Joule-Brayton Cycle Research Articles

A Dual-Mode Hybrid System Combining Solar Thermal With Pumped Thermal Energy Storage

A hybrid system that delivers renewable electricity generation and electricity storage capabilities is introduced. This dual-mode hybrid system is based on Pumped Thermal Energy Storage (PTES) which uses a heat pump to convert electricity into thermal energy that is transferred to silica particles which are stored in concrete silos. The stored heat is later converted back to electricity in a heat engine. The heat pump and heat engine use a closed Joule-Brayton cycle and fluidized bed heat exchangers. If the PTES system is co-located with an array of concentrating solar mirrors and a particle receiver, then the silica particles may also be heated up by the concentrating solar power (CSP) system. The PTES heat engine may also be used to convert the stored solar heat into electricity, thereby sharing this system between the PTES and CSP systems and reducing costs. However, this requires careful management of the heat engine off-design parameters. A thermodynamic model is used to evaluate the performance of the dual mode PTES-CSP hybrid system. The model accounts for turbomachinery efficiency, and approach temperature and pressure loss in heat exchangers, as well as other sources of inefficiency, such as motor-generator losses, and air fan power. The hybrid system also requires the evaluation of the turbomachinery efficiency and pressure ratio at off-design conditions since the CSP system operates over different temperature ratios than the Carnot Battery. Several design variables and design modifications are investigated, such as pressure ratios and maximum temperatures.

Study on a novel hydrogen liquification process applying mixed-refrigerant for pre-cooling and cryogenics

Reducing the energy consumption of hydrogen liquefaction process is an urgent issue to improve the economy of liquid hydrogen transportation. A novel large-scale hydrogen liquefaction system, with a capacity of 100 TPD, is proposed in this paper. The pre-cooling system is composed of a mixed-refrigerant (MR) refrigeration cycle and a CO2–NH3 cascade refrigeration cycle. Due to the auxiliary pre-cooling effect of the CO2–NH3 cascade cycle, temperature of the pre-cooled hydrogen can be as low as −200.9 °C. A modified MR Joule Brayton cycle with an additional compressor is used as the cryogenic system to cool the hydrogen from −200.9 °C to −252.2 °C. Besides, a four-stage ortho-to-para conversion (OPC) process is utilized. Performance of the novel system is investigated and optimized using the Aspen HYSYS software. According to the results, the lowest specific energy consumption (SEC) of the proposed process is 6.15 kWh/kgLH2 and the exergy efficiency is as high as 67.4%. Based on the energy analysis, the best system coefficient of performance is 0.1751 with a 96.3% of p-H2 in the liquid hydrogen. In addition, compared to the initial conceptual system, the proposed system exhibits significant performance enhancements, a 20% reduction in SEC and a 27.9% increase in exergy efficiency. A sensitivity analysis is conducted to assess the impact of refrigerant composition and hydrogen pressure on the system, resulting in the determination of the optimal proportions of refrigerant components and the optimal inlet pressure. Results of the study can provide theoretical reference for the further development of large-scale hydrogen liquefaction technology.

Reducing industrial hydrogen demand through preheating with very high temperature heat pumps

Decarbonising industry while maintaining economic competitiveness and improving living standards is one of the main challenges of reaching net zero targets, and low-carbon process heating will play a key role in this. In this work we investigate the potential to reduce the energy demands of hydrogen-based industrial heating systems using very high temperature reverse Joule-Brayton cycle heat pumps as preheaters, considering their economics and technical challenges. A thermodynamic process model is used to assess performance at temperatures of 300–500 °C, and cost optimisation is used to conduct cost-benefit analysis of preheating green hydrogen using heat pumps. It is found that over this temperature range, heat pump coefficient of performance lies in the range 1.4–1.7, with the turbine meeting 30–40% of the compressor load. At the electricity prices currently paid by heavy industry in Western Europe, levelised cost of heat from these heat pumps would be less than 4.5p/kWh. Using 500 °C heat pumps as preheaters in hydrogen heating systems could reduce hydrogen demands by over 20% and provide savings on the cost of green hydrogen of at least 8% out to 2050. With process heat accounting for three-quarters of industrial energy use and half of this being at temperatures above 400 °C, these savings are significant and suggest that very high temperature heat pumps could make an important contribution to industrial decarbonisation.

