Desiccant-assisted multistage air compression systems: Performance improvement and humidity control

Abstract

Novel desiccant-assisted systems have been evaluated for reducing the work required in multistage air compression processes. While traditional inter-cooling is generally achieved by placing heat exchangers between compression stages, the systems herein proposed are based on harvesting heat rejection to drive a desiccant cooling system. This cooling effect is then used to cool the air between the compression stages below ambient temperature, and also to pre-cool the air prior admission to the first stage, allowing for a reduction of the compression work. In addition, desiccant dehumidification is also used to control the humidity of the air in the compression system. A model based on steady-state heat and mass transfer balances across all components is presented and computationally implemented for a two-stage compression system. Numerical results are analyzed in terms of a performance factor, showing that some configurations can achieve a reduction in compression work almost 60% greater than that achieved with conventional inter-cooling systems. A final test-case was also presented, based on inlet conditions extracted from weather data of Rio de Janeiro, Brazil, demonstrating that the proposed compression schemes could be used as a viable option for reducing compression work in multi-stage systems. The use of a waste-heat-driven desiccant-assisted system for reducing compression work and controlling humidity, is an important addition to applications of desiccant cooling.