No abstract

In this study, three different gas turbine cogeneration systems that are preheating air, preheating air-fuel and simple cycles where steam injected in to combustion chamber are analyzed. The effects of steam injection on thermoeconomic performance are calculated and obtained. By using the first law of thermodynamics, the exergy analysis and economic methods, simulation programs written by the authors in FORTRAN code are obtained to use for the analyses. Thermoeconomic performance of these three different cycles for different stage and variable mass of injected steam are obtained and compared with literature. The effects of injection steam in to combustion chambers of those three cycles for variable compressing ratios, on power, efficiencies, product price and performances are obtained. Consequently, the advantages and the disadvantages of injection steam are evaluated. The results obtained in this study are compared with the results available in the literature. Injection steam into combustion chamber increases the electricity efficiency and electricity power but decreases the heat power of the cycles. Also the produced electricity price for per kWh is increasing.

The purpose of this article is to evaluate four different gas turbine cogeneration cycles which are basic, absorption cooling, air heating and air fuel heating cogeneration cycles by using the most important six evaluation criteria for different excess air coefficient, different compression rates, and different compressor inlet air temperatures. These six evaluation criteria are electrical heat ratio, exergy efficiency, incremental heat rate, artificial thermal efficiency, fuel energy saving ratio, and specific fuel consumption. It is seen that the air-fuel heating cogeneration cycle is the most efficient among the cycles examined for a certain compressor compression ratio, followed by the air heating, basic, and absorption cooling cycles.

There is a need for cooling by using the waste heat energy in food industry. Absorption cycles can be driven by waste thermal, geothermal, solar or industrial processes energies. In this study, cascade refrigeration system is thermodynamically modeled, and analyzed by using first law of thermodynamics, and exergy method. Thermodynamic properties such as pressure, temperature, entropy, enthalpy, exergy, mass flow rate in each stream are calculated for 50, 75, 100• C and for 0.8, 1.0, and 1.5 MPa pump pressure. A computer program is used that was prepared in FORTRAN by the author for the analyses. It is found that the compression-absorption cascade cooling cycle is appropriate for most of the kind of waste heat applications. Increase of the generator inlet heat temperature increases the generator inlet heat, the absorber outlet heat and the condenser 2 outlet heat energies and decreases the coefficient of performance of the absorption and the overall cycles. The generator heat decreases with increase of the pump pressure. Also increase of the pump pressure decreases the coefficient of performance of the absorption and the overall cycles. Increase of the pump pressure and the generator temperature decreases the exergetic coefficient of performance. Increase of the generator temperature and pump pressure increases the generator inlet exergy. It is concluded that increase of the generator temperature and the pump pressure increases the total destructed exergy of the cycle.

Ammonia-water power cycles are important for efficient utilization of low temperature heat sources such as geothermal, solar, waste heat sources, etc. For some special conditions ammonia-water power cycle is an important and economical option. This paper presents an exergetic analysis of a combined power and cooling cycle that uses ammonia-water mixture as working fluid. Such cycles, use solar or geothermal energy or waste heat energy from a conventional power cycle. Ammonia-water power cycle can be used as independent cycles to provide power output and cooling. For a range (25-55 Bar) of boiler pressure the performance of the combined power and cooling cycle is investigated. The exergy of the boiler is very low compared to its energy. There is a boiling process and a heat transfer process at low temperature, both of which destruct the energy given to the boiler, so that the energy efficiency is low; however the exergy efficiency is higher than the energy efficiency. Increasing the turbine inlet pressure decreases the energy and exergy efficiencies.

The electrical energy consumption is increasing in our country and in the world. The electrical energy and heat energy are primary energies and has a vital role on industry and our lives. The production of these two energies in different cycles leads to energy loss and low efficiency. With the production of both in the same cycle, the efficiency increases a lot, and the energy losses and emission values decrease a lot. By installing cogeneration system to produce electrical and heat energy, the energy consumption costs can be reduced importantly. The cycle in which the fuel and the air entering into combustion chamber is heated by the heat taken from the exhaust gases at the outlet of the gas turbine is analyzed by using exergy analysis method and, first and second laws of thermodynamics. The heat energy remained in the exhaust gases are used to produce in steam production, after some heat energy is consumed to heat the air and the fuel, in this cycle. The performance analysis of the devices that make up the cycle such as turbine, recuperator compressor, combustion chamber, and heat exchanger and for the whole cycle and were obtained and discussed. Exergy efficiency, exergy losses and other performance parameters of the devices were obtained and discussed.

Original scientific paper In this study eight methods are evaluated for a gas turbine cogeneration cycle to improve the efficiency. These methods are increasing gas turbine inlet air temperature, cooling the inlet air of the compressor, air preheating, fuel preheating, increasing compressor inlet air pressure, increasing air excess rates, steam injection, and humidification of the inlet air of the compressor. These methods are studied in order to compare their effects on the performance of the systems. The effects of these methods on the exergetic efficiency depend on the kind of the cogeneration cycle. By combining recuperation, preheating fuel and steam injection methods high efficiency can be achieved. The combined methods give the best results under variable heat demands of the market. An appropriate combination of the efficiency improvement methods may increase the exergetic efficiency about 20 %. The results show that efficiency improvement methods must be applied together whenever it is possible. Keywords: cogeneration; efficiency; improvements Poboljšanje učinkovitosti kogeneracijskih sustava plinske turbineIzvorni znanstveni članak U radu se procjenjuje osam metoda za poboljšanje učinkovitosti kogeneracijskog ciklusa plinske turbine. Tim se metodama povećava temperatura ulaznog zraka plinske turbine, rashlađuje ulazni zrak kompresora, predgrijava zrak, predgrijava gorivo, povećava tlak ulaznog zraka kompresora, povećava brzina viška zraka, ubrizgava para i vlaži ulazni zrak kompresora. Te se metode istražuju kako bi se usporedilo njihovo djelovanje na performanse sustava. Učinci tih metoda na egzergetsku učinkovitost ovise o vrsti kogeneracijskog ciklusa. Kombiniranjem metoda rekuperacije, predgrijavanja goriva i ubrizgavanja pare može se postići visoka učinkovitost. Kombinirane metode daju najbolje rezultate kod različitih potreba tržišta za toplinom. Odgovarajućom kombinacijom metoda za poboljšanje učinkovitosti može se povećati egzergetska učinkovitost za oko 20 %. Rezultati pokazuju da se metode za poboljšanje učinkovitosti moraju primijeniti zajedno kada je god to moguće.

Internal combustion engines use generally fossil fuel products. World resources of it is limited. Renewable alternative energy sources are getting important solution for energy demand. Hazelnut oil ethyl ester is obtained from raw hazelnut and mixed with diesel oil in certain proportions to use in a four-stroke direct injected single cylinder diesel engine. In this study the effects of the mixture of diesel oil with hazelnut oil ethyl ester on the engine performance and exhaust gas emissions are investigated for the first time in literature. The fuel injection system is regulated to use the mixture in the engine for the investigation. The results show that, the mixture with 25% ethyl ester extracted from hazelnut oil can be used as an alternative fuel without any change or regulation of the diesel engine.