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.     

超低排放燃煤电厂低低温电除尘器协同脱汞研究

通过调整某660 MW超低排放燃煤电厂低低温省煤器烟气温度,测试了煤中汞质量分数和电除尘器出入口烟气中各形态汞的质量浓度,分析了不同烟气温度下汞形态的变化特征。结果表明:低低温省煤器烟气温度会影响汞的形态分布,烟气温度降低时Hg~0向Hg~(2+)或Hg_p转变;低低温电除尘对Hg~0和Hg~(2+)具有协同脱除作用;低低温省煤器出口烟气温度为90℃时,低低温电除尘器入口Hg~(2+)和Hg_p的质量分数最高,低低温电除尘器总汞脱除率为84.4%,出口烟气中Hg~0和Hg~(2+)的质量浓度最低,此工况下低低温电除尘器对汞的协同脱除效果最佳;低低温省煤器停运时,低低温电除尘器出口烟气Hg~0和Hg~(2+)的质量浓度高于其他工况。     

燃煤烟气脱汞吸附剂综述

概述了我国燃煤烟气中脱汞吸附剂的研究现状,综述了活性炭、改性活性炭、飞灰、钙基吸附剂、矿物类吸附剂、金属类吸附剂,以及一些新型吸附剂对汞的脱除效果。指出活性炭对汞的脱除效率高,但成本也高;飞灰吸附剂脱汞的成本虽然低但脱除效率也低。文中还介绍了其它新型吸附剂的发展,指出寻找廉价高效吸附剂的必要性及开发烟气中污染物的联合脱除吸附剂的研究方向。     

金属氧化物改性凹凸棒石脱除烟气中的单质汞

利用固定床反应器在模拟烟气条件下研究凹凸棒石天然吸附剂对单质汞的脱除能力,并利用金属氧化物Mn O2和Co3O4对凹凸棒石进行改性,制备出金属氧化物改性的矿物吸附剂,研究了烟气组分对改性吸附剂脱汞效果的影响.结果表明,Mn O2和Co3O4改性后的凹凸棒石极大地提高了脱汞效率,由原来的12.2%分别提高到了87.9%和84.1%;O2和HCl促进单质汞的脱除,氧气体积分数为4%时,其脱汞率分别提高至92.1%和88.1%,HCl体积分数为10×10-6时,脱汞率分别提高至90.1%和90.7%;SO2和NO竞争吸附降低单质汞的脱除效率,SO2体积分数为400×10-6时,Mn O2和Co3,O4改性后的凹凸棒石其脱汞率分别降至84.7%和64.5%,NO体积分数为50×10-6时,其脱汞率分别降至86.1%和81%.     

模拟煤气中铁基吸附剂脱汞实验研究

在固定床吸附机理研究试验台上,利用汞在线分析仪研究了铁基吸附剂在氮气和模拟煤气气氛下对单质汞的吸附作用。实验结果表明,N2气氛下,铁基吸附剂的煅烧抑制了吸附剂对单质汞的脱除;铁基吸附剂在模拟煤气气氛下有着较高的脱汞效率,脱汞效率能够长时间维持在90%以上;吸附床温度会影响Fe2O3吸附剂对单质汞的吸附,随着吸附床温度升高,Fe2O3吸附剂的脱汞效率先升高后下降。     

复合稀土的添加对平板式脱硝催化剂汞氧化性能的影响

汞是大气环境的重要污染源,燃煤电厂烟气中汞的脱除成为近年来环保领域的研究热点之一。通常,烟气中的汞主要以三种形态存在:颗粒汞(Hg~P)、气态二价汞(Hg~(2+))和单质汞(Hg~0)。其中,Hg~p可以通过除尘设备脱除,Hg~(2+)可在除尘设备和湿法脱硫设备中除去,Hg~0的脱除难度较大。通过对选择性催化还原(SCR)脱硝催化剂进行改性,在SCR装置中同时实现氮氧化物(NO_x)和Hg~0的脱除,是一种较为新颖的技术手段。复合稀土的添加,改善了催化剂在低温段(300℃)的脱硝性能,从而拓宽了催化剂的脱硝活性窗口。同时,有效提高平板式脱硝催化剂的汞氧化性能,最大汞氧化效率分别达到47.6%和53.5%。此外,采用XRD、N_2-吸附脱附、耐磨强度测试对催化剂进行分析,当添加15%的复合稀土时,对催化剂的晶型、孔结构、耐磨强度影响较小;但添加30%复合稀土时,催化剂耐磨强度显著降低。因此,平板式脱硝催化剂适合的复合稀土添加量为15%。     

