US3446701A - Apparatus for impregnating and chemically converting cellulose-containing materials - Google Patents

Description

May 27, 1969 R. A. LLOYD 3 ,7

APPARATUS FOR IMPREGNATING AND CHEMICALLY CONVERTING CELLULOSECONTAINING MATERIALS I Filed Dec. 28, 1967 Sheet of s INVENTOR.

ROGER A. LLOYD APPARATUS FOR IMPREGNATING AND CHEMICALLY CONVERTING CELLULOSE-CONTAINING MATERIALS Filed Dec. 28, 1967 y 7, 1969 R. A. LLOYD 3,446,701

Sheet 2 of3 klllilllllllllllllllfl INVENTOR. .ROGER A. LLOYD May 27, 1969 Filed Dec. 28, 196

R. A.- APPARATUS FOR IMPREG CONVERTING 'CELLULOSE- LLOYD NATING AND CHEMICALLY CONTAINING MATERIALS Sheet of 3 INVENTOR. ROGER A. LLOYD WWW United States Patent US. Cl. 162237 1 Claim ABSTRACT OF THE DISCLOSURE An apparatus is disclosed for impregnating and chemically converting cellulose-containing particulate materials. The materials to be chemically converted flow through a hopper, an evacuated conveyor tube, a slurrying chamber, a rotary valve, a high pressure-low temperature impregnating conveyor tube, a draining conveyor tube, and then into a high pressure-high temperature reactor conveyor tube.

A nonexclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States.

Cross reference to related application This application is a continuation-in-part of application Ser. No. 369,037, filed May 20, 1964, and now abandoned.

BACKGROUND OF THE INVENTION ifield of the invention This invention relates to an apparatus for impregnating and chemically converting cellulose-containing materials wherein the environmental changes in pressure and temperature occur in two separate zones. In accordance with the invention, the first change is from an ambient temperature-ambient pressure zone to an amibent temperature-high pressure zone and thence to a high temperaturehigh pressure zone.

Description of the prior art Various processes and apparatus have been developed. These developments all have in common the fact that the pressure and temperature changes occur in the same zone. The result is that highly corrosive-high temperature conditions exist throughout the greater portion of the process or apparatus.

Objects An object of the present invention is to provide a method for carrying out a chemical reaction, involving 'at least one corrosive reactant, wherein the corrosive eifects are minimized by restricting them to one phase of the process. Another object is to provide a novel apparatus for carrying out such a process. A further object is to provide 'an apparatus in which the reactants are mixed in one zone under essentially nonreactive conditions and then transferred to another zone in which the reaction is caused to take place. Still another object is to provide an apparatus in which separate control of the conditions is maintained in each of several zones. Other objects and advantages will become apparent to those skilled in the art from the description of the invention which follows.

3,446,701 Patented May 27, 1969 Summary In general, the present invention relates to an apparatus for chemically treating particulate material with a liquid reagent. The apparatus is particularly suitable for continuous treatment with a corrosive reagent, as in the acid hydrolysis of wood chips or other cellulose-containing material, where it is necessary to minimize the corrosive effect of the reaction which takes place at high temperatures and pressures.

Essentially, the apparatus is comprised of several independent, but serially interconnected, subsystems or zones in which the particulate material is subjected to an individual phase of its total treatment, with mechanical provision made to prevent the process in each subsystem from interfering with the processes taking place in the other subsystems. Thus, the principal improvement in the presently described invention resides in a separation of the zone in which the pressure is raised from the zone in which the temperature is raised while the high pressure is maintained. In addition to restricting the zone of corrosion, the herein disclosed apparatus also permits the continuous impregnation and chemical conversion of cellulose-containing materials. Although the present invention is particularly directed toward prehydrolyzing sawdust, wood chips, and the like, the apparatus is also suitable for other chemical processes such as wood hydrolysis and chemical pulping processes.

Corrosion can be a serious problem with rotary valves, screw feeders, and other devices that are used for injecting corrosive solids into pressure vessels. The problem is much more serious when injection has to be performed at elevated temperatures. This invention provides a means for carrying out this injection in two steps. Solids containing corrosive liquor are injected into a high-pressure zone while at low temperature and then are transferred into the high-temperature zone and the highly corrosive area through a simple gate valve arrangement.

Brief description of the drawings FIGURE 1 represents a schematic diagram of the overall apparatus used for the continuous prehydrolysis of wood particles;

FIGURES 2 and 3 are partial, cut-away views of the inlet and outlet ends, respectively, ofthe impregnating tube;

FIGURE 4 represents a schematic diagram for valving the wood particles between the draining conveyor tube and the reactor conveyor tube; and

'FIGURE 5 represents a schematic diagram showing the systems for controlling the discharge cycle.

Description of the preferred embodiments As shown in FIGURE 1, the charge material of wood particles is fed continuously from hopper 1 through meter and rotary valve mechanism 2 into evacuated conveyor tube 3, driven by motor 64. Here a suflicient vacuum is maintained by conventional means (not shown), and retention time provided, to cause an optimum removal of air from the wood particles. At the end of evacuated conveyor tube 3 the wood particles are discharged into slurrying chamber 4 where they are picked up in the lowpressure circulating acid liquor system, in which the acid is continuously circulated by means of pump 51 and carried into the pockets of impregnating valve 5, described in detail in US. Patent No. 3,251,511. The wood particles are then displaced degrees by the rotor (not shown) of the impregnating rotary valve 5, driven by motor 65, and then swept out of the aforesaid pockets through pipe 52 by an up-flowing high-pressure stream of acid liquor, circulated by means oflpump 20. Thus,

as a result of the structure and operation of valve 5, as described in detail in the above mentioned US. Patent No. 3,251,511, the low pressure-ambient temperature acid liquid circulating subsystem is maintained functionally separate from the subsequent high pressure-ambient temperature impregnating zone in conveyor tube 6. By means of valve 5, it is therefore possible to transfer the slurry to tube 6 without having any of the slurry forced back into the circulating acid liquor system.

This high-pressure-ambient temperature stream of acid liquor then carries the wood particles into impregnating conveyor tube 6, driven by motor 66, with a suitable retention time provided therein for acid liquor to impregnate the wood particles at ambient temperature and under high pressure. At the exit end of tube 6 the particles leave in a slurry and are conveyed into draining conveyor tube 7 throuhg pipes 26 and 28. Screw conveyor 7a is driven by means of motor 67. An adequate retention time is provided in tube 7 to permit the aforesaid particles to be drained of acid liquor. The particles, which are now in an atmosphere of high-pressure air, are discharged from draining tube 7 through air and steam lock 8 into reactor conveyor tube 9, which is at a steam pressure approximately equal to the air pressure in the draining tube. After the particles enter reactor tube 9 they are rapidly brought to the temperature of the steam atmosphere so that they are now in a high temperature-high pressure atmosphere, and after a controlled retention time (determined by the speed of screw 9a) the particles are discharged through solenoid valve 10 and collected in cyclone-type receiver 11. Screw 9a can be driven independently or, by means of belt 68, from motor 67.

The temperature and retention time provided by reactor tube 9 are the critical variables of the process. The desired temperature establishes the operating steam pressure, which in turn determines the air pressure in draining tube 7 and the pressure available for impregnation. By limiting the high temperature zone to the reactor tube, the highly corrosive area is confined.

Special chamber 12 is provided in the low-pressure acid liquor circulation system for defoaming. Level control 13 associated with slurrying chamber 4 maintains the proper liquid level in the low-pressure system by the on and off control of piston pump 14. Liquid level probe 15 in sump 31 of draining tube 7 control the liquid level in the highpressure system by operating solenoid valve 16 in suction line 53 from the low-pressure system to acid liquor supply tank .17.

To control the retention time of the chips in impregnating tube 6 it is necessary to control the rotational 1 speed of screw 6a as well as the velocity of the acid liquor passing through the length of said tube. There are several piping arrangements that could be used for the high-pressure acid liquor system to achieve this control of liquor velocity. The one illustrated in the flow diagram is least complicated. The drained liquor from draining tube 7 passes through pipe 54 to pump 18 and is then divided into two streams. Part of the liquor enters impregnating tube '6 at the exit end through pipe 55 and is recirculated to draining tube 7. The rest passes through pipe 56 to meter '19 and pipe 57 and then completely through impregnating tube 6 before being recirculated to draining tube 7.

Referring to FIGURE 2, all of the acid liquor entering impregnating tube 6 through pipe 52 with the chips is immediately removed through rotary screen 6c, which is attached to conveyor tube shaft 6b at the inlet end of impregnating tube 6, and pipe 58 and is recirculated through pump 20 (FIGURE 1) and impregnating valve 5 (FIGURE 1). FIGURE 2 illustrates a partial view of impregnating tube 6 cut away to show rotary screen 60 and the features that make it self-cleaning. Acid liquor from the interior of the tube passes through the entire area of rotary screen 6c at a comparatively low velocity, carrying with it wood particles 21 that tend to plug rotary screen 60. This screened liquor leaves the tube" through port 23. Most of the clear liquor entering impregnating tube 6 through port 23 passes through only the screen area directly opposite port 22 and therefore passes through at a comparatively high velocity, taking with it any particles that were tending to plug rotary screen 60.

FIGURE 3 illustrates the exit end of impregnating tube 6 cut away to show the provisions made for discharging the particle slurry. The bulk of the particles leave through bottom port 24 and transfer line 26. Constriction 25 limits the rate of discharge into slurry transfer line 26 and thus prevents line plugging. impregnating tube 6 is sloped slightly to encourge any entering air bubbles to migrate to the exit end of the tube. Port 27 and transfer line 28 are provided to remove this air as fast as it accumulates. The diameter of constriction 29 is just large enough to accommodate the largest wood particle. To prevent permanent clogging at constrictions 25 and 2 9, a spoked wheel 30 is attached to conveyor screw shaft 6b. The spokes sweep across the orifices continually to break up particle agglomerates.

Draining tube 7 also has its exit end elevated slightly higher than the inlet end to encourage liquor draining into sump 3-1. The entire interface 59 between sump 31 and the main body of draining tube 7 is perforated and provides draining area.

FIGURE 4 is a diagram showing a means for valving the wood particles from draining tube 7 into reactor tube 9. Gates 32 and 32' of gate valves 33 and 33 of steam lock 8 are operated by compressed air released through three- way solenoid valves 34 and 35. Vent valve 36 is operated simultaneously with air valve 3 4 and vent valve 37 with air valve 35. FIGURE 4 shows gate valves 33 and 33 in their so-called normal positions, which they would assume more than half of the total cycle time. The frequency of the valving cycles is controlled by timer 38. When timer 38 times out, it starts synchronous motor 39a which drives cam 39b. The open section on this adjustable cam determines the duration of the motivating pulse for repositioning valve gates 32 and 32'. When the cam follower leaves the open section and the switch is again activated, timer 38 is reset, motor 39a is stopped, and step-switch 41 is repositioned. This last repositioning activates synchronous motor 40a and adjustable cam 40b.

I The open section in this cam determines the duration of the motivating pulse for the return stroke of valve gates 32 and 3 2'. The speed of motor 40a largely determines the duration of valve gates 32 and 32 in the abornormal position. When the cam follower 61 leaves the open section of cam 40b and the switch is again activated, stepswitch 41 is repositioned, motor 40a stops, and a complete cycle is ended and a new one started.

A convenient and successful way to continually discharge solids from a pressure vessel is through a variable orifice with which the discharge rate can be controlled. However, if the particle size of the solids is large compared to the required discharge rate, this method cannot be used successfully. The schematic diagram shown in FIGURE 1 indicates that solenoid valve 10 is used to discharge the wood particles wherein a quantity of said particles may be permitted to build up in the enlarged section 62 above solenoid valve 10 and intermittently said valve is opened and the particles discharged along with some steam. To prevent any influential drop in pressure during a discharge operation, a solenoid valve in the steam line to reactor tube 9 may be opened simultaneously with discharge valve 10'. An uncontrolled drop in pressure could adversely affect the operation of gate valves 33 and 33' and the control of temperature. This means for controlling the discharge cycle and pressure in reactor tube 9 is described below with reference to FIG- URE S.

Timer 42 establishes the frequency of the discharge cycles. When this timer times out, synchronous motor 430 is activated and drives adjustable cam 43!). The open section of adjustable cam 43b determines the duration of discharge through solenoid valve and steam injection through solenoid valve 44. When the cam follower 63 leaves the open section and the switch is again activated, timer 42 is reset and motor 43a is stopped. The temperature in reactor tube 9 is controlled through a thermocouple primary element (not shown), a pneumatic controller and pneumatic valve 45. Pressure switch 46 operates a holding coil in two-circuit relay 48. If the pressure in reactor tube 9 exceeds the maximum desired operating pressure, .both steam solenoid valves 44 and 49, the latter being in the pneumatic valve line, are closed. Hand valve 47 is adjusted so that the quantity of steam injected through valve 44 is somewhat less than that required to maintain the proper temperature and pressures in reactor tube 9. Pneumatic valve 45; can then control temperature and by-pass line 50 (FIGURE 1) will equalize the pressure between draining tube 7 and reactor tube 9'.

Air for the system is provided from any suitable source (not shown) throughinlet line 69- and is distributed to the various components of the system through lines 70, 71, 72, and 73. Pressure in the several air lines is controlled by means of valves 74, 75, and 76.

In addition to the novel aspects of its, apparatus, the process of this invention is unique in its means of impregnation, in its method of introducing solids into a high-pressure-high temperature zone, and the high degree of control it affords to reaction time.

Having thus disclosed my invention, what I claim is:

1; Apparatus for continuously impregnating and chemically treating cellulose-containing materials in a circulating liquor comprising: i

(a) A first conveyor constituting an evacuation chamber for continuously transferring cellulose-containing material from a source of said material connected to said first conveyor and to a slurrying chamber connected to said first conveyor;

(b) Vacuum means connected to said first conveyor for removing occluded air from said cellulose-containing material;

(c) Pumping means connected to said slurrying chamber for continuously circulating treating liquor to and away from said slurrying chamber;

(d) A rotary valve connected to said slurrying chamber for continuously transferring slurry to a second conveyor connected to said rotary valve, said second conveyor constituting an impregnating chamber, said rotary valve being provided with means for transferring slurry to said second conveyor without introducing slurry into the circulating treating liquor;

(e) Means connected to said second conveyor for applying high pressure-ambient temperature air to cause t'he 'tre ating liquor to impregnate the evacuated cellulose-containing material;

(f) A third conveyor constituting a draining chamber conec'ted to said second conveyor, said third conveyor being provided with means to receive and collect excess treating liquor drained from the impregnated cellulose-containing material;

(g) Means for maintaining said third conveyor under high pressure-ambient temperature;

(h) A fourth conveyor constituting a reaction chamber;

(i). Means for transferring drained cellulose-containing material from the third conveyor to the fourth conveyor;

(j) Means for introducing high temperature-high pressure steam into the fourth conveyor;

(k) Means connected between the third and fourth conveyors for preventing passage of said high temperature-hig h pressure steam from said fourth to said third conveyor; and

(1) Means connected to the fourth conveyor for discharging treated cellulose-containing material therefrom.

References Cited UNITED STATES PATENTS 2,999,784 9/1961 Hullmann 162-53 X 3,076,501 2/1963 Schinn 16 2-63 X 3,165,436 1/1965 Bennett 162-68 X 3,278,367 10/1966 Loebel 162-53 X HOWARD R. CAINE, Primary Examiner.

US. Cl. X.R. 162-53, 69

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