US2779475A - Fluid driven centrifugal machine - Google Patents

Description

United States Patent FLUID DRIVEN CENTRIFUGAL MACHINE Charles A. Olcott, West Milford, N. J.

Application January 14, 1950, Serial No. 138,657

4 Claims. (Cl. 210--71) This invention relates to centrifugal machines and more specifically to fluid-driven machines of the centrifugal type.

It is the principal object of this invention to provide novel and improved means for improving the operation and efiiciency of fluid-driven centrifugal machines and particularly of centrifugal machines used in the manufacture of sugar.

In the manufacture of sugar, centrifugal machines are utilized which go through many complete operating cycles each hour. In each cycle, the machine is accelerated to full speed, allowed to run at this speed for a few minutes and then quickly brought to rest. During the unloading operation, the machine is turned at low speed. While various forms of drive have been used, a hydraulic or water drive is used extensively for centrifugals drying slow draining materials requiring relatively high centrifugal force. The maintenance charges of hydraulic centrifugals are very low and they have been found to be the most economical type for drying certain types of material, such as corn sugar.` Water driven centrifugals have the further advantage that they usually have fewer moving parts than any other type. On the other hand, the usual water-driven centrifugal has the following disadvantages: (l) its rate of acceleration with any reasonable amount of power is low, (2) its overall efficiency is not as high as that of the electrically driven machines, and (3) frequently, insufficient torque for the low speed required for unloading is available when the only source of usable power is that required to keep the centrifugal running at full speed (this is particularly true in the case of slow drying materials). The present invention in one of its primary aspects is concerned with the problem of reducing these three disadvantages and thus improving the competitive position of the waterdriven centrifugal,

lt has heretofore been proposed to reduce the abovementioned disadvantages by providing a water motor for a centrifugal with two bucket wheels, one wheel being larger than the other and both wheels being driven by jets at substantially the same high water pressure, The large Wheel is normally used for booster purposes to provide acceleration and its size is so proportioned with respect to the velocity of the water at its jet that the that the power of this wheel is negligible at the normal running speed of the centrifugal (which for practical purposes is almost the safe driving speed). The small wheel develops its maximum power at or near the normal running speed of the machine and little power at the lower speeds. Normally, the large wheel is used, either alone or in conjunction with the small` wheel, during the acceleration period only and the small Wheel alone is used to provide power at the normal running speed. Because of the above-mentioned characteristic of the large wheel (negligible power at the centrifugals normal running speed), the machine cannot exceed its safe speed even though, through human carelessness or through` ICC non-operation of the valve or valves controlling the admission of water to its driving jet, the large wheel has water applied thereto at the normal running speed. This safety feature is tremendously important as centrifugals which greatly exceed their safe running speeds are liable to blow themselves to pieces. l v

The use of such a water motor having large and small bucket wheels is effective in producing the desired results but it involves the expense inherent in providing two wheels instead of one for each centrifugal. While this expense is justified in many situations, there isa distinct advantage and reduction in cost, especially in a completely new installation where there are a large number of centrifugals to be attached to the pumping system, in reducing the number of impulse wheels required for the installation.

It is a further object of this invention to reduce the number of water wheels required in multi-centrifugal installations without sacrificing the above-mentioned safety feature. 3

The above and related objects `are attained in accordance with the invention by providing, in an exemplary embodiment thereof, a centrifugal machine (which may form part of a large installation of similar machines) which has two driving means for a single water wheel. These driving means comprise a pair of nozzles to produce a corresponding pair of jets. The first nozzle has applied thereto fluid at a relatively low pressure which, when acting alone (i. e. with the other nozzle turned off) drives the Water wheel at maximum power (for this nozzle) during the acceleration period but which produces substantially no power at or above the normal running speed. The second` nozzle is used for the normal running of the machine and it has applied thereto a relatively high pressure which is suliicient toproduce maximum power (for this nozzle alone) at or near normal running speed of the centrifugal. By way of example,

the low pressure is at least forty percent less than` the high pressure. Normally the iirst nozzle alone (or this nozzle plus the second nozzle) is used for the accelera tion of the machine but only the second or high pressure nozzle is used for the normal running of the centrifugal. Any suitable valve means can lbe used for turning `on and off the nozzles at the appropriate times in the cycle.

