moving beyond colour

Moving beyond colour

Alfa Laval bleaching processes for fats and oils

Bleaching is one of the key processes in fats and oils refining, designed to remove not only pigments, but also a wide range of other impurities.

Most crude fats and oils contain impurities that have to be removed for both commercial and health reasons. Modern industrial bleachingtechnologies are the way to do this.

Flexible paths to bleaching results

Bleaching processes for fats and oils 3

Bleaching – simple yet complexThe bleaching of fats and oils isnormally carried out after either alkalinerefining or degumming, and preparesthe oil for the final deodorizationprocess. In the case of crude palm oil,bleaching is the initial stage of thewhole refining process.

At first glance, bleaching seems arelatively simple process that consistsof mixing the oil with a powder, stirringfor some minutes and then removingthe powder again.

However, this process is quite complexboth in theory and in practice. And theterm “bleaching” is in fact a somewhatmisleading description for a complexrefining process in which the removalof pigmentation is no longer the mostimportant purpose.

Getting rid of impuritiesThe prime focus in modern bleachingprocesses is now on the removal of awide range of different impurities, ofwhich pigmentation is only one. Suchimpurities can virtually all be removedusing new processes in whichcombinations of different bleachingagents are used to bind specificimpurities. These are then removedwhen the bleaching agent issubsequently filtered out.

Efficient bleaching makes it possible to● remove certain pigments such as

carotinoids and chlorophyll● decompose and partially remove

oxidation products● remove contaminants such as soaps

and trace metals● remove traces of phosphatides● remove polycyclic aromatic

hydrocarbons and other pollutants.

All these substances can have adverseeffects on both the quality and stabilityof your final product, and thereforehave to be removed to ensure that theproduct is commercially attractive.

Bleaching agentsThe most commonly used way tobleach fats and oils is to treat themwith surfactant powdery materials.These bind (also known as “adsorb”)the pigmented substances in the oils to the extensive surface area providedby them being in powder form.

4 Bleaching processes for fats and oils

Dry bleachingDry bleaching is the methodtraditionally used for fats and oils.Although most common in Europe andAsia, it is a process that industryexperts throughout the world arefamiliar with, and provides a viablesolution in many processing situations.

Before it is mixed with bleaching earth,the oil is heated. If the process requiresit, a citric acid solution is mixed withthe hot oil to bind trace metals anddecompose any residual soaps.

After this treatment, the oil is mixedwith bleaching earth, activated carbon

The Alfa Laval advantage forbleaching process operatorsincludes● flexibility● exceptional reliability● low energy costs● easy operation.

Modern bleaching processes use asubstantial range of different bleachingagents in order to remove a wide rangeof specific impurities, in addition to thepigments.

The agents normally used include● natural bleaching earths (used with

only limited colour-reducing effect but are particularly useful in treating animal fats)

● acid-activated bleaching earths (widely used for removing all kinds of impurities)

● activated carbon (used to remove polyaromatic hydrocarbons and ensure removal of a wide range of specific pollutants)

● synthetic amorphous silica compounds (used largely in wet bleaching, with a focus on selectively removing phosphatides, trace metals and soaps).

Wide range of usesBleaching also reduces the number ofsubstances that can affect the tasteand smell of the fats and oils. It istherefore used in refining andprocessing fats and oils that includesoybean, palm, rapeseed, sunflower,palm kernel and coconut oil, as well asfish oil and lard.

However, the increasing quantities ofenvironmental pollutants and otherimpurities often found in raw materialsof all kinds mean that bleaching israpidly becoming an obligatory part oftreating all fats and oils.

This means that bleaching is crucial ifyou wish to ensure high-qualityproducts, and is therefore normallyincluded in all refining sequences.

Heat exchangersAlfa Laval plate heat exchangers areideal for heating and cooling the oilefficiently, both before and after thebleaching process.

Heat recovery using an economizer isalso used in cases where the oilsubsequently undergoes dewaxing.

The basis for modern bleaching


Mixing in the bestAt the Prikolotnoye Oil Extraction plant in the Kharkov region of Ukraine, Alfa Lavalsupplied a full package of modern refinery equipment. A dry bleaching plantfeaturing a multi-dosing system was part of the order.

The flexibility of the design, along with Alfa Laval technical experience, meant thatthe company was also able to build its own best ideas into the system. As Andrey Nepochatov, head of the refinery plant, pointed out, “Alfa Laval reallylistened to what we wanted. They not only supplied us with highly efficientequipment, but also made suggestions about how we could get the most out of it.And they made sure that our ideas about special mixing and dosing were alsoincorporated. The system now all works perfectly.”

Bleachingearth

To atmosphere

Economizer

Cooler

Day tank

Acid mixer

Bleachingreactor

Crude oil

Bleached oil

Spentearth

Heater

Steam

Water

Water

Citric/phosphoricacid

Transportationsystem


Dosingunit

Dosingunit

Bleaching earth Activated carbon

Vacuum

Vacuum

Pressureleaf filter

Slop oil

Cyclone

Oilcollector

Steam

Spargingsteam

Steammanifold

Steam

Spentearth

Pressureleaf filter

Polishing filters

Filter aidM

Optional

Buffer tank

P ecoatingtank

r

Dry bleaching

or a mixture of these two. This is doneunder vacuum to prevent oxidation,and in the presence of sparging steam.

