evaporation technology
TRANSCRIPT
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GEA Wiegand
GmbH
GEA Evaporat ion Technologies
EvaporationTechnology
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Research and Development
GEA Wiegand has its own Research an d Developmen t Centre,
wh ere num erous laboratory and pilot plants are available for
detailed analyses and testing in the field of evaporation and
distillation. At the R&D Centre, imp ortant p hysical character-
istics such as boiling p oint elevation, su rface tension, solubility
and maximum achievable concentration are determined.
Certain pilot plants are available as mobile un its and can there-
fore be installed at a custom er s site. Data is capt ured and
plant op erating behaviour m odelled by mean s of the latest com-
puter programs.
The tests are performed in different types of tubular and plate
evap orators an d d istillation column s. To da te, more than 3,000
produ ct categories have been tested through our p lants. The
alphabetical list of produ cts tested ranges from acetone/ alcohol
mixtures to zinc dichloride.
Evaporation Technology
Contents
Research and Development 2
Reference Products f rom GEA Wiegand Evaporation Plants 3
Evaporator Types 4
Special Evaporator Types 11
Quant it ies and Concentration Ratios in Evaporat ion Plants 14
Energy Efficiency of Evaporation Plants 15
Criteria for the Design Selection, Arrangement and
Operating Modes of Evaporation Plants 19
Evaporation Plant Components 19
Measuring and Control Equipment 22
Manufacture, Transport, Erection, Commissioning
and After-sales Service 23
Due to ongoing research and de-
velopment work spanning many
decades, and the experience of
several thousand installed refer-
ences, GEA Wiegand continues to
provide the broadest technical ex-
pertise and the respected ability
to offer the best solution for almost
any product, evaporation rate,
operating condition or application.
Evaporation p lants are used as a thermal separation techno-
logy, for the concentra tion or sepa ration of liquid solu tions,
suspensions and emulsions.
A liquid concentrate that can still be pu mp ed is generally the
desired final prod uct. Evaporation m ay how ever also aim
at separa ting the volatile constituents, or distillate, as would
be the case in a solvent separation system. During these pro-
cesses, it is usual that p rodu ct qualities are maintained and
preserved.
These, together w ith many other requirements result in a w ide
variety of evaporator types, operating modes and a rrangemen ts.
GEA Wiegand has substantially contributed to the d evelop-
men t of evaporation techn ology. The first Wiegand evap orator,
built in 1908, was a paten ted mu ltiple-effect circulation eva-
porator. This concentrated liquids in a gentle and efficient m an-
ner in a wa y un par alleled in its time. It was easy to control and
had a compact arrangement.
Further techn ical dev elopm ents led to the first Wiegand falling
film eva por ator, built in 1952, which combined these consider-
ably improv ed, essential characteristics with new process
possibilities, especially in the field of evaporating heat-sensitive
prod ucts. At the sam e time, the therm al efficiency of evap ora-
tion plants was considerably improved.
Thanks to its advan tages, the falling film evapor ator has virtu -
ally replaced other evap orator typ es in ma ny fields. Forced
circulation a nd circulation eva pora tors still have som e signifi-
cance, whereas special types such as spiral tub e, coun terflow
or stirrer evaporator s are only used in special circumstan ces.
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The following list show s group s of produ cts
that are su ccessfully concentrated in more
than 4.000 GEA Wiegand evap oration plants.
Add itional prod ucts are detailed in ou r refe-
rence lists.
Reference Products from GEA Wiegand Evaporation Plants
Chemical and Pharmaceut ical Industries
Caustic solutions Caustic soda solution, caustic potash solution
Organic acids Ascorbic acid, citric acid
Inorganic acids Phosp horic acid, nitric acid
Saline solutions Ammonium nitrate, ammonium sulph ate, sodium
sulphate
Amines Urea, diethyl amine
Alcohol Methano l, ethanol, glycerine, glycol, isopropano l
Organic products Aromatic compou nd s, acetone, caprolactam w ater,
synth etic glue, aromas
Pharmaceutical Enzymes, antibiotics, dru g extracts, sugar substitu tes,
solutions sorbitol, sorbose and glu conate
Suspensions Kaolin, calcium carbonate
Waste water Process waste wa ter, wash an d r insing water, oil
emu lsions, etc.
