DE102008064116A1 - Process and apparatus for producing clathrate hydrate - Google Patents

Abstract

The invention relates to a device and its use for producing clathrate hydrate comprising an adjustable temperature surface (tempering surface) which can be brought into contact with water or an aqueous solution and a hydrate-forming gas. The tempering surface forms a channel through which a mixture of substances containing water and hydrate-forming gas can be passed.

Description

The The invention relates to a device for producing clathrate hydrate, having a surface with adjustable temperature (Tempering), with water or an aqueous Solution and a hydrate-forming gas are brought into contact can.

About that In addition, the invention relates to the use of the invention Device for producing clathrate hydrate.

Under Clathrate hydrate, hereinafter also referred to as hydrate for short is understood to be compounds of water and at least one another substance that is present under standard conditions as a gas. The In this case, water forms a lattice structure in whose cavities the gas molecules are included as so-called. Gastgas. hydrates occur in nature in large quantities. So is a significant one Part of the world natural gas reserves bound in the form of methane hydrate, the in permafrost soils or in the depths of the seas, in particular at the continental slopes, forming deposits. In technical processes, hydrates often occur unintentionally on. For example, they arise at correspondingly low temperatures and high pressures in natural gas or oil-bearing pipelines, where they form plugs and can lead to blockages.

hydrates are generally at relatively high pressures and low temperatures thermodynamically stable, with the exact stability conditions depend on the type of trapped gas and hydrate structure. The distances between the guest gas molecules are much smaller than in a free gas under the same conditions. For this reason, in more recent considerations, the thought to synthesize hydrates to save space, safe and under certain conditions also comparatively inexpensive to store or transport.

To simplify the handling during storage and transport and to minimize the cooling power requirement, it is advantageous if the hydrate is thermodynamically stable at the highest possible temperature and the lowest possible pressure. It is therefore attempted to exploit the effect of the anomalous stability or self-preservation of hydrates, as he said 1 for methane hydrate is apparent. At atmospheric pressure, methane hydrate is stable below a temperature of 193K. When the temperature rises and the pressure remains constant, the rate of dissociation continuously increases until about 242 K. At temperatures between 242 K and 271 K an anomaly is visible. This is because the rates of dissociation are falling sharply again, although the exact reasons for this behavior have not yet been adequately researched and are still largely unknown. At temperatures greater than 271 K, the dissociation rate rises sharply again. From a technical point of view, ie with regard to pressure and temperature level and the associated dissociation rate, the range of anomalous stability between 242 K and 271 K is thus particularly advantageous.

In a technical publication ( Zhang, G., Rogers, RE: "Ultra-stability of gas hydrates at 1 atm and 268.2 K", Chem. Eng. Sci. 63 (2008) 2066-2074 ) it is described that the self-preservation of methane hydrate is enhanced when it has been formed on cold surfaces with very good thermal conductivity and is in cylindrical block form. Self-preservation is particularly pronounced when the surfactant sodium dodecyl sulfate (SDS, C ₁₂ H ₂₅ NaO ₄ S) is used to prepare the methane hydrate. Although the production process with a metal cylinder in the semibatch mode disclosed in the publication is suitable for carrying out laboratory experiments, it can not be used for large-scale hydrate production.

To produce hydrate with sufficient formation rates, especially on an industrial scale, a subcooling under the thermodynamic equilibrium is generally necessary. In the patent US 5,362,467 For example, for the production of carbon dioxide hydrate, a process which appears suitable for use on an industrial scale is disclosed. In this case, a metal edge is introduced into a solution consisting of water and carbon dioxide, which is cooled and thus ensures local supercooling of the solution. Hydrate deposits in lump form on the metal edge, while at the same time the heat of formation is dissipated via the metal. After a period of hydrate formation, the metal profile is heated until the hydrate lump falls. This sequence can be periodically repeated to produce hydrate. However, in order to bring it into a favorable and defined form for storage and transport, it is necessary to press the hydrate thus produced in a subsequent process step, for example, into a cylindrical block or to comminute it into cylindrical pellets. In addition to the more favorable bulk material properties, the cylindrical block or pellet form, as stated above, has a positive effect on the hydrate stability.

task It is the object of the present invention to provide a device of the generic type Type and use of this device, which allow Clathrate hydrate with increased self-preservation in large-scale Scale, but with less effort than the state of Technique required to produce.

