CA1210907A - Method for use in continuous digestion of finely divided cellulose-containing material - Google Patents
Method for use in continuous digestion of finely divided cellulose-containing materialInfo
- Publication number
- CA1210907A CA1210907A CA000443128A CA443128A CA1210907A CA 1210907 A CA1210907 A CA 1210907A CA 000443128 A CA000443128 A CA 000443128A CA 443128 A CA443128 A CA 443128A CA 1210907 A CA1210907 A CA 1210907A
- Authority
- CA
- Canada
- Prior art keywords
- liquor
- zone
- impregnation
- flow
- chips
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
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
- D21C3/00—Pulping cellulose-containing materials
- D21C3/22—Other features of pulping processes
Landscapes
- Paper (AREA)
- Processes Of Treating Macromolecular Substances (AREA)
- Polysaccharides And Polysaccharide Derivatives (AREA)
Abstract
Abstract of the Disclosure The invention relates to a method for use in continuous digestion of finely-divided cellulose-containing material, such as wood chips.
According to the invention said finely-divided material is fed in a liquid-filled treatment vessel as a continuous chip pillar through a feeding zone, a heating and impregnation zone, a digesting zone, and a washing zone, the temperature in the heating and impregnation zone being kept lower than in the digesting zone. In order to ob-tain stable temperature and chemical profiles in these zones the liquor fed in with the chips is caused to flow through the chip pillar in the feeding zone in the direction of feed of the chips with such velocity before said liquor is withdrawn that said chip pillar is fed through the subsequent impregnation zone, where a flow of impregnation liquor in counter-current to the advancing chip pillar is so regulated that the heat-capacity flow of said impreg-nation liquor is at least equal to the heat-capacity flow of the advancing chip pillar.
According to the invention said finely-divided material is fed in a liquid-filled treatment vessel as a continuous chip pillar through a feeding zone, a heating and impregnation zone, a digesting zone, and a washing zone, the temperature in the heating and impregnation zone being kept lower than in the digesting zone. In order to ob-tain stable temperature and chemical profiles in these zones the liquor fed in with the chips is caused to flow through the chip pillar in the feeding zone in the direction of feed of the chips with such velocity before said liquor is withdrawn that said chip pillar is fed through the subsequent impregnation zone, where a flow of impregnation liquor in counter-current to the advancing chip pillar is so regulated that the heat-capacity flow of said impreg-nation liquor is at least equal to the heat-capacity flow of the advancing chip pillar.
Description
9~7 A method for use in continuous digestion of finely-divided cellulose-containing material The present invention relates to a method for use in con-tinuous digestion of finely-divided cellulose-containing material, e.g. wood chips, by feeding said finely-divided material in a liquid-filled treatment vessel as a contin-uous chip pillar through a feeding zone, an impregnation zone, a digesting zone and a possible washing zone with the temperature in the impregnation zone being kept lower than that in the digesting zone.
The object of the present invention is to make it possible to maintain sufficiently sharp temperature boundaries and sufficiently large temperature differences between the feeding zone, the impregnation zone and the digestion zone in continuous pulp cooking with the intention of obtaining effective impregnation of the finely-divided cellulose-con-taining material with cooking chemicals before the digesting reactions commence and also that the temperature of the liquor used to feed in the finely-divided material shall be kept lower than its boiling point at normal atmospheric pressure.
In the production of pulp from wood chips it is of great importance that the chips are impregnated to a sufficient extent with cooking chemicals before the temperature of said chips is raised to such a level that the rate of the digesting reactions becomes significant. 5ince the rate of diffusion increases as the temperature rises the temperature during impregnation should be as constant and high as poss-ible but nevertheless lower than the temperature at which the rate of the digesting reactions becomes significant.
In order to obtain a pulp of consistent and high quality ~f~
9~
and with the desired properties the temperature of the chips and the liquor with which they are to be impregnated should be raised to the most suitable impregnation temper-ature and held at this level for a known and sufficiently long time before the temperature is raised to the cooking temperature.
To maintain such a temperature profile in a continuously operating pulp digester has been a major problem. Especially in digesters in which the chips are fed in at the top and in which lt is desired to maintain an impregnation zone above the digesting zone and with a temperature lower than the cooking temperature instability in the temperature pro-file occurs because the hot liquor and possibly also chips force their way up from the digesting zone into the impreg nation zone in a variable and unforeseeable fashionO This instability in the temperature profile and chemical profile not only results in variations in the impregnation and cooking times but also causes variations in the temperature of the liquor used in feeding in the chips with difficulties in said feeding in as a consequence.
