Flue Gas Research Articles

Promoting elemental mercury immobilization performance from smelting flue gas over a wide temperature range via cobalt-doped copper sulfide adsorbents

Copper sulfide (CuS) sorbent exhibits great potential for gaseous elemental mercury (Hg0) decontamination, but it still suffers from a narrow operating temperature. Therefore, designing advanced CuS sorbents that have a high activity level for capturing Hg0 and thermal stability at a high temperature range is challenging. Herein, we propose a metal doping strategy to fabricate a bimetallic sulfide adsorbent. Benefiting the unique structure and composition, a mesoporous structure and an abundance of unsaturated sulfur sites ensure that CuxCo(1–x)Sy provides a desirable level of adsorption for Hg0. The experimental results indicate the optimum Co doping mass concentration of 5 %. The Cu0.95Co0.05Sy not only performs satisfactory Hg0 adsorption at elevated temperatures (Hg0 average adsorption efficiency of over 97.3 %, Hg0 average adsorption rate of over 2.7 μg/g/min), but also presents an exciting regeneration and recycle performance (a Hg0 adsorption efficiency of over 94 % after 10 cycles). The adsorption capacity of Cu0.95Co0.05Sy at the breakthrough threshold of 25 % reaches 5.22 mg/g, surpassing most of metal sulfide sorbents for Hg0 immobilization at 150 °C. As far as Hg0 adsorption is concerned, the composition of typical smelting flue gases has almost no effect. According to further studies, unsaturated coordination short-chain sulfur (S22−) sites are essential for adsorption of Hg0 and are capable of directly forming α-HgS from Hg0. In both the contrast experiment and density functional theory calculations, the cobalt doping strategy enhances the thermal stability of the active S22− ligand and the Hg0 adsorption properties. This study not only provide a prospective adsorbent for Hg0 sequestration at wide temperature range, but also explores a method of utilizing gaseous contaminants for resource utilization.

Development of efficient CO2 adsorbents: Synthesis and performance evaluation of dopamine-modified halloysite nanotubes loaded with ZIF-8

Carbon capture, utilization, and storage (CCUS) is a crucial technology for achieving carbon reduction targets. The key to CCUS technology lies in developing and designing efficient and low-cost CO2 capture materials. Metal-organic frameworks (MOFs) have emerged as promising CO2 adsorbents in the field of carbon capture. However, high agglomeration of nanoparticles and high cost have severely hindered the application of MOF-based solid adsorbents. This study employs an in-situ growth method to prepare a novel “corncob-shaped” PHNT@ZIF-8 composite material. During the reaction process, surface modification of halloysite nanotubes (HNT) enhances the interaction between HNT and ZIF-8. The resulting PHNT@ZIF-8 exhibits an enhanced CO2 adsorption capacity of 1.48 mmol/g. Notably, the functionalized PHNT@ZIF-8 as CO2 adsorbents demonstrated significant adsorption properties: a high specific surface area of 409.74 m2/g, good selectivity in simulated flue gas composition of 15%/85% (CO2/N2) (39.1), excellent thermal stability, and superior regenerability. Moreover, PHNT@ZIF-8 adsorbs CO2 primarily through van der Waals forces, which involve low energy and are easily reversible. After eight adsorption–desorption cycles, CO2 capacity retention rate remains as high as 93% (1.37 mmol/g). This work enriches the repertoire of solid CO2 composite adsorbents, providing a novel pathway for enhancing CO2 adsorption performance.

Smoke control and temperature distribution of tunnel fires under longitudinal ventilation combined with shaft exhaust

