Desulfurization Wastewater Research Articles

Synergistic Modification of Ti/PbO2 Electrodes with Metal Ions (Nd, Al, Bi) and STAB Surfactant for Electrocatalytic Treatment of Desulfurization Wastewater

In this study, PbO2 electrodes are modified by co-doping with different metallic elements (Nd, Al, Bi) and stearyl trimethyl ammonium bromide (STAB) using the electrodeposition method. The modified electrodes, designated as Ti/PbO2-Nd-STAB, Ti/PbO2-Al-STAB, and Ti/PbO2-Bi-STAB, are then applied in the electrochemical degradation of desulfurization wastewater. The surface morphology, crystal structure, and elemental valence of the prepared electrodes are analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Their electrochemical performance and stability are assessed by linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and accelerated life testing (ALT). The results reveal that modification with metallic elements and STAB significantly enhances the physicochemical and electrocatalytic performance of the Ti/PbO2 electrode. Among the modified electrodes, the Ti/PbO2-Nd-STAB electrode exhibits the most compact and homogeneous surface morphology, the highest oxygen evolution potential (OEP, 2.33V vs. SCE), the lowest chlorine evolution potential (CEP, 1.44V vs. SCE), the largest electrochemically active surface area, the lowest charge transfer resistance, the highest electrochemical stability, and a prolonged accelerated life (65h, which is 17h longer than that of the unmodified electrode). Further, the optimal electrochemical oxidation process parameters for desulfurization wastewater are determined as follows: current density = 50mA/cm2, temperature = 35 ℃, electrode spacing = 3.0cm, and stirring rate = 300rpm. After 300min of electrolysis, the Ti/PbO2-Nd-STAB electrode achieves a Cl− removal rate of 86.9% and a chemical oxygen demand (COD) removal rate of 71.2%. After 10 cycles, the Cl− and COD removal rates decrease by 2.8% and 1.8%, respectively. Besides, Tafel curve analysis indicates that the chlorine evolution reaction follows the Volmer-Tafel mechanism, with the recombination of adsorbed Cl− ions on the surface oxidation film being the rate-determining step. Overall, the Ti/PbO2-Nd-STAB anode exhibits immense application potential in the treatment of desulfurization wastewater.

Investigation of Nitrogen Removal in Flue Gas Desulfurization and Denitrification Wastewater Utilizing Halophilic Activated Sludge.

In the process of flue gas desulfurization and denitrification, the generation of high-sulfate wastewater containing nitrogen is a significant challenge for biological wastewater treatment. In this study, halophilic activated sludge was inoculated in a Sequencing Batch Reactor to remove nitrogen from wastewater with a high sulfate concentration (60 g/L). With the influent concentration of 180 mg/L, the removal rate of total nitrogen was more than 96.7%. The effluent ammonium nitrogen concentration was lower than 1.94 mg/L, and the effluent nitrate nitrogen and nitrite nitrogen concentrations were even lower than 0.77 mg/L. The salt tolerance of activated sludge is mainly related to the increase in the content of ectoine in microbial cells. The Specific Nitrite Oxidation Rate is quite low, while the Specific Nitrite Reduction Rate and Specific Nitrate Reduction Rate are relatively strong. In the system, there are various nitrogen metabolic processes, including aerobic nitrification, anaerobic denitrification, and simultaneous nitrification-denitrification processes. By analyzing the nitrogen metabolic mechanisms and microbial community structure of the reaction system, dominate bacteria can be identified, such as Azoarcus, Thauera, and Halomonas, which have significant nitrogen removal capabilities.

