US3629002A

US3629002A - Method and apparatus for extracting sugar from bagasse

Info

Publication number: US3629002A
Application number: US782815A
Authority: US
Inventors: Willy Kaether; Hans-Dieter Backofen
Original assignee: BMA Braunschweigische Maschinenbauanstalt AG
Current assignee: BMA Braunschweigische Maschinenbauanstalt AG
Priority date: 1968-12-11
Filing date: 1968-12-11
Publication date: 1971-12-21
Anticipated expiration: 1988-12-21

Abstract

A method and apparatus for extracting sugar from bagasse in which extraction is effected by an aqueous liquid, the crude bagasse being fed into one end of a diffusion trough and discharged at its other end. The layer of bagasse is treated in two stages for which purpose the diffusion trough is divided into two zones, an entry zone and a diffusion zone. When in the entry zone the bagasse receives a thermal treatment and before leaving the same is subjected to pressure by passage beneath a pressure and a conveyor roller. In order to facilitate passage of the bagasse layer through the diffusion zone the bottom comprises a series of rollers, certain, preferably alternate, rollers being driven. The roller bed may be made up of large diameter (driven) rollers and relatively small (nondriven) rollers consisting of a perforated drum and serving to collect the extraction liquor so that it can be directly pumped back into the recirculation line to the sprays.

Description

United States Patent [72] Inventors Willy Kaether Braunschweig-Melverode; Hans-Dieter lBackofen, Braunsehweig, both of Germany [2]] Appl. No. 782,815 [22] Filed Dec. 11, 1968 [45] Patented Dec. 21, 1971 [73] Assignee Braunschweigische Maschinenbauanstalt Braunschweig, Germany [54] METHOD AND APPARATUS FOR EXTRACTING SUGAR FROM BAGASSE 13 Claims, 8 Drawing Figs.

[52] U.S. Cl 127/5, 23/270 B, 127/3, 127/43 [51] lnt.Cl Cl3d1/12, C13d 1/08 [50] Field of Search 127/3-8, 43-45; 23/270 B [56] References Cited UNITED STATES PATENTS 2,686,192 8/1954 Bonotto 23/270 X 3,275,472 9/1966 Tantawi et al. 127/5 3,475,214 10/1969 Kaether et al. 127/3 X FOREIGN PATENTS 565,928 7/1960 Belgium 23/270 B Primary ExaminerMorris O. Wolk Assistant ExaminerD. G. Conlin Attorneys-Curt M. Avery, Arthur E. Wilfond, Herbert L.

Lerner and Daniel J. Tick ABSTRACT: A method and apparatus for extracting sugar from bagasse in which extraction is effected by an aqueous liquid, the crude bagasse being fed into one end of a diffusion trough and discharged at its other end. The layer of bagasse is treated in two stages for which purpose the diffusion trough is divided into two zones, an entry zone and a diffusion zone. When in the entry zone the bagasse receives a thermal treatment and before leaving the same is subjected to pressure by passage beneath a pressure and a conveyor roller In order to facilitate passage of the bagasse layer through the diffusion zone the bottom comprises a series of rollers, certain, preferably alternate, rollers being driven. The roller bed may be made up of large diameter (driven) rollers and relatively small (nondriven) rollers consisting of a perforated drum and serving to collect the extraction liquor so that it can be directly pumped back into the recirculation line to the sprays.

PATENIEU BECZ] an SHEET 1 SF 2 N & a s & u s Q METHOD AND APPARATUS FOR EXTRACTING SUGAR FROM BAGASSE This invention relates to a method of extracting sugar from bagasse which as it is continuously conveyed through a diffusion trough is sprayed on the countercurrent principle with extraction liquid from liquor containers disposed beneath the trough, and also to apparatuses for carrying out this method.

A method and apparatus for the extraction of sugar is known in which sugar cane, from which sugar is to be extracted, after being crushed into bagasse, is first treated thermally, thereby effecting the plasmolysis of the cells which have not yet been opened by the preceding mechanical treatment of the sugar cane, in order to make these permeable to the sugar juice and thus to facilitate the extraction operation. After such treatment, in known methods and apparatuses the bagasse is passed by suitable conveyor means into a diffusion trough, through which it is moved at uniform speed. The bottom of the heretofore known diffusion troughs which carry the bagasse is generally formed of a movable or stationary sieve, beneath which juice containers, extending over the entire length and width of the trough, are disposed side by side to receive the extraction liquid from liquor sprays located above the bagasse layer. The extraction liquid on passing through the layer of bagasse is extracted from the liquor containers by a pump associated with each container and returned to the bagasse layer upstream of the respective container.

in this manner the extraction liquid passes cyclically in countercurrent through the bagasse layer from one liquor container to the next, or from one liquor spray to the next, and is increasingly enriched with sugar in the direction of the charging side of the diffusion trough,

Movement of the bagasse through the diffusion trough may be heavy drag chains interconnected by conveyors bars which move over the perforated (sieve) bottoms of the diffusion trough, or by means of rotating sieve belts.

