Flue Gas Desulfurization Research Articles

Effect of Mineral Admixtures on Physical, Mechanical, and Microstructural Properties of Flue Gas Desulfurization Gypsum-Based Self-Leveling Mortar.

The production of flue gas desulfurization gypsum poses a serious threat to the environment. Thus, utilizing gypsum-based self-leveling mortar (GSLM) stands out as a promising and effective approach to address the issue. β-hemihydrate gypsum, cement, polycarboxylate superplasticizer, hydroxypropyl methyl cellulose ether (HPMC), retarder, and defoamer were used to prepare GSLM. The impact of mineral admixtures (steel slag (SS), silica fume (SF), and fly ash (FA)) on the physical, mechanical, and microstructural properties of GSLM was examined through hydration heat, X-ray diffractometry (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) analyses. The GSLM benchmark mix ratio was determined as follows: 94% of desulfurization building gypsum, 6% of cement, 0.638% each of water reducer and retarder, 0.085% each of HPMC and defoamer (calculated additive ratio relative to gypsum), and 0.54 water-to-cement ratio. Although the initial fluidity decreased in the GSLM slurry with silica fume, there was minimal change in 30 min fluidity. Notably, at an SS content of 16%, the GSLM exhibited optimal flexural strength (6.6 MPa) and compressive strength (20.4 MPa). Hydration heat, XRD, and Raman analyses revealed that a small portion of SS actively participated in the hydration reaction, while the remaining SS served as a filler.

Stabilization and Release Characteristics of Heavy Metals in Desulfurization Sludge from Coal-Fired Power Plants

ABSTRACT The leaching risk of heavy metals from flue gas desulfurization (FGD) by-product sludge of coal-fired power plants is high, and there is an urgent need for effective treatment using solidification. In this paper, dithiocarbonates (DTC), 2,4,6-tri-mercapto-S-triazine trisodium salt (TMT-15) curing agent, fly ash and cement were used to cure the desulfurization sludge and study the environmental release characteristics of heavy metals before and after curing. The results show that all four curing agents had a good curing effect. The best chelating agent was DTC, and the best curing conditions were achieved at a liquid-to-solid ratio of 3:1 and a mass fraction of 8%. The leaching concentrations of As, Pb, Cd, Cr, Ni, Cu, Zn, and Hg were reduced by 87.95%, 100%, 85.29%, 86.17%, 70.11%, 95.06%, 90.28%, and 98.44%, respectively, after curing. In the environmental release characteristics test, the leaching concentrations of heavy metals in the cured sludge were lower than those of the original samples at different pH values and temperatures, indicating better stability. The mass fraction had the greatest effect on the leaching concentration of heavy metals, followed by the pH value and temperature.

An assessment of inorganic components in condensable particulate matter as a function of surface aggregation, spatial suspension state and particle size

Experimental studies assessed the removal efficiency and fine-size distribution of CPM coupled with compositional analysis across air pollution control device systems (APCDs) at an ultra-low emission (ULE) power plant. The findings indicated total CPM emissions were reduced to a minimum of 0.418 mg/m3 at the Wet Electrostatic Precipitator (WESP). The Wet Flue Gas Desulfurization (WFGD) showed the highest removal efficiency (98%) across all particle sizes, notably in the ultra-micron range. Selective Catalytic Reduction (SCR) demonstrated a mere 34% overall efficiency, with a negative removal rate in the ultra-fine particle range. The WESP effectively removed CPM only in sub-micron and ultra-micron sizes, but significantly increased water-soluble ions formation in ultra-fine spatially suspended CPM (CPMspa), leading to overall negative efficiency. Thus, the removal efficiency of the ultra-fine particle range was most affected among the three particle size ranges when the flue gas went through the APCDs. Major metal elements and water-soluble ions were more readily removed by APCDs due to their surface aggregation, while the removal of trace elements like Hg and Se was limited. Reducing SO42-/NH4+ formation in SCR, and optimizing WESP spray system operations based on flue gas components are essential steps in controlling CPM concentration in ULE power plants.

