JPH05195466A - Method for oxygen delignification improved by cleaning press - Google Patents

Abstract

PURPOSE: To provide a method to achieve high delignification selectivity of pulp in a process of high concentration oxygen delignification process. CONSTITUTION: A method to achieve high delignification selectivity of pulp in a process of high concentration oxygen delignification comprises each following process; applying the first amount of alkaline material to a pulp by washing the pulp with a solution of alkaline material to condense the pulp to high concentration of at least 18 weight % in a wash press, distributing substantially uniformly the first amount of alkaline material through the washed pulp, extracting pressate from the wash press, applying a total amount of alkaline material of at least about 0.8-7 weight % by a measure of weight of oven dry pulp where the total amount contains even the first amount, delignifing oxygen for the alkaline material containing high concentration pulp, and obtaining a high delignification selectivity and oxygen delignification pulp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wood pulp, and more specifically, it distributes an alkaline substance to a brown raw material pulp before oxygen delignification to improve the strength of the pulp after the oxygen delignification. It relates to a process which makes it possible to obtain highly delignified pulp without adversely affecting it.

[0002]

BACKGROUND OF THE INVENTION Wood contains most cellulose and hemicellulose fibers and amorphous non-fibrous lignin that functions to keep the fiber portions together. The hemicellulose and cellulose are often collectively referred to as holocellulose. When wood is treated to produce pulp, it is converted to a fiber mass by removing most of the lignin from the wood. Thus, the process of making paper as well as paper products generally involves a pulping process in which the wood, usually as wood chips, is converted to a fiber mass. Several different pulping processes are known in the art and are generally classified as mechanical, chemical or semi-chemical processes. Chemical pulping processes involve a great variety of steps, such as the bisulfite process, the soda process and the kraft process. The chemical pulping process generally introduces wood chips into a digester where the chips are digested in a chemical liquor. In the Kraft process, the cooking liquor contains a mixture of sodium hydroxide and sodium sulfide. After a predetermined cooking time, the softened and delignified wood chips are removed from the cooking liquor to produce a pulp fiber mass. This pulp made by the chemical pulping process is called "brown stock". Typically, the brown stock is washed to remove the cooking liquor and then processed to produce unbleached grade paper products or bleached to produce high brightness paper products.

In principle, many bleaching processes for brown raw materials require further delignification of the brown raw material, since the chromophores on the lignin cause the coloring of the pulp.
For example, the brown raw material can be further delignified by reacting it with elemental chlorine in an acidic medium or with hypochlorite in an alkaline solution. After these steps, it is typically reacted with chlorine dioxide to give a fully bleached product. Oxygen delignification is a frequently used pulp bleaching method these days because it uses inexpensive bleaching agents and forms by-products that can be incinerated in recovery boilers to reduce environmental pollution. Oxygen delignification often involves a bleaching process that uses chlorine or chlorine dioxide, but requires less bleach and produces less environmental pollutants. The reason is that bleaching is also achieved in the oxidation step. In some bleaching processes, the pulp is bleached while maintaining the pulp consistency low to the medium level. Pulp concentration is a measure of the percentage of solid fiber material in the pulp. Pulp with a concentration of less than about 10% by weight has a medium to low concentration
(The low to medium range of pulp consistency). The method requiring bleaching at a low concentration such as a medium concentration is described in the following patents or publications.
U.S. Pat.No. 4,198,266 to Kirk et al., U.S. Pat.No. 4,431,480 to Markham et al.
rough), U.S. Pat. No. 4,220,498, and Kirk et al., "Low-consistency Oxygen Delignification in a Piperine Reactor-A Pilot Study".
in a Pipeline Reactor-A Pilot Study), TAPPI, 1978, May. Each of the above references describes an oxygen delignification process that is operated on pulp at a medium level of low consistency.

