Production of energy from municipal solid waste

Production of Energy from MSW

1.1. Introduction

The start of civilization has seen the human race generating

waste as bones and other parts of animals they slaughter for

their food or the wood they cut to make their shelters , tools,

carts etc. the advancement of civilization has witnessed the

waste generation getting enhanced, and becoming more complex in

nature. The beginning of industrial era has had enormous effects

on the life style of people which have started changing with the

availability of many consumer products and services in the

market. The manufacturing and usage of vast range of products as

well as management of the resulting waste give rise to emission

of green house gases. This has led not only to the pollution of

air and water but has affected the planet Earth through global

warming.

Rapid migration of rural populations to urban centers, in

search of better opportunities of livelihood, has resulted in an

over whelming demographic growth in many cities worldwide. The

situation is more pronounced especially in Asia and Africa. The

projected rate in North America is less because it has already

recording the growth rate of > 70%. Also in Europe, the situation

is similar. But in Africa and Asia, around 35% of the population

presently is urban fig (1.1). Asian countries are experiencing an

urban growth of approximately 4% per year. This growth rate is

expected to continue for several more years, and by 2025, 52% of

Asian population is likely to be living in urban centers. As in

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Asia, Africa’s population is mainly rural at present. However,

Africa is also experiencing a high rate of urbanization at 4-5%

per annum, and by 2025, urbanization is likely to be similar to

Asia. The high rate of urbanization can lead to serious

environmental degradation in and around several cities [1].

Figure 1.1: urban

growth rate [2]

Pakistan has an estimated 2.61% population growth rate per year[3], which is the highest in Asia. Today, Pakistan is the 6th most

populous country in the world with a population of approx. 180

million. By 2020, Pakistan’s population is expected to reach the

210 million mark - a situation that will burden its limited

resources making it difficult for the country to meet the

requirements of its people [4].

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This alarming growth rate is causing immense pressure on the

country’s resources. As the population of Pakistan is increasing

day by day, so the waste generated by them is also increasing day

by day. We must develop the alternative sources of energy like

the “energy from municipal solid wastes [4].

1.2. Waste and its types:

Waste (also known as rubbish. Trash, refuse, garbage, junk) is

any unwanted or useless materials. Or it may also be defined as

“any materials unused and rejected as worthless or unwanted” and

“a useless or profitless activity; using or expending or

consuming thoughtlessly or carelessly”. It may be solid waste,

liquid waste or gaseous waste.

1.2.1. Solid Waste

It is defined as “Non-liquid, non soluble materials ranging from

municipal garbage to industrial wastes that contain complex and

sometimes hazardous substances”. It may include sewage sludge,

Demolition& construction wastes, ashes, industrial waste, medical

waste, dead animal and agriculture refuse [5].

1.2.2. Domestic wastes

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Are generated by household activities such as cooking, cleaning,

repairs, interior decoration, and used products/ materials such

as empty glass/ plastic/ metal containers, packing stuff,

clothing, old books, newspapers, old furnishings, etc. commercial

wastes are the waste generated in offices, whole sale stores,

shops, restaurants and hotels, vegetable, fish and meat markets,

warehouses and other commercial establishments. Institutional

wastes are generated from institutions such as schools, colleges,

hospitals, research institutions. The waste includes mostly

paper, cardboards etc, and hazardous wastes. Municipal wastes are

wastes generated due to municipal services such as street

sweeping, and dead animals, market waste and abandoned vehicles

or parts; also includes already mentioned domestic wastes,

institutional wastes and commercial wastes. Garbage includes

animals and vegetable wastes due to various activities like

storage, preparation and sale, cooking and serving; theses are

biodegradable [1].

1.2.3. Ashes

Residues from the burning of wood, charcoal, coke for coking and

the heating in the houses, institutions and small industries.

Ashes consist of fine powders, cinders and clinker often mixed

with small pieces of metal and glass.

1.2.4. Rubbish

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Apart from garbage and ashes, other solid wastes produced in

households, commercial establishments, and institutions.

1.2.5. Bulky wastes

Bulky wastes are large household appliances such as cookers,

refrigerators and washing machines as well as furniture, crates,

vehicle parts, tyres, wood, trees and branches. The bulky

metallic wastes are sold as scrap metal but some portion is

disposed as sanitary landfills.

1.2.6. Street wastes

Street wastes include paper, cardboard, plastic, dirt, dust,

leaves and other vegetable matter collected from streets,

walkways, alleys, parks and vacant plots. Municipal waste

includes street waste also.

1.2.7. Dead animals

It includes animals that die naturally or killed by accident. It

does not include carcass and animals parts from slaughterhouses

as they are considered as industrial wastes.

1.2.8. Construction and demolition wastes

Some quantities of the major components of the construction

materials such as cement, bricks, cement plaster, steel, rubber,

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stone, timber, plastic and iron pipes are left out as waste

during construction as well as demolition. About 50% of the waste

is not currently recycled and 70% of the construction industry is

not aware of recycling techniques.

1.2.9. Industrial wastes

These are non-hazardous solid material discarded from

manufacturing processes and industrial operations, and are not

considered as municipal wastes. However, solid wastes from small

industrial plants and ash from power plants are frequently

disposed of at municipal landfills [1].

Similarly, the industrial waste is made up of a wide variety

of non-hazardous materials that result from the productions of

goods and products. Commercial and institutional, or industrial

waste is often a significant portion of municipal solid waste,

even in small cities and suburbs.

Some of the wastes referred to as Special wastes include (i)

Cement kiln dust, (ii) Mining waste, (iii) Oil and gas drilling

mud and oil production brines, (iv) Phosphate rock mining,

beneficiation, and processing waste, (v) Uranium waste, and (vi)

Utility waste(i.e., fossil fuel combustion waste). These are

generated in large volumes and are believed to cause less risk to

human health and the environment than the wastes specified as

hazardous waste [1]. The table shows the major industrial wastes

and their sources in Pakistan:

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Table 1.1: Industrial wastes and

their sources [1]

Sr. No. Waste Source

1 Steel and Blast Furnace Conversion of steel

2 Brine mud Caustic soda industry

3 Copper slag By product from smelting of

copper

4 Fly ash Coal based thermal power

plant

5 Kiln dust Cement plants

6 Lime sludge Sugar, paper, fertilizer,

tanneries, soda ash,

calcium carbide industries

7 Mica scrape waste Mica mining areas

8 Phospho gypsum Phosphoric acid plant,

ammonium phosphate

9 Red mud/ bauxite Mining and extraction of

alumina from bauxite

10 Coal washery dust Coal mines

11 Iron tailing Iron ore

12 Lime stone waste Lime stone quarry

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Beside these, industrial waste water discharge from industries in

the country has been estimated at 6.25(in 2010) to a projected

value of 12.50 million cubic meters/ annum (in 2025). A combined

pollution load(BOD, COD & TDS) in waste water discharged to

inland water bodies has been estimated at 28.6 (in 2010) to a

projected value of 58.6 million tons/annum [6]. Degradation of

water quality, both for human consumption and irrigation, due to

industrial waste water discharge with high pollution load and its

resulting impacts on public health and environment are most

obvious. In a recent SDPI survey of 38 polluted sites in the

country, it was shocking to observe, waste water from industrial

estates and industrial units being discharged into agriculture

fields most for cash crops but also in the few, for food crops

and vegetables, both on large and small scale [7]. Water and soil

are known and well established pathways for toxic chemicals

(metals non metals & organics) getting into food chain and

ultimately into human bodies, besides, to a lesser extent through

air.

1.2.10. Medical waste (or Hospital waste)

It refers to the waste materials generated at health care

facilities, such as hospitals, clinics, physician’s offices,

dental practices, blood banks, and veterinary hospitals/clinics,

as well as medical research facilities and laboratories. The

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medical waste is defined as “any solid waste that is generated in

the diagnosis, treatment, or immunization of human beings or

animals, in related research, or in the production or testing of

biological.” For example, the following trash constitutes medical

waste: blood soaked bandages, culture dishes and other glassware,

discarded surgical gloves, discarded surgical instruments,

discarded needles used to give shots or draw blood, cultures,

stocks, swabs used to inoculate cultures, removed body organs

(e.g., tonsils, appendices, limbs), and discarded lancets.

Several health hazards are associated with poor management of

medical wastes like injury from sharps to staff and waste

handlers associated with health care establishments, Hospital

Acquired Infection (HAI) of patients due to spread of infection,

and Occupational risk associated with hazardous chemicals, drugs,

unauthorized repackaging and sale of disposable items and

unused/date expired drugs. This waste is highly infectious and

can be a serious threat to human health if not managed in a

scientific manner. It has been roughly estimated that of the 4 kg

of waste generated in a hospital at least 1 kg would be infected[1].

Around 250,000 tons of medical waste is annually produced from

all sorts of health care facilities in the country, revealed

Sikandar K Sherwani, a lecturer of microbiology at the Federal

Urdu University [8].

1.2.11. Hazardous waste

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The waste that is dangerous or potentially harmful to human

health or the environment is called hazardous waste which can be

in the form of liquids, solids, gases, or sludge. The discarded

commercial products like cleaning fluids or pesticides, or the

by-products of manufacturing processes can also be hazardous [1].

This hazardous waste may include the medical waste, some

industrial waste and other is the agricultural waste, which

mostly include pesticides. According a study conducted by GTZ on

“inventory of obsolete pesticides in Punjab, Sindh and

Baluchistan” by Mr. wolfgang A Schimpf, it has been estimated

that the stocks of outdated pesticides lying in Pakistan is

between 1,000 to 1,500 tons [3].

1.2.12. E-wasteElectronic waste or e-waste is referred to the end-of-life

electronic and telecommunication equipment and consumer

electronic to be specific, computers, laptops, television sets

DVD players, mobile phones etc, which are to be disposed. UN

estimates that between 20 and 60 million tons of e-waste are

generated worldwide every year at approximately 12 million tons

of this comes from Asian countries.

E-waste is the fastest growing segment of MSW streamed e-

waste equals 1% of solid waste on average in developed countries

which grew to 2% by 2010. In developing countries, e-waste is

0.01% to 1% of the total solid waste. Globally, computer sales

continue to grow at > 10% rates annually. Sales of DVD players

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are doubling year over year. As a result a high percentage of

electronics are ending up in the waste stream releasing dangerous

toxins into the environment. These are a division of WEEE (Waste

Electrical and Electronic Equipment). The categories under WEEE

are: large household appliances, small appliances, IT and

telecommunication equipment, electrical and electronic tools,

medical devices. Monitoring and control instruments and so on.

Most of the equipment is made of components, some of which

contain toxic substances. If proper processing and disposal

methods are not followed, these substances affect human health as

well as the environment. For example, cathode rays tube contains

large amounts of carcinogens such as lead, barium, phosphorus and

other heavy metals. If they are broken or disposed in an

uncontrollable manner without taking safety precautions, it can

result in harmful effects for the workers, and pollute the soil,

air and ground water by releasing toxins. Special care is

warranted during recycling and land filling of e-waste as they

are prone to hazards [1].

1.3. Degradation time for some daily wastes

Table 1.2: wastes and their time

to degenerate [5]

Type of wastes Approximate time it takes to

degenerate

Organic waste such as A week or two

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vegetable and fruit peels,

leftover foodstuff, etc

Paper 10-30 days

Cotton cloth 2-5 months

Wood 10-15 years

Woolen item 1 year

Tin, aluminum, and other

metal items such as cans

100-500 years

Plastic bags One million years

Glass bottles Undetermined

1.4. Quantity and Composition of waste generated

While Pakistan’s population has increased to more than 160

millions, lack of adequate infrastructure is creating

environmental hazards. In Pakistan, sources of waste include

households, commercial areas, institutions, construction and

demolition sites, industrial areas and agricultural disposals.

Factors that affect waste generation in the country are size and

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type of the community and level of communities ‘income. Solid

waste generated mostly ends up in empty plots, place of

generation, in drains causing blockage in sewage system or on

road sides. Composition of solid waste generally comprises of

plastic and rubber, metal, paper and cardboard, textile waste,

glass, food waste, animal waste, leaves, grass, straws, fodder,

bones, wood and stones, as shown in the table below. Apart from

this, substantial amount of hospital waste is also produced in

the country [9].

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Table 1.3: Quantity of waste generated in

Pakistan [9]

Seri

es

No.

Description Tons per Day % Weight

1 Paper 69.1 5.04

2 Glass 30 2.19

3 Ferrous metal 0.3 .02

4 Non ferrous

metal

6.5 0.47

5 Film plastic 177.3 12.94

6 Rigid plastic 76.0 5.55

7 Organics 917.9 67.02

8 Textiles 13.7 1.00

9 Others 79.0 5.77

Tota

l

1369.8 100.0

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According to various studies conducted on waste management in the

country, about 54,888 tons of solid waste is generated daily in

urban areas of Pakistan and 60% of it is collected by municipal

authorities. However, according to official estimates, 30% to 50%

of solid waste generated within most cities is not collected [3].

The amount of waste generated strongly depends on the level

of consumption and lifestyle besides population. That in Pakistan

shows a particular trend that increases in waste generation has

occurred in accordance with the city’s social and economic

development (JICA, 2005:2008). The Ministry of Environment and

Urban Affairs Division, Government of Pakistan (1996) Revealed

that the average rate of waste generation from municipalities

varies from 0.283kg/capita/day to 0.613 kg/capita/day or from

1.896 kg/capita/day to 4.29 kg/capita/day in all selected cities

from Sibi to Karachi. In related to nine cities, the average of

waste generation from nine cities ranges from 115 ton/day of DG

Khan to 5000 ton/day of Lahore [9] as shown in the figure below:

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Figure 1.2: Waste generation and

collection in major cities of Pakistan [9]

Waste generation is roughly estimated based on the population and

an estimated average generation rate of 0.6 kg/capita/day, since

no detailed study on the nine cities in the Punjab is available[9].

