Novel desolventization process yielding superior defatted meal

Abstract

A desolventization process of the residual solid material obtained after the specific solvent extraction of the oil contained in oleaginous vegetable materials for producing plant-based meal of superior nutritional quality. In particular, the proteins of the meal obtained by the innovative desolventization process are less denatured compared to existing processes. Additionally, compared to current processes, the present desolventization process is more economical, more flexible, requires less footprint and less utilities (electricity and water), produces less effluents and is safe. Furthermore, the desolventized meal obtained by the novel desolventization process is very homogeneous, in particular, it contains less fines and / or less burned particles than meal produced with current desolventization processes.

Description

NOVEL DESOL VENTIZATION PROCESS YIELDING SUPERIORDEFATTED MEALFIELD OF THE INVENTION

[0001] The present invention relates to a novel desolventization process of the residual solid material obtained after the specific solvent extraction of the oil contained in oleaginous vegetable materials such as, for example, soybean, rapeseed or sunflower. Said residual solid material, or “extraction residue” contains flammable solvent, in most instances commercial hexane, which must be completely removed in order to obtain a useful edible meal. The present novel desolventization process is able to produce plantbased meal of superior quality from such extraction residue. In particular, the meal obtained by the innovative desolventization process is very homogeneous, contains no over-toasted particles and less fines than meals produced by existing desolventization processes. The proteins of the meal obtained by the innovative desolventization process are less denatured and have superior nutritional value compared to meal produced by existing desolventization processes. Additionally, compared to existing desolventization processes, the present desolventization process is more economical, more flexible, safer for continuous operation, provides a buffer capability, requires less footprint and less utilities (electricity and water), and produces less effluents.BACKGROUND OF THE INVENTION

[0002] Protein rich plant-based feed and food products, in particular defatted meals with high protein content derived from soybean, rapeseed and to less extend sunflower are increasingly in demand in order to replace and / or complement protein rich products from animal origin. Such steady increasing demand is induced by environmental, ethical, and economic reasons.

[0003] Replacing animal-based protein food by plant-based protein food in the human diet is recognised as healthy by a large fraction of the public which further fosters the high demand of plant-based defatted meal. Furthermore, the feed meal industry also demands high quality plant-based protein meal, in particular for aquaculture and poultry.

[0004] Commercially, the most prevalent plant-based defatted meals are derived from soybean even if other crops such as rapeseed and sunflower are also increasingly used. Those oleaginous vegetable materials are primarily cultivated and harvested for their edible oil content which is mainly solvent extracted. The solvent extraction yields edible oil (after proper desolventization and refining) and a solvent laden defatted residue which must be completely desolventized to produce a defatted meal rich in protein since typically about 25% to 35% of the mass of the oleaginous vegetable material is oil and has been extracted, all other components (protein, sugars, fibres, etc.) remaining in the residue. The resulting defatted meal is therefore naturally enriched in protein. Thus, both the starting extraction residue and the final meal still contain all the sugars both simple and complex (saccharides, oligosaccharides, starches, fibres, etc.) as well as the other components of the original oleaginous vegetable material because only the fatty matters have been extracted during the solvent extraction process.

[0005] Therefore, large volume of relatively inexpensive protein-rich meal is available from those crops. The meal is valorised as such but is also used as starting material for various processes aiming at transforming the meal in specific feeds and foods products for example protein concentrates or protein isolates.

[0006] Amongst plant-based protein rich meal, (or “meal” as from now on) the strongest demand surge is for applications requiring proteins of high quality i.e., proteins that are less denatured during the desolventization of the extraction residue. Such high- quality proteins are needed for food applications and for special feed applications for example tailored for fish and monogastric animals. Both applications command higher retail prices.

[0007] For example, in the field, and in the case of soybean, a high-quality meal is known as “white-flake meal” because white, bland, and fluffy in comparison to standard meal which is typically a brown and coarse material having a characteristic strong odour (usually designated as “beany” or “toasted”).

[0008] Typically, standard meal is resulting from a desolventization realised under atmospheric pressure and including an intensive steam stripping step of the residue. High- quality meal results from a desolventization realized under reduced pressure and necessitating a less intensive steam stripping; alternatively, often in the case of soybean, high-quality meal can also be obtained by a process including a sudden high-temperatureflash-stripping of the residue followed by a moderate steam stripping under reduced pressure of the remaining solvent contained in the residue.

[0009] However, it is well known that the existing desolventization processes generate defects in the resulting meal such as protein degradation and / or over-toasted meal particles and / or excessive amount of problematic fines.

[0010] Standard meal is obtained from the desolventization of extraction residue under atmospheric pressure realised typically in a DTDC (Desolventizer Toaster Dryer Cooler) or in a serial combination of a DT (Desolventizer Toaster) and a DC (Dryer Cooler). For concision, the following description will focus on DTDC, being understood that the same principles and conclusions will apply to a desolventization operated with a single DTDC or two distinct but serially connected pieces of equipment (a DT and a DC).

[0011] DTDC are tall vertical towers comprising several stacked horizontal trays on which the processed residue is laying while simultaneously gently mixed and pushed by rotating sweep arms to cascade, via an opening made in each tray, to the next tray positioned directly below. The residue is firstly pre-desolventized on one or more pre-desolventizing tray(s) where the solvent is only thermally evaporated by contacting the processed residue on a heated surface. After this pre-desolventization on one or more pre-desolventizing trays, the residue is contacted with stripping steam while continuously cascading on several stripping trays directly positioned below the one or more pre-desolventizing tray(s). In fact, the bulk of the solvent is removed on those stripping trays by the stripping steam directly contacted to the residue. During this stripping, a substantial fraction of the stripping steam condenses in the processed residue. Consequently, the processed residue must be dried with hot air and then cooled, respectively on one or more drying tray(s) and cooling tray(s) also located directly below the stripping trays.

