US3741864A - Continuous digester check valve - Google Patents

Abstract

THE COMBINATION WITH A PRESSURIZED VESSEL FOR CONTINUOUSLY DIGESTING WOOD CHIPS IN A CHEMICAL SOLUTION WITH A PUMP FOR FORCING THE CHIPS AND SOLUTION INTO THE VESSEL AND A VALVE WHICH IS BIASED TO ITS CLOSED POSITION AND A CONTROL FOR THE VALVE WHICH OPENS THE VALVE WHEN THE

PUMP IS OPERATING, THE VALVE BEING CLOSED WHEN THE PUMP IS NOT OPERATING.

Description

' "June 26, 1973 R. v. PENMNGTON 3,741 864 CONTINUOUS .DIGESTER CHECK VALVE Original Filed Aug. 31, 1966 OI lllllllllllll IIIII III|| United States Patent 3,741,864 CONTINUOUS DIGESTER CHECK VALVE Rohe Vester Pennington, Nashua, N.H., assignor to Improved Machinery Inc., Nashua, N.H.

Continuation of application Ser. No. 202,775, Nov. 29,

1971, which is a continuation of application Ser. No.

836,214, June 12, 1969, which in turn is a continuation of application Ser. No. 576,277, Aug. 13, 1966, all now abandoned. This application May 10, 1972, Ser. No.

Int. Cl. D21c 7/06 U.S. Cl. 162-246 1 Claim ABSTRACT OF THE DISCLOSURE The combination with a pressurized vessel for continuously digesting wood chips in a chemical solution with a pump for forcing the chips and solution into the vessel and a valve which is biased to its closed position and a control for the valve which opens the valve when the pump is operating, the valve being closed when the pump is not operating.

This is a continuation of application Ser. No. 202,775, filed Nov. 29, 1971, which is a continuation of application Ser. No. 836,214, filed June 12, 1969, which in turn is a continuation of application Ser. No. 576,277, filed Aug. 13, 1966 (all now abandoned).

This invention relates to the continuous digestion of fibrous material, and more particularly, to a novel check valve for preventing pulp blow-back from the pressurized continuous digester vessel used in the digestion process.

The pulping of wood or other fibrous materials is carried out by digesting particles of fibrous material, such as wood chips, in a highly heated pressurized chemical solution as in the well known kraft process for the manufacture of wood pulp. In continuous digestion processes, the solid raw material is continuously fed into the reaction vessel or digester, is treated by heating under pressure in a digester chemical solution as it moves throughout the length of the digester, and is discharged as pulp at the other end of the digester. The pressure within the digester is often as high as 150 to 175 p.s.i., and must be carefully controlled for safety reasons.

In many processes, the wood chips and chemical solution are mixed in a supply tank and then forced, as a mixture, into the pressurized digester. It has been known that one of the least expensive methods of forcing the wood chip chemical mixture into the pressurized vessel would be to use a conventional non-fluid sealing pump such as a centrifugal pump. The use of such a non-fluid sealing pump, however, has been considered to be too hazardous since, if the pump should stop, the super-heater, highly pressurized chemical mixture within the digester would be blown back through the pump and would severely injure or kill persons in the nearby area. In presently existing continuous digestion systems, therefore, the mixture is fed into the digester using some type of fluid sealing, positive feeding device such as a rotary pocket or intersecting double screw feeder. These devices, although generally satisfactory in operation, are extremely expensive in that they require close tolerance and massive construction.

It is, accordingly, a primary object of the present invention to provide a positive fail-safe check valve which will automatically seal the inlet of the digester whenever the pump forcing the mixture into the digester is not operating, as well as to close upon the occurrence of other system failures. Other objects include providing a simple, relatively inexpensive valve which can be coupled with a centrifugal pump to provide a cheap, safe, and efiicient means for forcing chips and chemicals into a continuous pulp digester.

The invention, in general includes a check valve, preferably biased by (gravity towards its closed position, mounted in the digester inlet line between the pump and the digester inlet, and control means coupled with the pump for overcoming the bias and opening the valve when the pump is operating and automatically closing the valve when the pump stops. In preferred embodiments there is provided a rotary valve with a rotor with a through passageway of constant volume mounted in a cylindrical housing, both the passageway and housing having edges capable of shearing wood chips interposed between them. A large counterweight is preferably secured directly to the rotor in position for rotating it into the closed position and for shearing wood chips in order to do so. A hydraulic control system is provided for rotating the rotor against the bias of the counterweight, such system being responsive to pump operation so that the rotor remains in open position only so long as the pump is operating.

Other objects, features and advantages will appear from the following detailed description of a preferred embodiment of the invention, taken together with the attached drawings thereof in which:

FIG. 1 is a diagrammatic drawing of pulp digesting apparatus including a valve system constructed according to the present invention shown in open position;

FIG. 2 is a diagrammatic view of the valve system of FIG. 1 in closed position; and,

FIG. 3 is a detailed cross-sectional view of the valve element of FIG. 1 in open position.

Referring more particularly to the drawings, there is shown in FIG. 1 pulp digesting apparatus, generally designated 10, including a positive digester check valve, generally designated 12, and control system generally designated 13 constructed according to the present invention. As illustrated, pulp digesting apparatus 10 includes a substantially cylindrical pressurized vessel or digester 14, generally of the order of ten or more feet in diameter and one hundred or more feet in length. Digester 14 includes an inlet 16 in the base thereof through which the wood chip-liquid mixture, initially provided in a storage tank 18, is forced into the digester by means of a centrifugal pump 20. An inlet pipe system, designated 22, extends from storage tank 18 to inlet 16. Digester check valve 12 is mounted in pipe system 22 intermediate pump 20 and inlet 16 of the digester. At the upper end of digester 14 is provided a discharge outlet 26 through which the drained, digested chips or slurry may be discharged to a discharge mechanism (not shown) at the lower end of a substantially vertical downflow pipe 28.

As illustrated, digester check valve 12 comprises a rotary valve including valve member in the form of a rotor 32, having a passageway 34 extending radially therethrough, rotatably mounted in a substantially cylindrical housing 36 having a pair of circumferentially spaced ports, outlet port 38 and inlet port 40, respectively. The valve is opened and closed by rotating rotor 32 relative to housing 36 for about degrees to move the opposite ends of passageway 34 into and out of communication with ports 38 and 40. With this arrangement, passageway 34 remains of constant volume during rotor movement, so that it does not compress material therein during valve closing. The peripheral edges of ports 38 and 40 and the cooperating edges of passageway 34 are sufiiciently hardened to act as cutting edges for shearing Wood chips which may be positioned between them during valve closing, so that closing of the valve is not prevented thereby. Although a rotary valve as preferred, a slide valve with a sliding member having a through passageway of constant volume could also be used.

The control system 13 includes an elongated beam 42 secured to one axial end of check valve rotor 32. One end of beam 42, designated 44, supports a large gravity actuated counterweight 46. The other end, designated 48, is connected to a vertically acting hydraulic piston 50' and cylinder 52. Piston 50 is actuated by a double hydraulic pump 54 driven by means of gears 56, from the output shaft 58 of the same motor 60 used to actuate centrifugal pump 20. Hydraulic fluid from pump 54 is fed to and from cylinder 52 to actuate piston 50' therein through the hydraulic system shown in the drawings. An air system could also be used although a hydraulic system is preferred.

One output line of double pump 54, designated 62, is connected to the upper or live end of cylinder 52; the other output line, designated 64, to energize a spring biased hydraulic control valve 66. The inlet 68 of control valve 66 is connected to the live end of cylinder 52. One outlet 70 of control valve 66 is closed off; the other outlet 72 of valve 66 connects to a discharge line 74 leading to a fluid discharge and supply tank 76. The hydraulic system also includes a pair of control orifices 78 and 80 pro vided, respectively, in pressure control lines 82 and 84 connecting each of the outlets of pump 54 to tank T6 so that fluid flows continuously through said orifices when A hydraulic pump 54 is operating. Fluid supply lines 86, 87 connect supply tank 76 to the inlet of pump 54.

