WO1997040308A1

WO1997040308A1 - Process for recovering low molecular volatile compounds from hydrocarbon-containing liquids

Info

Publication number: WO1997040308A1
Application number: PCT/NO1997/000112
Authority: WO
Inventors: Kåre G. Breivik; Tore Andreas Torp; Ola Ruch; Reidar Vik
Original assignee: Den Norske Stats Oljeselskap A/S
Priority date: 1996-04-25
Filing date: 1997-04-25
Publication date: 1997-10-30
Also published as: NO304483B1; AU2654197A; NO961667D0; NO961667L; GB9823183D0; GB2329189A

Abstract

A process for recovering vapors of low molecular volatile compounds released during processing, storage or transportation of a hydrocarbon-containing liquid. The low molecular volatile compounds are separated from the hydrocarbon-containing liquid and are subjected to a hydration reaction in contact with water under hydratred-forming pressure and temperature conditions in a hydration zone to form hydrates of hydratable compounds among the low molecular volatile compounds, whereupon the formed hydrates are withdrawn from the hydration zone for storage or further treatment. The hydrates are preferably stored as a suspension or slurry in a light oil used for cooling purposes in the process.

Description

Process for recovering low molecular volatile compounds from hydrocarbon-containing liquids

The present invention relates to a process for recovering vapors of low molecular volatile compounds released during processing, storage or transportation of a hydrocarbon-con¬ taining liquid. The recovered vapors are particularly useful as an energy source, e.g. as a fuel for engines, boiler plants, heating plants, etc.

Handling of hydrocarbon-containing liquids often involves release of low molecular volatile compounds, comprising gases such as H₂S, low molecular sulphides and C0_Z, light hydrocar¬ bons such as methane, ethane, propane, isobutane, n-butane, isopentane, and n-pentane, and possibly lesser amounts of heavier hydrocarbons (C₆₊) as well. Venting of such hydrocarbon compounds into the atmosphere represents an environmental pro¬ blem. Besides, the hydrocarbon compounds represent a valuable energy source if they can be recovered in a convenient way.

Situations and handling operations which may bring about losses of substantial amounts of low molecular volatile com¬ pounds are for instance burning (flaring) of excess gas on oil production localities and in oil refineries; loading of crude oil in oil tankers at a land terminal; flushing of ship tanks with crude oil after unloading of crude oil; reloading of tankers at a land terminal; filling of bunker oil in ship tanks; and loading of product tankers with refined oil pro¬ ducts such as gasoline, diesel oil, fuel oil, etc. at a refinery. Other operations which could be mentioned are loading of tank lorries at oil stores; unloading of tank lorries at filling stations, e.g. petrol stations, and in stationary tanks feeding heating plants, etc.; and filling of fuel tanks in vehicles.

During an operation such as loading of crude oil in oil tanks at a land terminal, vapors released from the crude oil will blend with a non-combustible gas utilized as a neutral gas (traditionally mainly N₂ and C0₂), which gas has been intro- duced into the empty crude oil tanks as a security precaution during a preceding unloading of oil. In connection with the present invention, such blend of light hydrocarbon vapors from the crude oil (HC vapor or HC gas) and such neutral gas will 5 be designated as "VOC vapor" (VOC = "Volatile Organic Com¬ pounds"). Such VOC vapor which is vaporized from the oil is today usually vented to the atmosphere.

An earlier proposal for solving the problems connected with o release of VOC vapor during load handling has consisted in condensing the heavier components of the VOC vapor and pumping the condensate back into the oil at a point where the hydro¬ static pressure is sufficiently high to allow the condensate to be absorbed in the oil. However, the lighter fractions of s the VOC vapor, such as methane and ethane, are not easily absorbed in the oil and therefore have had to be vented to the atmosphere. In addition to this latter disadvantage, the suggested solution would in many cases merely transfer the problem to the next stage of the transportation chain, where o the crude oil must again be handled. Processes of this kind are described for example in GB 2,289,054 and in US 2,978,876 (1961).

