Experimental studies on gas-phase mercury oxidation removal and denitration of coal combustion with NH_4 Br addition

In order to remove gas-phase mercury and NOx from flue gas, experimental studies on flue gas mercury oxidation removal and denitration of Guizhou anthracite combustion with NH4Br addition were carried out. The influence of NH4Br addition on the ignition temperature and combustion characteristics was studied using a thermogravimetric analyzer. The effects of the NHaBr addition amount on gas-phase mercury oxidation and removal were investigated in a bench scale of 6 kW fluidized bed combustor （FBC）. Mercury concentrations in flue gas were determined by the Ontario hydro method （OHM） and the mercury mass balance was obtained. Results show that the NH4Br addition has little influence on the ignition temperature of Guizhou anthracite. With the mercury mass balance of 95.47%, the proportion of particulate mercury Hg^p, gaseous mercury Hg^0 and Hg^2＋ are 75.28%, 11.60% and 13. 12%, respectively, as raw coal combustion. The high particulate mercury Hg^p in flue gas is caused by the high unburned carbon content in fly ash. When the NH4Br addition amount increases from 0 to 0. 3%, the concentration of gaseous Hg^0 and Hg^2＋ in flue gas decreases continuously, leading to the Hg^p increase accordingly. The oxidation rate of Hg^0 is positively correlated to the Br addition amount. It demonstrates that coal combustion with NH4Br addition can promote Hg^0 oxidation and removal. NOx concentration in flue gas exhibits a descending trend with the NHaBr addition and the removal rate reaches 17.31% with the addition amount of 0.3%. Adding NH4Br to coal also plays a synergistic role in denitration.

吸附脱汞技术及其应用现状综述

重金属汞是燃煤烟气关键污染物之一,其毒性已被国际社会所高度关注。从吸附剂合成手段、量子化学微观模拟、工程示范类测试等3个方面评述了现有脱汞技术的研究方法,认为对原材料改性处理是主要的吸附剂合成方法,而量子化学研究重点在于吸附剂表面的吸附机理,工程示范测试则更倾向于检测和探索选择性催化还原法等技术的脱汞效率。此外,从辅助脱汞技术、协同脱汞技术、循环可再生脱汞技术以及其他新型脱汞技术等4个方面对吸附脱汞技术未来的研究进行了展望,综合推测循环可再生脱汞技术是未来脱汞技术的潜在发展方向。

汞氧化剂加入对燃煤电厂汞及卤素排放影响试验研究

为掌握燃煤电厂添加溴化物的脱汞规律以及对其它副产物的影响,在某600MW燃煤机组上开展掺烧溴化钙的应用研究,采用美国环保局(Environmental Protection Agency,EPA)30B方法对湿法脱硫系统(wet flue gas desulfurization,WFGD)前后烟气进行汞浓度及形态测试,并对相关副产物中的汞浓度进行分析。结果表明:溴化钙的加入,大幅提高了烟气汞氧化率、以及飞灰的汞富集因子,当溴/煤比为28.3mg/kg时,整体脱汞率可达到96.8%。通过EPA 26A方法对选择性催化还原脱硝(selective catalytic reduction,SCR)、静电除尘器(electrostatic precipitator,ESP)、WFGD前后烟气进行卤素浓度及形态测试,发现溴化钙的添加,并不会导致卤素排放增加,烟气中的溴均以HBr的形式存在,而HBr极易溶于水,脱硫后均未检出溴排放。对产物的浸出毒性和热稳定性试验结果表明,溴化钙添加后对飞灰、石膏等副产品的浸出毒性,以及石膏中汞的热稳定性都没有明显影响,但提高了飞灰中汞的热稳定性。此外,该文还对烟气汞浓度测试方法、飞灰中溴浓度测试方法进行分析,并结合试验结果推测主要的反应路径。综合来看,汞氧化剂添加技术能够提升电站整体脱汞效率,并且未发现明显负面影响。

Mercury removals by existing pollutants control devices of four coal-fired power plants in China

