Water introduced into the refrigeration plant does not evaporate like the refrigerant and thus it collects in the cold side of the plant. Usually the water is introduced by opening of the plant in connection with for example service and by leaks in low- pressure components. In the case of a continuous leak the refrigerant in the cold side will gradually increase its content of water. On NH3 plants, as the water content increases the refrigerant changes evaporating temperature resulting in a reduction in plant efficiency. Also the water can react chemically with the refrigerant and oil, thus creating undesirable by-products. Often the corrosion created by the water itself and the by-products result in additional leaks, thus allowing the entry of more water.

Traditionally water purging on an NH3 plant is done by filling a vessel with water- contaminated refrigerant. The refrigerant is evaporated and returned to the system while the water remains in the vessel. When sufficient water has collected in the vessel, the vessel is isolated from the rest of the system and the water is drained.

On HCFC and HFC plants drying filters are used.

To remove the refrigerant from the water/refrigerant mixture, heat is added, thus evaporating the refrigerant. Usually the energy is taken from the hot side of the refrigeration plant resulting in an energy efficient, or even energy neutral, solution to the problem. However with changes in the operating conditions of the plant, it is possible that the heat influx to the purger vessel increases very rapidly. This results in

a violent boiling in the vessel and in some cases the boiling is so violent that the water is carried out of the vessel and back into the system. The key to a successful purging is to avoid these violent boil-ups, but with the existing solutions this has proved to be difficult to control, usually requiring extensive valve/automation fitting.

Air can be present in the refrigeration plant, also introduced by leaks and service openings of the plant. The air will be compressed in the compressor and fed to the condenser, but unlike the refrigerant the air does not condense thus staying in the condenser. The air will take up space in the condenser and will occupy surface that was to condense refrigerant. Furthermore the mixing of air and refrigerant will change the condensing temperature. Both these factors reduce the efficiency of the condenser and thus of the entire plant.

Usually air is purged manually or by automatic air purgers commercially available.

In US 4,304, 102 a refrigeration purging system for removal of non-condensable gases such as air and condensable contaminants such as water is disclosed. A portion of the refrigerant in the refrigeration system is placed in a first purge chamber which condenses contaminants such as water leaving non-condensables such as air and a small portion of the refrigerant at the top of the chamber. The non-condensables and remaining refrigerant are extracted from the first chamber and pumped to a higher pressure and passed to a second purge chamber wherein the remaining refrigerant is condensed and returned to the first purge chamber. The non-condensable gases remaining are released to the atmosphere. The condensable contaminants are extracted from the first purge chamber, and the condensed refrigerant is returned to the refrigeration system. A control system for regulating the operation of the pump in relation to the amount of non-condensable gases in the first purge chamber is disclosed together with means for controlling the flow of condensed refrigerant between the two purge chambers.

US 5,031, 410 describes a thermal purge apparatus for a chiller removing air, moisture and other non-condensables from the chiller system refrigerant by causing chilled

system refrigerant vapour to condense in a purge tank as result of its creating heat exchange with a second and different refrigerant employed in a discrete purge refrigeration circuit. Chiller refrigerant circulates from the chiller condenser to, through and out of the purge tank in a free-flowing circulatory manner as a result of temperature and pressure gradients which develop between the interiors of the chiller condenser and the purge tank when the purge apparatus is in operation.

Both documents describe separation of liquid refrigerant and liquid water which is achieved only because the liquid refrigerant has a higher density than water. The separation cannot in this way be 100% efficient and the water leaving the system may contain refrigerant which may evaporate to the atmosphere.

It is the object of the invention to provide an efficient purge apparatus, with an efficient water purger and an efficient non-condensables gas purger, where loss of refrigerant from the refrigeration plant is minimized, with a device that is self- regulating, thereby offering trouble-free operation regardless of the plant operating conditions.

This can be achieved if the recovery tank comprises a shell, which shell is open at the bottom, which shell at the top comprises a restricted outlet where the shell surrounds the heating means, which heating means evaporates refrigerant inside the shell, where evaporated refrigerant is discharged through the restricted outlet, where evaporated refrigerant partly surrounds the heating means.

