An analytical model for a combined heat and power (CHP) system driven by deep geothermal energy based on heat pipes was developed. The dynamic heat extraction characteristics of the heat pipes are obtained through numerical calculations based on the heat pipe-geothermal rock layer model. By analyzing the thermodynamic and thermo-economic performance of the direct expansion CHP system, the effects of heat pipe structure (heat pipe diameter, length, and insulation layer length), operating time, and geothermal temperature gradient on the performance of the system are investigated. The results show that, lower steam condensation temperature of the heat pipes leads to greater heat extraction, which helps shorten the investment recovery of the system. However, reducing the condensation temperature also decreases thermal efficiency of the CHP system. Moreover, there exists an optimal steam condensation temperature that minimizes the system’s levelized cost of electricity (LCOE). The heat extraction rate from the heat pipes declines rapidly in the first five years, and then gradually stabilizes. To maintain stable heat extraction over long term (30 years) and avoid interference between adjacent heat pipes, the center distance between any two heat pipes should be kept above 80 meters. The economic performance of the CHP system is closely related to the structural parameters of the heat pipes. At an optimal steam condensation temperature, increasing the heat pipe diameter and length, and selecting target zones with higher geothermal gradients can effectively reduce both the investment payback period and the LCOE.

Based on the application of micro-channel printed circuit heat exchangers in fields such as thermoelectric power generation and aerospace, a high-efficiency, low-resistance, and easy-to-manufacture transverse slotted channel is proposed using the theory of boundary layer re-development, and the heat transfer is enhanced. Numerical simulations are employed to study the flow and heat transfer characteristics of both straight and slotted channels. The mechanisms of heat transfer enhancement and flow resistance reduction in the transverse slotted channel are investigated. The results show that the entrance effect can significantly enhance heat transfer with a minimal increase in flow resistance. The transverse slotted channel creates multiple entrance effects in the slotted regions by inducing flow separation, which leads to periodic boundary layer redevelopment, thereby greatly enhancing local convective heat transfer. Additionally, due to the relatively small velocity gradient in the slotted regions, local resistance is effectively reduced. As a result, the proposed transverse slotted channel improves the heat transfer capability of the channel by 2.24%~2.59%, reduces the resistance by 6.66%~7.91%, and increases the overall heat transfer performance by 9.87%~11.02%.

For a supercritical carbon dioxide (S-CO₂) recompression Brayton (RB) system with two-stage compression and intercooling process, two system models with different layouts are constructed. The effects of key parameters such as low-pressure stage pressure ratio and split ratio on the system performance are explored. The results indicate that, the minimum and optimum splitting ratios exist for the RB cycle, the two-stage compression cycle of the main compressor (TCIP-RB), and the two-stage compression cycle of the recompressor (RTCIP-RB) under the design conditions. Moreover, the thermal efficiency of the TCIP-RB cycle is higher than that of the other two cycles within a certain range of split ratios. When the above three systems adopt the optimal split ratios, the maximum efficiency of the TCIP-RB cycle is 50.95%, which surpasses that of the RB and RTCIP-RB cycle by 3.20% and 3.98%, respectively. At different low-pressure stage pressure ratios, TCIP-RB and RTCIP-RB cycles have an optimal split ratio to maximize the thermal efficiency of the system, and the maximum thermal efficiency decreases with the increase of the low-pressure stage pressure ratio.

As an emerging large-scale electricity storage technology, the Carnot battery has the advantages of low cost, large capacity, and being free from geographical limitations. Aiming at the current situation that the low discharge cycle efficiency restrains further improvement of round-trip efficiency of the Carnot battery, combined with the heat demand of the thermally integrated Carnot battery and the relatively high discharge efficiency of the Kalina cycle, a heat pumped-Kalina cycle Carnot battery system driven by extraction steam of a coal-fired power station is proposed. A thermodynamic model of the Carnot battery system is established, and the influences of thermal energy storage temperature, temperature difference in thermal energy storage, and ammonia mass fraction on thermodynamic performance of the Carnot battery are mainly studied. The results show that, with different temperature differences of thermal energy storage and at different temperatures, the round-trip efficiency can reach 44.8%~108.0%. With the increase of the ammonia mass fraction, the round-trip efficiency will be significantly improved. However, when the ammonia mass fraction exceeds 90%, the efficiency will drop sharply, and the Kalina cycle is close to a one-component cycle. Therefore, when designing a Carnot battery based on the Kalina cycle, the ammonia mass fraction should be controlled within 80%~90%.

