CA2240861C - A storage silo for lime mud product - Google Patents
A storage silo for lime mud product Download PDFInfo
- Publication number
- CA2240861C CA2240861C CA002240861A CA2240861A CA2240861C CA 2240861 C CA2240861 C CA 2240861C CA 002240861 A CA002240861 A CA 002240861A CA 2240861 A CA2240861 A CA 2240861A CA 2240861 C CA2240861 C CA 2240861C
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- Canada
- Prior art keywords
- lime
- liquor
- lime mud
- green liquor
- mud
- 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.)
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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C11/00—Regeneration of pulp liquors or effluent waste waters
- D21C11/0064—Aspects concerning the production and the treatment of green and white liquors, e.g. causticizing green liquor
- D21C11/0078—Treatment of green or white liquors with other means or other compounds than gases, e.g. in order to separate solid compounds such as sodium chloride and carbonate from these liquors; Further treatment of these compounds
-
- 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
- Y02P40/00—Technologies relating to the processing of minerals
- Y02P40/40—Production or processing of lime, e.g. limestone regeneration of lime in pulp and sugar mills
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- Paper (AREA)
- Treatment Of Sludge (AREA)
Abstract
Process for preparation of white liquor. Black liquor is burned and the smel t is dissolved to make a green liquor. The green liquor is pressure filtered before it is causticised to produce white liquor. The white liquor is pressure filtered and the lime sludge is washed and dried in the filter. The lime sludge has a dry substance of 75-85 % when it is brought to a storage container before it is dispensed to the lime oven. A storage container for lime sludge. The container comprises an upper part which opens downwards, a lower discharge part which opens upwards and a discharge end with an discharge opening which open s downward.
Description
A Storage Silo for Lime Mud Product The present invention relates to a method of producing white liquor by dissolving chemical smelt obtained from evaporating and burning of block liquor, by causticizing the green liquor formed in the dissolution, by separating lime mud (calcium carbonate) and burning it to lime (calcium oxide) to be used in causticizing of green liquor. The method of the invention is characterized in that a) before causticizing, suspended solids are directly removed irorn green liquor by pressure filtration to get green liquor with a suspended solids, i.e. dregs content of less than 20 mgli, b) lime mud (calcium carbonate) is separated directly by pressure filtration while the lime mud cake is simultaneously washed and dried to pro-duce a lime mud product with a dry solids content of 75-88% by weight. anti c) the lime mud product is led to a storage silo from where i'c is dis-charged and fed 'as an even flow to a lime kiln and burned to lime (calcium oxide).
It is an object of the invention to provide an improved method by simplifying the soda recovery plant and the causticizing process of a sulphate pulp mill, to improve the quality of the product, white liquor, and to decrease the amount of green liquor dregs and resulting weak liquor. In addition, purer green liquor and a drier lime mud product is obtained.
In present causticizing processes employed at sulphate pulp mills, the smelt from a recovery boiler is dissolved in a smelt dissolves in weak liquor and other process waters to give green liquor. Green liquor is usually leci via an equalizing tank to a green liquor clarifies. In the green liquor clarifies dregs are separated. Clarified green liquor is led to a green Liquor tank and then to a lime slakes. The dregs separated in the green Liquor clarifies are led by a pumping system to a dregs filter and the resulting dregs cake is dumped, and the filtrate is led to a weak liquor tank. In the lime slakes burnt lime is slaked with green liquor to form a lime mud-white liquor mixture, lime milk. This mix-ture is led to a causticizing tank where the causticizing reaction is completed From the causticizing tank lime milk is led to a white liquor filter from where fil-trated clarified white liquor is led to a digester. The separated solids. limp r~irl~l, and part of the white liquor are led to a lime mud silo and suspended in warm water. After filtration, the dry solids content of time mud is about 30-40°,~~ F=rorn the silo the lime mud suspension is led to a lime mud filter from where th;:
Irme mud, washed with water, is led to a lime kiln and burned. After the filter the dry solids content of lime mud is generally at least about 70%. The filtrate ob- .
tained from the wash filter is led to a weak liquor tank. Burnt lime obtained from the lime kiln is led to (ime storage from where the burnt time is fed to the , lime slaker.
