Proportional Flow Controller for Liquids W I L L I A M R. WILKINSON' AND H A R O L D A. BEATTY Chemical Research Laboratory, Ethyl Corporation, Detroit, Mich. arrangemciit of the slot, the guide plate, and the dividcr plate is shown schematically in Figure 2. The divider plate has a sharp edge, and is notched t o fit closely around the guide plate, so that it cuts the falling film into two separate parts, each of which flows out of one end of the tray into tlie lon-er conipartment. That compartment in turn is divided on thc bottom by a vertical plate, underneath the movable tray, ~vvhichkeeps the two liquid streams separated as they spill from thc, tray. The dividing tray, which is supportcd' on 1iorimiit:d rails as shown, can be moved by a rod projecting through a packing gland in the side of the lower compartment, and its position is indicated by a pointer on the rod. The length of the tray, and the position of the divider plate, may be designed so t'hat the floir- can be split into any ratio over the required range, which can be anyir-here between zero and total reflux.
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PERENKIAL problem in fractional distillations is the accurate control of reflux ratio with a variable throughput. In the laboratory, manual control guided by visual observation of the flow is usually satisfactory. In pilot-plant and larger installations this method is impractical and hence many contrivances have been devised and described for automatic division of the flow in a given ratio. These generally fall into two classes, the intermittent take-o$ type and the proportional condensing surfnce type. C:irter and Johnson (3)describe a device employing a funnel moved magnetically; Brunn ( 2 ) uses a two-way valve and capillaries; Podbielniak (4)has an intermittently-opening valve seated in the take-off tube; Berg (1) describes a proportional condensing area device. Most reflux ratio controllers are difficult and expensive to build, contain delicate moving parts which get out of order, and are intermittent in operation or of such M nature that the ratio may be varied only by stages. A proportional flow controller free from these defects has been developed in this laboratory and used successfully on a 5-inch diameter column for one year. I t operates on the principle of directing a downflow of liquid into a uniform, free-falling sheet or curtain which is split into two part's by a movable divider.
The liquid head in the upper compartment is determined by the input rate and the slot dimensions, and the only variable in the liquid sheet leaving the slot is its velocity. Thus the instrument is independent of variations in throughput, within the limit set by the maximum available height above the slot. The upper and lower compartments are connected by vent lines, so that unequal gas pressures cannot develop. The vent from the upper compartment also acts as an~oyerflowline into one end of the overflow compartment, in case the rate of flow becomes greater than the capacity of the slot. The guide plate below the slot maintains the continuity and uniformity of the falling film, and this constitutes the essential feature ahich makes the device workable. Kithout it, the velocity of the liquid will usually be insufficient to f o h a continuous sheet of its own accord. The slot itself is formed of two V-edged plates as shown in Figure 1. The plates were made as shown because the edges must be parallel and straight, snd with the soft brass which was used, this shape appeared t o offer the best chance of obtaining these qualities. A thin hardened plate,
The device consists of an upper and a lower compartment separated by a horizontal plate, as shown in the schematic crosssectional views of Figure 1. This plate contains a narrow slot through which the entire liquid condensate flows by gravity, the liquid flow being indicated by arrows on the drawings. Just below and parallel to the slot is fixed a vertical sharp-edged guide plate which collects the liquid as a uniform falling film. The guide plate extends down into a movable tray having a vertical divider plate perpendicular to the guide plate; the 1
Present address, R. T. Vanderbilt Co., East Norwalk, Conn.
Left, end view.
Right, ride view
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
926
TRAY
Figure 2.
Flow Controller
ground to a sharp edge, would be at least as satisfactory, and probably better than the shape shown in Figure 1. Although the direction of the V as shown does not make the slot self-cleaning, it is necessary to have it as shown in order to feed all the liquid to the guide plate. (A disk-type metal filter with low pressure drop was used on the feed line to remove any scale or sediment from the liquid.) With the exception of the slot, which must be fixed accurately, none of the dimensions are critical, and they may be varied to suit the individual requirements. The plates are adjustable, so that the liquid head necessary to maintain the proper flow does not become unreasonable. The
Vol. 18, No. 11
plates are adjusted a t both ends, two feeler gages being used to ensure parallelism. The slot width is determined by the allowable liquid head and the density, viscosity, and surface tension of the liquid. A spacing of 0.0045 inch in a 4-inch long slot is sufficient to carry a flow of 5 to 25 gallons of gasoline per hour at a maximum head of 15 inches, and to provide a continuous sheet of liquid. This slot \vas tested with gasoline a t reflux ratios in the range of 1 to 30. The ratios predicted from the position of the divider were obtained with an accuracy varying from * l % a t a ratio of 1 to * 10% a t a ratlo of 30, throughout the entire range of 5 to 25 gallons per hour. This degree of precision is entirely adequate for distillation work, but can be further increased by lengthening the slot. While the present device was designed for reflux control, it is evidently applicable to many installations where it is desired to split a liquid stream into two parts of given, constant ratio. Its advantages include: no moving parts in operation; wide and continuous range of ratios, independent of throughput, pressure, viscosity, etc.; continuous, rather than intermittent, operation with relatively low holdup. LITERATURE CITED
(1) Berg, L., ISD. ENQ.CHEM.,ANAL.ED., 18, 54 (1946). (2) Brunn, J. H., Ibid., 7, 359 (1935). (3) Carter, A. 9.. and Johnson, F. W., U.5.Patent 2,251,185 (July 29, 1941). (4) Podbielniak Centrifugal Contactor Co., Circ. 22 (Nov. 1942).
Improved Apparatus for Karl Fischer W a t e r Determination RICHARD KIESELBACH Bakelite Corporation, Bound Brook,
TFHE
need for excluding atmospheric moisture from a Karl ischer titration is well known; it is equally necessary, for high precision pork, to protect the apparatus used from moisture before the titration. Several types of apparatus to accomplish this end have been proposed. Almy, Griffin, and Wilcox (1) suggested a stopper drilled to take the buret tip, stirrer, and electrodes, and machined to fit into an ordinary Erlenmeyer flask. Wernimont and Hopkinson (4)modified this apparatus by machining the stopper to a standard taper, which with a standardtaper flask gives a more nearly air-tight joint, and replaced the glass stirrer with stainless steel for the sake of durability. More recently, an all-glass apparatus n a s described by Zerban and Sattler (6), in which magnetic stirring is used with a semi-ballneck flask having a side neck for the electrodes. The apparatus shown in Figure 1 is an all-glass modification of Wernimont and Hopkinson’s apparatus. In use, it is held by a clamp on the upper portion and connected by the standard-taper 10/30joint t o an automatic buret of the overhead reservoir type. The use of a seating-type joint prevents trapping of an air bubble at this point. A radio tube base and a cable connector afford a convenient and positive means of electrical connection to the titrimeter. The one-piece construction of the apparatus eliminates possibility of leakage and adds t o convenience of assembly. A glass stirrer is used, since stainless steel is subject to corrosion by the reagent. Less than 5 seconds are required by an experienced operator to remove the flask from the apparatus and unstopper and connect the next flask to be titrated; this feature is also found in the first two types cited. All else being equal, the speed of this operation determines the degree of precision obtainable in the titration. The dimensions of the apparatus permit use of a 250-ml. Erlenmeyer flask with a 24/40 standard-taper joint, but it could be modified to accommodate other sizes. For small-scale titrations, a vessel in the form of a test tube with a 24/40 joint will permit titration of volumes down to about 5 ml. A solvent-resistant grease should be used on the buret stopcock and the 10/30 joint, to prevent serious leakage. The 24/40 oint should not be greased, since a slight amount of outward air eakage is necessary to permit addition of the reagent; it is some-
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times necessary to grind a slight groove in the male joint to t,his end. An efficient moisture trap should be used on the air inlet of the buret. (The drying tube usually supplied with the buret is too small to be effective.) The stirrer should be connected to the motor with a short length of soft-rubber tubing to prevent damage due t o misalignment. Care should be taken to ensure that the stirrer paddles clear the electrodes. A drop or two of light machine oil in the glass bearing will reduce wear. The electrodes should be kept covered with a spare flask between titrations, that flask being kept stoppered when not in use. TITRIMETER
Serfass (3) has described an electronic titrimeter suitable for detecting end points in conductometric and potentiometric titrations, featuring the use of a “magic eye” electron ray tube for the indicating instrument. MeKinney and Hall ( 2 ) modified the circuit by introducing a voltage doubler, giving a brighter image in the eye. This circuit, although it has the advantage of simplicity and low cost, suffers from two faults which diminish its usefulness. Because it is not isblated from the power line, and because of an inefficient filter circuit, the magic eye image is fuzzy and very susceptible t o interferences such as that caused by a stirrer motor. In addition, flickering of the eye is sometimes caused by a ground to the electrodes through the operator’s body and a conducting film on the surface of the buret, when the buret is connected to the titration vessel, as in a Karl Fischer titration. These disadvantages may be eliminated by adding a power transformer, choke, and condenser, in accordance with the diagram shown in Figure 2. A clear, sharp image in the magic eye results from elimination of alternating current component through the improved filter circuit, the by-pass condenser between the grid and cathode of the magic eye tube, and the connection maimaining the heater of the triode a t the same direct current potential as the cathode. Although the low potential side of the circuit is grounded, no deflection of the eye is caused by grounding the buret through the operator’s body. This effect is eliminated by reduction of the above-ground potential of the
