Optimal Compressor Pressure Ratio Research Articles

A novel zero carbon emission system based on the complementary utilization of solar energy and hydrogen

A novel zero carbon emission combined power and hydrogen system is developed in this paper, which integrates power generation, hydrogen production, and energy storage. The novel combined system is composed of solar power tower subsystem, supercritical carbon dioxide recompression Brayton cycle subsystem, hydrogen gas turbine subsystem, hydrogen production subsystem and thermoelectric generator subsystem. Considering the solar instability, three operating modes are set for the combined system: pure hydrogen mode, solar‑hydrogen hybrid mode and pure solar energy mode. Comprehensive energy, exergy and economic analyses are performed for the combined system. The effects of five key parameters on the system performance are investigated. Taking the maximum exergy efficiency and the minimum levelized cost of energy as the objective function, the key parameters are optimized by the genetic algorithm. Results show that in pure hydrogen mode, the thermal and exergy efficiency of the combined system are 44.79% and 45.49%, respectively. Compared with pure hydrogen mode, the levelized cost of energy is reduced by 44.76% and 75.16% in solar‑hydrogen hybrid and pure solar energy mode. There is an optimal compressor pressure ratio to make the combined system have better thermodynamic and economic performance. Parameter optimization results show that for pure solar mode, the levelized cost of energy of the combined system is 75.4% and 56.3% lower than that of pure hydrogen mode, solar‑hydrogen hybrid mode respectively in the levelized cost of energy optimal design. The derived significant contributions of this work highlight strong potentials for combined system based on solar energy‑hydrogen complementary utilization.

Power and efficiency optimizations for an open cycle two-shaft gas turbine power plant

In finite-time thermodynamic analyses for various gas turbine cycles, there are two common models: one is closed-cycle model with thermal conductance optimization of heat exchangers, and another is open-cycle model with optimization of pressure drop (PD) distributions. Both of optimization also with searching optimal compressor pressure ratio (PR). This paper focuses on an open-cycle model. A two-shaft open-cycle gas turbine power plant (OCGTPP) is modeled in this paper. Expressions of power output (PP) and thermal conversion efficiency (TCE) are deduced, and these performances are optimized by varying the relative PD and compressor PR. The results show that there exist the optimal values (0.32 and 14.0) of PD and PR which lead to double maximum dimensionless PP (1.75). There also exists an optimal value (0.38) of area allocation ratio which leads to maximum TCE (0.37). Moreover, the performances of three types of gas turbine cycles, such as one-shaft and two-shaft ones, are compared. When the relative pressure drop at the compressor inlet is small, the TCE of third cycle is the biggest one; when this pressure drop is large, the PP of second cycle is the biggest one. The results herein can be applied to guide the preliminary designs of OCGTPPs.

Effect of climate and component performance on optimized recuperated air Brayton cycles for nuclear microreactor power conversion

Thermodynamic analyses were performed to evaluate recuperated open air Brayton cycles for nuclear microreactors operating with a power output of 3 MWe. Specifically, the efficiencies of the recuperated air Brayton cycles were compared under steady-state operating conditions for different climate conditions, reactor types, turbomachinery efficiencies, and recuperator performance. Recuperator minimum approach temperatures of 5, 10, and 15 °C were evaluated using an effectiveness-number of thermal units approach to encompass the expected range of different heat exchanger designs. Optimal compressor pressure ratio and optimum thermal efficiencies are presented for turbine efficiencies of 80%, 85%, and 90%; compressor efficiencies of 70%, 75%, 80%, and 85%; and turbine inlet temperatures of 500 °C, 650 °C and 850 °C corresponding to different reactor types. Effects of climate on the thermal efficiency of the recuperated air Brayton cycles show the largest effect on the recuperated cycle due to the change in ambient temperature, whereas the humidity of the ambient air has a negligibly small effect. An exergy analysis utilizing a high-performing compressor and turbine and a recuperating heat exchanger with a 10 °C minimum approach temperature showed that the compressor, recuperating heat exchanger, and the ambient heat rejection accounted for nearly 72% of the exergy destruction. The effect of pressure drop through the heat exchangers was quantified in terms of compressor pressure ratio and heat exchanger performance.

