US3834982A

US3834982A - Method and apparatus utilizing the effects of cavitation in the treatment of fibrous suspensions

Info

Publication number: US3834982A
Application number: US00285860A
Authority: US
Inventors: A Belonogov; G Vorobiev; A Efimov; I Vjukov; L Gorbachev; R Solonitsyn
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-09-01
Filing date: 1972-09-01
Publication date: 1974-09-10
Anticipated expiration: 1991-09-10
Also published as: FR2199765A5; DE2241673A1; GB1407046A; DE2241673C2

Abstract

SUSPENSIONS OF FIBROUS MATERIALS ARE TREATED BY POSITIONING A NON-STREAMLINED SOLID CYLINDRICAL BODY, CROSSWISE IN A REACTOR SUCH THAT THE CYLINDER IS DISPOSED IN A HYDRODYNAMIC FLOW OF THE SUSPENSION TO PRODUCE A TWO DIMENSIONAL PLANE CONTRACTION OF THE FLOW. THIS CAUSES CAVITATION FORCES TO BE ESTABILISHED IN THE THUS CONTRACTED FLOW AND THESE FORCES ACT ON THE SUSPENSION TO EFFECT ANY ONE OR MORE OF VARIOUS TREATMENTS SUCH AS RESINATION, BEATING, BLEACHING, WASHING, ETC.

Description

3,83%,982 THE EFFECTS OF cAvITATIoN; N THE TREATMENT or F'IBRous susrznsrons 4 ROVICH ET AL US UTILIZIN p 10, 1974 R. ALEXAND METHOD AND APPARAT G Filed Sept. 1. 1972 .2 sheets-sheet 1 o 2 lm I m. no H 7% M C I a 2 .H ,U .m A Jfl M W 1 v y w M n 4 .H w w w A F a m w W 1:3: m? m M w M I p 1974 R. ALEXANDROVICH EI'AL "8,834,982

IETHOD AND APPARATUS UTILIZING THE EFFECTS OF CAVITATION IN THE TREATMENT OF FIBROUS SUSPENSIONS,

Filed Sept. 1, 1972 2 Sheets-Sheet a United States Patent 3,834,982 METHOD AND APPARATUS UTILIZING THE EFFECTS OF CAVITATION IN THE TREAT- MENT OF FIBROUS SUSPENSIONS Rem Alexandrovich Solonitsyn, ulitsa Andreya Malyshko 45, kv. 31, Kiev, U.S.S.R.; Ivan Elizarovich Vjukov, Grazhdansky prospekt 98, korpus 2, kv. 129; Leonid Alexeevich Gorbachev, ulitsa 3, Internatsionala 3, kv. 141; and Anatoly Mikhailovich Belonogov, ulitsa Bela Kuna 23, kv. 171, all of Leningrad, U.S.S.R.; and Gennady Afanasievich Vorobiev, Chuksin tupik 4, kv. and Alexandr Vasilievich Efimov, ulitsa Starogo Gaya 6, korpus 1, kv. 58, both of Moscow, U.S.S.R. Filed Sept. 1, 1972, Ser. No. 285,860 Int. Cl. D21b N00 US. Cl. 162-1 19 Claims ABSTRACT OF THE DISCLOSURE Suspensions of fibrous materials are treated by positioning a non-streamlined solid cylindrical body, crosswise in a reactor such that the cylinder is disposed in a hydrodynamic flow of the suspension to produce a two dimensional plane contraction of the How. This causes cavitation forces to be established in the thus contracted flow and these forces act on the suspension to effect any one or more of various treatments such as resination, beating, bleaching, washing, etc.

This invention is concerned with a method of treating suspensions of fibrous materials, such as pulp and its intermediate products, mechanical woodpulp and other fibrous materials used in the manufacture of paper, cardboard and cellulose derivatives, as well as with an apparatus for carrying said method into effect.

In the pulp-and-paper manufacturing practice, methods and devices are known for effecting a number of technological processes associated with the treatment of fibrous materials. Among them there are such processes as deresination of chemical and semichemical pulp, simultaneous beating and deresination of chemical pulp and paper pulp, bleaching, chlorination and simultaneous beating and chlorination of chemical, semichemical and woodpulp, an enhancement of the reactivity and activation of chemical pulp for the chemical processing thereof, acetylation of the chemical pulp, washing of the chemical pulp and woodpulp, impregnation of plant fibres, deflocculation of wood pulp prior to casting on paperand cardboard machines, cleaning waste-water from fibrous materials.

The prior-art methods of deresination of chemical pulp are effected by oxidizing resinous substances with oxygen or by removing the resin together with small fibres by fractionation, or else by separating the superficial resin from the fibrous mass by the action of chemical reagents with subsequent washing of the chemical mass on vacuum filters. The above-mentioned deresination methods, however, have found no Wide industrial application in view of their inadequate efficiency. Thus, oxidation of resinous substances with oxygen involves fibre losses, considerable expenditures of chemicals amounting to 50 percent by weight of the fibre and a necessity of increasing production areas. The removal of resin from small fibres by fractionation with a sufficient extent of deresination results in considerable fibre losses and calls for the use of rather complicated equipment.

Among the methods now in use the most effective proves to be that of separating the superficial resin from fibrous suspensions by an intensive intermixing thereof with chemical reagents. Even this method, however, features material disadvantages, since a required degree Patented Sept. 10, 1974 of deresination can be attained only with a high expenditure of chemicals.

The known method of beating the chemical pulp with a concurrent deresination thereof is effected by crushing, cutting and brooming the fibres between the crossing bars of the beating equipment, with an intense intermixing of the fibrous suspension with chemical reagents introduced into the chemical pulp flow being treated before the beating stage. In the process of beating the resin contained in the chemical-pulp fibres, depending on the chemical employed, either passes into a dispersed state or coagulates and precipitates on the surface of the apparatus. Further the emulgated resin is removed from the technological treatment pulp flow with the use of washing apparatus, and the resin deposited on the apparatus is removed therefrom either by washing them with resin-dissolving agents or mechanically.

The now-existing methods for a concurrent beating and deresination are not free from a number of disadvantages, viz. the beating process leads to shortening of the fibre, and therefore high physico-mechanical characteristics of the semifinished product can be attained only by increasing specific consumption of energy for beating. Moreover, the resin deposited on the surface of the equipment, calls for the cleaning thereof so that the technological process should necessarily be of a periodical character.

The known method of bleaching fibrous materials is effected by treating the fibrous suspension with bleaching agents, an intensive intermixing being a prerequisite. Complete interaction of the reacting components is mandatory. This condition, however, can be attained only by a long duration of the process, of the order of 2.5 to 3.5 hours and by the use of cumbersome equipment. Bleaching towers up to 30 m high and 6 m diameter require great capital and maintenance investments. Essential fluctuations in the quality characteristics of the resulting product give rise to overexpenditures of costly chemicals due to a slow rate of diffusion processes on which the bleaching is based.

