GB2176713A - Process and plant for deodorising and/or physical refining of high-boiling liquids - Google Patents

Abstract

The deodorizing and/or physical refining of high-boiling liquids such as edible oils, fats, glycerides and other high-boiling esters as well as fatty acids takes place at a working pressure of less than 10 mbar at a liquid temperature of 180 to 280 DEG C. For a significant increase in the liquid throughput under these working conditions in conventional plants equipped with plate columns or the like without a simultaneous increase in the quantity of stripping steam and/or the capital investment and operating cost of the vacuum unit, the steam once utilized as stripping steam in the one or "old" plant part 10, after cooling and substantial removal of volatile matter, is again introduced as stripping steam into another, "new" plant part 30 and used therein for stripping volatile matter from already pretreated or from untreated liquid, whereupon it is again cooled, substantially freed from volatile matter and fed to the vacuum unit. Because of the low pressure loss, a single-stage or multi-stage falling-film column is especially provided as the other or "new" plant part. <IMAGE>

Description

SPECIFICATION Process and Plant for Deodorizing and/or Physical Refining of High-boiling Liquids The invention is directed to the deodorizing and/or physical refining of high-boiling liquids, i.e., edible oils, fats, glycerides and other high-boiling esters as well as fatty acids. To this end the invention provides a novel process and a novel plant for carrying out the process.

More in detail, the invention is directed to a process for deodorizing and/or physical refining of high-boiling liquids such as edible oils, fats, glycerides and other high-boiling esters as well as fatty acids, in which the liquid, which has been heated to atemperatureof 180to 280"C, is treated at a working pressure of less than 10 mbar in a part of the plant with stripping steam, the steam laden with volatile matter is collected, cooled and finally, after separation of most of the volatile matter, withdrawn by a vacuum unit which ensures the working pressure.

Known processes of this type are conducted, for example, in simple distillation apparatus, in continuously operating columns having overflow plates, in continuously operating bubble-plate columns, or in continuously operating columns having overflow plates and wire cloth packings with low pressure losses. The term "plate column or the like" is to comprise all of these conventional plants.

Typically, about 15 to 40 kg of stripping steam is required in such plants for the treatment of it of liquid.

The steam which is laden with volatile matter is mostly cooled in a jet condenser where the condensate is circulated. For the deodorizing and/or physical refining of edible oils, this condensate predominantly consists of free fatty acids. A separate coolant circuit is provided for indirect cooling of the circulating condensate, so that the condensate at a temperature of c. 50 to 800C according to its solidification point is sprayed into the flow of steam laden with volatile matter.

Typically, such jet condensers are operated at an overhead pressure of about 3 to 10 mbar.

The vacuum unit of such conventional plants for deodorizing and/or physical refining of edible oils is mostly designed for a pressure range from about 2 to 8 mbar.

Furthermore, the deodorizing and/or physical refining of edible oils according to the principle of continuous counter-current falling-film strippingsteam distillation in an externally imposed temperature field in a single-stage falling-film column (see the DE-OS 2,941,101) or in multi-stage falling-film columns (see the DE-PS 3,227,669) has sump of the final zone. In such single-stage or multi-stage falling-film columns the pressure loss across all of the stages may be maintained below 2.0 mbar.

In all of these known processes, irrespective of whether they operate with the conventional plate columns or the like or with the modern single-stage or multi-stage falling-film columns, the steam introduced as stripping steam is contacted with the treated liquid only once. After cooling and separation of most of the volatile matter this once-used steam is withdrawn by the vacuum unit.

In practical use the problem frequently arises that the existing older plants operating with a plate column or the like for deodorizing and/or physical refining of high-boiling liquids, in particular of edible oils, should be retrofitted at minimum capital investment cost for a higher liquid throughput.

