Increasing the Efficiency and Level of Environmental Safety of Pro-Environmental City Heat Supply Technologies by Low Power Nuclear Plants

In connection with the current prospect of decarbonization of coal energy through the use of small nuclear power plants (SNPPs) at existing TPPs as heat sources for heat supply to municipal heating networks, there is a technological need to improve heat supply schemes to increase their environmental friendliness and efficiency. The paper proves the feasibility of using the heat-feeding mode of ASHPs for urban heat supply by heating the network water with steam taken from the turbine. The ratio of electric and thermal power of a “nuclear” combined heat and power plant is given. The advantage of using a heat pump, which provides twice as much electrical power with the same heat output, is established. Taking into account that heat in these modes is supplied with different potential, the energy efficiency was used to compare these options. To increase the heat supply capacity, a scheme with the use of a high-pressure heater in the backpressure mode and with the heating of network water with hot steam was proposed. Heat supply from ASHPs is efficient and environmentally friendly even in the case of significant remoteness of heat consumers.

Performance of Gas-Steam Combined Cycle Cogeneration Units Influenced by Heating Network Terminal Steam Parameters

The determination of source-side extracted heating parameters is of great significance to the economic operation of cogeneration systems.This paper investigated the coupling performance of a cogeneration heating and power system multidimensionally based on the operating characteristics of the cogeneration units,the hydraulic and thermodynamic characteristics of the heating network,and the energy loads.Taking a steam network supported by a gas-steam combined cycle cogeneration system as the research case,the interaction effect among the source-side prime movers,the heating networks,and the terminal demand thermal parameters were investigated based on the designed values,the plant testing data,and the validated simulation.The operating maps of the gas-steam combined cycle cogeneration units were obtained using THERMOFLEX,and the minimum source-side steam parameters of the steam network were solved using an inverse solution procedure based on the hydro-thermodynamic coupling model.The cogeneration operating maps indicate that the available operating domain considerably narrows with the rise of the extraction steam pressure and flow rate.The heating network inverse solution demonstrates that the source-side steam pressure and temperature can be optimized from the originally designed 1.11 MPa and 238.8°C to 1.074 MPa and 191.15°C,respectively.Under the operating strategy with the minimum source-side heating parameters,the power peak regulation depth remarkably increases to 18.30%whereas the comprehensive thermal efficiency decreases.The operation under the minimum source-side heating steam parameters can be superior to the originally designed one in the economy at a higher price of the heating steam.At a fuel price of$0.38/kg and the power to fuel price of 0.18 kg/(kW·h),the critical price ratio of heating steam to fuel is 119.1 kg/t.The influence of the power-fuel price ratio on the economic deviation appears relatively weak.

Experimental Study on the Performance of ORC System Based on Ultra-Low Temperature Heat Sources

This paper discussed the experimental results of the performance of an organic Rankine cycle(ORC)system with an ultra-low temperature heat source.The low boiling point working medium R134a was adopted in the system.The simulated heat source temperature(SHST)in this work was set from 39.51°C to 48.60°C by the simulated heat source module.The influence of load percentage of simulated heat source(LPSHS)between 50%and 70%,the rotary valve opening(RVO)between 20%and 100%,the resistive load between 36Ωand 180Ωor the no-load of the generator,as well as the autumn and winter ambient temperature on the system performance were studied.The results showed that the stability of the system was promoted when the generator had a resistive load.The power generation(PG)and generator speed(GS)of the system in autumn were better than in winter,but the expander pressure ratio(EPR)was lower than in winter.Keep RVO unchanged,the SHST,the mass flow rate(MFR)of the working medium,GS,and the PG of the system increased with the increasing of LPSHS for different generator resistance load values.When the RVO was 60%,LPSHS was 70%,the SHST was 44.15°C and the resistive load was 72Ω,the highest PG reached 15.11 W.Finally,a simulation formula was obtained for LPSHS,resistance load,and PG,and its correlation coefficient was between 0.9818 and 0.9901.The formula can accurately predict the PG.The experimental results showed that the standard deviation between the experimental and simulated values was below 0.0792,and the relative error was within±5%.

