US2706390A - Bleaching plant - Google Patents

Description

April 19, 1955 R. J. JOHANSEN BLEACHING PLANT Sheets-She Filed Oct. 19, 1953 /NVENTOR.'

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Rolf Jamar Jo/mflsen,

- ,(Mv- ATTOfiWfVS} April 19, 1955 R. J. JOHANSEN 2,706,390

BLEACHING PLANT Filed Oct. 19, 1953 2 Sheets-Sheet 2 //VV/V7'0R:

Rolf Jamar Jo/mnsen BYMM A0 7 ATTORNEYS United States Patent Ofifice 2,706,390 Patented Apr. 19, 1955 BLEACHING PLANT Rolf Jomar Johansen, Karlstad, Sweden, assignor to Aktiebolaget Kamyr, Karlstad, Sweden, a company of Sweden Application October 19, 1953, Serial No. 386,959

Claims priority, application Sweden October 18, 1952 6 Claims. (CI. 6827) This invention relates to a plant for bleaching cellulosic pulp, comprising at least one high bleaching tower and at least one washing filter in which pulp is washed before it is introduced into the bleaching tower.

It is an object of the invention to provide a bleaching plant adapted for the feed of pulp in the upward direction through the bleaching tower or towers.

Another object is to provide suitable means for the transfer of pulp from the top of a preceding bleaching tower to the bottom of a following tower and for washing the pulp and mixing new bleaching agents into it during said transfer.

Still another object of the invention is to make possible a positioning of the filter or filters at a low level in the bleach plant, thereby gaining advantages in respect of building costs and ease of attendance to the filters.

A further object is to provide an advantageous combination of filter type used and the means for supply of pulp to the filter and for feeding of pulp from the filter to the bottom end of a following bleach tower.

Another object of the invention is to take advantage of the height difference between the ends of a bleach tower by having the pulp therefrom generate a superatmospheric pressure necessary for the operation of a rotary sieve filter located near the bottom of the tower.

A further object is to provide a feeding device suitable for the introduction of high density pulp into the lower end of a bleaching tower.

Still another object of the invention is to provide a feeding device forming a reliable lock or check valve in a feed tube carrying pulp under high pressure to the lower end of a bleaching tower.

A preferred form of the bleaching plant according to the invention is illustrated in the drawings and hereinafter more fully described.

In the drawings:

Fig. 1 is an elevational view, partly in section, of a part of the bleaching plant, and

Fig. 2 shows on a larger scale and in closer detail a part of Fig. 1 where certain means have been represented symbolically.

Referring to Fig. 1, the numerals 11 and 13 designate high concrete towers in which bleaching reactions take place during the continuous movement of the pulp through the towers in the upward direction. The pulp is to be transferred from the top of the tower 11 to the bottom of the tower 13, and during this passage the reaction products resulting from the preceding bleach step are to be washed off and a new bleaching agent is to be mixed into the washed pulp. The washing is carried out on a pressure air filter 15 located in the vicinity of the lower part of the tower 13 and preferably placed on a floor somewhat elevated above the ground floor. The filter 15 consists of a rotary cylindric drum 17 having a perforated shell,,and of a cover enclosing the drum and forming a pulp vat 19 into which the drum is partly immersed, and also a closed hood 21 surrounding the upper part of the drum which in operation carries a continuous pulp web 23. The hood 21 has a pressure air inlet 25 which is connected by means of a pipe 27 to a fan or low pressure compressor 29 serving to compress air taken from the atmosphere to a low superatrnospheric pressure. The air thus introduced into the hood 21 is pressed through the pulp web 23 and displaces water therein. Said water passes through the perforated shell of the sieve drum into the interior thereof, and therefrom it flows down into a box 26. Washing water is sprinkled over the pulp web through sprinkle tubes 28. The washed and dewatered pulp web is brought out of the pressure hood 21 and is taken off the sieve drum by means of a roller 29. The density of the pulp at this stage is of the order of 8 to 15 per cent dry content.

Pulp continuously discharged at the top of the tower 11 and diluted, if desired, is supplied to the above-described filter through a vertical drop tube 31, the lower end of which opens into a container 33, and from there the pulp is fed by means of a pump 35 through a pipe 37 to the pulp vat 19 of the filter. The drop tube 31 is open to the atmosphere at its upper end, and the diluted pulp falling down therein carries with it air which will be somewhat compressed on account of the height difference between the ends of the tube, and the high drop velocity. The tube 31 debouches in the container 33, whereby air and pulp are separated by cyclonic action. The air under a low superatmospheric pressure thus obtained is let off through a pipe 39 connected to the centre of the upper side of the container 33. Said pipe 39 is connected to the pipe 27 and therefore, said air is conveyed to the hood 21. Consequently, the fan 29 need only supply a part of the pressure air demand of the filter 15, and in certain cases said fan may be stopped or omitted. The greater part of the white water collected in the box 26 goes through a pipe 41 back to the container 33 and is held in circulation in order to dilute the pulp to a density convenient for the operation of the filter. A lesser part of the white water flows over an overflow down into the pipe 43 and is carried off by means of pump 44 and pipe 46 whereby the reaction products formed in the bleach tower 11 and washed off by the filter 15 are finally disposed of.

From the filter 15 the pulp drops down into a mixer 45, preferably designed as a conveyer screw, where the chemicals required for the bleaching in the tower 13 may be mixed in. From the end of the mixer 45 the pulp is brought through a valve 47 forming a locking device, into a conduit 49, the upper part of which extends vertically downwards from said valve and the lower curved end of which is connected to a stirring device 51. Steam from a steam pipe 53 is introduced into said stirring device in order to heat the pulp to the temperature required for the following bleaching reaction. Instead of or in addition to steam, a gaseous bleaching agent, such as chlorine gas, may be introduced into the stirring device and mixed into the pulp by the same. The stirring device 51 is directly connected to the point of the conical bottom of the bleach tower 13. At its upper end said tower is provided with a discharge means formed as a rotary scraper.

The valve 47 consists of a stationary housing having a pulp inlet 55 at its upper side and a pulp outlet 57 at its lower side, and of a cylindrical or slightly conical rotor or plug 59 rotary in said housing about a horizontal axis and driven in the clock-wise direction. Said plug has a number of pockets which in operation are each successively put in communication with the inlet 55, closed, put into communication with the outlet 57, closed again, and so on. In their upper position the pockets are filled with pulp coming from the mixer 45, and in their lower position the pockets are emptied of their pulp contents. In this way, small quantities of pulp are successively transferred from the inlet to the outlet of the valve, while maintaining the pressure difierence existing therebetween, i. e. the valve acts as a lock. Said pulp quantities drop through the outlet 57 down into the conduit 49 and join the solid column of pulp present in the lower part thereof.

A pipe 61 for the supply of air under pressure from a compressor tank 63 is connected to the upper end of the conduit 49. Inserted in said pipe 61 is a control valve 65 which, in a manner to be described more closely further down, is controlled by a level feeling device 67, so that it admits air when the pulp in the conduit 49 rises above a desired level and cuts oil or chokes the air when the pulp drops below said level. In this way, an always air-filled space 66 is maintained in the upper part of the conduit 49 and in the outlet 57, so that the pockets of the plug 59 are sure to be emptied of their contents when they face downwards. The pulp in the conduit 49 is under a high hydrostatic pressure, and if said air-filled space 66 were not present, no pulp would be conveyed to the tower, but the pulp in the tower would instead move backwards up through the valve when the same is turned. The pressure of the air supplied through the pipe 61 must be higher than the hydrostatic pressure caused by the pulp in the tower 13, because not only said pressure but also the friction in the conduit 49 and in the stirring device 51 must be overcome before the pulp moves. Usually the pressure is of the order of 2 to 3 atmospheres overpressure. The pressure air supply is controlled in such a manner that there is no risk of the conduit 49 and the stirrer 51 being blown free of pulp. Practically no air accompanies the pulp, but all pressure air supplied to the space 66 is fed out through the valve 47, the pockets moving upwardly on the left side of the rotary plug 59 being completely filled with pressure air. Instead of letting this air expand in the inlet 55 in counter-current to the pulp introduced therein, said air is conveyed to the pressure air filter 15. To this end, the valve housing is provided with an air outlet 69 located at such a point on the lateral side thereof that said air outlet 69 never communicates through the plug pockets with the pulp inlet 55 or the pulp outlet 57. A pipe 71 connects the air outlet 69 to the container 33 in which, as mentioned above, a low superatmospheric pressure prevails. When a plug pocket reaches said air outlet 69, the air filling therein expands to said lower pressure and the greater part of the air is transferred to the container 33. Fibres that may be entrained are separated olf therein, and from there said air is fed to the pressure filter together with air under low pressure derived from other sources. In the filter 15 the air is used for maintaining the pressure difference between the outer and inner side 3% the sieve drum required for a proper operation of the ter.

The pipe 61 has a shut-off valve 75, and between the steam pipe 53 and the valve 65 there is provided a pipe connection with a shut-off valve 77. By closing the valve 75 and opening the valve 77, steam instead of air may be supplied as the fiuid for driving the pulp downwards in the conduit 49 and into the bleach tower 13. If desired, air and steam may be supplied simultaneously through the control valve 77.

Referring to Fig. 2, the level feeling device symbolically represented by 67 in Fig. 1, comprises a screw or impeller 79 so constructed that an axially directed reaction force is exerted thereupon when it rotates in contact with the pulp in the conduit 49. The screw 79 is attached to a horizontal shaft 83 extending through the wall of the conduit 49 and sealed thereto by a packing box 85. The shaft is journalled in two bearings 87, 89 allowing an axial displacement of the shaft and is driven by an electric motor 91. Pivotally secured to a bracket 93 is a bell crank lever, the vertical part 95 of which bears with a point 97 against the end of the shaft 83, and the horizontal part of which serves to operate electric switches 101, 103. A weight 105 is displaceably arranged on the lever part 99, whereby the point 97 may be brought to bear against the end of the shaft 83 with a force of adjustable magnitude. The direction of rotation of the shaft is such that the reaction force from the pulp strives to displace the impeller 79 to the right. In the shown position, in which the impeller touches the pulp rather slightly, the two opposed axial forces balance each other. When the pulp level rises, the reaction force on the impeller will increase and the shaft screws itself outwardly, causing the lever 99 to close the switch 101. When the pulp level sinks below the shown position, the impeller will work in air, the weight 105 pushes the shaft to the left and the lever 99 closes the switch 103.

Secured to the spindle of the valve 65 is a toothed gear segment 107 in engagement with a gear keyed to the shaft of an electric motor 109. The current to said motor is thrown in by a reversing contactor 111 controlled by the switches 101, 103. A stop pin 113 restricts the movement of the gear segment 107 to about 90 degrees and may preferably form the operating lever of a limit switch for interrupting the current when the gear segment has reached one or the other of its end positions. In the shown position in which the switches 101, 103 are open, the motor 109 is at standstill. When the switch 103 is closed, the motor runs clockwise and the valve 65 is turned in the closing direction. This movement continues until the switch 103 opens or the valve 65 reaches its fully closed position. When the switch 101 is closed, the motor 109 runs counter-clockwise and the valve 65 is turned in the opening direction, until said switch opens again or the valve 65 reaches its fully opened position.

By the above-described control means the air supplied through the pipe 61 to the conduit 49 is controlled in such a manner that in the long run the supplied air quantity is equal to the air quantity discharged through the pockets of the rotary valve, and the control means work rapidly enough to prevent the pulp level from deviating too much from the desired level of equilibrium predetermined by the position of the feeler means 79.

I claim:

1. In a bleach plant for cellulosic pulp, a wash filter, a reaction tower, the top of said reaction tower being considerably above the top of said wash filter, a device for feeding pulp of high density from the wash filter to the bottom of the reaction tower, said device comprising a conduit having a vertical tubular part, the lower end of said part being connected to the bottom of the tower, a valve connected to the upper end of said vertical part, said valve having a pocketed plug rotary about a horizontal axis, means for supplying pulp from the filter to the upper side of said plug, and means for the supply of a gaseous fluid to the lower side of said plug.

2. In a cellulose bleach plant, a bleach tower having a pulp inlet at its bottom and pulp discharging means at its top, a feeder device for supplying pulp to said tower inlet, comprising a housing and a pocketed plug rotary therein about a horizontal axis, said housing having an inlet at its upper side and an outlet at its lower side, a conduit extending downwardly from said feeder outlet and connecting the same to the bleach tower inlet, means for supplying a gaseous fiuid under pressure to said conduit, and means responsive to the pulp level in said conduit for controlling the content of gaseous fiuid in said conduit.

3. In a plant for bleaching cellulosic pulp, a high reaction tower arranged for continuous flow of pulp therethrough, a conduit for the supply of pulp to the bottom of the tower, said conduit having a substantially vertical part, a rotary valve inserted in said part of the conduit at the level of the lower part of the tower, a tube for the supply of pressure air connected to said conduit at a point below the rotary valve, a controllable valve in said tube, pulp level feeling means located below said rotary valve in said conduit and controlling said last mentioned valve in such a manner as to maintain a filling of pressure air in a space of said conduit located between the rotary valve and said pulp level feeling means.

4. In a plant for bleaching cellulosic pulp, a high bleach tower, a pressure wash filter, said filter being located at a level below the middle of the height of the bleach tower, said filter comprising a rotary sieve drum and a cover for maintaining an atmosphere of air under pressure over a part of the outer periphery of the sieve drum, and means for feeding pulp from said filter to the bottom of said bleach tower, said means comprising a valve, a conduit leading from the valve to the tower, and a source for air under pressure connected to said conduit, said valve consisting of a housing having a pulp inlet at its upper side, a pulp outlet at its lower side and an air outlet at its lateral side, and of a plug rotary in said housing about a horizontal axis and having pockets each capable of communication successively with said pulp inlet, said pulp outlet and said air outlet and with only one thereof at a time, said pulp outlet being connected to said conduit and communicating means between said air outlet and said filter cover.

5. In a plant for bleaching cellulose pulp, two high reaction towers located at the side of each other, a rotary pressure wash filter, said filter being located at the level of the lower part of the towers, means for conveying pulp from the top of the first tower to said filter, said means comprising a vertical drop tube for generating pressure of the pulp supplied to the filter, means for feeding washed pulp from said filter to the bottom of the second tower, said means comprising a vertical conduit, a valve inserted in said conduit, said valve comprising a housing having a pulp inlet on one side thereof, a rotary plug having pockets for the transfer of pulp 5 from one side of the valve to the other, and a pressure air supply connected to said conduit below said valve.

6. In a plant for bleaching cellulosic pulp, a bleach tower having a pulp outlet at its top, a substantially vertical drop ,tube extending along the greater part of the height of the bleach tower, a wash filter comprising a rotary sieve drum and positioned at a level lower than the middle of the height of the bleach tower, the upper end of said drop tube being connected to said outlet of the tower and the lower end thereof being connected to the wash filter for supply of pulp thereto under pressure, a second bleach tower having a pulp inlet at its bottom, a pulp feeder comprising a housing having an upper inlet and a lower outlet, and a pocketed rotor turnable in said housing for transferring pulp from the inlet to the outlet thereof, said pulp feeder being located at a lower level than the wash filter, means for conveying washed pulp from the filter to the inlet of said feeder, means connecting the outlet of said feeder to the pulp inlet of the second tower, and means for supplying a gaseous fluid under pressure to the outlet of the feeder.

References Cited in the file of this patent UNITED STATES PATENTS 2,383,684 Richter Aug. 28, 1945

Claims (1)

1. IN A BLEACH PLANT FOR CELLOSIC PULP, A WASH FILTER, A REACTION TOWER, THE TOP OF SID REACTOR TOWER BEING CONSIDERABLY ABOVE THE TOP OF SAID WASH FILTER, A DEVICE FOR FEEDING PULP OF HIGH DENSITY FROM THE WASH FILTER TO THE BOTTOM OF THE REACTION TOWER, SAID DEVICE COMPRISING A CONDUIT HAVING A VERTICAL TUBULAR PART, A LOWER END OF SAID PART BEING CONNECTED TO THE BOTTOM OF THE TOWER, A VALVE CONNECTED TO THE UPPER END OF SAID VERTICAL PART, SAID VALVE HAVING A POCKETED PLUG ROTARY ABOUT A HORIZONTAL AXIS, MEANS FOR SUPPLYING PULP FROM THE FILTER TO THE UPPER SIDE OF SAID PLUG, AND MEANS FOR THE SUPPLY OF A GASEOUS FLUID TO THE LOWER SIDE OF SAID PLUG.

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