Argon condensation system and method

Patent metadata

Field	Value
Publication number	US-10082333-B2
Application number	US-201514754801-A
Country	US
Kind code	B2
Filing date	Jun 30, 2015
Priority date	Jul 2, 2014
Publication date	Sep 25, 2018
Grant date	Sep 25, 2018

Abstract

An argon reflux condensation system and method in which a plurality of once-through condensers are connected to an argon column of an air separation plant to condense argon-rich vapor streams for production of reflux to the argon column. Condensation of the argon-rich vapor streams is brought about through indirect heat exchange with crude liquid oxygen streams that partially vaporize and are introduced into a lower pressure column of the plant for further refinement. The flow rate of the crude liquid oxygen streams are sensed and controlled at locations in the air separation plant where the crude liquid oxygen is in a liquid state and in proportion to the size of the once-through heat exchangers. Prior to flowing into the once-through condensers, the partially vaporized crude oxygen stream enters a phase separator which separates the crude oxygen vapor from the crude liquid oxygen. The separated crude oxygen vapor bypasses the once-through condensers and is mixed with the vaporized oxygen stream that exits the one-through condensers. Feed stream flow rate to the argon column is controlled in response to air flow rate to the plant and product flow rate is controlled in response to the feed stream flow rate to the argon column.

First claim

What is claimed is:

1. An argon condensation system for an air separation unit having an argon column, a lower pressure column and a higher pressure column, said argon condensation system comprising:
a plurality of once-through heat exchangers connected to an argon column such that argon-rich vapor streams composed of argon-rich vapor column overhead are condensed within condensation passages of the once-through heat exchangers to produce an argon-rich liquid product stream and an argon-rich liquid reflux stream that is returned to the argon column as reflux;
a phase separator configured to separate a partially vaporized crude oxygen feed stream into at least one crude oxygen vapor stream and one or more crude liquid oxygen streams, wherein the partially vaporized crude oxygen feed stream originates as a crude liquid oxygen column bottoms from the higher pressure column that is partially vaporized as it is directed to the phase separator;
one or more crude liquid oxygen feed conduits disposed between the phase separator and vaporization passages of the once-through heat exchangers and configured to direct the one or more crude liquid oxygen streams to the plurality of once-through heat exchangers and wherein the one or more crude liquid oxygen streams are partially vaporized in the vaporization passages of the once-through heat exchangers through indirect heat exchange with the argon-rich vapor streams to produce one or more partially vaporized crude liquid oxygen streams;
one or more crude oxygen vapor conduits disposed between the phase separator and the lower pressure column and configured to direct the at least one crude oxygen vapor stream from the phase separator to the lower pressure column;
a reflux control valve positioned between the condensation passages of the once-through heat exchangers and the argon column to control a reflux flow rate of the argon-rich liquid reflux stream;
a feed flow transducer is connected to the crude argon feed conduit to sense the feed stream flow rate of the crude argon feed stream and configured to produce a crude argon signal referable to the feed stream flow rate; and
a crude argon flow controller responsive to the crude argon signal and a feed stream set point, the feed stream set point being a function of the air flow rate into the air separation unit multiplied by a crude fraction;
wherein the crude argon flow controller is configured to control the argon reflux valve such that when the feed stream flow rate is above the feed stream set point, the reflux control valve opening decreases to in turn decrease the reflux flow rate of the argon-rich liquid reflux stream and thereby cause the argon-rich liquid to back up into the condensation passages, an increase in pressure of the argon-rich vapor stream and within the argon column and a decrease in the feed stream flow rate of the crude argon feed stream and when the feed stream flow rate is below the feed stream set point, the reflux control valve opening increases to in turn increase the reflux flow rate of the argon-rich liquid reflux stream and thereby cause a decrease in the pressure of the argon-rich vapor stream and within the argon column and an increase in the feed stream flow rate of the crude argon feed stream; and
wherein the argon-rich vapor column overhead is produced through distillation of a crude argon feed stream and is fed from the lower pressure column to the argon column.