Model and Design of Cogeneration System for Different Demands of Desalination Water, Heat and Power Production

In order to improve the energy efficiency, reduce the CO2 emission and decrease the cost, a cogenera- tion system for desalination water, heat and power production was studied in this paper. The superstructure of the cogeneration system consisted of a coal-based thermal power plant （TPP）, a multi-stage flash desalination （MSF） module and reverse osmosis desalination （RO） module. For different demands of water, heat and power production, the corresponding optimal production structure was different. After reasonable simplification, the process model ot each unit was built. The economical model, including the unit investment, and operation and maintenance cost, was presented. By solving this non-linear programming （NLP） model, whose objective is to minimize the annual cost, an optimal cogeneration system can be obtained. Compared to separate production systems, the optimal system can reduce 16.1%-21.7% of the total annual cost. showing this design method was effective.

Optimal Scheduling Method of Cogeneration System with Heat Storage Device Based on Memetic Algorithm

Electric-heat coupling characteristics of a cogeneration system and the operating mode of fixing electricity with heat are the main reasons for wind abandonment during the heating season in the Three North area.To improve the wind-power absorption capacity and operating economy of the system,the structure of the system is improved by adding a heat storage device and an electric boiler.First,aiming at the minimum operating cost of the system,the optimal scheduling model of the cogeneration system,including a heat storage device and electric boiler,is constructed.Second,according to the characteristics of the problem,a cultural gene algorithm program is compiled to simulate the calculation example.Finally,through the system improvement,the comparison between the conditions before and after and the simulation solutions of similar algorithms prove the effectiveness of the proposed scheme.The simulation results show that adding the heat storage device and electric boiler to the scheduling optimization process not only improves the wind power consumption capacity of the cogeneration system but also reduces the operating cost of the system by significantly reducing the coal consumption of the unit and improving the economy of the system operation.The cultural gene algorithm framework has both the global evolution process of the population and the local search for the characteristics of the problem,which has a better optimization effect on the solution.

Off-Design Simulation of a CSP Power Plant Integrated with aWaste Heat Recovery System

Concentrating Solar Power(CSP)plants offer a promising way to generate low-emission energy.However,these plants face challenges such as reduced sunlight during winter and cloudy days,despite being located in high solar radiation areas.Furthermore,their dispatch capacities and yields can be affected by high electricity consumption,particularly at night.The present work aims to develop an off-design model that evaluates the hourly and annual performances of a parabolic trough power plant(PTPP)equipped with a waste heat recovery system.The study aims to compare the performances of this new layout with those of the conventional Andasol 1 plant,with the aim of assessing the improvements achieved in the new design.Based on the results,it can be concluded that the new layout has increased the annual generated power to almost 183 GWh(an increase of about 7.60% is achieved compared to the Andasol 1 layout that generates 169 GWh annually).Additionally,the proposed installation has achieved an efficiency of 20.55%,which represents a 7.87% increase compared to the previous design(19.05%).The Levelized Cost of Electricity(LCOE)of the new layout has been reduced by more than 5.8% compared to the Andasol 1 plant.Specifically,it has decreased from 13.11 to 12.35 c/kWh.This reduction in LCOE highlights the improved cost-effectiveness of the newlayout,making it amore economically viable option for generating electricity compared to the conventional Andasol 1 plant.

Simulation and performance analysis of organic Rankine cycle combined heat and power system

To improve the overall thermal efficiency of the organic Rankine cycle（ ORC）, a simulation study was carried out for a combined heat and power（ CHP） system, using the Redlich-Kuang-Soave（ RKS） equation of state. In the system,R245 fa was selected as the working fluid. A scroll expander was modeled with empirical isentropic expansion efficiency.Plate heat exchangers were selected as the evaporator and the condenser, and detailed heat transfer models were programmed for both one-phase and two-phase regions. Simulations were carried out at seven different heat source temperatures（ 80,90, 100, 110, 120, 130, 140 ℃） in combination with eight different heat sink temperatures（ 20, 25, 30, 35, 40, 45, 50,55 ℃）. Results showthat in the ORC without an internal heat exchanger（ IHE）, the optimum cycle efficiencies are in the range of 7. 0% to 7. 3% when the temperature differences between the heat source and heat sink are in the range of 70 to90 ℃. Simulations on CHP reveal that domestic hot water can be produced when the heat sink inlet temperature is higher than40 ℃, and the corresponding exergy efficiency and overall thermal efficiency are 29% to 56% and 87% to 90% higher than those in the non-CHP ORC, respectively. It is found that the IHE has little effect on the improvement of work output and efficiencies for the CHP ORC.

