JP2986137B2 - Green liquor crystallization - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a process for producing cellulose pulp which produces two or more liquid streams of different sulphidities, in particular, by controlling the sulfur content and producing liquid streams of very different sulphides, The present invention relates to a method for producing cellulose pulp that effectively collects chemical substances. This application was filed in 1992 5
U.S. patent application Serial No. 07 /
It corresponds to 887,004 CIP.

[0002]

2. Description of the Related Art As described in the above-mentioned parent application, during the process of producing cellulose pulp and during the recovery of chemical substances, the degree of sulfidation is significantly different. It is highly desirable to have more than one type of liquid flow. According to the present invention, there is provided a method by which such streams can be effectively and widely produced, including producing streams that can be controlled to be essentially free of sulfur. Can be

[0003] Part of the method according to the invention involves treating the "black liquor". As used herein and in the claims, the term "black liquor" refers to the process of producing cellulose pulp, typically a sulfate process, a sulfidation process, or other process that includes sulfur as part of the pulping chemical. Should be understood to have a broad meaning, including liquids containing dissolved lignin resulting from the cooking of cellulose in the manner described above. The liquid that processes the pulp is referred to as "white liquor." In this specification and in the claims, the term "white liquor" is intended to broadly include, unless otherwise specified, all liquids typically used in pulping processes where some sulfur is used. .
The white liquor is for the sulfate or sulphide process and is an essentially pure stream of NaOH at various points during the cooking or processing (i.e., at some point during the cooking, a sulfur-containing white liquor is used. But may be substantially free of sulfur).

[0004] In most embodiments of the invention, the black liquor is subjected to a heat treatment in its practice. The lignin in the black liquor is disrupted by heat treatment under pressure for a predetermined period of time, thereby being shown in U.S. Pat. No. 4,929,307, the description of which is incorporated herein by reference. Thus, it is known that gases containing organic sulfur compounds (typically dimethyl sulfide and methyl mercaptan) are generated.
The heat treatment may be performed between a typical pulp mill steamer and a recovery boiler, but is not limited to that area. The heat treatment is typically performed at a temperature of about 170-350C. 30-70 of sulfur in black liquor
As many as% are removed during the heat treatment. One purpose of the heat treatment is to reduce the sulfur content of the black liquor entering the recovery boiler or similar recovery process and to minimize corrosion problems. Also, the viscosity of the black liquor is reduced by this heat treatment. The sulfur-containing gas resulting from the heat treatment is advantageously used according to the invention.

[0005] One of the most basic features of the present invention is
A recovery system that burns the black liquor to produce a melt and then melts the melt to produce a green liquor, wherein the concentration and temperature are such that the sodium carbonate in the green liquor is a monohydrate or Control in such a way as to crystallize into decahydrate crystals. Then, when the crystals are removed from the green liquor, the resulting green liquor has a high degree of sulfurization. The withdrawn sodium carbonate crystals are used to form a substantially sulfur-free sodium hydroxide-containing liquid, which can be used in a very wide variety of different ways in a pulp mill.

In accordance with one aspect of the present invention, there is provided a method of recovering and utilizing chemicals during the manufacture of cellulose pulp using sulfur-containing chemicals. The method comprises the following steps: (a) heat treating the black liquor obtained from the production of the cellulose pulp to drive off some of the sulfur-containing compounds as a gas therefrom. (B) burning the heat-treated black liquor to produce a melt; (C) dissolving the melt with a liquid to produce a green liquor; (D) adjusting the concentration of the green liquor and controlling the temperature to crystallize the sodium carbonate to form crystals. (E) removing sodium carbonate crystals from the green liquor to produce a first stream of green liquor having a high degree of sulfidation; And (f) causticizing the sodium carbonate crystals to produce a liquid containing sodium hydroxide.

[0007] The first green liquor stream may be causticized to produce a first white liquor having a high degree of sulfidation, the degree of sulfidation of which is determined by the sulfur-containing gas generated in step (a). Can be further increased by raising the degree of sulfidation to greater than 50% by contacting with water.

