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1.
Abstract Selective catalytic reduction (SCR) technology increasingly is being applied for controlling emissions of nitrogen oxides (NO x) from coal-fired boilers. Some recent field and pilot studies suggest that the operation of SCR could affect the chemical form of mercury (Hg) in coal combustion flue gases. The speciation of Hg is an important factor influencing the control and environmental fate of Hg emissions from coal combustion. The vanadium and titanium oxides, used commonly in the vanadia-titania SCR catalyst for catalytic NO x reduction, promote the formation of oxidized mercury (Hg 2+). The work reported in this paper focuses on the impact of SCR on elemental mercury (Hg 0) oxidation. Bench-scale experiments were conducted to investigate Hg 0 oxidation in the presence of simulated coal combustion flue gases and under SCR reaction conditions. Flue gas mixtures with different concentrations of hydrogen chloride (HCl) and sulfur dioxide (SO 2) for simulating the combustion of bituminous coals and subbituminous coals were tested in these experiments. The effects of HCl and SO 2 in the flue gases on Hg 0 oxidation under SCR reaction conditions were studied. It was observed that HCl is the most critical flue gas component that causes conversion of Hg 0 to Hg 2+ under SCR reaction conditions. The importance of HCl for Hg 0 oxidation found in the present study provides the scientific basis for the apparent coal-type dependence observed for Hg 0 oxidation occurring across the SCR reactors in the field. 相似文献
2.
Data on the effect of several combustion modifications on the formation of nitrogen oxides and on boiler efficiency were acquired and analyzed for a 110 MW gas fired utility boiler. The results from the study showed that decreasing the oxygen in the flue gas from 2.2% to 0.6% reduced the NO x formation by 33% and also gave better boiler efficiencies. Flue gas recirculation through the bottom of the firebox was found to be ineffective. Staged combustion was found to reduce the NO x emissions by as much as 55 % while decreasing the efficiency by about 5%. Adjustment of the burner air registers reduced the NO x formation by about 20 ppm. The lowest NO x emissions of 42 ppm (at about 3% O 2) in the stack was obtained for air only to one top burner and 0.5% oxygen in the flue gas. 相似文献
3.
Sodium hypochlorite (NaClO) has been widely used as a chemical additive for enhancing nitrogen oxide (NO x; NO + NO 2), sulfur dioxide (SO 2), and mercury (Hg 0) removals in a wet scrubber. However, they are each uniquely dependent on NaClO (aq) pH, hence making the simultaneous control difficult. In order to overcome this weakness, we sprayed low liquid-to-gas (L/G) ratio (0.1 L/Nm 3) of NaClO (aq) to vaporize quickly at 165 °C. Results have shown that the maximized NO x, SO 2, and Hg 0 removals can be achieved at the pH range between 4.0 and 6.0. When NO x and Hg 0 coexist with SO 2, in addition, their removals are significantly enhanced by reactions with solid and gaseous by-products such as NaClO (s), NaClO 2(s), OClO, ClO, and Cl species, originated from the reaction between SO 2 and NaClO (aq). We have also demonstrated the feasibility of this approach in the real flue gases of a combustion plant and observed 50%, 80%, and 60% of NO x, SO 2, and Hg 0 removals, respectively. These findings led us to conclude that the spray of NaClO (aq) at a relatively high temperature at which the sprayed solution can vaporize quickly makes the simultaneous control of NO x, SO 2, and Hg 0 possible. Implications: The simple spray of NaClO(aq) at temperatures above 165 °C can cause the simultaneous removal of gaseous NOx, SO2, and Hg0 by its quick vaporization. Their maximized removals are achieved at the pH range between 4.0 and 6.0. NOx and Hg0 removals are also enhanced by gaseous and solid intermediate products generated from the reaction of SO2 with NaClO(aq). The feasibility of this approach has been demonstrated in the real flue gases of a combustion plant. 相似文献
4.
This paper reports the development of a rapid, continuous technique for analyzing fixed nitrogen species (NH 3, HCN, CH 3NH 2, etc.). The technique uses a platinum catalyst at low pressure in combination with a conventional chemiluminescent NO x analyzer. Previous workers observed that conventional stainless steel catalysts, and platinum catalysts operated at atmospheric pressure, do not reliably convert NH 3 to NO. The most serious problem was the variation in the efficiency of these catalysts with operating conditions. Changes in temperature, gas composition, or X NH3 could change the conversion efficiency from 99.9% to <30%. The new conversion technique, however, is quantitative up to several thousand ppm NH 3 in either O 2/He or O 2/CO 2/N 2. 相似文献
5.
