Oxyfuel coal combustion by efficient integration of oxygen transport membranes

Oxyfuel combustion is considered to be an energy efficient process for carbon capture and storage in power plants. Compared to cryogenic air separation, oxygen supply by means of an oxygen transport membrane (OTM) is more energy efficient. This paper describes possible implementations of an OTM into an oxyfuel process, in particular that is three-end and four-end integration of the membrane whereby the focus is put on overall cycle efficiency and possible measures to improve cycle efficiency. Starting from a simple conservative integration of the membrane, several steps for improvement of the process efficiency are shown. With a three-end integration the maximum achievable efficiency is 40.1%, with a four-end integration of the membrane an overall efficiency of 40.7% including CO2 compression with 90% capture can be achieved for a hard coal fired power plant of 1210 MWth compared to 45.9% efficiency for a reference power plant without carbon sequestration. In this case the effective energy demand for oxygen production can be reduced to 26 kWh/tO226 kWh/tO2. In a process variant in which the expansion turbine for the oxygen depleted air is co-fired, the combined efficiency reaches 46.1%.Although OTM operation in four-end design is preferable due to higher achievable net efficiencies, OTM operation in three-end design is likely to be technically viable at first since up to now no membrane material is available which withstands contact with flue gas.