SO2 Removal Efficiency Research Articles

Removal characteristics of SO3 in the low-low temperature electrostatic precipitator

ABSTRACT As SO3 endangered the industrial equipment and environment in the coal-fired power plants, it was necessary to give full play to the SO3 removal effect in a low-low-temperature electrostatic precipitator (LLT-ESP). The relationship between SO3 and fly ash particles was investigated during the cooling process. In addition, the SO3 removal performance in the LLT-ESP was further analyzed. The migration and deposition of SO3 into fly ash particles were promoted with the decrease in the gas temperature and the fly ash particle size, as well as the increase in the SO3 concentration. As the temperature of the gas decreased below the acid dew point (ADP), the H2SO4 vapor tended to migrate into fly ash particles with smaller sizes. The SO3 mass concentration increased significantly in fly ash particles whose sizes ranged from 0.03 to 0.26 μm. When the operating voltage turned up, the SO3 removal efficiency was increased from 43.2% to 60.1%. The increase in the inlet fly ash concentration promoted the SO3 removal, and the removal efficiency increased by nearly 20%. When the gas temperature was below the ADP, it had little influence on the SO3 removal efficiency.

A new absorbent system for reducing chlorine gas escape and enhancing pollutants removal during ship exhaust wet scrubbing

Using chlorine-containing oxidants to remove pollutants in the exhaust gas of ships is normally accompanied by Cl2 escape, which poses a significant threat to the environment and the health of the crew. This paper proposes a method to solve the problem of Cl2 escape in a single NaClO solution system using BAD (a new amide absorbent, C12H25NO). The electrostatic potential (ESP) theoretical calculations, FT-IR and UV–vis spectra tests showed that the strong field effect interaction between BAD and Cl2, which can form a stable symmetrical structure similar to a “sandwich”, results in a strong binding ability of BAD to Cl2. The effects of the initial pH, the concentration of NaClO solution, aeration time, and some operating parameters on the loss of active chlorine (AC) components were studied. Under the same conditions, a two-phase composite absorbent system with the addition of BAD can reduce the loss of AC components by 32.67% on average and up to 56.12%. It also can effectively capture the Cl2 escaping with the gas flow and keep it in the system, which enhances the oxidation of NO by Cl2 at the gas–liquid interface. It also has a strong ability to remove pollutants for a long period, as the removal efficiencies of SO2, NO, and NOx within 20 mins were 97.84%, 77.98%, and 76.01%, respectively. The results show that the BAD-NaClO two-phase composite absorbent system can effectively reduce Cl2 escape, and it is a sustainable wet treatment scheme for ship exhaust gas with great application prospects.

Conversion of medical waste into value-added products using a novel integrated system with tail gas treatment: Process design, optimization, and thermodynamic analysis

The COVID-19 pandemic has generated substantial medical waste (MW), posing risks to society. Based on widespread MW incineration, this study proposes an integrated system with tail gas treatment to convert MW into value-added products with nearly zero emissions. Herein, steam generators and supercritical CO2 cycles were used to recover energy from MW to produce high-temperature/pressure steam and electricity. A simple power generation cycle achieved a net electricity efficiency of 22.4% through optimization. Thermodynamic analysis revealed that the most energy and exergy loss occurred in incineration. Furthermore, a pressurized reactive distillation column purified the resultant tail gas. The effects of inlet temperature, pressure, liquid/gas ratio, and recycle ratio on the removal and conversion efficiencies of NO2 and SO2 were evaluated. Nearly 100% of the SO2 and 75% of the NO2 generated by the incineration of MW have been converted into their acid forms. Based on the proposed tail gas treatment unit, high-purity CO2 (∼98% purity) was finally obtained.

