Abstract
CO2-based trans-critical and supercritical cycles have received more and more attention for power generation in many applications such as solar and nuclear energy due to the desirable thermal stability and properties of CO2 and the high efficiency and compact size of the plant. In this study, two combined cycles driven by the flue gas exhausted from the LM2500+ gas turbine, CO2-TC+OTC (organic trans-critical cycle) and CO2-TC/OTC, which can achieve a good trade-off between thermal efficiency and utilization of the waste heat, are investigated. Parameters optimization is carried out by means of genetic algorithm to maximize the net power output of the combined cycle and the effects of the key parameters on the cycle performance are examined. Results show that the exergy efficiency of CO2-TC+OTC is about 2% higher than that of CO2-TC/OTC. In CO2-TC+OTC, the recuperation process of CO2 causes the largest exergy loss; in CO2-TC/OTC, the largest exergy loss occurs in the heat recovery vapor generator, followed by the intermediate heat exchanger due to the larger variation of the specific heat capacity of CO2 and organic fluid in the heat addition process.
Highlights
Recovering waste heat from the engines, gas turbines and industrial processes such as cement, glass and metallurgy and so forth, can effectively improve energy utilization efficiency, reducing fossil fuel consumption and CO2 emissions
In CO2 -trans-critical cycle (TC)/organic trans-critical cycle (OTC), the largest exergy loss occurs in HRVG, followed by intermediateheat heat exchanger (IHE)
This study aims to compare the thermodynamic performance of two combined cycles that is, CO2 -TC+OTC and CO2 -TC/OTC, for waste heat recovery
Summary
Recovering waste heat from the engines, gas turbines and industrial processes such as cement, glass and metallurgy and so forth, can effectively improve energy utilization efficiency, reducing fossil fuel consumption and CO2 emissions. In addition to the direct heat utilization of waste heat, such as preheating air and raw materials, building heating and so forth, power recovery is another practical option, especially for the medium-to-high temperature waste heat sources. Organic Rankine cycle (ORC) and organic trans-critical cycle (OTC) prove to be the promising technologies for the heat to power conversion under the low-to-medium temperature heat sources [1], which is mainly attributed to the lower critical temperature and the dry or isentropic characteristics of the organic working fluids. Carbon dioxide (CO2 ) has attracted more and more attention due to its high thermal stability. It is environmentally friendly, non-corrosive, non-toxic, non-flammable, easy to obtain and with the desirable heat and mass transfer properties
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