Extraction plants have also been constructed which consist of a diffusion trough, in which both the thermal preparation of the crude bagasse before the diffusion operation and also the extraction operation itself, following said preparation, are carried out in the same trough. The zone in which the thermal preparation of the bagasse is carried out is not separated by any mechanical means from the adjoining extraction zone in the common trough.

For the thermal preparation of the crude bagasse (the application for a short time of a higher temperature than in the adjoining diffusion operation for reasons of plasmolysis and bacteriological operations), extraction liquid, which had already passed through the diffusion zone in countercurrent and already possessed the sugar content which is attainable in practice in the diffusion zone, was fed as so-called circulation liquor to the first, thermal preparation zone after the aforesaid rise in temperature.

Plants of this type have the following disadvantages:

In order to work economically and without excessively large and consequently expensive installations, the bagasse layer in the diffusion trough has a height of about 1.5 to 1.8 meters in the region of the thermal preparation zone. The temperature of the sugar-containing circulating liquor for the preparation of the bagasse in the first part of the diffusion trough cannot be raised indefinitely without detrimental effects on the quality of the sugar and the overall yield of sugar. In order to reach the desired higher temperature of the crude bagasse for a short period before the extraction, the consequently restricted temperature drop between the crude bagasse and the circulating liquor therefore requires a quantity of circulating liquor which amounts to a multiple of the extraction liquor and which then, with the degree of crushing of the crude bagasse desired in each particular case, is not able, because of the volume thereof, to pass through the bagasse bed, which has a height of about 1.5 to 1.8 meters, on account of the resistance to its flow. Interruptions in operation or inadequate heating of the bagasse, with its detrimental consequences, are then unavoidable.

Another disadvantage of such installations, in which both the thermal preparation zone and the adjoining diffusion zone are accommodated in the same trough, is that in the transition zone between the thermal preparation zone and the diffusion zone there is a continuous, harmful mixing of circulating liquor and extraction liquid, which impairs the degree of extraction.

To avoid these disadvantages, the expedient was adopted of removing the thermal preparation from the diffusion trough and carrying it out in a separated station with a separate mechanical drive, this being known as the maceration stage. In a maceration stage of this type it was then possible to work with substantially smaller, i.e. shallower layers of bagasse than indicated above and also to operate at the desired temperatures for the circulating liquor and with correspondingly larger amounts of the latter.

Separately working stations of this type however require additional conveyor means, which take up a great deal of space and are costly.

Another disadvantage of known sugar extraction plants consists of the type of transport for the bagasse through the diffusion trough. The great depth of the layer of bagasse which is necessary for extraction of this type and the great overall length of such diffusion troughs, namely about 40 to 50 meters, which are indispensible if the desired degree of extraction from the bagasse is to be achieved, lead to considerable frictional forces between the rough bottom of the diffusion trough, which is constructed for example as a sieve, and the bagasse on the one hand, and between the heavy drag chains with their conveyor elements, which are constructed as conveyor bars and slide along on or in the plane of the sieve bottom, and the bottom on the other hand. The forces occurring in a diffusion trough of this type because of the frictional conditions are so great that they necessitate very heavy conveyor chains, up to eight such chains being disposed side by side so as to slide on the sieve bottom, while each chain entails tractive forces of up to 30,000 kg. The chain drive units must consequently also be very sturdy and expensive to build, while in particular the gears used in the transmissions are exposed to heavy loads. Drive units complying with these requirements entail considerable expense, which constitutes an important part of the total cost of known extraction plants. In addition, the concentration of such large forces constitutes a continuous danger to operational reliability and to the operators.

Moreover, the sieve bottom in known installations and also the chains sliding over them are subject to considerable wear because of the entrained sand and the heavy friction occurring between parts, and necessitate expensive replacement after a relatively short time.

The problem underlying the invention consists in obviating the above-mentioned disadvantages of known sugar extraction methods and apparatus and in particular to provide a method, and also apparatuses for carrying out this method, which while entailing investment and operating costs which are lower than those of known methods and apparatuses, provide an at least equivalent extraction yield and, in contrast to the previous situation, now make it possible to build installations of practically unlimited length without additional cost increasing considerably with length.