One of the known methods for bleaching fibrous suspension in a medium of bleaching agents resides in ultrasonic treatment of such suspension. Ultrasonic bleaching ensures better conditions for the penetration of the bleaching agent into the material being treated, but this method fails to find industrial applications due to high power consumption and low efficiency of ultrasonic converters.

The process of chlorinating the chemical pulp prior to bleaching thereof is aimed at oxidizing the lignin contained in the chemical pulp by elementary chlorine. In this respect it is common practice to mix the chemical pulp suspension with gaseous chlorine. The process efficiency and the quality of the resulting product depend on the intensity of mixing the chemical pulp with chlorine and on the uniformity with which the latter is distributed in the suspension. Known in the art is a method of kinetically mixing the chemical pulp with chlorine in aerators; this method, however, suffers from a number of disadvantages residing in a considerable consumption and incomplete utilization of chlorine, high costs of equipment and complexities in the manufacture of aerators.

The processes of bleaching and beating the suspension of fibrous materials can be combined by subjecting the fibrous material to a simultaneous action of bleaching agents and mechanical treatment in bleaching apparatus. Such a procedure, however, failed to find any wide industrial application due to high power consumption and lack of appropriate equipment.

A known method for enhancement of the reactivity of the chemical pulp intended for further chemical processing is effected by treating its fibres either chemically or mechanically. The main problem to be solved in the production of high-reactivity chemical pulp resides in ensuring most complete destruction of low-reactivity sheathings of the fibres and loosening of the cell membrane structure. Such chemical pulp, in the course of chemical processing thereof, exhibits higher ability of forming viscose solutions. It is known to increase the pulp reactivity by refining it on a Jordan mill prior to casting on press machines. This process, however, requires thorough control for precluding shortening of the fibres and disturbance of their adsorption properties. A method is known for increasing the reactivity of the chemical pulp by treating it in an ultrasonic field; but industrial applications of ultrasonic treatment procedures prove to be excessively expensive. It should also be pointed out that ultrasonic treatment of chemical pulp suspensions produces rather weak effects on the structure of cell membranes of the fibres.

Thus, a noticeable increase in the reactivity of the chemical pulp by treating the pulp suspension with the use of ultrasonic techniques with a frequency of 400 kHz. can be attained only after a period of 30 to 60 min, with the suspension concentration being not higher than 0.32 to 0.325%.

With the frequency of the treatment brought down to 20 or 30 kHz. and intensity more than 5 v./cm. and the same period of treatment, the concentration of the suspension being treated has to be reduced to 0.l0 .2%.

For enhancing the intensity of ultrasonic effects, investigations were carried out as to the possibility of treating the suspension under high static pressures; this, however, makes the process equipment more complicated and the process itself becomes less effective.

Known in the art is a method of increasing the reactivity of the chemical pulp by treating the suspension by means of an electrohydraulic shock. This method of electrohydraulic treatment is based on the origination of shock waves and displacements with an electric spark-over in a liquid. Hydraulic pulses originating due to an electric discharge in the liquid consist of two shocks. The first, which is the main and more powerful one, is a hydraulic shock whose shape is similar to that of current pulses; the steeper the pulse and the higher the amplitude, the shorter and more powerful the main hydraulic shock is. The main hydraulic shock is accompanied by side eifects, butthe main destructive force in the electrohydraulic effect is attributable to the hydraulic shock. The electrohydraulic shock is a powerful means for treating materials in a liquid and therefore currently it is known to be used mainly in metal working. Thus, electrohydraulic devices are known for knocking out cores from castings. As to the treatment of chemical pulp, there is a danger that the fibre could be simply destroyed, this producing a deleterious effect on the properties of the pulp thus processed. It is therefore necessary to control the force and depth with which the chemical pulp fibres are treated and obviate particularly strong effects on the fibre structure. To this end, it is necessary to make use the minimum limit of the permissible power of the electrohydraulic effect, this, however, being inexpedient from both the economical and technical standpoint.

The known method of activation of the chemical pulp for any kind of chemical processing, such as production of cellulose acetate, viscose rayon, nitrocellulose, cellulose ethers, fibre and other products, comprises singleor two-stage cooking of woodpulp, followed by multistage cleaning and single or multistage refining. Said sequence of operations ensures the required chemical composition of the resulting cellulose, but the latter is far from being always well processable and giving finished products of an adequate quality. Besides chemical composition, the supramolecular structure of the chemical pulp, a looser or denser structure of its macromolecules prove to be decisive for the chemical processing thereof.

Laboratory methods are known in the art for activating the chemical pulp by inclusion techniques. In accordance therewith, the chemical pulp is allowed to swell in water or alkali and then the latter is displaced by a polar liquid (such as acetone or methanol), for which purpose the pulp is Washed with a 5 to 20-fold volume of the last-mentioned agents. The latter agent is likewise displaced but with a non-polar liquid such as benzene, for which purpose the chemical pulp is washed With an approximately equal amount of this solvent. The above method requires the use of several agents in a quantity considerably exceeding the weight of chemical pulp and therefore this method failed to find industrial application.

It is known to activate the chemical pulp by vacuum inclusion with glycerol; but complexity of the process equipment and high power consumption associated therewith are also a hindrance for the industrial implementation of such process.

One of the present-day methods of acetylating the chemical pulp consists in treating the mixture being acetylated with the use of ultrasonics. This method allows the obtaining of a final product featuring sufliciently high physical and chemical homogeneity with a lower consumption of chemicals. But the complexity of ultrasonic devices, high specific power consumption conditioned by a low efficiency of the devices and low output capacity are essential disadvantages inherent in this acetylation method.

The known method of impregnating plant fibres with solutions of chemical agents widely employed in pulp and paper industry such as impregnation of chopped cane and straw or wood chips is conducting while coo-king. The impregnation depth is vital for the quality of the resulting product and for the uniformity of treatment of the plant fibres. When immersed into the impregnating liquid, wood tracheids, bast fibres of chopped cane and straw, plant fibres of semifinished products behave as a system of deadended capillaries. Air contained in the fibres offers the main obstacle to the impregnation of material. The air contained in the fibre capillaries is urged by the impregnating liquid further into the fibre and the air thus compressed oifers an increasing resistance to the impregnation. Air dissolution is a lengthy process and therefore deep impregnation of fibres is possible only when there is no air in the capillaries thereof.

There exist a number of impregnation methods envisaging only partial removal of air from fibre capillaries with the use of vacuum techniques or preliminary steam treatment of the material. Vacuum techniques are effective only with a definite moisture of the material, require highly tight equipment, involves higher power consumption and greater number of operations in the process. Preliminary steaming of the material under treatment leads to a dilution of the Working solution, to higher consumption of steam and greater time required for the entire process and also requires high uniformity of the steam treatment.

