A novel compressed carbon dioxide (CO₂) energy storage system based on gas-liquid phase change was proposed to promote the development of large-scale and high-efficiency energy storage technology. The overall pressure level of the proposed system is lower than the critical pressure of CO₂, which effectively reduces the difficulty of component manufacturing and improves the economic performance of system. Thermodynamic and economic analyses of the system were carried out and results show that the energy storage efficiency of system is 65.35% under typical design conditions and the investment payback period is about 5.50 years. The results of exergy analysis show that the maximum exergy destruction belongs to turbine which is 1.23 MW, and the evaporator has the minimum exergy efficiency which is 9.41%. The results of parameter analysis show that increasing the CO₂ condensation temperature, compressor isentropic efficiency and turbine isentropic efficiency, or decreasing the temperature difference between the cold end and hot end of heat exchanger 2, and the temperature difference between the cold end of heat exchanger 3, can improve the energy storage efficiency and shorten the investment payback period of the proposed system.

Syngas purification technologies for various pollutants in syngas were mainly reviewed, and the technologies can be classified into hot and cold gas purification according to different treatment methods and different treatment temperatures. For solid particulate pollutants, physical removal is used for both hot and cold gas purification; for tar treatment, physical separation is generally used for cold gas purification, while the methods such as adding catalysts during high-temperature thermal cracking or gasification process are used in hot gas purification; based on a good water-solubility of nitrogenous pollutants, most of cold gas purification technologies use water, acid or organic solvents to absorb directly, while hot gas purification usually uses catalytic oxidation; compared with nitrogenous pollutants, cold gas purification for sulfurated pollutants, not only can use liquid solvents to absorb, but also can use solid adsorbents such as porous carbon materials to absorb, and metal oxides are considered to have good adsorption properties for sulfurated pollutants at high temperatures. For chlorine compounds removal, cold gas purification is applied through following two mechanisms, such as ammonium chloride (NH₄Cl) deposition and absorption of hydrogen chloride (HCl) vapor, hot gas purification is applied through metals depositing with halides as halide salts.

For the unstability issue arising from the high ratio of renewable energy sources in power grid under the background of carbon neutralization, the demand features of various scenarios in the power grids for energy storage were introduced. The characteristics and development status of electrochemical energy storage technologies including supercapacitors, alkali-metal-ion capacitors and batteries, flow batteries, other secondary batteries, and hydrogen-based energy were discussed. The challenges and prospects of electrochemical energy storage technologies for large-scale energy storage in power grids were analyzed. Finally, it is figured out that the electrochemical energy storage technologies should be developed in the direction of "high performance, high safety and low cost".

As a new combustion technology, oxygen-enriched combustion can effectively improve the clean utilization of biomass fuel and provide high-concentration CO₂ flue gas for carbon capture and utilization. At present, the technology is still in the stage of research demonstration at home and abroad. By systematically sorting out the basic characteristics of biomass fuels, the characteristics of biomass oxygen-enriched combustion and related engineering research status were high lighted, and its development trend of this technology was analyzed. Results show that oxygen-enriched combustion can reduce heat loss and improve combustion stability and boiler operation efficiency to a certain extent. It can effectively control the temperature inside the furnace and alleviate the problem of pollutant emissions by dynamically adjusting the recirculation ratio through flue gas recirculation. There may be technical problems in the oxygen enrichment system, air distribution system, slag formation of the heating surface and the sealing of the whole furnace, etc., and main measures to prevent risks are to select appropriate oxygen injection and oxygen mixing mode, dynamic adjustment of oxygen and air distribution mode, anti-slagging treatment and sealing transformation. The efficient utilization of biomass energy coupled carbon capture and storage technology based on oxygen-enriched combustion is expected to become the direction of the transformation and development of biomass power plants.

This paper provides a comprehensive review of the research progress in lignocellulosic biomass pyrolysis technology. The pyrolysis mechanism of various biomass raw materials are summarized, the composition and properties of the products are analyzed, and the regulation, modification and application of the products are reviewed with emphasis. The results indicate that future research directions should focus on the following aspects: technological improvement, committed to improving biomass pyrolysis technology, enhancing energy conversion efficiency and product selectivity; diversification of products, in addition to the main energy products generated by biomass pyrolysis, such as biochar, bio-oil, and biogas, developing high-value chemicals and materials, including bio based chemicals, special chemicals, and high-performance materials should also be focused on; integration with other energy conversion technologies to establish a multi-energy co-supply system by combining biomass pyrolysis with the processes like biomass fermentation, photocatalysis, electrolysis, and energy storage technologies.

