Laying down the right combination

Recovering solvents from fats and oils processes

If a solvent extraction plant is to be run economically and in an environmentally responsible way, it is important to handle thesolvents used to extract the fats and oils from their source material with maximum efficiency.

This is a thermally intensive process, which makes it crucial to use energy efficiently. Alfa Lavalprovides economical, versatile solutions with itsrange of compact, high-efficiency heat exchangers.

The benefits – pure and simpleAlfa Laval heat exchangers can improve condensation and evaporation

in solvent processes, irrespective of make and capacity of the plant.

Recovering solvents from fats and oils processes 3

Expanding plant capacityThe equipment in an extraction plantalways has an optimum operatingprofile. As soon as the productionlevels anywhere in the processing chainexceed these parameters, bottlenecksstart to occur. These cause a generalimbalance in the system, which resultsin higher energy usage and/or highersolvents losses.

Alfa Laval heat exchanger solutions arethe key to solving these imbalances bymaking it simple to boost theevaporation and condensationcapacities of any part of the plant.Improving the way these thermal dutiesare carried out re-establishes thebalance in the plant’s processingactivities, with important financialbenefits.

Improving heat recoveryThe amount of energy recovered in thefirst-stage evaporator, the DTDC hotgas/miscella economizer, drops assoon as capacity is increased and theheat transfer area thus becomesinsufficient. This means moreevaporation is required in subsequentstages. Alfa Laval evaporators are idealfor boosting this capacity and returningenergy recovery levels to figures thatare as good as new or even better.

Improving solvent recoverySolvent recovery levels can beimproved in most circumstances.Compact heat exchangers make itpossible to boost recovery in twoways. Firstly, Alfa Laval systems enablevery close temperature approaches,which minimize the amount of non-condensable gases that are passed onto the vapour scrubbing system. Thismeans each individual condenser iscapable of condensing more solventthan a corresponding shell-and-tubeunit, resulting in a lower overall load onthe vapour scrubbing system.

Secondly, a plate heat exchanger canbe used to cool the mineral oil in thevapour scrubbing system moreeffectively, giving it a larger absorptioncapacity.

Replacing corroded unitsShell-and-tube heat exchangers areusually made of carbon steel. Thismeans that corrosion always becomesa problem sooner or later, even withhigh-quality water. The compactnessand efficiency of Alfa Laval heattransfer solutions make it possible touse stainless steel, titanium or othermaterials for all heat transfer areas, andto do so in a cost-effective way thatmakes them an ideal solution forreplacing corroded units.

New plantsCompact heat exchangers are moreefficient, easier to maintain and moreversatile than traditional heatexchangers. Including such Alfa Lavalequipment in the specifications for anew extraction plant means lowerconstruction and installation costs andmuch less piping.

And when the time comes to increaseplant capacity, it is an easy, straight-forward matter to upgrade existingcompact heat exchangers.

The basic principle behindsolvent recovery

4 Recovering solvents from fats and oils processes

Solvents are used to extract fats andoils from many raw materials. Thesolvent most commonly used ishexane, a toxic substance, that mustbe recovered to the greatest extentpossible for reasons of operatingeconomics, environmental responsibilityand general safety.

The basic processing principleTo prepare an oil seed for solventextraction, a series of operations arecarried out to expose the part of theseed that contains the oil. The solidsthat result from this preparation aretransported to the extractor where theyare brought into contact with thesolvent. Two flows thus leave theextractor – the solids and thesolvent/oil miscella. Solvent must berecovered from both streams.

The solids are typically processed in aunit called the desolventizer (DTDC),whose main function is to flash thevolatile solvent from the solid phase byuse of direct steam injection. Thevapour leaving the DTDC must becleansed and condensed.

The miscella flow that leaves theextractor goes to the distillationprocess. This normally takes place inthree stages, including two evaporatorsand one distillation column. Thehexane is removed from the oil in thedistillation system, and the oil therebyconcentrated to nearly 100%.

All condensed hexane is sent to thesolvent separation/storage vessel,where hexane is separated from water

and sent back for reuse in the process.The crude oil is then sold or refined stillfurther. Any remaining exhaust vapourfrom the system is sent on to a vapourscrubbing system.

The economics of a solvent extractionfacility thus depend largely on theinvestment cost and operatingefficiency of the solvent recoverysystem. Making the right choiceregarding the heat exchangers in thissystem is, in fact, a key to efficiencyand profitablility.

Solventseparation/

storage

Extractor DistillationOil to degumming/refining

Solidsfrom

preparation

Miscella

Wet solids

Solvent

Hotgas

Solvent/water

Desolventizer(DTDC)

Meal topreparation

Solvent recovery overview

Recovering solvents from fats and oils processes 5

Alfa Laval is able to bring the benefitsof all our heat exchanger know-how,experience and technology to bear onmeeting solvent recovery needs.

Alfa Laval heat exchangers make itpossible to● save money

Unique designs provide substantially higher thermal efficiency than traditional shell-and-tube units, which means less heat transfer area is needed. This also makes it financially viable to build the heat exchangers in stainless steel, titanium or special alloys.

