US3537953A - Pulping process including the transfer of wood chips from a first to a second digesting liquor - Google Patents

Description

Nov. 3, 1970 K. J. BROWN ETAL 3,537,953

PULPING PROCESS INCLUDING THE TRANSFER OF WOOD CHIPS FROM A FIRST TO A SECOND DIGESTING LIQUOR Filed Nov. 20, 1967 2 Sheets-Sheet 1 nuuqnn INVENTOR.

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Nov. 3, 1970 K. J. BROWN ETAL 3,537,953

PULPING PROCESS INCLUDING THE TRANSFER OF WOOD CHIPS FROM A FIRST TO A SECOND DIGESTING LIQUOR Filed Nov. 20, 1967 2 Sheets-Sheet 2 FICLZ.

ATTORNE Y.

TORS.

United States Patent O 11.5. CI. 162-52 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a pulping process for making pulp from wood chips. The process consists of mixing wood chips with a first treating liquor under pressure and thereafter partially converting said chips to pulp, transferring the chips to a second liquor without comingling the two liquors by the use of a transfer valve in which the chips are placed in a pocket which rotates past a series of ports, wherein one port the chips are introduced to the valve, the next port permits drainage of the first liquid, the following port allows for low pressure addition of a second treating liquor and a next port permits high pressure treating liquor to withdraw the chips, and finally heating the partially converted chips in the presence of the second liquor to fully convert the chips to pulp.

An object of this invention is to provide a novel pulping process.

A more specific object of this invention is to provide a process for treating wood chips with two liquors.

Another object of this invention is to treat wood chips with two treating liquors under pressure.

Yet another object of this invention is to treat the wood chips with the two treating liquors without mixing or contaminating the two liquors.

Still another object of this invention is to treat wood chips in a totally closed system.

In accordance with the invention, it has now been discovered that the above and other objects of this invention may be accomplished in the following manner.

Basically, the process consists of a series of steps, the first of which is to introduce wood chips to a first treating liquor under pressure to form a first reaction mixture. Then the first reaction mixture is heated under pressure to partially convert the wood chips to pulp. Next, the partially converted chips are transferred from the first liquor to a second treating liquor to form a second reaction mixture. This transfer is accomplished by the use of a transfer valve wherein the chips are collected in a rotating pocket, carried past a port where the first liquor is drained from the chips, carried past a next port Whereby the second treating liquor is introduced under low pressure, and finally carried to an exit port whereby the second liquor withdraws the chips from the valve under high pressure. Finally, the second reaction mixture is heated under pressure to complete conversion of the chips into pulp and the pulp is withdrawn from the treating liquor. In an embodiment of this invention, a quantity of the first liquor is introduced into the pocket of the transfer valve prior to introduction of the first reaction mixture to cushion the shock of the high pressure system filling the pocket. Also, in an embodiment of this invention, the second fluid remaining in the pocket after withdrawal of the chips from the valve is drained to prohibit any co-mingling of the two treating liquors.

In a preferred embodiment of this invention, the first reaction mixture containing the first treating liquor and the wood chips is formed by first forming a mixture of Patented Nov. 3, 1970 chips and water. After this first mixture of chips and water is formed, the chips are transferred to the treating liquor by the use of a transfer valve similar to that employed when the chips are transferred from the first treating liquor to the second treating liquor. The purpose of this second transfer valve is to insure a perfectly closed system in which the first treating liquor is isolated from external atmosphere and pressure.

In the drawings:

FIG. 1 is a flow diagram showing one emboiment of the present invention.

FIG. 2 is a flow diagram showing a second embodiment which is located at section AA of FIG. 1.

As shown in FIG. 1, wood chips are introduced to a feeder valve by placing the chips in a hopper 10 and allowing the conveyor 11 to deposit the chips into the feeder valve 14. A quantity of a first treating liquor is introduced into the feeder valve 14 through pipe 16 wherein a first reaction mixture is formed. This reaction mixture is withdrawn from the feeder valve 14 through pipe 18 and is introduced into a pretreater 20 through inlet 22. The amount of wood chips contained in the treating liquor is relatively low and a major portion of the treating liquor is returned through exit 24 and line 16 to feeder valve 14 where more chips are brought into the system and more of the first reaction mixture is formed. As the chips pass through the pretreater 20, the chips are partially converted into pulp. This is accomplished by heating the reaction mixtures, such as by heater 25. It is preferred to heat this first reaction mixture at a temperature ranging from about 100 C. to 140 C. at a pressure ranging approximately from about 100 p.s.i. to 200 p.s.i. The heating step takes approximately 20 minutes to 120 minutes. At this point, the wood chips are partially converted into pulp. After the reaction mixture has been heated as above, it is preferable to cool the mixture prior to transfer and further processing. Ideally, the reaction mixture should be cooled to approximately to C. after the heating step and prior to transfer of the mixture to the following steps. The cooled and partially converted wood chips suspended in the first liquor are withdrawn from the pretreater 20 through outlet 26 and are introduced into a transfer valve 28. This transfer valve is described and claimed in a co'pending commonly owned application S.N. 684,258 filed of even dated and now Pat. No. 3,433,- 392.

Basically, the transfer valve contains a rotating inner member which contains pockets, such as those shown in FIG. 1 and identified as pockets 30, 32, 34, 36, 38 and 40. At each of these positions, the pockets communicate with ports which permit introduction and removal of various fluids.

Since the first reaction mixture coming from outlet 26 of pretreater 20 is under high pressure, it is a preferred embodiment to fill pocket 30 with a quantity of first treating liquor contained in tank 43. Quantities of the first treating liquor under low pressure are. pumped through pipe 42 to fill pocket 30, with an overflow re;

the wood chips coming from outlet 26 of pretreater 20 are introduced into pocket 32. The already present first treating liquor cushions the shock of the high pressure reaction mixture and permits substantially longer lifefor the valve. Pocket 32 contains a screen which partially covers the area communicating between the pocket 32 and the port, whereby the treating mixture containing the chips is allowed to enter the pocket, but only the treating liquor is allowed to exit therefrom through pipe 46.-

Further rotation of the pocket to pocket 34 permits draining of the residual first treating liquor through lines 3 48 and 50 which return the first treating solvent to tank 43. At this point, the wood chips are effectively free from treating solution since the ratio of treating solution employed to wood chips is fairly high. Next the pocket rotates to the position shown by pocket 36 where a quantity of the second treating liquor is inroduced from tank 53 through line 52. Overflow liquor is returned to tank 53 through pipe 54. At this point, the pocket contains wood chips and a quantity of second treating liquor which is present to absorb the shock of the addition of high pressure second treating liquor.

Rotation of the pocket to the position shown by pocket 38 permits withdrawal of the chips from the system. High pressure second treating liquor is introduced through pipe 56 into pocket 38, whereby the chips are withdrawn and passed to the digester 64 through pipe 58 and introduced into digester 64 at inlet 66. Since the quantity of second treating liquor is substantially greater than the amount of wood chips carried, much of the second treating liquor is recycled through exit 68 of digester 64 and back to pocket 38.

Now that the second reaction mixture has been formed by the partially converted chips and the second treating liquor, the balance of the reaction is carried out in the digester 64. It is necessary to heat the reaction mixture to bring about the conversion of the chips to wood pulp, such as by the use of the heater 70. Normally this heating period will last from 60 to 120 minutes at a temperature ranging from 140 to 200 C. and at pressure of 12.0 to 250 p.s.i. Due to the large quantities of wood chips being processed, a certain time lag is necessary in some instances to bring the reaction mixture up to temperature. Preferably, this is accomplished in approximately 30 to 90 minutes.

After the wood chips have been completely converted into pulp, it is necessary or desirable to cool the reaction mixture by counter-current washing with quantities of the second treating liquor, as shown by cooler 72. Normally, this cooling period lasts from approximately 30 to 90 minutes. At this point, the chips have been converted into pulp and may be withdrawn from the systern through pipe 74.

In a preferred embodiment of the present invention, additional care must be taken to preserve the first treating liquor. As the process has been described above, the second treating liquor is effectively isolated from contamination by other materials and is contained in a closed system. Because of the operation of most feeder valves, it is possible for outside air to contaminate the first treating liquor. This is particularly undesirable when the first treating liquor is sensitive to oxygen, or, in some instances contains dissolved gases which have vapor pressures lower than air. Recent developments in the pulping industry include systems wherein certain gases are dissolved in a pretreating liquor or first treating liquor to catalyze and assist in the partial conversion of the wood chips to pulp.

Shown in FIG. 2 is a preferred embodiments of the present invention wherein the first treating liquor is effec tively maintained in a closed system. With reference to FIG. 1, pipes 16 and 18 are sectioned at the point shown in FIG. 1 as A-A. At this point, the system shown by the flow diagram of FIG. 2 is inserted. The wood chips are inserted into feeder value 14 of FIG. 1 and mixed with water or other inert fluids. This suspension of chips is then introduced into a transfer valve of the type described above whereby the chips are transferred to a quantity of the first treating liquor whereby the first reaction liquor described above is then transferred to pretreater 20 of FIG. 1.

As shown in FIG. 2, the pipe 18 transfers the suspension of wood chips in water to transfer valve 76. The operation of this valve is similar to the transfer valve 28 of FIG. 1 and the above mentioned co-pending commonly owned application filed of even date again describes the nature of the valve.

In the operation of transfer valve 76, various pockets 78, 80, 82, 84, 86 and 88 rotate about six ports which are in communication with the pockets shown in FIG. 2. A supply of water or other fluid being used to introduce the wood chips to the system is stored in tank 99. a quantity of this water is piped through pipe 90 to fill pocket 78, with an overflow line returning to tank 99 through pipe 92. Rotation of the pocket through the position shown by pocket 80 permits introduction of the wood chips and water under relatively high pressure. The presence of low pressure water supplied by tank 99 as described above permits the introduction of high pressure suspensions through pipe 18 at inlet 94 of the port in communication with pocket 80 without the accompanying shock of a high pressure fiuid filling an empty pocket. This is done to increase the useful life of the valve. Again, as described above, pocket 80 contains a screen which permits the inlet 94 to introduce the chips and water while permitting only water to be withdrawn from outlet 96 and return the water through pipe 16.

Next, the pocket rotates to the position shown by pocket 82 whereby the water remaining in pocket 82 is drained through lines 98 and 100 to tank 99. At this point, the wood chips are effectively free from major quantities of water.

Rotation of the pocket to the position shown by pocket 84 permits the first introduction of the first treating liquor. Quantities of this liquor, stored in tank 103, are passed through pipe 102 to fill pocket 84, with overflow being returned to tank 103 through pipe 104. This is done under low pressure.

As the pocket rotates to the pocket 86, quantities of first treating liquor under high pressure are introduced at point 106 through pipe 16 to withdraw the chips contained in pocket 86. These withdrawn chips exit through outlet 108 and are carried in pipe 18 to the pretreater 20 shown in FIG. 1 whereupon they are introduced to the pretreater 20 through inlet 22.

Final rotation of the pocket to the position shown by pocket 88 permits drainage of the pocketthrough line 112 to tank 103, thereby maintaining a closed system and preventing co-mingling of the Water and the first treating liquor. This draining may be accomplished as shown in FIG. 2 by introduction of fluid through pipe 110, thereby forcing the liquor contained in pocket 88 through line 112 to tank 103 or, in the alternative, line 110 may be a second drain line connecting with line 112 or going directly to tank 103.

Thus the wood chips have been introduced into the system to form the first reaction mixture without contamination by outside atmosphere. The first treating liquor has not been comingled with any other fluids, and any gases dissolved in the first treating liquid and maintained therein by the pressure of the system have not been permitted to escape. This is important not only from the economic loss occasioned by escaping gases, but as an additional safety factor when these gases may be toxic or otherwise undesirable pollutants.

It will become apparent to those skilled in the art that many modifications and further embodiments of the present invention may be employed without departing from the spirit of the invention.

What is claimed is:

1. A process for preparing pulp from wood chips, comprising the steps of:

introducing wood chips to a first treating liquor under pressure to form a first reaction mixture;

heating said first mixture under pressure to partially convert said chips to pulp;

transferring said partially converted chips from said first liquor to a second treating liquor to form a second reaction mixture by introducing said first mixture into a transfer valve in which said partially converted chips are collected in a rotating pocket, carried past a port through which said first liquor is drained from said partially converted chips, carried past a next port through which a second treating liquor under low pressure is added to said partially converted chips, and carried to an exit port through which said second liquor withdraws said partially converted chips from said valve under high pressure with the proviso that said pocket is filled with said first liquor under low pressure prior to introduction of said first mixture thereto in sulficient quantity to cushion the shock of said first mixture;

heating said second mixture under pressure to complete conversion of said partially converted chips into pulp; and

withdrawing said pulp from said second treating liquor.

2. The process of claim 1 wherein the second fluid remaining in said pocket after withdrawal of said partially converted chips from said valve is drained therefrom prior to introduction of any first treating liquor into said pocket, thereby preventing substantially any co-rningling of said first treating liquor with said second treating liquor.

3. The process of claim 2 wherein said first reaction mixture is heated to from 100 to 140 C. at a pressure of from 100 to 200 p.s.i. for a period of time ranging from 20 minutes to 120 minutes.

4. The process of claim 3 wherein said first reaction mixture is cooled to about 80 to 100 C. after said heating step and prior to transfer said mixture to said transfer valve.

5. The process of claim 2 wherein said second reaction mixture is heated for from 60 to 120 minutes at a tem perature of 140 to 200 C. and at a pressure of from 120 to 250 p.s.i.

6. The process of claim 5 wherein the time required to bring said second reaction mixture to said temperature ranges from 30 to 90 minutes.

7. The process of claim 1 wherein said chips are cooled by counter-current washing by cooled second liquor for from to minutes prior to withdrawal of the chips from said second treating liquor.

8 The process of claim 1 wherein said first reaction mixture is formed by first forming a mixture of chips and water, and therefore transferring said chips to said first treating liquor by introducing said mixture of chips and water to a transfer valve in which said chips are collected in a rotating pocket, carried past a port through which said water is drained from said chips, carried past a next port through which said first treating liquor is introduced under low pressure to said pocket, and carried past an exit port, through which said first treating liquor withdraws said chips from said valve under high pressure, with the proviso that a quantity of water is introduced into said pocket prior to introduction of said mixture of water and chips, and with the further proviso that all of the first treating liquor remaining in said pocket after withdrawal of said chips from said valve is drained therefrom prior to introduction of any water into said pocket, thereby preventing substantially all co-mingling of said water with said first treating liquor.

References Cited UNITED STATES PATENTS 3,180,789 4/1965 Fuchiwaki 162-17 3,383,277 5/1968 Gordon et al. l62-l9 3,411,986 11/1968 Buchberger et al. 162-246 3,445,328 5/1969 Laakso l62-19 S. LEON BASHORE, Primary Examiner T. G. SCAVONE, Assistant Examiner US. Cl. X.R. l62l9, 60, 246

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