Differential Scroll Drive

Abstract

A driven centrifuge mechanism for separating intermixed liquids and solids including a hollow bowl supported for rotation about an axis with a smaller inner diameter at one end and a larger at the other end and a helical conveyor scroll extending through the center for moving solids to a solids opening at one end of the bowl and a liquid opening at the other end of the bowl and a drive at one end of the bowl connected to the bowl and to the scroll for driving the bowl off a main drive motor at a constant speed and for varying the speed of the scroll relative thereto with the main drive motor driving a hydraulic pump which drives a hydraulic motor and through a differential gear means drives the scroll with the speed between the hydraulic pump and motor variable so as to be able to control the speed of the scroll.

Description

BACKGROUND OF THE INVENTION

The invention relates to a centrifuge mechanism for separating solids and liquids from a mixture and controlling the speed of the separator for optimum separation.

Centrifuge separators of this type have been employed in various industries and operate with a mechanism wherein a solid or perforated bowl centrifuge rotates at an optimum separation speed and has an axial screw conveyor or scroll extending coaxially therethrough. The screw conveyor functions to move the solids toward one end of the bowl for a discharge and liquids are discharged at the other end. An unseparated mixture of liquids and solids is supplied to the bowl coaxially through the conveyor to be fet at the processing speed of the conveyor. Control of the speed of the feed may be provided and an important factor is the speed of the scroll. With variant consistencies of the mixture and varying speeds of separation within the bowl, the speed of the screw conveyor must be controllable independent of the bowl speed. Various mechanisms have been provided heretofore to control the speed of the screw conveyor, and each of these structures have encountered disadvantages. Without control of the speed of the screw conveyor scroll, the mixture will not separate properly and matting and jamming can occur within the bowl. Also, because of the relative speed of the screw conveyor, an agitation and resuspension of the solids occurs as they progress toward the solid discharge end of the bowl. Rapid sedimentation without resuspension is essential for effective and efficient separation.

Also, it is essential to be able to control the speed of the conveyor scroll without providing a mechanism which results in the substantial loss of energy or power, for purposes of reducing the initial cost of the mechanism, the operating cost and the space requirements.

It is accordingly an object of the present invention to provide an improved centrifugal separating mechanism for the separation of intermixed liquids and solids which has an improved drive arrangement that results in an enhanced separation function of the machine.

A still further object of the invention is to provide an improved centrifugal separator and drive which effects a saving in power consumption, space and cost for devices heretofore available.

It will be apparent from the description of the invention that alternate embodiments may be employed within the scope and spirit of the invention, and other objects and advantages will become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments in the claims, specification and drawings in which:

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a somewhat schematic side elevational view, taken partially in section, of a structure constructed and operating in accordance with the principles of the present invention; and

FIG. 2 is a schematic showing of a portion of the drive mechanism.

DESCRIPTION

As illustrated in FIG. 1, the separator includes an elongate cylindrically shaped imperforate bowl 10 which is driven by shaft 41 and is supported for rotation about a central axis on end bearings 14 and 15. Surrounding the bowl is a casing 11 which is provided with a solids discharge outlet 12 at one end and a liquid discharge outlet 13 at the other end, and these outlets are lead from solids discharge ports 12a at one end of the bowl 10 and liquid discharge ports 13a at the other end of the bowl.

The bowl is driven in rotation for centrigugal separation of liquids and solids from a mixture fed therein.

Within the bowl is a rotating conveyor scroll 19 having helical lands thereon for moving the solids toward the solids discharge ports 12a. The scroll 19 rotates coaxial with the bowl 10, but at a slightly slower speed being supported the shaft 18 supported on one end on bearing 24 and on the other end on a bearing not shown.

A mixture of liquids and solids is supplied in a continual flow to the bowl through an inlet line 20 which feed axially inwardly past a feed control valve 22 within the scroll and the mixture passes radially outwardly through feed ports 21 in the scroll body.

