US2021394A - Apparatus for dispensing highly volatile liquids - Google Patents

Description

NOV. 19, 1935. H. N W 2,021,394-

APPARATUS FOR DISPENSING HIGHLY VOLATILE LIQUIDS Filed March 11, 1955 HENRY N. WADE 7D /NVENTOR ORNE) Patented Nov. 19, 1935 UNITED STATES PATENT OFFICE APPARATUS FOR DISPENSING HIGHLY VOLATILE LIQUIDS ment in most cities. From these buried tanksthe liquid is withdrawn by means of .a pump which must usually deliver the liquid at a pressure materially. above the vapor pressure.

The use for this purpose of a pump placed at or above the surface of the earth is attended with some difliculty. The liquid body in the storage tank rapidly comes into vapor-pressure equilibrium with the'overlying vapors. Thereafter, any attempt to draw liquid from the tank by suction lift from an elevated pump causes more or less vaporization of the liquid in the pump suction pipe, the pressure on the liquid in this pipe being necessarily brought below the vapor pressure in the very act of producing the suction. This vaporization renders the operation of any pump ineflicient and uncertain and may entirely prevent the use of the centrifugal type of pump which is most desirable for handling extremely volatile liquids.

. .This difliculty may be avoided by locating the pressure pump itself at or below the .bottom of the tank, as in a deep pit, in a well inside the tank, or in a well exterior to the tank and connected with it by piping. 'lither of these arrangements, however, is unduly expensive as to installation and renders repairs or replacements awkward and dimcult.

I A method of lifting the liquid to the pump suction which has had some practical application is to increase the pressure in the vapor space in the storage tank by introducing air or other fixed gas. A serious objection to this method is the obvious explosion hazard resulting from the 4 use of air, which is ordinarily the only gas avail- .applies equallyto the use of other fixed gases is that these gases slowly dissolve in the liquid and tend to separate therefrom when the pressure is reduced, giving rise to gas pockets and other dis- 50 turbances to the subsequent utilization of the liquid. v The object of the present invention is to proable forthis purpose. Another objection which the liquid contained in the tank, without the use of any extraneous material for accomplishing this pressure increase. It is obvious that such increased vapor pressure may be utilized to deliver an unbroken stream of liquid to the suction of a 5 pump located at the surface and to prevent vaporization in this stream, thus ensuring a constant supply of liquid to the suction of the pump and its eflicient and dependable operation at all times.

The form of the invention contemplated in the present application is illustrated in the attached drawing, which shows in a diagrammatic manner a suitable assemblage of apparatus.

Referring to the drawing, I is a closed storage 15 tank placed materially below the ground level indicated'at 2. A filling pipe 3 having a hand valve 4 provides for introducing the volatile liquid body indicated at 5.

A relatively small secondary tank or receiver 6 20 is placed above ground and its pipe connected in its lower part with the suction of a pump I having a discharge pipe 8 provided with a valve 20.

A pipe 9 connects the bottom of receiver 6 with the lower portion of the interior of tank I. A 2 pipe l0 connects the top of the receiver with the suction side of agas compressor l l which is actuated by an electric motor l2. 'The receiver is provided with a float I! attached to a pivoted.

arm H which extends through a packed gland to 30 the exterior of the receiver. A valve IS in pipe in is so connected to this arm that it is closed when the liquid in the receiver stands at some preferred level, say one-half its depth, and opens when the liquid falls materially below this level. 35 The motor I2 is connected by suitable leads It with a source of electrical energy not shown,

' these leads passing through a switch I! which is so coupled to arm I l as to be in the closed position when valve I5 is open and in the open posi- 40 tion when this valve is closed.

The compressor discharge'is connected with the vapor space in the top of the tank by a pipe l8.

In starting up the described system, receiver 6 which is arranged to drain freely into tank I will be empty, float l3 wfll be down, valve I! will be open and switch I! will be closed. On

supplying power to the electrical circuit and hav- 5o ing valve 2!) closed, the compressor will withdraw vapor from the receiver and return it to the storage tank, thus creating a pressure difference which causes liquid to rise through pipe 8 and 1111' the receiver up to the level at which the float operates to open switch I! and stop the compressor.

