Internal Compression vs. External Compression in Air Separation Plants

1) First, consider investment cost. Specifically, if an air separation plant is installed, which is more expensive, internal compression or external compression? Generally speaking, the difference in investment cost mainly includes the following: Comparing the internal compression process’s liquid oxygen pump and air compressor with the external compression process’s oxygen compressor. Overseas, the internal compression process is considered to offer significantly higher cost-performance, reflecting the market situation. This is because foreign oxygen concentrators are very expensive. For example, the price of an imported oxygen turbine compressor (turbine oxygen generator) of the same specifications is approximately three times that of a domestic counterpart. Meanwhile, the air compressor required for the internal compression process is 1.5 times the price of a corresponding domestic turbine oxygen compressor. In comparison, the cost of the liquid oxygen pump is almost negligible. Given such a significant cost gap, it’s natural to choose an air separation plant using the internal compression process. First, the turbine oxygen compressor used in the external compression process can easily use the same product, offering superior performance, low price, and excellent safety. However, the internal compression process generally requires an imported air compressor, as domestic units cannot fully meet performance requirements. Consequently, air separation plants using the internal compression process are more expensive. In reality, the investment cost of the internal pressure process is higher than that of the external pressure process, primarily due to the following factors:
2) Heat Exchanger
Since air separation units using internal compression processes require medium- and high-pressure plate-fin heat exchangers, this will result in a change in investment costs. Advanced medium- and high-pressure heat exchangers are relatively high in quality and reliability, but also relatively expensive, which in turn increases costs.
3) Expander
Air separation units using internal compression processes require medium-pressure expanders. Imported expanders offer higher efficiency and reliability. If an imported product is chosen, the typical configuration is to equip one unit with one core assembly. If a domestic unit is chosen, for operational reliability, one active unit and one standby unit should be used. With this configuration, the cost of equipping an imported unit is still higher than that of a domestically produced unit.
4) Valves
5) Operating costs are divided into three components: operating energy consumption, spare parts, and maintenance costs.
6) Safety and Reliability