This means can be manual or automatic. Separate sources for the two pressures can be provided or, if desired, a single source with a pressure boosting device in a line to one of the nozzles can be used instead. If, by chance or accident, the first nozzle is left on during the normal running interval of the centrifugal (in addition to the second nozzle), no harm is done because the first nozzle does not produce any appreciable torque at this speed.

The invention will be more readily understood by referring to the following description taken in connection with tbe accompanying drawings forming a part thereof, in which:

Fig. l is a schematic view of a fluid-driven centrifugal machine assembly in accordance with the invention, the driving means including a single bucket wheel and a pair of nozzles supplied with fluid at different pressures;

Fig. 2 is a graphical representation showing the efciency of the fluid wheel, with the first nozzle alone operating it, plotted against centrifugal speed; and

Fig. 3 is a graphical representation, similar to that of Pig. 2, for the second nozzle alone.

Referring more specifically to the drawing, Fig. l shows, in schematic form and by way of example for illustrative purposes, a uid-driven, sugar-centrifugal machine assembly 10 in accordance with the invention. The assembly comprises a centrifugal machine 11 provided with `a rotating basket l2 for the sugar-bearing material Patentes Jan. 2s, naar'` and a spindle 13 attached to the basket, the latter carrying an impulse member 14 in the form of a bucket wheel. he spindle 13 may be either in one piece or it may be in two pieces with a coupling between the impulse member 14 and the basket 12. A housing 15 surrounds the upper part of the machine 11. Driving iluid for the bucket wheel 14 is admitted to the housing 15 through a nozzle 16 (called nozzle No. l) and a nozzle 17 (called nozzle No. 2) from appropriate sources to be described below. The bucket wheel 14 can be, for example, one of the conventional impulse wheel types known as a Pelton wheel. The machine is braked at the desired times by suitable brake members 18 surrounding the spindle 13.

Fluid is supplied to the nozzles 16 and 17 from a fluid pressure supply 19 which can be a tank holdinga suitable supply of water to apply to the intake of pressure pumps 20v and 21. A pipe 22 leading to a water main, for eX- ample, supplies fluid for the tank 19. The motor 23 is of suitable power and speed to drive the pumps 2i) and 21. As an alternative, any other kind of driving member can be used, such as a turbine or a connection to another driven shaft by pulleys.

ri`he water pump 21 draws water from the tank 19 by means of pipe 24 and builds up a relatively high pressure so, by way of example, it has been shown as a two-stage centrifugal pump. The pump 20 is also connected to draw water or other iluid from the tank 19 (through the pipe 25) but as only about one half the pressure is built up by this pump as is produced by the pump 21, it has been shown as only a single stage pump. The reason for the pressure difference will be explained below.

In the output line 26 of the pump 21 is a valve 27 adapted, when operi, to admit Water or other uid to the nozzle 17, thus delivering a high pressure jet to impinge on the buckets of the impulse wheel 14. Similarly, the

output line 28 of the pump 2b is provided with a valve 29 to admit fluid to the nozzle 16 which in turn will deliver a relatively low pressure jet to the buckets of the impulse wheel 14.

VValves 27 and 29 can be opened and closed in the usual manner, either manually or by any suitable automatically operated device shown in the prior art. EX- amples of appropriate automatic valve operating means are disclosed in a copending application of Frederick Stindt, Ser. No. 637,245, filed December 26, 1945, and which issued as Patent 2,517,452 on August 1, 1950. This Stindt application also describes in greater detail the background theory of water wheels.

rl`he impulse wheel 14 is `preferably of such a diameter that, when running at the highest safe speed of the centrifugal machine (which for maximum design efficiency is about the same as the normal running speed), the buckets travel with a linear velocity about 48% of the velocity of the Huid in the jet from nozzle 17. The pressure at nozzle 16 supplied by pump 2li is preferably such as to provide a jet having a velocity suliicient to exert a driving torque on wheel 14 at all speeds up to the highest safe running speed of the centrifugal machine but insufficient to provide any substantial driving torque at any speed appreciably above the highest safe running speed.