Elton US Pat. No. 4,806,203
No. 4,529,097 discloses a preferred alkaline extraction for chlorinated pulp, where the timely removal of alkaline solution is an essential step to prevent redeposition of dissolved lignin on the pulp. If the process is too short or too long, the method provides little benefit. Oxygen delignification of wood pulp can be carried out on high concentrations of fluff pulp in a pressure reactor. During the oxygen delignification stage, the pulp consistency is typically maintained within the range of about 20-30% by weight. Gaseous oxygen is about 80 to about 100 psig
Is introduced into the high-concentration pulp at a pressure of and is reacted with it. GA smook's Handbook for Pulp and
Paper Technologists), Chapter 11.4 (1982).
In a previous oxygen delignification operation, the pulp after cooking was washed and dewatered to form a high concentration mat, which was then treated with an alkaline solution over the surface of the mat. Coated with a thin film or layer of solution. The amount of alkaline solution applied to the mat is about 0.8-7% of the oven dried pulp. The previously utilized concentrated oxygen delignification methods have several drawbacks. In particular, the application of an alkaline solution to a mat of high-concentration pulp does not evenly distribute the solution throughout the fiber mat and is not compatible with the general porosity of such mats. As a result of this non-uniform distribution, certain areas of the concentrated matte, usually its outer portion, are exposed to excess amounts of the alkaline solution. It is believed that this excessive exposure results in non-selective degradation of the holocellulose, producing at least in part a relatively low strength pulp. On the other hand, other parts of the concentrated mat, typically its inner parts, are not fully exposed to the alkaline solution and do not give a certain degree of delignification. Thus, overall performance is reduced.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of achieving high delignification selectivity of pulp during a high concentration oxygen delignification process, in which method the oxygen delignification is carried out. Pulp has higher strength and lower lignin content than is achieved by conventional methods. In addition, a wash press is used to apply a quantity of alkaline material to the pulp while reducing the amount of solids on the pulp entering the oxygen delignification reactor.

[0006]

According to the present invention, unbleached pulp is washed in a washing press with a solution of an alkaline substance to a consistency of at least about 18% by weight, whereby An amount of alkaline material is applied to distribute the first amount of alkaline material substantially uniformly over the pulp. This uniformly distributed first amount of alkaline material is compared to processes in which the alkaline material is applied to high-concentration pulp or to relatively low amounts of low-concentration pulp to achieve high-concentration oxygen delignification. Is sufficient to help increase the selectivity of the. According to one aspect of the invention, the pulp is a brown raw material, which raw material is washed with a sufficient amount of alkaline material such that the first amount applied to the pulp is equal to its total amount. Prior to passing to the wash press, the pulp is mixed with dilution water to obtain a low consistency pulp having a concentration of less than about 5% by weight, preferably in the range of about 1 to 4.5% by weight. The washing press thickens the pulp and discharges the pressate. At least a portion of this pressate can be used as the dilution water. The pressate can include an alkaline material, in which case a portion of it can be utilized to wash the pulp prior to introducing the pulp to the wash press. Ideally, the wash press operates under a substitution ratio of at or near a dilution factor of 0 and as close to 1 as possible, thus minimizing the amount of total alkali required. However, since it is difficult to achieve and maintain these values in industrial operation, the wash press has a dilution factor of 0.4 or less, preferably less than 0.25 and at least about 0.5, preferably about 0.
It should work above 75.

In the second embodiment, a split alkaline material addition sequence is used to apply the total amount of alkaline material to the pulp. A first amount of the alkaline material is applied to the pulp in the wash press, while a second amount is applied to the concentrated pulp. This reduces the amount of alkaline material used in the wash press. For either aspect, a predetermined amount of pressate can be retained in the storage tank. This amount of pressate can be recycled directly to the pulp / dilution water mixing stage and returned continuously. The total amount of this alkaline material applied to the pulp is generally about 0.8 to 7% by weight, based on oven dried pulp.
, The pulp is then subjected to oxygen delignification to achieve a high degree of delignification. The present invention relates to a method of treating a brownstock pulp with an alkaline material prior to concentrated oxygen delignification, in which method the amount of solids and alkaline material deposited on the pulp is minimized. The pulp is processed substantially uniformly. U.S. patent application Ser. No. 07 / 489,845 demonstrated that the selectivity of delignification of pulp undergoing a high concentration oxidation step can be enhanced by a substantially uniform distribution of alkaline material throughout the pulp. This distribution is accomplished by mixing the alkaline material and the low consistency pulp before pressurizing the pulp to a high consistency. Thus, a reduction of more than 50%, and generally at least 60% or more, of the K value in pulp undergoing the oxidation stage can be achieved without essentially damaging the cellulose portion of the pulp.

Embodiments of the present invention provide an unexpectedly high improvement in delignification selectivity as compared to a method of sprinkling concentrated pulp with alkaline material after being discharged from a press or other thickening device. Prove. From a pulp K number in the range of about 10 to 26 (depending on the type of wood and the type of pulping carried out on a particular wood) when released from the oxidation reactor, after oxygen delignification, about It is shown by a reduction of 5-10, which increases the viscosity of the pulp to about that of the input pulp.
With a variation from 19 cps to at least about 13 cps for the oxygen delignified pulp. These data are summarized and illustrated in the graph of FIG. 1 for softwood pulp. This patented method is successful but requires the use of larger amounts of alkaline material compared to the method applied by spraying. Most of the alkaline material is retained in the pressate. The process of the present invention uses a wash press to introduce alkaline material into the pulp, and by using a smaller amount of alkaline material than the patented method of distributing alkaline material, the alkalinity throughout the pulp is reduced. Equivalent results have been achieved with a uniform distribution of the substance. Furthermore, the same amount of alkaline material was distributed substantially uniformly throughout the pulp, thus providing similar advantages associated with increased selectivity of delignification of the pulp via a subsequent oxygen delignification step. It can be achieved.

