US3367495A

US3367495A - Floatation apparatus and recovery and utilization of wood fines from mill wastes

Info

Publication number: US3367495A
Application number: US398259A
Authority: US
Inventors: Norman S Lea; James S Brawn
Original assignee: Scott Paper Co
Current assignee: Kimberly Clark Tissue Co
Priority date: 1964-09-22
Filing date: 1964-09-22
Publication date: 1968-02-06
Anticipated expiration: 1985-02-06
Also published as: FI46751C; SE342478B; FI46751B

Description

Feb. 6, 1968 Filed Sept. 22, 1964 N. S. LEA ETAL FLOATATION APPARATUS AND RECOVERY AND UTILIZATION OF WOOD FINES FROM MILL WASTES 3 Sheets-Sheet 1 r I8 RAW MATERIAL I ALTERNATE OR LOGS OF PULP WOOD I SUPPLEMENTAL FEED-| sAwDUsT,e. 4 FROM; H '2 I KERF OF SAW AT I I I SAWMILL, OUTSIDE BARK AR lCl-HPPER FINES AND| E S K BARK I OTHER SELECTED L wAsTEs J l7 2 I l3 0 PRO E'TTSSQ CHI RI ERS ERRD DU PS T I FDR HEA I REMO/EDINPURlTIES 4 I PRIOR W W ART j CHIP SCREEN I l5 FLOATATION DEVICE- ,REMOVING UNDERsIzE I REMOvAL OF BARK, ICH'PSSMALL FRAG REJECTS KNOTS DIRT COM- IMENTs OFBARK. CHIPPER FINES I I PREssION WOOD AND IKNOTSID'RT AN D OTHER FRAGMENTS COMPRESSION W OF IMPURITIEs 2| l6 7 AccEPTsNORMAL ACCEPTS sIzE WOOD CHIPS UPGRADED GOOD WOOD FINES DEWATERINO DEvIcE- WATER REMOVING WATER FROM WOOD FINES DEWATERED WOOD FINES I I T A PRODUCT- DIOESTER- figigf GOOD QUA ITY PULP PM FOR SEMI-CHEMICAL FOR MAKING PAPER CHEMICAL PULPING FIGJ INVENTORS NORMAN S. LEA JAMES S. BRAWN Feb. 6, 1968 N. s. LEA ETAL 3,367,495

FLOATATION APPARATUS AND RECOVERY AND'UTILIZATION OF WOOD FINES FROM MILL WASTES Filed Sept. 22, 1964 3 Sheets-Sheet 2 i 79 a 78 3 I o I a [1L i l I 6| 1' FIGZ INVENTORS NORMAN S. LEA JAMES S BRAWN Feb..6, 1968 N. s. LEA ETAL FLOATATION APPARATUS AND RECOVERY AND UTILIZATION OF WOOD FINES FROM MILL WASTES Filed Sept. 22, 1964 3 Sheets-Sheet 5 INVENTORS NORMAN S. LEA

FIGB

FIGA

JAMES S. BRAWN United States Patent Office FLOATATION APPARATUS AND RECOVERY AND UTILIZATION OF WOOD FINES FROM MILL WASTES Norman S. Lea and James'S. Brawn, Everett, Wash., as-

signors to Scott Paper Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Sept. 22, 1964, Ser. No. 398,259 7 Claims. (Cl. 209-163) This invention pertains to the recovery and utilization of pulpable wood fractions from mixtures of fine particles of wood and bark. A particularly valuable application of the invention is concerned with the recovery of relatively bark-free wood chips from chipper fines and/ or sawdust.

In the preparation of paper from wood, parts of logs with much, but not all, of the bark removed are reduced to chips of varying size in apparatus known as a chipper. Among the chips are particles of wood, dirt, bark, knots and compression wood that are very small, e.g. small enough to pass through a A" screen. If good quality paper is desired, these should be separated by any suit able method or means from the larger, normal-sized wood chips. Following such separation, the larger chips are subjected to any of various treatments, such as chemical or semi-chemical pulping to convert them to wood pulp. By various subsequent treatments which constitute no part of the present invention and which are wellknown to those skilled in the art, paper is manufactured from the pulp.

