Study On The Pollutant Emission Characteristic Under The Dynamic Compound Combustion Of Coal-pulverized Coal

The circulating fluidized bed boiler,which dues to its wide adaptability of fuel,low pollutant emissions and large range of load regulation,has been developed rapidly in our country.The circulating fluidized bed boiler unit occupy a larger proportion.Simultaneously,wind and solar power generation grid-connected on the power generation massively.Wind and solar power generation that have uncertainty and intermittence put forward higher requirement for dispatching of power grid.It creates a pair of prominent contradiction.On the one hand,the power grid requires the unit have the ability adjust to the load quickly.On the other hand,the circulating fluidized bed load regulation rate is slower because of the large thermal inertia.This is the inherent characteristic of the circulating fluidized bed,and can not be solved by the adjustment of combustion.Address this issue,this paper presents the coal-pulverized coal dynamic compound combustion technology.The technology use the characteristics of fast heat release from pulverized coal combustion and introduces the right amount of pulverized coal into the CFB boiler combustion dynamically,so the load change rate of CFB boiler can be improved.Depending on a 240t/h high temperature and high pressure,single drum transverse type,single furnace,natural circulation,full steel frame PI type circulating fluidized bed boiler in a thermoelectric plant,the pulverized coal feeding point is arranged at the coal feeding port and the secondary air inlet of the 240t/h circulating fluidized bed boiler,a series of dynamic compound combustion experiment of coal-pulverized coal are carried out in the research,the dynamic load variation characteristics and pollutant emission characteristics of CFB boiler under compound combustion mode are studied.The composite combustion experiment consists of two parts:low calorific value coal-high calorific value pulverized coal and single quality coal-pulverized coal combined combustion experiment.For low calorific value coal-high calorific value pulverized coal dynamic composite combustion experiment,the influence of the different pulverized coal location,the calorific value of pulverized coal and the step heat ratio of pulverized coal to coal on the emission concentration of CO,NO_X and SO₂ were investigated.In order to observe the relationship between load change rate and NO_X,SO₂ emission,the load change rate of the working condition and the average value of NO_X and SO₂ emission are plotted and the Pearson correlation coefficient is analyzed.The correlation of the bed temperature,oxygen content and NO_X and SO₂ emission concentration in this test is compared.The single quality coal-pulverized coal combined combustion test study the effect of different primary and secondary step air volume ratios and raw coal particle size changes?by changing the proportion of pulverized coal in the raw coal to simulate changes in raw coal particle size?for load change rates and CO,NO_X and SO₂ emissions concentration.The result and analysis show that when the pulverized coal were injected at the secondary air inlet,the response rate of boiler load is faster;CO emission concentration is lower,the average value is 141.5mg/m3;the NO_X and SO₂concentration are higher,the average value are 164mg/m3 and 3495.5mg/m³.Compared with 19.30MJ/kg pulverized coal,CO emissions decrease by about8-11mg/m³ while NO_X and SO₂ emission increase by 9-10mg/m³ and130-160mg/m³ when 27.17MJ/kg pulverized coal is injected.The change rate of boiler load increases with the increase of pulverized coal step.When the step heat proportion of pulverized coal and the step heat coal increase,the concentration of CO emission decrease,and the concentration of NO_X and SO₂also increase.When the the step heat proportion of pulverized coal and coal is1:1,the CO emission is about 135mg/m³,NO_X and SO₂ are 155mg/m³ and3625mg/m³.The correlation between NO_X and SO₂ emission concentration and bed temperature is higher than that of oxygen content.In the process of dynamic combined combustion of single coal,When the secondary air inlet and the the coal feeding port are fed into the pulverized coal,The load response rate and NO_X emission concentration increase with the increase of primary air ratio;The emission concentration of CO decreases with the increase of primary air ratio;SO₂ emission always rises with the increase of primary air ratio.The concentrations of CO and NO_X and SO₂ are lower.When the proportion of pulverized coal becomes larger,the particle size becomes thinner,the load response rate becomes faster.