Removal of fine particles in wet flue gas desulfurization system by heterogeneous condensation

A novel process to remove fine particles with high efficiency by heterogeneous condensation in a wet flue gas desulfurization (WFGD) system is presented. A supersaturated vapor phase, necessary for condensational growth of fine particles, was achieved in the SO₂ absorption zone and at the top of the wet FGD scrubber by adding steam in the gas inlet and above the scrubbing liquid inlet of the scrubber, respectively. The condensational grown droplets were then removed by the scrubbing liquid and a high-efficiency demister. The results show that the effectiveness of the WFGD system for removal of fine particles is related to the SO₂ absorbent employed. When using CaCO₃ and NH₃·H₂O to remove SO₂ from flue gas, the fine particle removal efficiencies are lower than those for Na₂CO₃ and water, and the morphology and elemental composition of fine particles are changed. This effect can be attributed to the formation of aerosol particles in the limestone and ammonia-based FGD processes. The performance of the WFGD system for removal of fine particles can be significantly improved for both steam addition cases, for which the removal efficiency increases with increasing amount of added steam. A high liquid to gas ratio is beneficial for efficient removal of fine particles by heterogeneous condensation of water vapor.     

硫磺装置尾气提标改造方案的研究

硫磺回收及尾气处理装置烟气中含有高浓度的二氧化硫,比较了动力波烟气洗涤技术、空塔喷淋碱洗技术、喷射文丘里湿气洗涤技术(WGS)、超重力烟气脱硫技术吸收烟气中的二氧化硫,从烟气净化指标、系统压降、核心设备连续运行周期、运行费用和装置投资方面进行比较,得出喷射文丘里湿气洗涤技术(WGS)优于其他三种方案。     

祥光铜业废水处理与烟气超低排放技术的发展历程

介绍了祥光铜业从建设初期至今废水处理与烟气超低排放技术的发展过程.通过对全厂水资源的统一调配,对生产废水循环利用和梯度利用,最终实现了生产废水的资源化和减量化.在烟气治理方面,遵循分而治之的思路,根据各工序产出的烟气性质不同,对烟气处理系统不断优化,采用布袋除尘、高温陶瓷膜除尘、湿法洗涤除尘、高浓度SO2制酸、钠碱法脱...     

耦合热泵的FCC脱硫湿烟气脱白净化及余热回收系统设计分析

根据某80万吨/年催化再生烟气参数,结合低温浆液喷淋与热泵技术,设计了耦合热泵的FCC脱硫湿烟气脱白净化系统,建立了烟气-脱硫液-热泵的余热回收路线。使用Aspen Plus与热力学模型进行了流程模拟与分析。结果表明,低温环境下,系统具有良好的烟气脱白能力。低温浆液喷淋强化了脱硫塔的脱硫除尘性能,同时回收了烟气中的水分,设计工况下,系统回收水量为1.47t/h。本系统无需额外热源,烟气热量驱动可实现脱白。灵敏度分析表明,系统在烟气流量82%～124%范围内都能消除湿烟羽。系统具备余热回收再利用能力,模拟结果显示,盈余热量1.87MW,投资回收期4.88年,经济优势显著。     

Experimental investigation on removal of coal-fired fine particles by a condensation scrubber

The removal of coal-fired fine particles by heterogeneous condensation of water vapor in a scrubber was investigated. Supersaturated vapor phase necessary for the condensation growth of fine particles was achieved in the scrubbing zone as well as in the top of the scrubber by means of steam addition in the gas inlet and above the scrubbing liquid inlet, respectively. The condensation grown droplets were then removed by the scrubbing liquid and high-efficient demister. Influences of the steam addition amount, the temperature difference between the inlet gas and scrubbing liquid, and the liquid-to-gas ratio, etc. on removal efficiency were examined. The results show that with a steam addition amount of flue gas, number removal efficiencies of more than 60% and 70% can be attained for the two cases of steam addition, respectively. For the cases with steam addition in the gas inlet of scrubber, higher temperature difference between the inlet gas and scrubbing liquid enhances the removal of fine particles. Under the conditions of steam addition above the scrubbing liquid inlet, the removal efficiency decreases with increasing temperature difference. The removal efficiency can be effectively improved by increasing the liquid-to-gas ratio for both steam addition modes.     