2. The argon condensation system of claim 1 further comprising:
one or more crude liquid oxygen flow transducers disposed downstream of the higher pressure column and upstream of the phase separator at a location where the crude liquid oxygen column bottoms stream is in a liquid state and configured to sense liquid flow rates of the crude liquid oxygen column bottoms stream, and to produce flow signals corresponding thereto;
one or more crude oxygen flow control valves positioned downstream of the flow transducers to control the liquid flow rates of the crude liquid oxygen column bottoms stream; and
crude liquid oxygen flow controllers responsive to the flow signals and configured to control the flow control valves such that the flow rates of the crude liquid oxygen column bottoms stream are controlled to attain flow rate set points.

3. The argon condensation system of claim 2 wherein:
a level transducer is connected to the higher pressure column to sense a level of the crude liquid oxygen column bottoms in the higher pressure column and to generate a level signal referable to the level of the crude liquid oxygen column bottoms; and
a level controller is responsive to the level signal and configured to generate the flow rate set points such that the flow rate set points decrease as the level of the crude liquid oxygen bottoms decreases and vice-versa and the level is maintained at a constant height within the higher pressure column.

4. The argon condensation system of claim 1 wherein phase separator is disposed at a prescribed height above the once-through heat exchangers such that the liquid level in the phase separator provides the liquid head required to drive flow of the at least one crude liquid oxygen stream through the once-through heat exchangers.

5. The argon condensation system of claim 1 wherein the pressure in the phase separator is maintained at a pressure above the pressure of the lower pressure column and at or above the pressure required to drive flow of the at least one crude liquid oxygen streamthrough the heat exchangers.

6. The argon condensation system of claim 1 wherein phase separator is disposed at a prescribed height relative to the once-through heat exchangers and the phase separator is maintained at a prescribed pressure such that the liquid head in the phase separator combined with the maintained pressure of the phase separator drives the flow of the crude liquid oxygen through the heat exchangers.

7. The argon condensation system of claim 1 wherein the one or more partially vaporized crude liquid oxygen streams exiting the plurality of once-through heat exchangers each comprise 10% or more liquid.

8. The argon condensation system of claim 1 wherein the one or more partially vaporized crude liquid oxygen streams exiting the plurality of once-through heat exchangers collectively comprise 20% or more liquid.

9. The argon condensation system of claim 1 wherein the vaporization surface areas of the once-through heat exchangers are of equal size.

10. The argon reflux condensation system of claim 1 wherein:
temperature transducers are positioned to sense temperatures of the partially vaporized crude liquid oxygen streams; and
the crude argon flow controller is responsive to the temperature transducers such that feed stream flow rate decreases when the temperatures of the partially vaporized crude liquid oxygen streams are above a predetermined level indicative of dry out within the vaporization passages.

11. The argon reflux condensation system of claim 1 further comprising a product flow control subsystem for controlling a product stream flow rate, the product flow control subsystem further comprises:
a product flow control valve connected to a product outlet of the argon columns;
a product flow transducer connected to the product outlet, upstream of the product flow control valve, to sense the product stream flow rate of the argon-rich product stream and configured to produce a product signal referable to the product stream flow rate;
a product flow controller responsive to a product flow rate set point and the product signal, the product flow rate set point being a function of feed flow rate of the crude argon stream multiplied by a product fraction; and
the product flow c

Assignees

• Handley James R
• Powell Brian S
• Howard Henry E
• Chakravarthy Vijayaraghavan S
• Shelat Maulik R
• Falta Steven R
• Praxair Technology Inc

Inventors

• Handley James R
• Powell Brian S
• Howard Henry E
• Chakravarthy Vijayaraghavan S
• Shelat Maulik R
• Falta Steven R

Classifications

• F25J3/04672 Primary

  having a top condenser · CPC title

• F25J3/04715

  The auxiliary column system simultaneously produces oxygen · CPC title

• F25J3/04678

  cooled by oxygen enriched liquid from high pressure column bottoms · CPC title

• F25J3/04848

  Control strategy, e.g. advanced process control or dynamic modeling · CPC title

• F25J3/04412

  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 title