Evaporators

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TechnologySchmidt technology is know-how.

Know-how for the design of evaporationplants. It is distinguished by high qualityresults from the competence andcreativity of our engineers. With overone hundred years of experience asmanufacturers of heat exchangers andplants for thermal processing, we havehad a major influence on the technologyof evaporation. In processing liquidswith suspended solids, Schmidt hasmade major contributions to the state ofthe art.

• We have been designing plants withplate evaporators for more than 40years, and have been guided by thefollowing objectives:

- to design plants which deliver thebest possible product quality

- to provide economical systemswith low operating cost

• Schmidt designs, manufactures andinstalls complete turnkey plants formany different feed streams, takinginto account their inherent productcharacteristics.

In close cooperation with ourcustomers, we develop the mostappropriate process for the productto be treated. When required, wealso act as an engineering partnerand manage the overall technicaldesign of the plant.

• Schmidt technology is the result ofextensive research and develop-ment. In the early 80's, motivated bya growing need for better, moreflexible evaporation systems, wedeveloped the SIGMASTAR® eva-porator.

• Since its design is fundamentallynew, the SIGMASTAR® has beenawarded patents in many countries.The unique characteristics ofSIGMASTAR® evaporation plantsallow Schmidt to supply equipmentto many different and diverseindustries. The performance of theSIGMASTAR®, on widely differentproducts, far surpassed the mostoptimistic projections.

Areas of ExpertiseSchmidt concentration plants are usedin the food, chemical, fermentation, andpharmaceutical industries. They arealso used for waste treatment. Wemanufacture plate & frame designs,with energy saving options such asthermal vapour recompression (TVR).

Fine Chemicals andPharmaceuticalsWe have provided systems for acids(citric acid, etc.) bases (sodium hydrox-ide, etc.) salt solutions (ammoniumnitrate, ammonium sulphate, aluminiumsulphate, magnesium chloride), aminesolutions (urea, etc.), alcohols, (glycol,methanol, glycerine, etc.), aromaticcompounds (toluol, xylene, etc.), rawand intermediate products for syntheticmaterials and fibres (caprolactamwater), synthetic glue, pharmaceuticalproducts (sorbitol, sorbose, enzyme so-lutions, antibiotics, monosodium gluta-mate), as well as many types of wastewater.

Organic Natural ProductsWe have built plants for processingstick water, hide and bone glue, proteinhydrolysates, technical and photo-graphic gelatines, oils, molasses, slops,yeasts, yeast extracts, wort, drugextracts, hops extracts, plant extracts,tanning extracts, corn steep water,glucose, dextrose, fructose, and wastewaters from potato and wheat starches.

Effluent TreatmentApplicable to many types of effluentfrom all branches of industry.

Foods and BeveragesWe have delivered systems for fruitjuices, fruit purees, pulp concentrates,vegetable juices and purees, tomatojuice, vegetable extracts, pectin, ediblegelatines, malt extracts, sorghum ex-tract, beer wort, cane and beet sugar,liquid sugar, dealcoholised wine andbeer and aroma recovery for manydifferent kinds of products.

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The SIGMASTAR® Evaporator Plate• Figure 2 shows a variation of the

SIGMASTAR®-90 plate; the partitio-ned SIGMASTAR®-45 plate. Thisplate allows two products to be pro-cessed simultaneously. On the rightis the correspondingly partitionedsteam plate. Steam can enter eitherthe left, the right or both sides of theplate, the condensates exit from thebottom of the corresponding side(s)of the plate.

• The SIGMASTAR®-90 and theSIGMASTAR®-45 can be combinedin many different ways to increasethe flexibility of our plants, especiallyfor small duties.

• As the dimensions of both plates areidentical, the same frame supportscan be used. Expansions and modi-fications involving both plate typesare possible at any time.

