Inverse Brayton Cycle Research Articles

Waste heat recovery of a combined Brayton and inverse Brayton cycle for gas turbine based multi-generation hydrogen and freshwater purposes: 4E comparison with a simple coupled Brayton and inverse Brayton cycle

Using gas turbine cycles in power generation layouts can lead to a significant amount of waste energy. The combined Brayton and inverse Brayton cycle (IBC), which are used in such systems, has a considerable amount of waste energy in the heat rejection stage and exhausted gas, which has not been considered in previous studies. In the present research, a simple coupled Brayton and IBC (Configuration 1) is compared with a multi-generation system (Configuration 2) in which a hot water unit, a thermoelectric generator (TEG), and an absorption chiller are added to Configuration 1 for the waste energy utilization of combined Brayton and IBC. Furthermore, the power produced in IBC and TEG is directed to a proton exchange membrane electrolyzer and a reverse osmosis desalination unit for hydrogen and potable water outputs. Results show that although the total investment cost rate of Configuration 2 is higher than that of Configuration 1, the fuel cost rate, environmental cost rate, and exergy destruction cost rate of Configuration 2 are lower. Furthermore, at the best performance point, Configuration 2 has exergy efficiency and unit cost of products equal to 40.77% and 63.19 $/GJ. They are higher than Configuration 1 by 5% and 2%, respectively. Hence, with Configuration 2, a higher exergy efficiency with a lower fuel consumption and environmental cost rate is accessible.

4E optimization comparison of different bottoming systems for waste heat recovery of gas turbine cycles, internal combustion engines, and solid oxide fuel cells in power-hydrogen production systems

Gas turbine cycles (GTC), internal combustion engines (ICE), and solid oxide fuel cells (SOFC) are three important sources of waste energy, and although some studies have been done about their waste heat recovery (WHR) systems individually, there is a lack of a study comparing them to select the best solution. In the present research, the steam Rankine cycle, CO2 supercritical Brayton cycle (SBC), inverse Brayton cycle (IBC), and air bottoming cycle are used for WHR of high-temperature exhausted gas of 500 kW natural gas-fueled GTC and ICE. Furthermore, the organic Rankine cycle (ORC), trilateral cycle, organic flash cycle, Kalina cycle, and CO2 SBC are utilized for the WHR of the SOFC-gas turbine (GT). The performance of 13 proposed configurations is compared through 4E (energy, exergy, exergy-economic, and environmental) three-objective optimizations. Considering exergy efficiency, total cost rate, and unit cost of products as target functions, the SOFC-GT-ORC system has the best performance with exergy efficiency, total cost rate, and unit cost of 64.74%, 92.51 $/h, and 19.03 $/GJ. Furthermore, GTC-IBC and ICE-IBC have the best performance in their respective categories.

4E comparison and optimization of natural gas or solar-powered combined gas turbine cycle and inverse Brayton cycle in hydrogen and freshwater multi-generation systems

Replacing fossil fuel-based systems with renewable energy resources is a method to enhance the performance of the layout and reduce environmental pollution. The gas turbine cycle (GTC) is one of the main sources of consuming natural gas (NG) in a combustion chamber (CC). In the present study, the theoretical performance of a 500 kW CC-based gas turbine cycle is improved by replacing the NG CC with a solar power tower (SPT) and converting it into a multi-generation system. The waste heat recovery of GTC is done by a hot water unit and an inverse Brayton cycle (IBC), and then the energy of the heat rejection stage of IBC and the exhausted gas of the system is recovered by a thermoelectric generator (TEG) and an absorption chiller. Afterwards, the produced power of IBC and TEG is fed to a proton exchange membrane electrolyzer and a reverse osmosis desalination unit for hydrogen and potable water outputs. 4E optimization shows that the exergy efficiencies of the CC-based system (Configuration 1) and the SPT-based system (Configuration 2) are equal to 37.2% and 9.12%, respectively. However, the economic performance of Configuration 2 is better. In this case, the total cost rate and unit cost of multi-generation in Configuration 2 are 142.1 $/h and 15.14 $/GJ in comparison with 145.5 $/h and 31.58 $/GJ for Configuration 1. In addition, the fossil fuel consumption and emissions of Configuration 2 are zero, while the fuel and environmental cost rate make up 54.76% of the total cost rate of Configuration 1.

