Limestone-gypsum Flue Gas Desulfurization Research Articles

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.

Emissions of air pollutants from sintering flue gas in the Beijing-Tianjin-Hebei area and proposed reduction measures

Iron and steel manufacturing, especially the sintering process, is highly energy- and pollution-intensive, and is responsible for substantial emissions of major air pollutants in China, including particulate matter (PM), sulfur dioxide (SO2), and nitrogen oxides (NOx), which poses challenges to air quality improvement in the country. In this study, we carried out a comprehensive analysis of the temporal and spatial characteristic of SO2, NOx, and PM emission concentrations, quantified the standard-reaching rate and air pollutant emissions factors, as well as discussed the spatial distribution and potential reduction measures of emission amounts based on the hourly online monitoring data and basic information collected from sintering head process in the Beijing-Tianjin-Hebei region (BTH) in 2017. We found that there was a downward trend of monthly emission concentrations during September to December 2017, in response to the emission control policies. By comparing with the emission standard implemented in 2017, the standard-reaching rate of PM, NOx, and SO2 were 74.7%, 23.5%, and 62.5% respectively, higher relative to the ultra-low emission standard. The emission factors of PM, NOx, and SO2 were calculated at different sintering machine scales, and were found to be lower than previous estimates. The emissions of SO2, NOx, and PM from sintering machine heads in the BTH region amounted to 14.2 kt, 143.2 kt and 46.3 kt respectively, Tangshan and Handan accounted for over 60% of the total emission amounts. The most popular technologies applied for PM and SO2 removals are electrostatic precipitators and limestone-gypsum flue gas desulfurization with an average removal efficiency of 71.8% and 90.3%. The potential of NOx reduction is huge, more effective technical measures shall be adopted to further reduce the NOx emission amount during the sintering process.

Limestone-Gypsum Wet Flue Gas Desulfurization Wastewater Treatment

In this paper, chemical precipitation process is used for the treatment of the desulfurization wastewater generated by the waste gas treatment system of the limestone-gypsum flue gas desulfurization process of a thermal power plant. After one year of operation, the technology is reliable and stable. The removal rate of suspended matter, COD, fluoride, mercury and sulfate reached 99.5%, 98.3%, 87.5%, 99.8% and 85.6% respectively, and the corresponding effluent concentrations were 54 mg/L, 20 mg/L and 9.6 mg/L, 0.04 mg/L, 980 mg/L. Finally, the effluent quality of the system is better than the discharge requirements of “Discharge standard of wastewater from limestone-gypsum flue gas desulfurization system in fossil fuel power plants” (DL/T997-2006). In addition, the total electricity and chemical charges per ton of wastewater treatment were 6.50 yuan, which is lower than most of the engineering project under the same discharge requirements. Therefore, the process has certain engineering advantages.

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.

Abatement of Fine Particle Emission by Heterogeneous Vapor Condensation During Wet Limestone-Gypsum Flue Gas Desulfurization

The fine particles in desulfurized flue gas comprise coal-fired fine particles from combustion and generated fine particles from desulfurization. The abatement of fine particle emission by heterogeneous vapor condensation during wet flue gas desulfurization (WFGD) is experimentally investigated in this paper. A supersaturation atmosphere, which is necessary for heterogeneous vapor condensation, is established by increasing the humidity and reducing the temperature of the flue gas before WFGD. The improvement of the removal of coal-fired fine particles and the inhibition of generated fine particles formation in desulfurization process by heterogeneous vapor condensation were studied, and the influences of inlet flue gas parameters on the emission of total fine particles, including coal-fired fine particles and generated fine particles during desulfurization, are examined. The results indicate that the total emission of fine particles in desulfurized flue gas can be significantly decreased via heterogeneous...

A concise algorithm for calculating absorption height in spray tower for wet limestone–gypsum flue gas desulfurization

In this paper, a concise model for wet limestone–gypsum flue gas desulfurization system with spray tower has been presented, aiming at the prediction of the absorption height in a spray tower. The equations of droplet motion and mass balance were incorporated and developed to simulate the droplet movement, distribution and mass transfer of SO2 in the absorption section. The calculation results were in good agreement with the plant values of the absorption height. The influences of operating parameters on the absorption height were analyzed. The results show that absorption height declines with increasing liquid–gas ratio and pH value of the slurry, and increases with increasing droplet diameter, gas flow rate, gas temperature, inlet SO2 concentration and absorption efficiency, respectively. As the most sensitive parameter, the droplet diameter is crucial for the good prediction of absorption height. This model can provide engineering guidance to design a spray tower absorber.

Reduction of Freshwater Usage of a Coal Fired Power Plant with CCS by Applying a High Level of Integration of All Water Streams

Abstract The integration of the recently built 1 070 MW coal-fired unit in Rotterdam (Netherlands) with the proposed new 250 MW demonstration carbon capture unit of the Rotterdam Opslag en Afvang Demonstratieproject (ROAD) would lead to a substantial reduction in freshwater usage. This is partly due to the power plant design, the most relevant features being the seawater direct cooling and the limestone gypsum Flue Gas Desulfurization (FGD); and partly due to the high level of integration. This paper describes the water and waste streams of the capture plant, including quality and (re-) use in the power plant. The implications for a full scale capture are discussed.

Elucidation of the Mechanism of Reaction between S2O82–, Selenite and Mn2+ in Aqueous Solution and Limestone-Gypsum FGD Liquor

The mechanism of reaction between peroxodisulfate ion (S2O8(2-)), selenite (Se(IV)O3(2-)) and Mn(2+) as an inhibitor of selenite oxidation was studied using aqueous solutions composed of commercial reagents, as well as limestone-gypsum flue gas desulfurization (FGD) liquors sampled from coal fired power plants. The oxidation of selenite to selenate (Se(VI)O4(2-)) is promoted by the sulfate ion radical (SO4(-)) which results from decomposition of S2O8(2-). In the presence of Mn(2+), selenite oxidation was prevented due to the difference in rates of reaction with SO4(-). The ratio of the oxidation rate constants of selenite and Mn(2+) with SO4(-) was determined over a temperature range of 40-60 °C, and was found to be little influenced by the various coexisting components in FGD liquors.

Kinetic Analysis of Paper White Mud Dissolution at Constant pH

One of the most important steps in the wet limestone–gypsum flue gas desulfurization (WFGD) process is limestone dissolution, which provides the dissolved alkalinity necessary for SO2 absorption. Accurately evaluating the rate controlling step in sorbent dissolution process is important in the design and efficient operation of WFGD plants. In the present work, the kinetics of paper white mud(PWM) in dissolution process has been studied by using a pH-stat method. The results obtained indicated that PWM dissolution in WFGD conditions obeys the modified shrinking core model. PWM dissolution kinetics follows the film diffusion and surface reaction control and the rate controlling step of PWM is film diffusion control. The activation energies of PWM in film diffusion and surface reaction steps are 11.9±0.7 kJ/mol and 13.7±1.3 kJ/mol, respectively.

Experimental study on the oxidative absorption of Hg0 by KMnO4 solution

The wet FGD system is widely recognized as the co-effective removal system for oxidized Hg vapor species and SO2. In this study, a purpose-built device was designed for this experiment and several factors potentially affecting the Hg0 removal efficiency were systematic investigated, including different types of oxidants, pHs and concentrations of potassium permanganate, reaction temperatures, Hg0 inlet concentrations, O2, SO2 and NO concentrations, and different types of absorption solutions. Results indicate that pHs and KMnO4 concentrations, reaction temperatures, SO2 and NO concentrations all have a strong influence on the removal of Hg0, and the inlet concentrations of Hg0 and O2 contribute little to the removal of Hg0. SO2 could significantly inhibit the removal of Hg0, the negative effect is serious especially at lower SO2 concentration, and SO2 could lead to the re-emission of Hg0. Hg0 could be removed effectively by using CaCO3+KMnO4 solution, when the KMnO4 concentration in the CaCO3+KMnO4 solution was 1.5mmol/L, the removal efficiencies of SO2, NO and Hg0 were 100%, 40.69% and 90.58%, respectively. So, considering the application to the practical engineering, adding 1.5–2mmol/L KMnO4 into limestone–gypsum flue gas desulfurization systems is necessary. This technology is a promising method for the simultaneous removal of NO, SO2 and Hg0.

Sulfite Oxidation Catalyzed by Cobalt Ions in Flue Gas Desulfurization Processes

This paper presents an experimental study of calcium bisulfite oxidation, a key step in the wet limestone-gypsum flue gas desulfurization (FGD) process, in the presence of catalysts (e.g., cobalt ions and a mixture of ferrous and cobalt ions). A fundamental approach is followed, by reproducing a simplified synthetic FGD liquor in which both catalyst ions, alone or mixed together, are present. A laboratory-scale apparatus is used, in which sulfurous solution is contacted with a gas phase at a fixed oxygen partial pressure (21.3 kPa) and at different temperature levels (25, 45, and 55 °C). The experimental results are analyzed using the theory of gas-liquid mass transfer with chemical reaction, showing that the slow reaction regime is explored and the transition from the kinetic to the diffusional subregime is identified. The experimental results are compared with those obtained in the presence of other catalytic species (manganese and ferrous ions), showing that cobalt is effective in catalyzing the oxidation of calcium bisulfite to sulfate, but to a minor extent with respect to iron and manganese.

Particle Separation with a Hydro-Cyclone Separator in a Wet Limestone Gypsum FGD Process

A hydro-cyclone was applied to the separation of gypsum, a byproduct of the wet limestone gypsum flue gas desulfurization (FGD) process, that uses limestone as the raw material. Using a high slurry concentration, similar to that used in an actual plant, the effect of the inlet shape and ceiling clearance of the hydro-cyclone was examined, and a model for predicting the efficiency of separation is proposed.The results indicate that the 50% cut size decreases when the inlet width ratio is decreased. Over the entire range of inlet width ratio, the limestone content of the blow-down flow decreased by approximately half, compared with that of the feed, and it was confirmed the purity of the gypsum could be improved by decreasing the limestone content.When the ceiling clearance of the hydro-cyclone was changed, an optimum ceiling clearance for obtaining a minimal cut size was found.A model for predicting the slurry concentration that is proportional to the solid throughput of a hydro-cyclone and the improvement in gypsum purity in an actual plant is proposed. The results of this calculation model agreed well with experiment data.

D304 DEVELOPMENT OF DOUBLE-CONTACT-FLOW SCRUBBER FOR FLUE GAS DESULFURIZATION

Chugoku Electric Power Co., Inc. and Heavy Mitsubishi Heavy Industries, Ltd. developed a new type of absorber, the Double-Contact-Flow Scrubber (DCFS). DCFS is an easily maintainable absorber of simple construction with low initial cost and low power consumption for the wet limestone-gypsum flue gas desulfurization process. Absorbent slurry is spouted up from special type of nozzles located at the bottom of the absorber, creating a pillar of absorbent slurry to achieve a good gas-liquid contact. The only internal components of the absorber are the header pipes and nozzles, resulting in the simplicity of construction with lower cost, as well as easy maintenance due to the lack of scale deposits. This paper shows the performance results of DCFS operation.

Effect of Ammonium Concentration on SO2 Absorption in a Wet Limestone Gypsum FGD Process.

To investigate the effect of the ammonium concentration on SO2 absorption with a chemical reaction in the wet limestone-gypsum flue gas desulfurization (FGD) process, the SO2 absorption rate in limestone slurry was studied by using a stirred tank reactor at a constant pH, high temperature (50°C) and under the presence of ammonium. An absorption model with a reaction plane and the presence of ammonium in the liquid based on the film model was also proposed for an actual FGD plant.For the SO2 absorption rate depending on the concentration of ammonium, the experimental values agreed quite well with the results calculated with the absorption model, taking the presence of ammonium in the liquid into consideration.

Catalytic oxidation of calcium bisulfite in the wet limestone–gypsum flue gas desulfurization process

A study on the oxidation of calcium sulfite catalyzed by Mn 2+ is presented in this paper. A laboratory-scale well-mixed thermostated reactor was used, with continuous feeding of both gas and liquid phase. The gas phase was a mixture of oxygen and nitrogen, with O 2 partial pressure varying from 5.1 to 40.5 kPa. The liquid phase was obtained by mixing inside the reactor two separate aqueous solutions, one obtained by dissolving Ca(OH) 2 into a SO 2 solution, and the other one containing manganous sulfate. The temperature was kept constant in all the experiments at 45°C. The results show that increasing catalyst concentration, the transition takes place from slow kinetic to slow diffusional and eventually to fast reaction regime.

Limestone-gypsum flue gas desulfurization process: Hiroshi Kuroda, Tsukasa Nishimura, Taiki Hashimoto, Masakatsu Nishimura, Osamu Kanda, Shigeru Nozawa, Kure, Japan assigned to Babcock-Hitachi Kabushiki Kaisha

Limestone-gypsum flue gas desulfurization process: Hiroshi Kuroda, Tsukasa Nishimura, Taiki Hashimoto, Masakatsu Nishimura, Osamu Kanda, Shigeru Nozawa, Kure, Japan assigned to Babcock-Hitachi Kabushiki Kaisha