CFD-DEM simulations of a gas-solid-liquid fluidization system: Effects on the flow field and particle behavior of semi-dry desulfurization fluidized bed

Gas-solid-liquid multiphase flow systems have been widely applied in energy engineering, petrochemical industries, biochemical industries and food industries, etc., which usually involve multi-physical processes and multi-reaction stages. As a typical gas-solid-liquid multiphase flow system, the semi-dry flue gas desulfurization fluidized bed has been widely applied by small and medium-scale thermal power plants for its advantages of excellent mixing effect, relatively high efficiency and low cost. This study focused on the fluid hydrodynamics, wet particle motions and the transfer efficiency (SO2 removal efficiency) in a fluidized bed via two-way coupled CFD-DEM numerical simulations with the implementation of different semi-dry desulfurization stages (“constant-rate” absorption stage, “falling-rate” absorption stage and solid absorption stage) as well as the liquid bridge force. To avoid the fast evaporation of small droplets, simulations based on larger particles (Geldart group D) were also conducted to clarify the influence of varying liquid volume contents. Results revealed that the existence of liquid layers would partly enhance the desulfurization efficiency, while in this case the bed exhibits poor fluidization characteristics. Adding humification water in the solid absorption stage would transform the reaction stage from solid absorption stage to “constant-rate” absorption stage, which improves the desulfurization efficiency significantly. It could also be summarized that the increase of Ca/S molar ratio would enhance the desulfurization efficiency partly, but the improvement would not be obvious when the Ca/S molar ratio is greater than a certain range.

Numerical simulation on gas-droplet flow characteristics and spray evaporation process in CFB-FGD tower

Nozzle arrangement in the nozzle spray system has a significant impact on the gas-droplet flow characteristics and the temperature distribution within the circulating fluidized bed flue gas desulphurization (CFB-FGD) tower, which is critical to the SO2 removal efficiency. The effects of spray direction, nozzle number and nozzle spray angle on gas-droplet distribution and temperature distribution inside the FGD tower are investigated with numerical simulation based on a Eulerian-Lagrangian mathematical model. An optimal nozzle arrangement scheme is proposed to improve the contact between gas and water droplets and the flue gas temperature distribution. Results show that upward spray direction is beneficial to the interaction between water droplets, improving gas-droplet flow characteristics and spray evaporation process, and water droplets number trapped by tower wall could be reduced in the water droplets evaporation. With the increase in nozzle number, it is conducive to the contact between flue gas and water droplets to increase the evaporation efficiency of water droplets, as well as the uniformity of temperature distribution inside the tower. With nozzle spray angle increases from 30° to 120°, flue gas velocity decreases, water droplets number trapped by the tower wall increases. The temperature distribution at different cross-section is the most uniform when the nozzle spray angle is 60°.

The application of two-phase composite absorbent systems consisting of BAD and seawater resources in the wet treatment of ship exhaust gas

The impact of ship emissions on the environment cannot be ignored and should be controlled. The possibility of applying seawater electrolysis technology and a novel amide absorbent (BAD, C12H25NO) to the simultaneous desulfurization and denitrification of ship exhaust gas is entirely confirmed by using various seawater resources. Concentrated seawater (CSW) with high salinity can effectively reduce the heat generated during electrolysis and the escape of chlorine. The initial pH of the absorbent can greatly affect the NO removal capacity of the system, and the BAD could keep the pH range suitable for NO oxidation in the system for a long time. The use of fresh seawater (FSW) to dilute the electrolysis of concentrated seawater (ECSW) to make an aqueous oxidant is a more reasonable scheme; the average removal efficiencies of SO2, NO, and NOx were 97.10%, 75.41%, and 74.28%, respectively. The synergistic effect of HCO3 -/CO3 2- and BAD was shown to further restrict NO2 escape.

