7027056 Bagasse as Alternate Fuel[1]

7/31/2019 7027056 Bagasse as Alternate Fuel[1]

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INTRODUCTION

Need for alternative fuel

Industrial growth over the past century has seen an ever-increasing demand

on the earths fossil fuel resources such as coal & oil .These fuels have been

favoured due to their ease of extraction & cost-effective conversion into usable

energy. However recent discussion into the effects of fossil fuels on the

environment have encouraged investigation into renewable energy sources as away of alleviating negative environmental effects & their existing nature.

Reasons for low utilization of biomass

Biomass is comparable to solar energy in one respect that it occurs in a

highly diffused form, scattered throughout the country. Just as concentrating solar

energy at one point is difficult to collect & transport the relatively light biomass

from its point of origin to a centrally located processing facility. Although it is

stated above that the biomass either in the form of agro-waste or in the form of dry

grass had no commercial value, it still needs to be collected & transported by

somebody to the processing facility just a few Km away, cost about Rs.1000/ton.

In addition to the above expense, one should not expect a farmer to surrender this

agro-waste to a processing plant without any payment.

Because villagers are seen to use biomass, as a free of cost material for a

variety of purposes, even the so-called experts make the mistake of considering

plant biomass as a no-cost raw material for industrial scale processing operations

too. This lack of awareness of the ground realities has done more harm than good

to cause of biomass energy.


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What is BAGASSE?

Sugarcane is a seasonally-grown food and feed crop, the processing of

which creates bagasse, a low-cost biomass material, as its by-product. Bagasse is acommodity that is readily available for usein 1992, 610 million tons of bagasse

was produced worldwide. It is suitable for production of energy, ethanol, animal

feeds, paper products, composite board, and building materials; and it is a feed

stock for fluidized-bed production of a range of chemicals.

Selection of Bagasse as an alternative fuel

Biomass is a readily available renewable resource that has been usedthroughout the past as a source of heat energy by means of combustion. In recent

there has been increased research into the feasibility of converting biomass such as

bagasse into other form of usable energy.

Bagasse is comprised of lingo cellulosic residues & is a by-product of many

agricultural activities. Bagasse is essentially the fibrous waste left after the sugar-

cane has been extracted for crystallizing into sugar. The fraction of bagasse

obtained from raw cane crushed is approximately 20% - 30%.

Previously, bagasse was burned as a means of solid waste disposal.

However, as the cost of fuel oil, natural gas & electricity increased after the energy

crisis in 1970, special attention was paid to alternative fuels in an efficient way.

Consequently, conception of bagasse combustion changed & it has come to be

regarded as biomass fuel rather than refuse. The actual tendency is to use bagasse

as fuel, especially for cogeneration of electric power & steam, to increase its

contribution to the countrys energy supply.

This report will investigate that food waste recycling rate just was 1% &

how the sugar industry is using the principles of cleaner production to minimize

waste from the cane milling process by using the energy stored in bagasse to

power the process & in many cases add green energy to the main electricity grid. It


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will also investigate the economical & environmental effects of other options

available to process the bagasse into usable products such as FUEL.

Renewable energy program Govt. of INDIA1. The Indian Renewable Energy Development Agency (IREDA) was set up by

the Ministry of Energy in 1987 to provide assistance to manufacturers &users

of renewable energy system.

2. In 1992, the Ministry of Non-conventional Energy Sources (MNES) was

established as a department in the Ministry of Energy.

3. The Ministry implements the Integrated Rural Energy Program transferred to

it from the Planning Commission.4. A National Program on Biogas Development is a major Program of Ministry.

Waste collected (% by weight)

Industry waste

51%food waste

40%

others

9%

Industry waste food waste others


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PROPERTIES OF BAGASSE

Physical properties

1. White & light green.

2. It is odorless.

3. The typical specific weight is 250 Kg/m3.

4. The main content: - 45% moisture, 50% cellulose - (27.9% hemicellulose,

9.8% lignin & 11.3% cell contents) & 6% others.

5.

Energy content: - 19400 KJ/Kg dry ash free.

Chemical properties

The percentage distribution by dry wt. of major elements composing the

bagasse is present in the below table.

Components C H O N S Ash

% by wt

(dry basis)

49 6.5 42.7 0.2 0.1 1.5

Chemical formula

Estimation of the chemical formula of bagasse:-

1. The percentage distribution of the elements with & without the water

contained.

Give: - !00 Kg bagasse based on 45% of moisture content.

Component C H O N S Ash

Weight in Kg

(without water)27 3.6 23.5 0.11 0.055 0.735

Weight in Kg

(with water)27 8.5 63.5 0.11 0.055 0.735


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2. Computering the molar composition of the elements neglecting the ash

component.

Components C H O N S

Atomic weight 12 1 16 14 32

Moles (without water) 2.25 3.6 1.47 0.008 0.002

Moles (with water) 2.25 8.5 3.97 0.008 0.002

3. Setting up the computation table to determine the normalized mole ratio.

Components C H O N S

Moles ratio (without water) 1125 1800 735 4 1

Moles ratio (with water) 1125 4250 1985 4 1

4. Approximate chemical formula of bagasse.

Without water: - C1125H1800O735N4S

With water : - C1125H4250O1985N4S

Bagasses are the fibrous residue of the cane stalks after crushing & consist

mainly of cellulose, pentosans & lignin. Its final composition after milling

depends on method of harvesting as well as age & type of cane. On average it is

assumed to have 50% moisture, 47.7% fiber & 2.3% soluble solids. The Gross

Calorific Value (GCV) of dry ash free bagasse is 19400 KJ/ Kg while bagasse

with 50% moisture content has GCV of 9600 KJ/Kg & Net Calorific Value (NCV)

of 7600 KJ/Kg.GCV is also know as the Higher Heat Value(HHV) & the NCV as the

Lower Heat Value(LHV) it assumes that water formed by combustion & water of

the fuel constitution remains in vapour form. In industrial practice it is not

practicable to reduce the temperature of the combustion products below dew point


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to condense the moisture present & recover its latent heat, thus the latent heat of

the vapour is not available for heating purposes & must be subtracted from the

HCV.


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OVERVIEWOF SUGARINDUSTRIES

Dry matter productivity of some selected agricultural crop(1)

CROP DRY MATTER YEILD

Wheat 4.4

Rice 8.4

Corn 8.4

Barley 4.2

Oats 4.0

Rye 3.4

Soybean 5.7

Sugarcane 49.4

Sugarcane bagasse has been reported to contain 48% cellulose. It thus

implies that the total world production of 233.942 million tons of bagasse from

15,895 hectares would yield 112.29 million tons of cellulose. These data indicate

that based on per unit of land area sugarcane is the most productive cellulose

producing crop. The majority of bagasse produced in small or large scale factories

is generally used as fuel in the same factory where it is produced. It has been

estimated that 10-15% of the bagasse from any sugar mill could be made available

for feeding animals, using the rest as fuel for factory furnaces. Most of the sugar

mills burn bagasse to generate steam & electricity. One ton of bagasse when

burned is equal in fuel value to one barrel of fuel oil.


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Sugar industries scenario in INDIA

Sugar industry is the second largest industry after textile in India. India also

stands among the first five countries of sugar production in the world. The annual

turnover of the sugar industry is around 5500 crores of rupees and the totalinvestment is around 3500 crores of rupees. It also employs directly or indirectly

of about 1.75 crores people in India.

Crushing capacity of sugar mills vary from about 1500-5000 tonnes per

day, while that of the 'Khandasari' Mills vary from 20-200 tonnes per day.

The process of sugar production involves following steps.

1.

Cleaning of canes.2. Milling of canes.

3. Extraction of juice

4. Concentration of juice

5. Removal of impurities by addition of calcium phosphate, lime and double

carbonization or double sulphination.