The washing press comprises two synchronous, counter-rotating dewatering rolls, which rolls are and are so shaped as to have a dewatering section, a washing section and a final extraction section. Is designed. Pulp is introduced into the wash press at a low concentration of about 3.5% by weight in solution with dilution water. In the first dewatering section, the concentration is increased to about 10% by weight and a pad is formed on the roll.
In the wash section, wash water is introduced into the unconstrained side of the pad and begins to pass through it, displacing the dilution water in the pad. In the extraction (or consolidation) part, additional dilution water and wash water are displaced from the pad to increase the pulp consistency.
This pulp then exits the press at a high consistency in the range of about 25-35% by weight. In order to understand the present invention, it is necessary to be familiar with the terms and conditions associated with pulp washing.
The term "dilution water" is used to describe the water that is combined with the pulp as it leaves the press. The term "wash water" means the water added to the press independent of the pulp.

[0010] The term "dilution factor"
Means an amount of wash water added to the wash press that exceeds the amount required to displace the amount of water that exits the press with the pulp at the wash press outlet concentration.
The dilution factor (DF) would be 0 for the amount of wash water needed only to displace only the amount of water leaving the press with the pulp. This factor is expressed as the amount of water per pound of air-dried (AD) fiber, where 1 pound AD fiber equals 0.9 pounds of oven-dried (OD) fiber. This dilution factor is calculated according to the following formula. DF = WT-((0.9 lb OD fiber / 1 lb AD fiber) x (100
-C) / C] where WT is the amount of wash water used (expressed in pounds per pound of AD fiber) and C is the concentration of pulp exiting the wash press. For example, for pulp with 0 DF and a 28% consistency, the amount of wash water needed to replace the amount that exits the press with the pulp is calculated as follows. 0 = WT- [0.9 x (1-0.28) /0.28], or WT = water 2.31
Pounds / pound AD fiber. Amounts of water above this value of 2.31 give the excess released from the wash press as pressate.

The term "displacement ratio" refers to the washing press divided by the maximum change that can occur, ie the difference between the concentration of a component in the wash water and the concentration of the same component in the dilution water. It refers to the fraction that represents the actual change in the concentration of the component dissolved in the dilution water associated with the exiting pulp. The substitution ratio (DR) can be calculated from the following formula. _{DR = (X OUT -X IN)} / - with (X _W X _IN) where, X _OUT is the concentration of a particular component with the dilution water exiting with the pulp, X _IN during the wash press X _W is the concentration of the same component in the incoming dilution water and X _W is the concentration of the same component in the wash water. When X _OUT = X _W , the substitution ratio is 1, while for substitution ratios less than 1, X _OUT = (DR) (X _W ) + ((1-DR) (X _IN ) For example, , DR is 0.75, X _OUT = 0.75 (X _W ) +0.25 (X
_IN ) while DR is 0.5, X _OUT =
It becomes 0.5 (X _W ) +0.5 (X _IN ).

Usually, the concentration of unwanted components in the wash water is
Pulp whose degree is substantially lower than its concentration in the dilution water
, When removing components such as black liquor solids,
The concept of cleaning applies. However, in the present invention,
How is the concentration of components (eg alkaline substances) in the wash water
To a concentration higher than its concentration in the dilution water to
Whether it can be added to this rather than removed from the pulp
Use these relationships to show. From the formula shown above
As is clear, the dilution factor is 0 and the substitution ratio is 1.
Theoretically, the
All alkaline substances (concentration X _WIn) the cleaning pre
It will be retained in the pulp as it exits the soot. this
Industrial operation of the washing press, contained in the pulp
It is not possible to completely replace the dilution water with the wash water
However, this process requires a dilution factor of about 0.4 or less and 0.5
The above substitution ratio should be used. With this,
The following three advantages are obtained over the clear method. 1) A very small amount of alkaline material from the cleaning press
It is only lost during the resset, 2) the concentration of alkaline substances in the wash water (X_w)
Achieves a quick response to pulp changes by
3) Thorough washing occurred in the press, and no
Carryover of other impurities into the oxidation reactor
Substantially reduced.

Another advantage of this embodiment of the process of the invention is that the control method and equipment for the introduction of the alkaline substance are simplified in that only one point of addition is required. Is. Accordingly, the present invention provides high performance, high strength delignified wood pulp from kraft pulp or pulp produced by other chemical pulping processes. A preferred starting material is unbleached pulp obtained by cooking wood chips or other fibrous materials in a cooking liquor, for example by the Kraft or Kraft AQ processes. Referring to FIG. 2, a wood chip 1 and a white liquor 2 containing sodium hydroxide and sodium sulfide are introduced into a cooking shaving 3. A sufficient amount of white liquor should be added to the digester to substantially coat the wood chips. The contents of the cooked sesame are then heated at a temperature and for a time sufficient to allow the white liquor to substantially impregnate the wood chips and substantially complete the cooking reaction. This wood chip cooking process is well known as kraft cooking or kraft process, and the pulp produced by this method is known as kraft pulp or kraft brown raw material. Depending on the lignocellulosic starting material, the results of this delignification obtained by the known Kraft process can be improved by the use of the extended delignification process or the Kraft-AQ process. Moreover, these processes are preferred to achieve the greatest degree of reduction of the K number of the pulp without adversely affecting the strength and viscosity properties of the pulp during this cooking stage.

When utilizing the Kraft-AQ process, the amount of anthraquinone in the cooking liquor should be at least about 0.01% by weight, based on the oven dry weight of the wood to be pulped, generally 0.02 to about 0.1. Amounts in the range of% are preferred. The presence of anthraquinone in the kraft pulp process contributes to the substantial removal of the lignin without adversely affecting the desired strength properties of the remaining cellulose. Also, this ancillary cost of anthraquinone is partly eliminated by the cost savings of the chemical reagents used in the bleaching process, which involves oxygen delignification of the pulp. In addition to or in addition to the Kraft-AQ method, extended delignification techniques such as Kamyr MCC method, Beloit RDH method and Sands superbatch method (S
unds Super Batch Method) is used. These techniques also provide the ability to remove large amounts of lignin during cooking without adversely affecting the desired strength properties of the remaining cellulose. The digestive sesame 3 produces a black liquor containing a reaction product of lignin solubilization together with the brown material 4. This digestion step is typically a washing step in which dissolved organics and cooking reagents are removed for recycling and recovery purposes, and screening is performed by passing the pulp through a screening apparatus to remove fiber bundles that have not been separated during pulping. Involves steps. The brown raw material 4 is then guided to the blow tank 5.

The brown raw material 6 discharged from the blow tank 5 is washed in a washer 7, generally with an effluent 8 produced by washing pulp downstream of the oxygen delignification reactor. The washed pulp 9 exits the washer 7 at a concentration of about 15-18% by weight and is sent to a dilution tank 10 where it is diluted to a concentration of about 3.5% by weight. The starting point dilution water is supplied by filling the tank 10 with water 11. The pulp / diluted water stream 12 is then directed to a wash press 13 where alkaline material is added to the pulp. A preferred cleaning press 13 is the Displacement Press available from Sunds Defibrator AB of Sundsvall, Sweden.
It is DP. Other two-roll presses are available, but as noted above, they must have a combination of pulp dewatering, washing and displacement parts. The Sands device has 2
It contains two synchronous, counter-rotating dewatering rolls in a pressure vat with one pulp inlet. A pad of pulp having a concentration of about 10% by weight is formed on the roll at the end of the dewatering section.

A solution of sodium hydroxide 14, oxidized white liquor or other equivalent alkaline material is used to wash the pulp in the wash press 13. This solution 14 is preferably prepared by mixing concentrated alkaline material with the effluent of the bleached pulp wash water. This solution 14 is then introduced to the unconstrained side of the pulp pad and migrates through the pulp pad, displacing the dilution water therein. By operating with a substitution ratio close to 1 and a dilution factor close to 0, much of the alkaline material used to wash the pulp is distributed substantially uniformly over the pulp, and Held in. As noted above, the wash press 13 should be operated under a dilution factor of less than 0.4 and a substitution ratio of at least about 0.7 to achieve the desired distribution of alkaline material on the pulp. The alkaline material containing this pulp is then
Exit the wash press 13 at a concentration of 35% by weight. In many preferred embodiments, pulp 15 has a concentration of about 28-29% by weight. The wash press 13 compares, for example, with the use of chests to add alkaline material to the pulp,
It makes it possible to reduce the amount of alkaline substance used to apply a given amount on the pulp. Also, the cleaning press
The amount of organic and / or inorganic solids on the pulp exiting 13 is reduced so that most of these contaminants are not carried by the pulp in the oxidation reactor. Thus, smaller amounts of chemical reagents are consumed during the oxidation reaction with the pulp. Further, as compared to known scrubbers, a smaller amount of alkaline material is introduced into the liquid recovery system of this plant due to the release of the pressate or due to the "breakthrough" of the pressate into the scrubber effluent. Brought out.

