Countercurrent Liquid-Solid Extraction THE KENNEDY CONTINUOUS PILOT PLANT FRANK LERMAN, ANGUS B. KENNEDY, AND JEROME LOSHIN Vrclcan Copper and Supply Company, Cincinnati, Ohio Numerous pilot plant runs on over 20 dieerent lcinds of extractable solids have been made to demonstrate the effectiveness of the Kennedy extraction system for con- tinuous, countercurrent extraction and product recovery. The continuous pilot plant, of yp e 316 stainless steel con- struction, has proved the versatility, efficiency, and flexi- bility of the Kennedy extractor, and has indicated the quality of the products obtainable. The pilot plant has been an invaluable demonstration unit and also has given excellent data for use in design of commercial units . iMaterials heretofore considered unsuitable fbr continuous solvent extraction have been readily and thoroughly ex- tracted. A full program of pilot plant work has been scheduled for the coming months, involving several new extractable materials. ARLY in th e development work on the Kennedy extrac- E ion system at the Vulcan Copper and Supply Company, the need was recognized for a continuous pilot plant that could duplicate closely commercial solvent extraction and recovery operations. Previous pilot plant and commercial installations built by Angus B. Kennedy, inventor of the extractor, already had indicated the versatility and flexibility of the Kennedy ex- tractor. The first installation of this type was built in 1927 in Charlottes- ville,Va., for the extraction of natural dyes and tanning extracts from bark and wood. This machine was of rather crude construction, but clearly demonstrated a considerable saving over the leach tubs and autoclave methods of extraction in gen- eral use. In later years, the extractor was redesigned for the solvent ex- traction of vegetable oils, and a number of patentable improve- ments were incorporated at that time; these greatly increased the efficiency of the apparatus. In 1941, a small brass extractor of this improved design was installed at the WoIf Company’s plant, Chambersburg, Pa. The capacity of this small pilot extractor was approximately 1 cubic foot of solids per hour for a through- put time of 1hour. Its prime purpose was to furnish design da ta for the large com- mercial plant, which was subsequently installed at Hershey, Pa., for the extraction of cocoa butter from cocoa residues. This extractor was used also to solvent extract various vegetable oil- bearing materials, such as tung kernels (I), soybeans, and flax- seed, and to rarrv out certain special liquid-solid contacting op- erations, such as the water washing of cellulose acetate and t recovery of zein from corn proteins. The commercial solvent extraction plant for the recovery cocoa butter from flaked cocoa beans, expeller cake, filter cak hulls, and foots has been in operation for 6 years at the so plant of the Hershey Estates, Hershey, Pa It ha s a capacity 50 tons per day of expeller cake. A small brass extractor was installed at the Eastern Regio Research Laboratory of the U. S. Department of Agriculture Philadelphia, Pa., to extract vitamins from various vegetab materials. Its capacity is approximately 1 cubic foot per hour solids for 1 hour’s throughput contacting time. Recently, a pi plant of steel construction, with an extractor of about four tin the capacity of the previous pilot units, was built and operat at the Northern Regional Research Laboratory of the U. Department of Agriculture at Pcoria, Ill., for tho extraction soybeans with alcohol. A large srale Kennedy extractor mas built and installed on t West Coast for the acid M ashing and water neutralization of p tin for peal: war requiremonts. Cypress wood was used as t substitute construction material; it resisted the acid corrosion the emergency period. It was to extend and confirm these previousextractions, to t extractions of numerous other materials using various solven and to obtain basic operating data for the design of commerc installations for processing specific materials that the prese continuous extraction and recovery pilot plant has been bu on the grounds of the Vulcan Copper and Supply Company Cinrinnati. DESCRIPTION OF THE KENNEDY PILOT PLANT The pilot plant is installed in a concrete building, 35 feet lo by 19 feet 6 inches wide, with a roof of corrugated sheet me sloping from 22 feet to 15 feet above the concrete floor. An jacent concrete building, 22 feet 6 inches long by 18 feet wi with the roof sloping from 23 feet to 14 feet high, houses preparation equipment. This equipment consists of a corruga roller mill and a flaking mill for cracking and flaking the see beans, or kernels in preparation for extraction. Near th joint buildings is a solvent storage building of similar constr tion. The layout of equipment in the preparatioii and extracti buildings is shoi5 n in Figures 1, 2, an d 3. 1753
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Countercurrent Liquid - Solid Extraction - The Kennedy Continuous Pilot Plant
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5/14/2018 Countercurrent Liquid - Solid Extraction - The Kennedy Continuous Pilot Plant - slidepdf.com
1?54 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 4
r1
VAPOR
DETECTOR Ii-F L O O R P L A N
KENNEDY PI LOT SOLVENT EXTRACTION PLANT
Figure 1
The Kennedy extraction syst,em is designed around the Ken-
nedy extractor , a cross section of which is shon-n in Figure 4.
