GB2231136A - Gas separation - Google Patents

Abstract

The present invention provides a process for the removal of undesirable fire extinguishing vapours, such as halocarbons, from substantially enclosed spaces, such as rooms in a building, and without contaminating the atmosphere, by condensation. There is also provided condensing apparatus for performing said process.

Description

Gas SeParation The present invention relates to the separation of gases.

It has been recognised for a number of years that halogenated hydrocarbons (also referred to as halocarbons herein, the tern including perhalo compounds as well as partially substituted compounds), such as CFC's (chlorofluorocarbons), pose a threat to the upper atmosphere, and to the ozone layer in particular. The ozone layer comprises somewhat unstable molecules of three oxygen atoms. These molecules have, up until now, been safe in the upper atmosphere. However, with the advent of halogenated hydrocarbons, this is no longer the case. These compounds are sufficiently stable and light to reach the upper atmosphere and are capable of serving as catalysts to break down the molecules of ozone. Thus, a small amount of halogenated hydrocarbon can serve to destroy a large amount of ozone.This is particularly important, as the ozone layer serves as the primary defence against cancer-inducing ultraviolet rays from the sun.

Halogenated hydrocarbons are used in such diverse industries as aerosol packaging, refrigerator manufacturing and fire extinguishers. There is no particular danger to the atmosphere where the halocarbons are kept separate from the atmosphere. For example, refrigeration units recyle the halocarbon and release none to the atmosphere. Thus, there is little danger from this particular source. Nevertheless, a danger can arise during the manufacture of refrigeration units if a spillage occurs. This can also happen in the manufacture of aerosols.

The situation is far more serious with respect to fire extinguishers. A fire extinguisher is specifically intended to release a large amount of inert halocarbon to extinguish, or at least to prevent the spread of, a fire. The inevitable result is that the halocarbon reaches the open atmosphere and eventually contaminates and destroys the ozone layer.

In all of these cases, and in any other instance where halocarbons may be released into the atmosphere, it is desirable that the threat somehow be averted.

The present invention provides a process for averting such atmospheric contamination comprising the condensation of the halocarbon, or halocarbons, or undesirable fire extinguishing vapours, from a substantially enclosed space.

Suitable examples of enclosed spaces which may be subjected to the process of the invention include manufacturing plants and buildings, rooms or tunnels in which a fire extinguisher has gone off. The process is particularly applicable in buildings having a fixed installation fire extinguishing system having a totak- flood facility.

Such fixed installation systems are specifically designed to smother a fire by flooding with an inert gas, or foam. thereby to completely exclude oxygen, or at least to sufficiently reduce the concentration of oxygen to hinder or prevent appreciable combustion. In such cases. not only is it desirable to prevent the vapour, such as BTM (bromotrifluoromethane). from contaminating the atmosphere, but it is also desirable to recover as much as possible for recycling, thus saving unnecessary expense in manufacture.

It will be appreciated that apparatus for performing the process of the invention may be introduced into the enclosed space at need, or may be located there permanently. It is equally possible for a portal to be provided in, for example, the room, the apparatus being attached thereto permanently or as needed. If the apparatus is only connected to the portal in times of need, it is generally preferable that the portal is sealed when not in use, so as to prevent the escape of undesirable gases by that route. Combinations of the above are possible, and it may be necessary to use several condensers where large-areas are concerned.

It will be apparent that the present invention also provides condensation apparatus adapted to condense a halocarbon, halocarbons or fire extinguishing gases from the atmosphere of a substantially enclosed space. Such apparatus may be any that is suitable. It is generally preferred that cryogenic or refrigeration apparatus be used, although it is also envisaged that pressure condensation units may be used in certain circumstances.

Whilst it is possible that halocarbon refrigeration units be used in accordance with the invention, it is generally preferable that liquid nitrogen is used as the refrigeration agent. Other agents may also be used, but liquid nitrogen is generally effective to remove most halocarbons from the atmosphere.

Typical halocarbons which may be separated from the atmosphere in accordance with the present invention include the group known as Halons. This group includes bromochlorodifluoromethane, bromochloromethane, dibromodifluoromethane and dibromotetrafluoroethane (designated as 1211, 1011, 1202, 1301 and 2402 respectively).

Gases subject to the present invention tend to be vapours of low boiling point liquids. Such liquids tend to boil somewhere between -900C and ambient temperaturs,- especially between -700C and OOC.

The condensing apparatus of the invention suitably condenses the halocarbon from the atmosphere and returns the purified air back to normal circulation. However, it is quite likely that some halocarbon contamination will linger, and so it is preferred to filter the air before it is returned. When the condensing unit involves refrigeration, it may also be desirable to warm the air before return, primarily for reasons of comfort.

The halocarbon separated from the atmosphere is likely to be contaminated with other components found in air, such as water and carbon dioxide. The apparatus of the invention may comprise suitable filters to remove such contaminants, as both tend to be solids at the low temperatures envisaged, but it is not essential to use such filters. However, the apparatus will usually comprise filters at least to exclude particulate matter, such as smoke or other suspended atmospheric materials (e.g. dust), which may interfere with the condensation process.

In order that the condensed halocarbons be as pure as possible, it is preferable that other contaminants (such as described above) be removed before the final condensation stage. This may, for example, involve F pre-cooling stage, conveniently to just below O-C, to remove any moisture. Instead of a pre-cooling stage. an anhydrous filter could also be used, or the filter could be employed together with a pre-cooling stage in order to ensure complete removal of atmospheric moisture. In the final stage, it is preferred that the halocarboncontaminated air is clean and dry before condensation.

The condensed vapours collected may then suitably be treated for recycling for further use. In order to achieve this, the condensation chamber of the apparatus is suitably a self-contained sealable unit. This can then be transported when filled to a processing plant.

In accordance with a further aspect of the present invention, there is provided apparatus for condensing vapours from a gas contained in a substantially enclosed space, the gas comprising such components as halocarbons or fire extinguishing vapours. the apparatus comprising: inlet means: means to draw said gas through said inlet means; said inlet means conducting said gas to condensing means: collecting means to collect any condensate from said condensing means; and outlet means to permit exit of uncondensed gases.

. The apparatus described above suitably further comprises one or more types of filter in the inlet to remove unwanted contaminants (as described previously).

Filter means may also suitably be incorporated in the outlet to screen out any residual uncondensed vapours.

The collecting means is suitably in the form of a cannister which can be sealed after filling. for recycling or disposal. The apparatus as a whole is suitably attachable to a portal in the enclosed space, so as to be able to withdraw the contaminated atmosphere therethrough.

The condensing means may be any suitable. or known in the art. Suitably, a pipe-within-pipe system is used the gas being conducted through the inner pipe, and a refrigerant, such as liquid nitrogen, in the outer pipe serving to cool and condense the vapour(s). In a preferred embodiment, the gas containing the vapour is also pressurised, thus facilitating condensation.

Suitable apparatus for use in accordance with the present invention is illustrated in the accompanying drawings in which: Figure 1 represents the apparatus schematically; and Figure 2 shows the essential components of a suitable refrigeration apparatus for use in accordance with the invention.

Claims (2)

1. A process for the removal of a halocarbon, or halocarbons or undesirable fire extinguishing vapours, from a substantially enclosed space, comprising condensation of the vapour.

2. Apparatus for condensing vapours from a gas contained in a substantially enclosed space, the gas comprising such components as halocarbons or fire extinguishing vapours. the apparatus comprising: inlet means; means to draw said gas through said inlet means; said inlet means conducting said gas to condensing means; collecting means to collect any condensate from said condensing means; and outlet means to permit exit of uncondensed gases.

3 Apparatus according to claim 2 comprising cryogenic condensing means.