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The purpose of this study is thermo-economic analysis of a combined fuel cell and micro gas turbine power plant cycle for using in small scale CHP systems. Since the fuel cell is the main source of power generation in hybrid systems, in this study, complete electrochemical, thermal and thermodynamic calculations are performed to obtain more accurate results; and unlike most studies, the cell temperature is not assumed constant. The performance analysis of the hybrid system shows that increasing the pressure and air to fuel ratio, causes to loss of electrical efficiency and increase in the electricity price because of reduction in cell and turbine inlet gas temperatures. The other results of this study show that considering the economic life of the system, making use of this type of hybrid systems is economical and generates less electricity price in comparison with micro gas turbine.

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The waste heat management in heavy industry significantly increase productivity in this sector. Organic Rankine cycles (ORCs) are appropriate technology for the conversion of low quality thermal energy to electrical power. The Organic Rankine Cycle(ORC) applies the principle of the steam Rankine cycle, but uses organic working fluids with low boiling points can be used to recover heat from lower temperature heat sources. In this study the performances of three different organic Rankine cycles (ORCs) systems including the basic ORC (BORC) system, the single-stage regenerative ORC (SRORC) system and the double-stage regenerative ORC (DRORC) system using five different working fluids under the same waste heat condition are optimized by thermo-economic method using genetic algorithm. The results indicate that the R113 has the best performance between fluids. The optimized turbine inlet temperature and pressure in comparison with when exergy efficiency uses only, decreases. By changing basic Rankine cycle to the single-stage regenerative and the double-stage regenerative cycles, 12.5% and 18.75% change in specific power cost occurs respectively. Also results indicate that, as superheat degree in turbine inlet increases, the specific power cost increase and the exergy efficiency of system decreases.

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Waste heat recovery systems, which make use of waste sources for their input energy, have considerable importance in industry since they utilize streams, which will be disposed to nature if not employed. Ship’s engines are one of the places, where a large amount of energy is wasted in different forms. In the present article, the idea of making use of these loss streams and consequently producing useful power in the outlet is proposed in the form of two systems. In the first system, the only stream of exhaust gases is utilized, while in the second system, the jacket cooling water is used together with the engine exhaust gases. Screening in the working fluids is conducted in order to select appropriate fluids, which have suitable characteristics in the physical, safety, and environmental aspects. The analyses indicate that using R600a presents the highest net power output, which reaches to the value of about 575 kW at the most. Comparison of the two introduced systems shows that preheating the working fluid by the jacket cooling water makes the better operation of the system and the power output is increased up to about 31-58% in different fluids. The lowest payback period in the systems is achieved through the use of R600a as the working fluid, which is about 3.48 year in the second system.