Those skilled in the art can select an appropriate amount (ie, concentration and flow rate) of alkaline material 14 to be added to the wash press in this step to achieve a predetermined amount of alkaline material distribution throughout the pulp. In particular, the aqueous sodium hydroxide solution 14 has an OD after its concentration has been increased by the washing press.
Combined with the pulp in an amount sufficient to provide at least about 0.8 to about 7% by weight sodium hydroxide on the pulp, based on the pulp. As mentioned above, other sources of alkaline material having an equivalent sodium hydroxide content may be used, for example oxidized white liquor. The wash press 13 contains a residual liquid 16 from the pulp, also called pressate or wash filtrate.
To remove. Also, alkaline material that was not retained on the pulp due to less than ideal displacement would be included in this pressate 16. This pressate 16
Is sent to a storage tank or seal tank 17, which can be used to hold all the pressate 16 from the wash press 13 to achieve smooth continuous operation of the process. Dilute tank 10 with at least a portion 18 of pressate 16
Recycle to. At start-up, the storage tank 17 is filled with a suitable source of dilution water 11, typically fresh water. During the continuous operation of this process, a portion 18 of the pressate is returned to the dilution tank 10 to make up substantially all of the dilution water. Thus, stream 11 is utilized only at start-up (ie, before the pressate is produced by the wash press 13) or only when additional dilution water needs to be used. Also, a portion 19 of the pressate can be used as part of stream 8 in the washer 7 to wash pulp in the distillation section of the wash press 13. It is also possible to utilize a split shower with some of the wash water provided by stream 8 and a portion of stream 19 in washer 7, as shown. A portion 19 of the pressate can be discharged to the recovery system of the plant as needed to maintain the balance of water in the dilution tank / wash press circulation loop.

For situations where a significant amount of alkaline material is introduced into the pressate due to incomplete replacement of the wash water 14 in the pulp, the alkaline material in the wash water 14 Can be increased to compensate for such incomplete substitutions. Recirculating the pressate to the dilution tank increases the concentration of alkaline material in the dilution water,
Thus, the pulp / dilution water stream 12 is allowed to have a high concentration of alkaline material. This recirculation enhances the retention of alkaline material in the pulp to a given level at the expense of a slight reduction in the degree of cleaning action, and undesired material on the pulp 15 exiting the wash press. Lowers carryover. One of ordinary skill in the art having the benefit of this disclosure will, through routine experimentation, determine that a predetermined amount of the wash should be applied to the pulp based on the actual dilution factors and substitution ratios used to operate the wash press 13. The concentration of the appropriate alkaline substance in the water 14 can be determined. Similarly, in the second embodiment of the invention, shown in FIG. 2, some of the total amount of alkaline material to be applied to the pulp for high concentration delignification in the oxidation reactor 21 is as described above. Is added to the cleaning press 13.

In US patent application Ser. No. 07 / 637,100 (the contents of which are incorporated herein by reference), for example, by mixing a low concentration pulp with a solution of an alkaline substance, about half the predetermined amount of the alkaline substance is added to the pulp. The application of the other half of the amount by applying to the high-concentration pulp, followed by application to the high-concentration pulp in a substantially uniform distribution, is significantly less than that of applying the total alkaline material to the low-concentration pulp. It was demonstrated that a high delignification selectivity could be achieved. Furthermore, the amount of alkaline material required to apply a given amount to the pulp can be reduced compared to the case where the whole is applied to low-concentration pulp, while the high concentration of a part of the alkaline material is reduced. Is applied to the pulp such that the method quickly modifies or adjusts the total amount to be applied to the pulp to compensate for changes in the properties of the pulp or to change the degree of oxygen delignification of the pulp. Is possible. Examples 6-9 of this patent application exemplify the advantages obtained by the addition of the alkaline substance by the split addition method. FIG. 3 of the present invention shows the effect of increasing the percentage (%) of alkaline material used in the treatment of high consistency pulp. The horizontal solid line approximating the zero viscosity change value corresponds to the baseline viscosity achieved with the total alkaline material applied to the low consistency pulp. Two horizontal dashed lines on either side of the 0 solid line indicate boundaries with typical ± 6% shifts in viscosity. As is apparent from FIG. 3, the amount of alkaline material applied to the high-concentration pulp is about the total amount applied to the pulp.
Above 50%, the viscosity of the delignified pulp decreases below tolerance. The selectivity advantage of high delignification is also diminished due to the application of 50% or more alkaline material to the high consistency pulp. Therefore, at least about 50%, preferably about 55-90% of the alkaline material should be applied to the low consistency pulp with the balance applied to the high consistency pulp.

