Chunli Tang

Effect of Two-Level Over-Fire Air on the Combustion and NOx Emission Characteristics in a 600 MW Wall-Fired Boiler

This paper accomplishes a numerical investigation on the effect of two-level over-fire air (OFA) on the combustion and NOx emission in a supercritical 600 MW wall-fired boiler. Different arrangements of two-level OFA nozzles and different airflow ratios between the two layers are set to examine NOx emission and the carbon content in fly ash. According to the simulation results, the two-level OFA case releases the NOx between the single upper layer and the single lower layer of the two-level OFA nozzles in operation. Moreover, the two-level OFA arrangement gives a lower carbon content in fly ash than the single-level OFA cases. In addition, both low NOx emissions and low carbon content in fly ash can be obtained simultaneously when the two levels of OFAs are injected from Layers 1 and 4 with rlower at 0.5.

Energy analysis of a lignite predrying power generation system with an efficient waste heat recovery system

ABSTRACT Lignite has been extensively used for electricity generation in many regions worldwide. However, its high water content has obviously negative effect on plant thermal efficiency. Performance of lignite-fired power plant can be improved by predrying the lignite before combustion. In addition, recovery of waste heat from the dryer and the power generation system will enhance the plant thermal efficiency further. In the present study, a new lignite predrying power generation system integrated with an efficient waste heat recovery system was proposed. Both dryer exhaust waste heat and steam turbine exhaust latent heat were recovered to heat boiler feed water. Energy analysis indicates that system performance is improved significantly. The plant thermal efficiency increases linearly with drying degree and then increases at a lower rate. The generation of unused dryer exhaust changes the variation tendency of system performance with drying degree.

Influence of operating conditions on ammonium bisulfate deposition in the rotary air preheater of coal-fired power plants

To achieve the maximum NOx reduction in coal-fired power plant, excess ammonia is injected into the selective catalytic reduction reactor, which leads to the formation of ammonium bisulfate due to the reaction between ammonia escaping from the selective catalytic reduction reactor and SOx in the flue gas. Ammonium bisulfate can condense in the rotary regenerative air-preheater, which would adversely affect the safe and efficient operation of the air-preheater. An improved radian number is proposed to estimate the ammonium bisulfate deposition. The operating conditions or modes of the air-preheater, i. e., air-flow bypass, cold-end protection and different splitting fluid sector arrangements, are comparatively studied to analyze the temperature and ammonium bisulfate deposition distributions. The hot air re-circulation is not helpful to mitigate the ammonium bisulfate deposition in medium matrix layer. The splitting gas sector arrangement would cause more serious plugging problem, but the splitting air sector arrangements can alleviate the ammonium bisulfate deposition. To increase the air bypass rate is more effective than the splitting air sector arrangements to alleviate the plugging problem. The improved radian number is more reasonable to reflect the ammonium bisulfate deposition compared with the original radian number.

A study on air-cooling waste heat recovery from molten slag of slag-tap boilers

For a better utilization of Zhundong coals which have high fouling and slagging tendency, the slag-tap boiler has attracted much attention. To avoid the high sensible heat loss of discharged molten slag, an air-cooling waste heat recovery system is proposed. Energy and economic analyses are conducted to investigate the effectiveness of heating the desulfurized flue gas by hot air and the influences of partially substituting the secondary air by hot air on heat transfer of air preheater and thermal efficiency of boiler. A case study is performed by referring to a typical 50 MW cyclone boiler with nine types of low fusion temperature coals. The results show that for coals with low ash content, the temperature increment of desulfurized flue gas can be over 7 ℃. While for coals with high ash content, the flue gas temperature can be heated to more than 70 ℃, and the surplus hot air can be sent to the furnace. When the hot air is introduced to partially substitute the secondary air, an instantaneous impact on the air preheater will give rise to a decrement of quantity of heat transferred and increments of temperatures of exit flue gas and hot secondary air. The variations of these thermodynamic parameters become smaller with increasing hot air temperature. After introduction of hot air, the thermal efficiency of boiler can increase, resulting in a decrease of fuel consumption rate. In addition, the heating surface area of air preheater can be reduced.

Numerical simulation on the slag flow and heat transfer characteristics of the cyclone barrel for a cyclone-fired boiler

ABSTRACT A numerical simulation coupled with the user-defined function (UDF) is conducted on a cyclone-fired boiler. The thermal boundary condition is established for the cyclone barrel. The effects of the temperature of critical viscosity and the refractory material thickness on slag behavior are investigated. The results show that the temperature of critical viscosity is closely related to the location where the slag begins to form in the cyclone barrel. The refractory material thickness remarkably influences the surface temperature of the refractory material, and the solid slag thickness adapts to the variation of the refractory material thickness.

Comparative Study of Three Modes of Flue Gas Treatment for Power Plants

AbstractFlue gas treatment systems have been widely installed in power plants to recover the remaining energy from the exhaust flue gas and to address pollutant emissions by heating the cleaned flu...