CA1322827C - Process and equipment for pretreatment of cellulosic raw-material - Google Patents
Process and equipment for pretreatment of cellulosic raw-materialInfo
- Publication number
- CA1322827C CA1322827C CA 590344 CA590344A CA1322827C CA 1322827 C CA1322827 C CA 1322827C CA 590344 CA590344 CA 590344 CA 590344 A CA590344 A CA 590344A CA 1322827 C CA1322827 C CA 1322827C
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- Canada
- Prior art keywords
- solution
- penetration
- chips
- vacuum
- raw
- Prior art date
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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C1/00—Pretreatment of the finely-divided materials before digesting
- D21C1/10—Physical methods for facilitating impregnation
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- Paper (AREA)
- Chemical And Physical Treatments For Wood And The Like (AREA)
- Chemical Or Physical Treatment Of Fibers (AREA)
- Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE:
The invention concerns a process and an equipment for pretreatment of cellulosic chip-formed raw-material by impregnation. In the process, first a vacuum treatment is carried out withou preceeding moistening treatment, and as soon as possible after the vacuum treatment penetration, is carried out with a solution of chemicals or with water at the atmospheric or a higher solution pressure. In this way the fiber cavities can be filled optimally, which promotes a uniform and adequate diffusion of the solution into the fiber walls significantly. The process can be carried out, e.g., in a device which comprises a tank for the treatment of the raw-material and therein a feed opening for the solution as well as an opening for removal of the raw-material, which opening communicates preferably with a reception tank, where the atmospheric or a higher pressure prevails.
The invention concerns a process and an equipment for pretreatment of cellulosic chip-formed raw-material by impregnation. In the process, first a vacuum treatment is carried out withou preceeding moistening treatment, and as soon as possible after the vacuum treatment penetration, is carried out with a solution of chemicals or with water at the atmospheric or a higher solution pressure. In this way the fiber cavities can be filled optimally, which promotes a uniform and adequate diffusion of the solution into the fiber walls significantly. The process can be carried out, e.g., in a device which comprises a tank for the treatment of the raw-material and therein a feed opening for the solution as well as an opening for removal of the raw-material, which opening communicates preferably with a reception tank, where the atmospheric or a higher pressure prevails.
Description
~32%8~7 Process and equipment for pretreatment of cellulosic raw-material The present invention concerns a process and an equip-S ment for pretreatment of chip-formed wood or other cellu-losic raw-material by impregnation. ~he invention is in particular concerned with the penetration of the fibrous cell system, taking place as the first step in the impreg-nation. As the penetration solution, it is possible to use a solution of chemicals or water.
In the technique for -the production of paper fibers, the object of the impregnation of the wood chips is to provide a desired amount of solution as uniformly distributed in the fiber walls in the chips. In this way, the detaching of the fibers while they remain a~ intact as possible and of suitable quality or the dissolution of liqnin and of other encrust materials in a later stage of the process is pxomoted. The fa~tors affecting the impregnation are indefinite and difficult to control, which may result, e.g., in an overdosage of time and chemicals when attempts are made to guarantee an acceptable final result.
In the technical literature in this field, it is sug-gested that impregnation takes place as a joint effect of two physical fa~tors, penetration and diffusion, which starts immediately after the solution has reached contact with the chips.
The penetration begins prim~rily from the cut faces of a chip, from which the solution penetrates into the fiber cavities. Owing to the counter-pressure caused by the air present in the cavities, the penetration slows down and stops soon. Almost the only factor that is men-tioned as a factor that promotes the penetration is an in-crease in the difference in pressure betw~en the solution and the air present in the fiber cavities by reducing the component pressure of the air or by increasing the pres-sure of the liquid.
Compared to penetration, diffusion is very slow. In . .
In the technique for -the production of paper fibers, the object of the impregnation of the wood chips is to provide a desired amount of solution as uniformly distributed in the fiber walls in the chips. In this way, the detaching of the fibers while they remain a~ intact as possible and of suitable quality or the dissolution of liqnin and of other encrust materials in a later stage of the process is pxomoted. The fa~tors affecting the impregnation are indefinite and difficult to control, which may result, e.g., in an overdosage of time and chemicals when attempts are made to guarantee an acceptable final result.
In the technical literature in this field, it is sug-gested that impregnation takes place as a joint effect of two physical fa~tors, penetration and diffusion, which starts immediately after the solution has reached contact with the chips.
The penetration begins prim~rily from the cut faces of a chip, from which the solution penetrates into the fiber cavities. Owing to the counter-pressure caused by the air present in the cavities, the penetration slows down and stops soon. Almost the only factor that is men-tioned as a factor that promotes the penetration is an in-crease in the difference in pressure betw~en the solution and the air present in the fiber cavities by reducing the component pressure of the air or by increasing the pres-sure of the liquid.
Compared to penetration, diffusion is very slow. In . .
2 ~
diffusion the ions are transferred into the fiber walls in the solution because of differences in the concentra-tions of chemicals. The diffusion proceeds along liquid connections formed by the water which has penetrated into the fibrous cell system or which wa~ present in said cell system.
Raising of the temperature of the penetration solution promotes the mobility of the ions. However, the chemical concentration of the penetration solution has a declsive significance for the progress of the diffusion into the interior parts of the chips, because the diffu-sion is always retarded when the moisture contained in the chips dilutes the solution and when its chemical content is reduced as chemicals are absorbed into the cell walls.
Thus, the amount and the coverage of the penetration ha~e a highly essential importance for the initiation and progress of the diffusion as well as for the ~ufficiency an~ uniformity of the dosage of chemicals in the fiber walls, which is the ultimate goal.
It has been suggested that the amount of air contained in the cell systems in chips be reduced by means of vacuum produced mechanically or by means of steaming. However, only steaming is employed in the industry.
Steaming impregnation is a simple, but not adequate -or controlled process if a good and uniform penetration of the chips is desired. For example, it has been proved that, as a result of absorption with the cookin~ liquor, the chemical concentrations in diferent parts of a chip particle varied within wide limits and that a considerably long diffusion time with preheating is required before a concentration necessary for the chemical reactions can be obtained in the inner parts.
~ he use of a vacuum in order to ~emove air has been suggested, e.g., in the Finnish Patents 11,~87 and 30,091, and in the Swedi~h Patent 135,529.
The publication SE 135~529 deals with a continuous pro-cess and with equipment for impregnation of th~ chips with liguid. The impr2gnation takes place so that chips are , , :
~ 3 ~
fed continuously into the top portion of a tower, where it enters into a vacuum. The lower end of the to~er, whose top end is closed, is placed in water, so that the chip column sinks in the tower slowly downwards and is S submerged in the water, being impregnated at the same time. Thereat the pressure of the water surrounding the chips becomes gradually higher, until it reaches the atmospheric pressure as the chips are discharged out of the tower. When a chip particle sinks into water, tne 1Q pressure of the air present in the fiber cell system is the same as the pressure of the surrounding water, whereby no penetration dependent on pressure gradient takes place.
However, the effect of factors that retard penetration, which evolve rapidly, starts immediately.
In the process of the publication FI 30,091 the start-ing material is first predried to about 18 %, and air is removed from it almost completely at an absolute pressure lower than 100 mmHg (about 0.13 bar) and at a temperature of 85 to 90C. If a higher temperature is used, according to the patent, the vacuum-treatment pressure can be in-creased up to an absolute pressure of 200 mmHg (a~out 0.26 bar).
As compared with the very high variations in the con-~; ten~s of air and water in the chips, the changes in the density of the wood material are, as a rule, confined to the range of ~ 5...10 %, because attempts are made to use the same species of wood and to avo.id the parts that are most difficult to impregnate, such as the resinous heart-wood of conifer trees.
The moisture content of the chips varies within very wide limits. The chips arriving in the fiber production can normally contain water at a level of 30 to 120 % of the dry matter of the chips. In mechanical production processes, the defibration is successful best when the 3~ chips are filled with water. In chemic~l processçs, the desired dosage of chemicals must be provided throughout the chips as uniformly diffused. Thereat, the quantity and the chemicals content of the solution to be penetrated ~3~32~
into the fiber cell system free from watere have an essential effect on the diffusion.
In the cited processes, the impregnation takes place almost exclusively by means of diffusion. Penetration cannot be utilized therein almost at all, being usable at the maximum partially and occasionally.
The invention proposes a process for the pretreatment of cellulosic chip-formed raw-material, which comprises:
a) removing air out of the raw-material by means of vacuum treatment, wherein said vacuum treatment is carried out without preceding substantial moistening of the raw-material, b) bringing the raw-material into contact with a penetration solution, the temperature of which is lower than the boiling point of the solution at said vacuum, where the solution is allowed to penetrate into the raw-material for about 5 minutes at said vacuum, and c) exposing the raw material and the penetration solution to a pressure of atmospheric or above for a time sufficient to allow the solution to penetrate into the chips.
Here, "moistening" means steamin~, washing, or any other, conventional aqueous treatment.
The penetration is carried out rapidly after the vacuum treatment at the atmospheric or a higher solution pressure so that the ~iber cavities in -the raw-material do not have time to be closed substantially before the penetration. The more rapidly the penetration is carried out, the better. Depending on the conditions and on the species of wood, the vacuum-treated raw-material is subjected to solution pressure, e.g., within about 5 min., best e.g., in 1 min., most appropriately in 0,5 min~ from P~ ' c~ ~.322~27 - 4a -the vacuum treatment.
The passing of the penetration solution into contact with the raw-material is started preferably while the vacuum is still effective. Optimal1y, the vacuum is maintained during the whole of the passing of solution.
After the desired quantity of solution has been brought into contact with the raw-ma~erial, a pressure impact may be applied to the solution additionally.
The vacuum that is used is, e.g., 0.1 to 0.5 bar, optimally 0.2 to 0.4 ba~. Thereat, the temperature of the penetration solution is e.g., 35 to 85C, optimally 45 to 75C.
The concentration of chemicals in the penetration solution is advantageously~regulDted in accordance with the i 1,~
~ - ~
~322~7 raw-material or in accordance with the quantity of the solution to be penetrated.
According to an embodiment, the penetration solution is passed to among the raw-material in the same vessel in which the vacuum treatment was carried out, whereinafter the raw-material is transferred into a reception tank of a higher pressure, where the penetration is completed.
After the penetration, it is advantayeous to separate the proportion of the raw-material that did not ~ink into the solution from the rest o~ the raw-material.
