Continuous process for the dry fractionation of edible oils and fats

Abstract

Continuous process for the dry fractionation of edible oils and fats using one or more crystallizers connected in series, which process comprises the following steps: a) providing a melted fat; b) continuously feeding the molten oil or fat into the first of one or more series-connected crystallisers in which the fat is gradually cooled using heat exchangers containing a cooling medium to form a crystal slurry, each of the one or more crystallisers having a temperature gradient such that the temperature at the point at which the molten or partially crystallised fat enters one of the crystallisers is higher than that at the point at which the slurry leaves the crystalliser; c) continuously removing the slurry from the last of said one or more crystallizers; d) separating the crystal slurry by filtration into a filter cake and a filtrate; the process further comprising the step of at least partially melting grease deposits deposited on the heat exchangers.

Description

FIELD OF THE INVENTION

[0001] The invention relates to the modification of edible oils and edible fats by continuous fractionation in the absence of organic solvents. BACKGROUND OF THE INVENTION

[0002] The physical properties of edible oils and fats, as obtained from agricultural sources, do not necessarily meet the requirements of the food industry.

[0003] Consequently, several modification processes have been developed. In a hydrogenation process, a liquid oil is converted into a solid fat that can be used as a hard fat in margarines and shortenings and whose stability is also increased. In the interesterification process, the physical properties of the material to be interesterified are modified, for example, by lowering its melting point to avoid a sticky mouthfeel. These processes modify an oil or oil mixture and result in a single product. The fractionation process, on the other hand, separates the oil or fat into a stearin fraction with a higher melting point and an olein fraction with a lower melting point, both of which can yield further products through subsequent fractionation. Accordingly, the range of oil and fat products that can be produced through fractionation is very broad.

[0004] Various fractionation processes for edible oils and fats have been developed. Solvent fractionation processes use solvents such as acetone, nitropropane, or hexane. However, since these solvents are flammable, their use requires explosion-proof equipment, which is expensive. Further costs arise from the removal of the solvent from the various fractions by distillation and from solvent loss. Accordingly, solvent fractionation is only used for the production of high-value specialty products. Detergent fractionation also exists, but due to advances in dry fractionation, detergent fractionation can be considered obsolete.

[0005] In dry fractionation, it is common practice to heat the fat to be fractionated to approximately 10°C above its melting point to extinguish the crystal memory. The fat is then slowly cooled below its melting point, whereupon crystals form and grow. Once a sufficient degree of crystallization has been achieved, the crystal slurry is separated by filtration into a filter cake (the stearin) and a filtrate (the olein). Two types of crystallization process are used. One process involves dispensing the melt into trays and not agitating it during cooling. Such a process has been described in EP 1 028 159A and can be advantageously applied to oils such as palm kernel oil.The other type, used for palm oil, anhydrous milk fat and various other oils, fats and butters, uses large crystallization vessels equipped with heat exchangers and a stirrer.

[0006] What both types have in common is that filtration efficiency determines the yield of both fractions and the properties of the stearin. If the residual olein content in the filter cake is high, the stearin yield is high, but the properties of the stearin are less pronounced. Since, in palm oil fractionation, olein has a higher economic value than palm stearin, and the economic value of stearin depends little on its properties, it is advantageous to aim for maximum filtration efficiency. This can be achieved by using a membrane filter press in a batch process, as described in US Pat. No. 5,198,123. A continuous filtration process using a conical sieve centrifuge equipped with a co-rotating screw has been described in US Pat. No. 4,542,036.

[0007] With the increasing production of palm oil, dry fractionation processes have become very important. Palm olein is a valuable cooking oil, with palm oil middle fractions being used in confectionery applications, and palm stearin is increasingly used as a component in interesterification reaction mixtures used for the production of trans-free hard fats for margarines and shortenings. Often, these dry fractionation processes are integrated into palm oil refineries so that they can share facilities and infrastructure. These refinery processes, such as degumming, bleaching, and physical refining, are all continuous processes and, in this respect, differ from current fractionation processes, which are invariably batch processes.

[0008] Continuous fractionation processes have been developed from solvent fractionation processes. US Pat. No. 4,127,597 A describes a process for fractionating tallow into three distinct fractions: a hard, solid fraction with a high melting point, a plastic, solid fraction with physical and thermal properties similar to those of cocoa butter, and a liquid oil fraction, comprising: (a) dissolving the tallow in a suitable solvent, the solvent to tallow ratio being sufficient to solubilize the tallow and effect fractionation at a crystallizable solute concentration and temperature ratio; (b) continuously feeding the solution to one or more crystallizers; (c) circulating the solution through the crystallizers at a first preselected equilibrium crystallization temperature range;(d) limiting the nominal residence time of the solution in the crystallizers at this first equilibrium crystallization temperature to a maximum of 10 minutes; (e) crystallizing a hard, high-melting-point solid, thereby forming a crystallized circulating stream; (f) continuously withdrawing a portion of this crystallized stream at the first preselected equilibrium crystallization temperature to obtain a crystallized hard, high-melting-point solid and a filtrate; (g) continuously recirculating, at the first preselected equilibrium crystallization temperature, the crystallized stream not withdrawn in step (f), together with the aforementioned continuously fed solubilized tallow;(h) repeating steps (f) and (g) until the total amount of solubilized tallow has been fed to the crystallizers and the total amount of crystallized stream has been withdrawn from the crystallizers; (i) circulating the filtrate from the aforementioned first crystallization through the crystallizers at a second preselected equilibrium crystallization temperature range; (j) limiting the nominal residence time of the filtrate solution in the crystallizers at the equilibrium crystallization temperature to a maximum of 10 minutes; (k) crystallizing a plastic solid having physical and thermal properties similar to those of cocoa butter, thereby forming a crystallized circulating stream; (i) continuously withdrawing a portion of the crystallized stream at this second preselected equilibrium crystallization temperature to obtain a crystallized plastic solid and a filtrate;(m) Continuously recirculating at the second preselected equilibrium crystallization temperature the crystallized stream not removed in step (I); (n) Repeating steps (I) and (m) until the entire amount of crystallized stream is removed from the crystallizers; and (o) Removing the solvent from the filtrate from the aforementioned second crystallization to obtain a liquid oil fraction. According to US 4,594,259 A, suitable confectionery fats can be obtained by continuously fractionating palm oil using an acetone to fat ratio of about 5:1 to about 8:1 and employing two or more fractionation stages.

[0009] US 4,839,191 A describes a process for the solvent fractionation of fats into at least two fractions comprising a first high melting point glyceride fraction and a second fraction which is an oil, at temperatures above 10°C, the process comprising the following steps: (a) dissolving the fat in a solvent which is a binary azeotropic solvent mixture, the solvent ratio being 1.5 to 8.0 ml of solvent per gram of fat; (b) crystallizing the solution from step (a) at 10-15°C; (c) separately collecting a solvent phase and the precipitate formed in step (b); (d) extracting the precipitate from step (c) by contacting it with fresh solvent cooled to about 2°C below the temperature of step (b) using at least about 8% of the original volume of solvent;(e) collecting a solvent phase and a precipitate from step (d), which precipitate is a hard fat fraction with a melting point above 40°C; and (f) combining the solvent phases from step (c) and step (e) and removing the solvent therefrom to obtain an oil fraction that is liquid above 10°C. This process can be carried out either as a batch process or as a continuous process.

[0010] The preference for the use of solvents is quite understandable, as fats crystallize much faster from a solvent such as acetone than from the melt. Furthermore, the solvent dilutes the olein present in the filter cake, so that for a given filtration efficiency, the stearin contains less olein, resulting in its properties being less affected by olein than in the absence of the solvent. Furthermore, the solvent fractionation processes listed above predate the development of current efficient filtration systems using, for example, a membrane filter press.

[0011] Apart from these technological reasons, there are also physicochemical reasons. The fractional crystallization of fats from a melt is a very complex process, as fats are mixtures of very different triacylglycerol molecules. Accordingly, the fat crystals formed during fractionation are mixed crystals containing several different molecular entities, and their compositions evolve as crystallization progresses. In this respect, the fractional crystallization of fats differs fundamentally from other industrial crystallization processes, such as those used for p-xylene, terephthalic acid, sugar, citric acid, etc. These processes are primarily purification processes aimed at the formation of pure crystals.Another factor complicating fat crystallization is that fat crystals can have different morphologies, and crystallization conditions must be such that only a single polymorph is formed. Furthermore, oils and fats—and this is especially true for palm oil—invariably contain partial glycerides, such as diacylglycerols, which can impair crystal growth by attaching to a growth site on the crystal and temporarily hindering the attachment of additional triglyceride entities.

[0012] US 5 874 599 A describes a process for the crystallization of polymorphic fat molecules in a pseudo-equilibrium process, wherein the crystallization is carried out in a dry fractionation system by selecting and adjusting the flow rate, shear rate and temperature in such a way that the crystal form of the product is a kinetically stable crystal form, while the σ value during crystallization is maintained below 0.5 for a period of at least 12 hours, where: σ = 1 - SC / SE, where SC is the percentage of solids in the crystallizer at the crystallization temperature and SE is the percentage after stabilization for 48 hours at the exit temperature from the crystallizer. The process uses a single crystallizer, wherein the degree of crystallization is close to equilibrium (solubility).When palm olein was used as a starting material, the fractionation process yielded approximately equal amounts of top and bottom fractions and could be continued for 60-70 hours without any problems of scaling, slurry stability, polymorphic form, or viscosity.

[0013] US 6,383,456 B1 describes an apparatus for fractionating a melt of mixed triglycerides, which apparatus comprises: a heat exchanger for subcooling the melt of mixed triglycerides; a nucleator for controlling the energy and condition of the melt of mixed triglycerides, the nucleator having an inlet and an outlet and including a stirring device, the inlet of the nucleator being connected to the heat exchanger; and a crystallizer connected to the outlet of the nucleator. In this process, the nucleation stage is separated from the crystal growth stage. The examples in US Patent US 6,383,456 B1 are not limited to anhydrous milk fat, but also include lard, tallow, and palm kernel oil, but do not include the fractionation of palm oil or its fractions.