The mercury removals by existing pollution control devices and the mass balances of mercury in four coal-fired power plants of China were carried out based on a measurement method with the aluminum matrix sorbent.All the plants are equipped with a cold-side electrostatic precipitator （ESP） and a wet flue gas desulfurization （FGD） in series.During the course of coal stream,the samples,such as coal,bottom ash,fly ash,gypsum and flue gas,were collected.The Hg concentrations in coals were measured by CVAAS after appropriate preparation and acid digestion.Other solid samples were measured by the RA-915 ＋ Zeeman Mercury Spectrometer.The vapor phase Hg was collected by a sorbent trap from flue gas and then measured using CVAAS followed by acid leaching.The mercury mass balances were estimated in this study were 91.6%,77.1%,118% and 85.8% for the four power plants,respectively.The total Hg concentrations in the stack gas were ranged from 1.56–5.95 μg/m 3.The relative distribution of Hg in bottom ash,ESP,WFGD and stack discharged were ranged between 0.110%–2.50%,2.17%–23.4%,2.21%–87.1%,and 21.8%–72.7%,respectively.The distribution profiles were varied with the coal type and the operation conditions.The Hg in flue gas could be removed by ESP and FGD systems with an average removal efficiency of 51.8%.The calculated average emission factor was 0.066 g/ton and much lower than the results obtained ten years ago.

高纯海绵铂的短流程制备工艺研究及应用

针对传统王水溶解—氯化铵反复沉淀法精炼铂工艺中存在的不足展开研究,考察不同还原剂及其浓度对粗氯铂酸铵中铑、铱去除率的影响,研究了无需蒸干的脱硝工艺并尝试量化脱硝终点。结果表明,采用10%水合肼+5%盐酸对粗氯铂酸铵中铑、铱的一步去除率较高,一步铑去除率达91.18%,铱去除率达95.88%;采用40%酒精+8%尿素溶液脱硝时间仅为1.3 h,脱硝用时缩短89.2%以上,并且烧损合格率达到95%以上,为最佳的脱硝工艺,可以将溶液电位590~600 mV作为脱硝终点的判断依据。该工艺应用后,海绵铂的精炼周期缩短约75%,铂的直收率提高0.26个百分点,可稳定产出合格的高纯海绵铂,具有良好的推广应用价值。

Mercury oxidation and adsorption characteristics of potassium permanganate modified lignite semi-coke

The adsorption characteristics of virgin and potassium permanganate modified lignite semi-coke （SC） for gaseous Hg were investigated in an attempt to produce more effective and lower price adsorbents for the control of elemental mercury emission. Brunauer-Emmett- Teller （BET） measurements, X-ray powder diffraction （XRD） and X-ray photoelectron spectroscopy （XPS） were used to analyze the surface physical and chemical properties of SC, Mn-SC and Mn-H-SC before and after mercury adsorption. The results indicated that potassium permanganate modification had significant influence on the properties of semi-coke, such as the specific surface area, pore structure and surface chemical functional groups. The mercury adsorption efficiency of modified semi-coke was lower than that of SC at low temperature, but much higher at high temperature. Amorphous Mn7＋, Mn6＋ and Mn4＋ on the surface of Mn-SC and Mn-H-SC were the active sites for oxidation and adsorption of gaseous Hg~, which oxidized the elemental mercury into Hg2＋ and captured it. Thermal treatment reduced the average oxidation degree of Mn2＋ on the surface of Mn-SC from 3.80 to 3.46. However, due to the formation of amorphous MnOx, the surface oxidation active sites for gaseous Hg0 increased, which gave Mn-H-SC higher mercury adsorption efficiency than that of Mn-SC at high temperature.

