WO2016065427A1 - Reducing axial temperature gradients - Google Patents

Reducing axial temperature gradients Download PDF

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Publication number
WO2016065427A1
WO2016065427A1 PCT/AU2015/050683 AU2015050683W WO2016065427A1 WO 2016065427 A1 WO2016065427 A1 WO 2016065427A1 AU 2015050683 W AU2015050683 W AU 2015050683W WO 2016065427 A1 WO2016065427 A1 WO 2016065427A1
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WO
WIPO (PCT)
Prior art keywords
hydrogen storage
solid state
temperature
vessel
state hydrogen
Prior art date
Application number
PCT/AU2015/050683
Other languages
French (fr)
Inventor
Stephanie Maya Moroz
Jordan Christopher Pierce
Matthew Campbell Greaves
Krista DUMUR
Original Assignee
Hydrexia Pty Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AU2014904355A external-priority patent/AU2014904355A0/en
Application filed by Hydrexia Pty Ltd filed Critical Hydrexia Pty Ltd
Publication of WO2016065427A1 publication Critical patent/WO2016065427A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C11/00—Use of gas-solvents or gas-sorbents in vessels
    • F17C11/005—Use of gas-solvents or gas-sorbents in vessels for hydrogen
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/32—Hydrogen storage
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P90/00—Enabling technologies with a potential contribution to greenhouse gas [GHG] emissions mitigation
    • Y02P90/45—Hydrogen technologies in production processes

Definitions

  • the invention relates to a hydrogen storage unit which can be used for solid metal hydride absorption/adsorption and desorption of hydrogen and particularly a unit including a means for reducing the temperature gradients along the axis of the unit.
  • Hydrogen may be stored for use as a fuel or for other purposes.
  • Some hydrogen storage units include an enclosed volume carrying a bed of hydrogen storage material such as catalysed MgH 2 or other high temperature metal hydride (and various alloys).
  • hydrogen storage material such as catalysed MgH 2 or other high temperature metal hydride (and various alloys).
  • Typical hydrogen storage materials must be held within a narrow band of operating temperatures in the vicinity of 365°C to operate effectively.
  • a temperature gradient of less than 20°C is required within the bed of a hydrogen storage material during absorption/adsorption in order to ensure all the material absorbs/adsorbs the full amount of hydrogen it is chemically capable of. If the temperature of the coldest material is more than 20°C below the temperature of the hottest material in the bed, the catalyst will chemically react with the hydrogen to form a hydride, thereby decreasing its effectiveness. If this temperature difference is significantly more than 20°C, the resulting kinetics will be substantially slowed and the absorption/adsorption will not proceed to completion in a practical time.
  • a hydrogen storage system will be exposed to duty cycles varying from full desorption flow capacity of the system to periods of inactivity for an extended period of time.
  • a hot and partially desorbed cylinder is susceptible to migration of solid hydrogen from the hot zones of the cylinder to the cold zones if it is paused. If the cold zones of the cylinder drop below the equilibrium temperature of absorption, free molecules of gaseous hydrogen will be consumed, with the hot zones breaking its metal hydride bonds to account for the drop in pressure caused by absorbing zones.
  • the first and second ends of the cylinder although having insulating layers at both ends, will cool down extensively over time, as compared to the middle of the bed which has temperature staying almost constant throughout, thus resulting in a large temperature gradient along the length of the cylinder.
  • Prior art discusses methods of obtaining excellent thermal conductivity and high diffusion rate of hydrogen by having a thermal management controller that determines whether the cylinder is absorbing or desorbing and from that, deciding whether to cool or heat up the cylinder by routing to different heat exchangers.
  • Prior art also discusses the use of bundles of filaments using metal, synthetic high polymer, allowing metal hydride to absorb and desorb hydrogen in the spaces between the filament bundles. The filaments are capable of transferring heat and improve the thermal conductivity between the hydrides and or between the hydrides and the cylinder.
  • Prior art also discusses having small chambers extending in the axial direction of the cylinder with a hydrogen permeable carbon fibre sheet.
  • a plurality of aluminium fins are also used, with the fins projecting from the inner wall towards the centre of the cylinder, parallel to the axis of the cylinder. These fins are capable of distributing heat from the middle of the bed to other parts of the cylinder.
  • the thermal conductivity can also be improved by having a hydrogen storage mixture made up of hydrogen storage alloy granules and metal fibres and/or non-hydrogen-absorbing alloy fibres.
  • Prior art also discusses a possible method of improving the decline in thermal conductivity with the use of a compact of hydrogen adsorption alloy as the material matrix, which is composed of a metal hydride in which all surfaces of fine particles of hydrogen absorption alloy are completely coated with a dissimilar metal by plating, without affecting reactivity and a porous material of high thermal conductivity is infiltrated with the fine particles of alloy to be formed into a compact by compression moulding.
  • An important design consideration for hydrogen storage cylinders is to achieve high temperature uniformity along the axis of the cylinder. This promotes even desorption of the solid state hydrogen storage material, such as a metal hydride bed, and minimises migration of solid hydride from hot zones to cold zones (through hydride formation occurring due to the transfer of hydrogen from hotter zones to cooler zones, and the subsequent absorption of hydrogen in cooler zones) during periods of inactivity. As a result of "end effects" (defined as higher relative heat loss at the ends of the vessel to the middle of the vessel), the temperature at each end of the cylinder tends to be much lower than the middle of the vessel.
  • a solid state hydrogen storage and/or supply vessel comprising: a cylindrical shell portion having a first end and a second end, the first end and the second end defining an axis therebetween, the cylindrical shell having at least one inner compartment for a solid state hydrogen storage material; a fluid communication port for transmission of hydrogen gas to the at least one compartment; a heating element for heating the hydrogen storage material to desorb hydrogen from the hydrogen storage material; a temperature control system for monitoring temperature at locations corresponding to at least a first axial point and a second axial point and to provide a temperature profile along the axis; a heating apparatus for heating the solid state hydrogen storage material and being responsive to the temperature control system to maintain the temperature profile within a set temperature range.
  • solid state hydrogen storage and/or supply vessel comprising: a cylindrical shell portion having a first end and a second end, the first end and the second end defining an axis therebetween, the cylindrical shell having at least one compartment for a solid state hydrogen storage material; a fluid communication port for transmission of hydrogen gas to the at least one inner compartment; a heating element for heating the hydrogen storage material to desorb hydrogen from the hydrogen storage material; a temperature control system for monitoring temperature at locations corresponding to at least a first axial point and a second axial point and to provide a temperature profile along the axis; and a heating apparatus for heating the solid state hydrogen storage material at least at locations near or corresponding to at least the first axial point and the second axial point, the heating apparatus being responsive to the temperature control system to maintain the temperature profile within a set temperature range.
  • the temperature range is about 10°C. More preferably the temperature range is about 5°C.
  • the hydrogen storage and/or supply vessel is cylindrical in shape, and may be capped at either or both ends with an end cap such as a rounded, domed, or hemispherical cap.
  • the axis runs from a first end cap and through the cylindrical shell portion defined by a wall to the second end cap, such that the axis is oriented parallel to the cylindrical walls of the cylindrical shell portion.
  • the inner compartment of the cylindrical shell contains the hydrogen storage material in a bed of material, the heating element heating the bed to desorb hydrogen from the hydrogen storage material.
  • the heating apparatus is configured for heating the solid state hydrogen storage material along the axis at least at locations near or corresponding to at least the first axial point and the second axial point.
  • the heating apparatus acts as a differential heating apparatus to balance the temperature profile along the axis.
