Several important aspects are described in this paper. The occurrences of trace elements (TEs) in coal are introduced. Four main groups of trace element content level, say, >50, 10-50, 1-10 and < 1 ppm, can be drawn. Trace elements partitioning in emission streams; enrichment in submicron particles; vaporization and emission in flue gas; and the mobility and leaching behavior of trace elements in coal and combustion waste are summarized. The mechanisms of trace element transformation during combustion are illustrated as following: the vaporized metals at high temperature near the combustion flame will subsequently nucleate or condense at a lower temperature downstream. These metals form a suspended aerosol along with particles. The conversion of vaporized components into various solid and/or liquid forms is the key factor influencing the final trace elements' transformation/partitioning behavior. Finally, current trace element emission control technologies are briefly introduced. To control trace elements in particle phase, electrostatic precipitators and fabric filters are mainly used. To control trace elements in vapor phase, spray dryer absorbers, wet scrubbers, condensing wet scrubbers, wet scrubbers and solid sorbent injection should mainly be used. Research needs are identified and potentially promising research topics on trace elements emission are proposed as following: (1) trace element speciation and enrichment in coal and coal ash. (2) Trace elements partitioning in combustion process. (3) Mechanisms of transformation and control technologies for easily vaporized TEs during combustion.

Numerical modeling of a front wall pulverised coal fired utility boiler is presented in this paper. Comparison between the pre-dictions and measurements in the boiler is addressed. The accordance of the calculation results with the experimental data at several operating conditions validates the models and algorithm employed in the computation. The need to improve burner or boiler design with the objective of producing Nox abatement while avoiding some negative side effects is also the motivation for the prediction of furnace performance for different boiler operating conditions. The predicted results also lay a foundation for the boiler operating expert system

The mechanism of detailed chemical reactions in combustion is very complicated, especially when the formation of a pollutant such as NOx is considered. Based on regression analysis, a simplified fuel-NOx model is developed for premixed flame. The new model iS available for a wider range of temeperature and fuel-air ratios compared with De Soete's (1975) fuel NO model. The reduction CHi species on NO iS considered so that the model can be used in both fuel-lean and fuel-rich combustion systems. After a great simulation of a one-dimensional premixed flame system using Miller and Bowman'S (1989, Prog. Energy Combust. Sci., 15, 287) detailed elementary reaction model, the calculation of all the reaction rates is presented based on regression analysis.Copyright