Some advantages of the rising-film SIGMASTAR®-90 andSIGMASTAR®-45 are:

- superior product distribution due tothe thermo-siphon principle. Asproduct boils and rises in the tube,fresh product automatically rises tore-fill the tube. This distribution tech-nique operates independently of thefeed rate, and allows a high degreeof flexibility and the possibility ofpartial-load processes

- very short residence time; product isin the SIGMASTAR® plate for lessthan a second. This is due to theshort flow distance and the highproduct film velocity. This featureguarantees a gentle treatment of theproduct

- low pressure losses across thetubes, a benefit of the short tubelength

- high vapour velocity in the rising film,which allows the processor toachieve high concentrations andviscosities

- clearly defined product flow path.There is no chance of local over-concentration

- high heat transfer co-efficients areobtained even when the feed tempe-rature is lower than the boiling tem-perature

- compared to other evaporatorsystems less expensive for highgrade materials

Due to their special construction,SIGMASTAR® evaporators can be usedfor nearly all evaporation processes.Especially for problem products (e.g.viscous streams, slurries, and liquidswith fouling tendencies) which cannotbe processed with falling-film evapora-tors, the SIGMASTAR® evaporator per-forms smoothly and successfully.

Fig. 1 : SIGMASTAR®-90 Evaporator Plate

• The heart of the SIGMASTAR® eva-porator is the SIGMASTAR® rising-film plate (Fig. 1). SIGMASTAR®

plates have a heat transfer surfaceof 0,9 m2 and are approximately0,9 m wide, 1,8 m high. Only twotypes of plate are needed, a "steam"plate and a "product" plate. TheSIGMASTAR® plate has longitudinalcorrugations that are sinusoidal andextend over the full width of theplant. Looking at two plates, alignedin such a way that the projectingpoints touch, vertical channels areformed which are almost circularand can be considered as singletubes.

• Product enters the lower part of theevaporator plate and floods thetubes. In this manner, every tubehas equal access to the productfeed. Steam condenses on one sideof the plate, product boils on theother. The vapours generated in thetube channels create a thin, high –velocity film which rises to the top ofthe plate.

• Since Service steam cannot crosscorrugation peaks in the transversedirection, we employ a distributionarea in the upper part of the plate.Here the corrugation is arranged topermit vapour to flow in the trans-verse direction, and to the channels.The cross-sectional flow area is thesame on both sides of the plate.

Fig. 2: SIGMASTAR®-45 Evaporator Plates

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The SIGMASTAR® Evaporator

Fig. 3 : SIGMASTAR®-90 Evaporator

Figure 3 shows an assembled SIGMA-STAR®-90 evaporator. The evaporatorplates are fitted in a frame. Perimeterbolts clamp the fixed and movablecovers together. This compresses thegasket seal at the edges of the plate.The function of the flooded lower pro-duct chamber is to distribute the productevenly to the tubes.

• The rising-film evaporation creates atwo-phase flow: The generatedvapours induce a product film on thetubes. The resulting mixture of liquidand vapours flows to the channel atthe top of the plate. From there itflows forward to the fixed cover ofthe frame and into a downstreamvapour/liquid separator.

• The steam enters through twochannels at the top of each side ofthe plate. Heating steam is distri-buted across and along the plate,condensate is discharged at eachside of the bottom.

• Since all connections and steaminlets are on the fixed frame, it is noproblem to open the unit or torearrange the evaporation surface.

• Furthermore, it is possible to directsteam to all four steam inlet areas.When all four steam inlets are used,a portion of the steam passes to therear of the plate pack allowing theSIGMASTAR® to be used for largerevaporation capacities and at highervacuum.

Besides the possibility of a largenumber of operating variations, theSIGMASTAR®-45 plate presents theadvantage that different effects orstages can be incorporated into a singleframe. An extremely compact systemcan be built at reasonable cost.

• Figure 4 shows a 2-stage unit with adownstream condenser as an exam-ple. In the first evaporation stage,the raw product is pre-concentratedby means of a mixture of vapoursand motive steam. In the secondstage, concentration is continued bymeans of vapours coming from thefirst stage. The vapours boiled off ofthe product in the second stage arecondensed by means of coolingwater in the condenser.