Present causticizing processes generally use a large green liquor cfarifier to separate dregs from green liquor, which involves major investment and emptying costs. Moreover, the dregs suspension produced has a low dry solids content.
In present causticizing processes, time mud and white liquor are usually separated in a tube filter comprising perforated tubes that are covered with filter cloth and hang in the lime mud suspension, and through which white liquor is pressed. The dry solids content of the removed lime mud is about 30-35%. In the next wash step Time mud is washed by diluting with water and subsequent concentration. The dry solids content of the produced lime mud is about 35%. The Time mud suspension is filtered and the time mud washed by displacement in a vacuum filter, generally giving the removed lime mud a dry solids content of at least about 70%, but less than 75%.
A method of separating white liquor and Time mud, and green liquor and green liquor slurry, in two steps is knawn for example from publication FI
87,347. The lime mud containing white liquor obtained in the first step, and correspondingly the green liquor slurry, is diluted with water and possibly stored, and in the second filtering step pure lime mud, and correspondingly relatively dry green liquor waste is obtained, and quite large amounts of weak liquor.
Publication FI 923,127 discloses a method of filtering the causticiz-ing product and of increasing the dry solids content of the separated suspen-sion. the separation of white liquor and the washing and drying of the lime mud usually taking place in one process step. A pressure filter is preferably used as filter. the lime mud dry solids content after filtration being high, about 75%. The lime mud can then be dried by e.g. pressurized air. No mention is made ' whether the resulting lime mud can be stored, or if it can be transferred to a kiln as an even flow. ' Variations in properties of filtered, washed and dried lime slurry, i.e.
dry solids content, residual alkali, and particle size and structure, cause changes in the quality of burnt Time in known causticizing processes. Addition-ally, variations in lime slurry dosage affect lime burning. The even feed of the invention improves the use of a lime kiln and reduces variations in product quantity, i.e. burnt lime. The properties of burnt lime, e.g., particle size, affect lime slaking and the causticizing reaction.
The method of the invention is also simpler than known methods: a significant part of the equipment used in known methods can be omitted. Green liquor is filtered directly in one device, and the suspended solids, i.e.
dregs content of clarified green liquor is less than 20 mg/I, a further advantage being the high dry solids content, 55-75% by weight, of the separated dregs. Cleaner green liquor affects advantageously the rest of the causticizing process as the amount of harmful suspended solids reduces. White liquor and lime mud are also separated, and lime mud washed and dried, with a single device, the dry solids content of the lime mud product being high, 75-85% by weight. The dregs content of white liquor is generally less than 20 mg/I. Only about 0.8-1 m3 per ton of dry lime mud of wash water is needed. Moreover, the residual alkali of the lime mud can be adjusted, for example to less than 0.1 % by weight calculated as Na20. Good quality green liquor used in the causticizing reaction produces a purer and more homogeneous lime mud. Feeding a homogeneous lime mud product from a lime mud storage silo to a kiln simplifies kiln adjustment and reduces the need for drying energy thereby lowering costs. It may be mentioned that the yield of white liquor is high.
The invention also relates to a storage silo for a lime mud product applicable to the method of the invention.
Accordingly, an aspect of the invention provides for a storage silo for a lime mud product, the silo comprising of an upper part that opens downwards and a discharge part at a lower end of said silo, said discharge part opening upwards and having a discharge end that opens downwards, said discharge end comprising a discharge outlet.
In the following the method and the storage silo of the invention will be described in greater detail.
Figure 1 shows the process steps of the method of the invention.
Figure 2 shows filtration and washing steps in a pressure filter applicable to the method of the invention.
3a Figure 3 shows a lime mud storage silo applicable to the method of the invention.
