US2356407A - System for forming and storing hydrocarbon hydrates - Google Patents

Description

Aug. 22, 1944.

AQ J. L. HuTcHlNsoN SYSTEM FOR FOBMING AND STORING HYDROCARBON HYDRATES Filed Aug. 15,

2 Sheets-Sheet 1 i SQ Zire/Pfahl- /QPMWPJIMIZHMSM Aug. 22, 1944. A. J. L. HUTCHIN'SQN 2,356,401

SYSTEM FOR FORMING AND STORING HYDROCARBON HYDRATES Filed Aug.' 15. 1941 2 Sheessheet 2 d @v /m@ y u i I HCE/rre Jaim Patented Aug. 22, 1944 SYSTEM FORFORMING AND STDRING HYDROCABBON HYDRATES Arthur J. L. Hutchinson, Los Angeles, Calif., assignor to The Fluor Corporation, Ltd., Los Angeles, Calif., a corporation of California Application August 15, 1941, Serial No. 407,036

18 Claims.

This invention relates to improved methods for treating and storing normally volatile hydrocarbons such as natural gas, refinery gases and the like, and is a continuation-impart of my copending application Serial No. 392,186, iiled May 6, 1941, on Fractionation of hydrate-forming hydrocarbons. Y

The'customary method of maintaining these gases for fuel and other industrial purposes, is to store them in gaseous phase, using large-volume holders characterized by their great size and space requirements, as well as their susceptibility to rupture leading to immediate and violent combustion of liberated gas. Another method, more recently commerclalized, involves liquefaction of the gases and storing the hydrocarbons in liquid phase. That type of system is characterized by the expensive and special steel containers required to withstand pressure at extremely vlow temperatures, and even higher equipment and operating costs necessary lor refrigeration. of liquid" gas at temperature sumciently low, say in the neighborhood of minus 160" F., to maintain the hydrocarbon vapor pressures within practicable limits.

The general method employed according to the invention involves conversion of the hydrocarbons into their solid hydrates, i. e. water-addition products, which are characterized by'their capacity .for stabilization at considerably higher temperatures (and even proportionately less refrigerating costs) than those required for liquid phase storage i'orA corresponding vapor pressures o! the stored materials. A further important advantage of this method is that the hydrates, as such, are not combustible, and that while liberated hydrocarbons resulting from dissociationV of the hydrates will burn, their rate of liberation ordinarily is sufficiently slow to prevent violent combustion or explosion. Not only do` the hydrates lend themselves with particular advantage to storage under favorable temperature and pressure conditions to maintain the hydrocarbons in non-explosive condition, but they also permit ready liberation of the hydrocarbons for use from storage, and separation of moisture from the liberated gas by reason of the tact that the hydrates can be dissociated simply by reduced pressure or increased temperature controls, or a combina- .tion of both, and their water content remains as 50 residue.

Among different objects, the present invention aims to provide certain improvements and innovations with respect to the conditions and methoci bywhich the hydrates initially are formed (CL 26o-676) for storage or other disposal, and the manner in which the formed hydrates may be transferred from one zone to another, and specifically from the -converter or hydrate forming zone to a storage chamber or other vessel. It is desirable that the hydrates be formed in particle or crystal sizes better adapting the hydrates to transmission in a carrier medium, and to reduce the hydrate particle sizes to an extent permitting maximum quantity storage in a volume of given size. For the purpose of causing the hydrates to form as small crystals, I propose to contact the gas and water in the presence of a non-aqueous carrier, preferably by first emulsifyi'ng the water with the carrier to reduce the water to a state of iine particle dispersion within the carrier. In `addition to its fun tion as a dispersing medium for the water,l non-aqueous carrier also serves effectively as a heat absorbingrnedium (i. e. for heat of hydrateformation) and as a ushing medium to constantly remove the hydrates from the conversion zone, and at the rate at which they are formed. 'The carrier further serves efi'ectively as a transmission medium for the hydrates in conveying them, for example, from the converter to the storage zone. As will later appear, circulation of the carrier liquid between the two zones provides a simple method for continuous withdrawal of the hydrates from the converter, and continuous accumulation of the hydrates in the storage zone.

Certain aspects of the invention are to be regarded Y as independent of any particular disposition to be made VIof the hydrates removed from the 40 gas compression system adapted to replace and serve the purposes 'of the relatively expensive compressor plants now in operation. It is made possible-by the invention to dispense entirely with mechanical compression of the gas, by the simple expedient of converting relatively lower pressure gas into hydrated form, transferring the hydrates to what may be termed a pressure generator, and therein heatingthe-hydrates to release the gas at relatively-high pressure, all in a continuous or intermittent type operation and with little required mechanlcal equipment.

