| China is a large energy consumer and coal is the most important component of China's primary energy consumption structure.Pollutants emission due to coal utilization is one of the most important causes of atmospheric pollution in China.Adhering to the development concept of"Green waters and green mountains are gold and silver"and drived by the important national needs such as the improvement of regional atmospheric environmental quality and green development,China has made important breakthroughs in the theory and technology of stationary source pollutant removal.With the realization of ultra-low emissions of conventional pollutants from coal-fired power plants?PM<5mg/m3,SO2<35mg/m3,NOx<50mg/m3?,emission problems of special fine particles such as condensable particulate matter?CPM?formed by condensation of H2SO4,NOx,NH3,VOCs and other components have become increasingly prominent.At present,the existing control technologies of particulate matter in coal-fired fuel gas mainly focuse on the filterable particle matter?FPM?,but there are few studies on CPM.CPM can be generated in large quantities in high humidity flue gas after wet desulfurization,which is difficult to be removed efficiently by the traditional particulate control technology.A number of studies at home and abroad showed that the removal efficiency can be effectively improved by increasing the size of fine particles.Therefore,it is of great theoretical significance,academic value and application prospect to study the growth mechanism of CPM and to explore the methods to strengthen the rapid condensation and agglomeration growth of condensable fine particles.In order to solve this problem,by means of experimental research,calculation and analysis,weight comparison and engineering verification,this paper studied evolution of condensable fine particle size distribution in simulated flue gas by external regulation,so as to explore the method of enhancing the efficient removal of CPM.Firstly,the evolution mechanisms of different particle sizes and concentration of sulfuric acid aerosol,sulfate aerosol,ash-salt droplets as progressive particles of different components were studied in growth tube.It was found that the particle size distribution of sulfuric acid aerosol was approximately normal,with the largest number concentrations at 0.04?m.When NH3 was introduced,sulfate aerosols were produced,which to some extent promote the growth of sulfuric acid aerosols.At increased ammonia concentration from 10 ppm to 30 ppm,the peak of growth factor shifted rightward and increased from 1.21 to 1.35 and the range of growth factor>1was significantly broadened due to joint action of multiple mechanisms.Continuing adding fly ash,ash-salt droplets system formed,in which the CPM with smaller size adhered to the surface of fly ash,increasing the viscosity and making it easier for particles to aggregate and grow.Based on this,the growth rate of CPM in the process of condensation and agglomeration was calculated and analyzed.It was found that the temperature and moisture content of flue gas had a great influence on the condensation growth rate,because both cooling and humidification were beneficial to increase the water around the particles.It was easier for particles to contact and absorb the surrounding water,resulting in condensation growth enhancement,but there were little effect on the rate of agglomeration growth.For the CPM formed of NH3 and SO3,the evolution mechanism of particle size distribution during the process of growing was explored by adjusting the external field conditions such as temperature,flow rate,atomizing liquid and electrical discharge.It was found that cooling flue gas could enhance the CPM growth due to vapor condensation.At decreased temperature from 45°C to 30°C,the median diameter of CPM increased by 15%.In addition,the growth and agglomeration of CPM can be further enhanced when an external electrical field was utilized.The size range of growth factor>1 can be broadened,and the peak growth factor significantly increased at 8 kV applied voltage.Meanwhile,the univariate analysis method and neural network algorithm were used respectively to analyze the data of CPM growth.The results showed that cooling and electrical discharg have great effects on the growth and reduction of the number concentration of CPM,among which cooling is the most effective way to promote the growth of CPM.Finally,based on the above research results,a phase-change condensation cooperative water collection device was installed after the wet desulfurization tower of a combined heat and power coal-fired unit.The growth process and removal effect of fine particle were explored by changing temperature of the fuel gas.The influence of the temperature drop on the water recovery in high-humidity flue gas was calculated and the corresponding energy utilization was analysed.The effect of this device combined with wet electrostatic precipitator on the final pollutant emissions was tested at last.The results showed that both the mass concentration and number concentration of fine particles at the oulet of the wet desulfurization tower decreased greatly by installing a phase-change condensing cooperative water collection device.When the temperature drop?T was changed from 2.9?to 4.6?,the total number concentration decreased from 55.7%to 86.5%.According to theoretical calculations,the amount of condensed water can reach 1.92 t/h when the temperature of fuel gas drops by 5?.The mass concentration of SO3 at the wet electrostatic precipitator outlet can almost be kept below 0.5mg/m3. |
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