WO2016135133A1

WO2016135133A1 - A vehicle comprising a storage system and a combustion engine, the storage system comprising a container and at least one storage vessel

Info

Publication number: WO2016135133A1
Application number: PCT/EP2016/053754
Authority: WO
Inventors: Mathias WEICKERT; Stefan Marx; Ulrich Müller; Lena Arnold
Original assignee: Basf Se
Priority date: 2015-02-27
Filing date: 2016-02-23
Publication date: 2016-09-01

Abstract

The invention is related to a vehicle (2) comprising a storage system (1) and a combustion engine (4), the storage system (1) comprising a container (3) with a first interior (5) and at least one storage vessel (7) with a second interior (9), wherein the at least one storage vessel (7) is disposed in the container (3) and the at least one storage vessel (7) comprises a storage vessel wall (15) separating the first interior (5) from the second interior (9), wherein the first interior (5) comprises a first gas and the second interior (9) comprises a second gas and a sorption medium (17), and the first gas comprises an exhaust gas from the combustion engine (4) and the second gas comprises a fuel for the combustion engine (4), wherein the first interior (5) comprises at least two boxes (21), each comprising a third interior (23) and a box wall (25) separating the third interior (23) from the first interior (5), and wherein the at least two boxes (21) partly enclose the at least one storage vessel (7), each of the at least two boxes (21) encloses the at least one storage vessel (7) at least partly, referring to the cross-sectional circumference (27) of the at least one storage vessel (7), and each of the at least two boxes (21) encloses the at least one storage vessel (7) only partly, referring to the length in longitudinal direction (29) of the at least one storage vessel (7). The invention is further related to a process for operation of a vehicle (2).

Description

A vehicle comprising a storage system and a combustion engine, the storage system comprising a container and at least one storage vessel

Description

The invention relates to a vehicle comprising a storage system and a combustion engine, the storage system comprising a container with a first interior and at least one storage vessel with a second interior, wherein the at least one storage vessel is disposed in the container. Owing to the increasing scarcity of oil resources, research is increasingly being made to unconventional fuels such as methane, ethanol or hydrogen for operating an internal combustion engine or a fuel cell. For this purpose, vehicles comprise a storage vessel for keeping a stock of the fuel. For the storage of gas in stationary and mobile applications, the gas is stored in pressure vessels, often referred to as compressed natural gas (CNG) technique or in sorption stores, often referred to as adsorbed natural gas (ANG) technique. Sorption stores are also known as ANG tanks. ANG has the potential to replace compressed natural gas CNG in mobile storage applications such as in vehicles. In ANG-applications a porous solid is packed in a storage vessel to increase the storage density, enabling lower pressure operation with the same capacity or higher capacities at the same storage pressure.

Sorption, covering adsorption and absorption, is an exothermic process. Any sorption or desorp- tion is accompanied by a temperature change in an ANG-storage system. The heat of sorption has a detrimental effect on performance during both filling cycles and discharge cycles. A temperature increase as high as 80°C can occur during the filling cycle. A filling cycle normally will be performed at a fuel station, at least for mobile applications, where the released sorption heat can be removed. Contrary to the filling cycle, the rate of discharge is dictated by the energy demand for desorption.

Such storage vessels comprise sorption media, which is also referred to as adsorbent medium, adsorbent, adsorber or absorber. The gas is stored by adsorption on the sorption medium, in the cavities between individual particles of the sorption medium and in parts of the vessel, which are not filled with sorption medium. Alternatively or additionally the gas can be absorbed by the sorption medium. The filled storage vessel can be pressurized or non-pressurized. Selection of a suitable vessel depends on the applied maximum pressure. The higher the storage pressure the more gas can be stored per volume.

The sorption capacity of the solid, defined by the ratio of the mass of the sorbed gas or liquid to the mass of the solid, strongly depends on temperature and is reduced with increasing temperature. In the aim of a maximal exploitation of the storage space, the temperature profile estab- lished in the storage vessel during the filling procedure has to be taken into consideration. An efficient sorption allows a reduced filling time as the same amount of gas can be stored in a shorter time period. Hence, the maximum amount of stored gas can be increased when the available filling time is limited. During filling the storage vessel with gas two sources are relevant for a temperature increase in the vessel. These are the heat due to compression of the gas and the heat liberated as a result of the exothermic sorption. The amount of generated heat directly depends on the amount of sorbed gas. The more gas is sorbed on the sorption medium, the more heat is liberated. And with an increasing sorbed amount of gas on the solid, the sorption rate, defined as amount of gas sorbed per unit of time, is reduced.

In turn, desorption is an endothermic process and heat has to be supplied when gas is taken from the storage vessel. Heat management is therefore of great importance when storage vessels with sorption medium are used. Due to their large surface areas, in particular metal-organic framework materials (MOFs) are of interest for applications in gas storage. Advantageously, pulverulent materials are processed to compact shaped bodies. These can be handled more conveniently and especially in a safer manner. Shaped bodies allow better exploitation of volumes available in apparatuses or vessels and reduce pressure drops. Prerequisite for a successful use for shaped bodies are preliminari- ly a high sorption capacity, adequate thermal and mechanical stability and high abrasion resistance.

US 2008/0290645 A1 discloses absorbent media for gas or heat in a predetermined length of a polygon or curvilinear and preferably honey comb cross-sectioned shape with gas absorbant media packed therein. Hexagonal tubes are installed along the radial or longitudinal axis of a fuel tank.

US 7,637,292 B2 describes an apparatus wherein the compression heat for refueling of an on board vehicle tank is evacuated from the interior of the on board tank by a heat absorber within the tank through a radiator external to the tank in which a coolant circulates from the heat absorber within the tank to the external radiator. The external radiator is powered by the mechanical energy of refueling gas, which traverses a turbine from the high pressure depot to the low pressure on board tank. US 2014/029061 1 A1 discloses a natural gas storage system including a container, a natural gas adsorbant positioned in the container and a heating mechanism to selectively thermally activate the adsorbant.

According to WO 2013/130401 A1 a natural gas adsorption device includes at least one porous, flexible container that is permeable to natural gas, a natural gas adsorption material having a volume average diameter larger than the average pore diameter of the container and a storage tank enclosing the container and the natural gas adsorption material.

