US 3085742 A
Description (OCR text may contain errors)
A ril 16, 1963 F. T. E. PALMQVIST 3,08
APPARATUS FOR MAINTAINING CONSTANT FLOW RESISTANCE IN A CENTRIFUGAL EXTRACTOR Filed Feb. 25. 1958 INVENTUR. fie ik f oo or manue/ Qo/mywsl By I .7,'. M vW -K AT T 0 R N E 1 3,085,742 APPARATUS FOR MAENTAINING QONSTANT FLOW RESKSTANQE IN A CENTRHFUGAL EXTRACTOR Fredrik Teodor Emanuel Palmqvist, Soina, Sweden, assignor to Aktiebolaget Separator, Stockholm, Sweden, a corporation of Sweden Filed Feb. 25, 1958, Ser. No. 717,518 Qlaims priority, application Sweden Feb. 28, 1957 7 Claims. (Cl. 23315) The present invention relates to an improved apparatus for maintaining constant flow resistance in the centrifugal extractor adapted for throughflow passage of two or more media which, during the throughfiow, influence each other chemically or physically.
A centrifugal extractor is, in principle, a centrifugal separator in which an extraction process is carried out. An example of such a separator is that disclosed in Swedish Patent No. 146,598 and the corresponding US. Patent No. 2,879,282, issued March 24, 1959. In this separator, an extraction with the current is carried out in one step. By centrifugal extractors, however, is usually meant such apparatus in which an extraction is carried out in several steps and countercurrently, mixing and separation taking place in each step.
The extractors mentioned above as examples are intended for use in continuous operation. To this end, it is desirable that the extraction process for which the extractors are used be automatically regulated. According to the present invention, the variations which may occur in the various extraction media during the extraction process are utilized for this purpose. These variations may appear in the form of a changed flow resistance or pressure drop in the extractor, due, for instance, to a change in the viscosity or the specific gravity of the media. A change in specific gravity thus causes a displacement of the boundary level between the media with accompanying change of the throughflow areas for them. A change in viscosity or specific gravity may indicate a change in the extraction process, which change it is desired to avoid. As an example may be mentioned washing of soap in an extractor with an aqueous solution of an electrolyte. On certain conditions, the viscosity-electrolyte content curve in soap is U-shaped. This means that, in one case (one leg of the curve), the viscosity decreases when the electrolyte content of the soap is increased and, in another case (the other leg of the curve), the viscosity increases when the electrolyte content of the soap is increased. A certain quality of the soap corresponds to a certain viscosity in one of the legs of the curve or to a certain electrolyte content. Therefore, if it is desired to maintain a certain quality of the soap leaving the extractor, it is necessary to maintain a certain viscosity in the soap and, accordingly, a certain flow resistance or pressure drop in the extractor. The adjustment of this quality may thus be effected by regulating the concentration of the electrolyte solution flowing through the extractor.
The principal object of the present invention is to solve the regulating problem mentioned above.
An apparatus made according to the invention comprises a dosing means for feeding one of the media (herein called the first medium) through the extractor at a constant rate (constant quantity per unit of time), a means for mainaining in the path of the first medium a constant pressure at the inlet to or the outlet from the extractor, a meter for the pressure drop of the first medium during the how through the extractor, a means for maintaining in the path of the second medium a constant pressure at the inlet to or the outlet from the extractor, and a device operated by the indications of Patented Apr. 16, 1963' the pressure drop meter for regulating the second medium as to its composition or its temperature or the rate at which it is fed through the extractor. It is obvious that many different extraction processes can be regulated with this apparatus, such as extraction of colored constituents and excess sulphuric acid from sulphonic acid for the manufacture of detergents, degumming of fatty oil with water (the viscosity of the gum is kept constant), and refining of mineral oil with sulphuric acid (the specific gravity of the sludge is kept constant).
In one embodiment of the invention, means are provided for keeping a constant pressure at the outlet of the first medium from the extractor, and the dosing means for the first medium is provided at the inlet of this medium into the extractor.
In another embodiment of the invention, means are provided for keeping a constant pressure at the outlet of the second medium from the extractor, and the regulating device for the second medium is provided at the inlet of this medium into the extractor.
It is advantageous to combine these two embodiments, and in this combination embodiment it is possible to obtain a regulation of the composition of the second medium by arranging, between the regulating device for this medium and the inlet of this medium into the extractor, a dosing means for feeding this medium through the extractor at a constant rate, and by using as a regulating device a mixer having inlets for two or more different components, at least one of these inlets being arranged to be controlled by the indications of the pressure drop meter.
