PULP PUMP

Abstract: A centrifugal pump for pumpinp a pulp suspension, where the pump comprises a housing (10) with an inlet and an outlet for the pulp suspension and on a rotary shaft mounted an impeller with pump blades (15), which extend from a hub (16) outward along a wheel disc (17), where openings (19) for the discharge of gas are formed in the wheel disc (17). The hub (16) behind the wheel disc (17) is provided with vacuum pump blades (50), which are surrounded by a divisible vacuum pump housing (51) comprising an outer cylindric wall (52), which is eccentric in relation to the vacuum pump blades (50), a front wall (54) with a suction opening (55) for gas and a rear wall (53) with an exhaust opening (56) for gas. The rear wall (53) is axially movable for adjusting vacuum by means of a gap (65) between the lateral edges of the vacuum pump blades (50) and the rear wall (53). A gas passage (59) is provided between the wheel disc (17) and the front wall (54) for communication between the openings (19) in the wheel disc (17) and the gas suction opening (55). The gas exhaust opening (56) is connected to a gas outlet (58).

Description: Pulp pump This invention relates to a centrifugal pump for pulp suspensions of lignocellulosic material. The in vention , more precisely, refers to a pump where gas, such as air, is separated from the pulp in the pump. Gas following along with the pulp causes problems at pumping with centrifugal pumps. The gas in the pulp collects to bubbles, which accumulate in front of the impeller whereby the capacity of the pump deteriorates. This problem can be overcome in that the gas is evacuated from the space in front of the impeller, for example by means of vacuum pumps of the kind of liquid ring pumps. These pumps are often a separate vacuum pump, the suction line of which is connected to the sealing space of the pulp pump. They can also be designed as a separate vacuum impeller in the form of a liquid ring impeller located on the shaft of the pulp pump so that a common drive for both impellers is obtained. In the cases when a separate vacuum pump is used, the pulp pump is relatively complicated and expensive due to the fact that several components are comprised in the system. When a separate liquid ring impeller of conventional kind is placed on the same shaft as the pulp pump, the capacity of the liquid ring impeller is restricted for space reasons. The present invention implies that the aforesaid problems can be eliminated in that the vacuum impeller is integrated in the impeller of the pulp pump. The structure is compact and simple, and the capacity of the vacuum pump can be easily controlled. The arrangement is formed so that it can easily be combined with a separate vacuum pump, so that both pumps can be used in parallel Alternatively, the separate vacuum pump can be coupled in at operation drop-out of the integrated vacuum pump according to the invention in order thereby to ensure the accessability for the centrifugal pump. The characterizing features of the invention are apparent from the attached claims. The invention is described in greater detail in the following with reference to the accompanying Figures illustrating an embodiment of the invention. Fig. 1 is a section through a centrifugal pump according to the invention; Fig. 2 is a section according to A-A in Fig. 1. Fig. 3 shows a portion of Fig. 1 on an enlarged scale. The centrifugal pump shown comprises a pump housing 10 with an inlet 11 and an outlet 12 for the pulp suspension. Such pumps are used at relatively high pulp concentration, for example 8-12%. On a rotary shaft 13 in the pump housing 10 an impeller 14 with pump blades 15 is located, which extend from a hub 16 outward along a wheel disc 17. On the rear side of the wheel disc 17 rear blades 18 are located. The wheel disc 17 is formed with openings 19 for discharging gas which has collected in front of the impeller. The openings preferably are formed as slits extending from the hub 16 outward. Behind the wheel disc 17 the hub 16 is provided with vacuum pump blades 50, which are surrounded by a vacuum pump housing 51. This vacuum pump housing 51 comprises an outer cylindric wall 52, a rear wall 53 and a front wall 54. In order to render mounting and disassembling possible, the vacuum pump housing with its walls is divisible, preferably into two parts, an upper and a lower half. The cylindric wall 52 is eccentric in relation to the vacuum pump blades 50, so that a liquid ring pump is formed. In the front wall 54 a suction opening 55 for gas, and in the rear wall 53 an exhaust opening 56 for gas are located. These openings 55, 56 are placed spaced from each other in the circumferential direction, for gas suction into the vacuum pump housing and, respectively, gas exhaust from the vacuum pump housing. This effect is brought about by the rotation of the vacuum pump blades and the volume variation in the circumferential direction of the vacuum pump housing as a consequence of that the cylindric wall 52 is located eccentrically . The exhaust opening 56 communicates with a chamber 57 behind the rear wall 53 for gas evacuation through a gas outlet 58. On the rear side of the impeller 14 between the wheel disc 17 and the front wall 54 of the vacuum pump housing a gas passage 59 is located for communication between the openings 19 in the wheel disc 17 and the suction opening 55. In a sealing housing 60 in the pump housing 10 outside the outer wall 52 a dilution chamber 61 is located. This chamber 61 is provided with an inlet 62 for the supply of dilution liquid. Through openings 63 in the front wall 54, located preferably in the division surfaces in the divided vacuum pump housing 51, the chamber 61 communicates with the passage 59, whereby the supplied dilution liquid is utilised both as drive liquid to the liquid ring in the vacuum pump and as flushing liquid in the gas passage 59. The chamber 61 communicates also via a rear opening 67 in the rear wall 53 with a rear space 68 for a shaft sealing 69. The supplied flushing liquid can thereby also be utilized for external flushing of the sealing 69 in the space 68 The rear wall 53 of the vacuum pump housing 51 is axially adjustable in the sealing housing 60 by means of an adjusting device 64 for setting an axial gap 65 between the lateral edges of the vacuum pump blades 50 and the rear wall 53 for vacuum control . An additional connection opening 66 in the sealing housing 60 to the dilution chamber 61 preferably can be provided for rendering it possible to couple-in a vacuum system or a vacuum pump coupled in parallel (not shown). When a pulp suspension is pumped from the inlet 11 to the outlet 12, gas included in the pulp will collect in front of the impeller 14. The vacuum pump integrated in the hub 16 then will suck the gas through the openings 19 in the wheel disc 17 and therefrom via the gas passage 59 into the vacuum pump through the suction opening 54. By the pumping effect brought about by the vacuum pump blades 50 together with the rotating liquid ring in the vacuum pump housing 51 eccentric with the hub 16, the gas is pumped out through the exhaust opening 56 and evacuated through the gas outlet 58. By adjusting the gap 65 the capacity of the vacuum pump can be controlled. By inreasing the gap width the liquid leakage through the gap will increase, whereby the capacity of the vacuum pump is reduced, and vice versa. When a separate vacuum pump shall be used, it is coupled to the connection 66 in order to de-air the gas passage 59 via the openings 63 and dilution chamber 61. This separate vacuum pump can then serve in parallel with the integrated vacuum pump according to the invention or be coupled-in at operation drop-out of the integrated vacuum pump. Thereby the drive of the centrifugal pump is ensured. The invention, of course, is not restricted to the embodiments shown, but can be varied within the scope of the claims.

