US3085624A

US3085624A - Continuous digester

Info

Publication number: US3085624A
Application number: US856211A
Authority: US
Inventors: Anton J Horstman
Original assignee: Bauer Brothers Co
Current assignee: Bauer Brothers Co
Priority date: 1959-11-30
Filing date: 1959-11-30
Publication date: 1963-04-16
Anticipated expiration: 1980-04-16
Also published as: DE1283666B; FI43033C; FI43033B; GB892277A

Description

2 Sheets-Sheet l ll'll'lll A. J- HORSTMAN CONTINUOUS DIGESTER April 16, 1963 A. J. HORSTMAN 3,085,624

CONTINUOUS DIGESTER Filed Nov. 50, 1959 2 Sheets-Sheet 2 E; BYjjpm/w Q m United States Patent 3,085,624 CONTINUOUS DIGESTER Anton J. Horstman, Springfield, Ohio, assignor to The gainer Bros. Co., Springfield, Ohio, a corporation of Filed Nov. 30, 1959, Ser. No. 856,211 14 Claims. (Cl. 162-237) This invention relates to the art of producing pulp from a raw material such as wood chips, and particularly to apparatus for digesting the raw material in a continuously operating system.

The object of the invention is to simplify the construction as well as the means and mode of operating digesters, whereby such digester-s may not only be economically manufactured, but will be more eflicient and satisfactory in use, adaptable to a wide variety of applications, and be unlikely to get out of order.

An object of the invention is to provide for continuous movement of the raw materials through a vertical type digester as heretofore known in batch type operations, it being an especial although not limited object in this connection to adapt existing batch type digesters to operation in a continuous system.

Another object of the invention is to achieve to a high degree the advantages of continuous digestion, including increased pulp production per cubic foot of digester space, decreased production costs having regard to steam consumption, maintenance, chemical consumption, raw mate rial consumption and labor, and uniformity of product.

A further object of the invention is to provide a system adapted to treat any of the presently used raw materials and which may be operated to produce any of the known types of chemical and semi-chemical pulps.

Still another object of the invention is to provide in a system of continuous digestion as described controls regulating the quantity to be produced, the cooking temperature, time of cook, quantity of cooking liquor and the concentration of the latter.

A still further object of the invention is to provide a generally new digester in which a descending column of raw material has a portion of the bottom thereof con tinuously removed and forced from the digester, a related object in this connection being to provide for positive movement of the raw material through the system in all except the digester where gravity flow occurs through successive heating, cooking and discharge zones.

A further object of the invention is to provide a digester apparatus possessing the advantageous structural features, the inherent meritorious characteristics and the mode of operation herein mentioned.

With the above and other incidental objects in view as will more fully appear in the specification, the invention intended to be protected by Letters Patent consists of the features of construction, the parts and combinations thereof, and the mode of operation as hereinafter described or illustrated in the accompanying drawings, or their equivalents.

Referring to the accompanying drawing wherein is shown one but obviously not necessarily the only form of embodiment of the invention, 1

FIGS. 1 and 2 are diagrams which, when placed in side by side relation with FIG. 2 to the right of FIG. 1,

ice

comprise a single diagrammatic view of a continuous digesting system in accordance with the illustrated embodiment of the invention.

The movement of fluids and solids through the system is indicated by solid lines. Broken lines denote electrical connections.

Referring to the drawings, and first identifying major components of the system, a cylindrical tank-like vessel is vertically arranged and forms the digester. The vessel is closed and has a generally rounded configuration at its ends for service as a pressure vessel. At the top thereof is an inlet fitting 11. At the bottom is an outlet fitting 12. Also at the top of the tank or digester, and tangentially arranged to the fitting 11, are inlet

fittings

13 and 14 for the admission to the digester respectively of a chemical liquor and steam. Installed atop the fittings 11 in closing relation thereto is a rotary inlet valve 15. In overlying communicating relation to the top of valve 15 is a conveyor 16 for the raw materials which, in the illustrated instance and for convenience of designation, may be considered wood fragments or chips. The conveyor 16 is supplied by a chip distributing conveyor 17 and by means of a rotary screw 18 or the like feeds raw and untreated wood chips into the inlet valve 15, the movement of the chips occurring at a predetermined rate and any overflow being discharged at 19' for return to the distributing conveyor 17 The valve 15 is a unit comprising an outer stationary housing and an inner rotary valve element having circumferential pockets. These, in response to rotation of the inner valve element, receive incoming raw chips from the conveyor 16, carry them through a distance of within the valve unit until registering with the inlet fitting 11, and at this point drop the contained chips through the inlet fitting into the interior of digester vessel 10'. The rotation of the inner valve element is continuous in the operation of the system, being elfected from a suitable power source through a valve stem or shank 21.

