Wet Flue Gas Desulfurization System Research Articles

Control strategy optimization for wet flue gas desulfurization system during load cycling dynamic processes: Energy saving and environmental impact

To accommodate high penetration of fluctuating renewable power within the power grid, thermal power plants often engage in load cycling dynamic processes. When thermal power plants operate under low loads and load cycling dynamic processes, large ratio of auxiliary power is consumed in wet flue gas desulfurization (WFGD) system, because the slurry flowrate cannot be regulated appropriately. In this study, dynamic models of SO2 generation and WFGD system were developed, and coupled with the dynamic model of a thermal power plant. An optimization control strategy for slurry pumps under fixed-speed mode was presented. Then, model to determine the optimal slurry flowrates with changing parameters of flue gas and slurry was derived, and a control strategy to regulate inverter slurry pumps was proposed. The auxiliary power consumption during load cycling dynamic processes decreases significantly with optimization control strategies, although the cumulative SO2 emissions increases. When the control strategy optimization for slurry pumps under fixed-speed mode was implemented, the energy-saving potential is 19.00%, 20.39%, 22.06% and 23.05% during load decreasing processes under load cycling rate of 0.5%, 1.0%, 1.5%, and 2.0% Pe0 min−1, and that value under the control strategy to regulate inverter slurry pumps is 33.20%, 34.45%, 35.04% and 37.07%, respectively.

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.

Improving Fine Particle Removal Using a Single-Channel Slit Bubbling Device in Wet Flue Gas Desulfurization System.

To improve the cleanliness of coal-fired power plants' particulate matter emissions, a novel device (single-channel slit bubbling particle removal device (SCSB-PRD)) is proposed to improve the wet flue gas desulfurization system's (WFGDs) collaborative particle removal effect. Actual coal-fired flue gas was used to test the particle removal performance. The results showed that the flue gas temperature had no obvious effect on the scrubbing effect of the SCSB-PRD. The scrubbing space, scrubbing liquid volume, and flue gas flow rate effectively changed the gas-liquid flow state, and the bubbling state was the key factor in particle removal. The jet-bubbling contact state was more conducive to removing particles than the foam bubbling state. The jet-bubbling state improved the removal efficiency of fine particles by approximately 30% compared to the foam bubbling state. The device operated in a single stage, and the removal performance of the particulate matter reached more than 60%. Even the submicron particles had a satisfactory removal performance of greater than 50%. The particulate matter concentration at the outlet of the WFGDs was reduced to less than 10 mg/m3, which provides a feasible transformation path for ultraultra-low emissions of particulate matter from coal-fired power plants.

Predictor-Based Active Disturbance Rejection Control of Wet Flue Gas Desulfurization System With Delay Robustness and Simplified Tuning

Predictor-Based Active Disturbance Rejection Control of Wet Flue Gas Desulfurization System With Delay Robustness and Simplified Tuning

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.

Improvement of the reduction of condensable particulate matter in flue gas scrubbing process

Condensable particulate matter (CPM) is characterized by complex composition, non-negligible emission concentration, and fine or ultrafine in size after conversion to particles, which is difficult to remove. Current methods to control CPM are not fully developed and mainly focus on synergistic removal of CPM in existing air pollution control devices, such as CPM reduction through scrubbing processes in wet flue gas desulfurization (WFGD) systems. In this work, an experimental system including a simulated WFGD scrubber, also referred to as the primary scrubber (PS), and a secondary scrubber (SS) was built to explore measures to improve the CPM reduction performance during scrubbing. The operating parameters of the liquid-to-gas (L/G) ratio and the spray temperature in the two scrubbers were tuned in the experiments. The results indicated that CPM could be reduced in the PS by conversion to filterable particulate matter (FPM), and captured by the spray droplets through the effects of dissolution and condensation, but the reduction was not very efficient. In the SS, the reduction performance of CPM could be further improved due to increased dissolution of CPM caused by increased opportunities for gas-liquid contact, and increased condensation of CPM due to lower spray temperature. The FPM transformed from the CPM in the PS could also be reduced in the SS by the effects of diffusiophoresis and thermophoresis contributed by water vapor condensation. An increase in the L/G ratio could improve the CPM reduction.