  • the heating apparatus is external to the cylindrical shell portion. In an alternative embodiment, the heating apparatus is internal to the cylindrical shell portion. The skilled addressee will appreciate that whether the heating apparatus is internal or external will depend on the nature of the heating apparatus and the specifics of the design of the vessel.
  • the vessel further comprises an inner compartment for containing the solid state hydrogen storage material, the inner compartment having an internal wall and an outer wall, and being in fluid communication with the fluid communication port; wherein a peripheral space is defined between the cylindrical shell portion and the inner compartment, and the heating apparatus is located external to the outer wall of the inner compartment. That is, the heating apparatus is located within the peripheral space.
  • the heating apparatus may be located external to the vessel, internal to the vessel, in the peripheral space, or in a combination of these locations.
  • the heating apparatus is fitted at different positions along the axis at least at a location near or corresponding to the first axial point and/or a location near or corresponding to the second axial point.
  • the heating apparatus may include a plurality of heating units each of which may be independently located external to the vessel, internal to the vessel, in the peripheral space, or in a combination of these locations depending on the design of the vessel.
  • the heating units provide heat energy to a location near or corresponding to the first axial point and a location near or corresponding to the second axial point.
  • the heating units may be electrical heaters or oil heaters.
  • the heating apparatus comprises at least one band heater fitted to the location corresponding to the first axial point and at least one band heater fitted to a location corresponding to the second axial point.
  • the heating apparatus includes an oil heater.
  • the oil heater may include heating pipes that pass through the solid state hydrogen storage material at various locations, for example heating pipes may project into the solid state hydrogen storage material at a location near or corresponding to the first axial point and/or at a location near or corresponding to the second axial point. Heating oil may then be caused to flow through these pipes to provide thermal energy at or near the first and/or second axial points.
  • heating pipes may be located external to the vessel. Heating oil is circulated through the heating pipes to control the temperature as necessary.
  • the heating pipes may be attached to an external wall of the vessel at a location near or corresponding to the first axial point and/or at a location near or corresponding to the second axial point. Heating oil may be caused to flow through these pipes to provide thermal energy at or near the first and/or second axial points.
  • the oil heater may comprise pipes that pass through the peripheral space external to the outer wall of the inner compartment.
  • the pipes may be in contact with the outer wall of the inner compartment at a location near or corresponding to the first axial point and/or at a location near or corresponding to the second axial point. Heating oil may be caused to flow through these pipes to provide thermal energy at or near the first and/or second axial points.
  • the heating apparatus comprises an oil heater and an electrical band heater.
  • the oil heater provides heat energy to the solid state hydrogen storage material internal to the vessel and the electrical band heater provides heat energy to the solid state hydrogen storage material from external to the vessel.
  • the oil heater provides heat energy to the solid state hydrogen storage material internal to the vessel and at least one electrical band heater provides heat energy to the solid state hydrogen storage material from a peripheral space within the vessel.
  • the oil heater, the electrical band heater or heaters, or both may provide heat energy to a location near or corresponding to the first and/or second axial points
  • solid state hydrogen storage and/or supply vessel to store and supply hydrogen.
  • Figure 1 shows the temperature profile along the axis of a solid state hydrogen vessel according to the present invention.
  • Figure 2 shows the temperature profile along the axis of a solid state hydrogen vessel relying on external insulation.
  • Figure 3 shows the temperature profile along the axis of a solid state hydrogen vessel having insulated front and rear domes.
  • Figure 4 shows the temperature profile along the axis of a solid state hydrogen vessel having copper extrusions and internal insulation.
  • Figure 5 shows the temperature profile along the axis of a solid state hydrogen vessel having aluminium extrusions along the length of the vessel.
  • Figure 6 shows a plot of temperature vs. time for the middle and each end of a solid state hydrogen vessel relying on external insulation during periods of inactivity.
  • the present invention is directed to a solid state hydrogen storage and/or supply cylinder that is able to maintain a high degree of temperature uniformity along the axis of the cylinder.
  • One of the problems with the hydrogen storage cylinders of the prior art is that due to higher relative heat loss from the ends of the storage vessel compared with the middle portion of the vessel, the temperature at each end of the cylinder can be much lower than the temperature at the centre of the vessel.
  • Solid state hydrogen storage and/or supply vessels typically store hydrogen in an adsorbed solid form as a metal hydride. Accordingly, hydrogen storage and/or supply vessels typically comprise a solid metal-hydride bed, wherein the metal-hydride bed may include one or more high temperature metal hydrides. Hydrogen can then be released through the application of heat which drives a hydrogen desorption reaction, releasing hydrogen. Thus, a heating element may be provided to heat the hydrogen storage material to desorb hydrogen from the metal- hydride bed. The hydrogen can then be supplied to the appropriate location.
  • hydrogen storage and/or supply vessels comprise a cylindrical centre portion and dome ends.
  • the dome ends are usually heavily insulated to minimise loss of heat through the ends of the vessel.
  • the main pathway for heat loss is through the vessel shell, particularly at either end of the vessel shell.
  • Hydrogen absorption and desorption are temperature dependent. Therefore, the establishment of a temperature profile exhibiting a significant temperature differential between the centre of the vessel and the ends of the vessel can have a negative impact on hydrogen absorption and desorption.
  • a hot and partially desorbed cylinder is susceptible to migration of solid hydrogen from the hot zones of the cylinder to the cold zones if it is paused. If the cold zones of the cylinder drop below the equilibrium temperature of absorption, free molecules of gaseous hydrogen will be consumed, with the hot zones breaking its metal hydride bonds to account for the drop in pressure caused by absorbing zones. Maintaining a degree of uniformity to the temperature profile along the axis of the hydrogen storage and/or supply vessel is therefore important for promoting even desorption of hydrogen and minimises migration of the solid hydrogen from the hot zones to the cold zones during periods of inactivity.
  • the present invention is directed towards a solid state hydrogen storage and/or supply vessel comprising a means for axial heating.
  • the means for axial heating can be activated to attenuate a temperature differential in the temperature range along the axis of the hydrogen storage vessel. For example, if a temperature difference results due to one of the ends of the vessel being cooler than the centre of the vessel, heat energy can be applied to that end of the vessel to raise the temperature and thus reduce the temperature differential between that end of the vessel and the centre of the vessel.
  • a solid state hydrogen storage and/or supply vessel comprising: a cylindrical shell portion having a first end and a second end, the first end and the second end defining an axis therebetween; the cylindrical shell having at least one inner compartment for a solid state hydrogen storage material; a fluid communication port for transmission of hydrogen gas to the inner compartment; a heating element for heating the hydrogen storage material to desorb hydrogen from the hydrogen storage material; a temperature control system for monitoring a temperature at locations corresponding to at least a first axial point and a second axial point; a heating apparatus for heating locations corresponding to the first axial point and the second axial point, the heating apparatus being responsive to the temperature control system to maintain the temperature profile within a set temperature range.
  • the vessel can be filled by supplying hydrogen at pressure to the fluid communication port whereby the hydrogen is absorbed by the hydrogen storage material.
  • the hydrogen storage material is heated by heating elements within the hydride bed.
  • hydrogen flows out of the vessel.
  • the inner compartment has an internal wall and an outer wall, and is in fluid communication with the fluid communication port.
  • the inner compartment of the storage unit is constructed to contain hydrogen storage material.
  • the cylindrical shell portion may act as an outer vessel that may surround at least a substantial portion of, or totally contain the inner compartment and may be spaced therefrom to define a peripheral volume around the inner compartment.
  • the inner compartment may include a compartment wall and end pieces, the end pieces engaging the outer vessel wall to support the inner compartment within the outer vessel.
