氮氧化物污染控制——排烟脱硝

本文阐述排烟脱硝的方法,即以烟道气或工业废气中净化氮氧化物的方法。排烟脱硝的方法繁多,目前有还原法、吸收法以及吸附法三大类。但是,根据工业化排烟脱硝方法的经济评价得出,应用氨作还原剂选择性催化还原氮氧化物的方法,是脱除氮氧化物最经济和最有效的方法,其脱除氮氧化物的效率高达90％以上。由于能源结构的变化,研究与开发湿法脱除氮氧化物的技术,将进一步加快,尤其是湿法联合脱硫脱硝的技术。     

燃煤锅炉固态还原剂选择性非催化还原法脱硝

介绍固态还原剂选择性非催化还原法(PSNCR)脱硝的系统构成和工艺流程,与选择性催化还原法(SCR)、选择性非催化还原法(SNCR)、臭氧氧化法脱硝进行对比分析。对在天津市某区2×29 MW供热燃煤链条炉增设PSNCR脱硝设备前后的氮氧化物(NO_x)排放质量浓度进行监测。结果表明,燃煤锅炉NO_x排放值小于170 mg/m~3;与SCR、SNCR、臭氧氧化法相比,对供热燃煤链条炉,PSNCR在造价、运行费用、占地面积等方面具有优势。     

燃煤热水锅炉SNCR+SCR脱硝系统运行常见问题及对策分析

目前广泛应用的氮氧化物处理技术有选择性催化还原法(Selective Catalvtic Reduction,SCR)和选择性非催化还原法(Selective Non-catalytic Reductior,SNCR),本文介绍了承德热力集团有限责任公司某集中供热热水锅炉房4台燃煤热水锅炉(2台58MW和2台64MW)...     

水泥行业烟气脱硝技术浅析

近年来,随着我国经济的快速发展和工业化水平的显著提高,大气污染状况日益严重,我国SO2的排放量已经位居世界第二位,NOx排放量也在持续增长。烟气脱硫、脱硝已成为我国的一项重要任务,水泥厂排放的NOx是目前最主要的NOx来源之一,如果不加以控制,我国未来的酸雨污染可能将由硫酸型向硫酸/硝酸复合型发展,氮氧化物排放的影响日益突现,烟气脱硝已势在必行。水泥厂烟气的脱硝技术主要有选择性催化还原法(SCR)和选择性非催化还原法(SNCR)。有效控制煤燃烧造成的大气污染。控制煤燃烧过程中的氮氧化物排放,需要选择合理的烟气脱硝技术。介绍了水泥厂氮化物的生成途径,综述了各种脱硝技术方法及相关技术问题,对于高效烟气脱硝装置的选择有着实际意义。     

氮氧化物的污染和治理

氮氧化物能导致酸雨、雾霾和光化学烟雾等一系列环境问题。燃煤电厂和柴油车尾气是我国氮氧化物的主要来源。针对这2种主要来源,氨选择性催化还原法(NH3-SCR)因其技术相对成熟高效,已成为我国控制氮氧化物的主流技术。     

谈水泥和混凝土用脱硝粉煤灰中氨的控制

正近年来,随着我国固体废弃物资源化利用政策的支持,电厂排放粉煤灰资源化利用的传统技术已形成了规模化、工业化生产,被广泛地应用于建筑、建材领域,粉煤灰已成为我国建筑工程发展中制备建筑材料不可缺少的材料之一。但是随着大气环保的防治要求,燃煤火电厂选用选择性催化还原法(SCR)脱硝技术以防治氮氧化物(NO_X)等排放造成的污染,而SCR法脱硝过程中的副反应使电厂排放的脱硝粉煤灰中含有氨氮物质。     

29 MW燃气锅炉低氮改造工程

结合北京某供热厂29 MW燃气锅炉低氮改造工程,简要介绍了烟气再循环和选择性催化还原法(SCR)技术原理,详细说明了烟气再循环系统设置、燃烧器改造和SCR系统还原剂与催化剂选择依据。并根据环保监测烟气排放数据,指出现阶段可采用低氮燃烧器+烟气再循环技术作为燃气锅炉氮氧化物控制主流技术,SCR技术的应用可使锅炉高负荷时满足更低的氮氧化物排放要求。     

