烟气冷凝过程中雾化碱性浆滴脱硫实验研究.pdf

烟气冷凝过程中雾化碱性浆滴脱硫实验研究 ＊ 孙金栋 许淑惠 陈 欣 北京建筑工程学院城市建设工程系, 北京 100044 吴 宏 北京航空航天大学工程热物理系, 北京 100083 摘要 简要分析了雾化 Ca OH2浆滴对 SO2气体的吸收过程。 在竖直单管冷凝换热器内利用喷入雾化碱性浆滴, 研 究了影响SO2气体吸收的主要因素, Ca S 值、反应器入口 SO2浓度、雾化空气量、烟气进口温度、烟气雷诺数都会影响 对SO2气体的吸收效果。 实验表明, 雾化碱性浆滴强化了烟气冷凝脱硫效果。 关键词 Ca OH 2浆滴 烟气冷凝 脱硫 雾化 ＊北京建筑工程学院青年科研资金重点资助项目; 北京市“供热、供 燃气、通风与空调工程”重点实验室支持项目 1 引言 湿法烟气脱硫技术是工业应用中常见的脱硫方 法。在脱硫剂方面 ,由于石灰的廉价易得 ,常选用钙 基脱硫剂。由于固体 Ca OH2和 CaO 的利用率和脱 硫率较低, 往往采用喷入雾化碱液, 来提高烟气脱硫 效率 。本研究是基于烟气冷凝基础上进行的雾化碱 液脱硫 ,这一过程中既包含有雾化碱液的脱硫 ,又包 含有凝结液对 SO2气体的吸收。在烟气冷凝过程中, 由于雾化碱液的加入 ,使得整个脱硫过程变得复杂 。 2 雾化浆滴脱硫过程分析 实验过程中 ,把 Ca OH2浆液雾化喷入竖直单 管冷凝反应器, 烟气在冷凝反应器中同时完成两方面 任务 一方面通过冷凝烟气,使得烟气温度降低,大量 显热和水蒸汽凝结潜热释放出来 , 被回收利用 ; 另一 方面 ,雾化 Ca OH2浆滴吸收烟气中的 SO2气体, 实 现烟气脱硫的目的。这两个过程不是完全孤立的 ,两 者互相影响 。碱性浆滴的喷入 , 降低了烟气温度, 有 利于烟气的凝结过程 ; 水蒸汽的凝结, 增强了对 SO2 气体的吸收。显然这是一个复杂的传热传质过程和 化学反应过程。 烟气冷凝时雾化浆滴脱硫过程可以从两个方面 来考虑 在主流气道浆滴吸收 SO2气体过程 ; 在反应 管壁凝结液膜吸收 SO2气体过程 。在主流气道浆滴 吸收 SO2气体过程可以简化为以下几个部分 1 SO2从气相向液滴表面的扩散过程; 2 SO2在液 滴表 面被 吸收 ; SO2溶 解形 成 H2SO3,进而离解成 HSO - 3和 SO 2- 3; 3 浆滴内 Ca OH 2离解为 Ca 2和 OH- , 并向 HSO - 3和SO 2- 3扩散 ,生成CaCO3水合物。 由于存在部分碱性浆滴溶入凝结液膜,提高了凝 结液膜的碱性, 在反应管壁凝结液膜吸收 SO2气体过 程已区别于单纯烟气冷凝时凝结液对 SO2气体的吸 收。为了简化分析, 可以看作是形成了浓度被稀释的 碱性混合液膜, 其吸收反应机理近似于碱性浆滴的吸 收反应过程 。我们以 Ca OH2浆滴对 SO2气体的吸 收为主考虑脱硫过程 。 浆滴与 SO2气体的反应是一个极为复杂的过程, 建立一个数学模型把这些因素都考虑在内是很困难 的。一部分学者认为外部二氧化硫的质传递控制着 整个吸收过程 [ 1] 。一部分学者则考虑更多的因素影 响着吸收过程, 包括外部二氧化硫的质传递 ,二氧化 硫在浆滴表面的吸收 ,在浆滴内部液相的二氧化硫和 石灰颗粒的反应等因素 [ 2～ 3] 。由于液相传质速度很 快,浆滴可以被认为是一个良好的反应器 。 雾化液滴喷入高温烟气中 ,存在着液滴的蒸发问 题。液滴能否蒸发取决于烟气中水蒸汽是否达到饱 和状态,如烟气中水蒸汽达到饱和, 液滴就不能蒸发, 反之则可以蒸发。由于实验过程中要实现烟气的凝 结换热,也就是说,烟气中的水蒸汽要被冷却成水 ,显 然只有达到饱和温度水蒸汽才可能凝结成水 ,在换热 壁面处烟气中水蒸汽达到饱和 ,在此忽略液滴的蒸发 问题, 认为液滴在下降过程中, 近似于没有发生蒸发 过程 。 3 实验系统 实验系统由 5 部分组成 燃烧设备、 冷凝反应器、 凝结液收集装置 、 雾化喷液装置和测试装置。实验系 统如图1 所示。 40 环 境 工 程 2005年 6 月第23 卷第3 期 图 1 雾化碱液烟气冷凝脱硫实验系统图 1锅炉; 2SO2标准气瓶; 3烟气控制阀; 4烟气加热管; 5烟 气控制阀; 6烟气预冷器; 7冷却水出口; 8套筒式实验段; 9 冷却水进口; 10凝结液收集管; 11碱液箱。 天然气经燃气量表进入锅炉, 燃烧后生成的烟气 与SO2标准气瓶提供的二氧化硫气体混合 ,经过均速 管流量计和补偿式微压计测量流量 ,与套管换热器内 的冷却水进行逆流换热并形成凝结液膜 ,并吸收烟气 中的 SO2气体。冷凝后的烟气由引风机排出, 凝结液 由凝结液收集器收集。在冷却水进、出口和换热器 进、 出口烟道上都布置了水银温度计和测温铂电阻, 以测定进 、 出口水温变化及混合气体的进、 出口温度。 在实验段内喷入碱液 ,雾化碱液由竖直烟道顶部 的喷嘴进入实验段, 并与 SO2气体发生反应。其中喷 嘴的气端是由空压机提供雾化空气 ,配置的 Ca OH2 浆液由潜水泵送入喷嘴的水端。气路和水路都有阀 门控制 。浆滴直径控制在 0. 05 ～ 0. 1 mm 之间, 以使 浆滴和烟气充分接触 。 实验管 段采用套管换热器, 内 管 38 mm , 长 1 500 mm 。 实验药品 Ca OH2颗粒分析纯 95以上, 硫酸盐 0. 2。实验过程中 , 调节 Ca S 、 SO2浓度、 混合烟气流速等因素 ,收集凝结液滴与反应液滴的混 合液, 进行处理分析 , 通过烟气分析仪对烟气进行分 析测定。 4 实验结果分析 4. 1 喷入碱液对脱硫效果的影响 我们对单纯利用冷凝烟气脱硫与单纯喷入碱液 脱硫进行了对比实验 。