Combustion systems coal from

The high temperatures in the MHD combustion system mean that no complex organic compounds should be present in the combustion products. Gas chromatograph/mass spectrometer analysis of radiant furnace slag and ESP/baghouse composite, down to the part per biUion level, confirms this behef (53). With respect to inorganic priority pollutants, except for mercury, concentrations in MHD-derived fly-ash are expected to be lower than from conventional coal-fired plants. More complete discussion of this topic can be found in References 53 and 63. 

Step 4 Define the System Boundaries. This depends on the nature of the unit process and individual unit operations. For example, some processes involve only mass flowthrough. An example is filtration. This unit operation involves only the physical separation of materials (e.g., particulates from air). Hence, we view the filtration equipment as a simple box on the process flow sheet, with one flow input (contaminated air) and two flow outputs (clean air and captured dust). This is an example of a system where no chemical reaction is involved. In contrast, if a chemical reaction is involved, then we must take into consideration the kinetics of the reaction, the stoichiometry of the reaction, and the by-products produced. An example is the combustion of coal in a boiler. On a process flow sheet, coal, water, and energy are the inputs to the box (the furnace), and the outputs are steam, ash, NOj, SOj, and CO2. 

Straight combustion of coal-based syngas fuels in boilers is a fully developed technology with likely few opportunities for expanded coal utilization in the long-term. There are few advantages to such systems from an environmental standpoint as process schemes simply move environmental controls upstream from the boiler. Steam boilers can tolerate some levels of contaminants, including chlorines, particulates, and sulfur. 

Now, assume that there are other exergy flows into the system, which are required to make the process work. These amount to 410kj/mol of electricity, and comes from the combustion of coal (C is 410 kj/mol). How do the answers to a and b change What if the efficiency of electricity generation is 25% ... 

There are several approaches available to a utility to construct a boiler that will meet New Source Performance Standards. These approaches can be classified according to the position in the combustion system at which pollutant control technology is applied. Precombustion control involves removal of sulfur, nitrogen, and ash compounds from the fuel before it is burned. For coal combustion this approach involves the application of coal-cleaning technology. Combustion control relies on modifications to the combustion process itself or the addition of material to the combustion process to reduce pollutant formation or capture the pollutants formed in the combustion chamber. Examples of combustion control include staged combustion, boiler limestone injection, and fluidized-bed combustion with limestone addition. Post-combustion control involves removal of pollutants after they have been formed but before they are released into the atmosphere. Traditionally, flue gas desulfurization has meant the application of postcombustion control either alone or in conjunction with another... 

Synthetic liquid fuels derived from coal and shale will differ in some characteristics from conventional fuels derived from petroleum. For example, liquid synfuels are expected to contain significantly higher levels of aromatic hydrocarbons, especially for coal-derived fuels, and higher levels of bound nitrogen. These differences can affect the combustion system accepting such fuels in important ways. In continuous combustors, i.e. gas turbines, the increased aromatics content of coal-derived fuels is expected to promote the formation of soot which, in turn, will increase radiation to the combustor liner, raise liner temperature, and possibly result in shortened service life. Deposit formation and the emission of smoke are other potential effects which are cause for concern. Higher nitrogen levels in synfuels are expected to show up as increased emissions of N0X (NO+NO2) An earlier paper presented results of an experimental study on the effect of aromatics and combustor... 

Illite -H2O-H2 System. Vaporization of potassium from the highly acidic illite system, in neutral atmospheres, is expected to provide a relatively insignificant source of alkali in most coal combustion systems. However, in the presence of reactive combustion gases, such as H2O and H2, thermodynamic considerations predict a significant KOH partial pressure. In addition, an increase in the K-pressure should result from a reduction in the O2 pressure, in the presence of H2. However, KMS experiments did not indicate formation of KOH or additional K in the presence of H2 gas. Thus, thermodynamic equilibrium does not appear to have been established in this heterogeneous system, even though the temperatures were sufficiently high to have normally ensured a rapid approach to equilibrium. 

The second method that particles may be emitted from the combustion system is through the production of particles in the combustion process. For example, in the combustion of solid fuels, like coal, for example, ash is normally produced. The airborne portion of the ash, usually referred to as fly ash, may be carried out of the combustor by the exhaust gases. The use of OEC should reduce fly ash emissions because of more-complete combustion of the fuel compared with an air/fuel system. 

Blander, M. Pelton, A. D. Computer Assisted Analyses of the Thermodynamic Properties of Slags in Coal Combustion Systems, ANL/FE-83-19, Argonne National Laboratory, Argonne, IL, 1983 Available from NTIS, U.S. Dept. of Commerce, Washington, D.C. 

Availability of empirical data on the behavior of coals to be characterized from working plants or model combustion systems similar to those used in practical operation Elimination of the Si02 share of the ash which does not participate in the slagging process. 

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