Case Studies of Energy Saving and CO₂Reduction by Cogeneration and Heat Pump Systems

This paper describes two case studies: 1) a cogeneration system of a hospital and 2) a heat pump system installed in an aquarium that uses seawater for latent heat storage. The cogeneration system is an autonomous system that combines the generation of electrical, heating, and cooling energies in a hospital. Cogeneration systems can provide simultaneous heating and cooling. No technical obstacles were identified for implementing the cogeneration system. The average ratio between electric and thermal loads in the hospital was suitable for the cogeneration system operation. An analysis performed for a non-optimized cogeneration system predicted large potential for energy savings and CO2 reduction. The heat pump system using a low-temperature unutilized heat source is introduced on a heat source load responsive heat pump system, which combines a load variation responsive heat pump utilizing seawater with a latent heat-storage system (ice and water slurry), using nighttime electric power to level the electric power load. The experimental coefficient of performance (COP) of the proposed heat exchanger from the heat pump system, assisted by using seawater as latent heat storage for cooling, is discussed in detail.

Thermo-economic Investigation of an Enhanced Geothermal System Organic Rankine Cycle and Combined Heating and Power System

As a potentially viable renewable energy, Enhanced Geothermal Systems(EGSs) extract heat from hot dry rock(HDR) reservoirs to produce electricity and heat, which promotes the progress towards carbon peaking and carbon neutralization. The main challenge for EGSs is to reduce the investment cost. In the present study, thermo-economic investigations of EGS projects are conducted. The effects of geofluid mass flow rate, wellhead temperature and loss rate on the thermo-economic performance of the EGS organic Rankine cycle(ORC) are studied. A performance comparison between EGS-ORC and the EGS combined heating and power system(CHP) is presented. Considering the CO_(2)emission reduction benefits, the influence of carbon emission trading price on the levelized cost of energy(LCOE) is also presented. It is indicated that the geofluid mass flow rate is a critical parameter in dictating the success of a project. Under the assumed typical working conditions, the LCOE of EGS-ORC and EGS-CHP systems are 24.72 and 16.1 cents/k Wh, respectively. Compared with the EGS-ORC system, the LCOE of the EGS-CHP system is reduced by 35%. EGS-CHP systems have the potential to be economically viable in the future. With carbon emission trading prices of 12.76 USD/ton, the LCOE can be reduced by approximately 8.5%.

Fabrication and testing of phase change heat sink for high power LED

A novel phase change heat sink was fabricated for packaging cooling of high power light emitting diode （LED）. 3D structures as enhanced boiling structure in the evaporation surface were composed of a spiral micro-groove along circumferential direction and radial micro-grooves which were processed by ploughing-extrusion （P-E） and stamping, respectively. Meanwhile, the cycle power of refrigerant was supplied by wick of sintered copper powder on internal surface of phase change heat sink. Operational characteristics were tested under different heat loads and refrigerants. The experimental results show that phase change heat sink is provided with a good heat transfer capability and the temperature of phase change heat sink reaches 86.8 ℃ under input power of 10 W LED at ambient temperature of 20 ℃.

