Such an apparatus is described in DE-PS 36 10 780 the relevant contents of which are to be considered a part of the present disclosure. That apparatus has been very successful in practice. However, since its conception, environmental and technical requirements as regards decontamination of air and gases to be released into the atmosphere and of gases or vapours for industrial use have become ever more stringent.

The applicant has recognised this need. Intensive further research and development work over more than a decade has brought to light new inventive concepts which taken alone or in combination can be employed to improve the efficiency and performance characteristics of the prior art apparatus and render such and simitar apparatus suitable to a variety of new uses.

Whereas the prior art apparatus had been conceived primarily for the decontamination of dust-laden air withdrawn from sandblasting, shotblasting and gritblasting operations and plant, the apparatus improved according to

the present invention can be useful quite generally for removing entrained solid and liquid particles from contaminated air and other gases or vapours such particles being not limited to inorganic solid matter such as that derived from sand-, shot-and gritblasting but also organic and inorganic particles derived from all kinds of industrial operations, including mining and metallurgy, cutting of rock and stone, comminution processes, whether of inorganic material such as ores, cement, or lime or pigments, or organic matters such as coal, organic chemicals or food or feed stuffs such as cereals, where dust may constitute a fire and explosion hazard. However, the invention has also been applied to the decontamination of gases and vapours contaminated by entrained liquids and solids in connection with the decontamination of air in paint shops, the removal of flyash and other contaminants from flue and exhaust gases etc. Because of improved contact between the gases or vapours and the scrubbing liquor and the effective subsequent disentrainment of the scrubbing liquor, the invention may even be employed for the removal of vapours or gaseous contaminants from a gas or vapour phase, e. g. in waste gas (e. g. flue gas) decontamination or in the purification of gases for industrial, e. g. chemical processes, whether or not the substances thus removed are to be discarded or otherwise disposed of or even be recovered for further use.

In accordance with the present invention the apparatus as set out in the introductory paragraph includes one or more or a combination of one or more of the following integers: a) at least one outwardly bulging liquor catching formation on a peripheral wall of the downstream disentrainment chamber, said catching formation extending radially from an axis of spin imparted to the flow of vapour or gas phase inside the disentrainment chamber, including a collecting and return passage, for directing disentrained scrubbing liquor including any contaminants contained therein towards the sump;

b) the propelling device is a centrifugally acting fan mounted coaxially with a central axis of the gas or vapour forwarding passage at the far end thereof and is freely exposed in the disentrainment chamber, likewise coaxially with the central axis of that chamber, that axis being is also the axis of spin imparted on the gas or vapour phase; c) a baffle provided between the sump and the gas or vapour forwarding passage, moderating the exposure of the scrubbing liquor in the sump to the agitating effect of the gas or vapour phase in the inlet chamber.

Preferably, at least two, more preferably all three of the aforegoing integers are present in combination.

Integer a), i. e. the outwardly bulging liquor catching formation serves to promote a more effective disentrainment of the liquid droplets and any solid particles contained in the droplets or still entrained in the gas or vapour flow.

This disentrainment results from the spin imparted on the gas or vapour flow by the gas or vapour propelling device and resulting centrifugal forces urging the liquid and solid particles against the peripheral wall of the disentrainment chamber and henceforth into the outwardly bulging liquor catching formation, forming a pocket, wherein the particles become caught.

Preferably, such catching formation commences substantially in tangential relationship to the portion of the peripheral wall which is upstream of the liquor catching formation in relation to the direction of spin, and from there expands progressively in the direction of spin radially to the axis of spin, terminating in a particle catching wall which is inwardly directed, preferably approximately radially, and links up, in the direction of spin, with the peripheral wall.

Preferably, the peripheral wall of the disentrainment chamber, except for the liquid catching formation (s) is of circular cross section, e. g. of cylindrical or frustoconical shape, preferably the former.

Also preferably the lowermost level of the liquid catching formation is above the level of the propelling device. It was found to be advantageous to prolong the contact in the disentrainment chamber between the spinning, liquor laden gas stream emerging from the propelling device and the contaminants in the gas stream in order to promote the transfer of the contaminants into the scrubbing liquor droplets and thereby enhance the scrubbing effect before enhancing the disentrainment of the droplets in the liquid catching formation.

Preferably, a single liquid catching formation is provided.

The aforesaid features pertaining to the liquid catching formation have been found to greatly contribute to the efficiency and completeness of the disentrainment of liquid and solid particles in the disentrainment zone as compared with the prior art apparatus of DE-PS 36 10 780. This was not to be expected.

In contrast to the prior art apparatus in accordance with DE-PS 36 10 780, the centrifugally acting fan, mounted at the far (downstream) end of the gas or vapour forwarding passage, in accordance with feature b), is freely exposed to the interior of the disentrainment zone. The prior art screen formation surrounding the fan, and the jacket surrounding that screen formation have thus both been dispensed with, resulting in an unexpected greatly improved throughput capacity and cleaning efficiency and an elimination of caking and clogging problems. The previously expected clogging up of the drainage holes between the disentrainment chamber and the inlet chamber and of the walls of the former, surprisingly did not become a problem.

A further improvement has resulted from the elimination of the vented encasement of the fan motor and the replacement of the latter by a simple waterproofed motor. This, moreover, resulted in improved cooling and easier cleaning.

As regards integer c), the purpose of the baffle is to regulate the effect of the cyclonic inrush of air, gas or vapour into the inlet chamber onto the surface of the scrubbing liquor in the sump so as to, on the one hand, cause adequate entrainment of scrubbing liquor in the forwarded gas phase for effective scrubbing action whilst, on the other hand, mitigating against the formation of waves and liquid surging as occurs with the prior art apparatus of DE-PS 36 10 780. In contrast to that prior art, where the length of the gas or vapour forwarding passage is telescopically adjustable, the length and position of the gas or vapour forwarding passage according to the present invention is preferably fixed.

Also in preferred embodiments of the present invention the inlet chamber includes spin inducing guide formations, for example worm-like ridges or webs projecting inwardly from the peripheral walls of the inlet chamber.

These ridges or webs may extend downwardly into the sump.

As in the case of the prior art apparatus of DE-PS 36 10 780, the apparatus as a whole is preferably substantially in the form of an upright cylinder, preferably having a substantially constant diameter, although it would be within the scope of the present invention for changes in diameter to occur at various levels, either stepwise or progressively.

The preferred apparatus according to the invention includes means for continuously or intermittently separating contaminant accumulating in the sump form scrubbing liquor in the sump. This may take place in the sump itself or in means external of the sump, e. g. as more fully disclosed in the

copending application of the same date entitled:"Gas Scrubbing and Scrubbing Liquor Recovery Apparatus".

Details of the means for separating off contaminants will depend on the nature of the latter, in particular, on whether the contaminants are solid or liquid or vaporous or gaseous and on whether they form a phase separate and distinct from the scrubbing liquor phase.

Quite generally, the invention may be used with procedures involving the addition into the sump or separator and concentrator vessel of various additives and auxiliaries, e. g. substances which in a manner known per se promote deemulsification and/or act as anti-foaming agents and/or as coagulants.

The invention will now be further described and explained by way of non- limiting example, with reference to the accompanying drawings, wherein Fig. 1 represents a diagrammatic vertical section of an embodiment of an apparatus in accordance with the invention; Fig. 2 represents a horizontal section through the disentrainment chamber along line ll-il in Fig. 1; Fig. 3 represents a partly sectionalised side elevation of a removable external contaminant separator and concentrator vessel for separating contaminants from the scrubbing liquor and recycling the latter into the system.

Referring now to Figures 1 and 2 of the drawings, the gas scrubber apparatus 1 in its preferred embodiment according to the invention as illustrated is composed of a number of basically cylindrical sections flanged together one on top of the other. The bottom section is the scrubbing liquor sump 2 onto which, by means of flanges 3, the inlet chamber 4 is fitted. The inlet chamber

4 has a gas or vapour feed passage 5 which enters horizontally and eccentrically and substantially in a tangential direction to the cylinder walls of inlet chamber 4.

Concentrically about the central axis 7 of the basically cylindrical apparatus 1 a slightly frustoconical gas or vapour forwarding passage 6, having its wider open bottom end slightly below the feed passage 5, tapers towards the gas or vapour propelling device 8. This takes the form of a centrifugal fan, likewise coaxial about the central axis 7 and opening directly and without any obstructions into the bottom end of the downstream disentrainment chamber 9 fitted by flange connections 12 to the top of the inlet chamber 4. The disentrainment chamber 9 is followed in upward direction by an outlet chamber 10 flange fitted at 13 to the top of the disentrainment chamber and terminating at its top in a slightly narrower gas outlet vent 11. A horizontal baffle 14 is fitted at the level of the flanges 12, partitioning the disentrainment chamber 9 from the inlet chamber 4. Near the outer walls of the apparatus the baffle includes a series of peripheral drainage apertures 15 which allow for substantially unimpeded drainage of disentrained liquor downward from the bottom of the disentrainment chamber through the inlet chamber 4 back into the sump 2. The fan 8 is driven by a coaxially fitted drive motor 16 supported on mounting brackets 17 spanning the downstream disentrainment chamber 9.

Just above the mounting brackets 17 thecylindricalwatt 19 of the disentrainment chamber bulges outwardly to form a liquor catching formation 18 which, viewed in the direction of spin 22 of the gas or vapour inside the disentrainment chamber and imparted by the spin 23 of the fan 8 flares radially outwardly until it terminates in an end wall 20 serving as a particle catching wall leading radially back towards the cylindrical peripheral wall 19.

Near that end wall 20 the catching formation has a drainage hole and passage 21, leading downward into the inlet chamber 4 and serving to return

scrubbing liquor and contaminants disentrained in the liquor catching formation downwards back towards the sump 2.

It is important to note that in contrast to the prior art apparatus according to DE-PS-36 10 780 the centrifugally acting fan 8 is mounted completely freely exposed in the bottom end of the disentrainment chamber 9, a feature which has been found to contribute greatly to the efficiency of the apparatus.

Further, in accordance with the invention, a baffle 24 mounted on a central pillar 26, adjustably fitted in a support sleeve 28 held by the support bracket 27 is held at a predetermined level above the scrubbing liquor level 25 in the sump 2. This baffle 24 serves to regulate the effect of the cyclonic inrush of air through the feed passage 5 and is designed to allow adequate entrainment of scrubbing liquor in the forwarded gas phase whilst mitigating excessive wave action in the sump. The level of baffle 24 is normally adjusted on the basis of experience at the time when the apparatus is set up for a particular industrial application and usually does not require further adjustment once the apparatus is taken into operation.

The sump 2 is frustoconically shaped at its bottom to promote a concentration of the contaminant sludge collecting at the bottom of the sump. On one side the sump comprises an open ended funnel-like inlet formation 30 through which the scrubbing liquor level can be observed and replenished when the need arises to make up mainly for evaporated losses.

As in the case of the prior art apparatus according to DE-PS-36 10 780 a perforated screen 31 is provided against the cylindrical wall of the inlet chamber 4, approximately opposite to the inlet end of the feed passage 5.

In order to further promote the cyclonic movement of the gas or vapour flow in the inlet chamber, the inside of the cylindrical wall of the inlet chamber comprises worm-like spin inducing invertly directly ridges.

The gas or vapour scrubbing apparatus described so far with reference to Figs. 1 and 2 operates as follows: The fan 8 spinning at high speed induces a suction effect by means of which the gas or vapour, e. g. dust laden air, is drawn in the direction of the arrow 60 with a spin into the inlet chamber 4 where, partly guided by the baffle 24, as shown by arrows 61 and 62, the gas sweeps over parts of the scrubbing liquor surface 25 in the sump and picks up a percentage of scrubbing liquor in droplet form before rising through the gas or vapour forwarding passage 6 in the direction of arrow 63 into and through the fan 8.

Inside the inlet chamber the gas already experiences a substantial degree of spin and cyclonic action causing mainly the larger dust particles to be urged against the cylindrical wall of the chamber and becoming disentrained and to drop down into the sump 2.

The fan 8 expels the air and gas laden with dust and entrained scrubbing liquor in the direction of arrow 64 at high speed and the gas continues to spin as indicated by arrow 22 in the disentrainment chamber 9 as the gas progressively rises towards the outlet vent 11 as indicated by arrows 65 and 66. As the gas and vapour phase rises, the entrained droplets and solid particles are progressively urged by centrifugal forces towards the cylindrical wall 19 and eventually into the outwardly bulging liquor catching formation 18. At that stage the liquor droplets have become thoroughly contacted with the contaminants in the gas or vapour phase, i. e. solid particles in the event of dust, or even vaporous or gaseous contaminants. These droplets settle out against the wall of 18 and the end wall 20 and drain downwards towards the liquor collecting and return passage 21 and from there back into the inlet chamber and down into the sump 2. Liquor settling out against the wall 19 likewise drains in downward direction under the action of gravity and passes through the apertures 15 of the baffle 14 to return to the sump 2.

The nature and composition of the scrubbing liquor will depend on the nature of the gases and vapours to be scrubbed and the contaminants to be removed therefrom. In many cases, particularly in the case of dust laden air withdrawn from sand or grit blasting chambers, the scrubbing liquor will be an aqueous liquor, more particularly water with or without additives. Additives may include wetting agents. They may also include anti-foaming agents to avoid excessive foaming in the sump. Additives may also be added which promote the segregation and aggregation of contaminants (whether liquid or solid) from the aqueous liquor in the sump. In accordance with preferred embodiments a separation of aqueous scrubbing liquor and contaminants accumulating in the sump is to be brought about in order to permit the scrubbing liquor to be used over and over again in the scrubbing process performed in the scrubbing apparatus. In accordance with the prior art apparatus described in DE-PS 36 10 780 such separation was confined to the sump itself where the higher density solids progressively settled and accumulated at the bottom of the sump which from time to time was removed from the bottom of the apparatus for removing and discarding the accumulated deposit and cleaning.

In accordance with the embodiment illustrated in the drawings, the separation of scrubbing liquor from contaminants has been transferred to an external contaminant separator vessel 33, which in this case takes the form of a free standing tippable waste container having a base 34 supporting a waste bucket hinged to the base via a hinge axis 35, its front wall taking the form of an oblique discharge wall over which, when the bucket is tipped around the hinge axis 35, the contents are discharged. Close to the rear wall 39 an internal partition 37 is provided, hinged to the inside of the side walls of the bucket at hinge point 38. The partition divides the bucket into a sludge settling chamber 53 and a clear liquor chamber 50.

At the designed liquid level 54 inside the bucket, the partition 37 comprises an overflow weir 40 shielded from the chamber 53 by a preceding baffle 42, the bottom edge of which forms an underflow weir 41. Rearward angular movement of the partition beyond the vertical position is prevented by one or more stop formations 45. Angular forward movement is possible as indicated by the arrow 44. A meandering path 43 is defined by the gap between the baffles 42 and 37 and the underflow and overflow weirs 41,40.

To the outside of the apparatus 1 a sludge pump 46 is mounted which through an intake pipe 47 withdraws sludge from near the bottom region 29 of the sump 2 and discharges it through a discharge pipe 48 onto a discharge baffle 49, mounted just above the liquor level 54 inside the sludge settling chamber 53 of the bucket. Sludge settles out in that chamber to an ever increasing level 52 whereas the supernatant clarifie liquor proceeds (path 43) into the clear liquor chamber 50. From there the clear liquor is picked up by a return pipe 51 and returned into the sump 2.

Some further details of the contaminant separator vessel are apparent from fig. 3 where it is shown that the partition 37 is hung inside an upwardly open- ended hinge pin support 100. It is also shown there that the tipping bucket is hinged to the support base 34 via a hinge bracket 101 coacting with the hinge pin 35. The support base 34 is rearwardly extended by an extension 108 to which, at hinge point 109, an upright locking lever 102 is hinged which carries a catch 104 coacting with a locking pin 103 mounted to the bottom end of the rear wall 39 of the bucket. Near the top of rear wall 39 an eye 110 is provided to which a locking loop 105 for the top of the lever 102 is articulated.