Removal of elemental mercury by KI-impregnated clay

This study described the use of clay impreg- nated by KI in gas phase elemental mercury （Hg°） removal in flue gas. The effects of KI loading, temperature, 02, SO2 and H20 on Hg°removal were investigated using a fixed bed reactor. The Hg° removal efficiency of KI-clay with 3% KI loading could maintain at a high level （approxi- mately 80 %） after 3 h. The KI-clay demonstrated to be a potential adsorbent for Hg° removal when compared with activated carbon based adsorbent. 02 was found to be an important factor in improving the Hg° removal. 02 was demonstrated to assist the transfer of KI to I2 on the surface of KI-clay, which could react with Hg° directly. NO and SO2 could slightly improve Hg° removal, while H20 inhibited it greatly. The results indicated that after adsorption, most of the mercury escaped from the surface again. Some of the mercury may have been oxidized as it left the surface. The results demonstrated that the chemical reaction primarily occurred between KI and mercury on the surface of the KI-clay.

燃煤电厂污染控制设备脱汞效果及汞排放特性试验

为了解燃煤电厂汞的排放规律以及现有的污染控制设备对烟气中汞的协同脱除效果,采用安大略法对江西省内4台机组进行汞排放及控制试验研究,得到现阶段燃煤电厂配置条件下汞的排放特性。研究结果表明:未投入汞氧化剂的机组污染控制设备协同脱汞效率在69.01%~75.63%,投入汞氧化剂的机组脱汞效率可达89.69%;SCR脱硝装置对烟气总汞的减排效果不明显,但能促使Hg0成为易于脱除的Hg^(2+)和颗粒态汞,机组投入汞氧化剂后可大幅提高Hg^0氧化为Hg^(2+)的比率;除尘器可以脱除全部的颗粒态汞,其协同脱汞效率平均值为24.37%;湿式脱硫系统对Hg^(2+)的脱除效率为88.39%;烟气经过脱硝、除尘、湿式脱硫装置后,最终排放气体中汞的质量浓度在3.91~8.89μg/m^3,远小于国家排放标准限值。

中国活性焦烟气净化研究分析

根据973项目研究成果,结合文献资料,对中国活性焦用于烟气脱硫、脱硝和脱汞、以及联合脱除的研究现状,活性焦烟气净化工业应用情况进行了综述和分析,并提出了今后研发应用几点建议。

湿法烟气脱硫系统的脱汞性能研究

通过测量湿法烟气脱硫（WFGD）系统进出口烟气中汞的浓度，考察了采用NH3·H2O、NaOH、Na2CO3、Ca（OH）2、CaCO3等5种脱硫剂时系统的脱汞性能，并在脱硫液中添加KMnO4、Fenton试剂、K2SzO8／CuSO4、Na2S进行试验．结果发现：燃煤烟气中气态总汞主要成分是单质汞，二价汞所占比例不超过409／6；常规wFGD系统能高效脱除烟气中的气态二价汞（Hg^2＋），脱除效率高达81．11％～92．60％，而对气态总汞的脱除效率仅为13．27％～18．26％，经WFGD系统后单质汞略有增加；脱硫剂种类对脱汞效果影响不明显，提高液气比有利于提高wFGD系统的脱汞效率；KMnO4、Fenton试剂、K2S2O8／CuSO。和Na2S等添加剂均可提高脱汞效率，但不同添加剂的效果有所不同，其中Na2S效果最为显著，脱汞效率最高可达67％．

纳米氧化锌在模拟煤气下吸附单质汞的实验研究

采用均匀沉淀法制备纳米氧化锌吸附剂,并采用BET、XRD、XPS等分析手段对其进行表征。在固定床吸附实验台上,研究了吸附剂在N2和模拟煤气气氛下对单质汞的吸附特性,分析气体成分对纳米氧化锌脱汞性能的影响。结果表明,纳米氧化锌在纯N2气氛下的脱汞效率较低,以物理吸附为主;H2S的加入可以显著提高纳米氧化锌对汞的吸附,停止通入H2S后,脱汞效率仍能维持较长时间;CO和H2通过促进纳米氧化锌脱硫进而促进对汞的脱除。随着温度的提高,纳米氧化锌表面形成的单质硫逐渐减少,抑制了吸附剂对单质汞的吸附脱除。