6. Concentration of juice to syrup by evaporation.

7. Crystallization.

8. Separation of sugar through centrifuge i.e. by centrifugation of crystals.

9. Final packaging and handling of sugar.

Sugar cane synthesis the maximum solar residue and energy into biomass like

sugar, cellulose, lignin and pentosans.


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Profile of Indian sugar Industry

Year No of Mills Sugar production

in lakh tons

Consumption of Sugar

in lakh tons

1950-51 138 11.34 10.98

1955-56 143 18.92 19.73

1960-61 143 30.28 21.13

1970-71 216 37.46 40.27

1975-76 253 42.62 36.87

1980-81 314 51.16 49.70

1985-86 341 70.16 70.59

1991-92 392 134.64 106.26

The sugar companies comes under the Board of Industrial & Financial

Reconstruction (BIFR)(6).

As per the information provided by the BIFR as on 30-06-2003 , 44

companies involving 76 sugar mills are registered with BIFR . The state-wise

break up is as follows

Sr. no. STATE No. of Sugar Mills

1. Andhra Pradesh 3

2. Bihar 4

3. Kerala 1

4. Karnataka 5

5. Madhya Pradesh 3

6 Maharashtra 4

7. Orissa 1

8. Punjab 2

9. Rajasthan 110. Tamil Nadu 8

11. Uttar Pradesh 43

12. West Bengal 1

Total 76


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TREATMENTOFBAGASSE

A.) Improvement of the calorific value of bagasse(7)

(1.) Using flue gas drying

The existing sugar surplus and an acute energy shortage in India have

prompted the examination of co-generation possibility using available surplus

bagasse, and ways of saving more bagasse for off-season co-generation.Out of 20% condensation loss in the boiler efficiency, 14% of the loss is

due to the moisture in bagasse, which is around 50%. Reducing the bagasse

moisture would help to increase the calorific value of bagasse, resulting in an

increase in the quantity of bagasse saved. This reduction in bagasse moisture

could be achieved in two ways:

1. by mechanically increasing the pressure on the mill rollers.

2. by using various sources of energy and equipment to dry the bagasse.

An energy efficient way to reduce the bagasse moisture is to use the heat

from the flue gas. Over the years, rotary dryers, flash dryers, swirl burner system

and other means of drying bagasse were tried with varying degree of success.

After looking at the various options available, the Andhra Sugars Ltd.

installed an induced draft flash dryer at the Sugar Unit - I during the 1999 / 2000

season and had achieved substantial bagasse moisture reduction, bagasse saving

and an increase in boiler efficiency. Based on the data and experience gathered, a

forced draft flash dryer was commissioned during the 2000/2001 season at the

Sugar Unit - II. The operation of this dryer had been smooth since its


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commissioning and had resulted in substantial bagasse moisture reduction, bagasse

saving and boiler efficiency increase.

The installation of bagasse dryers at the two Sugar Units resulted in bagasse

saving that had enabled co-generation for four months during the off-season andincreased the energy generated from 12.5 to 16.4 million units per year.

(2.)Through the implementation of modified Java method mill setting

The Java method of mill settings was known since before the World War

II and it experienced good results for mill performances.

To obtain good overall extraction several conditions are specified by the

Java method, e.g.:1. Operate the mills at a very low rotation(2.51.5 rpm, gradually decreased

from the ultimate to the ensuing mills).

2. The actual fibre loadings should be as low as possible (gradually increased

to the ensuing mills).

3. The top roller lifts should be limited precisely as calculated.

With steam turbines the mill rotations will be higher and approximately the

same throughout the tandem; and consequently also the fibre loadings.

When MILL MATERIAL BALANCE is used as base for the mill settings

calculation, which modifies the method with the inclusion of the same average

value of fibre loadings throughout the tandem; the main objective of the Java

method could be achieved although steam turbines are used as the drives.

The said MMB calculation defined the flow of material (mass and volumes)

to and from each of the mill in the tandem individually; therefore the result could

be used as base and reference for individual setting of the mills.

Bases for calculation are quantity and quality of cane to be crushed,

quantity of mixed juice and imbibition water, and the dimensions of all the rollers


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in use, the average analysis of the extracted juices and the last mill bagasse

analysis.

Numerous calculations are required to complete a comprehensive MMB,

but with the use of a computer simulation it becomes simple and easy. Beside theextractions it could also simulate the last mill bagasse for low moisture content

even when a higher imbibition rate is applied. This means an improvement of the

net caloric value of bagasse as fuel for the boilers could be projected (by formula:

NCV = 4250 10 s 48 w).

An example of last mill bagasse produced by a tandem of 5 mills with

steam turbine drives is compared here.

Average bagasse analysis during campaign (mills were set without MMB):

Moisture = 50.23%

Caloric value = 1818 kcal/kg.

Average bagasse analysis when mills were set based

Moisture = 48.30%

Caloric value = 1920 kcal/kg.

It is concluded that with the proper mill settings based strictly on MMB

(modified Java method) the caloric value of bagasse will certainly increase and the

total bagasse consumed as fuel for the boilers for process requirement will be

reduced and additional excess bagasse will be obtained that could be used for

other purposes.

The potential for power generation from bagasse alone is estimated about

4,000 MW.

In view of its tremendous potential in power production, the Government

launched a National Program on Bagasse-based co-generation in 1994. At that

time, only 3 sugar mills in Tamil Nadu had the capacity to export about 5 MW of


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electrical power to the grid. As of now, 16 sugar mills based on bagasse have been

exporting surplus power to the extent of 56 MW.

A sugar mill can produce surplus power of 150 kWh per MT cane, under

ideal conditions. Study of a co-generation plant in the south of India shows thatprice realization varies from US Cents 5 to 6 per kWh. Also, during the crushing

season, they utilize bagasse and lignite in the ratio of 90:10 whilst during off-

season the ratio works out to 40:60.

Some of the concerns of bagasse-based co-generation plants are related to:

1. Optimum boiler / turbine configuration

2.

Round-the-year operation offering firm tie-up for power3. Alternate fuels

4. Energy efficient sugar processing

5. Efficient bagasse storage, handling and retrieval system

6. Effective grid interface systems

B.)Biological treatment and storage method for wet bagasse for year round

biomass supply (10).

Successful industrial operations need year-round supplies of the seasonally-

produced and harvested bagasse. The harvesting season for sugarcane is

approximately six months. Industries operate a 300 tpd bagasse particleboard

plant, a year-round operation that requires over 54,000 dry tons (equivalent to over

120,000 tons wet) of bagasse stockpiled on an ongoing basis. The collection,

transportation, and storage of this seasonal product for year-round use present a

difficult problem in bagasse utilization.

A biological treatment, FERLAB has been developed which quickly

ferments the soluble residual sugars and other low molecular weight extractable,

while it maintains low bale temperatures and reduces long-term fermentation

losses in storage. The FERLAB treatment was combined with a self-ventilating


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piling method of wet-baled bagasse to reduce fermentation losses and bagasse

moisture contents. To test the treatment, six 100-ton bagasse bale piles were

constructed. Bale temperatures, fermentation losses, and moisture contents were

monitored for four and one-half months.Ventilation of baled bagasse piles reduced moisture content from 55% to

25%. The FERLAB treatment reduced dry matter losses during storage. The

FERLAB process consists of a proprietary mixture of thermophilic microbes. A

schematic of the process is shown in Fig below.

Chemical analyses of the wet and conventionally pre-dried stored bagasse

showed that the FERLAB-treated bagasse had 66% lower extractive contents and

significantly higher relative alpha cellulose and lignin contents, which suggestsreduced acid hydrolysis of higher molecular weight cellulose and lignin during

storage.