[0014] EP 1 818 088A describes a dry fractionation process for edible oils and fats, comprising the following steps: melting the oil or fat to be fractionated; cooling the molten oil or fat in a crystallizer comprising a crystallizer vessel, a stirrer or a stirrer assembly and a drive, thereby producing a slurry of crystals in a mother liquor; and subsequently separating these crystals from the mother liquor, the drive providing the stirrer or a stirrer assembly with an oscillating motion and / or a rotating motion about an axis, with the proviso that each point of the stirrer or a stirrer assembly moves at substantially the same linear velocity; and describes in its examples the continuous fractionation of palm oil.Furthermore, the gentle stirring inherent in this process surprisingly leads to the formation of crystals of almost uniform size, whereas standard crystallizers comprising a stirrer consisting of a rotating shaft with laterally extending blades produce several diverse populations of crystals of varying sizes. This means that secondary nucleation of the crystallizing melt is suppressed, i.e., no or hardly any nuclei are formed once the initial nuclei have begun to grow. Furthermore, EP 1 818 088A describes that, contrary to what has been generally accepted, temperature homogeneity within a crystallizer is not a prerequisite for the formation of easily filterable crystals. The temperature gradient observed in Example 3 of EP 1 818 088A is such that it allows continuous operation.

[0015] A possible arrangement of a continuous dry fractionation process is shown in Fig. 6 of EP 1 818 088A, in which there are three crystallizers connected in series, each with a temperature gradient. Accordingly, the first crystallizer is fed with molten fat, and a filter-ready crystal slurry exits the third crystallizer. Since the type of agitator used causes little vertical movement of the slurry, this arrangement approximates a plug-flow situation.

[0016] However, the operation of such a continuous dry fractionation process over an extended period of time will inevitably lead to an incrustation of solidified fat on the cooling elements used in the process, since the surface of the heat exchanger must be significantly colder than the oil to achieve heat transfer. This leads to a decrease in their cooling capacity. Eventually, the incrustation will be such that the cooling capacity will be insufficient and will require the interruption of the fractionation process to remove the solidified fat from the cooling elements. Therefore, the arrangement with three crystallizers connected in series, as in Fig. 6 of EP 1 818 088A, in practice only a semi-continuous dry fractionation is used. Further prior art can also be found in DE 11 2007 000 184 T5.

[0017] Plug flow is also desired in the continuous dewaxing process of edible oils, where the same encrustation is observed. Oils such as sunflower seed oil can contain variable amounts of waxes (esters between fatty acids and fatty alcohols), some of which have melting points above 70°C. These can cause the oil to become cloudy upon cooling. Since this is considered undesirable, the high-melting waxes are removed by cooling the oil, as this allows the waxes to crystallize so that they can be removed by filtration. Compared to the dry fractionation of edible oils and fats, the dewaxing process is quite simple. The molecules to be crystallized are less complex, they are quite distinct from the solvent (triglyceride oil), and a filter aid is invariably used to facilitate filtration.

[0018] In continuous dewaxing, such plug flow is generally implemented using a compartmented crystallizer. Warm oil containing dissolved waxes enters from the top, and oil containing wax crystals exits the vessel at the bottom, with the temperature profile remaining the same throughout the vessel. However, these vessels are prone to encrustation of the cooling coils at the bottom of the vessel due to wax deposits. These deposits reduce heat transfer and shift the cooling load to the top of the vessel. This causes the oil in the upper compartment to become so cold that freshly added oil is severely supercooled, resulting in the formation of numerous small wax crystals. This requires more filter aid due to the wax crystals that have formed by slowly cooling the oil from above its cloud point to below its cloud point. Encrustation of the cooling coils should therefore be avoided. SUMMARY OF THE INVENTION

[0019] Therefore, it is an object of the invention to provide a continuous dry fractionation process with which encrustation problems can be adequately overcome.

[0020] It is an advantage of the continuous dry fractionation process of the present invention that such a continuous dry fractionation process is provided which can be integrated into an edible oil refinery, thus reducing energy requirements and saving on infrastructure.

[0021] Another advantage of the continuous dry fractionation process of the present invention is that it reduces the investment required for a given fractionation capacity.

[0022] It is also an advantage of the continuous dry fractionation process of the present invention that fractions with more uniform and better properties are obtained.

[0023] It is yet another advantage of the continuous dry fractionation process of the present invention that a higher olein yield is obtained compared to a batch process.

[0024] Surprisingly, the incrustation found with some products using the process of EP 1 818 088A can be effectively combated by interrupting the flow of cooling medium through the heat exchanger and at least partially melting this incrustation, for example, by electrically heating the heat exchanger or by pumping hot water or blowing steam through the heat exchangers, without interrupting the continuous operation of the process. This is not a measure that a person skilled in the art would consider taking, since once cooling has started in dry fractionation, a person skilled in the art would be reluctant to interrupt it, considering the system sacrosanct.