燃煤电厂脱硫系统的脱汞特性研究

作为未来潜在的多污染物排放控制装置,烟气脱硫系统对汞赋存价态和脱除效率的影响成为目前汞污染控制研究的热点。对2种具有代表性的脱硫系统[湿法脱硫(WFGD)和新型整体一体化脱硫(NID)]进行了汞测试。试验结果表明:WFGD系统对烟气中氧化态汞的脱除效率达到74.68%,但对烟气中单质汞的脱除效率很差,氧化态汞在全汞中所占的比例是决定WFGD全汞脱除效率的关键因素;NID系统对烟气中单质汞的脱除效率高达99.97%,对氧化汞的脱除效率为79.03%,对总汞的脱除效率是83.52%,这说明NID系统可以非常有效地控制燃煤电厂汞的排放。

410t/h煤粉锅炉的汞排放及其NID系统除汞特性研究

对配备有NID系统的410t／h燃煤电站锅炉的煤、底渣、飞灰进行取样，测定了样品中汞的含量。采用Ontario-Hydro方法测定了NID前和ESP后烟气中汞的形态。实验结果表明，汞主要以飞灰形式排放，占总汞量的90％，烟气汞占10％。NID前和ESP后的烟气中，汞的浓度分别为21．3μg/m^3～22．4μg/m^3和1．93μg/m^3～3．67μg/m^3，说明该NID系统对烟气中汞具有相当高的脱除效率，达到83．6％-90．9％。对汞的化学形态研究表明，NID前烟气汞主要以Hg^2＋形式存在，占气态汞量的67％；ESP后烟气中Hg^2＋占气态汞量的71．8％-85．1％，Hg^0的含量为零，说明烟气中Hg^0在NID系统中经历一系列的氧化还原反应后．被氧化成Hg^2＋并吸附脱除。

垃圾填埋场渗滤液中的汞及现场污水处理设施对其的去除

渗滤液一直是困扰垃圾填埋场的一个主要问题,处理不当会对周围生态环境造成严重的污染。垃圾中混入的汞淋滤进入渗滤液将会造成水体的汞污染。对贵阳市高雁垃圾卫生填埋场产生的渗滤液原液和不同处理单元过程中汞的含量进行了调查分析,结果表明该填埋场渗滤液原液中的汞含量为79.4ng·L-1,处于国内外的中低水平,就汞而言污染并不严重。经过处理,渗滤液有近2/3的汞被去除了。渗滤液原液中的汞主要以颗粒态为主,随着处理单元过程,这一比例逐渐降低。渗滤液中的汞含量与填埋垃圾汞含量、pH、以及填埋物质对汞的吸附有关。

模拟煤气中氧化铁吸附单质汞的影响因素

在固定床吸附机理研究实验台上,利用汞在线分析仪研究了超声波辅助沉淀法制备的氧化铁吸附剂在N2和模拟煤气气氛下对单质汞的吸附作用,分析煤气中气体成分对氧化铁吸附剂脱汞性能的影响.实验结果表明:氧化铁吸附剂在纯N2气氛下的脱汞效率较低;H2S可以促进氧化铁吸附剂对汞的吸附脱除,脱汞效率能够长时间维持在90%以上;在吸附床温度为150℃条件下,模拟煤气中的还原性气体CO和H2对氧化铁吸附剂的脱汞性能影响不大;模拟煤气中水蒸气抑制了氧化铁吸附剂对单质汞的吸附脱除;随着吸附床温度的升高,氧化铁吸附剂的脱汞效率先增高,而后逐渐降低.

活性焦脱汞实验研究

针对吸附剂对气态汞吸附效果的影响,比较了不同活性焦吸附剂对气态汞的吸附性能,对同种活性焦吸附剂不同吸附方式进行脱汞实验研究,分析了活性焦脱汞效率随时间的变化趋势;粒径和接触面积对吸附剂脱汞性能的影响。结果表明:样本活性焦最大吸附率出现在最开始,且随着吸附时间的增加,活性焦的吸附率逐渐减小,直到吸附量接近饱和,2种活性焦的饱和汞吸附量分别达到了1.137μg/g和0.792μg/g;随着活性焦质量的增加,最大吸附率及吸附饱和时间也随之增加;改变吸附方式可将最大吸附率由原来的20%左右提高至近40%,即增加吸附剂与汞的质量比可提高吸附剂的最大吸附率,增加吸附剂与含汞气体的接触面积可更好地提高吸附剂的脱汞效率。

