US1971816A

US1971816A - Method and apparatus for the control of evaporating processes

Info

Publication number: US1971816A
Application number: US485455A
Authority: US
Inventors: Hecht Max; David S Mckinney
Original assignee: EUGENE G CAMPBELL
Current assignee: EUGENE G CAMPBELL
Priority date: 1930-09-30
Filing date: 1930-09-30
Publication date: 1934-08-28
Anticipated expiration: 1951-08-28

Description

Aug 28, 1934.- M. HECHT ET AL METHOD AND APPARATUS FOR THE CONTROL OF EVAPORATING PROCESSES 2 Sheets-Sheet 1 Filed Sept. 30,1950

INVE' 'TORS 5% ugh Aug. 28, 1934., HECHT ET AL 1,971,816

METHOD AND APPARATUS FOR THE CONTROL OF EVAPORATING PROCESSES Filed Sept. 30, 1930 2 Sheets-Sheet 2 INVENTORS Patented Aug. 28, 1934 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR THE CON- TROL OF EVAPORATING PROCESSES Max Hecht and David S. McKinney,

Pittsburgh,

assignors of one-third to Eugene G.

38 Claims.

The present invention relates broadly to the method of controlling the concentration of dissolved substances in liquids undergoing evaporation, and to apparatus effective for controlling suchconcentration. One of the objects of the invention is to so control the concentration of dissolved substances as to enable the production of the vapor phase of a liquid, which vapor phase is of predetermined quality or purity.

Although the broad features of the present invention' are applicable to processes other than evaporating processes, it will, for purposes of a clearer understanding, be described in connection with sucha process and to the control of the factors governing evaporation in such manner that the production of steam of predetermined quality or purity may be continuously produced. As applied to a heat exchanging operation effective for producing evaporation, it is applicable to the evaporation of liquids in closed containers at any practical or operable temperatures and pressures in which the liquid and vapor phases are co-existent and where both of the phases contain substances which confer electrical conductance characteristics thereupon.

For purposes of the present invention it may be pointed out that the conductance of an aqueous solution depends only on the ions of the dissolved substances, the specific conductance of a solution being a measure of the total of ionized substances present therein, taking into consideration the kinds and quantity of the ions present. The present invention is predicated primarily on the control of the factors entering into the processes involved by means of the conductance of the liquid and vapor phases.

While it has heretofore been proposed in the art to which the present invention relates to make use broadly of the conductance principle for controlling the chemical composition of different mixtures and for indicating the dissolved substances present in liquids, it has not been proposed, insofar as we are aware, to utilize the conductance method for controlling automatically the factors verning an evaporating process. Furthermore, t those familiar with the art it will be appreciated that it has heretofore not been practical to measure continuously the concentration within a container of dissolved substances in liquids undergoing evaporation in boilers, evaporators,

and distillers, nor has it been practical to measure continuously the concentration of dissolved salts entrained from the liquid in the steam or vapor discharged from boilers, evaporators and distillers without condensing and cooling the vapor in such manner as to prevent inaccuracies in the conductance measurements.

In accordance with the present invention, the liquid and vapor are preferably withdrawn from a closed container-of the character referred to, and cooled and condensed under pressure in suitable heat exchangers in such manner as to prevent contact of the cooled supplies or samples with atmospheric gases. Such samples then have their electric conductance measured under conditions 85 of substantially no alteration of the dissolved substances and gas content, for the reason that the measurements are made in closed containers and the cooling and condensing operations are so carried out as not to result in loss of the relation of liquid to dissolved substances such as would be experienced, for example, by flashing of the liquid. Throughout the specification and claims the portions continuously withdrawn from the closed container and cooled will be referred to as samples, it being understood that such samples are essentially representative of the liquid and vapor within the container itself.

When a liquid such as water is evaporated, the vapor phase of the liquid may contain gases norso mally dissolved in the liquid. These gases include carbon dioxide, ammonia, and hydrogen sulphide, the carbon dioxide being the more generally met with gas. Such gases may also be evolved when the liquid is subjected to boiling because of chemical re-actions of substances dissolved in the liquids. Such gases confer electrical conductance characteristics upon the liquid and vapor phases, and in order to obtain a true measure of the dissolved substances other than gases, a correction for the conductance of the gases is necessary. The present invention in its preferred embodiment, therefore, contemplates correcting the measured conductance of the vapors for the gases contained therein in such manner that the conductance utilized for purposes of control is a true measure of the substances mechanically entrained in the vapor as the vapor disengages from the vapor disengaging surface of the liquid. This may be accomplished in any desired manner, as disclosed for example in Transactions of the A. S. M. E. vol. 53, No. 8, May-August, 1931, and more particularly pages 148 and 157.

All natural water supplies contain dissolved'l05 substancesincluding both salts and gases. These substancesfconcentrate when the water is evaporated in closed containers, and a portion of the salts may be entrained in the vapor discharged from the container. The deleterious effect of the entrainment of such salts in steam is well recognized not only by reason of the corrosion thereby occasioned, but by reason of the deposition of such materials in the apparatus connected to the evaporator, boiler or distiller. All such products, when present beyond a predetermined maximum, produce well recognized economic losses in the utilization of the steam.

To those versed in the art, it is known that as the concentration of the dissolved and suspended substances increases as a result of continuous or substantially continuous evaporation of water, the ability to produce a pure quality of steam decreases. Operators are aware that the concentration of such substances in water in the equipment requires close attention. The customary practice in producing steam from fuel fired boilers and evaporators is to maintain the steam production at the desired rate while maintaining a substantially constant water level and substantially constant pressure. The contemplated purity of the vapor is usually obtained by manually adjusting the concentration of the dissolved salts in the water by either a periodic or a continuous blow down. With steam heated evaporators, the customary practice is to maintain a substantially constant water level, and to adjust the rate of steam production by controlling the rate of heating steam supplied, the rate of vapor withdrawn, and the pressure in the vapor space of the evaporator. More especially with the continuous blow down system, the heat content of the drained water has been conserved by passing it through a heat exchanger and transferring the heat to the incoming-water supplied to the equipment, an occasional chemical test or density test being resorted to to assist in the regulation of the amount of water blown down. Ordinarily, however, the rate of blow down represents a fixed percentage of the rate of water supplied to the equipment. While conductivity recorders have been utilized for measuring the concentration of the blow off, provision has not been made for automatically controlling the factors governing evaporation by means of the conductivity itself.

In the accompanying drawings we have shown more or less diagrammatically, for purposes of explanation and understanding only, one embodiment of the invention. In the drawings:

Figure 1 is a diagrammatic view illustrating one embodiment of the invention;

Figure 2 is a detail view, on an enlarged scale and in greater detail, of a portion of the indicating and controlling mechanism 57 illustrated in Figure 1;

Figure 3 is a detail view, on an enlarged scale, of a portion of one indicator 57 of Figure 1; and

Figure 4 is a detail view representing diagrammatically a proportional step controller through which part of the control may be effected.

In accordance with the present invention there may be provided a closed container 2 such as a boiler, distiller or evaporator within which the steam. or vapor disengages from the liquid. For

sake of simplicity, the heat transfer surfaces of the container 2, as well as certain auxiliary equipment such as pumps, injectors, safety valves, heaters, dry pipes and the like, have been omitted. The normal liquid level or steam disengaging surfacewithin the container is indicated by the dotted line 3, although it will be understood that the liquid level may be maintained at any desired point within the container as is customary in the art.

For supplying liquid to the container 2 there is indicated a supply pipe 4 communicating at one end with a suitable source of liquid (not shown) and at the other end with a heat exchanger 5. This heat exchanger has a discharge connection 6 constituting the inlet to the container 2, and provided with a liquid supply regulating valve '7.

Also communicating with the container 2 is a drain connection 8 containing a primary blow down valve 9 and a secondary blow down valve 10, the drain 8 leading to any desired point. Communicating with the drain intermediate the primary and secondary blow down valves is a bypass connection 11 containing a by-pass blow down control valve 12 adapted to control the amount of liquid permitted to enter the coil 14. within the heat exchanger 5. The coil at its outlet end is connected to the drain pipe 8 through a suitable line 15 provided with a discharge controlling valve 16. I

The vapor space within the container is in communicationwith a steam ofitake pipe 1'7 controlled by a valve 18, this valve being utilized only in the case of evaporators.

.Suitably connected to the container 2 is a water column 19 including a water gauge glass 20 permitting visual observation of the apparent water level within the container. We preferably utilize a water column having incorporated therein a high and low water alarm. These may comprise a float 21 having a rod 22 projecting therefrom into a whistle 23 effective for giving an audible signal of unduly high or low water level within the container. It is preferred to provide the rod 22 with a valve 24 permitting the escape of steam into a chamber 25 when the water level within the container is low. The pressure of such steam is effective against a plunger 26 within the chamber 25 for moving the plunger outwardly and causing the plunger rod 27 to operate a switch 28 and bring the switch arm into engagement with a contact 29. At such time as the switch is closed, current is delivered to a by-pass control motor 30 from suitable line wires L and L representing a source of proper potential current. Energization of the motor 30 is efiective through a suitable connection 31 for closing the by-pass blow down valve 12 and thereby preventing further blow off and consequent further emptying of the boiler.

The construction so far described with respect to the drain and blow down system is such that either an automatic continuous or intermittent blow down may be obtained, or a manual intermittent blow down. When a manual intermittent blow down is desired, the primary blow down valve 9 is opened, the secondary blow down valve 10 is opened, and the by-pass control valve 12 is closed. This condition is maintained for the desired blow down interval, after which the primary and secondary blow down valves are closed. When an automatic blow down is desired, the secondary blow down valve is maintained closed, the primary blow down valve open, and the bypass control valve 12 opened. Included within the connection 15 on the discharge side of the valve 16 may be an orifice plate 32 efiective for limiting the maximum discharge of water from the container. In accordance with the preferred embodiment of the invention the orifice is of such size as not to permit over 25% of the feed water supplied to the container to be drained therefrom. The inclusion of such an orifice, and of an automatic by-pass control of the character described insures safety in the operation of the apparatus in that a complete drainage of water from the container is hindered to a greater degree than in apparatus as heretofore provided.

By reason of the heat exchanger 5, it will be apparent that the heat of the continuously blown down liquid is transferred to the liquid being supplied to the container whereby the heat of the blow off is conserved.

Disposed within the liquid space of the container 2 is a sampling device 33 of such construction as to be efiective for withdrawing a representative sample of liquid from the entire container. Such a sampling device may comprise a series of tubes 34 of different lengths communicating at one end with the liquid space of the container at different distances from the ends thereof, and at the other end with a header 35 the discharge from which is controlled by a sampling valve 36 within a sampling pipe 37. The sampling pipe throughout a portion of its length is formed into a coil 38 disposed within a casing 39 having inlet and outlet connections 40 and 41 respectively for a cooling fluid, the cooling fluid being so controlled as to effect temperature reduction of the sample to the desired extent.

The sampling pipe 37 on the discharge side of the coil 38 is preferably provided with a valve 42 effective for so controlling the water flow as to prevent flashing of any part of the water. The cooled sample water is discharged from the valve 42 into a conductance electrode chamber 43 of suitable construction provided with conductance elements 44 of suitable commercial type arranged for insertion in pressure pipes or containers. The'provision of a conductance electrode chamber of the character indicated is desirable in that it maintains the sample liquid out of contact with the atmosphere until after it has passed the conduci mce element 44 by means of which the conductivity is determined.

The steam offtake pipe 17 is likewise provided, preferably below the valve 18, with a steam sampler 45 generally similar to the sampler 33 before described. The portions collected by the various sampling tubes are delivered to a header 46 the discharge from which is controlled by a valve 4'1 connected into a vapor sampling line 48. Similarly to the liquid sampling line, the vapor sampling line is provided with a coil 49 within a suitable shell 50 having cooling fluid inlet and outlet connections 51 and 52' respectively. Not only is it desirable to so control the cooling fluid as to reduce the sample of vapor to condensate at a definite temperature, but it is desired to so control the cooling fluid that the temperature of the condensed vapor sample will be within the range of the temperature compensator hereinafter described. The coil 49 discharges through a valve 53 into a conductance electrode chamber 54, similar to the conductance electrode chamber 43, and provided with conductance elements 55.

The apparatus thus far described comprises means for continuously obtaining a representative sample of the vapor and cooling it to a predetermined temperature range and for also obtaining a representative sample of the liquid and similarly cooling such sample. The sampling devices used in accordance with the present invention are disclosed and claimed in the copending applicationof E. G. Campbell, Serial No. 485,571, flled September 30, 1930. The representative samples thus obtained are continuously available within conductance electrode chambers of such type that atmospheric contamination prior to conductivity measurements is prevented, and

the control of the liquid sample is such that there is no loss of the relation of liquid to dissolved substances such as would result from flashing.

The conductance elements within the conductance electrode chambers constitute means for obtaining automatic control of the factors governing the evaporating conditions. As indicated more particularly in Figure 2 of the drawings, the conductance elements 55, which are conveniently in the form of a conductivity cell are suitably connected by wires 56 to an alternating current Wheatstone bridge 57 of any well known balanced type. The use of a balanced Wheatstone bridge permits the use of a very sensitive detecting instrument, such as a galvanometer 58, and the high sensitivity of the detecting instrument makes it necessary to pass only a very minute current through the electrode circuit. Inasmuch as the polarization error is diminished with the reduction of current through the electrode circuit, the use of an alternating current Wheatstone bridge with a high sensitivity detecting instrument reduces the polarization error to a negligible quantity, even when using electrode or conductance element spacing and construction which permit the permanent installation thereof within the conductance electrode chamber. The operating current for the Wheatstone bridge, as is customary with this type of instrument, may be derived from line wires L and L' through a suitable transformer T, through transformer leads 59. One side of the Wheatstone bridge circuit preferably includes a temperature compensating resistance 60 and a carbon dioxide compensator shunted resistance 61.

An alternating current balanced type Wheatstone bridge of the character diagrammatically illustrated, and of well known commercial type, such'for example as disclosed in the patent to Keeler, No. 1,472,125 of October 30, 1923,.also ordinarily comprises a synchronous motor 62 effective for driving a chart, recorder or the like not shown, and suitably connected to a shaft 63 one direction or the other. Mounted upon the shaft 63 is a maximum concentration control cam 64 and a minimum concentration control cam 65. These control cams while carried by the shaft for movement therewith, are also preferably of the type adjustable one with respect to the other to a limited extent as permitted by a slot 66 and clamping screw 67.

Upon rotation of the shaft 63 in one direction, the maximum alarm cam 64 will be operative for engaging switch 68 and thereby controlling a

circuit including wires

69 and 70 leading to .a proportional step controlled 71 (Figs. 1 and 4). Operation of the shaft 63 in the opposite direction will be efiective for causing the minimum alarm cam 65 to actuate switch 72 and thereby close a circuit including wires '70 and 73 to the proportional step controller 71.

The proportional step controller 71 controls current flow in the circuits including the line wires L and L, the wires 74 and the respective wires '75 leading to regulating motor 76.

The Wheatstone bridge and its associated parts as illustrated more particularly in Figure 2 of the drawings, constitute what will hereinafter be termed a vapor indicator 57. The liquid indicator connected to the conductance elements 44 is of generally similar construction to that before described with the exception that the carbon dioxide compensator shunted resistance is omitted from the liquid indicator. The liquid indicator is designated by the reference character 57, and parts thereof corresponding to the parts of the vapor indicator 57 are designated by the same reference numerals having, however, a prime affixed thereto. In the vapor indicator 57 the

switches

68 and 72 are carried by a fixed portion of the apparatus. In the liquid indicator 57, however, the switches 68' and 72' are carried by a segment 77 comprising a worm wheel section 78' loosely surrounding the shaft 63' and meshing with a worm 79 on shaft 80 of theregulating motor 76. Thus when the regulating motor rotates in one direction, the sector 77 will be swung clockwise to thereby correspondingly change the relationship between the switches 68' and 72 and the control cams 64 and 65'. The relationship of the parts, as disclosed, for example, in the patent to Keeler No. 1,472,125 of October 30, 1923 is such that when the conductivity of the vapor sample increases to such an extent as to cause the maximum control cam 64 to close the switch 68, the motor 76 will be effective for rotating the sector 77 in a clockwise direction, whereby a lesser movement of the control cam 64' in a counterclockwise direction will be efiective for closing the switch 68. At the same time a greater movement of the control cam 65 in a clockwise direction will be required to close the switch 72'. As the conductivity of the sample in the conductance electrode chamber 54 decreases, the motor 76 will be operated in the reverse direction whereby a greater movement of the control cam 64' and a lesser movement of the control cam 65 will be effectiv for closing the switches 68' and 72 respectively.

With the switch 68' closed, a circuit including wires 69' and 70 to a proportional step controller 71' will be closed, while with the switch 72 closed a circuit including the wires 70' and 73' to such proportional step controller 71 will become energized. The proportional step controller controls a circuit 81 to a motor 82 having an operative connection 83 to valve 16; a second circuit 84 to motor 85 having an operative connection 86 to valve 7; and a third circuit 87 to motor 88 having an operative connection 89 to the valve 18 in the steam offtake pipe 17. The circuits are such that when the maximum control cam 64' closes the switch 68, thereby indicating too high a conductivity in the conductance electrode chamber 43, the motor 82 will become efiective for further opening the valve 16 to thereby increase the rate of blow down; the motor 85 will be effective for opening the valve '7 to permit a faster feed water supply to the container 2; and the motor 88 will he efiective for partially closing the valve 18 to thereby-increase the pressure within the container and decrease the rate of evaporation. When the minimum control cam 65' closes switch 72 a reverse operation will occur. At this time motor. 82 will tend to close the valve 16 to reduce the quantity of blow off; the motor 85 will tend to close the valve '7 to thereby restrict the rate of feed water supply and the motor 88 will open the valve 89 to decrease pressure within the container 2 and permit the rate of evaporation to increase.

The nature of one type of commercial proportional step controller is diagrammatically illustrated in Fig. 4. The

wires

69, 70 and 73 are connected to an electrical device 90 similar in character to a galvanometer, so that when current is supplied by way of the switch 68 or by way of the switch 72, the rotative element of the device 90 is swung or deflected in one direction or the other, depending upon which switch is closed. The deflection or arcuate movement of the rotative element of the device 90 corresponds to the amount of unbalancing in the circuit. This rotative element carries a pair of horizontally extending

arms

91 and 92, insulated one from the other and normally bearing against an annular contact member 93. This annular contact member is connected to a wire which is supplied with current from the line wires L and L through wires 74. A circuit is completed through one or the other of the wires 75 when the

arm

91 or 92 comes in contact with a continuously rotating

cam

94 or 95 respectively. The

cams

94 and 95 are actuated by current from the line wires L and L so as to rotate continuously; and the peripheries of these rotating cams may constitute a logarithmic spiral or any other desired contour. The cams are efiective during rotation for re-centering either the arm 91 or the arm 92, it being apparent that the time interval during which a cam is in engagement with its respective arm will depend upon the amount of displacement of the arm. The earns 94 and 95 are electrically connected through wires 75 to the motor 76. Accordingly, the time interval during which current is supplied to the motor for rotating it in one direction or the other will be exactly proportional to the amount of displacement of the

arms

91 and 92.

From the foregoing it will be apparent that the vapor indicator 57 is responsive to the conductivity of the vapor sample, the mechanism of the indicator being efiective for adjusting the position of the switches of the liquid indicator 57'. The operation of the liquid indicator in turn is effective for controlling, in direct accordance with the position of the switches 68' and 72, the factors governing evaporating conditions within the container.

1 As to the motor 30 connected to the valve 12,

it will be apparent that after it has been caused to close such valve by reason of the plunger rod 27, the valve will remain closed until the desired water level within the container 2 is restored and the pressure relieved from plunger 26 and it returns to a position which will permit opening of the switch. The valve 12 will then be opened manually. While automatic means might be provided, if desired, for restoring the previous conditions with respect to the valve 12, the necessity of manual re-positioning insures the intervention of the operator and thereby affords him an opportunity to definitely asc rtain the water conditions within the container Jefore changing the position of the parts.

The provision of the temperature compensator resistance 60 in the vapor indicator 57, and the corresponding temperature compensator resistance 60' (not shown) in the liquid indicator 57' makes it possible to adjust the indicators to the actual temperature of the samples in case the control of the cooling fluid to the shells 50 and/or 39 is not such that the samples are reduced to the temperature for which the indicators are set. The provision of the carbon dioxide compensator shunted resistance 61 in the indicator 57 makes the necessary correction for the carbon dioxide content and thereby prevents untimely actuation of the maximum control cam 64 such as would occur if the carbon dioxide content were high enough to produce a conductivity such that the maximum control cam 64 would be rotatedin such direction as to close the switch 68.

The use of proportional step controllers enables the desired increment of movement of the vari ous motors to be obtained, as will be well understood in the art so that a more or less complete movement of the valves in one direction or the other, "or of the sector 77 in one direction or the other may be obtained in accordance with the actual conductivity of the samples.

It will be apparent that the conductance units of the indicators may be calibrated in termsof the dissolved substance per million parts of water permitting the recorded conductance to be interpreted in terms ofparts per million by weight or in grains per gallon, which terms are customarily used by workers in measuring the concentration of dissolved substances in water.

Having thus explained the general construction and operation of an evaporating system embodying the present invention, it may be assumed, by way of example only, that it is desired to generate steam in a steam boiler from water in which the concentration on the average is 5000 parts of dissolved salts per million parts of water, the supply of water to the boiler having a concentration of 100 parts of dissolved salts per million parts of water. To maintain these conditions, an average blowing down of the concentrated water in the boiler of 2.0% of the boiler feed rate will be required. It may be further assumed that it is desired to produce steam which will have entrained therein dissolved salts from the boiler water in the range between 5 and 15 parts of salt per million parts of condensed steam. It will be understood that the expressions of amounts of dissolved salts may be transposed readily to conductance unit values from a suitable calibration curve, since the indicator may be marked in conductance values. In such case the steps to be taken are as follows:

1. The control cams of the vapor indicator 5'? are adjusted in such manner that the maximum control cam 64 will actuate the switch 68 for a conductance equivalent of 15 P. P. M. and the minimum control cam 65 will actuate the switch 72 for the conductance equivalent of 5 P. P. M.

2. The control cams of the liquid indicator 57 may be so adjusted that the maximum control cam 64 will close the switch 68' for the conductance equivalent of 5000 P. P. M., while the minimum control cam 65' will close the switch '72 for the conductance equivalent of 4000 P. P. M.

Having properly set the parts in the manner pensation for the conductance of both water and steam samples for temperature and the additional compensation of the steam for the dissolved gas conductance enables an accurate measurement to be obtained of the dissolved salts in both of the samples.

The utilization of control cams of the general character referred to operable in the manner set forth for obtaining a selective valve operation automatically in accordance with the conductance of the samples maintains automatically the conditions essential to the production of the desired steam quality and purity.

By utilizing the synchronous motors of the respective indicators for obtaining a continuous graphic record of the conductance, and particularly a continuous record of the conductance of the steam corrected for the conductance of dissolved gases and for temperature, there is provided data available at all times for calculating the steam quality.

All of the foregoing constitute advantages characteristic of the present invention.

While we have hereinbefore illustrated and described a preferred embodiment of the present invention and have explained the same in connection with the evaporation of water, it will be understood that the utility of the invention is not limited to the system shown or to the evaporation of water, and thatchanges in the apparatus, the method and the liquid being treated may be made without departing either from the spirit of our invention .or the scope of our broader claims.

We claim: 1

1. In the method of changing the phase of liquids, the steps comprising applying heat to the liquid to transform a portion thereof into the vapor phase, withdrawing a vapor sample, and controlling the dissolved substance concentration in the main body of the liquid by the conductance of such sample.

2. In the method of changing the phase of liquids, the steps comprising applying heat to a liquid to change the phase thereof, withdrawing a portion of the vapor produced by such change of phase, maintaining such sample out of contaminating contact with the atmosphere until the conductivity thereof has been determined, and controlling the dissolved substance concentration in the main body of the liquid by the conductance of such sample.

3. In the method of changing the phase of liquids, the steps comprising changing a portion of a liquid from the liquid phase to the vapor phase, withdrawinga sample of the vapor so produced, and controlling the quality of the vapor 115 being changed from the liquid phase to the vapor phase in accordance with the conductance of such sample.

4. In the method of changing the phase of liquids, the steps comprising changing a portion 129 of a liquid body from the liquid phase to the vapor phase, withdrawing a sample of the vapor so produced, cooling and condensing said sample to a predetermined temperature range, measuring the conductance of said cooled and condensed 25 sample, and controlling the vapor quality in accordance with the conductance of said sample.

5. In the method of changing the phase of liquids, the steps comprising subjecting a liquid to evaporating conditions to produce a change of 130 phase of a portion of the liquid, withdrawing a liquid sample and a vapor sample, and controlling the dissolved substance concentration in the main body of the liquid in accordance jointly with the conductance of the vapor sample and l35 the conductance of the liquid sample.

6. In the method of changing the phase of liquids, the steps comprising subjecting a liquid to evaporating conditions to produce a change of phase of a portion of the liquid, withdraw- I ing a liquid sample and vapor sample, and controlling the dissolved substance concentration in the main body of the liquid in accordance with the conductance of both of said samples.

7. In the method *of changing the phase of 1 5 liquids, the steps comprising subjecting a liquid body to evaporating conditions, replacing liquid of the body by liquid of lower dissolved substance concentration, withdrawing a liquid sample and a vapor sample, measuring the conductivity of 1 said samples, and controlling such replacement in accordance with both the conductance of the vapor sample and the conductance of the liquid sample.

8. In the method of changing the phase of liquids, the steps comprising subjecting a liquid body to evaporating conditions, withdrawing a liquid sample and a vapor sample, measuring the conductivity of said samples, and controlling the quality of the vapor produced in accordance with the conductance of both of said samples.

9. In the method of changing the phase of liquids, the steps comprising subjecting a body of liquid to a phase changing operation, replacing liquid of the body by liquid of lower dissolved substance concentration, withdrawing samples of the liquid and vapor resulting therefrom, cooling said samples under pressure while maintaining the same free from atmospheric contamination, and controlling such replacement in accordance jointly with the conductance of the vapor sample and the conductance of the liquid sample. I

10. In the method of changing the phase of liquids, the steps comprising subjecting a body of liquid to a phase changing operation, withdrawing samples of the liquid and vapor resulting therefrom, cooling said samples under pressure while maintaining the same free from atmospheric contamination, and controlling the quality of the vapor being changed from the liquid phase to the vapor phase in accordance with the conductance of both of said samples.

11. In the method of changing the phase of liquids, the steps comprising subjecting a body of liquid to a phase changing operation, and controlling the quality of the vapor being changed from the liquid phase to the vapor phase by the conductivity of the vapor produced by the phase changing operation.

12. In the method of changing the phase of liquids, the steps comprising subjecting a body of liquid to evaporating conditions, replacing .liquid of the body by liquid of lower dissolved substance concentration, controlling the quality of the vapor being changed from the liquid phase to the vapor phase by modifying such replacement in accordance with the conductance of the liquid, and modifying such control in accordance with the conductance of the vapor produced by the phase changing operation.

' 13. In the method of changing the phase of liquids, thesteps comprising subjecting a body of liquid in a container to evaporating conditions, replacing liquid of the body by liquid of lower dissolved substance concentration, and modifying such replacement by and in accordance with the conductance of both the vapor and liquid phases of the liquid.

14. In the method of changing the phase of liquids, the steps comprising subjecting liquid to evaporating condtions, replacing a portion of the liquid by liquid of lower dissolved substance concentration, withdrawing samples of both the liquid and vapor phases so produced, and changing such replacement by and in accordance jointly with the conductance of the vapor sample and the conductance of the liquid sample.

15. In the method of changing the phase of liquids, the steps comprising subjecting liquid to evaporating conditions, withdrawing samples of both the liquid and vapor phases so produced, and controlling the quality of the vapor being changed from the liquid phase to the vapor phase by and in accordance with the conductance of both of said samples.

16. In the method of changing the phase of liquids, the steps comprising delivering a liquid to a container, subjecting the liquid therein to factors effective for producing a phase change, and controlling the rate of liquid delivery by and in accordance with the conductance of the vapor produced by such phase change.

17. In the method of changing the phase of liquids, the steps comprising maintaining a substantially constant body of liquid by delivering and withdrawing to and from a container liquid quantities, subjecting the liquid in the container to factors effective for producing a phase change, and controlling the liquid supply and withdrawal in accordance with the conductance of the vapor produced by such phase change.

18. In the method of changing the phase of liquids, the steps comprising maintaining a substantially constant body of liquid by delivering to and withdrawing from a container liquid quantities, subjecting the liquid within the container to factors efiective for producing a phase change, controlling the quality of the vapor phase so produced in accordance with the conductance of the liquid phase, and modifying the control of the quality of the vapor phase in accordance with the conductance of the vapor phase.

19. Apparatus for producing a liquid phase change, comprising a container, means for continuously withdrawing from said container a vapor sample and cooling such sample under pressure thereby condensing such sample, and means for measuring the conductance of such sample without contamination thereof by the atmosphere.

20. Apparatus for producing a liquid phase change, comprising a container, means for withdrawing from said container a vapor sample and cooling such sample under pressure thereby condensing such sample, and means for measuring the conductance of such sample without contamination thereof by the atmosphere.

21. Apparatus for producing a phase change, comprising a container, means for continuously withdrawing from said container liquid and vapor samples, and cooling said samples under pres sure thereby condensing such sample, and means for measuring the conductance of such sample without contamination by the atmosphere.

22. Apparatus for producing a phase change, comprising a container, means for withdrawing from said container liquid and vapor samples, and cooling said samples under pressure thereby condensing such sample, and means for measuring the conductance of such sample without contamination by the atmosphere.

23. Apparatus for producing a phase change, comprising a container, means for withdrawing from said container representative liquid and vapor phase samples, and means for measuring the conductance of said samples prior to contamination thereof by the atmosphere.

24. Apparatus for producing a phase change, comprising a container having a liquid supply, a liquid discharge and a vapor ofitake, and means for controlling said discharge by the conductance of the vapor produced.

25. Apparatus for producing a phase change, comprising a container having a liquid supply, a liquid discharge and a vapor oiftake, and means for controlling the supply by the conductance of the vapor produced.

. 6.- pparatus for producing a phase change,

comprising a container. having a liquid supply, a liquid discharge and a vapor ofitake, and means for controlling said discharge and supply by the conductance of the vapor produced.

27. Apparatus for producing a phase change in liquids, comprising a container having liquid and vapor phases coexistent therein, means for determining the conductance of the vapor phase, and means for changing the dissolved substance concentration in the liquid phase in accordance with the conductance of the vapor phase.

28. Apparatus for producing a phase change in liquids, comprising a container having liquid and vapor phases co-existent therein, means for determining the conductance of the liquid phase, valve mechanism for controlling the rate of liquid supply, valve mechanism for controlling the rate of liquid discharge, and means for regulating said valve mechanism to increase one rate as the other rate is decreased in accordance with changes in the conductance of the liquid phase.

29. Apparatus for producing a phase change in liquids, comprising a container having liquid and vapor phases co-existent therein, means for determining the conductance of the vapor phase, and means for changing the dissolved substance concentration in the liquid phase in accordance with the conductance of the liquid phase, there being means modifying the changing of said concentration in accordance with the conductance of the vapor phase.

30. In a phase changing apparatus, means for continuously obtaining representative samples of liquid and vapor, and means for measuring the conductance of said samples'to determine the dissolved substance concentration therein.

31. In the method of changing the phase of liquids, the steps comprising withdrawing a vapor sample, making a conductance correction for the temperature of such sample, and controlling the dissolved substance concentration of the liquid by the corrected conductance of such sample.

32. In the method of changing the phase of liquids, the steps comprising withdrawing a vapor sample, correcting the conductance of such sample for carbon dioxide, and controlling the dissolved substance concentration in the liquid by the corrected conductance of such sample.

33. In the method of changing the phase of liquids, the steps comprising withdrawing a vapor sample, correcting the conductance of such sample for temperature and carbon dioxide, and controlling the dissolved substance concentration in the.liquid by the corrected conductance of such sample.

34. In the method of changing the phase of liquids, the steps comprising withdrawing a vapor sample, correcting the conductance of such sample for contained gases which confer conductance characteristics upon the liquid, and controlling the dissolved substance concentrationin the liquid by the corrected conductance of such sample. 35. In the method of changing the phase of liquids, the steps comprising changing a portion of a liquid body from the liquid phase to the vapor phase, withdrawing a sample of the vapor so produced, cooling said sample under pressure while maintaining the same free from atmospheric contamination, and controlling the quality of the vapor being changed from the liquid phase to the vapor phase in accordance with the conductance of the vapor sample.

36. In the method of changing the phase of liquids, the steps comprising maintaining a substantially constant body of liquid by delivering to and withdrawing from a container liquid quantities, subjecting the liquid in the container to factors effective for producing a phase change, and controlling the quality of the vapor phase so produced in accordance with the conductance of the vapor produced by such phase change.

37. In the method of controlling the dissolved substance concentration of liquid subjected to evaporating conditions, the steps comprising replacing a portion of the liquid being treated by liquid of lower dissolved substance concentration, maintaining such replacement normally continuous, and controlling such replacement by the conductance, corrected for temperature, of a sample of the liquid being treated.

38. In the method of controlling the dissolved substance concentration of water subjected to evaporating conditions, the steps comprising applying heat to water to vaporize the same,'conducting off vapor thus generated, replacing a portion of the water by water of lower dissolved substance concentration, continuously withdrawing a sample of the vapor generated, and continuously controlling said replacement of water by the conductance of such vapor sample.

MAX HECI-I'I'. DAVID S. MCKINNEY.