The continuous extractor consists of a series of enclosed ex-
traction chambers or sections; into each of these is fitted an im-
peller wheel assembly for moving the solid materials through
the liquid. Each impeller wheel assembly consists of a n en-
closed hub (the lower portion of the hub is partially submerged
in the liquid), four curved blades of perforated metal, an d a shaft
extending through bearings in th e sides of t he extractor n-alls.
Th e impeller wheel assemblies are driven fr om th e outside by a
common drive shaft through a xyorm and gear arrangement.
SXTRACTIOS AK D RECOVERY PROCESS
The process is as shown in Figure 5. Khen the solid material
being processed is required in flake form for extraction, IL 1sfirst put through tlie corrugated rolls of the cracking mill. Se xi ,the moisture content is adjusted to give the best, flaking prop-erties, a nd then t,he ma,t,erial s flakcd i o the desired thiclrness bypassing it one or more times through the smooth rolls of th eflaking mill.
The material, reduced t o the most suitable form and size forextraction, is placed in t he feed'hopper of the Kennedy extractor.From here, controlled quan titi es a re fed a t a COnSTant rate b>- afeed screm conveyer into the first extrac tion section of tlie cx -tractor. The material then is carried through the extrac-to r in countercurrent flow to t.he solvent.
Each portion of immersed solid material in a section iscollected by an ,impeller blade and carried through theliquid in that section. As the solids are carried up thecurved wall of that section, they are slightly compressedbetween the wall and the curved blade to form a wedge,which is lift ed above th e liquid level and sloughs off theblade into the next section. Thi s slight compression anddraining, through lifting the solids above the liquid level,reduce t8he mount of ent rain ed liquid carried over to t,hesucceeding section.
On striking th e liquid surface in the succeeding section,the wedge readily breaks up and disperses. Th e solidsimmersed in th e liquid of thi s section as distinct particlesare again collected by an impeller blade an d moved th roughthe liquid.
The cycle in each section of dispersion, immersion, andcollection of the solid in the liquid, of movement t,hroughthe liquid, and of the compression, lifting, and draining ofthe solids is the basis of the intimate and thorough con-tacting betm-een solid and liquid for exhaustive extractionof solute.
The extracted solids arc gravity drained of a good partof the entrained solvent while being carried up the dragchain conveyer, and then are dropped into a collecting canwith a perforated false bottom for separating additionalliquid drainings.
The drained batch fed int.0 thdryer n-here soporization t akscmicontinuouseither atmospvacuum conditivapor is carrieddryer through jacketed filte
Here, in passina cloth-covererated metal the vapors deentrained dusflowing int,o heing system.
The solvent fextractor is pumthe weigh tanksp o r t i o n i n gthrough the tuheat exchangeby controlled hor steam flowshell side, theleaves a t the deperature for eIt then flows
drag chain convtion of the extr actor at. an inte rmediate level and givwash t,o h e extracted residue on t ,he lower flights of the as they are carried upward. The solvent collects at ththe conveyer, which serves as the last wsidue extraction, and then overflow from seciion t,o section of the in countercurrent movement t,o the solids.
The solvent, containing the extracted material in leaves the filter section with a small content of fines, icomparable t,o th c amount of fines in th e solid feed mamost of the smaller particles are carried along with thsolid residues. A large portion of th e fines entr aineliquid are removed in the self-filtering operation in t he as the solvent fiows through tlie solid materials betxeenof the extractor ; also the coarser fines settle out ' of the liqsections (particularly the filter section) and are carried b
On leaving the extrac tor, the extract liquor flows by grathe miscella receiver; from the bottom of the receiver it ,iby a proportioning pump through a laboratory SparkHere the remaining fines are deposited on the prccoatdisks covering the filter plates. The fi ha te flo~vsntotank.
The solvent recovery unit of the pilot plant was deseparate vater-immiscible solvents from nonvolatilextracts, such as is normally the case in extracted vegeand animal fat recovery operations. Extractions involvimiscible solvents, or volatile or solid extracts, requirrecovery equipment, axmilable in t,he laboratories andtion pilot plant elsen-here in the VuIcan plant.
In . norcoveries.
Figure 2. View in PreparationR iiilding
cumulai'edof solvenliquor is pcarried byfrom the wat a constausually tmore time
of inflow to-throughthtube of therising-filmtor and thentrainmerator. Frthc vaporvent iscarrcondensersliquid, ofcentrated 90% extratemperaturu u m o pflows to tt h e s t rcolumn.
5/14/2018 Countercurrent Liquid - Solid Extraction - The Kennedy Continuous Pilot Plant - slidepdf.com
September 1948 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 1755
Figure 3. View i n Extraction Building
Here, the liquid flows down through the packed strippingcolumn (filled with Raschig rings) in countercurrent flow tostripping steam. Th e stripping column is jacketed so that theheat required to vaporize the residual solvent may be addedthrough the shell of the column. Th e vaporized solvent and thestripping steam pass through an entrainment separator abovethe stripping column and from there to the condensing system.Th e solvent-free extr act flows into a vacu um oil receiver.
Th e condensate is collected in one of two vacuum con densatereceivers and flows from th em t o a decanter for separating waterfrom solvent so tha t the latter may be re-used. The vapors fromthese condensers flow t o a large water-cooled, tube-in-shell ventcondenser before venting to the air. When the condensation isunder vacuum, th e vapors are carried through a steam jet ejectorto t he vent condenser.
SPECIAL DESIGN FEATURES
In the pilot plant all items that contact solvent, miscella, oroil are made of type 316 stainless steel. This materia l was chosen
because it is resistant to the widest variety of liquids, solids, or
vapors th at may be involved in the processing.
The extractor throughput time can be varied from 30 to 90
minutes by adjusting the variable speed drive. The capacity of
the extractor ranges from 1 to cubic foot per hour of solid
material, depending on the throughput time. With the usual
oil-bearing materials, having densities from 20 to 30 pounds per
cubic foot, this amounts to about 7 to 30 pounds per hour. The
feed screw and drag chain conveyer are synchronized with the
extractor drive. To meet special requirements outside the op-
erating ranges mentioned, adjustments and changes in the ex-
trac tor can be made readily by changing sprockets and gears.
The number of sections in thc pilot extractor are fixed. However, means are available to de termine the proper numb er of sec
tions for a commercial machine. To decrease the number o
effective extraction sections, the feed hopper assembly of the
pilot unit may be moved to discharge into an intermediate sec
tion. T o increase the numbe r of extracting sections, the extracted
solids discharged from one run may be used ns th e feed materia
for a subsequent run.
Th e solvent feed rat e can be varied froin 0.5 to 11 gallons pe
hour by adjusting the solvent feed pump. Th e solvent ra te
used depends on the concentratio n of solute desired in th e ex
trac t liquor and t he am ount of solvent carried from the extracto
by the wet extracted material.
In the design of the vacuum dryer, the advantages of operating
on a continuous basis were counterbalanced by the high cost of
devices fo r continuously charging and discharging the materiainto and from a vacuum. A compromise between b atch and con
tinuous operation was obtained by uring a continuous dryer with
a throug hput cap acity of about G times that of the extractor and
providing vapor-tight feed and discharge hoppcrs with cnough
volume to allow an 8-hour run of wet extracted material. Th
holdup time in the drying section can be varied from 20 t o 9
minutes.
The oil and solvent recovery system, when operating at 1
inches of mercury absolute pressure, can recover from 3 to 1
pounds of oil per hour, depending on th e original concentra tion
of oil in the miscella. Both th e evaporator and stripping column
heating jackets are piped to allon the use of either steam or ho
water as a heating medium.
5/14/2018 Countercurrent Liquid - Solid Extraction - The Kennedy Continuous Pilot Plant - slidepdf.com
1756 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 40,
LXTRACTFDSOU@ /
RECEIVER__Figure 4. Schematic Drawing of L ulcan P i lo t Plant Extractor
Solids impeller dimensions: 14 impellers are 8 inches in diameter X 6inches in width: 1 impaller is 11 25 inches in diameter X 6 inches i n w.idth:each impeller has 4 blades of 24-gage stainless steel, perforated with
1/16-inch h ole s, on '/sa-inch cent ers
The introduc tion of complete an d modern safety eyuipnient,
and practices mas one of the foremost considerat,ions in the de-
sign of the plant. Electrical equipment in the extraction and
solvent storage buildings is of Class I, Group D rating. A flam-
mable vapor detector samples the air in sequence from eight
critical points in the pilot plant. If the flammable solvent con-centra tion in t,he air reaches 40% of t he lower explosive limit, an
alarm sounds, all motors are shut' off, vent louvres below the
windows autoinatically open, an d th e vent,ilation blower changes
rhe air i n the building 30 times an hour instead of th e 10 times an
hour for normal operation.
All equipment, mctal supports, and window frames are
grounded positively. TThcncvcr flanimahle solvent is present, in
the building, only nonspariting tools are used and only minor
repairs are permitted. Other safety features, impor tant but
beyond t>he cope of t,his paper, were incorporated in the extrac-
tion plant'. As careful a safety engineering j o b was done for the
preparation and solvent.storage buildings.
OPERATION O F THE UNIT
The pilot plant' was operated for the first, 6 months on one,
two, an d occasionally three %hour shifts per d ay for a 5-dag XI-eek.