Theoretically, if there were no losses and if the water motor were 100% eiiicient, the pressure from pump 20 should be one-quarter of the pressure from pump 21, but due to various losses and due to the fact that the water wheel is designed for maximum efliciency with the high pressure from nozzle 17, the effect of pressure at nozzle 16 ot only one-quarter of that at nozzle 17 would be that the jet from nozzle 16 at the one-quarter pressure would actually have a braking effect tending to slow down the bucket wheel, which is not desired. This braking elect arises principally from the leading surface of the bucket 141 striking the low pressure jet at au angle. It has been found from experiments that the pressure at nozzle 16 should be about one half of the pressure at nozzle 17. With such pressures, efficiency curves for nozzles Nos. 1 and 2 like those shown in Figs. 2 and 3, respectively, are typical. Assuming a normal running speed of R. P. M., it should be noted that the eiciency (and hence power as applied to the bucket wheel) of nozzle No. l (the low pressure nozzle 16) is negligible at and slightly above 1800 R. P. M. while the efficiency (and hence power) of nozzle No. 2 (the high pressure nozzle 17) is a maximum at 1800 R. P. M. It should also be noted that at speeds substantially above 1800 R. P. M., the power of the two nozzles together is less than the power produced by nozzle No. 2 alone.

In the preferred form of normal operation, the ma chine is started and accelerated to its highest safe running speed by opening valves 27 and 29. The jet from nozzle No. l has such a size and such a pressure that it works at its highest eliiciency in delivering power to wheel 14 when the machine is running at about twothirds of the highest safe running speed (or at about 1200 R. l?. M. asy shown in Fig. 2). When the machine is accelerated to its highest safe running speed (1800 R. P. M.), then valve 2,9 is closed (either manually or automatically) and the machine is allowed to run at full speed (1800 R. P. M.), being driven by the jet from nozzle 17, which jet has such a size and such a pressure that it reaches its maximum eiliciency at this full speed, as shownr in Fig. 3.

If through` failure of the arrangement for closing valve 29, either through manual negligence or failure of an automatic device to function, the valve 29 should remain open after the machine is run at its highest safe speed, then this jet from nozzle 16 would not have any effect of increasing the speed of the machine above its safe speed because the Water from this jet would not be traveling fast enough to exert any driving torque on the buckets of the wheel 14 in excess of the drag resulting from the leading side of the buckets hitting the jet.

In an alternative form of operation, the low pressure nozzle No. 1 can be used alone during acceleration and the high pressure nozzle No. 2 used alone during the normal running of the centrifugal.

Various changes can be made in the embodiments described above without departing from the spirit of the invention as indicated by the claims.

What is claimed is:

1. A heavy centrifugal machine for separating solids from liquids and being of the type which is adapted to be cyclically rapidly accelerated from rest to a normal run ning speed which is substantially the highest safe speed of said machine, allowed to run at this speed for a time period normally less than an hour and quickly brought to rest, comprising a basket, a spindle for supporting said basket, a water wheel for driving said spindle, a pair of nozzles to produce jets for driving said wheel, pumping means for supplying water at a relatively low pressure to one of said nozzles, and additional pumping means for supplying water at a relatively high pressure to the other of said nozzles, said low pressure nozzle being of such size and said low pressure being sufficiently below said high pressure that the jet having the low pressure water has its maximum driving eiciency at a speed which is far below the normal running speed of said machine and has substantially reduced eiciency at the normal running speed ofsaid machine, and said high pressure nozzle being of such size and said high pressurey being suilicientlarge that the jet having the high pressure water has its maximum driving etliciency at the normal running speed of said machine.

2. The combination. of elements as in claim 1 in which said low pressure is at least 40% less than said high pressure.

3. The method of driving a sugar centrifugal machine of the water wheel type provided with .two driving nozzles which comprises applying water at relatively low pressure to one of said nozzles during the acceleration period, and applying water at relatively high pressure to 5 6 the other of said nozzles during the normal running wherein the said low pressure is at least 40% less than period while maintaining the 10W pressure nozzle closed, said high pressure. said low pressure nozzle being of such size and said low p pressure being suciently below said high pressure that References Cited in the me 0f hS Patent the jet produced by said low pressure nozzle has its 5 UNITED STATES PATENTS maximum driving eiciency at a speed which is far below the speed, of said machine during its normal running lcfaane light' g3g period and has substantially reduced eiciency at said 7 306625 Hals Dsc' 29 1942 normal running speed, and said high pressure nozzle be- Zen ing of such size and said high pressure being sufficiently l0 2517452 Stmdt Aug' l 1950 large that the jet produced by said high pressure nozzle OTHER REFERENCES has its maximum driving eiciency at the speed of said Hydraulic Motors, Churchs John Wiley and Sons, machine during its normal running period. 1st edition, 1908, p. 71

4. The combination of method steps as in claim 3 and

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