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

Problems commonly occur when the coal type and/or the load are changed in utility boilers. To solve these problems, a new pulverized coal burner, namely, a burner with continuously variable concentrations of coal dust by using a set of blades, is developed in this study. Gas-solid twophase flow downstream of the burner was measured by three-dimensional particle dynamics anemometer (3D PDA). The results show that the particle concentration biased degree of the burner can be continuously adjusted between 1 and 3 by changing the angle between the blades and the primary air flow, over a range of 0-20

The efficient use of pulverized coal is crucial to the utility industries. The use of computational fluid dynamics (CFD)-based numerical models has an important role in the design of new boiler furnaces or in retrofitting situations. The results of CFD simulations can be used to better understand the complex processes occurring within the boiler furnace. The use of these results to support boiler operation and training of operators requires that the CFD models can be easily accessed and the results are easily analysed. This paper discusses two ways to simulate the heat transfer process in boiler furnaces. The method directly applying CFD results is employed, in which the grid for solving the energy equation is the same as the flow grid in the CFD simulation while radiation heat transfer is solved in another relatively coarse grid. Comparison of the prediction results between CFD and Heat Transfer code (Simple model) is performed under boiler full load (100%) with one side wall fouling, as well as for different boiler loads (100, 98 and 95 per cent boiler full load, respectively). Finally, the flexible use of the results of CFD and the simple model for pulverized coal-fired boilers is presented. To facilitate the use of the system, a user-friendly interface was developed which enables the user to manipulate new calculations and to view results, namely performing'what-if' analysis. Copyright ~ 2000 John Wiley & Sons, Ltd.

mechanism including Hg reactions involving HgO was proposed. Among those reactions involving HgO, the progress of reaction HgO +HCl→HgCl+OH is HgO+HCl→TS1(HgClOH)→M(HgClOH)→TS2(HgClOH)→HgCl+OH, in which the controlling step is HgO+HCl→TS1(HgClOH)→M(HgClOH). The progress of reaction HgO+HOCl→HgCl+HO2 is HgO+HOCl→M(HgClOOH)→TS(HgClOOH)→HgCl+ HO2, in which the controlling step is M(HgClOOH)→TS(HgClOOH)→HgCl+HO2. Four other reactions are one-step, with no intermediates formed. The performance of the model was assessed through comparisons with experimental data conducted by three different groups. The comparison shows that model calculations were in agreement with only one set of all the three groups experimental data. The deviation occurs due to the absence of accurate rate constants of existing echanism, the adding of reactions involving HgO, as well as the exclusion of heterogeneous Hg oxidation mechanism. Analyses by quantum chemistry and sensitivity simulations illustrated that the pathway Hg+ClO=HgO+Cl is more significant than some of the key reactions in the kinetic mechanism proposed in the literature, which indicates the necessity of including reactions involving HgO in the mercury speciation kinetic mechanism. Studies on the effects of oxygen show that O2 weakly promotes homogeneous Hg oxidation, especially under the condition of low Cl2 concentration. In all cases, 1.5–6.0% of the mercury is predicted to be present as HgO.