CA1313325C - Method and apparatus for improving the control and treatment of fibre suspension flow - Google Patents

Abstract

ABSTRACT

The present invention relates to a method and an apparatus for optimizing the control and treatment of fibre suspension flow. The invention is mainly intended to be applied in connection with pumping of high-consistency pulp in pulp and paper industry. There are several earlier known means for controlling the function of the so called MC-pumps. The most usual is either a so called level control in which the level of the pulp container is controlled by throttling the flow leaving the pump to maintain at the desired level, or a constant-flow control, whereby the flow leaving the pump is maintained constant. In both cases the pressure loss in the valve grows high because the pulp proceeding as a plug flow frequently has to be pressed through the throttle opening of the valve. Additionally, there has been a risk that the valve will clog completely, especially with small flow amounts. The said problems are eliminated or minimized by the apparatus (19) according to the invention, in which in close proximity to the flow side surface of the valveelement (19) a fluidizing element (22) is arranged, which fluidizes the pulp to a liquid state so that the pulp can flow through the valve opening (16) and not clog it.

Description

13~33~5 METHOD AND APPARATUS FOR IMPROVING THE CONTROL
AND TREATMENT OF FIBRE ~USPENSION FLOW

The present invention relates to a method and an apparatus for improving the control and treatment of fibre suspension flow. Ths method and apparatus 5 according to the invention are particularly su-~able to be used for mixing chemicals and for simultaneously controlling the pumping of high consistency pulp in the pulp and paper industry.
Medium and high consistency pulp (consistency 8 - 30/O) forms a very stiff material; it can be so stm that one can stand with ordinary shoes on the pulp and 10 not sink into the pulp. The reason for it is that fibres wi~h the length on of a few millimetres form a strong three-dimensional fibre ne~work. The fibres are ratherrigid and when they rest on each other they form a strong structure.
High consistency pulp is still generally pumped by a displacement pump or a screw pump. When the pulp is pumped by such pumps, no control valve is 15 used in the discharge side. There are tnro reasons for this. Firstly, high consistency pulp is relatively stiff and the pumps produce pulses. If there is athrottling at the discharge side, the pulses can break structures. Secondly, a displacement pump works even if there is no pulp or so little pulp in the suction side that it would only partly fill compartments of the pump.
High consistency pulp can, however, be changed momentarily into a flowing state by breaking fibre network by bringing shear forces to the suspension.
This is called fluidization of high consistency pulp. Normally fluidization is effected by some kind of powerful rotor. For example, in high consistency pump the rotor effects the fluidization in the su~tion duct of the pump. Fluidization is a reversible 2s process, and as soon as the rotor is stopped or the pulp is no longer in the range of the rotor, the fibre network is formed again and the suspension becomes againa substantially solid material.
The present invention and prior art will be described with reference to the accompanying drawings. In the drawings:
30 Figs. 1a and 1b are schematic illustrations of prior art pumping arrangements.
Fig. 2 is a schematic illustration of a typical mixing arrangement according to the prior art.
Fig. 3 is a sectional side view of a preferred embodiment of an adjustable mixing valve according to the present invention.

1~1332S

Fig. 4 is a fragmentary detail of a valve arrangement according to Fig. 3 from the upstream side.
Fig. 5 is a schematic illustration of a pumping arrangement including an adjustable mixing valve according to the present invention.
5 Fig. 6a and 6b are graphs of flow-through curves of a valve according to the prior art and a valve according to ~he invention with pulps of dmerent consistencies compared with the flow-throush curves of water.
Fig. 7 is a graph showing the comparison of corresponding valves in relation to the amount of pulp flow-through to the amount of water flowing through as a function of pressure difference prevailing across the valve.
Lately a new type of high consistency pump has become used in the mills, cf. e.g. US-patent publication 4,435,122. This new kind of pump is a centrifugalpump, in which high consistency pulp is fluidized, in other words changed into aflowing state, just before the pulp reaches the range of the pump impeller. With15 this technique in pumping high consistency pulp it is usually necessary to provide a control valve in the discharge side of the pump according to Fig. 1 in order to ensure that there is always pulp in the suction side of the pump or that the amount of pulp to be pumped is correct. This is due to the fact that a centrifugal pumpalways has to have its inlet opening filled with pulp and thus its operation is most 20 often controlled in such a way that the pulp level in the vessel prior to the pump is maintained substantially constant by means of throttling the discharge of thepump.
If the capacity of a pump is adjusted by a control valve according to Fig.
1, the head of the pump is considerably lowered in the control valve because of 25 the rigid character of the pulp. In controlling the flow of high consistency pulp, the resistance i.e. pressure drop is often several bars even with the best valves known.
In pulp mills a pulp pump is often followed by yet another device, namely a mixer for mixing chemicals into the pulp, for example, in bleaching. The mixing 30 may be effected either in a separate mixer or in a high consistency pump. When chemicals are mixed in a medium/high consistency pump, they are added either before the pump or at the outer rim of the impeller. If this is done, a separatemixer is not necessary, as the same device may serve both as a mixer and a pump. However, ~ the chemicals are in the form of gases they cannot be added 313~5 before the pump as centrifugal pumps pumping medium or high consistency pulp are usually provided with means for separating gas from pulp whereby the chemicals would be the first gases to be separated.
Often a pump cannot be used as a mixer for several reasons. These 5 include, for example, material problems or the fact that the amount or the quality of the chemicals is such that the chemicals cannot be added into the pump.
Hereby one has to use a separate mi~(er according to Fig. 2. There are cases in which a part of the chemicals may be fed to the pump and the rest to the mixer or all chemicals to the mixer depending on the situation.
A mixer for use in connection with medium or high consistency pulps is described in Finnish published patent application Fl-68688. It consists of a substantially cylindrical casing with an axial inlet opening and an axial outletopening and protrusions on the inner surface, of an axially rotating rotor which has protrusions on the outer surface, and of a feed duct for chemicals which opens 15 to a substantially annular mixing zone between the rotor and the casing. Saidmixer, although very practical and reliable is, however, rather complicated to manufacture of special material. This kind of a mixer has still a severe drawback relatin3 to its operation. After being efficiently mixed with the chemicals and having started to rotate in the mixing ~one due to the rotation of the rotor the pulp 20 leaves the annular mixing 70ne in a direction coaxial with the rotor whereby the rotational movement of the pulp continues and the pulp tends to form a rotating annulus on the wall of the flow channel. Also, the pressure in the pulp decreases rapidiy as the flow area of the pulp suddenly increases. The result of these twofactors is that the gases, i.e. most often the chemicals, tend to separate in the 25 middle of the flow starting to form gas bubbles. Thus the mixing of the chemicals with the pulp is not as efficient and even as could be expected.
As one can note from the foregoing, there are several different devices in connection with the pulp pump, namely the pump itself, the control valve and a chemical mixer. A purpose of the present invention is to combine these devices 30 in such a way that the result would be most economical from the point of view of both the manufacturer of the devices and their users.