In operation, control system 13, when centrifugal pump 20 operates, rotates the rotor 32 of digester check valve 12 from its closed position, shown in FIG. 2, in which the ends of passageway 34 are spaced apart from ports 38 and 40 for preventing back-flow through the valve, to its open position shown in FIGS. 1 and 3, in which the ends of passageway 34 are in communication with ports 38 and 40 and there maintains it, permitting wood chips to flow into the digester, since, when centrifugal pump 20 is running, its driving motor 60 will also operate hydraulic pump 54. Under these conditions, pressurized hydraulic fluid from outlet 62 of pump 54 forces piston 50 downward, rotating beam 42 against the bias of the gravity counterweight 46 and opening valve 12. Fluid from the other outlet 64 of pump 54 moves control valve 66 to the left (as viewed in FIG. 1) against its spring bias to the position shown in FIG. 1 in which position the valve is closed and no fluid from cylinder 52 can dump therethrough to permit valve 12 to open.

If for any reason, centrifugal pump 20 stops or control system 13 fails, pressure on piston 50 will be released so that digester check valve 12 will be immediately closed by counterweight 46 to prevent the wood chip-chemical mixture within pressurized digester 14 from blowing back through the pump, the counterweight being effective during valve closing, to shear wood chips interposed between the cooperating cutting edges of passageway 34 and ports 38 and 40. Specifically, as hydraulic pump 54 operates only when motor 60 is also driving centrifugal pump 20, when motor 60 stops, the pressure in the hydraulic pump outlet lines 62 and 64 immediately drops because of continued flow through orifices 78 and 80. The decrease in pressure in outlet line 64 allows control valve 66 to open in response to its spring bias and permits pressurized fluid within cylinder 52 to flow rapidly through valve 66 to supply tank 76. This decrease in pressure in cylinder 52 allows counterweight 46 to drop, closing valve 12. Should valve 66 stick in its closed position as shown in FIG. 1, fluid flow through orifice 78 will release piston to permit digester check valve 12 to close, although at a slightly slower rate than that with hydraulic valve 66 open.

When motor and centrifugal pump 20 are restarted, thereby activating hydraulic pump 54, control valve 66 will close and the pressure in cylinder 52 will increase to force piston 50 downwardly, thereby reopening digester check valve 12. Other embodiments of the invention within the spirit thereof and the scope of the appended claim will occur to those skilled in the art.

What is claimed is:

1. In combination with a pressurized vessel for continuous digestion of wood chips having an inlet pipe through which a wood chip-liquid mixture is introduced thereinto;

a non-fluid-sealing centrifugal pump having a shaft for forcing said mixture through said inlet pipe into said vessel;

an operating valve connected to said inlet pipe between said pressurized vessel and said non-fluidsealing centrifugal pump for closing said inlet pipe for preventing back flow of said mixture from said pressurized vessel, said operating valve being movable between an open position and a closed position and including a gravity counterweight biasing said operating valve towards said closed position; and

control means coupling said pump means and said valve and responsive to said pump means for permitting the bias of said valve to close said valve when said pump means is not operating and for overcoming said bias and opening said valve in response to the operation of said pump means;

said control means including an hydraulic cylinder and piston secured to said operating valve in position for opening said valve against the gravity bias thereof, a double fluid pump mechanically coupled with said centrifugal pump shaft by gears for directly operating said centrifugal pump, and a control valve having an open non-energized position and a closed energized position;

said double fluid pump having one pressure outlet connected to said cylinder and piston to open said operating valve in response to the operation of said centrifugal pump, and another pressure outlet connected to said control valve to energize said control valve;

said control valve being connected to said cylinder and piston to open said cylinder and piston to fluid discharge when not energized by said double fluid pump.

References Cited UNITED STATES PATENTS 1,933,017 10/1933 Iansa 162-52X 2,067,479 I/ 1937 Dahlstrand 10340 FOREIGN PATENTS 138,930 1/1953 Sweden 162-246 S. LEON BASHORE, Primary Examiner R. V. FISHER, Assistant Examiner US. Cl. X.R. 16225 2

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