SE439939B - Continual sulphite or bisulphite process for cellulose boiling - Google Patents

Abstract

The invention refers to a continual sulphite or bisulphite process for cellulose boiling, where the boiling fluid containing the mass is removed from the cooker eventually via a concentration step and a subsequent defibration step and defibration occurs mainly at the cookers pressure entirely or mainly without washing and the mass is cooled prior to defibration. With the purpose of bettering it at similar continual processes with insufficient defibration of the mass after boiling, which on the one hand is an evidently unnecessary large use of effect through continued defibration and on the other hand as a worsening of the masses strength properties, the invention is characterized by the defibration occurring in the temperature area of between 90-120 degrees C.<IMAGE>

Description

79o9ss9-ß 2 writing with reference to the accompanying Figures 1 and 2.

Figure 1 schematically shows a boiler used in the method according to the invention. According to one embodiment, the chips are pneumatically transported through the pipe 41 to the chip cyclone 11.

From the cyclone, the chips fall into the chip funnel 12 and further onto the measuring device 13, which may be a double screw feeder according to Figure 1 with the task of keeping the chip flow constant. From the double screw feeder, the chips fall into a feed device 14 provided with pockets, the purpose of which is to serve as a pressure barrier between the astringent vessel 15 and the pressure in the atmosphere. From the low-pressure feeder device, the chips fall into said astringent vessel 15, which is provided with a transport screw for feeding the chips further in the direction of the arrow a to the high-pressure feeder device 16 and from there on via the bellows equalizer 17 and the pipe 18 to the impregnation device 19.

According to the described embodiment, this consists of a cylindrically inclined vessel 19 provided with the transport screw 61 for the movement of the chips in the direction of the arrow d. In the impregnation vessel, the surfaces of the impregnation solution are at, for example, the levels b and c, whereby b is level with the outlet opening and the position of c is determined by the pressure difference between the steam drum A and B.

From the impregnation vessel 19 the chips fall and also the amount of impregnation solution corresponding to the amount of solution introduced into the impregnation vessel via the boiler's bellows equalizer 20 and the normally open shut-off valve 21 falls into the digester 22. In the digester the chips form a chip column, the upper surface of which is represented by the dashed line e. The liquid assumes such a position that its upper surface forms the plane f. The surface height of the chip is measured by the radioactive measuring device 60, according to which the amount of mass which should be removed from the digester is regulated so that the surface height e is kept constant. The surface height f of the liquid, which can also be lower than said plane e.g. f '(shown in broken lines), is kept constant by regulating the outflow via the line 52. Of course, the amount of chips and / or cooking solution fed to the digester 22 can also be regulated. The pulp is removed from the bottom of the digester either via line 42 or line 43. To facilitate the discharge of the pulp, a rotating bottom plow is arranged in the bottom of the digester, the wings 24 of which move the pulp to the center of the digester and from there to the blow pipe 42 or 44. 42 and 44, respectively, a concentrator 27 and 28, respectively, has been provided, the task of which is to remove liquid from the mass and thus make it thicker. The concentrator for the construction can be e.g. a tubular or cylindrical piece 27, 28.

Inside this outer jacket and at a given distance from its inner surface another tube or inner jacket of screen plate has been arranged, in which the mass is introduced from the blow tube 42, 44 and further from here to the defibrator 29, 30. The screen tube and the concentrator have closed ends and the water which has flowed through the cracks in the walls of the screen pipe can be removed through the pipe sockets 62, 63. The above-mentioned inner jacket can advantageously be made of screen-type screen plate with the elongated cracks in the direction of movement of the mass.

In the concentrator, the space between the outer and inner jacket can be divided into two parts or chambers, e.g. through a partition in the radial direction of the tube 28, 29. In this case, with the aid of clocks or other devices (not shown in the drawing), the leaving liquid can only be taken from one of the chambers at certain times, according to the drawing e.g. the left chamber and the left pipe socket 63. The right chamber is then at rest and the cracks in its inner jacket are cleaned. In the following stage, the left chamber is at rest and the liquid is taken from the right chamber and the right pipe socket 62, 63. The working and resting stages can thus be varied.

A defibrator 29 and 30, respectively, has been arranged in the blow tube, through which the mass is led in defibrated form to the blow tube 43 and 45, respectively, and further to the blow container (not shown in the drawing). When mass flows continuously in the blow tube, the defibrator can is considered to follow almost immediately after the digester, despite the rather short blow tube 42 and 44, respectively, when no blow vessel is present between the digester and the defibrator. The defibrator can be e.g. and s.k. plate painter type equipped with regulator for the grinding gap.

According to Figure 2, the impregnation vessel can also be provided with the screw 31 for immersing the chips in the impregnation solution, in case the chips are so dry that it does not sink by its own weight.

When the blowpipes 42, 43, the concentrator 27 and the defibrator 29 are in use, the blowpipes 44, 45, the concentrator 28 and the defibrator 30 may be out of use and first put into use e.g. when operational disturbance occurs in the blow pipes 42, 43, the concentrator 27 and / or the defibrator 29 and until the disturbance has been removed. The operation of the paired facilities can thus, if necessary, be changed or used at the same time.

According to Figure 1, the boiling liquid, which consists of an aqueous solution of some soluble base (ammonium, sodium or magnesium) and sulfur dioxide from the recovery and chemical manufacturing plant (not exposed in the figure) is passed through line 46 to the boiling solution vessel 32. , which can also be a pressure vessel depending on the properties of the boiling solution at the temperature in question. From the container 32, the boiling solution is led by means of a pump (not shown in the figure) via the line 47, the heat exchanger 33 and further via the line 48 to the impregnation bead 19, below the surface c. The boiling solution is heated to the impregnation temperature, suitably 90 ° C. ~ 13o ° c and must be allowed to 1oo ° c - 12o ° c, immediately or practically immediately before it reaches the impregnation chamber, the solution flowing continuously through the heat exchanger 33 and from there via the tube 48 to the vessel 19. Hereby For example, the boiling solution will no longer be hot in the pipes or any intermediate container, which could have harmful consequences in terms of the composition of the boiling solution and especially in the hot state when chemical reactions and the like. has a great tendency to take place.

The spent cooking solution or the so-called the effluent is removed from the digester through strainer devices 23 to the conduit 52 and further to the expansion vessel 34, where it is allowed to expand.

The resulting steam flows via lines 53 and 54 or 53 and 55 to the basin vessel 15, where it is used to heat the chips. The part of the line 55 present at the supply device 14 is not exposed in the drawing. If necessary, the separated residual liquor can be led via the line 56 to the following expansion vessel 35, from where the expanded steam flows via the lines 57 and 57a, for example to the washing water heating (not exposed in the figure).

Alternatively, the steam can also be led to the chip heating via lines 57 and 57b. The separated effluent is led via line 58 c to the evaporator housing (not shown in the drawing) for further treatment.

The amounts of steam needed to keep the boiler pressure and temperatures up can be conducted at the points indicated by arrows 49, 50 and 51 (not all of which are shown in the drawing), via pipes and valves to the system. To cool the pulp to a suitable blowing and defibrating temperature, the effluent from the laundry (not shown in the drawing) is led to the bottom of the digester via line 59, which communicates with the wings of the bottom plow 24. Via in these nozzles placed the solution spreads over the bottom of the cooker.

¶ \ .O C) V) CO (N * Q l OI! The devices and parts described above and later here may be known per se and used in the cellulose industry, so not all of them are described in more detail here.

In addition to the above-mentioned components, the system includes a large number of shut-off and control valves, adjusting devices as well as other aids and pipelines, pumps, etc.

With the method according to the invention and the plant described above, on a factory scale, cellulose has most recently been produced for newsprint and printing paper instead of the sulphate pulp used hitherto. Of the results obtained, the following may be mentioned as examples: raw material: factory chips, 60% pine, 40% spruce cooking solution: SO2 content 4%, pH 4.3 Pulp: kappa number 95 yield 66% pallor 61.5 SCAN extract 0.4 dichloromethane demolition 2.3 m2 degree of grinding 260 / SR When using the above-mentioned cellulose pulp as a paper ingredient instead of sulphate pulp, the paper and printing presses have been shown to function normally without detected disturbances. This means a significant saving in wood consumption when comparing e.g. between 45% yield of sulphate pulp and 65% yield of bisulphite pulp with corresponding properties.

The said good properties of the cellulose pulp depend, among other things, on on the following factors. Prior to impregnation, primary high-pressure evaporation is achieved with the highest possible air escape from the chips, which requires proper impregnation before cooking and low rejection, sufficiently even cooking conditions, and proper and performed defibrillation under correct conditions. When the defibrator is located immediately or practically immediately after the boiler, the mass can be fed to the defibrator with the advantage of the boiler pressure.

Immediately after cooking, the pulp then arrives in a more suitable form to the defibrator with less energy consumption during defibration. By making the mass suitably thick, the grinding gap in the defibrator can be kept larger than otherwise. It also follows that the majority of the fibers are defibrated only by ironing against each other. In this case, the gap of the defibrator will encounter fewer fibers in the mass passing through the defibrator and will therefore cause less damage to these. Mass properties, for example, "its pallor also improves the fact that the sulfur dioxide coming from the boiling zone in the gaseous form through the barrier solution of the impregnation zone 19 cannot come into contact with non-impregnated chips.

The decomposing changes in the cooking solution are promoted by added organic substances, which impairs the properties of the resulting cellulose. In such circumstances, it has generally been considered disadvantageous to allow any residual products from the boiler to circulate back to it. However, the residual steam obtained here is to such an extent “particularly particularly free of harmful sulfur dioxide that the steam can be circulated back in the process. This means significant savings in heating costs.

Due to the above reasons, however, only steam is circulated back. Residual solution etc. products are not recycled.

The examples given above of course include only an application of the invention, which can be varied to a large extent within the scope of the patent claims. Said pH range 3.5-4 constitutes e.g. no limit, but the pH value can also be lower.

The devices for the construction can also be different, e.g. the feeder device can be provided with pockets instead of a double screw, the pocket feeder devices 14 and 16 can be plug screws instead of a pocket feeder, the strainer device 23 can consist of only one strainer disc, which is arranged in the cooker wall instead of a self-cleaning strainer, etc.

The present invention can be used e.g. in a continuous sulphite or bisulphite process for cellulose boiling, where the boiling solution consists of an aqueous solution of one or more so-called soluble bases, such as ammonium, sodium and magnesium, as well as sulfur dioxide, and where the fibrous raw material consists of some coniferous tree or mixture of coniferous trees, in order to produce cellulose with high yield and high quality paper properties, the pulp being removed from the digester at the defibration stage, the defibration mainly takes place at the boiler pressure between the temperature 9o-12o ° c and completely or mainly in the washing state.

The defibration can take place at any particular consistency using such a bit distance in the defibrator 29, 30 that the degree of grinding of the pulp does not change significantly. The mass concentration during defibration can also be kept as high as possible, e.g. by concentrating the same.

For carrying out the process, a continuous boiler 22 can be built together with associated plants, the defibrator

Claims (1)

1. 7 79o9s3ø ~ ß 29, 30 is placed in the mass ledninu emanating from the digester or s.k. the blowpipe 42, 44 immediately or practically taqet immediately after the digester. The defibrator 29, 30 can be of so-called plate grinder type, provided with a control device for the grinding gap. Between the bottom of the digester 22 and the defibrator 29, 30 a concentrator 27, 28 can be arranged to thicken the mass to the desired consistency. The concentrator 27, 28 can for the construction be a pipe, in which an inner jacket consisting of a screen plate is arranged and to which pipe the necessary pipe sockets 62, 63 for the discharge of the separated liquid are connected. The inner jacket may be made of a screen plate type with slots, the oval openings of which run in the direction of movement of the mass. Continuous sulphite or bisulphite process for cellulose boiling, in which the cooking liquid containing the pulp is removed from the digester, optionally via a concentration stage and a subsequent defibration step, and the defibration takes place substantially at the digester pressure completely or substantially without washing and the pulp is cooled before defibration. , that the defibrillation takes place in the temperature range 90 - 120OC.