Solidification and Release Characteristics of Heavy Metals in Gypsum from Coal-Fired Power Plants

Heavy metals in flue gas desulfurization (FGD) gypsum from coal-fired power plants are at risk of releaching during the processes of stockpiling and resource utilization. In this study, the effects of organosulfur chelators dithiocarbamate (DTC) and trisodium trithiocyanate-15 (TMT-15) on the solidification characteristics of heavy metals in desulphurized gypsum under different mass fractions, pH values, water contents and reaction times were investigated. The chemical composition and morphology were analyzed by inductively coupled plasma atomic emission spectrometer (ICP-AES) and scanning electron microscope (SEM). The experiments showed that both DTC and TMT-15 were effective at stabilizing the heavy metals in the FGD gypsum, with more than a 50% curing effect for all the heavy metals except Pb. DTC showed a better stabilization for Pb, Hg, Cu, Zn, and Cr, and TMT-15 showed a better curing effect for Cd. The solidified gypsum had good heavy metal stability in low-water-content environments. Increasing the mass fraction, reaction time, and pH decreased the heavy metal leaching, and the mass fraction had the greatest effect on the total heavy metal leaching concentration, followed by the reaction time and pH value.

Mechanical insights into desulfurization by peroxymonosulfate oxidation via a non-reactive oxygen species pathway

Air pollution by sulfur dioxide (SO2) remains a pressing concern for both the environment and human health. Desulfurization enhanced by persulfate based advanced oxidation processes (PS-AOPs) has been proven to be a feasible method. However, the inherent contradiction between the rapid diffusion mass transfer of SO2 in the “gas-liquid-gas” phase and the limited lifespan of reactive oxygen species (ROS) can not be ignored. Excessive investment in PS is required to sustainably generate ROS to achieve continuous desulfurization performance, which may lead to excessive PS consumption. To address this issue, whether PS can achieve the oxidation absorption of SO2 via a non-reactive oxygen species pathway was investigated. Experimental and computational results demonstrated that peroxymonosulfate (PMS) instead of peroxydisulfate (PDS) had a great SO2 removal performance, the utilization of PS could be effectively achieved by maintaining a 1:1 molar ratio of PMS and removed SO2. The presence of HOO bonds in the PMS introduced a partial positive charge to the oxygen atom, making the PMS polar and more susceptible to be attacked by the nucleophile HSO3-. So SO2 underwent a series of processes including dissolution, dissociation, one-oxygen atom transfer, and ionization before ultimately being converted into SO42- ions, effectively achieving its removal from flue gas. This study may presents a novel approach for achieving high-efficiency flue gas desulfurization.

Improvement on engineering properties of alkali-activated paste with calcined oyster shell ash and flue gas desulfurisation gypsum

To reduce environmental pollution and conserve natural resources, calcined oyster shell ash (COSA), class F fly ash (FFA) and flue gas desulfurisation gypsum (FGDG) were used in an attempt to improve the engineering properties of alkali-activated ternary cementitious paste. The COSA – obtained by calcining crushed oyster shells at 800°C for 3 h and then grinding to pass through a no. 100 sieve – was used to substitute FFA at rates of 2.5, 5.0 and 7.5 mass%. The alkali solution used was 10M sodium hydroxide and sodium silicate with a modulus of 2.5. The hardened paste with 7.5% COSA, 1% FGDG and ratio of weight of added water to dry binder of 0.09 at 56 days had the highest compressive strength of 62 MPa. Microstructural analyses (scanning electron microscopy and energy-dispersive X-ray spectroscopy) showed that the resulting calcium aluminosilicate hydrate gel was found to have a compact microstructure, which improved the compressive strength of specimens. In summary, COSA successfully replaced natural limestone as a calcium oxide activator to manufacture an alkali-activated ternary cementitious paste containing FFA and FGDG.

Synthesis and utilization of polyol-modified high specific surface area Ca(OH)2: an investigation.

