Biomass

Dr. Basudev Pradhan

What is Biomass?Biomass is biological material derived from living, or recentlyliving organisms. In the context of biomass for energy this isoften used to mean plant based material, but biomass canequally apply to both animal and vegetable derived material.

Chemical compositionBiomass is carbon based and is composed of a mixture of organicmolecules containing hydrogen, usually including atoms ofoxygen, often nitrogen and also small quantities of other atoms,including alkali, alkaline earth and heavy metals. These metalsare often found in functional molecules such as the porphyrinswhich include chlorophyll which contains magnesium.

Plant material The carbon used to construct biomass is absorbed from the

atmosphere as carbon dioxide (CO2) by plant life, using energy from the sun.

Plants may subsequently be eaten by animals and thus converted into animal biomass. However the primary absorption is performed by plants.

If plant material is not eaten it is generally either broken down by micro-organisms or burned:

If broken down it releases the carbon back to the atmosphere, mainly as either carbon dioxide (CO2) or methane (CH4), depending upon the conditions and processes involved.

If burned the carbon is returned to the atmosphere as CO2. These processes have happened for as long as there have been

plants on Earth and is part of what is known as the carbon cycle.

Fossil fuels Fossil fuels such as coal, oil and gas are also derived from

biological material, however material that absorbed CO2 from the atmosphere many millions of years ago.

As fuels they offer high energy density, but making use of that energy involves burning the fuel, with the oxidation of the carbon to carbon dioxide and the hydrogen to water (vapour). Unless they are captured and stored, these combustion products are usually released to the atmosphere, returning carbon sequestered millions of years ago and thus contributing to increased atmospheric concentrations.

The difference between biomass and fossil fuels The vital difference between biomass and fossil fuels is one

of time scale. Biomass takes carbon out of the atmosphere while it is

growing, and returns it as it is burned. If it is managed on a sustainable basis, biomass is harvested as part of a constantly replenished crop. This is either during woodland or arboricultural management or coppicing or as part of a continuous program of replanting with the new growth taking up CO2 from the atmosphere at the same time as it is released by combustion of the previous harvest.

This maintains a closed carbon cycle with no net increase in atmospheric CO2 levels.

Sources of Biomass

Biomass

Energy cropsNatural

vegetable growth

Organic wastes and

residues

Forest residueAgricultural

crop residuesAnimal waste Urban waste

Municipal solid waste

Sewage liquid waste

Industrial waste

Categories of biomass materials Biomass for energy can include a wide range of materials. There are five basic categories of material: Virgin wood, from forestry, arboricultural activities or

from wood processing Energy crops: high yield crops grown specifically for

energy applications Agricultural residues: residues from agriculture

harvesting or processing Food waste, from food and drink manufacture,

preparation and processing, and post-consumer waste Industrial waste and co-products from manufacturing

and industrial processes.

Virgin wood

Virgin wood consists of wood and other products such as bark and sawdust which have had no chemical treatments or finishes applied. Wood may be obtained from a number of sources which may influence it's physical and chemical characteristics.

Energy crops Energy crops are grown specifically for use as fuel and

offer high output per hectare with low inputs. Different classes of energy crops are,

Short rotation energy crops

Grasses and non woody energy corps

Agricultural energy crops

Aquatics

Agricultural residues Agricultural residues are of a wide variety of types, and

the most appropriate energy conversion technologies and handling protocols vary from type to type. The most significant division is between those residues that are predominantly dry (such as straw) and those that are wet (such as animal slurry).

Sources of agricultural residues Many agricultural crops and processes yield residues

that can potentially be used for energy applications, in a number of ways. Sources can include:

Arable crop residues such as straw or husks

Animal manures and slurries

Animal bedding such as poultry litter

Most organic material from excess production or insufficient market, such as grass silage.

Wet Residue These are residues and wastes that have a high water

content as collected.

This makes them energetically inefficient to use for combustion or gasification, and financially and energetically costly to transport. It is therefore preferable to process them close to production, and to use processes that can make use of biomass in an aqueous environment. They include,

Animal Slurry

Grass Silage

Dry residues These include those parts of arable crops not to be

used for the primary purpose of producing food, feed or fiber, used animal bedding and feathers. They are generally,

Straw

Corn Stover

Poultry litter

Food waste There are residues and waste at all points in the food

supply chain from initial production, through processing, handling and distributions to post-consumer waste from hotels, restaurants and individual houses

It has been calculated that about a third of all food grown for human consumption in the UK is thrown away.

