Environmental chamber measurements of mercury flux from coal utilization by-products

An environmental chamber was constructed to measure the mercury flux from coal utilization by-product (CUB) samples. Samples of fly ash, FGD gypsum, and wallboard made from FGD gypsum were tested under both dark and illuminated conditions with or without the addition of water to the sample. Mercury releases varied widely, with 7-day experiment averages ranging from −6.8 to 73 ng/m² h for the fly ash samples and −5.2 to 335 ng/m² h for the FGD/wallboard samples. Initial mercury content, fly ash type, and light exposure had no observable consistent effects on the mercury flux. For the fly ash samples, the effect of a mercury control technology was to decrease the emission. For three of the four pairs of FGD gypsum and wallboard samples, the wallboard sample released less (or absorbed more) mercury than the gypsum.     

Mercury in gypsum produced from flue gas desulfurization

Wet flue gas desulfurization (FGD) technologies used to remove sulfur dioxide (SO₂) from combustion gases can be effective in capturing oxidized mercury (Hg). Depending on the FGD process, a large portion of this Hg may be incorporated into the FGD slurry and its solid byproducts including synthetic gypsum, a material commonly used in the manufacturing of wallboard. The potential for atmospheric and groundwater releases of Hg arises during the manufacturing processes, during the preparation and use of the manufactured products, and eventually upon disposal of the wallboard or other products. In this paper, the fate and mobility of Hg in FGD products and process streams were investigated. Experimental approaches, including leaching studies and size separation techniques, were used to investigate products including FGD-outlet slurry and wallboard production line samples. Results of the experiments reported here indicate that, in a number of cases, Hg mobility is limited. Further, the agent responsible for the immobilization appears to be not the finer particles of gypsum itself but an iron-rich phase, such as iron coated clay minerals or iron oxide/hydroxide particles, probably introduced with the limestone used to form the SO₂-capture reagent.     

脱硫建筑石膏三相分析方法研究及应用

从脱硫建筑石膏各相所具有的水化和脱水特性角度,利用卤素水分测定仪,提出一种用于脱硫建筑石膏相组成分析的简单而有效的方法.就残余二水石膏及无水石膏含量对脱硫建筑石膏性能的影响进行试验研究,对相组成在煅烧设备及煅烧工艺改进方面的应用进行探讨,从而肯定了相分析的重要性及有效性.     

Mercury speciation in gypsums produced from flue gas desulfurization by temperature programmed decomposition

Temperature programmed decomposition was used to identify mercury (Hg) species in gypsum samples produced from flue gas desulfurization in two Spanish power stations (A and B). As stricter emission control/reduction policies, particularly those focusing on Hg, are being implemented, wet flue gas desulfurization (FGD) technologies used for the removal of SO₂ can result in the co-removal of highly-soluble oxidized Hg. The amount of Hg retained in FGD products may increase in the future if these units are optimized for co-capture. For this reason, it is important to identify the mercury species in FGD products not only to determine the potential risk when the wastes are finally disposed of, but also to understand the behaviour of mercury during combustion and therefore to improve the technologies for mercury removal. Different mercury species were identified in the gypsum samples. In power station A, HgS were the most probable Hg species, whereas in power station B the main compound was Hg halogenated compounds.     

Alternative calcium-sulfate-bearing materials as cement retarders: Part II. FGD gypsum

The aim of this paper is to investigate the possible displacement of natural gypsum (CaSO₄·2H₂O) in cement with an alternative setting retarder, such as the industrial by-product derived from flue gas desulfurization process called FGD gypsum. These calcium-sulfate-bearing materials (CSBM), alone or in mixtures, were ground with clinker both in laboratory and industrial scale to examine their influence on the physical and mechanical properties of cement, as well as on the industrial production line of cement. From the present work, it is extracted that the use of mixtures of sulfate-bearing materials with gypsum seems to be advantageous for the actual control of setting time. The addition of FGD gypsum increases setting time without affecting compressive strength profile. During the industrial trial, the formation of hemihydrate form of calcium sulfate dihydrate has a profound regulatory effect on the setting and strength performance of the cement partially replaced with FGD gypsum.     