The very small particles separated from the larger chips are known as chipper fines. conventionally, they are separated from the larger chips by screening and are then burned to recover whatever heating value they may possess. If the good wood could be recovered from the chipper fines substantially free of the other chipper fines components, especially bark, substantial economic benefits would result, for the potential value of the paper that could be produced from the good Wood exceeds the value of the chipper fines as fuel.

Various obstacles have discouraged the recovery and utilization of the good wood contained in the chipper fines. First of all, the separation of the small particles of good wood from the bark and other impurities in the chipper fines can be difficult and costly. Secondly, attempts at producing wood-pulp from the chipper fines without removal of impurities have resulted in undesirably low grades of paper. Thirdly, it has been generally believed that if normal-sized chips are cooked along with very small chips, such as might be recovered from the chipper fines, the yield increase would not be sufiicient to justify the cost of recovering the good wood from the chipper fines.

Exemplary of various factors contributing to the problem of separating good wood from the back and other impurities in chipper fines is the reported observation that both bark and wood chips tend to float on the surface of water. This frustrates attempts to use simple floatation or float-sink separation processes in which a mixture of two solid materials having respective specific gravities greater than and less than water are delivered to the surface of a body of water and are then separately recovered therefrom after the heavier material has sunk beneath the surface. Of course, it has been observed that if chips of certain kinds of Wood and bark are delivered to the surface of water and allowed to stand long enough, the wood will become water-logged and sink before the bark does. However, the period of time required for the wood to absorb the necessary amount of water by normal capillary action unduly protracts the treatment and renders rapid separation impossible. Recently, it has been proposed that special float-sink separation procedures involving vacuum and heat treatments and specialized floatation Patented Feb. 6, 1968 media be used to hasten the separation of mixtures of bark and wood chips. As is well known, however, the employment of heat, vacuum and specialized media introduce additional complexities and cost factors which it would be desirable to avoid, if possible. Consequently, there is still a need for additional methods and apparatus of a simple, economical, rapid and efficient nature for separating good wood fragments from fragments of bark and other impurities.

It is the principal object of the present invention to fulfill the above need. Another object is to provide methods and means for separating chips of wood and bark by floatation without the necessity of resorting to vacuum treatment, heat treatment or specialized floatation media. Still another object is to provide methods and means whereby bark chips may be caused to sink and good wood chips float in water to facilitate their separation. A further object is to provide a consistently efiicient float-sink separation process for separating mixtures of very small good wood and bark fragments despite relatively wide and frequent variations in the ratio of bark to good wood in said mixtures. Another object is to provide methods and means for upgrading, e.g. lowering the percentage of various impurities, such as bark, knots and compression wood, in particulate mixtures of wood and one or more of these impurities, the mixtures being characterized by particles which will pass through a screen with A" openings. Still another object is to provide an integrated process for recovering pulpable wood from chipper fines and for converting the recovered wood to pulp. Another object is to provide a process for recovering good wood from chipper fines and for converting said chipper fines to pulp in the presence of one or more additional woody materials. Still other objects and advantages of the invention will suggest themselves to persons skilled in the art upon consideration of the explanations which follow.

According to the present invention, it has been found that chipper fines, sawmill sawdust and other selected wood wastes may be upgraded and converted to good pulp in the presence or absence of normal-size wood chips, e.g. those which will be retained on a screen with A" to openings. Thus, material whose value has been largely wasted by burning it as fuel may now be more beneficially utilized by converting it to pulp which displays good strength properties and is readily bleached.

According to the present invention, mixtures of fine particles of waste wood and impurities, e. g. particles small enough to pass through a screen with openings of approximately 4, are submerged in an aqueous bath; a generally downwardly directed force is applied to the mixture in the bath for forcibly conducting the mixture downwards in the bath; the mixture is then released from the downwardly directed force. Upon completion of the above operations, the good wood has a tendency to rise in the bath while the impurities sink or at least remain an appreciable distance below the surface. It has been found that the performance of the above operations will cause a predominant proportion of the good wood in the mixture to rise to the surface while a predominant proportion of the impurity or impurities fails to so rise. Consequently, the invention facilitates the recovery from the surface of the bath of good wood freed of a substantial proportion of the impurity or impurities in the original mixture.