According to the invention, this problem is solved through the fact that the diffusion trough is subdivided into at least two zones, and that the crude bagasse is thermally prepared in the first, or entry, zone and is compressed at the end of this zone. By dividing the diffusion trough, in accordance with the invention, into two zones by means of the compression of the bagasse at the end of the entry zone, the expensive construction of a separately working maceration stage is avoided and an economically more favorable accommodation of the thermal preparation of the bagasse in the diffusion trough itself is made possible without any harmful mixing of circulating liquor and extraction liquid occurring. in addition, as will be described below, the compression of the bagasse before entering the diffusion zone brings advantages of such a nature that according to the invention the step of compressing the bagasse can be applied even to extraction plants in which the maceration stage is in the form of a structurally separate unit.

Since the crude bagasse introduced into the inlet zone still constitutes a relatively loose layer, according to another feature of the invention it is advantageous, in the interest of a continuous and extensive extraction operation, for the speed of travel of the bagasse in theinlet zone to be higher than in the adjoining diffusion zone This difference in the speed of travel has the advantage that the depth of the bagasse layer in the inlet zone is less than that in the diffusion zone, so that the spraying of the bagasse in the entry zone leads to a desiredly rapid thermal preparation.

The reduction in the speed of travel of the bagasse is brought about according to the invention at the transition from the entry zone to the diffusion zone, where the bagasse is simultaneously subjected to pressure to extract the liquor.

To enable the relatively thin layer of bagasse in the entry zone to be effectively compressed and to ensure an increased depth of layer of the bagasse which is required for the diffu sion zone, according to another feature of the method of the invention the bagasse is dammed up at the end of the entry zone.

Starting with an apparatus consisting essentially of a diffusion trough and having liquid spray distributors supplied from liquor containers arranged side by side over the entire length and width of the trough, and disposed beneath the bottom of the trough, in accordance with this invention the diffusion trough is divided into at least one entry zone and one diffusion zone, which together form a constructional unit, the bagasse being subjected to thermal preparation by spraying in passage through the entry zone, and between the entry Zone and the diffusion zone there is provided means such as a conveyor roller for applying the necessary pressure. Provision of a compression and conveyor roller between the entry and diffusion zones enables the expensive drag chains required in known devices for conveying the bagasse, together with the appertaining conveyor bars and the heavy drives which they require, to be dispensed with,

The extraction plant of this invention thus works with a new type of preparation station, which is in the form of an entry zone and in which the bagasse is not only prepared by the in troduction of the heated circulating liquor, which has already passed through the diffusion trough as extraction liquid, but is also subjected to additional preparation by mechanical compression by means of a roller, into a compact, coherent mass at the end of the entry zone, i.e. prior to entry into the diffusion zone, after it has first been dammed up by the action of the compression and conveyor roller at the end of the entry zone.

On entering the diffusion zone the bagasse consequently has, as a result of the measures according to the invention, a consistency which in known diffusion troughs frequently can only be achieved at the end of the diffusion operation, on discharge from the diffusion trough, as the consequence of frequent spraying with extraction liquid. Owing to the fact that the bagasse is compressed into a compact, coherent mass it is in fact made possible for the compression roller disposed at the transition from the entry to the diffusion zone to be used for conveying the bagasse through the diffusion zone.

The provision of this conveyor roller at the entry to the diffusion zone not only serves to extract liquor from the bagasse leaving the entry zone, whereby effective separation of the cir culating liquor from the extraction liquid is achieved, but also the additional purpose of separating two different stages of the process, while at the same time serving as a means for conveying the bagasse into the diffusion zone and acting as a dam to increase the depth of the layer.

This compression of the: bagasse leads at the same time to an improvement of the extraction, since more intimate contact between the extraction liquid and the bagasse is achieved through the reduction in size of the cavities within the bagasse layer.

Since liquid passes through the bagasse in its passage through the diffusion zone and since the wet surface has a certain ability to slide, according to another feature of the invention the compression and conveyor roller is provided on its periphery with axially extending webs in order to increase the grip of the rollers on the bagasse so that it will more effectively transmit movement to the bagasse.

The conveyor roller may be mounted in a fork which pivots about a horizontal axis, so that it will rise and fall with changes in depth of the bagasse layer and thus automatically accommodate itself to operating conditions at all times.

Through the provision of a roller, which may be provided with a brake mechanism at the outlet end of the diffusion zone, particularly effective and desirable extraction of water from the bagasse is effected before it leaves the diffusion zone because of the cooperation of said roller with the bottom of the diffusion zone, as a consequence of a prearrangement of the bagasse layers through the brake action of the roller.