Water, Air Emissions, and Cost Impacts of Air-Cooled Microturbines for Combined Cooling, Heating, and Power Systems： A Case Study in the Atlanta Region

The increasing pace of urbanization means that cities and global organizations are looking for ways to increase energy efficiency and reduce emissions. Combined cooling, heating, and power （CCHP） systems have the potential to improve the energy generation efficiency of a city or urban region by providing energy for heating, cooling, and electricity simultaneously. The purpose of this study is to estimate the water consumption for energy generation use, carbon dioxide （CO2） and NOx emissions, and economic impact of implementing CCHP systems for five generic building types within the Atlanta metropolitan region, under various operational scenarios following the building thermal （heating and cooling） demands. Operating the CCHP system to follow the hourly thermal demand reduces CO2 emissions for most building types both with and without net metering. The system can be economically beneficial for all building types depending on the price of natural gas, the implementation of net metering, and the cost structure assumed for the CCHP system. The greatest reduction in water consumption for energy production and NOx emissions occurs when there is net metering and when the system is operated to meet the maximum yearly thermal demand, although this scenario also results in an increase in greenhouse gas emissions and, in some cases, cost. CCHP systems are more economical for medium office, large office, and multifamilv residential buildings.

Robust optimal dispatch strategy of integrated energy system considering CHP-P2G-CCS

Integrated energy systems(IESs)can improve energy efficiency and reduce carbon emissions,essential for achieving peak carbon emissions and carbon neutrality.This study investigated the characteristics of the CHP model considering P2G and carbon capture systems,and a two-stage robust optimization model of the electricity-heat-gascold integrated energy system was developed.First,a CHP model considering the P2G and carbon capture system was established,and the electric-thermal coupling characteristics and P2G capacity constraints of the model were derived,which proved that the model could weaken the electric-thermal coupling characteristics,increase the electric power regulation range,and reduce carbon emissions.Subsequently,a two-stage robust optimal scheduling model of an IES was constructed,in which the objective function in the day-ahead scheduling stage was to minimize the start-up and shutdown costs.The objective function in the real-time scheduling stage was to minimize the equipment operating costs,carbon emission costs,wind curtailment,and solar curtailment costs,considering multiple uncertainties.Finally,after the objective function is linearized with a ψ-piecewise method,the model is solved based on the C&CG algorithm.Simulation results show that the proposed model can effectively absorb renewable energy and reduce the total cost of the system.

Optimized scheduling of integrated energy systems for low carbon economy considering carbon transaction costs

With the introduction of the“dual carbon”goal and the continuous promotion of low-carbon development,the integrated energy system(IES)has gradually become an effective way to save energy and reduce emissions.This study proposes a low-carbon economic optimization scheduling model for an IES that considers carbon trading costs.With the goal of minimizing the total operating cost of the IES and considering the transferable and curtailable characteristics of the electric and thermal flexible loads,an optimal scheduling model of the IES that considers the cost of carbon trading and flexible loads on the user side was established.The role of flexible loads in improving the economy of an energy system was investigated using examples,and the rationality and effectiveness of the study were verified through a comparative analysis of different scenarios.The results showed that the total cost of the system in different scenarios was reduced by 18.04%,9.1%,3.35%,and 7.03%,respectively,whereas the total carbon emissions of the system were reduced by 65.28%,20.63%,3.85%,and 18.03%,respectively,when the carbon trading cost and demand-side flexible electric and thermal load responses were considered simultaneously.Flexible electrical and thermal loads did not have the same impact on the system performance.In the analyzed case,the total cost and carbon emissions of the system when only the flexible electrical load response was considered were lower than those when only the flexible thermal load response was taken into account.Photovoltaics have an excess of carbon trading credits and can profit from selling them,whereas other devices have an excess of carbon trading and need to buy carbon credits.

Simulation Analysis of Flue Gas Waste Heat Utilization Retrofit Based on ORC System

Recovery of waste heat from boiler flue gas is an effective way to improve energy utilization efficiency.Taking a heating station heating project as an example,the existing heating system of this heating station was analyzed for its underutilized flue gas waste heat and low energy utilization rate.Rankine cycle is an effective waste heat recovery method,and a steam boiler organic Rankine cycle(ORC)cogeneration waste heat utilization method is proposed.The system model simulation is constructed and verified.First,a thermodynamic model was constructed in MATLAB and five suitable work gases were selected to analyze the effects of evaporation temperature and condensation temperature on the network and thermal efficiency of the waste heat cycle power system.Secondly,the ORC model is invoked in TRNSYS to construct the improved cogeneration system,and the rationality of the remaining heat utilization methods is determined by calculating and analyzing the thermal performance,economy,and environmental protection of the improved system.The simulation results show that the system can generate about 552,000 kWh of electricity per year,and improving the energy utilization rate from 0.72 to 0.78.

