Study And Application Of Low NO_x Combustion Technology In Tangential-Firing Pulverized Coal Boiler

In China, coal-dominated energy structure would exist for a long period of time. Nitrogen oxides produced by coal-fired boilers leads to serious environmental pollution, which have to be solved urgently. In this paper, a serious of low NOx combustion technologies is presented, by taking account of China's main coal-fired boiler furnace and the concentration of nitrogen oxides emission, combined with increasingly stringent emission standards as well as the development trend for both state and local government. These technologies will meet different stages of the corresponding emission standards and provide solutions for China's incremental stages for the implementation of the nitrogen oxide emission reduction. Numerical simulation, laboratory research and chemical kinetics analysis methods are used to conduct a comprehensive in-depth study on a series of low-NOx combustion technology such as the separated over fire air, fuel reburning and advanced reburning. Mechanism of NOx reduction, the design methods and principles for low NOx technologic l upgrading on existed coal-fired boiler are presented. In addition, advanced low-NOx combustion technology and the impact of the factors required for NOx reduction reaction mechanism model are discussed.Based on the mechanism of NOx production, a variety of factors and optimization principle are analyzed. A representative coal- fired boiler is set as a case, key factors on separated over fire air low NOx combustion technology is analyzed in deep. According to the new NOx emissions standards for state and local, it is proposed that SOFA is an effective and low-cost transformation of technologic l upgrading on existed coal-fired boiler, hence, numerical simulation method for the design and modification of the optimal operation is provided.Facing to the more stringent NOx emissions standards, use low-NOx reburning fuel combustion technology on overall classification on the basis of the air will further reduce NOx emissions. Different fuels for reburning are studied such as natural gas, petroleum gas and biomass gasification gas with tar. Results show that: For natural gas reburning, HCCO, CH2 and CH3 radical is the main active substance on NO reduction. Reaction temperature and OH, H, O are key factors for a group of active substances production; Under the same conditions, NO restore by petroleum gas reburning are better than natural gas reburning. This is because a large number of free radicals HCCO and H, OH active groups involved in the reaction during petroleum gas reburning for NOx reduction.On the basis of fuel reburning, advanced reburning can achieve the same level of a significant reduction as SCR does in NOx emissions. Reaction time, reaction temperature, excess air ratio in reburning zone and NSR, are the main factors for NO reduction; In order to simulate the NO distribution discipline along the length of reactor, GRI-SNCR reaction mechanism model is been tried and proved by experiment. Then, this reaction mechanism can be used to carry out in-depth analysis of advanced reburning; It can be seen from reactant generation rate analysis: Under rich fuel condition, NH2 is the main activity radical for NO reduction. Under oxidizing atmosphere, most NH2 are oxidized to HNO, and finally to NO. Therefore, during advanced reburning, reaction between NH2 radical and NO is competitive reaction strongly dependent on the atmosphere, NH2 can reduced NO to N2, and also be oxidized to NO.