Fluidized Bed Combustion Ash Research Articles

Decolorization of Coking Wastewater by Mineral Adsorbents

The decolorization of coking wastewater is an urgent issue for coking wastewater treatment. Using mineral adsorbents to deal with the coking wastewater is an effective way to solve the above problem. In this paper, fluidized bed combustion (FBC) ashes, diatomite and clinoptiolite were used to decolorize the coking wastewater. UV-Vis was used to estimate the decolorization efficiency of the FBC ashes. The materials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the sequence rule for the decolorization effect of three mineral adsorbents is FBC ashes > diatomite > clinoptiolite. In addition, the chroma of treated coking wastewater reduced from 320 times to less than 5 times in the comparison of raw wastewater. It is much lower than the chroma of GB8978-1996 1A discharge standard. The excellent decolorization effect of FBC ashes might be due to large contains of CaO and f-CaO.

Study on the Utilization of FBC Ashes as Cement Admixture

Compared with ordinary Pulverized Coal Combustion (PC) fly ashes, Fluidized Bed Combustion (FBC) ashes have some special properties. The effect of FBC ashes content on the strength of cement mortar was studied, and the physical properties of FBC ashes-cement mortar with 30% FBC ashes were also investigated. The results show that the flexural and compressive strength at 7 and 28 days of the mortar gradually decreases with the increase of FBC ashes content. Under the same dosage, the strength of FBC ashes-cement mortar is greater than that of PC fly ashes-cement mortar. The FBC ashes-cement system presents a normal setting time but poor soundness with more than 3.5% SO3. This work confirms that the properties of FBC ashes-cement system are superior to those of PC fly ashes-cement system when SO3 content is no more than 3.5%.

Effect of Coal Combustion By-products on Phosphorus Runoff from a Coastal Plain Soil

Coal combustion by-products can lower soil phosphorus (P) solubility, but few studies have assessed their effect on runoff P. A soil with elevated P content was amended with fluidized bed combustion ash, flue gas desulfurization gypsum, and anthracite refuse ash at rates of 0–40 g kg−1 soil, and runoff from small plots was monitored over 3 years. In the first year, by-products lowered dissolved P in runoff by up to 47% below the untreated control; however, effects did not persist into the remaining years of the study. Total P losses were not significantly affected by coal combustion by-products, likely because of elevated particulate P losses. Water-extractable P was up to 40% less in treated soils than in untreated soils across the 3 years. Results demonstrate that although coal combustion by-products readily lower P solubility in soils, their impact on P losses in runoff can be undermined by erosional processes.

Assessing the effects of FBC ash treatments of metal-contaminated soils using life history traits and metal bioaccumulation analysis of the earthworm Eisenia andrei

Earthworms ( Eisenia andrei) were exposed, in controlled conditions, to metal-contaminated soils previously treated in situ with two types of fluidized bed combustion ashes. Effects on this species were determined by life history traits analysis. Metal immobilizing efficiency of ashes was indicated by metal bioaccumulation. Ashes-treated soils reduced worm mortality compared to the untreated soil. However, these ashes reduced both cocoon hatching success and hatchlings numbers compared to the untreated soil. In addition, sulfo-calcical ashes reduced or delayed worm maturity and lowered cocoon production compared to silico-alumineous ones. Metal immobilizing efficiency of ashes was demonstrated for Zn, Cu and to a lesser extent Pb. Only silico-alumineous ashes reduced Cd bioaccumulation, although Cd was still bioconcentrated. Thus, although ash additions to metal-contaminated soils may help in immobilizing metals, their use might result, depending on the chemical nature of ashes, to severe detrimental effects on earthworm reproduction with possible long term consequences to populations.