Simulation and optimization of a combined cycle power plant with low heating value fuel gas

Combined cycle power plant (CCPP) usually plays an important role in balancing byproduct gas generation and consumption in integrated iron and steel plant. The low heat value fuel gases, such as blast furnace gas (BFG) or mixed gas with Coke oven gas (COG) and BFG, are preferred to be used in high-efficient CCPP for power generation. In practice, the general heat value of mixed gas can be set in the range of 3500–4400[Formula: see text]kJ/Nm3. This paper presents a methodology to simulate operating parameters of CCPP with BFG. A generic model of gas turbine with open loop stage cooling employing air is used to simulate the performance of gas turbines cycle under different compressor pressure ratios and turbine inlet temperatures (TIT). The isentropic efficiencies for gas compressor and gas turbine are supposed to be constants and set corresponding to published industrial experience. The steam cycle is composed of classical double-pressure heat recovery steam generator (HRSG) and steam turbines according to gas turbine outlet temperature. Specific work, gas turbine cycle efficiency, cogeneration thermal efficiency and coolant air flow requirements are evaluated to find the optimal compressor pressure ratio and TIT. The research results are useful to select the optimum operating parameters of CCPP with BFG. Performance features were estimated with the help of compression ratios 12.5–20 and combustor exit temperature 1150–1350[Formula: see text]C.

ЗАМКНУТЫЕ МИКРОГАЗОТУРБИННЫЕ ДВИГАТЕЛИ С ОКИСЛИТЕЛЕМ-ВОЗДУХОМ В ЭНЕРГОУСТАНОВКАХ ПОДВОДНОЙ ТЕХНИКИ

Under the conditions of the Arctic, in the development of deposits on the shelf of the seas and oceans, a significant role is assigned to underwater equipment, which must have both sufficient power supply and the ability to work for a long time in isolation from the places of permanent deployment. Among the various types of power plants for these purposes, closed micro-gas turbine plants (CMGTP) with a high specific power are of interest. The paper analyzes the characteristics of the operating cycles of various CMGTP schemes, and CMGTP with heat recovery was chosen as the base one, as it is more economical compared to a simple cycle CMGTP and capable of operating in a single-circuit scheme on organic fuel using air as an oxidizer. A mixture of nitrogen, fuel combustion products and oxygen are used as a working medium of the engine. The surplus working medium is removed from the cycle by the compressor overboard. A further increase in the efficiency of a simple cycle by deep utilization of the heat of exhaust gases in a turbocompressor utilizer (TCU) consisting of an overexpansion turbine driving a booster compressor and a regenerator with a gas cooler located between them is proposed. It has been established that the efficiency of CMGTP with TCU and heat regeneration is 1.15... 1.25 times higher than that of the base CMGTP with regeneration, and the specific power increases 1.3... 1.5 times with the optimal compressor pressure ratio in the engine.

Proposal and assessment of a novel combined heat and power system: Energy, exergy, environmental and economic analysis

This research aims at developing a small-scale novel cogeneration system to satisfy all of the electrical and heating demands of a typical residential complex. The proposed system is integrated of a gas turbine cycle (GTC) and a Kalina cycle (KC). A comprehensive parametric study is presented for evaluating the proposed system from energy, exergy, environmental and economic (4E) points of view. The system’s governing equations are solved and validated through developing a high-accuracy computational code in Engineering Equation Solver (EES) software. The effects of some important design parameters (including compressor pressure ratio, base ammonia concentration, generator pressure and condenser pinch point temperature difference) are investigated on four appropriate criteria of energy efficiency (ηth), exergy efficiency (ηex), levelized total emissions (LTE) and levelized total costs (LTC). Furthermore, two economic methods, payback period (PP) and net present value (NPV), are also investigated. The results show that, the simulation outputs at base design conditions are as ηth = 69.43%, ηex = 37.90%, LTE = 87998 kg/kW, LTC = 8958 $/kW, PP = 3.34 years and NPV = 878679 $. The results of parametric analysis reveal that there is an optimal compressor pressure ratio which leads to maximum ηth and ηex and minimum LTE and LTC. The combustion chamber of GTC has the maximum share in system’s total exergy destruction (with 55.95% of total exergy destruction). Also, the entire KC has a low contribution of 3.396% in total exergy destruction.