The known method of washing the chemical pulp after the treatment thereof with solutions of chemicals when manufacturing paper cardboard and cellulose derivatives in the course of chemical processing is performed by diluting the suspension of fibrous material with water, intensive stirring thereof and subsequent dehydration to a definite concentration. The chemicals contained in the fibres pass into the solution which is separated at the dehydration stage. The quality of the Washing is very important, and in some cases even proves to be decisive. For example, when preparing cellulose nitrates, thorough washing is a decisive factor for the required quality of the finished product. In this case even traces of acids remaining after the washing render the chemical pulp unfit for storage.

With the above-described methods of washing the process takes from 8 to 10 hours with the washing water repeatedly changed and the fibres mechanically agitated.

The washing can also be performed with the use of ultrasonic techniques. With a high flow rate, however, such washing technique is quite complicated and economically unreasonable.

The known method of mercerizing cellulose fibres when preparing spinning solutions is effective by mixing these fibres with a caustic soda solution. Both periodic and continuous action apparatus are used for the purpose, the promising being that which ensures continuous mercerization of the cellulose, the process being run with the cellulose continuously mixed with caustic soda. The main disadvantage of the known method resides in that fails to ensure rapid and uniform diffusion of the reagent into the fibre.

The most important stage of the technological process for the preparation of viscose rayon is known to be not only mercerization but also dissolution of cellulose xanthate. The dissolution process conditions are decisive for the quality of viscose rayon and are to a great extent responsible for the ultimate properties of the rayon produced. Incomplete dissolution, inhomogeneity of the viscose rayon cause considerable difficulties for the maturing and filtering the solution, as well as for shaping the fibre.

Cellulose xanthate can be dissolved by making use of additional mechanical effects such as crumbling, agitation and crushing it, or subjecting it to ultrasonic treatment. The now-existing methods take from 3 to 5 hours for their accomplishment, and ultrasonic treatment is economically inexpedient.

The known method of dyeing the paper pulp and introduction of fillers is carried out with the suspension of fibrous materials being intermixed with the pigments introduced thereinto. It is most preferable to make use of mineral pigments such as titanium dioxide, red oxide, lead yellow molybdate, raw umber, and the like. Wide industrial application of this pigment, however, is limited due to poor dispergation of the aggregated particles and nonuniform distribution of the dye in suspension with a high number of visible inclusions of dye particles over 35-40 micron in size. Poor distribution of certain dyes in the suspension of fibrous materials is caused by the presence of strong agglomerates of pigment therein, which cannot be dispersed under stirring.

Methods are known in the art for dispersing and stirring the colorants with the use of ultrasonic treatment and also by intermixing with surfactant additives. However, the use of surfactants causes foaming of the fibrous suspension which results in poor properties of paper while ultrasonic treatment renders the process materially more expensive.

Defiocculation of the paper pulp before casting on a paper machine is an important stage of final preparation of a homogeneous fibrous suspension when making highquality paper, such as condenser paper and paper of other special grades. Usually deflocculation of the paper pulp is effected by passing the fibrous suspension through narrow elongated slits in a metallic knot catcher screen. Agglomerated fibres left on the screen are removed from the process and further directed for utilization in paper of inferior grades or are disposed of as waste. Deflocculation of the paper pulp is also performed in the process of dispersing fibre agglomerates by subjecting the suspension to highfrequency oscillations. A method of treating the pulp in centrifugal-pulsation apparatus has become most widespread in industry. The generation of oscillations in the suspensions by the known methods for the realization of the above process suffers from a number of disadvantages such as complexity of apparatus design, inadequate quality of cleaning and a possibility of agglomerate formation after the cleaning, as well as high maintenance and service costs and low efficiency of the existing method. A method for cleaning waste water from fibrous mass by flotation is widely employed in the pulp and paper industry. The known method is based on air flotation residing in the action of molecular forces contributing to the adhesion of emulgated, fine disperse and other substances with air bubbles introduced into the waste water. Air bubbles floating up to the surface of the waste water make up a foam-like layer saturated with the substance being floated. In the flotation process use is made of chemical additives promoting foam formation and conferring to the substances being floated an ability of sticking to the air bubbles, thereby expelling them from the water.

For the flotation process to be effective it is necessary that waste water should be energetically agitated and saturated with air bubbles in the presence of flotation chemical additives. The methods of cleaning waste water by flotation now in use have a number of disadvantages, these being lengthy flotation periods coming to 10l5 minutes, high consumption of flotation reagents of from 5 to 50 g. per cu. in. water, low degree of clarification (to 96%), and a low concentration of substances in the fioatant (0.5 to 1.0%). The realization of these methods require expensive and complicated apparatus. These methods cannot cope with the large amount of waste water to be cleaned.

Known at present is the use for treating liquids of cavitation forces arising in the hydrodynamic flow of the liquid (cf., e.g., the materials pertinent to FRG application No. 1,557,212; Cl. 12c, 4/01 of May 26, 1967).

The cavitation arising in the liquid flow is used for intermixing liquid pulverized and gaseous components. The liquid treatment is accomplished by the creation of cavitation with the liquid being passed through a jet nozzle and another component being supplied into the cavitation zone characterized by a high vacuum. The device for realization of such method is made as a conventional injector. These methods and devices, however, are inapplicable for treating suspensions of fibrous materials, since cavitation forces arising in such hydrodynamic flow are of low intensity. The embodiment of the contraction mem her as a jet nozzle provides for a volumetric one-dimensional contraction of the flow with a periodic recurrence of vortex flow separation. Though with such flow around body cavitation takes place its erosion activity is negligibly small.

The erosion activity is used here and hereafter to imply the intensity of cavitation to erosion effect.

A number of experimental and theoretical investigations in the field of cavitation have proved the erosion activity of cavitation to be in an exponential dependence from the value of the pressure pulsations within the cavitation zone. The pulsation of pressures in its turn also depends on the form of the flow restriction and kind of the body within the flow. The cavitation resulting due to the constriction of the flow by the jet nozzle is weak and sufiices only for intermixing any given components in the liquid. Moreover, injection of some other component into the cavitation zone disturbs its structure, the degree of vorticity of the cavitation void, and leads to a considerable decrease in the Strouhal vortex wake number. This still further reduces the erosion activity of cavitation.

It is likewise a well-known fact that supplying gaseous components into the cavitation zone is undesirable, since it brings about a change in the very character of the cavitation process and a diminution of the erosion activity to zero.

It is clear from the above-stated that the application of cavitation which originates in a hydrodynamic flow of injector devices for treating suspensions of fibrous materials is impossible in view of low erosion activity of such cavitation.

It is an object of the present invention to provide a method of treating suspensions of fibrous materials which would allow intensification of various technological processes conducted in the pulp-and-paper industry.

Another object of the invention is to provide an apparatus for treating suspensions of fibrous materials, which, while being simple in design, features high output capacity, low power requirements, and ensures a possibility of the cavitation field intensity to be controlled within a wide range.