Many food materials are processed at some stage to remove components that are inedible or not required such as peel/skin, shells, husks, cores, pips/stones, fish heads, pulp from juice and oil extraction, etc

Many manufactured foods and drinks, and cheese and other dairy products generate large quantities of organic waste material. It has been estimated that up to 92% of ingredients used in brewing ultimately become waste, principally spent grains, and the dairy industry uses around 40 million m3 annually, mainly for cleaning, which produces effluent containing high levels of organic residues

Food preparation on both the commercial and domestic scale yield residues and waste, used cooking oils and food that has had to be disposed of because it has gone bad, for health and safety reasons or because it is surplus to requirements.

Food waste can be divided into dry waste and wet waste, however the majority is of relatively high moisture content.

Industrial waste and co-products Many industrial processes and manufacturing

operations produce residues, waste or co-products that can potentially be used or converted to biomass fuel. These can be divided into woody materials and non-woody materials.

Woody wastes and residues

Non-woody wastes and residues

Forms of biomass and wood fuel Raw biomass typically has a low energy density as a

result of both its physical form and moisture content. This makes it inconvenient and inefficient for storage and transport, and also usually unsuitable for use without some kind of pre-processing

There are however a range of processes available to convert it into a more convenient form. Depending on the biomass itself, and the purpose to which it is to be put, this may consist of

Physical preprocessing Conversion by thermal or chemical process

In this way raw biomass is converted into what can be described as a 'biomass fuel‘ For example, virgin wood (above) is a simple form of

biomass and for many applications may require relatively straightforward processing. For ease of handling, transport and storage it may be cut into a number of physical forms, as best suit the requirements of the next handling or processing stage

Pre-processing forestry and arboricultural residues

Pre-processing may be required to change the physical form or to reduce the moisture content.

As harvested, forest derived biomass tends to be of a range of lengths and size, and is of relatively low density. Physical pre-processing can consist of

Cutting to uniform length

Chipping

Grinding or shredding

Reducing moisture content.

Conversion technologies There are a number of technological options available

to make use of a wide variety of biomass types as a renewable energy source. Conversion technologies may release the energy directly, in the form of heat or electricity, or may convert it to another form, such as liquid biofuel or combustible biogas. While for some classes of biomass resource there may be a number of usage options, for others there may only one appropriate technology

Thermal conversion technologies

Chemical Conversion technologies

Thermal conversion These are processes in which heat is the dominant

mechanism to convert the biomass into another chemical form. The basic alternatives are separated principally by the extent to which the chemical reactions involved are allowed to proceed:

Combustion

Gassification

Pyrolysis

Combustion Combustion is the process with which everyone is

familiar by which flammable materials are allowed to burn in the presence of air or oxygen with the release of heat.

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What is combustion? The basic process is oxidation.

Combustion is the simplest method by which biomass can be used for energy, and has been used for millennia to provide heat. This heat can itself be used in a number of ways:

Space heating

Water (or other fluid) heating for central or district heating or process heat

Steam raising for electricity generation or motive force.

Combustion of biomass material When the flammable fuel material is a form of

biomass the oxidation is of predominantly the carbon (C) and hydrogen (H) in the cellulose, hemicellulose, lignin, and other molecules present to form carbon dioxide (CO2) and water (H2O)

Oxidation of other elements into gasses, ash or slag The above, and other, molecules within the biomass also

contain other atoms in different quantities and some of these too can be oxidized, with the oxide released as gas in the flue gasses, or as solid as ash or slag.

All carbohydrates, such as cellulose, also contain oxygen in the molecular structure.

Other atoms potentially found in biomass include: Nitrogen (N) Phosphorus (P) Potassium (K) Silicon (Si) Sulphur (S).

Gasification Gasification is a partial oxidation process whereby a

carbon source such as coal, natural gas or biomass, is broken down into carbon monoxide (CO) and hydrogen (H2), plus carbon dioxide (CO2) and possibly hydrocarbon molecules such as methane (CH4).

What is gasification? This mix of gases is known as 'producer gas' or product

gas (or wood gas or coal gas, depending on the feedstock), and the precise characteristics of the gas will depend on the gasification parameters, such as temperature, and also the oxidizer used. The oxidizer may be air, in which case the producer gas will also contain nitrogen (N2), or steam or oxygen.

Applications Gasification technology can be used for:

Heating water in central heating, district heating or process heating applications

Steam for electricity generation or motive force

As part of systems producing electricity or motive force

Transport using an internal combustion engine.

