2. Evaporation
• The purpose of the evaporation system is
to remove water from the thin stillage.
• The evaporation system boils the thin
stillage using a tube and shell heat
exchanger called the Calandria, which has
an attached separator. This is the first
stage (effect) of the evaporation process.
• The stillage entering the system consists
of approximately 92% water and 8%
solids.
3. Evaporation
• The heat source for the evaporation
system is the MVR (mechanical vapor re-
compressor).
• The product is pumped from the
Calandria to the North and South
Finishers which are also tube and shell
heat exchangers.
• From the finishers the product is sent to
the syrup storage tank.
4. Evaporation
• The evaporation system produces syrup,
(Condensed Distillers Soluble) which is
thickened stillage. Through a process of heating
the stillage and boiling off the water, the
entrained liquid and vapor are separated and the
syrup solids are concentrated. The syrup has a
target of 30 to 32% solids in the final product.
5. Evap Preheater
• The evap pre-heater is a spiral scroll type
heat exchanger.
• The evaporator pre-heater is used to
preheat the thin stillage entering into the
evaporator.
• The heat source for the pre-heater is
evaporation condensate.
6. Evap Pre-heater
• The pre-heater
can be bypassed
for repair and
cleaning if
necessary.
• The evaporation
process will work
with out the pre–
heater online, but
will not operate
as efficiently.
8. The Science of Evaporation
• The Calandria and finishers are falling film
evaporators.
• In this type of evaporator, liquid and vapors
flow downwards in parallel flow. The stillage
is heated to a boiling temperature. An even
thin film enters the heating tubes via a
distribution device in the head (top) of the
evaporator, flows downward at boiling
temperature, and is partially evaporated.
9. The Science of Evaporation
• The weight of the liquid in the tubes as
well as the downward movement of the
vapor keeps the product moving
downward.
• The successful operation depends on
an even distribution of liquid at the top
of the Calandria.
10. The First Stage of Evaporation
• The evaporation system boils the
thin stillage using a tube and shell
heat exchanger called the Calandria,
which has an attached Separator
tank.
• The stillage from the pre-heater is
feed into the Calandria and re-
circulated by four pumps.
11. The First Stage of Evaporation
• A liquid level is maintained in the bottom
of the Calandria and Separator. This
level can be checked with a sight glass
located on the side of the Separator and
should be less than 1/3rd
the way up the
sight glass. This liquid is re-circulated
back through the Calandria, with a
portion being drawn off and sent to the
Finishers.
12. The Second Stage of
Evaporation
• Instead of one exchanger and one
separator like the first stage the second
stage is setup with two exchangers and
one separator.
• The two exchangers are also falling film
type evaporators and are called the North
and South Finishers.
• There is a tank between the Finishers that
is the separator.
13. The Second Stage of Evaporation
• The heat exchangers and separator
function in the same way as the first stage.
• A liquid level is maintained in the bottom
of each Finisher and the separator tank.
• That liquid is re-circulated back to the top
of the Finishers with a portion being drawn
out and sent to the syrup storage tank.
14. The MVR
• MVR is an acronym for Mechanical Vapor
Re-Compressor.
• During mechanical vapor recompression,
the vapor of an evaporator is
recompressed to a higher pressure by
means of a mechanically driven
compressor.
• Steam from the MVR is the heat source
for evaporation.
16. Evap Condensate
• Steam is injected on the shell side of the
Calandria and Finishers.
• The steam is subsequently condensed as
it transfers its energy to the stillage and
the condensate is collected in the Evap
Condensate tank.
• From here the condensate is pumped
through the Evap pre-heater and to the
Recycle water tank.
17.
18. The Separator Tanks
• As mentioned before each stage of
evaporation has a separator tank.
• The purpose of the separator is to remove
the water droplets from the steam vapor
as it is drawn out the top of the vessel to
the suction of the MVR.
19. The Separator Tanks
• The vapor is drawn up through Chevrons.
• The Chevrons are mist eliminators that are are
highly effective in removing liquid entrainment
from gas streams.
• They providing high efficiency and low pressure
drop.
20. The Separator Tanks
• The chevrons can
remove fine droplets with
efficiencies approaching
100%.
• They also provide
excellent resistance
against fouling in
applications with high
solids loading.
21. Storage
• The process syrup tank is used to supply syrup
to the wet feed.
• Syrup being drawn from the evaporators is
pumped to the process syrup tank.
• The syrup tank works as a surge tank.
• We pump the syrup we make into it and pump
out what we need for the wet feed.
• What we don’t use is sold to various customers.
Editor's Notes
First stage evap is divided into three sections (North, South, and Middle). Using pumps (603 A, B & C) the stillage is pumped to the top of each Calandria section in the up flow tubes. At the top of the Calandria, the stillage overflows out of the up tubes and spills into the down flow tubes. The stillage forms a thin layer in the down tubes as it gravity flows down.
On the shell side of the Calandria is vapor. Vapor from second stage is pulled into the shell side by the condensing of the vapor on the tubes. The non-condensable are removed through the non-condensable line to the final condensers. This vapor heats the tubes that the stillage flows in. Unlike the three compartments on the tube side, the shell side is just one compartment.
