JP2876428B2 - Batch digestion method for pulp - Google Patents

Abstract

A method for improving pulp brightness utilizes a combination of a distributed total white liquor charge during the warm fill, hot fill and cooking stages of a batch cooking process and low cooking temperatures during the cooking stage. The high total white liquor charge ranges between 15 % AA &tilde& 35 % AA, while the cooking temperatures range between 150 &tilde& 168 DEG C._________________________

Description

Description: TECHNICAL FIELD The present invention relates to a method for improving the final shine of pulp,
In particular, the present invention relates to rapid displacement replacement heating (Rapid Displacement heating).
nt Heating (RDH) for both the cooking temperature of the cooking system and the replenishment of white liquor.

(Background technology)

Rapid Drain Displacement Heating ("RDH") is a low energy batch cooking method for making kraft pulp.
By combining the inherent effects of batch cooking with the energy efficiency of a continuous digester, RDH removes waste black liquor from cooked digesters to pre-treat wood chips in a continuous cook process. Reuse. Thus, both the heat and chemicals of these waste liquors are reclaimed and used for the next cook process. The pre-treatment of pre-treating fresh wood chips in a subsequent cook process begins with a low temperature liquor (about 80-130 ° C.), followed by a high temperature liquor (about 130-165 ° C.). The hot liquor is heated to a high temperature as possible digester, after which the temperature is raised to the final cooking temperature ⁽³ 170 ° C.) by steam.

RDH and other alkaline cooking methods produce pulp that is relatively dark in color. The pulp is usually bleached to a high degree of brilliance for white pulp for writing or printing paper or cardboard, since the use of pulp and paper usually requires a high contrast. Is done. Pulp color results from changes in the lignin component of the raw materials that occur during the pulp manufacturing process. Unfortunately, the use of high cooking temperatures in the RDH process and the use of low strength black liquor creates a problem of poor bleachability, after which the usual ECF and TCF bleaching steps must be used. Have to be. Higher cooking temperatures and the use of weaker black liquor promote the condensation reaction and cause lignin to condense with lignin extract and other wood extracts. As a result, the bleaching potential of the pulp is reduced.

Therefore, there is a need for alternative RDH cooking processes in the RDH cooking process to eliminate such negative side effects and to improve the bleachability of the pulp.

[Disclosure of the Invention]

The present invention provides a method for improving the shine of pulp. Based on a variation of the batch cooking process utilizing rapid drainage heating, the method of the present invention provides a method for preparing a white liquor solution (% active alkalinity (AA) or effective alkalinity (E
A)), or alternatively, adding NaOH to both the warm liquor filling stage and the initial hot liquor filling stage, and to produce pulp with improved bleachability, at temperatures higher than previously used in batch-type operations. Combines cooking wood chips at low temperatures. Therefore, the replenishment of the total white liquor of 15% AA to 35% AA is performed at the warm liquor filling stage,
The hot liquor filling phase and the cooking phase are dispensed in predetermined amounts. When using a cool pad in practicing the present invention, cool white liquor is added to black liquor discharged from the cool liquor accumulator. Basically, white liquor is added at all stages of the batch cooking process before the actual cooking process.

During chip cooking, white liquor and black liquor are present in the digester. The cooking temperature is low and ranges from 150C to 167C. Combining the supply of high AA or EA white liquor with the low cooking temperature improves the final shine of the pulp. As a result, the use of contaminants and bleaching chemicals in the pulp milling operation is reduced.

[Brief description of drawings]

FIG. 1 shows a schematic diagram of a digester and its associated devices used in current RDH cooking systems.

2A, 2B, and 2C are diagrams of white liquor, that is,
Figure 3 shows the addition of white liquor at various stages of the RDH cooking process. In FIG. 2A, plot A
Represents the case where a small amount of white liquor was added at the start of the warm liquor filling mode. Plot B represents the cooking stage and shows the presence of white liquor in the digester during the actual cooking of the chips.

FIG. 2B shows the continuous addition of white liquor to black liquor at each stage of the RDH cooking process, starting with warm liquor filling and continuing to the end of hot liquor filling.

FIG. 2c shows the continuous addition of white liquor at each RDH stage. It involves the addition of white liquor from the waste displacement tank to the wash filtrate.

FIG. 3 shows a stage 3 RDH system without the addition of white liquor between the warm liquor filling mode and the hot liquor filling mode.

FIG. 4 shows the RD of step 3 when white liquor was added between the warm liquor filling mode and the hot liquor filling mode.
Shows the H system.

