Closed loop single mixed refrigerant process

• US 5,657,643 A
• Filed: 02/28/1996
• Issued: 08/19/1997
• Est. Priority Date: 02/28/1996
• Status: Expired due to Term

• Current Assignee: Black & Veatch International Company (Black & Veatch Corporation)
• Original Assignee: The Pritchard Corporation
• Inventors: Price, Brian C.
• Primary Examiner(s): KILNER, CHRISTOPHER B
• Application Number:
  US08/607,942
• Time in Patent Office: 538 Days
• Field of Search: 62/612, 62/623
• US Class Current: 62/612
• CPC Class Codes: F25B 1/10 with multi-stage compression with cascade operation F25B7/00
• CPC Class Codes: F25B 9/006 the refrigerant containing more than one component F25B9/004 takes precedence
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• CPC Class Codes: F25J 1/0052 by vaporising a liquid refrigerant stream
• CPC Class Codes: F25J 1/0092 Mixtures of hydrocarbons comprising possibly also minor amounts of nitrogen
• CPC Class Codes: F25J 1/0212 as a single flow MCR cycle
• CPC Class Codes: F25J 1/0262 Details of the cold heat exchange system constructional details F25J5/00, construction of cold-exchangers in general F28
• CPC Class Codes: F25J 1/0291 Refrigerant compression by combined gas compression and liquid pumping
• CPC Class Codes: F25J 2220/64 Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general
• CPC Class Codes: F25J 2290/32 Details on header or distribution passages of heat exchangers, e.g. of reboiler-condenser or plate heat exchangers

Abstract

An improved closed loop single mixed refrigerant process and system for cooling a fluid material through a temperature range exceeding 200° F. by heat exchange with a single mixed refrigerant in a closed loop refrigeration cycle comprising: compressing the mixed refrigerant in a first stage compressor; cooling the compressed mixed refrigerant from the first stage compressor to produce a first mixture of a first condensed portion of the mixed refrigerant, and a gaseous refrigerant; separating the first condensed portion of the mixed refrigerant from the gaseous refrigerant; passing the gaseous refrigerant to a second stage compressor and further compressing the gaseous refrigerant; cooling the second stage compressed gaseous refrigerant to produce a second mixture of a second condensed portion of the gaseous refrigerant and a second gaseous refrigerant; separating the second condensed portion of the gaseous refrigerant and the second gaseous refrigerant; combining the first condensed portion of the mixed refrigerant with the second condensed portion of the gaseous refrigerant and the second gaseous refrigerant; charging the compressed mixed refrigerant to a refrigeration zone where the compressed mixed refrigerant is cooled to produce a liquid, mixed refrigerant, and expanded to produce a low temperature coolant; passing the low temperature coolant in countercurrent heat exchange with the compressed mixed refrigerant and the fluid material to produce the liquid, mixed refrigerant, a cooled, liquid, fluid material and gaseous mixed refrigerant; and recycling the gaseous mixed refrigerant to the first stage compressor.

Claims

1. A closed loop single mixed refrigerant process for cooling a fluid material through a temperature range exceeding 200°

F. by heat exchange with a single mixed refrigerant in a closed loop refrigeration cycle comprising;

compressing gaseous mixed refrigerant in a first compressor;

passing the compressed gaseous mixed refrigerant from the first compressor to a first heat exchanger to cool the mixed refrigerant and produce a first mixture of a first condensed portion of the mixed refrigerant, the first condensed portion being rich in higher boiling components of the mixed refrigerant and a gaseous refrigerant;

separating the first condensed portion of the mixed refrigerant from the gaseous refrigerant;

passing the gaseous refrigerant to a second compressor and further compressing the gaseous refrigerant to produce a second compressed gaseous refrigerant;

passing the second compressed gaseous refrigerant to a second heat exchanger to cool the compressed gaseous refrigerant and produce a second mixture of a second condensed portion of the gaseous refrigerant and a second gaseous refrigerant

separating the second condensed portion of the gaseous refrigerant and the second gaseous refrigerant;

combining the first condensed portion of the mixed refrigerant with the second condensed portion of the gaseous refrigerant and the second gaseous refrigerant to reconstitute the mixed refrigerant;

charging compressed mixed refrigerant to a refrigeration zone where the compressed mixed refrigerant is cooled to produce a cooled, substantially liquid, mixed refrigerant, passed to an expansion valve and expanded to produce a low temperature coolant;

passing the low temperature coolant in countercurrent heat exchange with the compressed mixed refrigerant and the fluid material in the refrigeration zone to produce the cooled, substantially liquid, mixed refrigerant, a cooled, substantially liquid, fluid material and gaseous mixed refrigerant; and

recycling the gaseous mixed refrigerant to the first stage compressor.

2. The process of claim 1 wherein the fluid material is natural gas.

3. The process of claim 2 wherein the mixed refrigerant contains compounds selected from the group consisting of nitrogen and hydrocarbons containing from 1 to about 5 carbon atoms.

4. The process of claim 3 wherein the mixed refrigerant comprises nitrogen, methane, ethane and isopentane.

5. The process of claim 2 wherein the mixed refrigerant is compressed to a pressure from about 100 to about 250 psia in the first stage compressor.

6. The process of claim 3 wherein the compressed mixed refrigerant from the first stage compressor is cooled to a temperature below about 135°

F.

7. The process of claim 2 wherein the first condensed portion is equal to from about 5 to about 25 mole percent of the mixed refrigerant.

8. The process of claim 2 wherein the gaseous refrigerant is compressed to a pressure from about 450 psia to about 650 psia in the second stage compressor.

9. The process of claim 2 wherein the compressed gaseous refrigerant from the second compressor is cooled to a temperature below about 135°

F.

10. The process of claim 2 wherein the cooled compressed gaseous refrigerant from the second compressor is separated into a liquid portion and a gaseous portion.

11. The process of claim 10 wherein the liquid portion, the gaseous portion and the first condensed portion are combined to produce the compressed mixed refrigerant.

12. The process of claim 3 wherein the natural gas is:

a) withdrawn from the refrigeration zone;

b) passed to a heavy liquids separation zone wherein at least a major portion of natural gas constituents containing six or more carbon atoms are removed from the natural gas; and

c) returned to the refrigeration zone.

13. The process of claim 2 wherein the liquefied natural gas is recovered from the refrigeration zone at a temperature from about -230°

F. to about -275°

F.

14. The process of claim 1 wherein the first stage compressor and the second stage compressor comprise a first compressor and a second compressor.

15. In a closed loop single mixed refrigerant process for cooling a fluid material through a temperature range exceeding 200°

F. by heat exchange with a single mixed refrigerant in a closed loop refrigeration cycle comprising;

compressing gaseous mixed refrigerant in a compressor to produce a compressed mixed refrigerant;

Cooling the compressed mixed refrigerant to produce a mixture of a condensed portion of the mixed refrigerant and a gaseous refrigerant;

separating the condensed portion of the mixed refrigerant;

combining the condensed portion of the mixed refrigerant and the gaseous refrigerant to reconstitute the mixed refrigerant;

charging the mixed refrigerant to a refrigeration zone wherein the mixed refrigerant is passed in countercurrent heat exchange with a low temperature coolant to produce a substantially liquid mixed refrigerant;

passing the substantially liquid mixed refrigerant through an expansion valve to produce the low temperature coolant;

charging the fluid material to the refrigeration zone wherein the fluid material is passed in countercurrent heat exchange with the low temperature coolant;

recovering the fluid material in a substantially liquid phase;

recovering the mixed refrigerant after the countercurrent heat exchange in a substantially gaseous phase; and

recycling the gaseous mixed refrigerant to the compressor, the improvement comprising;

compressing the gaseous mixed refrigerant in a first stage compressor;

cooling the compressed mixed refrigerant from the first stage compressor to produce a first stage mixture of a first stage condensed liquid refrigerant rich in higher boiling point components of the mixed refrigerant and a first stage gaseous refrigerant;

separating the first stage condensed liquid refrigerant from the first stage gaseous refrigerant;

compressing the first stage gaseous refrigerant in a second stage compressor;

cooling the compressed first stage gaseous refrigerant to produce a second stage mixture of a second stage ;

condensed liquid refrigerant and a second stage gaseous refrigerant;

separating the second stage condensed liquid and the second stage gaseous refrigerant;

combining the first stage condensed liquid refrigerate, the second stage condensed liquid refrigerant and the second stage gaseous refrigerant to reconstitute the compressed mixed refrigerant; and

charging the compressed, reconstituted, mixed refrigerant to the refrigeration zone.

16. The improvement of claim 15 wherein the fluid material is natural gas.

17. The improvement of claim 15 wherein the mixed refrigerant contains compounds selected from the group consisting of nitrogen and hydrocarbons containing from 1 to about 5 carbon atoms.

18. The improvement of claim 17 wherein the mixed refrigerant comprises nitrogen, methane, ethane and isopentane.

19. The improvement of claim 17 wherein the mixed refrigerant is compressed to a pressure from about 100 to about 250 psia in the first stage compressor.

20. The improvement of claim 17 wherein the first stage condensed liquid refrigerant is equal to from about 5 to about 25 mole percent of the mixed refrigerant.

21. The improvement of claim 15 wherein the first stage gaseous refrigerant is compressed to a pressure from about 450 psia to about 650 psia in the second stage compressor.

22. The improvement of claim 15 wherein the natural gas is:

a) withdrawn from the refrigeration zone;

b) passed to a heavy liquids separation zone wherein at least a major portion natural gas constituents containing six or more carbon atoms are removed from the natural gas; and

c) returned to the refrigeration zone.

23. The improvement of claim 15 wherein the liquefied natural gas is recovered from the refrigeration zone at a temperature from about -230°

F. to about -275°

F.

24. The improvement of claim 15 wherein the first stage compressor and the second stage compressor comprise a first compressor and a second compressor.

25. A closed loop single mixed refrigerant system comprising:

a) a mixed refrigerant suction drum;

b) a first compressor having an inlet in fluid communication with a gaseous mixed refrigerant outlet from the mixed refrigerant storage drum;

c) a first condenser having an inlet in fluid communication with an outlet from the first compressor;

d) a first refrigerant separator having an inlet in fluid communication with an outlet from the first condenser;

e) a second compressor having an inlet in fluid communication with a gaseous refrigerant outlet from the first refrigerant separator;

f) a second condenser having an inlet in fluid communication with an outlet from the second compressor;

g) a second refrigerant separator having an inlet in fluid communication with an outlet from the second condenser and a liquid refrigerant outlet from the first refrigerant separator;

h) a refrigeration vessel including a first heat exchange passageway in fluid communication with a gaseous refrigerant outlet from the second refrigerant separator and a liquid refrigerant outlet from the second refrigerant separator, a second heat exchange passageway in fluid communication with a source of a fluid material which is to be cooled, a third heat exchange passageway countercurrently positioned in the refrigeration vessel with respect to the first heat exchange passageway and the second heat exchange passageway, and an expansion valve in fluid communication with an outlet from the first heat exchange passageway and an inlet to the third heat exchange passageway;

i) a recycled refrigerant line in fluid communication with an outlet from the third heat exchange passageway and an inlet to the mixed refrigerant suction drum; and

,

j) a product line in fluid communication with an outlet from the second heat exchange passageway.

26. The system of claim 25 wherein the first compressor and the second compressor comprise a two stage compressor.

27. The system of claim 25 wherein the liquid refrigerant outlet from the first refrigerant separator is in fluid communication with the inlet to the second refrigerant separator via the second condenser.

28. The system of claim 25 wherein at least a portion of the fluid material is withdrawn from an intermediate portion of the second heat exchange passageway, passed to a heavy liquids removal section and returned to the second heat exchange passageway after removal of heavy liquids.

29. The system of claim 25 wherein the fluid material in the product line is passed through an expansion value to further cool the fluid material.