Simultaneous removal of SO2, NO and Hg0 using porous carbon/heat-coactivated persulfate system

A novel simultaneous removal technique of SO2, NO, and Hg0 using porous carbon/heat-coactivated persulfate (PS) system was proposed. A series of experiments and theoretical analysis were conducted to explore simultaneous removal process of Hg0, SO2, and NO. Study demonstrates that the developed porous carbon/heat-coactivated PS system gains larger free radical yield and higher pollutants simultaneous removal efficiency than other comparison systems, which are associated with the synergism between porous carbon and heat. High temperature plays a vital role in this co-activation system. Both SO4−· and ·OH play an important role in NO and Hg0 removal, but ·OH is more important for NO removal while SO4−· is more important for Hg0 removal. Both NO and Hg0 removal processes meet pseudo-first-order rapid reaction kinetics, and their removal processes are controlled by mass transfer. Removal efficiencies of NO and Hg0 are increased first and then are decreased with increasing PS concentration, temperature and porous carbon concentration. Increasing pH and concentrations of SO2, NO and Hg0 reduce the NO and Hg0 removal efficiencies. The highest simultaneous removal efficiency of Hg0, SO2, and NO is up to 98.4% for Hg0, 100% for SO2, and 89.3% for NO under an optimized test condition.

Simultaneous removal of NO and SO2 by Fe(II)/peracetic acid oxidation system: Operating conditions, removal efficiency and removal mechanism

The request of synergistic control of PM2.5 and O3 pollution has made NO and SO2 emission control a hot topic again in the field of atmospheric environment. An advanced oxidation process (AOPs) for simultaneous removal of SO2 and NO from the flue gas of small and medium-sized boilers and kilns by Fe(II) activated peracetic acid (PAA) was investigated. The influences of operating parameters like reaction temperature, initial pH, concentrations of PAA and Fe(II) on SO2 and NO removal efficiency in Fe(II)/PAA system were studied. The NO removal efficiency was increased with higher PAA concentration and lower initial pH. Changes in reaction temperature and Fe(II) concentration had a dual effect on NO removal efficiency. The SO2 removal efficiency can be stably maintained above 99 % under all operating conditions, which is of great significance for practical engineering applications. Results indicated that the maximum removal efficiency of 92.3 % for NO and 99.5 % for SO2 were obtained under the optimal conditions of 100 mM PAA, 10 mM Fe(II), operating temperature 45 °C and initial solution pH 2.4. PAA was confirmed to play a major role in NO removal rather than coexistent H2O2. According to the electron paramagnetic resonance (EPR) technology, methyl phenyl sulfoxide (PMSO)-based probe experiments and radicals quenching experiments, reactive oxidizing species such as CH3C(O)O·, CH3C(O)OO·, ·OH and FeIVO2+ were generated in the Fe(II)/PAA system, where organic radicals (R-O•) were confirmed to be the major ones affecting NO oxidation. Ion chromatographic analysis revealed that SO42- and NO3- were the main products of SO2 and NO removal, and the mechanism of SO2 and NOx oxidation and removal by Fe(II)/PAA system was thus elucidated, which would promote the industrial application of this novel method.

Simultaneous oxidation and absorption of nitric oxide and sulfur dioxide by peroxymonosulfate activated by bimetallic metal-organic frameworks

SO2 and NO from coal combustion are the main precursors of acid rain, regional haze, and photochemical smog. Advanced oxidation strategies can be used to simultaneously remove SO2 and NO from flue gas under a low temperature. Two metal-organic frameworks (MOFs), FeBDC and CuFeBDC, were synthesized and used to activate peroxymonosulfate (PMS) for the oxidation and absorption of flue pollutants. The characterization results revealed that MOFs contained the redox pairs Fe(II)/Cu(I) and Fe(III)/Cu(II). Fe(II)/Cu(I) initiated firstly the PMS activation. Then, the Fe(II-III-II) and Cu(I-II-I) redox cycles continuously activated PMS and generated reactive species. MOFs-PMS removed 76.6 % and 86.5 % of NO in the presence of FeBDC and CuFeBDC catalysts, respectively. 100 % of SO2 was removed. CuFeBDC exhibited the efficient catalytic properties for the removal of NO and SO2 in PMS solution, and could be recycled and regenerated. After five cycles, the removal efficiencies of NO and SO2 were 71.2 % and 100 %, respectively, and NO and SO2 emissions in the outlet were lower than the emission limit when using CuFeBDC-PMS. During the oxidation and absorption process, NO and SO2 were first oxidized to NO2- and SO32- as intermediates, then formed the final products of NO3- and SO42-. Radical scavenging experiments and electron paramagnetic resonance measurements revealed that both radical (SO4-•, •OH) and non-radical pathways (1O2) contributed to the efficient oxidation of NO/ SO2. 1O2 was the predominant reactive oxygen species for the removal of NO, while SO4-• and •OH were responsible for the removal of SO2.

The assessment of response surface methodology (RSM) and artificial neural network (ANN) modeling in dry flue gas desulfurization at low temperatures

The performance of a flue gas desulfurization (FGD) system is characterized by SO2 removal efficiency () and reagent conversion (). Achieving a near-perfect reaction environment has been of concern in dry FGD (DFGD) due to the low reactivity compared to the wet and semi-dry units. This study will appraise output responses using modeling by response surface methodology (RSM) and artificial neural networks (ANN) approaches. The impacts of input parameters like hydration time, hydration temperature, diatomite to hydrated lime (Ca(OH)2), sulfation temperature and inlet gas concentration will be studied using a randomized central composite design (CCD). ANN fitting tool mapped the CCD metadata using the Levenberg-Marquardt (LM) algorithm activated by the hyperbolic tangent (tansig) function. The hidden cells ranged from 7 to 10 to ascertain the effect node architecture on modeling accuracy. Validation of each procedure was assessed using root mean square error (RMSE), mean square error (MSE) and R-Squared studies. The outcomes presented a more accurate 5-10-2 ANN model in the mapping of the DFGD from R2 data of = 0.993 and = 0.9986 with a mapping deviation from the RMSE values of = 0.48465; = 0.44971 and MSE results of = 0.23488; = 0.20229.

The simultaneous removal of NO and SO2 over MnO2 material via the multi-stage fluidized bed process at low temperatures

To overcome the easy poisoning and deactivation of denitrification catalysts by SO2 at low temperatures, the bench-scale multi-stage fluidized bed (MSFB) process with the active MnO2 medium (feeding rate of 0.3–1.2 kg/h) is designed and applied to simultaneously remove the NO and SO2 from flue gas of medium/small industrial boilers in the low-temperature range of 100 – 200 °C, which demonstrates excellent and stable removal efficiency of both NO and SO2 even in the presence of 10 vol% water. In the MSFB system, the fluidized MnO2 particles in different layers flow against the simulated flue gas stage by stage, and the deactivated MnO2 will be continuously discharged and replaced with fresh MnO2 to keep the system effective and steady. The MnO2 medium acts as both denitrification (DeNOx) catalyst and desulfurizer, and the limited backmixing and layered arrangement of the MSFB system ensure the high removal capacity and sufficient utilization of MnO2 material. The multiple structural characterizations further reveal that the active MnO2 is gradually consumed by SO2 to form MnSO4 stage by stage with decreased specific surface and pore volume, accounting for its gradually decreased removal efficiency of both NO and SO2 stage by stage. And the deactivated MnO2 can be easily regenerated by aqueous ammonia with the conversion of MnSO4 to active MnO2. The demonstrated advantages of the MSFB system with MnO2 will provide a promising technical route for the simultaneous removal of NO and SO2 from low-temperature flue gas in industry.

