Extraction Sugar

8/2/2019 Extraction Sugar

1/37

EXTRACTION

andSUGAR INDUSTRY

APPLICATIONS


2/37

EXTRACTION

1-LEACHING(SOLID EXTRACTION)

a) GENERAL INFORMATION

b) FACTORS INFLUENCING THE RATE OF EXTRACTION

c) LEACHNG EQUPMENT

2- LIQUID-LIQUID EXTRACTION

a) EXTRACTION PROCESS

b) CLASSIFICATION OF EXTRACTION EQUIPMENT

- STAGE-WISE EQUIPMENT FOR EXTRACTION

- DIFFERENTIAL CONTACT EQUIPMENT FOR EXTRACTION

EXTRACTION IN SUGAR INDUSTRY APPLICATIONS

1- THE FXED-BED OR ROBERT DFFUSON BATTERY

2- CONTNUOUS DFFUSON BATTERES


3/37

EXTRACTION

Extraction is the method of removing one constituent from a

solid or liquid by means of a liquid solvent.Extraction techniquesfall into two categories.The first is called leaching or solidextraction and the is second called liquid extraction.


4/37

LEACHING (SOLID

EXTRACTION)

A-GENERAL INFORMATIONLeaching is concerned with the extraction of soluble constituent

from a solid by means of a solvent.The process may be usedeither for the production of a concentrated solution of a valuable

solid material,or in order to remove an insoluble solid ,such as apigment ,from a soluble material with which it is contaminated.


5/37

B-FACTORS INFLUENCING THE

RATE OF EXTRACTIONThe selection of the equipment for an extraction process isinfluenced by the factors which are responsible for limiting the

extraction rate.There are four important factors to be considered:

Particle size: The smaller the size ,the greater is the interfacialarea between the solid and liquid,and therefore the higher is therate of transfer of material and the smaller is the distance the

solute must diffuse within the solid.

Solvent:The liquid chosen should be a good selective solvent andits viscosity should be sufficiently low for it to circulate freely.

Temperature:In most cases,the solubility of the material which isbeing extracted will increase with temperature to give a higherrate of extraction.Further ,the diffusion coefficient will be expected

to increase with rise in temperature and this will also improve therate of extraction.

Agitation of the fluid:Agitation of the solvent is importantbecause this increases the eddy diffusion and therefore thetransfer of material from the surface of particles to tha bulk of the

solution.


6/37

LEACHNG EQUPMENT

When the solids form an open ,permeable mass

throughout the leaching operation ,solvent may bepercolated through an unagitated bed of solids.Withimpermeable solids or materials that dissintegrate during

leaching,the solids are dispersed into the solvent and arelater separated from it.Both methods may be either batchor continuous.


7/37

In some cases the rate of the solution is so rapid that onepassage of solvent through the material is sufficient ,butcountercurrent flow of solvent through a battery of tanks is morecommon.In this method, fresh solvent is fed to the tankcontaining the solid that is most nearly extracted;it flows throughthe several tanks in series and is finally withdrawn from the tankthat has been freshly charged.such a series of tanks is called anextraction battery.

Leaching by percolation through stationary solid beds

Stationary solid-bed leaching is done in a tank with aperforated false bottom to support the solids and permitdrainage of the solvent.Solids are loaded into thetank,sprayed with solvent until their solute content isreduced to the economical minimum,and excavated.


8/37

Moving-bed leaching

In the machines that are used for this type ofleaching, the solids are moved through the solvent withlittle or no agitation.The bollman extractor (figure a)contains a bucket elevator in a closed casing.There areperforations in the bottom of each bucket.At the topright-hand corner of the machine ,the buckets are

loaded with flaky solids such as soybeans and aresprayed with appropriate amounts of half miscella asthey travel downward.Half miscella is the intermediatesolvent containing some extracted oil and some smallsolid particles.As solids and solvent flow cocurrentlydown the right-hand side of the machine ,the solvent

extracts more oil from beans.


9/37

Simultaneously the fine solids arefiltered out of the solvent, so that cleanfull miscella can be pumped from theright hand sump at the bottom of thecasing.As the partially extracted beansrise through the left side of the machine

,a stream of pure solvent percolatescountercurrently through them.Itcollects in the left-hand sump and ispumped to the half-miscella storagetank.Fully extracted beans are dumpedfrom the buckets at the top of the

elevator into a hopper from which theyare removed by paddle conveyors.

