EP1462185A1

EP1462185A1 - Detergent injection system

Info

Publication number: EP1462185A1
Application number: EP03006600A
Authority: EP
Inventors: Eskil Eriksson; Jan Hamrefors; Kenneth Stig Lindqvist
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2003-03-25
Filing date: 2003-03-25
Publication date: 2004-09-29

Abstract

The invention relates to a method to introduce an additive into a washing chamber (12) of a CO₂ dry cleaning system. The additive is transferred from an additive reservoir (18) into a CO₂ transfer line (11) connecting a CO₂ storage tank (4) with said washing chamber (12). Gaseous CO₂ from said CO₂ storage tank (4) is introduced into said CO₂ transfer line (11) and said additive is propelled into said washing chamber (12) by said gaseous CO₂.

Description

The invention relates to a method to introduce an additive into a washing chamber of a CO₂ dry cleaning system wherein said additive is transferred from an additive reservoir into a CO₂ transfer line connecting a CO₂ storage tank with said washing chamber.
Dry-cleaning using liquid carbon dioxide is known as an environmentally friendly cleaning technique with favourable cleaning properties which can be used to remove contaminants from garments or textiles as well as from metal, machinery, workpieces or other parts. It is further known that the cleaning performance of carbon dioxide dry-cleaning can be improved by the addition of detergents, surfactants or other additives.
There are several possibilities for the introduction of such additives: For example, the additives can be premixed in CO₂ and stored in high-pressure cylinders. But that requires a complicated manufacturing process and the filling of the cylinders has to be carried out at a specialty gas plant by a person with gas filling experience. Further, there might occur changes in the concentration of the additive in the CO₂ during use of the mixture.
Instead of premixing the additive into CO₂, other carrier fluids, for example gaseous nitrogen, may be used. However, the disadvantages with respect to the filling procedure and the distribution of the mixtures remain the same.
US patent 6,129,451 discloses another method to add a surfactant or a detergent to a carbon dioxide dry cleaning system. The additive is pumped from a supply source into a mixing reservoir having a capacity of 2 liters. During pumping of the additive the vent valve of the mixing reservoir is open to the atmosphere. Liquid carbon dioxide is then pumped into the reservoir and thoroughly mixed with the detergent. The mixture is transferred to the washing chamber under the force of a liquid carbon dioxide pump and dispersed into the washing chamber.
A thorough mixing of the additive with the liquid CO₂ requires that the maximum solubility of the additive in CO₂ is known. That means that in the method according to US 6,129,451 the necessary capacity of the mixing reservoir may vary from additive to additive. Further, according to US 6,129,451 the mixing reservoir is open to the atmosphere when the additive is pumped into it, meaning that a low pressure pump can be used which is cheaper than a high pressure pump. However, since in the next process step liquid CO₂ is injected into the mixing reservoir without preceeding pressurisation of the reservoir to a pressure above the triple point of CO₂, there is a certain risk of dry ice formation.
Therefore, it is an object of the invention to provide a method to introduce an additive into a CO₂ dry cleaning system.
This object is achieved by a method to introduce an additive into a washing chamber of a CO₂ dry cleaning system wherein said additive is transferred from an additive reservoir into a CO₂ transfer line connecting a CO₂ storage tank with said washing chamber, wherein gaseous CO₂ from said CO₂ storage tank is introduced into said CO₂ transfer line and wherein said additive is propelled into said washing chamber by said gaseous CO₂.
CO₂ dry cleaning is typically carried out at pressures above 35 bars up to more than 70 bars. The injection of the additives directly into the pressurized washing chamber thus requires a high pressure pump. Therefore, according to a preferred embodiment of the invention during the transfer of the additive into the CO₂ transfer line the pressure within the CO₂ transfer line does not exceed 20 bars, preferably does not exceed 10 bars. It is then possible to use a low pressure pump to pump the additive out of the additive reservoir.
The CO₂ transfer line advantageously comprises a segment of increased diameter and the additive is fed into that segment or very close to that segment. For example the CO₂ transfer line may comprise a kind of bulb. The segment of increased diameter is not aimed for mixing the additive with CO₂, but provides a sufficient volume in order to assure that enough additive can be pumped into the CO₂ transfer line by using a low pressure pump or can be pushed into the CO₂ transfer line by an excess pressure in the additive reservoir. The capacity of that segment or bulb should be high enough that the pressure in it does not exceed a certain maximum pressure, which for example is determined by the maximum pressure of the low pressure pump or the excess pressure in the additive reservoir. It is apparent for the man skilled in the art that the orientation of the bulb can be chosen in several ways. But preferably the bulb is vertically oriented with the inlet for the additive and the CO₂ near or at the bottom of the bulb .
It is further advantageous to depressurize the washing chamber prior to injecting the additive into it. Depressurization means that the pressure is lowered to a value below the excess pressure in the additive reservoir or below the maximum pressure that can be achieved by the low pressure pump which is used to pump the additive from the additive reservoir into the CO₂ transfer line. Due to the pressure difference between the CO₂ transfer line and the washing chamber the additive can then be easily pushed into the washing chamber by gaseous CO₂.
For example, after a wash cycle, the CO₂ transfer line or the bulb contain a pressure of typically 17-20 bar. By opening the CO₂ transfer line to the washing chamber for only a couple of seconds, prior to the injection of the additive into the CO₂ transfer line or the bulb, it is assured that the bulb and the CO₂ transfer line are ending up at ambient or even lower pressure, depending on the pressure within the washing chamber.
