US2089992A - Continuous bleaching process and apparatus - Google Patents

Description

Aug. 17, 1937. J. CAMPBELL ET AL CONTINUOUS BLEACHING PROCESS AND APPARATUS Filed March 14, 1932 5 Sheets-Sheet 1 31 INVENTORS JOHN CAMPBELL LANCELOT O. ROLLESTON GEORGE A. SMITH Y 1 4 6 H EIR ATTOYRNEY 1937. J. CAMPBELL ET AL 2,089,992

CONTINUOUS BLEACHING PROCESS AND APPARATUS Filed March 14, 1932 1 z. Sheets-Sheet 2 INVENTORS JOHN CAMPBELL v GEORGE ASH/TH BY HEIR ATTORNEY LANCELOT 0.. RDLLESTON 1937- J. CAMPBELL ET AL CONTINUOUS BLEACHING PROCESS AND APPARATUS Filed March 14, 1932 3 Sheets-Sheet 3 EUNEW ENVENTORS JOHN CAPIPBELL LAFJCELOT O. IVOLLEJTON GEORGE A. SMITH THEIR ATTORNEY Patented. Aug. 17, 1937 UNITED STATES.

aoaasaz conrmvovs nrlmcnmc raocsss AND ARATUS APP John Campbell, Lancelot 0. Rolleston; and George A. Smith, Glens Falls, N. Y., assignors to Inter- I national Paper Company, New York, N. 2., a corporationof New York Application March 14, 193?, Serial No. 598,582

, 9 Claims.

This invention is concerned with a continuous bleaching process and suitable equipment for conducting the process in the bleaching of pulp and similar fibrous, cellulosic materials. The

equipment forming a part of the invention is particularly suited to a process in which the material is subjected to a vacuum and then to reaction with a gaseous bleaching agent, such as chlorine, in the manner set forth in the pending application of John Campbell and Lancelot O. Rolleston Serial No. 487 ,758 filed October 10, 1930, Patent No. 1,957,937.

The apparatus is not limited to the conduct of this type of process, however, but may be uti- 5 lized in conjunction with various other processes,

as will more clearly appear hereinafter.

A feature of the invention is the utilization of an elongated reaction chamber or conduit in such a Way that the material to be bleached may 20 be continuously introduced at one point and removed at another and in the course of transit through the chamber may be subjected to treatment under varying pressure conditions. A vacuum may, for example, be produced at one point 5 in the chamber and pressure above atmospheric at another while the material is continuously advancing. This is permitted by the fact that the material as it is introduced and removed from the chamber, in accordance with the invention, serves to form a substantially air-tight plug. Furthermore it is so tightly packed within the chamber that substantial pressure differences may be maintained at points in the chamber only a short distance apart.

A single unit of the apparatus may be employed in a cyclic manner to subject the same mass of material to a series of successive treatments. A better and more economical bleaching action may be obtained by. subjecting the material to only a partial bleaching during each treatment. This is preferably accomplished, however, by the employment of a plurality of bleaching chambers connected in series. A further feature of theinvention is in the interconnection and utilization of a plurality of reaction chambers to efiect an efficient and economical multi-stage bleaching operation.

Other features and advantages of the invention will appear from the detailed description of certain illustrative forms of the same which will now be given in conjunction with the accompanying drawings in which:

Fig. 1 isa schematic view, in vertical section, of a bleaching unit constructed in accordance with the invention.

Fig. 2 is a diagrammatic view illustrating a plurality of the units shown in Figure 1 connect,- edin series for a multi-stage bleaching operation, and

Fig. 3 is a viewsimilar to Figure 1 showing a modified form of construction for the feeding of the material to be bleached.

Referring now particularly to Figure 1 there is shown a mainreaction chamber III which is formed preferably of steel or similar strong, durable material and is lined on its interior surfaces with any suitable material resistant to the action of the bleachingagent, such as chlorine or the like. For this purpose a lining ll formed of tile or stoneware or, if desired, rubber, glass,bakelite or the like, may be employed. The chamber is preferably formed with a slight taper from top to bottom, the bottom being slightly larger than the top, so as to avoid any tendency of the material to arch or become blocked in its travel through the chamber. At its top the chamber is provided with a tapered neck 12 having a flared or funnel shaped receiving portion or hopper I 3. Within the narrow, slightly-tapered neck there is provided a feed screw l4 having a relatively tight fit with the sides of the neck.

' This screw is carried by a shaft l5 having a bearing I6 'within the funnel I3 and carrying a bevel gear H at its upper end. A motor ill or other suitable source of power may be adapted to drive the shaft l5 at an appropriate speed through a pinion l9 cooperating with the gear H. The lower end of the feed screw may communicate with a flared portion of the neck which serves to deliver the material to be bleached into the cham- The pulp or other material to be bleached may be received in the form of slush from the mill or may otherwise be in a mixture of relatively low concentration. In this form it may be passed to any suitable form of dehydrating equipment such as a screw press, wet machine, centrifugal drier or the like. There is conventionally illustrated in Figure 1 a screw press 2i adapted to receive the stock in a hopper ,22 and force it by means of a screw 23 through small openings at the discharge end of the press. .A motor 24 may be provided to drive the feed screw. Water expressed from the stock may drain into the bottom of the press and may be withdrawn by means of a pipe 25. The partially dried pulp may be discharged into the hopper 26 of any suitable form of ,pulper or disintegrator or breaker 21. Here the stock is broken intorelatively small lumps or nodules of substantially dry material having its moisture 70 up into small lumps by the breaker 21.

content in the form of a film lining the interior and exterior surfaces of the fibers and having a certain amount of air within and between the cells, in the manner explained in the before-men- 5 tioned pending application. The breaker 21 is adapted to discharge the nodules directly into the hopper l3. Here they are seized by the feed screw and forced into the chamber at a suitable rate of feed.

At the lower end of the chamber it converges along a portion 28 toward a narrow discharge neck 23. Within this neck is mounted another feed screw 30 adapted to withdraw the material from the chamber and discharge it through the outlet 3| into any appropriate form of vessel for further disposition. A motor 32 may be provided for driving the feed screw 30 through gearing 33. The feed screws I 4 and 30 should be driven at appropriate relative speeds so as to insure introductlon and removal of the material at the same rate. It will be understood that suitable reduction gearing is provided between the motors and the feed devices.

For the purpose of removing the air from the material introduced into the chamber a vacuum pump 34 is provided. This may be connected through one or more branches 35 with the interior of the chamber. A single connection is sufiicient although it is considered preferable to employ a plurality as shown. This has various advantageous effects. It insures a somewhat better removal of the air from the pulp and at the same time avoids the development of a rapid rush of air toward a single small opening. Such a rush of air would be apt to cause some of the fibrous material to enter the pipe or tube also and thus clog it. Several branches, particularly near the top of the chamber, may conveniently enter on opposite sides at any desired number of points. 40 As shown the ends of the pipes are preferably beveled slightly or otherwise formed with downwardly facing openings to-assist in preventing clogging of the ends.

At a point further down the chamber a suitable gaseous bleaching agent, such as chlorine gas, may be introduced. For this purpose the gas may be led from a storage vessel 36 where it may be held under suitable pressure, preferably inliquid form. One or more tubes or pipes 31 may serve to introduce the gas into the chamber at a point removed from that at which the air is being withdrawn. Any convenient number of by-pass lines 38 may be provided to connect the lower portion of the chamber with the upper portion. This is to enable any chlorine which remains in the material,- as it approaches the discharge end of the chamber, to be drawn into the vacuum zone to react with the fresh material at this point. The chlorine introduced in this way will react so quickly with the material to produce non-gaseous products that no appreciable increase in pressure will result. It will benoted that the chlorine resistant lining is not provided on any of the surfaces above the main chamber since the chlorine will not find its way above this.

The operation of the apparatus may be briefly set forth as follows: The watery stock is first introduced into the hopper 22. It will be reduced to a suitable state of dryness and broken In this state it is supplied to the feed screw H which forms it into a comparatively solid plug filling all of the spaces between the screw and the walls of the neck I2. This serves to substantially prevent the entry of air which would interfere with atmospheric pressure. The pressure might be atmospheric or below so long as it is greater than the pressure establishedby the partial vacuum but a more rapid and thorough penetration of the gas into the cells of the material will take place if it is introduced under a slight superatmospheric pressure of, say, 10 to 25 pounds, more or less. This is possible without appreciable interference with the establishment of a vacuum higher up for several reasons. In the first place the material, as it is packed into the chamber, is so dense that it affords a quite effective seal between thevarious zones of the cham-- her. The gas under pressure at one point will be prevented, by the packing of the material itself, from leaking into the vacuum zone in any substantial quantities. Furthermore the gas in reacting with the cellulose fibres and the coloring matters will produce non-gaseous compounds which will instantly reduce the volume and pressureof the gas. Thus as any gas finds its way from the zone adjacent the point of inlet it will be rapidly consumedand will be more or less completely eliminated before it reaches the vacuum zone. Any free chlorine remaining in the material as it approaches the bottom of the chamber will be conducted by the by -pass lines 38 to the top of the chamber where it will be rapidly consumed by the fresh material. As the bleached or partially bleached material reaches the bottom of the chamber it is removed by the feed screw 30 and passed to any suitable equipment for further disposition. If any air is admitted through the plug formed around the screw 30 it will simply tend to assist in sweeping-the excess chlorine through the by-pass lines 38. It may be found desirable to provide a small opening 39 adjacent the bottom of the chamber for the purpose of admitting a regulated amount of air to effect the removal of the excess gas in this way before the material is discharged from the chamber.