[0012] Thus, in such atmospheric pressure DTDC comprising stacked horizontal trays, only a small fraction of the solvent is thermally evaporated on the pre-desolventizing tray(s), typically the residue will still contain about 20% (w / w) to about 25% (w / w) of solvent after the pre-desolventizing tray(s), for a typical starting residue containing about 30% (w / w) of solvent. Most of the solvent must be stripped by contacting the partially desolventized residue with stripping steam which substantially condenses into the processed residue. Then, this extra moisture must be evaporated by contacting dry hot air to the residue. Finally, after cooling of the processed residue to a temperature close to room temperature, a standard meal is obtained. The residence time is thus relatively long. Thoseprocessing conditions are thus characterized by high humidity combined to high temperature maintained during a long period of time and those processing conditions result into a substantial denaturation of the proteins contained in the standard meal and to the apparition of unfavourable organoleptic properties. The proteins contained in such standard meal are less digestible and less nutritive for monogastric animals. Furthermore, in a DTDC, the processed residue lays on heated pre-desolventizing horizontal trays and despite agitation by sweeping arms, some extraction residue particles tend to stick on the surface of those horizontal heated trays which results in the production of over-heated and / or burned particles of meal that will be collectively designated as over-toasted meal particles. The meal produced by the DTDC process is thus not fully homogeneous and includes degraded meal having substantially denatured proteins.

[0013] Therefore, other desolventization processes of the extraction residue are utilized to produce meal of higher quality. Currently, two major desolventization processes are commercially in use to produce high quality meal: the flash-loop pre-desolventization process which is mainly used to pre-desolventize extraction residue derived from soybean and the vacuum operated DTDC process which can be used to desolventize extraction residues derived from any seeds / beans. The flash-loop process represents about 60% to about 70% of the high quality soybean meal market. The flash-loop process is a pre- desolventization because even if it removes a large fraction of the solvent contained in the residue, the remaining solvent contained in the pre-desolventized residue must still be removed by steam stripping usually operated under reduced pressure. However, those two processes are not fully satisfactory.

[0014] Indeed, in the flash-loop process, a pre-desolventization is realized by stripping the residue with superheated hexane vapours requiring special and expensive equipment and safety measures. The residence time is very short which may appear as an advantage. However, it represents a practical inconvenience, as there is no buffer capacity for an efficient regulation based on the incoming extraction residue production. Such buffer capability is critical because the solvent laden extraction residue is difficult to store (due to its flammable solvent content) and thus must be continuously and rapidly desolventized. Furthermore, the resulting pre-desolventized residue is brittle which is caused by the sudden removal of a substantial fraction of the solvent and water from the residue resulting in a very porous and fragile material. It leads to a meal (white-flake) containing a large fraction of fines (up to 30%) after the full completion of the desolventization process.

[0015] Those fines are particularly damageable in case of further extraction of the white-flake meal to produce other protein products since they tend to block the extractor screen and furthermore those fines also tend to be entrained in the extraction solvent which results in equipment fouling, in particular, the solvent distillation section. In that case, white-flake meal resulting from a desolventization process including a flash-loop pre- desolventization must be sieved to remove the fines which represents a substantial material loss of about 20% to about 30% as well as an additional processing step and logistic constrains. Typically, the sieved fines fraction is blended in standard meal and thus valorised at a substantial lower price than white-flake meal which induces a significant economic disadvantage.

[0016] Furthermore, any power outages are particularly catastrophic for a flash-loop pre-desolventization process because the processed residue is moving through a narrow and long tube before reaching the superheated hexane stripping zone. Any power outage will then require the manual cleaning of this narrow and long tube (from 50 to 200 meters of length) which is particularly difficult due to its limited access. Indeed, even if this narrow tube is provided with some inspection holes, accessing inside the tube remains difficult, especially at high elevation. Furthermore, their opening for cleaning represents a safety risk as the narrow tube is loaded with solvent vapours which cannot be evacuated prior to said opening.

[0017] The vacuum operated DTDC process makes use of a desolventizer relatively similar in construction than a classical atmospheric DTDC, but this one is maintained under vacuum and may contain more pre-desolventizing trays where the solvent is removed only thermally. Thus, such vacuum-desolventizers are also tall vertical towers comprising several stacked horizontal trays on which the processed residue is laying while simultaneously gently mixed and pushed by rotating sweep arms to cascade, via an opening made in each tray, to the next horizontal tray positioned directly below. However, due to the poor thermal transfer coefficient of those pre-desolventizing trays, the thermal evaporation of the solvent remains moderate and, in consequence, stripping steam is still abundantly used to remove a substantial fraction of the residual solvent originally contained in the residue. Consequently, such vacuum operated DTDC still contains several strippingtrays where a substantial fraction of the solvent is removed by contacting the residue with stripping steam. Consequently, those vacuum operated DTDC are very large because provided with many inefficient pre-desolventizing trays and several stripping trays.Furthermore, since the stripping steam substantially condenses in the residue, a drying is still necessary after the vacuum steam-stripping desolventization step. The experience and usage of such equipment show that the larger the equipment, the more difficult it is to maintain a constant and sufficient vacuum and to avoid any leakage. This issue represents a major running expense and a safety concern because any air ingress into the vacuum desolventizer constitutes a fire or an explosion risk. Another disadvantage of the vacuum- desolventizer process is its high energy demand because in order to limit the size and cost of the equipment, vacuum-desolventizers are equipped with a limited number of pre- desolventizing trays. Therefore, in practice, still most of the solvent of the residue must be stripped with stripping steam, and since a substantial fraction of this stripping steam condense in the residue this one must be evaporated at the cost of additional energy demand and protein degradation. Indeed, the residue is still exposed to significant moisture and temperature during a long period when processed in such vacuum operated DTDC and therefore the protein of the meal obtained by such process are still degraded even if the extend of this degradation is minimized compared to atmospheric desolventization. The reduction of the exposure to moisture at high temperature would require adding a large number of inefficient pre-desolventizing trays. However, this would further increase the size, cost and running expenses of the equipment and further amplify the presence of overtoasted meal particles. Therefore, in practice, a compromise is found between acceptable equipment size, cost, and meal quality.

[0018] Thus, both desolventizing processes described above, aiming at producing high quality meal, i.e. the desolventization including a pre-desolventization in a flash-loop or the desolventization process based the vacuum operated DTDC, include a final vacuum steam stripping of the residual hexane still present in the pre-desolventized residue. However, since the remaining residual hexane after the flash-loop is usually relatively low the final vacuum steam stripping is rapid and consequently the protein denaturation remains moderate even if, of course, substantial quality variations are observed depending on the particular production facility. In the case of vacuum operated DTDC process, the residual hexane after the pre-desolventizing trays is usually higher (about 20%) and therefore more protein degradation will occur during the final vacuum steam stripping since this one will be more intensive. Furthermore, this vacuum steam stripping is always realized in the same vessel than the thermal desolventization taking place on the pre-desolventizing trays. Hence, the same vacuum is applied for both steps (i.e., the thermal desolventization andthe final steam stripping) and this vacuum cannot be individually set for best results. Once more a compromise has to be applied. In the flash-loop process, this final steam stripping is realized in an independent small vacuum steam-stripping desolventizer. Therefore, the vacuum that can be achieved in such small vacuum desolventizer is usually better than in a large vacuum desolventizer containing many inefficient pre-desolventizing horizontal trays and, therefore, this situation is more favourable for a rapid final desolventization which, consequently, is again beneficial for the protein quality contained in the meal.

[0019] Therefore, despite the merits of the existing desolventization technologies, there remains a need in the field for a new desolventization process of extraction residue delivering homogeneous meal containing no or a limited quantity of fines and over-toasted particles and containing proteins of better quality. Furthermore, the innovative desolventization process should offer a buffer capability, a reduced footprint, less safety concerns and be economical, ideally requiring less energy than existing desolventization technologies.SUMMARY OF THE INVENTION

[0020] It has been surprisingly observed that the desolventization process according to the present invention and including a thermal pre-desolventization making use of one or more atmospheric or vacuum operated disc dryer(s) is able to deliver high quality meal economically and safely. The meal delivered by the present invention if of higher quality that the one delivered by current desolventization processes because it does not contain over-toasted particles, contains less fines and its proteins are less denatured.

[0021] The process according to the present invention for the desolventization of an extraction residue containing flammable solvent comprises the following steps: a) a thermal pre-desolventization of the residue to obtain a partially desolventized residue, b) a steam stripping desolventization of the partially desolventized residue obtained in step (a) to obtain a fully desolventized residue containing less than 0.05% (w / w) of flammable solvent, c) an optional moisture adjustment of the fully desolventized residue obtained in step (b) to obtain a moisture adjusted fully desolventized residue, and, d) cooling the fully desolventized residue of step (b), or the moisture adjusted fully desolventized residue ofstep (c) to obtain a meal, characterized in that the thermal pre-desolventization step (a) is realized in one or more disc dryer(s).

[0022] The present invention also encompasses the process as previously described wherein the extraction residue contains flammable solvent in a concentration ranging from 20% (w / w) to 40% (w / w) and wherein said flammable solvent is any flammable solvent used for the specific extraction of fatty matters from oleaginous vegetable material.

[0023] The present invention also encompasses the process as previously described wherein the moisture content of the residue decreases during step (a) and increases during step (b) and wherein the relative desolventization intensities of step (a) and of step (b) are adjusted to obtain a fully a desolventized residue after step (b) having a moisture content ranging from 10% (w / w) to 12.5% (w / w).

[0024] The present invention also encompasses the process as previously described wherein the flammable solvent is commercial hexane comprising at least 50% (w / w) of n- hexane.

[0025] The present invention also encompasses the process as previously described wherein the flammable solvent is commercial isohexane comprising at least 50% (w / w) of 2-methylpentane.

[0026] The present invention also encompasses the process as previously described wherein the thermal pre-desolventization of step (a) of the extraction residue is realized in at least two disc dryers connected in series or in parallel.

[0027] The present invention also encompasses the process as previously described wherein the absolute pressures applied during the thermal pre-desolventization of step (a) ranges from 400 mbara to 1,000 mbara.

[0028] The present invention also encompasses the process as previously described wherein the thermal pre-desolventization of step (a) is realized at atmospheric pressure and said thermal pre-desolventization is reducing the content of flammable solvent contained in the extraction residue by at least 50%.

[0029] The present invention also encompasses the process as previously described wherein the thermal pre-desolventization of step (a) is realized at reduced pressure and said thermal pre-desolventization is reducing the content of flammable solvent contained in the extraction residue by at least 70%.

[0030] The present invention also encompasses the process as previously described wherein the thermal desolventization of step (a) is occurring progressively without flash evaporation and wherein the residence time of the residue in the one or more disc dryer(s) is ranging from 10 to 60 minutes.

[0031] The present invention also encompasses the process as previously described wherein the meal obtained in step (d) does not contain over-toasted particles and less than 30% of fines.

[0032] The present invention also encompasses the process as previously described wherein the meal obtained in step (d) has protein quality parameters (PDI, KOH solubility) at least 10% superior to the typical protein quality parameters of meal obtained with a DTDC (Desolventizer Toaster Dryer Cooler) having stacked horizontal trays.

[0033] The present invention also encompasses the process as previously described wherein the buffer capacity during the thermal pre-desolventization of step (a) is at least 10 minutes.

[0034] The present invention also encompasses the process as previously described wherein, for a given capacity, the effluent generated during step (c) is reduced by at least 10% compared to the effluent generated during the cooling step of DTDC (Desolventizer Toaster Dryer Cooler) having stacked horizontal trays.

[0035] The present invention also encompasses the process as previously described wherein, for a given capacity, the energy demand is reduced by at least 10% compared to the energy demand of a desolventization process realized with DTDC (Desolventizer Toaster Dryer Cooler) having stacked horizontal trays.

[0036] The present invention also encompasses the process as previously described wherein, the extraction residue of step a) contains from 20% (w / w) to 40% (w / w) of simple and complex sugars (including polysaccharides).BRIEF DESCRIPTION OF THE FIGURES

[0037] FIG. 1 is a block diagram representing one embodiment of the process according to the present invention.

[0038] FIG. 2 is a block diagram representing a preferred embodiment of the process according to the present invention.

[0039] FIG. 3 is a block diagram representing one embodiment of the process according to the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0040] Disc dryers are pieces of equipment designed and used for the dewatering and drying of animal by-products such as meat, bones, offal, feather, and blood. Such disc dryers can be used at atmospheric pressure or under reduced pressure. For example, they are sometimes used under reduced pressure to dry fish by-products. In those applications, the disc dryers are used for the removal of a non-flammable liquid. Disc dryers are also easy to clean and sanitize since the discs and other internals are easily accessible and located in a single vessel having one compartment. In disc dryers, the processed material is conveyed horizontally though a series of rotating vertical discs. The horizontal conveyance is provided by paddles installed at the tip of the discs. The discs are hollow and heated typically with heating steam. In disc dryers, the dried material does not lay on the discs but is continuously mixed and agitated in the open space around the discs.

