Latest ArticlesAs an emerging high-moisture solid waste treatment method, smoldering disposal technology shows unique advantages in the disposal of high-moisture and low-calorific sludge. However, its self-sustaining propagation process is easily affected by material characteristics and operating parameters, and there is a risk of propagation instability caused by the attenuation of reaction intensity. Taking high-moisture sludge (moisture content >65%) as the disposal object, this study systematically investigates the effects of the mixing ratio of quartz sand to sludge (2:1~5:1) and air Darcy velocities (5~8 cm/s) on smoldering propagation under biomass conditioning, and explores the boundary of biomass conditioning ratio for complete smoldering propagation. The results show that under the condition of a fixed Darcy flow rate of 5 cm/s, the critical biomass conditioning ratio linearly increases from 4% to 10% and the critical unit calorific value of the smoldering system remains stable at approximately 0.339 MJ/kg when the sand-sludge mixing ratio is increased from 2:1 to 5:1. When the sand-sludge mixing ratio is fixed at 3:1, the critical biomass conditioning ratio linearly decreases from 6% to 2% when the air Darcy velocity increases from 5 cm/s to 8 cm/s, corresponding to a linear decrease in critical unit calorific value from 0.339 MJ/kg to 0.172 MJ/kg. The material exhibits collapse characteristics after smoldering disposal, and the biomass conditioning ratio has no significant effect on the top collapse height when it exceeds the critical value. These results can provide reliable scientific references for solving the efficient smoldering disposal of high-moisture sludge.
In-factory testing of chloride ions in urea for urea-to-ammonia hydrolysis systems in power plants is a crucial task, and how to quickly and accurately detect chloride ions content remains an urgent problem to be solved. This study has proposed a new method for determining the mass concentration of chlorides in urea using silver chloride spectrophotometry. This method is simple and fast, capable of detecting the chloride content in a set of urea samples in about 20 minutes, with a detection range of 0.07 mg/L to 2.00 mg/L and a detection limit of 0.02 mg/L. Eighteen repeated tests were conducted on a 10% urea solution with a chloride ion mass concentration of approximately 0.05 mg/L. The results indicated a relative standard deviation of 8.30%. The recovery rate of spiked tests in the 10% urea solution ranged from 86% to 110%. Both the accuracy and sensitivity of this method meet the quality requirements for urea used in the urea-to-ammonia hydrolysis systems in thermal power plants, making it a suitable method for determining chlorides in urea.
To improve the comprehensive energy utilization efficiency of solar thermal power generation, this paper presents a novel linear Fresnel reflector (LFR) concentrated solar polygeneration system using supercritical carbon dioxide (S-CO2) Brayton cycle and organic Rankine cycle (ORC), which is designed for producing electricity, fresh water and hydrogen.
By using the Ebsilon code, the operation performance of the polygeneration system is investigated.
The results show that the output power and Brayton cycle efficiency of the polygeneration system are 50.0 MW and 44.0%, respectively. The hydrogen production rate and freshwater production rate of the polygeneration system are 18.34 kg/h and 311.61 t/h, respectively. The LFR solar section, Brayton cycle, ORC hydrogen production section and multistage flash desalination facility can achieve the coordinated operation effectively during a long term.
The economic performance evaluation results show that for the polygeneration system, its levelized costs of electricity, hydrogen and freshwater are 0.72 yuan/(kW·h), 28.8 yuan/kg and 7.75 yuan/t, respectively, revealing the economic feasibility of the polygeneration system.
To enhance the heat exchanger efficiency in a carbon dioxide energy storage system, a printed circuit heat exchanger (PCHE) was employed as the core heat transfer component, with binary nitrate molten salt (solar salt) serving as the cold-side fluid and supercritical carbon dioxide (S-CO2) as the hot-side fluid. This study aims to investigate the key factors influencing the internal heat transfer process in PCHE and optimize the dominant structural parameters governing its thermal performance, thereby addressing the performance bottlenecks of heat exchangers in such energy storage systems.
Three key structural parameters of the Zigzag PCHE, such as channel diameter, turning angle, and number of turning cycles, were selected as independent variables. The overall heat transfer coefficient K (a core indicator of heat transfer capacity) and the ratio of the overall heat transfer coefficient to pressure drop K/ΔP (a key metric for evaluating the trade-off between heat transfer and flow resistance) were designated as response variables. A three-factor, three-level response surface methodology (RSM) was established to quantitatively analyze the effects of the three structural parameters and their pairwise interactions on the response variables. Parameter optimization of the heat exchange channels was subsequently performed based on the analytical results.
Within the specified parameter ranges (channel diameter: 1.0~2.0 mm, turning angle: 5°~30°, number of turning cycles: 6~10), the results indicate that reducing the channel diameter, increasing the turning angle, or increasing the number of turning cycles can effectively improve the heat transfer efficiency of the Zigzag PCHE. Statistical analysis shows that the channel diameter has a highly significant impact on both K and K/ΔP, and the interaction between the channel diameter and the number of turning cycles also significantly influences these two response variables. The optimal parameter set for achieving the maximum K value (1 313 W/(m2·K)) was determined to be a channel diameter of 1.003 mm, a turning angle of 29.71°, and 9.935 turning cycles. Furthermore, the optimal combination for the comprehensive performance factor K/ΔP was found to be a channel diameter of 2.0 mm, a turning angle of 9.407°, and 6 turning cycles, yielding a K/ΔP value of 0.453 7 W/(m2·K·Pa) and a corresponding K value of 801.7 W/(m2·K). A comparative analysis reveals that the optimized PCHE volume is reduced by approximately one-tenth compared to conventional shell-and-tube heat exchangers.
This study confirms that variations in the channel diameter, turning angle, and number of turning cycles significantly affect the thermal performance of zigzag PCHEs. The response surface methodology proves effective in optimizing the channel structural parameters to enhance heat transfer performance. Moreover, PCHEs demonstrate remarkable compactness advantages in CO2 energy storage systems, making them well-suited for space-constrained operational environments. The findings provide reliable theoretical and data-driven support for the rational selection and engineering design of heat exchangers in related fields.
Coal-fired power generation coupled with biomass is one of the efficient carbon-reduction technologies for coal-fired units. As a typical energy plant, arundo donax has the characteristics of high yield, strong environmental adaptability and high calorific value, and can be used for large-scale coal-fired power generation. To investigate the effect of co-firing arundo donax in a pulverized-coal boiler on NOx emissions and explore the migration pathways of fuel nitrogen during the co-combustion of coal and arundo donax, a co-combustion reaction model of arundo donax and coal was established with a two-stage plug flow reactor (PFR). The formation characteristics and reaction mechanisms of nitrogen oxides during co-combustion of the arundo donax and coal in a pulverized-coal boiler were studied, focusing on exploring the influences of co-firing ratio, over-fire air (OFA) ratio, and OFA position on the formation characteristics of nitrogen oxides. The results show that the NOx emission can be reduced by co-firing arundo donax, and the mass concentration of NOx decreases with the increase in co-firing ratio of arundo donax. The NOx conversion rate and NOx mass concentration first decrease and then increase with the increase in over-fire air ratio, and there is an optimal over-fire air ratio (around 33%) to minimize NOx emissions. Delaying the position of the OFA leads to a decrease in both the NOx conversion rate and NOx mass concentration. By studying the NOx formation characteristics and the nitrogen migration pathways during co-combustion of coal and arundo donax, theoretical guidance can be provided for parameter setting and reducing exhaust NOx emissions in the co-combustion of arundo donax for coal-fired power generation.
As the working medium of turbine speed-control systems in power plants, phosphate ester fire-resistant fluid (FRF) plays a vital role in the normal operation of steam turbines. During operation, the deterioration of FRF may result in an increase in acid value, a decrease in volume resistivity, and the formation of oil sludge, and the degree of decomposition and deterioration varies among different oils. The chemical composition of different kinds of FRF samples was analyzed, the deterioration process of different phosphate ester molecules was simulated, and their aging-resistance properties were tested. The results show that the performance of FRF with tris-(dimethylphenyl) phosphate as the main component is more stable than that of FRF with tert-butylphenyl phosphate as the main component. During the production of FRF, the content of dimethylphenyl in triaryl phosphate should be increased, and the content of phenyl and tert-butyl phenyl should be reduced.
With the growing integration of renewable energy sources into the power grid, frequency fluctuations have become a significant challenge. To address this, hybrid energy storage systems (HESS) are used to assist thermal power units in responding to automatic generation control (automatic generation control, AGC) commands. This paper proposes a novel hybrid power distribution strategy based on stochastic model predictive control (SMPC) to enhance the regulation performance of thermal power units in AGC applications, particularly under fluctuating power demands. The aim is to optimize the power allocation between the thermal power unit and the HESS to improve the accuracy, stability, and efficiency of the regulation process, ensuring a more reliable response to AGC signals.
The proposed strategy first constructs a power demand model for the HESS system, consisting of lithium titanate batteries for high-power storage and lithium iron phosphate batteries for energy storage, based on a Markov probability matrix, which simulates the response of the thermal power unit to AGC commands. An adaptive mechanism is introduced to dynamically adjust the state transition probabilities in real-time, enhancing the accuracy of power demand predictions during AGC fluctuations. Additionally, a scene tree generation method is proposed, which combines probability thresholds with stratified sampling to transform the probability distribution output by the adaptive Markov model into a finite set of scenarios for optimization. This method is designed to better handle the uncertainty of power demand predictions under multiple future scenarios, addressing the inherent variability of AGC command responses. Finally, the strategy integrates the above components into an SMPC controller, which optimizes power distribution between the thermal power unit and HESS in real-time, considering the stochastic nature of power demands and control parameters.
Simulation experiments demonstrate that the proposed strategy significantly outperforms traditional frequency regulation strategies, which do not incorporate power prediction, and static SMPC strategies that lack dynamic correction of state transition probabilities. The performance index Kp is improved by 14.1% and 7.5%, respectively, showing that the SMPC strategy with adaptive power demand forecasting can achieve more precise and stable regulation performance. Additionally, the model's ability to handle uncertainty in power demand prediction allows for more accurate and timely responses to AGC fluctuations, resulting in better coordination between the thermal power unit and the HESS.
The proposed strategy effectively enhances the collaborative regulation performance between the thermal power unit and HESS, offering strong application potential. Further optimization of the model can improve its robustness and adaptability in practical applications, advancing the implementation of this technology.
In order to better cope with the impact of the rapid development of new energy on the existing power grid structure and improve the stability and economy of thermal power unit operation, this paper proposes to construct a dual-layer optimization model of fire storage frequency regulation based on real-time power prediction of thermal power units and fuzzy control allocation of energy storage power.
The upper layer of the model utilizes frequency deviation decomposition and real-time power prediction of thermal power to optimize the power benchmark, effectively overcoming the response delay of the unit. The lower layer introduces a fuzzy logic control strategy to achieve adaptive and precise power allocation between the thermal unit and the energy storage system. On this basis, multi-objective genetic algorithm is used to optimize the energy storage capacity configuration scheme, and the frequency modulation performance under different control strategies is quantitatively evaluated based on indicators such as system frequency fluctuation. Taking a 600 MW thermal power unit as the research object, the optimal energy storage configuration was obtained through algorithm as follows: flywheel energy storage power of 8.5 MW and capacity of 1.3 MW·h, and lithium battery energy storage power of 3.6 MW and capacity of 14.6 MW·h. The total investment cost corresponding to this configuration is 2.027 7×109 yuan, and the actual income during the 400 s frequency modulation cycle is 850.95 yuan.
After simulation verification using MATLAB/Simulink, it was found that under step disturbance, the dual layer optimization strategy of fire storage coordination reduces the frequency fluctuation of the system to 4.826×10–2 Hz, which is 38.53% lower than the independent frequency regulation of the fire power unit. The average absolute deviation of power fluctuation is reduced to 4.224 MW, which is 32.57% lower than the independent operation. Under continuous disturbance, the frequency fluctuation of the system decreased by 19.31%, the average absolute deviation of power fluctuation decreased by 78.71%, and the actual contribution of electricity increased by 0.527 MW·h. The results show that the thermal-storage coordinated dual layer optimization control strategy presented in this paper effectively mitigates system frequency and power fluctuations, thereby alleviating the frequency regulation pressure on thermal power units. Concurrently, it enhances the utilization efficiency of the energy storage system and improves the economic viability of frequency regulation services.
This research thus provides a novel technical direction for the flexible transformation of thermal power plants, enabling them to play a more supportive and complementary role in future power systems dominated by renewable energy sources.
The large-scale integration of renewable energy poses significant challenges to the peak-shaving capacity of coal-fired units. To enhance operational flexibility and address energy flow conflicts in typical coal-fired systems coupled with compressed air energy storage systems during peak shaving, this study investigates a 660 MW coal-fired unit using EBSILON software. Three energy storage schemes and two energy release schemes are proposed and evaluated through thermo-economic analysis, focusing on thermal-time decoupling capability, peak-shaving paradox elimination, and system performance. The results show that during energy storage, the scheme utilizing intermediate-pressure cylinder exhaust for thermal oil heating achieves the highest thermal storage gain ratio (1.370) and the lowest heat rate (8 814.976 kJ/(kW·h)). During energy release, the scheme absorbing heat from No.3 high-pressure heater drain outlet yields the minimum heat rate (7 547.945 kJ/(kW·h)). After 8 hours of operation, the system retains 38.503 MW·h of utilizable thermal energy and reduces the peak-shaving paradox index to –0.041. Parameter optimization improves the round-trip efficiency of the compressed air energy storage system by 2.702 percentage points and increases the unit’s peak-shaving depth by 2.481%. This study provides a viable solution for synergistic optimization of coal-fired units and energy storage systems.
To address the demand for flexibility and economy in power grids with high penetration of renewable energy, this paper proposes a coordinated dispatch optimization model and scheduling strategy for multi-type energy storage systems considering peak-valley electricity prices and renewable energy fluctuations.
Based on mixed integer linear programming (MILP) and the non-dominated sorting genetic algorithm II (NSGA-II), a dual-objective optimization dispatch model is constructed, aiming to minimize system costs and maximize renewable energy utilization rate. The model is validated using typical daily load and wind-solar power output data from different seasons in Hebei region to evaluate its economic performance and renewable energy accommodation effectiveness.
The results show that the model demonstrates good robustness and can adapt to fluctuations in wind-solar power and load. The optimal energy storage output is 3 000 MW in spring and 2 000 MW in summer, autumn, and winter. The renewable energy utilization rate remains above 85% in all seasons, and the total system cost is controlled at around 15 000 yuan.
By integrating multi-season scenarios, multi-type energy storage, and multi-objective optimization, this study achieves coordinated improvement in both economic performance and renewable energy accommodation, effectively enhancing grid flexibility and reducing the curtailment rate of wind and photovoltaic power.
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