US1946851A - Method of vaporizing mercury - Google Patents

Description

Feb. 13, 1934. J. J. GREBE METHOD OF" VAPORIZING MERCURY Filed July 31. 1930 2 Sheets-Sheet l 1 III] Fig. 2

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ATTORNEY Fig. 6

Feb. 13; 1934. J J, GREBE 1,946,851

METHOD OF VAPORIZING MERCURY Filed July 31. 1930 2 Sheets-Sheet 2 INVENTOR ATTORNEY Patented Feb. 13, 1934 UNITED STATES METHOD OF VAPORIZING MERCURY John J. Grebe, Midland, Mich-., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Michigan Application July 31, 1930. Serial No. 472,026

Claims.

The present invention relates to methods for vaporizing mercury.

Many attempts have been made to vaporize mercury and use the vapor thereof, e. g., in a 5 power cycle, whereby it was anticipated that higher economy would be realized in contrast with the use of steam alone for this purpose. It has been attempted to vaporize the mercury by boiling same in metal tubes exposed to the heat of a furnace, to expand the mercury in a turbine, to condense the expanded mercury vapor in heat exchange relation with boiling water, to utilize the steam so obtained in a heat engine adapted to generate power therefrom and to return the condensed mercury to the mercury boiler. Various diificulties have been encountered and some overcome, but it still remains true that it is not yet practicable to boil a body of liquid mercury in a metal tube since the mercury does not wet such a tube, the heat transmission co-eficient is low and mercury has a pronounced tendency to bump, and further, that the amount of mercury required, even in the best installations as yet worked out, amounts to several pounds per kilowatt capacity. The difiiculty with boiling the mercury and the large investment per kilowatt in mercury constitutes heavy handicaps to an otherwise attractive power cycle development.

I have invented a method of removing these two handicaps in a simple and easily controlled manner.

To the accomplishment of the foregoing and related ends, the invention, then, consists of the methods and means hereinafter fully described and particularly pointed out in the claims, the annexed drawings and the following description setting forth in detail several modes and means for carrying out the invention, such disclosed modes and means illustrating, however, but several of various ways in which the principle of the invention may be used.

In order to vaporize mercury I take advantage of the well-known phenomenon that if a liquid be introduced, preferably in the form of spray, into superheated vapor thereof, the liquid will desuperheat the vapor and the superheat of the vapor will be converted into latent heat or" evaporation of the liquid so introduced. I am thereby able to eliminate the boiling of a body of liquid mercury in contact with a metal surface and to construct a boiler which operates with very little mercury. I accordingly vaporize the mercury by introducing it, preferably in the form of a fine spray, into superheated mercury vapor preferably in the form of a current thereof, controlling the rate of introduction of the liquid mercury relative to the heat available in the superheat of the mercury vapor or otherwise available so that the liquid mercury so introduced will be either vaporized to substantial completeness, or suniciently so to satisfy the limitations of the particular vaporizing equipment chosen for carrying out the step. I may introduce the liquid mercury into a current of presuperheated mercury vapor in such amount as to substantially desuperheat the latter and also substantially completely to vaporize the mercury introduced, or I may introduce the liquid mercury in excess, or again, I may introduce less than enough liquid mercury to fully desuperheat the vapor. I may furthermore, introduce the liquid mercury into a current of mercury vapor while heating such vapor, that is, the mercury vapor may be absorbing heat from a heat source at the same time that the liquid mercury is absorbing heat from the vapor.

Inasmuch as the latent heat requirement for evaporation is large relative to the heat capacity of mercury vapor, even when considerably superheated, I may introduce the mercury to be vaporized in successive portions into a current of mercury vapor subjected to indirect heat absorbing relation with a source of heat, such as an extended tubular passageway in a furnace, whereby the vaporization with superheat will be done in successive stages. A variety of arrangements may be employed and a number of them are illustrated in the drawings.