[0041] The solvent extraction of the oil contained in oleaginous vegetable materials (such as soybean, rapeseed, or sunflower) is currently realised with commercial hexane (also known as extraction hexane) which is a highly flammable solvent. Commercial hexane is a mixture containing mostly saturated hydrocarbon having 6 carbons, mainly n- hexane and branched isomer of hexane. It’s prevalence in this field (close to 100%) is justified by its efficiency to specifically extract fatty matters, its low cost, its moderate boiling point, its low latent heat of evaporation and its immiscibility with water, making it straightforward to recover it from the condensed solvent / water vapours originating from desolventizer.

[0042] Isohexane is sometimes used as solvent presenting the advantage of having a lower boiling point than commercial hexane. However, isohexane is more expensive and less available than commercial hexane and therefore its usage is limited to specific applications.

[0043] Various alternative biodegradable solvents have been evaluated with preliminary positive results, but their commercial usage is still limited due to their high cost. However, any alternative solvent will likely remain flammable because carbon-based.Indeed, non-flammable solvents containing chlorine and / or other halogen element(s) are not used in the industry due to their prohibitive cost and potential toxicity.

[0044] Consequently, the present invention is limited to the desolventization of deoiled extraction residue containing any flammable solvent able to specifically extract fatty matters from oleaginous vegetable materials. Typically, the extraction residue will contain about 30% of flammable solvent when entering the desolventization process.

[0045] In the context of the present invention, the terms “residue” or “extraction residue” designate the residual solid material obtained after the specific solvent extraction of the oil contained in an oleaginous vegetable material such as soybean, rapeseed or sunflower for example. The solvent chosen must be as specific as possible to exclusively extract the fatty matters, but no other components present in the oleaginous vegetable material such as sugars and / or proteins for example. The residue is soaked with a flammable solvent, in most instances commercial hexane. Usually, directly after the oil solvent extraction, the residue contains about 30% of flammable commercial hexane.

[0046] In the context of this invention, the terms “processed residue” mean that the residue is in the process of being desolventized and / or moisture adjusted and / or cooled and therefore will contain a lower concentration of flammable solvent than directly after the oil solvent extraction of the oleaginous vegetable material. As a matter of fact, when the residue is fully processed it will contain a very low quantity of flammable solvent (typically less than 0.05% w / w), specific moisture content (typically about 10% to about 12.5 % depending on the oleaginous vegetable material) and be cooled at about room temperature. It can therefore be safely handled, transported, and stored. At this stage, the processed residue has been transformed into meal.

[0047] Thus, in the context of this invention, a meal is a deoiled oleaginous vegetable material which has been completely desolventized, moisture adjusted and cooled. Furthermore, the term “meal” encompasses standard meal and high quality meal. Furthermore, the defatted meal obtained by the present invention still contains the other components of the original oleaginous vegetable material, from which it is derived, including proteins, simple and complex sugars, vitamins, fibres, minerals and some residual oil. Typically, the meal will contain about 20% (w / w) to about 40% (w / w) of simple and complex sugars (including polysaccharides), the remaining components being mostly proteins (also usually in the range of about 20% (w / w) to about 50% (w / w), water (in the range of about 10% (w / w) to about 12.5% (w / w)) and various other matters listed above. As a matter of fact, the composition is highly variable depending on the nature of theoleaginous material and on the preparation before the solvent extraction i.e., if this preparation includes a dehulling step.

[0048] Despite the antagonism between deoiled vegetable extraction residue laden with flammable solvent and animal products containing water and no flammable solvent, it has been attempted to evaluate the performance of a desolventization process making use of a disc dryer for the thermal pre-desolventization of vegetable extraction residue. It must be noted that given the difficulty to transport solvent laden extraction residue from an oleaginous vegetable material solvent-extraction facility to a facility processing animal byproducts, such endeavour was not routine experimentation at all, but rather highly uncertain.

[0049] Such endeavour was also uncertain because it is difficult to predict the efficacy of a disc dryer compared to the one of a desolventizer of the DTDC type or to the efficacy of a flash-loop since the conceptions and the destination usages of those pieces of equipment are very different and many aspects of their construction is even opposite. Since disc dryers are used in the field of the dewatering of animal by-products, it can be assumed that its design is optimized for this precise application which is in fact less demanding because animal product does not contain carbohydrates. Hence, animal products are much less sensitive to the Maillard reaction when heated in humid conditions. Indeed, the presence of a very substantial quantity of sugars in the extraction residue amplifies the degradation of the proteins and the apparition of unfavourable organoleptic properties during the desolventization.

[0050] As a matter of fact, because disc dryers are used and designed to remove water, one can expect high specific thermal transfer coefficient and thus even more degradation of the residue if the pre-desolventization of extraction residue would be attempted with such disc dryer. In particular, an abundant production of over-toasted meal particles would be very probable. However, in the hypothesis that the disc dryer would be characterized by low thermal transfer coefficient, one may expect less degradation of the residue during the pre-desolventization but an increase in energy consumption and the need of an even bulkier pieces of equipment than the current DTDC.

[0051] Thus, the dewatering performances of animal products delivered by disc dryers are not suggesting that quality vegetable meal (i.e. homogeneous, having good organoleptic properties, containing no or a small quantity of over-toasted particles, having undegraded protein compared to meal produced by known processes) could be obtained if a disc dryer is used to thermally desolventize an extraction residue. Such uncertainties, and as a matterof fact deterrent factors, explains that no experimentation to this end has been attempted even if those technologies are intensively in use in their respective fields since many decades.

