Biomass & Biofuels (Final) (1)

8/16/2019 Biomass & Biofuels (Final) (1)

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BIOMASS

ANDBIOFUELS


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Biomass:

The material of plants and animals, including their wastes and

residues, is called biomass.

It is organic, carbon-based, material that reacts with oxygen incombustion and natural metabolic processes to release heat.

Heat, especially if at temperatures >400oC, may be used to generate

work and electricity.

Biofuels:

The initial material may be transformed by chemical and biological

processes to produce biofuels, i.e. biomass processed into a more

convenient form, particularly liquid fuels for transport.

Methane gas, liquid ethanol, oils etc. are some examples.

Bioenergy:

The term bioenergy is sometimes used to cover biomass and biofuels

together.


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Domestic Use:

Biomass provides about 13% of mankind’s energy consumption, includingmuch for domestic use in developing countries but also significant amountsin mature economies; this percentage is comparable to that of fossil gas.

The domestic use of biofuel as wood, dung and plant residues for cooking isof prime importance for about 50% of the world’s population.

Industrial Use

The industrial use of biomass energy is currently comparatively small formost countries, except in a few sugarcane-producing countries where cropresidues (bagasse) burnt for process heat may be as much as 40% ofnational commercial supply.

In some industrialized countries, the increasing use of biomass and wastesfor heat and electricity generation is becoming significant, e.g. USA (about2% of all electricity at 11 GWe capacity); Germany (at 0.5 GWe capacity)and in several countries for co-firing with coal.

World’s Total Installed Electricity

Generation Capacity: 5331.045 GWInternational Energy Statistics (2011)


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CO2 Associated with Biomass:

If biomass is to be considered renewable, growth must at least keep pace

with use.

The firewood consumption and forest clearing is significantly outpacing tree

growth in ever increasing areas of the world.

The carbon in biomass is obtained from CO2 in the atmosphere via

photosynthesis.

When biomass is burnt or digested, the emitted CO2 is recycled into theatmosphere, so not adding to atmospheric CO2 concentration over the

lifetime of the biomass growth.

Energy from biomass is ‘carbon neutral’. This contrasts with the use of fossil

fuels, from which extra CO2 is added to the atmosphere.

The heat energy available in combustion ranges from about 8 MJ/kg

(undried ‘green’ wood) and 15 MJ/kg (dry wood), to about 40 MJ/kg (fats

and oils) and 56 MJ/kg (methane).


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Natural & Managed Biomass Systems

Natural and Managed Biomass Systems


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Principles of Successful Biomass Systems

1. Every biomass activity produces a wide range of products and services. For

instance where sugar is made from cane, many commercial products can be

obtained from the otherwise waste molasses and fiber. If the fiber is burnt,

then any excess process heat can be used to generate electricity. Washings and

ash can be returned to the soil as fertilizer.

2. Some high-value fuel products may require more low-value energy tomanufacture than they produce, e.g. ethanol from starch crops & hydrogen.

Despite the energy ratio being >1, such an energy deficiency need not be an

economic handicap provided that process energy can be available cheaply by

consuming otherwise waste material, e .g. straw, crop fiber, forest trimmings.

3. Biofuel production is only likely to be economic if the production process

uses materials already concentrated , probably as a by-product and so available

at low cost or as extra income for the treatment and removal of waste.


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4. Biofuels are organic materials, so there is always the alternative of using

these materials as chemical feedstock . For instance, palm oil is an important

component of soaps; many plastic and pharmaceutical goods are made fromnatural products.

5. Poorly controlled biomass processing or combustion can certainly produce

unwanted pollution, especially from relatively low temperature combustion,wet fuels and lack of oxygen supply to the combustion regions. Modern

biomass processes require considerable care and expertise.

6. The use of sustainable biofuels in place of fossil fuels abates the emission of

fossil-CO2 and so reduces the forcing of climate change.

7. The main dangers of extensive biomass fuel use are deforestation, soil

erosion and the displacement of food crops by fuel crops.

Principles of Successful Biomass Systems


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Biofuel ClassificationMoisture Content:

If m is the total mass of the material as it is and m0 is the mass when

completely dried,

Dry basis moisture content w = m−m0 /m0

Wet basis moisture content w = m−m0 /m

When harvested, the wet basis moisture content of plants is commonly

50%, and may be as large as 90% in aquatic algae including seaweed (kelps).

The presence of moisture in biomass fuel usually leads to a significant loss

in useful thermal output because evaporation uses 2.3 MJ/kg of water and

the subsequently reduced combustion temperature increases smoke and air

pollution. Classification of Carbon-Based Fuels:

These are classified by their reduction level.

When biomass is converted to CO2 and H2O, the energy made available is

about 460 kJ per mole of carbon (38 MJ per kg of carbon nearly equal to 16

MJ per kg of dry biomass), per unit of reduction level R.


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Biofuel Classification Sugars (R = 1) have a heat of combustion of about 450 kJ per 12 g of carbon

content.

Fully reduced material, e.g. methane CH4 (R = 2) has a heat of combustion

of about 890 kJ per 12 g of carbon.

Following are the three broad classes of biomass energy process. Each class is

further divided into subclasses.

A: Thermochemical Heat:

1- Combustion:

It involves direct combustion for immediate heat.

Dry homogeneous input is preferred

2- Pyrolysis:

Biomass is heated either in the absence of air or by the partial combustion

of some of the biomass in a restricted air or oxygen supply.

Based on the temperature, type of input material and treatment process,

the products consist of gases, vapors, liquids and oils.


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Biofuel Classification3- Thermochemical Processes:

These involve sophisticated chemical control and industrial scale of

manufacture; methanol production is such a process, e.g. for liquid fuel.

B: Biochemical:

1- Aerobic Digestion:

In the presence of air, biomass generates heat with the emission of CO2, but

not methane.

This process is of great significance for the biological carbon cycle, e.g.

decay of forest litter, but is not used significantly for commercial bioenergy.

2- Anaerobic Digestion:

In the absence of free oxygen, certain micro-organisms can obtain their ownenergy supply by reacting with carbon compounds of medium reduction

level to produce both CO2 and fully reduced carbon as CH4.

Other names of this processes are fermentation and digestion.

The product of digestion is biogas.


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Biofuel Classification3- Alcoholic Fermentation:

Ethanol is a volatile liquid fuel and may be used in place of refined

petroleum.

Ethanol can be produced with fermentation process.

4- Biophotolysis:

Photolysis is the splitting of water into hydrogen and oxygen by the action

of light.

Commercial exploitation of these effects has not yet occurred.

C: Agrochemical:

1- Fuel Extraction:

Occasionally, liquid or solid fuels may be obtained directly from living or

freshly cut plants.

Production of natural rubber latex is a well known similar process.


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Biofuel Classification2- Biodiesel and Esterification:

Rudolph Diesel designed his original 1892 engine to run on variety of fuels,

including natural plant oils.

High viscosity and combustion deposits as compared to petroleum-baed

diesel fuel are the difficulties.

To overcome these difficulties, vegetable oil is converted to the

corresponding ester.


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Biofuels Production Processes

Biofuel Production Processes


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Energy Farming:

Energy Farming means the production of fuels or energy as a main orsubsidiary product of agriculture (fields), silviculture (forests),aquaculture (fresh and sea water), and also of industrial or social

activities that produce organic waste residues, e.g. food processing,urban refuse.

It is found best to integrate the energy and biofuel production withcrop or other biomass material products.

Example:Energy farming in the sugarcane industry; the process depends uponthe combustion of the crushed cane residue (bagasse) for powering themill and factory operations. With efficient machinery there should beexcess energy for the production and sale of by-products, e.g. molasses,

chemicals, animal feed, ethanol, fibre board and electricity. Commonlythe ethanol becomes a component of transport fuel and the excesselectricity is sold to the local grid.


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Sugar Cane Agro-Industry

Sugar cane argo-industry; process flow diagram


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Advantages & Disadvantages of Energy Farming

Advantages Large potential supply of fuels and energy intensive products

Variety of crops

Variety of uses (including transport fuel and electricity generation)

Efficient use of by-products, residues and wastes

Link with established agriculture and forestry encourages integrated farming

practice Establishes agro-industry that may include full range of technical processes, with

the need for skilled and trained personnel

Environmental improvement by utilizing wastes

Fully integrated and efficient systems need have little water and air pollution (e.g.

low sulfur content) Encourages rural development

Diversifies the economy with respect to product, location and employee skill

Greatest potential is in tropical countries.


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Disadvantages:

May lead to soil infertility and erosion

Variety of crops may compete with food production

Bulky biomass material handicaps transport to the processing factory

Pollutant emissions from poorly controlled processes

Poorly designed and incompletely integrated systems may pollute water

and air

Large-scale agro-industry may be socially disruptive

Foreign capital may not be in sympathy with local or national benefit

A major disadvantage is that energy crops may substitute for necessary food

production. For example, the grain farms of the United States grow about 10%of the world’s cereal crops, and export about one-third of this. A sudden

change to producing biofuels, e.g. ethanol from corn, on a large scale would

therefore decrease world food supplies before alternatives could be

established.


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Possible Remedies:

The obvious strategy to avoid these drawbacks:(a) To always grow plants that can supply both human foods (e.g. grain) and

energy (e.g. straw)

(b) To decrease dramatically the feeding of animals from crops

(c) To use all resources more efficiently.

l h li i


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Alcoholic Fermentation

Alcohol Production Methods:

Ethanol C2H5OH is produced using following sources:1- Directly from sugarcane: Commercial sucrose is removed from the cane

juices, and the remaining molasses used for the alcohol production process.

C12H22O11 + H2O 4C2H5OH + 4CO2

2- From Sugar Beet: Sugar beet is a mid latitude root crop for obtaining majorsupplies of sugar.

3- From Starch Crops: Starch crops, e.g. grain and cassava can be hydrolyzed to

sugars. Starch is composed of chains of glucose units, made by plants and

providing a major energy source for animals.

4- From Cellulose: cellulose comprises about 40% of all biomass dry matter.

Apart from its combustion as part of wood, cellulose is potentially a primary

material for ethanol production on a large scale by hydrolysis process.

yeast

Al h li F i


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Alcoholic Fermentation

Ethanol production

Bi


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BiogasBiogas is a mixture of methane (CH4) and carbon dioxide (CO2) evolved from

digesters, including waste and sewage pits; to utilize this gas, the digesters are

constructed and controlled to favor methane production and extraction.

Energy Availability:

The energy available from the combustion of biogas is between 60 and 90% of

the dry matter heat of combustion of the input material.

Processes Involved:

Decaying biomass and animal wastes are broken down naturally to elementary

nutrients and soil humus by decomposer organisms, fungi and bacteria. The

processes are favored by wet, warm and dark conditions. The final stages are

accomplished by many different species of bacteria classified as either aerobic

or anaerobic.In closed conditions, with no oxygen available from the environment,

anaerobic bacteria exist by breaking down carbohydrate material. The carbon

may be ultimately divided between fully oxidised CO2 and fully reduced CH4.

Nutrients such as soluble nitrogen compounds remain available in solution, so

providing excellent fertilizer and humus.


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Biogas Systems• Simple oil drum gas digester

Digesters at higher temperatures proceeds more rapidlythan at lower temperatures, with gas yield rates doubling

at about every 5oC of increase.


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Biogas Systems

• Indian gobar gas digester


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Biogas Systems

• Chinese Dom digester


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THANK YOU

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Biomass & Biofuels (Final) (1)