Converting Waste Agricultural Biomass into Energy … Waste Agricultural Biomass into Energy Source Report on Assessment of Environmentally Sound Technologies (ESTs) for Waste Agricultural

Converting Waste Agricultural Biomass into Energy Source

Report on

Assessment of Environmentally Sound

Technologies (ESTs) for

Waste Agricultural Biomass (WAB)

In District Sanghar, Pakistan

By: Prof. Dr. Rasool Bux Mahar

Institute of Environmental Engineering & Management Mehran University of Engineering & Technology

Jamshoro, Pakistan

United Nations Environmental Programme International Environmental Technology Centre

Osaka/Shiga, Japan

2

PREFACE

Rapid increase in demand and consumption of fossil fuels and its consequent

impact on climate change and environment has put greater emphasis on development

of alternative and renewable sources of energy. Waste biomass, as a renewable energy

source, presents a viable solution for meeting our energy demands. It addresses the

climate change issues as well as reduces our dependence on fossil fuels. In developing

countries this could be developed as a versatile source of energy for domestic as well

as industrial/commercial purposes.

Biomass is a broad term, which generally refers to any plant or animal matter.

The main categories of biomass are; agriculture residues (referred to hereafter as

waste agricultural biomass), forestry residues, wood (both from forests and firewood

plantations), animal residues, organic wastes from cities and dwellings. The

discussions in this guideline pertain only to waste agricultural biomass.

In this Report district Sanghar, which is one of the largest districts of province

Sindh, Pakistan was selected as the study area for the assessment of the technology

for converting waste agricultural biomass (WAB) into energy/ resource.

This report is divided into three parts. Part- I is Introduction, Part- II is

proposed environmentally sound technologies (ESTs) for converting WAB into

energy/resource in Sanghar and Part- III is assessment of environmentally sound

technologies.

3

TABLE OF CONTENTS Description Page

Preface 2 Part- I INTRODUCTION 1.1 Biomass

6

1.2 Biomass Energy 7 1.3 Waste Agricultural Biomass (WAB) 7 1.3.1 Field residue 7 1.3.2 Process residue 7 1.4 Why To Use Waste Agricultural Biomass? 7 1.5 Study Area 8

1.6 Environmentally Sound Technologies (ESTs) 10 1.7 Environmental Technology Assessment (EnTA) 10 1.8 Purpose and Scope EnTA 11 1.9 Criteria for Critical Analysis of EST

11

Part- II PROPOSED ENVIRONMENTALLY SOUND TECHNOLOGIES (ESTS) FOR CONVERTING WAB INTO ENERGY/RESOURCE IN SANGHAR

2.1 Proposed Technologies for District Sanghar 14 2.2 Direct Combustion 14 2.3 Biomass Pellets 16 2.3.1 Description of the Pelleting Process 17 2.3.2 Feedstock Grinding 18 2.3.3 Moisture Control 18 2.3.4 Extrusion 18 2.3.5 Cooling 19 2.3.6 Packaging 19 2.4 Energy Requirements For Pellet Manufacture 19 2.6 Composting 19 2.7 Advantages Of Composting 21 2.8 Disadvantages Of Composting 21 2.9 Composting Systems 21 2.9.1 Windrow/pile Composting – Turning 22 2.9.2 Windrow/pile Composting – Active Aeration, 22 2.9.3 Windrow/pile Composting – Passive Aeration, 23 2.9.4 Windrow/pile Composting – Static Piles, not Aerated 23 2.9.5 In-vessel Composting 24 2.9.6 Vermi-composting 24

2.10 Gasification 24 2.11 Principle Of Operation 24 2.12 History On Gasification 27 2.13 Types Of Gasifiers 27 2.13.1 Moving Bed Gasifier 27 2.13.2 Entrained Flow Gasifier 28 2.13.3 Fluidized Bed Gasifier 29

4

2.14 Common Biomass Feedstock For Gasification 29 2.14.1 Fuel-wood 29 2.14.2 Biomass Briquettes 30 2.14.3 Agriculture Residue 30 2.15 Advantages Of Gasification 30 2.16 Disadvantages Of Gasification 31 2.17 Anaerobic Digestion 31 2.18 Principle Of Operation 32 2.18.1 Hydrolysis 32 2.18.2 Acetogenesis 32 2.18.3 Methanogenesis 32 2.19 History Of Anaerobic Digestion 33 2.20 Energy Conversion 33 2.21 Conditions And Variables Influencing AD 34 2.23 TYPES OF DIGESTERS 36 2.24 Advantages Of Anaerobic Digestion 36 2.25 Disadvantages Of Anaerobic Digestion 37

Part- III ASSESSMENT OF ENVIRONMENTALLY SOUND TECHNOLOGIES

3.1 Problem Statement 40 3.2 Steps By Step Assessment of ESTs 45 3.2.1 Screening tier 45 3.2.2 Scoping tier 45 3.2.3 Detailed assessment tier 47 CONCLUSION & RECOMMENDATION 50

5

PART- I

INTRODUCTION

6

PART- I

INTRODUCTION

1.1 BIOMASS

The word biomass is the combination of two “Bio”, which is the prefix

indicating the action of living organisms and the “Mass”, which is the matter in the

body. Biomass is the mass of living organisms and recently dead matter like wood,

leaves, stalks, straw and other organic matter. It is accessible on a renewable basis,

and also includes agricultural crops and their residues, animal wastes (dung), wood

and wood residues, aquatic plants and organic portion of the municipal solid waste

(garbage). The basic step in the constitution of the biomass is photosynthesis, which

can be symbolized as Eq. (1.1).

OHOOHCkJOHCO lchlorophyl22612622 662800126 ++ →++ (1.1)

Photosynthesis is the chemical process, in which the small portion of the

sunlight is absorbed by chlorophyll of green plant cells, which is consumed by it to

generate carbohydrates (sugars) from water and carbon dioxide. Fig. 1.1 indicates the

interaction of the solar energy and the biomass. Only green plants are capable of

photosynthesis, where as other living organisms either consumes green plants or their

by-products and generate biomass.

Fig. 1.1: Interaction of sun and biomass during photosynthesis

7

1.2 BIOMASS ENERGY

The energy obtained from the floras and their residues and fauna’s waste is

known as biomass energy. In other words biomass energy is the accumulation of the

solar energy into the animals, plants and their different types of wastes. By the

definition of the biomass the fossil fuels do not considered as biomass energy, though

their origin is biomass. One of the reasons is that the fossil fuels are not renewable

source of energy; second they are long term decayed organisms forming after several

million years under certain conditions of pressure, temperature, etc.

1.3 WASTE AGRICULTURAL BIOMASS (WAB)

The agricultural residues are referred as the Waste Agricultural Biomass,

which may be assorted as field residues and process residues.

1.3.1 Field residue

It is the matter leftover in an agricultural field after the crop has been reaped

e.g. leaves, straw, stalks, roots etc.

1.3.2 Process residue

It is the matter leftover after the processing of the crop at the mills or factories

into a valuable resource e.g. husks, sugar cane fiber (bagasse), seeds, groundnut

shells, maize cobs etc.

1.4 WHY TO USE WASTE AGRICULTURAL BIOMASS?

There are several social, economical and environmental benefits of the waste

agricultural biomass to be uses as the fuel. Following are the few important points to

be considered;

� The waste agricultural biomass is a clean, renewable source of energy, and is

the replacement of a non-renewable energy sources.

� It is free from worldwide price variations and supply doubts, as it is domestic

fuel and is available on the periodic basis, hence provides the energy security.

� The use of waste agricultural biomass can substantially reduce the carbon

emissions if managed in a suitable manner. Its management includes

collection, processing, transportation and use for energy recovery technology.

� It will enhance energy security by utilizing locally available resources mean

while decreasing the dependency to the fossil fuels.