Optimization and analysis of a hydrogen liquefaction process integrated with the liquefied natural gas gasification and organic Rankine cycle

Combination of the hydrogen pre-cooling and liquefied natural gas gasification processes is forward-looking in the hydrogen liquefaction industry. To enhance the cold energy utilization, a hydrogen liquefaction process integrated in conjunction with a liquefied natural gas gasification process assisted by an organic Rankine cycle is designed. Furthermore, a simplified refrigeration system incorporating a dual-pressure Joule-Brayton cycle is developed to provide efficient cryo-cooling for the hydrogen. A binary mixture consisting of ethylene and propane is preferred as the working fluid for the organic Rankine cycle when liquefied natural gas gasification pressure is 30 bar, which results in 2.2% and 15.5% improvement in the liquefied natural gas cold energy utilization compared to the organic Rankine cycle with the pure refrigeration as the working fluid and the hydrogen pre-cooling process without the organic Rankine cycle, respectively. In the proposed cryo-cooling process using two Joule-Brayton cascade cycles, the utilization rate of the input exergy reaches 48.84%. The exergy loss generated in the compressors and coolers accounts for approximately 66.2% of the total exergy loss. Therefore, they are regarded as the priority targets for improving the hydrogen liquefaction system. After the optimization of the proposed process using the genetic algorithm, optimal results are obtained with a specific energy consumption of 6.59 kWh/kgH2 and an exergy efficiency of 47.0%.

The Water-Enhanced Turbofan as Enabler for Climate-Neutral Aviation

A significant part of the current aviation climate impact is caused by non-carbon-dioxide emissions, mainly nitrogen oxides (NOx) and contrails. It is, therefore, important to have a holistic view on climate metrics. Today’s conventional, but already well-developed, aero-engines are based on the Joule–Brayton cycle, and leave only limited room for improvement in climate impact. The revolutionary Water-Enhanced Turbofan (WET) concept represents a technical step change addressing all relevant emissions by implementing the Cheng cycle, which combines the gas turbine cycle with a Clausius–Rankine steam cycle. This paper builds upon previous publications regarding the WET concept, and outlines the evolution since then. Promising WET configurations are evaluated according to their ability to reduce global warming potential compared to an evolutionarily advanced turbofan engine. A quantitative approach to estimate reduction of NOx emissions through steam injection is presented. The impact on the creation of contrails is considered using the Schmidt-Appleman criterion. In conclusion, all three climate-relevant emissions can be reduced with the WET concept compared to a technologically similar turbofan in terms of CO2 (up to 10%), NOx (more than 90%), and contrails (more than 50%). The resulting in-flight climate impact can be reduced by more than 40% when using fossil kerosene, paving the way to climate-neutral aviation.

Techno-economic analysis of recuperated Joule-Brayton pumped thermal energy storage

This article describes a techno-economic model for pumped thermal energy storage systems based on recuperated Joule-Brayton cycles and two-tank liquid storage. Models have been developed for each component, with particular emphasis on the heat exchangers. Economic metrics such as the power and energy capital costs (i.e., per-kW and per-kWh capacity) and levelized cost of storage are evaluated by gathering numerous cost correlations from the literature, thereby enabling estimates of uncertainty. It is found that the use of heat exchangers with effectivenesses up to 0.95 is economically worthwhile, but higher values lead to rapidly escalating component size and system cost. Several hot storage fluids are considered; those operating at the highest temperatures (chloride salts) improve the round-trip efficiency but the benefit is marginal and may not warrant the additional material costs and risk when compared to lower-temperature nitrate salts. Cost-efficiency trade-offs are explored using a multi-objective optimization algorithm, yielding optimal designs with round-trip efficiencies in the range 59–72% and corresponding levelized storage costs of 0.12 ± 0.03 and 0.38 ± 0.10 $/kWhe. Lifetime costs are competitive with lithium-ion batteries for discharging durations greater than 6 h under current scenarios.

