脱硫灰用作钙质材料制备蒸压加气混凝土砖块

为实现半干法脱硫灰的资源化利用,采用半干法脱硫灰作为蒸压加气混凝土砖块中的钙质材料。对脱硫灰进行预处理,使其在含水量20%条件下消化2 h后,烘干。在其他条件不变情况下,掺入经过预处理后的脱硫灰,砖块的抗压强度会有明显的提高。增加经过预处理后的脱硫灰的掺入量,可以在不影响砖块的抗压强度性能的基础之上,降低砖块的干燥收缩值和导热系数,同时提高砖块的抗冻性能和保温隔热性能。     

烧结脱硫灰制备蒸压加气混凝土砌块的研究

研究了烧结烟气半干法脱硫灰复掺粉煤灰、水渣/水泥,辅之外加剂,制备蒸压加气混凝土砌块的可行性.实验结果显示,当脱硫灰掺入量25%,粉煤灰掺入量45%,水渣和水泥掺入量均15%,铝粉掺入量0.04%,水料比0.6,稳泡剂掺入量0.0012%,烧碱掺入量1%,无需额外添加石膏,采用蒸压养护12.5 h(其中抽真空时间为0....     

密相塔半干法烟气脱硫塔内加湿降温及其对脱硫效率的影响

为了实现密相塔半干法脱硫工艺的精确加湿进一步提高系统脱硫效率,利用推导出的传热传质计算方法,得到烟气温度降低和加水量的关系.结合3组密相塔半干法工程实际数据,发现理论计算值和实测值误差区间仅为2.9％ ～5.4％.通过选取河北某钢厂210 m2烧结烟气密相塔半干法脱硫项目实际在线检测数据,发现循环脱硫灰含湿量为3％的系统脱硫效率整体高于含湿量为5％和4％的样品,最大值达93.56％.通过粒度分析、扫描电镜、X射线衍射及差热-热重对2种不同含湿量的循环脱硫灰进行表征,结果表明,含湿量为3％的循环脱硫灰较含湿量为5％的样品粒径小、比表面积大,无团聚现象,物相分析还证实相对于含湿量为5％样品,其Ca(OH)2和结晶水含量少,几乎都是CaSO4和CaS03干态物质,因此脱硫反应进行彻底,脱硫效率较高.     

烧结烟气脱硫剂性能的研究

为了提高脱硫效率和合理利用烧结过程中产生的机头灰,在半干法烟气脱硫剂生石灰中,加入一定量的烧结机头灰作为脱硫催化剂。在测定机头灰与生石灰化学成分、粒度和比表面积的基础上,研究和分析了机头灰与生石灰的质量配比对于脱硫效率的影响。结果表明,脱硫剂与机头灰在粒径分布和比表面积上都较接近,但经过消化活化后的混合脱硫剂的比表面积明显增大。当机头灰添加量为脱硫剂质量的2%～5%时,脱硫效率提高了2%～3%。机头灰与生石灰的胶凝反应以及机头灰中Fe2O3的催化作用是主要的作用机理。     

CFB烧结烟气脱硫灰亚硫酸钙热氧化条件优化

循环流化床(CFB)是一种常用的半干法烟气脱硫工艺,该工艺的副产物主要为脱硫灰。含有大量亚硫酸钙的脱硫灰较难被利用,致使大量脱硫灰堆积,给环境保护和企业生产带来了巨大的压力。亚硫酸钙的存在限制了脱硫灰在建材领域的应用,只有将其氧化为硫酸钙才能实现其资源化。脱硫灰热氧化主要采用了立式管式炉,分别考察了反应温度、反应状态、氧含量、水汽的含量对亚硫酸钙氧化的影响。结果表明:温度对脱硫灰氧化的影响最大,其次为气体流速、氧含量和水汽含量。反应温度与反应速率呈正相关;增加氧气含量可以提高反应速率,但当氧含量高于30%时,反应速率趋于稳定;反应器温度在350℃时,亚硫酸钙开始缓慢反应,在400℃、无预热气速为75 mL·min~(-1)时,亚硫酸钙最大转化效率达到86%,预热处理后最大转化率达到90%;当水汽量0.88 g·L~(-1)时,水汽量的增加会抑制氧化的进行;当水汽含量0.88 g·L~(-1)时,则会促进反应的进行。以上结果对指导脱硫灰热氧化处理和节能环保具有理论与实践意义。     

