Cleaning during Combustion

Cleaning during combustion can involve modification of the manner in which coal is burned or, alternately, the use of pollutant-absorbing substances which can be injected into the combustion chamber. 

Clean combustion consists of removing the pollutants from coal as it is burned. This can be accomplished by controlling the combustion parameters (fuel, air/oxygen, and temperature) to minimize the formation of pollutants and/or by injecting pollutant-absorbing substances into the combustion chamber to capture the pollutants as they are formed (Martin, 1986). 

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There are strong incentives to develop processes for removing sulfur from coal before combustion (precombustion cleaning), during combustion, or after combustion (postcombustion cleaning)... 

Thus, there are (1) precombustion cleaning, (2) cleaning during combustion, (3) postcombustion cleaning, and (4) cleaning by conversion. 

Control of sulfur dioxide emissions from stationary sources (such as power plants) usually takes one of three forms fuel cleaning, also known as fuel beneficiation removal of sulfur during combustion or flue gas processing. 

The concept of clean coal is based on the idea that coal can be cleaned of its toxic ingredients by selective burning or washing before it is used as a fuel, thereby reducing the amount of pollutants emitted during combustion. The remaining pollutants can then be collected and stored rather than released into the environment. 

Precombustion control involves removal of sulfur compounds from fuel prior to combustion. Control during combustion employs techniques to minimize the formation and/or release of SO2 and N0X during the combustion process. Finally, SO2 and N0X can be removed from the combustion flue gas using various postcombustion control methods. This chapter discusses the potential of mitigating acid deposition through precombustion cleaning of coal to remove sulfur compounds. 

In the works devoted to study and development of MEISs numerous examples on their application to the analysis of various problems were certainly presented. They are formation of harmful substances during fuel combustion and cleaning of combustion products from these components, fuel processing, atmospheric pollution with anthropogenic emissions, stationary and nonstationary flow distribution in hydraulic systems, etc. These examples should illustrate practical efficiency of MEISs, their capabilities for revealing specific features of the modeled process and determining directions of its improvement. 

The nozzles should be kept clean and in good conditions. Extra cooling air for the nozzle could be useful during combustion. 

Coal can be utilized in ways that are cleaner and often more energy-efficient than those used in the past. In the various technologies, the cleaning can occur precombustion, during combustion, postcombustion, or by conversion of the coal to another fuel. 

This is an idealized representation of a detergent. Calcium carbonate is suspended in oil with a sulfonate or phenate. The excess calcium carbonate provides a base reserve to oils and neutralizes acids that are formed during combustion. Detergents are also effective at keeping surfaces in the engine clean. The metals used to make detergents are typically calcium, magnesium, and sodium. Calcium is the most common. 

NOx emission from coal combustion can be reduced through measures during combustion, cleaning of the flue gases or a combination of both. There is currently a total installed capacity of over 150 GWe equipped with combustion measures, mainly low NOx burners and air staging in furnace. The rates of NOx reduction in, for example, the FRG have been 25-40%. Higher reduction rates have been obtained with advanced low NOx systems. To achieve further NOx reduction, /flue gas treatment is necessary. The most common process presently in use is selective catalytic reductions (SCR). A capacity of 35 GWe was equipped with SCR by the end of 1989. Most SCR plants in operation are designed to achieve about 80% NOx reduction to meet emission standards of 200 mg/m. ... 

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