High-temperature Thermal Power Research Articles

The thermal shock resistance of in-situ synthesized mullite absorption and storage integrated ceramics for solar thermal power generation

Solar high-temperature thermal power generation systems require thermal storage materials with excellent thermal shock resistance due to the large temperature difference during operation (in the range of 20–800 °C). In this study, mullite-based absorption and storage integrated ceramics were prepared using low-cost bauxite and kaolin as raw materials and Fe2O3 as additive. The effect of Fe2O3 on the thermal shock resistance of mullite-based ceramics was investigated. The results showed that the absorption and bending strength of sample BK4 (bauxite: 50 wt%, kaolin: 50 wt%, Fe2O3: additional 11 wt%) increased by 2.98% (89.8%) and 8.00% (147.10 MPa), with a storage thermal density of 1185.75 kJ kg−1 after 30 thermal shock cycles. The mechanism for the excellent thermal shock resistance of the ceramics is revealed from the aspect of the changes in phase and microstructure of the samples induced by the changes in the mass transfer rate during the thermal shock process. It was calculated that a unit volume of BK4 (with a raw material cost of about 154.22 USD) could generate 974.95 kW h of electricity (saving 119.92 kg of coal) when used in a solar thermal storage system.

Recent progress in the microstructurally based creep modelling of Ni-based alloy 617

ABSTRACT Solid solution strengthened (SSS) Ni-based superalloys, such as A617, show superior creep resistance at 700°C. Established for many years in land- and aero-based gas turbines, these materials are increasingly being considered for use in high-temperature thermal power plants. Apart from SSS, the creep strength in A617 stems from γ’ and carbide precipitates. In this work, a microstructurally based creep model for A617 is presented. Mobile dislocations in the model interact with fine grain-interior precipitates, and grain boundaries act as dislocation sources/sinks. The model is capable of simulating creep curves and time-to-rupture (TTR) diagrams based on the evolution of mobile dislocations. At lower stresses, the accuracy of modelled TTR can be improved by adding diffusion creep to dislocation creep. The simulated evolution of dislocation densities is realistic compared to the literature data. The reduction of area of ruptured samples was included in a damage factor, enabling the consideration of creep ductility.

Exergoeconomic and Environmental Evaluation of a Ground Source Heat Pump System for Reducing the Fossil Fuel Dependence: A Case Study in Rome

By 2050, the European Commission aims to achieve a 90% reduction in greenhouse gas emissions within the construction sector due to new targets set for greenhouse gases by the Commission. One of the most effective solutions for mitigating the environmental impact of buildings is to integrate renewable-energy systems such as air-to-water heat pumps or geothermal heat pumps. Several works in the literature investigated the advantages of heat pumps, particularly ground source heat pumps, for specific contexts. Furthermore, the evaluation can encompass not only energy considerations but also exergetic aspects, and this paper makes a significant contribution to the latter. The study presented here applies exergy analysis to a geothermal heat pump system that is interconnected with photo-voltaic and solar collector systems in a building located in Rome. Feasibility and environmental assessments were also conducted. It is evident that the exergy efficiency obtained is much lower than the energy efficiency. The heat pump demonstrates higher exergy efficiency by producing high-temperature thermal power compared to a constant dead state at relatively low temperatures. Following the heat pump, the adiabatic mixer exhibits the second highest exergy efficiency, trailed by two heat exchangers. Compared to a conventional plant case, the money saved is EUR 16,772 per year, translating to a Payback Period of 23 years. Furthermore, the average annual reduction in fossil fuel emissions is estimated at 26.2 metric tons of CO2.

