Coal pollution mitigation

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Emissions controls at a coal fired power plant Figure 1- Sample Layout of Emissions Controls at a Coal Power Plant (7315637538) (cropped).jpg
Emissions controls at a coal fired power plant

Coal pollution mitigation, sometimes labeled as clean coal, is a series of systems and technologies that seek to mitigate health and environmental impact of burning coal for energy. Burning coal releases harmful substances that contribute to air pollution, acid rain, and greenhouse gas emissions. Mitigation includes precombustion approaches, such as cleaning coal, and post combustion approaches, include flue-gas desulfurization, selective catalytic reduction, electrostatic precipitators, and fly ash reduction. These measures aim to reduce coal's impact on human health and the environment.

Contents

The combustion of coal releases diverse chemicals into the air. The main products are water and carbon dioxide, just like the combustion of petroleum. Also released are sulfur dioxide and nitrogen oxides, as well as some mercury. The residue remaining after combustion, coal ash often contains arsenic, mercury, and lead. Finally, the burning of coal, especially anthracite, can release radioactive materials. [1]

Mitigation technologies

Mitigation of coal-based pollution can be divided into several distinct approaches. Coal pollution mitigation seek to minimize negative impacts of coal combustion. [2]

Precombustion

Prior to its combustion, coal can be cleaned by physical and by chemical means.

Physical cleaning of coal usually involves gravimetric processes, often in conjunction with froth flotation Such processes remove minerals and other noncombustible components of coal, exploiting their greater density vs that of coal. This technology is widely practiced.

Coal can also be cleaned in part by chemical treatments. The concept is to use chemicals to remove deleterious components of coal, leaving the combustible material behind. Typically, coal cleaning entails treatment of crushed coal with acids or bases. This technology is expensive and has rarely moved beyond the demonstration phase. During World War II, German industry removed ash from coal by treatments with hydrofluoric acid and related reagents. [2]

Post-combustion

The wastes produced by the combustion of coal can be classified into three categories: gases, particulates, and solids (ash). The gaseous products can be filtered and scrubbed to miminize the release of SOx, NOx, mercury:

Electrostatic precipitators remove particulates. Wet scrubbers can remove both gases and particulates.

Ash

The solid residue, coal ash, requires separate set of technologies but usually involves landfilling or some immobilization approaches. Reducing fly ash reduces emissions of radioactive materials.

Carbon capture

Several different technological methods are available for carbon capture:

Satellite monitoring

Satellite monitoring is now used to crosscheck national data, for example Sentinel-5 Precursor has shown that Chinese control of SO2 has only been partially successful. [7] It has also revealed that low use of technology such as SCR has resulted in high NO2 emissions in South Africa and India. [8]

Combined cycle power plants

A few Integrated gasification combined cycle (IGCC) coal-fired power plants have been built with coal gasification. Although they burn coal more efficiently and therefore emit less pollution, the technology has not generally proved economically viable for coal, except possibly in Japan although this is controversial. [9] [10]

Case studies

In conjunction with enhanced oil recovery and other applications, commercial-scale CCS is currently being tested in several countries.[ by whom?] Proposed CCS sites are subjected to extensive investigation and monitoring to avoid potential hazards, which could include leakage of sequestered CO2 to the atmosphere, induced geological instability, or contamination of water sources such as oceans and aquifers used for drinking water supplies. As of 2021, the only demonstrator for CCS on a coal plant that stores the gas underground is part of the Boundary Dam Power Station.[ citation needed ]

The Great Plains Synfuels plant supports the technical feasibility of carbon dioxide sequestration. Carbon dioxide from the coal gasification is shipped to Canada, where it is injected into the ground to aid in oil recovery. A drawback of the carbon sequestration process is that it is expensive compared to traditional processes.

The Kemper County IGCC Project, a proposed 582 MW coal gasification-based power plant, was expected to use pre-combustion capture of CO2 to capture 65% of the CO2 the plant produces, which would have been utilized and geologically sequestered in enhanced oil recovery operations. [11] However, after many delays and a cost runup to $7.5 billion (triple the initial budget), [12] the coal gasification project was abandoned and as of late 2017, Kemper is under construction as a cheaper natural gas power plant. [13]

The Saskatchewan Government's Boundary Dam Integrated Carbon Capture and Sequestration Demonstration Project will use post-combustion, amine-based scrubber technology to capture 90% of the CO2 emitted by Unit 3 of the power plant; this CO2 will be pipelined to and utilized for enhanced oil recovery in the Weyburn oil fields. [14]

An oxyfuel CCS power plant operation processes the exhaust gases so as to separate the CO2 so that it may be stored or sequestered Oxyfuel CCS fossil fuel power plant operation.png
An oxyfuel CCS power plant operation processes the exhaust gases so as to separate the CO2 so that it may be stored or sequestered

An early example of a coal-based plant using (oxy-fuel) carbon-capture technology is Swedish company Vattenfall’s Schwarze Pumpe power station located in Spremberg, Germany, built by German firm Siemens, which went on-line in September 2008. [15] [16] The facility captures CO2 and acid rain producing pollutants, separates them, and compresses the CO2 into a liquid. Plans are to inject the CO2 into depleted natural gas fields or other geological formations. Vattenfall opines that this technology is considered not to be a final solution for CO2 reduction in the atmosphere, but provides an achievable solution in the near term while more desirable alternative solutions to power generation can be made economically practical. [16]

Other examples of oxy-combustion carbon capture are in progress. Callide Power Station has retrofitted a 30-MWth existing PC-fired power plant to operate in oxy-fuel mode; in Ciuden, Spain, Endesa has a newly built 30-MWth oxy-fuel plant using circulating fluidized bed combustion (CFBC) technology. [17] Babcock-ThermoEnergy's Zero Emission Boiler System (ZEBS) is oxy-combustion-based; this system features near 100% carbon-capture and according to company information virtually no air-emissions. [18]

Other carbon capture and storage technologies include those that dewater low-rank coals. Low-rank coals often contain a higher level of moisture content which contains a lower energy content per tonne. This causes a reduced burning efficiency and an increased emissions output. Reduction of moisture from the coal prior to combustion can reduce emissions by up to 50 percent. [19] [ citation needed ]

In the late 1980s and early 1990s, the U.S. Department of Energy (DOE) conducted projects called the Clean Coal Technology & Clean Coal Power Initiative (CCPI). [20] [21]

Financial impact

Whether carbon capture and storage technology is adopted worldwide will "...depend less on science than on economics. Cleaning coal is very expensive." [22]

Cost of converting a single coal-fired power plant

Conversion of a conventional coal-fired power plant is done by injecting the CO2 into ammonium carbonate after which it is then transported and deposited underground (preferably in soil beneath the sea). [23] This injection process however is by far the most expensive. Besides the cost of the equipment and the ammonium carbonate, the coal-fired power plant also needs to use 30% of its generated heat to do the injection (parasitic load). A test-setup has been done in the American Electric Power Mountaineer coal-burning power plant.

One solution to reduce this thermal loss/parasitic load is to burn the pulverised load with pure oxygen instead of air. [23]

Cost implications for new coal-fired power plants

Newly built coal-fired power plants can be made to immediately use gasification of the coal prior to combustion. This makes it much easier to separate off the CO2 from the exhaust fumes, making the process cheaper. This gasification process is done in new coal-burning power plants such as the coal-burning power plant at Tianjin, called "GreenGen".

Country by country experiences

Local pollution standards include GB13223-2011 (China), India, [24] the Industrial Emissions Directive (EU) and the Clean Air Act (United States).

China

Since 2006, China releases more CO2 than any other country. [25] [26] [27] [28] [29] Researchers in China are focusing on increasing efficiency of burning coal so they can get more power out of less coal. [30] It is estimated that new high efficiency power plants could reduce CO2 emission by 7% because they won't have to burn as much coal to get the same amount of power. [30]

As of 2019 costs of retrofitting CCS are unclear and the economics depends partly on how the Chinese national carbon trading scheme progresses. [31]

India

Pollution led to more than 2.3 million premature deaths in India in 2019, according to a new Lancet study. Nearly 1.6 million deaths were due to air pollution alone, and more than 500,000 were caused by water pollution. India has developed instruments and regulatory powers to mitigate pollution sources but there is no centralized system to drive pollution control efforts and achieve substantial improvements," the study said adding that in 93% of the country, the amount of pollution remains well above the World Health Organization (WHO) guidelines. [32]

Canada

In 2014 SaskPower a provincial-owned electric utility finished renovations on Boundary Dam's boiler number 3 making it the world's first post-combustion carbon capture storage facility. [33] The renovation project ended up costing a little over $1.2 billion and can scrub out CO2 and toxins from up to 90 percent of the flue gas that it emits. [33]

Japan

Following the catastrophic failure of the Fukushima I Nuclear Power Plant in Japan that resulted from the 2011 Tōhoku earthquake and tsunami, and the subsequent widespread public opposition against nuclear power, high energy, lower emission (HELE) coal power plants were increasingly favored by the Shinzō Abe-led government to recoup lost energy capacity from the partial shutdown of nuclear power plants in Japan and to replace aging coal and oil-fired power plants, while meeting 2030 emission targets of the Paris Agreement. 45 HELE power plants have been planned, purportedly to employ integrated gasification fuel cell cycle, a further development of integrated gasification combined cycle. [34] [35]

Japan had adopted prior pilot projects on IGCC coal power plants in the early-1990s and late-2000s.

U.S.

In the United States, clean coal was mentioned by former President George W. Bush on several occasions, including his 2007 State of the Union Address. Bush's position was that carbon capture and storage technologies should be encouraged as one means to reduce the country's dependence on foreign oil.

During the US Presidential campaign for 2008, both candidates John McCain and Barack Obama expressed interest in the development of CCS technologies as part of an overall comprehensive energy plan. The development of pollution mitigation technologies could also create export business for the United States or any other country working on it.

The American Reinvestment and Recovery Act allocated $3.4 billion for advanced carbon capture and storage technologies, including demonstration projects.

Former Secretary of State Hillary Clinton has said that "we should strive to have new electricity generation come from other sources, such as clean coal and renewables", and former Energy Secretary Dr. Steven Chu has said that "It is absolutely worthwhile to invest in carbon capture and storage", noting that even if the U.S. and Europe turned their backs on coal, developing nations like India and China would likely not.

During the first 2012 United States presidential election debate, Mitt Romney expressed his support for clean coal, and claimed that current federal policies were hampering the coal industry. [36]

During the Trump administration, an Office of Clean Coal and Carbon Management was set up within the United States Department of Energy, but was abolished in the Biden administration.

See also

Health and environmental impact of the coal industry

Related Research Articles

<span class="mw-page-title-main">Gasification</span> Form of energy conversion

Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (CO2). This is achieved by reacting the feedstock material at high temperatures (typically >700 °C), without combustion, via controlling the amount of oxygen and/or steam present in the reaction. The resulting gas mixture is called syngas (from synthesis gas) or producer gas and is itself a fuel due to the flammability of the H2 and CO of which the gas is largely composed. Power can be derived from the subsequent combustion of the resultant gas, and is considered to be a source of renewable energy if the gasified compounds were obtained from biomass feedstock.

<span class="mw-page-title-main">FutureGen</span> Cancelled coal power station project

FutureGen was a project to demonstrate capture and sequestration of waste carbon dioxide from a coal-fired electrical generating station. The project (renamed FutureGen 2.0) was retrofitting a shuttered coal-fired power plant in Meredosia, Illinois, with oxy-combustion generators. The waste CO2 would be piped approximately 30 miles (48 km) to be sequestered in underground saline formations. FutureGen was a partnership between the United States government and an alliance of primarily coal-related corporations. Costs were estimated at US$1.65 billion, with $1.0 billion provided by the Federal Government.

In industrial chemistry, coal gasification is the process of producing syngas—a mixture consisting primarily of carbon monoxide (CO), hydrogen, carbon dioxide, methane, and water vapour —from coal and water, air and/or oxygen.

<span class="mw-page-title-main">Fossil fuel power station</span> Facility that burns fossil fuels to produce electricity

A fossil fuel power station is a thermal power station which burns a fossil fuel, such as coal, oil, or natural gas, to produce electricity. Fossil fuel power stations have machinery to convert the heat energy of combustion into mechanical energy, which then operates an electrical generator. The prime mover may be a steam turbine, a gas turbine or, in small plants, a reciprocating gas engine. All plants use the energy extracted from the expansion of a hot gas, either steam or combustion gases. Although different energy conversion methods exist, all thermal power station conversion methods have their efficiency limited by the Carnot efficiency and therefore produce waste heat.

<span class="mw-page-title-main">National Energy Technology Laboratory</span> United States research lab

The National Energy Technology Laboratory (NETL) is a U.S. national laboratory under the Department of Energy Office of Fossil Energy. NETL focuses on applied research for the clean production and use of domestic energy resources. It performs research and development on the supply, efficiency, and environmental constraints of producing and using fossil energy resources while maintaining affordability.

<span class="mw-page-title-main">Flue gas</span> Gas exiting to the atmosphere via a flue

Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases, as from a fireplace, oven, furnace, boiler or steam generator. It often refers to the exhaust gas of combustion at power plants. Technology is available to remove pollutants from flue gas at power plants.

<span class="mw-page-title-main">Carbon capture and storage</span> Collecting carbon dioxide from industrial emissions

Carbon capture and storage (CCS) is a process in which a relatively pure stream of carbon dioxide (CO2) from industrial sources is separated, treated and transported to a long-term storage location. For example, the burning of fossil fuels or biomass results in a stream of CO2 that could be captured and stored by CCS. Usually the CO2 is captured from large point sources, such as a chemical plant or a bioenergy plant, and then stored in a suitable geological formation. The aim is to reduce greenhouse gas emissions and thus mitigate climate change. For example, CCS retrofits for existing power plants can be one of the ways to limit emissions from the electricity sector and meet the Paris Agreement goals.

An integrated gasification combined cycle (IGCC) is a technology using a high pressure gasifier to turn coal and other carbon based fuels into pressurized gas—synthesis gas (syngas). It can then remove impurities from the syngas prior to the electricity generation cycle. Some of these pollutants, such as sulfur, can be turned into re-usable byproducts through the Claus process. This results in lower emissions of sulfur dioxide, particulates, mercury, and in some cases carbon dioxide. With additional process equipment, a water-gas shift reaction can increase gasification efficiency and reduce carbon monoxide emissions by converting it to carbon dioxide. The resulting carbon dioxide from the shift reaction can be separated, compressed, and stored through sequestration. Excess heat from the primary combustion and syngas fired generation is then passed to a steam cycle, similar to a combined cycle gas turbine. This process results in improved thermodynamic efficiency, compared to conventional pulverized coal combustion.

<span class="mw-page-title-main">Oxy-fuel combustion process</span> Burning of fuel with pure oxygen

Oxy-fuel combustion is the process of burning a fuel using pure oxygen, or a mixture of oxygen and recirculated flue gas, instead of air. Since the nitrogen component of air is not heated, fuel consumption is reduced, and higher flame temperatures are possible. Historically, the primary use of oxy-fuel combustion has been in welding and cutting of metals, especially steel, since oxy-fuel allows for higher flame temperatures than can be achieved with an air-fuel flame. It has also received a lot of attention in recent decades as a potential carbon capture and storage technology.

<span class="mw-page-title-main">Chemical looping combustion</span>

Chemical looping combustion (CLC) is a technological process typically employing a dual fluidized bed system. CLC operated with an interconnected moving bed with a fluidized bed system, has also been employed as a technology process. In CLC, a metal oxide is employed as a bed material providing the oxygen for combustion in the fuel reactor. The reduced metal is then transferred to the second bed and re-oxidized before being reintroduced back to the fuel reactor completing the loop. Fig 1 shows a simplified diagram of the CLC process. Fig 2 shows an example of a dual fluidized bed circulating reactor system and a moving bed-fluidized bed circulating reactor system.

Carbon capture and storage (CCS) is a technology that can capture carbon dioxide CO2 emissions produced from fossil fuels in electricity, industrial processes which prevents CO2 from entering the atmosphere. Carbon capture and storage is also used to sequester CO2 filtered out of natural gas from certain natural gas fields. While typically the CO2 has no value after being stored, Enhanced Oil Recovery uses CO2 to increase yield from declining oil fields.

The milestones for carbon capture and storage show the lack of commercial scale development and implementation of CCS over the years since the first carbon tax was imposed.

<span class="mw-page-title-main">Bioenergy with carbon capture and storage</span>

Bioenergy with carbon capture and storage (BECCS) is the process of extracting bioenergy from biomass and capturing and storing the carbon, thereby removing it from the atmosphere. BECCS can theoretically be a "negative emissions technology" (NET), although its deployment at the scale considered by many governments and industries can "also pose major economic, technological, and social feasibility challenges; threaten food security and human rights; and risk overstepping multiple planetary boundaries, with potentially irreversible consequences". The carbon in the biomass comes from the greenhouse gas carbon dioxide (CO2) which is extracted from the atmosphere by the biomass when it grows. Energy ("bioenergy") is extracted in useful forms (electricity, heat, biofuels, etc.) as the biomass is utilized through combustion, fermentation, pyrolysis or other conversion methods.

The Kędzierzyn Zero-Emission Power and Chemical Complex was a proposed facility in Kędzierzyn-Koźle, Poland. It was planned to combine the functions of power and heat generation with chemical production and carbon capture and storage. The project was proposed by a consortium of chemicals producers, including Zakłady Azotowe Kędzierzyn and the electricity company Południowy Koncern Energetyczny. The facility would have produced synthesis gas by gasification of hard coal. Gas produced by the plant would have been used for power and heat generation, or for the production of other chemicals.

GreenGen is a project in Tianjin, China that aims to research and develop high-tech low-emissions coal-based power generation plants.

<span class="mw-page-title-main">Kemper Project</span> Power station in Mississippi, US

The Kemper Project, also called the Kemper County energy facility or Plant Ratcliffe, is a natural gas-fired electrical generating station currently under construction in Kemper County, Mississippi. Mississippi Power, a subsidiary of Southern Company, began construction of the plant in 2010. The initial, coal-fired project was central to President Obama's Climate Plan, as it was to be based on "clean coal" and was being considered for more support from the Congress and the incoming Trump Administration in late 2016. If it had become operational with coal, the Kemper Project would have been a first-of-its-kind electricity plant to employ gasification and carbon capture technologies at this scale.

<span class="mw-page-title-main">Hydrogen Energy California</span> Alternate energy and hydrogen power project

Hydrogen Energy California (HECA) was a proposed alternative energy hydrogen power project developing with support from the U.S. Department of Energy in Kern County, California which was not approved for construction.

Coal gasification is a process whereby a hydrocarbon feedstock (coal) is converted into gaseous components by applying heat under pressure in the presence of steam. Rather than burning, most of the carbon-containing feedstock is broken apart by chemical reactions that produce "syngas." Syngas is primarily hydrogen and carbon monoxide, but the exact composition can vary. In Integrated Gasification Combined Cycle (IGCC) systems, the syngas is cleaned and burned as fuel in a combustion turbine which then drives an electric generator. Exhaust heat from the combustion turbine is recovered and used to create steam for a steam turbine-generator. The use of these two types of turbines in combination is one reason why gasification-based power systems can achieve high power generation efficiencies. Currently, commercially available gasification-based systems can operate at around 40% efficiencies. Syngas, however, emits more greenhouse gases than natural gas, and almost twice as much carbon as a coal plant. Coal gasification is also water-intensive.

Lower-temperature fuel cell types such as the proton exchange membrane fuel cell, phosphoric acid fuel cell, and alkaline fuel cell require pure hydrogen as fuel, typically produced from external reforming of natural gas. However, fuels cells operating at high temperature such as the solid oxide fuel cell (SOFC) are not poisoned by carbon monoxide and carbon dioxide, and in fact can accept hydrogen, carbon monoxide, carbon dioxide, steam, and methane mixtures as fuel directly, because of their internal shift and reforming capabilities. This opens up the possibility of efficient fuel cell-based power cycles consuming solid fuels such as coal and biomass, the gasification of which results in syngas containing mostly hydrogen, carbon monoxide and methane which can be cleaned and fed directly to the SOFCs without the added cost and complexity of methane reforming, water gas shifting and hydrogen separation operations which would otherwise be needed to isolate pure hydrogen as fuel. A power cycle based on gasification of solid fuel and SOFCs is called an Integrated Gasification Fuel Cell (IGFC) cycle; the IGFC power plant is analogous to an integrated gasification combined cycle power plant, but with the gas turbine power generation unit replaced with a fuel cell power generation unit. By taking advantage of intrinsically high energy efficiency of SOFCs and process integration, exceptionally high power plant efficiencies are possible. Furthermore, SOFCs in the IGFC cycle can be operated so as to isolate a carbon dioxide-rich anodic exhaust stream, allowing efficient carbon capture to address greenhouse gas emissions concerns of coal-based power generation.

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Further reading