Changes in soil properties in a fluvisol (calcaric) amended with coal fly ash

Fluidized bed combustion ash (FBC) is a by-product from coal-fired power stations used for many decades in concrete, cement and brick manufacturing and more recently for trace metal immobilization and pesticide retention in soils. Moreover FBC ash has been recommended by some authors as a soil amendment in agriculture for its nutrient supply. In this study silico-aluminous (SiAl) and sulfo-calcic (SCa) fly ashes have been added to a fluvisol (calcaric) sampled in the Rhine River plain (Germany) in order to investigate the physical, chemical and physico-chemical possible modifications of the amended soil. Earthworms were introduced into microcosms hydrated with a solution of water and CaCl 2 (3.7 10 − 4 mg/L; pH = 6.2) and stabilized during 7 and 14 weeks. Batch leaching tests were performed during 6 weeks on the amended soil in order to obtain data on the mobilization potential of major elements (NH 4 +, Na +, K +, Mg 2+, Cl −, Ca 2+, NO 3 −, SO 4 2−, PO 4 3−, H 4SiO 4) and trace elements (Sr, Ba, V, Zn, Cu, Co, As, Ni, Mo, Cr, Cd, Pb) during ash–soil–water interactions. The main modification is an increase in pH (≈ 12) of soil water in soil amended with sulfo-calcic ash, whereas soil pH only slightly changes in the other soil as compared to control soil. This alkaline pH causes a strong mortality of the macrofauna and a higher mobility of Co, Ni and V on the contrary to Cr, Cu, Pb and Zn which are less mobile and more strongly retained by soil. Soil physico-chemical properties remain generally similar to control soil in soil amended with silico-aluminous ash (SiAl) but show major differences in the case of soil amended with sulfo-calcic ash (SCa). The sulfo-calcic ash therefore seems less adapted to integration in soils from an agricultural and farming point of view, contrary to the silico-aluminous ash which increases the cation exchange capacity, thus improving the nutrient and water reserve for plants.

X-ray powder diffraction-based method for the determination of the glass content and mineralogy of coal (co)-combustion fly ashes

The relevance of Al–Si glass in a number of fly ash applications, such as use as a pozzolanic material, zeolite synthesis, and geopolymer production, necessitated research towards investigation of methods for an easy and consistent determination of the glass content in this coal (co)-combustion by-products. A glass standard-addition X-ray powder diffraction (XRD)-based method is proposed in this study as an alternative to the non straightforward procedure of conventional methods for determining the amorphous components, mainly by difference of the total mass and the addition of quantified crystalline species. A >99% Al–Si glass slag sample was selected as a standard for glass. A number of glass standard/fly ash mixtures were performed on Fluidized Bed Combustion (FBC) and pulverized coal combustion (PCC) fly ashes and subsequently analyzed by XRD. The method provides results closer to quantitative proportions of the Al–Si amorphous material of this (co)-combustion by-product, with a range of values <3% when compared with those obtained by the conventional Reference Intensity Method (RIM) method, demonstrating suitability and consistence of the procedure. Furthermore, by the proposed method, the requirement of previous determination of the mineral phases of conventional techniques is avoided. Coupled with the easy calculations, this allowed a fast determination of the glass content of (co)-combustion fly ash. The mineralogy of FBC and PCC fly ash was also investigated using the RIM method. The occurrence and proportions of the crystalline components in fly ash are in line with the combustion technology and their inherent operational parameters, especially the (co)-combustion temperature. The FBC fly ash shows the highest content of relic phases from feed coal (quartz, illite, calcite, and feldspars) and lower contents of amorphous components. The PCC fly ash are characterized by the highest proportions of mullite and Al–Si glass and low contents of quartz an other relict phases. The occurrence and distribution of anhydrite and Fe-oxide species appears to be related to the content of Ca and Fe in the feed fuels, showing slightly higher contents in FBC than in PCC fly ash.