Solid waste in Punjab is generally composed of plastic and

rubber, metal, paper, and cardboard, textile waste, glass, food

waste, animal waste, leaves, grass, straws and fodder, bones,

wood, stones and fines of various extents. A typical distribution

of waste fractions is given in the following figure

This shows that organic material account for more than half of

total waste even though the composition of waste changes from the

point of generation to the final disposal sites

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Figure 1.3: Composition of waste in major

cities of Pakistan [9]

1.5. Municipal Waste Collection Services

The responsibility of solid waste management rests basically with

the municipalities. Traditionally, in Pakistan’s large cities,

the local Government collects waste from households in middle to

high-income areas and is in charge of street sweeping. Solid

waste collection services by the government in Punjab’s cities

averages only 50 percent of waste generated: however, for cities

to be relatively clean, at least 75% of these quantities should

be collected. The uncollected waste remains on street or road

corners, open spaces and vacant plots, etc., polluting the

environment continuously. The rate and amount of the waste

collected in all the selected cities are given in the following

table (JICA, 2005: 11-12). The available fleet for the waste

collection and transport typically is composed of handcarts,

donkeys and bulla carts for primary collection; and open trucks,

tractors/trolleys systems, arm roll containers/trucks for the

secondary collection and transport. A number of municipalities

have hired the sweepers and sanitary workers. Workers collect the

solid waste from small heaps and dustbins with the help of heel

borrow and brooms and store it at formal and informal depots and

then carry out the sweeping of the streets and roads. The

proportion of the waste collected is much less in many other

areas of the country, particularly in poorer areas, where the

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only means of solid waste disposal is often informal scavenging

by people and animals, local self-help for the disposal to

informal (technical illegal)dumping sites [9].

1.6. Solid waste management

4R’s (recycle, refuse, reuse and reduce) has to be followed for

the solid waste management.

Refuse: Instead of buying new containers from the market, use the

ones that are in the house. Refuse to buy the new items though

you may think they are prettier than the ones you already have.

Reuse: Do not through away the soft drink cans and bottles; cover them with homemade paper or paint on them and use them as

pencil stand or as small vases.

Recycle: Use the shopping bags which are made of cloth or jute, which can be used over and over again.

Reduce: Reduce the generation of unnecessary waste. E.g. carry your own shopping bag when you go to the market and put all your

purchase into it [5].

1.7. Waste management in Pakistan

Before promulgation of the local government in 2001, the

provincial Public Health Engineering Department (PHED) was

responsible for the development and maintenance of water and

sanitation services including solid waste management. Under the

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recently prevailing system of local government, it is the

responsibility of Town/Tehsil Municipal Administration (TMAs);

however the sighting of disposal facilities is primarily the

function of Zila Council. Paid sanitary workers are employed by

TMAs to sweep the streets and collect the trash at a specified

place from where it is taken to the dumping site by ht municipal

carrier.

In addition to these there are some private entrepreneurs

who have entered the field. Private sector is involved in waste

management activities in the country may be divided into formal

and informal categories. The formal sector consists of govt.

organization and non government organization (NGOs). The informal

sector is significant in size as it consists of thousands of

itinerant traders (called kabarias or kabari-wallas) spread

throughout the cities who are engaged in collection of waste

material of different kinds.

Private sector firms have initiated projects based on

organic and in-organic waste management. Organic waste is used to

produce organic fertilizer. Inorganic waste is first sorted into

paper, plastic, tin, etc, and it is then sold to respective

industries where it is recycled to make products such as; Plastic

Wood and Tetra Sheets. Unplanned urbanization, poor sanitation

and drainage system, inadequate human and capital resources for

collecting waste, unavailability of official dumping sites,

absence of weigh bridges for exact measurement of waste coming at

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sites, and almost negligible presence of recycling processes have

negatively impacted waste management in the country.

In Pakistan there is immense potential to convert waste into

resources for the economy. In this regard, some NGOs and private

firms have already stepped into the industry. These organizations

collect waste and reprocess it to produce fertilizers, plastic

bottles, and tetra packs. A private firm has established a

recycling facility in Lahore where it is engaged to produce

refuse-derived fuel (RDF) based on the concept of waste to

energy. Similarly an NGO in Karachi encourages people to sell

their waste to them and prepares soil conditioning fertilizer.

Thus the government of Pakistan is aware of the role of waste

management industry. However there is a need of more pro-active

approach, likely to be based on public private partnership to

help this industry provide a cleaner environment while adding

value to economy [10].

1.8. Solid waste recycling

In fact, presently none of the municipalities have formal

recycling systems in place. The mostly informal classification

activities take place at various step of the cycle, from the

source to the disposal site. What happens normally is that the

main recyclable items such as paper, plastic, glass and metals

are retained by the people themselves, which are later sold to

stree hawkers or waste dealers for recycling. The recyclable

20


mixed with discharged waste are picked up by the scavengers who

make trips to two to three different dumps and earn approximately

Rs to 200/day. As a whole, however, according to estimates the

amount of recyclable waste varies from 1000 tones/year in sibi to

513743 tons/year in Karachi. The city-wise potential for the

waste recycling is given in the following table (JICA, 2005: 12)[9].

1.9. Solid waste treatment

Besides there being a great number of illegal dumping sites at

any open space, the “official” disposal sites are far from being

acceptable from an environment point of view. Delivered garbage

is dumped without any base protection from potential leachate

infiltration into ground water; leach ate collection and

treatment nor collection and control or gas evacuation/ flaring

system- those being the minimum requirements for an acceptable

practice. The presence of waste pickers on the sites is hindering

a more efficient operation of them and is critical from a public

health perspective (IP: 14-5).

Treatment and disposal technologies such as sanitary land

filling, composting and incineration are comparatively new

concepts in Pakistan. Open dumping is the most common practice

throughout Pakistan and dumpsites are commonly set on fire to

reduce the volume of accumulating waste, hence adding to the air

pollution caused by the uncovered dumped waste itself. The

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practice of sanitary land fling is still in its infancy in

Pakistan and the first site has yet to be developed. At present,

there is no landfill regulation or standards that provide a basis

for compliance and monitoring, but national guidelines for these

standards are being prepared by the consultant under the National

Environmental Action Plan Support Program (NEAPSP) [9].

1.10. Legal and institutional framework

regarding Solid Waste Management in Pakistan

Presently the legal rules and regulations dealing with solid

waste management in Pakistan are as follows:

Current

Section 11 of Pakistan Environmental Protection Act

prohibits discharge of waste in an amount or concentration

that violates the National Environmental Quality Standards.

Draft Hazardous Substances Rules of 1999.

Islamabad Capital Territory Bye Laws, 1986 by Capital

Development Authority Islamabad.

Section 132 of the Cantonment Act 1924 deals with Deposits

and disposals of rubbish etc.

Provision contained in the Local Government Ordinance, 2001

Required

The rules and guidelines that are yet to be introduced include:

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Basic Recycling rules

Waste Management rules

E-waste Management rules

Development of Environmental Performance Indicators (EPI)

Eco-Labeling guidelines Assessment Approaches

Guidelines for Environmentally Sound Collections and

Disposal

Guidelines for model landfill site [11].

2.1. Waste to energy

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Waste to energy (WtE) or energy from waste (EfW) is the process

of creating energy in the form of electricity or heat from the

incineration of waste source. WtE is a form of energy recovery.

Most WtE processes produce electricity directly through

combustion, or produce a combustible fuel commodity, such as

methane, methanol, ethanol, or synthetic fuels [12].

Figure 2.1: heating values

of various fuels [13]

There are various methods used for the production of energy from

waste, some of them are listed below:

2.2. Thermal technologies

2.2.1. Incineration

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Incineration, the combustion of organic material such as waste

with energy recovery is the most common WtE implementation. All

new WtE plants in developing countries must meet strict emission

standards including those on nitrogen oxides (NO), sulpher

dioxide (SO2), heavy metals and dioxins[14][15]. Hence modern

incineration plants are very vastly different from the old types,

some of which neither recovered energy nor materials. Modern

incinerators reduce the volume of the original waste by 95-96 %,

depending upon composition and degree of recovery of materials

such as metals from the ash for recycling [16].

Concerns regarding the operation of incinerators include

fine particulate, heavy metals, trace dioxin and acid gas

emissions, even through these emissions are relatively low [17]

from modern incinerators. Other concerns include toxic fly ash

and incinerators bottom ash (IBA) management [18]. Discussions

regarding waste resource ethics include the opinion that

incinerators destroy valuable resources and the fear that they

may reduce the incentives for recycling and waste minimization

activities. This is open to question, however, as the Refuse

Derived Fuel (RDF) is produce by recycling centres (MRFs), which

make their money from selling on recoverable material, and the

name Residue Derived Fuel (RDF) even suggests that it’s made from

what’s left over, not the materials being pulled out. It is not

in the interests of the MRF operators to give away for free the

very materials they could otherwise sell. Incinerators have

electric efficiencies on the order of 14-28%. The rest of the25


energy can be utilized for e.g. district heating, but is

otherwise lost as waste heat.

The method of using incineration to convert municipal solid

waste (MSW) to energy is relatively old method of waste to energy

production. Incineration generally entails burning an RDF to boil

water which powers steam generators that make electric energy to

be used in our homes and businesses. One problem associated with

incinerating MSW to make electrical energy, is the potential for

pollutants to enter the atmosphere with the flue gases from

boiler. Theses pollutants can be acidic and in the 1980s were

reported to cause environmental damage by turning rain into

acidic rain. Since then, the industry has removed the problem by

the use of lime scrubbers and electro-static precipitators on

smokestacks. The limestone mineral used in these scrubbers has a

Ph of approximately 8 which means it is a base. By passing the

smoke through the lime scrubbers, any acids that may be in the

smoke are neutralized which prevents the acid from reaching the

atmosphere and hunting our environment [19].

2.2.2. Pyrolysis

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Pyrolysis is a thermochemical decomposition of organic material

at elevated temperatures without the participation of oxygen. It

involves the simultaneous change of chemical composition and

physical phase, and is irreversible. The word is coined from the

Greek derived elements pyr “fire” and lysis “separating”.

Pyrolysis is a case of thermolysis, and is most commonly

used for organic materials, being, therefore, one of the

processes involved in charring. The pyrolysis of wood which

starts at 200-300 degree C, [20] occurs for example in fires where

solid fuels are burning or when vegetation comes into contact

with lava in volcanic eruption. In general, pyrolysis of organic

substances produces gas and liquid products and leaves mostly

carbon as the residue, is called carbonization.

The process is used heavily in the chemical industry, for

example, to produce charcoal, activated carbon, methanol and

other chemicals from wood, to convert ethylene dichloride into

vinyl chloride to make PVC, to produce coke from coal, to convert

biomass into syngas and biochar to turn waste into safely

disposable substances, and for transforming medium weight

hydrocarbons from oil into lighter ones like gasoline. These

specialized uses of pyrolysis may be called various names, such

as dry distillation, destructive distillation or cracking.

27


Figure 2.2: Simplified depiction

of pyrolysis chemistry [20].

Pyrolysis also plays an important role in several cooking

procedures, such as baking, frying, grilling and caramelizing. In

addition, it is a tool of chemical analysis, for example, in mass

spectrometry and in carbon-14 dating. Indeed many important

chemical substances, such as phosphorous and sulfuric acid, were

first obtained by this process. Pyrolysis has been assumed to

take place during pyrography. In their embalming process, the

ancient Egyptians used a mixture of substances, including

methanol, which they obtained from the pyrolysis of wood.

Pyrolysis differs from other high-temperature processes like

combustion and hydrolysis in that it usually does not involve

reactions with oxygen, water, or any other reagents. In practice,

it is not possible to achieve a completely oxygen-free

atmosphere. Because some oxygen is present in any pyrolysis

system, a small amount of oxidation occurs.

28


The term has also been applied to the decomposition of

organic material in the presence of superheated water or steam

(hydrous pyrolysis), for example, in the steam cracking of oil[20].

2.2.3. Plasma gasification

It is a process to convert organic matter into syngas by using

plasma processing. Plasma gasification technologies use an

electric arc gasifier (plasma torch) to create a high-temperature

ionized gas which breaks organic matter primarily into syngas and

solid waste (slag) [21][22][23][24] in a controlled vessel (plasma

converter-either furnace or reactor). Its main use is as a waste

treatment technology as it allows full decomposition and

disintegration of organic components; however, it is also tested

for the biomass and solid hydrocarbons, such as coal, oil shale[25], gasification. The process is intended to be a net generator

of electricity, depending upon the composition of input wastes,

and to reduce the volumes of waste being sent to landfill sites[26].

A plasma torch uses inert gases (steam) and metal electrodes

(copper, tungsten, hafnium, zirconium, etc.). Relatively high

voltage, high current electricity is passed between two

electrodes, spaced apart, creating an electrical arc. Pressurized

inert gas is ionized when passing through the arc creating

plasma. The temperature of the plasma torch can be in the range

29


4000-25000 degree Fahrenheit; [27] at these temperatures molecular

bond break down into basic elemental components in a gaseous

from, and complex molecules are separated into individual atoms.

This process is called molecular dissociation and molecular

dissociation using plasma is called plasma pyrolysis.

2.2.4. Thermal depolymerization

Thermal depolymerization (TDP) is a deploymerization process

using hydrous pyrolysis for the reduction of complex organic

materials (usually waste products of various sorts, often biomass

and plastic) into light crude oil. It mimics the natural

geological processes thought to be involved in the production of

fossil fuels. Under pressure and heat, long chain polymers of

hydrogen, oxygen, and carbon decompose into short-chain petroleum

hydrocarbons with a maximum length of around 18 carbons.

Thermal depolymerization is similar to other processes which use

superheated water as a major step to produce fuels, such as

direct hydrothermal liquefaction [28].

2.3. Non thermal technologies

2.3.1. Anaerobic digestion

It is a three step process as given below:

Hydrolysis

30


In the first step (hydrolysis), the organic matter is enzymolyzed

externally by extracellular enzymes (cellulase, amylase, protease

and lipase) of microorganisms. Bacteria decompose the long chains

of the complex carbohydrates, proteins and lipids into shorter

parts. For example, polysaccharides are converted into

monosaccharaides. Proteins are split into peptides and amino

acids.

Acidification

Acid-producing bacteria, involved in the second step, convert the

intermediates of fermenting bacteria into acetic acid (CH3COOH),

hydrogen (H2) and carbon dioxide (CO2). These bacteria are

facultatively anaerobic and can grow under acid conditions. To

produce acetic acid, they need oxygen and carbon. For this, they

use the oxygen dissolved in the solution or bounded-oxygen.

Hereby, the acid-producing bacteria create an anaerobic condition

which is essential for the methane producing microorganisms.

