JP2003515084A - Hydrate storage and transport - Google Patents

Abstract

  (57) [Summary] Methods and devices for storing or transporting hydrates. The hydrate slurry is stored or transported at an elevated pressure of up to 20 bar, preferably up to 10 bar, and at a temperature above the temperature at which the liquid in the slurry solidifies or freezes.

Description

Detailed Description of the Invention

TECHNICAL FIELD This invention relates to the storage and transportation of fuel gas, especially natural gas in the form of hydrates.

BACKGROUND OF THE INVENTION Gas hydrates are physically trapped or engaged in an expanded lattice of water molecules.
Other light gases, such as light hydrocarbons and N _2, CO ₂ is, when appropriately contacted with water at boosted pressure and / or low temperatures, the gas hydrate can. The oil and gas industry has long sought to control hydrate formation in production and transportation equipment because solid or concentrated hydrates block flow channels and interfere with oil and gas production and transportation. I've been Moreover, the production of associated natural gas in oil production facilities where there is no convenient and cost effective way to transport the associated natural gas to consumers has long been considered a nuisance. Such associated gases have traditionally been processed by combustion, which is environmentally unfavorable and a waste of valuable natural resources.

However, since the volumetric solid natural gas hydrate contains more than 150 volumetric units of natural gas, the conversion of natural gas into hydrates is at present not the case of fuel gas transportation or It is known as a safe, convenient and cost effective method of storage. However, in order to maintain the hydrate in a suitable form to prevent dissociation of the fuel gas during transportation or storage, the hydrate must be kept at a suitable low temperature and / or high pressure, which Things are expensive.

US Pat. No. 3,514,274 discloses an example of a method of transporting hydrates, in which natural gas, under suitable conditions, contacts solid particles of propane hydrate,
Crystals of natural gas hydrate are made in liquid propane. The natural gas hydrate and liquid propane are cooled to about -40 ° C and kept at this temperature to keep the hydrate stable during storage and shipping. However, cooling the hydrate to such a temperature and keeping the hydrate at this temperature requires considerably expensive equipment and is associated with high operating costs.

In US Pat. No. 3,975,167, the hydrate is placed and transported in a container submerged at an appropriate depth in the sea to maintain the transported hydrate in a stable form, The sea provides the required elevated pressure and reduced temperature to maintain the hydrate in a stable form. However, submersible vessels that provide cargo with ambient pressure and temperature conditions are expensive, have relatively small carrying capacities, and are limited to areas where a suitable depth of water is available during use.

SUMMARY OF THE INVENTION According to a first aspect of the present invention there is provided a method of transporting a hydrate which comprises maintaining the hydrate at an elevated pressure of substantially between 2 bar and 20 bar. It

According to a second aspect of the present invention there is provided a method of storing a hydrate which comprises maintaining the hydrate at an elevated pressure of substantially between 2 bar and 20 bar.

[0008] A considerable amount of hydrate, for example 150 m ^{3 to} 500 m ³ or more, is added to about 20 bar.
Containers that can be supported at pressures up to are inexpensive and provide a convenient means of storing or shipping hydrates in a stable form.

The hydrate is preferably in the form of a slurry of hydrate particles in a liquid. Slurries are much more convenient than solid hydrates for pumping into and out of pressure vessels for storage or shipping. Forming the hydrate in the form of a slurry is particularly convenient when the hydrate is produced on a coastal platform, and being able to pump the hydrate through, for example, a pipe is useful for moving solids. The platform is a valuable space because it requires less space than the required conveyor belts, air conveyors, etc.
The slurry may be substantially 40% -70% liquid by volume, but 45%-
It is preferably 65% liquid. Increasing the liquid component increases the fluidity of the slurry but reduces the proportion of hydrate in the slurry or the proportion of slurry in the hydrate.

The hydrate is preferably maintained at a temperature at which the liquid in the slurry solidifies or freezes, above 0 ° C. for water, and the slurry is maintained in a pumpable form.

[0011]     (Embodiment of the invention)   The present invention will now be described by way of example with reference to the accompanying drawings.

FIG. 1 shows one or more pressure vessels, preferably our previous patent application WO 97/26
A hydrate production plant 10 as shown is shown at 494. The plant 10 receives a supply 11 of water and a supply 12 of hydrate-producing gas 12. The plant 10 may be onshore or integrated into offshore production facilities. The plant 10 may be provided at or adjacent to a fixed or floating production facility. The hydrate-producing gas supplied may be associated natural gas.

The hydrate slurry exiting the plant 10 is generally at a temperature of substantially 2 ° C. to 10 ° C. and is substantially 20 bar to 200 bar, more typically 45 bar to 100 bar.
Is the pressure of. The ratio of water in the hydrate / water slurry exiting plant 10 will vary from about 50% to substantially 99%, depending on the particular type of plant used. When using a plant as illustrated in our earlier patent application WO 97/26494, the proportion of water in the hydrate slurry produced will be greater than 90%. In this situation, it is preferable to separate the water from the slurry in order to increase the hydrate content of the remaining slurry. Increasing the concentration of hydrate in the slurry increases the amount of effective fuel gas transported for a volume of hydrate slurry.

The hydrate slurry from plant 10 is sent to separator 20 via conduit 21. Separator 20 may have any suitable form. It can be, for example, a liquid cyclone, a screen or a small concentration of hydrate floating on the water surface,
It may be a device that can settle the slurry in a tank such as using an arm or scraper to physically remove the hydrate floating on the water surface.
The water removed from the slurry by the separator may be recycled by feeding it into the plant 10 with the water feeding from the feed 11. This recycled water contains hydrate trace elements that enhance hydrate formation within the plant 10.

The hydrate slurry is delivered via conduit 31 from plant 10 or preferably separator 20 to one or more hydrate storage or transport tanks 30.

FIG. 2 is an equilibrium curve for temperature and pressure conditions where natural gas hydrate is stable.
The hydrate is stable at temperatures and pressures above this curve. This curve is slightly different for hydrates of other gases such as methane, and if additives such as salts are included in the slurry. As can be seen from FIG. 2, the natural gas hydrate must be substantially stored at temperatures above 7 bar or above the freezing point (273 K) of water in the slurry to stay stable. . Additives such as salts may be added to the slurry to reduce the temperature at which the water in the slurry freezes.

The hydrate slurry can be stored at temperatures below 273 K by adding salt.

Since the hydrate slurry generally exits the plant 10 at a pressure higher than the pressure stored in the container 30, even if the pressure in the separator 20 is lost, a means for increasing the pressure is generally used. Not necessary for. However, the temperature at which the hydrate slurry leaves the plant 10 is higher than the required temperature in the vessel 30, so a cooler (not shown) known in the art may be used. The cooler is preferably used to cool the hydrate slurry leaving the plant 10. When the separator 20 is used, it is preferable to arrange a cooler between the plant 10 and the separator 20 because a slurry having a high water ratio can be easily cooled.

The hydrate slurry is a temperature slightly above 0 ° C. at which it does not freeze when the liquid in the slurry is water and a pressure below 20 bar, preferably for example 2 bar to 7 bar.
It is preferably stored or transported at a pressure below 10 bar, such as bar.

FIG. 3 shows a container 30 for storing or shipping a hydrate slurry. Container 30
Preferably has a cylindrical structure with substantially hemispherical or dome-shaped end portions. In this example, the container 30 is made from carbon steel sections about 2-3 cm thick welded to withstand elevated pressures of up to 20 bar or more conveniently 10 bar. However, the container 30 may be made of any suitable material such as a plastic material, a composite material, or other metal such as aluminum or an alloy such as stainless steel. The container 30 may be internally coated or lined to prevent deterioration due to corrosion and other chemical effects. The container 30 has a hydrate slurry inlet port 34, a hydrate slurry outlet port 35, and a pressure relief valve 36 that releases the pressure within the container 30 when it exceeds a predetermined value considered safe for the particular container. It is provided. In this example, the container 30 has a cooler 37.
The cooler 37 pumps a cooling fluid, which in this example is a mixture of glycol and water, throughout the container 30 to keep the hydrate slurry in the container 30 cold. The cooling fluid is pumped through a conduit 38 in thermal contact within the coil 30, in this example, around the container 30, in thermal contact with the container 30. The container 30 is also provided with an insulating layer 40.

The size and number of containers 30 depends on the amount of hydrate slurry stored and / or transported. The 3 m diameter containers 10 m to 20 m long are very cost effective as they can be pre-assembled and supplied directly to storage locations or suitable vehicles or vessels for serving. However, larger or smaller containers 30 may be used.

In a preferred application, the hydrate slurry produced in the plant 10 and passed through the separator 20 is stored in one or more vessels 30, which are onshore, for example on or adjacent to the platform. Alternatively, it may be located offshore. If desired, the hydrate slurry may be added to the outlet port (s) 3 of the storage tank 30.
5 to the inlet port (s) 34 of one or more similar vessels 30 of the vehicle or ship 34 of FIG. The ship 50 illustrated in FIG. 4 has a plurality of containers 30 extending end to end and stacked within the hold of the ship. A manifold (not shown) is provided for delivering the hydrate slurry to the inlet port 34 and removing the hydrate from the outlet port 35. The hydrate slurry is then transported to the destination and exits the exit port (s) 35 of the shipping container 30 and the inlet port (s) 34 of one or more similar container (s) 30. The hydrated slurry is pumped to and stored at its destination.

Alternatively, one or more containers 30 may be provided on the vehicle or ship only, and the vehicle or ship may be provided until the desired amount of hydrate slurry is received in the container (s) 30. It is kept in the hydrate slurry plant 10. The vehicle or ship is then transported to its destination and held there, while the hydrate slurry is gradually used.

The present invention may be used to provide fuel gas storage, for example to meet changing demands. The hydrate slurry produced in the plant 1 of FIG. 1 is pumped via conduit 31 to one or more hydrate storage vessels 30. The hydrate in the slurry in the container 30 is kept in a stable state by being kept at the increased pressure as in the previous example. The separator 20 is preferably provided to separate the liquid from the hydrate slurry produced in the plant 10 before it is sent to the storage container 30. The liquid separated from the hydrate slurry by the separator 20 is
It may be recycled to the liquid inlet 11 of the plant 10. This recycled liquid is
It may contain trace elements of hydrate that will enhance hydrate formation in plant 10. Additionally or alternatively, a cooler may be used to cool the hydrate slurry produced in the plant 10 before it is fed into the container 30.

When fuel gas demand is low, excess fuel gas may be fed into the inlet 12 of the plant 10 and converted to a hydrate slurry stored in a container 30. When the demand for fuel gas increases, the hydrate slurry stored in the container 30 is returned to the fuel gas by heating or releasing the pressure in the container 30. Fuel gas is then fed to the demand source.

This method is particularly suitable for use in accommodating daily fluctuations in fuel gas demand.

The present invention may also be used to store fuel gas at or adjacent to onshore or offshore oil and gas production facilities. FIG. 5 shows an offshore facility. The production facility illustrated in FIG. 5 is an offshore platform 60, but this example is equally applicable to floating facilities. The oil and gas produced are routed through a pipeline 61 to one or more pipes 62 to a tanker or land receiving station.
Sent by. Pump 62 is typically powered by gas produced in the production facility. However, during the lifetime of the producing oil and gas wells, most of the fuel gas is produced during the early life of the wells, and during the subsequent well life.
Little is left to move pump 62. However, the problem is that the excess fuel gas produced during the early life of the well is stored as hydrate slurry in the storage container 30 and to operate the pump 62 during the subsequent life of the well. The solution is to return the stored hydrate slurry to fuel gas. The generation equipment of FIG.
There is a hydrate production plant 10, which pumps the produced hydrate slurry to one or more vessels 30 via conduit 41. If desired, the hydrate slurry produced in plant 10 may be separated and / or cooled before being sent to storage container 30. In the example of FIG. 5, the storage container 30 is located below the surface of the water, and relatively high pressure (about 10 bar at a depth of about 90 m) and low temperature (typically 2-3 ° C.) cause the hydrate in the slurry. Helps stay stable. When fuel gas is required, container 3
The hydrate slurry in 0 is returned to the fuel gas, for example by releasing the pressure in tank 30 or by injecting hot water into tank 30. The fuel gas is the conduit 6
Returned to platform 60 via 3 to drive pump 62.

Many modifications may be made to the examples described above without departing from the scope of the present invention. For example, the hydrate may be supplied to a slurry in which the liquid component is supplied essentially by oil or liquid hydrocarbons rather than water. Since oil or liquid hydrocarbons solidify at the low temperatures at which ice freezes, the hydrate slurry in the oil or liquid hydrocarbons in vessel 30 is determined by the low temperature and hydrate equilibrium curves. The resulting low pressure is maintained, while maintaining the slurry in a pumpable form.

A slurry of hydrate particles in an oil or liquid hydrocarbon is produced by feeding a hydrate production plant 10 with a mixture of water, fuel gas and oil and / or liquid hydrocarbon. Water and fuel gas are consumed in the plant 10 to produce hydrates that leave the plant 10 as oil or liquid hydrocarbons as a slurry.

[Brief description of drawings]

[Figure 1]   FIG. 1 schematically shows an apparatus for making a hydrate slurry.

[Fig. 2]   It is a figure which shows a hydrate equilibrium curve.

[Figure 3]   FIG. 3 schematically shows a container for storing and shipping hydrates.

[Figure 4]   It is a figure which shows the some container mounted in the ship.

[Figure 5]   FIG. 1 shows a device for storing hydrates in a coastal oil and gas production facility.

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE, TR), OA (BF , BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, G M, KE, LS, MW, MZ, SD, SL, SZ, TZ , UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, C H, CN, CR, CU, CZ, DE, DK, DM, EE , ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, KG, K P, KR, KZ, LC, LK, LR, LS, LT, LU , LV, MA, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, S G, SI, SK, SL, TJ, TM, TR, TT, TZ , UA, UG, US, UZ, VN, YU, ZA, ZW (72) Inventor Borill Philip Arthur             British Warwickshire Sheave             34 34 hf warwick             D'Drose Park Denette Close               12 (72) Inventor Martin Paul Anthony             United Kingdom Leicestershire Ellie 11             3 Elwie Lauborough Outwoods             Road 66 F-term (reference) 3E072 EA10

Claims (16)

[Claims] 1. A method of transporting a hydrate slurry, which comprises substantially 20 bar.
Holding the slurry at an elevated pressure up to and holding the slurry at a temperature above the temperature at which the liquid in the slurry solidifies or freezes. 2. A method of storing a hydrate slurry, which comprises substantially 20 bar.
Holding the slurry at an elevated pressure up to and holding the slurry at a temperature above the temperature at which the liquid in the slurry solidifies or freezes. 3. Process according to claim 1 or 2, characterized in that it comprises holding the slurry at a boosted pressure of substantially up to 10 bar. 4. A method according to claim 3, characterized in that it comprises holding the slurry at a pressure of substantially 2 to 7 bar. 5. The method according to claim 1, wherein the slurry contains 40% to 75% liquid. 6. The method of claim 5, wherein the slurry contains 45% to 65% liquid. 7. A method according to any one of claims 1 to 6, characterized in that the liquid in the slurry consists essentially of water. 8. A method according to any one of claims 1 to 6, characterized in that the liquid in the slurry consists essentially of liquid hydrocarbons. 9. Process according to claim 8, characterized in that the liquid in the slurry consists essentially of petroleum. 10. The method according to claim 1, wherein the hydrate in the slurry is a natural gas hydrate. 11. The hydrate slurry is produced in a hydrate producing means, and the produced hydrate slurry passes through a separator before the hydrate slurry is transported or stored. The method according to any one of claims 1 to 10, characterized in that the liquid is separated from the hydrate slurry. 12. A container for storing or transporting a hydrate slurry, the container being at an elevated pressure of substantially up to 20 bar and above the temperature at which the liquid in the slurry solidifies or freezes. A container configured to keep a slurry at a temperature. 13. Container according to claim 12, characterized in that it contains the hydrate slurry at an elevated pressure of up to 20 bar and above the temperature at which the liquid in the slurry solidifies or freezes. 14. A vehicle comprising the container according to claim 12 or claim 13. 15. A ship comprising the container according to claim 12 or claim 13. 16. A method of storing or shipping a hydrate, substantially as described below with respect to the accompanying drawings.