Calcium hydroxide (Ca(OH)2) finds widespread use in the petrochemical industry, particularly in flue gas desulfurization applications. However, its conventional usage is limited by its inherently low specific surface area, hampering its efficiency. To address this limitation, this study aims to develop a simple and industrially scalable preparation process for Ca(OH)2 with a high specific surface area, thereby enhancing its effectiveness in various applications. This study aimed to develop a preparation process for making Ca(OH)2 with a high specific surface area, suitable for industry and easy to make. Ca(OH)2 with a specific surface area of 41.555 m2/g was successfully synthesized by incorporating polyols during lime digestion. The prepared high specific surface area Ca(OH)2 is more than five times the specific surface area of ordinary Ca(OH)2. Incorporation of polyols within the lime digestion process induces a reduction in both Ca(OH)2 grain size and particle dimensions, concurrently amplifying the specific surface area and optimizing mass transfer efficiency. Specifically, the desulfurization breakthrough time for Ca(OH)2 subject to a 15% triethanolamine modification was notably extended to 879s, surpassing the desulfurization breakthrough time of unaltered Ca(OH)2 by more than tenfold. Moreover, the modified Ca(OH)2 exhibited remarkable efficacy in neutralizing acidic wastewater. A new approach for the preparation of high-performance Ca(OH)2 is proposed in this study, which could facilitate the industrial production of Ca(OH)2 with high specific surface area.

Integration effects of soil amendments and cover crops on dryland no‐till corn

AbstractA field study was carried out at the Mississippi Agricultural and Forestry Experiment Station near Pontotoc to evaluate the synergistic impacts of broiler litter (BL) and inorganic fertilizer nitrogen (N) with flue gas desulfurization (FGD) gypsum and lignite in the presence of winter cover crops (WCCs) on dryland no‐till corn (Zea mays L.) in Falkner silt loam soil. The experimental design was a split‐plot randomized complete block design with three replications. The main plots were WCC and winter fallow (WF), and the subplots were fertilization treatments. Fertilization treatments included BL, inorganic fertilizer N, FGD gypsum and lignite with BL, FGD gypsum and lignite with inorganic fertilizer N, and an unfertilized control. BL, FGD gypsum, and lignite were applied at the rates of 13.4, 3.4, and 3.4 Mg ha−1, respectively. Inorganic fertilizer N was applied to corn at 168 kg N ha−1. BL increased soil carbon (C), soil infiltration, and resulted in higher corn grain yield compared to both inorganic fertilizer N and unfertilized control in 2020 and 2022. Averaged across fertilization treatments, WCC improved soil moisture, soil C, and soil infiltration by 16%, 19%, and 25% at the 0‐ to 15‐cm depth, respectively, and increased corn grain yield by 25% as compared to WF in 2022. Cover crops boosted corn grain yield during drier years. The combination of FGD gypsum and lignite with BL increased corn grain yield by 15% in 2020 and 13% in 2022 compared to BL alone. This approach can be considered to promote the sustainability of agroecosystems.

Ionic liquid for simultaneous desulfurization and dehydration of flue gas: Data‐driven thermodynamics and mechanisms

Ionic liquid for simultaneous desulfurization and dehydration of flue gas: Data‐driven thermodynamics and mechanisms

Comparing Electrochemical Passivation and Surface Film Chemistry of 654SMO Stainless Steel and C276 Alloy in Simulated Flue Gas Desulfurization Condensates.

This research examines the behavior of electrochemical passivation and the chemistry of surface films on 654SMO super austenitic stainless steel and C276 nickel-based alloy in simulated condensates from flue gas desulfurization in power plant chimneys. The findings indicate that the resistance to polarization of the protective film on both materials initially rises and then falls with either time spent in the solution or the potential of anodic polarization. Comparatively, 654SMO exhibits greater polarization resistance than C276, indicating its potential suitability as a chimney lining material. Mott-Schottky analysis demonstrates that the density of donors in the passive film formed on 654SMO exceeds that on C276, potentially due to the abundance of Fe oxide in the passive film, which exhibits the characteristics of an n-type semiconductor. The primary components of the passive films on both materials are Fe oxides and Cr oxides. The formation of a thin passive film on C276 in the simulated condensates is a result of the low Gibbs free energy of nickel oxide and low Cr content. The slower diffusion coefficient of point defects leads to the development of a thicker and more compact passive film on the surface of 654SMO.

