Thermodynamic Analysis of a Regenerative Brayton Cycle Using H2, CH4 and H2/CH4 Blends as Fuel

Considering a simple regenerative Brayton cycle, the impact of using different fuel blends containing a variable volumetric percentage of hydrogen in methane was analysed. Due to the potential of hydrogen combustion in gas turbines to reduce the overall CO2 emissions and the dependency on natural gas, further research is needed to understand the impact on the overall thermodynamic cycle. For that purpose, a qualitative thermodynamic analysis was carried out to assess the exergetic and energetic efficiencies of the cycle as well as the irreversibilities associated to a subsystem. A single step reaction was considered in the hypothesis of complete combustion of a generic H2/CH4 mixture, where the volumetric H2 percentage was represented by fH2, which was varied from 0 to 1, defining the amount of hydrogen in the fuel mixture. Energy and entropy balances were solved through the Engineering Equation Solver (EES) code. Results showed that global exergetic and energetic efficiencies increased by 5% and 2%, respectively, varying fH2 from 0 to 1. Higher hydrogen percentages resulted in lower exergy destruction in the chamber despite the higher air-excess levels. It was also observed that higher values of fH2 led to lower fuel mass flow rates in the chamber, showing that hydrogen can still be competitive even though its cost per unit mass is twice that of natural gas

Economic Study of Solar Thermal Plant based on Gas Turbines

The goal of this thesis is to carry out an economic analysis of solar thermal plant based on gas turbines. Throughout the project , there is a brief overview of different technologies used today in CSP without going into greater depth in most of them, but emphasizing solar tower technology with solar hybrid gas turbines. Having explained the reason why this technology has been chosen, possible configurations currently found in the solar panorama will be considered. Then, with the help of a thermodynamic software, called IPSE, all necessary data will be extracted for further economic evaluation. All configurations tested are hybrid using a fuel support based on Brayton cycle. Before carrying out the economic analysis, it will attempt to optimize the electrical efficiency and see how it affects to the levelized cost of electricity. Finally, all the configurations studied will be compared considering economic and energetic aspects.Outgoin

Detailed analysis of the effect of the turbine and compressor isentropic efficiency on the thermal and exergy efficiency of a Brayton cycle

Energy and exergy analysis of a Brayton cycle with an ideal gas is given. The irreversibility of the adiabatic processes in turbine and compressor is taken into account through their isentropic efficiencies. The net work per cycle, the thermal efficiency and the two exergy efficiencies are expressed as functions of the four dimensionless variables: the isentropic efficiencies of turbine and compressor, the pressure ratio, and the temperature ratio. It is shown that the maximal values of the net work per cycle, the thermal and the exergy efficiency are achieved when the isentropic efficiencies and temperature ratio are as high as possible, while the different values of pressure ratio that maximize the net work per cycle, the thermal and the exergy efficiencies exist. These pressure ratios increase with the increase of the temperature ratio and the isentropic efficiency of compressor and turbine. The increase of the turbine isentropic efficiency has a greater impact on the increase of the net work per cycle and the thermal efficiency of a Brayton cycle than the same increase of compressor isentropic efficiency. Finally, two goal functions are proposed for thermodynamic optimization of a Brayton cycle for given values of the temperature ratio and the compressor and turbine isentropic efficiencies. The first maximizes the sum of the net work per cycle and thermal efficiency while the second the net work per cycle and exergy efficiency. In both cases the optimal pressure ratio is closer to the pressure ratio that maximizes the net work per cycle

Another view on the optimization of the Brayton cycle with recuperator

Bezdimenzijski izrazi za rad, termički stupanj djelovanja, dovedenu toplinu i značajku entropijske produkcije u Braytonovom ciklusu s rekuperatorom su prikazani kao funkcije sedam ulaznih parametara: omjer tlakova, omjer temperatura, efikasnost rekuperatora, izentropski stupnjevi djelovanja kompresora i turbine, bezdimenzijski pad tlaka u komori za izgaranje i rekuperatoru te izentropski koeficijent. Izvedeni su izrazi za omjere tlakova koji maksimiziraju ili minimiziraju razmatrane veličine.Budući da nije moguće maksimizirati sve veličine pri jednoj vrijednosti omjera tlakova, definirana su tri kriterija optimizacije: (i) maksimalni rad, (ii) maksimalni termički stupanj djelovanja i (iii) maksimum njihove težinske sume. Za svaki kriterij dana su dva dijagrama iz kojih se može odabrati optimalni omjer tlakova i očitati sve osnovne veličine koje definiraju Braytonov ciklus. U slučaju kriterija maksimalnog termičkog stupnja djelovanja, kada je efikasnost rekuperatora manja od određene vrijednosti, Braytonovo ciklus bez rekuperatora je bolji nego onaj s rekuperatorom. U slučaju ostala dva kriterija, Braytonov ciklus s rekuperatorom je uvijek bolji od onog bez rekuperatora, bez obzira na vrijednost efikasnosti rekuperatora.Nondimensional expressions for the work output, thermal efficiency, heat input, and entropy generation number in the Brayton cycle with a recuperator are given as functions of seven input parameters: pressure ratio, temperature ratio, recuperator effectiveness, turbine and compressor isentropic efficiencies, nondimensional pressure drop in the combustor and recuperator and the ratio of specific heat capacities. The expressions for pressure ratios which maximize or minimize the considered quantities are derived. Since it is not possible to maximize all the quantities at a unique value of pressure ratio, three optimization criteria: (i) maximum work output, (ii) maximum thermal efficiency, and (iii) maximum of their weighted sum are defined. For each criterion two diagrams from which one can select optimal pressure ratio and read out all basic quantities defining the Brayton cycle are provided. In the case of criterion of maximum thermal efficiency, when the recuperator effectiveness is lower than the certain limit, the Brayton cycle without a recuperator is better than that with it. In the case of other two criteria, the Brayton cycle with a recuperator is always better than that without it, regardless of the value of the recuperator effectiveness

a vector optimization methodology applied to thermodynamic model calibration of a micro gas turbine chp plant

Abstract This paper is focused on the validation of a cogeneration plant based on micro gas turbine. The experimental data related to design working point are compared to thermodynamic model results using a multi-variable multi-objective methodology depending on a genetic optimization algorithm (MOGA-II). The result with lowest Euclidean norm in objective functions space represents the operating conditions closest to experimental data, and it highlights at the same time the reliability of chain measurement. Finally, this preferred result is plotted on turbomachinery performance maps in order to validate indirectly the methodology outcomes

Carnot Cycle and Heat Engine Fundamentals and Applications II

This second Special Issue connects both the fundamental and application aspects of thermomechanical machines and processes. Among them, engines have the largest place (Diesel, Lenoir, Brayton, Stirling), even if their environmental aspects are questionable for the future. Mechanical and chemical processes as well as quantum processes that could be important in the near future are considered from a thermodynamical point of view as well as for applications and their relevance to quantum thermodynamics. New insights are reported regarding more classical approaches: Finite Time Thermodynamics F.T.T.; Finite Speed thermodynamics F.S.T.; Finite Dimensions Optimal Thermodynamics F.D.O.T. The evolution of the research resulting from this second Special Issue ranges from basic cycles to complex systems and the development of various new branches of thermodynamics

Design considerations on a small scale supercritical CO2 power system for industrial high temperature waste heat to power recovery applications

Existing industrial processes are energy intensive environments with a multitude of waste heat streams at different temperature levels whose recovery would undoubtedly contribute to the enhancement of the sustainability of the industrial sites and their products. In particular, the geographical distribution and size of the available waste heat potential is very widespread with most sources being small to medium size, up to 1 MW and fewer of larger size above 1 MW. Among the waste heat to power conversion approaches, the usage of bottoming thermodynamic cycles based on carbon dioxide in supercritical phase (sCO2) provides significant advantages compared to more conventional technologies such as the Organic Rankine Cycle (ORC) systems that are nowadays commercially available even at small scale (~10 kWe). However, unlike the large sCO2 systems that are already on the market (~ MWe), medium and small size ones are still under development. In the current work, the challenges involved in the design of a small scale sCO2 system are considered through thermodynamic analysis (1st and 2nd law) as well as by a preliminary turbomachinery design based on the similarity approach. With reference to a simple regenerative cycle architecture, the study provides details on the design parameters and performance trends as well as on the operational and manufacturing constraints that the compressor imposes to the theoretical values

New energy conversion techniques in space, applicable to propulsion

The powering of aircraft with laser energy from a solar power satellite may be a promising new approach to the critical problem of the rising cost of fuel for aircraft transportation systems. The result is a nearly fuelless, pollution-free flight transportation system which is cost-competitive with the fuel-conservative airplane of the future. The major components of this flight system include a laser power satellite, relay satellites, laser-powered turbofans and a conventional airframe. The relay satellites are orbiting optical systems which intercept the beam from a power satellite and refocus and redirect the beam to its next target

Liquid-Flooded Ericsson Power Cycle

In this paper, the use of liquid flooding is examined to create a high efficiency Ericsson Power Cycle. The introduction of significant amounts of liquid into the compression and expansion processes of a gas leads to quasi-isothermal behavior approximating that of an Ericsson cycle. A thermodynamic model is presented and various working fluid pairs are examined under operating conditions suitable for solar thermal power generation. The Liquid-Flooded Ericsson Cycle (LFEC) can be manufactured with fixed volume ratio machinery currently mass produced for the refrigeration industry. In this manner low cost, distributed solar thermal generation can be promoted. The thermodynamic performance of the LFEC is compared to that of other power cycles proposed for solar thermal systems. It is shown that for sufficiently high component efficiencies the Liquid-Flooded Ericsson Cycle provides higher thermal efficiencies than any other power cycle currently under consideration