Finnish Patent Application No. 52366 describes a method to alleviate this problem by maintaining an essentially hori-zontal current of cooled liquor over the whole cross-section of the chip pillar in the lower part of the impregnation zone by means of withdrawing liquor at the periphery of the chip pillar, cooling it and returning it to the middle of said pillar. This method, however, has the drawback, among others, that it entails an increased heat requirement for the cooking process because the heat which rises together with the liquor and chips from the digesting zone and which is removed by cooling must be replaced by additional heating in the digesting zone. For this and other reasons it is now usual to employ a separate impregnation vessel which, how-ever, increases the cost of' the plant.
A precondition for the maintenance of a stable temperature and chemical profile in a continuously operating digester is that the chips are packed into a continuous pillar to such a degree that the freedom of movement of the indivi-dual chips in relation to each other is eliminated and that the feeding of the chips is so arranged that there is a stable flow of liquor through said pillar.
Because the chips in a digester in which the chips are intro-duced at the top are normally packed only by the nett weight of the overlying chips, the packing pressure on the upper part of` the chip pillar is very low. Moreover, the flow vel-ocity of the liquor is so low that laminar flow occurs. As is known the flow resistance with laminar flow depends on the viscosity of the fluid so that the flow resistance de-creases as the temperature of the liquor rises. With turbu-lent flow of the liquor, on the other hand, the flow resis-tance is independent of the viscosity of the liquor. When hot liquor is given the opportunity of displacing cold liquor from a chip pillar in which there is a low packing pressure and through which the normal liquor flow is low very unstable flow conditions are created. This circumstance is the decisive cause of the problem of maintaining a well-defined impregnation zone with a lower temperature above the digesting zone in current digesters.
According to the present invention in a digester in which the chips are introduced at the top,well-defined zones with respect to temperature rise are obtained for charging, im-pregnation and digesting with stable temperature and chem-ical profiles.
lZ~LV~9o~9 Thus in its broadest aspect this invention provides sharp temperature boundaries can be maintained between the charging zone and the impregnation zone and between the impregnation zone and the digesting zone even when these zones are present in the same pres-sure vessel with charging at the top.
The liquor intended for impregnation of the chips is heat-ed to a temperature somewhat higher than the desired impregnation temperature before being fed into the outlet end of the impregnation zone. This heating is performed, using heat from liquor withdrawn from the outlet of the digesting zone, by means of indirect counter-current heat exchange and by possible admixture. In order to achieve an even chemical concentration and temperature o~er the whole cross-section of the chip pillar impregnation liquor is cir-culated at the outlet of the impregnation zone by wlthdrawing liquor at the periphery of the pillar and returning it to the middle of the pillar. In the impregnation zone a flow of impregnation liquor is maintained in counter-current through a continuous chip pillar in such quantity that the heat-capacity flow of the impregnation liquor is at least as large as the heat-capacity flow of the chip feed~This is achieved by means of withdrawing from the inlet of the impregna-tion zone a flow of liquor of such magnitude that its heat capacity flow is at least as large as the heat-capacity flow of the chips fed into the digester and the liquor fed in with them. Stable liquor flow is maintained in the impregnation zone by means of mak-ing its cross-section so small that turbulent flow conditions exist in the current of liquor in question. In order to maintain in the impregnation zone a continuous chip pillar in which the freedom of :~L2~L~9~' movement of the individual chips i5 eliminated and ~Ihich is contin-uously fed through that zone counter-current to the impregnation liquor and further through the digesting zone and washing zone to the discharging zone the chips are compressed and subjected to a sufficient force in the direction of feed before being fed into -the impregnation zone. ~his is achieved by causing the liquor fed in with the chips to flow in the direction of feed of the chips through a sufficiently long chip pillar with - 4a -0g~
sufficient velocity before said liquor is withdrawn at the periphery of the chip pillar adjacent to the inlet of the impregnation zone.
The impregnation liquor is withdrawn for the main part separately from the liquor used to feed in the chips and therefore extractives which are transferred to khe impreg-nation liquor from the chips during their passage through the impregnation zone can be separated from a relatively small flow of liquor. The flow cross-section for the chips and liquor fed in increases successively up to the point where said liquor is withdrawn and consequently a sufficient feeding force is obtained even with a relatively low flow of said liquor. This also confers a high degree of self-regu-lation of the level of the chip pillar in the digester since the flow of liquor fed in automatically falls as said level tends to rise.
The present invention is described in greater detail in the following with reference to the accompanying drawings, in which:
Figure 1 illustrates diagrammatically in cross-section a digester for embodiment of the invention when impregnation is carried out with a fresh liquor of cooking chemicals, Figure 2 shows a similar view of a digester which has been modified so that impregnation is carried out with liquor withdrawn from the digesting zone with desired admi~ture of a fresh liquor of cooking chemicals, Figure 3 illustrates a graph which shows how the relative pressure compressing and feeding the chip pillar at the outlet of the charging zone depends on the relative pres-sure fall in the charging zone of the liquor fed in with the chips, Figure 4 illustrates a graph which shows how the relative level of the chip pillar in the charging zone depends on the relative pressure fall in the charging zone of the liquor fed in with the chips, and Figure 5 illustrates a graph which shows how the flow of liquor which is fed in with the chips depends on the level of the chip pillar in the charging zone of the digester.