In this way boiling of refrigerant will take place around the heating means inside the shell where a bubble of evaporated refrigerant is formed in the top of the shell. The bubble of evaporated refrigerant is discharged from the shell through the restricted outlet. During normal operation a balance between the size of the steam bubble inside the shell and the opening in the restricted outlet is established. If no heat is generated by the heating means, the liquid level inside the shell and outside the shell will be equal because no boiling takes place under the shell. If very strong boiling take place because the heating means are overheated, maybe because the heating means are part

of the condenser in the refrigeration system where rapid boiling can take place, the rapid boiling will create a big steam bubble inside the shell, and the level of liquid refrigerant inside the shell will be lowered because of increasing pressure. This means that the active heating surface that is in contact with the liquid refrigerant is reduced, and the boiling as such is also reduced. If rapid boiling in the refrigerant inside the shell leads to evaporation of water inside the shell, condensation will form on the inside of the shell. The boiling is self-adjusting and over-boiling is avoided. The content of water in the liquid refrigerant remains as liquid water and is not evaporated by the boiling. So the water content in the recovery tank increases. The invention put forward uses a thermodynamic/fluid mechanic balance to regulate the boiling process in the water purger. The heat required for the boiling of the refrigerant can either be from hot refrigerant liquid or from the air purging process.

The recovery tank may comprise means for adjusting the level of liquid refrigerant in the tank by opening a connection to feed contaminated refrigerant into the recovery tank. By keeping the level of liquid refrigerant constant in the recovery tank, the self- regulating process inside the shell can be held constant.

Evaporated refrigerant can be led from the recovery tank to a suction line. In this way refrigerant is returned to the refrigeration plant, maybe directly to the compressor in order to be compressed and returned to the circuit.

Heating means may be heated by liquid condensing refrigerant. By using condensing refrigerant, no external energy source is necessary. Mostly energy from the condensing process is wasted, but with the invention the energy can be used for recovery of the refrigerant.

Instead, the heating means may be heated by a mixture of gas and liquid refrigerant coming from a point in the condenser where non-condensable gases may be collected.

In this way most of the foreign gases that are found in a refrigeration plant can be collected, for example from the top of the condenser unit, and led directly to the heating means inside the shell where the refrigerant and the non-condensable gases are

heat exchanged to the surrounding mixture of gas and refrigerant. Inside the heating element, refrigerant condenses where the non-condensable gases remain as gas.

From the heating means the mixture of condensed refrigerant and non-condensable gases may be fed to a float valve from which float valve non-condensable gases are led to an air purger. In this way the non-condensable gases are separated from the liquid refrigerant.

Liquid refrigerant may be led from the float valve through a thermodynamic liquid trap to a liquid refrigerant return line. By using the thermodynamic liquid trap only liquid substances are allowed to pass. Non-condensable gasses, which are still part of the mixture, will be returned to the float valve from which it can escape. By using the thermodynamic liquid trap, it is assured that absolutely only liquid refrigerant is returned to the refrigeration plant.

The heating element may be formed as a coil placed inside the shell. One possible way of forming the heating means is by placing the coil inside the shell, because the coil is one way of forming the big surface and making an efficient heat transfer.

The bottom of the recovery tank may be connected through a valve to a water purge line, which valve is closed during normal operation and opened after closing the inlet and boiling away the content of refrigerant. In this way all refrigerant can be boiled away from the water content in the recovery tank. When water only is left, the valve can be opened and the recovery tank can be drained.

The invention is described in more detailed below, with reference to the attached figures where Fig. 1 shows a fist embodiment of the water purger.

Fig. 2 shows a second embodiment of the invention for a combined water and non- condensable gas purger.

Fig. 1 shows a recovery tank 2 which contains liquid refrigerant 4 and evaporated refrigerant 6. The recovery tank 2 comprises a shell 8 with a restricted outlet 10, which shell 8 comprises heating means 12, which heating means 12 are connected to an energy supply by connections 14 and 16. Outside the recovery tank 2 there are means 18 for adjusting the level of liquid refrigerant 4 into the recovery tank 2. The means 18 are working together with the valve 20 which can open for a supply line 22 for refrigerant. At the top of the recovery tank 2 there is an outlet for refrigerant gas which is sent via a valve 24 to an outlet 26 and maybe to a suction line.