In one embodiment of the invention the bagasse is supported in the region of the compression and conveyor roller on a perforated slide plate over which the bagasse is pushed by the action of the conveying rollers and through which the liquid can pass into the receiving vessels beneath it In another embodiment support of the bagasse in the region of the compression and conveyor rollers is by means of a rotating plate conveyor, so that the frictional losses occurring between the moving bagasse and the bottom supporting it are reduced to a minimum.

To enable the circulating liquid accumulating in the entry zone to be easily discharged, the bottom of the diffusion trough in the entry zone consists of a downwardly inclined conveyor belt formed by rotating sieve surfaces or of conveyor chains which are disposed above a stationary perforated bottom and operate at a conveying speed greater than the peripheral speed of the conveyor rollers, in order to achieve the previously mentioned, desirable difference between the conveying speed in the entry zone and that in the diffusion zone.

It has already been mentioned elsewhere that an important object of the invention consists in replacing the known expensive conveyor devices for transporting the bagasse through the diffusion trough in a manner which is advantageous to the carrying out of the method, while reducing the previously described frictional losses in the diffusion zone to about 30 percent of the values previously known. The power required for the heavy drive means for conveying the bagasse may thereby also, according to the invention, be reduced so that at the same times an operationally reliable extraction plant requiring less maintenance and far less expensive to construct is produced.

According to this invention the bagasse is conveyed through the diffusion zone by a series of rollers arranged at intervals and mounted to revolve about horizontal axes transverse to the directional of movement of the bagasse. Transport of the bagasse through the diffusion zone thus consists of a simple roller grid, which works only with rolling friction instead of sliding friction, so that the above described disadvantages of previously known conveyor devices for the bagasse are avoided.

The new type of preparation by compression of the bagasse at the: end of the entry zone before it passes into the diffusion zone makes it possible for the mass of bagasse prepared in this manner to be fed to the roller grid provided with gaps for discharge of the extraction liquid, so that the breaking down and pulling apart of the bagasse on its lower side when passing through the diffusion zone are avoided and the use of a roller grid is made possible. The harmful passage of large amounts of bagasse through the roller grid into the extraction liquid is thereby avoided, and the formation of a compact bundle of bagasse enables the latter to be transported over the roller grid. Only the compression of the bagasse at the end of the entry zone makes it possible for a bagasse layer which is flat on its upper side to pass through the diffusion zone despite the considerable action of the friction on the sidewalls, so that varying depths of the bagasse layer stream and consequently different diffusion results for individual zones of the bagasse are avoided. At the same time, depending on the degree of crushing of the bagasse, the compression of the latter at the end of the entry zone is effected to the extent to which it would in any case by adjusted in accordance with experience in previously known diffusion troughs, at the outlet ends of the latter, through the continuous spraying with extraction liquid.

These advantages achieved by the compression of the bagasse in accordance with the invention before it enters the diffusion zone are of such great importance to the profitability and the perfect performance of the sugar extraction operation that, as previously stated above, even in the case of diffusion troughs in which the maceration takes place in an apparatus separate from the diffusion trough this compression of the bagasse in accordance with the invention can also be effected.

In the diffusion zone therefore the perforated bottom grids which were previously usually employed, together with the chains and conveyor elements sliding over them and also their heavy drives, are replaced by a roller grid, over which the bagasse layer of a height of about 1.5 meters is transported by the action of the compression and conveyor rollers, while a further reduction of frictional losses and further conveying of the bagasse can be achieved through the fact that the rollers are provided with a drive and that either groups or all of the driven rollers are associated with the drive.

After passage through the bagasse layer, the extraction liquid sprayed onto the surface of the bagasse passes through the axial gaps between the rollers into the receiving containers disposed beneath the roller grid, whence it is conducted in countercurrent to the adjacent liquor distributor in the direction opposite the direction of transport of the bagasse.

The roller grid, depending on the crushing of the sugar cane to be effected, may be made up of rollers of different diameter. Drive may be imparted to alternate rollers, the driven rollers having a diameter greater than that of the nondriven or guide rollers, all the rollers being arranged with their upper surfaces lying in one plane, so that the bagasse bed, which is already compressed at the end of the entry zone, is transported in a nondestructive manner over the roller grid. Because of the different diameters of the individual rollers, the gaps between the individual lines of contact of the bagasse bed and the roller grid are at the same time relatively small, so that the compressed bagasse bed is not broken up or torn apart and the disadvantageous consequences which would be entailed by washing of particles of bagasse out of the mass of bagasse by the extraction liquid, are avoided, the nondriven rollers filling the gaps between the driven rollers, thereby evening out the transport path for the bagasse bed.

The large diameter driven rollers may have roughening surfaces. In one arrangement the driven rollers are formed with peripheral grooves over which bars are secured extending over the entire length of the rollers. Such bars not only provide the desired increase of friction between the rollers and the bagasse but facilitate extraction of the liquid.

