5. Auxiliaries

5.1 Air separation unit

The air separation unit produces the oxygen required for the gasification process. It is only required for IGCC plants running on oxygen. Depending on technical and economic choices, oxygen purity of 85-95% is required. Higher purity is not useful for the gasification process and would have a prohibitive additional energy cost.

Of the various techniques available, cryogenic distillation is generally preferred because of its lower cost. It is based on the differences in boiling temperatures of the various constituents of air (mainly oxygen, argon and nitrogen). Argon/nitrogen separation is generally not carried out, as these two gases have the same inertial properties in combustion processes