US 2008/0168776 A1 reports on a hydrogen storage tank system based on gas adsorption on high-surface materials comprising an integrated heat exchanger. The gas storage system, storing gas by cryo-adsorption, comprises an insulating container and storage vessels. A cooling fluid is provided to remove heat when the storage vessels are being filled with the gas. For gas storage systems a complete emptying of the storage vessel is not possible and a residual amount of gas always remains in the storage vessel when a minimum gas pressure level is required for example for the operation of a combustion engine of a vehicle. This residual amount of gas is higher for storage systems comprising sorption media than for storage systems without sorption media. Further, the residual amount of gas strongly depends on temperature.

It is an object of the present invention to provide a vehicle comprising a sorptive storage system and a process for operation of the vehicle, which enables the reduction of the residual amount of gas still present in the storage vessel when a minimum storage pressure is reached. Further, the storage system should have a small internal pressure drop and the homogeneity of the internal temperature profile is to be improved. This object is achieved by a vehicle comprising a storage system and a combustion engine, the storage system comprising a container with a first interior and at least one storage vessel with a second interior, wherein the at least one storage vessel is disposed in the container and the at least one storage vessel comprises a storage vessel wall separating the first interior from the second interior, wherein the first interior comprises a first gas and the second interior comprises a second gas and a sorption medium, and the first gas comprises an exhaust gas from the combustion engine and the second gas comprises a fuel for the combustion engine, wherein the first interior comprises at least two boxes, each comprising a third interior and a box wall separating the third interior from the first interior, and wherein the at least two boxes partly enclose the at least one storage vessel, each of the at least two boxes encloses the at least one storage vessel at least partly, referring to a cross-sectional circumference of the at least one storage vessel, and each of the at least two boxes encloses the at least one storage vessel only partly, referring to a length in longitudinal direction of the at least one storage vessel.

The object is further achieved by a process for operation of a vehicle comprising a storage sys- tern and a combustion engine, the storage system comprising a container with a first interior and at least one storage vessel with a second interior, the at least one storage vessel is disposed in the container and the at least one storage vessel comprises a storage vessel wall separating the first interior from the second interior, wherein the first interior comprises a first gas, and the second interior comprises a second gas, which is contacted with a sorption medium, wherein at least part of the second gas is conducted from the second interior to the combustion engine and the second gas is combusted in the combustion engine to form the first gas, and wherein the first gas is conducted from the combustion engine into the first interior and a stream of the first gas is led through the first interior in cross-flow to a longitudinal direction of the at least one storage vessel.

By means of the invention, heat of the exhaust gas from the combustion engine is used to increase the temperature of the at least one storage vessel comprising the second gas and the sorption medium. At a higher temperature, a reduced residual amount of the second gas is required to remain in the at least one storage vessel in order to provide a predetermined minimum storage pressure, which is necessary to operate the combustion engine. For a combustion engine in for example of a three-wheeler a minimum storage pressure of typically 4 bar is needed. Thus, by means of the invention, the effective storage capacity of the storage system is enhanced.

The container preferably comprises a container wall with a top part and an undermost part, at least one of the at least two boxes touches the top part of the container wall and at least one of the at least two boxes touches the undermost part of the container wall, and for every two adjacent boxes, the first of the two adjacent boxes touches the top part of the container wall and the second of the two adjacent boxes touches the undermost part of the container wall. By the contact of the least two boxes with the undermost part of the container wall and the top part of the container wall, respectively, a change of the flow direction of the stream of the first gas at the container wall is enforced. A direct flow path of the first gas in the longitudinal direction along the container wall from one end of the container to another opposing end of the container is blocked by the at least two boxes. More preferably, each of the at least two boxes touches the container wall in a way that at least 30 % of the length of a cross-sectional circumference of the container is touched or covered by one of the at least two boxes, more preferably 50 to 95 %, particularly preferably 60 to 90 % and most preferably 75 to 90 %, for example 85 %.

Preferably, a first gap is provided between the first of the two adjacent boxes and the undermost part of the container wall and a second gap is provided between the second of the two adjacent boxes and the top part of the container wall. By this position of the two adjacent boxes in the container, having an offset to each other in vertical direction, the flow direction of the first gas within the container meanders at least once. When the stream of the first gas reaches the first of the two adjacent boxes, the flow is diverted downward a first side of the first of the two adjacent boxes, passes through the first gap and at an opposing second side of the first of the two adjacent boxes, the flow is directed from the bottom part of the container to the top part of the container. Here, the stream of the first gas flows substantially in parallel to the second side of the first of the two adjacent boxes and also in parallel to a first side of the second of the two adjacent boxes. The stream of the first gas is again deflected at the top part of the container wall, passes through the second gap between the second of the two adjacent boxes and the top part of the container wall and flows downward along a second side of the second of the two ad- jacent boxes. Alternatively, it is possible with an inverse overall flow direction of the first gas that the stream of the first gas firstly reaches the second of the at least two boxes, providing the second gap at the top part of the container wall, while the above-described principle of flow pattern within the container is still satisfied. Cross-flow is understood to led the stream of the first gas through the first interior, wherein a flow direction of the stream of the first gas and the longitudinal direction of the at least one stor- age vessel enclose an angle β in a range from 60° to 120°, preferably 80° to 100°, more preferred 85° to 95°, particularly preferred 88° to 92° and most preferred 90°.

Depending on the installation space available and the maximum permissible storage pressure in the at least one storage vessel, different cross-sectional areas are suitable for the at least one storage vessel, for example the circular, elliptical or rectangular. Preferably, the at least one storage vessel has a cylindrical shape, more preferably with a longitudinal extension being longer than a radial extension. The diameter of the at least one storage vessel is preferably between 5 and 50 cm and the inner volume of the at least one storage vessel is preferably be- tween 5 and 20 L. The length in longitudinal direction of the at least one storage vessel preferably corresponds to the length in longitudinal direction of the container and is preferably between 50 cm and 150 cm, more preferably between 80 cm and 1 10 cm.

Even though several forms of the container are applicable, the container preferably has a cu- boid form. Preferably, also each of the at least two boxes has a cuboid form.

Preferably, the at least one storage vessel is mounted in a horizontal position and also the container is mounted in a horizontal position. The container preferably comprises an inlet and an outlet, the inlet and the outlet being arranged at the container wall on opposing sides of the container. The inlet is preferably connected with an exhaust gas outlet of the combustion engine by a connecting pipe. Typically, the inlet and the outlet are provided at opposing end surfaces of the container. Referring to a cuboid container, the end surfaces are the surfaces with the smallest area, referring to all surfaces of the cuboid.

