BIOMASS ENERGY UNIT-III

BIOMASS ENERGY UNIT-III
Wednesday, December 27, 2017

BIOMASS ENERGY Energy from Biomass Biomass as Renewable Energy Source
Types of Biomass Fuels Solid, Liquid, Gas Biomass Conversion Techniques Photosynthesis Wet Process Dry Process Biogas Generation Factor Affecting Bio-digestion Classification of Biogas Plant Continuous Batch Fixed Dome Types 8. Advantages & Disadvantages. Wednesday, December 27, 2017Wednesday, December 27, 2017

BIOMASS AS A renewable energy source
Biomass is a renewable energy source that is derived from living or recently living organisms. Biomass includes biological material, not organic material like coal. Energy derived from biomass is mostly used to generate electricity or to produce heat. Thermal energy is extracted by means of combustion, torrefaction, pyrolysis, and gasification. Biomass can be chemically and biochemically treated to convert it to a energy-rich fuel. Biomass today serves many markets that were developed with fossil fuels and modestly reduces their use. Uses - Industrial process heat and steam, Electrical power generation, Transportation fuels (ethanol and biodiesel) and other products. Wednesday, December 27, 2017Wednesday, December 27, 2017

Biomass energy Biomass energy (or) bioenergy, is the energy stored in non-fossil organic materials such as ….. wood straw vegetable oils wastes from the forest, Agricultural wastes industrial sectors wastes. Wednesday, December 27, 2017Wednesday, December 27, 2017

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Composition of Urban Garbage
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Recycling advantages If you drink 2 cans of soft drink per day in aluminum cans and cans are not recycled ,you waste more energy than is used daily by one human in the lesser developed countries Recycling one aluminum can saves enough energy to run a TV for 3 hours Recycling of all paper used in the Sunday edition of the New York Times would save 75,000 trees per year Wednesday, December 27, 2017Wednesday, December 27, 2017

Bio Energy Bioenergy consists of biomass (biological mass) used in the production of energy; CO2 + H2O >--solar energy and chlorophyll  CH2O + O2, or carbohydrate and oxygen While biomass combustion releases CO2 into the atmosphere, new plants require CO2 to grow, balancing the process for no net CO2 over a long time Nonrenewable energies come from combustion of coal, oil, and natural gas. Their creation took millions of years, and we are using it faster than it was produced and faster than it is being created. Renewable energies come from the sun. Collection is from natural occurrences. While the energy is free, it costs money to collect it. Nuclear and geothermal energies aren’t renewable but are treated that way since the quantity is so large. Wednesday, December 27, 2017Wednesday, December 27, 2017

Energy in Biomass Only a small amount energy in sunlight converted into biomass by plants. Conversion efficiency varies: Sugar cane: 2% Corn: 1% Typical forest: 0.8% Most food plants: <0.8% Maximum theoretical efficiency: 10% Wednesday, December 27, 2017Wednesday, December 27, 2017

Bio Energy(From Biomass)
Direct firing, co firing, and gasification are forms of bio power Ethanol can be made from grain or soybeans, and methanol can be made from cellulose (wood) Liquid fuels are essential for transportation vehicles due to high energy density in the tank! May be intentionally grown (coppicing) such as poplar trees or might use waste byproducts Biomass satisfied 4% of energy demand in 1990 Biomass can serve as a bridge from fossil fuels, although it is an inefficient producer of energy (~1%) Wednesday, December 27, 2017Wednesday, December 27, 2017

Energy Extraction and Preparation
Dry biomass may have some residual moisture but only requires physical preparation like chipping to fire it Some research is being done to see if long trees can be directly fired on a metal conveyor belt Wet biomass can absorb more heat energy from a furnace than it can supply; the biomass must be externally dried to burn Small biomass pellets are made from wood scraps and sawdust There are pellet-burning stoves with a screw conveyor feed Wednesday, December 27, 2017Wednesday, December 27, 2017

Dry Biomass Dry biomass consists of tree chips, paper, various other plant matter such as corn, soybean, sorghum, sunflower, oats, barley, wheat and hay When first cut, the sap may absorb energy, and the mass should dry Spread on fields in the sun Placed in oven heated by what would otherwise be waste heat Using solar thermal energy air-heaters Wednesday, December 27, 2017Wednesday, December 27, 2017