FIG. 5 shows a plot of D1 brightness versus total (D100 + D1) chlorine supplementation for best case and baseline case RDH pulses. Plot A is RDH pulp R3 (0.225 Kappa coefficient)
Represents Plot B is RDH pulp R4 (0.27 Kappa coefficient)
Represents Plot C represents RDH pulp R7 (0.225 Kappa coefficient). Plot D represents RDH pulp R8 (0.27 Kappa coefficient).

FIG. 5A shows the relationship between D1 luminance and D1 = supplement of chlorine oxide.
Plot A represents RDH pulp R3 (0.225 Kappa coefficient).
Plot B represents RDH pulp R4 (0.27 Kappa coefficient). Plot C represents RDH pulp R7 (0.225 Kappa coefficient). Plot D represents RDH pulp R8 (0.27 Kappa coefficient).

Figure 6 shows the D100 for all 0.225 Kappa factor bleach.
The relation between the total chlorine supply amount and the D1 luminance in the stage and the D1-stage is shown. Plot A represents RDH pulp R3. Plot B
Represents RDH pulp R12. Plot C represents RDH pulp R7.

FIG. 6A shows the relationship between D1 luminance and the supply amount of chlorine dioxide at the D1 stage. Plot A represents RDH pulp R3 (0.225 Kappa coefficient). Plot B shows RDH pulp R12 (0.225 Kapp
a coefficient). Plot C shows RDH pulp R7 (0.225 Ka
ppa coefficient).

FIG. 7 shows the D100 for all 0.27 Kappa factor bleach.
The relationship between the total chlorine replenishment amount and the D1 luminance at the stage and the D1 stage is shown. Plot A represents RDH pulp R4. Plot B is R
Represents DH pulp 12. Plot C represents RDH pulp R8.

FIG. 7A shows the relationship between the D1 luminance and the chlorine dioxide supply amount in the D1 stage. Plot A represents RDH pulp R4 (0.27 Kappa coefficient). Plot B shows RDH pulp R12 (0.27 Kappa
Coefficient). Plot C shows RDH pulp R8 (0.27 Kappa
Coefficient).

[Best mode for carrying out the invention]

The present invention provides a method for improving pulp bleachability based on a modification of existing RDH cooking systems for wood chip digestion. In particular, the method involves the replenishment of white liquor starting at the start of the RDH cooking cycle and continuing until the time reaches the temperature stage of the process. In the time leading up to the temperature stage, the actual cook begins. The method of the present invention is also based on the use of somewhat lower cooking temperatures for actual cooks as compared to the cook temperatures commonly used in the RDH pulp manufacturing process.

According to the invention, a total white liquor replenishment of about 15% AA to 35% AA is distributed over the warm black liquor filling phase, the initial hot black liquor filling phase, and the cooking phase. In use, Cool Pat or Cool Liquor Accumulators also accept White Liquor. The present invention, in addition to using dispensed white liquor, uses a low cooking temperature of about 150C to 167C. The result is a pulp having improved final brightness when bleached with a combination of bleaching chemicals.

The operational stages of a typical RDH cooking system are as follows. That is, (1). Chip filling, (2). Filling of cold black liquor, (3). Filling of warm black liquor, (4). Hot black liquor filling, (5). The time to reach a certain temperature, (6). Time at a certain temperature, (7). Drainage replacement, (8). Pump out. For the basic principles of RDH operation, see US Patent No. 4,578,149 (issued March 25, 1986).
, The entire contents of which are incorporated herein by reference. Therefore, the details of the operation of the RDH are in the range required for those of ordinary skill in the art to consider various variations of the RDH cooking system for producing bleachable grade pulp described herein. Are described.

Figure 1 shows the type of RDH required for digestion of pulp.
1 schematically shows an apparatus for use. It should be understood that this figure shows very general features of a cooking device. As detailed below, variations and changes to this system may,
It is possible. For example, many devices such as gauges, pressure relief ports, pumps and valves have been omitted to simplify the drawing. FIG. 1 is used to illustrate an existing RDH cooking process, which facilitates understanding of a method improvement in accordance with the principles of the present invention.

Referring to FIG. 1, there is shown a digester 10 of the type commonly used for chemical digestion of wood chips.
The digester 10 has a truncated bottom 12. The inflow valve 14 regulates the inflow of various reaction liquors flowing into the digester 10. Although not shown, the contents of the digester 10 are ultimately obtained by discharging cooking liquor via a heat exchanger or steam sprayer connected to the digester 10 by a valve-controlled line. Heated to cooking temperature.

