Method and apparatus for impregnation of fiber material by pressure pulsation

#The invention relates to an apparatus and method for impregnating fiber material with treatment liquid, especially with digesting liquid, before treatment of the fiber material, especially before digestion thereof. The pre-impregnation of fiber material with treatment liquid constitutes a very important part of the delignifying process in the production of pulp, the object of the pre-impregnation being to replace the air or gas content of the fiber material with the impregnation liquid. Conventionally, the air or gas is replaced by the utilization of steam at a small super-atmospheric pressure, followed with the submersion of the fiber material in treatment liquid at higher pressure and temperature. Also, initial vacuum treatment and pressing, followed by submersion in treatment liquid, is known. Whatever prior art conventional methods are utilized, a certain amount of equipment is necessary. it is desirable -- both for economical and space saving reasons -- to limit the amount of impregnation equipment necessary as much as possible. At the same time, no decrease in the efficiency of the impregnation process is tolerable.

#Swedish Pat. No. 174,656 teaches the impregnation of fiber material by pressure variations of the impregnating liquid. According to the teachings of this Swedish patent, the readily-impregnable fiber material is led away from an impregnation chamber more quickly than the less readily-impregnable fiber material. The impregnation vessel is a long, sloping structure to which a mixture of fiber material and digesting liquor at pressure is fed by means of one assembly, and is withdrawn by means of another assembly. A conveyor for the impregnated fiber material is disposed within the impregnation vessel, and the air that is displaced is withdrawn, and the pressure variations are obtained by means of a vacuum pump and/or a liquor tap-off means. The structure of the Swedish patent is relatively complex, a great deal of accessory equipment being necessary.

#According to the apparatus and method of the present invention, impregnation through pressure variations may take place with the utilization of a minimum amount of accessory equipment. Essentially, according to the present invention, the only accessory equipment that is necessary is a valve in a conduit in the treatment vessel (and various pressure sensitive and time and pressure responsive control means for the valve) and a screening device. A conventional continuous digester or other treatment vessel and conventional pocketed-rotor transfer device, such as devices produced by Kamyr Inc., may be utilized, along with a feed system such as shown in U.S. Pat. No. 3,802,956. The apparatus, according to the present invention, includes a relatively low pressure first system including a source of fiber material in treatment liquid, a means for continuously removing liquid from the first system to maintain the system at relatively low pressure, means for transferring fiber material in treatment liquid in the first system to a second relatively high pressure system (said means including a conventional Kamyr high pressure pocketed-rotor transfer device), a conventional Kamyr high pressure vertical fiber material treatment vessel (i.e., digester), the second pressure system including an upper impregnation portion of the fiber material treatment vessel, means for selectively allowing or blocking communication between the second system and the fiber material treatment vessel so that the pressure in the second system is substantially as high as the treatment vessel pressure when communication between the second system and the the treatment vessel is allowed, and so that the pressure in the second system becomes significantly reduced when communication between the second system and the treatment vessel is terminated, and timing means for controlling the selective communication means to control the relative times the second system is exposed to high and low pressure so that impregnation of fiber material with treatment liquid takes place in the second system. The fiber material and liquid in the first system may be at a small super-atmospheric pressure of about 1 atmosphere, while the digester pressure (and the pressure phase in the second system during the high pressure thereof) is about 10 atmospheres. The conventional transmission device utilized for providing transfer of fiber material and liquid from the first system to the second system operates so that the flow between the first system and the second system is substantially continuous. (Steam treatment of the fiber material before it is actually fed to the transmission device is possible to remove the majority of the air in the fiber material.) Complete impregnation of the fiber material with treatment liquid takes place in the second system.

#FIG. 1 is a schematic showing of exemplary apparatus for effecting fiber material impregnantion with treatment liquid according to the present invention;

#FIG. 2 is a perspective view of the high pressure transfer device of FIG. 1; and

#FIG. 3 is an exploded perspective view illustrating certain parts of the transfer device of FIG. 2.

#Exemplary apparatus, according to the present invention, is shown schematically in FIG. 1. The major component parts of the apparatus of FIG. 1 include a relatively low pressure system (or defining means) 10 including a source 11 of fiber material in treatment liquid, means 12 (a screen device) for continuously removing liquid from the first system 10 to maintain the system at relatively low pressure, a second relatively high pressure system (or defining means) 13 including an upper impregnation chamber 14 of a conventional high pressure continuous treatment vessel (i.e., Kamyr digester) 15, means 16 for transferring fiber material and the impregnation liquid in the first system to the second system and boosting the pressure thereof, the means 16 comprising a conventional high pressure transfer device having a pocketed rotor, means 17 for selectively allowing or blocking communication between the second system and the fiber material treatment vessel 15 so that the pressure in the second system 13 is substantially as high as the treatment vessel pressure when communication between the second system 13 and the treatment vessel 15 is allowed, and so that the pressure in the second system 13 becomes significantly reduced (by removal of liquid therefrom -- indirectly -- by screening means 12) when communication between the second system and the treatment vessel is terminated, and timing means 18 for controlling the selective communication means 17 to control the relative times that the second system 13 is exposed to high and low pressure so that impregnation of fiber material with treatment liquid takes place in the second system 13.

#The first system 10 includes an inlet line 19 to the transfer device 16, an outlet line 20 from the transfer device 16, a pump 21 disposed in the outlet line, and an outlet line 22 for liquid from the screening means 12. The screening means 12 may be any conventional dewatering device. The second system 13 includes an inlet line 23 to the transfer device 16, a pump 24 being disposed in the inlet line 23, and an outlet line 25 extending from the transfer device 16 opposite the inlet line 23. The outlet line 25 need not be in the form of a constant diameter conduit, but may bulge into a vessel, tank, or other suitable means (shown in dotted line in FIG. 1). The line 25 is connected to the feed-in 26 for the impregnation chamber 14.

#As shown in the drawings, the impregnation chamber 14 and the feed-in 26 therefor are substantially the same as an individual chamber in my copending application Ser. No. 592,659 now U.S. Pat. No. 4,028,171. A pipe 27 extends a significant distance past the top 28 of chamber 14 into the chamber 14, and rotatable shaft 29 driven by a motor 30 extends into the chamber 14, a scraper device or distribution means 31 being provided at the end of the shaft 29 just above the outlet from the chamber 14 into the vessel 15. Fiber material in chamber 14 establishes a certain level 32 therein, and in order to provide screenless withdrawal of liquid from chamber 14, a withdrawal conduit 33 is disposed above the level 32 (that is above the bottom of the inlet 27). A more or less "stilling well" is provided in the chamber 14. The conduit 33, of course, is connected to the inlet line 23 to the transfer device 16.