Method for improved startup of an air separation unit having a falling film vaporizer

Patent metadata

Field	Value
Publication number	US-11320198-B2
Application number	US-202016911945-A
Country	US
Kind code	B2
Filing date	Jun 25, 2020
Priority date	Jun 25, 2020
Publication date	May 3, 2022
Grant date	May 3, 2022

Abstract

A method for starting up an air separation plant having a higher-pressure column, a lower-pressure column, and a falling film vaporizer disposed within a lower section of the lower-pressure column is provided. The method can include the steps of: introducing a cooled and compressed air stream into the higher pressure column; withdrawing an oxygen-enriched liquid stream from a bottom section of the higher-pressure column and introducing said oxygen-enriched liquid stream to an upper section of the lower-pressure column; and exchanging heat between nitrogen gas coming from a top section of the higher-pressure column and liquid oxygen from the lower-pressure column within the falling film vaporizer. During a start-up period, flow of liquid oxygen is at least reduced to the closed core. This reduces the available heat exchange area during start up, which increases ΔT and ΔP in the condenser/reboiler.

First claim

I claim:

1. A method for starting up an air separation plant having a higher-pressure column, a lower-pressure column, and a falling film vaporizer disposed within a lower section of the lower-pressure column, the method comprising the steps of:
introducing a cooled and compressed air stream into the higher pressure column;
withdrawing an oxygen-enriched liquid stream from a bottom section of the higher-pressure column and introducing said oxygen-enriched liquid stream to an upper section of the lower-pressure column; and
exchanging heat between nitrogen gas coming from a top section of the higher-pressure column and liquid oxygen from the lower-pressure column within the falling film vaporizer,
wherein the falling film vaporizer comprises an open core and a closed core,
wherein during a start-up period, flow of liquid oxygen is at least reduced to the closed core as compared to during a steady state operation.

2. The method as claimed in claim 1 , wherein the lower-pressure column has a first pressure set point during startup and a second pressure set point during steady state operation, wherein the first pressure set point is at least 1 psig higher than the second pressure set point.

3. The method as claimed in claim 1 , wherein the air separation plant further comprises a liquid oxygen pump and distribution means that are configured to transfer liquid oxygen from the lower section of the lower-pressure column to the falling film vaporizer.

4. The method as claimed in claim 3 , wherein the distribution means are further configured to selectively transfer the liquid oxygen to the open core without sending any liquid oxygen to the closed core during the start-up period.

5. The method as claimed in claim 4 , wherein the distribution means are further configured to transfer the liquid oxygen to the closed core during a steady state operation.

6. The method as claimed in claim 1 , further comprising withdrawing a liquid oxygen product from the lower-pressure column.

7. A method for operating an air separation plant having a higher-pressure column, a lower-pressure column, and a falling film vaporizer disposed within a lower section of the lower-pressure column, the air separation plant having a start-up operation and a steady state operation, the method comprising the steps of:
introducing a cooled and compressed air stream into the higher pressure column;
withdrawing an oxygen-enriched liquid stream from a bottom section of the higher-pressure column and introducing said oxygen-enriched liquid stream to an upper section of the lower-pressure column;
exchanging heat between nitrogen gas coming from a top section of the higher-pressure column and liquid oxygen from the lower-pressure column within the falling film vaporizer;
withdrawing a liquid oxygen product from the lower-pressure column,
wherein the falling film vaporizer comprises an open core and a closed core,
wherein during the start-up operation, the method further comprises:
flowing liquid oxygen to only the open core of the falling film vaporizer;
increasing a pressure set point for the lower-pressure column as compared to steady state operation; and
reducing the flow rate of liquid oxygen product from the lower-pressure column as compared to steady state operation.

Assignees

• Air Liquide

Inventors

• Kong Paul

Classifications

• F25J2205/60

  using adsorption on solid adsorbents, e.g. by temperature-swing adsorption [TSA] at the hot or cold end · CPC title

• F25J3/0409

  of oxygen · CPC title

• F25J3/04478

  for controlling purposes, e.g. start-up or back-up procedures (F25J3/04496 takes precedence) · CPC title

• F25J3/04818

  Start-up of the process · CPC title

• F25J3/04412 Primary

  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 title