Transient simulation and thermodynamic analysis of pumped thermal electricity storage based on packed-bed latent heat/cold stores

Pumped thermal electricity storage is a promising large-scale electricity storage technology that uses thermodynamic cycles and thermal energy storage to achieve electricity storage and release. At present, for pumped thermal electricity storage based on the Joule-Brayton cycle, packed beds filled with sensible heat storage media are widely adopted as the thermal store, while they usually suffer from low energy storage densities and large volumes. In this paper, the thermodynamic feasibility of packed-bed latent heat/cold stores is explored to replace the packed-bed sensible heat/cold stores in pumped thermal electricity storage. A numerical model of a 10.5 MW/5 h storage system based on packed-bed latent heat/cold stores is established. The energy and exergy analysis of components is carried out. The effect of compression ratios, porosities, isentropic efficiencies, and inlet velocities on the systematic thermodynamic performance is investigated and optimal conditions are also investigated. It is concluded that the energy storage density of the system increases from 232.5 kWh/m3 to 245.4 kWh/m3 when packed-bed sensible heat/cold stores are replaced by latent ones. Furthermore, the power density of the system based on packed-bed latent heat/cold stores is 216.5 kW/m3, and the round-trip efficiency reaches 84.7%, which is competitive in large-scale electricity storage technologies.

Implications of Phase Change on the Aerodynamics of Centrifugal Compressors for Supercritical Carbon Dioxide Applications

Abstract Closed Joule–Brayton cycles operating with carbon dioxide in supercritical conditions (sCO2) are nowadays collecting a significant scientific interest, due to their high potential efficiency, the compactness of their components, and the flexibility that makes them suitable to exploit diverse energy sources. However, the technical implementation of sCO2 power systems introduces new challenges related to the design and operation of the components. The compressor, in particular, operates in a thermodynamic condition close to the critical point, whereby the fluid exhibits significant non-ideal gas effects and is prone to phase change in the intake region of the machine. These new challenges require novel design concepts and strategies, as well as proper tools to achieve reliable predictions. In this study, we consider an exemplary sCO2 power cycle with the main compressor operating in proximity to the critical point, with an intake entropy level of the fluid lower than the critical value. In this condition, the phase change occurs as evaporation/flashing, thus resembling cavitation phenomena observed in liquid pumps, even though with specific issues associated with compressibility effects occurring in both the phases. The flow configuration is therefore highly nonconventional and demands the development of proper tools for fluid and flow modeling, which are instrumental for the compressor design. The paper discusses the modeling issues from the thermodynamic perspective, then highlighting their implications on compressor aerodynamics. We propose tailored models to account for the effect of the phase change in 0D mean-line design tools as well as in fully three-dimensional (3D) computational fluid-dynamic (CFD) simulations: the former was previously validated for sCO2 compressors, the latter is validated in this paper against experiments of compressible flows of supercritical sCO2 in nozzles. In this way, a strategy of investigation is built-up as a combination of mean-line tools, industrial design experience, and CFD for detailed flow analysis. The investigation reveals that the potential onset of the phase change might alter significantly the performance and operation of the compressor, both in design and in off-design conditions, according to three main mechanisms: incidence effect, front-loading, and channel blockage.

Transient analysis and control of a heat to power conversion unit based on a simple regenerative supercritical CO2 Joule-Brayton cycle

Supercritical carbon dioxide (sCO2) heat to power systems are a promising technology thanks to their potential for high efficiency and operational flexibility. However, their dynamic behaviour during part-load and transient operation is still not well understood and further research is needed. Additionally, there is not enough literature addressing suitable control approaches when the objective is to follow the dynamics of heat load supplied by the topping process to maximise the power recovery. The current research aims to fill these gaps by proposing a one-dimensional transient modelling formulation calibrated against the major components of a 50 kWe sCO2 test facility available at Brunel University London. The dynamic analysis showed that the system quickly adapts to a 2800s transient heat load profile, proving the flexible nature of the sCO2 system investigated. The turbine by-pass, during startup and shutdown modes of operation, enabled gradual and safe build-up/decline of the pressures and temperatures throughout the loop. The regulation of the inventory in the range 20–60 kg allowed a 30% variation of the turbine inlet temperature with lower penalties on system performance than the turbomachinery speed control. The designed proportional-integral inventory controller showed a rapid response in the control of the turbine inlet temperature around the set point of 773 K during large variations of the heat load.

