Search Results (37)

Mercury poses serious hazards to human health. Carbon nanotube (CNT) is a potential material for elemental mercury (Hg⁰) adsorption removal, however, it shows susceptibility to SO₂ and H₂O. Herein, CNT is first decorated with Fe₂O₃ then modified with MnCl₂ (MnCl₂-Fe₂O₃@CNT) to enhance SO₂ and H₂O resistance. The Hg⁰ removal performance and physical–chemical properties of samples are comprehensively studied. MnCl₂(10)FeCNT (10 wt% MnCl₂ content) has a high specific surface area (775.76 m²·g⁻¹) and abundant active chlorine (35.01% Cl* content) as well as oxygen species (84.23% O_α content), which endows it with excellent Hg⁰ adsorption capacity (25.06 mg·g⁻¹) and good SO₂ and H₂O resistance. Additionally, the superparamagnetic property can enable MnCl₂(10)FeCNT to be conveniently recycled. After fifth regeneration, MnCl₂(10)FeCNT can still achieve >90% Hg⁰ removal. The abundant active chlorine and oxygen species over MnCl₂(10)FeCNT are responsible for Hg⁰ removal with HgCl₂ as the primary product. This work demonstrates the enhancement of CNT’s resistance to SO₂ and H₂O by Fe₂O₃ and MnCl₂ modification, which has potential application in flue gas mercury removal. Full article

Co-combustion is regarded as an effective means for high-efficiency utilization of low-quality fuels. However, low-quality fuel has problems such as low energy density and high water content. The fuel quality and blending performance can be further optimized by the pretreatment of low-quality fuel, for example, calorific value, hydrophobicity, and NO conversion rate. Based on the idea of co-upgradation, this study systematically investigates the effects of integrated upgrading on fuel quality and hydrophobicity under different conditions. In this study, lignite and wheat straw were selected as research objects. The co-upgrading experiments of wheat straw and lignite were conducted at reaction temperatures of 170 °C, 220 °C, and 270 °C in flue gas and air atmospheres with biomass blending ratios of 0%, 25%, 50%, 75%, and 100%. SEM (scanning electron microscopy) and nitrogen (N₂) adsorption analyses showed that under low-temperature and low-oxygen conditions, organic components from biomass pyrolysis migrated in situ to cover the surface of lignite, resulting in a gradual smoothing of the fuel surface and a decrease in the specific surface area. Meanwhile, water reabsorption experiments and contact angle measurements showed that the equilibrium water holding capacity and water absorption capacity of the lifted fuels was weakened, and hydrophobicity was enhanced. Combustion kinetic parameters and pollutant release characteristics were investigated by thermogravimetric analysis (TGA) and isothermal combustion tests. It was found that co-upgradation could effectively reduce the reaction activation energy and NO conversion rate. Characterized by Raman spectroscopy (Raman) and X-ray photoelectron spectroscopy (XPS), in situ migration of organic components affected combustion reactivity by modulating changes in N-containing product precursors. The results showed that the extracted fuel with a 75% biomass blending ratio in the flue gas atmosphere exhibited the best overall performance at 220 °C, with optimal calorific value, combustion reactivity, and hydrophobicity. These findings may provide important theoretical foundations and practical guidance for the optimization of industrial-scale upgrading processes of low-quality fuels. Full article

This study investigates the emission characteristics and environmental impacts of pollutants from bagasse-fired biomass boilers through the integrated field monitoring of two sugarcane processing plants in Guangxi, China. Comprehensive analyses of flue gas components, including PM_2.5, NOx, CO, heavy metals, VOCs, HCl, and HF, revealed distinct physicochemical and emission profiles. Bagasse exhibited lower C, H, and S content but higher moisture (47~53%) and O (24~30%) levels compared to coal, reducing the calorific values (8.93~11.89 MJ/kg). Particulate matter removal efficiency exceeded 98% (water film dust collector) and 95% (bag filter), while NOx removal varied (10~56%) due to water solubility differences. Heavy metals (Cu, Cr, Ni, Pb) in fuel migrated to fly ash and flue gas, with Hg and Mn showing notable volatility. VOC speciation identified oxygenated compounds (OVOCs, 87%) as dominant in small boilers, while aromatics (60%) and alkenes (34%) prevailed in larger systems. Ozone formation potential (OFP: 3.34~4.39 mg/m³) and secondary organic aerosol formation potential (SOAFP: 0.33~1.9 mg/m³) highlighted aromatic hydrocarbons (e.g., benzene, xylene) as critical contributors to secondary pollution. Despite compliance with current emission standards (e.g., PM < 20 mg/m³), elevated CO (>1000 mg/m³) in large boilers indicated incomplete combustion. This work underscores the necessity of tailored control strategies for OVOCs, aromatics, and heavy metals, advocating for stricter fuel quality and clear emission standards to align biomass energy utilization with environmental sustainability goals. Full article

The present study analyzes the combustion process of mixed biomass pellets in a domestic boiler. For the purposes of the research, experimental measurements of flue gases are combined with numerical simulations based on computational fluid dynamics (CFD). Special attention is given to the impact of the ratio between primary and secondary air on the combustion process, emission characteristics, and thermal balance. The results show that an air distribution ratio of 60/40 (primary/secondary) leads to more complete combustion, reducing emissions of carbon monoxide (CO) and nitrogen oxides (NOx), while also improving the efficiency of the boiler. The analysis of the numerical modeling results shows that CO emissions decrease by 12% and NOx emissions by 27%. The calculated model is validated using experimental data on flue gas temperature, oxygen (O₂) and carbon dioxide (CO₂) concentrations, and combustion efficiency, and a high degree of correspondence between theoretical and actual measurements is established. The simulations reveal the dynamics of the temperature field, the movement of flue gases, and the role of turbulence in the combustion chamber. Optimization of the air distribution is proven to improve the combustion process and reduce the harmful emissions generated. The obtained results highlight the potential of mixed biomass pellets as a sustainable alternative to conventional fuels, provided that combustion parameters are precisely regulated. They can serve as a foundation for the enhancement of biomass-based heating systems in order to achieve higher efficiency and environmental sustainability. A market research study is also conducted, revealing that mixed pellets are preferred due to their high calorific value, low cost, and low ash content. Full article

This present study covers a complex approach to study a hybrid separation technique: membrane-assisted gas absorption for CO₂ capture from flue gases. It includes not only the engineering aspects of the process, particularly the cell design, flow organization, and process conditions, but also a complex study of the materials. It covers the spinning of hollow fibers with specific properties that provide sufficient mass transfer for their implementation in the hybrid membrane-assisted gas absorption technique and the design of an absorbent with a new ionic liquid—bis(2-hydroxyethyl) dimethylammonium glycinate, which allows the selective capture of carbon dioxide. In addition, the obtained hollow fibers are characterized not only by single gas permeation but with regard to mixed gases, including the transfer of water vapors. A quasi-real flue gas, which consists of nitrogen, oxygen, carbon dioxide, and water vapors, is used to evaluate the separation efficiency of the proposed membrane-assisted gas absorption technique and to determine its ultimate performance in terms of the CO₂ content in the product flow and recovery rate. As a result of this study, it is found that highly permeable fibers in combination with the obtained absorbent provide sufficient separation and their implementation is preferable compared to a selective but much less permeable membrane. Full article

The thermodynamic equilibrium of the gas-phase system in lead smelting flue gas was studied using FactSage 8.2 software, and the effects of temperature, the main components of the gas phase, and other factors on the SO₃ content in the equilibrated flue gas were investigated. In addition, experimental research was conducted on a solid-phase catalysis experimental platform to investigate the effect of lead smelting ash on SO₂ catalytic oxidation. The results show that temperature and initial O₂ content in flue gas have a significant impact on the equilibrium concentration of SO₃, while the initial SO₂ content in flue gas has a relatively small impact on the equilibrium concentration of SO₃; the fly ash from the lead smelting flue promotes the conversion of SO₂ to SO₃ in the flue gas. SO₃-suppression experiments show that PbS can adequately inhibit SO₃ formation in a simulated flue gas environment, and the content of SO₃ after adding PbS under different oxygen contents and SO₂ atmospheres does not exceed 0.6%. Through the method of thermodynamic simulation and experimental verification, this study reveals the catalytic oxidation mechanism of SO₂ in lead dust and proposes the use of PbS as an in situ SO₃ inhibitor. Full article

The municipal solid waste incineration (MSWI) process plays a crucial role in managing the risks associated with waste accumulation and promoting the sustainable development of urban environments. However, unstable operation of the MSWI process can lead to excessive pollutant emissions, deteriorating air quality, and adverse impacts on public health. Flue gas oxygen content is a key controlled variable in the MSWI process, and its stable control is closely linked to both incineration efficiency and pollutant emissions. Developing a high-precision, interpretable model for flue gas oxygen content is essential for achieving optimal control. However, existing methods face challenges such as poor interpretability, low accuracy, and the complexity of manual hyperparameter tuning. To address these issues, this article proposes a flue gas oxygen content model based on a Bayesian optimization (BO) main–compensation ensemble modeling algorithm. The model first utilizes an ensemble TS fuzzy regression tree (EnTSFRT) to construct the main model. Then, a long short-term memory network (LSTM) is employed to build the compensation model, using the error of the EnTSFRT model as the target value. The final output is obtained through a weighted combination of the main and compensation models. Finally, the hyperparameters of the main–compensation ensemble model are optimized using the BO algorithm to achieve a high generalization performance. Experimental results based on real MSWI process data demonstrate that the proposed method performs well, achieving a 48.2% reduction in RMSE and a 53.1% reduction in MAE, while R² increases by 140.8%, compared to the BO-EnTSFRT method that uses only the main model. Full article

Oxy-fuel combustion is a promising way to avoid process-based CO₂ emissions. In this paper, the operational range of a new semi-industrial oxy-fuel combustion chamber for pulverized biomass is analyzed. This approach is used to gain a deeper understanding of the combustion setup and to examine the differences between air and oxy-fuel combustion on an industrial scale. Both analyzed parameters—flame spread and temperature distribution—have a significant influence on heat transfer in commercial boilers. The stability of various operating conditions is assessed by monitoring the CO content in the flue gas via a gas analyzer unit. For stable operation using walnut shells as fuel in an air atmosphere, an overall air-to-fuel ratio of 1.57–1.75 and a local air-to-fuel ratio of 0.75–0.95 provide the most stable conditions. A high swirl number of $0.9$ is found to be critical for stability, as the increased fuel momentum entering the combustion chamber promotes a fuel jet-dominated swirl flame. For the corresponding oxy-fuel combustion with the same volume flows and three different oxygen concentrations between 27% and 33%, stable combustion behavior is also observed. Using a camera setup to analyze flame shape and spread, it is observed that the flame formed with an oxygen content of 33% most closely resembles the flame shape achieved under air combustion conditions. However, the combustion temperatures most closely match those of the air operating condition when the oxygen content is 27%. Overall, it is shown that the approach for corresponding oxy-fuel conditions features similar flame shapes to oxy-fuel combustion with flue gas recirculation in a semi-industrial combustion chamber. Full article

Algae communities as primary producers are essential elements of aquatic ecosystems and contribute significantly to oxygen production, carbon dioxide fixation, and nutrient transport processes in water bodies. The use of algae-based carbon capture and storage technologies does not produce harmful by-products that require disposal, and the resulting algal biomass can be valuable across various industrial sectors. In this study, model experiments were conducted to develop sequential absorption–microalgae hybrid CO₂-capture methods. To facilitate CO₂ capture from flue gases, wood biomass ash (WBA), an agricultural by-product, was utilized for its alkaline properties, while the flue gas scrubbing medium was regenerated by algae that restored alkalinity during their growth. In our experiments, one of our goals was to determine the optimal conditions for achieving maximum algal biomass growth in the shortest possible time. The suitability of WBA for flue gas cleaning was tested via simulation of CO₂ introduction. Moreover, a method was developed to determine the dissolved inorganic carbon content with the use of an OxiTop device monitoring the changes in pressure. The applied device was a closed, static, and pressure-based respirometer originally designed to determine the biological activity of microorganisms in both solid and liquid samples. In addition, the effects of CO₂-enriched WBA extract on algae cultivation were also analyzed, confirming that it imposed no growth inhibition and identifying the concentration (10% WBA) that optimally promoted algal growth. The optimal initial algal concentration and nutrient conditions for maximum growth were also determined. Full article

To investigate the safe, stable, and economically viable operation of a boiler under ultra-low-load conditions during the deep peaking process of coal-fired units, a numerical simulation study was conducted on a 660 MW front- and rear-wall hedge cyclone burner boiler. The current research on low load conditions is limited to achieving stable combustion by adjusting the operating parameters, and few effective boiler operating parameter predictions are given for very low-load conditions, i.e., below 20%. Various burner operation modes under ultra-low load conditions were analyzed using computational fluid dynamics (CFDs) methods; this operation was successfully tested with six types of pulverized coal combustion in this paper, and fitting models for outlet flue gas temperature and NO_x emissions were derived based on the combustion characteristics of different types of pulverized coal. The results indicate that under 20% ultra-low-load conditions, the use of lower burners leads to a uniform temperature distribution within the furnace, achieving a minimum NO_x emission of 112 ppm and a flue gas temperature of 743 K. Coal type 3, with the highest carbon content and a calorific value of 22,440 kJ/kg, has the highest average section temperature of 1435.76 K. In contrast, coal type 1 has a higher nitrogen content, with a maximum cross-sectional average NO_x concentration of 865.90 ppm and an exit NO_x emission concentration of 800 ppm. The overall lower NO_x emissions of coal type 3 are primarily attributed to its reduced nitrogen content and increased oxygen content, which enhance pulverized coal combustion and suppress NO_x formation. The fitting models accurately capture the influence of pulverized coal composition on outlet flue gas temperature and NO_x emissions. This control strategy can be extended to the stable combustion of many kinds of coal. For validation, the fitting error bar for the predicted outlet flue gas temperature based on the elemental composition of coal type 6 was 8.09%, whereas the fitting error bar for the outlet NO_x emissions was only 1.45%. Full article

To reduce the mercury content in flue gas from coal-fired power plants and to obtain high-performance, low-cost mercury adsorbents, a novel composite material was prepared by structural design through the in situ growth method. Functionalization treatments such as the modification of functional groups and multilayer loading of polymetallic were conducted. These materials include the MOF material UiO-66 and modified biochar doped with Fe/Ce polymetallic, both of which contain unsaturated metal centrals and oxygen-containing functional groups. On the basis of obtaining the effects of adsorption temperature and composite ratio on the Hg⁰ removal characteristics, coupling and synergistic mechanisms between the various types of active centers included were investigated by using a variety of characterization and analysis tools. The active adsorption sites and oxidation sites were identified during this process, and the constitutive relationship between the physicochemical properties and the performance of Hg⁰ removal was established. The temperature-programmed desorption technique, Grand Canonical Monte Carlo simulation, and adsorption kinetic model were employed to reveal the mechanism of Hg⁰ removal. The results showed that the UiO-66-Br@MBC composite adsorbent possessed an excellent Hg⁰ removal performance at adsorption temperatures ranging from 50 to 250 °C, and targeted construction of adsorption and oxidation sites while maintaining thermal stability. The Hg⁰ removal by the composites is the result of both adsorption and oxidation. The micropores and small pore mesopores in the samples provide physical adsorption sites. The modified biochar acts as a carrier to facilitate the full exposure of the central metal zirconium ions, the formation of more active sites, and the process of electron transfer. The doping modification of the Br element can enhance the overall redox ability of the sample, and the introduced Fe and Ce polymetallic ions can work in concert to promote the oxidation process of Hg⁰. The excellent regulation of the ratio between adsorption and oxidation sites on the surface of the composite material finally led to a significant boost in the samples’ capacity to remove Hg⁰. Full article

The technology for the selective catalytic reduction of NO_x by CO (CO-SCR) has the capability to simultaneously eliminate CO and NO_x from industrial flue gas and automobile exhaust, thus making it a promising denitrification method. The advancement of cost-effective and high-performing catalysts is crucial for the commercialization of this technology. Mn-based catalysts demonstrate enhanced catalytic efficiency under conditions of low temperature and low oxygen content when compared to other transition metal-based catalysts, indicating significant potential for practical applications. This review outlines the diverse Mn-based catalysts, including bulk or supported MnO_x catalysts, bulk or supported Mn-based composite oxide catalysts, and the use of MnO_x as dopants. Subsequently, the synthesis methods and catalytic mechanism employed by Mn-based catalysts are presented. The following section examines the impact of O₂, H₂O, and SO₂ on the catalytic performance. Finally, the potential and implications of this reaction are deliberated. This work aims to offer theoretical guidance for the rational design of highly efficient Mn-based catalysts in the CO-SCR reaction for industrial applications. Full article

Dense-phase-tower desulfurization technology is an emerging semi-dry flue-gas desulfurization ash process, i.e., the flue gas is allowed to enter the desulfurization tower from the bottom up and, at the same time, is sprayed with a desulfurizing agent that undergoes an acid–base reaction with the flue gas in the ascent process. The calcium sulfite and calcium sulfate produced by the reaction and the part of the desulfurization agent that is not involved in the reaction will enter the subsequent dust removal system, and what is retained is the by-product desulfurization ash. This desulfurization ash contains a large amount of calcium sulfite, which leads to its unstable nature; it is easily oxidized and expands in volume, and, if used in the field of building materials, it will lead to cracking and other problems, so it is difficult to effectively use it. In order to solve this problem, XRF, XRD, and iodometric and other analytical methods were used to determine the specific composition of desulfurization ash, and the muffle furnace and vertical tube furnace were used to study the thermal oxidative modification of calcium sulfite in desulfurization ash, to investigate the effects of the oxygen content, reaction temperature, medium flow rate, and chloride content on the oxidation of calcium sulfite, and to analyze the thermodynamics in the high-temperature oxidation reaction. The results showed that the oxidation rate of calcium sulfite increased with higher reaction temperatures. Increased oxygen content promoted the oxidation rate, particularly at low oxygen levels. The oxidation rate of calcium sulfite correlated positively with the medium flow rate until a rate of 75 mL·min⁻ was reached. At a reaction temperature of 420 °C and a gas flow rate of 85 mL·min⁻¹, the oxidation conversion efficiency exceeded 89%. Chloride content significantly reduced the oxidation rate of calcium sulfite, although this inhibition weakened at temperatures above 500 °C. Kinetic analysis suggested that the oxidation reaction of calcium sulfite predominantly occurred below 500 °C. These findings have both theoretical and practical implications for the thermal oxidation treatment and disposal of desulfurization ash. Full article

As an indispensable component of coal-fired power plants, boilers play a crucial role in converting water into high-pressure steam. The oxygen content in the flue gas is a crucial indicator, which indicates the state of combustion within the boiler. The oxygen content not only affects the thermal efficiency of the boiler and the energy utilization of the generator unit, but also has adverse impacts on the environment. Therefore, accurate measurement of the flue gas’s oxygen content is of paramount importance in enhancing the energy utilization efficiency of coal-fired power plants and reducing the emissions of waste gas and pollutants. This study proposes a prediction model for the oxygen content in the flue gas that combines the whale optimization algorithm (WOA) and long short-term memory (LSTM) networks. Among them, the whale optimization algorithm (WOA) was used to optimize the learning rate, the number of hidden layers, and the regularization coefficients of the long short-term memory (LSTM). The data used in this study were obtained from a 350 MW power generation unit in a coal-fired power plant to validate the practicality and effectiveness of the proposed hybrid model. The simulation results demonstrated that the whale optimization algorithm–long short-term memory (WOA-LSTM) model achieved an MAE of 0.16493, an RMSE of 0.12712, an MAPE of 2.2254%, and an $R^2$ value of 0.98664. The whale optimization algorithm–long short-term memory (WOA-LSTM) model demonstrated enhancements in accuracy compared with the least squares support vector machine (LSSVM), long short-term memory (LSTM), particle swarm optimization–least squares support vector machine (PSO-LSSVM), and particle swarm optimization–long short-term memory (PSO-LSTM), with improvements of 4.93%, 4.03%, 1.35%, and 0.49%, respectively. These results indicated that the proposed soft sensor model exhibited more accurate performance, which can meet practical requirements of coal-fired power plants. Full article

The cement industry is regarded as one of the primary producers of world carbon emissions; hence, lowering its carbon emissions is vital for fostering the development of a low-carbon economy. Carbon capture, utilization, and storage (CCUS) technologies play significant roles in sectors dominated by fossil energy. This study aimed to address issues such as high exhaust gas volume, low CO₂ concentration, high pollutant content, and difficulty in carbon capture during cement production by combining traditional cement production processes with cryogenic air separation technology and CO₂ purification and compression technology. Aspen Plus^® was used to create the production model in its entirety, and a sensitivity analysis was conducted on pertinent production parameters. The findings demonstrate that linking the oxygen-enriched combustion process with the cement manufacturing process may decrease the exhaust gas flow by 54.62%, raise the CO₂ mass fraction to 94.83%, cut coal usage by 30%, and considerably enhance energy utilization efficiency. An exergy analysis showed that the exergy efficiency of the complete kiln system was risen by 17.56% compared to typical manufacturing procedures. However, the cryogenic air separation system had a relatively low exergy efficiency in the subsidiary subsystems, while the clinker cooling system and flue gas circulation system suffered significant exergy efficiency losses. The rotary kiln system, which is the main source of the exergy losses, also had low exergy efficiency in the traditional production process. Full article