● save space The compact design of Alfa Laval heat exchangers means that transportation, erection and installation costs are drastically reduced compared with shell-and-tube units. When designing and building a new extraction plant, the floor space needed is less and the loads vastly reduced. In an existing plant, minimal installation modifications are required.

● reduce maintenance Most of the heat transfer surfaces are easily accessible for cleaning by simply opening or pulling apart the unit. The special Alfa Laval heat exchanger designs also create high turbulence in the channels. This not only reduces fouling during operation, but also makes subsequent chemical cleaning very effective.

● ensure flexibilityPlate heat exchangers provide the flexibility to adjust capacity by simply adding or removing plates while maintaining the existing frame. This allows continuous optimization of theprocess parameters and is a major advantage in relation to the fixed capacity of shell-and-tube heat exchangers.

AlfaCondThe world’s first tailor-made plate condenser, AlfaCond,was developed specifically for condensing vapours underlow pressure/vacuum conditions in evaporation anddistillation systems. The compact design makes itavailable to suit specific applications and capacityrequirements. Features include semi-welded plates, largeconnections and unique channel spacing.

AlfaVapThe compact AlfaVap rising film evaporator is widely usedwithin many applications. With its economic efficiency,the plate evaporator replaces conventional large andexpensive shell and tube units. Features include semi-welded plates, large connections and wide channels.

Compabloc®

This versatile welded plate heat exchanger can be usedas a condenser, evaporator, re-boiler and liquid-to-liquidexchanger.

Spiral heat exchangerThese welded heat exchangers are ideal forcondensation, reboiling and liquid-to-liquid duties,particularly at very low pressures and/or high volumeflows.

Semi-welded plate heat exchangerA full range of semi-welded heat exchangers for varyingcapacities.

Environmental concernsGovernment regulations constantly demand less solvent release into theatmosphere. Alfa Laval heat exchangers are the perfect way to comply with suchregulations due to their unique design and very close temperature approaches.

6 Recovering solvents from fats and oils processes

steam injection. The vapour mixtureleaving the DTDC – the DTDC hot gas– consists of steam, hexane and smallquantities of air, together with somefine material. The DTDC hot gas isused to regeneratively evaporate themiscella in the economizer, and is itselfalso condensed in this unit. Theremaining vapour flow is handled in a

Fines

Safety condenser

CW/coolant out

CW/coolant In

Tosolvent/water

separation

Hot waterscrubber

Solvent vapour mixture

(DTDC hot gas)

Meal to preparation

To fines separation

Miscella

Hot gas/miscella

economizer

CW out

CW In

CW/coolant out

CW/coolant In

To vapourscrubbing system

Miscella/hexane vapour

Cyclone

Primary condenser Vent condenser

DTDC

Wet solids from extractor

Tosolvent/water

separation

Hot gas condensation

Example flow diagram – Condensation

Condensing DTDC hot gasThe solid material leaving the extractor,often wet flakes, is saturated withhexane. This hexane must be removedbefore the solids can be sold as mealor reused.

The removal process takes place in theDTDC, using vaporization with direct

Growth at lower costThanakorn Vegetable Oil Products Co.Ltd. has been producing edible oilproducts in Thailand since 1977.Specializing in soybean oil and ricebran oil, the company is recognizedas the most progressive in its field.

Over the years, the Thanakornextraction plant has increased itscapacity by more than 250%. As partof this expansion, the company hasinstalled more and more plate heatexchangers to replace and augmentthe original shell-and-tube units.Today, Alfa Laval equipment serves ina wide range of different installationsas evaporators, condensers,economizers, chillers and reboilers.

The compactness and efficiency ofAlfa Laval plate heat exchangers haveplayed an important part inThanakorn’s expansion programme.As the Deputy Managing Director, MrSek Boonbunloo, notes, “Our mainbenefits ... are lower installation costcompared with the shell-and-tubeunits, higher heating exchangeefficiency and smaller spacerequirements. This will supportexpansion of our production capacitywithout enlarging the building.”

Recovering solvents from fats and oils processes 7

series of condensers that comprise aprimary condenser, a vent condenserand, in some cases, a safetycondenser.

Any non-condensables that remainafter this circuit continue on to thevapour scrubbing system.

Use Alfa Laval technology to● boost condensation● reduce the load on the vapour ● scrubbing system● replace corroded units

Miscella evaporation anddistillation

8 Recovering solvents from fats and oils processes

DTDC hotgas

Crude oilCrude

degummed oil

Crude degummed oil Condensate

Condensate

CondensateCrude oil Condensate

Miscella Miscella

Miscella

Crude oil

Steam Steam

Steam

Steam

Hot gas/miscella economizer

(1st stage)

Evaporator(2nd stage)

Vap

our

/liq

uid

sep

arat

or

Vap

our

/liq

uid

sep

arat

or

Vap

our

/liq

uid

sep

arat

or

Strippingcolumn

Steam

To solvent water separation

Solvent liquid/vapour mixture

Vent condenser Primary condenser Stripper condenser

To vapourscrubbing

system

To vapourscrubbing

system

CW/coolant out

CW/coolant In

CW out

CW In

CW/coolant out

CW/coolant In

Removing solvent from the miscellaThe miscella leaving the extractor isconcentrated in stages. First it ispreheated and then regeneratively

evaporated in the economizer usingthe DTDC hot gas as the heatingsource. The miscella then passes tothe second-stage evaporator, whichoperates using steam. A steam

stripping column extracts anyremaining hexane and concentrates theoil to its final required level. Vaporizedhexane gas from the evaporators andthe stripping column must then becondensed.