Numerical and theoretical investigations of heat transfer characteristics in helium-xenon cooled microreactor core

Helium-xenon cooled microreactors are a vital technological solution for portable nuclear reactor power sources.To exam-ine the convective heat transfer behavior of helium-xenon gas mixtures in a core environment,numerical simulations are conducted on a cylindrical coolant channel and its surrounding solid regions.Validated numerical methods are used to determine the effect and mechanisms of power and its distribution,inlet temperature and velocity,and outlet pressure on the distribution and change trend of the axial Nusselt number.Furthermore,a theoretical framework that can describe the effect of power variation on the evolution of the thermal boundary layer is employed to formulate an axial distribution cor-relation for the Nusselt number of the coolant channel,under the assumption of a cosine distribution for the axial power.Based on the simulation results,the correlation coefficients are determined,and a semi-empirical relationship is identified under the corresponding operating conditions.The correlation derived in this study is consistent with the simulations,with an average relative error of 5.3%under the operating conditions.Finally,to improve the accuracy of the predictions near the entrance,a segmented correlation is developed by combining the Kays correlation with the aforementioned correlation.The new correlation reduces the average relative error to 2.9%and maintains satisfactory accuracy throughout the entire axial range of the channel,thereby demonstrating its applicability to turbulent heat transfer calculations for helium-xenon gas mixtures within the core environment.These findings provide valuable insights into the convective heat transfer behavior of a helium-xenon gas mixture in a core environment.

Optimizing Grids Demand Reduction through Enhanced Heat Transfer in Low-Temperature Waste Heat Driven ORC Systems

With increasing awareness of energy conservation and environmental protection, the Organic Rankine Cycle (ORC) system has gained significant attention. This technology enables the recovery of industrial waste heat, waste incineration heat, and renewable energy sources such as geothermal heat, biomass energy, and solar energy at lower temperatures. However, the low-grade heat source utilized in ORC systems faces a challenge to achieving high power generation efficiency and output power. Therefore, enhancing the power generation capacity of ORC systems is a key research focus in this field. An entranced heat exchanger ORC system with the screw expander driven by the low-temperature heat source is established to investigate the relevant performance. Hot water temperature from 77°C to 132°C is adopted for performance analysis, while the environmental temperature is approximately 25°C. Refrigerant R245fa is selected as the working fluid, and the screw expander is employed for power generation. It is worth noting that the entranced heat exchanger ORC system has significant potential for low-temperature heat recovery. Experimental results indicate that the maximum power output is 12.83 kW, which is obtained at around 105°C hot water inlet temperature. Correspondingly, the average power output remains 11.75 kW, revealing the system’s high stability for power generation. The implementation of a plate heat exchanger for enhanced heat transfer has enabled a 50% reduction in system size compared to traditional shell-tube type ORC systems. Besides, economic calculations demonstrate substantial benefits associated with the ORC system. The calculations indicate an internal benefit of 560,000 RMB/year, accompanied by notable external benefits such as an energy saving and emission reduction potential of up to 784 t CO2 per year. Moreover, the payback period is 2.23 years. It shows a remarkable improvement in terms of performance and excellent economic benefits. As a result, the novel ORC presents a promising alternative for low-grade heat utilization as compared to conventional small-scale ORC systems.

Analysis and Economic Evaluation of Hourly Operation Strategy Based on MSW Classification and LNG Multi-Generation System

