GB2110952A - Gas scrubbing and demisting - Google Patents

Abstract

A purifier for purifying spray mist containing air through contact with purifying water comprises one or more concave guide surfaces (5) extending downwardly from one or more purifying water flowdown walls and one or more inlet passage (22) defined along an upper portion or portions of the guide surface or surfaces to provide passage for the spray mist containing air. The arrangement may be installed in the floor (13) of a paint spray booth. 2 concave surfaces back to back may be used as shown; Fig. 9 shows them in facing arrangement and Figs. 10, 11 show a single such surface. <IMAGE>

Description

SPECIFICATION Spray mist containing air purifier The present invention concerns a purifier for spray mist containing air in a spray booth in which spray painting is applied to automobiles or the like.

Overspraying in the paint spray booth produces a mist of superfluous paint suspended in the air which adheres to the interior walls of the booth and in particular deteriorates atmospheric environment for the workers. To avoid these undesirable consequences the following measures are taken: 1) The booth is provided at the ceiling with means to supply fresh air.

2) The booth is provided with a grating floor; blowers and exhaust plenum chambers are also provided in order to withdraw the spray mist containing air downwardly from the floor for separating the spray mist from the air and release of the resu Iting clean air to the ambient atmosphere.

3) Purifying water is used to contact the spray mist containing air underneath the grating floor and upstream of the blower in order to trap the spray mist in the air thereby cleaning the latter.

4) The water which has trapped the spray mist is led to a separating bath in which spray sludge is separated from the water, the resulting clean water being recirculated by pumps for further use.

Commonly practised methods of bringing the spray mist containing air into contact with purifying water in the measure (3) above include a target method as shown in Fig. 1 of the accompanying drawing, a deflection method as shown in Fig. 2, and mixtures of the above two methods as shown in Figs. 3 and 4. In these figures,A indicates the spray mist containing air, W indicates the purifying water, 1 indicates a target plate and 2 indicates a deflector plate. While the four methods as shown have their advantages and disadvantages, the problem common to all is that the spray mist separating efficiency is not satisfactory and in particular they are unable to carry out complete separation of a spray mist having small particle diameters (10 microns or less).

An object of the present invention is to avoid the disadvantages of the prior art, and to achieve a higher spray mist separating efficiency.

An example shown in Fig. 5 is now considered with respect to inertia separation relied on for the main separating function, as far as Stokes' law of resistance is applicable. In this Fig. 3 indicates a concave guide surface for purifying water and spray mist containing air, 4 indicates an inlet to the guide surface, 0 indicates the centre of curvature of the guide surface 3, a an effective centric angle thereof, Ran effective radius derived by subtracting 1/2 of the transverse dimension b of the inlet 4 from the radius of curvature of the guide surface and V indicates air flow velocity at the inlet4.Disregarding reduction of the air flow velocity for primary approximation and supposing R 2 b, the distance X(d) by which parti cites of the spray mist move radially outwardly by centrifugalfornes within the centric angle of rad. is derived from the followingequztion.

X(d)= a(pplpl)y .d2 (1) 18y Wherein di is particle diameter (m), pp is particle density (kg/m3), p is air density (kg/m3 ), and zy is kinetic viscosity coefficient of air.

Where X(dc)=b, in which dc is a critical diameter for trapping, particles whose diameters d are greater than dc get trapped in the water and those whose diameters d are smaller than dc remain in the air. In other words, the smaller the diameter, the more difficult is the particle to trap.

Measures to decrease the critical diameter for trapping require the foregoing equation (1) to be modified by (1) increasing ex, or increasing circumferential length L, (2) decreasing X(d) orb, or (3) increasing v. The present invention lays stress on the above alternative (1).

In a purifier for spray mist containing air in a spray booth according to the invention, a concave guide surface is defined extending downwardly from a purifying waterflowdown wall to guide the purifying water and spray mist containing air, the guide surface having a continuous arc or like shape including a vertical or like surface at an intermediate position between top and bottom ends thereof and tangents extending from the top and bottom ends in horizontal directions or in directions slightly inclined therefrom, and inlet passage means is defined along an upper portion of the guide surface to provide passage for the spray mist containing air.

The nature of the above-mentioned concave guide surface is briefly described referring to Figs. 6a, 6D, 6e and 6d. As seen, the guide surface may have an upper starting point at P1, P2 or P3 and a lower terminal point at Q1, Q2 or Q3. Points P1 and Q1 are at positions right above and below the centre of curvature O of a circuleE, respectively. Points P2, P3, Q2 and Q3 are at positions from which tangents extend at angles of 40 degrees or less, preferably 30 degrees or less and more preferably 15 degrees or less, to the horizontal.

The shape of the guide surface 5 relative to the circle E may be such that the guide surface 5 coincides with the circle E as in Fig. 6a, an upper half of the guide surface 5 departs outwardly from the circle E as in Fig. 6b, a lower half thereof departs from the circle E as in 6c, or both upper and lower halves depart from the circleE as in Fig. 6d. The examples of Figs. 6b to 6d may have a deflected guide surface.

While there is no restriction in principle to the degree of departure from the circle, the centre of curvature or the radius, the degree of departure preferably is minimal. Number 6 in the drawings indicates flowdown walls for the purifying water.

As will be understood from the foregoing examples, the critical diameter for trapping of spray mist particles is considerably decreased according to the invention compared with that in the prior art by providing a concave guide surface of sufficient circumferential length, which istheoretical ly supported by the equation (1). In other words, the simple strut tural improvements inthe guide surface alone result in advantagesoverthe known construction that smaller particles are separated at title sameseparat- ing efficiency while the particles of the sarne size are separated at a higher separating efficiency.

For the foregoing solution (2) the inlet passage for introducing the spray mist containing air may be divided. In particular, the inlet passage divided into two has advantages (1 ) that the particle diameter for trapping is smaller than in the prior art since the inlet dimension b is halved while the flow velocity remains the same, (2) that with the diameter for trapping unchanged, that is the dimension b remaining the same as in the undivided inlet, the flow velocity Vis a/1/2 and pressure loss therefore is 1/2 thereby saving energy, and (3) that the flow velocity may be determined at a median between those in the cases (1 ) and (2) above. (Q=S x v) In practising the invention it is perfectly in order to employ measure (3) in combination with measures (1)and(2).

In the drawings already mentioned and de scribed :- Figs. 1,2,3 and 4 are sectional views each showing a principle of a known purifier for spray mist containing air, Fig. 5 is a view showing inertia separation, Figs. 6a, 6b, 6cant 6d are sectional views each showing an example of concave guide surface.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Fig. 7 is a vertical section of a purifier according to the invention in its near entirety; Fig. 8 is a vertical section of a principal portion of a modified purifier; Fig. 9 is a section of an alternative embodiment of purifier; Fig. 10 is a section of another alternative embodiment of purifier; and Fig. 11 is a section of yet another embodiment of purifier.

Referring to Figs. 7 and 8, 7 indicates a spray booth, 8 indicates walls, 9 a grating floor, 10 an object to be painted such as an automobile body, 11 indicates a dolly, 12 purifying water supply headers, 13 wash trays gently sloping toward drain ports and 14 and 15 indicate continuous elongate partition plates whose outer surfaces act as flowdown walls 6.

16 indicates inclined bottom plates, 17 a drain channel and 18 a duct leading to an exhaust plenum chamber. Broken lines A shown air flows and solids lines Wshown water flows. Dots indicate particles of spray mist. 19 indicates continuous elongate tub-like guide plates in the form of circular arcs extending# over 1800 and defining concave guide surfaces 5 on inside face thereof 20 indicates downwardly wind ing target plates which may be omitted. 2f indicates guide plates defining a passage 22 to introduce spray mist containing air along upper portions of the guide surfaces 5. The guide plates 21 also receive overflows of purifying water. The flowdown walls 6 and the inlet passage 22 have a common opening 23 to the spray booth 7.In these embodiments the two guide plates 19 are arranged back to back to greatly facilitate removal of paint sludge adhering to the guide surfaces 5 though wEe ope#n#sextencling over )80". Preferablythe guide surfaces s are coated with Teflon (R.T.M.) or other material effective to prevent adhesion thereto of fine particles of paint.

Purification of the spray mist containing air is effectively carried out by inertia separation at the guide surfaces 5 and by impact separation at the target plates 20.

Fig. 9 shows a modified purifier in which the two guide plates 19 are frontally opposed to each other and have a common target plate 20. A centre supply header 12 is disposed between air guide plates 21 to cause the purifying water to flow over through openings 23 at the tops of the guide plates 21.

The modification shown in Fig. 10 comprises one opening 23, one guide plate 19 and one guide plate 21.

In Fig. 11, the flowdown wall 6 and the inlet passage 22 communicate with the spray booth 7 via respective openings 23' and 23".

While the target plate or plates 20 as shown in Figs. 8 and 9 are omitted from the embodiments of Figs. 10 and 11, the latter embodiments are provided with winding target plates as shown in Fig. 8 or a flat target plate at right angles to the air and water flows as shown in Fig. 9.

Claims (6)

1. A purifier for purifying spray mist containing air through contact with purifying water, in which at least one concave guide surface is defined extending downwardly from at least one purifying water flowdown wall to guide the purifying water and spray mist containing air, the guide surface having a continuous arcuate or the like shape including a vertical or the like surface at an intermediate position between top and bottom ends thereof and tangents extending from the top and bottom ends in horizontal directions or in directions slightly inclined therefrom and an inlet passage means defined along an upper portion of the guide surface to provide passageforthe spray mist containing air.

2. A purifier as claimed in claim 1, in which the guide surface is in form of a circular arc having a centric angle of 1800 or approximately 1800.

3. A purifier as claimed in claim 2, in which the flowdown wall and the inlet passage means have a common opening to a spray booth.

4. A purifier as claimed in claim 1, in which the inlet passage means has a bottom upper surface also acting as a flow surface for the purifying water.

5. A purifier as claimed in claim 1, 2 or 3, in which the inlet passage means for introducing the spray mist containing air is branched right and left at a transversely intermediate position of the opening.

6. A purifier constructed and arranged to operate substantially as herein described with reference to and as illustrated in any of Figs. 7 to 11 ofthe accompanying drawings.