US2850882A

US2850882A - Method and apparatus for handling volatile liquids

Info

Publication number: US2850882A
Application number: US550703A
Authority: US
Inventors: Jesse B Starnes
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1955-12-02
Filing date: 1955-12-02
Publication date: 1958-09-09
Anticipated expiration: 1975-09-09
Also published as: GB812998A; DE1100060B; FR1168949A; BE553071A

Description

Sept. 9, 1958 J.'B. STARNES 2,350,832

METHOD AND APPARATUS FOR HANDLING VOLATILE LIQUIDS Filed Dec. 2, 19555 s Sheets-Sheet 1 Fill Connecfion iary Fill Line Auxiliary Fill Line it 8 3 l0 ID a; 1 l 420 3c 3;: a 62s:

INVENTOR. JESSE B. STARNES Non-Regulal'ed Pressure Pipeline A T TOR/V5 V P 1958 J. B. STARNES 2,850,882 METHOD AND APPARATUS FOR HANDLING VOLATILE LIQUIDS Filed Dec. 2, 1955 3 Sheets-Sheet 2 I MAE-f w I 147% Ia? do IN V EN TOR. JESSE B. STARNEYVS A TTOR/VEV Sept. 9, 1958 J. B. STARNES METHOD AND APPARATUS FOR HANDLING VOLATILE LIQUIDS Filed Dec. 2, 1955 3'Sheets-Sheet 3 IN V EN TOR. I

JESSE BA. STARNES BY A TTORNE'Y United States Patent METHOD AND APPARATUS FOR HANDLING VOLATILE LIQUIDS Jesse B. Starnes, Snyder, N. Y assignor to Union Carbide Corporation, a corporation of New York Application December 2, 1955, Serial No. 550,703

13 Claims. (Cl. 62-52) friction and to an increase in fluid velocity. Such pressure drop will be apparent even when the pump is immersed in the body of liquid and intake piping is eliminated. Heat will also be added to the liquid inside the pump due to turbulence of the moving liquid, to friction of the moving pump parts, and to heat conduction along the pump drive. All these factors tend to cause vaporization of a portion of the liquid before it can be discharged from the pump.

If vaporization is allowed to occur before or Within the pump, it may prevent priming or cause loss of prime (i. e., it may cause vapor binding). Furthermore, a small amount of vaporization, insuflicient to result in priming difliculties, is detrimental to good pump performance. In rotary pumps, vaporization causes cavitation of the rotor, and in reciprocating pumps, severe impact or knocking occurs which accelerates wear and fatigue on both pump and drive. The presence of vapor within the pump also reduces its pumping rate so that more power is consumed and more operating time is required for a given transfer of liquid.

The usual procedure to avoid these pumping difliculties is to first subcool the liquid with respect to its pressure by rapidly increasing the gas pressure above the liquid immediately prior to pumping. Subcooling is the procedure of adjusting the pressure-temperature conditions of the liquefied gas so that it is substantially below its boiling point at the existing pressure. This allows the liquid to be handled and transported with some pressure drop without flashing or excessive evaporation. To subcool a body of liquid by abstracting heat would obviously require a colder fluid to absorb the heat removed, plus expensive heat transfer equipment. It is thus more convenient to increase the static pressure above the body of liquid in order to prevent boiling and suppress vaporization. The degree of subcooling required for good pump performance depends upon a number of factors. Important considerations are heat leak and pressure drop in the piping,

pump without attendance and with pressure regulation in the storage vessel to meet the fluctuating pressure requirements during pumping and non-pumping periods.

Such liquefied gases are normally stored at or near their boiling point, and it has in the past required continuous attending and a high degree of skill on the part of a trained operator to maintain the transfer operation without vapor binding. The steps of precooling the pump and subcooling the liquid in the storage tank had to be performed manually with a high measure of care to avoid poor pump operation with consequent lowering or stoppage of pumping rates and increasing power losses. Excessive subcooling often occurred resulting in high pressure conditions in the storage tank with attendant loss of product through safety devices.

The principal object of this invention, therefore, is the provision of a method and apparatus by means of which a body of highly volatile liquid stored at or near its boiling point can be subcooled by pressure building for withdrawal purposes completely automatically and reliably, so as to eliminate or reduce the influence of the operators attentiveness and skill upon the efiiciency of the subcooling operation. This results in lower maintenance, reduced operating costs and greater dependability.-

Another object of this invention is to provide for the automatic return to normal storage pressure at the terof the storage vessel pressure between prescribed limits.

A body of liquid stored at low temperature andnear its boiling point will gradually build pressure due to unavoidable heat leak unless vapor is withdrawn. The tank pressure is usually maintained below the desired upper limit by periodically withdrawing vapor which 'may be either blown to the atmosphere, delivered to gas-phase storage or supplied to a consuming means. If the liquid is stored at or above the pressure at which it is con sumed, then vapor may be conveniently released into a In such cases an automatic valve responsive supply line. to tank pressure is generally adequate. If the liquid is stored at low pressure, however, it may be necessary to compress the excess vapor before itsdisposal. In instances where compression is needed, the compressor automatic controls are responsive to storage tank pressure as disclosed in U. S. patent to Van Fleet, et al. 2,435,332. When the same body of liquid is also subcooled prior: to withdrawal, the tank pressure is preferablyv raised above the standby upper limit, and new upper and lower limits must be established at a pressure range which provides sufficient subcooling of the liquid. The lower limit will. be prescribed by the minimum subcooling pressure. I Tank pressure will be maintained below the upper limit ,in

the same manner as described with respect to lower range control. It is to be understood that the upper limit controls describedherein for the storage vessel are pro vided in addition to the usual over-pressure safety devices. In general practice, safety devices are not made subject to adjustment or operation in response to an operating control system, but rather are considered to be for emergency purposes only. 7

