US2185048A - Mercury boiler feed arrangement - Google Patents

Description

Dec. 26, 1939. Q w ob 2,185,048

MERCURY BOILER FEED ARRANGEMENT Filed May 20, 1939 Inventor: Qrla L. Wo ci, b fiu/aycfx H i s Attorney.

Patented Dec. 26, 1939 UNITED stares r'rssr omcs New York Application May 20, 1939, Serial N0. 274,782

' 5 Claims. (01 103-111) The present invention relates to mercury boiler feed arrangements including a pump, particular ly a low suction head pump for forcing mercury liquid into a boilei. In such arrangement speear means have to be provided for returning mercury liquid l'eaking along the pump shaft.

The objeet (if my invention is to provide an improved construction and arrangement of the type above specified whereby leakage of mercury along the pump shaft may be readily returned into the system. I

For a consideration of what I believe to be novel in my invention, attention is directed to the following description andthe claims appendedthere'to in connection with the accompanying drawing. v 1

The single figure of the drawing illustrates an arrangement embodying my invention.

The arrangement comprises a mercury boiler Ill for producing mercury vapor. An elastic fluid turbine H has an inlet conduit I 2 with a valve l3- connected "to the boiler to receive mercury vapor therefrom and a discharge conduit I4 connected to a condenser I5 in which the exhaust fluid fromthe'turbine is condensed. 1 During normal operationthe condensate is discharged from thecondenser through a conduit l6 and forced into the boiler ID by means including a pump I! with a discharge conduit l8 having a valve l9. The pump is of the impeller type and comprises a pump casing 25 in which an impeller 21 is located and secured to a vertical shaft 22 driven by a motor 23. The lower end of the casing forms an inlet and the upper portion of the casingforms a sealing chamber 24. A mercury liquid seal is formed between the chamber 24 and the'motor' 23 to prevent leakage of mercury liquid into the oil lubricated motor bearings and also to prevent air from coming in contact with and oxidizing the hot leakage mercury entering chamber 24 from the impeller. This seal comprises a rotary sealing cup 25 secured to the shaft 22'and a stationary sealing vane 26 projecting into the sealing cup 25. Sealing liquid, in the present instance mercury, is fed to the sealing cup by a conduit 21 in which is located a cooler 26a and a valve 26b which is opened to produce a small continuous mercury flow into the cup The channel 21 is connected to a conduit 28, one end of which is connected to the aforementioned. condenser discharge conduit l5 through a valve'29, normally closed, and the other end of the conduit 28 is connected to pump discharge conduit .l8 ahead of the valve l9 as regards direction of now oiliquid through the conduit it. The valve 23 is opened when the valve I9 is closed to recirculate the mercury While the pump is running to prevent f overheating and alsofor sealing the turbine shaft when it is sta tionary' besides acting as a vent for steam or air in case the impeller of the pump becomes bound with same.

The inlet of the pump I? is connected through a U-shaped sealing conduit to a sump 3| to receive liquid therefrom through an overflow 32 formed within the sump. The inlet of the sump is connected to the condenser discharge conduit 65. The leg of the U-shaped sealing conduit tlliwhich is connected to the sump 3| has an enlarged portion 33.

During operation, mercury flows into the overflow 32 in the sump and through the U-shaped sealing conduit 33 and the inlet of the pump ll to be forced by the pump through the conduit l3 into the boiler I0. Thus, normally, the condenser l5 forms the source of supply for mercury. When the plant is put out of operation the mercury liquid is drained into a storage tank 34 which in the present instance is located ata level below the condenser and boiler. The tank 36 is connected tothe system by means of twosurge tanks 35 and 35 having upper portions connected by a pressure equalizing conduit 31 and by a conduit 38 to the condenser l5, normally to maintain vacuum in the tanks 35, 35. The surge tanks are connected to the storage tank 34 by a conduit 39 which has a lower portion projecting into a downward extension 40 of the bottom of the storage tank 34, thus forming a liquid seal. The upper end of the conduit to has branches M, 42 projecting into the surge tanks 35 and 36 respectively and forming over-- flows therein. The bottom portions of the tanks 35 and 35 are connected by a branched conduit 43 to the enlarged portion 33 of the sealing con- 'duit 30. An upper portion of the tank 34 is connected by a conduit M having a valve 45 to a source of gas, preferably inert gas, under pressure. In order to force'mercury from the storage tank 34 into the system the valve 45 is opened whereby mercury liquid from the storage tank 34 is forced through the conduit 39 into the surge tanks 35, 35 whence it flows through the conduit 43 and the sealing conduit 30 to the pump inlet.

I During operation some of the mercury liquid in the pump leaks into the sealing chamber 24. From this chamber the liquid is returned into the, system by means including a U-shaped s l which has one leg connected to the chamber and another leg connected to the aforementioned U- shaped seal 30, preferably to the enlarged portion 33 thereof, that is, to the leg of the seal 30 which is connected to the sump 3|. More specifically this U-shaped sealing conduit for returning leakage from the pump into the system comprises a leg 46 connected bya conduit 41 to the chamber 24 and a leg 48 connecting the lower end of the leg 46 to the enlarged conduit portion or chamber 33 at a point somewhat below the level of the center of the impeller 2| of the pump. The leg 46 has an upperopen end extending beyond the connection with the conduit 41 and enclosed in a chamber 49. The chamber 49 has an upper portion connected to a conduit 50 with a valve 5! for receiving gas, preferably inert gas of atmosheric pressure or pressure slightly above atmosphere. The bottom of the chamber 49 is connected to the conduit 39 by a conduit 52 forming a U-shaped seal at the lower end and including a valve 53.

