Biomass as a Source of Energy-379

7/30/2019 Biomass as a Source of Energy-379

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Biomass as a Source of EnergyBooklet No. 379

Agriculture and Bio-energy: ABES-1ContentsPreface

I. IntroductionII. Concept of BiomassIII. Types of Biomass

1. Fuel biomass2. Feed biomass3. Organic fertilizer biomass4. Fibre biomass5. Chemical biomass

IV. Sources of BiomassV. CombustionVI. PyrolysisVII. Destructive Distillation

VIII. GasificationIX. Anaerobic Bio-gasification

1. Advantages2. Process3. Feasibility

X. Alcoholic FermentationXI. Production of Biomass

Preface

In many developing countries wood has been used as a fuel. The situation is growing sodesperate that wood is poached from forest reserves. As a result the ecosystem is degrading

deplorably. So, in order to protect the natural environment, there is every necessity of producingalternative source of energy for the needs of the people. Biomass is the best alternative as it isavailable in plenty and production of energy from biomass is also less costly.

Dr. K.T. Chandy, Agricultural &Environmental Education

I. Introduction

In India, the concept of energy as "Shakti" has been at the focus of philosphic, scientificand metaphysical thought from time immemorial. The conventional energy sources like fossilfuels, crude oil, natural gas etc. are dwindling fast. The world stock of non-renewable naturalsources indeed have decreased. There is every necessity of going for renewable alternative

resources for energy. The energy crisis of 1973 left scientists to accelerate the renewableenergy programmes. The important renewable energy sources are sun, wind, tides, waves,biomass, hydro-power (from water) charcoal, peat, fuelwood, geothermal energy etc. Thepattern of energy consumption in India shows that 56.5 % of total energy is from the commercialsources like coal, oil & electricity and remaining 43.5% is non-commercial energy. Fire wood,charcoal, agricultural residues, vegetable wastes, cow dung, urban and industrial wastes, forestresidues are the main sources of this non-commercial energy. The most efficient utilization ofthese resources comes when they are converted to biomass by appropriate technologies. The


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non-commercial biomass fuels are the main sources of energy available in the rural areas. The80% of our population resides in villages are dependent on this non-commercial biomass fuels.

II. Concept of Biomass

The term biomass refers to all organic matter generated through photosynthesis and

other biological processes. The ultimate source of this renewable biomass is the inexhaustiblesolar energy which is captured by plants through photosynthesis. It includes both terrestrial aswell as aquatic matter such as wood, herbaceous plants, algae, aquatic plants and residues, likestraw, husks, corncobs, cow dung, saw-dust, wood shavings and other wastes like disposablegarbage, night soil, sewage solids, industrial refuse etc. In spite of all these biomass resourcesavailable in India, they are not being properly utilized. In fact, a large amount of it is disposed offby burning in open fields causing serious air pollution.

In order to utilise these resources properly, biomass should be converted to energywhich can meet a sizeable percentage of the country's demands for fuel as well as energy.Three main approaches can be adopted for generation and proper utilization.

1. Collection of agricultural and forest residues to produce fuels, organic manures and chemicalfeed stock.2. Collection of urban and industrial wastes as fuel in boilers and as a feedstock for producingmethane and some liquid fuels.3. Growth of some specific energy plants for use as energy feed stock and cultivation ofcommercial forestry, aquatic and marine plants for different products.

By a number of processes, the collected wastes can be converted into solid, liquid andgaseous fuels. The technologies include thermal, thermo-chemical and bio-chemicalconversions. The actual processes in these technologies are combustion, pyrolysis, gasification,alcoholic fermentation, liquefaction etc.

The main products of conversion technologies are energy (thermal, steam, electricity),solid fuels (charcoal, combustibles) and synthetic fuels (methanol, methane, hydrogen gas etc.).These can be used for different purposes like cooking, lighting, heating, water pumping,electricity generation and as industrial and transport fuels.

III. Types of Biomass

Depending on the nature and availability of these wastes and organic residues they canbe utilized in different manners as described here.

