Note: Descriptions are shown in the official language in which they were submitted.
~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
. .
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
1 1
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~
1 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~
13
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
14
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 .~
16
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
17
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~
18
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
1 9
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,~
21
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
22
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.
