CO2 capture from natural gas power plants using selective exhaust gas recycle membrane designs

Abstract

This paper describes membrane processes to capture the CO2 produced by combustion gas turbines in natural gas combined cycle power plants. Because combustion turbines typically use a large excess of air, the resulting turbine exhaust gas is relatively dilute (only 3–4% CO2), making subsequent CO2 capture difficult and costly. Previously, we’ve shown that a membrane process can be used to selectively recycle CO2 to the combustion step, which significantly increases the CO2 content in the exhaust gas. In this way, selective exhaust gas recycle (S-EGR) makes CO2 capture energetically easier. Here, various membrane design concepts incorporating S-EGR are described and compared. A combination of S-EGR with non-selective exhaust gas recycle (EGR) is shown to offer advantages in reduced capital, while retaining most of the energy benefits of S-EGR alone. For all of the membrane designs analyzed, the energy and cost of capture vary with the capture rate. Generally, if flue gas compression is not used, the lowest capture cost ($/tonne CO2) for membranes occurs at partial capture rates of 60–70%. Of the process designs studied, the lowest cost of capture (∼$44/t) is achieved by an integrated turbine/membrane design that would require changes to existing turbines.