GB2149900A - Refrigeration apparatus - Google Patents

Abstract

Refrigeration apparatus for use in hazardous environments e.g. an offshore oil rig, comprises a condenser 3 and an evaporator 12 interconnected to form a closed cycle for circulation of fluid, a compressor 1 for circulating the fluid round the cycle, and a branch pipeline 16 selectively engageable to interrupt the cycle by directing the fluid round a further cycle including the compressor 1 and the evaporator 12 without passage through the condensor 3, wherein each of the components of the apparatus is adapted or selected for use in hazardous environments. <IMAGE>

Description

SPECIFICATION Refrigeration apparatus This invention relates to refrigeration apparatus and to a container having the refrigeration apparatus.

The present invention has been developed particularly for refrigerated containers for use in offshore environments, but is of relevance in other areas where the stringent offshore safety requirements are not applicable.

Hitherto, refrigerated containers for offshore use have employed an evaporator section in the form of large plates through which refrigerant fluid passes to provide heat-exchange with the air in the container. The distribution of the cooled air throughout the container is effected by natural convection, and the evaporator plates are large to allow a substantially even temperature throughout the container.

Refrigeration apparatus is subject to frosting of the evaporator, with consequent loss of efficiency, and the evaporator must therefore be defrosted periodically. This has been done either by heating the evaporator electrically, which of course renders the container temporarily unusable for refrigerated storage and causes large volumes of water to be deposited from the plates, or by mechanically scraping the plates to remove ice; this latter method is inefficient.

According to the present invention there is provided refrigeration apparatus for use in hazardous environments, comprising a condenser and an evaporator interconnected to form a closed cycle for circulation of fluid, a compressor for circulating the fluid round the cycle, and a branch pipeline selectively engageable to interrupt the cycle by directing the fluid round a further cycle including the compressor and the evaporator without passage through the condenser, wherein each of the components of the apparatus is adapted or selected for use in hazardous environments.

By creating said further cycle provision is made for passing gaseous fluid through the evaporator, where the fluid condenses to a liquid, giving out latent heat. This latent heat defrosts the evaporator and avoids the need for electric heaters which carry a fire risk.

The refrigeration apparatus also generally includes an expansion valve which is also bypassed by the branch pipeline.

The evaporator is preferably of the "mesh" type having a number of through passages each of which presents a large surface area to the external air, rather than of the solid plate type. In this way the evaporator can be disposed in a single location within the container instead of extending across a large area, as with plate evaporators, and the defrosting does not then result in heating of the entire container. The container may therefore be defrosted without adversely affecting the contents, and without the need for their removal during the operation.

One or more fans can be provided to move air past the evaporator to provide even and effective distribution of the cooling effect of the apparatus throughout the container, and the fan or fans can be deactuated when defrosting is taking place, so as to prevent heat dispersion.

A drainage channel can be provided to collect melted ice from the evaporator during defrosting, the channel preferably leading the melted ice to a disposal or storage area outside the container.

An embodiment of this invention will now be described by way of example with reference to the accompanying drawing which is a schematic diagram of refrigeration apparatus of the present invention.

Referring to the drawing, refrigeration apparatus of this embodiment has a compressor 1 driven through an anti-static belt from a flameproof motor (not shown), the motor and belt being disposed within cast iron explosionprotected housings. The compressor 1 is connected through a discharge pipe 2a, through which high pressure discharge vapour flows, with an air-cooled condenser 3. A flameproof solenoid valve 4 is also connected in this line.

The pipe 2a has a safety high-prssure cut-out switch 5.

Adjacent the condenser 3 and downstream of it is a receiver 6 which is connected to the condenser 3 through a pipe 2d which carries high pressure liquid from the bottom of the condenser 3 to a top entry of the receiver 6.

Connected to the pipe 2d is a pressure regulator valve 8a which operates as a liquid backup valve to reduce the condenser surface area during low ambient and light load conditions, thereby maintaining a constant condensing pressure to assist with the defrost cycle. Between the pipe 2d and the pipe 2a is a further pipe 7 which has a pressure differential valve 8. The valve 8 operates in conjunction with the valve 8a, so that the valve 8a closes down to back up pipes 2a and 2d and opens up to by-pass discharge vapour to the receiver 6. A constant receiver pressure is thereby maintained to permit the expansion valve (as hereafter described) to operate efficiently.

