Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
Spent stillage lS the grain slurry remaining aftercompletion of the fermentation and distillation processes in the
production of distilled liquors. Stillage has for years been
-treated to produce a conglomerate of particulate material suitable
for animal consumption.
Spent stillage is initially a slurry consisting of over
90~ water which is first mechanically treated to separate the
liquid from the solid materials by mechanical means, such as
centrifuging or pressing. The liquid phase is further concentrated
by evaporation providing a syrup including about 55% water. The
solid materials or cake from the mechanical separation step and
the syrup are mixed together to form a wet mixture which is then
dried using dispersion or flash drying to reduce the moisture to
about 10%.
In the past the flash drying processes that were used
included limited air volumes, high drying chamber inlet air temp-
eratures and material circulation techniyues which often caused
the emission of substantiaI amounts of smoke and odors during the
drying operation.
The process and apparatus of the present invention is
an improvement in the dispersion drying operation which uses sub-
stantially more air and lower temperatures to obtain a dried
material which is improved in its nutrient value. The process is
- carried out with a substantial reduction in smoke and odor and in
fire and explosion hazards.
SUMMARY OF THE INVENTION
Broadly, the present invention is an improvement in a
stillage flash drying process in which cake, syrup and recycled
stillage material having a moisture content of over about 10% is
introduced into a large-volume rapidly-moviny air column heated
to a temperature in the range of about 325F to about 425F, is
3~
mixed with the air, is carried a distance to a separator means
where the particulate material is separated from the air and
collected. Substantially all the material is then recycled a
large number of times with the moisture content being reduced
during each pass to dry the material until the moisture content
is reduced to the desired level.
It is a feature of the process that the product has
improved nutritive value. It is also a feature that the process
produces less smoke and odors.
BRIEF DESCRIPTION OF T~IE DRAWI~GS
Fig. 1 is a top plan view of the drying and Fig. 2 is
an elevational view of apparatus that is used to practice the
process of this invention.
DESCRIPTION OF THE PREFERRED EM DIMENT
Referring to Figs. 1 and 2, air entering furnace 1 is
heated and is caused to pass through the system in a generally
counterclockwise path in which the air passes from furnace 1
through vertical mixing and drying column 2, through column
extension duct 3, to Y-shaped duct section 4 where the air splits
into two streams which flow along entrance ducts 6 and 7 to cyclone
upper separator sections 8 and 9 of separator units 10. Two
separator units are preferred but one, two or more may be used.
The air passes around the cyclone entrance sections 8 and 9
causing the heavier stillage material to move to the outer peri-
pheries of the separator sections 8 and 9 while the air is drawn
off through the centered upper outlets 11 and 12 through cyclone
exit conducts 13 and 14 and then down vertical air fan intake
duct 16 through fan 17 and exhaust pipe 18. The exit temperature
of the air is normally in the range of 150F. to 200F.
Turning now to the flow pattern of the stillage material,
wet material is fed into the system through down pipe 19 onto
horizontal conveyor 21 where it is mixed with recycled stillage
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grain in a ratio from 5-40/1, then ~ed further in subsequent
conveyors 22 or mixer~ of appropriate length, orientation and
capacity (not shown) and then fed by gravity, mechanical or
pneumatic means (not shown) along feed chute 23 into the vertical
column 2. Concentrated stillage syrup can be applied to the grain
before or after the wet cake stillage is added to the recycled
grain in whole or in part and at various points along the mixing
conveyors or at a mixer immediately prior to introduction to the
dryer column 2. The introduced material is mixed with and carried
along by the heated gas stream until it is centrifugally separated
in the separator portions 8 and 9 of the separator units 10. The
separated and partially dried material then descends through
cylindrical sections 26 and conical section 27 of the separator
units 10 until the material reaches the bottom and is discharged
through rotary locks 28.
During operation all the material is recirculated in
the range of from 5-40 times with the composite mixture extracted
at substantially the same rate off conveyor 21 as the rate of
input of new material through pipe 19. Normally, drying down to
about 10% is desired; however, it should be noted that each
discrete portion of the material exiting pipe 31 is not exactly
at 10% moisture but the average moisture content will be in the
neighborhood of 10~. For example, if the system were operated
with a 5,000 lbs./hr. input at 64% moisture and the material made
only one pass about 54% of the moisture would have to be removed
to bring the moisture down to 10%. However r if two passes were
used in which the moisture reduction on the first pass was from
64% to 14% and from 14% to 6% on the second pass, about half
the material would be extracted down to a 14% moisture content
and one half down to a 6% moisture content thus providing the
desired average of 10%. Again looking at averages, the average
inlet moisture would drop to 39%. Thus, it is seen that as a
larger number of passes is used, the average inlet moisture con-
tent is lowered. It should also be noted that with a greater
volume of material in the system a large percent change in input
flow through pipe 19 will have a lesser effect on the moisture
content of the extracted mixture unless the large increase or
decrease in input is continued for a substantial period of time.
The larger the number of recYcle passes that are used
the less water is extracted from each individual grain or particle
during each drying pass. A plurality of passes, each interrupted
by the time required to convey the material between passes, pro-
vides a retention time in the system adequate for proper moisture
equilibration in each particle which is in part accomplished by
moisture migration from the inside of the particles to their out-
side surface areas. The fact that the drying and evaporation can
be more efficiently accomplished with lower temperatures and
higher velocities of gas movement than previously employed is
due in part to the use of step-by-step moisture extraction starting
with removal of moisture from the outside of the particle, migration
of interior moisture to the surface and the subsequent removal of
the migrated moisture. The system may, for example, have 25,000
to 200,000 lbs./hr. in circulation with an input and corresponding
output of 5,000 lbs./hr.
Mixing of air and material is improved by drawing heated
air up auxiliary duct 32 tangentially into ports 33 and 34 in the
walls of column 2.
The introduction of tangential air increases turbulence,
mixing and retention time of heavier particles. Though air is
preferred as a drying medium process, superheated steam, other
gases or mixture or gases can be used.