The present invention contemplates obtaining similar benefits by applying about half of the total alkaline material during treatment in the wash press 13 described above. Thereafter, an additional second amount of alkaline material is applied to the washing press 13 by known spraying methods.
It is applied to the high-concentration brown raw material 15 coming out of the pulp, and the entire amount of a given alkaline substance is applied to the pulp before oxygen delignification. This second amount of alkaline material is the remaining amount (again, again, required to achieve the desired degree of delignification of the subsequent oxygen delignification step carried out on the concentrated pulp treated with alkaline material. Approximately half of the total amount) is applied. As mentioned above, the total amount of alkaline material actually applied to the pulp is generally 0.
It is in the range of 8 to 7% by weight, preferably about 1.5 to 4% by weight (relative to South American softwood) and about 1 to 3.8% by weight (relative to hardwood). In another embodiment of FIG. 2,
About half of these amounts are preferably applied to each of the low and high consistency pulps. Thus, about 0.5-2
% By weight, preferably about 0.5-1 for hardwood pulp.
9% by weight and 0.75 to 2% by weight for softwood pulp
Is applied to the pulp in each of the alkaline treatments of the low and high consistency pulps.

The split addition method of the present invention further improves controllability of the addition of alkaline materials to the pulp. The high-concentration alkaline treatment step allows the rapid modification or adjustment of the total amount of the alkaline material present in or on the pulp introduced into the oxygen delignification reactor 21. Easy controllability of both the amount of alkaline material added to the wash water of the press and the amount of alkaline material sprinkled on the high-concentration pulp gives optimum responsiveness to changing delignification requirements. give. The requirements are to compensate for variations in the properties of the input brown material (ie wood type, K number and viscosity) or to modify the degree of oxygen delignification of a particular pulp. The exact total amount to be added can be changed easily and quickly. The pulp 15, which has been sufficiently treated with alkaline material, is then sent to the oxygen delignification reactor 21 where it is contacted with gaseous oxygen 22 by any of a number of well known methods. Suitable conditions for oxygen delignification of the present invention include about 80 to about 100 psig for the high density pulp.
Gaseous oxygen is introduced under a pressure of 1, while maintaining the temperature of the pulp within the range of about 90-130 ° C. The average contact time between the concentrated pulp and the gaseous oxygen is in the range of about 15 minutes to about 60 minutes. After oxygen delignification in the reactor 21, the delignified pulp is washed to remove dissolved organic matter and produce a high quality, low colored pulp. As mentioned above, the effluent from this wash stage can be recycled for use in the washer 7 or for introduction into the dilution tank 10 as stream 11. Preferably, part of this flow is
It is utilized as stream 14 after addition of concentrated sodium hydroxide or oxidized white liquor. The oxygen delignified pulp can be used to make unbleached brown stock paper products, or can be subsequently sent to a bleaching stage to make fully bleached products.

An additional benefit of the present invention can be obtained during the subsequent bleaching of oxygen delignified pulp 23. Such bleaching can be carried out using a wide variety of bleaching agents such as ozone, peroxides, chlorine, chlorine dioxide, hypochlorite and the like. When utilizing the known chlorine / chlorine dioxide bleaching method to increase the whiteness of the pulp treated with an alkaline material as described above, as compared to the bleaching of oxygen delignified pulp by known techniques, Substantially reduce the amount of total active chlorine used. The total amount of chlorine-containing reagents used according to the invention is small compared to the amount required for the same starting pulp which has not been treated with alkaline material in the wash press. Similarly, when the chlorine / chlorine dioxide treated pulp is subjected to an alkali extraction treatment, the alkali substance required at this stage is compared with the bleaching process for pulp which is not uniformly bound to the alkali substance at a low concentration. The quantity is substantially reduced. The amount of alkaline material used in this extraction step will also be saved for pulp treated with alkaline material in a wash press as described herein. In addition to providing the cost advantages associated with reducing the amount of chemical reagents required for such treatments, the method of the present invention can also mitigate the extent of environmental pollution caused by the use of chlorine. This is because the amount of chlorine used is saved. Furthermore,
Due to the lower usage of chemical reagents in this part of the apparatus, the amount of pollutants in the wastewater from this treatment plant is correspondingly reduced, which is a wastewater treatment facility and the associated costs. Results in similar savings.

[0023]

EXAMPLE 1 A mathematical model was used to illustrate the method of the present invention for softwood pulp as described in FIG. 2 using a wash press operating at a dilution factor of 0 and a substitution ratio of 0.95. In this embodiment, the pressurizing material portion 19 was used as the washing water 8 for the washing device 7. The applicable flow rates were as follows.

