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Analysis and solutions for abnormal speed during load rejection test of 660 MW ultra-supercritical dual intermediate pressure cylinder cogeneration unit
ZHANG Jinxu;CHEN Guoqing;YU Qiang;WANG Chen;CHEN Jian;HU Yun;JIANG Guoan;HE Xinrong;[Objective]Load rejection test is a core procedure in the startup and acceptance of coal-fired power units, serving to verify dynamic regulation safety under sudden load loss conditions, which directly impacts grid reliability and must strictly comply with industry standards. To address the technical gap in speed control during load rejection for China's first 660 MW ultra-supercritical dual-intermediate-pressure cylinder cogeneration unit, a 50% load rejection test and abnormal mechanism study were conducted.[Methods] In this study, the pre-verification and formal tests of the unit load rejection were completed first. Based on the dynamic energy balance model of the steam turbine rotor and Ebsilon thermal system simulation, the causes of the abnormal speed surge were analyzed, a systematic optimization scheme was proposed, and the effectiveness of the scheme was verified through a repeated test.[Results] In the pre-verification phase, the closing times of 12 key steam valves all met the design requirements, and the main steam valve tightness test, as well as the over-speed protection control(OPC) and electrical overspeed tests, were all qualified. However, in the first formal test, after the unit was disconnected from the grid, the high-pressure and intermediate-pressure regulating valves closed rapidly, yet the maximum speed surged to 3 183 r/min, exceeding 106% of the rated speed, and the test was terminated. The study revealed that the closing time of the butterfly valve in the intermediate pressure cylinder connecting pipe was 850 ms, which failed to meet the design requirements and resulted in continuous work done by the steam; meanwhile, the main and reheat steam temperatures were 62 ℃ and 67 ℃ lower than the design values, and the high-pressure heater(HP heater) was not put into operation, leading to excessive work done by the intermediate and low-pressure cylinders. The coupling of these three factors intensified the speed surge. After optimization, the closing time of the butterfly valve was shortened to 350～370 ms. Meanwhile, the HP heater system was put into operation, and the main and reheat steam temperatures were controlled to be ≥590 ℃. In the repeated 50% load rejection test, the maximum speed of the unit reached 3 135 r/min, which was no more than 105% of the rated speed, the speed stabilized at the rated value within 60 seconds, and all parameters met the specification requirements.[Conclusion] This study reveals for the first time the multi-factor coupling mechanism of speed surge during load rejection of dual intermediate pressure cylinder units. The established technical system of "valve dynamic optimizationthermal parameter matching-system balance regulation" fills the industry gap, provides a replicable scientific paradigm for the safety acceptance of similar high-parameter CHP units, and has important academic value and engineering significance for improving the adaptability of new-type coal-fired power units to extreme working conditions and ensuring the stable operation of the energy and power system.
Research progress on high-value chemical utilization technology of carbon dioxide
CAO Xinyue;GAO Zhanyan;YANG Yingju;SU Yi;HUANG Jun;WU Dawei;SHEN Teng;CHEN Miao;LIU Jing;[Objective] In the context of the carbon neutrality target, the continuous growth of total CO2 emissions and installed capacity of new energy has led to a surge in energy storage demand. It is a highly promising large-scale longterm energy storage technology to utilize renewable energy to drive the conversion of CO2 into high-value-added fuels or chemicals and store them in the form of chemical energy.[Methods] This paper reviews the research progress of energy storage technologies based on high-value utilization of CO2, including energy storage via catalytic hydrogenation of CO2 to synthesize carbon-based fuels, electrochemical energy storage, and energy storage via microalgal CO2 fixation. It systematically analyzes the characteristics of various technical routes for energy storage based on high-value CO2 utilization, addresses key challenges such as catalyst development and system integration, and evaluates the adaptability of various technologies under different scenarios.[Results] The high-value utilization of CO2 requires at the technical level that products have high energy density, excellent energy storage efficiency, and compatibility with existing industrial infrastructure. At the economic level, it demands low raw material costs, high product added value, and feasibility of large-scale application. At the environmental level, it necessitates achieving a closed carbon cycle, low lifecycle carbon emissions, and resource recycling value. Liquid products from the high-value utilization of CO2, such as methanol, dimethyl ether and polyhydric alcohols, have a higher energy density, enabling more efficient storage as chemical energy in liquid fuels, easier transportation and simpler utilization in existing infrastructure. The energy storage technology via electrocatalytic CO2 reduction to formic acid or formate is characterized by mild reaction conditions(ambient temperature and pressure), low energy consumption, and rapid response, making it suitable for small and medium-sized energy storage scenarios. The energy storage technology via microalgal CO2 fixation achieves the synchronization of carbon fixation and energy production through photosynthesis, and can use industrial wastewater and flue gas as raw materials, boasting both environmental friendliness and resource recyclability. The above three technical routes have their own focuses and complement each other, allowing differentiated selection based on energy storage scale, scenario requirements, etc., to fully cover diversified energy storage needs.[Conclusion] In general, the energy storage technology based on high-value utilization of CO2 provides key technical support from an overall perspective for the diversified utilization of renewable energy, energy conservation and emission reduction, and the construction of new energy storage systems under the carbon peaking and carbon neutrality goals.
Comparative study of different metaheuristic algorithms in optimizing the structure of heat pipe heat exchangers
ZHAO Yang;HUANG Linbin;TAN Rui;ZHU Xuchu;MA Kai;WANG Yuetong;[Objective] The heat pipe heat exchanger has the effect of saving energy and reducing consumption in coalfired power plants, but how to obtain the optimal efficiency with the least manufacturing materials is an engineering application problem. At present, for the structural optimization of heat pipe heat exchanger, it is necessary to break through the problems of no basis for algorithm selection, dependence on experience for parameter setting and difficulty in landing theoretical solutions, find out the parameter sensitivity law in the optimization process and establish a new perspective of "theory-engineering" evaluation. [Methods] In this paper, the gas-gas heat pipe heat exchanger selected for the air preheater of a 90 t/h CFB boiler is taken as the research object, and a multi-constraint optimization model with the goal of reducing the metal consumption is constructed. Three algorithms, constrained genetic algorithm(CGA), particle swarm optimization(PSO) and linear population size reduction success-history based adaptive differential evolution(L-SHADE), are selected. The system comparison is carried out under the same conditions. The coupling effects of population size, iteration times and randomness on performance are quantitatively analyzed innovatively, and the post-evaluation mechanism of ' rounding the theoretical optimal solution to the engineering standard specification ' is first proposed to simulate the real manufacturing constraints. [Results] Studies have shown that all three algorithms have optimal parameter intervals. Although CGA algorithm can effectively deal with constraints, its convergence speed is not as fast as PSO algorithm and L-SHADE algorithm. PSO has the highest computational efficiency under the premise of ensuring the quality of the solution. After rounding the theoretical continuous solution according to the manufacturing standard, the metal consumptions calculated by CGA, PSO and L-SHADE algorithms are 0.592 m3, 0.586 m3 and 0.588 m3, respectively, which are 24.30%, 25.06% and 24.81% lower than the initial design. Although the performance of the algorithm in the theoretical space is different, the three final schemes tend to be consistent after the engineering specifications are rounded, which reveals the performance convergence between the ideal model and the actual constraints. [Conclusion] Although the final engineering schemes are similar, PSO has become the first choice due to its excellent efficiency and stability. The method described in this paper significantly improves the engineering applicability of the optimization design.
Comparative study on economic indicators of deep peaking operation for super/subcritical units
QIAO Liang;XU Zhen;BAI Yuan;[Objective] In order to further enhance the peak-shaving capability of coal-fired power units, so as to meet the peak-regulation demands of the power system and achieve optimization of economic indicators. [Methods] This paper selects eight types of units, namely 600 MW and 300 MW, with supercritical wet cooling, supercritical air cooling, subcritical wet cooling, and subcritical air cooling as research objects. The influence of load rate on heat consumption rate and comprehensive plant electricity consumption rate areanalyzed, and the variation characteristics of coal consumption for power supply under different conditions such as load rate, power supply load, and load reduction process of different types of units are discussed.[Results]The research results indicate that the heat consumption rate and the comprehensive plant power consumption rate increase with the decrease of load rate. Except for supercritical air-cooled units and subcritical wet cooled units, which have a slightly higher coal consumption for 600 MW units than 300 MW units at a load rate of 100%, all four types of units show a lower coal consumption for 600 MW units than 300 MW units under other load rate conditions(e.g., the average difference for supercritical wet cooling units is 7.55 g/(kW·h)). When the unit decreases from full load to a load rate of 50%, the coal consumption for power supply shows a relatively gentle upward trend(e. g., the growth rate for supercritical wet cooling units is about 7.00%). When the unit decreases from a load rate of 50% to a load rate of 30%, the coal consumption for power supply shows a more severe upward trend(e. g., the growth rate for supercritical wet cooling units is about 19.76%). Supercritical wet cooling units have better energy-saving benefits during deep peak shaving processes. For supercritical wet cooling units, if the unit operates for less than 300 MW for a long time, the energy-saving advantage of 300 MW units is better than that of 600 MW units; if the unit needs to frequently reduce load operation from full load state, the regulating energy advantage of a 600 MW unit is better than that of a 300 MW unit(e. g., when reducing 200 MW from full load, the average coal consumption growth rate for 600 MW units is 3.11%, significantly lower than the 19.45% for 300 MW units). [Conclusion]This study can provide guidance for the development of more reasonable scheduling strategies for coalfired power units, reduce energy consumption and emissions during peak shaving, and achieve energy conservation and consumption reduction in unit operation.
Research on low-load stability of biomass gas-coupled coal-fired boiler based on CFD
ZHAO Jun;WANG Jiajun;LI Tao;LIU Sanju;GONG Xun;[Objective] To evaluate the flow and combustion stability of a coal-fired boiler coupled with biomass gas under low-load conditions, and to provide a basis for flexible regulation of thermal power units. [Methods] A Computational Fluid Dynamics(CFD) model of a 640 MW supercritical tangential firing boiler was established, and studies under different loads and different co-firing ratios were conducted. A series of steady-state simulations were conducted under multiple load conditions(70%, 50%, 30%), each with biomass gas co-firing ratios of 5%, 10%, 15% and 25%. According to the theoretical flow characteristics of tangentially fired boilers, stability coefficients were constructed and used in combination with velocity field, temperature field, ignition temperature, ignition distance, temperature distribution, and flue gas emissions to comprehensively evaluate the stability of each operating condition. [Results] The results show that under 70% and 50% load conditions, the variation in stability coefficients with increasing co-firing ratio was small, and the internal flow structure and combustion field remained symmetrical and uniform, indicating good system stability. Under the 30% load condition, significant instability occurred when the co-firing ratio was 10%, with deviations in velocity and temperature stability coefficients reaching 61.53% and 10.19%, respectively. Further increases in the co-firing ratio led to some improvement in stability, but performance remained inferior to that under medium and high loads. Increasing the co-firing ratio reduced the ignition temperature and ignition distance of pulverized coal, enhanced combustion intensity, and elevated furnace temperature, with the most pronounced temperature rise observed at 30% load. In terms of emissions, co-firing biomass gas effectively reduced CO2 and NOx concentrations at the furnace outlet across all operating conditions, with maximum reductions of 26.98% and 50.6%, respectively. [Conclusion] These findings indicate that appropriately increasing the co-firing ratio can improve combustion stability and emission performance under low-load conditions.
Data driven based strategy of plant-level load dispatch for the coal-fired power plant
DIAO Bing;BI Zhiying;XU Jing;China Wuzhou Engineering Group Corporation Ltd.;[Objective] Driven by the carbon peaking and carbon neutrality goals, coal-fired units are transitioning from baseload to flexible regulation power sources, resulting in prolonged low-load operation and a significant increase in net standard coal consumption. Scientifically allocating loads among multiple units to minimize plant-level energy consumption has become a critical issue for the thermal power industry. [Methods] This study takes six units of three types(1 000, 600 and 300 MW) from a virtual power plant as the research objects, a data-driven plant-level load optimization strategy is proposed. Grey relational analysis is employed to screen key parameters affecting the net standard coal consumption rate, and an XGBoost-based coal consumption characteristic prediction model is constructed. With the objective of minimizing the plant-level net standard coal consumption rate, an adaptive parameter differential evolution algorithm based on historical success is introduced to dynamically solve the optimal load dispatch scheme satisfying grid load commands. [Results] The results indicate that the relative error of the proposed coal consumption rate prediction model fluctuates within 0.05%. The plant-level load allocation optimization strategy proposed in this paper achieves minimized overall energy consumption under varying total load demands. The coal-saving potential exhibits a trend of first increasing and then decreasing with the total load. When the plant-level load reaches 2 600 MW, the net standard coal consumption rate under the optimized load dispatch is only 312.29 g/(k W·h). Compared to conventional dispatch modes, it demonstrates a maximum coal-saving potential of 1.92 g/(k W·h), effectively reducing both plant-wide fuel consumption and carbon emissions. [Conclusion] The proposed data-driven plant-level load allocation strategy proposed herein offers a low-cost, high-efficiency technical pathway for thermal power plants to unlock energysaving potential under flexible operating conditions. This provides support for establishing a new power system that is clean, low-carbon, safe, and efficient.
Comprehensive energy efficiency analysis of multiple ultra-supercritical units and load distribution strategy
ZHANG Haifeng;LIU Qingtong;CHEN Guoqing;YIN Ge;GAO Xinglong;ZHOU Xiaoming;[Objective] The plant-level electric load distribution mode of coal-fired power plant affects its economy. In order to reveal the difference of energy efficiency characteristics of multiple ultra-supercritical units in a power plant and the influence of electric load distribution on the economy of the whole plant, the optimal electric load distribution strategy is proposed to realize the energy saving and efficiency increase of the whole plant operation. [Methods] In this paper, the 2 × 1 000 MW ultra-supercritical single-reheat unit in the first phase and the 2 × 1 000 MW ultra-supercritical doublereheat unit in the second phase of a power plant are taken as the object. Based on the Ebsilon software platform, the thermal system models of the first and second phase units are established. The variation of coal consumption and heat consumption rate of the first and second phase units is simulated under the condition of pure condensation with 5 % step size and 30%THA ～ 100%THA, a total of 15 load points. [Results] The results show that when the electric load is between 300 MW and 1 000 MW, the coal consumption rate of the first stage unit is 277.1 ～ 310.9 g/(kW·h), and the maximum difference is 33.8 g/(kW·h). The coal consumption rate of the second phase unit is 266.8 ～ 297.6 g/(kW·h), and the maximum difference is 30.8 g/(kW·h). At low load, the influence of unit electric load change on coal consumption rate is more significant. The coal consumption rate of the first-stage unit decreases more under low load; under high load, the economy of the second-stage unit is better. Under the total load of 2 200 MW, the heat consumption rate of the first-stage multi-load scheme is 30.26 kJ/(kW·h) lower than that of the second-stage. [Conclusion] The load distribution of the unit needs to be dynamically optimized. When the total load is low, it is preferentially borne by the first-stage unit. As the total load increases, the load ratio of the second-stage unit needs to be gradually increased. The high-load period is dominated by the second-stage unit, which can significantly reduce the coal consumption of the whole plant.
Study on the impact of phase change material thermal storage systems on peak-shaving performance of large thermal power units
SUN Xiaoqi;LI Debo;FANG Lijun;JIN Fengchu;XUE Tianhu;[Objective] To enhance the peak-shaving flexibility and grid load response capability of large-scale thermal power units, and to address the issue of insufficient deep peak-shaving capacity of conventional coal-fired units under high-penetration renewable energy integration, this study explores a deep integration pathway between a hightemperature phase change thermal storage system and the thermodynamic cycle of a 1 000 MW ultra-supercritical coalfired unit. [Methods] Based on the EBSILON Professional 17.0 simulation platform, a coupled unit-PCM thermal storage thermodynamic model was established with Al-12 Si eutectic alloy selected as the thermal storage medium. Three steam extraction schemes were designed for the charging stage(A: main steam; B: reheat steam; C: main + reheat steam), and three heat release paths were designed for the discharging stage(a: deaerated water to lowpressure cylinder inlet; b: No. 3 HP heater inlet → No. 1 HP heater outlet; c: No. 3 LP heater inlet → No. 1 HP heater outlet), forming nine coupled schemes. Comprehensive comparisons were conducted from multiple perspectives, including peak-shaving capacity, thermal efficiency, standard coal consumption, exergy efficiency, and round-trip efficiency.[Results] The results indicate that Scheme A-b exhibits the best overall performance: at a 90 MW chargingdischarging load, the peak-shaving capacity reaches 173.95 MW, with an exergy efficiency of 43.92% and a round-trip efficiency of 50.10%, all outperforming the other schemes, while achieving the lowest standard coal consumption. Among the charging schemes, Scheme A provides the largest peak-shaving capacity; among the discharging schemes, Scheme b demonstrates the optimal peak-shaving performance and thermal efficiency. [Conclusion] Reasonable selection of main steam thermal storage coupled with high-pressure regenerative heat release paths can significantly broaden the unit's load regulation range and enhance ramp rates under safe operation, offering a feasible technical pathway for flexibility retrofitting of large-scale thermal power units and renewable energy accommodation.
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Introduction
Electric Power Technology and Environmental Protection
Bimonthly issued
CN 32-1808/X
ISSN 1674-8069
Governed by:
China Energy Investment Group Co., Ltd.
Sponsored by:
China Energy Group Science and Technology Research Institute Co., Ltd.
Academic support：
State Key Laboratory of Low-carbon Smart Coal-fired PowerGeneration and Ultra-clean Emission
Columns:
Thermal Energy Engineering, Clean Power Generation, New Energy Generation, Integrated Power Generation.
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