WO2010069472A1

WO2010069472A1 - Method and device for producing clathrate hydrate

Info

Publication number: WO2010069472A1
Application number: PCT/EP2009/008646
Authority: WO
Inventors: Robert Eckl; Henning Marius Exner
Original assignee: Linde Aktiengesellschaft
Priority date: 2008-12-19
Filing date: 2009-12-04
Publication date: 2010-06-24
Also published as: DE102008064116A1

Abstract

The invention relates to a device and to the use thereof for generating clathrate hydrate, comprising a surface having an adjustable temperature (temperature control surface) that can be brought into contact with water or an aqueous solution and a gas forming hydrate. The temperature control surface forms a channel through which a material mixture comprising water and a gas forming hydrate can be fed.

Description

description

Process and apparatus for producing clathrate hydrate

The invention relates to a 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.

Moreover, the invention relates to the use of the device according to the invention for the production of clathrate hydrate.

Clathrate hydrate, which is also referred to below as hydrate for short, is understood as meaning compounds of water and at least one further substance which is present as a gas under standard conditions. In this case, the water forms a lattice structure in whose cavities the gas molecules are enclosed as so-called guest gas. Hydrates occur in nature in large quantities. So is a significant part of

World natural gas reserves bound in the form of methane hydrate, which forms deposits in permafrost or in the depths of the seas, especially on the continental slopes. In technical processes, hydrates often occur unintentionally. 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 thermodynamically stable at relatively high pressures and temperatures, with precise stability conditions depending on the nature of the entrapped 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, the idea is pursued in recent considerations to synthetically produce hydrates in order to store or transport gases in a space-saving, safe and, under certain conditions, comparatively inexpensive way or to transport them.

To simplify the handling during storage and transport and to minimize the cooling power requirement, it is advantageous if the hydrate at the highest possible Temperature and lowest possible pressure thermodynamically stable. It is therefore attempted to exploit the effect of the anomalous stability or self-preservation of hydrates, as can be seen from FIG. 1 for methane hydrate. 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 in terms of 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., 63 (2008) 2066-2074) it is described that the self-preservation of methane hydrate is reinforced when it has been formed on cold surfaces with very good thermal conductivity and is in a cylindrical block shape. 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 US Pat. No. 5,362,467, a process is disclosed specifically for the production of carbon dioxide hydrate which appears to be suitable for use on an industrial scale. 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. To put it for storage and transportation in a cheap and However, it is necessary to bring the hydrate thus produced in a subsequent process step, for example, to a cylindrical block or to comminute 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.

Object of the present invention is to provide a device of the generic type and a use of this device, which allow clathrate hydrate with increased self-preservation on an industrial scale, but with less effort than required in the prior art to produce.

According to the invention, the stated object is achieved in that the tempering surface forms a channel through which a substance mixture containing water and hydrate-forming gas can be passed.

The device according to the invention makes it possible to guide water and hydrate-forming gas very specifically along the tempering surface. At a correspondingly low temperature, therefore, a dense and largely homogeneous hydrate forms on the tempering surface. Preferably, the channel is designed with a circular cross section in which hydrate deposits as a cylindrical block. On account of its favorable surface-to-volume ratio, its dense structure and the symmetrical and homogeneous structure without significant mechanical stress states, such a hydrate has an inherently higher stability and is therefore also particularly suitable for transport and storage purposes under the conditions of abnormal self-preservation , Conceivable, however, are other cross sections, such as rectangular or oval.

In order to be able to set the temperature of the temperature control surface, the invention provides that the channel can be flowed around by a heat transfer medium, through which heat can be diverted from the temperature control surface or led to the temperature control surface. Furthermore, an electric heater is proposed, which is arranged along the channel in order to conduct heat to the temperature.

Hydrate formation normally occurs under elevated pressure. According to the invention, the temperature control surface is therefore arranged in a reactor (hydrate reactor) which is designed to be pressure-resistant to absorb the prevailing hydrate during the pressures can.

A preferred embodiment of the device according to the invention provides that the hydrate reactor is designed as a tube bundle heat exchanger, wherein the

Temperature control surface is formed by the inner surfaces of a plurality of straight tubes.

Another preferred embodiment provides that the tempering is designed as a wall of a bore in a suitably made of metal reactor body. A bore (temperature control channel), through which a heat transfer medium can be guided or in which an electrical heating device is installed, can be arranged parallel to the bore having the temperature control surface. In order to improve the heat transfer between a tempering channel and the tempering surface, a further development of the device according to the invention provides an insert which consists of a metal with high thermal conductivity (eg copper or aluminum) and expediently with the tempering channel and the tempering surface direct connection stands. This insert can be flush with the tempering or protrude into the bore having the tempering.

A further preferred embodiment of the device according to the invention provides that the hydrate reactor is designed as a plate heat exchanger, wherein a channel formed by a temperature control surface 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), wherein an aerosol is formed. 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 hydrate pellet production (NGHP) by process development unit (PDU) ", Proceedings of the 5th International Conference on Gas Hydrates, 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 can be operated at a pressure and temperature level at which hydrate formation already occurs. The resulting hydrate crystals or crystallization nuclei ensure an acceleration of the reaction rate in the subsequent hydrareactor. The upstream mixing device is in this embodiment, a primary reactor, while the hydrate reactor acts as a secondary reactor.

