基于热力学平衡计算的燃煤电厂烟气中SO3形态研究

Reseach on SO3 morphological characteristics in flue gas of coal-fired powerplants based on thermodynamic equilibrium calculation

SO3是燃煤电厂烟气排放常见污染物之一,对系统设备稳定运行和大气环境质量有较大影响。为深化相关研究,基于热力学及酸露点理论建立了SO3形态转化计算模型,计算了不同烟气温度、湿度和SO3浓度的形态特征,确定了常规燃煤电厂烟气中SO3形态的分布特征,结果表明:燃煤电厂烟气中SO3主要以SO3气体、H2SO4气体和H2SO4气溶胶3种形态存在,形态转化基于化学反应和物理反应2个过程,化学反应指气态SO3与H 2 O结合形成气态H2SO4的过程,物理反应指在烟气温度降至酸露点以下时气态H2SO4通过均相或非均相成核形成H2SO4气溶胶的过程。此外,假设烟气湿度为8%,烟气温度低于202℃时,全部以H2SO4形态存在;烟气温度高于495℃时,全部以SO3形态存在;烟气温度低于95℃时,基本以H2SO4气溶胶的形态存在。结合常规燃煤电厂烟气湿度和温度的分布情况,则SO3形态的分布特征为:烟气脱硝装置前段,主要以SO3气体形态存在;脱硝装置至空预器段,SO3气体和H2SO4气体共同存在;空预器至脱硫装置段,H2SO4气体和H2SO4气溶胶共同存在;脱硫装置后段主要以H2SO4气溶胶形态存在,粒径<0.1μm。

SO3 is one of the common pollutants discharged from coal-fired power plants,which has a great impact on the stable operation of system equipment and the quality of atmospheric environment.In order to deepen the relevant research,SO3 morphologic transformation calculation model was established based on thermodynamics and acid dew point theory.The morphologic characteristics of different flue gas temperature,humidity and SO3 concentration were calculated,and the distribution characteristics of SO3 morphologic characteristics in flue gas from conventional coal-fired power plants were determined.The results show that SO3 in flue gas of coal-fired power plants is mainly composed of SO3 gas,H2SO4 gas and H2SO4 aerosol.The transformation of SO3 is based on chemical reaction and physical reaction.The chemical reaction is that SO3 gas reacts with H 2 O gas to H2SO4 gas and the physical reaction is that H2SO4 gas condenses to H2SO4 aerosol by homogeneous and heterogeneous nucleation when flue gas temperature is lower than dew point,respectively.In addition,assuming the valve of humidity is 8%,when the flue gas temperature is lower than 202℃,higher than 495℃and lower than 95℃,SO3 exists in the form of H2SO4 gas,SO3 gas and H2SO4 aerosol,respectively.Furthermore,combined with the distribution of flue gas humidity and temperature in conventional coal-fired power plants,the distribution characteristics of SO3 are as follows:SO3 gas,SO3 gas and H2SO4 gas,H2SO4 gas and H2SO4 aerosol,H2SO4 aerosol exist the section ahead denitrification device,between denitrification device and air preheater,between air preheater and rear section of desulfurization unit,respectively.What is more,the particle size of H2SO4 aerosol is less than 0.1μm.