System and method for enhanced recovery of argon and oxygen from a nitrogen producing cryogenic air separation unit

Patent metadata

Field	Value
Publication number	US-10663222-B2
Application number	US-201815962245-A
Country	US
Kind code	B2
Filing date	Apr 25, 2018
Priority date	Apr 25, 2018
Publication date	May 26, 2020
Grant date	May 26, 2020

Abstract

A moderate pressure air separation unit and air separation cycle is disclosed that provides for up to about 96% recovery of argon, an overall nitrogen recovery of 98 percent or greater and limited gaseous oxygen production. The air separation is configured to produce a first high purity oxygen enriched stream and a second lower purity oxygen enriched stream from the lower pressure column, one of which is used as the refrigerant to condense the argon in the argon condenser, with the resulting vaporized oxygen stream used to regenerate the temperature swing adsorption pre-purifier unit. All or a portion of the first high purity oxygen enriched stream is vaporized in the main heat exchanger to produce the gaseous oxygen products.

First claim

What is claimed is:

1. A method of separating air to produce one or more nitrogen products and one or more high purity oxygen products in a cryogenic air separation unit, the method comprising the steps of:
compressing a stream of incoming feed air to produce a compressed air stream;
purifying the compressed air stream in an adsorption based prepurification unit configured to removing water vapor, carbon dioxide, nitrous oxide, and hydrocarbons from the compressed air stream to producing a compressed and purified air stream;
splitting the compressed and purified air stream is split into at least a first part of the compressed and purified air stream and a second part of the compressed and purified air stream;
cooling the first part of the compressed and purified air stream to a vapor air stream at a temperature suitable for rectification in a cryogenic distillation system and partially cooling the second part of the compressed and purified air stream;
expanding the partially cooled second part of the compressed and purified air stream in a turbine to form an exhaust stream;
rectifying the liquid air stream and exhaust stream in a cryogenic distillation column system having a higher pressure column having an operating pressure between 6.0 bar(a) and 10.0 bar(a) and a lower pressure column having an operating pressure between 1.5 bar(a) and 2.8 bar(a), the higher pressure column and the lower pressure column being linked in a heat transfer relationship via a condenser reboiler, wherein the rectifying step produces a first oxygen enriched stream from the lower pressure column having a first oxygen concentration greater than or equal to 99.5 percent oxygen, a second oxygen enriched stream from the lower pressure column having a second oxygen concentration greater than 93 percent and lower than the first oxygen concentration, a nitrogen overhead stream from the lower pressure column; and a condensed nitrogen stream from the condenser-reboiler;
rectifying an oxygen-argon stream extracted from the lower pressure column in an argon column arrangement, the argon column arrangement having at least one argon column and an argon condenser and wherein the argon column is configured to produce a third oxygen enriched stream and an argon-enriched overhead;
subcooling an oxygen enriched kettle stream from the higher pressure column and the condensed nitrogen stream from the condenser-reboiler via indirect heat exchange with the nitrogen overhead stream from the lower pressure column;
returning the third oxygen enriched stream from the argon column to the lower pressure column;
directing the argon-enriched overhead from the argon column and the second oxygen enriched stream to an argon condenser;
condensing the argon-enriched overhead in the argon condenser against the second oxygen enriched stream from the lower pressure column to produce a crude argon stream or a product argon stream, an argon reflux stream and an oxygen enriched waste stream;
wherein the method recovers greater than 30 percent of the argon in the feed air stream; and
wherein the method produces one or more nitrogen products and recovers greater than 98 percent of the nitrogen contained in the feed air stream; and
wherein the method produces one or more high purity oxygen products including a high purity pumped oxygen stream from the first oxygen enriched stream at a pressure greater than or equal to 3.4 bar(a).

2. The method of claim 1 wherein the adsorption based pre-purifier unit is a multi-bed temperature swing adsorption unit configured to purifying the compressed air stream, the multi-bed temperature swing adsorption unit is configured such that each bed alternates between an on-line operating phase adsorbing the water vapor, carbon dioxide, nitrous oxide, and hydrocarbons from the compressed air stream and an off-line operating phase where the bed is regenerated with the oxygen enriched waste stream having greater than 90.0 percent oxygen content.

3. The method of claim 1 , further comprising the step of subcooling the second oxygen enriched stream via indirect heat exchange with the oxygen enriched waste stream prior to directing the second oxygen enriched stream to the argon condenser.

Assignees

• Kromer Brian R
• Handley James R
• Prosser Neil M
• Praxair Technology Inc

Inventors

• Kromer Brian R
• Handley James R
• Prosser Neil M

Classifications

• F25J3/0423

  Subcooling of liquid process streams · CPC title

• F25J2270/14

  External refrigeration with work-producing gas expansion loop · CPC title

• F25J3/04187

  Cooling of the purified feed air by recuperative heat-exchange; Heat-exchange with product streams (arrangements of cold exchangers F25J5/002) · CPC title

• F25J2245/50

  the recycled stream being oxygen · CPC title

• F25J3/04406

  using a dual pressure main column system (F25J3/0446, F25J3/04624, F25J3/04636 and F25J3/04715 take precedence) · CPC title