  • the compartment wall is preferably cylindrical and the end pieces conical, frusto-conical or hemispherical in shape.
  • the inner compartment wall is substantially cylindrical and the cylindrical shell portion forms an outer vessel wall that totally encloses the inner compartment.
  • the outer vessel may include a substantially cylindrical interior wall concentrically surrounding the inner compartment defining a peripheral volume which is an annular space between the inner compartment and the outer vessel.
  • the inner compartment fluidly communicates with the peripheral volume around the inner compartment during receipt of hydrogen so that the peripheral volume is pressurised.
  • the heating means of locations along the axis may be achieved by application of heat external to the outer wall of the inner vessel.
  • band heaters may be fitted to the ends of the outer wall of the inner vessel and used to eliminate any significant temperature difference along the axial length of the inner vessel. Alternatively, the heating may be applied at locations external to the vessel, on the vessel shell.
  • the temperature of the hydrogen storage and/or supply vessel in the centre of the vessel is monitored with a temperature control system, such as those that are standard in the art.
  • a separate independent temperature control system monitors the temperature at the ends of the cylinder shell with a temperature control system, such as those that are standard in the art.
  • the temperature control systems may be a closed loop system to allow a quick response to changes in the environment to ensure that the temperature profile is maintained within specified parameters. It is preferred that the temperature gradient between an end of the vessel and the centre of the vessel is maintained within a temperature range of 10°C. For example, the temperature difference between any one end of the vessel and the temperature at the centre of the vessel is less than about 10°C. It is also preferred that the temperature profile over the axis of the vessel does not exceed a temperature differential of greater than 10°C.
  • the hydrogen storage material is magnesium hydride
  • this operating temperature is dependent on a number of parameters such as the type of solid state storage material used, or the system operating conditions such as the internal pressure of the system.
  • the operating temperature for a hydrogen storage and supply system is going to be between 50°C and 450°C, depending on the solid state hydrogen storage material and the operating conditions of the system.
  • a temperature control system is employed.
  • This temperature control system monitors the internal temperature at the centre of the hydride bed and interfaces with a heating element to maintain the temperature at approximate 365°C. While this is effective at maintaining the temperature at the centre of the vessel, it can be ineffective at maintaining the temperature of the hydride bed at the ends of the hydride bed. As discussed, end effects result in the ends of the vessel cooling more rapidly than the centre of the vessel. Thus hydride material located further from the vessel centre cools more rapidly than that located nearer the centre, with the hydride material at the ends cooling most rapidly. To address this issue, additional temperature control systems are employed. In this embodiment, separate independent temperature control systems are used to maintain the ends of the cylinder shell at a constant temperature of approximately 365°C. The presence of this additional temperature control system lessens the impact of the preferential cooling due to "end effects".
  • each of the temperature control systems may be integrated with a temperature control system that regulates the temperature at the centre of the hydride bed.
  • each of the temperature control systems i.e. the first temperature control system which regulates the temperature at the centre of the hydride bed, the second temperature control system which regulates the temperature at a first end of the hydride bed, and the third temperature control system which regulates the temperature at a second end of the hydride bed
  • the heating means may be achieved by application of heat to an appropriate location.
  • band heaters are fitted to the ends of the vessel shell and used to suppress any significant temperature difference along the axial length of the hydrogen storage material.
  • a closed control loop on the band heaters will result in a quick response to changes in the environment to ensure the temperature gradient is always within an acceptable range.
  • the use of local band heaters act as an active control to heat up the ends of the cylinder, preventing the axial temperature gradient from being outside the specified range, and at the same time ensuring that the invention is cost efficient and easy to fabricate, without interfering with the internals of the cylinder.
  • a person skilled in the art will appreciate that other forms of applying heat to the vessel may also be used. These other forms may include suitable internal means or other suitable external means.
  • the present invention may be used with solid state hydrogen cylinder packs for replacement of compressed gas MCP's or with solid state hydrogen storage system packaged in a shipping container.
  • the present invention may also be used in a solid state hydrogen storage systems: for interface with a high temperature fuel cell for waste heat recovery, for interface to an internal combustion engine for waste heat utilisation, for refuelling applications, or for PEM fuel cell applications.
  • the present invention is applicable in any situation that includes hydrogen storage or hydrogen supply and where there is a desire to minimise an axial temperature difference.
  • Figure 1 shows the axial temperature profile of a hydrogen storage and/or supply vessel
  • the hydrogen storage and/or supply vessel 100 including a metal hydride storage material 102 according to the present invention.
  • the hydrogen storage and/or supply vessel 100 is fitted with external band heaters 104 and 106 at each end of the cylindrical shell portion of the vessel.
  • the temperature differential between the end of the vessel shell and the centre of the vessel is maintained within approximately 1°C.
  • the hydrogen storage and/or supply vessel includes insulation 108 and 110 in the domed ends of the cylindrical shell portion and insulation 112 external to the cylindrical shell portion.
  • FIGS 2, 3, 4 and 5 show the axial temperature profiles of hydrogen storage and/or supply vessels 200, 300, 400, and 500 each including metal hydride 202, 302, 402, and 502.
  • hydrogen storage and/or supply vessels 200, 300, 400, and 500 use prior art strategies to maintain heat.
  • the vessel 200 of Figure 2 has external insulation 212 and H 2 gas 213 is free to accumulate in the domed ends;
  • the vessel 300 of Figure 3 has insulated front and rear domes 308 and 310 as well as external insulation 312;
  • the vessel 400 of Figure 4 has copper extrusions 414, internal insulation 408 and 410, and external insulation 412;
  • the vessel 500 of Figure 5 has aluminium extrusions 516 along the length of the vessel 500 as well as both internal insulation 508 and 510, and external insulation 512.
  • the temperature differentials exceed 10°C.
  • Figure 2 where only external insulation was utilised exhibits the greatest temperature differential of about 46°C.
  • the present invention both minimises the temperature differential of the temperature range in a temperature profile, and provides a simple and cost effective way of doing so. While other prior art mechanisms may also reduce the temperature differential in comparison with only using external insulation, the prior art approaches are difficult to implement with regards to both retrofitting an existing vessel, and fabricating new vessels. For example, the presence of additional fins or metal extrusions inside the cylinder pose fabrication difficulties, and modification of the material matrix of the bed can result in changes to the weight and density of the bed, the efficiency of the absorption/desorption processes, and potentially contaminate the product.
  • Figure 6 shows a plot of temperature vs. time for a solid state hydrogen vessel relying on external insulation during periods of inactivity.
  • the flow rate drops to zero beginning a period of inactivity.
  • the temperature at the centre of the cylinder is regulated by the control system and remains constant.
  • the temperature at the top of the vessel drops to a temperature in excess of 20°C colder than the centre.
  • the temperature at the bottom of the cylinder drops to over 40°C colder than the centre.
  • One key feature of the invention is that a highly uniform cylinder temperature can be achieved with relatively low power.
  • the band heaters at the ends of the vessel are accounting for the higher heat loss due to the end effects.
  • the power requirement of each band heater is as low as 30W, 0.2% of the total power. This power requirement can be satisfied with low cost heaters. And since the power density is so low, there is minimal chance the band heaters can overheat the cylinder above its design temperature.
  • Another key feature of the invention is that by using band heaters to minimise the temperature gradient in the vessel shell there is a much lower requirement for internal insulation to minimise heat loss due to the end effects. Therefore, more space in the vessel is available to be filled with metal hydride (instead of insulation), yielding a reduction in the cost of the storage unit per kg of hydrogen stored that offsets the additional cost of the band heaters and control.
