JPS5982488A - Improved method and apparatus for oxygen delignification - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION This invention relates to the oxygen delignification of fibrous materials, and more particularly, to the oxygen delignification of fibrous materials, and more particularly to the oxygen delignification of medium consistency bleachable grade pulps and others using a substantially horizontal tubular reaction zone. The present invention relates to the oxygen delignification of fibrous materials.

In the oxygen delignification of fibrous materials, it is desirable to achieve rapid and homogeneous delignification of the pulp stock. Level-delignification of the pulp stock results in greater pulp strength. It is also desirable to introduce alkaline chemicals into the pulp stock to maintain the pH level within some optimum range. Steam is typically introduced into the mixture of pulp stock, oxygen, and alkaline chemicals to heat the mixture to a temperature at which the delignification reaction begins.

It is preferred to carry out the oxygen delignification reaction on the pulp at a medium concentration, i.e. 8-20% concentration.

Such delignification systems are compatible with much existing mill equipment, including pulp washing equipment and thickening equipment, as such equipment is designed to operate in the medium concentration range. Delignification systems using medium consistency pulps are preferable to delignification systems using low consistency pulps (i.e. 1-5% consistency) because the latter require larger reaction volumes to maintain acceptable pulp residence times. This is because a large amount of power is required to pump a large volume of pulp and to steam the pulp to heat it in a reactor.

An effective, relatively low cost apparatus for oxygen delignification of medium consistency pulps consists of at least one, but preferably two or more, substantially horizontal tubular reaction zones, each of which It has stirring and transport means, such as a screw, extending along at least part of its length and is driven by a single motor. The reaction zone has one inlet for the pulp to enter, one outlet for the delignified pulp to exit the reaction zone, and preferably multiple outlets for the lye, steam and oxygen to enter the reaction zone. orifice. Although the screw may take many different forms, commonly used screws have a solid shaft around which extends a single helical blade that agitates and transports the pulp.

In such a reaction zone, the temperature ranges from 80°C to 160°C.
℃, an alkaline chemical agent of 1-20% calculated as Na2O is added to the moisture-free material, and the oxygen partial pressure is 3O-200psi (2,1-111k
lI/cTL2). Appropriate residence time is 5-1
It has been found that 20 minutes. Such devices and methods are more fully described in European Application Serial No. 80604340.5, filed December 2, 1980.

The first horizontal reaction tube in such equipment typically receives feedstock in somewhat compressed form from a concentrate pump, which pump provides a single conduit that is substantially full of feedstock during pumping operations. Pump the raw material through. This is in contrast to reaction zones, which are typically operated to provide space for gas to collect along its length at the top of the reaction zone. As a result, a portion of the horizontal reaction zone is required to loosen this compacted pulp and expose the mass to oxygen so that the delignification process can begin.

Thus, the delignification reaction does not begin until the pulp stock has moved through a portion of the reaction zone and the screw has had an opportunity to agitate and cleave the pulp mass.

Therefore, longer reaction times are required to delignify the pulp. These long reactions result in the need for larger and therefore more costly reaction equipment.

Various reactor designs that combine oxygen with the pulp stream prior to the reaction zone have been proposed for oxygen delignification of pulp. For example, Richter U.S. Pat. No. 4,093
, No. 511 is a defibrator (def 1brato
r) He teaches a reaction system in which pulp and oxygen gas are strongly mixed using a bottle mixer, and this is a reaction system in which the gas and 79! These then flow upwardly through the vertical reaction zone. Kriep et al., TAPPI, June 1981, pp. 87-90 and Jarman, U.S. Pat.
No. 161,421 teaches a similar system using a high shear mixer to create an emulsion of gas and pulp prior to a vertical reaction zone. Renato 9's TAPPI, 1
August 981, pp. 51-54, teaches an analogous system. Finally, U.S. Pat. No. 4J 98,266 to Kirk et al.
In one embodiment of the invention, the US patent teaches the use of a high shear mixer to combine oxygen with the pulp stream prior to the reaction zone.

However, all of the above oxygen reactors require high shear mixers to disperse or emulsify the oxygen gas into the pulp. High shear mixers require significant horsepower to achieve proper distribution of oxygen. Moreover, high shear mixing in the presence of oxygen and IL-potash at elevated temperatures may lead to pulp fiber damage, which reduces pulp strength. Another disadvantage of the aforementioned groups is that the high intensity dispersion of oxygen gas in the pulp sometimes creates foamy conditions, which reduces the washing efficiency when the dissolved solids are washed from the fibers following delignification. That's true.

Accordingly, there exists a need in the art for delivering pulp to a horizontal reaction zone in a form that has already been cleaved so that the pulp mass has easier access to oxygen within the reaction zone.

Furthermore, there is a need to be able to initiate the delignification process before the pulp enters the horizontal tubular reaction zone, thus reducing the length of the reaction zone and thus the cost and making the reactor more efficient. Finally, a need exists for a system that achieves proper mixing of oxygen and pulp without creating high shear forces that are detrimental to pulp strength.

SUMMARY OF THE INVENTION The present invention provides an apparatus for continuous delignification of fibrous materials, such as medium consistency pulp, which utilizes one or more reaction zones, but which The pulp stock enters the reaction zone after being mixed with oxygen and alkaline chemicals, thus ensuring that the delignification process has already started and the compaction state of the pulp has been reduced. This improves the rate of oxygen delignification within the reaction zone, thereby increasing the efficiency and reducing the size and cost of the required equipment. Another advantage of the present delignification system is that oxygen is added to the pulp mass at a single point in close proximity to the concentrate pump, rather than being added only in the reaction zone, where the working pressure is Substantially greater than pressure. Therefore, the solubility of oxygen is at a higher value and the delignification reaction proceeds at an increased rate. Another advantage of the device of the invention is that it utilizes the moment when the pulp mass is retained in the conduit connecting the pump with the first reaction zone. Yet another advantage of the present invention is that proper mixing of pulp and oxygen is achieved without the use of high intensity mixers.

Although the present invention is specified and best suited for delignifying pulps of medium consistency, i.e., 8-20% consistency, the apparatus is also suitable for delignifying pulps of medium consistency, i.e., between about 8% and 8%. It should be understood that it may also be used to delignify materials. Additionally, although the present invention provides for the use of filters in conjunction with one or more substantially horizontal tubular reaction zones, other reactors may be used, such as vertical columns. be understood.

゛ The present invention comprises a first substantially horizontal tubular reaction zone having an inlet and an outlet, a screw for stirring and transporting the fibrous material through the reaction zone to the outlet, and a screw for transporting the fibrous material into the first reaction zone. There is provided a continuous oxygen delignification apparatus for fibrous materials of the type having at least a thick feed pump for pumping and a connecting conduit for transferring the material from the pump to the inlet of a first reaction zone. be.

The improvement includes an oxygen supply conduit communicating with the connecting conduit for introducing oxygen into the connecting conduit, and an oxygen supply conduit for mixing with the fibrous material flowing the oxygen introduced into the connecting conduit into the reaction zone. a series mixer mounted in a connecting conduit downstream of the conduit.

In one embodiment of the invention, alkaline chemicals and/or steam are introduced into this connecting conduit to maintain the optimal H value of the pulp solution while heating it to the desired temperature.

Preferably, the series mixer used in this connecting conduit is a static mixer so that the energy imparted to the pulp suspension by the concentrate pump itself is used to perform the mixing operation. Static mixers do not create high shear forces that are detrimental to sweet pulp strength. Surprisingly, it has been discovered that proper mixing of pulp and oxygen may be achieved using static mixers rather than the high intensity mixers taught in the prior art.