新型一体化半干法脱硫系统同时脱汞的试验研究与微观机理分析

对某台安装有新型一体化烟气脱硫（NID）系统的燃煤电站锅炉的煤、底渣、飞灰进行取样，测定了样品中汞的含量．并采用Ontario—Hydro方法测定了NID系统前后烟气中汞的形态．利用比表面积及孔隙度分析仪、X衍射仪、扫描电镜和能谱仪对NID系统中各种灰的物理化学特性进行了分析，揭示了NID半干法脱硫系统同时脱除烟气中Hg的微观机理．结果表明：在NID半干法脱硫系统中，消石灰与飞灰可以充分混合，脱硫塔内飞灰循环倍率高，混合灰表面始终有新鲜的脱硫剂Ca（0H）2，而且脱硫塔内有水合硅酸钙形成，颗粒团聚严重，对脱除烟气中的SO2和Hg非常有利．NID半干法脱硫系统对烟气中总汞的脱除效率高达86．6％～92．2％，对燃煤电站汞排放的控制效果显著．

磁性活性炭吸附剂脱汞性能研究

为了制备同时具有优良脱汞性能和磁分离特性的磁性活性炭(MAC),采用共沉淀法制备Fe^(3+)和Fe^(2+)的不同离子配比及不同磁质量分数的MAC,并对其进行比表面积、磁化强度、扫描电镜、X射线衍射、热失重试验等分析,得到Fe^(3+)和Fe^(2+)摩尔比为1∶1,磁质量分数为25%的MAC具备良好的磁分离特性和脱汞性能。在固定床试验台上对MAC进行脱汞性能影响试验,结果表明:γ-Fe_2O_3是MAC上主要的磁性物质,O_2和HCl的存在均能加强元素汞的氧化脱除,促进MAC对汞的吸附,且其含量越高脱汞性能越好;SO_2对MAC的脱汞效率无明显影响,接触初期在MAC表面产生竞争吸附现象,造成脱汞效率先降低后升高现象;水蒸气减弱了MAC对汞的吸附效果。

褐煤半焦脱除燃煤烟气中元素态汞的试验研究

为制备廉价的燃煤烟气中气态Hg0污染物的吸附材料,在小型固定床反应器上对3种原料褐煤半焦(NM-SC,SX-SC,SD-SC)、两种高锰酸钾改性半焦(Mn-SC,Mn-H-SC)的除汞性能进行试验研究。结果表明:3种原料半焦的除汞效率均随吸附温度的升高而降低,呈现出典型的物理吸附特征;NM-SC的孔隙结构最为发达,在低温时的除汞效率明显高于另外两种原料半焦;改性半焦Mn-SC和Mn-H-SC低温时的除汞效率较差,但高温时的除汞效率远高于NM-SC,呈现出典型的化学吸附特征,其中Mn-H-SC在140℃时的除汞效率可长时间稳定在80%左右;增加吸附剂用量,可提高Mn-H-SC的除汞效率;增加Hg0初始浓度会提高Mn-H-SC的单位质量汞容积量。

竹活性炭吸附溶液中汞离子的试验研究

利用竹活性炭吸附去除溶液中的汞离子,考察了溶液pH值、汞离子初始浓度、活性炭投加量和吸附温度对竹活性炭吸附汞离子的影响,研究了竹活性炭吸附溶液中汞离子的吸附动力学行为。结果表明:竹活性炭吸附溶液中汞离子是一个吸附与解吸并存的物理吸附过程,20℃下竹活性炭的除汞效率明显高于80℃,是放热反应,低温利于吸附;溶液pH值是影响竹活性炭吸附汞离子的最重要因素,酸性环境可明显提高活性炭的除汞效率;活性炭的微孔和小中孔是汞离子的主要吸附位,平均孔径为2nm的竹活性炭除汞效率能够达到99%以上。竹活性炭对汞离子的吸附动力学行为遵循准二级动力学方程,相关系数高于0.99。