新型半干法烟气脱硫的实验及机理研究
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摘要
半干法烟气脱硫工艺与传统的湿法烟气脱硫工艺相比具有投资费用低、能耗小、脱硫产物为干态、易于处理等优点。本文通过阅读大量的文献发现：吸收剂利用率低和脱硫效率低是限制半干法烟气脱硫应用的重要原因。因此，必须完善半干法烟气脱硫技术以提高脱硫效率和石灰的利用率，才能使其具有经济性上的竞争力。本文在喷雾干燥烟气脱硫工艺的基础上，结合循环流化床烟气脱硫和烟气悬浮脱硫等技术，开发了一种新型的半干法烟气脱硫工艺。该工艺结构简单，投资低，运行费用省，而且还可除去其它有害气体甚至重金属等，非常适合在国内推广应用。
石灰浆液雾化喷嘴是半干法烟气脱硫装置的关键部件，喷嘴的雾化性能对于系统的脱硫效率至关重要。喷嘴雾化特性主要包括石灰浆滴的粒径大小、分布以及喷雾角等。本文研制了一种新型低能耗的双流体雾化喷嘴，利用FAM激光测粒仪对不同气液比、不同浆液浓度下石灰浆液喷嘴的雾化特性进行了研究。结果发现这种喷嘴能耗低、寿命长、雾化性能好，具有较好的负荷适应性，在半干法烟气脱硫领域具有广阔的应用前景。
本文就运行参数对脱硫效率的影响进行了试验研究并分析了其机理，研究了增湿水对脱硫的强化作用。首先对两种脱硫剂进行对比试验，选用效果较好的一种作为整个试验研究的脱硫剂。主要研究了Ca/S、出口距绝热饱和温度的温差、入口二氧化硫浓度、烟气在吸收塔内的流速、石灰浆滴的粒径大小、有无脱硫灰再循环等运行参数对脱硫效率的影响，研究了增湿水对脱硫的强化作用以及脱硫塔轴向中心温度分布的情况。结果发现，对系统脱硫效率影响最为明显的参数是脱硫塔出口的趋近绝热饱和温度，其次为钙硫比，得出了最佳的运行参数范围；趋近绝热饱和温度一般选为10℃左右，钙硫比一般选为1.5。提高循环倍率可以提高脱硫塔和系统的脱硫效率，当运行参数保持基本工况值，钙硫比为1.5，循环倍率为10时，脱硫塔内的效率为75％左右，系统脱硫效率高达92％。增湿水的喷入点应当在石灰浆液恰好干燥位置，喷入量应为系统总耗水量的30％左右，在不进行脱硫灰渣循环情况下，当运行参数保持基本工况值，钙硫比为1.5，脱硫塔和系统的脱硫效率分别可以达到72％和87％。
本文还研究了添加剂对半干法烟气脱硫系统性能的影响。吸湿性添加剂、H_2O_2、蔗糖可以提高系统的脱硫效率，甲酸和苯酸效果不明显。对于本文的新型半干法烟气脱硫，当采用合适的添加剂，在没有脱硫灰渣再循环和增湿水的情况下，系统即可达到90％以上的脱硫效率。根据成本核算，采用NaOH和CaCl_2作为添加剂的相对成本基本相同而且较低。
本文考虑常速阶段、降速阶段、脱硫塔内干燥后阶段以及布袋除尘器的脱硫反应过程，建立了半干法烟气脱硫整体化模型。脱硫塔内气液反应模型同时考虑了气相阻力、液相传质阻力和石灰的溶解阻力。通过模型分析确定了半干法烟气脱硫工艺各阶段的反应机理。结果表明，在脱硫塔内石灰浆滴干燥的常速阶段初期，控制脱硫反应进行的阻力环节是石灰的溶解阻力。在常速阶段之后的时间内，反应过程为气膜扩散阻力所控制。当反应进行到降速阶段，限制脱硫反应的阻力环节是反应物向反应区域的扩散阻力。而在脱硫塔内干燥后阶段和布袋除尘器中气固反应的控制阻力为SO_2通过脱硫产物层的扩散。模型计算结果与试验结果吻合较好，本模型的建立可以用来指导半干法烟气脱硫装置的设计，预测现有脱硫装置的脱硫效率。
该工艺不仅适用于电站锅炉，还适用于垃圾焚烧锅炉、余热发电站以及各种燃煤或燃油
浙江人学博】：学位论义
的工业锅炉等所产生的酸性烟气净化。本系统不仅可用于新建锅炉，而且可以用于现有锅炉
的改造。脱硫塔可以同布袋除尘器配合使用也可以与电除尘器配合使用，都完全能够满足锅
炉排放标准的要求。
从本文的结果可以看出，如果继续提高循环倍率，脱硫塔的脱硫效率仍然有很大的提升
空问。另外，如果同时采用灰渣循环、分级喷水增湿和添加剂等强化脱硫反应的措施，脱硫
塔和系统的脱硫效率应该比单纯采用循环、分级喷水增湿和添加剂时还要高。浙汪大学热能
所正在对各种促进脱硫效率的措施进行综合优化研究，相信达到 95％的脱硫效率是不难实
现的。
More recently, semi-dry flue gas desulfurization techniques using finely divided lime slurry as sorbents for SO2 have drawn increasing interest. These semi-dry FGD techniques are projected to have lower capital and operating costs than the conventional wet FGD techniques. Further more, the waste product is dry powder rather than wet sludge. This offers potential advantages in the areas of waste handling and disposal. While there is an obvious economic benefit for these systems in terms of lowering of capital cost requirements, the higher operating costs incurred due to poor sorbent utilization may make them uneconomical for application to medium or high-sulfur coal application. With these factors in mind, current technologies of semi-dry flue gas desulfurization are reviewed while focus on the removal efficiency and utilization of calcium-based sorbents. The technologies include spray drying, Circulating Fluidized Bed, Gas Suspend Absorption and New Integrated Desulfurization. Since particulate collection device also have some effect on sulfur removal, these subjects are also reviewed. The preceding literature review points two major