US2872314A - Method of making pulp - Google Patents

Description

3 Sheets-Sheet 1 N. H. SANDBERG METHOD ,OF MAKING'PULP FiledJuly 12, 1 954 fzWEil/ZWR Ne /s H. Sane/berg QMWQ r AJTd/EWEY Feb. 3, 1959 N. H. SANDBERG METHOD OF MAKING PULP 3 Sheets-Sheet 2 Filed July 12, 1954 MFEAIY'QZ /Ve/$ H. Sana/bar BY 9 Qoapva 4n% mam/2y F 3, 1 9 N. H. sANDBERG 2,872,314

METHOD O MAKING P LP 3 Sheets-Sheet 3 Filed July 12, 1954 ran 1m A/e/s H. Sanaberg BY Q W 81 United States Patnt Mnrnon on MAKING PULP Nels H. Sandberg, St. Paul, Minn, assignor to Waldorf Paper Products Co., Ramsey County, Minn, a cor-pa ration of Minnesota Application July 12, 1954, Serial No. 442,873

7 Ciaims, (Cl. 92--6) This invention relates to an improvement in pulp mak ing process, and has as its object the formation of paper and paper pulp from wood chips in a continuous operation.

For many years efforts have been made to devise a successful continuous process for making paper pulp from wood chips. Probably the biggest problem lies in the treatment of the wood chips before being made into pulp. The chips must be impregnated with liquid prior to defibration. If the chips are soaked in impregnating liquor in the absence of elevated pressures and tempera tures, the time required for impregnation is excessive. On the other hand, if the raw chips are subjected to the pressures and temperatures necessary to cook the chips, the surface portions only of the chips are impregnated prior to the start of the cooking operation; and the heart, or core, of each chip remains more or less uncooked, resulting in an inferior product.

Chips are successfully cooked in batches in digesters by inserting the chips in the digester and subjecting them to a long slow cooking process. if necessary, the pressure and temperature can be gradually increased during the process. Unfortunately, however, this is a batch process rather than a continuous process, and extreme difficulties are experienced in producing similar conditions in a continuous process.

Efforts have been made to produce the pulp by passing the chips through a series of chambers of varying pressures and temperatures in the presence of impregnating liquor. For example, the chips may be subjected to gradually increasing pressures and temperatures in the series of chambers through which the chips pass. Obviously, however, this process is complicated by the necessity of providing a pressure seal between the chambers, and in transferring the chips from a chamber of lower pressure to a chamber of higher pressure. Rotary transfer valves have been used for this purpose but it is difiicult to maintain a constant feed of chips through the various chambers and transfer valves, and the cost is high due to --the necessity of driving the various transfer valves, and

the cost of maintaining the same.

The object of the present invention lies in the provision of-a continuous method of producing paper pulp in which the pressure may remain constant throughout the chip impregnating, cooking, and defibrating process. In this process, the chips maybe thoroughly impregnated with liquor to the cooking process without any deleterious effect upon the chips,'while still maintaining the same pressure in the impregnating chamber and in the cooking chamber. As a result, the chips may move continuously through the impregnating chamber and the. cooking chamber without the necessity of intervening seals or pressure locks.

A feature of the present invention lies in the provision of a hydrostatic impregnating tube or chamber which is filled with liquor, and into which the raw chips are fed.

' This chamber includes a means for continuously-moving the chips from one end of the chamber to the other. As the chips pass through this chamber, they are subjected to relatively high pressure, but the temperature is maintained below the cooking temperature of the chips. The movement of the chips through this chamber is sufliciently slow so that the chips will be thoroughly impregnated with the liquor. The chips are then continuously fed to a preheating or cooking chamber which is maintained at a steam pressure equal to the hydrostatic pressure of the impregnating chamber. However, after the chips have been removed from the impregnating liquor, the temperature increases to that corresponding to the pressure of saturated steam.

A feature of the present invention resides in the use of a hydrostatic chamber having an inlet and an outlet which are above the liquid level in the chamber so that the chips passing therethrough are completely submerged during the impregnating process. As a result, while the steam used for maintaining an equalized pressure throughout the system produces a corresponding steam temperature in the preheating or cooking chamber, the temperature 'defibrator of the Aspmnd type, from which the fibers are exhausted to atmospheric pressure. The pulp thus formed may be further refined, if desired, and supplied to a paper making machine where it is made into a suitable paper or paperboard.

An added feature of the present invention lies in the provision of a system in which the raw chips are subjected for a short period of time to the action of elevated pressure and temperatures immediately before they are immersed in impregnating liquor. This step is of considerable importance in the process, as the chips have a tendency thereafter to absorb liquor much more quickly when immersed.

These and other objects and novel features of the present invention will be more clearly and fully set forth in the following specification and claims.

In the drawings forming a part of the present invention:

Figure l is an end elevational view, partly in section, showing the apparatus used in the method of forming paper pulp.

Figure 2 is a side elevational view, partly in section, of the apparatus illustrated in Figure 1.

Figure 3 is a vertical sectional view through the inlet end of the apparatus.

' Figure 4 is a vertical sectional view through the outlet end of the apparatus.

The apparatus used in the production of paper pulp by my method includes, in general, a hydrostatic pressure impregnating tube orchamber, illustrated in general by the letter A, a preheating or cooking chamber, illustrated in general by the letter B, and a defibrator C. These elements are connected together in series to form a continuous apparatus.

Wood chips are supplied from a suitable source of supply, not illustrated in the drawings. These chips are conveyed by any suitable means to the upright inlet pipe to into which they fall by gravity. Obviously, a conveyor may be provided in the inlet pipe ll) if desired.

The inlet pipe it is connected to the upper end of a rotary transfer valve ll. This valve, in the form illustrated, includes a generally cylindrical pocketed rotor 7.2 rotatably mounted upon a horizontal axis 13 and enclosed within a housing 14. A motor 15 or other suitable drive means acts to rotate the rotor 12 to move the pockets 16 beneath the inlet pipe 10, to receive chips therefrom, and then to invert the filled pockets above the valve outlet pipe 17, into which the chips are dropped.

The lower end of the valve outlet pipe 17 communicates with an inclined inlet feed pipe 19 which communicates at its lower end with a horizontally extending hydrostatic tube or impregnating chamber 20. A spiral conveyor 21 is provided in the feed pipe 1.9 to insure the movement of the chips downwardly into the impregnating chamber. A motor or similar drive means 22 is connected to the spiral conveyor 21 to the As is best illustrated in Figure 2 of the drawings, the elongated impregnating chamber is provided with a spiral conveyor 23 which is rotatablysupported by suitable bearings on an end plate 24 closing the inlet end of the chamber 20, and on an end plate 25 closing the outlet end of the chamber 20. A motor 26 is provided externally of the chamber 20 and connected to the shaft 27 of the conveyor 23 for driving the same.

The conveyor 23 operates at a proper speed to retain the chips in the impregnating chamber for a suitable length of time to insure proper impregnation. This time depends upon the thickness and size of the chips being used, the type of wood used, and upon the pressures and temperatures employed. However, in any event, the temperatures should not be sufficient to tend to cook the chips, and the time must be sufficient to insure impregnation of the heart or core of the chips.

As is illustrated in Figure 2 of the drawings, the conveyor 23 is terminated short of the outlet end of the impregnating chamber and includes opposed bladed portions 29 on opposite sides of the outlet relation thereto. The bladed portions 29 are arranged to feed the chips from the impregnating chamber to the outlet pipe 33 at the outlet end of the impregnation chamber. A spiral conveyor 31 is provided in the outlet pipe 30 which is designed to carry the chips upwardly from the impregnation chamber to a point above the liquid level in this chamber. The liquid level is indicated in general by the numeral 32. The chips within the impregnation chamber are thus at all times below the level of the impregnating liquid.

As indicated in Figure 4 of the drawings, the chips are delivered by the conveyor 31 to an upright pipe 33 communicating with the interior of the preheating or cooking chamber B. This chamber may comprise a single elongated tube 34, or a series of connected elongated tubes such as 34, 35, 36, and 37. in other words, in the formation of certain types of pulp, only one such cylinder is required. In other installations, and in producing other types of pulp, a series of such tubes are desirable.

When the apparatus is to be used in the production of pulp used in the formation of paper of perhaps a thickness of 0.009 inch, commonly known as 9 point paperboard and designed for use in the production of corrugated board, a single preheating or cooking chamber may be used. From a practical standpoint, the length of tube which may be used is limited by the length of spiral conveyor which can be conveniently supported and used. As an example, the use of a spiral conveyor of a length much greater than thirty feet may be considered impractical, due to the fact that a longer conveyor would require a correspondingly heavier supporting shaft, correspondingly heavier bearings, and would add a proportionally greater weight. Thus, while it is understood that such limitations are only arbitrary, there are indeed actual practical limits to the length of the cooking chambers and spiral conveyors. It is usually easier to provide a series of connected cooking chambers than to elongate a single chamber beyond predetermined limits.

The length of the cooking chamber depends partially upon the type of pulp which is to be formed therein. If a pulp such as that used in the formation of the nine point paperboard used in fabrication of corrugated board is to be produced, the chamber may be relatively short,

as a higher lignin content is desirable. However, in the formation of bleached pulp, where a lower lignin content is necessary, a much longer cooking time is preferable. Obviously, the shorter the cooking period, the lower the cost of the process, and accordingly, a minimum cooking time is desirable.

it is usually impossible or impractical to produce chips which are identical in size and thickness. Therefore, while a cooking period of a predetermined length will produce complete penetration of the great majority of the chip-s, small proportion of thicker chips may not be completely penetrated, leaving a small percentage of raw fibers in the heart or core of the chips. This difficulty may be overcome by cooking the chips for a longer period; but in some types of product this longer cooking period may not be necessary or economically advantageous. By lengthening the cooking period, a greater percentage of the lignin will be removed from the pulp, which is desirable in some pulps and not so desirable or necessary in others.

From the foregoing discussion, it will be evident that the apparatus may be provided with a single cooking or preheating chamber, or a series of them, depending upon the type of product to be made. By providing a series of connected chambers, a high volume of production may be maintained without the necessity of reducing the cooking time. When the cooking time is relatively long, the feed screw of a single cylinder would travel so slowly that the volume of production would be greatly reduced.

It is also possible to provide pressure seals between various cooking chambers, if it is desired. However, in most instances the temperatures in the impregnating and the cooking chambers can be properly differentiated without maintaining pressure differentials. In the drawings, a transfer valve to and a suitable driving motor 40 is shown between the chambers 3 and 35, with connecting pipes 41 and 42 between the chambers 35, 36, and 36, 37. These connecting pipes could also include transfer valves such as 40 if desired, or, alternatively, the transfer valve 40 could be omitted if preferred.

The outlet end of the lowermost cylinder or tube 37 is connected by a downwardly extending connection 43 to a lateral connection 44 which preferably includes a feed screw 45 leading to a defibrator C of the Asplund type. This defibrator is a patented apparatus, being shown in Patent 2,145,851, and acts to thoroughly separate the fibers. The pulp remains under elevated pressure and temperature until the pulp leaves the defibrator, at which time it is usually exhausted to atmospheric pressure.

As is evident from the drawings, the cooking chambers 34, 35, 36, and 37, are provided with spiral conveyors 47, 49, 50, and 51, respectively, so as to convey the pulp at a uniform but variable speed through these chambers. These conveyors are driven by a suitable source of power 52 connected to the conveyors by a chain or chains 53. The arrangement shown is merely illustrative, and all of the conveyors may be gear connected to operate in unison if preferred. A conveyor motor 54 drives the outlet conveyor 31 in outlet pipe 30.

A steam supply pipe 55 is connected to branches 56 and 57. One branch 56 leads to the inlet pipe 19, above the'liquid level therein, and the other branch 57 communicates with the outlet pipe 30 above the liquid level indicated by the dotted line 32 therein. These pipes cause steam to exert a pressure upon the treating liquid within the impregnating chamber 20 without raising the temperature of the liquid to an excessive degree. Specific examples will be more clearly described.

Steam is also supplied to the cooking or preheating chambers 34, 35, 36, and 37. Steam manifolds 59 are shown extending along these chambers from the inlet end thereof, and steam connections 60 lead from the manifolds 59 to the interior of the chambers. This arrangement is provided to equalize the temperature within the cooking chambers from end to end thereof.

As specific examples of the manner in which the process may be carried out, aspen chips about seven-sixteenths of an inch in length and about three-sixteenths inch in thickness are supplied to the inlet pipe 10. The chips vary in width over substantial limits. The chips usually contain fifty percent to eighty percent oven dry Wood, or contain from twenty percent to fifty percent moisture.

The chips pass through the transfer valve 11 and are, for a short period of time, exposed to a pressure of perhaps one hundred twenty-five pounds steam pressure at a corresponding temperature of three hundred forty-four degrees Fahrenheit. The time during which the chips are subject to this temperature and pressure is insufficient to burn or injure the chips, and insufiicient to tend to cook them, the time normally being limited to a few seconds.

The chips then are urged into the liquor within the impregnating chamber 2%. This liquor comprises a solution of, for example, one hundred fifty grams of sodium sulphite per liter of water. Also, in solution is forty-five grams of sodium hydroxide per liter of water.

The purpose of this arrangement is to consume between ten and twelve percent sodium sulphite based on the oven dry wood inserted. The sodium hydroxide assists in breaking down the wood structure and acts as a buffering agent to maintain the pH of the solution at about 7.

The chips are retained in the impregnating chamber for a time sufficient to produce the degree of saturation desired without coo-king the chips. in the present example, the chips are cooled by impregnation, the average temperature of the liquor being well above room temperatures, or about two hundred forty degrees Fahrenheit, and the time being approximately fifteen minutes. During this time, impregnation is substantially complete.

Heating the chips has a tendency to expand the air cells in the wood, while the pressure tends to compress these cells. When the chips enter the impregnating liquid, they are cooled sutficiently to cause a partial vacuum to be created within the chips, tending to draw the impregnating liquid into the chips.

The chips are elevated above the liquid level, and drop into a single cooking chamber 34. During this time, the chips are subjected to the same pressure (one hundred twenty-five pounds) and at a corresponding saturated steam pressure of about three hundred forty-four degrees Fahrenheit. The spiral conveyor operates at a proper speed to maintain the chips in the chamber 34 for a time of between fifteen and twenty minutes. The chips are thoroughly preheated during this time,'entering the chamber at about thirty percent oven dry wood, and leaving at about twenty-five percent over dry wood, the increase in moisture content being due to condensation. While still maintained at the same pressure and temperature, the chips are directed through the connection 43, the connection 44, and into the defibrator C. After defibration, the fibers pass through an orifice to atmospheric pressure.

To tabulate the above example, the conditions may be listed as follows:

1 Percentage of sodium sulphite is based on amount of oven dry wood.

As a second example of a pulp made by the process, bleached pulp, or pulp prepared for bleaching, may be de- 6 scribed. This process is very similar to that previously described; but as any discolored fibers resulting from incomplete cooking will detract from the quality of the pulp, the cooking time is lengthened.

Wood chips about three sixteenths inch in thickness are fed to the transfer valve and into the inlet 19. For a few seconds these chips are subjected to one hundred fifty pounds pressure and a corresponding saturated steam temperature of about three hundred fifty-eight degrees Fahrenheit. The chips are then submerged in liquor which is of an average temperature of about two hundred forty-five degrees Fahrenheit. Actual temperature readings of the surface temperatures vary, highest reading being at the inlet end (perhaps two hundred fifty to two hundred seventy-five degrees Fahrenheit) and being lower at the outlet end (perhaps two hundred forty to two hundred fifty degrees Fahrenheit).

The liquor in which the chips are impregnated may comprise two hundred fifty grams of sodium sulphite per liter of water. impregnation of the chips is complete in fifteen to twenty minutes. The impregnated chips are Withdrawn from the liquor and delivered to the cooking chamber where they remain for about forty-five to sixty minutes. In order to provide a regular how of pulp, two or three cooking chambers such as 34 and 35, or 34, 35, and 36, are used in series.

in this example, a greater amount of sodium sulphite is absorbed by the chips, the amount consumed being about fourteen to fifteen percent based on the oven dry wood. The cooked chips are defibrated while still subjected to elevated temperatures and pressures, as in the previous example.

Kraft pulp may also be produced through the use of proper impregnating liquor. For example, the chips may be impregnated with a liquor as follows:

Active alkali as sodium hydroxide grams per liter 96 Causticity percent 74 Sulphidity do 32.9 insert ingredients or impurities do 3.1

The chips are fed through the transfer valve 11 and subjected for a short time to one hundred fifty pounds per square inch pressure and a corresponding saturated steam temperature. The chips are then immersed in the liquor, and conveyed through the impregnating chamber while at a hydrostatic pressure of substantially one hundred fifty pounds, the liquor being approximately at an average temperature of two hundred forty-five degrees Fahrenheit. The time required for impregnation is approximately fifteen minutes.

The chips are then conveyed through the outlet 34 and into the cooking chamber where they are cooked for ap proximately the same length of time (fifteen minutes). While cooking they are subjected to a pressure of one hundred fifty pounds per square inch and a corresponding saturated steam pressure.

By using a liquor containing sixty to seventy grams per liter active chemical as sodium hydroxide, and substituting this liquor for that used in the production of kreft, a soda cook may be provided. The pressures and temperatures may be approximately the same as those in the last example.

In a similar manner, various types of pulp maybe produced by varying the pressures, temperatures, and liquor. In general, the higher the steam pressure, the quicker the chips will be prepared for defibration. For example, tests have been made using as much as three hundred pounds hydrostatic pressure upon the chips being impregnated, and impregnation was complete in about five minutes, at about one hundred fifty degrees Fahrenheit. Pressure as low as one hundred pounds have also been successfully employed.

v By placing the chips under hydrostatic pressure while being impregnated, the pressure necessary to impregnate the chips is produced, while at the same time the temperature is not excessive. The system has the advantage that the only pressure seal necessary is at the inlet transfer valve where the chips are relatively dry and may be easily handled. The short heating period between the transfer valve and the impregnation chamber also has been found important, as the impregnating liquor is actually drawn into the chips when they are submerged. The cooking operation atelevated temperatures may then take place without the requirement of pressure locks or seals between these operations.

In usual practice, it has not been found necessary tosubject the chips to zones of different pressure. However, in some instances it may be difficult to increase the hydrostatic pressure in the impregnating chamber without raising the temperature above that desired in this portion of the apparatus. In this case, the partially cooked chips may pass through a second transfer valve such as 40 to a cooking area of higher temperatures and pressures. Also, if necessary, the cooking zone can be divided into a series of chambers of different increasing temperatures and pressures.

In accordance with the patent statutes, the principles of construction and operation of the method of making pulp have been described and while it has been endeavored to set forth the best embodiment thereof, it is desired to have it understood that obvious changes may be made within the scope of the following claims without departing from the spirit of the present invention.

I claim:

1. A method of producing pulp from wood chips including the continuous steps of immersing the chips below the liquid level of impregnating liquor at an above atmospheric hydrostatic pressure and at an above room temperature elevated temperature which is substantially below the temperature of saturated steam at the pressure employed by maintaining steam under pressure upon the liquid level of the liquor, and then cooking the impregnated chips by the action of temperatures substantially corresponding to the temperature of saturated steam at the pressure employed to produce pulp.

2. The process described in claim 1 and including the further step of defibrating the chips after they have been subjected to the higher temperature, while still maintaining the same pressure.

3. A method of producing pulp from wood chips including the continuous steps of subjecting the chips for a short period to the action of above atmospheric pressure at a temperature corresponding to that of saturated steam at that temperature, the temperature being surficient to cook the chips, but the period being insufficient to materially cook the chips, immersing the heated chips below the surface of impregnating liquor at a hydrostatic pressure equal to the above mentioned above atmospheric pressure, the liquor being at an above room temperature substantially below the first mentioned temperature, and cooking the impregnated chips at said elevated pressure and at a temperature substantially equal to the first mentioned temperature.

4. The method of producing pulp from wood chips including the continuous steps of subjecting the raw chips to steam pressure and a corresponding saturated steam pressure for a short interval of time insufiicient to tend to cook the chips, the pressure being substantially at least one hundred pounds per square inch, immersing the chips below the surface of liquor at a hydrostatic pressure substantially equal to said steam pressure, moving the chips from immersion, submitting the chips again to said steam pressure and corresponding saturated steam temperature until the impregnated chips are cooked, and defibrating the chips while still at an elevated pressure and temperature.

5. The process described in claim 4 and in which the liquor includes a solution of sodium sulphite.

6. The method described in claim 4 and in which the chips are moved continuously through the steps described.

7. The process described in claim 4 and in which the liquor includes water, sodium sulphite, and sodium hydroxide.

References Cited in the file of this patent UNITED STATES PATENTS 40,696 Lyman Nov. 24, 1863 1,679,336 Dunbar July 31, 1928 1,880,587 Traquair et al. Oct. 4, 1932 1,915,812 Wollenberg June 27, 1933 1,938,802 Braun et al Dec. 12, 1933 2,008,892 Asplund July 23, 1935 2,024,689 Groombridge et al Dec. 17, 1935 2,145,851 Asplund Feb. 7, 1939 2,323,194 Beveridge et al June 29, 1943 2,422,522 Beveridge June 17, 1947 2,425,024 Beveridge Aug. 5, 1947 2,427,495 Deuchler Sept. 16, 1947 2,474,862 Richter July 5, 1949 2,673,690 Segl Mar. 30, 1954

Claims (1)

1. A METHOD OF PRODUCING PULP FROM WOOD CHIPS INCLUDING THE CONTINUOUS STEPS OF IMMERSING THE CHIPS BELOW THE LIQUID LEVEL OF IMPREGNATING LIQUOR AT AN ABOVE ATMOSPHERIC HYDROSTATIC PRESSURE AND AT AN ABOVE ROOM TEMPERATURE ELEVATED TEMPERATURE WHICH IS SUBSTANTIALLY BELOW THE TEMPERATURE OD SATURATED STEAM AT THE PRESSURE EMPLOYED BY MAINING STEAM UNDER THE PRESSURE UPON THE LIQUID LEVEL OF THE LIQUOR, AND THEN COOKING THE IMPREGNATED CHIPS BY THE ACTION OF TEMPERATURES SUBSTANTIALLY CORRESPONDING TO THE TEMPERATURE OF SATURATED STEAM AT THE PRESSURE EMPLOYED TO PRODUCE PULP.

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