[0025] It has surprisingly been found that, in a first aspect of the present invention, the above-mentioned objects can be achieved by means of a continuous process for the dry fractionation of edible oils and fats using one or more crystallizers connected in series, which process comprises the following steps: a) Providing melted fat; b) continuously feeding the molten oil or fat into the first of one or more series-connected crystallisers in which the fat is gradually cooled using heat exchangers containing a cooling medium to form a crystal slurry, each of the one or more crystallisers having a temperature gradient such that the temperature at the point at which the molten or partially crystallised fat enters one of the crystallisers is higher than that at the point at which the slurry leaves the crystalliser; c) continuously removing the slurry from the last of said one or more crystallizers; d) separating the crystal slurry by filtration into a filter cake and a filtrate; the process further comprising the step of at least partially melting grease deposits deposited on the heat exchangers.

[0026] In a preferred embodiment of the first aspect of the present invention, the process further comprises the step of continuously cooling the molten fat in a cooler to a temperature above the cloud point of the fat before the molten fat enters the first of the one or more crystallizers, wherein the cooler comprises at least one heat exchange element, which may be integrated or separate.

[0027] Further described is an oil fraction produced by the process of the present invention.

[0028] Specific and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as detailed in the claims.

[0029] Although there have been continuous improvements, changes, and developments in the devices in this field, it is believed that the present concepts represent significant new and novel improvements, including departures from previous practices, resulting in the provision of more efficient, stable, and reliable devices of this type.

[0030] The above and other features, characteristics, and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is merely exemplary in nature and is not intended to limit the scope of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be described with respect to specific embodiments and with reference to specific drawings, but the invention is not limited thereto but only by the claims.

[0032] Furthermore, the terms first, second, third, and the like are used in the specification and claims to distinguish between similar elements and not necessarily to describe a sequence, whether temporal, spatial, rank, or otherwise. It should be understood that the terms so used are interchangeable under appropriate circumstances, and that embodiments of the invention described herein are capable of functioning in sequences other than those described or illustrated herein.

[0033] Furthermore, the terms above, below, above, below, and the like are used in the specification and claims for purposes of explanation and not necessarily to describe relative positions. It should be understood that the terms so used are interchangeable under appropriate circumstances, and that embodiments of the invention described herein are capable of operation in orientations other than those described or illustrated herein.

[0034] It should be noted that the term "comprising," as used in the claims, should not be interpreted as being limited to the means listed below; it does not exclude other elements or steps. It should therefore be interpreted as specifying the presence of the recited features, integers, steps, or components as recited, but does not preclude the presence or addition of one or more further features, integers, steps, or components, or groups thereof.

[0035] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic, as described in connection with the embodiment, is included in at least one embodiment of the present invention. Therefore, the appearances of the phrases "in an embodiment" or "in the embodiment" in various places throughout this specification do not necessarily refer to the same embodiment, but may do so. Furthermore, the particular features, structures, or characteristics may be combined in one or more embodiments in any suitable manner as would be obvious to one of ordinary skill in the art having ordinary knowledge from this specification.

[0036] Similarly, it should be appreciated that in describing exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the description and promoting understanding of one or more of the various aspects of the invention. However, this method of description should not be interpreted as reflecting an intent that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, aspects of the invention lie in fewer than all of the features of a single previously described embodiment.Therefore, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention.

[0037] While some embodiments described herein further include some, but not other, features included in other embodiments, combinations of the features of various embodiments are intended to be within the scope of the invention and constitute various embodiments, as understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments may be employed in any combination.

[0038] In the description provided herein, numerous specific details are set forth. However, it will be understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures, and techniques have not been shown in detail in order not to obscure this description.

[0039] The invention will now be described with a detailed description of various embodiments of the invention. It is clear that other embodiments of the invention may be configured according to the knowledge of those skilled in the art without departing from the true spirit or technical teaching of the invention, since the invention is limited only by the terms of the appended claims.

[0040] The oil or fat to be used in the process according to the invention can be of vegetable or animal origin. Examples of vegetable oils and fats are palm oil, various palm oil fractions, shea butter, mango kernel fat, hydrogenated edible oils such as soybean oil or rapeseed oil (canola), and even lauric fats such as palm kernel oil and coconut oil. The process of the invention can also be applied to winterization, i.e., the removal of high-melting-point triglycerides from, for example, cottonseed oil. Examples of animal oils and fats are oils and fats that are already fractionated, such as lard, beef tallow, mutton tallow, anhydrous milk fat, chicken fat, and fish oil.

[0041] The oil or fat to be fractionated is preferably at least partially refined. Accordingly, it should no longer contain the mucilage present in crude oil, as these can impair crystallization, and the free fatty acid content should also preferably be reduced to below 0.5 wt% by alkali refining or vacuum steam stripping.

