Gypsum Flue Gas Research Articles

Microbial Response to Sodic Soil Amendments: Flue-Gas Gypsum, By-Product Lime, and Langbeinite

ABSTRACT Amendments are commonly applied to soil to ameliorate sodic conditions, but their effect on improving microbial activity depends on the severity of sodicity and the types and rates of amendments applied. Changes in metabolic activity in response to three chemical amendments (flue-gas gypsum (FG), spent lime, and langbeinite) applied at three rates to two sodic soils were measured using infrared gas analyzer during 76 days of incubation. Spent lime had the greatest influence on microbial activity at rates of 33.6 and 67.2 Mg ha−1, and at the highest rate of application (67.2 Mg ha−1) cumulative respiration was over two times greater than the control for both soils. High rates of langbeinite yielded the lowest respiration but were not significantly different than the control and the FG had no significant influence on respiration. The use of spent lime increased microbial activity which, in turn, may improve soil health through increased microbial activity.

Growth of indoor fungi on gypsum.

To have a better understanding of fungal growth on gypsum building materials to prevent indoor fungal growth. Gypsum is acquired by mining or as a by-product of flue-gas desulphurization or treatment of phosphate ore for the production of fertilizer. Natural gypsum, flue-gas gypsum and phosphogypsum therefore have different mineral compositions. Here, growth of fungi on these types of gypsum was assessed. Conidia of the indoor fungi Aspergillus niger, Cladosporium halotolerans and Penicillium rubens were inoculated and observed using microscopic techniques including low-temperature scanning electron microscopy. Elemental analysis of gypsum was done using inductively coupled plasma atomic emission spectroscopy and segmented flow analysis. Moisture content of the gypsum was determined using a dynamic vapour sorption apparatus. Aspergillus niger, C. halotolerans and P. rubens hardly germinated on natural gypsum and flue-gas gypsum. The latter two fungi did show germination, outgrowth, and conidiation on phosphogypsum, while A. niger hardly germinated on this substrate. Other experiments show that C.halotolerans and P. rubens can develop in pure water, but A. niger does not. The observations show that the lack of germination of three indoor fungi is explained by the low amount of phosphor in natural, flue-gas and laboratory-grade gypsum. Additionally, C. halotolerans and P. rubens can develop in pure water, while conidia of A. niger do not show any germination, which is explained by the need for organic molecules of this species to induce germination. Indoor fungal growth is a potential threat to human health and causes damage to building materials. This study possibly helps in the application of the right type of gypsum in buildings.

A concise algorithm for calculating absorption height in spray tower for wet limestone–gypsum flue gas desulfurization

In this paper, a concise model for wet limestone–gypsum flue gas desulfurization system with spray tower has been presented, aiming at the prediction of the absorption height in a spray tower. The equations of droplet motion and mass balance were incorporated and developed to simulate the droplet movement, distribution and mass transfer of SO2 in the absorption section. The calculation results were in good agreement with the plant values of the absorption height. The influences of operating parameters on the absorption height were analyzed. The results show that absorption height declines with increasing liquid–gas ratio and pH value of the slurry, and increases with increasing droplet diameter, gas flow rate, gas temperature, inlet SO2 concentration and absorption efficiency, respectively. As the most sensitive parameter, the droplet diameter is crucial for the good prediction of absorption height. This model can provide engineering guidance to design a spray tower absorber.

The Treatment and Recycling of FGD Waste

At present, wet lime - gypsum flue gas desulfurization (FGD) technology is very common in the field of gas desulfurization technology. In addition, wet carbide slag - gypsum FGD and Magnesia FGD are also used. In the process of eliminating SO2, with the first two technology, the byproducts of desulfurization wastewater and gypsum will be produced; With Magnesia FGD, the byproducts of magnesium sulfite and magnesium will be produced. The way to utilize desulfurization wastewater, gypsum and magnesium comprehensively and to achieve circular economy is worth exploring.