8

� The proper consumption of waste agricultural biomass decreased green house

gas (GHG) emissions, achieved by decreasing the open field burning and

methane discharges due to decomposing of the WAB available into the field.

� It will reduce the problem of waste agricultural biomass management and

disposal.

� In addition to the environmental benefits the proper utilization of the WAB

can potentially increases the profit to the farmers/ landowners.

� Management of the WAB creates new job opportunities.

1.5 STUDY AREA

The area selected for UNEP project was Sanghar district, which is one of the

largest districts of province Sindh, Pakistan. The district Sanghar lies between 25° to

30° North latitudes and 70° to 13° East longitudes. From the Province map of Sindh

by districts as in Fig. 1.2, it can be observed that the district Sanghar is bordered on

the East by India, North by Khairpur District, North-west by Nawabshah district, and

South by Tando Allahyar, Mirpurkhas and Umerkot districts and on the West by

Matiari district. The total area of the district is about 2439704 Acres.

Fig. 1.2: Map of Sindh Province by districts

9

The district Sanghar principally is an agrarian district except the large part of

Taluka Khipro and some part of Taluka Sanghar, which comes on the left side of Nara

Canal and is known as Thar Desert. The rest of the part of the district is very fertile.

Wheat, Cotton, Sugarcane and Rice are main crops of the district. Groundnuts,

Vegetables, Pulses, Maize, Bananas and many other crops are also grown there.

District Sanghar has great importance due to Political, Economic and Cultural

causes. There exist many small industries like cotton factories, flour mills, rice mills,

oil mills, ice factories, match factories & only one large sugar mill. People of district

Sanghar are very hospitable. The climate there in summer is dry and hot, where as in

winter it is dry and cold. The temperature in the region ranges from 43°C to 6°C in

summer and winter respectively. The district average out receives 12mm of the

rainfall annually.

The district Sanghar is administratively sub-divided into six Talukas; these are

Sanghar, Sinjhoro, Shahdadpur, Tando Adam, Jam Nawaz Ali, and Khipro as shown

in Fig. 1.3.

Fig. 1.3: Map of district Sanghar by Taluka

The total area, number of dehs, number of Union Councils and population of

each Taluka of district Sanghar is given in Table 1.1. It is to be noted that the

population for the year 2010 was estimated by using the growth rate of 2.47%

between the censuses of 1981 and 1998 [District Profile (2005)]. There are total 59

10

union councils are in district Sanghar. In order to get the representative data, each of

them was considered as a unit area for the survey.

Table 1.1: Area and population of district Sanghar by Taluka

S# Name of taluka Area (Acre)

No of Dehs

No of Union

Councils

Population by census

1998

Population in 2010

01 Sanghar 590782 69 11 262050 362459

02 Sinjhoro 217070 88 8 196849 272275

03 Shahdadpur 108377 47 13 327408 452860

04 Tando Adam 107688 28 10 255941 354009

05 Jam Nawaz Ali 115021 51 4 88908 122975

06 Khipro 1300766 78 13 321874 445206

Total 2439704 361 59 1453030 2009784

1.6 ENVIRONMENTALLY SOUND TECHNOLOGIES (ESTs)

Environmentally Sound Technologies ESTs can be defined as those

technologies that protect the environment, are less polluting, use all resources in a

more sustainable manner, recycle more of their waste and products and handle

residual waste in a more sustainable manner than the technologies for which they are

substitutes.

ESTs include a variety of cleaner production process and pollution prevention

technologies, as well as end-of-pipe and monitoring technologies. Apart from just

technologies, they can be considered as total ‘systems’ that may include knowledge

and skills transfer, operating procedures, goods, services and equipment, and also

organizational and managerial procedures.

1.7 ENVIRONMENTAL TECHNOLOGY ASSESSMENT (EnTA)

EnTA is conceived as a system for technology assessment focusing on not just the

environmental performance of the various processes and components of the technology,

but also on its cultural and socio-economic consequences. Simply put, EnTA is a system

to facilitate the identification and selection of the ‘best possible technology option’.

11

1.8 PURPOSE AND SCOPE OF EnTA

EnTA targets planners, decision makers in the government and private sectors,

communities through community leaders and community-based organizations, and

other stakeholders to enable them to arrive at an informed consensus on the proposed

technology intervention. More specifically, the purpose of EnTA for different users is

as described below:

� Decision makers and managers in industry – To identify/recognize

environmental implications of the proposed technology intervention,

potentially avoiding adverse financial and legal issues

� Development planners and government sector officials – To identify and thus

address implications of technology based development and integrate it in

planning

� Community and non-government organizations – To ensure that the rights and

responsibilities of communities are given due consideration where technology-

based development is being planned

� Stakeholders in sustainable development – To enable citizens to ensure that

environmental outcomes are recognized and suitable modifications are

implemented for a more positive technology-based development

1.9 CRITERIA FOR CRITICAL ANALYSIS OF EST

The EST criteria begin with four basic requirements:

1. Environmental soundness

a. Protecting the environment

b. Less polluting and handles wastes in a more acceptable manner

c. Uses resources in a more sustainable manner

d. Accepts by-products and wastes as inputs

2. Economic viability

a. Lesser capital costs

b. Availability of financial incentives / rebates for raising capital

c. Lesser operating and maintenance costs

d. Leads to additional monetary savings from operation

12

3. Social and cultural acceptability

a. Protects and enhances social aspects

b. Culturally acceptable and/or enhancing

4. Characterization (of technologies) by sufficient and verified information

13

PART- II

PROPOSED ENVIRONMENTALLY SOUND

TECHNOLOGIES (ESTs) FOR

CONVERTING WAB INTO

ENERGY/RESOURCE IN SANGHAR

14

2.1 PROPOSED TECHNOLOGIES FOR DISTRICT SANGHAR

The following five technologies are proposed for converting Waste

Agricultural Biomass (WAB) into energy/ material source:

1. Direct Combustion

2. Biomass Pellets

3. Composting

4. Gasification

5. Anaerobic Digestion

2.2 DIRECT COMBUSTION

The simplest way, and oldest way, of generating electricity from biomass is to

burn it. This is called direct combustion. Direct combustion systems burn biomass in

boilers to produce high pressure steam. This steam turns a turbine connected to a

generator. As the steam causes the turbine to rotate, the generator turns and electricity

is produced. Most of the world’s biomass power plants use direct combustion. In

some cases, the steam from the plants is also captured to heat water and buildings.

These are known as cogeneration facilities. Direct combustion processes can be used

to convert various raw fuel materials besides wood, including municipal garbage and

crop wastes. If they burn woody materials, these commonly take the form of

woodchips, bark or sawdust that originates as waste by-products of forest industries.

Although this technology is dependable and proven, its efficiency is limited.

Direct combustion systems typically have thermal efficiencies around 20 per cent.

These efficiencies can be increased through cogeneration. Biomass cogeneration

refers to the combustion of a mixture of fossil fuels such as coal and biomass fuels.

Direct combustion is the main process of converting the biomass to the useful

form of energy. Technology for direct combustion can generate heat, electricity or

both (Cogeneration or combined heat and power, CHP). Biomass direct combustion is

generally based on the Rankin cycle, where a steam turbine is employed to drive the

generator. This type of system is well developed, and available commercially around

the world. Most bioelectricity plants today are direct-fired. In direct combustion,

steam is generated in boilers burning solid biomass which has been suitably prepared

(dried, baled, chipped, formed into pellets or briquettes or otherwise modified to suit

the combustion technology). Direct combustion technologies may be divided into

fixed bed, fluidized bed and dust combustion see Fig 2.1.

15

Fig. 2.1: Direct combustion technologies

In fixed bed systems, the biomass fuel burns in a layer on a grate which moves

to transport the fuel through the furnace towards ash removal. Fixed bed technologies

are reliable and generally have relatively low investment costs compared with other

direct combustion technologies. However, a given fixed bed boiler design can usually

handle only a limited range of biomass fuel types.