The above `features and objects'o the invention, as welllas various additional as ects, will be understood ,to'better advantage from the follow- M ing detailed description of certain typical and siiied condition in the carrier.

illustrative systems. Throughout the description reference is had to the accompanying drawings,

' ly within the range of methane. ethane, the propanes and butanes, together with ilxed gases such as hydrogen sulphide. carbon dioxide.' helium,

oxygen, and nitrogen. Depending upon its nory mal condition, the gas may or may not be precooled before its introduction to the converter. although some cooling ci the gas ordinarily will be required to bring the gas and water mixture in the converter within the temperature range at which hydrate formation will occur under the existing pressure. The pressure in the converter may be held between about 400 to 650 lbs. per sq. in., and the temperature of the gas and water or emulsion inlet streams regulated so that, with or without additional cooling, the temperature in the converter will range between about to 40 the hydrates, and, as stated, va kerosene distillate appears best suited for the purpose.

Rapid formation of-the' hydrates results from contacting the gas and moisture in the converter. the solid hydrates settling to the base of the converter and being carried through the outlet Il to the discharge lineil. Fixed gases and unconverted hydrocarbons are withdrawn through line I8, the inlet Ita of which is shielded by a baille Il to prevent line i8 from becoming clogged by hydrate formation within its inlet. The gases discharged through line It may again be treated in a second stage converter (not shown) in the manner described for the treatment of the raw gas in line i0, or given. any other suitable dis- .posal. With provision made for suillcient time and intimacy of contact between the gas and' v water, it is possible to convert into hydrates and in a single stage, substantially all hydrocarbon constituents of the gas capable of hydration.

Various methods may be employed for preventing congesting accumulations of hydrates tending to remain in the converter, as .by building up on its walls. By passing a suitable heating iluid through the chamber jacket IBI (which otherwise may serve as a heat insulating medium for the chamber), the chamber wall may be warmed to a temperature at which the hydrates F. Water introduced tothe converter through linemI2 may be passed through cooler I3, or bypass line I4, and suitably discharged into the gaseous'aimosphere within the converter in finely divided form-or mist, as through spray' nozzles Il. It -is desirable 'that the water and gas be brought into intimate contact for the dual purposes of assuring their effective interaction in forming the hydrates, and to cause the hydrates to form as small crystals better adapted to suspension in the carrier medium and to close packing in the storage zone. Dispersion ofthe water en e or emulsion as spray or mist in an atmosphere of the gas. establishes'a condition suitable for the accomplishment of these purposes in the initial formation of the hydrates.

As previously indicated, the water may be inf troduced to the converter alone or in dispersed or emulsified condition in a non-aqueous carrier 'liquid which may serve both to maintain the moisture initially in a state of ilne, particle division or dispersion, and to provide a liquid medium within which solid hydrates are carried out of the converter to the storage zone, as will later appear. Accordingly, the liquid introduced through line I2 may consist of around 1%. to 1 parts oi water in a non-aqueous liquid carrier,

preferably one immiscible with water so that the latter is present in at least substantially emul- While anysuitable carrier liquid may be used. I preferably employ a mineral oil distillate or fraction such as kerosene, or a relatively heavy kerosene distillate. Mineral oil carrier is particularly suitable by reason of its availability, ease of handling in the circulation system, and its adaptability to rather close adjustment of its specific gravity. In order to maintain the hydrates most effectively sus.

pended in the carrier during transference of the hydrates from the converter to the storage zone, it is desirable that the Specific' gravity of the carrier be-adiusted to correspond closely or substantially to the specific gravity of the hydrates. The mineral .oil fraction maybe particularly selected for specific gravity correspondence, with storage purposes contacting the wall will melt and thus cause .all 'the hydrates to gravitate through the outlet I0 to the discharge line. '-Hydrate accumulations may also be prevented by continuously flushing the wall of the converter with a suitable liquid, preferably the non-aqueous hydrate carrier. Thus, astream of the carrier being pumped through line 20 into the upperinteriorof the converter, may be sprayed downwardly and directly against the chamber wall through an annular nozzle 2i.

It wi'llbe'unde'rstood that a-circulation of the carrier liquid in such manner as to convey the hydrates from the converter to the storage zone, may be maintained in any suitable manner, and, more specifically. by the introduction of the carrier liquid directly into the converter, as explained, or in a circulating system which receives the hydrates after their discharge from the converter. According to the typical system illusl trated, the hydrates removed through the converter outlet I6 into the discharge line I1 are met by a stream of the carrier liquid being pumped through line 22 and discharged through nozzle 23 into conduit i1. and acting to with-i draw and entrain by ejector action, the hydrates being produced in the converter.

The hydrate-carrier stream iiows through line 24 into a suitablestorage zone 25, shown typically as a vessel or tank 2l, which for hydrate will have considerably large volume. Within storage zone 25 the carrier liq.- uid is separated from the hydrates, as by depositing the latter on the foraminous iioor 21 through which the carrier liquid drains to the,

outlet 2l. The liquid then recirculates through line 28 to -be forced by pump 20 through a cooler 30 and then 'to line 22, the primary purpose of the cooler being to remove from the carrier liquid, heat of formation of the hydrates generated in the converter Il. It may be mentioned that the heat of hydrate formation may be removed elsewhere in the system, as by passing a cooling fluid through the converter Jacket lli or by a heat exchanger in the discharge line I1.

l.The hydrates are maintained in the. storage zone 25 under stabilizing temperature and presassaeo'z sure conditions which, by reason of the properties and vapor pressure characteristics of the hydrates, do not necessitate the high pressure required in the converter Il. Accordingllh be,- yond valve 32 in the discharge line and in the storage zone, the pressure may be reduced sumciently low to obviate necessity for using high pressure or special steel storage vessels (as required, for example, in low temperature, liquid phase storage). Typically, the hydrate storage pressure may be around 25 lbs. per sq. in., or even lower, depending upon the most economical balance of decreasing pressure, and increasing refrigeration costs.

The hydrate storagetemperature required to keep the hydrate lvapor pressure desirably low, may be maintained in any suitable manner, Vas by passing a cooling or refrigerating fluidin heat transferring relationA with the stored hydrates. For example, cooling iluid introduced through line 33 may be circulated through line 34 in the storage vessel jacket 35 to the outlet line 36, or the circulation may occur through a cooling coil 31 within the storage zone itself. It is contemplated that the hydrate carrier liquid may in some instances be employed as the storage zone cooling medium, with or without cooling of the carrier liquidin addition to that occurring in heat exchanger 30. Thus, the carrier liquid is shown to be capable of circulation through line 31| into the storage chamber jacket 35, or cooling coil 31, thence to be recirculated through line 38. As will be understood, the hydrates may be maintained indefinitely in the storage zone.

When it is desired to release the hydrocarbons from -the storage zone for use as fuel gas or other purposes, dissociation of the hydrates may be effected by either pressure reduction, or heating, or a combination of both. By opening the normally closed valve 4D in the outlet line ll, the pressure may be reduced suiliciently. to cause dissociation of the hydrates without heating,v or at least supplying any substantial amount of heat. On the other hand, the stored hydratesv may be heated to release the hydrocarbons at a pressure above their normal storage pressure. as will be more particularly dealt with in describ- V ing the embodiment of the invention shown in Fig. 3. Usually it is preferred to heat the stored hydrates in a manner that will assure-substantially uniform dissociation of all the hydrates, so that the released gas will contain the hydrocarbons in substantially their normal relative proportions. For this purpose, aheating iluid may be introduced through line 33 and circulated either through the storage chamber jacket 3 5 or coil 31. The heat-inguid may be circulated through lines 33 and 33 bypump v23 (the exchanger 30 in this instance serving as a heater) and the hydrate carrier liquid may be used `tion from the liberated hydrocarbons is involved,

due to the fact that the hydrate water'of combination remains in the storage zone (vaporisa-- tion of the hydrateshaving the eileci: of cooling in the tail gas stream, which'are capable of conversion to hydrates and storage in their hydrated form. Fractionatlng column 64 may be taken as the nal fractionating zone in a straight run or cracking plant, and in which the vapors leaving the fractionating column through line I5 are subjected to nai condensation in condenser 45. Gasoline condensate is collected in the receiver 51, from which the xed gases and uncondensed hydrocarbons are discharged through line 48. These gases then are compressed by the compressor 4S to a pressure, e. g. 400 to 650 lbs. per sq. in., at which the hydrates will form in the converter il. After passage through the cooler 5l?, the gas enters the converter through line ida, all as previously described.-

Fig. 3 illustratesa further variational adaptation of the invention `for the dual or individual purposes of forming and storing the hydrates,

,extending column to which the hydrocarbon gas is. introduced through line 54 to ilow upwardly vwithin the converter, countercurrently to a stream of waterl or. water and v'carrier emulsion, ied'to the converter through line 55 andsprayed downwardly from the nozzles 55a. Fixed andl non-hydrated gases are intermittently or continuously withdrawn from the converter through the valved line 56. Thesolid hydrates leave thel base of the converter throughline 51, and are discharged through heat exchanger 59 into the vessel S0 within which the hydrates may be contained temporarily, or stored for an extended length'of time. In this instance vthevessel 50.

isV intended to serve also as a pressure generator and therefore will have suiilcient'strength to withstand high pressures. separated from the hydrates in vessel 50 is recirculated by its own pressure to the converter through line- 5l, heat exchanger 53 line 55 and the cooler 52, makeup water and anyexcess carrier liquid being supplied through line 63.', The

Vhydrates and carrier .liquid from-vessel 53 are.. pumped by pump 58 through'line 51,1 heatexchanger 53 into pressure generator 5I. `It is understood that in normal operation pressure the residual water andthereby preventing itsv vaporization).

Fig. 2 illustrates the described hydrateconversion and' storage system in. conjunction with a refinery producing uncondensed hydrocarbons' 3l generator 3 0 would be maintained at a higher pressureA than converter. It will be understood that the storage vessel or pressure generator '6l will be provided witheany 'suitable Employing a heating coil- 34. Jor any other suit-' able source of heat, the. temperature of the hy-4 drates in vessel may be raised `above their' critical temperature offormation, whereupon they will dissociate and release the hydrocarbons 'in gaseous phase, and also increase the pressure o! the hydrocarbon gas.V as additional hydrates are dissociated in the chamber, kto as highs. value as may be desired. tor example to 1,000

The carrier liquid.

lbs. per sq. in., or above. A corresponding back pressure may be maintained by a suitable control valve Il permitting the gas to be released through line It under highV pressure and for whatever purpose the high pressure gas may be needed. Suitable means, such as a system of baiiies til, may be used to separate liquid entrainxnent from the outlet gas.

It will be observed thattransference oi hydrates from the converter tothe pressure generator, and the release oi high pressure gas from the generator, may proceed continuously, onintermittently. That is to say, the hydrate-carrier stream may be continuously circulated to maintain continuous delivery of hydrates to the pres- .sure generator. and the hydrates therein may continuously be heated to cause their dissociation into 'high pressure gas. When operated in this manner, the continuous withdrawal oi carrier liquid from the base of the generator may be controlled by a suitable valve 61 operated by the conventionally illustrated float mechanism Il,

which 4maintains a minimum level of the liquid in lthe base of the pressure vessel. Excessive water concentrations in the carrier oil, and resulting from residual water after vaporization `unrated carrier liquid with water into said hydrate-forming zone.

6. The process Vthat includes, converting normally gaseous hydrate-forming hydrocarbons into their solid hydrates in a hydrate forming zone, removing the hydrates from said zone in a water-immiscible carrie'r liquid into a second zone, separating the carrier liquid from the hydrates, and' recirculating the separated, carrier liquid to remove additional hydrates from said forming zone.

of the hydrocarbons in the pressure generator,

may be suitably removed, as by a separator dia'- grammatically shown at 12.

Operating on an intermittent cycle, the Dressure vessel l0 may more or less completely be filled with hydrates, valves t9 and 1I closed (the oat operated valve 61 iq this instance not being used), and the accumulated hydrates then heated to generate and release the hydrocarbon gas under the desired high pressure.

I claim:

l. I'he process that includes, converting normally gaseous hydrate-forming hydrocarbons into their solid hydrates in 8 hydrate formi!!! zone, removing the'hy'drates from saidzone in a carrier liquid into a second zone, and separating the carrier liquid from the hydrates.

2. The process that includes, converting'normally gaseous hydrate-forming hydrocarbons into their solid hydrates in a hydrate forming zone, removing the hydrates iromsaid zone in a carrier liquid into a second zone, separating the carrier liquid from the hydrates, and maintaining the hydrates in said second zone under stabilizing temperature and pressure conditions. 3. 'l'he process that includes, converting normally gaseous hydrate-forming hydrocarbons into their solid hydrates in a hydrate forming zone, removing the hydrates from said zone in many g s 7. The process that includes, converting normally gaseous hydrate-forming hydrocarbons into their solid hydrates ina hydrate forming zone, removing the hydrates from said zone in a water-immiscible carrier.l liquid into a second zone, separating the carrier liquid from the hydrates, storing the hydrates in saidsecond zone, andI later dissociating the stored hydrates.

8. The process that includes, .converting-normally gaseous hydrate-forming hydrocarbons into their solid hydrates in a hydrate forming zone, and removingl the resulting hydrates from said zone in a water-immiscible carrier liquid.

9. The process that includes, converting normally gaseous hydrate-forming hydrocarbons into their solid hydrates in a hydrate forming zone, andremoving the resulting hydrates from said zone in a stream oi mineral oil.

10. 'I'he process that includes, converting normally gaseous hydrate-forming hydrocarbons into their solid hydrates within a hydrate forming zone by contacting the hydrocarbons with a preformed intimate mixture of water and a water-immiscible carrier liquid, the water in said mixture being in finely divided condition. Y

ll. The proc that includes, -converting norhydrategiorming hydrocarbons .lid hydrates within a hydrate forminto their ing zone and in the presence of a water-im.

misciblecarrier liquid containing small water particles, and removing the resulting hydrates from said zone to a second zone in a stream of said carrier liquid.

12. The process that includes, converting normally gaseous hydrate-forming hydrocarbons into'thelr solid hydrates within a hydrate forming zone by contacting said hydrocarbons with a a carrier liquid into a second zone. separating the carrier liquid from the hydrates, and recirculating the separated lcarrier liquid to remove additional hydrates from said forming zone.

4. The process that includes, converting normally gaseous hydrate-forming hydrocarbons into their solid hydrates in a hydrate forming i.

zone, removing the hydrates from said zone in a water-immiscible carrier liquid into a ,second zone, and separating the carrier liquid from the y hydrates.

'v 5. The process Y Y mally gaseous hydrate-forming hydrocarbons that includes,v converting nori into their solid hydrates in a hydrate forming zone, removing the hydrates from'said zone in a water-immiscible carrier liquid into a second zone, separatlng'the carrier liquid from the hy- Y drates, and introducing la mixture of the seppreformed emulsion oi'.water and a water-immiscible carrier liquid in which the water is in finely divided condition.

1-3. The process that includes, converting normally gaseous hydrate-forming hydrocarbons into their solid hydrates within a hydrate forming zone by contacting said hydrocarbons with an emulsion of water and a water-immiscibie carrier liquid, and removing the resulting hydrates from said zone to a second zone in a stream of said carrier liquid.

l4 The process that includes, converting normally gaseous vhyd'ratei.'orming hydrocarbons into theiry hydrates' within a hydrate forming zone by contacting said hydrocarbons with water, introducing to said `zone a water-immiscible carrier liquid, removing the hydrates from said zone in a stream of the carrier liquid into a second zone .maintained under relatively low pressure, separating the carrier liquid from the hydrates, and recirculating the separated carrier liquid through a cooling zone into said hydrate forming zone.

l5. The process that includes, con' erting normally gaseous hydrate-forming drocarbons into their hydrates within a hydrate forming zone by contacting said hydrocarbons with water A aiasaaor in thepresence of mineral oil carrier liquid, rey moving the hydrates from said zone in a stream of the carrier liquid into a second lower pressure convertingrelatively low pressure normally gasleous hydrate-forming hydrocarbons into their zone, separating the carrierA liquid from the hyheating and dissociating the hydrates in said second zone to release the hydrocarbons at apressure higherpthan the pressure'of the hydrocarbons before their conversion to hydrates.

l'l. The process of developing hydrocarbon gas under high pressure that includes, continuously solid'iiydrates within la hydrate-forming zone, continuously pumpingv a mixture of mineral oil carrier liquid and the resulting hydrates into a second higher pressure zone, 'and continuously heating and dissociating the hydrates in said second zone to release the hydrocarbons at a pres-V sure higher ythan the pressure of the hydrocarbons before their conversion to' hydrates.

18. The process of developing hydrocarbon gas under` high pressure that includes, converting relatively low pressure normally vgaseous hydrate-forming hydrocarbons into their solid hydrates within a hydrate-forming zone, transferl ring the resulting hydrates into a second zone in a stream of carrier liquid,land heating and dissociating the lwdrates in said second zone-to release the hydrocarbons at a pressure higher y 20 .than the pressurev of the hydrocarbons before their conversion `to hydrates. y ARTHURJ. L. HUTCII-IINSON.

Images