Among those various processes performed in the pulpand-paper industry that can be intensified by the method of the invention, deresination of the chemical pulp, bleaching of woodpulp and chemical pulp, chlorination of chemical pulp, increasing of the reactivity of chemical pulp for further chemical processing thereof, simultaneous beating and deresination of chemical pulp,-simultaneous beating and bleaching of chemical pulp, activation and acetylation of the chemical pulp for further chemical processing thereof, impregnation of fibrous materials, washing of the chemical pulp, mercerization and dissolu tion of cellulose xanthate, dyeing of the paper pulp, cleaning of waste water from fibrous materials and deflocculation of the paper pulp, and others can be mentioned.

The above and other objects are accomplished in that when treating suspensions of fibrous materials by subjecting the suspension to the action of cavitation forces that are created in a contracting hydrodynamic flow of the suspension to be treated, according to the invention, the cavitation forces in the hydrodynamic flow of the suspension being treated are created by immersing in said flow of at least one solid that causes a two-dimensional plane contraction of the said flow.

For the deresination of fibrous materials, dispersing agents can be introduced into the suspension flow, upstream the contraction thereof, in an amount of 0.5 to 1.0 percent by weight of the fibre, it being advantageous to combine the procedures of the deresination and beating of the fibrou materials.

For the bleaching of fibrous materials, bleaching agents can be introduced into the suspension flow upstream the contraction thereof, it being advantageous to combine the procedures of bleaching and beating of the fibrous materials.

For chlorinating the fibrous materials, gaseous chlorine can be introduced into the suspension flow upstream of the contraction thereof.

For increasing the reactivity of the fibrous materials, surfactants can be introduced into the suspension flow upstream the contraction thereof.

For activating the fibrous materials, inclusion agents can be introduced into the suspension flow upstream the contraction thereof.

For acetylating the fibrous materials, a catalyst can be introduced into the suspension flow upstream the contraction thereof.

For impregnating the fibrous materials, an impregnating cooking liquor can be introduced into the suspension flow upstream the contraction thereof.

For washing the fibrous materials, water can be introduced into the suspension flow upstream the contraction thereof.

For mercerizing the fibrous materials, alkali can be introduced into the suspension flow upstream the contraction thereof.

For dissolving cellulose xanthate, a solvent can be introduced into the suspension fiow upstream the contraction thereof.

For dyeing the fibrous materials, a pigment can be introduced into the suspension flow upstream the contraction thereof.

For cleaning Waste water from fibrous materials, air can be introduced into the suspension flow upstream the contraction thereof.

The above and other objects are also accomplished in that in an apparatus for treating suspensions of fibrous materials, comprising a reactor having a shell accommodating a member for contracting the flow in the suspension of fibrous materials pump-fed along a system of pipes, and for creating cavitation forces in the suspension, said member accommodated in the reactor shell and adapted for being immersed into the suspension flow,

is shaped as a cylinder and arranged near the entrance portion of the reactor equidistantly from the side walls thereof in such a manner that the line generating the cylindrical surface of said member is normal to the direction of the suspension travel; the reactor from the side of the suspension entrance being associated with the system of pipes by means of an eifuser and from the side of the suspension exit, by means of a diffuser.

Moreover, at the olfuser entrance, over the periphery thereof, nozzles can be provided for supplying chemical agents into the flow of the suspension of fibrous materials. For increasing the erosion activity of the cavitation forces, the cylindrical surface of said member immersed into the suspension flow can be coated with a layer of elastic material, or, else, a vibrator can be arranged in the reactor past the said cylindrical body coaxially therewith.

For measuring the erosion activity of the cavitation forces it is preferable that a pickup unit should be arranged in the reactor.

The essence of the present invention resides in the following.

The prior-art methods are based on the use of hydrodynamic cavitation in the flow of the suspension of fibrous materials, this cavitation originating in the place of the flow contraction as the suspension moves around bodies of a certain shape, the latter inducing the cavitation.

Cavitation cores are bubbles of air present in the micro- -macro-, submicropores and capillaries of the fibres. With a sharp pressure drop past the member immersed in the flow, the cavitation cores grow to bubbles from 0.1 to 1.0 mm. in size, while in the increased pressure zone the dimensions of the cores sharply diminish. With the bubbles enclosed within the cavitation void, shock waves of score thousands of atmospheres originate in the microvolumes of the suspension. These pulses cause repeated deformations of the fibres. The fibre walls become delaminated and fibrillated, this contributing to the development of the active surface area of the fibre and, hence, to a more rapid penetration of the chemical agents into the fibre. The fibres that have undergone the cavitation effect easily react with other components introduced into the suspension and therefore the reaction speeds of the process are in fact determined by the speeds of the chemical reactions proper.

The cavitation forces are manifested in the action of instantly changing pressure gradients, in intensive stirring under the effect of shock waves and microfiows, and are thus responsible for the erosion activity with respect to the suspension being treated. Therefore the creation of an erosion-active stage of cavitation in the hydrodynamic flow of the suspension being treated is of great interest.

According to the invention, for inducing the cavitation, it is suggested that a non-streamlined cylindrical solid should be arranged in the contracting hydrodynamic fiow.

As is known, such a flow features plane two-dimensional vortex wakes which extend over the entire cross-section of the suspension flow. The void has maximum vorticity which determines the degree of rarefaction thereof, and the vortex wakes in case of the cylindrical solid are strictly periodic in obeyance with the Strouhal number. The above features taken in combination determine the maximum erosion activity of the cavitation void. The cavitation caused by the flow moving around the cyllindrical member arranged across the path of the suspension corresponds to the plane two-dimensional vortex wake.

Investigations have shown the erosion activity of the hydrodynamic cavitation created by solids of other shapes to be 8 to 12 times less than that observed in the wake past the cylindrical solid.

It should be pointed out that the intensity of cavitation in. the two-dimensional plane flow can be increased in case the amplitude of pulsations of the Strouhal number is actively changed by superimposing into the field of 9 hydrodynamic pulsations an additional pulse synchronous with said field.

The erosion activity of the hydrodynamic flow cavitation which originates when the flow is contracted by the cylindrical body exceeds the intensity of cavitation induced by other known methods.

Insofar as the potential cores of cavitation are located directly within the fibres, this particular circumstance makes it possible, under the conditions which cause hydrodynamic, separation or flow cavitation (and only such cavitation), easily effect stripping of low-reactivity layers of the cell membrane and thus increase the active surface area of the fibres without the accumulation of low-molecular fractions.

The selectivity of the process is favored by the structure of the chemical pulp fibres, since the primary membrane (low-reactivity layer) is more porous than the inner layer of the secondary membrane, While the outer layer of the secondary membrane is more porous than the inner layer of the secondary membrane.