One or possibly both of the means for keeping constant pressure may consist merely of outlets from the extractor to the atmosphere. 'In general, however, it is preferable that one of such means consist of an outlet to the atmosphere and the other of a means which keeps a constant pressure higher than the atmospheric pressure. Means of the latter kind (automatic valves) are well known.
The invention is described in greater detail in connection with the accompanying drawing, in which FIGS. 1-5 are schematic views of various embodiments.
Referring now to FIG. 1, the reference numeral 1 designates the extractor in which there are shown, for the sake of simplicity, only two liquid layers 2 and 3, one of which is represented by a blank surface and the other by a hatched surface. In reality, these layers form two cylinders which are concentric with one another, and the drawing symbolizes one half of an axial section through these cylindrical (actually somewhat conical) liquid layers. The layer 2 is assumed to consist of the light liquid and the layer 3 of the heavy liquid, although the case could as well be in the reverse. The light liquid is fed into the extractor independently of the counter-pressure at a constant rate (quantity by volume per unit of time) through a feed line 4 by means of a dosing device or pump 5, such as a positive pump, for instance a gear or piston pump. A positive pump means here a pump whose volumetric throughput is proportional to the number of revolutions of the pump. From the extractor .1, the light liquid is fed out through a discharge line 6 against a constant pressure which is maintained by means such as a valve 7. The valve 7 may, if desired, be replaced by an outlet to the free atmosphere, if this outlet opens at a suitable radial distance from the axis of rotation of the extractor. The free atmosphere here also represents a constant pressure. In the feed line 4, between the pump or dosing device 5 and the extractor 1, is a manometer 8 whose indications, through an operative connection 9, actuate a regulator or control device 10 in the feed line 11 for the heavy liquid. As the discharge pressure for the light liquid is kept constant by the valve means 7, changes in the meter 8 indicate changes in the pressure drop within the extractor and, therefore, changes in the viscosity or specific gravity of the liquids, as mentioned above. From the extractor, the heavy liquid leaves through a discharge line 12 which, at a distance from the axis of rotation of the extractor, opens through an outlet 13 into the free atmosphere, the latter, as previously mentioned, representing a constant pressure. Thus, the vented outlet 13 constitutes in effect a means in the discharge line 12 for maintaining a constant pressure in this line.
Let it now be assumed that a disturbance occurs in the extractor, for instance, because the viscosity of the light liquid increases so as to cause an undesired condition in the extraction process. The heavy liquid must now be influenced in such a way as to restore the extraction process to the condition desired. When this has been done, the viscosity of the light liquid will have resumed its normal value. Assuming that the viscosity of the light liquid decreases as the temperature of the heavy liquid increases, the regulator 10 may be adapted to increase the heating of the heavy liquid when the viscosity of the light liquid increases and the manometer 8 thus indicates an increased pressure.
Of course, the regulator 10 may also take the form of a flow regulator, if the quantity of the heavy liquid supplied per unit of time changes the viscosity or the specific gravity of the light liquid.
The embodiment shown in FIG. 2 differs from that according to FIG. 1 in that a constant pressure is kept at the inlet side for the heavy liquid by means in the form of a valve 14 and that the manometer 8 actuates a control device or regulator 10a in the discharge 11116.12. of the heavy liquid. The regulator 10a functions in this case to control the discharge rate of heavy liquid from the extractor by regulating the throttling of the line 12 in order to influence, as in the preceding case, the viscosity or the specific gravity of the light liquid. On the other hand, this embodiment does not make it possible to influence the nature of the heavy liquid before entering the extractor.
In the FIG. 3 embodiment, the light liquid is fed into the extractor at a constant pressure through valve 7:: and is discharged at a constant rate through pump 5a. In this case, the constant pressure must be kept so high that, in spite of the pressure drop variations that may occur before the pump 5a, a pressure remains which is sufficiently high to ensure that the pump 5:: always feeds out a fixed quantity per unit of time. As to the heavy liquid, the circumstances here are the same as in the FIG. 1 embodiment, except that the manometer 8a actuates the regulator from the discharge line 6 for the light liquid.
In the embodiment shown in FIG. 4, the apparatus associated with the light liquid is the same as in FIG. 3, while the apparatus associated with the heavy liquid is the same as in FIG. 2, except that the manometer 8a in the FIG. 4 embodiment actuates the regulator 10a from the discharge line 6 for the light liquid.
