Comparison of micro gas turbine heat recovery systems using ORC and transcritical CO2 cycle focusing on off-design performance
Suk Young Yoon, Min Jae Kim, In Seop Kim, Tong Seop Kim
Session: Session 1A: CO2 Power System
Session starts: Wednesday 13 September, 10:30
Presentation starts: 12:10
Room: Building 27 - Lecture room 01
Suk Young Yoon (Graduate School, Inha University)
Min Jae Kim (Graduate School, Inha University)
In Seop Kim (Graduate School, Inha University)
Tong Seop Kim (Dept. of Mechanical Engineering, Inha University)
Micro gas turbines (MGT) are widely used for distributed generation due to the advantage of being able to produce electricity with high specific output. The exhaust temperature of MGT is still high almost 300oC in recently developed MGTs even though it is equipped with a recuperator at the turbine exit. One way to reduce the energy loss due to the high temperature gas exhaust is recovering the heat of the exhaust gas of the MGT and produce additional power using a bottoming cycle. In this study, we applied two heat recovery systems to an MGT and compared the performance of them. They are an organic Rankine cycle (ORC) and a transcritical CO2 cycle (tCO2). Toluene which is generally used for the high-temperature heat source is used as the working fluid of the ORC. For the tCO2 cycle, heat recuperation was adopted to maximize the bottoming cycle efficiency. System simulation was performed using HYSYS . Since MGTs usually operate to follow the electric power demand, an off-design performance is also important. Therefore, we also analyzed the off-design performance of the two bottoming cycles with the load variation of the MGT. The performance curve, the effectiveness-NTU method, and the Stodola’s equation  were used to model the off-design operations of all the bottoming cycle components such as a pump, a turbine and heat exchangers. According to the calculation result, the power output of ORC was higher than that of tCO2 cycle when MGT operates at a full load. However, since the power output variation with MGT load change is larger in the ORC, the power output of tCO2 becomes larger when MGT operates at part load below 80%. Accordingly, we can conclude that the tCO2 is suitable for the heat recovery system utilizing MGT exhaust gas in places where the MGT needs to operate at low loads during a lot of its operating hours. On the other hand, in applications where the MGT can operate at near full load conditions, the ORC is more suitable.
 Aspen Technology, AspenOne HYSYS, Ver. 7.2.
 In Seop Kim, Tong Seop Kim, Jong Jun Lee, 2016, “Off-design performance analysis of organic Rankine cycle using real operation data from a heat source plant” Energy Conversion and Management, Vol. 133, Issue 1, pp. 284-291.