Limestone-gypsum Wet Flue Gas Desulfurization Research Articles

Condensable Particulate Matter Removal and Its Mechanism by Phase Change Technology During Wet Desulfurization Process

Limestone-gypsum wet flue gas desulfurization (WFGD) played a key role in SOx removal and clean emissions. However, it would also affect the condensable particulate matter (CPM) removal and compositions. The effects of the WFGD system on the removal of CPM and the contents of soluble ions in CPM were investigated in a spray desulfurization tower at varied conditions. The results indicate that the emission concentration of CPM decreased from 7.5 mg/Nm3 to 3.7 mg/Nm3 following the introduction of cold water spray and hot alkali droplet spray systems. This resulted in a CPM reduction rate of approximately 51%, reducing the percentage of CPM in total particulate matter and solving the problem of substandard particulate matter emission concentrations in some coal-fired power plants. The concentrations of NO3−, SO42−, and Cl− among the soluble ions decreased by 41–66.6%. As the liquid−to−gas ratio of the cold water spray and hot alkali droplet spray increased, CPM came into contact with more spray, which accelerated dissolution and chemical reactions. Consequently, the CPM emission concentration decreased by 17.4–19%. The liquid−to−gas ratio has a great effect on the ion concentrations of NO3−, SO42−, Cl− and NH4+, with a decrease of 28–66%. The temperatures of the cold water spray and the hot alkali droplet spray primarily affect the ionic concentrations of SO42− and Ca2+, leading to a decrease of 32.3–51%. When the SO2 concentration increased from 0 mg/Nm3 to 1500 mg/Nm3, large amounts of SO2 reacted with the desulfurization slurry to form new CPM and its precursors, the CPM emission concentration increased by 57–68.4%. This study addresses the issue of high Concentration of CPM emissions from coal-fired power plants in a straightforward and efficient manner, which is significant for enhancing the air quality and reducing hazy weather conditions. Also, it provides a theoretical basis and technical foundation for the efficient removal of CPM from actual coal-fired flue gas.

On-line measurement of particle size in high-concentration limestone slurry pipeline by Monte-Carlo based ultrasonic attenuation model

Limestone-gypsum wet flue gas desulfurization (WLG-FGD) technology is wildly used to diminish sulfur dioxide emissions in coal-fired power plants, where the particle size of the limestone slurry is a crucial factor closely related to the desulfurization efficiency. The high-concentration Monte Carlo model (HC-MCM) was developed for attenuation spectrum prediction. In numerical simulations with a particle diameter range of 10–70 μm, the differential evolutionary (DE) algorithm was used for retrieving particle sizes with relative deviations that do not exceed 2 % in terms of a given diameter and distribution width. A through-transmission/pulse-echo dual-mode ultrasonic system has been established. The results indicate that the root mean square relative error (RMSRE) of the two modes’ attenuation spectra was 7.03 %. The relative deviations of DV90 are less than 8 % compared to the results obtained through the laser particle analyzer. Moreover, the fineness is within the specifications required for limestone slurry, indicating proper mill performance.

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.

Formation and migration of soluble ions in condensable particulate matter in limestone-gypsum wet flue gas desulfurization system

In this work, the emission characteristics of condensable particulate matter (CPM) and soluble ions in the inorganic components after wet flue gas desulfurization (WFGD) were investigated by adjusting the operating parameters of the limestone-gypsum WFGD system. Using a combination of US Method 202 and US EPA Method 5 as the primary measurement method, the study is an experimental study and analysis of the properties of CPM emitted from a limestone-gypsum WFGD system. Based on the measurement results, the influence of some important WFGD operating parameters on CPM emissions was evaluated. The results showed that CPM accounts for 84% of total particulate matter (TPM) emissions in desulfurized flue gas. The composition of CPM is primarily inorganic, comprising 96% of the components, with only a small portion being organic at 4%. The CPM that condensed to a solid state was generally less than 1 μm in diameter and mostly came from WFGD process. The analysis of soluble ions showed that Ca2+ and SO42- were the main ionic components in CPM. By adjusting the desulfurization operating parameters (inlet flue gas temperature, desulfurization solution temperature, desulfurization solution concentration), the concentration of soluble ions can be reduced to different degrees, so as to achieve the purpose of reducing CPM emission. This demonstrated that the CPM emission problem of limestone-gypsum WFGD system could be relieved by operating parameter optimization.

