Functioning of cryogenic air separation unit (ASU) is able to generate oxygen or nitrogen by liquefaction and separation of the atmospheric air. There is no denying the fact that ASU is considered one of the best techniques for generating high purity oxygen on a large scale. In order to do comparative evaluation of cryogenic air separation unit, we must discuss other techniques of air separation such as pressure swing adsorption (PSA) and membrane separation system. Most of these systems are used in wide range of industries depending on the focus and end results sought by businesses. Each of them has their own cons & pros.However, or evaluation will be based on three factors —energy consumption, costing and gas purity, which are discussed below:
Whether it ASU, PSA or membrane separation system, all of them run by consumption of electricity. To start with, it will not be wrong to say that operating ASU is energy-intensive in comparison with other techniques available for air separation. It is estimated that more than half of the power consumption goes into operating the liquefaction unit and one-third in running the air compressor. A great energy loss takes place in the use of air compressors and turbines. There is energy loss on a lesser scale in the distillation column and turbines. This is considered to be the major drawback of air separation unit . Innovation of ASU needs to be done that cut the energy losses and make the process more energy efficient. Comparatively, PSA and membrane processes run on a lot less energy. And, these processes incur a lot less loss of energy.
Costing of ASUs is way more than either pressure swing adsorption plants or membrane separation. To accomplish liquefaction requires use of sophisticated technological processes. Components used in fabricating an ASU like air compressor, purification unit , heat exchangers , expanders , cold boxy, argon welding and high grade stainless steel column are very expensive. It makes it capital-intensive equipment. On top of it, it is also known for consuming more energy that increases the operational costs. PSA and membrane separation techniques are less expensive but they are not fit for gas production the large scale with high purity.
Cryogenic air separation is the most efficient way of generating oxygen or nitrogen with the highest purity attainable. The process is able to generate oxygen with purity up to 99.7% and nitrogen with purity up to 99.99%. PSA and membrane separation systems can generate these gases with less scale and on a smaller scale.