In Figure 1, numeral 35 refers to a take-off line for feeding smelt to a smelt dissolver 1 from a recovery unit (not shown). The smelt dissolver for producing green liquor comprises an agitator 2. A line 27 for weak liquor also ends in the smelt dissolver. A line 3 for thick green liquor leads from the smelt dissolver to an equalizing tank 4 for green liquor feed, from where green liquor is fed by means of a pumping system 6 automatically to an intermittently oper-ating pressure filter 8. A conveyor 36 for lime mud or burnt lime ends in the equalizing tank 4 and can be employed to add liri~e mud or burnt lime used as additive in the filtration. A return line 9 for filtrated green liquor. a prefiltrate, ends in the equalizing tank 4, which comprises an agitator 5. A return fine 7 for pumping green liquor also ends in the equalizing tank and is used when no green liquor is fed in a filtering cycle. The pressure filter 8 separates sus-pended solids, i.e. dregs 37, from green liquor. Filtrated clarified green liquor is conveyed via a line 10 to an air separator 11 for green liquor, from where the green liquor is then led via a line 12 to a storage tank 13 for green liquor.
From the storage tank the green liquor is fed via a sine 14 to a lime slaker 15.
The green liquor dregs in the filter 8 are dried by diaphragm pressing and air.
Air is separated from clarified green liquor by the air separator 11.
An alternative is to add burnt lime or lime mud to green liquor via the conveyor 36 to the equalizing tank 4. Adding burnt Time or lime mud con tributes to the filtration and adds to filtrate capacity, which can also be influ enced by changing the feeding pressure of green liquor.
A fine 16 for a mixture of lime mud product and white liquor, lime milk, leads from the lime slaker 15 to a causticizing tank 17. Lime milk is con-veyed from the causticizing tank by means of a pumping system 19 via a fine 18 to a pressure filter 21 which separates white liquor and lime mud. A fine for feeding white liquor filtrate, a prefiltrate, also ends in the causticizing tank.
Filtered white liquor flows via a line 22 to a digester {not shown). From the pressure filter 21 weak liquor is led via a line 23 to an air separator 24 where air is separated from weak liquor and weak liquor is led via a fine 25 to a weak liquor tank 26, and then via a line 27 to the smelt dissoiver 2. The lime mud that was separated, air dried and washed with water in the pressure filter 21, is led by a conveyor 28 to a lime mud silo 29 from where the lime mud is dis-charged and fed by a conveyor 30 as an even flow to the inlet of a lime kiln 31.
The residua! alkali of the lime mud separated in the filter can be adjusted.
The burnt lime is conveyed from the lime kiln via a conveyor 32 to a lime silo 33 and from there the burnt lime is fed via a fine or a conveyor 34 to the lime slaker 15.
Figure 2 shows the principle of a pressure filter applicable to a method of the invention in different steps. fn step 1 slurry is fed via a distribu-for line and feeding lines to the chambers of a closed and sealed fitter plate pack, whereby the solids gather on the filter cloth forming a cake. The filtrate penetrates the cloth and flows to the filtrate space and from there via a tube in the plate to the collector line at the discharge side. Diaphragm pressing is used in filtering green liquor but not in filtering white liquor. After this.
in ~fep 2, the filtrate remaining in the chambers is pressed by means of chamber dia-5 phragms and pressure through the cloth to the filtrate side by leading pressing water through the tubes in the plates and the bottom plates to a space at~ove the rubber diaphragms. An alternative to diaphragm pressing is air cJryinc~
which can be used to replace the first diaphragm pressing in step 2 and to eliminate the second diaphragm pressing in step 4. Air drying is used as an alternative in filtering lime mud.
At the end of the pressing, in step 3, the cake remaining on the cloth is washed with water, whereby the water lifts the press diaphragms against the chamber plates, and the wash filtrate penetrates the filtrate side of the cake and the cloth. to the collector fine. Wash water is fed to the filter chambers via the same distributor line as the slurry. The dregs cake formed in filtering green liquor is not washed, whereas the lime mud cake formed in white liquor filtration is washed with warm water. After the cake has been washed, in step 4, the washing liquid remaining in the cake is pressed from it by a second diaphragm pressing to the filtrate side and is led to the air sepa-rator of the weak liquor tank. The second diaphragm pressing is sirnil~r to the first one. After the second diaphragm pressing, in stage 5, the cake is dried with pressure air coming from the distributor line. When air fills the chambers, it lifts the pressing diaphragms up and the water in the chambers is reraovc:d to the filtrate side. After air drying, in step 6, the filter plate pack is opened to an upper position and emptied by moving the filter cloth forward. The cake is discharged to conveyors on bath sides of the filter.
The structure of the storage silo and the discharger for limo rnud product play a significant role in successful storage. For continuous process . ing, it is vital to choose the right solution for a substance that is difficult to han dle. The structure of the storage silo is shown in detail in Figure 3.
A storage silo 100 for lime mud product consists of an upper part 110 and a discharge part 120 below it. The properties of the lime mud product determine the length and breadth of the upper part. The longitudinal walls of the upper part open downwards at an 1-2° angle, and the upper part is thermally insulated.
The longitudinal wails of the discharge part open upwards and advantageously at a 15-30°
angle for the normal pressure of the lime mud load not to disturb the operation of the discharges. The wall (spout) of the discharge end 7 30 of the dis-charge part opens downwards at a 30-60.° angle. The discharge opening in the spout is arched at spout level. The other end of the discharge hart is closed. The lower part is overlaid with an antiadhesive coating determined by the properties of the lime mud product; suitable coatings include epoxy resin and polyfluoroethylene. The wall angles of the discharge part are rounded.
The lime mud storage operates continuously and lime mud can be discharged at a desired even flow from the silo by using the right discharges.
If needed, the discharge of lime mud storage can be interrupted even with full storage, and lime mud discharge can be resumed even after several days.
In a test run with an about 20m' Time mud storage. the lime mud storage was filled with lime mud having a dry solids content of 76-30°.o by weight while the discharges was on, and then the discharges was hafted anti the lime mud was left in the silo for three days. in spite of winter conditions (-10EC), it was possible to discharge the lime mud as an even flow after the halt. The discharged lime mud had a dry solids content of 78-80% by weight.
The method of the invention offers following advantages compare d with known methods:
- less requirements on space and structure - less eqriipment to be maintained .
- higher dry solids content of green liquor slurry and less r~rcen liq-uor dregs waste - lower dregs content in clear green liquor - lower amount of circulating process impurities due to efficient rli-sect filtration of green liquor - less energy needed as the temperature of e.g. the filtrated white liquor remains high .
- higher dry solids content of lime mud - muse even use of lime kiln due to adjustable residual alkali and dry solids content of lime mud - lower suspended solids content in white liquor - less weak liquor per m3 of white liquor less drying energy needed in Time kiln. '
It is an object of the invention to provide an improved method by simplifying the soda recovery plant and the causticizing process of a sulphate pulp mill, to improve the quality of the product, white liquor, and to decrease the amount of green liquor dregs and resulting weak liquor. In addition, purer green liquor and a drier lime mud product is obtained.
In present causticizing processes employed at sulphate pulp mills, the smelt from a recovery boiler is dissolved in a smelt dissolves in weak liquor and other process waters to give green liquor. Green liquor is usually leci via an equalizing tank to a green liquor clarifies. In the green liquor clarifies dregs are separated. Clarified green liquor is led to a green Liquor tank and then to a lime slakes. The dregs separated in the green Liquor clarifies are led by a pumping system to a dregs filter and the resulting dregs cake is dumped, and the filtrate is led to a weak liquor tank. In the lime slakes burnt lime is slaked with green liquor to form a lime mud-white liquor mixture, lime milk. This mix-ture is led to a causticizing tank where the causticizing reaction is completed From the causticizing tank lime milk is led to a white liquor filter from where fil-trated clarified white liquor is led to a digester. The separated solids. limp r~irl~l, and part of the white liquor are led to a lime mud silo and suspended in warm water. After filtration, the dry solids content of time mud is about 30-40°,~~ F=rorn the silo the lime mud suspension is led to a lime mud filter from where th;:
Irme mud, washed with water, is led to a lime kiln and burned. After the filter the dry solids content of lime mud is generally at least about 70%. The filtrate ob- .
tained from the wash filter is led to a weak liquor tank. Burnt lime obtained from the lime kiln is led to (ime storage from where the burnt time is fed to the , lime slaker.
