WO1979000931A1 - Preparation of white liquor - Google Patents

Preparation of white liquor Download PDF

Info

Publication number
WO1979000931A1
WO1979000931A1 PCT/SE1979/000085 SE7900085W WO7900931A1 WO 1979000931 A1 WO1979000931 A1 WO 1979000931A1 SE 7900085 W SE7900085 W SE 7900085W WO 7900931 A1 WO7900931 A1 WO 7900931A1
Authority
WO
WIPO (PCT)
Prior art keywords
lime
liquor
pressure
white liquor
carried out
Prior art date
Application number
PCT/SE1979/000085
Other languages
French (fr)
Inventor
A Andersson
Original Assignee
A Andersson
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by A Andersson filed Critical A Andersson
Priority to BR7908084A priority Critical patent/BR7908084A/en
Publication of WO1979000931A1 publication Critical patent/WO1979000931A1/en

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D1/00—Oxides or hydroxides of sodium, potassium or alkali metals in general
    • C01D1/04—Hydroxides
    • C01D1/20—Preparation by reacting oxides or hydroxides with alkali metal salts
    • C01D1/22—Preparation by reacting oxides or hydroxides with alkali metal salts with carbonates or bicarbonates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/18—Carbonates
    • C01F11/181—Preparation of calcium carbonate by carbonation of aqueous solutions and characterised by control of the carbonation conditions
    • 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
    • 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

Definitions

  • This invention relates to a process of preparing white liquor for the preparation of pulp by means of the sulphate method. According to the invention the preparation is carried out in a closed plant at a pressure exceeding atmospheric pressure. In this way a number of advantages are obtained.
  • the 'slaked lime is partly soluble in water and gives a lime milk, which is led to a causticizing vessel, in which the calcium in the lime milk reacts with the carbonate in the liquor, so that the desired sodium hydroxide and lime sludge (calcium carbonate) are obtained according to the formula:
  • the lime sludge is filtered, washed and stored in order to be subsequently burned and recycled to the process as quick lime.
  • the white liquor obtained is led to the digestion.
  • the lime slaker 2 operates in principle as a slaker of a known type. Quick lime 3 and green liquor
  • the lime gravel formed is homogenized by means of a bottom agitator 6 and is scraped towards a discharge gate for discontinuous removal out of the system at 7.
  • the lime milk is led to the causticizing vessel (or vessels) 8, where it is reacted with the sodium carbonate of the green liquor under vigorous stirring with the agitator 9, forming sodium hydroxide and calcium carbonate (lime sludge).
  • the mixture is further led to a white liquor filter 10, which contains a filter insert 11 of a design known per se.
  • a white liquor filter 10 which contains a filter insert 11 of a design known per se.
  • the lime sludge is separated, sediments in the lower cylindrical portion of the vessel and falls down towards the bottom, where it is homogenized by an agitator 12 and led to a vessel 13 for washing, after which the lime sludge is stored in a silo 14.
  • the white liquor is collected in the white liquor tank 15.
  • a pressure release to atmospheric pressure is carried out.
  • it is ⁇ ossible to utilize the heat energy released at the pressure reduction in a way known per se.
  • the lime sludge is pumped from the silo 14 to a washing filter 18 to be thickened and freed from certain impurities influencing the re-burning process and the surrounding environment negatively. Finally the lime sludge is fed from the filter into the lime sludge re-burning furnace in order to be returned subsequently to the lime slaker as quick lime.
  • the finished white liquor 17 is pumped with the pump 16 as cooking liquor to the digester house.
  • the essential, feature of the invention is that the preparation of the white liquor is carried out at a pressure exceeding the atmospheric pressure.
  • the upper limit of the used pressure is not critical but is primarily decided by considerations as to apparatus and process technique. An apparatus which must withstand a very high pressure will of course be more complicated and expensive, as more solid constructions and materials are required. In practice it has been found that a pressure of up to about 1 MPa over atmospheric can be used with • advantage, and an overpressure of 200-500 kPa is " especially suitable.
  • the heat developed at the slaking of the lime raises the temperature of the green liquor above the boiling point.
  • Water is evaporated in a causticizing plant of conventional type with atmospheric pressure, and the normal temperature in such a slaker is 102- 103°C. In a closed plant at positive pressure the temperature will.be higher,, as no water vapour can escape, and normally the temperature will here be about 105-110°C.
  • the heat will be stored in the mixture of white liquor and slaked lime until these two components are transferred to their storage containers at atmospheric pressure. In certain cases it can also be suitable to operate at a still higher temperature, and the upper temperature limit is here only set by the critical temperature of water (374.2°C). It has been found that a-..s«itable temperature range is 105-170 C. How ⁇ ever, it is not necessary for the invention that the temperature is above the boiling point, but the most • important feature is, as already indicated, that the pressure is above atmospheric pressure.
  • the pl ' ant can be built in a compact way, as the principle with gravity feed need not be utilized.
  • reaction heat produced in the slaker can be retained throughout the whole system and can be utilized by means of e.g. a hot water scrubber at the pressure release in the white liquor tank and the lime sludge silo.
  • the invention has been described above as utilized in a complete plant for the preparation of white liquor. However, it should be noted that the invention can also be utilized for the slaker only, and thus on a process for preparing slaked lime (calcium hydroxide). Thus, here green liquor as such need not be used for slaking but instead water or some other water-containing liquid. Also here, the above-mentioned advantages will be gained in an analogous way by carrying out the process at a pressure above atmospheric pressure.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Paper (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

Abstract

A process for the preparation of white liquor for the sulphate pulping process, wherein quicklime is slaked with green liquor (4) and the slaked lime formed is reacted with the sodium carbonate in the green liquor (4) to sodium hydroxide in a causticizing process, the lime sludge formed being separated. According to the invention, the process from the slaking of the lime up to the separation of the white liquor (7) and lime sludge is carried out at a pressure above the atmospheric pressure. In a preferred embodiment, the process is also carried out at a temperature above the normal boiling temperature of the system.

Description

Preparation of white liquor
This invention relates to a process of preparing white liquor for the preparation of pulp by means of the sulphate method. According to the invention the preparation is carried out in a closed plant at a pressure exceeding atmospheric pressure. In this way a number of advantages are obtained.
In the preparation of pulp according to the sulphate method, it is necessary to recover the digestion chemicals for a satisfactory process economy. This is achieved by evaporating the black liquor obtained from the pulp digestion and burning it in a soda recovery boiler, the inorganic constituents of the liquor being obtained in the form of a melt.' The latter is dissolved in water, whereby green liquor is obtained, which i.a. contains sodium carbonate, which is not active in the digestion process. Therefore it is desired to convert as large a portion of the carbonate as possible to sodium hydroxide, which is included as an active constituent in the digestion liquor. Therefore causticizing of the green liquor with calcium hydoxide is carried out.
At the addition of quick lime (calcium oxide) to green liquor in a lime slaker the burnt lime reacts
VϋREAi?
_ OMPI exothermically with the water present in the green liquor so that slaked lime (calcium hydroxide) is ob¬ tained according to the reaction
CaO + H20 >Ca(OH)2 + heat
The 'slaked lime is partly soluble in water and gives a lime milk, which is led to a causticizing vessel, in which the calcium in the lime milk reacts with the carbonate in the liquor, so that the desired sodium hydroxide and lime sludge (calcium carbonate) are obtained according to the formula:
Ca(0H)2 + a2C03 > CaC03 (s) + 2NaOH
The lime sludge is filtered, washed and stored in order to be subsequently burned and recycled to the process as quick lime. The white liquor obtained is led to the digestion.
Up to now, preparation of white liquor has always been carried out in more or less open systems and at atmospheric pressure in continuously operating apparatuses. However, according to the present inven¬ tion, the process is carried out in a system, which is pressurized from the lime slaker up to the storage tank for the finished white liquor, said pressure be¬ ing higher than the atmospheric pressure. This constitutes an essential deviation from the previously known method for the preparation of white liquor and brings considerable advantages, as will be shown more in detail in the following specification.
The invention is illustrated more closely in the accompanying drawing, which shows schematically the system of the process and how the process is carried out. In the drawing it is shown how green liquor 4 is led through a pump 1 into a lime slaker 2. Quick lime
_ O 3 is introduced in the lime slaker 2 through a feeder adapted, to feed the lime into a vessel under positive pressure. Such feeding means are known to those skilled in the arf. The pump 1 for green liquor serves as a transport pump for green liquor, lime milk and the mixture of white liquor and lime sludge through the. whole system, and maintains a pressure above atmospheric pressure up to the storage tank 15 for white liquor. The lime slaker 2 operates in principle as a slaker of a known type. Quick lime 3 and green liquor
4 are supplied under vigorous stirring with the agitator 5 and react with each other under development of heat. The lime gravel formed is homogenized by means of a bottom agitator 6 and is scraped towards a discharge gate for discontinuous removal out of the system at 7.
The lime milk is led to the causticizing vessel (or vessels) 8, where it is reacted with the sodium carbonate of the green liquor under vigorous stirring with the agitator 9, forming sodium hydroxide and calcium carbonate (lime sludge).
The mixture is further led to a white liquor filter 10, which contains a filter insert 11 of a design known per se. Here the lime sludge is separated, sediments in the lower cylindrical portion of the vessel and falls down towards the bottom, where it is homogenized by an agitator 12 and led to a vessel 13 for washing, after which the lime sludge is stored in a silo 14. The white liquor is collected in the white liquor tank 15. In the silo 14 and the tank 15 a pressure release to atmospheric pressure is carried out. Here it is υossible to utilize the heat energy released at the pressure reduction in a way known per se. The lime sludge is pumped from the silo 14 to a washing filter 18 to be thickened and freed from certain impurities influencing the re-burning process and the surrounding environment negatively. Finally the lime sludge is fed from the filter into the lime sludge re-burning furnace in order to be returned subsequently to the lime slaker as quick lime.
The finished white liquor 17 is pumped with the pump 16 as cooking liquor to the digester house. As indicated above, the essential, feature of the invention is that the preparation of the white liquor is carried out at a pressure exceeding the atmospheric pressure. The upper limit of the used pressure is not critical but is primarily decided by considerations as to apparatus and process technique. An apparatus which must withstand a very high pressure will of course be more complicated and expensive, as more solid constructions and materials are required. In practice it has been found that a pressure of up to about 1 MPa over atmospheric can be used with •advantage, and an overpressure of 200-500 kPa is " especially suitable.
The heat developed at the slaking of the lime raises the temperature of the green liquor above the boiling point. Water is evaporated in a causticizing plant of conventional type with atmospheric pressure, and the normal temperature in such a slaker is 102- 103°C. In a closed plant at positive pressure the temperature will.be higher,, as no water vapour can escape, and normally the temperature will here be about 105-110°C. The heat will be stored in the mixture of white liquor and slaked lime until these two components are transferred to their storage containers at atmospheric pressure. In certain cases it can also be suitable to operate at a still higher temperature, and the upper temperature limit is here only set by the critical temperature of water (374.2°C). It has been found that a-..s«itable temperature range is 105-170 C. How¬ ever, it is not necessary for the invention that the temperature is above the boiling point, but the most •important feature is, as already indicated, that the pressure is above atmospheric pressure.
In the causticizing process calcium carbonate is formed and precipitates as lime sludge. At a higher temperature, the precipitated crystals will be bigger at an unchanged reaction time. This is due to the fact that the formation of new crystallization nuclei will decrease at increasing temperature and that smaller crystals will be more-easily redissolved. Due to this, the probability of a precipitation on bigger crystals already formed will increase, so that bigger crystals are obtained, which makes the separation of the lime sludge easier. In practical work, this will make possible a shortening of the time for causticiz- ing. Thus, for the growth of the crystals of calcium carbonate, a higher temperature in the closed system .is of a positive importance.
At higher temperatures, the solubility of the calcium carbonate is increased while it will decrease for calcium hydroxide. Theoretically, the content of carbonate ions in the white liquor will thus increase with rising temperature. However, this is counter¬ acted by the fact that an equilibrium will appear more rapidly owing to the higher temperature. The apparatuses used in the process, such as slaker, causticizing vessel, filters, etc. are of. a conventional design for carrying out chemical reac¬ tions at a positive pressure arid can easily be assembled by one skilled in the art. It is also easy to select suitable materials for the various apparatus parts.
As the slaking and causticizing processes are carrie'd'out at a pressure above the atmospheric pressure in the preparation of white liquor, the following prominent advantages are obtained:
1. The pl'ant can be built in a compact way, as the principle with gravity feed need not be utilized.
2. The necessary pipe system will be very much simplified in comparison with a conventional plant. 3. Only a minimum of movable parts are required, viz. in the basic design 1 green liquor pump, 5 agitator aggregates, 1 feed device for lime and 1 discharge device for lime gravel.
4. It should be possible to reduce the volume of the plant building to about half of what is required at present.
5. By closing the process, the system will be advantageous from an environmental point of view.
6. The reaction heat produced in the slaker can be retained throughout the whole system and can be utilized by means of e.g. a hot water scrubber at the pressure release in the white liquor tank and the lime sludge silo.
The invention has been described above as utilized in a complete plant for the preparation of white liquor. However, it should be noted that the invention can also be utilized for the slaker only, and thus on a process for preparing slaked lime (calcium hydroxide). Thus, here green liquor as such need not be used for slaking but instead water or some other water-containing liquid. Also here, the above-mentioned advantages will be gained in an analogous way by carrying out the process at a pressure above atmospheric pressure.
_OMPI •

Claims

' " Claims
1. A process for preparing white liquor, where¬ in water included in green liquor is reacted
Figure imgf000009_0001
calcium oxide and calcium hydroxide formed is reacted with sodium carbonate in the green liquor to sodium hydroxide and calcium carbonate, characterized in that the reactions are carried out at a pressure above atmospheric pressure.
2. The process of claim 1, characterized in that the reactions are carried out at a pressure of up to 1 MPa over atmospheric.
3. The process of claim 1 or 2, characterized in that the reactions are carried out at a pressure of 200-500 kPa over atmospheric.
4. The process of any one of claim 1-3, characterized in that the reactions are carried out at ■a temperature of 105-170°C, preferably 105-110°C.
PCT/SE1979/000085 1978-04-14 1979-04-09 Preparation of white liquor WO1979000931A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
BR7908084A BR7908084A (en) 1978-04-14 1979-04-09 PROCESS TO PREPARE WHITE LIQUOR

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE7804239A SE419997B (en) 1978-04-14 1978-04-14 SET TO PREPARE WHITE WHITE A PRESSURE AT THE ATMOSPHERE PRESSURE
SE7804239 1978-04-14

Publications (1)

Publication Number Publication Date
WO1979000931A1 true WO1979000931A1 (en) 1979-11-15

Family

ID=20334613

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1979/000085 WO1979000931A1 (en) 1978-04-14 1979-04-09 Preparation of white liquor

Country Status (5)

Country Link
JP (1) JPH0123596B2 (en)
CA (1) CA1163777A (en)
FI (1) FI64671B (en)
SE (1) SE419997B (en)
WO (1) WO1979000931A1 (en)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2541331A1 (en) * 1983-02-23 1984-08-24 Enso Gutzeit Oy WHITE CAUSTIFICATION PROCESS TO PRODUCE WHITE LIQUOR REUSABLE FOR THIS COOKING FROM GREEN LIQUOR FROM THE RECOVERY OF LAUNDRY USED IN CELLULOSE PULP COOKING
US4762590A (en) * 1985-03-19 1988-08-09 Enso-Gutzeit Oy Causticizing process
FR2679933A1 (en) * 1991-07-31 1993-02-05 Int Paper Co METHOD OF EXTINCTION AND CAUSTIFICATION IN ONE STEP FOR THE PRODUCTION OF CELLULOSE PULP.
WO1996026901A1 (en) * 1995-02-27 1996-09-06 Aeci Limited Production of precipitated calcium carbonate
WO1996026902A1 (en) * 1995-03-02 1996-09-06 Pretoria Portland Cement Company Limited Calcium carbonate precipitation method
US6627170B2 (en) * 1996-12-09 2003-09-30 Nippon Paper Industries Co., Ltd. Process for preparing calcium carbonate
US7097819B2 (en) 2000-01-18 2006-08-29 Nippon Paper Industries Co., Ltd. Method for producing calcium carbonate

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE463771C (en) * 1985-05-02 1998-09-30 Caustec Ab Apparatus and method for separating white liquor, mesa and possibly sludge using a rotating disk filter

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE109555C (en) *
DK2969C (en) * 1900-04-17 Richard Jaeger Procedure for Dry Leaching of Lime.

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE109555C (en) *
DK2969C (en) * 1900-04-17 Richard Jaeger Procedure for Dry Leaching of Lime.

