Mechanics of Solvent Extraction with the Immersion

Type Extractor
N. HUNT MOORE, Consulting Engineer, Memphis, Tennessee

p l~IOR to the early 1920's there was in operation

in Europe a nt~mber of batch solvent extraction
This space above the solvent enables the excess sol-
vent to drain from the extracted flakes (3).
plants. I n this period there developed out of The fresh solvent is introduced into the "up l e g "
these batch extraction plants several types of contin- and flows down, across, and up the " d o w n l e g " in a
uous solvent extractors. The two types that were in- true eountercurrent manner. The solvent, now rich
troduced into this c o u n t r y with the extracted oil, flows through a wedge wire or
were the Bollman and the a perforated metal screen and on out to a receiving
Hildebrandt (1). T h e tank. I t is necessary to fi!ter this miscella before it is
Bollman was of the basket sent to the distillation equipment (3).
type and the H i l d e b r a n d t There are two or more of these extractors in opera-
of the immersion type of tion in this country. One is in operation on soybeans
extractor. and one is in operation on pre-press cottonseed (1).
A cross-section view of Also a n u m b e r of immersion type of extractors are
a Hildebrandt E x t r a c t o r in operation on cottonseed in this country, modifica-
is shown in Figure 1. The tions of the I t i l d e b r a n d t and the Bonotto extractor.
flakes to be extracted are They are very similar in design and operation and
fed into the top of one of are m a n u f a c t u r e d b y the V. D: Anderson Company,
the legs and are conveyed Cleveland, 0., and the Allis-Chalmers M a n u f a c t u r i n g
downward through the Company, Milwaukee, Wis.
solvent by means of a per- Figure 2 shows an extractor similar to those mann-
forated screw. A t the bot- factured b y Allis-Chalmers, now in operation on cot-
tom of this leg a horizontal
screw carries the flakes
over to the other leg of the
N. H u n t Moore extractor (3). This " u p
l e g " is rifled to prevent
the mass of flakes from t u r n i n g with the screw and to
enable them to be conveyed u p w a r d through the sol-
vent to a point several feet above the solvent level.
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538
 THE JOURNAL OF THE AMERICAN OIL CHEMISTS' SOCIETY, NOVEMBER, 1953 539

tonseed. This type is now being used in both pre- IE

press and straight extraction of cottonseed (2, 4). I n
this extractor the flakes are fed into the inclined screw ~JLer
and introduced into the s.traight section of the ex-
tractor. The flakes travel down the e x t r a c t o r f r o m
plate to plate through these pie-shaped openings.
There are sweeps on each plate that are attached to a
central shaft. This central shaft revolves very slowly
( f r o m 1 to 3 r.p.m.) and rotates these sweeps. The
rotation of the sweeps causes the flakes to travel
around on the plate until they drop through the open-
ing in the plate. At the bottom of the extractor the
flakes are removed b y a drag-chain t y p e conveyor-
elevator. This conveyor-elevator is driven with a var-
GN
iable speed drive, which controls the rate at which the
flakes are removed f r o m the bottom of the extractor.
By v a r y i n g the speed of this conveyor, it is possible
to maintain a flake level in the top portion of the
extractor (4).
The flakes are raised in this conveyor-elevator to a
point several feet above the top of the extractor. I I e r e
they are discharged into an inclined drag. I n this
d r a g the extracted flakes are washed with fresh sol-
vent and are given two-minute drainage to remove
the excess solvent before they are discharged into the
solvent removal driers. The fresh solvent t h a t is in-
troduced into this d r a g drains b y g r a v i t y down the
back leg of the elevator and flows up the extractioI1
column eountercurrent to the descending flakes. This
~ L
oil rich solvent, or miseella, then enters a settling
head, where the larger particles of meal settle out be-
fore the miscetla flows down to a collection tank. The
oul"~l--Tk~E
.s
miscella is filtered before going to the distillation l MM[P..s [I EXI-RACTO~ ~ PLUS DISCHARGE
equipment.
Another modification of this extractor is the use of FIG. 3
a p l u g discharge on the bottom of the extractor. This
plug discharge consists of a h e a v y screw conveyor, drained off in a screen section ' and flows down to tile
driven b y a variable speed drive, and a cone that ap-
bottom of the extractor.
plies pressure against the spent flakes as they leave The inlmersion type of extractors have their advan-
the extractor. This pressure forms a tight plug t h a t tages and disadvantages when compared to basket ex-
prevents the liquid in the extractor f r o m draining out tractors. S o m e of the advantages are: a) much lower
with the extracted flakes. The solvent is introduced initial investment; b) g r e a t e r flexibility in moisture
into the bottom of the extractor and flows u p w a r d and particle size; and c) less building space. Some
countereurrent to the flakes. A flake level is main- of its disadvantages are: a) more fines due to the agi-
tained in the u p p e r p a r t of the extractor b y the regu- tation of the flakes during extraction ( 1 ) ; b) the
lation of the speed of the p l u g discharge conveyor necessity of providing l a r g e r filters f o r an i m m e r s i o n
(1). A n u m b e r of extractors of this design are being type of extractor; and c) more power requirement t o
operated oa pre-press cottonseed cake. drive extractor (1).
The plug discharge is r a t h e r critical as to moisture
and t e m p e r a t u r e of the flakes in the extractor. Be- I~EFERENCES
cause of troubles t h a t have been encountered some of 1. Cofield, E. P. Jr., "The Solvent E x t r a c t i o n of Oilseed," Georgia
Institute of Technology, Circular No. 28 ( 1 9 5 0 ) .
the p l a n t s h a v e recently added a drainage section to 2. Bilbe, C. W., " A Year of Cottonseed Solvent E x t r a c t i o n , " Oil
the conveyor elevator and are operating their plug Mill Gazeteer, 59, No. 1, 39-41 (].948).
3. Markley, K. S., a n d Goss, %V. H., " S o y b e a n Chemistry a n d Tech-
discharges as a conveyor only and are letting the sol- nology, pp. 268-175.
4. Moore, N. H u n t , "Exsolex Process in the Solvent Extraction of
vent fill the conveyor-elevator. The excess solvent is Cottonseed," Tile Cotton Gin a n d Oil Mill Press, April ( 1 9 5 0 ) .