| NOx emissions of coal-fired power is the key point of flue gas pollutants governance in our country.Selective catalytic reduction is adopted widely with high denitration efficiency, stable running and simple system device. In the engineering practice, the first inportant problem is how to make the ammonia and NOx in flue gas to be fully contact reaction, thereby improve the denitration efficiency of SCR system.It is combined the combination of simulation and theory analysis method in this paper.The main work content is as follows:Firstly, based on the basic chemical principle of SCR flue gas denitration, dynamics of SCR denitration microscopic reaction process is analysed. The gas diffusion mass transfer theory and the surface chemical reaction theory are applied to SCR denitration micro reaction process. Then the CFD software is used to establish the denitration system model structure and the simulation calculation.Based on BMCR conditions(maximum evaporation boiler), The simulation analysis of adding diversion structure(guide plate and rectifying grille) on the denitration system flow field and concentration field are studied. The coal-fired boiler under variable working conditions and the flue gas parameters(gas flow rate, gas temperature, nitrogen oxides generation) are studied.Under variable working conditionsa,the change of the flue gas parameters for simulating the effect of structure arrangement is analyzed. According to the urea ammonia spray phenomenon, The proposed Taylor analogy model and wave broken broken model are applied the simulation analysis under different nozzle outlet pressure conditions.The nozzle and the export of ammonia concentration field and flow field distribution are simulated.The results of test and analysis suggest that the denitration system and ammonia concentration in flue gas velocity distribution as the change of rectifier grating Angle is different, the flow nonuniformity along with the increase of the Angle, first fall after rise trend, inhomogeneity and ammonia concentration decreases with increasing Angle.For both the flow field and concentration field.Under the same conditions,it is existed the best point of view. Under variable working condition, along with the reduction in working condition, It is inhibitory effect on the flow field at the Angle of 30 ° rectifier grille, the velocity of non-uniform coefficient is increased gradually;But the non-uniform of ammonia concentration decreases continuously with the reduction in working condition, It is conducived to the catalytic reduction reaction.The non-uniformity of velocity decreases from 47.42% to 12.34%, but NH3 uniformity is not satisfied in the preliminary scheme. When the grid angle of 30°and 3 pieces of 1/4 circulate plates arranged in the reactor inlet corner spacing, the non-uniformity of velocity and mole fraction of NH3 are 8.27%and 9.53% respectively, which satisfy the technical requirements.The scheme can meet operation requirements under different loads. Under the condition of different nozzle pressure, When nozzle pressure increased, inlet velocity increased significantly, but at the same time the gas vortex characteristic intensity weaken, spray cone is smaller;A cone-shaped spray droplets along the axis of the nozzle basic symmetric distribution, with the increase of and nozzle distance, droplet particles decreases until broken, and the distribution of droplet more diffuse;Near the nozzle axis of droplets and the diameter of particles, the periphery of the droplet diameter smaller particles.When the nozzle pressure in 0.3~0.4MPa, the atomization uniformity is best. |
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