The digester illustrated in Figure 1 consists of an ex-tended cylindrical pressure vessel 11 which by means of extraction stainers 21, 22, 23, 24, 25 and 26 is divided into six zones, viz. a charging zone A, a feeding zone B, an impregnation zone C, a digesting zone D, a washing zone E and a discharging zone F.
Chips 50 are proportioned into an unpressurized charging hopper 15 so as to maintain a chip pillar of such height above the liquor level in said hopper that the chips are pressed down to a discharger (not shown) for further trans-port through a pipe 60 to a sluice feeder 14 together with liquor which is introduced into said hopper via a pipe 70 by means of a circulation pump 53. In the sluice feeder, which can be of known type, the chips are transferred to a pipe 61 to be fed into the charging zone of the digester via connection 38 together with liquor which is fed to the sluice feeder by a circulation pump 51. Cooking liquor which is introduced via a pipe 80 to the circulation for the feeding of chips to the sluice feeder and the charging liquor which is transferred from a circulation line 81 to a circulation line 71 when the chips in the sluice feeder are fed fro~ the pipe 60 to the pipe 61, are transported via pipe 72 by means of a pump 52 to the suction side of the pump 51 for the feeding of the chips from the sluice feeder to the digester. This liquor transport i~ regulated by the liquor level in the charging hopper 15.
In the transport of chips via the pipes 60 and 61 the liquor flows are so large compared to the chip flow and the flow velocities are so high that the chips are able to flow freely to the inlets to the sluice feeder and to the di-gester and with approximately the same velocity as the liquor.
In this manner chips together with the charged liquor flow through the charging zone A of the digester to the level 29 of the chip pillar at which the charged chips are packed and fed forwards by means of causing the charged liquor 41 to flow under turbulent flow conditions through a pillar of charged chips in the direction of feed of said pillar before said liquor is withdrawn at the periphery of the chip pillar via the strainer 21 and transported via the pipe 62 by means of the pump 51 back to the sluice feeder.
With this method for charging of the chips a high compres-sing and feeding pressure which is easy to determine and regulate can be applied to the chip pillar before said pil-lar is fed through the impregnation zone. By arranging that this pressure is evenly distributed over the whole cross-section of the chip pillar and attains its greatest value at the inlet to the impregnation zone C mechanical deform-ation of the chips can be avoided.
In order to obtain a high feeding pressure with even a rel-avtively low flow of charged liquor and to facilitate regu-lation of the level of the chip pillar in the digester the flow cross-section for the charged chips and liquor is in-creased successively from the charging point 38 to the ex-traction strainer 21 for the charged liquor 41.
Figure 3 shows how the feeding pressure PF on the chip pil-lar at the inlet to the impregnation zone depends on the pressure drop of the feeding liquor in the feeding zone where ~ p is the total pressure drop in the feeding zone and ~ P1 is the pressure drop in a section of the feeding zone adjacent to the extraction strainer 21.
~2~
Figure 4 shows how the level H of the chip pillar in the feeding zone can be determined with the aid of these pres-sure drops. The level is regulated either by changing the pulp discharge 63 or by varying the charging of chips 60.
The flow of impregnation liquor 42 through the impregnation zone C is regulated by changing the amount of liquor with-drawn from the strainer 22 at the inlet to the impregnation zone and the circulation by the pump 54 through the heat-exchanger 12, where heating takes place by means of' hot liquor 67 withdrawn from the outlet of the digesting zone, for feeding in to the outlet of the impregnation zone to~
gether with liquor 65 withrawn there. The ~low o~ heated impregnation liquor 75 is adjusted os that its heat-capa-city flow is somewhat greater than the heat capacity flow of the charged chips 50 and cooking liquor 80 but equal to or somewhat less than the heat-capacity flow of the liquor 67 extracted from the outlet of the digesting zone.
Extractives 82 are separated 16 from the impregnation liquor 69 which is withdrawn before said liquor is returned after heating to the outlet of the impregnation zone.
The impregnated chips and the liquor which are fed from the impregnation zone to the digesting zone are heated to the cooking temperature by means of withdrawing cooking liquor 66, heating said cooking liquor 13 and returning it to the inlet 34 of the digesting zone.
In the digester illustrated in Figure 2 impregnation is performed with liquor 101 withdrawn from the outlet of the digesting zone, the desired concentration of fresh cooking chemicals being obtained by regulation of this liquor flow 101. The flow of impregnation liquor 42 through the impreg-nation zone is regulated in this case by altering the flow of spent impregnation liquor 89.
~Z~ 7 ~he method according tothe invention offers many advantages:
1. Sharp temperature boundaries can be maintained between the charging zone and the impregnation zone and between the impregnation zone and the digesting zone even when these zones are present in the same pressure vessel with charging at the top.
