GB2085526A

GB2085526A - Apparatus for pumping foaming liquids

Info

Publication number: GB2085526A
Application number: GB8131511A
Authority: GB
Original assignee: Sala International AB
Current assignee: Metso Minerals Sala AB
Priority date: 1980-10-20
Filing date: 1981-10-19
Publication date: 1982-04-28
Also published as: ES8207285A1; ES506344A0; ZA817013B; SE420230B; AU541997B2; DE3141578A1; FI71975C; GB2085526B; AU7663281A; FI813241L; FI71975B; DE3141578C2; SE420230C

Abstract

An arrangement for pumping foaming or frothing liquids comprises a pump connected to a sump (3), and at least that part of the sump located nearest the pump casing (1) has the shape of a truncated cone (5) with the apex directed downwardly. The pump impeller is arranged to impart a swirling motion to liquid supplied to the sump (3) via an inlet (7), such as to create a swirl or whirlpool having an air core (C). Arranged in the sump is a vent pipe (17) which is open at the top and which has a bottom opening in the air core (C) of the swirl or whirlpool. In this way the upper part of the air core is prevented from becoming blocked by foam or froth deflected towards the centre of the swirl, and gases released from liquid in the lower part of the swirl always have a free passage out of the sump (3). The pump motor (13) may be positioned above or below the sump. <IMAGE>

Description

SPECIFICATION Apparatus for pumping foaming liquids The present invention relates to an arrangement in apparatus for pumping foaming or frothing liquids, said apparatus comprising an impeller; a pump casing arranged around the impeller and having an outlet opening connected to a discharge line for the pumped liquid; a sump which is connected to the pump casing and of which at least that part located nearest the pump casing has the shape of a truncated cone, with the apex directed towards said casing, and has a substantially vertical axis; and at least one liquidsupply line which discharges into the sump.

Great difficulties are constantly experienced when pumping foaming or frothing liquids, because of the gases enclosed in the foam or froth. Examples of such liquids are flotation concentrates and aqueous solutions of various substances, in particular surfactants, although liquids not containing water may also create large quantities of froth or foam. The pumping of frothing or foaming liquids is also particularly problematic in horizontal centrifugal pumps, since an air lock is liable to form at the centre of the impeller. Attempts have been made to solve this problem by using a centrifugal pump having a vertical axis, where the pump casing is connected directly to the bottom of the sump. The pump shaft passes through the inlet opening of the casing, and the pump-driving mechanism is mounted above the sump.The gases enclosed in the foam or froth can then escape through a swirl or whirlpool having an air core surrounding the pump shaft.

In such so-called vertical pumps it has been found of particular advantage when the part of the sump located nearest the pump-inlet opening is of frusto-conical configuration, with the apex directed downwardly. Such a sump affords particularly favourable conditions for the rotation of the impeller to impart a swirling motion to the liquid in the sump. As a result of this swirling motion, liquid and any solid particles present will be urged towards the conical wall of the sump by centrifugal force, the foam or froth being collected in the centre of the swirl and broken-up at the same time. It has been found particularly advantageous when the liquid is supplied tangentially, in the direction of the swirl.A pump of this kind, however, still has a venting effect on the foaming or frothing liquid, even when the liquid is supplied vertically, and also even when fed tangentially in counter-direction to the swirl.

As liquid is supplied to the pump sump, fresh bubbles can form as a result of air being entrained with the inflowing liquid. Bubbles of froth or foam may also be broken Up by the inflowing liquid.

Pump sumps of frusto-conical configuration often have a ring of some one decimeter width around the inside of the upper edge thereof, said ring partly serving as a structure reinforcement and partly to prevent liquid in the sump from being thrown over said edge by the strong swirling motion.

When pumping foam which is particularly tough and difficult to break-up, a pump of the aforedescribed kind has not been found totally satisfactory, however. The foam is not broken-up by the swirling motion quickly enough, and hence the centre of the whirlpool or swirl is filled with foam, and ultimately the foam or froth will run over the upper edge of the sump. The relatively light foam or froth does not obtain the same speed of rotation as the remainder of the swirl, and can therefore fail down into the centre of the swirl.

