US3347741A

US3347741A - Feeder for solid materials

Info

Publication number: US3347741A
Application number: US337458A
Authority: US
Inventors: Gibson T Hutchison
Original assignee: Crane Co
Current assignee: Crane Co
Priority date: 1964-01-13
Filing date: 1964-01-13
Publication date: 1967-10-17
Anticipated expiration: 1984-10-17

Description

Oct 17, 19 G. T. HUTCHISON FEEDER FOR SOLID MATERIALS Filed Jan. 13, 1964 United 3,341,741 Patented Get. 17, 196? 3,347,741 FEEDER FDR SOLID MATERIALS Gibson T. Hutchison, Maple Glen, Pa., assignor to Crane Co., Chicago, Ill., a corporation of Illinois Filed Jan. 13, 1964, Ser. No. 337,458 3 Claims. (Cl. 162--241) ABSTRACT OF THE DISCLOSURE An apparatus for feeding wood chips to a pulp digester comprising a transfer chamber and means for equalizing the pressure in the transfer chamber and the digester. There is also provided means for applying a vacuum to the transfer chamber for removing the air from within the intricacies and between the fibers of the wood chips while contained within the transfer chamber.

This invention relates generally to feeders for solid materials of the free flowing type.

While the invention is applicable broadly to feeding of such materials from a supply thereof to a vessel in which the pressure is greater than the pressure of the supply, it will be described hereafter as it is applicable specifically to the paper industry for the feeding of wood chips to a pulp digester.

In the paper industry,'pulp digesters in the past have involved a batch process in which the digester, a large tank, is filled with wood chips, a cooking liquor is added and the batch is heated at a cooking temperature. At the end of the cooking cycle, the chips and liquor are blown down to a blow tank wheresteam flashes to atmosphere or other points in the process, and the digester is emptied in preparation for another charge. Obviously, a continuous process for pulp digestion would have many advantages over the batch process, such as greater output by reason of the elimination of the heat up and blow down steps, improved quality by reason of better process control, and the adaptability of the process to automation. One of the main problems encountered in the provision of a satisfactory continuous digestion operation is the metering and is at an elevated pressure and temperature. Prior feeding devices for such an operation have involved the use of a screw feeder, a rotary valve, or combinations thereof. However, such devices have not proved to be entirely satisfactory. For example, drawbacks of rotary valves are that they jam up, it is is difiicult to control leakage, and there are excessive wear areas.

In accordance with the present invention there is provided a novel feeder which comprises a transfer chamber or lock positioned between the supply of the wood chips and the digester, a control valve for controlling flow of the solid material from the supply to the transfer chamber and a control valve for controiling flow from the transfer chamber to the digester. The control valves also serve to isolate various sections of the apparatus. Means are provided for equalizing the pressure in the transfer chamber and the digester prior to feeding of the material to the vessel, which pressure equalization permits a smooth flow of material. A feature of the feeding arrangement is that it may be used to meter the rate of chip feed. This is achieved by the provision of a time control for the transfer operation in conjunction with the size of the transfer chamber or lock.

The foregoing and other objects and features of the invention will become apparent from the following description in which the single figure is a diagram showing one form of apparatus provided in accordance with this invention.

The single figure of the drawing illustrates the invention as applied to a feeder for a continuous pulp digester. It will be evident that the invention is more generally useful, in that the solid material handled need not be wood chips and the pressurized vessel need not be a digester. Nevertheless, for simplicity, the description will be phrased consistently with the feeding of wood chips to a continuous pulp digester.

There is indicated at 2 a continuous digester, which may be of conventional construction. During operation, the digester 2 is maintained at an elevated cooking temperature and pressure condition. Digester 2 has an inlet connection 4 in the top thereof. Mounted above the digester 2 in alignment with the inlet connection 4 is a bin 6 containing a supply of wood chips which are to be fed to the digester and having an open bottom end. In vertical alignment between the open bottom end of the bin 6 and the 8 is connected to the bottom of the bin 6 for receiving flow therefrom and the lower conduit 12 is connected to the inlet connection 4 for flow of solid material into the digester.

A valve 14 is provided in conduit 8 for controlling the flow of solid material therethrough. Valve 8 may be of any suitable type, but preferably is of a type of gate valve used in the art for pulp stock flow control and having nozzles arranged to direct jets of liquid or steam to clear the seatin and sealing surfaces. Conduit 12 is provided with a similar valve 16 for controlling flow therethrough and closing off or opening this conduit. A transfer chamber or lock is defined in the vertical conduits between the upper and

lower valves

14 and 16.

Valves

14 and 16 are operated by suitable valve actuating power means 18 and 20, respectively, and are provided with

nozzles

22 and 24, respectively, to clear the seating surfaces.

Nozzles

22 and 24 are supplied with steam or liquid 28 and

control valves

30 and 32, respectively.

Means are provided for equalizing the pressures in the transfer chamber and the digester 2. Such means comprises a line 34 connected to the upper end of the transfer chamber, a line 35 connected between line 34 and the upper end of the digester 2 and a pressure equalization valve 38 connected in line 36 for controlling flow therethrough.

Means are Such be described as follows:

The first step in the cycle is that of filling the transfer chamber contained in the enclosed space between the

valves

14 and 16. In the filling step, only the inlet valve a 14 and the vent valve 40 are open, all the other valves being closed. Accordingly, the wood chips contained in the bin 6 will fall into the transfer chamber by gravity flow to fill the space between the

valves

14 and 16. During the filling step, the transfer chamber is vented to atmosphere through the vent valve 40 whereby both the bin 6 and the transfer chamber are at atmospheric pressure.

The next step is to close the valve 14 to trap the chips within a sealed transfer chamber or look. The closure is effected by operation of the valve actuating means 18 which moves a valve member to close the passage through conduit 8. During the closing movement of the valve member, vent valve 40 and control valve 34) are the only valves which are open. The open condition of control valve 30 permits the flow of high pressure liquid or steam from source 26 through line 28 to the nozzles 22. Accordingly, jets of fluid are directed to clear the valve gate and seat.

The next step is that of evacuation of the transfer chamber. In this step only the evacuation valve 46 is open Wherefore the vacuum source 42 is in communication with the transfer chamber through

lines

44, 36 and 34. The application of a vacuum to the transfer chamber reduces the pressure appreciably to below atmospheric pressure. This causes the air within the intricacies and between the fibers of the wood chips to be forced out, making easier the penetration of the heating steam and/ or cooking liquor in the subsequent steps of pulp digestion. The evacuation step may be optimized by reducing the pressure below the vapor pressure corresponding to the temperature of the chips so that water within the chips is vaporized, resulting in maximum expulsion of air from within the chips.

The next step is to equalize the pressures in the transfer chamber and the digester, the latter being at a pressure greater than that in the transfer chamber. In this step, all the valves are closed with the exception of the pressure equalization valve 3% which is open to provide communication through line 36 between the transfer chamber and the digester 2. This communication between the two chambers permits pressure equalization to take place. It is to be noted that some chip preheating takes place in the transfer chamber during this step, the degree of preheating being dependent upon the length of time allocated to this step. If desired, time greater than that required for pressure equalization may be taken.

After the pressure equalization step is completed, it is time to open the valve 16 to provide communication between the transfer chamber and the vessel. The valve opening is effected by operation of the valve actuating means 20 which moves a valve member to open the passage through conduit 12. During opening movement of the valve member, the pressure equalization valve 38 and the control valve 32 are the only valves which are open. The open condition of control valve 32 permits the flow of high pressure liquid or steam from source 26 through line 28 to the nozzles 24 whereby jets of fluid are directed to clear the valve gate and seat.

Upon the opening of valve 16, the feeding of the chips from the transfer chamber to the digester takes place. In this step, pressure equalization valve 38 and transfer valve 16 are open. The feed is by gravity flow from the transfer chamber downwardly through conduit 12 and inlet connection 4 into the digester. The feed is smooth by reason of the equalized pressure condition. If desired, the valve 52 may also be opened at this time to introduce cooking liquor into the transfer chamber.

After all the chips have dropped into the digester, the next step is to close valve 16. This closure is effected by operation of the valve actuating means 20 and, as in the case of the opening of this valve, the control valve 32 is open to permit the introduction of jets of fluid for clearing the valve gate and seat. Also, the pressure equalization valve 38 is open in this step.

After the valve 16 is closed completely, the transfer chamber is sealed at both ends. The next step is to relieve the pressure in the transfer chamber, which pressure is at the elevated pressure of the digester. In this step all the valves are closed with the exception of the pressure relief or vent valve 40. This valve 40' is left open a time sufficient to permit the pressure in the transfer chamber to drop to approximately atmospheric pressure.

The next step is to open the valve 14 in preparation for the feed of chips into the transfer chamber. This opening is effected by operation of the valve actuating means 18 which moves a valve member to open the passage through conduit 8. During this opening movement of the valve member, vent valve 40 and control valve 30 are the only valves which are open. The open condition of control valve 3!} permits the flow of high pressure liquid or steam from source 26 to the nozzles 22 whereby jets of fluid are directed to clear the valve gate and seat.

The apparatus is now in condition for another filling of the transfer chamber as discussed above. Accordingly, another charge of wood chips contained in the bin 6 will fall into the transfer chamber by gravity flow to fill the space between the same.

The above description of the operation covers one cycle, and it will be apparent that this cycle may be repeated to provide a continuous feed of chips to the digester at a desired rate. Preferably, the cycle may be time controlled with each step taking place a specified time interval and the cycle being repeated at regulated intervals thereby metering the feed rate. However, certain steps could be terminated in accordance with other measurements, such as, pressure, temperature or level.

It will be apparent that various of the above steps may be omitted when not required for a specific process. Moreover, the cycle, steps and arrangements described above may vary from one installation to another, depending on the raw stock, the end product and the overall process.