SO42−, Cl−, Br−, and TDS removal by semi continuous electrocoagulation reactor using rotating anode

In this study, the simultaneous removal of SO 4 2 − , Cl − , Br − , and TDS from saline lake water was investigated using an emerging electrocoagulation (EC) reactor in a batch and a semi-continuous electrocoagulation mode (batch recirculation system). The possibility of the EC process in salt removal and sludge production were evaluated. The EC continuous reactor with rotating anode was used and the effect of the impeller plate anode was validated. Several variables were estimated to set the optimum operating conditions for a batch system. The effects of variables such as rotation speed (rpm), retention time (min), recirculation flow rate, current density (mA/cm 2 ), inter space distance (mm), pH solution, and continuous flow system were optimized. These operational parameters were set at 75 rpm, 10 min, 4 L/min, 2 mA/cm 2 , pH 8, 1 cm 2 , and 0.25 L/min, respectively. Statistical analyses were performed to determine the optimal EC conditions. The results revealed that the maximum removal efficiency of SO 4 2 − , Cl − , Br − , and TDS were 90.2%, 93.4%, 90.8%, and 92.3%, respectively. Electrical energy, aluminum consumption, chemical reagents, and sludge production were calculated to achieve an operating cost per m 3 of $0.1766. The sludge and treated water were characterized, and the mechanism of the EC technology was assessed. The results revealed that treated water with the use of the EC process was very efficient, with a low overall consumption cost. • SO 4 2 − , Cl − , Br − , and TDS are limited via physical adsorption with Al hydroxides. • Impeller plates of rotating anodes were used. • EC rotation speed, retention time, pH, and current density were the key parameters. • The EC technology revealed efficiency in saline water treatment.

Structured packing improves wet scrubbing of airborne molecular contaminants in cleanroom make-up air units

The use of wet scrubbing to remove airborne molecular contaminants in cleanroom make-up air units has economic benefits and good application prospects. Still, problems with this method include low removal efficiency and large water consumption. To improve scrubbing performance, we built a full-scale scrubbing experiment platform using SO2 as the removal object. In addition, we applied structured packing in the scrubbing process to enhance the mass transfer between gas and liquid, and we tested the wet scrubbing removal efficiency and pressure drop under a variety of operating conditions. Results showed that under the condition of double-row spraying only, the SO2 removal efficiency increased with increasing liquid-gas ratio. The efficiency ranged from 57% to 83.9% and the pressure drop ranged from 6 to 15 Pa. After adding structured packing, the removal efficiency under different liquid-gas ratios improved significantly. Improvement was more apparent, ranging from 72.2% to 86.2%, when the liquid-gas ratio was low. The pressure drop also increased, ranging between 59 Pa and 100 Pa. In addition, we changed the packing thickness and the number of stages, and found that when the packing thickness was 0.2 m and the two-stage spacing was 0.15 m, removal efficiency improved up to 89.7%. The research results are significant for optimizing wet scrubbing performance and, at the same time, have practical engineering value for controlling the concentration of airborne molecular contaminants in the cleanrooms.

Simultaneous absorption of SO2 and NO from flue gas by ammonia solution with a wetted-wall column

In a self-designed wetted column, the effects of absorption concentration, initial pH, liquid-gas ratio, SO2 inlet concentration, NO inlet concentration on desulfurization and denitration efficiency were studied with ammonia solution. The results show that the removal efficiency of SO2 and NO can be improved by increasing the concentration of absorption liquid and liquid-gas ratio. The presence of SO2 can promote the removal of NO. Increasing SO2 concentration and NO concentration are not conducive to removing SO2. The liquid-phase and gas-phase mass transfer coefficients of SO2 in the system were determined. The results demonstrate that when inlet concentration of SO2 and NO is about 1100 mg/m3 and 500 mg/m3 respectively, the best technical parameters are 4 to 5 L/m3 for the liquid-gas ratio, 6.0 to 7.0 for the pH of absorption, 3%(wt) for Ammonia concentration. Under the best experimental conditions, the removal efficiency of SO2 can reach above 99%, and that of NO can reach above 50%.

