Retrofitting decommissioned coal-fired power plants (CFPPs) to the Carnot battery (CB) with thermal energy storage (TES) could be an effective way to help the grid absorb more renewable energy. Towards the parameter matching problem in reconstructing the retired CFPP into CB, this paper proposes the feedwater temperature adjustment method and the steam parameter adjustment method to adjust the structure of the Rankine cycle. The results show that the feedwater temperature adjustment method and steam parameter adjustment method can improve the round-trip efficiency of power-to-heat (P2H) type schemes by 0.29 % to 0.95 % and 0.91 % to 0.97 %, respectively. As for CB constructed by heat pump (HP) form, the two methods can improve the round-trip efficiency by 0.09 % to 0.38 % and 0.95 % to 1.02 %, respectively. The sensitivity analysis shows that the feedwater temperature adjustment method is suitable for P2H type schemes and sensitive to variations in exhaust steam pressure. While the steam parameter adjustment method is sensitive to the heat absorption parameter on the heat source side of the matching process, a 1.36 % increase in efficiency can be achieved by regulating the thermodynamic parameters. Under combined heat and power mode, the energy utilization efficiency of CB can reach the maximum of 79.86 % (P2H) and 94.30 % (HP), respectively. At this point, two adjustment methods mentioned above can still be used to obtain efficiency gains close to the power generation model at different heat supply loads. The discounted CO2 reduction factors of different methods can reach about 0.38 t/MWh (P2H) and 0.46 t/MWh (HP) under different design conditions, respectively. This work would be expected to provide a detailed reference for the utilization of decommissioned CFPPs retrofitted to CB for renewable energy consumption.

To address the issues of mismatched resistance and heat transfer characteristics in the rain zone of natural draft wet cooling towers (NDWCT), as well as the insufficient utilization of potential energy, this paper proposes a potential energy recovery model. This model quantifies the recoverable potential energy in the rain zone based on the distribution characteristics of water droplets in the NDWCT. The recovered energy is then used to drive fans, improving both the resistance and heat transfer performance of the NDWCT. Using the NDWCT of a 1000 MW nuclear power unit as the research object, eight types of water collection plates with a coverage rate of 25 % were designed. These plates are used to collect circulating water to drive water turbines, which in turn power the fans. Calculations show that all designs can recover more than 450 kW of potential energy from falling water. After determining the recoverable potential energy, the thermal performance of NDWCT, HNDWCT (High-level water collecting natural draft wet cooling tower), NDWCT with dry-wet hybrid rain zone, and NDWCT with both dry-wet hybrid rain zone and potential energy recovery was compared under different environmental crosswind conditions. The results show that the performance of HNDWCT declines sharply under higher crosswind speeds. When the crosswind speed reaches 8 m/s, its heat exchange capacity decreases by 51.6 % compared to windless conditions, leaving it at only 63.1 % of the heat exchange capacity of NDWCT, with an outlet water temperature 3.66 degrees C higher than that of NDWCT. In contrast, the cooling tower modified with the dry-wet hybrid rain zones and potential energy recovery technology was less affected by crosswinds, with cooling capacity reductions of 5.4 % and 10.3 % at 4 m/s and 8 m/s crosswinds, respectively, whereas NDWCT exhibited reductions of 7.1 % and 11.1 %. Additionally, the former demonstrated superior performance under all crosswind conditions, the outlet water temperatures under windless, 4 m/s, and 8 m/s crosswind conditions decreased by 0.49 degrees C, 0.65 degrees C, and 0.53 degrees C, respectively, with heat exchange capacity improvements of 4.4 %, 6.3 %, and 5.3 %. Compared to traditional dry-wet hybrid rain zone towers, the cooling tower with the dry-wet hybrid rain zones and potential energy recovery technology is less affected by environmental crosswinds. The outlet water temperature decreased by 0.11 degrees C, 0.2 degrees C, and 0.17 degrees C under windless, 4 m/s, and 8 m/s wind conditions, respectively.

Reserve sites for coastal nuclear power plants are gradually being depleted, prompting a shift towards the development of inland nuclear power stations. A new cooling system based on the integration of multiple cooling sources using a hybrid dry–wet cycle is proposed to achieve a balance between energy and water consumption for inland nuclear power stations. Comparative studies among all the available cooling systems were further conducted to analyze the cooling performance and economic viability. The case study results indicate that, in comparison to relative humidity, the cooling performance and circulating water consumption of cooling systems are more susceptible to changes in dry-bulb temperature. In arid and water-scarce regions, a Combined Natural Draft Hybrid Cooling System generally exhibits a monthly average circulating water consumption rate that is more than 270 kg/s lower than that of the natural draft wet cooling system, with an average monthly back pressure reduction of 0.11 kPa. When the dry-bulb temperature exceeds 13 °C, the net profit of wet cooling surpasses that of hybrid cooling. However, this scenario undergoes a reversal as the dry-bulb temperature decreases and local water prices rise. It is emphasized that hybrid cooling demonstrates minimal impact when subjected to changes in environmental conditions, offering extensive regional applicability.

Optimized design of the full structure is a key solution to improve the overall performance of proton exchange membrane fuel cells and advance their commercialization. This paper established a three-dimensional mathematical model of PEMFC, and obtained a series of simulation data collection under different structural parameters. On this basis, we derived the mapping relationship between the thickness of the diffusion layer and the output power using response surface analysis, and then obtained the optimal structural parameters by the BP neural network. The optimization provided a new type of gradient diffusion layer used in the PEMFC, i.e., a tapered diffusion layer. Compared with the fuel cell using a conventional diffusion layer under the same flow channel structure and operating conditions, the results show that the average power of the fuel cell using a gradient diffusion layer has been increased by 3.5 %. The overall heat transfer capacity increased by 10.3 %, and the oxygen utilization increased by 8.7 %. Finally, this paper analyzed the multi-physics field synergistic performance of PEMFCs with different diffusion layer structures, and found that the fuel cell with tapered diffusion layer has better synergistic performance in terms of temperature and concentration fields, and temperature and velocity fields.

Fouling is an important factor affecting the heat transfer performance of condensers in nuclear power plants. In response to the lack of experience in the current cleaning of condensers in nuclear power plants, this paper proposes a particle swarm optimization based LSTM method for predicting fouling thermal resistance and a dynamic optimization theory for condenser cleaning cycles. On the basis of LSTM and the PSO algorithm, compared with the prediction results of LSTM, the MAE, RMSE and MAPE values of PSO-LSTM decreased by 43.3%, 47.3% and 42.1%, respectively, while R2 increased by 26.4%. Considering the load loss and maintenance loss of the unit, as well as the economic loss caused by condenser scaling, the optimal cleaning time of the condenser glue ball system under different fouling rate and circulating water temperature was analyzed, and a calculation theory based on the unit output, the running loss cost of the glue ball and the minimum optimal cleaning cycle of the condenser was proposed. Results show that at rated flow, optimizing the cleaning cycle, with an annual operating time of 300 days, can save $0.45 million in operating costs per year.

The low-carbon energy system has introduced the urgent demand for the ability of peak-shaving for coal fired power plants (CFPPs). A novel and efficient integration concept of the high temperature molten salt thermal energy storage (TES) system with CFPP in the boiler side is proposed in this paper. The concept integrates the TES system with the 350 MW CFPP by extracting the main steam and the reheat steam to exchange heat with the molten salt to enhance the CFPP flexibility, which considers the safety and flexibility of the unit by splitting the heat exchange process of the reheat steam. The sensitivity of the novel concept to the critical design parameters has been analyzed. The power generation load of the novel integrated system can be reduced to 16.31 % of the rated load and the equivalent round-trip efficiency can reach 75.38-77.33 %. The relative value of the reheat steam flow rate flowing at the boiler side in the novel system varies from 0 to 16 % under off-design conditions. The power generation load of CFPP can be increased by 9.56 % THA under the heat discharg mode. The equivalent round-trip efficiency of the novel system can reach 67.61 %-84.87 % under off-design conditions, as well as the exergy efficiency of the TES system can reach 77.48 %-81.38 %. Finally, the levelized cost of delivery of the novel system reaches 135.35 USD/MWh, which can reduce CO2 emissions by 59.58-66.16 tons under different operating conditions (The storage capacity of TES system is 212.21MWh). The results demonstrate that the flexibility enhancement concept of CFPP based on molten salt TES proposed in this paper would be useful to respond to the significant increase in renewable energy.