Present causticizing processes generally use a large green liquor cfarifier to separate dregs from green liquor, which involves major investment and emptying costs. Moreover, the dregs suspension produced has a low dry solids content.
In present causticizing processes, time mud and white liquor are usually separated in a tube filter comprising perforated tubes that are covered with filter cloth and hang in the lime mud suspension, and through which white liquor is pressed. The dry solids content of the removed lime mud is about 30-35%. In the next wash step Time mud is washed by diluting with water and subsequent concentration. The dry solids content of the produced lime mud is about 35%. The Time mud suspension is filtered and the time mud washed by displacement in a vacuum filter, generally giving the removed lime mud a dry solids content of at least about 70%, but less than 75%.
A method of separating white liquor and Time mud, and green liquor and green liquor slurry, in two steps is knawn for example from publication FI
87,347. The lime mud containing white liquor obtained in the first step, and correspondingly the green liquor slurry, is diluted with water and possibly stored, and in the second filtering step pure lime mud, and correspondingly relatively dry green liquor waste is obtained, and quite large amounts of weak liquor.
Publication FI 923,127 discloses a method of filtering the causticiz-ing product and of increasing the dry solids content of the separated suspen-sion. the separation of white liquor and the washing and drying of the lime mud usually taking place in one process step. A pressure filter is preferably used as filter. the lime mud dry solids content after filtration being high, about 75%. The lime mud can then be dried by e.g. pressurized air. No mention is made ' whether the resulting lime mud can be stored, or if it can be transferred to a kiln as an even flow. ' Variations in properties of filtered, washed and dried lime slurry, i.e.
dry solids content, residual alkali, and particle size and structure, cause changes in the quality of burnt Time in known causticizing processes. Addition-ally, variations in lime slurry dosage affect lime burning. The even feed of the invention improves the use of a lime kiln and reduces variations in product quantity, i.e. burnt lime. The properties of burnt lime, e.g., particle size, affect lime slaking and the causticizing reaction.
The method of the invention is also simpler than known methods: a significant part of the equipment used in known methods can be omitted. Green liquor is filtered directly in one device, and the suspended solids, i.e.
dregs content of clarified green liquor is less than 20 mg/I, a further advantage being the high dry solids content, 55-75% by weight, of the separated dregs. Cleaner green liquor affects advantageously the rest of the causticizing process as the amount of harmful suspended solids reduces. White liquor and lime mud are also separated, and lime mud washed and dried, with a single device, the dry solids content of the lime mud product being high, 75-85% by weight. The dregs content of white liquor is generally less than 20 mg/I. Only about 0.8-1 m3 per ton of dry lime mud of wash water is needed. Moreover, the residual alkali of the lime mud can be adjusted, for example to less than 0.1 % by weight calculated as Na20. Good quality green liquor used in the causticizing reaction produces a purer and more homogeneous lime mud. Feeding a homogeneous lime mud product from a lime mud storage silo to a kiln simplifies kiln adjustment and reduces the need for drying energy thereby lowering costs. It may be mentioned that the yield of white liquor is high.
The invention also relates to a storage silo for a lime mud product applicable to the method of the invention.
Accordingly, an aspect of the invention provides for a storage silo for a lime mud product, the silo comprising of an upper part that opens downwards and a discharge part at a lower end of said silo, said discharge part opening upwards and having a discharge end that opens downwards, said discharge end comprising a discharge outlet.
In the following the method and the storage silo of the invention will be described in greater detail.
Figure 1 shows the process steps of the method of the invention.
Figure 2 shows filtration and washing steps in a pressure filter applicable to the method of the invention.
3a Figure 3 shows a lime mud storage silo applicable to the method of the invention.
In Figure 1, numeral 35 refers to a take-off line for feeding smelt to a smelt dissolver 1 from a recovery unit (not shown). The smelt dissolver for producing green liquor comprises an agitator 2. A line 27 for weak liquor also ends in the smelt dissolver. A line 3 for thick green liquor leads from the smelt dissolver to an equalizing tank 4 for green liquor feed, from where green liquor is fed by means of a pumping system 6 automatically to an intermittently oper-ating pressure filter 8. A conveyor 36 for lime mud or burnt lime ends in the equalizing tank 4 and can be employed to add liri~e mud or burnt lime used as additive in the filtration. A return line 9 for filtrated green liquor. a prefiltrate, ends in the equalizing tank 4, which comprises an agitator 5. A return fine 7 for pumping green liquor also ends in the equalizing tank and is used when no green liquor is fed in a filtering cycle. The pressure filter 8 separates sus-pended solids, i.e. dregs 37, from green liquor. Filtrated clarified green liquor is conveyed via a line 10 to an air separator 11 for green liquor, from where the green liquor is then led via a line 12 to a storage tank 13 for green liquor.
From the storage tank the green liquor is fed via a sine 14 to a lime slaker 15.
The green liquor dregs in the filter 8 are dried by diaphragm pressing and air.
Air is separated from clarified green liquor by the air separator 11.
An alternative is to add burnt lime or lime mud to green liquor via the conveyor 36 to the equalizing tank 4. Adding burnt Time or lime mud con tributes to the filtration and adds to filtrate capacity, which can also be influ enced by changing the feeding pressure of green liquor.
A fine 16 for a mixture of lime mud product and white liquor, lime milk, leads from the lime slaker 15 to a causticizing tank 17. Lime milk is con-veyed from the causticizing tank by means of a pumping system 19 via a fine 18 to a pressure filter 21 which separates white liquor and lime mud. A fine for feeding white liquor filtrate, a prefiltrate, also ends in the causticizing tank.
Filtered white liquor flows via a line 22 to a digester {not shown). From the pressure filter 21 weak liquor is led via a line 23 to an air separator 24 where air is separated from weak liquor and weak liquor is led via a fine 25 to a weak liquor tank 26, and then via a line 27 to the smelt dissoiver 2. The lime mud that was separated, air dried and washed with water in the pressure filter 21, is led by a conveyor 28 to a lime mud silo 29 from where the lime mud is dis-charged and fed by a conveyor 30 as an even flow to the inlet of a lime kiln 31.
The residua! alkali of the lime mud separated in the filter can be adjusted.
The burnt lime is conveyed from the lime kiln via a conveyor 32 to a lime silo 33 and from there the burnt lime is fed via a fine or a conveyor 34 to the lime slaker 15.
Figure 2 shows the principle of a pressure filter applicable to a method of the invention in different steps. fn step 1 slurry is fed via a distribu-for line and feeding lines to the chambers of a closed and sealed fitter plate pack, whereby the solids gather on the filter cloth forming a cake. The filtrate penetrates the cloth and flows to the filtrate space and from there via a tube in the plate to the collector line at the discharge side. Diaphragm pressing is used in filtering green liquor but not in filtering white liquor. After this.
in ~fep 2, the filtrate remaining in the chambers is pressed by means of chamber dia-5 phragms and pressure through the cloth to the filtrate side by leading pressing water through the tubes in the plates and the bottom plates to a space at~ove the rubber diaphragms. An alternative to diaphragm pressing is air cJryinc~
which can be used to replace the first diaphragm pressing in step 2 and to eliminate the second diaphragm pressing in step 4. Air drying is used as an alternative in filtering lime mud.
At the end of the pressing, in step 3, the cake remaining on the cloth is washed with water, whereby the water lifts the press diaphragms against the chamber plates, and the wash filtrate penetrates the filtrate side of the cake and the cloth. to the collector fine. Wash water is fed to the filter chambers via the same distributor line as the slurry. The dregs cake formed in filtering green liquor is not washed, whereas the lime mud cake formed in white liquor filtration is washed with warm water. After the cake has been washed, in step 4, the washing liquid remaining in the cake is pressed from it by a second diaphragm pressing to the filtrate side and is led to the air sepa-rator of the weak liquor tank. The second diaphragm pressing is sirnil~r to the first one. After the second diaphragm pressing, in stage 5, the cake is dried with pressure air coming from the distributor line. When air fills the chambers, it lifts the pressing diaphragms up and the water in the chambers is reraovc:d to the filtrate side. After air drying, in step 6, the filter plate pack is opened to an upper position and emptied by moving the filter cloth forward. The cake is discharged to conveyors on bath sides of the filter.