Preferred embodiments of the various methods and apparatus of the present invention will now be described in connection with the accompanying drawings, wherein:

FIGURE 1 is a schematic diagram of certain methods constituting a part of the invention;

FIGURE 2 is a vertical sectional view of floatation apparatus constructed in accordance with the invention, taken along section line 22 of FIGURE 3;

FIGURE 3 is an end view of the aforesaid floatation apparatus; and

FIGURE 4 is a partially broken out sectional view taken along section line 4-4 of FIGURE 2.

In a preferred embodiment of a method according to the invention, as shown in FIGURE 1, logs of pulp wood are passed through a barker 11 for removal of as much bark 12 as is practicable. The debarked logs are then processed in a chipper 13 wherein the logs are reduced to an assortment of chips of good wood, bark, knots, dirt, compression wood and other impurities. In accordance with conventional practice, the chips are separated into normal size and undersize chips. The usual method of separation is by means of a chipper screen 14. Usually the chipper screen has openings of about 41" or and the rejects 15, the material which passes through the screen, is referred to as chipper fines and is characterized substantially, if not completely, by fragments which will pass through a A" screen. The accepts 16, of course, are the larger, normal size chips which do not pass through the screen.

In accordance with prior art practice, the chipper fines are sent to the boiler house 17 where they are burned to recover whatever heat value they may contain. Contrary to prior art practice, the present invention involves subjecting chipper fines, or other fine wastes 18, or mixtures thereof to a treatment to separate various impurities therefrom, such as bark, knots, dirt, compression wood and other impurities.

The preferred, but not necessarily the only, method of separation is by floatation according to a new process and in a novel floatation device 19, which constitutes part of the present invention. The floatation device upgrades the chipper fines by separating them into rejects 20, constituting the bulk of the impurities originally present, and into accepts 21, constituting a substantial portion of the good wood originally present in the chipper fines. Water 23 is removed from the accepts 21 in any suitable dewatering device 22, while the rejects are sent to boiler house 17. The invention provides two alternate or complementary modes of dealing with the dewatered accepts or wood fines 24.

According to one mode of treatment, constituting the preferred mode, the dewatered wood fines 24 are combined or mixed with the accepts 16. Then the mixture of the small and large chips is converted to pulp 28 by any suitable method or means 27, such as by mechanical, semichemical or chemical pulping. It has been found that this mode of operation can increase production rates in chemical pulping processes, for the upgraded wood fines when added to normal chips in a ratio of up to about 1:10, tend to fill in the voids between the normal-sized chips, thus increasing the weight of material that can be placed in a digester of a given volume, with proportional increases in the amount of pulp produced per cook. Any chemical pulping technique or type of cooking liquor may be employed, e.g. soda, acid sulfite, kraft, NSSC and so forth. The weight ratio of active chemical(s) to wood (bone dry basis) charged to the digester may correspond with or differ from the ratios conventionally used in present day commercial operations for a given liquor or technique. However, the use of conventional ratios is preferred, thus necessitating slight but non-injurious simultaneous increases in the concentration of active chemicals in the liquor and decreases in liquor volume.

According to the second mode of treatment for the dewatered wood fines 24, the fines are placed in a digester 29 for conversion to pulp 28. The best method of conversion for this material appears to be acid sulfite pulping, employing conventional liquors, temperatures, pressures, concentrations and liquor to wood weight ratios. To facilitate circulation in downflow forced circulation digesters, it is recommended that the bottom strainer be covered with a layer of normal size chips to insure that the wood fines do not interfere with circulation. Otherwise, the cooking procedure and conditions are conventional.

