CA1140382A - Process for producing fiberboard wherein dissolved wood matter is separated from the process water - Google Patents
Process for producing fiberboard wherein dissolved wood matter is separated from the process waterInfo
- Publication number
- CA1140382A CA1140382A CA000349325A CA349325A CA1140382A CA 1140382 A CA1140382 A CA 1140382A CA 000349325 A CA000349325 A CA 000349325A CA 349325 A CA349325 A CA 349325A CA 1140382 A CA1140382 A CA 1140382A
- Authority
- CA
- Canada
- Prior art keywords
- water
- wood
- passing
- pulp
- fiber pulp
- 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
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F1/00—Wet end of machines for making continuous webs of paper
- D21F1/66—Pulp catching, de-watering, or recovering; Re-use of pulp-water
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
- C02F1/048—Purification of waste water by evaporation
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
- D21B1/00—Fibrous raw materials or their mechanical treatment
- D21B1/04—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres
- D21B1/12—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres by wet methods, by the use of steam
-
- 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
- D21C11/0021—Introduction of various effluents, e.g. waste waters, into the pulping, recovery and regeneration cycle (closed-cycle)
Landscapes
- Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Wood Science & Technology (AREA)
- Mechanical Engineering (AREA)
- Paper (AREA)
- Dry Formation Of Fiberboard And The Like (AREA)
Abstract
ABSTRACT
A method is disclosed for the separation of dissolved wood substances in process water resulting from the production of wet process wood fiber board.
The system includes, in turn, a preheater, a defibrator, a cyclone, a leaching device and a dewatering device for the ground fiber pulp. In the applicant's method the process water from the dewatering device is led back partly to the defibrator, and partly to an evaporation plant, from which generated water vapor is led to the preheater, thus creating a closed circulation water system including two paths. Surplus steam from the cyclone is led to the evaporation plant for energy generation in the evaporation plant, thus giving the closed water system one more path.
A method is disclosed for the separation of dissolved wood substances in process water resulting from the production of wet process wood fiber board.
The system includes, in turn, a preheater, a defibrator, a cyclone, a leaching device and a dewatering device for the ground fiber pulp. In the applicant's method the process water from the dewatering device is led back partly to the defibrator, and partly to an evaporation plant, from which generated water vapor is led to the preheater, thus creating a closed circulation water system including two paths. Surplus steam from the cyclone is led to the evaporation plant for energy generation in the evaporation plant, thus giving the closed water system one more path.
Description
1:~4V382 This invention is concerned with a method for the production of wet process wood fiber board for the early separation of dissolved wood sub-stances from the process water with the object of benefitting economically from it. It is an object of the invention to avoid quality problems on the end product, e.g. the wood fiber board. It is a further object of the invention to produce an ecologically acceptable waste water for direct discharge into a receiving body of water.
During conventional production of wet process wood fiber board, the wood fiber is freed firstly by preheating wooden chips and/or saw dust and secondly by grinding between two grinding discs, one of which rotates and the other of which is stationary. The grinding can be carried out in one or several steps (of which the finishing ones are called "refining steps"). The preheat-ing takes place in a special preheater by direct injection of steam, usually below 1 mpa and 200 degrees C. During the preheating and the grinding, wood substances are dissolved, which later follow the process water to the Fourdrinier machine and the final pressing of the fiber board, where the water phase is removed as vapor or liquid. The process water is subsequently puri-fied before any discharge from the mill is made. A common purification method is the treatment of the process water in a so called "aeration tank" to lower the B.O.D.7 content, for an average size factory, the investment sum for an aeration tank is about 15 million Swedish crowns. There is also an annual cost of about 4 million Swedish crowns. Despite these formidable expenscs there is no financial return on the investment made in this equipment. Tn order to decrease the water flow some mills have installed closed water systems for recirculating the water. In so doing, the continuously fed pulp will enricl the process water with respect to the B.O.D.7 content. The drawback with these systams are the quality problems on the finished fiber board in form of -- 1 -- , .
,;
8~
indentations caused by contamination of tne caul plates during the consolidat-ing final hot pressing. Furthermore, susoe ptible parts of the production line will be exFosed to significant corr~sion problems.