SNCR+SCR联合脱硝技术在煤粉炉的应用

SNCR+SCR联合脱硝技术是结合选择性非催化还原法(SNCR)技术投资低、选择性催化还原法(SCR)技术效率高的优点,有效避免选择性非催化还原法(SNCR)技术效率低、选择性催化还原法(SCR)技术投资高等缺点而发展起来的一种脱硝工艺技术。文章通过中国石油吉林石化公司动力二厂410 t/h高温高压煤粉锅炉脱硝项目案例,详细介绍SNCR+SCR联合脱硝技术。     

燃煤电厂锅炉脱硝研究

降低NOx氮氧化物温室气体排放量,可减少对自然生态环境冲击,并避免暖化现象继续扩大。脱硝系统可分为三类,包括:低氮氧化物燃烧器(low NOx burner)、选择性非触媒还原法(selective non—catalytic reduction)与选择性触媒还原法(selective catalytic reduction,SCR),考虑到减少燃煤电厂氮氧化物排放的脱硝系统的性能特点,综合比较以SCR的处理效率为最高。     

水泥工业烟气中氮氧化物脱除技术

阐述了水泥工业烟气中氮氧化物(NO_X)深度脱除的意义及必要性,介绍了当前水泥工业NO_X的排放标准、水泥厂NO_X的来源及常见NO_X脱除方法,简析了各种方法的优缺点。通过分析得出,选择性催化还原技术(selective catalytic reduction, SCR)是目前唯一可实现水泥工业烟气中NO_X超低排放的技术,但在实际过程中,SCR技术仍面临催化剂中毒、低温催化活性低的问题。     

Mercury emissions from coal-fired power stations: The current state of the art in the Netherlands

About 30% of the electricity produced in the Netherlands is generated by coal, all of which is imported. At the same time, the co-combustion of biomass is becoming increasingly important. For the last 25 years, the fate of the elements/trace elements in general and of mercury in particular has been studied in great detail. It appears that on average 50% of the mercury is removed in the ESP (particulate control) and 50% of the remainder is removed in the flue gas desulphurization (FGD), resulting in a total mercury removal of 75%. If a high dust selective catalytic reduction (SCR for NO(x) reduction) is present, the total removal can be up to 90%. The results indicate that on average the removal of mercury during the co-combustion of biomass is similar to that found for full coal-firing. The conclusion is that a modern coal-fired power station with the above-mentioned flue gas cleaning equipment also removes mercury up to 90%. These cleaning devices are being installed to reduce the emission of particulates, sulphur dioxide and nitrogen oxides. This means that mercury abatement can be increased while meeting the EU regulation for SO(2) and NO(x). The application of Best Available Technique (BAT) for coal-fired installations by 1-1-2008 will lead to a further increase in the construction and operation of FGD and DeNO(x) installations.     

Characterization of ozone decomposition in a soil slurry: kinetics and mechanism.

A series of soil slurry experiments were performed in a carefully conceived reactor set-up to investigate the characteristics of the catalytic decomposition of ozone on a sand and iron surface. Real time on-line monitoring of ozone in the reaction module was possible using flow injection analysis coupled with a computer-controlled UV detector and data acquisition system. The effects of the soil media and size, ozone dosage, pH and p-CBA as a probe compound were examined at the given experimental conditions. Two apparent phases existed, and ozone instantaneously decomposed within one second in the first phase. These were defined as the instantaneous ozone demand (ID) phase, and the relatively slow decay stage. The interactions of ozone with the soil organic matter (SOM) and metal oxides were attributed mostly to the instantaneous decomposition of ozone. From the probe (p-CBA) experiments, 60-68% of total p-CBA removal occurred during the ID phase. The generation of hydroxyl radicals (OH.) was demonstrated and was closely related with metal oxides as well as SOM. Metal oxides in soil surface were considered to have relatively faster reaction rate with ozone and provide more favorable reactive sites to generate higher amount of OH. than SOM. Even at one-tenth concentration of the sands, a goethite-induced catalytic reaction outfitted the removal rate ofp-CBA among all the soils tested. More than 40% of total p-CBA removal occurred on the soil surface. It was inferred that the radical reaction with the probe compound seemed to take place not only on the soil surface but also in the solid-liquid interface. Ozone decomposition and the reaction between OH. and p-CBA appeared to be independent of any change in pH.     