A preferred embodiment of the floatation apparatus of the present invention is illustrated in FIGURES 2, 3 and 4. In accordance with the invention, a floatation tank 30 is provided, having a closed bottom 31 and side and end

walls

32, 33, 34 and 35, respectively. Any of the aforesaid walls, in this case end wall 34, has a lip 36 which is situated below the upper edges of the adjoining wall portions. The elevation of the lip determines the intended level 42 of the surface of an aqueous floatation bath 43 which is to be maintained in the tank. Extending downwardly and laterally from the lip 36 and end wall 34 is a spillway 37.

The floatation apparatus of the invention may include a headbox or sluice box. The sluice box or headbox may be located within or without the tank 30 proper, and the walls of the headbox may be separate from and/or part of the walls of the tank. In the present embodiment, the rear and side walls of the headbox or sluice box are part of the respective upper portions of the rear and

side walls

35, 32 and 33 of tank 30. The front wall of the headbox in the present embodiment is a generally vertical bafiie 44 extending transversely of the tank from side wall 32 to side wall 33 and between

end walls

34 and 35. The baffle 44 has an upper edge 45 disposed above the intended level 42 of the floatation bath, side edges 46 and 47 joined to

side walls

32 and 33 respectively, and a bottom edge 48 disposed below the intended level of the floatation bath. Thus, the baffle divides the headbox and tank into separate chambers at the level of the lip 36 and for an appreciable distance below said level, but does not close off communication between lower portions of the headbox and tank. It is apparent therefore, that the baffle will effectively divide the surface and upper portion of the floatation bath into separate portions, while permitting communication between that portion of the bath 43 contained in the lower portion of the headbox and that bath 43 contained in the tank 30 proper.

In accordance with the present embodiment, the bottom wall of the headbox is a generally horizontal baffle 39 extending transversely of the tank 30 along end wall 35 from side wall 32 to side wall 33. Battle 39 extends longitudinally from end wall 35 to a position beneath and vertically spaced from the bottom edge 48 of bafile 44. It may, if desired, extend a short distance further into the tank 30. It should be observed that the bottom edge 48 of vertical baffle 44 and the adjoining portion of generally horizontal bafiie 39, as well as the adjoining portions of

tank side walls

32 and 33, form a generally horizontal passageway 40 between the headbox and the tank, which passageway is wholly situated at an appreciable distance below the level of lip 36 and is therefore similarly below the intended level 42 of the surface of the floatation bath to be maintained in tank 30. This passageway provides communication between the headbox beneath the intended level of the floatation medium.

The headbox 38 is provided with a means for delivering chips thereto, such as a chute 49 and star feeder 41. Other means, such as conveyors, open chutes and conduits of various types may also be employed supplementary to or in substitution for the chute 49 for evenly distributing feed material in the headbox at a controlled rate. Also, although the chute 49 is positioned to deliver the chips to the surface of the floatation bath, the chips may also be delivered to the headbox below the surface of the bath.

Associated with the headbox are means for inducing therein a downwardly directed flow of floatation medium and chips. The preferred means is a conduit and pumping system which will now be described. In the present embodiment, there is an outlet in tank 30 well below the surface of the bath at a location widely separated from the headbox. Outlet 60 is connected to the input side of a pump 64 via

conduits

61, 62 and 63. The discharge side of pump 64 is connected with a spray header conduit 50 via

conduits

65, 66 and 67. Conduit 50 extends transversely of the floatation device above the intended bath level 42. It has a plurality of transversely spaced branch conduits 59 extending into chute 49 and having outlets directed downwardly towards the intended level of the bath at a plurality of transversely spaced points. The concluit system and pump described above are adapted to direct a plurality of forceful downward sprays of floatation liquid against the surface of the floatation bath in the headbox at a plurality of transversely spaced points.

The downwardly directed flow of floatation medium and chips may be induced in a number of ways. For instance, the action of the sprays may be supplemented by downwardly directed mechanical agitation of the floatation medium in the headbox, or mechanical agitation may be substituted entirely for the action of the sprays. Vigorously pumping the floatation medium and chips out of the headbox may also be used to supplement or replace any of the modes mentioned above for inducing the requisite flow. It will be apparent therefore to persons skilled in the art that a wide variety of means may be employed for inducing the desired flow.