  • the temperature control system has been discussed as a system that provides overall temperature monitoring and control. That is, the temperature control system: (i) monitors the temperature of the hydride bed and at least the temperatures corresponding to a first axial point and a second axial point; and (ii) provides control over the heating element and the heating apparatus.
  • the temperature control system may comprise a number of interrelated elements that operate in a dependent manner.
  • the temperature control system may comprise a number of temperature control subsystems which work independently of each other.
  • the temperature control system of the solid state hydrogen vessel comprises: (i) a first temperature control subsystem to monitor the temperature of the hydride bed, this first temperature control subsystem can raise the temperature of the hydride bed through communication with the heating element; (ii) a second temperature control subsystem to monitor and control the temperature of the first axial point, this second temperature control subsystem can raise the temperature of the hydride material at the first axial point of the vessel through communication with the heating apparatus to provide heat at the first axial point to the hydride material; and (iii) a third temperature control subsystem to monitor and control the temperature of the second axial point, this third temperature control subsystem can raise the temperature of the hydride material at the second axial point of the vessel through communication with the heating apparatus to provide heat at the second axial point to the hydride material. While the above example illustrates three temperature control subsystems, it will be appreciated that additional subsystems comprising further monitoring and heating elements can be employed.
  • the temperature control system of the solid state hydrogen vessel comprises: (i) a first temperature control subsystem to monitor the temperature of the hydride bed, this first temperature control subsystem can raise the temperature of the hydride bed through communication with the heating element; (ii) a second temperature control subsystem to monitor and control the temperature of the first and second axial points, this second temperature control subsystem can raise the temperature of the hydride material at the first and second axial point of the vessel through communication with the heating apparatus to provide heat at the first and second axial points to the hydride material.
  • additional temperature monitors and heating elements can be employed with either the first or second temperature control subsystems.
  • each subsystem operates via a closed loop control mechanism to maintain the temperature of the respective location.
  • the temperature control system uses temperature sensors to determine the temperature at various locations along the defined axis. While the temperature sensors are located along this axis, the temperature sensors may be radially offset from the centre axis.
  • the temperature control system comprises at least: (i) a first temperature sensor to monitor the temperature of the hydride bed, the first temperature sensor being placed in the middle of the hydride bed in the centre of the vessel; (ii) a second temperature sensor located at a position corresponding to the first axial point in the centre of the centre of the hydride bed; and (iii) a third temperature sensor located at a position corresponding to the second axial point in the centre of the hydride bed.
  • the temperature sensors are all located in-line along the axis.
  • the temperature control system comprises at least: (i) a first temperature sensor to monitor the temperature of the hydride bed, the first temperature sensor being placed in the middle of the hydride bed in the centre of the vessel; (ii) a second temperature sensor located at a position corresponding to the first axial point near the surface of the hydride storage material; and (iii) a third temperature sensor located at a position corresponding to the second axial point near the surface of the of the hydrogen storage material.
  • the temperature sensors are all located along the axis in the direction defined by the axis, but the temperature sensors corresponding to the first and second axial points are located at a distance perpendicular from the axis.
  • the second and third temperature sensors may be located at various positions that are perpendicularly (i.e. radially) offset from the axis.
  • the second and third temperature sensors may be placed: at various distances offset from the central axis within the hydride bed, on the internal wall of the inner compartment, on the external wall of the inner compartment, on the internal wall of the vessel shell, or on the external wall of the vessel shell.
  • the person skilled in the art will appreciate that other locations may also be suitable depending on the arrangement of the vessel. It will be appreciated that the invention is not limited to the use of three temperature sensors. Additional sensors may be present within the hydride bed as necessary. Furthermore, additional temperature sensors may be placed in-line along the axis, radially offset from the axis, or both in-line along the axis and radially offset from the axis.
  • the position of the heating apparatus is not limited to the use of three temperature sensors. Additional sensors may be present within the hydride bed as necessary.
  • additional temperature sensors may be placed in-line along the
  • the heating apparatus which provides heat to the hydride bed at a position corresponding to the first and second axial points are band heaters. That is, the heating apparatus of the solid state hydrogen storage vessel comprises at least two band heaters. These band heaters are positioned at a location corresponding to the first and second axial points. The band heaters are located at a position that is perpendicularly (i.e. radially) offset from the central axis, such as adjacent to, or on the external wall of the inner compartment or the external wall of the vessel shell. Additional band heaters may be used and positioned at appropriate locations along the vessel.
  • the invention is intended to be applied to hydrogen storage vessels, hydrogen supply vessels or hybrid vessels, and reference to any is intended to be a reference to all unless the context requires otherwise.
  • a person skilled in the art will appreciate that the term 'vessel' is analogous to other terms used in the art and may, depending on context, be instead referred to as a cylinder, tank, unit, container, or other comparable terms.

Abstract

A solid state hydrogen storage and/or supply vessel comprising: a cylindrical shell portion having a first end and a second end, the first end and the second end defining an axis therebetween, the cylindrical shell having at least one inner compartment for a solid state hydrogen storage material; a fluid communication port for transmission of hydrogen gas to the at least one compartment; a heating element for heating the hydrogen storage material to desorb hydrogen from the hydrogen storage material; a temperature control system for monitoring temperature at locations corresponding to at least a first axial point and a second axial point and to provide a temperature profile along the axis; a heating apparatus for heating the solid state hydrogen storage material and being responsive to the temperature control system to maintain the temperature profile within a set temperature range.

Description

Reducing Axial Temperature Gradients
Field of the invention
The invention relates to a hydrogen storage unit which can be used for solid metal hydride absorption/adsorption and desorption of hydrogen and particularly a unit including a means for reducing the temperature gradients along the axis of the unit.
Background of the invention
Hydrogen may be stored for use as a fuel or for other purposes. Some hydrogen storage units include an enclosed volume carrying a bed of hydrogen storage material such as catalysed MgH2 or other high temperature metal hydride (and various alloys). There are a number of thermal challenges associated with such storage units. Typical hydrogen storage materials must be held within a narrow band of operating temperatures in the vicinity of 365°C to operate effectively.
Typically, a temperature gradient of less than 20°C is required within the bed of a hydrogen storage material during absorption/adsorption in order to ensure all the material absorbs/adsorbs the full amount of hydrogen it is chemically capable of. If the temperature of the coldest material is more than 20°C below the temperature of the hottest material in the bed, the catalyst will chemically react with the hydrogen to form a hydride, thereby decreasing its effectiveness. If this temperature difference is significantly more than 20°C, the resulting kinetics will be substantially slowed and the absorption/adsorption will not proceed to completion in a practical time.
Furthermore, due to irregular demand on hydrogen flow rate at a customer site, a hydrogen storage system will be exposed to duty cycles varying from full desorption flow capacity of the system to periods of inactivity for an extended period of time. With temperature difference as the driving force, a hot and partially desorbed cylinder is susceptible to migration of solid hydrogen from the hot zones of the cylinder to the cold zones if it is paused. If the cold zones of the cylinder drop below the equilibrium temperature of absorption, free molecules of gaseous hydrogen will be consumed, with the hot zones breaking its metal hydride bonds to account for the drop in pressure caused by absorbing zones. The first and second ends of the cylinder although having insulating layers at both ends, will cool down extensively over time, as compared to the middle of the bed which has temperature staying almost constant throughout, thus resulting in a large temperature gradient along the length of the cylinder.
Prior art discusses methods of obtaining excellent thermal conductivity and high diffusion rate of hydrogen by having a thermal management controller that determines whether the cylinder is absorbing or desorbing and from that, deciding whether to cool or heat up the cylinder by routing to different heat exchangers. Prior art also discusses the use of bundles of filaments using metal, synthetic high polymer, allowing metal hydride to absorb and desorb hydrogen in the spaces between the filament bundles. The filaments are capable of transferring heat and improve the thermal conductivity between the hydrides and or between the hydrides and the cylinder. Prior art also discusses having small chambers extending in the axial direction of the cylinder with a hydrogen permeable carbon fibre sheet. A plurality of aluminium fins are also used, with the fins projecting from the inner wall towards the centre of the cylinder, parallel to the axis of the cylinder. These fins are capable of distributing heat from the middle of the bed to other parts of the cylinder. The thermal conductivity can also be improved by having a hydrogen storage mixture made up of hydrogen storage alloy granules and metal fibres and/or non-hydrogen-absorbing alloy fibres. Prior art also discusses a possible method of improving the decline in thermal conductivity with the use of a compact of hydrogen adsorption alloy as the material matrix, which is composed of a metal hydride in which all surfaces of fine particles of hydrogen absorption alloy are completely coated with a dissimilar metal by plating, without affecting reactivity and a porous material of high thermal conductivity is infiltrated with the fine particles of alloy to be formed into a compact by compression moulding.
There are many drawbacks to the approach taken in the prior art. For example, additional fins or metal extrusions inside the cylinder pose difficulties for fabrication. Furthermore, in many instances a reduction in the temperature gradient is also insufficient to prevent the occurrence of concentration migration. Modification of the material matrix of the bed may cause changes to the weight and density of the bed, as well as potentially contaminating the product.
Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art. Summary of the invention
An important design consideration for hydrogen storage cylinders is to achieve high temperature uniformity along the axis of the cylinder. This promotes even desorption of the solid state hydrogen storage material, such as a metal hydride bed, and minimises migration of solid hydride from hot zones to cold zones (through hydride formation occurring due to the transfer of hydrogen from hotter zones to cooler zones, and the subsequent absorption of hydrogen in cooler zones) during periods of inactivity. As a result of "end effects" (defined as higher relative heat loss at the ends of the vessel to the middle of the vessel), the temperature at each end of the cylinder tends to be much lower than the middle of the vessel. Accordingly, in one aspect of the invention there is provided a solid state hydrogen storage and/or supply vessel comprising: a cylindrical shell portion having a first end and a second end, the first end and the second end defining an axis therebetween, the cylindrical shell having at least one inner compartment for a solid state hydrogen storage material; a fluid communication port for transmission of hydrogen gas to the at least one compartment; a heating element for heating the hydrogen storage material to desorb hydrogen from the hydrogen storage material; a temperature control system for monitoring temperature at locations corresponding to at least a first axial point and a second axial point and to provide a temperature profile along the axis; a heating apparatus for heating the solid state hydrogen storage material and being responsive to the temperature control system to maintain the temperature profile within a set temperature range. In another aspect of the invention there is provided solid state hydrogen storage and/or supply vessel comprising: a cylindrical shell portion having a first end and a second end, the first end and the second end defining an axis therebetween, the cylindrical shell having at least one compartment for a solid state hydrogen storage material; a fluid communication port for transmission of hydrogen gas to the at least one inner compartment; a heating element for heating the hydrogen storage material to desorb hydrogen from the hydrogen storage material; a temperature control system for monitoring temperature at locations corresponding to at least a first axial point and a second axial point and to provide a temperature profile along the axis; and a heating apparatus for heating the solid state hydrogen storage material at least at locations near or corresponding to at least the first axial point and the second axial point, the heating apparatus being responsive to the temperature control system to maintain the temperature profile within a set temperature range. Preferably the temperature range is about 10°C. More preferably the temperature range is about 5°C.
The hydrogen storage and/or supply vessel is cylindrical in shape, and may be capped at either or both ends with an end cap such as a rounded, domed, or hemispherical cap. The axis runs from a first end cap and through the cylindrical shell portion defined by a wall to the second end cap, such that the axis is oriented parallel to the cylindrical walls of the cylindrical shell portion.
The inner compartment of the cylindrical shell contains the hydrogen storage material in a bed of material, the heating element heating the bed to desorb hydrogen from the hydrogen storage material.
In an embodiment, the heating apparatus is configured for heating the solid state hydrogen storage material along the axis at least at locations near or corresponding to at least the first axial point and the second axial point. The heating apparatus acts as a differential heating apparatus to balance the temperature profile along the axis.
In an embodiment, the heating apparatus is external to the cylindrical shell portion. In an alternative embodiment, the heating apparatus is internal to the cylindrical shell portion. The skilled addressee will appreciate that whether the heating apparatus is internal or external will depend on the nature of the heating apparatus and the specifics of the design of the vessel. In a further alternative embodiment the vessel further comprises an inner compartment for containing the solid state hydrogen storage material, the inner compartment having an internal wall and an outer wall, and being in fluid communication with the fluid communication port; wherein a peripheral space is defined between the cylindrical shell portion and the inner compartment, and the heating apparatus is located external to the outer wall of the inner compartment. That is, the heating apparatus is located within the peripheral space.
In yet a further alternative embodiment, the heating apparatus may be located external to the vessel, internal to the vessel, in the peripheral space, or in a combination of these locations.
It is generally preferred that the heating apparatus is fitted at different positions along the axis at least at a location near or corresponding to the first axial point and/or a location near or corresponding to the second axial point.
In each of the above embodiments, the heating apparatus may include a plurality of heating units each of which may be independently located external to the vessel, internal to the vessel, in the peripheral space, or in a combination of these locations depending on the design of the vessel. Preferably, the heating units provide heat energy to a location near or corresponding to the first axial point and a location near or corresponding to the second axial point. The heating units may be electrical heaters or oil heaters.
In an embodiment, the heating apparatus comprises at least one band heater fitted to the location corresponding to the first axial point and at least one band heater fitted to a location corresponding to the second axial point. In an alternative embodiment, the heating apparatus includes an oil heater. The oil heater may include heating pipes that pass through the solid state hydrogen storage material at various locations, for example heating pipes may project into the solid state hydrogen storage material at a location near or corresponding to the first axial point and/or at a location near or corresponding to the second axial point. Heating oil may then be caused to flow through these pipes to provide thermal energy at or near the first and/or second axial points. In another arrangement, heating pipes may be located external to the vessel. Heating oil is circulated through the heating pipes to control the temperature as necessary. The heating pipes may be attached to an external wall of the vessel at a location near or corresponding to the first axial point and/or at a location near or corresponding to the second axial point. Heating oil may be caused to flow through these pipes to provide thermal energy at or near the first and/or second axial points.
In yet another arrangement, in the case where the vessel includes a peripheral space, the oil heater may comprise pipes that pass through the peripheral space external to the outer wall of the inner compartment. The pipes may be in contact with the outer wall of the inner compartment at a location near or corresponding to the first axial point and/or at a location near or corresponding to the second axial point. Heating oil may be caused to flow through these pipes to provide thermal energy at or near the first and/or second axial points.
In another embodiment, the heating apparatus comprises an oil heater and an electrical band heater. In a preferred arrangement, the oil heater provides heat energy to the solid state hydrogen storage material internal to the vessel and the electrical band heater provides heat energy to the solid state hydrogen storage material from external to the vessel.
In another arrangement the oil heater provides heat energy to the solid state hydrogen storage material internal to the vessel and at least one electrical band heater provides heat energy to the solid state hydrogen storage material from a peripheral space within the vessel.
