Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
  • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
  • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
  • C10L3/08—Production of synthetic natural gas
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
  • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
  • C10L3/10—Working-up natural gas or synthetic natural gas
  • C10L3/108—Production of gas hydrates
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C11/00—Use of gas-solvents or gas-sorbents in vessels
  • F17C11/007—Use of gas-solvents or gas-sorbents in vessels for hydrocarbon gases, such as methane or natural gas, propane, butane or mixtures thereof [LPG]

Definitions

• the present invention concerns a method as stated in the introductory of patent claim 1, for the production of gas hydrates stable for storage, particularly hydrates of natural gas or associated natural gas, for onshore and offshore transportation or for the storage of the same.
• US Patent 3,514,274 discloses a method for solving the transportation problem, in which natural gas is converted to hydrates and transported/stored in propane or other C 4 -C 5 hydrocarbons. i this case, the propane is used as a recyclable energy carrier, and the natural gas hydrate is dehydrated at the delivery point and converted to pure natural gas simultaneously with converting the propane to propane hydrate. Then, the propane hydrate can be used again for the production of natural gas hydrate, in which compressed and cooled natural gas is contacted with propane hydrate in a reactor, thus converting propane hydrate to propane carrier liquid and natural gas to natural gas hydrate.
• this method has the disadvantage that dead weight, i.e. propane, must be transported all the time.
• the main object of the present invention is to provide a method for the treatment of hydrate forming gases, such as natural gas or natural gas mixed with or enclosed in other hydrocarbons or water, or polluting gases or gas to be supplied to an industrial or biotechnical process that permits economically satisfactory storage, transportation and use of the gas without using pipeline or immediate transportation by tankers or tank cars, and without the need for use of pressure or any carrier liquid during transportation or storage.
• Another object of the invention is to provide a method that in addition is environmentally acceptable and that can be realized with an acceptable risk with respect to security and economy.
• the present invention concerns a method for the production of storage stable gas hydrates from water and hydrate forming gases, such as CO 2 , H 2 S, natural gas and associated natural gas, just to mention a few.
• natural gas is in general described as the gaseous component in the production process, but it should be evident that a person skilled in the art can apply the principle of the invention to consider hydrate forming gases other than natural gas, and the invention should for that reason not be regarded as limited to use of natural gas only.
• the present method for production of gas hydrates can be adapted to both onshore and offshore operation.
• the pressure and temperature conditions in the reactor are adjusted to favor hydrate formation, and the gas pressure prior to expansion is preferably adjusted to provide cooling during expansion by means of the Joule- Thomson effect.
• the reactor temperature is preferably decreased a few degrees below the equilibrium temperature, thus increasing the reaction rate for the formation of natural gas hydrate.
• a sub-cooling from 1 to 10°C is in most cases sufficient, and a typical sub- cooling varies from 2 to 6°C.
• the natural gas hydrate formed as fine powder, is transported out of the reactor either by the reactor gauge pressure or by means of a mechanical transportation apparatus. Any excess gas is then separated from the hydrate powder, e.g. in a cyclone, whereupon the separated gas is compressed, cooled and recirculated back to the hydrate reactor.
• the hydrate powder is then cooled partly by ordinary heat loss during flow in the transportation pipe and partly through expansion to a lower pressure and optionally further cooling in a heat exchanger.
• the cooled hydrate powder is then optionally transferred to an agglomeration step, such as pressing or pelletizing, to provide a more dense natural gas hydrate and to embed further gas in pores.
• the resulting hydrate particles can then optionally be provided with a protective ice shell by spraying them with water, whereupon the water will freeze and form ice.
• further cooling must be provided, e.g. by cooled gas flowing through the wetted hydrate particles.
• the ice shell will provide more fracture strength and thermal insulation.
• the ice shell can also be strengthened with reinforcing materials, such as fibers, to further strengthen the ice shell and therefore the hydrate particles.
• the hydrate particles are then cooled to a suitable storage temperature, and the particles can be stored or transported stable for a longer time, up to several weeks, at adiabatic conditions and at a pressure near atmospheric pressure.
