循环流化床大气污染物排放模型研究

Model research of air pollutant emission in circulating fluidized bed

随着国家对燃煤电厂大气污染物的排放要求日益严格,循环流化床锅炉因为煤种适应性好,大气污染物排放量低而越来越受到重视。为研究循环流化床大气污染物的排放规律,并对实际运行提供科学依据,从循环流化床锅炉燃烧机理入手,将入炉煤分为挥发分和待燃烧的即燃碳。SO2与NOx的生成也随之分为2部分:一部分随挥发分燃烧立即生成,另一部分随即燃碳燃烧生成。炉内SO2脱除量主要重视钙硫比,而炉内NOx自还原量则主要与炉内即燃碳量和一氧化碳浓度相关。以此为基础推导出了脱硫塔入口SO2浓度与NOx浓度模型。模型在某330 MW亚临界循环流化床的运行数据上得到验证,模型计算值与实际值拟合度较好,且较实际值提前2~4 min,消除了由于大气污染物测点位置原因带来的测量延迟,具有很好的预测效果。探究了炉内即燃碳量与脱硫塔入口SO2浓度和SNCR入口NOx浓度之间的关系,计算结果表明,在脱硫剂变化不大的情况下,即燃碳量变化趋势与脱硫塔入口SO2浓度变化趋势相同,与SNCR入口NOx浓度变化趋势相反。最后在原有运行数据上改变了风量和煤量后利用模型进行计算,结果表明煤量不变而风量提升会降低脱硫塔入口SO2浓度,但会提高SNCR入口NOx浓度,而煤量提升对大气污染物排放浓度的影响与风量提升相反,该计算结果对实际运行有一定指导作用。

With the country's increasingly strict requirements for the emission of air pollutants from coal-fired power plants,circulating fluidized bed boiler has attracted more and more attention because of its good adaptability to coal and low emission of air pollutants.In order to study the emission law of air pollutants in CFB and provide a scientific basis for the actual operation,and based on the combustion mechanism of CFB boiler,the coal in the boiler was divided into volatile and burning carbon.The formation of sulfur dioxide and nitrogen oxide was also divided into two parts,one was generated immediately with the combustion of volatile matter,the other was generated with the combustion of burning carbon.The amount of sulfur dioxide removal in the furnace mainly focused on the calcium sulfur ratio,while the amount of nitrogen oxide self reduction in the furnace was mainly related to the amount of burning carbon and carbon monoxide concentration in the furnace.On this basis,the models of SO 2 concentration and NO x concentration at the inlet of desulfurization tower were derived.The model has been verified on the operation data of a 330 MW subcritical circulating fluidized bed.The calculated value of the model is in good agreement with the actual value,and it is about 2-4 minutes ahead of the actual value,which eliminates the measurement delay caused by the location of the measurement points of air pollutants,and has a good prediction effect.The relationship between the amount of burning carbon in the furnace and the sulfur dioxide concentration at the inlet of the desulfurization tower and the nitrogen oxide concentration at the inlet of SNCR was studied.The calculation results show that the change trend of the amount of burning carbon is the same as that of the sulfur dioxide concentration at the inlet of the desulfurization tower and is the opposite with that of the nitrogen oxide concentration at the inlet of SNCR when the desulfurizer does not change much.At last,the model was used to calculate after changing the air volume and coal volume on the original operation data.The results show that the increase of air volume will reduce the sulfur dioxide concentration at the inlet of desulfurization tower under the condition of constant coal quantity,but increase the nitrogen oxide concentration at the inlet of SNCR.However,the effect of coal volume increase on the concentration of air pollutants emission is opposite to that of air volume increase.The calculation results have a certain guiding effect on the actual operation.