Comparative study of a bottoming SRC and ORC for Joule–Brayton cycle cooling modular HTR exergy losses, fluid-flow machinery main dimensions, and partial loads

Abstract Energy conversion efficiency increase in power plants with high-temperature gas-cooled reactors via implementation of the bottoming cycle was investigated under nominal and minimal thermal load of a high-temperature reactor (HTR). Heat transfer surface area and turbine outlet volumetric flow rate in bottoming cycles was also investigated. Water and two low-boiling point working fluids (ammonia and ethanol) were analyzed. Analyzed thermodynamic cycles consisted of a closed Joule-Brayton cycle with helium as working medium, which was investigated in configurations with heat regeneration, compressor intercoolers, and in a simple design. Organic versus steam Rankine cycles were compared; low-boiling point fluids under supercritical conditions in some configurations provide higher cycle energy efficiency than the gas-steam cycle. Volumetric flow rates in the last turbine stages were reduced against the steam turbine to 38% and 0.8% with ethanol and ammonia, respectively. The steam Rankine cycle configuration provided the smallest heat transfer surface increase compared with the base cycle.

Waste Heat Recovery in the EU industry and proposed new technologies

In the European Union (EU), industrial sectors use 26% of the primary energy consumption and are characterized by large amounts of energy losses in the form of waste heat at different temperature levels. Their recovery is a challenge but also an opportunity for science and business. In this study, after a brief description of the conventional Waste Heat Recovery (WHR) approaches, the novel technologies under development within the I-ThERM Horizon 2020 project are presented and assessed from an energy and market perspectives. These technologies are: heat to power conversion systems based on bottoming thermodynamic cycles (Trilateral Flash Cycle for low grade waste heat and Joule-Brayton cycle working with supercritical carbon dioxide for high temperature waste heat sources); heat recovery devices based on heat pipes (flat heat pipe for high grade radiative heat sources and condensing economizer for acidic effluents).

Design of a high-temperature heat to power conversion facility for testing supercritical CO2 equipment and packaged power units

This paper addresses the need of bridging between fundamental energy research and industrial exploitation of technologies by presenting a state of the art experimental facility to investigate pilot heat exchangers and plants dealing with high temperature waste heat recovery and conversion. The facility comprises a 830 kW process air heater with an exhaust mass flow rate of 1.0 kg/s at 70 mbarg and maximum temperature of 780 °C. The heater has a 2.0 m long test section for the installation and characterization of waste heat recovery heat exchangers. The heat sink is a 500 kW water dry cooler with full control of flow rate and temperature of the cooling stream. The high-temperature heat to power conversion facility hosts a 50 kWe power conversion unit based on the simple recuperated Joule-Brayton cycle with supercritical CO2 (sCO2) as working fluid. The packaged, plug and play sCO2 system utilizes a single-shaft Compressor-Generator-Turbine unit. The paper discusses the main design features of the test facility as well as operation and safety considerations.

Conceptual design and analysis of a novel process for hydrogen liquefaction assisted by absorption precooling system

Hydrogen liquefaction processes have effective function in the hydrogen supply chain. However low efficiency and high liquefaction costs are still the most important concerns about the liquefaction plants. In this study a new configuration for a hydrogen liquefier process is proposed and energy-exergy analyzed. The production rate of the liquid hydrogen (LH2) is 90 tons per day that can supply the required LH2 of at least 90 k-180 k hydrogen vehicles in an urban area that results in the reduction of pollutions caused by carbon dioxide emission. The process is simulated in Aspen HYSYS simulator. In addition, it is optimized thorough a trial and error approach that is a functional and simple method of complicated systems analysis. The process includes a mixed refrigerant (MR) refrigeration cycle that precools feed gas hydrogen from 25°C temperature to −199.9°C temperature. A new MR is used in a cascade Joule-Brayton cycle that deep-cools the low-temperature gaseous hydrogen from −199.9°C temperature to −252.2°C temperature in the cryogenic section of the plant. The novel process involves also an absorption refrigeration system (ARS) that cools some hydrogen streams in the precooling and cryogenic sections of the process. The consumed energy per kilogram of produced LH2 is achieved as 6.47kWh. This quantity is 2.89kWh in the ideal conditions. The exergy efficiency of the plant is evaluated to be 45.5% that is significantly more than the exergy efficiency of the in operating hydrogen liquefiers in the world. The energy analysis reveals that the coefficient of performance (COP) of the overall system is 0.2034. The achieved COP is a higher amount in compare to the other similar processes. A sensitivity analysis is done to show the effect of the various operation conditions of the process on the features of the plant. Accordingly, the optimum mass flow of the ARS is determined as 207kg/s for the proposed configuration. As well as, the effect of the change in the temperature approach of the heat exchangers and the changes in the adiabatic efficiency of the compressors and expanders on the SEC, COP, and the exergy efficiency of the overall plant is discussed. Furthermore, financial analysis of the plant estimates the capital expenditures (CAPEX), energy expenditures (EEX), and operational and maintenance expenditures (OMEX) as 25413 €2000, 7370 €2000, and 2033 €2000 respectively. These can be specially improved be improving of the exergy efficiency of the plant. The results implicates that the proposed configuration has better performance indicators than the in-service liquefiers. Therefore, LHL plant manufacturer can be considered it in the design and development of new plants. As well as, researchers may utilize its operating conditions to improve the proposed processes.

Ecological efficiency of finite-time thermodynamics: A molecular dynamics study.

We present a molecular dynamics simulation of a two-dimensional Carnot engine. The optimization of this engine is achieved through the velocity of the piston, allowing not only the optimization of power output but also some other figures of merit involving entropy production. The maximum power and maximum ecological efficiencies are computed. It is shown that the near ideal gas working substance displays an endoreversible Carnot-like engine behavior. This can be considered as a prove of the validity of the Carnot-like endoreversible model. An effective reversible cycle different than the Carnot one is obtained, in agreement with theendoreversiblehypothesis flexibility. We compare the efficiencies stemming from an ideal gas approximation with those of the simulation, and then we propose a suitable approximation to an endoreversible heat engine and to a reversible Joule-Brayton cycle which fits very well to the simulation results. Finally, we show that the maximum ecological efficiency η=1-τ^{3/4}, which is also very close to the upper bound of the low-dissipation heat engine under maximum ecological (and Omega) conditions, is close for describing the dynamics of the simulated cycle under maximum power and maximum ecological conditions in the so-named heat engine operability region.

Techno-economic assessment of Joule-Brayton cycle architectures for heat to power conversion from high-grade heat sources using CO2 in the supercritical state

Bottoming thermodynamic power cycles using supercritical carbon dioxide (sCO2) are a promising technology to exploit high temperature waste heat sources. CO2 is a non-flammable and thermally stable compound, and due to its favourable thermophysical properties in the supercritical state, it can achieve high cycle efficiencies and a substantial reduction in size and cost compared to alternative heat to power conversion technologies. Eight variants of the sCO2 Joule-Brayton cycle have been investigated. Cycle modelling and sensitivity analysis identified the Turbine Inlet Temperature (TIT) as the most influencing variable on cycle performance, with reference to a heat source gas flow rate of 1.0 kg/s and 650 °C. Energy, exergy and cost metrics for different cycle layouts have been compared for varying TIT in the range between 250 °C and 600 °C. The analysis has shown that the most complex sCO2 cycle configurations lead to higher overall efficiency and net power output but also to higher investment costs. Conversely, more basic architectures, such as the simple regenerative cycle, with a TIT of 425 °C, would be able to achieve an overall efficiency of 25.2%, power output of 93.7 kWe and a payback period of less than two years.