Heavy metal migration and enrichment in desulfurization wastewater during low-temperature triple effect evaporation process

Zero discharge of desulfurization wastewater from coal-fired power plants has become important. Desulfurization wastewater and gypsum from different stages of the low-temperature triple-effect evaporation process of a coal-fired power plant were collected and investigated. The results showed that after low-temperature triple-effect evaporation, the concentrations of Na+, Mg2+, K+, and Cl− in the desulfurization wastewater increased by 7.91, 7.15, 8.49, and 8.35 times, respectively. With the progress of low-temperature triple effect evaporation process, the concentrations of As, Cd, Co, Cr, Cu, Mn, Se, and Zn in the wastewater after the triple effects were 5.85, 75.44, 1.28, 2.34, 13.66, 5.58, 8.59, and 4.35 times higher than those in the raw wastewater. Mn and Se exceeded the emission limits by 40 and 10 times, respectively. After triple-effect evaporation, the concentrations of As, Cd, Co, Cr, Cu, Pb, Se, and Zn in gypsum decreased to 46%, 26%, 66%, 41%, 35%, 97%, 39%, and 51% of the raw gypsum, respectively. Compared with that of other metal sulfates, the solubility of PbSO4 was extremely low under low-temperature conditions, and some PbSO4 precipitated during the triple-effect evaporation process, leading to a gradual decrease in the Pb concentration in the liquid phase. The mercury compounds in gypsum after the first and second effects were the same as those in raw gypsum, both of which were HgS and HgO. After third effect, the mercury compound in gypsum also included HgSO4. In addition, owing to the promoting effect of the pH of desulfurization wastewater approaching 5.50 on the generation of HgS, the proportion of HgS gradually increased, and the proportion of HgO gradually decreased from the raw gypsum to the third effect gypsum. Therefore, the stability of the mercury compounds in gypsum was enhanced. It can provide a good reference for the migration and enrichment of heavy metals in the low-temperature triple-effect evaporation process, which is beneficial for the clean production and efficient utilization of coal.

Eggshell-enhanced biochar with in-situ formed CaO/Ca(OH)2 for efficient removal of Pb2+ and Cd2+ from wastewater: Performance and mechanistic insights

This study proposes a green and simple strategy for efficiently removing heavy metals from wastewater by activating biochar with eggshell and in-situ generating CaO/Ca(OH)2. Characterization results revealed that the composite carbon material (BCEg15) successfully incorporated CaO/Ca(OH)2 active sites compared to the raw biochar (BC). Additionally, eggshell activation increased the specific surface area and pore volume of BCEg15 by 4.36 and 6.80 times, respectively, compared to BC. These structural enhancements increased the maximum adsorption capacity of BCEg15 for Pb2+ and Cd2+ by 20.68 and 42 times, respectively, compared to BC. Importantly, the loading of CaO and Ca(OH)2 significantly enhanced the ion exchange and mineral precipitation capacities of the biochar. For instance, compared to BC, the adsorption capacities of BCEg15 attributed to ion exchange (Qe) for Pb2+ and Cd2+ rose by 403.12 mg/g and 197.65 mg/g, respectively, while the adsorption capacities attributed to mineral precipitation (Qp) increased by 19.60 times and 45.20 times, respectively. BCEg15 demonstrated excellent reusability, maintaining adsorption capacities of 461.18 mg/g for Pb2+ and 265.26 mg/g for Cd2+ after five cycles. Additionally, BCEg15 outperformed commercial activated carbon in treating heavy metals from desulfurization wastewater from coal-fired power plants, achieving a removal efficiency of 99.98 % compared to 48.22 %. The primary mechanisms by which BCEg15 removes Pb2+ and Cd2+ were identified as ion exchange, mineral precipitation, complexation with oxygen-containing functional groups, and interactions with π electrons. Density functional theory (DFT) was utilized to delve deeper into the microscopic mechanisms of adsorption. The findings showed that the O-top site of CaO exhibited the greatest stability for heavy metal adsorption. Electron density difference maps and partial density of states (PDOS) results revealed a denser electron cloud and greater orbital overlap between CaO and Pb2+ compared to Cd2+, suggesting a higher affinity and adsorption capacity for Pb2+, consistent with the experimental findings. This study presents an effective method for preparing adsorbents capable of removing Pb2+ and Cd2+ from wastewater and offers theoretical insights into the adsorption mechanisms of metal oxide-incorporated biochar.

