Numerical investigation on the flow, combustion, and NO_X emission characteristics in a 660 MWe tangential firing ultra-supercritical boiler

Abstract

A three-dimensional numerical simulation was carried out to study the pulverized-coal combustion process in a tangentially fired ultra-supercritical boiler. The realizable k-e model for gas coupled with discrete phase model for coal particles, P-1 radiation model for radiation, two-competing-rates model for devolatilization, and kinetics/diffusion-limited model for combustion process are considered. The characteristics of the flow field, particle motion, temperature distribution, species components, and NO x emissions were numerically investigated. The good agreement of the measurements and predictions implies that the applied simulation models are appropriate for modeling commercial-scale coal boilers. It is found that an ideal turbulent flow and particle trajectory can be observed in this unconventional pulverized-coal furnace. With the application of over-fire air and additional air, lean-oxygen combustion takes place near the burner sets region and higher temperature at furnace exit is acquired for better heat transfer. Within the limits of secondary air, more steady combustion process is achieved as well as the reduction of NO x . Furthermore, the influences of the secondary air, over-fire air, and additional air on the NO x emissions are obtained. The numerical results reveal that NO x formation attenuates with the decrease in the secondary air ratio (g 2nd ) and the ratio of the additional air to the over-fire air (g AA / g OFA ) was within the limits.

A Review of the Numerical Modeling of Pulverized Coal Combustion for High-Efficiency, Low-Emissions (HELE) Power Generation

“…54 Air staging is primarily applied to utility boilers such as overfire air (OFA). Many studies have investigated low-NOx burners and air staging with respect to the effects of the geometries and boiler operating conditions, including the burner geometry and fuel equivalence ratio, 55,56 air ratio of secondary and OFA, 57 stoichiometric ratio, 58 and air temperature. 59 2.2.2.…”

“…62 Tangentially fired combustion systems are generally used in boilers to improve the combustion characteristics, including flame stability and combustion efficiency, and to reduce NOx emissions. The low-NOx concentric firing system (LNCFS) 57,63 is chiefly incorporated for low-NOx technology in tangentially fired boilers. Figure 5 (a) shows that the coal stream injected with primary air and the direct-flow secondary air forms an inner flame, while the horizontally biased secondary air forms the outer circle flame to create fuel-lean zones in the vicinity of the furnace walls.…”

“…Extensive literature exists on the effects of boiler configuration or operating conditions on their performance, particularly NOx emissions at the pilot-scale and HELE utility boilers with one or more implemented low-NOx combustion technologies. Several numerical studies over the past decade have demonstrated the effectiveness of low-NOx combustion technologies, including low-NOx swirl burners, ,, the optimized ratio and position of OFA, LNCFSs, and air staging, , the sub air technique, HBC and OFA, the double-tangential-circle boiler, and advanced firing systems for down-fired boilers . Various parameters must be considered to evaluate their effects on low-NOx combustion in different boilers.…”

Experimental Investigation on Turbulent Flow Deviation in a Gas-Particle Corner-Injected Flow

“…Tangentially fired boilers are widely applied in coal-fired power plants in Asian countries, and the corner-injected flow is the fundamental configuration in tangentially fired boilers [1]. The four adjacent jets create an intensive rotation flow in the whole chamber, resulting in an increase in the momentum and energy transfer between coal and gas [2].…”

“…Obviously, the dispersed pulverized coal particles can achieve better combustion with an appropriate rotation flow in the furnace. However, there exists no standard design for the ideal tangential circle for the tangentially fired furnace [1][2][3][4][5][6][7][8]. The inner mechanism between gas and pulverized coal particles in mesoscale is vague, which is important for the dispersion and combustion of coal particles in the furnace.…”