High-power energy storage devices have significant advantages such as the high power density and rapid charge-discharge speeds. High-power energy storage devices have been widely used for a variety of applications requiring high power output and quick response time, such as grid frequency regulation, emergency starting for military armored vehicles, and energy recovery of port lifting equipment. Focusing on the mainstream power storage devices including supercapacitors, high-power metal ion batteries and metal ion hybrid capacitors, the basic working principles of various high-power electrochemical energy storage technologies were introduced, and the improvement strategies and research progress of domestic and foreign scholars in the electrode materials and electrolytes of high-power electrochemical energy storage devices were systematically summarized. Finally, the future research directions and application trends of high-power electrochemical energy storage technologies were forecasted.

In view of the problems, such as the near-critical state of CO₂ working fluid in the cold end of the supercritical CO₂ Brayton cycle, the physical properties change drastically with temperature, and the difficulties in design and operation control of the cold end heat exchanger, the straight channel printed circuit heat exchanger (PCHE) and the variable section channel PCHE applied to supercritical CO₂ power cycle cold end heat transfer were designed, and the flow and heat transfer characteristics of SCO₂ in PCHE of variable-section flow channel were analyzed, based on the method of segmented design of heat exchanger. SIMULINK was used to establish a simulation model of the heat exchanger, the influences of the inlet parameters on the SCO₂ outlet parameters of heat exchangers with different flow channel forms were studied when the inlet parameters deviated from the design working conditions. Results show that the designed flow channel section of gradual expansion in SCO₂ side can increase the heat transfer performance of PCHE, but the pressure loss will be increased. PCHE with flow channel cross-section of progressive expansion can better stabilize the outlet temperature of SCO₂ while the inlet parameters of the cold side and hot side deviate from the design working conditions, and the operating range of the cold end parameters can be broadened.

Considering the characteristics of high efficiency and zero carbon emissions of the semi-closed CO₂ cycle, and based on the semi-closed CO₂ power generation system integrated with liquefied natural gas (LNG) cold energy at present, an efficient utilization way of LNG cold energy was proposed. Results show that, for the base case, the energy consumptions of the air separation and compression processes are reduced by 70.4 and 75 MW, respectively, and with a net system efficiency of 63.76%, which is 9.48 percentage points higher than the conventional cycle. Furthermore, with optimization measures such as improving the system parameters and matching the heat capacities of regenerators, the net efficiency of the optimized case is further increased to 72.22%, and the exergy efficiency is 51.27%. Compared with the reference system Ⅱ of only integrating LNG cold energy within the power cycle, the exergy efficiency of cold energy utilization is improved by 28 percentage points.

The key technologies and research progress of lithium battery and supercapacitor hybrid energy storage system used for frequency regulation in auxiliary thermal power units were discussed, such as power/capacity optimization configuration of different types of energy storage, application of high-voltage cascade and modular multilevel (MMC) topology structure, and hybrid energy storage control strategies. The demonstration project of domestic hybrid energy storage assisted frequency regulation for thermal power units was introduced. Finally, the domestic development prospects of hybrid energy storage systems were prospected.

Fretting fatigue life prediction analysis for compressor material TC11 specimens was conducted to study its potential engineering application. The basic flow of fretting fatigue life prediction method based on critical surface method was combed, and the experimental results and prediction results were compared. Results show that the smaller radian of the tenon working surface will reduce the SWT critical interface parameter value of the contact area, which is conducive to the improvement of fretting fatigue life. The error dispersion band between the predicted results based on SWT critical interface parameters and the experimental values is within 2 times of the factor, which has reference significance for the prediction of fretting fatigue life of actual components of aeroengines and gas turbines.

The effects of different Pr_t models on the numerical simulations of turbulent heat transfer of supercritical carbon dioxide in horizontal tubes were systematically investigated using the SST k-ω turbulence model and the predictive capability of different Pr_t models was analyzed by comparing against experimental data. Results show that under the condition of low-level buoyancy, the constant turbulent Prandtl number of 0.85 exhibits a good predictive ability, and the maximum deviation for wall temperatures is less than 5 K. Under the condition of strong buoyancy, larger deviations appear for the predictions using Pr_t=0.85 and the existing models of variable turbulent Prandtl numbers that are corrected for supercritical heat transfer have been demonstrated to be invalid as well. Through in-depth analysis, the turbulent Prandtl number models have profound impacts on fluid flow & heat transfer of supercritical carbon dioxide in the boundary layer, and then determine the turbulent heat transfer performance.

In order to study the changes in levelized cost of energy and cost of electricity supply after the carbon capture, utilization and storage (CCUS) retrofit of a coal-fired power station, the current development trend of the electricity-carbon market was summarized and analyzed, and a simulation model was built to show the cost and benefit of CCUS application for 660 MW coal-fired power station. A sensitivity analysis was carried out using the cost of carbon capture cost and carbon trading price as variables. Results show that the predicted levelized cost of energy of the thermal power units after CCUS retrofit will fall to the range of 20% upward fluctuation of the regional coal trading benchmark price between 2034 and 2035. After 2039, the change rate of levelized cost of energy before and after the transformation will be negative, which means that the levelized cost of energy after transformation will be lower than the target of levelized cost of energy before transformation. In addition, although the carbon capture cost and carbon trading price will have more or less impacts on levelized cost of energy and power supply cost, the coupling effect of carbon capture cost and carbon trading price still has good economic results in the future for the CCUS retrofit projects of the thermal power units.

Since the pressure and temperature of the compressed air in the gas storage are constantly changing during gas storage process in the compressed air energy storage system, which directly affects the output power of the compressor and the actual gas storage capacity, the temperature rise effect of the compressed air under adiabatic condition of 15 m pipeline steel was analyzed by numerical solution of differential equation, taking a gas storage of pipeline steel as an example. And Fluent was used for simulation verification. Considering the temperature rise of the pipeline steel and different heat transfer conditions, the thermal calculation for the gas storage process of the long-distance pipeline steel of 3 024 m was carried out. The coupling calculation of the gas storage process and the work process of the compressor was processed to obtain the change rules of the pressure and temperature of the compressed air in the gas storage process, the output power of the compressor, the actual gas storage capacity of the gas storage and other parameters. Results show that the mass mean temperatures of the compressed air at the end of inflation were 315.39 K, 311.65 K, 301.52 K and 291.35 K, and the gas storage capacities were 244.64 t, 252.60 t, 275.77 t and 301.35 t, when the comprehensive heat transfer coefficients of 0 W/(m²·K), 1 W/(m²·K),5 W/(m²·K) and 25 W/(m²·K) were adopted respectively.

The simulation model of the direct-expansion PVT heat pump hot water system was developed based on its working principle by iteration algorithm to investigate the system performance under various environmental conditions. Results show that in Shanghai, Beijing, Lhasa, Lanzhou, Kunming and Guangzhou, the average COP of direct-expansion PVT heat pump hot water system on typical days in summer is 7.34, 7.30, 6.98, 8.18, 6.24 and 6.79, and the heating time for given amount of water is 275 min, 273 min, 279 min, 243 min, 314 min and 295 min, respectively. The average COP of direct-expansion PVT heat pump hot water system on typical days in winter is 5.59, 5.21, 6.05, 5.03, 6.48 and 5.43, and the heating time for given amount of water is 344 min, 364 min, 316 min, 376 min, 298 min and 359 min, respectively. In the above-mentioned cities, compared to pure photovoltaic modules, the annually-averaged electricity generation benefits of PVT modules are 9.28%, 8.56%, 10.42%, 10.01%, 7.70%, 7.64%, respectively.

In order to comprehensively evaluate the mixing effect and drag loss of static mixers in selective catalytic reduction (SCR) system, a comprehensive performance evaluation index combined the uniformity of flow field and drag characteristics-dimensionless mixing efficiency η was proposed. According to the field requirements, the comprehensive performance of the system was evaluated by numerical simulation method with circular, petal and SMV mixers as examples. Results show that the η of circular mixer, SMV mixer and petal-shaped mixer are 16.18%, 22.50% and 26.88%, respectively. The petal-shaped mixer has the best comprehensive performance. Under the condition of sequence arrangement, same direction layout and coverage rate of 37%, the overall performance of the petal-shaped mixer is the best, and its dimensionless mixing efficiency η is 28.60%, which is 6.40% higher than before optimization.

Taking the combined heat and power (CHP) supplying industrial steam as the research object, the dynamic model of the steam pipe network was developed. Then, the frequency regulation capability of CHP unit assisted with steam distribution system was studied. The exergy storage equivalent conversion rate of steam distribution system under different operating conditions was analyzed. Results show that, when the extraction valve is kept closing for 30 s, the user side steam pressure reaches the lower limit value, and the additional cumulative power generation is 307 kW·h. When the extraction valve is totally closed, the exergy storage equivalent conversion rate is 84.6%, 82.8% and 81.5% as the power load of CHP unit is 700 MW, 900 MW and 1 000 MW,respectively. The faster the action of the extraction valve is, the faster the CHP plant power rises. When the valve closing time is 5 s, the maximum CHP plant power climbing rate is 9.77 MW/s. The variable load rate increases when the CHP unit assisted steam distribution system in frequency regulation, and the operation flexibility of CHP unit can be enhanced.

In order to smooth the fluctuation of wind farm output power, considering the high-efficiency characteristics of solid oxide electrolytic cells (SOEC) for hydrogen production through water electrolysis, a kilowatt-scale SOEC stack model was constructed based on the actual data and its accuracy was verified. To address the non-linearity and time-lag characteristics of the SOEC system, a power control strategy based on model prediction was proposed to mitigate the power fluctuations in wind farms. Based on the operational data of a 15 MW wind farm, a wind farm output power decomposition method was proposed using the ensemble empirical mode decomposition method, so as to obtain charging power instructions of the SOEC system and conduct simulation verification on it. Results show that the power control effect of the SOEC system based on model prediction is very effective, which can realize the following change of charging power command, and the mean absolute percentage error is 1.674%, indicating that it has a high accuracy in suppressing wind power fluctuations.

A new deep conditional subdomain adaptive network (DCSAN) was proposed for the problems of insufficient labeled data and low diagnostic accuracy in the unsupervised cross-domain fault diagnosis field. The network mapped the confidence predicted by the classifier to the features extracted by the shared feature extractor to obtain the multimodal mapping features. And then the multi-kernel local maximum mean difference (MK-LMMD) was used to measure the distance between the multimodal mapping features in different domains. By minimizing the MK-LMMD and the loss functions of the classifier, the alignment of the corresponding sub-domain distributions in the source and target domains was achieved. The feasibility of the proposed method was verified on the bearing dataset of Jiangnan University. Results show that in six migration tasks under variable work conditions, the average diagnostic accuracy of the DCSAN model are 9.5%, 8.0% and 13.6% higher respectively than that of DAN, D-CORAL and DANN model. The proposed DCSAN model has certain effectiveness and superiority in sub-domain alignment and cross-domain adaptive fault diagnosis.

In order to effectively avoid potential imbalance between supply and demand caused by the "source and load" uncertainties, and promote the large-scale development of the virtual power plant, an operational optimization model considering "source and load" uncertainties was proposed based on Copula function, birandom chance-constrained programming algorithm and thermoelectric decoupling. Results show that this model can not only accurately characterize the "source and load" uncertainties and formulate the operational strategies with optimal economic benefits and full utilization of energy, but also provide the effective linkage between the operating costs and default risks, and offer a theoretical basis for decision makers to weigh the risks and economic benefits of energy supply.

In transonic flow, the derivation of recovery temperature in adiabatic film cooling effectiveness is still controversial. There are two different kinds of methods, namely, liner regression method (LRM) and dual liner regression technique (DLRT). LRM believes that the recovery temperature equals to adiabatic wall temperature for the uncooled model. But DLRT determines the recovery temperature from two cooled experiments which only differ in coolant temperature. To explore the difference between LRM and DLRT, experimental rig of transonic channel flow with a mainstream Mach number of 0.85 was built. Transient thermal measurements by infrared thermography were conducted for the uncooled and cooled cases. The mainstream total temperatures of experiments were 330 K and 345 K respectively. For cooled experiments, the blowing ratios was 1.0 and the coolant temperatures were 282 K, 287 K and 291 K respectively. Results show that the convective heat transfer coefficients processed by two methods are basically the same. However, the adiabatic film cooling effectiveness obtained by the two methods is qualitatively different, due to the difference of recovery temperatures.

To achieve effective integration of renewables and reduce the instantaneous power fluctuations of wind power, a hybrid energy storage system (HESS) combining lithium battery-based energy storage and flywheel-based power storage was used to stabilize wind power fluctuations. Firstly, the improved k-means algorithm was used to obtain the typical daily data, and empirical mode decomposition (EMD) was used to disassemble it to obtain the HESS flattening task. Based on the comprehensive consideration of power capacity and charging-discharging efficiency constraints of various energy storage systems, a coordinated HESS energy management system was constructed. Moreover, with the minimum costs of hybrid energy storage system and wind power opportunity compensation as the objective function, a baseline variable and fluctuation penalty coefficient were introduced for correction, and a HESS capacity allocation model for stabilizing wind power fluctuations was developed. Finally, with the actual grid-connected data, a configuration scheme with optimized smoothing effect and economic performance was obtained. Results show that the cumulative under-compensation of wind power in the proposed configuration scheme is reduced by 91.8%, and the economic performance is increased by 49.99%. The optimal wind-storage ratio is 1∶0.16, of which the flywheel and lithium battery is 1∶4.65.

