Thermodynamic Model of a Cascaded Organic Rankine Cycle Power Plant

Abstract

The Alternative Energy Lab at GE Global Research has fully developed a functional power plant to recover waste heat from a Jenbacher engine using a Cascaded Organic Rankine Cycle. This solution is required to produce additional electricity, by using the heat rejected by an engine without changing or disturbing its way of functioning. Therefore, it is particularly important that such systems can adapt to changes in the gas engine operating point and hence changes in the amount of waste heat given to the system. Moreover the system has to conserve a good e ciency when ambient conditions are changing. This novel cycle concept reaches a high e ciency by separating the recovery of high and low temperature sources of the J420 GS Jenbacher engine. Indeed the J420 GS is a 1451 kW gas engine working with biogas and rejecting heat to the ambient atmosphere through two temperature sources, which are potential sources for the CORE cycle: a low temperature source, constituted by the engine cooling water system and a high temperature source constituted by the exhaust gas stream going out of the engine. Scope of this thesis is the establishment of a thermodynamic model of the CO.Ra product. EBSILON will be the platform for the development of the model. This thesis is the rst work at GE Global Research Munich using this simulation software. Therefore, the main scope of this work is to nd out whether EBSILON is suitable or not to run ORC simulations both under design and off-design conditions. For this purpose, the current EBSILON component capabilities will be studied. To match the simulation requirements the standard components will be extended. Once the model is assembled in design and off-design mode, off-design simulations will be performed. The focus of the steady-state off-design simulations carried out in this study is on the one hand, the sensitivity analysis of the model and on the other hand the calculation of the rotary speed of pumps in order to operate the plant close to the design point.