Fe_3O_4磁性纳米颗粒结合贵金属脱汞技术研究进展

Fe_3O_4纳米颗粒由于其优秀的物理、化学性能及其特有的磁性能可作为吸附剂的磁性载体。贵金属(Pd、Pt、Au、Ag、Rh等)材料能与Hg发生汞齐反应形成合金,并可通过升温的方式释放出汞蒸气并获得再生,可作为活性物质。将Fe_3O_4磁性纳米颗粒与贵金属结合,可制得一类稳定、可再生、易分离的新型优秀吸附剂,对于脱除燃煤烟气中的Hg~0具有很好的应用前景。在固定床上考察了载Ag的Fe_3O_4纳米颗粒对Hg~0的吸附能力,其脱汞效率可达90%以上。     

燃煤机组超低排放改造对汞排放的影响

针对超低排放课题下汞排放的研究,采用标准安大略法对浙江某发电厂两台燃煤机组实施烟气超低排放改造并对改造前后进行汞排放测试,着重分析了超低排放改造后污染控制设备的协同脱汞作用。结果表明总汞脱除率得到了显著提高,主要是改变了烟气汞形态分布,提升了Hg~(2+)比例;SCR(催化还原脱硝)影响汞的形态分布,但不改变总汞含量;ESP(电除尘)能够大量地降低汞浓度;WFGD(温法脱硫)对气相中氧化汞的脱除效果较好,WFGD对Hg~0没有脱除效果。从测试结果来看,两台机组总汞脱除效率平均提升了13.9%,Hg~(2+)比例平均提升153.9%。证实了利用超低排放技术改造后污染物控制设备(除尘装置、脱硝装置、脱硫装置)协同脱汞是比较经济有效的措施。     

燃煤烟气脱汞吸附剂研究进展

概述了目前当今世界燃煤烟气中脱汞吸附剂的研究现状,介绍了碳基吸附剂、钙基吸附剂、石油焦、飞灰,以及一些新型吸附剂对汞的脱除效果。指出活性炭对汞的脱除效率高,但成本也高;飞灰吸附剂对汞脱除的成本低,但脱除效率也低。用于燃煤电厂汞吸附的吸附剂研究处于实验室研究阶段,因此开发价廉和高效脱汞吸附剂和吸附剂的再生等是吸附剂发展过程中的一个重要研究课题。     

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种脱硫荆时系统的脱汞性能,并在脱硫液中添加KMnO4,Fenton试荆、K2S2O8/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40%;常规WFGD系统能高效脱除烟气中的气态二价汞(Hg2+),脱除效率高达81. %～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、K2SzO8/CuSO4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Na:S效果最为显著,脱汞效率最高可达67%.     

Selective separation of hydrogen sulfide by pressure-swing adsorption

A pressure-swing adsorption process using molecular sieves as adsorbents was tested for the effective separation of hydrogen (H₂) from a gas stream containing 88 vol% of hydrogen sulfide (H₂S) and 12 vol% H₂. Molecular sieve type Y (sodium ion) exhibited the highest dynamic capacity, adsorption efficiency and saturation time.     

A review on the utilization of fly ash

Fly ash, generated during the combustion of coal for energy production, is an industrial by-product which is recognized as an environmental pollutant. Because of the environmental problems presented by the fly ash, considerable research has been undertaken on the subject worldwide. In this paper, the utilization of fly ash in construction, as a low-cost adsorbent for the removal of organic compounds, flue gas and metals, light weight aggregate, mine back fill, road sub-base, and zeolite synthesis is discussed. A considerable amount of research has been conducted using fly ash for adsorption of NO_x, SO_x, organic compounds, and mercury in air, dyes and other organic compounds in waters. It is found that fly ash is a promising adsorbent for the removal of various pollutants. The adsorption capacity of fly ash may be increased after chemical and physical activation. It was also found that fly ash has good potential for use in the construction industry. The conversion of fly ash into zeolites has many applications such as ion exchange, molecular sieves, and adsorbents. Converting fly ash into zeolites not only alleviates the disposal problem but also converts a waste material into a marketable commodity. Investigations also revealed that the unburned carbon component in fly ash plays an important role in its adsorption capacity. Future research in these areas is also discussed.     

Enhanced hydrogen adsorption in ordered mesoporous carbon through clathrate formation

Ordered mesoporous carbons were synthesized with a soft-template approach and modified with a water and tetrahydrofuran mixture having a H₂O/THF molar ratio of 17:1 as potential adsorbent media for hydrogen storage. Hydrogen adsorption equilibrium on the carbon adsorbents was measured gravimetrically at 270 K and hydrogen pressures up to 163 bar. Enhanced hydrogen adsorption was observed on the carbon adsorbents doped with 0.5 wt.% and 0.75 wt.% of H₂O/THF due to the combined effects of hydrogen adsorption on the carbon surface and formation of a binary H₂–H₂O–THF clathrate. Hydrogen adsorption capacities on the carbon adsorbents doped with 0.5 wt.%, 0.75 wt.% of H₂O/THF, and the pure carbon at 270 K and 163 bar are 0.747 wt.%, 0.646 wt.% and 0.585 wt.%, respectively. The hydrogen adsorption isotherms on all the doped carbon adsorbents are of typical Type III and can be well correlated by the Freundlich equation. A desorption hysteresis loop was observed on the carbon adsorbents doped with 0.5 wt.% and 0.75 wt.% of H₂O/THF, which was probably caused by the pore size difference during the adsorption and desorption steps.     

Separation dynamics of hydrogen isotope gas in mesoporous and microporous adsorbent beds at 77 K: SBA-15 and zeolites 5A,Y, 10X

The separation of a hydrogen isotope mixture on porous materials was studied using equilibrium and breakthrough experiments. The adsorption equilibria of H₂ and D₂ on SBA-15 with mesopores and molecular sieves 5A, Y, and 10X with micropores were measured at 77 K using the volumetric method. The breakthrough experiments of a H₂ and D₂ mixture in each adsorbent bed were carried out at various conditions of flow rate and pressure. The equilibrium ratio of D₂ to H₂ on mesoporous molecular sieves was larger than the ratio on microporous molecular sieves (SBA-15 > 10X > Y > 5A), but the difference among the adsorbents decreased with increases in pressure. On the other hand, the order of breakthrough separation factor showed the opposite result (SBA-15 < 10X < Y < 5A). The breakthrough separation factors for zeolite 10X was approximately equal to the equilibrium ratio of D₂ to H₂ at the corresponding partial pressures, whereas zeolites 5A and Y showed higher breakthrough separation factors than their equilibrium ratios. In SBA-15, the separation factors from breakthrough results were even smaller than the corresponding equilibrium ratio. In the microporous adsorbent with a limited pore size (zeolite 5A in the study), the diffusion mechanism contributed to the separation of hydrogen isotope gases as one of key factors.     

吸附协同等离子体作用的顺序式锅炉烟气脱硫脱硝工艺

针对锅炉（烟厂用锅炉等）烟气，提出了一种具有高脱除率和低能耗的顺序式烟气脱硫脱硝工艺。即在吸附剂颗粒表面利用活性N原子还原NO产生的活性0原子来继续氧化二氧化硫生成SO3，并通过化学反应动力学模拟研究了该工艺的可行性。NO／SO2/N2系统等离子体脱硫脱硝的模拟结果显示：NO有显著的脱除效果，SO2有少量转化为SO3，SO2脱除率随停留时间增加而增加。研究结果表明顺序式烟气脱硫脱硝是可行的，关键在于选用合适吸附剂来控制其表面的O2浓度和停留时间。     

褐煤焦吸附烟气中气态汞的实验研究

利用汞渗透管的汞蒸气发生装置和其他烟气成分模拟烟气条件,在小型固定床实验台上开展褐煤焦脱除Hg0的试验研究。结果表明:O2和HCl单独存在时均能够有效地促进单质汞在煤焦上的吸附,使煤焦的穿透率减少,吸附效率提高;SO2的存在会造成竞争吸附,抑制煤焦对Hg0的吸附;NO对煤焦吸附Hg0影响不大。随着入口汞浓度的增加,煤焦的穿透率增加;随着吸附反应温度的升高,煤焦的穿透增加,吸附效率降低。     

MTO催化剂中国专利技术进展（二）——SAPO系列分子筛

SAPO-34分子筛的结构特征,使其在MTO工艺中可以高选择性地将甲醇转化为乙烯、丙烯。纯的SAPO-34用作MTO催化剂时,催化效率相对较低,通常需要对SAPO-34进行酸性调整、酸中心调整以及孔口径尺寸调整等改性。通过将金属元素引入SAPO-34分子筛骨架上,改变分子筛酸性和孔口径大小,得到小孔口径和中等强度的酸中心,而孔口径变小限制了大分子的扩散,有利于小分子烯烃选择性的提高。认为采取复合改性的方法,是分子筛改性的最直接、最经济、最简便和最容易取得效果的方法。有时,将具有不同孔口径、不同结构的分子筛按一定比例进行物理复合,制成的复合分子筛的性能完全满足工艺要求,而其成本却是最低的。从SAPO-34分子筛、流化床SAPO分子筛、金属改性SAPO分子筛,SAPO分子筛的预处理,复合分子筛,核壳结构催化剂及催化剂的再生等方面,综述了MTO工艺用SAPO系列分子筛的中国专利技术进展。     

Economic assessment of biogas-to-electricity generation system with H2S removal by activated carbon in small pig farm

This study was conducted to assess the economic feasibility of electricity generation from biogas in small pig farms with and without the H₂S removal prior to biogas utilisation. The 2% potassium iodide (KI) impregnated activated carbon selected as H₂S adsorbent was introduced to a biogas-to-electricity generation system in a small pig farm in Thailand as a case study. With the average inlet H₂S concentration of about 2400 ppm to the adsorption unit, the H₂S removal efficiency could reach 100% with the adsorption capacity of 0.062 kg of H₂S/kg of adsorbent. Under the reference scenario (i.e., 45% subsidy on digester installation and fixed electricity price at 0.06 Euro/kWh) and based on an assumption that the biogas was fully utilised for electricity generation in the system, the payback period for the system without H₂S removal was about 4 years. With H₂S removal, the payback period was within the economic life of digester but almost twice that of the case without H₂S removal. The impact of electricity price could be clearly seen for the case of treated biogas. At the electricity price fixed at 0.07 Euro/kWh, the payback period for the case of treated biogas was reduced to about 5.5 years, with a trend to decrease at higher electricity prices. For both treated and untreated biogas, the governmental subsidy was the important factor determining the economics of the biogas-to-electricity systems. Without subsidy, the payback period increased to almost 7 years and about 11 years for the case of untreated and treated biogas, respectively, at the reference electricity price. Although the H₂S removal added high operation cost to the system, it is still highly recommended not only for preventing engine corrosion but also for the environment benefit in which air pollution by H₂S/SO₂ emission and impact on human health could be potentially reduced.     

超低排放脱硫塔和湿式静电对烟气污染物的协同脱除

试验测定不同负荷下脱硫吸收塔进出口和湿式静电出口烟尘、PM_(2.5)、SO_2、SO_3、汞和液滴等多种污染物的浓度,研究脱硫吸收塔和湿式静电对多种污染物的协同脱除机制。试验结果表明:脱硫吸收塔和湿式静电均可协同脱除烟气中的SO_2、烟尘、PM_(2.5)、SO_3、汞和液滴等。相比较而言,脱硫塔对SO_2和汞的脱除效率高,湿式静电对总尘、PM_(2.5)和液滴的脱除效率高,对SO_3的脱除二者基本相当。脱硫吸收塔和湿式静电对污染物的协同脱除效率较高。对烟尘、PM_(2.5)、SO_2、SO_3、汞和液滴的协同脱除效率可分别高达87.3%、85.8%、99.25%、94.00%、89.31%和79.10%。脱硫吸收塔产生的气溶胶、二次释放的汞和液滴,经湿式静电进行进一步脱除。脱硫吸收塔和湿式静电对多种污染物有较强的协同脱除作用。     

Effect of chlorine-repulsive molecular fragments on photocatalytic seawater splitting performance of BiVO4 for oxygen evolution

Photocatalysis to produce clean energy by splitting seawater have great practical importance for dealing with the energy crisis. However, seawater contains many Cl^? ions whose oxidation competes with the oxygen evolution reaction. In this work, we present a photocatalyst modified with S-containing molecular fragments on the surface to improve its efficiency in the oxygen evolution reaction in seawater splitting. We found that the oxygen evolution performance of BiVO₄ modified with S-containing molecular fragments was 1.7 times higher than the unmodified material. Based on this finding, the modification didn't affect the light absorption and charge separation efficiency of BiVO₄, but lead to a marked (83.6%) decrease of the effective chlorine concentration in the reactor after photocatalytic reaction. The results indicate that the surface modification with S-containing molecular fragments is an effective method to repel chlorine. This work provides a useful reference to improve the efficiency of photocatalysts in overall seawater splitting.