A modification of the above cycle which will tend to prevent chips from bridging or arching in the bin would involve opening the valve 14 just before the pressure in the transfer chamber has reached atmospheric in its decay during the pressure relief step. This will cause a small puff or surge of gas from the transfer chamber into the bin through the valve 14 to impose a slight shock or bump to the chips in the bin. This will minimize the possibility of the chips bridging in the bin.

In a modification of the apparatus, the pressure relief valve 34 ma I be connected to any place where heat may be used at atmospheric pressure, as for example, to perform some type of preheating. This would make use of the high temperature of the gases in the transfer chamber after the pressure equalization step.

It will be apparent that the apparatus in accordance with the invention has several advantageous features. For example, by pressure relieving the transfer chamber before connection to the bin, the apparatus avoids an explosion into the hopper. Also, by evacuating the transfer chamber through the valve 48, the air is removed from the chips very effectively since the evacuation is performed on a relatively small space. Prior pulp digestion apparatus have not used the evacuation step because of the large evacuating equipment requirements and the structural design problems involved in the evacuation of large vessels.

It is to be understood that various changes may be made in the details of the embodiment of the inventive concepts herein contained without departing from the scope of th invention. For example, while the pressure equalization in the described embodiment is achieved by connecting the digester so that it serves as a source of pressure equalizing vapor, this vapor source could be a separate source at the same pressure as the digester. Accordingly, it is not desired to be limited except as required by the following claims.

What is claimed is:

1. Apparatus for feeding wood chips to a pulp digester comprising a bin containing a supply of wood chips, a

digester, the pressure in said digester being higher than that in said bin, and means for transferring said chips from said bin to said digester including a transfer chamber, first conduit means connecting said bin and said transfer chamber, a valve in said first conduit means for controlling flow therethrough, second conduit means connecting said transfer chamber and said digester, a valve in said second conduit means controlling flow therethrough, third conduit means for equalizing the pressure in said transfer chamber and said digester connected between said digester and said transfer chamber and a valve for controlling flow through said last-mentioned conduit means, and means including a vacuum source connected to said third conduit means and a valve between said vacuum source and said third conduit means for controlling a vacuum to said transfer chamber to reduce the pressure therein appreciably below atmospheric pressure so as to remove the air from within the intricacies and between the fibers of the wood chips within said transfer chamber.

2. Apparatus according to claim 1 comprising means for venting said transfer chamber to atmosphere.

References Cited UNITED STATES PATENTS 691,975 1/1902 Schaaf 162-246 X 1,704,728 3/1929 De Cew 162-53 X 2,582,054 1/1952 Michon 162-246 X 2,858,212 10/1958 Durant 162-237 3,076,739 2/1963 Nettle 162-17 3,190,509 6/1965 Kirchhoefer 214-17.4 3,215,587 11/1965 Guerrieri 162-53 X S. LEON BASHORE, Acting Primary Examiner. HOWARD R. CAINE, Examiner.

Claims

1. APPARATUS FOR FEEDING WOOD CHIPS TO A PULP DIGESTER COMPRISING A BIN CONTAINING A SUPPLY OF WOOD CHIPS, A DIGESTER, THE PRESSURE IN SAID DIGESTER BEING HIGHER THAN THAT IN SAID BIN, AND MEANS FOR TRANSFERRING SAID CHIPS FROM SAID BIN TO SAID DIEGSTER INCLUDING A TRANSFER CHAMBER, FIRST CONDUIT MEANS CONNECTING SAID BIN AND SAID TRANSFER CHAMBER, A VALVE IN SAID FIRST CONDUIT MEANS FOR CONTROLLING FLOW THERETHROUGH, SECOND CONDUIT MEANS CONNECTING SAID TRANSFER CHAMBER AND SAID DIGESTER, A VALVE IN SAID SECOND CONDUIT MEANS CONTROLLING FLOW THERETHROUGH, THIRD CONDUIT MEANS FOR EQUALIZING THE PRESSURE IN SAID TRANSFER CHAMBER AND SAID DIGESTER CONNECTED BETWEEN SAID DIGESTER AND SAID TRANSFER CHAMBER AND A VALVE FOR CONTROLLING FLOW THROUGH SAID LAST-MENTIONED CONDUIT MEANS, AND MEANS INCLUDING A VACUUM SOURCE CONNECTED TO SAID THIRD CONDUIT MEANS AND A VALVE BETWEEN SAID VACUUM SOURCE AND SAID THIRD CONDUIT MEANS FOR CONTROLLING A VACUUM TO SAID TRANSFER CHAMBER TO REDUCE THE PRESSURE THEREIN APPRECIABLY BELOW ATMOSPHERIC PRESSURE SO AS TO REMOVE THE AIR FROM WITHIN THE INTRICACIES AND BETWEEN THE FIBERS OF THE WOOD CHIPS WITHIN SAID TRANSFER CHAMBER.