US3443905A - Apparatus for solvent extraction of subdivided solids - Google Patents

Description

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United States Patent Int. Cl. B01d 11/04 U.S. Cl. 23269 11 Claims ABSTRACT OF THE DISCLOSURE Apparatus for continuously extracting sugar from sugar cane. The apparatus has a circular chamber containing a bed of subdivided cane. The chamber and the bed of cane are rotated as a unit while solvent is recirculated therethrough counter-current to the direction of rotation of the chamber.

This is a continuation-in-part of application Ser. No. 489,022 filed Sept. 21, 1965, the latter of which is a continuation-in-part of application Ser. No. 237,575 filed Nov. 14, 1962, now Patent No. 3,248,263.

This invention relates to a new and improved apparatus for removing or extracting, by the use of a suitable solvent or solvents, soluble substances from sub divided solids by diffusion, leaching, or lixiviation.

More specifically, the apparatus of this invention is designed to carry out the removing and extracting procedure of the type referred to by a continuous operation, as distinguished from a batch operation, and to effect such removal or extraction by employing an essentially counter-current flow or movement between the mass of subdivided solid material undergoing treatment and the extracting solvent or solvents employed.

In systems of this type which employ solvent as the liquid extracting medium it necessarily follows that recovery of the soluble substance free from the solvent requires subsequent separation of the two, which is a costly procedure. Accordingly, an objective for an improvement in this art is that of securing the removal and recovery of the maximum quantity of soluble substance while employing for that purpose the smallest possible amount of solvent.

Theoretically, the counter-current relative movement of the solid material and the solvent is well suited to diffusion, leaching, and lixiviation procedures, and good practical usage has been made of such practice in the past. However, as far as these applicants know all prior art procedures of this general type which have employed counter-current relative movement between the solids and solvent to effect such extraction have left a great deal to be desired from the standpoint of providing a procedure which employs a solids and solvent relationship which adequately approaches the ideal for the most efficient extraction. Theoretically, the greatest efiiciency would be achieved, other circumstances permitting, if each drop of the liquid solvent were brought successively into diffusing, leaching, or lixiviating contact with each particle of the solid material, in that sequence or order establishing a true counter-current flow therebetween.

Whereas such an ideal operation is desirable in principle it poses an impossible problem from the practical standpoint, but, at the same time, it is to be understood that in this art improvement does lie in the direction of approaching as closely as possible the theoretically ideal flow contact relationship between the solids and the solvents.

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Another objective in this art is that of maintaining at all times best possible solids and solvent conditions with respect to the relative quantities of each throughout the entire mass of material undergoing treatment.

Based on these considerations the present invention proceeds upon the principle of providing an apparatus which establishes and maintains an elongated continuous uninterrupted mass of subdivided solid material to be treated of substantially rectangular cross-section, having substantially uniform bulk density and permeability throughout, said mass having its length extending horizontally, preferably on the circumference of a circle, but on a straight or other line if desired, its width defined by vertical side faces and its depth maintained at all times at a substantially constant dimension with the upper face thereof constituting a substantially horizontal even surface disposed at a level which gives to said mass a depth dimension of substantial magnitude. It is to be understood, however, that the solid material will become slightly compacted as it travels through the treatment zones, and to this extent the bulk density and permeability thereof will be slightly altered.

The apparatus of this invention assures the close lateral confinement of the side faces of said mass Without frictional or other disturbance. The apparatus includes confining side walls immediately adjacent the side faces of said mass to contact the same and contain the solvent placed thereon without relative movement between the side walls and said mass. The side walls thus confine the solvent to the desired downward travel throughout said mass without channeling or otherwise undergoing nonuniform fiow action. The downward flow of the solvent is therefore characterized as being carried out without disturbance or movement of the material of said mass such as would result from a relative sliding movement between the containing side walls and the mass itself. Such relative movement not only would continuously agitate and disturb the uniform character and disposition of the mass itself, thus producing channeling or other unwanted actions, but would also disturb the relatively quiescent downward movement of the solvent in a manner detrimental to the high efficiency resulting from this invention and, in addition, would prevent the successful practice of clarification procedures, hereinafter more fully explained, contemplated for this invention.

The apparatus of this invention accordingly provides means for continuously applying fresh subdivided solid material at one end of said mass and means for continuously removing, at a corresponding rate, spent solid material from the other end of said mass, while at all times maintaining conditions which will cause the material of said mass to be deposited in a condition of substantially uniform bulk density and permeability with a substantially level and even top surface and with a close non-channeling and supported contact with the side walls.

In addition, the apparatus of this invention provides for the desired gravitational passage of the solvent liquid through a limited and particular zone or portion of the mass so that fresh liquid first encounters the most spent material and also in such manner that the continuous stream of liquid fed to the top of said zone or portion of said mass comes in contact for diffusing, leaching, or lixiviating activity with a vertical column of said mass of substantial depth but of relatively small cross-sectional area. In addition, the zones of treatment are determined solely by the control of the supply of liquid solvent employed and not by partitions intersecting the mass. In other words, this invention provides that the mass from end to end shall be continuous, uninterrupted, and uniform and thus free of dividing walls or partitions or any other similar structures such as would create pockets or corners or other spaces that will not uniformly fill as required. Thus the continuous character of the mass renders it free from channeling or any tendencies which would interfere with the uniform flow, association, and contact between the solids and the liquids as required for this invention.

