节点文献
生物质燃烧氯的析出与控制研究
Study on Release and Control of Chlorine during Biomass Combustion
【作者】 郭献军；
【导师】 肖波；
【作者基本信息】 华中科技大学 ， 环境工程， 2009， 博士
【摘要】 在生物质燃烧过程中由氯引起的沉积、结渣和腐蚀问题已引起人们的关注。本文首次系统地对生物质氯的测试方法、生物质氯的赋存形态、生物质燃烧过程氯化物的析出规律、燃烧固氯机理与技术等一系列基础问题进行理论与实验研究，旨在开发出以工业废弃物为固氯剂的生物质燃烧固氯新技术。主要研究成果如下：1)首次系统研究了高温燃烧水解——氯离子选择电极法和艾氏卡剂熔样——硫氰酸钾滴定法测定生物质氯的影响因素，分析测量精度，确定最优测量参数。得出高温燃烧水解法的最优测试条件为燃烧温度900℃、燃烧时间20min、水蒸气量2mL／min、试样量0．5克、氧气量400～500mL／min；艾氏卡剂熔样法的最优测试条件为生物质试样1．5克，艾氏卡剂5克，从室温加热到500～600℃然后保持2小时。确定高温燃烧水解法为本研究所采用的测氯方法。2)采用统计和浸提实验研究了我国生物质氯的赋存形态。结果表明，生物质氯与挥发份和碳成指数减小，与灰分和硫成指数增加；且生物质氯的水浸提、酸浸提和碱浸提的浸出率普遍较高。得出生物质氯主要以无机态存在的结论。3)建立了固定床管式炉生物质燃烧氯化物析出实验装置和研究方法；确定了生物质燃烧过程氯析出的影响因素和影响关系；初步建立生物质燃烧过程氯析出的动力学模型。结果表明：生物质中氯析出率随燃烧温度的升高而增加，在不同温度区间，温度对氯析出率的影响程度不同；随着燃烧时间的增加氯析出率明显增加；随炉内气氛氧化性减弱，氯析出率明显降低；燃燃烧过程烟气中水蒸气可促进生物质氯的析出；生物质粒径对氯含量和氯析出都有一定的影响，随着试样粒径的增加，氯析出率呈降低趋势；生物质燃烧过程中氯的析出可用一级反应动力学模型来描述，棉秆和烟草氯析出的反应活化能分别为18．8437kJ／mol和19．7956kJ／mol，则它们可在较低温度下析出氯化物。4)通过固定床管式炉燃烧实验，研究了生物质燃烧过程氧化钙的固氯作用及影响因素，并对粉煤、赤泥和磷石膏的固氯效果进行实验研究；从化学反应热力学和动力学两方面分析氧化钙燃烧固氯机理。结果表明，在生物质燃烧过程中氧化钙、粉煤、赤泥和磷石膏都有较好的脱氯效果，高温和较长的燃烧时间大大降低了其脱氯效率，而较小的粒径和较多的固氯剂添加量有利于提高脱氯效果；在298K～1200K温度范围内，CaO-HCl脱氯反应可自发进行，反应限度很深，但生物质水分和空气中水分会使脱氯反应向水解反应方向进行，降低脱氯效率；收缩核模型可以较好地反映脱氯反应的动力学，预测反应温度、HCl气体浓度和CaO粒径对反应的影响。5)详细阐述生物质微米燃料特性及其燃烧技术；进行微米燃料悬浮燃烧固氯技术小试和中试研究。得出不同固氯剂的固氯效果、固氯剂添加量的影响与在管式炉实验条件下的固氯效果基本一致，在900℃燃烧时不同固氯剂的固氯效果依次为：磷石膏＞赤泥＞氧化钙＞粉煤；加入固氯剂不同程度改善了生物质燃烧灰结渣问题，且对烟气中二氧化硫的量影响不大；粉煤是理想的固氯剂，加入适量的粉煤不仅起到固氯作用，而且能改善灰的结渣问题，同时提高燃料燃烧热值。
【Abstract】 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.