The oil heater, the electrical band heater or heaters, or both may provide heat energy to a location near or corresponding to the first and/or second axial points
In a further embodiment of the invention there is provided a use of the solid state hydrogen storage and/or supply vessel to store and supply hydrogen. In another embodiment of the invention, there is provided a method of operating the solid state hydrogen storage and/or supply vessel of any one of the preceding claims, wherein the heating apparatus applies heat energy in response to the temperature range exceeding an allowed temperature differential value. As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps.
Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.
Brief description of the drawings
Figure 1 shows the temperature profile along the axis of a solid state hydrogen vessel according to the present invention. Figure 2 shows the temperature profile along the axis of a solid state hydrogen vessel relying on external insulation.
Figure 3 shows the temperature profile along the axis of a solid state hydrogen vessel having insulated front and rear domes.
Figure 4 shows the temperature profile along the axis of a solid state hydrogen vessel having copper extrusions and internal insulation.
Figure 5 shows the temperature profile along the axis of a solid state hydrogen vessel having aluminium extrusions along the length of the vessel.
Figure 6 shows a plot of temperature vs. time for the middle and each end of a solid state hydrogen vessel relying on external insulation during periods of inactivity. Detailed description of the embodiments
The present invention is directed to a solid state hydrogen storage and/or supply cylinder that is able to maintain a high degree of temperature uniformity along the axis of the cylinder. One of the problems with the hydrogen storage cylinders of the prior art is that due to higher relative heat loss from the ends of the storage vessel compared with the middle portion of the vessel, the temperature at each end of the cylinder can be much lower than the temperature at the centre of the vessel. Solid state hydrogen storage and/or supply vessels typically store hydrogen in an adsorbed solid form as a metal hydride. Accordingly, hydrogen storage and/or supply vessels typically comprise a solid metal-hydride bed, wherein the metal-hydride bed may include one or more high temperature metal hydrides. Hydrogen can then be released through the application of heat which drives a hydrogen desorption reaction, releasing hydrogen. Thus, a heating element may be provided to heat the hydrogen storage material to desorb hydrogen from the metal- hydride bed. The hydrogen can then be supplied to the appropriate location.
Typically hydrogen storage and/or supply vessels comprise a cylindrical centre portion and dome ends. The dome ends are usually heavily insulated to minimise loss of heat through the ends of the vessel. As a result, the main pathway for heat loss is through the vessel shell, particularly at either end of the vessel shell.
Hydrogen absorption and desorption are temperature dependent. Therefore, the establishment of a temperature profile exhibiting a significant temperature differential between the centre of the vessel and the ends of the vessel can have a negative impact on hydrogen absorption and desorption. In particular, as temperature difference is the driving force, a hot and partially desorbed cylinder is susceptible to migration of solid hydrogen from the hot zones of the cylinder to the cold zones if it is paused. If the cold zones of the cylinder drop below the equilibrium temperature of absorption, free molecules of gaseous hydrogen will be consumed, with the hot zones breaking its metal hydride bonds to account for the drop in pressure caused by absorbing zones. Maintaining a degree of uniformity to the temperature profile along the axis of the hydrogen storage and/or supply vessel is therefore important for promoting even desorption of hydrogen and minimises migration of the solid hydrogen from the hot zones to the cold zones during periods of inactivity.
In one aspect, the present invention is directed towards a solid state hydrogen storage and/or supply vessel comprising a means for axial heating. The means for axial heating can be activated to attenuate a temperature differential in the temperature range along the axis of the hydrogen storage vessel. For example, if a temperature difference results due to one of the ends of the vessel being cooler than the centre of the vessel, heat energy can be applied to that end of the vessel to raise the temperature and thus reduce the temperature differential between that end of the vessel and the centre of the vessel. In a preferred embodiment, there is provided a solid state hydrogen storage and/or supply vessel comprising: a cylindrical shell portion having a first end and a second end, the first end and the second end defining an axis therebetween; the cylindrical shell having at least one inner compartment for a solid state hydrogen storage material; a fluid communication port for transmission of hydrogen gas to the inner compartment; a heating element for heating the hydrogen storage material to desorb hydrogen from the hydrogen storage material; a temperature control system for monitoring a temperature at locations corresponding to at least a first axial point and a second axial point; a heating apparatus for heating locations corresponding to the first axial point and the second axial point, the heating apparatus being responsive to the temperature control system to maintain the temperature profile within a set temperature range.
The vessel can be filled by supplying hydrogen at pressure to the fluid communication port whereby the hydrogen is absorbed by the hydrogen storage material. During the removal of hydrogen from the hydrogen storage vessel (desorption), the hydrogen storage material is heated by heating elements within the hydride bed. Thus when the fluid communication port is opened, hydrogen flows out of the vessel.
In another embodiment, the inner compartment has an internal wall and an outer wall, and is in fluid communication with the fluid communication port. The inner compartment of the storage unit is constructed to contain hydrogen storage material. According to such units, the cylindrical shell portion may act as an outer vessel that may surround at least a substantial portion of, or totally contain the inner compartment and may be spaced therefrom to define a peripheral volume around the inner compartment. The inner compartment may include a compartment wall and end pieces, the end pieces engaging the outer vessel wall to support the inner compartment within the outer vessel. The compartment wall is preferably cylindrical and the end pieces conical, frusto-conical or hemispherical in shape. In one embodiment, the inner compartment wall is substantially cylindrical and the cylindrical shell portion forms an outer vessel wall that totally encloses the inner compartment. The outer vessel may include a substantially cylindrical interior wall concentrically surrounding the inner compartment defining a peripheral volume which is an annular space between the inner compartment and the outer vessel. In one aspect, the inner compartment fluidly communicates with the peripheral volume around the inner compartment during receipt of hydrogen so that the peripheral volume is pressurised. In the situation where there is an annular space between the cylindrical shell portion and the inner vessel, the heating means of locations along the axis may be achieved by application of heat external to the outer wall of the inner vessel. In this regard, band heaters may be fitted to the ends of the outer wall of the inner vessel and used to eliminate any significant temperature difference along the axial length of the inner vessel. Alternatively, the heating may be applied at locations external to the vessel, on the vessel shell.
The temperature of the hydrogen storage and/or supply vessel in the centre of the vessel is monitored with a temperature control system, such as those that are standard in the art. A separate independent temperature control system monitors the temperature at the ends of the cylinder shell with a temperature control system, such as those that are standard in the art. The temperature control systems may be a closed loop system to allow a quick response to changes in the environment to ensure that the temperature profile is maintained within specified parameters. It is preferred that the temperature gradient between an end of the vessel and the centre of the vessel is maintained within a temperature range of 10°C. For example, the temperature difference between any one end of the vessel and the temperature at the centre of the vessel is less than about 10°C. It is also preferred that the temperature profile over the axis of the vessel does not exceed a temperature differential of greater than 10°C.
In an exemplified embodiment, where the hydrogen storage material is magnesium hydride, it is desirable to maintain the hydride storage material at a constant temperature of approximately 365°C. A person skilled in the art will understand that this operating temperature is dependent on a number of parameters such as the type of solid state storage material used, or the system operating conditions such as the internal pressure of the system. Broadly, the operating temperature for a hydrogen storage and supply system is going to be between 50°C and 450°C, depending on the solid state hydrogen storage material and the operating conditions of the system. However, in this particular example, to ensure that the hydride material in the middle of the cylinder is maintained at a constant temperature of approximately 365°C, a temperature control system is employed. This temperature control system monitors the internal temperature at the centre of the hydride bed and interfaces with a heating element to maintain the temperature at approximate 365°C. While this is effective at maintaining the temperature at the centre of the vessel, it can be ineffective at maintaining the temperature of the hydride bed at the ends of the hydride bed. As discussed, end effects result in the ends of the vessel cooling more rapidly than the centre of the vessel. Thus hydride material located further from the vessel centre cools more rapidly than that located nearer the centre, with the hydride material at the ends cooling most rapidly. To address this issue, additional temperature control systems are employed. In this embodiment, separate independent temperature control systems are used to maintain the ends of the cylinder shell at a constant temperature of approximately 365°C. The presence of this additional temperature control system lessens the impact of the preferential cooling due to "end effects".