This is aided by the presence of the aforementioned ring around the upper edge of the sump. Those bubbles which are broken-up and dispelled in the lower part of the whirlpool will then be recreated by the formation of fresh bubbles between the sinking froth or foam and the inner wall of the swirl or whirlpool. When the load of liquid entering the pump is high, so much foam will be collected and deviated towards the centre of the whirlpool as to close the open air core. The gas released in the lower part of the whirlpool will then have no outlet. In this way, an airlock can be created in the sump, despite the fact that it is a vertical pump and the pump capacity decreases considerably. This results in the foam or froth running over the edges of the sump, down onto the ground.

An object of the present invention is to provide pumping apparatus in which the aforementioned disadvantages are at least substantially eliminated. To this end it is proposed to arrange in the sump, for venting the gases released from the foaming or frothing liquid, an elongate vent means or connecting passage having an upper opening against the surrounding atmosphere and a lower orifice located at least partially within the central swirl or whirlpool created in the sump during a pumping operation, i.e. the lower orifice at least partially covers the air core of the swirl or whiripool. The upper part of the vent means is suitably connected to a lid covering the sump.

Three advantages are afforded by the apparatus according to the invention; to wit, a) the vent means prevents foam or froth in the upper part of the sump from falling down into the air core of the swirl or whirlpool, b) the vent means forces all liquid and all bubbles to pass through a zone in the lower parts of the sump, where a vigorous swirling motion is created by the rotation of the impeller, and therewith a strong centrifugal force which contributes to separating liquid and foam or froth and to breaking-up the bubbles, and c) the vent means, above all, prevents foam or froth in the upper part of the sump from being deflected inwardly so as to completely close the air core of the swirl or whirlpool, which would prevent the escape of gases released in the lower part of the sump.

Suitably, the pump is a vertical pump having drive means mounted over the sump, so that the drive shaft passes through the inlet opening of the pump casing and also through the vent means, such as to provide an open air-gap between the drive shaft and the inner wall of the vent means.

This positioning of the drive means, however, is not a necessary feature of the invention, since the pump drive shaft may also pass the wall of the pump casing on the side remote from the inlet opening, For the satisfactoryfunctioning of the invention it is absolutely necessary for the impeller to impart a swirling motion to the liquid in the sump. When the pump shaft passes through the wall of the pump casing, the pump shaft may be substantially vertical and therewith coincide with the axis line of the truncated cone. The pump shaft and the axis of rotation of the impeller, however, may also deviate from the axis line of the truncated cone when considered suitable, provided that the main requisite of the invention is fulfilled, namely that the impeller imparts a swirling motion to the liquid in the sump.

In accordance with the invention, the area and length of the vent means can be varied within wide limits. The largest cross-dimension of the vent means, however, should not exceed half the diagonal of the truncated cone at its upper end, and neither should it be less than 1/1 ooth of this diagonal. In the majority of cases, the largest diagonal should not exceed 1/3rd of the largest cone diameter.

The length of the elongate vent means should not be less than 1/1 ooth of the depth of the sump, and neither should said length exceed 4/5ths of said depth, otherwise there is a risk of throttling the liquid flowing to the inlet opening of the pump casing. These extreme values relating to the length of the vent means can only be applied with certain vent cross-sections, otherwise no foam or froth-damping effect is obtained and/or the pump capacity is reduced.

A better venting effect is obtained when the length of the vent means is between 1/5th and 3/5ths of the depth of the sump, since in this case the overall effect obtained is not so dependent on the selection of correct dimensions with respect to the cross-section of the vent means. This dependency is still less when the length of the vent means is between 1/4 and 2/3rds of the depth of the sump.

Optimal venting can be expected when the length of the vent means is between 1/3rd and a half of the sump depth. The largest diagonal of the vent means should not then exceed 1/3rd of the largest diameter of the truncated cone.