Taking the offshore nuclear power platform as the application object, based on the design scheme of the secondary passive residual heat removal system (PRHRS), an experimental facility was designed and built. The start-up characteristics of the system were studied, and the evolution of important parameters of the system during the start-up process was analyzed. Results show that the PRHRS can establish stable natural circulation and effectively remove the heat generated from the U-type tubes in the steam generator under the studied working conditions. During the start-up process, the initial operation pressure only affects the process of the system reaching the asymptotic steady-state, but not the final steady-state of the system. The thermal stratification in the cooling water tank plays an important role in the evolution characteristics of the temperature at the outlet of the passive residual heat removal heat exchanger.

A parallel deep learning framework with adaptive optimization of weight parameters was proposed to address the accuracy and adaptability short comings of existing photovoltaic (PV) power prediction models when the data fluctuation patterns varied greatly in different application scenarios. The framework contained two parallel deep learning algorithm units such as Attention-Seq2Seq unit and Transformer unit and a weight parameter adaptive optimization unit. Based on the proposed parallel deep learning framework, the prediction of PV power generation was carried out and compared with the prediction results by Attention-Seq2Seq and Transformer models. Results show that the proposed framework not only can offset the lack of prediction accuracy and adaptability of single algorithm under different data fluctuation patterns, but also can effectively solve the long-distance dependence problem in time series prediction, which results in higher forecasting accuracy. The maximum reduction of average absolute error (E_MAE) and root mean square error (E_RMSE) is 41.18% and 45.59% in a typical day of summer, respectively,while the maximum reduction of E_MAE and E_RMSE arrives at 81.13% and 82.86%, respectively in a typical day of winter.

In order to study the dynamic characteristics of the water wall outlet parameters of ultra-supercritical boiler, the calculation model of the dynamic characteristics of the water wall system under supercritical pressure was established by using the frequency domain method. The experimental results show that the calculated values are in good agreement with the measured data. The lower furnace water wall of an ultra-supercritical boiler was calculated, and the dynamic characteristics under 75%THA load were obtained. The dynamic characteristics at heat flux, inlet enthalpy, inlet mass flow rate and outlet pressure step were studied. The effects of heat flux, inlet enthalpy, inlet mass flow, and outlet pressure step on the outlet fluid parameters were analyzed separately. Results show that the response time due to disturbance decreases when the inlet enthalpy, inlet mass flow rate, and heat flux increases; the response time due to disturbance increases when the inlet pressure and pipe section length increase.

An integrated energy system based on source side of thermal power plant was proposed,which takes thermal power units as the core, couples multiple renewable energy inputs such as biomass gasification, garbage gasification and dried sludge at the input end of the system, and supplies multiple energy products such as colding, heating, steam and electricity at the output end. By coupling the thermal balance model of the power plant with the renewable energy model and cooling/heating system model, an optimization configuration method was established with efficiency and economy as the objectives. The following two types of optimization logics, input optimization and output optimization, were adopted to analyze the impact of the main operating parameters of the integrated energy system on the economy and efficiency optimization goals from the input and output ends of the system. Results show that integrated energy transformation has positive significance for current thermal power plants.

Chemical-looping reforming of biomass using Cu-based oxygen carriers was analyzed in a thermogravimetric analyzer (TGA) and a small fluidized bed reactor respectively, and the influence of oxygen carriers and reactor temperature was studied. Results show that, compared with Fe-based oxygen carriers and quartz sand, the use of Cu-based oxygen carriers results in larger weight loss and weight loss rate, since Cu-based oxygen carriers can release oxygen at high-temperature and thus accelerate the pyrolysis and gasification of biomass. Meanwhile, higher temperature leads to higher gasification efficiency, gas yield, conversion efficiency and gasification rate. The Cu-based oxygen carriers appear good redox ability, anti sintering ability and high reactivity.