A sliding-bed particle solar receiver with controlling particle flow velocity for high-temperature thermal power generation

Various impeded flow particle receivers were proposed to prolong the particle residence time but always faced the risk of thermal deterioration and the difficulty of real-time particle velocity control. Herein, we reported a novel impeded flow particle receiver to solve above problems and further have the potential to control the particle velocity distribution, which could provide a heat source with better stability, better uniformity and higher temperature for subsequent thermal power generation and other thermal applications. In this receiver, the friction along the path and the gate valves at outlet act as the obstruction structures to allow the particles to move slowly and controllably in the form of a sliding-bed, which is why we call this receiver a sliding-bed receiver. The sliding-bed receiver's structural validity and operational characteristics at different working conditions were detailly investigated with both experimental and numerical methods. Experimental results showed that the outlet particle temperature and efficiency could reach 847 °C and 77.2% under a solar simulator of 4 kW. An optical and thermal coupling model was developed and revealed an improved particle temperature of 1350 °C and efficiency of 82% under higher incident power. The effects of the effects of the incident power distribution, the particle velocity distribution and the quartz glass on aperture on the receiver performance were detailly analyzed, which could also help optimize the design and operation of other particle receivers such as free-falling particle receivers.

AirSim을 이용한 화력발전소 고온 환경의 보일러 내부 점검용 드론 개발 및 검증을 위한 시뮬레이션

본 논문은 고온 환경의 화력발전소 보일러 내부 점검용 드론 개발을 위한 선행연구로 AirSim을 이용한 고온 환경에서의 시뮬레이션을 통해 드론이 정상적인 비행이 가능한지 검증 하였다. 고온의 비행 환경에서는 공기 밀도, 점성계수 등이 상온과 달라 공력특성이 달라지며 이에 따라 드론의 비행성능 또한 달라진다. 따라서 온도 변화에 따른 프로펠러의 공력 특성의 변화를 확인하기 위해 JBLADE를 통한 프로펠러 해석과 추력 테스트, 전기추진계통 성능예측모델을 통한 동작특성 예측을 수행하였다. 그리고 해석 및 성능예측 결과를 AirSim에 적용해 시뮬레이션을 진행하고 결과 분석을 통해 기체 재설계를 진행하였다. 재설계 결과 80°C의 환경에서 호버링 시 필요한 추력을 얻기 위해 재설계 전 최대 출력의 약 65% 사용하던 것이 52%로 감소함을 확인하였다.

Cellular automata simulation on the corrosion behavior of Ni-base alloy in chloride molten salt

Chloride molten salt is required to study its corrosion behavior since it is recommended to be used as heat transfer and heat storage material in high-temperature thermal power generation system. In this paper, a simplify model was established by the reaction of diffusive corrosive gas and metal substrate in a chloride molten salt. A cellular automaton model based on the stochastic approach is adopted to simulate the uniform corrosion and the migration of metallic element. The corrosion behavior is also simulated considering the practical working condition, such as oxygen, moisture and so on. By comparing the simulation results with experimental data, it proves that the cellular automata simulation is an effective alternative method to describe the high-temperature corrosion process of molten salts. Simulation results of 25,000 time steps is taken as a comparison of the 21-day corrosion which reflects the Cr distribution, and the growth of corrosion layer with the migration of Cr element was reproduced. The change of corrosion layer thickness is similar to the mass loss. The simulation method provides insight on the distribution of corrosion products, corrosion kinetics and morphologies for the long-term application.

Integrated Electrochemical-Thermal System for High Efficiency and Low Cost Hydrogen Compression

