US1887807A - Mercury vaporizing apparatus - Google Patents

Description

Nov. 15, 1932. J. J. GREBE MERCURY VAPORIZING APPARATUS Filed Sept. 30, 1929 2 Sheets-Sheet v, Q G Q7 W 0,J Va. Q

ercur 0 M Re Main BY |NVENT8RM v Q iW/ Nov. 15, 1932.

J. J. GREBE 8 1,887,807

MERCURY VAPORIZING APPARATUS Filed Sept. 30, 1929 2 Sheets-Sheet 2 Fig. 3 80011071 A B 0;

INVENTOR 122: wmu, f1.

ATTORNEY Patented Nov. 15, 1932 UNITED STATES PATENT OFFICE JOHN J. GREBE, F MIDLAND, MICHIGAN, ASSIGNOR TO THE DOW CHEMICAL COMPANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN MERCURY VAPORIZING APPARATUS Application filed September 30, 1929. Serial No. 396,101.

My invention relates to mercury boilers such as may be employed for vaporizing mercury under pressure in connection with the use of mercury vapor as a heating agent or for use in a heat energy cycle, such as in a power generating turbine.

Mercury has been vaporized in a tubular container exposed to furnace heat. The boiling point is high and the high furnace temperature required introduces danger of overheating the tubes, either locally or generally. It has been proposed to interpose be tween the heating surface forthe mercury and the fire a bath of a molten metal, such as lead or an alloy thereof in the form of a jacket about the mercury heating surface and contained in a metal vessel. Such proposal amounts to materially increasing the heat transfer path and heat flow resistance be- 80 tween the fire and the mercury and does not eliminate risk of overheating the vessel in which the molten metal jacket is contained. It also reduces the effective capacity per cubic unit .of space taken up,thereby increasing construction cost, and by extending heat 'radiat ing surfaces increases radiation losses.

In a copending application, Serial No. 393,867, filed September 20, 1929, H. H. Dow and J. J. Grebe have disclosed an improved method and means for vaporizing mercury employing a molten metal heat transfer agent positively circulated in a path including a separate heater for the molten metal and a tubular mercury boiler heated by the so cir "cu'1ated man; *Sucliiisystemrequirsme h -r r 12' h a vacuum pu p,

chanical or equivalent means adapted to circulate a molten bath of metal.

The present invention may be regarded as an improvement upon theabove cited dis closure in which improved method a molten metal heat transfer agent is employed. the same being boiled under a controlled pres sure at constant temperature. such boiling furnishing self-circulation of the heat transfer agent over the heat receiving surface exposed to the source of heat and over the mercurv boiler heating surface.

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

In said annexed drawings Fig. 1 illustrates a typical form of apparatus adapted to carry out my invention. Figs. 2 and 3 illustrate one alternative form thereof.

Referring to Fig. 1, as hereinbefore stated,- a typical form of apparatus, i. e. a tubular heater for the boiling metal bath, is there shown comprised of a plurality of tubes 1, joined at their lower ends by a tubular header 2 and at their upper ends by a tubular header or drum 3. A vapor dome 4 surmounts the drum 3 having an outlet 5. An inlet 6 is provided in the header 2. Otherwise the tubular heating unit so comprised of the tubes 1, header 2 and drum 3, and dome 4 is a closed vessel. Within the drum 3, piercing the end wall 7 thereof, is a tube or bundle of tubes 8 adapted to contain the mercury. These tubes may be connected with a mercury feed main 9 and with a mercury vapor main 10 as shown. The tubular heating element thus described is to be understood as set in a furnace or heating zone 11, shown in dashed lines, adapted to deliver heat to the boiling metal in the tubes 1. The vapor dome 4 is connected not'shown but indicated, and with an emergency relief valve 13 delivering into a condenser 14 from which a pipe 15 leads to the inlet 6 and header 2. When pipe 15 is exposed to temperatures below the freezing point of sodium (206 F.) it may be acketed or heat insulated in well known manner. The

details of insulating pipe 15 as well as other hot fluid pipes have been omitted from the drawings for clarity.

Any one or more of the metals of the sodium group may be employed as the boiling metal bath, but on account of cheapness and other characteristics the metals sodium or potassium, or an alloy o1- said metals, I regard at the present time preferable metal or metals to use. In order to establish a substantially fixed boiling temperature at an elevation well adapted to the use in question, I conduct the boiling of the metal heating agent under reduced pressure which is done by connecting the vapor dome with a vacuum pump or source of lower pressure. By interposing between the vacuum pump and the boiler a suitable condensing surface, such as indidicated by the coil 12, metal vapors accom panying inert gases will be condensed and drained back into the boiler. Given a tight vessel and having once eliminated fixed gases from same to the vacuum pump but little, if any, vapor flow will be in effect in condenser 12 and a small vacuum pump will be adapted to serve a number of boiler units, such as illustrated in Fig. 1 or equivalent thereto. Operating under reduced pressure corresponding to 28 inches of vacuum the boilin point of sodium is approximately 1200-F., a temperature well suited to generate mercury vapor under considerable pressure and superheat, as for instance at 180 lbs. guage pressure and a temperature approximating 1100 to 1150 F. It will be preferable to charge the boiler with less than enough sodium or other metal than requiredto fill same, so that the tubes containing the mercury may be exposed to the sodium vapors and/or the molten sodium and circulation of the sodium be active due to vapor formation in the tubes receiving the most heat. Whether the mercury vaporizing tubes will be heated by sodium vapor only, by boiling molten sodium only, or a mixture thereof, is obviously contingent upon the level of the molten sodium in the boiler. Such level, Wherever initially set, will fluctuate in operation. The oflice of the emergency relief valve and connected condenser is to relieve excess pressure which may be developed over the sodium in case of a sudden and marked reduction in demand for mercury vapor also consequent upon lag in effective control of heat supply to the furnace. Such relieved vapors will be condensed and automatically returned to the boiler by the condenser 14: which, as well as the condenser 12, may he air-cooled or otherwise.