In a preferred embodiment the washing chamber does not contain liquid CO₂ during the injection of the additive into the washing chamber. In that case first the additives are blown into the washing chamber by gaseous CO₂ and then liquid CO₂ is introduced into the chamber. Prior to entering liquid CO₂ the CO₂ transfer line, all additives should be pushed out of the transfer line in order to avoid freezing of the additives which might lead to clogging of the CO₂ transfer line.
But the invention can also be used when the washing chamber is already filled with liquid CO₂ and there is only need to add detergents or when the washing chamber is partly filled with liquid CO₂. In this case the pressure in the washing chamber must of course not exceed the pressure of the gas that is used to propel the additive into the washing chamber, for example the pressure in the washing chamber must not exceed the pressure available in the CO₂ storage tank.
Preferably the gaseous CO₂ used as propellant is withdrawn from the head space of the liquid CO₂ storage tank which is designed for replacing losses during the washing cycle with liquid CO₂. Since the CO₂ gas reserve in the CO₂ liquid storage tank is often small, the pressurization of the washing chamber to a pressure above the triple point is preferably not made by using gas from that storage tank, but the washing machine will have to provide gas that can be used to pressurize the washing chamber.
Instead of the liquid CO₂ storage tank which is designed for replacing losses during the washing cycle with liquid CO₂ and which has a pressure of about 17 to 20 bar, it is also possible to use gas from the internal high pressure working tank of the dry-cleaning machine as propellant.
Preferably, there is no deliberate mixing of the additive and the CO₂ prior to entering the washing chamber. Of course when the gaseous CO₂ propels the additive into the washing chamber some mixing of CO₂ and additive occurs. But according to the invention the major part of the mixing takes place in the washing chamber. For that reason it is advantageous to have a rotating drum or a rotating basket within the washing chamber which creates agitation of the liquid CO₂.
The agitation in the washing chamber could be improved by the use of baffles or other agitating means, preferably located on the outside of the basket. Flexible baffles, for example made of teflon, or baffles designed like brushes may be used.
It is preferred to spray the additive through a nozzle into the washing chamber, that is through an outlet that represents a restriction compared to the overall diameter of the CO₂ transfer line. Such a nozzle should be designed for the additive injection as well as for the transfer of liquid CO₂ into the washing chamber. To avoid the risk of clogging, for example by particles of frozen additive, it might also be advantageous to use a CO₂ transfer line with a straight tube end without any restriction in diameter.
Preferably the outlet of the CO₂ transfer line, which is for example provided with a nozzle, is designed to flow rates of 5 to 20 liters/minute of additive, preferably of flow rates between 10 and 15 liters/minute. A reasonable time to spray the required amount of additive into the washing chamber would be less than 10 seconds.
Preferably the injection time corresponds to the amount of detergent that shall be injected for each given wash situation. In that case a certain injection time and thus the amount injected result in a desired detergent concentration in the actual bath.
As mentioned above it is preferred to have a rotating basket perforated with holes within the washing chamber. The distance between the outer surface of the rotating drum and the inner walls of the washing chamber is typically about 20 to 50 mm. It has been found that the additive should be sprayed onto the outside of the rotating drum in order to thoroughly mix the additive and the liquid CO₂. Otherwise the additive might be introduced into some dead ends within the washing chamber which will never be reached by liquid CO₂, or where agitation will not be sufficient to mix the detergent with the CO₂.
The position of the spray nozzle respectively the CO₂ transfer outlet which is used to introduce the additive into the washing chamber should be optimized. It has been found that the degree of mixing of the additive and the liquid CO₂ within the washing chamber depends on several parameters, for example the spraying angle, the position of the additive outlet, the tubing sizes and the design of the spray nozzle. Advatageously the spraying direction should be perpendicular to the basket surface and the spraying point, that is the additive outlet, should be located in the lower half of the basket. Preferably the additive is sprayed at a four or five o'clock position onto the basket if the basket is rotated clockwise.
In case a motor to rotate the basket is located within the washing chamber it is preferred to provide the additive outlet with a kind of hood to avoid spraying possibly harmful additives onto the motor.
In one embodiment of the invention there is only one additive reservoir which contains a mixture of detergent, anti-static agent and perfume. But it is also possible to have different reservoirs for different additives. For example, when cleaning the objects in a two-bath cycle with a wash bath and a rinse bath, it is advantageous to use only detergents in the wash bath and different additives, e.g. perfume, anti-static, anti-bacterial agents, anti-flammables or impregnating/water-proof agents in the rinse bath.
Independent of the cleaning method the additive must be soluble in CO₂, must not be hazardous and the detergent should have good cleaning properties. Further the additives should preferably be in the liquid state at room temperature and should not become solid when in contact with CO₂ at temperatures of about-15°C.
The invention as well as further details and preferred embodiments of the invention are disclosed in the following description and illustrated in the accompanying drawings, in which the

figure: is a schematic drawing of the inventive detergent injection system.

The CO₂ dry cleaning system shown in the figure is of modular design. It comprises a supply unit 1, a detergent injection system according to the invention 2 and the washing machine 3. Each of the modules 1, 2, 3 essentially only contains equipment belonging to its own function.
Supply unit 1 includes all parts of the system which are necessary for the transfer of CO₂, in gaseous as well as in liquid form. For sake of simplicity in the figure only a CO₂ storage vessel 4 is shown and all necessary safety features have been omitted in module 1. For example module 1 has to contain safety features that will protect module 1, which is a low pressure unit, from back flow from module 3, which is a high pressure unit.
Storage vessel 4 contains CO₂ in liquid phase 5 and in the gaseous state 6. A CO₂ gas transfer tube 7 is connected to the head space 6 of storage vessel 4. The flow of CO₂ gas can be controlled by means of gas valve 8. Liquid CO₂ can be withdrawn from storage vessel 1 via liquid transfer tube 9 which is provided with valve 10. Of course, the valves 8 and 10 could be replaced by a 3-way valve that can be turned between gas and liquid inlet, thus providing gas or liquid on its outlet to transfer line 11.
CO₂ transfer line 11 connects gas transfer tube 7 as well as liquid transfer tube 9 with the washing chamber 12 of the washing machine 3. Within a portion 13 the inner diameter of transfer line 11 is increased to form a kind of bulb 13 with a volume of about one liter. Washing chamber 12 comprises a perforated basket 14 which is rotated in a clockwise direction. The end of CO₂ transfer line 11 is provided with a spray nozzle 15 which is directed to the outside of the perforated basket 14. Spray nozzle 15 is located in the lower half of rotating basket 14 and the angle between the vertical and the spray direction is between 30° and 60°, preferably about 45°. The spray direction is perpendicular to the outside of basket 14. Upstream of spray nozzle 15 transfer line 11 is provided with a valve 16 which is part of the washing machine and is a high pressure ball valve, controlled and actuated by the washing machine.
A three-way-valve 17 is interposed in transfer line 11 between CO₂ storage vessel 4 and bulb 13. An additive reservoir 18 contains a detergent or a mixture of detergents, anti-static and anti-bacterial agents and perfume. Three-way-valve 17 interconnects with the additive reservoir 18 by means of an additive transfer tube 19 and a hose 20. A low pressure pump 21 is interposed between the additive reservoir 18 and hose 20.
Further, additive transfer tube 19 or hose 20 comprise a safety relief valve 23 and a check valve 24 which are designed to handle a back pressure burst from the washing chamber 12 which might occur when 3-way valve 17 is in a position where it connects hose 20 with bulb 13 or if it risks leaking between hose 20 and bulb 13 independently of its position. Additional safety relief valves of appropriate size and design may need to be added. Also, if the pressure in the system downstream the low pressure pump 21 is too high, i.e. if the pressure in high pressure hose 20 is too high for the low pressure pump 21 to overcome, the additives will be able to flow back through a by-pass line 25 situated parallel to the low pressure pump 21.
The sequence of operation of the detergent injection system is as follows: The objects to be cleaned, for example garments or parts, are loaded into the basket 14 of the washing machine 3. Then the door of the washing chamber 12 is closed.
Three-way-valve 17 is turned to open the way from the additive reservoir 18 to transfer line 11.
After the previous wash cycle, the bulb 13 and transfer line 11 contain a pressure of typically 17-20 bar, because the transfer that has been made during that previous cycle left said pressure in the system: Either, a full transfer was made with injection of detergent into the washing chamber, followed by liquid CO₂ transfer from tank 4 and followed by purging of the lines with gaseous CO₂ with a pressure of 17-20 bar. Or only a detergent injection took place, for example if the machine did not need additional CO₂, which also left 17-20 bar in bulb 13.
By opening the valve 16 for only a couple of seconds, prior to the injection of additives into the bulb 13, it is assured that the bulb 13 and transfer line 11 are vented into the washing chamber 12, thus ending up at ambient or even lower pressure, given that the washing chamber 12 is at ambient pressure or has been evacuated.
Then valve 16 is closed and detergent is injected into the bulb 13. Low pressure pump 21 is started and additive is pumped from the additive reservoir 18 into transfer line 11 and in particular into bulb 13. Prior to starting pump 21 as well as during the pumping procedure the pressure in transfer line 11 is controlled by means of a pressure indicator 22. When the correct amount of additive is pumped into the bulb 13 low pressure pump 21 is stopped. The pressure increase measured by the pressure indicator 22 is directly related to the amount of additive pumped into the bulb 13 and thus can be used to determine the amount of additive in the bulb 13.
But it is also possible to use a liquid level indicator within the additive reservoir 18 or a flowmeter in order to measure the amount of additive transferred into transfer line 11. Finally, knowing the flowrate of the pump 21 or the volume per pump strike, if a piston pump is used, the amount of additives injected could be determined by measuring the pumping time or by counting the number of pump strikes.
During the injection of additives into the bulb 13, the pressure within the bulb 13 must be below the maximum pressure of the low pressure pump 21. Further, in order to save time it is advantageous to evacuate and then pressurize washing chamber 12 during additive injection into bulb 13. Valve 16 is closed during that period. The pressurization of the washing chamber 12 should be made to above the triple point of C02, but not higher than the pressure available from the storage tank 4 or whatever gas source is used for propelling the additives.
Next, three-way-valve 17 is turned to open the connection between the liquid CO₂ storage vessel 4 and transfer line 11. Valve 10 is closed and valve 8 is opened. Gaseous CO₂ flows from the head space 6 of storage vessel 4 into transfer line 11.
Then washing chamber valve 16 is opened for about 10 seconds. By means of the gaseous CO₂ the additive is propelled through transfer line 11 into the washing chamber 12 and sprayed on the outer surface of rotating basket 14. When the additive transfer is completed washing chamber valve 16 is closed.
Supply unit 1 is then used to transfer liquid CO₂ into washing chamber 12, but only the amount of CO₂ corresponding to losses due to venting after the previous wash cycle(s). Therefore, gas valve 8 is closed and valves 10 and 16 are opened. Liquid CO₂ is pushed by the over pressure in head space 6 of CO₂ storage vessel 4 through transfer line 11 into washing chamber 12. When enough CO₂ to make up for losses has been transferred into the washing chamber 12 from storage tank 4, the rest of the CO₂ needed for washing is filled into the washing chamber 12 from the internal high pressure storage tank of the washing machine itself. When there is enough liquid CO₂ in the washing chamber 12, the cleaning process can be started.
As described above, the amount of liquid CO₂ taken from tank 4 is only aimed to make up for losses during the previous wash cycle(s). The rest of the liquid CO₂ which is required for the bath is taken from the internal working tank (not shown in the figure) of the washing machine.
It is obvious for a person skilled in the art that several parts of the equipment used with the invention are preferably controlled by any kind of electrical or pneumatical means. For example, valves 8, 10, 16 and 17 and pump 21 may be controlled by a control unit.