The equipment in accordance with the invention is pro-vided with a common v ssel for vacuum treatment and for penetration, or separate vessels are p~ovided for them.
A common processing vessel may be, for example, a rotor that revolves in a housing and that it open at least at one end. The necessary connecting ducts are fitted on the circumference of the rotor housing.
When separate vessels are used for vacuum treatment and for penetration, between them it is possible to employ a transf~r duct whose final end forms a barometric lock between the vessels. In such a case, the transfer duct is preferably extended by a perforated penetration duct.
The final end of the transfer duct is appropriately pro-vided with equipment for the removal of contaminations.
On the other hand, at the final end of the perforation duct, it i~ appropriately possible to place an equip~ent for the removal o~ unpenetrated raw-material. Penetrati~n liquid can be fed into the transfer duct, in particular into its initial end.
The raw-material can also ~e passed into the vacuum-treatment tank through a feed-transfer duct passing through the penetration tank so that the initial e~d of the feed-transfer duct forms a barometric lock between the penetration tank and the vacuum-treatment tank. In such a case, the raw-material must, of course, pass through this lock so that it is substantially not moistened.
The chips are pretreated in accordance with the inven-tion without a moistening substantial from the practical .
- :~3~2~27 point of view. The walls of the cut-off fibers at the cut-off ends of the chips, in particular those o~ their parts that contain hemicellulose, viz., absorb water very rapidly and, when they becGme ~oll~n, contract or block the open cell cavities. Out of said reason, in connection with penetration, vacuum-treated chips should preferably also be surrounded with solution as rapidly as possible.
If the chips, however, end up in contaet with water before the pretreatment in accordance with the inventlon, this contact time should, depending on the circumstances, be at the maximum about 1 min., preferably, however, at the maximum about 20 to 30 or 5 to 15 seconds.
According to the process of the present invention, the best penetration is not achieved by means of maximum vacuum, but by making use of the temperaturë of the pene-tration liquid, which said temperat~re is, depending on the wood species, 35 to 85C. The magnitude of the vacuum pressure is determined so that vaporization of the liquid is still avoided. The necessary vacuum can be produced by means of normal equipment commonly used in the industry at a reasonable cost.
For example, with softwood, the vacuum is advantage-ously 0.2 to 0.3 bar, and the temperature of the water solution 55 to 70C.
When the water content of the chips is changed, the amount o the solution that is penetrated is changed in the same proportion, but the total guantity of pene-trated solution and water contained in the chips remain at the same level, i.e. said penetration procedure per~its equal filling of the cell system independently from th~
moisture content of the chips. The amount and uniformity of penetration are well reproducible in the process.
When the density of wood varies, the altered solids amount i~ measured in the form of a corresponding altera-tion in the penetration solution.
The nature and the p~ of the solution of chemicalshave no significant ~ffect on the penetration.
The concentration of the solution of chemicals has a .
, 7 minor e~rfect, which is insignificant under the conditions concerned.
If necessary, high concentrations of chemicals are also possible, because it is possible to use temperatures in which the ~olubilities of the chemicals are good.
In the following, the process in accordance with the invention and the d~vices for its application will be de-scribed in more detail with reference to the accompanyinq figures, wherein - Figure 1 lllustrates the effect of a treatment with a solution of chemicals or with water that precedes the vacuum treatment on the amount of chips that sink into the solution, - Figure 2 illustrates the dependence of the penetra-tion on the temperature of the solution or water, - Figure 3 illustrates the effects of the moisture and the density of the chips on the amount of ~olu-tion penetrated and on the penetration level, - Figure 4 illu~trates a vacuum penetration solution in accordance with an advantageous embodiment of the invention, - Figure 5 illustrates a vacuum penetration solution in accordance with another advantageous embodiment, ~ Figure 6 illustrates a fuxther vacuum penetration solution in accordance with an ad~antageous embodi-ment, and - Figures 7 and ~ illustrate the steps of operation of a continuous vacuum penetration device~
In the experiments that were carried out, factory-made chips were used.
For determination of the uniform.ity of penetration and the level of penetration, it was noticed that determina-tion of the proportion of the chips that sink into the solution or water was a sufficiently accurate procedure.
From Fig. 1 it is seen how high the negative effect is with a cooking-liquor treatment that precede~ the vacu-um treatment on the penetrability of cooking liquor.
The vertica1 axis represents the proportion of the chips ~ 3 2 ~ 8 ~J ~
that sink into the liquor as a percentage of the whole quantity of chips treated, and the horizontal axiQ repre-sents the duration of effect of the liquor as minutes.
In tAe test, pine chips were used whose moisture content was 21 %. The temperature of the treatment solution w~s 65C and the concentration 5 %.
The broken line 1 illustrates the proportion of the sinking chips during vacuum penetration when the chips are txeated with NSSC-solution. The broken line ~ illustrates the proportion of the sinking chips when the chips are treated with NaHSO3-solution. It is noticed that a treat-ment for one minute with NSSC-solution already reduces the amount of the sinking proportion by 24 %, and a treatment for three minutes by about 45 %. The corresponding rPduc-tions in ~he case of treatment with NaHSO3-solution were about 30 % and about 70 ~. In the test a procedure was used wherein the penetration was performed with a cooking liquor subjected to the atmospheric pressure and wherein the filling of the solution was started while the vacuum pressure that had prevailed was still effective.
An explanation of the phenomenon of Fig. 1 is that an aqueous solution has a remarkably rapid effect on the walls and surface properties of capillary cell cavities, whereby, at the cut faces of the chip~, the cell systems and in particular the capillaries in summer wood are con tracted relatively speakinq most rapidly. In this way, the amount of solution that is penetrated, i.e. the pro-portion of the chips that are sunk into the solution, is lowered rapidly as the soaking time i5 increased.
Fig. 2 illustrates the effect of the temperature of the solution on the penetration with different treatment times. The left v~rtical axis represents the amount of the chips that sink into the solution as a percentage of the entire quanity of chip~ treated, the horizontal axis represents the temperature of the solution as C, and the right vertical axis represents the duration of treatment as minutes. In the test the raw-material consisted of pine chips of a moisture content of 20 %, which said chips ~32~
were treated ~ith a 5-~ NaHS03-~olution. It is seen that when the temperature of the solution rises from 20 to 50C, the amount of the chips that sink into the solution (broken line 3) also increases significantly. Likewise, it is seen that a further raisi~g of the temperature does not have a major effect on the result. At the same time with the raising of the temperature of the solution, the treatment time (straight line 4) was shortened in the tests, in spite of which the proportion of sinking chips remained invariable and PYen became somewhat higher. It comes out fxom the results unambiguously that the lower limit of the economical operating temperature of th~ solu-tion is somewhere around 35 to 40C, whereas, according to the experiments, it is not so useful to heat the mate-rial to very hi~h temperatures, because the penetrationis not improved essentially. By means of heating, it is, however, possible to intensi~y the penetration decisively.
From Fig. 3 it is seen how the water content of the chips affects the amount of solution that is penetrated.
The horizontal axis represents the water content of the chips, and the vertical axis represents the amount of penetrated solution and the amount of chips ~hat sink into the solution, all as a percentage of the dry matter of the chips. In th~ series o tests, the concentration of the solution of chemicals was S % and the tPmperature 65C.
Th~ broken lines 1 to 3 illustrate the penetrations of pine chips 1. with sulphate solution, ~. with NSSC-solu-tion, and 3. with NaHS03-solution, as well as the broken line 4 illustrates birch chips treated with NSSC-solution.
From the broken lines 1 to 3, it comes out that solutions essentially different from each other are penetrated approximately in the same way irrespective o the moisture content of the chips.
With the same chip species, the penetration of a solu-tion of chemicals i5 determined in an almost linear way by the amount of water contained in the chips. This comes out best from an examination, at the various test points, of the joint efects of the chan~es in the water contained .
~ 3 ~
~ o as moisture in the chips and in the amount of water con-tained in the solution that penetrated into the chips.
In the pine chips, the total water quantity was within the range of 164 to 177 %, and in the birch chips within the range of 143 to 145 ~, respectively. The scatterlng from the average value was with pine chips + 4 % and with birch chips ~
The proportion of sinking chips, which was determined by means of a follow-up of the penetration level, was with pine chips 8~ to 89 % and wlth birch chips 100 %, irres-pective of the moisture of the chips (broken lines 5 ~ 6).
The clear difference in penetration level between the pine and birch chips, seen in Fig. 3, is mainly attribu-table to different densities of the chips, the density of pine being on the average 0.4 and that of birch O.S. Here density is understood as meaning the nominal density of the wood species as fully dry.
Since in the case of the different species of wood that are ordinarily used for fiber production, the density of the wood material proper is the same, 1.32 to 1.35, the higher density of birch, which is on the average one quarter higher than the density of pine, means a corres-pondingly smaller space of fiber cavities, which is also manifested in a corresponding change in the penetrated quantities of NSSC-solution shown in Fig. 3.
In a comparat~ve tPst carried out with the pine chips and the NSSC-solution quality us~d in Fig. 3, impregnation by means of steaming was studied. After a steaming time of five minutes, about four fifths of the quantity of so-lution that penetrated under vacuum in ~ive minutes wereabsorbed best into dry chips, initially rapidly and in a total of two hours. The penetration level was low in par-ticular in dry chips aftex steaming, only a small fraction of the amount that ~ank into the solution on vacuum pene-tration sank into the solution now. The solution of chem-icals was obviously concentrated in the surface portions of the chips, being diluted with the water ~ondensed from the steam.
~ 3~28 On the other hand, with the same species of wood, any variations in the quantity o~ wood material in the cell walls ~nd, at the same time, variations in density are measured as changes in the quantity of solution penetrated like above with varying water contents of the chips.
On the whole, as compared with variations in the water contents, variations in density are so little that for practical purposes it is mostly enough if the joint effect of the water content and the density of the chips is taken into account.
A characteristic feature of conifer wood is dependence of the density on the differences between spring wood and summer wood. The walls of summer-wood fibers are remark-ably thicker and the diameters of the cell cavity capil-laries are only a fraction of the corresponding dimensionsof spring-wood fibers. It has been noticed that the cap-illary action has a significant part in the penetration.
