US1949669A - Apparatus for treating fibrous material - Google Patents

Description

March 6, 1934. s. D. WELLS 1,949,669

APPARATUS FOR TREATING FIBROUS MATERIAL Filed June 20, 1932 Jzlim y 17. Walk JNM Gum/M443 Patented Mar. 6, 1934 PATENT, OFFICE 1,949,669 ArPAnArUs' FOR TREATING r'mnous MATERIAL Sidney D. Wells, Combined Locks, Wis.

Application June 20, 1932, Serial No. 618,372

10 Claims.

My invention relates to improvements in apparatus and method for the treatment of fibrous material.

In the treatment of fibrous material, especially by alkaline processes, marked advantages have been found when the cooking liquor is admitted to the digester at intervals or continuously during the cook instead of in one charge at the beginning of the cook. An important object of my invention therefore is to provide an apparatus in which the cooking liquor may be fed to the digester at intervals or continuously during the cook.

Another object of my invention is to provide a device of this character in which the cooking liquor may be admitted to the digester at known rates of flow.

A further object of my invention is the provision of a device of this character capable of feeding the cooking liquor at variable and controlled rates of flow.

Other objects and advantages of my invention will be apparent during the course of the following description.-

In the accompanying drawing, which forms a part of this specification and wherein like char- .acters of reference denote like'or corresponding parts throughout the same,

Figure 1 is an elevation of my improved apparatus showing the assembly more or less Figure 4 is an elevation or still another form of tank with which a proportioning pump is used. In the drawing, wherein for the purpose of illustration is shown a preferred embodiment of my invention, the numeral 10 designates a digester tank of any suitable construction and 11 indicates a heating tank'suitably spaced therefrom.

An annular strainer 12 is arranged within the steam space or 0011 of the heater through drip pipe'19.

Pipes 20 and 21 connect the top of the heater with the upper and lower end of the digester respectively and return the heated liquor to opposite "ends of the digester under the pressure of the pump 14.

A tank 22 holds the liquor charge and is connected at it top to the top of digester 10 by means of pipe 23 and at its bottom is connected to inlet 13 or the pump 14 by means of pipe 24. The flow of the liquor from tank 22 is controlled by means of valve 25 arranged in pipe 24 immediately below tank 22.

The top of tank 22 is connected to the steam main 17 by means of pipe 26 and pipe 27. A valve 28 is arranged in the steam pipe 27 adjacent the tank 22 and a similar valve 29 is arranged in pipe 26 above the steam pipe 2'7. An inlet conduit 30 enters tank 22 at the top and is con- 76 trolled by valve 31 to permit the flow of liquor to tank 22.

A suitable gauge glass 32 is arranged exteriorly of tank 22 and is in communication with the interior thereof. The glass may be graduated, or a scale 33 may be arranged in proximity to the glass to show the level of the liquor in the tank.

A conduit 34 connects the lower end of pipe 21 with the recovery room and is controlled by valve 35. A valve 36 may be arranged in the pipe 21 86 adjacent the top of the heating tank 11 and a similar valve 37 may be arranged in pipe 23 adjacent the top of tank 22. 1

The fitting 38 arranged at the bottom of the digester 10 connects pipe 21 with the valve controlled digester discharge pipe 39 and should be provided with -a suitable screen or grating to prevent the passage of chips into the connecting pipe. A

In operation the digester 10 is supplied with chips or' other fibrous material and a quantity of a suitable cooking liquor such as black liquor, or spent cooking liquor from a previous cook, or' even water. The cover is then bolted on and the cooking liquor is drawn from digester 10 through strainer 12 to heating tank 11 by. ump 14, where it is heated and forced through conduits 20 and 21 to the ends of the digester, and is again. circulated through the digester to strainer 12 and back to the heating tank. Obviously, pump 4 may be reversed and'tlie liquor Y drawn from the ends of the digester and forced into the digester through strainer 12-.

fee

,heater, and opening valves 3'7 and 35.

complished by stopping pump 14 and'opening valve 25 to allow the liquor to feed by gravity from tank 22 through pipes 24 and 13 and strainer 12 to the digester. It is preferred however to open valve 28 and admit steam pressure from main 17 to force the liquor from tank 22 to the digester. If the pump 14 is in operation during the introduction of liquor from tank 22 to the digester the liquor will be pumped through heater 11 to the ends of the digester and circulated by means of pump 14. The rate of flow of the black liquor may be readily controlled by valve 25 and determined by means of gauge glass 32 and scale 33.

While under pressure the black liquor is circulated through the heater by pump 14 until it is heated to a temperature of about 110 C. and

- until the chips in the digester are thoroughly impregnated with black liquor and all are of a substantially uniform moisture content. The excess of black liquor may then be run to the recovery room by closing valves 28 and 36, shutting down the pump, turning off the steam to the After sumcient liquor has passed out of the digester, leaving enough to maintain circulation if desired, tank 22 is filled with white liquor through pipe 30 and valve 31 and is connected into the system by having valve 37 open while valves 35, 28, 29 and 31 are kept closed. Valve 25.may be opened to the extent necessary to secure the desired rate of fiow of the white liquor into the digester during the cooking operation. During this cooking operation valve 35 is closed, valve 36 is open and pump 14 is in operation to form a continuous circulation of liquor through the digester and heater. Irrespective of the operation of pump 14, liquor will flow by gravity to the digester when the valve 25 is open, due to the fact that tank 22 has thesame pressure as the digester when valve 37 is open. v

While a stationary digester is illustrated, other types of digesters may be used, such as the tumbling digester or globe rotary digesters in which the trunnions are used for the admission and removal of liquor and gases. In place of the heater 11 steam may be added directly to the system.

In place oi the manual control of the rate of flow of liquor from tank 22 I may use a proportioning or measuring pump capable of pumping against the digester pressure, as illustrated in Figure 2. Control of the liquor flow may be obtained by changing the stroke of the pump illustrated at 40 in Figure 2. This may be accomplished in any suitable manner. For example, the motor crank 41 may be provided with a slot in which the pump connecting link 42 is adjustably secured as seen in Figure 2. Adjustment of the link 42 toward or away from the motor shaft shortens or lengthens the pump stroke. It will be seen therefore that the active cooking chemical may be injected into the system at any desired rate by adjustment of the pump stroke and of the valve 25. Superior results have been obtained when the cooking chemical is injected at a relatively high rate at the beginning of the cooking operation and at a lower rate. as the rate of consumption of the active chemical decreases, so that at no time is the active chemical absent, and at the same time the concentration will never exceed a critical concentration injurious to the fiber. In the case of kraft cooking the concentration of active chemical considered as NazO should never exceed three pounds per hundred pounds of 'total liquid in the system. With my arrangement I prefer to use not over two and as low as one pound per hundred pounds of total liquid. When the liquor is added in one charge in the usualmanner however, the concentration amounts to as high as six pounds pe hundred pounds of liquid.

Whether the rate of flow of the liquor is controlled by valve 25 or by proportioning pump 40, the rate of flow is chosen to be suflicient to prevent total exhaustion of the active cooking chemical at any time but not sufllciently great to produce a concentration injurious to the fiber quality. If exhaustion of the chemical occurs, precipitation of encrusting matter on the fibers results, with consequent staining of fiber, in-. creasein bleaching required and loss in flexibility. If concentration greater than a critical concentration occurs, tendering of fibers results with consequent loss in strength and toughness and,loss in yield. Consequently accurate control of the rate of flow of the active chemical is not only highly desirable but is necessary to the production of high grade pulp. I

For example, the following schedule for a five ton kraft pulp digester has been found to be very satisfactory.

,First fifteen minutes-120 cu. ft. liquor 8 cu. ft. per min.

Next thirty minutes-120 cu. ft. liquor 4 cu. ft.

per min.

Next thirty minutescu. ft. liquor 2 cm ft.

per

Next sixty minutes-60 cu.

per min.

Next thirty minutes-No liquor injection.

With the measuring pump shown in Figure 2, the tank 22 is under digester pressure-due to pipe 23 and valve 37, and consequently the back pressure against the pump is negligible and all that the pump need do is to regulate the rate of flow of the liquor and servein the capacity of a measuring device. No great amount of power is needed therefore to operate the pump 40? 120 In Figure 3 I have shown an open tank 22'. which may be substituted for tank 22. The liquor is fed to the tank through conduit 30' and is under atmospheric pressure in the tank. A float is arranged on a flexible member 43 which 125 passes over a pulley 44 arranged at the top of the tank and extends down the outside of the tank in proximity to a graduated inverted scale 45.

A weighted pointer 46 is secured to the end of the member 43 and indicates the quantity of the 130 liquor in' the tank.

The tank 22' is either open at the top or loosely covered and the pump 40' is capable of pumping against the pressure of the circulating system and cooking pressure in the digester.

In Figure 4 I have shown an adjustable proportioning and measuring pump 40, similar to that disclosed in Figure 2, used in conjunction with the open tank 22', and capable of pumping against the pressure in thedigester system.

The pumps 40, if accurately constructed will pump a known quantity of liquor and'therefore will not require a gauge or scale on the tank. The slot in the tank 41 may he graduated however to determine the proper adjustment of the 145 pump, and a tank gauge may be used if desired.

. Where the liquor is fed from tank 22 to the ft.'liquor 1 cu. ft.

digester under the steam pressure admitted flow due to the fact that the pressure diflerence between the digester and the tank is greatest at the begirming of the cook and constantly decreases as the cook progresses and the pressure in the digester rises. The flow of liquid for an opening of the proper size will therefore be greatest at the startof the cook and will constantly diminish as the digster comes up to pressure, when it will reach a constant flow until all of the liquor has entered the digester. This flow will therefore substantially automatically conform to the rate of the chemical consumption which is greates during the early stages or the cook and then diminishes as the cook proceeds;

While I have shown and described the preferred embodiment of my invention it is to be understood that various changes in the size, shape and arrangement of parts, and in the various steps of the method, may be resorted to without departing from the spirit of my invention or the scope of the subjoined claims.

Having thus described my invention what I claim and desire to protect by Letters Patent is:

1. In a device of the character described, a digester adapted to receive fibrous material, a tank connected to said digester and adapted to receive cooking liquor, and a measuring device arranged to feed liquor from the tank to the digester at a controllable rate.

2. In a device of the character described, a digester adapted to receive fibrous material,atank connected to said digester and adapted to receive cooking liquor, a measuring device arranged to feed liquor from the tank to the digester, andv digester adapted to receive fibrous material, a

heater connected to opposite ends of the digester, a circulating pump connecting the heater to the intermediate portion of the digester, a liquor tank connected to said digester, and means to feed liquor from said tank tosaid digester at a rate proportioned to the rate of consumption of the liquor in the digester.

5. In a device of the character described, a digester adapted to receive fibrous material, a heater connected to opposite ends of the digester, a circulating pump connecting the heater to the intermediate portion of the digester, a liquor tank, and a measuring device connecting the tank to the digester. and adapted to feed liquor from the tank to the digester at a controllable rate.

6. In a device of the character described, a di gester adapted to receive fibrous material, a heater connected to opposite ends of the digester, a circulating pump connecting the heater to the intermediate portion of the digester, a liquor tank, a measuring device connecting the tank to the digester and adapted to feed liquor from the tank to the digester, and means to vary the rate of flow of the liquor from the tank .to the digester.

7. The method of treating fibrous material in adigester which comprises admitting a substantially continuous flow of cooking liquor to said digester, and varying the flow of liquor in proportion to the rate of consumption of the liquor.

8. The method of digesting fibrous material which comprises substantially continuously feeding cooking liquor to the fibrous material, and substantially constantly diminishing the amount of liquor fed to the fibrous material as the digestion progresses.

9. In a device of the character described, a digester adapted to receive fibrous material, a tank adapted to receive cooking liquor, a heater connected to said digester, and a measuring devicev connecting the liquor tank to the heater and cooking liquor, a source of cooking liquor, means connecting the source of cooking liquor to the digester whereby liquor may be fed to the digester during the digestion period, means to accurately control the rate of flow of the cooking liquor to the digester, means to circulate the liquor through the digester, and means to heat the incoming liquor and the circulating liquor.

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