The Importance of Maintenance for Lime Flue Gas Desulfurization Systems

The successful, reliable operation of a power plant flue gas desulfurization (FGD) system depends largely on a good program of maintenance. Identifying the FGD equipment that is most critical to an FGD system’s overall reliability or its ability to meet emission regulations plays an important role in determining the extent of a maintenance program for a particular site. FGD maintenance programs vary considerably, depending on site-specific requirements and the support of plant owners. Many owners are reluctant to spend money on FGD maintenance because an FGD system is a nonproductive part of a power plant; however, a good maintenance program can result in longer equipment life, improved equipment performance, increased system availability, better safety, and lower operating costs. This paper uses wet and dry lime FGD systems to illustrate the advantages of good maintenance and the consequences of poor maintenance. Examples of specific tasks for preventive, scheduled, planned, and emergency maintenance are described. Also, because of the importance of FGD maintenance personnel, a section on organization and training is included.     

Development and Pilot Plant Evaluation of Silica- Enhanced Lime Sorbents for Dry Flue Gas Desulfurization

EPA’s efforts to develop low cost, retrofitable flue gas cleaning technology include the development of highly reactive sorbents. Recent work addressing lime enhancement and testing at the bench-scale followed by evaluation of the more promising sorbents in a pilot plant are discussed here.

The conversion of Ca(OH)₂ with SO₂ increased several-fold compared with Ca(OH)₂ alone when Ca(OH)₂ was slurrled with fly ash first and later exposed to SO₂ in a laboratory packed bed reactor. Ca(OH)₂ enhancement increased with the increased fly ash amount. Dlatomaceous earths were very effective reactivity promoters of lime-based sorbents. Differential scanning calorimetry of the promoted sorbents revealed the formation of a new phase (calcium silicate hydrates) after hydration, which may be the basis for the observed Improved SO₂ capture.

Fly ash/lime and diatomaceous earth/lime sorbents were tested in a 100 m³/h pilot facility incorporating a gas humidifier, a sorbent duct injection system, and a baghouse. The inlet SO₂ concentration range was 1000-2500 ppm. With once-through dry sorbent injection into the humidified flue gas [approach to saturation 10–20°C (18–36°F) in the baghouse], the total SO₂ removal ranged from 50 to 90 percent for a stoichiometric ratio of 1 to 2. Recycling the collected solids resulted in a total lime utilization exceeding 80–90 percent. Increased lime utilization was also investigated by the use of additives.     

Application of the Lime/Limestone Flue Gas Desulfurization Process to Smelter Gases

In this presentation, adaptation of the lime/limestone process for flue gas desulfurization (FGD) is discussed and how this process can be adapted to applications in the nonferrous smelting industry such as fugitive gases, copper reverberatory furnace gases, lead sintering gases, molybdenum roasting plant tail gases, and other weak SO₂ smelter gases. Different methods for particulate removal are also discussed with emphasis on how the particulate removal process can be integrated with the desulfurization process.     

生活垃圾焚烧烟气排放中二噁英对人体健康的风险评价

随着垃圾焚烧的广泛应用,由此产生的二次污染问题也日益显现出来,特别是二嗯英污染已引起世界的关注。这也是垃圾焚烧设施在环评阶段遭到周围公众反对的原因之一。文中介绍了二嗯英的危害、垃圾焚烧烟气中的二嗯英来源以及二嗯英的相关标准。以某垃圾焚烧发电厂为例,对垃圾焚烧烟气中的二嗯英类物质对人体健康的风险进行了评价,并提出了如何最大限度地减少垃圾焚烧处理过程中的二唔英排放量。     

对氯化氢环境空气质量标准的商榷

通过对现行大气中的氯化氢(HCl)质量标准的来源、毒理作用的分析、各类标准的比较及标准的可行性等几方面的阐述，指出了现行标准在执行中存在的缺陷，提出了应对现行大气中HCl的标准进行重新核定的建议。     

Assessing Sorbents for Mercury Control in Coal-Combustion Flue Gas

Abstract

Sorbent injection for Hg control is one of the most promising technologies for reducing Hg emissions from power-generation facilities, particularly units that do not require wet scrubbers for SO₂ control. Since 1992, EPRI has been assessing the performance of Hg sorbents in pilot-scale systems installed at full-scale facilities. The initial tests were conducted on a 5000-acfm (142-m³/min) pilot baghouse. Screening potential sorbents at this scale required substantial resources for installation and operation and did not provide an opportunity to characterize sor-bents over a wide temperature range.

Data collected in the laboratory and in field tests indicate that sorbents are affected by flue gas composition and temperature. Tests carried out in actual flue gas at a number of power plants also have shown that sorbent performance can be site-specific. In addition, data collected at a field site often are different from data collected in the laboratory, with simulated flue gas mixed to match the major components in the site’s gas. To effectively estimate the costs of Hg sorbent systems at different plants, a measure of sorbent performance in the respective flue gases must be obtained. However, injection testing at multiple facilities with large pilot systems is not practical.