Longitudinal segmental smoke exhaust is often used for fire tunnels longer than 5 km. With the combined effect of longitudinal ventilation in the main tunnel and fan suction in the exhaust shaft, the smoke exhaust path is different from that of a traditional single-tube tunnel. Findings reported in the literature is insufficient to support the rapid development of extra-long road tunnels. In this paper, a numerical model was established by FDS (Fire Dynamics Simulator), and a 1:15 model test platform was built for verification. The effects of different longitudinal velocities, exhaust velocities, bifurcation angles, and exhaust shaft slopes on tunnel fires were analyzed for the longitudinal ventilation combined with shaft exhaust smoke evacuation mode (LVSE). The results show that when the exhaust velocity is greater than 4.5m/s, increasing the exhaust velocity has a limited effect on reducing the smoke length downstream of the exhaust shaft. The bifurcation angle has a significant effect on the velocity distribution in the ventilation shaft and the main tunnel. When the bifurcation angle is less than 45°, the airflow in the main tunnel is more likely to enter the exhaust shaft, and the velocity in the exhaust shaft is more than 5m/s. It is more favorable to reduce the smoke length when the slope of the exhaust shaft is not less than 7%. The high-temperature flue gas collects and forms a vortex near the vent under the LVSE mode, which makes the temperature decay rate slower than that when only longitudinal ventilation is used. The temperature decay model for the LVSE mode is obtained. This study is intended to provide a reference basis for the fire safety design of extra-long road tunnels under the LVSE mode.

Modeling biomimetic absorbent compounds for capturing carbon dioxide

Carbon capture and storage is a critical component of negative emission technologies for achieving economy-wide carbon neutrality to mitigate climate change and limit global temperature increase. Removal of CO2 can be undertaken after the standard pollution controls. Yet, the separation of CO2 from flue gas via CO2 capture processes is challenging because a high volume of gas must be treated, the CO2 is dilute, the flue gas is at atmospheric pressure, trace impurities can degrade capture media, and the captured CO2 must be compressed. We present a computational study of a novel family of biomimetic materials for such carbon capture processes based on the Crassulacean Acid Metabolism. Phosphoenolpyruvate serves as a template for designing similar molecules for use as CO2 solvents with designed thermochemical properties.

Compaction Characteristics of Fly Ash and Pond Ash: A Comparative Analysis

This study investigates the compaction characteristics of Fly Ash and Pond Ash, which are by-products of coal combustion in thermal power plants. Thermal power plants generate three types of ash: (a) Fly Ash, (b) Pond Ash, and (c) Bottom Ash. Fly Ash consists of fine particles carried out of the boiler with flue gases, while Bottom Ash is the residue that settles at the bottom of the boiler. In most coal plants, Fly Ash is captured using electrostatic precipitators and other filtration equipment before the flue gases are released through the chimney. Pond Ash, on the other hand, is a by-product of thermoelectric power plants, often regarded as waste material, posing significant environmental disposal challenges. The compaction characteristics of Fly Ash and Pond Ash are influenced by various factors, including specific gravity, moisture content, compaction energy, layer thickness, and mold area. In this study, Fly Ash collected from NTPC Sipat , Chhattisgarh exhibited an Optimum Moisture Content (OMC) ranging from 18% to 27% and a Maximum Dry Density (MDD) ranging from 0.90 to 1.59 gm/cc under standard Proctor compaction energy. Similarly, Pond Ash demonstrated an OMC ranging from 33% to 46% and an MDD ranging from 0.856 to 1.248 gm/cc under the same conditions. The findings indicate that variations in these factors significantly affect the dry density of both Fly Ash and Pond Ash. The study also aims to determine the geotechnical properties of these materials, providing insights into their potential applications in engineering and environmental management

Molecular Engineering of Poly(Ionic Liquid) for Direct and Continuous Production of Pure Formic Acid from Flue Gas.

Electrochemical CO2 reduction reaction (CO2RR) offers a promising approach to close the carbon cycle and reduce reliance on fossil fuels. However, traditional decoupled CO2RR processes involve energy-intensive CO2 capture, conversion, and product separation, which increases operational costs. Here, we report the development of a bismuth-poly(ionic liquid) (Bi-PIL) hybrid catalyst that exhibits exceptional electrocatalytic performance for CO2 conversion to formate. The Bi-PIL catalyst achieves over 90% Faradaic efficiency for formate over a wide potential range, even at low 15% v/v CO2 concentrations typical of industrial flue gas. The biphenyl in PIL backbone affords hydrophobicity while maintaining high ionic conductivity, effectively mitigating the flooding issues. The PIL layer plays a crucial role as a CO2 concentrator and co-catalyst that accelerates the CO2RR kinetics. Furthermore, we demonstrate the potential of Bi-PIL catalysts in a solid-state electrolyte (SSE) electrolyzer for the continuous and direct production of pure formic acid solutions from flue gas. Techno-economic analysis suggests that this integrated process can produce formic acid at a significantly reduced cost compared to the traditional decoupled approaches. This work presents a promising strategy to overcome the challenges associated with low-concentration CO2 utilization and streamline the production of valuable liquid fuels and chemicals from CO2.

Capacities of sorbents prepared by impregnation of inorganic carriers with PEI using different methods

The study presented here focused on the research of adsorbents for the separation of carbon dioxide from flue gas or other waste gases. Specifically, it focused on the possibility of eliminating the permanent problem with the insufficient resistance of inorganic adsorbents to unwanted – parasitic – adsorption of moisture from the processed gas. Based on the promising data published in recent papers regarding the wet impregnation of adsorbents with branched polyethyleneimine (PEI), four methods for the preparation of PEI-impregnated zeolite were tested. Penetration of the agent into the porous structure of the zeolite was achieved by: applying ultrasound, applying vacuum, combining vacuum and overpressure and boiling off the solvent without further operation. The raw zeolite was characterized by X-ray fluorescence spectrometry and X-ray diffractometry and also subjected to textural analysis. The characterization of the impregnated products mainly included thermogravimetric analysis, textural analysis and organic elemental analysis. In addition to gravimetric screening, the adsorption capacities of raw zeolite and impregnated products were primarily determined using a pressure flow-through apparatus with a fixed bed adsorber. The experimental conditions were determined to be close to real industrial installations: temperature during adsorption 20 and 40 °C, pressure during adsorption 600 kPa and 15% volume fraction of CO2 in the gas. Desorption was carried out by a combination of thermal desorption at 80 °C and vacuum. By reproducing the impregnation procedures from the literature, a PEI loading in the range of 4.1–23.7% was achieved, which is significantly lower than the literature sources state for the same preparation procedures. The measurement of textural properties verified that, depending on the value of PEI loading, there is a gradual reduction of the specific surface area, the total pore volume and the virtual disappearance of micropores and small mesopores. Specifically, at a PEI loading of 4%, the BET surface area decreased compared to the pristine zeolite from 29.4 to 2.9 m2 g–1 and at the same time the total pore volume decreased from 0.13 to 0.02 cm3 g–1, etc. The measurement of capacities did not confirm almost any of the results published in the literature. Without exception, the adsorption capacity decreased with the amount of PEI introduced into the zeolite particles. E.g. if a gas with 80% relative humidity and a content of 15% CO2 was used at a pressure of 600 kPa and a temperature of 40 °C, the capacity (by mass) decreased due to impregnation from 2.4% (for raw zeolite) to 0.8% for the sample with PEI mass fraction of 19%. Tests using dry gas resulted in even more marked deterioration. Thus, one can only partially agree with the literature data in the sense that humidity slightly compensates the negative effect of PEI on capacity. The effect, where the capacity increases with increasing temperature due to the replacement of physical CO2 adsorption by its chemisorption in the PEI layer, was also not confirmed. For example, for the above sample, humidity and pressure, the capacity was 0.9% at 20 °C. The impregnation procedure based on boiling off the solvent turned out to be completely unusable and, despite repeated rigorous attempts to reproduce it, did not lead to a product with a measurable capacity. The results of the study can be summarized in the following sentence. The problem is not that the experiments did not lead to a positive result, but above all the fundamental discrepancy between the published data and the attempts to reproduce them.

Challenges and advantages in recovering waste energy from flue gases from biomass boilers

Challenges and advantages in recovering waste energy from flue gases from biomass boilers

Improving used Lubricant Oil Burner Performance: Effect of Swirled Flow of Internally Distributor Type on the Combustion and Flue Gas Temperature and Emission

This study aimed to experimentally investigate the combustion characteristics of used lubricant oil (ULO). A simple cylindrical burner of the natural draft vaporizing type, equipped with an internal air distributor, was designed and fabricated to achieve this objective. The burner’s efficiency was evaluated based on combustion temperature, flue gas temperature, and concentration levels. The key feature of this burner lies in the swirled flow of air combustion and ULO vapor within the combustion chamber, facilitated by the swirled flow air distributor type. Various air-fuel ratios (ϕ), ranging from 0.5 to 4, were considered in characterizing the burner’s performance. The results revealed increased combustion and flue gas temperatures in the radial airflow types. The highest temperatures achieved using the radial flow type are 930 oC and 410 oC for combustion and exhaust gas temperature, respectively. In contrast, the combustion chamber and exhaust gas temperatures are 980 oC and 465 oC for the swirled flow type, respectively. It was found that there is a decrease in the emission of CO and CO2 by volume under optimum conditions. This decrement was attributed to the swirled flow effects, which promoted a better mixture of air combustion and ULO vapor during combustion.

Sustainable Operation Strategy for Wet Flue Gas Desulfurization at a Coal-Fired Power Plant via an Improved Many-Objective Optimization

Coal-fired power plants account for a large share of the power generation market in China. The mainstream method of desulfurization employed in the coal-fired power generation sector now is wet flue gas desulfurization. This process is known to have a high cost and be energy-/materially intensive. Due to the complicated desulfurization mechanism, it is challenging to improve the overall sustainability profile involving energy-, cost-, and resource-relevant objectives via traditional mechanistic models. As such, the present study formulated a data-driven many-objective model for the sustainability of the desulfurization process. We preprocessed the actual operation data collected from the desulfurization tower in a domestic ultra-supercritical coal-fired power plant with a 600 MW unit. The extreme random forest algorithm was adopted to approximate the objective functions as prediction models for four objectives, namely, desulfurization efficiency, unit power consumption, limestone supply, and unit operation cost. Three metrics were utilized to evaluate the performance of prediction. Then, we incorporated differential evolution and non-dominated sorting genetic algorithm-III to optimize the multiple parameters and obtain the Pareto front. The results indicated that the correlation coefficient (R2) values of the prediction models were greater than 0.97. Compared with the original operation condition, the operation under optimized parameters could improve the desulfurization efficiency by 0.25% on average and reduce energy, cost, and slurry consumption significantly. This study would help develop operation strategies to improve the sustainability of coal-fired power plants.

In situ hydrolyzed microporous polymer membranes for additional free volume to facilitate CO2 permeation

Advancements in membrane separation technology play a pivotal role in separation processes closely associated with the environment and energy. However, presently available commercial polymeric membranes encounter the challenge of low permeability, impacting both separation efficiency and membrane module costs. Here, we propose a simple and effective in situ acid hydrolysis strategy to significantly enhance membrane permeability. Specifically, a tetrafluorinated monomer with hydrolyzable Schiff base groups (TFNAD) has been meticulously designed, synthesized, and copolymerized with commercial TFTPN and TTSBI, yielding a series of copolymers. Subsequently, in situ hydrolysis removes aniline from the membrane, freeing up the occupied free volume and creating additional channels for gas transport. This process substantially enhances gas permeability while preserving the desired selectivity. PIM-TFAD-30 showed a 68 % improvement in CO2 permeability with virtually no compromise in CO2/N2 selectivity compared to the pre-hydrolysis membrane. Meanwhile, PIM-TFAD-30 also displayed outstanding separation performance and plasticization resistance in simulated flue gas tests, demonstrating its potential for practical application. This facile and straightforward hydrolysis method opens up a new perspective for preparing and modifying polymeric separation membranes beyond gas separation.

A novel boiler partial flow arrangement and partial load control strategies of a S-CO2 coal-fired power generation system

This work aims to address the technical issue of continuously decreasing reheat temperature in the S-CO2 coal-fired power system under partial-load operation. A novel partial flow arrangement of heating surfaces that uses part of the cooling walls in the furnace chamber as reheating surfaces was proposed. The steady-state model of a 300 MW S-CO2 coal-fired power system was developed to predict the partial-load operating characteristics. It is found that the proposed partial flow arrangement can effectively alleviate reheat temperature deviation. For the deviation of 10 °C, the present boiler operating load can be reduced to as low as 40 % whereas at least an 80 % load ratio for the traditional arrangement. According to the effects of four regulation measures, the comprehensive control sequence is suggested as 1) flue gas damper angle, 2) split ratio of the stream to FGC, 3) burner angle, and 4) split ratio of the stream to recompressor. This strategy can stabilize the reheat temperature at 620 °C for the load ratio decreasing from 100 % to 37 %, and achieve the higher system thermal efficiency. For load ratios from 37 % to 20 %, the reheat temperature cannot remain stable, and adjusting the reheat temperature will decrease the thermal efficiency.

Enhancement of CO2 removal from flue gas in an oscillatory baffled column using potassium carbonate solution

One of the efficient methods for reducing CO2 emissions from flue gas streams in oil refineries and power plants is the CO2absorption process using alkali solution. Potassium carbonate (K2CO3) solution, as CO2 absorbent, was used in the present study due to its high CO2 absorption capacity. However, K2CO3 has a drawback which is represented by its slow reaction with CO2. To overcome this issue, an oscillatory baffled column (OBC) was utilized as a contactor to maintain a high degree of mixing in the CO2 absorption system and thereby increasing the reaction rate between K2CO3 and CO2 as well as enhancing the mass transfer rate. In this study the effect of different operation conditions of the process namely; inlet flue gas flow rate (15 % (v/v) CO2 balanced with N2) and oscillation conditions on CO2 absorption in a semi-batch OBC were investigated. The experiments were performed with range of modified Reynolds Number of Oscillation (Reo′ = 0⎼1450) and aeration rates (0⎼1 vvm) using K2CO3 (100 g/L, 0.72 M)0.1.8–3.5-fold of enhancement of CO2 absorption rates was achieved by using OBC with respect to that obtained by baffled column (BC) (only baffles without oscillation) and plane bubble column (PBC) (without baffles and oscillation), respectively.The use of K₂CO₃ as a solvent in an oscillating reactor (OBR) to remove CO₂ represents a new method due to the high reactivity of K₂CO₃ with CO₂, forming stable bicarbonate and carbonate compounds. OBR's enhanced mixing capabilities improve mass transfer rates and reaction efficiency, allowing for more effective CO2 capture compared to conventional reactors. This combination leverages the strengths of both the chemical reactivity of K₂CO₃ and the mechanical benefits of OBR, potentially leading to more efficient and scalable CO2 removal processes.

A Perspective on Electrochemical Point Source Utilization of CO2 and Other Flue Gas Components to Value Added Chemicals.

Electrochemical CO2 reduction reaction (eCO2RR) has been explored extensively for mitigation of noxious CO2 gas generating C1 and C2+ hydrocarbons and oxygenates as value-added fuels and chemicals with remarkable selectivity. The source of CO2 being a pure CO2 feed, it does not fully satisfy the real-time digestion of industrial exhausts. Besides the detrimental effect of noxious gas mixture leading to global warming, there is a huge capital investment in purifying the flue gas mixtures from industries. The presence of other impurity gases affects the eCO2RR mechanism and its activity and selectivity toward C2+ products dwindle drastically. Impurities like NOx, SOx, O2, N2, and halide ions present in flue gas mixture reduce the conversion and selectivity of eCO2RR significantly. Instead of wiping out these impurities via separation processes, new strategies from material chemistry and electrochemistry can open new avenues for turning foes to friends! In this perspective, the co-electroreduction will vividly discussed and supporting role of different heteroatom-containing impurity gases with CO2, generating highly stable C─N, C─S, C─X bonds, and highlight the existing limitations and providing probable solutions for attaining further success in this field and translating this to industrial exhaust streams.

In situ decorated Mn-FeOx amorphous oxides on filter felt by a polyphenol-assisted method for low-temperature NH3-SCR

The combination of dust filtration technology and selective catalytic reduction of nitrogen oxides can effectively reduce the energy consumption and footprint of the flue gas purification system. To fabricate the high efficiency and firmly bonded catalytic filter material, a novel polyphenol-assisted method was designed in this work for in situ decorating Mn-FeOx amorphous oxides onto the smooth polyphenylene sulfide (PPS) filter felt. The polyphenolic compounds are not only worked as the dispersant, but also the binder for Mn-FeOx catalysts to firmly anchor on PPS filter felts. The introduction of Fe3+ into catalyst precursors can increase the Mn4+ content, surface adsorbed oxygen, as well as surface acidity, which displays satisfactory denitration performance and SO2 tolerance at low temperatures. The Mn5Fe1-TA/PDA@PPS sample shows nearly 100 % NO conversion efficiency at 180 °C with only 10.11 % catalysts loading in the sulfur dioxide free flue gas. Furthermore, the green and efficient synthesis route makes the catalytic filter felts preserve the same gas permeability and thermal stability with the pristine PPS filter felt, which suggests that the Mn5Fe1-TA/PDA@PPS has great prospects for simultaneously removing of NOx and dust in practical applications.

Design and analysis of negative CO2 emission methanol synthesis process incorporating green hydrogen and blue hydrogen

Methanol (MeOH) production by integration of green and blue hydrogen is evaluated herein. From 2018 to 2023, methanol demand increased by 3.6 % due to its use in various chemical industries as an eco-friendly fuel and as a method of transporting hydrogen and capturing renewable CO2. Moreover, due to the continual decrease in the cost of renewable energy, research into the use of green hydrogen from electrolysis is being conducted. Most of this research has focused on producing methanol from the green hydrogen obtained from proton-exchange membrane (PEM) electrolysis along with CO2 emissions from power plants. The present study examines processes based on oxyfuel combustion with oxygen obtained from either the PEM or an air separation unit (ASU) to produce methanol. By using oxyfuel combustion, the carbon capture process (which accounts for 30–50 % of the blue hydrogen cost) and pure (>98.75 %) 7.45 tCO2/tH2 can be obtained by separating H2O from the flue gas. By using the PEM, green hydrogen can capture 0.35 tCO2/tMeOH of external CO2. Furthermore, a carbon techno-economic analysis (CTEA) and a sensitivity analysis are conducted to evaluate the sustainability and feasibility of the proposed processes. As a result, the levelized cost of methanol (LCOM) is $373.91/tMeOH for the Blue process and $428.78/tMeOH for the Blue + Green process, each of which is below the current market price of $500/tMeOH. If the PEM price continues to decrease, and the carbon credit increases by €300/tCO2, after 2030, the Blue + Green process will become more lucrative than the Blue-only process. Thus, by considering the continuous decrease in renewable energy prices, the production of methanol via a hybrid Blue + Green process is suitable for a sustainable future.

Variation profiles, formation mechanisms, and emission risks of brominated flame retardant compounds during cement kiln co-processing of hexabromocyclododecane-containing waste

Cement kiln co-processing technique has been suggested as a promising disposal method for hexabromocyclododecane (HBCD)-containing construction wastes. However, concerns persist regarding the potential emissions of secondary brominated flame retardant (BFR) compounds. To address this, we conducted both field and laboratory experiments to elucidate the emission characteristics and formation mechanisms of BFRs during the co-processing of HBCD-containing waste in cement kilns. In the field experiments, which examined a range of HBCD disposal dosages from 0 to 400 kg/day, the concentrations of new brominated flame retardants (NBFRs), polybrominated diphenyl ethers (PBDEs), and polybrominated biphenyls (PBBs) in the stack gas were 0.57–0.80, 0.68–51.56, 0.62–1.79 ng/Nm3, respectively. Over 77 % of the emitted BFRs can be sequestered within solid materials. Further laboratory experiments revealed that the alkaline substances present in cement kilns can absorb HBr thus inhibiting the formation of BFRs. The transformation mechanisms from HBCDs to BFRs were further explored to involve processes including structural re-arrangement, de novo synthesis, and precursor formation. Furthermore, the national annual emission risk associated with the disposal of HBCD-containing construction wastes via cement kilns has been assessed. The findings of our study furnish a critical scientific basis for the development of strategies for managing HBCD-containing waste in the future.

FLUE GAS RECIRCULATION AS A WAY TO IMPROVE THERMAL EFFICIENCY AND REDUCE EMISSIONS IN POWER BOILERS

This study investigates the impact of flue gas recirculation on key parameters of the fuel combustion process, such as heat release and adiabatic combustion temperature. Based on the mathematical processing of experimental data, equations were obtained that reflect the dependence of useful heat release and adiabatic combustion temperature on the gas recirculation coefficient. According to the results of the study, the useful heat release in the furnace increases proportionally with the growth of the recirculation coefficient. This indicates that an increase in the level of recirculation contributes to an increase in combustion thermal efficiency, improving heat exchange processes within the furnace. A similar trend is observed for the adiabatic combustion temperature. It was found that the adiabatic combustion temperature also increases with an increase in the recirculation coefficient, which indicates the significant influence of recirculation on raising the temperature parameters of the combustion process. The rise in combustion temperature is associated with improved fuel combustion and more complete utilization of its energy potential. This, in turn, can contribute to a reduction in emissions of harmful substances such as nitrogen oxides and carbon, which is an important factor for environmental safety.Thus, the results of the study demonstrate that flue gas recirculation has a significant impact on heat exchange processes and combustion temperature. This makes recirculation an effective tool for increasing thermal efficiency and reducing the environmental impact. The application of this method in modern energy systems not only improves production performance but also ensures compliance with environmental requirements. The study results confirm the feasibility of implementing flue gas recirculation to enhance overall efficiency and environmental safety in energy installations.

A Numerical and Experimental Performance Assessments of an Improved Natural Draft Biomass Cook Stove

ABSTRACT This article analyses the performance of an efficiently designed biomass cook stove using standard performance parameters. The investigation was first conducted using mathematical modeling developed in the ANSYS Fluent software. The results of primary air and the temperature profiles inside the combustion chamber were found through simulation. It revealed that the flue gas left the combustion chamber with an average velocity of 1.7 m/s. The average pot bottom and fuel bed temperatures were 650 K and 1100 K, respectively. A copper coil was wrapped around the combustion chamber wall to recover its waste heat. The recovered waste heat was utilized to warm the water flowing through the copper coil. The heated water could be used for other domestic applications. The fabricated design of the improved stove was experimented with water boiling test. The maximum thermal efficiency achieved was 42% with a firepower of 8.25 kW, after incorporating the waste heat recovery system, corresponding to 7.5 L test. The overall efficiency, which is the product of the modified combustion efficiency and the maximum thermal efficiency, was found to be 41.50%. The performance was found to be significantly better than that of a commercial biomass cook stove. The developed model was also evaluated for indoor CO, CO2 and PM emissions. The highest levels of CO2 and CO were 940 ppm and 23 ppm. The average amount of PM1, PM2.5 and PM10 found out to be 18 µg/m3, 20 µg/m3 and 35 µg/m3 respectively.

Carbothermal reduction of flue gas desulfurization ash through the utilization of waste heat from steel slag: Investigating performance and mechanism

Flue gas desulfurization ash is a significant solid waste generated by the steel industry, leading to environmental pollution. In response to this challenge, this study proposes a novel method for preparing CaS from desulfurized ash through carbothermal reduction using steel slag waste heat. Thermodynamic analysis using FactSage and non-isothermal thermogravimetric testing were conducted to confirm the feasibility of carbothermal reduction. The experiment successfully prepared CaS, with a molar ratio of C to CaSO3 of 1.5 or higher leading to complete reduction. The presence of reducing agent C replaced the decomposition reaction of CaSO3 with reduction, occurring at a temperature 60 K lower. Large scale thermogravimetric analysis experiments demonstrated that as the mass percentage of pulverized coal increased, the reduction reaction of CaSO3 shifted to a lower temperature zone, expanding the temperature range and achieving the theoretical value. Reduction rates of CaSO3 were 43.12 %, 76.9 %, and 99.3 % with ratios of CaSO3 to reducing agent C of 1:0.75, 1:1.5, and 1:3, respectively. Kinetic study results showed that the activation energy of CaSO3 reduction ranged from 90.669 kJ/mol to 136.059 kJ/mol within the conversion rate range of 0.2 to 0.9. When CaSO3 and carbon powder are mixed and subsequently added, the thermochemical decomposition reaction of CaSO3 is inhibited. This inhibition leads to the formation of stable CaS through the reduction of desulfurization ash by carbon.