[0042] The fat to be fractionated according to the invention should be molten. It may be somewhat cloudy, but its solid fat content should preferably be below 2% by weight, and more preferably below 1% by weight. One way of introducing the molten fat into the first of one or more crystallizers is to pump it from a shore or day tank. If the fractionation plant is an integral part of a refinery, a small intermediate storage tank will suffice. In edible oil fractionation, it is customary to raise the temperature of the fat to be fractionated about 10°C above its melting point. This heating step may also precede the process according to the invention, but if it is found unnecessary and / or if its omission is considered advantageous, the resulting process may still be within the scope of the invention.

[0043] If the temperature of the grease to be pumped from the bearing is more than 10°C above its cloud point, it may be advantageous to cool the grease in a simple cooler to just above its cloud point. Cooling it below its cloud point for extended periods is not recommended, as this may lead to deposition of grease crystals in the cooler. If the temperature of the grease is below its cloud point for a short period and this leads to deposition, this deposit will be melted out and removed by the continuous oil flow once its temperature is sufficiently high to melt the high-melting triglycerides comprising the deposit; this may be several degrees above the cloud point. In the process according to the invention, a temporary interruption of the cooling medium flow may also promote the at least partial melting of any crystalline deposits.

[0044] While the crystallizer described in US Pat. No. 5,874,599 maintains a substantially uniform temperature throughout the vessel, each of the one or more crystallizers to be used in the process according to the invention must exhibit a temperature gradient. At the point where the molten or partially crystallized fat, which may be the result of prior cooling of the fat in the cooler, enters the crystallizer, its temperature will be higher than at the point where the slurry leaves that crystallizer. Generally, the crystallizer is filled from the top and the crystal slurry leaves the vessel at its lowest point, but the process according to the invention is not limited to this arrangement. The establishment of this gradient places certain demands on the design of the crystallizer and, in particular, on its agitator.

[0045] While standard crystallization vessels used for the fractionation of edible oils and fats include an agitator comprising a rotating shaft to which agitator blades have been attached in such a way that these blades, upon rotation, exert a vertical force on the surrounding slurry, the agitator used in the process according to the invention should preferably not exert this vertical force and merely ensure contact between the crystal slurry and the heat exchangers present in the crystallization vessel. In this respect, the type of agitator described in EP 1 818 088A is very suitable; it is therefore incorporated by reference in its entirety. It also has the advantage that its linear velocity is low, which suppresses secondary nucleation and thereby leads to the formation of a homogeneous crystal population.In one of the embodiments described in EP 1 818 088A, the stirrer itself also serves as a heat exchanger. In another embodiment, the stirrer moves between stationary heat exchangers. Both embodiments are suitable for the process according to the invention.

[0046] Another type of stirrer that has been found to be highly useful in the process according to the invention is described in GB 2 053 019 A. Like the stirrers described in EP 1 818 088 A, it produces gentle stirring and exerts no net vertical force. Furthermore, it can be easily mounted inside a large crystallization vessel.

[0047] More standard rotating agitators can also be used in the process according to the invention, provided that the agitator rotates slowly and the agitator blades are not tilted obliquely, exerting only a radial force on the surrounding crystal slurry to force the slurry toward the heat exchangers. These heat exchangers can be spirally wound coils, as found in many existing crystallizers.

[0048] This means that these crystallizers can be retrofitted to implement the process according to the invention by replacing the stirring blades.

[0049] Although the cooling surfaces and agitators can be designed to minimize fouling, this often involves high fluid velocities. In the continuous dry fractionation process of the oils according to the invention, these high velocities must be avoided, as they have been found to lead to secondary nucleation, non-uniform crystal sizes, slow filtration, and a high residual oil content in the filter cake. Accordingly, the process of the invention includes devices for at least partially melting the grease deposits that have been deposited on the cooling surfaces of the heat exchangers in the one or more crystallizers and on the cooling surfaces of the at least one heat exchange element in the cooler.

[0050] One method for removing these deposits involves devices for electrically heating the cooling surfaces of the heat exchangers and / or the at least one heat exchange element of the cooler. To avoid simultaneous heating of the cooling medium, it is preferably drained from the heat exchanger and / or the at least one heat exchange element of the cooler before any current is applied to the electrical heating system.

[0051] Other methods include the possibility of heating by the Joule effect, induction, and the injection of small amounts of heating medium, such as hot water or steam, into the heat exchangers and / or the at least one heat exchange element of the cooler, sufficient to loosen any encrustations that may have formed on these heat exchangers and / or the at least one heat exchange element of the cooler. The injection of this small amount of heating medium will also melt and thus remove any encrustations that are barely visible to the naked eye but serve as a starting point for crystal growth. The removal of these encrustations requires less heat and less time than the removal of visible encrustations by at least partially melting the crystals that cause them to adhere to the surface of the heat exchangers.Since any resulting incrustations are unlikely to be detected during temperature differential measurements, their removal is preferably initiated by a programmable timer. Complete melting of the incrusted crystals has been found to be unnecessary. Once they no longer adhere to the outer surface of the heat exchanger, they are removed by the slowly stirred oil slurry. Partial melting of the incrustation by such shock heating has the advantage of requiring less heat and less time than complete melting, and has the additional advantage of not noticeably heating the bulk of the slurry contained in the crystallizer.