In fluidized bed boilers, the fuel burns in a constantly mixing suspension of

hot, inert, granular bed material (usually silica sand or dolomite) into which

combustion air enters from below. Because of the very effective mixing achieved,

fluidized bed plants are very flexible in their ability to burn different biomass fuel

types, although the fuel particle size must be relatively uniform. Fluidized bed

systems have high investment and operating costs.

In dust combustion, fuel in the form of small particles such as sawdust or crop

residue shavings is injected along with air into the combustion chamber, and

combustion takes place with the fuel in suspension.

16

2.3 BIOMASS PELLETS

Biomass may include any fuel derived from organic matter, such as wood, oil

crops, and agricultural & animal residues. Biomass pellets are produced from grinding

down wood, energy crops and crop byproducts such as straw. The quality of the pellet

will vary significantly depending on the quality of the original wood/crop etc. Fig. 2.2

shows the biomass pellets.

Fig. 2.2: Biomass Pellets

Biomass pellets and briquettes are made by compressing dry sawdust or crop

residue shreds under high pressure until the lignin softens and binds the material

together. The combination of low moisture content (typically below 10%) and highly

compressed material gives pellets a high volume energy density, typically three to

four times that of uncompressed. They are also clean, consistent and flow easily,

making them particularly attractive in domestic applications. The significantly lower

storage requirements make them attractive to urban applications. Pellets for domestic

and small scale applications are typically 6-8 mm diameter, while those for industrial

applications may be 10-12 mm. Above 25 mm diameter they are known as briquettes

and can resemble a fire-log in appearance and function, though with improved

storage, handling, and combustion properties.

There are two main types of pellet appliance available; these are smaller-scale

space heaters and larger scale water heaters suitable for a range of uses from top-up

space heating to complete space and water heating. Pellet stoves are far more efficient

than open fires or wood burning stoves. Pellet boilers work in much the same way as

“conventional” gas or oil boilers and are able to fire up automatically and be

17

controlled by time clocks etc. The ash created will be very small (<2% of total fuel

burnt) provided the pellet is of high enough quality.

Biomass pellets are generally a superior fuel when compared to their raw

feedstock. Not only are the pellets more energy dense, they are also easier to handle

and use in automated feed systems. These advantages, when combined with the

sustainable and ecologically sound properties of the fuel, make it very attractive for

use.

2.3.1 Description of the Pelleting Process

The process of manufacturing fuel pellets involves placing ground biomass

under high pressure and forcing it through a round opening called a “die.” When

exposed to the appropriate conditions, the biomass “fuses” together, forming a solid

mass. This process is known as “extrusion.” Some biomass (primarily wood) naturally

forms high-quality fuel pellets, while other types of biomass may need additives to

serve as a “binder” that holds the pellet together. However, the creation of the pellets

is only a small step in the overall process of manufacturing fuel pellets. These steps

involve feedstock grinding, moisture control, extrusion, cooling, and packaging. Each

step must be carried out with care if the final product is to be of acceptable quality.

Fig. 2.3 shows the flow diagram for biomass pellet making.

Fig. 2.3: Flow diagram for biomass pellet making

18

2.3.2 Feedstock Grinding

Standard-sized pellet mills generally require biomass that is ground to

particles that are no more than 3 millimeters in size. Several types of equipment are

available to carry out this task. If the biomass is quite large and dense (e.g., wood),

the material is first run through a “chipper,” and then run through a hammer mill or

similar device to reduce the particles to the required size. Smaller and softer biomass

(e.g., straw) can be fed directly into the hammer mill without first being chipped.

2.3.3 Moisture Control

Maintaining an appropriate moisture level in your feedstock is vital for overall

quality of the final pellets. For wood, the required moisture level of the feedstock is at

or near 15 percent. Other types of biomass have other requirements—you may need to

experiment a bit. Moisture can be removed from the feedstock by oven-drying or by

blowing hot air over or through the particles. If the feedstock is too dry, moisture can

be added by injecting steam or water into the feedstock.

2.3.4 Extrusion

The pellet is actually created in this step. A roller is used to compress the

biomass against a heated metal plate called a “die.” The die includes several small

holes drilled through it, which allow the biomass to be squeezed through under high

temperature and pressure conditions. If the conditions are right, the biomass particles

will fuse into a solid mass, thus turning into a pellet. A blade is typically used to slice

the pellet to a predefined length as it exits the die. Some biomass tends to fuse

together better than other biomass. Sawdust is an especially suitable feedstock for

pelleting because the lignin that is naturally present in the wood acts as a glue to hold

the pellet together. Grasses tend to not fuse nearly as well, and the resulting pellets are

less dense and more easily broken. The proper combination of input material

properties and pelleting equipment operation may minimize or eliminate this problem.

It is also possible to add a “binder” material to the biomass to help it stick together, or

to mix a fraction of sawdust, with similar results. Distillers Dry Grains (a product of

the corn ethanol industry) are reported to improve the binding properties of some

biomass.

19

2.3.5 Cooling

Pellets, as they leave the die, are quite hot (~150°C) and fairly soft. Therefore,

they must be cooled and dried before they are ready for use. This is usually achieved

by blowing air through the pellets as they sit in a metal bin. The final moisture content

of the pellets should be no higher than 8 percent.

2.3.6 Packaging

Pellets are typically sold in 18-kilogram bags, which can be easily filled using

an overhead hopper and conveyor belt arrangement. The bags should be clearly

labeled with the type of pellet, their grade (i.e., premium or standard), and their heat

content.

2.4 ENERGY REQUIREMENTS FOR PELLET MANUFACTURE

Pellet manufacture requires quite a bit of energy, both for drying damp

feedstock and for running the various pieces of machinery. Large plants typically burn

a portion of their feedstock to provide heat for drying, whereas smaller facilities often

use other means. As a rule of thumb, a pelletizer requires between 50 and 100

kilowatts of electrical demand for every ton per hour of production capacity. In

addition, electricity is usually needed to operate any chopping, grinding, drying,

cooling, and bagging equipment that is in use. If a reliable source of electricity is not

available, gasoline or diesel-based equipment is available.

2.5 ADVANTAGES OF BIOMASS PELLETS

Biomass pellets have following advantages:

� Low moisture content, typically <10%

� High volume energy density: 3-3.5 MWh/m3

� Many different designs of pellet store available off the shelf

� Usually low ash <1%

� Relatively compact storage requirements

2.6 COMPOSTING

Composting is the biological decomposition of organic materials by

microorganisms under controlled, aerobic conditions to a relatively stable humus-like

20

material called compost. Composting can happen in many different ways using a

variety of materials, methods, equipment, and scales of operation. For agricultural

operations the common materials or feed stocks that are composted are livestock

manures and bedding and various residual plant materials (straw, culls, on-farm

processing wastes, etc).

Traditionally some farmers allowed manure to pile up and it decomposed until

they were ready to use it. Some have referred to this as composting. Composting is

much more than just aging manure — it is a science. The decomposition occurs in a

well-managed process to obtain specific positive results a valuable product with a

minimum of negative environmental impacts. The composting process can be viewed

from Fig. 2.4.

Fig 2.4: The composting process

The nutrient content of compost will be quite different from the manure and

other feedstock that go into the mix. As water evaporates, the carbon breaks down and

is lost as carbon dioxide, the compost volume decreases and the phosphorous and

most other nutrients become more concentrated. Some nitrogen will be lost during

composting and some will convert from readily available forms (nitrate and ammonia)

to more stable organic forms that are slowly released to crops. It has been estimated

that less than 15% of the nitrogen in compost (that has been applied to the soil) will

be released in the first crop year compared to 50–60% for un-composted dairy

manure. The nutrient value of compost can be highly variable depending on the

materials being composted and the composting system used. The finished volume of

the compost is frequently 40– 60% of the original compost feedstock volume. The

compost process reduces the volume to be handled and transported to the field

21

utilization site. It also concentrates many of the nutrients in the compost material

compared to their concentrations in the original materials. Well-managed compost

reduces odors and runoff moisture to reduce potential environmental hazards.