In accordance with the present invention, a storage tank holding a body of volatile liquid at or near its boiling points 'at storage pressure, is provided with a dual pressure range control that includes a normal ,pressure range control operative during standby periods to hold the tank pressure within a relatively low pressure range and a tank pumping pressure range control operative during withdrawal periods to hold tank pressure between upper and lower limits of a relatively higher high pres sure range. The dual pressure range control is inter Patented Sept. 9, 1958.

connected with the controls for the liquid withdrawal pump, and is operative when a pumping period is initiated to render ineffectual the tank normal range control and to activate the tank pumping range control. Likewise, when the pumping period is terminated, the dual pressure range control is responsive to a condition sensed by the pump controls and is operative to effectuate inactivation of the tank pumping range control and to reinstate the tank normal pressure range control. When thetank pumping range control is activated, the pressure of the body of liquid in the tank is automatically increased to the higher pressure range, which is sufiiciently high to prevent vaporization from occurring either in piping to the liquid withdrawal pump or in the pump itself. In this way, subcooling is achieved in a reliable manner without the need for manual attention and operation.

In one aspect of the invention, when Warm pumps, i. e. uninsulated or other pumps which are allowed to warm up in the intervals between operations, are employed for liquid withdrawal, automatic subcooling can be accomplished by vapor relief control. The process of precooling a warm pump prior to usage normally prov-ides more than sufficient vapor for subcooling needs provided the pumping period is of relatively short duration, or the quantity of liquid withdrawn is a relatively small fraction of the storage volume. During standby periods, the tank normal pressure range vapor relief device is operative to hold tank pressure below an upper limit. When the pumping period is initiated, the automatic subcooling controls associated with the pump controls place the tank under control of the tank pumping range vapor relief control and vapor resulting from pump precooling and priming is directed into the tank and builds up the pressure to substantially above that existing prior to pump precooling and priming. If the pressure should reach the upper limit of the vapor relief device, sufficient vapor is released from the tank by such device to prevent further pressure rise.

In another aspect of the invention suited particularly to cold pumps-those which are immersed in the stored liquid or external thereto but well insulated, automatic subcooling is effected preferably by the use of pressure building coil control. A single range or dual range control can be provided. In either case, tank pressure is built up to a desired level by withdrawing a portion of liquid from the tank, vaporizing it in an evaporating coil and directing the resulting vapor into the vapor phase of the tank to raise the pressure to the desired level. A dual range pressure building control could be used, for example, to provide a subcooling range and a lower range for effecting transfer to other equipment by pressure difference alone. Admission of a high pressure gas from an external source would be employed for pressure building as an alternative to the pressure building coil control. In either arrangement, vapor relief devices and/or safety pressure release devices are usually required for safety reasons, these devices being set to function at a higher pressure than the subcooling range.

Combined vapor relief and pressure building control is a particularly attractive control for complete automatic operation of cold liquid distribution systems which operate with an intermittent pumping schedule. This system employs in addition to pressure building controls for subcooling, vapor relief controls to draw the tank pressure down between pumping operations in order to remove heat that was added to the stored liquid during pressure building and pumping. By removing the heat in this manner, the margin of pressure between the liquid saturation point and the limiting setting of safety devices is always adequate for the required degree of cooling.

These and other objects, features, and advantages will become apparent from the following description of the accompanying exemplary drawings, in which:

Fig. 1 is a schematic diagram of an automatic gas dispensing system embodying the invention, using warm 4 pump priming and dual-range vapor relief control for subcooling;

Fig. 2 is an electrical circuit diagram for the automatic controls of the apparatus illustrated in Fig. 1, which are pertinent to the present invention;

Fig. 3 is a schematic view of another embodiment of this invention, using a pressure building coil for subcooling;

Fig. 4 is a schematic view of still another embodiment of the invention, illustrating an automatically controlled dual-range pressure building circuit;

Fig. 5 is a schematic view of an embodiment of the invention, illustrating an automatic dual-range high pressure gas control;

Fig. 6 is a schematic view of another embodiment of the invention, showing a combined dual-range vapor relief and dual-range pressure building control; and

Fig. 7 is a simplified electric circuit diagram used in the system of Fig. 4.

In accordance with the present invention, there is provided; storage tank means S for storing a low boiling point liquefied gas in a condition substantially insulated against heat inflow from external sources, a vapor compressor L for control of storage tank pressure by removing vaporization from the storage tank and supplying this gas to the consumers pipe line in response to the pressure in the storage tank and with provision for maintaining such tank pressure at a higher level during the operating cycle of either cold converter filling pump P or P a cold converter or parallel-connected bank of cold converters C for delivering liquefied gas in response to the demand of the consumers pipe line, liquefied gas conduit means including the pumps P or P for transferring liquefied gas from the storage tank to the cold converter bank, vaporizing and superheating means associated with the cold converters and a pressure regulating manifold for withdrawing liquefied gas from the cold converters and supplying it in the gaseous phase to the consumers pipe line, and automatic pump control means comprising a liquid content responsive device associated with the converter or one converter of a bank and preferably including a closed hydraulic pressure system responsive to the change in weight of liquefied gas in the cold converter and operative to control the pumping of liquefied gas from the storage tank 5 to the co d converter or cold converter bank to maintain a level of liquefied gas therein between predetermined limits.