The embodiment shown in FIG. 5 is similar to that shown in FIG. 1, except that in FIG. 5 the control device 10 is arranged to regmlate the composition or concentration of the heavy liquid. Here, the heavy liquid is assumed to be an aqueous solution of a salt. In the line 11 is inserted a pump 15 which feeds a constant quantity of liquid per unit of time. The pump 15 is supplied with salt solution of fixed concentration, preferably concentrated salt solution, from a feed line 16 at a rate which is regulated by the control device or valve 10. Through a branch feed line 17, the pump 15 is supplied by unrestricted inflow with water at a rate corresponding to the difference between the throughput rate of the pump 15 and the rate of feed of salt solution through the line 16.
For a better understanding of the embodiment shown in FIG. 5, it may be assumed that a soap mass passes at a constant rate through the line 4 from the saponifying stage in a continuously operating soap factory. The soap mass is presumed to be in such a condition that an increase in its viscosity should be counteracted by increasing the salt content in an aqueous solution with which the soap is washed in the extractor 1. The soap, which in this case constitutes the lighter phase, corresponds to the layer 2, while the salt solution constitutes the heavier phase and corresponds to the layer 3. If the viscosity of the soap now increases, the manometer 8 indicates an increased pressure drop and actuates the regulator 10 through operating connection 9 to increase the supply of salt solution to the pump 15. As a result, the water quantity fed per unit of time to the pump 15 through the line 17 decreases. Thus, the salt solution fed by the pump 15 into the extractor 1 will have its salt content increased. When the increase has become sufiicient, the viscosity of the soap decreases to the value desired so that the intended balance in the washing or extraction process is attained.
It will be understood that the constant pressure maintaining means 7 (and 14) may be any conventional valve commonly used for this purpose. An example of such a valve is the diaphragm-operated valve in which the pressure on the diaphragm is varied through an operating connection 18 from a device 19 which senses changes in the pressure to be maintained constant. Thus, in FIGS. 1 and 2, for example, a pressure decrease in line 6 acts through the sensing device 19 and connection 18 to move the diaphragm so as to throttle the valve 7 and thereby restore the pressure to the desired value.
The operating connection 9 from the manometer 8 to the control device 10 may be any conventional systern for transmitting motion from an indicator to a remote control point, such as an electric or hydraulic servo system. As such systems are well known, a detailed description of the operating connection 9 is unnecessary.
1. In combination with a centrifugal extractor through which first and second media are adapted to flow while contacting and influencing each other, the extractor having separate feed and discharge lines for the respective media arranged to feed and discharge each medium separately to and from the centrifugal extractor, each line being located at one end of the extractor; apparatus for maintaining a constant flow resistance in the centrifugal extractor, comprising a constant delivery pump in one of said separate lines for the first medium and operable to feed said first medium through the extractor at a constant rate, means for maintaining a constant pressure in the other of said lines for the first medium, a pressure meter in said one line for the first medium and operable to indicate a variation in the pressure drop of the first medium as it flows through the extractor, said one line for the first medium being closed to atmosphere throughout the length of said one line between the extractor and said pump and meter, means for maintaining a constant pressure in one of said lines for the second medium, a control device in one of said lines for the second medium for so regulating the second medium in said flow thereof through the extractor as to influence the flow resistance of said first medium, and an operative connection between the control device and said meter and through which said device is operable by the meter in response to said variation to counteract said variation.
2. Apparatus according to claim 1, in which said pressure maintaining means for the first medium is in the discharge line for the first medium, said pump being in the feed line for the first medium.
3. Apparatus according to claim 1, in which said pressure maintaining means for the second medium is in the discharge line for the second medium, said control device being in the feed line for the second medium.
4. Apparatus according to claim 1, in which said pressure maintaining means for the first medium is in the discharge line for the first medium, said pump being in the feed line for the first medium, said pressure maintaining means for the second medium being in the discharge line for the second medium, and said control device being in the feed line for the second medium.
5. Apparatus according to claim 1, in which one of said pressure maintaining means includes an outlet from the extractor opening to atmosphere.
6. Apparatus according to claim 1, in which one of said pressure maintaining means includes an outlet from the extractor opening to atmosphere, the other of said pressure maintaining means including a valve for maintaining a constant pressure above atmospheric pressure.
7. Apparatus according to claim 1, in which the control device is a valve in the feed line for the second medium, the apparatus comprising also a branch feed linejoining said second medium feed line at a point between said valve and the extractor, whereby the second medium includes two components combined at said point, and a pump located in said second medium feed line between said point and the extractor and operable to feed said second medium through the extractor at a constant rate.
References Cited in the file of this patent UNITED STATES PATENTS 2,597,138 Trigg May 20, 1952 2,628,023 Dahlstedt Feb. 10, 1953 2,707,964 Monroe May 10, 1955 2,758,783 Podbielniak Aug. 14, 1956 2,961,154 Bergey Nov. 22, 1960