This process is called dry bleaching,because the bleaching reactoroperates at a vacuum of about 70 torr,which greatly reduces the humidity inthe oil.

After bleaching, the bleaching agent isnormally removed using pressure leaffilters. Naturally, the filter cake thataccumulates here still contains oil.Much of this can be recovered bysteam-blowing the contents of thesefilters.

Filtered oil collects in the buffer tank,which operates under the samevacuum as the bleaching reactor. Fromthere, oil goes via one of the polishingfilters to the next process step, or tostorage.

If it proves necessary to build up a filtercake in order to improve filtration, pre-coating can be accomplished byrecirculating the oil through the filter viaa precoating tank.

Dry bleaching has several distinctadvantages. These include● lower initial investment compared

with other types of bleaching● the use of plate heat exchangers for

heating and cooling means lower consumption of utilities compared with shell-and-tube solutions. This results in lower operating costs

● easy, straightforward control and operation

● only a minimum of space is required for installation

● minimal energy consumption.


Wet bleachingAs the name implies, wet bleaching isa bleaching process in which water isadded to the oil while it is in contactwith the bleaching agent in thebleaching reactor.

The presence of small amounts ofwater results in more efficient use ofthe relatively expensive bleaching earth.This greater efficiency results in lowerearth consumption as well asreductions of total oil losses.

This makes wet bleaching an attractivesolution on account of the overalleconomics of the process, eventhough the investment costs areslightly higher.

The water present during wetbleaching is introduced in the form of acitric acid solution, or by taking wet oilfrom the separation line. Adjustment iscarried out by careful control of theoperating vacuum in the bleachingreactor to determine how much of thewater subsequently evaporates.

Just add water

Bleachingearth

To atmosphere

Economizer

Cooler

Day tank

Acid mixer

Bleachingreactor

Crude oil

Bleached oil

Spentearth

Heater

Steam

Water

Water



Dosingunit

Bleaching earth

Vacuum

500 torr 70 torr

Vacuum

Pressureleaf filter

Slop oil

Cyclone

Oilcollector

Steam

Spargingsteam

Steammanifold

Steam

Spentearth

Pressureleaf filter

Polishing filters

Filter aidM

Dryer

Vacuum

Optional

Buffertank

P ecoatingtank

r

Even tiny amounts of water – anythingin excess of 0.5% – remaining in themixture after this will cause filtrationproblems later on. The oil therefore hasto be dried before filtration.

In terms of the equipment used, thebasic difference between wet and drybleaching installations is thereforewhether or not a dryer is locatedbetween the bleaching reactor and thefiltration system.

Wet bleaching

Vacuum

Oil outlet

Spargingsteam

Bleaching earthfrom dosing unit

Oil in


The advantages of wet bleachinginclude● more efficient use of the bleaching

earth● easy to combine with a silica

treatment process● highly flexible● low consumption of bleaching earth● reduced oil loss during filtration.

Alfa Laval bleaching reactor

Alfa Laval bleaching reactorsUnder normal atmospheric conditions,mixing the adsorbent into the oilresults in rapid oxidation, due to thelarge surface area of the activeadsorbents. It is important to avoidthis, which is why the design of Alfa Laval bleaching reactors ensuresthat the oil and bleaching earth areboth deaerated before being mixedtogether.

The spray curtain of oil entering thebleaching reactor from above, alongwith the special design of the reactor,prevents any of the bleaching agentbeing drawn up into the vacuumsystem above.

The reactor is divided into threecompartments to ensure uniformreaction times and avoid oil flow shortcuts inside the reactor.

It is not always possible to use steamto agitate the mixture. If not, thebleaching reactor can be equippedwith a mechanical agitation system.

Alfa Laval bleaching reactor designsare equally suitable for both dry andwet bleaching, with no modificationnecessary.


Two-stage bleachingThe two-stage bleaching process isessentially a combination of wet anddry bleaching, combined with highlyefficient two-step filtration.

The main idea behind two-stagebleaching is to ensure that the dosingand filtration of the necessaryadsorbents takes place between eachstage of treating the oil. This means

that the adsorption process can bemade significantly more efficient.This is because adsorption takes placeon a continuous basis until there isequilibrium between the concentrationof pigments and other impurities on thesurface of the adsorbent and theconcentration remaining in the oil. Assoon as this equilibrium is reached, theadsorbent is filtered out of the oil.

At the second stage fresh adsorbent isthen added to the treated oil until anew state of equilibrium is reached.This oil then passes through a second filtration stage.

