While waste to energy (WTE) is the third-most-preferred municipal solid waste approach behind source reduction/reuse and recycling/composting, some 29 million tons of MSW—12% of total generated—were combusted for energy recovery in 2011, according to “Municipal Solid Waste in the US: Facts and Figures.” The Energy Recovery Council—a national trade organization representing the WTE industry and communities owning WTE facilities—in its 2014 report indicates that there are 84 WTE facilities in the US, of which four are inactive but may return to active service at a later date; one is under construction.
Waste to Energy Defined
EPA depicts WTE as the conversion of non-recyclable waste materials into useable heat, electricity, or fuel through a variety of processes, including combustion, gasification, pyrolization, anaerobic digestion (AD), and landfill gas (LFG) recovery. After energy is recovered, about 10% of the volume remains ash and is typically landfilled. Mixed combined ash is used as alternative daily cover in landfills instead of soil.
While waste to energy (WTE) is the third-most-preferred municipal solid waste approach behind source reduction/reuse and recycling/composting, some 29 million tons of MSW—12% of total generated—were combusted for energy recovery in 2011, according to “Municipal Solid Waste in the US: Facts and Figures.” The Energy Recovery Council—a national trade organization representing the WTE industry and communities owning WTE facilities—in its 2014 report indicates that there are 84 WTE facilities in the US, of which four are inactive but may return to active service at a later date; one is under construction.
Waste to Energy Defined
EPA depicts WTE as the conversion of non-recyclable waste materials into useable heat, electricity, or fuel through a variety of processes, including combustion, gasification, pyrolization, anaerobic digestion (AD), and landfill gas (LFG) recovery. After energy is recovered, about 10% of the volume remains ash and is typically landfilled. Mixed combined ash is used as alternative daily cover in landfills instead of soil.
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Most WTE facilities combust special, non-hazardous wastes such as off-specification household products and goods that can’t be recycled. All types of waste—except radioactive wastes—can be combusted in a properly designed WTE, according to the Waste-to-Energy Research and Technology Council (WTERT), founded in 2002 by the Earth Engineering Center of Columbia University.
Under sponsorship of the InterAmerican Development Bank,
Columbia University’s Earth Engineering Center created a 228-page guidebook discussing various waste management technologies. Nickolas J. Themelis, Director of the Earth Engineering Center and chair of the Global WTERT Council, says while the US is not as “environmentally conscious” as Europe, there are various levels of commitment state-to-state. He adds that there are basically two major approaches to WTE conversion in the US: the moving grate, which entails a mass burn approach, and RDF, which entails pre-shredding—with a third being a rotary kiln.
Grate Combustion Waste to Energy
In grate combustion WTE, MSW bags and other wastes are discharged from collection vehicles into the waste bunker in a fully enclosed building, typically large enough to hold more than a week’s feedstock. An overhead claw crane loads the solids into the feed hopper of the WTE furnace, and a ram feeder at the bottom of the hopper pushes the wastes onto the moving grate, which can be inclined or horizontal, and air-cooled or water-cooled. The mechanical motion of the grate and the gravity force in the usual case of an inclined grate slowly moves the bed of solids through the combustion chamber.
The high-temperature oxidation in the combustion chamber reduces objects as large as a big suitcase to ash that’s discharged at the end of the moving grate. The heat contained in the combustion gases is transferred through the water-cooled furnace water wall and superheater tubes to the high-pressure steam that drives the turbine generator. The low-pressure steam from the generator exhaust can be used for district heating.
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Combustion has been tested and proven with over 600 plants worldwide, says Themelis. However, capital costs in building such plants are high, and the industry should search for ways to make them more productive, thus decreasing capital charge per ton of MSW processed. There are emerging technologies in China and northern Europe that seem less costly. A few technologies are showing potential for increased use.
The circulating fluidized bed process converts a bed of solids into a fluid by introducing a gas flow through the bottom of the bed. It is strong in China, where 40 plants have been constructed in the last 14 years. It is useful where there is a lot of food waste in the MSW.
Covanta’s CLEERGAS (Covanta Low Emission Energy Recovery Gasification) technology is also on a fast track, says Themelis. “From a theoretical point of view, it can cut down the capital costs,” he says. “You produce a gas which you burn more efficiently in a second chamber, and you need less excess air.”
CLEERGAS converts unprocessed, post-recycled MSW into a synthesis gas (syngas), which is then processed for very low-emissions energy recovery. How it works: MSW, which does not have to be pre-processed, is subjected to high temperatures and reduced air on the gasification platform where it undergoes a chemical reaction creating a synthesis gas. The syngas is combusted and processed through an established energy recovery system, followed by a state-of-the-art emissions control system.
