WO2006040541A1

WO2006040541A1 - Novel methods for the manufacture and use of gas hydrates

Info

Publication number: WO2006040541A1
Application number: PCT/GB2005/003908
Authority: WO
Inventors: Bahman Tohidi; Ross Anderson; Rahim Masoudi
Original assignee: Heriot-Watt University
Priority date: 2004-10-11
Filing date: 2005-10-11
Publication date: 2006-04-20
Also published as: GB0422521D0

Abstract

The use of clathrate compositions, having non-flammable host and non-flammable guest molecules, especially CO2 hydrate compositions, for fire fighting, is described. Methods for the manufacture of dry solid clathrates by allowing an excess of guest to react with an excess of host under clathrate forming temperature and pressure conditions are also described.

Description

NOVEL METHODS FOR THE MANUFACTURE AND USE OF GAS HYDRATES

Field of the invention

The present invention relates tσ the field of gas hydrates and other clathrate compounds. It provides novel uses for gas hydrates, and novel methods for cost effective manufacture of gas hydrates, in particular, high quality gas hydrates .

Background to the invention

Delivering water to a fire is a major obstacle in fire fighting, and particularly in forest fire fighting.

In the USA in 2002, 6.7 million acres of range and forest were destroyed by fire at a cost of $1.6 billion according to the National Interagency Fire Center.

The USA allocates over $1 billion a year to fight forest fires.

Fires in domestic and industrial premises also result in major costs. The British Automatic Sprinkler Association estimate that there are approximately 2500 warehouse fires in the UK per year, and that insurers report average claims of £50,000 per fire.

Home Office fire statistics show that there were 43, 600 fires recorded in 2001 in the UK in buildings other than dwellings, which includes retail distribution premises, industrial premises, restaurants, cafes and public houses. Water sprinkler systems have the disadvantage of a maximum practical working height limit of 10 metres.

Furthermore water sprinkler systems experience an inherent difficulty in delivering water to the base of the fire due to vaporisation, again reducing their effectiveness.

Lastly, in such systems water damage to the contents and building is unavoidable.

Therefore finding alternative fire fighting materials and methods of fighting fires is highly desirable. Clathrate compounds, in particular gas hydrates are a class of materials, having special physical characteristics, which have not previously been considered for use in this context.

Gas hydrates are ice-like crystalline compounds, which form through a combination of water and suitably sized 'guest' molecules under low temperature and elevated pressure conditions. Liquid 'hosts' other than water are known to form similar compositions with appropriate 'guest' molecules which may be gases or liquid. Such ^xhost/guest' compounds are generally described as clathrate compounds.

Within the hydrate lattice, water molecules form a network of hydrogen-bonded cage-like structures, enclosing the guest molecules which generally comprise of low-molecular diameter gases, for example methane, ethane, propane, carbon dioxide.

Although hydrate formation can pose serious flow assurance problems in oil and gas production, gas hydrates have great potential for positive applications, turning a long standing problem into a potential benefit. Two important properties of hydrates are their very high gas to solid ratio (Im³ of hydrate could contain up to 175m³ of gas at standard conditions) , and self-preservation effects combined with high heat of dissociation, which make them feasible to be transported at atmospheric pressure.

Solid hydrates thus present a novel means for gas storage, transportation and delivery, particularly suited to a wide variety of areas, including the exploitation of remote gas fields (through storage and transportation of natural gas in the form of solid hydrates) and CO₂ sequestration/storage (particularly in order to reduce the emission of greenhouse gases into the atmosphere, where one option that has been suggested is to store/sequester CO₂, particularly by injecting CO₂ into depleted oil reservoirs or saline aquifers for storage) .

A commercially viable production method for solid hydrate also allows applications involving certain properties of certain hydrate solids to be much more viable, such as the use of CO₂ hydrates for transportation/storage of CO₂ and in enhanced oil recovery, in particular their injection into heavy oil in order to reduce its viscosity.

However, a major barrier to the development of hydrate technology is the current lack of an economical means for the mass-production of solid hydrate in a manageable form.

Alternative methods to hydrate production have been patented. - A - US patent 5536893 describes a method for production of gas hydrates for transportation and storage where the gas in question is pressurized and cooled, supplied to a vessel to which water is added simultaneously to form fine water droplets that are dispersed in the gas. The temperature and pressure in the vessel are adjusted to produce hydrates. The hydrate is then withdrawn from the reactor then agglomerated. The agglomerated hydrate particles are transported or stored at adiabatic conditions at atmosphere pressure or at a slight gauge pressure at a temperature below 0 DEG C.

US patent 6082118 describes a method for the storage and transportation of gas hydrates as a slurry suspension under metastable conditions.

The patent application WO02079355 describes a hydrate production and dehydration device using a screw type extrusion-moulding machine, which dewaters and solidifies gas hydrate slurry and takes out the solidified gas hydrate under ambient pressure.

