US2106593A - Apparatus for determining the dew point of a vapor product - Google Patents

Description

1938- R. F. DENISTON ET AL 2,106,593

APPARATUS FOR DETERMINING THE DEW POINT OF A VAPOR PRODUCT Filed May 5, 1936 2 Sheets-Sheet 1 0/5771 1 A TE INVENTORJ W @mlmawg ORNEY Jan. 25, 1938. R. F. DENISTON ET AL 2,106,593

APPARATUS FOR DETERMINING THE DEW POINT OF A VAPOR PRODUCT Filed May 5, 1956 2 Sheets-Sheet 2 CONTROLLER 1 /0 Eff/DUE L M MQ INVENTORJ BY Z 2 IZATTORNEY Patented Jan. 25, 1938 UNITED STATES PATENT OFFICE APPARATUS FOR DETERMINING THE DEW POINT OF A VAPOR PRODUCT Application May 5, 1936, Serial No. 77,942

2 Claims.

This invention relates to a device for continuously testing the productoi' a continuously operating distilling, stabilizing, or fractionatin device.

An object of this invention is to provide a device capable of association with a iractionating device to continuously observe the dew point,.or temperature of total equilibrium vaporization of the product of such apparatus.

Another object is to permit the observation of such quality in such a manner as to permit it to be used for control oi the operation producing the product. Other objects and advantages are possessed by this invention, some of which will be referred to hereinafter and some of which will be obvious to those skilled in the art.

While pertinent to all distillation operations in which the end boiling point of the product must be controlled to avoid the inclusion of materials 50 heavier than desired, the discussion will be herein limited to motor gasoline for simplicity. Most of the desirable properties of gasoline are tied up with its end distillation point and its volatility. So great is the truth of this statement that freetionating equipment for the production of gasoline is practically always operated by the control of end boiling point on the one hand and total vapor pressure on the other. Methods for automatically observing, and recording total vapor pressure and basing the control onthat have been worked out for application to stabilizers and similar apparatus for the reduction of volatility or vapor pressure in excess of that desired. No

simple method has as yet been presented for the automatic control-oi end boiling point.

Methods at present used for the control of end boiling point involve periodic removal of a sample, manual distillation in a batch process-the A. S. T. M. distillation, interpretation of results,

and subsequent change of distillation conditions if the control test has shown this to be necessary. This method presents several difllculties. Considerable time elapses between tests, manual control is involved, and a chemists time is required for the distillation. The results 01' the test are not, in themselves, a direct measure of the characteristics desirable in the product. The nearest approach to automatic operation of which we are aware accomplishes automatic withdrawal and analysis of sample, but leaves the entire interpretation of results and adjustment for correction just where it was before.

This invention is based upon the discovery that 55 the dew point of a product may be continuously observed in a convenient manner, and the control of equipment automatically accomplished thereby.

The dew point oi. a vapor is the temperature at which initial condensation occurs when a whole,

completely vaporized sample is'cooled. Converse- 1y, when considering a material such as gasoline, which has a boiling range rather than a boiling point, it is the temperature at which a sample heated under non-vaporizing conditions, will just be 100% vaporized on releasing or "flashing." The dew point is thus a comparatively sensitive measure of heavy material in the product. It has the advantage of having a direct physical significance. Carburetion in an internal combustion engine, or analogous operations, are in reality flash vaporizations. equilibrium flash vaporization point, is directly responsible for completeness of vaporization under any given conditions and easily correlated therewith. No other commonly observed property is so directly a measure of this valuable characteristic of gasoline. Vapor pressure alone is only part of the story, because vapor pressure is highly sensitive to percentage of highly volatile components, and relatively insensible to high boiling components. A. S. T. M. distillation end point is not completely significant, because two gasolines of the same end point will vary greatly in ability to be volatilized under given conditions because of variation in relative amount oi! lighter components present. These two properties bear upon each other and thus compel interpretation oi. results and prevent simple automatic control from observation of such properties. Dew point is the one determinable property which ties these things together, and when it becomes possible to continuously observe and record the dew point, it is possible to continuously control still conditions in a simple and convenient manner without the necessity of an operator's interpretation of results.

We have devised an apparatus for continuously observing and recording the dew point and which lends itseli to such control. In order that this device may be more readily understood, reference is now made to the drawings attached to and made a part 0! this specification, in which Figure 1 shows the dew point apparatus and Figure 2 shows the manner in which it may be applied to still control.