Moreover, they reduce the compounds with a low molecular weight

into alcohols, organic acids, amino acids, carbon dioxide,

hydrogen sulphide and traces of methane. From a chemical

standpoint, this process is partially endergonic (i.e. only

possible with energy input), since bacteria alone are not capable

of sustaining that type of reaction

Methane formation

31


Methane-producing bacteria, involved in the third step, decompose

compounds with a low molecular weight. For example, they utilize

hydrogen, carbon dioxide and acetic acid to form methane and

carbon dioxide.

Under natural conditions, methane producing microorganisms

occur to the extent that anaerobic conditions are provided, e.g.

under water (for example in marine sediments), in ruminant

stomachs and in marshes. They are obligatory anaerobic and very

sensitive to environmental changes. In contrast to the acidogenic

and acetogenic bacteria, the methanogenic bacteria belong to the

archaebacter genus, i.e. to a group of bacteria with a very

heterogeneous morphology and a number of common biochemical and

molecular-biological properties that distinguish them from all

other bacterial general. The main difference lies in the makeup

of the bacteria’s cell walls

It is used as a part of the process to treat biodegradable

waste and sewage sludge. As part of an integrated waste

management system, anaerobic digestion reduces the emission of

landfill gas into atmosphere. Anaerobic digesters can also be fed

with purpose-grown energy crops, such as maize [29].

32


Figure 2.3: Steps involved in

anaerobic digestion process [30]

2.3.1.1. Symbiosis of bacteria in anaerobic

digestion

Methane- and acid-producing bacteria act in a symbiotical way. On

the one hand, acid producing bacteria create an atmosphere with

ideal parameters for methane-producing bacteria (anaerobic

conditions, compounds with a low molecular weight). On the other

hand, methane-producing microorganisms use the intermediates of

the acid-producing bacteria. Without consuming them, toxic

conditions for the acid-producing microorganisms would develop.

In practical fermentation processes the metabolic actions of

various bacteria all act in concert. No single bacteria are able

to produce fermentation products alone [29].

2.3.2. Fermentation

33

http://en.wikipedia.org/wiki/File:Stages_of_anaerobic_digestion.JPG


Fermentation is the process of extracting energy from the

oxidation of organic compounds, such as carbohydrates [31], using

an endogenous electron acceptor, which is usually an organic

compound. In contrast, respiration is where electrons are denoted

to an exogenous electron acceptor, such as oxygen, via an

electron transport chain. Fermentation is important in an

anaerobic condition when there is no oxidative phosphorylation to

maintain the production of ATP (adenosine triphosphate) by

glycolysis.

During fermentation, pyruvate is metabolized to various

compounds. Homolactic fermentation is the production of lactic

acid from pyruvate; alcoholic fermentation is the conversion of

pyruvate into ethanol and carbon dioxide; and heterolactic

fermentation is the production of lactic acid as well as other

acids and alcohols. Fermentation does not necessarily have to be

carried in an anaerobic environment. For example, even in the

presence of abundant oxygen, yeast cells greatly prefer

fermentation to oxidative phosphorylation, as long as sugars are

readily available for consumption (a phenomenon known as the

crabtree effect) [32].

Sugars ate the most common substrate of fermentation, and

typical examples of fermentation products are ethanol, lactic

acid, lactose, and hydrogen. However, more exotic compounds can

be produced by fermentation, such as butyric acid and acetone.

Yeast carries out fermentation in the production of ethanol in

34


beers, wines, and other alcoholic drinks, along with the

production of large quantities of carbon dioxide. Fermentation

occurs in mammalian muscles during periods of intense exercise

where oxygen supply becomes limited, resulting in the creation of

lactic acid [33].

2.3.3. Mechanical biological treatment (MBT)

A mechanical biological treatment system is a type of waste

processing facility that combines a sorting facility with a form

of biological treatment such as composting or anaerobic

digestion. MBT plants are designed to process mixed household

waste as well as commercial and industrial wastes [34][35].

Figure 2.3: Mechanical

biological treatment of waste [34]

35

http://en.wikipedia.org/wiki/File:Mechanical_biological_treatment_flowchart.jpg


2.3.4. Refused-derived fuel (RDF)

Refuse derived fuel (RDF) or solid recovered fuel/ specified

recovered fuel (SRF) is a fuel produced by shredding and

dehydrating solid waste (MSW) with a waste converter technology.

RDF consists largely of combustible components of municipal waste

such as plastic and biogradable waste RDF processing facilities

are normally located near a source of MSW and, while an optional

combustion facility is normally close to the processing facility,

it may also located at a remote location [36].

36


3.1. GASIFICATION PROCESS

Gasification processes involve the reaction of carbonaceous

feedstock with an oxygen-containing reagent, usually oxygen, air,

steam or carbon dioxide, generally at temperatures in excess of

800°C. It involves the partial oxidation of a substance which

implies that oxygen is added but the amounts are not sufficient

to allow the fuel to be completely oxidised and full combustion

to occur. The process is largely exothermic but some heat may be

required to initialise and sustain the gasification process.

The main product is a syngas, which contains carbon monoxide,

hydrogen and methane. Typically, the gas generated from

gasification will have a net calorific value of 4 - 10 MJ/Nm3.The

other main product produced by gasification is a solid residue of

non-combustible materials (ash) which contains a relatively low

level of carbon. Syngas can be used in a number of different

ways, for example:

Syngas can be burned in a boiler to generate steam which may

be used for power generation or industrial heating.

Syngas can be used as a fuel in a dedicated gas engine.37


Syngas, after reforming, may be suitable for use in a gas

turbine

Syngas can also be used as a chemical feedstock.

Gasification plants, based on syngas production, are relatively

small scale, flexible to different inputs and modular

development. Producing syngas to serve multiple end-uses could

complicate delivery of the plants but it could provide a higher

degree of financial security [37].

3.2. Gasification of Municipal Solid WasteThe most important reason for the growing popularity of thermal

processes for the treatment of solid wastes has been the

increasing technical, environmental and public dissatisfaction

with the performance of conventional incineration processes. MSW

is difficult to handle, segregate and feed in a controlled manner

to a waste-to-energy facility. MSW has a high tendency to form

fused ash deposits on the internal surfaces of furnaces and high

temperature reactors, and to form bonded fouling deposits on heat38


exchanger surfaces. The products of the combustion of MSW are

also very aggressive, in that the flue gases are erosive and the

relatively high levels of chloride containing species in the flue

gases can lead to high rates of metal wastage of heat exchange

tube surfaces due to high temperature corrosion.

While evaluating gasification or other thermal technologies,

the degree of pre-processing required in conversion of MSW into a

suitable feed material is a major criterion. Unsorted MSW is not

suitable for most thermal technologies because of its varying

composition and size of some of its constituent materials. It may

also contain undesirable materials which can play havoc with the

process or emission control systems.

The main steps involved in pre-processing of MSW include

manual and mechanical separation or sorting, shredding, grinding,

blending with other materials, drying and pelletization. The

purpose of pre-processing is to produce a feed material with

consistent physical characteristics and chemical properties. Pre-

processing operations are also designed to produce a material

that can be safely handled, transported and stored [37].

3.2.1. Chemical reactions

In a gasifier, the carbonaceous material undergoes several

different processes:

39


1. The dehydration or drying process occurs at around 100°C.

Typically the resulting steam is mixed into the gas flow and

may be involved with subsequent chemical reactions, notably

the water-gas reaction if the temperature is sufficiently

high enough (see step #5).

2. The pyrolysis (or devolatilization) process occurs at around

200-300°C. Volatiles are released and char is produced,

resulting in up to 70% weight loss for coal. The process is

dependent on the properties of the carbonaceous material and

determines the structure and composition of the char, which

will then undergo gasification reactions.

3. The combustion process occurs as the volatile products and

some of the char reacts with oxygen to primarily form carbon

dioxide and small amounts of carbon monoxide, which provides

heat for the subsequent gasification reactions. Letting C

represent a carbon-containing organic compound, the basic

reaction here is

C + O 2

CO2

4. The gasification process occurs as the char reacts with

carbon and steam to produce carbon monoxide and hydrogen,

via the reaction

C + H 2O

H2 + CO

40


5. In addition, the reversible gas phase water gas shift

reaction reaches equilibrium very fast at the temperatures

in a gasifier. This balances the concentrations of carbon

monoxide, steam, carbon dioxide and hydrogen

CO + H 2O

CO2 + H2

Figure 3.1:

Gasification of char [38]

In essence, a limited amount of oxygen or air is introduced into

the reactor to allow some of the organic material to be "burned"

to produce carbon monoxide and energy, which drives a second

reaction that converts further organic material to hydrogen and

additional carbon dioxide. Further reactions occur when the

formed carbon monoxide and residual water from the organic

material react to form methane and excess carbon dioxide. This

third reaction occurs more abundantly in reactors that increase

the residence time of the reactive gases and organic materials,41


as well as heat and pressure. Catalysts are used in more

sophisticated reactors to improve reaction rates, thus moving the

system closer to the reaction equilibrium for a fixed residence

time [38].

3.3. Types of gasifiers

3.3.1. Fixed bed gasifiers

Fixed bed gasifiers typically have a grate to support the feed

material and maintain a stationary reaction zone. They are

relatively easy to design and operate, and are therefore useful

for small and medium scale power and thermal energy uses. The two

primary types of fixed bed gasifiers are updraft and downdraft[37].

3.3.2. Updraught or counter current gasifier

The oldest and simplest type of gasifier is the counter current

or updraught gasifier shown schematically in Fig below:

42


Figure 3.1: Updraught or counter current gasifier [39]

The air intake is at the bottom and the gas leaves at the top.

Near the grate at the bottom the combustion reactions occur,

which are followed by reduction reactions somewhat higher up in

the gasifier. In the upper part of the gasifier, heating and

pyrolysis of the feedstock occur as a result of heat transfer by

forced convection and radiation from the lower zones. The tars

and volatiles produced during this process will be carried in the

gas stream. Ashes are removed from the bottom of the gasifier.

43


The major advantages of this type of gasifier are its

simplicity, high charcoal burn-out and internal heat exchange

leading to low gas exit temperatures and high equipment

efficiency, as well as the possibility of operation with many

types of feedstock (sawdust, cereal hulls, etc.) .

Major drawbacks result from the possibility of "channelling" in

the equipment, which can lead to oxygen break-through and

dangerous, explosive situations and the necessity to install

automatic moving grates, as well as from the problems associated

with disposal of the tar-containing condensates that result from

the gas cleaning operations. The latter is of minor importance if

the gas is used for direct heat applications, in which case the

tars are simply burnt.

3.3.3. Downdraught or co-current gasifiersA solution to the problem of tar entrainment in the gas stream

has been found by designing co-current or downdraught gasifiers,

in which primary gasification air is introduced at or above the

oxidation zone in the gasifier. The producer gas is removed at

the bottom of the apparatus, so that fuel and gas move in the

same direction, as schematically shown in Fig below:

44


Figure 3.2: Downdraught or co-

current gasifier[39]

On their way down the acid and tarry distillation products from

the fuel must pass through a glowing bed of charcoal and

therefore are converted into permanent gases hydrogen, carbon

dioxide, carbon monoxide and methane.

45


Depending on the temperature of the hot zone and the residence

time of the tarry vapours, a more or less complete breakdown of

the tars is achieved.

The main advantage of downdraught gasifiers lies in the

possibility of producing a tar-free gas suitable for engine

applications.

In practice, however, a tar-free gas is seldom if ever achieved

over the whole operating range of the equipment: tar-free

operating turn-down ratios of a factor 3 are considered standard;

a factor 5-6 is considered excellent.

Because of the lower level of organic components in the

condensate, downdraught gasifiers suffer less from environmental

objections than updraught gasifiers.

A major drawback of downdraught equipment lies in its

inability to operate on a number of unprocessed fuels. In

particular, fluffy, low density materials give rise to flow

problems and excessive pressure drop, and the solid fuel must be

pelletized or briquetted before use. Downdraught gasifiers also

suffer from the problems associated with high ash content fuels

(slagging) to a larger extent than updraught gasifiers.

Minor drawbacks of the downdraught system, as compared to

updraught, are somewhat lower efficiency resulting from the lack

of internal heat exchange as well as the lower heating value of

the gas. Besides this, the necessity to maintain uniform high

46


temperatures over a given cross-sectional area makes impractical

the use of downdraught gasifiers in a power range above about 350

kW (shaft power).

3.3.4. Cross-draught gasifierCross-draught gasifiers, schematically illustrated in Figure

below are an adaptation for the use of charcoal. Charcoal

gasification results in very high temperatures (1500 °C and

higher) in the oxidation zone which can lead to material

problems. In cross draught gasifiers insulation against these

high temperatures is provided by the fuel (charcoal) itself.

Advantages of the system lie in the very small scale at

which it can be operated. Installations below 10 kW (shaft power)

can under certain conditions be economically feasible. The reason

is the very simple gas-cleaning train (only a cyclone and a hot

filter) which can be employed when using this type of gasifier in

conjunction with small engines.

A disadvantage of cross-draught gasifiers is their minimal

tar-converting capabilities and the consequent need for high

quality (low volatile content) charcoal.

47


It is because of the uncertainty of charcoal quality that a

number of charcoal gasifiers employ the downdraught principle, in

order to maintain at least a minimal tar-cracking capability.

Figure 3.3: Cross-draught

gasifier [39]

3.3.5. Fluidized bed gasifierThe operation of both up and downdraught gasifiers is influenced

by the morphological, physical and chemical properties of the

48


fuel. Problems commonly encountered are: lack of bunkerflow,

slagging and extreme pressure drop over the gasifier

A design approach aiming at the removal of the above difficulties

is the fluidized bed gasifier illustrated schematically in Fig.

3.4.

Air is blown through a bed of solid particles at a sufficient

velocity to keep these in a state of suspension. The bed is

originally externally heated and the feedstock is introduced as

soon as a sufficiently high temperature is reached. The fuel

particles are introduced at the bottom of the reactor, very

quickly mixed with the bed material and almost instantaneously

heated up to the bed temperature. As a result of this treatment

the fuel is pyrolysed very fast, resulting in a component mix

with a relatively large amount of gaseous materials. Further

gasification and tar-conversion reactions occur in the gas phase.

Most systems are equipped with an internal cyclone in order to

minimize char blow-out as much as possible. Ash particles are

also carried over the top of the reactor and have to be removed

from the gas stream if the gas is used in engine applications.