Referring to the drawing, and particularly to Fig. l, a liquefied gas filling conduit 10 is provided for a pumping and measuring means which transfers a low boiling point liquefied gas from a transport means to storage tank means S which comprises an inner shell and an outer shell separated by insulating material, preferably of the powder-in-vacuum type disclosed in U. 5. Patent No. 2,396,459. An alternative connection 11 is provided for pumping liquid from the tank S to a transport means by use of pump P or for filling liquid into tank S, or for pumping liquid into converter C directly from a combined transport, pump, and measuring means. A conduit 13 is provided to complete a pump priming circuit, or to fill the storage tank S. Automatic pump P withdraws liquefied gas from tank 8 through conduits 14 and 15 and transfers it through conduit 16, conduit 17, check valve 18, conduit 19, a manifold 20, and conduits 21 to each of the parallel-connected cold converters C through their respective conduits 23. A flow equalizing means 22, preferably an adjustable hand valve, is provided in each line 21 for effecting a present equalization of the flow of liquefied gas to each of the cold converters.

Each cold converter C comprises an inner pressure vessel 24 surrounded by heat insulating material, preferably of the powder-in-vacuum type, and an outer shell 25. Base structures 26 support each cold converter. A liquefied gas space 27 is provided in the insulation of the cold converter and is in communication with the inner vessel 24 through

conduits

28 and 29 connecting to gas and liquid phases, respectively. Relief valves 30 are provided to vent gas from the storage, tank S and each cold converter C in the event of excessive pressures. Safety heads 31 are provided to vent gas from the insulating material of storage tank S and each cold converter C in the event of accidental leakage. Liquefied gas is drawn from the inner vessel 24 of each converter C through conduits 32, and passes through conduits 34 to a heating means 35 where it is vaporized and superheated. A flow equalizing means, preferably a hand valve 33, is provided in each line 34 and is preset to effect an equalization of the fiow of liquefied gas from each of the cold converters C. The vaporized and superheated product is then passed through conduits 36 to conduits 37 which are enclosed in the liquefied gas of spaces 27 to effect a vaporization of a portion of liquefied gas in that space and thereby increase the pressure in the inner vessel 24. After passing through conduits 37, enclosed in spaces 27, the vaporized gas is then passed through conduit 38, to a reheating means 39,

where it is reheated to a desired temperature. v

A conduit 40 conducts the gas to the inlet of a reducing valve 41 which maintains the discharge pressure at a desired value for the pipe line. Conduit 42 connects the outlet of valve 41 to the consumers regulated pipe line. A conduit 43 supplies gas at a non-regulated pressure from the inlet end of reducing valve 41 to the non-regulated pipe line. A gas storage receiver 44 isin communication with the upper portion of each cold converter vessel through conduit 45, a heating means 46, and a conduit 47 and serves to prevent excessive rates of variation of pressure caused by filling of the converters and by fluctuations in the consumers demand. When pressure in the gas storage receiver 44 and conduit is above a set value, gas flows from conduit 45 to conduit 42 through a back pressure valve 48 and a reducing valve 49 which are connected between conduit 45 and conduit 42. Preferential flow of gas through reducing valve 49 with respect to gas through reducing valve 41 is elTected by a setting of the reducing valve 49 to open at a pressure value higher than the pressure setting of reducing valve 41.

The automatic control of liquefied gas level in the cold converter bank is provided by supporting a cold converter base structure 26 atone side on a pivot or pivots 50 and at the other side on a bellows 51 which is apart of a closed hydraulic system 52. A pressure is developed in this closed hydraulic system by a portion of the weight of the cold converter and the liquefied gas contained therein.

A pressure actuated switch 53 operable by the hydraulic pressure in the closed system operates to start the automatic pumping cycle. When the pressure in the hydraulic system drops to below a predetermined value, due to the drop in the liquefied gas level in the bank of cold converters, the pressure switch 53 in the closed hydraulic system is connected in a control circuit hereinafter described to actuate three devices as follows. First, valve 54 opens in a conduit 55, thus opening the priming circuit path of flow of liquefied gas from the storage tank S through conduits 14 and 15, connecting bottom of tank S to inlet of pump P then through pump discharge conduit 16, conduit 56, connected thereto, and to conduit 55, valve 54, and a conduit 57, connecting to conduit 13. Next, a relay switch 101 of Figure 2 opens in the vapor compressor controls causing the storage tank S pressure to be controlled at a higher range. Then a time delay relay 102 of Figure 2 is actuated to provide thecooling interval before starting the pump P These actions constitute the start of a demand prime cycle.

After a predetermined time interval for bringing pump P to a proper temperature and the storage tank S to proper subcooling pressurejvby use of vapor formed in precooling, the pump P is started by the closing of the time delay 'relay switch 103 of Figure '2. Themessure of pump discharge acting on a pressure switch 58 connected to conduit 56 increases as the pump primes and liquid flow increases through the

conduits

16, 56, 55, 57, and 13, and when the setting of pressure switch 58 is reached, the solenoid valve 54 is closed. Liquefied gas passes into a surge chamber 59 also connected to conduit 56 and pressure rapidly increases to overcome the cold converter pressure acting on check valve 18. Liquefied gas is then delivered to the cold converters C from storagetank S through the liquefied'gas delivery

line comprising conduits

16, 17,19, 21 and 23. When the liquefied gas level inthe cold converter reaches a predetermined value, and the hydraulic pressure acting on pressure switch 53 increases to a preselected value, the switch actuates the control system to stop the automatic pump P for stopping the transfer of liquefied gas from the storage vessel, to keep the priming circuit path closed, and to permit vapor compressor control of the storage tank pressure at the normal lower pressure range.

If the automatic pumping system should fail causing an extreme drop in the liquefied gas level in the cold converter, a pressure switch 60 connected in the hydraulic circuit 52 is actuated which sets off an alarm system giving the consumer sufficient warning to start standby pump P before the cold converters are emptied. This standby pump P is connected in parallel with automatic pump P through conduits 61, 62 connecting between conduit 14 and the inlet of pump P conduits 63, 64 connecting discharge of pump P to conduit 17, and 65 connecting through conduit 12 to conduit 13. The standby pump line 63 is provided With a pressure switch 66 which automatically stops the standby pump when an excessive pressure is developed in conduit 63.