Thus, in the present invention both the specific features of the very process of hydrodynamic flow cavitation and those of the material to be treated are used to advantage.

The investigations carried out concerning the changes in the structure of the cell membrane of the chemical pulp have confirmed high effectiveness of the present method for treating fibrous materials.

An apparatus for the realization of the present method is disclosed hereinbelow.

The apparatus of the invention, wherein cavitation is made to take place will be here and hereafter referred to as a reactor. A specific feature of the present reactor resides in employing the erosion activity of the cavitation which originates in the wake past the cylindrical solid immersed in the flow. As has been pointed out above, such cavitation features maximum erosion activity.

The reactor is essentially a pipe rectangular in cross section, so that a member adapted to contract the suspension flow can easily be arranged therein. This cylindershaped member is arranged close to the entrance portion of the reactor, equidistantly from the side Walls thereof, in such a manner that the line generating the cylindrical surface of said member is normal to the direction of the suspension travel. Such arrangement of the cylinder provides for periodic formation of vortices in the plane two-dimensional suspension flow and for a free space in the reactor necessary for the creation of the required structure of the cavitation void.

An effuser and a diffuser associate the reactor with a system of pipes and ensure smooth motion of the suspension flow along the reactor without any additional hydraulic resistance.

Nozzles for supplying chemical agents are arranged at the effuser entrance over the periphery thereof in such a manner that they do not interfere with the cavitation zone structure and thus increase the erosion activity of the cavitation.

The coating of the cylindrical member surface with elastic material and provision of a vibrator in the reactor increase the erosion activity of the cavitation, since superpostion of additional pulsations of the cavitation void vortices onto the cavitation field, these pulsations being synchronous with said field, actively increases the amplitude of natural pulsations characterized by the Strouhal number.

A pickup arranged in the reactor for measuring the erosion activity of the cavitation field serves to determine optimum parameters of the hydrodynamic flow.

Given below is a detailed description of an exemplary embodiment of an apparatus of the present invention to be considered in conjunction of the accompanying drawings, wherein:

FIG. 1 is a schematic view of an apparatus for treating the suspension of fibrous materials;

FIG. 2 is a reactor of the herein-proposed apparatus as viewed substantially in a longitudinal section thereof; and

FIG. 3 is an alternative embodiment of the reactor.

The apparatus represented in the drawings, comprises: a reactor 1 (FIG. 1), a pump 3 communicating therewith via a pipe 2, a tank 5 for the suspension under treatment to recirculate, said tank communicating with said pump via a pipe 4, and an overflow tank 6 communicating with the tank 5 via a pipe 7. The reactor 1 communicates with the overflow tank 6 via the pipe 2 which incorporates an upright run 8. The overflow tank 6 communicates with a finished-product tank 10 via a pipe 9.

A rectangular cross-section shell 11 (FIG. 2) of the reactor accommodates a non-streamlined cylindrical member 12 located nearby the entrance thereof at equal distances a from the lateral walls of the shell. The element 12 is so positioned that the generatrix of its cylindrical surface is normal to the direction of the suspension flow (as indicated by the arrow A).

At the inlet of the suspension the reactor shell is connected to an effuser 13, and at the outlet thereof, to a diffuser 14.

Provided at the entrance of the effuser 13 around the periphery thereof are nozzles 15 for chemical reagents to feed into the flow of the suspension of fibrous materials.

An alternative embodiment of the reactor makes provision for a coating 16 (FIG. 3) on the cylindrical member 12 made of an elastic material, e.g., rubber as well as for a vibrator 17 located beyond the cylindrical element 12 and extending longitudinally along the reactor center line.

Provision is also made in the reactor 1 (FIG. 1) for a hydrophone pickup 18 adapted for measuring with its analyzer 19 the erosion activity of a cavitation field.

The apparatus described above operates as follows.

The fibrous suspension of the material under treatment, taken in a concentration of up to 8 percent is fed along a pipe 20 (FIG. 1) to the recirculation tank 5, wherefrom the suspension is fed via the pipe 4 into the pump 3 and, under a pressure of 30-40 m. H O developed by the pump, is fed along the pipe 2 through the efiuser 13 into the reactor 1. Through the nozzles 15 located in the effuser, chemical reagents are introduced into the flow of the suspension. At the place of expansion of the previously contracted flow, a hydrodynamical cavitation field is established which renders an intensifying effect upon the fibrous materials under treatment. The suspension of fibrous materials treated in the reactor, is fed via the diffuser 14 and the pipe 2 incorporating the upright run 8, into the overflow tank 6. Therefrom part of the flow in suspension is passed along the pipe 9 into the finishedproduct tank 10, while the main flow in suspension is directed to recirculation along the pipe 7 into the tank 5. The thus-treated suspension from the tank 10 is fed into the production cycle as indicated by the arrow B.

The degree of treatment of the suspension depends upon the adopted value of the recirculation factor according to which the pump delivery rate is selected.

The intensity of the cavitation field in the reactor is determined by means of the intensity analyzer 19 which receives a signal from the hydrophone pickup 18.

The intensity of cavitation is adjustable by varying the height of the upright run of the pipe 8. By appropriately altering the height of the column of the flow in suspension or the parameters thereof, one can attain such a value of the pressure effective in the reactor, that enables a cavitation field possessing the optimum erosion activity to be obtained.

The operating principle of the analyzer is based upon the fact that the maximum sound pressure measured by the instrument is directly proportionale to the erosion activity of a cavitation field.

When practicing some methods of the treatment of the fibrous suspension, such as increasing its reactivity, it is recommendable to increase the erosion activity of the 1 1 cavitation field which is rendered practicable with the use of the reactor illustrated in FIG. 3.

The erosion activity of cavitation in such a case may be enhanced by 6-8 times, this being attained with the total capacity of the apparatus remaining the same.

The apparatus illustrated in FIG. 1 is applicable in a technological process for carrying out operations involved in the treatment of the suspension of fibrous materials.

Given below are a number of specific exemplary operating conditions and parameters of some techniques employed in pulp-and-paper production practice for the treatment of the suspension of fibrous materials.

EXAMPLE 1 Let us consider an exemplary embodiment of the treatment process of the suspension of fibrous materials involved in deresination of the bleached hardwood sulphate pulp. The fibrous suspension of said material taken in a concentration of up to percent, is pump-fed into the reactor. A hydrodynamic cavitation field is established at the place of the flow contraction, which exerts its influence upon the extraction of resin from the fibre and emulsification of the former in a liquid medium. To reduce time spent for the deresination process, it is practicable to introduce some dispersing agents (taken in an amount of 0.5 to 1.0 percent of the total weight of the fibre) into the suspension upstream of the contraction of the flow thereof. As a result, the number of recirculation cycles of the suspension through the reactor may be reduced to 5 times.

As a result of the treatment by the herein-proposed method a 30-to-6O percent decrease in the content of resin in the pulp is attained, whereas the known methods reduce the resin content but by -15 percent with the same power consumption rate.