49


Figure 3.4: Fluidized bed

gasifier [39]

The major advantages of fluidized bed gasifiers, as reported by

Van der Aarsen (44) and others, stem from their feedstock

flexibility resulting from easy control of temperature, which can

be kept below the melting or fusion point of the ash (rice

husks), and their ability to deal with fluffy and fine grained

50


materials (sawdust etc.) without the need of pre-processing.

Problems with feeding, instability of the bed and fly-ash

sintering in the gas channels can occur with some biomass fuels.

Other drawbacks of the fluidized bed gasifier lie in the rather

high tar content of the product gas (up to 500 mg/m³ gas), the

incomplete carbon burn-out, and poor response to load changes.

Particularly because of the control equipment needed to cater for

the latter difficulty, very small fluidized bed gasifiers are not

foreseen and the application range must be tentatively set at

above 500 kW (shaft power) [39].

In a Bubbling Fluidized Bed (BFB), the gas velocity must be

high enough so that the solid particles, comprising thebed

material, are lifted, thus expanding the bed and causing it to

bubble like a liquid. A bubbling fluidized bed reactor typically

has a cylindrical or rectangular chamber designed so that contact

between the gas and solids facilitates drying and size reduction

(attrition). As waste isintroduced into the bed, most of the

organics vaporize pyrolytically and are partially combusted in

the bed. Typical desired operating temperatures range from 900°

to 1000 °C.

A circulating fluidized bed (CFB) is differentiated from a

bubbling fluid bed in that there is no distinct separation

between the dense solids zone and the dilute solids zone. The

51


capacity to process different feedstock with varying compositions

and moisture contents is a major advantage in such systems [37].

3.4. Other types of gasifiersA number of other biomass gasifier systems (double fired,

entrained bed, molten bath), which are partly spin-offs from coal

gasification technology, are currently under development. In some

cases these systems incorporate unnecessary refinements and

complications, in others both the size and sophistication of the

equipment make near term application in developing countries

unlikely. For these reasons they are omitted from this account.

3.5. Thermal capacity of different gasfiers

Gasification technology is selected on the basis of available

fuel quality, capacity range, and gas quality conditions. The

main reactors used for gasification of MSW are fixed beds and

fluidized beds. Larger capacity gasifiers are preferable for

treatment of MSW because they allow for variable fuel feed,

uniform process temperatures due to highly turbulent flow through

52


the bed, good interaction between gases and solids, and high

levels of carbon conversion. Table 1 shows the thermal capacity

ranges for the main gasifier designs [37].

Table no.4: thermal capacities of different gasifiers [37]

Gasifier design Fuel capacityDowndraft 1KW-1MWUpdraft 1.1MW-12MW

Bubbling fluidized bed 1MW-50MWCirculating fluidized bed 10MW-200MW

3.6. Advantages & Disadvantages of Gasification

3.6.1. Advantages

There are numerous solid waste gasification facilities operating

or under construction around the world. Gasification has several

advantages over traditional combustion processes for MSW

treatment It takes place in a low oxygen environment that limits

the formation of dioxins and of large quantities of SOx and NOx.

Furthermore, it requires just a fraction of the stoichiometric

amount of oxygen necessary for combustion. As a result, the

volume of process gas is low, requiring smaller and less

expensive gas cleaning equipment. The lower gas volume also means

a higher partial pressure of contaminants in the off-gas, which

favours more complete adsorption and particulate capture.

Finally, gasification generates a fuel gas that can be integrated

53


with combined cycle turbines, reciprocating engines and,

potentially, with fuel cells that convert fuel energy to

electricity more efficiently than conventional steam boilers.

3.6.2. Disadvantages

During gasification, tars, heavy metals, halogens and alkaline

compounds are released within the product gas and can cause

environmental and operational problems. Tars are high molecular

weight organic gases that ruin reforming catalysts, sulfur

removal systems, ceramic filters and increase the occurrence of

slagging in boilers and on other metal and refractory surfaces.

Alkalis can increase agglomeration in fluidized beds that are

used in some gasification systems and also can ruin gas turbines

during combustion. Heavy metals are toxic and accumulate if

released into the environment. Halogens are corrosive and are a

cause of acid rain if emitted to the environment. The key to

achieving cost efficient, clean energy recovery from municipal

solid waste gasification will be overcoming problems associated

with the release and formation of these contaminants [37].

3.7. Process description

The sun dried and preheated MSW is subjected to magnetic

separator, from separator it enters into the air classifier the

shredded waste will be conveyed and heaped in a hoper. The size

of hoper will depend upon the volume of the MSW to be contained.

54


The hoper is then connected to gasifier in which the gasification

takes place and the syngas produce.

Magnetic Separation

This is the most commonly used method when separating metallic

materials from wastes whether crushed or not. A permanent or

electro magnet is used. No power is required when we using a

permanent magnet but capacity is relatively small.

The efiiciency of collecting metallic elements from wastes can

vary according to the power of magnet, size of belt, and

thickness of motes on conveyor.

3.7.1. Gassifier

The gasifier is an internally heated vessel. The heating source

comprises of electrical coils. The primary purpose of gasifier is

to convert MSW into synthersis gas. The gasifier operates at an

internal pressure of 30 atm and internal temperature of 1200 °C.

The MSW enters the flidized bed gasifier almost at room

temperature. As it moves down the gasifier, through different

temperature zones, it becomes almost moisture free. During the

course of its download fall, it interacts counter currently with

steam and gasifies giving synthesis gas, tar and leaving behind

char. The char leaves from the gasifier at the bottom through

similar auger conveyer setting as described above, whereas, due

to high temperatrure inside the gasifier, the tar gets vaporized

55


and moves upward with the synthesis gas towards the outlet of the

gasifier where the suction is created.

3.7.2. Cyclon separator

Before entering the cyclone separator the gas first enters into

the heat exchanger in which it exchange heat with cold water and

the temperature of syngas is reduces, the heat obtained from the

syngas is used in the production of steam and the boiler load can

be reduce.

The gas is then passed through the cyclone separator to

remove any dirt particles larger than 3 micro meter size. The

dirt is collected at the bottom whereas the gas leaves from the

top.

3.7.3. Scrubber

Then the gas enters into the scrubber in which CO2 is removed

water is sprayed and solvent is used to separate the dust

particles and also use to minimize the CO2 so as to syngas is

used for burning purposes. The solubility of CO2 changes with the

temperature of the syngas thus it is important to maintain a

particular temperature of the syngas before it enters into the

scrubber, thus the CO2 is removed efficiently.

56


3.7.4. Knock out drum

Knock out vessels are used to slow down gasses and allow liquids

to "fall out" of the gas stream. Knock out drums can be installed

either in the waste gas header, or in the flare stack base

itself. Knock out drums can be configured in either a horizontal

or vertical arrangement. When horizontal, a knock out drum will

be constructed with one gas stream inlet, and two outlets, which

can then be joined with a manifold. Another configuration that

can be used is one inlet with a much larger outlet. A liquid

level gauge or indicator should always be included, as these

vessels must remain drained and free of excess liquid. In a

vertical arrangement the knock out drum can have a side inlet

with a larger exit which will slow down the gasses.

The gas stream enters into the knock out drum and moisture is

removed from it and thus moisture free gas obtained at the outlet

of the knock out drum.

57


4.1. Material balance on gasifier

58


N2-Balance

0.4/100 (2547/28) = nN2F6

NN2F6 = 0.36385 kg mole

C-Balance:

41.3/100 (2547/12) = nCOF6 + nCO2

F6

nCOF6 + nCO2

F6 = 87.659 kg mole

S-Balance

0.2/100(2547/32) = nH2SF6

nH2SF6 = 0.15918 kgmole

H2-Balance

F3 + 4.2/100 (2547/2) + 20.2/100(2547/18)

= nH2F6 + nH2S

F6

nH2F6 + nH2S

F6 =F3 + 53.487 + 28.5832

nH2F6 + nH2S

F6 = F3 + 82.07

O2-Balance

F 4 + 24.2/100 (2547/32) + 0.5x20.2/100

(2547/18) + 0.5F3 =0.5 nCOF6 + nCO2

F6

59


F4 + 19.2616 + 14.2915 + 0.5F3 = 0.5 nCOF6 +

nCO2F6

F 4 + 19.2616 + 14.2915 + 0.5F3 = 0.5 nCOF6 +

nCO2F6

Ash-Balance

F5 = 0.80(0.095)(2547)

F5 = 193.572 kg/hr

Total Ash

0.095x2547 = 241.965 kg/hr = 241.965/90.33 =

2.678 kg mol/hr

Chemical Reactions

2.2C + 0.6O2+H2O

2.2CO + H2

2.2 K mol of C require = 0.6 K mol of O2

1 K mol of C require = 0.6/2.2

60


87.659 K mol of C require = 0.6/2.2 (87.659)

F4 = 23.907 kg mol

F4 = 23.907x32 = 765.024

kg/hr

2.2 K mol of C require = 1 Kmol H2O

87.659 K mol of C require = 87.659/2.2

F3 = 39.845 kg mol

F3 = 39.845x18.01 =

717.608 kg/hr

From H2 Balance equation

F3+ 82.07 = nH2F6 + nH2S

F6

nH2F6 + nH2S

F6 = 23.907 + 82.07

nH2F6 + nH2S

F6 = 105.977

equation A

Equation of C- Balance gives

87.659 = nCOF6 + nCO2

F6

equation B

From O2 Balance equation

F4 + 19.2616 + 14.2915 + 0.5F3 = 0.5 nCO + nCO2

23.907 + 33.553 + 0.5 (39.845) = 0.5nCO + nCO2

61


77.382 =0.5 nCOF6 + nCO2

F6

equation C

By solving equation B and C

87.659 = nCOF6 + nCO2

F6

77.382 =0.5 nCOF6 + nCO2

F6

0.5CO = 10.276

nCO = 10.276/0.5

nCO = 20.553 kg mole

nCO + nCO2 = 87.659

20.553+ nCO2 = 87.659

nCO2 = 87.659- 20.553

nCO2 = 67.106 kg mol

From equation A

nH2F6 + nH2S

F6 = 105.977

nH2 + 0.15918 = 105.977

nH2 = 105.977- 0.15918

nH2 = 105.817 kg mol

Total gas produced

62


NCOF6 + nCO2 + nN2 + nH2 + nH2S + Ash

20.553 + 67.106 + 0.36385 + 105.817 + 0.15918 + 0.536 = 194.535

kg mol

Table no.4.1: Composition of gas out from gasifier

Components Kg mole Percentage (%)CO 20.553 10.5CO2 67.106 34.4N2 0.36385 0.18H2 105.817 54.394H2S 0.15918 0.0818Ash 0.5361 0.2755Total 194.535 100

[10.5(28) + 34.4(44) + 0.18(28) + 54.394(2) + 0.081(34) +

0.2755(90.33)]/100

Avg. Mol. Weight of produced gas = 19.49 kg/ kg mol

=

3791.487 kg/hr

Flow rate of gas = 193.995x19.24

= 3732.926 kg/hr

63


F2 + F3 + F4 = F5 + F6

2547+ 717.608 + 768.024 = 241.965 + 3791.656

4033 = 4033.621

4.2. Material Balance around Cyclone

64


Table no.4.2: Composition of gas in cyclone

Components Kgmole/hr Percentage (%)CO 20.553 10.565CO2 67.106 34.495H2 0.3638 0.187N2 105.817 54.394H2S 0.15918 0.0818Ash 0.5361 0.2755Total 194.535 100

Table no.4.3: Composition of gas Out from cyclone Components Kgmol/hr Percentage (%)

CO 20,533 10.587CO2 67.106 34.567N2 0.36385 0.1874H2 105.817 54.507H2S 0.15918 0.0819Ash 0.1340 0.06902

Total 194.133 99.999

Efficiency of cyclone separator = 75%

0.5361x0.75 = 0.4020 kg mol/ hr out

0.5361- 0.4020 = 0.1340 kg mol/ hr

65


4.3. Material Balance around Scrubber

66


Table no.4.4: Composition of gas in scrubber

Components Kg mol %CO 20.553 10.587CO2 67.106 34.567N2 0.36385 0.1867H2 105.817 54.507H2S 0.15918 0.0819Ash 0.1340 0.06902

194.133

67


Components Kg mole %CO 20.553 13.241CO2 20.1381 12.969N2 0.36385 0.2344H2 105.817 68.172H2S 0.15918 0.102H2O 8.1938 0.102

155.2186Table no.4.5: Composition of gas Out from Scrubber

Mol. Weight of syn gas out from scrubber = 11.44kg/kgmol

68


4.4. Material Balance around Knock out Drum

Table no.4.5: Composition of Gas in Knockout Drum

Components Kg mole %CO 20.553 13.24CO2 20.1318 12.969N2 0.36385 0.2344H2 105.817 68.172H2S 0.15918 0.102H2O 8.1938 5.278

155.2186

69


Components Kg mole %CO 20.553 13.9792CO2 20.1318 13.692N2 0.36385 0.2474H2 105.817 71.972H2S 0.15918 0.1082

Total 147.02Table no.4.6: Composition of gas Out from Knockout Drum

Total moisture removed = 147.5714 kg mole

70


5.1. Energy Balance around Gasifier

Cp of Syngas = 2.1 kj/kg. K

Cp of Biomass in at 343K = 2.072 KJ/Kg. K

Cp of O2 at 573K = .995 KJ/Kg.K

Cp of Steam = 2.017 KJ/ Kg.K

71


Energy in with biomass

H = mCpΔT

= 2547* 2.072(343-298)/3600

= 65.967 KW

Energy in with O2 at 573 K

H = mCpΔT

= 765.02 * .9959 (573-298)/3600

= 58.199 KW

Energy in with Steam

H = mCpΔT

=717.608 * 2.017 ((673-298) + 2350)/3600

= 624.144KW

Generation with Biomass

H = mCpΔT

= 2547 * 2.072 (1173-343)/3600

72


=1216.73KW

In – out + Generation= Consumption

(58.199 + 624.144 + 65.9673) – (1935.235 + 21.4192) + 1216.73 =

Consumption

8.621 KW = Consumption

5.2. Energy Balance on Heat Exchanger

73


Heat Load = m Cp ΔT

= 3791.48 * 2.03 (1173 -

873)/3600

= 641.39 KW

Assuming that

Heat in = Heat out

m Cp ΔT (gas) = m Cp ΔT (water)

3791.48 * 2.03 (1173 - 873) = m * 4.18 (371 - 298)

2309011.32 = m * 302

74


M (water) = 7567.055 Kg/hr

5.3. Energy Balance around Scrubber

Sp of gas at 873K = 2.0 KJ/Kg. K

Sp of gas at 831K = 1.99 KJ/Kg.K

Average Cp of bottom effluents = 0.7 KJ/Kg.K at 320K

Heat in by Gas = m Cp ΔT

=3787.48 *

2.0 (873 - 298)/3600

=1208.66 KW

Heat out by Gas = m Cp ΔT

= 1836 *

1.99 (813 - 298)

= 522.6 KW

75


Heat out by bottom effluents (Co2 + water + solids) = m Cp ΔT

= 150000 * 0.7 (320 - 298)/3600

= 641.666 KW

Heat Losses = In – Out

= 1208.666 – (522.6 + 641.666)

= 44.32 KW

5.4. Energy Balance around Knockout Drum

Sp of Gas at 810K = 1.96 KJ/Kg.K

Sp of Gas at 710K = 1.94 KJ/Kg.K

76


Sp of Moisture = 1.92 KJ/Kg.K

Heat in by gas = m Cp ΔT

=1836 * 1.96 (810 - 298)

= 509.99 KW

Heat out by gas = m Cp ΔT

= 374.87 KW

Heat out by Moisture = m Cp ΔT

= 147.571 * 1.96 (343 -

298)/3600

= 3.615 KW

Heat Losses = Heat in – Heat Out

= 509.99 – (374.87 + 3.615)

= 132.3 KW

77


6.1. Design of Gasifier

Operating temperature = 1473K

Operating pressure = 90 atm

Chemical Reactions

C + H2O 2CO

CO + H2O CO2 + H2

C + H2O CO + H2

Rate Determining Step

78


Thermodynamic study of these reactions shows that reaction 3 is

the slowest and rate determining step

C + H2O CO + H2

Order of Reaction

Order of reaction = 2

It is considered that the selected gasifier shows behavior of a

plug flow reactor.