With the method according to this invention a major part of the water is taken care of already after the dissolving and leachLng of wood sub-stanoe s from the ground wood fiber pulp by means of pressing to at least 60%
dry content. The substan oes, which are dissolved during the hydrolizing grind-ing, are separated from the prooess water in an evaporation plant. Part of the process water can, with advantage, be recirculated into the defibrator and become enriched with respect to dissolved wood substan oes.
The method according to the invention inclu~es, in sucoe ssive order a preheater, a defibrator, a cyclone, a leaching devioe and a dewatering devioe for the ground wood fiber pulp. Ihe invention is characterized by the fact that the pnocess water from the dewatering device is led back partly to the defibrator and partly to an evaporation plant, from which the generated water vapor is led to the preheater, thus creating a closed circulating water system which includes two paths.
The leading of surplus water vapor from the cyclone to the evapora-tion plant to be used as a souroe of energy, adds a third path to the closed water sysb~m.
According to the present invention, there is provided an improvement in the wet prooess production of wcod fiber board in which dissolved wood substances are separated f mm process water comprising heating wood source material selected from the group consisting of wood chips and sawdust in a preheater wi~l steam, passing the heated wood source material to a grinding zone of a difibrator wherein the wood source material is formed into wet fiber pulp comprising wood fibers and dissolved wood substan oes in water, passing the wet fiber pulp to a cyclone separator wherein steam is removed and
During conventional production of wet process wood fiber board, the wood fiber is freed firstly by preheating wooden chips and/or saw dust and secondly by grinding between two grinding discs, one of which rotates and the other of which is stationary. The grinding can be carried out in one or several steps (of which the finishing ones are called "refining steps"). The preheat-ing takes place in a special preheater by direct injection of steam, usually below 1 mpa and 200 degrees C. During the preheating and the grinding, wood substances are dissolved, which later follow the process water to the Fourdrinier machine and the final pressing of the fiber board, where the water phase is removed as vapor or liquid. The process water is subsequently puri-fied before any discharge from the mill is made. A common purification method is the treatment of the process water in a so called "aeration tank" to lower the B.O.D.7 content, for an average size factory, the investment sum for an aeration tank is about 15 million Swedish crowns. There is also an annual cost of about 4 million Swedish crowns. Despite these formidable expenscs there is no financial return on the investment made in this equipment. Tn order to decrease the water flow some mills have installed closed water systems for recirculating the water. In so doing, the continuously fed pulp will enricl the process water with respect to the B.O.D.7 content. The drawback with these systams are the quality problems on the finished fiber board in form of -- 1 -- , .
,;
8~
indentations caused by contamination of tne caul plates during the consolidat-ing final hot pressing. Furthermore, susoe ptible parts of the production line will be exFosed to significant corr~sion problems.
With the method according to this invention a major part of the water is taken care of already after the dissolving and leachLng of wood sub-stanoe s from the ground wood fiber pulp by means of pressing to at least 60%
dry content. The substan oes, which are dissolved during the hydrolizing grind-ing, are separated from the prooess water in an evaporation plant. Part of the process water can, with advantage, be recirculated into the defibrator and become enriched with respect to dissolved wood substan oes.
The method according to the invention inclu~es, in sucoe ssive order a preheater, a defibrator, a cyclone, a leaching devioe and a dewatering devioe for the ground wood fiber pulp. Ihe invention is characterized by the fact that the pnocess water from the dewatering device is led back partly to the defibrator and partly to an evaporation plant, from which the generated water vapor is led to the preheater, thus creating a closed circulating water system which includes two paths.
The leading of surplus water vapor from the cyclone to the evapora-tion plant to be used as a souroe of energy, adds a third path to the closed water sysb~m.
