Wet Flue Gas Desulphurization Research Articles

Investigation of Mazidagi phosphate ore in wet flue gas desulphurization

The employment of Mazidagi phosphate ore for wet flue gas desulphurization was investigated. The ore was exposed to sulfation processes in a three-phase double-stirred reactor to determine the effects of certain parameters on SO2 absorption. The absorption rate significantly increased with inlet SO2 concentration, gas flow rate, stirring speeds, and solid concentration but not with temperature. The absorption rate increases as the mass transfer coefficients and interface area value increase with stirring speeds. These parameters have also a prominent impact on the absorption rate depending on the dissolution rate of CaCO3. Based on these, the most effective parameters on SO2 absorption are liquid-phase stirring speed and suspension concentration, and the process is diffusion-controlled in the liquid phase. In addition, optimum conditions were determined, and then the ore was exposed to sulfation processes via a semi-batch operation mode. A comparison between raw and sulfated ore was examined for the changes in physical structure and chemical composition. Although the ratios of fluorapatite and carbonate-fluorapatite remained nearly constant, the ratio of calcite decreased significantly. It was determined from these investigations that the calcite in the phosphate ore has been converted into the CaSO3∙½H2O compound. Consequently, both the calcite in the phosphate ore was utilized effectively for wet flue gas desulphurization, and a phosphate-rich industrial product was obtained.

Research on enhancing separation of ultra‐fine droplets using turbulators between adjacent demister plates in WFGD systems

AbstractTo enhance the performance of demister applied in wet flue gas desulphurization systems, flow turbulators are equipped between adjacent plates to reconstruct flow field. Both experimental and numerical approaches are employed to investigate the influence of various kinds of turbulator configurations upon removal of droplets within the range of 5–50 μm obeying Rosin‐Rammler distribution. Turbulators including spoiler, square column, concave groove, perforated concave groove, and triangular and cylinder columns are compared, among which spoiler provided the highest overall efficiency while square column yields the best graded efficiency for 5 μm droplets group. Furthermore, moving the spoiler towards the core region of the demister ducts received better performance due to augmented interaction between spoiler and drainage channels, which performed an essential role in droplets collection. Based on this knowledge, spoilers are optimized by changing their angle of attack and size; the result is positive since overall separation efficiency can be improved to 100%, along with graded efficiencies for 10 and 5 μm groups achieving 95.97% and 27.26%, respectively, much higher than those of baseline demister without turbulators. This study indicates that inertial‐based demisters have great potential in separating ultra‐fine droplets through reorganizing turbulence field, thus extra system loss can be avoided by abandoning additional filter components.

Flue Gas Desulfurization Scrubbers in Heavy Diesel Combustion Plants

Through the purification technology of flue gas desulfurization, ultralow emissions of SO2 flue gas in industrial flue gas can be achieved. In this article, wet flue gas desulphurization (FGD) processes using limestone (calcium carbonate CaCO3) and caustic (sodium hydroxide NaOH) as absorption solution are introduced in terms of fluid mechanics and mass transfer phenomena as well as absorption unit processes. Also initial investment and operation costs are compared for wet flue gas desulphurization processes using limestone and and caustic.

Uncertainty and disturbance estimator-based model predictive control for wet flue gas desulphurization system

Uncertainty and disturbance estimator-based model predictive control for wet flue gas desulphurization system

High-efficient cyclic absorption of sulfur dioxide in Na-Mg-Ci3- compound system for wet flue gas desulfurization

Sulfur dioxide (SO2), as a primary pollutant in the air, has attracted much attention due to the adverse effects on the atmospheric environment and human health. The wet flue gas desulfurization (WFGD) has been proved to be the most effective method to control the emission of SO2. However, the traditional absorbents in WFGD posed the problems of limited recycling utilization and susceptible to oxidation. In this study, we proposed the Na-Mg-Ci3- compound system to repeatedly absorb SO2 for rounds. The results demonstrated that the compound system can integrate the absorption capacity of Na3Ci absorbent and the regeneration efficiency of Mg3Ci2 absorbent. We compared the performances of the compound systems with different alkaline earth metals (Li, Na, K), and the sodium was most suitable for the circulating desulfurization with the consideration of performance and economy. After that, we investigated the influence of ingredient proportions on the absorbent performance, and the results showed that the 0.4 mol/L Na3Ci and 0.2 mol/L Mg3Ci2 were the best combination for the compound system in these experiments. In this condition, the compound system had the excellent effective sulfur capacity and regeneration speed in the recycling process. Moreover, the anti-oxidation effect of sodium ascorbate was explored, and the reusability performance of compound system can be improved with antioxidants. This study contributes to providing a novel method for the removal and recycling of SO2 in the wet flue gas desulphurization.

