CZ20011674A3 - Process and apparatus for regulating atmosphere within an enclosed space - Google Patents

Abstract

A method and an apparatus for regulating an atmosphere in an essentially closed space are described. The atmosphere contains a condensable substance, inert gas and oxygen, and the method comprises the following steps: withdrawing said atmosphere from the space and passing the same, forming a process gas flow to a concentrator unit wherein said condensable substance is separated from the rest of said process gas flow; returning at least a part of said process gas flow to the space; and bringing said condensable substance from said concentrator unit to a condensation unit and condensing said condensable substance in said condensation unit.

Description

Method and apparatus for controlling the atmosphere in an enclosed space

Technical field

The present invention relates generally to a method and apparatus for controlling the atmosphere in a substantially enclosed space.

BACKGROUND OF THE INVENTION

It has been known from the past to neutralize, or rather render indifferent, spaces into which objects are fed and are continuously modified there. These spaces often contain condensable substances such as volatile organic compounds (VOCs), for example solvents, and hydrocarbons. The aim of the neutralization process is to control the atmosphere, for example by keeping the O ₂ level at a level at which the atmosphere is not explosive. Another reason to keep O ₂ at a low level is to maintain the quality of the objects being treated, because a high O _{2 level} can have a detrimental effect on the end result of the treatment.

A preferred inert gas supplied to the space is, for example, nitrogen. In this type of neutralization, a large stream of nitrogen into the neutralized space is often required, resulting in a large cost of nitrogen. Since solvent vapors are present in the space, the outgoing stream from the space will contain not only nitrogen and oxygen, but also, for example, solvent vapors. This entails additional solvent costs and also no environmental impact. Also, in many countries, stricter environmental pollution requirements have required investments in purification plants to keep VOC discharges low and thus continue their further processing.

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European Published Patent Application EP-0 094 172 discloses a method and apparatus for recovering solvent vapors from an oven or exciter chamber in which a mass balance relative to the chamber atmosphere is maintained. The atmosphere is drawn from the furnace at a substantially constant flow rate and the uncondensed gas stream is returned to the furnace at a rate that depends on sensed changes in solvent vapor concentration. Thus, the combined rate at which solvent vapors are formed in the furnace and with which the non-condensed gas stream is returned to the furnace balances the rate at which the furnace atmosphere is removed from the furnace.

A problem with the described method and apparatus is also that the requirements for low volumes of VOC discharges are not met in an inexpensive manner.

It is an object of the present invention to provide a method and apparatus for controlling the atmosphere in a substantially enclosed space with which the above-mentioned disadvantages of the prior art are avoided or at least minimized. The aim is also to propose a cheap solution to limit the amount of VOC discharged.

SUMMARY OF THE INVENTION

The present invention is based on the discovery that the outgoing gas stream can be cleaned in an inexpensive manner by a combination of a concentrator and a condensing device.

According to a first aspect of the present invention, there is provided a method of controlling an atmosphere in a substantially enclosed space, wherein said atmosphere comprises a condensable condenser. And the method comprises the steps of: a) removing said atmosphere from the space and transferring it to form a gas stream to a concentrator unit in which said condensable substance is separated from the atmosphere; the remainder of said gas stream; b) returning at least a portion of said gas stream to the space; and c) feeding said condensable substance from said concentrator unit to a condensation unit and condensing said condensable substance in said condensation unit.

According to a second aspect of the present invention there is provided an apparatus for controlling the atmosphere in a substantially enclosed space, said atmosphere comprising a condensable substance, and the apparatus comprising an inert gas source associated with said space and a condensing unit for condensing said condensable substance. wherein the apparatus further comprises a concentrator unit disposed between said space and said condensation unit to increase the level of condensable substance in the flow leaving the concentrator unit to the condensation unit compared to the level of condensable substance in the flow entering the concentrator unit from the space.

Further advantageous embodiments of the present invention are defined in the dependent claims.

The present invention will be described in more detail below by way of example only with reference to the accompanying drawings.

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BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a block diagram illustrating a device according to the present invention for maintaining a desired atmosphere in a substantially enclosed space;

Fig. 2 is a diagram illustrating in more detail the concentrator of Fig. 1; and

Fig. 3 is a block diagram illustrating an alternative embodiment of a device according to the present invention for maintaining a desired atmosphere in a substantially enclosed space.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, with reference to Figs. 1 and 2, a first embodiment of the apparatus and method of the present invention for treating objects in a substantially enclosed space will be described. The objects (not shown) to be treated are moved into and through the substantially enclosed space 2. Space 2 is generally well known in the art and includes openings for the objects to be treated, in some cases also some type of gas curtain or the like for the purpose of minimizing the amount of oxygen entering the space through the openings, and so on.