[0008] Step (e) may be performed by centrifugation or by various filtration methods such as vacuum filtration, disc filtration, or sidehill screening. Step (d) is performed to control the temperature to about 5-20 ° C to produce pure decahydrate crystals, or to control the temperature to about 35-90 ° C to produce monohydrate crystals. May be performed. Generally, steps (a)-(f) can be performed to produce a liquid containing sodium hydroxide that is substantially free of sulfur as a liquid containing sodium hydroxide.

[0009] The sodium hydroxide liquid stream can be used at many different locations within the pulp mill. For example, it may be used in a plant for bleaching cellulose pulp, or it may be added at a later stage of cooking. Alternatively, it can be used to scrub the gas generated in step (a), thereby resulting in a liquid containing sodium hydrogen sulfide. The liquid containing sodium hydrogen sulfide may be used as a buffer storage for sodium and sulfur or as a feed to a polysulfide generator.

[0010] Alternatively, the gas from step (a) may be used to form sulfuric acid, which is then used for bleaching or pre-performed acid hydrolysis, or in a pulp mill where pH control is desired. It may be used separately. Also, the white liquor stream produced by causticizing the green liquor is split into two, and only one of the streams is contacted with the sulfur-containing gas from step (a), which is then used in the early stages of the cooking. The other low sulphide white liquor stream is used at a later stage of cooking (eg, in the wash recycle path).

In accordance with another aspect of the present invention, there is provided a process for producing chemical pulp from ground cellulose fibrous material using white liquor in a pulping process involving a fluid containing sulfur. The method comprises the following steps: (a) Systematically removing sulfur from a sulfur-containing fluid. (B) forming a first stream containing sulfur compounds and sodium carbonate; (C) adjusting the solids concentration and temperature of the first stream to produce sodium carbonate crystals in the first stream; (D) separating the sodium carbonate crystals from the first stream and then causticizing the first stream to produce a white liquor. (E) increasing the degree of sulfidation of the first stream using the sulfur removed from step (a). (F) using the separated sodium carbonate crystals to form at least a second stream of white liquor having a relatively low sulfur content (the first stream having a sulfur content substantially greater than the sulfur content of the second stream); Having). (G) Chemically pulping the cellulosic material with the first and second streams of white liquor added at different points in the pulping process. And (h) washing the produced chemical pulp.

In accordance with yet another aspect of the present invention, there is provided a method of recovering chemicals from black liquor formed during pulping of cellulose with a sulfur-containing treatment fluid, comprising the steps of: ) Burn the black liquor to form a melt. (B) dissolving the melt in a liquid to produce a green liquor; (C) adjusting the concentration of the green liquor and controlling its temperature to crystallize sodium carbonate into monohydrate or decahydrate crystals. (D) removing the sodium carbonate crystals from the green liquor to produce a first stream of green liquor with a high degree of sulfidation. And (e) causticizing the sodium carbonate crystals to produce a liquid stream containing sodium hydroxide that is substantially free of sulfur.

[0013] The main object of the present invention is to produce pure sodium carbonate crystals from green liquor in a recovery path and then to ultimately produce a liquid stream of very different sulfidity during the production of cellulose pulp. To recover chemical substances effectively. This and other objects will become apparent upon examination of the detailed description of the invention and the appended claims.

An example of a cellulosic pulp production and chemical recovery apparatus according to the present invention is indicated generally by the reference numeral 10 in FIG. In a conventional steamer 11 (which may be a continuous steamer or a batch steamer), the cellulose ground fiber material is steamed to produce cellulose pulp. The cooking step involves the use of sulfur-containing chemicals, which may comprise a sulfate method, a sulfide method, and the like. During the cooking, a lignin-rich liquid, known as "black liquor", is produced, which is continuously or periodically discharged from the steamer 11 to the conduit 1.
2 and typically comprises one or more evaporation stages 13, 1
4 and then sent to a conventional recovery boiler 16. Further, according to the present invention, the black liquor is subjected to a pressure heat treatment for a predetermined time to reduce the sulfur content and the viscosity of the black liquor.
The heat treatment step indicated at 15 in FIG. 1 is basically as described in U.S. Pat. No. 4,929,307, in which the black liquor is applied for a predetermined time of about 170-3.
Subject to pressure heat treatment at a temperature of 50 ° C. By varying the time, temperature, etc., as much as 30-70% of the sulfur can be removed from the black liquor, after which the black liquor is sent to the recovery boiler 16.

