Balancing power in split mixed refrigerant liquefaction system

Patent metadata

Field	Value
Publication number	US-10935312-B2
Application number	US-201816053196-A
Country	US
Kind code	B2
Filing date	Aug 2, 2018
Priority date	Aug 2, 2018
Publication date	Mar 2, 2021
Grant date	Mar 2, 2021

Abstract

A split mixed refrigerant (“MR”) natural gas liquefication system, where low-pressure (“LP”) and medium pressure (“MP”) MR compressors are driven by a first gas turbine and a propane compressor and a high-pressure (“HP”) MR compressor is driven by a second gas turbine, is disclosed. The split MR liquefication system is configured to adjust the characteristics of the HP MR compressor to require less power when less power is available and more power when more power is available compared to the system's design point. Such adjustments allow for shifting the balance of power between the propane compressor and the HP MR compressor to improve LNG production efficiency.

First claim

The invention claimed is:

1. A method of operating a hydrocarbon fluid liquefaction system, the method comprising:
a. precooling a hydrocarbon feed stream by indirect heat exchange with a precooling refrigerant stream to produce a precooled hydrocarbon fluid stream having a temperature within a first predetermined range;
b. compressing the precooling refrigerant stream in a precooling compressor having at least one compression stage;
c. further cooling and at least partially liquefying the precooled hydrocarbon stream by indirect heat exchange against a second refrigerant stream to produce a cooled hydrocarbon fluid stream having a temperature within a second predetermined range;
d. compressing the second refrigerant stream in a compression sequence comprising a plurality of second refrigerant compression stages;
e. driving the precooling compressor and at least one second refrigerant compression stage of the plurality of second refrigerant compression stages with a first driver having a maximum available power;
f. driving the remaining second refrigerant compression stages of the plurality of second refrigerant compression stages with a second driver having a second maximum available power, wherein the maximum available power to each of the first and second drivers represents maximum utilization of fuel available to the first driver while step (e) is being performed and maximum utilization of fuel available to the second driver while step (f) is being performed; and
g. operating the at least one second refrigerant compression stage at a first power requirement, which results in a first combined power utilized by the first and second drivers, wherein one of the first driver and the second driver is operated at the maximum available power when the at least one second refrigerant compression stage is operated at the first power requirement;
h. adjusting the at least one second refrigerant compression stage to operate the at least one second refrigerant compression stage at a second power requirement, wherein operating the at least one second refrigerant compression stage at the second power requirement enables one of the first and second drivers to operate closer to the maximum available power than when the at least one second refrigerant compression stage is operated at the first power requirement and results in increased production of the cooled hydrocarbon fluid stream in step (c);
i. after performing step (h), operating the first and second drivers at a -second combined power that is greater than the first combined power.

2. The method of claim 1 , wherein step (e) comprises driving the precooling compressor and at least one second refrigerant compression stage of the plurality of second refrigerant compression stages with the first driver having the maximum available power, the at least one second refrigerant compression stage having a discharge pressure that is greater than any other compression stage of the plurality of second refrigerant compression stages.

3. The method of claim 1 , further comprising performing step (h) wherein an ambient temperature is outside a predetermined design ambient temperature.

4. The method of claim 1 , further comprising performing step (h) wherein an ambient temperature is above a predetermined design ambient temperature.

5. The method of claim 4 , wherein step (h) comprises decreasing the power requirement of the at least one second refrigerant compression stage.

6. The method of claim 1 , wherein step (g) comprises operating at least one second refrigerant compression stage at a first power requirement, which results in a first combined power utilized by the first and second drivers, one of the first and second drivers delivering maximum available power and another one of the first and second drivers not delivering maximum available power as result of compression demands of the at least one second refrigerant compression stage and the precooling compressor.

7. The method of claim 1 , wherein adjusting the power requirement of the at least one second refrigerant compression stage to a second power requirement comprises adjusting the position of a suction throttle valve in fluid flow communication with a suction side of the at least one second refrigerant compression stage.

8. The method of claim 7 , wherein adjusting the power requirement of the at least one second refrigerant compression stage to a second power requirement comprises changing the position of a set of adjustable inlet guide vanes located in the at least one second refrigerant compression stage.

9. The method of claim 1 , wherein adjusting the power requirement of the at least one second refrigerant compression stage to a second power requirement comprises changing a gear ratio of a variable speed gearbox located between the precooling compressor and the at least one second refrigerant compression stage on a drive shaft of the first driver.

10. The method of claim 1 , wherein the second refrigerant comprises a mixed refrigerant.

11. The method of claim 1 , wherein the precooling refrigerant consists of propane.

12. The method of claim 1 , wherein the precooling refrigerant stream consists of a mixed refrigerant.

13. A system comprising:
a precooling subsystem having a precooling compressor having at least one first refrigerant compression stage and at least one precooling heat exchanger, the precooling subsystem being adapted to cool a hydrocarbon feed stream by indirect heat exchange against a first refrigerant stream to produce a precooled hydrocarbon fluid stream;
a liquefaction subsystem having a plurality of second refrigerant compression stages and at least one liquefaction heat exchanger, the liquefaction system being adapted to at least partially liquefy the precooled hydrocarbon stream by indirect heat exchange against a second refrigerant stream to produce a cooled hydrocarbon fluid stream;
a first driver that drives the precooling compressor and at least one second refrigerant compression stage of the plurality of second refrigerant compression stages;
a second driver that drives the remaining second refrigerant compression stages of the plurality of second refrigerant compression stages;
means for changing a power requirement of the at least one second refrigerant compression stage; and
a controller adapted to measure a first power state of the first driver and a second power state of the second driver and to control the power requirement of the at least one second refrigerant compression stage, the first power state of the first driver, the second power state of the second driver, and a flow rate of at least one selected from the group of the hydrocarbon feed stream and the precooled hydrocarbon stream;
wherein when one of the first power state and the second power state is less than the maximum available power, the controller is adapted to adjust the means for changing the power requirement of the at least one second refrigerant compression stage, wherein the adjustment of the means for changing the power requirement of the at least one second refrigerant compression stage results in a reduction in a difference between the first power state and the second power state, an increase in a sum of the first power state and the second power state, and an increase in production of the precooled hydrocarbon fluid stream.

14. The system of claim 13 , wherein the at least one second refrigerant compression stage has a discharge pressure that is greater than any other second refrigerant compression stages of the plurality of second refrigerant compression stages.

15. The system of claim 13 , wherein the means

Assignees

• Air Prod & Chem

Inventors

• Ott Christopher Michael
• Berg Jonathan James
• Weist Annemarie Ott
• Wehrman Joseph Gerard

Classifications

• F25J1/0216

  using a C3 pre-cooling cycle · CPC title

• F25B5/00

  Compression machines, plants or systems, with several evaporator circuits, e.g. for varying refrigerating capacity (with cascade operation F25B7/00) · CPC title

• F25J1/0022 Primary

  Hydrocarbons, e.g. natural gas · CPC title

• F25J1/0087

  Propane; Propylene · CPC title

• F25J2230/24

  Multiple compressors or compressor stages in parallel · CPC title