WO2016026533A1 - Heat pump system - Google Patents

Heat pump system Download PDF

Info

Publication number
WO2016026533A1
WO2016026533A1 PCT/EP2014/067853 EP2014067853W WO2016026533A1 WO 2016026533 A1 WO2016026533 A1 WO 2016026533A1 EP 2014067853 W EP2014067853 W EP 2014067853W WO 2016026533 A1 WO2016026533 A1 WO 2016026533A1
Authority
WO
WIPO (PCT)
Prior art keywords
working fluid
heat exchanger
fluid line
line
refrigerant
Prior art date
Application number
PCT/EP2014/067853
Other languages
French (fr)
Inventor
Oddvar JØRSTAD
Original Assignee
Statoil Petroleum As
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Statoil Petroleum As filed Critical Statoil Petroleum As
Priority to PCT/EP2014/067853 priority Critical patent/WO2016026533A1/en
Publication of WO2016026533A1 publication Critical patent/WO2016026533A1/en

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
    • F25B2400/23—Separators

Definitions

  • the present invention relates to a heat pump system, and to a method of exchanging heat between two fluids.
  • Heat pump systems are commonly used in many industries.
  • One such application is the use of heat pump systems to refrigerate natural gas to liquid natural gas (LNG). This can occur on offshore structures prior to transportation of LNG.
  • LNG liquid natural gas
  • FIG. 2 A known system for the refrigeration of LNG is shown in Figure 2.
  • the compressor 202 compresses refrigerant, increasing the refrigerant pressure and temperature.
  • the high pressure refrigerant is then pre-cooled in pre-cooling heat exchangers 203 and 204.
  • the high pressure refrigerant enters a main cryogenic heat exchanger (MCHE) 205 at the lower end of the MCHE 205 and is further cooled before it exits the upper end of the MCHE 205.
  • the pressure and temperature of the cooled refrigerant is then reduced using expansion valve 206 so that the refrigerant can take up heat by evaporating at low temperature.
  • MCHE main cryogenic heat exchanger
  • the cold, low pressure refrigerant enters the upper end of the MCHE 205 as a two- phase flow. As it flows downwards inside the MCHE 205, it takes up heat from the cooled, high pressure refrigerant stream and from a natural gas stream by evaporation. The natural gas stream flows in parallel with the cooled, high pressure refrigerant stream, entering at the bottom and exiting at the top of the MCHE 205.
  • the warm, low pressure refrigerant exits the lower end of MCHE 205 as a single phase gas, and is first sent to a suction drum 207 before it returns to the compressor 202.
  • the warm, low pressure refrigerant exiting at the lower end of the MCHE 205 is at a temperature above its dew point (i.e. it is superheated).
  • the degree of superheating is typical in the order of 5 - 10 K above the dew point.
  • the main reason for superheating of the warm, low pressure refrigerant exiting the MCHE 205 is to ensure that the warm, low pressure refrigerant is a single phase gas, and hence that no liquid droplets enter the compressor, or that there is no build of liquid refrigerant in the suction drum.
  • the suction pump can be used to separate gas and liquid phases of the warm, low pressure refrigerant exiting the heat exchanger, so that only gas enters the compressor.
  • any liquid present in the warm, low pressure refrigerant exiting the heat exchanger can be pumped in parallel to the gaseous warm, low pressure refrigerant passing through the compressor.
  • the pumped liquid refrigerant can then re-join the compressed refrigerant.
  • the present invention provides a heat pump system comprising a compressor, the compressor being connected to a working fluid-cooling heat exchanger via a first working fluid line, the working fluid-cooling heat exchanger being connected to an expansion device via a second working fluid line, the expansion device being connected to a working fluid-heating heat exchanger via a third working fluid line, the working fluid-heating heat exchanger being connected to a separator via a fourth working fluid line, the separator being connected to the compressor via a fifth working fluid line, wherein: the system is configured such that working fluid in the fourth working fluid line is at or below its dew point; the separator is for separating liquid and gas phases of the working fluid in the fourth working fluid line; and the system comprises a liquid moving device configured to move the separated liquid in the separator to the first working fluid line.
  • the working fluid in the present system is not superheated when exiting the working fluid-heating heat exchanger.
  • This increases the efficiency of the heat exchange system, as the working fluid can be colder.
  • This increases the cooling possible in the working fluid-heating heat exchanger.
  • the working fluid in the fourth fluid line may be at its dew point. This is the temperature at which the energy efficiency of the system is optimised.
  • the working fluid in the fourth working fluid line may be 1 , 2, 5 or 10 K lower than its dew point, or may be 1 , 2, 5 or 10 K above its dew point.
  • the system may be configured such that working fluid in the fourth working fluid line comprises a mixture of gas and liquid phases.
  • the system of the present invention provides this increased efficiency in a reliable and robust manner: if the separator and/or liquid moving device were to stop working adequately or fail, then the system is still capable of being run with superheated working fluid exiting the working fluid-heating heat exchanger as an inbuilt fall-back solution.
  • the working fluid may be pure working fluid (nitrogen, methane, ethane, ethylene, propane, butane, etc.).
  • the present invention may be particularly relevant for a mixed working fluid (e.g. a mixture of one or more of nitrogen, methane, ethane, propane, butane, and pentane).
  • the ratio/mixture/content of the mixed working fluid can be varied in order to ensure that the working fluid in the fourth working fluid line is at or below its dew point for a desired temperature and/or pressure.
  • the present invention is particularly advantageous for a mixed working fluid, where it is more likely that one of the mix of working fluids will be at a temperature below its dew point.
  • the liquid moving device acts to move working fluid in parallel with working fluid passing through the gas cooler/condenser.
  • the separator may comprise a reservoir for storing liquid working fluid.
  • the liquid moving device may be connected to a liquid outlet of the separator.
  • the reservoir may have a capacity such that is sufficient to store the liquid working fluid exiting the working fluid- cooling heat exchanger. This size will depend on the capacity of the heat pump system, the type of working fluid and the temperature of the working fluid in the fourth working fluid line and the type of heat exchanger used.
  • the reservoir may be at least 20m 3 , 30m 3 , 40m 3 , 50m 3 , 60 m 3 or 70 m 3 .
  • the reservoir may have a maximum volume of 70 m 3 , 60 m 3 , 50 m 3 , 40 m 3 , 30 m 3 or 20 m 3 .