In one preferred embodiment, oxygen is introduced into the pulp in a connecting conduit upstream of a single series mixer. In another embodiment, one conduit in the bottom fu of the series mixer is placed to introduce the alkaline solution into the mixture, and then downstream a second series mixer mixes the alkaline solution with the pulp and oxygen. placed for. Steam may be introduced through one conduit downstream of the alkaline mixer, and a third series mixer may be utilized to mix the steam with the mixture of alkaline liquid, oxygen, and . In a third embodiment, a single feed conduit is connected to a connecting conduit through which the combination of oxygen, alkaline chemical, and steam is introduced upstream of a single series mixer. In one variation of the second embodiment of the invention, some or all of the oxygen may be predispersed in the alkaline liquid before it is introduced into the pulp. In all of these embodiments of the invention, the oxygen may be dispersed in one liquid upstream of the mixing elements prior to its introduction into the pulp. This solution consists of water, oxygen bleach r solution,
Alternatively, it may be an alkaline solution.

For horizontal reactor tubes, it is necessary that the concentrate pump be located below the water column of the reactor tube and that the connecting conduit slope upwardly from the pump to the reactor tube. This connecting conduit could be connected to the tube either at its underside or through the top of the tube. This height difference is necessary to prevent oxygen gas from flowing back through the conduit to the concentrate pump and collecting there, causing complications.

By placing the series mixer in an upwardly sloping conduit and introducing oxygen into the rich feedstock - close to the pump, the flow in the horizontal reaction tube is reduced due to the hydrostatic head and friction losses in the continuous conduit leading to the reaction tube. At one location where the pressure is substantially greater than the operating pressure, the oxygen is mixed with the pulp. Since the pressure is greater, more oxygen is dissolved and the oxygen delignification reaction initiated at a location near the pump occurs at an increased rate.

Another advantage of using the present invention exists when Kraft white liquor is used as the alkaline liquor and oxygen is predispersed in the alkaline liquor. The sodium sulfite in this white liquor is somewhat oxidized before it is added to the pulp. In this way, the white liquor does not end up reacting with some of the oxygen and picking up additional oxygen in the reaction zone or in the continuous conduit.

This taken up oxygen is not available for the delignification reaction at that point. Indeed, this pre-oxidized white liquor sometimes produces a more viscous and stronger pulp.

It is therefore an object of the present invention to ensure that before the pulp is introduced into the horizontal reaction zone for the first time, some time is spent during the delignification reaction in the conduit between the pump and the reaction tube; provides an improved apparatus for the oxygen delignification of fibrous materials, in which the size of the reaction zone or reaction zones, and thus the cost, is reduced; and at a relatively low cost and relatively low cost. It is an object of the present invention to provide a device for oxygen membrane lidanization that can be easily manufactured.

Other objects and advantages of the invention will become apparent from the following description, drawings, and claims.

FIG. 1 is a schematic flow diagram depicting the overall apparatus of the present invention utilizing a plurality of horizontal reaction tubes; FIG. Figure 1 is a schematic representation of an embodiment; Figure 1 is a schematic representation of one connecting conduit forming part of a third embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS -1 As shown in FIG.
ξ is contained within a pulp source 10 which communicates with a thick stock pump 12 . Pump 12 may be a Mayno progressive cavity pump available from Robin Ant 8 Meyer, Springfield, Ohio. - Pump 12 may also be a Crowbar rotor thick stock pump manufactured by Ingersoll Rand Co. of Nashua, New Hampshire, a thick stock pump manufactured by Wallenpomff Co. of Warren, Massachusetts, or any other pump known in the art. It may be a type of concentrated pump or a high concentration pump.

Connecting conduit 14 connects pump 12 to first or main reaction tube 18
It extends to the entrance 16. The main reaction tube 18 includes an outlet 20 that communicates with a substantially vertical conduit 22 that communicates with an inlet 24 of a second reaction tube 26 .

The second reaction tube 26 is ultimately connected to the nozzle chamber 62 for subsequent reactions'!, if desired! 28.
30 may be connected.

The first reaction tube 18 and, if used, the subsequent reaction tubes 26.2Ej, 30 each include a screw 64 with drive means, preferably an electric motor. Preferably, screw 64 has a helical vane design. Each reaction tube 18. 26. 28.30 also optionally includes an alkaline liquid supply line 68 and includes a steam supply line 4o.