Bollman extractor


10/37

In the Rotocel extractor,illusratedin figure b, a horizontal basket isdivided into walled compartments

with a floor that is permeable to theliquid.The basket rotates slowlyabout a vertical axis.Solids areadmitted to each compartment atthe feed point;the compartmentsthen successively pass a number ofsolvent sprays, a drainage section,and a discharge point at which thefloor of the compartment opens todischarge the extracted solids.Theempty compartment moves to thefeed to point to receive its next loadof solids.To give countercurrentextraction, fresh solvent is fed onlyto the last compartment before the

discharge point, and the solids ineach preceeding compartment arewashed with the effluent from thesucceeding one.

Rotocel extractor


11/37

Dispersedsolid leaching

Solids that form impermeable beds, either before or duringleaching , are treated by dispersing them in the solvent bymechanical agitation in a tank or flow mixer.The leached residueis then separate from the strong solution by settling or filtration.Small quantities can be leached batchwise in this way in anagitated vessel with a bottom drawoff for settled residue.


12/37

LIQUID-LIQUID EXTRACTION

The separation of the components of a liquid mixture bytreatment with a solvent in which one or more of the desiredcomponents is preferentially soluble is known as liquid-liquidextraction. In this operation, it is essential that the liquid-mixturefeed and solvent are at least partially if not completely immiscibleand, in essence, three stages are involved:

1-Bringing the feed mixture and the solvent into intimatecontact,

2-Seperation of the resulting two phases,3-Removal and recovery of the solvent from each phase.

It is possible to combine stages 1 and 2 into a single pieceof equipment such as a column which is then operatedcontinuously. Such an operation is known as differentialcontacting. Liquid-liquid extraction is also carried out instagewise equipment, the prime example being a mixer-settler unit in which the main features are the mixing of thetwo liquid phases by agitation, following by settling in a

separate vessel by gravity.


13/37

Important applications of liquid-liquid extraction

include the separation of aromatics from kerosene-basedfuel oils to improve their burning qualities and theseparation of aromatics from paraffin and naphthenic

compounds to improve the temperature-viscositycharacteristics of lubricating oils. It may also be used toobtain, for example, relatively pure compounds such asbenzene, toluene, and xylene from catalytically producedreformates in the oil industry, in the production of

anhydrous acetic acid in the extraction of phenol from coaltar liquors, and in the metallurgical and biotechnologyindustries.


14/37

EXTRACTION PROCESSES

All liquid-liquid extraction operations, may be carried out eitheras a batch or continuous process.

In the single-stage batch process illustrated in the figure, thesolvent and solution are mixed together and then allowed toseparate into the two phases-the extract E containing the requiredsolute in the added solvent and the raffinate R, the weaker solution

with some associated solvent. With this simple arrangement mixingand seperation occur in the same vessel.

Fig.single-stage batch extraction


15/37

A continuous two-stage operation is shown in figure, where themixers and separators are shown as separate vessels.

Fig.Multiple-contact system with fresh solvent


16/37

CLASSIFICATION OF

EXTRACTION EQUIPMENTEssentially there are two types of design by which effective

multistage operation may be obtained:

1-Stage-wise contactors, in which equipment includes a seriesof physical stages in which the phases are mixed and separated,and;

2-Differential contactors, in which the phase are continuouslybrought into contact with complete phase separation only at theexits from the unit.


17/37

STAGE-WISE EQUIPMENT FOR

EXTRACTIONThe mixer settler

In the mixer-settler, the solution and solvent are mixed bysome form of agitator in the mixer, and then transferred to thesettler where the two phases separate to give an extract and araffinate. In the settler the separation is often gravity-

controlled, and the liquid densities and the form of thedispersion are important parameters.