In the embodiment of Fig. 1, vapor relief control isemployedfor automatically subcooling the liquid in storage tank S during pumping periods, since vapor for pressure building is availableduring precooling of the warm automatic pump P The vapor relief control is here shown as a vapor compressor system delivering the evaporation due to insulation heat leak or excessive pressure build-up within the storage tank to the consumers regulated pressure pipe line at a proper regulated pressure.

It should be understood that other equivalent vapor relief devices, such as vent valves, could also be used.

Line 68 from the upper portion of storage tank S supplies such gas to the inlet of a vapor compressor L. Pressure switches 69 and 70 connected to line 68 and responsive to tank S pressure control the operation of the single vapor relief device, compressor L. Pressure switch 70 controls the pressure within the normal pressure range (e. g., 28-30 p. s. i.) by closing at the upper limit (30 p. s. i.) to energize the vapor compressor for withdrawingvapor from the tank and by reopening at the lower limit (28 p. s. i.) to de-energize the compressor to terminate vapor withdrawal. Pressure switch 69 operates similarly but at a higher range (e. g., 35-37 p. s. i.). Filters F are preferably provided in the line on both sides of the vapor compressor. When the vapor is compressed to line pressure, it is passed through compressor discharge conduit 71 to the consumers regulated pipe line 42. A compressor discharge overpressure disconnect pressure switch 72 is connected to line 71. A cold liquefied gas detecting temperaure-operated switch 73 is preferably placed in conduit 68 to stop the vapor compressor L in the event the storage tank S is over filled.

Simplified electrical control circuits are diagramed' in Fig. 2, and include current supply lines L1 and L2 which supply power to the control circuits. When the liquefied gas level control switch 53 in line 117, which is connected across power lines L1 and L2, is closed to initiate a pumping period, the circuit through line 117 is energized causing relay 126 in line 117 to close contactors 131 in a line 134 connected across power lines L1 and L2. The closing of contactors131 energizes the operating coil of solenoid valve 54 which is in series with the closed contacts of the automatic pump priming pressure switch 58 in line 134. Normally, operation of the vapor compressor L is under control of the low range pressure switch 70, for the switches are placed in parallel in a circuit 68a containing a controller coil 147, and the pressure under the control of pressure switch 70 is not allowed to reach the setting of pressure switch 69. For the sake of simplicity the vapor relief device is shown schematically as an element VRD in line 68. The closing of pressure switch 53, however, energizes the tank pumping pressure range relay 137 which opens contactors 101 in the vapor relief control circuit 680, thereby taking the pressure switch 70 out of operation and placing operation of the vapor relief device under control of the tank pumping pressure range control switch 69. The closing of pressure switch 53 also energizes time delay relay 102 in line 117 and at the conclusion of a predetermined time period, contactor 103 closes and effects energization of pump motor controller operating coil 135 in line 130 connected across lines L1 and L2. Energization of coil 135 starts the motor which operates the automatic pump P When the liquid withdrawal is completed, the setting of the pressure switch 53 is reached and its contactors in line 117 are opened.

Relays

137, 102 and 126 are de-energized, respectively to close contactors 101 and place the vapor relief device under the control of pressure switch 70, to open contactors 103 to terminate operation of pump P by tie-energization of motor controller coil 135, and to open contactors 131 in line 134.

Installations, such as cold pump installations, in which there is no appreciable pressure building effect during pump priming require some other type of pressure building for subcooling. Such pressure building is usually accomplished by means of a pressure building coil which evaporates'a liquid fraction withdrawn from the main body of liquid and reintroduces the vapor into the vapor phase of the tank. Installations which do not require pressure building except during pumping are exemplified in the embodiment shown in Fig. 3. Liquid from storage tank S is withdrawn and pumped against a higher pressure by a cold pump indicated generally at 200. The pump may be mounted directly in, or in a part of, the storage tank S holding the liquid supply, or it may be immersed in a special liquid container or forechamber 201, as shown in Fig. 3. The forechamber 201 is supplied with liquefied gas by a pipe 202 controlled by a valve 203. A vent or pressure equalizing connection 204 from an intermediate part I of the forechamber 201 connecting to the storage tank S at an upper portion thereof is provided to remove vapor and allow free flow of liquid into the forechamber and to maintain the desired level of liquid therein. Connection 204 is controlled by a stop valve 205. Liquid is discharged from the pump by way of connection 206.

The pressure building circuit includes liquid withdrawal line 202 that is connected to the bottom of the tank and has a branch connection 207 leading to an evaporation coil 208. A solenoid valve 209 in branch connection 207 controls flow of liquid into the evaporating coil. Vapor resulting from evaporation of liquid in coil 208 is delivered to the top of the storage tank S into the gas phase of the tank by conduit 210. Valve 209 can be placed on the inlet side (as shown) or the discharge side of the evaporating coil 208. This valve is operated by a pressure switch 211 that is responsive to tank pressure and is operative when pressure in the tank falls below a predetermined value to close a pair of contactors 211a in series in an electrical circuit 215 With another pair of contactors 212 and with the operating coil 209a of the solenoid valve. The opening and closing of contactors 212 is regulated by the liquid withdrawal pump controls through a relay 213. Thus, when the pump is being primed or operated, relay 213 operating normally open contactors 212 is energized and closes contactors 212, thereby placing the solenoid valve 209 under control of the pressure switch 211. Switch 211 is set above the normal operating pressure of the tank Shut below the setting of a vapor relief device 214 which is required for safety reasons. The normal pressure will remain low due to high consumption rates and to frequent refilling with liquid saturated with respect to a low pressure. Therefore, if the pressure in the tank S is below the lower setting of pressure switch 211 when the pumping period is begun, and contactors 212 are closed, the switch closes contactors 211 and causes energization of coil 209a thereby opening the solenoid valve to allow liquid flow into the vaporizer. When the tank pressure reaches its upper setting, pressure switch 211 opens its contacts and causes the solenoid valve 209 to close, thereby preventing excessive build-up. The circuit 215 extends across two current supply lines L1 and L2.

In cases where stored liquid is also required to be transferred not only by pumping but also by pressure difference alone, the dual range automatic pressure building system illustrated in Fig. 4 is applicable. The pressure building circuit is similar to that shown in Fig. 3, except that the solenoid valve 209 controlling liquid flow through the evaporating coil 208 is shown on the discharge side of the coil in line 210. In addition to the tank pumping pressure range control, pressure switch 211, which is a controller for a higher pressure range than the normal operating minimum for delivery by pressure difference alone, a tank normal pressure range control is provided in the form of a second pressure switch 216 having a lower pressure setting than the pressure switch 211 and having contactors 216a arranged in parallel therewith in circuit 215 in such a manner as to normally complete a circuit through coil 209a of the solenoid valve 209 when closed by tank pressure falling below its lower setting. When this occurs, solenoid valve 209 opens, liquid fiows into evaporating coil 208 and pressure is built up above the lower setting of switch 216 by delivery of vapor into top of the tank. Pressure switch 216 opens the circuit when tank pressure reaches its upper setting to terminate pressure building. When the pump circuit is energized for pump withdrawal, relay 213 therein closes contactors 212 and the higher range control switch 211 overrides the lower range control switch 216 to obtain subcooling as described in reference to Fig. 3.

Pressure building for subcooling may also be accomplished by the admission of high pressure gas into the vapor space of the storage tank S as shown in Fig. 5. A source of gas at substantially higher pressure than the tank pressure must be available. The principal advantage of this system over the pressure building coil system is that high rates of pressure building may be achieved without extensive equipment. In Fig. 5, high pressure gas is supplied from a source (not shown) to the tank S through a connection 221 having

parallel branch connections

219 and 220. A tank normal pressure range control comprising a pressure operated valve 218 controlled by upstream (tank) pressure is disposed in branch connection 219 and a tank pumping pressure range control comprising a pressure operated valve 222 controlled also by upstream (tank) pressure is disposed in branch connection 220. If the pressurizing gas is at a pressure considerably above the normal working range of the tank, the

valves

218 and 222 are preferably pressure reducing valves so as to prevent admission of high pressure gas into the low pressure system.

A normally closed solenoid valve 209 is disposed in connection 220 in series with the higher pressure range control valve 222 and serves to maintain such control valve inoperative except during subcooling periods. Consequently, the lower pressure range control valve responds to tank pressure to admit high pressure gas when needed to maintain tank pressure above a predetermined lower limit. When the liquid withdrawal pump control circuit is energized, relay 213 therein acts to close normally open contactors 212 in the circuit of the coil 209a of solenoid valve 209. The solenoid is energized and causes valve 209 to open, thereby placing control of tank pressure under the tank pumping pressure range control valve 222, which acts in response to tank pressure to maintain a predetermined minimum pressure at a higher range in the tank.

It is sometimes desirable to draw tank pressure down between pumping operations in order to remove heat added to the liquid during a pressure building and pumping operation. By removing heat after a pumping operation, the margin of pressure between the liquid saturation point and the limiting setting of vapor relief safety devices is always adequate for the required degree of pressure building needed for subcooling. Such recooling of the liquid in the storage tank by vapor withdrawal is especially advantageous if the vapor is withdrawn. to a consuming means rather than being vented to the atmos phere.

Fig. 6 shows an installation in which vapor relief control is combined with pressure building control to provide such recooling between pumping operations. The vapor relief device, which is here shown for purposes of simplicity as a solenoid valve 225 in a vapor relief conduit 230, is under control of a low pressure range pressure switch 226 during normal operation and under control of a high pressure range pressure switch 227 during pumping periods, both switches being responsive to tank pressure and having upper and lower limit settings at which they respectively open and close the vapor relief device as in Fig. 1. Pressure building for both withdrawal by pressure dilference only and by pumping against a higher pressure is eifected, as in Fig. 4, by a pressure building circuit including evaporating coil 208 connected to the bottom of the tank for liquid withdrawal by

connections

207 and 202 and to the top of the storage tank S for vapor delivery by conduit 210 having

branch connections

228 and 229, which both lead to a conduit 231. Conduit 231 and vapor relief conduit 230 have a common connection 232 with the top of the storage tank. Branch connection 228 has therein a pressure operated valve 233 responsive to tank pressure, which serves as the low range pressure building control, and branch connection 229 has a pressure switch 234 which regulates the operation of the high pressure range control valve 235, also in connection 229. The vapor relief circuit and the pressure building control circuit control are interconnected with the pump control circuit by means of relay 236 which actuates a plunger 237 which simultaneously opens normally closed switch 238 in the vapor relief circuit 240 connected across power supply lines L1 and L2 and closes a normally open switch 239 in the pressure building circuit 241 also connected across power supply lines L1 and L2.

As an alternative to the pressure building coil 208 and conduit 207 of Fig. 6, a source of high pressure gas may be employed to pressurize the tank through line 210 as described in Fig. 5. In this case, a pressure reducing control is preferably used in line 229 to replace high range pressure building switch 234, the latter being omitted entirely. The circuit 241 from contacts 239 will then connect directly to solenoid valve 235, and valve 235 will function as an on-oif device for high range pressure building circuit 229.

Liquid is delivered to the storage tank S at a tank delivery pressure, normally at or near atmospheric pressure. With the pressure controls of Fig. 6, the tank pressure will be initially raised to a low pressure withdrawal level by the low range pressure operated valve 233 which opens below its lower limit setting and allows liquid to flow from the bottom of the tank into evaporating coil 208 and'vapor resulting from evaporation of such liquid to flow into the top of the tank by way of

conduits

210, 228, 231 and232 until tank pressure reaches the upper limit setting of valve 233. At this pressure, valve 233 closes. The low pressure range vapor relief switch 226 is set at a lower limit that is usually higher than the upper limit setting of valve 233, so as maintain tank pressure within the range required for withdrawal by pressure difierence.

When the liquid withdrawal pump control circuit is energized, relay 236' in such circuit opens switch 238 in the vapor relief control circuit 230 so as to inactivate pressure switch 226 and thereby to place pressure relief valve 225 solely under the control of the high pressure range switch 227. At the same time relay 236 closes switch 239 in the pressure building circuit to bring the opening and closing of valve 235 in branch connection 229 under control of the tank pumping pressure range control, pressure switch 234. The higher range vapor control switch 227 will be set to open relief valve 225 at a setting above the upper pressure building limit setting. When, therefore, a pumping period is terminated, relay 236 acts to restore control of the vapor relief valve 225 to the lower pressure range .pressure switch 226. This will cause valve 225 to remain open until vapor phase pressure in the tank is reduced to the lower limit setting of switch 227. Resulting evaporation recools the liquid so that'the equilibrium pressure of the liquid is maintained within or below the lower pressure control range.

If it is not essential to maintain a. minimum pressure in the low range, i. e. if withdrawal by pressure difference is not required, then low range pressure building control 233 and circuit 228 may be omitted. The operation of the remaining components will be the same as described above. During standby periods, .the tank pressure is under the control of low range vapor relief switch 226, and pressure building is not used. During a pumping cycle, the reversal of

contacts

238 and 239 places the tank pressure under the combined control of high range vapor relief switch 227 and thepressure building switch 234.

An exemplary circuit for a pressure building system such as that of Fig. 5 is diagramed in Fig.7 to show the interconnection between the automatic pressure building circuit end an automatic pumping circuit. The pump motor PM is controlled by a starter 242 whose contacts 243 are magnetically operated by a coil 244. The circuit to coil 244 is momentarily established by a start switch 245, and a holding circuit is subsequently established through auxiliary contacts 246 and a normally closed contact of a stop switch 247 in parallel with the start switch 245 in pump control circuit 248 connected across power supply lines L1 and L2. Auxiliary contacts 246 are closed by energization of coil 244. The start switch 245 may be manually operated or automatically operated by a liquid level gage, for example.

The normally closed stop switch 247 may be operated.

manually or automatically tobreak the holding circuit to terminate the pumping operation. The pressure building control circuit 249 includes a coil 251 on a solenoid valve 250 which regulates flow through the pressure building coil (not shown in this figure), a pairof pressure switches 252 and 253 in parallel in the circuit, and a switch 254 in series in the circuit of pressure switch 253 and itself operated by relay 255 in the pump control circuit 248. Operation of the control circuits is believed evident in view of the description of Figue 4 above. It will also be apparent that the subcooling controls are thus interconnected. with the pump controls so that priming, pumping and subcooling are all initiated and terminated by

switches

245 and 247. 1 r

It is to be understood that the controls provided by this invention are equally applicable to subcooling techniques other than those shown and described above. For instance, the pressure-building gas produced by evaporation of container liquid could be generated within the contained as well as without the container, as has been illustrated. A coil, which is heated electrically or otherwise, as by passage of a warm fluid therethrough, could be immersed in the liquefied gas in the container or disposed externally in surrounding relation to the liquefied gas in the container. The operation of this vaporizing coil could be regulated by a normally inoperative control means, such as a pressure switch, which is responsive to container pressure and which is interconnected with the liquid pump control means so as to be rendered operative during pumping periods This application is a continuation-in-part of my application, Serial No. 415,118, filed March 9, 1954 and now U. S. Patent No. 2,725,722 as of December 6, 1955.

It will be understood that various modifications may be made in the above-described embodiments without departing from the spirit and scope of the present invention as defined in the following claims.

What is claimed is:

1. In a system for storing and pumping a liquefied gas, a heat insulated container for holding a liquefied gas normally at a predetermined lower operating pressure range; pumping means associated with said container for withdrawing liquid therefrom and pumping it against a pressure substantially higher than container pressure; pump control means operative when energized and deenergized to initiate and terminate pumping periods, respectively; normally inoperative container pressure control means responsive to container pressure for maintaining container pressure at a predetermined higher operating pressure range within selected limits; and means connected with said pump control means and said container pressure control means and operative when said pump control means are energized to render said container pressure control means operative during pumping periods.

2. In a system for storing and pumping a liquefied gas, a heat insulated container for holding a liquefied gas normally at a predeterminde lower operating pressure range; pumping means associated with said container for withdrawing liquid therefrom and pumping it against a pressure substantially higher than container pressure; pump control means operative when energized and deenergized to initiate and terminate pumping periods, respectively; pressure building means having a connection with the container for delivering gas under pressure to said container; normally inoperative fluid flow control means having an operative element responsive to pressure in the container and controlling the quantity of gas in said container to maintain pressure therein at a predetermined higher operating pressure within selected limits; and means connected with said pump control means and said fluid fiow control means and operative when said pump control means are energized to render said fluid flow control means operative during pumping.

3. A system as defined in claim 2, wherein said pressure building means includes a vaporizer connected at one end to the gas space of the container through said connection and connected at its other end with the liquid space of said container through another connection; and said flow control means includes a pressure building valve in one of said connections operatively controlled by said operating element.

4. In a system for storing and pumping a liquefied gas, a heat insulated container for holding a liquefied gas normally at a predetermined lower operating pressure range; pumping means associated with said container for withdrawing liquid therefrom and pumping it against a pressure substantially higher than container pressure; pump control means operative when energized and de-energized to initiate and terminate pumping periods, respectively; pressure building means having a connection with the container for delivering gas under pressure to said container; normally inoperative fluid fiow control means having an operating elements responsive to pressure in the container for controlling admission of gas into said container for building and maintaining pressure therein at a predetermined higher operating pressure within selected limits; vapor relief means for venting vapor from said container when container pressure exceeds a predetermined value above said lower operating pressure but below said higher operating pressure; and means connected with said pump control means, said vapor relief means and said fluid flow control means and operative when said pump control means are energized to render said fluid flow control means operative and said vapor relief means inoperative during pumping periods.

5; In a system for storing and pumping a liquefied gas, a heat insulated container for holding a liquefied gas; pumping means associated with said container for withdrawing liquid therefrom and pumping it against a pressure substantially higher than container pressure; pump control means operative when energized and de-energized to initiate and terminate pumping periods, respectively; a dual-range automatic pressure control means for said container including means operative when said pump control means are de-energized to hold container pressure at a predetermined lower operating pressure within selected limits and other means operative when said pump controls are energized to hold container pressure at a predetermined higher operating pressure within selected limits.

6. In a system for storing and pumping a liquefied gas, a heat insulated container for holding a liquefied gas normally at an operating pressure; warm pumping means for withdrawing liquid therefrom and pumping it against a pressure higher than container pressure; pump control means operative when energized and de-energized to Initiate and terminate pumping periods, respectively; said pumping means having a connection with the gas space of said container for delivering evaporation vapor in said pumping means to said gas space; vapor relief means having a connection with the gas space of said container; first operating means connected with said vapor relief means and responsive to container pressure to effect with drawal of vapor from said gas space when pressure in said container exceeds a predetermined smaller value above said operating pressure, second operating means connected with said vapor relief means and responsive to container pressure to effect withdrawal of vapor from said gas space when pressure in said container exceeds a predetermined larger value above said operating pressure; and means connected with said pump control means and said operating means and operative when said pump control means are energized to render said first operating means inoperative and said second operating means operative.

7. In a system for storing and pumping a liquefied gas, a heat insulated container for holding a liquefied gas; pumping means associated with said container for withdrawing liquid therefrom and pumping it against a pressure substantially higher than container pressure; pump control means operative when energized and de-energized to initiate and terminate pumping periods, respectively; pressure building means having connection means with the container for delivering gas under pressure to the gas space of said container; flow control means for said connection means; said flow control means including normally operative means responsive to container pressure for admitting gas for pressure building into said container when pressure therein falls below a predetermined lower operating pressure and for stopping such admission when container pressure exceeds a predetermined value above said predetermined lower operating pressure; said flow control means also having normally inoperative means responsive to contalner pressure for admitting gas under pressure into said container when pressure therein falls below a predetermined higher operating pressure and for stopping such admission when container pressure exceeds a predetermined value above said predetermined higher operating pressure; and means connected with said pump control means and said flow control means and operative when sald pump control means is energized to render said normally inoperative means operative during pumping periods.

8. In a system for storing andpumping a liquefied gas, a heat insulated container for holding a liquefied gas;- pumping means associated with said container for withdrawing liquid therefrom and pumping it against a pressure substantially higher than container pressure; pump control means operative when energized and de-energized to initiate and terminate pumping periods, respectively; means including a conduit connected to the gas space of said container for supplying gas for pressure building to said space; a pressure-building valve controlling flow through said conduit; a dual range valve control means including normally operative means responsive to container pressure for opening said valve when pressure in said container falls below a predetermined lower operating pressure and for closing said valve when pressure in said container exceeds a predetermined value above said predetermined lower operating pressure; normally inoperative means responsive to container pressure for opening said valve when pressure in said container falls below a predetermined higher operating pressure and for closing said valve when pressure in said container exceeds a predetermined value above said predetermined higher operating pressure; and means connected with said pump control means and said dual range value control means and operative when said pump control means are energized to render said normally inoperative means operative during pumping periods.

9. In a system for storing and pumping a liquefied gas, a heat insulated container for holding a liquefied gas; pumping means associated with said container for withdrawing liquid therefrom and pumping it against a pressure substantially higher than container pressure; pump control means operative when energized and de-energized to initiate and terminate pumping periods, respectively; means including a pair of branch connections leading to the gas space of said container for supplying gas for pressure building thereto; a lower range pressure-building valve controlling flow through one of said branch connections; a higher range pressure-building valve controlling flow through the other branch connection; valve actuating means for each of said valves responsive to container pressure for opening its respective valve when pressure is below a pre-selected lower limit setting for the valve and for closing said valve when pressure is above a preselected upper setting for the valve; other valve means normally closing the flow path through said other branch connection; and means connected with said pump control means and said other valve means and operative when said pump control means are energized to open said flow path through said other branch connection to place the container under control of the higher range pressure-building valve during pumping periods.

10. In a system for storing and pumping a liquefied gas, a heat insulated container for holding a liquefied gas; pumping means associated with said container for withdrawing liquid therefrom and pumping it against a pressure substantially higher than container pressure; pump control means operative when energized and de-energized to initiate and terminate pumping periods, respectively; pressure building means including a vaporizer connected with the gas and liquid spaces of the container; a pressure-building valve controlling flow through said vaporizer; normally operative means responsive to contamer pressure to effect opening of said pressure building valve when pressure in the container falls below a predetermined lower operating pressure and closing of such valve when pressure in the, container exceeds a predetermined value above said lower operating pressure; and normally moperative means responsive to container pressure to eifect opening of said pressure building valve when pressure in the container is below a predetermined higher operating pressure and closing of said pressure building valve when pressure in the container rises above a predetermined value above said higher operating pressure, and means connected with said pump control means and with said normally inoperative means and operative when said pump control means are energized to render said normally inoperative means operative during pumping periods.

11. In a system for storing and pumping a liquefied gas, a heat insulated container for holding a liquefied gas; pumping means associated with said container for withdrawing liquid therefrom and pumping it against a pressure substantially higher than container pressure; pump control means operative when energized and de-energized to initiate and terminate pumping periods, respectively; means including a conduit adapted to be connected at one end to a source of gas under pressure and connected at its other end with the gas space of said container through a pair of branch connections leading to said space; a lower range pressure-building valve controlling flow through one of said branch connections; a higher range pressurebuilding valve controlling flow through the other branch connection; valve actuating means for each of said valves responsive to container pressure for opening its respective valve when pressure is below a preselected lower limit setting for the valve and for closing said valve when pressure is above a preselected upper setting for the valve; other valve means normally closing the flow path through said other branch connection; and means connected with said pump control means and said other valve means and operative when said pump control means are energized to open said other valve means and the flow path through said other branch connection to place the container under control of the higher range pressure-building valve during pumping periods.

12. In a system for storing and pumping a liquefied gas, a heat insulated container for holding a liquefied gas; ptunping means associated with said container for withdrawing liquid therefrom and pumping it against a pressure substantially higher than container pressure; pump control means operative when energized and de-energized to initiate and terminate pumping periods, respectively; pressure-building means having connection means with the container for delivering gas for pressure building to the gas space of said container; flow control means for said connection means; said flow control means having normally operative means responsive to container pressure for controlling the admission of gas to said container to maintain a substantially constant lower operating pressure Within selected limits and having normally inoperative means responsive to container pressure for controlling the admission of gas to said container to maintain a substantially higher operating pressure within selected limits; vapor relief means operative to vent vapor from the gas space of said container; normally operative means responsive to container pressure for operating said vapor relief means when container pressure exceeds a predetermined value above said lower operating pressure but below said higher operating pressure; normally inoperative means responsive to container pressure for opening said vapor relief means when container pressure exceeds a predetermined value above said higher operating pressure; and means connected with said pump control means and said pressure buildinglmeans and operative when said pump control means are energized to render said last-mentioned normally operative means inoperative and both of said normally inoperative means operative during pumping periods.

13. In a system for storing and pumping a liquefied gas, a heat insulated container for holding a liquefied gas; pumping means associated with said container for withdrawing liquid therefrom and pumping it against a pressure substantially higher than container pressure; pump control means operative when energized and de-energized to initiate and terminate pumping periods, respectively; pressure building means including heating means operative upon container liquid for generating gas to be mixed with the gas above the liquefied gas in the container for pressure building purposes; normally inoperative control means responsive to container pressure for regulating operation of said heating means; and means connected with 16 said pump control means and said normally inoperative control means and operative when said pump control means are energized to render said normally inoperative control means operative during pumping periods.

References Cited in the file of this patent UNITED STATES PATENTS 2,363,200 Pew et al Nov. 21, 1944 2,397,657 Goddard Apr. 2, 1946 2,435,332 Van Vleet et al Feb. 3, 1948 2,464,835 Thayer et al Mar. 22, 1949 2,544,734 St. Clair Mar. 13, 1-951 2,725,722 Ahlstrand et a1 Dec. 6, 1955 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N00 2,850,882 v September 9 1958 Jesse B., Starnes It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 10, line 48, for "end" read e and line '71, for "Figue" read m Figure column ll line 45, for "predeterminde" read w predetermined line 61, after "pumping" insert periods =-=o Signed and sealed this 3rd day of February 1959,

SEAL l ttest:

KARL 9 AXLINE ROBERT C. WATSON Attesting Ofljicer. Commissioner of Patents

Claims

1. IN A SYSTEM FOR SORTING AND PUMPING A LIQUENFIED GAS, A HEAT INSULATED CONTAINER FOR HOLDING A LIQUEFIED GAS NORMALLY AT A PREDETERMINED LOWER OPERATING PRESSURE RANGE; PUMPING MEANS ASSOCIATED WITH SAID CONTAINER FOR WITHDRAWING LIQUID THEREFROM AND PUMPING IT AGAINST A PRESSURE SUBSTANTIALLY HIGHER THAN CONTAINER PRESSURE; PUMP CONTROL MEANS OPERATIVE WHEN ENERGIZED AND DEENERGIZED TO INITATE AND TERMINATE PUMPING PERIODS, RESPECTIVELY; NORMALLY INOPERATIVE CONTAINER PRESSURE CONTROL MEANS RESPONSIVE TO CONTAINER PRESSURE FOR MAINTAINING CONTAINER PRESSURE AT A PREDETERMINED HIGHER OPERATING PRESSURE RANGE WITHIN SELECTED LIMITS; AND MEANS CONNECTED WITH SAID PUMP CONTROL MEANS AND SAID CONTAINER PRESSURE CONTROL MEANS AND OPERATIVE WHEN SAID PUMP CONTROL MEANS ARE ENERGIZED TO RENDER SAID CONTAINER PRESSURE CONTROL MEANS OPERATIVE DURING PUMPING PERIODS.