[0024]

[Table 1] Process flow rate Pulp concentration NaOH (Pong Figure 2 liquid (gpm) pulp (t / d ) (%) d / h) 9 504.2 580.8 18 209.5 12 2726.5 580.8 3.5 1533.8 14 247.9 ---- 1213.3 15 312.2 580.8 28 1159.8 16 2662.2 ---- 1587.3 19 440.0 ---- 262.0

Thus, Table 1 shows that at a flow rate of 580.8 t / d, the pulp exiting the wash press has a concentration of 28% and contains 1159.8 lbs / hr of sodium hydroxide.
This gives an amount of sodium hydroxide to be applied to the pulp of about 2.4%. If the wash press could operate at a replacement ratio of 1, then all alkali added to the wash press by stream 14 would be applied to the pulp exiting the press in stream 15. For operation below a replacement ratio of 1, some of the alkaline material added to the wash press by stream 14 will be lost in the pressate. Example 2 The graph of Figure 4 is presented to illustrate the transfer of alkaline material to the pulp when operating at various substitution ratios. This is a mathematical model for a wash press operating at a dilution factor of 0 and shows how the amount of alkaline material applied to the pulp changes as the substitution ratio changes. In this model, the pressate is recycled as stream 18 to the dilution tank and as part of stream 8 to brown stock scrubber 7. Thus, these results show the advantage of increasing the amount of alkaline material retained on the pulp due to recycling. While the invention described herein has been fully described to satisfy the above objects, it is understood that many modifications and aspects can be devised by one skilled in the art, and the claims above all include these. It is intended that all such modifications and aspects of the invention be included within the true spirit and scope of the invention.

[Brief description of drawings]

FIG. 1 Pulp viscosity and its K of softwood pulp treated with alkaline substances and delignified with oxygen according to the invention.
It is the graph which showed the relationship with a value compared with the conventional typical thing.

FIG. 2 is a diagram schematically showing the method of the present invention.

FIG. 3 is a graph showing the relationship of the change in viscosity (%) to the proportion of total alkaline substances applied to pulp at high concentrations.

FIG. 4 is a graph showing the percentage (%) of alkaline material retained on the pulp for the operation of the wash press at various substitution ratios.

[Explanation of symbols]

 1 ... Wood chips 2 ... White liquor 3 ... Digestion typo 4,6 ... Brown raw material 5 ... Blow tank 7 ... Washer 8 ... Outflow Liquid 9 ... Washed pulp 10 ... Dilution tank 11 ... Water 12 ... Diluting water flow 13 ... Washing press 14 ... Sodium hydroxide solution 15 ...・ High-concentration brown material 16 ・ ・ ・ Residual liquid (pressate) 17 ・ ・ ・ ・ Seal tank 21 ・ ・ ・ ・ Reactor 22 ・ ・ ・ ・ ・ ・ Gaseous oxygen 23 ・ ・ ・ ・ ・ ・ Oxygen delignified pulp

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Stuart Titaretto, South Carolina, USA 29045 Elgin Hickory Hill Trail 116 (72) Inventor Spencer Dovely Aqes, NJ 08501 Allentown Crosswicks-Erisdill Road 110 (72) Inventor Bruce F Griggs 29223 Columbia, South Carolina United States Sweet Gum Road 208

Claims (21)