Claims: Claims 1. A centrifugal pump for pumping a pulp suspension, where the pump comprises a housing (10) with an inlet and an outlet for the pulp suspension and mounted on a rotary shaft an impeller, the pump blades (15) of which extend from a hub (16) outward along a wheel disc (17), and openings (19) for the discharge of gas are formed in the wheel disc (17), c h a r a c t e r i z e d in that the hub (16) behind the wheel disc (17) is provided with vacuum pump blades (50), which are surrounded by a divisible vacuum pump housing (51) comprising an outer cylindric wall (52), which is eccentric in relation to the vacuum pump blades (50), a front wall (54) with a suction opening (55) for gas and a rear wall (53) with an exhaust opening (56) for gas, that the rear wall (53) is axially mo able for the adjustment of vacuum by means of a gap (65) between the lateral edges of the vacuum pump blades (50) and the rear wall (53), that a gas passage (59) is located between the wheel disc (17) and the front wall (54) for communication between the openings (19) in the wheel disc (17) and the gas suction opening (55), and that the gas exhaust opening (56) is connected to a gas outlet (58). 2. A centrifugal pump as defined in claim 1, c h a r a c t e r i z e d in that a dilution chamber (61) is located outside the outer wall (52)for the supply of dilution liquid to the gas passage (59) via openings (63) in the front wall (54) . 3. A centrifugal pump as defined in claim 2, c h a r a c t e r i z e d in that the dilution chamber (61) via a rear opening (67) communicates with a rear space (68) for external flushing of a shaft sealing (69) in said space (68) 4. A centrifugal pump as defined in any one of the preceding claims, c h a r a c t e r i z e d in that a connection opening (66) is provided for rendering it possible to couple-in a vacuum control system or a vacuum pump coupled in parallel.

Inventors: DANIELSSON PETER, FORSLUND KJELL, DANIELSSON, PETER, FORSLUND, KJELL
Applicants: DANIELSSON PETER, FORSLUND KJELL, VALMET FIBERTECH AB, DANIELSSON, PETER, FORSLUND, KJELL
Application year: 1999
Main classification: F04D7
IPC codes: F04D7, F04D29, F04D31