Claims

Method to introduce an additive into a washing chamber of a CO₂ dry cleaning system wherein said additive is transferred from an additive reservoir into a CO₂ transfer line connecting a CO₂ storage tank with said washing chamber, characterized in that gaseous CO₂ from said CO₂ storage tank (4) is introduced into said CO₂ transfer line (11) and that said additive is propelled into said washing chamber (12) by said gaseous CO₂.
Method according to claim 1, characterized in that during said transfer of said additive into said CO₂ transfer line (11) the pressure within said CO₂ transfer line (11) does not exceed 20 bars, preferably does not exceed 10 bars.
Method according to any of claims 1 or 2, characterized in that said CO₂ transfer line (11) comprises a segment (13) of increased diameter and that said additive is transferred into said segment (13).
Method according to any of claims 1 to 3, characterized in that said washing chamber (12) does not contain liquid CO₂ during the injection of said additive into said washing chamber (12).
Method according to any of claims 1 to 4, characterized in that liquid CO₂ is transferred from said CO₂ storage tank (4) into said washing chamber (12).
Method according to any of claims 1 to 5, characterized in that said washing chamber (12) comprises a rotatable basket (14) and that said additive is blown onto the outer surface of said rotatable basket (14).
Method according to any of claims 1 to 6, characterized in that different types of additives are stored in one single additive reservoir (18).