Waste-to-energy plant

Building that incinerates unusable garbage

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A waste-to-energy plant is a waste management facility that combusts wastes to produce electricity. This type of power plant is sometimes called a trash-to-energy, municipal waste incineration, energy recovery, or resource recovery plant.

Modern waste-to-energy plants are very different from the trash incinerators that were commonly used until a few decades ago. Unlike modern ones, those plants usually did not remove hazardous or recyclable materials before burning. These incinerators endangered the health of the plant workers and the nearby residents, and most of them did not generate electricity.

Waste-to-energy generation is being increasingly looked at as a potential energy diversification strategy, especially by Sweden, which has been a leader in waste-to-energy production over the past 20 years. The typical range of net electrical energy that can be produced is about 500 to 600 kWh of electricity per ton of waste incinerated.[1] Thus, the incineration of about 2,200 tons per day of waste will produce about 1,200 MWh of electrical energy.

Operation

Most waste-to-energy plants burn municipal solid waste, but some burn industrial waste or hazardous waste. A modern, properly run waste-to-energy plant sorts material before burning it and can co-exist with recycling. The only items that are burned are not recyclable, by design or economically, and are not hazardous.

Waste-to-energy plants are similar in their design and equipment with other steam-electric power plants, particularly biomass plants. First, the waste is brought to the facility. Then, the waste is sorted to remove recyclable and hazardous materials. The waste is then stored until it is time for burning. A few plants use gasification, but most combust the waste directly because it is a mature, efficient technology. The waste can be added to the boiler continuously or in batches, depending on the design of the plant.

In terms of volume, waste-to-energy plants incinerate 80 to 90 percent of waste. Sometimes, the residue ash is clean enough to be used for some purposes such as raw materials for use in manufacturing cinder blocks or for road construction. In addition, the metals that may be burned are collected from the bottom of the furnace and sold to foundries. Some waste-to-energy plants convert salt water to potable fresh water as a by-product of cooling processes.

Cost

The typical plant with a capacity of 400 GWh energy production annually costs about 440 million dollars to build. Waste-to-energy plants may have a significant cost advantage over traditional power options, as the waste-to-energy operator may receive revenue for receiving waste as an alternative to the cost of disposing of waste in a landfill, typically referred to as a "tipping fee" per ton basis, versus having to pay for the cost of fuel, whereas fuel cost can account for as much as 45 percent of the cost to produce electricity in a coal-powered plant, and 75 percent or more of the cost in a natural gas-powered plant. The National Solid Waste Management Association estimates that the average United States tipping fee for was $33.70 per ton.

Pollution

Waste-to-energy plants cause less air pollution than coal plants, but more than natural gas plants.[2] At the same time, it is carbon-negative: processing waste into fuel releases considerably less carbon and methane into the air than having waste decay away in landfills or bodies of water.[3]

Waste-to-energy plants are designed to reduce the emission of air pollutants in the flue gases exhausted to the atmosphere, such as nitrogen oxides, sulfur oxides and particulates, and to destroy pollutants already present in the waste, using pollution control measures such as baghouses, scrubbers, and electrostatic precipitators. High temperature, efficient combustion, and effective scrubbing and controls can significantly reduce air pollution outputs.

Burning municipal waste does produce significant amounts of dioxin and furan emissions[4] to the atmosphere as compared to the smaller amounts produced by burning coal or natural gas. Dioxins and furans are considered by many to be serious health hazards. However, advances in emission control designs and very stringent new governmental regulations, as well as public opposition to municipal waste incinerators, have caused large reductions in the amount of dioxins and furans produced by waste-to-energy plants.

Waste-to-energy plants produce fly ash and bottom ash just as is the case when coal is combusted. The total amount of ash produced by waste-to-energy plants ranges from 15% to 25% by weight of the original quantity of waste, and the fly ash amounts to about 10% to 20% of the total ash.[1] The fly ash, by far, constitutes more of a potential health hazard than does the bottom ash because the fly ash contains toxic metals such as lead, cadmium, copper, and zinc as well as small amounts of dioxins and furans.[5] The bottom ash may or may not contain significant levels of health hazardous materials. In the United States, and perhaps in other countries as well, the law requires that the ash be tested for toxicity before disposal in landfills. If the ash is found to be hazardous, it can only be disposed of in landfills which are carefully designed to prevent pollutants in the ash from leaching into underground aquifers.

