Production of liquid oxygen and/or liquid nitrogen

• US 4,152,130 A
• Filed: 03/16/1978
• Issued: 05/01/1979
• Est. Priority Date: 03/19/1977
• Status: Expired due to Term

• Current Assignee: Air Products and Chemicals Incorporated (Linde Plc)
• Original Assignee: Air Products and Chemicals Incorporated (Linde Plc)
• Inventors: Theobald, Alan
• Primary Examiner(s): Yudkoff, Norman
• Application Number:
  US05/887,101
• Time in Patent Office: 411 Days
• Field of Search: 62/13-15, 62/18, 62/30, 62/38
• US Class Current: 62/646
• CPC Class Codes: F25J 2205/02 using simple phase separation in a vessel or drum
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2205/60 using adsorption on solid adsorbents, e.g. by temperature-swing adsorption [TSA] at the hot or cold end
• CPC Class Codes: F25J 2205/68 Cooling the adsorption vessel
• CPC Class Codes: F25J 2205/70 Heating the adsorption vessel
• CPC Class Codes: F25J 2210/06 Splitting of the feed stream, e.g. for treating or cooling in different ways
• CPC Class Codes: F25J 2215/44 Ultra high purity nitrogen, i.e. generally less than 1 ppb impurities
• CPC Class Codes: F25J 2245/50 the recycled stream being oxygen
• CPC Class Codes: F25J 2270/90 External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
• CPC Class Codes: F25J 3/04157 Afterstage cooling and so-called "pre-cooling" of the feed air upstream the air purification unit and main heat exchange line F25J3/04618 takes precedence
• CPC Class Codes: F25J 3/04181 Regenerating the adsorbents
• CPC Class Codes: F25J 3/04296 Claude expansion, i.e. expanded into the main or high pressure column
• CPC Class Codes: F25J 3/04345 and comprising a gas work expansion loop
• CPC Class Codes: F25J 3/04393 using multiple or multistage gas work expansion
• CPC Class Codes: F25J 3/04412 in a classical double column flowsheet, i.e. with thermal coupling by a main reboiler-condenser in the bottom of low pressure respectively top of high pressure column
• CPC Class Codes: F25J 3/04854 Safety aspects of operation
• CPC Class Codes: F25J 3/0486 of vaporisers for oxygen enriched liquids, e.g. purging of liquids
• CPC Class Codes: Y10S 62/94 High pressure column

Abstract

Liquid oxygen and/or liquid nitrogen are made by removing carbon dioxide and water vapor from air, compressing the purified air in a re-cycle compressor and dividing the purified compressed air into first and second streams. Part of the first stream is expanded in a first expander and the refrigeration produced is used to cool both the first and second streams in a first heat exchanger. On leaving the first heat exchanger, the second stream is expanded in a second expander and the refrigeration produced is used to liquify at least part of the remainder of the first stream. The liquid stream is expanded and introduced into a fractionation column from which liquid nitrogen and/or liquid oxygen can be withdrawn. Expanded air from the first and second expanders is returned to the re-cycle compressor although part of the expanded air from the second expander is preferably introduced into the fractionation column. The invention is particularly suited to installations producing in excess of 100 tons of liquid per day and, at this size, preferred designs offer an estimated 51/2 to 9% power savings over the known prior art.

Claims

1. A method for producing at least one liquid product from the group of liquid oxygen and liquid nitrogen comprising the steps of:

(a) drying and removing carbon dioxide from a feed air stream to form a dry, carbon dioxide-free feed air stream;

(b) compressing said dry, carbon dioxide-free feed air stream in at least one recycle compressor to a pressure above 425 psia;

(c) dividing said compressed feed air stream into first and second feed air streams;

(d) dividing said first feed air stream into a sidestream and a remaining stream;

(e) expanding said sidestream to a lower pressure and temperature, and cooling said remaining stream and said second stream in heat exchange relationship with said expanded sidestream;

(f) expanding said second stream, after cooling in clause (e), to a lower pressure and temperature, and further cooling said once cooled remaining stream in heat exchange relationship with a first portion of said expanded second stream;

(g) expanding said twice cooled remaining feed air stream to a lower pressure, and injecting said expanded and cooled remaining feed air stream at least partially as a liquid, into a distillation column as a first feed air stream to the column;

(h) injecting a second portion of said expanded second stream into said distillation column as a second air feed stream to said column;

(i) recycling the exapnded streams of steps (e) and (f) to said recycle compressor as recycled feed air streams along with said initially dry carbon dioxide-free feed air stream;

(j) separating said first and second feed air streams in said distillation column and producing both liquid oxygen and liquid nitrogen in said column; and

(k) withdrawing at least one of said liquid oxygen and liquid nitrogen from said distillation column as liquefied product.