[0052] Nonetheless, despite those contrary expectations, several pre-desolventization trials of extraction residue have been attempted using a standard disc dryer. Rapeseed solvent extraction residue has been stored in hermitical containers and transported from Belgium to Denmark in the facility of one of the major manufacturers of disc dryers. Experiments have been performed on a standard pilot-sized disc dryer. The solvent concentration of the extraction residue was 30% at the collection time which is fully typical. The extraction residue contained 30% (w / w on a dry basis) of simple and complex sugars (including polysaccharides) and 13.5% of water. After transportation, the residue has been mixed and homogenized and the concentration of the solvent in the residue has been measured once more to verify if no evaporation occurred during the transportation. However, the same concentration of 30% in solvent has been determined. The solvent is commercial hexane which is the typical solvent currently used in any solvent extraction facility.

[0053] Despite those contrary expectations, it has been surprisingly observed that excellent pre-desolventization of the extraction residue has been obtained with the disc dryer while the resulting final meals obtained after the final steam-stripping desolventization, the moisture adjustment and the cooling were homogeneous, did not contain any over-toasted particles, contained limited amounts of fines and possessed protein of superior quality. If operated at atmospheric pressure, the remaining solvent after the thermal pre-desolventization of the residue was low, in the range of about 5% to about 15% which is significantly lower than the values obtained with current stacked trays desolventizers (DTDC) having steam heated horizontal pre-desolventizing trays. Furthermore, the equipment can be put under vacuum. The vacuum was maintained steady without air leaks causing safety concerns. When a vacuum of 500 mbara was applied, the thermal pre-desolventization improved even further and produced a pre-desolventized residue containing about 5% of solvent. Furthermore, this experimentation has revealed that for a given capacity, a disc dryer about half the size of a vacuum operated DTDC will be adequate. Therefore, maintaining a constant vacuum in such significantly smaller volume is considerably simplified and safer. The smaller size of the disc dryer generates less heat loss than much larger horizontal trays desolventizer. Furthermore, leakage risks are typically divided by a factor of two. Therefore, the present process, making use of discdryer for the pre-desolventization of extraction residue is also safer than current vacuum desolventization processes known in the field and more energy efficient while simultaneously delivering better quality meal after the completion of the subsequent steps following the thermal pre-desolventization.

[0054] Thus, it has been observed that the specific heat-transfer occurring in a vacuum operated disc dryer is superior to the one taking place in a vacuum desolventizer of the DTDC type making use of horizontal pre-desolventizing trays. However, very surprisingly, such superior thermal efficiency of a disc dryer is not accompanied by the production of an excess of over-toasted particles. As a matter of fact, the opposite was observed even if, in the experimentations realized with the disc dryer, the thermal pre-desolventization trials were intense because in all experiences, at least 100% more solvent was evaporated compared to the quantity of solvent typically thermally evaporated on the pre- desolventizing trays of a DTDC.

[0055] Hence the present desolventization process making use of vacuum or atmospheric operated disc dryer for the thermal pre-desolventization step is more compact and use globally less energy than current desolventization processes known in the field. This is due to the fact that, a substantially larger fraction of solvent is evaporated during the pre-desolventization step and hence the final steam-stripping step is less intense. Therefore, less water condenses in the residue during the final steam-stripping which, consequently, decreases the energy needed to dry the residue. For the same reason, the residue is less exposed to combined heat and moisture during the present desolventization process which is beneficial for the quality of the meal, in particular its protein digestibility and solubility.

[0056] Experimentation have been realized with a single disc dryer. However, the present invention also encompasses a residue desolventization including a pre- desolventization realised with several disc dryers connected in series or in parallel. For example, such lay-out may be beneficial in production facilities with variable capacities depending on harvesting period. For some applications it may be advantageous to realise two or more pre-desolventization in two or more separate disc dryers connected in series, each disc dryers having a given operating temperature and / or reduced pressure. Therefore, the innovative desolventization process is flexible. As a matter of fact, this flexibility also resides in the fact that, in the present invention, the steam-stripping desolventization step is realised in an independent steam-stripper desolventizer and hence, any adequate temperature and pressure can be selected which offer a greater flexibility than if both thethermal pre-desolventization and the steam-stripping desolventization are realized in the same vessel as it is the case for a DTDC.

[0057] As a matter of fact, the protein quality of the pre-desolventized residues has not been directly measured because its value is not relevant since only the final meal will be consumed as feed or food.

[0058] Thus, several pre-desolventized residues have been classically desolventized by steam-stripping, and then moisture adjusted and cooled to obtain final meals. It has been observed that the protein quality of the meal produced by the present desolventization process making use of disc dryer(s) for the thermal pre-desolventization step compares favourably to the protein quality obtained by conventional desolventization processes.

[0059] Indeed, two protein quality indictors PDI (Protein Dispersibility Index) and KOH solubility, which assess the availability and digestibility of the proteins are increased, which is commensurate with a better pre-desolventization and a less intense steam-stripping desolventization. Depending on the sample, it has been observed an improvement of those protein quality indicators ranging from 10% to 30% compared to typical meal obtained with a prior art DTDC. Furthermore, it has been observed that the more solvent is evaporated during the thermal pre-desolventization (with the disc dryer), the higher is the increase of protein quality indicators of the final meal. Even if those results have been obtained for meal derived from rapeseed extraction residue, it is expected that meal derived from other oleaginous vegetable material and obtained with the present desolventization process will benefit of a similar protein quality improvement. However, it is difficult to determine if the present desolventization process will deliver meal having better protein quality parameters than the ones produced by the desolventization process including a flash-loop pre-desolventization step. It is believed that any improvement will be marginal because the flash-loop pre-desolventization step removes already a substantial fraction of the solvent. Furthermore, such flash-loop pre-desolventization step is mostly used for treating soybean extraction residue which proteins quality parameter values do not compare directly to the ones of meal derived from rapeseed extraction residue. However, the desolventization process according to the present invention generated a rapeseed meal that is less brittle and that contains less fines than the soybean meal (known as white flakes) produced by a desolventization process including a flash loop pre-desolventization step. It is believed that this advantage will be conserved when extraction residue derived from other oleaginous vegetable materials will be desolventized by the process according to thepresent invention because its thermal pre-desolventization is softer and more progressive which generate a less brittle pre-desolventized residue.