Abstract Efforts to develop multipollutant control strategies have demonstrated that adding certain oxidants to different classes of Ca-based sorbents leads to a significant improvement in elemental Hg vapor (Hg 0), SO 2, and NO x removal from simulated flue gases. In the study presented here, two classes of Ca-based sorbents (hydrated limes and silicate compounds) were investigated. A number of oxidizing additives at different concentrations were used in the Ca-based sorbent production process. The Hg 0, SO 2, and NO x capture capacities of these oxidant-enriched sorbents were evaluated and compared to those of a commercially available activated carbon in bench-scale, fixed-bed, and fluid-bed systems. Calcium-based sorbents prepared with two oxidants, designated C and M, exhibited Hg 0 sorp-tion capacities (~100 μg/g) comparable to that of the activated carbon; they showed far superior SO 2 and NO x sorption capacities. Preliminary cost estimates for the process utilizing these novel sorbents indicate potential for substantial lowering of control costs, as compared with other processes currently used or considered for control of Hg 0, SO 2, and NO x emissions from coal-fired boilers. The implications of these findings toward development of multipollutant control technologies and planned pilot and field evaluations of more promising multipollutant sorbents are summarily discussed. 相似文献
6.
低温选择性催化还原(SCR)脱硝是国内外脱硝技术研发的热点,但目前主要集中在实验室小试范围,无法完全反映催化剂在实际烟气中的运行状况。在30 t/h循环流化床燃煤锅炉脱硫除尘装置后建设了2 000~5 000 m3/h的SCR脱硝中试装置,经系统研究发现,中试使用的蜂窝式催化剂对SO2和NO具有很强的吸附能力,且反应温度、喷氨速率和气体空速均会影响催化脱硝效率。为期5 d的连续运行实验结果表明,催化剂的脱硝效率一直稳定在30%~50%,并未发现明显的失活,这证明设计除雾除尘器、较大的混合器、混合器与反应器间较长的管路均有利于缓解催化剂因SO2、H2O和飞灰中的碱性金属导致的失活。 相似文献
7.
A series of iron–manganese oxide catalysts supported on TiO 2 and titanium nanotubes (TNTs) were studied for low temperature selective catalytic reduction (SCR) of NO with NH 3 in the presence of SO 2. The results showed that the specific surface area and the amount of Brønsted acid sites were highly correlated. The results also demonstrated that higher Mn 4+/Mn 3+ ratios and larger specific surface areas might be the main reasons for the excellent performance of MnFe-TNTs catalyst after SO 2 poisoning. The SO 2 poisoning effect could be minimized by reducing the GHSV, increasing the reaction temperature, or increasing the [NH 3]/[NO] molar ratio. The results also indicated that the formation of ammonium sulfate had a stronger effect on the NO conversion efficiency as compared to the formation of metal sulfate. Thus operating the low temperature SCR at above 230 oC to avoid the formation of ammonium sulfate would be the priority choice when SO 2 poisoning is a concerned issue.? Implications: Low-temperature selective catalytic reduction (SCR) has attracted increasing attention due to that it can reduce the energy consumption for the SCR process employed in industries such as steel plants and glass manufacturing plants. However, it also suffers from the sulfur dioxide (SO 2) poisoning problem. This study investigates the possibility of using titania nanotubes (TNTs) as the support of Mn/Fe bimetal oxide catalysts for low-temperature SCR to reduce the SO 2 poisoning. The results indicated that the MnFe-TNT catalyst can tolerate SO 2 for a longer time as compared with the MnFe-TiO 2 catalyst. 相似文献
8.
Currently, activated coke is widely used in the removal of multiple pollutants from industrial flue gas. In this paper, a series of novel FexLayOz/AC catalysts was prepared by the incipient wetness impregnation for NH3-SCR denitrification reaction. The introduction of Fe-La bimetal oxides significantly improved the denitrification performance of activated coke at mid-high temperature, and 4% Fe0.3La0.7O1.5/AC exhibited a superior NOx conversion efficiency of 90.1% at 400 °C. The catalysts were further characterized by BET, SEM, XRD, Raman, EPR, XPS, FTIR, NH3-TPD, H2-TPR, et al., whose results showed that the perovskite-type oxide of LaFeO3 and oxygen vacancies were produced on the catalysts’ surfaces during roasting. Fe-La doping enhanced the amount of acid sites (mainly Lewis and other stronger acid sites) and the content of multifarious oxygen species, which were beneficial for NOx removal at mid-high temperature. Moreover, it was investigated that the effect of released CO from activated coke at mid-high temperature on the NOx removal through the lifetime test, in which it was found that a large amount of CO produced by pyrolysis of activated coke could promote the NOx removal, and long-term escaping of CO on the activated coke carrier did not have a significant negative impact on catalytic performance. The results of the TG-IR test showed that volatile matter is released from the activated coke while TG results showed that the weight loss rate of 4% Fe0.3La0.7O1.5/AC only was 0.0015~0.007%/min at 300–400 °C. Hence, 4% Fe0.3La0.7O1.5/AC had excellent thermal stability and denitrification performance to be continuously used at mid-high temperature. Finally, the mechanisms were proposed on the basis of experiments and characterization results. 相似文献
9.
Abstract The speciation of Hg in coal-fired flue gas can be important in determining the ultimate Hg emissions as well as potential control options for the utility. The effects of NO x control processes, such as selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR), on Hg speciation are not well understood but may impact emissions of Hg. EPRI has investigated the reactions of Hg in flue gas at conditions expected for some NO x control processes. This paper describes the methodology used to investigate these reactions in actual flue gas at several power plants. Results have indicated that some commercial SCR catalysts are capable of oxidizing elemental Hg in flue gas obtained from the inlets of SCR or air heater units. Results are affected by various flue gas and operating parameters. The effect of flue gas composition, including the presence of NH 3, has been evaluated. The influence of NH 3 on fly ash Hg reactions also is being investigated. 相似文献
10.
Abstract Air pollutants were collected in Logan, Cache County, UT, in February 1993 during two periods of atmospheric inversion accompanied by fog. The following atmospheric species were determined: (1) gaseous SO 2, NO 2 (semi-quantitatively),HNO3, NH3, and HF; (2) fine particulate SO 4 =, NO 3 -, NH 4 +, F–, H +, C, Si, S, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, Pb, Se, Br, and Sr, and; (3) fine particulate mass, which was calculated. The major components of fine particulate matter were carbonaceous material, ammonium nitrate, and ammonium sulfate, while the soil component was small. Calculated, fine particulate mass averaged 80 μg/m 3 and reached concentrations as high as 120 μg/m 3. SO 2/So x and NO 2/NO y mole ratios generally varied between 0.2 and 0.1 during inversions. These ratios also showed moderate but consistent diurnal patterns. The emission inventory for Cache County indicates sources of SO 2 and NO x but not significant amounts of primary sulfate and nitrate. The observations reported here indicate there is significant conversion of SO 2 and NO x in the presence of excess oxidants to sulfuric and nitric acid that are neutralized by excess ammonia. 相似文献
11.
The nitrogen oxides (NO x) reduction technology by combustion modification which has economic benefits as a method of controlling NO x emitted in the combustion process, has recently been receiving a lot of attention. Especially, the moderate or intense low oxygen dilution (MILD) combustion which applied high temperature flue gas recirculation has been confirmed for its effectiveness with regard to solid fuel as well. MILD combustion is affected by the flue gas recirculation ratio and the composition of recirculation gas, so its NO x reduction efficiency is determined by them. In order to investigate the influence of factors which determine the reduction efficiency of NO x in MILD coal combustion, this study changed the flow rate and concentration of nitrogen (N 2), carbon dioxide (CO 2) and steam (H 2O) which simulate the recirculation gas during the MILD coal combustion using our lab-scale drop tube furnace and performed the combustion experiment. As a result, its influence by the composition of recirculation gas was insignificant and it was shown that flue gas recirculation ratio influences the change of NO x concentration greatly. Implications: We investigated the influence of factors determining the nitrogen oxides (NO x) reduction efficiency in MILD coal combustion, which applied high-temperature flue gas recirculation. Using a lab-scale drop tube furnace and simulated recirculation gas, we conducted combustion testing changing the recirculation gas conditions. We found that the flue gas recirculation ratio influences the reduction of NO x emissions the most. 相似文献
13.
Pentachlorobenzene (PeCB) in simulated flue gas was destructed by a commercial V 2O 5-WO 3/TiO 2 catalyst in this study. The effects of reaction temperature, oxygen concentration, space velocity and some co-existing pollutants on PeCB conversion were investigated. Furthermore, a possible mechanism for the oxidation of PeCB over the vanadium oxide on the catalysts was proposed. Results show that the increase of gas hourly space velocity (GHSV) and the decrease of operating temperature both resulted in the decrease of PeCB removal over the catalyst, while the effect of the oxygen content in the range of 5-20% (v/v) on PeCB conversion was negligible. PeCB decomposition could be obviously affected by the denitration reactions under the conditions because of the positive effect of NO but negative effect of NH 3. The introduction of SO 2 caused the catalyst poisoning, probably due to the sulfur-containing species formed and deposited on the catalyst surface. The PeCB molecules were first adsorbed on the catalyst surface, and then oxidized into the non-aromatic acyclic intermediates, low chlorinated aromatics and maleic anhydride. 相似文献
14.
Abstract A novel process for removal of nitrogen oxides (NO x) from flue gases with iron filings reduction following complex absorption in iron-ethylenediaminetetraacetic acid aqueous solution is proposed. The reaction mechanism involved in the process is discussed briefly. The parameters influencing the process, including the concentration of ferrous chelates, initial pH, amount of iron filings, temperature, flow rate of the flue gas, and inlet nitric oxide concentration and oxygen content of the flue gas, are researched in detail. The optimal NO x removal conditions are established. The regeneration and circular utilization of the absorption solution also is studied. 相似文献
15.
This paper reports the results of over 2 years of measurements of several of the species comprising atmospheric SOx (= SO2+ SO42−) and NOy (= NO+ NO2 + PAN + HNO3+ NO3−+ organicnitrates + HONO + 2 N2O5 …) at Whiteface Mountain, New York. Continuous real-time measurements of SO 2 and total gaseous NOy provided data for about 50% and 65% of the period, respectively, and 122 filter pack samples were obtained for HNO 3, SO 2 and aerosol SO 42−, NO 3−, H + and NH 4+. Concentrations of SO 2 and NOy were greatest in winter, whereas concentrations of the reaction products SO 42− and HNO 3were greatest in summer. The seasonal variation in SO 42− was considerably more pronounced than that of HNO 3and the high concentrations of SO 42− aerosol present in summer were also relatively more acidic than SO 42− aerosol in other seasons. As a result, SO 42− aerosol was the predominant acidic species present in summer, HNO 3was predominant in other seasons. Aerosol NO 3− concentrations were low in all seasons and appeared unrelated to simultaneous NOy and HNO 3concentrations. These data are consistent with seasonal variations in photochemical oxidation rates and with existing data on seasonal variations in precipitation composition. The results of this study suggest that emission reductions targeted at the summer season might be a cost-effective way to reduce deposition of S species, but would not be similarly cost-effective in reducing deposition of N species. kwAcid deposition, seasonal variation, sulfate, nitrate, nitric acid, sulfur dioxide, oxides of nitrogen, hydrogen peroxide, ozone, air pollution, Adirondack Mountains 相似文献
16.
零价汞的高效去除是燃煤烟气汞污染控制过程中的关键环节。为了促进烟气中的零价汞转化为易于去除的氧化态汞,分别考察了在有HCl存在时,几种过渡金属氧化物(Cu、Fe、Mn、Co和Zr)对零价汞氧化的催化作用,以筛选出性能较好的催化组分;为提高催化剂的抗SO2性能,分别尝试了利用几种金属元素(Sr、Ce、W和Mo)对催化剂进行掺杂改性的方法。结果表明,锰氧化物的催化作用最好,其最佳使用温度在573 K左右;SO2对零价汞的催化氧化有明显抑制作用,在无SO2及1 400 mg/m3SO2时锰催化剂对零价汞催化氧化效率分别为93%和78%。而Mo改性的锰氧化物催化剂的抗硫性能大幅提高,在1 400 mg/m3SO2存在的情况下其对零价汞的催化氧化效率可达到90%以上,较其他改性元素高。 相似文献
17.
Pilot-scale tests were conducted to develop a combined nitrogen oxide (NO x) reduction technology using both selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR). A commercially available vanadium- and titanium-based composite honeycomb catalyst and enhanced urea (NH 2CONH 2) were used with a natural-gas-fired furnace at a NO x concentration of 110 ppm. Changes in SNCR chemical injection temperature and stoichiometry led to varying levels of post-furnace ammonia (NH 3), which acts as the reductant feed to the downstream SCR catalyst. The urea-based chemical could routinely achieve SNCR plus SCR total NO x reductions of 85 percent with less than 3 ppm NH 3 slip at reductant/NO x stoichiometries ranging from about 1.5 to 2.5 and SCR space velocities of 18,000 to 32,000 h ?1. This pilot-scale research has shown that SNCR and SCR can be integrated to achieve high NO x removal. SNCR provides high temperature reduction of NO x followed by further removal of NO x and minimization of NH 3 slip by a significantly downsized (high-space velocity) SCR. 相似文献
18.
ABSTRACT At conditions typical of a bag filter exposed to a coal-fired flue gas that has been adiabatically cooled with water, calcium hydroxide and calcium silicate solids were exposed to a dilute, humidified gas stream of nitrogen dioxide (NO 2) and sulfur dioxide (SO 2) in a packed-bed reactor. A prior study found that NO 2 reacted readily with surface water of alkaline and non-alkaline solids to produce nitrate, nitrite, and nitric oxide (NO). With SO 2 present in the gas stream, NO 2 also reacted with S(IV), a product of SO 2 removal, on the exterior of an alkaline solid. The oxidation of S(IV) to S(VI) by oxygen reduced the availability of S(IV) and lowered removal of NO 2. Subsequent acidification of the sorbent by the removal of NO 2 and SO 2 facilitated the production of NO. However, the conversion of nitrous acid to sulfur-nitrogen compounds reduced NO production and enhanced SO 2 removal. A reactor model based on empirical and semi-empirical rate expressions predicted rates of SO 2 removal, NO 2 removal, and NO production by calcium silicate solids. Rate expressions from the reactor model were inserted into a second program, which predicted the removal of SO 2 and NO x by a continuous process, such as the collection of alkaline solids in a baghouse. The continuous process model, depending upon inlet conditions, predicted 30-40% removal for NO and 50-90% removal for SO 2. These x 2 results are relevant to dry scrubbing technology for combined SO 2 and NO x removal that first oxidizes NO to NO 2 by the addition of methanol into the flue duct. 相似文献
19.
The atmospheric chemical process was simulated using the Carbon Bond 4 (CB-4) model, the aqueous-phase chemistry in Regional Acid Deposition Model and the thermodynamic equilibrium relation of aerosols with the emission inventories of the Emission Database for Global Atmospheric Research, the database of China and South Korea and the Mesoscale Model version 2 (MM5) meteorological fields to examine the spatial distributions of the acidic pollutant concentrations in East Asia for the case of the long-lasting Yellow Sand event in April 1998. The present models simulate quite well the observed general trend and the diurnal variation of concentrations of gaseous pollutants, especially for O 3 concentration. However, the model underestimates SO 2 and NO x concentration but overestimates O 3 concentration largely due to uncertainty in NO x and VOC emissions. It is found that the simulated gaseous pollutants such as SO 2, NO x, and NH 3 are not transported far away from the source regions but show significant diurnal variations of their concentrations. However, the daily variations of the concentrations are not significant due to invariant emission rates. On the other hand, concentrations of the transformed pollutants including SO 42−, NH 4+, and NO 3− are found to have significant daily variations but little diurnal variations. The model-estimated deposition indicates that dry deposition is largely contributed by gaseous pollutants while wet deposition of pollutants is mainly contributed by the transformed pollutants. 相似文献
20.
High concentrations (>15 μm 3 cm ?3) of CaSO 4, Ca(NO 3) 2 and (NH 4) 2SO 4 were selected as surrogates of dry neutral, aqueous neutral and dry acidic inorganic seed aerosols, respectively, to study the effects of inorganic seeds on secondary organic aerosol (SOA) formation in irradiated m-xylene/NO x photooxidation systems. The results indicate that neither ozone formation nor SOA formation is significantly affected by the presence of neutral aerosols (both dry CaSO 4 and aqueous Ca(NO 3) 2), even at elevated concentrations. The presence of high concentrations of (NH 4) 2SO 4 aerosols (dry acidic) has no obvious effect on ozone formation, but it does enhance SOA generation and increase SOA yields. In addition, the effect of dry (NH 4) 2SO 4 on SOA yield is found to be positively correlated with the (NH 4) 2SO 4 surface concentration, and the effect is pronounced only when the surface concentration reaches a threshold value. Further, it is proposed that the SOA generation enhancement is achieved by particle-phase heterogeneous reactions induced and catalyzed by the acidity of dry (NH 4) 2SO 4 seed aerosols. 相似文献
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