Mechanical properties of solid waste-based composite cementitious system enhanced by CO2 modification

Utilizing CO2 to modify solid waste and produce high-performance cementitious material is a promising strategy. In this study, circulating fluidized bed fly ash (CFBFA), calcium carbide slag (CS) and flue gas desulphurization gypsum (FGDG) were prepared by mixing CO2 to produce cementitious materials. The impacts of CO2 on mechanical properties and carbonation reaction mechanism of composite materials were investigated. The results shown that the microstructure and mechanical properties of the gelling materials were improved by CO2 modification. When the CO2 mass transfer conditions as followed: CO2 flow rate was 1.5 L/min, stirring rate at 600 r/min, and stirring time at 20 min, compressive strength of modified material was 22 % higher than that of the non-CO2 modified material. Additionally, the density increased by 3.2 %, and porosity was reduced by 34.1 %. Among them, TG/DTG analysis found that the highest effective fixed CO2 rate was 11.1 %. The ultrasonic nondestructive testing also shown that the structure of the CO2-modified cementitious material was significantly better than that of the CFBFA-CS-FGDG composite cementitious system, and the ultrasonic loss rate was reduced by 9.4 %. Therefore, the use of CO2 to modify the composite system was of great significance for the realization of CO2 storage and the improvement of the properties of composite materials. One interesting future possibility is solid waste-based grouting materials production at energy plants: CFBFA, CS and FGDG can be used to capture CO2 from flue gases, thus improving the strength of produced grouting materials.

High-Performance Porous Organic Polymers for Environmental Remediation of Toxic Gases.

Sulfur dioxide (SO2) is a harmful acidic gas generated from power plants and fossil fuel combustion and represents a significant health risk and threat to the environment. Benzimidazole-linked polymers (BILPs) have emerged as a promising class of porous solid adsorbents for toxic gases because of their chemical and thermal stability as well as the chemical nature of the imidazole moiety. The performance of BILPs in SO2 capture was examined by synergistic experimental and theoretical studies. BILPs exhibit a significantly high SO2 uptake of up to 8.5 mmol g-1 at 298 K and 1.0 bar. The density functional theory (DFT) calculations predict that this high SO2 uptake is due to the dipole-dipole interactions between SO2 and the functionalized polymer frames through O2S(δ+)···N(δ-)-imine and O═S═O(δ-)···H(δ+)-aryl and intermolecular attraction between SO2 molecules (O═S═O(δ-)···S(δ+)O2). Moderate isosteric heats of adsorption (Qst ≈ 38 kJ mol-1) obtained from experimental SO2 uptake studies are well supported by the DFT calculations (≈40 kJ mol-1), which suggests physisorption processes enabling rapid adsorbent regeneration for reuse. Repeated adsorption experiments with almost identical SO2 uptake confirm the easy regeneration and robustness of BILPs. Moreover, BILPs possess very high SO2 adsorption selectivity at low concentration over carbon dioxide (CO2), methane (CH4), and nitrogen (N2): SO2/CO2, 19-24; SO2/CH4, 118-113; SO2/N2, 600-674. This study highlights the potential of BILPs in the desulfurization of flue gas or other gas mixtures through capturing trace levels of SO2.

Enhancing Pb2+ removal efficiency in flow-through systems using flue gas desulfurization gypsum-based porous materials: Experimental and numerical studies

This study addresses the poor permeability of flue gas desulfurization (FGD) gypsum in water remediation and further explores its potential for resource utilization. FGD gypsum-based porous materials (FGPMs) were prepared using different foaming behavior as permeable reactive barrier (PRB) media materials. The dynamic removal performance of Pb2+ was investigated, and a numerical model was developed to validate the results. The findings reveal that the adsorption mechanisms of FGPMs primarily involve ion exchange and surface precipitation. Pb2+ does not alter the structure or functional groups of the materials. By optimizing the foaming behavior to enhance pore connectivity, the adsorption capacity increased from 8.78 mg/g to 13.42 mg/g, thereby extending the service life of the PRB. The presence of closed and capillary pores hinders the dynamic removal performance of Pb2+. Furthermore, the FGPMs exhibit superior removal performance at low flow rates, low concentrations, and high column heights, as confirmed by the numerical model. These results offer valuable insights for designing and optimizing FGD gypsum-based adsorption processes to remove Pb2+ from wastewater efficiently.