利用干法半干法烟气脱硫灰热分解钾长石的实验研究

探讨了目前干法半干法脱硫灰综合利用当中存在的诸多问题.提出了利用该类灰渣热分解钾长石矿,生产以钾、钙、硅和镁为主的土壤营养调节剂.并对最佳的物料配比、焙烧条件和助剂的种类及含量进行了实验研究,利用广州恒运集团公司产出的脱硫灰,在1 050℃下焙烧2 h,使烧成物在酸性条件下最大可溶K2O达6.49%、有效CaO达32.28%、SiO2达13.83%、MgO达1.68%.烧成物料的PH值为9.6,是一种安全、适用于偏酸性土壤使用的复合元素土壤营养调节剂.     

利用拜耳法赤泥和氟化钙污泥制备烧结砖块

拜耳法赤泥是用氢氧化钠溶解铝土矿生产氧化铝过程中产生的固体废弃物。针对拜耳法赤泥的强碱性、重金属含量高等特点,提出了一种利用酸性氟化钙污泥进行共同烧制砖块的方法。以砖块的氟离子浸出量、铬离子浸出量、抗压强度、砖块密度及烧失量5个变量为评价指标,利用主成分分析法对五个指标进行综合评分,并研究了以氟化钙污泥与赤泥比,黏土添加量、铝灰添加量、黏结剂添加量、烧结温度为自变量对综合评分的影响。利用响应面法(RSM)对实验数据进行分析,得出最佳实验条件依次为氟化钙污泥与赤泥比=61.1%,黏土添加量=21.4%,铝灰添加量=15%,黏结剂添加量=2.5%,烧结温度=1 000℃。此条件下所得砖块对应的氟离子浸出量为0.33 mg·L~(-1),铬离子浸出0.034 mg·L~(-1),抗压强度5.73 MPa,烧失量9%,砖块密度1.07 g·cm~(-3)。可用做非承重砖。     

半干法烧结烟气脱硫灰的氧化改性

半干法烧结烟气脱硫灰中含有大量CaSO_3,而CaSO_3对于脱硫灰的稳定性具有重要影响,限制了脱硫灰的处理和综合利用。为了解决该问题,采用低温静态氧化改性实验和高温动态焙烧改性实验,在掺加和不掺加催化剂条件下,对含CaSO_3的脱硫灰进行了氧化改性研究,并结合热重实验考察了半干法烧结烟气脱硫灰中CaSO_3的高温动态氧化改性效果。结果表明,在低温为45、75和90℃时,掺入不同催化剂对半干法烧结烟气脱硫灰中CaSO_3进行氧化改性2 h,效果依次为:MnO_2Fe_2O_3不掺催化剂V_2O_5,且CaSO_3的氧化率均低于2.2%;在不掺催化剂的条件下,在350℃以上焙烧30~60 min,CaSO_3的氧化率均可达到85%以上。结合热重分析结果发现,选择合适的焙烧温度和时间对提高CaSO_3的氧化率有重要作用。     

半干法烧结烟气脱硫灰中亚硫酸钙氧化研究

针对半干法烧结烟气脱硫灰因CaSO3含量高难以有效综合利用的问题,采用静态和动态氧化实验,结合热重-差热分析探讨了半干法烧结烟气脱硫灰中CaSO3的氧化效果.实验结果表明,在沮度为45～90℃,以MnO2、Fe2O3、V2O3为催化剂时,脱硫灰中CaSO3的氧化率不超过3%,催化效果好差为MnO2Fe2O3V2O5;在温度为400～500℃、气固比(空气体积流量与脱硫灰质量比)为0.02～0.06m3/(g·h)、反应时间为30～60min、无外加催化剂时.脱硫灰中CaSO,3的氧化率为40.4%～100.0%;温度在450℃以上时,CaSO3氧化率均在80%以上.     

烟气中多种污染物协同脱除的研究

烟气中多种污染物协同脱除是烟气净化领域的研究热点.在现有烟气脱硫技术研究的基础上,对活性焦干法、多级增湿半干法、氧化性添加剂湿法以及等离子体湿法这4种烟气污染物协同脱除技术进行了系统的研究.研究发现,以活性焦为载体添加适当的催化剂能够实现在高效脱硫基础上的同时脱硝;多级增湿半干法技术提高了脱硫剂颗粒在吸收塔内反应全过程的含湿均匀性,通过添加复合促进剂可以提高反应速率,强化烟气中SO_2、NO_X等污染物协同脱除;在传统的湿法烟气脱硫技术中,向脱硫剂中加入KMnO_4和NaClO_2等强氧化剂或者采用等离子体前置氧化,能够有效的将难吸收的NO氧化成NO_2、HNO_2和HNO_3,最终实现同时脱硫脱硝.     

半干半湿法脱硫灰循环利用中试试验研究

半干半湿法脱硫产生的脱硫灰中混有大量有效钙和粉煤灰 ,本文对其进行了循环利用机理分析及试验研究 ,证实脱硫灰循环大大提高了钙的利用率 ,降低了钙硫比 ,但循环倍率增加到 2倍以上时 ,脱硫效率增速变缓。脱硫灰的循环利用对降低脱硫运行费用是非常有效的。     

双喷嘴矩形喷动床流体力学及脱硫性能的实验研究

针对半干法烟气脱硫方法,提出了一种新型的双喷嘴矩形喷动床半干法脱硫技术.在相同的静床层高度下,研究了最小喷动速度、最大喷动压降和喷动高度;在相同的Ca/S比、进气SO2浓度、进口温度、绝热饱和温差条件下,以消石灰为脱硫剂,研究了脱硫性能,并与传统柱锥形喷动床进行了比较.结果表明,矩形喷动床拥有更好的流动性能和脱硫率,得出了实验条件下矩形喷动床的最佳操作范围.     

Resource Recovery from Flue Gas Desulfurization Systems

The cost effective benefits of yielding a flue gas desulfurization (FGD) sludge predominantly composed of CaSO₄·2H₂O, have been previously established. The recovery of this material as FGD by-product gypsum has been demonstrated abroad. Recently U.S. wallboard manufacturers have recognized the viability of this recovery practice. Such techno-economic decision making variables as a) by-product specification, b) transportation costs, and c) location of suitable FGD systems enable the recognition of FGD by-product recovery. Recent investigations of resultant solids content and chloride washing reflect the technical possibility of delivering a suitable product. Commercial and economic factors favor recovery based upon rising disposal and transportation costs. Existing and near term proposed systems surface the technical and commercial problems faced by utilities considering recovery.

Generation of an oxidized FGD sludge consisting of 90⁺% CaSO₄·2H₂O and dewatered to 80⁺% solids is technically achievable by air sparging within the FGD system. Although the product is suitable for land disposal, electric power utilities should consider and evaluate by-product recovery. U.S. wallboard manufacturers have established technical criteria for FGD by-product gypsum. Percent CaSO₄·2H₂O, final solids content, particle size, and chloride content are primarily technical parameters. Technology exists within the FGD industry to satisfy these criteria and results are discussed.

Economic factors comparing mining costs, transportation costs, and disposal costs are developed for specific utility projects. Such comparison established generalized financial criteria for a given utility to develop the economic reasonableness of considering FGD byproduct recovery.

End product user perspectives are presented providing electric utilities with a realistic appreciation for by-product recovery potential. Location of existing wallboard plants highlight potential recovery regions. Quality control problems are discussed in terms of generating a by-product rather than a disposable material.     

Mercury emission and plant uptake of trace elements during early stage of soil amendment using flue gas desulfurization materials

A pilot-scale field study was carried out to investigate the distribution of Hg and other selected elements (i.e., As, B, and Se), i.e., emission to ambient air, uptake by surface vegetation, and/or rainfall infiltration, after flue gas desulfurization (FGD) material is applied to soil. Three FGD materials collected from two power plants were used. Our results show Hg released into the air and uptake in grass from all FGD material-treated soils were all higher (P < 0.1) than the amounts observed from untreated soil. Hg in the soil amended with the FGD material collected from a natural oxidation wet scrubber (i.e., SNO) was more readily released to air compared to the other two FGD materials collected from the synthetic gypsum dewatering vacuum belt (i.e., AFO-gypsum) and the waste water treatment plant (i.e., AFO-CPS) of a forced oxidation FGD system. No Hg was detected in the leachates collected during the only 3-hour, 1-inch rainfall event that occurred throughout the 4-week testing period. For every kilogram of FGD material applied to soil, AFO-CPS released the highest amount of Hg, B, and Se, followed by SNO, and AFO gypsum. Based on the same energy production rate, the land application of SNO FGD material from Plant S released higher amounts of Hg and B into ambient air and/or grass than the amounts released when AFO-gypsum from Plant A was used. Using FGD material with lower concentration levels of Hg and other elements of concern does not necessary post a lower environmental risk. In addition, this study demonstrates that considering only the amounts of trace elements uptake in surface vegetation may under estimate the overall release of the trace elements from FGD material-amended soils. It also shows, under the same soil amendment conditions, the mobility of trace elements varies when FGD materials produced from different processes are used.     

An Assessment

Extensive research has determined that adipic acid, when used as an additive to a limestone flue gas desulfurization (FGD) system, will improve the performance of the system. Both SO₂ removal and limestone utilization can be greatly increased by the buffering effect of adipic acid. Successful testing in laboratory, bench, pilot, prototype, and full scale systems has demonstrated the benefits of this technology for new and retrofit applications. Although adipic acid does degrade in the scrubber, no significant operating problems or environmental impacts have been identified. Economic estimates have shown the adipic acid enhanced limestone FGD system to be economically attractive when compared to conventional FGD systems. In addition, further research is underway to decrease the cost of using additives in FGD systems.     

Sulfur Gas Emissions From Stored Flue Gas Desulfurization Sludges

The emissions of volatile sulfur-containing compounds from 13 flue gas desulfurization (FGD) sludge field storage sites have been characterized. Sulfur gas emissions from the sludge surfaces were determined by measuring the sulfur gas enhancement of sulfur-free sweep air passing through a dynamic emission flux chamber placed over selected sampling sites. Samples of the enclosure sweep air were cryogenically concentrated in surface-deactivated Pyrex “U” traps. Analyses were conducted by wall-coated, open-tubular, capillary column, cyrogenic gas chromatography using a sulfur-selective, flame photometric detector. Several major variables associated with FGD sludge production processes were examined in relation to the measured range and variations in sulfur fluxes including: (a) the sulfur dioxide scrubbing reagent used, (b) sludge sulfite oxidation, (c) “unfixed” or “fixed” FGD sludge, and (d) ponding or landfill storage. The composition and concentration of the measured sulfur gas emissions were found to vary with the type of sludge, the effectiveness of rainwater drainage from the landfill surface, the method of impoundment, and the sulfate/sulfite ratio of the sludge. Hydrogen sulfide, carbonyl sulfide, dimethyl sulfide, carbon disulfide, and dimethyl disulfide were identified in varying concentrations and ratios in the FGD sludge emissions. In addition, up to four unidentified organo- sulfur compounds were found in the emissions from four FGD sludges. The sulfur flux from one FGD storage pond was analyzed by gas chromatography-single ion monitoring mass spectrometry. In addition to the four identified sulfur compounds, this flux contained large concentrations of benzene, toluene, and α-pinene. The measured, total sulfur emissions ranged from less than 0.01 to nearly 0.3 kg of sulfur per day for an equivalent 100 acre (40.5 hectare) sludge impoundment surface.     

Differential partitioning and speciation of Hg in wet FGD facilities of two Spanish PCC power plants

This paper evaluates the speciation and partitioning of mercury in two Spanish pulverised coal combustion power plants (PP1 and PP2), equipped with wet limestone-based flue gas desulphurisation facilities (FGD) operating with forced oxidation and re-circulation of FGD water streams. These plants are fed with coal (PP1) and coal/pet-coke blends (PP2) with different mercury contents. The behaviour, partitioning and speciation of Hg were found to be similar during the combustion processes but different in the FGD systems of the two power plants. A high proportion (86-88%) of Hg escaped the electrostatic precipitator in gaseous form, Hg²⁺ being the predominant mercury species (68-86%) to enter the FGD. At this point, a relatively high total Hg retention (72% and 65%) was achieved in the PP1 and PP2 (2007) FGD facilities respectively. However, during the second sampling campaign for PP2 (2008), the mercury removal achieved by the FGD was much lower (26%). Lab-scale tests point to liquid/gas ratio as the main parameter affecting oxidised mercury capture in the scrubber. The partitioning of the gaseous mercury reaching the FGD system in the wastes and by-products differed. In the low mercury input power plant (PP1) most of the mercury (67%) was associated with the FGD gypsum. Moreover in PP2 a significant proportion of the gaseous mercury reaching the FGD system remained in the aqueous phase (45%) in the 2007 sampling campaign while most of it escaped in 2008 (74%). This may be attributed to the scrubber operating conditions and the different composition and chemistry of the scrubber solution probably due to the use of an additive.     

Flue gas desulfurization: the state of the art

Coal-fired electricity-generating plants may use SO2 scrubbers to meet the requirements of Phase II of the Acid Rain SO2 Reduction Program. Additionally, the use of scrubbers can result in reduction of Hg and other emissions from combustion sources. It is timely, therefore, to examine the current status of SO2 scrubbing technologies. This paper presents a comprehensive review of the state of the art in flue gas desulfurization (FGD) technologies for coal-fired boilers. Data on worldwide FGD applications reveal that wet FGD technologies, and specifically wet limestone FGD, have been predominantly selected over other FGD technologies. However, lime spray drying (LSD) is being used at the majority of the plants employing dry FGD technologies. Additional review of the U.S. FGD technology applications that began operation in 1991 through 1995 reveals that FGD processes of choice recently in the United States have been wet limestone FGD, magnesium-enhanced lime (MEL), and LSD. Further, of the wet limestone processes, limestone forced oxidation (LSFO) has been used most often in recent applications. The SO2 removal performance of scrubbers has been reviewed. Data reflect that most wet limestone and LSD installations appear to be capable of approximately 90% SO2 removal. Advanced, state-of-the-art wet scrubbers can provide SO2 removal in excess of 95%. Costs associated with state-of-the-art applications of LSFO, MEL, and LSD technologies have been analyzed with appropriate cost models. Analyses indicate that the capital cost of an LSD system is lower than those of same capacity LSFO and MEL systems, reflective of the relatively less complex hardware used in LSD. Analyses also reflect that, based on total annualized cost and SO2 removal requirements: (1) plants up to approximately 250 MWe in size and firing low- to medium-sulfur coals (i.e., coals with a sulfur content of 2% or lower) may use LSD; and (2) plants larger than 250 MWe and firing medium- to high-sulfur coals (i.e., coals with a sulfur content of 2% or higher) may use either LSFO or MEL.     

Air-substrate mercury exchange associated with landfill disposal of coal combustion products

Previous laboratory studies have shown that lignite-derived fly ash emitted mercury (Hg) to the atmosphere, whereas bituminous- and subbituminous-derived fly ash samples adsorbed Hg from the air. In addition, wet flue gas desulfurization (FGD) materials were found to have higher Hg emission rates than fly ash. This study investigated in situ Hg emissions at a blended bituminous-subbituminous ash landfill in the Great Lakes area and a lignite-derived ash and FGD solids landfill in the Midwestern United States using a dynamic field chamber. Fly ash and saturated FGD materials emitted Hg to atmosphere at low rates (-0.1 to 1.2 ng/ m2hr), whereas FGD material mixed with fly ash and pyrite exhibited higher emission rates (approximately 10 ng/m2hr) but were still comparable with natural background soils (-0.3 to 13 ng/ m2hr). Air temperature, solar radiation, and relative humidity were important factors correlated with measured Hg fluxes. Field study results were not consistent with corresponding laboratory observations in that fluxes measured in the latter were higher and more variable. This is hypothesized to be partially an artifact of the flux measurement methods.