Fig. 2 shows an alternative embodiment of the invention. Here the components shown with numbers increased by 100 are the same as those shown in Fig. 1 ; thus the numbers up to 132 refer to the description in Fig. 1. In Fig. 2, the inlet line 114 may be connected to the top of a condenser (not shown) where non-condensing gases will concentrate. A mixture of the non-condensable gases and refrigerant is led through the line 114 to heating means 112 and further through the line 116 where all the refrigerant condenses to a liquid by heat transfer to the refrigerant surrounding the heating element, and where the non-condensable gases are still contained in gaseous form in the line 116 where the line 116 is connected to a float valve 134 from where gases are led via a line 136 to a valve 138 to another line 140, which could be open to the atmosphere. Liquid refrigerant is led via a line 142 to a thermodynamic liquid trap 144 from which the liquid refrigerant is returned to the refrigeration plant over line 146. From the thermodynamic liquid trap 144 gases are returned via the line 142 to the float valve 134 and to the line 136. In this way the non-condensable gases are efficiently isolated.

The invention involves a system to purge water and gaseous contamination from refrigeration plants. Water from refrigeration plants is a wide-spread problem resulting in, among other things, temperature glide in the refrigerant (NH3), ice in expansion valves (HCFCm, HFC etc. ), but mainly corrosion and possibly chemical reactions.

Non-condensable gases (hereafter referred to as air) in the refrigeration plant will collect in the condenser, blanking out the heat transfer area and thus affecting condenser performance and in the end plant efficiency. The proposed system involves

a self-regulating heat exchanger that can be used for water purging alone or as a combined air/water purger.

The refrigerant is boiled away from the water with the use of a coil 12,112 at the bottom of the tank 2. This is a well-known technology, but in the invention put forward the coil 12,112 is partially enclosed in an additional shell 8,108 that is open at the bottom. At the top of the enclosing shell 8,108 a small pipe 10,110 is fitted.

When the refrigerant evaporates, the gas will escape through the small pipe 10,110.

The pressure loss involved in the passage of the small pipe 10,110 (possibly fitted with an orifice) lowers the liquid level in the partial shell 8,108. In this way the liquid level will drop further as the capacity of the coil 12,112 increases and thus reduces the efficient area resulting in a capacity control of the coil 12,112. This function efficiently prohibits the violent boiling up mentioned above.

During operation of the water purger, a float valve 18,118 maintains the liquid level in the tank 2,102. While feeding refrigerant to the tank 2,102 the valve 18,118 also feeds water to the tank 2,102 as it is mixed up in the system charge. The refrigerant is evaporated from the tank 2,102, while the water remains. When water needs to be purged from the tank 2,102, the valve 20,120 in the float valve 18,118 is closed and the tank 2,102 is left to boil away remaining refrigerant. When it is estimated that all (most) refrigerant has been evaporated, the valve 24,124 to the suction line 26,126 is closed, and the water can be drained from the bottom of the tank 2,102 by opening a valve 30, 130.

The purger comes in two variants, a simple water purger and a combined air/water purger. The simple water purger uses a heat source that most likely will be the condenser liquid, and thus the coil 8,108 is connected between the condenser and the float/expansion valve that feeds the low-pressure system.

In the combined air/water purger the heat source is different from the simple water purger. However the water purge side remains the same. From the condenser, gas is led from the points where non-condensable gases usually collect and is fed to the coil.

The gas led from this point is a mixture of refrigerant gas and non-condensable gases.

This means that when the gas mixture enters the coil 8,108, the refrigerant will condense and the non-condensable gases will not. The resulting non-condensable gas/refrigerant liquid mixture is fed to a float valve 134. This valve 134 allows gas to escape to the air purge 140 while the liquid refrigerant is drained from the bottom and returned to the system.

In the liquid refrigerant return line 142 a thermodynamic liquid trap 144 is mounted.

This component, from the compressed air/steam industry, allows only liquid to pass and will thus ensure that only condensed refrigerant is returned to the system by line 146.

Variants of the invention can be the simple water purger and the combined air/water purger. The simple water purger will most likely use condenser liquid as a heat source, but any hot liquid or gas can be used. The combined air/water purger uses the cooling of the non-condensable gas/refrigerant mixture and the condensing of the refrigerant as heat source.