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Cryogenic Oxygen Plants

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Cryogenic oxygen plants are oxygen generating plants in the cryogenic process. We all know that there are basically two processes used in gas plants to produce pure oxygen-one is the cryogenic process and the other is the non cryogenic process.

While the cryogenic process is suitable for large scale gas plants as well small sized gas plants, the non cryogenic process involving the PSA technique is more suitable for small sized plants. Cryogenic gas plants are suitable for producing oxygen for industrial and medical uses and available in large, bulky sizes and also small sized cylinders. In other words, cryogenic oxygen plants are available in low purity which is approximately 95% and high purity which is almost 99.6+%. There are oxygen-only plants, and multi-product configurations like oxygen, nitrogen, argon etc.

What is Cryogenic Oxygen?

Cryogenic oxygen is oxygen in liquid state and it is very cold. In cryogenic oxygen plants, oxygen is produced, stored and maintained in a liquid state at a substantially constant pressure.

The Cryogenic Process

Commercial oxygen produced in cryogenic gas plants use the cryogenic distillation process originally developed in 1895. This cryogenic process produces oxygen that is 99+% pure. The steps involved are as follows:

Compression

The air is compressed using a multi-stage compressor, which is then passed through a water-cooled after cooler to condense any water. Before compression, air is pretreated to remove impurities. Once the impurities are removed, the air is submitted to fractional distillation, where the components are separated in several stages. In the cryogenic process, a cryogenic section is required to provide the low temperatures required to liquefy the gas components. Once the liquid oxygen is separated, it is purified and stored.
The air passes through a molecular sieve adsorber, containing zeolite and silica gel-type adsorbents. These adsorbents adsorbs the carbon dioxide, heavier hydrocarbons, and any remaining traces of water vapor.

Separating

Air is separated into its major components in this step. The portion of the pretreated air is diverted through a compressor, where its pressure is cooled and allowed to expand to nearly atmospheric pressure. This expansion rapidly cools the air using the cryogenic technique.
The air stream which is part liquid and part gas enters the base of the high-pressure fractionating or distillation column. As the air moves up the column, it loses additional heat. The oxygen continues to liquefy, leading to the formation of oxygen-rich mixture in the bottom of the column, and other gases like nitrogen and argon flow to the top as a vapor. The oxygen at the top is the liquid oxygen mixture, also known as crude liquid oxygen, which is almost 99.5%.

Purifying

The oxygen at the bottom is about 99.5% pure. Newer cryogenic distillation units are used to recover more of the argon/nitrogen from the low-pressure distillation column, and this improves the oxygen purity to about 99.8%. If higher purity is needed, additional fractionating columns may be added to further refine the oxygen product.

Distributing

The purified cryogenic oxygen produced is distributed to the end users in gas pipelines from nearby air separation plants or transported in cylinders and storage tanks to specified destinations. It is transported in large, insulated tanks, usually made of two shells and the air is evacuated between the inner and outer shell to obstruct heat loss.

Oxygen Grades at Cryogenic Oxygen Plants

The Compressed Gas Association, formed in USA with the intention to work for the development and promotion of safety standards and safe practices in the industrial gas industry, establishes grading standards for both gaseous oxygen and liquid oxygen. These standards are based on the amount and type of impurities present.

Gas grades are called Type I and range from A to F. The grade A stands for 99.0% pure and grade F stands for 99.995% pure. Liquid grades are called Type II. These also range from A to F. However, the types and amounts of impurities in liquid grades are different from the gas grades. The most commonly produced grades of oxygen are Type I Grade B and Grade C and Type II Grade C which is 99.5% pure. They are used in steel making and in the manufacture of synthetic chemicals.

Applications of Cryogenic Oxygen

Combustion
Glass industry
Metal fabrication
Pulp and paper industry
Chemical industry
Medical
Waste water treatment.

Equipment required in cryogenic oxygen plants

Suction Filter
Air Compressor
After Cooler
Chilling Unit
Oil Absorber
Moisture Separator
Molecular Sieve Battery
Expansion Engine
Air Separation Column
Liquid Oxygen Pumps

Tags:- Cryogenic Gas Oxygen Plant, Cryogenic Oxygen Plant, Cryogenic Oxygen Plant Supplier

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