A case analysis and treatment measures of high moisture content in wet desulphurization gypsum

China’s thermal power plant wet FGD (flue gas desulphurization) produces more than 80 million tons of gypsum each year. The factors affecting the quality of wet desulphurization gypsum are limestone quality, flue gas dust, gypsum slurry pH, slurry quality, gypsum water content, desulphurization system design features, and operating conditions, etc. There are many reasons for high gypsum moisture content, and the analysis and solution are particularly complex. Through a case analysis of a power plant with high moisture content of desulphurization gypsum, the main reasons are that the unit has been operating under low load conditions for a long time with low sulphur coal, limestone supply slurry is high, slurry pH is high, and the volume of gypsum crystals generated is small, resulting in gypsum dehydration difficulty and high moisture content. The measures were to add the crystal seeds into the slurry and to lower the operation pH. The slurry quality is improved, and the gypsum dehydration returns to normal. The design margin of the desulphurization system is large, even in a long-term low sulphur and low load operation. There are no similar cases, and this situation generally does not attract attention. It is worth further analysis and reference.

Flexible Control of Wet Desulphurization Process Based on Frequency Retrofit

To assist in the absorption of renewable energy, coal-fired power plants need to operate over a wide range of loads, which exacerbates the challenge of the time delay in the wet desulphurization process. Therefore, this paper proposes a new control structure based on frequency retrofit and a corresponding model predictive controller to change the traditional idea of wet desulphurization control. This structure provides faster control actions, thus reducing time delay directly. And it makes the original discrete control variable continuous, enabling most control methods. The field application to the wet flue gas desulphurization system reveals the practical prospects of the proposed control structure and simulations have been conducted to verify the merits of the proposed control scheme based on data collected from a 1000 MW power plant.

FGD (FLUE GAS DESULPHURIZATION) SYTEM -OVER VIEW

Advantage of using dry FGD (FLUE GAS DESULPHURIZATION) System instead of the WET FGD System in terms of efficiency and cost-effective solution. Though, the high cost of expensive slaked/quick lime required as reagent in dry FGDs, considering the capital cost of the project and considering the Water saving (useful in the water scarcity area) the Dry FGD system shall be recommended.

Wet Flue Gas Desulphurization (FGD) Wastewater Treatment Using Membrane Distillation

The use of waste incineration with energy recovery is a matured waste-to-energy (WtE) technology. Waste incineration can reduce the volume and mass of municipal solid waste significantly. However, the generation of high volumes of polluting flue gases is one of the major drawbacks of this technology. Acidic gases are constituents in the flue gas stream which are deemed detrimental to the environment. The wet flue gas desulphurization (FGD) method is widely employed to clean acidic gases from flue gas streams, due to its high efficiency. A major setback of the wet FGD technology is the production of wastewater, which must be treated before reuse or release into the environment. Treating the wastewater from the wet FGD presents challenges owing to the high level of contamination of heavy metals and other constituents. Membrane distillation (MD) offers several advantages in this regard, owing to the capture of low-grade heat to drive the process. In this study the wet FGD method is adopted for use in a proposed waste incineration plant located in Ghana. Through a mass and energy flow analysis it was found that MD was well matched to treat the 20 m3/h of wastewater generated during operation. Thermal performance of the MD system was assessed together with two parametric studies. The thermal efficiency, gained output ratio, and specific energy consumption for the optimized MD system simulated was found to be 64.9%, 2.34 and 966 kWh/m3, respectively, with a total thermal energy demand of 978.6 kW.

