Method for compressing an incoming feed air stream in a cryogenic air separation plant

Patent metadata

Field	Value
Publication number	US-10533564-B2
Application number	US-201916381046-A
Country	US
Kind code	B2
Filing date	Apr 11, 2019
Priority date	Oct 3, 2012
Publication date	Jan 14, 2020
Grant date	Jan 14, 2020

Abstract

A method for compression of an incoming feed air stream using at least two variable speed compressor drive assemblies controlled in tandem is provided. The first variable speed drive assembly drives at least one compression stage in the lower pressure compressor unit driven while the second variable speed drive assembly drives higher pressure compression stage disposed either in the common air compression train or the split functional compression train of the air separation plant. The first and second variable speed drive assemblies are preferably high speed, variable speed electric motor assemblies each having a motor body, a motor housing, and a motor shaft with one or more impellers directly and rigidly coupled to the motor shaft via a sacrificial rigid shaft coupling.

First claim

What is claimed is:

1. A method for compression of an incoming feed air stream to a cryogenic air separation plant, the method comprising the steps of:
(a) compressing the incoming feed air stream in a multi-stage compressor of a common air compression train driven directly by a double ended first variable speed electric motor assembly configured to operate at speeds of between 5000 rpm and 9000 rpm, wherein the multi-stage compressor further comprises a first compression stage or first compressor unit directly and rigidly coupled to one end of the double ended first variable speed electric motor assembly, and a second compression stage or second compressor unit directly and rigidly coupled to the other end of the double ended electric motor assembly, with the first compression stage or first compressor unit and the second compression stage or second compressor unit arranged in series and driven directly by the double ended first variable speed electric motor assembly, wherein the first compression stage or first compressor unit is configured to produce a first compressed air stream and the second compression stage or second compressor unit is configured to receive and further compress the first compressed air stream to produce a second compressed air stream;
(b) purifying the compressed feed air streams to remove impurities and produce a compressed and purified feed air stream;
(c) splitting the compressed and purified feed air stream into two or more portions in a split functional air compression train, the two or more portions including a turbine air stream moving through a turbine air circuit and a boiler air stream moving through a boiler air circuit;
(d) further compressing the boiler air stream in a third compressor unit and a fourth compressor unit arranged in series within the boiler air circuit and driven by a second variable speed electric motor assembly configured as a double ended second variable speed motor assembly, wherein the third compressor unit is directly and rigidly coupled to one end of a second variable speed electric motor assembly and the fourth compressor unit is directly and rigidly coupled to the other end of the second variable speed electric motor assembly;
(e) further compressing the turbine air stream in one or more additional compressor units disposed in the turbine air circuit;
(f) directing the further compressed boiler air stream and the further compressed turbine air stream to a primary heat exchanger configured to cool the boiler air stream and turbine air stream to temperatures suitable for rectification in a distillation column system of the cryogenic air separation plant;
(g) expanding the further compressed and cooled turbine air stream in a turbo-expander;
(h) directing the further compressed and cooled boiler air stream and the expanded turbine air stream to a distillation column system of the cryogenic air separation plant to produce liquid and gaseous products; and
(i) adjusting the speed of the first variable speed electric motor assembly in response to changes in operating conditions of the cryogenic air separation plant and a measured flow rate of air in the incoming feed air stream and thereafter adjusting the speed of the second variable speed electric motor assembly in response to the speed of the first variable speed electric motor assembly and a discharge pressure, the discharge pressure selected from the group consisting of a measured pressure in the turbine air circuit, a measured pressure in the boiler air circuit, or a measured pressure in the common air compression train; and
wherein the ratio of the speed of the first variable speed-electric motor assembly to the speed of the second variable speed electric motor assembly before the adjustment in step (i) is different than the ratio of the speed of the first variable speed-electric motor assembly to the speed of the second variable speed electric motor assembly after said adjustments in step (i).

2. The method of claim 1 wherein the first compression stage or first compressor unit is directly and rigidly coupled to one end of the double ended first variable speed electric motor assembly via a sacrificial rigid shaft coupling and the second compression stage or second compressor unit is directly and rigidly coupled to the other end of the double ended electric motor assembly via another sacrificial rigid shaft coupling.

3. The method of claim 1 further comprising one or more higher pressure compressors disposed in the common air compression train and further configured to compress the second compressed air stream to form a final compressed feed air stream and wherein the step of purifying the compressed feed air streams to remove impurities and produce a compressed and purified feed air stream further comprises purifying the final compressed feed air stream to remove impurities and produce a compressed and purified feed air stream.

4. The method of claim 1 wherein the step (i) further comprises adjusting the speed of the first variable speed electric motor assembly in response to changes in operating conditions of the cryogenic air separation plant and a measured flow rate of air in the incoming feed air stream and thereafter adjusting the speed of the second variable speed electric motor assembly in response to the speed of the first variable speed electric motor assembly and two or more discharge pressures, the two or more discharge pressures selected from the group consisting of a measured pressure in the turbine air circuit, a measured pressure in the boiler air circuit, or a measured pressure in the common air compression train.

5. The method of claim 4 wherein the speed of the first variable speed electric motor assembly is reduced such that the cryogenic air separation plant is turned down and a reduced volumetric flow of the incoming feed air stream to the cryogenic air separation plant is between about 50% to 70% of a designed volumetric flow of the incoming feed air stream for the cryogenic air separation plant, and wherein the reduced volumetric flow of the incoming feed air stream is compressed in the multi-stage compressor of the common air compression train, and wherein the speed of the second variable speed electric motor assembly is adjusted in response to the reduced speed of the first variable speed electric motor assembly and two or more discharge pressures.

6. The method of claim 1 wherein the speed of the first variable speed electric motor assembly is adjusted in response to changes in operating conditions of the cryogenic air separation plan, the measured flow rate of air in the incoming feed air stream, and one or more process limits and wherein the speed of the second variable speed electric motor assembly is thereafter adjusted in response to the discharge pressure, the one or more process limits and the speed of the first variable speed electric motor assembly.

7. The method of claim 1 wherein the speed of the first variable speed electric motor assembly is adjusted in response to changes in operating conditions of the cryogenic air separation plan, the measured flow rate of air in the incoming feed air stream, and one or more compression stage limits and wherein the speed of the second variable speed electric motor assembly is thereafter adjusted in response to the discharge pressure, the one or more compression stage limits and the speed of the first variable speed electric motor assembly.

8. The method of claim 1 wherein the speed of the first variable speed electric motor assembly is adjusted in response to changes in operating conditions of the cryogenic air separation plan, the measured flow rate of air in the incoming feed air stream, and one or more electric motor assembly limits associated with the first variable speed

Assignees

• Howard Henry E
• Schwarz Carl L
• Abdelwahab Ahmed F
• Rosen Lee J
• Degenstein Nick J
• Chen Reh Lin
• Praxair Technology Inc

Inventors

• Howard Henry E
• Schwarz Carl L
• Abdelwahab Ahmed F
• Rosen Lee J
• Degenstein Nick J
• Chen Reh-Lin

Classifications

• F04D29/266

  mounting compressor rotors on shafts · 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

• F25J3/04018 Primary

  of main feed air · CPC title

• F25J3/04884

  Arrangement of reboiler-condensers · CPC title

• F25J3/0429

  of feed air, e.g. used as waste or product air or expanded into an auxiliary column · CPC title