GB2207742A - Refrigeration system - Google Patents

Abstract

This invention relates to a refrigeration system particularly for use in corrosive environment wherein exposed apparatus can deteriorate rapidly. The system is for drawing heat from a walled storage area, and comprises a refrigeration cycle in which the condenser 6 is disposed adjacent the inside face of a wall of said walled area. This arrangement allows heat exchange across the wall to the external environment, the condenser being insulated from the storage area. The compressor 14 is disposed within a housing which is closed to the ambient environment and kept cool by its own evaporator 46. A heat exchanger 62, which accumulates heat from the compressed discharge fluid during the refrigeration cycle, gives out heat during the defrost cycle, which heat together with particular defrost discharge route for compressed discharge fluid provides a rapid defrost cycle. <IMAGE>

Description

11Refrigeration System" This invention relates to a refrigeration system, especially but not exclusively for use in a corrosive environment.

Refrigerated containers are used for example in the offshore oil and gas industries, and their refrigeration systems generally have the condenser and compressor housed in a compartment external of the storage area of the container.

The compartment is open to the environment through vents or the like to allow heat extracted from the storage area to be dissipated. However, the offshore environment is extremely corrosive and the apparatus in the compartment can deteriorate rapidly.

According to the present invention there is provided a refrigeration system for drawing heat from a walled area, comprising a refrigeration cycle in which the condenser is disposed adjacent the inside face of a wall of said walled area for heat exchange across said wall and insulated from said area, and the compressor is disposed within a housing which is closed to the ambient environment.

Preferably a secondary refrigeration cycle is provided to remove heat from the interior of said housing. The heat thus removed may be dissipated from a secondary condenser disposed adjacent a door or other opening of said walled area. The secondary refrigeration cycle may share the compressor of the main cycle.

The condenser preferably comprises a number of pipes each of which can be selectively deactivated, by a closing each pipe at each end, to isolate it from the others in accordance with the effect of ambient conditions on the pipework or in the event of damage or for maintenance.

Preferably also the condenser extends substantially across each of two opposite walls when the walled area is cuboidal.

Further according to the present invention there is provided a refrigeration system comprising a refrigeration cycle and a defrost cycle, wherein heat is removed from the refrigerant and stored during the refrigeration cycle, and given out to the defrost fluid during the defrost cycle.

Preferably, the defrost cycle shares certain pipework and the compressor of the refrigeration cycle; the compressed discharge fluid of the defrost cycle is circulated through the evaporator instead of the condenser, a servo-valve closing the line through the condenser and opening a second line to the evaporator which second line avoids any expansion valve.

Preferably, a heat exchanger accumlates the heat from compressed discharge fluid of the refrigeration cycle and gives out heat to discharge fluid upstream of the compressor and evaporator. The exchanger during the refrigeration cycle acts as a heat accumulator, preferably accumulating heat from the compressed fluid discharge pipe with which the exchanger is also in contact.

The heat exhanger may be in the form of an insulated tank filled with a fluid, preferably water, and anti-freeze mixture.

The exchanger is preferably disposed in the same closed housing as the compressor, with the secondary refrigeration cycle additionally removing from the housing any heat leaked from the exchanger.

fPreferably, fluid from the refrigeration cycle is drawn into the defrost cycle and through the heat exchanger by the pressure in the pipe feeding the compressor. Owing to the low line pressure during defrost and the cut off of fluid supply to the condenser, the fluid throughput of the secondary refrigeration cycle may be slight during the defrost cycle but the rapidity of defrost prevents overheating of the closed housing.

The secondary condenser of the door or other opening, instead of dissipating heat removed by the secondary refrigeration cycle, may be part of the primary refrigeration and defrost cycles and dissipate heat acquired either from the evaporator during the primary refrigeration cycle or from the heat exchanger during the defrost cycle.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is an end sectional view of one wall of a refrigerated container having a refrigeration system of the invention; Fig. 2 is a circuit diagram of one embodiment of the refrigeration system of the present invention; and, Fig. 3 is a circuit diagram of a second embodiment of the refrigeration system of the present invention.

Referring to Figs 1 and 2 of the drawings, a cuboidal refrigerated container for use on an offshore oil production platform has a steel side wall 2 which is lined on its inside by sheets of insulating material 4 in a manner which leaves a space between it and the wall 2. In that space are disposed condenser pipes 6 of the refrigeration system, the pipes 6 being held in close proximity to the steel wall 2 by heat-conductive material 8 which surrounds the pipes 6 and is spread along the wall 2 in order to enhance the transfer of heat from the pipes 6 to the wall 2.

The pipes 6 are provided along opposite walls of the container, and four separate pipes 6 run along each wall.