In said drawings: Fig. 1 represents broadly in part section an apparatus for introducing the mercury in the form of a spray into a current of mercury vapor. Fig. 2 represents partly in cross section a vaporizer in which the mercury is introduced through a tube, the outer surface of which is in contact with mercury vapor. Fig. 3 represents a cross section of the simple form of vaporizer shown in Fig. 2. Figs. 4, 5, 6, '7, 8, and 11 represent diagrammatically a variety of evaporator hookups adapted to carry out my invention.

Figs. 9 and 10 represent mod fications of Fig. 2.

Fig. 12 is a diagrammatic representation of an alternative method of introducing liquid mercury wherein excess is automatically returned to the mercury feed pump.

Describing the above listed drawings in greater detail, Fig. 1 illustrates a vapor pipe 1 intcwhich a smaller pipe 2 carrying a spray nozzle 3 is introduced, whereby a spray of liquid mercury may be injected via pipe 2 and nozzle 3 into pipe 1. In Fig. 2 is illustrated a heating tube 1 into which a small tube 2 is inserted. If now heat be applied to tube 1 and mercury injected through the fine bore tube 2, it will be vaporized initially in tube 1. The vapor therein will, if the rate of heating is suflicient relative to the rate of feed of liquid mercury, superheat the vapor therein, which superheated vapor will then transmit heat to the mercury in tube 2 and an equilibrium condition may be reached by proper control in which the mercury will be vaporized entirely or largely in the fine bore tube 2 and the vapor thereof will be superheated in tube 1, redelivering a part of of its heat to the mercury in tube 2, finally issuing through the extension tube 1:0 to any further point of use. A cross section of the tubes 1 and 2 is shown in Fig. 3.

In Fig. 4 I show diagrammatically a turbine generator unit 5, a condenser 6, a boiler feed pump 7 and a furnace or heating zone 8. In such furnace I set the initial mercury preheater 9, together with a plurality of superheaters 1. One coil-type initial heater 9 and three coil-type superheaters 1 are indicated. The pump 7 delivers the liquid mercury via pipe 2 to the initial heater 9 in which it is heated and may even be partially vaporized. The products of this step are then injected into a current of superheated mercury vapor through the aspirator or injector 3, thereby acting to recirculate mercury vapor through the superheaters 1 via the headers la, lb, and 10, whereby a continuous current of mercury vapor superheated in the heaters l is brought to the aspirator 3 and there mingled with mercury and distributed via the header 1a to the heaters l. A branch vapor main 1a: conducts superheated mercury vapor to the turbine.

Fig. 5 represents a modification of my vaporizer or boiler in which an initial vaporizer coil 9 is followed by a series of superheater coils 1a, 1b, 1c, 1d, 16. Liquid mercury from the condenser is delivered to each of said coils via the pipe 2 through the T-valves 2a, whereby a portion is vaporized in 9 to furnish an initial current of vapor. Such vapor is then superheated in la, whereupon an additional quantity of mercury is injected and vaporized at 3a. The thus augmented mercury vapor is again superheated in heater 11), after which an additional portion of mercury is introduced at 3b, after which the still further augmented mercury vapor current is again superheated and again augmented in the following heaters and injectors until it is delivered as superheated vapor through the pipe 13: leading to the turbine. Here no aspirating action of the injectors 3 is required, it being erely necessary to supply the liquid mercury at a pressure sufficiently above the terminal vapor pressure desired to insure injection thereof at all points. The expansion of the mercury into vapor is here depended upon to set up the flow of vapor in the system.

A further modification of my mercury boiler is shown in Fig. 6 in which the recirculation of mercury vapor in the heater system is provided for by a booster pump 13, the liquid mercury being introduced via the supply pipe 2 at a plurality of points 3 in the flow of superheated vapor, a portion of which latter is withdrawn from pipe 1r by the pump 13 and is returned to the heater system via pipe 1.

In Fig. '7 the liquid mercury is supplied through the pipe 2, a portion being introduced therefrom into an initial vaporizing coil 9 contained in a jacket 9a. This Jacket receives superheated mercury vapor from the pipe 1a, such superheated mercury vapor being produced by augmenting the portion vaporized in 9 by introduction of further liquid mercury into the succeeding heaters, in which heaters such additional portions of mercury are successively vaporized. The vapor leaving the jacket 9a is then superheated in the final heater 1e for delivery to the turbine via pipe lac.

In Fig. 8 is shown still another modification having close relationship with that shown in Fig. '7. Here, instead of the jacket 9a about the coil 9, a vapor pipe 9a surrounds initial vaporizing pipe 9. Such construction may be as detailed in Figs. 9 and 10. In Fig. 9 mercury in the small bore tube 9 is heated by the mercury vapor sur rounding same, which mercury vapor receives its heat from the furnace through the walls of the outer pipe 9a. Fins or other extended configuration of the surface of pipe 9 may be employed. In Fig. 10 a plurality of small mercury vaporizing pipes 9 are shown as contained within the larger pipe 9a.

It has been found that bumping may be overcome and the heat transfer co-efficient between mercury and the wall of a heating tube greatly increased by passing liquid mercury at a high velocity over the heating surface. This is provided for automatically in the construction shown in Figs. 9 and 10 where small bore heating tubes are employed in which the formation of vapor imparts to the mercury a high velocity, giving it a scrubbing action, thereby absorbing the heat rapidly from the tube wall. Mercury vapor itself is dense and the rate of transmission of heat between the tube wall and vapor is high. It is therefore ideally suited to take heat from the wall of the tube 9a and deliver it to the outer surface of the tubes 9.

In Fig. 11 is shown diagrammatically a more complete set-up of a turbine generator unit 5, a condenser water boiler 6, a boiler feed pump '7 and a vaporizer unit similar to that shown in Fig. 8. Such vaporizer unit as well as others herein described may contain as many successive stages of introduction of mercury as required for the pressure and temperature conditions employed. Instead of using the boiler indicated in Fig. 8 any other type, including those previously described, may be employed provided that mercury is therein vaporized in direct contact with superheated mercury vapor.

Fig. 12 represents diagrammatically a method of introducing liquid mercury into the vaporizing system at a number of points in such manner that any excess so introduced will be automatically returned to the mercury feed pump.

In this figure the feed pump is indicated at 7, drawing mercury from the hot well 6 and delivering via the header 2 to a plurality of spray nozzles 3 in a tubular heating system 1. Under normal operation the so introduced liquid merturn header lg to the trap 1h, in turn delivering to the hot well 6 or pump 7. In this arrangement, as in the others described, the tubes into which the mercury is introduced may be in the heating zone so that vaporization of the mercury by desuperheating the vapor occurs accompanied by coincident heating of the mercury vapor whereby a larger proportion of liquid mercury may be introduced at e ch point of introduction,

thereby limiting the number of points of introh ing such excess liquid as provided for in Fig. 12 at outlets located between the inlets for liquid, the vapor will have an opportunity to acquire superheat before reaching the next succeeding point of introduction, and, further, by such arrangement, necessity for close control is obviated since an excess of liquid may be systematically introduced, separated and recirculated. It should be noted that with this method of vaporization not only will the liquid mercury so introduced be vaporized by superheat of the vapor into which it is introduced, but it may absorb heat by radiation from the heating surface or by contact therewith, such contact, however, not being between a body of the mercury and the heating surface, but between a film of mercury and the heating surface whereby bumping is avoided. Where such a film does not actually contact with the heating surface, it will be separated therefrom by a film of vapor. Such film of vapor will be acquiring heat from the heating surface and delivering it to the mercury in contact therewith. The separated mercury at boiler temperature may be returned directly to the pump suction by the automatic trap lb or through a preheater or be otherwise reintroduced into the feed line 2.

In the control of my improved method of vaporization various procedures may be followed. One such procedure will involve control of the heat input responsive to load, for example, responsive to the rate of flow of vapor from the mercury boiler to the power mover through a flow meter, or responsive to the pressure of the vapor after the superheater or vaporizer system. The latter method of control will act to maintain a set pressure at the power mover. The supply of liquid mercury to the boiler will be controlled to keep a constant quantity of mercury in the system and may be made responsive to pressure in the vaporizing system, i. e. to supply more as the pressure rises and less as it falls. The mechanisms for such control are well understood and will not be herein described.

A distinguishing feature of my improvements comprises the vaporization of liquid mercury by direct contact with mercury vapor as heating agent, preferably by mingling with superheated vapor, liquid mercury preferably in the form of a spray. In this manner I am able to eliminate the presence of any consequential weight or vol ume of liquid mercury in the vaporizer, restricting such liquid mercury to the small amount in the condenser, hot well, pump, and boiler feed lines. As a result, I am able to reduce the mercury requirements of a power system of the character described to a fraction of a pound f inercury per kilowatt capacity, a highly desirable advantage from the standpoint of initial costs of mercury and a necessary condition if any large development in this field is to be made possible with a limited supply of available mercury. I have further obviated difficulties of bumping when boiling mercury in a body in contact with a heating surface, and, further, by reducing the weight of mercury in the system have correspondingly reduced the economic and other hazards following leakage or loss of the entire mercury charge through accident or faulty manipulation of equipment.

Although I have described various means for accomplishing the vaporization of mercury in accordance with my invention, it is obvious that various other means and arrangements may be employed without departing from the spirit of the invention so long as liquid mercury is vaporized by contact with a current of superheated mercury vapor.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the means and the steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

I therefore particularly point out and distinctly claim as my invention:-

1. The method of vaporizing mercury which comprises causing a current of mercury vapor to traverse a heating zone wherein the same is superheated by transfer of heat from an external source and simultaneously injecting into said current successive small portions of liquid mercury, whereby such liquid is vaporized by the superheat of the vapor.

2. The method of vaporizing mercury which comprises circulating a current of mercury vapor under superatmospheric pressure in a closed system, heating such vapor to superheat the same, simultaneously injecting successive small portions of liquid mercury into said current, whereby to vaporize such liquid by the superheat of the vapor, and withdrawing the vapor so generated for delivery to a point of use.

3. The method of vaporizing mercury which comprises preheating a body of liquid mercury, injecting successive small portions of such preheated liquid into a current of superheated mercury vapor under superatmospheric pressure, whereby to vaporize such liquid by the superheat of the vapor, simultaneously supplying heat from an external source to resuperheat the vapor, recirculating a portion of the superheated vapor for vaporizing additional liquid mercury and withdrawing the balance of the vapor for delivery to a point of use.

4. The method of vaporizing mercury which comprises preheating a body of liquid mercury, injecting successive small portions of such preheated liquid into a current of superheated mercury vapor under superatmospheric pressure, whereby to vaporize at least the major part of such liquid, tapping on unvaporized liquid and returning the same to the supply source for liquid mercury, supplying heat to said vapor current to resuperheat the vapor, recirculating a portion of the superheated vapor for vaporizing additional liquid mercury and withdrawing the balance of the vapor for delivery to a point of use.

5. The method of vaporizing mercury which comprises preheating a body of liquid mercury, injecting successive small portions of such preheated liquid into a current of superheated mercury vapor under superatmospheric pressure, whereby to vaporize at least a major part of such liquid, removing unvaporized liquid mercury, supplying heat to said vapor current to resuperheat the vapor, recirculating a portion of the super-- heated vapor for vaporizing additional liquid mercury and withdrawing the balance of the vapor for delivery to a point of use.

JOHN J. GREBE.

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