The pump suction is now flooded with the liquid retained in receiver 6 and valve 20 may be opened and the pump started. As the level in the receiver is reduced by pump withdrawal of liquid the float acts to close switch l1, starting the compressor, and the supply in the receiver is thus reestablished and is continuously maintained.

In dealing with volatile liquids such as pure propane or pure butane, consisting of a single component, the effect of the operation of the compressor is to maintain a temperature difference between the vapor spaces in the receiver and the tank. The liquid is lifted into the receiver by the reduction of pressure in its vapor space. This pressure reduction produces evaporation of liquid in the receiver and consequent reduction of vapor temperature by conversion of sensible heat into latent heat of evaporation. The vapor drawn through the compressor is heated by the work of compression and is delivered into the vapor space of the tank at a temperature higher than that of the liquid body in the tank. When the system is in static equilibrium, the temperature of the vapor and of the upper surface of the liquid body in the tank will be such that the vapor pressure of the liquid in this upper surface balances the vapor pressure of the liquid in the receiver plus the hydrostatic head of the liquid column between the two liquid levels. The slightly heated upper layer of liquid tends to remain at the top of the liquid in the tank and will not difluse through the liquid body because its specific gravity is reduced by heating. The heat from this upper layer can be transmitted to the liquid body only by the excessively slow process of downward conduction through the liquid itself.

In practice the receiver should be provided with effective heat insulation to prevent absorption of heat from the surrounding atmosphere, the temperature of the liquid in the receiver being usually materially below atmospheric.

In handling liquids consisting of two components, such as propane and butane in'the commercial grades of liquefied petroleum gas, the lifting of the liquid from the tank to the receiver does not depend solely on maintenance of temperature difierence. The vapor withdrawn from such a mixture will, by the well known laws of partial evaporation of mixtures, be relatively rich in the more volatile and poor in the less volatile constituent of the mixture. Thus the vapor returned to the tank will, in the case of propanebutane mixtures, contain a higher mol percent of propane than does the body of liquid in the tank. his has the effect of building up on the upper surface of the liquid body a thin layer of liquid relatively rich in propane and which in consequence has a higher vapor pressure at a given temperature than the liquid passing into the receiver at the same temperature.

This layer tends toremain distinct because of the lower specific gravity of the propane constituent, and lacking any cause for disturbance of the liquid body, mixture can occur only through slow downward diffusion. Thus in' this case a pressure difiference may be maintained between the tank and the receiver even though there be no actual temperature difference between the two liquid bodies, because the top layer of liquid in the tank, which is the controlling factor in fixing the vapor pressure in the vapor 10 space of the tank, is richer in propane than the upper surface of the liquid in the receiver, which has been deprived of some of its propane by withdrawal of vapor to the compressor,

While I have described a highly specific arrangement of apparatus, I would have it understood that the substance of my invention lies in the withdrawal of vapor from the liquid passing from the storage tank to the pump suction and the return of this vapor in a compressed condition to the vapor space of the tank, and that the limits of the invention are defined solely by the scope of the appended claims.

I claim as my invention:'

1. A storage and delivery system for highly volatile liquids comprising in combination: a closed storage tank; a closed receiver arranged substantially above said tank; a pump arranged to have its suction flooded by liquid from said receiver; a compressor arranged to withdraw vapor from said receiver and to return said vapor in a compressed condition to the vapor space of said tank, and means responsive to changes in liquid level in said receiver for controlling the operation of said compressor.

2. A storage and delivery system for highly volatile liquids comprising in combination: a closed storage tank; a closed receiver arranged substantially above said tank; a pump arranged to have its suction flooded by liquid from said receiver, and means for withdrawing Vapor from said receiver and for returning said vapor in a compressed condition to the vapor space of said tank.

3. A storage and delivery system for highly volatile liquids comprising in combination: a closed storage tank; a pump arranged substantially above said tank; a channel affording communication between the lower portion of said tank and the suction of said pump, and means for withdrawing vapor from liquid passing through said channel and for returning said vapor in a compressed condition tothe vapor space of said tank.

4. A storage and delivery system for highly volatile liquids comprising in combination: a closed storage tank; a pump arranged substantially above said tank and adapted to deliver said liquid under pressure; a receiver arranged substantially above said tank and communicating with the bottom of said tank and with the suction of said pump, and means for withdrawing vapor from said receiver and for delivering said vapor to the vapor space of said tank.

' HENRY N. WADE.

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