Tracing the interaction of acid mine drainage with coal utilization byproducts in a grouted mine: Strontium isotope study of the inactive Omega Coal Mine, West Virginia (USA)

Abstract In order to ameliorate acidic discharge, the inactive Omega Coal Mine, West Virginia was partially filled by injection of a grout consisting of 98% coal utilization byproducts (CUB), including fluidized bed combustion ash and fly ash, and 2% Portland cement. In this study, discharge chemistry and Sr isotope ratios were determined to identify and quantify the extent of interaction between mine waters and the CUB–cement grout. Eight sampling sites were monitored around the downdip perimeter of the mine. The major and trace element chemistry of the discharges was generally not sufficient to distinguish between discharges that interacted with grout and those that did not. Elements that showed the most separation include K and As, which were elevated in some waters that interacted with CUB–cement grout. In contrast, the Sr isotope ratios clearly distinguished discharges from grouted and non-grouted areas. Discharges that bypassed the grouted portions had 87 Sr/ 86 Sr ratios ranging from 0.71510 to 0.71594, while two discharges that interacted with grout had ratios in the range of 0.71401–0.71456. The Treatment Inlet, which includes both grouted and ungrouted discharges, yielded intermediate isotopic ratios. Leaching experiments on CUB–cement grout, coal and surrounding rocks are consistent with the isotopic trends observed in the discharges. Based on these results, waters that interacted with grout received 30–40% of their Sr from the CUB–cement grout material. These results suggest that the grout material is chemically eroding at a rate of approximately 0.04% per year. This novel application of the Sr isotope system illustrates its ability to sensitively track and quantify fluid interaction with coal and CUB-based grout.

Potential use of stockpiled circulating fluidized bed combustion ashes in controlled low strength material (CLSM) mixture

This paper presents the results of an experimental investigation carried out to evaluate the potential use of stockpiled circulating fluidized bed combustion (CFBC) ashes in developing controlled low strength material (CLSM) in which stockpiled CFBC ash was partially or fully replaced with Class F fly ash. Prior to develop CLSM mixture, basic material characterization of stockpiled CFBC ash was executed to identify the physical, chemical, and mineralogical changes due to aging process of the stockpiled ashes. For CLSM mixture, stockpiled CFBC ash was replaced with five different percentages of Class F fly ash by weight (20%, 40%, 60%, 80%, and 100%). Tests were performed to measure fresh and hardened properties of CLSM mixtures. It was found that the stockpiled CFBC ash can be effectively used in developing CLSM mixtures with restricted use of portland cement and fly ash in the direction of sustainable development.

Utilization of blended fluidized bed combustion (FBC) ash and pulverized coal combustion (PCC) fly ash in geopolymer

In this paper, synthesis of geopolymer from fluidized bed combustion (FBC) ash and pulverized coal combustion (PCC) fly ash was studied in order to effectively utilize both ashes. FBC-fly ash and bottom ash were inter-ground to three different finenesses. The ashes were mixed with as-received PCC-fly ash in various proportions and used as source material for synthesis of geopolymer. Sodium silicate (Na 2SiO 3) and 10 M sodium hydroxide (NaOH) solutions at mass ratio of Na 2SiO 3/NaOH of 1.5 and curing temperature of 65 °C for 48 h were used for making geopolymer. X-ray diffraction (XRD), scanning electron microscopy (SEM), degree of reaction, and thermal gravimetric analysis (TGA) were performed on the geopolymer pastes. Compressive strength was also tested on geopolymer mortars. The results show that high strength geopolymer mortars of 35.0–44.0 MPa can be produced using mixture of ground FBC ash and as-received PCC-fly ash. Fine FBC ash is more reactive and results in higher degree of reaction and higher strength geopolymer as compared to the use of coarser FBC ash. Grinding increases reactivity of ash by means of increasing surface area and the amount of reactive phase of the ash. In addition, the packing effect due to fine particles also contributed to increase in strength of geopolymers.