It will be appreciated that the additional temperature control systems, which regulate the temperature at each of the ends of the hydride bed, may be integrated with a temperature control system that regulates the temperature at the centre of the hydride bed. Alternatively, each of the temperature control systems (i.e. the first temperature control system which regulates the temperature at the centre of the hydride bed, the second temperature control system which regulates the temperature at a first end of the hydride bed, and the third temperature control system which regulates the temperature at a second end of the hydride bed) operate independently on a closed circuit control loop.
The heating means may be achieved by application of heat to an appropriate location. For example, in one embodiment band heaters are fitted to the ends of the vessel shell and used to suppress any significant temperature difference along the axial length of the hydrogen storage material. A closed control loop on the band heaters will result in a quick response to changes in the environment to ensure the temperature gradient is always within an acceptable range. In this embodiment, the use of local band heaters act as an active control to heat up the ends of the cylinder, preventing the axial temperature gradient from being outside the specified range, and at the same time ensuring that the invention is cost efficient and easy to fabricate, without interfering with the internals of the cylinder. A person skilled in the art will appreciate that other forms of applying heat to the vessel may also be used. These other forms may include suitable internal means or other suitable external means.
In a non-limiting disclosure, the present invention may be used with solid state hydrogen cylinder packs for replacement of compressed gas MCP's or with solid state hydrogen storage system packaged in a shipping container. The present invention may also be used in a solid state hydrogen storage systems: for interface with a high temperature fuel cell for waste heat recovery, for interface to an internal combustion engine for waste heat utilisation, for refuelling applications, or for PEM fuel cell applications. Broadly, the present invention is applicable in any situation that includes hydrogen storage or hydrogen supply and where there is a desire to minimise an axial temperature difference. Figure 1 shows the axial temperature profile of a hydrogen storage and/or supply vessel
100 including a metal hydride storage material 102 according to the present invention. In this case, the hydrogen storage and/or supply vessel 100 is fitted with external band heaters 104 and 106 at each end of the cylindrical shell portion of the vessel. In this case the temperature differential between the end of the vessel shell and the centre of the vessel is maintained within approximately 1°C. In this embodiment the hydrogen storage and/or supply vessel includes insulation 108 and 110 in the domed ends of the cylindrical shell portion and insulation 112 external to the cylindrical shell portion.
Figures 2, 3, 4 and 5 show the axial temperature profiles of hydrogen storage and/or supply vessels 200, 300, 400, and 500 each including metal hydride 202, 302, 402, and 502. In these cases, hydrogen storage and/or supply vessels 200, 300, 400, and 500 use prior art strategies to maintain heat. In particular, the vessel 200 of Figure 2 has external insulation 212 and H2 gas 213 is free to accumulate in the domed ends; the vessel 300 of Figure 3 has insulated front and rear domes 308 and 310 as well as external insulation 312; the vessel 400 of Figure 4 has copper extrusions 414, internal insulation 408 and 410, and external insulation 412; and the vessel 500 of Figure 5 has aluminium extrusions 516 along the length of the vessel 500 as well as both internal insulation 508 and 510, and external insulation 512. As can be seen in all of the above cases, the temperature differentials exceed 10°C. Figure 2 where only external insulation was utilised exhibits the greatest temperature differential of about 46°C.
The present invention both minimises the temperature differential of the temperature range in a temperature profile, and provides a simple and cost effective way of doing so. While other prior art mechanisms may also reduce the temperature differential in comparison with only using external insulation, the prior art approaches are difficult to implement with regards to both retrofitting an existing vessel, and fabricating new vessels. For example, the presence of additional fins or metal extrusions inside the cylinder pose fabrication difficulties, and modification of the material matrix of the bed can result in changes to the weight and density of the bed, the efficiency of the absorption/desorption processes, and potentially contaminate the product.
Figure 6 shows a plot of temperature vs. time for a solid state hydrogen vessel relying on external insulation during periods of inactivity. At the start of the graph the flow rate drops to zero beginning a period of inactivity. The temperature at the centre of the cylinder is regulated by the control system and remains constant. The temperature at the top of the vessel, drops to a temperature in excess of 20°C colder than the centre. The temperature at the bottom of the cylinder, drops to over 40°C colder than the centre.
The plot shown in Figure 6 was obtained during paused desorption of a cylinder. The enclosed region on the plot clearly shows that when the desorption is paused, and the heaters turn off, due to no heat being absorbed by the endothermic reaction, the ends of the cylinder decrease in temperature faster than the middle of the bed, leading to a temperature gradient along the bed. This might in turn lead to hydrogen redistribution when desorption is restarted, which is shown in the table above for desorption paused at 75% completion. The flow-rate does not go back to its initial value, due to some of desorbing hydrogen having been re-absorbed by the colder materials at the ends.
One key feature of the invention is that a highly uniform cylinder temperature can be achieved with relatively low power. The band heaters at the ends of the vessel are accounting for the higher heat loss due to the end effects. For a typical 15kW heated cylinder design, the power requirement of each band heater is as low as 30W, 0.2% of the total power. This power requirement can be satisfied with low cost heaters. And since the power density is so low, there is minimal chance the band heaters can overheat the cylinder above its design temperature.
Another key feature of the invention is that by using band heaters to minimise the temperature gradient in the vessel shell there is a much lower requirement for internal insulation to minimise heat loss due to the end effects. Therefore, more space in the vessel is available to be filled with metal hydride (instead of insulation), yielding a reduction in the cost of the storage unit per kg of hydrogen stored that offsets the additional cost of the band heaters and control.
The discussion below relates to specific components and arrangements of preferred embodiments. The temperature control system: The temperature control system has been discussed as a system that provides overall temperature monitoring and control. That is, the temperature control system: (i) monitors the temperature of the hydride bed and at least the temperatures corresponding to a first axial point and a second axial point; and (ii) provides control over the heating element and the heating apparatus. Thus, the temperature control system may comprise a number of interrelated elements that operate in a dependent manner. Alternatively, the temperature control system may comprise a number of temperature control subsystems which work independently of each other.
For example, in one embodiment the temperature control system of the solid state hydrogen vessel comprises: (i) a first temperature control subsystem to monitor the temperature of the hydride bed, this first temperature control subsystem can raise the temperature of the hydride bed through communication with the heating element; (ii) a second temperature control subsystem to monitor and control the temperature of the first axial point, this second temperature control subsystem can raise the temperature of the hydride material at the first axial point of the vessel through communication with the heating apparatus to provide heat at the first axial point to the hydride material; and (iii) a third temperature control subsystem to monitor and control the temperature of the second axial point, this third temperature control subsystem can raise the temperature of the hydride material at the second axial point of the vessel through communication with the heating apparatus to provide heat at the second axial point to the hydride material. While the above example illustrates three temperature control subsystems, it will be appreciated that additional subsystems comprising further monitoring and heating elements can be employed.