Clearly the roller grid may function as the sole means of conveying the bagasse through the diffusion trough, the rollers above the bagasse bed operating only as compression rollers.

The driven or larger rollers are preferably hollow, being perforated to allow the extraction liquid to enter the interior of the rollers (unless of its own accord it passes out on the bottom side of the rollers and at the same time flushes out any particles of bagasse adhering to the surface of the rollers) from which it is discharged through hollow axles connected to a suction extraction plant.

To prevent small particles of bagasse (e.g. when operating with small cut sizes) passing through the gaps between the rollers into the receiving containers beneath, perforated guide plates or other slide surfaces, which may be adjustable both in respect of their height and their angle of inclination, are disposed between the individual rollers.

The constructional simplification and increased profitability of diffusion troughs, which constitute an object of the invention, may also be achieved in the case of conventional installations provided with a bottom carrying the bagasse and consisting of a sieve. Although as a general rule extraction plants of this type are provided with expensive, disadvantageous, conveyor chains and with conveyor bars extending transversely to the direction of the movement of the bagasse, the division of the diffusion trough into at least two zones, of which the first serves as entry zone for the thermal preparations of the crude bagasse, also provides for these installations the previously mentioned considerable advantages. it is therefore also within the scope of the invention to adopt the measure of dividing known diffusion troughs, provided with sieve bottoms, into at least two zones, namely an entry zone and a diffusion zone, while here again through the provision of a compression and conveyor roller in the transition zone between the inlet zone and the diffusion zone the advantages according to the invention which have already been mentioned above are likewise achieved. In this connection it is entirely feasible for existing diffusion troughs provided with sieve bottoms to be converted in this manner and provided with the features according to the invention.

In the event of the compression and conveyor rollers provided being insufficient to overcome the frictional forces occurring between the bagasse layer and the sieve bottom, it is also possible, as a replacement for expensive drag chains, for the sieve bottom also to be composed of an endless driven conveyor belt. Because of the considerable length of diffusion troughs, it may be convenient for this endless conveyor belt, which is perforated like a sieve, to be replaced by a plurality of shorter conveyor belts driven independently of one another.

The invention is illustrated in the accompanying drawings, in which:

FIG. I is a side elevation of a form of construction of the diffusion trough in accordance with one embodiment of the invention;

FIG. 2 is a plan view of the entry end of the diffusion trough shown in FIG. 1;

FIG. 3 is a detail view of the transition zone between the entry zone and the diffusion zone of the diffusion trough shown in FIG. I, with a rotating plate conveyor disposed beneath the compression and conveyor roller;

FIG. 4 is a side elevation of another form of construction of the diffusion trough according to the invention;

FIG. 5 is a cross section of a number of rollers which carry the bagasse and which have the same diameter;

FIG. 6 is a cross section of a number of rollers carrying the bagasse and having different diameters;

FIG. 7 is a cross section of a roller provided with peripheral grooves; and

FIG. 8 is a longitudinal section, partly broken away, of the roller shown in FIG. 7.

Referring to FIG. 1, the diffusion trough 11 consists of three zones, an entry zone 12, a transition zone 13 and a diffusion zone 14. In the diffusion trough 11 all the zones are combined to form a constructional unit having common sidewalls 16. Within the diffusion zone 14, the bottom support for the bagasse consists of a series of perforated rollers or drums, indicated generally at 17 disposed parallel to one another and spaced apart, with their axes of rotation at right angles to the direction of movement of the bagasse, the rollers 17a having imparted thereto an intermittent rotary motion to advance the bagasse layer, and associated with which are idler (nonrotary) rollers 17b, the purpose of which is to prevent material falling through the gaps between rollers 17a. Liquor containers 18, which are arranged side by side over the entire length and width of the diffusion trough 11 are disposed beneath the conveyor rollers 17, said containers being intended to receive the extraction liquid percolating through the bagasse layer. The extraction liquid collecting in the containers 18, which are of inverted conical shape, is drawn off by circulating pumps 19, one to each container, the pressure branches 20 of each pump ending above the spray distributors 21. The spray distributors 21 are distributed over the diffusion zone of the diffusion trough and in each case are upstream of the liquor container 18 feeding them, referred to the direction of movement of the bagasse.

Material entering the entry zone 12 is received on a downwardly inclined conveyor belt 22 composed of perforated plates and which operates at a speed greater than the peripheral speed of a compression and conveyor roller 23 at the entry to the transition zone 13. On its periphery the roller 23 is provided with axially extending radial webs 23a. Beneath the conveyor roller 23 is a perforated slide plate 25 over which the bagasse from conveyor 22 passes. As shown in FIG. 3, however, this may be replaced by a rotating plate conveyor 26.