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2541331A1 (en) * 1983-02-23 1984-08-24 Enso Gutzeit Oy WHITE CAUSTIFICATION PROCESS TO PRODUCE WHITE LIQUOR REUSABLE FOR THIS COOKING FROM GREEN LIQUOR FROM THE RECOVERY OF LAUNDRY USED IN CELLULOSE PULP COOKING
US4627888A (en) * 1983-02-23 1986-12-09 Enso-Gutzeit Oy Causticizing method
US4762590A (en) * 1985-03-19 1988-08-09 Enso-Gutzeit Oy Causticizing process
FR2679933A1 (en) * 1991-07-31 1993-02-05 Int Paper Co METHOD OF EXTINCTION AND CAUSTIFICATION IN ONE STEP FOR THE PRODUCTION OF CELLULOSE PULP.
WO1996026901A1 (en) * 1995-02-27 1996-09-06 Aeci Limited Production of precipitated calcium carbonate
WO1996026902A1 (en) * 1995-03-02 1996-09-06 Pretoria Portland Cement Company Limited Calcium carbonate precipitation method
AP663A (en) * 1995-03-02 1998-08-19 Pretoria Portland Cement Ltd Calcium carbonate precipitation method.
AU709774B2 (en) * 1995-03-02 1999-09-09 Pretoria Portland Cement Company Limited Calcium carbonate precipitation method
US6036933A (en) * 1995-03-02 2000-03-14 Pretoria Portland Cement Company Limited Calcium carbonate precipitation method
US6627170B2 (en) * 1996-12-09 2003-09-30 Nippon Paper Industries Co., Ltd. Process for preparing calcium carbonate
US7261869B2 (en) 1996-12-09 2007-08-28 Nippon Paper Industries Co., Ltd. Processes for preparing calcium carbonate
US7097819B2 (en) 2000-01-18 2006-08-29 Nippon Paper Industries Co., Ltd. Method for producing calcium carbonate

Also Published As

Publication number Publication date
JPH0123596B2 (en) 1989-05-08
SE7804239L (en) 1979-10-15
JPS55500189A (en) 1980-04-03
FI64671B (en) 1983-08-31
SE419997B (en) 1981-09-07
CA1163777A (en) 1984-03-20
FI791164A (en) 1979-10-15

Similar Documents

Publication Publication Date Title
CN1315730C (en) Getting alkali from salt solution and calcining sesquicarbonate of soda
US4470876A (en) Kraft overload recovery process
GB1576130A (en) Continuous production of lithium carbonate
US4280987A (en) Method for treatment of Bayer liquor
WO1979000931A1 (en) Preparation of white liquor
US4504356A (en) Continuous process of removing silica from spent pulping liquors
US2238456A (en) Purification of magnesium base liquors
US6074521A (en) Method of separating impurities from lime and lime sludge
US4093508A (en) Process for recovering chemicals from the waste liquors of sulfate cellulose digestion and the waste waters of bleaching
US3650888A (en) Pollution controlled polysulfide recovery process
US4627888A (en) Causticizing method
NO180054B (en) One-step procedure for leaching and causticizing
US7468176B2 (en) Feeding device and process and feeding system which utilize the feeding device
US4762590A (en) Causticizing process
US1699845A (en) Process of treating waste sulphite liquor
US6123806A (en) Process for kraft chemical recovery
US2628155A (en) Method for the recovery of spent liquors from the cooking of cellulose from raw material containing silica
US3120464A (en) Decolorizing kraft waste liquors
US2734037A (en) Method of introducing sulfite waste
US2029616A (en) Process for preparing alkali sulphite or alkali bisulphite solutions from waste liquors obtained in the digestion of cellulose with alkali sulphur compounds
AU5288093A (en) Process for dividing the sulphide content of the green liquor for the production of white liquors having high and low sulphidity respectively
FI73754C (en) Process for the preparation of boiling chemicals for cellulose production.
US1856558A (en) Process of treating waste sulphite liquor
US3216788A (en) Flash evaporation of pulp liquor to eliminate calcium salts
JP2713429B2 (en) Method and apparatus for performing a sulfate pulp process

Legal Events

Date Code Title Description
AK Designated states

Designated state(s): BR DE JP US