Numerical simulation of fuel staged swirl combustion in the invert furnace of boiler on advanced ultra-supercritical steam parameters

The paper considers the schemes of Kuznetsky lean coal combustion for the M-shaped boiler. With such a boiler profile, it is possible to significantly reduce the length of main steamlines, which is especially important for the advanced ultra-supercritical parameters of the superheated steam. The furnace in this boiler unit is performed downward (invert). In this work, the aerodynamics of 6 combustion schemes was simulated by means of computational fluid dynamics. All considered schemes were designed on the basis of direct-flow burners and nozzles. For the most aerodynamically reasonable scheme the thermal processes in the boiler furnace firing Kuznetsky lean coal have been simulated by means of computational hydrodynamics. The simulation results showed a high efficiency of fuel burnout: loss due to unburned combustible equaled 0.1%, carbon-in-ash loss equaled 0.8%. Carbon monoxide concentration at the furnace outlet in conversion to excess air equal α = 1.4 amounted 226 mg/m3, the nitrogen oxides concentration in the flue gases (in conversion to normal conditions) equaled 424 mg/m3. It is appropriate to use the results obtained in this research in the development of new solid fuels combustion schemes.

Oxidation Behavior and Kinetics Parameters of a Lean Coal at Low Temperature Based on Different Oxygen Concentrations

The method of dividing the “three zones” of spontaneous combustion in goaf by oxygen volume fraction is the most widely used and effective method at present. However, the oxygen volume fraction method does not consider the influence of methane concentration in goaf, which is only applicable to low-gas goaf, not high-gassy goaf. In this work, the oxidation behavior and kinetics parameters of a lean coal at low temperatures under five different oxygen concentrations, including methane and its kinetics during low-temperature oxidation, were studied using temperature programming tests and thermogravimetric tests. The results showed that the decrease of oxygen content improves the adsorption capacity of coal to absorb different atmospheres at the initial stage. In the whole reaction process, there is a negative correlation between the strong-to-weak order of exothermicity and adsorption capacity, with a significant increase in apparent activation energy E. A marked hysteresis of the precipitation time of CO and CO2 and a decrease in their precipitation amount and a rise in the initial temperature for the generation of CO and CO2 were found.

Concentration, distribution and occurrence of mercury in Chinese coals

Mercury in coals is one of the important sources of atmospheric mercury, which is potentially harmful to the ecological environment. Based on the data of 970 coal samples, the concentration, spatial distribution and occurrence of mercury in Chinese coals were analyzed. The main conclusions are as follows: The distribution of mercury concentration in Chinese coalfields is uneven; medium and high mercury coals are mainly distributed in southwest China and eastern Inner Mongolia. The mercury concentrations in various coal-forming periods are as follows: K (0.320 mg/kg) > P2 (0.220 mg/kg) > C3 (0.179 mg/kg) > J (0.177 mg/kg) > D (0.165 mg/kg) > P1 (0.136 mg/kg) > C1 (0.090 mg/kg) > E (0.086 mg/kg) > T3 (0.066 mg/kg). The mercury concentrations in different coal ranks are as follows: Lignite (0.164 mg/kg), long flame coal (0.078 mg/kg), non-caking coal (0.256 mg/kg), weakly caking coal (0.086 mg/kg), gas coal (0.151 mg/kg), fat coal (0.122 mg/kg), coking coal (0.171 mg/kg), lean coal (0.393 mg/kg), meagre coal (0.161 mg/kg), anthracite (0.160 mg/kg). Sulfide bound state is the main form of mercury in coals, and pyrite is the main occurrence medium.