After the wood chips are added to the digester 10, cool black liquor (temperature of about 70 ° -95 ° C.) is supplied from a cool liquor accumulator (A tank) to a pump 18 through a pipe 20 controlled by a valve 22. Is discharged to the bottom of the digester 10 through the inflow valve 14.

Next, warm black liquor (at a temperature of about 90 ° -150 ° C.) is discharged from the warm liquor accumulator 24 through the valve 22, through the valve 14 and to the bottom of the digester 10 by the pump 18. While this warm liquor is being filled, some of the black liquor is discharged from digester 10,
It is returned to the cool liquor accumulator 16 by the pipe 26.

Hot black liquor (temperature between 150 ° and 168 ° C.) is then discharged from the hot liquor accumulator (C-tank) 28 to the bottom of the digester 10 using the valve 14 by the pump 30 controlled by the valve 32. During the filling of hot black liquor, black liquor is discharged from digester 10 and passes through lines 34 and 36, respectively, to warm liquor accumulator 24 and hot liquor accumulator 28.
Returned to

During the filling of the hot liquor, hot white liquor stored in the hot white liquor accumulator 38 is pumped by the pump 30 where the hot white liquor merges with the hot black liquor from the hot liquor accumulator 28. The combined liquor is then sent through valve 32 to the base of digester 10.

After hot liquor filling is complete, the inlet and outlet valves to the digester 10 close when the ticking of the temperature phase begins. Steam is injected into the digester 10 and the temperature rises to an average cooking temperature of about 170 ° C. The temperature of the digester is maintained at this temperature until the wood chips are digested, depending on the supply of white liquor and the H coefficient.

When the cooking step is completed, the washing filtrate (temperature of about 70 to 85 ° C.) stored in the drainage replacement tank (D tank) 40 is discharged to the digester 10 using the pump 42 and the valve 44. There, the contents are washed and digester 10
Is cooled. When the wash filtrate is added to the digester 10, the waste liquor is drained and returned to the warm liquor accumulator 24 and the hot liquor accumulator 28 via lines 46 and 48, respectively. When all of the wash filtrate has been used, its drain replacement mode ends. It is based on the dilution factor of the washing solution. After the drainage replacement is completed, the digested pulp is discharged from the digester 10 to a discharge tank using the pump 50.

Current RDH cooking systems use a cooking temperature of 170 ° C. or higher for rapid cooking, accelerating the condensation reaction. As a result, the pulp becomes normal ECF and T
When subjected to CF bleaching, bleaching problems arise.

Thus, the present invention overcomes these problems and improves the bleachability of pulp by modifying the wood chip cooking process. This improved RDH process
It utilizes a combination of high alkalinity (ie, white liquor replenishment) and low cooking temperature. In particular, white liquor is added during the warm liquor filling stage and the first hot liquor filling stage. This method contrasts with existing RDH cooking processes. Existing methods add white liquor only in the middle of the hot liquor filling mode.

Further, when a cool pad is used in the present invention, white liquor is added to cool black liquor sent from a cool liquor accumulator (ie, A tank). Thus, from the start of the RDH cooking process to the time to the temperature stage, white liquor is added to black liquor at each stage. The addition of white liquor at each stage, also called a white liquor chart (profiling), is shown in FIGS. 2A, 2B and 2C and is described in detail below.

In FIG. 2A, plot A shows the addition of a small amount of white liquor as warm black liquor exits the B tank, the warm liquor accumulator and flows into the digester, at the start of the warm liquor filling mode.
When the A-tank, cool pad, is used, white liquor can also be added thereto. When using two hot liquor accumulators C1, C2, at the end of the hot liquor filling mode, a mixture of white liquor and black liquor remains in the digester. Plot B represents the cooking stage and shows the presence of white liquor in the digester during the actual cooking of the chip. Black liquor also exists during the cooking process.

FIG. 2B shows that white liquor is continually added to black liquor at each stage of the cooking process, starting with the filling of warm liquor and ending with the filling mode of hot liquor.

FIG. 2C illustrates the continuous addition of white liquor through various stages, including the addition of white liquor to the wash filtrate from the drainage displacement tank.

The concentration of organic material dissolved in the first hot liquor filling operation (C1, C2 tanks with black liquor) is compared between hot liquor filling operation and white liquor addition during hot liquor filling operation. Was.

FIG. 3 shows a stage 3 RDH system. In that case, no white liquor was added during the warm and hot liquor filling modes. Only warm black liquor is warm liquor accumulator (B tank) 24
Exits and flows through line 56 to line 20 and then to digester 10 during the warm liquor fill mode.

Although this RDH system has two hot liquor accumulators 28 (C1 tank) and 58 (C2 tank),
Some RDH pulp manufacturing processes use only one hot liquor accumulator. In practicing the present invention, the white liquor profile formation process can be applied to any number of systems having a black liquor accumulator.

As shown in FIG. 3, during the first hot liquor filling mode,
The hot black liquor exits the hot liquor accumulators 28 and 58 via lines 60 and 62, respectively, and flows to the digester 10 via lines 64 and 20. In the middle of hot liquor filling time, hot white liquor accumulator 38
Hot white liquor accumulator from line 66
Mix with the hot black liquor that has left the hot liquor accumulator 58. The mixture is then
Flows through 4 and 20 to digester 10.

FIG. 4 shows a stage 3 RDH system, in which white liquor is added between the warm liquor filling mode and the hot liquor filling mode. First, white liquor is added to the warm black liquor leaving the warm liquor accumulator 24 via line 70 during warm liquor filling. The warm liquor flows to the digester 10 via lines 56,20. During the warm liquor filling mode, cool white liquor or hot white liquor is used.

During the first hot liquor fill mode, hot white liquor from hot white liquor accumulator 38
72 mixes with the black liquor leaving the hot liquor accumulator 28, and further through the lines 62 and 66
Is mixed with black liquor that has left the hot liquor accumulator 58. The mixture of hot white liquor and black liquor flows from the two hot liquor accumulators 28,58 to the digester 10 via lines 64,20.

 The result of the comparison is as follows.

When white liquor is not added during hot liquor filling operation and hot liquor filling operation (Fig. 3) When white liquor is added during hot liquor filling operation and hot liquor filling operation (Fig. 4) White liquor replenishment: 1.5% for C1 black liquor
1.5 for AA C2 Black Liquor
% AA This case study clearly demonstrates that during the first hot liquor filling operation, the concentration of dissolved organic components is adjusted by adding white liquor to the hot liquor filling line. The concentrations of the organic components dissolved in the C1 black liquor and the C2 black liquor were 13.1 respectively.
% To 10.1% and from 14.9% to 9.8%.

In the RDH process, in order to maximize the effect of bleachability and promote lignin removal, warm black liquor (temperature between about 70 ° and 150 ° C, its intensity is 3-20g / IA
A) and hot black liquor (temperature is about 100 ° ~ 168 ° C
The strength of 8-30 g / IAA) must be reinforced by white liquor or combination with NaOH solution.

As shown in the previous figures, warm and hot black liquor is changed using white liquor profiling. These liquors are also modified by profiling of sodium hydroxide (NaOH). The addition of white liquor or NaOH controls the total concentration of dissolved solids (TDS) and the strength of black liquor using a combination of black liquor, white liquor and NaOH. Black liquor temperature is about 50
° -150 ° C, black liquor strength is 1-18g / I
The wash filtrate replacement step, as retained in the AA, is enhanced with a combination of white liquor or NaOH solution.

The following examples illustrate the invention in its preferred embodiment, but the invention is not limited thereto.

As shown below, Tables 1, 1A, 2, 2A, 3, and 3A show the conditions and pulp production results for several cooks used in producing RDH pulp for subsequent bleaching studies. A summary of the pulp production results is shown in Table 3B.

Five (5) RDH pulp (R3, R4, R7, R8, R23) were bleached using the (0) (D100) (E0) (D) sequence. However, each of the five RDH pulps initially used oxygen delignification in a stirred reactor using the conditions shown below in Table 4.

When studying bleaching, D10 for pulp R3, R7, R12
When calculating chlorine dioxide in a zero step, a 0.225 kappa coefficient was used. For pulp R4, R8, R12, a 0.27 Kappa coefficient was used. The following Tables 5 to 10 show the (D100) (E0) of the pulp that was delignified with oxygen by these cooking treatments.
(D) Bleaching conditions and results are shown. The chlorine dioxide solution concentration was adjusted by a factor of 0.92 during bleaching to compensate for the loss of chlorine dioxide when filling reactors and polyethylene bags.

As shown in FIGS. 5 and 5A, increasing the kappa coefficient did not reduce the chlorine dioxide requirement of stage D1. The best case RDH pulp (R3, R4) showed a brightness 1.5 to 2.0 higher than the baseline case RDH pulp (R7, R8) at the same chlorine dioxide replenishment rate.