Thermal efficiency and specific work optimization of combined Brayton and inverse Brayton cycle: A multi-objective approach

Thermal efficiency and specific work optimization of combined Brayton and inverse Brayton cycle: A multi-objective approach

Gas turbine cogeneration concepts for the pressureless discharge of high temperature thermal energy storage units

Power-to-heat technology allows the leveling of high electrical power production peaks by converting excess electrical energy into high-exergy heat and storing it in a high-temperature thermal energy storage (HTS). When electricity is needed, a gas turbine process can be used for an efficient discharge in decentralized usage scenarios. As a novelty of this work, different configurations of the Brayton cycle are presented and investigated, which permit a pressureless storage discharge and thus a cost-efficient and scalable HTS unit. The processes enable combined heat and power generation (CHP) to increase the total efficiency of the system. Stationary process simulations are conducted with the software EBSILON®Professional to thermodynamically analyze four process designs. The influence of the HTS outlet temperature, process-internal pressure conditions, as well as other component-specific efficiencies are examined in separate parameter studies. Based on state-of-the-art components, the process variants show electrical efficiencies above 29% and total efficiencies about 87% for an HTS outlet temperature of 900 °C. By reducing thermal losses, closed processes can increase the total efficiency to 97%. Two processes can be determined as suitable for CHP. The open externally heated Brayton cycle achieves the highest electrical efficiency of 33.14% at the design point, while the closed inverse Brayton cycle is achieving the highest total energetic and exergetic efficiency.

Energy and exergy analyses of a new atmospheric regenerative Brayton and Inverse Brayton cycle

A regenerative Brayton & Inverse Brayton cycle has been already proposed to improve the thermal efficiency of the standard Brayton cycle as a Brayton &Inverse Brayton cycle did. All processes in the bottoming cycle take place at sub-atmospheric pressure. A new arrangement of the processes has been introduced in the present study to decrease the flow rate through the bottoming cycle. The new arrangement of the processes also performs an atmospheric exhaust airflow through the regenerator. Thermal performance of the new cycle is compared with that in the original regenerative Brayton & Inverse Brayton cycle. Performances of the two cycles are compared at different pressure-ratios of the compressors. Calculated results show that the thermal efficiency, the specific net output power, the specific heat supplied to the combustion chamber, and the total rate of exergy destruction are no longer strongly dependent on the pressure-ratio of the second compressor and are weakly dependent on the pressure-ratio of the first compressor in the new cycle. Meanwhile, the specific net output power of the new cycle is considerably greater than that in the original one (30%–250%). The new cycle is recommended to use at moderate pressure-ratios of the first and second compressors.

Comparative Exergy Analysis of Units for the Porous Ammonium Nitrate Granulation

The article deals with the study on the efficiency of units for porous ammonium nitrate production. The ways which increase the effective implementation of energy resources are determined by including the ejector recycling module, heat and mass exchangers that utilize principles of regenerative indirect evaporative cooling, and the sub-atmospheric inverse Brayton cycle. Mixed exergy analysis evaluates all flows of the system contour as those of the same value. The target parameter for determining the efficiency of both systems is the ratio of the unit’s productivity to the exergy expenditures to produce the unit mass of the product. As a result, it is found that the mentioned devices and units enable to increase the efficiency of the basic scheme by 87%.

Power and Efficiency Optimization for Open Combined Regenerative Brayton and Inverse Brayton Cycles with Regeneration before the Inverse Cycle.

A theoretical model of an open combined cycle is researched in this paper. In this combined cycle, an inverse Brayton cycle is introduced into regenerative Brayton cycle by resorting to finite-time thermodynamics. The constraints of flow pressure drop and plant size are taken into account. Thirteen kinds of flow resistances in the cycle are calculated. On the one hand, four isentropic efficiencies are used to evaluate the friction losses in the blades and vanes. On the other hand, nine kinds of flow resistances are caused by the cross-section variances of flowing channels, which exist at the entrance of top cycle compressor (TCC), the entrance and exit of regenerator, the entrance and exit of combustion chamber, the exit of top cycle turbine, the exit of bottom cycle turbine, the entrance of heat exchanger, as well as the entrance of bottom cycle compressor (BCC). To analyze the thermodynamic indexes of power output, efficiency along with other coefficients, the analytical formulae of these indexes related to thirteen kinds of pressure drop losses are yielded. The thermodynamic performances are optimized by varying the cycle parameters. The numerical results reveal that the power output presents a maximal value when the air flow rate and entrance pressure of BCC change. In addition, the power output gets its double maximal value when the pressure ratio of TCC further changes. In the premise of constant flow rate of working fuel and invariant power plant size, the thermodynamic indexes can be optimized further when the flow areas of the components change. The effect of regenerator on thermal efficiency is further analyzed in detail. It is reported that better thermal efficiency can be procured by introducing the regenerator into the combined cycle in contrast with the counterpart without the regenerator as the cycle parameters change in the critical ranges.

