Method and use of an apparatus for pumping a medium

Abstract: The present invention discloses a method and a centrifugal pump for pumping fiber suspensions of the pulp and paper industry in which the fiber suspension is caused to flow into a centrifugal pump housing in which space a vortex flow is created to prevent the suspension from forming a strong fiber network and from causing blockage of the system. The centrifugal pump includes a housing provided with one inlet (22) and at least two non-symmetrical outlets (92, 94), at least one of the outlets being preferably provided with a means for regulating the flow through the outlet. The centrifugal pump further includes an impeller/rotor (78, 80) for moving the suspension through the several outlets (92, 94) towards further processing devices.

Description: The present invention relates to a method of pumping a 5% to 25% consistency fiber suspension of a pulp and paper industry by means of a centrifugal pump. The present invention relates further to the use of a centrifugal pump for pumping a 5 % to 25 % consistency fiber suspension of a pulp and paper industry and for dividing said medium consistency fiber suspension into at least two partial streams of said medium consistency fiber suspension. A method according to the preamble of claim 1 and a centrifugal pump having a housing, an inlet channel, an impeller arranged on a shaft within the housing and a fluidizing rotor arranged substantially coaxially with the housing on the shaft and extending into the inlet channel, are known from EP-A-0 300 251. The pulp and paper industry often requires that a fiber suspension is conveyed from a vessel or a pipe continuously or intermittently to several places, e.g. from a storage tank simultaneously to two or more processing devices. When the consistency of the suspension is low, i.e. up to about 5 per cent, dividing of the flow itself does not cause any problems, but when the consistency is higher than about 5% there is only a small amount of free liquid between the fibers and the fibers form a strong fiber network. The strength of the network depends mainly on the consistency. The characteristics of medium or high consistency fiber suspensions are quite different from those of a true liquid and the handling thereof becomes more difficult the higher the consistency is. As stated, when the consistency is low, usually less than 5 %, it is possible to arrange a number of branch pipes to a pulp line beginning from the centrifugal pump outlet, whereby the suspension flowing in the pipe is able to flow freely into each branch pipe. In other words, the fiber network is not of sufficient strength to prevent the flow from dividing in a junction point. But when the consistency is high, e.g. about 8 to about 25 per cent, the fiber suspension forms a strong fiber network and dividing the fiber suspension in a pipeline into several branch pipes or other conduits is mostly impossible without special measures. When a high consistency fiber suspension arrives, usually in form of a plug flow, at a junction point in the pipeline, the fiber network is too strong to be dispersed. The rigid fiber network tends also to adhere to the pipe resulting in clogging of the pipeline. The above described problem in dividing the pulp flow is avoided by subjecting the flow to a field of shear forces of sufficient strength in the junction point so that the bonds between the fibers are loosened or broken and at least partially turbulent flow is created in which there exist no fiber networks that would prevent the division of the suspension. In high consistency fiber suspension, (above about 5% to 8%) sufficient shear forces are generated by a mechanical member arranged at or in the vicinity of the junction point. In many practical applications the above described dividing apparatus has been placed in a conduit closely after or downstream of the pump. The pressure drop in the dividing apparatus, particularly when the consistency of the pulp suspension is high, is often so high that the pressure created by the pump is almost totally lost in the dividing apparatus. Up to now, there have been known devices designed solely for dividing the flow of fiber suspension. In other words, the known devices must be located in a pipeline downstream of a pump that is creating at least the pressure difference required for causing the pulp to flow through the dividing apparatus. However, in this known apparatus pressure loss occurs in the pipeline. The known apparatus is complex and wastes the more energy the higher the consistency of the pulp is. At this stage it is worth noticing that in many cases the pulp transfer distances are quite short in a pulp mill so that only a slight increase in pulp pressure is needed to ensure a continuous pulp flow, pipe junctions or dividing apparatus excluded. The known apparatus may work satisfactorily when all the branch pipes are open, i.e. valves are kept open and the pulp may flow freely through the valves. But problems are to be expected when one should decrease the flow i.e. adjust the opening of the valve, as there may be a need to change the flow depending on different factors in a pulp mill. There may also be a need to vary the pressure. SU-1 571 299 A1 discloses a pump which separates abrasive particles from a liquid by centrifugal force. EP-A-0 300 251 discloses a pump having one fiber suspension outlet and several outlets for liquid only. Each of these liquid outlets is provided with a filter surface so that no fibers can be discharged through these liquid outlets. The object of this known pump is to separate liquid and to thicken the pulp. An object of the present invention is to provide a method of pumping a 5% to 25% consistency fiber suspension of a pulp and paper industry by means of a centrifugal pump by which the flow of a fiber suspension may be divided and the suspension be transferred in a controlled and reliable manner. More specifically, the object of the present invention is to provide a method by which the flow of a fiber suspension may be divided into several partial streams and be simultaneously moved by said pump via several flow channels to different places or locations in the pulp treating system. The applications for such a pump are numerous. The pump may be used, for instance, to transfer fiber suspensions simultaneously to a number of storage tanks, to a number of feed pipes or to recirculate a portion of the pulp. Thus, it is also an object to provide a use of a centrifugal pump for pumping a 5 % to 25 % consistency fiber suspension of a pulp and paper industry and for dividing said medium consistency fiber suspension into at least two partial streams of said medium consistency fiber suspension. The objects underlying the present invention are achieved by the method as defined in claim 1 and by the use of a centrifugal pump as defined in claim 9. The invention is particularly useful in applications where there is a need to have a by-pass flow of a desired volume or of a desired pressure from a device to some other place in the process or, for instance, back to the suction piping of the pump or to the suction vessel of the device. The method of the present invention comprises the steps of connecting an inlet channel of the pump to the source of the suspension; introducing the flow of the suspension through the inlet channel into the housing of the pump; fluidizing the suspension being pumped in the inlet channel; pumping the suspension out of the pump; dividing the 5% to 25% consistency fibre suspension into partial streams of substantially equal composition by creating a pressure difference between the inlet and each of the at least two pulp outlets of the pump for discharging the suspension as substantially homogenous partial streams through said pulp outlets; and creating a field of turbulence sufficient for ensuring that local fibre concentrations, e.g. plugs or settled fibres, are avoided in the pump housing from the inlet channel to each of the outlets. The centrifugal pump used is provided with a housing, an inlet channel, an impeller arranged on a shaft within the housing, and a fluidizing rotor arranged substantially coaxially with the housing on the shaft and extending into the inlet channel, at least two fiber suspension outlets for discharging the fiber suspension, and wherein the fiber suspension outlets are disposed in the housing at different axial locations and/or radial locations and/or circumferential locations with respect to the rotational axis of the pump for dividing the suspension being pumped into partial streams of substantially equal composition. The method and also the use of a centrifugal pump in accordance with the present invention result in a number of additional advantages. One advantage of providing a great number of outlet openings in the vortex chamber is that the most suitable outlet can be chosen and the rest closed. In other words, as the outlets are non-symmetrically arranged, one is able to choose the outlet giving just the correct pressure and/or volume flow. Another advantage is that any solid, liquid or gas can be fed through one or more of the openings or ducts into the vortex chamber. The medium to be fed may, for instance, be dilution liquid or chemicals. Accordingly, it is not necessary that all the openings or ducts in the vortex chamber, excluding the inlet opening for the pulp, are used as outlet openings for the pulp. Still, one of the most important advantages relates to the reliable and cost efficient operation of the dividing centrifugal pump. The flow regulating means may be arranged so close to the housing that the risk of clogging is practically negligible, also the power consumption of this type of centrifugal pump is significantly lower than that of an ordinary pump in combination with the dividing apparatus of the prior art. The invention is described in detail below with reference to the accompanying drawings which illustrate preferred embodiments of the apparatus for carrying out the method of the invention, in which: FIG. 1 is a cross sectional view along line A-A of Fig. 2 of an embodiment of a centrifugal pump used in accordance with the present invention; FIG. 2 is a longitudinal cross sectional view of an embodiment of a centrifugal pump used in accordance with the present invention; FIG. 3 is an end view of another embodiment of a centrifugal pump