US1858591A - Apparatus for making pulp - Google Patents

Description

May 17, 1932. R. w. HOVEY APPARATUS FOR MAKING PULP Filed NOv.3, 1928 3 Sheets-Sheet 1 w A' A I I i mmwlill I}: I--- I illxllll- I--- I I Alf A! A IAII. A |Am C V a I II INVENTOR REX.VV.H

721/ G ATIURNEiZ May 17, 1932.

R. W. HOVEY APPARATUS FOR MAKING PULP Filed Nov.3, 1928 3 SheetsSheet 2 INVENTOR- REX.WHOVEY BY. 1%

ATTORNEYS y 1932- R. w. HOVEY 1,858,591

APPARATUS FOR MAKING PULP Filed Nov.3,. 1928 5 SheetsSheet 3 .INVENTOR REXWHOVEY ATTORNEYS V Patented May 17, 1932 UNITED STATES an W. HOVEY, OF ST. JOHN, NEW BRUNSWICK, CANADA APPARATUS FOR MAKING PULP Application fled November 3, 1828, Serial No. 817,084, and in Canada July 15, 1826.

This invention relates to a process of making paper pulp, and is filed as a continuation,-

In part, of ap lication Serial No. 132,239

filed August 28t 1926.

T In the ordinary method of cooking wood to make sulphite pulp the chips or ligno celluloss products are packed in a di ster and cooked with a bisul hite liqui such as Ca(HSO and 1.86, Steam is applied,

usually, to the bottom of the digester and the whole mass is heated up, during which time the cooking liquor penetrates the chips. The heat ap lied is increased to a cooking temperature 0? about 140 to 150 C. and the wood is cooked for a period of eight hours or more,

depending upon the character of the pulp desired and the temperature employed.

In raising the temperature of the mass in the digester to a cooking temperature, it has been found that the mass of chips is heated very unevenly. When steam is applied at the bottom of the digester the heat rises at the centre of the digester and this central zone, from the bottom upwards, together with a space occupying the upper portlon of the digester, becomes heated much more rapidly than the annular space at the outside of the digester especially towards the bottom.

No satisfactory circulating means has been found to circulate the heated liquor so that all parts of the digester will be heated uniformly. I have found, by experiment, that there is a difference of as much as C.- between the temperature at the upper part of the digester and that at the lower outer portion of same.

One of the objects of the present invention is to provide a method of circulating the liqnor in the digester in such amanner that the temperature becomes, substantially, uniform throughout the entire body of the di' gester. When this uniform temperature is maintained the chips are heated uniformly. penetration is uniform and cooking becomes uniform with the result that the chips may be satisfactorily cooked in much less time than is ordinarily employed. The cooking time is not only reduced but a much better and more uniform product is produced and an increased yield is obtained. This uniformity of product also results in easy bleaching with a very considerable reduction in the quantity of bleach re uired.

The maintenance oi uniform cooking temperatures leads to other beneficial results.

Usually, wood products are either overcooked, which results in weaker pulp and a distinctloss in yield, or they are not cooked I uniformly, which results in coarse pulp and to excessive screeninglosses. I have found that by cooking wood at uniform temperatures I can dissolve out the lower sugars and a portion of the lignins and still retain practically all of the cellulose of the lignins, sugars and other so-called impurities, without deleteriously affecting the character of the pulp for certain purposes.

I can, also produce a pulp which is easily hydrated and which is particularly adapted for the making of parchment like papers. For example, when 1t is desired to Produce a sulphite pulp for mixing with ground wood for making newsprint, or when it is desired to produce an unbleached pulp for making (6 papers of the kraft type, I find that increased strength may be obtalned, along with a very considerably increased yield, by cooking the wood in such a manner as to retain all of the cellulose and somewhat less than half of the lignins, along with a certain percentage of the sugars, pentosans and other products.