Municipal Solid Wastes (MSW)
Municipal waste streams may have anything in it that people want to throw away -- it’s a mix Air blast and magnetic separation can select different streams to go in various piles Permanent magnets first extract the steel and iron Alternating current electromagnets use the eddy current effect to remove nonferrous metals (Al, Cu) Light paper and plastic will stratify in an air column to remove them from heavier substances (metal and bottles) Hand sorting can pick out some of what’s left Without this process, pollutants aren’t removed Wednesday, December 27, 2017Wednesday, December 27, 2017

Industrial Waste Streams (IWS)
Industrial wastes differ from municipal wastes in that they are often separated or categorized as outputs from specific processes It’s relatively easy to have “pure” waste streams all of one material, like wood strips, pallets, trim scrap Paper products are a possibility, but dioxin content can cause air pollution Any wet waste stream will require drying before burning Could require more energy to dry than can be extracted from it Wednesday, December 27, 2017Wednesday, December 27, 2017

Wet Biomass Wet biomass tends to be in water or to stay moist
Examples are water plants, animal wastes, and biodiesel oil Treated with hydrogasification at high pressure and low temperatures to produce a gas or biofuel oil Wednesday, December 27, 2017Wednesday, December 27, 2017

Animal Wastes Average manure production for fully bred cows and pigs is 40 kg and 2.3 kg wet weight per day (a thing I never wanted to know) Manure lagoons at Consolidated Animal Feeding Operations (CAFO) pose a stored pollution problem Lagoon dam breaches have poisoned nearby streams and killed thousands of fish in NC Anaerobic digestion allows methane gas recovery Wednesday, December 27, 2017Wednesday, December 27, 2017

Municipal Sewer Plants
The same processes for farm animal wastes can be used at city sewer plants 40 billion Btus of methane per 100,000 people per year Florida methane could yield 20 trillion Btus per year Cost would be $6 to $8 per million Btu At present, filtered sewage sludge is often bulk dumped (sprayed) on agricultural pastures The methane gas from a sewage lagoon can be recovered by a bioenergy process, reducing the sludge before disposal A cruise ship is like a small city -- where does the sewage go? Wednesday, December 27, 2017Wednesday, December 27, 2017

BIOFUEL Plants use photosynthesis to grow and produce biomass.
Also known as biomatter, biomass can be used directly as fuel or to produce liquid biofuel. Agriculturally produced biomass fuels, such as biodiesel, ethanol and bagasse (often a by-product of sugar cane cultivation) can be burned in internal combustion engines or boilers. Typically biofuel is burned to release its stored chemical energy. Research into more efficient methods of converting biofuels and other fuels into electricity utilizing fuel cells is an area of very active work. Wednesday, December 27, 2017Wednesday, December 27, 2017

LIQUID BIOFUEL Liquid biofuel is usually either a bioalcohol such as
ethanol fuel or a bio-oil such as biodiesel and straight vegetable oil. Biodiesel can be used in modern diesel vehicles with little or no modification to the engine and can be made from waste and virgin vegetable and animal oil and fats (lipids). Pure vegetable oils can be used in modified diesel engines. In fact the Diesel engine was originally designed to run on vegetable oil rather than fossil fuel. A major benefit of biodiesel is lower emissions. The use of biodiesel reduces emission of carbon monoxide and other hydrocarbons by 20 to 40%. Wednesday, December 27, 2017Wednesday, December 27, 2017

Biodiesel Fuel Biodiesel is liquid fuel oil that can be burned in diesel engines Made by transforming animal fat or vegetable oil with alcohol . Fuel is made from rapeseed (canola) oil or soybean oil or recycled restaurant grease. Directly substituted for diesel either as neat fuel or as an oxygenate additive Wednesday, December 27, 2017Wednesday, December 27, 2017

Bio-refinery A facility that integrates biomass conversion processes and equipment to produce fuels, power, and chemicals from biomass. Analogous to today's petroleum refineries It is based on the “Sugar Platform“ and the “Thermo chemical Platform“ Wednesday, December 27, 2017Wednesday, December 27, 2017

E-Diesel Uses additives in order to allow blending of ethanol with diesel. Ethanol blends of 7.7% to 15% and up to 5% Additives that prevent the ethanol and diesel from separating at very low temperatures or if water contamination occurs. Wednesday, December 27, 2017Wednesday, December 27, 2017

Jatropha Biodiesel from Jatropha Seeds of the Jatropha nut is
crushed and oil is extracted The oil is processed and refined to form bio-diesel. Wednesday, December 27, 2017Wednesday, December 27, 2017

Gaseous Biomass Methane is the primary biogas
Aside from sewage, there’s termites, livestock flatulence, swamps, etc. Landfill gas is primarily methane but contains CO2 and other gases from plastics, etc. 80% of odors humans find offensive are the result of nitrogen- or sulfur-bearing compounds. The nitrogen and sulfur atoms are rearranged into smaller molecules that give off odor when they're volatilized as gases into the air, as little as one part per billion - needs to be present for sensitive noses to notice. --- Doug Mason of Continuum Chemical Corporation in Houston, TX Wednesday, December 27, 2017Wednesday, December 27, 2017

Gasification A process that uses heat, pressure, and steam to convert materials directly into a gas composed primarily of carbon monoxide and hydrogen. Gasification technologies rely four key engineering factors 1. Gasification reactor atmosphere (level of oxygen or air content). 2. Reactor design. 3. Internal and external heating. 4. Operating temperature. Wednesday, December 27, 2017Wednesday, December 27, 2017

Gasification Typical raw materials - coal, petroleum-based materials, and organic materials. The feedstock is prepared and fed, in either dry or slurried form, into a sealed reactor chamber called a gasifier. The feedstock is subjected to high heat, pressure, and either an oxygen-rich or oxygen-starved environment within the gasifier. Wednesday, December 27, 2017Wednesday, December 27, 2017

Modified Waste Vegetable Fat
Designed for general use in most compression ignition engines . The production of MWVF can be achieved in a continuous flow additive process. It can be modified in various ways to make a 'greener' form of fuel Wednesday, December 27, 2017Wednesday, December 27, 2017

Methane Methane, CH4, is a likely future hydrogen gas source
The four H atoms allow more hydrogen to be produced per molecule of methane Cracking or pyrolysis changes the molecules to yield hydrogen and CO, which is also combustible The combination of methane and COx is known as biogas and can be made from acetic acid, produced from glucose by microorganisms Methane hydrates exist in cold, deep water in the ocean, but are difficult to extract without methane release Wednesday, December 27, 2017Wednesday, December 27, 2017

Energy Conversion Conversion from biomass to heat requires some extraction if the fuel stream is contaminated with polluting substances Typical processes are the following: Direct combustion Anaerobic Digestion Fermentation Pyrolysis Other less-used techniques Wednesday, December 27, 2017Wednesday, December 27, 2017

Gasifier Plant Wednesday, December 27, 2017Wednesday, December 27, 2017

Gasification Products of gasification :
* Hydrocarbon gases (also called syngas). * Hydrocarbon liquids (oils). * Char (carbon black and ash). Syngas is primarily carbon monoxide and hydrogen (more than 85 percent by volume) and smaller quantities of carbon dioxide and methane Wednesday, December 27, 2017Wednesday, December 27, 2017

Types of Gasifiers Updraft Gasifier

Types of Gasifiers Downdraft Gasifier

Types of Gasifiers Twin-fire Gasifier

Types of Gasifiers Cross draft gas producers

Gobar gas Gobar gas production is an anaerobic process Fermentation is carried out in an air tight, closed cylindrical concrete tank called a digester Wednesday, December 27, 2017Wednesday, December 27, 2017

Conversion Technologies
Biomass conversion is mainly in two subgroups – thermal related process and biological related process Many conversion types take into account the different feedstock going in due to the wide range of feedstock and the endproduct – heat, power, fuel, chemicals, and materials. Wednesday, December 27, 2017Wednesday, December 27, 2017

Biochemical Conversion
Plant matter – hemicellulose, cellulose, lignin Pretreatment Hydrolysis Sugar Fermentation In biochemical conversion – plants are the main feedstock. Plants are made up of mostly these three parts – hemicellulose, cellulose, and lignin. Cellulose is protected in a sheath of the other two so goes through a form of pretreatment using acid or catalysts. Wednesday, December 27, 2017Wednesday, December 27, 2017

Thermo chemical Conversion
Gasification, Pyrolysis, Direct Hydrothermal Liquefaction Carbon monoxide and Syngas (Hydrogen) Thermochemical conversion is just like combustion but more efficient. Taking the solid biomass – converting it into a gas or a liquid end product. Gasification uses 1/3 the amount of oxygen needed for combustion and creates carbon monoxide and synthetic gas – hydrogen. Direct hydrothermal liquefaction uses a catalyst and high temperatures to create an oily substance. Wednesday, December 27, 2017Wednesday, December 27, 2017

Thermo chemical Processes
Processes Evaluated Biochemical Processes Lower Temperature Lower Rate Anaerobic Digestion Ethanol Fermentation Hydrolysis Thermo chemical Processes Higher Temperature Higher Rate Gasification Pyrolysis Catalytic Cracking Plasma Arc Wednesday, December 27, 2017Wednesday, December 27, 2017

Conversion Techniques: 1.Direct Combustion
Refuse Derived Fuel (RDF) can be fired (burned) directly or in combination with conventional fuels Some processing, such as cleaning, chopping, etc. may be needed for handling or air pollution avoidance Fluidized grate furnaces blow air in beneath the grate, and this keeps the burning mass in seething flotation as it burns Wednesday, December 27, 2017Wednesday, December 27, 2017

Conversion Techniques: 2.Anaerobic Digestion
Bacteria produce acetic acid (found in vinegar) Methane gas 50% to 80%, $2.50/kft3 (1976) Microgy Cogeneration Systems, Inc. is building a 25 MW digestion plant Essex Junction Wastewater Treatment facility in Essex Junction, Vermont treats 1.7 million gallons of waste water per day and will produce 400 MW electricity per year to reduce plant costs. Price of electricity is estimated at $0.02 per kWh Wednesday, December 27, 2017Wednesday, December 27, 2017

Conversion Technique : 3. Fermentation
Enzymes can change cellulose into sugars, which can then be fermented into alcohol Cane sugar, C6H12O6  2C2H5OH + 2CO2 Fermentation of corn or other biomass will produce ethanol The use of food stocks in this way might be seen as a poor use of food Brewery spillage or waste and outdated soda can be filtered, cleaned, and reprocessed to produce fuel It is denatured with 15% gasoline to discourage drinking and avoid Federal liquor law taxes Fermentation of “stillage” refuse can also produce methane Wednesday, December 27, 2017Wednesday, December 27, 2017

Conversion Technique: 4. Pyrolysis
Fast pyrolysis is heating biomass without oxygen to decompose it into vapors, aerosols and char The liquid has ~one-half the heating value of fuel oil The process is tuned to produce liquid rather than charcoal Low-quality “producer” gas can be cleaned to remove CO2 and N2, then this “synthesis” gas reacted as H2 + CO  CH3OH to yield methanol Wednesday, December 27, 2017Wednesday, December 27, 2017

Conversion: Other Techniques
Hydrogasification Low temperature and high pressure produces ethane & methane plus CO2 A catalyst aids the process Hydrogenation Waste + Steam and CO forms low-sulfur oil having Btu/pound heating value Used to make peanut butter and margarine Wednesday, December 27, 2017Wednesday, December 27, 2017

Issues and Trends Environmental considerations
Biomass conversion plants are often fought by some as a source of pollutants Less polluting than a coal plant MSW may contain heavy metals and should not be burned Paper colored inks often contain heavy metals Trash production can be decreased by careful purchases, conservation, reusing, and recycling If these waste reduction practices are followed, there is less available for bioenergy Wednesday, December 27, 2017Wednesday, December 27, 2017

Environmental Benefits
Reduction of waste Extremely low emission of greenhouse gases compared to fossil fuels Ethanol is Carbon neutral and forms a part of the carbon cycle Growing variety of crops increases bio-diversity Wednesday, December 27, 2017Wednesday, December 27, 2017

Socio-Economic Benefits
Helps developing economies by promoting agrarian communities Increase in jobs Increase in trade balance (Indian perspective) due to lesser dependence on foreign resources Wednesday, December 27, 2017Wednesday, December 27, 2017

Biofuel value chain Biomass resources Supply systems Conversion
End products Oil bearing plants Agricultural crops and residues Woody biomass Industrial and municipal waste Harvesting, collection, handling, and storage Chemical (transesterification) Transportation fuels (biodiesel, bioethanol) Physical chemical (extraction) Solid fuels (wood pellets, charcoal) Biochemical (fermentation) Heat Electricity Thermochemical (gasification) High added-value chemicals (pharmaceuticals, polymers) byproducts Wednesday, December 27, 2017Wednesday, December 27, 2017

Analyses the different biomass energy technologies
choose the better technologies for the local necessity Wednesday, December 27, 2017Wednesday, December 27, 2017

i Photosynthesis Photosynthesis is the process by which chlorophyll containing organisms – green plants, algae, and some bacteria – capture energy in the form of light and convert it to chemical energy. Virtually all the energy available for life in the Earth’s biosphere, the zone in which life can exist, is made available through photosynthesis. A generalized, unbalanced, chemical equation for photosynthesis is CO2 + 2H2A+ light energy= (CH2O)+H2O+A2 Wednesday, December 27, 2017Wednesday, December 27, 2017

Photosynthesis Contd…
The formula H2A represents a compound that can be oxidised, i.e. from which electrons can be removed and CH2 is a general formula for the carbohydrates incorporated by the growing organism. In the vast majority of photosynthetic organisms – that is, algae and green plants – H2A is water (H2O) and A2 is oxygen (O2); in some photosynthetic bacteria however, H2A is hydrogen sulphide (H2S). Photosynthesis involving water is the most important Wednesday, December 27, 2017Wednesday, December 27, 2017

Photosynthesis consists of two stages: 1. A series of light-dependent reactions that are temperature-independent 2. A series of temperature-dependent reactions that are light independent. The rate of the first series, called the light reaction, can be increased by increasing light intensity (within certain limits) but not by increasing temperature. In the second series, called the dark reaction, the rate can be increased by increasing temperature (within certain limits) but not by increasing light intensity. Wednesday, December 27, 2017Wednesday, December 27, 2017

Most plants utilise the C3 photosynthesis route, the C3 determining the mass of carbon contained in the plant material. Another photosynthesis pathway is represented by C4 plants, which accumulate a significantly greater dry mass of carbon than do C3 plants, giving a biomass with increased potential for energy conversion. Examples of C3 species are poplar, willow, wheat and most other cereal crops, while the perennial grass, Miscanthus, sweet sorghum, maize and artichoke, all use the C4 route. Traditionally, the biochemical conversion of biomass into liquids, such as ethanol, has been undertaken sugar/starch feedstocks, such as cereals. The conversion of cellulose into glucose via acid/enzymatic hydrolysis and the subsequent conversion of glucose into alcohol,using fermentation, is more easily undertaken with highcellulose content biomass, than with lignin-rich biomass i.e. woody species, which is not so easily converted Wednesday, December 27, 2017Wednesday, December 27, 2017

What is a 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. Wednesday, December 27, 2017Wednesday, December 27, 2017

CONTINOUS TYPE BIOGASS PLANT
In continuous type biogas plant, the supply of the gas is continuous and the digester is fed with biomass regularly. Continuous biogas plants may be single stage, double stage or multiple stage. Digestion of waste materials in a single chamber or digester is called single stage process, in two chambers or digester is called multi stage process. In double stage process, acidogenic and methanogenic stage are physically separated into two chambers. Thus, the first stage of acid production is carried out in a separate chamber and only diluted acids are fed into the second chamber where biomethanation takes place. In single stage ,acidogenic and methanogenic stage are carried out in the same chamber without barrier. Wednesday, December 27, 2017Wednesday, December 27, 2017