The temperature of the first gas entering the container at the inlet is lower than the temperature of the first gas at the outlet. The temperature difference of the first gas between the inlet and the outlet is usually more than 100°C. The first gas has a temperature of preferably at least 300°C when entering the first interior, more preferably at least 400°C and most preferably between 430 °C and 470°C.

The first gas is led through the container comprising the at least one storage vessel and the heat transfer from the first gas to the second gas occurs substantially at the storage vessel wall. Due to the at least two boxes being present in the container and partly enclosing the at least one storage vessel, the path for the first gas flowing through the container is determined. The at least two boxes block the direct and shortest way through the container and the stream of the first gas is led in cross-flow to the longitudinal direction of the at least one storage vessel and preferably in cross-flow to the overall flow direction of the first gas.

With the given path for the stream of the first gas through the container in cross-flow to the at least one storage vessel a higher amount of heat reaches the parts of the at least one storage vessel, which are closer to the outlet of the container than to its inlet. The way of the stream of the first gas through the container is elongated and the flow velocity is enhanced by means of the at least two boxes. The temperature profile in the container and in the at least one storage vessel is rendered more homogeneous in a vertical as well as in a horizontal direction.

As the dependency of the sorption capacity on temperature is not linear, the specific temperature profile in the container has a pronounced effect on desorption and thus on the residual amount of gas remaining in the at least one storage vessel. Especially for temperatures of more than 80°C a further increase in temperature leads to only limited further desorption as the sorp- tion capacity is already significantly reduced at these high temperatures. The temperature profile in the container is also crucial for the amount of heat that is transferred via the container wall to the environment and which is therefore lost for the intended heat transfer to the at least one storage vessel. In order to achieve a more homogeneous temperature profile in longitudinal direction of the at least one storage vessel, which is preferably the horizontal direction, the flow velocity of the first gas is enhanced along the storage vessel wall compared to a storage system without the at least two boxes. Due to the increased flow velocity the convective heat transfer along the storage vessel wall becomes more dominant in relation to the heat conduction towards the interior of the at least one storage vessel, labeled as second interior of the storage system; this heat conduction is driven by the temperature difference between the first gas and the second gas.

It is important to transfer the heat along the length in longitudinal direction of the at least one storage vessel outside of the at least one storage vessel as heat conductivity inside the at least one storage vessel is quite limited due to the sorption medium.

The resulting cross-flow improves the homogeneity of the temperature profile in vertical direction, where in general the temperature increases from the bottom to the top. The area of the storage vessel wall, which is not covered by the at least two boxes is exposed to the stream of the first gas and available as heat transfer area. For an improved heat transfer, the storage vessel wall is brought in direct contact with the stream of the first gas coming from the combustion engine. The invention also reduces safety risks as due to a more homogeneous temperature distribution a local overheating of parts of the storage vessel wall is avoided.

The overall pressure drop in the first interior, referring to the first gas, substantially resulting from the presence of the at least two boxes in the container, is preferably less than 20 mbar, more preferably less than 15 mbar and most preferably less than 10 mbar. Higher pressure drops within the container would interfere with the operation of the combustion engine, as the exhaust gas is preferably directly led into the container. Instead of leading the exhaust gas completely from the combustion engine into the container, it is also possible to use a bypass for leading exhaust gas from the combustion engine into the container, wherein the bypass comprises at least 50 % by volume, referring to the total amount of exhaust gas produced by the combustion engine.

Preferably the at least two boxes are arranged serially in longitudinal direction of the at least one storage vessel. Typically, the stream of the first gas entering the container firstly reaches a first of the at least two boxes before reaching a second of the at least two boxes.

Size and form of the gaps between the at least two boxes and the container wall predominantly determine the internal pressure drop of the container, referring to the stream of the first gas. When the container has a cuboid form, the gaps preferably have a rectangular form in radial cross-sectional view, radial referring to the container, and are provided directly next to the con- tainer wall. The area of each gap in radial cross-sectional view is preferably 1 % to 10 % of the total radial cross-sectional area of the container, more preferably 1 % to 5 %, most preferably 2 % to 4 %, for example 3 %, independently from the form of the gap. The area of the gap, which is a partial area of the total area of the container cross-section can also be divided into more than one continuous parts.

A width of the gaps, measuring a shortest distance between the box wall and the container wall, is preferably less than 2 cm, more preferably less than 1 .5 cm and most preferably less than 1 .1 cm, for example 1 cm. At the sides of the gaps, at least one support, preferably two supports at each box can be provided in order to hold the corresponding box in a fixed position within the container.

A shortest distance between two adjacent boxes is preferably more than 10 mm, more preferably more than 0.5 cm, and most preferably between 0.5 cm and 2 cm, for example 1 cm, refer- ring to a length of 1 m in longitudinal direction of the container. The same ratios of the shortest distance and the length apply for other lengths of the container.

Typically, the container has a length in longitudinal direction from 80 to 120 cm, for example 1 m and a width and height in the range from 20 to 40 cm, preferably from 25 to 35 cm, for example 32 cm.

In order to further elongate the way of the stream of the first gas through the container, each of the at least two boxes preferably encloses the at least one storage vessel completely, referring to the cross-sectional circumference of the at least one storage vessel. By this measure, the storage vessel wall and the stream of the first gas are only in contact with each other in the crossflow mode and the stream of the first gas does not flow directly along the storage vessel wall in longitudinal direction of the at least one storage vessel. The stream of the first gas, flow- ing in vertical direction along the storage vessel wall, increases the homogeneity of the temperature profile in vertical direction in the container and in the at least one storage vessel. The cross-section refers to the radial cross-section of the at least one storage vessel. Preferably, 10 % to 30 % of the area of the storage vessel wall, referring to the sum of the storage vessel wall of all storage vessels present in the container, more preferably 15 % to 25 % and most preferably 18 % to 22 %, are directly available as heat exchange area for the first gas.

The first interior is a space, which is limited by the container wall, the storage vessel wall and the box wall. The second interior is a space, which is enclosed by the storage vessel wall. The third interior is generally a space which is limited by the storage vessel wall and the box wall. As at least two boxes are present in the container, also at least two separate third interiors exist. Preferably, all boxes have the same dimensions and more preferably, edges of different boxes are parallel to each other.