Parametric Study on Thermoelectric Power Generator and Microturbine Combined Power Generation System

Microturbine is an important power equipment for distributed energy system with the advantages of compact structure, light weight, low noise, and so on. However, its power generation efficiency is still too low while its cost is too high to be widely applied. Thermoelectric material is a solid-state energy converter which can directly convert thermal energy into electrical energy without affecting the original thermodynamic cycle. It is expected to significantly improve the system’s efficiency and reduce the power generation cost by integrating the thermoelectric generators into the microturbine system. In this study, a thermodynamic model is developed for the thermoelectric power generator and microturbine combined power generation system. The numerical results showed that the addition of thermoelectric power generators can increase the power output of microturbine system by 1-2 times. Increasing the figure of merit value of TEGs and turbine inlet temperature improve the power output and efficiency of the combined system, but there is an optimal compressor pressure ratio for the combined system.

Preliminary conceptual exploration about performance improvement on supercritical CO2 power system via integrating with different absorption power generation systems

Supercritical CO2 (sCO2) power system has been investigated by many scholars due to its attractive advantages of higher efficiency, compact system structure and eco-friendly working fluid. In this paper, some preliminary conceptual exploration about performance improvement on sCO2 power system by integrating with two types of absorption power generation (APG) systems are conducted. Parameter analysis, genetic algorithm (GA) optimization and exergy analysis are carried out quantitatively for the proposed combined sCO2/APG systems based on the self-built simulation platform from the viewpoints of thermodynamics and economics. Parameter analysis results reveal that there exist optimal compressor pressure ratio to maximize the thermal efficiency or minimize the total product unit cost. Higher turbine inlet temperature and lower absorber temperature could contribute to the overall system performance. In addition, compared with the stand-alone sCO2 system, improvements of 5.98% and 5.07% in thermodynamics as well as promotion of 4.24% and 2.19% in economics can be obtained for sCO2/LiBr-H2O system and sCO2/ammonia water system, respectively. Furthermore, exergy analyses show that the main exergy destructions occur in the reactor and the cooler and the proposed combined sCO2/APG system could effectively reduce around half of the exergy destruction within the cooler of the stand-alone sCO2 system.

Thermodynamic optimisation for open regenerated inverse Brayton cycle (refrigeration/heat pump cycle)

The thermodynamic performances for the model established in Part 1 of this paper are optimised by adjusting the mass flowrate. When the optimisation is performed with the constraints of the fixed power input and the plant size, the coefficient of performance can be maximised again by properly allocating the fixed flow area among the compressor inlet and the expander outlet. The coefficient of performance of refrigeration can be maximised again by properly allocating the fixed heat conductance inventory among the hot and cold side exchangers and the regenerator. The obtained maxima reach its maxima at optimal compressor pressure ratio. When the heat conductance distribution of the regenerator is fixed for the heat pump, the coefficient of performance can be maximised again by properly allocating the fixed heat conductance inventory between the hot and cold side exchangers. The obtained maxima reach its maxima at optimal compressor pressure ratio.

Efficient cycles for carbon capture CLC power plants based on thermally balanced redox reactors

