CA1135101A - Method for secondary heat recovery in batchwise cellulose digesting - Google Patents
Method for secondary heat recovery in batchwise cellulose digestingInfo
- Publication number
- CA1135101A CA1135101A CA000349532A CA349532A CA1135101A CA 1135101 A CA1135101 A CA 1135101A CA 000349532 A CA000349532 A CA 000349532A CA 349532 A CA349532 A CA 349532A CA 1135101 A CA1135101 A CA 1135101A
- Authority
- CA
- Canada
- Prior art keywords
- cooker
- steam
- liquor
- digesting
- cooking liquor
- 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
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/02—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents
-
- 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
- D21C11/00—Regeneration of pulp liquors or effluent waste waters
- D21C11/06—Treatment of pulp gases; Recovery of the heat content of the gases; Treatment of gases arising from various sources in pulp and paper mills; Regeneration of gaseous SO2, e.g. arising from liquors containing sulfur compounds
-
- 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
- D21C7/00—Digesters
- D21C7/08—Discharge devices
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Extraction Or Liquid Replacement (AREA)
- Paper (AREA)
- Polysaccharides And Polysaccharide Derivatives (AREA)
- General Preparation And Processing Of Foods (AREA)
- Jellies, Jams, And Syrups (AREA)
- Artificial Filaments (AREA)
Abstract
METHOD FOR SECONDARY HEAT RECOVERY
IN BATCHWISE CELLULOSE DIGESTING
Abstract of The Disclosure There is disclosed a method for secondary heat recovery in batchwise cellulose digesting in digesters, the cooking liquor being conducted, during the final stage of the digesting cycle, to an equa-lizing tank standing under pressure. The novel feature of this method is, that cooking liquor or steam, expanded from cooking liquor is con-ducted, under flow control, from the equalizing tank for utilizing in the digesting process, in auxiliary processes or in heat recovery aggregates for internal use of its heat content. In one preferred embodiment of the method, cooking liquor is conducted from the equa-lizing tank to a first flash cyclone, from where there is discharged a first steam flow and a first liquid flow, which is fed to a second flash cyclone, from where there is discharged a second steam flow and a second liquid flow.
IN BATCHWISE CELLULOSE DIGESTING
Abstract of The Disclosure There is disclosed a method for secondary heat recovery in batchwise cellulose digesting in digesters, the cooking liquor being conducted, during the final stage of the digesting cycle, to an equa-lizing tank standing under pressure. The novel feature of this method is, that cooking liquor or steam, expanded from cooking liquor is con-ducted, under flow control, from the equalizing tank for utilizing in the digesting process, in auxiliary processes or in heat recovery aggregates for internal use of its heat content. In one preferred embodiment of the method, cooking liquor is conducted from the equa-lizing tank to a first flash cyclone, from where there is discharged a first steam flow and a first liquid flow, which is fed to a second flash cyclone, from where there is discharged a second steam flow and a second liquid flow.
Description
11~35iU~ ~
The present invention relates to a method for secondary heat recovery in batchwise digesting of cellulose in digesters, the cooking liquor being conducted, during the final stage of the digesting cycle, to an equalizing tank standing under pressure.
Methods for secondary heat recovery in the pulp in-dustry are known. These are based on the recovery of heat from the expansion steam from the blowing tank, or from material flows, which originate directly from the digester. These methods are disadvantageous in that the material and heat flows to the heat recovery system are discontinuous, which means, that it will be difficult to control the process. Further the secon-dary heat is recovered as warm water, which is normally avail-able in excess o~f the normal needs of the plant(process). Asthe material and heat flows according to said methods aredis-continuous, there is needed an accumulating tank for the odor-ous foul gases liberated in the system so that subsequent treat-- ments may be effected. It is possible to eliminate the dis-continuity in the liberating of the foul gases on such occa-sions, when foul gases are not liberated by feeding air to the system.
In the Finnish Patent Specification No. 18,429 a cellulose digesting method is disclosed, according to which cook-ing liquor is conducted, after the digestion is terminated, un-der substantially the same pressure and temperature as that, which was prevailing in the digester, to a separate tank, and according to which any steam left in the pulp remaining in the digester is transferred to one or several steam accumulators.
As there is no disclosure of how to utilize the heat content of the cooking liquor practically in the method suggested, this has not been applied practically.
j 35 The heat economy is growing in importance in the pulp industry, and many efforts have been made to improve the same, ,~
..
f,, ~' ' .
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especially in the kraft pulping industry. The pres~nt inven-tion provides a method of the type mentioned at the introduction, which is characterized by a good heat economy, and which permi-ts blowing of the pulp at a relatively low temperature, prefer-ably within the range 90 - 105C, which means so called "cold blow", and in which the pulp may be prewashed within the digester.
According to the present invention there is provided in the batchwise digesting of cellulose in a cooker from which a cellulose mass is to be discharged, the method which comprises feeding cooking liquor and cellulose to said cooker to digest the cellulose, feeding cooking liquor, during a final stage of said digesting, from the cooker to an equalizing tank maintained under pressure, thereafter degassing the cooker to substantially atmospheric pressure, feeding washing liquor, during said de-gassing, to the cooker and there prewashing the cellulose mass at a ]ow temperature, and conducting a steam flow from the equalizing tank to the cooker to discharge its content oE cel-lulose mass at a temperature of 90 to 105C, thereby providing a cold blow.