In this study,a model of combined cooling,heating and power system with municipal solid waste(MSW)and liquefied natural gas(LNG)as energy sources was proposed and developed based on the energy demand of a large community,andMSW was classified and utilized.The systemoperated by determining power by heating load,and measures were taken to reduce operating costs by purchasing and selling LNG,natural gas(NG),cooling,heating,and power.Based on this system model,three operation strategies were proposed based on whether MSW was classified and the length of kitchen waste fermentation time,and each strategy was simulated hourly throughout the year.The results showed that the strategy of MSW classified and centralized fermentation of kitchen waste in summer(i.e.,strategy 3)required the least total amount of LNG for the whole year,which was 47701.77 t.In terms of total annual cost expenditure,strategy 3 had the best overall economy,with the lowest total annual expenditure of 2.7730×108 RMB at LNG and NG unit prices of 4 and 4.2 RMB/kg,respectively.The lower heating value of biogas produced by fermentation of kitchen waste from MSW being classified was higher than that of MSW before being classified,so the average annual thermal economy of the operating strategy of MSW being classified was better than that of MSW not being classified.Among the strategies in which MSW was classified and utilized,strategy 3 could better meet the load demand of users in the corresponding season,and thus this strategy had better thermal economy than the strategy of year-round fermentation of kitchen waste(i.e.,strategy 2).The hourly analysis data showed that the net electrical efficiency of the system varies in the same trend as the cooling,heating and power loads in all seasons,while the relationship between the energy utilization efficiency and load varied from season to season.This study can provide guidance for the practical application of MSW being classified in the system.

Optimization of Intermittent Variable Power Microwave Heating Process for Blueberry Pulp

To improve heating uniformity and anthocyanin content of the blueberry pulp under microwave heating,the intermittent variable power microwave heating technology was introduced in the study.The effects of technology parameters in terms of high microwave intensity heating time,intermittent time,low microwave intensity and low microwave intensity heating time on the blueberry pulp quality parameters(heating uniformity,average moisture content,the highest temperature and anthocyanin content)were investigated by using the response surface method.The results showed that the longer heating time under different microwave intensities resulted in the poorer heating uniformity.The intermittent stage promoted heat and mass transfer within the pulp and reduced the temperature difference and moisture gradient within the pulp,which enhanced desired uniformity of temperature and moisture distribution before entering the low microwave intensity heating stage.Therefore,the longer the intermittent time,the greater the heating uniformity.The optimal parameters were developed as high microwave intensity of 4 W·g^(-1),high microwave intensity heating time of 9.86 min,intermittent time of 10 min,low microwave intensity of 2.2 W·g^(-1)and low microwave intensity heating time of 6 min.This research might provide guidance for microwave heating berry fruits.

Improving the performance of a thermoelectric power system using a flat-plate heat pipe

A gravitational flat-plate heat pipe is designed and fabricated in this paper to serve as a heat spreader to diffuse the local heat source to the hot side of the thermoelectric power module.Based on this, an experimental test for the thermoelectric power generation system is conducted to study the influences of the heat spreader on the temperature uniformity and power generation performance when exposing to a local heat source.In addition,the effects of the heating power, inclination angle, and local heat source size on the power generation performance of the thermoelectric power module using a flat-plate heat pipe as a heat spreader are examined and compared with that using a metal plate.The results indicate that the gravitational flat-plate heat pipe has considerable advantages over the metal plate in the temperature uniformity.The superiority of temperature uniformity in the improvement of power generation performance for the thermoelectric power system using a heat pipe is demonstrated.Particularly, the heat pipe shows good adaptability to placement mode and the local heat source size, which is beneficial to the application in the thermoelectric power generation.

A Financial Approach to Evaluate an Optimized Combined Cooling, Heat and Power System

Iran’s removing subsidy from energy carrier in four years ago leads to spike electricity price dramatically. This abrupt change increases the interest on distributed generation (DG) because of its several benefits such as lower electricity generation price. In Iran among all type of DGs, because of wide natural gas network infrastructure and several incentives that government legislated to support combined cooling, heat and power (CCHP) investors, this type of technology is more prevalent in comparison with other technologies. Between existing CCHP technologies, certain economic choices are to be taken into account. For different buildings with different load curves, suitable size and operation of CCHP should be calculated to make the project more feasible. If CCHP does not well suited for a position, then the whole energy efficiency would be plunged significantly. In this paper, a model to find the optimal size and operation of CCHP and auxiliary boiler for any users is proposed by considering an integrated view of electricity and natural gas network using GAMS software. Then this method is applying for a hospital in Tehran as a real case study. Finally, by applying COMFAR III software, useful financial parameters and sensitivity analysis are calculated.