Two-stage filtrationThe filtration section in Alfa Laval two-stage bleaching takes place in twostages, featuring three alternating filtersworking in cycle for maximum

Filter aid

Bleachingearth

To atmosphere

Economizer

Day tank

Acid mixer

Bleachingreactor

Crude oil

Spentearth

Heater

SteamWater

Water



Dosingunit

Bleaching earth/silica

Vacuum

500 torr 70 torr

70 torr

Vacuum

Cooler

Bleached oil

Pressureleaf filter

Slop oil

Cyclone

Oilcollector

Steam

Spargingsteam

Steammanifold

Steam

Spentearth

Pressureleaf filter

Polishing filters

Bleachingreactor


Bleaching earth

Vacuum

Spargingsteam

Steammanifold

Dryer

Vacuum

Spentearth

Pressureleaf filter


Dosingunit

Activated carbon

M

Optional

Buffertank

P ecoatingtank

r

Two-stage bleaching

Two into one does go


Using synthetic silica compoundsTwo-stage bleaching is particularlyrelevant if you wish to use syntheticamorphous silica compounds as anadsorbent. These are particularlyeffective for removing phosphatides,trace metals, gums and soaps. Usingsynthetic silica also makes it possibleto cut back considerably onwastewater effluent from refining edible oils.

The best performance using syntheticsilica compounds normally requires thepresence of small amounts of water.This means that it is possible to extenda wet bleaching plant by adding asynthetic silica dosing systemupstream.

Multiple dosingAlfa Laval experience has shown that inmany fats and oils bleaching installa-tions, the best results are achieved byusing a combination of bleachingadsorbents. The percentages of thedifferent additives used are altereddepending on the type of oil, its qualityand the adsorbents used. This makesit possible to use a substantial range ofdifferent adsorbents with differentcharacteristics.

As an example, Alfa Laval bleachingreactors can be equipped with up tothree dosing systems, for maximumflexibility.

efficiency, with the almost saturatedfilter being used for prefiltration of theincoming oil.

This is because used bleaching earthfrom normal filtration processes stillretains an estimated 20% of itsadsorption capabilities. Alfa Laval two-stage filtration systems ensure moreefficient exploitation of these relativelyexpensive filtration agents.

On the customer’s wavelengthAfter carrying out a series of preliminary investigations, tests, etc., under the supervisionof Production Manager Niels Jørgen Eriksen, Fiskernes Fiskeindustri A.m.b.a. in Skagen(Denmark) awarded Alfa Laval the contract to deliver and install the process equipmentneeded to ensure that there are no traces of toxic pollutants in the company’s fish oilproducts.

Niels Jørgen Eriksen noted that “the Alfa Laval project has met our needs, and we aredefinitely satisfied with the results to date. The challenges involved in removing toxicpollutants have shown us the clear benefits of talking to experts who are really on ourwavelength.”

Dosing systemsThe way the bleaching agent is addedto the reactor is crucial for maximumefficiency. The dosing of the bleachingearth is set by changing howfrequently the two valves above andbelow the dosing chamber open and close.

Alfa Laval dosing systems aredesigned to ensure a smooth,proportional flow, with an accuracy of±0.03% in relation to the oil flow.

Alfa Laval provides the most straight-forward dosing solution currentlyavailable. It provides greater dosingaccuracy, lower operating costs, lessmaintenance and fewer spare parts.

The advantages of two-stagebleaching include● the best bleaching results for oils

otherwise often considered difficult● possibilities for using cheaper

bleaching agents and first-stageadsorbents, thus reducing operating costs

● reduced bleaching agent loading, resulting in lower costs

● high degree of flexibility.

Control systemsAlfa Laval supplies bleaching plantswith a wide selection of different levelsof automation to match customerrequirements.

These range from relatively simplemanually operated configurations withlocal control loops to fully automatedplants based on SCADA controltechnologies.

Service countsAlfa Laval operates with a highlysophisticated Nonstop Performanceconcept made possible by our worldwide network of service andspare parts distribution centres in morethan fifty countries throughout theworld.

Our expertise ensures that any servicework required is carried out with theabsolute minimum of disturbance tooperations.

Process know-howOne of the key advantages of workingwith Alfa Laval to install, update andextend your bleaching systems andequipment is our extensive practicalexperience.

Alfa Laval’s proven ability to design andcalculate a wide range of process configurations to meet specific customer requirements can provideyou with the benefits of our vast bodyof accumulated know-how.


Nonstop Performance

Alfa Laval engineering services include● installation design in full accordance

with international standards● installation supervision● commissioning and start-up● operator training● documentation● comprehensive spare parts packages● operational, maintenance and service

support.

Full controlAlfa Laval has full control over theentire supply chain associated with thecompany’s equipment. This means wecan provide customers with promptresponses, excellent availability andlead times that are second to none.

Engineering servicesAlfa Laval provides a wide range ofsupplementary engineering servicesthat can help ensure that your newinstallation comes on line as rapidlyand efficiently as possible.

We can also provide you with considerable savings by ensuring fullcompliance with the relevant nationaland international regulations for designcodes, safety procedures and bestengineering practice.

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Alfa Laval in briefAlfa Laval is a leading global provider ofspecialized products and engineeredsolutions. Our equipment, systems andservices are dedicated to helping customers to optimize the performanceof their processes. Time and time again.

We help our customers to heat, cool, separate and transport productssuch as oil, water, chemicals, beverages, foodstuffs, 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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