Thus according to the invention the cooking liquor or steam, expanded from cooking liquor is conducted, under flow control, from the equalizing tank for utilizing in the digest-ing process, in auxiliary processes or in heat recovery ag-gregates for external use of its heat content.
From the equalizing tank the hot cooking liquor is conducted to one or several flash cyclones. These stand under lower pressure than the equalizing tank for cooking liquor.
The steam generated in the 1, ~` j - 2 -1 cyclones cc~n be utilized partly in the digesting plant at the beginnin~
The present invention relates to a method for secondary heat recovery in batchwise digesting of cellulose in digesters, the cooking liquor being conducted, during the final stage of the digesting cycle, to an equalizing tank standing under pressure.
Methods for secondary heat recovery in the pulp in-dustry are known. These are based on the recovery of heat from the expansion steam from the blowing tank, or from material flows, which originate directly from the digester. These methods are disadvantageous in that the material and heat flows to the heat recovery system are discontinuous, which means, that it will be difficult to control the process. Further the secon-dary heat is recovered as warm water, which is normally avail-able in excess o~f the normal needs of the plant(process). Asthe material and heat flows according to said methods aredis-continuous, there is needed an accumulating tank for the odor-ous foul gases liberated in the system so that subsequent treat-- ments may be effected. It is possible to eliminate the dis-continuity in the liberating of the foul gases on such occa-sions, when foul gases are not liberated by feeding air to the system.
In the Finnish Patent Specification No. 18,429 a cellulose digesting method is disclosed, according to which cook-ing liquor is conducted, after the digestion is terminated, un-der substantially the same pressure and temperature as that, which was prevailing in the digester, to a separate tank, and according to which any steam left in the pulp remaining in the digester is transferred to one or several steam accumulators.
As there is no disclosure of how to utilize the heat content of the cooking liquor practically in the method suggested, this has not been applied practically.
j 35 The heat economy is growing in importance in the pulp industry, and many efforts have been made to improve the same, ,~
..
f,, ~' ' .
~13Sl~ ;
especially in the kraft pulping industry. The pres~nt inven-tion provides a method of the type mentioned at the introduction, which is characterized by a good heat economy, and which permi-ts blowing of the pulp at a relatively low temperature, prefer-ably within the range 90 - 105C, which means so called "cold blow", and in which the pulp may be prewashed within the digester.
According to the present invention there is provided in the batchwise digesting of cellulose in a cooker from which a cellulose mass is to be discharged, the method which comprises feeding cooking liquor and cellulose to said cooker to digest the cellulose, feeding cooking liquor, during a final stage of said digesting, from the cooker to an equalizing tank maintained under pressure, thereafter degassing the cooker to substantially atmospheric pressure, feeding washing liquor, during said de-gassing, to the cooker and there prewashing the cellulose mass at a ]ow temperature, and conducting a steam flow from the equalizing tank to the cooker to discharge its content oE cel-lulose mass at a temperature of 90 to 105C, thereby providing a cold blow.
Thus according to the invention the cooking liquor or steam, expanded from cooking liquor is conducted, under flow control, from the equalizing tank for utilizing in the digest-ing process, in auxiliary processes or in heat recovery ag-gregates for external use of its heat content.
From the equalizing tank the hot cooking liquor is conducted to one or several flash cyclones. These stand under lower pressure than the equalizing tank for cooking liquor.
The steam generated in the 1, ~` j - 2 -1 cyclones cc~n be utilized partly in the digesting plant at the beginnin~
2 of the next digesting cycle and in separate auxili~ry processes. In
3 this way live steam is saved compared with a conventional system. The ~ rest of the expanded steam is conducted to surface condensers, i.e.
a heat recovery a,ggregate, in which hot water iB produced. The odorous 6 foul gases and the methanol gases llberated with the expanded steam can 7 be conducted to a foul gases purification system thanks to the flow 8 control by a well known multi step condenser process.
9 After the discharge of the cooking liquor the secondary heat in the liquor remaining in the chips is recovered by relief gassing, 1 known per se. ~he pressure in the digester is lowered to a value some-12 what above atmosperic pressure. The steam flow generated is conducted l3 to a heat recovery aggregate together with or instead of a steam flow, 14 coming from a flash cyclone, to which liquor is fed from the equilizing tank, which last steam flow is controlled, in order that the combined 16 steam flow is kept substantially constant. ~he free liquor in the 17 digester is suctioned out through a sieve in the digester bottom.
18 The digester is then filled with filtrate from the pulp washer 19 and i6 blown empty by the aid of steam, expanded from the equilizing tank. Thus there is provided a prewash of the pulp.
21 The filtrate, i.e. the washing liquid is fed, preferably, to 22 the digester at a relatively low temperature, i.e. preferably at such 23 a temperature, that the temperature in the mixture of washing liquid 24 and pulp will be 105C or lower. The content of the digester can be blown preferably at a temperature of 90 - 105C, which means "cold 26 blow7l.
27 It is advantageous to feed washing liquid to the digester 28 through a sieve in the bottom of the digester in order to distribute 29 washing liquid evenly in the bottom of the digester.