used in accordance with the present invention; FIG. 4 is a side view of an embodiment of a centrifugal pump used in accordance with the present invention; FIG. 5 is a longitudinal cross sectional view of an embodiment of a centrifugal pump used in accordance with the present invention; FIG. 6 shows yet another embodiment of a centrifugal pump which can be used in accordance with the present invention; and FIG. 7 shows still another embodiment of a centrifugal pump which can be used in accordance with the present invention. Figs. 1 and 2 illustrate a preferred embodiment of a centrifugal pump which can be used in accordance with the present invention. This kind of a pump is very suitable for pumping medium consistency fiber suspensions. In fact, this embodiment is a novel modification of a fluidizing centrifugal pump, so called MC-pump, sold and manufactured by A. Ahlstrom Corporation, Finland. In accordance with Fig. 1 the housing of the centrifugal pump comprises two axially spaced housing portions, i.e. spiral portions 88 and 90, the radii of which preferably increase towards the respective outlet openings 94, 92. However, said spiral portions may well be circular except the outlets extending from said portions in a preferably tangential direction. It is understood that the dimensions of one spiral portion may differ from those of another spiral portion and the number of spiral portions as well the number of outlet openings may exceed the two shown. As shown in Fig. 2 the spiral portion 90 houses the impeller 80 of the centrifugal pump, whereby the pressure in the outlet opening 92 is much higher than that in the outlet 94. In fact, the pressure in outlet 92 corresponds to the pressure of an ordinary MC pump. The other outlet 94 is arranged in front of the impeller 80, whereby only the rotation created by both the suction of the centrifugal impeller and the fluidizing rotor 78 causes the pulp to flow through the outlet 94, the pressure remaining very low. In case there is a need to adjust the pulp flow through the openings, the outlet openings 94, 92 may also be provided with valves 76, as shown in Fig. 1, or the valves may be omitted. Fig. 2 shows clearly how to arrange several outlet openings 92, 94 in a centrifugal pump such that the pressure in the outlet openings varies. The spiral portions 88 and 90, the number of which may exceed two, are equal or different in size, each including at least one outlet opening 92, 94 and optionally a valve (not shown) in connection with said opening. Spiral portion 88 is arranged in connection with the inlet channel 22 of the pump, said channel 22 having a clearly smaller diameter than that of the impeller 80. In said inlet channel there is the fluidizing rotor 78, which preferably extends through said inlet channel 22 into the pulp vessel. However, it is also possible to arrange an independent rotor extending in the inlet channel or, it is also possible to shorten the inlet channel such that a rotor located entirely in the pulp vessel, drop leg or like creates a sufficient shear force field to make the pulp flow into the pump and, in combination with the shear force field created by the impeller, to make the pulp flow through the outlets of the pump. It is also possible to combine new outlets in the centrifugal pump shown such that at least one of the spirals shown may be divided circumferentially in a number of smaller spiral portions each having an outlet of its own. Thereby the pulp flows received from the centrifugal pump may have either substantially the same pressure and volume flow or a lower or a higher pressure and/or volume flow. Although shown in Figs. 1 and 2, the fluidizing rotor 78 is not necessary if the pump impeller is capable of pumping the medium without the aid of the rotor 78. The fluidizing rotor is only needed when a medium consistency fiber suspension or like medium is to be pumped by the centrifugal pump. Fig. 3 shows how the pump housing 96 may be provided with one or more substantially tangential 97 and 98 and/or radial 100 outlet duct or that the duct or ducts may be directioned half tangentially/half radially 102, whereby the direction of the outlets 98, 100, 102 may be chosen such that they extend always toward the free sides of the centrifugal pump and not downwardly towards the floor or towards some apparatus located near the pump. Also, the diameter of the outlets 100, 102 and/or 98 may differ as shown. Fig. 3 also shows an outlet 99 arranged in connection with the inlet channel 22 of the centrifugal pump. The different ducts receive pulp from the pump in different pressures and as the diameter of the ducts also varies the volume flows in the ducts are seldom equal. It is worthwhile noticing that the volume flow from a duct may be set constant by means of arranging the diameter of the duct to give a certain volume flow at a certain pressure. Fig. 4 shows how the outlet openings may extend from the housing 104 not only in a radial direction, as illustrated in Fig. 3, but also in an axial direction 108 or in a direction 110 between radial and axial. Figs. 3 and 4 show that the outlet openings 98, 100, 102, 106, 108, 110 may have any desired direction and that the