1. Fuel biomassBy some processes and procedures, biomass products like fuel gas, liquid fuels,

gaseous fuels etc. are obtained, which are given here

a. Biomass from plants or animal origin are directly burnt for cooking and other purposes.Municipal and sewage wastes, industrial wastes and agricultural wastes are converted to energywhich can meet the demand for energy in rural sector.

b. Paddy straw and rice husk can be profitably converted to fuel gas by thermal decomposition(Combustion)


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c. Ethanol, which is used as a liquid fuel can be produced from carbohydrates by alcoholicfermentation.

d When wood and agricultural residues are heated in the absence of air (pyrolysis), charcoal isthe resultant product which can be used as a fuel more advantageously than wood.

e By the process of gasification, gas is evolved which can be used as a fuel for engines.

f Biogas, which is popular in rural areas is produced by anaerobic fermentation from farmwastes.

2. Feed biomassConventionally, crop residues are used as cattle-feed. However, some of them with high

percentage of lignin or non-digestible constituents need certain treatments such as soaking inwater, alkali/alcohol to make their use as a fuel. The oil-cakes of various crop seed like cotton,rubber, tobacco etc. can also be used as a feed after extraction of toxic materials.

3. Organic fertilizer biomass

Dry fermented slurry can be used as a direct organic fertilizer for crop land.

4. Fibre biomassThe fibrous agricultural wastes and residues are being profitably utilised for making pulp

for cheap grade paper.

5. Chemical biomassHighly siliconous agricultural residues like rice husk and rice straw can be converted into

useful chemicals like morphous silicon, silicate products and solar grade silicon. Furfural ananother chemical can be produced from biogases, cotton seed hulls, corn-cobs, flax fibres, oathulls etc., which is used as a solvent for some petroleum products.

IV. Sources of Biomass

Important sources of biomass and their characteristics are given here.

A. Crop residue and farm wastesThe straw of cereals and pulses, stalks and seed coats of oil seeds, stalks and sticks of

fibre crops, pulp and wastes of plantation crops, peelings, pulp and stalks of fruits andvegetables and other wastes like sugarcane trash, rice husk, molasses, coconut shells etc.comes under this category.

Most of the crop residues have a higher ash content and mainly constitutes carbon,oxygen and hydrogen. Volatile matter content is 60-75%. The agricultural residues are

hygroscopic in nature. Ash content varies from 0.5 to 2.8 per cent.

B. Industrial wastesThese wastes include wastes from paper mills, chemical mills etc. for eg., paper wastes,

plastic wastes, textile wastes, gas, oil, paraffins, cotton seeds and fibres, bagasse etc. Plasticand rubber wastes have good calorific value.


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C. Forest wastesLogs, chips bark and leaves together constitute forest wastes. Sawdust is the forest

based industry waste. Forest products are also used as a. domestic fuel in many developingcountries.

D. Logging residuesTree tops, small stems and roots removed from a standard logging operation and broken

debris generally considered as logging residues. It contains 40-50% moisture, 50% carbon, 40%oxygen and mtrogen 5%.

E. Residues of wood product industriesBark, knots, sawdust etc. are obtained from wood product industry. Moisture content of

these residues is around 20% with 67% volatile matter and 11 % organic carbon.

F. Residues from pulp and paper industriesThe bark and black liquor produced in pulp and paper factories can be used as major

source of energy in the paper industry. Moisture content varies from 5-10% with organic. carbon

8-11 per cent.

G. Municipal solid wastesGenerally municipal solid wastes refer to a mixture of domestic, small construction and

demolition wastes left out within a community. Composition of municipal solid wastes is given ina Table 1. It shows the heterogenic nature of these waste mixture.

Table 1 : Composition of municipal solid wastesSl.No Component Percentage

(weight)

1 Paper 41.0

2 Metals 8.2

3 Glass, Stones, Ceramics 11.24 Plastic, rubber 4.95 Garbage, yard wastes 24.0

6 Miscellaneous 10.7

Total 100%

H. Municipal sewage sludgesThe sludges contain 95% water, and 5% organic matter and nutrients as the main

constituents. These can be utilized for the production of methane through anaerobic digestion.

I. Animal wastesThe moisture content of the manures ranges from 60 to 85 percent. The nitrogen varies

from 0.3 to 0.9 %, phosphorus 0.05-0.1 % and potassium 0.12 to 0.8% Available statisticsindicates production of 1300 million tonnes of dung annually from all types of animals. Of thetotal produced, 84% is of cow and buffalo dung and 13% goat and sheep droppings. Dung isused as a fuel in the form of cakes and biogas.

Availability of biomass resources in India along with their coal equivalent is shown inTable 2.


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Table 2. Major biomass resources in India

Sl.No Biomass Availability(tonnes/yr)

Coal equivalent(tonnes/yr)

1 Agricultural residues

1 Rice straw 9.0 58.4

2 Rice husk 19.9 15.73 Jute sticks 2.5 2.3

4 Wheat straw 50.5 37.5

5 Cattle dung 1,335.0 128.0

Agro-industrial bi-products

1 Bagasse 28.1 22.42 Molasses 2.1 0.8

3 Oil seed cakes 6.7 0.94 Saw dust 2.0 3.4

Forest products1 Mahua flowers 1.0 0.4

2 Leaves, tops etc. 3.3 3.0

The different processes that are followed in our country to make these wastes into auseful fuel are discussed.

V. Combustion

Agricultural residues-fired thermal power plants of small capacity are becoming popularwith agro-processing industries. Thus, sugar mills use bagasse (bi-product, wastes of sugarmills) for meeting their energy needs and rice mills bum husks. Combustion involves burning ofbiomass fuels in the presence of air to generate heat energy. Main products of combustion areash and fuel gases. Usually fuels are burnt on hot furnace. The heat generated is used to drive

steam engines and also for irrigation & thrashing purposes.

VI. Pyrolysis

When wood and agricultural residues are heated in the absence of air they breakdowninto a complex mixture of liquids involves heating organic matter at a high temperature of 540-1100oC in the absence of air for several hours. The earthen kilns or pit kilns or brick kilns orportable steel kilns are used for this process of which portable steel kilns make good charcoal.

Charcoal has a high calorific value, easy to transport, store and distribute and moreefficient in burning and has a characteristic feature of creating less pollution. From eight tonnesof wood, around one tonne of charcoal can be made. The gases that are produced during the

process of pyrolysis can be converted or synthesized into methanol and liquids which are usedas fuels. Depending on the temperature, the degradation stages of pyrolysis are given in Table3.

Table 3 : Different stages of degradation in pyrolysis

Sl. No Temperature Product

1 0-170 Evaporation of moisture

2 170-270 Evolution of carbon monoxideand carbon dioxide


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3 270-400 Evolution of methanol

4 400-500 Charcoal with optimum carboncontent

VII. Destructive Distillation

The destructive distillation is carried out in long steel retorts. Only the wood wastes suchas branches, trunks of trees are used as raw materials. The process involves decomposition ofwood at high temperatures in the absence of air. At an initial temperature of 230C, the moistureis evaporated and then the temperature is raised to 370C and maintained I for 6 hours. At theend of this period, wood is converted to charcoal which is cooled in the absence of air for 48hours. After cooling, they are spread in open sheds, two days for drying and is ready for supplyto consumers. The vapours of the volatile matters that are formed during the distillation processsubsequently condensed to tar, methanol, acetic acid, methyl acetate, oil and gas. The uses ofthese distillation \ products are detailed here.

1. Charcoal -Apart from its use as a fuel, charcoal is used as a source of carbon in makingcarbon-di-sulphide.

2. Methanol -It is used as a solvent and an antifreeze for automobiles.3. Acetic acid -It is used as a raw material for the manufacture of acetic anhydride, sodiumacetate, cellulose acetate, ethyl acetate, butyl acetate etc.4. Methyl acetate -is a solvent used in paint industry.5. Tar -A product of tar known as "pitch" is used as rubber softener.6. Oils -They are used as solvent and insecticide.7. Gases -Gases are used as fuel for heating wood distillation and fuel for boilers.

VIII. Gasification

Gasification is a process of degradation of carbonaceous material (wood wastes) undercontrolled air or pure oxygen at a high temperature of l000C. As a result of gasification high

amount of gases are produced. Biomass gasification is done in gasifiers designed m variousways. Types of gasifiers are generally classified based on the physical conditions of the feedstocks in the gasifiers. Fixed bed gasifier, stired bed gasifier, tumbling bed gasifier, fluidized bedgasifier etc. are in use.

In course of gasification, a number of chemical reactions takes place. As soon as thebiomass is ignited four distinct zones are set-up in the gasifier-unit. Biomass when introducedinto the gasifier, it enters into drying zone where the temperature is 200-400C. The products ofthis zone are vapours of tar, organo-chemicals, and liquid oils. After drying zone it enters intopyrolysis zone, temperature of 400- 750C. Pyrolysis results in char, organic liquids and somegases. At 750-l000C, mainly gases like carbon-di-oxide, carbon monoxide, hydrogen,methane etc. are produced which is called as gasification zone. The oxidation zone which is at

l000-l400oC also produces gases like nitrogen, carbon-di-oxide, hydrogen etc. When the processof oxidation is over, with the steam treatment, ash, an inert material is formed. The wholeprocess is depicted in Fig. l.