[0052] A person skilled in the art will be familiar with several ways of implementing this short burst of heating medium, e.g., hot water or steam. Preferably, the cooling medium (e.g., cooling water) is first drained from the heat exchangers and / or the at least one heat exchange element of the cooler, so that when steam is blown into the empty elements, it condenses on the inner surfaces of these elements, heating their surfaces and at least partially melting adhering crystals.

[0053] The sequence of draining, injecting heating medium (or electrical heating), and returning to cooling mode is preferably automated and can be triggered by a small temperature difference between the incoming and outgoing cooling water or by an increase in the temperature difference between the oil and the cooling water, as caused by a drop in the heat exchange rate. It can also be programmed on a regular time basis, focusing on developing encrustations that are not apparent by measuring temperature differences. If the heat exchangers or heat exchange elements consist of long, spirally wound coils, it may be advantageous to divide them into several superimposed, smaller units, which is an aspect to consider when retrofitting an existing crystallizer for the process according to the invention.Emptying such smaller units is faster and can be limited to the one that is actually encrusted. In addition, the use of several smaller units facilitates temperature control in the crystallizer. Accordingly, the temperature of the cooling medium, e.g., cooling water, can be controlled to a higher level in the top unit than in the lower units. In new crystallizers, the size (surface area) of the various heat exchangers and heat exchange elements can be taken into account to determine how much heat needs to be removed in that particular section of the crystallizer. In the upper section of a large crystallizer, or the first of one or more crystallizers, only perceptible heat needs to be removed to reduce the temperature of the molten fat to below its cloud point.When the fat begins to crystallize, the crystals are initially quite small, meaning they don't grow very quickly. Accordingly, cooling should be such that the temperature doesn't drop too quickly, as this will lead to excessive supersaturation and increase the risk of new nuclei forming. The heat exchange capacity of the vessel can be greater in the area where the primary crystallization occurs, as this is where most of the latent heat of crystallization will be released and must be removed.

[0054] To promote plug flow of the crystallized fat, it can be made to flow from one crystallizer to the next, as in Fig. 6 of EP 1 818 088A. If a large vessel is used as a crystallizer, it can be divided into compartments, but since the stirring process does not induce any vertical movement, this compartmentalization is by no means mandatory. Indeed, in such large crystallizers, the crystals formed at the top should be able to slowly sink freely to the bottom and grow as the temperature decreases from top to bottom in the crystallizer.

[0055] If multiple crystallizers connected in series are used in the process according to the invention, the crystals can only sink to the bottom of each separate crystallizer. The crystal slurry must be transferred to the next crystallizer, and provided they are positioned slightly above the other, this transfer can be accomplished by gravity. If this is ineffective, a pump is required for the transfer. Care should be taken in selecting the pump so that it does not crush the fat crystals.

[0056] The slurry leaving the crystallizer must be separated into a stearin fraction and an olein fraction by filtration. If the filtration is a batch process, as in the case of a membrane filter press, a small intermediate storage vessel is required. To prevent the slurry from settling, this vessel is preferably equipped with an agitator, which will keep the crystals suspended; this also ensures that the filter press feeds at a constant viscosity. If the filtration system operates continuously, the intermediate storage vessel is unnecessary.

[0057] The filter cake must be melted before the stearin can be pumped to the stearin storage tank. If the fractionation unit is part of a refinery complex, the heat required to melt the stearin can be provided at low cost by the refinery, similar to the heat required to melt the encrusted crystals, which can be provided by the refinery. One heat source could be the latent heat released in deodorizer scrubbers. Typically, the scrubber condensate is cooled with cooling water in a heat exchanger before being sent to a scrubber distillate storage tank. Instead, the heat exchanger could be fed with boiler feedwater to generate low-pressure steam, which can be beneficially used to melt the stearin filter cake.

[0058] Carrying out the process according to the invention and producing fractions within the specification means that the crystallizer throughput and the temperatures and flow rate of the cooling medium must be carefully coordinated. No precise rules can be established in this regard, but it has been found that starting with a rather low feed rate of molten fat, e.g., less than 75% of the designed capacity, and gradually increasing this feed rate is an effective way of starting up the process according to the invention. During this start-up, the temperature of the cooling medium flowing through the heat exchanger in the uppermost compartment or the first of one or more crystallizers should be slightly lower than the temperature of the molten fat fed into that compartment or crystallizer.The temperature of the cooling medium flowing through the heat exchanger in the lowest compartment or the last of one or more crystallizers should be just below the filtration temperature. The other cooling medium temperatures should be in between. Lowering the temperatures of this cooling medium will result in more heat removal, and this can be adjusted by increasing the feed rate until filtration problems arise and / or fraction properties begin to deviate from the target.