  • Having a large reservoir allows the heat pump system to be less sensitive to tilt and movement of heat pump system.
  • a large reservoir may ensure that only gas working fluid enters the compressor and only liquid fluid enters the liquid moving device. The issue of tilt and movement may be particularly important when the heat pump system is used off-shore, for example on a boat or floating platform.
  • the fifth working fluid line and the separator may be arranged such that only gaseous working fluid may enter the fifth working fluid line.
  • the separator may be arranged vertically.
  • a fifth fluid line may be connected to an upper end of the separator.
  • the liquid moving device may be connected to the lower end of the separator.
  • the separator may be housed within a suction drum.
  • a suction drum may be present between the working fluid-heating heat exchanger and the compressor.
  • the suction drum ensures operational flexibility during transient states such as during start-up or rapid capacity changes, and can ensure sufficient demisting of the working fluid. Since a suction drum is typically present in known heat pump systems, by placing the separator in the suction drum, or providing a suction drum with an in-built separator, existing heat pump systems and designs may easily be updated.
  • the working fluid-cooling heat exchanger may comprise a main heat exchanger and the working fluid-heating heat exchanger may comprise the main heat exchanger, the main heat exchanger comprising a first working fluid path connecting the first working fluid line to the second working fluid line and a second working fluid path connecting the third working fluid line to the fourth working fluid line, the first and second working fluid paths being arranged to allow heat to be exchanged therebetween.
  • the main heat exchanger may be a MCHE.
  • the main heat exchanger may be configured such that working fluid in the first path moves in a general direction opposite to a general direction of working fluid in the second path.
  • the main heat exchanger may be arranged such that the first and second paths are oriented such that working fluid in the first and second paths moves in a generally vertical direction.
  • the main heat exchanger may be arranged such that the first and fourth working fluid lines are connected to a lower end of the main heat exchanger and the second and third working fluid lines are connected to an upper end of the main heat exchanger. Since in the present invention, working fluid exiting the main heat exchanger comprises liquid and gas, this arrangement may be preferable.
  • the main heat exchanger may be arranged such that the first and fourth working fluid lines are connected to an upper end of the main heat exchanger and the second and third working fluid lines are connected to a lower end of the main heat exchanger.
  • the main heat exchanger may comprise a third path for passage of a non-working fluid, such that heat may be exchanged between the working fluid and the non-working fluid.
  • the main heat exchanger may comprise more than one path for passage of non- working fluid through the main heat exchanger, e.g. fourth, fifth, etc. passages. This may allow passage of more than one non-working fluid through the main heat exchanger.
  • the third path may be arranged such that the general direction of the non-working fluid is opposite the general direction of the working fluid in the second path.
  • non-working fluid may be input into the third path at the lower end of the main heat exchanger and may be output from the upper end.
  • non-working fluid may be input into the third path at the upper end of the main heat exchanger and may be output from the lower end.
  • the working fluid cooling heat exchanger may comprise a pre-cooling heat exchanger and the main heat exchanger
  • the first working fluid line may comprise a first portion connecting the compressor to the pre-cooling heat exchanger and a second portion connecting the pre-cooling heat exchanger to the main heat exchanger.
  • the pre-cooling heat exchanger allows working fluid entering the main heat exchanger from the first working fluid line to be sufficiently cool, so that in the main heat exchanger the working fluid passing through the second path can cool both the working fluid in the first path and the non-working fluid.
  • the pre-cooling heat exchanger may comprise a first heat exchanger and a second heat exchanger.
  • the first heat exchanger may cool the working fluid to the ambient temperature.
  • the second heat exchanger may cool the working fluid below the ambient temperature.
  • the first heat exchanger may be a gas cooler.
  • the second heat exchanger may be a condenser.
  • the liquid moving device may be connected to the first or second portion of the first working fluid line. Preferably, the liquid moving device is connected to the second portion of the first working fluid line.
  • the liquid moving device may be connected to an intermediate working fluid line connecting the first heat exchanger and the second heat exchanger.
  • the liquid moving device may be connected to the third working fluid line.
  • the third working fluid line may have pressure approximately equal to, or slightly greater than, the liquid working fluid in the separator.
  • the heat pump system may be a refrigeration system for refrigerating a non-working fluid, and the working fluid may be a refrigerant.
  • the non-working fluid may be natural gas.
  • the output of the third path in the main heat exchanger may be LNG.
  • the working fluid- cooling heat exchanger may be/comprise a condenser.
  • the working fluid-heating heat exchanger may be/comprise an evaporator.
  • the specific temperatures and pressures of the working fluid line may vary, as is known the art.
  • the specific temperature of the dew point of the working fluid exiting the working fluid-heating heat exchanger is thus dependent on many different factors. For the present invention, it is the temperature of the working fluid relative to its dew point that is important.
  • the expansion device may be a device or means suitable for expanding the refrigerant.
  • the expansion device may comprise an expander and/or an expansion valve.
  • the liquid moving means may be a pump.
  • the liquid moving means may be an ejector.
  • the invention provides a method of exchanging heat between a working fluid and a non-working fluid using a heat pump system
  • the heat pump system comprising a compressor, the compressor being connected to a working fluid-cooling heat exchanger via a first working fluid line, the working fluid-cooling heat exchanger being connected to an expansion device via a second working fluid line, the expansion device being connected to a working fluid-heating heat exchanger via a third working fluid line, the working fluid-heating heat exchanger being connected to a separator via a fourth working fluid line, the separator being connected to the compressor via fifth working fluid line, the method comprising: allowing the temperature of the working fluid in the fourth working fluid line to be at or below the dew point of the working fluid; separating liquid and gas phases of the working fluid present in the fourth working fluid line; and moving the separated liquid to the first working fluid line.