The crushed sugar cane passes by way ofa conveyor belt 27 into a filling hopper 28 disposed above a distribution spout 29, which is mounted to swivel about a vertical axis 30 and is supported at its free end on rollers 31 running on a rail 32.

Bagasse passing through the entry zone is subjected to the action of heated circulating liquor for the purpose of thermal preparation, the liquor being discharged as a spray from pipes 33 above the conveyor belt 22. Opposite the discharge end of the spout 29 is a baffle plate 34, beneath which the bagasse passes on to the conveyor belt 22. When the bagasse is transferred from the spout 29 to the conveyor belt 22, intensive rearrangement of the bagasse layers takes place because of the falling movement, and this has the effect that the temperature of the bagasse is rapidly raised by the hot liquor from the pipes 33.

The fact that instead of a separate preparation stage, thermal pretreatment of the bagasse is effected in the course of its restratification on passing from the discharge spout to the con veyor belt 22 and also during its passage through the entry zone at increased speed and with reduced layer height not only enables this separate treatment apparatus to be dispensed with but in addition results in the diffusion trough ll accord ing to the invention having a relatively short length compared with conventional diffusion troughs. In addition, the thorough mixing and intensive wetting in the region of the entry zone results in a particularly favorable increase in degrees Brix. The circulating liquor withdrawn from the containers l8 can moreover be returned to the bagasse at the entry zone either entirely or partly after suitable reheating.

On leaving the entry zone 12 the bagasse is subjected to compression by the conveyor roller 23, which results in almost complete extraction of the liquor and furthermore the bagasse is given a consistency which enables it to be transported through the adjoining diffusion zone by means of the rollers 17 without the lower side of the bagasse being broken up. In addition to its conveying action, the roller 23 simultaneously achieves an effective separation of the operation zone from the difiusion zone, avoiding undesirable mixing of circulating liquor with extraction liquid.

After leaving the transition zone 13 the compressed bagasse layer is carried along by the rollers 17 at a constant rate of travel while simultaneously being sprayed with extraction liquid which, due to the roller 23 is kept at a lower rate than the speed of travel within the entry zone, in the direction of the outlet end 35 of the trough 11. During its passage through the diffusion zone the bagasse is fed with extraction liquid by the spray distributors 21, the latter extending over the entire width of the diffusion trough, distributors 2] being supplied with liquor through the delivery branches from the circulating pumps 19.

At the end of the diffusion zone M is a braking roller 37 carried in a fork 36 mounted to pivot about a horizontal axis, the roller 37 applying pressure to the washed bagasse to extract water from it so that after passage through a centrifugal roller 38 downstream of roller 37, the bagasse can then be fed to a suitable firing apparatus.

The embodiment of FIG. 4 differs from that of FIG. I in that the diffusion trough 11 does not have an entry zone corresponding to that of FIG. 1, but works with a maceration stage separated structurally from the diffusion trough. Consequently, the speed of travel of the bagasse in the section situated upstream of the roller 23 is not higher than in the diffusion zone situated downstream thereof, since the thermal preparation has already taken place. It will be seen however that the FIG. 4 embodiment has a compression and conveyor roller 23 in accordance with the invention, the advantages of which are set out above. Clearly the depth of the bagasse layer upstream of the roller 23 is greater than in the diffusion zone following said roller, the diffusion zone having a length of about 45 meters and the bagasse passing through it in a period of time adapted to its diffusion behavior. As a consequence of the compression which takes place before the bagasse enters the diffusion zone and under the influence of the continuous spraying of the bagasse bed with extraction liquid, gradual shrinking of the height ofthe bagasse layer takes place, so that a compact, concentrated mass is produced.

In the FIG. 4 arrangement the roller 23 is mounted, similar to the brake roller 37, in a fork 39 for pivotal movement about a horizontal axis, so that the rollers will rise and fall with the height of the bagasse layer at any moment, which is dependent on throughput.

The base of the diffuser trough of FIG. 4 is made up of rollers of different diameters, each roller 17a of larger diameter alternating with a roller 17b of smaller diameter, the rollers 17:: being driven in order to assist the conveying movement produced by the compression and conveyor roller 23.

