Flue Gas Desulphurisation Waste Research Articles

Utilisation of FGD gypsum for silicate removal from scheelite flotation wastewater

Silicate removal from scheelite flotation wastewater by flue gas desulphurisation waste (FGD gypsum) has been investigated. Systematic laboratory-scale experiments were conducted to evaluate silicate removal and formation mechanism of calcium silicate. Precipitation test results showed that silicate removal reached 90% at an initial silicon concentration of 2650 mg/L when the dose of FGD gypsum exceeded 20 g/L. Equilibrium speciation analysis showed that solution pH is the key factor affecting silicate removal. Silicate removal could be effectively improved to 95% when pH was reduced to 10. Kinetic analysis showed that reaction rate peaked in 60 s and attained equilibrium after 240 s. Scanning electronic microscopy coupled with energy dispersive spectroscopy (SEM-EDS) results confirmed the formation of calcium silicate and described its morphology features. The continuous pilot-scale test (100 mL/min) further demonstrated the feasibility of utilizing FGD gypsum for silicate removal. Similar results were observed in laboratory-scale experiments. Treatment cost totalled 0.18 $/m3.

Response of salt tolerance of different salt-tolerant plants to flue gas desulphurization waste and a comprehensive evaluation of salt tolerance of plants

为探讨施用脱硫废弃物对生长在盐土和碱土上的不同植物耐盐特性的影响, 并建立综合评价指标体系, 对不同植物的耐盐指数进行综合评价。本试验在2008-2010年期间, 分别在碱土区和盐土区2个试点, 以施与不施脱硫废弃物为主处理, 选用9种不同耐盐植物为副处理开展了田间裂区试验, 观测分析了各耐盐植物的出苗特征、生长生理特征、产量等指标及土壤盐分、养分、碱化度(ESP)等性质, 从而建立包括植物生长、生理指标、土壤指标和经济指标的综合评价指标体系, 并应用TOPSIS法对不同耐盐植物的耐盐指数进行综合评价。结果表明: 与CK相比, 施用脱硫废弃物能显著改善各耐盐植物的生长发育, 提高出苗率、相对生长速率(株高)和相对生物量, 增加自由水和束缚水的比值(F/B), 且在碱土上效果优于盐土。不同类型耐盐植物之间差异显著, 表现出各自的耐盐、碱特性。同时施用脱硫废弃物种植耐盐植物可提高土壤有机质增加速率和全盐、碱化度的降低速率。同样地, 对盐碱土的改良效果表现为碱土优于盐土, 不同耐盐植物之间差异显著。通过综合评价把不同耐盐植物分为强、较强、中和弱4个耐盐等级。与CK相比, 施用脱硫废弃物可提高耐盐植物的耐盐等级, 扩展耐盐植物在盐碱地上的种植范围。由此可知, 耐盐植物的耐盐特性受植物类型、盐碱地类型、改良措施等因素影响。因此, 从生态经济的角度寻求合理的综合评价方法来确定耐盐植物的耐盐特性具有重要科学意义, 可为进一步优化盐碱地生态修复模式提供理论支持。

EARLY AGE POROSITY AND PORE SIZE DISTRIBUTION OF CEMENT PASTE WITH FLUE GAS DESULPHURISATION (FGD) WASTE

This paper is part of a wide-ranging investigation on the use of flue gas desulphurisation (FGD) waste in cement-based materials. It reports the results on the porosity and pore size distribution of cement paste containing varying amounts of simulated FGD waste. The water to binder ratio was 0.5. The binder consists of cement and simulated FGD. The FGD is a combination of fly ash and gypsum ranging from 0% to 100%. Cement in the pastes was partially replaced with 25% FGD (by weight). The porosity and pore size distribution of cement pastes was determined during the early stage of hydration. Increasing the amount of gypsum does not increase the pore volume. However, increasing the amount of gypsum in the paste leads to an increase in the threshold diameter and a decrease in the percentage of small pores in the paste, both indicating a coarser pore structure. The results of this investigation were compared with data at longer curing periods.

