Study On Release And Control Of Chlorine During Biomass Combustion

The chlorine-related problem of ash deposition and slagging and corrosion is interesting.In this paper,a series of key problems on the method of measuring chlorine in biomass,the occurrence characteristics of chlorine in biomass,the chlorine emission properties and the mechanism and technology of removal chlorine during biomass combustion were systemically studied by the intergation of theory and experiment. The technology of removal chlorine using industrial waste was presented.The results are following:1)The methods of measuring chlorine in biomass such as pro-hydrolysis—chlorine ion-selective electrode method (PHCIE) and aldrin melt sample—potassium thiocyanate titration method (AMST) were systemically studied for the first time,as well as these factors affecting determination of chlorine in biomass.At the same time,the precision and the optimal parameters of the two methods were presented.The results are as follows: the optimal parameters of PHCIE are combustion temperature of 900℃,combustion time of 20 minutes,steam flow of 2mL/min,biomass sample quality of 0.5g,oxygen flow of 400⁵00mL/min.The optimal parameters of AMST are biomass sample quality of 1.5g, aldrin quantity of 5g,heating from room temperature to 500～600℃and retaining 2 hours.The PHCIE was selected to serve the work.2)The occurrence characteristics of chlorine in biomass were studied by statistics and extracting tests. The results show that there are exponentially decreasing relationship of chlorine and volatile and carbon element, exponentially increasing relationship of chlorine and the content of ash and sulfur element.The extracting rate of chlorine in biomass by water,acid and alkali is obviously high.The results show that chlorine in biomass is mainly inorganic.3)The experimental system of tube furnace was set up.The emission characteristics of chlorine during biomass combustion was studied by the test system,and the mechanism of gas chlorine formation and chlorine precipitation kinetic model during biomass combustion were also presented.The results are as follows: precipitation rate of chlorine in biomass increases with combustion temperature, the effect of temperature on the precipitation rate of chlorine are differen in various temperature range. The precipitation rate of chlorine increases with combustion time and water content in flue gas. At the same time ,the precipitation rate of chlorine decreases with oxidation combustion atmosphere decreasing and biomass particle size increasing.The chlorine precipitation kinetic model during biomass combustion is to obey fisrt-order reaction kinetics.The activaton energy of the samples of cotton and tobacco are respectively 18.8437kJ·mol^-1 and 19.7956 kJ·mol^-1,showing chlorine in the samples can release in a low temperature. 4)The effect of calcium oxide,powdery coal,red mud and phosphogypsum on removal chlorine were studied in detail by the combustion experimental system of tube furnace. Based on chemical reaction thermodynamics and kinetics, the mechanism of removal chlorine by calcium oxide was studied. The results are as follows:The removal chlorine performances of calcium oxide ,powdery coal,red mud and phosphogypsum are good.Especialy, less particle size and more additive increase the removal chlorine performance.But a high temperature and a long combustion time decrease the performance.In the temperature range of 298K¹200K,the removal chlorine reaction of CaO - HCl is spontaneous chemical reaction , and the reaction limits are deep.But water in biomass and air can decrease performance of removal chlorine.The chemical reaction model of shrinking core can well explain the kinetics of removal chlorine,forecast the effects of temperature and HCl-content and particle size of calcium oxide.5)The biomass micron fuel (BMF) and the suspension technology of BMF combustion were presented in detail,and the technical studies on removal chlorine during BMF combustion were carried by small-scale and pilot-scale tests.The results of the tests are consistent with that of tube furnace.In the temperature of 900℃,the performances of different additive are following: phosphogypsum> red mud >calcium oxide>powdery coal.The additives improve the ash slagging and slightly affect the content of sulfur dioxide in flue gas.Comparing the different additives,powdery coal is an better additive for not only removal chlorine,but increasing the value of biomass.