[0059] In general, it can be stated that the process according to the invention is surprisingly more productive on a crystallizer volume basis and results in better selectivity than prior art batch processes. It is also more energy-efficient compared to these batch processes, since the crystallizer no longer needs to be heated and cooled, but can maintain its operating temperature thanks to continuous operation. The occasional encrustation that occurs with some products can be effectively managed without seriously interrupting the continuous operation of the process according to the invention. It is also possible to use the one or more crystallizers of the process according to the invention in batch mode, but then there is little need for encrustation removal. However, this can be useful during a period of frequent inventory changes. EXAMPLE 1

[0060] This example concerns an experiment using a crystallizer according to the Fig. 4C in EP 1 818 088A . The capacity of the crystallizer was 35 tons, the liquid level was 3.3 m above the bottom of the vessel and the cooling surface was 5.5 m 2 per ton of oil. The crystallizer was filled with palm oil with an iodine value (IV) of 51.6 by pumping the oil from a storage tank in which the oil temperature was maintained at 60°C by a plate heat exchanger that cooled the oil to just below 40°C.

[0061] The experiment began as a batch process, but when the oil temperature at the crystallizer outlet reached approximately 26°C, the crystallization process was made continuous by feeding oil at a temperature of approximately 40°C from the top of the crystallizer at a rate of 7 to 8 tons per hour and draining a crystal slurry with a solid fat content (SFC) of approximately 7 wt% from the bottom of the crystallizer to an intermediate storage vessel that fed the batch membrane filter press. The experiment continued for 63 hours, during which time 14 filtrations were performed. The yield of olein was 84 wt%, and its iodine value (IV) varied between 55.6 and 57.5.

[0062] The temperature of the slurry leaving the intermediate storage vessel varied between 24.7°C and 25.3°C, averaging 25.1°C. Its mean SFC was 8.4 wt%. This is slightly higher than the mean SFC of the slurry leaving the crystallizer, which was 7.3 wt%. This slight increase in solid fat content may be due to the slightly supercooled slurry leaving the crystallizer and / or the fact that the slurry temperature was reduced from a mean of 26.1°C to a mean of 25.1°C in the intermediate storage vessel.

[0063] The temperature difference of the cooling water in the plate heat exchanger was monitored, and if this temperature dropped significantly, the cooling water flow was interrupted, allowing warm oil at 58-60°C to flow through the heat exchanger and melt any crystal deposits in the heat exchanger. A 2-minute interruption of the cooling water flow was found to be sufficient to completely remove any deposits, and the hot oil entering the crystallizer during this 2-minute period did not disrupt its operation. During the 63 hours of continuous operation, the cooling water flow was interrupted 5 times.

[0064] Crystal deposits on the cooling elements in the crystallizer were also melted by passing hot water through them for a period of 10 minutes. This was done twice throughout the experiment. A visual inspection of the cooling elements after the experiment showed that they were free of any serious encrustation. This means that continuous operation could have been extended.

[0065] The experiment demonstrates several advantages of the process according to the invention. The melting of crystal encrustations barely interrupts the function of the crystallizer and, surprisingly, allows it to operate continuously and consistently over a long period of time. Compared to the batch process carried out in a similar crystallizer, the continuous process has a throughput that is 20 to 25% higher. Energy consumption is reduced by up to 30%, and surprisingly, less filter capacity is required for the continuous process according to the invention, since the resulting crystal cakes exhibit significantly higher permeability during filtration. In addition, the crystal cakes exhibit greater compactibility during cake compaction in the filter, and up to 3 wt.% more olein (on a 100% cake basis) can be recovered, which also offers economic advantages. EXAMPLE 2

[0066] In this example, two crystallizers were used in series, as described in Example 1. The first crystallizer was filled with palm oil with an iodine value of 51.6 by pumping the oil from a storage tank, where the oil temperature was maintained at 55°C, through a plate heat exchanger, which cooled the oil to 36°C.

[0067] The experiment was started as a batch process, but when the oil temperature at the crystallizer outlet reached approximately 26°C, the crystallization process was made continuous by continuously feeding oil at a temperature of approximately 36°C from the top of the first crystallizer at a rate of 3 to 3.5 tons per hour and flowing a crystal slurry with a solid fat content (SFC) of approximately 13-15 wt% and a temperature of approximately 20°C from the bottom of the first crystallizer to the top of the second crystallizer, where it further crystallized, yielding a slurry with a solid fat content (SFC) of approximately 23-26 wt% and a temperature of approximately 15-16°C at the outlet of the second crystallizer. From there, the slurry was continuously transferred to an intermediate storage tank that fed the batch membrane filter press.The experiment continued for 190 hours, during which time 38 filtrations were performed. The olein yield was 61.3 wt% and its IV varied between 61.5 and 63.4.

[0068] The temperature of the slurry leaving the intermediate storage tank varied between 14.8°C and 15.4°C, averaging 15.1°C. Its mean SFC was 26.3 wt%. This is slightly higher than the mean SFC of the slurry leaving the second crystallizer, which was 24.4 wt%. This slight increase in solid fat content is similar to that observed in Example 1.

[0069] As in Example 1, the temperature difference of the cooling water in the plate heat exchanger was monitored, and if this temperature dropped significantly, the cooling water flow was interrupted, allowing warm oil at 55-58°C to flow through the heat exchanger and melt any crystal deposits in the heat exchanger. Again, a 2-minute interruption of the cooling water flow was found to be sufficient to completely remove any deposits, and the hot oil entering the crystallizer during this 2-minute period did not disrupt operation. During the 190 hours of continuous operation, the cooling water flow was interrupted 12 times.

[0070] Passing hot water through the cooling elements for a period of 15 minutes also melted crystal deposits on the cooling elements in the crystallizer. During the 190 hours of continuous operation, the hot water was passed through the bundles seven times.

[0071] This example therefore illustrates that the process according to the invention can be successfully carried out with two crystallizers in series. It also demonstrates the product advantages of the process according to the invention.

[0072] Table 1 below summarizes the analytical and performance data of both examples.

[0073] Table 1 further illustrates the surprising observation that all performance parameters of the continuous fractionation process according to our invention and all product properties as achieved by the process according to our invention are improved compared to the batch fractionation process carried out in the same crystallizer vessel. QUOTES CONTAINED IN THE DESCRIPTION

[0074] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature EP 1028159 A US 5 198 123 A US 4 542 036 A US 4 127 597 A US 4 594 259 A US 4 839 191 A US 5 874 599 A US 6 383 456 B1 DE 11 2007 000 184 T5 EP 1818088 A GB 2 053 019 A EP 1818008 A

Claims

[1] Continuous process for the dry fractionation of edible oils and fats using one or more crystallizers connected in series, which process comprises the following steps: a) providing a melted fat; b) continuously feeding the molten oil or fat into the first of one or more series-connected crystallisers in which the fat is gradually cooled using heat exchangers containing a cooling medium to form a crystal slurry, each of the one or more crystallisers having a temperature gradient such that the temperature at the point at which the molten or partially crystallised fat enters one of the crystallisers is higher than that at the point at which the slurry leaves the crystalliser; c) continuously removing the slurry from the last of said one or more crystallisers; d) separating the crystal slurry by filtration into a filter cake and a filtrate; the process further comprising the step of at least partially melting fat deposits deposited on the heat exchangers. [2] A continuous process according to claim 1, wherein the continuous process further comprises the step of continuously cooling the molten fat in a cooler to a temperature above the cloud point of the fat before the molten fat enters the first of the one or more crystallizers, the cooler comprising at least one heat exchange element. [3] Process according to claim 2, wherein the at least partial melting of the grease incrustations in the cooler is effected by temporarily interrupting the flow of the cooling medium to the at least one heat exchange element of the cooler or by electrically heating the surface of the at least one heat exchange element of the cooler. [4] Process according to claim 3, wherein the temporary interruption of the cooling medium flow is initiated by a temperature difference circuit. [5] A process according to claim 3, wherein the temporary interruption of the cooling medium flow is initiated by a programmable timer. [6] Process according to claim 1, wherein said step of at least partially melting the fat deposits comprises electrically heating the surface of the heat exchangers. [7] Process according to claim 1 or 2, wherein a heating medium which is sufficiently hot to at least partially melt the grease incrustations which may have been deposited in the heat exchangers used in step b) and to at least partially melt the grease incrustations on the at least one heat exchange element of the cooler is caused to flow through the heat exchangers and / or the at least one heat exchange element of the cooler. [8] Process according to claim 7, wherein said heat exchangers and / or the at least one heat exchange element of the cooler are at least partially drained before a heating medium is caused to flow through the heat exchangers and / or the at least one heat exchange element of the cooler. [9] Process according to claim 7 or 8, wherein the heating medium is steam. [10] A process according to claim 9, wherein the steam has been generated in the scrubber of a vacuum stripping unit in a nearby refinery complex. [11] Process according to claim 7 or 8, wherein the heating medium is heated water. [12] A process according to claim 11, wherein the heated water has been heated by being used as a cooling medium in a nearby refinery complex. [13] Process according to any one of claims 7 to 12, wherein the switching from cooling medium to heating medium in the heat exchangers and / or the heat exchange elements of the cooler is initiated by a decrease in the temperature difference between the outgoing and incoming cooling medium. [14] A process according to any one of claims 7 to 12, wherein the switching from cooling medium to heating medium is initiated by a programmable timer. [15] A process according to any one of the preceding claims, wherein the agitators of the one or more crystallizers exert substantially no net vertical force on the contents of the crystallizers. [16] A process according to any one of the preceding claims, wherein the agitators also act as a heat exchanger. [17] A process according to any one of the preceding claims, wherein the design of the one or more crystallizers promotes plug flow. [18] Process according to claim 17, wherein the one or more crystallizers are divided into compartments. [19] A process according to any one of the preceding claims, wherein the stearin cake resulting from the filtration of the finally produced crystal slurry is melted by a heating medium recovered from upstream oil treatments in a nearby refinery complex, such as degumming and / or deodorization.