Such a method of boiling mercury has marked advantage over anything heretofore proposed. The mercury heating surface is entirely removed from exposure to high temperature furnace heat permitting the use of small thin-walled tubes and the use of flash evaporation, thereby eliminating the phenomenon of bumping which has been found troublesome when boiling mercury. The active circulationof the mercury which acconr panies flash evaporation, e. in small bore tubes, impinges the mercury forcibly upon the heating surface with which it does not effectively contact when at ut, increasing thereby the heat transfer cosicat markedly natural course depending upon the method of supplying the heat. If the furnace temperature be higher on the left hand side, the circulation will be upwards in the tubes adjacent that side and downwards in the tubes to the rear, or if the source of heat be on either face of the tube assembly and all tubes thereof more or less equally exposed, the tubes may be provided with a partition facilitating the upward circulation of the boiling metal on one side and the downward circulation on the other side of said partition, i. e. the boiling metal will rise in all the tubes in that side thereof in the face of the assembly of tubes adjacent the principal source of heat and fall in the other side thereof, the partition separating the rising and falling currents in the tubes. Various modifications and details of design and construction will be obvious to those skilled in the art, certain of which I proceed to describe.

Fig. 2 is a side view of a unit element of a mercury boiler employing my invention and Fig. 3 is a vertical cross-section on line AB of Fig. 2 showing three such units set parallel in a battery. The condensers, source of vacuum, and return connections are omitted for the sake of clearness.- The boiler elements here illustrated are suited for use in the convection passes of a multiple unit boiler and each such unit is comprised of the tubes 1, joined at the bottom by the oval header 2 and at the top by a like oval header 3 containing the mercury boiling tubes. The flow of the furnace gases is shown by the waving arrows as from left to right and a plurality of such individual units may be set side by side in the convection pass of a furnace in which arrangement the front tubes may or may not be exposed to direct radiated heat from the fire. The level of the molten boiling metal is indicated at CD as one level therefor. Selfcirculation will be upward in the front tubes and downwards in the back tubes as indicated by the arrows.

It will be seen that my improved invention, by providing for active natural circulation of the boiling metal heating agent at a controlled relatively fixed pressure and temperature, insures against overheating of the metal ves el exposed to the furnace heat. For the high temperatures herein contemplated, alloy steel is advantageously ap licable, such material being available s owing strength, rigidity, and durability at a red heat; The compact arrangement of heating units permits the use of a'limited weight and vol ume of the boiling metal bath and a subdivision of the total weight and volume thereof molten metal of low. specific gravity, a vacuum pump connected to the vapor space 0 sai drum, a condenser interposed between said drum and said pump,a pressure'relief valve and means including a condenser to return vapors vented thereby to said header, v

means to heat said tubular members, a bundle of tubes inserted within said drum and means to supply mercury to said tubes and to remove mercury vapor therefrom.

' JOHN J. GREBE.

evaporation of the mercury the volume and I weight of the mercury in the boiler may be reduced to a low figure which is very desirable in view of the high cost of mercury and the great danger of large loss if-a large weight thereof be employed. Such restriction of the weightof mercury per unit of heat delivered to the point of use further practicalizes the prespective employment of mercury vapor; since if large relative weight were required the limited supply of available mercury would likewise limit its use. Further, by boiling the mercury in a plurality of separate vessels, any one of which may be cut out in emergency, the risl: of mercury loss and hazard arising therefrom maybe greatly reduced.

Other arrangements and details of construction than those herein disclosed" will be obvious to thoseskilled in the art without departing from the spirit ofgny invention. 7

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

I therefore ,particularlypoint out and distinctly claim as my invention 1. In a mercury boiler, the combination of in a generally vertical position, a hea er connecting the lower ends of said members, a transverse, inclined vapor drum connecting the upper ends thereof, said tubular members, header and drum being adapted to contain-a body of molten metal of low s ific gravity,- a vacuum pump connected to t e vapor space of said drum and a condenser interposed betweemsaid drum and said pump, means to heat said tubular members, a bundle of tubes inserted within said. drum and means to supply mercury to said tubes and to remove mercury vapor therefrom.

2. In a mercury boiler, the combination of a bank of tubular members disposed in a generally vertical position, a header connecting the lower ends of-said members, a transverse inclined vapor drum connectin the upper ends thereof, said tubular mern header and drum being adapted to contain abody of Signed by me this 26th day of September,

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