What is the difference between internal compression and external compression in air separation?

Basically, in the case where the product compressor is a liquid pump – the liquid product is compressed first and then reheated using a plate heat exchanger; this is known as an internal compression process. In contrast, in this approach, the gas that has been reheated by the plate heat exchanger is then compressed by a compressor to reach the desired conditions; this is called external compression. Each method has its advantages and disadvantages, and the choice depends on the direction of your investment

There are two ways to pressurize oxygen: by using an oxygen compressor or an liquid oxygen pump. The former compresses gaseous oxygen, and the compression takes place outside the cryogenic tank； The latter uses liquid oxygen as the compression medium, which is compressed inside a cryogenic tank. They are referred to as external pressurization process and internal pressurization process, respectively. The internal compression process is a type of process in which liquid oxygen pumps are used to compress oxygen products. Depending on the medium compressed by the rotary booster, the process configurations can be divided into air circulation and nitrogen circulation. Depending on the location where the expanded air enters the tower, the internal compression process can be further divided into a process where the expanded air enters the top of the tower and a process where it enters the bottom of the tower. The internal compression process can also be divided into a single-pump internal compression process and a dual-pump internal compression process, depending on the compression conditions of the product. The dual-pump internal compression process involves, based on the user’s requirements for high-pressure oxygen and high-pressure nitrogen, compressing and vaporizing them respectively using an oxygen liquid pump and a nitrogen liquid pump inside a cryogenic tank, before delivering them.

A review of the technological development of large and medium-sized air separation units produced by Hangyang Air Separation Equipment: http://bbs.hcbbs.com/viewthread.php?tid=45787&highlight=%B4%F3%D6%D0%D0%CD%BF%D5%B7%D6%C9%E8%B1%B8%C1%F7%B3%CC There is a comprehensive overview available here, which can provide an approximate understanding of air separation processes.

What was explained upstairs is quite easy to learn*. Additionally, I’ve heard that the internal compression process is safer than the external compression process – is that true?

There is a clear explanation in the oxygen production worker Q&A

Yes, internal compression is relatively safe, has low maintenance costs and requires fewer operators, but accordingly its investment cost is higher than that of external compression processes

The internal compression process has the following three advantages: 1. The external compression process involves compressing oxygen in its gaseous state at normal conditions, which generates high temperatures; whereas the internal compression process involves compressing liquid oxygen in its liquid state at low temperatures. Clearly, the internal compression process is safer compared to the former； 2. Oxygen compressors require numerous safety measures during design and manufacturing, which increases their cost; in particular, imported oxygen compressors are very expensive ； Moreover, the cost of the liquid oxygen pumps and air compressors required for the internal compression process is significantly lower ； 3. Air separation units with an internal compression process can produce a large amount of liquid products alongside gaseous products. Given the increasing demand for liquids in today’s market, such air separation units have a significant advantage in terms of operating costs. There is also the comprehensive consideration of which process to choose, as well as the volume of the product gas, the pressure of that gas, and the amount of investment required for the equipment

Gaseous oxygen is more reactive than liquid oxygen. Operationally, external compression is more dangerous than internal compression.

Compressed liquid oxygen is safer; oil must be strictly avoided during gas compression, as even a tiny spark can cause problems. . .

If the user requires oxygen products at a high pressure and with a high flow rate, internal compression is preferred; comparatively, using pumps to compress large flow rates to high pressures is safer than using compressors.