Fig. 4 : SIGMASTAR®-45 Multisection Evaporator

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Single and Multiple Effect EvaporationIn a similar way this vapour can be usedto heat a further effect; thus two, threeor multiple effect evaporators can beconstructed.

With such evaporators the water eva-porated per unit mass of steam approa-ches the theoretical optimum of 2:1 withdouble effect plants, 3:1 with tripleeffect plants and so on. Thus with anincreasing number of effects thespecific steam consumption decreases.The necessary temperature differenceper effect is achieved by progressivelylowering the operating pressure (i.e. in-creasing vacuum).

• However, lower operating costs en-tail a higher initial investment. Themost profitable balance depends onthe individual application criteria(concentration, performance, annualproduction times, length of pro-duction, product data, cost andavailability of energy, etc.).

Fig. 7 : 1-Effect Plant

The evaporation of liquids is, indepen-dent of evaporator type, always associ-ated with high energy costs. Thus theenergy cost is the major in the overalloperating cost.

By using multiple effect plants and byjudicious use of thermal and mechanicalrecompression the energy consumptioncan be reduced. (Specific steam con-sumption under 3%).

Single Effect Evaporation

The steam requirements for singleeffect evaporation are approximatelythe same as the water removed, i.e. theheat contents of the vapour leaving theplant is roughly the same as that in theheating steam. The resistance to heattransfer occurring on the heat transfersurface requires a driving force indi-cated by a temperature difference; thusthe vapour temperature is always lessthan the steam temperature.

Multiple Effect Evaporation

In multiple effect evaporators the sameheat energy is used several times. Thisis effected by progressively lowering thetemperature from stage to stage. Freshsteam is used to heat the first effect.The vapour product, at a lower tempe-rature, is used as heating medium forthe second effect which operates at aneven lower temperature.

Fig. 8a : 3-Effect Plant

Evaporation with Vapour RecompressionThe reuse of heat, effected in themultiple effect evaporator, can also beachieved by means of thermal or mech-anical recompression.

• The use of thermal vapour recom-pression (thermocompression) can,for example, be used to give a tripleeffect evaporator the same energyeconomy as a quadruple effect plantwith a corresponding reduction ininvestment.

Fig. 8b : 3-Effect Plant with Thermocompression

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• The use of mechanical vapourrecompression allows almostcomplete energy recovery and atheoretical zero steam consumption.The operating costs are low but thetechnically complex plant isexpensive.

Vapour RecompressionThese are effectively heat pumpsystems wherein low pressure / tem-perature vapours are recompressed tothe pressure / temperature of theheating steam permitting their reuse. Atthis point we must distinguish betweenthermal and mechanical vapour recom-pression.

Thermal VapourRecompression (TVR)This type of plant has steam ejectors ascompressors. These, having no movingparts, are simple and inexpensive.

• The steam ejector consists essen-tially of a steam nozzle which dis-charges a high-velocity jet across asuction chamber that is connectedto the vapour-liquid separator. Thevapour is entrained by the steamand carried into a venturi-shapeddiffuser which converts the velocityenergy of the steam into pressureenergy. This resultant vapour is thenused as the heating medium for thiseffect.

• Thermocompressors recompressingonly a portion of the vapour, do notrepresent the ultimate in energyconservation. Under certain condi-tions (e.g. high load, long operatingtimes, low electricity costs) mech-anical vapour recompression be-comes the preferred energy savingalternative.

Fine Chemicals and PharmaceuticalsFields of applicationWe have provided systems for acids(citric acid, etc.), bases (sodium hydrox-ide, etc.), salt solutions (ammonium ni-trate and ammonium sulphate), alu-minium sulphate, magnesium chloride,amine solutions (urea, etc.), alcohols(glycol, methanol, glycerine, etc.), aro-matic compounds (toluol xylene, etc.),raw and intermediate products forsynthetic materials and fibres (capro-lactam water), synthetic glue, pharma-ceutical products (sorbitol, sorbose,enzyme solutions, antibiotics, mono-sodium glutamate, as well as manytypes of waste water.

An example of a typicalinstallationConcentration plant with SIGMASTAR®

evaporators for the concentration ofvegetable oil with the simultaneousrecovery of extraction solvent.Evaporator capacity : 1,500 kg/h

of solvent

Final product: solvent-free vegetable oil

• For this particular concentrationplant, we took special measuresbecause of the specific problemswhich typically occur during theextraction phase.

• Due to the azeotropic nature of themixture, concentration must be donein two effects at different processpressures in order to achieve acomplete separation.

• A comprehensive cooling and con-densation system guarantees mini-mum solvent concentrations in theexhaust gases. The special con-struction of the gaskets ensures amaximum service life.

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Organic Natural Products

Fields of applicationSchmidt evaporators are used for pro-cessing stick water, hide and boneglues, hydrolysed proteins, technicaland photographic grade gelatines, oils,molasses, slops, yeasts, yeast extracts,wort, drug extracts, hops extracts, plantextracts, tanning extracts, corn steepwater, glucose, dextrose, fructose andpotato waste water.

A typical installationConcentration plant with SIGMASTAR®

evaporators for glucose.

Evaporation capacity: 10,000 kg/hConcentration: 33 to 85 % total solidsSpecific steam economy: approx. 27 %

• For this product, the extremely highviscosity required a special plantarrangement. The product flowsthrough the effects in the sequence4-3-2-1 counter current to theheating steam. Low evaporationtemperatures and a final flash coolerprevented thermal damage to theproduct. Condensate streams fromthe various effects are used forinter-effect heating thereby reducingsteam consumption.

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Another typical installationConcentration plant with SIGMASTAR®

evaporators for hydrolysed proteins

Evaporation capacity : 4,000 kg/hConcentration : from 8-12 to

50-58 % t. s.Steam Economy : approx. 22 %

• For this product, consideration ofmany product specific characteris-tics led us to choose a 3-1-2arrangement. Discharging theproduct at the slightly highertemperature of the second effectenabled a trouble-free achievementof the final concentration. A thermo-compressor ensured optimum eco-nomy. Continuous operation coup-led with extremely short residencetimes maintain the highest productquality.This plant has as an additionalfeature full automatic control forstart-up, operation, shut-down andcleaning-in-place.

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API Schmidt-Bretten GmbH & Co. KGLangenmorgen 4, D-75015 Bretten-Gölshausen, Phone (0)7252/53-0, Fax (0)7252/53-200

http://www.APISchmidt-Bretten.de - E-Mail: info@apischmidt-bretten.de

The Netherlands: Schmidt-Bretten Ned. B.V., Apolloweg 7 D/E, NL-8938 AT Leeuwarden, Phone (31) 58 - 288 55 80, Fax (31) 58 - 288 50 05France: S.A.R.L. Schmidt-Bretten France, Z.A.C. de la Croix Prunelle, F-27220 Saint-André-de-I'Eure, Phone (33) 232 - 60 26 80, Fax (33) 232 - 60 28 77

Spain: Schmidt-Bretten Espana S.L., c/ San Isidro, 22. Oficina 300, E-08940 Cornella de Llobregat (Barcelona), Phone (34) 93 - 377 84 17, Fax (34) 93 - 474 11 51Romania: Schmidt-Bretten Romania SRL, Sos. Vergului, Nr. 59, Sect. 2, Bucuresti / Romania, Phone (40) 21 - 255 21 95, Fax (40) 21 - 255 33 36

India: Schmidt-Bretten (I) Pvt. Ltd., Filtron House, 6-Sitabag Colony, Singhagad Road, Pune-411 030 / India, Phone (91) 20 -433 8642, Fax (91) 20 - 433 7913USA: API Schmidt-Bretten Inc., 2777 Walden Avenue, Buffalo, N.Y. 14225 / USA, Phone (1) 716684-6700, Fax (1) 716 684-2129

02/2003