WO1986004603A1

WO1986004603A1 - Process for refining of vegetable oil

Info

Publication number: WO1986004603A1
Application number: PCT/SE1986/000040
Authority: WO
Inventors: Staffan Julin; Kenneth Carlsson; Anders HILLSTRÖM; Claes Johansson; Anders FREDRIKSÉN
Original assignee: Alfa-Laval Food & Dairy Engineering Ab
Priority date: 1985-02-04
Filing date: 1986-02-03
Publication date: 1986-08-14
Also published as: SE8500480D0; AU5519286A; EP0209587A1; SE8500480L

Abstract

In a process for steam refining and/or deodorization of vegetable oil this is led to a column (1) provided with inlet (2) and outlet (3) for the oil, and inlet for stripping steam (41-43) and outlet (5) for an outgoing gas flow, in which column (1) there is maintained a temperature of 180-270oC and a pressure of 0.067-1.33 kPa, at which the said stripping steam is blown directly into the oil for stripping of relatively volatile components, partly such that are present in the oil, and partly such which are formed in the oil under influence of the prevailing temperature, at which the stripped components are led away in a first gas flow. The invention is characterized in that the oil is led from the column (1) to a first container (14) provided with inlet (3) and outlet (15) for the oil and inlet (44) for stripping steam and outlet (21) for an outgoing gas flow, connected to a source for a low pressure, preferably the upper part of the column (1) such that mainly the same pressure prevails also in the first container (14), which also is provided with a unit (20) for indirect cooling, at which the said stripping steam is blown directly into the oil for stripping remaining volatile components, which are brought to be led away in a second gas flow, while the oil is at the same time cooled indirectly by a cooling medium.

Description

Process for refining of vegetable oil

The present invention relates to a process and an apparatus for steam refining and/or deodorization of vegetable oil, which is led to a first vessel, provided with inlet and outlet for the oil, and inlet for stripping steam and outlet for an outgoing gas flow, in which container there is maintained a temperature of 180-270°C and a pressure of 0.067-1.33 kPa, at which the said stripping steam is blown directly into the oil in order to strip relatively volatile components from the oil, partly such that are present in the oil and partly such that are formed in the oil under influence of the prevailing temperature, at which the stripped components are led away in a gas flow.

Such processes and corresponding apparatuses for carrying through the same are known since long in a number of variations. A register of processes and corresponding appara¬ tuses, which are present on the market is given by H. Stage in an article in "Seifen-Ole-Fette- achse" Vol. 105, No. 14, 15, 16, 18 (1979). In this publication it is stated, that disconti¬ nuous as well as continuous processes are existing, of which the latter nowadays seems to be the most usual. If the process is to be carried through effectively, it is demanded that the vessel, i.e. the reactor, is designed in such a way, that fundamentally the counte current principle is applicable as relates to the flow of oil and the flow of stripping steam. The vessel is therefore often designed as a vertical column, with inlet for the oil at the upper end and outlet for the same at the lower end. Such a column is usually divided into a number of sections arranged vertically after each other. The sections can have the form of bubble cap trays or other kind of trays known from the distillation technique. The stripping steam is usually led into each such section by way of separate inlets, while the oil flows through the sections from above. The oil is released from relatively volatile components, partly such that are present in the oil provided to the container, and partly such that are formed under influence of the prevailing temperature when the oil flows through the sections following each other.

One problem when carrying through processes of the kind mentioned introductory means, that relatively volatile com¬ ponents may be formed in the oil when the same has left the column, but still has essentially the same temperature as in the column. These components then remain in the oil and may give rise to bad taste and odour. A usual method of cooling the oil is to let the same heat the incoming oil led to the column in a heat exchanger. When such a heat exchanger is dimensioned in a reasonable way, the hot oil coming from the column can not be cooled so rapidly, that the formation of rela- tively volatile parts is hindered completely. Regenerative cooling of oil from the column by oil being led to the container involves a limitation of the possibility for cooling, if one changes from one quality of oil i.e. kind, to another. In such a case the outgoing oil from the column cannot be cooled with the incoming oil during the change, since a mixing of the kind of oils would be obtained in such a case. In this case a separate possibility for cooling is needed, usually in the form of a separate heat exchanger.

