US2069490A - Distillation control - Google Patents

Description

Feb. 2, 1937. M. R. FENSKE 6 DISTILLATION CONTROL Filed Sept. 15, 1933 2 Sheets-Sheet 1 RICE/V6? Co/mavsm M aim Feb. 2, 1937. M. R. FENSKE DISTILLATION CONTROL Filed Sept. 13, 1933 2 Sheets-Sheet 2 Z] M W V merrezmnmke Patented Feb. 2, 1.937

I DISTIILATION coN'raoL Men-ell B. Fenske, State College, Pa, assignor to Pennsylvania Petroleum Research tion, a corporation of Pennsylvania Corpora- Application September 13, 1933, Serial No. 689,331

12 Claims. (01. 196-132) This invention pertains generally to distillation, and particularly to acontrol therefor. It will be described in connection with the fractional distillation of mineral oils. However, it is to be understood that it is applicable to distillation processes in general.

In designing towers or columns, for instance for batch distillation, it is more or less the general practice to take into consideration the high- J est reflux ratio which will be required to separate the most diflicultly separable fractions. When this reflux ratio is determined and chosen it will aflord an adequate reflux for all fractions. but for all except the most difllcultly separable 5 fraction the reflux will obviously be more copious than is required, and the product will be taken oil at a lowerv rate than is necessary; Furthermore considerable heat is wasted in the excessive reflux since it must be revaporized and recondensed.

Since time is a very important element in the cost of operation it will be seen that unless some controlof the reflux ratio is afforded the process must be regarded as being relatively inefilcient.

A practice which has been followed to a con- 5 siderable extent involves the manual control of the reflux ratio according to what the operator by experience determines to be appropriate for the particular fraction coming off at the moment. This at best can be namore than a mere approximation. Furthermore; uniformity of results depends upon the operators approximating ability remaining constant from the beginning to the end of his shift and from da to day, and when different operators control he same piece of equipment, upon their respective approximating abilities being the same. It can be seen that under this practice. a really satisfactory control is not realized since it is too largely dependant upon the human element.

m In the-fractionation of compositions such as mineral oils, particularly upon a plant scale, practically none of the fractions comprise a constant boiling substance. The selection of the desired reflux ratio or ratios for each fraction 5 therefore; not only involves the-time element but also the desired temperature spread in the prodnot, for it will be recognized that the larger the reflux ratio the narrower will be the spread and vice versa.

so By way of explanation, a constant-boiling substance might be either a pure chemical compound or any mixture of compounds whose vapor is of the same composition as the liquid.

A pure chemical compound is characterized by 55 having a flxed boiling point at any given pressure.

A flxed boiling point is likewise a characteristic of a constant-boiling mixture but the pressure at which the vapor is of the same composition as .the liquid is usually also fixed.

In other words a constant-boilin substance 5 might be deflnedas one whose initial boiling point and end boiling point are the same at a given pressure.

The temperature spread of a substance is the difference in temperature measured in degrees between its initial boiling point and its end boiling point.

It follows that a constant-boiling substance has a zero temperature spread, whereas a mixture of compounds whose vapor is not of the same composition as the liquid (and therefore separable by fractional distillation) has a temperature spread greater than zero.

A feature of this invention therefore relates to an accurate reflux ratio control.

A further feature relates to a control which affords a product of the desired temperature spread.

A further feature of the invention relates to a new and novel process and apparatus for the automatic control of the reflux ratio for each fraction and of the temperature spread of the -fraction.

A further feature of the invention relates to a control of the quantity of reflux and of the quantity of product, said control being responsive to the temperature spread of the product.

A further feature of the invention relates to a control for the reflux ratio which automatically varies the reflux ratio in accordance with requirements.-

Further features of the invention reside in the construction, arrangement and combination of parts, and in the steps, and combinations and sequences of steps, all of which together with other features will become more apparent to persons skilled in the art as the specification proceeds and upon reference to the drawings in which: I

Fig. l is a semi-diagrammatic illustration of an embodiment of the invention.

Fig. 2 illustrates a modified form of control column.

Fig. 3 illustrates a further form of control column. i

Fig. 4 illustrates a means for varying the resistance of the galvanometer circuit at different temperatures.

Fig. 5 illustrates means for obtaining different voltages across the galvanometer circuit.

Referring now more particularly to Figure 1 of the drawings at I0 is conventionally illustrated a distilling tower having associated therewith the usual condenser ll, areflux line l2, and a'product line I3. Exhausting means is also conventionally illustrated at I4.