Any convenient means may be employed to introduce additional liquid to tank 30 to make up for that lost by overflow over the lip 36. According to the present embo'diment of the invention a make-up liquid supply conduit 75 provided with a valve 76 opens into the tank 30 through end wall 35.

Means may be provided for removing accumulations of material from the lower portion of tank 30. In the present embodiment, the means include a transversely extending channel 68 fitted to the bottom 31 of the tank. A conveyor 69 extends through channel 68, through first vertical conveyor guide means 70, through upper horizontal conveyor guide means 71, through a second vertical conveyor guide means 72, and back into channel 68. The vertical guide means 70 and 72 are fully enclosed, are substantially leakproof and are joined by liquid-tight connections to

tank walls

33 and 32 respectively. The conveyor discharge port 73 and driving means 74 are located above lip 36 and therefore are also above the intended surface level of the floatation bath in tank 30 and in the vertical conveyor guides.

Any suitable means for removing accumulations from the bottom 31 of the tank 30 may be employed. The means described above are preferred because they prevent any substantial flow of floatation medium out of the bottom of the tank, because they are eificient and because they may operate on a continuous basis. The use of means which operate intermittently or manual clean-out are possible, but automatic continuously operating means are considered best for high volume commercial operations.

The preferred embodiment of the present invention includes certain features which, though not deemed essential to the broadest concepts of the invention, nevertheless render the present embodiment unusually eflicient. For instance, it has been found desirable that the baflle 39 incline upward from its point of attachment to end wall 35 and extend a short distance, e.g. l or 2 inches, beyond baflle 44. Also, it has been found that the best yields are obtained when the depth of the baffle 44 beneath the surface of bath 43 is about 4 m6 inches, although other depths have been employed. Further, it has been found desirable to provide a plurality of vertical flow regulation baffles 77, 78 and 79 in tank 30, extending from side wall 32 to side wall 33 between

end walls

34 and 35. The bafiles should have their upper edges positioned a short distance, e.g. about an inch, below the intended level 42 of the surface of the floatation bath and their bottom edges should be spaced from the bottom and end wall 34 of the tank. Furthermore, it has been found that the convergence of the

end walls

34 and 35 towards the bottom of the tank reduces the area from'which accumulations of sunken material must be removed, thus facilitating the removal operations. Still another of the advantageous features of the present embodiment is the placement of the headbox 38 and the lip 36 at opposite ends of the tank 30, so that there will be a relatively straight-line flow of floatation liquid and floated material from one end of the tank to the other. Moreover, the vertical distance between

bafiles

44 and 39 should be relatively short, e.g. 3" to 5", if the best effect is to be obtained from the baflle 39 in turning the flow of floatation liquid and chips from a downward flow to a generally horizontal flow as it departs from the headbox. Finally, although embodiments of the invention have been constructed in which there is no horizontal baflie, and such embodiments have been able to make a worthwhile separation, a horizontal baffle is of considerable benefit, and its use is therefore recommended.

The operation of the floatation device of the present invention is relatively straight-forward. Water is customarily employed as the floatation medium, although other floatation media known to persons skilled in the art may also be used. The use of fine particles of any species of wood suitable for commercial processes of making paper is contemplated. Generally speaking, the feed material will contain not only fragments of good wood, but also the various impurities previously mentioned. The fragments may vary widely in size and shape, but the feed material will be characterized by a substan-' tial proportion of fragments which will pass through a quarter inch screen. Such fragments are available not only in the form of chipper fines, but also in the form of sawmill kerf sawdust and other selected mill wastes.

The feed material 56 is delivered to the headbox 38 through chute 49, which drops the feed on the surface of the floatation bath adjacent the sprays 51. The sprays beat downwardly upon the fragments and submerge them. The generally downward flow in the headbox induced by the sprays 51 conducts the fragments downward in the headbox. The flow of liquid and fragments generally follows the direction indicated by the arrows in FIGURE 2. The flow passes under the baffle and out into tank 30, where it is released from the downwardly directed force produced by the sprays 51. Then, a portion of the fragments 57, which is mostly good wood, rises to the surface and flows out of tank 30 over lip 36 and through chute 37, as indicated by the arrows in FIGURE 3. The good wood exiting tank 30 via chute 37 is recovered by any suitable means forming no part of the present invention. Another portion 58 of the fragments of feed material, containing mostly one or more of the impurities, such as bark, dirt, compression wood and knots, sinks to the bottom of tank 30. The impurities pile up in the bottom of the tank 30 and are gradually withdrawn therefrom through channel 68.

The rate of flow of floatation medium from conduit 50 should be suflicient to maintain a positive flow of floatation medium from the headbox to the tank 30 and over the lip. Generally, increased velocity of flow is associated with increased yields and a somewhat increased content of sapwood in the accepts, since sapwood sinks quite slowly. The percent of bark in the accepts, however, remains reasonably stable over a relatively wide range of velocities'Temperature does'not appear to be a critical feature, and the process will ordinarily be carried out at ambient temperatures, e.g. about O-40 C. and at the prevailing atmospheric pressure. The floatation medium must, of course, have a specific gravity inter.- mediate between the desired and undesired components of the feed material. The rate of introduction of feed material to headbox should be such as to keep in step with the rate of disappearance of feed material from the headbox. The latter rate, of course, is dependent upon the flow rate and pressure of the floatation medium issuing from conduit 50. Generally speaking, the higher the pressure, the better.

The following examples illustrate, but are not intended to limit the invention. All parts are by weight unless the contrary is indicated.

Example 1 Hemlock, white fir and lodgepole pine, in a weight ratio (bone dry basis) of 60 parts to 28 parts to 12 parts, is debarked, reduced to chips and sized with a chip screen having A openings to produce A1" accepts and %i" chipper fines or rejects. The chipper fines constitute approximately 2.7% of the weight of the chips fed to the chip screen. The moisture content of the chipper fines varies from about 47 to 62% and averages about 53%. The bark content averages about 0.62%.

The above-described chipper fines are processed in a floatation unit constructed in accordance with the invention. The unit is 24" wide, 4 deep and 8' long. The floatation tank or cell is divided into two retention chambers of approximately equal volume, as previously described. The floatation bath is water, which is maintained at a depth of about 3 in the retention chambers. The baflle between the headbox and floatation tank proper extends vertically about 5" beneath the surface of the floatation bath. The rate of feed of chipper fines is about 12 B.D. pounds per minute and water is sprayed into the headbox at a rate that varies from 75120 g.p.m. and is usually about 75-100 g.p.m.

The accepted material which floats on the surface of the bath, has an average moisture content of about 66% and an average bark content of about 0.17%. The rejects have a moisture content of about 63%. The yield, pounds of B.D. (bone dry) accepts divided by the sum of pounds B.D. accepts plus pounds B.D. rejects, is 63.81%.

Example 2 The procedure of Example 1 is repeated, substituting s'awmill kerf sawdust and blends of chipper fines and sawmill kerf sawdust for the chipper fines. Similarly, successful results are obtained.

Example 3 The procedure of Example 1 is repeated, except that the vertical underwater extension of the baffle between the headbox and floatation tank proper is varied from 4" to 6". The system continues to operate successfully.

Example 4 Accepted material produced in Example 1 is given a sulphite digester treatment utilizing ammonia base acid. 4.54 kg. of 47.2% B.D. hemlock chips are placed over the bottom strainer in a downflow forced circulation digester. 120.86 kg. of the accepted material produced in Example 1, 32.25% B.D. are charged to the digester over the hemlock chips, thus making a total charge of 41.31 B.D. kg. 215 liters of ammonia base cooking acid having a tot-a1 S content of 7.80% and a combined S0 content of 0.85% are employed in an approximate acid to wood ratio of 5.1: 1 for cooking the digester charge in accordance with the following schedule and conditions:

COOKING DATA Time (Hrs: pH Total Comb. Temp., 0.