Example flow diagram - Distillation

Solving the space problemCaramuru Alimentos Ltda., a majorBrazilian processor of soybeans,operates crushing plants in both SãoSimão and Itumbiara. Expansion ofcapacity at the company’s São Simãoplant meant that condensationprocesses could not keep up, andhexane solvent was therefore beingpassed to the vacuum system.

Better recovery was needed, butspace considerations made a shell-and-tube installation impractical.Applying Alfa Laval know-how inevaporation and condensationtechnologies provided a solution witha semi-welded M20-MW plate heatexchanger installed in parallel withexisting units.

Not only was the productionbottleneck effectively removed, butthe space-saving Alfa Laval solutionalso kept installation costs to aminimum.

This is done in a primary condenserand then a vent condenser. Vapourthat leaves the stripping column istreated in the stripper condenser, andnon-condensables from both proceedto the vapour scrubbing system.

Imco

pa, B

razi

l

Recovering solvents from fats and oils processes 9

Use Alfa Laval technology to● boost evaporation● improve heat recovery● boost condensation● reduce the load on the stripping

column● reduce the load on the vapour

scrubbing system● replace corroded units

Vapour scrubbing

Vapour scrubbingThe exhaust from the entire solventrecovery system is combined and sentto the vapour scrubbing system. Thisexhaust vapour is scrubbed to removeresidual hexane, using mineral oil in anabsorption column. Lean mineral oil isbrought into contact with the hexane-rich vapour, which is then absorbed.

The rich mineral oil is thenregeneratively heated by lean mineraloil once more in a steam heater, beforeentering a stripping column where thehexane is removed with steam.

This hexane is recovered bycondensation. The lean mineral oil isthen cooled, first regeneratively usingthe rich mineral oil and then normally ina series of two coolers, one usingcooling water and the other a coolant.

10 Recovering solvents from fats and oils processes

To solvent/water separation

Solvent/vapourmixture

Steam

Lean mineral oil

Steam

Vapours toatmosphere

Non-condensablesfrom system

Condensate

Rich mineral oil

Rich mineral oil

Lean mineral oil

Absorptioncolumn

Strippingcolumn

Stripper condenser

CW/coolant in

CW/coolant out

CW/coolant out

CW/coolant In

CW in

CW out

p g g p

Example flow diagram – Vapour scrubbing

Use Alfa Laval technology to● increase mineral oil absorption

capacity● reduce hexane loss into the

atmosphere● anticipate and meet more

demanding environmental regulations

● replace corroded units

Alfa Laval heat exchangers can have agreat impact on both new and existingsolvent recovery systems.

They allow you to optimize existingplants now operating at greatercapacity than they were designed for,as well as making it possible to expandyour existing production line. This canbe done with only a minimum ofalterations to the installation and majorequipment, and with limited capitalinvestment.

Compact heat exchanger solutionsalso provide opportunities for makingnew plants smaller, lighter, moremaintenance-friendly and more suitablefor future expansion.

The Alfa Laval range of equipment forsolvent recovery processes includes:● AlfaCond, the world's first tailormade

plate condenser● AlfaVap, the tailor-made rising film

evaporator● Compabloc, the versatile welded

plate heat exchanger● Spiral heat exchanger, the welded

spiral channel heat exchanger● Semi-welded plate heat exchanger,

the complete range for varying capacities

Recovering solvents from fats and oils processes 11

Solutions for more than just onesolvent processIn addition to the typical seed oilextraction process shown here, Alfa Laval can help you with solventrecovery from other fats and oilsprocesses such as solventfractionation, extraction from fish meal,extraction of oil from spent bleachingearth and others.

Your solution provider for fats andoils processesAlfa Laval is a leading supplier ofequipment and processing technologyto the fats and oils industries. Weprovide process knowledge indegumming, neutralization, bleaching,dry dewaxing, deodorization,deacidification, modification processesand more, while delivering such Alfa Laval equipment as our PXseparators, MX mixers, the SoftColumndeodorization system and a full rangeof compact heat exchangers.

Challenge us to show you the right combination

Alfa Laval in brief

Alfa Laval is a leading global provider ofspecialized products and engineeredsolutions.

Our equipment, systems and servicesare dedicated to helping customers tooptimize the performance of theirprocesses. Time and time again.

We help our customers to heat, cool,separate and transport products such asoil, water, chemicals, beverages, food-stuffs, starch and pharmaceuticals.

Our worldwide organization worksclosely with customers in almost 100countries to help them stay ahead.

How to contact Alfa LavalUp-to-date Alfa Laval contact details forall countries are always available on ourwebsite at www.alfalaval.com

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