Enhancing aerosol emission reduction in an ammonia-based WFGD system with tray implementation

Operating parameter optimization is a viable strategy to reduce aerosol emissions from an ammonia-based wet flue gas desulfurization (ammonia WFGD) system. But the optimization techniques typically cause SO2 removal efficiency reduction. Multi-hole trays can be installed in the scrubber to balance the aerosol emission control and the desulfurization efficiency. The experimental results show that the tray installation alone can barely enhance aerosol emission control. However, the tray installation can improve the SO2 removal efficiency to spare more space for operating parameter optimization. The smaller hole size favors the SO2 removal with a particular hole ratio. Optimizing the liquid-to-gas ratio (L/G) works well with tray installation to realize aerosol emission reduction, with the aerosol reduction rate over 50 %. The improvement brought about by the tray installation only works within a specific L/G range, beyond which the tray cannot make up for the desulfurization efficiency reduction caused by L/G optimization. The best aerosol emission reduction rate was achieved at L/G = 8 L/m3 with the tray installation of 35 % hole ratio and 10 mm diameter, with the desulfurization efficiency maintained above 90 %. The tray with 35 % hole ratio and 20 mm diameter can be employed at L/G = 8 L/m3 for better aerosol emission if the SO2 removal efficiency below 90 % is acceptable. The choice is due to desulfurization efficiency and aerosol emission control demand.

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.

Study on the Effects of Wet Flue Gas Desulfurization on Particulate Matter Emission from Industrial Coal-Fired Power Plants

This study aimed to investigate the effects of wet flue gas desulfurization (WFGD) on particulate matter (PM) emissions in coal-fired power plants (CFPPs) using an electrical low-pressure impactor (ELPI). The investigation was conducted on five industrial CFPPs of various loads in China to clarify the influence factors of WFGD on PM10 emissions. After WFGD, the proportion of PM2.5 to PM10 in the outlet flue gas increases, which showed that the WFGD system is selective in the capture of PM, with a significant effect on the capture of large particle sizes. The investigation found that four spray layers have a better effect on the capture of particles than two spray layers. Additionally, the investigation also found that unit load is not the main factor affecting the efficiency of PM10 capture by WFGD. Instead, the factors affecting the capture efficiency of PM10 by WFGD are the inlet flue gas temperature and the dust concentration. Relatively higher inlet flue gas temperature and lower inlet dust concentration will both result in higher emission of PM0.1~1 from the WFGD outlet. These findings suggest that a matched integration of WFGD and CFPP is essential for ultra-low PM emission control and green industry development.

Experimental Investigation of Removal of SO3 from Flue Gas with Modified Fly Ash Adsorbents.

The removal of nonconventional pollutants in coal-fired power plants, such as SO3, has been receiving more and more attention. However, due to its unique nature, it is difficult to remove SO3 effectively with the widely used wet flue gas desulfurization systems. Nowadays, dry-sorbent injection technology has become a promising method for SO3 emission control in coal-fired power plants. The removal characteristics of SO3 from flue gas with modified fly ash adsorbents were investigated in a fixed-bed reactor. Factors affecting the adsorption efficiency of SO3 were studied, including modification method, modified fly ash adsorbent particle size, reaction temperature, and flue gas component. Combined with adsorbent characterization analysis, the adsorption kinetics of SO3 by modified fly ash adsorbents were carried out with four different adsorption kinetics models. The results show that the SO3 adsorption efficiency of the fly ash samples increases after modification; the best SO3 removal performance of fly ash was achieved when 1.5 mol/L NaOH solution was used, with the highest SO3 adsorption efficiency of up to 98.3%. The modified fly ash adsorbent particle size, water vapor content, and the addition of NO have little effect on the adsorption efficiency of SO3. As the reaction temperature increases from 250 to 450 °C, the SO3 adsorption efficiency first increases and then decreases, with an optimal reaction temperature of 350 °C. The addition of SO2 would compete with SO3 for adsorption and inhibit the uptake of SO3 by the adsorbent. Adsorption kinetics data show that external mass transfer and chemical adsorption are the main critical mechanisms affecting the adsorption efficiency of the modified fly ash adsorbent in the SO3 removal process compared to internal diffusion.

