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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
Bleaching processes for fats and oils 5
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.
Bleaching earth Activated carbon
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.
6 Bleaching processes for fats and oils
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
500 torr 70 torr
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.
Bleaching earthfrom dosing unit
Bleaching processes for fats and oils 7
The advantages of wet bleachinginclude more efficient use of the bleaching
earth easy to combine with a silica
treatment process highly