Gasifiers demand oxygen, provided as air, pure oxygen, or combination of the two. The use of pure oxygen reduces the volume flows through the IGT gasifier and through downstream equipment, which reduces investment costs. Also the Autothermal Reformer (see below) is, for the same reason, preferably fired by oxygen. As the production of oxygen is expensive, there will likely be an eco­nomical optimum in oxygen purity. Oxygen-enriched air could be a compromise between a cheaper oxygen supply and a reduced downstream equipment size.

Cryogenic air separation is commonly applied when large amounts of O2 (over 1000 Nm3/h) are required. Since air is freely available, the costs for oxygen production are directly related to the costs for air compression and refrigeration, the main unit operations in an air separation plant. As a consequence, the oxygen price is mainly determined by the energy costs and plant investment costs (van Dijk et al. 1995; van Ree 1992).

The conventional air separation unit is both capital and energy intensive. A potential for cost reduction is the development of air separation units based on conductive ionic transfer membranes (ITM) that operate on the partial pressure differential of oxygen to passively produce pure oxygen. Research and develop­ment of the ITM are in the demonstration phase (DeLallo et al. 2000). Alternative options are membrane air separation, sorption technologies, and water decompo­sition, but these are less suitable for large-scale application (van Ree 1992).