Low temperature gasification If the gasification takes place at a relatively low

temperature, such as 700ºC to 1000ºC, the product gas will have a relatively high level of hydrocarbons compared to high temperature gasification. As a result it may be used directly, to be burned for heat or electricity generation via a steam turbine or, with suitable gas clean up, to run an internal combustion engine for electricity generation.

High temperature gasification Higher temperature gasification (1200ºC to 1600ºC)

leads to few hydrocarbons in the product gas, and a higher proportion of CO and H2.

This is known as synthesis gas (syngas or biosyngas) as it can be used to synthesize longer chain hydrocarbons using techniques such as Fischer-Tropsch (FT) synthesis.

If the ratio of H2 to CO is correct (2:1) FT synthesis can be used to convert syngas into high quality synthetic diesel biofuel which is completely compatible with conventional fossil diesel and diesel engines.

PyrolysisPyrolysis is the precursor to gasification, and takes place

as part of both gasification and combustion. It consists of thermal decomposition in the absence of oxygen. It is essentially based on a long established process, being the basis of charcoal burning

Products of pyrolysis: The products of pyrolysisinclude gas, liquid and a sold char, with the proportions of each depending upon the parameters of the process.

Applications Applications for pyrolysis include:

Biomass energy densification for transport or storage

Co-firing for heat or power

Feedstock for gasification.

Lower vs. higher temperature pyrolysis Lower temperatures (around 400ºC) tend to produce

more solid char (slow pyrolysis), whereas somewhat higher temperatures (around 500ºC) produce a much higher proportion of liquid (bio-oil).

Chemical conversion Processes A range of chemical processes may be used to convert

biomass into other forms, such as to produce a fuel that is more conveniently used, transported or stored, or to exploit some property of the process itself.

Biochemical conversion As biomass is a natural material, many highly efficient

biochemical processes have developed in nature to break down the molecules of which biomass is composed, and many of these biochemical conversion processes can be harnessed.

Biochemical conversion makes use of the enzymes of bacteria and other micro-organisms to break down biomass. In most cases micro-organisms are used to perform the conversion process:

Anaerobic digestion Fermentation Composting Trans esterification

Anaerobic Digestion Anaerobic digestion (AD) is the process whereby bacteria break down organic

material in the absence of air, yielding a biogas containing methane.

About anaerobic digestion The products of this process are:

Biogas (principally methane (CH4) and carbon dioxide (CO2))

A solid residue (fiber or digestate) that is similar, but not identical, to compost.

A liquid liquor that can be used as a fertilizer.

Using the outputs from the anaerobic digestion of biomass material

Methane can be burned for heat or electricity generation.

The solid residue of the AD process can be used as a soil conditioner, however its properties:

Will depend on the AD feedstock used

May or may not contain useful levels of nitrate or phosphate

May be contaminated with heavy metals.

The solid residue can, alternatively, be burned as a fuel, or gasified.

Fermentation Fermentation is the process used in brewing and wine

making for the conversion of sugars to alcohol (ethanol CH3CH2OH). The same process, followed by distillation, can be used to obtain pure ethanol (bioethanol) for use as a transport biofuel.

Conventional fermentation processes for the production of bioethanol make use of the starch and sugar components of typically cereal or sugar (beet or cane) crops.

Second generation bioethanol precedes this with acid and/or enzymatic hydrolysis of hemicellulose and cellulose into fermentable saccharides to make use of a much larger proportion of available biomass

Using bioethanol (Bio)ethanol can be readily added to conventional

petrol in concentrations up to 10%, but most European manufacturers' vehicle warranties only cover up to a 5% bioethanol/95% petrol blend.

Composting Similarly to anaerobic digestion, though making use of

different bacteria, composting is the aerobic decomposition of organic matter by micro organisms. It is however typically performed on relatively dry material rather than a slurry

Using composting for heat and power Instead of, or in addition to, collecting the flammable

biogas emitted, the exothermic nature of the composting process can be exploited and the heat produced used, usually using a heat pump.

Trans esterification

This chemical conversion process can be used to convert straight and waste vegetable oils into biodiesel.

Problems with using vegetable oils as fuel Vegetable oils and animal fats are triglycerides: esters of

glycerol with three fatty acid chains. Although some unmodified vegetable oils have been used as fuel in internal combustion engines, in general the viscosity is significantly higher than that of conventional diesel and a number of modifications are required to a vehicle's fuel system (including heaters, additional filters and modified injectors) to use them.

Even then, the lack of a transport fuel specification for straight vegetable oil (SVO) and concerns about long term engine reliability using SVO as a fuel, make this inadvisable for the present

Converting vegetable oils into biodiesel Instead, SVO and filtered waste vegetable oil (WVO) can

be reacted with methanol (or ethanol) to change the triglyceride esters into methanol (or ethanol) monoesters, each with single fatty acid chains making fatty acid methyl ester (FAME), commonly known as biodiesel.

Although not all oils and fats are suitable for this process, depending on such chemical characteristics as degree of saturation of the fatty acid chains (iodine number), melting point, etc., many oils have been successfully used, including rape seed oil, palm oil and soybean oil.

Both virgin oil and waste oil can potentially be used. However WVO needs both to be filtered before use and assayed for iodine number and free fatty acid concentration before use

Basic Process : therm0-chemical conversion• Conversion of solid fuels into combustible

gas mixture called producer gas (CO + H2 + CH4)

• Involves partial combustion of biomass• Four distinct process in the gasifier viz.

• Drying • Pyrolysis• Combustion• Reduction

What is Biomass Gasification?

Biomass Gasifiers

Downdraft Gasifier

Gasification flow diagram

Bubbling fluidized bed gasification

Particulars Rice Husk Woody Biomass

CO 15-20% 15-20%

H2 10-15% 15-20%

CH4 Upto 4% Upto 3%

N2 45-55% 45-50%

CO2 8-12% 8-12%

Gas C.V. (kcal/Nm3) Above 1050 Above 1100

Gas generated in Nm3/kg

of biomass

2 2.5

Producer Gas - Composition?

Applications

Power Generation Thermal Applications

o Irrigation Pumping

o Village Electrification

o Captive Power (Industries)

o Grid-fed Power from Energy

Plantations on Wastelands

o Simultaneous Charcoal and

Power Production

o Hot Air Generators

o Dryers

o Boilers

o Thermic Fluid Heaters

o Ovens

o Furnaces & Kilns

Gasifier Plant

Indicative Schematic – Power Gen

Biodiesel plant

Biodiesel is a liquid fuel produced from non-edible oil seeds as Jatropha, karanja, jajoba, etc which can be grown on wasteland. Viscosity 20 times higher than diesel, to solve by trans-esterification (raw vegitablesoils are treated with alcohol to form methyl or ethyl ester(monoester or biodiesel)

Schematic of the Transesterification process

Biodiesel – Final ProductBiodiesel 100%

Glycerin

BioDiesel is here

Using biodiesel The biodiesel produced can be used on its own or

mixed with petroleum based diesel fuel as a 5% biodiesel/95% fossil diesel blend and used by unmodified, conventional diesel engines

In USA, anhydrous ethanol (10%)+petrol (90%)~ gasohol

In India 18 M tonnes sugar production per year, ethanol ~1700 M litres, 1200 M litres for chemical sector, leaving 500 M litres sufficient for 5% blending with petrol in our country

Biogas and biogas technologyBiogas:Biogas is a renewable energy derived from organic wastes such as cattle dung, human waste, etc. It is a safe fuel for cooking, and lighting. Left over digested slurry is used as enriched manure in agriculture lands.

Biogas technology:Biogas is produced from wet biomas through a biological conversion process that involves bactrial breakdown organic matter by micro-organisms to produce CH4, CO2 and H2O......”anaerobic digestion” in three steps

•Hydrolysis by celluolytic bacteria/hydrobytic bacteria), pH(6-7), temp(30-40°C)•Acid formation ( acetic acid)•Methane formation

Factor affecting biogas production

Solid–to-water ratioCattle dung (gobar) contains 18% solid matter+82% water. Anaerobic fermentations better if slurry contain 9% solid, so digester feed is prepared by mixing water in 1:1 weight ratio, to increase the solid matter, crop residues, weed plants may be mixed

Volumetric loading rate (1-1.5 kg/m3/day)

Temperature (35-38°C, deceases below 20°C stop below 8°C)

Seeding

pH value(6.8- 7.8)

Carbon –to –nitrogen ratio(30:1)

Retention time (120 litre digester , fed 5 litre per day, retentation time24 days)

Stirring digester contents

Calorific values of commonly used fuels

Commonly used fuels

Calorific values in Kilo calories

Thermal efficiency

Bio-gas 4713/M3 60%

Dung cake 2093/Kg 11%

Firewood 4978/Kg 17.3%

Diesel (HSD) 10550/Kg 66%

Kerosene 10850/Kg 50%

Petrol 11100/Kg ---

Biogas Production Potential from different Wastes

Raw Materials for Gasification

Average maximum biogas production from different feeds

Sl. No. Feed StockLitre /kg of dry matter

% Methane content

1. Dung 350* 60

2. Night-soil 400 65

3. Poultry manure 440 65

4. Dry leaf 450 44

5. Sugar cane Trash 750 45

6. Maize straw 800 46

7. Straw Powder 930 46

* Average gas production from dung may be taken as 40 lit/kg. of fresh dung when no temperature control is provided in the plant. One Cu. m gas is equivalent to 1000 litres.

What is Biogas Plant

Basically Methane & CO2 Gas Producer.

Methane – Odorless, Colorless, Good Calorific Value, Green House Gas

Sources : Animal Manures, excreta, kitchen waste, Industrial Chemical Processes, Sea Water Bed, etc.

Animal Manure & Excreta contributes around 16 %of the total global methane emission.

Components of the bio-gas production plant

There are two major models - fixed dome type and floating drum typeBoth the above types have the following components

(i) Digester : This is the fermentation tank. It is built partially or fully underground. It is generally cylindrical in shape and made up of bricks and cement mortars.

(ii) Gas holder: This component is meant for holding the gas after it leaves the digester. It may be a floating drum or a fixed dome on the basis of which the plants are broadly classified. The gas connection is taken from the top of this holder to the gas burners or for any other purposes by suitable pipelines.

(iii) Slurry mixing tank: This is a tank in which the dung is mixed with water and fed to the digester through an inlet pipe.

(iv) Outlet tank and slurry pit: An outlet tank is usually provided in a fixed dome type of plant from where slurry in directly taken to the field or to a slurry pit. In case of a floating drum plant, the slurry is taken to a pit where it can be dried or taken to the field for direct applications.

Points to be considered for construction of a biogas plant

Site selection: While selecting a site for a bio-gas plant, following aspects should be considered:

The land should be levelled and at a higher elevation than the surroundings to avoid water stagnation

Soil should not be too loose and should have a bearing strength of 2 kg/cm2

It should be nearer to the intended place of gas use (eg. home or farm).

It should also be nearer to the cattle shed/ stable for easy handling of raw materials.

The water table should not be very high.

Adequate supply of water should be there at the plant site.

The plant should get clear sunshine during most part of the day.

The plant site should be well ventilated.

A minimum distance of 1.5m should be kept between the plant and any wall or foundation.

It should be away from any tree to prevent root interference.

It should be at least 15m away from any well used for drinking water purpose.

Availability of raw materials : The size of the biogas plant is to be decided based on availability of raw material. It is generally said that, average cattle yield is about 10 kg dung per day. For eg. the average gas production from dung may be taken as 40 lit/kg. of fresh dung. The total dung required for production of 3 m3 biogas is 3/0.04= 75 kgs. Hence, a minimum of 4 cattle is required to generate the required quantity of cow dung.

Schematic of a typical Biogas Plant

Floating dome type Bio-gas Plant

A KVIC Type Biogas Plant

Fixed dome type Bio-gas Plant

Benefits of Biogas Plants

Contributes substantially in reducing Global Warming.

Cost effective replacement for Fossil Fuels.

This Smoke Free gas emits less carbon dioxide as compared to other fuels.

A very efficient and environmentally friendly solution for disposing off various organic matter.

METHANE

Contributes largely in Global Warming

Traps 21 times more heat than CO2

Over the 100 years – 25 times more temperature impact than that by CO2

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Biogas Plant Traps Methane

Fuel Carbon Dioxide.

Biogas Plants – Reduction in Global Warming

Simple sketch of household biogas plant

Deenbandhu biogas plant

Biogas Bottling Plant

BGFP Project at Village – Talwade, Taluka- Trimbakeshwar, District- Nashik (Maharashtra)

Conclusions

India has second largest biogas programme in the world at ruraland as well as urban levels.

Many technologies/models have been successfully developed inIndia for biogas programme.

There is need to develop a sustainable renewable energyprogramme on biogas for replacing petroleum products byutilization of biogas in the country.

This will help in green energy technology and reducing greenhouse gases emissions.

Biogas is a potential renewable energy source for rural India and

other developing countries.

Biogas generation and subsequent bottling will cater the energy

needs of villages, supply enriched manure and maintain village

sanitation.

The bottling system will work as a decentralize source of power

with uninterrupted supply using local resources, generate ample

opportunities for employment and income of the rural people.

Biogas flame

THANK YOU