2.7 ADVANTAGES OF COMPOSTING

Composting has following advantages:

� Reduce/eliminate pathogens

� Reduce volume and moisture content

� Reduces viable weed seeds

� Reduces insect larvae (fly problems)

� Reduce odor

� Stabilize organic components and nutrients

� Produce a soil amendment/fertilizer

2.8 DISADVANTAGES OF COMPOSTING

Composting has following disadvantages:

� Pathogen control requires high temperatures and good aeration

� Often requires additional bulking material (carbon)

� Long processing time

� Poorly run processes achieve very little

� Land required for composting and storage areas

� May require large investment

� Requires more labour

2.9 COMPOSTING SYSTEMS

There are many different methods and types of equipment and structures

suitable for composting. These include:

1. Windrow/pile composting – turning

2. Windrow/pile composting – active aeration

3. Windrow/pile composting – passive aeration

4. Windrow/pile composting – static pile

5. In-vessel composting

6. Vermi-composting

22

2.9.1 Windrow/pile Composting – Turning

There are several advantages of turning the compost windrow. Thorough

turning will ensure that there is a uniform mix of the feedstock materials throughout

the windrow. This reduces the likelihood of hot spots where there is overheating or

accumulation of high moisture materials that reduce microbial activity. The frequency

of turning can be managed to respond to changes in moisture or temperature as

required. The moisture content of the windrow usually decreases after turning. If the

compost has become too dry, water can be added when turning to increase the

moisture within the windrow and to increase the composting activity of the

microorganisms. Turning adds air spaces and oxygen in the windrow.

Turning at regular intervals during the initial 2–3 weeks of composting is

advisable to reach and maintain temperatures above 55ºC for 15 days. This

temperature is known to kill most pathogens and weed seeds.

2.9.2 Windrow/pile Composting – Active Aeration,

Static pile Active aeration of windrows requires more careful design for

appropriate airflows, and usually a more expensive system than turned windrow

systems. The most common design of this system is to place aeration pipes along the

length of the windrow with adequate holes for proper airflow. The pipes and middle

portion of the base of the windrow is then covered with a porous material such as

wood chips. The windrow is then placed on top of the aeration bed. Proper mixing of

the feedstock materials and optimum moisture contents are critical to success since

these windrows are usually not turned therefore not disturbing the aeration system).

Fans are attached to the ventilation tube and air is either blown into the windrow

(positive pressure) or vacuumed out of the pipe (negative pressure). When using a

negative pressure, biofilters may be needed to remove the odors from the exhausted

air. The aerated windrows also need to be covered with an insulated blanket of

material to allow adequate heating of the surface of the materials that need to be

composted. This covering is frequently straw or mature compost and is 6-12 in. thick

over the whole windrow.

2.9.3 Windrow/pile Composting – Passive Aeration,

Static piles sometimes known as PAWS (Passive Aeration Windrow System),

this system involves the insertion of aeration pipes into or under the pile. The

23

feedstock materials are usually piled on a bed of coarse material such as wood chips

and/or aerated pipes to improve aeration. The air is permitted to flow passively

through the pipes and the coarse material under the pile.

PAWS allows better aeration than the static piles and can achieve higher

temperatures, but can be subject to many of the same problems especially if the

mixing is inadequate or if the feedstock materials are of improper C:N ratio or

moisture. The aeration pipes make it difficult to turn the piles as a means of correcting

problems such as hot spots. As a result the degree of composting may vary throughout

the pile.

2.9.4 Windrow/pile Composting – Static Piles, not Aerated

This is a very low management system where you pile it and leave it. While it

is the easiest and least expensive composting system, it can also be the most

troublesome and produce the poorest quality compost. When there is no turning of a

windrow, the uniform mixing of feedstock materials and the moisture content going

into the windrow are very critical. There needs to be enough void space (porosity) in

the materials to allow air to penetrate the windrow. Water is released as the feedstock

breaks down, but if there is insufficient airflow, this water goes to the bottom of the

pile creating anaerobic conditions near the bottom of the pile. This problem is

increased if the windrow is not covered to prevent the inclusion of rainwater. Under

hot, dry weather conditions, the surface layer of the windrow can become too dry for

microorganisms to work effectively. Turning the pile would mix it to create more

uniform moisture content throughout the windrow.

Windrows that are not turned and do not have mechanical aeration systems,

frequently do not reach adequate temperatures to kill pathogens and weed seeds. This

is especially true in anaerobic zones within the centre of the windrow, as well as near

the surface of the windrow, where temperatures are well below the temperatures

required for pathogen kill (55ºC).

2.9.5 In-vessel Composting

In-vessel composting systems include a group of composting methods. They

have the greatest amount of design requirements. They range from concrete channels

with mechanical mixers to rotating steel drum type systems. Many are continuous

flow and designed for high capacity commercial composting operations. Frequently

24

they are contained in buildings designed for the purpose. High initial cost and

continuous management are disadvantages. They are usually used for high volume or

central composting systems and require a higher level of management than other

systems discussed here. Some designs use rectangular concrete channels that may

have aerated floors and be turned either with turners that travel on overhead rails or in

some on-farm cases by using multiple channels and tractor-loaders to turn and move

the material from one channel to another.

2.9.6 Vermi-composting

Vermi-composting is worm composting. Common worm species for this type

of composting are Eisenia foetida and Lumbricus rubellus. These are sometimes

called "red wigglers" or manure worms. These worms are added to the feedstock

materials to assist in the decomposition of the organic matter and transform it into

worm castings. This type of composting does not reach high temperatures but

research is showing that there can be good kill of pathogens and weed seeds.

2.10 GASIFICATION

Gasification is a thermo-chemical process in which carbonaceous (carbon-

rich) feed stocks such as coal or biomass are converted into a gas consisting of

hydrogen and carbon monoxide (and lesser amounts of carbon dioxide and other trace

gases) under oxygen depleted, high pressure, high-heat and/or steam conditions. The

resulting gaseous compound is called Syngas.

2.11 PRINCIPLE OF OPERATION

Biomass gasification is a thermo-chemical conversion process in which a solid

biomass fuel e.g. wood is converted into a combustible gas. In a biomass gasifier,

biomass is burned in a limited amount of air. The amount of air supplied is less than

the amount of air required for complete burning. This converts the biomass (which

consists of carbon, hydrogen, oxygen, etc) into an inflammable mixture of gases

known as producer gas/ wood gas.

25

Fig 2.5: A typical biomass gassifier

The producer gas consists of carbon monoxide (CO), hydrogen (H2), and

methane (CH4), along with carbon dioxide (CO2) and nitrogen (N2). In a gasifier

biomass is progressively heated from the ambient temperature to a temperature of

around 1100 oC. The main reactions which take place in a gasifier are:

1. DRYING: Biomass fuels usually contain up to 35% moisture. When the

biomass is heated to around 100oC, the moisture gets converted into steam.

2. PYROLYSIS: After drying as the biomass is heated it undergoes pyrolysis.

Pyrolysis is the thermal decomposition of biomass fuels in the absence of

oxygen. Biomass decomposes into solid charcoal, liquid tars and gases.

26

Fig 2.6: Pyrolysis of carbonaceous fuels & Gasification of char

3. OXIDATION: Air is introduced in a gasifier in the oxidation zone. The

oxidation takes place at about 700-1400 oC, in which the solid carbonized fuel

reacts with oxygen in the air producing carbon dioxide and releasing heat.