Odor pollution can be a problem when the plant location is not isolated. Some plants store the waste in an enclosed area with a negative pressure, which prevents unpleasant odors from escaping, and the air drawn from the storage area is sent through the boiler or a filter. However, not all plants take steps to reduce the odor, resulting in complaints.

An issue that affects community relationships is the increased road traffic of garbage trucks to transport municipal waste to the waste-to-energy facility. Due to this reason, most waste-to-energy plants are located in industrial areas.

Landfill gas, which contains about 50% methane, and 50% carbon dioxide, is contaminated with a small amount of pollutants. Unlike at waste-to-energy plants, there are little or no pollution controls on the burning of landfill gas. The gas is usually flared or used to run a reciprocating engine or microturbine, especially in digester gas power plants. Cleaning up the landfill gas is usually not cost effective because natural gas, which it substitutes for, is relatively cheap.

See also

References

Introduction

Our first responsibility with respect to waste is to minimize it. Once we&#;ve done what we can to reduce, recycle, and reuse, we still have to do something with the residual. Converting waste to energy through incineration, gasification, or pyrolysis is a trash management strategy that can also reduce greenhouse gas emissions by reducing methane generation from landfills and releasing energy that can substitute for that generated by fossil fuels. However, it also can contaminate air, water, and land with toxic pollutants.

Project Drawdown&#;s Waste to Energy solution involves the combustion of waste to produce electricity and usable heat. It replaces conventional electricity-generating technologies such as coal, oil, and natural gas power plants. The magnitude of impact varies substantially depending on the baseline used. Key considerations include the caloric content of waste, the waste's methane generation potential, likely alternative disposal pathways, and the fossil fuels being displaced.

Conversion of waste to energy has seen wide adoption in Europe, the US, and Japan, and adoption is growing rapidly in China. Organisation for Economic Co-operation and Development (OECD) countries are most likely to see significant growth in market penetration moving forward. The primary barriers are high capital cost and the unreliable availability of municipal solid waste with a high heating value.

We consider waste-to-energy a &#;transition solution.&#; It can reduce greenhouse gas emissions, but social and environmental costs are high. It can help move us away from fossil fuels in the near term, but is not part of a clean energy future.

Methodology

We present waste-to-energy adoption in two ways: in terawatt-hours of electricity generation and in metric tons of waste produced.

Total Addressable Market

We based the total addressable market for the Waste to Energy solution on projected global electricity generation from to . The total addressable market is different for our two scenarios because Scenario 2 projects extensive electrification of transportation, space heating, etc., dramatically increasing demand and therefore production of electricity worldwide.

We estimated current adoption (the amount of functional demand supplied in ) at 0.54 percent of generation (142 terawatt-hours).

Adoption Scenarios

We calculated impacts of increased adoption of waste-to-energy from to by comparing two scenarios with a reference scenario in which the market share was fixed at current levels.

• Scenario 1: We based this scenario on the average yearly adoption of six custom scenarios derived from conservative adoption scenarios from the International Energy Agency (IEA, a) ETP 4DS and 6DS, Greenpeace () Energy [R]evolution and Advanced Energy [R]evolution scenarios, and different scenarios supported on the methodology suggested by Monni et al. (), applying different caps to waste-to-energy use. The solution supplies 340.32 terawatt-hours of electricity in (1 percent of total generation).
• Scenario 2: We based this scenario on the average yearly adoption of two custom scenarios derived from IEA (a) ETP 2DS and IEA (b) ETP Annex 1 methodology. The solution supplies 104.92 terawatt-hours of electricity in (<1 percent of total generation).

Emissions Model

Our assessment provided a regionally explicit forecast of waste-to-energy adoption and climate impacts, in terms of avoided methane and carbon dioxide emissions. We used the first-order decay method recommended by the Intergovernmental Panel on Climate Change (IPCC) to estimate total emissions reduction for conversion of waste to energy compared with sending the waste to a landfill.

Financial Model

All monetary values are presented in US$.