There are also plants for carrying through a process of the kind mentioned introductory in which there is provided a cooler for cooling of the oil before it leaves the column. Such an apparatus has certain disadvantages. It is constructively difficult to avoid, that such a cooler is exposed to strong vibrations, which brings about- a mechanical load on the apparatus. It is also difficult to clean and carry through maintainance on a cooler of this kind.

The aim of the present invention is to achieve a process and an apparatus of the kind mentioned introductory, which is simple and flexible and does not have any of the disadvantages which were mentioned above when relating the prior art. According to the invention such a process is characterized in that the oil is led from said column to a container, provided with inlet and outlet for the oil and inlet for stripping steam and outlet for the outgoing gas flow. The container is connected to a source of low pressure, preferably the upper part of the column, such that mainly the same pressure prevails in the column as In the con¬ tainer. The container is also provided with a unit for indirect cooling. The said stripping steam is blown directly into the oil in order to drive off remaining volatile components, which are brought to leave the container as a second gas flow, while the oil is cooled indirectly by a cooling medium at the same time. In a suitable embodiment the said cooling medium is brought to circulate in a circulation path by a pump, which path comprises the said unit and a second container. In some cases it may be suitable to arrange a throttle valve in the circulation path before the inlet to the second container, such that the cooling medium may be brought to circulate at such a pressure, that it is in liquid form in the said unit, but at least partly changes to steam form in the second container. The cooling medium may consist of many different liquids, but in practice water is often suitable. If the oil is cooled with water, it may be of advantage that the water is brought to leave the second container In the form of steam. The steam is led to a steam pipe, which is maintained under a chosen, constant pressure, at which the steam formed from the water with advantage is used to drive an aggregate, comprising steam ejectors in order to achieve the needed low pressure in the column and the first container. This aggregate is very steam demanding, and must alternatively be provided with steam from an external steam source, that is usually a steam boiler of some kind.

In a preferred embodiment of the process according to the invention the flow of cooling medium is controlled in dependence on the temperature of the oil, which leaves the first container, with the aim of keeping this temperature on a desired, sufficiently low level in the range of 170°C, preferably by actuating the said throttle valve. This actuation may take place manually or in the form of an automatic controlling by way of a regulator.

Alternatively one can maintain the temperature of the oil, which leaves the first container on a desired level by arranging a further circulation path for the cooling medium, in which a determined part of the same is circulating without passing and giving off heat in the second container.

Other possibilities for controlling are of course possible. The oil, which leaves the first container is usually sufficiently warm to give off heat to the oil, which is led into the column, by way of a heat exchanger.

The design of an arrangement for carrying through the process according to the invention has principally been described above. Apart from that it may be suggested, that the said second container preferably is arranged such that a feed pipe for cooling medium, preferably water, is connected to the said circulation path in such a way, that the level of cooling medium in the second container is kept constant, for example by means ofa float, which influences a valve in the inlet pipe.

The unit for indirect cooling in the second container is suit- ably arranged as mainly vertical standing thin plate pairs, within which the cooling medium is brought to circulate, at which diffusors for steam are arranged at the lower, horizontal limitations of the plate pairs. In a preferred embodiment of an arrangement according to the invention the said plate pairs are arranged mainly in parallel, close to each other, in such a way that, seen in a cross section, a relatively high pair is followed by two somewhat lower pairs, followed by a relatively high pair at and so on. Diffusors for steam are arranged in parallel with the plate pairs, between a relatively high and a somewhat lower plate pair.

The cooling medium flows within the plate pairs and the oil in the flow paths formed between the parallel plates. Usually cooling medium and oil are brought to flow in counter-current flow. It is suitable to arrange said diffusors closer to the lower than to the relatively higher plate pair. The stripping steam makes the oil, which flows along the longitudinal direction of the plate pairs to flow also vertically upwards between a relatively high and a somewhat lower plate pair and down between two somewhat lower plate pairs, i.e. according to the "Mammoth Pump Principle" .

When starting a plant with such a design of the cooling elements in the first container the oil will at the start be standing so low in the first container, that it cannot flow over the somewhat lower plate pairs. In order to make the diffusors to distribute steam between the somewhat lower plate pairs in this operation step, although in a limited extent, it is suitable to arrange the diffusors in such a way, that a few of the diffusors are directed in between the said lower plate pairs.

