A new concept for generating mechanical work from gas permeation

Abstract

Large amounts of energy are available from gas concentration gradients in thermal power plant exhaust. For example, the energy potential of carbon dioxide and water vapor gradients from flue gas and cooling towers of coal-fired and natural gas-fired power plants represents 1–2% of the plant's overall capacity. In this paper, we introduce a novel membrane-based gas permeation process for using concentration gradients of gas mixture to generate useful mechanical work in the form of compressed gas flow. The concept is experimentally validated using a simple binary gas mixture of nitrogen and water vapor with commercially available polydimethylsiloxane membranes. Power density from water vapor flux of 57 mW/m2 and power density from net gas flux of 11.5 mW/m2 are observed under relatively conservative laboratory test conditions. Fundamental transport dynamics are modelled and used to simulate the response of the system to membrane properties and feed concentrations, and up to 600 mW/m2 is reported for the cases considered. The possibility of recovering energy from exhaust gases may open up new opportunities for improving power plant efficiency and sustainability.