It would, of course, be possible to combine all the above mentioned three D devices together, but there is one factor which makes it practically impossible. As explained above, the chemicals may be mixed within the pump. In such a case, 13~33~5 the pump perhaps should be manufactured of a more durable material, but not always. However, when pumping medium or high consistency pulp the control valve should be arranged so close to the pump impeller that the fluidized pulp would not have time to reverse back into plug flow by forming a fibre network. It 5 is to be noted at this stage that the discharge duct of a centrifugal pump is always tangential in order not to resist the flow out of the pump. On one hand, this kind of tangential arrangement would be impossible in case high consistency pulps were to be pumped, as the distance from the impeller blades maintaining the fluidized state at a sufficient level to the throttling arrangement arranged in a 10 tangential discharge duct would be long enough for allowing the pulp to form flbre network, whereby an ordinary valve would either cause a high pressure loss or beentirely clogged. On the other hand the discharge duct could be arranged substantially radially, whereby the above defined distance would be minimized, but the sharp turn in the volute flow from circumferential to radial would bring about 15 a considerable drop in pressure substantially equalling the drop in an ordinary valve.
One basic object of the invention is to rninimizs the flow resistance of an adjustable valve or a stationary throttling by means of arranging a fluidizing rotor in connection with said throttling so that the high consistency pulp flows in a 20 fluidized state through the throttling. Fig. 6a shows in principle, how dramatically the capacity of the present throttling arrangements decreases while the consistency is increased. Fig. 6b is a graph showing the capacity of a throttling arrangement provided wi~h a fluidizator. The reliability and the adjustability of the throttling arrangement improve particularly with small spread angles, enabling a25 far more accurate control of the pump resulting in a more even and steady flow and pressure conditions in the discharge of the pump.
The most attractive object of the pre ent invention is to eliminate the need of a separate mixer in addition to a separate throttling by means of a new kind of throttling arrangement and to utilize the fluidizing properties of said throttling 30 arrangement by means of feeding chemicals prior to the throttling as well as to lower the total resistance of the system and to reduce the need of space.
The present invention brings about the following advantages over the prior art.
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- The throttling arrangement functions at high consistencies (15 - 30/0) - The throttling arrangement functions even at small spread angles without clogging and evenly with no need for over-spreading even at the starting point.
- The capacity of thc throttling arrangement with pulp of a consistency of 15 5 - 20% practicaliy equals the capacity with water and operates at lower pressure ciifferences than the present pulp valves when adjusting pulp flows (cf. Fig. 7).
- The separate throttling arrangements and mixers made of special materials are replacsd by a valve mixer.
- The total pressure loss diminishes.
10 - It is possible to raise the consistency level of the mixture up to a consistency of 25 - 30% such being impossible with the known devices.
- The construction of the throttling arrangement is such that it works regardless of the rate of inlet flow.
In the systems according to the prior art (Fig. 1) the aim has been to place 15 the throttling arrangement in a small pipe close to the discharge side of the pump.
Thus a high flow rate is achieved at the throttling arrangement, which makes thethrottling arrangement operate better and prevents the Glogging. A throttling according to the invention and the arrangement using it can be placed anywhere in the piping. This kind of arrangement makes it possible to arrange the purnp to 20 the most appropriate location and arrange the valve mixer to another location best for its operational purposes.
The arrangement utilizing th0 invention enables mixing of chemicals without the pump being the only place where the chemicals may be added. In many cases in bleaching process, part of the chemicals can be added in the pump and 25 the rest in the control valve. No separate mixer is needed. Thus the arrangement according to the prior art (Fig. 2) is essentially simplified.
A significant advantage of the present invsntion resides in the great possibilities for adjusting the volumetric flow. Because it is possible to fluidize the high consistency pulp just in front of the valve element, the valve opening can be 30 throttled to its minimum and yet the pulp flow continues, in other words it is possible to reach low flow amounts ev~n at high consistencies.