Over the past five years, fixed-bed characterization testing, modeling studies, and bench-scale injection testing have been undertaken to develop a low-cost technique to characterize sorbent performance in actual flue gas and subsequently to project normalized costs for Hg removal prior to full-scale demonstration. This article describes the techniques used and summarizes field-testing results from two plants burning Powder River Basin (PRB) coal for commercial activated carbon and several other sorbent types. Full-scale projections based on the results and data collected on larger-scale systems also are included.     

Estimating Costs of Flue Gas Desulfurization Systems for Utility Boilers

In September 1973, PEDCo-Environmental Specialists was awarded a study by the U. S. Environmental Protection Agency to evaluate the cost of controlling sulfur dioxide and particulate emissions from selected utility boilers. Since that time, PEDCo has conducted additional studies for the U. S. EPA, state and local control agencies, and private industry on the costs of control technology and the reliability of sulfur dioxide control systems. Current work includes determining the feasibility and environmental impact of converting selected utility boilers to coal-firing to conserve the nation’s gas and oil supplies. This paper presents an overview of the status and costs of flue gas desulfurization (FGD) systems, and the factors relating to the variability in costs. It is based in part upon work performed in developing detailed FGD cost estimating manuals for EPA.     

Current Status of the ADVACATE Process for Flue Gas Desulfurization

The following report discusses current bench- and pilot-plant advances in preparation of ADVAnced siliCATE (ADVACATE) calcium silicate sorbents for flue gas desulfurization. It also discusses current bench- and pilot-plant advances in sorbent preparation. Fly ash was ground in a laboratory scale grinder prior to slurring in order to decrease the slurring time needed for the sorbent to be reactive with SO₂. Reactivity of ADVACATE sorbents with SO₂ in the bench-scale reactor correlated with their surface area.

ADVACATE sorbents produced with ground fly ash were evaluated in the 50 cfm (85 m³/h) pilot plant providing 2 s duct residence time. ADVACATE sorbent was produced by slurrying ground fly ash (median particle size of 4.3 µm) with Ca(OH)₂ at the weight ratio of 3:1 at 90°C (194°F) for 3hto yield solids with 30 weight percent of initial free moisture. When this sorbent was injected into the duct with 1500 ppm SO₂ and at 11°C (20°F) approach to saturation, the measured SO₂ removal was approximately 60percent at a Ca/S stoichiometric ratio of 2. Previously, when ADVACATE sorbent was produced at 90°C (194°F) and at the same fly-ash-to-Ca(OH)₂ weight ratio using unground fly ash, removal under the same conditions in the duct was approximately 50 percent following 12 h slurring. The report presents the results of pilot-scale recycle tests at the recycle ratio of 2. Finally, the report discusses future U.S. Environmental Protection Agency plans for commercialization of ADVACATE.     

The Feasibility of Wet Scrubbing for Treating Waste-to-Energy Flue Gas

The selection of Hue gas treatment processes in the waste-to-energy industry has generally followed the trend of the coal-fired power industry. The highly favored process for both industries is the dry scrubber (spray absorber) followed by a fabric filter. As more attention is focused upon increasingly greater efficiencies, lower outlet concentrations, heavy metals emissions, and toxic organic pollutant emissions, the advantages of wet scrubbing become more pronounced. This paper provides an objective technical and economic evaluation of selected wet scrubbing and dry scrubbing systems for a generic waste-to-energy facility. The advantages and disadvantages of wet scrubbing are discussed and translated into cost benefits or penalties.     

喷射鼓泡法烟气脱硫工艺

对以喷射鼓泡反应器为主设备，石灰石浆液为脱硫剂的湿法烟气脱硫工艺进行了实验研究，结果表明主要参数[烟气压降Δp、ф（液气）比、吸收液pH值、进气SO2浓度]对脱硫效率均有较大的影响。     

Use of Seawater in Flue Gas Desulfurization

For seasite power plants using seawater for condenser cooling, Bechtel developed a new process to remove better than 90 percent of flue gas SO₂ using seawater and lime. Tests demonstrate that marine life is not affected by the effluent from this unique scrubbing process; therefore, the aqueous effluent containing reacted products (gypsum) in solution at low concentration is suitable for discharge to the sea.     

Modeling of Dry Injection Flue Gas Desulfurization

Dry processes for controlling sulfur dioxide emissions by injecting sodium based sorbents in the ductwork ahead of a bag filter are effective and more simple alternatives to conventional FGD processes. This paper presents a fundamental kinetic model of the dry injection process. Experimental data from pilot scale tests are reported. The model is shown to be applicable to the dry injection process. However, further experimental work is recommended to get a better understanding of the reaction mechanisms.     

对锅炉烟气处理的技术改造

对锅炉烟气处理工艺进行了改造，运行结果表明，改造后的处理效果明显提高，解决了烟尘及SO2排放浓度的超标问题，实现了达标排放。     

Investigation of a Mercury Speciation Technique for Flue Gas Desulfurization Materials

Abstract

Most of the synthetic gypsum generated from wet flue gas desulfurization (FGD) scrubbers is currently being used for wallboard production. Because oxidized mercury is readily captured by the wet FGD scrubber, and coal-fired power plants equipped with wet scrubbers desire to benefit from the partial mercury control that these systems provide, some mercury is likely to be bound in with the FGD gypsum and wallboard. In this study, the feasibility of identifying mercury species in the FGD gypsum and wallboard samples was investigated using a large sample size thermal desorption method. Potential candidates of pure mercury standards including mercuric chloride (HgCl₂), mercurous chloride (Hg₂Cl₂), mercury oxide (HgO), mercury sulfide (HgS), and mercuric sulfate (HgSO₄) were analyzed to compare their results with those obtained from FGD gypsum and dry wallboard samples. Although any of the thermal evolutionary curves obtained from these pure mercury standards did not exactly match with those of the FGD gypsum and wallboard samples, it was identified that Hg₂Cl₂ and HgCl₂ could be candidates. An additional chlorine analysis from the gypsum and wallboard samples indicated that the chlorine concentrations were approximately 2 orders of magnitude higher than the mercury concentrations, suggesting possible chlorine association with mercury.     

冲天炉烟气除尘净化技术

针对冲天炉熔炼过程中产生污染物的特性，提出了一种净化效率高且经济可行的冲天炉烟气多级复合除尘净化技术。     

重金属离子在腐植酸上吸附的研究

对4种代表性重金属离子在腐植酸上吸附、pH对竞争吸附的影响及其吸附机理进行了研究。结果表明，Cu2＋、Pb2＋、Zn2＋的吸附等温线为F型，而Cd2＋等温线为L型；2．5＜pH＜3．5时，竞争吸咐次序为Cu2＋＞Pb2＋＞Cd2＋＞Zn2＋；pH＞5．0时，Cd2＋＞Cu2＋＞Zn2＋＞Pb2＋；Cu2＋在腐植酸上的吸附主要是以与腐植酸形成配合物的方式相互结合。     

Silica-Enhanced Sorbents for Dry Injection Removal of SO2 from Flue Gas

Novel silica-enhanced lime sorbents were tested in a bench-scale sand-bed reactor for their potential for SO₂ removal from flue gas. Reactor conditions were 64°C (147°F), relative humidity of 60 percent [corresponding to an approach to saturation temperature of 10°C (18°F)], and inlet SO₂ concentration of 500 or 1000 ppm. The sorbents were prepared by pressure hydration of CaO or Ca(OH)₂ with siliceous materials at 100°C (101 kPa) [212°F (14.7 psi)] to 230°C (2793 kPa) [446°F (405 psi)] for 15 min to 4 h. Pressure hydration fostered the formation of a sorbent reactive with SO₂ from fly ash and Ca(OH)₂ in a much shorter time than did atmospheric hydration. The conversion of Ca(OH)₂ in the sand-bed reactor increased with the increasing weight ratio of fly ash to lime and correlated well with B.E.T. surface area, increasing with increasing surface area. The optimum temperature range for the pressure-hydration of fly ash with Ca(OH)₂ was between 110 and 160°C (230 and 320 °F). The pressure hydration of diatomaceous earth with CaO did not offer significant reactivity advantages over atmospheric hydration; however, the rate of enhancement of Ca(OH)₂ conversions was much faster with pressure hydration. Scanning electron microscope (SEM) and x-ray diffraction studies showed solids of different morphology with different fly ash/lime ratios and changing conditions of pressure hydration.     

循环流化床烟气脱硫多层喷水技术

东南大学热能工程研究所建立了我国目前最大的循环流化床烟气脱硫试验装置，脱硫塔直径为600mm,处理烟气量达2000m^3/h。在此试验台上进行了循环流化床烟气脱硫多层喷水的试验研究，试验表明在多层喷水条件下，趋近饱各温度△T有较大降低，脱硫效率明显提高，提高了Ca的利用率，降低了运行费用。     

剩余污泥对酸性大红G的吸附

以剩余污泥为吸附剂,研究其对模拟废水中酸性大红G的吸附条件及吸附机理。结果表明,剩余污泥对酸性大红G的吸附是一个快速过程,吸附时间可控制在30 min;其吸附过程同时受液膜扩散和颗粒内扩散的影响,可以用假二级动力学模型进行描述和预测;Freundlich方程可以较好地描述剩余污泥对酸性大红G的吸附行为。污泥未调pH时,对pH<2的溶液中酸性大红G的吸附性能良好;污泥pH为1时,对实验范围(pH<11)溶液中的酸性大红G均可有效吸附;污泥投加量增加,酸性大红G去除率升高,但污泥对酸性大红G的吸附量下降。