These plants are economic, simple and easy to operate
These plants are economic, simple and easy to operate. these plants are generally for small and medium size biogas plants. However ,the two stage biogas plants are costlier, difficult in operation and maintenance but they produce more gas. Thes plants are preferred for larger biogas plant system. The important features of continuous type biogas plants are: (i) Gas production is continuous. (ii) Retention period is less (iii) Less problems as compared to batch type. (iv) Small digestion chambers are required Wednesday, December 27, 2017Wednesday, December 27, 2017

Fixed Dome Type Plant (11)

Advantages of Fixed-dome plants
Low construction cost, no moving parts, no rusting steel parts, hence long life (20 years or more), underground construction, affording protection from winter cold and saving space, creates employment locally. Disadvantages: Plants often not gaslight (porosity and cracks), gas pressure fluctuates substantially and is often very high, low digester temperatures. Fixed-dome plants can be recommended only where construction can be supervised by experienced biogas technicians Wednesday, December 27, 2017Wednesday, December 27, 2017

Floating-drum Plants Floating-drum plant 1. Mixing tank with inlet pipe. 2. Digester. 3. Overflow on outlet pipe. 4.Gasholder with braces for breaking up surface scum. 5. Gas outlet with main cock. 6. Gas drum guide structure. 7. Difference in level = gas pressure in cm WC. 8. Floating scum in the case of fibrous feed material. 9. Accumulation of thick sludge. 10. Accumulation of grit and stones. 11. Water jacket with oil film. Wednesday, December 27, 2017Wednesday, December 27, 2017

Floating-drum Plants contd…
Floating-drum plants (Figure) consist of a digester and a moving gasholder. The gasholder floats either direct on the fermentation slurry or in a water jacket of its own. The gas collects in the gas drum, which thereby rises. If gas is drawn off, it falls again. The gas drum is prevented from tilting by a guide frame. Advantages: Simple, easily understood operation, constant gas pressure, volume of stored gas visible directly, few mistakes in construction. Wednesday, December 27, 2017Wednesday, December 27, 2017

Disadvantages: High construction cost of floating-drum, many steel parts liable to corrosion, resulting in short life In spite of these disadvantages, floating-drum plants are always to be recommended in cases of doubt. Water-jacket plants are universally applicable and especially easy to maintain. The drum won't stick, even if the substrate has a high solids content. Up to 15 years; in tropical coastal regions about five years for the drum), regular maintenance costs Wednesday, December 27, 2017Wednesday, December 27, 2017

BATCH TYPE BIOGAS PLANT
Batch type biogas plants are appropriate where daily supplies of raw waste materials are difficult to be obtained. A batch loaded digester is filled to capacity sealed and given sufficient retention time in the digester. After completion of the digestion, the residue is emptied and filled again. Gas production is uneven because bacterial digestion starts slowly, peaks and then tapers off with growing consumption of volatile solids. This difficulty can overcome by having minimum to digester so that at least one is always in operation. This problem can also minimize by connecting batch loaded digester in series and fed at different times so that adequate biogas is available for daily use. Wednesday, December 27, 2017Wednesday, December 27, 2017

The salient features of batch-fed type biogas plants are:
(i) Gas production in batch type is uneven. (ii) Batch type plants may have several digesters for continuous supply of gas. (iii) Several digesters occupy more space. (iv) This type of plants require large volume of digester, therefore, initial cost becomes high. (v) This plant needs addition of fermented slurry to start the digestion process. Wednesday, December 27, 2017Wednesday, December 27, 2017