Study on the automatic control method for evaporation treatment of wet flue gas desulfurization wastewater in power plants

ABSTRACT DRFNN is used to predict the evaporation state of wastewater, and incremental PID algorithm is combined to adjust the control quantity. By real-time monitoring the state and parameter changes of wastewater evaporation treatment process, online adjusting and optimizing the parameters of DRFNN and incremental PID, the automatic control of desulfurization wastewater evaporation treatment is completed. The experimental results show that this method can achieve more accurate and reliable automatic control, short control time, strong ability to deal with emergencies, and can converge to stability in a short time. This method can effectively reduce the number of early alarms and failures of the system and save maintenance costs. The IAE values of chloride ion (Cl) and mercury (Hg) in this method are 0.3558 and 0.3872, respectively, which proves that the difference between the actual output and the expected output of this method is very small, which proves that the system in this paper has high accuracy.

Treatment of Se-Impacted Wastewater Using a Three-Dimensional Packed Bed Electrochemical Reactor

Selenium is an essential element for flora and fauna in trace amounts. It plays a crucial role in bolstering photosynthesis and facilitating thyroid hormone metabolism. However, excessive consumption of selenium can result in health concerns such as reproductive complications and cancer. Selenium usually coexists with minerals such as copper and coal in the natural environment. The associated activities, such as copper mining and coal combustion, have greatly accelerated the mobilization of selenium. The selenium released through coal combustion is mostly captured in the flue gas desulfurization (FGD) wastewater as inorganic selenite and selenate.Our lab previously validated the viability of direct electrochemical reduction (SeDER) to remove dissolved selenite from a simplified FGD water matrix using planar gold and graphite cathodes, where more than 94% of the aqueous selenite can be converted to elemental Se(0) deposited on the cathode surface. Graphite is eventually selected for its low material cost, decent removal performance, and minimum secondary pollution as compared to gold and other non-noble metal cathodes. This direct electrochemical deposition process provides many benefits that existing biological and indirect electrochemical methods lack, such as zero chemical addition and low to zero solid generation. However, this method is only suitable for wastewater with elevated temperatures necessary to generate conductive Se(0) for continuous reduction. The inclusion of a heating process adds complexity to the design, impeding the scalability of the SeDER system. Furthermore, the application of SeDER is constrained to Se-impacted wastewater with an elevated temperature.In this study, we propose a novel reactor design utilizing electrochemical reduction to treat Se-impacted wastewater at ambient temperature. The electrodes we used are made of graphite for the reasoning stated above. The reactor consists of a pair of planar graphite anode and cathode, and the inner chamber is filled with cylindrical graphite particle electrodes (PEs) separated by a nylon spacer to create an anodic chamber and a cathodic chamber. The PEs act as an extension of the planar electrodes, which offers numerous reaction sites and minimizes the travel distance for selenite ions to reach the electrode surface. In our 120-mL batch test with 0.1-mM selenite in 100-mM phosphate buffer, the exact system without filler removed 0% selenite at room temperature, while the filled 3D system removed on average 50% of the selenite in 3 hours. Using the same 3D system, we then investigated performance enhancement with a recirculating operation. The total working volume is fixed at 200 mL, while the flow rate and the applied voltage vary. The flow rate is set at the values with hydraulic retention time (HRT) fixed at 15 min, 30 min, and 60 min. The system-applied voltage is set at -1.9V (just enough for selenite reduction), -2.1V, and -2.3V. We found that the shortest HRT combined with -2.1V system applied voltage yielded the highest selenite removal performance in all tests, with an average of 47% removal in 3 hours. We hypothesized that the shorter HRT provides a faster flow rate that refreshes the PE’s surface from insulative Se(0) deposition, which provides sustainable reaction sites for the incoming selenite. At -2.1V, the potential is negative enough to allow selenite reduction while fewer parasitic reactions (e.g., hydrogen evolution reaction) occur compared to that under -2.3V.With the selected system voltage and flow rate, we eventually explored competing ion behavior and switched from a simplified water matrix to simulated Se-impacted wastewater. We found that of all the commonly found competing ions (i.e., sulfate, nitrate, and chloride), chloride significantly impacts selenite removal, with performance dropping to 10% removal in 3 hours. Nitrate slightly decreased the selenite removal, with an average Se removal performance of 23%. Sulfate, on the other hand, resulted in an increase in selenite removal after addition. We hypothesize that a high sulfate concentration in simulated wastewater could help alleviate the repulsing force from the cathode surface for the selenite ions. The double layer of the PEs could also be compressed by the high ionic strength, which decreases the capacitance and promotes selenite reduction. To confirm this hypothesis, we conducted an electrochemical impedance study to analyze the effect of competing ions on reaction kinetics and capacitance. We also performed surface analysis for the wasted planar electrodes and PEs to investigate the change in morphology and observed possible chemical residue. These characterizations will help us develop a regeneration protocol in long-term operation and help us scale up our prototype to manage actual Se-impacted wastewater.

Atomization and desulfurization characteristics of limestone slurry in a non-uniform electric field

Electrohydrodynamic atomization (EHDA) of limestone slurry is anticipated to significantly enhance desulfurization efficiency and reduce desulfurization wastewater discharge. In this study, a visual electrospray experimental system is established to obtain the characteristics of EHDA. Initially, the breakup modes of the slurry are investigated, identifying three distinct modes: dripping mode, microdripping mode, and oscillating microdripping mode. The electric field shortens the liquid thread, reducing secondary droplet formation in the oscillating microdripping mode. Furthermore, it is found that a slight increase in droplet size and an initial decrease followed by stabilization in generation frequency with voltage increasing in the oscillating microdripping mode. In addition, the nondimensionalized droplet size prediction formulas for each breakup mode are provided. Subsequent desulfurization characteristic experiments in an absorption tower reveal optimal desulfurization efficiency in the oscillating microdripping mode. The relationship between desulfurization efficiency and droplet size is discussed, highlighting the pivotal role of the gas-liquid contact area in determining desulfurization efficiency. The present work is expected to provide theoretical guidance for efficient desulfurization.

Microbial osmotic pressure desalination system for desulfurization wastewater from coal-fired power plants: A pilot study

The treatment of desulfurization wastewater has emerged as a critical area of research due to the significant water consumption and drainage volume associated with thermal power plants, which account for 30 %–40 % of industrial water usage. The desalination and treatment of this wastewater generate desulfurization byproducts, posing environmental risks and incurring high operational costs. This study established a pilot-scale desalination system based on the principle of microbial osmotic pressure for the treatment of desulfurization wastewater from power plants. The desulfurization wastewater primarily contains Cl−, SO42−, Mg2+, Ca2+, and Na+ ions. The microbial osmotic pressure device reduced the water conductivity from 26,000 μs/cm to below 8000 μs/cm, achieving a total salt removal rate of 70 %. The removal rates for Cl−, SO42−, Mg2+, Ca2+ and Na+ were 69.10 %, 76.55 %, 73.0 %, 35.34 % and 52.80 %, respectively. The desalinated water from the osmotic pressure device then undergoes aerobic removal of organic compounds, followed by membrane filtration and reverse osmosis for further desalination. The effluent conductivity is <1000 μs/cm, meeting the standards for reuse water. The microbial osmotic pressure device enriched salt-absorbing halobacteria and was dominated by norank_f__Bacteroidetes_vadinHA17, Trichococcus, Acidovorax, Soehngenia, and norank_f__Hungateiclostridiaceae. Compared to traditional processes, the biological desalination process demonstrates lower operational and annual maintenance costs under conditions of regular addition of microbial agents and liquid activators to sustain the desalination bacterial community. Future research could focus on desalination microbial cultivation methods to improve stability and reduce costs.

Multi-stage calcium-based chemical oxo-precipitation application to treat boron-containing flue gas desulfurization wastewater from coal-fired power plant

Chemical oxo-precipitation (COP) is a peroxo-aided process that was successfully applied to remove boron from the solution in the previous report. In this study, three-stage Ca-based COP was introduced to treat boron-contained flue gas desulfurization (FGD) wastewater that came from coal-fired power plants in Taiwan. Operating parameters, including pHi, [H2O2]i/[B]0, and [Ca]i/[B]0 (‘i’ represents the stage number) were optimized to reach the permissible effluent boron concentration of 5 mg/L. The effect of sulfate and magnesium in boric acid solution as the interference ions was preliminary investigated. The presence of sulfate and high magnesium concentration ([Mg]0/[B]0 > 0.5) are negatively affected the deboronation process due to the consumption of calcium and hydrogen peroxide, respectively, to form the unrequired precipitate. The optimum condition was resulting in residual boron concentration of 2.5 mg/L reached under the pH1 = pH2 = 10.5, pH3 = 11.0, [H2O2]1/[B]0:[H2O2]2/[B]0:[H2O2]3/[B]0 = 2:2:2, [Ca]2/[B]0:[Ca]3/[B]0 = 1.5:1. FTIR and RAMAN analysis show that most of the boron was removed via Ca(B(OH)3OOH)2 and CaB(OH)3OOB(OH)3 precipitation at 1st and 2nd stage. However, the predominated formation of metal peroxide, metal carbonate, and metal sulfate at 3rd stage provided different removal mechanism of boron through adsorption and co-precipitation. It can be concluded that Multi-stage Ca-based COP has a big potential to be applied to treat boron-contained industrial wastewater, but the re-adjustment is needed due to the varying concentration of wastewater components.

Sulfite permeability and sulfur accumulation in a sulfite depolarized electrolyser

Sulfur dioxide or sulfite depolarized electrolyser is considered a promising technology for green hydrogen production. A sulfite depolarized electrolyser adopting sulfite wastewater is developed for both hydrogen production and wastewater treatment in our project, e.g. flue gas desulfurization wastewater and lead plate pre-desulfurization solution. Sulfite permeability and sulfur accumulation are primary challenges of the sulfite depolarized electrolyser for long-term stability. The electrochemical behaviors of SO32− reduction are investigated particularly here, which exhibits a 3.06-electron route on the homemade Pt-Pd/C catalyst. The reduction of SO32− to S0 is observed using an electrochemical quartz crystal microbalance. The sulfite diffusion coefficients of three proton exchange membranes are also determined. A frequent polarity inverted electrolysis is developed to remove the sulfur deposits and keep cell stability. Adopting a lead plate pre-desulfurization solution as the anolyte, both the fresh and repaired sulfite depolarized electrolyser can achieve a remarkable current density of > 500 mA/cm2 at 2.0 V. 200 h long-term test indicates excellent anodic depolarization and long-term stability for hydrogen production. The strategy may shed light on the further development of industrial applications.

The potential of coupled water electrolysis with electrochemical wastewater treatments

The coupled water electrolysis is a promising strategy for green hydrogen production. Pollutants are attractive feedstocks for the fungible anode reactions of the sluggish oxygen evolution reaction, with the advantages of trash-to-treasure and cost reduction. There is an urgent need for real waste sample tests from the view of both contaminant abatement and electrochemical hydrogen production. This work offers a systematic evaluation of the coupled water electrolysis with real wastewater, where four real wastewater with sulfur element compounds in different states are taken as examples. The technical and economic potentials are evaluated particularly based on the coupled water electrolysis performances, including cell voltage, current density, hydrogen production rate, hydrogen electricity consumption, and pollution abatement. The coupled water electrolysis with the refractory wastewater, e.g. the desulfurization wastewater from coal-fired power plants and the H acid wastewater, does not show advantages from the view of hydrogen production, due to the high overpotential and limited current density. Nevertheless, hydrogen is a high-value-added byproduct for operation cost reduction from the view of wastewater treatment. The readily oxidizable pollutants, e.g. sulfite and sulfide, exhibit notable potentials for anodic depolarization and electricity consumption reduction of hydrogen production. However, the coupled water electrolysis adopting the sulfide spent caustic stream may suffer a low hydrogen production rate for sulfide to sulfur. The coupled water electrolysis adopting sulfite wastewater indicates excellent potential for both space-time yield and electricity consumption for hydrogen production. This work may offer a reference for the systematic evaluation and selection of coupled water electrolysis with real wastewater.

Separation of Chloride and Sulfate Ions from Desulfurization Wastewater Using Monovalent Anions Selective Electrodialysis.

The high concentration of chloride ions in desulphurization wastewater is the primary limiting factor for its reusability. Monovalent anion selective electrodialysis (S-ED) enables the selective removal of chloride ions, thereby facilitating the reuse of desulfurization wastewater. In this study, different concentrations of NaCl and Na2SO4 were used to simulate different softened desulfurization wastewater. The effects of current density and NaCl and Na2SO4 concentration on ion flux, permselectivity (PSO42-Cl-) and specific energy consumption were studied. The results show that Selemion ASA membrane exhibits excellent permselectivity for Cl- and SO42-, with a significantly lower flux observed for SO42- compared to Cl-. Current density exerts a significant influence on ion flux; as the current density increases, the flux of SO42- also increases but at a lower rate than that of Cl-, resulting in an increase in permselectivity. When the current density reaches 25 mA/cm2, the permselectivity reaches a maximum of 50.4. The increase in NaCl concentration leads to a decrease in the SO42- flux; however, the permselectivity is reduced due to the elevated Cl-/SO42- ratio. The SO42- flux increases with the increase in Na2SO4 concentration, while the permselectivity increases with the decrease in Cl-/SO42- ratio.

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.

Migration and distribution characteristics of typical organic pollutants in condensable particulate matter of coal-fired flue gas and by-products of wet flue gas desulfurization system.

The wet flue gas desulfurization (WFGD) system of coal-fired power plants shows a good removal effect on condensable particulate matter (CPM), reducing the dust removal pressure for the downstream flue gas purification devices. In this work, the removal effect of a WFGD system on CPM and its organic pollutants from a coal-fired power plant was studied. By analyzing the organic components of the by-products emitted from the desulfurization tower, the migration characteristics of organic pollutants in gas, liquid, and solid phases, as well as the impact of desulfurization towers on organic pollutants in CPM, were discussed. Results show that more CPM in the flue gas was generated by coal-fired units at ultra-low load, and the WFGD system had a removal efficiency nearly 8% higher than that at full load. The WFGD system had significant removal effect on two typical esters, especially phthalate esters (PAEs), with the highest removal efficiency of 49.56%. In addition, the WFGD system was better at removing these two esters when the unit was operating at full load. However, it had a negative effect on n-alkanes, which increased the concentration of n-alkanes by 8.91 to 19.72%. Furthermore, it is concluded that the concentration distribution of the same type of organic pollutants in desulfurization wastewater was similar to that in desulfurization slurry, but quite different from that in coal-fired flue gas. The exchange of three organic pollutants between flue gas and desulfurization slurry was not significant, while the concentration distribution of organic matters in gypsum was affected by coal-fired flue gas.

Experimental and theoretical study on recovered nano amorphous selenium as efficient adsorbents for mercury capture from flue gas

The cost-effective removal of gaseous elemental mercury from coal-fired flue gas is crucial for environmental protection. In this study, nano amorphous selenium (nano-a-Se) adsorbent was recovered from desulfurization wastewater to remove Hg0 in flue gas. The results indicate that nano-a-Se has a high efficiency in the amorphous form with a saturated adsorption capacity of 2034.32 mg g−1. The Se utilization ratio of nano-a-Se reached 80% of the theoretical limit. Meanwhile, nano-a-Se exhibited high resistance to NO and SO2 poisoning. Moreover, the Hg0 removal mechanism of nano-a-Se was analyzed by experimental analysis and density functional theory (DFT) calculations. The results demonstrate that nano-a-Se can convert Hg0 into stable mercury selenide, a high-value by-product with little risk of mercury re-release. Therefore, nano-a-Se is expected to be a novel adsorbent with high efficiency in capturing Hg0, which can help realize the resource utilization of toxic elements from the environment.

High-performance of Mg2+ additive for addressing NH3 escape in inorganic ammonia carbon capture

The urgency to reduce the energy consumption of organic amine carbon capture, while the inorganic ammonia carbon capture (IACC) and co-production of ammonium fertilizer eliminates the desorption energy consumption. Inhabiting NH3 escape at the end of IACC process requires a large amount of water consumption, and there is a lack of corresponding process parameters and technical routes. In this paper, Mg2+, one of major components in desulfurization wastewater, was used as an NH3 inhibitor. It’s found that the addition of MgCl2 can increase the total NH3 absorption rate by 13.02 % and reduce the total NH3 escape rate by 87.02 %. Furthermore, the effects of six process parameters in the forward and reverse NH3 mass transfer experiments could be distinctly quantified by the normalization method to determine the differentiation between priority and others. It’s concluded that NH3 can enter the first solvent shell of Mg2+ to replace some H2O based on the first-principles calculations, which is the main cause for the decrease of NH3 diffusion coefficient. Finally, simulation with Aspen Plus was applied to construct the complete process route, and the Arrhenius formula for the Mg(OH)2 nucleation was used to refine the reaction kinetic parameters of the simulation. The heat and water balance of IACC could achieve within this system, and the excellent NH3 inhibition effect of added Mg2+ was verified, which could effectively keep from the NH3 escape within 3 ppm.

Study on the evaporation performance of concentrated desulfurization wastewater and its products analysis

Concentrated desulfurization wastewater evaporation technology exhibited significant superiority in desulfurization wastewater zero discharge. Nevertheless, changes of physical and chemical properties of the concentrated wastewater shifts evaporation mode during wastewater evaporation, which may cause difficulty in disposing of evaporation products. In this work, the rotary spray drying pilot test experimental platform was utilized to investigate the evaporation performance of concentrated desulfurization wastewater. The results indicate that, while the evaporation rate of concentrated wastewater is lower than that of non-concentrated wastewater, its lower free water volume resulting in the improved evaporation performance. Increasing the inlet flue gas temperature, gas-liquid ratio, and prolonging the residence time of flue gas can promote droplet evaporation. Besides, the evaporation products were analyzed by various characterization techniques. The elemental composition and particle size of concentrated wastewater evaporation products change. At a moisture content of 2 %, the Flowability Function is 3.57 (2 < FF < 4), indicating a cohesive nature and poorer flowability compared to the non-concentrated wastewater.

Experimental study on the application of nanofiltration concentrated water in the preparation of burning-free bricks

ABSTRACT The realization of zero discharge of desulfurization wastewater has become a major trend in the environmental protection of power plants. After the desulfurization wastewater is treated by the nanofiltration process, a certain amount of nanofiltration concentrated water will be produced. Based on the water quality and quantity analysis of nanofiltration concentrate, this study proposes to apply nanofiltration concentrate to the preparation of free-sintering brick to realize the resource utilization of nanofiltration concentrate. The results show that the optimal ratio of the cement-to slag ratio ratio is 1:0.8, the 28d strength of the solidified body is 18.64MPa, the water absorption rate is 15.9%, and the water-soluble chloride ion content is 4.8%. In order to further optimize the production technology to improve the performance of the curing body, the later experiments optimized the curing formulation with the water-reducing agent sodium lignosulfonate as an admixture and obtained the optimal addition ratio of sodium lignosulfonate which was 0.2%. Finally, an economic evaluation was conducted and the use of nanofiltration concentrate for the preparation of free sintering brick could bring considerable economic benefits to the power plant while achieving the purpose of reducing environmental pollution and reducing the investment cost of environmental management.

火电厂高镁硬度脱硫废水预处理技术研究

火电厂高镁硬度脱硫废水预处理技术研究

A Study on Mechanism of Evaporation Reduction of Desulfurization Wastewater in Air Cooling Tower

It’s a new technology for the concentration and reduction of desulfurization wastewater by the indirect air cooling tower. In this paper, indoor experiments are conducted to explore the evaporation characteristics of the evaporation tower and the evaporation law of desulfurization wastewater in the filler and analyze the factors affecting the evaporation characteristics, and a power plant adopting this technology is tested to verify the conclusion of the indoor experiments. The results show that the evaporation rate of the evaporation tower is positively correlated with the cross-sectional wind speed, water spray density, packing height and other parameters, and the influence of the interrupted wind speed on the evaporation rate is the most significant. The difference of vapor pressure has a positive linear relationship with that of mass fraction of the air in inlet and outlet, and the results of model test conform to those of actual one basically. On the condition of ventilation rate of 817.56m3/s, the evaporation efficiency of a mechanical ventilation cooling tower with a drenching area of about 400m2 can reach 16.2-18.4t/h, which basically meets the engineering needs of desulfurization wastewater concentration and reduction in millions of thermal power plants.