The storage vessel is preferably a pressure vessel and the storage vessel wall is preferably not permeable for gas; otherwise no pressure within the storage vessel could be established. A maximum storage pressure in the at least one storage vessel depends on the application and type of the vehicle as well as on the embodiment of the at least one storage vessel. Even though applications with storage pressure of up to 250 bar exists, preferably, the second gas is stored in the at least one storage vessel at a pressure of up to 100 bar, preferably the maximum storage pressure is between 30 and 90 bar, most preferably between 60 and 80 bar.

The wall of the at least one storage vessel can be made from any material as for example metal such as aluminum, steel, fabric, fiber, plastic or composite material. Fiber composite material, aluminum and steel are preferred.

Generally, at least one opening is provided in the storage vessel wall for each storage vessel in order to provide an inlet and/or an outlet for filling the second gas into the at least one storage vessel. Preferably the inlet and the outlet at the storage vessel wall are provided at the same half of the at least one storage vessel. The half can also be named as side or end. The inlet and the outlet can be located in the same position in the storage vessel wall and combined in one construction part or adapter. Generally, processes for gas storage by means of porous solids are described in more detail for example in WO-A 2005/003622, WO-A 2003/064030, WO-A 2005/049484, WO-A 2006/089908 and DE-A 10 2005 012 087.

The close arrangement of the inlet and the outlet is especially advantageous on order to estab- lish a flow-through in the at least one storage vessel, for example during filling of the at least one storage vessel with the second gas, which is further described in WO 2014/057416. For a flow-through regime in the at least one storage vessel a flow-through is established in the sec- ond interior during filling and a gas flow of the second gas through the outlet at the storage vessel wall exceeds 0 kg/h, preferably 50 kg/h and more preferably 100 kg/h during filling.

Preferably, also the box walls are not permeable for gas. The at least two boxes might be manufactured from the same material as the container wall. A preferred material for the box wall is aluminum. Nevertheless, the third interior within the at least two boxes do not have to be completely sealed towards the first interior as the boxes predominantly serve for leading the stream of the first gas and not for separating the first gas from the second gas or from the environment. The boxes can also be an assemblage of baffles. In the case where the boxes are constructed from single baffles, the third interior is preferably a space which is limited by the storage vessel wall, the box wall and the container wall.

Correspondingly, it is preferred that the container wall is not permeable for gas. Nonetheless, small amounts of the first gas might escape from the container through the container wall in other locations than the points where the first gas is intended to be led into and out of the container. It is further preferred that the container wall has a heat transfer coefficient a of at least 10 W/(m^2»K) in order to minimize heat losses towards the surroundings of the container.

In order to minimize the heat loss towards the surroundings of a container, the container wall preferably comprises a double wall. The slot between two walls of the double wall is preferably filled with a gas, for example air.

The container wall can be equipped with high temperature insulation material such as graphite, ceramics or microporous thermal insulation material. Preferably, the high temperature insulation material is at least provided between the container wall and the box wall.

The container can also be configured as a drawer, wherein a compartment, which comprises the at least one storage vessel and which is open towards one direction, preferably not having a top cover, is arranged in a movable manner in a shell enclosing the compartment. In a closed position, the shell covers the open side of the compartment.

More than one storage vessel can be disposed in the container. Preferably, the storage system comprises at least three storage vessels, more preferably the storage system comprises four storage vessels.

Preferably the fuel is selected from the group consisting of natural gas, shale gas, town gas, methane, ethane, hydrogen, propane, propene, ethylene, carbon dioxide and combinations thereof. In a particularly preferred embodiment, the second gas comprises methane and/or hydrogen to an extent of more than 70 % by volume. For the purpose of the present invention, the term "gas" is used in the interest of simplicity, but gas mixtures are likewise encompassed. The gas can also comprise small amounts of the liquid. The sorption medium can generally be disposed in the at least one storage vessel in form of powder, pellets, shaped bodies or monoliths or combinations thereof. As pellets extrudates are preferred. When the sorption medium is present as a bed of pellets, the ratio of the permeability of the pellets to the smallest pellet diameter is at least between 1 -10^-11 m²/m and 1 -10^-16 m²/m, preferably between 1 -10^"12 m²/m and 1 -10¹⁴ m²/m, and most preferably 1 -10^"13 m²/m.

In an alternative embodiment, it is further preferred that the sorption medium is present in at least one monolith and the at least one monolith has an extension in one direction in space in the range from 5 cm to 50 cm. A monolith is understood to be a shaped body with a greater size compared to known sizes of for example pellets.

The at least one storage vessel can be filled by only one monolith made of the sorption medium, wherein a longest extension of the one monolith in longitudinal direction of the monolith is in the range from 50 cm to 150 cm, more preferably in a range from 80 to 1 10 cm. Preferably a diameter of the one monolith, referring to its cross-section, is in a range from 5 to 50 cm, more prefer- ably from 10 to 15 cm, especially in the case where the storage system comprises four storage vessels. Typically, when the at least one storage vessel comprises only one monolith, the longest extension of the one monolith does not differ from the length in longitudinal direction of the at least one storage vessel by more than 30 %, more preferably by more than 20 %, most preferably by more than 10 % but is always shorter than the length in longitudinal direction of the at least one storage vessel, as the one monolith is arranged within the at least one storage vessel. The same ratios applies for the diameter of the one monolith and the diameter of the at least one storage vessel.

In an alternative embodiment, more than one monolith made of the sorption medium are provid- ed in the at least one storage vessel. Preferably, three to ten monoliths are provided in the at least one storage vessel, most preferably five to six. For this embodiment, a ratio between a longest first extension of each of the at least two monoliths in a radial direction and a longest second extension of each of the at least two monoliths in the axial directions is equal to or greater than 5, axial and radial referring to the at least one storage vessel. Preferably, each of the at least two monoliths has a disk-like shape and the at least two monoliths are arranged one next to the other in longitudinal direction of the at least one storage vessel. Preferably, in a cross-sectional view, the form of the circumference of the at least one storage vessel corresponds to the form of the circumference of each of the at least two monoliths. Assuming a longitudinal central axis of the at least one storage vessel, the at least one monolith comprises an opening in axial direction, axial referring to the central axis of the at least one storage vessel. Preferably, the at least one monolith is completely traversed by the opening. Further, the at least one monolith comprises preferably in addition to the opening hollow channels in the axial direction and a cross-sectional area of each hollow channel is smaller than a cross-sectional area of the opening. Preferably, the longest diameter of the opening is in the range from 0.3 % to 20 % of the longest diameter of the radial cross-sectional area of the at least one storage vessel. It is further preferred when the opening in the at least one or the at least two monoliths is arranged centrally with respect to the at least one storage vessel. The at least one monolith can comprise at least one spacer providing an open space, which is free of the sorption medium, between the monolith and the storage vessel wall or between two of the monoliths.

Preferably, the sorption medium is selected from the group consisting of activated charcoals, zeolites, activated alumina, silica gels, open pore polymer foams, metal hydrides, metal organic frameworks and combinations thereof.

Preferably, the sorption medium is selected from the group consisting of activated charcoals, zeolites, activated alumina, silica gels, open pore polymer foams, metal organic frameworks and combinations thereof, particularly preferably the sorption medium is a metal-organic framework.

Zeolites are crystalline aluminosilicates having a microporous framework structure made up of AI04 and Si04 tetrahedra. Here, the aluminum and silicon atoms are joined to one another via oxygen atoms. Possible zeolites are zeolite A, zeolite Y, zeolite L, zeolite X, mordenite, ZSM (Zeolites Socony Mobil) 5 or ZSM 1 1. Suitable activated carbons are in, particular, those having a specific surface area above 500m² g-¹, preferably about 1500m² g-¹, very particularly preferably above 3000m² g-¹. Such an activated carbon can be obtained, for example under the name Energy to Carbon or MaxSorb. Metal-organic frameworks (MOF) are known in the prior art and are described for example in US 5,648,508, EP-A 0 700 253, M. O'Keeffe et al., J. Sol. State Chem., 152 (2000), pages 3 to 20, H. Li et al., Nature 402, 1 (1999), page 276, M. Eddaoudi et al., Topics in Catalysis 9, (1999), pages 105 to 1 1 1 , B. Chen et al., Science 291 , (2001 ), pages 1021 to 1023, DE-A 101 1 1 230, DE-A 10 2005 053430, WO-A 2007/054581 , WO-A 2005/049892 and WO-A 2007/023134. The metal-organic frameworks (MOF) mentioned in EP-A 2 230 288 A2 are particularly suitable for storage vessels. Preferred metal-organic frameworks (MOF) are MIL-53, Zn-tBu-isophthalic acid, AI-BDC, MOF 5, MOF-177, MOF-505, MOF-A520, HKSUST-1 , IRMOF-8, IRMOF-1 1 , Cu- BTC, AI-NDC, AI-AminoBDC, Cu-BDC-TEDA, Zn-BDC-TEDA, AI-BTC, Cu-BTC, AI-NDC, Mg- NDC, Al-fumarate, Zn-2-methylimidazolate, Zn-2-aminoimidazolate, Cu-biphenyldicarboxylate- TEDA, MOF-74, Cu-BPP, Sc-terephthalate. Greater preference is given to MOF-177, MOF- A520, KHUST-1 , Sc-terephthalate, AI-BDC and AI-BTC. Apart from the conventional method of preparing the MOFs, as described, for example, in US 5,648,508, these can also be prepared by an electrochemical route. In this regard, reference may be made to DE-A 103 55 087 and WO-A 2005/049892. The metal organic frameworks prepared in this way have particularly good properties in respect of the sorption and desorption of chemical substances, in particular gases.

Particularly suitable materials for the adsorption in storage vessels are the metal-organic framework materials MOF A520, MOF Z377 and MOF C300. MOF A520 is based on aluminum fumarate. The specific surface area of a MOF A520, measured by porosimetry or nitrogen adsorption, is typically in the range of from 800 m²/g to

2000 m²/g. The adsorption enthalpy of MOF A520 with regard to natural gas amounts to 17 kJ/mol. Further information on this type of MOF may be found in "Metal-Organic Frameworks, Wiley-VCH Verlag, David Farrusseng, 201 1 ". MOF Z377, in literature also referred to as MOF 177, is based on zinc-benzene-tribenzoate. The specific surface area of a MOF Z377, measured by porosimetry or nitrogen adsorption, is typically in the range from 2000 m²/g to 5000 m²/g. The MOF Z377 typically possesses an adsorption enthalpy between 12 kJ/mol and 17 kJ/mol with respect to natural gas. MOF C300 is based on copper benzene-1 ,3,5- tricarboxylate and for example commercially available from Sigma Aldrich under the trade name Basolite® C300.

WO-A-03/102000 describes in general terms the conversion of metal-organic framework powder into shaped bodies like pellets with a resistance to pressure in the range from 2 to 100 N. In an example pellets which have a resistance to pressure of 10 N are made by means of eccen- trie press.

To form shaped bodies several routes exist, among them molding the pulverulent material alone or in combination with a binder and/or other components into a shaped body, for example by pelletizing. In the context of the present invention, the term "molding" refers to any process known to the expert in the field by which a porous material, i.e. any powder, powdery substance, array of crystallites etc., can be formed into a shaped body that is stable under the conditions of its intended use.

While the step of molding into a shaped body is mandatory, the following steps are optional. The molding may be preceded by a step of mixing. The molding may be preceded by a step of preparing a paste-like mass or a fluid containing the porous material, for example by adding solvents, binders or other additional substances. The molding may be followed by a step of finishing, in particular a step of drying. The step of molding, shaping or forming may be achieved by any method known to a person skilled in the art to achieve agglomeration of a powder, a suspension or a paste-like mass. Such methods are described, for example, in Ullmann's Enzyklopadie der Technischen Chemie, 4th Edition, Vol. 2, p. 313 et seq., 1972, whose respective content is incorporated into the present application by reference.

In general, the following main pathways can be discerned: briquetting or tableting, i.e. mechani- cal pressing of the powdery material, with or without binders and/or other additives, granulating (pelletizing), i.e. compacting of moistened powdery materials by subjecting it to rotating movements, and sintering, i.e. subjecting the material to be compacted to a thermal treatment. The latter is limited for the material according to the invention due to the limited temperature stability of the organic materials.

Specifically, the molding step according to the invention is preferably performed by using at least one method selected from the following group: briquetting by piston presses, briquetting by roller pressing, binderless briquetting, briquetting with binders, pelletizing, compounding, melting, extruding, co-extruding, spinning, deposition, foaming, spray drying, coating, granulating, in particular spray granulating or granulating according to any process known within the processing of plastics or any combination of at least two of the aforementioned methods. Briquetting and/or pelletizing are in particular preferred.