Three approaches to transport and delivery hydrogen at large scale have been identified by the US Department of Energy [1]. Each of the approaches requires the presence of high-pressure hydrogen compression systems. Currently DOE set its fueling station pressure targets at approximately 875 bar with flow rates up to 100 kg/h [1]. Among the other targets for hydrogen compression systems, DOE identified the uninstalled cost target for the FY 2020 at 275,000 $, the energy requirement at 1.6 kWh/kg, availability equal to 85% and annual maintenance cost equal to 4% of the uninstalled cost[1] [1]. The current mechanical compressors cannot achieve the DOE targets and they have several additional drawbacks working at the specified operating conditions, especially in terms of reliability, efficiency and investment and lifetime costs. Valid alternative processes are represented by electrochemical compression (EC) systems and thermal compression systems, exploiting the properties of suitable hydrogen absorption materials. A two-stage hybrid compressor system is proposed, with a first stage (lower pressure) EC, coupled in series with a second stage (higher pressure) metal hydride (MH) thermal compression system. The EC operates at compression ratios on the order of 10-20, reaching pressures of about 100-200 bar. Molecular hydrogen is oxidized at the anode producing protons and electrons. They are driven through the proton exchange membrane and combine with electrons at the cathode to deliver high pressure hydrogen. The outlet pressure is maintained at relatively low values (≤ 100-200 bar) in order to avoid hydrogen back diffusion. The second stage of the system, operating at higher pressures, is comprised of a thermal compression system, based on MH materials. Such compounds absorb hydrogen in an exothermic chemical reaction and release the absorbed hydrogen in the reverse endothermic chemical reaction. Their equilibrium pressure is a direct exponential function of the operating temperature. Therefore, providing high temperature thermal power during the desorption process, the hydrogen pressure can be increased without the use of electricity. The paper presents the results obtained from a project funded by DOE, involving Greenway Energy, Savannah River National Laboratory and Sustainable Innovation. An electrochemical system, using Nafion-117® membrane, was successfully tested at high operating temperatures (≈ 150 °C) and pressures up to 100 bar, representing the baseline configuration for the first stage of the compression system. The second stage of the compressor, based on metal hydride systems, was tested using a commercially available Ti1.1CrMn material as the baseline alloy, achieving pressures on the order of 500-600 bar at temperatures on the order of 150 °C. A novel heat transfer system was also identified and designed to recover the available waste heat from the electrochemical system and drive the thermal compression process in the MH system. Overall system efficiency and costs were also assessed, with the results presented and discussed.

Integrated Hybrid Electrochemical and Thermal Metal Hydride Systems for Low-Cost and Efficient High Pressure Hydrogen Compressors

The United States Department of Energy (DOE) has identified three scenarios to transport and delivery hydrogen at large scale [1]. Each of the approaches requires the presence of high pressure hydrogen systems. Currently DOE set its fueling station pressure targets at approximately 875 bar with flow rates up to 100 kg/h [1]. Among the other targets for hydrogen compression systems, DOE identified the uninstalled cost target for the FY 2020 at 275,000 $, the energy requirement at 1.6 kWh/kg, availability equal to 85% and annual maintenance cost equal to 4% of the uninstalled cost[1] [1]. The current mechanical compressors cannot achieve the DOE targets and they have several additional drawbacks working at the specified operating conditions. Valid alternative processes are represented by electrochemical compression (EC) systems and thermal compression systems, exploiting the properties of suitable hydrogen absorption materials. Here, an alternative two-stage hybrid compressor system is proposed, with a first stage (lower pressure) EC, coupled in series with a second stage (higher pressure) metal hydride (MH) thermal compression system. The EC operates at compression ratios on the order of 10-20, reaching pressures of about 100-200 bar. Molecular hydrogen is oxidized at the anode producing protons and electrons. They are driven through the proton exchange membrane and combine with electrons at the cathode to deliver high pressure hydrogen. The outlet pressure is maintained at relatively low values (≤ 100-200 bar) in order to avoid hydrogen back diffusion. The second stage of the system, operating at higher pressures, is comprised of a thermal compression system, based on MH materials. Such compounds absorb hydrogen in an exothermic chemical reaction and release the absorbed hydrogen in the reverse endothermic chemical reaction. Their equilibrium pressure is a direct exponential function of the operating temperature, determined by the Van’t Hoff equation. Therefore, providing high temperature thermal power during the desorption process, the hydrogen pressure can be increased without the use of electricity. The paper presents recent results obtained from the project, funded by the DOE-FCTO, involving Greenway Energy, Savannah River National Laboratory and Sustainable Innovation. A techno-economic model of the hybrid system was developed and adopted to identify the initial baseline system configuration. Several MEA concepts have been examined for the EC, to find the optimized solution to be coupled with the MH system. The baseline system is currently based on Nafion(R) 117 membranes, operating at temperatures of 150 oC and pressures up to 100 bar. Results show suitable voltage and current density values of the EC, reaching adequate technical performance of the EC system and ability to be paired with the MH compressor. Long term tests of the EC system are planned to be run, to assess the performance time degradation of the Nafion(R) membrane at the operating conditions of interest. Specific techno-economic analyses have also been carried out for the MH system, identifying two existing MH material formulations, based on Ti hydrides, as the baseline candidates for the current application. A new finned tube configuration was selected to realize an effective heat exchange between the heat transfer fluid (i.e. water at pressures of 7-7.5 bar) and the MH material. Detailed transport models were developed to simulate the performance of the MH configuration. The adopted solution demonstrated the ability to transfer the heating and cooling (sensible and latent) power required to desorb and absorb hydrogen in the MH system in about 10 minutes for half a cycle. A matching operating point between the EC system and the MH system was also identified to recover the waste heat available from the EC system into the MH system at about 130-150 oC, without any additional external heating power. The system, integrating an electrochemical compressor with a pure thermal compressor, demonstrated the potential to closely approach the DOE 2020 technical targets for high pressure compression.