In Figure 1, which is diagrammatic, 3 is a pipe through which the distillate product to be tested is introduced in condensed or partially condensed form to coil 4, placed in heating bath 6, which is filled with a suitable liquid and heated by The dew point, or 100% iectrlcal heater: lne heated to ell. b a

which is is likewise r vaporate from the pan 3 to the gas stream. bel w the dew pol the pan regularly be comes hes. --until it filled. Above the dew a 3 becomes lighten-until empty.

in weight pan i3 is employed to cm. temperature of the bath and indiwe and record point. Any

nose. 2 e orefe to employ an inductance ce it enables us to dispense wit mov springs, etc, mounted. in the vapor stream 5; exposed to possible gumming and. corrosion. The inductance bridge consists of solenoid coils l8 surrounding solenoid core M, which supports the pan, and solenoid coils ll surrounding core i8. The inductance bridge is actuated by a source of alternating current 20, which also supplies the various heating services. Without considering in detail the makeup of the inductance bridge, which is well known, its properties are such that when actuated by alternating current as shown, the two cores are suspended at certain points as determined by their weights, the properties of the coils, etc., and any change in the position of one is followed by a corresponding proportional change in the position of the other. Thus, when coil 1 is below the dew point and pan l3 becomes heavy, core l4 moves down, and a corresponding movement of core i8 relayed by contacts l9 admits current to auxiliary heater 2!. When coil 1 is above the dew point, pan 13 becomes lighter, and core I8 is correspondingly moved to cut out heater II. The bath in heating vessel 8 and coil 1 immersed therein are thus kept at the dew point of the vapor analyzed, proportions of bath and coil being so selected that hunting is minimized. It is of course understood that while direct contacts are shown at I9, it will probably be preferable to employ some convenient form of relay system, the direct contacts being shown for simplicity. Since the bath in vessel 8 is maintained at the dew point of the substance analyzed, it is simple to observe the temperature of the bath or in the trap ID by any convenient form oi thermocouple as 22, here shown in the bath near trap ID, to which is attached the indicating and recording pyrometer designated by 23.

in diagrammatic form how this dew point, in this apparatus r the control of a distillation gure 24 is a. columnar still, to which feed reduced by pipe 26, and heated by coal Residue is withdrawn through pipe ET, v "ors pass overhead through pipe 29 to receiver 30. Distillate awn through pipe 3!, and pipe end a continuous sample of dis point analyzer comprising vessels rap Hi, as previously described. rmocouple 22 observes the dew pols; and instrument 23 indicates and records it. In this set-up however, instrument 2! has an additional function. Condensate from drum 3!) is returned by pump 33 through pipe 34 as wet re for on rol of top temperature of tower eturned being controlled by valve 23 in this case is also a control instrument, so designed that when the dew point exceeds a predetermined maximum, admitted to tower 24, and when too low, less is admitted. capable of so acting are own, and of many forms, and 1' part of this invention, and motion is consequently indicated onnection between instrument 23 r vur l product is 32 is provide.' tillate to a use i that equivalents of the device disclosed will occur to those skilled in the art, and it our intention to claim all that is move} 5. ermn, except as limited by the following claims.

We claim:

Means for continuously observing the dew point of a continuously flowing stream of vaporizable substance comprising means Ior continuously sampling said stream, means for converting said sample to a slightly superheated vapor, a tube through which said vapor flows, a heater to maintain said tube at a temperature below the dew point of said vapor, said tube including a trap, pan in said trap, means to direct condensate formed in said tube on said pan, an auxiliary heater for said tube, means responsive to the weight of the condensate in said pan to control said auxiliary heater to add more heat in response to an increase and less heat in response to a decrease in condensate, whereby said tube is maintained at the dew point temperature of said vapor, and means to observe the temperature of the tube.

2. Means for continuously observing the dew point of a flowing stream of vaporizable substance, comprlsing means to extract a sample therefrom, means to convert such sample to a slightly superheated vapor, means to cool such vapor to a controlled temperature, means to collect any condensate so formed in a position exposed to uncondensed vapors, means actuated by the amount of condensate collected to so control the cooling temperature that the condensate amount tends neither to decrease nor increase, and means to observe the controlled temperature.

ROBERT F. DENISTON. WENDELL P. HAWTHORNE.

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