Generally, the total alkaline material loading is 1-20% by weight calculated as Na2O of the bath dry weight of the raw fibrous material. Examples of alkaline materials suitable for use in connection with the present invention include hydroxide, sodium carbonate, sodium borate compounds, ammonia, Kraft white liquor, oxidized Kraft white liquor, and mixtures thereof, but Other known alkaline pulp treating fluids may also be used. The steam introduced through the steam supply pipe raises the temperature inside the reaction tubes 18, 26, 28.30 to 80°C-1.
Preferably it is sufficient to maintain the temperature within the preferred temperature range of 60°C.

The oxygen delignification system described thus far is of known design and is disclosed and discussed in great detail in European Patent Application Serial No. 8030a340.5, filed December 2, 1980. Improvements in this system include connecting conduit 14 and concentrate pump 12 in communication with a source of oxygen under pressure.
This consists of adding a continuous oxygen supply pipe 42 at a position close to the.

Downstream of this rich feed pump 12 there is arranged a means for mixing oxygen with the feed, which is preferably a static mixer 44 in series. An example of such a static mixer is the Komax triple action static mixer of Long Beach, California. The oxygen supplied through line 42 may be pre-dispersed in gaseous form in a liquid such as water, oxygen bleach solution, or some alkaline solution, and may be pre-dispersed at a point near the inlet of mixer 440. Preferably, it is supplied.

As shown in FIG. 1, concentrate pumps are typically of the horizontal discharge type. Since the pump 12 must be located at a height below the height of the main reaction tube, the connecting conduit 14 must, in addition to the substantially horizontal section 48, include an upwardly sloping section A6. The height difference is necessary to prevent oxygen gas present above the feed in the main reaction tube 18 from migrating backwards from the reaction tube toward the rich feed pump 12. The series mixer 44 is connected to the horizontal portion 4 of the connecting conduit 14.
Although shown mounted along 8, it may alternatively be located along the sloped portion of the connecting conduit.

The operation of the oxygen delignification system shown in FIG. 1 is as follows. Pulp from pulp source 10 is pumped by concentrate pump 12 through connecting conduit 14 to main reaction tube 18 . Oxygen is introduced into connecting conduit 14 through feed line 42 downstream of concentrate pump 12 and just upstream of the inlet to mixer 44 . The oxygen and feedstock are mixed as the feedstock flows through the direct static mixer, at which point the oxygen delignification process begins. Therefore 2, entrance 1
6 to the main reaction tube 18 contains dissolved oxygen and evenly dispersed oxygen gas within the feed slurry and is not delivered as a somewhat compressed mass containing no oxygen at all.

Therefore, the length of the main reaction tube 18 can be shorter than that required for systems without oxygen mixing occurring in the connecting conduits.

Once the partially delignified pulp enters the main reaction tube 18, alkaline liquid is introduced into the pulp through feed line 38 and steam is introduced into the pulp through feed line 40. Optionally, some or all of the steam or alkaline chemicals may be added to the pulp prior to the concentrate pump. Optionally, additional oxygen may be introduced into main reaction tube 18 via supply line 50.

Main reaction benefit 1 in which the pulp is driven by the screw 64
As it moves along the length of 8, it further reacts with the oxygen and alkaline solution present in the tube. The temperature is maintained by steam so that the delignification process continues at the appropriate rate. The pulp passes through the outlet 20 to the main reaction tube 18
exits through vertical conduit 22 and falls through inlet 24 into a second reaction tube. The delignification process continues in the same manner until the delignified pulp is deposited into the blow zone 62.

In some cases, only one reaction tube is required to achieve the desired degree of degreasing.

A second embodiment of the invention is shown in FIG.
receives feedstock via connecting conduit 141 from a pump (not shown). The connecting conduit 1a' is an oxygen source and an oxygen supply pipe 42'
connected through. Conduit 14' communicates with the alkaline liquid source via alkaline supply line 52, and 1° supply lines 42', 52.5 which communicate with the steam source via steam supply line 54.
A series stationary mixing element 11A, 44 downstream of each of A
Now, Otsu/ICL is about to be placed.

These elements may be three separate mixers or may consist of elements within a single mixer. Another inlet 16' may be attached to the reaction tube '18 to pump the feed into the reaction tube from below.

Oxygen supply line 42' is preferably upstream of alkaline liquid supply line 52 and steam supply line 54. If an alkaline strainer or steam is added before oxygen addition, a loss in pulp yield or a decrease in pulp strength or viscosity may occur. Furthermore, the oxygen pipe 42'
is near the concentrate pump (not shown) and mixing element 4
It is preferred to maintain a position immediately upstream of the dA inlet so that the oxygen enters the feed at a point where relatively high pressure is present. It is desirable to add alkaline liquid and steam to the connecting conduit 14' to raise the p'H and temperature within the connecting conduit to optimal levels that improve the delignification rate.

In operation, conduit 14' transports the pulp to the thick stock pump (
thick stock pump), and the pulp is sent from pipe 42'
The oxygen is mixed with the pulp in mixer 44A to initiate the delignification reaction. The pH level and temperature of the mixture is maintained by injecting alkaline chemicals and steam into the feed through lines 52,54.

After each injection, the mixture is mixed by mixers 44B, 44G to maintain homogeneity of the mixture. The pulp mass entering reactor 18 can have access to oxygen gas in the reactor more easily than would be the case without the improvements of the present invention.

A variation of the second embodiment of the invention is also depicted in FIG. 2, in which some or all of the oxygen is
The alkaline solution 52 may be supplied to the alkaline solution 52 through . Preferably, the oxygen is delivered using a venturi system, injector, diffuser, or small static mixer (motionless mixer).
Dispersion into an alkaline solution using as well as other known methods.

A third embodiment of the present invention is shown in FIG. 6, in which the continuous conduit 11L'' supplying feedstock from a pump (not shown) to the main reaction tube (not shown) includes a single feed line 56. The supply piping 56 is connected to a distribution ring 58, or other suitable gas Preferably it ends with a dispersion device, which has nozzles arranged around its inner periphery for distributing the oxygen.

As with the previously discussed embodiments, the feed line 56 and distribution ring 58 are located adjacent to the thick stock pump and upstream of the motionless mixer 44. is preferred.

In operation, feedstock flowing from the pump receives a mixed stream of oxygen, steam and alkaline solution via piping 56 and ring 58. This charge is immediately mixed with the feedstock by mixer 44 to initiate a delignification reaction throughout the pulp flowing downstream of ring 58. The pulp entering the reactor tube has already been partially delignified and is at the optimum pH level and temperature.

A system such as that shown in Figure 3 provides the lowest cost form of the invention and provides a gas-liquid heat mixture to be injected into the connecting conduit 14''. Oxygen gas is used as the oxygen source. If so, the gas can be well dispersed in the alkaline liquid using Venturi-type systems, syringe diffusers, or small motionless mixers, as well as other known methods. Another advantage is that
When white liquor is used as an alkaline liquor, the sodium sulfite in the white liquor reacts with oxygen and becomes somewhat oxidized before it is added to the pulp. In some cases this results in improved pulp viscosity and strength.

Although the methods and apparatus described herein constitute preferred embodiments of the invention, the invention is not limited to these precise methods and apparatus, but rather includes the invention as defined in the claims. It should be understood that changes may be made without going out of scope.

[Brief explanation of the drawing]

FIG. 1 is a horizontal flow diagram depicting the overall system of the present invention using a plurality of horizontal reaction tubes, and FIG. FIG. 6 is a schematic representation of a connecting conduit forming part of a third embodiment of the invention. Patent Applicant: The Black Clawson Company (1 other person) Continued from page 1 ■ Applicant: Air Products and Chemicals, Inc. 538 P.O. Box 538 Allentown, Pennsylvania, United States of America

Claims (1)

Claims: 1. A first substantially horizontal tubular reaction zone including at least an inlet and an outlet, a means for agitating and transporting fibrous material into said first reaction zone to said outlet; in a continuous delignification apparatus for fibrous materials of the type comprising means for pumping fibrous material into said first reaction zone and conduit means for conveying fibrous material from said pumping means to said inlet; means for introducing oxygen into said conduit means such that an oxygen delignification reaction is initiated in the fibrous material flowing through said conduit means; and means for introducing oxygen from said conduit means into said fibrous material in said conduit means. a stationary mixing (motionless mixer) means located within said conduit for mixing. 2. Apparatus according to claim 1, wherein said pumping means is located at a height below said reaction zone and said conduit means slopes upwardly into said tubular reaction zone. 3. The apparatus of claim 2 further comprising means for introducing a 3° alkaline chemical into said conduit means. 7. The apparatus of claim 6 further comprising means for introducing 4° steam into said conduit means. 5. Apparatus according to claim 6, wherein said means for introducing an alkaline chemical agent is located downstream of said oxygen introducing means and at least partially upstream of said static mixing means. 6. Apparatus according to claim 4, wherein said steam introduction means are located downstream of said oxygen introduction means and at least partially upstream of said static mixing means. 7. The static mixing means comprises a series static mixer comprising a plurality of mixer elements, each of which is connected to the oxygen introduction means, the alkaline chemical agent introduction means, and the steam introduction means, respectively. 2. A device according to claim 1, located downstream of and in close proximity to one of the devices. 8. joined to said conduit means upstream of said mixing means and in communication with said means for introducing oxygen, alkaline chemical and steam so that oxygen, alkaline chemical and steam are mixed together before entering said conduit; 3. The device of claim 2, further comprising a supply conduit adapted to. 9. said oxygen further comprising a supply conduit joined to said conduit upstream of said static mixing means, said oxygen supply conduit comprising means in said supply conduit for dispersing oxygen in said liquid flowing through said supply conduit; A device according to claim 1, characterized in that it is in communication with introduction means. 10. The oxygen introduction comprises a dispersion ring mounted in the conduit for injecting oxygen into it, so that the oxygen is evenly distributed within the fibrous material flowing through the conduit means. , an apparatus according to claim 1. 11. In a process for continuous oxygen delignification of fibrous materials, of the type in which the material is pumped through one conduit by a thick stock pump to the reaction zone at a concentration of 8 to 20%: introducing the material into the material while it is flowing through the conduit to the reaction zone, and agitating the fibrous material within the conduit to mix the material with the oxygen; A step-by-step method to initiate the oxygen membrane nignin reaction without subjecting the material to high shear forces. 12. introducing an alkaline chemical agent into the mixture of fibrous material and oxygen in the conduit, and agitating the fibrous material within the conduit to mix the alkaline agent with the fibrous material and oxygen; 12. The method of claim 11 further comprising each step. 13. Introducing steam into the mixture of fibrous material, oxygen and alkaline chemical agent in the conduit, and agitating the fibrous material in the conduit to mix the steam with the fibrous material and oxygen. 13. The method of claim 11 or 12, further comprising the steps of: 14. Pumping the fibrous material through a thick stock pump in a conduit to a substantially horizontal reaction zone, introducing an alkaline chemical into the fibrous material, and introducing oxygen into the fibrous material. 8 into the reaction zone and transport the fibrous material through the reaction zone while agitating the fibrous material to mix the material with oxygen and alkaline chemicals and throughout the reaction zone. - In a continuous oxygen delignification process of fibrous material of the type maintaining a concentration of 20%; the pump is positioned below the level of the reaction zone and the fibrous material is passed into the reaction zone through an upwardly inclined conduit. pumping, introducing oxygen into the material as the material is pumped through the upwardly sloped conduit, and agitating the material to remove the oxygen as the material is pumped through the upwardly sloped conduit. An improvement comprising steps that are mixed with the above materials to initiate an oxygen delignification reaction without creating high shear forces in the fibrous material. 15. Claim 11 or 14, wherein the oxygen introduction step consists of introducing oxygen gas into the material.
The method described in section. 16. The method of claim 11, wherein the step of introducing oxygen comprises introducing oxygen dispersed in a liquid. 17. The method of claim 16, wherein said liquid is selected from the group consisting of water, oxygen bleaching liquid, and alkaline solution. 18. 8-20% of the fibrous material in the conduit
Claim 1 further comprising the step of maintaining the concentration at
The method according to item 1 or item 14.