There are in principle two eariier known types of control arrangements of pulp pumping. Fig. 1a shows a so called principle of level control, in which the output D f the pump 2 is adjusted by the thro~tling arrangement 1 so that the level of the pulp in the pulp container remains constant. Fig. 1b illustrates a so called principle of flow contrsl, in which the pump 2 is attached to the pulp container 3 and thereafter there is a flow indicator 5 arranged in the flow passage through which a pulp flow passes, which flow is maintained constant by the throttling 5 arrangements 6. In both cases the valve is disposed considerably far from the pump and in any case so far that medium/high consistency pulp has time to form a rigid fibre network and to change into plug flow. The subsequent pressing of the pulp through the throttling arrangement involves a great loss of pressure.
Additionally, even by bringing a throttling arrangement as close to the pump as 10 possible It is not possible to completely avoid the pulp frorn beginning to solidify, because the formation of the fibre network begins already in the pump itself just after the fluidization zone of the pump.
Fig. 2 shows another arrangement according to prior art, for admixing bleaching chemicals to the suspension. The arrangement comprises pulp tank 3, 15 a pump 2, a level control valve 1 and a mixer 7 following the valve 1 in the direction of pulp flow. The mixer can be the fluidizing mixer shown in Finnish patent application F1 850854 cited above. Drawbacks of this arrangement are a considerable overall loss of pressure of the devices especially with high consistency pulps, and the costs of the devices made of special materials.
20 Additionally, the fluidizing mixer, if used, does not mix the chemicals in the suspension evenly.
Figs. 3 and 4 disclose an arrangement in accordance with the invention in which a valve 10 comprises in general a substantially cylindrical or sometimes almost ball shaped chamber 13 provided with an inlet 14 connected to an inlet 25 pipe 11 and an outlet 15 connected an outlet pipe 12. The iniet pipe 11 may be mounted at its other end to a fluidizing centrifugal pump, but any type of pump capable of delivering medium/high consistency pulp may be used. The inlet 14 of the chamber 13 may be provided with an inlet opening 23 for chemicals throughwhich opening, for instance, bleaching chemicals may be beforehand added into 3~ the pulp flow prior to mixing. The opening for the chemicals may, however, belocated almost anywhere upstream of said throttling arrangement. The outlet 15 is provided with a throttling 16 i.e. an area having a reduced diameter with respect to both the chamber 13 and the outlet pipe 12. According to Fig. 3, a substantially radial shaft 21 protrudes through the wall of the chamber 13 and the outlet pipe 12. According to Fig. 3 a substantially radial shaft 21 protrudes through the wallof the chamber 13 and a fluidizing element 22 is attached to the other end of said shaft 21 inside the chamber 13. The fluidizing element may be a rotor having a number of more or less axially located blades. The blades are preferably formed 5 of a lengthy steel plate having a generally rectangular cross-section and having radially an inner and an outer edge. The blades may, however, be of any appropriate form as long as the center of tha rotor is open. The blades are arranged with said inner edge locating a~ a radial distance from the axis of therotor 21 in such a way that the center of the rotor is open, thus allowing the fiber 10 suspension to flow through the center of said rotor, whereby the rotor itself causes as little resistance to the flow as possible. The blades may be either straight axial or somewhat arcuate thus forming a cylinder, ball or barrel shaped envelope surface during rotation. The direction of the shaft 21, however, may differ from the radial direction relative to the inlet 14 and outlet 15 i.e. it may be inclined with 15 respect to the axial direction of the chamber 13 so far that ~ is clearly non-axially disposed within said chamber. The reason for this is the mixing ability, as, while the direction of the shaft is non-axial, the fiber suspension flow through the apparatus due to the pressure created by the pump prior to the throttling arrangement prevents the rotor from forming a gas bubble in the middle of the 20 flow. A characterizing feature of a fluidizing, centrally open rotor is that it tends to separate gas from liquids. But as the rotational movement the rotor causes in the suspension is not coaxial with the main flow direction, a gas bubble is not able to grow in the middle of the rotor.
The operation of the apparatus is such that the fiber suspension flow from 25 a pump, for instance, from a fluidizing centrifugal pump, is introduced to chamber 13 through inlet 14 and simultaneously chemicals are fed through opening 23, either located in connection with the throttling arrangement or somewhere upstream thereof, to the fiber suspension. The fluidizing element i.e. the rotorwhile rapidly rotating causes the fiber suspension to fluidize whereby the chemicals 30 are efficiently being mixed throughout the suspension and are capable of contacting each fiber of the suspension. Due to the feed pressure created by thepump the suspension flows through the apparatus towards the outlet being provided with the throttling wheraby the pressure dmerence over the throttling ,i .
~. . ~ ..

