The invention has particular application to the treatment of air contaminated by vapour from the lubricating oils used in hot rolling plant for metal, especially aluminium, forming. In this context, attempts to decontaminate the air have involved scrubbers using water or solvents for the lubricating oil, but these have not worked satisfactorily and also generate a disposal problem in the form of undesirable liquid products from the scrub liquor.

It is an object of the present invention to provide an improved process for removal of such contamination from a gas or air.

According to the invention there is provided a method of treating gas, and in particular air, contaminated with a noxious vapour from a process liquor in a hot working environment, which method comprises passing the gas through a scrubber device in which the gas is exposed to a spray of cold droplets of the same process liquor as that which in vapour form comprises the contaminant.

By"cold"we mean a temperature low enough to cause significant condensation onto the droplets of vapour from the liquor in the gas. Preferably, the cold liquor supplied to the scrubber device is chilled to a temperature as close as practicable to the solidification temperature of the liquor.

Preferably the scrubber device comprises a vortex chamber having at least one tangential inlet port for the contaminated gas and an axial outlet port through which the treated gas emerges and, within the chamber, a liquid spray generator which is fed with the said process liquor and which generates a spray of droplets of the process liquor so as to fill a substantial proportion of the vortex chamber with droplets.

Preferably the liquid spray generator is of the type in which opposed jets of liquid impinge upon each other and are disrupted to form a spray of droplets and the liquor is supplied to the liquid spray generator under conditions in which the flow is at least partially turbulent, preferably under conditions for which the Reynolds number is greater than 12,000, so that the droplets in the spray are projected outwardly from, and transverse to the flow direction of, the opposed jets of liquor with a random distribution of the angular relationship between the direction of movement of the droplets relative to the direction of flow of the said opposed jets of liquor.

A method and specific construction of apparatus embodying the invention will now be described by way of example and with reference to the drawing filed herewith which is a diagrammatic cross sectional view of the apparatus.

The apparatus comprises a vortex chamber gas/liquid contactor 11 of the type described in patent GB 2282983.

The contactor 11 is connected to receive air from a fume hood 31 which is positioned to collect and draw air from a metal forming hot rolling mill, indicated diagrammatically at 32.

The contactor 11 comprises a cylindrical vortex chamber 12 which has a tangential gas inlet port 13 and an axial gas outlet port 14. A liquid feed pipe 15 divides into two branches 16 and 17 which enter into the vortex chamber 12 and terminate in two axially opposed nozzles 18 and 19, respectively. The opposed nozzles are, in this example, aligned with the central axis of the vortex chamber 12. A baffle 20 extends across the lower part of the vortex chamber 12 and the portion of the vortex chamber below the baffle 20 forms a sump 21 for liquor 22 which is withdrawn through an outlet 23 and re-circulated by a pump 24 to the feed pipe 15 via a chiller 33.

Contaminated air is drawn from the hood 31 by pump 34 and fed to the tangential inlet 13 of the vortex chamber 12 via gas feed pipe 35.

In this example, the sump 21 is filled with a liquor which is the same as that used for lubrication in the hot rolling mill 32 and thus, in vapour form, comprises the major contaminant of the air being withdrawn from the hood 31.

The pump 24 is such as to drive the liquor through the feed pipe 15 and branches 16,17 so that the flow of the opposed liquor jets emerging from the nozzles 18,19 is turbulent, having a Reynolds number in excess 12,000.

Under these conditions, the impinging jets of liquor at 25 are formed into a spray of droplets which are projected in all directions outwardly from, and transverse to the flow direction of, the opposed jets of liquor. Because of the turbulence in the impinging liquor jets, there is a random distribution of the angular relationship between the direction of movement of the droplets relative to the direction of flow of the said

opposed jets of liquor. The vortex chamber 12 is, in this way, very effectively filled with chilled droplets of liquor which are collected by their impact on the outer wall of the chamber. The collected droplets flow down the outer wall and into the sump 21, from which this collected liquor is available for re-circulation.

The contaminated air entering the vortex chamber 12 via the tangential inlet port 13 is caused to swirl through the chamber 12 and ultimately exit axially by outlet port 14. The air is thus subjected to a particularly effective scrubbing interaction with the spray of chilled droplets of the liquor. Liquor in vapour form in the air is condensed onto the droplets and thus carried with them into the sump 21, whilst the air, now significantly decontaminated, is released via outlet 14.

It will be appreciated that the chill applied by the chiller 33 must be sufficient to achieve the required degree of effectiveness in condensation of vapour onto the chilled droplets in the vortex chamber 12. In practice, it may be convenient to arrange for the chilling applied by chiller 33 to reduce the temperature of the liquor to reasonably close to its solidification temperature.

The volume of liquor in the sump 21 will gradually increase as operation of the apparatus continues. Also there will be some accumulation in the liquor in the sump 21 of other contaminants trapped by the scrub action.

Provision (not shown) is therefore made for withdrawal/replacement of this liquor. The withdrawn liquor is conveniently treated, as by distillation, steam stripping, or membrane separation for example, to remove contaminants and the recovered liquor reused. It will be

appreciated that some of the recovered liquor may be reused as lubricant in the hot rolling mill.

The invention is not restricted to the details of the foregoing example. For instance, there may be circumstances in which it is not air which is contaminated but some other gas such as, for example, an inert gas used to protect the plant over which it is circulated. The method and apparatus can equally well be applied to the decontamination of such a gas.

The decontamination may require more than 1 stage of treatment in a vortex chamber gas/liquid contactor. Such multiple stage decontamination may readily be applied, for example, by choosing any suitable multiple stage version as described in patent GB 2282983.

For forming the spray of droplets within the vortex chamber 12, a spray generator as described in GB 2347098 may advantageously be used in place of the nozzles 18, 19.