[Claims] 1. A method of achieving high delignification selectivity of pulp during high concentration oxygen delignification, comprising the step of adding pulp to a high concentration of at least about 18% by weight of alkaline material in a wash press. Applying a first amount of alkaline material to the pulp by washing with a solution to distribute the first amount of alkaline material substantially evenly over the washed pulp; The pressate is drawn off and is at least about 5% based on the oven dry weight of the pulp.
A total amount of 0.8 to 7% by weight of the alkaline substance is supplied to the high-concentration pulp (the total amount includes the first amount), and the alkaline substance containing the high-concentration pulp is subjected to oxygen delignification to obtain a high degree of deoxidation A method as described above, comprising the steps of obtaining a lignin-selective and oxygen delignified pulp. 2. The pulp is a brown raw material, and the method further comprises in said washing press a solution of alkaline material in a sufficient amount such that the first amount applied to said brown raw material is equal to said total amount. The method of claim 1, further comprising the step of washing the brown material. 3. The method further comprises mixing the pulp with dilution water to obtain a low consistency pulp having a concentration of less than about 5% by weight, directing the pulp to the wash press, to which an alkaline material is applied. The method of claim 1, further comprising the step of: 4. A low concentration of said mixed pulp is in the range of about 1 to 4.5% by weight and said method further recycles at least a portion of the pressate from said wash press to said dilution in said mixing step. The method according to claim 3, further comprising the step of using as water. 5. The method of claim 4, wherein substantially all of said dilution water consists of pressate. 6. The method of claim 1, wherein the method further comprises the step of storing the pressate withdrawn from the wash press and continuously circulating a portion of the pressate directly to the pulp / diluting water mixing step. Method. 7. A step of applying a second amount of alkaline material to said high-concentration pulp, the sum of the amounts of said first and second alkaline materials being the total amount of alkaline material provided to said high-concentration pulp. The method according to claim 1, which is equal. 8. The process of claim 1 wherein the pulp concentration is increased to a value in the range of about 25-35% by weight prior to oxygen delignification. 9. The oxygen delignification step reduces the K value of the high-concentration pulp by an amount exceeding 50% to obtain high delignification selectivity without significantly damaging the cellulose component of the pulp. A method according to claim 1 for obtaining. 10. The method of claim 9, wherein the K value is reduced from a value in the range of about 10-26 prior to delignification to a value in the range of about 5-10 after the delignification. 11. The pulp is unbleached softwood pulp,
The total amount of alkaline material applied to the pulp is about 1.5-4.
8. The method of claim 7, wherein the first and second amounts are each in the range of about 0.75 to 2% by weight. 12. The pulp is unbleached hardwood pulp,
The total amount of alkaline material applied to the pulp is about 1 to 3.8.
8. The method of claim 7, wherein the first and second amounts are each in the range of 0.5% to 1.9% by weight. 13. The pressate comprises an alkaline substance,
The method of claim 1 and also including the step of washing said pulp with at least a portion of said pressate prior to applying alkaline material to said pulp in said wash press. 14. The method of claim 1, further comprising operating the wash press at a dilution factor of about 0.4 or less and a substitution ratio of at least about 0.5. 15. The method of claim 14, wherein the dilution factor is about 0.25 or less and the substitution ratio is at least about 0.75. 16. A method for achieving high delignification selectivity of unbleached pulp during high-concentration oxygen delignification, which comprises mixing unbleached pulp with dilution water to obtain about 1 to 4.5% by weight. %
By obtaining a low-concentration pulp having a concentration in the range of, by introducing the pulp into a washing press, and washing the pulp with a solution of an alkaline substance in the washing press to a high concentration of at least about 18% by weight. A first amount of alkaline material is applied to the pulp while the wash press is run at a dilution factor of at or near 0 and a substitution ratio as close to 1 as possible to remove the first amount of alkaline material. Disperse substantially uniformly throughout the washed pulp, withdraw the pressate from the wash press, recirculate at least a portion of the pressate as dilution water to the mixing step, the unbleached pulp in the wash press. At least about 0.8 to 7 based on the oven dry weight of the pulp by washing the pulp with a solution of a sufficient amount of the alkaline material that the first amount applied to the pulp is equal to the total amount. A total amount of wt% alkaline material is fed to the high-concentration pulp and the alkaline material containing high-concentration pulp is oxygen delignified to obtain high delignification selectivity and oxygen delignified pulp, each The above method including the steps. 17. The method of claim 16 further comprising the step of storing the pressate withdrawn from the wash press and continuously circulating a portion of the pressate directly to the pulp / dilution water mixing step. 18. A method for achieving high delignification selectivity of unbleached pulp during high-concentration oxygen delignification, which comprises mixing unbleached pulp with dilution water to obtain about 1 to 4.5 weight%. %
A low concentration pulp having a concentration of 10% by weight, leading the pulp to a wash press, and washing the pulp with a solution of the alkaline substance to a high concentration of at least about 18% by weight in the wash press. Applying a first amount of alkaline material while operating the wash press under a dilution factor of at or near 0 and a substitution ratio as close to 1 as possible to clean the first amount of alkaline material Substantially uniformly distributed over the entire pulp, withdrawing the pressate from the wash press, recirculating at least a portion of the pressate as dilution water to the mixing step, and releasing the wash press from the wash press. A second amount of alkaline material is applied to the consistency pulp, wherein the sum of the first and second amounts is at least about 0.8 to 7% by weight based on the oven dry weight of the pulp. Comprising the steps of oxygen delignifying the alkaline material containing a high concentration of pulp equal to the total amount of alkaline material on the concentration pulp to obtain high delignification selectivity and oxygen delignified pulp. Method. 19. The pulp is a softwood pulp and the total amount of alkaline material applied to the pulp is about 1.5-4% by weight.
And the first and second amounts are each about 0.
19. The method according to claim 18, which is in the range of 75-2% by weight. 20. The pulp is a hardwood pulp and the total amount of alkaline material applied to the pulp is about 1 to 3.8% by weight.
And the first and second amounts are each about 0.
19. The method according to claim 18, which is in the range of 5-1.9% by weight. 21. The first amount of alkaline material applied to the pulp in the wash press is at least 50-90 of its total amount.
19. The method of claim 18, which is in the range of%.