Nitrogen removal from wastewater by a catalytic oxidation method

The ammonia-containing waste produced in industries is usually characterized by high concentration and high temperature, and is not treatable by biological methods directly. In this study, a hydrophobic Pt/SDB catalyst was first used in a trickle-bed reactor to remove ammonia from wastewater. In the reactor, both stripping and catalytic oxidation occur simultaneously. It was found that higher temperature and higher oxygen partial pressure enhanced the ammonia removal. A reaction pathway, which involves oxidizing ammonia to nitric oxide, which then further reacts with ammonia to produce nitrogen and water, was confirmed. Small amounts of by-products, nitrites and nitrates were also detected in the resultant reaction solution. These compounds came from the absorption of nitrogen oxides. Both the minimum NO2- selectivity and maximum ammonia removal were achieved when the resultant pH of treated water was near 7.5 for a feed of unbuffered ammonia solution.     

凹凸棒石负载MnO_x和FeO_x催化剂催化还原NO的性能

通过浸渍法制备了以FeOx和MnOx为活性组分,凹凸棒石(PG)为载体的选择性催化还原(selective catalytic reduction,SCR)脱硝催化剂;在固定床石英玻璃反应器上利用模拟烟气进行催化剂催化还原NO的活性评价。结果表明:凹凸棒石负载MnOx催化剂的SCR脱硝性能好于凹凸棒石负载FeOx催化剂的,其中Mn10/PG催化剂脱硝效率200℃达到84.6%,250℃增加到94.4%。     

Catalytic decomposition of hydrogen peroxide and 2-chlorophenol with iron oxides

The aim of this study was to examine the catalyzed decomposition of hydrogen peroxide and 2-chlorophenol (2-CP) in the presence of iron oxides. Granular ferrihydrite, goethite, and hematite were selected as catalysts in this study. 2-CP was used as the model compound because it is a typical toxic compound and has not been investigated in the catalytic decomposition by iron oxides. The catalytic activity for hydrogen peroxide decomposition followed the sequence: granular ferrihydrite > goethite > hematite. However, hematite exhibited the highest activity in catalyzing 2-CP oxidation. The oxidation efficiency of 2-CP corresponded with the inverse sequence of specific area and pHpzc of the iron oxides. The catalytic activity of granular ferrihydrite was affected significantly by the mixing speed and particle size for its large value of Thiele modulus (phi) and Damkohler number (Da). The strong diffusion resistance for granular ferrihydrite was attributed either to its microporous structure or to the formation of oxygen in the pores of the iron oxide leading to the unexpected catalytic activity of granular ferrihydrite to hydrogen peroxide and 2-CP.     

Interaction patterns of major air pollutants in Hong Kong territory

Air pollution in a metropolitan city like Hong Kong is a major obstacle to improve air quality and living environment due to the high population density and the vehicle emission increases. The high air pollutant levels impose harm to the human health and impair the city image. The characteristic analysis of air pollutants is very important and necessary to pollutant monitoring, forecasting and controlling. In this study, the interaction patterns of principle air pollutants, e.g. nitrogen dioxide (NO(2)), nitric oxide (NO), nitric oxides (NO(x)) and ozone (O(3)), a secondary pollutant, are investigated based on the measured database in four selected areas, which covers two urban types (i.e. residential area, mixed residential/commercial/industrial area) in Hong Kong, during the period of 1999-2001. The study involves analyzing the chemical and physical properties, the characteristics of air pollutants and the factors affecting such interactions using statistical method. The results reveal several routines in urban air pollutants' variations, interaction and trends from macro aspect.     

热煤气中氨的脱除(Ⅰ)

热煤气净化是ＩＧＣＣ、ＭＣＦＣ发电技术的关键，热煤气含有（２～３）×１０－３的氨，文章介绍了氨催化分解的反应机理，选择金属催化剂的经验法则及国内、国外的研究者对氨催化分解催化剂的筛选工作。最后得出Ｎｉ是氨催化分解最有效的活性组分，开发高效率、高的耐受性的高温Ｎｉ基催化剂是今后工作的方向。     

Electrocatalytic reduction of nitrate in water

Nitrate (NO(3)(-)) contamination of groundwater is a common problem throughout intensive agricultural areas (nonpoint source pollution). Current processes (e.g., ion exchange, membrane separation) for NO(3)(-) removal have various disadvantages. The objective of this study was to evaluate an electrocatalytic reduction process to selectively remove NO(3)(-) from groundwater associated with small agricultural communities. A commercially available ELAT (E-Tek Inc., Natick, MA) carbon cloth with a 30% surface coated Rh (rhodium) (1microg x cm(-1)) was tested at an applied potential of -1.5 V versus standard calomel electrode (SCE) with a Pt auxiliary electrode. Electrocatalytic reduction process (electrolysis) of NO(3)(-) was tested with cyclic voltammetry (CV) in samples containing NO(3)(-) and 0.1M NaClO(4)(-). Nitrate and NO(2)(-) concentrations in test solutions and groundwater samples were analyzed by ion chromatography (IC). The presence of Rh on the carbon cloth surface resulted in current increase of 36% over uncoated carbon cloths. The electrocatalysis experiments using Rh coated carbon cloth resulted in reduction of NO(3)(-) and NO(2)(-) on a timescale of minutes. Nitrite is produced as a product, but is rapidly consumed upon further electrolysis. Field groundwater samples subjected to electrocatalysis experiments, without the addition of NaClO(4)(-) electrolyte, also exhibited removal of NO(3)(-) on a timescale of minutes. Overall, results suggest that at an applied potential of -1.5 V with respect to SCE, Rh coated carbon cloth can reduce NO(3)(-) concentrations in field groundwater samples from 73 to 39 mg/L (16.58 to 8.82 mg/L as N) on a timescale range of 40-60 min. The electrocatalytic reduction process described in this study may prove useful for removing NO(3)(-) and NO(2)(-) from groundwater associated with nonpoint source pollution.     

Atmosphere pollutants and mortality rate of respiratory diseases in Beijing

In this paper, we apply the method of Granger causality, which is more accurate than classical correlation analysis method, to determine whether the main air pollutants--Nitrogen oxides (NO(x)), SO(2) (Sulfur Dioxide), CO (carbon monoxide), TSP (total suspended particulates), PM(10) (particulate matter smaller than 10 microns)--and the mortality of respiratory diseases of the residents in Beijing have causal relationship. After ensuring NO(x), SO(2) and CO as the responsible substances, we use the time series method to construct the autoregressive integrated moving average model (ARIMA) of the pollutants, so that we could predict the amount of the pollutants from 2005 to 2008. Then we use the predicted value of pollutants as the input of the neural network model and obtain the output as the change of the death rate of respiratory diseases from 2005 to 2008. In the end, reducing the amount of pollutants by 10% and inputting the data in the neural network model, we make the prediction to evaluate the level of the pollutants and concluded that NO(x) is the most important pollutant to control.     

Minimizing bromate formation with cerium dioxide during ozonation of bromide-containing water

This work investigated the effect of several metal oxides including alpha-FeOOH, alpha-Fe(2)O(3), gamma-FeOOH, and CeO(2) on bromate formation potential (BFP) during ozonation of bromide-containing water. Results indicate that CeO(2) could most effectively minimize the BFP among these metal oxides taking ozonation alone as control. The BFP minimization by O(3)/CeO(2) favored a relatively low Br(-) concentration (i.e., <1.0mgL(-1)) and pH<7. Water temperature ranging from 5 to 25 degrees C had no significant impact on the percent reduction of BrO(3)(-). Further investigation indicates that the effective BFP minimization can be ascribed to neither the surface adsorption of BrO(3)(-) or Br(-) on CeO(2) nor the surface reduction of BrO(3)(-) to HOBr/OBr(-) by CeO(2). It seems to have relationship with the activity of surface Ce(IV) sites. The CeO(2) can lower the concentration of H(2)O(2) which is formed during ozone decomposition and promotes BrO(3)(-) formation. Another possible reason for the BFP minimization is that the CeO(2) could possibly reduce BrO() to HOBr/OBr(-) during the decomposition of H(2)O(2).