As the lifting force of the solution in a capillary is in-versely pxoportional to the second power of the radius of the capillary, the capillary filling of the fiber cell system starts strongest and mos~ rapidly in the portion of summer wood, provided that a sufficient amount of solu-tion is available in the fiber cavities. It is apparent that the solution pressure formed removes remaining air, and the summer-wood fibers are filled ~irst. This has its significance in view of the initiation of the diffusion and of equali7ation of the chemicals in the thick-wall fibers in th~ summer wood. Said assumption is supported, e.g., by the penetration-promoting effect of a vacuum maintained during filling of solution, which had been noticed in the tests.
Birch has no corre~ponding di~ferences in the struc-tures o~ the cell systems of summer wood and spring wood.
In the tests, this came out clearly in a better level and speed of penetration of birch as compared with pine chips.
Occasional structural differences in wood, such as knots and inclusions caused by resin, have no major sig-nificance quantitatively. Unpenetrated portions in cell . .
, ~
, 2~
syst~ms are, in a way, taken into account in a way similar to the cell-wall material, i.e. they have the same effect as an increasing density has.
The vacuum penetration device 10 that is shown sche-matically in Fig. 4 consists of a penetration tan~ 11,into which the chips are introduced through the feed open-ing 12, to which either a globe valve 13 used for the feed of chips or a chamber feeder or a high-pressure feeder can be connected. At the lower end of the tank 11, there is an outlet opening 14 for the material, and therein a globe valve 15. Vacuum pressure is produced into the tank 11 by means of a connecting duct 16, which is, by means of a valve 17, connected either directly with a vacuum pump or with an intermediate vacuum tank, which is provided so as to accelerate the removal of air. The tank 11 is further provided with a connecting duct 18, through which the penetration solution can be passed into the tank 11 by means of a valve 19, e.g., from a pressure accumulator.
The equipment in accordance with Fig. 4 is used so that the tank 11 is filled through the feed opening 12, - whereupon the valve 13 is closed and the valve 17 is opened and air is sucked out of the chips present in the t~nk 11. The vacuum pressure is allowed to sink to a value at which the penetration solution to be fed in the next step does not yet start vaporizing. In the fillir.g, the vacuum pressure is settled, depending on the species of wood and on the arrangement of equipment, in 0.5 to 5 minutes, whereupon the valve 17 is closed and the valve 19 is opened, said latter valve letting the penetration solution into the tank as rapidly as possible. It is also possible to keep the valve 17 open and to allow the vacuum pressure to act in a way intensifying the pene-tration during the filling o the solution. In the tests it has been noticed that such a filling is penetrated rapidly and uniformly in a few minutes.
If an increased equipment capacity is desired, it is possible to discharge the filling by means of positive pressure into a pressurizec1 reception tank, wherein the ;
' , . -~3~2~
penetration i~ completed and the diffusion of chemicals can be started by rai~ing the temperature.
~ he equipment 20 shown schematically in Fig. 5 is intended for penetration of, e.g., birch chips and of other hardwood chips of corresponding cell systems which takes place as a continuous flow treatment. The penetra-tion part consists of an arc-shaped transfer duct ~1, which extends in its upper part as a vacuum chamber 22.
The lower ends of the transfer duct, which act as baromet-ric vacuum locks, are arranged in the tank 23 for thecooking li~uor. The level o~ the liquor is kept constant, and, owing to the ~acuum pressure produced in the vacuum chamber 22, the cooking li~uor rises in the ends of the transfer duct 21 placed in the soaking basin 23 to the height h corresponding to the vacuum pres~ure and forms vacuum locks. The chips are fed by means of a screw con-veyor 24, at which the ~urrounding tube 25 is perforated in order that the air surrounding the chips should be able to escape before the chips are transferred onto the end-less conveyor in the transfer duct 21. From the risingpart of the conveyor 21, the chips are discharged onto the screw conreyor 26 in the vacuum chamber 22. By adjusting the transfer speed of the conveyor 26, the chips can be given the desired time of ~tav in the vacuum chamber 22, from which the endless conveyor 21 again transfers the chips down into the cooking-liquor basin 23. At the turn 27 of the conveyo~ 21, it is advantageous to provide sepa-ration of sand etc. corresponding contaminations from th~
chips. At the turning point 28, the portion of the chips that sinks into the solution i5 discharged out sf the transfer duct 21 onto the bottom of the basin 23 ~o as to be shifted further to the process. The portion that does not sink into the solution, consisting mainly of bark- !
covered, knotty, etc. poorly penetrated chips, is removed from the surface of the basin 23. By crushing this chip portion further, usable raw-material can be recovered from it.
As regards its construction and operation, the e~uip-~22~7 ment described above is simpler than the solution of Fig.4 with its numerous valYes. ~oreover, the cost of produc-ing the vacuum is lower in this case, because most of the air carried along with the chips is already separated in the screw feeder 24 and does not enter into the vacuum system. Actually the only drawback of the equipment in accordance with this em~odiment of the invention is the fact that the chips must already be in contact with the cooking liquor before the vacuum treatment, in the screw feeder 24 and in the lower end of the transfer duct 21.
However, it has been noticed that, if dimensioned correct- -ly, the conveyor portions inside the liquid are so short that the time of stay of the chips in the solution remains at the level of 5 to 15 seconds. It does not yet have a great signiicance in the treatment of chips made of easily penetrable wood. The wetting of the chips is re-duced further by the air that surrounds the chip particlPs and that is discharged in the feeder 24 as well as by the vacuum, which starts being effective rapidly increasing from the lower end of the conveyor 21.
In the embodiment of equipment shown in Fig. 6, the ~-drawback of principle mentioned in relation to the device shown in Fig. 5 has been eliminated. The chips are taken alternatingly from two intermediate tanks 41, which can be subjected to vacuum pressure, into a vacuum chamber 42, from which a spiral feeder 43 eeds the chips sub-jected to vacuum pressure into a conveyor 45, which acts a~ the same time as a barometric ~acuum lock b~tween the vacuum chamber and the chip-reception tank 46. The con-struction of the conveyor 45 is such that it pulls thechips rapidly from the vacuum into the pressurized basin space. Sand, which is heavier than the chips, and other contaminations are separated at the point 47. By means of a conveyor spiral 48 oper~ting at an adjustable cpeed, the time of sta~ of the chips is regulated so as to com-plete the penetration. At the point 49, the portion of the chips that does not sink into the solution can be se-parated, e.g., for crushing. The penetrated chips are tran~ferred into the process by means of the conveyvr 50.
In the reception basin 46, the surface level of the solu-tion is kept in~ariable. When a certain dosage of chemi-cals is penetrated into the chips, the solution is fed at the level of the surface formed by the effect of the vacu-um at the barometric lock to the point 51, i.e. the dif-ference in height h ~etween the solution surfaces corres-ponds to the vacuum pressure in the vacuum chamber 43.
In the sluicing 52 of the chips, it is possible to use globe or di~c valves, sluice feeders or plug screws suit-able for the treatment of chips, and for application of vacuum 53, conventional hlocking means can be used.
In Fig. 6, it is possible to imagine that the equip-ment components 41, 52 and 53 are ~ubstituted for, e.g.
in the penetration of birch chips, by a plug screw press, which feeds the chips into the Yacuum chamber 42.
The equipment described above is suitable for continu-ous penetration of chips, in particular when a certain uniform dosage of chemicals is aimed at. If penetration with water is concerned, the varying requirement of water is taken care of by control of the water leYel in the reception tank.
Figures 7 and 8 are schematical illustrations of two operating positions of a vacuum penetration device, whose principle of operation is the same as in the device shown in Fig. 4 but in which the chip treatment space is a revolving rotor.
Fig. 7 illustrates the starting situation, in which any transfer solution that remained in the rotor 60 after the preceding processinq bat~h has been removed through the duct 61 and in which the chips are ~illed through the filling opening 62 while the punched plate placed at the other end of the rotor is in the position S. In Fig. B, in the position S o~ the screen plate Gf the rotor, the chips ar first acted upon by vacuum through the duct 63.
~ The penetration solution ox water is introduced through -~ the duct 64, and after the filling, either immediately or after a certain i~cubation time, the treated chips are :~, . .
~:, - ~ ~ 2 .~
transfe~red, by means oP a solution taken from the recep-tion tank through the duct 65, through the duct 66 into said reception tank. In the reception tank, it is advan-tageous, even though not necessary, to maintain a liquid pressure of a few bars. In stead of the reception tank, the further treatment of the chips can also be carried out by using the barometric vacuum lock of the equipment em-bodiments illustrated in Figs. 5 and 6. If penetration with water is concerned, the duct 64 is not needed.
The arrangement of equipment de~cribed above is suit-able, e.g., for the treatment of chips for production of refiner mechanical fibers with water, to which said water it is advantageou~ly possible, if necessary, to dissolve chemicals which improve the cont.rol of pH, th~ yield of fiber, or the colour.
In said devices provided with a rotor, the penetration space must be made relatively small out of constructional reasons. On the other hand, advantages that are obtained are short and rapid vacuum-treatment or svlution-filling times and thereby good handling capacity. Rapid and in-tensive pressure variations on removal of air and on pen-etration of solution into its place promote opening of the ring pores between the fibers, which improves the leval and the speed of penetration.
If necessary, the process of the invention provides the possibility to adjust the dosage of chemicals in the chips, determined in relation to the dry matter, to the desired level by adjusting the concentration of chemical~
in the solution to be penetratedO In the following, some examples will be given o the measurement apparatu~es and auxiliary devices necessary in that connection, which are suitable for use in connection with all of the above em-bodiments of equipment for vacuum penetration, the purpose of these examples b2ing to illustrate the requirements to - 35 be imposed on said embodiments.
For the measurement of the water content and ~nsity of the chips as well as for the transfer and conversion of the measurement results to the control of the chemical :~ 3 2 ~, ~ 2 1 concentration of the solution to be penetrated, as a rule, the apparatuses used for said purposes are suitable.
The storage circulation time of chips is normally some weeks. Thereat, extreme conditions of water contents are equalized, and the variations in moisture content in the chips coming to use occur as wave-like variations. Since the denslty of the wood material in the fiber walls is, with all of the wood species that are concerned, practi-cally the same, 1.32 to 1.35, with some simplification, it i~ possible to ~tart from the assumption that a flow or batch of chips that represents the same species of wood and the same density and that has been treated at a stand-ardized volume always contains the same weight quantity of dry matter of wood per unit of volume. Thereat~ it can also be considered that the total volume of the cell cavities and pores remains at the same level. It follows from this that the difference in weight between the weight of the chips that is measured in each particular case and the weight of the dry matter of the chips, to be considered invariable, which latter weight also includes the varia-tions in the density of the wood material, can be adopted as the joint quantity of the water contained in the chips and of the density differing from the average, which said joint value, when subtracted from said total volume of the cell cavities, gives the cavity volume free from water and ~rom variations in wood density, i.e. the solution volume - in which the desired chemical dosage must be present as dissolved.
Under the above prerequisites, the concentration of chemicals lk (~) in the solution to be penetrated is de-termined on the basis of the desired chemical dosage b [%
of dry matter) and of the joint effect a (~ of dry matter~
of the water content and density o~ the chips from the formula lk = 100~ ab, wherein the value of the factor n is a factor derived from the density of the wood material concerned. Based on experience, the factor n may be made to include an apparatus-specific correction or a correc-tion derived from a desired security or similar factor~
I ~.32~2~
For example, wlth conier wood at a density 0.~, the value of the factor n is without corrections 176, and wlth birch at a density 0,6 correspondingly 93. In the formula it is essential that the quantity or the filling density of the chips has no effect on the result.
For constant monitoring of the water content and the weight of chips, e.g., a measurement apparatus is suitable wherein the water content is determined by means of neu-tron radiation and the weight by means of qamma radiation.
If constant monitoring of variation3 in the density of the chips is necessary, in the measurement area of the con-veyor belt the chip flow must be of invariable volume or the measurements mu~t be carried out in a measurement space, in which case the filling density of the chip~ can be made invariable more readily. Variations in the densi-ty of the chips are normally o~ an order of a few per cent so that in most cases it is enough to make corrections to the density only after a certain limit has been surpassed or when the wood species or quality is changed remarkably.
In the embodiments of equipment described, rapid and pre-cise treatment of a continuous flow of chips is possible.
A considerably simpler embodiment of equipment, which, yet, operates with sufficient accuracy, is obtainPd when, on the chips, only the variation in the weight of chips present in an invariable volume and invariable filling density ls determined either continuously or by the batch of treatment. In this embodiment, ~nd so also in the em-bodiment of equipment described above, frozen chips do not cause an error of measurement, but difficulties in the treatment of the chips both in the measurement stage and in the penetration stage could be avoided best by mPlting the chips and by partly drying the surface moisture, e.g., by means of a warm flow of air. When the wood species or quality is changed essentially, a corresponding correc-tion is made to the control factor. Said mode of opera-tion is advantageous in particular when high-yield pulps are produced by means of penetration devices of the type illustrated in Figs. 7 a~d 8.
, - .
1 3?~h~J~7 It i5 possible to make use of the measurement results obtained from the changes in the quantity of penetrable solution, which ~aid changes are caused by variations in the water co~tent and density of the chips. Thereat the solution volume of the ~olution penetrable in a flow or batch of chips to be treated is used in the control of the chemical content of the penetration solut~on for the next chip batch as a guide for the ~olution volume in which the desired chemical dosage must be contained. The error pro-duced by the delay in this procedure has no significancein practice, because in the chip stores, which are changed relatively slowly, the greatest local differences in moisture content are equalized, and in the chips taken to production the moisture level can be chararterized as varying in wave form in stead of abrup~ moisture differ-ences. The process can be accomplished by means of simpl~
embodiments of equipment, and therein the control of the regulation of the chemical concentrations in the solution is obtained rom measurement of the factually penetrable cavity volume in the chip ~uality that is being treated at each particular time.
In the embodiments of equipment described above as examples, the chemical concentration of the solution is regulated by means of dosage devices in a separate solu-tion mixer by means o~ a control obtained from changes inthe quantity of penetrable solution, which said changes are caused by the water content, dPnsity, and local blocks in the chips. The chemical content of the solution to be penetrated required in each particular case is obtained, e.g., by mixing concentrated chemical solution and chemi-cal solution obtained from a later stage in the process or waste liquor or waste water in a proportion that yields the desired chemical concentration. The concentration of the concentrated solution is adjusted close to the satura-tion point of the chemical concerned at the treatmenttemperature used in each particular case.
High chemical concentrations ~re needed when a higher water content in the chips reduces the "free" fiber cavity -, , .
- ~22~7 space. In such a case, an improved sclubility of chemi-cals of relatively high penetration temperatures is of advantage. If the "free" cavity space in wet chipc is not sufficient even when concentrated solution~ are used, by means of a uniform and ~aximally high concentration of chemicals in the chip cell system, a favourable starting situation has been created for diffusion.
For the regulation and transfer of quantities of solu-tions, it is advantageously possible to use, e.g., metering pumps.
In the mixer, connecting ducts are required, besides for intake of said solution components, also for passing the solution mixture into the penetration space and for recirculation of the chip transfer solution.
The chip transfer solution is taken from the reception tank preferably out of the cylinder surrounding the ex-tended and perforated discharge pipe for the chips, where-at the concentration of the transf~r solution is the samq ~ or, having ~een used in tXe preceding penetration, almost - 20 the same. It is also advantageous to use the transfer solution for the preparation of the solution to be pene-trated when, with an increasing water content in the chips, the chemical concentration must be increased. When dilution is needed for the solution mixtures, it is pos-sible to use, e.g., washing waters and waste ~olutions in consideration of their contents of heat and chemicals and the advantages provided by recirculation in the process.
In the reception tank, the penetrated chips are surrounded by a warm solution, whose chemical concentration corres-ponds to the average level of the solution concentrationsof the preceding penetration batches, and the diffusion of the chemical ions into the walls of the chip cell sys-tems filled with solution can start immediately. The ob-jective of the impregnation, a desired chemical dosage adequately and uniformly diffused in the wood matsrial, i5 achieved ~n a fraction of the time that is usually re-quired in practical impregnation when the major part of the chemicals must be obtained from a solution placed . . . .
~, . .
: : .
, ~3~2~7,~
outside the chip particle by means of diffusion.
Intensified penetration reduces the formation of knotter pulp. Further, the amount and quality of knotter pulp can be affected, as was described above, ~y treating S the partly unpenetrated chips, which do not sink into the solution, separately. The separation can be carried out advantageously in the chip reception tank. The incom~
pletely penetrated portion of the chips, to be removed from the top portion of the tank, is preferably reduced to splinters and, after a separate prolonged solution treatment, returned to the process or, in a repeated sepa-ration, the knotty or any other poorly defibrizable part of the raw-material is removed.
Separation of mechanical contaminations before the 15 Yacuum treatment of the first stage by washing with water cannot be carried out in the process of the invention.
In the treatment stages themselves, the chips are, how-ever, subjected to mixing and pressure variations taking place in the solution, which detach contaminations that adhere to the chips quite efficiently. If the requirements imposed on the purity of the chips cannot be met in said tr~atment, a normal purification treatment is carried out in connection with the further transfer of the chips.
By means of the process and the embodiments cf equip-ment in accordance with the invention described above, nadequate solution filling that is equalized throughout the - chips can be penetrated into the chips rapidly and und~r control. By means o a control obtained from the joint effect of the moisture and, if necessary, density o the chips, the concentration of chemicals can be regulated, when desired, so that the dosage of chemicals in the chips as calculated per its dry matter re~ains practically at ` the same desired level. Thereby a favourable starting situation has been created for completion of uniform and complete impregnation of the chips, i.e. for slow diffu-sion of chemical ions: maximally high concentration of chemicals and temperature in the solution as well as short - distance to the reaction points. A controlled and very - ~
~22~,7 rapid balanced impreqnation of the chips improves th~ pro-duct quality indirectly and provides economies of raw-material and energy. At the same time, the time taken by the process cycle is shortened essentially. In this way, S for example, the capacity of existing digesting plants can be improved advantageollsly.
The procedure is suitable for use in alkaline and neu-tral digesting processes. It is in particular suitable for the production of high-yield and chemi-mechanical pulps, whereat attempt~ are made to obtain a high yield and a good fiber quality by means of a little dosage of chemicals and short-time heating, possi~ly carried out in a steam phase. ~urther, the use of this process is advantageous in impregnation objects wherein li~tle quan-tities of chemicals must be distributed uniformly in theraw-material. The objective may be, for example, stabi-lization of hemicellulose and the use of catalysts or bleaching chemicals. In mechanical production of fibers, the chips may be penetrated with hot water, to which small amounts of chemicals may have been added. The procedure increases the possibilities of using a wood or chip qual-ity inferior to the customary quality, e.g. dried-up sawmill chips in TMP-, CTMP- and CMP-processes.
Besides for the production of fibers, the pretreatment of raw material in accordance with the invention can, with the arrangement~ described above, be used in impregnation of a porous cellulosic raw-material, e.g., in the produc-tion of boards or when the raw-material is modified chem-ically, e.g. in converting wood to sugar, or in general in utilization of the constituents of wood.
Above, some advantageous example~ have been givPn of the numerou~ modifications that are included in the scope of the invention, said modification~ being restricted by the accompanying patent claims only.
diffusion the ions are transferred into the fiber walls in the solution because of differences in the concentra-tions of chemicals. The diffusion proceeds along liquid connections formed by the water which has penetrated into the fibrous cell system or which wa~ present in said cell system.
Raising of the temperature of the penetration solution promotes the mobility of the ions. However, the chemical concentration of the penetration solution has a declsive significance for the progress of the diffusion into the interior parts of the chips, because the diffu-sion is always retarded when the moisture contained in the chips dilutes the solution and when its chemical content is reduced as chemicals are absorbed into the cell walls.
Thus, the amount and the coverage of the penetration ha~e a highly essential importance for the initiation and progress of the diffusion as well as for the ~ufficiency an~ uniformity of the dosage of chemicals in the fiber walls, which is the ultimate goal.
It has been suggested that the amount of air contained in the cell systems in chips be reduced by means of vacuum produced mechanically or by means of steaming. However, only steaming is employed in the industry.
Steaming impregnation is a simple, but not adequate -or controlled process if a good and uniform penetration of the chips is desired. For example, it has been proved that, as a result of absorption with the cookin~ liquor, the chemical concentrations in diferent parts of a chip particle varied within wide limits and that a considerably long diffusion time with preheating is required before a concentration necessary for the chemical reactions can be obtained in the inner parts.
~ he use of a vacuum in order to ~emove air has been suggested, e.g., in the Finnish Patents 11,~87 and 30,091, and in the Swedi~h Patent 135,529.
The publication SE 135~529 deals with a continuous pro-cess and with equipment for impregnation of th~ chips with liguid. The impr2gnation takes place so that chips are , , :
~ 3 ~
fed continuously into the top portion of a tower, where it enters into a vacuum. The lower end of the to~er, whose top end is closed, is placed in water, so that the chip column sinks in the tower slowly downwards and is S submerged in the water, being impregnated at the same time. Thereat the pressure of the water surrounding the chips becomes gradually higher, until it reaches the atmospheric pressure as the chips are discharged out of the tower. When a chip particle sinks into water, tne 1Q pressure of the air present in the fiber cell system is the same as the pressure of the surrounding water, whereby no penetration dependent on pressure gradient takes place.
However, the effect of factors that retard penetration, which evolve rapidly, starts immediately.
In the process of the publication FI 30,091 the start-ing material is first predried to about 18 %, and air is removed from it almost completely at an absolute pressure lower than 100 mmHg (about 0.13 bar) and at a temperature of 85 to 90C. If a higher temperature is used, according to the patent, the vacuum-treatment pressure can be in-creased up to an absolute pressure of 200 mmHg (a~out 0.26 bar).
As compared with the very high variations in the con-~; ten~s of air and water in the chips, the changes in the density of the wood material are, as a rule, confined to the range of ~ 5...10 %, because attempts are made to use the same species of wood and to avo.id the parts that are most difficult to impregnate, such as the resinous heart-wood of conifer trees.
The moisture content of the chips varies within very wide limits. The chips arriving in the fiber production can normally contain water at a level of 30 to 120 % of the dry matter of the chips. In mechanical production processes, the defibration is successful best when the 3~ chips are filled with water. In chemic~l processçs, the desired dosage of chemicals must be provided throughout the chips as uniformly diffused. Thereat, the quantity and the chemicals content of the solution to be penetrated ~3~32~
into the fiber cell system free from watere have an essential effect on the diffusion.
In the cited processes, the impregnation takes place almost exclusively by means of diffusion. Penetration cannot be utilized therein almost at all, being usable at the maximum partially and occasionally.
The invention proposes a process for the pretreatment of cellulosic chip-formed raw-material, which comprises:
a) removing air out of the raw-material by means of vacuum treatment, wherein said vacuum treatment is carried out without preceding substantial moistening of the raw-material, b) bringing the raw-material into contact with a penetration solution, the temperature of which is lower than the boiling point of the solution at said vacuum, where the solution is allowed to penetrate into the raw-material for about 5 minutes at said vacuum, and c) exposing the raw material and the penetration solution to a pressure of atmospheric or above for a time sufficient to allow the solution to penetrate into the chips.
Here, "moistening" means steamin~, washing, or any other, conventional aqueous treatment.
The penetration is carried out rapidly after the vacuum treatment at the atmospheric or a higher solution pressure so that the ~iber cavities in -the raw-material do not have time to be closed substantially before the penetration. The more rapidly the penetration is carried out, the better. Depending on the conditions and on the species of wood, the vacuum-treated raw-material is subjected to solution pressure, e.g., within about 5 min., best e.g., in 1 min., most appropriately in 0,5 min~ from P~ ' c~ ~.322~27 - 4a -the vacuum treatment.
The passing of the penetration solution into contact with the raw-material is started preferably while the vacuum is still effective. Optimal1y, the vacuum is maintained during the whole of the passing of solution.
After the desired quantity of solution has been brought into contact with the raw-ma~erial, a pressure impact may be applied to the solution additionally.
The vacuum that is used is, e.g., 0.1 to 0.5 bar, optimally 0.2 to 0.4 ba~. Thereat, the temperature of the penetration solution is e.g., 35 to 85C, optimally 45 to 75C.
The concentration of chemicals in the penetration solution is advantageously~regulDted in accordance with the i 1,~
~ - ~
~322~7 raw-material or in accordance with the quantity of the solution to be penetrated.
According to an embodiment, the penetration solution is passed to among the raw-material in the same vessel in which the vacuum treatment was carried out, whereinafter the raw-material is transferred into a reception tank of a higher pressure, where the penetration is completed.
After the penetration, it is advantayeous to separate the proportion of the raw-material that did not ~ink into the solution from the rest o~ the raw-material.
The equipment in accordance with the invention is pro-vided with a common v ssel for vacuum treatment and for penetration, or separate vessels are p~ovided for them.
A common processing vessel may be, for example, a rotor that revolves in a housing and that it open at least at one end. The necessary connecting ducts are fitted on the circumference of the rotor housing.
When separate vessels are used for vacuum treatment and for penetration, between them it is possible to employ a transf~r duct whose final end forms a barometric lock between the vessels. In such a case, the transfer duct is preferably extended by a perforated penetration duct.
The final end of the transfer duct is appropriately pro-vided with equipment for the removal of contaminations.
On the other hand, at the final end of the perforation duct, it i~ appropriately possible to place an equip~ent for the removal o~ unpenetrated raw-material. Penetrati~n liquid can be fed into the transfer duct, in particular into its initial end.
The raw-material can also ~e passed into the vacuum-treatment tank through a feed-transfer duct passing through the penetration tank so that the initial e~d of the feed-transfer duct forms a barometric lock between the penetration tank and the vacuum-treatment tank. In such a case, the raw-material must, of course, pass through this lock so that it is substantially not moistened.
The chips are pretreated in accordance with the inven-tion without a moistening substantial from the practical .
- :~3~2~27 point of view. The walls of the cut-off fibers at the cut-off ends of the chips, in particular those o~ their parts that contain hemicellulose, viz., absorb water very rapidly and, when they becGme ~oll~n, contract or block the open cell cavities. Out of said reason, in connection with penetration, vacuum-treated chips should preferably also be surrounded with solution as rapidly as possible.
If the chips, however, end up in contaet with water before the pretreatment in accordance with the inventlon, this contact time should, depending on the circumstances, be at the maximum about 1 min., preferably, however, at the maximum about 20 to 30 or 5 to 15 seconds.
According to the process of the present invention, the best penetration is not achieved by means of maximum vacuum, but by making use of the temperaturë of the pene-tration liquid, which said temperat~re is, depending on the wood species, 35 to 85C. The magnitude of the vacuum pressure is determined so that vaporization of the liquid is still avoided. The necessary vacuum can be produced by means of normal equipment commonly used in the industry at a reasonable cost.
For example, with softwood, the vacuum is advantage-ously 0.2 to 0.3 bar, and the temperature of the water solution 55 to 70C.
When the water content of the chips is changed, the amount o the solution that is penetrated is changed in the same proportion, but the total guantity of pene-trated solution and water contained in the chips remain at the same level, i.e. said penetration procedure per~its equal filling of the cell system independently from th~
moisture content of the chips. The amount and uniformity of penetration are well reproducible in the process.
When the density of wood varies, the altered solids amount i~ measured in the form of a corresponding altera-tion in the penetration solution.
The nature and the p~ of the solution of chemicalshave no significant ~ffect on the penetration.
The concentration of the solution of chemicals has a .
, 7 minor e~rfect, which is insignificant under the conditions concerned.
If necessary, high concentrations of chemicals are also possible, because it is possible to use temperatures in which the ~olubilities of the chemicals are good.
In the following, the process in accordance with the invention and the d~vices for its application will be de-scribed in more detail with reference to the accompanyinq figures, wherein - Figure 1 lllustrates the effect of a treatment with a solution of chemicals or with water that precedes the vacuum treatment on the amount of chips that sink into the solution, - Figure 2 illustrates the dependence of the penetra-tion on the temperature of the solution or water, - Figure 3 illustrates the effects of the moisture and the density of the chips on the amount of ~olu-tion penetrated and on the penetration level, - Figure 4 illu~trates a vacuum penetration solution in accordance with an advantageous embodiment of the invention, - Figure 5 illustrates a vacuum penetration solution in accordance with another advantageous embodiment, ~ Figure 6 illustrates a fuxther vacuum penetration solution in accordance with an ad~antageous embodi-ment, and - Figures 7 and ~ illustrate the steps of operation of a continuous vacuum penetration device~
In the experiments that were carried out, factory-made chips were used.
For determination of the uniform.ity of penetration and the level of penetration, it was noticed that determina-tion of the proportion of the chips that sink into the solution or water was a sufficiently accurate procedure.
From Fig. 1 it is seen how high the negative effect is with a cooking-liquor treatment that precede~ the vacu-um treatment on the penetrability of cooking liquor.
The vertica1 axis represents the proportion of the chips ~ 3 2 ~ 8 ~J ~
that sink into the liquor as a percentage of the whole quantity of chips treated, and the horizontal axiQ repre-sents the duration of effect of the liquor as minutes.
In tAe test, pine chips were used whose moisture content was 21 %. The temperature of the treatment solution w~s 65C and the concentration 5 %.
The broken line 1 illustrates the proportion of the sinking chips during vacuum penetration when the chips are txeated with NSSC-solution. The broken line ~ illustrates the proportion of the sinking chips when the chips are treated with NaHSO3-solution. It is noticed that a treat-ment for one minute with NSSC-solution already reduces the amount of the sinking proportion by 24 %, and a treatment for three minutes by about 45 %. The corresponding rPduc-tions in ~he case of treatment with NaHSO3-solution were about 30 % and about 70 ~. In the test a procedure was used wherein the penetration was performed with a cooking liquor subjected to the atmospheric pressure and wherein the filling of the solution was started while the vacuum pressure that had prevailed was still effective.
An explanation of the phenomenon of Fig. 1 is that an aqueous solution has a remarkably rapid effect on the walls and surface properties of capillary cell cavities, whereby, at the cut faces of the chip~, the cell systems and in particular the capillaries in summer wood are con tracted relatively speakinq most rapidly. In this way, the amount of solution that is penetrated, i.e. the pro-portion of the chips that are sunk into the solution, is lowered rapidly as the soaking time i5 increased.
Fig. 2 illustrates the effect of the temperature of the solution on the penetration with different treatment times. The left v~rtical axis represents the amount of the chips that sink into the solution as a percentage of the entire quanity of chip~ treated, the horizontal axis represents the temperature of the solution as C, and the right vertical axis represents the duration of treatment as minutes. In the test the raw-material consisted of pine chips of a moisture content of 20 %, which said chips ~32~
were treated ~ith a 5-~ NaHS03-~olution. It is seen that when the temperature of the solution rises from 20 to 50C, the amount of the chips that sink into the solution (broken line 3) also increases significantly. Likewise, it is seen that a further raisi~g of the temperature does not have a major effect on the result. At the same time with the raising of the temperature of the solution, the treatment time (straight line 4) was shortened in the tests, in spite of which the proportion of sinking chips remained invariable and PYen became somewhat higher. It comes out fxom the results unambiguously that the lower limit of the economical operating temperature of th~ solu-tion is somewhere around 35 to 40C, whereas, according to the experiments, it is not so useful to heat the mate-rial to very hi~h temperatures, because the penetrationis not improved essentially. By means of heating, it is, however, possible to intensi~y the penetration decisively.
From Fig. 3 it is seen how the water content of the chips affects the amount of solution that is penetrated.
The horizontal axis represents the water content of the chips, and the vertical axis represents the amount of penetrated solution and the amount of chips ~hat sink into the solution, all as a percentage of the dry matter of the chips. In th~ series o tests, the concentration of the solution of chemicals was S % and the tPmperature 65C.
Th~ broken lines 1 to 3 illustrate the penetrations of pine chips 1. with sulphate solution, ~. with NSSC-solu-tion, and 3. with NaHS03-solution, as well as the broken line 4 illustrates birch chips treated with NSSC-solution.
From the broken lines 1 to 3, it comes out that solutions essentially different from each other are penetrated approximately in the same way irrespective o the moisture content of the chips.
With the same chip species, the penetration of a solu-tion of chemicals i5 determined in an almost linear way by the amount of water contained in the chips. This comes out best from an examination, at the various test points, of the joint efects of the chan~es in the water contained .
~ 3 ~
~ o as moisture in the chips and in the amount of water con-tained in the solution that penetrated into the chips.
In the pine chips, the total water quantity was within the range of 164 to 177 %, and in the birch chips within the range of 143 to 145 ~, respectively. The scatterlng from the average value was with pine chips + 4 % and with birch chips ~
The proportion of sinking chips, which was determined by means of a follow-up of the penetration level, was with pine chips 8~ to 89 % and wlth birch chips 100 %, irres-pective of the moisture of the chips (broken lines 5 ~ 6).
The clear difference in penetration level between the pine and birch chips, seen in Fig. 3, is mainly attribu-table to different densities of the chips, the density of pine being on the average 0.4 and that of birch O.S. Here density is understood as meaning the nominal density of the wood species as fully dry.
Since in the case of the different species of wood that are ordinarily used for fiber production, the density of the wood material proper is the same, 1.32 to 1.35, the higher density of birch, which is on the average one quarter higher than the density of pine, means a corres-pondingly smaller space of fiber cavities, which is also manifested in a corresponding change in the penetrated quantities of NSSC-solution shown in Fig. 3.
In a comparat~ve tPst carried out with the pine chips and the NSSC-solution quality us~d in Fig. 3, impregnation by means of steaming was studied. After a steaming time of five minutes, about four fifths of the quantity of so-lution that penetrated under vacuum in ~ive minutes wereabsorbed best into dry chips, initially rapidly and in a total of two hours. The penetration level was low in par-ticular in dry chips aftex steaming, only a small fraction of the amount that ~ank into the solution on vacuum pene-tration sank into the solution now. The solution of chem-icals was obviously concentrated in the surface portions of the chips, being diluted with the water ~ondensed from the steam.
~ 3~28 On the other hand, with the same species of wood, any variations in the quantity o~ wood material in the cell walls ~nd, at the same time, variations in density are measured as changes in the quantity of solution penetrated like above with varying water contents of the chips.
On the whole, as compared with variations in the water contents, variations in density are so little that for practical purposes it is mostly enough if the joint effect of the water content and the density of the chips is taken into account.
A characteristic feature of conifer wood is dependence of the density on the differences between spring wood and summer wood. The walls of summer-wood fibers are remark-ably thicker and the diameters of the cell cavity capil-laries are only a fraction of the corresponding dimensionsof spring-wood fibers. It has been noticed that the cap-illary action has a significant part in the penetration.
As the lifting force of the solution in a capillary is in-versely pxoportional to the second power of the radius of the capillary, the capillary filling of the fiber cell system starts strongest and mos~ rapidly in the portion of summer wood, provided that a sufficient amount of solu-tion is available in the fiber cavities. It is apparent that the solution pressure formed removes remaining air, and the summer-wood fibers are filled ~irst. This has its significance in view of the initiation of the diffusion and of equali7ation of the chemicals in the thick-wall fibers in th~ summer wood. Said assumption is supported, e.g., by the penetration-promoting effect of a vacuum maintained during filling of solution, which had been noticed in the tests.
Birch has no corre~ponding di~ferences in the struc-tures o~ the cell systems of summer wood and spring wood.
In the tests, this came out clearly in a better level and speed of penetration of birch as compared with pine chips.
Occasional structural differences in wood, such as knots and inclusions caused by resin, have no major sig-nificance quantitatively. Unpenetrated portions in cell . .
, ~
, 2~
syst~ms are, in a way, taken into account in a way similar to the cell-wall material, i.e. they have the same effect as an increasing density has.
The vacuum penetration device 10 that is shown sche-matically in Fig. 4 consists of a penetration tan~ 11,into which the chips are introduced through the feed open-ing 12, to which either a globe valve 13 used for the feed of chips or a chamber feeder or a high-pressure feeder can be connected. At the lower end of the tank 11, there is an outlet opening 14 for the material, and therein a globe valve 15. Vacuum pressure is produced into the tank 11 by means of a connecting duct 16, which is, by means of a valve 17, connected either directly with a vacuum pump or with an intermediate vacuum tank, which is provided so as to accelerate the removal of air. The tank 11 is further provided with a connecting duct 18, through which the penetration solution can be passed into the tank 11 by means of a valve 19, e.g., from a pressure accumulator.
The equipment in accordance with Fig. 4 is used so that the tank 11 is filled through the feed opening 12, - whereupon the valve 13 is closed and the valve 17 is opened and air is sucked out of the chips present in the t~nk 11. The vacuum pressure is allowed to sink to a value at which the penetration solution to be fed in the next step does not yet start vaporizing. In the fillir.g, the vacuum pressure is settled, depending on the species of wood and on the arrangement of equipment, in 0.5 to 5 minutes, whereupon the valve 17 is closed and the valve 19 is opened, said latter valve letting the penetration solution into the tank as rapidly as possible. It is also possible to keep the valve 17 open and to allow the vacuum pressure to act in a way intensifying the pene-tration during the filling o the solution. In the tests it has been noticed that such a filling is penetrated rapidly and uniformly in a few minutes.
If an increased equipment capacity is desired, it is possible to discharge the filling by means of positive pressure into a pressurizec1 reception tank, wherein the ;
' , . -~3~2~
penetration i~ completed and the diffusion of chemicals can be started by rai~ing the temperature.
~ he equipment 20 shown schematically in Fig. 5 is intended for penetration of, e.g., birch chips and of other hardwood chips of corresponding cell systems which takes place as a continuous flow treatment. The penetra-tion part consists of an arc-shaped transfer duct ~1, which extends in its upper part as a vacuum chamber 22.
The lower ends of the transfer duct, which act as baromet-ric vacuum locks, are arranged in the tank 23 for thecooking li~uor. The level o~ the liquor is kept constant, and, owing to the ~acuum pressure produced in the vacuum chamber 22, the cooking li~uor rises in the ends of the transfer duct 21 placed in the soaking basin 23 to the height h corresponding to the vacuum pres~ure and forms vacuum locks. The chips are fed by means of a screw con-veyor 24, at which the ~urrounding tube 25 is perforated in order that the air surrounding the chips should be able to escape before the chips are transferred onto the end-less conveyor in the transfer duct 21. From the risingpart of the conveyor 21, the chips are discharged onto the screw conreyor 26 in the vacuum chamber 22. By adjusting the transfer speed of the conveyor 26, the chips can be given the desired time of ~tav in the vacuum chamber 22, from which the endless conveyor 21 again transfers the chips down into the cooking-liquor basin 23. At the turn 27 of the conveyo~ 21, it is advantageous to provide sepa-ration of sand etc. corresponding contaminations from th~
chips. At the turning point 28, the portion of the chips that sinks into the solution i5 discharged out sf the transfer duct 21 onto the bottom of the basin 23 ~o as to be shifted further to the process. The portion that does not sink into the solution, consisting mainly of bark- !
covered, knotty, etc. poorly penetrated chips, is removed from the surface of the basin 23. By crushing this chip portion further, usable raw-material can be recovered from it.
As regards its construction and operation, the e~uip-~22~7 ment described above is simpler than the solution of Fig.4 with its numerous valYes. ~oreover, the cost of produc-ing the vacuum is lower in this case, because most of the air carried along with the chips is already separated in the screw feeder 24 and does not enter into the vacuum system. Actually the only drawback of the equipment in accordance with this em~odiment of the invention is the fact that the chips must already be in contact with the cooking liquor before the vacuum treatment, in the screw feeder 24 and in the lower end of the transfer duct 21.
However, it has been noticed that, if dimensioned correct- -ly, the conveyor portions inside the liquid are so short that the time of stay of the chips in the solution remains at the level of 5 to 15 seconds. It does not yet have a great signiicance in the treatment of chips made of easily penetrable wood. The wetting of the chips is re-duced further by the air that surrounds the chip particlPs and that is discharged in the feeder 24 as well as by the vacuum, which starts being effective rapidly increasing from the lower end of the conveyor 21.
In the embodiment of equipment shown in Fig. 6, the ~-drawback of principle mentioned in relation to the device shown in Fig. 5 has been eliminated. The chips are taken alternatingly from two intermediate tanks 41, which can be subjected to vacuum pressure, into a vacuum chamber 42, from which a spiral feeder 43 eeds the chips sub-jected to vacuum pressure into a conveyor 45, which acts a~ the same time as a barometric ~acuum lock b~tween the vacuum chamber and the chip-reception tank 46. The con-struction of the conveyor 45 is such that it pulls thechips rapidly from the vacuum into the pressurized basin space. Sand, which is heavier than the chips, and other contaminations are separated at the point 47. By means of a conveyor spiral 48 oper~ting at an adjustable cpeed, the time of sta~ of the chips is regulated so as to com-plete the penetration. At the point 49, the portion of the chips that does not sink into the solution can be se-parated, e.g., for crushing. The penetrated chips are tran~ferred into the process by means of the conveyvr 50.
In the reception basin 46, the surface level of the solu-tion is kept in~ariable. When a certain dosage of chemi-cals is penetrated into the chips, the solution is fed at the level of the surface formed by the effect of the vacu-um at the barometric lock to the point 51, i.e. the dif-ference in height h ~etween the solution surfaces corres-ponds to the vacuum pressure in the vacuum chamber 43.
In the sluicing 52 of the chips, it is possible to use globe or di~c valves, sluice feeders or plug screws suit-able for the treatment of chips, and for application of vacuum 53, conventional hlocking means can be used.
In Fig. 6, it is possible to imagine that the equip-ment components 41, 52 and 53 are ~ubstituted for, e.g.
in the penetration of birch chips, by a plug screw press, which feeds the chips into the Yacuum chamber 42.
The equipment described above is suitable for continu-ous penetration of chips, in particular when a certain uniform dosage of chemicals is aimed at. If penetration with water is concerned, the varying requirement of water is taken care of by control of the water leYel in the reception tank.
Figures 7 and 8 are schematical illustrations of two operating positions of a vacuum penetration device, whose principle of operation is the same as in the device shown in Fig. 4 but in which the chip treatment space is a revolving rotor.
Fig. 7 illustrates the starting situation, in which any transfer solution that remained in the rotor 60 after the preceding processinq bat~h has been removed through the duct 61 and in which the chips are ~illed through the filling opening 62 while the punched plate placed at the other end of the rotor is in the position S. In Fig. B, in the position S o~ the screen plate Gf the rotor, the chips ar first acted upon by vacuum through the duct 63.
~ The penetration solution ox water is introduced through -~ the duct 64, and after the filling, either immediately or after a certain i~cubation time, the treated chips are :~, . .
~:, - ~ ~ 2 .~
transfe~red, by means oP a solution taken from the recep-tion tank through the duct 65, through the duct 66 into said reception tank. In the reception tank, it is advan-tageous, even though not necessary, to maintain a liquid pressure of a few bars. In stead of the reception tank, the further treatment of the chips can also be carried out by using the barometric vacuum lock of the equipment em-bodiments illustrated in Figs. 5 and 6. If penetration with water is concerned, the duct 64 is not needed.
The arrangement of equipment de~cribed above is suit-able, e.g., for the treatment of chips for production of refiner mechanical fibers with water, to which said water it is advantageou~ly possible, if necessary, to dissolve chemicals which improve the cont.rol of pH, th~ yield of fiber, or the colour.
In said devices provided with a rotor, the penetration space must be made relatively small out of constructional reasons. On the other hand, advantages that are obtained are short and rapid vacuum-treatment or svlution-filling times and thereby good handling capacity. Rapid and in-tensive pressure variations on removal of air and on pen-etration of solution into its place promote opening of the ring pores between the fibers, which improves the leval and the speed of penetration.
If necessary, the process of the invention provides the possibility to adjust the dosage of chemicals in the chips, determined in relation to the dry matter, to the desired level by adjusting the concentration of chemical~
in the solution to be penetratedO In the following, some examples will be given o the measurement apparatu~es and auxiliary devices necessary in that connection, which are suitable for use in connection with all of the above em-bodiments of equipment for vacuum penetration, the purpose of these examples b2ing to illustrate the requirements to - 35 be imposed on said embodiments.
For the measurement of the water content and ~nsity of the chips as well as for the transfer and conversion of the measurement results to the control of the chemical :~ 3 2 ~, ~ 2 1 concentration of the solution to be penetrated, as a rule, the apparatuses used for said purposes are suitable.
The storage circulation time of chips is normally some weeks. Thereat, extreme conditions of water contents are equalized, and the variations in moisture content in the chips coming to use occur as wave-like variations. Since the denslty of the wood material in the fiber walls is, with all of the wood species that are concerned, practi-cally the same, 1.32 to 1.35, with some simplification, it i~ possible to ~tart from the assumption that a flow or batch of chips that represents the same species of wood and the same density and that has been treated at a stand-ardized volume always contains the same weight quantity of dry matter of wood per unit of volume. Thereat~ it can also be considered that the total volume of the cell cavities and pores remains at the same level. It follows from this that the difference in weight between the weight of the chips that is measured in each particular case and the weight of the dry matter of the chips, to be considered invariable, which latter weight also includes the varia-tions in the density of the wood material, can be adopted as the joint quantity of the water contained in the chips and of the density differing from the average, which said joint value, when subtracted from said total volume of the cell cavities, gives the cavity volume free from water and ~rom variations in wood density, i.e. the solution volume - in which the desired chemical dosage must be present as dissolved.
Under the above prerequisites, the concentration of chemicals lk (~) in the solution to be penetrated is de-termined on the basis of the desired chemical dosage b [%
of dry matter) and of the joint effect a (~ of dry matter~
of the water content and density o~ the chips from the formula lk = 100~ ab, wherein the value of the factor n is a factor derived from the density of the wood material concerned. Based on experience, the factor n may be made to include an apparatus-specific correction or a correc-tion derived from a desired security or similar factor~
I ~.32~2~
For example, wlth conier wood at a density 0.~, the value of the factor n is without corrections 176, and wlth birch at a density 0,6 correspondingly 93. In the formula it is essential that the quantity or the filling density of the chips has no effect on the result.
For constant monitoring of the water content and the weight of chips, e.g., a measurement apparatus is suitable wherein the water content is determined by means of neu-tron radiation and the weight by means of qamma radiation.
If constant monitoring of variation3 in the density of the chips is necessary, in the measurement area of the con-veyor belt the chip flow must be of invariable volume or the measurements mu~t be carried out in a measurement space, in which case the filling density of the chip~ can be made invariable more readily. Variations in the densi-ty of the chips are normally o~ an order of a few per cent so that in most cases it is enough to make corrections to the density only after a certain limit has been surpassed or when the wood species or quality is changed remarkably.
In the embodiments of equipment described, rapid and pre-cise treatment of a continuous flow of chips is possible.
A considerably simpler embodiment of equipment, which, yet, operates with sufficient accuracy, is obtainPd when, on the chips, only the variation in the weight of chips present in an invariable volume and invariable filling density ls determined either continuously or by the batch of treatment. In this embodiment, ~nd so also in the em-bodiment of equipment described above, frozen chips do not cause an error of measurement, but difficulties in the treatment of the chips both in the measurement stage and in the penetration stage could be avoided best by mPlting the chips and by partly drying the surface moisture, e.g., by means of a warm flow of air. When the wood species or quality is changed essentially, a corresponding correc-tion is made to the control factor. Said mode of opera-tion is advantageous in particular when high-yield pulps are produced by means of penetration devices of the type illustrated in Figs. 7 a~d 8.
, - .
1 3?~h~J~7 It i5 possible to make use of the measurement results obtained from the changes in the quantity of penetrable solution, which ~aid changes are caused by variations in the water co~tent and density of the chips. Thereat the solution volume of the ~olution penetrable in a flow or batch of chips to be treated is used in the control of the chemical content of the penetration solut~on for the next chip batch as a guide for the ~olution volume in which the desired chemical dosage must be contained. The error pro-duced by the delay in this procedure has no significancein practice, because in the chip stores, which are changed relatively slowly, the greatest local differences in moisture content are equalized, and in the chips taken to production the moisture level can be chararterized as varying in wave form in stead of abrup~ moisture differ-ences. The process can be accomplished by means of simpl~
embodiments of equipment, and therein the control of the regulation of the chemical concentrations in the solution is obtained rom measurement of the factually penetrable cavity volume in the chip ~uality that is being treated at each particular time.
In the embodiments of equipment described above as examples, the chemical concentration of the solution is regulated by means of dosage devices in a separate solu-tion mixer by means o~ a control obtained from changes inthe quantity of penetrable solution, which said changes are caused by the water content, dPnsity, and local blocks in the chips. The chemical content of the solution to be penetrated required in each particular case is obtained, e.g., by mixing concentrated chemical solution and chemi-cal solution obtained from a later stage in the process or waste liquor or waste water in a proportion that yields the desired chemical concentration. The concentration of the concentrated solution is adjusted close to the satura-tion point of the chemical concerned at the treatmenttemperature used in each particular case.
High chemical concentrations ~re needed when a higher water content in the chips reduces the "free" fiber cavity -, , .
- ~22~7 space. In such a case, an improved sclubility of chemi-cals of relatively high penetration temperatures is of advantage. If the "free" cavity space in wet chipc is not sufficient even when concentrated solution~ are used, by means of a uniform and ~aximally high concentration of chemicals in the chip cell system, a favourable starting situation has been created for diffusion.
For the regulation and transfer of quantities of solu-tions, it is advantageously possible to use, e.g., metering pumps.
In the mixer, connecting ducts are required, besides for intake of said solution components, also for passing the solution mixture into the penetration space and for recirculation of the chip transfer solution.
The chip transfer solution is taken from the reception tank preferably out of the cylinder surrounding the ex-tended and perforated discharge pipe for the chips, where-at the concentration of the transf~r solution is the samq ~ or, having ~een used in tXe preceding penetration, almost - 20 the same. It is also advantageous to use the transfer solution for the preparation of the solution to be pene-trated when, with an increasing water content in the chips, the chemical concentration must be increased. When dilution is needed for the solution mixtures, it is pos-sible to use, e.g., washing waters and waste ~olutions in consideration of their contents of heat and chemicals and the advantages provided by recirculation in the process.
In the reception tank, the penetrated chips are surrounded by a warm solution, whose chemical concentration corres-ponds to the average level of the solution concentrationsof the preceding penetration batches, and the diffusion of the chemical ions into the walls of the chip cell sys-tems filled with solution can start immediately. The ob-jective of the impregnation, a desired chemical dosage adequately and uniformly diffused in the wood matsrial, i5 achieved ~n a fraction of the time that is usually re-quired in practical impregnation when the major part of the chemicals must be obtained from a solution placed . . . .
~, . .
: : .
, ~3~2~7,~
outside the chip particle by means of diffusion.