The FERLAB/wet self-ventilating bagasse storage provided easier handling

and lower transportation costs (drying reduced the weights). Reduced moisture

content increased the Btu content of mill-run bagasse from 3,130 Btu/lb to 5,586

Btu/lb. The stored bagasse at 25% moisture content can provide not only year-

round boiler fuel, but also raw material for an air-fluidized-bed reactor system to

produce low Btu gasses and chars, tar/oils which can be used as a substitute for

phenol in adhesives and other chemicals. Bagasse also can be stored for year-

round methanol production. These bio energy products reduce the storage

problems and transportation costs unique to biomass fuels. The FERLAB/wet self

ventilating storage is an alternate to current wet storage.


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Schematic of the FERLAB treatment for biological drying of bagasse(10)

.


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5

A COMPARATIVESTUDYBagasse as an Alternative Fuel to Coal for Industrial Uses

Introduction

The usage of coal as a fuel in industries results in the generation of gaseous

emissions. The total coal reserves (as on 1-1-1998) have been assessed by

Ministry of Coal (MOC) at 206.24 billion tonnes but bulk of these (87%) reserves

are non-coking coals of inferior grade. The Ministry of Environment & Forests

(MOEF) has imposed restrictions on the usage of non-coking coal with high ashcontents in view of huge fly ash generation. The need of the hour in todays world

is to globally phase-out coal as a fuel source. Since the deficit of coal

consumption over its availability is expected to continue and much of the available

coal is of inferior grade and likely to find restricted use in the future due to the

MOEF regulations, it would be desirable to choose a suitable fuel to substitute

coal. The alternate fuel should have advantages in terms of utility, financial

savings, less pollution loads etc. The various substitute materials currently being

utilized are fuel oil, locally available cheaper agro-residues such as bagasse, husk,

briquettes, wood etc.

Bagasse is a by-product/waste in the sugar industry. Its use as a fuel is

restricted because of its low Calorific Value (CV). Theoretically the thermal

efficiency of bagasse can be improved when mixed with waste oil in the optimum

ratio of 4:1. This optimum ratio was arrived at such that, the prescribed minimum

stack height (30m) attached to the boiler is not altered.

The present study is oriented towards:

Exploring the feasibility of using bagasse as an alternate fuel to coal and its

comparison vis--vis coal with respect to both technical and economical

aspects


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Incorporating provision for any future changes in the inputs used for

cost analysis

Problem Formulation and ResultsMinistry of Coal (MOC) has classified the non-coking coal into A, B, C, D,

E and F grades based on its useful CV. The useful CV in Kcal/kg according to the

MOC classification is defined by the formula:

8900 138(% ash content +% moisture content)

In the case of coal having a moisture less than 2% and a volatile content

less than 19%, the useful CV shall be the value arrived at as above reduced by

150 Kcal/kg for each reduction in volatile content below 19% fraction pro-rata .

Pollutant emissions

The emission rates of coal and bagasse are found out for direct firing

of these fuels such that, the stack height for the emission do not exceed the

stipulated minimum stack height 30 m . The assumptions made in the calculation

of pollutant emissions are:

1. No pollution control equipment is needed for the minimum stack height of

30m.

2. Fly ash generation from bagasse is 0.081 kg per each kg of bagasse fired

while that of the coal is 75% of coal ash content.

3. The only emissions generated and discharged through the stack are due to

the fuel firing.

With the above assumptions, the minimum fuel inputs are back calculated

and are given in Table below. The three types of coal selected from literature with

ash and moisture contents 43.12% & 3.84%, 34.38% & 6.04% and 25.19% & 6.0

% respectively are designated as C1, C2, & C3 types for the purpose of present

study. As per the MOC classification of non-coking coals, the above-designated


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Economics

The economic returns involved in the alternative usage of optimum BWO

as fuel for coal and/or bagasse alone are compared. The utilization cost of steam

from the fuels attempted for the study is calculated @ 2.5 US $ or Rs. 108.60 per1000 kg of steam and is shown in Table-3. The purchase costs of bagasse, D-,

& F-grade coals are taken as Rs. 150 per 1000 kg, Rs. 594 and Rs. 415

respectively. Using this information, the Net Utility Value (NUV) of the fuels

attempted is calculated as the difference of its steam utility value (SUV) and

purchase costs.

Table: Net utility value of various fuels

FuelQOF

(KPH)

PC

(Rs.)

SUV

(Rs.)

NUV

Rs.(SUV-PC)

Bagasse 432 64.80 338.83 274.03

Optimum BWOmix (4:1)

346 51.90 629.88 577.98

C1 type Coal 108 44.82 779.75 734.93

C2 type Coal 135 56.03 886.18 830.15

C3 type Coal 185 110.00 1000.21 890.21

QOF: Quantity of Fuel; PC: Purchase Cost; SUV: Steam Utility value.

Analysis Results & Discussion

Considering the above results, the monthly saving/expenditure on the

attempted fuel for the user is calculated with the assumption of 21 working hours a

day and 30 working days per month. The results are:

1. The usage of optimum BWO mix as fuel in place of bagasse result in a

net saving of Rs. 1.915 lakhs per month or Rs. 22.98 lakhs per annum.

2. The financial loss to the user due to the non-usage of bagasse as fuel is Rs.

1.726 lakhs per month or Rs. 20.716 lakhs per annum.


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6

BIOMASS GASIFICATIONFACILITY

USINGBAGASSE

The reactor operates at a pressure of 2 MPa and feed rate of 90 dry tonne

bagasse per day. It consists of a refractory-lined fluidized bed which utilizes

alumina beads as the inert bed media. Air and steam are fed into the reactor

through separate distributors in order to control temperature and gas composition.

Airflow is typically maintained at approximately 30% of that required for

complete combustion. Steam for the process is supplied by the sugar mills

bagasse-fired boiler. A plug-screw feeder is used to sufficiently increase the

bagasse density so as to seal the feed system against the pressure of the gasifier.

The plug exiting the screw feeder falls onto a water-cooled shredding auger which

breaks up the plug and conveys the bagasse into the reactor. Raw gas exiting the

top of the reactor passes through a refractory-lined cyclone to remove entrained,

unreacted char and ash particles. In the operations reported here, the process

stream is dropped from reactor pressure to near ambient conditions before entering

a product gas flare where it is combusted and vented to atmosphere. The process

operated in an air-blown mode, with no steam added, at a nominal reactor

temperature and pressure of 840C and 300 KPa, respectively. Bagasse from the

factory at ~50% moisture was dried to ~25% wet basis. Wet fuel feed rate to the

reactor was approximately 1.1 t/ hr. An average gas composition determined over

the period of operation was 4% H2, 10% CO, 18% CO2, 3.3% CH4, ~1% C2s and

higher hydrocarbons, and the balance N2. The higher heating value of the gas was

3.7 MJ m3. Carbon conversion efficiency was estimated to be ~96%. Resulting in

an additional 60 hours of operation. Testing using air and steam was carried out at

a reactor temperature and pressure of 860C and 500 KPa. Wet fuel feed rate was


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1.6 t/hr with a reduced moisture content of 17%. Steam addition resulted in

improved gas quality and higher heating value. Composition was determined as

8.5% H2, 12% CO, 18% CO2, 7% CH4, ~1% C2s and higher hydrocarbons, and the

balance N2 with a higher heating value of 5.8 MJ m

3(10)

.

Process schematic of bagasse gasifier(10)

.

Fouling Of Boiler(10)

Boilers fired with fuels having high levels of potassium or sodium (alkali

metals), particularly in the presence of chlorine and sulfur, are susceptible to

fouling and slagging. Sugarcane leaves and tops are expected to contain much

higher levels of alkali compounds than bagasse; therefore using such fuels might

cause significant problems in bagasse boilers.