C+O2 = CO2 + 406 kJ/g.mol

4. REDUCTION: At higher temperatures and under reducing conditions several

reactions take place which results in formation of CO, H2 and CH4.

CO2 + C = 2CO -172.6 kJ/g.mol

C+H2O = CO + H2 -131.4 kJ/g.mol

CO2+H2 = CO +H2O -41.2 kJ/g.mol

C+2H2 = CH4 +75 kJ/g.mol

Typical composition of producer gas is presented in Table 1.1. The producer

gas so obtained is a low calorific value gas with typical higher heating value (HHV)

in the range of 5.4-5.7 MJ/m3 (Kishore, 2008). The producer gas can be directly

burned in a burner to provide thermal energy or it can be used as a fuel in an engine to

provide mechanical power or electricity.

Table 2.1 Composition of producer gas (TERI, 2006)

Component Composition (%)

Carbon monoxide 18 – 22

Hydrogen 13 – 19

Methane 1 – 5

Heavier hydrocarbons 0.2 - 0.4

Carbon dioxide 9 – 12

Nitrogen 45 – 55

Water vapor 4

27

2.12 HISTORY ON GASIFICATION

Gasification is an old technology with a long history of development. The

process was mainly used from the mid-1800’s through the early-1900’s to produce

“town gas” from coal for heating and lighting purposes. The subsequent development

of natural gas fields soon replaced “town gas." World War II brought a resurgence of

gasification when petroleum starved Europeans used wood gas generators to power

vehicles. But the need for liquid fuels remained and German engineers devised a way

to make synthetic liquid fuel from gasified coal.

The 1970’s brought The Arab Oil Embargo and the “energy crisis” which

prompted the U.S. government to support industrial scale gasification projects. From

this development came the first Integrated Gasification Combined Cycle (IGCC)

electric generating plant. Presently, several IGCC power plants are operating

throughout the world. And crude oil price spikes and geopolitical instabilities in major

oil-producing countries have generated serious interest in using gasification for GTL

(Gas to Liquid) synthetic fuel processes.

2.13 TYPES OF GASIFIERS

Many design variations of Gasification Reactors (Gasifiers) exist, however,

depending upon the type of flow conditions present in the equipment, they all fall into

one of three general categories:

2.13.1 Moving Bed Gasifier:

Dry carbon fuel is fed through the top of the gasifier. As it slowly drops

through the vessel, it reacts with steam and oxygen as they flow in opposite in

directions over the bed. The fuel goes through the process until it is completely spent

leaving behind low temperature syngas and molten ash. Trace contaminants are later

scrubbed from the syngas.

28

Fig 2.7: Moving Bed Gasifier

2.13.2 Entrained Flow Gasifier:

Fuel can be fed dry or wet (mixed with water) into the gasifier. The reactants

(steam and oxygen) flow uni-directionally upwards through the gasifier, as the stages

of gasification take place, until high temperature completed syngas exits the top of the

reactor. Molten slag drops out at the bottom.

Fig 2.8: Entrained Flow Gasifier

29

2.13.3 Fluidized Bed Gasifier:

Steam and oxygen flow upwards through the reactor tower while fuel is

injected into, and remains suspended in, this stream while gasification takes place.

Moderate temperature syngas exits the while dry (un-melted) ash is evacuated at the

bottom.

Fig 2.9: Fluidized Bed Gasifier

2.14 COMMON BIOMASS FEEDSTOCK FOR GASIFICATION

A large type of biomass feedstock have been tried and tested in fixed bed

gasifies. The chemical composition, size, bulk density, moisture content, ash

properties are some of the important parameters that determines suitability of a

biomass resource for use in fixed bed gasifies. The common biomass feedstock used

in fixed-bed gasifies are:

2.14.1 Fuel-wood

Dried fuel-wood having moisture content less than 20 % and cut into suitable

size is the most common biomass feedstock used for gasification. Fuel wood obtained

from Prosopis Juliflora, eucalyptus, casurina, acacia, neem, mango have been found to

be good gasification material.

30

2.14.2 Biomass Briquettes:

Due to low bulk densities (50-200 kg/m3), many non-woody biomass residues

poses problem in direct utilization in fixed-bed gasifies. Such biomass materials can

be densified and converted into briquettes (density: 800-1200 kg/m3) and can then be

easily used in gasifiers. Briquettes made from sawdust, coffee husk, groundnut shells,

pulverized mustard stalk, and cotton sticks are found to be good feedstock for fixed

bed gasifiers.

2.14.3 Agriculture Residue:

Several agriculture residues have been successfully used directly (without

densification) in fixed bed gasifiers. However, it should be noted that utilization of

some of these materials necessitates modification in the design of gasifiers which are

designed primarily for utilization of fuelwood or biomass briquettes. Some of the

prominent agriculture residues which have been used in fixed-bed gasifiers are:

coconut shells, stalks such as mustard, arhar and cotton, rice husk, cashew nut shell,

corn cob, etc.

2.15 ADVANTAGES OF GASIFICATION

� Feedstock flexibility

� Product flexibility

� Near-zero emissions

� High efficiency

� Energy security

� Gasification plants produce significantly lower quantities of criteria air

pollutants.

� Gasification can reduce the environmental impact of waste disposal because it

can use waste products as feed stocks generating valuable products from

materials that would otherwise be disposed as wastes.

� Gasification's byproducts are non-hazardous and are readily marketable.

� Gasification plants use significantly less water than traditional coal-based

power generation, and can be designed so they recycle their process water,

discharging none into the surrounding environment.

31

2.16 DISADVANTAGES OF GASIFICATION

� Complex multi-stage process

� Up-front processing of feedstock

� Syngas must be cleaned/purified

� Initial setup is expensive

2.17 ANAEROBIC DIGESTION

Anaerobic digestion is one of the most important biological methods used for

stabilization of liquid organic sludge from sewage works, highly concentrated

effluents from biochemical and food processes. It is becoming more common now for

processing of livestock wastes and solid municipal wastes.

Fig 2.10 Biogas Plant

32

2.18 PRINCIPLE OF OPERATION

Anaerobic digestion is a natural process which takes place in the absence of

oxygen. Controlled digestion is normally accelerated by increasing reactor

temperature into the mesophilic range (normally for anaerobic digestion between 30-

37ºC), or into the thermophilic regime (normally for thermophilic anaerobic digestion

between 55-65ºC). The decomposition of organic material consists of three basic

processes as follows;

2.18.1 HYDROLYSIS

The first step in anaerobic decomposition is enzymatic hydrolysis. It occurs in

the substrate, out with the cells, by the action of extra cellular enzymes produced by

bacteria. The result of hydrolysis is the formation of sugars from carbohydrates,

amino acids from proteins, and fatty acids from lipids. Soluble organic compounds are

fermented to a relatively small variety of end products. These include formate,

acetate, propionate, butyrate, lactate, succinate, ethanol, carbon dioxide, and hydrogen

gas.

2.18.2 ACETOGENESIS

Products of hydrolysis are degraded by acetogenic bacteria to their final

metabolic products of volatile fatty acids (predominantly acetates), CO2 and

hydrogen. During this phase a fast growth of acetogenic bacteria occurs, thus mixing

of the substrate positively affects this process.

2.18.3 METHANOGENESIS

Production of methane and CO2 from intermediate products is accomplished

by methanogenic bacteria. Approximately 70% of the methane is formed from volatile

fatty acids. The remaining 30% is produced from hydrogen and carbon dioxide.

Methanogenesis is critical to the entire digestion process, since it is the slowest

biological reaction of the digestion. Overloading of the reactor, temperature changes

or large ingresses of oxygen usually result in cessation of methane production, an

increasing fatty acids concentration and results in the production of only CO2.