Gas turbine combined cooling, heating and power (CCHP) technology has excellent development and application prospects. However, there are many problems such as low efficiency in partial load operation, strong coupling of thermal-electrical output and inflexible regulation of thermoelectric ratio etc. To solve these problems, a novel CCHP system based on gas turbine and constant-pressure compressed air energy storage (CAES) was developed. The thermodynamic models of components such as the compressor, combustion chambers, turbine, waste heat boiler, heat exchanger, injector and water pumps/turbine, were developed and used to analyze the operational characteristics of the CCHP system under an extraction-release gas flow regulation strategy. Results show that when the extraction-release coefficient is between 0 and 0.2, the CCHP system has a thermoelectric ratio regulating range of 0.58-2.27. During the variable load operation process, the primary energy utilization rate of the CCHP system changes within the range of 58.1%-59.5%, and the exergy efficiency is no less than 32.2%. For the developed CCHP system, the high comprehensive energy efficient and flexibility can be achieved under wide operating conditions.

In order to investigate the effect of substrate negative bias voltage on the structure and properties of the ion plating coatings, AlCrN films were deposited on SP-700 titanium alloy by three different ion plating processes. The morphology, phase composition, micro-hardness, wear resistance and electrochemical corrosion resistance of the coatings were measured by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Vickers microhardness tester, reciprocating friction and wear tester, white light interference 3D surface profiler and electrochemical workstation. The corrosion behavior of the coating in HF solution with mass fraction of 5% was measured by immersion corrosion method. Results show that the surface of the ion plating coating is compact, mainly composed of cubic (Cr,Al) N phase and cubic Al phase, and its microhardness is high, the friction coefficients of the coatings are lower during friction and wear process, the wear mass loss of the specimen in the process 2 is the smallest, and the relative wear resistance reaches 902.26. The corrosion resistance of AlCrN coating in NaCl solution with mass fraction of 3.5% is similar to that of titanium alloy substrate. The corrosion resistance of AlCrN coating in HF solution is better.

During chemical looping combustion, oxygen carrier plays a crucial role as the carriers of oxygen and heat. Design of oxygen carrier has always been the emphasis and difficulty in chemical looping technology research. Chemical looping combustion usually occurs in a fluidized bed reactor. Since the chemical stress caused by chemical reactions has the greatest contribution rate to the abrasion of oxygen carrier, the life of oxygen carrier is significantly shortened and the effective components run away. From the perspective of oxygen carrier structure design, the anti-abrasion mechanism of different composite oxygen carriers was qualitatively evaluated. The core-shell structure inhibits the phase separation of the active components and avoids the deactivation of oxygen carrier caused by surface abrasion of the active components. The addition of Al₂O₃ fiber and "rivet" inhibits crack growth and slows down the abrasion of the material. The addition of fuel ash improves the skeleton strength of the composite oxygen carriers, and the resistance to abrasion and slagging aggregation of oxygen carriers. The synergistic effect of the composite oxygen carrier increases the reactivity and slows down the sintering agglomeration phenomenon. From the perspective of abrasion dynamics and service life, the abrasion conditions of different oxygen carriers were quantitatively compared. By logarithmically fitting of the Gwyn abrasion dynamics equation, fitting parameters K and n of different oxygen carriers were calculated, which reflects the abrasion mechanism and abrasion patterns.

Biohydrogen production technologies such as photolysis of water, photo fermentation, dark fermentation, and coupled dark-photo-fermentation were mainly reviewed. The hydrogen production mechanism, technological advantages and disadvantages, influencing factors and research status of each method were analyzed. At the same time, the types and characteristics of biohydrogen production reactors were compared. The results show that biohydrogen production has great potential in low-grade energy treatment and advanced energy production. Finally, some suggestions on the development of biohydrogen production technology were given.

In order to further build a clean, low-carbon, economical and energy-saving energy supply system, a distributed energy system with wind, solar and multi-energy storage was established. For an office park in Beijing, DeST simulation software was used to predict user load and local wind and solar conditions. An adaptive optimal operation strategy was proposed to maximize the comprehensive benefits of economy, energy-saving and environmental protection. The exhaustive search method and genetic algorithm were used to optimize the optimal scheduling scheme of the system. Meanwhile, using the electric heating operation strategy as a comparison, the comprehensive benefits of the system under several different operation strategies were compared and analyzed. Results show that the average comprehensive benefit under the traditional following electrical load operation mode is 0.41 on average; under the adaptive optimization operation strategy, the average comprehensive benefit of the scheduling scheme obtained by genetic algorithm can reach 0.5, and the average comprehensive benefit of the operation scheme obtained by the exhaustive search method can reach 0.51.

The Eco-Indicator 99 method was used as an exergoenvironmental index evaluation method to conduct the environmental analysis of the conventional coal-fired unit (scheme 1), coal-fired carbon capture power system (scheme 2) and solar-assisted coal-fired carbon capture power system (scheme 3).The life cycle assessment of coal and each equipment was conducted, and the exergoenvironmental indices of the three schemes were compared. Results show that system exergy efficiency is characterized by scheme 3>scheme 1>scheme 2. Considering the power penalty induced by carbon capture and storage (CCS) and the solar power compensation to the unit power, the specific environmental impact of electricity is indicated with scheme 2>scheme 1>scheme 3. The power consumption of CCS system results in a decrease in the net power output of the system, the environmental impact of producing 1 kW·h of electricity is reflected with scheme 2>scheme 3>scheme 1. The exergoenvironmental indices show that only the boiler generates pollutants and play a dominant role in the environmental impact. The environmental impact can be reduced by reducing pollutant generation. For boilers, small turbines and other equipment, the environmental impact can also be cut down by improving the exergy efficiency.

The heat transfer coefficient calculation models and methods for outer surface of steam pipe, main stop valve, control valve and outer casing of steam turbines were established. The heat transfer coefficient calculation formulas for inner surface of steam pipe, main stop valve, control valve, high pressure (HP) outer casing, intermediate pressure (IP) outer casing and low pressure (LP) outer casing of steam turbine, and the composite heat transfer coefficient of the outer surface of the insulation structure and the outer surface of the LP outer casing were given. The calculation model of the heat transfer process of the steam pipe, the metal inner wall of the HP outer casing and the IP outer casing and the double-layer casing wall of the outer wall of the thermal insulation structure, the metal inner wall of the main stop valve, control valve and the double-layer spherical wall of the outer wall of the thermal insulation structure, and the single-layer cylinder wall of the LP outer casing of steam turbine were established. Considering that the inner surface temperature and outer surface temperature of the inner metal wall and the outer surface temperature of the outer wall of the thermal insulation structure were both undetermined, the iterative method was used to determine the surface temperature of these steam turbine components, the heat transfer coefficient and the heat flow density of the heat transfer process. The calculation and analysis of the external surface heat transfer coefficient of the steam pipes, main stop valve, control valve, HP outer casing, IP outer casing and LP outer casing of the steam turbine were completed. The calculation results of the heat transfer coefficient, heat flux density and equivalent surface heat transfer coefficient of the metal inner wall outer surface of these steam turbine components during the heat transfer process were obtained, providing heat transfer boundary conditions for finite element numerical calculation of temperature field and stress field of these steam turbine components.

The thermal numerical simulation of the fuel axial staged model combustion chamber was carried out, so as to analyze the effects of jet nozzle angle and equivalence ratio on the velocity field, temperature field, residence time, turbulent kinetic energy distribution and pollutant emission of the model combustion chamber. Results show that with the increase of jet equivalence ratio, except for 45°, obvious backflow appears at the downstream of jet nozzle when the angle comes to 90° and 135°, and the flue gas residence time in the combustion chamber increases. With the decrease of jet nozzle angle, the residence time of the primary combustion zone increases, and the residence time of the secondary combustion zone decreases, but the total residence time increases. With the increase of jet nozzle angle and jet equivalent ratio, the high turbulent kinetic energy region in the combustion chamber increases. Compared with jet nozzle angle of 90° and 135°, the NO_x mass fraction at jet angle of 45° is higher when the jet equivalent ratio is low, indicating that under certain operating conditions, the emission characteristics are lower when the jet angle is 45°.

In order to select the optimal working fluid for the organic Rankine cycle (ORC)power generation system driven by a vapor-liquid two-phase hybrid geothermal fluid with the heat source temperature of 140 ℃, six dry working materials were selected and a system model was built in MATLAB. The influence of each working fluid evaporation temperature on the system thermodynamic performance was analyzed. The variation of the optimal evaporation temperature with the heat source temperature under different steam mass fractions was compared. The influence of heat source mass flow rate on the system net output power and the influence of evaporation temperature on the recharge temperature were studied. Results show that considering the effect of thermodynamic performance, physical and chemical stability, thermal source matching and system recharge temperature on geothermal ORC power generation system, R601a (isopentane) is the best suitable material for ORC power generation system driven by 140 ℃ vapor-liquid two-phase hybrid geothermal fluid as heat source.