The invention will now be described further with reference to the four attached figures, of which figure 1 schematically shows a flow chart of a plant for steam refining and deodorization; figure 2 shows a horizontal cross section through a unit for indirect cooling in a container according to the inven¬ tion; figure 3 shows (enlarged) a cross section through four plate pairs and two diffusors; figure 4 shows the flow chart in figure 1 with some operational data. In figure 1, 1 denotes a column with an inlet 2 and an outlet 3 for oil, inlet 4 1 , 42 and 43 for stripping steam to the column on different levels, i.e. sections, in this case in the form of trays with baffles, between which the oil is brought to flow from section to section downwards meeting stripping steam, which is distributed by diffusors not shown in detail. The necessary low pressure in the column is achieved by way of an aggregate, connected to the top of the column and comprising a first steam ejector, or booster 6, a first condenser 7 and a second steam ejector 8, a second condenser 9, a water ring pump 10 and a third condenser 11. The aggregate is provided with steam from a steam pipe 12. The oil forwarded to the column 1 is preheated to the necessary temperature in a heat exchanger 13 which is heated by heating medium from a generator not shown in the drawing.

A container 14 is arranged to receive oil from the outlet 3. This container is provided with an outlet 15 for oil, connected to a pump 16 and a pipe 17, which is connected to a heat exchanger 18, in which the oil leaves the remaining heat to an arriving oil flow 19. The container 14 is in the interior provided^" with a unit 20 for indirect cooling of the oil in the container, and a pipe 21, connected to the upper part of the column, for evacuation of a gas flow from the said container. There is furter an inlet 4 for stripping steam to a diffusor in the container 14. The unit 20 is a part of a circulation path consisting of a pipe 22, a second container 23, a pipe 24, a circulation pump 25 and a pipe 26 connected to the unit 20. In the pipe 22 there is also in this case a throttle valve 27. By way of a supply pipe 28- a pump 29 provides the second container 23 with water, such that the level, which is detected by a level sensor 30 in the container 23 and is controlled by a valve 31 in the pipe 28 is kept constant. The container 23 is by way of an outlet 32 connected to a steam pipe 33, in which the pressure is kept constant by means of a pressure sensing means 34 and a regulating valve 35. The trottle valve 27 is in this case controlled by a temperature sensing means 36 arranged in the outlet 15 for cooled but still relatively warm oil (about 170°C), in such a way that this oil is kept at a constant desired temperature in a way which is described in the following.

In figure 2 there is shown a container 14 with a unit 20 seen from above, partly in section. The unit 20 consists in this case of nineteen parallel plate pairs 37, located vertically. The plate pairs are arranged such, that parallel flow paths for the oil are formed, while the cooling media flows in parallel in groups of plate pairs, in the shown unit in groups of each three plate pairs. In such a way the cooling media flows in the same direction in the three plate pairs 37a, 37b and 37c and in the other direction in the three plate pairs 37d, 37e and 37f etc. The path of the oil is marked with arrows. The oil path is caused partly by guide plates 38 and partly due to the fact that the plate pairs have a different height, in the way that is shown in figure 3, from which may be seen that for example the plate pairs 37a and 37d are relatively high, while the plate pairs 37b and 37c located between them are relatively lower.The sign + means, that the oil flows in a direction again the viewer and the sign - that is flows away from the viewer. In parallel w-ith the plate pairs there are two diffusors 39, 40 for stripping steam arranged in such a way, that a larger steam flow is distributed between the plate pairs 37a and 37b and between the plate pairs 37c and 37d (thick arow) than between the plate pairs 37b and 37c. This is obtained by locating the diffusors in the vicinity of the lower limitations of the plate pairs 37b and 37c but somewhat displaced towards the plate pairs 37a. The reason for this is, that it is desired, that steam shall be distributed in the oil also during a starting step or otherwise, when the oil is not standing so high, that it reaches the top of the somewhat lower plates 37b and 37c. In normal operation the latter is the case and the oil is, according to the "Mammoth Pump Principle" , driven by the steam upwards between the plates 37a-37b and 37c-37d, respectively, and made to flow downwards between the plates 37b-37c. This flow is superposed the main flow direction of the oil in parallel with the plate pairs.

It should be emphasized, that the plant in the figures only shows an example of a plant for carrying through the process according to the invention. Many other embodiments are possible within the scope of the claims. If one for example choses to generate steam in the second container, this steam may for example be used for different purposes. In the example shown in the figure, steam from the container 23 is used to drive the steam ejectors 6, 8, which often is of interest, and as stripping steam. Of course this Is not the only possible use.

Example

In figure 4 there is shown the same plant as in figure 1. Some operational data have been marked as an example. The vegetable oil is forwarded to the plant after some pretreatment steps and is heated by outgoing oil from 90°C to 150°C in a heat exchanger, and is thereafter heated to 250°G in a further heat exchanger, heated with heating fluid. In the column there is maintained, a pressure of 0.798 kPa. Stripping steam is blown into the oil in the sections, into which the column is divided, and which the oil successively passes on Its way down the column. The oil leaves the column at 245°C and is led into the container, where it is cooled to 170°C while stripping steam is blown in, and the oil leaves the plant through the first mentioned heat exchanger. Water is pumped around in the circulation path, which comprises the unit 20 and the third container 23 by way of the pump 25. The water arrives to the unit 20 at about 140°C, 1400 kPa, and leaves the unit at 180°C, 1200 kPa. This means that the water due to the throttle valve is kept at a pressure above the boiling point at the prevailing temperature. When the water flow has passed the throttle valve 27 a part of the same is transformed to steam due to the pressure 400 kPa prevailing in the container 23. The pressure 4 bar is maintained by way of the valve 35 in the steam pipe 33. The throttle valve 27 has for its task to control the water flow in the circulation path in such a way that the temperature of the outgoing oil is kept constant. This is possible since the flow capacity of the pump 25 is influenced by the counter pressure (the pump is in this case a centrifugal pump). The control of the valve 27 may be carried through manually, but is most efficiently done by way of a control circuit, where the temperature sensing means 36 by way of a regulator controls the valve 27. The level of water in the container 23 is maintained constant by feeding water, in this case with a temperature of 90°C by way of the pump 29, at which the level controller 30 controls the valve 31 in the supply pipe to the container 23. The steam which is created in the container 23 is used to drive the aggregate for achieving the necessary pressure of 0.798 kPa in the column, and as a stripping steam. Principally one can as suggested earlier use the steam in other ways. When starting the plant this is driiven entirely with steam, which is obtained through the steam pipe 33.

The plant according to the invention has many advantages. It is extremely flexible and simple to maintain, since it constitutes a separate unit. The first container may be designed as a unit where all connections are situated on the outside near the gable. This gable may easily be dismantled for inspection and clea- ning of the unit for cooling. The construction is especially robust and stable. The plant may be built up by units, which gives the plant large flexibility. Already existing plants for steam refining or deodorization, which miss arrangements for cooling during stripping with steam, may easily be completed with an arrangmement according to the invention. As mentioned intro- ductory cooling during stripping gives a good oil quality. The plant according to the invention is also characterized by a good heat economy even during change of oil quality or emptying of the plant.

Claims

1. Process for steam refining and/or deodorization of vegetable oil, which is led into a column, provided with inlet and outlet for the oil, and inlet for stripping steam and outlet for the outgoing gas flow, in which column there is maintained a temperature of 180-270°C and a pressure of 0.067-1.33 kPa, at which the said stripping steam is blown directly into the oil for stripping of relatively volatile components, partly such which are brought about by the oil and partly such that are formed in the oil during influence of the prevailing temperature, at which the components driven off are led away in a first gas flow, c h a r a c t e r i z e d i n that the oil is led from the said column (1) to a first container (14), provided with inlet (3) and outlet (15) for the oil, and inlet (44) for stripping steam and outlet (21) for an outgoing gas flow, connected in such a way to a source for low pressure, preferably at the upper part of the column, that essentially the same pressure as in the column prevails in the first container (14), which also is provided with a unit (20) for indirect cooling, at which the said stripping stream is blown directly into the oil for stripping of remaining volatile components, which are brought to leave the container as a second gas flow, while the oil is simultaneously cooled indirectly by cooling water, which by a pump (25) is brought to circulate in a circulation path, which comprises the said unit (20) and a second container (3) which circulation path before the inlet to the second container (23) comprises a throttle valve (27).