• heat is supplied to the natural gas hydrate to decompose same to form gas and ice.
• the water can, if desired, be recycled or discharged, without any environmetal risks.
• it is an advantage to recycle the water back to the gas hydrate production process, firstly because the water itself represents a low temperature reservoir, and secondly because the water, provided that it is kept at a temperature below +30°C, still contains seeds that promotes the reaction rate for the hydrate formation, as further described below.
• the gaseous particles can be stored as solid material in gas or surrounded by cooled water or a hydrocarbon based liquid.
• Hydrate particles with embedded gas can be transported from offshore storage vessels by boat, tankers, barges or floating containers towed by tugboats to the shore.
• hydrate particles are pumped from the storage vessels offshore through a pipeline to a tanker.
• the tanker can, but does not need to, be able to store the particles under gauge pressure.
• the particles can be transported to the shore as solid cargo or in water or in a hydrocarbon based liquid. Gas that escapes from the particles during transportation can be pressurized and/or used to operate the tanker and the cooling equipment.
• Hydrate particles can also be stored in underground storage rooms, such as large caverns blown in rock formations. This can be accomplished by cooling/refrigerating the underground storage cavern prior to the supply of gas hydrates, so that any naturally occuring water freezes and forms an isolating ice shell on the "vessel" walls. In this way, gas escape from the storage cavern can be prevented.
• the gas hydrate produced in accordance with the invention can be stored near atmospheric pressure, as descirbed in further detail below.
• the hydrate particles with embedded gas are after the transportation pumped or transferred by other ways from the tanker to one or several storage tanks onshore. The particles melts and the gas can escape. The melting can be accomplished using different types of heating, e.g.
• Cold melting water can be used as coolant for any power station, thus making the ordinary cooling towers reduntant.
• melting water and process water can be loaded.
• the water can have its origin from a former cargo.
• the melting water will be ballast for the tanker from the shore to an offshore platform.
• the tanker loads the particles at the platform, the melting water is unloaded.
• the vessels at the platform accept the melting water for use in the hydrate production.
• air may be remowed from the melting water and the process water and optionally pre-treated.
• the air removal can be effected onshore and/or offshore.
• the water can be used for injection to a reservoir.
• Figure 2 is a simple diagram illustrating a general method for production of hydrates in accordance with the invention
• Figure 3 is a simplified process flow sheet that illustrates the method for production of hydrate powder in accordance with the present invention
• Figure 4 illustrates an alternative method for providing a protecting ice shell on hydrate particles
• Figure 5 illustrates schematically an experimental arrangement to measure the storage stability of gas hydrates
• Figure 6 and 7 show temperature change and amount of gas emitted as a function of time during the testing of storage stability of natural gas hydrate in accordance with the experimental arrangement in Figure 5.
• Figure 1 shows a pressure/temperature diagram for a typical treated natural gas, applied as an example in the method in accordance with the present invention, the diagram provided with a equilibrium curve for hydrate.
• the gas in the example comprises, after the removal of heavier hydrocarbons, 92% methane, 5% ethane and the remainder propane.
• the treated gas can nevertheless contain small amounts of other gases, such as carbondioxide, oxygen or air, without adversely effecting the subsequent production of hydrates.
• the formation temperature for hydrate it is not 5 necessary that the formation temperature for hydrate be lower than 0°C.
• the formation pressure for natural gas hydrate is 104 bar at +20°C, whereas the formation pressure at 0°C will be about 8 bar. Hydrate formation will occur at the high pressure side/low temperature side of this curve. Water can establish two different lattice types, the first having an empiric formula of 8X •
• gas hydrates are unstable at atmospheric pressure, and even at -15 °C a 0 pressure of e.g. at least 4.5 bar is required to keep the hydrate exemplified in Figure 1 in a stable state.
• a hydrate To disintegrate a hydrate into its respective components, it is required to supply the hydrate with its dissociation heat, and will accordingly assume a meta stable state at adiabatic conditions in a cooled state, even at pressures close to atmospheric pressure.
• FIG. 1 illustrates in general a method for production of storage stable gas hydrates in accordance with the present invention.
• gas is pre- treated, e.g.
• process step 2 by removing heavier hydrocarbons from natural gas, and thereafter in process step 2 is supplied to a reactor 2 together with water pre-treated in process step 1.
• the gas and the water react in accordance with the equilibrium conditions in question for hydrate formation and forms gas hydrate, in most cases with a snow-like appearance.
• the formed gas hydrate is then transported to process step 2, in which any unreacted gas and water is removed from the formed hydrate particles, whereupon the hydrate particles optionally are compressed/agglomerated and provided with a protecting ice shell.
• the formed and optionally post-treated hydrate particles are then further transferred in process step 5 to a transportation or storage container, in which storage or transportation occurs at conditions close to adiabatic and at a pressure close to atmospheric.
• the hydrate can then be stored for a longer period of time or transported for long distances without the risk of the hydrate decomposes into its respective components.
• the reactor pressure and the respective initial pressures for gas and water can be determined as desired, depending on the total pressure loss in the system and the gas pressure available. With respect to the process heat balance, a general rule says that the lower the reactor pressure, the less energy is required to produce gas hydrates based on the total energy content in the hydrate.
• the reaction rate for the formation of gas hydrate will increase with the pressure, and accordingly the reactor pressure must also be adjusted in view of the type of gas supplied to the reactor.
• the gas hydrate formed in solid state is then transferred out from the reactor vessel, e.g. by means of a mechanical transportation apparatus or by means of the reactor gauge pressure.
• the hydrate particles 8a are separated from any unreacted gas, and liquidous water is removed.
• the hydrate particles with emedded gas are transported, as described above, optionally to equipment agglomerating or collecting the small particles to larger particles.
• the first hydrate particles are cooled and/or refrigerated in a refrigeration unit 11 prior to entering the agglomeration step 12. Cooling and freezing can be accomplished by pressure change, direct supply of cooled/refrigerated gas and/or indirect heat exchange.
• the purpose of the agglomeration is to agglomerate the hydrate to decrease its volume and simultaneously provide volume for gas storage in the particle pore volume.
• the compression or "agglomeration" can occur at pressure and temperature conditions chosen to achieve an optimum gas content and particle stability, i.e.
• Additives can be mixed with the hydrate particles to improve their properties. Depending on the process conditions chosen, the total mass percent of gas can in general be in the range from 10 to 40 percent of the particle weight. After the agglomeration, the hydrate particles 8b can be cooled and/or refrigerated, thus keeping the total gas content inside the particle.
• the diameter of the compressed hydrate particles varies with the method used for agglomeration and the degree of compression desired, but a typical particle diameter for agglomerated natural gas hydrate particles is for example 2-20 mm.
• the density will vary with the agglomeration method and degree of agglomeration, but a typical density is e.g. in the range from 850 to 950 kg/m 3 .
• the agglomerated hydrate particles are transported to an apparatus 13 that covers the gas impregnated particles with a pure ice shell by spraying the particles with water that freezes and forms an ice shell on the particles. For example, this can be accomplished by spraying the agglomerated particles 8b with water 15 via nozzles 16 whereas the particles are transported downstream by means of a mass transporter 14, e.g. a conveyor. The hydrate particles covered by ice are then cooled in a cooling apparatus 17.
• the ice shell thickness may be varied as required, but in general it is sufficient that the ice shell has a thickness from 0.5 to 1.5 mm.
• This process step of covering the hydrate particles with ice can be accomplished in several steps to further stabilize the hydrate particles by recirculating the partly ice-covered hydrate particles in stream 8c back to the same operation 13, or transporting the same to a following step (not illustrated).
• Cooling in the cooling apparatus 17 can for example be accomplished with a cooled methane based mixture at a pressure and a temperature outside the conditions favouring the hydrate formation.
• the ice shell has two major effects on the stability of a hydrate particle. Firstly, diffusion of gas from inside the particle to the environment is prevented because diffusion of gas through ice is negligble.
• the ice shell provides a protecting shell that withstands a higher internal pressure from the particle. It can be verified that a spherical ice shell (pure ice) having a diameter of 15 mm and a shell thickness of 1 mm is able to withstand an internal pressure of about 5 bar. This pressure is in theory sufficient to prevent a typical natural gas hydrate from decomposing at temperatures below -13°C at atmospheric pressure. However, experiments carried out in connection with the present invention has revealed that hydrates are stable even at temperatures as high as -1.5°C, but the stability will of course increase with decreasing temperature. To improve this effect further, the ice shell is optionally provided with reinforcing materials, such as fibers. The ice strength increases with decreasing temperature and with the use of fiber reinforcement.
• the fiber material can also be supplied at the first particle production by addition to the pressurized and cooled water or in other ways, e.g. by adding hydrate particles to the fiber material followed by mixing in a mixing unit, prior to the water spraying step. Moreover, the fiber material is optionally added in the agglomeration step when producing larger hydrate particles from the smallest gas filled hydrate particles.
• the produced, agglomerated and 5 cooled hydrate particles 8d, optionally provided with ice shell, are then ready for transportation or storage.
• FIG. 4 An alternative mode of providing an ice shell on the hydrate particles is illustrated in Figure 4.
• the hydrate particles 20 formed are wetted by spraying with water 21 in, for example, a separate chamber 22.
• cooled gas 25 e.g. natural gas
• the cooled gas cools the wetted hydrate particles to effect freezing of the water to establish a protecting ice shell on same, whereupon the hydrate particles covered by ice are removed from the tower in stream 26.
• Such gas containing hydrate particles can be produced at offshore platforms or onshore.
• the platforms can be temporary or permanent.
• the hydrate particles can be produced at a location close to hydrocarbon sources or other 0 locations.
• the gas supplied in this way can be natural gas or natural gas together with other constituents. It can also be pollution gas to be transported away for further treatment.
• Example 1 5 This example illustrates one alternative method for the production of hydrate from natural gas by using the method of production in accordance with the invention, in which a relatively high reactor pressure of about 50 bar is applied.
• Natural gas or associated gas is compressed and treated to remove components heavier than methane, ethane and propane in a manner known per se.
• the resulting 0 mixture comprises 92% methane, 5% ethane and 3% propane (mole percent).
• the natural gas hydrate formed having a snow like consistence, falls down toward the reactor bottom by the force of gravity and exits the reactor to an environmental pressure of about 10 bar.
• the individual hydrate particles then have a density of about 920 kg/m 3 and a gas content corresponding to 160-170 std.
• m 3 pure natural gas per m 3 hydrate powder and comprise of about 15 mass percent natural gas and the remainder water.
• the particle size is from 1 to 10 mm.
• the hydrate powder is withdrawn from the reactor by the gauge pressure in the reactor, whereupon unreacted gas and water is separated from the gas hydrate formed, preessurized, cooled and transferred back to the reactor 6; the volume stream of the recirculated gas is about 10 times as great as the amount of fresh gas fed to the reactor.
• the hydrate is then cooled to -15°C and compressed/agglomerated by pressing in a hydraulic press to a resulting particle size of about 5-15 mm, thus providing more embedded gas.
• the produced agglomerated natural gas hydrate is then transported by means of cooled natural gas to storage vessels or to a transportation vessel.
• test tube 31 The test tube 31, the closed cylinder 32 and the external container 34 at constant temperature were constructed to maintain almost adiabatic conditions in the test tube; i.e. heat was neither removed from nor added to the test tube.
• a temperature gauge 36 was attached to measure the temperature in the gas hydrate.
• the solid hydrate was stored in the test tube at minus 5°C for a long period of time. The solid hydrate was stable and gave no indication of decomposing to gas and ice; i.e. no gas emission from the test tube was measured.
• test tube temperature is shewn in Figure 6 and is an approach to the real temperature in the solid natural gas hydrate, as appears from the construction of the testing apparatus in
• test tube 31 and the surrounding cylinder 32 were moved to a third container 34 having a constant temperature of about +20°C.
• Figure 7 The results of this experiment is shown in Figure 7.
• test tube temperature increased rapidly to about +5°C.
• test tube temperature 0 increased to about +20°C (not shown).

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• Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Filling Or Discharging Of Gas Storage Vessels (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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Cited By (26)

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Citations (8)

• 1990
  • 1990-01-29 NO NO90900395A patent/NO172080C/no unknown
• 1991
  • 1991-07-08 EP EP91911763A patent/EP0594616B1/en not_active Expired - Lifetime
  • 1991-07-08 CA CA002113071A patent/CA2113071C/en not_active Expired - Fee Related
  • 1991-07-08 WO PCT/NO1991/000101 patent/WO1993001153A1/en active IP Right Grant

Patent Citations (9)

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