[0015] In the recovery boiler 16, the black liquor is burned, and the lignin therein gives a substantial calorific value. The combustion of the black liquor produces a melt, which contains the chemicals that are desired to be recovered. The melt is dissolved in the melt tank 17 with water or other liquid, as is conventional. According to the invention, the concentration of the liquid produced in the melt tank 17, known as the "green liquor", is controlled in a similar manner to the temperature, so as to produce essentially pure sodium carbonate crystals in the green liquor. I do. As illustrated in FIG. 1, the green liquor can be clarified in a finer 18 and crystals formed in a crystallizer 19.
Crystallizer 19 can provide temperature control by controlling the evaporation rate or other crystallization function, or the temperature control can be accomplished by heating and heating the green liquor as shown schematically at 20 in FIG. It can also be performed externally by cooling.

When essentially pure sodium dehydrated sodium carbonate crystals are formed, the concentration and temperature are controlled so that the amount of sodium carbonate in the green liquor is not too high for effective causticization after the green liquor. Then, the temperature is controlled to be about 5 to 20 ° C. If sodium monohydrate crystals are formed, the temperature is controlled to be about 35-90 ° C. The concentration of the green liquor is controlled by the amount of liquid added to the melt tank 17 so as to produce green liquor from the melt and / or after the green liquor is formed in the melt tank 17, Controlled by evaporation of the liquid (eg in crystallizer 19).

After the formation of sodium carbonate crystals in the green liquor, the crystals are separated. Separation is preferably performed with a centrifuge such as the hydrocyclone illustrated at 21 in FIG. The crystals discharged from the bottom of the hydrocyclone 21 into the conduit 22 are causticized with lime (CaO) in the causticizer 23, while discharging the green liquor into the conduit 24. Instead of the centrifuge 21, various filtration mechanisms such as a vacuum drum filter, a side hill screen, and a disc filter can be used.

The reaction involving reburned or fresh lime and sodium carbonate in the causticizer 23 is as follows: CaO + H ₂ O-- → Ca (OH) ₂ Na ₂ CO ₃ + Ca (OH ) ₂ --- → 2NaOH + C
aCO ₃

Preferably, the green liquor in conduit 24 is also causticized to conventional levels in causticizer 25 in a conventional manner, and the lime slurry from both causticizers 23 and 25 is lime kiln 26
Send to The product stream in conduit 28 from causticizer 23 is an essentially sulfur-free sodium hydroxide stream, while the white liquor in conduit 30 from causticizer 25 has a high degree of sulfidation, It has a higher degree of sulfidation than with conventional recovery methods.

The liquid in conduits 28, 30 can be used for a variety of different purposes. Typically, however, the white liquor in conduit 30 is used to cook the cellulose in the digester 11 and the relatively high sulphide white liquor in conduit 30 is used in the early stages of cooking, possibly involving impregnation. ). The essentially sulfur-free sodium hydroxide in conduit 28, as shown by conduit 32,
It may be used as "white liquor" at a later stage of the cooking in 1 (including the wash recirculation line), or may be used in the bleaching plant 33, as indicated by conduit 34.

The gas generated during heat treatment 15 is typically sent to a sulfur and fuel gas recovery block 36, where the fuel gas is separated into conduit 37, which may be used as a fuel gas in lime kiln 26. It is often introduced into kiln 26 through conduit 38. Sulfur-containing gases (typically dimethyl sulfide and methyl mercaptan) may be treated to produce hydrogen sulfide and the like, and as shown schematically by conduit 40 in FIG. It may be introduced (absorbed therein) and increase the degree of sulfidation of the white liquor in conduit 30 even further (eg, greater than 50%, typically about 60-90%). The processing in block 36 may be as described in the parent application (their descriptions are incorporated herein by reference).

FIG. 2 illustrates a modification of the method of FIG. In the modification of FIG. 2, components that correspond to those of FIG. 1 are illustrated with the same reference numerals simply prefixed with a “1”.

In FIG. 2, the white liquor in conduit 130 is split into two substantially identical streams, 42 and 43. Sulfur-containing chemicals, such as hydrogen sulfide, are absorbed into the white liquor in stream 42 and are used in the early stages of the steamer 111 or in an impregnation vessel (shown in dotted lines at 44 in FIG. 2). The low sulphide white liquor in conduit 43 is used at a later stage in steamer 111, for example, it may be added to wash recirculation path 46 associated with steamer 111, as shown by dotted line 45. Good.

FIG. 3 illustrates another way of using the material resulting from the heat treatment of the black liquor. In FIG. 3, components that correspond to components of the embodiment of FIG. 1 are indicated by the same reference numerals preceded only by "2".

The gas generated in the heat treatment step 215 of FIG.
It is sent to a sulfur and fuel and gas recovery unit 236, which typically produces hydrogen sulfide and is discharged into conduit 240. The hydrogen sulfide in conduit 240 may then be sent to conventional device 48 to convert the hydrogen sulfide to sulfuric acid. The sulfuric acid in conduit 49 may then be used in a bleaching step in the pulp mill (eg, bleaching plant 33) and / or may be used for acid hydrolysis that has been performed previously during the pulping step. . Sulfuric acid can also be used outside the mill if there is a clear sulfur imbalance in the mill.

FIG. 4 illustrates another modification. In the modification of FIG. 4, the structure corresponding to the structure of FIG. 1 is indicated by a reference number preceded only by "3".

The gas generated in conduit 50 from heat treatment 315 is sent to scrubber 51. The cleaning device 51 includes a causticizer 3.
The essentially sulfur-free sodium hydroxide produced in 23 is also sent. In this way, the washer 51 produces in the conduit 52 a liquid containing sodium hydrogen sulfide. The sodium hydrogen sulfide containing liquid may be sent to a conditioning (for sodium and sulfur) reservoir 53 or may be used as a feed stream for a polysulfide generator 54;
The resulting polysulfide is used during cooking and / or in other steps of the pulp mill.

[0028]

In one embodiment of the method described with reference to FIGS. 1-4, in a kraft pulp manufacturing operation, 102 tons of Na _{2 /} day were used to satisfy the cooking liquid conditions.
Requires S and 238 tons of sodium hydroxide per day. 26.4 tons of sulfur are removed in the outgassed gas generated during the heat treatment in step 15. The black liquor exiting the heat treatment stage 15 is burned in a recovery boiler 16 and the resulting chemical is added to the water in the melt tank 17 to produce a green liquor having a degree of sulfidation of about 15%. The solids content and temperature of the green liquor from the melt tank 17 were determined by adding Na ₂ CO ₃ .10H ₂ O
Alternatively, it is adjusted to such a level as to precipitate crystalline sodium carbonate in the form of Na ₂ CO ₃ .H ₂ O. Adjustment of the solids content may be performed during the melt dissolution step in tank 17 by controlling the amount of water added, or during the evaporation step following melt dissolution (eg, during 19), or both. The degree of crystallinity and subsequent removal of sodium carbonate is controlled by the solids content of the green liquor, the temperature at which the green liquor is cooled, and the concentration of other compounds such as sodium sulfide and sodium chloride in the green liquor. You. If the temperature is about 5-20
C., if the temperature is controlled to be about 35-90 ° C., while decahydrate sodium carbonate crystals are formed.
When controlled to be in ° C., a monohydrate type is formed. The amount of crystallized sodium carbonate will be about 189 tonnes per day as Na ₂ CO ₃ . The concentration of green liquor is also adjusted to produce good causticizing efficiency. Sodium carbonate crystals dissolve in aqueous solution until the appropriate concentration,
In the causticizer 23, it is separately causticized. The sodium carbonate yields a solution containing about 174 tons of essentially sulfur-free sodium hydroxide per day, which when causticized in causticizer 25, produces a white liquor having a sulfidity of about 25%. Will occur.