The space 2 is connected to the concentrator 5 via the outlet line 3 and the inlet line 6. A discharge valve 6 is provided in the inlet duct 4. The function of the valve will be described later.

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The concentrator 5 is further coupled to the cryogenic condensation device (CCP) 9 via an output line 7 and an input line 8.

Finally, a liquid nitrogen source 10 (LIN source) is also provided, which is connected to the CCP 2 via a line

11. The LIN source 10 is also connected to the space 2 via the evaporator 12 and the lines 13 and 14. The line 13 is also connected to the CCP 1.

The operation of the apparatus described above will be described in the following description. At the beginning, the level of O ₂ in space 2 exceeds the desired level, for example 3%. In order to reduce the O ₂ level, pure nitrogen is supplied to the space 2 from the LIN source 10 through the evaporator 12 and lines 13 and 14. The function of the evaporator 12 is thus to prevent liquid nitrogen from entering the space 2, which would otherwise damage the space and objects in it.

Nitrogen is supplied from the LIN source 10 to space 2 until the O _{2 level} in this space is reduced to the desired level. The objects to be treated, such as glass bottles or video tapes, are then routed into and through the space 2 through openings (not shown) provided for this purpose. Nitrogen is continuously fed to space 2 to maintain the oxygen level at the desired level as new oxygen continuously flows into space 2. To maintain the pressure in space 2, a gas stream that includes nitrogen, solvent vapors and oxygen will then be passed through a fan (not shown) from the space 2 through the outlet duct 3 and into the concentrator 5. The fan may be formed in any of the ducts 3 or ducts 4.

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The concentrator 5 will now be described in more detail with reference to FIG. 2. The gas stream enters the concentrator 5 through line 3 and is directed to one of the two cleaning beds 20a, 20b. A valve 21a, 21b, 21c, 21d is formed in each inlet and outlet of these beds, and through these valves a bed is selected to be used for cleaning the gas stream. The bed which is not used to purify the gas stream is then closed by valves 21a, 21b, 21c, 21d. For example, if a bed 20a is to be used, the valves 21a and 21b are open while the valves 21c and 21d are closed.

The beds 20a, 20b include some suitable cleaning material, such as zeolite or activated carbon. When the gas stream is passed through the bed, solvent vapors are separated from the gas stream and retained in the scrubbed beds. The gas stream cleaned in this way then leaves the concentrator via line 4.

The beds 20a, 20b are also connected to the guides 7 and 8 via valves 22a, 22b and 22c, 22d, respectively. These connections are used when the beds are to be cleaned, i.e. when they are saturated with solvent. The cleaning process will now be described in more detail.

The lines 2 and 8 together with the concentrator 5 and the CCP 9 form a substantially closed nitrogen system. A fan (not shown) is provided in line 2 for circulating nitrogen. A nitrogen heater 23 is also provided in the line 8. to enter the concentrator 5, see FIG. 2. The nitrogen entering the concentrator from line 8 is directed to one of the beds 20a, 20b, which is saturated with solvent and thus it is not used to clean the gas stream from the room

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2. The selection of the bed 20a, 20b is made by means of the valves 22a, 22b, 22c and 22d. Thus, when the bed 20a is used to purify the gas stream, the nitrogen from line 8 is directed to the saturated bed 20b, and vice versa. Thus, when the valve 21a is open, then the valve 22a must be closed, and vice versa, that is, the two valves 21a, 22a must not be opened at the same time. However, it is possible for the two valves 21a, 22b to be closed at the same time, for example when the bed 20a has already been cleaned, but the second bed 20b is still functional for cleaning the gas stream. The same applies to the second pair of valves 21b, 22b, and so on.

When heated nitrogen enters bed 20a or 20b from line 8, the solvent in the bed evaporates and exits with a stream of heated nitrogen leaving the concentrator 5 through line Z to CCP 9. · In this way the selected bed is cleaned and can then be used for cleaning the incoming gas stream from room 2. ·

The function of CCP 9 will now be described. · CCP 9, operates according to the principle of cryogenic condensation, which will now be explained. In a cryogenic condenser for condensing, for example, solvent vapors, the efficiency depends on the concentration of the solvent in the gas stream. At higher solvent concentrations, most of the cooling effect can be used to condense the solvent. At a lower concentration, a greater part of the cooling effect will be used to cool the nitrogen, resulting in less efficient utilization of the cooling capacity. In other words, in order to condense the same amount of solvent a much larger amount of liquid nitrogen (LIN) would be required for cooling in the absence of a concentrator.

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Thus, the incoming stream of nitrogen and solvent is cooled to a very low temperature, thereby condensing most of the solvent. The cooling is performed by liquid nitrogen supplied from the LIN source 10 via line 11. The CCP 9 then operates as a heat exchanger in which the liquid nitrogen from the LIN source 10 is vaporized, thereby cooling the stream of nitrogen and solvent coming from the concentrator 5.

The condensed solvent is collected and can then be returned to the neutralized space 2 and reused in the process by some suitable piping means shown in the figures by arrow 26. This reuse of solvent thus provides a cheap and efficient means of reducing solvent costs.

Due to the use of the concentrator 5, the cooling process in CCP 9 is a very efficient process because the nitrogen and solvent stream from the concentrator 5 contains a relatively large proportion of the solvent.

Evaporated pure nitrogen from the LIN source 10 after being used for cooling is then fed to space 2 as part of the nitrogen added through line 13.

In the usual operation, when limited amounts of oxygen penetrate into space 2, the nitrogen used for cryogenic condensation and the amount of nitrogen needed to neutralize space 2 are substantially in equilibrium, i.e. all the nitrogen used for cooling in CCP 9. directly into the inertia 2 and only small amounts or even no nitrogen must be used in CCP 9. which cannot be used in the inertia

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this to this to space to 2. this means space to 2. This means In addition to functioning as a capacitor, the CCP 9 actually also functions as an evaporator, which further improves the cost-effectiveness of the method and apparatus of the invention.

A second embodiment of the present invention will now be described with reference to Fig. 3. The only change from the embodiment described with reference to Figs. 1 and 2 is in the CCP 9. In the first embodiment, this device acted as a heat exchanger with two separate systems, see system associated with a concentrator 5 with a solvent condensation function. and a system, respectively, coupled to a LIN source 10 having a function for cooling the solvent-bearing nitrogen. In this second embodiment, the CCP operates in a different manner.

As can be seen in FIG. 3, the CCP 9 is still coupled to the LIN source 10 and the liquid nitrogen supplied through line 11 is used for cooling. However, instead of being fed into space 2, the vaporized nitrogen used for cooling is then fed to the concentrator 5 through line 8. This nitrogen is heated by the heater 23, see FIG. 2, before being fed to one of the beds 20a, 20b to be cleaned, as in the first embodiment. In this second embodiment, however, the ventilator (not shown) used to circulate nitrogen in line 8 can be discharged since the pressure from the LIN source 10 is sufficient to push nitrogen through the system.

After leaving the concentrator 5, the nitrogen used for bed cleaning is passed through line 7 to the CCP 9 in which the solvent is condensed. Then, nitrogen, now with only a minor proportion of the solvent, is fed to the neutralization space 2. Thus, the system comprising CCP 9, concentrator 5, and concentrator 5 and lines 8, 8 now no longer forms a closed nitrogen system.

This second embodiment provides several advantages. First, the fan in the conduit 8 can be discharged, which is a cost saving. Secondly, the nitrogen supplied through this line is clean, i.e. essentially free of oxygen as it comes substantially directly from the LIN source 10. This eliminates the risks associated with the heater 23, since very small amounts of oxygen in contact with it then may cause an explosion.

Referring now to Fig. 1, a self-regulating system of inert nitrogen coming from the CCP will be described.

9 and evaporator 12. As can be seen in this figure, two pressure regulators 28 and 29 are provided in line 13 and line 14 leaving the evaporator 12, respectively. The set pressure value of regulator 28 is slightly higher than that of regulator 29, for example, ie 200 mbar and 190 mbar. Nitrogen in line 13 then comes primarily from CCP 9, and only if there is not enough nitrogen from the device, i.e. the pressure drops in line 13 upstream of pressure regulator 28, will nitrogen be supplied from evaporator 12 and line 14, In this way, it is ensured that the nitrogen used for cooling is also used to neutralize the space 2, and that the nitrogen coming from the LIN source 10 through the evaporator 12 is only used if the nitrogen used for cooling is not sufficient to neutralize This therefore provides a very cost effective process for reducing the amount of liquid nitrogen (LIN) used.