EXAMPLE 2 Let us consider an exemplary embodiment of the treatment process of fibrous materials for a simultaneous beating and deresination of the unbleached sulphite pulp. The fibrous suspension in a concentration of up to 4 percent is pump-fed from the recirculation tank into the reactor. At the place of contraction of the flow in suspension a hydrodynamic cavitation field is established which produces fibrillating action upon the fibrous material to facilitate extraction of resin particles therefrom. The suspension recirculates through the reactor -20 times with the result that emulsification of the particles of resin occurs without adding chemical dispersing agents. Prior to being used in further production processes, the suspension of fibrous materials is dehydrated by a conventional method to a concentration of 6-7 percent.

As a result of the treatment by the proposed method, a 30-40-percent decrease in the pulp resin content, 2 to 3 SR increase in the beating degree and a S-percent increase in certain physico-mechanical characteristics are attained.

EXAMPLE 3 Let us consider an example of carrying into efiect the treatment process of the suspension of fibrous materials for bleaching the mechanical woodpulp. The fibrous suspension of that material taken at a concentration of 4 to 6 percent is pumped from the recirculation tank into the reactor. A hydrodynamic cavitation field is created at the place of contraction of the suspension flow to intensify the bleaching process. The components of the bleaching compound are introduced during 1.0-1.5 minutes through the nozzles located in the effuser, viz, sodium silicate, hydrogen peroxide and caustic soda. The latter is introduced in two steps with an intermediate checking the pH value of the medium until it reaches 10.2.

Control of the bleaching process, i.e., an increase in the whiteness of the woodpulp, is exercised by way of determining the whiteness of castings against the Zeiss leucometer.

The total duration of the bleaching process is 15 minutes at a suspension temperature of 45-50 C.

As a result of the treatment by the proposed method, the bleaching time is reduced 12-16 times and the degree of whiteness is increased by 5.5 units as compared to the now-existing bleaching methods, otherwise conditions being identical.

EXAMPLE 4 Let use consider an embodiment of the treatment process of fibrous materials for chlorination of sulphite pulp.

T he fibrous suspension of the material under treatment with a concentration of 3-4 percent at a temperature of 15-20" C. is pumped from the recirculation tank into the reactor.

A hydrodynamic cavitation field is established in the reactor at the place of contraction of the suspension flow to intensify the chlorination process.

Gaseous chlorine is uniformly fed through the nozzles located in the effuser throughout the chlorination process. The recirculation factor during the pulp chlorination process is from 15 to 20.

As a result of the treatment by the proposed method,

the general chlorination stages are reduced two times, theconsumption of chlorine and the chemicals used at the stages of bleaching and refining of said pulp is substantially diminished. The increase in whiteness by 2-5 units is accompanied by enhanced physico-mechanical characteristics by 4-6 percent and a 30-percent decrease in the degree of dirtiness.

EXAMPLE 5 Let us consider an exemplary embodiment of the treatment process of fibrous materials for simultaneous bleaching and beating of sulphite pulp.

The fibrous suspension of the material under treatment with a concentration of 3-4 percent at a temperature of 40-50 C. is pumped from the recirculation tank into the reactor.

A hydrodynamic cavitation field is established in the reactor at the place of contraction of the suspension flow to intensify the bleaching process and concurrently fibrillate the fibrous suspension. The number of recirculation in this case amounts to 10-15. 1

Bleaching chemicals are fed through the nozzles located in the efiuser. Upon treatment in the hydrodynamic cavitation field the pulp is washed by a conventional method.

As a result of the treatment by the proposed method, a 5-6 percent increase in the physico-mechanical characteristics of the finished product and an increment of whiteness by 9 units are obtained.

EXAMPLE 6 Let us consider an exemplary embodiment of the treatment process of fibrous materials aimed at increasing the reactivity of the pulp.

The fibrous suspension of the pulp to be chemically processed, taken at a concentration up to 4 percent and a temperature of 20 to 30 C., is pumped into the reactor.

A hydrodynamic cavitation field is established at the place of contraction of the suspension flow to exert influence upon the material under treatment. The number of recirculation in this case amounts to 25-30.

As a result of the treatment by the proposed method, an increase in the pulp reactivity from /11 percent CS /NaOI-I attainable by the now-existing method, to 60/11 percent Cs /NaOH, the resultant cellulose xanthate being essentially a transparent and fast-to-filter viscose solution.

Examinations of the fibre microstructure have proved also that its treatment in the hydrodynamic cavitation field is conducive to an intensive elimination of the unreactive layers of the cell wall and a uniform fibrillation of the fibre surface.

13 EXAMPLE 7 Let us consider an exemplary embodiment of the treatment process aimed at activating sulphate and sulphite refined pulp.

The fibrous suspension of the pulp with a concentration of 26 percent at a temperature of 4050 C. is pumped from the recirculation tank into the reactor, the number of recirculation amounting in this case to 25-30. A hydrodynamic cavitation field is established at the place of contraction of the suspension flow to exert influence upon the material under treatment.

Fed through the nozzles in the etfuser is an inclusion agent taken as a 3-percent glycerol solution in an amount of 2.0 to 5.0 percent of the fibre weight.

Upon dehydrating the pulp on filters, the inclusion agent is again introduced into the production cycle to further circulate therein.

Treating the pulp in the cavitation field in the medium of the inclusion agent consists in loosening its supramolecular structure so as to increase the accessibility of the macromolecules thereof.

As a result of the treatment by the proposed method, the following characteristics are attained which are compared with those resulting from the now-existing activation methods: viscosity, 400 centipoise (against 410 centipoise) at 50 C., optical density in a 30-mm. cuvette, 0.7 (against 1.1), filterability, 210 ml. (against 55 ml.). Acetylation of the thus-activated pulp is carried out at 50C. with the use of acetyloxide in the acetic-acid medium, sulphuric acid being the catalyst. The bath ratio is equal to 20, catalyst consumption, 2 per cent of the pulp weight, acetic acid-to-acetyloxide ratio, 85:15.

With the herein-proposed activation method, a possibility is rendered of extending the assortment of the semifinished products engaged in the manufacture of man-made fibres and films due to the use of low-grade cellulose.

EXAMPLE 8 Let us consider an exemplary embodiment of the treatment process of fibrous materials aimed at acetylating the pulp to be chemically processed.

The fibrous suspension of a distintegrated pulp with a concentration up to 5 percent at a temperature of 30 40 C. is pumped from the recirculation tank into the reactor. A hydrodynamic cavitation field is created at the place of contraction of the suspension fiow to intensify the acetylation process. The treatment takes 8-12 minutes to occur.

A catalyst is introduced in the suspension through the nozzles in the etfuser.

A non-preactivated pulp may be subjected to acetylation by the proposed method.