[0060] The innovative desolventization process including a pre-desolventization step realized in one or more disc dryer(s) still benefits of sufficient buffer capacity, considerably higher than the buffer capacity delivered by a desolventization process including a pre- desolventization step realized in a flash-loop. As a matter of fact, the buffer capacity of disc dryer is comparable and even higher than the one offered by a classic DTDC (a desolventizer based on several stacked horizontal trays). This is due to the fact that DTDC are compartmented in many compartments separated by horizontal trays. On the contrary, a disc dryer has a single cavity accommodating several vertical discs and a large quantity of residue. As a matter of fact, even if the global volume of the disc dryer is considerably smaller than an DTDC, about 50% smaller for a given capacity, its buffer capacity remains similar or even higher. For any commercial-scale installation integrating the desolventization process according to the present invention the buffer capacity will be largely in excess of 10 minutes.

[0061] It has been furthermore observed that the innovative process is particularly energy efficient compared to current technologies, in particular when compared to a DTDC of similar capacity. This is mainly due to the observed higher thermal transfer of the disc dryer. The main energy saving of the desolventization process according to the present invention originates in the fact that a substantial fraction of the solvent is removed during the thermal pre-desolventization. Consequently, in the process according to the present invention, the total energy input during the thermal pre-desolventization step will be in fact higher than the one consumed during the pre-desolventization realized in a DTDC and relying on horizontal pre-desolventizing tray(s). Indeed, in the present process, a much greater quantity of solvent is evaporated during the pre-desolventization step. However, this higher energy spending during the thermal pre-desolventization step allows substantial energy saving during the following steps of the process according to the present invention since both the steam-stripping desolventization step and the moisture adjustment step (in most instance a drying) will be less energy demanding and will allow, globally, a substantial energy saving. Indeed, since the present innovative process delivers a pre- desolventized residue containing less solvent, less stripping steam are required during the steam-stripping desolventization and consequently, less stripping steam condenses in the steam-stripped residue which results in a substantially less intensive moisture adjustment step (such as a drying in most instances) or even no moisture adjustment step at all. Thissaving is substantial because evaporating water is particularly energy demanding. Therefore, the desolventization process according to the present invention is able to save substantial amounts of energy compared to prior art processes even if paradoxically, more energy is spent during the thermal pre-desolventization step. This energy saving is a major advantage of the desolventization process according to the present invention and particularly unexpected since, simultaneously, meal of better quality is produced. For a given capacity, the energy saving is at least of 10% compared to a desolventization process of the prior art based on a DTDC, because, systematically, a deeper pre-desolventization will be realized.

[0062] Another shortcoming of current processes for the desolventization of extraction residues is the need for a substantial moisture adjustment step after the desolventization steps. This moisture adjustment step aims at adjusting the moisture content of the fully desolventized residue in order to obtain a meal that can be safely stored for an extended period of time without apparition of mould, yeast or other degradations. As a matter of fact, since meal is sold by weight, the maximal moisture still allowing a safe storage for an extended period of time is wished by the processors. The exact values depend on the processed vegetable material but for the most prevalent vegetable material (soybean, rapeseed and sunflower) it will typically ranges between 10% (w / w) and 12.5% (w / w). The experience shows that, in most instances, for the current processes used for the desolventization of extraction residues, depending on the processed vegetable material, a drying step is necessary after the steam stripping desolventization step. On the contrary, in a few instances, for some materials, a moisturising step may be necessary if for example too much moisture is evaporated during the thermal pre-desolventization step. Both situations induce additional energy consumption in the sense that the energy is consumed to evaporate too much water. The cause of such unfavourable situation is either insufficient thermal pre-desolventization systematically occurring in a DTDC, or excessive pre- desolventization occasionally occurring during the flash-loop pre-desolventization.

[0063] Typically, in a DTDC, the thermal pre-desolventization removes only a few percents of solvent and therefore, since a large fraction of the solvent must be removed by steam-stripping, it means that a substantial quantity of moisture will condense in the residue. Consequently, there is an excess of moisture in the fully desolventized residue and an energy demanding drying step is necessary. In this situation, there is a waste of energyto evaporate water that have been added to the residue during the intense steam-stripping desolventization.

[0064] Typically, during a flash-loop pre-desolventization, the solvent stripping which is realized at high temperature also removes a substantial quantity of moisture from the residue and the experience has shown that in some instances, even if some moisture was added to the residue during the steam-stripping step, the fully desolventized residue it too depleted in moisture. This induces a weight loss if this fully desolventized residue is cooled to yield a meal and thus represent a financial penalty. This situation also represents a waste of energy because a fraction of the energy injected during the flash-loop pre- desolventization has been wasted to evaporate an excessive amount of moisture contained in the residue.

[0065] It must be noted that for the two current pre-desolventization processes, involving either horizontal pre-desolventizing tray(s) of a DTDC or a flash-loop pre- desolventizer, it is difficult to adjust the quantity of moisture that is removed from the residue during the pre-desolventizing step by modifying process parameter(s). Indeed, those two currents pre-desolventization processes are not flexible enough. In the case of a pre-desolventization realized in a DTDC, one of the possibilities to increase the amount of removed solvent and water would be to rise the temperature of the pre-desolventizing tray(s). But this is not practical because it would further increase the amount of overtoasted particles. Adding more pre-desolventizing trays is a theoretical solution but is not realistic since this would result in very large and costly piece of equipment. A flash-loop pre-desolventizer is sized to operate with super-heated solvent (in most instance hexane) at a given high temperature and for a given very short residence time. Even if the temperature can be adjusted, the experience has shown that several flash-loop installations deliver excessively dry pre-desolventized residue.

[0066] In sharp contrast with current processes for the desolventization of extraction residues, the thermal pre-desolventization according to the present invention and making use of disc dryer(s) can be sized and fine-tuned with process parameters in order to adjust the remaining moisture level of the pre-desolventized residue to the extent that the final moisture level of the fully desolventized residue corresponds to the wished moisture range contained in the meal. Therefore, in this case, no moisture adjustment step is necessary, and a simple cooling step after the steam-stripping step will yield a meal having the wished moisture level. Thus, in the desolventization process according to the present invention,the extent of the pre-desolventization step can be adjusted with a much greater amplitude compared to currently available technologies. Indeed, the sizing of the disc dryer(s), the temperature of the residue, the residence time of the residue in the disc dryer(s) and the operating pressure can be adjusted widely, easily, and safely. However, the present invention is not limited to this precise embodiment and remains advantageous even if this optional optimization is not applied. If this optional optimization is not applied, a moisture adjustment step is needed after the steam-stripping desolventization step as depicted in Fig. 1. Fig. 1 is a block diagram of an embodiment of the desolventization process according to the present invention listing its successive steps: the thermal pre-desolventization of the residue in one or more disc dyer(s) to obtain a partially desolventized residue, the steam stripping desolventization of the partially desolventized residue to obtain a fully desolventized residue containing less than 0.05% (w / w) of flammable solvent, the moisture adjustment of the fully desolventized residue and the cooling of the fully desolventized and moisture adjusted residue to obtain a meal.

[0067] Thus, a particularly advantageous embodiment of the process according to the present invention even allow to suppress the moisture adjustment step i.e., the drying step or in some instance a hydration step. By adjusting the intensity of the two distinct desolventization steps it is possible to obtain a fully desolventized residue having the targeted moisture content right after the steam-stripping desolventization step. At this point the residue just needs to be cooled to a temperature close to room temperature to yield a meal having the targeted moisture level. Such optimization is the best mode of the present invention and requires adjustments that are much easier to implement in the present invention than with current desolventizing technologies. Such embodiment is depicted in Fig. 2. Fig. 2 is a block diagram of this preferred embodiment listing its successive steps: the thermal pre-desolventization of the residue in one or more disc dyer(s) to obtain a partially desolventized residue, the steam stripping desolventization of the partially desolventized residue to obtain a fully desolventized residue containing less than 0.05% (w / w) of flammable solvent and the cooling of the fully desolventized residue to obtain a meal.

[0068] Thus, more generally, in the desolventization process according to the present invention, the moisture adjustment after the steam-stripping step is optional as depicted in Fig. 3. Fig. 3 is a block diagram of one of the embodiments of the present invention listing its successive steps: the thermal pre-desolventization of the residue in one or more discdyer(s) to obtain a partially desolventized residue, the steam stripping desolventization of the partially desolventized residue to obtain a fully desolventized residue containing less than 0.05% (w / w) of flammable solvent, the optional moisture adjustment of the fully desolventized residue and the cooling of the fully desolventized and optionally moisture adjusted residue to obtain a meal.

[0069] This energy saving is a major advantage of the desolventization process according to the present invention and particularly unexpected since, simultaneously, meal of better quality is produced. For a given capacity, the energy saving is at least of 10% compared to a desolventization process of the prior art based on a DTDC, because, systematically, a deeper pre-desolventization will be realized.

[0070] Thus, compared to a classical desolventization process based on a DTDC, the present innovative desolventization process allows substantial energy savings the extend of them depending on the material processed and on various conditions. Consequently, less effluents are produced, in particular less solvent-laden vapours are generated during the steam-stripping step, and less contaminated air is generated during the drying step. Indeed, as processed residue always contains some dust and fines, the hot air exiting the drying step will not only be laden with moisture but with dust and fines as well. For a given capacity, the desolventization process according to the present invention will generate at least 10% less effluent compared to a desolventization process of the prior art based on a DTDC. Indeed, when the pre-desolventization is realized in a DTDC, the steam-stripping is systematically very intense which induce too much water condensation in the residue, hence an intense drying is necessary which generates a large volume of hot exhaust air containing fine, dust and volatile matters.

[0071] The thermal pre-desolventization step must be progressive to avoid any flashevaporation effect that is known to jeopardize the integrity of the processed residue by creating a fragile porous structure. Such problem is encountered in the flash-loop pre- desolventization process wherein a relatively large fraction of the solvent is removed in a very short time at high temperature and results, after the full completion of the desolventization process, in a meal containing a lot of fine and dust.

[0072] Accordingly, in the present invention, if the thermal pre-desolventization step is operated under reduced pressure, process adjustments are implemented to still obtain a progressive evaporation of the solvent without flash effect. In practice, the reduced pressure is preferably above 400 mbara and ranges thus between about 400 mbara and about1000 mbara (atmospheric pressure at sea level). For example, at 400 mbara , it has been observed that a retention time of about 10 minutes in the disc dryer(s) was necessary to remove 70% of the solvent (hexane) contained in rapeseed extraction residue heated at 60°C. In those conditions, no marked flash evaporation occurred. In those conditions, the final meal obtained after the completion of the full desolventization process contained some fine (about 10%) which is considerably less compared to existing process, notably the desolventization process including a flash-loop pre-desolventization. As a matter of fact, the fines created during the thermal pre-desolventization realized in disc dryer(s) and according to the present invention, are mostly due to mechanical mixing and are still relatively coarser while the resulting pre-desolventized residue is not particularly fragilized nor brittle. Applying reduced pressure lower than 400 mbara will increase the risk of having a more marked flash evaporation when the temperature of the processed residue is of the same (60°C) and the solvent is commercial hexane (containing mostly n-hexane isomer). It is believed that for other solvents, the reduced pressure threshold to avoid a flash evaporation may be shifted according to their boiling point but that no substantial flash evaporation will be observed as long as the needed residence time in the disc dryer(s) in order to remove about 70% of the solvent of the extraction residue is in excess of 10 minutes.

[0073] Accordingly, the residence time of the residue in the disc dryer in order to remove about 50% to 70% of the flammable solvent contained it the extraction residue should not be inferior to 10 minutes in order to avoid substantial flash evaporation of the solvent. However, the residence time of the residue in order to remove about 50% to about 70% of the flammable solvent should not be excessive in order to avoid too much mechanical degradation of the residue causing fine and dust. Accordingly, the residence time of the residue in the disc dryer in order to remove about 50% to about 70% of the flammable solvent contained it the extraction residue should not be in excess of 60 minutes.

[0074] The temperature of the extraction residue during the thermal pre- desolventization should be maintained as low as possible in order limit the degradation of the proteins contained is said residue. Typically, the temperature should not exceed much the boiling point of the flammable solvent contained in the extraction residue. At atmospheric pressure, the temperature of the extraction residue should not exceed the boiling point of the solvent contained in the residue by 10°C. At reduced pressure, the temperature of the extraction residue should not exceed the boiling point of the solventcontained in the residue and could even be below its boiling point. As a matter of fact, the temperature of the residue during the thermal pre-desolventization is adapted in order to obtain a proper pre-desolventization without apparition of over-toasted particles and excessive amount of fine with the goal of removing from about 50% to 70% of the solvent contained in the extraction residue within a residence time in the disc dryer ranging from about 10 minutes to about 60 minutes. Practically, for any type of extraction residue containing flammable solvent that was not processed before according to the present invention, a first orientation pre-desolventization test can be done according to the following protocol: pre-desolventization for 20 minutes, residue temperature equalling the boiling temperature of the solvent, atmospheric pressure. According to the remaining solvent content in the pre-desolventized residue obtained after the completion of this orientation test, those parameters can be adapted, for example by increasing the residence time and or the residue temperature if it has been observed that the amount of evaporated solvent in below expectation.

[0075] The second step of the process according to the present invention does not need to be detailed since desolventization by steam-stripping is an established desolventization technique well known by any skilled artisan in the field. Nonetheless, usually, the amount of stripping steam needed to fully desolventize the pre-desolventized residue obtained by the present invention can be divided at least two times compared to pre-desolventized residue originating from the pre-desolventizing trays of a DT. Conversely, the residence time can also be reduced considerably.

[0076] Thus, the meal delivered with the innovative desolventization process is homogeneous and does not contain burned particles, possesses proteins of superior quality and contains a limited quantity of fine (compared to white flakes). Furthermore, the new desolventization process including a pre-desolventization making use of one or more atmospheric or vacuum operated disc dryer(s) is compact, having a smaller footprint than the pieces of equipment in standard desolventization processes while still offering a substantial buffer capacity. Furthermore, new desolventization process including a pre- desolventization making use of one or more atmospheric or vacuum operated disc dryer(s) is able to deliver a pre-desolventized residue having respectively less than 10 % or less than 5 % of residual solvent. Hence, the final steam stripping desolventization step of such deeply pre-desolventized residue requires a less intense steam stripping compared to pre- desolventized residue obtained by conventional pre-desolventization. Therefore, theenergy demand for the final steam-stripping desolventization and moisture adjustment (in most instances a drying) of this deeply pre-desolventized residue, produced according to the present process, is reduced. The vacuum is easily maintained in the disc dryer(s) which has a substantially more compact volume for an equivalent capacity than a large compartmented DTDC. Indeed, for a given capacity, the internal volume of the disc dryer is at least the half of the internal volume of DTDC. Therefore, the energy demand to maintain a given vacuum in the innovative process making use of one or more disc dryer(s) is reduced compared to existing process. Safety is also greatly increased since the risk of leakage and air ingress in the vacuum operated disc dryer is nearly inexistant and power outage does not induce catastrophic consequence since it is easy to open the disc dryer(s), remove any material and clean each disc and any other internals. The above advantageous results are surprising and could not be expected before observations by experimentations.

Claims

CLAIMS1. A process for the desolventization of an extraction residue containing flammable solvent comprising the following steps: a) a thermal pre-desolventization of the residue to obtain a partially desolventized residue, b) a steam stripping desolventization of the partially desolventized residue obtained in step (a) to obtain a fully desolventized residue containing less than 0.05% (w / w) of flammable solvent, c) an optional moisture adjustment of the fully desolventized residue obtained in step (b) to obtain a moisture adjusted fully desolventized residue, and, d) cooling the fully desolventized residue of step (b), or the moisture adjusted fully desolventized residue of step (c) to obtain a meal, characterized in that the thermal pre-desolventization of step (a) is realized in one or more disc dryer(s).

2. A process according to claim 1 wherein the extraction residue contains flammable solvent in a concentration ranging from 20% (w / w) to 40% (w / w) and wherein said flammable solvent is any flammable solvent used for the specific extraction of fatty matters from oleaginous vegetable material.

3. A process according to claim 1 wherein the moisture content of the residue decreases during step (a) and increases during step (b) and wherein the relative desolventization intensities of step (a) and of step (b) are adjusted to obtain a fully a desolventized residue after step (b) having a moisture content ranging from 10% (w / w) to 12.5% (w / w).

4. A process according to claim 1 wherein the flammable solvent is commercial hexane comprising at least 50% (w / w) of n-hexane.

5. A process according to claim 1 wherein the flammable solvent is commercial isohexane comprising at least 50% (w / w) of 2-methylpentane.

6. A process according to claim 1 wherein the thermal pre-desolventization of step (a) of the extraction residue is realized in at least two disc dryers connected in series or in parallel.

7. A process according to claim 1 wherein the absolute pressures applied during the thermal pre-desolventization of step (a) ranges from 400 mbara to 1,000 mbara.

8. A process according to claim 1 wherein the thermal pre-desolventization of step (a) is realized at atmospheric pressure and said thermal pre-desolventization is reducing the content of flammable solvent contained in the extraction residue by at least 50%.

9. A process according to claim 1 wherein the thermal pre-desolventization of step (a) is realized at reduced pressure and said thermal pre-desolventization is reducing the content of flammable solvent contained in the extraction residue by at least 70%.

10. A process according to claim 1 wherein the thermal desolventization of step (a) is occurring progressively without flash evaporation and wherein the residence time of the residue in the one or more disc dryer(s) is ranging from 10 to 60 minutes.

11. A process according to claim 1 wherein the meal obtained in step d) does not contain over-toasted particles and less than 30% of fines.

12. A process according to claim 1 wherein the meal obtained in step d) has protein quality parameters (PDI, KOH solubility) at least 10% superior to the typical protein quality parameters of meal obtained with a DTDC (Desolventizer Toaster Dryer Cooler) having stacked horizontal trays.

13. A process according to claim 1 wherein the buffer capacity during the thermal pre- desolventization of step (a) is at least 10 minutes.

14. A process according to claim 1 wherein, for a given capacity, the effluent generated during step (c) is reduced by at least 10% compared to the effluent generated during the cooling step of DTDC (Desolventizer Toaster Dryer Cooler) having stacked horizontal trays.

15. A process according to claim 1 wherein, for a given capacity, the energy demand is reduced by at least 10% compared to the energy demand of a desolventization process realized with DTDC (Desolventizer Toaster Dryer Cooler) having stacked horizontal trays.

16. A process according to claim 1 wherein, the extraction residue of step (a) contains from20% (w / w) to 40% (w / w) of simple and complex sugars (including polysaccharides).

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