Effect of borax on the hydration and hardening of β-hemihydrate gypsum at high water–plaster ratio

The existing methods of preparing lightweight gypsum blocks are to make hollow slats or to make foamed blocks, both of which are defective and fail to meet the standards. In order to prepare lightweight gypsum blocks, this paper investigates the method of increasing the proportion of moisture to reduce the weight of gypsum blocks. To further understand the performance relation between β-hemihydrate gypsum (β-hemihydrate phosphogypsum and β-hemihydrate flue-gas desulfurization gypsum) and its products, the effect of borax on the hydration and hardening of β-hemihydrate gypsum at high water–plaster ratio was studied. The results showed that with an increase in borax dosage, the setting time of β-hemihydrate phosphogypsum (β-HPG) was evidently prolonged; the initial setting time increased from 15 to 62 min, and the final setting time increased from 22 to 93 min. The difference between the initial and final setting times also increased, and the fluidity of the gypsum slurry was improved. When the borax dosage reached 0.5%, the flexural strength of β-hemihydrate flue-gas desulfurization gypsum (β-HFGD) increased from 5.2 to 6.3 MPa and the compressive strength increased from 4.7 to 9.3 MPa after 28 d. By analyzing the changes in phase transition, hydration degree, infrared spectrum, particle size, and crystal microstructure during the hydration of β-hemihydrate gypsum, it was found that β-HPG was more sensitive to borax than β-HFGD at high water–plaster ratio and β-HFGD showed superior mechanical properties. The study findings will provide a theoretical basis for the application of β-hemihydrate gypsum products under humid conditions and expand the application range of gypsum products.

Investigation of iron oxide supported on activated coke for catalytic reduction of sulfur dioxide by carbon monoxide

In view of the low utilization rate of by-product in limestone-gypsum wet flue gas desulfurization process, a method of catalytic reduction of SO2 to elemental sulfur was proposed. In this work, supported iron catalyst using activated coke as supporter was prepared and characterized. Moreover, the performance of SO2 reduction using CO as reducing agent at various Fe loadings, temperatures, gaseous hourly space velocities and CO/SO2 molar ratios was studied. Research shows that, compared with other metals, the highest catalytic activity is achieved over Fe-based catalyst. The iron sulfide is the main active component during the catalytic reduction reaction, hence the catalyst needs to be presulfided before use. The micropores of activated coke become more abundant after loading Fe, whereas excessive increase of Fe loading may bloke the mesopores and weaken the catalytic activity. Higher reaction temperature, lower GHSV and a stoichiometric molar ratio are conducive to the improvement of SO2 conversion and S yield. The catalytic performance at lower temperatures was further improved by loading Co. When the Co loading is 4 wt%, the SO2 conversion rate reaches 90.9% at 400 °C because loading Co enhances the redox performance of the catalyst surface. The findings are instructive for the development of cost-effective carbon-based catalysts for resource recovery of sulfur.

Experimental Study on Desulfurization Characteristics of Dry Sorbent Injection at Low SO2 Concentrations

AbstractTo effectively reduce SO2 emissions, flue gas desulfurization methods are widely used in coal‐fired power plants. In desulfurization, the dry sorbent injection (DSI) technology has the advantages of high desulfurization efficiency, simple operation, convenient adjustment, and low initial investment. Here, a pilot‐scale experimental system was designed and built to investigate the desulfurization characteristics of the DSI technology. The influence of the residence time of the desulfurizer, the reaction temperature, the stoichiometric ratio of the desulfurization reaction, the particle size of the desulfurizer, the inlet SO2 concentration, the dust concentration, and the water vapor content in the flue gas on the desulfurization efficiency at low SO2 concentrations was studied by injecting NaHCO3 into the pipeline. The desulfurization efficiency can be significantly improved by reducing the desulfurizer particle size or increasing the water vapor content in the flue gas at low SO2 concentration. An empirical formula describing the dependence of the desulfurization efficiency on experimental parameters is given.

Evaluating the impact of gypsum as a novel bedding material on broiler performance, foot pad health, and fear response

