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Opinion of Kanchan Choudhury, IIT-Kharagpur, on LOX Production

Opinion of Kanchan Choudhury, IIT-Kharagpur, on LOX Production

The following comment, as told to Nityanand Jayaraman (slightly edited for style and clarity), pertains to the article ‘Vedanta’s Oxygen Output in Thoothukudi Is Less CSR, More Disaster Capitalism’ (The Wire Science, May 26, 2021).

Copper, steel, zinc and gold production facilities use GOX to enrich air in furnaces or in highly pure form as jets. In such metallurgical extraction, GOX is produced at between 5 bar and 30 bar pressures at the plant level. It is usual for an oxygen plant to produce 5-10% of the capacity as LOX, which is kept as reserve in case the plant shuts down – when it is vapourised and supplied to keep the production on.

The percentage of LOX is decided at the design stage. If, at some point, the quantum of LOX has to be increased, one can do that by reducing some gas production to free up some refrigeration capacity (in case of high-pressure gas only) and activate the stand-by turbine, if there is one, to liquefy some extra oxygen.

It is possible to enhance the liquid oxygen production by some fraction. If someone is producing 35 tpd of LOX out of total oxygen production of 500 tpd, it is possible for them to enhance LOX to some extent. But if they are saying they will convert the entire production to liquid oxygen, I find that hard to believe. It is not possible to convert the total capacity by any manipulation at the plant level.

Of course, external injection of liquid nitrogen (brought from outside) can enhance liquid oxygen production further. However, that is another process altogether. The gas plants are not designed to produce high quantities of liquid. The steel plants that are now supplying liquid oxygen for the ‘Oxygen Express’ are reducing production of gases, including nitrogen, and focusing on liquid oxygen. But they must do this without disturbing the purity of the oxygen in the distillation column and keeping strict vigilance on the operation of the compressor and the heat-exchanger. If some of them have stand-by turbines for cooling, they can operate that too.

But even then the production will be limited by the capacity of the other parts – the compressor, heat-exchanger, the distillation column etc. I can’t just enhance capacity by adding another turbine without caring for other parts. These components work in tandem with other components of the system. It’s like saying, “I want to eat more, so I’m adding another stomach.” But the rest of your body has to be able to cope. If you add an extra stomach, your liver will be overloaded and may not be able to supply the digestive juices. The heart won’t be able to pump, and the lungs will not be able to purify by providing sufficient oxygen to the blood.

All the facilities ought to work in perfect coordination in a process plant in order to maintain the oxygen purity required for medical use.

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