18/37

Combined mixer-settler units

Recent work has emphasised theneed to consider the combined mixer-settler operation.Thus WARWICK andSCUFFHAM give details of a design,shown in the figure in which the twooperations are effected in the one

combined unit. The impeller has swept-back vanes with double shrouds, andthe two phases meet in the draughttube. A baffle on the top of the agitatorreduces air intake and a baffle on theinlet to the settler is important in

controlling the flow pattern.Thisarrangement gives a good performanceand is mechanically neat. Figure.Mixer-settler


19/37

The segmented mixer-

settler.In segmented mixer-settler specially designedKnitMesh pads are used tospeed up the rate ofcoalescence. The centrallysituated mixer is designed to

give the required hold up,and the mixer is pumped atthe required rate to thesettler which is formed insegments around the mixer,each fed by individualpipework.

Figure.Segmented mixer-settler


20/37

Kuhni have recentlydeveloped a mixer-settler column which isa series of mixer-settlers in the form of acolumn. The unit

consists of a number ofstages installed one onthe top of another,each hydraulicallyseparated, and eachwith a mixing andsettling zone as shownin the figure. Fig.Khni mixer-settles column


21/37

Baffle-plate columns

These are simple cylindrical columns provided with baffles todirect the flow of the dispersed phase, as shown in the figure. Theefficiency of each plate is very low, though since the baffles canbe positioned very close together at 75-150 mm, it is possible toobtain several theoretical stages in a reasonable height.

Figure.Baffle-plate column


22/37

The Scheibel column

One of the problems with perforated plate and indeed packedcolumns is that redispersion of the liquids after each stage is verypoor. To overcome this, SCHEIBEL and KARR introduced a unit,shown in the figure, in which a series of agitators is mounted on acentral rotating shaft. Between the agitators is fitted a wire mesh

section which successfully breaks up any emulsions.

Figure.Scheibel column


23/37

DIFFERENTIAL CONTACT EQUIPMENT FOREXTRACTION

Spray columns

Two methods of operating spray columns are shown in nextfigure. Either the light or heavy phase may be dispersed. Inthe former case (a) the light phase enters from a distributor atthe bottom of the column and the droplets rise through the

heavier phase, finally coalescing to form a liquid-liquidinterface at the top of the tower. Alternatively the heavierphase may be dispersed, in which case interface is held at thebottom of the tower as shown in (b). Although spray towersare simple in construction, they are inefficient becauseconsiderable recirculation of the continuous phase takes place.As a result true countercurrent flow is not maintained and up

to 6 m may be required for the height of one theoretical stage.


24/37

Figure.Spray towers


25/37

Packed columns

The packing increasing the interfacial area, and considerablyincreases mass transfer rates compared with those obtainedwith spray columns because of the continuous coalescence andbreak-up of the drops. Packed columns are unsuitable for usewith dirty liquids, suspensions, or high viscosity liquids. They

have proved to be satisfactory in the petroleum industry.


26/37

Rotary annular columns and

rotary disc-columns

With these columnsmechanical energy is providedto form the dispersed phase.The equipment is particularlysuitable for installations wherea moderate number of stagesis required, and where thethroughput is considerable. A

well dispersed system isobtained with thisarrangement. The figureshows a rotary annularcolumn. Figure.Rotary annular column


27/37

Pulsed columns

In order to prevent coalescence of the dispersed drops,VAN DUCK and others have devised methods of providingthe whole of the continuous phase with a pulsed motion.This may be done, either by some mechanical device, or bythe introduction of compressed air.

The pulsation markedly improves performance ofpacked columns. There are advantages in using gauze-typepackings since the pulsation operation often breaks ceramic

rings.Pulsed packed columns have been used in the nuclearindustry.


28/37

Centrifugal extraction

If separation is difficult in a mixer-settler unit, a centrifugalextractor may be used in which the mixing and the separationstages are contained in the same unit which operates as adifferential contactor.

In the Podbielniak contactor,the heavy phase is drivenoutwards by centrifugal force and the light phase is displacedinwards. Referring to the next figure, the heavy phases entersat D, passes to J and is driven out at B. The light phase entersat A and is displaced inwards towards to shaft and leaves at C.The two liquids intermix in zone E where they are flowingcountercurrently through the perforated concentric elements

are separated in the spaces between. In zones F and G theperforated elements are surfaces on which the small droplets ofentrained liquid can coalesce, the large drops then being drivenout by centrifugal force.


29/37

Figure.Podbielniak contactor


30/37

The Alfa-Laval contactor shown in thefigure, has a vertical spindle and therotor is fitted with concentric cylindricalinserts with helical wings forming aseries of spiral passages. The twophases are fed into the bottom, thelight phase being led to the periphery

from which it flows inwards along thespiral, with the heavy phase flowingcountercurrently. High shear forces arethus generated giving high extractionrates.

Fig.Working principle ofAlfa-Laval centrifugalextractor


31/37

EXTRACTION IN SUGAR

INDUSTRY APPLICATIONS

Extraction is needed for sucrose extraction from beets

and cane.

Beets are washed and seperated from any remainingbeet leaves before processing.

The processing starts by slicing the beets into thin chips.The slicing is done with sharp knives which cut a V selectionslice 4 to 5 mm thickness to increase the surface area of thebeet to make it easier to extract the sugar.

The extraction takes place in diffusers. The two wellknown diffusers for sucrose extraction are The fixed-bed

or Robert diffusion battery and Continuous diffusionbatteries or Silver continuous diffuser.


32/37

THE FXED-BED OR ROBERT

DFFUSON BATTERY

This was developed primarily in the beet-sugar industry, but is

also used for the extraction of tanning extracts from tanbark,

for the extraction of certain pharmaceuticals from barks andseeds, and similar processes. It consists of a row of vessels filled

with the material to be extracted and through which water flowsin series.The piping is so arranged that the fresh water comes incontact with the most nearly extracted material, and the strongestsolution leaves from contact with the fresh material.Since eachcell is filled and discharged completely ,


33/37

one at a time, each cell in the battery changes its position in thecycle,and therefore the piping must be so arranged that water canbe fed to any cell, and the thick liquor drawn off from any cell, ascircumstances may dictate.The arrangement of valves and pipingbecame standardized in the beet industry and is generally found

an all forms of diffusion battery. Figure shows that is adiagrammatic illustration of the principle of a diffusion battery.Forevery vessel or cell there is a heater, because the diffusionprocess takes place more rapidly at higher temperatures.Twomain headers are necessary .One handles water and the otherhandles solution;and for every cell there must be three valves.In

figure shows that the valves that are open are shown as circlesand the valves that are closed are shown in solidblack.


34/37

Fig.Diagram of diffusion battery


35/37

Consider figure; Cell 1 is nearly exhausted and the cell 3 has justbeen charged.The space between the cossettes in cell 3 istherefore filled with air.Water is introduced into cell 1 and flowsdown through cell 2, and up through its heater.It would not beconvenient to pass the solution down through cell 3 because ofthe air which would be entrapped;and the charge is cold,therefore additional heating is desirable.Consequently, the liquid

flows from the heater of the cell 2 through the solution line, downthrough the heater of cell 3,and up through cell 3. A vent at thetop of this cell discharges air.When liquid appears at this vent,the valves are quickly changed to the position shown infigure.Liquid now flows down through cell 3, up through itsheater, and out t the process.The operation shown in figurecontinued until cell 1 is completely extracted.By this time another

cell to the right of those shown has been filled, cell 1 is dumped,water is introduced to cell 2, and the process continued.In adiffusion battery for beet cossettes there may be from 10 to 15cells.


36/37

CONTNUOUS DFFUSON

BATTERES

The next figure shows the Silver Continuous diffuser.The figureshows only three units; but actually the battery consists of 20 to

24 units arranged in two tiers, one above the other.The batteryconsists essentially of a series of closed troughs A,A,A, eachprovided with a helical screw B.Cossettes are intoduced into thebattery through chute C and are carried together with the liquid inthe direction indicated by the arrows.At the end of the first trough isa Wheel D with inclined perforated buckets on the inside.It is soarranged that the screw B discharges the cossettes into this wheel,where they are picked up by the buckets;drained free from juicelifted, and discharged through chute E which takes them into thesecond trough A. Here the helix carries them in the oppositedirection discharges them from this to another wheel which in turnforwards them to another trough A, and so on until they areexhausted and leave the battery.


37/37

Silver continuous diffuser:A,A,A, extraction trougs;B,conveyor for moving cossettes; C, feed chute; D, transferWheel; E, transfer chute for chips.

Documents

Extraction Sugar