33

2.19 HISTORY OF ANAEROBIC DIGESTION

Historical evidence indicates that the anaerobic digestion (AD) process is one

of the oldest technologies. However, the industrialization of AD began in 1859 with

the first digestion plant in Bombay. By 1895, biogas was recovered from a sewage

treatment facility and used to fuel street lamps in Exeter, England. Research led by

Buswell and others in the 1930s identified anaerobic bacteria and the conditions that

promote methane production. As the understanding of the AD process and its benefits

improved, more sophisticated equipments and operational techniques emerged. The

result was the used of closed tank and heating and mixing systems to optimize AD.

Regardless of improvements, AD suffered from the development of aerobic treatment

and low costs of coal or petroleum. While AD was used only for the treatment of

wastewater sludge digestion, developing countries such as India and China embraced

the technology. Small-scale AD systems were mostly used for energy and sanitation

purposes. Numerous failures were reported. Nevertheless, technical improvements

and increasing energy prices have led to a diversification of the waste treated and

larger size AD plants.

2.20 ENERGY CONVERSION

The anaerobic degradation of organic substances to its most reduced form,

methane (CH4), is a microbial process. The energy released, originally stored in the

substrate, and is predominantly recovered by the formed methane.

33g org. material = 22g CO2 + 8g CH4 + 3g biomass

The AD plant will provide biogas which will be used to generate two forms of

energy, electricity and heat, in combined heat and power (CHP) units of gas engines.

Anaerobic digestion is a proven technology but it is not a simple process. It requires

storage space for the raw and treated material, dosing pumps, a gas tight reactor with

heat exchanger and mixing facilities, a bio-gas reservoir, boiler and/or internal

combustion engine with an electrical energy generator. To make the process

economical, with a payback period of less than 5 years, a high percentage of biogas

has to be utilised. This target is achievable in larger plants, where electrical

energy/heat co-generation is the most practical design.

34

Table 2.2 Typical Composition of biogas gas

COMPONENT %

Methane, CH4 50–75

Carbon dioxide, CO2 25–50

Nitrogen, N2 0–10

Hydrogen, H2 0–1

Hydrogen sulfide, H2S 0–3

Oxygen, O2 0–2

2.21 CONDITIONS AND VARIABLES INFLUENCING AD

There are several conditions and variables that must be applied in order to

obtain a proper breakdown of the organic compounds. The operating parameters of

the digester must be controlled so as to enhance the microbial activity and thus

increase the AD efficiency. Some of these parameters are discussed briefly below;

2.21.1 Total Solid content

There are three different ranges of solid content: low solid (LS) AD systems

contain less than 10% Total Solid (TS), medium solid (MS) from 15-20% and high

solid systems (HS) range from 22-40%. When increasing the total solid content, the

volume of the digester decreases, due to lower water requirements.

2.22.2 Temperature

Anaerobic digestion can occur under two main temperature ranges: i.e.

Mesophilic conditions, between 20-45°C, usually 35°C and Thermophilic conditions,

between 50-65° C, usually 55°C. The optimum temperature of digestion may vary

depending on feedstock composition and type of digester, but in most AD processes it

should be maintained relatively constant to sustain the gas production rate.

Thermophilic digesters are more efficient in terms of retention time, loading

rate and nominally gas production, but they need a higher heat input and have a

greater sensitivity to operating and environmental variables, which make the process

more problematic than mesophilic digestion

35

The sterilization of the waste is also linked to the temperature. The higher it is

the more effective it is in eliminating pathogens, viruses and seeds.

2.22.3 Retention time

Retention time is the time needed to achieve the complete degradation of the

organic matter. The retention time varies with process parameters, such as process

temperature and waste composition. The retention time for waste treated in a

mesophilic digester ranges from 15 to 30 days and 12-14 days for thermophilic

digester.

2.22.4 pH

The optimal pH values for the acidogenesis and methanogenesis stages are

different. During acidogenesis, acetic, lactic and propionic acids are formed and, thus

the pH falls. Low pH can inhibit acidogenesis and pH below 6.4 can be toxic for

methane-forming bacteria. The optimal range for methanogenesis is between 6.6 to 7.

An optimal pH range for all is between 6.4 and 7.2.

2.22.5 Carbon to Nitrogen ratio (C: N)

The relationship between the amount of carbon and nitrogen present in organic

materials is represented by the C: N ratio. Optimum C: N ratios in anaerobic digesters

are between 20 and 30. A high C: N ration is an indication of a rapid consumption of

nitrogen by the methanogens and results in a lower gas production. On the other hand,

a lower C: N ratio causes ammonia accumulation and pH values exceeding 8.5, which

is toxic to methanogenic bacteria. Optimum C: N ratio of the feedstock materials can

be achieved by mixing waste of low and high C: N ratio, such as organic solid waste

mixed with sewage or animal manure.

2.22.6 Mixing

Mixing, within the digester, improves the contact between the micro-

organisms and substrate and improves the bacterial population's ability to obtain

nutrients. Mixing also prevents the formation of scum and the development of

temperature gradients within the digester. However excessive mixing can disrupt the

micro-organisms and therefore slow mixing is preferred.

36

In case of co-digestion, the different feedstocks should be mixed before

entering the digester to ensure a sufficient homogeneity.

2.22.7 Organic loading rate (OLR)/ Volatile Solids (VS)

OLR is a measure of the biological conversion capacity of the AD system.

Feeding the system above its sustainable OLR, results in low biogas yield due to

accumulation of inhibiting substances in the digester slurry (i.e. fatty acids). Under

such circumstances, the feeding rate of the system must be reduced. OLR is a

particularly important control parameter in continuous systems. Many plants have

reported system failure due to overloading. OLR is expressed in kg Chemical Oxygen

Demand (COD) or Volatile Solids (VS) per cubic meter of reactor. It is linked with

retention time for any particular feedstock and anaerobic reactor volume.

Volatile Solids (VS) represents the organic matter in a sample which is

measured as solid content minus ash content, as obtained by complete combustion of

the feed wastes. VS comprise the biodegradable VS (BVS) fraction and the refractory

VS (RVS). High VS content with low RVS is more suitable for AD.

2.23 TYPES OF DIGESTERS

Anaerobic digesters can be classified into the following three categories:

1. single-stage

2. multi-stage

3. batch

The temperature range of the digestion, mesophilic or thermophilic, as well as the

solid content also define the type of reactor used.

2.24 ADVANTAGES OF ANAEROBIC DIGESTION

� The methane produced by AD plants can be collected and managed in an

environmentally sound manner, by using it as a natural gas substitute either

directly, or in the production of hot water, steam or electricity. When

combusted, the methane is converted to CO2, which is much less damaging as

a greenhouse gas (methane is 21 times more powerful than CO2 as a

greenhouse gas).

37

� The methane produced in the digester will be used as an energy source. If it

displaces oil, natural gas or coal, used for the generation of electricity, this

waste management approach has significant greenhouse gas benefits.

� Anaerobic digestion is a net energy producing process. Surplus biogas can be

used to generate electricity and thus defray the cost of the process. Also, the

excess of heat can be sold for heating of large buildings and/or district heating

purposes.

� The compost product produced through the anaerobic digestion of organic

waste is a valuable soil amendment; when added to soil it can improve plant

growth, reduce soil erosion and nutrient runoff, alleviate soil compaction, and

help soil retain water. In addition, there is evidence that compost can suppress

diseases and ward off pests.

� Compost can also reduce the need for artificial fertilizers, which are derived

from natural gas, result in water contamination, and deplete soil health.

Further, greenhouse gases are created during their production and nitrous

oxide (N2O) is released during tillage. This harmful practice can be replaced,

in part, by returning nitrogen bound in organic waste to the soil.

� The quantifiable benefits of displacing artificial fertilizer include reducing the

significant CO2 emissions associated with their manufacture, and reducing the

N2O emissions released through their use.