The object of the present invention is to make it possible to maintain sufficiently sharp temperature boundaries and sufficiently large temperature differences between the feeding zone, the impregnation zone and the digestion zone in continuous pulp cooking with the intention of obtaining effective impregnation of the finely-divided cellulose-con-taining material with cooking chemicals before the digesting reactions commence and also that the temperature of the liquor used to feed in the finely-divided material shall be kept lower than its boiling point at normal atmospheric pressure.
In the production of pulp from wood chips it is of great importance that the chips are impregnated to a sufficient extent with cooking chemicals before the temperature of said chips is raised to such a level that the rate of the digesting reactions becomes significant. 5ince the rate of diffusion increases as the temperature rises the temperature during impregnation should be as constant and high as poss-ible but nevertheless lower than the temperature at which the rate of the digesting reactions becomes significant.
In order to obtain a pulp of consistent and high quality ~f~
9~
and with the desired properties the temperature of the chips and the liquor with which they are to be impregnated should be raised to the most suitable impregnation temper-ature and held at this level for a known and sufficiently long time before the temperature is raised to the cooking temperature.
To maintain such a temperature profile in a continuously operating pulp digester has been a major problem. Especially in digesters in which the chips are fed in at the top and in which lt is desired to maintain an impregnation zone above the digesting zone and with a temperature lower than the cooking temperature instability in the temperature pro-file occurs because the hot liquor and possibly also chips force their way up from the digesting zone into the impreg nation zone in a variable and unforeseeable fashionO This instability in the temperature profile and chemical profile not only results in variations in the impregnation and cooking times but also causes variations in the temperature of the liquor used in feeding in the chips with difficulties in said feeding in as a consequence.
Finnish Patent Application No. 52366 describes a method to alleviate this problem by maintaining an essentially hori-zontal current of cooled liquor over the whole cross-section of the chip pillar in the lower part of the impregnation zone by means of withdrawing liquor at the periphery of the chip pillar, cooling it and returning it to the middle of said pillar. This method, however, has the drawback, among others, that it entails an increased heat requirement for the cooking process because the heat which rises together with the liquor and chips from the digesting zone and which is removed by cooling must be replaced by additional heating in the digesting zone. For this and other reasons it is now usual to employ a separate impregnation vessel which, how-ever, increases the cost of' the plant.
A precondition for the maintenance of a stable temperature and chemical profile in a continuously operating digester is that the chips are packed into a continuous pillar to such a degree that the freedom of movement of the indivi-dual chips in relation to each other is eliminated and that the feeding of the chips is so arranged that there is a stable flow of liquor through said pillar.
Because the chips in a digester in which the chips are intro-duced at the top are normally packed only by the nett weight of the overlying chips, the packing pressure on the upper part of` the chip pillar is very low. Moreover, the flow vel-ocity of the liquor is so low that laminar flow occurs. As is known the flow resistance with laminar flow depends on the viscosity of the fluid so that the flow resistance de-creases as the temperature of the liquor rises. With turbu-lent flow of the liquor, on the other hand, the flow resis-tance is independent of the viscosity of the liquor. When hot liquor is given the opportunity of displacing cold liquor from a chip pillar in which there is a low packing pressure and through which the normal liquor flow is low very unstable flow conditions are created. This circumstance is the decisive cause of the problem of maintaining a well-defined impregnation zone with a lower temperature above the digesting zone in current digesters.
According to the present invention in a digester in which the chips are introduced at the top,well-defined zones with respect to temperature rise are obtained for charging, im-pregnation and digesting with stable temperature and chem-ical profiles.
lZ~LV~9o~9 Thus in its broadest aspect this invention provides sharp temperature boundaries can be maintained between the charging zone and the impregnation zone and between the impregnation zone and the digesting zone even when these zones are present in the same pres-sure vessel with charging at the top.
The liquor intended for impregnation of the chips is heat-ed to a temperature somewhat higher than the desired impregnation temperature before being fed into the outlet end of the impregnation zone. This heating is performed, using heat from liquor withdrawn from the outlet of the digesting zone, by means of indirect counter-current heat exchange and by possible admixture. In order to achieve an even chemical concentration and temperature o~er the whole cross-section of the chip pillar impregnation liquor is cir-culated at the outlet of the impregnation zone by wlthdrawing liquor at the periphery of the pillar and returning it to the middle of the pillar. In the impregnation zone a flow of impregnation liquor is maintained in counter-current through a continuous chip pillar in such quantity that the heat-capacity flow of the impregnation liquor is at least as large as the heat-capacity flow of the chip feed~This is achieved by means of withdrawing from the inlet of the impregna-tion zone a flow of liquor of such magnitude that its heat capacity flow is at least as large as the heat-capacity flow of the chips fed into the digester and the liquor fed in with them. Stable liquor flow is maintained in the impregnation zone by means of mak-ing its cross-section so small that turbulent flow conditions exist in the current of liquor in question. In order to maintain in the impregnation zone a continuous chip pillar in which the freedom of :~L2~L~9~' movement of the individual chips i5 eliminated and ~Ihich is contin-uously fed through that zone counter-current to the impregnation liquor and further through the digesting zone and washing zone to the discharging zone the chips are compressed and subjected to a sufficient force in the direction of feed before being fed into -the impregnation zone. ~his is achieved by causing the liquor fed in with the chips to flow in the direction of feed of the chips through a sufficiently long chip pillar with - 4a -0g~
sufficient velocity before said liquor is withdrawn at the periphery of the chip pillar adjacent to the inlet of the impregnation zone.
