Evaporation Technology

8/4/2019 Evaporation Technology

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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.


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.


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


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).


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.


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.


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.


Long operating p eriods continu ous cleaning of the heating

surface by the entrained beads and improved heat transfer.


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


12/2412

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.


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.


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.


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


13/2413

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.


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.


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.


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.


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


15/2415

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 %


16/2416


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.


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


17/2417


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


18/2418

Directly heated Thermal vapour recompression

2-effect design


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.



19/2419

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.


20/2420

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.



21/2421

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


22/2422

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.


23/2423

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.


24/24

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

Evaporation Technology

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