necneee.weebly.com€¦  · Web viewBIOGAS & GEOTHERMAL POWER GENERATING SYSTEMS. Bioconversion: The term Bioconversion, also known as biotransformation refers to the use of live

UNIT IVBIOGAS & GEOTHERMAL POWER GENERATING SYSTEMS

Bioconversion:

The term Bioconversion, also known as biotransformation refers to the use of live organisms often microorganisms to carry out a chemical reaction that is more costly or not feasible non biologically. These organisms convert a substance to a chemically modified form. An example is the industrial production of cortisone. One step is the bioconversion of Progesterone to 11-alpha-Hydroxyprogesterone by Rhizopus nigricans.

Another example of this is the conversion of organic materials, such as plant or animal waste, into usable products or energy sources by biological processes or agents, such as certain microorganisms, some Detritivores or enzymes.

The conversion of organic materials, such as plant or animal waste, into usable products or energy sources by biological processes or agents, such as certain microorganisms.

The Bioconversion Science and Technology group performs multidisciplinary R&D for the Department of Energy's (DOE) relevant applications of bioprocessing, especially with biomass. Bioprocessing combines the disciplines of chemical engineering, microbiology and biochemistry. The Group 's primary role is investigation of the use of microorganism, microbial consortia and microbial enzymes in bioenergy research.

New cellulosic ethanol conversion processes have enabled the variety and volume of feedstock that can be bioconverted to expand rapidly. Feedstock now includes materials derived from plant or animal waste such as paper, auto-fluff, tires, fabric, construction materials, municipal solid waste (MSW), sludge, sewage, etc.

Three different processes for bioconversion

1 - Enzymatic hydrolysis - a single source of feedstock, switchgrass for example, is mixed with strong enzymes which convert a portion of cellulosic material into sugars which can then be fermented into ethanol. Genencor and Novozymes are two companies that have received United States government Department of Energy funding for research into reducing the cost of cellulase, a key enzyme in the production cellulosic ethanol by this process.

2 - Synthesis gas fermentation - a blend of feedstock, not exceeding 30% water, is gasified in a closed environment into a syngas containing mostly carbon monoxide and hydrogen. The cooled syngas is then converted into usable products through exposure to bacteria or other catalysts. BRI Energy, LLC is a company whose pilot plant in Fayetteville, Arkansas is currently using synthesis gas fermentation to convert a variety of waste into ethanol. After gasification, anaerobic bacteria (Clostridium ljungdahlii) are used to convert the syngas (CO, CO2, and H2) into ethanol. The heat generated by gasification is also used to co-generate excess electricity.

3 - C.O.R.S. and Grub Composting are sustainable technologies that employ organisms that feed on organic matter to reduce and convert organic waste in to high quality feedstuff and oil rich material for the biodiesel industry.[3] Organizations pioneering this novel approach to waste management are EAWAG, ESR International, Prota Culture and BIOCONVERSION

that created the e-CORS system to meet large scale organic waste management needs and environmental sustainability in both urban and livestock farming reality. This type of engineered system introduces a substantial innovation represented by the automatic modulation of the treatment, able to adapt conditions of the system to the biology of the scavenger used, improving their performances and the power of this technology.

Biogas

Biogas typically refers to a mixture of different gases produced by the breakdown of organic matter in the absence of oxygen. Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste or food waste.

It is a renewable energy source and in many cases exerts a very small carbon footprint.

Biogas can be produced by anaerobic digestion with anaerobic bacteria, which digest material inside a closed system, or fermentation of biodegradable materials.

Biogas is primarily methane (CH4) and carbon dioxide (CO2) and may have small amounts of hydrogen sulphide (H2S), moisture and siloxanes. The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used for any heating purpose, such as cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.

Biogas can be compressed, the same way natural gas is compressed to CNG, and used to power motor vehicles. In the UK, for example, biogas is estimated to have the potential to replace around 17% of vehicle fuel. It qualifies for renewable energy subsidies in some parts of the world. Biogas can be cleaned and upgraded to natural gas standards, when it becomes bio methane.

Biogas

Biogas is formed by the anaerobic decomposition of putrescible organic material. Biogas CHP (combined heat and power or cogeneration) is the utilisation of biogas, typically in a biogas engine, for the production of electricity and useful heat, at high efficiency.

Clarke Energy is a distributor of GE Jenbacher biogas engines which are designed for robust operation on difficult gases such as biologically-derived ones.

What is biogas?

Biogas is a gas that is formed by anaerobic microorganisms. These microbes feed off carbohydrates and fats, producing methane and carbon dioxides as metabolic waste products. This gas can be harnessed by man as a source of sustainable energy.

Biogas is considered to be a renewable fuel as it originates from organic material that has been created from atmospheric carbon by plants grown within recent growing seasons.

Benefits of anaerobic digestion and biogas

Production of renewable power through combined heat and power cogeneration Disposal of problematic wastes Diversion of waste from landfill Production of a low-carbon fertiliser Avoidance of landfill gas escape and reduction in carbon emissions

Biogas formation

Biogas creation is also called biomethanation. Biologically derived gases are produced as metabolic products of two groups of microorganisms called bacteria and Archaea. These microorganisms feed off carbohydrates, fats

and proteins, then through a complex series of reactions including hydrolysis, acetogenesis, acidogenesis and methanogenesis produce biogas consisting mainly of carbon dioxide and methane.

Biogas composition

Biogas consists primarily of methane (the source of energy within the fuel) and carbon dioxide. It also may contain small amounts of nitrogen or hydrogen. Contaminants in the biogas can include sulphur or siloxanes, but this will depend upon the digester feedstock.

The relative percentages of methane and carbon dioxide in the biogas are influenced by a number of factors including:

The ratio of carbohydrates, proteins and fats in the feedstock The dilution factor in the digester (carbon dioxide can be absorbed by water)

Anaerobic digestion

Anaerobic digestion is the man-made process of harnessing the anaerobic fermentation of wastes and other biodegradable materials. Anaerobic microbes can be harnessed to treat problematic wastes, produce a fertiliser that can be used to replace high carbon emission chemical fertilisers. It also is the process that results in the production of biogas, which can be used to provide renewable power using biogas cogeneration systems.

Anaerobic digestion can occur at mesophilic (35-45˚C) or thermophilic temperatures (50-60˚C). Both types of digestion typically require supplementary sources of heat to reach their optimal temperature. This heat is most commonly provided by a biogas CHP unit, operating on biogas and producing both electricity and heat for the process.

Often, biogas plants that treat wastes originating from animal material, will also require the material to be treated at high temperature to eliminate any disease causing bacteria in the slurry. These systems pasteurise the slurry, typically at 90C for one hour, to destroy pathogens, and result in the provision of clean, high quality fertiliser.

Biogas engines

GE Jenbacher biogas engines are specifically designed to operate on different types of biogas. These gas engines are linked to an alternator in order to produce electricity at high efficiency. High efficiency electricity production enables the end user to maximise the electrical output from the biogas and hence optimise the economic performance of the anaerobic digestion plant.

Biogas engine electrical output

 There are 4 ‘types’ of GE Jenbacher gas engines with different levels of power output and electrical/thermal efficiency characteristics.

249-330kWe – Type 2 499-1,065kWe – Type 3 844-1189kWe – Type 4 1,600-3,000kWe – Type 6

Biogas CHP

Biologically-derived gases can be utilised in biogas engines to generate renewable power via cogeneration in the form of electricity and heat. The electricity can be used to power the surrounding equipment or exported to the national grid.

Low grade heat from the cooling circuits of the gas engine, typically available as hot water on a 70/90°C flow/return basis. For anaerobic digestion plants that are using a CHP engine, there are two key types of heat:

High grade heat as engine exhaust gas (typically ~450°C)

The low grade heat is typically used to heat the digester tanks to the optimum temperature for the biological system. Mesophilic anaerobic digesters typically operate at 35-40°C. Thermophilic anaerobic digesters typically operate at a higher temperature between 49-60°C and hence have a higher heating requirement.

You can find out more about biogas CHP efficiency here.

High temperature exhaust gas heat can either be used directly into a drier, waste heat boiler or organic rankine cycle unit. Alternatively it can be converted into hot water using a shell and tube exhaust gas heat exchanger to supplement the heat from the engine cooling systems.