Hybrid Thermo-Electrochemical System for Efficient and Low Cost High Pressure Hydrogen Compression

The United States Department of Energy (DOE) has identified three means to transport and delivery hydrogen at large scale [1]. Each of the approaches requires the presence of high pressure hydrogen systems. Currently DOE set its fueling station pressure targets at approximately 875 bar with flow rates up to 100 kg/h [1]. Among the other targets for hydrogen compression systems, DOE identified the uninstalled cost target for the FY 2020 at 275,000 $, the energy requirement at 1.6 kWh/kg, availability equal to 85% and annual maintenance cost equal to 4% of the uninstalled cost[1] [1]. The current mechanical compressors cannot achieve the DOE targets and they have several additional drawbacks working at the specified operating conditions. Valid alternative processes are represented by electrochemical compression (EC) systems and thermal compression systems, exploiting the properties of suitable hydrogen absorption materials. Here, an alternative two-stage hybrid compressor system is proposed, with a first stage (lower pressure) EC, coupled in series with a second stage (higher pressure) metal hydride (MH) thermal compression system. The EC operates at compression ratios on the order of 10-20, reaching pressures of about 100-200 bar. Molecular hydrogen is oxidized at the anode producing protons and electrons. They are driven through the proton exchange membrane and combine with electrons at the cathode to deliver high pressure hydrogen. The outlet pressure is maintained at relatively low values (≤ 100-200 bar) in order to avoid hydrogen back diffusion. The second stage of the system, operating at higher pressures, is comprised of a thermal compression system, based on MH materials. Such compounds absorb hydrogen in an exothermic chemical reaction and release the absorbed hydrogen in the reverse endothermic chemical reaction. Their equilibrium pressure is a direct exponential function of the operating temperature, determined by the Van’t Hoff equation. Therefore, providing high temperature thermal power during the desorption process, the hydrogen pressure can be increased without the use of electricity. The paper presents the results obtained from two combined projects, funded by DOE, involving Greenway Energy, Savannah River National Laboratory, University of South Carolina, NIST and Sustainable Innovation. A techno-economic high level model of the hybrid system has been developed in order to assess the performance of the system under different operating conditions and to evaluate the existing gap with the DOE techno-economic targets. Several MH materials have been examined, including rare earth based materials (such as LaNi5, MmNi5, etc) and Ti based MHs. The objective of the analysis was the minimization of: (1) operating temperature, (2) material cost and (3) required thermal power (i.e. material reaction enthalpy minimization). Three main existing material formulations, based on Ti compounds, have been downselected as the candidate materials having the best potential for the current application. The selected materials can reach equilibrium pressures on the order of 900 bar at temperatures on the order of 100-150 °C. Several MEA concepts have been examined for the EC, to find the optimized solution to be coupled with the MH system. Mainly the performance of systems comprised of more traditional PFSA membranes (such as Nafion® membranes) was compared with the one of more innovative polybenzimidazole (PBI) membranes. The latter membranes have shown long term stability, carrying out selected experimental tests. They also showed several other advantages over Nafion® membranes, especially in terms of integrated system performance. EC systems equipped with PBI membranes operating at about 170 °C and at current density of about 2.5 A/cm2 can provide the required thermal power to drive the MH system, recovering the waste power available from the EC system. This results in high energetic and exergetic efficiencies with no need for external thermal power. The hybrid system can closely approach the DOE targets even with the currently available systems, equipped with PBI membranes. The main existing gaps between the targets and the current performance have been identified and analyzed. Specific analyses have been carried out for the MH system, demonstrating that a material with reaction enthalpy on the order of 22 kJ/molH2 and raw material cost of about 1.5 $/kg can meet the targets. A high-throughput genome based technique has been developed and validated, including material synthesis, characterization and numerical modeling prediction. The technique is used and applied to develop new low reaction enthalpy and, especially, low cost MH materials for hydrogen compression systems.