Food and Beverage Industry
Dairy products Whole and skimmed milk, cond ensed milk, whey and
wh ey derivates, butterm ilk proteins, lactose solutions,
lactic acid
Protein solution Soya whey, nutrient yeast and fodd er yeast, wh ole egg
Fruit juices Orang e and other citrus juices, pomaceous juice,
red berry juice, tropical fruit juices
Vegetable juices Beetroot juice, tomato juice, carrot juice
Starch products Glucose, dextrose, fructose, isomerose, maltose, starch
syrup, d extrine
Sugar Liquid su gar, white refined sugar, sweetwater, inu lin
Extracts Coffee and tea extracts, hop extract, malt extract,
yeast extract, pectin, meat and bone extract
Hydrolisate Whey hydrolisate, soup seasoning, protein hydrolisate
Beer De-alcoholized beer, wort
Organic Natural Products Industry
Fermentation broth Glutamate, lysine, betain
Glue and gelatine Technical gelatine, edible gelatine, leather glue and
bone glue
Emulsions Miscella
Extracts Tanning extract
Stillage Whisky, corn, yeast, potato stillages, vinasses
Steep wat er Corn steep water, sorghu m steep water
Stick water Slaugh terhou se waste w ater, fish stick water, fruit peel
press water, beet chips, fibre press water, fibreboard
press water
Organic waste wat er Wash water, wheat and potato starch effluents, manu re
Blood Whole blood, blood plasma
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Two examples of suitable distribution systems,
above: Perforated bowl, below: Tubelet
Heating steam
Heating steam condensate
Cooling water
Deaeration
Product
Vapour condensate
Concentrate
1 Falling film evaporator
2 Preheater
3 Condenser
A
B
12 3
F
CC
CD
E
that w ill lead to incrustation and the build-up of deposits.
For comp lete wetting it is importa nt that a su itable distribution
system is selected for the head of the evapora tor.
Wetting rates are increased by using longer heating tu bes,
dividing the evaporator into several comp artments or by recir-
culating the p roduct.
Parti cular features
Best product quality du e to gentle evaporation, mostly
und er vacuum , and extremely short residence times in the
evaporator.
High energy efficiency due to m ultiple-effect arrangem ent
or heating by thermal or m echanical vapou r recompressor,
based upon the lowest theoretical temperature difference.
Simp le process control and automation due to their small
liquid content falling film evap orators react quickly to changes
in energy sup ply, vacuu m, feed quan tities, concentrations,
etc. This is an importa nt p rerequisite for a u niform final concen-
trate.
Flexible operation quick start-up and easy switchover
from operation to cleaning, uncomplicated changes of product.
Fields of appl ication
Capacity ranges of up to 150 t/ hr, relatively small floor space
requirement.
Particularly suited for temperature-sensitive products.
For liquid s which contain small quan tities of solids and h ave
a low to m oderate tendency to form incrustations.
D
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Evaporator Types
FORCED CIRCULATION EVAPORATORS
Design
Horizontal or vertical shell-and-tube heat exchanger or plate
heat exchanger as the calandria, with flash vessel/ separator
arranged above the calandria, circulation pum p.Vapour
Heating steam
Condensate
Product
Concentrate
Flash vessel /separator
Calandria
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CD
A
B
CC
D
E
F
CD
3
1c1a 1b
2
Operation
The liquid is circulated throu gh the caland ria by mean s of a
circulation pu mp , where it is superheated at an elevated p res-
sure, higher than its norm al boiling pressure. Upon entering
the separa tor, the pressu re in the liquid is rapidly redu ced
resulting in some of the liquid being flashed , or rapidly boiled
off. Since liquid circulation is maintained , the flow velocity in
the tubes and the liquid temp erature can be controlled to suit
the p roduct requirements ind epend ently of the p re-selected
temperature difference.
Parti cular features
Long operating p eriods boiling/ evaporation does not take
place on the heating su rfaces, but in the sep arator. Fouling du e
to incrustation and precipitation in the calandr ia is therefore
minimised.
Optimised heat exchange surface flow velocity in th e tubes
determined by the circulation pum p.
Fields of applicati on
Liquids with a h igh tend ency for fouling, highly viscous
liquids, as the high concentration step in mu ltiple-effect eva-
poration plants.
Forced circulation evaporators are optima lly suited a s
crystallising evap orators for saline solutions.
Heating st eam
Cooling water
Deaeration
Vapour condensate
Heat. steam cond.
Concentrate
Product
D
1a Calandria plate heat exchanger
1b Calandria vertical shell-and-tube
heat exchanger
1c Calandria horizontal shell-and-
tube heat exchanger
2 Separator
3 Condenser
2-effect falling film, forced circulation evaporation plant in counterflow
arrangement with downstream system for the purification of vapour conden-
sate by distillation of waste water containing salts and organic compounds.
Evaporation rate: 9,000 kg/hr concentrated to 65 % TS
1a 1b 1c
D
CD
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Heating st eam
Cooling water
Deaeration
Vapour condensateHeating steam condensate
Concentrate
Product
D
A
B
CD CC
E
F
Operation
Product and heating med ia are transferred in counterflow
throug h their relevant passages. Defined plate distances in con-
junction with special plate shapes generate strong turbulence,
resulting in op timum heat transfer.
Intensive heat transfer causes the prod uct to boil wh ile the
vap our form ed d rives the residu al liquid , as a rising film, into
the vapou r du ct of the plate package. Residu al liquid an d va -
pours are separated in the d ownstream centrifugal separator.
The wide inlet du ct and the up ward m ovement ensure op-
timu m d istribution over th e total cross-section of the hea t ex-
changer.
Parti cular features
Use of different heating m edia du e to p late geometries,
the system can be heated with both hot w ater as well as with
steam.
High product quality due to especially gentle and u niform
evaporation d uring single-pass op eration.
Little space required due to comp act design, short connec-
ting lines and sm all overall height of max. 3- 4 m.
Easy ins tallation requiring l ittle time due to pre-assem-
bled, transportable construction units.
Flexible evaporation rates by add ing or removing plates.
Ease of maintenance and cleaning as plate packages can
be easily opened .
Fields of appl icationFor low to m edium evaporation rates.
For liquids containing only small amounts of undissolved
solids and with no tendency to fouling.
For tempera ture-sensitive produ cts, for highly viscous
produ cts or extreme evaporation conditions, a produ ct circula-
tion design is chosen.
1 Plate calandria
2 Separator
3 Condenser
2
1 3
Multiple-effect plate evaporation plant for fructose.
Evaporation rate: 16 t/hr
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Evaporator Types
Operation
The liquid to be concentrated is sup plied to the bottom an d
rises to the top of the heating tubes in accordance with the
mam moth p um p or rising film principle. Due to the external
heating of the tu bes the liquid film on the inside w alls of the
tubes starts to boil releasing vap our. The liquid is carried to th e
top of the tubes as a result of the upward movement of the
vapours.
The liquid is separated from the vapou rs in the down stream
separator and flows through a circulation p ipe back into the
evapor ator, ensuring stable and un iform circulation. The larger
the temp erature difference between th e heating cham ber and
the boiling chamber, the greater the intensity of evaporation
and , consequ ently, the liquid circulation and h eat transfer
rates.
Where the boiling cham ber of the circulation evap orator is
divided into several separate chambers, each one equipp ed
with its own liqu id circulation system, the heatin g surface
required for high final concentration s can be considerably
reduced compared to an und ivided system.
The final concentration is only reached in the last cham ber. In
other chambers, the heat tran sfer is considerably higher d ue to
the lower v iscosities and boiling point elevations.
CIRCULATION EVAPORATORS
Design
Vertical shell-and-tu be heat exchanger of
short tube length, w ith lateral separator
arranged at the top.
Heating st eam
Deaeration
Cooling water
Heating st eam condensate
Product
Vapour condensate
Concentrate
1 Calandria
2Separator
3 Condenser
A
F
E
CC
CD
D
2
1
3
3-effect circulation evaporation plant for glycerine water.
Evaporation rate: 3,600 kg/hr
B
Parti cular features
Quick start-up and large specific capacity the liquid
content of the evapora tor is very low d ue to the relatively short
length and sm all diam eter of the heating tubes (1- 3 m).
Fields of appl ication
For the evaporation of prod ucts insensitive to high temp era-
tures, where large evaporation ratios are required.
For products which have a h igh tendency to foul and for
non-Newtonian p roducts, where the apparent viscosity may be
redu ced by the high velocities.
The circulation evaporator with divided boiling chamber
and top-mounted separator can be used as a high concentrator.
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Operation
The liquid is evenly d istributed over the heating tu bes by
means of a d istribution system an d flows as a th in film d own
the inside w alls. The external heating of the tubes cau ses the
liquid film to boil. The vapou rs formed are cond ensed as d istil-
late on the external walls of the cond ensate tubes an d flow
dow nw ards. Distillate and bottom prod uct are separately kept
and discharged from th e lower part of the evaporator.
Parti cular features
Particularly gentle product treatment due to very low
pressure/ temperature p rocessing, short produ ct residence
times and single pass operat ion. Distillation po ssible at
vacuu m p ressures ranging from 1 mbar to below 0.001 mba r.
Due to the integrated condenser tubes, there is no vap our flow
pressure loss.
Optimised design no mechanical wear and tear, as the
system has no rotating internal p arts.
Low investment cost.
Also suitable for high evaporation rates.
Fields of appl ication
Particularly temperature sensitive, non-aqueous solutions.
Special Evaporator Types
FALLING FILM, SHORT PATH
EVAPORATORS
Design
Vertical shell-and -tube hea t exchanger
equipped with concentrically arranged
condenser tubes within the heating tubes
and integrated separator in the lower part
of the unit.
FLUIDISIED BED EVAPORATORS
Design
Vertical fluidised bed heat exchan ger (on
the tu be side solid p articles such as glass
or ceram ic beads, or stainless steel wire
particles are entrained in the liquid),
flash/ vessel separator and circulation
pump.
Operation
Same principle as for the forced circulation eva por ator.
The upw ard m ovemen t of the liquid entrains the solid p articles,
which provide a scouring/ cleaning action. Together with the
liquid they are transferred through the calandria tubes.
At the head of the caland ria, the particles are separated from
the liquid an d are recycled to the caland ria inlet cham ber.
The superheated liquid is flashed to boiling tem peratu re in the
dow nstream separator and is partially evaporated.
Parti cular features
Long operating p eriods continu ous cleaning of the heating
surface by the entrained beads and improved heat transfer.
Fields of applicati on
For produ cts that have h igh fouling tend encies, where
fouling cannot be sufficiently prevented or retard ed in stan-
dard, forced circulation evaporators.
For liqu ids of low to m ediu m, viscosity.
Heating steam
Deaeration
Heating steam
condensate
Cooling water
Concentrate
Vapour condensate
Product
1 Fluidised bed calandria
2Separator
3 Condenser
A
E
F
B
CC
CD
D21 3
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Operation
As in falling film evap orators, the liquid is sup plied to the top
of the evaporator and is distributed over the evaporator tubes,
but the vap ours flow to the top in counterflow to the liquid.
Parti cular features
Partial di stillation amou nts of volatile constituents con-
tained in the p roduct to be concentrated can be stripped. Thisprocess can be enha nced by the sup ply of an entraining stream,
such as steam or inert gas, to the lower p art of the caland ria.
Fields of appl ication
This type of evapo rator, designed for sp ecial cases, is used to
enhance the m ass transfer between liquid and vapou r. If a gas
stream is passed in counterflow to th e liquid, chemical reac-
tions can be triggered.
COUNTERFLOW-TRICKLE
EVAPORATORS
Design
Shell-and-tube h eat exchan ger, lower p art
of caland ria larger than th at of e.g. the
rising film evaporator, top-moun ted sepa-
rator equipped w ith integrated liquid dis-
tribution system.
RISING FILM EVAPORATORS
Design
Vertical shell-and-tu be hea t exchanger
with top-mounted vap our separator.
Special Evaporator Types
Operation
The liquid to be concentrated is sup plied to the bottom an d
rises to the top in accordance with to the mam moth p um p
pr inciple, or rising film prin ciple.
Due to externa l heating, the liquid film starts to boil on the in-
side walls of the tubes and is partially evaporated d uring this
process. As a result of the up ward movement of the steam
bubbles, the liquid is transferred to the top. During the ascent
more and more vap ours form. The film starts to move along
the w all, i.e. the liquid rises. The vapou rs and liquid are then
separated in the top-mounted separator.
Parti cular features
High temperature difference between heating chamber
and boiling chamber in order to en sure a su fficient liquid
transfer in tubes of a length of 5 -7 m an d to cause the film to
rise.
High turbulence in the liqui d due to the upward m ove-
men t against grav ity. For this reason, rising film evapor ators
are also suited for prod ucts of high viscosity and those with
the tend ency to foul on the heating surface.
Stable high-performance operation based on produ ct re-
circulation w ithin a wid e range of cond itions.
Fields of appli cation
For large evaporation ra tios, for high viscosities and p ro-du cts having a tend ency to foul.
Can be u sed as a high concentrator in single pass operation
based on extrem ely short residen ce times.
Falling film counterflow
trickle evaporation plant
with rectification unit for
olive oil refining
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Operation
The liquid to be evapor ated flows as a boiling film from the
top to the bottom in pa rallel flow to the vap our. The expand ing
vap ours p rodu ce a shear, or pu shing effect on the liquid film.
The curv ature of the path of flow indu ces a secondary flow,
wh ich interferes with the mo vemen t along the tub e axis. This
additional turbulence considerably improves the heat transfer,
especially in the case of high viscosities.
Parti cular features
Small apparatus dimensions due to the spiral shape,
longer tube lengths an d consequently larger heating su rfaces
relative to the overall height of the unit can be obtained .
Large evaporation ratios du e to large temperatu re differ-
ences and single pass operation.
Fields of appl ication
For high concentr ations an d viscosities, e.g. for the concen-
tration of gelatine.
Operation
The liquid is supp lied to the vessel in batches, is caused to boil
while being continuously stirred an d is evaporated to the re-
quired final concentration.
If the evap orated liquid is continuously replaced by thin pro-
du ct, and if the liquid content is in this w ay kept constant, the
plant can be also operated in semi-batch mode.
Parti cular features
Low evaporation rate due to small heat exchange surface.For this reason, large temperatu re d ifferences between th e
heating jacket and the boiling chamber are requ ired. The pro-
duct properties permitting, the heating surface can be enlarged
by means of additional immersion heating coils.
Fields of applicati on
For highly viscous, pasty or p ulpy p roducts, whose proper-
ties are not negatively influen ced by a residence time of several
hours, or if particular p roduct p roperties are required by long
residence times.
It can also be used as a high concentrator dow nstream from
a continuou sly operating p re-evaporator.
SPIRAL TUBE EVAPORATORS
Design
Heat exchanger equipp ed w ith spiral
heating tubes and bottom-moun ted centri-
fugal separator.
STIRRER EVAPORATORS
Design
External, jacket heated vessel equipp ed
with stirrer.
Stirrer evaporator arranged as a high concentrator
for yeast extract. Evaporation rate 300 kg/hr
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Quantities and Concentration Ratios
in Evaporation Plants
To calculate continu ous evap oration p rocesses, mass
flow rates rather than volumetric quantities are used.
The unit kg/ hr is used for A, B and C. The ratios
indicated above d o not change.
A C
BInitial concentration cA
of t he product flow A kg/hr
cA
cB
Evaporated product , concentrate
Final concentration cB
of concentrate f low B kg/hr
The evaporation ratio is a measure for
the concentration process:e The evaporation rat io can also be defined as the ratio of theinitial and final concentrations (% weight dry substance).
Part of the solvent (C), is evaporated from t he
product flow (A).The residual amount (B), is
the evaporated product (concentrate):
A = B + C
e = A = cBB cA
The evaporated quantity C, can therefore
be defined as the dif ference between the
quantity of thin solution and concentrate:
C = A B
Vapour flow C [kg/hr]: Evaporated water,
solvent
Given
Quantity A to be
evaporated
Formula
C = A e 1
e
B = A 1
e
If the solvent is evaporated from th in solution A at an even rate, the
concentration rises slowly at first, but rises increasingly rap idly to the
theoretical maximum . At this point, no more solvent wou ld be left in
the solution. The lower the initial concentration cA, the steeper th e
increase of the concentration cu rve. This relationship is essential for th e
control of evap oration p lants, and in cases of high evap oration ratios,
for the separation of the evaporation p rocess into pre-evaporation an d
high concentration steps.
If the concentrat ions or the evaporation ratio is known,
the quantit ies can be calculated using the formulae in t he
table below:
Left: Increase of final concentration during the evaporation from
solutions at different in itial concentrations
Required
C
B
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Energy Efficiency of Evaporation Plants
The operating costs of an evap oration p lant are largely deter-
mined by the energy consump tion.
Under steady-state conditions there m ust be a balance between
the energy entering and leaving the system.
The energy consumption of the system can be tailored to meet the
customers individual requirements by intelligent thermal configura-
tions of the evaporation plant.
There are three ba sic possibilities to save en ergy:
Multiple-effect evap oration
Thermal vapou r recompression
Mechanical vapour recompression
App lication of one of these techniqu es will considera bly de-
crease the energy consu mp tion. Often it is feasible to combine
two of these possibilities to minimise capital and opera ting
costs. In highly soph isticated evap oration p lants all three tech-
niques may be applied.
5-effect falling film evaporation plant for apple juice concentrate, directly
heated, w ith aroma recovery. Evaporation rate: 12,000 kg/hr
Decrease of the specific steam consumption in % and increase of the approxi-
mate total heating surfaceF in relation to the number of effects
Mult iple-effect evaporation
If we consid er the h eat balance of a single-effect evap orator w e
find that the heat content (enthalpy) of the evaporated vapou r
is approximately equal to the h eat input on the h eating side. In
the common case of water evaporation, about 1 kg/ hr of
vapou r will be produced by 1 kg/ hr of live steam, as the speci-
fic evaporation heat values on the heating and produ ct sides
are about the same.
If the amou nt of vapour prod uced by primary energy is used
as heating steam in a second effect, the energy consum ption of
the overa ll system is red uced by abou t 50 %. This principle can
be continued over furth er effects to save even m ore energy.
The maximu m allowab le heating temp eratu re of the first effect
and the lowest boiling temp eratu re of the final effect form an
overall temp erature difference which can be divided a mon g the
individ ual effects. Consequ ently, the temp eratu re difference
per effect d ecreases with an increasing nu mber of effects. For
this reason, the heating su rfaces of the individu al effects mu st
be d imensioned accordingly larger to achieve the required eva-
poration rate, but w ith a lower temp erature difference ( t).
A first approximation shows that the total heating surface of
all effects increases prop ortionally to th e nu mber of effects.
Consequ ently, the investm ent costs rise considera bly wh ereas
the am oun t of energy saved becomes increasingly lower.
Live steam Vapour Specif. steam consumption
1-effect-plant 1 kg/h 1 kg/h 100 %
3-effect-plant 1 kg/h 3 kg/h 33 %
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Energy Efficiency of Evaporation Plants
Thermal vapour recompression
During therm al vapour recompression, vapou r from a boiling
chamber is recomp ressed to the h igher pressure of a heating
chamber in accordance w ith the heat p um p p rinciple. The sat-
urated steam temp erature correspond ing to the heating
chamber pressure is higher so that the vap our can be reused
for heating.
To this end, steam jet vapou r recompressors are used . They
operate according to the steam jet pu mp principle. They have
no m oving parts and are therefore not subject to wear and tear.
This ensures maximu m op erational reliability.
The use of a thermal vapour recompressor gives the same
steam/energy saving as an additional evaporation effect.
A certain steam qu antity, the so-called motive steam, is required
for operation of a thermal vap our recomp ressor. This motive
steam p ortion is transferred as excess vapou r to the next effect
or to the cond enser. The energy of the excess vapou rs app roxi-
mates the energy of the motive steam qu antity used.
3-effect falling film forced circulation evaporation plant heated by thermal
vapour recompressor for waste water from sodium glutamate production.
Evaporation rate: 50 t/hr
Heating steam
Cooling water
Deaeration
Service waterVapour condensate
Product
Concentrate
1, 2 Falling film evaporators
3, 4 Forced circulation evap.
5 Condenser6, 7 Preheaters
8 Thermal vapour recomp.
9 Feed tank
10 Condensate collection tank
11 Vacuum pump
1 2
3
4 5
11
6
7
8
9
10
F
D
E
CCCC
B
A
G
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Mechanical vapour recompression
Evaporation p lants heated by m echanical vapou r recompres-
sors require particularly low am oun ts of energy.
Whereas steam jet compressors only comp ress part of the
vap our, mechanical vapou r recompressors recycle all of the
vapou r leaving the evap orator. The vapour is recompressed to
the pressure of the corresponding h eating steam temperature
of the evap orator, using a m ere fraction of electrical energy
relative to the enthalpy recovered in the vapour. The operating
principle is similar to that of a heat p um p. The energy of the
vapou r condensate is frequently u tilized for the p reheating of
the prod uct feed. The amou nts of heat to be dissipated are
considerably redu ced, with the evap orator itself re-utilizing
the energy norm ally d issipated throu gh th e condenser cooling
water. Depend ing on the operating conditions of the plant, a
small quantity of add itional steam, or the conden sation of a
small quantity of excess vapou r may be required to m aintain
the overall evaporator heat balance and to ensure stable opera-
ting conditions.
Due to their simp licity and m aintenan ce friendly d esign, single
stage centrifugal fans are used in evap oration plants. These
un its are supp lied as high pressure fans or turbo-comp ressors.
They operate at h igh flow velocities and are th erefore suited
for large and very large flow rat es at vapou r compression
ratios of 1:1.2 to 1:2. Ration al speeds typ ically are 3,000 up to
18,000 rpm. For high pressu re increases, mu ltiple-stage com-
pressors can be used.
(See our sp ecial brochure Evap oration Technology u sing
Mechanical Vapou r Recompression).
1-effect falling film evaporation plant heated by mechanical vapour recom-
pression for wheat starch effluent. Evaporation rate: 17,000 kg/hr
Heating st eam
Cooling water
Product
Deaeration
Service water
Vapour condensate
Concentrate
1 Falling film evaporator
2 Condenser
3 Plate heat exchanger4 Vapour recompressor
5 Feed tank
6 Condensate collection tank
7 Vacuum pump
A
E
B
1 2
34
5
6
7
F
CC
D
G
CC
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Directly heated Thermal vapour recompression
2-effect design
Mechanical vapour recompression
Mass/energy flow diagrams of an evaporator with different types of heating
A
A
D
D
D D
A A
B
B
B B
CD
CDCC
CC CC
C
C
CC
E
A Product
B Concentrate
C Condensate
CC Vapour condensateCD Heating st eam
condensate
D Heating steam
E Electrical energy
If we consider the heat balance of a single-effect
evaporator we find that the heat content
(enthalpy) of the evaporated vapour (C) is ap-
proximately equal to the heat input (D) on the
heating side. In the common case of water eva-
poration, about 1 kg/hr of vapour will be pro-
duced by 1 kg/hr of live steam, as the specific eva-
poration heat values on the heating and product
sides are about the same.
If the amount of vapour produced by primary
energy is used as heating steam in a second
effect, the energy consumption of the overall
system is reduced by about 50 %. This principle
is repeated over further effects to save even
more energy.
A certain quantit y of live steam, the so-called
motive steam, is required for the operation of
a thermal vapour recompressor. This motive
steam quantity must be transferred to the next
effect or to the condenser as surplus residual
vapour. The surplus energy contained in the
residual vapour approximately corresponds to
the amount of energy supplied in the motive
steam.
The operation of evaporation plants heated by
mechanical vapour recompressors requires a
particularly low amount of energy. The
operating principle of a mechanical vapour
recompressor is similar to that of a heat pump.
Almost the entire vapour quantity is com-
pressed and recycled by means of electrical
energy. Only minimum quantities of live
steam are required, generally just during
start-up. The quantit ies of residual waste
heat to be dissipated are considerably reduced.
Energy Efficiency of Evaporation Plants
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Criteria for the Design Select ion, Arrangement
and Operating Modes of Evaporation Plants
Evaporation Plant Components
The core of any evapor ation plan t is the caland ria. For the
operation of the p lant, several add itional comp onents are re-quired.
The most imp ortant of these are condensers, preheaters,
pu mp s, fittings, vents, vacuu m systems and cleaning systems.
If substances are to be separated, the p lants are also equ ipp ed
with rectification colum ns, memb rane filtration un its, scrub-
bing and aroma recovery systems.
To gu arantee trou ble-free operation of the plant, state-of-the-
art measuring, control and computer m onitoring systems are
used.
Attention to detail, safety and p rotective equipm ent and t her-
mal and sound insulation ensure safe operation of the p lant.
GEA Wiegand designs, builds and supplies turnkey evaporation
plants. Our experience and expert knowledge of the performance of
each individual component enables us to select the right equipment
for each application so that the requirements of the entire evapora-
tion plant will be met.
The most import ant requirements are as follows:
Capacity and operating dat a such as qu antities, concentra-
tions, temperatures, annual operating hours, change of
product, control, automation.
Product properties such as tem peratu re sensitivity, viscosity
and flow p roperties, tend ency to foaming, fouling and p re-
cipitation, boiling p roperties.
Utility Requirements such a s steam, cooling w ater, electricity,
cleaning agents, parts exposed to wear and tear.
Selection of materials and surface finish.
Capital costs for interest and repayments.
Personnel costs for op eration an d maintenance.
Site conditions such as sp ace availability, climate for outdoor
installations, connections for energy and prod uct, service
platforms.
Legislative framework regarding h ealth and safety, prevention
of acciden ts, soun d p ropagat ion, environm ental protection
and others, depen ding on the specific project.
When d esigning evaporation p lants, various and often contra-
dictory requ irements mu st be taken in to consideration. These
determine the type of design, arrangement and the resulting
process and cost data.
GEA Wiegand ev aporation p lants are characterised by their
high quality, efficiency and design refinemen ts. Careful atten-
tion is paid to the above m entioned criteria in view of the ind i-
vidu al requirements. In ad dition, a strong emp hasis is placed
on reliability and ease of operation.
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Evaporation Plant Components
Preheaters and heaters
In most cases the produ ct to be evaporated mu st be preheated
to boiling temper atu re before it enters the calandr ia. As a rule
straight tu be preheaters or p late heat exchangers are u sed for
this duty.
Evaporators
The selection of the suitable type of evapor ator is depen den t
on the p articular case of each application and the prod uct pro-
perties.
Separators
Each evap orator is equipped with a unit for separating vap ours
from liquids. Depending on th e field of app lication d ifferent
typ es of separa tors are chosen, e.g. centrifugal separat ors, gra-
vitational separators or separators equipped with internals.
Essential d esign criteria are separa ting efficiency, pressu re loss
and frequency of cleaning.
Condensers
Where possible, the heat content of the vap ours p rodu ced
du ring evapora tion is used for heating dow nstream effects and
preheaters, or the vapou rs are recompressed and re-utilized as
the heating m edium . The residual vap ours from the last effect
of an evaporation p lant which cannot be used in this way mu st
be condensed. Evaporation plants can be equipped w ith
surface, contact or air-cooled cond ensers.
Deaeration/vacuum systems
Vacuum pu mp s are required for maintaining the vacuum in
the evaporation p lant. They d ischarge leakage air and n on-
conden sing gases from th e process, including d issolved ga ses
wh ich are introd uced in th e liqu id feed. For this app lication,
jet pump s and liquid ring pump s can be used d epending on
the size and the op erating m ode of the evaporation plant.
Pumps
Pum ps mu st be chosen in view of a wide ran ge of design con-
ditions an d ap plications. The main criteria for the selection of
pu mp s are produ ct properties, suction head conditions, flow-
rates and the pressure ratios in the evaporation plant.
For low-viscosity produ cts, centrifugal pu mp s are mostly u sed.
High ly-viscous prod ucts require the use of positive displace-
men t pu mp s. For liquid s containing solids or crystallised
produ cts, other pu mp typ es such as propeller pum ps are used.
The type, size, speed , mechanical seals and mat erial are deter-
mined by the p articular case of app lication and the relevant
conditions of use.
Cleaning systems
Depend ing on the p roduct, scaling and fouling m ight occur
after a certain operating time. Scale and fouling d eposits can
be remov ed by chemical cleaning in most cases. To this end ,
the evaporation plant is equipped with the necessary comp o-
nents, cleaning agent tan ks, additional pum ps an d fittings.
This equipment, ensu ring ease of cleaning withou t d isassembly,
is comm only referred to as Cleaning in Place or CIP.
Cleaning agents are chosen according to the type of dep osit.
The cleaning agen ts penetra te the incrustation, dissolve or
disintegrate it and completely clean an d, w here necessary, ste-
rilise the evap orator su rfaces.
Vapour scrubbers
A vapour scrubber is required wh ere the plant is not heated
with live steam but w ith discharge stream such as dryer ex-
haust vap ours. The vapou rs must be cleaned before they are
transferred into the heating chamber of the evaporation plant
in order to avoid contamination and fouling.
Condensate polishing systems
In spite of optimised droplet separation, the condensate
quality might not correspond to the requ ired pu rity especially
if the prod uct contains volatile constituents. Depend ing on
the case of app lication the cond ensate can be further p urified
by mea ns of a rectification colum n or a m embra ne filtration
system.
Materials
The materials of the evaporation plant are d etermined by the
requirements of the p roduct and the customers request.
Depending on the corrosion behaviour u nd er the relevant d e-
sign conditions, a w ide va riety of materials is used. Stainless
steels are most comm only used . For special requirements,
Ha stelloy, titanium , nickel, copper, graphite, rub berised steelor synth etic mat erials can also be used . As required th e design
and manu facture will comply w ith international standard
directives and codes.
Depiction of a 4-effect evaporation plant for corn stillage, consisting of a3-effect falling film evaporator and a single-effect forced circulation evapora-
tor. The plant is directly heated with dryer exhaust vapours. The vapours are
cleaned in a vapour scrubber.