Factors Affecting Biodigestion
Carbon/Nitrogen (C/N) Ratio The relationship between the amount of carbon and nitrogen present in organic materials is expressed by the carbon/nitrogen (C/N) ratio. A suitable C/N ratio plays an important role for the proper proliferation of the bacteria for the degradation process . It is generally found that during digestion, micro-organisms utilize carbon 25 to 30 times faster than nitrogen, i.e. carbon content in feedstock should be 25 to 30 times of the nitrogen content . Temperature Most digesters installed in the field lack mechanisms for temperature control and removal of dissolved oxygen. Hence, efficiency of these digesters is reported to be low, particularly during the winter months. There are different temperature ranges during which mesophilic and thermophilic bacteria are most active causing maximum gas yield. Generally, mesophilic bacteria are most active in the temperature range 35-40°C and thermophilic bacteria in the range 50-60°C. Wednesday, December 27, 2017Wednesday, December 27, 2017

pH Value Dilution and Consistency of Input
It is essentially a measure of the acidity and alkalinity of a solution before feeding to a digester. It is suggested that during anaerobic fermentation, micro-organisms require a natural or mildly alkaline environment for efficient gas production. An optimum biogas production is achieved when the pH value of input mixture in the digester is between 6.25 and 7.50. Dilution and Consistency of Input All waste materials fed to a biogas plant consist of solid substance—volatile organic matter and non-volatile matter (fixed solids)—and water. During anaerobic fermentation process, volatile solids undergo digestion and non-volatile solids remain unaffected. According to a finding by The Energy and Resources Institute (TERI) , fresh cattle waste consists of approximately 20% total solid (TS) and 80% water. TS, in turn, consists of 70% volatile solids and 30% fixed solid. For optimum gas yield through anaerobic fermentation, normally, 8-10% TS in feed is required. This is achieved by making slurry of fresh cattle dung in water in the ratio of 1:1. However, if the dung is in dry form, the quantity of water has to be increased accordingly to arrive at the desired consistency of the input (i.e., ratio could vary from 1:1.25 to even 1:2). If the dung is too diluted, the solid particles will settle down into the digester and if it is too thick, the particles impede the flow of the gas formed at the lower part of the digester. In both cases, gas production will be less than optimum. It is also ecessary to remove inert materials such as stones from the inlet before feeding the slurry into the digester. Otherwise, the effective volume of digester will decrease. Wednesday, December 27, 2017Wednesday, December 27, 2017

Hydraulic Retention Time
Loading Rate Loading rate is defined as the amount of raw materials fed per day per unit volume of digester capacity. It is an important parameter that affects gas yield. If the plant is overfed, acids will accumulate and methane production will be inhibited since micro-bacteria cannot survive in acidic situation. Similarly, if the plant is underfed, the gas production will also be low because of alkaline solution, which is also not a favourable condition for anaerobic bacteria . Hydraulic Retention Time Hydraulic retention time (HRT) is the average period that a given quantity of input material remains in the digester to be acted upon by the methanogens. In a cattle-dung plant, the retention time is calculated by dividing total volume of the digester by volume of input added daily. From the results of experiments, it is observed that the rate of gas generation is initially high and then, gradually, declines as the digestion approaches completion .Thus, the time required for 70-80% digestion is considerably less than that needed to achieve complete digestion. HRT is chosen to achieve at least 70-80% digestion. Wednesday, December 27, 2017Wednesday, December 27, 2017

Other Factors Affecting Biogas Yield
Toxicity Mineral ions, heavy metals and detergents are some toxic materials that inhibit the normal growth of pathogens in the digester. Small quantity of mineral ions (e.g., sodium, potassium, calcium, magnesium,)also stimulates the growth of bacteria, while very heavy concentration of these ions leads to toxic effects Detergents including soap, antibiotics, organic solvents etc. also inhibit the activity of methane producing bacteria and hence addition of these substances in the digester should be avoided. Other Factors Affecting Biogas Yield Agitation Agitation or mixing of digester contents significantly helps to ensure intimate contact between micro-organisms, which leads to improved fermentation efficiency. Coppinger suggested that effect of varying degrees of mixing of digester contents improves biogas production. Additives The additives seem to play an important role in biogas yield. Addition of 5% commercial charcoal to cattle dung slurry on dry weight basis raised the yield by 17 and 35% in batch and semi-continuous processes, respectively. The impact of adding inert materials such as vermiculite, charcoal and lignite bovine excreta as feed on biogas yield has also been reported. Wednesday, December 27, 2017Wednesday, December 27, 2017

Thank you for your attention!

BIOMASS ENERGY UNIT-III

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