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.

Prediction of inlet SO2 concentration of wet flue gas desulfurization (WFGD) by operation parameters of coal-fired boiler.

Circulating fluidized bed (CFB) boilers with wet flue gas desulfurization (WFGD) system is a popular technology for SO2 removal in the coal-fired thermal power plant. However, the long response time of continues emission monitoring system (CEMS) and the hardness of continuously monitoring the coal properties leads to the difficulties for controlling WFGD. It is important to build a model that is adaptable to the fluctuation of load and coal properties, which can obtain the SO2 concentration ahead CEMS, without relying on coal properties. In this paper, a prediction model of inlet SO2 concentration of WFGD considering the delay between the features and target based on long-short term memory (LSTM) network with auto regression feature is established. The SO2 concentration can be obtained 90s earlier than CEMS. The model shows good adaptability to the fluctuation of SO2 concentration and coal properties. The root-mean-squared error (RMSE) and R squared (R2) of the model are 30.11mg/m3 and 0.986, respectively. Meanwhile, a real-time prediction system is built on the 220 t/h unit. A field test for long-term operation has been conducted. The prediction system is able to continuously and accurately predict the inlet SO2 concentration of the WFGD, which can provide the operators with an accurate reference for the control of WFGD.

An Efficient Method for Heat Recovery Process and燭emperature燨ptimization

Flue gas heat loss accounts for a significant component of the overall heat loss for coal-fired boilers in power plants. The flue gas absorbs more heat as the exhaust gas temperature rises, which reduces boiler efficiency and raises coal consumption. Additionally, if the exhaust gas temperature is too high, a lot of water must be used to cool the flue gas for the wet flue gas desulfurization system to function well, which has an impact on the power plant’s ability to operate profitably. It is consequently vital to take steps to lower exhaust gas temperatures in order to increase boiler efficiency and decrease the amount of coal and water used. Desulfurization performance may be enhanced and water use can be decreased by reasonable flue gas characteristics at the entry. This study analyzed the unit’s energy consumption, investment, and coal savings while proposing four coupling strategies for regulating flue gas temperature and waste heat recovery. A graded flue gas conditioning and waste heat recovery plan was presented under the condition of ensuring high desulfurization efficiency, along with the notion of minimizing energy loss owing to energy inflow temperature difference. Numerical results show that the proposed methods improved the system performance and reduced the water consumption and regulated the boiler temperature.

Hybrid modeling and operating optimization method of oxidation process of wet flue gas desulfurization (WFGD) system

Wet flue gas desulfurization systems (WFGD) are the most popular method to remove the SO2 from the flue gas in China’s power plants. Most WFGD systems contain an oxidation subsystem, which is one of the most important subsystems. In this paper, a hybrid modeling and operating optimization method of oxidation process of WFGD system is proposed, verified and applied on the WFGD system of a typical 1000 MW unit. The influence of important parameters such as the diameter of droplets or bubbles, the liquid-gas ratio or the gas-gas ratio (the ratio of between oxidized air flow rate and flue gas flow rate) and the height of the natural oxidation zone or the slurry level on natural oxidation rate and forced oxidation rate are further explored. The application results show that the above method can significantly reduce the operating energy consumption of the oxidation fan by more than 25 %. Furthermore, field tests are also carried out on the WFGD systems of 130 t/h and 220 t/h circulating fluidized bed (CFB) units. The energy consumption can be reduced by 30.6 % and 37.5 %, respectively. The results will be helpful to reduce the auxiliary power consumption and additional CO2 emission of WFGD.