Potential for energy and emissions of asymmetric twin-scroll turbocharged diesel engines combining inverse Brayton cycle system

In this paper, a new combined cycle of asymmetric twin-scroll turbocharged diesel engine cycle and inverse Brayton cycle (IBC) for use is proposed. The use of a single asymmetric twin-scroll turbocharged diesel engine cycle is simple in structure and can improve the trade-off between low fuel consumption and nitrogen oxide emissions; however, both the engine exhaust gas recirculation (EGR) rate and the exhaust energy utilization should be further improved. A test bench experiment was performed to validate the numerical models of the single-cycle and combined-cycle approaches. Based on the models, the influence laws of the critical system parameters (turbine asymmetry and the IBC turbine throat area) on the engine performance characteristics were studied. The combined cycle was found to achieve improvements in both the engine EGR rate and the power. Given the same EGR rates at different engine speeds, the power improvement of the combined cycle was found to increase with increasing engine speed and decreasing turbine asymmetry, reaching a maximum of 5.00%. Moreover, further power improvements with an increasing IBC turbine throat area were observed, with the maximum power improvement of 5.78%. Compared with the power turbine, the combined cycle can utilize more waste heat at low and medium engine speeds; thus, the combined cycle is well-suited for use in heavy-duty diesel engines. The new combined cycle described in this report has great potential to provide substantial gains in both engine emissions and energy.

Strategy on performance improvement of inverse Brayton cycle system for energy recovery in turbocharged diesel engines

The inverse Brayton cycle is a potential technology for waste heat energy recovery. It consists of three components: one turbine, one heat exchanger, and one compressor. The exhaust gas is further expanded to subatmospheric pressure in the turbine, and then cooled in the heat exchanger, last compressed in the compressor into the atmosphere. The process above is the reverse of the pressurized Brayton cycle. This work has presented the strategy on performance improvement of the inverse Brayton cycle system for energy recovery in turbocharged diesel engines, which has pointed the way to the future development of the inverse Brayton cycle system. In the paper, an experiment was presented to validate the numerical model of a 2.0 l turbocharged diesel engine. Meanwhile, the influence laws of the inverse Brayton cycle system critical parameters, including turbocharger speed and efficiencies, and heat exchanger efficiency, on the system performance improvement for energy recovery are explored at various engine operations. The results have shown that the engine exhaust energy recovery efficiency increases with the engine speed up, and it has a maximum increment of 6.1% at the engine speed of 4000 r/min (the engine rated power point) and the full load. At the moment, the absolute pressure was before final compression is 51.9 kPa. For the inverse Brayton cycle system development in the future, it is essential to choose a more effective heat exchanger. Moreover, variable geometry turbines are very appropriate to achieve a proper matching between the turbocharging system and the inverse Brayton cycle system.

Thermochemical Biomass Conversion for Decentralized Power Generation with the Inverse Brayton Cycle

AbstractBiomass is an important energy source for decentralized power generation. The combination of a two‐stage thermochemical conversion unit with an inverse Brayton cycle (IBC) is the subject of current research activities. Several advantages are expected compared to commercially available concepts. A commercially proven turbocharger from the automotive industry is used for the IBC unit. No cost‐intensive gas cleaning is required due to an almost dust‐ and tar‐free biomass conversion. The influence of the feedstock characteristics on the thermochemical conversion, the emissions, and the overall plant performance is subject to process optimization studies. Furthermore, validation of the concept is the target of a demonstration phase planned for a later stage of the research activities.