After the first downward pass of the solvent liquid is accomplished, as above set forth, the liquid is continuously collected at a point below the treated zone or mass column and returned to the top of the mass and deposited on the next adjacent zone or column and thereafter again collected at the bottom and again returned to the top, repeatedly on and on progressively to the end that the liquid undergoes successive passes through the respective columns or zones in the diretcion moving from the end of the spent material toward the end where the fresh material is added to the mass.

In addition to the foregoing, the apparatus of this invention contemplates selectively locating the solvent distributors positioned above the mass longitudinally thereof so as to alter, within limits, the location of the solvent outlets, respectively, with respectto the collecting zones or tanks positioned below the mass.

It should be understood that any particular material undergoing treatment will have its own peculiar permeability characteristics, depending upon its nature and its preparation and, accordingly, the time interval for the passage of solvent therethrough will depend on the particular material being processed. The control of the ultimate destination of the solvent in the underlying solvent receiving zones or tanks must take into account this permeability factor and the rate of speed at which the material is moved relative to said zones or tanks. This involves a longitudinal adjustment of the solvent outlets with respect to the underlying solvent receiving zones or tanks.

The ideal operation of the apparatus requires that the solid material be so prepared that its permeability rate will permit just 100% of the overall solvent throughput to pass successively through each solvent outlet, each treatment zone of the said mass, and each bottom collecting zone, thus creating the longest possible effective path of solvent travel through the said mass without recirculation through any individual treatment zone; and this, while maintaining the maximum amount of solvent in contact with the said mass.

With the solid material thus prepared, there will be a certain position of the solvent outlets that will permit such operation without flooding of solvent at the top of the said mass.

If the preparation of the solid material is such that its permeability rate will not permit the passage of the said 100% of solvent throughput through each treatment zone, then the solvent outlets must be adjusted in the direction of solvent advance, and flooding at the top of the said mass will be avoided because part of the solvent will be advanced greater than one treatment zone.

If the permeability rate of the solid material is such that only 50% of the overall solvent throughput will pass through each treatment zone, there will in effect be created two separate paths of solvent travel, each skipping intermediate treatment zones, and this will result in an effective length of solvent travel one-half that at the said 100% operation.

Intermediate permeability rates will call for intermediate adjustments of the solvent outlets, and will result in intermediate lengths of elfective solvent travel.

If the preparation of the solid material is such that its permeability rate is so great that the maximum amount of solvent cannot be maintained in contact with the said mass at the said optimum 100% operation then the solvent outlets will be adjusted in a direction opposite that of the solvent advance, and there will be partial recirculation of solvent through each solvent outlet and treatment zone. In general, recirculation of solvent in a treatment zone of susbtantial depth results in reduced extraction that partially offsets the advantage of maintaining maximum contact of solvent and solids. Therefore, any preparation of the solid material that permits a solvent flow substantially in excess of the said 100% operation, with com sequent recirculation, will usually be found to be undesirable. However, in some instances recirculation may prove to be desirable, and the apparatus is capable of operation in such manner.

The flow of solvent should be such that the solvent quickly penetrates the top of the mass and passes downwardly withsome lateral spreading to contact the material constituting the particular column or zone of the mass selected for treatment by aparticular solvent outlet. The

slight pooling that occurs immediately beneath the outlets should be confined to this limited area and the solvent should quickly disappear as a result of its downward passage into the mass so that there will be no overall pooling on top, such that the solvent from the individual successive outlets can run and mix together.

A further feature of the invention is to provide an apparatus which permits the solvent at the point of highest concentration where it is removed tfrom the system to be filtered and thus cleansed by passage through the mass of material undergoing treatment which itself has previously been cleansed by washing with the same juice on a prior pass in the circulation.

As another feature of this invention an apparatus is provided which includes the mechanisms above referred to for diifusing, leaching, or lixiviating, which are espe cially adapted for use inextracting sugar from sugar cane. In this form of the invention a system is provided which employs diffusion, leaching, and lixiviation of the above describedtype, together with mechanism for processing the cane prior to its introduction into the diffuser, and an additional mechanism for receiving the spent cane and subjecting it to a pressing action for the recovery of a substantial portion of the residual juice. In a system of this type for processing sugar cane, it is highly important that such residual juice be recovered and returned to the diffusing process.

With respect to this aspect of the cane treatment, it is important to reduce the cane to a fiberized mass made up of individual fibers with associated pith. The cane is so prepared by subjecting it to the action of two novel pieces of equipment herein defined as a cane buster and a cane fiberizer.

In addition, the action with respect to the pressing of the spent cane, commonly called bagasse, may be carried out in apparatus of any suitable type serving as a bagasse press. The spent cane before pressing will hereinafter be called wet bagasse and after pressing pressed bagasse.

In the light of the foregoing, it may be understood that it is an object of this invention to provide an apparatus which is capable of carrying out an extraction for removal of soluble substances by the use of a suitable solvent or solvents from subdivided solid material by diffusion, leaching, or lixiviation, which is characterized as having a higher efiiciency productive of a greater yield with the minimum amount of solvent. By way of illustration and as applied to the diffusion of sugar from sugar cane, this -invention is cap-able of extracting high percentages of sugar when operated at a draft as low as approximately 100. As used here, draft should be understood to mean the weight of diffusion juice leaving the diffuser expressed as a percentage of the weight of the prepared cane entering the diffuser. Prepared cane is the total cane entering the diffuser, including trash, dirt, leaves, and any other foreign material.

A further object of this invention is to provide an apparatus for extracting sugar from sugar cane which produces juice of greater clarity.

It is a further object of this invention to provide an apparatus through the use of which juice may be extracted from sugar cane which is purer than such extracts of the

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