Enhancing deep learning for the comprehensive forecast model in flue gas desulfurization systems

The sulfur dioxide (SO2) emissions contribute to severe environmental pollution and respiratory problems, which make the limestone–gypsum wet flue gas desulfurization (WFGD) an increasingly important issue. The WFGD system consists of the flue gas system, the limestone slurry supply system, the oxidation air supply system, and the gypsum slurry discharge system, which have the characteristics of multivariable coupling, high dimension, nonlinear, large delay, and difficulty for parameters measurement, bringing great challenges and limitations for the traditional mechanism modeling of the WFGD system. To solve those issues above, in this study, an enhancing modeling method that integrates feature fusion and deep learning is proposed to predict the dynamics of SO2 emission in a WFGD system. Aiming at the problem that most of the existing modeling methods cannot fully and accurately extract the hidden features in WFGD system data, the convolutional neural network (CNN) method is responsible for extracting multiple spatial features including the local and global spatial features from WFGD system data, and the long short-term memory (LSTM) method mines the temporal relationship from the previous and current state of the WFGD system. Finally, the attention mechanism (AM) method is enhanced for the effective improvement of crucial information. Taking an actual coal-fired boiler as an illustration, the SO2 emissions at different time steps are predicted. The experiment results reveal that the proposed CNN-LSTM-AM model can fully and accurately extract system features and outperform other approaches in terms of prediction accuracy.

Emission characteristics of filterable particulate matter and condensable particulate matter from coal-fired power plants

Particulate matter (PM) emission has been widely concerned all over the world. The formation of condensable particulate matter (CPM) was affected by atmospheric temperature. An optimal-designed sampling device and monitoring method for particulate matter in high-humidity flue gas were applied to the particulate matter emission concentration of 12 ultra-low emission coal-fired units. The emission levels and composition characteristics of particulate matter and main inorganic ions in the flue gas were analyzed and evaluated. The results showed that the filterable particulate matter (FPM) concentration range was 0.81–7.52 mg/m 3 , and the condensable particulate matter concentration range was 1.10–12.25 mg/m 3 . The emission characteristics of CPM/FPM was significantly affected by different air pollution control devices. Preferable emission reduction result of condensable particulate matter may be realized by units equipping wet limestone-gypsum flue gas desulfurization and wet electrostatic precipitator. The certain correlation was showed between CPM/FPM and ash content. The inorganic ion concentration range was 1104–8240 μg/m 3 in condensable particulate matter. Ca 2+ concentration accounted for more than 45% of the cation concentration, and SO 4 2− concentration accounted for up to 97.81% of the anion concentration in CPM.

SOx removal and emission characteristics of WFGD system applied in ultra-low emission coal-fired power plants

In this paper, SOX (SO2 and SO3) removal and emission characteristics of wet limestone-gypsum flue gas desulfurization (WFGD) are investigated based on the data collected from 95 ultra-low emission coal-fired power units. The study shows that the overall removal efficiency of single-absorber is above 97.5%, in which the SO3 removal efficiency is between 31% and 70%. When the inner structures are installed into the spray absorber, the correlation between the inlet SO2 concentration and SOX removal efficiency becomes more obvious, however, with a tray absorber, the maximum SO2 removal efficiency of double-absorber reaches 99.74%, in which the SO3 removal efficiency is between 27% and 81%. With a normal spray absorber, the higher inlet concentration, the higher removal efficiency it reaches, while with a tray absorber, the result is opposite. With a single-absorber, there is little correlation between flue gas temperature drop and SO2 removal efficiency. Large temperature drop harms the improvement of overall SO2 removal efficiency but is beneficial to SO3 removal. By the calculation of SOX emission performance model, average emission performances of SO2 and SO3 are acquired, which are about 90–107 mg/(kW·h) and 81–97 mg/(kW·h), respectively.

Study on Spray Evaporation Treatment of Desulfurization Wastewater

Limestone-gypsum wet flue gas desulfurization (WFGD) often produces a certain amount of wastewater with complex water quality and heavy metal pollution which should be treated properly before release. Spaying the desulfurization wastewater into flue duct and using exhausted flue gas heat for evaporation is a promising and economical technology for achieving zero wastewater discharge in thermal power plant. To enable a more in-depth understanding on evaporation of FGD wastewater spray, a visual wind tunnel test rig based on the atomized droplet laser measuring system was built to reveal the impact factors on droplet thermal-fluid behavior. The dominant impact factors such as compressed air pressure and flow rate in air-blast spray nozzle, hot air temperature and velocity in the evaporation tunnel were analyzed to discuss the droplet size distribution and evaporation performance through alternating operate condition. A discrete mathematical model that combines both Eulerian and Lagrangian framework was established to validate the experiment result. It is concluded that introducing high pressure compressed air into the nozzle can contribute to the dispersion of droplets and enhance the evaporation rate. Proper flow rate in spray nozzle is required to avoid incomplete droplets evaporation. Air temperature and velocity in the evaporation tunnel apply positive impact on droplet size distribution and evaporation performance. Numerical simulation results of both dominant factors impact on evaporation behavior and total evaporation rate showed consistency with the experimental outcome.

Experimental research and engineering application on the treatment of desulfurization wastewater from coal-fired power plants by spray evaporation

The spray evaporation is a promising zero discharge technology for desulphurization wastewater treatment. In this work, a pilot-scale platform for the spray evaporation of desulfurization wastewater was built, the desulphurization wastewater was atomized by a rotary atomizer and evaporate in the evaporation tower, and the wastewater atomization and evaporation characteristics were investigated systematically. The results showed that the increase of atomizer rotating speed can improve the atomization effect of desulfurization wastewater, while the increase of its flow rate and total amount of dissolved solids (TDS) was not conducive to that. For the evaporation of desulfurization wastewater, the increase of flue gas temperature, gas-liquid ratio (the ratio of flue gas volume to desulfurization wastewater volume, Nm3 m−3) and atomizer rotating speed can promote its rapid evaporation, while the increase of wastewater TDS reduced the evaporation rate of wastewater droplets. On this basis, a bypass evaporation tower system was designed and constructed in a 330 MW coal-fired power plant to treat the desulphurization wastewater from limestone–gypsum wet flue gas desulfurization (WFGD) system, and the influence of wastewater evaporation on the flue gas and particle characteristics was investigated under different boiler loads. The results show that this evaporation system can ensure the evaporation effect of desulphurization wastewater under different boiler loads, lead to the reduction of flue gas temperature and the increase of humidity, reduce the concentration of SO2 and particles in flue gas, and enlarge the particle size at the outlet of evaporation tower. This work can provide a reference for the desulphurization wastewater treatment in coal-fired power plants.

Case analysis and preventive measures of limestone-gypsum wet flue gas desulfurization slurry poisoning for 320MW unit

The slurry poisoning of the desulfurization system is a difficult problem in the current desulfurization operation. This paper analyzes the abnormality of the limestone-gypsum wet flue gas desulfurization slurry poisoning of a 320MW unit, and proposes a solution. Through the test method, the slurry composition and gypsum quality the analysis was carried out and effective measures were taken according to the actual situation to solve the slurry poisoning phenomenon and ensure the safe operation of the desulfurization system, which is of great significance to the flue gas emission standard of the desulfurization system of the power plant.

A formulation additive for simultaneously improving flue gas desulfurization efficiency and gypsum quality

The effects of different additives, including MgSO4, MnSO4, adipic acid, citric acid, benzoic acid, succinic acid and acrylic acid on SO2 removal from a limestone-gypsum wet flue gas desulfurization (FGD) system and gypsum characteristics were investigated. An optimized formulation additive for simultaneously improving flue gas desulfurization efficiency and gypsum quality was found. This formulation additive was successfully applied in an industrial-scale FGD system of a local coal power plant (600 MW, Shanghai Wujing Power Plant, China), and the gypsum quality was improved. The optimized formulation additive was acrylic acid, MnSO4 and citric acid mixed at a ratio of 1:1:2, which can simultaneously achieve an increased desulfurization efficiency of 97.02% and a low gypsum moisture content of 4.32%. Moreover, MnSO4 and acrylic acid were found to be most effective for improving SO2 removal, and citric acid contributed to gypsum particles with more uniform sizes and regular shapes, as well as good dewatering characteristics.

A novel drying tower technology for zero liquid discharge of desulfurization technology

ABSTRACT The wet limestone/gypsum flue gas desulfurization (WFGD) technology has been attracting much interest, while handling with wastewater produced in WFGD is indispensable but difficult. Zero liquid Discharge (ZLD) technology is to recycle water content and reuse salt content of wastewater, which has becoming developing trend because of the strict wastewater emission regulation in China. However, existing ZLD technology cannot realize low investment and low power consumption. Therefore, in this paper, a novel drying tower applied in ZLD system was proposed. Wurster fluidized bed was introduced into drying of desulfurization wastewater and high gas-liquid heat transfer can be achieved with inert particles as immediate heat carrier. Industrial experiment and numerical simulation were applied to verify the feasibility of this novel drying tower, research flow structure in tower and offer optimization for future operation. The results indicate that this novel drying tower applied for a 300 MW power plant performs well in ten-day pilot run. Through numerical simulation applying computational particle fluid dynamics (CPFD), gas-solid-liquid flow structure of inner circulation is detected. With the increase of particle size, the evaporation efficiency increases firstly and then decreases while power consumption increases. The working condition with particle size of 1.6 mm performs best. With more bed material in dryer, higher efficiency and pressure drop can be obtained. Overall considering working effect, bed material of 380 kg is recommended for future operation. In simulation range, high efficiency and low power consumption can be obtained with higher wind supply ratio of central part. With the work of experiment and simulation, the novel drying tower is proved to be applicable and recommended operating parameters for future operation are offered through simulation results.

Energy conservation and efficiency improvement by coupling wet flue gas desulfurization with condensation desulfurization

Limestone–gypsum wet flue gas desulfurization (WFGD) is the most effective desulfurization technique. However, to achieve ultralow SO2 emissions, the efficiency of WFGD should be improved and its energy consumption reduced. To address these aims, a technology of coupling WFGD with condensation desulfurization using a condensing heat exchanger (CHE) was proposed in this study. The results show that, as the WFGD approaches the limiting desulfurization efficiency, a small increase in the efficiency may cause a high energy consumption. However, the energy consumption can be reduced significantly through the synergistic absorption of SO2 during the wet flue gas condensation. The synergistic absorption efficiency is affected by the SO2 concentration at the inlet of the CHE, flue gas flow, and the amplitude and rate of temperature drop. Injecting Ca(OH)2 into the flue gas during wet flue gas condensation can form dispersive heterogeneous cores of Ca(OH)2 in the flue gas, thereby enhancing SO2 mass transfer and improving the desulfurization efficiency considerably. The increased amount of Ca(OH)2 is small, and the unreacted Ca(OH)2 can be fully utilized by collecting the condensed solution and returning it to the WFGD system. When the coupling desulfurization technology is applied to achieve ultralow SO2 emissions, at inlet SO2 concentrations of 2000 and 4000 mg/Nm3, the circulating pump power consumption decreases by 351–449 kW and 1661.5–2125.5 kW for 300- and 1000-MW units, respectively, demonstrating the significant energy-saving potential of the coupling desulfurization technology.

Model-Free Adaptive Control of pH Value of Wet Desulfurization Slurry under Switching of Multiple Working Conditions

In limestone-gypsum wet flue gas desulfurization process, the change process of pH value of slurry in absorption tower is a typical nonlinear system with time delay and various uncertainties, so it is difficult to establish an accurate mathematical model of slurry pH control process. According to the pH control process of the slurry of wet flue gas desulfurization process, a model-free adaptive control algorithm based on compact form dynamic linearization (CFDL-MFAC) is designed to realize the tracking control of the pH value of the slurry. Due to various interference factors in the pH control process of slurry in absorption tower, it is easy to cause jump change of control system parameters and even structure. Therefore, a model-free adaptive control algorithm based on switching strategy is proposed in this paper. According to different working conditions, several model-free adaptive controllers are established. The stability of the algorithm is analyzed for the two cases of fixed system parameters and jumping system parameters. It was found that the model-free adaptive controller based on the switching strategy can switch multiple controllers under the condition of system parameter jump, so as to realize the fast tracking control of the slurry pH value of the system absorption tower under different working conditions. Through this method, the overshoot can be reduced and the control quality can be improved.

Analysis and Treatment Measures of Continuous Emission Monitoring System Fouling in a Coal-Fired Power Plant after Ultra-Low Emission Transformation

Scanning electron microscopy (SEM) micro-morphology analysis, X-ray diffraction (XRD) and energy-dispersive X-ray diffraction (EDX) component analysis were conducted on the fouling of continuous emission monitoring system (CEMS) sampling tube at the outlet of limestone-gypsum wet flue gas desulfurization (WFGD) of unit 1 in a 600 MW supercritical coal-fired power plant in Inner Mongolia Autonomous Region. The results show that the main component of fouling was ammonium dihydrogen phosphate, which was generated by the reaction between phosphoric acid in the phosphoric acid titration device and the NH3 escaping from the selective catalyst reduction (SCR) denitrification system, and corresponding treatment measures were taken. It indicates that the average value of ammonia escape was reduced from 1.79 ppm to 1.54 ppm through the ammonia injection optimization test of the SCR denitrification system (at the load of 410 MW of the unit), which effectively reduced the generation of fouling. This research provides reference for improving the reliability of coal-fired unit operation after ultra-low emission transformation.

Emission Characteristics of Soluble Ions in Fine Particulates in Limestone–Gypsum Wet Flue Gas Desulfurization System

Limestone-gypsum wet flue gas desulfurization (WFGD) process has a significant influence on the emission characteristics of soluble ions in particulates. In this study, a simulated limestone-gypsum WFGD platform was used to study the emission characteristics of water-soluble ions in flue gas after desulfurization. The experimental results indicated that the entrainment of desulfurization slurry droplets was the main source of water-soluble ions emission while water-soluble ions cannot be carried by vaporous water in flue gas. The limestone-gypsum desulfurization process can form soluble ionic particles with particle size less than 1 μm. In addition to Ca2+, Mg2+, SO42- and Cl-, which were the main ion components in the slurry, NH4+ was also the main ion composition of the soluble ionic particles, indicating that the entrainment and evaporation of slurry droplets and condensation of volatile components were the formation mechanism of the soluble ionic particles. Reducing the gas velocity and liquid-gas rat...

Field test of SO3 removal in ultra-low emission coal-fired power plants.

Under the extensive implementation of ultra-low emission (ULE) facilities in coal-fired power plants of China, sulfur trioxide (SO3) has received increasing attention due to its impact on human health and operation safety of power plants. However, systematic research and evaluation for controlling SO3 emission in various ULE facilities are still lacking. Here, a systematic study was conducted based on 378 in situ performance evaluation tests carried out in 148 coal-fired power plants. The results illustrate that the SO2/SO3 conversion rate of the selective catalytic reduction devices can be controlled within 1% before and after ULE retrofit. Also, the synergistic removal efficiency of SO3 in the low-low-temperature electrostatic precipitator and the wet electrostatic precipitator can be higher than 70%. The removal efficiency of SO3 in the wet limestone-gypsum flue gas desulfurization scrubber is 33-64% before ULE and 31-81% after, and the average efficiency of the double scrubbers is 8.7% higher than that of the single scrubber. Due to the different SO3 removing abilities of various technologies, the overall efficiency of SO3 removal is in the range between 27 and 95% adopting different ULE technical routes. Average concentration of SO3 emission can be decreased by 51.8% after ULE application.

Promotion of conversion activity of flue gas desulfurization gypsum into α-hemihydrate gypsum by calcination-hydration treatment

The massive accumulation of flue gas desulfurization (FGD) gypsum produced in the wet limestone-gypsum flue gas desulfurization process not only encroaches on lands but also causes serious environmental pollution. The preparation of α-hemihydrate gypsum (α-HH) is an important way to achieve high-value utilization of FGD gypsum. Although the glycerol-water solution approach can be used to produce α-HH from FGD gypsum under mild conditions, the transition is kinetically unfavorable in the mixed solution. Here, an easy pretreatment was used to activate FGD gypsum by calcination and hydration to readily complete the transition. The pretreatment deteriorated the crystallinity of FGD gypsum and caused it to form small irregular flaky crystals, which dramatically increased the specific surface area. Additionally, most of the organics adsorbed onto FGD gypsum surfaces were removed after pretreatment. The poor crystallinity, increased specific surface area, and elimination of organics adsorbed onto crystal surfaces effectively improved the conversion activity of FGD gypsum, thereby promoting dihydrate gypsum (DH) dissolution and α-HH nucleation. Overall, the phase transition of FGD gypsum to α-HH is facilitated.

Investigation on Removal Characteristics of SO3 Acid Mist during Limestone-Gypsum Desulfurization Process

With the increasing attention on SO3 emission in coal-fired power plants, the removal of SO3 acid mist in a limestone-gypsum wet flue gas desulfurization (WFGD) system was investigated. The generation properties of SO3 acid mist were analyzed with an experimental system, and the effects of flue gas properties and technologies for ultralow emission on the SO3 removal in WFGD systems were investigated with a pilot plant. The results revealed that the sizes of SO3 acid aerosols generated by homogeneous nucleation were principally less than 0.1 μm, and it had a positive impact on the coagulation and growth of fly ash particles via the collision. When the gas temperature at the inlet of the scrubber went up, the removal efficiency of the WFGD system on SO3 acid mist was decreased, and the decline was more obvious as the temperature fell below the dew point of the acid. Higher concentrations of SO3 and fly ash before desulfurization were beneficial for the improvement of SO3 removal. Furthermore, technologies f...

Improving the removal of fine particles by chemical agglomeration during the limestone-gypsum wet flue gas desulfurization process

Coal-fired power plants are considered a major source of fine particle emissions in China. Aimed to improve the removal efficiency of fine particles during the limestone-gypsum wet flue gas desulfurization (WFGD) process, a novel technology using chemical agglomeration to abate the emission of fine particles is presented herein. The relationship between fine particle emission and the proportion of fine particles in the desulfurization slurry was studied. Additionally, the influence of chemical agglomeration on fine particle size distribution, both in the flue gas and slurry was experimentally investigated. When chemical agglomeration agents were added to the desulfurization slurry, the fine particle removal performance as well as the effects of the operation parameters was also explored via the simulated experimental facility. The results revealed that the fine particles in both the desulfurization slurry and flue gas were significantly enlarged after the addition of the agglomeration agents. This was more marked in the submicron particles. Thus, the proportion of fine particles (< 10 μm) in the slurry decreased from 31.1% to 22.6%. An increase in the desulfurization slurry temperature and liquid-to-gas ratio aided the reduction in fine particle emission. Moreover, the addition of an agglomeration agent in the slurry did not affect the desulfurization efficiency of the desulfurization tower and even promoted the WFGD process. Thus, the proposed chemical agglomeration technique reduced the fine particle emission of the WFGD system by ~30%, while a desulfurization efficiency >90% was maintained.