US3076739A

US3076739A - Manufacture of pulp from fibrous substances

Info

Publication number: US3076739A
Application number: US754317A
Authority: US
Inventors: Nettel Frederick
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-08-11
Filing date: 1958-08-11
Publication date: 1963-02-05
Anticipated expiration: 1980-02-05

Description

Feb. 5, 1963' F. NETTEL MANUFACTURE OF PULP mou FIBROUS SUBSTANCES Filed Aug. 11, 1958 United States Patent Ofiice 3,076,739 Patented Feb. 5, 1963 3,076,739 MANUFACTURE OF PULP FROM FIBROUS SUBSTANCES Frederick Nettel, 173 Chapel Road, Manhasset, N.Y.

Filed Aug. 11, 1958, Ser. No. 754,317 7 Claims. (Cl. 162--17) This invention deals with improvements in the conversion of fibrous substances, in particular wood, straw, bagasse for examples, into pulp. Known processes work either on the batch system or the continuous system. In the batch system the raw material in form of chips or cuttings is fed into large so-called digester containers where it is subjected to the action of suitable chemicals (liquor) in the presence of steam at pressures mostly above atmospheric for long periods, being discharged periodically. Continuous digesters use tubes through which the raw material is moved by mechanical means, mostly screws. The disadvantages of the batch digesters are principally in the slowness of the action, the losses incurred in steam and time-when filling them, heating them and discharging them. The continuous digesters are more flexible in operation, give more uniform pulp, but they require complicated, expensive and often unreliable means for feeding the raw material into the pressure space of the digesters consisting of one or more tubes through which the processed material is moved mostly by screws arranged inside the digester tubes. The devices used for bringing the raw material into the pressure space are either power-driven screws, or power-driven multi-cell rotary feeders. Such devices require much power and have to be designed to operate at widely different speeds to regulate the digester output, which makes them unduly expensive in first costs and in maintenance, because of wear.

It is known to be advantageous, and even necessary in some cases, to impregnate the raw chips before cooking. This is done in known continuous digesters either by presoaking the chips or cuttings with liquor prior to pressing the material into the pressure zone, or by using the first tube as impregnating tube into which liquor is fed together with steam. Pre-soaking at atmospheric pressure does not give satisfactory results because the liquor generally has to be at elevated temperatures to be chemically really effective.

Using the first tube as impregnating tube is expensive in the sense that the chips or cuttings do not have to be moved for good impregnation. Besides, the recovery of surplus liquor from the impregnating tube without clogging in the piping is known to cause difficulties. Re-circulating the liquid after re-fortificating it during the impregnation is known to be advantageous, economical and because it shortens the necessary cooking time.

It is the main object of this invention to provide in substantially continuous digesters simple and cheap means for impregnating the raw material, while at the same time eliminating the complicated and costly devices for bringing the material from a space (hopper) under atmospheric pressure into the pressure zone or zones of the digesters. In general it may be said that I attain this principal object of my invention, as well the other objects thereof which will hereinafter appear, by providing a plurality of closed chambers, preferably two in number, each with valved connections with a source of raw material, for example an open hopper, and with the pressure zone of the digester. The raw material is fed into said chambers in sequence, beginning with the first chamber with its valve to the digester closed. After filling is completed, the valve to the hopper is also closed and steam is admitted and liquor circulated through said chamber so that impregnation of the raw material is achieved. While this takes place, the valves of the second chamber to the digester and to the hopper were kept closed, however, when the impregnation in the first chamber starts, the valve of the second chamber to the hopper is opened and filling starts, and when completed, impregnation in the second chamber proceeds in the same manner as described for the first chamber. In the meantime impregnation in the first chamber has been completed to a desired degree, whereupon surplus liquor is drained from it and then its valved connection to the first digester tube of the continuous digester is opened and the contents discharged into the latter. When this discharge is completed, the impregnation in the second chamber has also been completed and surplus liquor is drained from it. Then the valved connection of the first chamber with the digester is closed and the valved connection of the second chamber with the digester tube is opened and feeding of the latter from the second chamber begins. Now the pressure in the first chamber is suitably relieved, its valved connection with the hopper opened and filling from the hopper is repeated. The cycle is now closed and is repeated in the same manner over and over again, resulting in a substantially continuous feeding of the digester, because the switching over of feeding from one chamber to the other which by themselves operate on the batch principles can be completed in a few seconds. It is another object of my invention to provide the valves for the material, liquor and steam with controls which operate these elements in the sequence indicated above, completing the operating cycle in a predetermined and adjustable time, called for the purposes of this specification the cycle time.

It is a further object of my invention to vary the cycle tilme in relationship with the required output of the digester p ant.

The volume (chip capacity) of the sluice-impregnation chambers is determined by the nature of the raw material to be processed, the type of liquor used, and the product quality desired. At present an impregnation period, i.e. a residence time of the chips in each chamber, of not less than ten percent of the whole pulping cycle time is preferred.

It is immaterial for the purposes of my invention whether impregnation takes place at the same or a pressure difierent from that which prevails in the digester tubes. Obviously, the pressure in the chambers will be equalized with that in the digester tubes when the valved connections to the latter are opened. It is also immaterial for the purposes of my invention what fibrous raw material is used and what chemical composition the liquor has.

In the drawing affixed to this specification and forming part thereof, an embodiment of this invention is illustrated diagrammatically by way of non-limiting example as follows:

It shows a digester with two closed sluicing and impregnation chambers and two cooking tubes. 1 is the open hopper with outlet conduits 2 and 3 and interposed gate valves 4 and 5. 6 and 7 are the two closed sluicing and impregnation chambers with outlet conduits 8 and 9 with interposed gate valves Y10 and 11. Conduits 8 and 9 discharge into conduit 12 which is connected to the one end of the first cooking tube 13 with internal screw 14- which is driven by a motor 15. At the other end of tube 13 a conduit 16 connects with the second cooking tube 17 which is essentially of the same design as the tube 13, also driven by a motor 18. The conduit 19 is connected with the discharger 26 for the cooked pulp which leaves the plant through pipe 21. At the lower end of the hopper 1 two valved

steam pipes

21 and 22 are provided to facilitate the discharge of the raw chips from the hopper. The

valved pipes

23 and 24 serve to admit steam under pressure into the chambers 6 and 7, and the valved pipe 25 permits to connect the chambers 6 and 7 with the atmosphere. Also connected with both chambars are liquor impregnating and circulating means consisting of

liquor tanks

26 and 27 from which liquor can be pumped by

pumps

28 and 29 driven by motors 28 and 29' through the

pipes

30 and 31 with valves 30 and 31' into the upper parts of the chambers 6 and 7. The liquor returns to said tanks via the

pipes

32 and 33. Fresh (white) liquor is fed into said tanks through the valved pipes 34 and 35. All the valves shown, with the exception of those in

pipes

21, 22, 34 and 35, are power operated from a common control cylinder 36, driven by a motor 37. This cylinder receives an operating medium, for example oil under pressure, at 38. The control connections to each of said valves are indicated diagrammatically only by broken lines. Steam may also be admitted to the first cooking tube through the valved pipe 3?. The drawing shows the plant at a moment when the chamber 7 is discharging into the digester While the chamher 6 is being filled. Obviously the valves in pipes 21, 22., 34 and 35 may also be power operated from the cylinder 36, if desired. Starting, and operating of the plant, assuming both chambers 6 and 7 empty and the gate valves 4, 5, 10 and 11 closed, proceeds after starting the motor 37 of the control as follows; gate valve 4 is opened and chamber 6 filled, assisted by steam jet from pipe 21. Gate valve 4 closed, steam admitted through pipe 23, pump 23 started by motor 28' and valve 30' opened, so that impregnation of the chips in the chamber 6 can proceed, and by keeping the pump in operation recirculation of the liquor impregnation is speeded and improved. In the meantime, after starting impregnation in chamber 6, gate valve is opened and filling of chamber 7 starts in the same way, and when completed, gate valve 5 is closed, steam admitted through pipe 24, pump 29 started by motor 29' and valve 31 opened, so that impregnation in the chamber 7 proceeds in the same manner as described above for chamber 6. In the meantime impregnation in the chamber 6 has been completed, whereupon the pump 28 is stopped, valve 30 closed, so that surplus liquor is drained from chamber 6 via pipe 32 into the liquor tank. Thereafter gate valve is opened and the impregnated chips are discharged into the cooking tube 13, assisted by steam jet from pipe 23. After the chamber 6 is empty, the impregnation which has been proceeding in the chamber 7', is also completed so that surplus liquor is drained from it via pipe 33 by stopping pump 29 and closing valve 31. Now gate valve 10 is closed and the steam pressure in the chamber 6 is relieved either to the atmosphere via pipe 25 with 3-way valve or by opening gate valve 4 slowly, thereby loosening and moistening the chips at the entrance of chamber 3, making it ready for the next filling. After gate valve 10 has been closed, the gate valve 11 is opened and discharge of the chamber 7 into the digester begins immediately, practically without interruption of the feeding of the digester. The feeding and impregnation cycle is now completed and is repeated by the filling of the chamber 6.

For regulating the output in continuous digesters it is known to regulate the speed of the motors and 18 and thereby the speed at which the pulp is moved through the cooking tubes by the screws 14. Obviously, it is necessary to correlate the feeding from the chambers 6 and 7 with the required output and this is achieved by my invention by regulating the speed of the motor 37 driving the control cylinder 36.

The use of sluices to introduce materials into a pressure zone is known per se. This invention teaches as new the combination of special sluice chambers With continuous digesters, and effecting an important part of the pulping process, i.e. the impregnation of the raw material, under the simultaneous application of liquor and steam under pressure Within two or more alternatingly operating sluice chambers, with predetermined time intervals provided for the impregnation, eliminating also the heavy 4 power demand for operating known devices such as screw feeders or multi-cell feeders.

Manifestly, variations may be resorted to, equivalents of parts introduced, and parts may be used without others Within the broad scope of my invention and its features.

Having now described my invention, I claim:

1. Method of producing pulp from fibrous materials in a continuous digester by subjecting them to the chemical action of a liquor and steam, comprising the steps of charging the comminuted raw material into the inlet of a first chamber, thereafter closing the inlet and outlet of said first chamber so as to isolate it, admitting steam and liquor under pressure into said isolated chamber, circulating the liquor through said first chamber in a substantially closed first circuit so as to impregnate the raw material therein, then draining surplus liquor from said first isolated chamber while maintaining the inlet closed, then opening the outlet of said first isolated chamber, then discharge the contents of said first chamber into the pressure zone of the digester, repeating said steps with a second chamber and the same digester, the filling of the second chamber with said raw material being timed to occur during the impregnation of said raw material in the first isolated chamber, and thereafter repeating the cycle alternatingly with the first and second chambers and with the same relative timing, with the liquor circulating through said second chamber means in a second substantially closed circuit.

2. Method of producing pulp from fibrous raw materials in a high pressure continuous digester by subjecting them to the chemical action of a liquor and steam, comprising the steps of closing the outlet of a first cham ber, charging the comminuted raw material into the inlet of said first chamber, thereafter closing the inlet of said first chamber so as to isolate it, admitting steam and liquor under low pressure into said isolated first chamber, circulating the liquor through said first chamber in a first substantially closed circuit so as to impregnate the raw material therein, then draining surplus liquor from said first isolated chamber while maintaining the inlet closed, opening the outlet of said first isolated chamber to the higher pressure zone of the digester so as to admit this higher pressure to the first chamber, then discharge the contents of said first chamber into the digester under the higher pressure, repeating said steps with the second chamber and the same digester, the filling of the second chamber with said raw material being timed to occur during the impregnation of said raw material in the first isolated chamber, and thereafter repeating the cycle alternatingly with the first and second chambers and with the same relative timing with the liquor circulating through said isolated second chamber in a second substantially closed circuit.

3. In a continuous digester for comminuted fibrous material, the combination of a digester in which the fibrous material is subjected to the action of steam and liquor under pressure for chemical treatment of said material, open container means for the raw material, two chambers each having an inlet and outlet, conduit means including first valve means for connecting selectively each of the said inlets of said two chambers with said open container means, conduit means including second valve means for selectively connecting each of the outlets of said two chambers with the digester, a source of liquor, conduit means including third valve means forming a first substantially closed circulatory path for said liquor through the said first chamber and a second substantially closed circulatory path for said liquor through said second chamber, pumping means for circulating the liquor separately through each of said circulatory paths, conduit means including fourth valve means for introducing steam under pressure into, and for withdrawing steam from said chambers, control means for operating the valve means and pumping means in said conduit means in predetermined sequence and in repetitive cyclic order, said control means including means for closing the second valve means, means for opening the first valve means between said open container means and said first chamber for filling it with raw material, means for then closing the first valve means serving said first chamber, means for then opening the third and fourth valve means to the first chamber for liquor and steam, means for then energizing the pumping means serving the first chamber for circulating liquor through said chamber so as to effect impregnation of the raw material during a predetermined period, means for then opening said first valve means between said open container means and the second chamber for filling said second chamber with raw material while impregnation is proceeding in said first chamber, means for then closing said first valve means to said second chamber after filling of said second chamber with raw material, means for then opening the third and fourth valve means serving the second chamber for introducing liquor and steam into said second chamber, means for then energizing the liquor pumping means serving the second chamber so as to effect impregnation of the raw material therein during a predetermined period, means for then closing said third and fourth valve means serving said second chamber, means for then deenergizing said pumping means for the second chamber, means for then opening the second valve means from the first chamber soas to discharge the contents of said first chamber into the digester, means for then closing said second valve means from the first chamber, means for then opening the second valve means serving the second chamber so as to discharge the contents of the second chamber into the digester, mean-s for then closing said second valve means for the second chamber, means for opening the first valve means to the first chamber while the impregnation of the raw material is proceeding in said second chamber.

4. In a continuous digester as set forth in claim 3, valved conduit means for introducing into said closed chambers steam of difierent pressure than prevails in the digester tubes and to maintain said different pressure at least during part of the time While impregnation takes place in said chambers.

5. In a continuous digester as set forth in claim 3, valved steam conduits connectable to both said chambers, to relieve rcssure in the said chambers to a space of lower pressure.

6. In a continuous digester as set forth in claim 3, a liquor tank interposed in the circuit of liquor circulation and valved conduit means for introducing fresh liquor into the said circuit.

7. In a continuous digester as set forth in claim 3, means for regulating the digester output by valve control means disposed to complete the cycling operation of the valves in time intervals decreasing with increasing output of the digester.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. METHOD OF PRODUCINT PULP FROM FIBROUS MATERIALS IN A CONTINUOUS DIGESTER BY SUBJECTING THEM TO THE CHEMICAL ACTION OF A LIQUOR AND STEAM, COMPRISING THE STEPS OF CHARGING THE COMMINUTED RAQ MATERIAL INTO THE INLET OF A FIRST CHAMBER, THEREAFTER CLOSING THE INLET AND OUTLET OF SAID FIRST CHAMBER SO AS TO ISOLATE IT, ADMITTING STEAM AND LIQUOR UNDER PRESSURE INTO SAID ISOLATED CHAMBER, CIRCULATING THE LIQUOR THROUGH SAID FIRST CHAMBER IN A SUBSTANTIALLY CLOSED FIRST CIRCUIT SO AS TO IMPREGNATE THE RAW MATERIAL THEREIN, THEN DRAINING SURPLUS LIQUOR FROM WITH A SECOND CHAMBER AND THE SAMME DIGESTER THE FILLING CLOSED, THEN OPENING THE OUTLET OF SAID FIRST ISOLATED CHAMBER, THEN DISCHARGE THE CONTENTS OF SAID FIRST CHAMBER INTO THE PRESSURE ZONE OF THE DIGESTER, REPEATING SAID STEPS WITH A SECOND CHAMBER AND THE SAME DIGESTER, THE FILLING OF THE SECOND CHAMBER WITH SAID RAW MATERIAL BEING TIMED TO OCCUR DURING THE IMPREGNATION OF SAID RAW MATERIAL IN THE FIRST ISOLATED CHAMBER, AND THEREAFTER REPEATING THE CYCLE ALTERNATINGLY WITH THE FIRST AND SECOND CHAMBERS AND WITH THE SAME RELATIVE TIMING, WITH THE LIQUOR CIRCULATING THROUGH SAID SECOND CHAMBER MEANS IN A SECOND SUBSTANTIALLY CLOSED CIRCUIT.