This allows heat to be dissipated through the wall facing away from the sun, or other source of direct heat. Any of the eight pipes 6 can be deactivated selectively for this purpose, or for maintenance.

The pipes 6 meet at their inlet end in an 8-way discharge distribution manifold 10 and at their outlet end in a return manifold 12. The distribution manifold is fed with fluid from a compressor 14 which is housed in a sealed compartment external of the storage area of the container and having no vent to the ambient environment.

The fluid flows from the compressor 14 to an oil separator 16, from which excess oil is returned to the compressor 14 through a solenoid valve 18. The compressed fluid passes from the separator 16 to the 8-way distribution manifold 10 in which it is divided into eight streams which pass one into each of the pipes 6. Only one of the pipes 6 is shown in Fig. 2, for clarity. The pipes 6 pass along the inner face of the opposite walls of the container as described above, allowing the fluid to lose heat through the walls into the ambient environment.

The pipes 6 converge in the return manifold 12 from which the fluid passes through a receiver 20, a shut-off valve 22, a drier 24 and a solenoid valve 26. The solenoid valve 26 is thermostatically controlled and is actuated when the internal temperature of the container falls to a predetermined temperature.

A sight glass 28 is disposed between the drier 24 and the solenoid valve 26 for checking the amount of liquid in the line.

The fluid passes to a forced-draught evaporator 30 within the storage area of the container, and hence returns to the compressor 14. A thermostatic expansion valve 32 is provided between the solenoid valve 26 and the evaporator 30 in a balance line 34 which senses the fluid pressure at the outlet of the evaporator 30 and thus evaporator 30 pressure drop.

A defrost line 36 branches from the main line from a point between the oil separator 16 and the solenoid valve 18 to the inlet of the evaporator 30 through a solenoid valve 38.

In normal use of the cycle the valve 18 is open and the valve 38 closed so that the defrost line in inoperative, but when defrosting of the evaporator 30 is required the valve 38 is opened and the valve 18 closed to divert the hot compressed fluid directly to the evaporator 30 through the line 36, bypassing the condenser pipes 6.

A secondary line 40 extends from a point upstream of the defrost line 36 to carry a proportion of the compressed fluid around the frame of a door of the container at 42. In conventional refrigerated containers the door edges tend to frost up, and the line 40 prevents this. From the door frame 42 the line passes through a capillary tube 44 to an evaporator 46 disposed within a sealed compartment external of the storage area of the container. The compartment houses the compressor 14 and electrical equipment controlling and driving the cycle. This compartment would otherwise tend to heat up, and the evaporator 46 removes that excess heat. A fan is provided to maintain air movement around the compartment and over the evaporator 46.

It will be noted that the evaporator 46 will continue to operate even when the main evaporator 30 is defrosting, as the line 40 branches from the main line upstream of the line 36.

The compartment housing the compressor 14, electrical equipment and evaporator 46 is sealed from the outside environment, so these items are protected from corrosion by salt water and other substances. Similarly the condenser pipes 6 are internal of the compartment wall 2, and therefore also protected from corrosive effects.

Referring to Fig. 3 of the drawings, there is shown a second embodiment of the circuit and features common with the embodiment of Figs 1 and 2 bear the same reference numerals.

In the second embodiment, secondary line 52 supplys only the evaporator 46, which is disposed within the sealed compartment external of the storage area of the container.

Line 52 branches off upstream of the evaporator 30 and rejoins the main refrigeration cycle just upstream of the compressor 14. The evaporator 46 is fan-assisted and provided with a balance line 50 and an upstream expansion valve 51.

During both refrigeration and defrost cycles the compressor 14 discharges high pressure super-heated refrigerant gas and oil through line 57 to the oil separator 16 where the oil settles out and accumulates. Oil is then forced under discharge pressure at a temperature equal to the super heated gas through an outlet at the base of the separator 16 into line 53, returning to the low pressure side of the compressor, this line 53 being the door heater circuit which is disassociated from the door heater 42. The fluid for the door heater circuit passes from the oil separator 16 past a shut off valve 56 filter 55 and a sight glass 54 before circulating through the door heater 42 and returning to the compressor 14 via its low pressure side.

The compressed discharge fluid also continues from the oil separator 16 through a three-way servo-valve 60 to the distribution manifold 10, passing on the way through a heat exchanger 62 which removes heat from the compressed fluid.

The heat exchanger 62 comprises an insulated tank containing water and anti-freeze. The heat exchanger 62 is in the sealed compartment which also houses the compressor 14 and electrical equipment and evaporator 46. This compartment would tend to heat up were it not for the evaporator 46 removing additional heat.

The heat exchanger 62 is provided as a heat accumulator during the refrigeration cycle. This heat can then be given out on defrost. This combined with a particular discharge route for compressed discharge fluid provides a rapid defrost cycle of as little as three minutes rather than the 30 minutes defrost time required for the embodiment of Figs 1 and 2.

However, defrost frequencies and intervals are controlled by a timer (not shown) and the minimum defrost period is preferably ten minutes as this ensures total defrost even in the worst conditions. The evaporator's 30 temperature progressively increases with a corresponding increase in pressure causing the compressor 14 motor to cut out on overload. A pressure relief valve 72 is located in a line 73 running between the discharge of the compressor 14 and the condensor 6 to prevent this by dumping high pressure gas into the condensor 6. The valve 72 is pre-set to maintain sufficient pressure for defrosting the evaporator 30.

To defrost the evaporator 30 in the embodiment of Fig. 3, compressed discharge fluid flows directly from the compressor 14 via line 57 to the oil separator 16 and through line 70 straight to the evaporator 30, line 70 having been opened by actuation of the servo-valve 60 the same valve 60 having closed the line to the condensor 6.

The high pressure fluid travels through the evaporator 30 to suction pipe 71 of 1/2 inch diameter that connects the evaporator 30 to the compressor 14.

The servo-valve 60 is actuated by the opening of a pilot valve 66 which drops the pressure to the suction pressure of pipe 71 and thus moves the internal piston of the servovalve 60.

The pilot valve 66 is activated by the defrost switch and timer which also opens a solenoid gas boost valve 68 situated on a line 61 that passes from the receiver 20 to line 71 and the compressor 14. This line 61 passes through the heat exchanger 62 and, on opening valve 68, the suction pressure of line 71 draws fluid from the receiver 20, through the heat exchanger 62, into the compressor 14.

Fluid from the receiver 20 removes the heat from the heat exchanger 62 and, on being dumped in the compressor 14, the heated fluid heats the total compressed discharge fluid passing along line 57 to the evaporator 30. This heated fluid speeds the defrost cycle. Generally, on opening valve 68, only gas at the top of the receiver 20 is removed, but any liquid also drawn off is evaporated during its passage through the heat exchanger 62. The gas boost increases the total charge of the fluid and a non-return valve 72 prevents any migration back to the condenser 6 from the receiver 20.

When the gas boost valve 68 opens on defrost, receiver 20 pressure eventually equals suction pressure generated by the suction valve of the compressor 14 which suction pressure is also the pressure of the secondary evaporator 46; the system is therefore mainly in a static pressure state.

Modifications and improvements may be made without departing from the scope of the invention.

Claims (14)

1. A refrigeration system comprising a refrigeration cycle and a defrost cycle, wherein heat is removed from the refrigerant and stored during the refrigeration cycle, and given out to the defrost fluid during the defrost cycle.

2. A refrigeration system according to Claim 1, wherein the defrost cycle shares a compressor with the refrigeration cycle, and in the defrost cycle compressed discharge fluid is circulated through the evaporator.

3. A refrigeration system according to either Claim 1 or 2, wherein a heat exchanger accumulates the heat from compressed discharge fluid of the refrigeration cycle and gives out heat to discharge fluid upstream of the compressor.

4. A refrigeration system according to either Claim 3, wherein the heat exchanger comprises an insulated tank, filled with a fluid and anti-freeze mixture.

5. A refrigeration system according to any one of the preceding Claims, wherein the heat exchanger is disposed within a housing which is closed to ambient environment and contains the compressor and secondary refrigeration cycle, which cycle removes heat from the interior of the housing.

6. A refrigeration system according to any one of Claims 3 to 5, wherein fluid from the refrigeration cycle is drawn into the defrost cycle and through the heat exchanger by the pressure in the pipe feeding the compressor.

7. A refrigeration system for drawing heat from a walled area, comprising a refrigeration cycle in which the condenser is disposed adjacent the inside face of a wall of said walled area for heat exchange across said wall and insulated from said area, and the compressor is disposed within a housing which is closed to the ambient environment.

8. A refrigeration system according to Claim 7, wherein a secondary refrigeration cycle is provided to remove heat from the interior of said housing.

9. A refrigeration system according to Claim 8, wherein the heat removed by the secondary refrigeration cycle is dissipated from a secondary condenser disposed adjacent a door or other opening of said walled area.

10. A refrigeration system according to any one of the Claims 7 to 9, wherein the condenser comprises a number of pipes each of which can be selectively deactivated to isolate it from the others.

11. A refrigeration system according to any one of the Claims 7 to 10, wherein the condenser extends substantially across each of two opposite walls when the walled area is cuboidal.

12. A refrigeration apparatus incorporating the refrigeration system of any one of Claims 1 to 6 with the refrigeration system of any one of Claims 7 to 11.

13. A refrigeration system substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

14. A refrigeration system substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.