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A rough gauge of fouling potential is the amount of potassium and sodium

compounds per unit of fuel energy; e.g., kilograms of Na2O and K2O per GJ. The

figure below plots concentrations of total alkali compounds (expressed as K2O

and Na2O), sulfur (as SO3), and chlorine per unit fuel energy, for four differentbiomass feedstock sugarcane bagasse produced by milling; diffusion; unprocessed

banagrass (a cultivar of elephantgrass); and processed (chopped and leached)

banagrass, along with an estimate of each fuels potential to cause fouling.

Whereas bagasse contains relatively low- to- moderate levels of alkali

compounds (~0.05 to 0.15 kg per GJ), sulfur, and chlorine, and normally does not

promote excessive fouling in boilers, unprocessed banagrass contains very high

levels of alkali compounds (~0.7 kg per GJ), sulfur, and chlorine, and isanticipated to readily foul boilers.

Concentration of total alkali, sulfur, & chlorine for four different biomass fuels &

fuel fouling/slagging potential(10)

.


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7

OPTIMIZATION OFBOILEREFFICIENCYUSINGBAGASSE ASFUEL

Introduction(8)

The designs referred to as fuel cell and horseshoe boilers were those

typically used for bagasse combustion. In these boilers, bagasse is gravity-fed

through chutes and burned as a pile. Nowadays, bagasse is burned in spreader

stoker boilers, replacing the combustors that use pile type approaches, and

improving combustion efficiency. Furthermore, the use of additional heat transfersurfaces, as air heaters, economizers, etc. allows for a reduction of the stack

temperature below 200oC. With these improvements, efficiency of the boilers can

be increased up to 70%. Special attention has been paid to the optimization of

stoichiometric ratio as well as the stack gases temperature, for their influence on

the principal heat losses and, consequently, on the overall efficiency of the boiler.

Boiler and fuel characteristics

The experiments were carried out in three RETAL boilers shows a detailed

sketch of the main thermal surfaces of these facilities. The total height and depth

of the boiler are 10.6 and 10.92 m, respectively, and the width (not shown in the

figure) is 8 m. Summarizing the main characteristics, a nominal steam power of 45

t/h is achieved for an approximate bagasse consumption of 22 t/h; with a pressure

and temperature of the superheated steam of 1.9 MPa and 320 8C, respectively.

Bagasse fed to these boilers enters the furnace through five fuel chutes and is

spread mechanically. The major part of the bagasse characterized by small and

light pieces, burns in suspension. Simultaneously, large pieces of fuel are spread in

a thin even bed on a stationary grate. An average ultimate (dry) analysis of the fuel

used in the tests gave a 46.27% (in weight) of carbon, 6.4% of hydrogen,


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Sketch of a RETAL bagasse-boiler(8)


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43.33% of oxygen, 0% of nitrogen, 0% of sulfur, and 4% of ash. The moisture

content of the bagasse ranged from 48 to 52% for all the analyzed samples.

Operational test procedureMore than 60 tests were performed, attending the ASME recommendations

for solid and liquid fuels. Each test comprised three stages, namely: preparation,

measurements, and laboratory analysis. According to the standard procedures, one

should wait at least 24 h after startup of the boiler and 2 h after cleaning of the

bottom ash, the ash hopper located in the U-turn of the flue gas duct and the heat

transfer surfaces before starting a test. The boiler should reach, and maintain, a

steady state for at least 8 h before starting the test. The fuel chute and thestationary grate must also be cleaned 1 h before starting, and the speed of rotation

of the spreader stokers fixed. Some trays have to be placed in the proper locations

for refuse collection, and the fly ash wet scrubber has to be cleaned as well.

Boiler measurements and laboratory analyses are performed along the

following 9 hours. The first four hours are dedicated to measure all the boiler

parameters every 15 minutes. Every half hour, stack gas composition (O2, CO, and

CO2) is determined and bagasse samples collected for the determination of their

moisture and ash contents. The furnace temperature is also measured every 15 min

using water-cooled suction pyrometers. The sampling and measurement locations

are shown in fig.

Laboratory work begins with refuse collection from all the different

locations (ash bottom, ash hopper and web scrubber). In the following five hours,

moisture and ash contents of the bagasse and solid samples from the fly ash

hoppers, wet scrubber, and bottom ash hopper are analyzed. When all the data are

assembled, a statistical analysis determines the mean and standard deviation for

each parameter. If a steady state has not been achieved in the boiler, the test must

be rejected.


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As it is well-known, the overall efficiency of a boiler can be calculated

using both direct and indirect methodologies. The direct measurement of the

bagasse consumption is always subjected to many error sources. For this reason, in

the present study, efficiency has been calculated using the indirect methodology.In general, this method relates the efficiency () of the boiler with the different

heat losses through the equation

(%) = 100 - qi

where qi = q2 + q3 + q4 + q5: In this equation, q2 represents the exhaust gases heat

loss, q3 and q4 are the chemical and fixed carbon loss, respectively, and q5 the

conduction heat loss from the external walls of the boiler. To quantify the heat

losses, the following equations are used [2]:

Here, Ieg and Iea are the exhaust gases and external air enthalpy,

respectively, b the stoichiometric ratio at the exit of the boiler, QP l the bagasse

heating value (as received), HCC the carbon heat of combustion, HCO

C the CO

heat of combustion, AP the ash contents of bagasse from ultimate analysis (asreceived) and RCO/f is the rate of kilograms of CO produced during the combustion

of one kilogram of fuel.

The stoichiometric ratio, = ma/f/moa/f is defined as the ratio of the actual

air-to-fuel mole number ratio (ma/f) to the theoretical one (moa/f) for the same


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experimental conditions. In turn, the actual air-to-fuel mole number ratio (ma/f ) is

defined as the theoretical number of moles of air plus the extra moles due to

excess air needed to achieve the complete combustion of one mole of bagasse (in

moleair/molefuel). In order to more accurately reproduce the physical influence ofthe different parameters and heat losses in the statistical models, two

stoichiometric ratios have been defined, namely: stoichiometric ratio at the

furnace, f; and stoichiometric ratio at the exit of the boiler, b. It should be

pointed out that in the case ofb; the amount of surrounding air in-leakage into the

boiler due to non-air tightness, ; is also included in the total air mole number.

Ai refers to Afa; Aah and Aba; which correspond to ash percentages in the fly

ash, ash hopper and bottom ash, respectively, obtained through laboratory analysis

combusting and weighting the different samples of refuse collected in a special

oven following the methodology of ASME. In the same way, a i refers to the ratios

of ash in the fly ash, afa; ash hoppers, aah; and bottom ash, aba with respect to the

total ash in the fuel, in kgash in refuse/kgash in fuel. From a mass balance of ash in the

boiler, considering Gi as the refuse collected per time unit in the different locations

in fly ash, Gfa; ash hopper, Gah; and bottom ash, Gba; respectively, in kgrefuse/s, the

following equation can be written

the different ash ratios ai; in fly ash, afa; ash hoppers, aah; and bottom ash, aba; are

defined by

and hence

To calculate the conduction heat loss, q5; from the external wall to the

surrounding area, the total heat lost (including radiation) has to be considered. In


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Eq. (5),T is the total heat transfer coefficient in kW/(m2C), F is the total heat

transfer area of the external wall in m2, ti and tea are the external wall and external

air temperature (K), respectively. It has to be noted that in Eq. (5), the fuel

consumption, B; has to be included for dimensional homogeneity. The unknownfuel consumption in Eqs. (4) and (5) is calculated by an iterative procedure.

Waste heat recovery scheme

Over the years, the boiler has been redesigned, mostly by modifying its

combustion systems according to the changes in fuel type. Attention has been paid

to heat losses respect to the exhaust gas, because they can reach up to 30% of the

total energy in the fuel. To obtain the optimal value for the exhaust gases

temperature, it is necessary to use additional heat transfer surfaces such as an

economizer, air heater, bagasse dryer, or some combination of them. However, the

addition of new elements increases the investment and operating costs of the boiler

and hence, the importance of establishing the optimal stack temperature. To solve

this problem, a minimum total cost (Z) has to be found through the equation

where i is the type of recuperative heat transfer surface (furnace water-walls, super

heater, generating tubes, air heater, economizer, and bagasse dryer); P i the annual

cost of 1 m2 of the surface i ($/(m2 yr)); Fi the heat transfer area of surface i (m

2),

Pef the equivalent fuel-oil cost ($ s/(yr kg)) and Bef the equivalent fuel-oil

consumption (kg/s). This fuel-oil equivalence means the amount of commercial

fuel oil with an average heating power (QPef ) of 41,868 kJ/kg (and its price at the

oil market), needed to yield the same energy as the total bagasse consumed to

produce a given steam power. Once the efficiency is determined using the indirect

method, the total bagasse consumption, B; is calculated by


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where Dsh is the measured steam power in t/h and Ish and Ieec are the superheated

steam and the fed water enthalpy, respectively. The equivalent fuel-oil

consumption Befis determined by

Using the common methodology to calculate the minimum value of a function, the

equation obtained to determine the optimal stack temperature, considering all the

heat transfer surfaces is

In this equation, T is the stack temperature; P and F define, respectively, the cost

and area for all thermal surfaces considered. Subscript w indicates furnace water-

walls; sh super heater, gt generating tubes; AH the air heater; ec the economizer,

and bd the bagasse dryer.

RESULTS AND DISCUSSION

Bagasse heating value determination

In general, bagasse has a broad range of heating values, extending from

6500 to 9150 kJ/kg (as received). Due to the importance of this parameter in the

determination of the efficiency of a boiler, it was carefully determined using a

calorimeter on more than 1000 samples collected during the tests. Results yielded

an average heating value for the bagasse of 7738 +/- 100 kJ/kg, as received.

However, in most sugar mills, it is not possible to carry out such a determination

in their laboratories. An alternative method has been considered, calculating the

heating value using the well-known equation [2]


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taking into account the general chemical composition, but considering bagassemoisture and ash contents from the samples measured in the laboratory tests. The

above equation provides a means for quickly determining the heating value of

bagasse (as received) with a high confidence level, good accuracy, and avoiding

the more difficult and time consuming experimental measurements. In contrast to

the ultimate fuel analysis, bagasse moisture and ash contents are relatively easy to

measure and are accessible to every sugar mill.

Optimization of boiler operation

The determination of the bagasse moisture and ash contents need to be

performed only once during the test. The analysis of exhaust gas composition is

measured at the beginning and at the end of the test. To carry out the boiler

optimization for different operational regimes, experimental measurements have

been obtained from the full tests according to the ASME procedure. As a

consequence of the experimental results, some important simplifications on both

the fixed carbon loss, q4; and conduction heat loss, q5; are considered.

From the experimental tests, it is concluded that q5 shows only a strong

dependence on steam power. For this reason, a simplified equation relating q5

with the steam power commonly used in this type of boilers was considered,

namely

Considering the physical influence of the fixed carbon loss (q4) on the

remaining heat losses (q2 and q3), it must be the first of all the heat losses to be

evaluated in the efficiency calculation. For the terms inside the brackets in Eq. (4),


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experimental measurements during the tests performed demonstrated the validity

of the following inequality

which means that the terms corresponding to ash hopper and bottom ash can be

neglected when compared to the fly ash one.

The terms [100 Ai] in Eqs. (4) and (15) are, by definition, the unburned

fuel (carbon) for the refuse collected in the different locations. Having in mind that

q4 is expressed as an unburned loss, it is convenient at this moment to introduce

the relation Cuf= [100 - Afa] as the unburned carbon in the fly ash. For this reason,

Eq. (4) can be rewritten as

the last parameter, Teg; is needed to calculate the exhaust gases enthalpy in Eq. (2).

The influence of the stoichiometric ratio in the furnace (f) and steam power (Dsh)

on the unburned carbon in the fly ash, Cuf; has been plotted. As can be seen, the

unburned carbon increases with increasing steam power and decreases withincreasing stoichiometric ratio in the furnace. As steam power is raised at a

constant stoichiometric ratio, both the amount of bagasse fed and the combustion

air flow rate increase, since the air volumetric flow rate per unit weight of bagasse

is fixed. This, in turn, increases the average gas velocity in the furnace and the

fraction of fuel that burns in suspension, rather than in the bed on the stationary

grate. The shorter residence time available for combustion in suspension results in

an increased unburned carbon carryover and poorer combustion performance.

Therefore, when steam power and bagasse consumption are increased, a higher

stoichiometric ratio in the furnace is needed to achieve the same carbon

conversion (Cuf): Taking into account all the experimental data, a statistical model

is fitted


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reproducing the experimental dependence of Cufon both the stoichiometric ratio at

the furnace, f ; and the steam power, Dsh: In this equation Dsh has units of t/h.

Once q4 is calculated, q3 and q2 can also be evaluated. To determine the chemical

carbon heat loss (q3); the parameter RCO/f needs to be calculated by the equation

CO/C being the CO-to-C molecular weight ratio. CP

and SP

are the carbon andsulfur contents of bagasse from ultimate analysis.

Performance of the unburned carbon in fly ash vs. stoichiometric ratio at the exit

of the furnace (f) for different values of steam power.


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The statistical model relating carbon monoxide, expressed as a fraction of

the total carbon oxides, to both fand Dsh; is

It is important to note that the physical parameters measured in the tests are the O2,

CO and CO2 concentration in the exhaust gases, which are used to calculate the

stoichiometric ratio, b; at the exit of the boiler applying the equation [2]

where O2; CO and CO2 are the stack gases composition analysis. This equation is

obtained using the combustion reactions as a function of the mole number,

However, Eqs. (17) and (18) are correlated to the stoichiometric ratio at the

furnace exit,f ; because of the physical dependence of both Cuf and CO on f

rather than on b: These two stoichiometric ratios are closely related throughout

the air in-leakage, ; by

Air in-leakage, ; represents the leakage of surrounding air, due to non-air

tightness, into the boiler and can be calculated by

where nom is the air in-leakage at the nominal steam power (Dnom sh = 45 t/h).

This parameter, nom

; was previously determined for all boilers tested andyielded a roughly constant value of 0.2.

Finally, to calculate the exhaust gases heat loss, q2; the exhaust gas

enthalpy, Ib; needs to be known. This enthalpy depends on the stack temperature,

Teg. Relating Teg to fand Dsh; the following equation is obtained.


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Even when the dependence of Teg

on Dsh

is weak, it is noteworthy that the

stack temperature is raised as the steam power decrease. When the steam power is

decreased for a constant stoichiometric ratio at the furnace, combustion air flow

rate also decreases, reducing the average gas velocity in the furnace as well as the

heat transfer in the waste heat recovering scheme. As a result, a higher exhaust

gases temperature is measured at the exit of the boiler.

If the set of Eqs. (17), (18) and (22) is introduced into the methodology to

calculate the heat losses q4; q3 and q2; their individual contributions to the overallboiler efficiency can be analyzed. This influence is shown in Fig. 5(a), (b) and (c)

for three different levels of stoichiometric ratio at the exit of the boiler, b : 1.45,

1.5 and 1.8, respectively, considering a fixed constant bagasse moisture of 50%

and an ash content of 4% (dry). In all these figures, the stoichiometric ratio at the

furnace exit, f ; has also being included. The evolution off as a function of

steam power derived from Eqs. (20) and (21) and its dependence on the level of

the stoichiometric ratio at the boiler exit, b; can be easily verified. Comparing the

three figures, it is evidenced that, as the stoichiometric ratio at the exit of the

boiler increases, the heat losses have different behavior; the exhaust gases heat

loss, q2; undergoes a significant rise, while q3 and q4 decrease. Even though Eqs.

(17), (18) and (22) are valid for Dsh of 20 t/h, it can be seen that for low

stoichiometric ratios, Fig. 5(a), (b =1:45); experimental data is only available for

steam flows above 30 t/h.

On the other hand, as can be observed in this figure, at higher steam

powers, q5 decreases, as predicted by Eq. (14). As the total heat transfer area is a

fixed value (for each boiler) and the external wall temperature is roughly constant

irrespective of the steam power, then the total heat lost to the surroundings (in

kW) is nearly constant as well. However, as an increase in the steam power is


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related to higher fuel consumption, a reduction in the conduction heat loss is

finally achieved, according to the behavior also predicted by Eq. (5).

All these features are summarized, where the overall efficiency, ; is

plotted as a function of the stoichiometric ratio at the exit of the boiler and thesteam power, demonstrating the global effect of heat losses on boiler efficiency

(Eq. (1)). Data for only four values of the stoichiometric ratio are displayed, for

clarity. It is concluded that the highest efficiency is reached for a steam power

value in the vicinity of the nominal one, 45 t/h and for low values of b (1.45).

This result is supported by the fact that the largest heat loss in these boilers is that

corresponding to the exhaust gases, q2. However, again for this value of b; a

decrease of the steam power below 30 t/h, causes the unstable combustion regime

described before, which finally results in flame extinction. On the contrary, for b

of 1.5 and 1.6, a nearly flat behavior of the efficiency with respect to the steam

power is reached, for the whole range, with values quite close to those achieved

for the lowest stoichiometric ratio, b. It is for this reason that, including in the

analysis the results obtained for all the boilers tested, the optimal value of the

stoichiometric ratio at the exit of the boiler, b; has been determined to range from

1.5 to 1.55, which allows for a full coverage of the whole range of steam powers.

It should also be noted that, prior to this experimental research, engineers and

boiler operators used to run the boilers at higher stoichiometric ratio values at the

exit of the boiler, even exceeding 1.8, loosing a large amount of thermal energy

resulting in a lower efficiency.


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Calculated heat losses (q2, q3, q4, q5) vs. steam power for three levels of

stoichiometric ratio at the exit of boiler (b):a) 1.45,b) 1.5, &c) 1.8.


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Optimization of heat recovery scheme

Boiler design optimization is a very complex problem, requiring some

assumptions to simplify its mathematical treatment. In this study, to optimize the

waste heat recovery scheme, the speed of the flue gas, steam, water and air floware supposed to have their optimal values for all the heat transfer surfaces studied.

At the same time, the furnace exit gas temperature is kept constant at 900 8C and

the steam power is fixed at the nominal value of 45 t/h. It is also necessary to

consider the specific heat at the exit of the boiler and its average value at the

different heat transfer surfaces to be independent of the stack temperature. The

heat transfer coefficients should also be considered as independent of the

optimized temperature. To solve Eqs. (9) and (12), a thermal analysis of all theheat transfer surfaces in the boiler was first performed followed by a coupled

mathematical and graphical analysis.

where subscript 1 means hot gas and 2 refers to the cold fluid (water, steam or air).

A summary of the heat transfer coefficients for the different surfaces studied is

presented in Table 1. Note that for the bagasse dryer, the volumetric heat transfer

coefficient is given in kW/ (m3 K).

Heat transfer coefficients used for the different surfaces studied

Generatingtubes

Air heater EconomizerSuperheater

Bagassedryer

k(kW/(m2K) 0.041 0.014 0.057 0.054 0.1014

A typical value for the stack temperature for boilers that burn common fuel

oils and coal ranges between 150 and 300 C to avoid acid corrosion. However,

sulfur contents in bagasse are negligible, yielding a low dew point temperature for

the exhaust gases, around 60 C, based on experimental determinations. Therefore,


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keeping the external pipe temperature in the last equipment over 70 C (or the

stack temperature over 80 C) the problem of acid deposition is avoided Teg; varies

between 80 and 100 C for all the cases analyzed, except when a bagasse dryer is

taken into account. The optimal stack temperature is slightly higher than 60C;which is permissible when the last recuperative piece of equipment is the bagasse

dryer, because acid deposition on the previous heat transfer surface (in this case

the economizer) will never occur. The optimal value for bagasse moisture, W; is

near 41% when a bagasse dryer is taken into account.


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8

FASTPYROLYSIS OFBAGASSETOPRODUCEBIO OILFUELFORPOWER GENERATION

Introduction

It is a well-established fact that combustion of fossil fuels such as coal, oil

and natural gas for power generation is a significant contributor to global

warming. On the other hand biomass has long been identified as an alternate

sustainable source of renewable energy. However, power generation using a solid

fuel has had significant limitations with respect to materials handling requirementsand efficient energy conversion. Converting biomass fuel into a liquid addresses

these issues and makes possible the use of higher efficiency combined cycle

systems for power generation. Fast pyrolysis technology is a unique process that

converts solid biomass waste materials, such as bagasse, into a relatively clean

burning liquid fuel called BioOil that is also carbon dioxide and greenhouse gas

(GHG) neutral. The nearest term commercial application for BioOil is as clean

fuel for generating power and heat from small stationary diesel engines, gas

turbines and boilers.

Fast Pyrolysis of biomass

Fast Pyrolysis (more accurately defined as thermolysis) is a process in

which biomass material, such as bagasse, is rapidly heated to high temperatures in

the absence of air (specifically oxygen). The bagasse decomposes into a

combination of solid char, gas, vapors and aerosols. When cooled, most volatiles

condense to a liquid referred to as BioOil. The remaining gases comprise a

medium calorific value non condensable gas.

BioOil is a liquid mixture of oxygenated compounds containing various

chemical functional groups, such as carbonyl, carboxyl and phenolic. BioOil is


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made up of the following constituents: 20-25% water, 25-30% water insoluble

pyrolytic lignin, 5-12% organic acids, 5-10% non-polar hydrocarbons, 5-10%

anhydrosugars and 10-25% other oxygenated compounds.

In this particular fast pyrolysis process, biomass feedstock is introducedinto a thermolysis reactor having a bed of inert material, such as sand, with a

height to width ratio greater than one. The biomass is shredded to sufficiently

small dimensions so that its size does not limit significantly the production of the

liquid product fraction. Simultaneous introduction of pre-heated, non-oxidizing

gas at sufficient linear velocity performs two principal functions: firstly, as a

medium for fluidizing the hot sand bed and secondly, to cause automatic

elutriation of the product char from the fluidized bed reactor. The process includesremoving the elutriated char particles from the effluent reactor stream and rapidly

quenching the gas, aerosols and vapors to produce a high conversion yield of

liquid BioOil. For maximum yield of liquid, the thermolysis reaction must take

place within a period of a few seconds at temperatures ranging from 450C to

500C. The products must then be quenched as soon as possible to prevent

cracking of the newly produced BioOil.

BIO THERM Flow sheet


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Fast Pyrolysis heat and mass balance

Feedstock for the fast Pyrolysis process can be any biomass waste material

i.e. bagasse. To maximize yield and minimize process development risk,

DynaMotive has focused near term BioOil production from sugarcane bagasse.Preparation includes drying the feedstock to less than 10% moisture content

to minimize the water content in the BioOil and then grinding the feed to small

particles to ensure rapid heat transfer rates in the reactor.

When processing bagasse feed stocks, the conversion yield to liquid BioOil,

solid char and non-condensable gas is approximately 62%, 26% and 12% by

weight, respectively, on an as fed basis. The heat required for thermolysis is the

total heat that must be delivered to the reactor to provide all the sensible, radiationand reaction heat for the process to proceed to completion.

The heat of reaction for the fast Pyrolysis process is marginally

endothermic. When operating the pilot plant using prepared feedstock, the total

heat requirement to produce BioOil at a 62% yield rate (including radiation and

exhaust gas losses) is approximately 2.5 MJ per kilogram of BioOil produced. The

net heat required from an external fuel source, such as natural gas, is only 1.0 MJ

per kilogram of BioOil produced. This applies when the non-condensable gases

produced in the process are directly injected into the reactor burner. This

represents approximately 5% of the total calorific value of the BioOil being

produced.

Bio Oil Analysis

BioOil is a dark brown liquid that is free flowing. It has a pungent smoky

odor. BioOil contains several hundred different chemicals with a wide-ranging

molecular weight distribution. The following Table below lists the properties of

BioOil produced by the BioTherm pilot plant, derived from bagasse biomass feed

stocks.


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Table:DynaMotive BioOil Properties

Biomass Feedstock Bagasse

Moisture wt% 2.1

Ash Content wt% 2.9

BioOil Properties

pH 2.6

Water Content wt% 20.8

Lignin Content wt% 23.5

Solids Content wt% < 0.10

Ash Content wt% < 0.02

Density kg/L 1.20

Calorific Value MJ/kg 15.4

Kinematic ViscositycSt @20C

57

cSt @80C 4.0

The density of BioOil is high, approximately 1.2 kg/liter. On a volumetric

basis BioOil has 55% of the energy content of diesel oil and 40% on a weight

basis.

The solids entrained in the BioOil principally contain fine char particles

that are not removed by the cyclones. As can be seen, the solids in the BioOil havebeen reduced significantly to levels of approximately 0.1% by weight. The ash

content in these solids ranges from 2% to 20%, depending on the ash content in

the feedstock.


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Table: BioOil Composition

Biomass Feedstock Bagasse

BioOil Concentrations wt%

Water 20.8Lignin 23.5

Glyoxal 2.2

Hydroxyacetaldehyde 10.2

Levoglucosan 3.0

Formaldehyde 3.4

Formic acid 5.7

Acetic acid 6.6

Acetol 5.8

Market Competitiveness

In the proprietary DynaMotive process, BioOil and char are commercial

products and the non-condensable gases are recycled back into the process. No

waste is produced in the DynaMotive process. The overall simplicity of the

technology gives DynaMotive significant competitive advantages over other

Pyrolysis technologies in terms of capital and operating costs. DynaMotiveprocess also produces higher quality fuel and higher yields of BioOil compared to

competing technologies. DynaMotives target cost for BioOil production is $5 per

gigajoule (GJ) based on a 400 tonne per day (tpd) commercial plant. The earliest

and most appropriate market application for BioOil is as a clean fuel to produce

green power and heat in boilers, kilns, gas turbines and diesel engines.

DynaMotive is also developing higher value fuel and chemicals

applications for BioOil including ethanol blended fuels, diesel/BioOil emulsions

and catalytic upgrading of BioOil to synthesis gas, which can be converted to

synthetic transport fuels and bio methanol for use in hydrogen fuel cells.


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Bio Oil Application as a Fuel in Gas Turbine Engines

As a clean fuel, BioOil has a number of advantages over fossil fuels:

1. CO2 / Greenhouse Gas Neutral because BioOil is derived from biomass

(organic waste), it is considered to be greenhouse gas neutral and cangenerate carbon dioxide credits.

2. No SOx Emissions As biomass does not contain sulfur, BioOil produces

virtually no SOx emissions and, therefore, would not be subjected to SOx

taxes.

3. Low NOx BioOil fuels generate more than 50% lower NOx emissions

than diesel oil in gas turbines.

4.

Renewable and Locally Produced BioOil can be produced in countrieswhere there are large volumes of organic waste.

As BioOil has unique properties as a fuel, it requires special consideration and

design modifications. Some of these properties are presented and are compared to

those of diesel fuel.

Table:Typical Properties of BioOil Compared to Diesel Fuel

BioOil Diesel

Calorific Value MJ/kg 15-20 42.0

Kinematic Viscosity3 9

@ 80C

2 4

@ 20C

Acidity pH 2.3 - 3.3 5

Water wt% 20 25 0.05 v%

Solids wt%


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BioOil. These tests not only revealed the feasibility of operation but also

demonstrated that similar performance could be achieved for BioOil and diesel.

Although CO and particulate emissions were higher than diesel, testing revealed

that NOx emissions were about half that from diesel fuel and the SO2 emissionslevels were so low as to be undetectable by the instrumentation.

Pyrolysis Oil NOx Emission Reduction

The engine being utilized for this program is the 2.5MW OGT2500

industrial gas turbine engine. The OGT2500 offers distinct technical advantages

over other engines. Unlike aero-derivative engines, it has been designed as an

industrial engine with durability being one of the main design criteria and not

weight. In addition to its ruggedness, the distinct silo type combustion system

allows for easy access and modifications to the entire combustion system, which is

one of the critical systems for the adaptation of the engine to BioOil.

Application of Pyrolysis Oil to Gas Turbine Operation.


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BioOil has an energy density approximately half that of diesel fuel.

Therefore, to meet the same energy input requirement, the flow rate must be

double. This requires design changes to the fuel system to be able to control higher

flow rates and also modify the fuel nozzle to accommodate this larger flow. Thislower energy density also can affect combustion since physically there must be

twice as much fuel in the combustion chamber as with diesel.

Higher viscosity of the fuel reduces the efficiency of atomization, which is

critical to complete combustion. Large droplets take too long to burn. Proper

atomization is addressed in three ways. Firstly, the fuel system is designed to

deliver a high-pressure flow since atomization is improved with larger pressure

drops across the fuel nozzle. Secondly, the fuel is pre-heated to lower the viscosityto acceptable levels. Thirdly and most importantly, the fuel nozzle has been

redesigned to improve spray characteristics. These design improvements are

important for complete combustion and effectively reducing CO emissions.

Due to its relatively low pH, material selection is also critical for all

components wetted by BioOil. This does not require the use of exotic materials;

however, it does eliminate some standard fuel system materials. Typically, 300

series stainless steels are acceptable metallic materials and high-density

polyethylene (HDPE) or fluorinated HDPE for polymers.

Although looked at as a contaminant for diesel fuel, the water content in

BioOil has some advantages. Firstly, it is helpful in reducing the viscosity, since it

is a relatively low viscosity fluid. As well, it is a factor in lowering thermal NOx

emissions.

The solids content is a combination of ash and char fines which have

carried-over to the liquid part of the BioOil. The effect of these solids is to cause

sticking of close tolerance surfaces. They can result in particulate emissions

because of the long residence time required to fully combust. It is important that

the solids level in the BioOil is controlled to be less than 0.1 wt%.


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The ash content in the fuel represents the material that cannot be

combusted. Depending on the elements in the ash, it can result as a deposit on the

hot gas path components that will reduce the turbine efficiency. This operational

problem is a familiar one with the use of low-grade fuel oils that also have highash content. The solution is a turbine wash system. This typically consists of two

separate systems in which an abrasive medium is injected during operation to

physically scrub off the deposits. This allows turbine cleaning without any

downtime. The second system is an offline process,, which injects a cleaning fluid

and allows a soak period to loosen the deposits that are then removed when the

engine is started.

Due to the poor ignition characteristics of BioOil, one other key designrequirement is a BioOil specific ignition system or process. To overcome this, the

OGT2500 system starts on diesel fuel flowing through the primary channel in the

fuel nozzle. Following a warm -up period, BioOil is fed into the secondary

channel at an increasing rate while the diesel fuel flow is reduced until 100%

BioOil flow is achieved.

Converting biomass wastes produced from agriculture and forestry

operations to a liquid BioOil, using DynaMotives fast Pyrolysis technology, has

been demonstrated at the pilot plant level as a reliable and repeatable process. Test

programs to demonstrate BioOil application as a fuel in gas turbine engines, diesel

engines and boilers are underway with a host of engine manufacturers. To-date the

results have been most encouraging.


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9

APPLICATIONS

Locomotives

Compared to oil , coal or even wood , the calorific value of bagasse

being very low & most locos have large auxillary tenders to carry it . Since

it is so fibrous , much of the fuel passes from the fire box straight through

the boiler tubes unburned & burns up in the air .

Electricity generation(9)

India, which accounts for around 85% of South Asian electricity

generation, is facing serious power problems with current generation is about 30%

below demand. New options have to meet the challenge and need to invest heavily

in new electric generating capacity. Overall, Indian power demand is projected to

increase to 1,192 billion-kilowatt hours (BkWh) in 2020, around three times the

378 BkWh consumed in 1996.

Net Electric Output Calculations for Combustion of Bagasse:

Combining of all thermal efficiencies of equipment involved equates the

total thermal efficiency for the total system:

overall= comb * boil * gen

Overall thermal efficiencies for the standard combustion steam cycle and

integrated gas combined cycle technologies reported in were used in the following

calculations:

Net electric output =overall * fuel * LHVfuel * Pparasitic

Where

fuel = mass flow of entering fuel and

Pparasitic = amount of electricity consumed by plant equipment


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Parasitic electricity consumption was neglected due to lack of information on

exact equipment parameters and for ease of calculation. However, for a true

account of net electricity these should be included in the calculations. Fuel = 100 tonne bagasse per hour; LHV = 7600 kJ/kg

Net electricity output = 7600 kJ/kg *0.35 *100 000 kg/hr *1 hr/3600 s

= 73.89 MW.

Ethanol production(9)

Ethanol is produced through the fermentation of sugars by yeast. The most

commonly used yeasts come from the Saccharomyces and Zymomonas genii and

use the Embden-Meyerhof and Entner-Doudoroff pathway respectively. Glucose

is bio-chemically converted to the intermediate pyruvic acid, the next step is non

oxidative decarboxylation and acetaldehyde formation catalyzed by

decarboxylase. This is followed by acetaldehyde reduction catalyzed by

dehydrogenase to form ethanol. The net chemical reaction is that of the following:

C6H12 O62CH3CH2OH + 2CO2

The fermentation is carried out non-aseptically at 23 to 32C. Antibiotics

may be added to control possible contaminants. Because the overall reaction is

exothermic, cooling is required. The fermentation can take on average 40 to 50

hours. Carbon dioxide is normally vented; if it is to be recovered the vent gas is

scrubbed with water to remove entrained ethanol and then purified using activated

carbon. The out-gassing of the carbon dioxide from the fermentor provides

sufficient agitation for small tanks. Mechanical agitation may be added for large

fermentation tanks. The Theoretical yield of ethanol from bagasse is stated as

111.5 US gallons per US ton of bagasse.

Essentially, there are three basic steps in ethanol production from bagasse:


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1. Feed preparation involves the separation of cellulose and hemicellulose

(sugar containing components) from the unwanted solid waste (lignin);

2. Fermentation xylose and glucose from the hemicellulose and cellulose

respectively are fermented by yeast (generally a species such asSaccharomyces cerevisiae) to generate ethanol.

3. Product finishing centrifuging and distillation operations are used to

separate the solid waste and broth from the ethanol product. The resultant

product stream is usually a minimum of 95% ethanol.

There are two specific technologies used in the conversion of bagasse to

ethanol: (1) two-stage dilute-acid process, and (2) enzyme-based process. Figure

below shows the two-stage dilute-acid process flow diagram; this consists of four

basic unit operations: first stage hydrolysis; second stage hydrolysis; ethanol

fermentation; and product purification.

Two-stage Dilute-acid Process Flow Diagram


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Ethanol is currently the most commonly used fuel alternative throughout

the world, used primarily as an octane booster to prevent early ignition and to

extend gasoline. It also helps to prevent air pollution by acting as an oxygenate,

reducing carbon monoxide and ozone. . Moreover, ethanol from product of thesugar industry by its use in the transport sector can also play a critical role in

reducing GHGs. Ethanol can be used as a 10% gasoline blend in the automobiles

without any modification to the engines. It can also be used as a diesel blend in

stationery engines and automobiles along with an additive. India consumes nearly

6000 billion liters of gasoline and 42000 billion liters of diesel. Ethanol, which is

currently, produced from molasses has the capacity to substitute more than 1000

million liters of gasoline per annum. To meet additional demand of ethanol othermethods such as direct production from cane juice and bagasse can be explored.


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10

CONCLUSION

India one of the leading sugarcane producers in the world realizing the

potential of bagasse, a by-product of the sugar industry, for power generation, has

come up with various programs and incentives to boost the sector.

India produces nearly 40 million metric tonne (MMT) of bagasse, which is

mostly used as a captive boiler fuel other than its minor use as a raw material in

the paper industry. Sugar mills in the country especially in the private sector haveinvested in advanced cogeneration systems by employing high-pressure boilers

and condensing cum extraction turbines. These sugar mills have been able to

export power in the season as well as in the off-season by using bagasse or any

other locally available biomass and to some extent coal. Off-season operation has

been more lucrative by exporting power which otherwise earlier was non-existent

except some operation and maintenance work. High technology has made these

sugar mills efficient by improving the economic viability of the mills in terms of

higher production of units of electricity per unit of bagasse.

Environmental benefits

The sugar mills showing interest in cogeneration projects, it has benefited

the environment by reducing the greenhouse gases (GHGs) in the atmosphere in

terms of the usage of biomass as fuel. Bagasse and other biomass, which are

renewable, can play a major role in substituting fossil fuel for future power

generation. There is a potential of 3500 MW bagasse based cogeneration potential

and 16500 MW other biomass power potential in the country. A typical 2500 TCD

sugar mill having a cogeneration potential of 22 MW exports nearly 0.3 million

units of electricity in the season with a gross generating capacity of more than 150


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million KWhs in a year and thus can offset nearly 0.166 million tonne of carbon

dioxide. The Clean Development Mechanism (CDM) can be an effective tool in

the sugar sector creating a major impact by the way of technological and financial

transfer between India and developed countries and can help start the transitiontowards truly environmentally, economically and socially sustainable energy

systems.


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REFERENCES

1. D.S Chahal. Food, Feed & Fuel from Biomass, reprint 1991, pp.23.

2. N.H.Ravindranath, K.Usha Rao, Bhaskar Natranjan. Renewable Energy &

Environment, 2nd reprint 2001 pp.106, 242.

3. L.A Ekal, S.H Pawar. Advances in renewable energy technologies, 1st reprint

pp.35, 194.

4. S.Rao, Dr. B.B.Parulekar. Energy Technology, 2nd edition, 1997.

5. G.D Rai. Energy Resources, 3rd edition, 1999.

6. http://164.100.24.208/Is/committeeR/Food/27.pdf

7. M.Narendranath & G.V.S. Prasada Rao. Improvement of the calorific value of

bagasse using flue gas drying, & T.Sumohandoyo ,by JAVA method mill

setting, www.greenbusinesscentre.com/casestudies/sugar/sugar-case%20study

8. Jorge Barroso, Felix Barreras, Hippolyte Amaveda, On the optimization of boiler

efficiency using bagasse as fuel, www.fuelfirst.com

9. http://bioproducts-bioenergy.gov/pdfs/bcota/abstracts/30/z130.pdf

10.G.A.Grozdits. Biological treatment & storage method for wet bagasse,

S.Turn. Demonstration-Scale biomass gasification facility operates on bagasse.

International Cane Energy news, July 1997

Newsletter of the International Cane Energy Network.

7027056 Bagasse as Alternate Fuel[1]

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