The structure of the storage silo and the discharger for limo rnud product play a significant role in successful storage. For continuous process . ing, it is vital to choose the right solution for a substance that is difficult to han dle. The structure of the storage silo is shown in detail in Figure 3.
A storage silo 100 for lime mud product consists of an upper part 110 and a discharge part 120 below it. The properties of the lime mud product determine the length and breadth of the upper part. The longitudinal walls of the upper part open downwards at an 1-2° angle, and the upper part is thermally insulated.
The longitudinal wails of the discharge part open upwards and advantageously at a 15-30°
angle for the normal pressure of the lime mud load not to disturb the operation of the discharges. The wall (spout) of the discharge end 7 30 of the dis-charge part opens downwards at a 30-60.° angle. The discharge opening in the spout is arched at spout level. The other end of the discharge hart is closed. The lower part is overlaid with an antiadhesive coating determined by the properties of the lime mud product; suitable coatings include epoxy resin and polyfluoroethylene. The wall angles of the discharge part are rounded.
The lime mud storage operates continuously and lime mud can be discharged at a desired even flow from the silo by using the right discharges.
If needed, the discharge of lime mud storage can be interrupted even with full storage, and lime mud discharge can be resumed even after several days.
In a test run with an about 20m' Time mud storage. the lime mud storage was filled with lime mud having a dry solids content of 76-30°.o by weight while the discharges was on, and then the discharges was hafted anti the lime mud was left in the silo for three days. in spite of winter conditions (-10EC), it was possible to discharge the lime mud as an even flow after the halt. The discharged lime mud had a dry solids content of 78-80% by weight.
The method of the invention offers following advantages compare d with known methods:
- less requirements on space and structure - less eqriipment to be maintained .
- higher dry solids content of green liquor slurry and less r~rcen liq-uor dregs waste - lower dregs content in clear green liquor - lower amount of circulating process impurities due to efficient rli-sect filtration of green liquor - less energy needed as the temperature of e.g. the filtrated white liquor remains high .
- higher dry solids content of lime mud - muse even use of lime kiln due to adjustable residual alkali and dry solids content of lime mud - lower suspended solids content in white liquor - less weak liquor per m3 of white liquor less drying energy needed in Time kiln. '
Claims (3)
1. ~A storage silo for a lime mud product, the silo comprising of an upper part that opens downwards and a discharge part at a lower end of said silo, said discharge part opening upwards and having a discharge end that opens downwards, said discharge end comprising a discharge outlet.
2. ~A storage silo as claimed in claim 1, characterized in that longitudinal walls of the upper part open downwards and longitudinal walls of the discharge part open upwards, and an inside of the discharge part is overlaid with an antiadhesive coating.
3. ~A storage silo as claimed in claim 2, characterized in that the antiadhesive coating is a fluorocarbon polymer.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI956153A FI105933B (en) | 1995-12-20 | 1995-12-20 | A process for preparing white liquor |
| FI956153 | 1995-12-20 | ||
| PCT/FI1996/000676 WO1997022752A1 (en) | 1995-12-20 | 1996-12-19 | Process for filtering white liquor and a storage container for lime sludge |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2240861A1 CA2240861A1 (en) | 1997-06-26 |
| CA2240861C true CA2240861C (en) | 2007-03-13 |
Family
ID=38008068
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002240861A Expired - Lifetime CA2240861C (en) | 1995-12-20 | 1996-12-19 | A storage silo for lime mud product |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2240861C (en) |
-
1996
- 1996-12-19 CA CA002240861A patent/CA2240861C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| CA2240861A1 (en) | 1997-06-26 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |
Effective date: 20161219 |