Model‐free adaptive control based on switching mechanism for multi‐input multi‐output wet flue gas desulfurization system

SummaryThe wet flue gas desulfurization (WFGD) process is a complex controlled system with nonlinear and time‐varying characteristics. There are a variety of external disturbances in the desulfurization process, which can easily cause a jump in system parameters and even structure. In response to this problem, a model‐free adaptive control scheme based on a switching mechanism is proposed, and the convergence analysis is given. In the scheme, firstly, the operating conditions of the WFGD system are divided into n kinds based on multiple external disturbances, and the mathematical models of the multi‐input multi‐output WFGD system under different operating conditions are established. Then the MFA controllers of the WFGD system under multiple operating conditions are established, respectively. Finally, a switching index function is designed to switch the controller of the WFGD system according to different operating conditions, so that the desulfurization system is always controlled by the most appropriate controller. In the simulation experiment, according to the actual data of the WFGD system of a 1000 MW coal‐fired power station in Beijing, the modeling test and algorithm simulation of the WFGD system under three operating conditions are carried out. The simulation results show that this method can effectively reduce the transient error of the WFGD system output and improve the desulfurization effect.

Zero-valent bimetallic catalyst/absorbent for simultaneous facilitation of MgSO3 oxidation and arsenic uptake

Cobalt (Co)-based catalysts can efficiently reduce the heat waste from sulfate concentration by enhancing sulfite oxidation during wet flue gas desulfurization system. However, arsenic (As) can poison such catalysts and migrate into the sulfate by-products, resulting in severe secondary pollution. In this study, a zero-valent Co/iron (Fe)-based nanoparticle (NZV-Co2Fe1) was fabricated and applied as a bifunctional catalyst/adsorbent. The catalytic stability of the Co-based catalyst was enhanced by the introduction of Fe because the poisonous effect of As was substantially suppressed because of the high adsorption capacity of Fe for As. Compared with the noncatalytic benchmark, the presence of 0.5 g/L NZV-Co2Fe1 can increase the rate of MgSO3 oxidation by approximately 12-fold even at a high concentration of As (2.5 mg/L). The Langmuir model was fitted to the As adsorption isotherms, indicating that As uptake is a single-layer adsorption process. The pseudo-second-order kinetic model indicated that As was removed through chemisorption. The oxidation pathway of As(III) involves reactive radicals (mainly OH, SO4− and SO5−) and ligand-to-metal charge transfer between SO32− and Co2+. The availability of MgSO3 improved the removal efficiency at high concentrations of As(III) (1 mg/L). These results indicate that using NZV-Co2Fe1 as a catalyst to purify the by-products of flue gas desulfurization can effectively prevent secondary pollution.

Enhanced Efficiency of the Sieve Tray in a Desulfurization Spray Scrubber

The wet flue gas desulfurization (WFGD) system is widely used in coal-fired power plants worldwide. Improving its efficiency is very important for economical running. In this study, SO2 removal by the spray scrubber by adding a new sieve tray was studied and compared to that by the traditional spray scrubber without a sieve tray (the WFGD system). The effects of gas flow rate, liquid flow rate, inlet SO2 concentration, and pH value on both types of scrubbers were evaluated. Pore diameter and porosity of the sieve tray in the sieve-tray spray scrubber were determined, and its enhanced efficiency under different experimental conditions was calculated. The results showed that the enhanced efficiency increased with the increasing liquid flow rate, gas flow rate under the same liquid/gas ratio (L/G), and pH value. Compared to the spray scrubber without a sieve tray, the sieve-tray spray scrubber had significantly higher efficiency. The enhanced efficiencies were mostly between 20% and 60% in the experimental range.

Limestone-based dual-loop wet flue gas desulfurization under oxygen-enriched combustion

Oxygen-enriched combustion is the most promising CO2 emission reduction technology for coal burning. However, the sharp increase in CO2 and SO2 concentrations in flue gas after oxygen-enriched combustion poses a new challenge to the subsequent wet flue gas desulfurization (WFGD) system. In this study, limestone-based dual-loop WFGD technology was used to solve this problem. Using a small dual-loop falling-film WFGD experimental system, the effect of CO2 concentration on limestone dissolution, SO2 absorption, SIV oxidation, and CaSO4 crystallization during limestone-based dual-loop WFGD was investigated in detail and compared with single-loop WFGD. The results show that, although an increase in CO2 concentration is beneficial to SO2 absorption in the single-loop WFGD system, it is not conducive to limestone dissolution, SIV oxidation, and CaSO4 crystallization. Compared with single-loop WFGD, in the low pH region of dual-loop WFGD, increasing the CO2 concentration can also improve the SO2 absorption efficiency. However, it had no obvious effect on limestone dissolution, SIV oxidation, and CaSO4 crystallization. In the high pH region of the dual-loop WFGD, although an increase in CO2 concentration is not conducive to SO2 absorption, the SO2 absorption efficiency is still higher than that of single-loop WFGD. The negative effect of increasing the CO2 concentration on limestone dissolution, SIV oxidation, and CaSO4 crystallization can be effectively solved by introducing slurry from the high pH region into the low pH region. Therefore, compared with single-loop WFGD technology, dual-loop WFGD is more suitable for flue gas desulfurization after oxygen-enriched combustion.

Effect of wet flue gas desulfurization on the concentrations and component profiles of condensable particulate matter from ultralow emission coal-fired power plants

This study investigated effect of wet flue gas desulfurization (WFGD) on the concentrations and component profiles of condensable particulate matter (CPM). This research was carried out in two ultralow emission coal-fired power plants (CFPPs), which were equipped with pulverized coal furnaces (PC), in Hunan province, China. The CPM concentrations were measured following the US EPA Method 202. The stack emissions of filterable particulate matter (FPM) met the Chinese ultralow emission standards, and the CPM concentrations from CFPP A and B were respectively 12.12 and 17.64 mg/Nm3. In the WFGD system, the removal efficiencies of the FPM and CPM were respectively 80% and 91% in CFPP A, 83% and 81% in CFPP B. SO42− accounted for the largest fraction of the total detected water-soluble ions in the CPM. Alkanes were the main component of the organic fraction in the CPM, which accounted for 95% in CFPP A and 92% in CFPP B. The removal efficiency of inorganic components from the CPM in CFPP A and B were 81% and 92%, respectively, possibly because the water-soluble ions could be dissolved and removed in the slurry; however, due to the limited solubility of alkanes and esters, the removal efficiency of organic components from the WFGD in CFPP A and B were only 17% and 31%, respectively. The emission factors (EFs) of the CPM for CFPP A and B range from 0.090 to 0.979 kg/(t of coal).

Deep neural network-based optimal selection and blending ratio of waste seashells as an alternative to high-grade limestone depletion for SOX capture and utilization

• Wet flue gas desulfurization process was optimized using waste oyster shell. • Deep neural network–based surrogate model is used to cost optimization. • Seashells with low-grade limestone could fully replace high-grade limestone. • At an optimal blending ratio, total annualized cost could be reduced by US$788,469. • The results facilitate cost-effective and eco-friendly SO x capture and utilization. In wet flue gas desulfurization system, the resource depletion of high-grade limestone, used as conventional SO x absorbent, is becoming serious for SO x capture and utilization. This paper proposes optimal selection and blending ratio of waste seashells as an alternative to high-grade limestone depletion using a deep neural network (DNN)-based surrogate model. Cost optimization proceeds as follows: data generation, data preprocessing, development of DNN-based surrogate model, and derivation of cost optimal selection and blending ratio. First, a process model is developed to generate the datasets, which are gypsum purity according to selection and blending ratio of each seashell and limestone. In addition, a mathematical model is proposed to calculate the total annualized cost (TAC) considering the pretreatment cost of seashell, and the TAC is added to the datasets to predict the gypsum purity as well as TAC. Second, the generated datasets are preprocessed to intensify prediction performance of the DNN-based surrogate model using the z-score normalization method. Third, a DNN-based surrogate model is developed to predict the gypsum purity and TAC according to the selection and blending ratio. Finally, the cost optimal selection and blending ratio are derived from 2.4 billion data generated by the developed DNN-based surrogate model under two constraints: gypsum purity and total SO x absorbent consumption. As a result, the derived selection and optimal blending ratios are low-grade limestone (80.86%), oyster shells (10.78%), scallop shells (0.216%), cockle shells (0.323%), clam shells (2.426%), and mussel shells (5.391%), reducing the TAC by US$788,469.