The mixing device can be arranged as a separate reactor upstream of the hydrate reactor or integrated into the hydrate reactor. If the hydrate reactor is designed as a shell-and-tube heat exchanger, its inlet or inflow zone can be equipped, for example, with a static mixing element or with one or more gas nozzles.

Furthermore, the device according to the invention has a device for separating the hydrate of water and hydrate-forming gas-containing mixture (hydrogenation sludge) formed on the temperature control surface, as well as lines and a pump for recycling the mixture of hydrate separated before the tempering. If a gas phase arises during the separation or if the substance mixture is in the form of an aerosol, the device according to the invention comprises a compressor via which the gas phase or the aerosol can be returned.

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 water and a hydrate-forming gas-containing mixture is passed through the channel formed by the tempering, wherein the temperature of the temperature control surface on a lower value is set at which is due of subcooling forms under the thermodynamic equilibrium clathrate hydrate on the tempering surface and accumulates; 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 can be lowered at a given temperature or the solubility of the hydrate-forming gas in the water can be increased. According to the literature, some additives also have a positive effect on the self-preservation of the hydrate. Among others, tetrahydrofuran and sodium dodecylsulfate are mentioned in the literature as suitable additives.

In the course of the hydrate formation process, the cross section of the channel formed by the tempering surface is increasingly reduced, whereby at the same time the pressure loss across the channel increases. The invention provides to use the magnitude of this pressure loss to determine the time at which the temperature of the temperature control surface is raised to the upper value.

With the aid of the invention, a multiplicity of different clathrate hydrates can be produced. In particular, however, it is suitable for the production of carbon dioxide and methane hydrate as well as hydrates of other hydrocarbons, such as ethane, propane and butane and mixtures of these constituents (for example natural gas).

In the following, the invention with reference to three, schematically illustrated in Figures 2 to 4 embodiments will be explained.

FIG. 2 shows a device according to the invention for producing methane hydrate, the hydrate reactor being designed as a shell-and-tube heat exchanger.

FIG. 3 shows a possible cross-sectional shape of a channel formed by a tempering surface. FIG. 4 shows another possible cross-sectional shape of a channel formed by a tempering surface.

In FIG. 2, methane is introduced into the mixing device M via line 1 and the compressor V1, which is also supplied with water via line 2 and the pump P1. In the mixing device M, a dispersion is produced from methane 1 and water 2, which is transferred at a pressure of about 60 bar via line 3 into the hydrate reactor H designed as a tube bundle heat exchanger where it is passed through the tubes of the tube bundle R. With the help of the cooling water 4, the inner surfaces of the tubes, which constitute a tempering surface, maintained at a temperature of about 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 5 now flows heating water in the hydrate reactor H and ensures an increase in the Temperierflächentemperatur to about 10 ⁰ C. At this temperature, a thin layer of the hydrate formed in the vicinity of the tempering dissociated. As a result of the inflowing dispersion, the hydrate is pressed out of the tube bundle with a cylindrical block mold which is favorable for high self-preservation and passes via the line 6 into the separator S. With the exception of the detachment process from the tempering surface, the stability conditions are always present in all apparatuses since otherwise dissociation begins , In the separator S, the hydrate is separated from the dispersion and forwarded via line 7, for example in a memory (not shown) on. Via the line 8 and the pump P2, a liquid phase obtained in the separator is fed back into the mixing device M, while a likewise resulting gas phase is recirculated via line 9 and the compressor V2.

The cross-sectional shape shown in FIG. 3 for a channel formed by a tempering surface 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. FIG. 4 shows a solid metal block A ₁ with a central bore B, the wall of which represents a temperature control surface T and through which a substance mixture comprising a water and a hydrate-forming gas can be conducted. 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.

Claims

claims

Anspruch [en] An apparatus for producing clathrate hydrate comprising an adjustable temperature surface (tempering surface) that 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 mixture can be passed.

2. Apparatus according to claim 1, characterized in that the temperature of the temperature control surface by indirect heat exchange with a heat transfer medium and / or by means of electrical devices is adjustable.

3. Device according to one of claims 1 or 2, characterized in that the temperature control surface is arranged in a pressure-resistant reactor (hydrate reactor)

4. Apparatus according to claim 3, characterized in that the hydrate reactor is designed as a tube bundle heat exchanger or as a plate heat exchanger.

5. Device according to one of claims 1 to 4, characterized in that it comprises a mixing device in which a solution or a dispersion or an aerosol can be produced from water and a hydrate-forming gas.

6. Device according to one of claims 1 to 5, characterized in that it comprises a device for separating the hydrate formed on the heating surface of water and hydrate-forming gas-containing mixture.

7. Use of a device according to one of claims 1 to 6, characterized in that a: a water and a hydrate-forming gas-containing mixture is passed through the channel formed by the temperature control surface, wherein the temperature of the temperature control surface is set to a lower value at due to hypothermia under the thermodynamic equilibrium clathrate hydrate forms and attaches to the tempering surface; 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.

8. Use of a device according to claim 7, characterized in that the water and a hydrate-forming gas-containing mixture is produced with the addition of tetrahydrofuran and / or sodium dodecyl sulfate.

9. Use of a device according to claim 7 or 8, characterized in that the size of the pressure loss over a channel formed by the temperature control surface is used for determining the time at which the temperature of the temperature control surface is raised to the upper value.