points that hinder the adoption of semi-dry scrubbing technologies: poor sorbent utilization and low SC>2 removals. Anything that can be done to overcome these limitations has the potential to improve the economic feasibility of semi-dry scrubbing processes. On the bases of great number of international and national references, one novel semi-dry flue gas desulfurization, which is new in China and suitable for the current situation in China, is presented in this paper. A bench scale test facility was designed and built. The process features simple design, operational reliability, low maintenance costs and removal of heavy metal.
At the same time, its key components-atomizer has been researched in detail. The distribution characteristic of droplet size in space at different deepness of lime slurry and the quality rate of gas and liquid has been measured by the advanced FAM laser particle size-measuring instrument and analyzed to conclude the regularity of atomization.
An experimental study has been performed on the semi-dry FGD. The influence of operation parameters on SOz removal has been investigated. The approach to saturation temperature and Ca/S mole ratio influence SCh removal strongly. The optimum operating parameters have been got. The optimum approach to saturation temperature is about 10癈, the optimum CA/S ratio 1.5, the optimum recycle ratio 5, and the optimum humidified water is about 30 percent of total water evaporated.
The effects of additives were studied directly in the semi-dry FGD process. Hygroscopic additives had significant effects on improving lime utilization and SC>2 removal; Buffer additives had little or no effect. The mechanisms responsible for improvements in performance with the use of additives were investigated and discussed. Experiments showed that over 90% removal of SCh could be achieved in this semi-dry FGD process with the appropriate use of additives and operating conditions.
An integral mathematical model was put forward to predict semi-dry FGD tower and fabric filter. The model of FGD tower was based on film theory and treated the atomized slurry droplet as a
sphere with the fluid phase uniformly distributed around the discrete individual sorbent particle. Both the gas phase mass transfer and liquid phase mass transfer coefficients were included in the tower model along with a relationship to predict the resistance to lime dissolution. This approach was said to allow predictions of the mass transfer coefficients and to model the enhancement due to increasing solid concentration as evaporation proceeds. It was investigated that there are different control mechanisms in different steps of the process. Efficiency predictions using this model have been compared with the test data taken from the pilot semi-dry/fabric filter facility. It can be seen that the calculated results from the model agreed well with the experimental results.
石灰浆液雾化喷嘴是半干法烟气脱硫装置的关键部件，喷嘴的雾化性能对于系统的脱硫效率至关重要。喷嘴雾化特性主要包括石灰浆滴的粒径大小、分布以及喷雾角等。本文研制了一种新型低能耗的双流体雾化喷嘴，利用FAM激光测粒仪对不同气液比、不同浆液浓度下石灰浆液喷嘴的雾化特性进行了研究。结果发现这种喷嘴能耗低、寿命长、雾化性能好，具有较好的负荷适应性，在半干法烟气脱硫领域具有广阔的应用前景。
本文就运行参数对脱硫效率的影响进行了试验研究并分析了其机理，研究了增湿水对脱硫的强化作用。首先对两种脱硫剂进行对比试验，选用效果较好的一种作为整个试验研究的脱硫剂。主要研究了Ca/S、出口距绝热饱和温度的温差、入口二氧化硫浓度、烟气在吸收塔内的流速、石灰浆滴的粒径大小、有无脱硫灰再循环等运行参数对脱硫效率的影响，研究了增湿水对脱硫的强化作用以及脱硫塔轴向中心温度分布的情况。结果发现，对系统脱硫效率影响最为明显的参数是脱硫塔出口的趋近绝热饱和温度，其次为钙硫比，得出了最佳的运行参数范围；趋近绝热饱和温度一般选为10℃左右，钙硫比一般选为1.5。提高循环倍率可以提高脱硫塔和系统的脱硫效率，当运行参数保持基本工况值，钙硫比为1.5，循环倍率为10时，脱硫塔内的效率为75％左右，系统脱硫效率高达92％。增湿水的喷入点应当在石灰浆液恰好干燥位置，喷入量应为系统总耗水量的30％左右，在不进行脱硫灰渣循环情况下，当运行参数保持基本工况值，钙硫比为1.5，脱硫塔和系统的脱硫效率分别可以达到72％和87％。
本文还研究了添加剂对半干法烟气脱硫系统性能的影响。吸湿性添加剂、H_2O_2、蔗糖可以提高系统的脱硫效率，甲酸和苯酸效果不明显。对于本文的新型半干法烟气脱硫，当采用合适的添加剂，在没有脱硫灰渣再循环和增湿水的情况下，系统即可达到90％以上的脱硫效率。根据成本核算，采用NaOH和CaCl_2作为添加剂的相对成本基本相同而且较低。
本文考虑常速阶段、降速阶段、脱硫塔内干燥后阶段以及布袋除尘器的脱硫反应过程，建立了半干法烟气脱硫整体化模型。脱硫塔内气液反应模型同时考虑了气相阻力、液相传质阻力和石灰的溶解阻力。通过模型分析确定了半干法烟气脱硫工艺各阶段的反应机理。结果表明，在脱硫塔内石灰浆滴干燥的常速阶段初期，控制脱硫反应进行的阻力环节是石灰的溶解阻力。在常速阶段之后的时间内，反应过程为气膜扩散阻力所控制。当反应进行到降速阶段，限制脱硫反应的阻力环节是反应物向反应区域的扩散阻力。而在脱硫塔内干燥后阶段和布袋除尘器中气固反应的控制阻力为SO_2通过脱硫产物层的扩散。模型计算结果与试验结果吻合较好，本模型的建立可以用来指导半干法烟气脱硫装置的设计，预测现有脱硫装置的脱硫效率。
该工艺不仅适用于电站锅炉，还适用于垃圾焚烧锅炉、余热发电站以及各种燃煤或燃油
浙江人学博】：学位论义
的工业锅炉等所产生的酸性烟气净化。本系统不仅可用于新建锅炉，而且可以用于现有锅炉
的改造。脱硫塔可以同布袋除尘器配合使用也可以与电除尘器配合使用，都完全能够满足锅
炉排放标准的要求。
从本文的结果可以看出，如果继续提高循环倍率，脱硫塔的脱硫效率仍然有很大的提升
空问。另外，如果同时采用灰渣循环、分级喷水增湿和添加剂等强化脱硫反应的措施，脱硫
塔和系统的脱硫效率应该比单纯采用循环、分级喷水增湿和添加剂时还要高。浙汪大学热能
所正在对各种促进脱硫效率的措施进行综合优化研究，相信达到 95％的脱硫效率是不难实
现的。
More recently, semi-dry flue gas desulfurization techniques using finely divided lime slurry as sorbents for SO2 have drawn increasing interest. These semi-dry FGD techniques are projected to have lower capital and operating costs than the conventional wet FGD techniques. Further more, the waste product is dry powder rather than wet sludge. This offers potential advantages in the areas of waste handling and disposal. While there is an obvious economic benefit for these systems in terms of lowering of capital cost requirements, the higher operating costs incurred due to poor sorbent utilization may make them uneconomical for application to medium or high-sulfur coal application. With these factors in mind, current technologies of semi-dry flue gas desulfurization are reviewed while focus on the removal efficiency and utilization of calcium-based sorbents. The technologies include spray drying, Circulating Fluidized Bed, Gas Suspend Absorption and New Integrated Desulfurization. Since particulate collection device also have some effect on sulfur removal, these subjects are also reviewed. The preceding literature review points two major points that hinder the adoption of semi-dry scrubbing technologies: poor sorbent utilization and low SC>2 removals. Anything that can be done to overcome these limitations has the potential to improve the economic feasibility of semi-dry scrubbing processes. On the bases of great number of international and national references, one novel semi-dry flue gas desulfurization, which is new in China and suitable for the current situation in China, is presented in this paper. A bench scale test facility was designed and built. The process features simple design, operational reliability, low maintenance costs and removal of heavy metal.
At the same time, its key components-atomizer has been researched in detail. The distribution characteristic of droplet size in space at different deepness of lime slurry and the quality rate of gas and liquid has been measured by the advanced FAM laser particle size-measuring instrument and analyzed to conclude the regularity of atomization.
An experimental study has been performed on the semi-dry FGD. The influence of operation parameters on SOz removal has been investigated. The approach to saturation temperature and Ca/S mole ratio influence SCh removal strongly. The optimum operating parameters have been got. The optimum approach to saturation temperature is about 10癈, the optimum CA/S ratio 1.5, the optimum recycle ratio 5, and the optimum humidified water is about 30 percent of total water evaporated.
The effects of additives were studied directly in the semi-dry FGD process. Hygroscopic additives had significant effects on improving lime utilization and SC>2 removal; Buffer additives had little or no effect. The mechanisms responsible for improvements in performance with the use of additives were investigated and discussed. Experiments showed that over 90% removal of SCh could be achieved in this semi-dry FGD process with the appropriate use of additives and operating conditions.
An integral mathematical model was put forward to predict semi-dry FGD tower and fabric filter. The model of FGD tower was based on film theory and treated the atomized slurry droplet as a
sphere with the fluid phase uniformly distributed around the discrete individual sorbent particle. Both the gas phase mass transfer and liquid phase mass transfer coefficients were included in the tower model along with a relationship to predict the resistance to lime dissolution. This approach was said to allow predictions of the mass transfer coefficients and to model the enhancement due to increasing solid concentration as evaporation proceeds. It was investigated that there are different control mechanisms in different steps of the process. Efficiency predictions using this model have been compared with the test data taken from the pilot semi-dry/fabric filter facility. It can be seen that the calculated results from the model agreed well with the experimental results.
引文
1．国家环保局，“1999年中国环境状况公报“，2000
2．国家环保局，“中国环境年鉴”，2000
3．国家环保局科技标准司，燃煤SO2控制技术现状及综合评价
4．杨成勋，燃煤电厂的脱硫技术，湖南电力，No．4，1994，p：46—50
5．张新生等编，燃煤烟气脱硫，中国地质大学出版社，1991
6．岑可法，倪明江，骆仲泱等，循环流化床锅炉理论、设计与运行。北京：中国电力出版社，1998
7．江哲生．中国洁净煤发电技术的展望．第十四届国际匹兹堡会议及煤炭利用研讨会论文(单行本)，太原，1997：2-4
8．章名耀，李大骥，蔡宁生等，关于我国发展先进燃煤发电技术的建议．动力工程，1994，14(2)：1-8
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11．戴和武，谢可玉，王伟藜．控制燃煤硫的污染与动力煤全硫比价划分．洁净煤技术，1997，3(1)：13-17
12．郝吉明，贺克斌．中国燃煤二氧化硫污染控制战略．中国环境科学．1996．16(3)：208-212
13．韩笑钊等，烟道气脱硫概述，安徽化工，1995，No．5，p：40-43
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15．能源部火电厂脱硫技术考察团，美国芬兰所开发的火电厂脱硫技术，中国电力，1994(7)
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17．唐恒等，烟气脱硫技术的现状和发展，江苏理工大学学报，1999(1)，p：44—47
18．陶邦彦，对我国电站烟气脱硫的研讨，发电设备，1997，No．5，p：4—10
19．《中国环境年鉴》编辑委员会．中国环境年鉴—1996．北京：中国环境年鉴社，1996：p115，p477，p481，p492
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21．中国环境科学学会．脱硫技术．北京：中国环境科学出版社，1995：p30-31
22．高翔，新型余热回收、除尘脱硫多功能烟气净化装置的基础研究，[学位论文]，杭州：浙江大学，1995
23．高翔等．新型多功能烟气净化装置的开发．环境科学学报，1999(4)：363-367
24．芮素生，成玉琪，叶显彬．中国煤炭开发利用现状与发展洁净煤技术．中国洁净煤技术发展研讨会论文选集，北京，1994
25．潘惠正．中国洁净煤技术发展研讨会致开幕词．中国洁净煤技术发展研讨会论文选集，北京，1994
2．国家环保局，“中国环境年鉴”，2000
3．国家环保局科技标准司，燃煤SO2控制技术现状及综合评价
4．杨成勋，燃煤电厂的脱硫技术，湖南电力，No．4，1994，p：46—50
5．张新生等编，燃煤烟气脱硫，中国地质大学出版社，1991
6．岑可法，倪明江，骆仲泱等，循环流化床锅炉理论、设计与运行。北京：中国电力出版社，1998
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