AERATION SYSTEM

Background and Summary ofthe Invention

This invention relates to a centrifugal pump, and more particularly to a pump which conditions the fluid handled by the pump by introducing air into this fluid. A pump of this description may be used for the production of an air and water mixture to be admitted to a tank holding a quantity of sewage The air so introduced facilitates the removal of oil and other pollutants including solid particles which tend to separate out as a surface scum with the introduction of air and liquid to the tank. The aerated liquid produced by the pump of course may be used for other purposes. This application is a continuation-in-part of prior filed application entitled

IMPELLER PUMP WITH VANED BACKPLATE FOR CLEARING DEBRIS, filed September 6, 1994 as Serial No. 08/300,995.

It is known in the art that aeration of liquids is a useful procedure relied upon in pollution control operations. A known procedure, by way of example, is the

aeration of sewage contained in a holding tank, with such tending to produce separation of pollutants in the liquid in the tank either as a scum or as sediment. A convenient approach for introducing such air would be to introduce air in the desired quantity to the suction or intake side of the pump during a pumping operation, with the pump then tending to produce a mixture of air and liquid which is expelled from the pump The problem with this approach is that the addition of significant quantities of air to the intake of the pump will cause the pump to lose outlet pressure and stop pumping. Pump performance is also affected. U.S. 3,663,117 discloses a so-called aeration pump, wherein air is introduced against the front side of a pump impeller in a centrifugal pump, with the impeller vanes therein then producing mixing of the air and liquid pumped to produce aeration of the

liquid. Such a system, because of the relatively high pressure condition existing adjacent the periphery of the impeller, requires a source of air at superatmospheric pressure to be supplied to the pump chamber. In another system, the liquid discharged from a pump is supplied to an air saturation tank, and this tank in turn being supplied air from a compressed air source whereupon the air and water is then mixed. The need for an air compressor and other equipment adds to the complexity and expense of any system requiring a source of pressurized air.

A general object of this invention is to provide an improved method and apparatus for conditioning a liquid by the introduction of air into the liquid, with the air on introduction becoming dissolved in the liquid or entrained as a fine dispersion therein.

Another general object is to provide an improved sewage treatment method which utilizes recycled sewage conditioned with air in the treatment process.

Yet a further object is to provide an improved pump operable upon operation to produce a mixture of fluid and air, which operates without the requirement of a pressurized source of air.

A more specific object is the provision of such a pump, which employs air at atmospheric pressure introduced into a seal chamber in the pump, and structure within the seal chamber producing an air liquid mixture which under the action of the pump impeller moves to the periphery ofthe impeller and then to the pump discharge. Brief Description ofthe Drawings

These and other objects and advantages are obtained by the invention, which is described herein below in conjunction with the accompanying drawings, wherein:

Fig. 1 is a cross sectional view of a centrifugal pump featuring a construction for a seal chamber in the pump as contemplated by the invention;

Fig. 2 is a schematic drawing illustrating a sewage treatment system

utilizing a pump as described and shown in Figs. 1 and 2; and Fig. 3 is a view ofthe front of a backplate portion in the pump.

Detailed Description ofthe Preferred Embodiment Referring now to the drawings, and first of all more particulariy to Fig. 1, indicated generally at 10 is a centrifugal pump. The pump has a casing 12. Casing 12 includes a front casing section 14, with an intemal pump chamber wall 16 defining a pump

chamber having the usual volute configuration. Also part of the casing is a back casing

section 18. These two casing sections are secured together in the pump. The back casing section includes a backplate portion 22 and a motor bracket portion 24.

A rotatable impeller 30 located within the pump chamber produces, on rotation, movement of the liquid being pumped or the pumpage. This liquid enters the pump chamber through an inlet opening or intake 32. Pressurized pumpage leaves the pump through pump discharge 34. The impeller has a front 35 and a back 36.

The impeller is detachably mounted, as by a fastener 38, on a forward end of a motor-driven impeller shaft 40. This shaft extends rearwardly, or outwardly from the back ofthe impeller, to a suitable power means such as an electric motor. Backplate portion 22 has an inner wall 44, referred to as a seal chamber wall, which in general outline has a conical tapered or flaring shape. This wall and the back ofthe impeller bound what is referred to as a seal chamber or cavity 46. The seal chamber has a smaller diameter end located directly forwardly of hub 48. By reason ofthe taper of

the seal chamber wall, the seal chamber enlarges progressing from this end to the opposite or large diameter end ofthe seal chamber or from left to right in Fig. 1. This is only one type of seal chamber, others are possible.

Hub 48 extends about an opening 50 which receives the impeller shaft.

Seal structure exposed to the seal chamber seals the shaft and casing, and this structure comprises a stationary seal 52 and a rotary seal 54 which rotates with the impeller shaft. A compression spring 56 urges the rotary seal against the stationary seal. With the construction described, liquid within the seal chamber is prevented from leaking outwardly past the backplate. During operation ofthe pump, part ofthe liquid being pumped flows into the seal chamber by moving about the periphery of the impeller and across the impeller's outer back margin. It is conventional to utilize this circulating fluid to produce cooling of the seal structure just described.

The back of the impeller may be provided with vanes indicated at 60. These vanes, when viewed in a direction extending toward the back of the impeller, ordinarily arcuately curve about the axis of the impeller shaft. By the inclusion of these vanes, a swirling action is introduced to the pumpage liquid which circulates in the seal chamber.

An air-introduction passage is provided along the inside of a conduit 72 having one end 72a which opens to the seal chamber and an opposite end 72b which opens to the atmosphere. Indicated at 74 is an adjustable valve which can be adjusted to control the amount of air introduced to the seal chamber by the conduit.

During operation of the pump and rotation of the impeller, pumpage is drawn in through the suction ofthe pump 32 and discharged at the periphery ofthe impeller through discharge 34. A negative or subatmospheric pressure is produced in an annular region extending about the impeller shaft adjacent the seal structure for the shaft comprising stationary and rotary seals 52, 54. Spring 56 functions to keep the seal faces in engagement against the action of this negative pressure. The negative pressure is effective to draw

atmospheric air into the seal chamber into the negative pressure region through air- introduction conduit 72, with the amount of such air being controllable through controlling the adjustment of valve 74 (or by using a properly sized orifice). Mixing of this air with the pumpage circulating at the rear ofthe impeller, and transporting of the mixture outwardly from the seal chamber to the stream of fluid being discharged from the pump at discharge 34, is promoted by stationary vane structure which is part ofthe back casing section 18.

Further explaining, and referring also to Fig. 3, equally circumferentially distributed about axis 80 ofthe impeller shaft are multiple (namely six in the embodiment of the invention illustrated) outer vane segments 86. In frontal outline, as illustrated in Fig. 3, each of these outer vane segments has a shape which roughly may be described as a truncated triangle, and includes a base 86a and opposite sides 86b, 86c. Each vane projects outwardly from the seal chamber wall with its front face 86d extending at only a slight angle relative to a plane peφendicular to the axis ofthe shaft compared to the slope ofthe inclined pump seal chamber wall, which extends at a greater angle with respect to this plane. By reason of this incline, each outer vane segment has an increasing height or greater projection from the inclined pump seal chamber wall progressing in a radially

inward direction on the seal chamber. Explaining a typical construction, face 86d might extend at an angle of approximately 10° with respect to a plane perpendicular to the axis of the shaft. In comparison, the tapered seal chamber wall might extend at an angle of approximately 35° with respect to this perpendicular plane. These specific values herein are given only as exemplary, and are subject to variation depending upon pump construction.

Distributed circumferentially about the shaft axis are multiple (three in the embodiment shown) inner vane segments 90. These extend inwardly on the seal chamber wall from the inner ends of alternate ones of the outer vane segments. Each inner vane segment has an arcuate, concavely curving base 90a, and opposite sides 90b, 90c, with these sides forming extensions of sides 86b, 86c of an outer vane segment. Sides 90b, 90c diverge from each other progressing in a radially inward direction. The front face 90d of an inner vane segment (refer to Fig. 1) inclines away from the tapered seal chamber wall progressing in a radially outward direction. As a result, these inner vane segments have increasing height increasing radially outwardly on the seal chamber. With the seal chamber wall inclining at an angle of approximately 35° with respect to a plane extending peφendicular to the axis of the impeller shaft, the face of an inner vane segment might incline at a somewhat greater angle with respect to this plane, for example, an angle of 45°.

The sides ofthe outer vane segments need not join with the faces of these respective vane segments at a shaφ angle, but over a slight round, which tends to reduce excessive turbulence in the circulation of pumpage moving over the vanes.

In the pump illustrated, a fluid circulation line or conduit is shown at 102, equipped with a valve 104. The conduit connects at one end with the interior ofthe pump casing at the periphery ofthe impeller. The opposite end connects with the seal chamber in

the region of the seal chamber having a subatmospheric pressure. By including the circulation line, the amount of pumpage circulated to the seal chamber to be mixed with air

may be increased over that which circulates to this seal chamber by moving over the periphery ofthe impeller. Optionally, liquid may be introduced to the seal chamber by a line connected to a pressurized water source.

Describing the operation ofthe pump, the vane structure on the back ofthe impeller together with the normal rotation of the impeller causes pumpage within the seal chamber to swirl about as the impeller rotates. As this pumpage moves over the stationary vane structure projecting from the rear wall of the seal chamber, a vortexing action results

tending to move debris, and also mixed pumpage and air, from the region of the seal chamber adjacent the impeller shaft radially outwardly, with this fluid and debris ultimately being expelled from the seal chamber by way of the back vanes 60 to become intermixed with the principal pumpage being pumped by the pump which is being discharged at discharge 34.

A sewage system which utilizes the pump as described is illustrated in Fig.

2. Referring to this figure, a tank for containing a volume of sewage is illustrated at 110. Sewage is introduced to the tank from a raw sewage feed 114 introducing the sewage to the tank through a header box 116.

Effluent from the tank is removed through a conduit 120. A portion of this effluent is recycled through a conduit 122 to the intake of pump 10 above described. Fluid discharged from this pump travels through a conduit 124 to be returned to header box 116 and reintroduced to the tank 110 through conduit 126.

Air is introduced to the effluent through conduit 72.

Air introduced into the pump through operation of the impeller is thoroughly mixed with the liquid sewage. Much ofthe air is mixed to become dissolved in the liquid sewage. Air not actually dissolved is felt to be contained in the liquid in the air bubbles sized below 150 microns.

The introduction to the tank of the recycled stream of sewage containing dissolved air and air dispersed as finely entrained bubbles, has the effect, as earlier discussed, of producing a separation in the tank, with pollutants separating as a sludge which if floating can be removed from the tank as a drawof

The system in Fig. 2 can be further simplified by introducing the air into the pump supplying the raw feed, thus eliminating the need for a recycle flow, and further reducing the complexity ofthe system.

With the construction described, appreciable quantities of air may be introduced into the pumpage with introduction of air in an amount exceeding approximately 15% by volume ofthe pumpage handled having been attained. While an embodiment ofthe invention has been described, it is obvious that variations and modifications are possible without departing from the instant invention as claimed herein.