The impregnation liquor is withdrawn for the main part separately from the liquor used to feed in the chips and therefore extractives which are transferred to khe impreg-nation liquor from the chips during their passage through the impregnation zone can be separated from a relatively small flow of liquor. The flow cross-section for the chips and liquor fed in increases successively up to the point where said liquor is withdrawn and consequently a sufficient feeding force is obtained even with a relatively low flow of said liquor. This also confers a high degree of self-regu-lation of the level of the chip pillar in the digester since the flow of liquor fed in automatically falls as said level tends to rise.
The present invention is described in greater detail in the following with reference to the accompanying drawings, in which:
Figure 1 illustrates diagrammatically in cross-section a digester for embodiment of the invention when impregnation is carried out with a fresh liquor of cooking chemicals, Figure 2 shows a similar view of a digester which has been modified so that impregnation is carried out with liquor withdrawn from the digesting zone with desired admi~ture of a fresh liquor of cooking chemicals, Figure 3 illustrates a graph which shows how the relative pressure compressing and feeding the chip pillar at the outlet of the charging zone depends on the relative pres-sure fall in the charging zone of the liquor fed in with the chips, Figure 4 illustrates a graph which shows how the relative level of the chip pillar in the charging zone depends on the relative pressure fall in the charging zone of the liquor fed in with the chips, and Figure 5 illustrates a graph which shows how the flow of liquor which is fed in with the chips depends on the level of the chip pillar in the charging zone of the digester.
The digester illustrated in Figure 1 consists of an ex-tended cylindrical pressure vessel 11 which by means of extraction stainers 21, 22, 23, 24, 25 and 26 is divided into six zones, viz. a charging zone A, a feeding zone B, an impregnation zone C, a digesting zone D, a washing zone E and a discharging zone F.
Chips 50 are proportioned into an unpressurized charging hopper 15 so as to maintain a chip pillar of such height above the liquor level in said hopper that the chips are pressed down to a discharger (not shown) for further trans-port through a pipe 60 to a sluice feeder 14 together with liquor which is introduced into said hopper via a pipe 70 by means of a circulation pump 53. In the sluice feeder, which can be of known type, the chips are transferred to a pipe 61 to be fed into the charging zone of the digester via connection 38 together with liquor which is fed to the sluice feeder by a circulation pump 51. Cooking liquor which is introduced via a pipe 80 to the circulation for the feeding of chips to the sluice feeder and the charging liquor which is transferred from a circulation line 81 to a circulation line 71 when the chips in the sluice feeder are fed fro~ the pipe 60 to the pipe 61, are transported via pipe 72 by means of a pump 52 to the suction side of the pump 51 for the feeding of the chips from the sluice feeder to the digester. This liquor transport i~ regulated by the liquor level in the charging hopper 15.
In the transport of chips via the pipes 60 and 61 the liquor flows are so large compared to the chip flow and the flow velocities are so high that the chips are able to flow freely to the inlets to the sluice feeder and to the di-gester and with approximately the same velocity as the liquor.
In this manner chips together with the charged liquor flow through the charging zone A of the digester to the level 29 of the chip pillar at which the charged chips are packed and fed forwards by means of causing the charged liquor 41 to flow under turbulent flow conditions through a pillar of charged chips in the direction of feed of said pillar before said liquor is withdrawn at the periphery of the chip pillar via the strainer 21 and transported via the pipe 62 by means of the pump 51 back to the sluice feeder.
With this method for charging of the chips a high compres-sing and feeding pressure which is easy to determine and regulate can be applied to the chip pillar before said pil-lar is fed through the impregnation zone. By arranging that this pressure is evenly distributed over the whole cross-section of the chip pillar and attains its greatest value at the inlet to the impregnation zone C mechanical deform-ation of the chips can be avoided.
In order to obtain a high feeding pressure with even a rel-avtively low flow of charged liquor and to facilitate regu-lation of the level of the chip pillar in the digester the flow cross-section for the charged chips and liquor is in-creased successively from the charging point 38 to the ex-traction strainer 21 for the charged liquor 41.
Figure 3 shows how the feeding pressure PF on the chip pil-lar at the inlet to the impregnation zone depends on the pressure drop of the feeding liquor in the feeding zone where ~ p is the total pressure drop in the feeding zone and ~ P1 is the pressure drop in a section of the feeding zone adjacent to the extraction strainer 21.
~2~
Figure 4 shows how the level H of the chip pillar in the feeding zone can be determined with the aid of these pres-sure drops. The level is regulated either by changing the pulp discharge 63 or by varying the charging of chips 60.
The flow of impregnation liquor 42 through the impregnation zone C is regulated by changing the amount of liquor with-drawn from the strainer 22 at the inlet to the impregnation zone and the circulation by the pump 54 through the heat-exchanger 12, where heating takes place by means of' hot liquor 67 withdrawn from the outlet of the digesting zone, for feeding in to the outlet of the impregnation zone to~
gether with liquor 65 withrawn there. The ~low o~ heated impregnation liquor 75 is adjusted os that its heat-capa-city flow is somewhat greater than the heat capacity flow of the charged chips 50 and cooking liquor 80 but equal to or somewhat less than the heat-capacity flow of the liquor 67 extracted from the outlet of the digesting zone.
Extractives 82 are separated 16 from the impregnation liquor 69 which is withdrawn before said liquor is returned after heating to the outlet of the impregnation zone.
The impregnated chips and the liquor which are fed from the impregnation zone to the digesting zone are heated to the cooking temperature by means of withdrawing cooking liquor 66, heating said cooking liquor 13 and returning it to the inlet 34 of the digesting zone.
In the digester illustrated in Figure 2 impregnation is performed with liquor 101 withdrawn from the outlet of the digesting zone, the desired concentration of fresh cooking chemicals being obtained by regulation of this liquor flow 101. The flow of impregnation liquor 42 through the impreg-nation zone is regulated in this case by altering the flow of spent impregnation liquor 89.
~Z~ 7 ~he method according tothe invention offers many advantages:
1. Sharp temperature boundaries can be maintained between the charging zone and the impregnation zone and between the impregnation zone and the digesting zone even when these zones are present in the same pressure vessel with charging at the top.
2. Independent of the temperature in the impregnation zone the temperature of the charging liquor can be kept so low that the charging arrangements preceding the sluice feeder can be made unpressurized.
3. A sufficiently high and constant temperature for effec-tive impregnation can be maintained in the impregnation zone without the temperature becoming so high as to cause the start of lignin dissolution which is undesirable in this zone.
4. The requirement of the process for external heat is low since the only requirement is for the heat needed for heating of the finely-divided material and the cooking liquor from the impregnation temperature to the digesting temperature.
5. A high packing pressure on the chip pillar can be main-tained in the impregnation zone without entailing an ex-cessively high compressive force on the cooked chips, which is necessary in order that the chips can be continuously fed through the digester as a continuous pillar and that suffi-cient quantities of liquor can be fed in counter-current through the impregnation zone and through the washing zone.
6. since the chips on entering the digester are quickly compressed and reach maximum packing when they pass the ex-traction strainer for the charging liquor the transport of `` ~z~a7 fine solid material (sawdust) to said extraction strainer is reduced. Using the present method it is thus possible to minimize the circulation of fine material in the char-ging arrangement. This not only increases the charging capacity and reduces the need for cleaning but also in-creases the yield since undesired decomposition of the fine material is reduced. Chips of comparatively low qual-ity can therefore be utilized without giving rise to operational difficulties.
7. During the pressurized part of the cooking process the chips are surrounded the whole time by liquor. The impreg-nation of the chips is therefore effective and even since absorption of gas is eliminated and since the impregnation liquor which surrounds the chips in the impregnation zone is continuously and rapidly changed because of the high relative flow between the liquor and chips.
8. The force compressing and feeding the chips and also the level of the chip pillar in the inlet to the digester can easily be determined and regulated.
Mechanical deformation of the chips is reduced to a minimum since the chips are not at any stage of the charging into the digester exposed to a higher mechanical pressure than is required to obtain a continuous and even feeding of said chips.
10. The extractives contained in the chips are transferred to the impregnation liquor and can be separated from said liquor at a comparatively low temperature before the impreg-nation liquor is fed into the digesting zone.
11. Even unsteamed chips can be effectively impregnated and fed as a continuous pillar through the digester.
~Z~9~'7 12. The required plant is simple since the whole cooking process can be carried out in a single pressure vessel.
Mechanical deformation of the chips is reduced to a minimum since the chips are not at any stage of the charging into the digester exposed to a higher mechanical pressure than is required to obtain a continuous and even feeding of said chips.
10. The extractives contained in the chips are transferred to the impregnation liquor and can be separated from said liquor at a comparatively low temperature before the impreg-nation liquor is fed into the digesting zone.