The rotary reactor differs from most alternative chemical looping combustion (CLC) reactor designs because it maintains near-thermal equilibrium between the two stages of the redox process by thermally coupling channels undergoing oxidation and reduction. An earlier study showed that this thermal coupling between the oxidation and reduction reactors increases the efficiency by up to 2% points when implemented in a regenerative Brayton cycle. The present study extends this analysis to alternative CLC cycles with the objective of identifying optimal configurations and design tradeoffs. Results show that the increased efficiency from reactor thermal coupling applies only to cycles that are capable of exploiting the increased availability in the reduction reactor exhaust. Thus, in addition to the regenerative cycle, the combined CLC cycle and the combined-regenerative CLC cycle are suitable for integration with the rotary reactor. Parametric studies are used to compare the sensitivity of the different cycle efficiencies to parameters like pressure ratio, turbine inlet temperature, carrier-gas fraction and purge steam generation. One of the key conclusions from this analysis is that while the optimal efficiency for regenerative CLC cycle was the highest of the three (56% at 3bars, 1200°C), the combined-regenerative cycle offers a trade-off that combines a reasonably high efficiency (about 54% at 12bars, 1200°C) with much lower gas volumetric flow rate and consequently, smaller reactor size. Unlike the other two cycles, the optimal compressor pressure ratio for the regenerative cycle is weakly dependent on the design turbine inlet temperature. For the regenerative and combined regenerative cycles, steam production in the regenerator below 2× fuel flow rate improves exhaust recovery and consequently, the overall system efficiency. Also, given that the fuel side regenerator flow is unbalanced, it is more efficient to generate steam from the fuel side regenerator than from the air side regenerator.

Power and power density analyzes of an endoreversible modified variable-temperature reservoir Brayton cycle with isothermal heat addition

The mistakes in recent literatures are analyzed, and a new model for an endoreversible closed modified Brayton cycle with isothermal heat addition coupled to variable-temperature reservoirs is established using finite-time thermodynamics in this paper. The range of isothermal heat addition modification is determined, and the analytical formulae of the dimensionless power output, thermal efficiency and dimensionless power density of the cycle are derived. The effects of the cycle parameters on the global performances of power output and power density and the performances at maximum power design and maximum power density are analyzed by numerical calculations. The results show that there exist optimal compressor pressure ratios, respectively, which lead to maximum dimensionless power output and maximum dimensionless power density, that the optimal compressor pressure ratio and the thermal efficiency at maximum power design are always smaller than the corresponding ones at maximum power density design, and that dimensionless power output and maximum specific volume at maximum power design are always bigger than the corresponding ones at maximum power density design. The results imply that the power density design possesses the advantages such as smaller equipment volume and higher thermal efficiency at the cost of disadvantages such as bigger compressor pressure ratio and power output loss. Maximizing the power density gives a compromise between power and the size of the engine. The calculations also show that an endoreversible closed modified Brayton cycle with isothermal heat addition cannot work at the maximum thermal efficiency design point.

Ecological performance analysis of an endoreversible modified Brayton cycle

An endoreversible closed modified simple Brayton cycle model with isothermal heat addition coupled to variable-temperature heat reservoirs is established using finite-time thermodynamics. Analytical expressions of dimensionless power output, thermal efficiency, dimensionless entropy generation rate and dimensionless ecological function are derived. Influences of cycle thermodynamic parameters on ecological performance and optimal compressor pressure ratio, optimal power output, optimal cycle thermal efficiency and optimal entropy generation rate corresponding to maximum ecological function are obtained and compared with those corresponding to maximum power output. The results show that cycle thermal efficiency improvement and entropy generation rate reduction are obtained at the expense of higher compressor pressure ratio and a little sacrifice of power output at maximum ecological function. The compromises between power output and entropy generation rate and between power output and cycle thermal efficiency, respectively, are achieved.

Maximum useful energy rate and efficiency of a recuperative Brayton cogeneration plant

A thermodynamic model was developed to analyze the performance of cogeneration plant based on irreversible recuperative Brayton cycle. A parameter, dimensionless total useful energy rate (DTUER), was used as the criterion for performance optimization of cogeneration plant. The effects of cycle parameters, internal irreversibilities, and recuperator efficiency on maximum DTUER and on the efficiency at maximum DTUER were numerically investigated. The relation between DTUER and cogeneration efficiency was also analyzed. The results show that there exists an optimal compressor pressure ratio which maximizes the DTUER. It is also found that there exists an optimal power-to-heat ratio which results in a dual-maximum DTUER.