The white liquor in conduits 30, 130 is split into two substantially identical streams 42,43. One stream in conduit 43 has a degree of sulfidity of about 25%, and at a later stage of the cooking,
For example, it is used in the steamer 111. For the other stream in conduit 42, a gas stream containing primarily hydrogen sulfide (and possibly sulfur-free fuel gas) contacts the white liquor and substantially increases its sulphidity, exceeding 50% (In this example, about 74
%). This white liquor with a high degree of sulfidation can be
11 used in the initial stage of steaming (or impregnation vessel 44).

It will be appreciated that the present invention provides various methods for effective chemical recovery and pulping during cellulose pulping. While the invention has been shown and described herein in what is presently considered to be the most practical and preferred embodiment, it will be apparent to those skilled in the art that many modifications may be made within the scope of the invention. The scope of the invention should be consistent with the broadest interpretation of the following claims so as to encompass all equivalent processes and methods.

[Brief description of the drawings]

FIG. 1 is a schematic flow chart illustrating an example of a method for recovering and utilizing a chemical during the production of a cellulose pulp according to the present invention.

FIG. 2 is a partial process diagram illustrating details of a steamer and components equivalent to those in FIG. 1 for performing the correction method according to the present invention.

FIG. 3 is a partial process diagram illustrating the heat-treated portion of FIG. 1, illustrating the components used to implement another modification in accordance with the present invention.

FIG. 4 is a partial flow chart similar to FIG. 3 for implementing a further modification according to the invention.

[Description of Signs] 11 Steamer 13 Evaporator 14 Evaporator 15 Heat treatment device 16 Recovery boiler 17 Melt tank 18 Green liquor clarifier 18 Green liquor crystallizer 20 Temperature controller 21 Centrifugal separator 23 Sodium carbonate causticizer 25 Green liquor causticizer 26 Lime kiln 33 Bleaching plant 36 Sulfur / fuel gas recovery unit 48 Sulfuric acid production unit 51 Cleaning unit 53 Adjustment storage unit 54 Polysulfide production unit 111 Steamer 215 Heat treatment unit 236 Sulfur / fuel gas recovery unit 315 Heat treatment unit 323 Sodium carbonate causticizer

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Joseph R. Phillips Glens Falls, NY, USA Ridge Center, Kamiya, Inc. (no address), Incorporated Notice (72) Inventor Brian F. Greenwood Glens Falls, New York, USA Ridge Center, Kamiya, Inc. (no address), Incorporated Notice (72) Inventor Janty. Richardsen Glens Falls, NY, USA Ridge Center, Kamiya, Inc. (no address), Incorporated Notice (72) Inventor Jay. Wayne Shambury Glens Falls, Ridge Center, New York, USA, Kamiya, Inc. (no address) noticed (72) Inventor Tuomo Nikanen Glens Falls, Ridge Center, New York, United States, Kamya, Inc. (56) Noticed (56) References JP-A-50-123902 (JP, A) JP-A-49-2902 (JP, A) JP-A-52-27802 (JP, A) JP-A-51-116205 (JP, A)

Claims (19)