Hoviever, the demand for applying the Kennedy system to an
increasing number of extraction problems has necessit,ated a 3-
shift, 24-hour per day operation of the pilot plant since the first
of this year. Operation for 5 days per week has been continued,
except on special, urgent occasions.
The extraction pilot plant is under the direct control of the
head of the Research and Development Depar tment; he is re-
sponsible also for the operation of th e Dist'illation Pilot Plan t
and Laboratory, a nd the Fermentation a nd Biochemical Labora-
tory of the Vulcan organization. The engineers of the Kennedy
Extraction Division work closely with him in coordinating and
scheduling the pilot pla nt runs. Close contact is kept also with
representatives of various companies interested in t he specific
runs or for whom th e investigations are being made.
They
are assisted by chemical engineering students of two or more
years' training in the cooperative course at the University of
Cincinnati. Th e shift supervisor and an assistant operator are
assigned for each shift t,o run the plant,. Another assistant is
scheduled each shift to carry out th e required analyt,icalwork onsolid and liquid samples of materials, taken prior to and after
processing, or from intermediate processing steps. Anot,her engi-
neer on the day shift correlates these dat a and prepares th e formal
reports.
I n starting up, th e solvent is pumped from a drum outside the
building: by a hand pump into one of the weigh tanks. The ex-
tractor sections are filled wit,h solvent. Then wit,hout further
solvent flow, the snlid material is fed int o the extractor. -4fter
The shift supervisors are graduate chemical engineers.
the solids work through t,lie ext,ractor and st
discharge, solvent flow is resumed at the req
rate and proper temperat,ure. This start-up
dure is used t o build up equilibrium concentr
quickly. Another 2 to.4 hours are required
mally to reach dynamic equilibrium in the e
tor. Runs are then continued from 4 to 24
depending on what specific information or quof product is desired. The recovery syabembe operated concurrently with t'he extractor, b
frequently operated during the clean-out per
the preparatory period for a succeeding ruii.
DATA OBTAINED
During extraction operation, hourly weight
ings ar e taken for solids and solvent feed rate
extrac t liquor and solids residue discharge
to obtain material balances. Samples o
liquid and solid discharged materials also are taken h
for analysis t o obtain a niaterial balance for the extract ma
Fines remaining in th e ex ti~act iquor can he measured b y w
ing the cake of th e filter plates af te r the run or, better, by e
ing a gall011or more liquid saniple during the run for labo
filtration, drying, and iveighing.Liquid and solid saniples at intermediate stages of extr
are taken through t hr quick-opening st~mpli ng x t s lo
above the junction point between Pach pair of extractio
tions. These saniples are taken only at the end of each
avoid upsetting material equilibrium during that run.
solid samples are drained t o a uniform extent by placing o
sorbent paper toweling before analysis. The liquid sanipl
settled or filtered free of fines before analysis. Analyses o
material and final extracted material are run in t,riplicate.
centrations in intermetliat,e srctioris are usually th e res
single analysis.
The recovery equipment, both for the e stra cttd residue an
ext,racted material, is operated chiefly to duplicate, on a
tinuous basis, cornniercial operations to ensure t,hat comp
product quality may be attained. Ternpcrature wid va
conditions are measured and maintained cloaely.The concent,ration of th e ext ract liquor after evaporatio
before stripping is an example of t>hegood agreement be
theory, pilot plant operat,ion, and coinmercial design.
laboratory equilibrium data for a typical vegetable oil in a
petroleum solvent (Sj, the equilibrium concentration at. 1an d 20 inches of mercury vacuum is 9394 oil. In the des
a commercial installation for these conditions, a value of
oil concentration was used. The pilot plant evapora tor,
operated at this given temperature and vacuum, consis
discharges a concentrated oil-solvent liquor containing Fro
to 927, il.
For each series of runs made on a given type of ma
(covering a period from 2 days t o a month or more),
search Department report is prepared, This report pr
briefly but thoroughly t,he n-ork accomplished, the dat a ob b
and the conclusions drawn. Da ta usually are prepared
lows: a general summa ry of conditions and results for eac
an over-all material balance sheet of input and output
extract,or; and the analytical results on concentrations of
in solid and liquid at, intermediate and t erminal points of t
tractor . An over-all solube balance sheet is the n pres
Examples of thcse dat a sheets are shown in Tables I to IV .
Charts which show the solute concent,rations plotted a
extractor section number on semilog paper a re included wi
da ta sheets. Such charts are valuable for design purpos
ext,rapolation or inte rpolation of the curves indicates the
of increasing or decreasing the number of extraction sec
Comparison between curves shows the effects of changes
5/14/2018 Countercurrent Liquid - Solid Extraction - The Kennedy Continuous Pilot Plant - slidepdf.com