  • the method may comprise storing the separated liquid working fluid.
  • the method may comprise allowing only gaseous working fluid into the fifth working fluid line.
  • the method may include providing and/or using any or all features of the heat pump system described above.
  • Moving the separated liquid may comprise pumping the separated liquid.
  • FIG. 1 shows an embodiment of the heat pump system of the present invention
  • Figure 2 shows an example of a prior art heat pump system.
  • FIG. 1 shows a refrigeration system 1.
  • the refrigeration system 1 comprises a compressor 2, the compressor being connected to a refrigerant-cooling heat exchanger 3, 4, 5 via a first refrigerant line 1 1.
  • the compressor 2 compresses refrigerant to a high pressure, and doing so raises its temperature.
  • the refrigerant-cooling heat exchanger 3, 4, 5 comprises a first heat exchanger 3, a second heat exchanger 4 and a main heat exchanger 5.
  • the first heat exchanger 3 cools the compressed refrigerant to the ambient temperature.
  • the second heat exchanger 4 cools the compressed refrigerant below the ambient temperature.
  • the main heat exchanger 5 further cools the compressed refrigerant.
  • the refrigerant-heating heat exchanger 3, 4, 5 is a condenser.
  • the refrigerant-cooling heat exchanger 3, 4, 5 is connected to an expansion valve 6 via a second refrigerant line 12.
  • the expansion valve 6 is connected to a refrigerant-heating heat exchanger 5 via a third refrigerant line 13. At the expansion valve 6 the pressure of the refrigerant is reduced and its temperature is decreased.
  • the main heat exchanger 5 is also the refrigerant-heating heat exchanger 5.
  • the main heat exchanger 5 comprises a first refrigerant path connecting the first refrigerant line 1 1 to the second refrigerant line 12 and a second refrigerant path connecting the third refrigerant line 13 to a fourth refrigerant line 14.
  • the first and second refrigerant paths are arranged to allow heat, but not refrigerant, to be exchanged therebetween.
  • the refrigerant- heating heat exchanger 5 is an evaporator.
  • the main heat exchanger 5 also comprises a third path for passage of natural gas, such that heat, but not fluid, may be exchanged between the refrigerant and the natural gas.
  • the third path is arranged such that the general direction of flow of the natural gas is opposite the general direction of flow of the refrigerant in the second path.
  • the refrigerant in the first path moves in a general direction opposite to a general direction of refrigerant in the second path.
  • the main heat exchanger 5 is arranged such that the first and second refrigerant paths, and the third path, are oriented such that refrigerant in the first and second paths, and the natural gas in the third path, moves in a generally vertical direction.
  • the main heat exchanger 5 is arranged such that the first 11 and fourth 14 refrigerant lines are connected to a lower end of the main heat exchanger 5 and the second and third refrigerant lines are connected to an upper end of the main heat exchanger 5. Further, the natural gas is input (in gaseous form) into the third path at the lower end of the main heat exchanger 5 and is output (as LNG) from the upper end.
  • the refrigerant cooling heat exchanger 3, 4, 5 also comprises a pre-cooling heat exchanger 3, 4.
  • the first refrigerant line 1 1 comprises a first portion 1 1 1 connecting the compressor to the pre-cooling heat exchanger 3, 4 and a second portion 112 connecting the pre-cooling heat exchanger 3, 4 to the main heat exchanger 5.
  • the refrigerant-heating heat exchanger 5 is connected to a separator 7 via the fourth refrigerant line 14.
  • the separator 7 is connected to the compressor 2 via a fifth refrigerant line 15.
  • the warm, low-pressure refrigerant exiting the second refrigerant path is not super- heated (at or below its dew point).
  • the refrigerant in the fourth refrigerant line 14 contains both liquid and gaseous refrigerant.
  • the separator 7 acts to separate these two phases.
  • the separator 7 is housed within a suction drum.
  • the separator 7 comprises a reservoir for storing the separated liquid refrigerant.
  • a pump 8 is connected to the reservoir.
  • the reservoir has a capacity of between 20 and 70 m 3 .
  • the fifth refrigerant line 15 and the separator 7 are arranged such that only gaseous refrigerant may enter the fifth refrigerant line 15.
  • the separator 7 is arranged vertically with the fifth fluid line 15 being connected to an upper end of the separator 7 and the pump 8 being connected to the lower end of the separator 7.
  • the pump 8 pumps refrigerant in parallel with refrigerant passing through the condenser 2.
  • the pump 8 is connected to the second portion 112 of the first refrigerant line 1 1.
  • the refrigerant used in the refrigeration system 1 is a mixed refrigerant.
  • the refrigerant in the present system 1 is not superheated when exiting the refrigerant-heating heat exchanger 5, the refrigerant in the fourth refrigerant line being 0 - 2 K lower than its dew point.
  • the system may be configured such that refrigerant in the fourth refrigerant line 14 comprises a mixture of gas and liquid phases.
  • refrigerant in the fourth refrigerant line 14 comprises a mixture of gas and liquid phases.
  • the temperature of the refrigerant in the fourth refrigerant line may be 10°C to 40°C and the pressure may be 5 to 10 bar.
  • the temperature of the refrigerant in the fourth refrigerant line may be -50°C to - 30°C and the pressure may be 2 to 5 bar.
  • the temperature of the refrigerant in the fourth refrigerant line may be 10°C to 40°C and the pressure may be 1 to 2 bar.
  • the temperature of the refrigerant in the fourth refrigerant line may be -60°C to -50°C and the pressure may be 2 to 3 bar.
  • the temperature of the refrigerant in the fourth refrigerant line may be -85°C to -75°C and the pressure may be 2 to 3 bar; for a methane, ethane and propane mixed refrigerant, the temperature of the refrigerant in the fourth refrigerant line may be -60°C to -50°C and the pressure may be 2 to 3 bar; for a methane, ethane, propane and butane refrigerant, the temperature of the refrigerant in the fourth refrigerant line may be -30°C to -20°C and the temperature may be 2 to 5 bar, and/or the temperature may be 0°C to 10°C and the pressure may be 5 to 10 bar.
  • a methane, ethane, propane and butane refrigerant may have a temperature of 0°C to 10°C and a pressure of 5 to 10 bar, and/or a temperature of 10°C to 40°C and a pressure of 30 to 40 bar in a fourth refrigerant line of one circuit; and a nitrogen, methane, ethane and propane refrigerant may have a temperature of -60°C to -50°C and a pressure of 2 to 3 bar in a fourth refrigerant line of the other circuit.

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Steam Or Hot-Water Central Heating Systems (AREA)

Abstract

A heat pump system (1) comprising a compressor (2), the compressor (2) being connected to a working fluid-cooling heat exchanger (3, 4, 5) via a first working fluid line (11), the working fluid-cooling heat exchanger (3, 4, 5) being connected to an expansion device (6) via a second working fluid line (12), the expansion device (6) being connected to a working fluid-heating heat exchanger (5) via a third working fluid line (13), the working fluid-heating heat exchanger being connected to a separator (7) via a fourth working fluid line (14), the separator (7) being connected to the compressor (2) via a fifth working fluid line (15), wherein: the system (1) is configured such that working fluid in the fourth working fluid line (14) is at or below its dew point; the separator (7) is for separating liquid and gas phases of the working fluid in the fourth working fluid line (14); and the system (1) comprises a liquid moving device (8) configured to move the separated liquid in the separator (7) to the first working fluid line (11).

Description

Heat Pump System
The present invention relates to a heat pump system, and to a method of exchanging heat between two fluids.
Heat pump systems are commonly used in many industries. One such application is the use of heat pump systems to refrigerate natural gas to liquid natural gas (LNG). This can occur on offshore structures prior to transportation of LNG.
A known system for the refrigeration of LNG is shown in Figure 2. The compressor 202 compresses refrigerant, increasing the refrigerant pressure and temperature. The high pressure refrigerant is then pre-cooled in pre-cooling heat exchangers 203 and 204. The high pressure refrigerant enters a main cryogenic heat exchanger (MCHE) 205 at the lower end of the MCHE 205 and is further cooled before it exits the upper end of the MCHE 205. The pressure and temperature of the cooled refrigerant is then reduced using expansion valve 206 so that the refrigerant can take up heat by evaporating at low temperature.
The cold, low pressure refrigerant enters the upper end of the MCHE 205 as a two- phase flow. As it flows downwards inside the MCHE 205, it takes up heat from the cooled, high pressure refrigerant stream and from a natural gas stream by evaporation. The natural gas stream flows in parallel with the cooled, high pressure refrigerant stream, entering at the bottom and exiting at the top of the MCHE 205.
The warm, low pressure refrigerant exits the lower end of MCHE 205 as a single phase gas, and is first sent to a suction drum 207 before it returns to the compressor 202.
The warm, low pressure refrigerant exiting at the lower end of the MCHE 205 is at a temperature above its dew point (i.e. it is superheated). The degree of superheating is typical in the order of 5 - 10 K above the dew point. The main reason for superheating of the warm, low pressure refrigerant exiting the MCHE 205 is to ensure that the warm, low pressure refrigerant is a single phase gas, and hence that no liquid droplets enter the compressor, or that there is no build of liquid refrigerant in the suction drum.
It is also known that, in a heat pump system comprising a suction pump, the suction pump can be used to separate gas and liquid phases of the warm, low pressure refrigerant exiting the heat exchanger, so that only gas enters the compressor.
It is also known that, any liquid present in the warm, low pressure refrigerant exiting the heat exchanger can be pumped in parallel to the gaseous warm, low pressure refrigerant passing through the compressor. The pumped liquid refrigerant can then re-join the compressed refrigerant.
In the LNG business it is usually desirable to avoid new technology solutions that are not verified in full scale operation, and to avoid introducing further complexity into systems, so as to ease manufacture and to minimise the potential for leakage of working fluid for example. Further, it is usually desirable to minimise the volume of working fluid in a system, so as to reduce the demands on the system during warm-start up, reduce the make-up demand, and reduce the filling of refrigerant of safety reason, for example.
In one aspect, the present invention provides a heat pump system comprising a compressor, the compressor being connected to a working fluid-cooling heat exchanger via a first working fluid line, the working fluid-cooling heat exchanger being connected to an expansion device via a second working fluid line, the expansion device being connected to a working fluid-heating heat exchanger via a third working fluid line, the working fluid-heating heat exchanger being connected to a separator via a fourth working fluid line, the separator being connected to the compressor via a fifth working fluid line, wherein: the system is configured such that working fluid in the fourth working fluid line is at or below its dew point; the separator is for separating liquid and gas phases of the working fluid in the fourth working fluid line; and the system comprises a liquid moving device configured to move the separated liquid in the separator to the first working fluid line.
Thus, in operation the working fluid in the present system is not superheated when exiting the working fluid-heating heat exchanger. This increases the efficiency of the heat exchange system, as the working fluid can be colder. This increases the cooling possible in the working fluid-heating heat exchanger. The working fluid in the fourth fluid line may be at its dew point. This is the temperature at which the energy efficiency of the system is optimised. However, the working fluid in the fourth working fluid line may be 1 , 2, 5 or 10 K lower than its dew point, or may be 1 , 2, 5 or 10 K above its dew point. Hence, the system may be configured such that working fluid in the fourth working fluid line comprises a mixture of gas and liquid phases.
Despite the advantages the present invention achieves, in comparison to
conventional heat pump systems the additional separator and liquid moving device increases the complexity of the system, increases the volume of working fluid in the system, which can be disadvantageous, as mentioned above.
Due to the increased efficiency of the system, production of cooled non-working fluid can be increased, and/or compressor work can be decreased, by 2-3%. Further, it can allow for a reduction in the size and weight of the heat pump system, for the same production capacity. Operation of the heat pump where evaporation occurs throughout the whole working fluid-heating heat exchanger (i.e. where there is no superheating of the working- fluid) contributes to this increased efficiency. The increased efficiency in turn allows the heat exchanger to have a reduced area of heat-exchange surface, and so may be smaller in size and hence cheaper, lighter, etc.
However, a heat exchanger operating with evaporation occurring throughout the entirety of the working fluid-heating heat exchanger is not usually advisable for offshore or hybrid floating LNG heat pump systems. In these cases, since temporary or permanent tilts may be present, it is usually advisable to ensure that all the working fluid has evaporated some distance from the outlet of the working fluid-heating heat exchanger. It is this which motivates the superheating of the working fluid and which reduces the efficiency of typical systems.
Further, the system of the present invention provides this increased efficiency in a reliable and robust manner: if the separator and/or liquid moving device were to stop working adequately or fail, then the system is still capable of being run with superheated working fluid exiting the working fluid-heating heat exchanger as an inbuilt fall-back solution.
The working fluid may be pure working fluid (nitrogen, methane, ethane, ethylene, propane, butane, etc.). The present invention may be particularly relevant for a mixed working fluid (e.g. a mixture of one or more of nitrogen, methane, ethane, propane, butane, and pentane). The ratio/mixture/content of the mixed working fluid can be varied in order to ensure that the working fluid in the fourth working fluid line is at or below its dew point for a desired temperature and/or pressure. The present invention is particularly advantageous for a mixed working fluid, where it is more likely that one of the mix of working fluids will be at a temperature below its dew point.
The liquid moving device acts to move working fluid in parallel with working fluid passing through the gas cooler/condenser.
The separator may comprise a reservoir for storing liquid working fluid. The liquid moving device may be connected to a liquid outlet of the separator. The reservoir may have a capacity such that is sufficient to store the liquid working fluid exiting the working fluid- cooling heat exchanger. This size will depend on the capacity of the heat pump system, the type of working fluid and the temperature of the working fluid in the fourth working fluid line and the type of heat exchanger used. For example, the reservoir may be at least 20m3, 30m3, 40m3, 50m3, 60 m3 or 70 m3. The reservoir may have a maximum volume of 70 m3, 60 m3, 50 m3, 40 m3, 30 m3 or 20 m3.
Having a large reservoir allows the heat pump system to be less sensitive to tilt and movement of heat pump system. A large reservoir may ensure that only gas working fluid enters the compressor and only liquid fluid enters the liquid moving device. The issue of tilt and movement may be particularly important when the heat pump system is used off-shore, for example on a boat or floating platform.
The fifth working fluid line and the separator may be arranged such that only gaseous working fluid may enter the fifth working fluid line. The separator may be arranged vertically. A fifth fluid line may be connected to an upper end of the separator. The liquid moving device may be connected to the lower end of the separator. The separator may be housed within a suction drum. In conventional heat pump systems, a suction drum may be present between the working fluid-heating heat exchanger and the compressor. The suction drum ensures operational flexibility during transient states such as during start-up or rapid capacity changes, and can ensure sufficient demisting of the working fluid. Since a suction drum is typically present in known heat pump systems, by placing the separator in the suction drum, or providing a suction drum with an in-built separator, existing heat pump systems and designs may easily be updated.
The working fluid-cooling heat exchanger may comprise a main heat exchanger and the working fluid-heating heat exchanger may comprise the main heat exchanger, the main heat exchanger comprising a first working fluid path connecting the first working fluid line to the second working fluid line and a second working fluid path connecting the third working fluid line to the fourth working fluid line, the first and second working fluid paths being arranged to allow heat to be exchanged therebetween. The main heat exchanger may be a MCHE.
The main heat exchanger may be configured such that working fluid in the first path moves in a general direction opposite to a general direction of working fluid in the second path.
The main heat exchanger may be arranged such that the first and second paths are oriented such that working fluid in the first and second paths moves in a generally vertical direction.
The main heat exchanger may be arranged such that the first and fourth working fluid lines are connected to a lower end of the main heat exchanger and the second and third working fluid lines are connected to an upper end of the main heat exchanger. Since in the present invention, working fluid exiting the main heat exchanger comprises liquid and gas, this arrangement may be preferable.
The main heat exchanger may be arranged such that the first and fourth working fluid lines are connected to an upper end of the main heat exchanger and the second and third working fluid lines are connected to a lower end of the main heat exchanger.
The main heat exchanger may comprise a third path for passage of a non-working fluid, such that heat may be exchanged between the working fluid and the non-working fluid.
The main heat exchanger may comprise more than one path for passage of non- working fluid through the main heat exchanger, e.g. fourth, fifth, etc. passages. This may allow passage of more than one non-working fluid through the main heat exchanger.
The third path may be arranged such that the general direction of the non-working fluid is opposite the general direction of the working fluid in the second path.
Further, the non-working fluid may be input into the third path at the lower end of the main heat exchanger and may be output from the upper end. Alternatively, the non-working fluid may be input into the third path at the upper end of the main heat exchanger and may be output from the lower end.
The working fluid cooling heat exchanger may comprise a pre-cooling heat exchanger and the main heat exchanger, and the first working fluid line may comprise a first portion connecting the compressor to the pre-cooling heat exchanger and a second portion connecting the pre-cooling heat exchanger to the main heat exchanger. The pre-cooling heat exchanger allows working fluid entering the main heat exchanger from the first working fluid line to be sufficiently cool, so that in the main heat exchanger the working fluid passing through the second path can cool both the working fluid in the first path and the non-working fluid.
The pre-cooling heat exchanger may comprise a first heat exchanger and a second heat exchanger. The first heat exchanger may cool the working fluid to the ambient temperature. The second heat exchanger may cool the working fluid below the ambient temperature.
The first heat exchanger may be a gas cooler. The second heat exchanger may be a condenser.
The liquid moving device may be connected to the first or second portion of the first working fluid line. Preferably, the liquid moving device is connected to the second portion of the first working fluid line.
The liquid moving device may be connected to an intermediate working fluid line connecting the first heat exchanger and the second heat exchanger.
The liquid moving device may be connected to the third working fluid line. The third working fluid line may have pressure approximately equal to, or slightly greater than, the liquid working fluid in the separator.
The heat pump system may be a refrigeration system for refrigerating a non-working fluid, and the working fluid may be a refrigerant. The non-working fluid may be natural gas. The output of the third path in the main heat exchanger may be LNG. The working fluid- cooling heat exchanger may be/comprise a condenser. The working fluid-heating heat exchanger may be/comprise an evaporator.
Depending on the specific working fluid used, and the specific type of heat pump system used (e.g. a cascade system, a single stage system, a mixed working fluid system, a single working fluid system, etc.) the specific temperatures and pressures of the working fluid line may vary, as is known the art. The specific temperature of the dew point of the working fluid exiting the working fluid-heating heat exchanger is thus dependent on many different factors. For the present invention, it is the temperature of the working fluid relative to its dew point that is important. The expansion device may be a device or means suitable for expanding the refrigerant. For example, the expansion device may comprise an expander and/or an expansion valve.
The liquid moving means may be a pump.
The liquid moving means may be an ejector.
In another aspect the invention provides a method of exchanging heat between a working fluid and a non-working fluid using a heat pump system, the heat pump system comprising a compressor, the compressor being connected to a working fluid-cooling heat exchanger via a first working fluid line, the working fluid-cooling heat exchanger being connected to an expansion device via a second working fluid line, the expansion device being connected to a working fluid-heating heat exchanger via a third working fluid line, the working fluid-heating heat exchanger being connected to a separator via a fourth working fluid line, the separator being connected to the compressor via fifth working fluid line, the method comprising: allowing the temperature of the working fluid in the fourth working fluid line to be at or below the dew point of the working fluid; separating liquid and gas phases of the working fluid present in the fourth working fluid line; and moving the separated liquid to the first working fluid line.
The method may comprise storing the separated liquid working fluid. The method may comprise allowing only gaseous working fluid into the fifth working fluid line. The method may include providing and/or using any or all features of the heat pump system described above.
Moving the separated liquid may comprise pumping the separated liquid.
Certain preferred embodiments will now be described by way of example only and with reference to the accompanying drawings, in which
Figure 1 shows an embodiment of the heat pump system of the present invention,
Figure 2 shows an example of a prior art heat pump system.
Figure 1 shows a refrigeration system 1. The refrigeration system 1 comprises a compressor 2, the compressor being connected to a refrigerant-cooling heat exchanger 3, 4, 5 via a first refrigerant line 1 1. The compressor 2 compresses refrigerant to a high pressure, and doing so raises its temperature. The refrigerant-cooling heat exchanger 3, 4, 5 comprises a first heat exchanger 3, a second heat exchanger 4 and a main heat exchanger 5. The first heat exchanger 3 cools the compressed refrigerant to the ambient temperature. The second heat exchanger 4 cools the compressed refrigerant below the ambient temperature. The main heat exchanger 5 further cools the compressed refrigerant. The refrigerant-heating heat exchanger 3, 4, 5 is a condenser.
The refrigerant-cooling heat exchanger 3, 4, 5 is connected to an expansion valve 6 via a second refrigerant line 12. The expansion valve 6 is connected to a refrigerant-heating heat exchanger 5 via a third refrigerant line 13. At the expansion valve 6 the pressure of the refrigerant is reduced and its temperature is decreased.
The main heat exchanger 5 is also the refrigerant-heating heat exchanger 5. The main heat exchanger 5 comprises a first refrigerant path connecting the first refrigerant line 1 1 to the second refrigerant line 12 and a second refrigerant path connecting the third refrigerant line 13 to a fourth refrigerant line 14. The first and second refrigerant paths are arranged to allow heat, but not refrigerant, to be exchanged therebetween. The refrigerant- heating heat exchanger 5 is an evaporator.
The main heat exchanger 5 also comprises a third path for passage of natural gas, such that heat, but not fluid, may be exchanged between the refrigerant and the natural gas. The third path is arranged such that the general direction of flow of the natural gas is opposite the general direction of flow of the refrigerant in the second path.
The refrigerant in the first path moves in a general direction opposite to a general direction of refrigerant in the second path.
The main heat exchanger 5 is arranged such that the first and second refrigerant paths, and the third path, are oriented such that refrigerant in the first and second paths, and the natural gas in the third path, moves in a generally vertical direction.
The main heat exchanger 5 is arranged such that the first 11 and fourth 14 refrigerant lines are connected to a lower end of the main heat exchanger 5 and the second and third refrigerant lines are connected to an upper end of the main heat exchanger 5. Further, the natural gas is input (in gaseous form) into the third path at the lower end of the main heat exchanger 5 and is output (as LNG) from the upper end.
The refrigerant cooling heat exchanger 3, 4, 5 also comprises a pre-cooling heat exchanger 3, 4. The first refrigerant line 1 1 comprises a first portion 1 1 1 connecting the compressor to the pre-cooling heat exchanger 3, 4 and a second portion 112 connecting the pre-cooling heat exchanger 3, 4 to the main heat exchanger 5.
The refrigerant-heating heat exchanger 5 is connected to a separator 7 via the fourth refrigerant line 14. The separator 7 is connected to the compressor 2 via a fifth refrigerant line 15. The warm, low-pressure refrigerant exiting the second refrigerant path is not super- heated (at or below its dew point). Thus, the refrigerant in the fourth refrigerant line 14 contains both liquid and gaseous refrigerant. The separator 7 acts to separate these two phases.
The separator 7 is housed within a suction drum. The separator 7 comprises a reservoir for storing the separated liquid refrigerant.
A pump 8 is connected to the reservoir. The reservoir has a capacity of between 20 and 70 m3. The fifth refrigerant line 15 and the separator 7 are arranged such that only gaseous refrigerant may enter the fifth refrigerant line 15. The separator 7 is arranged vertically with the fifth fluid line 15 being connected to an upper end of the separator 7 and the pump 8 being connected to the lower end of the separator 7.
The pump 8 pumps refrigerant in parallel with refrigerant passing through the condenser 2. The pump 8 is connected to the second portion 112 of the first refrigerant line 1 1.
The refrigerant used in the refrigeration system 1 is a mixed refrigerant.
In operation the refrigerant in the present system 1 is not superheated when exiting the refrigerant-heating heat exchanger 5, the refrigerant in the fourth refrigerant line being 0 - 2 K lower than its dew point. Hence, the system may be configured such that refrigerant in the fourth refrigerant line 14 comprises a mixture of gas and liquid phases. For example, for a nitrogen, methane, ethane, propane, butane and pentane mixed refrigerant, the temperature of the refrigerant in the fourth refrigerant line may be 10°C to 40°C and the pressure may be 5 to 10 bar. Further, for a nitrogen, methane, ethane and propane mixed refrigerant the temperature of the refrigerant in the fourth refrigerant line may be -50°C to - 30°C and the pressure may be 2 to 5 bar. Further, for an ethane, propane and butane mixed refrigerant the temperature of the refrigerant in the fourth refrigerant line may be 10°C to 40°C and the pressure may be 1 to 2 bar. Further, for a nitrogen, methane, ethane and propane mixed refrigerant the temperature of the refrigerant in the fourth refrigerant line may be -60°C to -50°C and the pressure may be 2 to 3 bar. Further, in a cascade process, for a nitrogen, methane and ethane mixed refrigerant, the temperature of the refrigerant in the fourth refrigerant line may be -85°C to -75°C and the pressure may be 2 to 3 bar; for a methane, ethane and propane mixed refrigerant, the temperature of the refrigerant in the fourth refrigerant line may be -60°C to -50°C and the pressure may be 2 to 3 bar; for a methane, ethane, propane and butane refrigerant, the temperature of the refrigerant in the fourth refrigerant line may be -30°C to -20°C and the temperature may be 2 to 5 bar, and/or the temperature may be 0°C to 10°C and the pressure may be 5 to 10 bar. Further, in a dual mixed refrigerant process, a methane, ethane, propane and butane refrigerant may have a temperature of 0°C to 10°C and a pressure of 5 to 10 bar, and/or a temperature of 10°C to 40°C and a pressure of 30 to 40 bar in a fourth refrigerant line of one circuit; and a nitrogen, methane, ethane and propane refrigerant may have a temperature of -60°C to -50°C and a pressure of 2 to 3 bar in a fourth refrigerant line of the other circuit.

Claims

A heat pump system comprising a compressor, the compressor being connected to a working fluid-cooling heat exchanger via a first working fluid line, the working fluid- cooling heat exchanger being connected to an expansion device via a second working fluid line, the expansion device being connected to a working fluid-heating heat exchanger via a third working fluid line, the working fluid-heating heat exchanger being connected to a separator via a fourth working fluid line, the separator being connected to the compressor via a fifth working fluid line, wherein:
the system is configured such that working fluid in the fourth working fluid line is at or below its dew point;
the separator is for separating liquid and gas phases of the working fluid in the fourth working fluid line; and
the system comprises a liquid moving device configured to move the separated liquid in the separator to the first working fluid line.
A heat pump system as claimed in claim 1 , wherein the separator comprises a reservoir for storing liquid working fluid.
A heat pump system as claimed in claim 1 or 2, wherein the fifth working fluid line and the separator are arranged such that only gaseous working fluid may enter the fifth working fluid line.
A heat pump system as claimed in any preceding claim, wherein the separator is housed within a suction drum.
A heat pump system as claimed in claim any preceding claim, wherein the working fluid-cooling heat exchanger comprises a main heat exchanger and the working fluid- heating heat exchanger comprises the main heat exchanger, the main heat exchanger comprising a first working fluid path connecting the first working fluid line to the second working fluid line and a second working fluid path connecting the third working fluid line to the fourth working fluid line, the first and second working fluid paths being arranged to allow heat to be exchanged therebetween.
A heat pump system as claimed in claim 5, wherein the main heat exchanger is configured such that working fluid in the first path moves in a general direction opposite to a general direction of working fluid in the second path.
7. A heat pump system as claimed in any preceding claim, wherein the working fluid cooling heat exchanger comprises a pre-cooling heat exchanger and a main heat exchanger, and the first working fluid line comprises a first portion connecting the compressor to the pre-cooling heat exchanger and a second portion connecting the pre-cooling heat exchanger to the main heat exchanger.
8. A heat pump system as claimed in claim 7, wherein the liquid moving device is connected to the first or second portion of the first working fluid line.
9. A heat pump system as claimed in any of claims 5 to 8, wherein the main heat exchanger comprises a third path for passage of a non-working fluid, such that heat may be exchanged between the working fluid and the non-working fluid.
10. A heat pump as system claimed in claim 9, wherein the third path is arranged such that the general direction of the non-working fluid is opposite the general direction of the working fluid in the second path.
1 1. A heat pump system as claimed in any preceding claim, wherein the heat pump system is a refrigeration system for refrigerating a non-working fluid, and the working fluid is a refrigerant.
12. A heat pump system as claimed in any preceding claim, wherein a non-working fluid of the heat pump system is natural gas.
13. A method of exchanging heat between a working fluid and a non-working fluid using a heat pump system, the heat pump system comprising a compressor, the compressor being connected to a working fluid-cooling heat exchanger via a first working fluid line, the working fluid-cooling heat exchanger being connected to an expansion device via a second working fluid line, the expansion device being connected to a working fluid-heating heat exchanger via a third working fluid line, the working fluid-heating heat exchanger being connected to a separator via a fourth working fluid line, the separator being connected to the compressor via fifth working fluid line,
the method comprising:
allowing the temperature of the working fluid in the fourth working fluid line to be at or below the dew point of the working fluid;
separating liquid and gas phases of the working fluid present in the fourth working fluid line; and
moving the separated liquid to the first working fluid line.
14. A method as claimed in claim 13, further comprising storing the separated liquid working fluid.
15. A method as claimed in claim 13 or 14, comprising allowing only gaseous working fluid into the fifth working fluid line.
PCT/EP2014/067853 2014-08-21 2014-08-21 Heat pump system WO2016026533A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/EP2014/067853 WO2016026533A1 (en) 2014-08-21 2014-08-21 Heat pump system

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP2014/067853 WO2016026533A1 (en) 2014-08-21 2014-08-21 Heat pump system

Publications (1)

Publication Number Publication Date
WO2016026533A1 true WO2016026533A1 (en) 2016-02-25

Family

ID=51383735

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/EP2014/067853 WO2016026533A1 (en) 2014-08-21 2014-08-21 Heat pump system

Country Status (1)

Country Link
WO (1) WO2016026533A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106441964A (en) * 2016-09-14 2017-02-22 中海石油气电集团有限责任公司 Floating type test platform of natural gas liquefaction system

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE69808087T2 (en) * 1997-06-12 2003-05-28 Costain Oil Gas & Process Ltd TWO-STAGE COLD CIRCUIT WITH MULTICOMPONENT COLD AGENT
WO2006007278A2 (en) * 2004-06-23 2006-01-19 Exxonmobil Upstream Research Company Mixed refrigerant liquefaction process
WO2008118703A1 (en) * 2007-03-26 2008-10-02 The Boc Group, Inc. Closed cycle mixed refrigerant systems
WO2011119697A1 (en) * 2010-03-25 2011-09-29 Linde Aktiengesellschaft Nitrogen rejection and liquifier system for liquified natural gas production

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE69808087T2 (en) * 1997-06-12 2003-05-28 Costain Oil Gas & Process Ltd TWO-STAGE COLD CIRCUIT WITH MULTICOMPONENT COLD AGENT
WO2006007278A2 (en) * 2004-06-23 2006-01-19 Exxonmobil Upstream Research Company Mixed refrigerant liquefaction process
WO2008118703A1 (en) * 2007-03-26 2008-10-02 The Boc Group, Inc. Closed cycle mixed refrigerant systems
WO2011119697A1 (en) * 2010-03-25 2011-09-29 Linde Aktiengesellschaft Nitrogen rejection and liquifier system for liquified natural gas production

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106441964A (en) * 2016-09-14 2017-02-22 中海石油气电集团有限责任公司 Floating type test platform of natural gas liquefaction system
CN106441964B (en) * 2016-09-14 2018-10-02 中海石油气电集团有限责任公司 A kind of test platform of floating natural gas liquefaction system

Similar Documents

Publication Publication Date Title
RU2505762C2 (en) Liquefaction method and device
KR101281914B1 (en) Natural gas liquefaction process
CN105716369A (en) Integrated pre-cooled mixed refrigerant system and method
CN103635761A (en) Refrigeration device
CN104520660A (en) System and method for natural gas liquefaction
US10030908B2 (en) Natural gas liquefaction process
KR20170112946A (en) Vessel
US11624555B2 (en) Method and system for cooling a hydrocarbon stream
KR101831177B1 (en) Vessel Including Engines
JP5971548B2 (en) Refrigeration equipment
KR101742285B1 (en) BOG Re-liquefaction Apparatus and Method for Vessel
US20190162469A1 (en) Method and system for cooling a hydrocarbon stream
CN104019626B (en) The cold method and device preparing liquefied natural gas of a kind of azeotrope two-stage system
US20140060111A1 (en) Process for liquefying a hydrocarbon-rich fraction
BR112020019239A2 (en) SYSTEM AND METHOD OF LIQUEFACING OF MIXED REFRIGERANT WITH PRE-COOLING
KR101357720B1 (en) Refrigeration system and refrigeration method for liquefying natural gas
WO2015063837A1 (en) Refrigeration cycle device
WO2016026533A1 (en) Heat pump system
KR101858510B1 (en) Boil-Off Gas Re-liquefaction System and Method
Gadhiraju et al. Natural gas liquefaction processes
JP4879606B2 (en) Cold supply system
US20210116173A1 (en) Standalone high-pressure heavies removal unit for lng processing
CN105605882A (en) Method for composite refrigeration natural gas liquefaction
KR100469537B1 (en) Cryogenic multi-refrigerating system
Gadhiraju et al. Constant-temperature refrigeration processes

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 14753102

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 14753102

Country of ref document: EP

Kind code of ref document: A1