2.25 DISADVANTAGES OF ANAEROBIC DIGESTION

� Relatively complicated process, the centralized plant has to be run by

specialists

� Complete volatile solids destruction of the waste does not occur in anaerobic

digester

� Possible problems resulting from explosive gas production from aerobically

digested sludge

� Cost of construction of AD is expensive

38

� Difficulty of storage of gas (corrosive)

� Significant consumption of water

� Storage of fertilizer is difficult

� Problem of management of the sludge

� Does not destroy all pathogens

� High operating cost due to temperature management

� Longer start-up time to develop necessary biomass inventory

� May require alkalinity and/or specific ion addition

� May require further treatment with an aerobic treatment process to meet

discharge requirements

� Increased potential for production of odors and corrosive gases.

39

PART- III

ASSESSMENT OF ENVIRONMENTALLY

SOUND TECHNOLOGIES

40

3.1 PROBLEM STATEMENT

Transforming biomass waste into a source of energy is very important from

reduction of the pollution. Resource augmentation by utilizing waste biomass has

emerged as a major issue in both developed and developing countries. There are three

important motivational factors for converting waste biomass into a resource:

1. Economic Benefit

Huge costs can be avoided which are otherwise required to manage huge

volumes of waste through conventional waste management practice, viz.: collection,

transportation, treatment and proper disposal.

2. Energy/ Material Production

Waste biomass contains precious resources which could be obtained in the

form of material or energy to reduce pressure on natural resources which are required

to support economic development and improved living standards. This could also be

in line with strategies for poverty alleviation through income generation activities and

through reducing costs for obtaining energy to support livelihoods.

3. GHG Mitigation

These reductions take place on two accounts. Burning or decomposition of

waste biomass produces GHG emissions and proper management of waste biomass

would reduce these GHG emissions. So far, most of the waste biomass is left in the

fields and to clear the land for planting next crop, farmers use open burning, which

creates local air pollution as well as GHG emissions (CO2). The waste biomass that is

left over the months, gets rotten and generates methane; thus creating GHG emissions.

Hence, converting that waste biomass into an energy source, GHG emissions, which

are caused due to open burning or from rotten waste biomass, could be avoided in

addition to the GHG emissions which are offset due to use of this alternative energy

source.

41

The total quantity of all the nine selected residues for district Sanghar is

represented in Table 3.1 below. As an aggregate the total quantity of the WAB in

district Sanghar is 2533 kilo-tons.

Table 3.1: Total quantity of WAB in district Sanghar (kilo-tones)

S No

Name of Taluka

Crop Residue

San

ghar

Sin

jhor

o

Sha

hdad

- pu

r

Tan

do

Ada

m

Jam

Naw

az

Ali

Khi

pro

TO

TA

L

1 Wheat Straw 73.17 137.43 113.83 52.87 29.62 86.60 494

2 Cotton Stalks 229.18 318.19 315.14 127.78 114.48 318.36 1423

3 Cotton Gin Waste 10.31 14.32 14.18 5.75 5.15 14.33 64

4 Sugarcane Tops 68.16 58.92 39.00 46.77 17.73 22.22 253

5 Baggase 33.40 28.87 19.11 22.92 8.69 10.89 124

6 Rice Straw 7.40 20.19 2.82 4.33 6.66 9.34 51

7 Rice Husk 3.37 9.18 1.28 1.97 3.03 4.24 23

8 Canola Straw 5.32 2.66 2.62 2.18 0.73 1.50 15

9 Banana Plant 1.41 4.62 28.21 48.81 2.09 1.78 87

TOTAL 432 594 536 313 188 469 2533

The overall characteristics of the biomass for the selected nine residues of

district Sanghar are represented in Table 3.2 below.

42

S

No

Nam

e of

Sam

ple

Moi

stur

e (%

)V

olat

ile a

t 55

0 C

(%

)O

rgan

ic

(%)

Ash

(%

)D

ensi

ty

(kg/

m3)

HC

V

(kca

l/kg)

% C% H

% N% O

% S

1B

ana

na P

lant

5.97

58.9

677

.33

16.7

130

032

0138

.31

5.35

0.3

933

.18

0.10

2B

agga

se3.

1173

.09

92.1

64.

7225

639

1044

.65

5.54

0.18

41.7

90.

00

3C

ano

la9.

0962

.40

81.3

89.

5427

835

2539

.66

5.32

0.20

35.2

70

.93

4C

ott

on

Sta

lks

4.85

60.4

685

.17

9.98

1263

3649

42.8

45.

630.

0836

.20

0.42

5M

aize

Co

b4.

5868

.68

88.7

06.

7390

437

9244

.69

6.16

1.04

36.

720.

09

6R

ice

Hus

k4.

8058

.44

74.6

220

.58

1010

3418

36.8

55.

551.

703

0.30

0.22

7R

ice

Str

aw3.

3360

.20

77.9

318

.75

674

3349

36.3

94.

961.

013

5.35

0.22

8S

aw D

ust

7.68

63.7

286

.02

6.30

800

3659

44.3

95.

940.

4135

.16

0.12

9S

uga

rcan

e T

ops

2.43

64.8

183

.96

13.6

214

5736

3929

.92

3.720.15

50.0

30.

14

10W

heat

Str

aw

4.33

61.3

581

.04

14.6

431

134

4340

.83

5.34

0.8

333

.80

0.24

11C

ott

on

Gin

Wa

ste

4.55

58.0

774

.68

20.7

731

932

6839

.87

5.0

61.

7027

.47

0.60

Tab

le 3

.2: O

vera

ll C

hara

cter

istic

s of

WA

B

43

The available energy of all the nine residues is represented in Table 3.3. The

total energy equivalent in district Sanghar was estimated as 38 PJ, where as the

available energy potential was 21.5 PJ, which is equal to 56% of the total energy

equivalent in district Sanghar. It can be observed that, by using available energy of

waste agricultural biomass, we can generate about 1192 million units of electricity by

installing the power plant of 150 MW. Moreover the same number of units can be

generated if the decentralized approach is adopted for each Taluka.

Table 3.3: Total energy potential of WAB in district Sanghar

Nam

e of

T

aluk

a

San

ghar

Sin

jhor

o

Sha

hd-

adpu

r

Tan

do

Ada

m

Jam

N

awaz

A

li

Khi

pro

TOTAL

Total Energy Equivalent (TJ) 6528 8919 8027 4653 2833 7059 38,018

Available Energy Equivalent (TJ) 2813 4690 4282 3235 2078 4365 21,464

Electricity Generation (MWh) 156250 260580 237883 179742 115469 242505 1192,429

Pant Size (MW) 20 33 30 23 15 31 151

The true sense of the Waste Agricultural Biomass is the energy that we can

obtained from the disposed off agricultural residues. The quantity and energy of

disposed off WAB, that can be obtained from cotton stalks, sugarcane tops, rice straw

and banana plant in each Taluka of district Sanghar was 1088 kilo-tons and 16,385 TJ

respectively as shown in Table 3.4 below.

