Dynamic modeling of multistage compression cooled by a supersonic ejector cycle

The energy storage at large scale is a worldwide issue, many research works are done in order to bring satisfactory solutions. It is in this context that the The Government of the Wallonia, through the Departement des Programmes de Recherche - Direction des Programmes regionaux lauched the CAES-CET project, Compressed Air Energy Storage Cooled by Ejector Technology project. Both UCLouvain (Université catholique de Louvain) and ULB (Université libre de Bruxelles) has been engaged into the project. CAES is a low cost technology for storing large quantities of electrical energy in the form of high-pressure air. The project aims to evaluate the techno-economical feasibility of the storing of compressed air energy. The air is compressed using a three stage compressor with inter-cooling between each stages. The cooling between the first and second stage is made with a supersonic ejector cycle using R134A as refrigerant. This type of technology aim to decrease the full electric consumption of the cycle for given compression characteristics of the compressor. This paper consists of two main parts. The "steady modeling" part which consists of the modeling and sizing of the elements of the cycle. For the sizing of the elements of the cycle, a set of ambient conditions, called the reference conditions are applied to the system. The cycle under these conditions is called the reference case. The air between the first and second stage of compression is cooled by a supersonic ejector cycle, between the two other stages the air is cooled by a water cycle. The second part of this paper is the dynamic modeling of the cooling system between the first and second stage of compression. This research work aims to characterize the dynamic behavior of this cycle when three time varying disturbances are applied. The first case study is the closing of the evaporator electro-valve which feeds the secondary inlet of the ejector. The second case of study is the loss of the water cooling system in the condenser. Finally, the last case is the study of the change in the ambient air conditions at the inlet of the compressor during a given time period of three hours.