All of the foregoing may be regarded as standard equipment. The exhausting means may or may not be used depending upon whether or not tower I0 is to be operated at sub-atmospheric pressures.

The equipment illustrated is of the batch type. The invention, however, is equally applicable to the continuous type of equipment. In the latter case a separate control column controls the temperature spread of each product stream taken off.

The reflux ratio is of course the ratio of the reflux to the product. For a given amount of condensate delivered by condenser I I the smaller the the amount of product drawn ofi the larger will be the amount of reflux as well as the reflux ratio, and vice versa. It follows that the reflux ratio may be controlled by controlling the rate at which the product is withdrawn from the system.

In a normally controlled system, as previously pointed. out, the rate of withdrawal of product during the separation of any fraction is a matter of guess work and there is no accurate control of the temperature spread of the fraction.

In accordance with this invention the temperature spread of the product (or a fixed part or parts thereof) is employed to control the rate at which the product is withdrawn. The temporature spread of the product may be set at anydesired value. For a constant boiling liquid fraction it will obviously be zero. For fractions having finite boiling ranges the spread may be held constant at any desired value up to the point where no reflux is returned to the tower. In other words the reflux ratio may be varied between infinity, in which case there would be no product and all the condensate would return as reflux, and zero, in which case there would be no reflux and all of the condensate would be removed as product.

The term temperature spread" for the purposes of this specification and the claims will include a zero spread, and the terms phase composition differential and temperature differential to be hereinafter employed includes a zero differential.

The control of the temperature spread of the product is accomplished through the use of a control column through which at least a portion of the product flows preferably (though not necessarily) continuously on its way to the receiver or other destination. The product as it passes through a suitable receptacle or still at the bottom of the column is maintained at a boiling temperature. The vapors pass up through the column, which has a suitable number of theoretical perfect plates for instance between 4 and 10, and the phase composition differential (which will be referred to hereinafter as being measured in terms of temperature differential) between vertically spaced points in the column, for instance between the top and bottom, is employed to control a valve in the product line. The valve in the product line controls the rate of flow of .pro'duct and thus the reflux ratio, which in turn determines the temperature spread.

By phase composition differential is meant difference in composition within either or both the control column. This may be zero or greater than zero.

By temperature differential is meant difference in temperature within either or both phases between points spaced longitudinally of the control column. This may be zero or greater than zero.

In the case of a mixture whose vapor is not of the same composition as the liquid at the pressure obtaining in the control column each phase is caused to vary in composition longitudinally of its flow as the normal result of fractionation, each phase becoming richer in the lighter constituents from the bottom to the top of the column. As a result the temperature decreases from the bottom to the top of the column.

In the case of a constant-boiling substance, since separations cannot be made by fractionation, each phase remains uniform in composition and the two phases are of the same composition throughout the control column. As a result the temperature is uniform from the bottom to the top of the column.

Since the temperature differential between any two longitudinally spaced points in the control column is a measure of the phase composition dififerential between these two points, for purposes of simplicity in description temperature differential will be referred to.

For a constant boiling fraction both the temperature differential and temperature spread will be zero. For a fraction which is further separable by fractionation the temperature diiferential will have a value greater than zero and will be dependent upon the temperature spread of the product flowing through the receptacle. By closing the valve (partially or completely) when the temperature differential and consequently the temperature spread is larger than desired and opening the valve (partially or completely) when the temperature differential and consequently the temperature spread is smaller than is desired, the reflux ratio is automatically varied according to the requirements for separation of the fraction. As a result the capacity of the equipment is increased and each fraction is taken oil" with a desired temperature spread. This spread need not be the same for each fraction, but may be different as will hereinafter appear.

Referring to Figure 1 of the drawings at 16 is illustrated a flask having a relatively long stem i1 and a. bulb l8. The upper portion of stem I1 is surrounded by a condenser l9 and above the condenser a branch tube 20 is illustrated. Bulb l8 at its bottom communicates with an S-shaped draw off tube 2!, the highest point 22 of which is so positioned with respect to bulb I8 as to maintain a desired liquid level in bulb l8.

Stem I'I contains a suitable column packing material which is illustrated as being supported by a helical spring 24 having its ends 25 fused into the walls of stem H. In order that the control column may be compact and yet contain a reasonable number of perfect plates, I prefer to use a packing material 26 which requires a very small height per theoretical plate, for instance single helical turns of about inch diameter and small pitch made from very small diameter rod and of any suitable material such as metal or glass. However, any other packing may be employed. In fact any type of column may be adapted to this particular use.

A tube 28 communicates with stem l1 below condenser l9 and adjacent the top of packing 26. Tube 28 is connected to product line 63 on the outlet side of an electrically controlled valve 23 in said product line. The connection of tube 1 .24 to line I3 is such that product will flow therethrough in preference to continuing through line I3 Any means may be provided for this purpose, for instance such as that illustrated. An adjustment screw or valve 38 is provided in tube 28 so that the flow therethrough may be regulated. The rest of the product flowing through valve 28, oi course, continues on throu h line l3 and is delivered to any suitable destination, for instance, a receiver illustrated at 3|.

Valve 28 is provided with a constant flow oriflee 82, which is controlled by an adjustment screw 33, and a variable flow orifice of substantially greater capacity 34 which is controlled by a movable valve element 35 operated byxsolenoid 38.

Theflow through orifice 32 need only be substantiallyiust sufficient to keep the tube 28 filled,

since it is primarily provided so that the control column may be supplied, with condensate even though the orifice 34 is closed.

Any means may be provided to respond to the temperature differential between desired vertically spaced points in the control column. For

instance a thermocouple junction may be posltioned at each point and a galvanometer may be connected in series with thesejunctions and may be made to respond to any current set up by a difi'erence ofv temperature at the junctions. The relative position of the responsive element of the galvanometer may be made to control an external circuit which may be made to operate the solenoid 86.

Such an arrangement is shown in the drawings wherein a single strand of wire (which may be bareii the packing 26 is non-conductive) is shown threaded down through stem l1 and out through bulb l8. This strand of wire between terminals 38 and 38 is composed of two different suitable metals or alloys of metals, the portion 48 between junctions 4| and 42Jbeing of one metal and the portions 43 and 44 being of the other metal. If the remainder of the circuit is composed of a metal other than that of the portions 43 and 44 the terminals 38 and 39 should obviously be maintained at substantially the same temperature, which may be room temperature.

The remainder of the circuit as shown comprises wire 48 in which is inserted rheostat 41, coil 48 oil galvanometer 49 and wire 58. Galvanometer 48 is of a well known type and is merely illustrated diagrammatically. An essential feature of galvanometer 48 is that coil 48 rotates in response to and through an arc proportional to current flow, and returns to its original position upon the cessation of such fiow.

-Coil 48 carries a mirror which is adapted to reflect a beam of light from a light source 52 in the general direction of a photoelectric cell 53, said beam being directed on or off, of said cell depending upon the position of coil 48.

Since it is desired to concentrate the beam on the photoelectric cell for all values of current above a certain point, a stop 55 is provided for .coil 48, said stop limiting the rotation of coil- 48 in a manner to obtain these results.

Cell 53 is a part of a vacuum tube relay circuit; This circuit comprises a three element tube 51 having a plate 58, a grid 59, and a filament 60. The filament is illustrated as being supplied with alternating current from a transformer SI for the purposes of heating. The conventional potentiometer 52 with sliding tab 53 is shown connected across the filament terminals, the tap being connected to the minus 18 terminal.

The input circuit includes a potentiometer 54 connected across a suitable voltage source with the plus terminal connected to the filament through tap 63 and potentiometer 52. Potentiometer 54 has two sliding taps 55 and 55, tap 55 being connected to grid 59 through cell 53, and tap 68 being connected to grid 59 through the grid leak 61. Tap 65 is directly connected to the cathode 68 of cell 53 and grid, is dii-ectly connected to the anode 58 of cell 53. The

Assuming the distillation equipment to be in operation, product will flow through pipes l3 and 28 into and down through the control column and into bulb i8; where it will be brought to a boiling temperature by any suitable heating means. Such means has been illustrated as a heating element 88, connected across a source 8| through a current control 82. The vapors ascend through the control column and if the product is further separable by fractionations rectification takes place with the result that points 4| and 42 will have a different temperature. The temperature differential between points 4| and 42 will of .course depend upon the temperature spread of the product. If the temperature spread is zero as in the case of a constant boiling liquid, the temperature diflerential will also be zero. If the temperature spread has some value above zero, the temperature difierential will also have a value above zero and proportional to the temperature spread.

A diiierence in temperature at points 4| and 42 generates an electromotive force which causes a current flow through the galvanometer, and coil 48 .rotates through an are proportional to the current flow. Whether or not the beam of light will be brought to rest upon the photoelectric cell 53 will depend upon the value of the temperature dififerential and the setting of the instrument. The setting is accomplished by means of rheostat 41 which controls the amount of currentfor' any temperature difierential. The beamof light is brought to rest on cell 53 when and as long as the desired temperature spread is exceeded, whether it be zero or of a finite value.

The relay circuit is so arranged and adjusted that when cathode 68 is not energized, suflicient current. may flow through the output circuit to energize relay 1| to hold contacts 13 and 14 apart. This permits orifice 34 to remain open and product may flow freely therethrough. Current in the output circuit may be adjusted at tap 56 which controls the normal grid bias.

Let us assume that a temperature spread of 10 F. is desired in the product. In this case coil 48, by means of rheostat 41. would be set so that the light beam would fall just to one side of Now should the spread increase beyond 10 degrees, the increased temperature differential would ircrease the electromotive force generated by the thermocouple which in turn would increase the current through galvanometer 49 to further rotate coil 48. This would bring the beam of light onto cell 53 thereby making the cell conductive. This would increase the grid bias in view of the position of tap 65 sumciently to cut down the current in the output circuit to the point where relay 'II would be in effect 'deenergized. Orifice 34 would be immediately closed due to the release of armature I2 thereby causing contacts I3 and I4 to close the circuit through'solenoid 36.

The closing of orifice 34 decreases the rate of fiow of product and consequently increases the reflux ratio. A part of the product however flows continuously through the control column and as soon as the increased reflux ratio has brought the product back to a 10 spread the light beam will move to one side of cathode 69. Orifice 34 will then open to increase the rate of flow of product. When the spread again exceeds 10 F. orifice-34 willclose and the cycle will be repeated.

In view of the high sensitivity of thermocouple and galvanometer circuits it will require only a very small change in the temperature differential to open or close orifice 34. This sensitivity may be increased by increasing the spacing between the cathode 69 and the mirror 5|, since the greater this spacing the smaller will be the necessary movement of coil 48 to bring the light beam on or oif cathode 69. Since the product preferably flows continuously and in very small amount through the control column, the fresh product will be brought to boiling immediately upon entering bulb I8 and the vapors and reflux of the control column will follow closely those of the fresh products. As a result, the temperature differential will follow closely the temperature speed.

Condenser I9 is provided preferably to completely reflux vapors which flow up above the control column. The complete reflux of these vapors prevents their escape and they are eventually delivered to receiver 3| as condensate. With a control column of the type shown in Figure 1 scrubbing is effected not only by condensate but also by the fresh product. The fresh product in descending through the control column reaches a temperature close to boiling before it enters bulb I8.

The control of the flow of the product may of course be accomplished in other suitable ways and different theories of operation may be devised. For instance in batch distillation it may be desired to set the opening at orifice 32 so that with orifice 34 closed the reflux ratio will be such as to take care of the most difiiculty separable fraction. In this case orifice 34 would control the reflux ratio for each of the other fractions as required.

The new product after flowing down through the control column will comprise the upper stratum of liquid in bulb I 9, will cause the outflow of old product through tube 22 and will be the first to vaporize. All of the fractions are completely miscible and therefore there will be no separation due to differences in density.

Although it is'preferred to pass only a small part of the product through the control apparatus for the'reasons set forth above, anyportion or all of the product may be so employed without departing from the spirit of the invention.

In the above description it has been assumed that the distilling apparatus is being operated at atmospheric pressure. Therefore the mouth of stem I I has been described as being open. In this case any change in atmospheric pressure will affect the distilling column and the control column equally and the precision of the control will remain the same.

When operating with sub-atmospheric pressures the mouth of stem I1 is closed, for instance by a cork 94 (through which passes the wire 43) and the control column is exhausted to the same extent as the distilling column by the vacuum apparatus I4. This is illustrated by connecting tube 95, which connects with tube 29, to vacuum line 96. Line 96 connects the output side of condenser II to vacuum apparatus I4.

For any distillation above atmospheric pressure the control column would also be operated at the same pressure as the distilling column.

Many other modifications might be devised by persons skilled in the art upon becoming familiar with this invention. For instance it will at once occur to a skilled electrician that the external circuit may be varied in a vast number of ways to accomplish a control of the rate of flow of product.

A different type of control column is shown in Figure 2 in which the flask 99 has a stem 9| without a product inlet and a bulb 92 having an inlet 93 at the bottom, and an overflow 94 at the side. Otherwise the control column of Figure 2 is essentially the same as that shown in Figure 1.

In operation the product enters at 93 and overflows at 94 and is kept boiling while in bulb 92.

In any case the volume of liquid in the bulb is preferably small so that this volume may at all times be representative of the product coming off.

A further type of control column is illustrated in Figure 3, in which flask 96comprises a stem 91 and a bulb 98. Bulb 98 has an S-shaped overflow 99 similar to that of bulb I8 of Figure 1.

Stem 91, at its top I99, is connected and sealed to a relatively larger portion I9I having a product inlet I92 at its top I93. A tube I94 has a portion I95 which extends down into portion I9I through its top I93 to which it is sealed. Tube I94 is substantially axially aligned with stem 91 and has an end I96 which is spaced from the end I99 of stem 91.

Tube I94 is provided with a condenser I91, a side tube I98 for connection to vacuum apparatus, and may or may not be closed with cork I99 depending upon whether they distillation is at subatmospheric or atmospheric or superatmospheric pressure as previously described.

In operation the product enters at I92 and flows down around portion I95 of tube I94 before it enters the top of the columnat I99. Vapors from the column ascend into tube I94 and are at least partially condensed in portion I95 since.

the product will generally enter at a temperature below boiling. The heat transfer to the product raises the temperature thereof so that it enters the column at a temperature nearer boiling. If all of the vapor is not condensed in portion I95 the rest is referably completely condensed by condenser I91. The latter form of flask is preferred if the product becomes substantially cooled before it reaches the control column.

According to the previous description, as long as the setting at rheostat 41 remains constant the fraction or fractions will come off with a temperature spread which will not vary substantially,

depending of course upon the care with which the apparatus is constructed. If it is desired to change the temperature spread iTor any traction it is merely necessary to adjust rheostat 41, to

reduce the resistance or the galvanometer circuit if it is desired to narrow the spread, or to increase the resistance if it is desired to widen the spread.

Since the temperature diilerential is proportional to the temperature spread it is possible to operate a pyrometer with the same, but preterably with a separate, thermocouple. The pyrometc: may then be calibrated in terms of temperature spread. This is illustrated in Figure 1 7 tion coming'ofl.

It is, of course, possible to control any other device or instrument by means of the temperature difl'erential' between spaced points in the control As previously pointed out, the control is equally applicable to either batch or continuous distillation. In the case or continuous distillation each product stream whether taken oil? at the top or at the side of the column has its temperature spread controlled by a separate control column in the manner above described. Thus the temperature spread of each product may be varied independently oi the other products.

Although it is preferred that the product flow continuously through the control column so that the character of the liquid therein may follow closely that o! the product, this is not an absolutely essential feature. For instance the control column might be employed only at intervals to adjust the rate of flow of the product, as by setting the opening of a valve or otherwise, or the control column might be employed tooperate any other type of transmitting means such as an indicator or gauge from which the rate of flow of product might be controlled normally. The pyrometer III is an example of the latter. Or the control column may be employed merely to make a record of the temperature spread as by operating pyrometer III, many types of which are adapted to make permanent records.

When'using the batch method it may be desired to change the temperature spread of succeeding fractions automatically. To accomplish this it is merely necessary to automatically vary the resistance of the galvanometer circuit as the temperatures which bound the fractions are reached. Any suitable arrangement may be provided for this purpose.

In Figure 4, for instance, is shown at I I2 a plurality of well known temperature controlled switching devices H3, H4, H5, and H6. Each of said switching devices II3 to H6 has an element responsive to temperature (not shown) which is inserted in the vapors at the top of the main column or between the main column and the condenser as illustrated at H2 in Figure 1.

As is well known these switching devices rotate through an are when a certain temperature is reached. This temperature may be set at any desired valve. The rotatable element of each switch II3 to H6 comprises a disc-like member H1, 3, I I3, and I respectively. Each disc-like member, as illustrated, carries two mercury switches, member II1 carrying switches, I2I and I22, member II8 carrying switches I23 and I24, member II9 carrying switches I26 and I26, and member I20 carrying switches I21 and I23. All of the switches are shown in cold position.

Switches I22, I24, I26, and I23 are inserted in a common series circuit between terminals I23 and I30. This circuit comprises resistance I31, wire I3I, resistance I36, switch I22, wire I32, switch I24, wire I33, switch I23, wire I34, switch I28, and wire I35. Switches I22, I24, I26, and I23 are closed in the positions shown.

Switche I2l, I23, I25, and I21 are shown in open position. Switch I 2| controls a circuit between wire I3I and wire I32 which circuit includes a resistance I33. Switch I23 controls a circuit between wire I,3I and wire I33, which circuit includes a resistance I39. Switch I25 con trols a. circuit between resistance I31 and wire I34. Switch I21 controls a circuit between terminal I29 and wire I35 which circuit includes a resistance I40. Switching devices H3, H4, H5, and H6 respond in order as the temperature increases and for the purposes of illustration it will be assumed that switching device I3 rotates at 200 C., switching device 4 at 250 C., switching device H5 at 300 C. and switching device I I6 at 350 C. No particular significance is attached to the temperatures chosen, to the number of switching devices employed, or to the sequence in which the temperature spread is increased or decreased, all of which are described in detail for the purposes of illustration.

The device of Figure 4 may be connected in series with the galvanometer circuit in any suitable manner, for instance by opening the circuit at point I42 on wire'50, and inserting a. single pole double through switch I43, which in one position connects the ends I44 and I45 of wire directly and in the other position connects the terminals I23 and I30 in series between ends I44 and I45.

The rheostat 41 is adjusted so as to afford the desired temperature spread for the fractions which come ofl under 200 C. When 200 C. is reached switching device II3 rotates clockwise. This opens switch I22 thus breaking the previous lyclosed circuit between wires I3I and I32, and closes switch I2I, thus closing a new circuit between wires I3I and I32 through resistance I38.

' The eflect of this is to substitute resistance I38 for resistance I36. Resistance I38 may be of any desired value and will be larger than resistance I36 if the temperature spread is to be larger between 200 C. and 250 C. or is smaller if the spread is to be smaller. Resistance I38 may be fixed or variable but preferably has a set value with respect to resistance I36 so as to automatically set the device for the desired new spread without further adjustment.

When the temperature reaches 250 C. switching device II4 rotates clockwise. This opens switch I24 and thus the previously existing circuit between wires HI and I33 through resistance I38 is broken. This also closes switch I23 thus closing a new circuit between the same wires through resistance I39. The net efiect of this is to substitute resistance I39 for resistance I38. Resistance I33 may be larger or smaller according to the temperature spread desired between 250 C. and 300 C.

Upon reaching 300 C. switching device rotates clockwise. Switch I26 opens to open the previously established circuit through resistance I39 and switch I25 closes to directly connect resistance I31 to wire I34. The net effect of this is to reduce the resistance between terminals I29 and I30 below that of the first circuit by the amount of the resistance I 30. The spread will obviously be narrower than at any time previous.

When 350 C. is reached switching device IIB rotates clockwise to open switch I28 and close switch I21. The opening of switch I28 opens the previously established circuit between terminals I29 and. I30 and the closing of switch l21 directly connects terminals I29 and I30 through resistance I40. The net effect of this is to 'substitute resistance I40 for resistance I31. If resistance I40 is smaller the spread will be made still narrower. If resistance I40 is larger the spread will be larger than just previous and obviously may be of any desired value.

No'attempt has been made to exhaust all of the possible combinations of resistances and switches which are unlimited. From the foregoing it will be seen that any desired sequence of temperature spreads may be obtained.

Switches H3, H4, H5, and H5 return automatically to their original positions when the temperature drops back below 200 0., 250 0., 300 C., and 350 C. respectively. Since a fall in temperature below 200 C. generally accompanies the charging of a new batch, the device will automatically set itself to repeat the foregoing sequence with the new batch.

Othermeans may be provided to obtain the desired sequence of temperature spreads. For instance it is possible to vary the resistance of the galvanometer circuit at desired time intervals by means of clock mechanism. However, varying the resistance with the temperature at certain temperatures is to be preferred in batch distillation.

A means for obtaining different voltages across the galvanometer is illustrated in Figure 5. In this figure flask I6of Figure 1, and its appurtenances have been substantially reproduced except for the thermocouples I41, I48, I49, and I50. Each of the latter thermocouples has a pair of junctions I5I, I52, I53, and I54 respectively. The spacing between junctions is different for each pair. It follows that the temperature differential' between each pair of thermocouple junctions will be different and consequently the voltage developed by each pair will be different. These different voltages may be availed of to vary the temperature spread by connecting selected thermocouples across the galvanometer. This may be done manually or automatically, for instance by a clock mechanism.

As illustrated in the drawings one set of thermocouple terminals is connected to a common terminal I56 and the terminals of the other set are connected to the spaced fixed contacts I51, I58, I59, and I60 respectively of a rotary switch IBI. The galvanometer 49 is. connected between themovable contact I62 of switch I6I and terminal I56.

The different voltages obtained from the thermocouples may be availed of for any desired purpose. For instance thermocouples I41, I48, I49, and I50 may be standardized so that the temperature spread of the product may be varied fixed amounts. For instance, the temperature spread might be 5 C. when thermocouple I41 is in circuit, 10 C. when thermocouple I48 is in circuit, C. when thermocouple 449 is in circuit and C. when thermocouple I50 is in circuit.

Switch I6I may be operated manually for in stance by the knob I64 or automatically for instance by the clock mechanism illustrated generally at I65. Any clock mechanism would be suitable and it is therefore not illustrated in detail. Knob I64 may correspond to the knob for manually setting the hand or hands when a clock mechanism is employed. This would afford both manual and automatic operation.

The invention in its broader aspects includes the rectification of any vapors of the character producing the product. Such vapors for instance not onlyfiinclude vapors of the product itself as it is drawn off from the column either in an overhead or side stream, but also the vapors passing up through the main column which after beingrectified and condensed form such product. The temperature differential between spaced points in the rectifying means for the particular vapors would then control the rate at which the product of such vapors would be withdrawn and consequently the reflux ratio affecting the particular product. In this case it is merely necessary to transfer the thermocouple to the proper section of the main column. Such section for each vapor is preferable one over which the vapor flows just prior to being condensed since it is then in a relatively pure state. For instance, the main column itself, or parts thereof might be used for the same purpose as the separate control column.

While the invention has been described in connection with the control of the flow of product from a distillation column it is to be understood that the invention may be employed for any purpose whatsoever. For instance, it would be possible to employ the control column to control the rate of condensation or the temperature 'spread of the condensate in any section of a fractional condensation system. In this case the column would control the rate of flow of cooling fluid through the particular section of the fractional condenser and thus control the temperature spread of the liquid condensed therein. A part of the condensate would of course flow through the column so that the proper spread might be maintained.

Other uses will suggest themselves to persons skilled in the art upon becoming familiar with this invention.

Several distillation columns might be controlled by a single control column particularly if their operation characteristics were substantially the same. The product of one column might control the operation of all columns or a. part or'all of the product of two or more columns might be mixed before entering the control column.

Although certain embodiments of the invention have been described in detail it is to be understood that the invention is not limited thereto. Therefore, changes, omissions, additions, substitutions and modifications may be made without departing from the spirit thereof, and the claims are intended to be limited only as required by the prior art.

I claim:

1. The combination with apparatus adapted for the fractional distillation of a liquid and having means for varying the temperature spread of the product produced thereby, of a device for controlling said means and thus the temperature tus, said device comprising a control column, a

still for said control column, means for continuously flowing at least a portion of said product produced by said first-mentioned apparatus through said still, means for vaporizing at least a portion of said product as it flows through said still, means for causing said product vapors to flow through said column countercurrently to liquid reflux under at least substantially adiabatic conditions, and means responsive to temperature differential between spaced points having at least a portion of the contacting section of said control column vtlierebetween for controlling said first-mentioned means. 2. In combination, fractionating apparatus, means associated with said apparatus for controlling the temperature spread of the product produced thereby, a control column adapted to operate under at least substantially adiabatic conditions, means fordelivering vapors of the character producing said productto said control column, means in said control column for subjecting said vapors to fractionating conditions, a plurality of means each responsive to temperature diflerential between a separate pair of spaced points in said column, the spacing between each pair of points being different from that of the others, means for selectively connecting a translating device to said means of said plurality of means, and means for connecting said translating device to said first-mentioned means for controlling the same.

3. A method comprising fractionating a liquid mixture under conditions in which the temperature spread between the initial and end points of a product of said fractionation is subject to variation through a control of said fractionation,

subjecting vapors of said product to further fractionating conditions, measuring phase composition diilerential efl'ected by said last mentioned fractionation, andcontrolling said first mentioned fractionation in accordance with increase or decrease in said phase composition diflerential so as to maintain substantially constant the temperature spread of said product.

"4. Incombination, means for fractlonating a liquid mixture, means for varying the temperature spread between the initial and end points of a product of said fractionation, means for subjecting vapors of said product to further fractionating conditions, means responsive to change in phase composition difierential between a pair of spaced points having at least a part of said last mentioned fractionating conditions therebetween, and means for connecting said last mentioned means to said-second mentioned means to control said second mentioned means in accordance with increase or decrease in said phase foo composition differential so as to maintain substantially constant the temperature spread of said product.

5. A method comprising fractionating a liquid mixture under conditions in which the temperature spread between the initial and end points of a product of said fractionation is subject to variation through a control of said fractionation, subjecting vapors of said product to further fractionating conditions, measuring phase composition diflerential efiected by said last mentioned fractionation, and controlling said first mentioned fractionation to maintain a substantially constant .temperature spread of said product by causing said temperature spread to decrease when said phase composition differential increases above the value in phase composition differential at which the desired temperature spread is obtained and by causing said temperature spread to increase when said phase composition differential decreases below the value in phase composition differential at which the desired temperature spread is obtained.

6. In combination, means for fractionating a liquid mixture, means for varying the tempera-. ture spread between the initial and end points of a product of said fractionation, means for subjecting vapors of said product to further fractionating conditions, means responsive to change in phase composition differential between a pair of spaced points having at least a part of said last mentioned fractionatingconditions therebetween, and means for connecting said last mentioned means to said mond mentioned means in a manner to decrease said temperature spring with increase in said phase composition differential and to increase said temperature spread with decrease in said phase composition differential to maintain the temperature spread of said product substantially constant.

. 7. A method comprising subjecting vapors of the charactenproducing a product of a fractionating tower to fractionating conditions by intimately contacting said vapors with countercurrently flowing liquid reflux in a contacting path, said vapors and said liquid reflux entering said contacting path at longitudinally spaced points, and controlling the degree of fractionation effected by said fractionating tower in producing said product through a phase composition differential measured between a second set of spaced points, said second set of spaced points being in said contacting path and bracketed by said flrst mentioned spaced points.

8. A method comprising separately subjecting vapors'of a product of a fractionating tower to further fractionating conditions by intimately contacting said vapors with countercurrently flowing liquid reflux in a contacting path, said vapors and said liquid reflux entering said contacting path at opposite ends thereof, and increasing and decreasing the degree of fractionation eiTected by said iractionating tower in promentioned vapors with countercurrently flowing liquid reflux in a separate contacting path, said last mentioned vapors and last mentioned liquid reflux entering said separate contacting path at opposite ends thereof, and employing differ-- ence in temperature between longitudinally spaced points in said separate contacting path to control the proportion of liquid reflux to vapors in said first mentioned distillation, said spaced points being positioned between the point of entry of said second mentioned vapors and the point of entry of said second mentioned liquid reflux into said separate contacting path.

'10. A method forcontrolling the temperature spread between the initial and end points of a product of the fractional distillation of a liquid mixture in which fractional distillation vapors of said liquid mixture are countercurrently contacted with liquid reflux comprising, subjecting vapors of said product to further fractionating conditions by intimately contacting said last mentioned vapors with countercurrently flowing liquid reflux in a contacting path, said last mentioned vapors and last mentioned liquid reflux entering said contacting path at opposite ends thereof, and increasing and decreasing the proportion of liquid reflux to vapors in said first mentioned fractional distillation withincrease and decrease respectively in temperature differential between longitudinally spaced points in said contacting path, said spaced points being positioned between the points of entry of vapors and liquid reflux into said contacting path.

11. The combination with fractlonating apparatus having means for varying the temperature spread of a product produced thereby, of a device for controlling said means and thus the temperature spread of the product produced by said apparatus, said device comprising a control column, means for flowing vapors of said product through said control column countercurrently to liquid reflux, and means responsive to change in temperature differential between spaced points having at least a portion of the contacting section of said control column therebetween for controlling said first mentioned means in a manner to decrease said temperature spread with increase in said temperature differential and to increase said temperature spread with decrease in said temperature differential.

The combination with fractionating apparatus having means for varying the temperature spread of a-product produced thereby, of a device for controlling said means and thus the temperature spread of the product produced by said apparatus, said device comprising a control column, means for flowing vapors of said product through said control column countercurrently to liquid reflux, means responsive to change in temperature differential between spaced points having at least a portion of the contacting section of said control column therebetween for controlling said first mentioned means in a manner to decrease said temperature spread with increase in said temperature differential and to increase said temperature spread with decrease in said temperature difierential, and means responsive to change in temperature of product vapors delivered by said fractionating tower for changing the sensitivity of said last mentioned means to change the value of the temperature spread.

. MERRELL R. FENSKE.

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