In general, several different types of hydrate forming processes exist. They mostly cover the formation of slurry hydrates, a time-consuming process involving low formation rates of dry hydrate from water droplets. Furthermore, practical problems regarding the implementation of these methods exist, due to their complexity and the high expenses involved in their implementation.

Currently no known efficient process exists for forming dry solid hydrates, a potentially more manageable and economical alternative to the existing processes which generally use hydrate slurries or require dewatering of hydrate slurries for the transportation, storage and use of hydrates.

It is the object of the current invention to provide a method for the formation of dry solid hydrates, which could be converted to, for example, a pellet form for various application purposes. The technology could, amongst other uses, improve the economics of several gas hydrate applications, including applications as described hereafter. It also allows the introduction of novel applications of certain gas hydrates as described hereafter.

It is a further object of the current invention to provide novel uses for clathrate compositions, especially CO₂ hydrate compositions, and novel CO₂ hydrate compositions.

Description of the invention

Clathrates for fire fighting

According to a first aspect the present invention provides the use of a clathrate composition comprising at least one non-flammable host and at least one non-flammable guest for fighting fires. By combining two non-flammable materials in a clathrate composition the fire fighting benefits of both, together with the (typically) high heat of dissociation of the clathrate can be utilised. Preferably the clathrate composition is a CO₂ hydrate composition. The main advantage of using CO₂ hydrate, which has CO₂ as the guest and water as the host, for fire fighting is that they offer the combination of two main fire fighting agents, namely water and CO₂. CO₂ hydrate has a higher latent heat (i.e. heat sink capacity) and better chance of reaching the base of the fire. Preferably the CO₂ hydrate composition is used in the form of a dry solid.

Preferably the non-flammable clathrate composition is in the form of pellets. The size of pellets can be chosen to suit the selected method of delivery of the clathrate composition to a fire. Alternatively the clathrate composition can be provided as a powder. A powder form has the benefit of maximising the surface area of hydrate composition in immediate contact with the hot and burning substances at the locus of the fire. However a powder form is more easily deflected from a target fire than more substantial particles such as pellets. Alternatively the clathrate composition may be in the form of a slurry, with clathrate particles distributed in a non-flammable liguid, for example water.

CO₂ gas hydrates, for example in the form of pellets or in the form of powder or other forms or shapes, can have a major impact in tackling fires, especially forest and warehouses fires. Solid clathrates, particularly in the form of pellets, have a better chance of reaching to the base of the fire. CO₂ hydrates are also a more effective fire fighting agent than water, as they combine both CO₂ and water, which are two effective fire fighting agents.

As fire sprinkler systems have a very restricted working height (< 10m) due to water vaporisation, their use in high roofed structures such as warehouses is very problematic. Hydrates delivered to the site of a fire in the form of solid (e.g., powder, pellet, block, etc) are, however, a very effective fire-fighting tool. The advantage of a non¬ flammable clathrate solid over water in fire fighting is in its greater efficiency, as the clathrate solids are less affected by the flow of hot air and have more resistance to evaporation due to high latent heat content, whereas water, as mentioned, tends to vaporise. Also, being solids, preferably in pellet form, they are expected to face less air resistance and more readily reach the base of a fire.

This greater efficiency of solid CO₂ hydrate, particularly in the form of pellets, enables less material to be used to extinguish a fire. Thus the material cost disadvantage when compared with water is minimised.

CO₂ hydrates act to extinguish a fire first by dissociation, an endothermic process absorbing energy and heat, and then evaporation of the released water, again absorbing energy. Additionally, the disassociation of the hydrate releases both carbon dioxide and steam which do not support combustion of a flame. Since the dissociation process for hydrates is endothermic (energy absorbing) it requires heat, in this case in the form of fire conditions, to occur. As the rate of hydrate dissociation is a function of the heat intensity, the dissociation will slow down significantly when the fire is extinguished, so that the product should act as a "smart" fire-fighting material. A small fire would be extinguished using an appropriate amount of CO2 hydrate, after which dissociation of the hydrate would slow down to very low rates, whereas water sprinklers tend to have to be left on.

Furthermore, the fighting of fires within inhabited buildings such as office blocks will be aided. So long as due attention is paid to the quantity of carbon dioxide released by the solid hydrate, preferably in the form of pellets, being less than the maximum level acceptable to support life, then this innovation can be used within inhabited environments. This minimises the risk to life, unlike conventional CO₂ extinguishers.

The reported examples of ineffectiveness of water in fighting warehouse fires and forest fires, resulting in significant destruction and loss of assets, illustrates a need for a more effective system. Insurance premiums would therefore be lower when utilising a more effective fire- fighting system.

The present invention also provides a fire extinguishing apparatus comprising a non-flammable clathrate composition as extinguishing medium. Preferably the fire extinguishing apparatus comprises a CO₂ hydrate composition as extinguishing medium. The fire extinguishing apparatus may for example be a hand held fire extinguisher. Alternatively it may be a sprinkler type system. The sprinkler type system may be, for example, fitted to a building such as a warehouse and be designed to distribute hydrate over a wide area, either automatically in response to an indication of a fire or when activated manually. The apparatus may, for example, deliver a CO₂ hydrate composition in the form of a powder or pellets. The non-flammable clathrate such as, for example, a CO₂ hydrate composition may also be delivered from the apparatus in the form of a slurry in a non¬ flammable liquid such as water for example.

In particular, a combination of CO₂ and water (two effective fire fighting agents) produces CO₂ hydrate which has a high latent heat for melting (around 1.7 times that of ice) . This produces water and CO₂ upon dissociation, which have their conventional fire fighting effects. As delivering water to the fire is a major obstacle in forest fire fighting, it can be seen that producing solid CO₂ hydrates will have a major impact in tackling fires. This invention could be used complimentary to other fire fighting options. For example, the heat intensity and temperature of forest fire could be reduced by C02 hydrates and then the fire is tackled by conventional means such as water.

Any method of production for solid CO₂ hydrate or other non¬ flammable clathrates can be used to manufacture appropriate compositions for use in fire fighting.

CO₂ hydrate is formed by interaction of water and CO₂ under appropriate temperature and pressure conditions as described in the following references, for example:

1. Deaton WM, Frost EM. Gas hydrates and their relation to the operation of natural gas pipe lines. US Bur Mines Monogr. 1946; 8 : 101-108.

2. Larson SD. Phase Studies Involving the Two-Component Carbon Dioxide-Water System, Involving the Carbon

Dioxide Hydrate. PhD Thesis. Champaign, IL: Univ. of Illinois; 1955.

Preferably the method of the invention described hereafter is utilised, as it provides currently the most cost effective and stable method for the manufacture of non¬ flammable clathrates, especially CO₂ hydrate.

Preferably, in manufacturing an appropriate CO₂ hydrate for use in fire fighting, liquid CO₂ could be used, as this can improve the hydrate formation process. Preferably, and in addition, adding promoters, for example some surfactants, can improve the gas-to-solid ratio of the produced hydrates and/or improve its stability.

The present invention also provides a composition for fighting fires comprising a non-flammable clathrate in combination with a wettable porous solid. Preferably the composition comprises CO₂ hydrate and a wettable porous solid. Preferably the wettable porous solid is silica gel particles or porous glass beads. It is possible to form clathrates such as CO₂ hydrate in combination with porous media as described hereafter, i.e., porous glass beads, silica gel etc to promote the reaction rate and control the powder or pellet sizes. Such a composition has the clathrate formed within the pores and on the surface of the porous solid.

The produced CO₂ hydrate composition is then delivered to the fire, and the fire is consequently extinguished. The hydrate is delivered to the base of the fire through gravity, or through any appropriate mechanical means.

Novel production process for clathrates

According to a second aspect the present invention provides, a method for the manufacture of a dry solid clathrate, comprising the steps of: providing at least one guest and at least one clathrate host; and, allowing the said guest and the said host to react under clathrate forming temperature and pressure conditions, the said guest being in excess of the quantity required to convert all of the said host to the clathrate. Preferably the guest is selected from methane, ethane, propane, butane, carbon dioxide, and combinations thereof or natural gas or hydrocarbon reservoir fluids. Preferably the host is water. When the guest is a gas and the host is water the product is a dry solid gas hydrate.

The expressions "dry solid clathrate" or "dry solid gas hydrate" means that the clathrate or hydrate produced according to the method is substantially free from separable liquid, for example water. In other words the hydrate solid will not have any free visible liquid attached to it. That is to say that the solid product, kept under suitable temperature and pressure conditions, for preventing decomposition of the hydrate composition concerned, will not produce free water on, for example, filtration. Similarly if subjected to mild centrifugation, at a speed (i.e. force) which is insufficient to cause its decomposition, no free water will be produced.

Materials other than water can be used to form clathrates. For example liquid ammonia is known to form clathrate compositions. It will be understood that in the description of preferred and alternative aspects and uses of the method that follows expressions such as "hydrate" or "gas hydrate" can refer to other clathrates formed with appropriate guests and hosts.

Preferably the hydrate is produced in a preferably cylindrical hydrate reactor with a stirring blade using the following procedure. Alternatively any system which allows for the agitation of water and gas under controllable pressure and temperature conditions can be used, and the use of a reactor within the description contained herein is to be taken to include any such system.

Water is pre-loaded up to preferably around 25-30% of the volume of the reactor. Alternatively, water (preferably pre- cooled) could be sprayed into the reactor containing gas with or without make-up gas. Any water/gas volume ratios which leaves enough space for gas/liquid guest compound, permits efficient mixing, and prevents substantial localised water accumulation is suitable.

In the description of the invention contained herein water is used, but any other fluid which can be used as a component for gas hydrate formation can be used in place of water, as can water which contains additives.

The reactor should be operated in excess gas conditions.

The gas from which it is desired to form hydrate in gas or liquid form is then charged to the reactor, preferably while the stirrer (agitator) is on. For example, if it is desired to produce natural gas hydrate in order to facilitate the transport or storage of that natural gas, then natural gas should be introduced, and if the production of methane hydrate for neutron moderation is desired, then methane should be introduced, or if CO₂ hydrate for fire fighting is desired, then CO₂ should be introduced.

Additional promoters or other materials may be added. Suitable promoters can include surfactants, which can improve the gas-to-solid ratio of the produced hydrate, hydrate promoters, compounds that will help hydrate nucleation, growth and stability. Preferably the stirrer is revolving at around 1000 rpm, as this presents an ideal balance between a low rpm, which does not generally give good mixing, and a high rpm, which although ensuring good mixing does not prolong the working life of the stirrer. Any degree of revolution which ensures good mixing can be used. Other mechanisms for mixing could be used to improve mass and heat transfer necessary for hydrate formation.

Preferably the stirrer revolves until an elevated pressure of around 200-2500 psia at 0-15 ⁰C is reached in the reactor

(depending on the type of hydrate forming compound) , as high pressure and low temperature conditions promote hydrate formation. Higher pressures can be used, but are generally uneconomical due to the high equipment costs involved. However, temperature conditions which are too low should be avoided as ice may form and reduce the rate of hydrate formation. Preferably those pressure and temperature conditions, which promote the formation of the particular hydrate being manufactured, should be used. The reactor may be run under constant pressure conditions.

The stirrer has two important functions, being firstly to push hydrates to the reactor wall and to compact them through centrifugal force and secondly to ensure a good- water gas interface.

The system is kept within these limits for preferably between 2 to 3 hours. The time which the mixture should be kept under the above conditions is preferably that which is sufficient to achieve vapour-liquid equilibria. Following this, the system temperature is reduced to preferably between 0.2 and 0.5 °C, preferably whilst stirring continues. The temperature to which the system should be reduced is preferably that which is as low as possible to achieve whilst avoiding the freezing of the water or other liquid initially added to the system along with the gas from which the hydrate is desired.

The drop in temperature causes the system pressure to decrease. It is possible to compensate the pressure drop by introducing more gas to the system or run the reactor at constant pressure conditions. Solid hydrate is consequently formed as the system cools down and the pressure drops. In the cases where a large stirring implement is used, the solid hydrate is initially pushed toward the reactor wall by the stirrer. Stirrer could be designed to combine draining hydrates with mixing and collecting unreacted water for spraying inside the reactor.

Once the pressure within the system has stabilised (or there is no significant gas intake, in case of constant pressure operation) , or once the stirrer is prevented from moving due to the solid hydrate formation, it is possible to inject more gas in order minimise the remaining free water within the system.

The system is then left for preferably between 4 and 5 hours. The time should preferably be that which is sufficient to ensure the stabilisation of system pressure.

Following this the system is depressurised by discharging any free gas left in the reactor. During depressurisation, the system temperature is preferably reduced to help the formed gas hydrate to become more rigid and stable, and also to encourage any remaining trapped free water to form solid hydrates .

The produced dry solid hydrate, which is often very solid and rigid, can then removed from the reactor.

The produced solid hydrate can be discharged in block form, if some initial discharge preparation/device is implemented within the hydrate reactor design. Such a device could take the form of, for example, an internal metal basket contained within the reactor. The produced solid hydrate could also be discharged in the form of crushed hydrate particles.

Following the discharge it is preferable that the produced solid hydrate is immediately transferred to a cool room with adequate low temperatures in order to prevent and minimise any dissociation.

The produced hydrate can then be next converted to the appropriate form for uses in the various applications described herein. Generally this will be a powder or a pellet. There are several known methods which could be used, such as those involving, rolling, those involving the use of a fluidized bed, and those involving compression moulding (more fully described at, for example, http://nippon.zaidan.info/seikabutsu/2002/00223/contents/040 .htm) .

Pellets produced using the novel process disclosed herein can be characterised by particle size, using a pellet machine which is able to produce various sizes of pellets, with varying stability and particle size distribution. The effect of their particle size and distribution, in conjunction with their stability can be optimised for use in particular applications.

It is also possible to combine the hydrates with oil or water to form hydrates in oil or hydrate in water slurry as described by other researchers.

Desirably a non-organic wettable porous solid is provided in contact with the liquid during the reaction of the gas and the hydrate forming liquid.

Preferably the wettable porous solid is silica gel particles or glass beads. Preferably the non-organic wettable porous solid is water wettable and the liquid is water. Preferably the wettable porous solid is present in sufficient quantity to absorb substantially all of the hydrate forming liquid.

Hydrate forming processes utilising organic material such as activated carbon as an absorbent have previously been employed. The use of non-organic material is preferred in the present invention, providing consistent processing and product quality. In addition, for example, where the hydrate product is a CO₂ hydrate, which may be employed for fire fighting, use of non-flammable materials is desired.

Preferably, where a wettable porous solid is used, it is present in sufficient quantity to absorb substantially all of the hydrate forming liquid.

For example a good water-gas interface is obtained by using water-wet porous materials, for example silica gel or porous glass beads, or other porous non-organic particles, to improve the rate of hydrate formation, by increasing the interface between gas and water to improve mass transfer. By using sufficient porous material the system is not over saturated with water. That is to say that the relative amounts of water and water-wet porous material is chosen so that the water is substantially disposed within the pores and on the surface of the water-wet porous particles leaving spaces in between. Where the system is not highly over saturated, water is retained in the pores and the gas occupies the space between the grains .

This provides excellent surface contact between water and gas, maximising the rate of hydrate formation and generally eliminating the need for any mixer (stirrer) . However a stirrer can be employed if desired. The porous media itself takes up some space (volume) , reducing the gas content per volume. However, this is not significant in the case where highly porous materials are used and is easily compensated by the increased rate of reaction. The same considerations regarding the benefits of increased liquid contact with gas apply when a liquid other than water is being employed to make a clathrate compound.

The presence of porous media also surprisingly increases the gas intake to levels higher than conventional bulk hydrate formation. It is believed that the gas can be adsorbed into the pores or onto the surface of the porous particles as well as forming hydrate complexes. In other words part of the gas stored is believed to be due to capillary adsorption and part due to hydrate formation. This use of porous media is not restricted to the novel method of forming dry solid gas hydrates described above but can also be used to improve the gas holding capacity of hydrates manufactured by any other hydrate forming process.

Thus according to a third aspect of the invention there is provided a clathrate composition comprising at least one guest and at least one host in combination with a non¬ organic wettable porous solid. In this context, in combination, means that the clathrate is formed within the pores and on the surface of the porous solid. Additionally as described above some of the guest material (usually a gas) may be stored by capillary adsorption.

Preferably the non-organic wettable porous solid is silica gel particles or porous glass beads. Such clathrate (or gas hydrate) compositions can find utility in the transport or storage of gases.

The described methods above avoid complex multi-stage high- pressure dehydration processes required in current slurry methods, and significantly reduces manufacturing costs by an estimated up to 25 %. This makes the use of hydrates made by the method of the invention for transportation, storage or other uses particularly advantageous.

Brief Description of the Drawings

Further preferred features and advantages of the present invention will appear from the following detailed description of some experiments and examples illustrated with reference to the accompanying photographs in which: Fig 1 shows a charcoal fire in a domestic barbecue apparatus; and,

Figs 2 to 4 show the fire being extinguished following application of a CO₂ hydrate composition.

Experimental Results Description of Preferred Embodiments and Examples

CO₂ hydrates for fire fighting

Some preliminary tests have been conducted using a BBQ

(barbeque) set-up to assess and compare the relative effectiveness of CO₂ hydrates and water in extinguishing burning charcoal.

The CO2 hydrates used were in the form of hydrate mass rather than pellets but still proved effective in fire fighting.

The results, as shown the Figures 1 to 4, demonstrate the potential superiority of CO₂ hydrates to water.

Figure 1 shows a charcoal fire in a barbeque apparatus. In Figure 2 CO₂ hydrate masses (light coloured) have been dropped on the fire. The tests showed that CO₂ hydrates were quite heat resistant, as illustrated in Figure 2.

Dissociation occurred at a steady rate allowing them to remain effective within the fire for a relatively long time period.

Hydrate dissociation generated very little liquid water, instead producing water vapour and CO₂ gas that extinguished the burning charcoal in a short time period, as illustrated in Figures 3 where the fire is partially extinguished, and Figure 4 where it is almost completely extinguished.

When the fire was almost entirely extinguished, (Figure 4) the rate of hydrate dissociation reduced significantly, although sufficient dissociation remained to prevent re- ignition of the fuel, even when a highly flammable liquid, kerosene, was added.

In addition, very little free liquid water was produced during the extinguishing process, which suggests that water damage could be significantly reduced if CO₂ hydrates are used for fire fighting. When the test was repeated with liquid water, the water was found to extinguish the fire locally, producing bursts of water vapour. However, although the resulting water vapour reduced the system temperature, most of the liquid water rapidly pooled below the burning charcoal, where it became far less effective in extinguishing the fire. As a result, the charcoal was able to re-ignite.

The fact that solid CO₂ hydrates remain within the fire, generally on the top of burning materials as they are solid, as opposed to liquid water which can flow away, is an important factor in the effectiveness of hydrates in fire fighting, in addition to their high heat capacity. This property of hydrates which will result in fire control and significant reduction in flame temperature and heat intensity could facilitate the application of conventional fire fighting methods (e.g., water spraying) . This could be a significant advantage, as the fire- extinguishing agents will remain in the direction of hot fluid and flame movement, releasing CO₂ and water vapour, absorbing the heat released, reducing the system temperature and starving the fire from air and oxygen. Also, the proportionate release of water will minimise water damage which could be very important in some types of fire.

Gas hydrate production

In one embodiment of the current invention the method disclosed herein for producing dry solid hydrate is implemented using a hydrate reactor, a cool room, a crusher, a pellet machine and temperature probes and pressure transducers.

The hydrate reactor is any hydrate reactor specifically designed for the production of hydrates at high pressure conditions, containing a preferably rectangular or U-shaped blade stirrer for efficient mixing and transfer and compaction of hydrates on the wall of the reactor. A cylindrical reactor would be suitable. The reactor consists of a cylindrical vessel (for example, 500, 1000, 2000, or more cm³) , a test fluid inlet and outlet, a stirrer (with a variety of blades, and stirrer design), a coolant jacket (or external cooling bath) , and temperature/pressure recording equipment preferably controlled by a computer.

The cool room is necessary for the mass processing and storage/preservation of produced dry solid hydrates at low temperature and ambient pressure. The hydrate-crushing machine is necessary for crushing and converting the produced solid hydrate blocks to homogeneous small hydrate particles, such as powder. An ice-crushing machine could be used for this purpose, in the case of C02 hydrates.

The pellet machine is necessary for forming the crushed hydrate solids into pellets, as pellets, due to their size, combine the benefits of ease of transportation and storage.

Temperature probes and pressure transducers are necessary for the accurate and reliable measurement and monitoring of the pressure and temperature of the system during the staged hydrate pellet production process.

The cooling jacket or bath is necessary to control the temperature of the reactor, and computer recording device to record the conditions of the system at any time.

The novel method of production described above in the description is then implemented using this described equipment.

Following production the produced hydrate is discharged from the reactor and transferred to the cool room immediately to prevent or minimise hydrate dissociation.

The hydrate crusher is used to convert the solid hydrate to small particles, if necessary.

Following this the pellet machine is used to convert the hydrate to pellet form, if required. Examples of Hydrate use for the storage, transportation and sequestration of gas and for reducing the emission of greenhouse gases

Further uses for gas hydrate, for example in the form of pellets created using the novel method of production described herein, include gas transport and sequestration.

Although any method of production for solid hydrate can be used to manufacture hydrates appropriate for storage or sequestration, the method described herein is preferred, as it provides currently the most cost effective and stable method for the manufacture of solid hydrate.

For example, in the case of gas storage, the gas is transformed into solid hydrate, and preferably into hydrate pellets using the method of production disclosed herein.

The preferable conditions for the storage of this solid hydrate are low temperature below water freezing point (ideally -5 to -10 °C) , and atmospheric pressure.

Gas sequestration/storage can be applied to reduce the emission of greenhouse gases such as CO₂ into the atmosphere. In the case of gas sequestration, the proposed method can be used for CO₂ storage/transport, where the CO₂ is transformed into hydrate using the method described above, as it provides currently the most cost effective and stable method for the manufacture of solid hydrate.

There are considerable gas resources in the form of associated or non-associated gas in various parts of the world that can secure a low carbon fossil fuel supply for years to come. However the locations of these reserves inhibit their development due to the costs of transporting gas to where it can be processed. Many countries have considerable natural gas resources waiting for exploration and exploitation. Often these resources are to be found in offshore deepwater and remote fields, where gas transportation remains a major challenge.

Pipelines are considered too expensive due to the great distances and depths involved, and the small size of individual fields. Currently, natural gas is transported by pipeline which costs ~£1 million per km, so a cost-effective gas hydrate transportation alternative is attractive for small to medium sized gas fields. As an alternative, liquid natural gas (LNG) transportation technology is very costly due to its requirements for extreme refrigeration.

Natural gas hydrate non-pipeline technology is an alternative to conventional liquefied natural gas (LNG) and pipeline transportation for bringing stranded gas to the market from small to medium sized gas fields.

In various other industries a cost effective method for the storage of gas is a priority.

Gas can be stored and transported more easily and cost effectively when it is in hydrate form. The method of the invention provides an efficient and cost effective way of obtaining such hydrates. For example CO₂ is currently transported either as gas along pipelines or is compressed to form the liquid for transport by tanker or pipeline. By forming into the hydrate by the method of the invention the gas can be conveniently transported with the prospect of CO₂ removal at source being realised. For example CO₂ from a combustion process, such as at a power station, is separated from flue gases, transformed into solid hydrate, and disposed of accordingly.

In particular it can be used for the transportation of natural gas, through the conversion of that natural gas into hydrates (preferably pellets, as these hydrate pellets represent a highly compressed form of that natural gas) , and therefore represent a very economical solution to some of the problems inherent in transportation of large gas volumes. It is also possible to combine the hydrates formed in excess gas conditions with oil/condensate or water and form hydrates in oil or hydrates in water slurries.

In the case of natural gas, the formation of such hydrate pellets is carried out using the novel procedure described herein to produce dry NG solid hydrate pellets. In this case, again, using small amounts of promoters, for example surfactants, can improve the gas to solid ratio of the produced hydrates. The NG hydrates can also be transported at more feasible conditions, for example at temperatures around -5 to -10 °C and at atmospheric pressure, than LNG, which generally requires a temperature of around -160 °C.

In particular gas hydrates should preferably be transported in the form of pellets loaded in a thermally insulated carrier. The preferred characteristics of the carrier mechanism are those which reduce the heat supply to the hydrate by conduction, convection and radiation. The transportation capacity could be improved by using a mixture of different sizes of pellets, which would help in reducing the convectional heat transfer. This eliminates the need for expensive pipelines or high pressure liquid carriers.

The application of methane hydrates as neutron moderators

Gas hydrate, preferably manufactured using the novel method disclosed herein, can also be utilised as a neutron moderator in high power neutron sources and processes, in order to regulate the intensity of the produced neutron beams.

For example, in nuclear engineering, a neutron moderator is a medium which reduces the velocity of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a chain reaction. Commonly used moderators include deuterium, hydrogen and graphite. In a thermal nuclear power reactor, the nucleus of a heavy fuel element such as uranium absorbs a slow moving free neutron, becomes unstable, and then splits into two smaller atoms. The fission process for uranium atoms yields two smaller atoms, one to three fast-moving free neutrons, plus an amount of energy. Because more free neutrons are released from a uranium fission event than are required to initiate the event, the reaction can become self sustaining - a chain reaction under controlled conditions which can produce a tremendous amount of energy. However, the newly released fast neutrons must be slowed down before they can be absorbed by the next fuel atom. This slowing down process is caused by collisions of the neutrons with atoms of an introduced substance called a moderator.

Furthermore, an explanation of neutron sources, their uses, can be found at http://www.sns.gov/aboutsns/intro.htm. Preferably and in particular, methane hydrates have shown great potential as a neutron moderator for high power neutron sources, generally used in the microanalysis of compounds and biological materials.

However, methods for their simple and widespread production are currently lacking.

Therefore, development of such techniques would greatly benefit research and development in the pharmaceutical and biotech industries.

Hydrates and in particular methane hydrates, preferably in the form of pellets (as the size of methane hydrate pellets has a strong effect on moderator performance) are manufactured, using the novel method disclosed herein. These pellets are then used as a neutron moderator within a neutron source.

Benefits of current: invention

Hydrate pellets for fire fighting

COz hydrate is particularly suited to fighting fire. The novel method disclosed herein can be used to manufacture CO2 hydrates for fire fighting, for example in the form of pellets.

The market for this innovation is global, and applies to both interior and exterior fires.

Novel production process for gas hydrates The novel process disclosed herein can be easily scaled-up for industrial use.

The novel process disclosed herein is particularly applicable to the oil and gas industries, forestry, environmental agencies, biotechnology, and scientific communities .

The prime advantage will be through the use of a low cost dry solid hydrate production route.

A cost-effective method for solid hydrate production will have a significant impact on the economic and practical viability of various applications of gas hydrates, such as transportation.

The novel process disclosed herein will avoid complicated multi-stage high pressure dehydration processes, which are the major drawback of previously proposed slurry methods, such as those patented by Advantica (former British Gas) (WO 00/56684, TW480321), Mobil Oil Corporation (US6082118), and the Kobe Shipyard and Machinery Works, Japan (WO02079355) . These methods have not yet been industrialised, most likely due to their complexity and the high expenses involved.

Solid hydrate for the storage,transportation and sequestration of gas, and for reducing the emission of greenhouse gases

Legislation passed at the Kyoto summit requires the reduction of CO₂ emissions to the atmosphere. CO₂ produced as a by-product of industry can be converted to dry CO₂ hydrates for transportation, destined either for disposal through sequestration and/or for enhanced oil recovery, or as previously mentioned, a fire-fighting agent.

Solid hydrate for gas storage and transportation as solid gas hydrates

The novel hydrate pellet production technology should have a significant effect on the economics of this process.

It is estimated from initial market research that the market for natural gas transportation and CO₂ sequestration could be in the range of 100s of millions of pounds.

Furthermore, the invention described herein could be applied to the storage and transport of any gas, making any industry within which such items are an issue eminently more profitable.

The application of methane hydrates as neutron moderators

The Spallation Neutron Source under construction in the USA, which will provide the most intense pulsed neutron beams in the world for scientific research and industrial development is planned for completion in 2006 at a total cost of $1.4 billion.

The neutron moderator is a key component.

A neutron moderator methane hydrate application offers a technical advantage at reasonable price to universities and research institutes. Furthermore, methane hydrate has shown great potential as a neutron moderator for high power neutron sources used in microanalysis of compounds and biological materials.

Claims

1. Use of a clathrate composition comprising at least one non-flammable host and at least one non-flammable guest for fighting fires.

2. Use of a clathrate composition according to claim 1 wherein the clathrate composition is a CO₂ hydrate composition.

3. Use of a clathrate composition according to claim 1 or claim 2 wherein the clathrate composition is a dry solid clathrate composition.

4. Use of a clathrate composition according to claim 1 or claim 2 wherein the clathrate composition comprises a clathrate distributed in a non flammable liquid.

5. Use of a clathrate composition according to any one of claims 1 to 3 wherein the clathrate composition is in the form of pellets.

6. Use of a clathrate composition according to any one of claims 1 to 3 wherein the clathrate composition is in the form of a powder.

7. A composition for fighting fires comprising a non¬ flammable clathrate in combination with a wettable porous solid.

8. A composition according to claim 7 wherein the non¬ flammable clathrate is CO₂ hydrate.

9. A composition according to claim 7 or claim 8 wherein the wettable porous solid is non-organic.

10. A composition according to claim 9 wherein the wettable porous solid is silica gel particles or porous glass beads.

11. A fire extinguishing apparatus comprising a non¬ flammable clathrate composition as extinguishing medium.

12. A fire extinguishing apparatus according to claim 11 wherein the non-flammable clathrate composition is a CO₂ hydrate composition.

13. A fire extinguishing apparatus according to claim 11 or claim 12 wherein the apparatus is a hand held fire extinguisher.

14. A fire extinguishing apparatus according to claim 11 or claim 12 wherein the apparatus is a sprinkler system.

15. Preparation of a CO2 hydrate composition for fighting fires comprising the step of reacting CO₂ and water wherein the CO₂ is in excess of the quantity required to consume all the water.

16. Preparation of a CO₂ hydrate composition for fighting fires according to claim 15 wherein the CO₂ is used in liquid form.

17. A method for the manufacture of a dry solid clathrate, comprising the steps of: providing at least one guest and at least one clathrate host; and, allowing the said guest and the host to react under clathrate forming temperature and pressure conditions, the said guest being in excess of the quantity required to convert all of the said host to the clathrate.

18. A method according to claim 17 wherein the guest is methane, ethane, propane, butane, carbon dioxide, and combinations thereof or natural gas or hydrocarbon reservoir fluids .

19. A method according to claim 17 or 18 wherein the host is water.

20. A method according to any one of claims 17 to 19 wherein the method further comprises providing a non¬ organic wettable porous solid in contact with the host.

21. A method according to claim 17 wherein the wettable porous solid is selected from, silica gel or glass beads.

22. A method according to claim 17 or claim 18 wherein the wettable porous solid is present in sufficient quantity to absorb substantially all of the host.

23. A method according to any one of claims 17 to 22 wherein the method further comprises stirring the host with an agitator.

24. A method according to claim 23 where the agitator is stirred at about lOOOrpm during the bulk of hydrate formation.

25. A method according to any one of claims 17 to 224 wherein temperature and pressure conditions of 200-2500 psia and 0-15deg C are used to form the clathrate.

26. A method according to any one of claims 14 to 22 wherein after the bulk of clathrate formation the temperature is adjusted to between 0.2 to 0.5deg C to complete reaction.

27. A method according to claim 23 wherein the temperature is reduced further before the product is removed from the reactor.

28. A method according to any one of claims 17 to 25 wherein the host occupies 25 to 30% of the volume of a reactor used to carry out the method.

29. A method according to any one ^• of claims 17 to 28 wherein surfactants, or other clathrate promoters are used to promote clathrate nucleation, growth or stability.

30. A method according to any one of claims 17 to 29 wherein the reaction is carried out at constant pressure conditions.

31. A method according to any one of claims 17 to 29 wherein additional guest is added after reaction is apparently complete.

32. Use of a dry solid clathrate manufactured by a method according to any one of claims 17 to 31 for the transport or storage of gases.

33. A clathrate composition comprising at least one guest and at least one host in combination with a non¬ organic wettable porous solid.

34. A clathrate composition according to claim 33 wherein the non-organic wettable porous solid is silica gel particles or porous glass beads.