Argon condensation system and method

Patent metadata

Field	Value
Publication number	US-10060673-B2
Application number	US-201514754786-A
Country	US
Kind code	B2
Filing date	Jun 30, 2015
Priority date	Jul 2, 2014
Publication date	Aug 28, 2018
Grant date	Aug 28, 2018

Abstract

An argon reflux condensation system and method in which a plurality of once-through heat exchangers 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 plant where the crude liquid oxygen is in a liquid state and in proportion to the size of the once-through heat exchangers. 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 reflux condensation system for an air separation unit having an argon column, a lower pressure column and a higher pressure column, said argon reflux 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 argon-rich liquid reflux stream returned to the argon column as reflux, the argon-rich vapor column overhead produced through distillation of a crude argon feed stream fed from the lower pressure column to the argon column;
crude oxygen feed conduits connected between the higher pressure column and vaporization passages of the once-through heat exchangers such that a plurality of crude liquid oxygen streams composed of a crude liquid oxygen column bottoms of the higher pressure column 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 partially vaporized crude liquid oxygen streams introduced into the lower pressure column;
crude liquid oxygen flow transducers positioned within the crude liquid oxygen feed conduits at locations where the crude liquid oxygen streams are in a liquid state to sense liquid flow rates of the crude liquid oxygen streams, the crude liquid oxygen flow transducers configured to produce flow signals, each referable to a liquid flow rate within a crude liquid oxygen feed conduit associated therewith;
crude oxygen flow control valves positioned within the crude liquid oxygen feed conduits downstream of the flow transducers to control the liquid flow rates;
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 streams are controlled to attain flow rate set points;
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.

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

3. The argon reflux condensation system of claim 1 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 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.

5. The argon reflux condensation system of claim 4 , wherein the crude liquid oxygen flow controllers are responsive to the temperature transducers such that when the temperatures are unequal, the flow rate set points are biased so as to maintain the temperatures at an equal level.

6. The argon reflux condensation system of claim 1 wherein:
temperature transducers are positioned to sense temperatures of the partially vaporized crude liquid oxygen streams;
a temperature controller is responsive to the temperature transducers and configured to generate control valve signals to control the opening of the reflux control valves such that the 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;
the crude argon flow controller also generates control valve signals to control the opening of the reflux control valve; and
a low select connected to the temperature controller and the crude argon flow controller passes the control valve signals generated by either the temperature controller or the crude argon flow controller of lower amplitude.

7. The argon reflux condensation system of claim 6 wherein the crude liquid oxygen flow controllers are responsive to the temperature transducers such that when the temperatures are unequal, the flow rate set points are biased so as to maintain the temperatures at an equal level.

8. The argon reflux condensation system of claim 4 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 controller configured to control the product flow control valve and thereby maintain the product stream flow rate at the product flow rate set point.

Assignees

• Falta Steven R
• Powell Brian S
• Howard Henry E
• Chakravarthy Vijayaraghavan S
• Praxair Technology Inc

Inventors

• Falta Steven R
• Powell Brian S
• Howard Henry E
• Chakravarthy Vijayaraghavan S

Classifications

• F25J3/048 Primary

  Argon recovery · CPC title

• F25J2250/20

  Boiler-condenser with multiple exchanger cores in parallel or with multiple re-boiling or condensing streams · CPC title

• F25J3/04715

  The auxiliary column system simultaneously produces oxygen · 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

• F25J3/04848

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