Flue Gas Desulfurization (FGD) gypsum is a byproduct of the coal-fired power plant process commonly used to remove sulfur dioxide emissions from the flue gas. FGD gypsum has numerous industrial, agricultural, and environmental applications. This study aimed to explore a novel approach involving the use of FGD gypsum combined with different litter treatments as bedding for broiler production. It focused on performance metrics, including adjusted feed conversion ratio (AFCR) and average body weight (BW), foot pad dermatitis (FPD), and fear response over 5 consecutive flocks. A total of 1,800 one-day-old Ross 708 chicks were randomly assigned to 24 pens (75 birds/pen), divided into 6 treatment groups (4 pens/treatment), with 5 replications and raised until 42 d old (d). Treatments were gypsum that was decaked (D), rotovated (E), and rotovated then windrowed (F) between flocks. Control treatments using pine shavings were decaked (A), rotovated (B), and windrowed postrotovating (C). AFCR, average BW, and mortality were used as a measure of production. Foot pad dermatitis scores were taken on d42 using a scale of 0 (absence), 1 (mild), and 2 (severe). Response to observer and human approach test were used to measure fear response. Data were analyzed as a 2-way ANOVA (Proc Glimmix) for the main effects of bedding type and litter treatment. Means were identified using Tukey's HSD. No effect of bedding type or litter treatment was found for AFCR, BW, or mortality. FPD scores 2 and 1, were higher with pine shavings than gypsum (P = 0.01 and P = 0.01, respectively). While FPD scores 0 were higher for gypsum than the pine shaving (P = 0.01). No difference in fear response was found among birds raised on any of the gypsum litter treatments and any of the pine shaving litter treatments. Overall, the use of gypsum as bedding results in equivalent production and fear response to pine shavings, while increasing FPD quality when compared to pine shaving.

Comparing the Photocatalytic Oxidation Efficiencies of Elemental Mercury Using Metal-Oxide-Modified Titanium Dioxide under the Irradiation of Ultra-Violet Light

Since the signing of the Minamata Convention in 2013, attempts have been primarily focused on reducing the emission of elemental mercury (Hg0) from coal-fired power plants (CFPPs). The most cost-effective measure for controlling the emission of mercury involves oxidizing Hg0 to mercury oxides, which are then removed using wet flue gas desulfurization (WFGD). Thus, novel photocatalysts with the best properties of photocatalytic ability and thermal stability need to be developed urgently. In this study, titanium dioxide (TiO2)-based photocatalysts were synthesized through the modification of three metal oxides: CuO, CeO2, and Bi2O3. All the photocatalysts were further characterized using X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence, and ultraviolet-visible spectrometry. The photocatalytic oxidation efficiencies of Hg0 were evaluated under an atmosphere of N2 + Hg0 at 100–200 °C. The photocatalytic reactions were simulated by kinetic modeling using the Langmuir–Hinshelwood (L–H) mechanism. The results showed that Bi2O3/TiO2 exhibited the best thermal stability, with the best oxidation efficiency at 200 °C and almost the same performance at 100 °C. L–H kinetic modeling indicated that photocatalytic oxidation reactions for the tested photocatalysts were predominantly physical adsorption. Additionally, the activation energy (Ea), taking into account Arrhenius Law, decreased dramatically after modification with metal oxides.

Current Status of Zero Liquid Discharge Technology for Desulfurization Wastewater

Desulfurization wastewater is industrial wastewater with a high salt content, high metal ions, and high hardness produced by flue gas desulfurization of the limestone-gypsum method in coal-fired power plants. This paper summarizes the source of desulfurization wastewater, water quality characteristics, water quality impacts, and other factors, combined with the current status of research worldwide to introduce the advantages and shortcomings of the existing desulfurization wastewater treatment technology. In addition, zero liquid discharge technology as a novel method to treat desulfurization wastewater is also summarized. It mainly includes evaporation and crystallization, flue gas evaporation, membrane distillation removal, etc. Finally, this manuscript looks forward to the future development direction of desulfurization wastewater based on its existing technology and emission standards.

Numerical simulation of particle erosion coupled with flue gas desulphurization in the spouted bed

The addition of an axial swirl vane (ASV) and multi-jet distributor plate (MDP) to a conventional spouted bed (CSB) to form an integrated multi-jet swirling spouted bed (IMSSB) combined with internally reinforced components not only optimized its desulphurization efficiency but also exacerbated the erosion of particles on the bed and the internal components. Coupled study of the particle erosion and desulphurization reaction in the flue gas desulphurization process of an IMSSB was carried out based on the CPFD numerical simulation. The results show that: the desulfurization efficiency of IMSSB is increased by 16.6% compared with that of the CSB; in terms of wall erosion, the maximum erosion rate in IMSSB is about four times that of CSB; the erosion condition increases in the vane from the center to the edges; particle erosion is most severe in the fountain area.