Flue Gas Desulfurization Technology Research Articles

Dynamic learning of flue gas desulfurization process using deep LSTMs neural network

SO2 emissions are known to pose great harm to both human health and atmospheric air, and flue gas generated from coal-fueled power plant is the prime source of sulfur dioxide. For this reason, flue gas desulfurization (FGD) technology has found wide applications in most coal-fired power stations. Correctly describe the dynamic behavior of an FGD process is the precondition of controlling it effectively. However, FGD process modeling is by no means an easy task, as the underlying process dynamics are highly nonlinear in nature, meanwhile time-delay effect is significant therein. Long short-term memory (LSTM) network possesses remarkable long-term memory capability, hence it is anticipated to have a powerful identification capability. In this paper, the connection between deep learning and system identification is established, further a unidirectional/bidirectional LSTM deep network is designed and employed to identify a real FGD process. Simulation results clearly demonstrate the effectiveness of deep learning-based identification approach, and the superiority of deep LSTMs over other conventional identification models is also verified.

Economic and carbon emission analysis of two typical denitrification systems for sintering process in the iron and steel industry

The transition of the Chinese iron and steel industry to ultralow emissions has accelerated the development of denitrification technologies. Considering the existing dual carbon targets, carbon emissions must be considered as a critical indicator when comparing denitrification systems. Consequently, this study provided a comprehensive cost-benefit model for denitrification in the steel industry, encompassing additional carbon emissions resulting from the implementation of denitrification systems. Activated-carbon adsorption and selective catalytic reduction (SCR) systems are two efficient techniques for controlling NOx emissions during sintering. Based on this model, a cost-benefit analysis of these two typical systems was conducted, and the results indicated that the unit flue-gas abatement costs of SCR and activated-carbon adsorption systems were 0.00275 and 0.0126 CNY/m3, and the unit flue-gas abatement benefits were 0.0072 and 0.0179 CNY/m3, respectively. Additionally, the effect of operational characteristics on operating costs, including duration and material prices, was analyzed. When treating the flue gas, the two systems released 0.0020 and 0.0060 kg/m3 of carbon dioxide, respectively. The primary sources of carbon emissions from the SCR and activated-carbon adsorption systems are the production of reducing agents and system operations, respectively. Furthermore, considering the features of the activated carbon adsorption system for simultaneous desulfurization, a SCR- wet flue gas desulfurization (WFGD) technology route was developed for comparison with the activated carbon adsorption system.

Multi-scale numerical analysis of Ca-based desulfurizer dynamics characteristics and SO2 absorption processes in industrial-scale SDA-FGD reactor

Spray dry absorption flue gas desulfurization technology is widely employed to control sulfur dioxide emissions from industrial pollutant gases. This study employs the multiphase particle-in-cell method to numerically simulate gas–solid heat transfer, SO2 removal processes, and the effect of operating conditions in the SDA reactor. The flue gas desulfurization model used has been experimentally validated. The results indicate that flue gas and slurry droplets exhibit swirling flow along the reactor walls, forming gas vortices at the top and near the outlet. The temperature and Reynolds number of slurry droplets show minimal variation when particle size is below 43 μm. The heat transfer coefficient of slurry droplets is notably higher at the reactor top and increases with the slip velocity of the droplets. Furthermore, the CaSO3 volume fraction increases with longer residence times of the slurry droplets in the reactor. When the height and diameter of the main reaction area are lower than 14 m and 8.5 m, respectively, the SO2 mass fraction in the central area undergoes significant changes. The SO2 inlet concentration is negatively correlated with desulfurization efficiency, whereas the slurry injection speed, along with the diameter and height of the main reaction region, are positively correlated with desulfurization efficiency. Among these factors, the SO2 inlet concentration and the height of the main reaction region have the most substantial impact on desulfurization efficiency.

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.

ZIF-67-derived Co@NC as an efficient catalyst for magnesium sulfite oxidation in the flue gas desulfurization process

Magnesium desulfurization is a wet flue gas desulfurization (WFGD) technology widely used in China, however, the low oxidation rate of magnesium sulfite (MgSO3), a byproduct of WFGD, causes the subsequent oxidation and crystallization process to require amount energy. Here, we prepared a cobalt-based nitrogen-doped porous carbon catalyst (Co@NC) using ZIF-67 as a precursor for the efficient catalytic oxidation of MgSO3 generated during magnesium desulfurization. The performance of Co@NC catalysts obtained at an optimal calcination temperature of 650 °C showed that the catalysts with oxidation rates up to 0.1332 mmol·L−1·s−1 of MgSO3 were considerably better than those previously studied, which outperformed the catalysts described in earlier research by a considerable margin. Further studies revealed that the Co@NC’s exceptional catalytic activity was attributed to both its special porous structure and the exposed active Co sites in the organic skeleton. The uniformly dispersed Co species act as the active sites of the Co@NC that can be fully contacted with the reactant. The presence of 0.5 g·L−1 Co@NC increases the MgSO3 oxidation rate by about 14 times compared to the noncatalytic benchmark. A practical tactic is furnished by this research for energy saving and emission reduction in the WFGD process, especially for the efficient oxidation and resource conversion of the by-product MgSO3.

Research on the characteristics of flue gas purification reaction in spouted bed

Semi-dry flue gas desulfurization and purification technology is a promising flue gas treatment technique. This study numerically investigated the influence of factors such as nozzle expansion angle, and fluidized particles diameter on the purification of SO2 and HF in the spouted bed. The study showed that in nozzle expansion angles of 5-25°, the 10° expansion angle is optimal for SO2 and HF purification efficiency. The fluidized particles' diameter affects purification efficiency. Desulfurization and defluorination efficiency are optimal when the ratio of fluidized particle diameter to slurry droplet diameter is 15. When Ca(OH)2 accounts for 0.005–0.01 of the slurry, desulfurization and defluorination efficiency are most cost-effective. According to the principle of chemical equilibrium, a higher Ca/S ratio facilitates a complete reaction with SO2 and HF, ensuring effective purification of the flue gas. The optimal Ca/S ratio is 2.5, with a desulfurization efficiency of 93.55% and a defluorination efficiency of 99.79%.

Development of emission reduction measures of trace gas emissions from coal-fired power plants in Indonesia

Most of Indonesia’s electricity demand is supplied by coal fired power plants (CFPPs) which can potentially emit huge amounts of air pollutant gases such as NOx and SO2 gas. The country has committed to reduce Greenhouse Gases (GHGs) emission by 2030 through Nationally Determined Contributions but some emission reduction measures may also reduce air pollutant gases. Flue Gas Desulfurization (FGD) and Atmospheric Fluidized Bed Combustion (AFBC) are the leading control technologies for reducing SO2 and NOx emissions that can be installed in the CFPPs. This study aims to determine the pollution load of SO2 and NOx gases in 2030 generated from CFPPs operation with (reduction scenario) and without FGD and AFCB control technology (business as usual (BAU)). The gas pollution load was calculated using the Atmospheric Brown Clouds- Emissions Inventory Manual (ABC-EIM) procedure. Based on the BAU scenario, the emission load accounted of 1,440,192 tons/year for NOx and 613,121 tons/year for SO2 in 2030. After implementing the control technology scenarios in 2030, the NOx emission load is projected to decrease to 579,610 tons/year, and the SO2 emission load decrease to 77,920 tons/year. The application of AFBC and FGD control technologies can potentially reduce NOx and SO2 emissions load from CFPPs operation in 2030 thus it can help to improve air quality in the future.

CFD analysis of the spray droplet parameters effect on gas-droplet flow and evaporation characteristics in circulating fluidized bed desulfurization tower

The circulating fluidized bed flue gas desulfurization (CFB-FGD) process is a promising semi-dry flue gas desulfurization technology. The gas-droplet flow characteristics and droplets evaporation characteristics are critical to improving the desulfurization efficiency of the FGD tower. The effects of droplet parameters, including spray droplet diameter, spray droplet velocity, spray droplet mass flow rate and spray angle are investigated. Two evaluation indices, the coefficient of variation of droplet concentration (CV) and droplet mass-weighted life, are adopted to evaluate mixing degree of gas-droplet and droplet evaporation time, respectively. Results show that as the spray droplet diameter increases from 40 µm to 80 µm, the amount of water droplets trapped by tower wall increases from 3% to 21%. Increasing the spray droplet velocity and spray droplet mass flow rate could effectively increase the turbulent kinetic energy, which could improve the turbulent mixing ability. Moreover, droplet with smaller diameter and high velocity are beneficial to improving the temperature distribution uniformity. When the spray droplet mass flow rate exceeds 2.7 kg/s, the temperature in the tower would be lower than the dew point temperature, resulting in corrosion of the tower wall. Furthermore, the evaporation rate of droplets decreases with the increase of droplet diameter, spray droplet velocity and spray mass flow rate, while increases with the increase in the spray angle. This study would provide a better reference for the optimum operating scheme in practical applications.

Process compatible desulfurization of new suspension preheater cement production: Rapid catalytic oxidation of trace SO2 over V2O5-based catalysts in preheater environment

Efficient capture of sulfur dioxide (SO2) in the preheater of the cement production system is the key to achieving process compatible flue gas desulfurization (FGD). Herein, the rapid oxidation of trace SO2 over V2O5-based catalysts in the preheater environment was realized to enhance the SO2 capture capacity of limestone in raw meal, and the catalytic efficiency was further improved by 45.2%, 56.1% and 61.9% after introducing TiO2/MnO2/CeO2 as cocatalysts, respectively. The V2O5-based catalysts had superior catalytic behavior only when the flue gas temperature exceeded 500 °C, while the composition variation of flue gas had a minor influence on SO2 oxidation. Finally, a maximum SO2 oxidation efficiency of 68.1% was achieved in the presence of 4.0% O2, 25.0% CO2 and 15.0% H2O at 600 °C. Furthermore, the mechanism of SO2 catalytic oxidation over V2O5-based catalysts was deduced based on the results of XRD, BET, XPS and Raman, and V5+ was identified as the primary vanadium species for SO2 oxidation. The results provide a deeper insight into the catalytic oxidation of SO2 in the preheater environment, and then facilitate the improvement of process compatible FGD and available dry FGD technologies for cement industry.

Study on thermal regeneration of saturated activated coke coupled with SO2 carbothermal reduction to produce elemental sulfur

The large-scale development of dry flue gas desulfurization technology with carbonaceous adsorbents is limited due to the long process flow, high energy consumption, and narrow application range of sulfuric acid as a by-product. This study focused on the innovative preparation of elemental sulfur from saturated activated coke (SAC) by one step thermal regeneration coupled with SO2 carbothermal reduction. The experimental results showed that the rapid rise in temperature in SAC causes rapid SO2 desorption, resulting in a larger instantaneous SO2 concentration and smaller carbon loss. At temperature higher than 550 °C, most of the adsorbed sulfur converted into gaseous SO2, and a small amount was converted into elemental sulfur with a selectivity of 3.69%. In the temperature range of 650–950 °C, the rapid desorption of SO2 coupled with carbothermal reduction improved the selectivity of elemental sulfur and achieved a near-complete conversion at 950 °C of 93.7%. Furthermore, the re-absorption performance of regenerated AC at 750 °C reached the maximum value of 67.27 mg/g and approached the original AC value of 66.44 mg/g. According to the trade-off between elemental sulfur selectivity and re-adsorption activity, the optimal reaction temperature was determined at 750–850 °C.

Process compatible desulfurization of NSP cement production: A novel strategy for efficient capture of trace SO2 and the industrial trial

Cement industry contributes to more and more SO2 emission due to utilization of alternative raw materials and fuels, whereas the available calcium-based dry flue gas desulfurization (FGD) technologies present low efficiency due to slow reversible de-SO2 reactions and short gas-solid contact time in the preheater. In the present study, the SO2 capture potentials of CaCO3, CaO, and Ca(OH)2 in the preheater environment were maximized by introducing V2O5-based catalyst and selecting optimal reaction temperature, and the de-SO2 mechanism was extensively discussed. The results showed that the de-SO2 efficiency of calcium-based adsorbents increased by 10–57 times as SO2 was effectively oxidized to SO3 in the presence of V2O5-based catalyst, then maximum de-SO2 efficiency of 75.5% was achieved using Ca(OH)2 and V2O5-CeO2 at 600 °C. Furthermore, CaCO3 assisted by V2O5-CeO2 also had a de-SO2 efficiency of 65.6%. Subsequently, a novel process compatible FGD technology was designed to maximize the de-SO2 ability of raw meal in the preheater by adding V2O5-based catalyst and humidification, the SO2 concentration of flue gas reduced from 1000 mg/Nm3 to less than 100 mg/Nm3 in the industrial-scale trial, as more sulfur was solidified into clinker in the form of alkali sulfate without reducing its properties. This novel process compatible de-SO2 strategy is of real significance for reducing SO2 emission of cement industry at low economic cost.

Hybrid Modeling and Real-time Predictive Scheduling of Wet Flue Gas Desulfurization for Energy Saving and Life Extension

Sulfur dioxide (SO2) is one of the most important air pollutants emitted by power plants and ironworks. To effectively remove SO2 from flue gas, wet flue gas desulfurization (WFGD) technology is widely adopted by most of China’s coal-fired power plants. However, one of the most important issues of WFGD is the relatively high energy consumption, with the main contribution from the power consumed by circulating pumps in the absorber. In this paper, hybrid modeling and real-time predictive scheduling of a wet flue gas desulfurization (WFGD) system for energy saving and life extension are proposed. The hybrid model is based on the mechanism of the SO2 absorption process and modified based on the operation data using a particle swarm optimization (PSO) algorithm. The prediction model can describe the SO2 absorption process well, and the root-mean-square error (RMSE) of the model is 2.20 mg/m3. Effects of parameters such as the inlet SO2 concentration, pH, flue gas flow rate, and combinations of circulating pumps on the outlet SO2 concentration are further explored. The optimal combination of circulating pumps under different conditions is calculated. Finally, a real-time predictive scheduling strategy is proposed and evaluated under different parameter settings. The system shows the best performance when the upper limit, the target of outlet SO2 concentration, and the lower limit are set to 30, 15, and 10 mg/m3, respectively. The energy consumption of the system is 2564.6 kW, which is 10.6% lower than that before optimization.

Sources apportionment of water-soluble inorganic salts in CPM from coal-fired power plants with different emission control technologies

Different control technologies to reduce emissions of sulfur oxides and nitrogen oxides from coal-fired boilers have been adopted globally, leading to significant reductions in these gas emissions, especially over the past several years in China. Comparatively, little attention has been paid to the potential effects of these control technologies on particulate matter (PM) emissions, especially condensable particulate matter (CPM), which is harmful to the atmosphere and human health. In this study, we measured filterable and condensable PM emissions in five coal-fired commercial-scale boilers installed with SNCR or SCR for NOx control and wet, semidry, or dry flue gas desulfurization (FGD) for SO2 emission controls. Water-soluble ionic components in PM were analyzed. The experimental results show that the CPM accounts for 55.9% to 95.1% of total particulate matter (TPM) and is composed primarily of water-soluble SO42- and NH4+, with (NH4)2SO4 being the dominant CPM aerosols. Experimental results also reveal that the flue gas emission control technology significantly affects CPM emission from coal-fired boilers. Since the production of (NH4)2SO4-rich CPM results from the use of ammonia solution for NOx reduction, boilers emit more CPM with SNCR than with SCR because the former operates with a higher ammonia/NOx ratio than the latter. Additionally, the CPM emission is related to the FGD technology installed. Boilers installed with wet FGD emit the lowest CPM, followed by semidry and dry FGDs, because of their decreased capabilities of dissolving and absorbing water-soluble components.

Characteristics of the particulate matter and its toxic substances from different stationary coal-fired sources

Condensable particulate matter (CPM) and uncaptured fine filterable particulate matter (FPM) from various stationary coal-fired sources cause haze weather to harm human health. In this study, we measured the emissions of FPM, CPM, and polycyclic aromatic hydrocarbons (PAHs) from household stoves, small-capacity boilers, and industrial-scale circulating fluidized bed (CFB) boilers. CFB systems installed with dry and semidry flue gas desulfurization (FGD) systems and ammonia-based NOx control systems (SCR/SNCR) emit lesser filterable PM but substantially higher CPM than household stoves and small-capacity boilers. The results indicate that these air emission control technologies have side effects on promoting the generation and emission of CPM, which is rich in (NH4)2SO4 and NH4HSO4. CFB boilers with wet FGD technology exhibit lower CPM emission, suggesting the positive effects of dissolving and absorbing of gypsum slurry on CPM emission. Various small coal-fired stoves burning different types of coal do not significantly affect CPM but the PAHs emissions. Based on the data of this investigation, we estimated the emission inventory of CPM from various stationary coal-fired sources, aiming to provide valuable insights into setting priorities for improving the atmospheric environment in China.

Modelling of absorption process by seawater droplets for flue gas desulfurization application

• A new model for calculating the mass transfer coefficient between the droplet and the gaseous phase has been implemented. • The new model takes additional physical parameters such as surface renewal intensity. • With the newly-implemented model in 3D CFD simulations better results are achieved. Flue gas desulfurization technology for sulfur dioxide removal from exhausts of combustion processes is becoming more widespread as allowed emission levels keep getting lowered. Spray scrubbers have gained traction in coastal and maritime applications, where seawater can be used as a scrubbing liquid. Detailed numerical models are required for accurate replication of processes in these applications, with complex physical and chemical phenomena considered. Among them, mass transfer modeling between phases has proven to be particularly important for obtaining accurate simulation results. Present work investigates a new model for calculating liquid side mass transfer coefficient in falling droplets, which considers additional parameters such as surface renewal rate, Reynolds number, and droplet diameter, compared to simplified and more common approaches. Initial modelling was performed on a single droplet level, followed by the implementation in the computational fluid dynamics framework and expansion to the entire spray. Desulfurization efficiencies for real cases modelled with the new approach were compared with the experimental data and the previously used penetration theory model results. The newly implemented model investigated the influence of operational parameters such as water and gas flow, sulfur dioxide concentration, droplet size, and distribution on desulfurization efficiency. The results obtained by the new model showed the expected trend of increased efficiency with the water flow increase, as well as greater sensitivity to operational conditions in different cases. Furthermore, compared to the previously used model, the present work more accurately replicated removal efficiencies in simulations of seawater spray scrubber applications, which is beneficial in designing new and more efficient equipment.

Evolution of the physicochemical properties and SO2 adsorption performance of powdered activated coke during adsorption–desorption cycle

The use of carbonaceous adsorbent to remove SO2 from flue gas is regarded as the most environmentally friendly flue gas desulfurization technology presently known because of the extensive pores and rich functional groups characterizing the adsorbents. The main purpose of this work is to clarify the effects of the thermal regeneration temperature and cycle times on SO2 adsorption performance by analyzing the physicochemical properties of carbon adsorbent and to reveal the synergistic relationship between adsorbent mass loss and gas release. Commercial powdered activated coke (PAC) prepared from coal was used. Experimental results show that the influence of the regeneration temperature on the physicochemical properties of the adsorbent leads to different variation trends in the circulating desulfurization performance. The regeneration rates of the regenerated PACs after 10 cycles at 250/450/650/850 °C were 37.71%, 72%, 118.66%, and 148.06%, respectively. Pore blockage and oxygen accumulation on the carbon surface are the reasons for the decline in the desulfurization performance of regenerated PAC at 250–450 °C. Pore development, primarily in the form of micropores, and the inhibition of surface oxidation cause the optimization of the desulfurization performance of regenerated PAC at 650–850 °C. The release of carbon atoms in CO2/CO gas during regeneration causes loss of PAC mass; meanwhile, oxygen atoms mainly originate from the adsorption process. This study systematically clarifies the relationship between the physicochemical properties of PAC and the evolution of SO2 cyclic adsorption properties, which provides guidance for the design of regeneration parameters for desulfurization systems.

Thermodynamic study of regenerative barium-based materials towards barium sulfide for catalytic sulfur dioxide reduction

Flue gas with high SO2 content presents a series of human health and environmental problems, which prompted Flue Gas Desulfurization (FGD) technologies widely utilised in industries. However, the conventional FGD using absorbents or adsorbents could generate secondary sulfur-containing pollutants. Thus, a regenerative FGD reaction system that eliminates secondary pollutants while recovering valuable S has been researched. Ba-based materials, viz. Ba(OH)2, BaCO3 and BaO as the precursors, are involved in a regenerative BaS/BaSO4 reaction system of this research. Current thermodynamic study via minimization of Gibbs free energy explored the feasibility of BaS production from these Ba-based materials and reviewed its potential in SO2 reduction to S. Formation of BaS from Ba-based materials was feasible but the yield depends strongly on the temperature and sulfidizing agent used. Compared to BaCO3-systems, Ba(OH)2- and BaO-systems showed better performance in BaS synthesis due to their high equilibrium conversion, even at temperatures< 773 K. Besides, H2S is a better sulfidizing agent for BaS synthesis due to higher BaS yield (maximum 99%). Synthesis routes of different Ba-systems were confirmed by their respective Keq profiles. The feasibility of BaS catalyst in SO2 reduction to S was proven by the excellent SO2 reducing activity and high S yield (100%) at 273 – 1173 K with S8 and S2 as major products. BaS regeneration via H2 was also validated by high BaS yield (100%) at 473 – 1273 K.

Research on Flue Gas Desulfurization and Denitrification Technology and Energy Conservation and Environmental Protection in Thermal Power Plants

Research on Flue Gas Desulfurization and Denitrification Technology and Energy Conservation and Environmental Protection in Thermal Power Plants

Application of Flue Gas Desulfurization and Denitration Technology in Thermal Power Plants and Energy Saving and Environmental Protection

Application of Flue Gas Desulfurization and Denitration Technology in Thermal Power Plants and Energy Saving and Environmental Protection

Numerical simulation study on gas-solid flow characteristics and SO2 removal characteristics in circulating fluidized bed desulfurization tower

Circulating fluidized bed flue gas desulfurization technology is widely used in the world. The computational particle fluid dynamics (CPFD) numerical simulation method was used to study the gas-solid two-phase flow and desulfurization characteristics in the circulating fluidized bed desulfurization tower. The CPFD method is based on the MP-PIC method, which uses the stochastic particle method for the particle phase and the Euler method for the fluid phase to solve the dense particle flow. The established model was firstly verified by the experimental results of gas-solid flow field and desulfurization efficiency. Then, the effects of flue gas parameters on the flow field in the desulfurization tower and the effects of flue gas parameters, SO2 inlet concentration, and Ca/S on desulfurization efficiency were numerically simulated. An effective optimization scheme was also proposed to improve the desulfurization efficiency. The research results showed that the CPFD simulation results were in good agreement with the experimental results, which proved the reliability of the method. The particle motion state in the bed of the desulfurization tower presents a core-annular flow. As the flue gas inlet flow increased, the distribution of flue gas and particles has a serious deviation, and the desulfurization efficiency also decreased. The desulfurization efficiency will decrease with the increased of SO2 inlet concentration and increased with the increased of Ca/S. According to the distribution of SO2 concentration in the bed, three characteristic desulfurization zones can be proposed, namely, the initial mixing process zone, the high-efficiency desulfurization process zone, and the low-efficiency desulfurization process zone. Installing a baffle at the bottom of the desulfurization tower can optimize the distribution of gas-solid two-phase flow in the bed and the desulfurization efficiency.