These older single-stage plants mostly operate at an overhead pressure of about 3 to 10 mbar in the jet condenser and require about 1.5 to 4.0 wt.% of stripping steam, based on the liquid throughput. In particular, the already existing vacuum unit, which is in most cases designed for a pressure of about 2 to 8 mbar, is to be retained. The capacity of the vacuum unit determines the allowable flow rate of stripping steam and thus practically determines the purifying capacity of the plant, because the quantity of stripping steam used must be discharged from the vacuum unit and consequently has a decisive influence on the steam requirements of the vacuum unit.In practical use, it is estimated that at a cooling-water injection temperature of 2500 the consumption of steam for the compressioncondensation of the vapours, which are to be withdrawn and consist almost exclusively of steam, amounts to about six times the quantity of stripping steam.

Based on a process of the kind specified above, it is the object of the instant invention to achieve a considerable increase in the liquid throughput in the deodorizing and/or physical refining of edible oils, fats, glycerides and other high-boiling esters as well as fatty acids in conventional plants equipped with plate columns or the like, while at the same time the quantity of stripping steam and/or the capital investment and operating costs of the vacuum unit must not be increased. Furthermore, a plant for carrying out this improved process shall be provided.

The solution of this object in accordance with the invention is a process comprising the measures specified in claim 1 or claim 2 and, respectively, a plant comprising the features specified in claim 14.

Advantageous embodiments and further improvements of the invention will be apparent untreated liquid, is thereupon cooled again and substantially freed from volatile matter and is supplied to the vacuum unit. Preferably, the other or "new" part of the plant is a single-stage or multistage falling-film column, and the steam cooled in the jet condenser of the one or "old" part of the plant and largely freed from volatile matter is introduced into the sump of said falling-film column.

The plant according to the invention for carrying out the novel process provides at lesat the following equipment: - a plate column or the like; - a first jet condenser communicated to the head of said plate column; ~at least one falling-film column; - a vapour conduit leading from the head of said first jet condenser to the sump of said falling-film column; - a second jet condenser communicated to the head of the falling-film column; - a live-steam introducing conduit into the plate column or the like; and - a vapour withdrawing conduit leading from the head of the second jet condenser to the vacuum unit.

The following explanations specifically refer to the deodorizing and/or physical refining of palm oil, but the basic experience may readily be transferred also to other trig lycerides and the like. In addition to the fatty acid glycerides, palm oil and other vegetable oils contain a proportion of light ends in the order of about 5 wt.%. The main proportion consists of free fatty acids in addition to a great number of further components such as water, pigments, stabilizers, odorous and/orflavouring compounds and the like. In the course of the counter-current stripping steam treatment these light ends and -degradation products such as hydrocarbons, methyl ketones and aldehydes concentrate in the stream of vapours.In conventional plate columns it is possible at a temperature of 2600C and a working pressure of 2.5 mbar and with an amount of stripping steam of 1.5 to 3 wt.% of the palm oil throughput to reduce the light ends content in the treated oil to less than 0.03 wt.%.

In the jet condenser, the stream of vapours is contacted with a spray jet of recirculated condensate which consists substantially of fatty acids and has a temperature of about 50 to 80 C, in the case of palm oil of 60 to 800C. Thereby the organic components contained in the gas stream stream discharged from the jet condenser may be utilized for the additional deodorizing and/or physical refining of 1.5 to 2.5 times the amount of palm oil without constituting an additional load on the vacuum unit.

In practical deodorizing and/or physical refining of high-boiling liquids, in particular of edible oils, this results in a considerable cost saving, because the costs for the provision and withdrawal of the stripping steam constitute the greatest cost factor.

In accordance with the process of the invention, it is possible to deodorize and/or physically refine threetimes the quantity of liquid without any increase in the stripping steam cost as compared to conventional processes.

Forthe purpose of increasing the liquid throughput, the supplementation of conventional plants equipped with plate columns or the like by an additional single-stage or multi-stage falling-film column including a second jet condenser has in many cases proven cheaper than the setting-up of a completely new plant with the desired throughput.