EXTERNAL CHEMICAL SHRINKAGE OF PASTES CONTAINING FLUE GAS DESULPHURISATION (FGD) WASTE

The effect of including flue gas desulphurisation (FGD) waste on total chemical shrinkage of cement paste up to 7 days is reported. The FGD wastes were obtained from different plants located in different countries which vary in compositions. Also simulated FGD wastes were prepared in the laboratory which is a blend of fly ash and gypsum. Pastes were prepared with water to binder ratio of 0.5. The binder consists of cement and FGD. Cement was replaced with 25% (by weight) of different FGD materials. The results reported show varying trend depending upon chemical composition. Using calcium sulphate based FGD waste in cement paste, both the short and long-term total chemical shrinkage were reduced. For paste containing SiO2-Al2O3-CaSO4 based waste the total chemical shrinkage was reduced.

Preliminary examinations of mechanistic control in the solidification of flue gas desulphurisation sludge and pulverised fuel ash

Abstract Cement‐based solidification of pulverised fuel ash and flue gas desulphurisation waste i s examined using mix designs adapted from a commercial process. Monoliths augmented with up to 3.75%w/w Portland cement exhibited dimensional stability and unconfined compressive strengths exceeding 2 MPa at 84 days set. Total aqueous‐extractable metals of 0.1–1.7 mg 1‐1, determined using rapid dynamic leach tests, indicated minimal, but progressive removal of cationic species from solidified waste forms at 7, 28 and 84 days. Distinction between the mechanistic processes of solidification and cation fixation is evidenced by microstructural investigations suggesting that well‐developed ettringite crystallites, formed in the presence of available sulphate, are instrumental in controlling the leachability of metals from waste matrices.

The disposal of flue gas desulphurisation waste: sulphur gas emissions and their control

Flue gas desulphurisation (FGD) equipment to be fitted to UK coal-fired power stations will produce more than 0.8 Mtonnes of calcium sulphate, as gypsum. Most gypsum should be of commercial quality, but any low grade material disposed as waste has the potential to generate a range of sulphur gases, including H2S, COS, CS2, DMS and DMDS. Literature data from the USA indicates that well-oxidised waste with a high proportion of calcium sulphate (the main UK product of FGD) has relatively low emissions of sulphur gases, which are comparable to background levels from inland soils. However, sulphur gas fluxes are greatly enhanced where reducing conditions become established within the waste, hence disposal strategies should be formulated to prevent the sub-surface consumption of oxygen.

Biological Denitrification of Waste Water from Wet Lime–Gypsum Flue Gas Desulphurization Plants

Waste water from flue gas desulphurization by the wet lime-gypsum process is characterized by high contents of nitrate (150–300 mg/l N) and chloride (10–30 g/l Cl) and high temperature (40–50°C). Continuous and batch experiments with biological denitrification were performed with suspended cultures in lab-scale reactors fed with synthetic waste water with chloride concentrations up to 30 g/l Cl. Process temperatures in the range of 30–50°C were investigated. Acetate was added as carbon source. The results of the experiments show that biological denitrification was feasible at the extreme environmental conditions prevailing in wet lime–gypsum flue gas desulphurization waste water. Stable continuous denitrification was performed at chloride concentrations up to 30 g/l and at temperatures up to 45°C. A temperature optimum of 40°C was found for nitrate removal. At 50°C the denitrification had ceased in the reactors. In batch experiments an increased tendency to intermediate nitrite accumulation at increased temperatures and increased chloride levels was observed. This indicates that efforts should be made to equal out load variations in high chloride and high temperature biological denitrification in order to avoid periodical nitrite accumulation.

Fishery Enhancement Reef Building Exercise

Abstract The constructive use of coal-fired power station waste products for building artificial reefs is being explored for the first time in the U.K. at present, the practice of sea dumping of raw pulverised fuel ash (PFA) from coal combustion is under review and the use of consolidated PFA blocks offers a possible alternative. the planned fitting of flue gas desulphurisation (FGD) plant in the U.K. will additionally produce large quantities of gypsum. to test the environmental compatability of such materials in marine structures, an experimental reef has been constructed off the central south coast of the U.K. Fifty tonnes of blocks made from different combinations of PFA, gypsum, FGD waste water sludge, cement and gravel using standard concrete as the control material, were deployed. the site selected is remote from prominent sea bed features in an area of flat sand with limited species variety.The preliminary studies leading to the licensing of this project included bioassay experiments with diatom c...

Characterization and leaching studies of FGD waste by-products

To develop a data base for the planning of effective flue gas desulphurization (FGD) by-product management, a laboratory study was undertaken to evaluate the following FGD material characteristics: (a) chemical and mineralogical composition; (b) leaching behavior and evolution of leachate chemistry with time; (c) nature and extent of geochemical interactions between FGD leachate and clay liner materials. The FGD by-product materials used in the study were produced as part of the limestone/hydrate lime sorbent injection process evaluation test runs at one of Ontario Hydro's coal-fired thermal generating stations. The major constituents of the waste material are free lime, anhydrite, calcite, and quartz, with minor amounts of magnetite and mullite. The presence of unreacted free lime imparts strong exothermic properties to this material. Leaching tests indicate that the waste material is highly alkaline but nonhazardous under the environmental protection act of the Ontario government. Modeling of leachate/clay liner interactions indicates that calcareous tills may serve as suitable liner materials at an FGD waste disposal site, where high leachate alkalinity is maintained. However, in the event of the leachate alkalinity being neutralized by CO 2(g) or other processes with a corresponding drop in pH, most rock-forming minerals and clay minerals may be usede as liner materials.

Ammonia-based flue gas desulphurization waste solution as a nitrogen fertilizer

A flue gas desulphurization product based on the absorption of sulphur dioxide by an ammoniacal solution (Am-FGD) was evaluated as a nitrogenous fertilizer. Evaluation was by field trial using barley and rye-grass as test crops. The Am-FGD solution was added to the soil either one week before sowing the barley, at sowing, or one week after. In the grass experiment, the Am-FGD solution was added to the soil surface or sprayed on the plants shortly after the first and after the second cut.The results indicate that nitrogen in the Am-FGD solution had the same fertilizer value as nitrogen in calcium-ammonium-nitrate (CAN). The toxic effect of sulphite is avoided or reduced to insignificant levels when direct contact of the Am-FGD solution with the plants is avoided. When added in combination with CAN there might even be a slight positive effect. The plant content of inorganic elements was unchanged by the experimental treatments.

Inorganic element uptake by barley from soil supplemented with flue-gas desulphurisation waste and fly-ash

Inorganic element uptake by barley from soil supplemented with flue-gas desulphurisation waste and fly-ash

Oxidation of sulphite originating from flue gas desulphurization waste in soil

The rate of catalyzed oxidation of sulphite originating from flue gas desulphurization (FGD) waste was studied under varying conditions. The pH dependence was examined in aqueous solution at the pH range of 5 to 8, the effect of soil moisture was studied in sieved soil of different moisture contents, and the oxidation of sulphite to a soil as FGD waste, was measured at different depths in a field experiment. The experiments that the half-lives of sulphite in aqueous solution were between 0.5 and 2 hours and that the oxidation rate was highest at the lowest pH. In sieved soil the half-lives of sulphite were in the range of 3 to 20 days with the oxidation rate at the highest moisture content, indication that oxygen availability was the limiting factor. The slowest decrease of the sulphite concentration was found at a soil depth of 8-10 cm which was the where the highest background concentration of sulphite was found in control plots, too.

Inorganic element uptake by barley from soil supplemented with flue gas desulphurization waste and fly ash

To evaluate the influence of waste products from coal- and oil-fired power plants on the inorganic element content of plants, barley was grown in pots each with 22 kg of sandy loam supplied with increasing amounts of six waste products. The plants were harvested at maturity and analysed for a number of inorganic elements. The salinity of the soil was the limiting factor for the amount added in terms of plant growth. Concerning the quality of the plants as fodder, addition of the waste to the soil at levels of about 0.5% by weight increased the Se concentration of the barley from a level deficient for animals to that approaching sufficiency for animals. The increase in Cd from the flue gas desulphurization (FGD) products was deemed undesirable, even though the concentrations following this single addition were far from toxic. All other increases in element concentrations were without any biological significance.