Method And Apparatus For The Removal Of Entrained Gases From Mineral Slurries, Pulps, Liquids, And The Like

Abstract

A deaerator comprising a rotating chamber having a nozzle exhausting by centrifugal force the liquid of an entrained gas/liquid feed into an outer liquid body while the entrained gases are withdrawn from the interior of the chamber through a separate gas outlet under a reduced pressure.

Description

In the design of a liquid handling system which usually involves the use of various pumps, agitators, beaters and other devices which tend to entrain air or other gases in being operated, it usually follows that a substantial amount of gas is suspended as bubbles in the liquid. This results in both the liquid and gaseous phase being present which may have an adverse effect on either the process treating steps or the instrumentation or both. If measurements are required to be taken and the instruments used are sensitive to entrained gases, then it is a necessity for this entrained gas to be eliminated to permit accurate measurements to be taken.

While there are deaerating systems in the prior art that make use of vacuum and centrifugal force or a combination thereof to remove entrained air from liquids, they usually discharge through a pipe or scoop which dips into the rotating fluid and picks off the bottom layer. The pipe is subjected to severe and rapid abrasive wear since it must be stationary relative to the fluid. The pipe produces turbulence within the liquid body and may be the origin of reaeration. None of the prior art devices are as free from abrasion difficulties or turbulence reaeration as the present invention. The patent to Rich, U.S. Pat. No. 3,371,059, is directed to apparatus for the treatment of liquids to separate gas therefrom by combined use of centrifugal and elastic wave energy. The liquid to be treated is fed centrally into a rotating drum which throws the heavier liquid to the outside of the drum leaving a center hollow portion containing bubbles. This center portion is subjected to elastic wave energy to break the bubbles and a pair of stationary pipes are positioned with an inlet of each within the outer layer of rotating gas free liquid where the liquid is withdrawn. The patent to Humfeld et al., U.S. Pat. No. 2,542,031, is directed to a fermentor for submerged cultures having both aeration and foam breaking devices. The foam breaker comprises a pair of cones and a disc located above the normal liquid level in the vessel. The patent to Diamant et al., U.S. Pat. No. 3,249,554, is directed to apparatus for breaking foam and comprises the drawing of foam through a rotating impeller which serves to beat the foam and reduce its volume. The patent to Forrester, U.S. Pat. No. 2,908,652, is directed to apparatus for defoaming liquids and comprises a cylindrical tank under reduced pressure. An outlet for discharge of de-aerated liquid is provided in the bottom. A vertically positioned rotating shaft is axially positioned in the tank and a plurality of vertically disposed horizontal paddles mounted thereon for agitation of the liquid to be treated. The patent to Gates, U.S. Pat. No. 2,366,513, is directed to a method of breaking foam by separating the foam from the liquid and subjecting it in the form of a relatively small stream to impact against a surface and allowing the liquid and gas components to separate. None of the prior art workers have been able to provide a suitable dearation system to remove entrained gas from a liquid stream.

It is an object of this invention, therefore, to provide an improved deaeration system.

It is a further object of this invention to provide a deaeration system for use with liquids containing abrasive solids.

A still further object of this invention is to provide a deaeration system which has a minimum amount of reaeration after deaeration.

A further object of the invention is to provide a deaeration system which is easy to maintain and operate and which is readily and economically manufactured.

In accordance with the invention there is provided a deaerator comprising an outer liquid receiving tank and an inner concentrically positioned rotating hollow chamber having an enlarged portion connecting a centrally positioned inlet. The enlarged portion is provided with one or more nozzle openings positioned about the largest diameter thereof and means producing a reduced pressure within the enlarged portion of the chamber. A plurality of nozzle openings may be provided or a single annular slot as the discharge for deaerated liquid into the outer body of liquid below the normal operating level of the liquid.

For a better understanding of the preent invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

In the drawings:

FIG. 1 is an elevational view partly in cross section of a deaerator according to the present invention;

FIG. 2 is a cross sectional view to an enlarged scale showing the details of the rotating vacuum seal;

FIG. 3 is a view along line 3--3 of FIG. 1; and,

FIG. 4 is a cross sectional view in elevation partly broken away to conserve space showing another form of the rotating chamber arrangement.

