The present invention is concerned with a method relating to discontinuous treatment of fi.bre material , where the fibre material after a first treatment is transferred via a rotary feed valve to a further treatment.

It is known practice in the treatment of fibre material to use rotary feed valves for transfer of the material between various treatment stages, whereby the different treatment liquids of the process can be kept separated from one another to a great extent. The transfer between different circuits of circulating liquid is effected by the rotary feed valve having a rotor formed with one or several pockets, which rotor is brought into different positions where communication is established between circulation lines connected to differ- ent treatment vessels. Thus, it is known, for example, in connection with digestion of fibre material and subsequent washing to transfer the fibre material from several dis- continuously operated digesters via a rotary feed valve to a subsequent continuously operated washing step. In the ^' rotary feed valve, treatment liquid such as digesting liquor is hereby separated from the fibre material and returned to the digesters or withdrawn for separating off the digesting chemicals in separate subsequent treatment stages. The fibre material in the rotary feed valve is fed to the subsequent washing vessel through a separate circulation line.

The object of the present invention is to improve this method, in order continuously to utilize the heafcontent contained in the treatment liquid such as the digesting liquor. Another object is to reduce dilution in the circuit of circulating washing liquid, and further object are to reduce losses of dry substance and the BOD-load.

This is achieved by endowing the method of the inven¬ tion with the characteristic features stated in the appended claims.

The invention will hereinafter be described nearer in conjunction with the appended drawings which show embodi¬ ments constituted by various systems to which the method of the invention is. applied. Figure 1 shows diagrammatical an overall view of a digester house where the digester vessels via a rotary feed valve are connected to subsequen treatment stages, the diagram showing a plant for 1 ow yiel Figure 2 shows. a plant similar to that presented in Figure but modified for high yield. Figure 3 shows diagrammatical a further plant with another type of rotary feed valve.

Figures 4a - 4c show diagrammatically the rotary feed valv of the plant in Figure 3 in three different positions.

Th-e plant diagrammatically shown in Figure 1 has two treatment vessels, such as digesters 10, 12, through a lin 14 connected to a rotary feed valve 16 of a construction known per se, as disclosed, for example, in the Swedish ^" patent application 7609782-3. In the embodiment according to Figure 1 , the rotary feed valve 16 has two positions, in which a pocket arranged in the rotary feed valve inter- connects two lines attached at diametrically opposed place Attach.ed at the side opposed to linel4 is a line 18 which ^• connects the rotary feed valve with an accumulator 20. Fib material and treatment liquor from the digesters 10, 12 wh through the line 14 are introduced into the rotary feed valve 16 will be separated from one another in the same by the rotary valve being provided with an appropriate screening means so that the treatment liquor through the line 18 is fed into the accumulator 20 whereas the fibre material remains in the pocket of the rotary ^" valve. A port of the treatment liquor may be recycled to the digesters v a pump not labelled in detail and line 22.-

In the second position of the rotary feed valve 16 the fibre material contained in the pocket of the rotary valve will be fed through a line 24 into a blow tank 26 by becom displaced out of the pocket by means of liquid which throu lines 30, 28 is recycled as deducted liquid from a filter-

-euipped washing station 32 positioned behind the blow tank. The blow tank 26 and the washing station 32 are connected to a line 34 which feeds fibre material to the washing sta¬ tion. A portion of the recycled exhaust liquid may be fed into the blow tank 26. From the_washing station.32 the fibre material or pulp is discharged to subsequent stages of treatment or utilization through a line 36.

Attached to the top of the digesters 10, 12 via a line 38 is a cyclone 40 for removal of gases from th.e digesters 10, 12. The liquid portion from the cyclone 40 is conducted over a line 42 to the top portion of the blow tank while the gaseous phase- is fed to a condensor 44 from which a line 46 leads to a decanting vessel 48. Gases obtained from this decanting vessel are conducted in a line 50 to combustion, for example, while recovered turpentine is withdrawn via a line 52 and residual liquid phase via a line 54 is fed to a subsequent separation by expulsion, as will be described in more detail more below. Th'fe top portion of the blow tank 26 may be connected through ^' a line 56 to the discharge line 50 for ^' those gases which shall be removed from the process. From the pressure accumulator 20 disposed according to the invention the treatment liquid, such as the digesting liquor, obtained from the first, discontinuous treatment, is fed through a line 58 to a flash tank 60. Phases separated in the tank or receptacle 60 are fed to an evaporation sta¬ tion 62 via lines 64, 66, and the concentrate obtained from the evaporation station 62 is supplied to an expelling device 64, to which also the line 54 from the de.canting vessel 48 is connected for feed of liquid obtained in said vessel . Gases from the expelling device 64 are conducted through a line 66 to the gas discharge line 50 whereas the liquid phase is recycled via line 68 to the washing station 32.

In the process illustrated in Figure 1 and described in conjunction therewith there is obtained after the dis¬ continuous treatment in the vessels 10, 12 in the continua¬ tion behind the rotary feed valve 16 a continuous treatment

of both the fibre material and the extracted treatment liquid. Here the pressure accumulator 20 serves as a sto for the extracted treatment liquid, from which liquid th preponderant portion of the heat content can be utilized, for example by setting free vapour by expansion, while a the same time a subsequent treatment with flashing, eva¬ poration and expulsion, permits effective recovery of the chemical constituents in the treatment liquid.

The plant shown diagrammatically in Figure 2 where the same refere-nce numerals are employed for details havi a counterpart in Figure 1, differs from the plant of Figure 1 by the fibre material from the rotary feed valve 16 being fed through the line 24 to a combined washing ^' and. blow tank 70 from which the fibre material via line 72 is fed to a final washing station 74. Furthermore the outlet line 18 from the rotary feed valve 16 is not connected directly with the accumulator 20 but to the ret line 22 for digesting liquor, a line 18a starting from sa line to the accumu.lator 20. Connected to the line 18a is also a branch 28a from that line 28 which feeds washing liquid to the rotary feed valve-for displacement of fibre material therefrom. The equipment shown in the top portio of Figure 1 for separating the gaseous and liquid phases one another and the equipment for concentration by evapor tion and expulsion are identical in Figure 2 for which re they have been omitted in the latter figure, as will be understood from the dotted lines set out in Figures 1 and

In the plant shown in Figure 3, one digester 100 only is shown, which digester by a line 102 is connected to a rotary feed valve 104. A line 106 may, for example, come from other, discontinuously operated digesters in th system. A line 108 may lead from the top portion of the digester to a decanting system of the type shown at 40 an the following items in Figure 1. The shown rotary feed valve 104 is of the type where the valve pocket takes three positions. In the pos tion represented by continuous lines, the line 102 is in

connection with ^' an outlet line 110 for the digesting liquor. In the next-following position of the clockwise rotating feed valve 104 a line 112 which supplies washing liquid from a subsequent washing station which will be described more below, is connected with a line 114 which together with the line 110 is connected to a pressure accumulator 116. The washing liquid supplied through the line 112 expels the ^' residual digesting liquor from the pocket of the rotary feed valve and washes at the same time the fibre material in the pocket in counter-current to the direction in which the digesting liquid was extracted. As- is marked diagrammatically in the figure, the extractions of liquid from the rotary feed valve, 104 is effected by means of appropriate screens dis¬ posed at the liquid outlets. In the third position of the feed valve pocket, a line 118 which recycles liquid from the pressure accumulator 116, is connected with a line 120 for transfer of the fibre material to a blow tank 122. From the blow tank 122 gases are carried off through a line 124 for combustion, for example, while the fibre material, via a line 126 is fed to a final washing station 128. From the final washing station pulp is discharged through a line 130, washing water being fed to the washing station 128 via a line 132.

From the pressure accumulator 116 the liquor is introduced into a flash tank 134 via a line 136, and gases separated off from the flash tank are fe~d through a line 138 to a preliminary evaporation station 140 to which also the discharge from the bottom of the flash tank 134 is fed through a line 142; through a line 144 steam is-fed to the preliminary evaporation station 140. From the prelimina¬ ry evaporation station 140 the liquor is discharged via a line 146 to a liquor container 148 wherein separation is effected of e.g. soap which is removed in a line 150, 152 denoting the final liquor discharge. The preliminary evapora- tion equipment 140 is connected with an expulsion device 154 from which starts a line 156 for non-condensable gases which

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are conducted to combustion, for example, a line 158 bei provided for drainage of purified condensate which can b used ^' as washing water by the line 158 being connected to the line 132. In the plant presented in Figure 3 thus firstly t heat from the digesters is recovered by the digesting liquor discharged to the pressure accumulator steam bein released continuously by expansion, which expansion stea may be used, fo example, for preliminary concentration evaporation of -the same digesting liquor. Steam from the last step of the preliminary concentration by evaporatio can be used _. for expulsion of the secondary condensate pr duced by the evaporation and for driving off gases from formed turpentine mother lye. The expulsion of the conde sate may be carried out under atmospheric pressure, for example, and the expelled condensate may, as mentioned above, be used in the washing station as washing water. gases which are set free in connection with the expulsio and non-condensable gases from the degasifying of the digester and the blow tank are conducted to common combu The condensate from the condenser of the expelling appar may also be concentrated in a separate concentrating col for recovery of by-products, in which connection turpenti may be decanted also from the condensate ahead of the sai concentrating column in order to produce-, methanol in liq phase. The methanol liquid obtained from the concentrati column may also be burned together with those non-conden gases which are produced in various parts of the system. other or complementary way of utilizing the heat energy i to employ the digesting liquor from the pressure accumul in some other digester for filling with liquid.

The rotary feed valve 104 shown in Figure 3 is sh in more detail in the Figures 4a - 4c. In Figure 4a, the is shown the body of the valve 104 in position for fillin the valve feeder or pocket 160, the material arriving th the line 102 and remaining in the pocket 160, whereas th

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digesting liquor escapes through the screen 162 into the line 110. The valve pocket 160 is provided with an interior screen plate 164 disposed in spaced relation to the pocket 160 and which between itself and the wall of the valve pocket 160 forms liquid channels 166 for quicker drainage of liquid from the fibre material in the valve pocket 160. In the nextfol 1 owing position which is shown in Figure 4b ^' , washing liquid is supplied through the line 112 which liquid displaces the residual digesting liquor in the valve pocket 160 thrσugh a screen plate 168 and the line 114.

In the nextfollowing position which is shown in Figure 4c the line 118- is connected with the line 120 whereby fibre material and was ^' hing liquid in the valve 160 are displaced . by means of liquor fetched from the pressure accumulator 116 and supplied via the line 118.

It is clear that the shown and described embodiment is an example only of realization of the invention and that the same can be changed and varied within the scope of the appended claims.