Investigation On NOx Control And Combustion Optimization For Large Capacity Utility Boilers

Energy and Environment are very important topics for human's development, especially for China - a country with great coal resource. The pollution from coal combustion has been the biggest pollution source in China. This work was involved in the low NOx combustion technology for the large capacity utility boilers, a set of low NOx pulverized coal combustion approaches have been developed in this work by the means of experiments, numerical simulation and field tests.The formation characteristics of the NOx precursor from various types of Chinese coal were investigated using a drop-tube furnace, and experiments on the NOx formation and destruction mechanisms were also studied experimentally. A particle model was developed to simulate the release of volatile fuel-nitrogen and its subsequent conversion to nitrogen oxide during the devolatilization. The different devolatilization models were employed, one is the two competing reactions model and the other is the universal model. The conversion efficiencies of volatile fuel-nitrogen to nitric oxide and the amount of char-nitrogen are presented.In this work, the detailed experiments on the NOx emission characteristics of a 600 MW capacity boiler with concentric firing system were carried out, the numerical approaches employing the joint PDF method were used to simulate the NOx formation process in the furnace. The performance of the concentric firing system on the flow field, coal combustion and NOx emission were evaluated, which shows that concentric firing system has some effects on the reduction of NOx emission, also the prevention of furnace slag, but its effect is limited.The two-stage high temperature desulphurization method using the CaS as the intermedium is developed in this work to obtain the simultaneous reduction of NOx and SOx in the pulverized coal fired furnace. The experimental results show that it is possible to perform such a two-stage high temperature desulfurization in the pulverized coal fired furnace if a deep air stage can be employed in the lower furnace. Such a deep air stage may lead to the dangerous high temperature corrosion and serious furnace slag.To avoid the high temperature corrosion and serious furnace slag caused by deep air stage, a novel low NOx combustion configure named as "the Compound multi-function combustion system" was developed by the author, it has much betterperformance than that of the concentric firing system. A number of boilers firing coals with low ash fusing temperature (ST is about HOOT?) met serious furnace slag problem, the compound multi-function combustion system has solved their problems and achieved a NO* emission reduction of 35%.In this work, the detached-eddy-simulation (DES) approach was employed to study the turbulent flow in the fuel rich-lean separator and the gas-solid multiphase jet from the exit of a fuel rich-lean burner. The vortex shedding process was simulated and its effect on the fuel rich-lean separate performance was evaluated. Combined with the stochastic particle tracking method, the particle motion characteristics in the gas-solid fuel rich-lean jet was tracked, which show the fuel-rich stream and the fuel lean stream will not mix quickly downstream of the exit of the nozzle, the fuel rich-lean combustion can be kept in a rather long distance from the nozzle. Compared with the Reynolds Average Navier Stocks (RANS) method, DES method can give more information about the vortex structure of the gas-solid jet. DES can be used for numerical simulation in large geometry, it will find its more wide employment in the combustion science.Usually, the Particle Doppler anemometry is employed to study the gas-solid two-phase flow, but it cannot do measurements in the gas-solid flow with high solid concentration. In this work, a novel fiber probe was employed to investigate the gas-solid two-phase flow structure downstream of the exit of two low NO* burner nozzle. The gas solid interaction was studied, the solid concentration and particle size distribution contours downstream of the nozzle were obtained. The...