outlet 99 may also be connected to the inlet channel 22 instead of to the volute of housing. Fig. 5 shows schematically how one of the branch ducts 112 from the housing 114 may be directly connected to the suction vessel 116, drop leg or like device. A portion of the medium introduced into the centrifugal pump is returned via said duct 112 back to the suction vessel 116, for instance, for keeping the bottom layer in said vessel moving, i.e. for preventing the solids of the medium from accumulating at the bottom of the vessel 116. Another application for a duct 112 is where the capacity of the pump exceeds the need in the processing line, whereby a portion of the pulp has to be returned back to the pulp vessel. Yet another possible application for a duct leading back to the suction vessel is where the pulp is to be heated by steam, whereby the branch pipe 112 from the vortex chamber could be led through a steam heater back to the suction vessel 116. In such a case the heated pulp does not necessarily need to be introduced into the bottom portion of the vessel 116. Also the recirculation may be used for compressing the pulp in the vessel 116 downwardly by means of feeding the recirculated, preferably degassed pulp on top of the pulp in said vessel. Fig. 6 shows two outlet ducts 119, 120 arranged in the spiral 122 at different radial distances from the axis of the centrifugal pump, leading to different pressures in the outlet ducts. Fig. 7 shows four outlet ducts 124, 126, 128, 130 arranged in the housing 132 at different locations along the outline of an imaginary spiral so that different pressures result in addition to the radial location also at different circumferential locations. An important feature of the present invention is that the regulating means i.e. valves or other throttling means, in case they are used, are disposed at a short distance from the inner surface of the vortex chamber. The suitable distance has proven to be less than d and preferably less than d/2, when d represents the diameter of the respective outlet. The reason for this is the fact that a thick fiber suspension, for instance, a high consistency pulp, tends to form a rigid fiber plug inside the outlet openings i.e. inside the outlet channel leading from the outlet opening to the valve while the valve is closed or greatly throttled. If the outlet channel from the housing to the regulating means is too long the turbulence created by the rotor/impeller in the housing/inlet channel does not extend all the way to the valve thus allowing the fiber suspension filling the outlet channel to settle and to form a rigid fiber plug inside the channel. Equally, when the size of the plug inside the channel is allowed to increase, the pressure created by the vanes of the centrifugal pump is unable to push the plug through the valve when the valve is opened. To avoid these problems, the valves are preferably located in close vicinity to the vortex chamber. Regulation of the flow may, in addition to the valves, be achieved in several other ways. The outlets or outlet openings may be different in size (Fig. 1) or they may be arranged in the vortex chamber such that the pressures acting in the openings are different in magnitude (Figs. 6, 7). The embodiments illustrated in Figs. 1 to 7 are only exemplary as the number, location and direction of the outlets may greatly differ from the ones shown. Also the direction of the shaft 40 of the centrifugal pump may be either vertical, horizontal or inclined depending on the location of the centrifugal pump. The centrifugal pump may be secured to any convenient part of the vessel containing the medium to be pumped. It is also noted that the method and the centrifugal pump in accordance with the invention are intended to cover embodiments wherein the number of regulating means, i.e. valves, is less than the number of outlets. The direction of the outlet channels may also vary greatly as they may be arranged, not only as illustrated either radially or tangentially, but also in any direction therebetween. Further, the ducts shown may also be used to feed gas, liquid or solids into the pump housing, to be mixed with the medium to be pumped. In a preferred embodiment, bleaching chemicals of a pulp mill are introduced into the pump and the pulp is pumped further so that the main flow goes to the bleaching tower and a smaller flow is introduced back to the pulp vessel to keep the pulp in the bottom thereof movable. Also dilution liquid may be fed into the pump to lower the consistency of the pulp. Finally, it is to be remembered that though all the examples and embodiments above are described in connection with pumping pulp, the pump in accordance with the invention may well be used for pumping all kinds of liquid mediums that need to be delivered from a vessel or the like to a number of different locations. It is thus understood that the preferred embodiments illustrated and described above are for illustrative purposes only and are not to be considered as limiting the scope of the invention which is properly delineated only in the appended claims. Reference signs in the claims are intended for better understanding and shall not limit the scope.

Claims: A method of pumping a 5% to 25% consistency fiber suspension of a pulp and paper industry by means of a centrifugal pump, comprising the steps of connecting an inlet channel of the pump to the source of the suspension; introducing the flow of the suspension through the inlet channel into the housing of the pump; fluidizing the suspension being pumped in the inlet channel; and pumping the suspension out of the pump; characterized by dividing the 5% to 25% consistency fibre suspension into partial streams of substantially equal composition by creating a pressure difference between the inlet and each of the at least two pulp outlets of the pump for discharging the suspension as substantially homogenous partial streams through said pulp outlets; and creating a field of turbulence sufficient for ensuring that local fibre concentrations, e.g. plugs or settled fibres, are avoided in the pump housing from the inlet channel to each of the outlets. The method as recited in claim 1, characterized in that said fibre suspension is a medium consistency (8 % to 25 %) fiber suspension of the pulp and paper industry. The method as recited in claim 1 or 2, characterized in the step of controlling said flow of said suspension through said outlets by providing at least one of said outlets with means for regulating said flow of fiber suspension through said outlet. The method as recited in claim 3, characterized in that said turbulence field is extended toward said regulating means so that said partial fiber flow is prevented from forming a fiber network adjacent said regulating means. The method as recited in claim 3, characterized in that said flow through said outlets is regulated by providing said outlets with unequal diameters. The method as recited in claim 3, characterized in that the flow through said outlets is regulated by providing unequal pressures in said outlets. The method as recited in claim 1 or 2, characterized in the step of returning a partial flow of said fiber suspension from said housing back to said source of fiber suspension. The method as recited in claim 7, characterized in that said partial flow returned to the pulp source flows through a heat exchanger. Use of a centrifugal pump for pumping a 5 % to 25 % consistency fiber suspension of a pulp and paper industry and for dividing said medium consistency fiber suspension into at least two partial streams of said medium consistency fiber suspension, the pump having a housing (86, 96, 104, 122, 132), an inlet channel (22), an impeller (80) arranged on a shaft within the housing (86, 96, 104, 122, 132), and a fluidizing rotor (78) arranged substantially coaxially with the housing (86, 96, 104, 122, 132) on the shaft and extending into the inlet channel (22), at least two fiber suspension outlets (92, 94, 97, 98, 99, 100, 102, 106, 108, 110, 112, 119, 120, 124, 126, 128, 130, 134) for discharging the fiber suspension, and wherein the fiber suspension outlets are disposed in the housing (86, 96, 104, 122, 132) at different axial locations and/or radial locations and/or circumferential locations with respect to the rotational axis of the pump for dividing the suspension being pumped into partial streams of substantially equal composition. Use of a centrifugal pump as recited in claim 9, characterized in that said fiber suspension has a consistency of 8 % to 25 %. Use of a centrifugal pump as recited in claim 9 or 10, characterized in a fluidizing rotor (78) extending substantially coaxially with said housing and extending into said inlet channel (22). Use of a centrifugal pump as recited in claim 11, characterized in that said fluidizing rotor (78) is attached to said shaft. Use of a centrifugal pump as recited in claim 11, characterized in that the fluidizing rotor (78) and/or the impeller (80) comprise vanes extending from said shaft towards said outlets (92, 94) for creating turbulence in said housing and pressure difference between said housing and said outlets (92, 94). Use of a centrifugal pump as recited in claim 9 or 10, characterized in that at least one of said outlets (94, 98, 99, 100, 102, 108, 110, 112, 119, 120, 124, 126, 128, 130) is provided with means (76) for regulating the flow of the fibre suspension. Use of a centrifugal pump as recited in claim 14, characterized in that said means (76) are disposed adjacent said outlets (94, 98, 99, 100, 102, 108, 110, 112, 119, 120, 124, 126, 128, 130) for regulating the flow of the fibre suspension. Use of a centrifugal pump as recited in claim 9 or 10, characterized in that the respective diameters of said outlets (94, 98, 99, 100, 102, 108, 110, 112, 119, 120, 124, 126, 128, 130) are unequal. Use of a centrifugal pump as recited in claim 9 or 10, characterized in that the housing (86, 96, 104, 122, 132) includes a housing portion (88, 90) having a circular cross section. Use of a centrifugal pump as recited in claim 15, characterized in that said regulating means (76) is positioned so that the distance between said regulating means (76) and said outlet (94, 98, 99, 100, 102, 108, 110, 112, 119, 120, 124, 126, 128, 130) is less than the diameter of said outlet (94, 98, 99, 100, 102, 108, 110, 112, 119, 120, 124, 126, 128, 130). Use of a centrifugal pump as recited in claim 9 or 10, characterized in that the housing (86, 96, 104, 122, 132) includes a housing portion (88, 90) having the shape of a spiral and that the outlets (94, 98, 99, 100, 102, 108, 110, 112, 119, 120, 124, 126, 128, 130) are arranged at different peripheral locations along said spiral. Use of a centrifugal pump as recited in claim 9 or 10, characterized in a plurality of second outlets (94, 98, 99, 100, 102, 108, 110, 112, 119, 120, 124, 126, 128, 130) being arranged at different radial distances from said axis of the housing. Use of a centrifugal pump as recited in claim 9 or 10, characterized in that at least one of said outlets (99) is connected to the inlet channel (22) of said centrifugal pump. Use of a centrifugal pump as recited in claim 9 or 10, characterized in another housing portion (88) axially displaced relative to the housing portion (90) and in communication therewith, each said housing portion (88, 90) having at least one outlet (92, 94) therein. Use of a centrifugal pump as recited in claim 9, 10 or 22, characterized in that said housing portion (88, 90) is one of circular, spiral, formed of a number of spiral portions and a combination thereof. Use of a centrifugal pump as recited in claim 9, 10 or 22, characterized in that at least one of said outlets (94, 98, 99, 100, 102, 108, 110, 112, 119, 120, 124, 126, 128, 130) of said housing (86, 96, 104, 122, 132) is used for introducing a fluid into said housing (86, 96, 104, 122, 132). Use of a centrifugal pump as recited in claim 11, characterized in that said fluidizing rotor (78) extends through said inlet channel (22) into the source of the fibre suspension. Use of a centrifugal pump as recited in claim 9 or 22, characterized in that said outlets (94, 98, 99, 100, 102, 108, 110, 112, 119, 120, 124, 126, 128, 130) extend from the housing (86, 96, 104, 122, 132) one of tangentially, axially and radially or in a direction therebetween.

Inventors: NISKANEN TOIVO, REPONEN VOITTO, TIMPERI JUKKA, VESALA REIJO, VIKMAN VESA, NISKANEN, TOIVO, REPONEN, VOITTO, TIMPERI, JUKKA, VESALA, REIJO, VIKMAN, VESA
Applicants: AHLSTROEM OY, A. AHLSTROM CORPORATION
Application year: 1991
Main classification: F04D7
IPC codes: F04D15, F04D7, F04D29