According to the present invention, there is provided an improvement in the wet prooess production of wcod fiber board in which dissolved wood substances are separated f mm process water comprising heating wood source material selected from the group consisting of wood chips and sawdust in a preheater wi~l steam, passing the heated wood source material to a grinding zone of a difibrator wherein the wood source material is formed into wet fiber pulp comprising wood fibers and dissolved wood substan oes in water, passing the wet fiber pulp to a cyclone separator wherein steam is removed and
- 2 ~
~U382 passing the fiber pulp to a leaching device where m the fiber pulp is leached and passing the leached fiher pulp to a dewatering device wherein a portion of the water containing dissolved wood substances in the leached fiber pulp is removed and passing the dewatered leached pulp to a pulp holding device in preparation for further grinding and dewatering and hot pressing into fiber board, the improvement comprising taking off sufficient water in the dewatering device to provide a dewatered leached fiber pulp having a dry content of at least 60% by weight, and passing a portion of said water containing dissolved wcod substances taken off at the dewatering device back through the defibrator, and passing another portion of said water containing dissolved wccd substanoe s taken off at the dewatering device to an evaporator wherein it is heated to evaporate the water as steam which is passed to the preheater and to separate therefrom the dissolved wood substances as an evaporation residue, and passing the steam remDved in the cyclone separator to the evaporator and utilizing said steam as a Source of heat therein, thereby creating three closed loops in the prooe ss water system.
The method according to the invention is easily visualized by the attached schematic drawing which is in the nature of a flow sheet. Ihe parts of the apparatus used are numbered as follows:-1. Preheater 2. Defibrator
~U382 passing the fiber pulp to a leaching device where m the fiber pulp is leached and passing the leached fiher pulp to a dewatering device wherein a portion of the water containing dissolved wood substances in the leached fiber pulp is removed and passing the dewatered leached pulp to a pulp holding device in preparation for further grinding and dewatering and hot pressing into fiber board, the improvement comprising taking off sufficient water in the dewatering device to provide a dewatered leached fiber pulp having a dry content of at least 60% by weight, and passing a portion of said water containing dissolved wcod substances taken off at the dewatering device back through the defibrator, and passing another portion of said water containing dissolved wccd substanoe s taken off at the dewatering device to an evaporator wherein it is heated to evaporate the water as steam which is passed to the preheater and to separate therefrom the dissolved wood substances as an evaporation residue, and passing the steam remDved in the cyclone separator to the evaporator and utilizing said steam as a Source of heat therein, thereby creating three closed loops in the prooe ss water system.
The method according to the invention is easily visualized by the attached schematic drawing which is in the nature of a flow sheet. Ihe parts of the apparatus used are numbered as follows:-1. Preheater 2. Defibrator
3. Cyclone
4. Leaching device - 2a -4038~
5. Dewatering device ~pTess)
6. Evaporation plant
7. Pulp chest Wood chips and/or saw dust are fed by a conventional screw-feeder into the preheater 1, in which water vapor is injected. After the preheating, the wood fibers are fed into the grinding zone of the defibrator 2 and the fibers are defibrated to pulp. The pulp is led to the cyclone 3, and, there-after, to the leaching device ~ and the dewatering device 5, which preferably is a screw-press, and, finally, to the pulp chest 7. After the pulp chest 7, the pulp is further ground in a refiner and led to the Fourdrinier machine and the hot press, in which the finished wood fiber board is produced. The latter steps of production are not included in Figure 1. Since they are conventional and well-known to those skilled in the pulp mill art. The water that is squeezed out of dewatering device 5 is, depending on the circumstances, divided between the defibrator 2 and the evaporation plant 6. The generated water vapor from evaporation tank 6 is led to the preheater 1. The cyclone 3 is connected with the evaporator 6, to which the excess water vapor can be fed and used as a source of energy.
The method according to the invention has scveral advantages.
(a) The total amount of contamination in the process water will be low because the contaminants have been concentrated in the water that has al-ready been separated in the dewatering device. The contamination is then fod to the evaporation plant.
(b) Excessive quantities of water into the defibrator can be reduced by recirculating the water from the dewatering device to the defibrator.
The amount of recirculated water is settled by the concentration of dissolved wood substances, which in turn are settled by the water vapor pressure and temperature, plus the type of wood.
_ 3 -i . !
~U~82 ~ c) The yield of the process is affected positively since the defibrator is fed with water which already contains dissolved wood substances.
In the reaction wood (in the defibrator) ~ wood fiber + dissolved wood substances the dissolving of wood is retarded, which increases the yield of wood fiber in relation to wood. The system is economically advantageous, as the amount of water, containing the main part of in the process dissolved and suspended substances, is only a few percent of the total amount of process water. A fur-ther enrichment by evaporation is therefore economically interesting. The evaporation residue can be used either as a fuel or sold as feedstuff for cattle.
