US1969421A - Production of paper pulp - Google Patents

Description

Aug 7, 1934. P. A. PAULSON 1,969,421

PRODUCTION PAPER PULP Filed Nov. 5. 1932 AdLme Patented Aug. 7, 1934y UNITED STATES PATENT OFFICE This invention relates` to' the production of paper pulp and particularly to improvements in the sulphite process.

In the manufacture of paper making pulp by the sulphite process the cooking of the wood with the bisulphite acid and steamV usually takes place in a battery of two or more digesters. 'I'he time allowed for the lling, cooking and emptying a digester is vdivided by the number of digesters in use so that the starting of a digester takes place at equal intervals. If, for instance, twelve hours is allowed for a complete cycle, and there are four digesters, then a digester is started every three hours. It thus follows that there are always three digesters cooking when one is being started'.

The cooking takes place 'under a pressurel of from 60 to 80 lbs. per square inch. The digesters are equipped at the bottom with steam pipes to supply the necessary steam for obtaining the required temperature and pressure.

In common practice )the digesters are also equipped with relief valves at the top. These valves serve to relieve acid gases and liquor from the digesters during the cooking process in order that sufficient steam may find room in the digesters to raise the charge to the required temperature. 'I'he relief valves are as a rule operated by hand and require skillful operators as well as considerable attention if the best results are to be obtained.

A principal object of the invention is to provide a method of operation and a system of apparatus which will eliminate the necessity for highly skilled operators, and will render the various phases of the cooking process nearly automatic in their operation.

A further object of the invention is to provide a method of operation in which the conditions will be more regular and uniform than in the previously known methods.

Another object of Athe invention is to decrease the time' required for the cooking cycle of operations.

A further object of the invention is to provide for the impregnation of the wood chips with acid liquor of the greatest possible strength.

Briefly, the invention comprises the provision of a common relief line into which the individual relief valves ofa battery of digesters open, and which is provided with an automatic pressure control device whereby a uniform pressure will always be maintained in the common relief line. The invention also comprises the provision of means for supplying to each digester a uniform predetermined flow of steam during the rst stage of the cooking period until the desired teniperature'is reached, and thereafter supplying a smaller uniform predetermined flow of steam sufficient to maintain the desired temperature.

'Ihe invention makes it unnecessary for the operator to adjust either of the relief valves or steam supply valves. The operator has only to open the relief valves wide and the automatic pressure 'regulator on the common relief main 66 will insure a. uniform pressure on all of the digesters at the same time.

The provision of a common relief main and of two different steam supply means of predetermined capacity makes it possible uniformly and regularly to bring the digesters to full working pressure and temperature in the shortest possible time.

Furthermore, by buildingy up the pressure in a digester starting the cycle, by means of acid relief gases from other digesters of the battery, it results that the wood chips vare impregnated with acid liquid of the highest possible strength and at the maximum'pressure, since the attaining of the necessary pressureis not dependent upon the supplying' of steam to the digester whichhas the effect of weakening the strength of the acid in proportion as it builds up the temperature.

In ordinary practice it takes from two to six hours to bring a digester to full working pressure. With my method of the invention it can be done in from ten to fifteen minutes. When the digester has been filled with chips and acid, the operator will open the relief valve and the pressure from the other digesters already relieving will enter the newly filled digester at the top and bring up the pressure on it almost immediately.

The steam entering the bottom of the digester is madeto go through a nozzle or orifice of a predetermined size that will bring the contents of the digester to the desired temperature in a specified time. A smaller nozzle or orifice that will just maintain the correct temperature is then used until the cook is finished.

The invention will be more particularly described for the purpose of illustration with reference to the accompanying drawing which is a diagrammatic representation of a system of ap- -paratus embodying the principles of the invention.

The apparatus shown comprises a battery of three digesters ,1, each having an acid supply line 2, and a discharge line 3 leading to the blowpit. Each digester is provided at the top with a relief line and valve 4 leading into a com- 110 mon relief main 5, leading to an acid reclaiming system, not shown. In therelief main between the battery of digesters and the acid reclaiming system is located an automatic pressure control valve 6, adjusted to maintain in the relief main the pressure necessary for proper cooking.

Each digester is supplied with steam inlets '7 at the bottom. The steam inlets are'fed from a source of steam 8, through an arrangement which permits the steam to be supplied either through a small orifice of predetermined capacity S), or a larger orifice of predetermined capacitylO.

A manhole opening for admitting the wood chips into the digester and cover 1l are provided oneach digester. l

'I'he method of operation after the establishment of a regular cycle may be as follows: After an emptied digester is filled with Wood chips and acid andthe covervll has been bolted on, the relief valve 4, which has been closed during ythe emptying and filling operations, is opened Wide. Acid gases and liquor from the other digesters which are at this time in the cooking stage enter the newly filled digester through valve 4 and bring it up to full pressure almost immediately. It is to be noted that the operator does not have to manipulate orv adjust valve 4 for any purpose until it is closed at the vend of the cooking operation.

After relief valve 4 is opened, the operator opens the valve supplying steam to the digester through the larger orifice l0, the size of which is calculated to supply sufficient steam to bring the contents of 'the digester to the desired maximum temperature in. a predetermined time. After the maximum temperature is reached the valve supplying steam through orifice 10 is closed and that supplying steam through the smaller orifice 9 is opened. The size -of the smaller orice is calculated to admit suflicient steam to maintain the contents of the digester at the desired maximum temperature.

I claim: y

1. A method of making wood pulp by the sulphite process which comprises filling a digester forming one of a battery of digesters with Wood chips and bisulpliite liquor, bringing the upper portion of said digester into free communication with the upper portions of the other digesters of the battery which are undergoing cooking, passing steam into said digester at a predetermined constant rate until the contents of the digester reach the desired maximum temperature, and thereafter passing steam into said digester at a lower predetermined constant rate adapted to maintain the contents of the digester at the .desired maximum temperature.

2. Apparatus for the manufacture of Wood pulp by the sulphite process including a battery of digesters, a common header, means for bringing the upper portion of each of said digesters into communication with said common header for the passage of gases and liquids between said digesters, and means for maintaining a predetermined maximum pressure on said common header.

3. Apparatus for the manufacture of Wood pulp by the sulphite process including a battery of digesters, means for supplying steam to said digesters, said means including a xed orifice of predetermined size adapted to supply steam at a rate sufficient to bring the contents of the digesters to the desired temperature in a predetermined period of time, and a second fixed orifice of predetermined sizeadapted to supply steam at a rate sufficient to maintain the contents of the digesters at the desired temperature, a common header, means for bringing the upper portion of each of said digesters into communication with said common header for the passage of gases and liquids between said digesters, and means for maintaining a predetermined maximum pressure on said common header.

4. A method of making wood pulp by the sulphite process which comprises filling a digester forming one of a battery 0f digesters with wood chips and bisulphite liquor, bringing the upper portion of said digester into free communication with the upper portions of the other digesters of the battery which are undergoing cooking' and thereafter supplying steam to said digester while maintaining said free communication throughout the cooking period whereby all of the digesters undergoing cooking are maintained at the same pressure.y

5. In the production of wood pulp by the suli

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