According to Covanta, the CLEERGAS advanced control system is proven in a commercial operating environment to yield predictable and stable syngas from variable MSW fed into the gasifier. It has been processing 350 tons per day (tpd) of post-recycled MSW and has demonstrated “superior reliability” at more than 95% availability. The CLEERGAS process is designed to require less air than waste combustion for higher energy recovery efficiency, reduced boiler fouling and corrosion, and minimal formation of pollutants. A standard 300-tpd CLEERGAS modular plant will produce 6–8 MW of clean, renewable energy.
Themelis says it’s quite possible for different technologies to work side-by-side as long as a municipality can effectively separate the wastes into recyclables, compostables, and combustibles. The capital investment and ROI are major driving factors in WTE endeavors. One approach to affordability may be putting a tax on landfills like some European countries. “That provides a tremendous incentive,” says Themelis. “Europe has the carbon credit. When you take something from landfill to waste-to-energy, according to our estimates, you save from one ton, to a half ton of carbon dioxide, depending on the efficiency of collecting landfill gas. That would add to the value of waste-to-energy. Anything that produces energy at less carbon dioxide is more desirable and valuable.”
Most WTE facilities combust special, non-hazardous wastes such as off-specification household products and goods that can’t be recycled. All types of waste—except radioactive wastes—can be combusted in a properly designed WTE, according to the Waste-to-Energy Research and Technology Council (WTERT), founded in 2002 by the Earth Engineering Center of Columbia University.
Under sponsorship of the InterAmerican Development Bank, Columbia University’s Earth Engineering Center created a 228-page guidebook discussing various waste management technologies. Nickolas J. Themelis, Director of the Earth Engineering Center and chair of the Global WTERT Council, says while the US is not as “environmentally conscious” as Europe, there are various levels of commitment state-to-state. He adds that there are basically two major approaches to WTE conversion in the US: the moving grate, which entails a mass burn approach, and RDF, which entails pre-shredding—with a third being a rotary kiln.
Grate Combustion Waste to Energy
In grate combustion WTE, MSW bags and other wastes are discharged from collection vehicles into the waste bunker in a fully enclosed building, typically large enough to hold more than a week’s feedstock. An overhead claw crane loads the solids into the feed hopper of the WTE furnace, and a ram feeder at the bottom of the hopper pushes the wastes onto the moving grate, which can be inclined or horizontal, and air-cooled or water-cooled. The mechanical motion of the grate and the gravity force in the usual case of an inclined grate slowly moves the bed of solids through the combustion chamber.
The high-temperature oxidation in the combustion chamber reduces objects as large as a big suitcase to ash that’s discharged at the end of the moving grate. The heat contained in the combustion gases is transferred through the water-cooled furnace water wall and superheater tubes to the high-pressure steam that drives the turbine generator. The low-pressure steam from the generator exhaust can be used for district heating.
While waste to energy (WTE) is the third-most-preferred municipal solid waste approach behind source reduction/reuse and recycling/composting, some 29 million tons of MSW—12% of total generated—were combusted for energy recovery in 2011, according to “Municipal Solid Waste in the US: Facts and Figures.” The Energy Recovery Council—a national trade organization representing the WTE industry and communities owning WTE facilities—in its 2014 report indicates that there are 84 WTE facilities in the US, of which four are inactive but may return to active service at a later date; one is under construction.
Waste to Energy Defined
EPA depicts WTE as the conversion of non-recyclable waste materials into useable heat, electricity, or fuel through a variety of processes, including combustion, gasification, pyrolization, anaerobic digestion (AD), and landfill gas (LFG) recovery. After energy is recovered, about 10% of the volume remains ash and is typically landfilled. Mixed combined ash is used as alternative daily cover in landfills instead of soil.
[text_ad]
Most WTE facilities combust special, non-hazardous wastes such as off-specification household products and goods that can’t be recycled. All types of waste—except radioactive wastes—can be combusted in a properly designed WTE, according to the Waste-to-Energy Research and Technology Council (WTERT), founded in 2002 by the Earth Engineering Center of Columbia University.
Under sponsorship of the InterAmerican Development Bank,
Columbia University’s Earth Engineering Center created a 228-page guidebook discussing various waste management technologies. Nickolas J. Themelis, Director of the Earth Engineering Center and chair of the Global WTERT Council, says while the US is not as “environmentally conscious” as Europe, there are various levels of commitment state-to-state. He adds that there are basically two major approaches to WTE conversion in the US: the moving grate, which entails a mass burn approach, and RDF, which entails pre-shredding—with a third being a rotary kiln.
Grate Combustion Waste to Energy
In grate combustion WTE, MSW bags and other wastes are discharged from collection vehicles into the waste bunker in a fully enclosed building, typically large enough to hold more than a week’s feedstock. An overhead claw crane loads the solids into the feed hopper of the WTE furnace, and a ram feeder at the bottom of the hopper pushes the wastes onto the moving grate, which can be inclined or horizontal, and air-cooled or water-cooled. The mechanical motion of the grate and the gravity force in the usual case of an inclined grate slowly moves the bed of solids through the combustion chamber.
The high-temperature oxidation in the combustion chamber reduces objects as large as a big suitcase to ash that’s discharged at the end of the moving grate. The heat contained in the combustion gases is transferred through the water-cooled furnace water wall and superheater tubes to the high-pressure steam that drives the turbine generator. The low-pressure steam from the generator exhaust can be used for district heating.
[text_ad]
Combustion has been tested and proven with over 600 plants worldwide, says Themelis. However, capital costs in building such plants are high, and the industry should search for ways to make them more productive, thus decreasing capital charge per ton of MSW processed. There are emerging technologies in China and northern Europe that seem less costly. A few technologies are showing potential for increased use.
The circulating fluidized bed process converts a bed of solids into a fluid by introducing a gas flow through the bottom of the bed. It is strong in China, where 40 plants have been constructed in the last 14 years. It is useful where there is a lot of food waste in the MSW.
Covanta’s CLEERGAS (Covanta Low Emission Energy Recovery Gasification) technology is also on a fast track, says Themelis. “From a theoretical point of view, it can cut down the capital costs,” he says. “You produce a gas which you burn more efficiently in a second chamber, and you need less excess air.”
CLEERGAS converts unprocessed, post-recycled MSW into a synthesis gas (syngas), which is then processed for very low-emissions energy recovery. How it works: MSW, which does not have to be pre-processed, is subjected to high temperatures and reduced air on the gasification platform where it undergoes a chemical reaction creating a synthesis gas. The syngas is combusted and processed through an established energy recovery system, followed by a state-of-the-art emissions control system.
According to Covanta, the CLEERGAS advanced control system is proven in a commercial operating environment to yield predictable and stable syngas from variable MSW fed into the gasifier. It has been processing 350 tons per day (tpd) of post-recycled MSW and has demonstrated “superior reliability” at more than 95% availability. The CLEERGAS process is designed to require less air than waste combustion for higher energy recovery efficiency, reduced boiler fouling and corrosion, and minimal formation of pollutants. A standard 300-tpd CLEERGAS modular plant will produce 6–8 MW of clean, renewable energy.
Themelis says it’s quite possible for different technologies to work side-by-side as long as a municipality can effectively separate the wastes into recyclables, compostables, and combustibles. The capital investment and ROI are major driving factors in WTE endeavors. One approach to affordability may be putting a tax on landfills like some European countries. “That provides a tremendous incentive,” says Themelis. “Europe has the carbon credit. When you take something from landfill to waste-to-energy, according to our estimates, you save from one ton, to a half ton of carbon dioxide, depending on the efficiency of collecting landfill gas. That would add to the value of waste-to-energy. Anything that produces energy at less carbon dioxide is more desirable and valuable.”
Combustion has been tested and proven with over 600 plants worldwide, says Themelis. However, capital costs in building such plants are high, and the industry should search for ways to make them more productive, thus decreasing capital charge per ton of MSW processed. There are emerging technologies in China and northern Europe that seem less costly. A few technologies are showing potential for increased use.
The circulating fluidized bed process converts a bed of solids into a fluid by introducing a gas flow through the bottom of the bed. It is strong in China, where 40 plants have been constructed in the last 14 years. It is useful where there is a lot of food waste in the MSW.
Covanta’s CLEERGAS (Covanta Low Emission Energy Recovery Gasification) technology is also on a fast track, says Themelis. “From a theoretical point of view, it can cut down the capital costs,” he says. “You produce a gas which you burn more efficiently in a second chamber, and you need less excess air.”
CLEERGAS converts unprocessed, post-recycled MSW into a synthesis gas (syngas), which is then processed for very low-emissions energy recovery. How it works: MSW, which does not have to be pre-processed, is subjected to high temperatures and reduced air on the gasification platform where it undergoes a chemical reaction creating a synthesis gas. The syngas is combusted and processed through an established energy recovery system, followed by a state-of-the-art emissions control system.
According to Covanta, the CLEERGAS advanced control system is proven in a commercial operating environment to yield predictable and stable syngas from variable MSW fed into the gasifier. It has been processing 350 tons per day (tpd) of post-recycled MSW and has demonstrated “superior reliability” at more than 95% availability. The CLEERGAS process is designed to require less air than waste combustion for higher energy recovery efficiency, reduced boiler fouling and corrosion, and minimal formation of pollutants. A standard 300-tpd CLEERGAS modular plant will produce 6–8 MW of clean, renewable energy.
Themelis says it’s quite possible for different technologies to work side-by-side as long as a municipality can effectively separate the wastes into recyclables, compostables, and combustibles. The capital investment and ROI are major driving factors in WTE endeavors. One approach to affordability may be putting a tax on landfills like some European countries. “That provides a tremendous incentive,” says Themelis. “Europe has the carbon credit. When you take something from landfill to waste-to-energy, according to our estimates, you save from one ton, to a half ton of carbon dioxide, depending on the efficiency of collecting landfill gas. That would add to the value of waste-to-energy. Anything that produces energy at less carbon dioxide is more desirable and valuable.”