The dynamic characteristics of key parameters were investigated in this study, which reflected the operational flexibility and efficiency of thermal power units during load regulation. A refined model of the cold end of the unit was proposed. Simultaneously, an innovative exploration was conducted into the coordinated achievement of flexible load regulation and the promotion of energy-efficient operations. Two variables, the variable load rate and cooling water flow, were selected, and the continuous dynamic characteristics of unit energy consumption during load adjustment were determined. The ratio of total variable load coal consumption to load regulation and variable load time was defined as the average regulated coal consumption BZ, which was introduced to enhance the intuitive evaluation of flexibility and efficiency. It was shown that with the increase in variable load rate, there was a decrease observed in the total coal consumption during the variable load process. This trend was consistent with earlier publications. Concurrently, a reduction in cooling water flow had resulted in an increase in power generation coal consumption and a decrease in coal consumption for circulating cooling water pumps. The elevated rate of load variation was attributed to the increased flow of cooling water. A decrease of 14.9 % in back pressure was noted with the increase in the flow of the cooling water. As a result of this reduction in back pressure, the coal consumption rate for power generation was decreased by 1.334 g/kWh, reflecting a decrease of 0.43 %. Additionally, a reduction in total coal consumption of 0.16 t during variable load operation was witnessed, while a 1.97 % increase in the variable load rate was recorded. The optimal flexibility and coal-saving effect were achieved under the conditions of 30 MW/min and 60000 t/h, with Delta BZ = -50 g/(MW & sdot;s). Finally, the feasibility of the proposed scheme was verified through the case of a 350 MW unit.

Deaerator is one of the most important equipment for steady state and dynamic operation of power plants. The deaerator energy storage utilization process is one of the most essential ways to enhance the variable load rate of power plants. The purpose of this study is to improve the dynamic simulation performance of the deaerator during unit load changes by constructing a more reasonable deaerator model, aiming to provide guidance for practical operations. In this paper, a thermal mass microelement algorithm is proposed for the heat transfer between droplets and steam in the deaerator, followed by segmental modeling of the deaerator. By comparing with the operation data of a power plant, the steady state operation error of the deaerator model is within 0.6 %. Subsequently, the unit load variation process is simulated and the dynamic variation accuracy of the model proposed in this paper is enhanced by 1-2 % compared to the lumped parameter model. The dynamic characteristics of the deaerator are obtained by simulating the step and ramp changes of the deaerator boundary conditions and the deaerator start-up process. In addition, during the simulation of condensate throttling, the maximum power of the unit using the deaerator model in this paper is 0.2-1.5 MW larger than that of the lumped parameter model.

Two new types of printed circuit heat exchanger (PCHE) channels are proposed based on the typical airfoil fin PCHE channel proposed in literatures (standard channel) to further improve the thermal-hydraulic performances of airfoil fin PCHE channel. The small shuttle fins and oval fins are employed between the adjacent two airfoil fins of two novel channels, respectively. Using supercritical CO2 as the working fluid, the thermal-hydraulic performances and enhancement mechanisms of the novel channels are numerically investigated. The results show that the channel with shuttle fins has the best comprehensive performance. The Nusselt number of the channel with shuttle fins is 6.7-26% larger, and the f-factor is 8.3-18.6% larger than that of the standard channel under the selected conditions, which leads to a 3-19.1% increase in the PEC (comprehensive performance evaluation criteria). The Nusselt number of the channel with oval fins is 9-27.3% larger, and the f-factor is 26.6-43.4% larger than that of the standard channel, which leads to a 1-15.3% increase in the PEC. The applications of small fins between the adjacent two fins can effectively reduce the low-velocity region area and enhance the local disturbance, thereby effectively improving the thermal-hydraulic performance. The enhancement mechanism of the novel fin PCHE channel structure can be well explained by the principle of field synergy. It can be found that the synergies of the temperature gradient field and the velocity field in two novel channels are significantly improved.

The cold-end system of a nuclear power plant is a key complex node connecting the power generation system with the variable environmental conditions, and its operation, economy, and stability have become the main obstacles to further improving the performance of the first and second circuits. The current research on the interactions between the cold-end system and the thermal cycle of nuclear power mainly adopts the micropower model, while the existing condenser model does not take into account the influence of the turbine exhaust resistance and exhaust flow and other factors on the condenser vacuum change caused by the change in the circulating water flow rate and temperature in determining the optimal vacuum. This ignores the interactions between the equipment and the interconnections between the parameters, which results in the reduction of the model’s accuracy. This paper takes a nuclear power unit as an example, adopts the “constant flow calculation” method to calculate the heat balance of the two-loop thermal system of the nuclear power plant, and constructs an integrated simulation model of the reaction environment variables, the cold-end system, and the thermal cycle. Taking the circulating water temperature and flow rate as variables, the errors of the separate condenser model and the coupled model in circulating water parameter changes were obtained under the condition of satisfying the thermal system operation, and the circulating water temperature and flow rate change ranges applied by the separate condenser model were analyzed in order to reduce the amount of calculations when the unit power error was 1%. The results show that the circulating water temperature is 4 °C, the applicable range of the circulating water flow rate is 42 m3/s to the rated flow rate, the applicable range of the circulating water temperature is 20 °C, the applicable range of the circulating water flow rate is 32.12 m3/s to the rated flow rate, the applicable range of the circulating water temperature is 26 °C, the applicable range of the circulating water flow rate is 38.63 m3/s to the rated flow rate, the applicable range of the circulating water temperature is 30 °C, and the applicable range of the circulating water flow rate is 45 m3/s to the rated flow rate. At a circulating water temperature of 26 °C, the applicable range of the circulating water flow is between 38.63 m3/s and the rated flow; at a circulating water temperature of 30 °C, the applicable range of the circulating water flow is between 45.64 m3/s and the rated flow.

As a renewable energy power generation method, concentrating solar power generation has a broad application prospect. Weather and fluctuation significantly affect the output power of concentrating solar power generation. A heat storage system can stabilize this fluctuation and generate continuous and stable power. Therefore, the research on heat storage systems is of great significance to the development of concentrating solar power generation. This paper mainly studies the operating characteristics of the heat storage system based on solar energy in simultaneous charging, the influence in the change in solar radiation intensity on the charging power and the discharging outlet temperature, and the feasibility of the heat storage tank as an inertial link to stabilize the fluctuation in solar energy and the discharging outlet temperature. In this study, an experimental system for heat storage was established, in which solar energy was used as the heat source, water was used as the heat transfer fluid, and paraffin was used as the phase change heat storage material. When the initial temperature is 50 °C and the charging flow rate is maintained at 0.7 m3/h, at the same time the discharging flow rate is 0.1 m3/h, 0.3 m3/h, and 0.5 m3/h, respectively. The results show that when the solar radiation intensity is lower than 548 W/m2, the curve of heat storage power is almost parallel to the curve of solar radiation intensity; when the solar radiation intensity is lower than 535 W/m2, the moving direction of the thermocline will change; the average discharging outlet temperature in each case is higher than the phase change temperature of the phase change material and this system can continuously supply hot water at more than 69 °C for more than 3 h 32 min; and increasing the discharging flow rate will increase the whole charging and discharging time, thicken the thermocline, and disturb the temperature field in the tank. The experimental analysis will be conducive to profoundly understanding the operation characteristics of the thermocline heat storage tank under the solar heat source and has reference value for the subsequent design of a more efficient heat storage system.

Natural draft hybrid cooling (NDHC) for thermal power generating units is proposed to achieve a balance of energy and water consumption for arid areas. This study examines the two main design forms of hybrid cooling with airside in serial and parallel heat exchange based on the same tower shell and heat transfer areas. Taking full consideration of the thermal cycle of the power generating unit, simplified simulation models for different cooling systems are established to show the influences of ambient conditions and marketing factors. Results show that both the hybrid cooling designs have a better cooling efficiency than either dry cooling or wet cooling. Expanded inlet areas of hybrid cooling in the parallel heat exchange design bring high heat transfer performance. As for the serial design, the higher temperature of the air at the outlet of the dry section maintains a larger airside mass flow rate, obtaining a high-efficient cooling system. The hybrid cooling in the serial design type relies more on the heat transfer performance of the wet section and is more sensible to ambient humidity, while the performance of hybrid cooling in the parallel design mainly depends on the dry section and is more easily affected by ambient temperature. Considering the unit cost variations of coal and water treatment, hybrid cooling in the parallel design has a wider range of applications compared with the serial design. With the growth in coal cost, there exist more benefits with the serial design.

火力发电干湿联合冷却兼具湿冷散热能力大和空冷节水的优势,同时,还可依据机组负荷条件和电厂的环境气象条件变化,调节不同的冷却方式,使机组具有更好的灵活性和环境适应性.为掌握火力发电干湿联合冷却性能,在干冷段和湿冷段并联和串联运行2种模式下,建立联合冷却系统实验台;开展不同运行条件下,联合冷却系统干冷段和湿冷段热负荷分配的实验研究,以及不同运行模式下耗水量与冷却能力的变化规律;采用单变量分析法,研究环境温度、环境湿度等因素对联合循环系统性能的影响.结果表明,环境湿度升高后,系统不同运行模式受到循环水蒸发速率下降的影响,散热量、耗水量有所降低;得到环境温度升高所导致的散热量随系统换热温差减小的定量结果;揭示出耗水量随着湿冷段和干冷段热负荷分配比例的变化规律.研究结果为不同气象条件下,干湿联合冷却系统运行模式和热负荷分配比例的优化提供了实验基础.

Improving the efficiency of energy utilization is a necessary way to control the total amount of fossil energy and thus, achieve the goal of carbon peaking by 2030 and carbon neutrality by 2060. Thermal power generation accounts for nearly 50% of the total installed power generation capacity. The optimization of energy savings of existing thermal power-generating units under full working conditions has a key role in energy efficiency improvement. The introduction of a new physical quantity, entransy, provides a new perspective for connections of operating parameters of the system with the multifields and structural parameters of heat- and mass-transfer surfaces. This paper summarizes the results of the application of the entransy theory in thermal power generation systems recently, focusing on the heat, flow, and mass entransy dissipation-based optimization on the tail flue of boiler and cold-end systems. Then, an outlook on the problems to be solved and the energy-saving potentials, as well as optimization targets of each key subsystem, is provided to offer references for further improving the operating conditions of thermal power units during the energy transition period.

Crosswind has an adverse impact on the performance of an indirect dry cooling system. In order to mitigate the adverse influence, this study redistributed the circulating cooling water among air-cooled heat exchanger sectors so that the performance of the indirect dry cooling system could be improved. An evolution strategies algorithm combined with numerical effectiveness-based heat exchanger model was established to minimize the operation costs of the whole system. Based on a 660 MW practical power plant, optimal circulating cooling water operation strategies under varied crosswind speeds and ambient temperatures were calculated to show its application. According to the calculated results, the performance of the indirect dry cooling system could be enhanced by optimizing circulating cooling water distribution under any crosswind speed, especially under high ambient wind speeds. There is a slight promotion of the coal savings with a rise in ambient temperature: improvements of about 5%. The standard coal consumption rate could save as much as 2.50 g/kWh under crosswind speed of 10 m s−1 and ambient temperature of 32 °C, compared to the 0.1 g/kWh under crosswind speed of 2 m s−1 and ambient temperature of 32 °C.

For thermal power generation, the natural draft hybrid cooling system (NDHCs) with airflows in parallel design gives a multi-objective solution for water saving, performance enhancement and maintenance issues, like corrosion, by switching the loads of wet and dry sections. Performances of dry and wet sections interact with each other in the highly integrated system, increasing the complexity of operation strategies. In this context the present paper examines eight different operation schemes to reveal the relationships of ambient conditions and operation schemes. Comprehensive comparisons in the view of cooling efficiency with a same water inlet temperature are conducted firstly. Results show that there exists energy-saving potentials of the water evaporated rate, cooling performances and the pump power for different schemes. Based on the practical boundary conditions, including those of weather data, operation hours and market factors, optimal operation strategies of hybrid cooling are designed to minimize the operation costs of the energy system. For the 660 MW power generating unit integrated with a natural draft dry cooling system (NDDCs), operation costs based on NDHC after optimization decreased about 0.8% in 2010 and 0.35% in 2018 compared with that of the basic system. When comparing with the designed operation modes of hybrid cooling, 0.07 million dollars is saved after optimization.

Natural draft dry cooling system (NDDCs) utilizes ambient air as cooling medium and is susceptible the ambient conditions. Natural draft wet cooling system (NDWCs) can provide adequate cooling capacity by consuming large amount of water but forms visible plumes. A novel natural draft hybrid cooling system (NDHCs) which consists of both dry and wet components is proposed in this study as a means to be in conflict with the protection and conservation of water resources. With full consideration of its control equations of flow, heat and mass transfer, an iterative algorithm is developed to predict the performance of NDHCs. Coupled to a practical coal-fired power unit, the annual performances of the three systems, as well as the trade-off of the water consumption rate and saved coal consumption rate are explored. The results indicate that during extreme hot days, NDHCs shows more priority over NDDCs and NDWCs. The annual performance of NDHCs is better than NDDCs and NDWCs due to its parallel connection of air, which brings more air passing through the tower. Compared with NDDCs, the playback period of the modification is only 1 year though there is a slightly underestimation due to the structure difference of tower. Furthermore, NDHCs can avoid plumes and further pollution caused by the plumes effectively, since the saturated/supersaturated air will be warmed by the air from dry section and within the sub-saturated region.

在电厂冷却塔的设计中,根据塔内外空气密度差计算塔内抽力应用较广泛,但缺少理论依据,且计算结果存在较大误差,Kr?ger算法考虑了相关作用因素的影响,计算精度较高,但计算形式复杂.以间接空冷自然通风冷却塔为模型,通过实验和数值模拟对比了塔内抽力密度差模型和Kr?ger模型的准确性,指出了后者计算抽力结果更准确的原因,其影响因素主要包括:冷却塔高度、环境大气温度及循环水进口温度.分析结果表明:当环境大气温度和循环水进口温度条件不变时,随冷却塔高度的增加,密度差模型较Kr?ger模型的相对误差随之增大,则计算的换热量误差亦增大.同理,在其他2个条件不变时,随环境大气温度的升高或随着循环水进口温度的降低,相对误差增大.分析结果为自然通风冷却塔抽力计算公式的适用范围以及不同条件下计算方法的选择提供了理论依据.

The recovery of waste heat from power generation by the utilization of energy cascade for district heating has become an important method to improve the energy saving of combined heat and power (CHP) plants. In this paper, a novel super high back pressure (SHBP) cascade heating scheme is proposed to recover waste heat further and tap the energy saving potential of multi-unit combined heating system. On this basis, the regulation progress under full heating conditions is simulated. It's concluded that the regulation progress can be divide into 4 stages, and the flow of extraction steam or the back pressure of turbines is adjusted to satisfy the varying heating demand. Furthermore, the detailed thermodynamic analysis of the novel cascade heating scheme is performed. The results indicate that, in the design condition, the heating process exergy efficiency of the SHBP scheme is improved by 10.4%, leading to an addition of 136.6 MW in generating power and a decline of 30.1% in the heating consumption rate. During the whole heating period, exhaust steam heat load ratio of the SHBP system reaches to 92.5%, which brings about the average heating consumption rate only 5.30 kg/GJ, and 72 thousand tons standard coal saved in total. (C) 2020 Elsevier Ltd. All rights reserved.