WO1993011359A1

WO1993011359A1 - Pump with built-in vacuum pump

Info

Publication number: WO1993011359A1
Application number: PCT/SE1992/000828
Authority: WO
Inventors: Ronny Höglund; Ulf Jansson
Original assignee: Kamyr Aktiebolag
Priority date: 1991-12-03
Filing date: 1992-11-30
Publication date: 1993-06-10
Also published as: AU3120793A; SE9103588D0; SE468293C; SE468293B; SE9103588L

Abstract

A pump for pumping pulp, comprising a main housing (1); a shaft (4) rotatable therein; a rotor (15) on the shaft (4) for fluidization of the pulp; an impeller (12) on the shaft (4) for pumping the pulp; a vacuum pump (23) having a vacuum pump housing (24), a vaccum impeller (26) on the shaft (4) and an end wall (10) of the vacuum pump housing (24), said end wall and an inner partition (9) between them defining a vacuum chamber (25) in which the vacuum impeller (26) and a liquid ring rotate; a gas passage system for withdrawing gas separated out of the pulp, said gas passage system comprising besides the vacuum chamber (25) gas passageways (20, 21, 22, 36) in the impeller (12), partition (9) and end wall (10); and a make-up air passageway (39) for supplying air from outside when the vacuum exceeds a predetermined value. According to the invention the make-up air passageway (39) is arranged in said end wall (10) of the vacuum pump (23), extends through the end wall (10) directly to said vacuum chamber (25) and opens into this radially inside the liquid ring and circumferentially at a distance from the conduit (36) of the gas passageway through which gas is evacuated from the vacuum chamber (25) to outside the pump.

Description

Pump with built-in vacuum pump

The present invention relates to a pump for pumping a suspension of cellulosic fibrous material, said pump comprising a main housing having a suspension inlet and a suspension outlet generally perpendicular to the inlet; a shaft rotatable about an axis of rotation; a rotor mounted to said shaft for rotation therewith for effecting fluidization of the suspension; an impeller mounted to said shaft for rotation therewith for effecting pumping of the fluidized suspension; a vacuum pump of liquid ring type including a vacuum pump housing, a vacuum impeller mounted to said shaft for rotation therewith, a partition mounted between said main housing and the vacuum pump housing to separate the vacuum impeller from said impeller for pumping the suspension, and an end wall of the vacuum pump housing, said end wall and partition between them defining a cylindrical vacuum chamber in which the vacuum impeller rotates together with a liquid ring; a gas passage system extending from an area in the main housing in front of its impeller where gas separated out of the suspension by said rotor is collected, to an area outside the vacuum pump housing, said gas passage system comprising besides said vacuum chamber gas passageways in said impeller, partition and end wall; and a make-up air passageway connected to said gas passage system for supplying air from outside the pump when the vacuum created by the vacuum pump exceeds a predetermined value.

The problems addressed by the invention are to be found in a make-up air passageway of the type described in US-4,776,758, corresponding to EP-0 298 949. The known make-up air passageway has several bends and extends through a plurality of construction elements to achieve connection with the gas passage system for evacuation of gas at a point prior to the vacuum pump. Such a make-up air passageway is time-consuming and complicated in manufacture, thus also increasing manufacturing costs. For special reasons the partition wall in front of the vacuum pump must be made as slim as possible and the radial part of the make-up air passageway formed in this partition wall is therefore relatively narrow. Under certain operating conditions there is a risk, when the make-up air passageway is closed, of the suspension penetrating into said radial part and back parts of the make-up air passageway and becoming lodged there due to the narrowness of the passages. The make-up air passageway must therefore be cleaned at regular intervals, work which is not only time-consuming but also difficult because of the many bends in the make-up air passageway.

The object of the invention is to substantially reduce the above-mentioned problems. The invention thus aims at simplifying manufacture of the make-up air passageway in the vacuum pump, simplifying cleaning of the make-up air passageway if it becomes clogged by suspension, and also reducing the risk of such clogging.

This is achieved according to the invention in that said make-up air passageway is arranged in said end wall of the vacuum pump, extends through the end wall directly to said vacuum chamber and opens into this radially inside the liquid ring and circumferentially at a distance from the conduit of the gas passageway through which gas is evacuated from the vacuum chamber to outside the pump.

The make-up air passageway according to the invention is thus considerably shorter than in the known arrangement, which is an advantage both from the manufacturing and the cleaning aspects. Moreover, it is located further away from the suspension impeller than before, thus contributing to decreasing the risk of clogging. The invention will be described in the following by way of example, with reference to the accompanying drawing in which

5 Figure 1 is a longitudinal sectional view of a suspension pump with a built-in vacuum pump, provided with a make-up air passageway in accordance with the invention.

With reference to Figure 1 it is shown therein a

10 suspension pump for pumping a suspension of a cellulosic fibre material, particularly paper pulp of medium consistency, i.e. about 6-15% dry solids. The suspension pump comprises a main housing 1 with a suspension inlet 2 and a suspension outlet 3. The outlet 3 is generally

15 perpendicular to the inlet 2. The suspension pump includes a shaft 4 rotatable about an axis of rotation 5 and driven by a motor 6. The inlet 2 is concentric with respect to the axis of rotation 5. The housing 1 has a cylindrical part 7 extending from the inlet 2 and, in

20 relation to the cylindrical part 7, a radially enlarged part 8 in which said suspension outlet 3 is disposed. A wall member closes the suspension pump at its end facing away from the suspension inlet 2, said wall member including a partition 9 and an end wall 10, through which

25 wall parts 9, 10 said shaft 4 extends. Seals 11 provide requisite sealing between the shaft 4 and end wall 10 of the housing.

The suspension pump comprises an impeller 12 of radial 30 wheel type mounted to said shaft 4 for rotation in the •_* ^• radially enlarged housing part 8. The impeller 12 has a plurality of front blades 13 with their side edges facing ^•~ the suspension inlet 2 and a plurality of rear blades 14 with their side edges facing the partition wall 9.

35

Further, the suspension pump is also provided with a fluidizing rotor 15 mounted to the shaft 4 via the impeller 12. The rotor comprises a plurality of blades 16 attached to the impeller 12 and extending at a distance from and parallel to the axis of rotation 5 and the cylindrical inside of the housing part 7. The suspension pump may be applied horizontally or vertically in an opening in the bottom of a container containing pulp of medium consistency. The rapid rotation of the rotor blades 16 sets the pulp in motion at such high speed and causes such turbulence in the pulp that this is fluidized to pumpable condition. The gas present in larger or smaller quantities in the fiber suspension will collect in front of the first impeller during the fluidization process, forming a gas bubble 19. The gas is evacuated via a system of gas passageways including, inter alia, a plurality of small axial holes 20 in the impeller 12, the inner part 21 of the space between the impeller 12 and the partition 9, and an annular passage 22 through the partition 9.

The suspension pump is also equipped with a vacuum pump

23 of liquid ring type including a pump housing 24 with a cylindrical vacuum chamber 25 and a rotating impeller 26 having a plurality of blades 27 defining pockets between them. The vacuum chamber 25 is defined by the partition wall 9 and end wall 10 and forms a part of said gas passage system. The impeller 26 of the vacuum pump is mounted to said shaft 4 for rotation with the suspension impeller 12 and rotor 15 about the axis of rotation 5. In order to obtain a suction action, the vacuum chamber 25 is arranged eccentrically in relation to the impeller 26, the vacuum chamber 25 containing a liquid ring which thus has the same eccentricity as the chamber 25 in that the liquid ring slides along the cylindrical inner side 30 of the chamber. The radial size of the liquid ring is adjusted such that its inner eccentric surface circumferentially lies completely within the span of the blades 27. The outer ends of the blades 27 are thus located within the liquid ring. Liquid for regulating the size of the liquid ring is supplied through a conduit 32. Since the liquid ring is eccentric in relation to the impeller 26, said blade pockets will gradually be enlarged on the suction side of the vacuum pump and gradually be decreased on its pressure side seen in the direction of rotation of the impeller.

Said annular passage 22 in the partition 9 opens into the vacuum chamber 25 through an arc-shaped gas inlet 35. The vacuum chamber 25 communicates with a conduit 36 for removal of the gas evacuated from the centre of the suspension pump. The conduit 36, which thus forms a part of said gas passage system, extends through the end wall 10 and includes an arc-shaped gas outlet 37 from the vacuum chamber 25. The gas outlet 37 is thus arranged on the inside of the end wall 10 and is displaced substantially 180° in circumferential direction in relation to the gas inlet 35. The gas inlet 35 and gas outlet 37 are arranged close to the hub 38 of the impeller 26, the gas inlet 35 becoming larger and the gas outlet 37 becoming narrower in circumferential direction in the direction of rotation of the impeller. The radially outermost edge of the arc-shaped gas outlet 37 determines the size of the liquid ring. Excess liquid will therefore be pressed out through the gas outlet 37.

When the pulp level is low in the pulp tower to which the pump is connected, the pressure at the inlet to the pump will be correspondingly low (atmospheric pressure and below), so that large and varying quantities of air in the pulp will be separated in the pump and disturbing pumping. The pressure at the centre of the impeller 12 is below atmospheric pressure and the air is evacuated by means of the vacuum pump 23. Since the quantities of air separated out vary from one time to another the pressure will also vary. In order to maintain constant pressure, therefore, make-up air is supplied via a passageway 39 provided with a pressure-sensitive valve 40 set at a predetermined under pressure, e.g. -0.4 bar. The built-in vacuum pump is dimensioned for a capacity enabling it to evacuate the largest quantity of air that can be separated out of the pulp at low pressure.

According to the present invention the make-up air passageway 39 is arranged in the end wall 10 of the vacuum pump, extending only through the end wall 10 and opening directly into the vacuum chamber 25, the orifice part 41 of the make-up air passageway 39 thus being disposed radially inside the liquid ring and spaced circumferentially from the gas outlet 37 of the conduit 36, preferably substantially 180° therebetween. The orifice part 41 is thus preferably disposed within the area formed by an axial projection of the opposite gas inlet 35 to the vacuum chamber 25. The orifice part 41 may have the same arc-shaped extension as said gas inlet 35. Generally the area of the orifice part 41 shall be equal to or less than the area of the gas inlet 35.

Claims

C L A I M S

1. A pump for pumping a suspension of cellulosic fibrous material, said pump comprising a main housing (1) having a suspension inlet (2) and a suspension outlet (3) generally perpendicular to the inlet (2); a shaft (4) rotatable about an axis of rotation (5); a rotor (15) mounted to said shaft (4) for rotation therewith for effecting fluidization of the suspension; an impeller (12) mounted to said shaft (4) for rotation therewith for effecting pumping of the fluidized suspension; a vacuum pump (23) of liquid ring type including a vacuum pump housing (24), a vacuum impeller (26) mounted to said shaft (4) for rotation therewith, a partition (9) mounted between said main housing (1) and the vacuum pump housing (24) to separate the vacuum impeller (26) from said impeller (12) for pumping the suspension, and an end wall (10) of the vacuum pump housing (24), said end wall and partition (9) between them defining a cylindrical vacuum chamber (25) in which the vacuum impeller (26) rotates together with a liquid ring; a gas passage system extending from an area in the main housing (1) in front of its impeller (12) where gas separated out of the suspension by said rotor (15) is collected, to an area outside the vacuum pump housing (24), said gas passage system comprising besides said vacuum chamber (25) gas passageways (20, 21, 22, 36) in said impeller (12), partition (9) and end wall (10); and a make-up air passageway (39) connected to said gas passage system for sypplying air from outside the pump when the vacuum created by the vacuum pump (23) exceeds a predetermined value, characterized in that said make-up air passageway (39) is arranged in said end wall (10) of the vacuum pump (23), extends through the end wall (10) directly to said vacuum chamber (25) and opens into this radially inside the liquid ring and circumferentially at a distance from the conduit (36) of the gas passageway through which gas is evacuated from the vacuum chamber (25) to outside the pump.

2. A pump as claimed in claim 1, characterized in that the make-up air passageway (39) extends linearly through the entire end wall (10) at least to its orifice part (41) at the vacuum chamber (25).

3. A pump as claimed in claim 1 or 2, characterized in that the make-up air passageway (39) opens into the vacuum chamber (25) within an area formed by an axial projection of the gas inlet (35) to the vacuum chamber (25) forming a part of the gas passage system disposed in said partition (9).

. A pump as claimed in claim 1, 2 or 3, characterized in that the area of the orifice part (41) of the make-up air passageway (39) is at most as large as the area of the gas inlet (35) to the vacuum chamber (25).

5. A pump as claimed in any of claims 1-4, characterized in that the orifice part (41) of the make¬ up air passageway (39) is displaced substantially 180° in circumferential direction in relation to the gas outlet (37) from the vacuum chamber (25) to said conduit (36).