Purification mechanism of corona discharge coupled with dimethyl sulfoxide microemulsion for simultaneous desulfurization and denitrification

In this study, a new absorbent dimethyl sulfoxide (DMSO) microemulsion is used, and corona discharge coupled with dimethyl sulfoxide microemulsion is proposed for simultaneous desulfurization and denitrification. This study solves the problem of low efficiency of simultaneous SO2 and NO purification and avoids the problem of easy poisoning of catalysts for simultaneous desulfurization and denitrification. In addition, it makes up for the defects of low efficiency and complex products of desulfurization and denitrification by plasma alone. In this study, the effects of different corona discharge voltages, DMSO microemulsion oil–water ratio and oxygen concentration on the simultaneous removal of SO2 and NO were investigated in detail. The study showed that increasing the voltage and oxygen concentration had a significant promotion effect on the degradation of NO, but the high oxygen concentration would release part of the captured SO2. Under the best experimental conditions, the SO2 removal efficiency could reach 93.4 % and the NO removal efficiency was 84.9 %. In addition, the adsorption energy calculations combined with different initial concentrations and different DMSO microemulsion temperatures illustrate that SO2 and NO react competitively with SO bonds in DMSO and OH bonds in isoamyl alcohol in DMSO microemulsions, with SO2 being preferentially adsorbed. Finally, this study explains in detail the mechanism of simultaneous SO2 and NO degradation, showing that the reactive species generated during corona discharge can excite microemulsions to produce more reactive radicals and active substances to further improve the removal of SO2 and NO.

A brand new two-phase wet oxidation absorption system for the simultaneous removal of SO2 and NOX from simulated marine exhaust gas

Marine engine exhaust emissions are increasingly harmful to the natural environment and human health and must be controlled. A self-synthesized amide (BAD, C12H25NO) in the laboratory shows a strong absorption capacity of nitric acid and nitrous acid, which may solve the problem that only using chlorine-based oxidant as an absorbent cannot completely absorb or retain NO2 produced by NO oxidation in previous studies. Based on Multiwfn and VMD (Visual Molecular Dynamics) program calculation, the formation mechanism of hydrogen bonds between BAD with nitric acid and nitrous acid was revealed by electrostatic potential (ESP) analysis and further confirmed by FT-IR (Fourier transform infrared spectroscopy) spectra research. Subsequently, simultaneous removal of SO2 and NOX from simulated flue gas was carried out by using NaClO/BAD as a two-phase composite absorbent, and the maximum removal efficiencies of SO2 and NOX were 98.9% and 86.6%, respectively. The recycling experiments and the engineering experiments showing that NaClO/BAD can solve the problem of absorption of NO2, and it can be a promising composite absorbent in wet desulfurization and denitrification of marine engine exhaust gas in practical applications.

Effect of amino acid additives in ammonia solution on SO2 absorption and ammonia escape using bubbling reactor for membrane contactor applications

Controlling the SO2 emissions is crucial because they result in several environmental problems and affect human health. Several techniques have been proposed for controlling SO2 emissions. Limestone or lime-based absorbents are widely used for SO2 removal. However, their low solubility limits their applications. Ammonia solution has attracted attention owing to its higher SO2 removal efficiency. However, owing to its high volatility, it has the propensity to escape, which can cause secondary environmental pollution. Therefore, we investigated the effect of six amino acid additives to improve the SO2 absorption performance and inhibit the ammonia escape in aqueous ammonia solution. The surface tension and theoretical breakthrough pressure of the amino acid-containing ammonia solutions was investigated to evaluate their applicability to a membrane contactor process. L-histidine (His) exhibited the best performance. Therefore, the effect of His concentration, inlet SO2 concentration, and absorption temperature on SO2 absorption performance was explored. The 13C nuclear magnetic resonance (NMR) and 1H NMR analyses were used to study the SO2 absorption mechanism. This study provides a strategy for preparing an eco-friendly and highly efficient SO2 absorbent that can overcome the disadvantage of current ammonia solutions for the removal of low-concentration SO2 from industrial gas emissions for the membrane contactor process application.

