燃煤过程汞析出及模拟烟气中汞吸附脱除试验和机理研究
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摘要
汞及其化合物是环境污染物控制的污染物种，煤燃烧是大气汞污染的一个主要来源，对其研究已成为当今环境研究的前沿问题。
本文系统介绍了汞的物化性质、危害、环境来源，着重叙述了煤中汞赋存特性以及国内外有关燃煤汞测量和控制的研究进展，并且在国外测试方法的基础上，完善并形成了一整套适于试验研究的采样、预处理方法和基于原子荧光光谱法(CVAFs)的分析技术。
利用加热装置(烘箱或马弗炉)进行了煤样的裂解或燃烧试验，加热温度越高，加热时间越长，半焦或灰渣中的的汞越少；在相同条件下，裂解与燃烧相比汞析出相对较少。在600～700℃以上加热，较短时间内煤样中的汞可基本析出，主要以气态方式进入烟气。
本文研究了煤在层燃、悬浮燃烧、流化床燃烧三种不同燃烧方式条件下，煤中汞的析出规律。三种燃烧条件下燃烧产物中气态、颗粒态汞分布相似，在燃烧区域内主要以单质汞形式存在，气态汞是燃煤汞排放的主要形式，但是又由于具体燃烧条件和煤种的不同而有差异。
在煤粉层燃条件下，随着温度升高，烟气中的零价汞含量逐渐降低，二价汞含量逐渐升高。层燃和悬浮燃烧两种条件下，二价汞(Hg_g~(2+))和零价汞(Hg_g~0)的形态分布规律相似，烟气中气态汞总量在10～15μg/Nm~3范围内，二价汞(Hg_g~(2+))占气态总汞的比例在40％以上，较低的烟气冷却速率可以促进零价汞向二价汞的转化。利用循环流化床形式将石煤和烟煤混合燃烧，烟气中的气态汞含量在6.8～9.3μg/Nm~3范围内，小于10μg/Nm~3。底渣中的汞含量很低，占汞总量的3％～7.6％；飞灰中的汞含量相对较高，烟气中汞含量相对较低，这与纯烟煤燃烧不同。加入石灰石后，飞灰汞含量增加了16％以上，烟气汞向大气的直接排放有所减少。
本文还采用固定床试验系统，采用吸附剂(活性炭、石灰、沸石、Ca(OH)_2、生物质半焦等)吸附的方法在模拟烟气条件下进行了各种烟气成分、浓度、温度等因素对吸附效果影响的研究。Hg~0浓度增加会促进活性炭的吸附作用；烟气成分SO_2对汞吸附有一定的抑制作用；而HCl对汞吸附有促进作用等，这一点也表明活性炭对Hg的吸附作用既包括物理吸附，同时也包括化学吸附的过程；C/Hg比增加后，吸附效率相应提高，单位吸附量降低，说明活性炭的利用率降低了；含碳量高的飞灰样品与含碳量低的飞灰相比，吸附量大，但是含碳量与飞灰的吸附能力不成比例；飞灰和活性炭在很多方面都很相似，活性炭在低温下吸附效果更好，飞灰也得到了同样的结果；熟石灰、石灰以及飞灰和熟石灰的混合物三种钙基类物质在SO_2存在时都表现出比在基本气体条件下较高的吸附量
浙江大学博士学位论文
和吸附效率;吸附剂经改性处理后可改善吸附效果，活性炭经过注氯化学处理后，吸附
性能显著成倍增加;沸石、膨润土和蛙石改性后，其单位吸附量均有不同程度增加。
通过模型计算，选取基本工况，对活性炭、飞灰、石灰等吸附剂的吸附过程进行了
模拟，结果基本吻合;通过模型分析，选取某些影响因素，预测了在一定运行条件下活
性炭吸附剂的吸附量和穿透曲线。结果表明，随着颗粒粒径增大，吸附量曲线上升幅度
减缓，吸附效率降低，较小的颗粒粒径对吸附的进行更有利;在保证一定c旧g比的条
件下，随着入口浓度增大，单位吸附量也相应增大，活性炭的利用率提高了;接触时间
延长后，吸附效率增加，吸附量曲线增长缓慢，吸附剂的单位吸附量降低。在较低的吸
附温度下，有利于吸附效率的增加，这是由物理吸附的特点决定的。本模型的建立可以
用来指导固定床汞吸附装置的设计，预测现有固定床除汞装置的脱除效率和计算吸附量。
影响燃煤电站汞排放的主要因素归纳起来有煤中汞含量，电站锅炉炉型，锅炉运行
条件，所采用的烟气清洁装置类型。利用汞排放修正因子，可以估算燃煤电站汞排放量。
Mercury has long been identified as a hazard to human health and the environment. Since coal-fired power plants represent a significant fraction of the anthropogenic emissions of mercury into the atmosphere, the speciation and control of mercury in coal-fired power plants is currently an active topic of research.
