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© Earthtoys Inc. 2002 2007
AUGUST 2008
+ COVER PAGE
INTERVIEWS
+ ROGER COX THE EVOPOD
+ RAINER WISCHINSKI SPINWAVE SYSTEMS
ALTERNATIVE ENERGY
+ THINFILM SOLAR CELLS HEADING FOR $1 PER WP
+ SOLAR PHOTOVOLTAICS MARKET POTENTIAL
+ SOLAR THERMAL AND EVACUATED TUBE TECHNOLOGY
+ GEOTHERMAL IS NOT WHAT MANY PEOPLE THINK IT IS
+ WASTETOENERGY (WTE) CONVERSION
+ FUTURE PERSPECTIVES OF NUCLEAR POWER
+ TIOGA ENERGY REPORT – SOLAR PPA
+ HOW TO INFORM PEOPLE AWAY FROM SUSTAINABLE
ALTERNATIVETRANSPORTATION
+ BEAT ONE HUNDRED MPG
THE ENVIRONMENT
+ LIGHTS OUT FOR INCANDESCENTS & HALOGENS
+ THE GREEN DATA CENTER
+ GREEN ROOFING OPTIONS AND ADVANTAGES
Generally, the greater the economic prosperity and the higher percentage of urban population, the greater the amount of solid waste produced. Reduction in the volume and mass of solid waste is a crucial issue especially in the light of limited availability
of final disposal sites in many parts of the world.
Salman Zafar, WastetoEnergy Consultant Aligarh, India
1. INTRODUCTION
The enormous increase in the quantum and diversity of waste materials generated byhuman activity and their potentially harmful effects on the general environment andpublic health, have led to an increasing awareness, worldwide, about an urgent needto adopt scientific methods for safe disposal of wastes. While there is an obviousneed to minimize the generation of wastes and to reuse and recycle them, thetechnologies for recovery of energy from wastes can play a vital role in mitigating theproblems. Besides recovery of substantial energy, these technologies can lead to asubstantial reduction in the overall waste quantities requiring final disposal, which canbe better managed for safe disposal in a controlled manner while meeting thepollution control standards.
Waste generation rates are affected by socioeconomic development, degree ofindustrialization, and climate. Generally, the greater the economic prosperity and thehigher percentage of urban population, the greater the amount of solid wasteproduced. Reduction in the volume and mass of solid waste is a crucial issueespecially in the light of limited availability of final disposal sites in many parts of theworld. Although numerous waste and byproduct recovery processes have beenintroduced, anaerobic digestion has unique and integrative potential, simultaneouslyacting as a waste treatment and recovery process.
2. WASTETOENERGY CONVERSION PATHWAYS
There are three main pathways for conversion of organic waste material to energy – thermochemical, biochemical and physicochemical. Thermochemical conversion, characterized by higher temperature and conversion rates, is best suited for lower moisture feedstock and is generally less selective for products. Thermochemical conversion includes incineration, pyro lys is and gas i f ica t ion. The inc inerat ion technology is the controlled combustion of waste with the recovery of heat to produce steam which in turn produces power through steam turbines. Pyrolysis and gasification represent refined thermal treatment methods as alternatives to incineration and are characterized by the transformation of the waste into product gas as energy carrier for later combustion in, for example, a boiler or a gas engine.
The bio chemical conversion processes, which include anaerobic digestion and fermentation, are preferred for wastes having high percentage of organic biodegradable (putrescible) matter and high moisture content. Anaerobic digestioncan be used to recover both nutrients and energy contained in organic wastes suchas animal manure. The process generates gases with a high content of methane (55–70 %) as well as biofertilizer. Alcohol fermentation is the transformation of organicfraction of waste to ethanol by a series of biochemical reactions using specializedmicroorganisms.
The physicochemical technology involves various processes to improve physical andchemical properties of solid waste. The combustible fraction of the waste is convertedinto highenergy fuel pellets which may be used in steam generation. Fuel pelletshave several distinct advantages over coal and wood because it is cleaner, free fromincombustibles, has lower ash and moisture contents, is of uniform size, cost effective, and ecofriendly.
2.1 Factors affecting Energy Recovery
The two main factors which determine the potential of recovery of energy from wastesare the quantity and quality (physicochemical characteristics) of the waste. Some ofthe important physicochemical parameters requiring consideration include:
l Size of constituents
l Density
l Moisture content
l Volatile solids / Organic matter
l Fixed carbon
l Total inerts
l Calorific value
Often, an analysis of waste to determine the proportion of carbon, hydrogen, oxygen,nitrogen and sulfur (ultimate analysis) is done to make mass balance calculations, forboth thermochemical and biochemical processes. In case of anaerobic digestion, theparameters C/N ratio (a measure of nutrient concentration available for bacterialgrowth) and toxicity (representing the presence of hazardous materials which inhibitbacterial growth), also require consideration.
2.2 Significance of Wasteto Energy (WTE) Plants
While some still confuse modern wastetoenergy plants with incinerators of the past,the environmental performance of the industry is beyond reproach. Studies haveshown that communities that employ waste toenergy technology have higherrecycling rates than communities that do not utilize wastetoenergy. The recovery offerrous and nonferrous metals from wastetoenergy plants for recycling is strong andgrowing each year. In addition, numerous studies have determined that wastetoenergy plants actually reduce the amount of greenhouse gases that enter theatmosphere.
Nowadays, wastetoenergy plants based on combustion technologies are highlyefficient power plants that utilize municipal solid waste as their fuel rather than coal,oil or natural gas. Far better than expending energy to explore, recover, process andtransport the fuel from some distant source, wastetoenergy plants find value in whatothers consider garbage. Waste toenergy plants recover the thermal energycontained in the trash in highly efficient boilers that generate steam that can then besold directly to industrial customers, or used onsite to drive turbines for electricityproduction. WTE plants are highly efficient in harnessing the untapped energypotential of organic waste by converting the biodegradable fraction of the waste intohigh calorific value gases like methane. The digested portion of the waste is highlyrich in nutrients and is widely used as biofertilizer in many parts of the world.
2.3 WastetoEnergy around the World
To an even greater extent than in the United States, wastetoenergy has thrived inEurope and Asia as the preeminent method of waste disposal. Lauding wastetoenergy for its ability to reduce the volume of waste in an environmentally friendlymanner, generate valuable energy, and reduce greenhouse gas emissions, Europeannations rely on wastetoenergy as the preferred method of waste disposal. In fact,the European Union has issued a legally binding requirement for its member States tolimit the landfilling of biodegradable waste.
The Confederation of European WastetoEnergy Plants (CEWEP) notes that Europecurrently treats 50 million ton of wastes at waste toenergy plants each year,generating an amount of energy that can supply electricity for 27 million people orheat for 13 million people. Upcoming changes to EU legislation will have a profoundimpact on how much further the technology will help achieve environmental protectiongoals. Describing the advances of waste toenergy, the German Ministry for theEnvironment cites drastic reductions in emissions of dioxin, dust and mercury.Twenty years ago, 18 Swedish wastetoenergy plants emitted a total of about 100grams of dioxins every year. Today, the collective dioxin emissions from all 29Swedish wastetoenergy plants amount to 0.7 of a gram. It is clear that Europe hasmade similar strides as the United States with respect to emissions reductions.
3. FEEDSTOCK FOR WASTETOENERGY CONVERSION PLANTS
3.1 Agricultural Residues
Large quantities of crop residues are produced annually worldwide, and are vastlyunderutilised. The most common agricultural residue is the rice husk, which makesup 25% of rice by mass. Other residues include sugar cane fibre (known asbagasse), coconut husks and shells, groundnut shells, cereal straw etc. Currentfarming practice is usually to plough these residues back into the soil, or they areburnt, left to decompose, or grazed by cattle. A number of agricultural and biomassstudies, however, have concluded that it may be appropriate to remove and utilise aportion of crop residue for energy production, providing large volumes of low costmaterial. These residues could be processed into liquid fuels or combusted/gasifiedto produce electricity and heat.
3.2 Animal Waste
There are a wide range of animal wastes that can be used as sources of biomassenergy. The most common sources are animal and poultry manures. In the past thiswaste was recovered and sold as a fertilizer or simply spread onto agricultural land,but the introduction of tighter environmental controls on odour and water pollutionmeans that some form of waste management is now required, which provides furtherincentives for wastetoenergy conversion. The most attractive method of convertingthese waste materials to useful form is anaerobic digestion which gives biogas thatcan be used as a fuel for internal combustion engines, to generate electricity fromsmall gas turbines, burnt directly for cooking, or for space and water heating. Foodprocessing and abattoir wastes are also a potential anaerobic digestion feedstock.
3.3 Sugar Industry Wastes
The sugar cane industry produces large volumes of bagasse each year. Bagasse ispotentially a major source of biomass energy as it can be used as boiler feedstock togenerate steam for process heat and electricity production. Most sugar cane millsutilise bagasse to produce electricity for their own needs but some sugar mills areable to export substantial amount of electricity to the grid.
3.4 Forestry Residues
Forestry residues are generated by operations such as thinning of plantations,clearing for logging roads, extracting stemwood for pulp and timber, and naturalattrition. Wood processing also generates significant volumes of residues usually inthe form of sawdust, offcuts, bark and woodchip rejects. This waste material is oftennot utilised and often left to rot on site. However it can be collected and used in abiomass gasifier to produce hot gases for generating steam.
3.5 Industrial Wastes
The food industry produces a large number of residues and byproducts that can beused as biomass energy sources. These waste materials are generated from allsectors of the food industry with everything from meat production to confectioneryproducing waste that can be utilised as an energy source. Solid wastes includepeelings and scraps from fruit and vegetables, food that does not meet quality controlstandards, pulp and fibre from sugar and starch extraction, filter sludges and coffeegrounds. These wastes are usually disposed of in landfill dumps.
Liquid wastes are generated by washing meat, fruit and vegetables, blanching fruitand vegetables, precooking meats, poultry and fish, cleaning and processingoperations as well as wine making. These waste waters contain sugars, starches andother dissolved and solid organic matter. The potential exists for these industrialwastes to be anaerobically digested to produce biogas, or fermented to produceethanol, and several commercial examples of wastetoenergy conversion alreadyexist.
3.6 Municipal Solid Waste (MSW)
Millions of tonnes of household waste are collected each year with the vast majoritydisposed of in landfill dumps. The biomass resource in MSW comprises theputrescibles, paper and plastic and averages 80% of the total MSW collected.Municipal solid waste can be converted into energy by direct combustion, or bynatural anaerobic digestion in the landfill. At the landfill sites the gas produced by thenatural decomposition of MSW (approximately 50% methane and 50% carbondioxide) is collected from the stored material and scrubbed and cleaned beforefeeding into internal combustion engines or gas turbines to generate heat and power.The organic fraction of MSW can be anaerobically stabilized in a highrate digester toobtain biogas for electricity or steam generation.
3.7 Sewage
Sewage is a source of biomass energy that is very similar to the other animal wastes.Energy can be extracted from sewage using anaerobic digestion to produce biogas.The sewage sludge that remains can be incinerated or undergo pyrolysis to producemore biogas
3.8 Black Liquor
Pulp and Paper Industry is considered to be one of the highly polluting industries andconsumes large amount of energy and water in various unit operations. Thewastewater discharged by this industry is highly heterogeneous as it containscompounds from wood or other raw materials, processed chemicals as well ascompound formed during processing. Black liquor can be judiciously utilized forproduction of biogas using UASB technology.
Table 1. Summary of Successful WastetoEnergy Plants in India based on Anaerobic Digestion
4. CONCLUSIONS
The wastetoenergy plants offer two important benefits of environmentally safe wastemanagement and disposal, as well as the generation of clean electric power. Wastetoenergy facilities produce clean, renewable energy through thermochemical,biochemical and physicochemical methods. The growing use of wastetoenergy as amethod to dispose off solid and liquid wastes and generate power has greatly reducedenvironmental impacts of municipal solid waste management, including emissions ofgreenhouse gases. Wastetoenergy conversion reduces greenhouse gas emissionsin two ways. Electricity is generated which reduces the dependence on electricalproduction from power plants based on fossil fuels. The greenhouse gas emissionsare significantly reduced by preventing methane emissions from landfills. Moreover,wastetoenergy plants are highly efficient in harnessing the untapped sources ofenergy from a variety of wastes.
REFERENCES
1. Gunasegarane, G.S., Energy from Dairy Waste, Bio Energy News, 6, 2002, pp26.
2. Sirviö, A., and Rintala, J. A., Renewable Energy Production in Farm Scale:Biogas from Energy Crops, Bio Energy News, 6, 2002, pp 16.
3. Rao, R.P., Energy from Agro Waste A Case Study, Bio Energy News, 3,1999, pp 21.
4. Mapuskar, S.V., Biogas from Vegetable Market Waste at APMC Pune, BioEnergy News. 1, 1997, pp 16.
5. Dhussa A.K., and Varshney, A.K., Energy Recovery from Municipal SolidWaste Potential and Possibilities, Bio Energy News, 4, 2000, pp 7.
6. http://www.undp.org.in/env.htm
7. http://www.recoveredenergy.com/d_wte.html
8. http://www.wte.org
9. http://www.earthtoys.com/
10. http://www.undp.org.in/programme/GEF/Mar%202003/article2.htm
11. http://www.undp.org.in/Programme/GEF/march00/page1214.html
12. http://www.mnes.nic.in
13. http://mnes1.delhi.nic.in/bionews
14. http://www.renewingindia.org/finren.html
Leather & Abattoir Industry WasteLocation Capacity Feed type Type of
reactor used
Biogas utilization
Rudraram, Andhra Pradesh
60 tpd Abattoir waste BIMA Boiler fuel
Melvisharam, TamilNadu
5 tpd Fleshing & primary sludge
CSTR Aerator operation
Melvisharam, TamilNadu
2 tpd Tannery fleshing &sludge UASB Boiler fuel
Dewas, Madhya Pradesh
1.2 1.5 tpd
Chromed leather dust UASB UASB
Vegetable Market Yard WasteVijayawda, Andhra Pradesh
20 tpd Vegetable market and slaughterhouse waste
UASB Power generation
Koyambedu, Tamil Nadu
30 tpd Vegetable waste BIMA Power generation
Municipal Wastewater/ SewageBhubaneshwar, Orissa
400 m3/d Domestic Sewage Fixed film Heating and illumination
Surat, Gujarat 0.5 MWe Domestic Sewage Anaerobic sludge
Power generation
Animal Agro ResidueKarur, Tamil Nadu 12000
m3/dBagasse wash water UASB Lime kiln
Ludhiana, Punjab 235 tpd Cattle manure BIMA Power generation
Fruit and Food Processing WasteDharmapuri, Tamil Nadu
12000 tpd Tapioca wastewater HUSMAR Power generation
[Stay Informed Subscribe to our Monthly Email Update] [Index] [Emagazine ] [News] [Libraries] [Products] [Search] [Advertise] [About Us]
© Earthtoys Inc. 2002 2007
AUGUST 2008
+ COVER PAGE
INTERVIEWS
+ ROGER COX THE EVOPOD
+ RAINER WISCHINSKI SPINWAVE SYSTEMS
ALTERNATIVE ENERGY
+ THINFILM SOLAR CELLS HEADING FOR $1 PER WP
+ SOLAR PHOTOVOLTAICS MARKET POTENTIAL
+ SOLAR THERMAL AND EVACUATED TUBE TECHNOLOGY
+ GEOTHERMAL IS NOT WHAT MANY PEOPLE THINK IT IS
+ WASTETOENERGY (WTE) CONVERSION
+ FUTURE PERSPECTIVES OF NUCLEAR POWER
+ TIOGA ENERGY REPORT – SOLAR PPA
+ HOW TO INFORM PEOPLE AWAY FROM SUSTAINABLE
ALTERNATIVETRANSPORTATION
+ BEAT ONE HUNDRED MPG
THE ENVIRONMENT
+ LIGHTS OUT FOR INCANDESCENTS & HALOGENS
+ THE GREEN DATA CENTER
+ GREEN ROOFING OPTIONS AND ADVANTAGES
Generally, the greater the economic prosperity and the higher percentage of urban population, the greater the amount of solid waste produced. Reduction in the volume and mass of solid waste is a crucial issue especially in the light of limited availability
of final disposal sites in many parts of the world.
Salman Zafar, WastetoEnergy Consultant Aligarh, India
1. INTRODUCTION
The enormous increase in the quantum and diversity of waste materials generated byhuman activity and their potentially harmful effects on the general environment andpublic health, have led to an increasing awareness, worldwide, about an urgent needto adopt scientific methods for safe disposal of wastes. While there is an obviousneed to minimize the generation of wastes and to reuse and recycle them, thetechnologies for recovery of energy from wastes can play a vital role in mitigating theproblems. Besides recovery of substantial energy, these technologies can lead to asubstantial reduction in the overall waste quantities requiring final disposal, which canbe better managed for safe disposal in a controlled manner while meeting thepollution control standards.
Waste generation rates are affected by socioeconomic development, degree ofindustrialization, and climate. Generally, the greater the economic prosperity and thehigher percentage of urban population, the greater the amount of solid wasteproduced. Reduction in the volume and mass of solid waste is a crucial issueespecially in the light of limited availability of final disposal sites in many parts of theworld. Although numerous waste and byproduct recovery processes have beenintroduced, anaerobic digestion has unique and integrative potential, simultaneouslyacting as a waste treatment and recovery process.
2. WASTETOENERGY CONVERSION PATHWAYS
There are three main pathways for conversion of organic waste material to energy – thermochemical, biochemical and physicochemical. Thermochemical conversion, characterized by higher temperature and conversion rates, is best suited for lower moisture feedstock and is generally less selective for products. Thermochemical conversion includes incineration, pyro lys is and gas i f ica t ion. The inc inerat ion technology is the controlled combustion of waste with the recovery of heat to produce steam which in turn produces power through steam turbines. Pyrolysis and gasification represent refined thermal treatment methods as alternatives to incineration and are characterized by the transformation of the waste into product gas as energy carrier for later combustion in, for example, a boiler or a gas engine.
The bio chemical conversion processes, which include anaerobic digestion and fermentation, are preferred for wastes having high percentage of organic biodegradable (putrescible) matter and high moisture content. Anaerobic digestioncan be used to recover both nutrients and energy contained in organic wastes suchas animal manure. The process generates gases with a high content of methane (55–70 %) as well as biofertilizer. Alcohol fermentation is the transformation of organicfraction of waste to ethanol by a series of biochemical reactions using specializedmicroorganisms.
The physicochemical technology involves various processes to improve physical andchemical properties of solid waste. The combustible fraction of the waste is convertedinto highenergy fuel pellets which may be used in steam generation. Fuel pelletshave several distinct advantages over coal and wood because it is cleaner, free fromincombustibles, has lower ash and moisture contents, is of uniform size, cost effective, and ecofriendly.
2.1 Factors affecting Energy Recovery
The two main factors which determine the potential of recovery of energy from wastesare the quantity and quality (physicochemical characteristics) of the waste. Some ofthe important physicochemical parameters requiring consideration include:
l Size of constituents
l Density
l Moisture content
l Volatile solids / Organic matter
l Fixed carbon
l Total inerts
l Calorific value
Often, an analysis of waste to determine the proportion of carbon, hydrogen, oxygen,nitrogen and sulfur (ultimate analysis) is done to make mass balance calculations, forboth thermochemical and biochemical processes. In case of anaerobic digestion, theparameters C/N ratio (a measure of nutrient concentration available for bacterialgrowth) and toxicity (representing the presence of hazardous materials which inhibitbacterial growth), also require consideration.
2.2 Significance of Wasteto Energy (WTE) Plants
While some still confuse modern wastetoenergy plants with incinerators of the past,the environmental performance of the industry is beyond reproach. Studies haveshown that communities that employ waste toenergy technology have higherrecycling rates than communities that do not utilize wastetoenergy. The recovery offerrous and nonferrous metals from wastetoenergy plants for recycling is strong andgrowing each year. In addition, numerous studies have determined that wastetoenergy plants actually reduce the amount of greenhouse gases that enter theatmosphere.
Nowadays, wastetoenergy plants based on combustion technologies are highlyefficient power plants that utilize municipal solid waste as their fuel rather than coal,oil or natural gas. Far better than expending energy to explore, recover, process andtransport the fuel from some distant source, wastetoenergy plants find value in whatothers consider garbage. Waste toenergy plants recover the thermal energycontained in the trash in highly efficient boilers that generate steam that can then besold directly to industrial customers, or used onsite to drive turbines for electricityproduction. WTE plants are highly efficient in harnessing the untapped energypotential of organic waste by converting the biodegradable fraction of the waste intohigh calorific value gases like methane. The digested portion of the waste is highlyrich in nutrients and is widely used as biofertilizer in many parts of the world.
2.3 WastetoEnergy around the World
To an even greater extent than in the United States, wastetoenergy has thrived inEurope and Asia as the preeminent method of waste disposal. Lauding wastetoenergy for its ability to reduce the volume of waste in an environmentally friendlymanner, generate valuable energy, and reduce greenhouse gas emissions, Europeannations rely on wastetoenergy as the preferred method of waste disposal. In fact,the European Union has issued a legally binding requirement for its member States tolimit the landfilling of biodegradable waste.
The Confederation of European WastetoEnergy Plants (CEWEP) notes that Europecurrently treats 50 million ton of wastes at waste toenergy plants each year,generating an amount of energy that can supply electricity for 27 million people orheat for 13 million people. Upcoming changes to EU legislation will have a profoundimpact on how much further the technology will help achieve environmental protectiongoals. Describing the advances of waste toenergy, the German Ministry for theEnvironment cites drastic reductions in emissions of dioxin, dust and mercury.Twenty years ago, 18 Swedish wastetoenergy plants emitted a total of about 100grams of dioxins every year. Today, the collective dioxin emissions from all 29Swedish wastetoenergy plants amount to 0.7 of a gram. It is clear that Europe hasmade similar strides as the United States with respect to emissions reductions.
3. FEEDSTOCK FOR WASTETOENERGY CONVERSION PLANTS
3.1 Agricultural Residues
Large quantities of crop residues are produced annually worldwide, and are vastlyunderutilised. The most common agricultural residue is the rice husk, which makesup 25% of rice by mass. Other residues include sugar cane fibre (known asbagasse), coconut husks and shells, groundnut shells, cereal straw etc. Currentfarming practice is usually to plough these residues back into the soil, or they areburnt, left to decompose, or grazed by cattle. A number of agricultural and biomassstudies, however, have concluded that it may be appropriate to remove and utilise aportion of crop residue for energy production, providing large volumes of low costmaterial. These residues could be processed into liquid fuels or combusted/gasifiedto produce electricity and heat.
3.2 Animal Waste
There are a wide range of animal wastes that can be used as sources of biomassenergy. The most common sources are animal and poultry manures. In the past thiswaste was recovered and sold as a fertilizer or simply spread onto agricultural land,but the introduction of tighter environmental controls on odour and water pollutionmeans that some form of waste management is now required, which provides furtherincentives for wastetoenergy conversion. The most attractive method of convertingthese waste materials to useful form is anaerobic digestion which gives biogas thatcan be used as a fuel for internal combustion engines, to generate electricity fromsmall gas turbines, burnt directly for cooking, or for space and water heating. Foodprocessing and abattoir wastes are also a potential anaerobic digestion feedstock.
3.3 Sugar Industry Wastes
The sugar cane industry produces large volumes of bagasse each year. Bagasse ispotentially a major source of biomass energy as it can be used as boiler feedstock togenerate steam for process heat and electricity production. Most sugar cane millsutilise bagasse to produce electricity for their own needs but some sugar mills areable to export substantial amount of electricity to the grid.
3.4 Forestry Residues
Forestry residues are generated by operations such as thinning of plantations,clearing for logging roads, extracting stemwood for pulp and timber, and naturalattrition. Wood processing also generates significant volumes of residues usually inthe form of sawdust, offcuts, bark and woodchip rejects. This waste material is oftennot utilised and often left to rot on site. However it can be collected and used in abiomass gasifier to produce hot gases for generating steam.
3.5 Industrial Wastes
The food industry produces a large number of residues and byproducts that can beused as biomass energy sources. These waste materials are generated from allsectors of the food industry with everything from meat production to confectioneryproducing waste that can be utilised as an energy source. Solid wastes includepeelings and scraps from fruit and vegetables, food that does not meet quality controlstandards, pulp and fibre from sugar and starch extraction, filter sludges and coffeegrounds. These wastes are usually disposed of in landfill dumps.
Liquid wastes are generated by washing meat, fruit and vegetables, blanching fruitand vegetables, precooking meats, poultry and fish, cleaning and processingoperations as well as wine making. These waste waters contain sugars, starches andother dissolved and solid organic matter. The potential exists for these industrialwastes to be anaerobically digested to produce biogas, or fermented to produceethanol, and several commercial examples of wastetoenergy conversion alreadyexist.
3.6 Municipal Solid Waste (MSW)
Millions of tonnes of household waste are collected each year with the vast majoritydisposed of in landfill dumps. The biomass resource in MSW comprises theputrescibles, paper and plastic and averages 80% of the total MSW collected.Municipal solid waste can be converted into energy by direct combustion, or bynatural anaerobic digestion in the landfill. At the landfill sites the gas produced by thenatural decomposition of MSW (approximately 50% methane and 50% carbondioxide) is collected from the stored material and scrubbed and cleaned beforefeeding into internal combustion engines or gas turbines to generate heat and power.The organic fraction of MSW can be anaerobically stabilized in a highrate digester toobtain biogas for electricity or steam generation.
3.7 Sewage
Sewage is a source of biomass energy that is very similar to the other animal wastes.Energy can be extracted from sewage using anaerobic digestion to produce biogas.The sewage sludge that remains can be incinerated or undergo pyrolysis to producemore biogas
3.8 Black Liquor
Pulp and Paper Industry is considered to be one of the highly polluting industries andconsumes large amount of energy and water in various unit operations. Thewastewater discharged by this industry is highly heterogeneous as it containscompounds from wood or other raw materials, processed chemicals as well ascompound formed during processing. Black liquor can be judiciously utilized forproduction of biogas using UASB technology.
Table 1. Summary of Successful WastetoEnergy Plants in India based on Anaerobic Digestion
4. CONCLUSIONS
The wastetoenergy plants offer two important benefits of environmentally safe wastemanagement and disposal, as well as the generation of clean electric power. Wastetoenergy facilities produce clean, renewable energy through thermochemical,biochemical and physicochemical methods. The growing use of wastetoenergy as amethod to dispose off solid and liquid wastes and generate power has greatly reducedenvironmental impacts of municipal solid waste management, including emissions ofgreenhouse gases. Wastetoenergy conversion reduces greenhouse gas emissionsin two ways. Electricity is generated which reduces the dependence on electricalproduction from power plants based on fossil fuels. The greenhouse gas emissionsare significantly reduced by preventing methane emissions from landfills. Moreover,wastetoenergy plants are highly efficient in harnessing the untapped sources ofenergy from a variety of wastes.
REFERENCES
1. Gunasegarane, G.S., Energy from Dairy Waste, Bio Energy News, 6, 2002, pp26.
2. Sirviö, A., and Rintala, J. A., Renewable Energy Production in Farm Scale:Biogas from Energy Crops, Bio Energy News, 6, 2002, pp 16.
3. Rao, R.P., Energy from Agro Waste A Case Study, Bio Energy News, 3,1999, pp 21.
4. Mapuskar, S.V., Biogas from Vegetable Market Waste at APMC Pune, BioEnergy News. 1, 1997, pp 16.
5. Dhussa A.K., and Varshney, A.K., Energy Recovery from Municipal SolidWaste Potential and Possibilities, Bio Energy News, 4, 2000, pp 7.
6. http://www.undp.org.in/env.htm
7. http://www.recoveredenergy.com/d_wte.html
8. http://www.wte.org
9. http://www.earthtoys.com/
10. http://www.undp.org.in/programme/GEF/Mar%202003/article2.htm
11. http://www.undp.org.in/Programme/GEF/march00/page1214.html
12. http://www.mnes.nic.in
13. http://mnes1.delhi.nic.in/bionews
14. http://www.renewingindia.org/finren.html
Leather & Abattoir Industry WasteLocation Capacity Feed type Type of
reactor used
Biogas utilization
Rudraram, Andhra Pradesh
60 tpd Abattoir waste BIMA Boiler fuel
Melvisharam, TamilNadu
5 tpd Fleshing & primary sludge
CSTR Aerator operation
Melvisharam, TamilNadu
2 tpd Tannery fleshing &sludge UASB Boiler fuel
Dewas, Madhya Pradesh
1.2 1.5 tpd
Chromed leather dust UASB UASB
Vegetable Market Yard WasteVijayawda, Andhra Pradesh
20 tpd Vegetable market and slaughterhouse waste
UASB Power generation
Koyambedu, Tamil Nadu
30 tpd Vegetable waste BIMA Power generation
Municipal Wastewater/ SewageBhubaneshwar, Orissa
400 m3/d Domestic Sewage Fixed film Heating and illumination
Surat, Gujarat 0.5 MWe Domestic Sewage Anaerobic sludge
Power generation
Animal Agro ResidueKarur, Tamil Nadu 12000
m3/dBagasse wash water UASB Lime kiln
Ludhiana, Punjab 235 tpd Cattle manure BIMA Power generation
Fruit and Food Processing WasteDharmapuri, Tamil Nadu
12000 tpd Tapioca wastewater HUSMAR Power generation
[Stay Informed Subscribe to our Monthly Email Update] [Index] [Emagazine ] [News] [Libraries] [Products] [Search] [Advertise] [About Us]
© Earthtoys Inc. 2002 2007
AUGUST 2008
+ COVER PAGE
INTERVIEWS
+ ROGER COX THE EVOPOD
+ RAINER WISCHINSKI SPINWAVE SYSTEMS
ALTERNATIVE ENERGY
+ THINFILM SOLAR CELLS HEADING FOR $1 PER WP
+ SOLAR PHOTOVOLTAICS MARKET POTENTIAL
+ SOLAR THERMAL AND EVACUATED TUBE TECHNOLOGY
+ GEOTHERMAL IS NOT WHAT MANY PEOPLE THINK IT IS
+ WASTETOENERGY (WTE) CONVERSION
+ FUTURE PERSPECTIVES OF NUCLEAR POWER
+ TIOGA ENERGY REPORT – SOLAR PPA
+ HOW TO INFORM PEOPLE AWAY FROM SUSTAINABLE
ALTERNATIVETRANSPORTATION
+ BEAT ONE HUNDRED MPG
THE ENVIRONMENT
+ LIGHTS OUT FOR INCANDESCENTS & HALOGENS
+ THE GREEN DATA CENTER
+ GREEN ROOFING OPTIONS AND ADVANTAGES
Generally, the greater the economic prosperity and the higher percentage of urban population, the greater the amount of solid waste produced. Reduction in the volume and mass of solid waste is a crucial issue especially in the light of limited availability
of final disposal sites in many parts of the world.
Salman Zafar, WastetoEnergy Consultant Aligarh, India
1. INTRODUCTION
The enormous increase in the quantum and diversity of waste materials generated byhuman activity and their potentially harmful effects on the general environment andpublic health, have led to an increasing awareness, worldwide, about an urgent needto adopt scientific methods for safe disposal of wastes. While there is an obviousneed to minimize the generation of wastes and to reuse and recycle them, thetechnologies for recovery of energy from wastes can play a vital role in mitigating theproblems. Besides recovery of substantial energy, these technologies can lead to asubstantial reduction in the overall waste quantities requiring final disposal, which canbe better managed for safe disposal in a controlled manner while meeting thepollution control standards.
Waste generation rates are affected by socioeconomic development, degree ofindustrialization, and climate. Generally, the greater the economic prosperity and thehigher percentage of urban population, the greater the amount of solid wasteproduced. Reduction in the volume and mass of solid waste is a crucial issueespecially in the light of limited availability of final disposal sites in many parts of theworld. Although numerous waste and byproduct recovery processes have beenintroduced, anaerobic digestion has unique and integrative potential, simultaneouslyacting as a waste treatment and recovery process.
2. WASTETOENERGY CONVERSION PATHWAYS
There are three main pathways for conversion of organic waste material to energy – thermochemical, biochemical and physicochemical. Thermochemical conversion, characterized by higher temperature and conversion rates, is best suited for lower moisture feedstock and is generally less selective for products. Thermochemical conversion includes incineration, pyro lys is and gas i f ica t ion. The inc inerat ion technology is the controlled combustion of waste with the recovery of heat to produce steam which in turn produces power through steam turbines. Pyrolysis and gasification represent refined thermal treatment methods as alternatives to incineration and are characterized by the transformation of the waste into product gas as energy carrier for later combustion in, for example, a boiler or a gas engine.
The bio chemical conversion processes, which include anaerobic digestion and fermentation, are preferred for wastes having high percentage of organic biodegradable (putrescible) matter and high moisture content. Anaerobic digestioncan be used to recover both nutrients and energy contained in organic wastes suchas animal manure. The process generates gases with a high content of methane (55–70 %) as well as biofertilizer. Alcohol fermentation is the transformation of organicfraction of waste to ethanol by a series of biochemical reactions using specializedmicroorganisms.
The physicochemical technology involves various processes to improve physical andchemical properties of solid waste. The combustible fraction of the waste is convertedinto highenergy fuel pellets which may be used in steam generation. Fuel pelletshave several distinct advantages over coal and wood because it is cleaner, free fromincombustibles, has lower ash and moisture contents, is of uniform size, cost effective, and ecofriendly.
2.1 Factors affecting Energy Recovery
The two main factors which determine the potential of recovery of energy from wastesare the quantity and quality (physicochemical characteristics) of the waste. Some ofthe important physicochemical parameters requiring consideration include:
l Size of constituents
l Density
l Moisture content
l Volatile solids / Organic matter
l Fixed carbon
l Total inerts
l Calorific value
Often, an analysis of waste to determine the proportion of carbon, hydrogen, oxygen,nitrogen and sulfur (ultimate analysis) is done to make mass balance calculations, forboth thermochemical and biochemical processes. In case of anaerobic digestion, theparameters C/N ratio (a measure of nutrient concentration available for bacterialgrowth) and toxicity (representing the presence of hazardous materials which inhibitbacterial growth), also require consideration.
2.2 Significance of Wasteto Energy (WTE) Plants
While some still confuse modern wastetoenergy plants with incinerators of the past,the environmental performance of the industry is beyond reproach. Studies haveshown that communities that employ waste toenergy technology have higherrecycling rates than communities that do not utilize wastetoenergy. The recovery offerrous and nonferrous metals from wastetoenergy plants for recycling is strong andgrowing each year. In addition, numerous studies have determined that wastetoenergy plants actually reduce the amount of greenhouse gases that enter theatmosphere.
Nowadays, wastetoenergy plants based on combustion technologies are highlyefficient power plants that utilize municipal solid waste as their fuel rather than coal,oil or natural gas. Far better than expending energy to explore, recover, process andtransport the fuel from some distant source, wastetoenergy plants find value in whatothers consider garbage. Waste toenergy plants recover the thermal energycontained in the trash in highly efficient boilers that generate steam that can then besold directly to industrial customers, or used onsite to drive turbines for electricityproduction. WTE plants are highly efficient in harnessing the untapped energypotential of organic waste by converting the biodegradable fraction of the waste intohigh calorific value gases like methane. The digested portion of the waste is highlyrich in nutrients and is widely used as biofertilizer in many parts of the world.
2.3 WastetoEnergy around the World
To an even greater extent than in the United States, wastetoenergy has thrived inEurope and Asia as the preeminent method of waste disposal. Lauding wastetoenergy for its ability to reduce the volume of waste in an environmentally friendlymanner, generate valuable energy, and reduce greenhouse gas emissions, Europeannations rely on wastetoenergy as the preferred method of waste disposal. In fact,the European Union has issued a legally binding requirement for its member States tolimit the landfilling of biodegradable waste.
The Confederation of European WastetoEnergy Plants (CEWEP) notes that Europecurrently treats 50 million ton of wastes at waste toenergy plants each year,generating an amount of energy that can supply electricity for 27 million people orheat for 13 million people. Upcoming changes to EU legislation will have a profoundimpact on how much further the technology will help achieve environmental protectiongoals. Describing the advances of waste toenergy, the German Ministry for theEnvironment cites drastic reductions in emissions of dioxin, dust and mercury.Twenty years ago, 18 Swedish wastetoenergy plants emitted a total of about 100grams of dioxins every year. Today, the collective dioxin emissions from all 29Swedish wastetoenergy plants amount to 0.7 of a gram. It is clear that Europe hasmade similar strides as the United States with respect to emissions reductions.
3. FEEDSTOCK FOR WASTETOENERGY CONVERSION PLANTS
3.1 Agricultural Residues
Large quantities of crop residues are produced annually worldwide, and are vastlyunderutilised. The most common agricultural residue is the rice husk, which makesup 25% of rice by mass. Other residues include sugar cane fibre (known asbagasse), coconut husks and shells, groundnut shells, cereal straw etc. Currentfarming practice is usually to plough these residues back into the soil, or they areburnt, left to decompose, or grazed by cattle. A number of agricultural and biomassstudies, however, have concluded that it may be appropriate to remove and utilise aportion of crop residue for energy production, providing large volumes of low costmaterial. These residues could be processed into liquid fuels or combusted/gasifiedto produce electricity and heat.
3.2 Animal Waste
There are a wide range of animal wastes that can be used as sources of biomassenergy. The most common sources are animal and poultry manures. In the past thiswaste was recovered and sold as a fertilizer or simply spread onto agricultural land,but the introduction of tighter environmental controls on odour and water pollutionmeans that some form of waste management is now required, which provides furtherincentives for wastetoenergy conversion. The most attractive method of convertingthese waste materials to useful form is anaerobic digestion which gives biogas thatcan be used as a fuel for internal combustion engines, to generate electricity fromsmall gas turbines, burnt directly for cooking, or for space and water heating. Foodprocessing and abattoir wastes are also a potential anaerobic digestion feedstock.
3.3 Sugar Industry Wastes
The sugar cane industry produces large volumes of bagasse each year. Bagasse ispotentially a major source of biomass energy as it can be used as boiler feedstock togenerate steam for process heat and electricity production. Most sugar cane millsutilise bagasse to produce electricity for their own needs but some sugar mills areable to export substantial amount of electricity to the grid.
3.4 Forestry Residues
Forestry residues are generated by operations such as thinning of plantations,clearing for logging roads, extracting stemwood for pulp and timber, and naturalattrition. Wood processing also generates significant volumes of residues usually inthe form of sawdust, offcuts, bark and woodchip rejects. This waste material is oftennot utilised and often left to rot on site. However it can be collected and used in abiomass gasifier to produce hot gases for generating steam.
3.5 Industrial Wastes
The food industry produces a large number of residues and byproducts that can beused as biomass energy sources. These waste materials are generated from allsectors of the food industry with everything from meat production to confectioneryproducing waste that can be utilised as an energy source. Solid wastes includepeelings and scraps from fruit and vegetables, food that does not meet quality controlstandards, pulp and fibre from sugar and starch extraction, filter sludges and coffeegrounds. These wastes are usually disposed of in landfill dumps.
Liquid wastes are generated by washing meat, fruit and vegetables, blanching fruitand vegetables, precooking meats, poultry and fish, cleaning and processingoperations as well as wine making. These waste waters contain sugars, starches andother dissolved and solid organic matter. The potential exists for these industrialwastes to be anaerobically digested to produce biogas, or fermented to produceethanol, and several commercial examples of wastetoenergy conversion alreadyexist.
3.6 Municipal Solid Waste (MSW)
Millions of tonnes of household waste are collected each year with the vast majoritydisposed of in landfill dumps. The biomass resource in MSW comprises theputrescibles, paper and plastic and averages 80% of the total MSW collected.Municipal solid waste can be converted into energy by direct combustion, or bynatural anaerobic digestion in the landfill. At the landfill sites the gas produced by thenatural decomposition of MSW (approximately 50% methane and 50% carbondioxide) is collected from the stored material and scrubbed and cleaned beforefeeding into internal combustion engines or gas turbines to generate heat and power.The organic fraction of MSW can be anaerobically stabilized in a highrate digester toobtain biogas for electricity or steam generation.
3.7 Sewage
Sewage is a source of biomass energy that is very similar to the other animal wastes.Energy can be extracted from sewage using anaerobic digestion to produce biogas.The sewage sludge that remains can be incinerated or undergo pyrolysis to producemore biogas
3.8 Black Liquor
Pulp and Paper Industry is considered to be one of the highly polluting industries andconsumes large amount of energy and water in various unit operations. Thewastewater discharged by this industry is highly heterogeneous as it containscompounds from wood or other raw materials, processed chemicals as well ascompound formed during processing. Black liquor can be judiciously utilized forproduction of biogas using UASB technology.
Table 1. Summary of Successful WastetoEnergy Plants in India based on Anaerobic Digestion
4. CONCLUSIONS
The wastetoenergy plants offer two important benefits of environmentally safe wastemanagement and disposal, as well as the generation of clean electric power. Wastetoenergy facilities produce clean, renewable energy through thermochemical,biochemical and physicochemical methods. The growing use of wastetoenergy as amethod to dispose off solid and liquid wastes and generate power has greatly reducedenvironmental impacts of municipal solid waste management, including emissions ofgreenhouse gases. Wastetoenergy conversion reduces greenhouse gas emissionsin two ways. Electricity is generated which reduces the dependence on electricalproduction from power plants based on fossil fuels. The greenhouse gas emissionsare significantly reduced by preventing methane emissions from landfills. Moreover,wastetoenergy plants are highly efficient in harnessing the untapped sources ofenergy from a variety of wastes.
REFERENCES
1. Gunasegarane, G.S., Energy from Dairy Waste, Bio Energy News, 6, 2002, pp26.
2. Sirviö, A., and Rintala, J. A., Renewable Energy Production in Farm Scale:Biogas from Energy Crops, Bio Energy News, 6, 2002, pp 16.
3. Rao, R.P., Energy from Agro Waste A Case Study, Bio Energy News, 3,1999, pp 21.
4. Mapuskar, S.V., Biogas from Vegetable Market Waste at APMC Pune, BioEnergy News. 1, 1997, pp 16.
5. Dhussa A.K., and Varshney, A.K., Energy Recovery from Municipal SolidWaste Potential and Possibilities, Bio Energy News, 4, 2000, pp 7.
6. http://www.undp.org.in/env.htm
7. http://www.recoveredenergy.com/d_wte.html
8. http://www.wte.org
9. http://www.earthtoys.com/
10. http://www.undp.org.in/programme/GEF/Mar%202003/article2.htm
11. http://www.undp.org.in/Programme/GEF/march00/page1214.html
12. http://www.mnes.nic.in
13. http://mnes1.delhi.nic.in/bionews
14. http://www.renewingindia.org/finren.html
Leather & Abattoir Industry WasteLocation Capacity Feed type Type of
reactor used
Biogas utilization
Rudraram, Andhra Pradesh
60 tpd Abattoir waste BIMA Boiler fuel
Melvisharam, TamilNadu
5 tpd Fleshing & primary sludge
CSTR Aerator operation
Melvisharam, TamilNadu
2 tpd Tannery fleshing &sludge UASB Boiler fuel
Dewas, Madhya Pradesh
1.2 1.5 tpd
Chromed leather dust UASB UASB
Vegetable Market Yard WasteVijayawda, Andhra Pradesh
20 tpd Vegetable market and slaughterhouse waste
UASB Power generation
Koyambedu, Tamil Nadu
30 tpd Vegetable waste BIMA Power generation
Municipal Wastewater/ SewageBhubaneshwar, Orissa
400 m3/d Domestic Sewage Fixed film Heating and illumination
Surat, Gujarat 0.5 MWe Domestic Sewage Anaerobic sludge
Power generation
Animal Agro ResidueKarur, Tamil Nadu 12000
m3/dBagasse wash water UASB Lime kiln
Ludhiana, Punjab 235 tpd Cattle manure BIMA Power generation
Fruit and Food Processing WasteDharmapuri, Tamil Nadu
12000 tpd Tapioca wastewater HUSMAR Power generation
[Stay Informed Subscribe to our Monthly Email Update] [Index] [Emagazine ] [News] [Libraries] [Products] [Search] [Advertise] [About Us]
© Earthtoys Inc. 2002 2007
AUGUST 2008
+ COVER PAGE
INTERVIEWS
+ ROGER COX THE EVOPOD
+ RAINER WISCHINSKI SPINWAVE SYSTEMS
ALTERNATIVE ENERGY
+ THINFILM SOLAR CELLS HEADING FOR $1 PER WP
+ SOLAR PHOTOVOLTAICS MARKET POTENTIAL
+ SOLAR THERMAL AND EVACUATED TUBE TECHNOLOGY
+ GEOTHERMAL IS NOT WHAT MANY PEOPLE THINK IT IS
+ WASTETOENERGY (WTE) CONVERSION
+ FUTURE PERSPECTIVES OF NUCLEAR POWER
+ TIOGA ENERGY REPORT – SOLAR PPA
+ HOW TO INFORM PEOPLE AWAY FROM SUSTAINABLE
ALTERNATIVETRANSPORTATION
+ BEAT ONE HUNDRED MPG
THE ENVIRONMENT
+ LIGHTS OUT FOR INCANDESCENTS & HALOGENS
+ THE GREEN DATA CENTER
+ GREEN ROOFING OPTIONS AND ADVANTAGES
Generally, the greater the economic prosperity and the higher percentage of urban population, the greater the amount of solid waste produced. Reduction in the volume and mass of solid waste is a crucial issue especially in the light of limited availability
of final disposal sites in many parts of the world.
Salman Zafar, WastetoEnergy Consultant Aligarh, India
1. INTRODUCTION
The enormous increase in the quantum and diversity of waste materials generated byhuman activity and their potentially harmful effects on the general environment andpublic health, have led to an increasing awareness, worldwide, about an urgent needto adopt scientific methods for safe disposal of wastes. While there is an obviousneed to minimize the generation of wastes and to reuse and recycle them, thetechnologies for recovery of energy from wastes can play a vital role in mitigating theproblems. Besides recovery of substantial energy, these technologies can lead to asubstantial reduction in the overall waste quantities requiring final disposal, which canbe better managed for safe disposal in a controlled manner while meeting thepollution control standards.