The "new" or other plant part to be additionally provided must ensure low pressure losses so that the suction capacity of the existing vacuum unit will suffice and the steam supply to the vacuum unit need not be increased. Even in a three-stage fallingfilm column, which in the direction of the tricklingdown oil has progressively decreasing trickle passage diameters from one stage to the next, the overall pressure loss is below 0.8 mbar with overall exchanger lengths of up to 20 m. In combination with a matching jet condenser, the overall pressure loss of the additional other plant part may be kept below 2.0 mbar, preferably below 1.4 mbar.

The amount of stripping steam put through the "old" plant part suffices-after substantial separation of volatile matter-for deodorizing and/ or physically refining approximately 1.5 to 2.5 times the quantity of liquid. There are several alternatives for conducting the liquid. Basically, it would be possible to put the total liquid quantity first through the old plant while decreasing the proportion of light ends down to a residual content of about 0.7 to 0.9% and then to feed the obtained liquid to the manifold in the head of the new plant part where the residual deodorizing and/or physical refining is conducted down to a light-ends content of less than 0.05%. However, this mode of operation is less expedient, because in most cases the capacity of the first jet condenser associated with the old plant will not suffice for the higher throughput so that great pressure losses may occur therein.

It has proven more expedient to maintain the conventional liquid throughput through the old explanation of the presentinvention~shall be incorporated herein by reference. For this process sequence, for example, a dual-stage falling-film column has proven satisfactory which is designed for a throughput of 10,000 kg/h of palm oil comprising 5% of fatty acids and which has trickle passage hydraulic diameters of 73 to 150 mm in the initial zone directly succeeding the liquid supply and has trickle passage hydraulic diameters of 25 to 33 mm in the final zone. For the initial zone, c. 2 theoretical plates are required, and for the final stage c. 6 theoretical plates are required, so that a total exchanger length of c. 8 to 16 m will be sufficient.

It is particuarly advantageous to treat the total liquid quantity first in the new plant part and to separate herein the major proportion of light ends down to a residual content of about 0.5%. To this end, merely about 2 to 3 theoretical plates are required. These may be implemented very easily in a single-stage falling-film column having comparatively wide trickle passage diameters. For this process sequence a falling film column having, for example, an exchanger length of merely 3 to 6 m has proven satisfactory, the diameters of the trickle passages being between 40 and 120 mm. For this process sequence it is especially preferred to use a single-stagefalling-film column having an exchanger length of about 4 m and trickle passage hydraulic diameters of 60 to 90 mm.For a throughput of 10,000 kg/h of palm oil, about 60 trickle passages having a diameter of 84 mm are required, which may easily be realized in an indirectly heated shell-and-tube column. The thus treated liquid is thereupon introduced into the oil plant part, where the content of light ends is reduced to below 0.05%, preferably to below 0.03%.

The resulting product may then be used as edible oil. This process sequence permits tripling of the oil throughput at minimum capital investment cost and is preferred in accordance with the invention.

Having regard to the high working temperatures of up to 2800C, the medium-pressure steam available from usual sources has proven to be insufficiently inert for use as stripping steam. Traces of lubricant separated from valves and the like may cause discolorations of the liquid. Residual amounts of air cause autoxidation and lead to the formation of peroxide. It is therefore preferred to use as stripping steam so-called inert steam produced from previously distilled and degasified water. This inert live steam is preferably introduced exclusively into the "old" plant part, for example into the plate column or the like.

The steam used once in the "old" plant part as stripping steam has a temperature of 50 to 800C after pressure loss in the heat exchanger should be minimized.

Moreover, it is possible in a manner known per se to effect degasification and partial dehydration of the liquid to be treated before the same is heated to the working temperature. Suitably, degasification is conducted at relatively low temperatures between 40 and 100"C, preferably between 60 and 80 C, and at a working pressure of about 100 to 280 mbar, preferably between 120 and 200 mbar. Under these conditions the crude oil is sufficiently degasified but not completely dried. Rather, a residual proportion of dissolved water in the order of 0.005 to 0.2 wt.% remains in the crude oil, said residue promoting the stripping of volatile matter at the provided working pressure of less than 10 mbar.

The invention is directed to the deodorizing and/or physical refining of high-boiling liquids, i.e., of edible oils, fats, glycerides and other high-boiling esters as well as fatty acids. "High-boiling" in this context means that the treated liquid would boil already above its decomposition temperature of about 3000C at a negative pressure of 12 mbar.

Suitable edible oils comprise, for instance, palm oil, soy bean oil, cotton seed oil, coconut oil, palm kernel oil, rape-seed oil, olive oil, wheat germ oil, hydrogenated fish oil and the like. Suitable fats comprise, for example, beef tallow, hog fat, mutton tallow and the like. Suitable glycerides comprise, in addition to the triglycerides, the mono- and diglycerides of any fatty acids, such as synthetic triglycerides which will melt at body temperature (for example bases for suppositories). Other high boiling esters comprise, for example, the esters of phthalic acid, sebacic acid and the like which may be used as plasticizers, as well as the esters of higher alcohols with fatty acids such as butyl stearate and similar esters.Suitable fatty acids are, for example, higher-boiling anhydrized fatty acids of fish oils and other hydrogenated fatty acids in order to remove the hydrogenation odour thereof. The process according to the invention is also suitable for removing the hydrogenation odour of other hydrogenated fats and oils.

Moreover, the invention might also be employed for the mild distillative purification of other, thermally sensitive compositions whose separable components have a vapour pressure higher by several powers of ten than that of the higher-boiling thermally sensitive substance.

Below, the plant for carrying out the process according to the invention will be explained by means of preferred embodiments thereof with reference to the drawing, in which Fig. 1 is a flow diagram of a plant in which the total liquid volume is initially put through the other, plant part, i.e., a multi-stage falling-film column; and Fig. 3 is an embodiment of the new plant part according to Fig. 2, wherein a degasification vessel, a jet condenser, a heat exchanger and the dualstage falling-film column are integrated in a single column section.

As will be apparent from Fig. 1, the overall plant for deodorizing and/or physical refining in its main portions~apartfrom the usual components of such plants such as pipelines, pumps, fittings, regulating means and the like, which are not specified in detail-mainly comprises the conventional one plant part including the degasification stage 4, the heat exchangers 27 and 28, a conventional column 10 equipped with overflow plates, the (first) jet condenser 14 thereof with condensate cooler 16, a vacuum-producing unit 22, 23, the stripping steam supply 12 and the discharge line 25 for the finished product; the other, new or additional plant part includes the single-stage falling-film column 30, the (second) jet condenser 32 thereof with condensate cooler 34, and the vapour withdrawal line 39 leading to the vacuum unit22.

As will be apparent in more detail from Fig. 1, the crude oil is fed from a storage tank 1 by means of the pump 2 through the line 3 to the head of the degasification stage 4. The degasification stage 4 may be a simple flash vessel or, preferably, may be designed as a trickling column, as illustrated schematically. For example, the degasification stage 4 is operated at a working pressure of 200 mbar. By means of the liquid level regulator in the sump of the degasification stage 4 it is ensured that a correspondingly high column of liquid is always provided at the intake side of the delivery pump, which is connected downstream of the stage 4 via the line 5, by means of which liquid column a slight overpressure may always be ensured in the pump 6.

It is thereby possible to prevent-even when the less expensive pumps equipped with packings are used as the delivery pump 6~oxygen from the air from re-entering into the already degasified oil.

From the delivery pump 6, the oil is passed through the line 7 to a heat exchanger 27 where heating of the degasified but still water-containing oil occurs by heat exchange with the hot finished oil. The crude oil preheated in the heat exchanger 27 is passed through the line 8 to the high-temperature heat exchanger 9 where heating to the working temperature takes place by heat exchange with a high-temperature heating medium.

The crude oil, which has been heated to the working temperature in the high-temperature heat exchanger, is then passed to the manifold disposed an exchanger length of from 3 to 6 m. Preferably, said trickle passages have a hydraulic diameter of about 80 to 100 mm with an exchanger length of about 3 to 4 m. For example, indirectly heated shell-and-tube columns, in which the liquid film trickles down the inner walls of the tubes, are well suited. In the embodiment described with reference to Fig. 1, a tube bundle having 60 tubes (inner diameter 84 mm, exchanger length 4 m) is provided inside the falling-film column 30, the liquid film trickling down the inner walls of said tubes.

Inside the falling-film column 30, heating medium flows about every single tube of the tube bundle, said heating medium being supplied from a predetermined source through the port 36 and being discharged through the port 37. At the provided temperature range, high-pressure vapour or a high-temperature oil such as, for example, "HT-oil" (higher aromatic compounds) may serve as heating medium, wherein the use of the hightemperature oil causes a temperature gradient on the side of the heating medium and is therefore preferred. As illustrated, the heating medium flows counter-current to the liquid film trickling down, so that optimum heat transfer is ensured, on the one hand, and superheating of the liquid is prevented, on the other hand.

The mixture collected in the head ofthefalling film column 30 and consisting of contaminated carrier steam, free fatty acids separated from the crude oil, degradation products and other light ends is withdrawn through line 31 and introduced into the jet condenser 32. The pump 33 withdraws the condensate accumulating in the sump of the jet condenser 32 and squeezes it into a recirculating line which passes through the cooler 34. Part of the condensate at a temperature of about 600C is blown into the vaporous stream. The remainder of the condensate is continuously withdrawn through the line 35. In the head of the jet condenser 32 there is furthermore provided a mist eliminator 38, for example a so-called "Euro-Form" eliminator, in which liquid material is eliminated. The vapours having passed through the mist eliminator 38 are supplied to the first booster stage of the vacuum unit 22, 23 via a sufficiently dimensioned vapour withdrawing line 39 so as to ensure minimum flow pressure losses. The suction side of this first booster stage 22 is kept at a pressure of 2 to 4 mbar.

The oil flowing down the inner walls of the tube bundles in the falling film column 30 is collected in the sump thereof and is withdrawn via line 24 leading to the manifold above the uppermost overflow plate 11 inside the plate column 10; if required, this supply line 24 may pass through a liquid level. The finished oil is finally withdrawn through line 25 from the sump of the plate column 10 and is squeezed by the pump 26 through the heat exchanger 27 where it releases the essential part of its sensible heat to the crude oil to be treated. In order to improve the storage stability of the finished oil, a complexing agent such as citric acid may be introduced into the partially cooled finished oil from a supply through the metering valve 29.To ensure good storage stability of the finished oil, further indirect cooling is finally effected by means of cooling water in the heat exchanger 28 down to the lowest possible temperature at which the corresponding finished oil may still be pumped. If applicable, polishing may subsequently be provided in an inert gas atmosphere.

The vapours collecting in the head of the plate column 10 are discharged through line 13 and passed into the (first) jet condenser 14. The vapours are cooled in contact wihh recirculating condensate, the organic components are condensed and substantially scrubbed. The condensate accumulating in the sump of the jet condenser is delivered by the pump 15 through the cooler 16, where it is cooled to c. 60"C. Part of the cold condensate is blown into the vaporous stream, and the remainder is withdrawn through line 17. A mist eliminator 18 provides for complete elimination of all liquid droplets.To ensure minimum flow pressure loss, a sufficiently dimensioned vapour conduit 19 extends from the head of the (first) jet condenser 14 via the heat exchanger 20 to the sump of the falling-film column 30; i.e., the vapours which accumulate in the head of the jet condenser 14 after substantial separation of volatile matter and which consist of more than 99.9% of water vapour, are re-introduced after heating to the working temperature of 180 to 280 C into the falling-film column 30 as stripping steam and flow through the trickle passages thereof in counter-current flow to the down-trickling crude oil. The heat exchanger 20 must likewise exhibit minimum pressure losses (below 1.3 mbar) and may, for instance, have longitudinal finned tubes on the water vapour side to be heated.

It is possible in a plant of the kind described to perform the physical refining of crude oil as well as the deodorizing of physically pre-refined oil.

Suitably, the respective operating conditions differ from each other as described, for example, in the DE-PS 3,227,669.

If the liquid was already previously neutralized chemically and only a deodorizing treatment is to be conducted, higherthroughputswill be possible in a given plant.

With reference to Fig. 2 a further embodiment of liquid communication with each other, and the associated jet condenser 65.

Again, the crude oil is supplied from a storage tank 1 by means of the pump 2 through the line 3 to the head of the degasification stage 4. The degasified material accumulating in the sump of the degasification stage 4 is withdrawn through line 5 and is partitioned as desired by means of the valve combination V1 and V2. One part is heated in the usual way in the heat exchanger 45 by heat exchange with the finished oil withdrawn from the sump of the bubble-plate column 40 and is supplied through line 47 to the high-temperature heat exchanger 48, where heating to the working temperature is effected by heat exchange with a high-temperature heating medium. Thereupon this part of the heated liquid is charged to the topmost bubble plate 41 of the bubble-plate column 40 and contacted in the usual way with stripping steam introduced through the stripping steam supply 42.

The finished oil is withdrawn through line 43 and is squeezed by the pump 44 through the heat exchangers 45 and 46. The heat exchanger 46 cools the finished oil to a temperature at which it is still just fluid and may be passed to further processing stages.

The vapours collecting in the head of the bubbleplate column 40 are discharged through the vapour line 51 and supplied to the (first) jet condenser 52.

Therein, condensation and scrubbing of the organic components takes place in contact with recirculating condensate, as has already been described. After passing through the mist eliminator 53 in the head of the jet condenser 52, the water vapour is withdrawn through the sufficiently dimensioned vapour line 54, again heated to working temperature in the heat exchanger 55 and subsequently introduced as stripping steam into the "new" plant part.

The "new" plant part comprises the falling-film columns 60 and 70, which are in mutual vapour and liquid communication. The initial zone is realized in the falling-film column 60, which has an exchanger length of 2 to 6 m. This column 60 is provided with trickle passages having a hydraulic diameter of 73 to 120 mm. Preferably, said trickle passages have a hydraulic diameter of about 84 to 108 mm with a trickle passage length of about 3 to 5 m. For instance, indirectly heated shell-and-tube columns, in which the liquid film trickles down the inner walls of the tubes, are well suited. In the embodiment described with reference to Fig. 2, a tube bundle with 60 tubes (inner diameter 84 mm, length 4 m) along whose walls the liquid film flows downwards is provided within the falling-film column 60.

The quantity of degasified liquid partitioned in high-temperature heating medium. The crude oil, which has been heated to the working temperature, is finally charged onto the manifold in the head of the falling-film column 60 and thence passed to the inner walls of the individual trickle passages. Within the falling-film column 60, heating medium flows around every single tube of the tube bundle, the heating medium being supplied from a predetermined source via the port 61 and being discharged via the port 62. The product accumulating in the sump of the column 60 contains about 10% of the initial proportion of contaminants.

This sump product is charged through line 63 onto the manifold in the head of the second falling-film column 70.

In this second falling-film column 70 the remaining proportion of contaminants is substantially stripped off. Since this proportion is relatively small, there occurs only a slight pressure loss. On the other hand, to ensure the required number of 5 to 6 plates, trickle passages having an exchanger length of 6 to 10 m and a trickle-passage diameter of 25 to 40 mm are provided. Preferably, these trickle passages have a hydraulic diameter of 28 to 35 mm at a trickle passage length of about 8 m.

In the embodiment described with reference to Fig.

2, this second falling-film column 70 includes a tube bundle having 150 tubes (inner diameter 33 mm, length 8 m) about which heating medium flows that is supplied via the port 71 and is discharged via the port 72. The crude oil flows down the inner walls of these tubes, wherein simultaneously the remaining low-boiling companion substances are separated, and finally reaches the sump of the falling-film column 70. The finished oil is withdrawn through the line 73 from the sump of the falling-film column 70 and squeezed by means of the pump 74 through the heat exchanger 75, where it releases the major proportion of its sensible heat to the crude oil to be treated.In order to achieve good storage stability, further indirect cooling with cooling water is finally effected in the cooler 76 down to the lowest possible temperature at which the finished oil may just be pumped.