Mercury removal from coal combustion by Fenton reactions. Paper B: Pilot-scale tests

This second paper in a series describes results of pilot-scale testing for mercury (Hg) removal from coal combustion flue gas using a scrubbing solution based on the Fenton reactions. The selected reagents contain hydrogen peroxide and iron salts. The mercury scrubbing was performed in a condensing heat exchanger (CHX) with flue gas generated by coal combustion in CANMET’s vertical combustor research facility (VCRF). Both the Ontario Hydro method and a Hg CEM were used for Hg sampling and speciation. The results, obtained with the combustion of three different pulverized coals – bituminous, sub-bituminous and lignite – showed that the CHX was very effective in removing oxidized mercury (Hg(II)). Concerning the performance of the scrubbing solutions, 30–40% of elemental mercury (Hg(0)) oxidation was achieved for the lignite coal, with the solution being preferably composed of FeCl₃ and H₂O₂ and with pH value between 1 and 3. Results also showed that better Hg removal results were achieved by combining sulphur removal and Hg removal in the same stage of the CHX. An additional test done on the pilot-scale research boiler with a conventional wet scrubber showed that the Hg removal capability using the Fenton reactions was not dependent on the configuration of the wet scrubber. Although the Hg(0) oxidation ratio was not particularly high compared to the achievements from bench-scale tests, considering the economic and non-toxic nature of the scrubbing solution and the readily available equipment, the current results are encouraging and deserve further work to develop a better understanding of the chemistry in order to determine if the method can be further optimized.     

Residence time distribution and dispersion of gas phase in a wet gas scrubbing system

Residence time distribution (RTD) of exhaust gas in a wet scrubbing system was investigated for application to the removal of SO _x , NO _x or dust included in exhaust gas. The mixing of gas phase in the wet scrubbing system was also examined by considering the axial dispersion coefficient of gas phase. Effects of gas amount (velocity), liquid amount (velocity) and solid floating materials on the residence time distribution (RTD) and axial dispersion coefficient of exhaust gas were discussed. The addition of solid floating materials could change the RTD and thus dispersion of exhaust gas in the scrubbing system. The mean residence time and axial dispersion coefficient of exhaust gas were well correlated in terms of operating variables.     

镁法烟气脱硫副产物热解回收MgO的研究

镁法烟气脱硫工艺是利用MgO浆液吸收烟气中的SO2,脱硫副产物经过热解还原为MgO后,可再次制浆从而实现吸收剂的循环利用。对某火电厂的脱硫副产物进行分析,发现每克干渣中含MgSO3 0.723 g（折算值）,具有良好的回收利用价值。分别考察了热解温度、恒温时间等热解条件对热解产物的影响,发现在热解温度750℃、恒温时间2 h时,MgO回收率可达到59.8%。热解温度低于750℃时,脱硫副产物单质硫析出占理论硫比例为6.0%;当热解温度达到900℃时,单质硫析出达到了24.0%。故在热解脱硫副产物时,应控制热解温度以减少单质硫的析出。     

臭氧低温氧化烟气脱硝过程中的氮平衡试验研究

臭氧氧化污染物协同脱除技术利用臭氧的强氧化性,将烟气中溶解度较低的NO _x 、Hg、VOCs等多种污染物氧化为高价态或易溶解的形式,并结合尾部湿法喷淋系统实现污染物的同时脱除。由于其具有温度窗口低、脱硝效率高、反应速率快及改造难度小等优点,在工业锅炉、窑炉及非电行业得到广泛应用。但是在此过程中的污染物实际转化路径,尤其是氮氧化物的输入/输出平衡,目前还未有详细的验证试验支撑。因此本文针对典型臭氧氧化脱硝过程,对污染物脱除过程中的氮氧化物输入/输出平衡及氮元素流向进行了分析试验。试验结果表明,气相输入的NO经过臭氧氧化耦合湿法喷淋后逐渐转化为液相中硝酸根和亚硝酸根离子。在不同O₃/NO摩尔比下,气相氮元素的减少量均以液相中硝酸根及亚硝酸根的增加量存在,不存在其他含氮形式。同时,吸收浆液中硝酸盐及亚硝酸盐的转化率也与烟气中NO _x 脱除率相匹配。在NO/SO₂同时氧化条件下,调节O₃/NO摩尔比,结合湿法喷淋系统可以实现NO _x /SO₂的协同高效脱除,同时系统满足氮元素输入/输出平衡,为臭氧氧化污染物协同脱除技术的工程应用推广提供了依据。     

碱性吸收剂脱除燃煤烟气中HCl的研究进展

氯是煤中的微量元素,在燃烧过程中以HCl气体的形式释放出来,对燃煤发电机组石灰石-石膏湿法脱硫设施造成不利影响。基于湿法脱硫吸收塔浆液中氯离子的物料平衡,本文提出了碱性吸收剂脱除燃煤烟气中HCl的技术思路,从碱性吸收剂种类、反应条件对脱除HCl的影响、HCl脱除机理方面对烟气脱氯技术进行了综述,指出了碱性吸收剂脱除燃煤烟气低浓度HCl的研究方向。     