Effect of amending high phosphorus soils with flue-gas desulfurization gypsum on plant uptake and soil fractions of phosphorus

Flue gas desulfurization (FGD) gypsum, a coal combustion by-product, can be used to decrease water-extractable soil P, thereby lowering the potential for P export to surface waters. This decrease results from a conversion of loosely bound inorganic P (IP) which is readily desorbable to water, to less soluble Al- and Fe-bound IP and, to a lesser extent, calcium-bound IP pools. Although this conversion has little effect on predictors of plant-available soil P (e.g., Mehlich-3 P), little is known about the plant uptake of P over several growth cycles after high P soils are amended with FGD. In a greenhouse experiment, we measured P uptake by ryegrass (Lolium perenne) using a modified Stanford–Dement procedure (three growth cycles), and the extent to which IP was being removed from each soil IP fraction (Hedley fractionation), for three soils treated with FGD gypsum (equivalent to 22.4 Mg ha^–1). Treatment with FGD decreased water extractable soil P 38 to 57%, but had little effect on Mehlich-3 soil P. During the first growth cycle, the shift from resin IP to less available Al, Fe, and Ca IP remained stable. Repeated growth cycles of ryegrass removed resin IP and thus, had a continued effect on lowering water-extractable P. After three growth cycles and harvests, ryegrass dry-matter production was not affected by FGD treatment (P > 0.05), although cumulative P uptake (20%) and P concentration of ryegrass tops (25%) were greater in FGD treated than untreated soils. Our results confirm that treatment of high P soils with FGD gypsum decreases water-extractable P by conversion to soil IP fractions that are stable with time, does not decrease plant production, and suggests that the potential for P export in surface runoff may be reduced for several years.     

Mineralogical and chemical properties of FGD gypsum from Florina,Greece

BACKGROUND: The aim of this work is to define the chemical and mineralogical composition of the fuel gas desulphurization (FGD) gypsum produced from the Meliti thermal power plant in the region of Florina in North West Greece, in order to investigate potential uses in the cement industry. Mineralogical and microprobe analyses were carried out on FGD gypsum samples collected from the Meliti 330 MW lignite‐fired power plant. RESULTS: Results show that the main component of the FGD gypsum is pure mineral gypsum (CaSO₄·2H₂O). The particle size of the gypsum ranges from 5 to 50 µm and the crystals are mainly of rhomboid shape. Microprobe analysis shows that the concentration of CaO and SO₃, which are the main components, range from 31.9%–32.5% and from 45.90–46.40%, respectively. CONCLUSION: This FGD gypsum can easily substitute the natural gypsum used in the production of cement. Copyright © 2007 Society of Chemical Industry     

烟气脱硫石膏资源化利用的研究进展

对湿法脱硫石膏和干法脱硫石膏研究现状进行了总结和分析。湿法脱硫石膏可以代替天然石膏直接利用,研究比较成熟;干法脱硫石膏的应用受到亚硫酸钙含量的影响,附加值低,资源化利用受到限制,而目前的研究也仅停留在试验阶段,不能够规模化高附加值利用。目前急需加强对干法脱硫石膏的应用研究,针对性地根据脱硫石膏成分的变化拓展利用渠道,提高附加值,达到资源化利用的目的。     

用于磷石膏煅烧的高温煅烧管设计

生产湿法磷酸副产磷石膏的综合利用是国内外共同关注的问题，高温煅烧后将其制成建筑石膏是磷石膏综合利用的主要途径之一，国内正待发展。介绍该技术中关键设备高温煅烧管的设计计算和结构处理，经铜化集团试用，基本上达到了设计要求，认为适当调整操作参数后，可用于生产不同品质的高温石膏。     

脱硫石膏联产水泥与硫酸技术

结合鲁北集团60kt／a水泥-40kt／a硫酸中试装置数据,介绍用电厂烟气脱硫石膏联产水泥与硫酸的原料性质、工艺流程、控制指标及成本构成。指出用脱硫石膏联产水泥与硫酸具有技术和经济可行性,既可减少环境污染,又可实现废物的资源化利用。     