To improve the reactive power compensation and voltage stability of doubly-fed wind farms, a zonal control method of reactive power and voltage in wind farms considering fuzzy multi-objective optimization was proposed. Based on the active power data, the wind farm was partitioned and dimensionality was reduced, and the reactive power optimization limits for each zone were calculated. The zonal reactive power margin index was defined to describe the safety margin of wind farm voltage operation. Taking into account both operation safety and stability, a fuzzy multi-objective optimization model for wind farm reactive power voltage was established. A self-adaptive genetic taboo algorithm that can quickly and globally optimize on a large scale has been proposed. the global timeliness of optimization was improved by redefining the crossover and mutation, and the accuracy of optimization was improved by introducing taboo algorithm. Finally, simulation verification was conducted using a doubly fed wind farm as an example. Results show that the proposed method can reserve sufficient reactive power margin for wind farms and significantly reduce voltage fluctuations within the system.

In order to achieve more accurate feedforward control for the superheated steam temperature with wide load operation, a predictive feedforward signal model based on physical guided neural network (PGNN) was proposed, and the load segment allocation of multiple models was determined based on gap measurement. The PGNN prediction method of multi-model gap measurement adopted the multi-model gap measurement method to reasonably divide the load section. Combined with the long short term memory neural network guided by the superheater mechanism, the strong coupling and large inertia superheated steam temperature wide load feedforward signal can be accurately predicted. Results show that when in the wide load of the unit, the nonlinear degree of the control object gradually increases with the load reduction, and more models are needed. The multi-model gap measurement PGNN feedforward control method can adopt feedforward signals suitable for the current working conditions under different working conditions, and improve the adjustment accuracy and stability of superheated steam temperature.

A coupled system based on reheated steam extraction and molten salt thermal storage was presented, and the operation processes and efficiency of the system were analyzed. In order to match the main steam temperature, electric heating was used to elevate the molten salt temperature after heat exchanging with extracted steam during the charging process. On this basis, the effects of average temperature difference in charging process, temperature difference of pinch point in discharging process and lower storage temperature of molten salt on system performance parameters were studied. Results show that with a fixed temperature difference of 10 K of the charging process, increasing the temperature difference of pinch point from 5 K to 15 K, the maximum equivalent round-trip efficiency reduces from 88.2% to 85.0%, and the optimal heat storage temperature will increase from 314 ℃ to 324 ℃. With fixed pinch point of 10 K, the round-trip efficiency decreased from 89.5% to 85.8% when the average temperature difference of the charging process increased from 5 K to 15 K. With both temperature differences of 10 K, the maximum equivalent round-trip efficiency is 87.1%, and the minimum load of the unit is reduced from 30% to 24.3%.

Based on the dynamic mesh technique, the vortex-induced vibration of wind turbine airfoil at 90° angle of attack was numerically studied by using the prescribed vibration method and the free vibration method respectively. Through the prescribed vibration calculation method, the vortex-induced vibration range of Du96-W-180 wind turbine airfoil at different amplitudes was determined, and the effects of changing the incoming flow velocity and changing the structural stiffness on the vortex-induced vibration range were compared. Through the free vibration calculation method, the vortex-induced vibration range of the airfoil at different inflow speeds was obtained. The influence of different structural damping on the vibration response of the airfoil at the frequency ratio r=0.93 and r=1.11 was compared, and the development and evolution process of the vortex-induced vibration of the airfoil were analyzed. Results show that vortex-induced vibration range at different frequency ratios is basically the same while changing incoming flow velocity and changing the structural stiffness. The free vibration numerical simulation verifies the vortex-vibration range of the forced vibration. When 6% structural damping is applied at different frequency ratios, the vibration of the airfoil exhibits two forms: vortex-induced vibration and forced vibration.

Extreme weather events become more frequent because of climate change, posing a threat to the security and stability of the electricity system. Current researches about strategic reserve generation units mainly focus on policy evaluations or modelling simulations from the perspective of unit costs and power sale income, which do not adequately account for the economic and social effects they can bring. In order to comprehensively analyze the economics of strategic reserve generation units, a cost-benefit analysis model was established from the perspective of the whole society, considering the benefits including the guarantees for the economic production, health benefits for residents and labor force level, and the costs of strategic reserve generation unit investment and operation, and Sichuan power restriction event was taken as a case study for analysis. Results show that the benefit for 1 kW·h electricity that can be brought by the strategic reserve generation units is 4.77 yuan/(kW·h) and the required costs for 1 kW·h electricity generated by building new strategic backup units and using units that are close to retirement were about 1.91 yuan/(kW·h) and 0.47 yuan/(kW·h), respectively. Thus it is economically feasible to build and operate the strategic reserve generation units from the whole society perspective. At the same time, the operating hours are the most critical factor affecting the cost of strategic reserve generation units, and if the operating hours are less than 89 hours in a year, the unit's cost of electricity will be higher than its social benefits.