11. Even unsteamed chips can be effectively impregnated and fed as a continuous pillar through the digester.
~Z~9~'7 12. The required plant is simple since the whole cooking process can be carried out in a single pressure vessel.
Claims (10)
1. A method for use in continuous digestion of finely-divided cellulose-containing material by feeding said finely-divided ma-terial in a liquid-filled treatment vessel as a continuous chip pillar through a feeding zone, a heating and impregnation zone, and a digesting zone, with the temperature in the heating and impregnation zone being kept lower than in the digesting zone, comprising causing the liquor fed in with the chips to flow through the chip pillar in the feeding zone in the direction of feed of the chips with such velocity before said liquor is with-drawn that said chip pillar is fed through the subsequent impreg-nation zone, where a flow of impregnation liquor in counter-current to the feed of the chip pillar is so regulated that the heatcapacity flow of said impregnation liquor is at least equal to the heat-capacity flow of the advancing chip pillar.
2. A method according to claim 1, in which the velocity of the impregnation liquor in relation to that of the chip pillar in the impregnation zone is kept so high that turbulent flow condi-tions prevail.
3. A method according to claim 1, in which the impregnation liquor which is introduced into the outlet end of the impregna-tion zone is heated by liquor withdrawn from the outlet of the digesting zone.
4. A method according to claim 1, in which the liquor and the finely-divided material in the feeding zone flow through a successively increasing flow cross-section up to the extraction strainer for the charged liquor.
5. A method according to claim 1, in which the impregnation liquor is withdrawn via a strainer either entirely or partly sepa-rate from the charging liquor.
6. A method according to claim 5, in which extractives in the impregnation liquor are separated out before the impregnation liquor withdrawn is returned or mixed with other liquor.
7. A method according to claim 1, in which the feeding pres-sure on the finely-divided material at the inlet to the impregna-tion zone and also the level of the continuous chip pillar, are determined by measuring the pressure drop of the charging liquor from a point in the charging zone and from a point in the feeding zone to a point adjoining the extraction strainer for the charging liquor.
8. A method according to claim 7, in which the feeding pres-sure is regulated by throttle regulation of the charging liquor or by regulation of the speed of rotation of the transport pump for said charging liquor or by regulation of the level of the continuous chip pillar.
9. A method according to claim 7, in which the level of the continuous chip pillar is regulated by regulation of the trans-port liquor for the finely-divided material to the sluice feeder.
10. A method according to claim 7, in which the level of the continuous chip pillar is regulated by regulation of the speed of rotation of said sluice feeder.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI824282 | 1982-12-14 | ||
| FI824282A FI66215C (en) | 1982-12-14 | 1982-12-14 | SAETTING VIDEO CONTAINER UPPSLUTNING AV FINFOERDELAT CELLULOSAHALTIGT MATERIAL |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1210907A true CA1210907A (en) | 1986-09-09 |
Family
ID=8516450
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000443128A Expired CA1210907A (en) | 1982-12-14 | 1983-12-13 | Method for use in continuous digestion of finely divided cellulose-containing material |
Country Status (12)
| Country | Link |
|---|---|
| JP (1) | JPS59137589A (en) |
| AT (1) | AT384631B (en) |
| AU (1) | AU548448B2 (en) |
| BR (1) | BR8306977A (en) |
| CA (1) | CA1210907A (en) |
| DE (1) | DE3344865C2 (en) |
| FI (1) | FI66215C (en) |
| FR (1) | FR2537621B1 (en) |
| NO (1) | NO161927C (en) |
| SE (1) | SE452175C (en) |
| SU (1) | SU1475491A3 (en) |
| ZA (1) | ZA838909B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5958181A (en) * | 1997-08-07 | 1999-09-28 | Ahlstrom Machinery, Inc. | Continuous cooking with a two-stage cool impregnation |
| US6179958B1 (en) | 1996-02-09 | 2001-01-30 | Kvaerner Pulping Ab | Method for continuous cooking of cellulose-containing fibre material |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| RU2447216C1 (en) * | 2011-01-17 | 2012-04-10 | Тарантин Сергей Анатольевич | Method of delignification of wood chips in manufacturing of cellulose |