Low-temperature adsorption technology for coal-fired flue gas pollutants can synergistically remove various pollutants and achieve near-zero emission. Focusing on the key equipment of this technology, flue gas spray cooling tower, ANSYS Fluent software is used to simulate the inside of the tower, and the impacts of various parameters are analyzed. The results indicate that, increasing the spray height effectively extends the contact time between flue gas and cooling water, thus significantly enhances heat exchange. Reducing the temperature of the cooling water strengthens the tower’s cooling capacity. Additionally, moderately reducing the inlet flue gas velocity increases its residence time in the tower, promoting more thorough heat exchange. Reducing the droplet diameter of the cooling water enhances the heat transfer efficiency by increasing the contact area. Enlarging the spray angle extends the residence time of cooling water within the tower and lengthens the contact duration with flue gas, boosting heat exchange. Increasing the cooling water flow rate expands the heat exchange area, further improving the heat transfer performance. The addition of packing material improves the heat exchange capacity of the tower while conserving cooling water. Comprehensively optimizing these parameters can substantially reduce the temperature of cooled flue gas, providing theoretical support for the design, manufacturing, and optimization of spray cooling towers in the low-temperature adsorption technology for coal-fired flue gas pollutants.

To achieve efficient coupling between coal-fired power plants (CFPP) and compressed air energy storage (CAES), a system that couples the flue-gas side of CFPP with CAES is proposed. During the energy release phase of this coupled system, the flue gas from CFPP is used to heat the high-pressure air before it enters the expander. This avoids introducing additional heat sources, which would increase costs, or extracting steam from the turbine side to heat the high-pressure air, which would affect the output of the thermal power unit. Subsequently, to reduce the effect of extracted flue gas on the operation of a single thermal power unit, a CAES coupled system sharing the flue gas of two thermal power units is established. Based on the above thermodynamic models of the systems, modeling is carried out using EBSILON software and performance analysis is conducted. Then, an optimal economic operation strategy for the plant-level coupled system is proposed. The results show that, at full load, compared with the steam-coupling scheme, the flue-gas-coupling scheme reduces the standard coal consumption rate by 2.15 g/(kW·h), increases the heat consumption rate by 37.06 kJ/(kW·h), raises the energy utilization coefficient by 0.33 percentage point, and decreases the auxiliary power rate by 0.20 percentage point. The overall electrical efficiency, round-trip efficiency, and CAES operating efficiency of the flue-gas-side coupling are all higher than those of the steam-side coupling. After the economic optimization of the plant-level coupled system, the net revenues of four typical days increase by 143 700, 157 600, 188 100 and 208 700 yuan, respectively.

In order to effectively improve the energy efficiency and operational flexibility of solar power generation, an integrated system coupling solar photovoltaic, solar thermal and compressed air energy storage is proposed. During the day, the compressed air energy storage system will store the photovoltaic abandoned power, and transfer the compression heat to the photothermal power station. At night, the compressed air energy storage system releases air and uses water supply of the photothermal power station to heat up, thereby increasing the power generation load of the unit. Based on the system simulation, the coupling scheme is analyzed thermodynamically and economically. The overall generation efficiency of the coupled system is 41.24%, while the overall exergy efficiency is 66.79%. The round-trip efficiency of the compressed air energy storage system is 72.14%, while the exergy efficiency of the compressed air system is 84.30%, both of which have increased significantly. The peaking depth of the coupled system is 7.02% in the daytime and 19.69% in the evening. In addition, the dynamic recovery cycle of the coupling scheme is 3.10 years, and the net present value is 41.350 6 million yuan.