In normal operation and in the position shown in Fig. 3, the bucket of the contaminant separator vessel 33 is secured against tipping. Once the sludge level 52 has risen so much that adequate clarification of scrubbing liquor is impeded, the sludge pump 46 is stopped and the feed pipe 48 and return pipe 51 are disconnected to permit removal of the separator vessel 33. This

is done, for example, by a forklift which engages underneath support 34 to pick up the vessel and carry it to a dumping and discharge place. There the loop 105 is raised and disengaged from the lever 102 which is pulled back in the direction 106 for the catch 104 to be released from the locking pin 103.

The bucket is then tipped in the direction 107 about the hinge axis 35 in order to discharge the contents of the bucket, in the course of which the partition 37 swings forward in the direction 44. In order to facilitate cleaning of the bucket, the partition 37 may be lifted off the hinge pin support 100.

While the separator vessel is removed and emptied, a second similar vessel may be set up next to the scrubbing apparatus, so that sludge separation may continue almost without interruption. Alternatively, sludge separation is temporarily interrupted until the original separator vessel is returned to its previous position.

With the arrangement just described it was found that the scrubbing liquor near the top of the sump 2 is relatively clear so that effective gas and vapour scrubbing may proceed in the apparatus. Due to this feature as well as the remaining features of the scrubbing apparatus a high degree of decontamination of the gas or vapour stream was found to be achievable.

Due to the effectiveness of the separation taking place in the contaminant separator vessel it was possible to minimise losses of scrubbing liquor with the discarded sludge so that not much more liquor is lost than is due to evaporation in the scrubbing apparatus.

Due to the relatively low scrubbing liquor content of the sludge at the stage of it being tipped out and dumped, it was found that the sludge can be dried very rapidly. This is of importance if the sludge is to be subjected to further treatment under dry conditions, e. g. by magnetic separation in order to recover or separate magnetic components or any other forms of solid separation treatments.

Although the contaminant separator vessel and ancillary details thereof and used in connection therewith have been described as part of a preferred embodiment of the present invention, it is to be understood that alternative forms of separating contaminants from the scrubbing liquor accumulating in the sump of the scrubbing apparatus are possible. This can be done by alternative constructions of external separator apparatus, i. e. apparatus provided outside the scrubbing apparatus proper. Alternatively, suitable means for separating contaminants could conceivably be provided inside the scrubbing apparatus as such, e. g. inside or connected to the sump 2.

The following are typical dimensions and operating parameters for apparatus according to the invention, although it will be understood that where circumstances so require the dimensions may be larger or smaller in a manner readily understood by those skilled in the art.

The invention has been successfully performed in apparatus having total heights of from about 2 to 5 meters and diameters from about 40 to about 200 cm, although there are in theory virtually no real limitations to these dimensions.

For apparatus of the above described dimensions the following ranges of fan dimensions have been found particularly suitable:- fan height appr. 40-150 mm, preferably,. 60-120 mm fan diameter appr. 20-120 cm, preferably 28-90 cm number of vanes 4 to 20, preferably 7-10 fan motor about 2-100 kW, preferably 2,2-75 kW.

Inlet air velocities have been between 10 and 80/sec., preferably 18-40 m/sec. and air exit velocities (ignoring any ducting) 5 to 20 m/sec, preferably 7-14 m/sec., depending on type and size of plant.

Typical capacities within the above dimension ranges are about 2000- 40 000 m3/hr.

Typically the rate of withdrawal of scrubbing liquor from the sump and dispersion thereof in the gas or vapour flow entering the inlet chamber lies in the range of about 0,3-20 L/min, preferably 0,5-10 L/min for apparatus of the aforesaid dimensions. This is equivalent to about 1-3, preferably 1,5 ml/m3 of gas or vapour throughput.

With sandblasting where dust problems are particularly severe, dust values in the purified air of below 1 mg/m3 have been measured as compared with about 5 mg/m3, using the prior art apparatus according to DE-PS 36 10 780.

Filter cartridges or bag filters can usually be dispensed with.