(d) The surplus energy from the cyclone can be utili~ed for evapora-tion, and the excess energy from the evaporation plant can, in turn, be used for preheating of the raw material or the process water.
(e) The economy of the process can be further improved by allowing the subsequent refining step to be made under optimum dry content, which posi-tively influences the energy construction.
(f) By separating dissolved wood substances from the process water in an early stage of the process, a relatively pure water is released from later steps in the process, which adds to higher product quality at the hot pressing to finished boards.
(g) An important condition in obtaining the preclictccl result is thilt the press, after the defibrator, is about to givc a dry contcnt of the fibcr pulp, that is about that which is to be present when, in the hot press, the final pressing and evaporation step to a finished fiber boarcl is to begin.
The following numerical Examples are mcant to provide a betlter uncler-standing of the enviromnental value of the method of the invention:-Production of 400 metric tons hardboard, utilizing the system according to the invention.
Dry content of the fiber pulp after the screw-press ~dewater device 5) - 60%.
The final process water for discharge to the receiving body of water contains about 6.5 kgs B.O.D.7 per metric ton of board.
The corresponding discharge. without utilizing the system according to the invention, would be about 27 kgs B.O.D.7 per metric ton board.
Production of 365 metric tons hardboard and 35 metric tons of semi-hardboard, utilizing the system according to the invention.
Dry content of the fiber pulp after the screw-press (dewatering device 5) - 60%.
The final process water for discharge in the receiving body of water contains about 7 kgs B.O.D.7 per metric ton board.
The corresponding discharge, without utilizing the system according to the invention, would be about 30 kgs B.O.D.7 per metric ton board.
:, .l,f~i..,
The method according to the invention has scveral advantages.
(a) The total amount of contamination in the process water will be low because the contaminants have been concentrated in the water that has al-ready been separated in the dewatering device. The contamination is then fod to the evaporation plant.
(b) Excessive quantities of water into the defibrator can be reduced by recirculating the water from the dewatering device to the defibrator.
The amount of recirculated water is settled by the concentration of dissolved wood substances, which in turn are settled by the water vapor pressure and temperature, plus the type of wood.
_ 3 -i . !
~U~82 ~ c) The yield of the process is affected positively since the defibrator is fed with water which already contains dissolved wood substances.
In the reaction wood (in the defibrator) ~ wood fiber + dissolved wood substances the dissolving of wood is retarded, which increases the yield of wood fiber in relation to wood. The system is economically advantageous, as the amount of water, containing the main part of in the process dissolved and suspended substances, is only a few percent of the total amount of process water. A fur-ther enrichment by evaporation is therefore economically interesting. The evaporation residue can be used either as a fuel or sold as feedstuff for cattle.
(d) The surplus energy from the cyclone can be utili~ed for evapora-tion, and the excess energy from the evaporation plant can, in turn, be used for preheating of the raw material or the process water.
(e) The economy of the process can be further improved by allowing the subsequent refining step to be made under optimum dry content, which posi-tively influences the energy construction.
(f) By separating dissolved wood substances from the process water in an early stage of the process, a relatively pure water is released from later steps in the process, which adds to higher product quality at the hot pressing to finished boards.
(g) An important condition in obtaining the preclictccl result is thilt the press, after the defibrator, is about to givc a dry contcnt of the fibcr pulp, that is about that which is to be present when, in the hot press, the final pressing and evaporation step to a finished fiber boarcl is to begin.
The following numerical Examples are mcant to provide a betlter uncler-standing of the enviromnental value of the method of the invention:-Production of 400 metric tons hardboard, utilizing the system according to the invention.
Dry content of the fiber pulp after the screw-press ~dewater device 5) - 60%.
The final process water for discharge to the receiving body of water contains about 6.5 kgs B.O.D.7 per metric ton of board.
The corresponding discharge. without utilizing the system according to the invention, would be about 27 kgs B.O.D.7 per metric ton board.
Production of 365 metric tons hardboard and 35 metric tons of semi-hardboard, utilizing the system according to the invention.