The process of centrifugal separation which occurs within the bowl is known to those versed in the art and need not be discussed further in detail, however, in operation, the mixture feeds in through the inlet 20 and out through the ports 21 to come into engagement with the inner surface of the rotating bowl 10, and as the solids centrifugally separate from the liquid the solids are conveyed by the scroll toward the smaller diameter end of the bowl, and the liquids flow toward the larger diameter end. The speed of rotation of the scroll for the proper speed of conveyance of the solids is essential for the operation and effective separation and continued satisfactory operation can be attained only by obtaining the proper speed of scroll rotation relative to the speed of rotation of the bowl and the speed of separation of the mixture of products therein.

The bowl is driven directly by a main drive motor 27 through suitable means such as V-pulleys and belts 26. In one form a fluid coupling 28 may be provided within the main drive motor, and the V-belt drive.

For driving the scroll at a controlled speed, a variable speed drive means perferably in the form of a planetary gear reducer 29 is provided. The gear reducer, and its associated mechanism, are driven off of the same main drive motor so that only a single main source of power need be provided. As shown in FIG. 2, the gear reducer in a preferred form embodies a planetary gearing with an output shaft 39 and a first input shaft 41 and a second input shaft 43. The planetary gears 32 are connected to the output shaft 39, and the first input shaft is connected to the sun gear 31, and the second input shaft 43 is connected to the sun gear 33.

The planetary gearing is driven through the input shaft 41 from the main drive motor 27. Control of the speed is attained through the second input shaft 43 which is driven by a hydraulic motor 34. The hydraulic motor is operated from a hydraulic pump 35 and connector lines 36 extend between the pump and motor. The pump is driven also by the main drive motor 27.

In a preferred form, the hydraulic pump 35 and hydraulic motor 34 are variable positive displacement types with the displacement of the pump and motor controlled by control members. Therefore, the pump may operate at a constant speed as driven by the motor 27, and the hydraulic motor 34 will operate at a speed determined by the setting of the displacement of the hydraulic pump 35. On the pump 35 or in the hydraulic lines 36 is a valve 37 which operates to reverse the lines so that the flow between the pump and motor can be set for operation in mode I or mode II. In mode I the sun gear member 33 is allowed to rotate in the same direction as the centrifuge bowl. The differential speed, which is the speed of the bowl minus the speed of the scroll, is determined from the equation:

The hydraulic drive is normally functioning in mode I as a retarder and power flow is such that the fixed displacement hydraulic motor is actually performing as a pump, and the variable displacement pump operates as a motor. This accomplishes energy recovery by hydraulic transmission from the sun gear back to the main drive motor.

In mode I the hydraulic drive may also function as a drive, wherein the hydraulic motor performs as a motor and the hydraulic pump performs as a pump.

In mode II the sun gear member 33 is driven in the opposite direction of rotation of the centrifuge bowl. In this mode the differential RPM is calculated from the equation:

In this mode the hydraulic drive functions as a drive, and the output of the hydraulic pump drives the hydraulic motor. The reduction ratio of the planetary gear reducer, of course, will be chosen as optimum relative to the required speed of the scroll relative to the bowl. For example, in a preferred arrangement the scroll may operate at a differential speed of 16 RPM (absolute speed of 3,784 RPM) while the bowl operates at 3,800 RPM, and the speed of the scroll may be adjusted upwardly or downwardly in accordance with the wetting of the hydraulic pump.

An advantage of this arrangement, as illustrated, is that the output hydraulic pressure of the pump is proportional to the torque required to drive the scroll. Thus, a pressure valve 38 is connected to the lines 36 to indicate fluid pressure and hence indicate the scroll drive torque. The valve 38 may be provided with an overload protection arrangement to prevent damages to drive mechanism, which limits torque on reducer 29, allows motor 34 to "free wheel" or which shuts down the entire mechanism at maximum torque. In the structure shown in FIG. 2, the pressure valve 38 is connected to the feed control valve supplying the mixture of solids and liquids to the separator. By thus decreasing the feed as the torque increases, uniform separation and uniform constant operating conditions can be maintained.

It will be appreciated that the drive arrangement is not positively limited to the exact separator shown, but may be used with different design separators.

Thus, with the arrangement of the instant invention, torque overload protection is obtained, only a single drive source need be provided, accurate differential speed control is obtained, torque overload possibility has been eliminated, and a compact power saving unit has been provided. Recovery of approximately 75 percent of the scroll horsepower consumption which is normally lost through structures of the prior art that employ separate braking devices, is attained.

Claims

I claim as my invention:

1. A driven centrifuge mechanism for separating inter-mixed liquids and solids comprising in combination,

a hollow bowl supported for rotation about an axis and having its inner diameter decreasing toward one end with a solids opening at said one end and a liquids opening at the other end,

a helical conveyor scroll coaxial within the bowl supported for rotation at a controlled speed different than the bowl for moving solids within said bowl toward the solids opening,

a feed means within the bowl for supplying a mixture of liquids and solids to the bowl,

a differential gear drive means having an output shaft connected to the scroll and having first and second input shafts, said first input shaft connected to the bowl,

motor means drivingly connected to the first input shaft for driving the bowl and first input shaft at a predetermined constant speed,

a hydraulic pump driven by said motor means and having an output, a hydraulic motor connected by fluid lines to the output of the hydraulic pump for being driven thereby and drivingly connected to the second input shaft of said gear drive means, and

means for controlling the relative flow displacement of said pump and said motor so that the speed of said second input shaft is controlled to thereby control the speed of said output shaft and control the speed of the scroll relative to the speed of the bowl.

2. A driven centrifuge mechanism for separating intermixed liquids and solids constructed in accordance with claim 1 wherein said pump is a positive displacement pump and with controlling means, varies the fluid direction and output of the pump relative to its driven speed.

3. A driven centrifuge mechanism for separating intermixed liquids and solids constructed in accordance with claim 1 wherein said differential gear drive means is a planetary gearing having sun gears.

4. A driven centrifuge mechanism for separating intermixed liquids and solids constructed in accordance with claim 3 wherein the sun gears are connected to the first and second input shafts respectively.

5. A driven centrifuge mechanism for separating intermixed liquids and solids constructed in accordance with claim 1 and including a liquid coupling between the motor means and said first input shaft.

6. A driven centrifuge mechanism for separating intermixed liquids and solids constructed in accordance with claim 1 and including a pressure sensing valve connected to the output of the hydraulic pump.

7. A driven centrifuge mechanism for separating intermixed liquids and solids constructed in accordance with claim 6 including a feed control valve connected to said feed means and connected to said pressure sensing valve and operated as a function of the pump pressure output to regulate the feed to the bowl.

8. A driven centrifuge mechanism for separating intermixed liquids and solids comprising in combination,

a hollow bowl supported for rotation about an axis and having its inner diameter decreasing toward one end with a solids opening and a liquids opening,

a helical conveyor scroll coaxial within the bowl supported for rotation at a controlled speed different than the bowl for moving solids within said bowl toward the solids opening,

a feed means within the bowl for supplying a mixture of liquids and solids to the bowl,

a variable speed output drive means having an output shaft connected to the scroll and having first and second input shafts,

motor means drivingly connected to the bowl and connected to the first input shaft for driving the bowl and first input shaft at a predetermined constant speed,

a hydraulic pump driven by said motor means,

a hydraulic motor connected by fluid lines to the hydraulic pump for being driven thereby and drivingly connected to the second input shaft of said gear drive means, and

means for controlling the relative flow displacement of said pump and said motor so that the speed of said second input shaft is controlled to control the speed of the scroll relative to the speed of the bowl.

9. A driven centrifuge mechanism for separating intermixed liquids and solids constructed in accordance with claim 1 wherein the controlling means includes a control valve means for controlling flow direction.