According to a further feature of the invention a drive which is particularly favorable from the point of view of economy and operating requirements is obtained when the rollers 17a are arranged and driven in groups. This can be ef fected by providing suitable operating cylinders 432 in which there is respectively reciprocated a piston to which an elongated piston rod 41 is connected. The reciprocatory rectilinear motion of the rods 41 is transformed to rotary motion of the rollers 17a through lever arms 40 respectively pivotally connected at one end to the rod 411 and having a conventional pawl and ratchet connection with the shaft of a respective roller at the other end thereof. Thus, the other end of the lever arms 40 may be hoop-shaped with a springbiased inwardly radially extending pawl, for example, meshing in the teeth of respective ratchet wheels mounted on the shafts of the rollers 17a to effect rotation of the rollers 17a in one given stroke direction of the piston rods 41. Of course, rotary motion of the rollers 17a can also be effected by a pistoncylinder-linkage system of the type employed for railroad locomotives for uniformly rotating the wheels thereof.

As represented diagrammatically at 50 in FIGS. 1 and d, the circulating liquor depositing in the container 18 is heated to desired temperature before being recirculated to the pipes 33 for spraying the bagasse passing through the entry zone.

FIG. 6 is an enlarged view of some of the rollers 17a and l7b of FIG. 4 with the lever arms 40 removed, and showing slide surfaces or guide plates 49, which may be perforated, that are located between the

rollers

17a and 17b to prevent small particles of bagasse (e.g. when operating with small cut sizes) from passing through the gaps between the rollers and into the receiving containers l8 therebeneath.

In the modification of FIG. 5, instead of

rollers

17a and 17b of different diameter, there are provided rollers 17 of equal diameter. Slide surfaces or guide plates 49 similar to those of the embodiments shown in FIG. 6 are provided between the rollers 17 for preventing passage of bagasse particles through the gaps between the rollers 17. The guide plate 49, located between the two left-hand rollers 17 of FIG. 5 is adjustably pivotable as indicated by the solid and broken line positions thereof.

The rollers 17 of the embodiment of FIG. 5, as well as the larger driven rollers 17a of the embodiment of FIG. 6 are preferably hollow and have a perforated peripheral surface 83 which permits extraction liquid to enter the interior of the respective rollers. The extraction liquid may then be discharged through a hollow axle 44 of the roller connected by a tube 45 to a nonillustrated suction extraction plant. The extraction liquid may also, however, merely discharge from the interior of the respective rollers through the perforations located at the underside thereof, at the same time flushing out any particles of bagasse adhering to the surface of the rollers.

As shown in FIGS. 7 and 8, the large diameter driven rollers l7a may be suitable modified with peripheral grooves 46 formed in the cylindrical wall 48 thereof and provided with peripherally spaced bars 47 extending over the entire length of the respective rollers and suitably secured thereto. The bars 47 provide a desired increase of friction between the rollers 17a and the bagasse while facilitating extraction of the liquid.

What is claimed is:

1. ln apparatus for extracting sugar from comminuted sugar cane the combination of a diffusion trough, spray means located above said trough for subjecting a layer of comminuted sugar cane in passage therethrough to treatment with an aqueous extraction liquid, said spray means operating on the countercurrent principle, screening means in the bottom of the trough over which the comminuted sugar cane is conveyed, containers beneath said screening means to collect extraction liquid from the comminuted sugar cane layer and from which the extraction liquid is recirculated via said spray means, means dividing said trough into a diffusion zone and a pretreatment zone, said spray means including sprays located both in said pretreatment zone and in said diffusion zone, the sprays of said pretreatment zone being adapted to eject a relatively large amount of extraction liquid at relatively high temperature as compared with the amount and temperature of the liquid ejected by the sprays in said diffusion zone, means for moving comminuted sugar cane in a relatively thin layer and at relatively high speed in said pretreatment zone into which the comminuted sugar cane is fed, as compared with the thickness and moving speed of the layer of comminuted sugar in said diffusion zone, so that said pretreated thin layer of comminuted sugar cane collects and forms a layer of increasing thickness compressible by said trough dividing means.

2. Apparatus according to claim 1 in which the bottom of the diffusion trough in the entry zone comprises a plate conveyor.

3. Apparatus according to claim 1 in which the rate of travel of the plate conveyor exceeds the peripheral speed of the compression and conveyor roller.

4. Apparatus according to claim 1 wherein the diffusion trough has sidewalls which are inclined inwardly towards their upper ends.

5. Apparatus according to claim 1 wherein the diffusion trough has a roller with an associated braking mechanism at the outlet end of the diffusion zone.

6. Apparatus according to claim I in which the bottom of the diffusion trough in the entry zones comprises a moving screen.

7. Apparatus according to claim 6 in which the rate of travel of the moving screen exceeds the peripheral speed of the compression and conveyor roller.