实验过程中 ,保持烟气进入实 验段时烟气温度在 85 ℃、烟气 Re 5 000、烟气中 SO2浓度为2 800 mg Nm 3 ,实验碱液取用质量分数 5 的Ca OH2水溶液。实验结果如图 2 所示。 烟气单纯冷凝脱硫 ,一般脱硫率在 30左右, 烟 气凝结效果是影响二氧化硫吸收的关键因素 ,凝结效 果越好,对二氧化硫的吸收效果越好。相对于烟气单 纯凝结脱硫效果 ,碱液脱硫效果较好, 利用雾化碱液 脱硫效果在 60左右 。由于单纯冷凝脱硫依靠 SO2 气体的扩散溶解和在凝结液中的离解反应,但是反应 进行缓慢, 同时凝结液形成的多少受多种因素限制, 因而导致依靠单纯冷凝脱硫吸收效果较差 。雾化浆 滴脱硫时 , 浆滴内 SO2分布梯度远远大于液滴, 甚至 在浆滴内某一点 ,浓度达到零, 因此浆滴的吸收率远 远大于液滴 ,并且 ,浆滴碱性越强, 溶解的 OH -越多, 浓度达到零的那一点越接近浆滴表面, 浓度梯度增 大,吸收率增大 。 图 2 烟气冷凝脱硫与碱液脱硫实验对比 1单纯冷凝脱硫; 2单纯碱液脱硫; 3碱液与冷凝混合脱硫。 烟气冷凝与雾化碱液混合脱硫效果相对较好。 由于雾化碱液的喷入, 有效降低了烟气温度 ,促进了 烟气的冷凝 ,同时也促进了凝结液对 SO2的吸收。烟 气冷凝过程的进行 ,烟气处于饱和状态 , 因而抑制了 浆滴的蒸发 ,部分浆滴将会溶入凝结液中 ,增大了凝 结液的碱性 ,有利于对SO2气体的吸收。 4. 2 Ca S 及 SO2浓度对 SO2吸收率的影响 在烟气进口温度 85 ℃、烟气流动 Re 约为5 000 左右 、 雾化空气量 0. 5 m 3 h 下 , 针对不同 SO 2入口浓 度下 ,Ca S 与 SO2吸收率的关系进行了实验 。实验结 果如图3 所示。 图 3 Ca S 与SO2吸收率的关系 图3 显示,随着Ca S 的增加,SO2的吸收率升高。 由于 Ca S 的增加, Ca OH2浆滴与 SO2接触反应的 几率增大,所以 SO2吸收率升高。但是, 脱硫效率与 Ca S 的增加并没有线性关系。随着 Ca S 的增加, 脱 硫效率增加趋势变缓 ,由于在 SO2浓度、 雾化空气量、 41 环 境 工 程 2005年 6 月第23 卷第3 期 烟气流速等条件不变的情况下, Ca S 增加 ,液气比也 随之增高。虽然增大了气-液相接触面积, 但此时浆 滴在通道内的滞留时间却大大缩短, 就单个液滴而 言,与 SO2的反应反而不充分。一般认为, 最佳 Ca S 在1. 5～ 2. 0 之间 。 实验结果显示烟气中 SO2浓度的增加导致吸收 率有所降低。根据气液溶解平衡理论可知,增大气相 分压力使液相的溶解分率减小 , 因而降低了反应速 率,致使吸收率下降 。当烟道中 SO2的浓度较低时, 只要暴露时间足够长 , 浆滴中已经电离出的 Ca 2便 可以完成吸收过程 ; 而当 SO2浓度较高时 , Ca 2 从 Ca OH2颗粒上的溶出速率低于 Ca 2和 SO2- 3的扩散 和反应速率 ,由于浆滴在烟道中的时间有限 ,导致实 际吸收效率下降 。 4. 3 雾化空气量对 SO2吸收率的影响 图 4 雾化空气量与 SO2吸收率的关系 实验条件为烟气进口 SO2浓度2 000 mg Nm 3 , 烟 气流动 Re 5 000,入口烟温 85 ℃。雾化空气量的增 加会导致雾化浆滴直径的减小 ,使浆滴的蒸发速度加 快,降低了浆滴的存在时间, 不利于 SO2的吸收。但 是,浆滴直径的减小将使总的反应面积增大 ,与气体 接触更加充分, 会使 SO2的吸收率增大。然而雾化空 气的增加造成烟气中 SO2的分压力降低、水蒸汽分压 力降低, 不利于烟气中水蒸汽的凝结 ,对 SO2的吸收 率有不利影响。在实验中雾化浆滴粒径可达到 0. 05 ～ 0. 1mm ,从实验结果看来, 雾化空气量的适当增加, SO2吸收率也有相应提高 。 4. 4 烟气雷诺数对 SO2吸收率的影响 实验条件为烟气进口 SO2浓度2 000 mg Nm 3 , 入 口烟温 85 ℃, 雾化空气量为 1. 0 m 3 h, Ca S 为 1. 7。 烟气雷诺数对 SO2吸收率的影响变化如图 5 所示 。 烟气雷诺数增加 ,使混合加剧。有利于 SO2在烟 气中的扩散 ,与浆滴的接触相对充分 ,有利于 SO2的 吸收。但是 ,在反应管段一定的情况下 , 烟气雷诺数 增加, 意味着烟气在反应管段存留时间缩短 ,即反应 时间降低, 反应不充分而导致 SO2的吸收率降低。由 于吸收率并不是随着烟气雷诺数的升高而升高,因此 在设计反应器时 ,烟气雷诺数的选定是一个重要设计 参数 。针对本实验状况 ,烟气雷诺数在4 000～ 5 000 左右是一个比较合适的范围。 图 5 烟气雷诺数与 SO2吸收率间关系 5 结论 1 相对于烟气单纯凝结脱硫效果 , 烟气冷凝与 雾化碱液混合脱硫效果较好, 雾化碱液有效地提高了 烟气脱硫效率。 2 随着 Ca S 的增加,SO2的吸收率升高。一般 认为 ,最佳 Ca S 在 1. 5～ 2. 0之间。 3 雾化空气量、 SO2浓度、烟气雷诺数也是影响 综合脱硫的因素 。 参考文献 1 Brogren C and Karsson H T . Modeling the absorption of SO2in a spray scrubber using the penetration theory . Chem. Eng . Sci. 1997. 52 18 3085～ 3099. 2 Rochelle G T. Comments on absorption of SO2into aqueous system. Chem. Eng. Sci. 1992. 47 12 3169～ 3171. 3 Hans T. Karlsson and Jonas Klingspor, Tentative Modeling of Spray-dry Scrubbing of SO2. Chem. Eng . Technol. , 1987. 10 102～ 104. 作者通讯处 孙金栋 100044 北京西城区展览路 1 号 北京建筑工 程学院城市建设工程系 电话 010 68322127 E -mail sunshine8177 sina. com 2004 -09 -22 收稿 42 环 境 工 程 2005年 6 月第23 卷第3 期 blue triphenylmethane dyesvaried little when acetic acid concentrations increased from 200 mg L to 1 200 mg L and dye concentration from 20 mg L to 100 mg L. It revealed that the biological decolorization of these cationic dyes seemed to be combined action of biosorption and subsequent biodegradation. The acetic acid concentration could enhance the color removal percentage of cationic red 6 B hemicyanine dyes. It could be the co -metabolism took place between 6 B and acetic acid. Keywords cationic dyes, biological decolorizaiton and aerobic process TREATMENT OF SAPONIN WASTEWATER BY PHYSICOCHEMICAL AND BIOCHEMICAL PROCESSXie Qingjie et al 26 Abstract The saponinwastewater is characterized by a strong dark color, high chemicaloxygen demand CODconcentration, low pH value and low biodegradability. Treatment of this wastewater by traditional activated sludge is essentially impossible. In the present work, combined physical, chemical and biological s were synergistically utilize to tackle the wastewater. The results show that CODCr, BOD5, chromaticity and SS can be reduced respectively from 23 250 mg L, 3 600 mg L, 216 times and 260 mg L to 92 mg L, 20 mg L, 20 times and 27 mg L by the process, and their average removal rates are 99. 7, 99. 4, 90. 7 and 90. 4 respectively ,which can meet the first-order of “ Overall Sewage Discharge Standards” GB8978 -1996. Keywords saponin, wastewater treatment, physicochemical and bio-chemical DEMONSTRATIONENGINEERINGRESEARCHONCONSTRUCTEDWETLANDFOR PURIFYING POLLUTED RIVER WATER FLOWING INTO DIANCHI LAKEDeng Futang et al 29 Abstract A demonstration engineering research on purifying the polluted riverwater flowing into Dianchi Lake using a composite constructed wetland system was implemented in thisproject. The resultsshown that the demonstration engineering system of the constructed wetland had a good applicability for treating the polluted river water flowing into Dianchi Lake. Under the normal running condition, the removal rate of CODMn, BOD5, TN and TP int the polluted river water could reach at 67, 74, 83 and 65 separately in the constructedwetland system. Keywords constructed wetland, polluted river water flowing into Dianchi Lake, sewage purification and demonstration engineering TREATMENT OF PRINTING AND DYEING WASTEWATER BY PRETREATMENT HYDROLYTIC ACIDIFICATION -AO PROCESSQin Lian et al 32 Abstract A printing and dyeing company in Changzhou adopts pretreatment -hydrolytic acidifcation -AO process to treat printing and dyeing wastewater. The running result shows the effect of the treatment is good and the process semmed to be fit for serveral different dyeing effluents. The effluent quality from the process meets the first class criterion specified in“ The National Discharge Standard of Pollutants” GB8978 -1996 . The cost of the treatment is 1. 851yuan R MB per ton wastewater. Keywords hydrolytic acidification, AO process and dyeing wastewater STUDIES ON PURIFYING DIESEL EXHAUST GASES WITH ATTAPULGITE CLAY Zou Jianguo et al 35 Abstract The attapulgtite clay was selected as absorbent for purifying diesel exhaust gas. Diesel exhaust gaswas allowed to pass through a jet bubble reactor JBR arragned in the exhaust system of the diesel engine, in which diesel particulates and other contaminantswere absorbed by the attapulgite clay solution. The absorbent slurry has colloid property and a strong affinity for the diesel particulates. It shows that under the experimental conition, the diesel particulates are removed by 71. 3, NOXby 80. 4, HC and SO2all by above 90 from the exhaust gas, the temperature of the exhaust gas decreases from 200～ 250 ℃ to about 55 ℃, and the gas resistance is 3. 5 kPa. Keywords attapulgite, purify, absorb and diesel exhaust gas EXPERIMENTAL STUDY ON NON -THERMAL PLASMA FOR THE OXIDATION OF METHANGE Yang Xiaoping et al 37 Abstract The capacitively coupled plasma for oxidation of CH4in dry air was studied and the removal efficiency of CH4and proucts of reaction were analysed. That was compared to caseswith catalyst in the reactor. The result indicates that when the catalyst was present, the CH4 removal efficiency was improved, the CO2selectivity was increased in the reaction product. The final products of CH4oxidationwere CO, CO2and H2O. Keywords plasma, catalyst, methane and capacitively coupled discharge EXPERIMENTAL STUDY ON DESULFURIZATION OF CONDENSING FLUE GAS BY FOG LYE Sun Jindong et al 40 Abstract Theory of SO2absorptionby Ca OH 2slurry droplet was analyzed. Factors influencing SO2absorption were studied by spraying fog lye in a vertical tube condensing exchanger, such as Ca S ration, inlet SO2concentration, air quantity of fog lye, inlet temperature and Reynolds 3 ENVIRONMENTAL ENGINEERING Vol. 23,No. 3, Jun. , 2005 number of flue gas. It was indicated that desulfurization of condensing fluegaswas intensified by fog lye. Keywords Ca OH 2slurry droplet, condensing flue -gas, desulfurization and spray PURIFICATION OF ORGANIC WASTE GAS FROM THE WIRE PRINTED DISTRICT OF PRINTED CIRCUIT BOARD PLANTLi Shanhong et al 43 Abstract The flowchart of the intermittent fixed be active carbon adsorption for purification of the organic waste gas was selected in accordance with the organic waste gas pollution problems from the wire printed district of the printed circuit board plant. Through the calculation ability of the causing cold and quantitites of the adsorption. some parameters of the activated carbon adsorption are designed, such as the gas velocity of the empty tower was about 0. 6 m s, the activated carbon is coconut. The activated carbon adsorption bed was designed as double story with drawers. After the adsorption bed purification, practical monitor testified the efficient of the benzene. toluene andxylene purifiedto 81. 59, 83. 50, 85. 43 by adsorption. The waste activated carbon was accumulated and desorption. The recycle organic products were mixed into the diesel oil to be used as fuel of motors. Keywords organic waste gas, production of printed criculit board, activated carbon adsorption and purification ATION OF ATMOSPHERIC POLLUTANTS DURING PRODUCTION OF POLYVINYL CHLORIDE AND TREATMENT MEASURESShi Lijuan et al 46 Abstract It is explained that the production position and features of vinyl chloride monomer during the production of polyvinyl chloride PVCby analyzing the manufacturing process of PVC. Based on which its treatment conditions are also analyzed, and finally high -efficient and feasible controlling measures are proposed. Keywords PVC, production of pollutant, influence and control measures APPLICATION OF AMMONIA PROCESS FLUE GAS DESULPHURIZATION TO COAL -FIRED BOILERZhou Jianhong et al 49 Abstract Taking the project of 75 t h pulverised coal combustion boiler as an example, this paper discusses the application of ammonia processflue gas desulphurization to the coal -fired boiler. The result shows that, with the desulphurization unit is put into operation, average desulphurization effect in the system has reached 95. 92percent, and sulfur dioxide content in the flue gas from the boiler has been reduced to less than 135 mg per cubic meter, which is far lower than the specified limits. This paper also discussed operating index, treatment effect and existing problems. Keywords desulfurization by ammonia process, FGD, coal-fired boiler and sulfur dioxide DESIGN PRINCIPLE OF MODERN SOLID WASTE LANDFILL SITE AND ITS APPLICATION Wang Yanming et al 51 Abstract The design principle of modern landfilling site is summarized herein. An example project called Shanghai Laogang Landfill Site Phase -Ⅳis referred to show the detailed application of the theory. Keywords modern landfilling, design principle, constructing by stages, developing plan, high dimension and double anti-seepaging layer STUDIES ANDTECHNICAL DESIGNS OF ON -SITE TREATMENT OF NIGHSOIL AND KITCHEN GARBAGEChen Zhulei et al 54 Abstract This paper offers a suitof disposal techniques at source of the night soiland kitchen garbage. A pilot -scale system. whichwasused to dealwith the night soil and kitichen garbage from one unit of a residential building for simulationwas designed according to the data of lab-scale trials. The system comprises vacuum collection, anaerobic digestion of solids, composting of digestive sludge and anaerobic -aerobic disposal of mixed sewage. Its handling capacity was0. 2 t d. The night soil and kitchengarbage can be collected at source and disposed at locale, synchronously, the bacterial fertilizer and methane can be produced through the system. Keywords night soil, kitchen garbage, vacuum collection and anaerobic digestion STUDY ONTECHNOLOGY OF OPTIMIZAITONTREATMENT OF LIVING RUBBISHES IN CITIES AND TOWNSLiu Dayi et al 57 Abstract The present situation of technology of treating living rubbish is synopsized, the technology of optimization treatment of living rubbish is put forward, and comparedwith the present technology. The engineering example indicates that the new technology has high efficency of treatment, it isworth popularizing. Keywords cities and towns, living rubbish and optimization treatment technology STUDY ONDETERMINING CONCENTRATIONOF TOTALVOLATILE ORGANICCOMPOUND IN 4 ENVIRONMENTAL ENGINEERING Vol. 23,No. 3, Jun. , 2005