CO2 and SO2 uptake by oil shale ashes

In the present research, CO2 and SO2 binding ability of different oil shale ashes and the effect of pre-treatment (grinding, preceding calcination) of these ashes on their binding properties and kinetics was studied using thermogravimetric, SEM, X-ray, and energy dispersive X-ray analysis methods. It was shown that at 700 °C, 0.03–0.28 mmol of CO2 or 0.16–0.47 mmol of SO2 was bound by 100 mg of ash in 30 min. Pre-treatment conditions influenced remarkably binding parameters. Grinding decreased CO2 binding capacities, but enhanced SO2 binding in the case of fluidized bed ashes. Grinding of pulverized firing ashes increased binding parameters with both gases. Calcination at higher temperatures decreased binding parameters of both types of ashes with both gases studied. Clarification of this phenomenon was given. Kinetic analysis of the binding process was carried out, mechanism of the reactions and respective kinetic constants were determined. It was shown that the binding process with both gases was controlled by diffusion. Activation energies in the temperature interval of 500–700 °C for CO2 binding with circulating fluidized bed combustion ashes were in the range of 48–82 kJ mol−1, for SO2 binding 43–107 kJ mol−1. The effect of pre-treatment on the kinetic parameters was estimated.

Pozzolanic reaction kinetics of coal ashes

The pozzolanic reactivity was determined by the hydration kinetics of pozzolanic reaction based on the fact that the hydration products of active SiO2 and Al2O3 with lime were soluble in dilute hydrochloric acid. The results show that the pozzolanic reaction of active SiO2 and Al2O3 of coal ashes follows apparent first-order kinetics. The reaction rate constant of FBC ashes is greater than that of PC ashes, while the activation energy of the former is lower than that of the latter. It is confirmed that the pozzolanic activity of fluidized bed combustion(FBC) ashes is significantly higher than that of PC ashes, and the reaction barrier of the former is lower than that of the latter, because the microstructures of FBC ashes, such as mineralogical composition, morphology and polymerization degree of [SiO4] and [AlO6] are more favorable to the pozzolanic activity development than those of PC ashes.

Potential use of stockpiled circulating fluidized bed combustion ashes in manufacturing compressed earth bricks

There is currently 123 million tons of coal combustion by-products produced in US each year. Among these include fly ash, bottom ash, boiler slag, and flue gas desulphurization material. Of that approximately 40% are utilized as a construction material in cement manufacturing, roadway construction, and others. However, the utilization of some ashes such as those produced by fluidized bed combustion has been limited due to their inherent high sulfate and carbon content. This paper is aimed at the evaluation of the potential use of stockpiled circulating fluidized bed combustion ash (SCFBCA) to develop compressed earth brick (CEB). Laboratory tests were conducted to determine the physical, chemical, and mineralogical properties with respect to SCFBCA. A series of tests were carried out to evaluate the properties of the bricks related to filler and binder types on compressive strength, density, and absorption. Test results indicate that SCFBCA can be used to manufacture CEB. Subordinately, test results may provide a means to reduce a waste disposal problem while providing the brick industry with a new, useful, low cost raw material.

Sonochemical treatment of FBC ash: A study of the reaction mechanism and performance of synthetic sorbents

This work explores the reaction mechanisms for the sonochemical-enhanced carbonation of fluidized bed combustion (FBC) ash. Ashes from Nova Scotia Power’s 165MWe circulating fluidized bed combustor (CFBC) as well as synthetic ash prepared directly from limestone have been used. Acetone tests were carried out using pure acetone as well as acetone/water mixtures (4:1 ratio). Tests with acetone demonstrated that, without previous hydration of the ash, significant carbonation is not achieved. Experiments were also conducted to determine the role of hydration temperature on the carbonation of FBC ash. X-ray diffraction (XRD) analysis of synthetic ash after sonication has also been carried out. Analysis of the data obtained revealed that the process is well described by a series reaction mechanism. Initial hydration temperature does not appear to significantly impact the carbonation of FBC ash. Synthetic ash does not behave like FBC ash due apparently to its extreme susceptibility to the size reduction capability of ultrasonics.

Disposal of Waste Liquor from 2,5-Dichlorodisulfanilic Acid Production

Three alternative procedures were worked out for disposal of waste liquor from production of 2,5-dichlorodisulfanilic acid [CAS No. 88-50-6]. This liquor is a hazardous liquid waste which, if discharged into a wastewater treatment plant without any treatment, inhibits processes of biological treatment. The first alternative utilizes stabilization/solidification technology by using fluidized-bed combustion ash. The second alternative consists in treating the liquor in a flow-through columnpacked with active carbon black as an adsorbent and discharging of the treated liquor, which already displays an acceptable chemical oxygen demand level after removal of organic pollutants by adsorption, into a wastewater treatment plant. The third alternative comprises of passing the waste liquor through the column with active carbon black and stabilization/solidification of the treated liquor by fluidized bed combustion ash. Efficiency of the liquor disposal in cases of stabilization/solidification was evaluated by determining dissolved organic carbon content, conductivity, pH, and ecotoxicity of test specimens' leachates. From results it follows that the proposed procedures represent efficient disposal of given liquid waste.

Effect of fluidized bed combustion ashes used in metal polluted soil remediation on life history traits of the oligochaeta Eisenia andrei

The aim of the present work was to investigate the effects of two fluidized bed combustion (FBC) ashes (silico-alumineous and sulfo-calcical) used as immobilizing agents for metals in contaminated soils, on the earthworm Eisenia andrei life history traits in OECD artificial soil. A significant mortality of either juveniles or mature worms was observed following silico-alumineous (>60% mortality) or sulfo-calcical (100% mortality) ashes addition. This effect was due to a transient pH rise of soil. No mortality occurred when worms were introduced eight weeks after soils were amended with FBC ashes. However, growth rates were significantly reduced for both treatments and both ashes exhibited sub-lethal effects likely to affect population dynamics. Thus, cocoon productions were reduced for both amendments and no hatching was recorded with sulfo-calcical ashes. Most of the harmful effects observed on worms growth and reproduction could be attributed to an increase of pH and/or an osmotic disturbance caused by FBC ashes, especially sulfo-calcical ones.

Forensic Examination of Severe Heaving of Embankment Constructed with Fluidized Bed Combustion Ash

Coal combustion by-products (CCB) are widely used as structural fill materials in embankment construction works. Fluidized bed combustion (FBC) units, which are used to burn coal, have an advantage over the conventionally used pulverized coal units because they can be used to burn even low-grade or high-sulfur content coal. FBC technology emerged from efforts to reduce the emission of pollutants. A roadway embankment was constructed in 1995 with 60% FBC ash, 35% stoker ash, and 5% Class-F fly ash as part of the South Russell Road extension work at Purdue University, West Lafayette, Indiana. The embankment length, maximum height, and crest width are approximately 200 m, 10 m, and 20 m, respectively. The side slopes are 3:1 (H:V). Heaving of the embankment was observed during and after construction, and the pavement exhibited severe damage at several locations. A forensic investigation of the possible causes and mechanisms for this swelling behavior was undertaken. X-ray diffraction and scanning electron microscopic studies were performed to compare the mineralogical phase composition of fresh samples and samples collected from the heaved embankment. The test results indicated that the formation of ettringite led to the swelling of the embankment, which caused cracking of the pavement. In addition, one-dimensional swelling tests on fresh FBC ash samples, as well as on samples collected from the embankment that underwent heaving, were conducted in a consolidometer to quantify the expansive behavior of this material.

Alkaline injection technology: Field demonstration

In December 2001, 2225 tonnes of fluidized bed combustion (FBC) ash were injected into an abandoned coal mine in eastern Oklahoma. Post-injection monitoring continued for 24 months, during which the mine system appeared to be reestablishing equilibrium with CO 2 in the mine headspace. Alkalinity and pH gradually increased, and as of December 2003 were roughly 65 ppm and 7.3, respectively. Metal concentrations were still significantly lower than pre-injection levels, but iron and manganese concentrations had increased from non-detect levels shortly after injection to roughly 30 ppm and 1.25 ppm, respectively. Aluminum, nickel, and zinc were less than pre-injection concentrations and did not appear to be increasing (roughly <PQL, 0.02 ppm, and 0.1 ppm, respectively). Arsenic and boron were not identified in concentrations that were of concern for protecting freshwater aquatic communities; however, selenium was well above the criterion continuous concentration and the maximum contaminant level. There were obvious improvements observed in the receiving environment—benthic habitat recovery and the return of fish species. However, additional monitoring is needed to determine the duration of the treatment and to evaluate the applicability of the treatment technology.

