US2130402A - Apparatus for chlorinating pulp - Google Patents

Description

Sept. 20, 1938. c. K. TExToR APPARATUS FOR CHLORINATING PULP Filed Dec. 11, 1955 /6722224; U52@ ff @a (7V-@MW Patented sept. 2o, 193s UNITED STATES APPARATUS FOR CHLORINATING PULP Clinton K. Textor, Cloquet, Minn., assignor to The Northwest Paper Company, Cloquet, Minn., a corporation of Minnesota Application December 11, 1935, Serial No. 53,886

2 Claims.

The present invention relates to apparatus in which gas is introduced into a liquid for an absorptlon or reaction with the liquid or material suspended therein. In particular it relates to 5 method and apparatus for treating cellulosic pulp With chlorine, to effect bleaching thereof, as is commonly practiced in paper mills.

Apparatus has been specially provided for the purpose of chlorinating pulp, but in many respects it is defective. There is known apparatus which is in many respects similar to that herein described, but certain defects therein have been overcome in the 'present invention. Time elhciency in thev process, apparatus cost and maintenance, and power costs are particular items in l which older practice has been improved.

The older apparatus involves an outer circular tank and/an inner concentric cylinder, open at both ends, with a propeller arranged to circulate a` pulp slurry either upwardlyl or downwardly through the inner cylinder and back through the annular space. Such apparatus provides a propeller at the bottom of the inner cylinder, and the depth of apparatus necessitates a bearing below the liquid level. Where chlorine is employed the corrosive action is destructive of the bearing structure and surfaces, or else a very expensive bearing must be provided. J

Another feature` of disadvantage in prior art structures is the use thereof involving much power to cause a downward flow at a velocity which overcomes the tendency of chlorine bubbles to rise. Such high downward velocity necessitates a high upward velocity in the circuit, and this tends to carry rising bubbles more quickly to the top.

The present invention aims to provide a structure in which bearings are eliminated below the liquid leVeLkand in which the velocity requirements of the moving stock are materially lessened,

thus to conserve power in operation. l

Another object of the invention is to permit circuitous flow of stock at a velocity upwardly which is very slow, and ata velocity downward which is not determined to overcome tendency of bubbles to rise.

Fig. 1 represents a vertical section through the so center of the apparatus.

Fig. 2 showsa horizontal cross-section on the line 2--2 of Fig. 1.

Fig. 3 shows a horizontal cross-section on the line 3 3 of Fig. 1.

It is to be understood that the illustrated example of the apparatus can be modied in numerous ways without departing from the invention herein described and claimed.

Generally the apparatus provides a liquid circuit. with an upward passage-way and a downward passage-way. Practically, this is accomplished by placing in the middle of a vessel a tubular shell with both ends open below the liquid level in the vessel. Where gas is introduced, such as chlorine for bleaching paper pulp in suspen. sion in the liquid, there are times in .the process where gas may be introduced faster than it is used or absorbed by the liquid, with the consequent `formation of bubbles or bodies of gas. These tend to rise and may be lost. For the entire downwardly moving column it has heretofore been proposed to use a highvelocity to prevent gas bubbles rising therethrough. Increasing `thel downward velocity in any apparatus also `in creases the upward velocity, and such bubbles of gas as get into the upward column are more quickly carried to the top and may be lost. Hence,` slow upward velocity andv high downward velocity are desirable for prior art apparatus', but these are quite antagonistic requirements in the apparatus employed heretofore.

The rst step in improvement over the older practice is to decrease the velocities of both colunms, giving less tendency to loss in the upward column. -The decrease in velocity of the downward column may be carried so far as to permit gas to rise in it. However, as a safe-guard a velocity seal is provided in the downward column above the point of introducing the gas. By constricting the column at. a narrow zone in an amount conditioned by the rate of flow in the column, the velocity can be made to bar the rise of gas and even hold below said constriction a pocket of the gas. As a further assurance for positive action of the seal, the circulating -means is locatedin the constricted zone.

For convenience of construction it is best located in the shell. Where a rotary propeller is used, it is most practical to use a cylindrical shell, and for this reason the vessel itself is Apreferably cylindrical. A propeller will function to maintain general circulation irrespective of its location in the shell. However, the higher the propeller is located vin the shell, the less it may` whip, and it may more easily be supported from outside the vessel. In a like manner the smallerl the propeller, the less. power it takes, and the less it stirs the column. The constriction of the column is made circular and is placed high, thus to aiord a small circular orice in which to lopropeller is in effect only for agitation and that A ported wholly from above ing. 23, into which stock may run into the vessel effort to-overcome friction. By making the upward column and the downward column sub-V stantially the same in cross-section the one balances the other and lessensthe work of the propeller. y For all the reasons above set forth the invention is most simply carried out in apparatus as iollows:

A vessel I preferably provides a deep cylindrical well-like container, such as one which isv about 27 feet deep and about 131/2 feet across. It may be made of Wooden staves for chlorination of paper pulp. Within it is formed a tubular shell I I, which is preferably cylindrical and concentric with the vessel I0. This may be about 9 feet in diameter. It also may be made of wooden staves, but openings I3 are provided at the top, and openings I4 at the bottom to permit circulation through it of liquid, the level of which is shown at line I5. A suitable bottom I8 is provided through whichv there is an outlet opening I1 for the pipe I8 with valve I9. On the bottom centrally is a bale cone 20, as of solid wood to direct the downwardly flowing liquid laterally, and to avoid stagnation. Similarly there is a fillet 2| at the outer edge of the bottom to move stock upwardly, and to avoid stagnation. `'Iv'he top of the vessel I8 has a closure 22 with openbe introduced as from chute 24.

Part way down in the shell there `is an annulus with lower and upper inclined faces `2li and 2'I4 forming a circular throat 28, having a short Y cylindrical wall 29. Within the throat is located a propeller on shaft 3I.

the liquid vlevel I5, as Driving means is by the bearing or mounting 32.

and a motor 35.

indicated by a gearing box 33 rlhe propeller has a depth corresponding closely throat, and its blades I to the short wall 29 of the 38 are wide and slightly inclined, and extend closely to the wall 29. Just above the annulus 25 there are holes 38 about 6 inches square' in the shell II, to provide for circulationwhen the level of liquid is below the bottom 39 of the top openings I3.

Tubes 40 for introducing gas are located ,toA

discharge the gas into the shell below the annulus 25. Preferably these are placed low, giving the gas some opportunity to rise and to react as it rises. Excess gas will not pass the .throat 28 in proper operation. Where chlorine is the gas used, rubber hose is suitable for the tubes 40. The ends 4I project downwardly at an angle as shown. Three 3A, inch rubber hose are suitable for the apparatus described when used for chlorinating paper pulp.

In j operation for chlorinating pulp, stock is I0 from chute 24, thus lling the vessel and the shell. A slurry of 21V/2% to 41/2% consistency is suitable. When the level reaches the holes 38 circulation may begin and chlorine may be introduced. The speed of the rotary propeller may vary and preferably is limited between that low speed which effectsr the velocity seal, and that high speed which tends to The shaft is supprevents gas rising carry gas bubbles down with the pulp, out-of the sneu and into the 11p-stream. This does not mean that action does not occur in the uptop. When `chlorination is suiliciently complete'y thevalve I9 may be opened, and circulation can continue until the'liquid level drops below the holes 38.

The holes 38 serve also to short circuit part of the stock. Where little or no bleaching action takes place above the level of the holes on the outside of the shell, there is no need for all the stock to travel up and over the top ofthe shell to be recirculated. Suitable gates may be provided over the Aholes 38 to close them in whole or in part. One such gate is illustrated as having guides 43 and 44, a gate member 45, and a controlling rod 46. Control of the gates may limit or prevent the short-circuiting of `part of the v and claimed, the apparatus being highly efiicient and greatly improved over the equipment used heretofore, as set forth in the appended claims. I claim:

l. Apparatus for treating liquid and pulp slurrieswith gas comprising a vessel, a vertical tubular shell -within said vessel open at thetop and bottom to liquid in said vessel for circuitous flow of liquid through said shell, means providing an annular constriction in the passage-way through said shell adjacent the upper end providing a reaction chamber below said constriction, propelling means located in and substantially lling the opening of said constriction for circulating the liquid, the opening of said constriction and the size of the propelling means being such that operation of the propelling means creates a velocity of the slurry at said constriction which through said constriction, and means for discharging gas into said-reaction chamber below said propelling means.

2. Apparatus for treating liquid and pulp slurries with gas, comprising a straight-sided vertical tubular vessel, a straight-sided vertical tubular shell within said vessel open at top and bottom to` liquid, lthe opening of said constriction and the size of the propeller being such that operation of the propeller creates a velocity of liquid at said l constriction which prevents gas rising through said constriction, and means for discharging gas into said reaction chamber below said propeller.

, CLINTON K. TEXTOR.

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