Intensified penetration reduces the formation of knotter pulp. Further, the amount and quality of knotter pulp can be affected, as was described above, ~y treating S the partly unpenetrated chips, which do not sink into the solution, separately. The separation can be carried out advantageously in the chip reception tank. The incom~
pletely penetrated portion of the chips, to be removed from the top portion of the tank, is preferably reduced to splinters and, after a separate prolonged solution treatment, returned to the process or, in a repeated sepa-ration, the knotty or any other poorly defibrizable part of the raw-material is removed.
Separation of mechanical contaminations before the 15 Yacuum treatment of the first stage by washing with water cannot be carried out in the process of the invention.
In the treatment stages themselves, the chips are, how-ever, subjected to mixing and pressure variations taking place in the solution, which detach contaminations that adhere to the chips quite efficiently. If the requirements imposed on the purity of the chips cannot be met in said tr~atment, a normal purification treatment is carried out in connection with the further transfer of the chips.
By means of the process and the embodiments cf equip-ment in accordance with the invention described above, nadequate solution filling that is equalized throughout the - chips can be penetrated into the chips rapidly and und~r control. By means o a control obtained from the joint effect of the moisture and, if necessary, density o the chips, the concentration of chemicals can be regulated, when desired, so that the dosage of chemicals in the chips as calculated per its dry matter re~ains practically at ` the same desired level. Thereby a favourable starting situation has been created for completion of uniform and complete impregnation of the chips, i.e. for slow diffu-sion of chemical ions: maximally high concentration of chemicals and temperature in the solution as well as short - distance to the reaction points. A controlled and very - ~
~22~,7 rapid balanced impreqnation of the chips improves th~ pro-duct quality indirectly and provides economies of raw-material and energy. At the same time, the time taken by the process cycle is shortened essentially. In this way, S for example, the capacity of existing digesting plants can be improved advantageollsly.
The procedure is suitable for use in alkaline and neu-tral digesting processes. It is in particular suitable for the production of high-yield and chemi-mechanical pulps, whereat attempt~ are made to obtain a high yield and a good fiber quality by means of a little dosage of chemicals and short-time heating, possi~ly carried out in a steam phase. ~urther, the use of this process is advantageous in impregnation objects wherein li~tle quan-tities of chemicals must be distributed uniformly in theraw-material. The objective may be, for example, stabi-lization of hemicellulose and the use of catalysts or bleaching chemicals. In mechanical production of fibers, the chips may be penetrated with hot water, to which small amounts of chemicals may have been added. The procedure increases the possibilities of using a wood or chip qual-ity inferior to the customary quality, e.g. dried-up sawmill chips in TMP-, CTMP- and CMP-processes.
Besides for the production of fibers, the pretreatment of raw material in accordance with the invention can, with the arrangement~ described above, be used in impregnation of a porous cellulosic raw-material, e.g., in the produc-tion of boards or when the raw-material is modified chem-ically, e.g. in converting wood to sugar, or in general in utilization of the constituents of wood.
Above, some advantageous example~ have been givPn of the numerou~ modifications that are included in the scope of the invention, said modification~ being restricted by the accompanying patent claims only.
Claims (16)
1. A process for pretreatment of cellulosic chip-formed raw-material in two stages, which comprises:
a) removing air out of the raw-material by means of vacuum treatment, wherein said vacuum treatment is carried out without preceding substantial moistening of the raw-material, b) bringing the raw-material into contact with a penetration solution, the temperature of which is lower than the boiling point of the solution at said vacuum, where the solution is allowed to penetrate into the raw-material for about 5 minutes at said vacuum, and c) exposing the raw material and the penetration solution to a pressure of atmospheric or above for a time sufficient to allow the solution to penetrate into the chips.
a) removing air out of the raw-material by means of vacuum treatment, wherein said vacuum treatment is carried out without preceding substantial moistening of the raw-material, b) bringing the raw-material into contact with a penetration solution, the temperature of which is lower than the boiling point of the solution at said vacuum, where the solution is allowed to penetrate into the raw-material for about 5 minutes at said vacuum, and c) exposing the raw material and the penetration solution to a pressure of atmospheric or above for a time sufficient to allow the solution to penetrate into the chips.
2. A process as claimed in claim 1, wherein the penetration solution starts being passed to the raw-material while the vacuum is still effective and, upon completion of the penetration, optimally a pressure impact is applied to the solution.
3. A process as claimed in claim 1 or 2, wherein the vacuum used is from about 0.1 to 0.5 bar, and the penetration solution has a temperature of from about 35 to 85°C.
4. A process as claimed in claim 1 or 2, wherein the vacuum used is from about 0.2 to 0.4 bar.
5. A process as claimed in claim 1 or 2, wherein the penetration solution has a temperature of from about 45 to 75°C.
6. A process as claimed in claim 1 or 2, wherein the penetration solution consist of a solution of chemicals, and the concentration of chemicals in the solution is adjusted in accordance with the moisture, with the moisture and density, or with the quantity of penetration solution, in accordance with the formula , where lk is concentration of chemicals, a is joint effect of moisture and density, b is dosage of chemicals, and n is a factor consisting of correction factors.
7. A process as claimed in claim 1 or 2, wherein the exposure of cellulose chip raw material in step (a) is carried out in a vacuum vessel and the penetration solution is thereafter added to the vacuum vessel, and wherein after addition of the penetration solution, the raw material and solution are transferred into a reception tank for completion of penetration under a pressure of at least atmospheric.
8. A process as claimed in claim 1 or 2, wherein the penetration solution comprises a saturated or almost saturated solution of chemicals as well as of a solution of chemicals obtained from the further processing of the raw-material other than washing water, or a combination thereof.
9. A process as claimed in claim 1 or 2, wherein the step b) is carried out within about 1 minute from the time of exposure to said vacuum.
10. A process as claimed in claim 1 or 2, wherein the step b) is carried out within about 0.5 minute from the time of exposure to said vacuum.
11. A process as claimed in claim 1 or 2, wherein the penetration solution used in said process prepares the cellulose pulp for an alkaline or neutral digesting process.
12. A process as claimed in claim 1 or 2, wherein the penetration solution used in said process prepares the cellulose pulp for the mechanical production of fibers.
13. A process as claimed in claim 1 or 2, wherein the vacuum in step (a) is from about 0.2 to about 0.4 bar, and wherein the penetration solution has a temperature of from about 35° to about 85°C.
14. A process as claimed in claim 3, wherein the penetrating liquid is a chemical solution and wherein the concentration of chemicals in the solution is adjusted in accordance with the moisture or with the moisture and density or with the quantity of chemical solution, in accordance with the formule , wherein lk is concentration of chemicals, a is joint effect of moisture and density, b is dosage of chemicals, and n is a factor of correction factors.
15. A process in claim 3, wherein the exposure of cellulose chip raw materia in step (a) is carried out in a vacuum vessel and the penetration solution is thereafter added to the vacuum vessel, and wherein after addition of the penetration solution, the raw material and solution are transferred into a reception tank for completion of penetration under a pressure of at least tmospheris.
16. A process in claim 6, wherein the exposure of cellulose chip raw material in step (a) is carried out in a vacuum vessel and the penetration solution is thereafter added to the vacuum vessel, and wherein after addition of the penetration solution, the raw material and solution are transferred into a reception tank for completion of penetration under a pressure of at least atmospheric.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI880560A FI80083C (en) | 1988-02-08 | 1988-02-08 | Method and apparatus for pre-treating cellulosic feedstock |
| FI880560 | 1988-02-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1322827C true CA1322827C (en) | 1993-10-12 |
Family
ID=8525866
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 590344 Expired - Fee Related CA1322827C (en) | 1988-02-08 | 1989-02-07 | Process and equipment for pretreatment of cellulosic raw-material |
Country Status (6)
| Country | Link |
|---|---|
| CA (1) | CA1322827C (en) |
| DE (1) | DE3990074C2 (en) |
| FI (1) | FI80083C (en) |
| FR (1) | FR2650604B1 (en) |
| SE (1) | SE507694C2 (en) |
| WO (1) | WO1989007170A1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI80083C (en) * | 1988-02-08 | 1990-04-10 | Antti Aho | Method and apparatus for pre-treating cellulosic feedstock |
| FI910577A (en) * | 1991-02-06 | 1992-08-07 | Antti Aho | REGLERING AV EN PROCESS. |
| FI934281A0 (en) * | 1993-09-29 | 1993-09-29 | Antti Aho | FOERBEHANDLING AV FLIS |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3076501A (en) * | 1956-11-08 | 1963-02-05 | Escher Wyss Ag | Apparatus for treating fibrous materials in the production of cellulose or semi-cellulose |
| DE1070013B (en) * | 1957-07-10 | 1959-11-26 | Escher Wyss G.m.b.H., Ravensburg | Method and device for the treatment of fibrous substances in the production of cellulose or semi-cellulose |
| US3215587A (en) * | 1963-01-21 | 1965-11-02 | Lummus Co | Continuous process and apparatus for delignification of cellulosic material |
| US3347741A (en) * | 1964-01-13 | 1967-10-17 | Crane Co | Feeder for solid materials |
| US3446701A (en) * | 1967-12-28 | 1969-05-27 | Us Agriculture | Apparatus for impregnating and chemically converting cellulose-containing materials |
| FI80083C (en) * | 1988-02-08 | 1990-04-10 | Antti Aho | Method and apparatus for pre-treating cellulosic feedstock |
-
1988
- 1988-02-08 FI FI880560A patent/FI80083C/en not_active IP Right Cessation
-
1989
- 1989-01-30 WO PCT/FI1989/000017 patent/WO1989007170A1/en active Application Filing
- 1989-01-30 DE DE3990074A patent/DE3990074C2/en not_active Expired - Fee Related
- 1989-02-07 CA CA 590344 patent/CA1322827C/en not_active Expired - Fee Related
- 1989-08-04 FR FR8910541A patent/FR2650604B1/en not_active Expired - Fee Related
-
1990
- 1990-08-08 SE SE9002601A patent/SE507694C2/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| FR2650604B1 (en) | 1995-02-10 |
| WO1989007170A1 (en) | 1989-08-10 |
| FR2650604A1 (en) | 1991-02-08 |
| SE507694C2 (en) | 1998-07-06 |
| SE9002601D0 (en) | 1990-08-08 |
| FI880560A (en) | 1989-08-09 |
| FI80083C (en) | 1990-04-10 |
| FI80083B (en) | 1989-12-29 |
| FI880560A0 (en) | 1988-02-08 |
| SE9002601L (en) | 1990-08-08 |
| DE3990074C2 (en) | 2000-03-16 |
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