Abstract
This paper presents an off-design analysis of a gas turbine Organic Rankine Cycle (ORC) combined cycle. Combustion turbine performances are significantly affected by fluctuations in ambient conditions, leading to relevant variations in the exhaust gases’ mass flow rate and temperature. The effects of the variation of ambient air temperature have been considered in the simulation of the topper cycle and of the condenser in the bottomer one. Analyses have been performed for different working fluids (toluene, benzene and cyclopentane) and control systems have been introduced on critical parameters, such as oil temperature and air mass flow rate at the condenser fan. Results have highlighted similar power outputs for cycles based on benzene and toluene, while differences as high as 34% have been found for cyclopentane. The power output trend with ambient temperature has been found to be influenced by slope discontinuities in gas turbine exhaust mass flow rate and temperature and by the upper limit imposed on the air mass flow rate at the condenser as well, suggesting the importance of a correct sizing of the component in the design phase. Overall, benzene-based cycle power output has been found to vary between 4518 kW and 3346 kW in the ambient air temperature range considered.
Highlights
In recent years, the accelerated consumption of fossil fuels caused many serious environmental problems, such as global warming, depletion of the ozone layer and atmospheric pollution
The electrical power output shows a similar trend for each fluid considered (Figure 4), indicating the best performances for benzene and toluene independently from the ambient air temperature considered
The power output is strongly affected by the hot gas mass flow rate, while the effects of the hot gas temperature are less evident since the maximum oil temperature is imposed to be equal to its limit
Summary
The accelerated consumption of fossil fuels caused many serious environmental problems, such as global warming, depletion of the ozone layer and atmospheric pollution. Organic Rankine Cycle (ORC) power plants have proved to be an attractive solution for the conversion of low/medium grade heat into electricity. This kind of cycle allows the usage of clean energy sources, such as solar radiation [2], geothermal water/steam [3,4], biomass [5]. Dry fluids are preferred because of the positive slope of their saturation vapour curve that prevents liquid formation during expansion [6] This choice is based on environmental impact: several studies on the fluid’s polluting properties can be found in literature, as in the work of Chen [7]. ORC power plants tend to have numerous advantages, such as reliability, quiet operation, long life and compact size [8]
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