| With the introduction of ultra-low emission policy,thermal power plants have carried out large-scale desulfurization and denitration transformation.The blockage of air preheater after selective catalytic reduction(SCR)is particularly prominent.The reason is that NH3 escaping after SCR denitration and ammonia bisulfate(ABS)generated by SO3 in flue gas are condensed and deposited in the air preheater.If the blockage of air preheater can be accurately judged and early warning can be put forward,it will help to guide the staff in the power plant to take corresponding measures in time to reduce the blockage of air preheater.In this paper,the blocking problem of air preheater is deeply studied,and the blocking early warning model of air preheater is proposed.Firstly,from the perspective of the whole process from the boiler to the SCR outlet,using the methods of SO3 reaction kinetics and denitration reaction kinetics,this paper establishes a model to predict the generation temperature of ABS in the air preheater according to the sulfur content in coal and SCR denitration parameters.The model solves the difficulty of calculating ABS generation temperature by measuring SO3 concentration and NH3 concentration in the past,and has passed the accuracy verification of the actual data of the power plant.The effects of different sulfur content in coal,different NH3/NOx molar ratio,different NOx concentration at SCR inlet and different denitration efficiency on ABS generation temperature were further studied.The results show that the increase of sulfur content in coal leads to the increase of SO3 concentration in flue gas and the rapid increase of ABS formation temperature;When the NH3/NOx molar ratio exceeds 0.9,continue to increase the NH3/NOx molar ratio,resulting in the rapid increase of ABS generation temperature;With the increase of NOx concentration at SCR inlet,the generation temperature of ABS increases;When the denitration efficiency exceeds 93%,continue to improve the denitration efficiency,resulting in the rapid increase of NH3 escape and the rapid increase of ABS generation temperature.Then,the temperature early warning model generated by ABS is applied to the following four air preheater schemes(air preheater not modified,air heater modified,3.5 bin modified and hot air circulation modified).Combined with the temperature field distribution of the air preheater obtained by(Computational Fluid Dynamics)CFD numerical simulation,the ABS temperature early warning of the air preheater under four schemes is obtained,and the lowtemperature acid corrosion zone,medium temperature ABS corrosion zone and hightemperature common ash deposition zone are established.After the air heater is put into operation,the overall temperature of the air preheater rotor rises significantly,reducing the ABS condensation height in the air preheater,which is conducive to soot blowing and alleviating ABS corrosion;3.5 split bin reconstruction and circulating air reconstruction will help alleviate low-temperature acid corrosion,but have no obvious effect on ABS mitigation,and may even expand the ABS condensation deposition area.If the temperature in split bin after reconstruction is increased to more than 197℃,it will help alleviate the condensation corrosion of ABS in air preheater.Finally,based on the big data of Distributed Control System(DCS)of power plant,an intelligent early warning model of air preheater blockage is proposed to early warning the pressure drop of air preheater.After comparing various models,it is found that the improved BP neural network model(PSO-BP)based on particle swarm optimization algorithm(PSO)has the best prediction effect on the pressure drop of air preheater,and the correlation coefficient is 0.98769.The model can better track the change trend of pressure drop of air preheater.In practice,the model can be used to compare the predicted value with the measured value of the power plant,reflect the blockage of the air preheater and give early warning. |
