Oxygen Transport Membranes for Ultra-Supercritical (USC) Power Plants With Very Low CO2 Emissions

Abstract

Coal combustion for electric power generation is one of the major contributors to anthropogenic CO2 emissions to the atmosphere. Carbon capture and storage (CCS) technologies are currently intensively investigated in order to mitigate CO2 emissions. The technique which is currently the most pursued is post combustion scrubbing of the flue gas, due to the potential to retrofit post combustion capture to existing power plants. However, it also comes with a substantial energy penalty. To reduce the energy demand of CO2 processing, the so-called oxyfuel technology presents an option to increase the concentration of CO2 in the flue gas. Here, the coal is burned in a mixture of oxygen and recycled flue gas. Hence, the flue gas primarily consists of CO2 and water vapor, which can be easily condensed. In general, there are two different techniques for oxygen production in oxyfuel power plants: cryogenic air separation (it is a method which can be easily implemented since it is already well established in industry) and a mixed metal oxide ceramic membrane (ITM or OTM) operating at high temperatures (it is a new process for O2 production, which is under development). In the last ten years, efforts in the efficient utilization of energy and reduction of emissions have indirectly stimulated research in mixed conducting membranes. In fact, the presently available cryogenic air separation process consumes a significant fraction of the generating plant's output and reduces its efficiency. Oxygen transport membrane (OTM) integration with an ultra-supercritical (USC) power plant is, indeed, considered a promising technology that will lead to economic and energy savings compared to the previous solution. In this paper, we discuss the actual potentialities and limits of OTM and their integration in USC power plants.

CO2 capture in advanced power plants fed by coal and equipped with OTM

“…We studied both these options (Gambini and Vellini, 2012); in this paper we have chosen only the second option because the energy performance of this solution are better.…”

“…This can be achieved with: (i) high absolute pressure ratio across the membrane which can be achieved with a strong air compression of the feed stream, and (ii) an high flow of sweep fluid on the permeate side in order to dilute the oxygen stream. In our membrane model, described in detail elsewhere (Gambini and Vellini, 2012), we have assumed bulk diffusion as the limiting step, according to literature (Ito et al, 2007).…”

“…To assess the thermodynamic performance of the options proposed, a comprehensive power plant simulation has been set up (Tonziello and Vellini, 2011;Gambini and Vellini, 2012). Heat and material balances have been evaluated with different commercial/non-commercial software:…”

“…Many studies have been also elaborated on coal-fired power plants in these last years and different power plant configurations for CO 2 capture have been proposed by many researcher (Stadler et al, 2010;Anantharaman and Bolland, 2011;Tonziello and Vellini, 2011;Gambini and Vellini, 2012). The goal of this paper is to compare energy and environmental performance (net efficiency and CO 2 specific emissions) for an IGCC and SSC integrated with OTM for oxygen production and to evaluate the economic impacts of such CO 2 emission abatement technologies.…”

Determination of technical and economic parameters of an ionic transport membrane air separation unit working in a supercritical power plant

“…This solution greatly reduces the auxiliary power of air separation unit by reducing the flue gas flow rate at the inlet to the cryogenic separation unit. The last and also the least studied method is the use of ion transport membranes (ITM) for air separation (Bredesen et al, 2004;Engels et al, 2010;Gambini and Vellini, 2012;Pfaff and Kather, 2009). These membranes are made of oxygen ion conductors operating at a temperature of 700-900 °C (950 °C).…”