Waste heat boilers produce steam typically at 8-15bar. Driers may be useful to reduce the moisture content of the digestate to assist in reducing transportation costs. Organic rankine cycle turbines are able to convert surplus waste heat into additional electrical output.

In the event that the local legislation requires for the destruction of pathogens in the digestate (such as the European Animal By-Products Regulations) there may be the requirement to heat treat the waste via pasteurisation or sterilisation. Here, surplus heat from the gas engine can be used in the pasteurisation unit.

The heat from the CHP engine can also be used to drive an absorption chiller to give a source of cooling, converting the system to a tri generation plant.

Minimum Flow Rate

The minimum gas flow rate to operate the smallest GE Jenbacher biogas engine at full load (J208 @249kWe)  is 127Nm3/hour at 50% methane.

Sectors

We have specific pages related to:

Agriculture Organic wastes Distilleries Mechanical biological treatment and anaerobic digestion of mixed wastes (MBT-AD) Landfill gas Sewage gas

Potential Contaminants

Biologically derived gases may include contaminants or impurities including water, hydrogen sulphide and siloxanes. Please discuss your gas quality expectations with your local Clarke

Energy office. GE provides specific guidelines on fuel gas quality in technical instruction documents.

Water

Biological gases contains water vapour due to the nature of the feedstock that produces the gas. The quantity of water is linked to the  temperature of the biological gas and the method of production. Above certain limits the moisture content of the biogas becomes a combustion challenge for the gas engines.

Water can be removed from the gas by using:

Gas dehumidification (drying) units. Ground tube dewatering

Hydrogen Sulphide

Hydrogen sulphide (H2S)  is derived as a by-product of the anaerobic digestion process of high sulphur feedstocks such as amino-acids and proteins. When burnt in a gas engine hydrogen sulphide can condense with water to form sulphuric acid. Sulphuric acid is corrosive to elements of gas engines and so must be limited to prevent adverse effects on the CHP engine.

Processes for the removal of hydrogen sulphide include

Activated carbon filters Low level oxygen dosing into digester head space (typically <1%) External biological scrubber towers Ferric chloride dosing into the digester

Siloxanes

In some cases biogas contains siloxanes. Siloxanes are formed from the anaerobic decomposition of materials commonly found in soaps and detergents. During the combustion process of the gas  that contains siloxanes, silicon is released and can combine with free oxygen or various other elements in the combustion gas. Deposits are formed containing mostly silica (SiO2) or silicates (SixOy). These white mineral deposits accumulate and must be removed by chemical or mechanical means.

Siloxanes are often problematic in landfill gas and sewage gas plants due to contamination that is often found associated with the organic wastes.

In source-segregated biodegradable waste and agricultural biogas plants, it is much less common to find problems associated with siloxanes.

Production

Biogas is produced as landfill gas (LFG), which is produced by the breakdown of biodegradable waste inside a landfill due to chemical reactions and microbes, or as digested gas, produced inside an anaerobic digester. A biogas plant is the name often given to an anaerobic digester that treats farm wastes or energy crops. It can be produced using anaerobic digesters (air-tight tanks with different configurations). These plants can be fed with energy crops such as maize silage or biodegradable wastes including sewage sludge and food waste. During the process, the microorganisms transform biomass waste into biogas (mainly methane and carbon dioxide) and digestate. The biogas is a renewable energy that can be used for heating, electricity, and many other operations that use a reciprocating internal combustion engine, such as GE Jenbacher or Caterpillar gas engines.[4] Other internal combustion engines such as gas turbines are suitable for the conversion of biogas into both electricity and heat. The digestate is the remaining organic matter that was not transformed into biogas. It can be used as an agricultural fertiliser.

There are two key processes: mesophilic and thermophilic digestion which is dependent on temperature. In experimental work at University of Alaska Fairbanks, a 1000-litre digester using psychrophiles harvested from "mud from a frozen lake in Alaska" has produced 200–300 liters of methane per day, about 20%–30% of the output from digesters in warmer climates.

Composition

The composition of biogas varies depending upon the origin of the anaerobic digestion process. Landfill gas typically has methane concentrations around 50%. Advanced waste treatment technologies can produce biogas with 55%–75% methane, which for reactors with free liquids can be increased to 80%-90% methane using in-situ gas purification techniques. As produced, biogas contains water vapor. The fractional volume of water vapor is a function

of biogas temperature; correction of measured gas volume for water vapor content and thermal expansion is easily done via simple mathematics which yields the standardized volume of dry biogas.

Typical composition of biogasCompound Formula  %

Methane CH4 50–75Carbon dioxide CO2 25–50

Nitrogen N2 0–10Hydrogen H2 0–1

Hydrogen sulphide H2S 0–3Oxygen O2 0–0

In some cases, biogas contains siloxanes. They are formed from the anaerobic decomposition of materials commonly found in soaps and detergents. During combustion of biogas containing siloxanes, silicon is released and can combine with free oxygen or other elements in the combustion gas. Deposits are formed containing mostly silica (SiO2) or silicates (SixOy) and can contain calcium, sulfur, zinc, phosphorus. Such white mineral deposits accumulate to a surface thickness of several millimeters and must be removed by chemical or mechanical means.

Practical and cost-effective technologies to remove siloxanes and other biogas contaminants are available.(broken link)

For 1000 kg (wet weight) of input to a typical biodigester, total solids may be 30% of the wet weight while volatile suspended solids may be 90% of the total solids. Protein would be 20% of the volatile solids, carbohydrates would be 70% of the volatile solids, and finally fats would be 10% of the volatile solids.

Benefits

In North America, use of biogas would generate enough electricity to meet up to 3% of the continent's electricity expenditure. In addition, biogas could potentially help reduce global climate change. High levels of methane are produced when manure is stored under anaerobic conditions. During storage and when manure has been applied to the land, nitrous oxide is also produced as a byproduct of the denitrification process. Nitrous oxide (N2O) is 320 times more aggressive than carbon dioxide and methane 21 times more than carbon dioxide.

By converting cow manure into methane biogas via anaerobic digestion, the millions of cattle in the United States would be able to produce 100 billion kilowatt hours of electricity, enough to power millions of homes across the United States. In fact, one cow can produce enough manure in one day to generate 3 kilowatt hours of electricity; only 2.4 kilowatt hours of electricity are needed to power a single 100-watt light bulb for one day. Furthermore, by converting cattle manure into methane biogas instead of letting it decompose, global warming gases could be reduced by 99 million metric tons or 4%.

Applications

Biogas can be used for electricity production on sewage works, in a CHP gas engine, where the waste heat from the engine is conveniently used for heating the digester; cooking; space heating; water heating; and process heating. If compressed, it can replace compressed natural gas for use in vehicles, where it can fuel an internal combustion engine or fuel cells and is a much more effective displacer of carbon dioxide than the normal use in on-site CHP plants.

Biogas Problems

The dangers of biogas are mostly similar to those of natural gas, but with an additional risk from the toxicity of its hydrogen sulfide fraction. Biogas can be explosive when mixed one part biogas to 8-20 parts air. When the tank is open for cleaning or repair work is being done open flames, sparks, and smoking should be avoided. If light is needed a flashlight or sunlight reflected off of a mirror should be used. Biogas leaks smell like rotten eggs (hydrogen sulfide). If someone enters a biogas digester they should always have someone with them in case they stop breathing due to low oxygen intake.

It is important that a biogas system never have negative pressure as this could cause an explosion or kill the digesting bacteria. Negative gas pressure can occur if too much gas is removed or leaked. Because of this biogas shouldn't be used at pressures below one column inch of water, measured by a pressure gauge.

Frequent smell checks must be performed on a biogas system. If biogas is smelled anywhere windows and doors should be opened immediately. If there is a fire the gas should be shut off at the gate valve of the biogas system.

Advantages of Biogas

1. Renewable Source of Energy: To begin with, biogas is considered to be a renewable source of energy. Since it often produced from materials that form sewage and waste products, the only time it will be depleted is when we stop producing any waste.

2. Non-Polluting: It is also considered to be non-polluting in nature. The production of biogas does not require oxygen, which means that resources are conserved by not using any further fuel.

3. Reduces Landfills: It also uses up waste material found in landfills, dump sites and even farms across the country, allowing for decreased soil and water pollution.

4. Cheaper Technology: Applications for biogas are increasing as the technology to utilize it gets better. It can be used to produce electricity and for the purpose of heating as well. Compressed Natural Gas (CNG) is biogas that has been compressed and can be used as a fuel for vehicles. Production can be carried out through many small plants or one large plant.

5. Large number of Jobs: Either way, work opportunities are created for thousands of people in these plants. These jobs are a blessing in rural areas, which are the targeted grounds for the use of biogas. In fact, biogas can easily be decentralized, making it easier to access by those living in remote areas or facing frequent power outages.

6. Little Capital Investment: Biogas are easy to set up and require little capital investment on a small scale basis. In fact, many farms can become self sufficient by utilizing biogas

plants and the waste material produced by their livestock each day. A single cow can provide enough waste material within a day to power a light bulb the entire day.

7. Reduces Greenhouse Effect: It also reduces the greenhouse effect by utilizing the gases being produced in landfills as forms of energy. This is a major reason why the use of biogas has started catching on. It recycles most forms of biodegradable waste and works on simple forms of technology.

Disadvantages of Biogas

1. Little Technology Advancements: First of all, the current systems in place used to create biogas are not as efficient as they get. Little new technology has been introduced for streamlining the process and making it more cost effective. As a result, large scale industrial production of biogas is still not on the energy map. Although it could solve the energy issues being faced by countries all over the world, very few investors are willing to put in the startup capital. It is also not the best idea to construct one biogas plant per house, which means that a central system will have to be put into place.

2. Contain Impurities: Biogas contains a number of impurities even after refining processes have been put into place. When compressed for use as fuel, these can become corrosive to the metal parts of engines.

3. Not Attractive on Large Scale: The process of using biogas on a large scale is not economically viable and it is very difficult to enhance the efficiency of biogas systems.

4. Unstable: It is also somewhat unstable, making it prone to explosions if the methane comes in contact with oxygen and become flammable in nature.

Even with all of the disadvantages present, countries have started to apply the uses of biogas in everyday life. Public transportation has been renewed and made efficient with the help of CNG. Remote locations that are off the electric grid receive a steady supply of power from these plants. The future use of biogas is bright, even with the problems it faces.

Anaerobic digestion definition

Anaerobic digestion is a biological process making it possible to degrade organic matter by producing biogas which is a renewable energy source and a sludge used as fertilizer.

The production of biogas is carried out in the environment in a natural way (e.g. gas of marshes - vegetable and animal matter decomposition where the formation of bubbles at water surface can be observed).

In the absence of oxygen (anaerobic digestion), the organic matter is degraded partially by the combined action of several types of micro-organisms. A succession of biological reactions (see diagram) led to the formation of biogas and sludge.

The bacteria which carry out these reactions exist in natural state in the liquid manure and the anaerobic ecosystems; it is not necessary to add more, they develop naturally in a medium without oxygen.

Anaerobic Digestion Diagram

Hydrolysis  

The organic macromolecules break up into simpler elements - solid waste thus is liquefied and hydrolyzed in small soluble molecules (e.g. the cellulose is transformed into soluble sugars such as glucose or cellobiose.

Acidogenesis

This process transforms these simple molecules into acids of weak molecular weight such as lactic acid and volatile fatty-acids from 2 to 5 carbon atoms. In parallel are produced low-weight molecular alcohol, such as bicarbonate ethanol and molecular hydrogen.

Acetogenesis 

The products resulting from fermentation require an additional transformation before being able to produce methane. It is here that intervene the acetogenes reducing bacteria and the sulfato-reducing bacteria, producing hydrogen sulphide (H2S)

Methanogenesis

The ultimate phase during which two types of methanogenes bacteria take over: the first ones (acetogenes) reduce methane acetate, CH4 and bicarbonate. The second ones, reduce methane bicarbonate.

Advantages of anaerobic digestion

Anaerobic digestion involves a considerable reduction in the organic load, thanks of the biological reactions, and the polluting load of the digested sludge. It is thus, a complete depollution. A correctly controlled anaerobic digestion leads to very high rates of purification.

It also has other advantages:

Economic advantages:

Additional income Autonomy in heat in a context of increase in the cost of fossil energies Diversification of outlets for crops Reduction of manure purchase thanks to valorisation of digested sludge

Agronomic advantages

Transformation of the liquid manure and the manure into a fertilizer, more easily assimilated by the plants, with reduction in the odours and the disease-causing agents

Organic waste processing for competitive prices Insect ellimination at the storage pit Odours supression

Environmental advantages

Biogas resulting by anaerobic digestion is a source of renewable energy because it replaces fossil energy

Reduction of pollution due to nitrogen stripping (please refer to the “Sludge” heading) Sustainable management of organic waste

Energy from Biomass

There are two distinct processes for obtaining energy from Bio mass, They are

1.Direct combustion

2.Indirect combustion

Methods of Biomass to Energy Conversion

Direct Combustion

Pyrolysis: thermal decomposition into gas or liquid

Involves high temperatures (500-900°C), low oxygen

Biochemical processes:

Anaerobic digestion by methanogens

Controlled fermentation produces alcohols:

Ethanol (grain alcohol)

Methanol (wood alcohol)

Anaerobic Digester

Converts animal or plant waste into methane

Typical wastes:

Manure (feed lots,pig farms, poultry)

Olive oil mill waste

Potato processing waste

Big deal: Agricultural Science Depts

Why Biomass? Lower greenhouse emissions, cleaner fuel, less dependency on foreign oil

Biofuels – ethanol, biobutanol, biodiesel

Biopower – methane, syngas to produce electricity

Bioproducts – converting byproducts or the different building blocks

Biorefineries – similar to petroleum refineries – just feedstock goes in, end product comes out

Fossil fuels are mainly made up of hydrocarbons – which are hydrogens and carbon while biomass is mainly carbohydrates – which are hydrogen, carbon, and oxygen which makes the conversion slightly different.

Biochemical Conversion

Feedstock

Supply

• Residues

• Dedicated Crops

Harvesting and

Handling Collection Processing StorageTransportation

ConversionThermochemicalCombustionGasificationPyrolysisOtherBiochemicalAnaerobic (fermentation) Anaerobic Digestion Alcohol FermentationAerobicCompostingActivated (oxygenated) waste treatmentDirect HydrogenPhysicochemical Oil extraction Hydrocarbon extraction

UtilizationBiopowerProcess and Space HeatingPower generationBiofuelsEthanolBiodieselMethanolPyrolisis liquidsBiogas (methane + CO2) including digester and landfill gas Synthesis gases (CO + H2)(for further refinement to liquid/gaseous fuels) HydrogenCharcoal Biomass solids OthersBioproducts Citric and other acids Composite materials FertilizerFibers Lubricants OthersPesticides Structural materials Surfactants

Plant matter – hemicellulose, cellulose, lignin

Pretreatment

Hydrolysis

Sugar Fermentation

Aerobic Digestion

Aerobic digestion is a process in which bacteria use oxygen to convert organic material into carbon dioxide. Products include nutrient-rich fertilizers and composts.

Anaerobic Digestion

Anaerobic Digestion is the decomposition of biomass by bacteria in the absence of oxygen. Biogas, or methane, is the primary product produced.

Fermentation

Fermentation is a biological process in which enzymes produced by microorganisms cause chemical reactions to occur. Products include ethanol, commercial levels of therapeutic and research enzymes, antibiotics, and specialty chemicals.

Thermochemical Conversion

Gasification, Pyrolysis, Direct Hydrothermal Liquefaction

Carbon monoxide and Syngas (Hydrogen)

Gasification

Gasification is a thermochemical process in which biomass at high heat is turned directly from a solid into a gaseous fuel called syngas (a mixture of carbon monoxide, hydrogen and some methane).

Pyrolysis

Pyrolysis is the thermal degradation of organic components in biomass in the absence of oxygen. Major products are oil, gas, and char.

The limitations for using biomass energy

• Either high technological level or catalytic combustion is needed.

• Large area is needed to grow plants for biomass energy use.

• When producing biomass fuel, large amount of waste will also produced.

The environmental problems are caused by biomass energy

• It will intensify air pollution.

• It may cause saltilization and decrease to total size of the arable land.

• The source of biomass can use fertilize soil, e.g., crop residues and animal manure.

• Cutting too many woods is a kind of deforestation can cause, soil erosion and natural disasters