Thermodynamic optimisation for open regenerated inverse Brayton cycle (refrigeration/heat pump cycle)

The thermodynamic performances for the model established in Part 1 of this paper are optimised by adjusting the mass flowrate. When the optimisation is performed with the constraints of the fixed power input and the plant size, the coefficient of performance can be maximised again by properly allocating the fixed flow area among the compressor inlet and the expander outlet. The coefficient of performance of refrigeration can be maximised again by properly allocating the fixed heat conductance inventory among the hot and cold side exchangers and the regenerator. The obtained maxima reach its maxima at optimal compressor pressure ratio. When the heat conductance distribution of the regenerator is fixed for the heat pump, the coefficient of performance can be maximised again by properly allocating the fixed heat conductance inventory between the hot and cold side exchangers. The obtained maxima reach its maxima at optimal compressor pressure ratio.

Thermodynamic analysis of an integrated power generation system driven by solid oxide fuel cell

A new integrated power generation system driven by the solid oxide fuel cell (SOFC) is proposed to improve the conversion efficiency of conventional energy by using a Kalina cycle to recover the waste heat of exhaust from the SOFC-GT. The system using methane as main fuel consists an internal reforming SOFC, an after-burner, a gas turbine, preheaters, compressors and a Kalina cycle. The proposed system is simulated based on the developed mathematical models, and the overall system performance has been evaluated by the first and second law of thermodynamics. Exergy analysis is conducted to indicate the thermodynamic losses in each components. A parametric analysis is also carried out to examine the effects of some key thermodynamic parameters on the system performance. Results indicate that as compressor pressure ratio increases, SOFC electrical efficiency increases and there is an optimal compressor pressure ratio to reach the maximum overall electrical efficiency and exergy efficiency. It is also found that SOFC electrical efficiency, overall electrical efficiency and exergy efficiency can be improved by increasing air flow rate. Also, the largest exergy destruction occurs in the SOFC followed by the after-burner, the waste heat boiler, the gas turbine. The compressor pressure ratio and air flow rate have significant effects on the exergy destruction in some main components of system.

Exergoeconomic performance optimization for a combined cooling, heating and power generation plant with an endoreversible closed Brayton cycle

Finite time exergoeconomic performance of a combined cooling, heating and power generation (CCHP) plant composed of one endoreversible closed Brayton cycle and one endoreversible four-heat-reservoir absorption refrigeration cycle is investigated by using finite time thermodynamics. Heat conductance distribution among hot-, cold-, thermal consumer-, generator-, absorber-, condenser- and evaporator-side heat exchangers and compressor pressure ratio are optimized by taking the maximum profit rate as objective. Numerical examples show that there exists a sole group of optimal heat conductance distribution among hot-, cold-, thermal consumer-, generator-, absorber-, condenser- and evaporator-side heat exchangers and an optimal compressor pressure ratio which lead to the maximum profit rate. The effects of design parameters on the optimal performance of the CCHP plant are discussed.

Exergoeconomic optimal performance of an irreversible closed Brayton cycle combined cooling, heating and power plant

A combined cooling, heating and power (CCHP) plant model composed of an irreversible closed Brayton cycle and an endoreversible four-heat-reservoir absorption refrigeration cycle is established by using finite time thermodynamics. The irreversibilities considered in the CCHP plant include heat-resistance losses in the hot-, cold-, thermal consumer-, generator-, absorber-, condenser- and evaporator-side heat exchangers as well as non-isentropic losses in the compression and expansion processes. Equations of exergy efficiency and profit rate of the CCHP plant are derived. Based on the finite time exergoeconomic analysis method, profit rate optimization is carried out by searching the optimal compressor pressure ratio and the optimal heat conductance distributions of the seven heat exchangers for a fixed total heat exchanger inventory and with the help of Powell arithmetic. The effects of some design parameters, including compressor and gas turbine efficiencies, ratio of heat demanded by the thermal consumer to power output, heat reservoir temperature ratios and price ratios on the optimal heat conductance distributions, optimal compressor pressure ratio, maximum profit rate and finite time exergoeconomic performance bound of the CCHP plant are discussed by numerical examples. The results obtained may provide some theoretical guidelines for the designs and operations of the practical CCHP plants.