The function of the valve 6 will now be described with reference to FIG. 1

Nitrogen permeates into the space 2 and therefore an inert gas, such as nitrogen, must also be fed into the space 2. Oxygen and nitrogen together with the solvent vapors are conducted as a gas stream from space 2 to concentrator 5. Nitrogen together with oxygen is then returned to space 2 through line 4. If all of this mixture of oxygen and nitrogen were returned, excess pressure would be created in space 2. Thus, some of this nitrogen-oxygen mixture is discharged through the valve 6 and into the environment. This has already been made readily practicable due to the fact that this nitrogen-oxygen mixture is substantially free of solvent vapors and therefore does not present any environmental risks.

Using the method and apparatus of the present invention, liquid nitrogen consumption (LIN) can be substantially reduced. It has been shown experimentally that LIN liquid nitrogen consumption can be reduced by a factor of 8 to 10. The number of times that nitrogen can be reused depends on In addition, the condensed solvent can be fed back into the process, thereby reducing the amount of solvent added.The liquid nitrogen (LIN) used to reduce the oxygen level can be used not only for this purpose but also for condensation of solvent after concentrator.

When only cryogenic condensation is used, discharge requirements (VOCs) often cannot be met. With the method and apparatus of the present invention in which a concentrator is also used, the amount of VOC discharged can be low so that the requirements are also met in countries with very strict discharging rules.

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Having read the foregoing description, it will be apparent to one skilled in the art that many modifications and modifications may be made to the scope of the appended claims. For example, although just two cleaning beds have been illustrated, it is clear that any number of such beds may be used. If only one scrubbing bed is used, the process operates intermittently, that is, the process continues to operate until the bed is saturated with solvent, and then the neutralization process is interrupted and the bed cleaning process is initiated.

It will also be appreciated that the method and apparatus of the present invention is not limited to VOCs such as solvents, but is also applicable to other types of condensable substances such as hydrocarbons.

Claims (9)

PATENTOVÉ Claims 1. ··! ··· · · · · · · · · · · · · · · · · · · · · · · · · A method of controlling an atmosphere in a substantially enclosed space, said atmosphere comprising a condensable substance, inert gas and oxygen, comprising the steps of: a) removing said atmosphere from the space and passing it on to form a gas stream into a concentrator unit in which said condensable substance is separated from the remainder of said gas stream; b) returning at least a portion of said gas stream to the space; and c) feeding said condensable substance from said concentrator unit to a condensation unit and condensing said condensable substance in said condensation unit. The method of claim 1, wherein said condensation in step c) comprises cryogenic condensation. The method of claim 1 or 2, wherein step a) comprises supplying a gas stream to a scrubbing bed in said concentrator unit, and wherein step c) comprises vaporizing said condensable substance and supplying said condensable substance from said scrubbing bed to said scrubber. condensing units via heated inert gas. The method of any one of claims 1 to 3, wherein step c) comprises supplying cold inert gas to the condensing unit to effect said condensation. • · · 9 · f · f · f The method of claim 4, further comprising the step of d) introducing said inert gas to effect said condensation into a space to neutralize the atmosphere therein. • 9 » 9 9 • • * • · ·· that »includes used The method of claim 4, further comprising the step of d) supplying said inert gas used to effect said condensation to a concentrator unit for vaporizing said condensable substance and supplying said condensable substance from said scrubbed to said condensation unit. a space (2), wherein said condensable substance, and An apparatus for regulating an atmosphere in a substantially enclosed atmosphere comprising the apparatus comprising a source with said space (2) and (10) an inert gas connected to a condensing unit (9) for condensing said condensable substance, characterized in that (5) a concentrator disposed between said condensation unit (9) for comprising a unit of space (2) and increasing the level of condensable substance in the flow leaving the concentrator unit to the condensation unit (9) compared to the level of condensable substance in the flow entering concentrator units from space (2). Device according to claim 7, characterized in that said concentrator unit (5) comprises at least one cleaning bed (20a, 20b) connected to said space (2) and said condensation unit (9). The apparatus of claim 8, wherein said at least one cleaning bed (20a, 20b) comprises zeolite.