US3477383A - Centrifugal pumps - Google Patents

Description

NOWU, 1939 P. J.RAwsoN ET AL 3,477,383

GENTRIFUGAL PUMPS Filed Math 27. 1968 United States Patent U.S. Cl. S-99 2 Claims ABSTRACT 0F THE DISCLOSURE A centrifugal pump of extreme simplicity, especially for pumping liquid metal, has an impeller comprising a simple cylinder (preferably of refractory material), which is supported in bearings above the highest level reached by the liquid being pumped.

This invention relates to centrifugal pumps, that is t9 say pumps in which a liquid is raised from an inlet to an outlet by virtue of pressure imparted to the liquid by the action of centrifugal force in a rotating impeller through which the liquid passes.

A conventional centrifugal pump can be considered as consisting of four main parts: a casing having an inlet for the liquid to be pumped; the impeller, mounted within the casing; a drive shaft coupled to the impeller; and a delivery tube connected to the outlet of the casing and extending upwards to the pump outlet through a vertical distance equal to the pumping head.

One object of the present invention is to provide a centrifugal pump in which the functions of all four of these parts are combined in a single impeller member, so as to produce a much simpler and cheaper pump than those known hitherto.

According to this invention, a centrifugal pump includes a non-horizontal rotatable hollow tubular impeller having at or adjacent its lower end an inlet for immersion in a liquid to be pumped, the impeller having also t an outlet at a level such as to be above the surface of said liquid so that, on rotation of the impeller, liquid can be caused to rotate in the impeller so as to generate a pressure on the inside surface of the impeller whereby to raise the liquid to said outlet.

Another object of the invention is to provide a pump suitable for use in connection with corrosive liquids, particularly those which must not be brought into contact with metallic parts of the pump. Such corrosive liquids include for example many liquid metals especially when at elevated temperatures: examples include molten metals or mixtures of metals, or liquid metals used as coolants in nuclear reactors.

It is therefore desirable that those parts of the pump coming into contact with the liquid should be in a form such that they can readily be made to withstand very high temperatures and severe corrosion. This suggests the need for components of very :much simpler design than is possible in conventional centrifugal pumps.

In particular, it is desirable to keep the bearingsas far away as possible from the liquid.

According to a preferred feature of the invention, therefore, the impeller is supported entirely above the outlet. Thus all the bearings can be above the highest point to which the liquid rises.

According to another preferred feature of the invention, all surfaces of the pump liable to come into contact with the liquid are of refractory material. In particular, those surfaces of the impeller liable to come into contact with the liquid are of refractory ceramic material.

ICC

Suitable refractory materials for use in connection with the pumping of hot molten metals include for example a refractory cement, fire-clay or ceramic chosen for the operational temperature and chemical conditions. The material must be capable of withstanding the centrifugal, pressure and thermal stresses exerted on it in operation.

Under some conditions it will however be possible to use non-refractory metals instead of refractory materials: and even when refractory materials must be used, it is only necessary that the actual surfaces, liable to be subjected to conditions which metals could not withstand, should be of refractory materials. Accordingly, the impeller and other refractory parts may be reinforced with metals: in particular, those parts of the outer surface of the impeller which are not immersed in corrosive liquid may be reinforced by an outer metallic sheath, or by a number of stay-bolts or the like suitably anchored to the outside of the refractory impeller tube.

Such metallic reinforcement may need to be cooled, and another object of the invention is to provide a simple and reliable method of cooling it without recourse to expensive and cumbersome special cooling equipment.

The pump preferably includes a drive unit mounted above the impeller and coupled thereto so as to rotate the impeller.

According to a further preferred feature of the invention, therefore, the drive unit is arranged to be operated by a compressed gaseous medium, the impeller being mounted for rotation in a flxed structure of the pump, and the fixed structure having openings to direct said medium from an exhaust of the.` drive unit down onto an external surface of a portion of the impeller below the outlet, whereby to cool said external surface.

One pump in a preferred form according to the invention, for pumping molten metal out of a furnace, will now be described by way of example and with reference to the accompanying drawing, which is a simplified sectional elevation showing the pump installed.

The pump includes a frame 10 carrying a compressedair drive unit 11, which is arranged to drive a hollow vertical shaft 12 which rotates in two spaced-apart bearings 13 in the frame 10. The frame 10 is supported by a xed structure 14 of a furnace.

A tubular impeller 16 is fixed coaxially, to and extends downwardly from, a rigid coupling 15 on the bottom end of the shaft 12. The impeller 16 consists of an upper tube 17 having radial outlet ports 18 below a blanking plate 19 which closes of the top end of the impeller, and a lower tube 20 which extends well below the highest possible level 21 of the surface of a -pool 23 of molten metal in the furnace. The outlet ports 18 are well above the level 21. The lower end of the lower tube 20, which is immersed in the pool 23, contains radial vanes 24 to help initiate rotation of the molten metal inside the impeller 16. The vanes 24 are retained in position by a ring 22 in the bore of the tube 20, and a baille plate 24A on top of the vanes 24 forces liquid metal passing the vanes to flow outwardly to the wall of the tube past the plate 24A.

Both the upper and lower tubes 17 and 20 of the impeller 16 are of a refractory ceramic material of a kind capable of withstanding the high temperature of the molten metal and resistant to corrosion thereby. The top of the lower tube 20 has a flange 20A, resting on a ring 25 which is above the level 21. The ring 25 is fixed to a tubular steel sheath 26 which is mounted coaxially around the upper tube 17 and which is separated therefrom by thermal insulation 27. The top end of the sheath 26 is fixed to the coupling 15, the sheath 26 and insulation 27 having holes 28 opposite the outlet ports 18 3 but much bigger so as to minimise contact of liquid metal with the sheath.