| JP5786087B2 (en) * | 2011-03-25 | 2015-09-30 | ヴァルメト アクチボラグ | Method and apparatus for adding treatment liquid to cellulosic material in downflow container |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1907001A1 (en) * | 1968-02-13 | 1969-09-11 | Sunds Ab | Method and device for heating fiber material |
| SE343344B (en) * | 1970-06-29 | 1972-03-06 | Kamyr Ab | |
| CA1002361A (en) * | 1973-01-03 | 1976-12-28 | James R. Prough | Digester control process and apparatus |
| US4071399A (en) * | 1976-09-01 | 1978-01-31 | Kamyr, Inc. | Apparatus and method for the displacement impregnation of cellulosic chips material |
-
1982
- 1982-12-14 FI FI824282A patent/FI66215C/en not_active IP Right Cessation
-
1983
- 1983-11-30 AU AU21847/83A patent/AU548448B2/en not_active Ceased
- 1983-11-30 ZA ZA838909A patent/ZA838909B/en unknown
- 1983-12-05 NO NO834466A patent/NO161927C/en unknown
- 1983-12-07 AT AT0427983A patent/AT384631B/en not_active IP Right Cessation
- 1983-12-12 DE DE3344865A patent/DE3344865C2/en not_active Expired
- 1983-12-12 FR FR8319839A patent/FR2537621B1/en not_active Expired
- 1983-12-12 SE SE8306853A patent/SE452175C/en not_active IP Right Cessation
- 1983-12-13 SU SU833677056A patent/SU1475491A3/en active
- 1983-12-13 CA CA000443128A patent/CA1210907A/en not_active Expired
- 1983-12-13 JP JP58234907A patent/JPS59137589A/en active Granted
- 1983-12-14 BR BR8306977A patent/BR8306977A/en not_active IP Right Cessation
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6179958B1 (en) | 1996-02-09 | 2001-01-30 | Kvaerner Pulping Ab | Method for continuous cooking of cellulose-containing fibre material |
| US5958181A (en) * | 1997-08-07 | 1999-09-28 | Ahlstrom Machinery, Inc. | Continuous cooking with a two-stage cool impregnation |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3344865C2 (en) | 1985-09-19 |
| FI66215B (en) | 1984-05-31 |
| FR2537621A1 (en) | 1984-06-15 |
| SE452175B (en) | 1987-11-16 |
| DE3344865A1 (en) | 1984-06-14 |
| AU548448B2 (en) | 1985-12-12 |
| NO161927C (en) | 1989-10-11 |
| BR8306977A (en) | 1984-07-24 |
| FR2537621B1 (en) | 1985-11-22 |
| ZA838909B (en) | 1984-07-25 |
| FI66215C (en) | 1984-09-10 |
| SE452175C (en) | 1990-03-26 |
| AT384631B (en) | 1987-12-10 |
| ATA427983A (en) | 1987-05-15 |
| SE8306853L (en) | 1984-06-15 |
| FI824282A0 (en) | 1982-12-14 |
| JPS59137589A (en) | 1984-08-07 |
| NO161927B (en) | 1989-07-03 |
| SU1475491A3 (en) | 1989-04-23 |
| SE8306853D0 (en) | 1983-12-12 |
| JPS6347836B2 (en) | 1988-09-26 |
| NO834466L (en) | 1984-06-15 |
| AU2184783A (en) | 1984-06-21 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4071399A (en) | Apparatus and method for the displacement impregnation of cellulosic chips material | |
| US4136831A (en) | Method and apparatus for minimizing steam consumption in the production of pulp for fiberboard and the like | |
| US3963561A (en) | Recirculation of unconsumed oxygen pulp bleaching gas | |
| US2474862A (en) | Process and apparatus for continuous digestion of fibrous materials | |
| US2876098A (en) | Process of and apparatus for the continuous manufacture of cellulose or hemicellulose from cellulosic fibrous materials | |
| EP1778910B1 (en) | Method for impregnating chips | |
| US7381302B2 (en) | Method and arrangement for impregnating chips | |
| US3041232A (en) | Method of continuous cellulose digestion and digester apparatus for practicing said method | |
| CA1210907A (en) | Method for use in continuous digestion of finely divided cellulose-containing material | |
| US3092338A (en) | Pulp refining apparatus | |
| SE502039C2 (en) | Methods and apparatus for continuous cooking of pulp | |
| US3434920A (en) | Apparatus for continuous digesting | |
| US7112256B2 (en) | Method for continuous cooking of chemical pulp to improve heat economy | |
| FI63610C (en) | REQUIREMENTS FOR CONTAINER UPPSLUTNING AV FINFOERDELAT MATERIAL | |
| US4093511A (en) | Apparatus for oxygen bleaching of pulp including recirculation of exhaust gases | |
| US4092212A (en) | Selective impregnation of heterogenous fiber material before digestion | |
| US3165436A (en) | Continuous impregnating and pulping process | |
| US2996421A (en) | Pulp manufacture | |
| WO2014184443A1 (en) | A system and method to regulate consistency in a blow or pulp tank | |
| US3441475A (en) | Continuous pulping apparatus | |
| US2008635A (en) | Process of and apparatus for producing pulp | |
| SU1051112A1 (en) | Apparatus for thermal processing of oil-bearing seeds | |
| US3723243A (en) | Continuous digester having selfregulating wood chip level | |
| US3076739A (en) | Manufacture of pulp from fibrous substances | |
| US4155805A (en) | Method for continuously digesting cellulosic fiber by evenly spreading the fiber material over the digestion vessel with steam |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |