Rotary kinetic fluid motors or pumps – Runner has spirally arranged blade or fluid passage – Extending along runner axis
Reexamination Certificate
2001-08-06
2003-04-22
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Runner has spirally arranged blade or fluid passage
Extending along runner axis
C415S001000, C415S143000, C415S169100, C416S176000
Reexamination Certificate
active
06551054
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to an improved method and apparatus for pumping liquids or various suspensions. The method, apparatus and rotor used in connection therewith are especially preferably suitable for pumping fiber suspensions of the paper and pulp industry at medium consistency (8-20%) and high consistency (over 20%). According to a preferred embodiment of the invention the method, apparatus and rotor used in connection therewith are suitable for pumping viscous and/or air-containing mediums. The method invention mainly relates to intensifying the pumping of liquids or various suspensions, but also to methods of eliminating the disadvantages caused by air and/or gases existing in and being absorbed into said medium. Especially the invention of the apparatus relates preferably to a construction utilized in connection with a centrifugal pump in order to increase the inlet pressure of the pump.
Prior art knows a large amount of centrifugal pumps that have been and still are used for pumping the fiber suspensions in the wood processing industry. The biggest group is presented by centrifugal pumps having a conventional basic construction with some in-essential changes therein to make them capable of pumping pulp. As an example of this kind of changes, e.g. mounting so-called inducers in front of the actual impeller for facilitating the flow of the pulp to the actual impeller of the pump may be stated. Despite many attempts and minor constructional changes, pumps of the described type are hardly capable of pumping a pulp at a consistency above 6-8%. The reason for this is both the increasing air content of the pulp as the consistency increases, whereby the air or gas bubble accumulated in the center of the impeller prevents the pulp from passing to the impeller, and the poor flow properties of thick pulp in the suction duct of the pump or from the pulp-containing space into the suction duct of the pump.
The second stage, entering the market in the late 1970-'s, was the so-called MC™ pump characterized in that in the inlet opening of the pump there is arranged a rotor most usually extending through the suction duct to some extent into the pulp container, the drop leg or the like, by means of which rotor bonds between fibers of the fiber suspension are being loosened by feeding energy in form of a shear force field into the pulp, whereby the flow of the pulp to the impeller of the pump is facilitated. The objective of these pumps was to make it possible to pump pulps at the consistency of 8-15%. The main problem was considered to be the poor flow properties of pulp at said consistency in the suction duct of the pump, due to which fact the invention was at that time related to methods of getting the pulp to flow in the suction duct of the pump to the impeller. Various embodiments of this kind of pump are described e.g. in U.S. Pat. Nos. 4,410,337, 4,435,193 and 4,637,779. All said solutions are characterized in that they both fluidize the pulp being pumped and remove therefrom gas, most usually air, that disturbs both the pumping and the further treatment of the pulp. The fluidizing is understood to mean breaking the pulp pieces in the fiber suspension into smaller parts to such an extent that the pulp starts behaving as a fluid. The fluidizing is effected by the blades of a rotor located inside the relatively long suction duct of the pump, which blades are located essentially at a radial plane and mainly axially, although some solutions have utilized rotor blades that are twisted to some extent. In all presented pump solutions the separation of gas is effected due to centrifugal force into the hollow center of the rotor in front of the impeller, wherefrom the gas is further removed through openings in the back plate of the impeller in most cases by means of suction created by a vacuum pump. Said suction or vacuum pump, most usually a so-called liquid ring pump, is located either separately from the actual centrifugal pump in connection with a drive of its own or alternatively on the same shaft with the centrifugal pump. As examples of the latter case, e.g. U.S. Pat. Nos. 5,078,573, 5,114,310, 5,116,198, 5,151,010 and 5,152,663 may be mentioned.
About the constructional details of prior art MC™ pumps it may be stated that in all said publications the rotor extends to some extent into the pulp-containing space. Most explicitly this has been described in U.S. Pat. No. 4,637,779, in which the rotor is mentioned to be extending into the tank for about 3 inches, i.e. about 75 mm. This dimension is really true as a maximum range, because the production program mainly includes pumps, the rotor of which does not extend even so deep into the suction chamber. The maximum dimension may be said to be about 0.5*the diameter of the suction duct, which ratio in reality is diminished as the diameter of the suction duct is increased. In practice, the diameter of the smallest MC™ pump is about 150 mm, whereby said ratio is fulfilled. As the diameter of the suction duct further increases, the factual extension of the rotor into the pulp chamber practically does not increase.
Because it was seen from practice, that said extension of the rotor into the chamber was not enough, U.S. Pat. No. 4,971,519 was made to protect a solution, in which the fluidizing rotor was made to extend into the chamber to an extent of at least the length of the diameter of the suction opening of the pump. In an embodiment described in said patent, the end of the fluidizing rotor was provided with blades feeding pulp towards the suction opening of the pump, by which blades a relatively large zone of moving pulp was effected in the vicinity of the suction opening in order to ensure that the pulp would not easily arch in the vicinity of the suction opening.
Now that a lot of practical experience has been gained on said MC™ pumps it has been noticed that the pumps working as such excellently and reaching at their best the consistency ranges up to about 15% can be developed further. The main consumption at the initial stage of developing the MC™ pumps was that the biggest obstacle of pumping a thick pulp is the friction between the wall of the suction duct and the pulp, which friction was attempted to be eliminated by fluidizing the pulp in the suction duct. A second problem was considered to be the discharge of the pulp from the suction chamber or drop leg into the suction duct, because the thick pulp gradually tends to fill the openings surrounded by sharp edges, i.e. including the suction opening. As a result, the fluidizing rotor was decided to be arranged to extend to a certain length into said chamber in order to make the rotor tear off the fibers and fiber flocs possibly attached to the edges of the openings and thus prevent the clogging of the suction opening. However, the old rules self-evident to a designer of centrifugal pumps were maintained, according to which rules the flow of the material being pumped has to be as laminar as possible when entering the pump to eliminate flow losses. References of this kind are still found, e.g. in said U.S. Pat. No. 4,637,779 wherein on column 2, pages 24-30 it is stated that a prior art apparatus generates in front of and around the suction inlet of the pump a “doughnut-shaped” turbulent, i.e. at least partly fluidized, zone which really is located in the vicinity of the edges of the suction inlet of the pump. In said US-publication said phenomena has been considered to disturb the pumping, believing in rules on pump design, and accordingly the tips of the rotor blades extending into the pulp chamber or the like of the MC™ pump have been twisted to give the pulp a force component acting towards the suction inlet. In the publication the utilization of said solution is based on giving the pulp flowing inwards a pressure that facilitates the removing of gas in front of the impeller.
The next confronted problem was the one familiar from pumping pulps of medium consistency by means of MC™ pumps, i.e. even if the pump and its rotor were
Peltonen Kari
Vesala Reijo
Vikman Vesa
Look Edward K.
McAleenan J. M.
Nixon & Vanderhye P.C.
Sulzer Pumpen AG
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