Flue Gas Desulfurization Sludge Research Articles

Preparation of Porous Porcelain with Treated Flue Gas Desulfurization (FGD) Sludges the Foaming Agent

The potential of treated FGD sludge as foaming agent in ceramic porcelain were studied. The effect of treated FGD sludge content on phase composition, porosity and mechanical strength of porous ceramic were investigated. The result showed that the addition of treated FGD sludge improve the porosity. However, the increased porosity significantly reduced the flexural strength in sample after sintering at 1200°C for 3 hours. The porous of ceramic porcelain produced in this study can be used for insulation in high temperature application.

Phase Transformation of FGD By-Product into Plaster Mould via Heat Treatment Process

Flue Gas Desulfurization (FGD) is a waste incineration process commonly used to eliminate sulfur dioxide (SO2) from flue gas power plants. FGD by-product recorded a rich gypsum content, also known as calcium sulfate dehydrate (CaSO4•2H2O), which has promising practical applications in plaster mould production. Plaster of Paris (POP) with a chemical composition of calcium sulfate hemihydrate (CaSO4•0.5H2O) is widely used in plaster mould production because of its quick setting and hardening upon moistened. Naturally, gypsum with 2 molecules of crystalline water can change to 1.5 molecules via the dehydration process. Various dehydration methods were conducted to transform FGD gypsum to hemihydrate. After undergoing different autoclave processes, the phase transition of FGD by-products was identified by X-ray diffraction (XRD) mode and compared with commercial POP. Chemical composition of FGD sludge contains a high amount of calcium oxide (CaO), sulfur trioxide (SO3) and boron trioxide (B2O3), as well as other impurities such as fluorine (F), chlorine (Cl), and magnesium oxide (MgO). Based on phase analysis, sample H1 to H5 show the percentage of hemihdyrate is 1.5%, 19.7%, 2.8%, 1.2%, and 46.1%, respectively, after different dehydration methods.

Characterisation Of FGD Sludge From One of Glass Industrial in Malaysia and Their Potential as Ceramic Mould

Flue Gas Desulfurization (FGD) is a waste incineration process used to eliminate sulfur dioxide (SO2) from flue gas power plants. Limestone/gypsum was injected into the plant to trap sulfur dioxide and change their chemical composition from calcium carbonate to calcium sulfate dehydrate, known as FGD sludge wet scrubber. Nowadays, it is necessary to overcome the environmental pollution caused by the massive production of FGD sludge waste through recycling. In this research, FGD sludge was characterised to reveal its chemical composition, crystalline phase, and FTIR spectra characteristics. FGD sludge recorded a moderate alkaline with a pH of 8.24. Based on the XRD result, FGD sludge was mainly composed of gypsum (CaSO4•2H2O) and anhydrite (CaSO4). XRF analysis also shows that FGD sludge was mainly composed of calcium oxide, sulfur trioxide, silica, and potassium oxide.

Mercury species and potential leaching in sludge from coal-fired power plants

Wet flue gas desulfurization (WFGD) sludge, generated from the WFGD effluent treatment process, is suitable for multiple uses in various industries. However, risk assessments of its utilization are limited. Systematic study of Hg species occurrences, partitioning and risks of leaching is required, and these concerns were addressed in the present study. Hg temperature-programmed decomposition (Hg-TPD) and an improved European Community Bureau of Reference (BCR) method indicated residual Hg in WFGD sludge was related to HgS, and the content of this fraction was from 2 to 3%. HgCl2, HgO and HgSO4 were assigned to the water/acid-soluble fractions, and reducible Hg was related to Fe species in the sludge. Leachate evaluation of the WFGD sludge indicated potentially high Hg leaching risk. WFGD sludge with higher Hg concentrations and smaller particulate diameters exhibited greater leaching potential. Leaching of Hg from WFGD sludge in China into the environment was estimated at 7.46 t/yr.