Referring now to the drawings and in particular to FIG. 1, there is shown a deaerator 10 which is seen to comprise generally an outer cylindrical tank 12 having a liquid outlet 14 centrally located in the bottom thereof and containing an inner rotatable chamber 62 with an inlet 16 communicating the interior of rotatable chamber 62 and from thence to the interior of tank 12 through ports 68. The top of tank 12 has attached thereto a bearing support plate 18 transversely of the top and secured thereto by means of bolts 20. Bolts 20 also secure to the support plate a cylindrical extension 22 of tank 12. The upper end of extension 22 is closed by top 23 except for a centrally positioned opening 24 therein. Also the extension has a horizontally positioned slot 26 in the side wall near the top to accommodate passage of drive belts 28 therethrough as will be explained as the description progresses.

A hollow cylindrical bearing housing 30 having upper and lower outturned mounting flanges 32 and 34 respectively has the lower flanges 34 bolted to the support plate 18 by means of bolts 36. Housing 30 also has at the lower extremity an inturned flange 38. The flange 38 has a stepped portion which supports the outer race of bearing 40. The upper extremity of housing 30 is provided with an annular shoulder which supports the outer race of bearing 42 in vertical spaced coaxial relation to bearing 40. The inner races of bearings 40 and 42 receive and support tubular member 44 for rotation. The upper end of member 44 is of a diameter greater than the opening in the inner race of bearing 42 and provides a shoulder which is supported vertically by bearing 42. The lower end of member 44 and the opening in the inner race of bearing 42 is of a smaller diameter and the larger diameter of the member above provides a shoulder which is supported by bearing 40. A seal in the form of an elastomer ring 46 is positioned in sealing relation between the inturned end of flange 38 and the O.D. of member 44.

A plate 48, having a center opening 50 therein, is secured to the top of housing 30 as by means of bolts 52. The center opening of plate 48 is of a size to accommodate the largest diameter of tubular member 44. The opening 50 is provided with a step forming a shoulder and a seal in the form of an elastomer ring 54 is positioned in sealing relation between the shoulder of opening 50 and the enlarged portion 56 of member 44. Member 44 above enlarged portion 56 is of a reduced diameter and has mounted thereon and secured thereto in suitable fashion a pulley 58 for rotation therewith. The lower end of member 44 is provided with external screw threads, shown dotted. A tubular extension 60 is threadedly attached to the lower end of member 44 and a splash plate 61 having a center opening receiving the lower end of member 44 is held against a shoulder therein in close proximity to the bottom of support 30 by the upper end of extension 60. To the lower end of extension 60 is attached the inner rotatable chamber 62 which is shown in the preferred form of a pair of spherical segments positioned for rotation about its axis of revolution. The chamber 62 is secured to extension 60 in suitable fashion and the inner and outer walls of the chamber 62 are covered by a coating 63 of elastomer to resist abrasion wear. The bottom of chamber 62 is provided with a clean-out opening 64 which is normally closed by a cover 66. The walls of chamber 62 are provided with a plurality of apertures 68 positioned in spaced relation about the largest diameter thereof in a plane normal to the axis of rotation. The apertures serve as nozzles to discharge deaerated liquid to the tank 12 below the liquid level 98 as will be explained. Apertures 68 may be a number of discrete openings or a continuous slot sized to provide an adequate flow rate of liquid therethrough.

The opening 24 in the top 23 of extension 22 is provided with a cap 70 having a central bore 72 therein and secured to the top 23 by screws 74. The bore 72 is threaded and the inlet pipe 16 is threadedly received in the upper end thereof. The lower end of bore 72 threadedly receives the center feed pipe 76 which passes downwardly inside tubular member 44, extension 60 and into the interior of vessel 62 terminating just above cover 66 of the clean-out opening on the bottom of the vessel. The cap 70 is provided with a downwardly directed annular slot 78 which receives the upper tubular end of tubular member 44 within slot 78. The inner diameter of member 44 is provided with a reduced diameter portion to provide a shoulder 79 at a position approximating the location of the pulley 58. The shoulder 79 supports a seal 80 which is held in place by a keeper 82 and a spring 84 bearing against the keeper 82 and a downwardly directed shoulder 86 on cap 70. The seal 80 provides a gas tight seal between the space 87 communicating the interior of vessel 62 and the ambient atmosphere. Cap is provided with a vacuum inlet 88 which is connected to a vacuum line 90. Vacuum inlet 88 communicates the inner bore of cap 70 which is in communication with the space 87 within tubular member 44 between which and the outside of cap 70 seal 80 acts. Referring to FIG. 2 it will be seen that seal 80 is made up of parts 80a, 80b and 80c which cooperate to provide the necessary sealing action.