钛石膏的改性处理和力学性能研究

采用破碎、干燥、粉磨、煅烧和陈化等处理工艺对钛石膏进行物理改性,研究了煅烧温度对钛石膏力学性能的影响,通过掺加硫酸钠、生石灰和硅酸盐水泥等外加剂对钛石膏进行化学改性,确定了外加剂掺加量的最佳配比,并对改性机理进行了探讨.结果表明,钛石膏经180 ℃煅烧3 h,掺加0.5%硫酸钠、3%生石灰和5%硅酸盐水泥,制得的试样力学性能可以达到:2 h抗折强度2.6 MPa、抗压强度3.2 MPa,绝干抗折强度4.58 MPa、抗压强度5.2 MPa.经改性后钛石膏试样的强度指标可以达到建筑石膏国家标准中1.6等级的要求.     

适用于制备粉体石膏建材的脱硫建筑石膏

通过对脱硫建筑石膏的三相分析,确定适用于制备粉体石膏建材的脱硫建筑石膏:二水石膏含量宜<4.00%,无水石膏(Ⅲ型)宜<5.00%.宜采用低温慢烧工艺对脱硫石膏原料进行煅烧.     

低水膏比时减水剂对β半水脱硫石膏力学性能的影响

研究了低水膏比时减水剂对β半水脱硫石膏力学性能的影响.结果表明:脱硫石膏脱水工艺最佳参数为烘干温度170℃,烘干时间6h和陈化时间5d.显微结构表明,β半水脱硫石膏颗粒表面为粗糙、不完整结构;烘干时无水石膏与半水石膏同时存在才具有较高的强度.当水膏比为0.28,减水剂掺量为0.9％～1％时,β半水脱硫石膏抗压强度达到最大值35 MPa,在此掺量下减水剂可有效减少成型时需水量和提高试块强度.     

脱硫石膏热处理制备注浆成型模具

石灰石-石膏湿法烟气脱硫技术以石灰石为原料吸收烟气中的二氧化硫,得到石膏晶体。在控制二氧化硫排放的同时,脱硫石膏的处理与综合利用也非常重要。以脱硫石膏为原料,分析脱硫石膏的成分,通过热处理使其脱水,并表征热处理过程对石膏物理性能的影响。将热处理后的石膏用于石膏模具的制作,并最终制备固体氧化物燃料电池阳极支撑体。燃料电池测试的结果显示,脱硫石膏可以用于管式固体氧化物燃料电池的制备。     

Post‐fire analysis of construction materials—gypsum wallboard

The objective of this research was to assess scientifically to what extent fire damaged gypsum wallboard (GWB) could be used to identify time, temperature and heat flux exposures of the incipient stages of an uncontrolled fire. Gypsum wallboard is commonly used on vertical and ceiling surfaces that frequently survive a building fire so permiting samples of the GWB to be removed for post‐fire analysis. The gypsum (calcium sulphate dihydrate) is a hydrated cystalline mineral that is chemically very stable and undergoes phase changes at temperatures found in the incipient stages of a building fire. Experiments are described in this paper that support the theory that thermally induced changes in GWB provide a quantitative method for determining time/temperature regimes that have occurred in a building fire. Copyright © 2000 John Wiley & Sons, Ltd.     

鞍钢钢渣矿渣制备人工鱼礁混凝土复合胶凝材料

以81.5％的矿渣、5％的钢渣、12.5％的脱硫石膏以及1％的水泥熟料,制备出了28 d抗压强度为56.75 MPa的低碱度胶凝材料,该胶凝材料可用于制备低碱度人工鱼礁混凝土.通过改变钢渣和脱硫石膏的掺量,研究了其掺量变化与试件强度的影响关系.实验结果表明:在该体系中,当钢渣掺量小于5％时,胶砂试块的强度随着钢渣的增加而提高;当钢渣掺量大于5％时,胶砂试块的强度随着钢渣掺量的增加而降低,并在钢渣掺基大于20％时快速下降.脱硫石膏的掺量对胶砂试块的强度影响更为显著;当脱硫石膏掺量达到12.5％时,与不含脱硫石膏的试样相比,抗压强度和抗折强度分别提高了168％和176％.利用XRD和SEM分析净浆的水化过程,结果表明,体系在早期水化主要生成AFt相和C-S-H凝胶,并对强度的增长起了主要作用.     

Recycling of FGD gypsum to calcium carbonate and elemental sulfur using mixed sulfate-reducing bacteria with sewage digest as a carbon source

A combined chemical and biological process for the recycling of flue gas desulfurization (FGD) gypsum into calcium carbonate and elemental sulfur is demonstrated. In this process, a mixed culture of sulfate-reducing bacteria (SRB) utilizes sewage digest as its carbon source to reduce FGD gypsum to hydrogen sulfide. The sulfide is then oxidized to elemental sulfur via reaction with ferric sulfate, and accumulating calcium ions are precipitated to calcium carbonate using carbon dioxide. Employing anaerobically digested-municipal sewage sludge (AD-MSS) medium as a carbon source, SRB in serum bottles demonstrated an FGD gypsum reduction rate of 8 mg dm⁻³ h⁻¹ (10⁹ cells)⁻¹. A chemostat with continuous addition of both AD-MSS medium and gypsum exhibited sulfate reduction rates as high as 1·3kg FGD gypsumm⁻³ day⁻¹. The increased biocatalyst density afforded by cell immobilization in a columnar reactor allowed a productivity of 152 mg SO₄ dm⁻³ h⁻¹ or 6·6kg FGD gypsum m⁻³ day⁻¹. Both reactors demonstrated 100% conversion of sulfate, with 75–100% recovery of elemental sulfur and as high as 70% COD utilization. Calcium carbonate was recovered from the reactor effluent upon precipitation using carbon dioxide. The formation of two marketable products—elemental sulfur and calcium carbonate—from FGD gypsum sludge, combined with the use of a low-cost carbon source and further improvements in reactor design, promises to offer an attractive alternative to the landfilling of FGD gypsum.     

Fire-Resistant joints in gypsum wallboard

In situations where joint failure in the protective gypsum membrane is critical to the fire resistance of the system, wallboard manufacturers recommend application of two layers of wallboard with joints in the face layer staggered with joints in the backerboard. Unfortunately, the additional weight load that a second layer of wallboard imposes on the building assembly renders the technique impractical in some situations. Two examples are wallboard ceilings attached directly to wood joist or wood truss floor systems or suspended by hanger wire to steel furring channels below these floor systems. Small-scale laboratory tests demonstrated that the installation of steel ‘Tee’ strips in the finished joint between adjacent gypsum wallboard panels significantly increased the resistance of the joint to passage of fire and hot gases. Use of these strips in the construction of gypsum wallboard protected building systems should provide a significant increase in the fire resistance of the entire assembly without greatly increasing the weight load imposed upon the assembly.     

Q相对脱硫石膏氯离子固化和抗压强度的影响

受限于高氯离子迁移性能,大量品质较低的脱硫石膏在石膏制品中无法被有效利用。本文研究了Q相(Ca₂₀Al₂₆Mg₃Si₃O₆₈)对脱硫石膏中氯离子迁移性能的影响规律与机理。结果表明,在脱硫石膏中以10%~30%(质量分数)的比例掺入Q相,其水化产物主要为二水硫酸钙、钙矾石和AH₃凝胶,脱硫石膏样品中氯离子固化率和绝干抗压强度均得到了较大提升。掺入30%的Q相对脱硫石膏性能提升效果最佳,此时氯离子固化率达19.55%,石膏的绝干抗压强度提升了约51.5%。结合XRD、SEM和综合热分析探明了Q相-脱硫石膏水化产物中钙矾石、AH₃凝胶对氯离子固化和石膏力学性能改善的作用机理。     

脱硫石膏的热处理及其对矿渣水泥若干性能的影响

研究了在不同温度下处理的脱硫石膏对矿渣水泥若干性能的影响，确定其在水泥基材料中循环利用的可行性。研究结果表明，经低温烘干焙烧处理的脱硫石膏，掺入到矿渣水泥中并控制适当的SO3掺量，水泥凝结时间正常，强度略有提高，并且明显降低了硬化水泥浆体的失水率和干缩率，可以有效防止收缩裂缝的产生：并进一步探讨了脱硫石膏对矿渣水泥性能的影响机理。