Chemical liquor is supplied to the vessel 10 in an amount to maintain a normal liquid level approximately as indicated by the line 22. Steam is admitted to the vessel and serves to wet the chips therein as well as to raise the internal pressure and temperature of the vessel interior above normal levels. As the wood chips drop into the upper end of the vessel 10 they are sprayed by liquor admitted through inlet fitting 13 which may comprise interiorly of the vessel a suitable nozzle. At the same time admitted steam wets and heats the chips in a substantially uniform manner. The digester vessel interior is, in accordance with the instant inventive concept, formed with Zones of which the upper interior of the vessel above the liquor 22 is considered the heating zone. At the lower end of the vessel in the area adjacent to outlet fitting 12 a discharge zone is formed, the upper end of this zone occurring approximately at the point of entrance into the sides of the vessel of

nozzles

23 and 24, these nozzles being supplied by a conduit 25 and directing fluid under pressure tangentially downward into the discharge zone.

Intermediate the heating zone and the discharge zone is the cooking zone wherein the wood chips are subjected to the combined effects of heat, pressure and chemical action in a manner to soften the chips and to free individual fibers, thereof. The wood chips form a column in the vessel 10. In a process of continuous movement, and

partly wetted by cooking liquor and steam, the column of chips passes downward out of the heating zone into the cooking zone of the digester and then finally into the discharge zone. During passage through the cooking zone the chips are digested to the extent desired by control of temperature and chemical concentration. The liquor to wood ratio in the cooking zone will be approximately five to one although this ratio is a variable depending on chip size, wood species and other factors. At the location of the

nozzles

23 and 24 the bottom of the column of chips and liquor is sluiced oif continuously by incoming jets of pressure fluid, this action serving to insure an even draw down of the column and also to provide a force for expulsion of the mixture of chips and liquor from the vessel through the outlet fitting 12.

The latter connects with a conduit 26 leading to a closed body 27 forming a part of a drainer device 28 which further includes a closed housing'29 through which extends feed screw means 31. The device 28 operates to separate the liquor from the chips, now a pulp-like material, with the released liquor draining off by way of a liquor outlet 32. The pulp material is advanced by the feed screw means 31 toward an outlet fitting 33 with liquor being continously released fromthe pulp and flowing on account of the inclined attitude of the drainer device back for discharge at the outlet 32. The pulp outlet 33 connects to a discharge or blow line 34 through a rotary valve 35 which is constructed like and functions like the inlet valve 15. A motor driven stem 36 turns a rotory valve element to conduct pulp material from the outlet 33 to the discharge line 34 where steam carried by the valve and flash steam from the discharge pulp carries the pulp to a blow tank. An inlet fitting 37 admits steam to the drainer device 28.

The separated liquor from the device 28 is used to supply the

nozzles

23 and 24 at the discharge zone of the digester vessel. Thus a line 38 leads from the liquor outlet 32 to a line 39 common to the

nozzles

23 and 24 and there is interposed in the line 38 a pump 41 providing for jet flow at the nozzles as described. Supplying a liquor to the digester vessels, the

nozzles

23 and 24 thus act as hydraulic mining nozzles. The liquid jets not only sluice ofi the bottom of the descending column of chips, as described, but also dilute the chip-liquor mixture. In this zone of the digester the liquor to wood ratio is substantially increased, as on the order of 40 or 50 to l on up to 200 to 1. The liquor entering the vessel by way of the mining nozzles forces liquor and chips out the bottom outlet of the digester since the steam pressure in the heating zone will not permit the liquor to be forced upward in the digester. In this latter connection it is to be noted that the digester and drainer device are disposed in and operate in a substantially pressure tight area the opposite limits of which are defined by the inlet valve unit and the outlet valve unit 35. Both of these valves are designed as described to operate in a manner to pass the wood chips or the treated pulp without however, permitting any material escape of pressure from the treatment area.

Steam for the establishing and maintaining of pressure in the system is drawn from a source 42 and supplied under control of a valve 43 to the drainer device 28 and to the digester vessel inlet 14, the latter being supplied by a line 44 in which is interposed a differential pressure transmitter 45 operating to maintain a predetermined difierence in pressure between the digester vessel and the drainer device. The transmitter 45 operates through an indicator device 46 to signal the steam pressure in the drainer and through such device to control the operation of steam inlet valve 43. A signaling and control system for digester pressure includes the pressure differential tarnsmitter 45, an element 48 sensing the pressure in the heating zone of the digester vessel, an indicator 49 showing digester pressure and a controlled steam valve 51.

Continuing to refer to the drainer device 28, the body.

27 thereof is adapted to dispose of surplus chips or pulp material through a conduit 52 which extends to the discharge zone of the digester vessel, there being a pump 53 disposed therein. Thus pulp supplied to the drainer device 28 in excess of the ability of feed means 31 and valve to dispose thereof is returned to the digester for recirculation, automatic controls being provided to adjust the rate of movement of the chips through the system in the event the oversupply to the drainer device is other than a temporary fluctuation. The feed means of the drainer is operated from a constant speed motor 54 driven at a speed in a predetermined relation to the speed of operation of the chip metering conveyer 16. The latter is in turn driven by a variable speed driving means 55 to which is attached a tachometer 56 and which is controlled by an electrical connection in which is an indicator 57. The device 57 is connected by a conductor to a chip level sensing means 58 stationed on one side of the digester vessel in the heating zone thereof in a position to receive gamma rays issuing from an emitter 59 located on the opposite side of the digester. The arrangement is one sensing the chip level within the digester, which level is indicated at 61 therein, with the variable speed driving means being controlled to increase and to reduce the speed of operation of the chip metering conveyer and thereby to increase and to reduce the rate of movement of raw wood chips to the digester.

Sensing the liquor level within the digester vessel is a device 62 electrically connected through a line 63 with an indicator 64 and operating through

respective connections

65 and 66 to control flow valve 67 and 68. Valve 67 is located in a line 69 constituting a bypass from the return liquor flow line 38 to a black liquor storage reservoir 71. Thus in response to a rising liquor level in the digester vessel above the desired normal the valve 67 opens whereby a part of the output of pump 41 is directed to storage tank 71 rather than being returned to the digester vessel. The valve 68 is located in a supply line 72 leading to the liquor inlet 13 at the top of the digester vessel. Liquor for supply line 72 is drawn from a supply tank 73 and placed under pressure by a pump 74. The valve 68 may operate in response to rising liquor level in the tank to shut oif supply through line 72, and, correspondingly, to re-open such line in response to a lowering liquor level.

The temperature of the liquor in the cooking zone of the digester vessel is sensed by thermostatic means 75. The cooking liquor is heated, both as a result of action by the admitted steam and by passage of the admitted liquor through a heat exchanger 76 in the supply line 72. However, should the heating provided be inadequate a supplemental supply of heated liquor is provided for in a secondary supply line 77 leading also to the inlet 13 and extending from the liquor recirculating line 38 as an extension thereof. Within the secondary supply line 77 is a heat exchanger 78. The thermostatic means electrically controls a valve 79 located in the line 77. Within heat exchanger 76 the flowing liquor is put into heat transfer relation to steam admitted to the heat exchanger from the source 42 under control of a valve 81. The latter is in turn electrically controlled through an indicator 82 receiving signals from a thermal means 83 concerning the temperature of the liquor beyond heat exchanger 76. In a similar manner liquor flowing through heat exchanger 78 is heated by steam from a valve 84 in turn controlled by thermal means 85 sensing the temperature of the liquor beyond the heat exchanger 78. Opening of steam valve 84 accordingly is dependent upon a prior opening of liquor flow control valve 79 and this is in turn responsive to the temperature of the cooking liquor in the digester vessel.

Flow of the raw material and treated pulp is a positive movement generated by motor driven feed means or by hydraulic pressure means, except in the case of descent of the column within. the digester vessel from the upper end or heating zone through the intermediate or cooking zone. While gravity flow through the digester normally is adequate the descending column may at times be slowed or have its movement impeded. With a continuous inflow of chips at the top of the digester a slowing of the descending column has the eifect of raising the chip level. The device 58 senses this raising chip level, as before seen, and, in addition to controlling the variable speed means 55 serves also to energize a valve 86 interposed in a line 87 serving also as an extension of the liquor circulating line 38 and located in advance of the valve 79. Beyond the valve 86, the line 87 supplies nozzles 23 and 24' installed in the side of the digester vessel in a manner similar to the

nozzle

23 and 24. Opening of the valve 86 admits a portion of the recirculating liquor under pressure to the nozzles 23 and 24'. These discharge the liquor in a jet flow against the sides of the column of chips, breaking up the column and facilitating movement of the chips to the outlet 12. The nozzles 2324' are located at an intermediate point or points above the discharge zone of the digester, the nozzles being provided in such number and at such locations as may be deemed desirable for best results.

In its broader aspects the invention contemplates a control also over the liquor make-up and supply. This portion of the system may comprise a bin 88 for dry chemical storage and a source 89 of dilution Water. A motor driven valve 91 dispenses dry chemicals from the bin 88 into a mixing tank 92. Water is admitted to the tank by a line 93 under control of a valve 94. A level transmitter 95 senses the level of chemical-water mixture in the tank 92, and, through an indicator 96, signals the motor driven valve 91 and the valve 94. An agitator 97 mixes the water and chemicals in the tank 92 and this mixture is drawn off by a pump 98 and delivered under control of a valve 99 to the aforementioned liquor supply tank 73 by way of a supply conduit 191. Opening and closing of the valve 99 is under control of a magnetic flow meter 102 in the line 101 in advance of the valve' and operating upon the valve through an indicator 103. The density or concentration of the mixture passed by valve 99 is variable by operation of a valve 104 controlling a by-pass 105 between the dilution supply line 93 and the line 101 in advance of pump 98. This valve operates through an indicator 106 under control of a density gauge 107 in the line 101.

The supply in liquor supply tank 73 is made up of the liquor admitted thereto by way of line 101 and also of liquor admitted thereto by a line 108 extending from the black liquor storage 71. A pump 109 is in the line 198 as is a control valve 111 responsive in its operation to a transmitter device 112 sensing the level in tank 73.

Further considering the system controls, pulp manufacture in accordance with the instant invention contemplates a control over the quantity of pulp to be produced, the cooking temperature, time of cook, quantity of cooking liquor and the concentration thereof. Quantity of production depends on the volume of chips being fed to the system. This volume is selected by adjusting the speed of the variable speed motor driving the chip metering conveyor 16. This adjustment is made to regulate the volume of chip movement in terms of tons per day, and the control may be eflected manually or automatically in response to changes in the chip level in the digester. The volume flow of chips to the digester also is related to quantity flow of liquor to the supply tank 73, there being a connection 113 from chemical liquor flow indicator 103 to control indicator 57.

Liquor quantity and concentration, which determine the percentage chemical being used, are adjusted manually to a predetermined ratio and then made subject to regulation. White liquor from the makeup tank 92 of a known or measured concentration is pumped through the quantity control valve 99 to the tank 73. The liquid level in this tank is maintained by the addition of black 6 liquor from tank 71 through the operation of transmitter 112 and valve 111. Water also could be used as a diluent. V

The cooking temperature within the digester is measured by thermal means 75. Responding to this temperature the thermal means 75 controls valve 79 and so varies the temperature of the incoming liquor. The temperature sensing means might also be used to control the quantity of admitted steam or both the steam admission and liquor temperature.

The time required for chips to pass through the system varies directly as the volume of the various components of the system and inversely with respect to the quantity of chips. Time through or in all components, except the digester, is not critical. Once the cooking'is complete the chief concern is in getting the pulp out of the system as quickly as possible. Under these conditions the only times requiring controlling are those in the heating and cooking zones. This control, that is control or the proportion of the total time in the digester that the solids spend in each zone, is exercised by regulating the chip and liquor levels in the digester in the manner described. Thus in the illustrated instance these levels are indicated by broadcasting gamma rays through the digester to suitable receivers from which signals are sent to control equipment. The liquor level is controlled by automatic adjust ment of the how of liquor into the vessel. Since the quantity of white liquor introduced into tank 73 is governed only by the production rate of the white liquor in tank 92 it follows that the total liquor flow is adjusted by varying the admission of diluent or in this instance the black liquor quantity.

- Pressures are obtained in the digester through introduction of steam. The steam pressure is manually set and automatically maintained. The steam is used to obtain a uniform heating and wetting of the chips entering the digester, and may also be used to operate chip distributing means within the digester.

In respect of chemical concentration, the density gauge 107 in the white liquor supply line 101 operates through the control indicator 106 to open and close valve 104 thus varying the proportion or concentration of chemicals to liquid in the white liquor, maintaining a constant ratio of chemical to wood.

In further respect of the temperature of the cooking liquor, steam in the heating zone is expected to bring the temperature of the chips up to cooking levels. These results are inconsistent, however, since chip moisture and steaming time are variables. Therefore, the heat brought into the digester with the liquor is here varied, firstly by flow of the main liquor supply through heat exchanger 76 and secondly by the secondary liquor flow through heat exchanger 78.

The steaming time and cooking factors are related and controlled by varying the liquor level. The liquor level for any given through put of chips is a measure of the cooking time since the level of the discharge zone is physically fixed by the digester construction.

The control of temperatures, pressures, chip and liquor levels, and liquor densities and flow rates, as well as chip volume supply, all are set to operate in a predetermined relation to one another. Hence the Several indicators which have been described in connection with the individual control systems are suitably arranged for comparison viewing. From these indicators, moreover, impulses may be delivered, as at the points indicated X to a data logging system or the like in which the information continuously sensed and acted upon in the digester system is fed into suitable recording apparatus for purposes of data comparison and computation.

From the above description it will be apparent that there is thus provided a device of the character described possessing the particular features of advantage before enumerated as desirable, but which obviously is susceptible of modification in its form, proportions, detail construction and arrangement of parts without departing from the principle involved or sacrificing any of its advantages.

While in order to comply with the statute the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise but one of several modes of putting the invention into effect, and the invention is therefore claimed in any of its forms or modifications within the le itimate and valid scope of the appended claims.

Having thus described my invention, I claim:

1. Apparatus for the continuous digesting of fragmentary fibrous solids, including a vertical digester vessel having inlet and outlet openings at the top and bottom thereof respectively, means for continuously admitting solids for treatment to the interior of said vessel by way of said inlet opening, means for supplying liquor and steam to the interior of said vesesl in the top portion thereof, the heated and wetted solids descending by gravity toward said outlet opening, and nozzles installed in the side of said vessel in the bottom portion thereof for introducing a fluid under pressure into said vessel adjacent the bottom thereof thus forcing the solids out of the vessel by way of said outlet opening under pressure.

2. Apparatus for the continuous digesting of frag mentary material, including a vertical digester vessel having upper, lower and intermediate interior zones, means for continuously admitting material for treatment to the upper zone of said vessel, the material forming a column descending by gravity through said intermediate zone to said lower zone, an outlet from said vessel communicating with the lower interior zone thereof, means for introducing heated fluid into said vessel at the upper interior zone and other means for directing pressure fluid inwardly of the vessel upon the descending column of material in said lower zone at the bottom of the vessel to force the material out of the vessel by way of said outlet.

3. Apparatus for the continuous digesting of fragmentary solids, including a vertical digester vessel having a continuously open outlet at the bottom thereof, means for introducing liquid, steam and solids for treatment into said vessel at the top therof, said solids forming a column descending by gravity in said vessel toward said outlet, and hydraulic liquid means at the bottom of the vessel for removing a portion of said column from the bottom thereof and placing it from the vessel through said outlet.

4. Apparatus according to claim 3, characterized in that said last named means includes nozzle means installed in said vessel adjacent to the bottom thereof for directing liquid in jet flow into the vessel toward the bottom.

5. Apparatus according to claim 3, characterized by means for separating the hydraulic liquid from the solids beyond said outlet and recirculating itdirectly to said hydraulic means.

6. Apparatus for the continuous digestin of fragmentary solids, including a vertical digester vessel having a continuously open outlet at the bottom thereof and an inlet at the top and preventing therebetween upper, lower and intermediate zones, at metering conveyer delivering material for treatment at a predetermined rate to said inlet, a valve between said. conveyor and said inlet passing the material while inhibiting a release of pressure from said vessel, means for admitting liquor and steam to said vessel, the mixture of liquor and fragmentary solids descending by gravity through said zones to said outlet, means for sensing the quantity of fragmentary solids in said vessel, means for responding to said last named means for varying the rate of delivery of said fragmentary solids to said inlet, means for admitting a hydraulic liquid to the lower zone of the digester, and means responsive to the quantity of solids for selectively diverting 8 a portion of the hydraulic liquid to other points in the digester below the upper zone.

7. Apparatus for the continuous digesting of fragmentary solids, including a vertical digester vessel having a continuously open outlet at the bottom thereof and an inlet at the top, a metering conveyer for delivering fragmentary solids at a predetermined rate to said inlet, a valve between said conveyer and said inlet for passing the solids while inhibiting a release of pressure from said vessel, means for admitting liquor and steam to said vessel, the mixture of liquor and material descending by gravity through the vessel to said outlet, means for sensing the quantity of solid material in said vessel, means for applying hydraulic pressure at selected points in said vessel, and means responsive to the quantity of solids in the vessel for diverting a part of the hydraulic pressure to other selected points.

8. Apparatus for the continuous digesting of the fragmentary solids, including a vertical digester vessel having a continuously open outlet at the bottom thereof, means for admitting the fragmentary solids to the top of the vessel, said means including a valve closing the upper part of the vessel against pressure escape therefrom, the fragmentary solids forming a column descending in said vessel to said oultet, means for admitting liquor and steam to the vessel above the column of fragmentary solids, a closed conduit for conducting the mixture of fluids and solids from said outlet, a closed drainer device having an inlet communicating with said conduit and an outlet, liquid being separated from the solid material in said device, a valve passing the solid material through said outlet without loss of pressure from said device, means for supplying steam to said drainer device, and means for maintaining a predetermined differential between the steam pressures in said digester vessel and in said drainer device.

9. Apparatus according to claim 8, characterized by means for returning the separated liquor from said drainer device to said digester vessel at the bottom of the latter for an increased proportion of liquor to solid material in the region of said vessel outlet.

10. Apparatus according to claim 8, wherein the said valve for controlling the outlet from said drainer device provides for a predetermined rate of discharge of the solid material, characterized by means for returning from said drainer device to said digester vessel solid material supplied thereto in excess of the quantity which may be discharged from said drainer device.

11. Apparatus useful in pulp production, including a vertical digester vessel having a single continuously open outlet at the bottom thereof, means for continuously and separately admitting steam, liquor andfragmentary solids to said vessel at the top thereof, the solid material and fluids forming a column descending by gravity through heating, cooking and discharge zones in said vessel and means for substantially increasing in said discharge zone the proportion of fluids to solid material, said means including inlets directing pressure fluid inwardly and downwardly in said vessel in the discharge zone thereof, the pressure fluid being supplied from a source other than the sources supplying materials to said vessel at the top thereof.

12. Apparatus according to claim 11, characterized by means for responding to the quantity of solids in said digester vessel for controlling the volume of fragmentary solids fed to the digester vessel and selectively to divert a portion of the pressure fluid supplied to said discharge zone to other points in the digester below the heating and cooking zones.

13. Apparatus useful in a continuous process of pulp production, including a pair of spaced apart rotary valves continuously operating to pass a predetermined volume of fragmentary solids and the like while inhibiting fluid pressure loss therethrough, and process equipment between said valves including a vertical digester vessel supplied With a cooking liquor and having an inlet at the top thereof receiving the solid material from one of said valves and having an outlet at the bottom, said equipment further including a drainer device intermediate said outlet and the other one of said valves for separating the liquor from the solid material, and means for returning to said digester vessel liquor separated in said drainer device and solid material supplied to said drainer device in excess of the rate of flow provided through the said other one of said valves.

14. Apparatus according to claim 13, wherein said digester vessel and said drainer device are supplied with steam, characterized by means for maintaining a prede- 10 termined pressure difierential between said digester vessel and said drainer device.

References Cited in the file of this patent UNITED STATES PATENTS 1,776,761 Morterud Sept. 23, 1930 2,001,022 How May 14, 1935 2,745,743 Knopf May 15, 1956 2,769,710 Becker Nov. 6, 1956 2,858,213 Durant et al. Oct. 28, 1958 2,870,209

Richter Jan. 20, 1959

Claims

7. APPARATUS FOR THE CONTINUOUS DIGESTING OF FRAGMENTARY SOLIDS, INCLUDING A VERTICAL DIGESTER VESSEL HAVING A CONTINUOUSLY OPEN OUTLET AT THE BOTTOM THEREOF AND AN INLET AT THE TOP, A METERING CONVEYER FOR DELIVERING FRAGMENTARY SOLIDS AT A PREDETERMINED RATE TO SAID INLET, A VALVE BETWEEN SAID CONVEYER AND SAID INLET FOR PASSING THE SOLIDS WHILE INHIBITING A RELEASE OF PRESSURE FROM SAID VESSEL, MEANS FOR ADMITTING LIQUOR AND STEAM TO SAID VESSEL, THE MIXTURE OF LIQUOR AND MATERIAL DESCENDING BY GRAVITY THROUGH THE VESSEL TO SAID OUTLET, MEANS FOR SENSING THE QUANTITY OF SOLID MATERIAL IN SAID VESSEL, MEANS FOR APPLYING HYDRAULIC PRESSURE AT SELECTED POINTS IN SAID VESSEL, AND MEANS RESPONSIVE TO THE QUANTITY OF SOLIDS IN