SYSTEM AND METHOD FOR REFRIGERATION OF CONTENTS OF AN LCO2 INTERMEDIATE STORAGE TANK AT A CO2 RECEIVING TERMINAL

Abstract

 A system 110 and a method for refrigeration of the contents of an intermediate liquid CO₂ (LCO₂) storage tank 10 at a CO₂ receiving terminal during offloading of LCO₂ into the storage tank are disclosed. The invention uses vaporisation of LCO₂ for vapour return to ship to provide for refrigeration of a fluid stream being withdrawn from storage tank 10, which fluid stream, after refrigeration thereof, is returned to the storage tank 10.

Description

FIELD OF THE INVENTION

[0001] The present invention generally relates to Carbon Capture and Storage (CCS) technology, and more particularly to a system and method for refrigeration of the contents of an intermediate liquid CO₂ (LCO₂) storage tank at a CO₂ receiving terminal during injection of LCO₂ into a pipeline connected to a long-term storage. The invention an injection stream being injected into a pipeline connected to a long-term storage to provide for refrigeration of a fluid stream being withdrawn from storage tank, which fluid stream, after refrigeration thereof, is returned to the storage tank.

BACKGROUND ART

[0002] In a CO₂ terminal for Carbon Capture and Storage (CCS), intermediate storage is provided for the liquefied CO₂ (LCO₂) prior to injection into a reservoir for long-term storage. Captured and liquefied carbon dioxide can be transported in the liquid phase (LCO₂) from various locations and customers by ship to CO₂ receiving terminals. The purpose of the buffer storage is to allow for continuous injection to the long-term storage reservoir despite intermittent LCO₂ cargo transfer from ship.

[0003] Handling of liquefied gases, e.g. LCO₂, below ambient temperature often requires mechanical refrigeration to maintain or lower the pressure in an intermediate storage, without venting the liquefied gas to atmosphere or another location. Natural heat ingress from the warmer ambient surroundings into the colder intermediate storage causes a pressure rise and/or generation of boil-off gas. In order to counteract the natural heat ingress, refrigeration could be applied. Refrigeration could also be applied in excess of the natural heat ingress to actively reduce storage pressure. However, high refrigeration duties imply high power input requirements.

[0004] It would be desirable to be able to reduce the power input requirements for the refrigeration required in a CO₂ terminal to counteract the natural heat ingress.

[0005] Accordingly, it is an object of the present invention to provide a system and a method enabling reducing the power input requirements for refrigeration in a CO₂ terminal to counteract the natural heat ingress.

SUMMARY OF THE INVENTION

[0006] The present invention uses cold LCO₂ present in the CO₂ terminal outside of the intermediate storage as a heat sink to aid the refrigeration. More particularly, the invention uses an injection stream of LCO₂ that is being injected into a pipeline connected to a long-term storage. The cold LCO₂ that is being injected into the pipeline does not need to stay cold, and can thus act as a heat sink to aid refrigeration. According to the present invention, LCO₂ that will be heated even without the invention as part of the normal operation of the terminal is used as a heat sink, thereby making use of a waste low-temperature resource.

[0007] Accordingly, in one aspect the invention relates to a system 110 configured to refrigerate LCO₂ contained in an intermediate LCO₂ storage tank 10 at a CO₂ receiving terminal, the system comprising: an intermediate LCO₂ storage tank 10; a fluid withdrawal conduit 40, connected to the intermediate LCO₂ storage tank 10 configured to withdrawing a fluid stream from the intermediate LCO₂ storage tank 10; an LCO₂ discharge conduit 17, 19, 31, one end of which is connected to the intermediate LCO₂ storage tank 10, and the other end is connected to a pipeline 2 connected to a long-term storge 1, said discharge conduit being configured to withdraw an LCO₂ discharge stream from the intermediate LCO₂ storage tank and to lead the stream to the pipeline 2; a first LCO₂ pump 15 arranged along the LCO₂ discharge conduit 17, 19, 31; a refrigeration unit 50 connected to the fluid withdrawal conduit 40 configured to refrigerate the withdrawn fluid stream from the intermediate LCO₂ storage tank 10; a fluid return conduit 42 connecting the refrigeration unit 50 with the intermediate LCO₂ storage tank 10 configured to convey a refrigerated and/or liquefied fluid stream from the refrigeration unit 50 to the intermediate LCO₂ storage tank 10, a sub-ambient refrigeration heat sink 70 arranged along the LCO₂ discharge conduit 17, 19, 31 at a location downstream of the first LCO₂ pump 15 configured to transfer heat from a refrigerant stream exiting the refrigeration unit 50 to the LCO₂ discharge stream; a refrigerant heating conduit 72 fluidly connecting the refrigeration unit 50 with the sub-ambient refrigeration heat sink 70 configured to convey to the sub-ambient refrigeration heat sink 70 the refrigerant stream exiting the refrigeration unit 50; and, a refrigerant return conduit 74 fluidly connecting the refrigeration unit 50 with the sub-ambient refrigeration heat sink 70 configured to return to the refrigeration unit 50 the refrigerant stream.

[0008] In another aspect, the invention relates to a method for refrigeration of the contents of an intermediate LCO₂ storage tank 10 at a CO₂ receiving terminal during injection of LCO₂ into a pipeline 2 connected to a long-term storage 1, said method comprising the following steps: A discharging a stream of LCO₂ from an intermediate LCO₂ storage tank 10 to be injected into a pipeline 2 connected to a long-term CO₂ storage; B subjecting the stream of LCO₂ from step A to pumping in a first pumping stage 15; C transferring heat from a refrigerant stream to the LCO₂ stream from step B; D withdrawing a fluid stream 40 from the intermediate LCO₂ storage tank 10; E refrigerating the withdrawn fluid stream from step D, thereby liquefying the withdrawn fluid stream and/or cooling the withdrawn fluid stream; and, F returning the fluid stream from step E to the storage tank 10, wherein, in step E, heat from the withdrawn fluid stream 40 is transferred to the refrigerant stream to be used as a heat source for the refrigeration of step E, and the LCO₂ stream from step B is used as a heat sink for the refrigeration of step E.

[0009] The invention can reduce the power requirements for the refrigeration by about 50% compared to using an ambient heat sink alone.

[0010] Further embodiments and advantages of the invention will be apparent from the following detailed description and appended claims.

[0011] In the present disclosure, same reference numeral is used both to denote the conduit and the stream flowing therein. For example, reference numeral 42 is used to both denote the fluid return conduit, and also to denote the fluid stream itself flowing in said conduit.

[0012] The term "long-term" as used herein denotes a storage intended to be permanent.

BRIEF DESCRIPTION OF THE ATTACHED DRAWING

[0013] 

Figure 1 shows an embodiment of the inventive system 110 as indicated by the dashed line which can be implemented into an CO₂ receiving terminal. The inventive system 110 in its most generic embodiment does not include the ambient cooling 64, 66, which in a preferred embodiment can be attached to the refrigeration unit 50; 51.

Figure 2 shows an embodiment of the inventive system 110 including a detailed embodiment of the refrigeration unit 51.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention provides refrigeration of an intermediate LCO₂ storage tank 10 during discharge from the storage tank of an LCO₂ stream to be injected into a pipeline connected with a long-term storage 1. As shown in Fig. 1, the cold LCO₂ from the intermediate storage that is being injected into the pipeline, can be used as an additional, sub-ambient heat sink for the refrigeration, since the injected LCO₂ does not need to stay cold.

[0015] By providing a sub-ambient heat sink for the refrigeration system, the temperature difference between the heat source (fluid 40 from the intermediate LCO₂ storage tank 10) and the heat sink (fluid 19 that is being injected into the long-term CO₂ reservoir 1 via pipeline 2) is reduced compared to using only an ambient heat sink 64, 66, which inherently improves refrigeration efficiency.

[0016] For operational reasons, it may be useful to bring the pressure in the intermediate storage tank 10 down even further than just through injecting the liquid while not loading, e.g. in preparation to receive a large cargo "parcel" where no vapour return at all is allowed. For example, it may be desirable for a ship 30 to reduce its pressure prior to leaving the terminal, and therefore not accept vapour return.

[0017] The refrigeration unit could, in principle, use any sort of refrigeration, including mechanical, thermoelectric, or absorptive refrigeration, mechanical refrigeration being generally preferred due to the current state of the art. The invention provides a lower-temperature heat sink compared to the ambient, and thereby increases refrigeration efficiency.

[0018] The ambient fluid used for ambient cooling could be sea water, fresh water and/or air.

[0019] The invention can reduce the power requirements for the refrigeration by about 50% compared to using ambient heat sinks alone.

LIST OF REFERENCE SIGNS USED

[0020] 

1

long-term CO₂ storage

2

pipeline

10

intermediate LCO₂ storage tank

15

first LCO₂ pump

17, 19, 31

discharge conduit

30

LCO₂ carrier ship

40

fluid withdrawal conduit

42

fluid return conduit

50; 51

refrigeration unit

64

ambient cooling inlet

66

ambient cooling outlet

70

sub-ambient refrigeration heat sink

72

refrigerant heating conduit

74

refrigerant return conduit

81, 83, 85, 87

refrigerant medium conduit

74, 85, 87, 81, 83, 72

closed refrigerant loop

91

refrigerant compressor

93

desuperheater

95

refrigerant receiver

97

expansion valve

99

evaporator

110

system

Claims

1. A system (110) configured to refrigerate LCO₂ contained in an intermediate LCO₂ storage tank (10) at a CO₂ receiving terminal, the system comprising:

- an intermediate LCO₂ storage tank (10);

- a fluid withdrawal conduit (40) connected to the intermediate LCO₂ storage tank (10) configured to withdrawing a fluid stream from the intermediate LCO₂ storage tank (10);

- an LCO₂ discharge conduit (17, 19, 31), one end of which is connected to the intermediate LCO₂ storage tank (10), and the other end is connected to a pipeline (2) connected to a long-term storge (1), said discharge conduit being configured to withdraw an LCO₂ discharge stream from the intermediate LCO₂ storage tank and to lead the stream to the pipeline (2);

- a first LCO₂ pump (15) arranged along the LCO₂ discharge conduit (17, 19, 31);

- a refrigeration unit (50; 51) connected to the fluid withdrawal conduit (40) configured to refrigerate the withdrawn fluid stream from the intermediate LCO₂ storage tank (10);

- a fluid return conduit (42) connecting the refrigeration unit (50; 51) with the intermediate LCO₂ storage tank (10) configured to convey a refrigerated and/or liquefied fluid stream from the refrigeration unit (50; 51) to the intermediate LCO₂ storage tank (10),

- a sub-ambient refrigeration heat sink (70) arranged along the LCO₂ discharge conduit (17, 19, 31) at a location downstream of the first LCO₂ pump (15) configured to transfer heat from a refrigerant stream exiting the refrigeration unit (50; 51) to the LCO₂ discharge stream;

- a refrigerant heating conduit (72) fluidly connecting the refrigeration unit (50; 51) with the sub-ambient refrigeration heat sink (70) configured to convey to the sub-ambient refrigeration heat sink (70) the refrigerant stream exiting the refrigeration unit (50; 51); and,

- a refrigerant return conduit (74) fluidly connecting the refrigeration unit (50; 51) with the sub-ambient refrigeration heat sink (70) configured to return to the refrigeration unit (50; 51) the refrigerant stream.

2. The system (110) of claim 1, wherein the refrigeration unit (50; 51) additionally comprises:

- an ambient cooling inlet (66) configured to enter a flow of an ambient fluid into the refrigeration unit (50; 51); and

- an ambient cooling outlet (64), configured to exit a flow of heated ambient fluid from the refrigeration unit (50; 51).

3. The system (110) of claim 2, wherein the refrigeration unit (50; 51) comprises:

- a refrigerant medium conduit (81, 83, 85, 87), connected to the refrigerant heating conduit (72), and to the refrigerant return conduit (74);

- an evaporator (99) arranged along the refrigerant medium conduit (81, 83, 85, 87) fluidly connected to the fluid withdrawal conduit (40), and to the fluid return conduit (42) configured to receive the withdrawn fluid stream (40), to transfer heat from the latter to the refrigerant medium stream in the evaporator (99), and to exit a cooled withdrawn fluid stream (42);

- a refrigeration compressor (91) arranged along the refrigerant medium conduit (81, 83, 85, 87) downstream of the evaporator (99) configured to compress a refrigerant medium stream exiting the evaporator (99), and to exit a compressed stream of refrigerant medium;

- a desuperheater (93) arranged along the refrigerant medium conduit (81, 83, 85, 87) downstream of the refrigeration compressor (91) configured to transfer heat from the compressed refrigerant medium stream to a flow of ambient fluid (64, 66), and to exit a cooled compressed refrigerant medium stream to the sub-ambient refrigeration heat sink (70);

- receiver (95) arranged along the refrigerant medium conduit (81, 83, 85, 87) downstream of the sub-ambient refrigeration heat sink (70) configured to receive the cooled compressed refrigerant medium stream;

- an expansion valve (97) arranged along the refrigerant medium conduit (81, 83, 85, 87) downstream of the receiver (95) fluidly connected with the evaporator (99) configured to exit an expanded stream of refrigerant medium to the evaporator (99).

4. A method for refrigeration of the contents of an intermediate LCO₂ storage tank (10) at a CO₂ receiving terminal during injection of LCO₂ into a pipeline (2) connected to a long-term storage (1), said method comprising the following steps:

A) discharging a stream of LCO₂ from an intermediate LCO₂ storage tank (10) to be injected into a pipeline (2) connected to a long-term CO₂ storage;

B) subjecting the stream of LCO₂ from step A to pumping in a first pumping stage (15);

C) transferring heat from a refrigerant stream to the LCO₂ stream from step B;

D) withdrawing a fluid stream (40) from the intermediate LCO₂ storage tank (10);

E) refrigerating the withdrawn fluid stream from step D, thereby liquefying the withdrawn fluid stream and/or cooling the withdrawn fluid stream; and,

F) returning the fluid stream from step E to the storage tank (10);

wherein, in step E, heat from the withdrawn fluid stream (40) is transferred to the refrigerant stream to be used as a heat source for the refrigeration of step E, and the LCO₂ stream from step B is used as a heat sink for the refrigeration of step E.

5. The method for refrigeration of claim 4, additionally comprising the step:

G) transferring heat to an ambient fluid from the refrigerant stream.

6. The method of claim 5, wherein the refrigerant is circulated in a closed refrigerant loop (74, 85, 87, 81, 83, 72), and wherein the refrigerant is vaporised in step E, said method additionally comprising the steps:

H) compressing the vaporised refrigerant stream from step E;
wherein, in step G, heat is transferred from the compressed vaporised refrigerant of step H; wherein, in step C, the compressed vaporised refrigerant stream from step H is condensed;

I) subjecting the condensed refrigerant stream from step C to expansion,
wherein, in step E, the refrigeration is achieved by vaporisation of the expanded condensed refrigerant stream from step I.

Drawing