Comparative study on direct and indirect methods for wet desulphurisation and denitrification based on micro-nano bubbles

ABSTRACT The wet desulphurisation and denitrification technique based on micro-nano bubbles, which is available by either D-method or I-method, is a promising novel process. By employing piped water, Na2SO3 aqueous solution and HA-Na aqueous solution as the absorption liquids, a comparative study was conducted in this article on D-method and I-method to analyze their performance, advantages and disadvantages. It was accompanied by an investigation of how initial pH and initial temperature values of the absorption liquids affected the removal efficiency. The results suggested a positive correlation between NO/SO2 removal efficiencies and pH values but a little improvement in the removal efficiency under alkaline conditions. Furthermore, heating the absorption liquids inhibited the removal of NO and SO2. When manipulated in the same experimental environment, D-method and I-method did not present a significant difference in the SO2 removal efficiency, while the former was remarkably more effective than the latter in removing NO. To put together, D-method had higher removal efficiency, but required a large-scale micro-nano bubble generator to process a large quantity of flue gas as the micro-nano bubble generator was subject to a limited inlet flow rate. Consequently, an increase in investment and operating costs was incurred, while this issue could be avoided by I-method.

Removal of multi-pollutants in flue gas via a new approach based on dielectric barrier discharge coupling MnCu/Ti oxidation

A dielectric barrier discharge (DBD) coupling MnCu/Ti oxidation and postpositioned wet electrostatic precipitator (WESP) system was built. The experimental results showed that WESP can significantly enhance the simultaneous conversion efficiency(ηC) of NO, SO2 and Hg0 by the DBD coupling MnCu/Ti reactor. The best simultaneous removal efficiency(ηR) of NO, SO2 and Hg0 reached 94.5%, 100% and 100%, respectively. The ratio of catalyst active component (Mn/Cu) and catalyst filling amount were optimized. The effects of catalyst active component ratio, filling amount, flue gas component and energy density (SED) on the ηC of NO, SO2 and Hg0 were determined. The effect of sodium humate (HA-Na) in the cleaning water on the ηR was also illustrated. Besides, we clarified the absorption mechanism and how WESP corona discharge oxidized NO, SO2 and Hg0, as well as the removal of NO2, SO2, and SO3 by HA-Na. Product analysis showed that NO2, SO2 and SO3 were converted into NO3- and SO42-, part of HgO was converted into Hg2+ in the cleaning water, and a small amount of Hg(NO3)2 and HgSO4 were converted into Hg2+, NO3- and SO42-.

Recycling of marble waste for desulfurization of flue gas accompanied by synthesis of gypsum and PoP

The suitability of marble waste (MARWAS) slurry as an alternative sorbent to limestone for wet flue gas desulfurization (WFGD) was studied by absorbing SO2 from air-SO2 mixtures in a semi-batch bubble column reactor. The concentration of SO2 at the inlet to- and exit from the reactor was measured using an infrared SO2 analyser (ZJRFAY36, Fuji, Japan). Percent removal efficiency (PRE) of SO2 and slurry saturation time (SST) were determined as functions of pertinent process variables. The maximum values of PRE and SST obtained were 99.8% and 40.83 min, respectively, for a slurry depth of only 3 × 10−2 m. Product gypsum was calcined to Plaster of Paris (PoP) using a modified electric furnace and characterized using XRD, TGA, and SEM analyses. A design criterion for the continuous absorption of SO2 using two semi-batch absorbers have been proposed that allows complete conversion of MARWAS and more than 99% PRE of SO2. The synthesized gypsum can be used to adjust the desired properties of cement products while the PoP as a construction material. A comparison of PRE of SO2 using MARWAS and limestone slurries showed its maximum value to differ by approximately± 1%. MARWAS slurry can, therefore, be favorably employed for the WFGD.