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BOIGAS AND BIOMASS

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History :-

Scientific interest in the manufacturing of gasproduced by the natural decomposition of organicmatter was first reported in the 17th century byRobert Boyle and Stephen Hale, who noted that

flammable gas was released by disturbing thesediment of streams and lakes. In 1808, SirHumphry Davy determined that methane was presentin the gases produced by cattlemanure.The firstanaerobic digester was built by a leper colony in

Bombay, India, in 1859. In 1895, the technology wasdeveloped in Exeter, England, where a septic tank wasused to generate gas for thesewer gas destructor lamp, a type ofgas lighting. Also

in England, in 1904, the first dual-purpose tank forboth sedimentation and sludge treatment was

http://en.wikipedia.org/wiki/History_of_manufactured_gashttp://en.wikipedia.org/wiki/Robert_Boylehttp://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Humphry_Davyhttp://en.wikipedia.org/wiki/Cattlehttp://en.wikipedia.org/wiki/Manurehttp://en.wikipedia.org/wiki/Leper_colonyhttp://en.wikipedia.org/wiki/Bombayhttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Exeterhttp://en.wikipedia.org/wiki/Englandhttp://en.wikipedia.org/wiki/Sewer_gas_destructor_lamphttp://en.wikipedia.org/wiki/Gas_lightinghttp://en.wikipedia.org/wiki/Sedimentationhttp://en.wikipedia.org/wiki/Sedimentationhttp://en.wikipedia.org/wiki/Gas_lightinghttp://en.wikipedia.org/wiki/Sewer_gas_destructor_lamphttp://en.wikipedia.org/wiki/Englandhttp://en.wikipedia.org/wiki/Exeterhttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Bombayhttp://en.wikipedia.org/wiki/Leper_colonyhttp://en.wikipedia.org/wiki/Manurehttp://en.wikipedia.org/wiki/Cattlehttp://en.wikipedia.org/wiki/Humphry_Davyhttp://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Robert_Boylehttp://en.wikipedia.org/wiki/History_of_manufactured_gas

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Definition:- It is an organicmatter produced by plant and

their derivatives & animalmanure.Bio-energy:- energy produced

from biomassBio- mass can be considered one form ofsolarenergy.Plants are grow byphotosynthesis.It is renewable energy sources because the organic

matter generated round the year.Fossil fuel like coal, petroleum products and naturalgas are not considered as bio mass since they areproduces from dead biomass under pressure and

temperature during several years.

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Bio mass resourcesclassification:

1. Biomass obtain from agriculturefields, crops, forests.

2. Biomass obtain from waste(Municipal waste, animal & humanwaste)

3. Biomass converted into liquid fuels

like methanol, ethanol.

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PHOTOSYNTHESISPROCESS

Biomass is produced inphotosynthesis processwhich convert solar energy into biomass energy.

This process only occurs in green plants.It is the process which combined CO2 from atmosphere withwater in presence of light energy toproduce carbohydrates( sugar ,starch, celluloses,etc) and oxygen.Photosynthesis process can be represented by the following equation:

6CO2 + 6H2O +light energy PHOTOSYNTHESIS C6H12O6 + 6O2

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ENERGY CONVERSIONFROM BIOMASS:-

There various methods for conversion of biomass intoenergy classified as follows:1. Direct combustion2.Thermo chemical conversion3. Biochemical conversion

DIRECT COMBUSTION:-Direct burning of biomass is the most straightforward methodof energy production. Mankind has burned wood and otherforms of biomass for thousands of years, to keep warm, tocook food, and eventually to forge weapons and other tools.

The energy released by direct combustion takes the form ofheat, and can be used to directly influence the temperature ofa small environment or to power steam-driven turbines to

produce electricity. Unfortunately, the burning of biomass isthe cause of a reat deal of ollution and has contributed to

http://library.thinkquest.org/20331/types/pollute.htmlhttp://library.thinkquest.org/20331/types/pollute.html

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THERMOCHEMICAL CONVERSION:The thermo chemical reactions can convert the organicbiomass into more valuable and convenient form ofproducts as gaseous and liquid fuels at different pressureand temperatures.

These processes are as below:Gasification :- Gasification is a process thatconverts biomass materials into carbon monoxide,hydrogen and carbon dioxide. This is achieved by reactingthe material at high temperatures (>700C), withoutcombustion, with a controlled amount ofoxygen. Theresulting gas mixture is called syngas (from synthesisgas or synthetic gas) or producer gas and is itself a fuel.

The power derived from gasification of biomass andcombustion of the resultant gas is considered to be a sourceofrenewable energy; the gasification offossil fuel

derived materials such as plastic is not considered to berenewable ener .

http://en.wikipedia.org/wiki/Carbon_monoxidehttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Syngashttp://en.wikipedia.org/wiki/Producer_gashttp://en.wikipedia.org/wiki/Renewable_energyhttp://en.wikipedia.org/wiki/Renewable_energyhttp://en.wikipedia.org/wiki/Producer_gashttp://en.wikipedia.org/wiki/Syngashttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Carbon_monoxide

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PYROLYSIS:-Pyrolysis involves theheating of biomass in the absence ofoxygen. Biomass such as wood oragricultural waste is heated to around

1000 degrees Fahrenheit and allowedto decompose into gas and charcoal(carbon). A major advantage of Pyrolysisis that carbon dioxide, one of the maindrawbacks to most biomass energyconversion processes, is not produced. Adisadvantage, however, is that the

biomass must be heated to relatively hightemperatures, a process that in and of

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BIOCHEMICAL CONVERSION:As biomass is a naturalmaterial, many highly efficient biochemical processeshave developed in nature to break down themolecules of which biomass is composed, and many

of these biochemical conversion processes can beharnessed.Biochemical conversion makes use of theenzymes of bacteria and other micro-organismsto break down biomass. In most cases micro-organisms are used to perform the conversionprocess: anaerobic digestion AND fermentation. Another way of breaking down biomass is by

breaking down the carbohydrates and simple sugars

to make alcohol. However, this process has not beenerfected et. Scientists are still researchin the

http://en.wikipedia.org/wiki/Anaerobic_digestionhttp://en.wikipedia.org/wiki/Fermentation_(biochemistry)http://en.wikipedia.org/wiki/Fermentation_(biochemistry)http://en.wikipedia.org/wiki/Anaerobic_digestion

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BIOGAS GENERATION:-

Biogas is produced by anaerobic decompositionof organic waste by suitable bacteria. It contains55-65 % of methane and remaining percent CO2and other impurities.

Main source of production of biogas are cropresidue, wet cow dung, vegetable waste, poultrydropping, other waste etc. Any organic materialwhich is easily bio degradable.

The material from which biogas is produced retains

its value as fertilizer can be used after certainprocessing.Biogas can be produced by digestion Pyrolysis.Digestion is a biological process that occurs in

absence of O2 and in presence ofanaerobicor anisms at normal ressure and tem erature (35-

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PRINCIPLE OF BIO GASPRODUCTION FROM WASTEBIOMASSS

There are four key biological and chemical stagesof anaerobic digestion:HydrolysisAcidogenesis

AcetogenesisMethanogenesisIn most cases, biomass is made up of largeorganic polymers. For the bacteria in anaerobicdigesters to access the energy potential of the

material, these chains must first be broken downinto their smaller constituent parts. Theseconstituent parts, or monomers, such as sugars,are readily available to other bacteria. The

process of breaking these chains anddissolvin the smaller molecules into solution

http://en.wikipedia.org/wiki/Hydrolysishttp://en.wikipedia.org/wiki/Acidogenesishttp://en.wikipedia.org/wiki/Acetogenesishttp://en.wikipedia.org/wiki/Methanogenesishttp://en.wikipedia.org/wiki/Methanogenesishttp://en.wikipedia.org/wiki/Acetogenesishttp://en.wikipedia.org/wiki/Acidogenesishttp://en.wikipedia.org/wiki/Hydrolysis

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Acetate and hydrogen produced in the first stagescan be used directly by methanogens. Othermolecules, such as volatile fatty acids (VFAs) with achain length greater than that of acetate must first

be catabolised into compounds that can be directlyused by methanogens.

The biological process ofacidogenesis results infurther breakdown of the remaining components byacidogenic (fermentative) bacteria. Here, VFAs arecreated, along with ammonia, carbon dioxide, andhydrogen sulfide, as well as other by-products. Theprocess of acidogenesis is similar to the waymilk sours.

The third stage of anaerobic digestion is

http://en.wikipedia.org/wiki/Catabolisedhttp://en.wikipedia.org/wiki/Acidogenesishttp://en.wikipedia.org/wiki/Hydrogen_sulfidehttp://en.wikipedia.org/wiki/Sour_milkhttp://en.wikipedia.org/wiki/Acetogenesishttp://en.wikipedia.org/wiki/Sour_milkhttp://en.wikipedia.org/wiki/Hydrogen_sulfidehttp://en.wikipedia.org/wiki/Acidogenesishttp://en.wikipedia.org/wiki/Catabolised

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The terminal stage of anaerobic digestion is thebiological process ofmethanogenesis. Here,methanogens use the intermediate products of thepreceding stages and convert them into methane,

carbon dioxide, and water. These componentsmake up the majority of the biogas emitted fromthe system. Methanogenesis is sensitive to bothhigh and low pHs and occurs between pH 6.5 andpH 8. The remaining, indigestible material the

microbes cannot use and any dead bacterialremains constitute the digestate.A simplified generic chemical equation for theoverall processes outlined above is as follows:

C6H12O6 3CO2 + 3CH4

http://en.wikipedia.org/wiki/Methanogenesishttp://en.wikipedia.org/wiki/Methanogenesis

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Advantages of biogasproduction1. Waste material available after processing

can be used as fertilizer.2.The biogas after removal of CO2

produces an excellent fuel as CH4 gas.3. Gas production is cheap.4. Sewage waste after production of biogas

is converted into less offensive slurry.

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Factors affectingproduction of biogas:-

Temperature & pressure Solid concentration and loading rate Retention period pH value Nutrients composition Toxic substance

Digester size & shape Stirring agitation of the content ofdigester

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Temperature & pressure:

Process of anaerobic fermentation and methaneforming bacteria works best in the temperaturerange of25-55 C and pressure about 1.1-1.2 bar

Rate of gas production increase with temperature

but percentage of methane reduced. 35-38 C isthe best range for methane production.

If the temperature is lower than 20 C rate of gasproduction sharply reduced and almost stop at 10C.

So, in cold climate ,it is necessary to heat thedigester to 35 C.

Solid concentration and loading rate:

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Retention period:It represents the time period for which thefermentable material remains inside the digester. This

period ranges from 35 days to 50days dependingupon atmospheric condition.

pH value or hydrogen ion concentration:

pH value indicates the degree of acidity or alkalinity ofa solution.pH value in the range 0-7 represents acidic solutionand in the range 7-14 indicates the alkaline solution.In the initial stage ofacid forming stage of

digestion, pH value may be around 6 or less,however during methane formation stagepHvalue higher than 7 is maintained sincemethane formers are sensitive to acidity.

For above reasons the optimum pH value of digestersolution between 7-8 is recommended.

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Toxic substances:

The presence of ammonia, pesticides , detergents,

heavy metals are considered as toxic substance tomicro-organisms since their presence reduces thefermentation rate. if digested slurry allowed toremain in digester beyond certain time, it become

toxic to micro-organism growth.

Digester size and shape:

It is found that the biogas production per unit volume

of digester is high when its diameter to depth ratioranges between 0.66 to 1.

Stirring or agitation of the content of digester:

Since bacteria in the di ester has ver limited ran e

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Classification of biogas plant:

Biogas plants are built in different size and shapesdepending upon process carried out.

These plants are mainly classified as:1. Continuous or batch type

2. Dome and drum type

Continuous & batch type biogas plant:

Continuous type biogas plant: in which biomass fed

regularly to the digester delivers the biogascontinuously.

They are two types namely as:1) Single stage continuous type plant: in this plant

conversion of biomass into biogas are carried out inthe sin le chamber .

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Then dilute acids are only fed into second chamberwhere the stage II of methane formation is carried out.

The biogas so produced is collected from the secondchamber.

Advantages of these plants is that it produce moreamount of biogas , required less space and lesserperiod of digestion as compared to single stage plant.

Disadvantages are that plant is costlier , difficult tooperate and maintain.

Single stage for small size plant

Double stage for larger size plant.

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Batch type biogas plant :- the biomass feeding isdone in batches with large time interval between thetwo consecutive batches.

a digester is loaded with feed and given sufficient

time (30-40 days) for digestion of biomass. Aftercompletion of digestion, the residue is emptied and itis again charged with the next batch of feed.in this type of plant biogas production is uneven.

Silent features of batch type plants are:

v Gas production is unevenv Need several digester for continuous supply of gasv

The cost and space required is highv Need addition of fermented slurr to start the

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Dome & drum type biogas plant:

Various models of dome and drum type of biogasplants have been developed by the various agencies.

These are mainly of two types:1) Floating drum type biogas plants.2) Fixed dome type biogas plants.

Floating drum type biogas plant (constant pressure

type):Many models of floating drum type biogas plants

have been developed in various countries. One ofthe model is discussed here.

Floating drum type KVIC model:a common obar as lant su ested b khadi

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Advantages of KVIC plant:

High gas production rate No problem of gas leakage

Work under constant pressure naturally. No problem of mixing of biogas with external air, thusno danger of explosion.

Disadvantages :

it has higher cost Heat is lost through metal gas holder. Requires painting of drum to avoid corrosion at least

twice a year. Re uired maintenance of i e and oint.

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Fixed dome type biogas plants:

In fixed dome type biogas plants, thedigester and the gas dome are combined andenclosed in the same chamber. These type ofplants are more economical compared tofloating dome type.

The digester is usually built below theground level, which is suitable in regionshaving cold climate.

total volume inside the dome remains

constant due to which it is also called asconstant volume t e bio as lant. So the

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1. Fixed dome type domestic biogasplant ( janta model or Chinese model):

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Flexible bag type biogasplant:

Fixed dome type

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Fixed dome typedeenbandhu model biogas

plant:

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Advantages of fixed dome type plant:

Cost is less as compared to floating type Loss of heat is negligible ( construction is under

ground) No corrosion problem It is maintenance free.

Disadvantages of fixed dome type plants:

Need skilled labour to operate Gas production/m3 of digester volume is less Gas production at variable pressure.

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Site selection for biogasplant:Minimum distance between gas production and gasconsumption.Should be made open space to utilize sun energysince the biogas production is high above 25 Ctemperature.

Sufficient amount of water is availableSufficient space is available for its operation andmaintenance.

Application of biogas:The composition of biogas are as below:

CH4 50-65%CO2 30-45%H2 and N2 5-10%H2S and O2 very small amount