In another exemplary embodiment, the temperature control system of the solid state hydrogen vessel comprises: (i) a first temperature control subsystem to monitor the temperature of the hydride bed, this first temperature control subsystem can raise the temperature of the hydride bed through communication with the heating element; (ii) a second temperature control subsystem to monitor and control the temperature of the first and second axial points, this second temperature control subsystem can raise the temperature of the hydride material at the first and second axial point of the vessel through communication with the heating apparatus to provide heat at the first and second axial points to the hydride material. It will be appreciated that additional temperature monitors and heating elements can be employed with either the first or second temperature control subsystems. In the embodiments where the temperature control system comprises a number of independent temperature control subsystems, each subsystem operates via a closed loop control mechanism to maintain the temperature of the respective location.
The position of the temperature sensors: The temperature control system (including any temperature control subsystems) uses temperature sensors to determine the temperature at various locations along the defined axis. While the temperature sensors are located along this axis, the temperature sensors may be radially offset from the centre axis.
For example, in one embodiment the temperature control system comprises at least: (i) a first temperature sensor to monitor the temperature of the hydride bed, the first temperature sensor being placed in the middle of the hydride bed in the centre of the vessel; (ii) a second temperature sensor located at a position corresponding to the first axial point in the centre of the centre of the hydride bed; and (iii) a third temperature sensor located at a position corresponding to the second axial point in the centre of the hydride bed. In this example, the temperature sensors are all located in-line along the axis.
In another exemplary embodiment, the temperature control system comprises at least: (i) a first temperature sensor to monitor the temperature of the hydride bed, the first temperature sensor being placed in the middle of the hydride bed in the centre of the vessel; (ii) a second temperature sensor located at a position corresponding to the first axial point near the surface of the hydride storage material; and (iii) a third temperature sensor located at a position corresponding to the second axial point near the surface of the of the hydrogen storage material. In this example, the temperature sensors are all located along the axis in the direction defined by the axis, but the temperature sensors corresponding to the first and second axial points are located at a distance perpendicular from the axis. The second and third temperature sensors may be located at various positions that are perpendicularly (i.e. radially) offset from the axis. For example, the second and third temperature sensors may be placed: at various distances offset from the central axis within the hydride bed, on the internal wall of the inner compartment, on the external wall of the inner compartment, on the internal wall of the vessel shell, or on the external wall of the vessel shell. The person skilled in the art will appreciate that other locations may also be suitable depending on the arrangement of the vessel. It will be appreciated that the invention is not limited to the use of three temperature sensors. Additional sensors may be present within the hydride bed as necessary. Furthermore, additional temperature sensors may be placed in-line along the axis, radially offset from the axis, or both in-line along the axis and radially offset from the axis. The position of the heating apparatus:
As stated previously, in a preferred embodiment, the heating apparatus which provides heat to the hydride bed at a position corresponding to the first and second axial points are band heaters. That is, the heating apparatus of the solid state hydrogen storage vessel comprises at least two band heaters. These band heaters are positioned at a location corresponding to the first and second axial points. The band heaters are located at a position that is perpendicularly (i.e. radially) offset from the central axis, such as adjacent to, or on the external wall of the inner compartment or the external wall of the vessel shell. Additional band heaters may be used and positioned at appropriate locations along the vessel.
The invention is intended to be applied to hydrogen storage vessels, hydrogen supply vessels or hybrid vessels, and reference to any is intended to be a reference to all unless the context requires otherwise. Furthermore, a person skilled in the art will appreciate that the term 'vessel' is analogous to other terms used in the art and may, depending on context, be instead referred to as a cylinder, tank, unit, container, or other comparable terms.
It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims

1. A solid state hydrogen storage and/or supply vessel comprising: a cylindrical shell portion having a first end and a second end, the first end and the second end defining an axis therebetween, the cylindrical shell having at least one inner compartment for a solid state hydrogen storage material; a fluid communication port for transmission of hydrogen gas to the at least one compartment; a heating element for heating the hydrogen storage material to desorb hydrogen from the hydrogen storage material; a temperature control system for monitoring temperature at locations corresponding to at least a first axial point and a second axial point and to provide a temperature profile along the axis; and a heating apparatus for heating the solid state hydrogen storage material and being responsive to the temperature control system to maintain the temperature profile within a set temperature range .
2. A solid state hydrogen storage and/or supply vessel comprising: a cylindrical shell portion having a first end and a second end, the first end and the second end defining an axis therebetween, the cylindrical shell having at least one inner compartment for a solid state hydrogen storage material; a fluid communication port for transmission of hydrogen gas to the at least one compartment; a heating element for heating the hydrogen storage material to desorb hydrogen from the hydrogen storage material; a temperature control system for monitoring temperature at locations corresponding to at least a first axial point and a second axial point and to provide a temperature profile along the axis; and a heating apparatus for heating the solid state hydrogen storage material at least at locations near or corresponding to at least the first axial point and the second axial point, the heating apparatus being responsive to the temperature control system to maintain the temperature profile within a set temperature range.
3. The solid state hydrogen storage vessel of claim 1 or 2, wherein the inner compartment has an internal wall and an outer wall, and is in fluid communication with the fluid
communication port; wherein a peripheral volume is defined between the cylindrical shell portion and the inner compartment, and the heating apparatus is external to the outer wall of the inner compartment.
4. The solid state hydrogen storage vessel of claim 1 or 2, wherein the heating apparatus is external to the cylindrical shell portion.
5. The solid state hydrogen storage vessel of any one of the preceding claims, wherein the heating apparatus comprises a band heater fitted to a location corresponding to the first axial point and a band heater fitted to a location corresponding to the second axial point.
6. The solid state hydrogen storage vessel of any one of the preceding claims, wherein the temperature range is about 10°C.
7. The solid state hydrogen storage vessel of any one of the preceding claims, wherein the temperature range is about 5°C.
8. The solid state hydrogen storage vessel of claim 1 or 2 wherein the heating apparatus comprises an oil heater.
9. The solid state hydrogen storage vessel of claim 8 wherein the oil heater includes heating pipes that pass through the solid state hydrogen storage material.
10. The solid state hydrogen storage vessel of claim 9 wherein the heating pipes pass through the solid state hydrogen storage material at locations near or corresponding to the first axial point and the second axial point.
11. The solid state hydrogen storage vessel of any one of claims 8 to 10 wherein the heating apparatus comprises an oil heater and an electrical band heater.
12. The solid state hydrogen storage vessel of claim 11 wherein the oil heater provides heat energy to the solid state hydrogen storage material internal to the vessel and the electrical band heater provides heat energy to the solid state hydrogen storage material from external to the vessel.
13. A method of operating the solid state hydrogen storage and/or supply vessel of any one of the preceding claims, wherein the heating apparatus applies heat energy in response to the temperature range exceeding an allowed temperature differential value.
14. The method of claim 13, wherein the temperature differential is about 10°C.
15. The method of claim 14, wherein the temperature differential is about 5°C.
16. Use of the solid state hydrogen storage and/or supply vessel of any one of claims 1 to 12, to supply hydrogen.
17. Use of the solid state hydrogen storage and/or supply vessel of any one of claims 1 to 12, to store hydrogen.
PCT/AU2015/050683 2014-10-30 2015-10-29 Reducing axial temperature gradients WO2016065427A1 (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2011103627A1 (en) * 2010-02-24 2011-09-01 Hydrexia Pty Ltd Hydrogen release system
WO2011103626A1 (en) * 2010-02-24 2011-09-01 Hydrexia Pty Ltd Hydrogen storage unit

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2011103627A1 (en) * 2010-02-24 2011-09-01 Hydrexia Pty Ltd Hydrogen release system
WO2011103626A1 (en) * 2010-02-24 2011-09-01 Hydrexia Pty Ltd Hydrogen storage unit

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