CA1262722A - Process for dispersing one fluid in another - Google Patents

Abstract

A Process for Dispersing One Fluid in Another Abstract A process for dispersing a first fluid in a second fluid having a relatively higher viscosity comprising the following steps:
(a) providing a confined zone having an opening at its upstream end, an opening at its downstream end, and a hypothetical central axis running from its upstream end to its downstream end;
(b) introducing the second fluid into the confined zone at the opening in its upstream end in such a manner that the second fluid passes from the opening in the upstream end through the opening in the downstream end;
(c) dividing the first fluid into a plurality of streams and introducing the streams into the second fluid co-currently therewith whereby:
(i) the number of streams is in the range of about 25 streams per square foot of a cross-section of the confined zone to about 1000 streams per square foot of the cross-section;
(ii) the cross-section is perpendicular to the axis; and (iii) the streams are about equidistant from one another, the distance between the streams being about 0.375 to about 2.5 inches.

Description

DESCRIPTIO~
_ rocess ~or Dispersin~ One Fluid ~n Another Technical Eield This invention relates to ~ process ~or dispersln~ a fluld, which may be a gas or llquid, into a high viscosity liquid.
Back~round Art In certain types of systems involving the reaction and/or blending of a material or fluid of relatively high viscosity with ~ second ~luid, it is desirable to uniformly disperse the second Eluid throughout the mass oE high viscosity material.
Such Q system is the bleaching of medium consistency pulp with gaseous oxygen or with aqueous solut~ons of chlorine dioxide, hydrogen peroxide, or sodium hypochlorite. The bleaching ~s intended to whiten and brighten the pulp without damaging the strength charRcteristics o~ the paper to be made from the pulp. The main light absorbing substances in wood pulp ~re the llgnin and resin components. Therefore, to make the pulp whiter, these substances must be removed. Oxidation, reduction, or hydrolysls make the lignln and resin components soluble so that they c~n be washed away by aqueous solutions. The initial solubllization of the bulk of the lignin ls carried out with non-oxidizing substances such as alkalies, sulfides, or sulfites; however, continu~tion of the dissolution by thls means is found to seriously degrade the carbohydrate fraction of the pulp, affecting bo-th strength and yield.

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~ 2 Since lignin is readily oxidi~ed by many substances, the remainder, then, is removed by oxidation and dissolution of the oxidized products in water and aqueous alkali. Chlorine, chlorine dioxide, hypochlorite, hydrogen peroxide, ozone, and oxygen can be used separately or in various comb1nations as oxidizing agen-ts.
Pulp bleachlng plants generally treat the pulp ln a continuous flow mode with a series of oxidizing agents. An alkaline treatment step is often provided between some of the oxidi7ing treatment steps with a water wash aEter each step.
A typlcal sequence would be to start with an aqueous chlorine treatment, then a water wash, an alkaline treatment, water wash~ aqueou~ chlorine dioxide tre~tment, and a finsl water wash. The apparatus in which these steps are conventlonally carried out are, in ~rder of use, a chlorination tower, a water washer, a steam mixer, a thlck stock pump, an upflow or downElow extraction tower, a water washer, a chlorine dioxide mixer, a chlorine dioxide tower, and a watsr washer.
It has been known for some time that the addition of about Eive kilograms of oxygen gas per metric ton of dry pulp to the process between the aqueous chlorine treatment step and the alkaline treatment step permits equivalent levels oE
bleaching to be obtained at reduced chlorlne dioxide(or other oxidant) requirements. The relatlvely high viscosity of the pulp makes it diEficult to disperse the oxygen gas uniEormly throughout the pulp. The reason ~or the difficulty lies in the fact that it is necessary to create turbulence in the v1scous material in order to obtain a good dispersion, and early mixing techniques were ~ust not up to this task.
Typlcally, the pulp entering the alkaline extraction tower is o medium consistency, containlng about ten to about fiEteen percent by weight of dry pulp admixed with an alkaline aqueous solution. Its flow characteristics, or viscosity, are comparable to that of ground meat or damp papier-mache. If the oxygen gas i8 not well dispersed within the pulp mass, it will not be able to reach most o~ the pulp and the desired reaction will not be able to tflke place in the portion of the pulp mass unexposed to the oxygen.
The Eirst commercial plants using oxygen with medium consistency pulp achieved adequate dispersion of the oxygen gas in the pulp by employing dynamic mechanical mixers. Such mixers, however, are complicated pieces of equipment with high capital~ maintenance, and operational costs.
_isclosure of the Inyention An ob~ect of the invention, therefore, is to provide a process which will disperse one fluid uniformly throughout another fluid where one of the fluids characteristically has a relatively high viscosity thus achieving an otherwise dlfficult to attain level of dispersion without mechanical mixing devices.
Other obJects and advantages will become apparent hereinafter.