The stripping steam, viz., the steam withdrawn from the first jet condenser 52 and heated to working temperature in the heat exchanger 55, is introduced through the stripping steam supply 77 into the sump of the falling film column 70. Therein, the stripping steam flows in counter-current relationship to the down-trickling liquid through the falling-film tubes and is collected in the head of the falling film column 70. A vapour line 78 leads from the head of the falling-film column 70 into the sump of the falling-film column 60, so that the vapour recirculating condensate. After passing through the mist eliminator 66 in the head of the jet condenser 65 the steam, which is substantially scrubbed of organic constituents, is withdrawn by the first booster stage 22 of the vacuum unit 23.

In accordance with a further embodiment of the invention, the "new" plant parts may be integrated in a single column section so as to allow spacesaving installation in existing plants. Such a column section is schematically illustrated in Fig. 3. As seen from top to bottom, such a column section 80 may comprise: a trickle column-type degasification stage 81, a jet condenser 82, a first falling-film column 83 having wider trickle passages, a second falling-film column 84 having narrower trickle passages, a pump 85 for withdrawing the finished oil, and a heat exchanger 86 for heating the crude oil in heat exchange with the finished oil.

Again, the crude oil is supplied from a storage tank 1 and charged via the pump 2 through line 3 onto the manifold of the degasification stage 81. The degasified material discharged from the degasification stage 81 is squeezed through the line 5 and the pump 6 into the heat exchanger 86 and passes through line 7 and the high-temperature heat exchanger to be charged onto the manifold of the falling-film column 80. Here, it is distributed to the wide trickle passages of this falling-film column 80 and is again fed from the sump thereof onto the manifold of the falling-film column 84. Stripping steam, i.e. the steam already utilized in the first plant part, is introduced after renewed heating to the working temperature through the stripping steam supply 87 into the sump of the column 84. This stripping steam first flows through the narrow trickle passages of the falling-film column 84, thereupon into the wider trickle passages of the falling-film column 83, and is finally cooled in the jet condenser 82 by contact with recirculated condensate and is substantially stripped from organic components. After passing through the mist eliminator 88, the cooled steam is supplied to the vacuum unit through the sufficiently wide vapour line 89.

On account of the short length of the lines, this structure ensures an especially low pressure loss.

Moreover, due to the comparatively moderate space requirements installation in existing plants is possible without extensive retrofitting.

Claims (1)

1. A process for deodorizing and/or physical refining of high-boiling liquids, viz., edible oils, fats, glycerides and other high-boiling esters as well as fatty acids, in which the liquid heated to a matter from already pretreated or from untreated liquid, is thereupon cooled again, substantially freed from volatile matter and supplied to the vacuum unit.

2. A process of deodorizing and/or physical refining high-boiling liquids, viz., edible oils, fats, glycerides and other high-boiling esters as well as fatty acids, in which the liquid heated to a temperature of 180 to 2800C is treated at a working pressure of less than 10 mbar in a conventional plate column or the like in counter-current flow with stripping steam, the steam laden with volatile matter is collected and is contacted with recirculating condensate at a temperature of 50 to 800C in a jet condenser at a pressure of less than 10 mbar, and is finally withdrawn by a vacuum unit which ensures the working pressure, characterised in that the steam after exiting from the jet condenser is again introduced as stripping steam into the sump of a single-stage or multi-stage falling-film column and is used therein for stripping volatile matter from already pretreated or from untreated liquid, is thereupon cooled again, substantially freed from volatile matter and supplied to the vacuum unit.

3. A process as claimed in claim 1 or claim 2, characterised in that a pressure of 2 to 8 mbar is maintained in the intake portion of the vacuum unit.

4. A process as claimed in any of the claims 1 to 3, characterised in that the pressure loss in the other plant part or, respectively, in the falling-film column including the second jet condenser associated therewith is kept at a level of less than 2.0 mbar, especially less than 1.4 mbar.

5. A process as claimed in any of the claims 1 to 4, characterised in that per unit of time a part of the heated liquid is introduced into the one plant part or, respectively, into the bubble-plate column or the like, and the other part of the heated liquid is fed to the other plant part or, respectively, the falling-film column.

6. A process as claimed in claim 5, characterised in that per unit of time, 1 part by weight of liquid is supplied to the one plant part or, respectively, the bubble-plate column or the like, and 1.5 to 2.5 parts by weight of liquid are supplied to the other plant part or, respectively, the falling-film column.

7. A process as claimed in claim 5 or claim 6, characterised in that as the other plant part or, respectively, as the falling-film column a multi-stage falling-film column is used which in its initial zone immediately succeeding the liquid supply has larger trickle passage hydraulic diameters than in the succeeding zone(s).

8. A process as claimed in any of the claims 1 to 4, characterised in that per unit of time, the total hydraulic diameter of 40 to 120 mm, especially of 60 to 90 mm, and an exchanger length of 3 to 6 m, especially of 3 to 4 m.

10. A process as claimed in claim 8 or claim 9, characterised in that a liquid charge of 1 to 3 m3 per hour and per meter of the trickle passage circumference is maintained in the falling-film column.

11. A process as claimed in any of the claims 1 to 10, characterised in that inert steam is used as stripping steam, said inert steam having been produced from previously distilled and deaerated water, and the live inert steam is exclusively introduced into the one plant part or, respectively, the plate column or the like.

12. A process as claimed in any of the claims 1 to 11, characterised in that the steam which has once been utilized as stripping steam, after substantial removal of volatile matter, is reheated to the working temperature of 180 to 2800C priorto being introduced again as stripping steam into the other plant part or, respectively, the falling-film column.

13. A process as claimed in any of the claims 1 to 12, characterised in that the liquid to be treated is degasified in a preliminary stage at a pressure of 60 to 280 mbar and a temperature between 40 and 100 C, and with the water content of 0.05 to 0.02 wt.% remaining under these conditions is contacted with the stripping steam.

14. A plant for carrying out the process as claimed in any of the claims 2 to 13, characterised by a plate column or the like, a first jet condenser in communication with the head of said plate column or the like, at least one falling-film column, a vapour conduit extending from the head of said first jet condenser to the sump of said falling-film column, a second jet condenser in communication with the head of the falling-film column, a live steam conduit leading into the plate column or the like, and a vapour withdrawing conduit leading from the head of the second jet condenser to the vacuum unit.

15. A plant as claimed in claim 14, characterised by a single-stage falling-film column whose trickle passages have constant hydraulic diameter through the entire exchanger length, and said hydraulic diameter being 40 to 120 mm, especially 60 to 90 mm.

16. A plant as claimed in claim 15, characterised in that the trickle passages have an exchanger length of 3 to 6 m, especially of 3 to 4 m.

17. A plant as claimed in claim 14, characterised by a multi-stage falling-film column comprising at least two serially operating counter-current falling film stripping-steam distillation zones in vapour and liquid communication with each other, of which the ensures at least six theoretical plates, the trickle passages have a hydraulic diameter of 25 to 33 mm.

19. A plant as claimed in claim 18, characterised in that in the initial zone the trickle passages have an exchanger length of 2 to 6 m, and in the final zone the trickle passages have an exchanger length of 6 to 10 m.

20. A plant as claimed in any of the claims 14 to 19, characterised in that a degasification vessel is additionally provided.

21. A plant as claimed in claim 20, characterised in that the degasification vessel, a heat exchanger for indirect heat exchange between the treated liquid and fresh liquid, the second jet condenser, and the single-stage or multi-stage falling-film column are integrated in a common column section (see Fig. 3).