44

Table 3.4 Energy potential of disposed off WAB in district Sanghar

Tal

uka

Name of Crop Residue

QPY (tons)

AF QDO (tons/year)

HCV (kcal/kg)

EDO (TJ/year)

Cotton Stalks 229177 0.25 57294 3649 875 Sugarcane Tops 68163 1.00 68163 3639 1038 Rice Straw 7403 0.80 5923 3349 83 Banana Plant 1415 1.00 1415 3201 19 S

ang

har

Sub- total 306157 ---- 132794 ---- 2015 Cotton Stalks 318193 0.45 143187 3649 2186 Sugarcane Tops 58917 0.80 47133 3639 718 Rice Straw 20188 0.75 15141 3349 212 Banana Plant 4619 1.00 4619 3201 62 S

injh

oro

Sub- total 401916 ---- 210080 ---- 3178 Cotton Stalks 315145 0.50 157572 3649 2406 Sugarcane Tops 38997 0.80 31198 3639 475 Rice Straw 2817 0.70 1972 3349 28 Banana Plant 28210 1.00 28210 3201 378

Sha

hda

dpur

Sub- total 385169 ---- 218952 ---- 3287

Cotton Stalks 127779 0.70 89445 3649 1366 Sugarcane Tops 46770 0.80 37416 3639 570 Rice Straw 4333 0.75 3249 3349 46 Banana Plant 48814 1.00 48814 3201 654

Ta

ndo

Ada

m

Sub- total 227696 ---- 178925 ---- 2635 Cotton Stalks 114480 0.80 91584 3649 1398 Sugarcane Tops 17728 0.80 14183 3639 216 Rice Straw 6660 0.75 4995 3349 70 Banana Plant 2092 1.00 2092 3201 28

Jam

Na

waz

Ali

Sub- total 140961 ---- 112854 ---- 1712 Cotton Stalks 318356 0.65 206931 3649 3160 Sugarcane Tops 22220 0.80 17776 3639 271 Rice Straw 9335 0.80 7468 3349 105 Banana Plant 1777 1.00 1777 3201 24 K

hipr

o

Sub- total 351689 ---- 233953 ---- 3559

GRAND TOTAL 1,813,588 ---- 1,087,558 ---- 16,385 Where,QPY = Quantity of WAB per year (tons), AF = Availability Factor,

QDO = Total Quantity of Disposed off WAB per year (tons), EDO = Energy in disposed off WAB per year (TJ)

45

3.2 STEPS BY STEP ASSESSMENT OF ESTs

The EST criteria may be applied towards TA in a three-tiered manner:

1. Screening tier

2. Scoping tier

3. Detailed assessment tier

3.2.1 Screening tier

The first tier could be a screening level assessment, that is based on

elimination, using certain qualifying criteria (go / no go) that are a must for a

technology to be classified as an EST. Table 3.5 represents the screening of all the

four technologies. It can be viewed that all the five technologies have been screened

out.

Table 3.5: Tier 1 (screening) criteria applied to identified technology systems

Technology

Criteria

Direct Combustion Composting Gasification Biogas

Pallets of

WAB Compliance with local environmental laws

Yes Yes Yes Yes Yes

Compliance with national environmental laws

Yes Yes Yes Yes Yes

Safe to use? Yes Yes Yes Yes Yes

Provides savings on resources?

Yes Yes Yes Yes Yes

3.2.2 Scoping tier

The second tier is essentially a scoping exercise and uses EST criteria and

indicators to rank technology alternatives (e.g. based on a weighted sum technique)

and allows short-listing of ESTs. The result of the scoping is shown in Table 3.6.

46

Sco

reW

eig

ht

x S

core

Sco

reW

eigh

t x

Sco

reS

core

Wei

ght

x S

core

Sco

reW

eigh

t x

Sco

reS

core

Wei

ght

x S

core

Sui

tabi

lity

of w

aste

ch

arac

teris

tics

for

tech

nolo

gy

appl

icat

ion

104

406

607

708

806

60P

ast

expe

rienc

e (u

nder

si

mila

r co

nditi

ons

)10

880

660

440

660

220

Land

req

uire

men

ts10

330

550

880

880

880

(Ove

rall)

po

lluta

nt

rem

ova

l effi

cien

cy10

330

660

990

880

770

Acc

epta

bilit

y (t

o t

he

publ

ic)

106

606

603

308

806

60In

com

e ge

nera

tion

pote

ntia

l7

749

428

428

749

642

289

318

338

429

332

Pal

lets

of W

AB

Wei

ght

Crit

eria

TO

TA

L = Σ

(W

eigh

t x

Sco

re)

Dire

ct

Com

bust

ion

Com

post

ing

Gas

ifica

tion

Bio

gas

Tab

le 3

.6: T

ier

2 (s

copi

ng)

crite

ria a

pplie

d to

tech

nolo

gy s

ystem

s

47

Table 3.7 shows the rankings given to the various technology systems options

based on the results from Table 3.6. It can be observed that the ranking of the

technologies is one to five is for biogas, gasification, pellets of biomass, composting

and direct combustion respectively. Now for the detailed assessment tier the top three

technologies were selected.

Table 3.7: Ranking the technology systems from results in Tier 2

Technology system Score Rank number

Biogas 429 1 Gasification 338 2 Pellets of WAB 332 3 Composting 318 4 Direct Combustion 289 5

3.2.3 Detailed assessment tier

The third tier is the analysis of short-listed alternatives on the basis of criteria

and indicators using a scoring/ranking framework. Of the first three ranked

technology systems shaded in Table 3.7 were short-listed and taken for further

assessment using the criteria in Tier 3 (detailed assessment criteria). Table 3.8 shows

the calculations for the technology systems’ assessments, once again using the

weighted sum method.

48

Sco

reW

eigh

t*

Sco

reS

core

Wei

ght*

S

core

Sco

reW

eigh

t*

Sco

reP

roce

ss s

tabi

lity

94

368

726

54Le

vel o

f aut

omat

ion

/ sop

hist

icat

ion

103

307

708

80E

stim

ated

use

ful l

ife10

880

880

880

Fue

l con

sum

ptio

n7

535

749

642

Ele

ctric

ity c

onsu

mpt

ion

73

216

425

35S

avin

gs in

ene

rgy

87

566

484

32C

apita

l inv

estm

ent

104

408

8010

100

Ope

ratio

n an

d m

aint

enan

ce c

osts

104

408

808

80F

inan

cial

ince

ntiv

es (

e.g.

reb

ates

from

go

vern

men

t)8

00

00

00

Pay

bac

k pe

riod

87

566

487

56N

PV

/ IR

R8

432

756

648

Sec

onda

ry c

onta

min

ant g

ener

atio

n9

436

981

654

Req

uire

PP

E fo

r st

aff?

75

356

427

49Le

vel o

f saf

ety

risk

for

wor

kers

and

co

mm

uniti

es7

428

749

321

Noi

se le

vels

nea

r in

stal

latio

n du

ring

oper

atio

n7

535

749

642

Odo

ur le

vels

nea

r in

stal

latio

n du

ring

oper

atio

n7

535

535

749

Per

son-

pow

er r

equi

rem

ents

53

154

204

20T

echn

ical

kno

wle

dge

requ

irem

ents

(q

ualif

icat

ions

/spe

cial

kno

wle

dge

need

ed)

106

609

907

70

670

991

912

Gas

ific

atio

nB

iog

asP

alle

ts o

f W

AB

TO

TA

L (Σ

wei

gh

t *

assi

gn

ed s

core

)

Cri

teri

aW

eig

ht

Tab

le 3

.8: R

esult

of T

ier

3 cr

iteria

to s

hort

-list

ed te

chno

logy

sys

tem

s

49

Figure 3.1 shows the star diagram by taking the results of tier 3. It can

be observed from the star diagram that of the three technology system option, biogas

has been found to be the most appropriate option of the three, followed by biomass

pellets and gasification respectively.

Figure 3.1: Star Diagram at Tier 3 Level of Assessment

50

CONCLUSION & RECOMMENDATION

From the detail assessment of the selected technologies following three

technologies were come out as most feasible and environmentally sound, sustainable

and economically viable.

1. Biogas

2. Biomass Pellets

3. Gasification

From the results of Tier 3 criteria to short-listed technology systems as in

Table 3.8, the score obtained by Biogas, Biomass Pellets and Gasification is in the

order of 991, 912 and 670 respectively. The gasification technology is less feasible

from the assorted technologies because of more sophistication, automation, capital

investment, safety risk for workers and requirements of technical knowledge. On the

other hand Biogas gasification is most feasible. The biomass pellets according to the

score comes at the second number. For pilot scale biogas (Anaerobic Digestion) is

recommended for pilot scale project in Sanghar.