Performance analyses and optimisation of the Joule-Brayton cycle via the mean cycle pressure criterion

Within the scope of developing a new method to optimise the use of economic and ecological thermal systems, a comparative study was conducted by means of different compression ratios and temperature ratios according to mean cycle pressure (MCP) criterion for the simple Joule-Brayton cycle. The results, when compared with the other performance criteria's results in the literature, show that the thermal efficiency and network at maximum MCP condition are approximately 1–2% more and 12–13% times less than other criteria, respectively. Moreover, the thermal efficiency that corresponds to the maximum MCP condition is nearly 15% more than the maximum network condition, and the network at the maximum MCP and maximum thermal efficiency conditions are equal. Thus, MCP criterion will give more useful and realistic information in terms of designing more efficient and smaller thermal systems.

Performance analyses and optimisation of the Joule-Brayton cycle via the mean cycle pressure criterion

Within the scope of developing a new method to optimise the use of economic and ecological thermal systems, a comparative study was conducted by means of different compression ratios and temperature ratios according to mean cycle pressure (MCP) criterion for the simple Joule-Brayton cycle. The results, when compared with the other performance criteria's results in the literature, show that the thermal efficiency and network at maximum MCP condition are approximately 1–2% more and 12–13% times less than other criteria, respectively. Moreover, the thermal efficiency that corresponds to the maximum MCP condition is nearly 15% more than the maximum network condition, and the network at the maximum MCP and maximum thermal efficiency conditions are equal. Thus, MCP criterion will give more useful and realistic information in terms of designing more efficient and smaller thermal systems.

Feasibility analysis of a solar field for a closed unfired Joule-Brayton cycle

Feasibility analysis of a solar field for a closed unfired Joule-Brayton cycle

APPLICATION OF A NOVEL THERMO-ECOLOGICAL PERFORMANCE CRITERION: EFFECTIVE ECOLOGICAL POWER DENSITY (EFECPOD) TO A JOULE-BRAYTON CYCLE (JBC) TURBINE

This study presents an application of a new performance analysis criterion named as Effective Ecological Power Density (EFECPOD) to a Joule-Brayton cycle (JBC) turbine. The turbine performance is expressed a single value by the proposed criterion using effective efficiency, effective power, cycle temperature ratio and volume. NOx formation and turbine dimensions are considered by the cycle temperature ratio and turbine volume, respectively. The turbine volume is also related to production cost of the heat engine. Therefore, the proposed criterion is essential for multi purpose optimization. Furthermore, this criterion can be developed and applied to the other gas cycle and heat engines. Also, the influences of engine design parameters such as cycle temperature ratio, pressure ratio, turbine speed, and equivalence ratio on the EFECPOD have been examined based on Finite-Time Thermodynamics Modelling (FTTM). In order to obtain realistic results, temperature-dependent specific heats for working fluid have been used and heat transfer and exhaust output losses have been taken into consideration. The results presented could be an essential tool for JBC turbine designers.

Thermodynamic analysis of a small scale combined cycle for energy generation from carbon neutral biomass

The aim of this paper is to investigate the thermodynamic performance of a novel small-scale power plant that employs a combined cycle for the energy generation from carbon-neutral biomass, such as pruning residues. The combined cycle is composed of an externally fired Joule Brayton cycle followed by a bottoming steam cycle. The topping cycle has the unique particularity of being composed of a cost-effective turbocharger taken from the automotive industry, in place of a more expensive commercial micro-turbine. The turbocharger can be either directly connected to the electric generator (after a few modifications) or coupled (without modifications) with a power turbine moving the generator. The use of solid biomass in the proposed plant is allowed by the presence of an external combustor and a gas-to-gas heat exchanger. The warm flue gases exhausted by the topping cycle are used in a bottoming cycle to produce steam, which can power a steam expander.This paper thermodynamically assesses the novel combined cycle in the configuration for the topping cycle that employs a turbocharger coupled with a power turbine capable of generating 30 kW of electrical power. Furthermore, the comparison between the performance obtained using the bottoming water Rankine cycle and a bottoming Organic Rankine Cycle is provided.