13~3325 causes the suspension to turbulate when passing the throttling further facilitating the mixing of chemicals.
There is yet another aKractive feature relating to the rotating fluidizing element and the following throttling. As the fluidizing rotor facilitates the flow 5 through said throttling i.e. tends to reduce the back pressure caused by the reduced diameter of the throttling it is possible to control the flow through the throttling by only controlling the degree of fluidization i.e. the strength of the sheer force field created by the rotor. Thus by adjusting the rotational speed of the fluidizing element it is easy to control the amount of resistance the throttling10 subjects to the flow of suspension.
In the embodiment shown, there is a throttling 16 being provided with a seat ring 17 for an adjustable calotte valve 19 with a V-opening 18, the inner and outer surface of which valve are a part of a spherical surface. The angular position of the calotte valve 19 is controlled by a control spindle 20 protruding from the chamber 13. According to Fig. 3, the control spindle 20 is coaxial withthe shaft 21 of the fluidizing element 22 so that said element rotates close to the inner side of the coved surface of the calotte valve 19. By means of this arrangement it is ensured that the fibers cannot clog the V-opening 1~ of the calotte valve 19.
The above described components are preferably situated in the chamber as described above in relation to the direction of the puip flow: firstly the chemicals feed opening, secondly the fluidizing element 22, then the calotte valve 19, andthen the throttling 16. It is however, also possible to position the throttling arrangement in the opposite disposition with the fluidizing element behind the valve 25 element in the direction of fiow so as to hinder the fibres which might stick on the edges of the valve opening. However, the feed opening for chemicals has to be arranged always upstream of the fluidizing element. Also, the directions of the shafts of the rotor and the throttling arrangement can differ from each other or one of the shafts can be within the o~her.
The throt~ling arrangement according to several embodiments of the invention functions in the foliowing way. With medium or high consistency pulp, when the pulp flow coming from the pump reaches the chamber of the throttling arrangement in the form of a plug flow, chemicals are introduced in said chamberbefore the pulp is subjected by the fluidizing element rotating within the chamber 1~133Z5 g to such an amount of shear forces that the bonds between the fibres forming a stiff fiber network, i.e. a pulp plug, loosen and the pulp flows like a fluid through the throttling arrangement. Simultaneously, as the fibers of the pulp suspensionare loose in the flow, the chemicals are emciently mixed with ths fibers in such a 5 way that each fiber will be in contact with the chemicals and, as it is impossible for the chemicals to be separated in the form of bubbles from the suspension, the mixing is even and the dosage of chemicals may be minimized. The loss of pressure caused by the throttling arrangement is consequently on a fraction of what it would be without fluidization. The most difficult situation is when the flow 10 channel defined by the valve element 19 and the throttling 16 is very small, in other words the volumetric flow is small. Hereby the fibres stick very easily on the edges of the flow channel and gather together forming in a short time a plug which clogs the throttling arrangement. It is, however, possible to design the fluidizing element so that it causes a pulse at the flow channel agains~ the normal 15 direction of flow, in other words it tends to draw off the fibre bundles formed on the edge of the opening and to re~urn them to the fluidizing area. If a rotatingrotor is involved, the fibre bundles can be loosened also by the total effect of the structure of the valve element and the rotational direction of the rotor.
Fig. 5 discloses an arrangement according to the present invention, in 20 which the throttling arrangement 10 is used as a mixer. A pump 2 is connectedto a pulp tank 3 and the pump is followed by the throttling arrangement 10 situated at an appropriate location and, according to the embodiment in the fixture is controlled by a level detector. The arrangement in Fig. 5 can well be compared to the arrangement in Fig. 2 because in both cases the same measures are 25 involved: control of the pump and minimizing of chemicals. The equipment in Fig.
5 is much simpler and an additional advantage is achieved by the higher outlet pressure compared to that of Fig. ?.
The throttling arrangement according to the invention can be employed, for example, in an apparatus in which pulp is led from the MC-pump to the thickener 30 which requires a certain counter pressure to function in the desired way.
Consequently, the consistency of thç pulp flow being throttled can easily be more than 15%, even 20%. To ensure the flow (in other words, to hinder the clogging at the throttle point) fluidization of pulp is required immediately before the throttling arrangement. The throttling arrangement is to be s~uated preferably exactly at the _~ , 10 13133%5 outlet opening of the thickener, because at the same time as the throttling arrangement throttles the flow, it also discharges the pulp from the thickener.
Similarly, the throttling arrangement can also be used in connection with other components treating high consistency pulp.
Fig. 6a represents the behaviour of a conventional valve at high consistency pulps. The test consistencies were 8, 10, 13 and 15%. The horizontal axis shows the spread angle of the throttling arrangement and the vertical axis the mass flow passing through the throttling arrangement. It will be appreciated from the graph that at a consistency of 10% the flow rate of the pulp significantly begins to 10 decrease at large spread angles and at a consistency of 15% the value of the pulp flow remains below half of the maximum value which is achieved by water.
Correspondingly, at low mass flows, the consistency of 15% requires a spread angle at least double the size of that of water even to star~ the flow. Thus thecontrol of small amounts of flow is most complicated, if not impossible by 15 conventional throttling arrangements.
Fib. 6b correspondingly represents the behaviour of ~he throttling arrangement according to the invention at high csnsistencies. It is seen in the same coordinates that at small spread angles the 15% pulp does not differ from water, so the adjustability is as good as that of water. At larger spread angles the 20 15% pulp requires a little larger spread angle than water, but the curve does not turn horizontal as occurred with the throttling arrangements according to the prior art.
Fig. 7 discloses comparative curves of the capacity (y-axis) of the throttling arrangement as a function of the pressure difference prevailing across the 25 throttling arrangernent. The curves show the Qpulp/Qwater relation of the volumetric flows, which with the throttling arrangements in accordance with the prior art (broken line curves) is weak already at the consistency of 10%. In other words a considerable pressure difference is required for the efficiency of the flow to reach a profitable value. At the consistency of 15% the pressure difference 30 required is even greater. By means of a throttlin~ arrangement according to the invention (solid cun/e) a considerably be~ter efficiency is achievsd. The maximum volumetric flow value is achieved at considerably lower pressure difference, less than half of the corresponding pressure difference of a throttling arrangement in accordance with the prior art.