Transformation pathways from calcium sulfite to α-calcium sulfate hemihydrate in concentrated CaCl2 solutions

The disposal of sulfite-rich flue gas desulfurization (FGD) scrubber sludge has been a tough problem. The sludge now finds its prospective utilization way by being transformed into α-calcium sulfate hemihydrate (α-HH). At low pH, atmospheric pressure and 95.0°C, the calcium sulfite hemihydrate (CSH) is oxidized and then changed to α-HH via calcium sulfate dihydrate (DH) in 2.50–3.50m CaCl2 solutions (i.e. CSH→DH→α-HH). Direct transformation from CSH to α-HH (i.e. CSH→α-HH) occurs in a 4.00m CaCl2 solution. The formation of DH at low CaCl2 concentrations is probably attributed to faster heterogeneous nucleation. The increment in CaCl2 molality lowers the water activity, and enlarges the supersaturation gap between DH and α-HH nucleation, which makes α-HH nucleation more competitive. Higher CaCl2 concentration favors the α-HH formation, and nucleation kinetics accounts for the transformation pathway evolution. The preparation of α-HH from the sulfite-rich FGD sludge is of great sense to electric power industry and environmental conservation.

Physico-chemical assessment of a fixated flue-gas desulfurization sludge cap emplaced along with other coal-combustion residues to abate acid mine drainage

Long term monitoring of the physical and chemical effects of using coal-combustion residues (CCRs), in particular fixated flue gas desulfurization (FGD) sludge, as a major component in the reclamation of a pyritic refuse deposit was undertaken to determine the beneficial and detrimental consequences of placing these controversial materials in an unrestricted environment. Monitoring wells, neutron probe access tubes, and weirs were installed before and after reclamation to observe hydrologic conditions and determine how the use of FGD sludge as a recharge barrier was affecting hydrochemical response to ambient weather conditions. Data were collected for six months prior to reclamation and then for an additional 13years (more intensively during the first 5years). Statistical analyses of water levels in the pyritic refuse deposit indicate a shift from precipitation- to barometric-controlled fluctuations. These findings, along with minimal variability in soil moisture within the CCR cap and transient perching of groundwater above the cap, are evidence that recharge of the refuse aquifer has been minimized. Statistically significant improvements in the quality of groundwater on-site and surface water leaving the site include long-term declines in acidity, As, and Fe concentrations within the refuse aquifer, attributed to a decrease in recharge of oxygenated water as supported by an analysis of calculated mineral saturation indices. Long-term declines in acidity and associated trace metals discharging from the site are attributed to the post-reclamation loss of sulfate salts brought to the surface by capillary forces. The results of this study indicate that strategic usage of CCRs in reclamation programs can produce beneficial effects, including acid drainage reductions, that are beyond those achieved using traditional reclamation approaches such as the utilization of mine spoil as capping and fill material.

Stabilization of Flue Gas Desulfurization By-Products with Fly Ash, Cement, and Sialite

Flue gas desulfurization (FGD) sludge is a by-product generated by air pollution control systems used in coal-fired power plants. The objective of this work was to stabilize FGD gypsum and FGD filter cake with Class C fly ash. The effectiveness of other additives, such as cement, cement kiln dust, and sialite was also investigated. The chemical, physical, and mineralogical properties of FGD gypsum and FGD filter cake were analyzed. Compaction, California bearing ratio (CBR), and unconfined compressive strength (UCS) tests were conducted on FGD gypsum and FGD filter cake with fly ash. The UCS tests were also conducted on FGD materials stabilized separately with cement, cement kiln dust, and sialite. This study investigated the environmental implications of these two types of FGD by-products with different additives. The test results indicated that both CBR values and UCS for FGD gypsum and filter cake increased with an increase in fly ash contents. FGD gypsum has the potential to be used in geotechnical fill and embankment directly, while FGD filter cake cannot be used directly in pavements without stabilization.

Utilization of coal combustion byproducts in building blocks

Some mechanical and durability properties of composite material produced with by-products of Orhaneli power plant (flue gas desulfurization sludge, fly ash and bottom ash), cement and hydrated lime were investigated. To improve the mechanical properties (compressive and flexural strength) of this material, steam curing was applied and the effect of chemical admixture (high water reducing agent) was investigated. Some physical properties and water resistance of the mixtures were also determined. Furthermore, microstructure of the specimens was investigated using scanning electron microscopy. Finally, to produce construction elements, prototypes of building blocks were manufactured by using some of these mixtures. All kind of power plant wastes (flue gas desulfurization sludge, fly ash, bottom ash) can be utilized with these mixtures, which consist of 90% of coal combustion byproducts. It seems to be a promising material for composite construction elements such as building blocks.

Metabolic Responses Induced by Serial Harvesting of Alfalfa Pasture Established on Amended Acid Soil

Alfalfa pasture has not been sustainable on the coastal plain of the United States because of its intolerance to soil acidity. This study examined the responses of alfalfa metabolism to differential amendments of acid soil and to serial harvesting. The soil was spatially amended with different quantities of flue gas desulfurization sludge and gypsum after liming to pH 7. The serial harvests oscillated the RNA synthetic activity of glutamate dehydrogenase (GDH) from an oxidized to a reduced state irrespective of the soil amendments. The amplitudes of the redox cycles changed from one harvest to the next, thus demonstrating improved regrowth persistence. The chlorophyll, hexose, nucleotide, and protein contents, and the fructose‐1, 6‐bisphosphatase activity, decreased and fluctuated inconsistently in the successive cuttings. Consideration of the metabolic responses per harvest showed that the alfalfa had optimized saccharide metabolism in the first harvest, optimized RNA metabolism in the second harvest, optimized saccharide and RNA metabolism in the third harvest, and depressed saccharide metabolism in the fourth harvest, thereby optimizing the regrowth potential of the alfalfa pasture. Sustainability of the pasture was conferred by the coordinate compensatory regulation of metabolism in response to the synergistic interaction between the differential amendments and the nitrogen (N) nutrient excreted by the alfalfa into the soil.

Sulfur and Carbon Cycling in a Flue Gas Desulfurization Sludge Disposal Site

Products of a power plant flue gas desulfurization scrubber are discharged into a pond as sludge consisting of calcite (initial δ13C 3.2–3.8‰), gypsum (initial δ34S 7.6–8.6‰), and aqueous solution. Reducing conditions exist below a boundary that appears to move vertically as a function of changes in pond water level. Under reducing conditions, bacteria partially reduce aqueous sulfate to low-δ34S sulfide, consuming organic carbon and generating low-δ13C bicarbonate. Under oxidizing conditions, sulfide is converted to sulfate, leading to calcite dissolution, gypsum precipitation, and isotopic re-equilibration of remaining calcite with dissolved bicarbonate near the pond surface. The gypsum has δ34S near 6‰, and calcite has δ13C as low as -1.7‰; the changes from initial values correspond to predictions based on isotopic balance and reaction stoichiometry. The pond largely contains the products of bacterial reduction. After the pond is abandoned, these products may adversely affect attempts to revegetate the site. Future bacterial reduction may be best controlled by dewatering and limiting the supply of organic matter in percolating surface water.

石炭灰・都市ゴミ焼却灰・脱硫スラッジ混合物からの鉛の溶出挙動

Lead in various wastes is thought to cause serious pollution when the wastes are discarded in the environment. Therefore, its elution behavior from various kinds of ashes has so far been investigated. Here, mixing various wastes at optimum ratio is expected to result in the inhibition of its elution.In the present study, first, elution behavior of lead, artificially added to the mixture of coal ash, municipal waste ash and flue gas desulfurization sludge was investigated by varying added amount of lead and mixing ratio. Remarkable inhibition effects by addition of flue gas desulfurization sludge to the mixture of the coal ash and municipal waste ash were found on the elution of lead. Second, the mechanism of the inhibition effects of lead was discussed by considering the effects of co-existing anions in the leachate. Chemical species of lead eluted were estimated by the stability of various lead complexes formed and their solubility products. It was suggested that lead carbonate formed by the reaction between lead ion produced from lead chloride added and carbonate ion eluted from the desulfurization sludge suppressed the elution of lead. Finally, the contribution of formation of ettringite or similar minerals during the curing process to the lead elution was discussed from the results on the effects of coal ash to municipal waste ash ratio on its elution.

Sulfur transformations related to Revegetation of flue gas desulfurization sludge disposal sites

This study investigated factors controlling redox conditions in flue gas desulfurization (FGD) sludge and identified ways to minimize the production of phytotoxic reduced sulfur (S) species at FGD sludge disposal sites. The oxidation of reduced FGD sludge (Eh ‐385 mV) appears to be a two‐step process mostly controlled by water content. Eighty percent of total sulfide (S‐2) in reduced sludge was oxidized within 20 h of exposure to air with constant water evaporation. When organic carbon (OC) was added to saturated oxidized sludge, the Eh dropped exponentially. Sulfate reduction began at an Eh of about ‐75 mV and reached a maximum at ‐265 to ‐320 mV. Water content, degree of mixing, concentration of OC, and temperature control the rate and extent of reduction of FGD sludge. This suggests that water saturation and OC inputs to revegetated disposal sites should be controlled, especially during warm temperatures, to prevent production of phytotoxic levels of S‐2.

99/01656 Simulation of the heavy metal releases of a bituminous coal-fired power station. Effects of the return of flue gas desulfurization sludges into the firing zone : Berger R. and Krabbe, H. J. VGB Kraftwerkstech., 1998, 78, (9), 100–106. (In German)

99/01656 Simulation of the heavy metal releases of a bituminous coal-fired power station. Effects of the return of flue gas desulfurization sludges into the firing zone : Berger R. and Krabbe, H. J. VGB Kraftwerkstech., 1998, 78, (9), 100–106. (In German)

Evaluation of Revegetation Techniques of a Saline Flue Gas Desulfurization Sludge Pond

AbstractCodisposal of flue gas desulfurization (FGD) sludge with low‐volume generating station waste simplifies disposal but creates a saline, high‐boron (B) waste that may be difficult to revegetate after site closure. Studies on a delta of waste material in a codisposal pond in eastern Arizona evaluated management techniques, amendments, and plants for revegetating this material. One study investigated leaching and ridging techniques and a second evaluated amendment with manure, wood shavings, and fly ash. Four salt‐tolerant grass species and four saltbushes (Atriplex spp.) were evaluated in the two studies. Criteria for success were high survival rates and growth, as measured by grass height and shrub height × width. Leaching salts and B from the waste was not necessary for establishment and growth of transplanted shrubs and grasses. Ridging was not a successful technique, due to limited moisture and high levels of salinity and B on these structures. Gardner saltbush [A. gardneri (Moq.) D. Dietr.] and a fourwing saltbush [A. canescens (Pursh) Nutt.] accession from the site were the most successful shrubs and alkali sacaton [Sporobolus airoides (Torr.) Torr. ‘Saltalk‘] was the most successful grass at this disposal pond. Amendment with manure, wood shavings, or fly ash did not increase plant survival. Growth of grasses was improved with all amendments and was greatest with manure, but growth of shrubs was not improved with any amendment.

Fly Ash Binders in Stabilization of FGD Wastes

This paper presents a study of the integrated management of solid wastes generated in a high-capacity power plant, i.e., coal combustion fly and bottom ash (BA) and flue gas desulfurization (FGD) sludges. Solidification/Stabilization (S/S) processes were tested by analyzing the influence of the variables: binder type, water needs, and land disposal scenario that affect the final solid leaching characteristics. A factorial design of experiments was used to study the influence of these variables in the final S/S solid. After characterization of the leachates according to European regulations, the chemical stability of the S/S solids was analyzed using a standard dynamic leaching test (DLT). A dynamic leaching model of the contaminants (sulfates) contained in the S/S matrix was formulated from the research on the long-term behavior of the solid matrix, establishing the parameters that have an effect on the mobility of the sulfate. One parameter, the effective diffusion coefficient [De (cm2/s)] and its logarithmic expression, the leaching index (LX), were evaluated for each S/S process. Values of 1.51 × 10−11 (cm2/s) ≤De≤ 2.14 × 10−9 (cm2/s) for 100 humidity-cured S/S wastes and 1.98 × 10−11 (cm2/s) ≤De≤ 4.36 × 10−11 (cm2/s) for water bath–cured S/S wastes were obtained for De, leading to LX values of 8.67 ≤ LX ≤ 10.82 and 10.36 ≤ LX ≤ 10.80, respectively. These values suggest that a high immobility was reached in some of the developed S/S processes. The validity of the leaching parameters obtained after a short-term landfill period (56 days) was confirmed after 1 year.

Selected Species and Amendments for Revegetating Saline Flue Gas Desulfurization Sludge: Greenhouse Study

Codisposing low-volume wastes from electrical generating stations with flue gas desulfurization (FGD) scrubber sludge simplifies waste disposal but produces a saline waste that presents unique challenges to revegetation. This greenhouse study identified plants and amendments for revegetating a saline FGD sludge disposal pond in eastern Arizona. Survival and growth of 16 sown accessions plus two vegetatively propagated accessions of inland saltgrass [Distichlis spicata var. stricta (Torr.) Beetle] were investigated in saline FGD sludge (ECₛₑ = 6.65 S m⁻¹). Amendments used included two soils from the disposal site, Claysprings gravelly clay (Typic Torriorthent) and Sheppard sand (Typic Torripsamment), composted steer manure, and N-P-K fertilizer. Soils and manure were added at 2:1 sludge/amendment (v/v). Plants were irrigated with a 1:1 mixture of disposal pond water and untreated well water (EC = 2.09 S m⁻¹). One accession of inland saltgrass, two cultivars of tall wheatgrass [Elytrigia pontica (Podq.) Holub ‘Largo’ and ‘Jose’], Altai wildrye [Leymus angustus (Trin.) Pilger ‘Praireland’l, tall rescue (Festuca arundinacae Schreb. ‘Alta’), and alkali sacaton [Sporobolus airoides (Torr.) Torr. ‘Saltalk’] show promise for revegetating saline FGD sludge disposal sites. Survival rates were the same in unamended sludge and in sludge amended with the clay soil or with N-P-K fertilizer. Plant dry matter produced was the same in unamended sludge and in sludge amended with either of the soils or with N-P-K. Although survival rates were significantly lower with manure than with any other amendment, due to high EC values, growth was significantly greater by all measurements, due to the high fertility of this treatment. Contribution from the Dep. of Soil, Water, and Environ. Sci., Univ. of Arizona, Tucson.

Plant Species for Revegetation of a Saline Flue Gas Desulfurization Sludge Pond

AbstractCodisposing saline wastewater from electrical generating stations with flue gas desulfurization (FGD) scrubber sludge simplifies waste disposal but produces a saline waste that will later require revegetation. This waste is low in macronutrients, contains high levels of salts and B, and has a fine texture. This study identified plants, based on germination test results, that show promise for sowing at an evaporation pond in eastern Arizona where scrubber sludge and wastewater are codisposed. Forty‐four grass, forb, and shrub accessions germinated on filter paper in saline water from the disposal pond. Dilutions of disposal pond water with untreated well water from the site ranged in EC from 0.17 to 3.03 S m−1. Our criteria for evaluating plants to be used in revegetating saline FGD sludge were: (i) ability to germinate in increasing levels of disposal pond water and (ii) ease of establishment from seed. The percentage of pond water that would reduce germination to 50% that of well‐water controls (P50) ranged as high as >100 for the most tolerant plants. Accessions that show promise for sowing at these types of saline waste disposal sites include: Elytrigia pontica ‘Jose’ and ‘Largo’, Atriplex gardneri, Puccinellia airoides, P. distans ‘Fults’, Festuca arundinacea ‘Alta’ and ‘Fawn’, Krascheninnikovia lanata, Kochia prostrata ‘Immigrant’, Panicum virgatum ‘Nebraska 28’, Sporobolus airoides ‘Saltalk’, Leymus angustus ‘Praireland’ and Elymus trachycaulus ‘Pryor’.

Systematic Investigation of the Compositional Variations in Solid Waste Products from Coal Combustion: ABSTRACT

A systematic study of the chemical and physical characteristics of feed coal, fly ash, bottom ash, feed limestone, and flue gas desulfurization sludge has been initiated at a Kentucky power plant. Two units at the power plant are sampled monthly for a two-year period. One unit bums a high-sulfur coal (3 wt % total S); the other unit burns a low-sulfur coal (<1 wt % total S). One focus of the study is to evaluate the variability in feed coal compositions and resulting variability in the composition of combustion solids. Major, minor, and trace element composition and mineralogy are determined on most samples. In addition, modes of occurrence, magnetic properties, stable and radiogenic isotopic composition, organic chemistry, and leachability under different conditions are determined on selected samples. Mass balance calculations show that most elements (data for Hg are not available) are retained in the solid waste products except for Se. The ratios of trace elements in the fly ash to bottom ash for both units are very similar to the order of element volatility reported in the literature. Ni, Cr, and Co show substantial enrichment in the magnetic fraction of the fly ash from the low-sulfur unit. Laboratory leaching ofmore » the fly ash and bottom ash shows that the magnetic particles are very rapidly dissolved by mild acids. Fission track results indicate that U is uniformly distributed within some fly ash cenospheres. Dark, iron-rich glass may have higher concentrations of U than does clear glass. The distribution of As appears to be uniform at low levels in most fly ash particles.« less

Cause and Remediation of Hydrogen Sulfide Emissions from a Sodium‐Based Flue Gas Desulfurization Sludge Disposal Pond

AbstractA flue gas desulfurization (FGD) sludge disposal pond with a history of H2S emissions to the atmosphere was studied to determine the cause of emissions and remediation strategies. The pond receives sludge and associated waters from a single‐pass Na2CO3 flue gas scrubber unit. The pond water is a sodic alkaline brine with large SO3 and S2O3 concentrations (&gt;5000 mg L−1), and hence, an elevated chemical O2 demand. The pond water H2S concentrations are small as a result of periodic H2O2 additions. The sediments, however, have as much as 3500 mg L−1 H2S in the pore water. The production of H2S appeared to originate from the sediments and diffuses through the anoxic water column with little oxidation. Large concentrations of the reduced sulfur species SO3 and S2O3 were present as a result of the flue gas desulfurization process and incomplete oxidation of H2S. The pond was reconstructed to circulate the water through an air injection system that was designed to oxidize the SO3 and S2O3 to SO4, and thereby reduce the chemical O2 demand. After the installation of the air injection system, emissions of H2S ceased and the concentrations of SO3 and S2O3 were reduced by at least a factor of 10 within 3 to 4 wk. The production of H2S in the sediments, however, did not appear to be affected, nor did it appear that it will be reduced in the future by the air injection system.

Effects of leaching on pore size distribution of solidified/ stabilized wastes

Chemical solidification/stabilization processes are commonly used to immobilize metals in fly ash and flue gas desulfurization (FGD) sludges and to convert these wastes into monolithic or granular materials with better handling properties and reduced permeabilities. This study evaluated the role of pore structure of solidified materials during leaching. The solidified material's initial pore structure, changes in the pore structure which result during leaching, and the effects of pore structure on leaching are discussed. It was found that pore structures varied depending upon the wastes used and the solidification mix formulations tested. After acetic acid leaching, the pore structures of samples changed remarkably. Total pore volumes and pore sizes increased. The percentage of larger pores (diameter greater than 6000 nm) increased from below 5% for before-leaching samples to above 23% for after-leaching samples. The higher the alkalinity in a sample, the greater the change of pore structure due to leaching. Changes in pore structure were primarily due to leaching of calcium hydroxide.