mohammad zoghi

In recent years, the use of Gas Turbine-Modular Helium Reactor (GT-MHR) which operates in accordance with closed Brayton cycle with helium fluid as working fluid has attracted researchers’ attention because of its high efficiency, high reactor safety, being economical, and low maintenance costs. In the present study, a combined system, including GT-MHR cycle, Kalina cycle and Ammonia-water absorption cycle is investigated with respect to energy, exergy, and exergoeconomic. As the bottoming cycle, Kalina cycle and absorption cycle are used in order to avoid energy wasted by gas turbine cycle and to increase efficiency of energy conversion. The results of the simulated model show that, in the basic input mode, the overall work is 304462 kW, the overall exergy destruction is 289766kW and the overall exergy efficeincy of cogeneration cycle is 0.689kW. Also reactor, turbine and compressor in helium cycle are the component to which more attention should be paid with respect to exergoeconomic because the highest amount of cost rate is related to these components. At the end, parametric analysis is carried out in order to evaluate the effect of the changing pressure ratio of helium compressor, input temperature of helium compressor, input pressure and temperature of turbine and mass fraction of the base mode of the Kalina cycle on the output parameters.

Organic Rankine Cycles are appropriate technology for the conversion of low quality thermal energy to electrical power. In this research the organic Rankine cycle was studied from energy, exergy and exergo-economic points of view, and it was simulated with hybrid solar and geothermal heat source in order to produce electricity and hot water. In this configuration, 90℃ geothermal brine was used to preheat the organic fluid and 150℃ solar fliud was used for organic fluid evaporation. Waste heat in condenser was also used to produce hot water. Simulation results show that power energy and exergy efficiency of combined heating are 0.566 and 0.156 and electrical energy and exergy efficiency are 0.057 and 0.065, respectively. Moreover, the amount of work output and total irreversibility are 50 and 671.1, respectively. Solar collector, the evaporator and condenser are the most important components from the exergo-economic point of view, due to the high initial cost rate and Exergy destruction. Parametric analysis result shows that the temperature increase in evaporator has positive effect on cycle operation and causes the increase in electricity efficiency and decrease in irreversibility. Also, the increase in pinch point temperature difference of evaporator has a negative effect on cycle operation. From economic point of view, the increase in evaporator and pinch point temperature difference of evaporator causes the decrease in capital coast rate. Also, the solar radiation change find to have positive effect on system operation, based on exergo-economic point of view, which causes the increase in energy and exergy efficiency.

Considering the daily increase of consumption and expense of nonrenewable energies such as natural gas and electricity, application of clean and renewable energies such as solar thermal energy nowadays has been highly taken into consideration. In this research, at first, simple steam Rankine cycle and two different configurations of combined steam and organic Rankine cycles with parabolic trough solar collector as heat source are simulated from energetic and exergetic point of view. First configuration was basic steam rankine cycle with parabolic trough solar collector (PTSC) as heat source, and other configurations of the combined cycle worked as follows: In the second configuration (combined cycle with intermediate heat exchanger), with the increase of steam condenser pressure, heat dissipation in condenser is used as heat source for bottoming organic Rankine cycle and in the third configuration (combined cycle without intermediate heat exchanger), reduced-temperature solar fluid moving output of steam rankine cycle acted as the organic Rankine cycle heat source. Simulation results in the basic input state show that third configuration has the maximum amount of work and irreversibility and second configuration has the minimum amount of work and irreversibility which in this case, increase in the steam cycle condenser pressure leads to the reduction of work of combined cycle with intermediate heat exchanger, even lower than the simple steam cycle. On the other hand, second configuration has the maximum solar energy and exergy efficiency among three configurations which is due to the reduction of collector area required in this configuration.

In this research, ammonia-water regenerative Rankine cycle driven by solar energy and LNG as it’s heat sink in condenser, is simulated from the energy, exergy and exergoeconomic point of view. A relatively new method is used to implement pinch temperature difference in heat exchangers which causes improving of the thermodynamic performance and output power of the system. Also heat exchangers are simulated by using heat transfer correlations of shell and tube heat exchanger in details. The results of based condition showed the suitable performance of natural gas cycle from the thermodynamic and exergoeconomic point of view and notifies the importance of using the natural gas cycle. Solar collector and condenser of ammonia-water cycle because of their high cost value, are introducing as the components that shoud be more concidered from the exergoeconomic viewpoint. The parametric analysis results show that in high inlet pressure of ammonia-water turbine, the exergy efficiency and the total cost of the system heve more suitable values while the net output power of the system decreases. Also by changing the ammonia mass fraction, changing of output parameters has a complicated patern. Finally by increasing the pinch temperature difference in heat exchangers, the decreased amount of system’s thermodynamic performance is more than the amount of system’s economical performance improvement.

In this study, at first the combined steam and organic Rankine cycles, have been stimulated with high-temperature wasted hot gases recovery, from the energy and exergoeconomic points of view. In the configuration of the combined cycles, the high-temperature wasted gases acts as the source of steam cycle evaporator, then the decreased temperature exhaust gas of the steam cycle evaporator, is used as the low temperature source of organic cycle evaporator. Afterward the effects of changing different parameters such as temperature of the evaporator and condenser of steam cycle and pinch temperature difference, on the amount of total output work, total irreversibility, energy efficiency, exergy efficiency and exergoeconomic variables have been checked. The results in base state show that, energy and exergy efficiency of combined cycles are 0.2782 and 0.5279 respectively and the amount of output work and total irreversibility are 71401kW and 43616kW respectively. Total exergoeconomic factor for the combined cycles is 12.47 percent, which represents a high exergy destruction in components and recommends raising the initial cost of components in order to improve the performance of system. The evaporator, turbine and condenser of steam cycle, are the components that should be considered from the perspective of the exergoeconomic, because they contains the maximum amount of total initial costs and the cost of exergy destruction.