The oxygen ratio in the air on a dry basis is about 20.95 % by volume and 23.20 % in terms of weight. Its boiling point at atmospheric pressure is about 90.2 Kelvin or 182.95 degrees centigrade. With the help of Cryogenic technology oxygen from the air is separated into pure form. For large-scale, oxygen production cryogenic technology is the only method available now.
The oxygen plant is designed based on below equipment:
- Air compressor: Axial compressor used for building up the air pressure sucking it from the atmosphere through a set of shifting filters.
- Refrigeration unit: Air is cooled by countercurrent oxygen and waste nitrogen streams.
- Moisture separator
- Air purification unit: It consists of adsorbers, a regeneration heater, post filters, a nitrogen vent silencer, and an air vent silencer.
- Cold box: It is a box enclosed with the main heat exchanger, medium-pressure column, low-pressure column, expansion turbine, Sub cooler, liquid oxygen circulation pumps, condenser-vaporizer, and Liquid oxygen filters (acetylene adsorbers).
- Liquid oxygen storage tank
- Gaseous oxygen storage tank
High-production oxygen plants are designed based on the cryogenic system where the air is cooled, condensed, separated and purified, and stored as liquid oxygen. Atmospheric air is filtered and compressed to high pressures. Moisture is separated as water and compressed air is passed to silica gel adsorbers. The gas is passed to main heat exchangers and passed to turbines for expansion of gas which results in a temperature drop below the critical temperature and pressure forming a liquid mixture and oxygen is collected as liquid oxygen.
Nitrogen Production Plant Flowsheet
Nitrogen plant consists of the following equipment
1. Air compressor
2. Refrigeration unit
3. Moisture separator
4. Air purification unit
- Post filters
- Regeneration heater
- Air vent silencer
- Nitrogen vent silencer
5. Cold box
- Main exchanger
- Medium pressure column
- Condenser vaporizer
- Waste nitrogen & air expansion turbine
- Liquid nitrogen/ gaseous nitrogen separator
6. Deriming heater
7. Nitrogen vaporizer
8. Liquid nitrogen storage tank
9. Pressurizing coil
Nitrogen from the air is separated by compressing air and expanding it at low temperature. By means of cryogenic technology, continuous removal of heat and compression will make nitrogen to change its phase from gas to liquid phase, the liquid phase nitrogen is stored at high pressure and transported in cylinders.