Waste generation rates are affected by socioeconomic development, degree ofindustrialization, and climate. Generally, the greater the economic prosperity and thehigher percentage of urban population, the greater the amount of solid wasteproduced. Reduction in the volume and mass of solid waste is a crucial issueespecially in the light of limited availability of final disposal sites in many parts of theworld. Although numerous waste and byproduct recovery processes have beenintroduced, anaerobic digestion has unique and integrative potential, simultaneouslyacting as a waste treatment and recovery process.
2. WASTETOENERGY CONVERSION PATHWAYS
There are three main pathways for conversion of organic waste material to energy – thermochemical, biochemical and physicochemical. Thermochemical conversion, characterized by higher temperature and conversion rates, is best suited for lower moisture feedstock and is generally less selective for products. Thermochemical conversion includes incineration, pyro lys is and gas i f ica t ion. The inc inerat ion technology is the controlled combustion of waste with the recovery of heat to produce steam which in turn produces power through steam turbines. Pyrolysis and gasification represent refined thermal treatment methods as alternatives to incineration and are characterized by the transformation of the waste into product gas as energy carrier for later combustion in, for example, a boiler or a gas engine.
The bio chemical conversion processes, which include anaerobic digestion and fermentation, are preferred for wastes having high percentage of organic biodegradable (putrescible) matter and high moisture content. Anaerobic digestioncan be used to recover both nutrients and energy contained in organic wastes suchas animal manure. The process generates gases with a high content of methane (55–70 %) as well as biofertilizer. Alcohol fermentation is the transformation of organicfraction of waste to ethanol by a series of biochemical reactions using specializedmicroorganisms.
The physicochemical technology involves various processes to improve physical andchemical properties of solid waste. The combustible fraction of the waste is convertedinto highenergy fuel pellets which may be used in steam generation. Fuel pelletshave several distinct advantages over coal and wood because it is cleaner, free fromincombustibles, has lower ash and moisture contents, is of uniform size, cost effective, and ecofriendly.
2.1 Factors affecting Energy Recovery
The two main factors which determine the potential of recovery of energy from wastesare the quantity and quality (physicochemical characteristics) of the waste. Some ofthe important physicochemical parameters requiring consideration include:
l Size of constituents
l Density
l Moisture content
l Volatile solids / Organic matter
l Fixed carbon
l Total inerts
l Calorific value
Often, an analysis of waste to determine the proportion of carbon, hydrogen, oxygen,nitrogen and sulfur (ultimate analysis) is done to make mass balance calculations, forboth thermochemical and biochemical processes. In case of anaerobic digestion, theparameters C/N ratio (a measure of nutrient concentration available for bacterialgrowth) and toxicity (representing the presence of hazardous materials which inhibitbacterial growth), also require consideration.
2.2 Significance of Wasteto Energy (WTE) Plants
While some still confuse modern wastetoenergy plants with incinerators of the past,the environmental performance of the industry is beyond reproach. Studies haveshown that communities that employ waste toenergy technology have higherrecycling rates than communities that do not utilize wastetoenergy. The recovery offerrous and nonferrous metals from wastetoenergy plants for recycling is strong andgrowing each year. In addition, numerous studies have determined that wastetoenergy plants actually reduce the amount of greenhouse gases that enter theatmosphere.
Nowadays, wastetoenergy plants based on combustion technologies are highlyefficient power plants that utilize municipal solid waste as their fuel rather than coal,oil or natural gas. Far better than expending energy to explore, recover, process andtransport the fuel from some distant source, wastetoenergy plants find value in whatothers consider garbage. Waste toenergy plants recover the thermal energycontained in the trash in highly efficient boilers that generate steam that can then besold directly to industrial customers, or used onsite to drive turbines for electricityproduction. WTE plants are highly efficient in harnessing the untapped energypotential of organic waste by converting the biodegradable fraction of the waste intohigh calorific value gases like methane. The digested portion of the waste is highlyrich in nutrients and is widely used as biofertilizer in many parts of the world.
2.3 WastetoEnergy around the World
To an even greater extent than in the United States, wastetoenergy has thrived inEurope and Asia as the preeminent method of waste disposal. Lauding wastetoenergy for its ability to reduce the volume of waste in an environmentally friendlymanner, generate valuable energy, and reduce greenhouse gas emissions, Europeannations rely on wastetoenergy as the preferred method of waste disposal. In fact,the European Union has issued a legally binding requirement for its member States tolimit the landfilling of biodegradable waste.
The Confederation of European WastetoEnergy Plants (CEWEP) notes that Europecurrently treats 50 million ton of wastes at waste toenergy plants each year,generating an amount of energy that can supply electricity for 27 million people orheat for 13 million people. Upcoming changes to EU legislation will have a profoundimpact on how much further the technology will help achieve environmental protectiongoals. Describing the advances of waste toenergy, the German Ministry for theEnvironment cites drastic reductions in emissions of dioxin, dust and mercury.Twenty years ago, 18 Swedish wastetoenergy plants emitted a total of about 100grams of dioxins every year. Today, the collective dioxin emissions from all 29Swedish wastetoenergy plants amount to 0.7 of a gram. It is clear that Europe hasmade similar strides as the United States with respect to emissions reductions.
3. FEEDSTOCK FOR WASTETOENERGY CONVERSION PLANTS
3.1 Agricultural Residues
Large quantities of crop residues are produced annually worldwide, and are vastlyunderutilised. The most common agricultural residue is the rice husk, which makesup 25% of rice by mass. Other residues include sugar cane fibre (known asbagasse), coconut husks and shells, groundnut shells, cereal straw etc. Currentfarming practice is usually to plough these residues back into the soil, or they areburnt, left to decompose, or grazed by cattle. A number of agricultural and biomassstudies, however, have concluded that it may be appropriate to remove and utilise aportion of crop residue for energy production, providing large volumes of low costmaterial. These residues could be processed into liquid fuels or combusted/gasifiedto produce electricity and heat.
3.2 Animal Waste
There are a wide range of animal wastes that can be used as sources of biomassenergy. The most common sources are animal and poultry manures. In the past thiswaste was recovered and sold as a fertilizer or simply spread onto agricultural land,but the introduction of tighter environmental controls on odour and water pollutionmeans that some form of waste management is now required, which provides furtherincentives for wastetoenergy conversion. The most attractive method of convertingthese waste materials to useful form is anaerobic digestion which gives biogas thatcan be used as a fuel for internal combustion engines, to generate electricity fromsmall gas turbines, burnt directly for cooking, or for space and water heating. Foodprocessing and abattoir wastes are also a potential anaerobic digestion feedstock.
3.3 Sugar Industry Wastes
The sugar cane industry produces large volumes of bagasse each year. Bagasse ispotentially a major source of biomass energy as it can be used as boiler feedstock togenerate steam for process heat and electricity production. Most sugar cane millsutilise bagasse to produce electricity for their own needs but some sugar mills areable to export substantial amount of electricity to the grid.
3.4 Forestry Residues
Forestry residues are generated by operations such as thinning of plantations,clearing for logging roads, extracting stemwood for pulp and timber, and naturalattrition. Wood processing also generates significant volumes of residues usually inthe form of sawdust, offcuts, bark and woodchip rejects. This waste material is oftennot utilised and often left to rot on site. However it can be collected and used in abiomass gasifier to produce hot gases for generating steam.
3.5 Industrial Wastes
The food industry produces a large number of residues and byproducts that can beused as biomass energy sources. These waste materials are generated from allsectors of the food industry with everything from meat production to confectioneryproducing waste that can be utilised as an energy source. Solid wastes includepeelings and scraps from fruit and vegetables, food that does not meet quality controlstandards, pulp and fibre from sugar and starch extraction, filter sludges and coffeegrounds. These wastes are usually disposed of in landfill dumps.
Liquid wastes are generated by washing meat, fruit and vegetables, blanching fruitand vegetables, precooking meats, poultry and fish, cleaning and processingoperations as well as wine making. These waste waters contain sugars, starches andother dissolved and solid organic matter. The potential exists for these industrialwastes to be anaerobically digested to produce biogas, or fermented to produceethanol, and several commercial examples of wastetoenergy conversion alreadyexist.
3.6 Municipal Solid Waste (MSW)
Millions of tonnes of household waste are collected each year with the vast majoritydisposed of in landfill dumps. The biomass resource in MSW comprises theputrescibles, paper and plastic and averages 80% of the total MSW collected.Municipal solid waste can be converted into energy by direct combustion, or bynatural anaerobic digestion in the landfill. At the landfill sites the gas produced by thenatural decomposition of MSW (approximately 50% methane and 50% carbondioxide) is collected from the stored material and scrubbed and cleaned beforefeeding into internal combustion engines or gas turbines to generate heat and power.The organic fraction of MSW can be anaerobically stabilized in a highrate digester toobtain biogas for electricity or steam generation.
3.7 Sewage
Sewage is a source of biomass energy that is very similar to the other animal wastes.Energy can be extracted from sewage using anaerobic digestion to produce biogas.The sewage sludge that remains can be incinerated or undergo pyrolysis to producemore biogas
3.8 Black Liquor
Pulp and Paper Industry is considered to be one of the highly polluting industries andconsumes large amount of energy and water in various unit operations. Thewastewater discharged by this industry is highly heterogeneous as it containscompounds from wood or other raw materials, processed chemicals as well ascompound formed during processing. Black liquor can be judiciously utilized forproduction of biogas using UASB technology.
Table 1. Summary of Successful WastetoEnergy Plants in India based on Anaerobic Digestion
4. CONCLUSIONS
The wastetoenergy plants offer two important benefits of environmentally safe wastemanagement and disposal, as well as the generation of clean electric power. Wastetoenergy facilities produce clean, renewable energy through thermochemical,biochemical and physicochemical methods. The growing use of wastetoenergy as amethod to dispose off solid and liquid wastes and generate power has greatly reducedenvironmental impacts of municipal solid waste management, including emissions ofgreenhouse gases. Wastetoenergy conversion reduces greenhouse gas emissionsin two ways. Electricity is generated which reduces the dependence on electricalproduction from power plants based on fossil fuels. The greenhouse gas emissionsare significantly reduced by preventing methane emissions from landfills. Moreover,wastetoenergy plants are highly efficient in harnessing the untapped sources ofenergy from a variety of wastes.
REFERENCES
1. Gunasegarane, G.S., Energy from Dairy Waste, Bio Energy News, 6, 2002, pp26.
2. Sirviö, A., and Rintala, J. A., Renewable Energy Production in Farm Scale:Biogas from Energy Crops, Bio Energy News, 6, 2002, pp 16.
3. Rao, R.P., Energy from Agro Waste A Case Study, Bio Energy News, 3,1999, pp 21.
4. Mapuskar, S.V., Biogas from Vegetable Market Waste at APMC Pune, BioEnergy News. 1, 1997, pp 16.
5. Dhussa A.K., and Varshney, A.K., Energy Recovery from Municipal SolidWaste Potential and Possibilities, Bio Energy News, 4, 2000, pp 7.
6. http://www.undp.org.in/env.htm
7. http://www.recoveredenergy.com/d_wte.html
8. http://www.wte.org
9. http://www.earthtoys.com/
10. http://www.undp.org.in/programme/GEF/Mar%202003/article2.htm
11. http://www.undp.org.in/Programme/GEF/march00/page1214.html
12. http://www.mnes.nic.in
13. http://mnes1.delhi.nic.in/bionews
14. http://www.renewingindia.org/finren.html
Leather & Abattoir Industry WasteLocation Capacity Feed type Type of
reactor used
Biogas utilization
Rudraram, Andhra Pradesh
60 tpd Abattoir waste BIMA Boiler fuel
Melvisharam, TamilNadu
5 tpd Fleshing & primary sludge
CSTR Aerator operation
Melvisharam, TamilNadu
2 tpd Tannery fleshing &sludge UASB Boiler fuel
Dewas, Madhya Pradesh
1.2 1.5 tpd
Chromed leather dust UASB UASB
Vegetable Market Yard WasteVijayawda, Andhra Pradesh
20 tpd Vegetable market and slaughterhouse waste
UASB Power generation
Koyambedu, Tamil Nadu
30 tpd Vegetable waste BIMA Power generation
Municipal Wastewater/ SewageBhubaneshwar, Orissa
400 m3/d Domestic Sewage Fixed film Heating and illumination
Surat, Gujarat 0.5 MWe Domestic Sewage Anaerobic sludge
Power generation
Animal Agro ResidueKarur, Tamil Nadu 12000
m3/dBagasse wash water UASB Lime kiln
Ludhiana, Punjab 235 tpd Cattle manure BIMA Power generation
Fruit and Food Processing WasteDharmapuri, Tamil Nadu
12000 tpd Tapioca wastewater HUSMAR Power generation
[Stay Informed Subscribe to our Monthly Email Update] [Index] [Emagazine ] [News] [Libraries] [Products] [Search] [Advertise] [About Us]
© Earthtoys Inc. 2002 2007
AUGUST 2008
+ COVER PAGE
INTERVIEWS
+ ROGER COX THE EVOPOD
+ RAINER WISCHINSKI SPINWAVE SYSTEMS
ALTERNATIVE ENERGY
+ THINFILM SOLAR CELLS HEADING FOR $1 PER WP
+ SOLAR PHOTOVOLTAICS MARKET POTENTIAL
+ SOLAR THERMAL AND EVACUATED TUBE TECHNOLOGY
+ GEOTHERMAL IS NOT WHAT MANY PEOPLE THINK IT IS
+ WASTETOENERGY (WTE) CONVERSION
+ FUTURE PERSPECTIVES OF NUCLEAR POWER
+ TIOGA ENERGY REPORT – SOLAR PPA
+ HOW TO INFORM PEOPLE AWAY FROM SUSTAINABLE
ALTERNATIVETRANSPORTATION
+ BEAT ONE HUNDRED MPG
THE ENVIRONMENT
+ LIGHTS OUT FOR INCANDESCENTS & HALOGENS
+ THE GREEN DATA CENTER
+ GREEN ROOFING OPTIONS AND ADVANTAGES
Generally, the greater the economic prosperity and the higher percentage of urban population, the greater the amount of solid waste produced. Reduction in the volume and mass of solid waste is a crucial issue especially in the light of limited availability
of final disposal sites in many parts of the world.
Salman Zafar, WastetoEnergy Consultant Aligarh, India
1. INTRODUCTION
The enormous increase in the quantum and diversity of waste materials generated byhuman activity and their potentially harmful effects on the general environment andpublic health, have led to an increasing awareness, worldwide, about an urgent needto adopt scientific methods for safe disposal of wastes. While there is an obviousneed to minimize the generation of wastes and to reuse and recycle them, thetechnologies for recovery of energy from wastes can play a vital role in mitigating theproblems. Besides recovery of substantial energy, these technologies can lead to asubstantial reduction in the overall waste quantities requiring final disposal, which canbe better managed for safe disposal in a controlled manner while meeting thepollution control standards.
Waste generation rates are affected by socioeconomic development, degree ofindustrialization, and climate. Generally, the greater the economic prosperity and thehigher percentage of urban population, the greater the amount of solid wasteproduced. Reduction in the volume and mass of solid waste is a crucial issueespecially in the light of limited availability of final disposal sites in many parts of theworld. Although numerous waste and byproduct recovery processes have beenintroduced, anaerobic digestion has unique and integrative potential, simultaneouslyacting as a waste treatment and recovery process.
2. WASTETOENERGY CONVERSION PATHWAYS
There are three main pathways for conversion of organic waste material to energy – thermochemical, biochemical and physicochemical. Thermochemical conversion, characterized by higher temperature and conversion rates, is best suited for lower moisture feedstock and is generally less selective for products. Thermochemical conversion includes incineration, pyro lys is and gas i f ica t ion. The inc inerat ion technology is the controlled combustion of waste with the recovery of heat to produce steam which in turn produces power through steam turbines. Pyrolysis and gasification represent refined thermal treatment methods as alternatives to incineration and are characterized by the transformation of the waste into product gas as energy carrier for later combustion in, for example, a boiler or a gas engine.
The bio chemical conversion processes, which include anaerobic digestion and fermentation, are preferred for wastes having high percentage of organic biodegradable (putrescible) matter and high moisture content. Anaerobic digestioncan be used to recover both nutrients and energy contained in organic wastes suchas animal manure. The process generates gases with a high content of methane (55–70 %) as well as biofertilizer. Alcohol fermentation is the transformation of organicfraction of waste to ethanol by a series of biochemical reactions using specializedmicroorganisms.
The physicochemical technology involves various processes to improve physical andchemical properties of solid waste. The combustible fraction of the waste is convertedinto highenergy fuel pellets which may be used in steam generation. Fuel pelletshave several distinct advantages over coal and wood because it is cleaner, free fromincombustibles, has lower ash and moisture contents, is of uniform size, cost effective, and ecofriendly.
2.1 Factors affecting Energy Recovery
The two main factors which determine the potential of recovery of energy from wastesare the quantity and quality (physicochemical characteristics) of the waste. Some ofthe important physicochemical parameters requiring consideration include:
l Size of constituents
l Density
l Moisture content
l Volatile solids / Organic matter
l Fixed carbon
l Total inerts
l Calorific value
Often, an analysis of waste to determine the proportion of carbon, hydrogen, oxygen,nitrogen and sulfur (ultimate analysis) is done to make mass balance calculations, forboth thermochemical and biochemical processes. In case of anaerobic digestion, theparameters C/N ratio (a measure of nutrient concentration available for bacterialgrowth) and toxicity (representing the presence of hazardous materials which inhibitbacterial growth), also require consideration.
2.2 Significance of Wasteto Energy (WTE) Plants
While some still confuse modern wastetoenergy plants with incinerators of the past,the environmental performance of the industry is beyond reproach. Studies haveshown that communities that employ waste toenergy technology have higherrecycling rates than communities that do not utilize wastetoenergy. The recovery offerrous and nonferrous metals from wastetoenergy plants for recycling is strong andgrowing each year. In addition, numerous studies have determined that wastetoenergy plants actually reduce the amount of greenhouse gases that enter theatmosphere.
Nowadays, wastetoenergy plants based on combustion technologies are highlyefficient power plants that utilize municipal solid waste as their fuel rather than coal,oil or natural gas. Far better than expending energy to explore, recover, process andtransport the fuel from some distant source, wastetoenergy plants find value in whatothers consider garbage. Waste toenergy plants recover the thermal energycontained in the trash in highly efficient boilers that generate steam that can then besold directly to industrial customers, or used onsite to drive turbines for electricityproduction. WTE plants are highly efficient in harnessing the untapped energypotential of organic waste by converting the biodegradable fraction of the waste intohigh calorific value gases like methane. The digested portion of the waste is highlyrich in nutrients and is widely used as biofertilizer in many parts of the world.
2.3 WastetoEnergy around the World
To an even greater extent than in the United States, wastetoenergy has thrived inEurope and Asia as the preeminent method of waste disposal. Lauding wastetoenergy for its ability to reduce the volume of waste in an environmentally friendlymanner, generate valuable energy, and reduce greenhouse gas emissions, Europeannations rely on wastetoenergy as the preferred method of waste disposal. In fact,the European Union has issued a legally binding requirement for its member States tolimit the landfilling of biodegradable waste.
The Confederation of European WastetoEnergy Plants (CEWEP) notes that Europecurrently treats 50 million ton of wastes at waste toenergy plants each year,generating an amount of energy that can supply electricity for 27 million people orheat for 13 million people. Upcoming changes to EU legislation will have a profoundimpact on how much further the technology will help achieve environmental protectiongoals. Describing the advances of waste toenergy, the German Ministry for theEnvironment cites drastic reductions in emissions of dioxin, dust and mercury.Twenty years ago, 18 Swedish wastetoenergy plants emitted a total of about 100grams of dioxins every year. Today, the collective dioxin emissions from all 29Swedish wastetoenergy plants amount to 0.7 of a gram. It is clear that Europe hasmade similar strides as the United States with respect to emissions reductions.
3. FEEDSTOCK FOR WASTETOENERGY CONVERSION PLANTS
3.1 Agricultural Residues
Large quantities of crop residues are produced annually worldwide, and are vastlyunderutilised. The most common agricultural residue is the rice husk, which makesup 25% of rice by mass. Other residues include sugar cane fibre (known asbagasse), coconut husks and shells, groundnut shells, cereal straw etc. Currentfarming practice is usually to plough these residues back into the soil, or they areburnt, left to decompose, or grazed by cattle. A number of agricultural and biomassstudies, however, have concluded that it may be appropriate to remove and utilise aportion of crop residue for energy production, providing large volumes of low costmaterial. These residues could be processed into liquid fuels or combusted/gasifiedto produce electricity and heat.
3.2 Animal Waste
There are a wide range of animal wastes that can be used as sources of biomassenergy. The most common sources are animal and poultry manures. In the past thiswaste was recovered and sold as a fertilizer or simply spread onto agricultural land,but the introduction of tighter environmental controls on odour and water pollutionmeans that some form of waste management is now required, which provides furtherincentives for wastetoenergy conversion. The most attractive method of convertingthese waste materials to useful form is anaerobic digestion which gives biogas thatcan be used as a fuel for internal combustion engines, to generate electricity fromsmall gas turbines, burnt directly for cooking, or for space and water heating. Foodprocessing and abattoir wastes are also a potential anaerobic digestion feedstock.
3.3 Sugar Industry Wastes
The sugar cane industry produces large volumes of bagasse each year. Bagasse ispotentially a major source of biomass energy as it can be used as boiler feedstock togenerate steam for process heat and electricity production. Most sugar cane millsutilise bagasse to produce electricity for their own needs but some sugar mills areable to export substantial amount of electricity to the grid.
3.4 Forestry Residues
Forestry residues are generated by operations such as thinning of plantations,clearing for logging roads, extracting stemwood for pulp and timber, and naturalattrition. Wood processing also generates significant volumes of residues usually inthe form of sawdust, offcuts, bark and woodchip rejects. This waste material is oftennot utilised and often left to rot on site. However it can be collected and used in abiomass gasifier to produce hot gases for generating steam.
3.5 Industrial Wastes
The food industry produces a large number of residues and byproducts that can beused as biomass energy sources. These waste materials are generated from allsectors of the food industry with everything from meat production to confectioneryproducing waste that can be utilised as an energy source. Solid wastes includepeelings and scraps from fruit and vegetables, food that does not meet quality controlstandards, pulp and fibre from sugar and starch extraction, filter sludges and coffeegrounds. These wastes are usually disposed of in landfill dumps.
Liquid wastes are generated by washing meat, fruit and vegetables, blanching fruitand vegetables, precooking meats, poultry and fish, cleaning and processingoperations as well as wine making. These waste waters contain sugars, starches andother dissolved and solid organic matter. The potential exists for these industrialwastes to be anaerobically digested to produce biogas, or fermented to produceethanol, and several commercial examples of wastetoenergy conversion alreadyexist.
3.6 Municipal Solid Waste (MSW)
Millions of tonnes of household waste are collected each year with the vast majoritydisposed of in landfill dumps. The biomass resource in MSW comprises theputrescibles, paper and plastic and averages 80% of the total MSW collected.Municipal solid waste can be converted into energy by direct combustion, or bynatural anaerobic digestion in the landfill. At the landfill sites the gas produced by thenatural decomposition of MSW (approximately 50% methane and 50% carbondioxide) is collected from the stored material and scrubbed and cleaned beforefeeding into internal combustion engines or gas turbines to generate heat and power.The organic fraction of MSW can be anaerobically stabilized in a highrate digester toobtain biogas for electricity or steam generation.
3.7 Sewage
Sewage is a source of biomass energy that is very similar to the other animal wastes.Energy can be extracted from sewage using anaerobic digestion to produce biogas.The sewage sludge that remains can be incinerated or undergo pyrolysis to producemore biogas
3.8 Black Liquor
Pulp and Paper Industry is considered to be one of the highly polluting industries andconsumes large amount of energy and water in various unit operations. Thewastewater discharged by this industry is highly heterogeneous as it containscompounds from wood or other raw materials, processed chemicals as well ascompound formed during processing. Black liquor can be judiciously utilized forproduction of biogas using UASB technology.
Table 1. Summary of Successful WastetoEnergy Plants in India based on Anaerobic Digestion
4. CONCLUSIONS
The wastetoenergy plants offer two important benefits of environmentally safe wastemanagement and disposal, as well as the generation of clean electric power. Wastetoenergy facilities produce clean, renewable energy through thermochemical,biochemical and physicochemical methods. The growing use of wastetoenergy as amethod to dispose off solid and liquid wastes and generate power has greatly reducedenvironmental impacts of municipal solid waste management, including emissions ofgreenhouse gases. Wastetoenergy conversion reduces greenhouse gas emissionsin two ways. Electricity is generated which reduces the dependence on electricalproduction from power plants based on fossil fuels. The greenhouse gas emissionsare significantly reduced by preventing methane emissions from landfills. Moreover,wastetoenergy plants are highly efficient in harnessing the untapped sources ofenergy from a variety of wastes.
REFERENCES
1. Gunasegarane, G.S., Energy from Dairy Waste, Bio Energy News, 6, 2002, pp26.
2. Sirviö, A., and Rintala, J. A., Renewable Energy Production in Farm Scale:Biogas from Energy Crops, Bio Energy News, 6, 2002, pp 16.
3. Rao, R.P., Energy from Agro Waste A Case Study, Bio Energy News, 3,1999, pp 21.
4. Mapuskar, S.V., Biogas from Vegetable Market Waste at APMC Pune, BioEnergy News. 1, 1997, pp 16.
5. Dhussa A.K., and Varshney, A.K., Energy Recovery from Municipal SolidWaste Potential and Possibilities, Bio Energy News, 4, 2000, pp 7.
6. http://www.undp.org.in/env.htm
7. http://www.recoveredenergy.com/d_wte.html
8. http://www.wte.org
9. http://www.earthtoys.com/
10. http://www.undp.org.in/programme/GEF/Mar%202003/article2.htm
11. http://www.undp.org.in/Programme/GEF/march00/page1214.html
12. http://www.mnes.nic.in
13. http://mnes1.delhi.nic.in/bionews
14. http://www.renewingindia.org/finren.html
Leather & Abattoir Industry WasteLocation Capacity Feed type Type of
reactor used
Biogas utilization
Rudraram, Andhra Pradesh
60 tpd Abattoir waste BIMA Boiler fuel
Melvisharam, TamilNadu
5 tpd Fleshing & primary sludge
CSTR Aerator operation
Melvisharam, TamilNadu
2 tpd Tannery fleshing &sludge UASB Boiler fuel
Dewas, Madhya Pradesh
1.2 1.5 tpd
Chromed leather dust UASB UASB
Vegetable Market Yard WasteVijayawda, Andhra Pradesh
20 tpd Vegetable market and slaughterhouse waste
UASB Power generation
Koyambedu, Tamil Nadu
30 tpd Vegetable waste BIMA Power generation
Municipal Wastewater/ SewageBhubaneshwar, Orissa
400 m3/d Domestic Sewage Fixed film Heating and illumination
Surat, Gujarat 0.5 MWe Domestic Sewage Anaerobic sludge
Power generation
Animal Agro ResidueKarur, Tamil Nadu 12000
m3/dBagasse wash water UASB Lime kiln
Ludhiana, Punjab 235 tpd Cattle manure BIMA Power generation
Fruit and Food Processing WasteDharmapuri, Tamil Nadu
12000 tpd Tapioca wastewater HUSMAR Power generation
