Sensitivity analysis of Double Transmission Double Expansion (DTDE) systems for assessment of the environmental impact of recovering energy waste in exhaust air from compressed air systems

This paper focuses on energy savings from compressed air that is removed (expanded) through muffles into the ambient environment. We present a novel analysis of the Double Transmission Double Expansion (DTDE) approach as part of thermodynamic cycles, a new collector system and a significant improvement in the internal construction of our Energy Harvester Unit (EHU). It means necessary research tests that will improve the environmental impact of any pneumatic machine operating on an industrial scale, and will also guarantee that the introduction of back pressure will not interfere with the normal operation of the machine. In this way, we are able to compensate for the over-scaling of the pneumatic machine. Analysis of DTDE thermodynamic cycles reveals a decrease in gauge pressure in dead volumes, which reduces ”dead work” in the operating cylinders within the associated devices. To connect our EHU with an operating machine, we need to develop a collector system. Such system is an intermediate installation that automatically starts the pressure level in the back pB to an acceptable level when the pneumatic machine operates in the same way as mentioned earlier. Thus, the waste of power pBV̇B is constant, so the volumetric flow V̇B should also work automatically. In this way we can adapt any operating condition of the exhaust part of the pneumatic machine to the necessary condition required by the EHU. Finally, the DTDE approach has been assessed using two environmental factors that analyse electricity consumption and decrease the operation time of the compressor. To prove this concept, industrial tests on a small scale have been carried out. We are also changing the internal construction of the EHU by introducing a slide-crank mechanism instead of the gear system (gear wheel rack) used previously. This modification ensures a significant improvement in electricity savings achieved, from 4% to 11%. Short calculations of annual cost savings (ACS) for the DTDE indicate savings of about 1/3 of the compressor’s operating costs. It brings more benefits in terms of practical solutions for energy management systems. According to the results, we are able to propose and analyse Closed Cycle (CC) and Exhaust Air Re-circulation (EAR) methods that manage the air power which exits through the machine outputs, i.e. mufflers. We were surprised by the amount of annual cost savings (ACS) for the new CC and EAR concepts compared to DTDE. However, we want to emphasise that CC and EAR calculations did not take into account losses due to leakages, friction along the length of the pipeline, as well as the low efficiency of the booster. Therefore, in practice, the real savings of the CC and EAR concepts are unknown and are still waiting for confirmation.