Reduction of Freshwater Usage of a Coal Fired Power Plant with CCS by Applying a High Level of Integration of All Water Streams

Abstract The integration of the recently built 1 070 MW coal-fired unit in Rotterdam (Netherlands) with the proposed new 250 MW demonstration carbon capture unit of the Rotterdam Opslag en Afvang Demonstratieproject (ROAD) would lead to a substantial reduction in freshwater usage. This is partly due to the power plant design, the most relevant features being the seawater direct cooling and the limestone gypsum Flue Gas Desulfurization (FGD); and partly due to the high level of integration. This paper describes the water and waste streams of the capture plant, including quality and (re-) use in the power plant. The implications for a full scale capture are discussed.

Kinetic Analysis of Paper White Mud Dissolution at Constant pH

One of the most important steps in the wet limestone–gypsum flue gas desulfurization (WFGD) process is limestone dissolution, which provides the dissolved alkalinity necessary for SO2 absorption. Accurately evaluating the rate controlling step in sorbent dissolution process is important in the design and efficient operation of WFGD plants. In the present work, the kinetics of paper white mud(PWM) in dissolution process has been studied by using a pH-stat method. The results obtained indicated that PWM dissolution in WFGD conditions obeys the modified shrinking core model. PWM dissolution kinetics follows the film diffusion and surface reaction control and the rate controlling step of PWM is film diffusion control. The activation energies of PWM in film diffusion and surface reaction steps are 11.9±0.7 kJ/mol and 13.7±1.3 kJ/mol, respectively.

Experimental study on the oxidative absorption of Hg0 by KMnO4 solution

The wet FGD system is widely recognized as the co-effective removal system for oxidized Hg vapor species and SO2. In this study, a purpose-built device was designed for this experiment and several factors potentially affecting the Hg0 removal efficiency were systematic investigated, including different types of oxidants, pHs and concentrations of potassium permanganate, reaction temperatures, Hg0 inlet concentrations, O2, SO2 and NO concentrations, and different types of absorption solutions. Results indicate that pHs and KMnO4 concentrations, reaction temperatures, SO2 and NO concentrations all have a strong influence on the removal of Hg0, and the inlet concentrations of Hg0 and O2 contribute little to the removal of Hg0. SO2 could significantly inhibit the removal of Hg0, the negative effect is serious especially at lower SO2 concentration, and SO2 could lead to the re-emission of Hg0. Hg0 could be removed effectively by using CaCO3+KMnO4 solution, when the KMnO4 concentration in the CaCO3+KMnO4 solution was 1.5mmol/L, the removal efficiencies of SO2, NO and Hg0 were 100%, 40.69% and 90.58%, respectively. So, considering the application to the practical engineering, adding 1.5–2mmol/L KMnO4 into limestone–gypsum flue gas desulfurization systems is necessary. This technology is a promising method for the simultaneous removal of NO, SO2 and Hg0.

Particle Separation with a Hydro-Cyclone Separator in a Wet Limestone Gypsum FGD Process

A hydro-cyclone was applied to the separation of gypsum, a byproduct of the wet limestone gypsum flue gas desulfurization (FGD) process, that uses limestone as the raw material. Using a high slurry concentration, similar to that used in an actual plant, the effect of the inlet shape and ceiling clearance of the hydro-cyclone was examined, and a model for predicting the efficiency of separation is proposed.The results indicate that the 50% cut size decreases when the inlet width ratio is decreased. Over the entire range of inlet width ratio, the limestone content of the blow-down flow decreased by approximately half, compared with that of the feed, and it was confirmed the purity of the gypsum could be improved by decreasing the limestone content.When the ceiling clearance of the hydro-cyclone was changed, an optimum ceiling clearance for obtaining a minimal cut size was found.A model for predicting the slurry concentration that is proportional to the solid throughput of a hydro-cyclone and the improvement in gypsum purity in an actual plant is proposed. The results of this calculation model agreed well with experiment data.

Bisulfite Oxidation Reaction Rate in a Bubbling Tank

In wet limestone gypsum Flue Gas Desulfurizers, flue gas is washed with CaCO 3 -water slurry on the wet walls of a vertical absorption tower, where SO 2 and O 2 are absorbed to form CaSO 3 and CaSO 4 . Though it is required to capture sulfur into calcium sulfate, which is neutral to the environment as deposited, CaSO 3 is not always oxidized completely there to CaSO 4 due to insufficient residence time of slurry on the wet walls and the low absorption rate of oxygen. The rest CaSO 3 should be oxidized in a bubbling tank just under the tower. Therefore appropriate air bubble injectors are required to supply oxygen, just as much as necessary and enough, into the slurry in the tank. Here is proposed an Air Rotary Sparger (ARS) for the vertically and horizontally uniform distribution of small air bubbles in the tank and its performance is investigated with a small-sized conventional paddle type model with a central air injection hole on the bottom and two ARS models.

Contaminant mobility in soils amended with fly ash and flue-gas gypsum: Intact soil cores and repacked columns

The impact of the land application of coal combustion by-products, fly ash (FA) and flue-gas desulfurization gypsum(FDG), to coarse-textured soils of the southeastern U.S.A. wasinvestigated using batch and dynamic column techniques. Two FAsamples, one an alkaline FA (Alk-FA) and the other an acidic FA(Acid-FA), were evaluated alone and in combination with FDG assoil amendments to an Appling loamy sand (Typic Hapludults). Theeffects of these waste products on clay dispersion, soilhydraulic conductivity (Ksat) and the migration ofcontaminants such as Arsenic (As) and Boron (B) were studiedusing intact soil cores and repacked soil columns. FA or combinationsof FA + FDG were applied to the surface of intact soil cores (10 Mg ha-1) and repacked soil columns or incorporated withinrepacked soil columns. The columns were saturated and thenleached for a prescribed number of pore volumes to simulateleaching conditions in the field. Effluent pH, electricalconductivity (EC), and turbidity were monitored and leachatefractions were collected for B, As, Ca, Mg, K and Na analysis.Both FA materials were ineffective at decreasing the inherentdispersibility of clay from the Ap horizon in batch tests.In fact, high application rates of the Alk-FA induced some claydispersion in the well-flocculated Bt soil materials, andcolumn results suggest that incorporating the Alk-FA within thesurface soil may actually reduce Ksat. In contrast,treatments with FDG were highly effective at inducing rapid clayflocculation in batch tests and eliminating effluent turbidityfor intact and repacked soil columns. Boron was readily mobilefrom both intact and repacked soil columns, a majority of whichleached from the columns within the first three pore volumes.Boron leaching was greater for combined treatments (FA + FDG),possibly indicative of enhanced solubilization in the presenceof FDG or sulfate (SO4 2-) competition for sorptionsites. Arsenic levels present in the leachates from FA and FDGcolumns were generally lower than control columns and roughlycorrelated with effluent turbidity. Combined treatments (FA +FDG) enhanced Mg and K leaching due to the added competition ofCa for cation exchange sites. Following leaching, the intactsoil cores were sectioned at 5 cm intervals and the pH and EC ofthe soil, as well as the vertical distribution of As and B, weredetermined. Levels of residual As were only slightly higher in the upper section of the FA-amended columns, showing little downward movement, but no clear trend in residual B was observed due to its greater mobility.

Catalytic oxidation of calcium bisulfite in the wet limestone–gypsum flue gas desulfurization process

A study on the oxidation of calcium sulfite catalyzed by Mn 2+ is presented in this paper. A laboratory-scale well-mixed thermostated reactor was used, with continuous feeding of both gas and liquid phase. The gas phase was a mixture of oxygen and nitrogen, with O 2 partial pressure varying from 5.1 to 40.5 kPa. The liquid phase was obtained by mixing inside the reactor two separate aqueous solutions, one obtained by dissolving Ca(OH) 2 into a SO 2 solution, and the other one containing manganous sulfate. The temperature was kept constant in all the experiments at 45°C. The results show that increasing catalyst concentration, the transition takes place from slow kinetic to slow diffusional and eventually to fast reaction regime.

Calcium Bisulfite Oxidation Rate in the Wet Limestone−Gypsum Flue Gas Desulfurization Process

In this paper oxidation of calcium bisulfite in aqueous solutions was studied, in connection with the limestone−gypsum flue gas desulfurization process. Experimental measurements of the oxidation rate were carried out in a laboratory scale stirred reactor with continuous feeding of both gas and liquid phase. A calcium bisulfite clear solution was used as liquid phase, and pure oxygen or mixtures of oxygen and nitrogen were used as gas phase. Experiments were carried out at T = 45 °C varying the composition of the liquid phase and the oxygen partial pressure. Manganous sulfate was used as catalyst. The analysis of the experimental results showed that the kinetics of bisulfite oxidation in the presence of MnSO4 follow a parallel reaction mechanism, in which the overall reaction rate can be calculated as the sum between the uncatalyzed rate (3/2 order in bisulfite ion) and the catalyzed reaction rate (first order in manganous ion).

Fluid bed biological nitrification and denitrification in high salinity wastewater

Wastewater from wet lime(stone)-gypsum flue gas desulphurisation (FGD) processes in coal-fired power plants contains nitrate. Where case selective catalytic reduction (SCR) of NOx is applied the wastewater can also contain ammonia. For the removal of both nitrate and ammonia, biological processes are an attractive option. A bottle-neck for application of biological processes might be the high chloride concentration and relatively high temperature of the wastewater. Therefore research work was performed in fluid-bed reactors at pilot-plant scale for both biological nitrification and denitrification. Biological nitrification was studied up to 34 gCl−/l and nitrite was the main product formed. Biological denitrification was effective up to at least 45 gCl−/l. Both nitrate and nitrite were removed effectively.

Fluid bed biological nitrification and denitrification in high salinity wastewater

Wastewater from wet lime(stone)-gypsum flue gas desulphurisation (FGD) processes in coal-fired power plants contains nitrate. Where case selective catalytic reduction (SCR) of NO x is applied the wastewater can also contain ammonia. For the removal of both nitrate and ammonia, biological processes are an attractive option. A bottle-neck for application of biological processes might be the high chloride concentration and relatively high temperature of the wastewater. Therefore research work was performed in fluid-bed reactors at pilot-plant scale for both biological nitrification and denitrification. Biological nitrification was studied up to 34 gCl − /l and nitrite was the main product formed. Biological denitrification was effective up to at least 45 gCl − /l. Both nitrate and nitrite were removed effectively.

Flue gas desulfurization gypsum improves orchardgrass root density and water extraction in an acid subsoil

In Appalachia, many soils are acidic, high in exchangeable aluminium, and low in calcium. Large amounts of high gypsum flue gas desulfurization (FGD) by-products are currently disposed of into landfills, although they have potential value as a soil amendment for the region. This study was conducted to determine if leaching an acid subsoil with a saturated solution of a FGD by-product can improve the subsoil as a rooting media for orchardgrass (Dactylis glomerata L.) which is widely used for pasture in the region. Orchardgrass was grown in soil from a pHc 3.8 (in 0.01 M CaCl2) Lily loam Bt horizon (fine loamy siliceous, mesic, Typic Hapludult) leached with two different rates of a saturated FGD by-product aqueous solution, as well as in soil that was limed, and an unamended soil. Water use by a clipped and partially enclosed vegetative canopy was measured in a growth chamber during two drying cycles. Small but consistent increases in water use were correlated with decreases in aluminium saturation of the soil. The effect was greatest during the second drying cycle. Increases in root biomass were also correlated with decreases in aluminium saturation. The effect of treatment on the pattern of water use altered after the first drying cycle when water uptake became most restricted in the unamended treatment. The manganese content of leaf tissue increased from 208 mg kg-1 to 570 mg kg-1 between the unaltered and highest leaching rate treatment. The highest level was still below the 2000 mg kg-1 that is considered toxic to grazing animals. These results suggest that the application of high gypsum FGD by-products to pastures in Appalachia has the potential to improve root growth and functioning in subsoil horizons, but some care may be needed to monitor forage quality.