The outlet ports 18 exhaust through the holes 28 into an annular trough 29 which is fixed to the frame 10. The trough 29 includes a cylindrical wall 34 around the up'per tube 17 of the impeller, and extending to approximately the level of the bottom of the ports 18 in the impeller. The trough 29 has a spout 30 whereby molten metal can pass to a channel 31. The trough 29 preferably has a lid 32 to reduce upward heat losses. The trough 29 and channel 31, or at least those parts thereof which are lia-ble to come into contact with the molten metal, are of a suitable refractory material.

In operation, the drive unit 11 rotates the impeller 16, imparting a centrifugal force to the liquid metal therein. The liquid metal in the impeller is thus urged towards the inside surface of the impeller and tends to rotate with the impeller. As the speed of rotation is increased, the pressure between the liquid metal and the impeller wall increases, so that a column of liquid metal rises up the impeller. The speed is increased to a value at which this column reaches the outlet ports 18, so that the liquid metal passes through them.

From the ports 18, the molten metal spills over the top of the wall 34 into the trough 29. The wall 34 acts as a Weir, giving automatic control of the flow into the trough 29.

The exhaust from the compressed air drive unit 11 passes through openings A in the frame 10 to the outside of the impeller sheath 26, which is thereby cooled.

The outside of the lower tube of the impeller is provided with small plates 33, which are so aligned that on rotation of the impeller, the blades 33 cause a local upward flow of molten metal: this tends to oppose the tendency of any vortex which may be generated around the tube 20, by virtue of rotation of the latter in the pool 23, to extend down as far as the lower end of the impeller.

An alternative to the blades 33 is the provision of ixed blades adjacent the tube 20. In some cases, however, it may be unnecessary to provide any means for limiting the extent of the vortex.

The insulation 27 may be omitted if there is no means for cooling external metallic reinforcement of the upper tube 17 (such as the sheath 26), or if no such external reinforcement is provided.

The liquid metal may be extracted from the trough 29 by any suitable means, for example a pipe.

Where reinforcements such as an external sheath or stay-bolts, or internal bolts or bars, is provided for the impeller tubes, the latter may be made in sections, joined or held together end-to-end by such reinforcement` The impeller may be made in the form of one continuous tube (in one piece or made up of sections), provided no metallic reinforcement which may be included in such a tube comes into contact with the liquid being pumped if the latter is likely to have a deleterious effect on the metallic parts.

Cooling of the metallic parts, where provided, may be by any suitable means, for example a separate forcedflow system for a liquid or gaseous coolant.

Should `it be necessary to control the atmosphere in contact with the liquid to be pumped, the whole pump may `be enclosed in a suitable gas-tight vessel having an inlet andan outlet for the liquid, the vessel then being filled with the desired atmosphere or evacuated.

A flow control mechanism, responsive to the level of molten metal in the trough 29, may be provided, either in place of the weir 34 or in addition to it. In one example of such a mechanism, a float valve in the trough 29 is arranged to control the speed of the drive unit 11.

Although in the example described herein it has been stressed that those parts of the pump liable to come into contact with the liquid metal must be of refractory material, it will be realised that this is only necessary where the temperature of the liquid metal, and its corrosion properties, demand. Pumps according to the invention can be used over a wide range of temperatures, from well below 0 C. to the highest melting points of metals (where such high temperatures are not too high for satisfactory materials to be found for the pump components). Thus for many purposes metals may in fact be used instead of (for example) ceramics for the impeller components to be in contact in the liquid metal and for the trough and associated parts.

The lowest temperatures at which the pump can operate will be limited by the eiciency of the pump.

It will be understood that pump's according to the invention need not incorporate a drive unit, but may be made so that they can be coupled to one at will.

The inlet need not be in the lower end face of the impeller, but may instead be in the side of the impeller near its lower end.

The vanes 24, though preferable, are not essential.

In some cases it is possible to support the impeller in one or more bearings below the level of the outlet ports 18, though this is not desirable Where high temperatures or corrosive conditions, for example in pumping hot molten metals, are anticipated.

The drive unit may be operated by a compressed gaseous medium other than air in certain special cases.

The coupling connecting the impeller to its drive shaft (in the drawing the coupling 15) may be made flexible instead of rigid if desired so as to overcome vibration problems.

We claim:

1. A centrifugal pump for raising molten metal, comprising:

a hollow rotor consisting of:

an upper portion comprising a cylindrical lining of refractory material, an insulating layer surrounding the lining, and a metal sheath surrounding the insulating layer for strengthening the upper portion, and

a lower portion consisting of a self-supporting cylinder of refractory material attached at its upper end to the lower end of the upper portion and which projects below the surface of the liquid metal; and

drive and supporting means for suspending the rotor from its upper end and for permitting liquid metal which rises inside the rotor to escape from the upper end of the rotor.

2. A centrifugal pump according to claim 1, wherein the internal radius of the lining of the upp'er portion of the rotor is greater than the internal radius of the lower portion of the rotor.

References Cited UNITED STATES PATENTS 913,179 2/ 1909 Wernette 103-99 1,361,938 12/1920 WaldrOn 103-99 2,528,210 10/ 1950 Stewart.

2,671,405 3/ 1954 Stoors 103-99 2,715,367 8/1955 Kodet et al.

3,075,459 l/ 1963 Hoelzer et al. 103-99 3,092,030 6/ 1963 Wunder.

3,150,597 9/ 1964 Steenhagen 103-99 3,304,066 2/ 1967 Vieceli et al. 103-99 HENRY F. RADUAZO, Primary Examiner U.S. C1. X.R. 103-103; 266-38

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