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Acco-rding to the present inventiorl, an improvement h~s been discovered in a process for dispersing a first fluid in ~ second fluid having a rel~tlvely higher viscosity comprising the following steps:
(a) providing a confined zone having ~n opening at its upstream end, an open1ng at lts downstream end, and a hypothetical centr~l axis running from its upstream end to its downstream end;
(b) ~ntroducing the second fluid into the confined zone at the opening in its upstream end in such a manner that the second ~.luid pa.sses from the opening ~n the upstream end through the opening in the downstream end:
~ c) dividing the ~irst fluid into a plurali$y of streams and introducing the streams into the second fluid co-currently therewith whereby:
(i) the number o~ streams is in the range of ~bout 25 streams per square foot of a cross-section of the confined zone to about 1000 streams per square foot of the cross-section;
(ii) the cross-section is perpendicular to the axis; and (iii) the streams are about equidistant Erom one another, the distance between the streams being about 0.375 to about 2.5 inches.
Brief DescriPtion of the Drawin~
Figure 1 is a schematic diagram of a view of a cross-sectlon taken frorn the upstream or downstream end of one embodiment of the invention.

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:2 2 ~2 Figure 2 is ~ side view cross-section of the same embodiment seen in F1gure 1.
Figure 3 is a schematic diagram of one of the small pipes shown in Figure 1 taken from the downstream end and showing two rows of outlet ports. The small pipe has been enlarged over its counterpart in Figure 1.
Figure 4 is a schematic diagram of an enlarged section oE Figure 3 showing some oE the outlet ports.
Figure 5 is a schem~tic diagram of a plan view cross-section of Figure 4 showing detail of the outlet portsn Detailed Description While the invention will be described in terms of an important application, i.e., pulp bleaching, it has application 1n many other industrial processes such as dispersing dyes in high viscosity polymers; dispersing additives 1n high vlscosity food materi~ls; and blending epoxy components, and other processes where dispers10n of one material in another is considered to be a critical Eactor. Liquld/liquid and gas/liquid mixtures are contemplated, the fluid havlng the relatively higher viscoslty, oE course, being R
liquid or semi-liquid. The liquid to be dispersed can also have ~ relatively high viscosity provicled that it i3 capable of belng passed through the second confined zones and the ports.
The process provides a series of steps whereby a plurality of small streams is introduced across the flow oE a high viscosity Eluid, the flow ~ .

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psttern belng achieved with minlmal pressure drop.
The number of streams is in the range of about 25 streams per square foot of cross-section of the confined zone to about 1000 streams per square foot of the cross-section. The cross-section used here is a cross-section perpendicular to the hypothetical central axis referred to above. The cross-section is selected at any point in the conEined zone at which all of the streams have been formed. This is usually between the mldpoint of the axis and the downstream end oE the zone, pre~erably closer to the midpoint. The preferred number of streams is in the range of about 50 to about 600 streams per square ~oot. The streams are about equidistant from one another, the dlstance between streams being about 0.375 to about 2.5 inches and preferably about 0.5 to about 1.7 inches. The dlrection of flow of these ~m~ll streams of liquid or gas bubbles ls deflned by the ~low of the relatively higher viscosity fluid.
The dlspersion can be enhanced with the use of A
m1xing device such as a static mixer located downstream of the apparatus used to carry out sub3ect process.
A typical static mlxer has a multipliclty of baffles located in a pipe. The baffles sequentially subdivide and mix material flowing through the pipe. The utilization of sub~ect process upstream oE the static mixer permlts a reduction in the number of baffles (or mixing elements) in the static mixer~
It is advantageous that the apparatus, which can be used to carry out the process of this ~26:~722 lnvention i5 low in capital cost, low in maintenance expense, and requires minlmum modifications to existlng pl~nt equipment. In addition to these advant~ges, the process itself is one in whtch medium consistency pulp can be proEitably treated (i) with oxygen prior to the first alkaline bleach stage or (ii) with other bleach chemic~ls such as chlorine dioxide, hypochlorite, or hydrogen peroxide in aqueous solutions, both resulting in a reductlon in the overall cost of bleach chemicals.
A preferred apparatus utilizes a series oE
relatively small diameter perforated or porous pipes within a relatively larger diameter pipe. The larger diameter pipe is referred to as the conined zone. The plpes are made o~ conventional materials such as stainless steel. In a typlcal pulp bleach~ng system employing oxygen in an oxidative extraction, the large pipe is placed between the thick stock pump and the first alkaline extraction tower. The main stream of pulp or pulp mass flowing through the large pipe comprises a mlxture of about 10 to about 15 parts by weight pulp solids with, the balance, a solutlon oE water and alkali, usually d~lute. This ls considered a medium consistency pulp. A plur~llty oE uniEorm continuous or dlscontinuous streams of oxygen flow in a downstream direction from the perforations or pores of the small diameter plpes. The flow rate of the pulp mass stream is about 150 to about lO00 metric tons of pulp sollds per day. The flow rate of the oxygen is about 800 standard cubic feet per hour (scfh) to about 5500 scfh.
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The small pipes are considered to be arranged in sets and there are several of these sets in the large pipe. Spacing between the small pipes in a set and between the sets themselves ls balanced so that brldging is avoided wlthout sacriflcing uniformity oE dispersion. The diameter and placement of the small pipes are also a factor affecting bridging. Bridging i~ caused by, ~or example, the accumulation o~ a highly viscous fibrous material in the path of flow, even-tually blocking it. It is of especial concern with medium consistency pulp bec3use the pulp begins to lose water as the bridge forms causing the brldging pulp to become lncreasingly more rlgid. The rate at which the bridge forms and the amount of bridge Çormation are a function of the nsture of the fibrous mass such as fiber length, the kind of fiber, prio~ treatment of the fiber, and the lubricating properties of the first fluid.
The small p1pes in each set are about equally spac~d from one another and about 1 to about 10 inches apart, preferably about 3 to about 5 inches apart. The sets of pipes are spaced apart from one another by about 1 to about 12 inches, preferably ~bout 3 to about 6 inches. It is also preferred that the pipes in each set are in a staggered relationship to the pipes in the other sets. In this case, if one were to take an upstream/ downstream cross-section throu~h one of the small plpes in a three set system, there would only be one pipe in the cross-section.

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There are about 2 to about 6 sets provided ln the con~ined zone and preFerably about 3 to about 5 sets and there are about 3 to about 8 small pipes per set, a'bout 2 to abou-t 6 small pipes per set being pre~erred.
Referrin~ to the Drawin~
In Figures 1 and 2, pipe 21 encloses the conEined zone. It is supported by flanges 22 and 23. Various braces and welds(not shown~ also provide support Eor the struckureO Annular chamber 24 is formed by ring 25 and closure rings 26. It has an lnlet pipe 27 and an outlet valve 28. Small pipes 1, 4, 7. 10, 13, and 16 represent the First set of sm~ll plpes; small pipes 2, 5, 8, 11~ and 14 represent the second set,and small pipes 3, 6, 9.
12, and 15, the third set. Hypothetical axis 2~ of pipe 21 runs from the upstream end to the downstream end. Small pipes 1, 2, and 3 as well as the other small pipes are perpendicular to hypothetical axis 29. The small plpes may also be inclined lnsofar as hypothetical axis 29 is concerned, the angle, of inclination lying in the range of about 20 to about 90. It is preferred that the angle be the same for all small pipes. F'urther, each set lies in its own plane and each plane bears a spaced relationship to each other plane. Whi'le a plane is ususally described RS two dimensional, i.e., without height or depth, in this context it is considered to have a height or depth equal to the diameter of t'he zones or pipes oF the set which lie in the plane. The plane bears the same angle of inclination as the pipes in the set, which lles in that plane. Both 7~2 ends of each small plpe ace open. These ends are referred to as ~nlet ports 30.
Figure 3 is an enlargement of one of the small pipes 2 throu~h 15 showing outlet ports 31 in æ staggered array. The small pipe has a hypothetlcal axis 32 which, of course, would be perpendicular to hypothetical axis 29 I~ shown in Figure 2.
Figure 4 is an enlargement of a section of the small pipe shown in Figure 3.
Figure 5 is a cross-section of the small pipes shown in Flgures 3 and 4. Axes 33 of outle~
ports 31 are at a ninety degree angle to each other, and perpendicular to hypothetical axis 32.
The angle is more particularly defined as follows: the centr~l axis o~ each outlet port is at an angle oE about 0 to about 9Q, and preferably about 45, from a hypothetical line 34 running downstream from the point at which the central axis of the outlet port meets the central axis o~ the small pipe, s~id hypothetical line belng perpendicular to the central axis of the small pipe, parallel to the central axis o~ the con~ined zone, and lying in the same plane as the central axis o~
the outlet port.
The following example illustrates the invention:
ExamPle Sub~ect process is carried out in the ~pparatus described above. The apparatus is located in a softwood, kr~ft pulp bleach plant using a conventional bleaching process. The normai flow ~;262~2 rate through the apparatus is 350 metric tons per day of pulp solids (or pulp mass on an air dried basis). Pulp mass Erom the washer ~ollowing the chlorine stage is made alkaline and is heated prior to being pumped into the bottom of a standard up~low alkaline extr~ctiotl reaction tower. The initial pulp mass is a mixture o~ 11 percent pulp solids and 89 percent water. The apparatus ls inserted into a Z4 inch diameter p~pe line, which carries the pulp mass into the bottom oE the up~low tower. Pipe 21 is 23.25 lnches in inner diameter and is 18 inches long. There are sixteen small pipes, placed as shown in the drawing, equidlstant from adJacent pipes. There are three sets of small pipes, the sets being spaced four inches apart. The small plpes are 0.30 lnch in inner diameter and 0.54 inch in outer diameter. They are Schedule 80 pipes made of AISI 304 stainless steel. Small p~pes 1 and 16 have one ro~ of outlet ports 31 and small pipes 2 through 15 have two rows o~ outlet ports 31. E~ch row o~ outlet ports 31 is centered on its small pipe, e.g. where the small pipe is 10.5 inches Long, thè row is only about 6.5 inches long and two inches at e~ther end of the pipe have no outlet p~rts. The lengths of each, i.e., pipe and row, are as ~ollows:

length of approx~mate small pipelength of row small PiPe no. (lnches) (inches) 1 and l6 10.5 6.5

2 and 15 15.5 11.0

3 and 14 19.0 15.0

4 and 13 21.0 18~0

5 and 12 23~0 20.0

6 and 11 24.0 21.0

7 and 10 ~5.0 22.0

8 and 9 25.0 22.0 Outlet ports 31 have inner diameters of 0.025 inch and are three lnches spart from adjacent outlet ports 31 in the same row. Thus, if all oE the outlet ports 31 in each of small pipes 2 to 15 were ln the same row, they would be 1.5 inches apart.
The axes of outlet ports 31 are at the angles shown ln Figure 5, the axes of outlet ports 31 in small pipes 1 and 16 being directed to the interlor of pipe 21. The number of streams per square foot of cross-section is 64.
Oxygen at a pressure of about 120 psig is introduced through inlet pipe 27 (one inch i.nternal diameter, Schedule 40) into annular chamber 24. It then passes into the small pipes through inlet ports 30 and out throu~h outlet ports 31 into pipe 21 (wall 0.375 Lnch thick). The amount of oxygen introduced is 4 kilograms per metric ton of pulp solids.
Lt is found that the quantity oE bleach chemicals required to achieve the plant's target 27~22 , .

brightness o~ 90 Elephro is subst~n~i~lly reduced, e.g., ~ reductlon of 18 percent in chlorine dioxide and of 8 percent ~n chlorine ls found.

Claims (7)

1. Claims l. A process for dispersing a first fluid in a second fluid having a relatively higher viscosity comprising the following steps:
   (a) providing a confined zone having an opening at its upstream end, an opening at its downstream end, and a hypothetical central axis running from its upstream end to its downstream end;
   (b) introducing the second fluid into the confined zone at the opening in its upstream end in such a manner that the second fluid passes from the opening in the upstream end through the opening in the downstream end;
   (c) dividing the first fluid into a plurality of streams and introducing the streams into the second fluid co-currently therewith whereby:
   (i) the number of streams is in the range of about 25 streams per square foot of a cross-section of the confined zone to about 1000 streams per square foot of the cross-section;
   (ii) the cross-section is perpendicular to the axis; and (iii) the streams are about equidistant from one another, the distance between the streams being about 0.375 to about 2.5 inches
2. 2. The process defined in claim 1 wherein the number of streams is in the range of about 50 to about 600 per square foot of cross-section.
3. 3. The process defined in claim 2 wherein the distance between the streams is about 0.5 to about 1.7 inches.
4. 4. The process defined in claim 1 wherein the second fluid is a pulp mass comprising a mixture of about 10 to about 15 percent by weight pulp solids and, the balance, an alkaline solution.
5. 5. The process defined in claim 4 wherein the first fluid is oxygen, said oxygen being introduced into the pulp mass in an amount of about 2.5 to about 7.5 kilograms of oxygen per metric ton of pulp solids.
6. 6. The process defined in claim 1 wherein the First fluid/second fluid dispersion is mixed downstream of the confined zone.
7. 7. The process defined in claim 6 wherein the mixing is performed with a static mixer.