Installation of a Concentrated Solar Power System for the Thermal Needs of Buildings or Industrial Processes

Solar energy is one of the main alternatives to carbon-intensive sources of energy. However, limited attention has been devoted to small-scale (<10 kW) concentrated solar power systems, which are capable to provide high-temperature heat to buildings or industrial processes. In this work, we describe the concentrated solar power system (7.4 kW thermal power) with dual axis solar tracker installed at Politecnico di Torino. The solar concentrator system is coupled to a sensible heat storage by a plate heat exchanger. Here, we provide preliminary data on the system efficiency and compare it to typical values obtained by flat plates or evacuated tubes collectors. The generated high-temperature thermal power is suitable for both domestic hot water, heating and cooling, and industrial purposes.

Design, simulation and experimental characterization of a novel parabolic trough hybrid solar photovoltaic/thermal (PV/T) collector

A novel hybrid solar concentrated photovoltaic thermal (PV/T) collector is designed, simulated, and tested. The PV/T system uses a parabolic trough to focus sunlight towards a nonimaging compound parabolic concentrator (CPC) that is formed of single junction Gallium Arsenide (GaAs) solar cells to simultaneously generate electricity and high temperature thermal power. The GaAs cells generate electricity from high energy photons and reflect low energy photons towards the high temperature absorber, thus maximizing the exergy output of the system. The two-stage design also allows the thermal absorber to reach a geometric concentration ratio of ∼60×, which is significantly higher than other PV/T systems and enables the absorber to reach high temperatures even under partial utilization of the solar spectrum. The modelled exergy efficiency with a thermal absorber operating at 500 °C is 37%. In the experimental setup, the maximum outlet temperature reached was 365 °C with a thermal efficiency of around 37%. The direct solar to electric efficiency from the GaAs cells was 8%. This design is capable of producing electricity directly along with high temperature thermal energy that can be stored for dispatchable electricity production and has the potential to significantly improve the exergy efficiency of parabolic troughs plants.

Study on an Improved Solar though Concentration PV/T System with an Extra Temperature Raising Stage

This paper proposes “an improved solar though concentration PV/T system with an extra temperature raising stage”, which adds reheating stage on the basis of cogeneration to achieve high-quality power output and high-temperature thermal power output. Two systems have been established. Output characteristics of 1.8m2 cogeneration and 15m2 extra temperature raising stage system with different opening widths of mirror are tested respectively through experiment, as well as output performance of 30m2 extra temperature raising stage system.