As a result of the treatment by the proposed method, highly substituted cellulose triacetate is obtained, featuring the degree of polymerization of about 500 which -15 times reduces the time spent for acetylation by the known method.

EXAMPLE 9 Let us consider an exemplary embodiment of the treatment process aimed at impregnating chopped straw and cane with solutions of chemicals.

The suspension of chopped straw or cane with a concentration up to 8 percent at 30-40 C. is pumped from the recirculation tank into the reactor. A hydrodynamic cavitation field is established at the place of contraction of the suspension How to intensify the impregnation process, the treatment period taking 3 to 5 minutes to occur.

An impregnation liquor of digester acid is introduced into the suspension through the nozzles in the effuser.

As a result of the treatment by the proposed method, the permeability of the fibers is increased which favourably tells on the pulp cooking rate. The impregnation 14 method by this method substitutes the maceration process.

EXAMPLE 10 Let us consider an exemplary embodiment of the treatment process of fibrous materials aimed at washing the cellulose to get it rid of chemical reagents.

The fibrous suspension with a concentration up to 4 percent at 2030 C. is pumped from the recirculation tank into the reactor. A hydrodynamic cavitation field is established at the place of contraction of the suspension flow to intensify the Washing process. Washing time is 15 to 20 minutes.

Wash water is introduced into the suspension through the nozzles in the etfuser. Upon the cavitation treatment, the pulp suspension is dehydrated by the known methods.

As a result of the treatment by the proposed method, washing time is reduced from 68 hours according to the known methods to 15-20 minutes. Simple construction and safe operation improve the labour conditions for the attending personnel.

EXAMPLE 1 1 Let us consider an exemplary embodiment of the treatment process of fibrous materials involved in mercerization of pulp.

The suspension of the pulp taken as a loose mass at a concentration up to 8 percent and a temperature of 30- 40 C., is pumped from the recirculation tank into the reactor. A hydrodynamic field is established at the place of contraction of the suspension flow to intensify the mercerization process.

Caustic soda is fed into the suspension through the nozzles in the effuser. The process takes 4 to 5 minutes to take place. Under the effect of the cavitation field possessing high erosion activity, conditions are established for a uniform swelling of the pulp and a complete dissolving of hemicelluloses.

As a result of the treatment by the proposed method, the quality of the finished product is improved and the content of the hemicellulose therein is increased. Thus, when treating the pulp in a caustic-soda solution with a concentration of 220 g./l. and the bath ratio of 20, the content of hemicellulose equals 2832 g./l. in the working solution and 3035 g./l. in the pressed-up solution.

EXAMPLE 12 Let us consider an exemplary embodiment of the process of dissolving cellulose xanthate.

The suspension of cellulose xanthate is pumped from the recirculation tank into the reactor. A solvent is introduced into the suspension through the nozzles in the effuser. A hydrodynamic cavitation field is established at the place of contraction of the suspension flow to intensity the process of a deep penetration of the solvent inside the polymer and destruction of the intermolecular bonds which contributes to a faster passing of xanthate into solution.

As a result of the treatment by the proposed method, a complete dissolution of cellulose xanthate within 20 minutes occurs, with the resultant easy-to-filter viscose solution with a viscosity of 50 sec. as measured by the ball method and a 9.5-percent cellulose and 6.7-percent caustic soda content.

EXAMPLE 13 Let us consider an exemplary embodiment of the treatment process of fibrous materials involved in dyeing the paper mass.

The suspension of the material to be dyed with a concentration up to 4 percent is pumped from the recirculation tank into the reactor. A mineral pigment is introduced into the suspension through the nozzles in the effuser. A hydrodynamic cavitation field is established at the place of contraction of the suspension flow to intensify the process of dyeing the paper mass. Under the ef fect .of the cavitation field, a dispersion of the pigment and a uniform intermixing thereof with the material being dyed take place.

As a result of the treatment by the proposed method, the quality and properties of the paper from such paper mass, as well as its aesthetic characteristics are substantially enhanced. When the suspension of fibrous materials is treated by the now-existing methods, paper castings, feature a fairly number of visible inclusions of aggregated particles 0.08-04 mm. in size, while the castings of the cellulose treated in the cavitation field wtihin the period of time twice as short, incorporate no inclusions of the pigment.

EXAMPLE 14 Let us consider an exemplary embodiment of the treatment process of the suspension of fibrous materials when defiocculating the paper mass.

The suspension of paper mass with a concentration up to 4 percent at 15-20 C. is pumped from the recirculation tank into the cavitation reactor. A hydrodynamic cavitation field is established at the place of contraction of the suspension flow under the effect of which the agglomerates of fibres formed Within the previous production processes, are dispersed.

The fibres of the paper mass, due to their having been charged with the like potential, in the cavitation field forms no flocs during further flow of the suspension. Thus, the paper mass is ready for casting on a paper machine. With a 5-fold recirculation, the content of agglomerates in the fibrous mass is 70-80 percent as low as that in the known methods of treatment.

EXAMPLE 15 Let us consider an exemplary embodiment of the treatment process of the suspension of fibrous materials when cleaning waste water of pulp-and-paper industry.

The stream of waste water containing fine fibres, is fed from the recirculation tank into the cavitation reactor. Air is introduced into the Waste water through the nozzles in the eifuser. A hydrodynamic cavitation field is established at the place of contraction of the waste water flow to intensify the process of saturating the waste water with fine-disperse air bubbles. Under the influence of pressure pulses arising during the closing of cavitation bubbles, the dispersing of the fibres being floated occurs as well as oversaturation of the suspension with air and dispersing large-sized air bubbles. An intense stirring of the suspension due to high degree of the flow turbulence in the caviation field adds to the foam formation. The separated mass of the fine-disperse air bubbles float up within the zone of laminar flow and entrain the particles of fibres contained in the waste water. The ascended layer of the substances being floated is then separated from the larified water.

As a result of the treatment by the proposed method of waste water containing acid, neutral or alkaline medium without the use of any flotation chemicals, a 5-6 percent increase in the concentration of the substances being floated is attained. Besides, the time spent for the process is cut down by 2 times as compared to the nowexisting methods.

The afore-considered examples testify to the fact that the treatment of suspensions of fibrous materials in a hydrodynamic cavitation field makes it possible to considerably intensify the majority of technological processes involved in pulp-and-paper industry, enables said processes to be run with the use of novel equipment at a drastically reduced expense for the manufacture and operation of production apparatus, allows high-quality products to be obtained at lower consumption of raw materials, power and time per unit of the finished product. The fact that the proposed method runs continuously and is simple to be carried out enable a possibility of a complete automation of the production process.

What is claimed is:

1. A method of treating suspension of fibrous materials, comprising a non-streamlined cylindrical solid body transversely in an elongated passageway in the hydrodynamic flow'of the suspension under treatment so as to cause a two-dimensional plane contraction of the How to produce cavitation forces in the thus-contracting flow and in the wake at the rear of the cylindrical surface of said non-streamlined body which cavitation forces act upon the suspension of fibrous materials.