Except when mercury is forced from the storage tank 34 to the surge tanks 35, 36, the valve 53 is normally open. The pressure difference in the outlet end of the conduit 52 which is normally under vacuum as it is in communication with the condenser l5 and the chamber 49 which is under pressure preferably slightly above atmosphere is maintained by the mercury seal in the U-shaped portion of the conduit 52. The difference in level of the liquid contained in the chamber 33 and in the leg 46 is substantially equal to the vacuum maintained in the condenser [5, it being assumed that the condenser I5 is under vacuum and the pump I! out of operation. Upon operation of the pump the level in the chamber 33 drops to a point near the connection with the leg 48 and near the horizontal plane through the center of the impeller by the amount of differential pressure between the designed suction or inlet head on the pump for the then existing discharge, and the amount of vacuum maintained in condenser I5. In any case, even with maximum vacuum in condenser 15, provided the pump is in normal operation and discharging the same amount of liquid in the discharge conduit 18 that is entering it through the conduit l6 and the U-shaped sealing conduit 30, the level in the chamber 33 will never reach such a height that the level in the leg 46 will approach the entrance of the conduit 41. The level in the chamber 33 is indicated by a stand pipe 54 connected to the U- shaped sealing conduit 30 and including a float 55. If the level rises to a certain point above the horizontal center line through the impeller, an upper portion of the float 55 actuates an alarm switch 56. Such rise of the mercury level may be caused, for example, if the pump I! is rendered inoperative and it also takes place during starting when mercury liquid is forced from the storage tank to the pump. Likewise there is a similar alarm switch 59 which the float 55 actuates if the pump attempts to pump itself dry with a consequent drop in level by the valves l9 being left open or too far open for the amount of return entering the pump from condenser l5. During starting the level indicator notifies the operator when to start the pump and also when to admit inert gas, such as nitrogen, by opening the valve 5| to the sealing chamber 24. The rotary mercury seal 25, 26 prevents leakage of gas into the atmosphere and'leakage of air into the sealing chamber. This is best accomplished by a gas pressure in the sealing chamber slightly above atmosphere. The avoidance of air leakage into the sealing chamber is important in mercury boilers because of the oxidation of mercury that would otherwise result. In case of an emergency shut-down of the pump with full vacuum'in the condenser, the mercury liquid in the chamber 33 will rise above its connection with the conduit 43 and the mercury liquid will be forced into the surge tanks 35, 36, the latter as stated before being under vacuum. As the level in the surge tanks rises to the height of the overflow pipes 4|, 42 the liquid will be returned through these overflows into the storage tank 34. During shut-down the vacuum in the condenser is ordinarily broken by the admission of inert gas such as nitrogen. The mercury liquid then draining into the chamber 33 of the sealing leg 30 causes considerable rise in level in the sealing leg 46. As the mercury level in this leg rises to the open upper end of the leg 46 above the connection with the conduit 41, the mercury liquid flows into the chamber 49, whence it is drained through the sealing conduit 52 to the storage tank 34. The upper end of leg 46 is located at a level near that of the rotary mercury seal 25, 26. The cross-section of the chamber 49 is large relative to that of the area of the open end of the leg 46. This enables the chamber to take large overfiow without much increase in head, thus preventing the mercury level in the pump sealing chamber 24 to rise above the sealing cup 25. I

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Mercury boiler feed arrangement comprising a source of mercury, a feed pump, means including a U-shaped sealing conduit connecting the inlet of the pump to the dischargeof the'condenser, and means including a U-shaped sealing pipe for returning leakage from the pump into said sealing conduit.

2. Mercury boiler feed arrangement compris+ ing a source of mercury, a feed" pump having a casing with a portion forming an inlet and another portion forming a sealing chamber, means including a liquid seal connecting the inlet to the condenser, and means forming another. liquid seal connecting the sealing chamber to the first liquid seal. 1

3. Mercury boiler feed arrangement compris- I ing a, condenser, a feed pump forming a sealing chamber, means forming a liquid seal connecting the inlet of the pump to the discharge of the condenser, means for draining leakage from the chamber to the liquid seal comprising a U-shaped sealing device having one leg connected to said liquid seal, and means connecting the other leg to the chamber and to a source of inert gas under pressure.

4. Mercury boiler feed arrangement comprising a source of mercury liquid,.a vertical pump having a shaft with an impeller, an inlet below the impeller and a sealing chamber above the impeller, means including a U-shaped sealing conduit having a first leg connected to the inlet and a second leg connected to the source, and means including a .U-shaped sealing pipe having a first leg connected to the sealing chamber and a second leg connected to the second leg of said conduit to return leakage from the chamber 'to the sealing conduit, and means forming an overflow for the first leg of the sealing pipe and having a liquid seal to receive mercury as the mercury level in the sealing chamber rises beyond a certain height.

ORLA L. WOOD.

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