粉煤灰综合利用过程中汞的二次释放规律研究

我国粉煤灰年产生量4亿t左右,近年来利用率稳定在65%～68%,主要利用方式包括建材生产、道路施工、建筑工程和农业利用.建材生产包括高温工序,可能存在粉煤灰中汞的二次释放.本研究设计实验模拟了水泥生产、蒸养砖生产的主要环境因素,利用程序升温脱附的方法研究粉煤灰利用过程中的汞迁移转化规律,并对全国范围内粉煤灰利用过程汞的二次释放量做出估算.研究发现,粉煤灰中的汞以HgCl2(Hg2Cl2)、HgS和HgO的形式存在;水泥生产过程中,粉煤灰中98%以上的汞会释放;蒸养砖生产过程中,粉煤灰中汞的平均释放率为28%,释放率主要受到粉煤灰中的HgCl2(Hg2Cl2)比例的影响.我国粉煤灰利用过程中的汞二次排放量由2002年的4.07 t.a-1增至2008年的9.18 t.a-1,其中水泥行业的贡献率占到96.6%.     

Effects of temperature and SO3 on re-emission of mercury from activated carbon under flue gas conditions

Mercury(Hg) is a toxic and bio-accumulating heavy metal that is predominantly released via the combustion of coal. Due to its toxicity, the Environmental Protection Agency(EPA)has introduced Mercury and Air Toxics Standards(MATS) Rule regarding allowable Hg emissions. In order to reduce emissions, power plants have widely adopted activated carbon(AC) injection. AC injection has proven to be an effective method to reduce Hg emissions, but the re-emission of previously adsorbed Hg during unit operation, likely due to changing temperature or flue gas composition, could be problematic. This study specifically examined the effects of temperature and sulfur trioxide(SO3) concentration,by ramping temperature and SO3 concentration independently and simultaneously, on AC samples that are already exposed to flue gas and saturated in presence of Hg, sulfur dioxide(SO2) and nitric oxide(NO). Of these two suspected factors to cause re-emission,temperature had the greater impact and resulted in re-emission of both elemental and oxidized Hg with a greater fraction of oxidized Hg, which can be attributed to elemental Hg being more strongly bonded to the AC surface. Surprisingly, exposing the samples to increasing concentrations of SO3 had nearly no effect under the conditions examined in this study, possibly as a result of the samples being already saturated with sulfur prior to the SO3 ramp tests to simulate transient conditions in the plant.     

燃煤烟气污染物控制装置协同脱汞特性研究

采用Ontario Hydro方法对某100MW燃煤机组进行了烟气汞取样测试,获得了选择性催化还原（SCR）脱硝装置、静电除尘器（ESP）和湿法烟气脱硫装置（WFGD）对烟气汞形态转化和脱除特性规律.借助程序升温脱附（TPD）、扫描电子显微镜分析（SEM）和X射线荧光光谱分析（XRF）等方法探究了飞灰对汞的吸附特性及吸附后汞的热稳定性.结果表明,在75% MCR和85% MCR不同的机组负荷下,SCR+ESP+WFGD对烟气总汞（Hg^T）的联合脱除率分别为92.83%、81.66%.SCR对元素汞（Hg⁰）的氧化率与燃煤氯（Cl）含量正相关,Cl含量为500mg/kg时,氧化率高达96.18%.ESP在完全脱除颗粒汞（Hg^P）的同时对Hg⁰和氧化态汞（Hg²⁺）的平均脱除率分别为12.73%和27.79%,ESP飞灰中的未燃尽炭和金属氧化物（Al₂O₃、Fe₂O₃）是吸附气态汞的关键组分,汞在飞灰表面主要以HgCl₂、HgS（红色）和HgO的形态存在,高于190℃时会分解再释放.WFGD对Hg²⁺的平均脱除率为91.10%,并能将部分Hg²⁺还原成Hg⁰,存在明显的汞二次释放问题.     

模拟湿地植物根系分泌物对酸性矿山废水沉淀物中Fe、Mn释放及形态的影响

为研究人工湿地处理酸性矿山废水(acid mine drainage,AMD)系统中植物根系分泌物对根际环境沉淀物中Fe、Mn活性的影响,评估人工湿地处理AMD时对Fe、Mn固持作用的稳定性及可靠性,选用植物根系分泌物中常见的柠檬酸、苹果酸及草酸来模拟植物根系分泌物对沉淀物中Fe、Mn的释放及形态影响。结果表明:3种有机酸对根际环境沉淀物中Fe、Mn的释放均产生不同程度的影响,相同浓度下的有机酸对Fe的影响顺序为:柠檬酸>苹果酸>草酸,对Mn的影响顺序为:柠檬酸>草酸>苹果酸。随着有机酸浓度的增加,沉淀物中Fe、Mn的释放量逐渐增加,且Fe的释放量大于Mn。形态分析结果表明,在有机酸参与前沉淀物中Fe、Mn主要以可还原态形式存在,当添加3种不同浓度的有机酸后,沉淀物中的可还原态Fe、Mn极不稳定,易向可交换态发生转变,而残渣态与可氧化态则较为稳定,说明沉淀物中残渣态与可氧化态的Fe、Mn在人工湿地中是Fe、Mn去除的重要途径。