Cascade refrigeration system with inverse Brayton cycle on the cold side

Low temperature refrigeration of cold stores poses some specific issues: single stage, vapour compression cycles have modest COP at low evaporation temperature; cold evaporator surfaces require de-frosting and a fan for air circulation; a part of the refrigeration load may be delivered at intermediate temperature levels, e.g. for the cold store loading dock.Cascade system may improve the COP and add flexibility on the temperature levels and working fluids, but the problems related to the cold evaporator surface remain unsolved.The refrigeration system presented herein features a cascade configurationcombining a vapour compression cycleand an inverse Braytoncycle. Both cycles use “natural” fluids, complying with strictest regulations. The top cycle uses Ammonia in order to increase efficiency, while the bottom cycle uses air, which directly circulates in the cold space and hence eliminates the cold heat exchanger. A detailed thermodynamic analysis allows a complete screening of the relevant design parameters for an overall system optimization.The results show that, notwithstanding the intrinsic gap of efficiency suffered by the Brayton cycle, the proposed system features an acceptable global performance and widens the implementation field of this technology. This system configuration shows a COP 50% higher than the corresponding simple Brayton cycle at temperatures of the refrigerated storage of −50°C.

Exergy Analysis for Brayton and Inverse Brayton Cycles with Steam Injection

Global economic and social development has led to the growth in demand for electrical power. Gas turbines play an essential role in many societies, and as the requirements for power generation increase, the power output and thermal efficiency of gas turbines must also increase. This paper presents one of the ways to improve the performance of the gas turbine with a study of exergy analysis of combined Brayton and inverse Brayton cycles with steam injected into the combustion chamber. The effect of variation of operating conditions (compression ratio and ambient temperature) on the performance of gas turbine (thermal efficiency, power) were investigated, the results were compared with the same cycle, but without injection with the analytical formulae of exergy and exergy destruction. The programming of performance model for gas turbine was developed utilizing the commercially available software IPSEpro. The analysis shows that the highest exergy destruction occurs in the combustion chamber. In addition, the performance has been improved by using steam injection by 11% in efficiency and 57% in power output and decrease linearly with the increase of the ambient temperature. However, steam injection increases the specific fuel consumption and heat rate. Thus, the thermodynamic parameters on cycle performance are economically feasible and beneficial for the gas turbine operations.

Usefulness analysis on regenerator and heat exchanger in Brayton & inverse Brayton cycles at moderate pressure ratio operation

A consistent methodology incorporating usefulness of the regenerator and heat exchanger for alternative forms of Brayton & Inverse Brayton cycle compared to the basic Brayton and regenerative Brayton cycles has been presented. An analytical study has been performed to explain why regenerator and heat exchanger might be useless at particular operational conditions. This analysis showed that regenerator and/or heat exchanger of the Brayton & Inverse Brayton cycle should be removed from the service at particular pressure ratio operations. Thermal performances of all unit arrangement were accordingly calculated at the moderate range of compressors’ pressure ratios. Analytical and computational findings showed that a particular unit arrangement including a regenerator between the two stages of expansion processes through turbines exhausting to the atmospheric pressure had a better thermal performance, i.e. at least 14% greater than all other unit arrangements, while the huge heat exchanger and second compressor could be eliminated for lower occupation space and start up process.

Exergetic performance optimization for new combined intercooled regenerative Brayton and inverse Brayton cycles

A new configuration of combined intercooled regenerative Brayton and inverse Brayton cycles with regeneration before the inverse cycle is proposed in this paper. By using the exergy analysis, the performance of the new configuration is investigated and optimized. The intercooling pressure ratio is optimized when the total pressure ratio (π) is fixed and π is optimized when it is variable. The effects of the main design parameters on the exergetic performance are analyzed. It is found that the intercooling and regenerative processes are beneficial to increase the exergy efficiency when π varies in a certain range; when the total pressure ratio is relatively high, the consumed work of the compressor is significantly decreased by the intercooling process and the regenerative process will save more fuel when the total pressure ratio is small; and the combustor produces the largest exergy destruction.