Suitably, the vent means is a cylindrical tube which is coaxial with the axis line of the truncated cone. This is not limitative of the invention, however, since the vent means or connecting passage may have a cross-sectional shape other than circulr, if no access can be had to a tube of suitable dimensions. Furthermore, it is not necessary for the vent means to be coaxial with the axis line of the truncated cone, but that the centre line of the pipe can deviate from said axis line when considered necessary, for example, for structural or design reasons. The vent means may also extend completely or partially outside the axis line of the truncated cone.

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 is a partly cut-away sectional view of a pump provided with an arrangement according to the invention, in which the drive means are mounted on top of the pump sump, and Figure 2 is a partly cut-away sectional view of a further embodiment of the invention, in which the pump drive means are mounted beneath the sump.

Figure 1 illustrates a pump having an arrangement according to the invention, comprising a pump casing 1 and an impeller (not shown) arranged for rotation in said casing. The pump casing is connected to a discharge pipe 2 by means of a bolt connection (not shown), and to a sump 3 via a flange connection 4. The part of the sump 3 located nearest the pump casing 1 is of frusto-conical configuration 5, with the apex directed towards the casing 1. The upper part of the sump consists of a cylinder 6, to which there is connected a substantially tangential liquid inlet 7.

The sump is supported by three legs 8, of which only two are shown in the Figures. The legs rest freely on a foundation 9, or may be bolted thereto.

The pump-drive means comprises a drive shaft 10, a bearing housing 11, a V-drive with belt-guard 12, and a pump motor 13. The bearing housing 11 and the pump motor 13 are bolted to a frame structure 14, which is firmly mounted on top of the sump. The sump is covered by a lid 1 5.

Arranged in the centre of the lid 1 5 is an opening 16 to the defining surfaces of which connect to a vent pipe or connecting passage 1 7 for gases released from the frothing liquid. The vent means 17 surrounds the drive shaft 10 and exhibits therebetween an air gap through which the released gases canvass from a lower opening 18, through the gap and out through the upper opening 1 6 and from there to the surrounding atmosphere. In this embodiment the axis line 1 9 of the truncated cone coincides with the rotary axis of the drive shaft and with the vertical.

The right-hand half of the Figure illustrates the function of the arrangement, by showing the various zones of liquid, froth or foam and free gas.

Rotation of the impeller creates a vigorous swirling motion, which propagates through the inlet opening of the pump and up into the sump.

This swirling motion is strongest in the part of the sump located nearest the inlet opening. As a result of centrifugal force, liquid and any solid particles present will be thrown up against the outer wall 5, 6 of the sump and there form an outer zone A comprising substantially solely liquid and any solid particles present..Located inwardly of the outer zone A is an inner zone B comprising froth or foam. The size of the bubbles present in the froth or foam zone increases towards the centre of the whirlpool or swirl.In the centre, surrounding the pump shaft, there is a central open air core (C) in the swirl or whirlpool which freely communicates with the surrounding atmosphere through the connecting passage or vent means 1 7. As will be seen from the Figure, in the illustrated embodiment there may exist a circular zone D of air in the angle between the lid 1 5 and the vent means 1 7. In order to prevent excessive quantities of air from being trapped in zone D, evacuation orifices 30 are arranged in the wall of the connecting passage or vent means 1 7.As will be seen from the drawing, the outer wall of the vent means 1 7 prevents foam or froth present in the upper part of zone B from penetrating and fully blocking the air core C in its uppermost part, such as to close the free passage to atmosphere for the gases released in the lower parts of the sump.

Figure 2 iilustrates a further embodiment of an arrangement according to the invention.

Corresponding elements have been identified with the same references as those used in Figure 1, and coincide in all details with the previously described embodiment. The difference between the Figure 2 embodiment and the Figure 1 embodiment resides in the fact that the pump drive-shaft 20 passes the wall of the pump casing 1 on the side thereof remote from its inlet opening. The bearing housing 21 of the drive shaft is firmly connected to a mounting flange 26 on the wall of the pump casing 1, via legs 25. The bearing 21 and the V-drive 22 of the pump are protected against leaking liquid by a stuffing box 27 and a slinger 28.

The V-drive 22 together with its belt guard must be particularly designed to protect the belt against falling liquid. The pump drive motor is mounted on one of the three legs 8 of the sump by means of a mounting plate, which cannot be seen in the drawing. The pump may also be driven in some other manner, not shown, for example via an angle gear or by a direct drive, flange-mounted motor.

In the embodiment of the invention illustrated in Figure 2, the drive shaft of the pump does not occupy space in the air core C, as in the case of the Figure 1 embodiment. In this way there is obtained a whirlpool or swirl with a larger open surface of the air core. On the other hand, movement of the pump shaft does not help to break-up the foam or froth. In order to afford the bearing housing, transmission and drive motor some protection against leaking liquid, the pump casing may be connected to the sump by means of an elbow pipe although the venting effect will then be weakened. The impeller, however, can still impart to the liquid in the sump a swirling motion even when the connection between pump casing and sump is not straight, although in this case said swirling motion is weaker than what would otherwise be the case. As will be understood, the venting effect obtained is, however, superior to that obtained with a sump which completely lacks any form of vent means or connecting passage 1 7.

The described embodiments are not restrictive, but can be modified within the scope of the following claims.

Claims

1. An arrangement in apparatus for pumping foaming or frothing liquids, comprising an impeller; a pump casing (1) arranged around said impeller and having an outlet opening connected to a discharge line (2) for pumped liquid; a sump (3) which is connected to the pump casing and of which at least that part located nearest the pump casing (1) has the shape of a truncated cone (5) with the apex directed towards said casing (1) and has a substantially vertical axis (1 9);; and at least one liquid supply line (7) discharging into the sump (3), characterized in that arranged in the sump (3) is an elongate vent means (17) for venting gases released from the foaming or frothing liquid, said vent means having an upper opening (16) against the surrounding atmosphere, and a lower opening (1 8) located at least partially within the air core (C) of the swirl or whirlpool created in the sump (3) when the pump is operating.

2. An arrangement according to claim 1, characterized in that the upper part of the vent means (17) connects with a lid (15) covering the sump (3).

3. An arrangement according to claim 1 or claim 2, characterized in that the upper part of the sump (3) has the form of a cylinder (6) which connects with the conical part (5).

4. An arrangement according to any one of the preceding claims, characterized in that the impeller is arranged to impart a swirling motion to liquid present in the sump (3).

5. An arrangement according to claim 4, characterized in that the pump drive-means (11, 12, 13) are mounted above the sump, and the drive shaft (10) passes through the inlet opening of the pump casing and through the interior of the vent means (17), so as to provide an air gap between the drive shaft (10) and the inner wall of said vent means (17).

6. An arrangement according to claim 4, characterized in that the pump drive shaft (20) passes through the wall of the pump casing (1) on the side thereof remote from the inlet opening.

7. An arrangement according to claim 5 or claim 6, characterized in that the rotary axis of the impeller coincides at least approximately with the centre line (19) of the truncated cone (5).

8. An arrangement according to any one of the preceding claims, characterized in that the vent means (17) is a cylindrical pipe.

9. An arrangement according to claim 5 and claim 8, characterized in that the cylindrical pipe (17) is concentrical with the pump shaft.

10. An arrangement according to any one of the preceding claims, characterized in that the largest cross dimension of the vent means (1 7) is between one 1/2 and 1/1 ooth of the diagonal of the upper part of the truncated cone (5).

11. An arrangement according to any one of the preceding claims, characterized in that the vent means (1 7) extends downwardly to between 1/1 ooth and 4/5ths of the depth of the sump (3).

12. An arrangement according to any one of the preceding claims, characterized in that the vent means (17) extends down to an extent between 1/5th and 3/4 of the depth of the sump (3).

13. An arrangement according to any one of the preceding claims, characterized in that the vent means (17) extends down to between 1/4 and 2/3rds of the depth of the sump (3).

14. An arrangement according to any one of the preceding claims, characterized in that the vent means (17) extends down to between 1/3rd and a half of the depth of the sump (3) measured from its upper edge.

1 5. An arrangement in apparatus for pumping foaming or frothing liquids substantially as herebefore described with reference to and as illustrated in Figure 1 or Figure 2 of the accompanying drawings.