The asked task is the device side according to the invention thereby solved, that the tempering surface forms a channel, passed through the mixture containing a water and hydrate forming gas can be.

The Device according to the invention allows water and hydrate-forming gas very targeted to the tempering to lead along. At correspondingly low temperature forms Therefore, at the tempering a dense and largely homogeneous hydrate. Preferably, the channel is circular Cross-section executed in which hydrate as cylindrical Block deposits. Alone because of its favorable ratio from surface to volume, its dense construction and the symmetric and homogeneous structure without significant mechanical Stress states, such a hydrate inherently higher stability and is therefore also for Transport and storage under conditions of abnormal self-preservation particularly suitable. However, other cross sections are also conceivable, such as rectangular or oval.

Around to be able to adjust the temperature of the tempering surface, the invention provides that the channel of a heat transfer medium can flow around, by the heat from the temperature control surface derivable or lead to the temperature is. Furthermore, an electric heater is proposed, the is arranged along the channel to heat to the temperature control surface should lead.

The Hydrate formation usually occurs under increased pressure. According to the invention, the tempering surface Therefore, in a reactor (hydrate reactor) arranged according to designed to be resistant to hydrate formation To be able to record pressures.

A preferred embodiment of the invention Device provides that the hydrate reactor as a tube bundle heat exchanger is executed, wherein the tempering through the inner surfaces of several straight tubes is formed.

A Another preferred embodiment provides that the tempering as a wall of a bore in a convenient manner made of metal reactor body executed is. Parallel to the temperature control surface having bore a further bore (tempering) can be arranged by a heat transfer medium feasible or in an electric heater is installed. To the heat transfer between a temperature control channel and the temperature control surface improve sees a development of the device according to the invention an insert made of a metal with high thermal conductivity (For example, copper or aluminum) and the more appropriate Way with the tempering and the tempering in direct connection stands. This insert can with the tempering finish flush or in the tempering projecting bore protrude.

A further preferred embodiment of the invention Device provides that the hydrate reactor as a plate heat exchanger is executed, wherein one of a temperature control surface formed channel is surrounded by cooling channels.

According to the invention, the device has a mixing device in which water and a hydrate-forming gas generates a mixture of substances and from which the generated mixture of substances can be conducted into a channel formed by the temperature control surface. The literature cites a variety of reactors that can be used as a mixer. The hydrate-forming gas can be dissolved in water (eg carbon dioxide) or dispersed (eg methane). In spray reactors, water can be atomized and sprayed into a gas atmosphere ( DE 69131299 T2 ), creating an aerosol. For dispersion or solution in the literature, the use of stirred reactors ( Iwasaki, T., Katoh, Y., Nagamori, S., Takahashi, S., Oya, N .: "Continuous natural gas hydrates pellet production (NGHP) by process development unit (PDU)", Proceedings of the 5th International Conference at Gas Hydrate, Trondheim / Norway, 2005 ) or static mixers ( Tajima, H., Yamasaki, A., Kiyono, F .: "Continuous Gas Hydrate Formation Process by Static Mixing of Fluids", Proceedings of the 5th International Conference on Gas Hydrates, Trondheim / Norway, 2005 ). Alternatively, the gas can also be injected into the water or by means of a bubble column ( Luo, Y.-T. et al .: "Study on kinetics of hydrate formation in a bubble column", Chem. Eng. Sci. 62 (2007) 1000-1009 ) are introduced.

A further embodiment of the device according to the invention provides that the mixing device at a pressure and temperature level is operable, in which hydrate formation already occurs. The resulting Hydrate crystals or crystallization nuclei provide in the following Hydroreactor for an acceleration of the reaction rate. The upstream mixing device provides in this embodiment Primary reactor while the hydrate reactor as Secondary reactor acts.

The Mixer can be upstream as a separate reactor the hydrate reactor or integrated into the hydrate reactor be. If the hydrate reactor designed as a tube bundle heat exchanger For example, its inlet or inflow zone may be with a static mixing element or with one or more gas nozzles be equipped.

Farther the device according to the invention has a device for the separation of the hydrate formed on the tempering surface mixture of water and hydrate-forming gas (hydrogenation sludge) as well as lines and a pump for recycling the separated from hydrate mixture in front of the tempering on. If there is a gas phase during the separation or is the substance mixture as an aerosol, so the inventive Device a compressor through which the gas phase or the aerosol is recyclable.

• a: ein Wasser und ein hydratbildendes Gas enthaltendes Stoffgemisch durch den von der Temperierfläche gebildeten Kanal hindurchgeleitet wird, wobei die Temperatur der Temperierfläche auf einen unteren Wert eingestellt wird, bei dem sich aufgrund von Unterkühlung unter das thermodynamische Gleichgewicht Clathrathydrat an der Temperierfläche bildet und anlagert;
• b: die Temperatur der Temperierfläche auf einen oberen Wert eingestellt wird, bei dem ein Teil des angelagerten Clathrathydrats in der Nähe der Temperierfläche dissoziiert;
• c: das Clathrathydrat durch nachströmendes Stoffgemisch aus dem Kanal herausgedrückt wird.

Furthermore, the invention relates to the use of the device according to the invention for generating clathrate hydrate, wherein the stated object is achieved in that

• a: a substance mixture containing water and a hydrate-forming gas is passed through the channel formed by the tempering surface, the temperature of the tempering surface being set to a lower value at which clathrate hydrate forms and attaches to the tempering surface due to subcooling under the thermodynamic equilibrium;
• b: the temperature of the tempering surface is set to an upper value at which part of the deposited clathrate hydrate dissociates in the vicinity of the tempering surface;
• c: The clathrate hydrate is forced out of the channel by an inflowing substance mixture.

The hydrate produced in this way has a high self-preservation because it is dense and largely homogeneous and has symmetrical block shape. By adding an additive, the hydrate formation pressure at a given temperature lowered or the solubility of the hydrate-forming Gases are increased in the water. According to the Literature, some additives also have a positive effect on self-preservation hydrate. Suitable additives are in the literature including tetrahydrofuran and sodium dodecyl sulfate called.

in the During the hydrate formation process, the cross section of the of Temperierfläche formed channel increasingly smaller, whereby at the same time the pressure loss across the channel increases. The invention provides, the size of this pressure loss use to set the time at which the temperature of the Temperature control surface is raised to the upper value.

With Help of the invention can be a variety of different Clathrathydrate be generated. In particular, however, it is for the production of carbon dioxide and methane hydrate and hydrates of other hydrocarbons, such as ethane, propane and butane and mixtures of these ingredients (eg natural gas).

In the following, the invention is based on three, in the 2 to 4 schematically illustrated embodiments will be explained in more detail.

The 2 shows a device according to the invention for the production of methane hydrate, wherein the hydrate reactor is designed as a tube bundle heat exchanger.

The 3 shows a possible cross-sectional shape of a channel formed by a tempering.

The 4 shows a further possible cross-sectional shape of a channel formed by a tempering surface.

In 2 will be over line 1 and the compressor V1 methane introduced into the mixing device M, via line 2 and the pump P1 is also supplied with water. In the mixing device M is made of methane 1 and water 2 produces a dispersion which is at a pressure of about 60 bar via line 3 transferred into the designed as a shell and tube heat exchanger hydrate reactor H where it is passed through the tubes of the tube bundle R. With the help of cooling water 4 the inner surfaces of the pipes, which constitute a tempering surface, are kept at a temperature of approx. 3 ° C. Under these conditions, methane hydrate forms, which accumulates on the tempering surface and forms a block in the form of a hollow cylinder in the tubes of the tube bundle R. As the time progresses, the flow cross-section available for the dispersion decreases more and more, due to continuous hydrate crystallization, until finally the pressure drop across the tube bundle R reaches a threshold value. This threshold serves as a signal for closing the obturator a and opening the obturator b. Instead of cooling water 4 now flows heating water 5 into the hydrate reactor H and ensures an increase in the Temperierflächentemperatur to about 10 ° C. At this temperature, a thin layer of the hydrate formed dissociates in the vicinity of the tempering surface. As a result of the inflowing dispersion, the hydrate is pressed out of the tube bundle with a cylindrical block mold favorable for high self-preservation and passes over the line 6 in the separator S. With the exception of the detachment process from the tempering surface, the stability conditions are always present in all apparatuses, otherwise dissociation starts. In the separator S, the hydrate is separated from the dispersion and via line 7 For example, in a memory (not shown) passed on. About the line 8th and the pump P2, a resulting liquid phase in the separator is fed back into the mixing device M, while a likewise resulting gas phase via line 9 and the compressor V2 is recirculated.

The in the 3 shown cross-sectional shape for a channel formed by a tempering consists of four circle segments K1-K4. Compared to a channel with a circular cross-section of the same area, the tempering surface is therefore larger, which leads to a better heat dissipation or supply.

4 shows a solid metal block A, with a central bore B, whose wall is a tempering T and through which a water and a hydrate-forming gas comprehensive mixture is conductive. Parallel to the bore B, the metal block A four more holes C1-C4, through which a heat transfer medium can be performed. To accelerate the formation of hydrate, the bores C1-C4 are connected to the tempering surface T via inserts E1-E4 having good thermal conductivity. The inserts E1-E4 are preferably made of aluminum or copper and protrude into the bore B in order to increase in this way the temperature T.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• US 5362467 [0007]
• - DE 69131299 T2 [0016]

Cited non-patent literature

• - Zhang, G., Rogers, RE: "Ultra-stability of gas hydrates at 1 atm and 268.2 K", Chem. Eng. Sci. 63 (2008) 2066-2074 [0006]
• - Iwasaki, T., Katoh, Y., Nagamori, S., Takahashi, S., Oya, N .: "Continuous natural gas hydrates pellet production (NGHP) by process development unit (PDU)", Proceedings of the 5th International Conference at Gas Hydrates, Trondheim / Norway, 2005 [0016]
• Tajima, H., Yamasaki, A., Kiyono, F .: "Continuous Gas Hydrate Formation Process by Static Mixing of Fluids", Proceedings of the 5th International Conference on Gas Hydrates, Trondheim / Norway, 2005. [0016]
• - Luo, Y.-T. et al .: "Study on kinetics of hydrate formation in a bubble column", Chem. Eng. Sci. 62 (2007) 1000-1009 [0016]

Claims (9)

Device for producing clathrate hydrate, comprising an adjustable temperature surface (tempering surface) which can be brought into contact with water or an aqueous solution and a hydrate-forming gas, characterized in that the tempering surface forms a channel through which a water and hydrate-forming gas containing substance mixture can be passed. Device according to claim 1, characterized in that that the temperature of the temperature control surface by indirect Heat exchange with a heat transfer medium or / and adjustable by means of electrical devices. Device according to one of claims 1 or 2, characterized in that the temperature control surface in a pressure-resistant reactor (hydrate reactor) is arranged Device according to claim 3, characterized in that that the hydrate reactor as a tube bundle heat exchanger or designed as a plate heat exchanger. Device according to one of claims 1 to 4, characterized in that it comprises a mixing device, in the solution of water and a hydrate-forming gas or a dispersion or an aerosol can be produced. Device according to one of claims 1 to 5, characterized in that it comprises a device for separation of the hydrate of water formed on the tempering surface and containing hydrate-forming gas mixture. Use of a device according to one of the claims 1 to 6, characterized in that a: a water and a Hydrate-forming gas-containing mixture by that of the Temperierfläche formed channel is passed, wherein the temperature of the temperature control surface to a lower value is set, which is due to hypothermia under the thermodynamic equilibrium clathrate hydrate at the tempering surface forms and attaches; b: the temperature of the tempering surface is set to an upper value at which part of the attached Clathrathydrate near the tempering surface dissociated; c: the clathrate hydrate by inflowing Mixture is pushed out of the channel. Use of a device according to claim 7, characterized in that the water and a hydrate-forming Gas-containing mixture with the addition of tetrahydrofuran or / and sodium dodecyl sulfate is produced. Use of a device according to claim 7 or 8, characterized in that the size the pressure loss over a through one of the temperature control surface formed channel is used to determine the timing at which the temperature of the temperature control surface on the upper Value is raised.