First, the physical and chemical properties, the distribution and occurrence characteristics of Chinese coal were presented in the paper. The information of mercury measurement and control in coal-fired power plants was introduced systematically. Based on Ontario-Hydro method, the method of the mercury sampling, disposal and analysis method (CVAFs) was established.
The coal sample was heated in heating oven, the mercury content of the residual after coal combustion or pyrolysis was investigated with different temperature and heating time. The results indicate that mercury in coal during coal combustion discharge faster than during coal pyrolysis. Nearly all of the mercury in coal samples discharge rapidly in gaseous state at high temperature (above 700℃) during coal combustion or pyrolysis.
The studies of the mercury transformation mechanism with different coal combustion mode were performed. Coal of grate firing, suspension firing and fluidi/ed bed firing experiments were carried out respectively in a quartz tube furnace, a bench-scale pulverized coal furnace and a pilot-scale CFB system. The experimental data showed that the speciation of mercury occurring under the above three systems were similar, however mercury behave differently because of the difference of the combustion conditions and coal species etc.
The data of coal grate firing and suspension firing shows that the gaseous mercury concentrations in the flue gas range from 10 and 15 (μg/Nm~(3), emissions of mercury are approximately 40% divalent mercury (Hg_(g)~(2+)) in the flue gas, and mercury in the ash was below 20%, which suggested that most of the mercury went into the flue gas in gaseous state. In addition, the cooling rate of hot flue gas is considered to be an important factor tending to increase the conversion ratio of elemental mercury (Hg_(g)~(0)) to divalent mercury (Hg_(g)~(2+)) with slower cooling rate.
Stone coal mixed with bituminous coal combustion in fluidized bed System showed that the gas phase concentration of mercury in the flue gases is 6.8-9.3 μg/Nm~(3), the content of mercury in ash and flue gas is about 90%, and in bottom ash, the content is very low. The effect of limestone as the additive into stone coal is obvious, it increases the content of mercury in ash and decreases the mercury content in flue gas.
The mechanisms and rate of elemental mercury (Hg~(0)) capture by activated carbons and
other sorbents such as fly ash, lime, zeolite, roseite and bentonite, have been studied using a bench-scale fixed-bed apparatus. The effects of inlet mercury concentration, flue gas composition, and adsorption temperature were investigated to determine the abilities to remove mercury in simulated flue gas streams. The amount of mercury adsorbed increased with increasing carbon content. Temperature had a tremendous impact on the adsorbed-phase mercury concentration, the adsorption capacities increased as the temperature decreased. These data are consistent with a physical adsorption mechanism. However the adsorption capacities were also affected by flue gas composition, SO_(2) HC1 and other flue gases, which suggested the mechanism is not purely physical, may be a combination of physisorption and chemisorption. Sorbents modified chemically resulted an increase of mercury removal capacity. Activated carbon were impregnated with chloride, The chloride content of chloride-impregnated AC increased slightly, which resulted an increase of mercury removal capacity.
A Theoretical model was developed to predict mercury removal based on sorbents characteristics as determined in laboratory fixed-bed reactor tests at different conditions. The simulation results indicated that the model is capable of describing the te
本文系统介绍了汞的物化性质、危害、环境来源，着重叙述了煤中汞赋存特性以及国内外有关燃煤汞测量和控制的研究进展，并且在国外测试方法的基础上，完善并形成了一整套适于试验研究的采样、预处理方法和基于原子荧光光谱法(CVAFs)的分析技术。
利用加热装置(烘箱或马弗炉)进行了煤样的裂解或燃烧试验，加热温度越高，加热时间越长，半焦或灰渣中的的汞越少；在相同条件下，裂解与燃烧相比汞析出相对较少。在600～700℃以上加热，较短时间内煤样中的汞可基本析出，主要以气态方式进入烟气。
本文研究了煤在层燃、悬浮燃烧、流化床燃烧三种不同燃烧方式条件下，煤中汞的析出规律。三种燃烧条件下燃烧产物中气态、颗粒态汞分布相似，在燃烧区域内主要以单质汞形式存在，气态汞是燃煤汞排放的主要形式，但是又由于具体燃烧条件和煤种的不同而有差异。
在煤粉层燃条件下，随着温度升高，烟气中的零价汞含量逐渐降低，二价汞含量逐渐升高。层燃和悬浮燃烧两种条件下，二价汞(Hg_g~(2+))和零价汞(Hg_g~0)的形态分布规律相似，烟气中气态汞总量在10～15μg/Nm~3范围内，二价汞(Hg_g~(2+))占气态总汞的比例在40％以上，较低的烟气冷却速率可以促进零价汞向二价汞的转化。利用循环流化床形式将石煤和烟煤混合燃烧，烟气中的气态汞含量在6.8～9.3μg/Nm~3范围内，小于10μg/Nm~3。底渣中的汞含量很低，占汞总量的3％～7.6％；飞灰中的汞含量相对较高，烟气中汞含量相对较低，这与纯烟煤燃烧不同。加入石灰石后，飞灰汞含量增加了16％以上，烟气汞向大气的直接排放有所减少。
本文还采用固定床试验系统，采用吸附剂(活性炭、石灰、沸石、Ca(OH)_2、生物质半焦等)吸附的方法在模拟烟气条件下进行了各种烟气成分、浓度、温度等因素对吸附效果影响的研究。Hg~0浓度增加会促进活性炭的吸附作用；烟气成分SO_2对汞吸附有一定的抑制作用；而HCl对汞吸附有促进作用等，这一点也表明活性炭对Hg的吸附作用既包括物理吸附，同时也包括化学吸附的过程；C/Hg比增加后，吸附效率相应提高，单位吸附量降低，说明活性炭的利用率降低了；含碳量高的飞灰样品与含碳量低的飞灰相比，吸附量大，但是含碳量与飞灰的吸附能力不成比例；飞灰和活性炭在很多方面都很相似，活性炭在低温下吸附效果更好，飞灰也得到了同样的结果；熟石灰、石灰以及飞灰和熟石灰的混合物三种钙基类物质在SO_2存在时都表现出比在基本气体条件下较高的吸附量
浙江大学博士学位论文
和吸附效率;吸附剂经改性处理后可改善吸附效果，活性炭经过注氯化学处理后，吸附
性能显著成倍增加;沸石、膨润土和蛙石改性后，其单位吸附量均有不同程度增加。
通过模型计算，选取基本工况，对活性炭、飞灰、石灰等吸附剂的吸附过程进行了
模拟，结果基本吻合;通过模型分析，选取某些影响因素，预测了在一定运行条件下活
性炭吸附剂的吸附量和穿透曲线。结果表明，随着颗粒粒径增大，吸附量曲线上升幅度
减缓，吸附效率降低，较小的颗粒粒径对吸附的进行更有利;在保证一定c旧g比的条
件下，随着入口浓度增大，单位吸附量也相应增大，活性炭的利用率提高了;接触时间
延长后，吸附效率增加，吸附量曲线增长缓慢，吸附剂的单位吸附量降低。在较低的吸
附温度下，有利于吸附效率的增加，这是由物理吸附的特点决定的。本模型的建立可以
用来指导固定床汞吸附装置的设计，预测现有固定床除汞装置的脱除效率和计算吸附量。
影响燃煤电站汞排放的主要因素归纳起来有煤中汞含量，电站锅炉炉型，锅炉运行
条件，所采用的烟气清洁装置类型。利用汞排放修正因子，可以估算燃煤电站汞排放量。
Mercury has long been identified as a hazard to human health and the environment. Since coal-fired power plants represent a significant fraction of the anthropogenic emissions of mercury into the atmosphere, the speciation and control of mercury in coal-fired power plants is currently an active topic of research.
First, the physical and chemical properties, the distribution and occurrence characteristics of Chinese coal were presented in the paper. The information of mercury measurement and control in coal-fired power plants was introduced systematically. Based on Ontario-Hydro method, the method of the mercury sampling, disposal and analysis method (CVAFs) was established.
The coal sample was heated in heating oven, the mercury content of the residual after coal combustion or pyrolysis was investigated with different temperature and heating time. The results indicate that mercury in coal during coal combustion discharge faster than during coal pyrolysis. Nearly all of the mercury in coal samples discharge rapidly in gaseous state at high temperature (above 700℃) during coal combustion or pyrolysis.
The studies of the mercury transformation mechanism with different coal combustion mode were performed. Coal of grate firing, suspension firing and fluidi/ed bed firing experiments were carried out respectively in a quartz tube furnace, a bench-scale pulverized coal furnace and a pilot-scale CFB system. The experimental data showed that the speciation of mercury occurring under the above three systems were similar, however mercury behave differently because of the difference of the combustion conditions and coal species etc.
The data of coal grate firing and suspension firing shows that the gaseous mercury concentrations in the flue gas range from 10 and 15 (μg/Nm~(3), emissions of mercury are approximately 40% divalent mercury (Hg_(g)~(2+)) in the flue gas, and mercury in the ash was below 20%, which suggested that most of the mercury went into the flue gas in gaseous state. In addition, the cooling rate of hot flue gas is considered to be an important factor tending to increase the conversion ratio of elemental mercury (Hg_(g)~(0)) to divalent mercury (Hg_(g)~(2+)) with slower cooling rate.
Stone coal mixed with bituminous coal combustion in fluidized bed System showed that the gas phase concentration of mercury in the flue gases is 6.8-9.3 μg/Nm~(3), the content of mercury in ash and flue gas is about 90%, and in bottom ash, the content is very low. The effect of limestone as the additive into stone coal is obvious, it increases the content of mercury in ash and decreases the mercury content in flue gas.
The mechanisms and rate of elemental mercury (Hg~(0)) capture by activated carbons and
other sorbents such as fly ash, lime, zeolite, roseite and bentonite, have been studied using a bench-scale fixed-bed apparatus. The effects of inlet mercury concentration, flue gas composition, and adsorption temperature were investigated to determine the abilities to remove mercury in simulated flue gas streams. The amount of mercury adsorbed increased with increasing carbon content. Temperature had a tremendous impact on the adsorbed-phase mercury concentration, the adsorption capacities increased as the temperature decreased. These data are consistent with a physical adsorption mechanism. However the adsorption capacities were also affected by flue gas composition, SO_(2) HC1 and other flue gases, which suggested the mechanism is not purely physical, may be a combination of physisorption and chemisorption. Sorbents modified chemically resulted an increase of mercury removal capacity. Activated carbon were impregnated with chloride, The chloride content of chloride-impregnated AC increased slightly, which resulted an increase of mercury removal capacity.
A Theoretical model was developed to predict mercury removal based on sorbents characteristics as determined in laboratory fixed-bed reactor tests at different conditions. The simulation results indicated that the model is capable of describing the te
引文
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