It may also be suitable to feed a controlled flow of washing - 3- ~135~0?~
1 liquid through a sieve in the bottom of the digeter, durlng the blowing 2 into the bottom cone of the digester in order to reduce the friction in 3 the flow through this part of the digester, whereby the discharge of
a heat recovery a,ggregate, in which hot water iB produced. The odorous 6 foul gases and the methanol gases llberated with the expanded steam can 7 be conducted to a foul gases purification system thanks to the flow 8 control by a well known multi step condenser process.
9 After the discharge of the cooking liquor the secondary heat in the liquor remaining in the chips is recovered by relief gassing, 1 known per se. ~he pressure in the digester is lowered to a value some-12 what above atmosperic pressure. The steam flow generated is conducted l3 to a heat recovery aggregate together with or instead of a steam flow, 14 coming from a flash cyclone, to which liquor is fed from the equilizing tank, which last steam flow is controlled, in order that the combined 16 steam flow is kept substantially constant. ~he free liquor in the 17 digester is suctioned out through a sieve in the digester bottom.
18 The digester is then filled with filtrate from the pulp washer 19 and i6 blown empty by the aid of steam, expanded from the equilizing tank. Thus there is provided a prewash of the pulp.
21 The filtrate, i.e. the washing liquid is fed, preferably, to 22 the digester at a relatively low temperature, i.e. preferably at such 23 a temperature, that the temperature in the mixture of washing liquid 24 and pulp will be 105C or lower. The content of the digester can be blown preferably at a temperature of 90 - 105C, which means "cold 26 blow7l.
27 It is advantageous to feed washing liquid to the digester 28 through a sieve in the bottom of the digester in order to distribute 29 washing liquid evenly in the bottom of the digester.
It may also be suitable to feed a controlled flow of washing - 3- ~135~0?~
1 liquid through a sieve in the bottom of the digeter, durlng the blowing 2 into the bottom cone of the digester in order to reduce the friction in 3 the flow through this part of the digester, whereby the discharge of
4 the digester is facilitated.
In such cases, when there are disturbances in a pulp plant, 6 for instance at a digester, so that the steam consumption is periodi-7 cally reduced, there is, according to the invention, a possibility to 8 conduct external high pressure steam, i.e. steam from the boiling house, 9 to the equilizing tank, in order to save this steam instead of blowing it into the free air.
11 The new method has many advantages, considering the steam 12 consumption of the plant, the process, the quality of the pulp, the 13 washing efficiency and the environmental protection, which will be t4 obvious from the following list.
Advantages relating to the steam consumption of the plant _________________________________________________________ 16 Theoretically 10~o of the latent heat of the digester content 17 is available in the form of a controlled secondary steam flow. Compared t8 to a conventional heat recove7y system there is thus provided a greater 19 freedom in the choice of utilization of the secondary heat. ~urther, the se~ondary heat is recGvered at a higher enthalpy level than before.
21 The variations in the primary steam flow to the digesting 22 plant can be reduced.
23 Process advantages 24 Generally it can be said, that the best features of the con-2S tinuous and the discontinuous batchwise digesting processes have been 26 combined.
Z7 'rhe secondary heat flow from the digesting plant can be fed, 28 more safely, to different auxiliary processes, as the flows are not 29 influenced by disturbances in the main process.
Improved pulp quality _____________________ ~ The method permits blowing of the digester at a low tempera-~
~ ~ 4 ~ ~13S~0~
"
~L~13S10~
1 ture (90 - 105 C). This socalled "cold blow" means, that the risk for 2 a ruptur~ in the fibre wall by violent expansion of liquid, bound in 3 the fibre, i8 reduced compared to the risk in conventional blow. In 4 this way the strength of the pul~ is improved.
~he variation of the Kappa-Number is reduced, as it is more 6 economical than previously to use a high water/wood-relationship in 7 the digesting 8 If there are disturbances in the subsequent process line 9 (washer, bleaching plant) this method gives an opportunity to let a completed digester charge wait in the digester without reducing the 11 Kappa-Number. Relief gassing of the digester to a pressure not too far l2 from atmospheric pressure and feed of filtrate from the washer lowers 13 the temperature of the pulp, which means, that the reaction velocity of 14 the digesting process is reduced below a level, where the Kappa-Number is influenced.
16 Improved washing efficiency ___________________________ 17 m e free cooking liquor with a high concentration of cooking t8 chemicals and components extracted from the wood are removed from the 19 digester and are rèplaced by a washing liquid with a lower concentration of said substances. Mixing of washing liquid and pulp is carried out 21 partly in the digester and partly in the blowing pipe and in the blowing ~2 tank. In the blowing tank there iB also a diffusion of chemicals from 23 concentrated cooking liquor, absorbed in the fibre to the more diluted 24 washing liquid. Hereby a dilution os obtained, and thus a washing effect.
It is possible to raise the temperature of the washing water 26 in the filtre washer without any greater risk for cooking in the suction 27 leg. The temperature of the washing liquid to ghe filtre is lower than 28 previously.
29 Improved environmental protection _ _ _ _ _ _ _ The foul gases from the digesting plant can be conducted for treatment as a constant, controlled flow.