For Plug Flow Reactor

Performance equation is due to second order reaction.

ɽ = dC∫ A / -rA

= CAo dXA / -r∫ A

-rA = K CAo

CA0 = initial concentration (kmol/m3)

CA = final concentration (kmol/m3)

XA = Fractional conversion

-rA = Reaction rate (kmol/m3.s)

k = Rate constant

Reaction Rate

Fractional conversion of C = Xc = 0.8

79


Initial concentration = CCo = 0.413 kmol/m3

Final concentration = CC =?

CC = CCo(1-XA/1+ᶓXA)

ᶓ = Fractional change in volume

ᶓ= (2-2)/2

ᶓ= 0

CC = CCo(1-Xc)

CC = 0.413(1-0.8)

CC = 0.0826 kmole/m3

Since reaction is second order the rate of reaction is

-rc = kCC2

-rc = k[CC][CH2O]

-rc = 1[0.0826][ CH2O]

= 0.0826x1.7859

-rc = 0.1475

PV = nRT

CH2O = P/RT

CH2O = 1234.8 psia/573K (8.314kJ/Kmol)

80


CH2O = 0.2591 psia Kmol/KJ.K

= 1.7859 Kmol/m3

Residence Time

ɽ = CAo ∫00.8dXA / -rA

= 0.413/ 0.1475 (0.8 - 0)

= 2.23 sec

A

emf depends on the shape of the particles. For spherical

particles emf is usually 0.4 – 0.45.If emf is unknown than Wen

and Yu found for many systems:

B

Using A & B and putting values in equation we get

81

(ρg−ρf)g=ρfu0

2

ΦsDpε3 [150 (1−ε)μ

ΦsDpu0ρf+1.75]

Φsεmf3 ≃

114

1−εmfΦS2εmf

3 ≃11

Remf=[ (33.7)2+0.0408Dp3ρf (ρp−ρf)g

μ2 ]−33.7Br=[ Dp3ρf (ρp−ρf)g

μ2 ]


Physical Properties of MSW

Density = ῥ = 120 Kg/ m3

Particle Dia = Dp = 60mm

Gas density =ῥg = 0.212 Kg/m3

Viscosity = Ug = 4.2 * 10-5 Ns/m

Br = 30474067

By putting these values in Equation A we get

Uₒ2 =3.88 m/s

For 2 * 105 > Re > 500

CD = 0.43

Uts = Dp[ 3.1 g (ῥp - ῥg)/ῥg]1/2

By putting values in the eqation we get

Uts = 7.86 m/s

Molar Flow Rate of Produced Gas = 0.05 Kgmol/sec

Volume of Solids

ɽ = Cco V/Fco

Fco = 7.832 * 10-3

V = (7.832 * 10-3) (2.23)/ 0.413

V= 0.0422 m3

82


V1 = 2547/ 25.173

= 0.028 Kgmol/hr

Volume of Produced gas

V2 = (0.0281 kgmol/sec)(22.4m3/kmol)(350psia)(14.7psia)(273)(1473)

=3.499 m3/sec

= (3.499 m3/sec) * 2.23 sec

V2 = 7.8 m3

Diameter of Gasifier

Volume of produced Gas = 7.8 m3

Π D2/4 * L = 7.8

Assuming

L = 4.5D

Π D2/4 (4.5 D) = 7.80

D3 = 2.206

D = 1.30m

Length Of Gasifier

L = 5.85m

10% more margin

L= 6.408m

83


Volume of Gasifier

Total volume of gasifier = volume occupied by solids + Volume

occupied by Produced Gas

= 0.042289 +

7.80

Total volume of Gasifier = 7.842289 m3

Insulation Jacket

Flow rate of gas in = 3791 kg/hr

Let consider the avg. of zone temperature inside the gasifier

Tavg = 1300K

Outlet temperature of gas = 1173K

(3791/3600) x2.1x (1300-1173)

Q = 280.84 KW

Consider water is coming out at 343K

Water remained for cooling

84


Q = m Cp ∆T

280.84 = mH2Ox (4.18)x (343-298)

mH2O = 1.49308 kg/sec

mH2O = 5375.11 kg/hr

Q = UA.ᶿm

A = Q/U ᶿm

The overall heat transfer coefficient for Jacketed vessel for

water and gas system ranges from 20-300 W/m2.0C

ᶿm = T1-T2/ln(T1/ T2)

When

Temperature in combustion zone = 2226.33K

Now

T = 2226.33 – 1173= 1053.33K

ᶿm = (1053.33-45)/ln(1053.33/45)

85


ᶿm = 319.800

So area required

A = Q/U ᶿm

A = 280.84x103/160x319.800

A = 5.489 m2

Thickness of Insulation:

Heat out by gases = 1935.235KW

Assuming 20% heat losses

Heat losses = 387.047 KW = 387047W

Length of Gasifier = 6.408m

Q/L =2 π (T1 – T2)/(ln (r1/ro))/ k1 + (ln (r2 / r1))/k2

Let

r = radius of refractory brick lining

r1 = inner radius of steel shell

r2 = outer radius of steel shell

D = 1.30m

86


ri = D/2 = 1.30/2 =0.65m

Let the thickness of steel shell be 0.02m then

r0 = 0.65+0.02 = 0.67m

k1 = thermal conductivity of bricks (aluminium) = 3.1 W/mK

k2 = thermal conductivity of steel = 4.5 W/mK

387047/6.408 = 2(3.142)(1173-298)/ (ln (0.65/rr))/3.1 +( ln

(0.67/ 0.65))/45

60400.593/1 = 5498.5/ln (0.65/rr)/3.1 + 6.7345x10-4

5498.5 = 60400.59 ln (0.65/rr/3.1) + 60400.59x 6.7345x10-4

5498.5 = 19484.061 ln(0.65/rr) + 40.6767

19484.061 ln(0.65/rr) = 5498.5 – 40.6767

ln(0.65/rr) = 0.28011

0.65/rr = e0.28011

rr/0.65 = 1/1.32327

rr = 0.65/1.32327

Dr = 0.491 m

Dr = 2(rr)

Dr = 2 * 0.491

Dr = 0.982 m

87


Thickness of insulation = ri-rr

= 0.65-0.491

Thickness of insulation = 0.159 m

Volume of Insulating Material:

Amount of material used = Areax Length

= π (Di2-Dr

2)/4 x 6.408

= π (1.302- 0.9822)/4 x 6.0404

= 3.142(1.69-0.9643)/4 x 6.0408

r = 3.443 m2

6.2. Heat Exchanger DesignThere are two purposes for installing the heat exchanger. First we want to heat the feed stream so preheating can reduce the load

88


on the furnace. Second, we want to reduce temperature of stream coming from the reactor. Syngas is on the tube side and water is on the shell side

Flow rate of syngas = 3791.48 kg/hr

Flow rate of water = 7567 kg/hr

Initial temperature of syngas = 1173K

Final temperature of syngas = 873K

Initial Temperature of water = 298K

Final temperature of water = 371K

Sp heat of syngas = 2.03 KJ/Kg-K

Sp of water = 4.18 KJ/Kg-K

Heat Load

Q = mCp (t1- t2)

Q = 3791.48 * 2.03 * (1173 - 873)

Q = 2309011.32/3600

Q = 641.392 KW

89


LMTD

∆tm = ∆t2 - ∆t1 / ln (∆t2 / ∆t1)

= 802 – 575 / ln (802/ 575)

= 682.217 K

Corrected LMTD

R = T1 – T2/t2 – t1

= (1173 - 873) / (371 - 298)

R = 4.10

S = t2 – t1 / T1 – t1

= 371 – 298 / 1173 – 298

S = 0.083

So from Graph Ft = 0.912

Corrected LMTD = ∆tm = ∆tm * Ft

= 409.217 * 0.912

= 373.205°

Suppose,

U = 30.05 W / m2 - K

Q =U A ∆tm

90


A = Q / U ∆tm

A = 641.392/ 30.05 * 682.217

= 0.0313 * 1000 = 31.30 m2

Now we must have shell diameter, no of tubes and length

of heat exchanger and diameter of tubes.

Let,

Outer dia. of the tubes = do = 40 mm = 0.04m

Inner Dia= di = 32mm = 0.032m

Tube Thickness = 4mm = 0.004m

Length of tube = L = 10 m

(suppose)

So,

Area of tube = π * do * L

= π * (0.04) * 10

= 1.256 m2

No. of tubes = Nt= total area / area of one tube

= 31.30/ 1.256

= 25 tubes

Now

91


Bundle Diameter

Db = d0 (Nt / Ki)1/h1

As the shell side fluid is relatively clean use 1,25 triangular

pitch

Db = 40 (25 / 0.249)1/2.207

Db = 42.04mm

Shell side Dia

Bundle dia clearance = 7.84 mm

Shell Dia = Ds = 50.781 mm

Tube Side Coefficient

Mean Temperature = 1173 + 873 / 2

= 1023K

= π/4 (32)2

= 803.84 mm2

Tube per Pass = 25/2 = 12.5 = 13

Total flow area = 13 * 803.84 *10-6

= 0.0104m2

Mass velocity:

92


Gs= 3791.48/ 3600 * 0.0104

= 100 Kg / sec m2

Density = 0.1681 Kgm-3

Linear Velocity= Ut=100/ 0.1681

= 594.88 ms-1

hi= 4200 (1.35 + 0.02t) Ut.8/ di

.2

= 1153.57

Hidi/Kf= jhRe Pr.33 (μ / μw)0.14

Viscosity of syngas = μ= 0.02257 mNs

Thermal Conductivity = Kf = 0.250 W/m ° C

= Re = di U l /μ

= 141780.17

Pr = Cpμ/ K

Pr= 0.5219

Neglect μ/ μio

93


L / di = 10 / 32* 10-3

= 312.5

Using Graph Jh= 5 * 10-3

Now putting the value in Equation we get

Hi = 4470.46 W / m2 °C

Baffle Spacing = Ds / 5 = 10.1562

Lb = 10.1562 mm

Tube Pitch = Pt = 1.25 * 40 = 50 mm

Cross- sectional Area = As = (Pt – do)Dslb/ Pt

= (50 – 40 ) * 50.781 * 10.1562 * 10-6 / 25

= 0.000206 m2

Mass Velocity = Gs= 7567.055 / 3600 * 0.000206

= 10203.68 Kg/ s. m2

EquivelantDia = de= 1.10/ de (Pt2 - 0.917 do

2)

= 1.10/40 (502 – 0.917 (40)2)

= 28.402mm

Mean Shell Side Temp = 371 + 298 / 2 = 334.5 K

Density = 1000 Kgm-3

μ = 0.8904 mNs/ m2

94


Heat capacity = Cp = 4.18 KJ/Kg.K

Thermal Cunductivity = K = 0.611 W / m.K

Re = Gsde/ μ

Re = 25477,223

Pr = Cp H/ K

= 4.18 *03 * 0.8904 * 10-3 / 0.614

= 6.09144

Choosing 25% Baffle cut

JH = 1.7 * 10-2

Without Viscosity Correction term

hs = JH * Re * Pr1/3 / de

hs = 216064 w / m2 °C

Overall Coefficient

1 / Uo= 1 / ho + do ln (do/ di)/2 Kw+ 1 / hi(do/ di)

1/Uo = 1/ 216064 + 0.04 ln (0.04 / 0.032) + 1/ 4470.46 (40/32)

1/Uo = 2608.16 W/m2 °C

Too much above the assumed value

Tube side Re = 141780 and using Graph jf= 4.2 * 10-3

95


Pressure Drop Calculation

For tube side

∆Pt = Np[ 8jf (L/di)(μ/μw) + 2.5 ] ρ ut2/2

= 80 Kpa

6.3. Design of Cyclon Separator

Flow Rate of gas=G = 3791.48 kg/hr

= 1.0532 kg/sec

96


Volume of product gas = 3.4999 m3/sec

Density of product gas =1.0532/3.499

= 0.3010 kg/m3

The optimum velocity of separation having range 10-20

Let

U = 15 m/sec

We know that

G = ῥUA

Inlet Duct Area of gas = G =ῥUA1

1.0532 = (0.3010)

(15)A1

A1 = 0.23m2

Diameter of cyclone:

Area of duct = Ai = 0.5xDcx 0.2Dc

0.23 = Ai = 0.1Dc2

Dc2 = 0.23/0.1

Dc2 = 0.23

Dc = 1.516 m

97


Length of upper section:

Lc = 1.5Dc

Lc = 1.5x1.516

Lc = 2.274 m

Length of lower Section:

Zc = 2.5Dc

Zc = 2.5x1.516

Zc = 3.79 m

Outlet Duct Area of gas:

Do = 0.5Dc

Do = 0.5x1.516

Do = 0.758 m

Ao = π/4 Do2

Ao = 3.14/4 (0.758)2

Ao = 0.451 m2

Dia of Dust Collector:

Dd = 0.357xDc

Dd = 0.357x1.516

Dd = 0.541 m

98


Effective no. of special Paths

The effective no. of special pattern taken by the gas within the

body of cyclone is

U = 15 m/s

N = 3.5

Terminal velocity of smaller particles:

Uo = 0.2

Thickness of Material used

Inner Diameter of duct = 0.765m

Volume of portion A

Volume = π (R2 – r2) * L

V1 = 3.14 * (0.7652 – 0.7582) * 2.274

= 0.076 m3

= 0.076 (3.28)3 = 2.686 ft3

Volume of portion B

V2= 1.489 ft3

99


Total Volume = 1.489 + 2.686 = 44.175 Ft3

Density of stainless steel = 489 and mass of steel used = 4.175 *

489 = 2041.86 lbs

Pressure drop in Cyclon

∆P = ρ /203(U1(1+2∅2(2rtℜ −1))+2 (u2 )2)

U1 = velocity at the inlet = 15 m/s

ῥ = density of gas = 0.3010 kg/m3

Ai = area of inlet duct

=0.5Dc x0.2Dc

=0.1Dc2

Where Dc = 1.516

Ai = 0.1x (1.516)2

Ai = 0.2298 m2

As = cyclone surface Area

As =π x Dcx (Lc+Zc)

Where

Lc = 2.274 m

Zc = 3.79 m

100


So

As = 3.14x1.516x (2.274+3.79)

As = 28.8660 m2

Fc = Friction factor = 0.005 for gases

φ=¿ fcAs/Ai

= (0.005x28.866)/0.2298

φ = 0.62806

rt = radius of circle to which the center line of inlet is

tangential

rt = Dc – (0.2xDc/2)

rt = 1.516 – (0.2x1.516/2) where Dc = 1.516 m

rt = 1.516 – 0.1516

rt = 1.3644 m

re = radius of exit pipe = Do/2 where Do = 0.758 m

re = 0.758/2

re = 0.379 m

Now the ratio

rt/re = 1.3644/0.379

rt/re = 3.6

101


By using rt/re and φ calculate∅ from graph (10.47)

(Reference ?)

∅ = 2

Area of exit pipe = Ae = π x re2

Ae = 3.14x0.3792

Ae = 0.451 m2

U2 = G/ ῥ xAe where ῥ = 0.3010kg/m3 and G = 1.0532 kg/sec

U2 = 1.0532/(0.3010x0.451)

U2 = 7.7583 m/sec

Putting all values and evaluate

∆P = 0.3010/203 (15(1+2(2)2)(2(3.6)-1)+2(7.75)2))

= 1.482x10-3(15(1+8 (6.2) + 2(60.0625)))

= 1.482x10-3[15 (55.8+120.125)]

= 1.482x10-3(2638.875) = 3.91Pa

7.1. Production cost

Total investment required for project

F.C.I = Fixed capital investment

W.C.I = Working capital investment

Total investment = F.C.I + W.C.I

102


7.2. Fixed Capital Investment

Total purchase cost

Total physical plant cost

7.3. Working Capital Investment

The capital which is necessary for the operation of plant is

called working capital investment.

7.4. Production Cost

Variable Cost

Fixed Cost

7.5. Estimation of Fixed Capital Investment

7.5.1. Total purchased cost

This includes cost of gasifier, belt, conveyor, magnetic

separator, and shredder.

7.5.2. Cost of Gasifier

Length of gasifier = 6.408 m

Diameter of gasifier = 1.30 m

Material of construction = stainless steel

Pressure = 30 atm

103


Material factor = 2

Pressure factor = 1.4

Bare cost = 30000$

Purchased cost = 30000x2x1.4

Purchased cost = 84000$

In year 2013

n = 9

Every year 2.5% increase

100% already so 1+ 0.025 = 1.025

Now

Purchased Cost of gasifier = 84000x (1.025)9

Purchased cost of gasifier = 104904$

7.5.3. Heat Exchanger

Heat transfer Area = A = 31.30 m2

Material of construction for shell = carbon steel

Material of construction for tubes = carbon steel

Type = Floating

Head

Pressure = 40 bar

104


Pressure Factor = 1.3

Type Factor = 1.0

Bare Cost = 15000$

Purchased Cost = 15000 x (1.0)

x1.3

Purchased Cost = 19500$

In Year 2013

n = 9

Every year increase 2.5%

100% already so 1+ 0.025 = 1.025

Now

Purchased Cost of Heat Exchanger = 19500x (1.025)9

Purchased Cost of Heat Exchanger = 24352.82$

7.5.4. Knockout Drum

S =1738.9 kg/hr

S =CxS0.6

S = 2900x (1738.9)0.6

S = 211045.45 kg/hr

= 211045.45x (1.025)9

105


= $263566.8552

7.5.5. Scrubber

In 1998 cost was $67700

In 2010 cost of scrubber = (cost of scrubber in 1998) (cost index

in 2010/cost index in 1998)

= 67700x (200/132)

=$102576

7.5.6. Cyclon Separator

In 1990 cost of cyclone separator was $35000

Cost index in 2010/Cost index in 1990 = 1582.9/924

=

1.713

Cost of cyclone in 2013 = $35000x1.713

=

$59955

106


7.5.6. Total Equipment Cost

=

104904.48+24352.82+263566.85+1025.76+59955

Total Equipment Cost = $555355.15

7.6. Estimation of Fixed Capital Cost

Typical factors for estimation of project

Fixed Capital Cost Elements

Items

Factors

Equipment Errection

0.45

Piping

0.45

107


Instrumentation

0.15

Electrical

0.10

Buildings, Process

0.10

Utilities

0.45

Storage

0.20

Site Development

0.05

Auxillary Buildings

0.20

Physical Plant Cost = Total equipment Cost

(1+0.45+0.45+0.15+0.10+0.10+0.45+0.20+0.05+0.20)

Physical Plant Cost = $1749368.7

Fixed Capital Cost

Design & Engineering

0.25

108


Construction Fee

0.05

Contingency

0.10

Fixed Capital = Physical Plant Cost

(1+0.25+0.05+0.10)

= $2449116.213

7.7. Estimation of Working Capital

Working Capital = 5% of fixed capital cost of

fixed capital used

Working Capital = $122455.81

Total Investments

Total Investments required = Fixed Capital + Working Capital

= 2449116.212 +

122455.818

= $2571572.023

Total Operating Cost = $2571572.023

7.8. Summary of Production Costs

7.8.1 Fixed Costs

109


Plant Attainment = 85%

Operating time = 365x0.85

= 310.25 days/yr

= 7446 hr/yr

Maintenance Cost = 10% of fixed Capital

= 0.10x (2449116.212)

= 244911.621

Operating Labour = 15% of total operating Cost

= 0.15x (2571572.023)

= 385735.80

Plant Overhead = 50% of operating labour

= 0.50x (385735.80)

= $192867.9

Capital charges = 10% of fixed Capital

Capital charges = 0.10x2449116.212

Capital charges = $244911.6212

Insurance = 1% of fixed Capital

= 0.01x2449116.212

Insurance = $24491.16212

110


Local taxes = 2% of fixed capital

= 0.02x2449116.212

Local taxes = $48982.3

Royalties and License fee = 5% of fixed capital

= 0.05x2449116.212

Royalties and License fee = $122455.81

Total fixed cost = $1154146.214

7.8.2. Variable Cost

Variable costs = Raw material + Miscellaneous

materials + Utilities

Raw Material Cost

MSW cost used = 1.27$/ton = 3000kg/hr

Total used cost = (3000 kg/hr)(1.27$/ton)

(1ton/1000kg)(7446hr/yr)

Total cost used = 28369.2$/yr

Oxygen Used = 23.907 kgmol

Oxygen cost = 12c/m3

(12c/m3)(1$/100C)(23.907kgmol/hr)(22.4m3/1kmol)(7446hr/year)

= $478494.97

111


Process water:

Cost of water used = 50c/ton

= 8139.86 + 39.845

= 8233.7kgmol/hr

Cost of water used = 148289.02

Total cost of water = (50c/ton)(1$/100c)

(148289.02kg/hr)(1ton/1000kg)(7446hr/yr)

Total cost of water = 552080$/yr

Total Raw Material Cost = 28369.2 + 148289.52 + 552080

Total Raw Material Cost = 728738.24$/yr

7.8.2.1. Miscellaneous Material Cost

Miscellaneous Material Cost = 10% of fixed Capital

=

0.10x2449116.212

Miscellaneous Material Cost = 244911.6212

7.8.2.2. Utilities

112


Utilities Cost = 5% of fixed Capital

= 0.05x2449116.212

= 122455.8

Total Variable Cost = 728738.24 +Miscellaneous Cost

+ Utilities Cost

= 728738.24 +

244911.6212 + 122455.8

Total Variable Cost = $367367.4212

7.8.3. Direct Production Cost

Direct Production Cost = Total Fixed

Cost + Total Variable Cost

Direct Production Cost = 1154146.214+

367367.4212

Direct Production Cost = $1521513.635

Sales Expenses + general OverHeads = 20% of direct

production cost

0.20x1521513.635

Sales Expenses + General Overheads = $304302.727

7.8.4. Annual Production Cost:

113


Total Fixed Cost + Total Variable Cost + Sales Expenses+ General

Overheads

= 1154146.214 + 367367.4212 + 304302.72

= 1825816.355$/year

7.8.5. Production Cost

Production Cost =

(Annual Production Cost)/(Annual Production Rate)

Production Cost =

(1825816.355$/year)(hr/147.028kg)(year/7446hr)

Production Cost =

1.667$/kg

114


8.1. Instrumentation and process controlThe important feature common to all process is that a process is

never in state of static equilibrium except for a very short

period of time. Process is a dynamic entity subject to continual

upset and disturbance which tend to drive it away from the

desired state of equilibrium; the process must then be

manipulated upon or corrected to derive some disturbances bring

about only transient effect of process behavior. These passes

115


away and they never occur again. Others may apply periodic or

cycle forces which may make the process respond in a cyclic or

periodic fashion. Most disturbances are completely random w.r.t

time and show no repetitive pattern. Thus, their occurrence may

be accepted but cannot be predicted at any particular time. If a

process is to operate efficiently the disturbances process must

be controlled.

A process is design for a particular objective or output and

is then found, sometimes by trial and error ans some time by

previous experience that control of a particular variable

associated with some stages of the process is necessary to

achieve the desired efficiency.

Each process will have associated with it a number of

variables which are likely to change at random. Each such change

will lead to changes in the dependent variable of the process.

One of which is selected as being indicative of successful

operation. One of the input variables will be manipulate d to

cause further changes in the output variables to restore the

optimal condition.

Process may be controlled more precisely to give more uniform and

high quality products by the application of automatic control,

which often leads to highest profits. Additionally, process which

response too rapidly, and is to be controlled by human operators,

can be controlled automatically, automatic control is also

beneficial in certain remote, hazardous or routine operations.

116


Automatically control processing systems which may too large and

too complex for effective direct human control.

Sensors to measure process conditions and valves to

influence process operations are essential for all aspects of

engineering practice. While sensors and valves are important in

all aspects of engineering, they assume greatest importance in

the study of automatic control, which is termed as process

control when applied in the process industries. Process control

deals with the regulation process by applying the feedback

principle using various computing devices, principally digital

computation. Process control requires sensors for measuring

variables and valves for implementing decisions; therefore, the

presentation of this material is designed to complement other

learning topics in process control.

Since successful process control requires appropriate

instrumentation, engineers should understand the principals of

common instruments introduced in this section. The descriptions

in this section cover the basic principles and information on the

performance for standard, commercially available instruments.

Thus, selection and sizing of standard equipment is emphasized,

not designing equipment “from scratch” [40].

8.1.1. Elements of automatic process

control

117


In the process control, four basic elements are normally

involved: process, measurement, evaluation (with a controller),

and control element (Fig8.1).

Fig

8.1: Basic control elements [40]

8.1.2. PROCESS

If we try to control the temperature during ladle furnace steel

making, the ladle furnace steelmaking can be abstracted as a

Process. Many dynamic variables may be involved in a process, and

118


it may be desirable to control all those variables at the same

time. There are single-variable processes, in which only one

variable is to be controlled. However, most industrial processes

are multivariable processes, in which many variables, perhaps

interrelated, may require regulation.

8.1.3. MEASUREMENT

Control is in nature to effect control of a dynamic variable in a

process. To perform control, we have to perform measurement, so

that we can have information on the variable itself. In general,

a measurement refers to the transduction of the variable into

some corresponding analog of the variable, such as a pneumatic

pressure, an electrical voltage, or current. A transducer is a

device that performs the initial measurement and energy

conversion of a dynamic variable into analogous electrical or

pneumatic information. Further transformation or signal

conditioning may be required to complete the measurement

function. The result of the measurement is a transformation of

the dynamic variable into some proportional information in a

useful form required by the other elements in the process-control

loop.

8.1.4. EVALUATION

The next step in the process-control sequence is to examine the

measurement and determine what action, if any, should be taken. A

controller is commonly used in this step to perform the

119


evaluation. The evaluation may be performed by an operator, or by

(electronic/pneumatic) signal processing, or by a computer.

Computer use is growing rapidly in the field of process control

because it is easily adapted to the decisionmaking operations and

because of its inherent capacity to handle control of

multivariable systems. The controller requires an input of both a

measured representation of the dynamic variable and a

representation of the desired value of the variable, expressed in

the same terms as the measured value. The desired value of the

dynamic variable is referred to as the setpoint. Thus, the

evaluation consists of a comparison of the controlled variable

measurement and the setpoint and a determination of action

required bring the controlled variable to the setpoint value.

8.1.5. CONTROL ELEMENT

The final element in the process-control loop is the device that

exerts a direct influence on the process, that is, that provides

those required changes in the dynamic variable to bring it to the

setpoint condition. This element accepts an input from the

controller, which is then transformed into some proportional

operation performed on the process. In our previous example, the

control element is the value that adjusts the outflow of fluid

from the tank. This element is also referred to as the final

control element [39].

8.1.6. Block Diagram

120


Each element in a process-control loop is represented in a block

diagram a separate step. Figure 1 is actually a block diagram

constructed from the element defined in the previous section. The

controlled dynamic variable in the process is denoted by C in

this diagram, and the measured representation of the controlled

dynamic variable is labeled CM. The controlled variable setpoint

labeled CSP and must be expressed in the same proportion as that

provided the measurement function.

In many cases, the controller block is presented in a fashion

that carr over from electronic feedback or servo analysis. This

presents the evaluation operation as a summation point that

outputs an error signal E = CM - CSP to the controller for

comparison and action.

To further illustrate, the block diagram concept in Fig. 8.2

shows a block diagram for a typical flow control system. In this

example, the dynamic variable is the flow rate that is converted

to electric current as an analog. The process is the flow, and

the measurement is to determine the difference of pressure. With

the setpoint in the controller, the flow process is controlled

through the control element, the valve [41].

121


Fig 8.2: A process-control system to regulate flow and the

corresponding block diagram [41]

8.2. Sensors

A sensor (also called detector) is a converter that measures a

physical quantity and converts it into a signal which can be read

by an observer or by an (today mostly electronic) instrument. For

example, a mercury-in-glass thermometer converts the measured

temperature into expansion and contraction of a liquid which can

be read on a calibrated glass tube. A thermocouple converts

temperature to an output voltage which can be read by a uy7. For

accuracy, most sensors are calibrated against known standards.

Sensors are used in everyday objects such as touch-sensitive

elevator buttons (tactile sensor) and lamps which dim or brighten

by touching the base. There are also innumerable applications for

sensors of which most people are never aware. Applications

122

http://en.wikipedia.org/wiki/Tactile_sensor

http://en.wikipedia.org/wiki/Standard_(metrology)

http://en.wikipedia.org/wiki/Calibration

http://en.wikipedia.org/wiki/Voltmeter

http://en.wikipedia.org/wiki/Thermocouple

http://en.wikipedia.org/wiki/Mercury-in-glass_thermometer

http://en.wikipedia.org/wiki/Electronics

http://en.wikipedia.org/wiki/Physical_quantity

http://en.wikipedia.org/wiki/Energy_conversion


include cars, machines, aerospace, medicine, manufacturing and

robotics.

A sensor is a device which receives and responds to a signal when

touched. A sensor's sensitivity indicates how much the sensor's

output changes when the measured quantity changes. For instance,

if the mercury in a thermometer moves 1 cm when the temperature

changes by 1 °C, the sensitivity is 1 cm/°C (it is basically the

slope Dy/Dx assuming a linear characteristic). Sensors that

measure very small changes must have very high sensitivities.

Sensors also have an impact on what they measure; for instance, a

room temperature thermometer inserted into a hot cup of liquid

cools the liquid while the liquid heats the thermometer. Sensors

need to be designed to have a small effect on what is measured;

making the sensor smaller often improves this and may introduce

other advantages. Technological progress allows more and more

sensors to be manufactured on a microscopic scale as micro

sensors using MEMS technology. In most cases, a micro sensor

reaches a significantly higher speed and sensitivity compared

with macroscopic approaches [42].

8.2.1. Temperature sensors

Temperature control is important for separation and reaction

processes, and temperature must be maintained within limits to

ensure safe and reliable operation of process equipment.

123

http://en.wikipedia.org/wiki/Macroscopic

http://en.wikipedia.org/wiki/Microelectromechanical_systems

http://en.wikipedia.org/wiki/Microscopic_scale


Temperatures can sense by many methods; several of the more

common are described below [43]

Table no.8.1: Summary of temperature sensors [43]

Criteria Thermocouple RTD Thermistor

Temperature

range

Very wide Wide Narrow

124


-450°F

+4200°F

-400°F +1200°F -100°F

+500°F

Interchangeab

ility

Good Excellent Poor to fair

Long term

Stability

Poor to fair Good Poor

Accuracy Medium High Medium

Repeatability Fair Excellent Fair to good

Sensitivity

(output)

Low Medium Very high

Response Medium to

fast

Medium Medium to

fast

Linearity Fair Good Poor

Self heating No Very low to

low

High

Point(end)

sensitive

Excellent Fair Good

Lead effect High Medium Low

Size/

packaging

Small to

large

Medium to

small

Small to

medium

125


Table no. 8.2. Temperature sensors advantages and disadvantages[43]

Sensors Advantages Disadvantages

Thermocoup

le

No resistance lead

wire problems

Fastest response

Simple, rugged

Inexpensive

High temperature

operation

Point temperature

sensing

Non-linear

Low voltage

Least stable,

repeatable

Least sensitive

RTD

Most stable,

accurate

Contamination

resistant

More linear than

thermocouple

Current source

required

Self-heating

Slow response time

Low sensitivity to

small temperature

126


Area temperature

sensing

Most repeatable

temperature

measurement

changes

8.2.2 Flow sensors

A flow sensor is a device for sensing the rate of fluid flow.

Typically a flow sensor is the sensing element used in a flow

meter, or flow logger, to record the flow of fluids. As is true

for all sensors, absolute accuracy of a measurement requires

functionality for calibration.

There are various kinds of flow sensors and flow meters,

including some that have a vane that is pushed by the fluid, and

can drive a rotary potentiometer, or similar devices.

127

http://en.wikipedia.org/w/index.php?title=Rotary_potentiometer&action=edit&redlink=1


http://en.wikipedia.org/wiki/Fluid

http://en.wikipedia.org/wiki/Flow_meter

http://en.wikipedia.org/wiki/Flow_meter

http://en.wikipedia.org/wiki/Sensor

http://en.wikipedia.org/wiki/Rate_of_fluid_flow


Other flow sensors are based on sensors which measure the

transfer of heat caused by the moving medium. This principle is

common for micro sensors to measure flow.

Flow meters are related to devices called velocimeters that

measure velocity of fluids flowing through them. Laser-based

interferometry is often used for air flow measurement, but for

liquids, it is often easier to measure the flow. Another approach

is Doppler-based methods for flow measurement. Hall Effect

sensors may also be used, on a flapper valve, or vane, to sense

the position of the vane, as displaced by fluid flow.

128

http://en.wikipedia.org/wiki/Hall_effect_sensor

http://en.wikipedia.org/wiki/Hall_effect_sensor

http://en.wikipedia.org/wiki/Photoacoustic_Doppler_effect

http://en.wikipedia.org/wiki/Air

http://en.wikipedia.org/wiki/Interferometry

http://en.wikipedia.org/wiki/Velocity

http://en.wikipedia.org/wiki/Velocimetry

http://en.wikipedia.org/wiki/Microsensor


Table no.8.3: Summary of flow sensors [44]

Sensor Visco

us

liqui

d

Slurr

y

Gas Output Pressu

re

loss

Accura

cy

%

full

scale

Full

range

Orifice Limite

d

Poor Good Squareroot

characteristic

High ±0.5 to

±2%

10-3 to

5.5×103

m3/hr

Venturi Limit

ed

Limit

ed

Goo

d

--do-- Minima

l

±0.5

to ±3%

1 to

5.5×103 m3/hr

Flow nozzle Limit

ed

Limit

ed

Goo

d

--do-- Minima

l

±0.5

to ±3%

1 to

5.5×103 m3/hr

Pitot tube Poor Poor Goo

d

--do-- Poor ±5to

±10%

10 to

104

m3/hrElectromagn

etic

Good Good Goo

d

Linear Minima

l

±2to

±5%

5.5×104 to

4.95×1

03

m3/hrVariable

area meter

Limit

ed

Limit

ed

Goo

d

Linear Averag

e

±0.5% 10-7to

5.5×103 m3/hr

129


Positive

displacemen

t

Good Good Goo

d

Linear Minima

l

±0.5

to ±1%

10-5to

5×102

m3/hrTurbine Limit

ed

Poor Poo

r

Linear Minima

l

±2to

±5%

05 to

4.95×1

02

m3/hr

8.2.3. Pressure sensors

A pressure sensor measures pressure, typically of gases or

liquids. Pressure is an expression of the force required to stop

a fluid from expanding, and is usually stated in terms of force

per unit area. A pressure sensor usually acts as a transducer; it

generates a signal as a function of the pressure imposed. For the

purposes of this article, such a signal is electrical.

Pressure sensors are used for control and monitoring in thousands

of everyday applications. Pressure sensors can also be used to

indirectly measure other variables such as fluid/gas flow, speed,

water level, and altitude. Pressure sensors can alternatively be

called pressure transducers, pressure transmitters, pressure

senders, pressure indicators and piezometers, manometers, among

other names.130

http://en.wikipedia.org/wiki/Function_(mathematics)

http://en.wikipedia.org/wiki/Transducer

http://en.wikipedia.org/wiki/Liquids

http://en.wikipedia.org/wiki/Gas

http://en.wikipedia.org/wiki/Pressure


Pressure sensors can vary drastically in technology, design,

performance, application suitability and cost. A conservative

estimate would be that there may be over 50 technologies and at

least 300 companies making pressure sensors worldwide.

There is also a category of pressure sensors that are designed to

measure in a dynamic mode for capturing very high speed changes

in pressure. Example applications for this type of sensor would

be in the measuring of combustion pressure in an engine cylinder

or in a gas turbine. These sensors are commonly manufactured out

of piezoelectric materials such as quartz.

Some pressure sensors, such as those found in some traffic

enforcement cameras, function in a binary (on/off) manner, i.e.,

when pressure is applied to a pressure sensor, the sensor acts to

complete or break an electrical circuit. These types of sensors

are also known as a pressure switch.

Table no. 8.4: Summary of pressure sensor [45]

Sensor Limits of

applicati

Accuracy Dynamics Advantag

e

Disadvant

age

131

http://en.wikipedia.org/wiki/Pressure_switch

http://en.wikipedia.org/wiki/Traffic_enforcement_camera

http://en.wikipedia.org/wiki/Traffic_enforcement_camera

http://en.wikipedia.org/wiki/Piezoelectric


onBourdon “c” Up to 100

MPa

1-5% of

full

span

-

-

- low

cost

with

reasonab

le

accuracy

-wide

limits

of

applicat

ions

-

hysteresi

s

-

affected

by shock

and

vibration

Spiral Up to 100

MPa

0.5% of

full

span

-

Helical Up to 100

MPa

0.5-1%

of full

span

-

-low

cost

-

differen

tial

pressure

- smaller

pressure

range

-

Temperatu

re

compensat

ion

needed

Bellows Typically

vacuum to

500 kPa

0.5% of

full

span

-

Diaphragm Up to 60

kPa

0.5-1.5%

of full

span

- - very

small

span

possible

- usually

limited

to low

pressure

(i.e.

132


below

8kPa)Capacitance/

Inductance

Up to 30

kPa

0.2% of

full

span

- - -

Resistive/

strain gauge

Up to 100

kPa

0.1-1%

of full

span

Fast - large

range of

pressure

-

Piezoelectr

ic

- 0.5% of

full

span

Very

fast

-Fast

dynamics

-

Sensitive

to -

temperatu

re

changes

8.2.4. Level sensor

Level sensors detect the level of substances that flow, including

liquids, slurries, granular materials, and powders. Fluids and

fluidized solids flow to become essentially level in their

containers (or other physical boundaries) because of gravity

whereas most bulk solids pile at an angle of repose to a peak.

133

http://en.wikipedia.org/wiki/Gravity

http://en.wikipedia.org/wiki/Wiktionary

http://en.wikipedia.org/wiki/Granular

http://en.wikipedia.org/wiki/Slurry

http://en.wikipedia.org/wiki/Liquids

http://en.wikipedia.org/wiki/Sensors


The substance to be measured can be inside a container or can be

in its natural form (e.g., a river or a lake). The level

measurement can be either continuous or point values. Continuous

level sensors measure level within a specified range and

determine the exact amount of substance in a certain place, while

point-level sensors only indicate whether the substance is above

or below the sensing point. Generally the latter detect levels

that are excessively high or low.

There are many physical and application variables that affect the

selection of the optimal level monitoring method for industrial

and commercial processes. The selection criteria include the

physical: phase (liquid, solid or slurry), temperature, pressure

or vacuum, chemistry, dielectric constant of medium, density

(specific gravity) of medium, agitation (action), acoustical or

electrical noise, vibration, mechanical shock, tank or bin size

and shape. Also important are the application constraints: price,

accuracy, appearance, response rate, ease of calibration or

programming, physical size and mounting of the instrument,

monitoring or control of continuous or discrete (point) levels[43].

134

http://en.wikipedia.org/wiki/Programming


http://en.wikipedia.org/wiki/Shock_(mechanics)

http://en.wikipedia.org/wiki/Vibration

http://en.wikipedia.org/wiki/Noise

http://en.wikipedia.org/wiki/Agitation_(action)

http://en.wikipedia.org/wiki/Density

http://en.wikipedia.org/wiki/Transmission_medium

http://en.wikipedia.org/wiki/Dielectric_constant

http://en.wikipedia.org/wiki/Chemistry

http://en.wikipedia.org/wiki/Vacuum


http://en.wikipedia.org/wiki/Temperature

http://en.wikipedia.org/wiki/Phase_(matter)


Table no.8.5: Summary of level sensor [46]

Sensor Limits of

applicati

ons

Accuracy Dynamics Advantage

s

Disadvanta

ges

Float Up to 1 m - - -can be

used for

switches

-cannot be

used for

sticky

fluids

which coat

the floatDisplacem

ent

0.3-3 m - - -good

accuracy

-limited

range

-cost of

external

mounting

for high

pressure

Different

ial

Essential

ly no

- - -good

accuracy

-large

range

-assumes

constant

density

-sealed

135


pressure upper

limit

-

applicabl

e to

slurries

with the

use of

sealed

lines

lines

sensitive

to

temperatur

e

Capacitan

ce

Up to 30

m

- - -

applicabl

e to

slurries

- level

switch

for many

difficult

fluids

-affected

by density

variations

8.3. On stream analyzers

The term analyzer refers to any sensor that measures a physical

property of the process material. This property could relate to

136


purity (e.g., mole % of various components), a basic physical

property (e.g., density or viscosity), or an indication of

product quality demanded by the customers in the final use of

material (e.g., gasoline octane for fuel heating value).

Analyzers rely on a wide range of physical principals; their

unifying characteristics is a greatly increased sensor complexity

when compared with the saturated temperature, flow, pressure and

level (T,F,P and L) sensors. In many situations, the analyzers is

located in a centralized laboratory and processes samples

collected at the plant and transported to the laboratory. This

procedure reduces the cost of analyzer, but it introduces long

delays before a measurement is available for use in plant

operations.

8.4. Control valves

Control valves are valves used to control conditions such as

flow, pressure, temperature, and liquid level by fully or

partially opening or closing in response to signals received from

controllers that compare a "setpoint" to a "process variable"

whose value is provided by sensors that monitor changes in such

conditions.[47]

The opening or closing of control valves is usually done

automatically by electrical, hydraulic or pneumatic actuators.

Positioners are used to control the opening or closing of the

actuator based on electric, or pneumatic signals. These control

137

http://en.wikipedia.org/wiki/Pneumatic_actuators

http://en.wikipedia.org/wiki/Hydraulic

http://en.wikipedia.org/wiki/Electrical

http://en.wikipedia.org/wiki/Control_valves#cite_note-1

http://en.wikipedia.org/wiki/Sensors

http://en.wikipedia.org/wiki/Liquid

http://en.wikipedia.org/wiki/Temperature


http://en.wikipedia.org/wiki/Fluid_dynamics

http://en.wikipedia.org/wiki/Valves


signals, traditionally based on 3-15psi (0.2-1.0bar), more common

now are 4-20mA signals for industry, 0-10V for HVAC systems, and

the introduction of "Smart" systems, HART, Fieldbus Foundation,

and Profibus being the more common protocols.

A control valve consists of three main parts in which each part

exist in several types and designs:

Valve's actuator

Valve's positioned

Valve's body

9.1. Future consideration

We have made the design of gasification plant to the best of our

knowledge. Although the energy balance around the plant yielded a

net positive energy of MW/hr, but after detailed analysis,

thorough study and research, we have come to a conclusion that

may be some aspects, which can be modified in order to improve

the overall efficiency of the plant. These can be summarized as

under:

1. The increased amounts of CO2 in the synthesis gas are big

factor in its relatively low heating value. This problem can

be overcome by feeding the gasifier with coal or coke along

with MSW. This will favor the following reaction:

138

http://en.wikipedia.org/wiki/Profibus

http://en.wikipedia.org/wiki/Fieldbus


CO2 + C

2CO

This will decrease the CO2 contents of the synthesis gas and will

ultimately increase the calorific value of synthesis gas.

2. Methane is a high calorific value gas. In the gasification

process, it yielded by the following reaction:

CO + 3H2

C2H4 + H2O

The above depicted reaction is a shift reaction in the forward

direction, depending on the pressure. Increasing the pressure

inside the gasifier can eventually increase the yield of methane

contents of the synthesis gas.

3. In the gasifier plant we have designed, the furnace is the

most energy consuming unit. This can be lower down by

heating the gasifier externally, using a part of synthesis

gas produced.

4. The synthesis gas produced, can be used to generate the

following fuels by Fischer-Tropsc process:

139


Methanol

Bio-diesel

Petroleum like fuels

140


References

1- P Jayarama Reddy “municipal solid waste management,

processing energy recovery, global examples”

2- http://news.bbc.co.uk/2/hi/science/nature/5054052.stm

3- Draft (guideline for solid waste management) june 2005,

Pakistan Environmental Protection Agency, JICA, UNDP, page

no. 5-16.

4- http://www.Pakistantoday.com.pk/2012/15/comment/editors-

mail/alarming-population-growth/

5- SHARISH, Solid Waste and its Management ppt.

6- Khan, Azher Uddin, “Evaluation of industrial Environmental

Management-Pakistan,”May,(2010

7- Khwaja, Mahmood A., Shahenn, Nazma and Yasmeen,

Farzana,”Mapping of Chemically polluted sites in

Pakistan,”SDPI, Islamabad, 2010(in preparation)

8- http://tribune.com.pk/story/26620/pakistan-produces-250000-tons-

of-medical-waste-annually/

9- Dr. Jeong, Hoi-seong & Dr. Kim, Kwang-Yim “ Koica-world

bank joint study on solid waste management in Punjab,

Pakistan

10- State Bank of Pakistan “Waste Management: Recent

Developments in Pakistan”.

11- Brief report on solid waste management in Pakistan

12- NW BIORENEW

141

http://nwbiorenew.com/Technologies.htm

http://tribune.com.pk/story/26620/pakistan-produces-250000-tons-of-medical-waste-annually/

http://tribune.com.pk/story/26620/pakistan-produces-250000-tons-of-medical-waste-annually/

http://news.bbc.co.uk/2/hi/science/nature/5054052.stm


13- Alexander Klein and Nickolas J. Themelis “Energy

Recovery from Municipal Solid Waste by Gasification.

14- "Waste incineration". Europa. October 2011.

15- "DIRECTIVE 2000/76/EC OF THE EUROPEAN PARLIAMENT AND OF

THE COUNCIL of 4 December 2000 on the incineration of

waste". European Union. 4 December 2000.

16- Waste to Energy in Denmark by Ramboll Consult

17- Emissionsfaktorer og emissionsopgørelse for decentral

kraftvarme, Kortlægning af emissioner fra decentrale

kraftvarmeværker, Ministry of the Environment of Denmark

2006 (in Danish)

18- Waste Gasification: Impacts on the Environment and

Public Health

19- Rosenthal, Elisabeth (12 April 2010). "Europe Finds

Clean Energy in Trash, but U.S. Lags". The New York Times.

20- Burning of wood , InnoFireWood's website. Accessed on

2010-02-06.

21- Moustakasa, K.; Fattab, D.; Malamisa, S.; Haralambousa,

K.; Loizidoua, M. (2005-08-31). "Demonstration plasma

gasification/vitrification system for effective hazardous

waste treatment". Journal of Hazardous Materials 123 (1–3): 120–

126. doi:10.1016/j.jhazmat.2005.03.038. (subscription

required). Retrieved 2012-03-08.

22- "How Stuff Works- Plasma Converter". Retrieved 2012-

09-09.

142

http://science.howstuffworks.com/environmental/energy/plasma-converter.htm

http://dx.doi.org/10.1016%2Fj.jhazmat.2005.03.038

http://en.wikipedia.org/wiki/Digital_object_identifier

http://en.wikipedia.org/w/index.php?title=Journal_of_Hazardous_Materials&action=edit&redlink=1

http://www.sciencedirect.com/science/article/pii/S0304389405001585



http://virtual.vtt.fi/virtual/innofirewood/stateoftheart/database/burning/burning.html

http://www.nytimes.com/2010/04/13/science/earth/13trash.html?scp=1&sq=trash&st=cse

http://www.nytimes.com/2010/04/13/science/earth/13trash.html?scp=1&sq=trash&st=cse

http://www.bredl.org/pdf/wastegasification.pdf

http://www.bredl.org/pdf/wastegasification.pdf

http://en.wikipedia.org/wiki/Ministry_of_the_Environment_of_Denmark

http://www2.dmu.dk/1_viden/2_Publikationer/3_fagrapporter/rapporter/FR442.pdf

http://www2.dmu.dk/1_viden/2_Publikationer/3_fagrapporter/rapporter/FR442.pdf

http://en.wikipedia.org/wiki/Ramboll

http://www.zmag.dk/showmag.php?mid=wsdps

http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2000:332:0091:0111:EN:PDF



http://europa.eu/legislation_summaries/environment/waste_management/l28072_en.htm


23- Kalinenko, R. A.; Kuznetsov, A. P.; Levitsky, A. A.;

Messerle, V. E.; Mirokhin, Z. B.; Polak; Sakipov, L. S.;

Ustimenko, A. B. (1993). "Pulverized coal plasma

gasification". Plasma Chemistry and Plasma Processing 13 (1): 141–

167. doi:10.1007/BF01447176. (subscription required).

Retrieved 2012-03-08.

24- Messerle, V. E.; Ustimenko, A. B. (2007). "Solid Fuel

Plasma Gasification". In Syred, Nick; Khalatov, Artem.

Advanced Combustion and Aerothermal Technologies. Environmental Protection

and Pollution Reductions. Springer Netherlands. pp. 141–156.

doi:10.1007/978-1-4020-6515-6. ISBN 978-1-4020-6515-6.

(subscription required). Retrieved 2012-03-08.

25- "The Recovered Energy System: Discussion on Plasma

Gasification". Retrieved 2008-10-20.

26- Bratsev, A. N.; V. E. Popov, A. F. Rutberg, S. V.

Shtengel’ (2006). "A Facility for Plasma Gasification of

Waste of Various Types". High temperature 44 (6): 823–828.


27- Huang, H.; Lan Tang, C. Z. Wu (2003). "Characterization

of Gaseous and Solid Product from Thermal Plasma Pyrolysis

of Waste Rubber". Environmental science & technology 37 (19): 4463–

4467. Retrieved 2013-03-12.

28- "Biomass Program, direct Hydrothermal Liquefaction" . US

Department of Energy. Energy Efficiency and Renewable

Energy. 2005-10-13. Retrieved 2008-01-12.

143

http://en.wikipedia.org/w/index.php?title=2005-10-13&action=edit&redlink=1

http://www1.eere.energy.gov/biomass/pyrolysis.html#thermal

http://pubs.acs.org/doi/abs/10.1021/es034193c



http://www.springerlink.com/index/R82T86R6625446Q8.pdf

http://www.springerlink.com/index/R82T86R6625446Q8.pdf

http://www.recoveredenergy.com/d_plasma.html

http://www.recoveredenergy.com/d_plasma.html

http://en.wikipedia.org/wiki/Special:BookSources/978-1-4020-6515-6

http://en.wikipedia.org/wiki/International_Standard_Book_Number

http://dx.doi.org/10.1007%2F978-1-4020-6515-6


http://www.springerlink.com/content/n0u2236g59w08236/

http://www.springerlink.com/content/n0u2236g59w08236/

http://dx.doi.org/10.1007%2FBF01447176


http://en.wikipedia.org/w/index.php?title=Plasma_Chemistry_and_Plasma_Processing&action=edit&redlink=1

http://www.springerlink.com/content/qx506h01079341l5/

http://www.springerlink.com/content/qx506h01079341l5/


29- Werner Kossmann, UtaPönitz, Stefan Habermehl “Biogas

Digest volume 1”

30- Anaerobic digestion , waste.nl. Retrieved 19.08.07

31- Klein, Donald W.; Lansing M.; Harley, John (2006).

Microbiology (6th ed.). New York: McGraw-Hill. ISBN 978-0-07-

255678-0.

32- Dickinson, J. R. (1999). "Carbon metabolism". In J. R.

Dickinson and M. Schweizer. The metabolism and molecular physiology

of Saccharomyces cerevisiae. Philadelphia, PA: Taylor & Francis.

ISBN 978-0-7484-0731-6.

33- Voet, Donald & Voet, Judith G. (1995). Biochemistry (2nd

ed.). New York, NY: John Wiley & Sons. ISBN 978-0-471-58651-

7.

34- Enviros (2006) Mechanical biological treatment website,

www.mbt.landfill-site.com, Waste Technology Home Page,

Accessed 22.11.06

35- Juniper (2005) MBT: A Guide for Decision Makers –

Processes, Policies & Markets, www.juniper.co.uk, (Project

funding supplied by Sita Environmental Trust), Accessed

22.11.06

36- Velis C. et al. (2010) Production and quality assurance

of solid recovered fuels using mechanical—biological

treatment (MBT) of waste: a comprehensive assessment

37- http://www.altenergymag.com/emagazine.php?

issue_number=09.06.01&article=zafar

144

http://www.altenergymag.com/emagazine.php?issue_number=09.06.01&article=zafar

http://www.altenergymag.com/emagazine.php?issue_number=09.06.01&article=zafar

http://www.tandfonline.com/doi/abs/10.1080/10643380802586980



http://www.juniper.co.uk/Publications/downloads.html

http://www.juniper.co.uk/Publications/downloads.html

http://www.mbt.landfill-site.com/




http://en.wikipedia.org/wiki/John_Wiley_%26_Sons



http://en.wikipedia.org/wiki/Taylor_%26_Francis




http://en.wikipedia.org/wiki/McGraw-Hill

http://highered.mcgraw-hill.com/sites/0072556781/information_center_view0/

http://www.waste.nl/content/download/472/3779/file/WB89-InfoSheet(Anaerobic%20Digestion).pdf


38- Kamka, Frank; Jochmann, Andreas (June 2005).

"Development Status of BGL-Gasification" (PDF).

International Freiberg Conference on IGCC & XtL Technologies

speaker Lutz Picard.

http://www.iec.tu-freiberg.de/conference/conference_05/pdf/

21_Picard.pdf. Retrieved 2011-03-19.

39- http://www.fao.org/docrep/t0512e/T0512e0a.htm

40- Smith and Corpio “Process Dynamics and Control.

41- Curtis D. Johnson: Process Control Instrumentation

Technology, 3rd Ed. John Wiley & Sons, Inc., 1988. ISBN 0-

471-85340-2.

42- M. Kretschmar and S. Welsby (2005), Capacitive and

Inductive Displacement Sensors, in Sensor Technology

Handbook, J. Wilson editor, Newnes: Burlington, MA

43- http://www.watlow.com/reference/guides/0205.cfm

44- http://enggyd.blogspot.com/2011/04/comparison-of-flow-

meters.html

45- Elastic hologram' pages 113-117, Proc. of the IGC 2010,

ISBN 978-0-9566139-1-2 here:

http://www.dspace.cam.ac.uk/handle/1810/225960

46- Sapcon Instruments. "Fly Ash Level Detection?".


47- Control valve tutorials Tutorials covering the sizing,

capacity and characteristics of control valves. Actuators,

positioners

145

http://www.spiraxsarco.com/resources/steam-engineering-tutorials/control-hardware-el-pn-actuation.asp

http://www.sapconinstruments.com/articles/article1.html

http://www.dspace.cam.ac.uk/handle/1810/225960

http://en.wikipedia.org/wiki/Special:BookSources/9780956613912

http://enggyd.blogspot.com/2011/04/comparison-of-flow-meters.html

http://enggyd.blogspot.com/2011/04/comparison-of-flow-meters.html

http://www.watlow.com/reference/guides/0205.cfm

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