The present invention approaches the above discussed problem 5 from another angle. It has been found that the problem can be solved thereby that the light hydrocarbon vapors which are released from hydrocarbon-containing liquids are recovered and then subjected to a hydration and an optional condensation, whereupon the gas hydrate thereby obtained is stored, prefer- o ably as a hydrate slurry, and is utilized as required as an energy source.

It is previously known to form gas hydrates by contacting gas and water under suitable temperature and pressure conditions. s A reference may be made e.g. to US 3,975,167, WO 93/01153, and WO 94/00713. References are also made to US 2,356,407, WO 96/34226, and WO 96/34227. Thus, the present invention provides a process for recovering vapors of low molecular volatile compounds released during processing, storage or transportation of a hydrocarbon-contai¬ ning liquid. The process is characterized in that the low 5 molecular volatile compounds are separated from the hydrocar¬ bon-containing liquid and are subjected to a hydration reac¬ tion in contact with water under hydrate-forming pressure and temperature conditions in a hydration zone to form hydrates of hydratable compounds among the low molecular volatile com- o pounds, whereupon the formed hydrates are withdrawn from the hydration zone for storage or further treatment.

The hydration reaction which takes place between the hydrat¬ able compounds in the vapor and the water is an exothermal s reaction and it will therefore be useful to remove the heat generated during the reaction in order to maintain the desired temperature conditions during the hydration. The hydrate- forming temperature conditions may be maintained by supplying a (first) cooling medium, of a temperature lower than the o selected operating temperature in the hydration zone, or optionally a cooling medium of the vaporizing type. When the hydrate has been formed, it can be further cooled by direct contact either with the same cooling medium or with a second cooling medium, whereupon the hydrate is stored at a reduced 5 temperature. The second cooling medium (and likewise the cooling medium when only one medium is utilized for both cooling operations) is preferably a hydrocarbon-containing liquid, in which case the hydrate can be stored in the form of a suspension or slurry of hydrate in such cooling liquid, 0 which then becomes a carrier liquid for the hydrate.

The cooling medium employed in the final cooling of the formed hydrate must not contain any substantial amounts of volatile compounds, as this might lead to problems due to release of 5 such volatile components during the storage of the hydrate in the form of a suspension or a slurry in the cooling medium. When both a first and a second cooling medium are used, each for one of the two cooling operations, the two cooling mediums may be circulated in separate cooling circuits. A hydrocarbon-containing liquid utilized as cooling medium must be highly liquid at the temperatures being used (see below) and is designated below as a "light oil". The light oil may for instance be a diesel oil or a condensate fraction of a crude oil. It is essential that the light oil should not con¬ tain or only contain insignificant amounts of components which would separate out as a wax or other solid or thick-flowing substance at the lowest temperatures in the process.

The hydration reaction is usually carried out at pressures in the range of 10 to 150 bars, usually from 30 to 100 bars, and at temperatures in the range of 0 °C to 10 °C, preferably in the range of 0 °C to 4 °C. After the finalizing cooling, the finished hydrate slurry usually has a temperature of from -10 °C to -20 °C, but it can also have a still lower tempera¬ ture, down to -40 °C, or even down to -60 °C. The hydrate slurry is stored at these temperatures, preferably at a tempe¬ rature of from -10 "C to -20 °C. The storage pressure will preferably be lower than 5 bars and it will most preferably be at about the atmospheric pressure.

Actual hydratable vapor components, given in order of increa¬ sing reactor pressure, are isobutane, propane, ethane, C0₂, methane and nitrogen. N-butane is also hydratable, when pre- sent in mixture with hydrocarbons having 1 to 3 carbon atoms. Heavier hydrocarbon components do not form hydrates, because there is no room for the large gas molecules in the voids of the hydrate grid. Mainly non-hydratable hydrocarbon molecules which may be present in the VOC vapor are pentanes and C_6t. These heavier hydrocarbon components will blend with a light oil utilized as a cooling liquid, and will thus be capable of serving as a part of the cooling medium in the hydration process and as a part of the carrier liquid in the finished hydrate slurry. Only minor amounts of nitrogen will form hydrates at the pressures which are useful in the present process.

As mentioned above, a non-combustible gas is used as a neutral gas on tankers, as a security precaution, during unloading of crude oil at a land terminal. This neutral gas usually con¬ tains a substantial amount of nitrogen and optionally some amount of carbon dioxide in addition. Although nitrogen is capable of forming hydrates, such formation of hydrates will only occur at a pressure which is higher than the pressure required by hydrate-forming hydrocarbons such as methane, ethane and propane, see in this connection Fig. 4 of US 5,434,330. Therefore, in processes of the present kind, a high content of nitrogen, and to a lesser degree of carbon dioxide, will have a thinning effect on the hydrocarbon content of gas mixtures in cargo oil tanks for crude oil. This leads to a lower partial pressure of the hydrocarbon components and consequently to reduced potentialities for separation of the hydrocarbon components as hydrates or condensates in VOC recovery processes. This is true in particular when loading of crude oil in empty tanks is started, and will result in loss of some of the hydrocarbon content in the VOC gas.

Therefore, instead of nitrogen or mixtures of nitrogen and carbon dioxide, obtained for example as exhaust gas from various machinery, it might be advantageous to utilize gas mixtures containing substantial amounts of hydratable or condensable hydrocarbons as a neutral gas during unloading of crude oil. This would prevent VOC vented during loading of crude oil from being thinned in respect of hydrocarbons, and from rendered more difficult to separate as hydrate or conden¬ sate. The result would be that the essential part of the VOC released during loading and transportation of crude oil could be recovered and utilized for useful purposes, especially as a fuel for engines and boilers. The gas processing equipment of the plant, including the hydration plant, will assist in securing control of the volumes of hydrocarbon gas mixtures in the oil tanks.

As gas mixtures for the above purpose one may advantageously employ gas released by dissociation of gas hydrate or by regasification of previously condensed gas components. The process of the invention is described in more detail below with reference to the drawings, wherein:

Fig. 1 shows schematically a plant for carrying out the process of the invention, Fig. 2 shows in more detail a plant for carrying out the process of the invention, and

Fig. 3 shows an alternative and preferred embodiment of the hydration unit of the plant shown in Fig. 2.

in the figures, identical reference numerals have been utilized for equivalent parts of the system.

Fig. 1 illustrates the basic features of the process of the invention. A hydrocarbon-containing liquid is supplied via a line 1 to a storage tank 3, where it is to be stored for a shorter or longer time. The tank is equipped with an outlet 2 for hydrocarbon-containing liquid. Volatile compounds vapor¬ ized from the hydrocarbon liquid in the tank 3 are passed via a line 6 to a hydration unit 10, which is equipped with a water inlet 14, a heat exchanger arrangement 40, an outlet 41 for unconverted volatile compounds, and a line 20 for convey¬ ing formed hydrate to a storage tank 4 for hydrate. In the hydration unit 10, the vapors of the volatile compounds are contacted under hydrate-forming pressure and temperature conditions with water supplied via the water inlet 14, whereby a hydration of hydratable compounds contained in the vapors takes place. The hydration reaction is exothermal and the hydration temperature is maintained at the desired level by cooling the hydration zone in the hydration unit 10 by means of the heat exchanger arrangement 40. When the desired amount of hydrate has been formed in the hydration unit 10 and the hydrate has been cooled down to the desired storage tempera¬ ture by means of the heat exchanger arrangement 40, the hydrate is passed from the hydration unit 10 via the line 20 to the storage tank 4 for storage. Said storage tank is equipped with a heat exchanger arrangement 42, the primary function of which is to keep the hydrate at the desired storage temperature, although it may also be used for disso¬ ciation of the hydrate by supplying thereto a hot dissociation medium. The storage tank 4 is further equipped with an outlet 20 for withdrawal of hydrate, and an inlet 43 for supply of a hot medium for releasing gas from the hydrate, as well as an outlet 33 for gas released from the hydrate, especially as a result of heat being supplied via the heat exchanger arrange¬ ment 42 or via the inlet 43 for hot medium.

A reference is now made to Fig. 2, wherein a crude oil tank 3 is loaded with crude oil via a line 1. In the oil tank the crude oil releases light hydrocarbon vapors as a result of agitation at relatively low pressure. The released hydrocarbon vapors blend with neutral gas, mainly N₂ and C0₂, having been introduced into the empty oil tanks as a security precaution. The crude oil tank 3 is equipped with vacuum and overpressure valves which open at given underpressures and overpressures, respectively, as a protection against overload and deformation of the tank walls. The vapor mixture (the VOC vapor) above the crude oil in the tank is transferred from the tank via a line 6 to a compressor 11, wherein it is compressed to a pressure in the range of 30 to 100 bars, e.g. to about 60 bars. The compressor 11 is controlled i.a. by the pressure in the crude oil tank 3. At relatively high pressure, or in the event of increasing pressure in the crude oil tank, the capacity of the compressor is increased, and at relatively low pressure or in the event of decreasing pressure, the capacity is reduced, whereby the pressure in the crude oil tank will at any time have a value between the setting values for the vacuum and overpressure valves, e.g. a value between -0.05 bar and +0.14 barg, respectively.

The compressed and possibly partially condensed vapor from the compressor 11 is passed via an inlet 13 to a hydration reactor 12, consisting for example of an elongated, vertical contai¬ ner. The VOC vapor is contacted in the reactor 12 with water supplied through a line 14 equipped with one or more nozzles, under conditions creating intimate contact between liquid and vapor, and under hydrate-forming pressure and temperature conditions. Soft water or sea water may be used as hydration water. During the hydration reaction which takes place between the water and hydrate-forming components of the VOC vapor, the water molecules form grid structures having voids in which gas molecules are entrapped. When the supplied water, atomized to fine droplets through nozzles, is introduced into the reactor 12 the hydrate is formed as small snow flake-looking crystal¬ line particles which are sinking slowly down through the reac¬ tor.

In this embodiment, heat which is released during the hydrate formation is recovered by a highly liquid hydrocarbon-con¬ taining cooling and carrier liquid which is supplied to the hydration reactor 12 in a cool state, i.e. with a temperature lower than a selected operating temperature for the hydration reaction. The cooling and carrier liquid, which is designated below as a "light oil", should preferably be introduced into the gas volume in the reactor as finely dispersed droplets. It is circulated in a pumping circuit comprising the reactor 12, an outlet in the bottom of the reactor, a line 15, a heat exchanger 16, a line 15, a heat exchanger 16, a pump 17, and a line 18 having an intake which is preferably situated in the top section of the reactor.

Any heavier hydrocarbon components of the VOC vapor which are condensed but not hydrated under the hydration conditions used, will circulate in the pumping circuit together with the light oil and will thus be incorporated as a part of the cooling liquid. A sieve 19 may be arranged in the reactor to recover the hydrate formed in the reactor 12.

The temperature in the reactor 12 must be sufficiently low to allow formation of hydrate from water and hydrate-forming components of the VOC vapor, i.e. lower than the equilibrium temperature for formation/dissociation of gas hydrate at the actual operating pressure, but not sufficiently low to allow water in the reactor to form ice instead of participating in hydrate formation together with the hydrate-forming components of the VOC vapor. The presence of free, unconverted water in the hydrate or in the cooling liquid will reduce the energy content and create problems in the handling of the hydrate mass, and such presence may create problems when the hydrate mass is cooled down to temperatures lower than 0 °C, because the free water will freeze to ice, which may result in a sintering of the hydrate mass and clogging of lines and ducts, 5 and lead to the formation of an unmanageable, hard or lumpy mass. Care should therefore be taken that water be not supp¬ lied in such amounts, relative to other material and energy streams to and from the reactor 12, which would lead to the formation of a hydrate product containing free water (in the o form of water or ice) in more than insignificant amounts.

Gas components that are not amenable to form hydrate under the contemplated hydration conditions, such as for instance excess nitrogen, oxygen, noble gases, hydrogen, any unconverted s hydrocarbons, and the like, are withdrawn from the top of the reactor 12. This gas, which will contain a certain amount of unconverted/non-hydrated hydrocarbons, may be flared, or, more preferably, be subjected to combustion in the propulsion engines or boilers of the vessel, so that their energy poten- o tial is utilized and the venting of hydrocarbons to the atmos¬ phere is reduced.

At an operation pressure of about 60 bars in the reactor 12, a temperature of 6 °C to 8 °C will be sufficiently low to bring 5 about hydrate formation in the reactor. However, the hydrate formation temperature should preferably be lower than that, and preferably down towards 0 °C. The temperature must not, however, be lower than the freezing point of the water. Addi¬ tion of supplementary amounts of cooling liquid to replace the o cooling liquid serving as carrier liquid in the withdrawn hydrate slurry can be made through a line 25 connected to the pumping circuit (the cooling circuit).

When an appropriate amount of hydrate has been formed in the 5 reactor 12, the feed streams of compressed VOC vapor and water to the reactor are shut off. At this stage of the hydration process the cooling and carrier liquid should be reasonably free from volatile components, as such components may contri¬ bute to a building up of a partial pressure of volatile compo- nents during the storage of the slurry of gas hydrate and carrier liquid, and such components will be released as gas if the total partial pressure of volatile components exceeds the storage pressure, which latter will usually be about 1 ata.

The temperature of the circulating light oil, which during the hydration reaction had the function of removing of reaction heat, is now lowered further so as to lower the temperature of the reactor contents to a temperature which is generally lower than 0 °C, and is preferably in the range of from -10 °C to - 20 °C. During this cooling, the pressure in the reactor decreases gradually as a result of the lowering of the tem¬ perature and the venting of gases, such as nitrogen gas. When the pressure has become sufficiently low, for example a little above the ambient pressure, a suspension or slurry of the formed hydrate in the light oil serving as cooling liquid is withdrawn from the reactor 12 via a gate (20a) and a line 20, and is passed to one or more thermally insulated storage tanks 4, which may be insulated slop tanks. The obtained hydrate slurry can be stored and handled by means of conventional sto¬ rage and transportation equipment for liquids and suspensions. In order to convey the hydrate slurry from the reactor to the storage tank(s), a remaining pressure in the reactor may be utilized, or pumps may be used (not shown in the figure). A slurry temperature of from -10 °C to -20 °C is considered sufficient for the hydrate slurry to be sufficiently stable to be stored adiabatically at atmospheric pressure in the ther¬ mally insulated storage tanks 4. If desired, the temperature of the hydrate slurry in the storage tanks 4 may be controlled by decanting carrier liquid from the hydrate slurry from the top of the storage tanks 4, cooling the carrier liquid in a heat exchanger, and returning the carrier liquid to a point near the bottom of the storage tanks.

The finished hydrate slurry stored in the storage tanks 4 will advantageously have the lowest possible content of carrier liquid which is consistent with the pumpability requirements, so as to obtain a maximum concentration of the hydrated VOC vapor in the hydrate slurry. Fig. 3 illustrates an alternative to the above described embo¬ diment of the hydration unit 10 shown in Fig. 2. The hydration reaction is carried out in similar way as in the plant shown in Fig. 2. However, in this case the pumping circuit comprises in addition a container 21, arranged at the upstream side of the heat exchanger 16. Hydrate which is formed in the reactor 12, and which is surrounded by or suspended in a light oil which served as cooling liquid for removal of the heat genera¬ ted during the hydration reaction, is withdrawn from the bottom of the reactor 12 through a line 15 and is passed via a line 26 to the container 21. Because the hydrate has a higher specific weight than the light oil in which it is suspended, the hydrate will tend to sink down through the light oil, and a lower zone 22 of hydrate slurry is therefore formed in the container 21, while a zone 23 consisting of light oil without any substantial amounts of hydrate is formed above said zone. The light oil in the zone 23 is passed via a line 24 to the heat exchanger 16 and is then passed via a pump 17 back to the reactor 12, more specifically to the top section thereof, in a similar way as the cooled light oil in the hydration unit shown in Fig. 2. In the embodiment shown in Fig. 3 the hydra¬ tion reaction can be completed and the hydrate particles recrystallized in a liquid bath ("fluidized bed") and it will not be necessary to use any sieve which might be clogged or might otherwise exhibit poor performance.

When an adequate amount of hydrate has been formed in the reactor 12, the supplies of water and compressed VOC vapor to the reactor are shut off in this embodiment also. In similar manner as in the hydration unit shown in Fig. 2, the tempera¬ ture of the circulating light oil, which serves as a cooling liquid for removal of reaction heat during the hydration reaction, is now further lowered to reduce the temperature of the hydrate slurry in the hydration unit to a temperature which is generally lower than 0 °C, and is preferably in the range of from -10 °C to -20 °C. Simultaneously with this cooling, the pressure in the reactor is gradually lowered, partly as a consequence of the lower temperature and partly through venting of gases, such as nitrogen gas, from the top of the reactor 12. Gas accumulating in the top section of the container 21 may be recirculated to the reactor 12 through a separate line (not shown). When the pressure in the hydration unit has become sufficiently low, e.g. slightly above the ambient pressure, the cooled hydrate slurry is withdrawn from the bottom of the container 21 via a line 20 and passed to one or more thermally insulated storage tanks 4, similarly as described earlier. For further details a reference is made to WO 96/34226, WO 96/34227, and NO 961666 of 25 April 1996, which are relating to similar embodiments and other embodi¬ ments of the reactor and of the hydration process.

As will be apparent from the above, the hydration of the VOC vapor from the crude oil tank(s) is carried out discontinuous- ly, as a batch treatment of the supplied VOC vapor, viz. in a hydration unit 10 comprising a compressor 11, a hydration reactor 12 and a cooling circuit comprising a cooler 16. Thus, if it should be desired to secure a reasonably steady with¬ drawal of VOC vapor from the crude oil tank(s) 3, it will be appropriate to have more than one production line for the formation of hydrate slurry. Thus, in practice, at least two such productions lines will be used, either with a common compressor 11, or with one compressor 11 each. By taking care that the individual production lines are at any time in diffe- rent stages of the process cycle, i.e. that the production lines start with the production of hydrate at different times, it can be obtained that the total hydration unit 10, compri¬ sing two or more parallel production lines working in diffe¬ rent "phases", receives a reasonably steady total supply of VOC vapor and delivers a reasonably steady stream of hydrate slurry to the storage tank(s) 4. Thus, it may be convenient to utilize 2 to 5 production lines, each with a separate hydra¬ tion reactor 12, for example three such production lines.

The hydrate slurry is kept stored in the thermally insulated cargo oil tanks (4) until it is to be transferred to another locality, or until it is to be used on the spot, for example as a fuel for engines, a boiler plant or other combustion plant. Hydrate which is stored adiabatically at the low tern- peratures in question will dissociate very slowly, even though it is not in astate of equilibrium. The reason why the hydrate is not in a state of equilibrium is that the equilibrium tem¬ perature of the hydrate will be substantially lower than the most useful storage temperatures of between -10 °C and -20 ^βC.

The storage tank(s) 4 are protected by means of overpressure and vacuum valves, or they may be vented to the atmosphere. Some form of agitation in the tanks may be contemplated. It 0 may also be useful to have agitators arranged at the outlets of the tanks.

Hydrate slurry may be pumped as required from the storage tank to one or more dissociation units 32. In addition to the s individual feed pumps 31, each of which is supplying its own dissociation unit 31, a separate transportation pump (not shown) may be installed within or near the thermally insulated storage tank for hydrate slurry, for delivery of the slurry to the feed pumps. This may be necessary to avoid an undesired 0 degree of dissociation of the hydrate in the lines leading to the feed pump. It may therefore be advantageous to have a certain pressure in the supply line from the storage tank, and it may also be advantageous to utilize a hydraulic accumulator to level out the pressure during changes in the hydrate 5 volume. Any leakages from a pressurized hydrate slurry line will not entail any serious and immediate explosion risk, since the hydrate is dissociating and releasing gas at a slow rate only, and with a large consumption of heat energy. Thus, a pressurized line containing hydrate slurry is not comparable o to a pressurized gas line.

Heat is supplied to the dissociation unit 32, so as to bring about a dissociation (melting) of the hydrate to gas, water and liquid hydrocarbons. The dissociation unit 32 has an 5 outlet 33 for dissociated product, which is transferred to a fuel-consuming unit, and it can also be equipped with an outlet 34 for water and an outlet 35 for light oil serving as carrier liquid in the hydrate slurry. This light oil may be recirculated to the hydration unit 10 for renewed use.

Claims

Patent claims

1. A process for recovering vapors of low molecular volatile compounds released during processing, storage or transportation of a hydrocarbon-containing liquid, characterized in that the low molecular volatile compounds are separated from the hydrocarbon-containing liquid and are sub¬ jected to a hydration reaction in contact with water under hydrate-forming pressure and temperature conditions in a hydration zone to form hydrates of hydratable compounds among the low molecular volatile compounds, whereupon the formed hydrates are withdrawn from the hydration zone for storage or further treatment.

2. A process according to claim 1, characterized in that the hydrate-forming temperature conditions are maintained during the hydrate formation by supplying a first cooling medium having a temperature lower than the selected operating temperature in the hydration zone, which cooling medium is optionally of the evaporative type.

3. A process according to claim 2, characterized in that the formed hydrate is further cooled, in direct contact with either the first cooling medium or a second cooling medium, and is stored at a lowered temperature.

4. A process according to claim 3, characterized by there being used as sole cooling medium, or as the second coo- ling medium, a highly liquid hydrocarbon-containing liquid, preferably a diesel oil or a condensate fraction of a crude oil, and that the hydrate is withdrawn in the form of a sus¬ pension or slurry of the hydrate in said liquid, which thus becomes a carrier liquid for the hydrate.

5. A process according to any of claims 2 to 4, characterized in that the cooling medium or mediums is/are constituted wholly or partly by condensed components of the vapors of low molecular volatile compounds subjected to hydration.

6. A process according to any of claims 1 to 5, characterized in that the hydration reaction is carried out at a pressure in the range of 10 to 150 bars, preferably in the range of 30 to 100 bars, and at a temperature in the range of s 0 °C to 10 °C.

7. A process according to claim 6, characterized in that the hydration reaction is carried out at a pressure of about 60 bars and at a temperature of 0 °C to 4 °C. 0

8. A process according to any of claims 1 to 7, characterized in that the formed hydrates are stored or further treated under pressure and temperature conditions at which the hydrates are stable or semi-stable, preferably at a s temperature below 0 °C and a pressure below 5 bars, most preferably at about the atmospheric pressure.

9. A process according to any of claims 1 to 8, characterized in that compounds, which under the hydrate- 0 forming pressure and temperature conditions are condensed to liquids but not converted to hydrates, are combined with the stored hydrates for storage or further treatment.

10. A process according to any of claims 1 to 8, 5 characterized in that compounds, which under the hydrate- forming pressure and temperature conditions are condensed to liquids but not converted to hydrates, are separated from the obtained hydrates, and are stored or further treated under pressure and temperature conditions at which the condensed o liquid is stable, preferably at a temperature below 0 °C and a pressure below 5 bars, most preferably at about the atmosphe¬ ric pressure.

11. A process according to any of claims 1 to 10, 5 characterized thereby that in cases where a neutral gas is required to replace liquid volumes, or for pressure levelling, a neutral gas is used which has a substantial content of hydratable or condensable, gaseous hydrocarbons.

12. A process according to claim 11, characterized by there being used as a neutral gas a gas mixture obtained by dissociation of gas hydrate or by regasification of previously condensed gas components.