A mixture comprising the porous material can be prepared in a mixer such as intensive mixers, rotary plates, marumerizers, and any other equipment known by a person skilled in the art. Preferred mixers are selected from the group consisting of intensive mixers, rotary plates, ball formers and marumerizers.

The molding can be carried out at elevated temperatures, for example in the range from room temperature to 300°C, and/or at superatmospheric pressure, for example in the range from atmospheric pressure to a few hundred bar, and/or in a protective gas atmosphere, for example in the presence of at least one noble gas, nitrogen, dry air with a relative humidity of preferably less than 45% or a mixture of two or more thereof. The shaped bodies can be formed for example in an excenter press. A compacting force is preferably between 1 kN and 3000 kN, more preferably between 1 kN and 300 kN and most preferably between 10 kN and 150 kN. For higher forces the permeability of the shaped bodies is unnecessarily reduced and for smaller forces no stable shaped bodies are obtained. The smaller the shaped body, the higher the applied force can be chosen. Preferably, the shaped body is produced with a pressing pressure in a range from 100 bar to 1000 bar, more preferably from 400 bar to 600 bar. The applied press can comprise an upper punch for compaction or it can compact from both sides with an upper punch and a lower punch. Further, the pressing can be performed under vacuum in order to avoid damaging the porous solid.

The step of molding can be performed in the presence of binders, lubricants and/or other additional substances that stabilize the materials to be agglomerated. As to at least one optional binder, any material known to an expert to promote adhesion between the particles to be mold- ed together can be employed. A binder, an organic viscosity-enhancing compound and/or a liquid for converting the material into a paste can be added to the pulverulent material, with the mixture being subsequently compacted. Suitably binders, lubricants or additives are, for example, aluminum oxide or binders comprising aluminum oxide, as described, for example, in WO 94/29408, silicon dioxide, as described, for example, in EP 0 592 050 A1 , mixtures of silicon dioxide and aluminum oxide, as described, for example, in WO 94/13584, clay minerals as described, for example, in JP 03-037156 A, for example montmorillonite, kaolin, bentonite, hallosite, dickite, nacrite and anauxite, alkoxysilanes as described, for example, in EP 0 102 544 B1 , for example tetraalkoxysilanes such as tetra- methoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, or, for example, trial- koxysilanes such as trimethoxysilane, triethoxysilane, tripropoxysilane, tributoxysilane, alkoxyti- tanates, for example tetraalkoxytitanates such as tetramethoxytitanate, tetraethoxytitanate, tetrapropoxytitanate, tributoxytitanate, or, for example, trialkoxytitanates, such as trimethoxyti- tanate, triethoxytitanate, tripropoxytitanate, tributoxytitanate, alkoxyzirconates, for example tetraalkoxyzirconates such as tetramethoxyzirconate, tetraethoxyzirconate, tetrapropoxyzir- conate, tetrabutoxyzirconate, or, for example, trialkoxyzirconates such as trimethoxyzirconate, triethoxyzirconate, tripropoxyzirconate, tributoxyzirconate, silica sols, amphiphilic substances, copper, graphite, ascorbyl palmitate, expanded natural graphite (ENG), silicon carbide, polysac- charides, fatty acids, alcyl silicon resins , metal-organic framework materials, where the metal- organic framework has a layer composition, or mixtures thereof.

Suitable binders are for example commercially available under trade names like Pural® SB (aluminum oxide), Ludox® AS 40 (colloidal silica), or Silres® MSE100 (methyl and methoxy groups containing polysiloxane).

Preferred binder, lubricants or additives are graphite, stearic acid, magnesium stearate, copper platelets, silicon carbide, expanded natural graphite (ENG), ascorbyl palmitate, polysaccharides, for example commercially available as Zusoplast PS1 , aluminium oxide, for example commercially available as Pural SB or mixtures thereof.

In a preferred embodiment, the shaped body comprises at least 1 % by weight of a binder and/or lubricant, which are selected from the group consisting of inorganic oxide, clay, concrete and graphite. Preferably the shaped body comprises less than 10% by weight of a binder and/or lubricant and most preferably, the shaped body comprises between 1.5% and 5% by weight of a binder and/or lubricant and most preferably between 2.5% and 3.5%. Alternatively, no binder or lubricant is used.

Further additives which can be used are, inter alia, amines or amine derivatives such as tetraalkylammonium compounds or amino alcohols and carbonate-comprising compounds, e.g. calcium carbonate. Such further additives are described, for instance, in EP 0 389 041 A1 , EP 0 200 260 A1 or WO 95/19222. Further, pore-forming agents such as organic polymers, preferably methylcellulose, polyethylene oxide or mixtures thereof can be added. Preferably, the shaped body comprises from 1 % to 50% by weight of further additives and more preferably from 3% to 20% by weight. Alternatively, no further additives are used. The term vehicle includes but shall not be limited to cars, trucks, ships, airplanes, motorcycles, three-wheelers and the like. Preferably, the vehicle is a three-wheeler. The inventive solution is in particular advantageous for three-wheelers as the amount of heat available from the exhaust gas is comparatively small, but can still be used with the inventive system due to a spatial proximity of the combustion engine and the storage system.

Brief description of the drawings

The present invention is described in more detail at hand of the accompanying drawings in which:

Figure 1 shows a storage system according to the invention;

Figure 2 shows a cross-sectional view of a storage system according to the invention comprising one storage vessel;

Figure 3 shows a storage system according to the invention comprising four storage vessels and

Figure 4 shows a schematic view of a vehicle according to the invention.

Figure 1 shows a storage system 1 according to the invention comprising a container 3 and a storage vessel 7, which are both mounted in a horizontal position. The container 3 has a container wall 31 and a first interior 5 and the storage vessel 7 has a second interior 9, which is filled with a sorption medium 17. The second interior 9 is enclosed by a storage vessel wall 15. The storage system 1 further comprises two boxes 21 , which are deposited within the container 3 and which at least partly enclose the storage vessel 7. Each of the two boxes 21 comprises a third interior 23, which is limited by the storage vessel wall 15 and a box wall 25.

Due to the two boxes 21 a path for a stream 19 of a first gas through the container 3 is determined. The first gas enters the container 3 via an inlet 1 1 and leaves the container 3 via an outlet 13. Within the container 3, a flow direction of the stream 19 changes between a horizontal direction, an upward direction and a downward direction.

The storage vessel 7 has a radial cross-sectional circumference 27 and a length in longitudinal direction 29. The two boxes 21 enclose the storage vessel 7 in a way that over the length in longitudinal direction 29 of the storage vessel 7 only part of the storage vessel wall 15 is cov- ered by the boxes 21 . In the positions where the boxes 21 are located, the complete cross- sectional circumference 27 of the storage vessel 7 is covered by the box 21.

Referring to the length in longitudinal direction 29, the boxes 21 are arranged serially. Concern- ing the vertical position of the boxes 21 , the boxes 21 are arranged with an alternating off-set, wherein a first of the two boxes 21 touches a top part 33 of the container wall 31 and a second of the two boxes 21 touches an undermost part 35 of the container wall 31.

The two boxes 21 are of the same size and due to their deviating vertical positions, a gap 37 is generated between each of the two boxes 21 and the undermost part 35 of the container wall 31 and the top part 33 of the container wall 31 , respectively. In order to provide the gap 37 and to hold each of the two boxes 21 in a fixed position in the container 3, the gap 37 is flanked by two supports 39. Figure 2 shows a cross-sectional view of the storage system 1 according to figure 1 . The radial cross-section is represented for a position, at which the first of the two boxes 21 encloses the storage vessel 7. In this illustrative embodiment, the gap 37 has a rectangular form and the box 21 is hold by the supports 39 at the sides of the gap 37. Figure 3 shows a cross-sectional view of a storage system 1 according to the invention, which comprises four storage vessels 7. A box 21 is traversed by all four storage vessels 7, which are arranged in parallel to each other. Despite the presence of four storage vessels 7 instead of only one storage vessel 7 as represented in figure 1 , this storage system 1 corresponds to the storage system 1 according to figure 1 .

Figure 4 shows a vehicle 2 according to the invention comprising a storage system 1 and a combustion engine 4. In this illustrative embodiment, the vehicle 2 is a three-wheeler. A second gas comprising a fuel for the combustion engine 4 is led from at least one storage vessel 7, being part of the storage system 1 , through a fuel pipe 43 to the combustion engine 4. The second gas is combusted in the combustion engine 4 leading to a first gas comprising an exhaust gas, which is formed in the combustion engine 4. The combustion engine 4 supplies energy to a drive axle 41 of the vehicle 2. The first gas is conducted from the combustion engine 4 via a connecting pipe 45 back to the storage system 1 , where the first gas passes through the first interior 5 surrounding the at least one storage vessel 7, transferring heat from the combustion carried out in the combustion engine 4 to the second gas still stored in the second interior 9 by means of the sorption medium 17. The first gas is conducted out of the storage system 1 via an exhaust pipe 47 to the surrounding of the vehicle 2, wherein the first gas possesses a lower temperature in the exhaust pipe 47 than in the connecting pipe 45. The exhaust pipe 47 may further comprise an exhaust gas catalytic converter.

Comparative example A three-wheeler comprises a storage system for the storage of natural gas, which is used as fuel. The storage system comprises four cylindrical storage vessels with storage vessel walls made of aluminum. The four storage vessels are arranged in parallel to each other in a horizontal position, forming a bundle of two upper storage vessels above two lower storage vessels. Each of the four storage vessels has an inner volume of 10 L, a length in longitudinal direction of 1 m and a diameter of 14 cm. The four storage vessels are filled with pellets of the MOF material C300, providing a bulk density of 500 g/L and an adsorption enthalpy, referring to natural gas, of 4 MJ. A maximum storage pressure in the storage vessels accounts to 60 bar. The four storage vessels are enclosed by a container of a cuboid form, having a length in longitudinal direction of 1 m and a height and width of 32 cm, respectively. The container wall is made of aluminum and has a thickness of 2 mm. A first gas, which is the exhaust gas of the combustion engine, enters the container at a first end and leaves the container at an opposing second end, wherein the distance between the first and the second end corresponds to the length in longitudinal direction of the container.

The three-wheeler has a fuel consumption of 1 .5 kg/h in average and thus an average mass flow of 1.5 kg/h is conducted from the storage vessels to the combustion engine and back to the container of the storage system.

While driving, the second gas, which is the fuel, desorbs from the sorption medium and therefore the temperature in the storage vessels decreases.

Without heating of the storage vessels, the mean temperature over the total volume of the stor- age vessels is -30°C when the storage vessels are continuously emptied until the pressure in the storage vessels is 4 bar.

Leading the first gas through the container without any further means for flow control, such as boxes, heat is predominantly transferred to the upper two storage vessels. On average, the part of the first gas reaching the lower two storage vessels has a temperature which is up to 200°C lower compared to the part of the first gas reaching the upper two storage vessels.

Further, already after a first quarter of the length in longitudinal direction of the container in flow direction of the first gas, the temperature of the first gas equals the temperature of the storage vessels.

Locally, especially in proximity to the inlet, where the first gas enters the container, the temperature at the storage vessel wall reaches up to 500 K, which can cause damage to the storage vessel wall, depending on its material. In proximity to the outlet, the temperature at the storage vessel wall is -15°C and the mean temperature over the total volume of the storage vessels is -10°C. 20 % by weight of the second gas, referring to the maximum storage capacity at 60 bar, have to remain in the storage vessel in order to maintain a minimum pressure level of 4 bar within the storage vessel being required for operation of the combustion engine. Example

The three-wheeler as described for the comparative example now comprises a storage system according to the inventions, which differs from the storage system according to the comparative example in that the storage system according to the invention additionally comprises five cuboid boxes in the container. The five boxes are arranged serially in longitudinal direction of the four storage vessels with a vertical offset to each other. Three adjacent lateral surfaces of each box are in sealing contact with the container wall, preventing a passage of the first gas along the storage vessel wall in longitudinal direction. A gap with a height of 1 cm is provided at a fourth lateral surface of each box at the top part or the undermost part of the container wall, respec- tively. The length of each box is 18.8 cm and a distance between two adjacent boxes is 1 . Thus, a flow channel with a width of 1 cm is provided in cross-flow over the four storage vessels. The flow path of the first gas through the container is elongated from 1 m to 2.2 m in comparison to the comparative example. A mean velocity of the stream of the first gas in the container is now 0.2 m/s. The residence time of the first gas in the container is 10 seconds at 50 % of the full load of the combustion engine.

The pressure loss in the container, substantially caused by the additional five boxes, is less than 10 mbar at full load of the combustion engine. The temperature of the first gas is 600 K at the outlet of the combustion engine. By a temperature reduction concerning the first gas from 600 K to 293 K, a heat flow of 130 watts is available.

1 10 watts are required to compensate for the temperature reduction due to desorption, when the storage pressure is reduced to 4 bar in the storage vessels and a mean temperature of 50° is established in the storage vessels.

Applying the five boxes for flow control in the container, the temperature of the first gas equals the temperature of the storage vessel wall not bevor reaching the last quarter, referring to the length in longitudinal direction, of the container. Local hotspots at the storage vessel wall in proximity to the inlet of the first gas show a reduced temperature of only 350 K, compared to the comparative example. In proximity to the outlet, the temperature at the storage vessel wall is 20°C. The mean temperature in the storage vessels, after desorption of the second gas and when the minimum storage pressure of 4 bar in the storage vessels is reached, is now 50°C.

Only 5 % by weight of the second gas, referring to the maximum storage capacity at 60 bar, are still entrapped in the storage vessel for providing the required minimum pressure level. List of reference numbers

1 storage system

2 vehicle

3 container

4 combustion engine

5 first interior

7 storage vessel

9 second interior

1 1 inlet

13 outlet

15 storage vessel wall

17 sorption medium

19 stream

21 box

23 third interior

25 box wall

27 cross-sectional circumference

29 length in longitudinal direction of the at least one storage vessel

31 container wall

33 top part

35 undermost part

37 gap

39 support

41 drive axle

43 fuel pipe

45 connecting pipe

47 exhaust pipe

Claims

1 . A vehicle (2) comprising a storage system (1 ) and a combustion engine (4), the storage system (1 ) comprising a container (3) with a first interior (5) and at least one storage ves- sel (7) with a second interior (9), wherein the at least one storage vessel (7) is disposed in the container (3) and the at least one storage vessel (7) comprises a storage vessel wall (15) separating the first interior (5) from the second interior (9), wherein the first interior (5) comprises a first gas and the second interior (9) comprises a second gas and a sorption medium (17), and the first gas comprises an exhaust gas from the combustion engine (4) and the second gas comprises a fuel for the combustion engine (4), wherein the first interior (5) comprises at least two boxes (21 ), each comprising a third in- terior (23) and a box wall (25) separating the third interior (23) from the first interior (5), and wherein the at least two boxes (21 ) partly enclose the at least one storage vessel (7), each of the at least two boxes (21 ) encloses the at least one storage vessel (7) at least partly, referring to a cross-sectional circumference (27) of the at least one storage vessel (7), and each of the at least two boxes (21 ) encloses the at least one storage vessel (7) only partly, referring to a length (29) in longitudinal direction of the at least one storage vessel (7).

2. The vehicle (2) according to claim 1 , wherein the container (3) comprises a container wall (31 ) with a top part (33) and an undermost part (35), at least one of the at least two boxes

(21 ) touches the top part (33) of the container wall (31 ) and at least one of the at least two boxes (21 ) touches the undermost part (35) of the container wall (31 ), and for every two adjacent boxes (21 ), a first of the two adjacent boxes (21 ) touches the top part (33) of the container wall (31 ) and a second of the two adjacent boxes (21 ) touches the undermost part (35) of the container wall (31 ).

3. The vehicle (2) according to claim 2, wherein a first gap (37) is provided between the first of the two adjacent boxes (21 ) and the undermost part (35) of the container wall (31 ) and a second gap (37) is provided between the second of the two adjacent boxes (21 ) and the top part (33) of the container wall (31 ).

4. The vehicle (2) according to any of claims 1 to 3, wherein the at least two boxes (21 ) are arranged serially in longitudinal direction of the at least one storage vessel (7).

The vehicle (2) according to any of claims 1 to 4, wherein each of the at least two boxes (21 ) encloses the at least one storage vessel (7) completely, referring to the cross- sectional circumference (27) of the at least one storage vessel (7).

The vehicle (2) according to any of claims 1 to 5, wherein the container (3) comprises an inlet (1 1 ) and an outlet (13), the inlet (1 1 ) and the outlet (13) being arranged on opposing sides of the container wall (31 ).

The vehicle (2) according to any of claims 1 to 6, wherein the storage system (1 ) compris es at least three storage vessels (7).

8. The vehicle (2) according to any of claims 1 to 7, wherein the container wall (31 ) comprises a double wall.

The vehicle (2) according to any of claims 1 to 8, wherein the vehicle (2) is a three wheeler.

The vehicle (2) according to any of claims 1 to 9, wherein the sorption medium (17) is selected from the group consisting of activated charcoals, zeolites, activated aluminia, silica gels, open-pore polymer foams, metal hydrides, metal-organic frameworks (MOF) and combinations thereof.

1 1 . The vehicle (2) according to any of claims 1 to 10, wherein the sorption medium (17) is present in form of at least one monolith and the at least one monolith has an extension in one direction in space in a range from 5 cm to 50 cm.

12. The vehicle (2) according to any of claims 1 to 1 1 , wherein the fuel is selected from the group consisting of natural gas, shale gas, town gas, methane, ethane, hydrogen, propane, propene, ethylene, carbon dioxide and combinations thereof.

13. A process for operation of a vehicle (2) comprising a storage system (1 ) and a combustion engine (4), the storage system (1 ) comprising a container (3) with a first interior (5) and at least one storage vessel (7) with a second interior (9), the at least one storage vessel (7) is disposed in the container (3) and the at least one storage vessel (7) comprises a stor- age vessel wall (15) separating the first interior (5) from the second interior (9), wherein the first interior (5) comprises a first gas, and the second interior (9) comprises a second gas, which is contacted with a sorption medium (17), wherein at least part of the second gas is conducted from the second interior (9) to the combustion engine (4) and the second gas is combusted in the combustion engine (4) to form the first gas, and wherein the first gas is conducted from the combustion engine (4) into the first interior (5) and a stream of the first gas is led through the first interior (5) in cross-flow to a longitudinal direction of the at least one storage vessel.

The process according to claim 13, wherein the first gas has a temperature of at least 300°C when entering the first interior (5).

The process according to claim 13 or 14, wherein the second gas is stored in the at least one storage vessel (7) at a pressure of up to 100 bar.