From FIGS. 6 and 6A, it can be seen that the feasible best case RDH pulp (R12) exhibits an intermediate brightness between the best case RDH pulp (R3) and the baseline case RDH pulp (R7).

Seventh and 7A illustrate that the viable best case RDH pulp (R12) exhibits an intermediate brightness between the best case RDH pulp (R4) and the baseline case RDH pulp (R8).

A summary of the results from this pulp bleaching study,
It is shown in Table 11. The most bleachable pulp was the best case pulp. The least bleachable pulp was the baseline case pulp, and the viable best case bleachability was somewhere in between. From this result, high alkalinity (white liquor is added in warm liquor filling mode and hot liquor filling mode, white liquor is also added in the cooking stage, and AA is supplied between 15% AA and 35% AA) and low temperature Cooking temperature (about 150 ℃
167167 ° C.) can be shown to improve the bleachability of the pulp and thus improve the final brightness of the pulp. During the RDH cook process, the strength of the black liquor must be maintained.

It will be apparent to those skilled in the art that various modifications and variations can be made to the preferred embodiment described herein. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its advantages. It is therefore intended that such changes and modifications be covered by the appended claims.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) D21C 3/02 D21C 11/00

Claims (11)

(57) [Claims] Claims 1. Cooking a lump of cellulosic material with a cooker liquor results in replacement of waste liquor generated in the digester (10), which becomes hot black liquor and warm black liquor in the accumulator (24,
28, 58), and collects and uses the heat of waste liquor, and uses the waste liquor of progressively higher temperature before cooking to replace the warm black liquor and hot black liquor with a drainage displacement pretreatment. The mass of cellulose material is preheated, and in order to make delignified pulp, in a batch type digestion method using a rapid drainage replacement heating method, the warm black liquor of the digestion method is used. 70-
Add white liquor to hot black liquor at 150 ° C, add white liquor to hot black liquor at 100-168 ° C in the hot black liquor pretreatment stage, add white liquor to cooking liquor in the cooking stage, and the total amount of white liquor added there is Between 15% active alkali and 35% active alkali, wherein the temperature of said cooking liquor is 150
A batch type digestion method for pulp, characterized in that the temperature is raised to ~ 165 ° C. 2. The method according to claim 1, wherein said white liquor solution is added in a predetermined amount to warm black liquor (temperature of 90 to 150 ° C.) and to hot black liquor (temperature of 150 to 165 ° C.). The batch digestion method for pulp according to 1. 3. The method of claim 3, wherein the white liquor is added to cool black liquor (70-90 ° C.) and the cellulosic material mass is pre-treated with the cool black liquor to which the white liquor is added before pre-treatment with warm black liquor. The method for batch digestion of pulp according to claim 1, wherein the pulp is digested. 4. A preferable total amount of white liquor is>
The batch digestion method of pulp according to claim 1, which is 20% AA. 5. A process for batch digestion of pulp according to claim 1, wherein the preferred cooking temperature is 150-165 ° C. (A). Introducing a wood chip into the digester (10); (b). Pre-treating the chips with warm black liquor below the cooking temperature; (c). Replacing the warm black liquor from the digester (10) with at least one volume of hot black liquor; (d). Raising the temperature of the digester (10) to the cooking temperature; (e). Maintaining said temperature until the chip is digested; (f). Replacing the contents of the digester (10) with the filtrate resulting from the washing of the pulp; (g). By applying gas pressure inside the digester (10) or by pumping it out
Emptying the contents of the digester (10), white liquor is added to the warm black liquor of 70 to 150 ° C used in the pretreatment step, and 100 to 1 in the replacement step.
White liquor is further added to the hot black liquor at 68 ° C.
2. The method according to claim 1, wherein a maximum temperature of .degree. C. is achieved.
A method of producing bleachable grade pulp according to the method of 1. 7. Pre-treating the chips with a mixture of cool black liquor and white liquor (or NaOH solution) prior to the step of pre-treating with warm black liquor.
The pulp manufacturing method according to claim 6. 8. The total white liquor used is 15% AA ~
7. The pulp manufacturing method according to claim 6, having a total amount of 35% AA. 9. The preferred total amount of white liquor added is> 20.
The pulp manufacturing method according to claim 8, wherein the pulp is% AA. 10. The pulp manufacturing method according to claim 6, wherein a preferred cooking temperature is 155 to 165 ° C. 11. The washing filtrate and white liquor (or NaOH).
The method for producing pulp according to claim 6, which comprises a step of replacing the contents of the digester (10) with a combination with the solution).