Understanding the Behavior of Calcium Compounds in Petroleum Coke Fluidized Bed Combustion (FBC) Ash

With growing understanding of the differences between solid residues from the fluidized bed combustion of petroleum coke and of coal, the significance of fuel-derived and sorbent-derived components of the ash has become clearer. It is well documented that hydration of the ashes is necessary prior to disposal or utilization or as a reactivation method. Initially, hydration of the lime was thought to involve water reacting only with CaO to form Ca(OH)2 but when the free lime content of the ashes is looked at before and after hydration, it is apparent that the process is more complex. Detailed analyses have shown that the free lime can decrease and vary within the same ash in different particle size ranges. The complexity of the reactions is reflected in problems with the assessment of the free lime content of the materials and the effect of hydration on different particle size fractions of the ash. The free lime content of the ash is significantly lower than expected based on the elemental analysis. Bed ash from the circulating fluidized bed combustion boilers owned and operated by the Nelson Industrial Steam Company Ltd. (NISCO) was examined in detail to elucidate the fate of calcium in the ash during hydration, using a range of techniques. The objective of the study is to determine the amount of CaO available for hydration/reactivation and to better understand interactions of Ca and other mineral components of the ash. Analysis results indicate that in NISCO ashes up to about 6% of the analytical CaO may be combined as acid soluble and insoluble OCCs (other calcium compounds). This implies up to about 10% less free lime than would be inferred from standard chemical analyses. About 1% of the missing CaO can be present as acid insoluble Ca and Mg vanadates, with up to 2% bound in soluble OCCs. The remaining 3-4% is still not accounted for. It is clear that even very minor quantities of mineral matter, other than CaO or CaSO4, associated mainly with the coarser size fractions, are important. The amount of bound water in the hydrated ash, other than that combined in portlandite or brucite, can be as large as 3-5%. This cannot be ignored when sample mass change on hydration or heating is used as a measure of the extent of CaO to Ca(OH)2 conversion.

Injection of Fluidized Bed Combustion Ash into Mine Workings for Treatment of Acid Mine Drainage

A demonstration project was conducted to investigate treating acid mine water by alkaline injection technology (AIT). A total of 379 t of alkaline coal combustion byproduct was injected into in an eastern Oklahoma drift coal mine. AIT increased the pH and alkalinity, and reduced acidity and metal loading. Although large improvements in water quality were only observed for 15 months before the effluent water chemistry appeared to approach pre-injection conditions, a review of the data four years after injection identified statistically significant changes in the mine discharge compared to pre-injection conditions. Decreases in acidity (23%), iron (18%), and aluminum (47%) were observed, while an increase in pH (0.35 units) was noted. Presumably, the mine environment reached quasi-equilibrium with the alkalinity introduced to the system.

Application of Pressurized Fluidized Bed Combustion Ash to Phosphorous Adsorbent

Typical calcium silicate powder, wollastonite, was mechano-chemically activated in air for 24h with a vibration ball-mill. The cakes of the vibration ball-milled wollastonite added with a fair amount of water and Pressurized Fluidized Bed Combustion (PFBC) ash were carbonated at 80°C in 0.33MPa CO2 for 3h. The removal efficiencies of phosphorous for the carbonated specimens were investigated by immersing them in Na2PO4 aqueous solution containing 5ppm phosphorous. After immersing the specimens for prescribed duration in the test solution, the remaining amount of phosphorous in a supernatant liquid was measured by an inductively coupled plasma spectroscopy or a molybdenum blue method. Ca ion concentrations dissolved from specimens were measured with a selective electrode instruction. The addition of PFBC ash containing calcium sulfate increased a pore volume of the consolidated wollastonite by carbonation and the Ca ion released into water. As a result, the removed efficiencies of phosphorous for the specimens markedly improved compared with those without PFBC ash. The removed rate of phosphorous showed large temperature dependence, and crystallization process are thought to be the rate determining one of the phosphorous elimination.