Evaporation rate: 130 t/hr
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1a
2a
3a
4b
6
3b
5
2b
1b
4a
4c
8
8
88
8
7
1a,b Falling film evaporator with centrifugal separator2a,b Falling film evaporator with centrifugal separator
3a,b Falling film evaporator with centrifugal separator
4a,b,c Forced circulation evaporator with flash vessel/
gravitational separator and circulation pump
5 Surface condenser6 Vapour scrubber
7 Vacuum pump
8 Product and condensate pum ps
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Measuring and Cont rol Equipment
The major goal of the evap oration p rocess is to achieve a con-
stant final concentration of th e prod uct. It is therefore imp ortant
to maintain all parameters, such as steam pressure, product
feed an d vacuum, w hich m ight influence the evaporation p lant
or alter the mass and heat balances.
In accordance w ith the technical and customers requirements,
GEA Wiegand evap oration plants are equipped with the rele-
vant m easuring and control systems. We sup ply conventional
control systems as w ell as process control systems.
1. Manual control
The plant is operated by means of manu ally operated valves.
Concentrate sam ples mu st be checked at certain intervals. This
type of control is suitable for simp le plants and for p rodu cts
wh ere slight variations in qua lity are acceptable.
2. Semi-automated cont rol system
The most important param eters such as steam pressure, product
feed quan tity, vacuum , final concentrate density and liquid
level are kept constan t by mean s of hard wa re controllers and
are recorded by a data recorder. Pump motors and valves are
manu ally operated from a control panel.
3. Semi-automated control system based on PLC control
The plant is operated by mea ns of softwa re controllers from a
programmable logic controller (PLC) with operating inputsand a da ta monitoring system p rovided by a PC. The control-
lers, motors and valves are manually operated from the PC.
Smaller program sequences such as cleaning mode are possi-
ble. All key m easured values are recorded and displayed on the
mon itor. Control and operating system s are chosen on th e basis
of GEA Wiegand specifications or customer specifications.
4. Automated cont rol system based on PLC control
As an extended version, the PLC system is used as au tomation
system for the program sequences of start-up, switch-over
to produ ct, produ ction, cleaning and shut-down .
The processes can be centrally operated and monitored on the
screen by means of a bus system. Set points and other key
param eters are entered into the fields show n on a graph ic dis-
play. The plant is self-mon itored an d is au toma tically switched
to a safe mode in th e event of operating trou ble. The use of a
mu ltiple operator station system increases the av ailability.
5. Process control system
The plant is controlled by one or several autom ation systems,
wh ich can also be integrated into existing p rocess structures.
The process control system is particularly suited for multiple
produ ct and batch p rocesses.
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Manufacture, Transport, Erect ion,
Commissioning and After-sales Service
Depending on the arrangement evaporation plants can be ex-
tremely comp lex, and therefore the first commissioning requ i-
res certain experience. Experienced sp ecialists are therefore
assigned to th is task, wh o are also available to train the custo-
mer s p ersonnel.
Each plant perm anen tly achieves its optimal perform ance if itis expertly ma intained . This service requires specialists wh o, if
required, immediately trace and eliminate faults so that p ro-
du ction losses caused by p eriods of standstill can be minimised.
Ou r trained service personn el are therefore available to you.
Thanks to their up -to-date training th ey are in a p osition to carry
out m aintenance and repairs quickly and thoroughly. Users
benefit from ou r spare p arts service, based on ou r plant refe-
rence num bers and a d escription of the item, spares can be
ordered on line or quotations requested for the required parts.
The GEA Wiegand manu facturing w orkshop
is situated in Beckum , Westpha lia. Covering
an a rea of more th an 6,500 m2, large parts of
our plants are manufactured and prep ared for
transport.
In some cases small plants are completelyassembled at the m anufacturing workshop
and are dispatched as compact or skid m oun-
ted u nits, ready for site connection. Most
plants, however, are assembled on site du e to
their size.
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GEA Wiegand GmbH Einsteinstrasse 915 D-76275 Ettlingen Germany Phone: +49 (0) 72 43/ 7 05-0E
05200405000/H
inkel&Junghans,Werbeagentur,KA
Evaporation plants
for the concentration of all types of liquid food , organic and
inorganic solutions, waste water and other typ es of liquid
prod ucts by means of thermal or mechan ical vapou r recom-
pressors, single-effect or mu lti-effect system s, with add itional
equip ment for heating, cooling, d egassing, crystallization,
rectification etc.
Membrane filtration
for the concentration of liquid food, process water, organic and
inorganic solutions and waste w ater, for the separation of im-
pu rities for upgr adin g and v aluable material recovery; based
on technology an d references by GEA Filtration, Hud son, USA.
Distillation/rectification plants
for the separation of mu lti-compon ent mixtures, e.g. for the
recovery of organic solvents, the recovery, purification an d
deh yd ration of bioalcohol of different qu alities.
Lines for the production of alcohol
from the treatment of raw m aterial, fermentation and distilla-
tion to stillage concentration and dry ing of spent p rodu cts.
Plants for crystallization
of special prod ucts as well as waste water containing salts.
Product studies, engineering
for plants includ ed in ou r range of produ cts.
Our Range of Products in Summary