2. A method as claimed in claim 1, comprising introducing chemical activators for the treatment process are introduced into the flow of suspension upstream of the contraction thereof.

3. A method as claimed in claim 2, wherein for deresinating the fibrous materials, dispersants in an amount of 0.5 to 1.0 percent of the fibre Weight are introduced into the flow of suspension upstream of the contraction thereof.

4. A method as claimed in claim 2, wherein for bleaching the fibrous materials, bleaching agents are introduced into the flow of suspension upstream of the contraction thereof.

5. A method as claimed in claim 2, wherein for chlori mating the fibrous materials, gaseous chlorine is introduced into the flow of suspension upstream of the contraction thereof.

6. A method of treating suspensions of fibrous materials, comprising introducing surfactants into the flow of suspension to enhance the reactive capacity of the fibrous materials of such suspensions, positioning a non-streamlined cylindrical solid body transversely in an elongated passageway in the hydrodynamic flow of the suspension under treatment so as to cause a two-dimensional plane contraction of the flow to produce cavitation forces in the contracting flow and in the wake at the rear of the cylindrical surface of said non-streamlined body which cavitation forces act upon the suspension of fibrous materials.

7. A method of treating suspensions of fibrous materials, comprising introducing inclusion substances into the flow ofsuspension to activate the fibrous materials of such suspension, positioning a non-streamlined cylindrical solid body transversely in an elongated passageway in the hydrodynamic flow of the suspension under treatment so as to cause a two-dimensional plane contraction of the flow to produce cavitation forces in the contracting flow and in the wake at the rear of the cylindrical surface of said non-streamlined body which cavitation forces act upon the suspension of fibrous materials.

8. A method of treating suspensions of fibrous materials, comprising introducing catalysts into the flow of suspension to activate the fibrous materials of such suspension, positioning a non-streamlined cylindrical solid body transversely in an elongated passageway in the hydrodynamic flow of the suspension under treatment so as to cause a two-dimensional plane contraction of the flow to produce cavitation forces in the contracting fiow and in the wake at the rear of the cylindrical surface of said non-streamlined body which cavitation forces act upon the suspension of fibrous materials.

9. A method of treating suspensions of fibrous materials, comprising introducing an impregnating solution into the flow of suspension, positioning a non-streamlined cylindrical solid body transversely in an elongated passageway in the hydrodyamic flow of the suspension under treatment so as to cause a two-dimensional plane contraction of the flow to produce cavitation forces in the contraction flow and in the wake at the rear of the cylindrical surface of said non-streamlined body which cavitation forces act upon the suspension of fibrous materials.

10. A method of treating suspensions of fibrous materials, comprising introducing water into the flow of suspension to wash the fibrous materials of such suspension, positioning a non-streamlined cylindrical solid body transversely in an elongated passageway in the hydrodynamic flow of the suspension under treatment so as to cause a two-dimensional plane contraction of the flow to produce cavitation forces in the contracting flow and in the wake at the rear of the cylindrical surface of said non-stream lined body which cavitation forces act upon the suspension of fibrous materials.

11. A method of treating suspensions of fibrous materials, comprising introducing alkali into the flow of suspension to mercerize the fibrous materials of such suspension, positioning a non-streamlined cylindrical solid body transversely in an elongated passageway in the hydrodynamic flow of the suspension under treatment so as to cause a two-dimensional plane contraction of the flow to produce cavitation forces in the contracting flow and in the wake at the rear of the cylindrical surface of said non-streamlined body which cavitation forces act upon the suspension of fibrous materials.

12. A method of treating suspensions of fibrous materials, comprising introducing solvents into the flow of suspension for dissolving xanthate in the suspension, positioning a non-streamlined cylindrical solid body transversely in an elongated passageway in hydrodynamic fiow of the suspension under treatment so as to cause a twodimensional plane contraction of the flow to produce cavitation forces in the contracting flow and in the wake at the rear of the cylindrical surface of said non-streamlined body which cavitation forces act upon the suspension of fibrous materials.

13. A method of treating suspensions of fibrous materials, comprising introducing pigments into the flow of suspension to dye the fibrous materials in such suspension, positioning a non-streamlined cylindrical solid body transversely in an elongated passageway in the hydrodynamic fiow of the suspension under treatment so as to cause a two-dimensional plane contraction of the flow to produce cavitation forces in the contracting flow and in the wake at the rear of the cylindrical surface of said nonstreamlined body which cavitation forces act upon the suspension of fibrous materials.

14. A method of treating suspensions of fibrous materials, comprising introducing air to cleanse waste water of the fibrous material of such suspension positioning a non-streamlined cylindrical solid body transversely in an elongated passageway in the hydrodynamic flow of the suspension under treatment so as to cause a two-dimensional plane contraction of the flow to produce cavitation forces in the contracting flow and in the wake at the rear of the cylindrical surface of said non-streamlined body which cavitation forces act upon the suspension of fibrous materials.

15. An apparatus for treating suspensions of fibrous materials, comprising: a reactor including an elongated shell having an entrance and an exit; a non-streamlined solid cylindrical member located in the reactor shell adjacent its entrance at equal distances from the lateral walls thereof; a first means to feed suspension into the reactor and continuously therethrough; an effuser which connects the reactor at said entrance with said first means; a second means to continuously discharge the treated suspension: and a diffuser which connects the reactor at said exit with said second means to remove the treated suspension; said cylindrical member being so positioned in the reactor shell that the generatrix of the cylindrical surface of said member is normal to the direction of flow of the suspension whereby said cylindrical member produces su stantial hydrodynamic cavitation in the wake at the rear of said cylindrical surface of said non-streamlined member.

16. An apparatus as claimed in claim 15, comprising nozzles at the inlet of the effuser located around the periphery thereof and adapted to feed chemical reagents into the flow of suspension of the fibrous materials.

17. An apparatus as claimed in claim 15, comprising a cylindrical surface of the said cylindrical member a layer of an elastic material.

18. An apparatus as claimed in claim 15, comprising a pickup in said reactor for measuring the erosion activity of a cavitation field produced by said cylindrical member.

19. An apparatus as claimed in claim 15 wherein said elongated passageway has a rectangular cross-section.

References Cited UNITED STATES PATENTS 3,420,454 1/1969 Brown, Jr. 162-5O FOREIGN PATENTS 268,162 10/1970 U.S.S.R. 16250 OTHER REFERENCES Williams et al., Some Factors Affecting the Inception of Cavitation, Symposium held at Natl Phys. Lab. on Sept. 14-17, 1955, Stimulate Interest in Ultrasonics for Wood Industries, Pulp and Paper, vol. 35, No. 1 (1961), p. 64.

S. LEON BASHORE, Primary Examiner P. CHIN, Assistant Examiner US. 01. X.R.