Search Results (71)

To compensate for the instability of renewable energy sources during China’s energy transition, large thermal power plants must provide critical operational flexibility, primarily through deep peaking. To investigate the combustion performance and wear and tear of a 600 MW pulverized coal boiler under deep peaking, the gas–solid flow characteristics and distributions of flue gas temperature, wall heat flux, and wall wear rate in a 600 MW tangentially fired pulverized coal boiler under variable loads (353 MW, 431 MW, 519 MW, and 600 MW) are investigated in this study employing computational fluid dynamics numerical simulation method. Results demonstrate that increasing the boiler load significantly amplifies gas velocity, wall heat flux, and wall wear rate. The maximum gas velocity in the furnace rises from 20.9 m·s⁻¹ (353 MW) to 37.6 m·s⁻¹ (600 MW), with tangential airflow forming a low-velocity central zone and high-velocity peripheral regions. Meanwhile, the tangential circle diameter expands by ~15% as the load increases. The flue gas temperature distribution exhibits a “low-high-low” profile along the furnace height. As the load increases from 353 MW to 600 MW, the primary combustion zone’s peak temperature rises from 1750 K to 1980 K, accompanied by a ~30% expansion in the coverage area of the high-temperature zone. Wall heat flux correlates strongly with temperature distribution, peaking at 2.29 × 10⁵ W·m⁻² (353 MW) and 2.75 × 10⁵ W·m⁻² (600 MW) in the primary combustion zone. Wear analysis highlights severe erosion in the economizer due to elevated flue gas velocities, with wall wear rates escalating from 3.29 × 10⁻⁷ kg·m⁻²·s⁻¹ (353 MW) to 1.23 × 10⁻⁵ kg·m⁻²·s⁻¹ (600 MW), representing a 40-fold increase under full-load conditions. Mitigation strategies, including ash removal optimization, anti-wear covers, and thermal spray coatings, are proposed to enhance operational safety. This work provides critical insights into flow field optimization and wear management for large-scale coal-fired boilers under flexible load operation. Full article

This paper presents and establishes a reaction kinetic model of Hg/Cl/C/H/O/N/S to investigate the reaction characteristics of mercury during coal combustion and elucidate its migration and transformation mechanisms in flue gas. Using CHEMKIN software, the influence of HCl, Cl₂, and other flue gas components on the mercury oxidation reaction rate is examined. Building on this, the mechanism of Hg homogeneous oxidation under the influence of multi-component and multi-reaction interactions is revealed. The results indicated that as Hg concentration increased, the transformation rate of mercury also increased. As the reaction temperature increases, the reaction rate of HCl and elemental mercury also increases, leading to a higher transformation rate of mercury at elevated temperatures. Additionally, an increase in Cl₂ concentration leads to a higher amount of HgCl₂ produced. When the Cl₂ concentration was 4 × 10⁻⁵ mol/L, the amount of mercury chloride produced was highest, increasing by 40% compared to the absence of Cl₂. As chlorine concentration increases, more Hg²⁺ is converted from Hg⁰, enhancing its capture and removal by existing technologies, which significantly contributes to environmental sustainability and mercury emission control in coal-fired power plants. It is also shown that the rate of change of HgCl₂ varies with different Cl₂ concentrations, with higher Cl₂ concentrations inhibiting mercury oxidation beyond a certain threshold. The reaction was most intense when the mercury concentration was 5 × 10⁻⁵ mol/L. At this concentration, the largest amount of HgCl₂ is produced. The mercury conversion rate curve remained consistent after adding NO and SO₂, with a HgCl₂ amount increasing as NO and SO₂ concentrations rose. This indicates that the addition of NO and SO₂ converts Hg⁰ to Hg²⁺, thereby improving mercury removal efficiency and contributing to sustainability. Full article

Fine particulate matter (PM) and sulfur trioxide (SO₃) from coal-fired flue gas pose significant environmental and health risks. While low-low temperature electrostatic precipitators (LLT-ESPs) enhance PM and SO₃ removal by cooling flue gas below the acid dew point, their efficiency is limited by incomplete agglomeration. This study proposes integrating turbulent agglomeration technology into LLT-ESP systems to improve collision and adhesion between droplets and particles. Experiments were conducted under three conditions: flue gas containing SO₃ alone, fly ash alone, and their mixture. Particle size distributions, mass concentrations, and removal efficiencies were analyzed using ELPI⁺ and PM samplers. Results showed that turbulent agglomeration reduced the number concentration of sulfuric acid droplets by 21.4% from 1.59 × 10⁷ cm⁻³ to 1.25 × 10⁷ cm⁻³ (SO₃-only case) and fine fly ash particles by 19.5% from 5.79 × 10⁶ cm⁻³ to 4.66 × 10⁶ cm⁻³ (fly-ash-only case). Although LLT-ESP combined with turbulent agglomeration has a certain removal effect in the case of individual pollutants, the overall effect is not unsatisfactory, especially for SO₃, whose mass-based removal efficiency was merely 16.2%. The value of the fly-ash-only case was 92.1%. Synergistic effects in the coexistence scenario (fly ash and SO₃) significantly enhanced agglomeration, increasing SO₃ and PM removal efficiencies to 82.9% and 97.6%, respectively, compared to 69.7% and 90.1% without turbulent agglomeration. The mechanism behind the efficiency improvement involved droplet–particle collisions, sulfate deposition, and improved particle charging. This work demonstrates that turbulent agglomeration optimizes multi-pollutant control in LLT-ESP systems, offering a feasible strategy for achieving ultra-low emissions in coal-fired power plants. Full article

Many coastal coal-fired power plants utilize seawater flue gas desulfurization (SWFGD) systems, which may pose risks of heavy metal attachment on suspended sediments. Understanding variations in suspended sediment concentration (SSC) is therefore useful for controlling marine pollution. We studied two power plants as examples of discharging SSC using continuous measurement techniques. Monitoring sites at intake and discharge points and the surrounding coastal areas of the power plants was conducted across seasons. The first case study, Linkou Power Plant, is located in a high-SSC region influenced by monsoon winds and wave activity. Results indicate that SSC levels at all the monitoring sites are correlated with environmental factors of wind and wave conditions, with strong positive correlations observed between the intake and discharge points. In contrast, the Dalin Power Plant is located within an international harbor, where the SSC levels are generally low; however, sudden increases in SSC are observed at the intake point due to disturbances from vessel activities. These sudden increases are not evident at the discharge point, suggesting a sink of SSC may occur within the system. These results demonstrate that the two studied power plants have limited effects on the increase in SSC; the SSC in the discharge point is mainly related to the SSC input at the intake point. Effective management of SSC at the intake may help mitigate coastal pollution caused by SSC discharge and reduce the risk of harmful substances adhering to suspended solids in the discharging wastewater. Full article

This study explores the potential of utilizing circulating fluidized bed boiler fly ash (CFBFA) in the production of composite gravels, with the aim of achieving performance comparable to natural gravel while promoting sustainability. CFBFA, activated by hydrated lime and gypsum, was investigated for its pozzolanic reaction and carbonation curing under simulated coal-fired power plant flue gas conditions (80 °C, 0.4 MPa, 15% CO₂, 85% N₂). The study focused on optimizing the ratios of gypsum and hydrated lime in CFBFA-based cementitious materials, with the goal of enhancing their mechanical properties and understanding the underlying hydration and carbonation mechanisms. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the mineral composition and microstructure of the composite gravels. The results revealed that the optimal gypsum-to-hydrated lime ratio for CFBFA composite gravels is 2:1, achieving a compressive strength of 9.01 MPa after 28 days of carbonation curing. Carbonation curing accelerated hydration, improving the material’s strength, stability, and microstructure. Additionally, the production of CFBFA composite gravels demonstrated significant environmental benefits, reducing Cumulative Energy Demand (CED) by 86.52% and Global Warming Potential (GWP) by 87.81% compared to cement road base materials. This research underscores the potential of CFBFA as a sustainable construction material, with insights into improving its mechanical performance and expanding its large-scale use through carbonation curing with flue gas. Full article

Limestone-gypsum wet flue gas desulfurization (WFGD) played a key role in SOx removal and clean emissions. However, it would also affect the condensable particulate matter (CPM) removal and compositions. The effects of the WFGD system on the removal of CPM and the contents of soluble ions in CPM were investigated in a spray desulfurization tower at varied conditions. The results indicate that the emission concentration of CPM decreased from 7.5 mg/Nm³ to 3.7 mg/Nm³ following the introduction of cold water spray and hot alkali droplet spray systems. This resulted in a CPM reduction rate of approximately 51%, reducing the percentage of CPM in total particulate matter and solving the problem of substandard particulate matter emission concentrations in some coal-fired power plants. The concentrations of NO₃⁻, SO₄²⁻, and Cl⁻ among the soluble ions decreased by 41–66.6%. As the liquid-to-gas ratio of the cold water spray and hot alkali droplet spray increased, CPM came into contact with more spray, which accelerated dissolution and chemical reactions. Consequently, the CPM emission concentration decreased by 17.4–19%. The liquid-to-gas ratio has a great effect on the ion concentrations of NO₃⁻, SO₄²⁻, Cl⁻ and NH₄⁺, with a decrease of 28–66%. The temperatures of the cold water spray and the hot alkali droplet spray primarily affect the ionic concentrations of SO₄²⁻ and Ca²⁺, leading to a decrease of 32.3–51%. When the SO₂ concentration increased from 0 mg/Nm³ to 1500 mg/Nm³, large amounts of SO₂ reacted with the desulfurization slurry to form new CPM and its precursors, the CPM emission concentration increased by 57–68.4%. This study addresses the issue of high Concentration of CPM emissions from coal-fired power plants in a straightforward and efficient manner, which is significant for enhancing the air quality and reducing hazy weather conditions. Also, it provides a theoretical basis and technical foundation for the efficient removal of CPM from actual coal-fired flue gas. Full article

To accommodate the integration of renewable energy, coal-fired power plants must take on the task of peak regulation, making the low-load operation of boilers increasingly routine. Under low-load conditions, the phase transition point (PTP) of the working fluid fluctuates, leading to potential flow instability, which can compromise boiler safety. In this paper, a one-dimensional coupled dynamic model of the combustion and hydrodynamics of a supercritical boiler is developed on the Modelica/Dymola 2022 platform. The spatial distribution of key thermal parameters in the furnace and the PTP position in the water-cooled wall (WCW) are analyzed in a 660 MW supercritical boiler when parameters on the combustion side change under full-load and low-load conditions. The dynamic response characteristics of the temperature, mass flow rate, and the PTP position are investigated. The results show that the over-fire air (OFA) ratio significantly influences the flue gas temperature distribution. A lower OFA ratio increases the flue gas temperature in the burner zone but reduces it at the furnace exit. The lower OFA ratio leads to a higher fluid temperature and shortens the length of the evaporation section. The temperature difference in the WCW outlet fluid between the 20% and 60% OFA ratios is 11.7 °C under BMCR conditions and 7.4 °C under 50% THA conditions. Under the BMCR and 50% THA conditions, a 5% increase in the coal caloric value raises the flue gas outlet temperature by 32.7 °C and 35.4 °C and the fluid outlet temperature by 6.5 °C and 9.9 °C, respectively. An increase in the coal calorific value reduces the length of the evaporation section. The changes in the length of the evaporation section are −2.95 m, 2.95 m, −2.62 m, and 0.54 m when the coal feeding rate, feedwater flow rate, feedwater temperature, and air supply rate are increased by 5%, respectively. Full article

To achieve the goals of carbon peaking and carbon neutrality, the retrofitting of existing coal-fired power plants is crucial to achieving energy-saving and emission reduction goals. A conventional recovery system of waste heat typically occurs downstream of the air preheater, where the energy quality in flue gas is low, resulting in limited coal-saving benefits. This study proposes a scheme involving a flue gas exchanger bypassing the air preheater and low-temperature economizers, which is used to transfer the waste heat from flue gas to primary and secondary air (System I). Additionally, a heat pump can be introduced to provide supplementary energy for primary and secondary air, as well as the condensate from the steam turbine (System II). The coal consumption rate and exergy efficiency are used to evaluate the two schemes. The results show that both waste heat recovery systems can increase the power output of the coal-fired unit by recovering waste heat. System II can boost power output by approximately 13.98 MW. The power increase in both waste heat recovery systems show a declining trend as the unit load decreases. This increased power is primarily attributed to the medium- and low-pressure cylinders, while the contributions from ultra-high-pressure and high-pressure cylinders are negligible. The increased power output for the medium-pressure cylinder ranges from approximately 3.49 to 3.58 MW, while the low-pressure cylinder has an increased power output of around 10.10 to 10.19 MW. The coal consumption rate is decreased from 250.3 g/(kW·h) to 247.5 g/(kW·h) under a full load condition for both systems, which can be augmented at lower load conditions. System II outperforms System I at 30% load condition, achieving a reduced coal consumption rate of 3.36 g/(kW·h). System I has an exergy efficiency of 40%, while System II shows a higher efficiency of 44%. Full article

Open absorption heat pumps are considered one of the most promising methods for efficiently utilizing low-grade waste heat, reducing energy consumption, and lowering greenhouse gas emissions. However, traditional heat pumps have significant limitations in the range of flue gas temperatures they can recover, and their relatively low system performance further restricts practical applications. In this study, we propose a novel double-section full-open absorption heat pump driven by flue gas from the desulfurization tower. By designing the absorber with a double-layer structure, the system can recover more latent and sensible heat from the flue gas, significantly enhancing its thermal recovery capability. Additionally, replacing the traditional LiBr/H₂O working pair with LiCl/H₂O significantly reduces the risks of solution crystallization and equipment corrosion. Through comprehensive research, the strengths and weaknesses of the system were explored. The results indicate that this system effectively recovers flue gas waste heat within the temperature range of 30–70 °C. Specifically, at a flue gas temperature of 70 °C and a flow rate of 3 kg/s, the system achieves a COP of 1.838, along with a heating capacity of 158.83 kW and a ROI of 34.1%. These metrics demonstrate that the system not only delivers high performance but also exhibits excellent economic viability. Additionally, when the solution temperature is lowered to 10 °C, the system’s maximum COP reaches 1.96, reflecting a significant 30.67% improvement over traditional heat pumps. These findings highlight the system’s potential for application in coal-fired power plants, where varying levels of power output can benefit from enhanced thermal recovery and efficiency. Full article

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. Full article

Oxy-fuel combustion technology replaces air with a mixture of pure O₂ and recycled flue gas for coal combustion, which leads to difficulties in the waste heat recovery of flue gas in the boiler tail of coal-fired power plants. This paper proposes a new integration scheme for waste heat recovery of flue gas in coal-fired power plants with oxy-fuel combustion CO₂ capture. By introducing an oxygen preheater, a recycled flue gas preheater, and a low-pressure economizer, the waste heat of flue gas is fully recovered to preheat oxygen, recycled flue gas, and feed water, respectively. The proposed scheme simultaneously ensures the safe operation of the recycled fan and improves the thermal performance of the coal-fired power plants. Compared to the air combustion configuration, the boiler’s efficiency and gross power efficiency in the oxy-fuel combustion configuration are increased by 0.42% and 1.29%, respectively. Due to power consumption for the added equipment, the net power efficiency is reduced by 10.41%. A techno-economic analysis shows that the cost of electricity for oxy-fuel combustion in coal-fired power plants has increased from USD 46.45/MWh to USD 80.18/MWh, and the cost of the CO₂ avoided reaches USD 43.24/t CO₂. 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 efficacy of spray dry systems compared to wet flue gas desulphurisation (FGD) units depends on applying a highly reactive scrubbing reagent. This study assessed sodium-based compounds derived from natural sources and waste by-products as potential agents for treating sulphur dioxide (SO₂). Sodium carbonate (Na₂CO₃) and sodium bicarbonate (NaHCO₃) were acquired from mineral deposits, whereas the black ash waste (Na₂CO₃·NaHCO₃) was obtained from the pulp and paper sector. The sorbents introduced in slurry form were subject to SO₂ absorption conditions in a lab-scale spray dryer, including an inlet gas phase temperature of 120–180 °C, flue gas flow rate of 21–34 m³/h, and sodium to sulphur normalised stoichiometric ratio (Na:S) of 0.25–1. The comparative performance was evaluated using the metric of %SO₂ ($\%{\eta }_{DeS{O}_X}$) removal efficiency. The results showed that NaHCO₃ had the highest overall result, with a removal efficiency of 62% at saturation. Black ash was the second best-performing reagent, with a 56% removal efficiency, while Na₂CO₃ had the lowest efficiency (53%). The maximum degree of SO₂ reduction achieved using NaHCO₃ under specific operating parameters was at an NSR of 0.875 (69%), a reaction temperature of 120 °C (73%), and a gas inlet flow rate of 34 m³/h. In conclusion, the sodium reagents produced significant SO₂ neutralisation, exceeding 50% in their unprocessed state, which is within acceptable limits in small- to medium-sized coal-fired power plants considering retrofitting pollution control systems. Full article

At present, there is a global rise in electricity consumption, leading to an accelerated depletion of natural resources due to the reliance on fossil fuels to fulfill this energy demand. Consequently, there exists a worldwide emphasis on enhancing the proportion of renewable energy sources in electricity generation. Biomass, as a renewable energy source, presents a viable alternative to certain fossil energy sources for combustion in electricity generation. This study focuses on a 660 MW coal-fired power plant as the subject of investigation, employing Aspen Plus simulation software (V11) to replicate the operational dynamics of the plant. A model of the direct mixed combustion biomass system within the coal-fired boiler is constructed, and its accuracy is validated against operational data obtained from the power plant. Moreover, a model elucidating the direct co-combustion of biomass in a coal-fired boiler, augmented by flue gas recirculation, was developed through the integration of biomass pre-treatment and flue gas recirculation technologies. This study explores the impacts of varying biomass blending ratios and flue gas recirculation on parameters, including flue gas volume, power generation efficiency, boiler performance, water vapor content, and emissions of pollutants. These findings indicate an inverse relationship between the mixing ratio and various performance metrics as follows: power generation, boiler efficiency, as well as NO_X and SO₂ content, with larger mixing ratios resulting in diminished values. Furthermore, the incorporation of flue gas recirculation was observed to mitigate furnace temperatures and suppress NO_X emissions. Full article

Combining biomass co-firing with oxy-fuel combustion is a promising Bioenergy with Carbon Capture and Storage (BECCS) technology. It has the potential to achieve a large-scale reduction in carbon emissions from traditional power plants, making it a powerful tool for addressing global climate change. However, mercury in the fuel can be released into the flue gas during combustion, posing a significant threat to the environment and human health. More importantly, mercury can also cause the fracture of metal equipment via amalgamation, which is a major risk for the system. Therefore, compared to conventional coal-fired power plants, the requirements for the mercury concentration in BECCS systems are much stricter. This article reviews the latest progress in mercury control under oxy-fuel biomass co-firing conditions, clarifies the impact of biomass co-firing on mercury species transformation, reveals the influence mechanisms of various flue gas components on elemental mercury oxidation under oxy-fuel combustion conditions, evaluates the advantages and disadvantages of various mercury removal methods, and finally provides an outlook for mercury control in BECCS systems. Research shows that after biomass co-firing, the concentrations of chlorine and alkali metals in the flue gas increase, which is beneficial for homogeneous and heterogeneous mercury oxidation. The changes in the particulate matter content could affect the transformation of gaseous mercury to particulate mercury. The high concentrations of CO₂ and H₂O in oxy-fuel flue gas inhibit mercury oxidation, while the effects of NO_x and SO₂ are dual-sided. Higher concentrations of fly ash in oxy-fuel flue gas are conducive to the removal of Hg⁰. Additionally, under oxy-fuel conditions, CO₂ and metal ions such as Fe²⁺ can inhibit the re-emission of mercury in WFGD systems. The development of efficient adsorbents and catalysts is the key to achieving deep mercury removal. Fully utilizing the advantages of chlorine, alkali metals, and CO₂ in oxy-fuel biomass co-firing flue gas will be the future focus of deep mercury removal from BECCS systems. Full article