Pressure coal combustion

Examples of the need for multimedia models are found in contemporary problem areas. Polynuclear aromatic hydrocarbons and metals are emitted into the atmosphere as trace impurities with the products of coal combustion. The organics have low vapor pressure and partially condense on emitted particulates in a stack plume. The particulates are transferred to the soil by dry deposition, rainout or washout. The metals manifest... 

Pulverized coal combustion systems are most commonly used in power plants. In pulverized coal combustion, temperatures typically reach around 1480 °C at atmospheric pressure. In the past couple of decades, fluidized bed combustion (FBC) technologies have been commercialized. These combustors often use limestone bed materials to capture sulfur gases. They operate at about 880 °C and usually at atmospheric pressure (Smoot and Smith, 1985), 38. 

Pressurized FBC may make possible the use of coal in turbocharged combustors and combined cycle power systems. Success is dependent on reducing the erosive and corrosive character of hot, pressurized flue gas generated from coal combustion before expanding it through the system s gas turbine. The problems to be overcome are manifold. The usual requirement for reducing particulate emissions to environmentally acceptable levels is supplemented with stringent... 

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. 

No experimental gasifier data was found to verify any of the simulation model results. However, limit cycle responses have been experimentally observed for the pressure in combustion chambers and boilers (20). This lends credence to our calculated results since coal combustion is an important factor in gasifier operation. 

Lipert, T. E. et al. (1981) Testing and verification of granular bed filters for removal of particulates and alkalies. High Temperature, High Pressure Particulate and Alkali Control in Coal Combustion Process Streams. In Proceedings U.S. DOE Contractors Meeting, CONF-810249, pp. 471-489. 

In a gasification-based power plant, the hot, high pressure coal gases from the gasifier turn a gas turbine. Hot exhaust from the gas turbine is then fed into a conventional steam turbine, producing a second source of power. This dual, or combined cycle arrangement of turbines is not possible with conventional coal combustion. It offers major improvements in power plant efficiencies. 

Pulverized coal combustion (PCC) involves grinding the feed coal to approximately <70 mm and injecting the powdered coal into the combnstor from either wall-mounted burners or comer-mounted (tangential) burners. Combustion takes place within a few seconds at flame temperatures up to 1500°C (2730°F). Supercritical PCC is a variation that seeks to improve thermal efficiency, from the typical values of up to about 40% for PCC to 43%-47% in supercritical systems through higher steam temperatures and pressures. 

Fluidized-bed combustion It accomplishes coal combustion by mixing the coal with a sorbent such as limestone or other bed material. The fuel and bed material mixture is fluidized during the combustion process to allow complete combustion and removal of sulfur gases. Atmospheric FBC (AFBC) systems may be bubbling (BFBC) or circulating (CFBC). Pressurized FBC (PFBC) is an emerging coal combustion technology. 

Havlica, J., Brandstetr, J., and Odler, I. (1998) Possibilities of utilizing solid residues from pressurized fluidized bed coal combustion (PFBC) for the production of blended cements. Cement and Concrete Research 28,299-307. 

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