Removal of heavy metals and suspended solids from wastewater from wet lime (stone)—gypson flue gas desulphurization plants by means of hydrophobic and hydrophilic crossflow microfiltration membranes

Wastewater from wet lime (stone)—gypsum flue gas desulphurization plants (FGD) for coal-fired boilers contains suspended solids (fine gypsum, silica, hydroxides of iron and aluminium) and soluble salts (chlorides and sulphates of calcium, sodium and magnesium). Moreover, traces of heavy metals such as As, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Se, Sn, and Zn are present in these wastewater streams. Most of these heavy metals and suspended solids have to be removed before discharging the wastewater, in order to fulfil the demands stated by the Dutch authorities. Therefore, a very efficient treatment method, based on coprecipitation of heavy metal hydroxides and sulphides followed by crossflow microfiltration (CMF) as a posttreatment, has been developed. The experiments were carried out on a pilot plant scale with actual wastewater from a FGD plant downstream of a coal-fired boiler. Two different types of membranes, a hydrophobic and a hydrophilic crossflow microfiltration membrane, were tested and compared with each other. The effect of membrane fouling as a function of fluid velocity and backwashing was investigated. Besides, the heavy metal concentration and the amount of suspended solids were determined before and after the CMF pilot plant. Finally, a simple and highly effective chemical cleaning method was developed.

Autoclave‐Free Formation of α‐Hemihydrate Gypsum

Flue gas gypsum may be converted to α‐hemihydrate by suspending the starting material in inorganic salt solutions of high concentration or in diluted sulfuric acid and maintaining the suspension at boiling, or near boiling temperature for a period of time. The crystal morphology of the produced α‐hemihydrate gypsum and, thus, its quality depend significantly on the composition of the liquid phase. Additions of different carbonic acids may improve the quality of the product distinctly. Under optimal working conditions the quality of the formed α‐hemihydrate gypsum is similar to that of a material produced in an autoclave.

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.

Treatment of Waste Water from Wet Lime (Stone) Flue Gas Desulfurization Plants with Aid of Crossflow Microfiltration

Abstract A treatment method has been developed to remove heavy metals such as As, Cd, Cr, Cu, Hg, Ni, Pb, Se and Zn very efficiently from waste water from wet lime(stone)-gypsum flue gas desulfurization plants (FGD). This method has been based on coprecipitation of heavy metal hydroxides and sulfides followed by crossflow microfiltration as a post-treatment. The experiments were carried out on pilot plant scale with actual waste water from a FGD plant downstream of a coal fired boiler. The effect of membrane fouling as a function of several process parameters was investigated. From SEM-EDS analysis it was found that the fouling layer on the membrane surface mainly consists of Mg-, Al-, Si-, Fe-compounds and gypsum. Membrane fouling could be decreased by periodical backwashing and by increasing the liquid velocity in the membranes. Moreover, a computer controlled start up procedure of the crossflow microfiltration unit was developed to minimize the effect of membrane fouling and to increase the operating t...

Heavy metal removal from waste water from wet lime(stone)—gypsum flue gas desulfurization plants

Waste water from wet lime(stone) gypsum flue gas desulfurization processes for coal-fired boilers contains suspended solids (gypsum, silica, hydroxides of iron and aluminum) and soluble salts (chlorides and sulfates of calcium, sodium and magnesium). Furthermore, small amounts of heavy metals such as As, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Se and Zn are present in these waste water streams. A treatment method has been developed to remove these heavy metals very efficiently. This method has been based on coprecipitation of metal hydroxides and sulfides. The hydroxide and sulfide precipitates are removed by a coagulation/flocculation technique followed by gravity settling. The coprecipitation can be carried out with sodium hydroxide or with lime. Both cases were investigated in two different pilot plants with synthetically composed waste water and with actual waste water from three different types of wet lime(stone)—gypsum flue gas desulfurization plants (lime—gypsum FGD plants without a prescrubber, one using seawater and another using river water as process water; a limestone—gypsum FGD plant with a prescrubber using river water as process water).