The financial inputs used in the model assume an average installation cost of US$6,795 per kilowatt. Since waste-to-energy conversation using incineration is a mature technology that has been in widespread use in OECD countries for decades, we applied a learning rate of 2 percent to first costs. We used an average capacity factor of 77 percent for waste-to-energy plants (based on historical data), compared with 57 percent for conventional technologies. We used fixed operation and maintenance costs of US$304.9 per kilowatt for waste-to-energy systems, compared with US$34.7 per kilowatt for conventional technologies.

Integration

We adjusted the total addressable market to account for reduced demand resulting from the growth of more energy-efficient solutions (e.g., LED Lighting and High Efficiency Heat Pumps) as well as increased electrification from other solutions, such as Electric Cars and High-Speed Rail. We calculated grid emissions factors based on the annual mix of different electricity-generating technologies over time. We determined emissions factors for each technology through a meta-analysis of multiple sources, accounting for direct and indirect emissions.

Adoption of the Waste to Energy solution is limited by the availability of municipal solid waste as a feedstock. This is a function of adoption of other waste management options, and is determined by our waste integration models. Landfill Methane Capture, Methane Digesters, Recycling, and Composting solutions all could affect the waste available for the Waste to Energy solution. The lower adoption trajectory in Scenario 2 is a result of the more substantial adoption of higher-priority solutions than in Scenario 1.

We converted metric tons of waste to terawatt-hours of electricity produced by multiplying an estimated heating value of waste and average efficiency of waste-to-energy plants.

Results

Scenario 1 avoids 6.27 gigatons of carbon dioxide equivalent greenhouse gas emissions. The net first cost to implement is US$244.81 billion from to , and the lifetime net operational cost is around US$79.08 billion.

Solution adoption is lower in Scenario 2 than in Scenario 1 because preferred Project Drawdown solutions have higher adoption. Scenario 2 results in carbon dioxide equivalent emissions reductions of 5.24 gigatons with a US$156.08 billion net first cost of implementation and US$10.32 billion in lifetime net operational costs.

Discussion

While preferable to landfilling, waste-to-energy conversion is seen as a bridge technology before other preferable waste management options become fully possible. Island nations may continue to use waste-to-energy conversation as an alternative to landfilling&#;employing more advanced technologies, such as plasma gasification, to limit the negative impacts.

Promotion of the Waste to Energy solution will be most successful where waste disposal and electricity costs are high and capital is readily available. Waste-to-energy conversion should be promoted appropriately in each region&#;s context, within a broader framework of integrated solid waste management. This is all the more important given the potentially significant public health risk that insufficiently regulated waste-to-energy conversion can pose (and historically has posed) to nearby communities. When appropriately strict pollution controls are in place, and when landfilling is a likely waste disposal alternative, waste-to-energy conversion will continue to provide an opportunity for societally beneficial greenhouse gas emissions reduction.

New waste-to-energy research in Europe and the US is relatively sparse as a result of the technology&#;s maturity. More active research is ongoing in East Asia and other regions. In general, research focuses on new technologies such as gasification, pyrolysis, and plasma-arc gasification. While these technologies are common in Japan, they have yet to become mainstream elsewhere.

References

Greenpeace. (). World Energy [R]evolution, a sustainable world energy outlook. Retrieved from: http://www.greenpeace.org/international/Global/international/publications/climate//Energy-Revolution--Full.pdf

IEA. (a). Energy Technology Perspectives - Towards Sustainable Urban Energy Systems. International Energy Agency. OECD/IEA, Paris, France. Retrieved from: https://www.iea.org/publications/freepublications/publication/EnergyTechnologyPerspectives_ExecutiveSummary_EnglishVersion.pdf

&#;&#;IEA. (b). Annex I: Municipal solid waste potential in cities. Retrieved November 14, , from http://www.iea.org/media/etp/etp/AnnexI_MSWpotential_web.pdf

Monni, Suvi, Riitta Pipatti, Antti Lehtila, Ilkka Savolainen, and Sanna Syri. (). Global Climate Change Mitigation Scenarios for Solid Waste Management. VTT Publications 603. Espoo. https://www.vtt.fi/inf/pdf/publications//P603.pdf

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