Improving the Energy Efficiency of Compressed Air Systems by Use of Pressure Equalizing Modules

Compressed air is a widely used energy carrier; however, its production is associated with a low energy efficiency. The utilization of isobaric compressed air receivers can increase the storage capacity significantly while simultaneously lower the energy demand. In this work, we propose a novel concept of an isobaric compressed air receiver based on pressure equalizing modules (PEQM), which combine different phase change materials for maintaining constant pressure as well as for storing heat. The PEQM can be placed into the receiver, and by the interaction of many modules, compressed air is stored isobarically. In a test plant, which emulates a compressed air system (CAS) with a fixed-speed oil-injected rotary screw compressor, a dryer, and a 250 l compressed air receiver, energy measurements are conducted. Since a pressure range may still be required for control purposes, the investigations in this paper are carried out within a pressure range of 2 bar. Based on the experimental results, the potential energy savings, due to equipping the receiver with PEQM, are determined theoretically. Approximately, 995 PEQM are fitting inside the receiver. They increase the storage capacity by 58.5% in a pressure range of 2 bar and lead to energy savings of around 9%. A major reason for the lower energy consumption is the stopping of the compressor, as the larger storage capacity allows more air to be used for a longer period of time. Based on that, isobaric compressed air receivers for CAS with fixed-speed compressors could be a promising measure to improve energy efficiency and should therefore be further developed.