Dry content of the fiber pulp after the screw-press (dewatering device 5) - 60%.
The final process water for discharge in the receiving body of water contains about 7 kgs B.O.D.7 per metric ton board.
The corresponding discharge, without utilizing the system according to the invention, would be about 30 kgs B.O.D.7 per metric ton board.
:, .l,f~i..,
Claims (3)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An improvement in the wet process production of wood fiber board in which dissolved wood substances are separated from process water comprising heating wood source material selected from the group consisting of wood ships and sawdust in a preheater with steam, passing the heated wood source material to a grinding zone of a difibrator wherein the wood source material is formed into wet fiber pulp comprising wood fibers and dissolved wood substances in water, passing the wet fiber pulp to a cyclone separator wherein steam is removed and passing the fiber pulp to a leaching device wherein the fiber pulp is leached and passing the leached fiber pulp to a dewatering device wherein a portion of the water containing dissolved wood substances in the leached fiber pulp is removed and passing the dewatered leached pulp to a pulp holding device in preparation for further grinding and dewatering and hot pressing into fiber board, the improvement comprising taking off sufficient water in the dewatering device to provide a dewatered leached fiber pulp having a dry content of at least 60% by weight, and passing a portion of said water contain-ing dissolved wood substances s taken off at the dewatering device back through the defibrator, and passing another portion of said water containing dissolved wood substances taken off at the dewatering device to an evaporator wherein it is heated to evaporate the water as steam which is passed to the preheater and to separate therefrom the dissolved wood substances s as an evaporation residue, and passing the steam removed in the cyclone separator to the evaporator and utilizing said steam as a source of heat therein thereby creating three closed loops in the process water system.
2. me process of claim 1 wherein the dewatering device is a screw press.
3. me process of claim 1 or 2 wherein the dewatering device removes sufficient water so that the dry content of the dewatered leached fiber pulp is greater than the dry content of fiber pulp which is used as feed to the hot pressing stage of a oonventional processing of fiber board.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE7903177-9 | 1979-04-10 | ||
| SE7903177A SE417847B (en) | 1979-04-10 | 1979-04-10 | PROCEDURE FOR SEPARATION OF DISSOLVED SUBSTANCES FROM THE PROCESSING WATER IN THE MANUFACTURE OF FIBER DISC |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1140382A true CA1140382A (en) | 1983-02-01 |
Family
ID=20337781
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000349325A Expired CA1140382A (en) | 1979-04-10 | 1980-04-08 | Process for producing fiberboard wherein dissolved wood matter is separated from the process water |
Country Status (5)
| Country | Link |
|---|---|
| CA (1) | CA1140382A (en) |
| FI (1) | FI801098A (en) |
| FR (1) | FR2453935B1 (en) |
| NO (1) | NO801000L (en) |
| SE (1) | SE417847B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE466605B (en) * | 1984-10-29 | 1992-03-09 | Kamyr Ab | CONSTRUCTION AND PROCEDURE KIT FOR MANUFACTURING MECHANICAL Pulp |
| US4692214A (en) * | 1984-10-29 | 1987-09-08 | Kamyr Ab | Apparatus for producing mechanical pulp with a refiner having its drive shaft connected to a steam turbine output shaft |
| US5053108A (en) * | 1989-06-28 | 1991-10-01 | Kamyr Ab | High sulfidity cook for paper pulp using black liquor sulfonization of steamed chips |
-
1979
- 1979-04-10 SE SE7903177A patent/SE417847B/en unknown
-
1980
- 1980-04-08 FI FI801098A patent/FI801098A/en not_active Application Discontinuation
- 1980-04-08 CA CA000349325A patent/CA1140382A/en not_active Expired
- 1980-04-08 NO NO801000A patent/NO801000L/en unknown
- 1980-04-10 FR FR8008042A patent/FR2453935B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| FR2453935B1 (en) | 1986-02-21 |
| SE417847B (en) | 1981-04-13 |
| FI801098A (en) | 1980-10-11 |
| NO801000L (en) | 1980-10-13 |
| FR2453935A1 (en) | 1980-11-07 |
| SE7903177L (en) | 1980-10-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |