US2711369A

US2711369A - Progressive explosion process of defibration

Info

Publication number: US2711369A
Application number: US216212A
Authority: US
Inventors: Birdseye Clarence
Original assignee: Process Evaluation and Development Corp
Current assignee: Process Evaluation and Development Corp
Priority date: 1951-03-17
Filing date: 1951-03-17
Publication date: 1955-06-21
Anticipated expiration: 1972-06-21

Description

June 21, 1955 c. BIRDSEYE 2,711,369

PROGRESSIVE EXPLOSION PROCESS OF DEFIBRATION v Filed March 17, 1951 2 Sheets-Sheet 9 IIIIBIIIII Q llll-llll INVIENTOR.

June 21,1955 j Y I 2,711,369

/ PROGRESSIVE EXPLOSION PROCESS OF DEF'IBRATION Filed March 17, 1951 2 Sheets-Sheet 2 INVENTOR.

ers of fibre in the larger chips to the direct action of steam or caustic vapor.

As the result of the second of these explosive reductions of pressure (that from 200p. s. i. to 100 p. s. i.) some of the residual chips will be entirely, and others partially disintegrated. In the meantime further heat penetration will be occurring in the freshly exposed layers of fibre in the still unexploded chips.

At the time of the third explosive pressure drop (that from 100 p. s. i. to atmospheric) the desired disintegration or defibration of all the product units in each chamber will be completed, and thereafter the now fibrous mass will be carried to the exit from the cylinder, and will be in form for any further desired treat' ment.

Under the above conditions I find that spruce chips of the size and nature commonly used in paper making require from about 30 to 60 seconds to pass through the entire length of the cylindrical cookerthe exact time required depending upon the diameter and length of the cylinder, the amount and maximum size of chips loaded into each pressure space or compartment, and the temperatures and pressures employed.

In the application of my process as described above no effort is made to remove from the fibers the lignin, terpenes or other non-cellulosic materials surrounding them. That can be done subsequently by any of several well-known commercial processes, or in any of several equally Well-known commercial types of equipment designed for that purpose.

In carrying out my improved process the chips will be more or less moist or wet when fed into the continuous cooker, and a certain amount of moisture will be added to the chips each time steam is fed into the compartments during the pressure-raising phase of the process. On the other hand, if the subsequent pressurelowering operations are accomplished by passing the chips under pop-valves to reduce progressively the pressures in the several compartments considerable moisture will be carried out of the cylinder as each explosive pressure-reduction is accomplished. The masses of fibers will therefore become somewhat dry and quite fluffy as the contents of each compartment is finally discharged from the cooker. If, on the contrary, the several pressure reductions within the cooker are accomplished by the addition of a cold water spray or other liquid to the compartments the product finally discharged from the cooker will be a fluid mixture of liquid and solids, which may subsequently be separated in any desired manner, as for instance, by means of a Fourdrinier belt.

Digestion (i. e. separation of cellulosic and noncellulosic materials) can, by a modification of my process, be accomplished simultaneously with the heating and exploding steps. One way in which digestion of the chips may be thus accomplished is by injecting, instead of steam, a caustic digestive fluid such as a solution of caustic soda or sodium sulphite into the cylinders under pressures of respectively 100, 200 and 300' p. s. i., and then explosively reducing the pressures within each chamber to 200, 100 and atmospheric by passing the chambers successively under properly regulated pop-valves. Thereafter, the cellulose fibers and the digestive fluid can be separated by any of several well-known commercial meanse. g. centrifuges, vibrating screens, or Fourdrinier belts.

Although I have hereinabove suggested the use of a modified McBean type continuous cooker, with heat and pressure supplied by the injection of either steam or a hot digestive fluid under pressure, I do not wish to be limited to such means, for my process of defibration by repeated explosions can be carried out in any suitable apparatus and with any available means of bringing about the successive explosions which characterize my process.

The advantages of my present process, as compared with such short-time-high-pressure-single-explosion methods as those disclosed in Masons U. S. patents (above identified) are numerous. As applied to the production of paper pulp: the enormous pressures and extremely high temperatures employed in the Mason process hydrolize some of the non-cellulosic constituents of the wood, and shorten and split the individual cellulose fibers. On the other hand, the lower pressures and temperatures of my improved processmade possible by progressive heat penetration and repeated less violent explosionspresent certain definite advantages; and the gradual build-up and step-down of pressures at opposite ends of a cylindrical cooker greatly simplify the construction and operation of that type of apparatus. This could not be used at all if pressures as high as 1000 p. s. i. were necessary Within it and throughout its length. As applied to such inorganic fibrous or laminated materials as asbestos rock and mica, my multiple, comparatively mild explosions have the great advantage of adequately fractionating relatively large units almost wholly along natural cleavage lines and with a minimum of breakage across the grain of the fibers or laminations.

The features and advantages of my improved process will best be understood and appreciated from the following description of apparatus for carrying it out as illustrated in the accompanying drawings in which:

Figs. 1 and 2 are complementary views, in elevation, partly in longitudinal section, of the apparatus, and

Fig. 3 is a diagrammatic view illustrating the general condition of the product in successive stages of the process.

As herein shown the apparatus includes an elongated, metal pressure cylinder It! horizontally disposed and provided throughout a part of its length with a steam jacket 11. An opening is provided near the intake end for a feed hopper 12 through which raw material, for

example pre-heated wood chips, may be introduced into the cylinder.

A series of compartments or chambers is formed within the cylinder 10 by pistons 13 securely affixed to a sprocket chain 14 in uniform spacing. The sprocket chain runs over sprocket wheels 15 and 16 and, of these, the wheel 16 may be driven from any convenient source of power to draw the pistons from left to right through the length of the cylinder in pressure tight relation and then return them freely from right to left outside the cylinder. In a cylinder having an effective length of 10 feet the pistons may be advanced at a rate of 10 to 20 feet per minute depending on the character of the raw material being treated.

The cylinder is provided in the portion shown in Fig. l with steam connections comprising pipes 17, 18 and 19 which enter the lower side of the cylinder in uniform spacing corresponding approximately to the spacing of the pistons 13. Substantially opposite each pipe in the cylinder is provided a pressure gauge 20. Each adjacent pair of pistons 13 forms a compartment, one of which in Fig. 1 is shown as being in communication with the pipe 17 by which it may be supplied with steam or vaporized caustic soda solution at pounds gauge pressure, for example. As these pistons are advanced the compartment is brought successively into communication with the pipe 18 supplying steam at 200 pounds and. then the pipe 19 supplying steam at 300 pounds. As the charge of wood chips is advanced in this manner the chips become permeated wholly or partly with steam or caustic solution at the pressures indicated and are now ready to be subjected to a series of defibrating explosions.

The cylinder is provided in the portion shown in Fig. 2 with connections 21, 22 and 23 to individual explosion chambers each controlled by an adjustable pressure-relief valve as indicated conventionally in the drawings. These. 7

connections are spaced to correspond approximately with the spacing of the pistons 13 and may be separated from the steam connections by any desirable length in the r progressive manner-a gaseous pressure of not less than tube through which the charge of chips may be con veyed while maintained under maximum steam pressure.

In the illustrated apparatus it may be assumed'that the I pressure-relief valve in the connection 21 is set at 2003 pounds. Consequently when the foremost cylinder defining the compartment passes the outlet of theconnection 21, the pressure therein is explosively dropped from 300 to 200 pounds and the effect upon the chips is to defibrate and disintegrate at least the surface layers of the chips in the charge. i ,7

As the piston-defined compartment is advanced the chips remain under 200 pounds steam pressure and if the chips have not been completely permeated hitherto by steam at that pressure, the newly exposed layers of fibre in the chips are quickly brought to that condition. When the connection 22 is reached the pressure in the compartment is again explosively reduced this time from 200 to a 100 pounds and again the exposed portion of the chips is defibrated and disintegrated, When the pistons reach the final connection 23 a third explosive reduction pressure takes place, this time from 100 pounds to atmospheric pressure, and in this final stage the chips are totally reduced to their constituent fibres. g

Fig. 3 illustrates diagrammatically the three steps of the process above described. .A typical chip 30 is indicated at the left-hand side of the figure asit is. introduced into the pressure cylinder and it may be assumed that,

the chip 31 represents the condition of the same chip after it has been subjected to the first explosive reduction in pressure. The fibres constituting the'surface portion of the chip have been loosened and separated from the body of the chip. The core of the chip and the fibres separated therefrom when subjectedto explosive pressure reduction from 200 to 100 pounds are represented at 32..

And finally, the group of disintegrated fibres 33 represents the ultimate conditionof the original chip.

After the final explosive reduction in pressure and a complete defibration of the chips the fibres are discharged from the right-hand end of the cylinder 10 and are directed through a discharge hopper 24 to a Wire mesh conveyer 25 horizontally disposed and adapted to remove the fibres from the apparatus while permitting intrained' liquid to drain away to a tank 26 disposedbeneath the conveyer. When a hot caustic solution is used, it will 100p; s. i. within fragments'of the material, and then intermittently reducing thersaid gaseous pressure thereby subjecting the fragments to a series of disintegrating explosions atprogressively decreasing pressures and so progressively exposing fresh layers of fibre directly to gaseous pressure.

3.. In a process of idefibrating wooden chips, the steps, of enclosing a collection of chips'in a pressure space, subjecting the collection to internal gaseous pressure greater than atmospheric, explosivelyfdisintegrating the chipszby a series of steps at progressively decreasing pressures thus removing surface fibres fromeach chip'and ex-.

posing fresh layers of fibre directly to, gaseous pressure, and f subjecting the. residual chips to m'oist ure at. all intermediate stages while: the original pressurespace.

45in a process of reducing wood chipslto their con- 7 stituent fibres, the'step of g space a collectio'nof chips of different sizes, subjecting Y r the collection to internal gaseous pressure ig'reater 'thanl atmospheric, and reducingthe'pressure progressively in ia seriesv of explosive stepsat progressively decreasing.

enclosing in .a compression pressures thereby converting someof the smaller chips to loose fibres and progressively removing surface fibres i fromthe larger chipsthus exposing fresh layers of'fibre directly to gaseous pressure. 5

carry with it the non-cellulosic material dissolved from I the chips.

The connections 21-43 each include a pressure relief valve as already explained, and are herein shown asleading upwardly to chambers27 which act v as muffiers and also serve to retain stray fibres that may be blown out:

of the pressure tube. If desired the pistons 13 may be enclosed throughout'a portion of their return run and thus the capacity, .of the apparatus" correspondingly increased. t I g While the exact pressures employed are of courseof secondary importance, they must in all cases be suflicient to cause explosive disintegration of the. fibrous product when suddenly reduced or released at successive stations in the process.

Having thus disclosed my invention and described in detail an illustrative manner of carrying it out, I claim as new and desire to secure byLetters Patent: 1

1. In a process of reducing fibrous material. to its constituent fibres, the steps of confining a predetermined charge of the material under vaporpressure of a hot] caustic solution at a pressure of approximately 300p. s. i.,

then advancing the'compressed charge to .a series of 1 decompression stations andexplosively reducing the vapor pressure of the charge first to approximately 200 p. 's. i., then to 100 p. s. i., thus exposing fresh layers of fibres at each step to direct action of hot caustic vapor, and finally to atmospheric pressure.

2. In a process of defibrating fibrous cellulose-yielding material, the steps of building up man intermittent'and g 5 In a process of jreducingl fibrouschips'to their con-v stituent fibres, the steps'of enclosingthe chips infafpressure chamber in a predetermined location, moving the} enclosed chips progressively in series from stationjto station, subjec tingthem to intermittently increasin'g steam j, pressures at certain"lstations,- and. subjectinglthem to exf l ,plosions underprogressiyely decreasing pressures at; sta

tions later in the {series thereby suceessively'cxppsi g;fresh layers of fibre inthe chips toflsteam pressure}.

. 6'. in,v a process of reducing fibrous cellulose-yielding material to its constituent. fibres, thelsteps of subjecting the material topredetermined initial pressurebf vappr'iof a. digestant'fiuid at approximately 390 p. s. {i.,- andIthen explosively reducing the internalpressure of thematerial gressively exposing" fresh layers of'jthe material directly 1 8.111 the defibration' the pieces to a hot caustic solution'at greater'than atmosj pheric pressure thereby dissolving the non-cellulosic mate- I rial from between the cellsof j the pieces, then explosively disintegrating the pieces in'a series of steps at progressively decreasing pressures andthereby'separating at least the. e surfacecellsof the pieces and exposing fresh layers of fibre dire ctly tothe action of hot caustic vapor, and then separating the loose cellsfromthecaustic solution.

r References Citediin the file ,of thisapatent 2,007,343' Scharmann et'al: July 9, 1935 .2,3s6,401 Joyce r Oct. 9, 1945 said chips are contained in the;

ot 1 pieces k of 7 fibrous T, vegetable materialgthe process comprising thejsteps of subjecting Aug. 23, 1932 'McBe'an July 9, 1946'

Claims

1. IN A PROCESS OF REDUCING FIBROUS MATERIAL TO ITS CONSITUENTS FIBERS, THE STEPS CONFINING A PREDETERMINED CHARGE OF THE MATERIAL UNDER VAPOR PRESSURE TO A HOT CAUSTIC SOLUTION AT A PRESSURE OF APPROXIMATELY 300P.S.I., THEN ADVANCING THE COMPRESSED CHARGE TO A SERIES OF DECOMPRESSION STATIONS AND EXPLOSIVELY REDUCING THE VAPOR PRESSURE OF THE CHARGE FIRST TO APPROXIMATELY 200 P.S.I.., THEN TO 100 P.S.I., THUS EXPOSING FRESH LAYERS OF FIBERS AT EACH STEP TO DIRECT ACTION OF HOT CAUSTIC VAPOR, AND FINALLY TO ATMOSPHERIC PRESSURE.