13~3325 The apparatus in accordance with the present invention operates efficiently in a far wider consistency range than the prior art mixers. Also, the energy expenditure of our apparatus is approximately one tenth of that of the competingmixers. The reason for this is the compact structure of our apparatus. The 5 volume of the chamber of our apparatus is very small and as the fluidizing element has an open center and as it rotat0s non~ ially with the chamber or at least with its outlet, the turbulence field it creates easily fills the entire chamber consuming minimal amount of energy for ~uidizing the suspension.
The above described arrangement according to the invention has thus 10 made it possible to avoid or minimize the drawbacks and defects of the devices according to the prior art by simplifying the apparatus by combining applicable components to a rational entity. However, only a few specially preferable embodiments have been referred to above and such are not intended to limit the scope of the invention of what is disclosed in the enclosed claims. It is, for 15 example, with a V-opening but in some cases the use of a slide valve as well as a ball or a disc valve can be justified. Similarly, It is not necessary for the fluidizing element to be a rotor as in the figures, but also another kind of vibrator can be used.
It is also clear that the material being used does not need to be high 20 consistency pulp, but the mixing is applicable also to diluted pulps or mere fluids.
Similarly, the substances or chemicals to be mixed can be either gaseous, liquids or solids.

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Claims (14)

1. A method of treating fiber suspensions having a consistency in the range of about 5-25% in an apparatus located within a pulp transfer line, said apparatus having an inlet with an axis connected to an inlet pipe, an outlet having an axis connected to an outlet pipe, the axes of said inlet and said outlet being coaxial, a chamber having an inner surface extending between said inlet and said outlet, a fluidizing rotor located within said chamber and extending transversely of the axes of said inlet and outlet, said rotor having an open center extending in the axial direction thereof, and a throttling located downstream in the direction of flow through said chamber from said fluidizing rotor, said throttling located adjacent to said outlet, wherein the method comprises the steps of:
feeding the suspensions from the pulp transfer line through said inlet into said chamber, within said chamber rotating said fluidizing rotor and subjecting said suspensions to shear forces and turbulence for loosening the bonds between individual fibers of said suspensions for fiuidizing said suspensions, generating the turbulences about an axis extending transversely of the axes of said inlet, said outlet and said throttling, flowing said suspension in a fluidized state through the open centre of said fluidizing rotor, flowing said suspension through said throttling in at least a partly fluidized state, and discharging said suspension from said outlet to the pulp line.

2. A method, as set forth in claim 1, minimizing the energy consumption of the fluidizing step by arranging the size of said chamber as small as possible relative to the diameter of the inlet or the outlet.

3. A method of treating fiber suspensions having a consistency in the range of 5-25% in an apparatus located within a pump transfer line, said apparatus having an inlet with an axis connected to an outlet pipe, the axes of said inlet and outlet being coaxial, a chamber having an inner surface extendingbetween said inlet and said outlet, a fluidizing rotor located within said chamber and having an axis extending transversely of the axes of said inlet and outlet, said rotor having an open center extending in the axial direction of said rotor, and a throttling located downstream from said fluidizing rotor in the flow through said chamber from said inlet to said outlet, the method comprising the steps of:
introducing chemicals into the suspension upstream from the fluidizing rotor, feeding the suspension from the pulp line through said inlet into said chamber, rotating said rotor about the axis thereof for subjecting the suspension to shear forces for loosening the bonds between individual fibers and fluidizing said suspension, at the same time flowing the suspension in a fluidized state through the open center of said fluidizing rotor for minimizing the resistance of said apparatus and fluidizing rotor to such flow, mixing the chemicals with the suspension during fluidizing of the suspension, flowing the suspension through said throttling in at least a partly fluidized state and rapidly increasing the flow area immediately downstream from said throttling for creating turbulence in the suspension, facilitating mixing of the chemicals due to the turbulence, and discharging the suspension from the apparatus into the pulp line.

4. A method, as set forth in claim 3, comprising the step of introducing the chemicals into the suspension upstream from the chamber.

5. A method, as set forth in claim 3, comprising the step of introducing the chemicals into the suspension within said chamber.

6. A method, as set forth in claim 3, wherein arranging the fluidized state to continue through said throttling for preventing fibers from forming flocs within said chamber or from attaching to the edges of said throttling.

7. A method, as set forth in claim 3, comprising the step of minimizing the energy consumption for fluidizing said suspension by arranging the size of said chamber as small as possible relative to the diameter of said inlet or outlet.

8. An apparatus for treating fiber suspensions having a consistency in the range of 5-25%, said apparatus comprising:
an inlet having and axis an arranged to be connected to an inlet pipe, an outlet having an axis and arranged to be connected to an outlet pipe, the axes of said inlet and said outlet being coaxial, a chamber having an inner surface extending between said inlet and said outlet for effecting the flow of the fiber suspension there between, a fluidizing rotor disposed within said chamber and having an axis extending generally transversely of the axes of said inlet and outlet, said rotor having an open center extending along the axis thereof for allowing said suspensions to flow therethrough from said inlet to said outlet, throttling means having a reduced diameter with respect to the diameter of said chamber and arranged downstream from said fluidizing rotor relative to the flow of the fiber suspension through said chamber; and said chamber having a diameter not greater than the diameter of said inlet pipe and said outlet pipe.

9. An apparatus, as set forth in claim 8, wherein said rotor comprises blades extending in the direction of and spaced radially outwardly from the rotor axis.

10. An apparatus, as set forth in claim 9, wherein said blades are arcuate blades defining a ball or barrel shaped envelope laterally enclosing theopen center of said rotor.

11. An apparatus, as set forth in claim 8, wherein said throttling is a valve member comprising a planar plate or an arched plate.

12. An apparatus, as set forth in claim 8, wherein the axis of said rotor extends perpendicularly to the axes of said inlet and outlet.

13. An apparatus, as set forth in claim 8, wherein said rotor is formed of blades having a radially inner edge and a radially outer edge, said inner edge being spaced radially outwardly from the axis of said rotor and said outer edge located adjacent to an inner surface of said chamber and said throttling.

14. An apparatus, as set forth in claim 8, wherein said chamber has an opening therein for introducing chemicals into said chamber, and said opening located upstream from said fluidizing rotor with respect to the flow of said fiber suspension from said inlet to said outlet.