Integrated membrane/heat exchanger module for use in exhaust gases

Oxygen separation using MIEC membranes (Mixed Ionic Electronic Conductor) needs a high temperature of appr. 850 °C. However, industrial flue gas streams containing often components able to react with the membrane material. Also BSCF (Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ) well known for its high oxygen permeation is blocked in a CO₂ atmosphere by forming of carbonate layers at the surface.

The approach shown here is based on a thermal integration of BSCF-membranes within a flue gas stream without a direct contact to the flue gas. For that purpose, a special ceramic sheath tube was developed to protect the membrane which is able to realize a heat exchange too. Besides, a connection to gas entry and outlet is possible at one open end of the sheath tube as shown in Fig. 1. Since the inner space of the sheath tube should be used as efficient as possible, a capillary bundle was built in according to Fig. 2. Fig. 3 represents the oxygen flux of such a bundle compared to a membrane tube with a 10 mm outside diameter. Obviously, the oxygen flux of the bundle is 3–4 times higher at low driving forces because of a smaller wall thickness and the higher membrane area at comparable space demand.

A “constructional approach” allows an integration of sensitive high-flux membrane materials in industrial processes characterized by critical gas components and different operation conditions. Therefore, a usage of process heat for production of oxygen by MIEC membranes seems to be possible for the majority of thermal processes.