(57) [Claims] (A) heat treating the black liquor obtained from the production of cellulose pulp to drive off some of the sulfur-containing compounds as a gas therefrom; and (b) burning the heat-treated black liquor to form a melt. (C) dissolving the melt in a liquid to produce a green liquor; (d) adjusting the concentration of the green liquor and controlling the temperature to crystallize sodium carbonate to produce crystals; e) removing sodium carbonate crystals from the green liquor to produce a first stream of green liquor having a high degree of sulfidation; (f) causticizing said sodium carbonate crystals to produce a liquid containing sodium hydroxide; g) causticizing the first green liquor stream to produce a first white liquor having a high degree of sulfidation; and (h) combining the first white liquor with the sulfur compound-containing gas obtained by performing step (a). Various processes to increase the degree of sulfidation by contact Ranaru, a method for recovering and utilizing chemicals when manufacturing cellulose pulp with chemicals containing sulfur. 2. The method according to claim 1, wherein the step (g) is carried out so that the sulfidity of the first white liquor is about 25
%, And step (h) is performed to increase the degree of sulfidation of the first white liquor to greater than 50%. 3. The method of claim 1, wherein step (e) is performed by centrifugation, vacuum filtration, disk filtration, or sidehill screening. 4. The method of claim 1 wherein step (d) is performed with a temperature control of about 5-20 ° C. to produce decahydrate crystals. 5. The method of claim 1, wherein step (d) is performed at a controlled temperature of about 35 to 90 ° C. to produce monohydrate crystals.
The method described in. 6. The method of claim 1, further comprising treating the cellulosic fibrous material in the slurry of the initial pulping stage with a first white liquor. 7. The method of claim 6, wherein steps (a)-(f) are performed to produce a liquid containing sodium hydroxide that is essentially free of sulfur as the liquid containing sodium hydroxide. 8. The method of claim 7, further comprising treating the cellulose slurry at a later stage of pulping using a stream of sodium hydroxide that is substantially free of sulfur. 9. The method of claim 7, further comprising the step of using a substantially sulfur-free sodium hydroxide stream in a cellulose pulp bleaching plant. 10. The method according to claim 1, wherein step (d) is performed by controlling the solids concentration by adjusting the amount of liquid added in step (c). 11. The method according to claim 1, wherein step (d) is performed after step (c) by controlling the evaporation of the green liquor to control the solids concentration. 12. The method of claim 1, wherein step (d) is performed such that the concentration of sodium carbonate in the green liquor is maintained at a level that is not too high for effective causticization. 13. The method of claim 1, wherein steps (a) to (f) are performed to produce a liquid containing sodium hydroxide that is essentially free of sulfur as the liquid containing sodium hydroxide. 14. The method of claim 13, further comprising the step of using a stream of substantially sulfur-free sodium hydroxide in a cellulose pulp bleach plant. 15. The gas from step (a) is transferred to step (f).
2. The method of claim 1 further comprising the step of washing with a sodium hydroxide containing liquid to produce a sodium hydrogen sulfide containing liquid. 16. The process according to claim 1, wherein sulfuric acid is formed using the gas of step (a), and the sulfuric acid is used in the bleaching of cellulose pulp or in a prior acid hydrolysis. 17. (a) heat treating the black liquor obtained from the production of cellulose pulp to drive off some of the sulfur-containing compound as a gas therefrom; and (b) burning the heat-treated black liquor to form a melt. (C) dissolving the melt in a liquid to produce a green liquor; (d) adjusting the concentration of the green liquor and controlling the temperature to crystallize sodium carbonate to produce crystals; e) removing sodium carbonate crystals from the green liquor to produce a first stream of green liquor having a high degree of sulfidation; (f) causticizing said sodium carbonate crystals to produce a liquid containing sodium hydroxide; g) Causticizing the first green liquor stream to produce a first white liquor having a high degree of sulfidation, comprising the steps of: recovering chemicals when producing cellulose pulp using sulfur-containing chemicals; It is a method to use Splitting the first white liquor into two different streams, contacting one of the streams with the sulfur component removed from the black liquor during step (a) and leaving the other stream untouched. How to have. 18. A method for producing chemical pulp from a ground cellulose fiber material using white liquor in a pulping step containing a sulfur-containing fluid, comprising: (a) deliberately removing sulfur from the sulfur-containing fluid; (B) forming a first stream containing a sulfur compound and sodium carbonate; (c) adjusting the solids concentration and temperature of the first stream to produce sodium carbonate crystals in the first stream; (d) forming said sodium carbonate crystals. Separated from the first stream,
Next, the first stream is causticized to form a white liquor, (e) the sulfurity of the first stream is increased using the sulfur removed in step (a), and (f) using the separated sodium carbonate crystals. Forming at least a second stream of white liquor having a relatively low sulfur content, said first stream having a sulfur content substantially greater than the sulfur content of said second stream; A chemical pulp manufacturing process comprising the steps of chemically pulping a cellulosic material using first and second streams of white liquor added at different locations, and (h) washing the resulting chemical pulp. 19. The method of claim 18 wherein steps (a)-(f) are performed such that the second stream of white liquor is substantially sulfur free sodium hydroxide.