Thermodynamic analysis of a hard coal oxyfuel power plant with hightemperature three-end membrane for air separation

摘要

Cryogenic air separation is a mature state-of-the-art technology to produce the high tonnage of oxygen required for oxyfuel power plants. However, this technology represents an important burden to the net plant efficiency (losses between 8% and 12%-points). High temperature ceramic membranes, associated with significantly lower efficiency losses, are foreseen as the best candidate to challenge cryogenics for high tonnage oxygen production. Although this technology is still at an embryonic state of development, the three-end membrane operation mode offers important technical advantages over the four-end mode that can be a good technological option in the near future. This paper analyzes the influence of both, the cryogenic and three-end high temperature membrane air separation units on the net oxyfuel plant efficiency considering the same boundary conditions and different equivalent thermal integrations. Moreover, the oxygen permeation rate, heat recovery, and required membrane area are also evaluated at different membrane operating conditions. Using a state-of-the-art perovskite BSCF as membrane material, net plant efficiency losses up to 5.1%-points can be reached requiring around 400,000 m_2 of membrane area. Applying this membrane-based technology it is possible to improve the oxyfuel plant efficiency over 4%-points (compared with cryogenic technology); however, it is still necessary to develop new ceramic materials to reduce the amount of membrane area required.