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The gasification process, thus, ultimately results in a number of gases which are inmixture. This mixture of gases referred to as producer gas, the composition of which is givenbelow.

Carbon monoxide -20-22%, Hydrogen -15-18%, Methan -2-4%, Carbon-di-oxide -9-11%

Nitrogen -50-53%.

Producer gas somewhat burnt like a natural gas which Ican be used as a fuel for engines.

IX. Anaerobic Bio-gasification

Degradation of organic matter in the absence of air to methane and carbon-di-oxide iscalled anerobic biogasification. In villages, cattle manure is used as a fuel for cooking purpose.So, preparation of biogas has become popular among rural people. Biogas can be utilized forcooking, lighting, operating diesel engines, water pumps etc. As cattle dung is the main rawmaterial for the production of biogas, this method has been given importance. The mainadvantages of the biogasification are given here.

A. AdvantagesThe biogas (also called as gober gas) production can be started by constructing a

permanent structures (tanks) at a convenient place at home. It can be manufactured with leastmaintenance. Initial investment is also cheap. Gober gas contains 60% methane and 40%carbon-di-oxide. The digested manure contains 1.5-2% nitrogen and other soil nutrients, whichcan be used as an organic fertilizer. The biogas can be easily purified to methane enriched fuelgas of high calorific value. The process of conversion of raw animal dung as well as someagricultural residues to biogas is detailed as follows.

B. ProcessThe conversion carbon-di-oxide and methane takes place by bacteria. The biogas from

cattle dung requires an optimum temperature of 35C. The biomass is kept in closed tankswhere the temperature is 35-38C and the conversion process is carried out anaerobically (inthe absence of air). The digestion time varies from 15-30 days. On an average biogas generatedfrom cattle dung is composed of 60% methane and 40% carbon-di-oxide. The basic structure ofthe biogas plant is given in Figure no. 2.


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When the cattle dung is used as feed stock, the biogas plant is 10 be filled with ahomogenous slurry made from a mixture of fresh dung and water in a ratio of 1:1. Subsequentdigestion changes results in the production and accumulation of gas in the empty space at theupper portion of the tank. The gas accumulated presses the slurry digester and displaces it intothe outlet displacement chamber. In other words, the slurry level in the digester falls where as inthe outlet chamber, it starts raising. The slurry from the outlet displacement chamber can beused as organic fertiliser. The gas outlet pipe will be connected to the gas utiliser points bypipelines.

C. FeasibilityMany developing countries are encouraging for installation of biogas plants to meet the

demand for fuel. India is one of the pioneer country in biogas technology where biogas researchand plant construction has been caused out over the past 30 years. In most of biogas plant,cattle dung is used for gas production. Though, biogas is used mainly for cooking and lightingpurposes, there are many other advantages also. It can be used in internal combustion enginesto power water pump and electric generators. The most economical benefits are minimizingenvironmental pollution and meeting the demand of energy for various purposes. In general, fivecattle produces enough dung to generate about 2m3 biogas to meet the demand of cooking andlighting for a family of four-five people.

X. Alcoholic Fermentation

Transformation of sugars into alcohols by fermentation is a common practice.Fermentation is carried out by a group of living organisms: yeasts or bacteria. Ethyl alcohol,commonly known as alcohol is one of the most important and popular industrial fermentedproducts. It is a liquid fuel, and can be used as an alternative to automobile fuels. The sugarenriched materials like cane sugar, beet sugar, fruit sugar, potato, com, rice or any other crop ofhigh sugar contents can be used as substrates mainly, along with starchy and ligno-cellulosicmaterials.

A Materials for fermentationFollowing are the types of substrates used for alcehot production.

1. Sugary materials

Examples of sugary materials like sugarcane and its biproducts (bagasse, molasses) andsugarbeet, fruit juice, sweet sorghum, sweet-potatoes etc. Sugarcane molasses is largely beingused in many countries for alcohol production. The yield of ethanol is directly proportional to theamount of sugar present.

2. Starchy materialsTapioca, maize, wheat, barley, oat, sorghum, rice and potatoes are the starchy materials

that are used in ethanol production. It has been estimated that 11.7 kg of corn starch can beconverted into about 7 liters of ethanol.


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3. Lignocellulosic materialsThe sources of cellulose and lignocellulosic materials are the agricultural wastes and

wood. On the basis of technology available today, about 409 litres of ethanol can be producedfrom one tonne of lignocellulose.

B Process of fermentation

Micro-organisms can grow on carbohydrates such as sugars, under anaerobicconditions. During anaerobic growth, sugars or other fermentable carbohydrates are oxidizedand ethyl alcohol is produced as a product of the fermentation process. Optimum temperaturerequirement for alcohol production is 30-38C and optimum pH ranges from 3 to 8. Properbalance of macro (nitrogen, phosphorus, potassium, sulphur etc.) and micro (iron, zinc,manganese, copper etc.) nutrients are required for the growth of micro-organisms.

When fermentation is over, which normally takes 4-10 days, the resultant productconsists of a mixture of alcohols and water. Ethanol (ethyl alcohol) can be recovered bydistillation process i.e. vaporization of alcohol-water mixture.

XI. Production of Biomass

Biomass production can be studied under these sub-heads.

1. Energy plantationsEnergy plantation is the practice of planting trees, purely for their use as fuel. Terrestrial

biomass i.e. the wood plants has been used since long time to generate fire for cooking andother purpose. In recent years, to meet the demand for energy, plantation of energy plants hasbeen re-emphasized. Government has started many plans like afforestation, agri-horticulturalpractices etc.. It has been estimated that at present, only l/7th of the world's total energy comesfrom biomass and a large amount of it remains untapped. In view of getting maximum biomassafforestation, forest management systems will have to be developed. These must include socialforestry, silvi-culture tree-use systems, drought tolerant, salt tolerant, pollutant resistant

plantations and high density energy plantations.

Annual plants in energy plantations should have fast growth, stress resistance, lesspalatable to cattle and other animals, high calorific value, absence of deleterious volatiles whensmoke comes out, high yield of biomass and should be disease and pest free.

2. Social forestryPlantation through social forestry has been much emphasized by the government of

India to meet the demand of fuel and fodder in rural areas. This includes planting trees alongroad sides, canals, railway lines and wastelands in village. Some of the important plants are

Acacia nilotica, Albizia lebbek, Cassia fistula, Eucalpytus globulus, Ficus glome rata, Morusalba, Ferminalia arjuna etc.

3. Silvi-culture energy farmsThese are known as short rotation forestry. These silviculture farms employ techniques

more similar to agriculture than forestry. The chief objective of energy plantation is to producebiomass from the selected trees and shrub species in the shortest possible time (generally 5-10years) and at the minimum cost, so as to satisfy local energy needs. This would certainly relievethe pressure on the consumption of fossil fuel like kerosene and prevent the destruction of plantcover, which is one of the primary component of life support system. Due to its high yield per


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unit area, smaller land requirements for biomass output, shorter life span, increased labourefficiency are the advantageous to adopt silviculture.

Different sources of biomass, their forms, their conversion process to respective formsof. energy are given in Table no. 4.

Table 4: Biomass as a source of energy

Sl.No Sources of biomass Forms of biomass

Conversionprocess

Forms ofenergy

A Plantations

1 Siviculture Fire wood Combustion Heat2 Energy plantation -do- Destructive

distillationCharcoal

3 Agriculture Carbohydrates

Ethanol

4 Energy crops Hydrocarbons Fermentation Fuel oil

5 Aquatic biomass Aquaculture Methanol6 Weeds Whole plant

bodyMethane

B Residues/wastes/weeds

1 Rural/urban wastes/industrial wastes

CombustionPyrolysis

Fire/fuelFuel oil

Fermentation Ethanol2 Forestry wastes -do- Combustion Fuel

Pyrolysis Oil gasGasification Gas

Fermentation Ethanol3 Agricultural wastes Wastes Fermentation Methane

4 Weeds & aquaticbiomass Wastes Fermentation Methane

5 Cattle dung Wastes Fermentation(biomass)

Methane

Thus production of biomass helps in developing cheaper source of energy fromunutilized agricultural residues, wastes, forest wastes, plantations etc. which is an alternativesource of energy for fossil fuel energies.

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Biomass as a Source of Energy-379