The formation and emission of SO₃ in coal-fired flue gas pose serious threats to both the safe and economical operation of power plants and the atmospheric environment. To solve this problem, the SO₃ removal performance of sodium-based, calcium-based and magnesium-based absorbents is investigated, and the performance variations of Na₂CO₃, Ca(OH)₂ and CaO under different operating conditions are studied. The results indicate that, under the coexistence of SO₂ and SO₃, the absorbers would react with SO₃ in the flue gas preferentially, and the effectiveness of SO₃ removal by various absorbents ranked from highest to lowest is as follows: Na₂CO₃>NaHCO₃>Mg(OH)₂>MgO>Ca(OH)₂>CaO. Under certain experimental conditions, the SO₃ removal efficiencies of all the absorbents could reach higher than 80% when the chemical equivalent ratio of absorbent to SO₂ reached 2:1. Pre-calcination treatment for the absorbents enhanced their pore structures, facilitating SO₃ diffusion into the absorbent and improving the SO₃ absorption efficiency. Increasing reaction temperature, chemical equivalent ratio, and initial SO₃ mass concentration can promote the SO₃ removal. Additionally, a moderate increase in H₂O volume fraction aided SO₃ removal. When the absorbent is significantly excessive, external diffusion is the main controlling step affecting the chemical reaction rate, while the type of absorbent has a relatively minor impact on it.

Constructing a large-scale virtual power plant (L-VPP) based on coal-fired units is a vital strategy for achieving “dual-carbon” goals by enabling renewable energy integration and supporting the transition of coal-fired power generation. A dynamic simulation model of the L-VPP and a source-storage frequency regulation control system model are established, which include a 350 MW coal-fired unit, a 100 MW photovoltaic unit, a 90 MW·h battery energy storage system, and internal loads. The frequency response characteristics of the L-VPP are analyzed for various control systems and at different load ramp rates of the coal-fired unit. The results reveal that, the load ramp rate of the coal-fired unit is a critical constraint on frequency response capability when storage capacity is limited. The complementary frequency response characteristics between the source and storage are obtained, leading to a coordinated control strategy that incorporates auxiliary power commands and cyclic determination mechanisms. Simulations demonstrate that the proposed strategy lowers the frequency nadir by 0.06 Hz and shortens the steady-state recovery time by 18.6%. Furthermore, to achieve a steady-state error within the frequency dead band, the load ramp rate of the coal-fired unit is increased from below 3.50 MW/min to 7.00 MW/min. This strategy offers technical guidance for the safe and efficient operation of large-scale virtual power plants.

Co-firing zero-carbon fuels in coal-fired power plants is one of the important paths to realize low-carbon emissions in power industry, and the common zero-carbon fuels blended at present are biomass, ammonia, and hydrogen, etc. The researches on co-firing zero-carbon fuels in coal-fired circulating fluidized bed (CFB) boilers are discussed, the technical principles and advantages of the technology are analyzed, and the future technical challenges and development trends of the technology are discussed, by combining the characteristics of biomass, ammonia and hydrogen fuels with the progress of the research on blending, to provide theoretical and technical support for the realization of low-carbon emissions from coal-fired boilers. Based on the fluidized combustion characteristics of CFB boilers, the basic fuel characteristics, combustion characteristics and pollutants emission characteristics of the three zero-carbon fuels after blending, problems and future development directions are analyzed. Although there are certain limitations and technical challenges in the co-firing of all three zero-carbon fuels, the optimization of the combustion process and the control of pollutant emissions can be realized through the organization of the gas-solid flow field, the deep grading of fuel or air, and the coupling of other technologies. Co-firing zero-carbon fuels in coal-fired CFB boilers is a feasible route for carbon emission reduction, which helps to develop a new generation of flexible low-carbon coal-fired power generation technologies in CFB boilers, and provides technical support for the promotion of low-carbon transformation of the energy structure in achieving “dual-carbon” target.