Energy from carbon dioxide: Experimental and theoretical analysis of power generation from membrane-based sweep gas permeation

Large amounts of energy are available from gas mixture gradients at exhaust sources such as power plant flue gases. Converting energy from exhaust to useful work, may open up new opportunities for improving power plant efficiency and sustainability. In this paper, we evaluate the novel concept of using sweep gas permeation of carbon dioxide CO2 across a membrane to generate power. Using a custom laboratory bench with a commercial polydimethylsiloxane membrane, power potential of up to 6.35 W/m(2) is experimentally observed from 192 g/ m(2)/h of CO2 flux against 2 bar applied pressure difference. This power is obtained from a pure CO2 feed, and assuming ideal energy conversion at key rotating machines (compressor and turbine). When more realistic feed concentrations of 20% CO2 are supplied, and the loss of nitrogen N-2 reverse flux is accounted for, power potential of 0.37 W/m(2) is observed from 29 g/m(2)/h net flux against 1 bar applied pressure. Fundamental transport dynamics are outlined and a numerical model is validated and used to simulate possible improvements from highly permeable and selective membranes, with certain predictions approaching 40 W/m(2). The model is also used to analyze the overall energy balance of the process, and it is shown that inefficiencies of the compressor and turbine impose important limitations on net power generation, unless operating conditions are carefully calibrated.