In a pulp of this character I do not desire nor do I obtain a hi h percentage of alpha cellulose, but I preface a pulp containing practically the entire cellulose content of the wood as alpha, beta and gamma cellulose, together with a portion of the lignin constituent and, also. a considerable percentage of the complex sugar content. I thus produce a pulp to yield approximately 55% to 65% of the total ligno-cellulose content. As the cellulose content ordinarily recovered in sulphite pulp is seldom more than 50% of the wood, it. will seen that greatly increased yield of material is obtained by my process. Fu rt-hermoi'e, I have found that the strength of such pulp is greatly increased and compares favorably with that of the pulp used in making kraft papers. In fact, fromno with a proportion 65 A .parts of the digester,

this product I can produce the equivalent of a kraft paper having the strength and crackling properties of kraft paper but with a brighter and much improved color.

The product made by slightly under cooking ligno-cellulose at a uniform temperature according to my process results in an entirely new type of pulp. In some cases, however, it may be necessary to subject a part of the fibres to a subsequent treatment after the cooking operation. This treatment consists in brushing or rubbing out a certain proportion of the'slightly undercooked fibres a high percentage of alpha cellulose, or slightly under cooked pulp containing a certain percentage of the lignins and other so-called impurities.

I believe that it is only possible to obtain such results by maintaining a perfect control of temperatures within the digester and this control of temperatures can only be accomplished through the proper circulation of the cooking liquor. By uniforni temperatures I refer to conditions in which the temperatures between any portions of the digester will not vary by more than 3 to 8 C. after the first hour from the commencement of the cook. A series of tests made in circulating cooking liquor according to my invention show temperature variations of less than 5 C. while the ordinary variation in temperature for a considerable portion of the cook ranges from 10 to 35 C. Such wide variations of temperatures would be fatal to the production of a satisfactory product from a slightly under cooked pulp and for all classes of pulpI have found that it is of the utmost importance to be able to maintain substantially perfect temperature control. If the ligno-cellulose material to be cooked was all of normal structure and temperatures could be maintained uniform throughout the digester, the quality of the pulp could be predetermined by the time' of cooking and the temperatures employed. I am able, by maintaining uniform temperatures to eliminate all variable or unknown factors excepting differences in the character of the wood. Assuming that the material to be cooked is of uniform quality,*I can produce a uniform quality of'well cooked pulp within a certain number of cooking hours and the time will be considerably, reduced over the time required for the ordinary cook.

If a pulp is desired containing a certain proportion of lignins or other impurities, the time of cookin is reduced or the'temperature is reduced an v the pulp is slightly widercooked. In such a case the normal 1i 0- cellulose material is cooked so that the fi res fall apart readily, but where abnormal structures appear the fibres will be in a slightly less cooked condition than the normal fibres. Consequently, it ma become necessary to treat theseabnormal bres in a somewhat different manner than the fibres from the normal structures. When a mass of such pulp is blown from the digester it is passed through the usual screening apparatus. The normal fibres will pass through the screen but the coarser and under cooked fibres will remain .on the screen. I find that these fibres only require a brushing or rubbing apart action in order to put them in substantially the same condition as the normal fibres. I, therefore, subject these fibres which will not pass through'the screen to a rubbin or brushingi action in a suitable machine an when this is one the product is mixed with the screened fibres and becomes a product of homogeneous material. In this manner I produce a chemical pulp which I believe is entirely new in this, industry and which contains, in addition to cellulose, a considerable percentage of partially cooked lignins, pentosans, hi her sugars and other products. These pro ucts appear to promote easy hydration and add strength to the finished paper. While this particular product is not intended to'be used as a bleached pulp for making high grades of writing papers and the like, it is very suitable for mixing with ground wood in the manufacture of news rint and may be made into archment and liraft papers. In fact, excel ent papers of the kraft type may be made from sulphite pulp of this character and may be more economically produced than kraft papers from 'the sodaprocess. It will be understood, however, that my process of circulating liquor in a digester may be applied equally as well to the soda process of cooking as to the bi-sulphite process.

- In carryin out my invention, a digester is filled with c ips and cooking liquor is then added. Steam is applied to the di ester in the usual manner, at the bottom. e steam and heat risein the digester through a central zone or core and this central zone' becomes very quickly heated. The heat, also, soon rises to the top of the digester and the natural tendency of the heat is to start a'downward circulation at or near the outer periphery of the digester. The chips are packed so tightly, however, and the bulk of the mass is so large that natural circulation is ineffective and a comparatively large annular zone between the central zone, afiected by the steam, and the periphery of the digester receives comparatively little heat for a long period. Temperature tests under ordinary cooking conditions show that, frequently, the temper ature within this annular zone is between O. and C. lower than the temperature at the top of the digester after about two hours from the commencement of the cook.

It is the purpose of my invention to circulatehot liquor within this annular zone in such a manner as to prevent any considerable variation in the temperature of the cooking liquor. I, therefore, provide a suitable header or like distributor somewhere below the top of the cookinglliquor in the digester and flow off into this points, a portion of the hot cooking liquor, carrying this hot cooking liquor through a suitable pump and pumping the hot liquor into a header or distributor at the bottom of the digester, said header having a series of openings into the digester within the annular zone located between the central steam zone of the digester and even to introduce hot liquor within the central axial zoneat the bottom of the digester. These steps have, however, proved ineffective as comparatively wide variations of temperature still result.

In carrying out my invention I have'illustrated a type of apparatus which may be employed.

Figure 1 is a sectional side elevation ofv a di ester with a liquor circulating means.

igure 2 is a sectional plan of the digester taken on the line 2-2 Figure 1.

Figure 3 is-a sectional plane of the digester taken on the line 33 Figure 1.

Figure 4 is a part sectional elevation of a digester of very large diameter in which the liquor distributing nozzles are arranged to circulate the li uor within a larger annular zone than that s own in Figure 1. V

Figure-5 is a sectional plan taken on the line 5-5 of Figure 4.

Figure 6 is a diagrammatic illustration of the rubbing or brushing device for the. sub-. sequent treatment of the uncooked pulp.

Referring more particularly to the drawings, 11 designates a digester shell with a relief valve 12 at the top and a pipe connection 13. at the bottom 14 which is preferably of conical form to facilitate discharge of-the material from the digester. Positioned near eader, at. a number of the to of the digester and encircling and space from same is the header pipe 15 which is provided with a plurality of inwardly projecting pipes 16 to allow liquor from the digester to flow therethrough into the header and down the vertically disposed pipe 17 into the suction or inlet side 18 of a power driven pump 18b. The ends of the pipes 16 within the digester are covered with screens 19 to prevent the pulp fibres from being drawn into the liquor circulating system. The outlet pipe 18a or discharge end of the pump is connected to a header pipe 20 or distributor of somewhat similar construction to the header 15, that is, it encircles the digester'and is provided with a pluralityof inwardly projecting pipes 21' which pass through the shell into the digester and which ma if necessary be provided at their open on s with screens 22a. The pipes 21 in the device shown in Figure 1 are preferably positioned so that they enter the digester through the conical-bottom and at a radius approximately half that of the maximum radius of the digester shell-for the reasons hereinafter stated. The heating medium, such as steam, is fed into the digester through the pipes 22 and 23 in the ordmary manner, so that its assage is upwardly through the centre of t e mass of material withinthe digester. Control valves 24 and 25 are provided in the pipes 22 and 23. Pipe 23' is also pump by means of the pipe28 which may be provlded with a control valve 29 so that, if desired, steam may be conveniently admitted to the liquor circulating distributor. The

cooking liquor in the digester must be maintained above the open ends of the pipes 16 while the circulating pump is in operation so that the liquor will be kept in circulation during the cook. In Figure 4 the bottom part of a digester of larger diameter than that shown in Fi gu're 1 is shown sothat the inwardly projecting pipes 21a are arranged to cover a much larger area or zone. In the drawings, I have shown two header plpes 20a connected together by means of a pipe 206. These headers are'spaced from one another and concentric with the shell of the digester. The pipes 210; are arranged so that their open ends zig-zag about a line 30 concentric with the shelland positionedapproximately midway between the central axis and the periphery of the digester. The inward ly projecting pipes are shown for illustrative purposes only and it will be readily understood that modifications may be made in the liquor circulating inlet and outlet means without departing from the spirit of the invention.

In operation, the digester is filled with wood chips or ligno-cellulose material and the digester is filled with cooking li uor, the level of which is above the open en of the inwardly projecting pipes at the top of the digester, Steam is then admitted throu h the pipes at the bottom of the digester, in t e usual manner. The steam passes upwardly through the charge in the direction indicated by the chain dotted arrows, heating the core or zone A. The heated liquor tendsto circulate in the usual manner and flows towards the wall of the digester at the top and then and the central axis of the digester the zone B is heated to the temperature of the rest of the digester and the chips within the said zone which, ordinarily, are undercooked, are brought into contact with the hot circulating liquor and uniformity of cook results. The temperatures within the digester being uniform the cooking of the pulp is-uniform, and, therefore, the treatment of pulp in a digester is simplified in that the cooking is reduced to a time temperature basis and a more uniform grade of pulp is provided within a shorter cooking time. \Vhen a product such as kraft or newsprint is desired containing a certain proportion of the li ins and other impurities the time of coo ing is reduced and the pulp is slightly under cooked. In such a case the normal ligno-cellulose material is cooked so that the fibres fall apart rapidl but where abnormal structures appear the bres are in a slightly less cooked condition than the normal fibres and are treated to a brushing or.

rubbing process in order to put them in the same condition as the normal fibres. In Figure 6 an apparatus is shown for accomplishing this object. The undercooked pulp is discharged from the digester throu h the pipe 23 into a blow pit (not shown) an from thence into a screening device 35 through the pipe 36. The screening device is shown diagrammatically in Figure 6 and is provided with two outlets 37 and 38, one for the fibres of the normal wood which pass through the screen and the other for the abnormal struc-- tures which do not pass through the screen and are further treated in a rubbing or brushing device of any of the well known types, one of which is illustrated diagrammatically'. The rubbing device shown consists of a casing 39 mounted on a bed plate 40 adapted to support the motors 41 and 42.

The armature shafts 43 and 44 project into the casing but are spaced from one another at their adjacent ends within the casing. Secured to the shaft 43 and rotating therewith within the casin is the disc 45 which is of dished form an is provided with pro ections 46 which guide the fibres fed into the centre of the casing from the pipe 38 through the opening 47 and through an aperture 48 formed in the disc. Secured to the armature shaft 44 is the disc 49 which is of similar shape to the disc 45. The material under treatment flows into the space 50 between the discs which are each provided with rubbing rin 51 secured to and adapted to rotate wit the discs. The rings are provided with projections 52 on their adjacent faces and the material must pass between the rings before being discharged from the 4 casing throu h the outlet 53, said outlet being connecte to the outlet 37 by means of the Y connection 54. The direction of rotation of the disc is shown by the arrows 55 and 56, that is they rotate in different directions so that the material passing between the discs is subjected to a vigorous rubbing or brushing treatment to reduce the lar er fibres to the same size as the fibres which have passed through the screen, so that the ulp produced is of practically uniform gra e and can be mixed with the normal wood fibres.

By providing for an upward circulation of the hot liquor withinthe annular zone between the central axis and the periphery of the digester, the charge is stirred up and loos ened in much the same manner as the charge within the central zone at the axis of the digester which comes within the influence of the steam. This. upward circulation counteracts the tendency of the chips to settle in a mass and thus the digester may be very much more easily and cleanly blown or discharged. The circulation of the hot liquor according to my invention also enables digesters to be packed or filled by modern filling systems which increase the quantity of the digester charge. Ordinarily, closely packed or filled digesters when cooked in the usual manner without any circulation of the liquor are not only difiicultto blow or discharge but chips within certain zones of the I digester are insufficiently cooked owing to the packing of the mass, non circulation of the hot liquor and other causes resulting from same. By using m y process chips in all parts of the digester are not only loosened by the .direction of circulation but are uniformly heated and penetrated and uniformly cooked.

Having thus described my invention, what I claim is An apparatus for cooking pulp which co1h-- my hand.

REX W. HOVEY.

Images