Coal Combustion

The USEPA's CCR Rule (USEPA, 2015a) is based on a risk assessment that evaluated potential risk to users of groundwater as drinking water.

From: Coal Combustion Products (CCP's) , 2017

Coal

Deepak Pudasainee , ... Rajender Gupta , in Future Energy (Third Edition), 2020

2.3.2.5 Solid waste

Coal combustion produces a large volume of solid wastes including bottom ash, fly ash, and gypsum (from limestone based flue gas desulphurization [FGD]). The impact of coal utilization on economics and environment can be reduced by using the coal combustion by-products in construction materials. Not all the coal combustion products are wasted; some are used beneficially, such as fly ash in cement kiln to produce clinker. The unused by-products containing higher concentration of toxic chemicals create the problem. The major environmental concern for coal combustion waste disposal is leaching of toxic pollutants, present in fly ash, into the waterbodies [21,22].

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Coal Combustion Residue Disposal Options

Richard W. Goodwin Ph.D., P.E. , in Combustion Ash Residue Management (Second Edition), 2014

Abstract

Coal combustion residues (CCRs) are presently regulated as solid waste (Subtitle D) under the Resource Conservation Recovery Act. Such classification promotes beneficial use by end-users i.e. mitigating excessive liability. According to the US Environmental Protection agency (USEPA), about 131  million tons of coal combustion residuals—including 71   million tons of fly ash, 20   million tons of bottom ash and boiler slag, and 40   million tons of flue gas desulfurization (FGD) material—were generated in the US in 2007. Of this, approximately 36% was disposed of in landfills, 21% was disposed of in surface impoundments, 38% was beneficially reused, and 5% was used as minefill. Stringent regulation, as Subtitle C (hazardous waste), would impose a perceived liability upon end-users; greatly reducing beneficial use opportunities. Mandatory use of synthetic liners—would not have prevented dike wall failure and fails to consider inherent engineering characteristics of CCRs.

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Air classification

J. Jow , in Coal Combustion Products (CCP's), 2017

Abstract

Coal combustion products (CCP) are fly ash, bottom ash (or boiler slag), and flue-gas desulfurization gypsum. All have three fundamental properties: chemical composition, mineral composition, and particle size distribution. Among these CCP and fundamental properties, fly ash has the largest volume, with an extremely broad range of particle sizes that exhibits large variability from plant to plant, even in different batches from the same plant. Air classification is used to classify fly ash into at least two or more fractions with consistent quality and desired particle size distributions, particularly fine particle size for high value utilization in selected applications. For better efficiency and lower separation cost to obtain the fine particles, fly ash from each electrostatic precipitator at the coal-fired power plant should be collected separately. Air classification can obtain the finest fly ash, maintain its spherical shape, and consume less energy than milling. Air classification is also more efficient than sieving for a large scale production.

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Storage of coal combustion products in the United States

A. Lewis , ... B. Hensel , in Coal Combustion Products (CCP's), 2017

20.4 Exposure pathways

Throughout the CCP risk assessment and damage case evaluation process conducted by the US EPA, several human and ecological exposure pathways have been identified and evaluated. The complete set of plausible exposure pathways associated with CCP exposure were articulated by the US EPA in its final risk assessment (US EPA, 2014a) and are depicted in Fig. 20.5. Note that the figure provided below is for exposure pathways associated with surface impoundment CCP storage, but landfill pathways are qualitatively similar. As noted above, in the most recent US EPA risk assessment, the impacts of the release of CCP constituents to groundwater and the subsequent discharge of contaminated groundwater to surface water were identified as key risk pathways for both human health and ecological endpoints. Prior risk assessments of CCPs had focused on "nonwater" exposure pathways and determined that the potential human health or ecological risk from exposure to CCPs via these pathways were minimal (US EPA, 1998). Most recently, the US EPA evaluated potential inhalation risks from fugitive dust generation at landfills and concluded that best practices for landfill management are unlikely to pose a risk to human health; more specifics on best practices for landfill management and potential fugitive dust risks are provided in Section 20.8.

Fig. 20.5. Key exposure pathways associated with CCP storage in surface impoundments.

 From US EPA. (2014a). Human and ecological risk assessment of coal combustion residuals (final) (1237 p.). Office of Solid Waste and Emergency Response (OSWER), Office of Resource Conservation and Recovery, December. Available from http://www.regulations.gov/#!documentDetail;D=EPA-HQ-RCRA-2009-0640-11993.

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Coal Combustion and the Environment

Paul Breeze , in Coal-Fired Generation, 2015

Coal combustion is a dirty process, releasing a range of pollutants including sulphur dioxide, nitrogen oxides, carbon dioxide, volatile organic compounds, ash and a range of heavy metals. If these are not controlled they can enter the atmosphere, causing damage to the environment and to human health. Air quality standards limit the amount of each of these that can be released into the atmosphere. Some pollutants can be removed by cleaning coal before combustion. Most are removed after combustion. The production of nitrogen oxides is controlled during combustion using special burners and they can be removed from flue gases using reduction reactions involving ammonia or urea. Sulphur dioxide is most commonly removed using a wet flue gas scrubber although dry techniques are also possible. Dust particles can be captured with an electrostatic precipitator or by using a baghouse filter. Heavy metals may be captured during these processes too, but new methods may be required to remove mercury when legislation controlling its emission comes into force.

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Introduction to the utilization of coal combustion products

R.A. Kruger , in Coal Combustion Products (CCP's), 2017

4.7 Utilization in South Africa

Coal combustion accounts for 85% of the electrical power generated in South Africa. The state-owned enterprise (Eskom) supplies 95% of the electrical power. A total of 35  Mt of coal ash (29   Mt fly ash and 6   Mt bottom ash) is generated, but only 11.6   Mt (9.9   Mt fly ash and 1.7   Mt bottom ash) are available for sale. Eskom has a zero-effluent discharge policy; therefore it uses the coal ash as a "sink" for their liquid effluents, making it unsuitable for use.

In total, 2.5   Mt (25%) of the available fly ash was sold in 2014. About 1% of the bottom ash is sold. Fly ash is almost exclusively applied in the cementitious market, with 72% used for cement extension and 26% in concrete (Fig. 4.2).

Fig. 4.2. Breakdown of the 2.5   Mt fly ash market for South Africa in 2014.

Due to the low sulfur content of the coal, no FGD is currently being produced, but FGD is being fitted to a 600   MW boiler of a power station currently under construction.

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Fossil fuels combustion and environmental issues

Jun Inumaru , ... Seiichi Ohyama , in Advances in Power Boilers, 2021

1.3.1.2 Combustion systems

Coal combustion systems include fixed-, fluidized-, and entrained-bed systems, as shown in Fig. 1.16 [25]. Typical examples of these combustion systems are explained as follows. A stoker furnace is a small furnace of a fixed-bed combustion system. In this system, lumps of coal are placed on a conveyor-type combustor and burned while moving. It is advantageous to be able to burn large lumps of coal without finely pulverizing them. In a fluidized-bed combustion system, grains of coal are injected into the bed medium (e.g., particles of limestone, silica, and ash) fluidized with an airflow and combusted. This system provides better heat transfer in the bed. Furthermore, it can be applied to in-furnace desulfurization by injecting limestone into the bed. However, it has problems in maintaining a stable fluidization when it is scaled up. A pulverized coal boiler system is an example of an entrained-bed combustion system in which pulverized coal and air are ejected from the center of the burner and burned. As this system uses coal particles pulverized to 30–40   μm, it provides high combustion efficiency and less excess air. Furthermore, as it allows the easy scaling up of a boiler, this system is now mainly used in coal-fired power plants.

Figure 1.16. Coal combustion system [26].

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Power boiler design

Masashi Hishida , ... Hitoshi Asano , in Advances in Power Boilers, 2021

4.2.6.1 History of stoker combustion

Coal combustion technology started by hand-scattering of coarse grain coal on a fire grate. In accordance with an increase in boiler capacity, mechanical stokers, for example, chain grate stoker, traveling grate stoker, inclined stoker, stepped stoker, spreader stoker, and so on, appeared. The first mechanical stoker with circular-plate type grate rotating around vertical axis was proposed by W. Brunton in 1819, while this first stoker was abandoned. Practical and efficient stoker was the traveling grate stoker developed by J. G. Bodmer in 1834. Since then, J. Jukes (1841), S. Hall (1845), R. F. Weller (1871), and so on developed successively various types stokers mentioned previously. The stoker combustion was one of the main boiler technologies, while pulverized coal combustion has successively expelled stokers from large-capacity power boilers. The stoker combustion has, on the contrary, shrunk successively in the power generation filed, while still remains mainstream in the field of incineration firing [6].

As mentioned earlier, stoker incinerators have conventionally been combustion-type and used as coal or bark incinerators, however, since the world's first stoker-type incinerator facility was established in 1873 in Manchester. This technology has gained attention as a way to counteract the rise of industry and increased waste processing problem. Continuous incinerators capable of operating around the clock started being built throughout the world from around 1950 [7]. Seventy-four percent of all stoker-type incinerators built as waste incinerators have been built within the last 10 years [8].

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Application of inorganic cements to the conditioning and immobilisation of radioactive wastes

F. Glasser , in Handbook of Advanced Radioactive Waste Conditioning Technologies, 2011

Case 2: Variability of fly ash

Coal combustion fly ash is also a very variable by-product. The ash composition reflects the mineral content of the coal, and the content of CaO (often present as mixtures of free lime and CaCO 3 in high-lime ashes) is particularly variable, depending on provenance. Thus large variations in fly ash composition and mineralogy are encountered worldwide. The low-lime ashes are characteristically rich in silica, alumina and iron oxide and have a high glass content, whereas the lime-rich ashes are more crystalline, with little or no glass, and may even contain some of the same crystalline minerals found in clinkers, e.g. dicalcium silicate, calcium aluminates, free lime and ferrite. Indeed, some lime-rich ashes are weakly cementitious when mixed with water and can be used for low-strength construction.

A potential concern about the lime-poor ashes is that, by reacting with calcium hydroxide furnished by cement activator, the ash will lower the internal pH. This process is described in more detail in subsequent sections, but the conclusions for nuclear waste are that (1) supplementary cementing materials have potential advantages in cemented waste matrices, such as control over thermally-induced cracking, but (2) specifications imposed by civil engineers, based on presently available data, may not provide sufficient information to predict long-term performance. Certainly blended cements should not be specified for use on the basis of improvement in short-term properties without also considering longer-term impacts. But an agreed procedure is needed to calculate the long-term impact of fly ash on the pH conditioning ability of cement solids.

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Large-scale integration of variable renewable resources

R Gómez-Calvet , ... J.M. Martínez-Duart , in Renewable-Energy-Driven Future, 2021

7.5.1 Coal phase-out

Coal combustion has historically been at the cornerstone of many country electricity mixes, but due to its high pollution emissions, the Emission Trading Systems, and its low efficiency conversion, it is being been displaced by other generation sources.

In the particular case of Europe, coal generation has shown its highest fall in 2019 which has been attributed to the EU's carbon cap-and-trade system, the Emission Trading System (EU-ETS) Scheme implemented at the beginning of the last decade. During the financial crisis the price on the EU carbon market was rather low, but it has risen from around €5 in 2017 to around €25 per tonne of emitted CO2 in 2019 [30], pushing coal power plants to halt generation. As an evidence of this fact, Fig. 7.12 shows the evolution of coal generation for Spain during a 5-year interval (the period between January 2015 to December 2019) in which it can be observed its progressive diminution during 2019. In addition, strict emissions regulations will make it very difficult to return to coal as a main source of power in Europe. Further analysis of power generation shows that this fall in coal generation has already been replaced mainly by additional renewables sources and natural gas. Not all European countries have shown a similar trend, and the fall in coal power generation has been much smaller in Central and Eastern Europe countries. Focusing attention in other continents, it has been noted a flattering of coal growth generation in China and 'a sharp turnaround in India, where coal power output is on track to fall for the first time in the last three decades' [31].

Figure 7.12. Coal generation in Spain during the last 5   years. Red line show a simple moving average taking one year (365 previous days) as interval for the analysis.

 Authors based on data from Red Eléctrica Española. Sistema de información del operador del sistema eléctrico en España, <https://esios.ree.es/en>; 2020 [accessed 01.11.20] [17].

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