Min.) S0 802 Front Center Back The cooking proceeds without any unusual problems. Bleachability of the product is about 6.10% C1 No. The

yield is 44.88% B.D. yield. The percent screenings is about 0.32%, which is much lower than the normal amount of screenings obtained from regular chips. When TAPPI handsheets of the pulp produced in accordance with this example are prepared with similar handsheets of unbleached Anacortes Alder, and are tested for Mullen, Tensile, Tear, Specific Volume and Freeness at beating times of 0, 10 and 30 minutes, the following results are obtained:

As can be seen from the above data, paper produced from upgraded chipper fines in accordance with the present invention compares favorably with that prepared from unbleached alder.

Example 5 Approximately two B.D. tons of the material recovered in accordance with Example 1 are thoroughly mixed with tons of 47% B.D., A" chips accepted by the chipper screen of Example 1. The upgraded chipper fines constitute approximately 5% by weight of the resultant mixture. The mixture is placed in a forced circulation plant digester and is cooked while approximately 38,800 gallons of acid sulfite cooking liquor are circulated. The cooking liquor is similar to that employed in example 4 and differs from conventional acid sulfite cooking liquors used for cooking normal-size chips only in that suitable adjustments have been made in the acid strength, both free and combined, to account for the presence of the chips, as explained below.

The mixture of 5% upgraded chipper fines and 75 (wet) tons of normal chips has essentially the same apparent volume as the 75 (wet) tons of normal chips would have alone. However, the B.D. weight and real volume of the mixture are greater than that of the normal chips alone. The total weight of wood is 5% greater. An upward adjustment of 5% in the percentage of free and combined S0 is needed to pompensate for the weight increase. However, the increased real volume of charge material decreases the number of gallons of cooking acid that can occupy the digester. The two tons of chipper fines occupy approximately 540 ft. of which 30% or 162 ft. is real volume. A loss of 162 ft. of digeste-r space which would otherwise be available for cooking liquor involves a reduction of 1,200 gallons from the normal 40,000 gallons of acid or a 3% reduction in the total charge of acid. Therefore, the acid strength, both free and combined is raised by 8% in order to maintain the same acid to wood ratio as is present when QQQlfi Wit AQu fines- The cooking schedule is as follows:

COOKING SCHEDULE Time (Hrs.:Min.) Circulation, Temperature, Pressure,

g.p.m. C. p.s.i.g

: 3, 550 104 100 I 3, 500 115 100 1 3, 200 122 100 2, 450 127 100 1 1, 900 131 100 I 1, 600 134 100 Z 1, 500 135 100 I 133 100 1 133 93 :30 128 65 A control cook with 75 tons (wet) of the chips alone, but without the 8% boost in concentration of the cooking liquor was carried out in a similar manner. The cooking schedule was as follows:

COOKING SCHEDULE In comparing the results of the two cooks described above, it is noted that circulation falls off sooner with the mixture of upgraded chipper fines and normal chips. Therefore, the control cook contains slightly fewer screenings. However, the cook with the upgraded chipper fines produces a pulp of normal chlorine number, dirt count and strength properties, and a higher yield of useable pulp. Therefore, it appears that advantageous results are obtained by admixing normal size chips with wood waste from which the impurities have largely been removed and by chemically digesting the resultant mixture.

What is claimed is:

1. Separatory apparatus of the flotation type, comprising: a tank, including a bottom, first and second end Walls, and a pair of side walls, said walls having upper edges and being joined to said bottom and to one another so as to contain a flotation medium; the first of said end walls having an overflow lip situated beneath the level of the upper edges of the remaining wall means whereby said lip maintains said flotation medium in said tank at a predetermined level; a generally vertical baffle member extending between said side walls at and for an appreciable distance below said predetermined level; a generally horizontal batfle member secured to the second of said end walls and extending from one of said side walls toward the other side wall and extending beneath said generally vertical baffle in vertically spaced relationship therewith; said baflie members, said second end wall and said side walls defining a sluice box, and said baflie members and said side walls defining a generally horizontal passage between the sluice box and tank proper; a plurality of spray means directed downwardly into said headbox from above said predetermined level at a plurality of transversely spaced points; an outlet in said tank at a location remote from said sluice box for the withdrawal of flotation medium therefrom; and means for recirculating said withdrawn flotation medium to said spray means under pressure; means in the bottom of said tank for the removal of accumulated solids therefrom; and means for supplying particulate material to the sluice box.