Synergetic removal characteristics of mercury for ultra-low emission coal-fired power plant

The synergetic mercury removal by flue gas treatment process in coal-fired power plants is widely accepted, but there is a lack of a corresponding model to describe mercury transformations. In this work, a model for mercury transformations is established in a flue gas treatment process model using Aspen Plus. The concentrations, mass flow rates, and normalized emission factors of mercury, NOX, particulate matters (PM), and SO2 are investigated in a 660 MW coal-fired power plant. The mercury oxidation efficiency of the selective catalytic reduction (SCR) unit is 56.9 %. The mercury removal efficiency of the electrostatic precipitator (ESP) and wet flue gas desulphurization (WFGD) units are 53.5 % and 34.4 %, respectively. The ultra-low emission system achieves 63.3 % removal of mercury. Approximately 53.5 % of mercury is retained in the fly ash. The emission factor of mercury is 0.0131 mg/kWh and increases to 0.0265 mg/kWh when the load decreases from 100 % to 50 %. The emission factors of PM, SO2 and NOX are 7.1, 97.1, and 142.9 mg/kWh at full load, and 10.9, 97.4, 150.0 mg/kWh at 50 % load, respectively. The proposed flue gas treatment process model is considered a feasible approach for quantitative evaluation of multi-pollutants emissions at plant level.

Impact of ultra-low emission retrofitting on partitioning and emission behavior of chromium in a Chinese coal-fired power plant.

Due to its low vapor pressure, chromium (Cr) mostly emitted as fly ash particles (especially PM2.5) into environment in coal-fired power plants (CFPPs). The ultra-low emission (ULE) control technologies used in current CFPPs may be beneficial to reducing both the regular pollutants and hazardous trace elements (e.g., Cr), but the insight into the removal efficiency of Cr by different upgrading air pollution cleaning devices (APCDs) and the environmental stability of the Cr-bearing wastes produced from those APCDs in the ULE CFPPs has rarely reported. This study investigated and compared the distribution and emission characteristics of Cr in a Chinese CFPP before and after ULE, and the leaching behavior of Cr after ULE retrofitting in combustion byproducts was also revealed. The results showed that Cr was primarily captured in bottom and fly ashes (80.85%), followed by gypsum (0.02%) and sludge from wet electrostatic precipitator (WESP) (4.52×10-4%), with only 3.02×10-8% emitted into the atmosphere. Additional WESP had a large removal efficiency of Cr with the value of 92.04%, and the overall Cr removal efficiency of selective catalytic reduction (SCR) equipment, electrostatic precipitator (ESP), wet flue gas desulphurization (WFGD) system, and WESP equipped after ULE retrofitting was 99.99%. Notably, although the mass percentage of Cr in WESP sludge was negligible, the concentration of Cr in WESP sludge was 324.04mg/kg. The leaching concentrations of Cr in combustion byproducts were in the descending order: fly ash>WESP sludge>bottom ash>gypsum. The atmospheric emission factor of Cr in the studied power plant was 1.08mg/t coal, which was significantly lower than those of the CFPPs before ULE retrofitting. Therefore, the ULE retrofitting for CFPP was beneficial to reduce Cr emissions. More attention should be paid to the subsequent processing problem of solid combustion byproducts, especially the WESP sludge.

Study on the condensable particulate matter removal characteristics of air pollution control devices in a Chinese ultra-low emission coal-fired generating unit

Condensable particulate matter (CPM) belongs to PM25. In addition, it is one of PM2.5 main contributors. But CPM emissions are often overlooked in coal-fired power plants. As a result, this paper studies the removal characteristics of (CPM) from air pollution control devices (APCDs) in a Chinese ultra-low emission coal-fired generating unit. The quality and content of flue gas particles, including CPM and filterable particulate matter (FPM), were measured at four points: the selective catalytic reduction (SCR) input, air preheater (APH) inlet, electric precipitator (ESP) outlet, and wet flue gas desulphurization (WFGD) outlet. The removal characteristics of each APCD were studied. Within the scope of this study, it is found that: ® CPM emission concentration accounts for 94.9% of total particle emission concentration, and is higher than the ultra-low particulate matter outflow guidelines for coal-fired power plants in China; ©WFGD has the highest CPM inorganic component removal radio of 97.02%, and ESP has the highest CPM organic component removal radio of 58.46%, among APCDs; ©SO4 2−, NH4 +, F−, and Cl− are the most abundant water-soluble ions in CPM.

A wet type flue gas desulphurisation system used in a coal-fired power plant: a case study

A wet type flue gas desulphurisation system used in a coal-fired power plant: a case study

A wet type flue gas desulphurisation system used in a coal-fired power plant: a case study

A wet type flue gas desulphurisation system used in a coal-fired power plant: a case study

An assessment of an ion exchange resin system for the removal and recovery of Ni, Hg, and Cr from wet flue gas desulphurization wastewater—a pilot study

The paper presents the results of a pilot-scale study investigating the efficiency of an ion exchange resin system in the removal of Ni, Hg, and Cr from flue gas desulphurisation wastewater, in the presence of competitive metals such as Ca, Mg, Al, Fe, and Mn. The core part of the ion exchange installation consisted of two columns that were filled with ion exchange resin with iminodiacetic functional groups (Purolite S930) and one column filled with resin with isothiouronium functional groups (Purolite S920). The results showed that Ni, Hg, and Cr were almost completely removed from the wastewater with nearly 100% efficiency. Purolite S930 almost totally removed Ni, reducing its content from 89.3 ± 35 μg dm−3 to below 0.1 μg dm−3, while Purolite S920 reduced the remaining Cr content from 2.2 ± 0.6 μg dm−3 and most of the Hg content, from 23.5 ± 6.6 μg dm−3 to below 0.1 μg dm−3. The competitive metals Ca, Mg, Mn, and Al showed low affinity to the studied ion exchange resins. The study also assessed speciation of ion forms and sorption mechanisms. Breakthrough curve analysis was also carried out, which revealed that the selectivity sequence of iminodiacetic resin was Ni > Cr > Hg > Fe > Al > Mn > Ca, Mg. Elution studies were performed on S930 resins that allowed the separation of two streams: one containing mostly Ni and Fe which can be subjected to Ni recovery and the other containing mostly Cr and Hg which can be separated.

Analysis of Desulfurization Characteristics in Coal-Fired Power Plant by Numerical Simulation and Computer Simulation

In this paper, the spray tower of a wet flue gas desulphurization system in a coal-fired power plant is studied. The flue gas and slurry droplet are two-way coupled with Euler-Lagrange method. The heat and mass transfer and the ion reaction in SO2 removal are also considered. The results show that the error between simulation removal efficiency and practical value is within 5% under the above models. Adjusting liquid-gas ratio and opening spray layer are beneficial to the SO2 removal, and the optimal liquid-gas ratio is 16 L/m3. Balance gas velocity is needed, because an overlarge velocity will significantly reduce removal efficiency.

Modified zeolite as a sorbent for removal of contaminants from wet flue gas desulphurization wastewater

The aim of the present work was to prepare and investigate the sorption efficiency of unwashed cationic surfactant-modified natural zeolite (Cp) for the simultaneous removal of selected inorganic compounds (NH4+, SO42−, NO3−, Fe, Mn, Zn, and Ni) from wet flue gas desulphurization (WFGD) wastewater. The Cp was modified using hexadecyltrimethylammonium bromide (HDTMA-Br) salt in an amount not exceeding its external cation exchange capacity (1.0 ECEC). The present analysis showed that the modification process was completed by forming an incomplete monolayer by the uptaken HDTMA ions. Fourier transform infrared (FTIR) and textural analysis indicated that the adsorbed HDTMA ions formed a disordered, macroporous structure onto Cp surface. Batch adsorption experiments with different sorbent dosages revealed an increase in the sorption efficiency of NH4+ and NO3− with the increase in the amount of modified Cp. The highest removal efficiency was observed at adsorbent dosage of 150 g/L. The studies also revealed, that the SO42− removal did not change significantly regardless the sorbent dosage. The kinetic tests showed that a substantial amount of inorganic compounds was removed within 2 h, and the sorption kinetics of each compound were best fitted to the pseudo-second order model. The studies of adsorption mechanism revealed that cation exchange, anion exchange with Br− counterion, electrostatic interaction between the surfactant and inorganic ions, as well as precipitation of insoluble salts might be involved simultaneously in the immobilization of NH4+, SO42−, NO3−, Fe, Mn, Zn, and Ni.

Waste heat utilization from boiler exhaust gases for zero liquid discharge of desulphurization wastewater in coal-fired power plants: Thermodynamic and economic analysis

Zero liquid discharge (ZLD) of wet flue gas desulphurization (WFGD) wastewater in coal-fired power plants (CFPPs) would contribute to sustainable development of fossil electricity generation. In the present work, improved flue gas-driven forced-circulation multi-effect distillation and crystallization (FCMEDC) systems were proposed for achieving low-cost ZLD of WFGD wastewater. Different types of integration scenarios were investigated, including FCMEDC systems driven by waste heat recovered from boiler and economizer exhaust gases, and incorporated with low-pressure economizer and flue gas bypass high-pressure economizer systems. Thermodynamic and techno-economic analysis models were developed for comprehensive evaluation of the technical and economic feasibility of the integrated ZLD schemes. The levelized cost of wastewater (LCOW) and operating expenditure (OPEX) were found to be significantly reduced by 41.5% and 53.6%, respectively, when plant auxiliary steam was substituted by boiler exhaust gas as the heat source in a 600 MW unit. A parametric study was further conducted to investigate the impact of wastewater salinity and flow ratio on the process design. The flue gas-driven FCMEDC system demonstrated favorable adaptability to variations in wastewater quality. Moreover, sensitivity analysis suggested that the LCOWs of the proposed ZLD systems were explicitly subject to the expected lifetime, brine disposal options, and brine pre-concentration. The methodology and results could provide insights into the process development of WFGD wastewater ZLD systems based on the FCMEDC technology.

Synthesis and Characterization of Zeolites Produced from Low-Quality Coal Fly Ash and Wet Flue Gas Desulphurization Wastewater.

This study investigated a low-energy-consuming procedure for the synthesis of zeolite materials from coal fly ash (CFA). Materials containing zeolite phases, namely Na–X, Na–P1, and zeolite A, were produced from F–class fly ash, using NaOH dissolved in distilled water or in wastewater obtained from the wet flue gas desulphurization process, under atmospheric pressure at a temperature below 70 °C. The influence of temperature, exposure time, and alkaline solution concentration on the synthesized materials was tested. In addition, chemical, mineralogical, and textural properties of the obtained materials were determined by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and cation exchange capacity (CEC). Cd(II), Ni(II), NH4+ cation, and Se(VI) anion sorption experiments were conducted to compare the sorption properties of the produced synthetic zeolites with those of the commercially available ones. Zeolitization resulted in an increase of CEC (up to 30 meq/100 g) compared to raw CFA and enhanced the ability of the material to adsorb the chosen ions. The obtained synthetic zeolites showed comparable or greater sorption properties than natural clinoptilolite and synthetic Na–P1. They were also capable of simultaneously removing cationic and anionic compounds. The structural, morphological, and textural properties of the final product indicated that it could potentially be used as an adsorbent for various types of environmental pollutants.

Spray drying absorption for desulphurization: a review of recent developments

Sulphur dioxide (SO2) abatement technologies, i.e. flue gas desulphurization (FGD), have proven effective in curtailing the harmful SO2 emissions resulting from coal combustion for electrical power generation. New regulations on these emissions now require some power utilities to retrofit new FGD units to existing coal-fired power plants to meet required emission standards. Wet FGD limestone scrubbing has been predominantly used over other competing technologies. However, the simplicity of the spray-drying absorption (SDA) technology has made it an attractive alternative to the wet scrubbing process. SDA offers huge savings on energy, water, operating cost and maintenance. Despite high cost of the sorbent (hydrated lime) used, recent advances in SDA process offer considerable economic and technical advantages ranging from improved sorbent utilization, better atomization and enhanced performance. Alternative sorbents and additives are continuously being explored for simultaneous removal of pollutant gases from flue gas. The performance improvement areas in a lime spray drying system include the use of inorganic salt additives, recycling of the dried product and the use of siliceous materials. This study is intended to review FGD systems applicable to coal-fired power plants, through a technical comparison between competing technologies. Additionally, a review of the spray-drying absorption process and operating parameters affecting their efficiency was carried out, together with a critical assessment of the literature published to date.