Performance analysis of a modified regenerative Brayton and inverse Brayton cycle

Regenerative Brayton and inverse Brayton cycle may particularly increase thermal efficiency compared to the corresponding non-regenerative one, while decreases the net output power. In this study, regenerative Brayton and inverse Brayton cycle has been modified by partially bypassing the airflow entering the regenerator. The influence of the bypass mass flow ratio on thermal efficiency and net output power of the modified cycle has been studied for varieties of compressors' pressure ratios. Results show that from operational point of view, more favorable output power with reasonable thermal efficiency can be generated with adjusting the bypass mass flow ratio. Meanwhile, for each compressor pressure ratio of the direct Brayton cycle, there is a particular bypass mass flow ratio, which results thermal efficiency and net output power independent of the compressor pressure ratio of the inverse Brayton cycle.

Thermodynamic analysis of the double Brayton cycle with the use of oxy combustion and capture of CO2

Abstract In this paper, thermodynamic analysis of a proposed innovative double Brayton cycle with the use of oxy combustion and capture of CO2, is presented. For that purpose, the computation flow mechanics (CFM) approach has been developed. The double Brayton cycle (DBC) consists of primary Brayton and secondary inverse Brayton cycle. Inversion means that the role of the compressor and the gas turbine is changed and firstly we have expansion before compression. Additionally, the workingfluid in the DBC with the use of oxy combustion and CO2 capture contains a great amount of H2O and CO2, and the condensation process of steam (H2O) overlaps in negative pressure conditions. The analysis has been done for variants values of the compression ratio, which determines the lowest pressure in the double Brayton cycle.

Performance optimisation for two classes of combined regenerative Brayton and inverse Brayton cycles

This paper proposes a new cyclic model of combined regenerative Brayton and inverse Brayton cycles. The new combined regenerative Brayton and inverse Brayton cycles recover heat energy after the working fluid leaves the turbine of the inverse Brayton cycle while the original combined regenerative Brayton and inverse Brayton cycles recover heat energy before the working fluid enters the turbine of the inverse Brayton cycle. Performance analysis and optimisation of the two classes combined cycles are carried out. Furthermore, the effect of the regenerator on the performance of the two combined cycles is analysed. It is found that the new combined cycle can obtain higher thermal efficiency and larger specific work than those of the original combined cycle at low compressor pressure ratio of the top cycle, and the regenerator can improve the performance of both the combined cycles. By theoretical analysis of this paper, it reveals that the new combined cycle will be well applied in the prospect, and the original combined cycle will be suited to low power output equipments. This paper aims at enriching the gas turbine theory and providing a possible way to save energy.

Thermodynamic optimization principle for open inverse Brayton cycle (refrigeration/heat pump cycle)

A thermodynamic model for an open inverse Brayton cycle (refrigeration or heat pump cycle) with pressure drop irreversibilities is established. There are seven flow resistances (or pressure drops) encountered by the working fluid stream for the inverse Brayton cycle. Two of these, the friction through the blades and vanes of the compressor and the expander, are related to the isentropic efficiencies. The remaining flow resistances are always present because of the changes in flow cross-section at the compressor inlet and outlet, heat exchanger inlets and outlets and expander inlet and outlet. The analytical formulae about the cooling load of refrigeration cycle, the heating load of heat pump cycle and other coefficients are derived, which indicate that the thermodynamic performance for open inverse Brayton cycle can be optimized by adjusting the mass flow rate (or the distribution of pressure losses along the flow path). It is shown that there are optimal air mass flow rates (or the distribution of pressure losses along the flow path) which maximize the cooling load of refrigeration cycle, and the optimal air mass flow rates are smaller than the one at the maximum power output of the direct Brayton cycle.

Energy performance optimization of combined Brayton and two parallel inverse Brayton cycles with regeneration before the inverse cycles

This paper proposes combined regenerative Brayton and two parallel inverse Brayton cycles with regeneration before the inverse cycles. Performance analysis and optimization for the combined cycle are performed based on the first law. The analytical formulae of thermal efficiency and specific work are derived. The performance analysis and optimization of thermal efficiency and specific work are carried out by adjusting the compressor pressure ratios of the bottom cycles. The influences of the effectiveness of the regenerator and other parameters on the optimal thermal efficiency and the optimal specific work are analyzed by numerical examples. It is found that the combined regenerative cycle can obtain higher thermal efficiency than that of the base cycle but with smaller specific work. It is revealed that if the effectiveness of regenerator equals to 0.9, the combined cycles will attain an optimal thermal efficiency of 51.2%.