A sustainable mediated electrochemical process for the abatement of NOx from simulated flue gas by using Ag(I)/Ag(II) redox mediators

Electrochemical removal of NO and NO₂ by using Ag(I)/Ag(II) redox mediator system in nitric acid medium by two-stage scrubbing process was investigated. Experiments were carried out for the complete removal of NO and NO₂ from the stimulated flue gas at room temperature and atmospheric pressure. The process parameters like current density, Ag(I) concentration, HNO₃ concentration, initial concentration of NO, Ag(I) concentration and temperature were studied and optimized. A removal efficiency of >99% was achieved using this sustainable redox process. Ag(II)/Ag(I) can be regenerated and reused for the scrubbing of waste gases continuously and there is no other gases emission during scrubbing.     

湿法烟气脱硫系统对细颗粒脱除性能的实验研究

针对石灰石-石膏法、双碱法、氨法等典型湿法烟气脱硫（WFGD）工艺,在喷淋脱硫塔中实验研究了WFGD系统对细颗粒的脱除作用;采用电称低压冲击器、场发射扫描电镜、X射线衍射仪等对WFGD系统前后烟气中细颗粒的浓度、粒径分布、形态、元素及物相组成进行了测试分析,考察了脱硫剂、液气比对WFGD系统脱除细颗粒性能的影响,并进行了利用蒸汽相变原理促进细颗粒凝结长大并高效脱除的实验研究。结果表明,脱硫剂对WFGD系统脱除细颗粒的性能具有重要影响,由于形成无机盐气溶胶细颗粒,采用CaCO₃、NH₃·H₂O脱硫剂时,WFGD系统对细颗粒的脱除效果明显不及Na₂CO₃脱硫剂和水洗涤,且颗粒形貌特征及元素组成发生明显变化;除NH₃·H₂O脱硫剂外,液气比对WFGD系统脱除细颗粒的影响不明显;在脱硫塔进口烟气、塔内脱硫液进口上方添加适量蒸汽建立蒸汽相变所需的过饱和水汽环境可显著促进细颗粒的脱除。     

喷淋洗涤条件下水汽饱和度分布特性

为在脱硫喷淋塔中借助蒸汽相变原理促进PM_2.5凝结长大,需要在塔内建立适宜的过饱和水汽环境。基于此,建立喷淋洗涤条件下气液两相热质传递模型,系统研究了操作参数对塔内饱和度分布特性的影响规律。结果显示,通过降低喷淋液温度、增加塔进口烟气含湿量,以及在喷淋区上方添加蒸汽均能够在塔内建立过饱和水汽环境;采用较大的液气比、较小的喷淋液滴直径有利于水汽饱和度的提高。获得了改变操作参数在脱硫喷淋塔内建立过饱和水汽环境的措施,对实际的脱硫除尘工艺的设计和运行具有指导意义。     

基于Aspen Plus的燃煤电厂烟气污染控制单元模拟

采用Aspen Plus软件对烟气污染控制单元进行模拟,以电厂实际运行数据验证模型的正确性,建模过程中考虑SO3转化和烟气中烟尘浓度的变化,并通过影响因素分析考察操作参数对污染物脱除效果的影响。结果表明,在选择性催化还原(SCR)脱硝过程中,部分SO2转化为SO3,除尘过程中飞灰对SO3有吸附作用,脱硫塔与除尘器对SO3和灰分脱除具有协同作用;SCR脱硝过程的最佳氨氮摩尔比范围为0.8~1.0,氨氮比低于0.6、反应温度低于400℃时,SO3浓度呈上升趋势;湿法脱硫过程中,入口烟气温度上升会阻碍SO2吸收和SO3去除;湿式除尘过程中,除尘效率随温度升高而降低,随气体流速增加先升高后降低,最佳流速为0.8~1.2 m/s。     

Modeling of ammonia-based wet flue gas desulfurization in the spray scrubber

A mathematical model of ammonia-based wet flue gas desulfurization process was developed based on the double film theory. The calculated results of the desulfurization system for two 220 t·h⁻¹ boilers per unit by this model were compared to that of corresponding measured data. It was found that the calculated results agree well with the measured data for the operating conditions of pH, liquid/gas ratio and SO₂ concentration. This model can provide predictions of the absorption performance of an ammonia-based wet flue gas desulfurization process and appears to be helpful for designing scrubbers for SO₂ absorption with ammonia absorbent.     

Effect of initial droplet size distribution on sulfur removal efficiency in FGD/SDA

Dry scrubbing with lime slurry in a spray dryer [spray dryer absorber (SDA)] has been an important technology for flue gas desulfurization (FGD). Mathematical models based on the heat and mass balances are used to predict SO₂ removal in the SDA as a function of initial size distribution of slurry droplets. Since the existence of moisture in the droplets appreciably enhances the SO₂ removal, its removal efficiency depends on the rate of drying as well as that of SO₂ removal itself, both depending on droplet diameter. With the increase in the geometric standard deviation (GSD) of the initial droplet size distribution, the efficiency of SO₂ removal first increases and then decreases, showing a maximum at a certain value of GSD. This trend is altered by the sorbent content of the droplets, expressed as stoichiometric ratio (SR). The decrease in SR makes the maximum move to higher GSD and reduces the variation in the efficiency with respect to GSD. For SR<0.73, a minimum efficiency also appears, ahead of the maximum. The results are well explained by the specific rates of both drying and SO₂ removal of the droplets.     

Cansolv~烟气脱硫-制酸技术在燃煤电厂烟气治理中的应用

介绍了中铝贵州分公司热电厂4台160 t/h循环流化床锅炉的烟气治理情况。项目包括烟气脱硫与硫酸生产2部分。烟气脱硫采用加拿大Cansolv可再生胺法,所获得的高纯度SO₂气体采用一转一吸工艺生产硫酸。介绍了装置的综合技术经济指标和运行情况。分析了该技术在电厂燃煤锅炉烟气治理中的优势及应用前景。     

燃煤电厂协同脱汞研究进展及强化措施

燃煤电厂是大气汞排放的重要源头,但是我国目前尚无完善的烟气汞控制方案。本文简要综述了国内外烟气脱汞技术研究现状,统计了国内污控设备（包括脱硝设备、除尘设备和脱硫设备）的装机容量。指出污控设备对烟气汞具有一定的协同脱除作用,但是受到我国煤质及运行条件等因素的制约,效果并不理想。本文结合国内某燃煤电厂的实测情况,提出了以下强化措施：①通过添加溴盐溶液,提高选择性催化还原（SCR）对烟气汞的氧化效率;②通过粉末活性炭与溴盐联合使用,强化静电除尘器（ESP）对烟气汞的协同脱除效率,脱汞效率可达90%以上;③通过精确控制脱硫浆液的pH值以及定期外排脱硫浆液,以降低其中汞的再释放率,维持湿法脱硫工艺（WFGD）稳定的烟气汞协同脱除效率;④通过优化和调整锅炉运行条件,提高现有污控设备体系的协同脱汞能力。     

Tentative modelling of spray-dry scrubbing of SO2

A 0.5 MW spray-dry scrubbing FGD pilot plant was used in the study of spray dryer performance over a wide range of operating conditions. Experimental findings were compared with a spray dryer model. During operation with large excesses of lime, the SO₂ absorption was limited by gas phase diffusion. At operation with a shortage of lime, the rate limiting step was the dissolution rate of lime. In addition, the flow regime in a spray dryer can be best described as well mixed. The SO₂ level in the flue gas was found to exert no direct effect on the efficiency of SO₂ removal. The observed effects are attributed solely to the changes in the drying process, due to the inter-dependence of slurry composition and SO₂ concentration.     

烟气排放控制技术的工艺现状

详细描述了LABSORB^TM再生式二氧化硫脱除工艺以及所用的EDV洗涤器设计。FCC装置可由一个简单的工艺采用：EDV洗涤器降低烟气中颗粒和SOx含量，不会引起堵塞或停车。该洗涤器可作为仅处理颗粒的设备(代替ESP)，当以后环保条例更严格时，也能转而处理SOx而不浪费任何组件。该洗涤器可使用LABSORB^TM工艺吸收剂，也可用苛性钠、碳酸钠、氢氧化镁甚至石灰为吸收剂。但二氧化硫含量较高时，LABSORB^TM可再生工艺可大幅度降低操作费用。LABSORB^TM工艺已成功地用于控制硫回收(SRU)装置的尾气排放，并用于控制全世界范围内22个FCC装置的排放，累计处理能力近158000m^3／d(1000000桶／d)。文中介绍用于FCC装置排放控制的苛性钠洗涤、可再生式洗涤以及常见的电除尘器(ESP)应用之间的差别，还详细描述这些系统及其除满足环保要求外的潜在优点。