8. In apparatus for extracting sugar from comminuted sugar cane, the combination of a diffusion trough; spray means located above said trough for subjecting a layer of comminuted sugar cane in passage therethrough to treatment with an aqueous extraction liquid, said spray means operating on the countercurrent principle; screening means in the bottom of the trough over which the comminuted sugar cane is conveyed; containers beneath said screening means to collect the extraction liquid from the comminuted sugar cane layer and from which the extraction liquid is recirculated via said spray means; means separating said diffusion trough into an entry zone and a diffusion zone, said spray means including sprays located in the entry zone by which the comminuted sugar cane is subjected to thermal preparation and in which a compression and conveyor roller is provided in the entry zone so that the comminuted sugar cane is subjected to pressure before entering the diffusion zone, said diffusion trou h, in the diffusion zone thereof, having a bottom which lI'lClU es a series of rollers mounted to revolve about spaced horizontal axes and over which the comminuted sugar cane layer is moved.

9. Apparatus according to claim 8 wherein means is provided for imparting drive to alternate rollers.

10. Apparatus according to claim 9 in which said alternate rollers are rotatably driven by said drive means, said rotatably driven rollers having a diameter larger than the diameter of the alternate rollers located between said rotatably driven rollers, the upper surfaces of all of said rollers lying in a common plane.

11. Apparatus according to claim 9 in which the driven rollers are arranged in groups, each group being driven from a common source of power.

12. Apparatus according to claim 9 comprising driven rollers whose surfaces are formed with circumferential grooves, in which axially extending bars are attached over the grooves.

13. Apparatus according to claim 9 wherein said alternate rollers are rotatably driven by said drive means, said rotatably driven rollers being hollow and perforated, and each thereof being mounted on an axle formed with an axial bore, and including suction means, and means connecting each of said bores to said suction means.

- A UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 9, Dated December 21, 1971 Inventor(s) Willy Kaether, et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet insert [30] Foreign Application Priority Data Germany" P 15 67 238.5 12/13/67 Signed and sealed this 20th day of August 197 (SEAL) Attest: v

MCCOY M. GIBSON, JR. A 7 C. MARSHALL DANN Attesting Officer I Commissioner of Patents 1 USCOMM'DC 50376-P59 U. 5. GOVERNMENT PRINTING OFFICE: 156! 0-Si5334,

FORM PO-1050 (10-69)

Claims

2. Apparatus according to claim 1 in which the bottom of the diffusion trough in the entry zone comprises a plate conveyor.
3. Apparatus according to claim 1 in which the rate of travel of the plate conveyor exceeds the peripheral speed of the compression and conveyor roller.
4. Apparatus according to claim 1 wherein the diffusion trough has sidewalls which are inclined inwardly towards their upper ends.
5. Apparatus according to claim 1 wherein the diffusion trough has a roller with an associated braking mechanism at the outlet end of the diffusion zone.
6. Apparatus according to claim 1 in which the bottom of the diffusion trough in the entry zones comprises a moving screen.
7. Apparatus according to claim 6 in which the rate of travel of the moving screen exceeds the peripheral speed of the compression and conveyor roller.
8. In apparatus for extracting sugar from comminuted sugar cane, the combination of a diffusion trough; spray means located above said trough for subjecting a layer of comminuted sugar cane in passage therethrough to treatment with an aqueous extraction liquid, said spray means operating on the countercurrent principle; screening means in the bottom of the trough over which the comminuted sugar cane is conveyed; containers beneath said screening means to collect the extraction liquid from the comminuted sugar cane layer and from which the extraction liquid is recirculated via said spray means; means separating said diffusion trough into an entry zone and a diffusion zone, said spray means including sprays located in the entry zone by which the comminuted sugar cane is subjected to thermal preparation and in which a compression and conveyor roller is provided in the entry zone so that the comminuted sugar cane is subjected to pressure before entering the diffusion zone, said diffusion trough, in the diffusion zone thereof, having a bottom which includes a series of rollers mounted to revolve about spaced horizontal axes and over which the comminuted sugar cane layer is moved.
9. Apparatus according to claim 8 wherein means is provided for imparting drive to alternate rollers.
10. Apparatus according to claim 9 in which said alternate rollers are rotatably driven by said drive means, said rotatably driven rollers having a diameter larger than the diameter of the alternate rollers located between said rotatably driven rollers, the upper surfaces of all of said rollers lying in a common plane.
11. Apparatus according to claim 9 in which the driven rollers are arranged in groups, each group being driven from a common source of power.
12. Apparatus according to claim 9 comprising driven rollers whose surfaces are formed with circumferential grooves, in which axially extending bars are attached over the grooves.
13. Apparatus according to claim 9 wherein said alternate rollers are rotatably driven by said drive means, said rotatably driven rollers being hollow and perforated, and each thereof being mounted on an axle formed with an axial bore, and including suction means, and means connecting each of said bores to said suction means.