Preferably, only a partial bleach is effected during each treatment of the pulp. A complete bleach may, in that case, be produced by passing the material several times through the same chamber. When discharged through the outlet 3| it may, for example, be washed and diluted to the state in which it was introduced into the hopper 22 and the same operation may be repeated. In the washing of the partly bleached material it may be treated with sulfur dioxide or caustic soda or both or with other similar treating agents. It will be found advantageous, as explained in the pending application already mentioned, to add certain alkaline substances, such as caustic soda, to the material prior to its passage through the chamber Ifl so that the gas may react with these substances and produce compounds which will assist in the bleaching of the material.

While the chamber III has been illustrated and described as being vertically disposed it will be understood that it may, if desired, be placed in a horizontal position. In lieu of forming it as a chamber of relatively large cross-section it might be formed as an elongated conduit of appropriate size to permit the material to be readily forced along. It should be of suitable height or length to insure a thorough bleaching of the material in transit.

The same reaction chamber may be utilized to effect two or more successive bleaching operations upon the same material, but it will be found preferable in most large scale production to provide a plurality of similar chambers arranged in series, as shown in Figure 2. This will enable the process to be conducted on an'absolutely continuous basis. There may, for example, be'provided three separate chambers 40, 4| and 42 in each of which the bleaching of the material may be only partially carried out. The raw, unbleached stock as received from the mill, or otherwise in a condition of low concentration, may be introduced into a tank 43. In this tank, or at aprevious point in the treatment of the pulp, suitable alkaline substances, such as caustic soda or any of the others mentioned in the pending Campbell and Rolleston application, may be added to the mixture. From the tank 43 the material is discharged into any suitable form of dehydrating equipment, such as a screw press 44. Here a large part of the water is expressed from the material and the latter is discharged in a suitable state of dryness into an appropriate breaker 45. The material emerging from the breaker should be in the form of small lumps, substantially uniform in size, expanded slightly to admit air into and between the cells. It is then handled and treated within the chamber 40 in the manner explained in connection with the chamber I0.

a -The partially bleached material is discharged into a tank 46 where it may be washed and diluted by the addition of a suitable quantity of water, preferably containing alkaline substances of the character previously referred to. This may be introduced through a pipe 41. -'I'he resoda or similar alkaline substances. The solution for this purpose may be derived in whole or in part from the screw press 44. Thus, the water which is expressed from the original stock at this point in the operation, still containing a considerable quantity of the original alkali, is used to advantage to treat the material prior to its final bleaching. The mixture in the tank 50 is again dehydrated by passing, for example, through a third screw press 52 and it is again broken into suitable lumps by a breaker 53. The water and alkali removed from the material in the press 52 may advantageously be employed as the source of the solution introduced through the pipe 41 into the tank 45 prior to the second bleaching action. The water removed by the press 48 will have lost the greater portion of its alkali content and may be simply discarded without any great loss. If desired, this water might again be'utilized after suitable concentration either by the evaporation of a part of the water It is then again broken into relatively or by the addition of alkali. Inasmuch as it will contain various undesirable impurities, however, it will be found preferable to discard it. Now, the material broken into lumps by the breaker 53 will be introduced into the final bleaching chammove traces of the bleaching agent and the products of the various bleaching reactions.

Referring now to Figure 3, a slightly modified form of apparatus is disclosed. The reaction chamber'55 may be of the same construction as the chamber ID of Figure 1. It is preferably also operated in the same way. Vacuum is produced adjacent the top of the chamber by means of a suitable vacuum pump 56 and chlorine or other bleaching gas is introduced from a storage vessel 51 at a lower point in the chamber. By-pass lines 58 may also be provided as before to conduct any unused-gas from the bottom of the chamber into contact with the fresh, unbleached material. In lieu of introducing and removing the pulp by means of feed screws, however, a form of reciprocating feed is employed. The material from the breaker is introduced into a hopper 59 associated with a cylinder 60. Within this cylinder is reciprocated a piston 6| operated in any suitable way by means of a crank arm 62 deriving power from a motor, or other convenient source. Upon each forward movement of the piston 6i, i. e., from the right, it will force a plug of the fibrous material into the top of the chamber. Upon retraction of the piston a new supply of the material will enter the cylinder. There will at all times be a plug in the forward or right-hand portion of the cylinder to serve as a seal, thus permitting a suitable vacuum to be developed adjacent the top of the chamber. Similar means may be provided for the discharge of the bleached material. For example, it may fall into a cylinder 63 connected with the bottom of the chamber and may be forced out of the cylinder by means of the piston 64 operated by a crank 65. A constant seal preventing access of air into the chamber or the escape of chlorineirom the chamber is provided by maintenance of a plug of the material at all times in the cylinder 63. In the operation of this form of equipment the pistons 6| and 64 are preferably driven in synchronism so that as the piston 6| forces a new charge of material into the chamber,- the piston 64 will be retracted and will permit a corresponding portion of the bleached material to descend into the cylinder'63. Due to the compressibility of the material in its dry state this relation in the operation of the pistons is not essential although the rate of introduction and discharge should be the same. In other respects the apparatus of Figure 3 may be utilized in the same way as that disclosed in Figure 1.

While several illustrative forms of the invention have been disclosed in considerable detail, it will be understood that various modiflcations'in the construction and operation of the several parts of the bleaching system maybe effected without departing from the general principles and a sence as to efi'ect a substantially air-tight sea] at the inlet and outlet, withdrawing the air from said .0 material as it passes through one portion of said chamber, and introducing a gaseous bleaching agent into said-material as it passes through a subsequent portion of said chamber.

2. A method of bleaching fibrous, cellulosic mal5 terial which comprises continuously forcing a body of the same in a substantially dry, solid mass through a reaction chamber, said material being so introduced and withdrawn as to effect a substantially air-tight seal at the inlet andoutlet, maintaining a substantial sub-atmospheric pressure adjacent the points of introduction and removal of the material, and introducing a gaseous bleaching agent under pressure at an intermediate point.

3. A method of bleaching fibrous, cellulosic ma-. terial which comprises continuously forcing a body of the same in a substantially dry state through a chamber, said material completely filling said chamber and forming a tightly packed moving mass, subjecting the material to a substantial sub-atmospheric pressure in one zone within the chamber, and introducing a gaseous bleaching agent under a higher pressure in a subsequent zone.

4. A method of bleaching fibrous, cellulosic material which comprises continuously forcing a body of the same in a substantially dry state through a chamber, said material completely filling said chamber and forming a tightly packed moving mass, maintaining a substantial sub-atmospheric pressure adjacent the two ends of said chamber, and introducing a gaseous bleaching agent under pressure at an intermediate point.

5. A multi-stage method of bleaching fibrous,

cellulosic material which comprises alternately concentrating the material and diluting it with an alkaline solution in at least three stages, utilizing the solution resulting from the-first concentration of the material to dilute it prior to the third stage, utilizing the solution resulting from the third concentration to dilute the material prior to the second stage, and subjecting the material in concentrated form and as a compact mass in each stage to the action of a gaseous bleaching agent.

6. A method of bleaching fibrous, cellulosic material which comprises continuously forcing the,

same in a substantially dry state through an elongated reaction chamber, said material being so introduced and withdrawn as to effect a substantially' air-tight seal at the inlet and outlet, subjecting the material at onepoint in the chamber to a substantial vacuum and introducing a gaseous bleaching agent into said chamber at a subsequent point.

7. Bleaching apparatus which comprises an elongated chamber having a larger cross sectional area at an intermediate'polnt than adjacent either end; means for continuously forcing a substantially dry, solid mass of material to be bleached at one point into said chamber, means for removing said material as a substantially dry, solid mass at another point, said chamber and said forcing and removing means being so constructed and arranged as to enable said dry, solid material to be forced through said chamber in said state and discharged therefrom, means for producing a vacuum in a portion of said chamber, and means for introducing a gaseous bleaching agent into a subsequent portion of said chamber.

8. Bleaching apparatus which comprises a chamber having an inlet and an outlet and having a gradually increasing cross sectional area.

throughout a portion from a point adjacent the inlet, means arranged at least in part adjacent the inlet for forcing a continuously advancing column of substantially dry material to be bleached into and through said chamber in such dry state, said means being adapted to form with said material a substantially airtight seal at said inlet andoutlet, means for maintaining a partial vacuum in a portion of said chamber, and means for introducing a gaseous bleaching agent into a subsequent portion of said chamber.

,9. Bleaching apparatus which comprises a chamber having an inlet and an outlet and having a gradually increasing cross sectional area throughout a portion from a point adjacent the inlet, means arranged at least in part adjacent the inlet for forcing a continuously advancing column of substantially dry material to be bleached into and through said chamber in such

Images