From the receiver pipe 2b passes through a filter drier 9, a sight glass 10 for checking fluid flow through the pipe, a flameproof solenoid valve 11 and an expansion valve 1 3 to an evaporator 1 2. The pipe 2b carries the sub-cooled liquid refrigerant to the expansion valve 1 3 and the evaporator 1 2. The evaporator 1 2 is connected to the compressor 1 along pipe 2c through a suction accumulator 18 and a suction pressure regulator valve 1 5.

The regulator 1 5 prevents the suction pressure from rising above a preset value and so prevents the motor from drawing excess current during high load conditions. A low pres sure switch 14 is connected between the valve 15 and the accumulator 18.

A further pipe 1 6 forming a hot gas by-pass line bridges between the pipe 2a, between the high pressure cut-out switch 5 and the solenoid valve 4, and the pipe 2b, between the expansion valve 1 3 and the evaporator 1 2.

The pipe 16 includes a flameproof hot gas bypass solenoid valve 17, so that it and the solenoid valve 4 can be selectively actuated and deactuated to divert refrigerant from the pipe 2a along the pipe 1 6 as required.

The evaporator 12 is located in a walk-in container for storage of food in offshore environments, for example on oil rigs, and is in the form of a mesh of similar type to a vehicie radiator, whereby fluid passing through it has a large surface area exposed for heat exchange with its environment. A pair of hazardous-duty fans (not shown) are actuable to create a flow of air through the evaporator 12.

In use, with the condenser solenoid valve 4 open and the hot gas by-pass solenoid valve 1 7 closed, the apparatus operates as a conventional refrigeration cycle with the evaporator 1 2 taking heat from the interior of the container by means of heat being transferred to the refrigerant from the air being circulated by the fans and passing across the evaporator.

The fans also maintain an even temperature distribution. The evaporator gradually becomes frosted up, at which point defrost takes place. The defrost is time initiated and pressure terminated, the time being set to initiate defrost every 6 hours. When defrost is initiated the control relay de-energises the condenser solenoid valve 4 and energises the hot gas solenoid valve 17, isolating the condenser 3 and the expansion valve 13 from the active part of the cycle and diverting the hot gas refrigerant vapour from the compressor 1 along the hot gas by-pass pipe 1 6 to the evaporator 12; thus the evaporator receives the hot gas refrigerant vapour which gives out its latent heat to the frosted evaporator 12, melting the ice formed on it.The condensed refrigerant passes from the evaporator 12 through the pipe 2c to the suction accumulator 18 and is drawn from the top of the accumulator 18 by the compressor 1 through the crankcase pressure regulator 1 5 thereby preventing the compressor pumping liquid.

Once the evaporator is defrosted the defrost termination pressure switch returns the system to the refrigeration cycle.

The water formed on the evaporator 1 12 during defrost drips into a drainage channel leading outside the container.

None of the components of the apparatus produces sparks or has exposed electricallyheated surfaces which could present a fire hazard. The solenoid valves each have a 240 volt coil within an explosion-protected and sparkproof housing, and the electrical system of the apparatus is controlled from a single control panel which is also enclosed in an explosion-protected and sparkproof housing. The apparatus of this embodiment allows the evaporator 1 2 to be defrosted without using hazardous equipment such as electric heaters; without having to scrape its surface manually, without causing accumulation of water in the container; and without causing the container interior to increase in temperature to a significant degree.

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

Claims (9)

1. Refrigeration apparatus for use in hazardous environments, comprising a condenser and an evaporator interconnected to form a closed cycle for circulation of fluid, a compressor for circulating the fluid round the cycle, and a branch pipeline selectively engageable to interrupt the cycle by directing the fluid round a further cycle including the compressor and the evaporator without passage through the condenser, wherein each of the components of the apparatus is adapted or selected for use in hazardous environments.

2. Refrigeration apparatus according to Claim 1, wherein the compressor is driven through an anti-static drive belt.

3. Refrigeration apparatus according to Claim 1 or 2, wherein the compressor is driven by a motor enclosed within an explosion-protected housing.

4. Refrigeration apparatus according to any one of the preceding Claims, wherein the branch pipeline is selectively engageable by means of one or more solenoid valves disposed within an explosion-protected housing.

5. Refrigeration apparatus according to any one of the preceding Claims, including also an expansion valve which is by-passed by the branch pipeline.

6. Refrigeration apparatus according to any one of the preceding Claims, wherein the evaporator has a heat-exchange surface which defines perforations for through passage of air.

7. Refrigeration apparatus according to Claim 6, wherein the evaporator has a heatexchange surface in the form of a mesh.

8. Refrigeration apparatus according to any one of the preceding Claims, wherein one or more fans are provided for moving ambient air over the evanorator.

9. Refrigeration apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawing.