US2944406A

US2944406A - Receipt and storage of liquefied gases

Info

Publication number: US2944406A
Application number: US808157A
Authority: US
Inventors: Carlton C Anderson
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1959-04-22
Filing date: 1959-04-22
Publication date: 1960-07-12
Anticipated expiration: 1977-07-12

Description

J l 12 19 0 C. C. ANDERSON RECEIPT AND STORAGE O F LIQUEFIED GASES Filed April 22, 1959 INVENTOR. CC. ANDERSON BY M W A TORNEVS pressor 76 and to close motor valves 81 and 82. In this manner pressure maintenance may be accomplished by the operation of compressor 17 alone. In this manner pressure maintenance in tank 3 is accomplished at a lesser cost than when both pumps are used. When liquid is present in tank 3, upon opening valves 35 and 41 in pipe 33, liquid at the pressure in tank 3 passes through this pipe and through an expansion valve 45 and through a spray nozzle 47 into a storage tank 42. This tank is a low pressure storage tank, that is, one designed to operate at a maximum pressure of, for example, 1 p.s.i.g. As the liquid in pipe 33 passes through expansion valve 45 and spray nozzle 47 into the zone of reduced pressure, further flash vaporizing and cooling takes place. On the final transfer of liquid propane into tank 42, the temperature of the liquid in tank 42 approaches its normal boiling temperature which is about --44;5 F. However, it is preferable to carry at least a little pressure above atmospheric in tank 42 so as not ever to be below atmospheric. V I

By operating tank 42 in such a manner that the liquid propane stored therein is maintained at a temperature at or very slightly above its normal boiling point, the tank is not constructed for pressure storage. In other words, tank 42 is a relatively inexpensive tank as compared to one constructed for storage of propane at atmospheric temperature. As liquid propane enters tank 42 through expansion valve 45 and spray nozzle 47, a portion of this propane vaporizes and the vapors so produced follow a compression and condensation cycle similar to that explained relative to tank 3. This cycle involves withdrawal of vapor through a pipe 49 with manually operable valves 51 and 87 being open for passage of vapor to the inlet of a compressor 53. When the propane in tank 42 reaches, for example, the aforementioned 1 p.s.i.g. pressure, a pressure controller 93 actuates a switch which starts a motor for driving compressor 53 for compression of the vapor from pipe 49. Compressor 53 discharges compressed propane through a pipe 54 into a pipe 55 for condensation in a condenser 57. Condensate therefrom passes through an open valve 59 and through an expansion valve 61 and a spray nozzle 63 into tank 42. Particularly when thissystem is being started up and all equipment is warm, or during the time propane for storage is entering the tank, the volume of vapors formed through the spray nozzles is very large. Thus, in tank 42, under this condition, this large volume of vapor is compressed in two compressors, that is, a compressor 77 in conjunction with compressor 53. Pressure controller 93 actuates in response to the aforementioned 1 p.s.i.g. and starts pumps 53 and 77 and opens motor valves 85 and 86 for pressure maintenance in tank 42. A valve 78 is opened manually to allow compressed propane from compressor 77 to enter manifold at a pressure of about 260 p.s.i.g. along with com pressed propane from compressor 53. The combined propane is condensed in condenser 57 and the condensate is flash vaporized in expansion valve 61 and spray nozzle 63. When the tank 42 and its accessories are cooled to the desired propane storage temperature, the volume of vapor formed through the sprays entering tank 42 is greatly reduced and the auxiliary compressor 77 will then not be needed. In this case the pressure controller 93 actuates to open the switch for stopping pump 77 and for closing valves 85 and 86. In this case, then, only the single compressor 53 is used.

One important point of my operation is the sizing of tank 3 for accommodating a shipment of liquefied propane at a rapid unloading rate and then transferring the propane from tank 3 through pipe 33 into tank 42 at a sufiiciently slow rate that compressor 53, which is a relatively small compressor, can maintain a pressure at or below the aforementioned 1 p.s.ig.

Similarly, when tank 3 is receiving a shipment of propane from pipe 1, excessively large volumes of vapor of the vented gas for subsequent use.

are formed and the two compressors 17 and 76 are required for pressure maintenance in this tank. Furthermore, under the condition that the liquid propane in pipe 1 is abnormally warm, or if propane flow through pipe 1 is greater than normal, pressure controller 79 starts compressor 76, and in extreme cases the controller opens valves 83 and 84 and compressor 77 is started manually. In this case manually operable valves 81a and 84a are opened and manually operable valves 83a and 78 are closed. However, if the propane is received from, for example, a pipe line which transports liquid propane at a temperature considerably below summer atmospheric temperature, it may be that a single compressor, such as compressor 17, is sufliciently large for pressure maintenance during filling of tank 3.

Under either of these aforementioned temperature con ditions, after the tank cars and/or trucks are unloaded or the complete pipe line slug has been received in tank 3, pump 17 alone can maintain proper pressure in tank 3. Afterthe shipmentphas been received in tank-3, transfer of the liquid propane from tank 3 through pipe 33 is started. However, it is usually preferable to start transfer of liquid into tank 42 as soon as suflicient liquid is present in tank 3 that a pump, as pump 39, is certain not to go on gas.

It is realized that such a storage tank as tank 42 must be properly insulated, as by insulation 43. -As desired, tank 3 is or is not insulated. In other words, it is not critical or essential that tank 3 be insulated. Whether tank 3 is or is not insulated may be determined for each individual installation, taking into consideration cost of insulating and maintenance versus increased operating costs without insulation. However, according to ambient temperature, temperature of propane received, etc. it may be desirable to operate the receiving tank at temperatures and pressures substantially below those mentioned hereinbefore. In such a case insulation would probably be required. In some cases an operating pressure in the receiving tank of p.s.i.g. (55 F.) might prove advantageous.

When storing butane, liquid ammonia, natural gasoline, or other high pressure liquids, corresponding temperatures and pressures will need be selected for the receiving tank, with or without insulation, as will be understood by those skilled in the art.

Under some conditions, the pressure of the propane in tank 3 is sufficient for transfer of the propane through pipe 33 into tank 42 without need of a transfer pump. However, under some conditions, it may be desired to provide a transfer pump. In this case a valve 41 is provided in pipe 33 and on either side of this valve a bypass pipe 37, containing a pump 39, is provided as illustrated. Suitable valves are provided in pipe 37 on opposite sides of pump 39.

Tank 3 is provided with a vent pipe 27 which contains a relief valve 29 for pressure relief in case of emergency. Similarly, tank 42 is provided with a vent pipe 67 which contains a relief valve ,69.

Vent pipes

27 and 67, as illustrated, connect with a pipe 31 which may lead to a flare for burning vented gas or it may lead to a useful disposal, such as a tank, for accumulation In case compressors 17, 76, '77 and 53 are driven by gas engines, these engines may be powered in part by the vented gas. The remaining fuel for operation of these engines can, if desired, be obtained from the propane being stored.

In tank 3 reference numeral 10 identifies liquid propane while reference numeral 12 identifies the vaporous propane. Similarly, in tank 42 reference numeral 65 identifies the liquid and reference numeral 66 identifies the vapor. Reference numeral 73 identifies a manifold pipe which contains the aforementioned valves 81, 83 and 85. Motor valves 83 and 84 are provided in their respective manifolds in case three compressors are ever needed for withdrawal of vapor from tank 3. This manieea makes for economy the need f r proviiicn. of only at minimum num r at compressors inni- I I The following example ill low pressure. storage of th' conventional high. pressun volumes. of. liquefied ropane.

B humanitaria P io ArtH- a. (2 :p-s.1.g-. o ns, Storage sta iidardflllliiddgal. tanks; 395' one dome-roof tank! 1 tanks required. Eachtank=37 tanssteelu tons steel. 'Itatjal steel (395 tanks)=l4,615 Total steel=1,348 tons. If i. .5

.1 1 Wetghtof; piping, etc, not included.

tank.

it-is thus seen that there is. a: marked saving; in-steel tonnage, i.6 14,615-- 1, 34i8'='13 267 tons ofstcel saved in, tanks alone. Muchless piping also is requiredgin-my system= than required foroperation of 395-. spacedpressure tanks. Valves and other equipment requirements. are also less. v

Au'additional safety feature isinvolved in the system 05 this invention. In case-of the unlikely occurrence of an extended failure of compressors; etc, the flare is'provided for vapor disposal. In case the low pressure storage. tank is full of liquid, a shutdown of 24 hours or more would berequired for the tank working pressure to be exceeded and the relief valves to open forventing. The

required for a part full tank to exceed working pres.- 9

sure varies with the level of the liquid, in the tank and the thickness of the insulation. The. least desirable. condinonis at such a time as. the tank is nearly empty. In

00 I V and 3 410013791. Receiving ere I 1 Dome-roof tank made of rings of progressively lighter plateup the Use Se -3, 300 bbl., 135x, l25"' receiving;tanksi Design pressure, 175 p.s.i.g. Working pressure, 160 p.s.i'.g. at 80 F; 180,000 bbl., 120' x 40 dome-roof. storage. tank Working pressure, 1; p.s.i.g. at -53 F. 1 3'! insulation- I j a mas er g'Ptm;

p.s.i. g. working pressure, 925 tons steer O e 2 b 1 remi' netank, 4

this casethe amount of vapor lost to the flare: is correbarrel volumes of liquefied propane with a one-tank storage capacity of 250,000 bbls; it is realized that installat-ions of other sizes, largeras well as smaller, canbe em- PI YQ n flthe esystenr as herein disclosed The

condensers

21 and 57 are, as desired, water cooled if suflicient cooling water is available, or they are air cooled. Preferably one or more blower fans provide air circulation in case the condensers are air cooled.

By providing four compressor units, as herein disclosed, operating costs are less than when a single unit is used for the receiving tank and a single unit for thestorage tank. With fourunits operating cost is less by operating only as much capacity as required. t

For the storage of 94,000 barrels of propane is the following:

10,000 bbl. min. slug size, 15,000 b.p.d. (438 g.p.m. receiving rate 1; lat -fi r setl Est.- ated investment c st. $6.00 Per barr ls s Estimated operating cost, $0c1 5 per barrel 01E throughput "Co parable convention-ah, i f i;

' High pressure storage, $19.00 per Barrel Gpe'rating costs-,neglig ible these examplesit is readilyicbserved that theca i- 'takinv'stndent is markedly less when the-"process of my jinventionisus'ed- Y unl ikelyioccurrence ofan extended failure of all compressor equipmentin suchlacase, the vented material The" vent pipes and 67 are provided mainly for the is passedthrough these vent lines and their corresponding relief valves to -a fi'eireorother' disposalas r'nentioned; For most in stallations the low pressure tank, su'ch as tank "42', should be insulated; and with a full tank of liquid .propane, "as" mentioned hereinbefore, a shutdown of=24 hours or more would be required for the tank working pressure'to beexceeded'. -"I- "ha-t= is, in case the-'liquid'were maintained in thetank at its normal" boiling point of 4.5- F'.,"24 hours or more would be requircd for-the 'peiat-ure oi -theteontents thereofato reach such 'a value that the-vapor'pr'essure'wou' be 1 p-.s.i-.-'g.'"fiThe'-nurnber oflhours reiquired-for 'the w the'tank when only partly filledare less than required for a full tank; The most-serious consideration from this 7-point of view would be when a tank is nearly empty; theiralrelativel y short time might be required for the vapor to be vented through the relief valves. However,

'in this casefif compressor repair were not quickly made,

only arelatively small amount of propane would be lost.

The system asherein disclosed probably has its greatest application in the storage of large volumes of liquid propane for natural, gas utility peak-shaving. By the term peak-shaving" is meant in case a utility has an armple volume of, for example, natural gas available for normal use but does not have a sufficient volume ofnatural gas for peak seasonal use, then the large stored volumeof propane satisfies the peak requirement. In such a case, propane is withdrawn from the storage tank, is vaporized and is admixed with suflicient air to bring down its B'.t.u.

content to that required for mixing with the availablenatural gas to meet contract requirements.

Thus, according to this invention, compressors 17 and 76 are sized to handle vapors produced by transfer of LPG at conventional unloading rates into the receiving tank, andthen the LPG is transferred from the receiving tank 3' to the storage tank 42 at a slow rate so that small capacity, and thus less costly, compressors 77 and 53 can be used for pressure maintenance in the storage tank during the transfer and for pressure maintenance during storage, 'i.e., without transfer of liquid from tank 3.- This latter pressure maintenance merely ofisets increase of pressure due to temperature radiation from the atmos-. phere through the insulation into the contents of the tank.

The switches herein disclosed in conjunction with the motors for driving the several compressors and the several motor valves may be pressure actuated apparatus. controllers can, be, if desired, pneumatic, electric output signal controllers. Furthermore, the controllers can be pneumatic output signal controllers, in which case the switches which open and close the power circuits to the motors driving the compressors are pneumatically operated switches. It is within the scope of this invention to use electrically actuated valves and switches. Ineither g upof th es'c ontents of The case the proper pressure controllers 79 and 93 are selected for pressure or for electrical actuation of equipment.

While certain embodiments of the invention have been described for illustrative purposes, the invention obviously is not limited thereto.

While two compressors are disclosed as being used in conjunction with the unloading tank and two compressors with the storage tank, it will be realized that more than two compressors, such as three or four compressors, or any desired number, can be used with the unloading tank, and also with thestorage tank. Obviously, when more than two compressors are used with either the;unlo ading tank or with the storage tank, piping and controls will be supplied accordingly.- While it is disclosed hereinabove that compressors 17, 76 and-77 can. be used. for compressing vapors from the unloading tank 3, with compressor 53, only, being employedon' vapors from the storage tank 42, it is realized that compressors 53, 77 and '76 under some conditions can be used on vapors from'thestorage tank.42 by opening

valves

83a, 81a, 78 and 84a, with, of

course, valves 81 and 82 being-closed. In this latter case valves 83 and. 84 obviously are disconnected from eontroller 79, and they can be opened manually, or-theycan be attached -to controller 93 for, operation therewith.

Iclaim: A, I

1; A method forthe liquid phase storage of an easily liquefiable,- normally gaseous fluid comprising reducing the pressure of, said material from a superatmospheric pressure to a lower superatmospheric pressure andat the lower pressure passing the material into a receiving zone. in a first spray flash vaporizing operation wherein liquid and vapor result, withdrawing flash vaporfrom said. receiving zone, compressing the withdrawn vapor, condensing the compressed vapor thereby producing a first condensate, reducing the pressure of said first condensate to said lower superatmospheric pressure and at the reduced pressure passing the condensate into said receiving zone in a spray flash vaporizing operation wherein liquid and vapor result, withdrawing liquid from said receiving zone, reducing the pressure of this withdrawn liquid from said lower superatmospheric pressure to a still lower superatmospheric pressure and at this latter pressure passing the liquid into astorage zone in a second spray flash vaporizing operation wherein liquid and vapor result, withdrawing flash vapor from said storage zone, compressing the latter withdrawn vapor, condensing the latter compressed vapor thereby producing a second condensate, reducing the pressure of said second condensate to said still lower superatmospheric pressure and at the still lower superatmospheric pressure passing the second condensate into said storage zone in a spray flashvaporizing operation wherein liquid and vapor result, and storing the liquid in said storage zone.

2. A method for storing liquefied petroleum gas comprising reducing the pressure of said liquefied gas from a superatmospheric pressure to a lower superatmospheric pressure and at the lower pressure passing the liquefied gas into a receiving zone in a firstspray flash vaporizing operation wherein liquid and vapor result, withdrawing flash vapor from the receiving zone, compressing the withdrawn vapor, condensing the compressed vapor thereby producing a first condensate, reducing the pressure of said condensate to said lower superatmospheric pressure and at the reduced: pressure passing the condensate into said receiving zone in aspray flash vaporiz ing operation wherein liquid and vapor result, withdrawing liquid from said receiving zone, reducing-the pres: sure ofv this withdrawn liquid from saidlower super: atmospheric pressure to a still lower superatmospheric pressure, and at this latter pressure passing the liquid into astorage zone in a second spray' flash vaporizing operation wherein liquid and vapor result, withdrawing flash vapor from said storage zone, compressing the latter withdrawn vapor, condensing the latter compressed vapor thereby producing a second condensate, reducing the 'pressureofi said second condensate to said second superatmospheric pressure and at this latter pressure passing thes'eCond' condensate-into said storage zone in a spray flash vaporizing operation wherein liquid and vapor result, and storing the liquid in said storage zone.

3. The method of claim 2 wherein said liquefied petroleum'g'as is propane.

I 4. The method of clai-m 2 wherein said liquefied petroleuni gas is butane.

5. The method of .claim 1 wherein said material is a natural gasoline.

6.-The method of-'c laim 1 wherein'said material is propane.

7. The method of claim 1 wherein said material is butane.

8. The method of claim 1 whereinsaid material is anhydrous ammonia. r

9. A method for storing liquefied petroleum gas come prising receiving said liquefied gas at a superatmospheric pressure, passing'the liquefied gas into a receiving zone wherein liquid and vapor result, withdrawing flash vapor from the receiving zone, compressing the withdrawn vapor, condensing the compressed 'vapor thereby producing a first condensate, reducing the pressure of said condensate and passing the condensate of reduced pressure into said receiving zone wherein liquid and vapor result, withdrawing liquid from said receiving zone, reducing the pressure of this withdrawn liquid to a second superatmospheric pressure, said second superatmospheric pressure being only slightly above atmospheric pressure, and at this latter pressure passing the liquid into a storage zone in a spray flash vaporizing operation wherein liquid and vapor result, withdrawing flash vapor from said storage zone, compressing the latter withdrawn vapor, condensing the latter compressed vapor thereby producing a second condensate, reducing the pressure of said second condensate to said second superatmospheric pressure and at this latter pressure passing the second condensate into said storage zone in a spray flash vaporizing operation wherein liquid and vapor result, andstoring the liquid in said storage zone. 7

References Cited in the file of this patent UNITED STATES PATENTS 2,487,863 Garretson Nov. 15, 1949 2,696,088 Twomey Dec. 7, 1954 2,884,763 lFaulk May 5, 1959