2. Apparatus in accordance with claim 1 wherein said tank is provided with means for the introduction of makeup flotation medium to replace that which is lost by overflow over said overflow lip.

3. Apparatus in accordance with claim 1 wherein said horizontal baffle member is inclined slightly upwardly as it extends away from said second end wall, and extends a short distance beyond said vertical bafiie member.

4. Apparatus in accordance with claim 1 wherein said end walls incline inwardly towards the tank bottom.

5. Apparatus in accordance with claim 1 wherein generally vertical flow regulation baffle means are provided in the tank proper, said baffle means extending transversely in said tank from one of said side walls to the other of said side walls and having upper edge means situated a short distance below the aforementioned predetermined level, and bottom edge means slightly spaced upwardly from the bottom of said tank.

6. Apparatus for separating wood fines of differing densities comprising a sluice box having an upwardly inclined bottom wall, said sluice box defining an exit port proximate the upper end of said bottom wall, a chamber communicating with said port and having Walls above the level of said port in said sluice box and adapted to contain a body of water extending above said port, channel means located proximate said sluice box and in fluid communication therewith to introduce wood fines therein, and conduit means in fluid communication with said sluice box to introduce substantially vertically downwardly into said sluice box an aqueous medium whereby fines entrained in such downwardly introduced aqueous medium are uniformly distributed through said sluice box exit port upwardly toward the surface of the fluid located in said chamber whereby fines of different densities readily separate in said fluid and are separately recoverable.

7. Apparatus as set forth in claim 6 including at least one vertically disposed baflie spaced from said sluice box and having a top face located above said exit port of said sluice box and below the top of the walls of said chamber and a bottom face located above the bottom of said chamber.

References Cited UNITED STATES PATENTS 450,063 4/1891 Fitch 209- 1,056,952 3/1913 Smith 209-162 1,937,190 11/1933 Chance 209-173 2,764,289 9/1956 Scheid 209173 3,042,198 7/1962 Slavich 20944 S. LEON BASHORE, Primary Examiner.

Claims

6. APPARATUS FOR SEPARATING WOOD FINES OF DIFFERING DENSITIES COMPRISING A SLUICE BOX HAVING AN UPWARDLY INCLINED BOTTOM WALL, SAID SLICE BOX DEFINING AN EXIT PORT PROXIMATE THE UPPER END OF SAID BOTTOM WALL, A CHAMBER COMMUNICATING WITH SAID PORT AND HAVING WALLS ABOVE THE LEVEL OF SAID PORT IN SAID SLUICE BOX AND ADAPTED TO CONTAIN A BODY OF WATER EXTENDING ABOVE SAID PORT, CHANNEL MEANS LOCATED PROXIMATE SAID SLUICE BOX AND IN FLUID COMMUNICATION THEREWITH TO INTRODUCE WOOD FINES THEREIN, AND CONDUIT MEANS IN FLUID COMMUNICATION WITH SAID SLUICE BOX TO INTRODUCE SUBSTANTIALLY VERTICALLY DOWNWARDLY INTO SAID SLUICE BOX AN AQUEOUS MEDIUM WHEREBY FINES ENTRAINED IN SUCH DOWNWARDLY INTRODUCED AQUEOUS MEDIUM ARE UNIFORMLY DISTRIBUTED THROUGH SAID SLUICE BOX EXIT PORT UPWARDLY TOWARD THE SURFACE OF THE FLUID LOCATED IN SAID CHAMBER WHEREBY FINES OF DIFFERENT DENSITIES READILY SEPARATE IN SAID FLUID AND ARE SEPARATELY RECOVERABLE.