1 The method according to the invention shall now be described 2 more in detail, reference being made to the accompanying figures, of 3 which 4 fi~ure 1 shows a temperature/time-diagram for a batchwise kra~t pulp di~esting with conventionnl heat recovery;
6 figure 2 shows a corresponding diagram for the method according to the 7 invention;
B fi~ure 3 shows, schematically, a plant for carTying out the method 9 according 'LO the invention.
In the conventional method there are the following steps:
11 1. A - ~ chip filling 12 2. B - C steam blowing l3 3. ~ - D filling of cooking liquor 14 4. D - E heating with low pressure steam
In such cases, when there are disturbances in a pulp plant, 6 for instance at a digester, so that the steam consumption is periodi-7 cally reduced, there is, according to the invention, a possibility to 8 conduct external high pressure steam, i.e. steam from the boiling house, 9 to the equilizing tank, in order to save this steam instead of blowing it into the free air.
11 The new method has many advantages, considering the steam 12 consumption of the plant, the process, the quality of the pulp, the 13 washing efficiency and the environmental protection, which will be t4 obvious from the following list.
Advantages relating to the steam consumption of the plant _________________________________________________________ 16 Theoretically 10~o of the latent heat of the digester content 17 is available in the form of a controlled secondary steam flow. Compared t8 to a conventional heat recove7y system there is thus provided a greater 19 freedom in the choice of utilization of the secondary heat. ~urther, the se~ondary heat is recGvered at a higher enthalpy level than before.
21 The variations in the primary steam flow to the digesting 22 plant can be reduced.
23 Process advantages 24 Generally it can be said, that the best features of the con-2S tinuous and the discontinuous batchwise digesting processes have been 26 combined.
Z7 'rhe secondary heat flow from the digesting plant can be fed, 28 more safely, to different auxiliary processes, as the flows are not 29 influenced by disturbances in the main process.
Improved pulp quality _____________________ ~ The method permits blowing of the digester at a low tempera-~
~ ~ 4 ~ ~13S~0~
"
~L~13S10~
1 ture (90 - 105 C). This socalled "cold blow" means, that the risk for 2 a ruptur~ in the fibre wall by violent expansion of liquid, bound in 3 the fibre, i8 reduced compared to the risk in conventional blow. In 4 this way the strength of the pul~ is improved.
~he variation of the Kappa-Number is reduced, as it is more 6 economical than previously to use a high water/wood-relationship in 7 the digesting 8 If there are disturbances in the subsequent process line 9 (washer, bleaching plant) this method gives an opportunity to let a completed digester charge wait in the digester without reducing the 11 Kappa-Number. Relief gassing of the digester to a pressure not too far l2 from atmospheric pressure and feed of filtrate from the washer lowers 13 the temperature of the pulp, which means, that the reaction velocity of 14 the digesting process is reduced below a level, where the Kappa-Number is influenced.
16 Improved washing efficiency ___________________________ 17 m e free cooking liquor with a high concentration of cooking t8 chemicals and components extracted from the wood are removed from the 19 digester and are rèplaced by a washing liquid with a lower concentration of said substances. Mixing of washing liquid and pulp is carried out 21 partly in the digester and partly in the blowing pipe and in the blowing ~2 tank. In the blowing tank there iB also a diffusion of chemicals from 23 concentrated cooking liquor, absorbed in the fibre to the more diluted 24 washing liquid. Hereby a dilution os obtained, and thus a washing effect.
It is possible to raise the temperature of the washing water 26 in the filtre washer without any greater risk for cooking in the suction 27 leg. The temperature of the washing liquid to ghe filtre is lower than 28 previously.
29 Improved environmental protection _ _ _ _ _ _ _ The foul gases from the digesting plant can be conducted for treatment as a constant, controlled flow.
1 The method according to the invention shall now be described 2 more in detail, reference being made to the accompanying figures, of 3 which 4 fi~ure 1 shows a temperature/time-diagram for a batchwise kra~t pulp di~esting with conventionnl heat recovery;
6 figure 2 shows a corresponding diagram for the method according to the 7 invention;
B fi~ure 3 shows, schematically, a plant for carTying out the method 9 according 'LO the invention.
In the conventional method there are the following steps:
11 1. A - ~ chip filling 12 2. B - C steam blowing l3 3. ~ - D filling of cooking liquor 14 4. D - E heating with low pressure steam
5. E - F heating with high pressure steam 16 6, ~ - G digesting 17 7. G - H tbp blowing 18 8. H - I bottom blowing 19 A - A 300 minutes incl. of 40 minutes intermed. time.
In figure 2 there is disclosed a process diagr~m for the new 21 method, carried out in plant disclosed in figure 3. m is plant comprises 22 a number of digesters, normally 8 - 12 units, of which only one digester 23 with reference 1 is 6hown. Circulation heating is provided by a heat 24 exchanger 2, which i9 provided with a circulation pump 3. External steam i8 fed to heat exchanger 2 through a line 4. The circulating cooking 26 liquor is returned to digester 1 via a line 5 with a valve 6. The line 5 27 i8 connected, via a line 7, provided with a valve 8, to an equalixing 28 tank 9, connected via a line 10, provided with a valve 11, to digester 1.