2. Process according to claim 1, c h a r a c t e r i z e d i n that the cooling medium is brought to circulate at such a pressure, that it is In liquid form in the said unit (20) but at least partly is transformed into steam form in the second container (23).

3. Process according to any of the claims 1 and 2, c h a ¬ r a c t e r i z e d i n that the water is brought to leave the second container (23) through an outlet (32) in the form of steam and is led to a steam pipe (33), which is kept under constant pressure, at which the steam formed by the cooling media is used preferably as stripping steam and to drive an aggregate, comprising steam ejectors (6, 8) in order to achieve the necessary pressure for the column and the first container (1, 14).

4. Process according to claim 3, c h a r a c t e r i z e d i n that the flow of water is controlled in dependence of the temperature of the oil which leaves the first container (14) in order to maintain this temperature on a desired level, preferably by actuating the said throttle valve (27).

5. Process according to any of claims 1-4, ch a r a c t e - r i z e d i n that the heat in the oil, which leaves the first container (14) heats the oil which is led into the column (1) by heat exchange (18).

6. Plant for steam refining and/or deodorization of vegetable oil according to claim 1, comprising a column (1), provided with inlet (2) and outlet (3) for the oil, and inlet (4¹-4³) for stripping steam and outlet (5) for an outgoing gas flow, arranged to maintain a temperature of 180-270°C and a pressure of 0.067-1.33 kPa, c h a r a c t e r i z e d i n that the first container (14) is provided with inlet (3) for oil coming from the column (1) and an outlet (15) for oil, and an inlet (44) for stripping steam and outlet- (21) for an outgoing gas flow, and a second container (23) and a circulation pump (25), which together with the unit (20) for indirect cooling forms a circulation path for cooling water, at which a throttle valve (27) is arranged in the said circulation path before the second container (23).

7. Plant according to claim 6, c h a r a c t e r i z e d i n an outlet (32) from the second container, connected to a steam pipe (33), arranged to be maintained under constant pressure by connection to an external steam source, at which the steam pipe (33) is connected to inlet (4 -4 ) for stripping steam and an aggregate comprising steam ejectors (6, 8) for achieving the necessary pressure in the column and in the first container (1, 14).

8. Plant according to claim 7, c h a r a c t e r i z e d i n that the said 'throttle valve (27) is arranged to control the flow and the circulation path in dependence of the temperature of the oil from the first container (14) such that the said temperature is maintained on the desired level.

9. Plant according to any of the claims 6-8, c h a r a c t e¬ r i z e d i n that a supply pipe (28) for water is connected to the said circulation path, in such a way that the level of cooling media in the second container (23) is maintained constant.

10. Plant according to any of claims 6-9, c h a r a c t e ¬ r i z e d i n that the unit (20) for indirect cooling is designed as mainly vertically standing relatively thin plate pairs (37), within which the cooling media is brought to circu- late, at which diffusors (39, 40) for stripping steam are arran¬ ged at the lower horizontal limitation of the plate pairs (37).

11. Plant according to claim 10, c h a r a c t e r i z e d i n that the said plate pairs (37) are arranged mainly parallel, close to each other, at which seen in a cross section, a relatively high plate pair (37a, 37d, 37g) is followed by two somewhat lower plate pairs (37b, 37c, 37f), which are followed by a relatively high plate pair and so on, at which diffusors (39, 40) for stripping steam are arranged in parallel with the plate pairs, between a somewhat higher and a somewhat lower plate pair (37a, 37b-37d, 37c).

12. Plant according to claim 11, c h a r a c t e r i z e d i n that the diffusors (39) are arranged closer to the lower (37b) than the relatively higher (37a) plate pairs, arranged such, that the stripping steam forces the oil, which flows in the longitudinal direction of the plate pairs also to flow vertically upwards between a relatively high (37a) and a somewhat lower (37b) plate pair and down between two somewhat lower plate pairs (37b, 37c), i.e. according to the "Mammoth Pump Principle" .

13. Plant according to claim 12, c h a r a c t e r i z e d i n that the diffusors (39, 40) also are arranged to distribute steam to the oil which is situated between the somewhat lower (37b, 37c) plate pairs in that case, when the level of the oil is such in the first container (14) that it cannot flow over the somewhat lower plate pairs (37b, 37c).