The interior of tank 12 is provided with a plurality of radially positioned vertical baffles 92 above and 94 below vessel 62. A horizontal baffle 96 is positioned within tank 12 above vessel 62 and below the normal liquid level 98. A motor 100 is mounted on the side of tank 12 exterior thereof by means of suitable motor mounts 102. The rotating shaft 104 of motor is fitted with a pulley 106 in which run belts 28 to provide transfer of rotary motion from motor 100 to vessel 62 via pulley 58.

An outlet 108 is connected to outlet 14. Pipe 108 is provided with an upright leg 110 which includes at the upper end thereof a chamber 112 which may conveniently contain sensors for measurement of the parameter of the deaerated liquid. Chamber 112 is provided with an overflow 114 the height of which establishes the normal liquid level 98 in tank 12. The side wall of tank 12 has an opening 116 therein which will serve as an overflow port to prevent level 98 from accidentally rising too high and damaging seal 46, bearing 40, etc. Cap 70 is provided with a lubrication tube 118 whereby lubrication may be supplied to seal 80.

In operation, a source of vacuum is connected to vacuum line 90. This may conveniently be an aspirator type pump. A feed slurry to be treated is introduced through pipe 16 into vessel 62 which is rotated by motor 100 through belts 28. Pipe 16 may be provided with a valve, not shown, to control the flow rate. The level of the liquid 77 in vessel 62 is normally at least as high as necessary to balance the vacuum drawn. The vacuum pump provides the reduced pressure in the rotating vessel necessary for start-up and exhausts gases removed from the process fluid through centrally located gas outlet passage 87 inside of shaft 44 through passage 88 and vacuum line 90. The incoming fluid to be deaerated is carried to the bottom surface of the rotating vessel. The fluid flows outward and assumes a level 77 within the vessel at which the centrifugal force acting on the fluid is just counteracted by the pressure differential between the interior of vessel 62 and the interior of tank 12 which is vented to atmosphere. During the time that the liquid is in the rotating vessel, it is acted upon by the combination of low ambient pressure and centrifugal force which causes the bubbles of entrained air and foam to move toward the center and be drawn off through the vacuum line. The deaerated liquid or slurry is exhausted through the peripheral apertures 68 in the walls of the rotating chamber, issues into the fluid body surrounding same well below the liquid level 98 to prevent re-aeration and is discharged from the bottom of tank 12 through the sensing chamber 112 which may house sensors on which entrained gas would normally have an adverse effect and finally exhausted at 114 for return to the process flow stream. Since the liquid or slurry passing through chamber 112 has been deaerated, measurements may be made by such sensors without the presence of entrained gases.

Excessive turbulence in the tank 12 sufficient to result in air entrainment is to be avoided. This is accomplished by operating the rotating chamber a sufficient distance below the surface of the liquid 98 and the use of baffles 92 and 94. The baffling, particularly below the rotating chamber, also serves to eliminate reverse pumping at the discharge 14 by impeding rotation of the fluid body.

While the shape of the rotating chamber does not materially influence the principle of operation, right cylindrical shapes at the periphery are subject to accumulation of heavy solids in the corners thereof during operation which converts same for all practical purposes to an internal conical section. The rate of rotation of the rotating chamber is not particularly critical, as it only influences the fluid depth 77 in of the rotating chamber. The rotational speed of the chamber establishes the "g" level in the fluid, and, hence, the depth of fluid required to counterbalance the vacuum. The vacuum is kept substantially constant by the vacuum pump.

The deaerator according to this invention can accept a wide range of flow rates and is adapted to being a part of a continuous treating system. The difference between the liquid level 98 in the tank and the level of pipe 114 is such as to provide a fluid head to counteract some reverse pumping action.

The size of discharge apertures in the periphery of the rotating chamber is governed in part by the flow rate desired. The aperture size can be varied over a wide range but should be kept toward the small end of the range, consistent with desired flow rates. It will be understood, of course, the larger the physical size of the deaerator, the greater the flow rate may be. On the other hand, increasing the size of the apertures to where they are excessively large in order to obtain the very high flow rates, might cause some fluid to recirculate at low flow rates. In such cases, larger equipment would preferably be used to provide the necessary flow rates.

It will be appreciated by those skilled in the art that many other mechanical configurations can be envisioned for supporting the bearings, effecting the vacuum seal, and providing the necessary rotation of the submerged inner chamber 62 with respect to the stationary outer tank 12. The specific embodiment just described is only intended to convey the basic principles of operation of the invention.

Claims

What is claimed is:

1. A deaerator comprising:

an inner gas-liquid receiving chamber having sidewalls and being of generally circular cross section, a centrally positioned gas-liquid inlet, a centrally positioned gas outlet and at least one liquid outlet peripherally positioned in the sidewalls, said inner chamber being rotatably mounted for relative rotation;

an outer liquid receiving tank surrounding said receiving chamber, and communicating with said liquid outlet of said inner chamber, a liquid outlet, and an overflow outlet defining a normal liquid level therein above and completely submerging the chamber when filled with a liquid with the liquid outlet of said chamber communicating the interior of said tank below the normal liquid level thereof; and,

a gas vacuum producing means connected to the gas outlet of said chamber to exhaust gases therefrom and maintain the chamber under a reduced pressure.

2. A deaerator according to claim 1 wherein the inner chamber is a pair of spherical segments.

3. A deaerator according to claim 1 wherein the inner chamber is a surface of revolution having its top and bottom surfaces converging from a maximum dimension along the axis of rotation to a minimum dimension at the periphery.

4. A deaerator according to claim 1 wherein the inner chamber is a double conical section, with the axes of revolution thereof coaligned and the bases abutting, mounted for rotation about the axes of revolution.

5. A deaerator according to claim 1 wherein the inner chamber has a plurality of spaced liquid outlets in the sidewalls thereof.

6. A deaerator according to claim 1 wherein the outer tank is provided with a plurality of radially extending baffles therein above and below the inner chamber.

7. The deaerator of claim 6 wherein the baffles are vertical.

8. The deaerator of claim 1, wherein the inner chamber is coated both inside and out with a coating of an elastomer and is provided with a bottom clean-out door.

9. The deaerator of claim 1 including an outlet conduit connected to the outlet of the outer tank and an sensor chamber positioned adjacent the normal liquid level of the tank connected to said outlet conduit.

10. The deaerator of claim 1 including rotary prime mover means operatively connected to said inner chamber for the rotary movement thereof.

11. A deaerator according to claim 1 wherein the gas outlet of said inner gas-liquid receiving chamber is located in the top thereof concentric with said gas-liquid inlet.

12. A deaerator according to claim 1 wherein the peripherally positioned outlet of the inner rotatable gas-liquid receiving chamber comprises a plurality of openings spaced about the periphery of said chamber which exhaust directly into the liquid receiving tank and wherein the gas-liquid inlet of the gas-liquid receiving chamber as well as the gas outlet is located at the top thereof.

13. A deaerator according to claim 12 wherein the gas-liquid inlet of the gas-liquid receiving chamber is positioned concentric with the gas outlet thereof.

14. The method of deaerating a slurry of suspended solid particles having a gas entrained therein comprising the steps of:

introducing the slurry to be deaerated into a rotating chamber immersed in a liquid bath;

centrifugally exhausting the liquid and solids peripherally from said chamber into the liquid bath by rotating the chamber at a rate sufficient to provide a hollow spinning annulus of liquid therewithin; and,

providing a reduced pressure within the chamber and the hollow interior of the spinning liquid body to extract gases released from the liquid body whereby a pumping action is produced therein which is self-pumping.