29 ~rom digester 1 there is drawn a line 12, provided with a valve 13, to a blowing tank, which is not shown. Line 10 is connected to a line 14
In figure 2 there is disclosed a process diagr~m for the new 21 method, carried out in plant disclosed in figure 3. m is plant comprises 22 a number of digesters, normally 8 - 12 units, of which only one digester 23 with reference 1 is 6hown. Circulation heating is provided by a heat 24 exchanger 2, which i9 provided with a circulation pump 3. External steam i8 fed to heat exchanger 2 through a line 4. The circulating cooking 26 liquor is returned to digester 1 via a line 5 with a valve 6. The line 5 27 i8 connected, via a line 7, provided with a valve 8, to an equalixing 28 tank 9, connected via a line 10, provided with a valve 11, to digester 1.
29 ~rom digester 1 there is drawn a line 12, provided with a valve 13, to a blowing tank, which is not shown. Line 10 is connected to a line 14
- 6 - ~13S10~
1 for ~eeding`of new cooking liquor This line is provided with a valve 1 2 A line 16, provided with a valve 17, is connected to the circulating - 3 line, with heat exchanger 2, to a sieve in the di~eOEter bcttom. The ~ bottom of the equalizing tank 9 is connected through a line 18, partly, via a line 19 to a first flash cyclone 20 and partly, via a line 21 to 6 a flash cyclone 22.
1 for ~eeding`of new cooking liquor This line is provided with a valve 1 2 A line 16, provided with a valve 17, is connected to the circulating - 3 line, with heat exchanger 2, to a sieve in the di~eOEter bcttom. The ~ bottom of the equalizing tank 9 is connected through a line 18, partly, via a line 19 to a first flash cyclone 20 and partly, via a line 21 to 6 a flash cyclone 22.
7 m e bottom of flash cyclone 20 is connected, via a line 23 to
8 flash cyclone 22. The steam outlet of flash cyclone 20 is connected,
9 via a line 24 to a steam pipe 25, coming from the top of digester 1.
The lines 24, 25 are also conneoted to the other digesters, which are 11 not shown. The steam outlet of flash cyclone 22 is connected via a line 12 27, to a line 28, coming from the top of digester 1, and provided with 13 a valve 29. Line 28 i9 connected to a heat recovery aggregate 30, from 14 where odorous foul gases are discharged through a line 31. From the liquid outlet of flash cyclone 22 a line 32 goes to a black liquor tank.
16 m e top of equalizing tank 9 is connected, via a line 34, with a valve 17 26 to the top of digester 1. m e top of digester 1 is connected, via a 18 valve 37 to line 28. A line 36, provided with valve 37 is connected to 19 li~e 1G. Line 19 is provided with a valve 38 Line 23 is provided with a valve 3~. Line 21 is provided with a valve 40.
21 me plant operates in the following way:
22 1. A - B chip filling 23 2. B - C steam blowing 24 3. C - D filling of cooking liquor 4. D - E heating with low pressure steam and stea~ from 26 flash cyclone 27 5. E - F heating with high pressure steam 28 6. F - G digesting 29 7. G - ~ discharge of cooking liquor 8. ~ - I top blowing to recovery system _ 7 _ ~13Sl~
1 9 I - J relief gassing to heat recovery a6greg~te 2 10. J - K feed of washing liquid 3 11. K - L increa~e of pressure for blowing of dlgester 4 12. L - M cold blow S 13. M - N final relief gassing 6 A - A 300 minutes incl. of 35 intermed. time.
7 A - B The cip filling is started by opening the digester valve and 8 starting the cip feed. Live steam and secondary steam from the line 24 are fed to the chip filler. When the correct chip level in the digester has been achieved, the valves are shut.
11 ~ - C During the steam blowing the chips are preheated in the diges-l2 ter by adding expanded steam from flash cyclone 20 through l3 valve 3~. At the same time air in the digester is forced out 14 through valve 37 in line 36. The preheating with steam from flash cyclone 20 is continued until the desired temperature 16 or pressure has been achieved in the digester, whereafter valve 17 35 in the line between the digester and the cyclone is shut.
t8 ~y a temperature control means the evacuating valve 37 is 19 shut, when the steam flow reaches the sensing point, of the control system, in iine 36.
21 C - D Cooking liquor is fed to the digester through the bottom 22 sieve. In order to increaee the feeding rate cooking liquor 23 can also be fed through a middle sieve. The black liquor charge 24 can be added, preferably through line 10, with flow control, from the equalizing tank for cooking liquor. ~y this mode of 26 operation live steam is saved.
27 When a sufficient amount of cooking liquor has been fed 28 through line 14 and line 10, valves 11, 15 and 17 are shut.
29 D - E Circulating pump 3 for cooking liquor is started. The indirect heating of cooking liquor with live steam is started with a temperature control, sensing the outlet temperature of the - 8 - 1135~01 1 cbokin~ liquor from heat exch~nger 2. Valve 6 is open and - 2 valve 8 is shut 3 Simultaneously live steam is ~ed to the digester from line 24 4 throu~h valve 33. The feed is interrupted automatically when the digester pressure has risen to a pressure close to that 6 in the flash cyclone.
7 The inert gases, accompanying the expanded stea~ from line 24 8 to the digester, are vented out of the digester via the 9 turpentine degassing line, the valve of which 35 is kept open to some degree during the heating period.
11 E - ~ The rest of the heating period to boiling temperature is 12 carried out indirectly in heat exchanger 2 by live steam.
13 ~ - G Digesting 14 G - H The discharge of free cooking liquor (part of the cooking liquor is bound in the chips) from the digester is carried 16 out during the digesting period in question by aid of the 17 circulating pump for cooking liquor. Valve 6 in the circulating t8 line for cooking liquor is shut, and the valve in the line 19 from heat exchanger 2 to the equalizing tank for cooking liquor and valve 17 on the suction side of pump 3 are opened. The 21 discharge is automatically interrupted when a level indicator 22 at a suitable level in the digester acts to shut valve 8 in 23 the line to the equalizing tank and shuts the circulating 24 pump.
25 H - I The pressure in the digester is lowered by opening valve 33 26 in line 25 from the digester to line 24. The steam valve 33 27 is controlled by a pressure controller, which shuts primarily 28 valve 38 in the pipe fo~r liquid feed from the equalizing tank 29 to cyclone 20, to compensate the load peak, caused by steam feed from the digester.
- 9- ~13Sl~
1 I - J When the pressure of the digester has been lowered down to a 2 value close to that in cyclone 20, valve 33 in line 25 from t 3 the digester will be automatically shut, and cyclone 20 i3 ~ again fed with liquid from the equalizing tank.
The rest of the pressure lowering in the digester i8 carried 6 out by degassing through valve 29 to the heat recovery aggre-7 gate for production of hot water. The load change of the 8 degassing from the digester is measured by a flow meter in 9 line 28. Variations in this flow are compensated primarily by changing the liquid flow to flash cyclone 22 by valve 40, 11 from which thus so much steam is produced, that the sum of l2 the steam flows in lines 27 and 28 will be substantially l3 constant. The steam flow to the heat recovery aggregate for 14 hot water production is measured by a flow meter.
If throttling of vlave 40 would not be enough, valve 29 is 16 ~ secondarily throttled in order to achieve a constant flow sum 17 to aggregate 10. If it is necessary for time reasons, the 18 degassing can be carried out simultaneously through valves 33 19 and 29. Then valve 33 is controlled by the pressure in line 24.
Valve 29 is controlled by the desired flow sum in lines 27 21 and 28.
22 J - K During the degassing period, washing liquid (filtrate from the 23 washer) is fed to the digester through valve 15. Valve 17 is 24 shut. The washing liquid is pumped in through the bottom sieve and the flow is controlled by a level controller, provided at 26 a suitable level. Even valves 35 and 29 in the line for de-27 ga~sing to the heat recovery aggregate are shut.
28 K - L The digester is put under pressure by opening valve 26 to the 29 equalizing tank for cooking liquor.
L - M The content of the digester is blown to the blowing tank.
en the total content has been blown out, valves 13 and 26 in the blowing pipe and the line from the equalizing tank are shut automatica]ly.
~o 1~L3Sl~
t M - N The digester is degassed once more to the heat recovery 2 aggre~ate by vlave 29. With atmospheric pressure in the 3 digester the cap is opened and the digester is ready for a 4 new digesting cycle.
Flash cyclone 20 operates as an integrated part of the 6 digesting system. It makes possible a return of degassing _-- 7 vapors and compensates the mementary degassings and heat 8 demands in the digestin~ plant.
9 The outgoing energy flow~ from the basic system are measured by three flow meters, provided in lines 23, 27 and 28. Data 11 from the flow measurements are fed to a control system, 12 primarily acting upon valve 40 and secondarily acting upon 13 degassing valves 29 and 35.
1~
- 11351C~
The lines 24, 25 are also conneoted to the other digesters, which are 11 not shown. The steam outlet of flash cyclone 22 is connected via a line 12 27, to a line 28, coming from the top of digester 1, and provided with 13 a valve 29. Line 28 i9 connected to a heat recovery aggregate 30, from 14 where odorous foul gases are discharged through a line 31. From the liquid outlet of flash cyclone 22 a line 32 goes to a black liquor tank.
16 m e top of equalizing tank 9 is connected, via a line 34, with a valve 17 26 to the top of digester 1. m e top of digester 1 is connected, via a 18 valve 37 to line 28. A line 36, provided with valve 37 is connected to 19 li~e 1G. Line 19 is provided with a valve 38 Line 23 is provided with a valve 3~. Line 21 is provided with a valve 40.
21 me plant operates in the following way:
22 1. A - B chip filling 23 2. B - C steam blowing 24 3. C - D filling of cooking liquor 4. D - E heating with low pressure steam and stea~ from 26 flash cyclone 27 5. E - F heating with high pressure steam 28 6. F - G digesting 29 7. G - ~ discharge of cooking liquor 8. ~ - I top blowing to recovery system _ 7 _ ~13Sl~
1 9 I - J relief gassing to heat recovery a6greg~te 2 10. J - K feed of washing liquid 3 11. K - L increa~e of pressure for blowing of dlgester 4 12. L - M cold blow S 13. M - N final relief gassing 6 A - A 300 minutes incl. of 35 intermed. time.
7 A - B The cip filling is started by opening the digester valve and 8 starting the cip feed. Live steam and secondary steam from the line 24 are fed to the chip filler. When the correct chip level in the digester has been achieved, the valves are shut.
11 ~ - C During the steam blowing the chips are preheated in the diges-l2 ter by adding expanded steam from flash cyclone 20 through l3 valve 3~. At the same time air in the digester is forced out 14 through valve 37 in line 36. The preheating with steam from flash cyclone 20 is continued until the desired temperature 16 or pressure has been achieved in the digester, whereafter valve 17 35 in the line between the digester and the cyclone is shut.
t8 ~y a temperature control means the evacuating valve 37 is 19 shut, when the steam flow reaches the sensing point, of the control system, in iine 36.
21 C - D Cooking liquor is fed to the digester through the bottom 22 sieve. In order to increaee the feeding rate cooking liquor 23 can also be fed through a middle sieve. The black liquor charge 24 can be added, preferably through line 10, with flow control, from the equalizing tank for cooking liquor. ~y this mode of 26 operation live steam is saved.
27 When a sufficient amount of cooking liquor has been fed 28 through line 14 and line 10, valves 11, 15 and 17 are shut.
29 D - E Circulating pump 3 for cooking liquor is started. The indirect heating of cooking liquor with live steam is started with a temperature control, sensing the outlet temperature of the - 8 - 1135~01 1 cbokin~ liquor from heat exch~nger 2. Valve 6 is open and - 2 valve 8 is shut 3 Simultaneously live steam is ~ed to the digester from line 24 4 throu~h valve 33. The feed is interrupted automatically when the digester pressure has risen to a pressure close to that 6 in the flash cyclone.
7 The inert gases, accompanying the expanded stea~ from line 24 8 to the digester, are vented out of the digester via the 9 turpentine degassing line, the valve of which 35 is kept open to some degree during the heating period.
11 E - ~ The rest of the heating period to boiling temperature is 12 carried out indirectly in heat exchanger 2 by live steam.
13 ~ - G Digesting 14 G - H The discharge of free cooking liquor (part of the cooking liquor is bound in the chips) from the digester is carried 16 out during the digesting period in question by aid of the 17 circulating pump for cooking liquor. Valve 6 in the circulating t8 line for cooking liquor is shut, and the valve in the line 19 from heat exchanger 2 to the equalizing tank for cooking liquor and valve 17 on the suction side of pump 3 are opened. The 21 discharge is automatically interrupted when a level indicator 22 at a suitable level in the digester acts to shut valve 8 in 23 the line to the equalizing tank and shuts the circulating 24 pump.
25 H - I The pressure in the digester is lowered by opening valve 33 26 in line 25 from the digester to line 24. The steam valve 33 27 is controlled by a pressure controller, which shuts primarily 28 valve 38 in the pipe fo~r liquid feed from the equalizing tank 29 to cyclone 20, to compensate the load peak, caused by steam feed from the digester.
- 9- ~13Sl~
1 I - J When the pressure of the digester has been lowered down to a 2 value close to that in cyclone 20, valve 33 in line 25 from t 3 the digester will be automatically shut, and cyclone 20 i3 ~ again fed with liquid from the equalizing tank.
The rest of the pressure lowering in the digester i8 carried 6 out by degassing through valve 29 to the heat recovery aggre-7 gate for production of hot water. The load change of the 8 degassing from the digester is measured by a flow meter in 9 line 28. Variations in this flow are compensated primarily by changing the liquid flow to flash cyclone 22 by valve 40, 11 from which thus so much steam is produced, that the sum of l2 the steam flows in lines 27 and 28 will be substantially l3 constant. The steam flow to the heat recovery aggregate for 14 hot water production is measured by a flow meter.
If throttling of vlave 40 would not be enough, valve 29 is 16 ~ secondarily throttled in order to achieve a constant flow sum 17 to aggregate 10. If it is necessary for time reasons, the 18 degassing can be carried out simultaneously through valves 33 19 and 29. Then valve 33 is controlled by the pressure in line 24.
Valve 29 is controlled by the desired flow sum in lines 27 21 and 28.
22 J - K During the degassing period, washing liquid (filtrate from the 23 washer) is fed to the digester through valve 15. Valve 17 is 24 shut. The washing liquid is pumped in through the bottom sieve and the flow is controlled by a level controller, provided at 26 a suitable level. Even valves 35 and 29 in the line for de-27 ga~sing to the heat recovery aggregate are shut.
28 K - L The digester is put under pressure by opening valve 26 to the 29 equalizing tank for cooking liquor.
L - M The content of the digester is blown to the blowing tank.
en the total content has been blown out, valves 13 and 26 in the blowing pipe and the line from the equalizing tank are shut automatica]ly.
~o 1~L3Sl~
t M - N The digester is degassed once more to the heat recovery 2 aggre~ate by vlave 29. With atmospheric pressure in the 3 digester the cap is opened and the digester is ready for a 4 new digesting cycle.
Flash cyclone 20 operates as an integrated part of the 6 digesting system. It makes possible a return of degassing _-- 7 vapors and compensates the mementary degassings and heat 8 demands in the digestin~ plant.
9 The outgoing energy flow~ from the basic system are measured by three flow meters, provided in lines 23, 27 and 28. Data 11 from the flow measurements are fed to a control system, 12 primarily acting upon valve 40 and secondarily acting upon 13 degassing valves 29 and 35.
1~
- 11351C~
Claims (8)
1. In the batchwise digesting of cellulose in a cooker from which a cellulose mass is to be discharged, the method which comprises feeding cooking liquor and cellulose to said cooker to digest the cellulose, feeding cooking liquor, during a final stage of said digesting, from the cooker to an equalizing tank maintained under pressure, thereafter degassing the cooker to substantially atmospheric pressure, feeding wash-ing liquor, during said degassing, to the cooker and there pre-washing the cellulose mass at a low temperature, and conducting a steam flow from the equalizing tank to the cooker to discharge its content of cellulose mass at a temperature of 90 to 105°C, thereby providing a cold blow.
2. The method of claim 1, in which said washing liquor is filtrate from a filter washer through which cooking liquor is fed to the cooker.
3. The method of claim 1, in which said low temper-ature does not exceed 105°C.
4. The method of claim 1, comprising also performing, after completion of the digesting, the step of withdrawing free liquor from the cooker by suction through a screen in the bottom of the cooker.
5. The method of claim 4, in which said washing liquor is fed to the cooker after said withdrawing step, the washing liquor being fed to the cooker through a screen in the bottom of the cooker in order to distribute the washing liquor evenly in the cooker bottom.
6. The method of claim 1, comprising also conducting cooking liquor under pressure from the equalizing tank to the cooker at an early stage of said digesting.
7. The method of claim 1, comprising also conducting cooking liquor from the equalizing tank to a flash cyclone from which a steam flow and a liquid flow are separately discharged and preheating the cellulose by passing steam to the cooker from said steam flow.
8. The method of claim 1, comprising also conducting cooking liquor from the equalizing tank to a first flash cyclone from which a first steam flow and a first liquid flow are separ-ately discharged, feeding said first liquid flow to a second flash cyclone from which a second steam flow and a second li-quid flow are separately discharged, and feeding to a heat re-covery system said second steam flow combined with a steam flow coming directly from said cooker.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI791205A FI63268C (en) | 1979-04-11 | 1979-04-11 | Procedures for emptying a batch cellulose cooker. |
| SE791205 | 1979-04-11 | ||
| SE7906540A SE435075B (en) | 1979-08-01 | 1979-08-01 | Process for the emptying of pulp from the boiler of a batchwise cellulose boiler |
| SE7906540-5 | 1979-08-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1135101A true CA1135101A (en) | 1982-11-09 |
Family
ID=26157029
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000349532A Expired CA1135101A (en) | 1979-04-11 | 1980-04-10 | Method for secondary heat recovery in batchwise cellulose digesting |
Country Status (8)
| Country | Link |
|---|---|
| AT (1) | AT375692B (en) |
| BR (1) | BR8002271A (en) |
| CA (1) | CA1135101A (en) |
| DE (1) | DE3013825A1 (en) |
| ES (1) | ES490518A0 (en) |
| FR (2) | FR2453934B1 (en) |
| NO (1) | NO157109C (en) |
| PT (1) | PT71072A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4975148A (en) * | 1988-12-06 | 1990-12-04 | Ahlstromforetagen Svenska Ab | Cold blow system for batch production of pulp |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE453673B (en) * | 1985-07-02 | 1988-02-22 | Kamyr Ab | SEE CONTINUOUS COOKING TO HEAT THE FIBER MATERIAL AT THE COOKER'S TOP |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NO115278B (en) * | 1962-03-03 | 1968-09-09 | Kamyr Ab | |
| US3515631A (en) * | 1965-07-14 | 1970-06-02 | Curt Fredrick Rosenblad | Method and system for flushing sulphite pulp digesters |
| US4138311A (en) * | 1977-02-10 | 1979-02-06 | International Paper Company | Method and apparatus for batch production of pulp including improved energy reclamation |
-
1980
- 1980-04-09 PT PT71072A patent/PT71072A/en not_active IP Right Cessation
- 1980-04-10 CA CA000349532A patent/CA1135101A/en not_active Expired
- 1980-04-10 NO NO801036A patent/NO157109C/en unknown
- 1980-04-10 DE DE19803013825 patent/DE3013825A1/en active Granted
- 1980-04-11 ES ES490518A patent/ES490518A0/en active Granted
- 1980-04-11 AT AT0197980A patent/AT375692B/en not_active IP Right Cessation
- 1980-04-11 FR FR8008225A patent/FR2453934B1/en not_active Expired
- 1980-04-11 BR BR8002271A patent/BR8002271A/en not_active IP Right Cessation
-
1984
- 1984-10-18 FR FR8415997A patent/FR2553797B1/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4975148A (en) * | 1988-12-06 | 1990-12-04 | Ahlstromforetagen Svenska Ab | Cold blow system for batch production of pulp |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2453934B1 (en) | 1985-08-23 |
| FR2553797B1 (en) | 1987-01-16 |
| DE3013825C2 (en) | 1987-03-26 |
| FR2453934A1 (en) | 1980-11-07 |
| ES8101160A1 (en) | 1980-12-01 |
| DE3013825A1 (en) | 1980-10-30 |
| BR8002271A (en) | 1980-12-02 |
| ATA197980A (en) | 1984-01-15 |
| NO157109B (en) | 1987-10-12 |
| AT375692B (en) | 1984-08-27 |
| PT71072A (en) | 1980-05-01 |
| FR2553797A1 (en) | 1985-04-26 |
| NO157109C (en) | 1988-01-20 |
| ES490518A0 (en) | 1980-12-01 |
| NO801036L (en) | 1980-10-13 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |