Systems and methods for hydrogen production

Abstract

The present invention relates to a system and method for producing hydrogen gas, the system comprising at least one gas transport vessel configured to transport at least hydrogen upwardly through water by buoyancy, and a heat transfer unit connected to an electrolysis unit and configured to transfer at least a portion of waste heat from the electrolysis unit to hydrogen gas transported by the gas transport vessel.

Description

[Technical field]

[0001] The present invention relates to systems and methods for producing hydrogen and optionally oxygen, in particular, systems and methods for producing hydrogen that utilize an electrolyzer and utilize excess heat from the electrolyzer to heat at least one of the produced gases. [Background technology]

[0002] Hydrogen gas is fundamental in many industrial processes, such as steel making and fertilizer production, and has recently emerged as the energy carrier in fuel cell based power generation, thus having the potential to become a major transportation fuel due to its unique energy content.

[0003] Fuel cell-based technologies and, for example, steelmaking using hydrogen gas, could be far superior from an environmental and sustainability point of view to the technologies used today, especially those and systems that rely on fossil fuels, but also on battery-based technologies. However, for hydrogen-based technologies to be attractive from an environmental and sustainability point of view, hydrogen must be produced by methods other than the production methods that dominate today, which use fossil fuels, mainly natural gas.

[0004] Water electrolysis is another method to produce hydrogen gas. Electrolysis itself is very clean, with only oxygen gas as a by-product, which also has high commercial value. However, the consumption of energy in the form of electricity has so far made electrolysis-based hydrogen production less attractive from a cost perspective compared to methods using fossil fuels. Another drawback with water electrolysis is that the electrolysis process and equipment are typically sensitive to impurities in the water. For example, seawater could not previously be used without extensive desalination and purification. However, as disclosed in Non-Patent Document 1, first published on March 18, 2019, methods and equipment have recently become available that allow seawater to be used directly for the electrolysis process.

[0005] Also, the efficiency of the electrolysis process has improved significantly in recent years, with electrical efficiencies of up to 80% reported for laboratory-scale prototypes. However, commercially available units typically have efficiencies significantly lower than 60%. Thus, significant improvements are needed to bring hydrogen production by electrolysis to cost parity with fossil fuel-based production.

[0006] The water electrolysis process is known to generate large amounts of heat, which must be removed via a cooling system. Typically, the heat generated can be considered waste heat with respect to the electrolysis production, but can also be used for lower grade applications, such as heating a home or facility, as with other industrial processes that generate heat.

[0007] US Patent No. 5,399,633 discloses a method and system in which waste heat from a water electrolysis process is recovered and provided to an electrochemical hydrogen pump that requires heat to initiate electrochemical hydrogen compression, thereby improving the efficiency of the overall system.

[0008] US Patent No. 5,399,633 discloses the production of hydrogen in an underwater plant, the main objective being to reduce the risk that the produced hydrogen or oxyhydrogen will ignite and cause an explosion. US Patent No. 5,399,633 discloses a method and system for generating power through the entrapment of gas bubbles. One gas source is described as a device that uses hydrolysis to produce hydrogen and oxygen from water and bubbles the produced gases through the water in the form of a gas mixture. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] US Patent Application Publication No. 16 / 953195 [Patent Document 2] International Publication No. 2014153249 [Patent Document 3] US Patent Application Publication No. 11 / 007690 [Non-patent literature]

[0010] [Non-Patent Document 1] Solar-driven,highly sustained splitting of seawater into hydrogen and oxygen fuels,Yun Kuang et al,PNAS April 2,2019 116(14)6624-6629 Summary of the Invention

[0011] It is an object of the present invention to provide a system and method for producing hydrogen, and optionally oxygen, in an environmentally and sustainably acceptable manner and at a cost that is competitive with fossil fuel based technologies.

[0012] This is achieved by a system according to claim 1 and a method according to claim 14. According to a first aspect of the present invention, a system for producing hydrogen gas is provided.

[0013] The system is configured to be placed within or associated with a water volume forming a water-filled gas rising column having a lower end and an upper end. an electrically driven electrolysis unit disposed adjacent a lower end of the water-filled gas riser column, the electrolysis unit being provided with a water inlet and at least one gas outlet, the electrolysis unit being configured, in use, to split water into hydrogen gas and oxygen gas in an electrolysis process during which process waste heat is generated; at least one gas transport vessel having at least one cavity and a gas inlet and a gas outlet communicating with the cavity, the vessel being configured to receive a quantity of hydrogen gas in the cavity and transport the hydrogen gas from the bottom to the top of the gas ascent column by buoyancy provided by the transported gas; - a gas connection means arranged at the lower end of the water-filled gas riser column and configured to provide a removable gas transport connection between the electrolysis unit and the gas inlet of the gas transport vessel; and a gas delivery means arranged at the upper end of the water-filled gas riser column and configured to provide a removable gas transport connection between the gas outlet and a gas collector. a heat transfer unit connected to the electrolysis unit and to the gas connection means or to the gas transport vessel and configured to transfer at least a portion of the waste heat from the electrolysis unit to the hydrogen gas in the gas connection means or to the hydrogen gas in the gas transport vessel.

[0014] According to one embodiment of the present invention, the heat transfer unit comprises a first thermal circuit arranged in contact with a heat generating part of the electrolysis unit thereby cooling the electrolysis unit, a second thermal circuit configured to heat the gas produced by the electrolysis unit, and a heat exchanger configured to transfer heat from the first thermal circuit to the second thermal circuit.

[0015] According to one embodiment of the invention, the heat transfer unit comprises a flow-through gas heater arranged between the electrolysis unit and the gas connection means. According to one embodiment of the invention, the heat transfer unit comprises an internal heating device disposed within the gas transport vessel and forming part of the second thermal circuit.

[0016] According to one embodiment of the invention, the internal heating device comprises a coil disposed inside the gas transport vessel. According to one embodiment, the internal heating device comprises a heating mantle disposed on at least a portion of the wall of the gas transport vessel.

[0017] According to one embodiment of the present invention, the gas transport vessel is equipped with a pressure regulating device configured to control the gas pressure within the cavity of the gas transport vessel relative to the external pressure, thereby controlling the buoyancy of the gas transport vessel while it is filled with heated gas received from the electrolysis unit and ascends in the gas ascending column.

[0018] According to one embodiment of the present invention, the pressure regulating device comprises: a control valve configured to provide fluid communication between the cavity and an exterior of the gas transport vessel or to a gas container separate from the cavity; an internal pressure sensor configured to provide a measurement of the pressure of a gas contained within the cavity; an external pressure sensor configured to provide a measurement of the pressure of the water surrounding the gas transport vessel; The internal and external pressure sensors are configured to affect adjustment of the control valve to control the pressure inside the cavity relative to the pressure outside the gas transport vessel such that a predetermined buoyancy is achieved.

[0019] According to one embodiment of the present invention, the pressure regulating device is configured to receive measurement data from the internal pressure sensor and the external pressure sensor and further comprises a control unit configured to control the control valve, the control unit having a stored pressure profile and configured to adjust the control valve according to the stored pressure profile.

[0020] According to one embodiment of the present invention, the gas transport vessel comprises: a non-compressible container provided with a main cavity; an expansion vessel capable of varying its volume and adapted to be influenced by both an internal pressure and an external pressure; - a pipe connecting a non-compressible container and an expansion vessel, the pipe being provided with a control valve; an internal pressure sensor configured to provide a measurement of the pressure of the gas contained within the main cavity, and an external pressure sensor configured to provide a measurement of the pressure of the water surrounding the gas transport vessel, The internal and external pressure sensors are configured to affect adjustment of the control valve, thereby controlling the flow of gas between the main cavity and the expansion vessel.

[0021] According to one embodiment of the present invention, - the incompressible container is double-walled and provides an insulating space between the inner and outer walls of the incompressible container; The incompressible container is provided with a differential pressure sensor configured to provide a measurement of the difference in gas pressure in the main cavity and the insulating space, and a second volume and pressure regulating valve configured to equalize the pressure between the main cavity and the insulating space.

[0022] According to one embodiment of the present invention, a system for producing hydrogen gas includes a belt having a plurality of gas transport vessels attached thereto, the belt configured to drive an electrical generator. According to a second aspect of the present invention, there is provided a combined system for producing hydrogen and oxygen gases, the combined system being configured to be disposed within or in connection with at least one water volume forming a first water-filled gas riser column having a lower end and an upper end, and a second water-filled gas riser column having a lower end and an upper end, the combined system comprising: an electrically driven electrolysis unit disposed adjacent a lower end of the first and second water filled gas riser columns and configured to be provided with a water inlet, a hydrogen gas outlet, and an oxygen gas outlet, the electrically driven electrolysis unit configured, in use, to split water into hydrogen gas and oxygen gas in an electrolysis process in which process waste heat is generated; a hydrogen subsystem, at least one hydrogen gas transport vessel having at least one cavity and a gas inlet and a gas outlet communicating with the cavity, the vessel being configured to receive a quantity of hydrogen gas within the cavity and transport the hydrogen gas from the bottom to the top of the first gas riser column by buoyancy provided by the transported gas; a hydrogen subsystem comprising: a hydrogen gas connection means provided at a lower end of the first water-filled gas riser column and configured to provide a removable gas transport connection between the electrolysis unit and a gas inlet of the hydrogen gas transport vessel; and a hydrogen gas delivery means provided at an upper end of the first water-filled gas riser column and configured to provide a removable gas transport connection between the gas outlet and a hydrogen gas collector; an oxygen subsystem, At least one oxygen gas transport vessel having at least one cavity and a gas inlet and a gas outlet communicating with the cavity, the vessel being configured to receive a quantity of oxygen gas in the cavity and transport the oxygen gas from the bottom to the top of the second gas riser column by buoyancy provided by the transported gas; an oxygen subsystem comprising: an oxygen gas connection means provided at a lower end of the second water-filled gas riser column and configured to provide a removable gas transport connection between the electrolysis unit and a gas inlet of the oxygen gas transport vessel; and an oxygen gas delivery means provided at an upper end of the second water-filled gas riser column and configured to provide a removable gas transport connection between the gas outlet and an oxygen gas collector; a heat transfer unit connected to the electrolysis unit and to the hydrogen gas connection means or to the hydrogen gas transport vessel, the heat transfer unit being configured to transfer at least a portion of the waste heat from the electrolysis unit to the hydrogen gas in the hydrogen gas delivery means or to the hydrogen gas in the hydrogen gas transport vessel; The heat transfer unit is further connected to the oxygen gas connection means or the oxygen gas transport vessel and configured to transfer at least a portion of the waste heat from the electrolysis unit to the oxygen gas in the oxygen gas delivery means or the oxygen gas in the oxygen gas transport vessel.

[0023] The composite system according to the second aspect may be configured according to any one of the above-listed embodiments of the system according to the first aspect. The systems according to the first and second aspects may comprise one or more structural elements for forming a water-filled gas rising column, i.e. by filling the structural elements with water, or alternatively, the system may be submerged in a volume of water, such as a lake, ocean or the like, forming a water-filled gas rising column.

[0024] Systems according to the first and second aspects may in some embodiments comprise one or more water-filled gas riser columns. According to a third aspect of the present invention, there is provided a method of operating the above-described system, wherein the electrolysis unit produces at least hydrogen gas, with resulting waste heat being generated, the method comprising: a) a gas transport vessel reaches a lower end of a gas riser column and is maintained there; b) transferring a quantity of gas from the electrolysis unit to a gas transport vessel; c) heating the gas during transport or after it is received by the gas transport vessel; d) releasing the gas transport vessel which moves upward in the gas lift column due to buoyancy; e) causing the gas transport vessel to move upwardly due to buoyancy, the upward movement being controlled by monitoring the internal gas pressure within the gas transport vessel and the external pressure outside the gas transport vessel and selecting a control valve setting to provide a predetermined buoyancy; f) delivering the gas from the transport vessel to a gas collector at the top of the gas riser column; g) transporting the gas transport vessel back to the lower end of the gas riser column.

[0025] The method may be used to operate a system according to the first aspect or the second aspect. When the method is used to operate a system according to the second aspect, the method steps for handling hydrogen gas are performed in the hydrogen subsystem and the method steps for handling oxygen are performed in the oxygen subsystem.

[0026] According to one embodiment of the invention, the method includes, in the step of transporting the gas transport vessel back to the lower end of the gas riser column, the gas transport vessel is filled with water and thereby caused to submerge.

[0027] According to one embodiment of the present invention, the method comprises a step in which the buoyancy of the gas transport vessel is utilized in driving a generator as the gas transport vessel moves upward to the top of the gas riser column.

[0028] According to one embodiment of the present invention, the gas transport vessel comprises an incompressible container provided with a main cavity, an expansion vessel capable of varying volume and configured to be affected by both internal and external pressures, and a piping connecting the incompressible container and the expansion vessel, the piping being provided with a control valve, and the method in the step of moving the gas transport vessel upwards by buoyancy includes the steps of monitoring the internal gas pressure in the gas transport vessel and the external pressure outside the gas transport vessel, and controlling the upward movement by selecting a setting of at least the pressure regulating valve to provide a predetermined buoyancy, - A pipe connecting the incompressible container and the expansion vessel, the pipe being provided with a control valve.

[0029] According to one embodiment of the present invention, the non-compressible container is double-walled, providing an insulating space between the inner and outer walls of the non-compressible container, and in the step in which the gas transport vessel moves upwards, the pressure regulating means is activated to equalize the air pressure in the main cavity and in the insulating space.

[0030] The present invention allows for a significant increase in the overall efficiency of the system for producing hydrogen gas, which will have a significant impact on lowering the production costs for the "green" production of hydrogen or a combination of hydrogen and oxygen.

[0031] One advantage of the present invention is that when partially submerged in the ocean, lake, etc. to form a water-filled gas rising column, both the pressure available at depth and the buoyancy from the gas produced are utilized to enhance the performance of the system.

[0032] One further advantage is that the system is scalable. A further advantage is that newly developed electrolysis units capable of operating on natural waters such as seawater can be utilized in a very efficient manner.

[0033] In the following, the invention will be described in more detail, by way of example only, with reference to the accompanying drawings, in which: FIG. [Brief description of the drawings]

[0034] [Figure 1] 1 is a schematic diagram of a hydrogen gas production system according to one embodiment of the present invention. [Figure 2a] FIG. 2 is a schematic diagram of a gas delivery vessel of a hydrogen gas generation system according to an embodiment of the present invention. [Figure 2b] FIG. 2 is a schematic diagram of a gas delivery vessel of a hydrogen gas generation system according to an embodiment of the present invention. [Figure 2c] FIG. 2 is a schematic diagram of a gas delivery vessel of a hydrogen gas generation system according to an embodiment of the present invention. [Diagram 3] 1 is a schematic diagram of a gas delivery vessel of a hydrogen gas generation system according to one embodiment of the present invention. [Figure 4] 1 is a schematic diagram of a combined hydrogen and oxygen gas production system according to one embodiment of the present invention; [Diagram 5] 1 is a schematic diagram of a gas container transport apparatus for a hydrogen gas generation system according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Terms such as "top," "bottom," "upper," "lower," "below," "above," and the like are used solely with reference to the geometric shapes of the embodiments of the invention as illustrated in the drawings and / or during normal operation of the devices and systems described, and are not intended to limit the invention in any way.

[0036] The system for producing gas according to the present invention is described as being at least partially operated in a vertical column submerged in water or filled with water. Water is the typical and preferred choice of liquid in which to operate portions of the system for several reasons, including but not limited to minimal cost and because water is the starting material for the electrolysis process that produces hydrogen and oxygen gas. However, the present invention is not limited to water and other liquids may be utilized.

[0037] According to one aspect of the invention, a system 100 for generating gas is provided. The system 100 for generating gas according to the invention is shown diagrammatically in FIG. 1 and comprises the main structural elements of a waterfilled gas rise column 110, an electrically driven electrolysis unit 120, a heat transfer unit 130 and at least one gas transport vessel 210 shown in more detail in FIGS. 2a-2c. An electrical connector 119, such as a power cable, is arranged to supply power to the electrolysis unit 120. The waterfilled gas rise column 110 may be, according to an embodiment of the invention, an actual structural element, for example an upright elongated cylinder of steel or reinforced concrete, as shown in FIG. 1 for example. Alternatively, the system 100 for generating gas is submerged in water and the waterfilled gas rise column 110 should be seen as part of the water volume in which the gas transport vessel 210 moves up and down, and does not necessarily need to be surrounded by another structural element. The electrolysis unit 120 is configured to split water into hydrogen gas and oxygen gas in an electrolysis process during use, and is provided with at least one water inlet 121 and at least one gas outlet 122, the at least one gas outlet 122 being provided at the lower end 111 of the water-filled gas riser column 110 and configured to direct the generated gas into the interior of the gas riser column 110. The water-filled gas riser column 110 extends vertically and is provided at its upper end 112 with a gas collector 170. The gas collector 170 is typically connected to a compressor 150 or other means for providing gas in pressurized form. The gas generated by the electrolysis unit 120 is directed to a gas outlet 122 in the gas riser column 110, the gas outlet 122 having the function of a gas docking device 123 adapted to connect to a gas inlet 223 of a gas transport vessel 210 as shown diagrammatically in FIG. 2a. The gas outlet 122, gas docking device 123, and gas inlet 223 of the gas transport vessel 210 form a gas connection means 125 that provides the ability to deliver gas to the gas transport vessel 210, or to a series of regularly arriving gas transport vessels 210, typically at regular intervals.The gas transport vessel 210 is configured to receive a predetermined amount of gas at the lower end 111 of the gas riser column 110, rise through the gas riser column 110 by buoyancy, and deliver the gas to the gas collector 170 on the upper end 112 of the gas riser column 110.

[0038] According to an embodiment of the present invention, the system 100 for generating gas comprises a plurality of gas transport vessels 210 connected to each other by an endless belt or belt-type or chain-like component 180 that extends over the length of the gas lift column 110 and is configured for the gas transport vessels 210 to move up and down between a lower end 111 and an upper end 112. According to one embodiment, the gas transport vessels 210 are configured to move up within the gas lift column 110 and move down outside the gas lift column 110. According to one embodiment, the endless belt device 180 comprises a generator 190 that is driven by the belt and is powered by the buoyancy of the gas transport vessels 210 rising within the gas lift column 110. Alternatively, the rotation or other motion generated by the belt device 180 may be used to directly drive, for example, a compressor or other type of machine.

[0039] The gas docking device 123 comprises a valve that regulates the flow rate and pressure of the gas and can completely close the gas outlet 122 when the gas transport vessel 210 receives a predetermined amount of gas and thereby moves upward from the lower end 111 of the gas riser column 110. The gas docking device 123 may be communicatively connected to and controlled by a central control unit.

[0040] The heat transfer unit 130 of the system 100 for generating gas is provided to transfer excess heat generated by the electrolysis unit 120 to the gas generated by the electrolysis unit 120 before the gas is introduced into the gas transport vessel 210, or alternatively, the heat transfer unit 130 is configured to transfer heat to the generated gas in the gas transport vessel 210. By heating the gas to be introduced or already introduced into the gas transport vessel 210, the buoyancy of the gas transport vessel 210 can be increased compared to the buoyancy provided by unheated gas.

[0041] According to one embodiment of the present invention, the heat transfer unit 130 functions as a cooling member for the electrolysis unit 120 and thereby as a heat collector, and typically comprises a first thermal circuit 131 in direct contact with the heat generating part of the electrolysis unit 120. The first thermal circuit 131 comprises a first heat carrying medium. The heat exchanger 132 transfers the generated heat by means of a second heat carrying medium to the second thermal circuit 133. The heat exchanger 132 as well as the first thermal circuit 131 and the second thermal circuit 133 operate according to principles well known in the field of heat exchangers and can for example comprise a number of pumps circulating the first and second heat carrying media in the first thermal circuit 131 and the second thermal circuit 133, respectively. The second thermal circuit 133 is positioned directly or indirectly to heat the gas produced by the gas transport vessel 210, and heating of the gas may be provided either upstream or downstream of the gas outlet 122, downstream meaning that heating takes place within the gas transport vessel 210.

[0042] According to one embodiment, the second thermal circuit 133 comprises a gas heater 134 located downstream of the electrolysis unit 120 and upstream but adjacent to the gas outlet 122. The gas heater 134 may be a flow-through gas heater of conventional design. The second thermal circuit 133 may also comprise one or more accumulators for storing the generated heat.

[0043] A gas transport vessel 210 according to an embodiment of the invention is shown diagrammatically in Figures 2a-2c and comprises a body 211 having an internal cavity 212. A gas inlet 223 is provided at a lower end of the gas transport vessel 210 and leads into the cavity 212. A gas outlet 225 is provided at an upper end of the gas transport vessel 210 and leads out of the cavity 212. The gas inlet 223 and gas outlet 225 are provided with control valves, inlet valve 223:1 and outlet valve 225:1, configured to receive and deliver gas, respectively, during use. The outlet valve 225:1 is a control valve further configured to function as a pressure regulating valve and configured to provide fluid communication, during use, between the cavity 212 and the exterior of the gas transport vessel 210 or to a gas container separate from the cavity 212. An exhaust outlet 224 provided with an exhaust valve 224:1 extends from the cavity 212 to the outside of the gas transport vessel 210 and is configured to open to exhaust water present in the main cavity during filling the cavity 212 with gas, typically prior to filling. The gas transport vessel 210 is further provided with an internal pressure sensor 227 configured to provide a measurement of the pressure of the gas contained in the cavity 212 and an external pressure sensor 228 configured to provide a measurement of the pressure of the water surrounding the gas transport vessel 210. The internal pressure sensor 227 and the external pressure sensor 228 are configured to affect the adjustment of the outlet control valve 225:1, forming a pressure regulator 229. Also optionally or alternatively, the exhaust valve 224:1 may be used to adjust the pressure in the cavity 212 and may be configured to be influenced by the internal pressure sensor 227 and the external pressure sensor 228. The internal pressure sensor 227, the external pressure sensor 228, the exhaust valve 224:1, and the outlet control valve 225:1 may be configured to interact mechanically, hydrodynamically, or electronically. Preferably, the internal pressure sensor 227 and the external pressure sensor 228 are electronic devices that provide a digitized output that can be received by a control unit (not shown) and used to calculate and send a desired setting to the outlet control valve 225:1 and / or the exhaust valve 224:1, where the outlet control valve 225:1 and / or the exhaust valve 224:1 are electronically or electrically controlled valves.The internal pressure sensor 227, the external pressure sensor 228, the outlet control valve 225:1, and optionally the exhaust valve 224:1 are utilized to control the pressure inside the cavity 212 relative to the pressure outside the gas transport vessel 210 so that a desired and predetermined buoyancy is achieved. The settings of the outlet control valve 225:1 and / or the exhaust valve 224:1 depend on the depth (giving pressure) at which the gas transport vessel 210 is located at a given moment during the upward movement of the gas transport vessel. Furthermore, by continuously or semi-continuously controlling the outlet control valve 225:1 and / or the exhaust valve 224:1 during the upward movement, the movement can be controlled and optimized for different scenarios. For example, but not limited to, optimizing for maximum gas delivery to the gas collector 170 and slow upward movement, or providing maximum force from the utilized buoyancy or otherwise utilizing upward force for fast upward movement. The gas transport vessel 210 may be provided with additional pressure and / or temperature sensors 241 to further control and regulate the upward movement of the gas transport vessel 210. Measuring the temperature within the gas transport vessel 210 may provide the same information as measuring the pressure. As will be appreciated by those skilled in the art, the details of the pressure regulator 229 may be varied and still provide the above functionality.

[0044] According to one embodiment, the control unit may have one or more pressure profiles stored, which provide optimal pressure settings at varying external pressures or water depths for different desired scenarios, e.g. optimizing for maximum gas delivery or maximum force as discussed above.

[0045] According to one embodiment, the second thermal circuit 133 provides heating of the gas in the gas transport vessel 210, which is shown diagrammatically in Fig. 2b. According to this embodiment, the gas transport vessel 210 is provided with an internal heating device 230. During a part of the operation, the second thermal circuit 133 is connected to the internal heating device 230 of the gas transport vessel 210, such that these parts of the gas transport vessel 210 functionally form part of the second thermal circuit 133.

[0046] According to some embodiments, the gas transport vessel 210 comprises an internal heating device 230 and means for connecting the internal heating device 230 to the heat transfer unit 130, whereby functionally the internal heating device 230 forms part of the second thermal circuit 133, with the second heat carrying medium flowing from the heat exchanger 132 to the heating device 230. The heating device 230 in operation is thereby the heat delivery part of the heat transfer unit 130. The waste heat generated in the electrolysis unit 120 is thereby transferred to the gas transport vessel 210 via the heat transfer unit 130. The means for connecting the heating device 230 of the gas transport vessel 210 to the heat transfer unit 130 may be in the form of a pair of docking devices 231 that connect to corresponding docking devices 137 provided in the gas riser column 110, the corresponding docking devices being provided with regulating valves and in fluid communication with the heat transfer unit 130. During operation, with the gas transport vessel 210 connected to the docking device 231 , heat is transferred to the gas and / or water contained within the gas transport vessel 210 .

[0047] According to one embodiment, shown diagrammatically in FIG. 2 b , the heating device 230 comprises a coil 230 b disposed inside the gas transport vessel 210 . According to an alternative embodiment, shown diagrammatically in FIG. 2 c , the heating device 230 comprises a heating mantle 230 c disposed on at least a portion of the wall 240 of the gas transport vessel 210 .

[0048] The functioning of the components of the system for producing gas according to the invention is illustrated by explaining the operating principle, which is also the method of operating the system. a) The gas transport vessel 210 reaches the lower end of the gas riser column 110 and the docking device 123 connects to the gas inlet 223 of the gas transport vessel 210 .

[0049] According to an embodiment of the present invention, the heating device 230 of the gas transport vessel 210 connects to a pair of docking devices 137 of the heat transfer unit 130. Alternatively, the gas heater 134 is activated.

[0050] b) The gas produced in the electrolysis unit 120 and having the pressure and temperature provided by the electrolysis unit 120 is transferred to the gas transport vessel 210. c) Heat is transferred from the heat transfer unit 130 via a heating device to the gas contained within the gas transport vessel 210. Alternatively, if a gas heater 134 is utilized for heating, the gas is heated during transport to the gas transport vessel 210.

[0051] d) The gas transport vessel 210 is released and begins to move upwards. e) The upward movement of the gas transport vessel 210 is controlled by controlling the gas pressure within the cavity 212 in relation to the external pressure experienced by the gas transport vessel 210. The gas pressure within the cavity 212 is provided by an internal pressure sensor 227 and the external water pressure is provided by an external pressure sensor 228. Data from the pressure sensors forms the basis for selecting settings of the exhaust valve 224:1 and / or the outlet control valve 225:1 to provide the desired and predetermined buoyancy.

[0052] f) Gas is delivered from the gas transport vessel 210 to the gas collector 170. g) The gas transport vessel 210 is transported back to the lower end of the gas riser column 110. Preferably, the valve of the gas transport vessel 210 is configured so that the vessel is filled with water and submerged at the lower end of the gas riser column 110.

[0053] According to one embodiment of the invention as shown diagrammatically in FIG. 3, the gas transport vessel 310 comprises an incompressible container 310:1 and an expansion vessel 310:2. The incompressible container 310:1 is configured so as not to be compressed or deformed during use and may be made, for example, of steel or reinforced plastic. The expansion vessel 310:2 is configured so as to be able to change volume and is affected by both internal and external pressure. The expansion vessel 310:2 may be in the form of, for example, a rubber bladder or the like. The incompressible container 310:1 and the expansion vessel 310:2 are connected by a pipe 340 provided with a control valve 343. The expansion vessel 310:2 is provided with an outlet 325 having an outlet control valve 325:1, corresponding to the outlet arrangement described with reference to FIGS. 2a-2b. The incompressible container 310:1 is preferably double-walled such that an insulating space 342 is formed between an inner wall 345 and an outer wall 344. The outlet 326 leads from the main cavity 312, which is the internal cavity, to the outside of the gas transport vessel 310 via the first volume and pressure regulating valve 324. The gas transport vessel 310 is provided with a gas inlet 323 provided with an inlet control valve 323:1, which is in fluid communication with either the main cavity 312 or the insulating space 342 via a second volume and pressure regulating valve 334, depending on how the second volume and pressure regulating valve 334 is set. The gas transport vessel 310 is further provided with an internal pressure sensor 327 configured to provide a measurement of the pressure of the gas contained in the cavity 312, and an external pressure sensor 328 configured to provide a measurement of the pressure of the water surrounding the gas transport vessel 310. The internal pressure sensor 327 and the external pressure sensor 328 are configured to affect the regulation of the control valve 343 and optionally the first volume and pressure regulating valve 324, and form the main part of the pressure regulating device. The internal pressure sensor 327, the external pressure sensor 328, the first volume and pressure regulating valve 324, and the control valve 343 may be configured to interact mechanically or fluid-dynamically.Preferably, the internal pressure sensor 327 and the external pressure sensor 328 are electronic devices providing digitized outputs that can be received by a control unit (not shown) and used to calculate and send desired settings to the control valve 343 and the pressure regulating valve 224, where the control valve 343 and the pressure regulating valve 224 are electronically or electrically controlled valves. The internal pressure sensor 327, the external pressure sensor 328, the first volume and pressure regulating valve 324, and the control valve 343 are utilized to control the pressure inside the main cavity 312 relative to the pressure outside the gas transport vessel 310. The incompressible container 310:1 may further be provided with a differential pressure sensor 329 configured to provide a measurement of the difference in gas pressure between the main cavity 312 and the insulating space 342. The differential pressure sensor 329 is configured to act on the second volume and pressure regulating valve 334 to regulate and equalize the pressure between the main cavity 312 and the insulating space 342. Alternatively, the differential pressure sensor 329 may be realized with separate pressure sensors in the insulating space 342 and the main cavity 312, or the internal pressure sensor 327 may be used for this purpose. As above, the differential pressure sensor 329 may be mechanically connected with the second volume and the pressure regulating valve 334. Preferably, the differential pressure sensor 329 is an electronic sensor and the communication with the second volume and the pressure regulating valve 334 is digital. A vent valve 347 may be provided at the top of the insulating space 342 and lead to the outside of the transport vessel 310. The vent valve 347 is configured to vent gas or air from the insulating space 342. The gas transport vessel 310 may also comprise other sensors, such as one or more temperature sensors 341 or further pressure sensors.

[0054] According to one embodiment, the gas transport vessel 310 comprises a central control unit and a power supply, and all pressure sensors and controllable valves are connected to and controlled by the central control unit.

[0055] The embodiments and alternatives described with reference to Figures 2a-b also relate, where technically feasible, to a gas transport vessel 310 comprising an incompressible container 310:1 and an expansion vessel 310:2. In particular, the gas transport vessel 310 comprises an incompressible container 310:1 and an expansion vessel 310:2, which may be provided with an internal heating device as described above.

[0056] The functionality of the components of the gas transport vessel 310, including the incompressible container 310:1 and the expansion vessel 310:2, is illustrated by explaining the operating principle, which represents one embodiment of a method of operating the system.

[0057] a) The gas transport vessel 310 reaches the lower end of the gas riser column 110 and the docking device 123 connects to the gas inlet 323 of the gas transport vessel 310. During the preceding downward transport, the main cavity 312 and the insulating space 342 of the gas transport vessel 310 are at least partially filled with water.

[0058] b) Gas produced in the electrolysis unit 120 is introduced through the gas inlet 323. In a first filling step, the second volume and pressure regulating valve 334 is set to direct the incoming gas into the insulating space 342. The filling of the insulating space 342 ends when the gas pressure in the insulating space 342 reaches or exceeds the ambient water pressure, at which point water is drained from the insulating space 342. In a second filling step, the second volume and pressure regulating valve 334 is set to direct the incoming gas into the main cavity 312. The first volume and pressure regulating valve 324 is open to the ambient water so that the water in the main cavity 312 can be forced out by the increasing gas pressure. The filling of the main cavity 312 ends when the gas pressure reaches or exceeds the ambient water pressure.

[0059] c) Heat is transferred from the heat transfer unit 130 to the gas contained within the gas transport vessel 310 via an internal heating device preferably configured such that only the gas within the main cavity 312 is directly heated. Alternatively, if a gas heater 134 is utilized for heating, the gas is heated during transport to the gas transport vessel 310.

[0060] d) The gas transport vessel 310 is released and begins to move upwards. e) The upward movement of the gas transport vessel 310 is controlled by controlling the gas pressure in the main cavity 312 in relation to the external pressure to which the gas transport vessel 310 is subjected. The first volume and pressure regulating valve 324 is normally closed during the upward movement. The gas pressure in the main cavity 312 is provided by the internal pressure sensor 327, and the external water pressure is provided by the external pressure sensor 328. The data from the pressure sensors forms the basis for controlling the release of gas to the control valve 343 and the expansion vessel 310:2, thereby controlling the buoyancy. The differential pressure sensor 329 can detect the pressure difference between the main cavity 312 and the insulating space 342 upon the release of gas by the control valve 343, and the second volume and pressure regulating valve 334 is used to stabilize the pressure between the main cavity 312 and the insulating space 342.

[0061] In a first use case, the valve is controlled to maintain the highest possible gas pressure in the main cavity 312 during the upward movement phase. Thus, the control valve 343 is controlled to release gas only to the expansion vessel 310:2 to provide just enough buoyancy to maintain positive buoyancy. Alternatively, a minimum buoyancy value may be defined and the control valve 343 is controlled to provide a buoyancy above the minimum buoyancy value.

[0062] In the second use case, the valve is controlled to maximize buoyancy. High buoyancy can be utilized to increase the speed of upward movement and / or to provide an upward force to a belt or the like attached to the gas transport vessel 310 to provide power generation from a belt system. Thus, the control valve 343 is controlled to release gas to the expansion vessel 310:2 to provide a large positive buoyancy. Typically, the rise of the gas transport vessel 310 should not be uncontrollably fast otherwise gas pressure in the main cavity 312 will be "wasted". Thus, a maximum buoyancy value can be defined and the control valve 343 is controlled to provide a buoyancy below the maximum buoyancy value. Alternatively, a buoyancy value set point or a preferred buoyancy value range is predetermined and the control valve 343 is controlled to provide a buoyancy within the predefined range. Buoyancy can be determined from measurements provided by the internal pressure sensor 327 and the external pressure sensor 328. The gas transport vessel 310 may further be provided with means for measuring the speed of upward movement.

[0063] f) At the top of the gas riser column 110, the outlet valve 325:1 is connected to the gas collector 170, the control valve 343 is opened, and gas is delivered from the main cavity 312 of the gas transport vessel 310. The second volume and pressure regulating valve 334 and / or the first volume and pressure regulating valve 324 are controlled to open the connection between the main cavity 312 and the insulating space 342, so that the gas contained in the insulating space 342 can also be delivered to the gas collector 170.

[0064] g) The gas transport vessel 310 is transported back to the lower end of the gas riser column 110, preferably by sinking the gas transport vessel 310 with negative buoyancy. Negative buoyancy may be achieved by opening the first volume and pressure regulating valve 324 to the surrounding water after the gas transport vessel 310 is released from the gas collector 170, and leaving the outlet valve 325:1 and the control valve 343 open, thereby filling the main cavity 312 with water. The second volume and pressure regulating valve 334 may be set to open between the main cavity 312 and the insulating space 342 so that the insulating space 342 also fills with water, and the exhaust valve 347 is opened to vent the gas.

[0065] According to one aspect of the present invention, a combined system 400 for producing hydrogen gas and oxygen gas is provided and is shown diagrammatically in FIG. 4. In the combined system 400, an electrically driven electrolysis unit 420 is provided with a water inlet 418, an electrical connector 419, a hydrogen gas outlet 422 and an oxygen gas outlet 421. The hydrogen gas outlet 422 and the oxygen gas outlet 421 lead to two separate subsystems, namely a hydrogen subsystem 410 and an oxygen subsystem 411, arranged in separate gas riser columns in the form of a first gas riser column 110 and a second gas column 110', comprising separate gas transport vessels or the like. Both subsystems are constructed according to the above description and the described embodiments and alternatives relate to both subsystems. Preferably, the heat transfer system 430 of the combined system 400 is configured to heat both hydrogen gas and oxygen gas using a heating device according to the above description. Given the density differences, the settings of the pressure regulating means to provide the desired buoyancy will be different for the hydrogen and oxygen subsystems, and such differences will be apparent to one of ordinary skill in the art in light of the teachings above.

[0066] According to one implementation of the present invention, the electrolysis unit 120 and the heat transfer unit 130 are submerged in an ocean, lake or reservoir at a depth ranging from 100 to 500 m, preferably 200 to 300 m. Preferably, the electrolysis unit 120 can process water from the ocean or lake directly or with some uncomplicated filtering such as the technique described in Non-Patent Document 1. A system operating at a depth of 200 m has an operating pressure of 2000 kPa (20 bar). The gas transport vessel can be submerged at a depth of 5 m. 3 ~20m 3 Preferably, the gas transport vessel is designed to have a cavity in the size range of 12m. If the gas transport vessel comprises an expansion vessel, the expansion vessel is preferably approximately the same size as the main cavity in its expanded state. FIG. 5 shows a schematic of a portion of a system utilizing 16 gas transport vessels 510 connected to a belt 580 to drive the belt 580 to produce hydrogen gas. The belt drives at least one generator 590 and may further comprise a number of support wheels 595 and other arrangements for temporarily storing the gas transport vessels separately at the top and bottom to facilitate gas delivery. The operation is preferably balanced so that the same number of gas transport vessels move up and down during operation. The expansion vessel preferably has a size of 12m. 3 Utilizing 16 gas transport vessels, the system may be designed to produce approximately 15000 kg / day of hydrogen, if each gas transport vessel receives an additional 5 kWh from heat transfer to the gas transported to the top, following the example of a 200 m working depth, the increased buoyancy utilized by the belt-driven generator is provided to the electrolysis unit as part of the required drive current, and the efficiency of the system increases by an order of magnitude of 10% or more compared to a gas generation system that does not utilize waste heat. The construction of such a system can utilize conventional construction techniques and materials, as well as at least those developed for offshore oil drilling and the like. The material of the main container of the gas transport vessel may be stainless steel or reinforced plastic, e.g. carbon fiber reinforced plastic. Suitable materials are commercially available.

[0067] The above-described embodiments should be understood as illustrative examples of the system and method of the present invention. Those skilled in the art will understand that various modifications, combinations and changes can be made to the embodiments. In particular, different part solutions in different embodiments can be combined in other configurations, if technically possible.

Claims

1. 1. A system (100) for producing hydrogen gas configured to be disposed within or associated with a volume of water forming a water-filled gas rising column (110) having a lower end (111) and an upper end (112), comprising: an electrically driven electrolysis unit (120) disposed adjacent the lower end (111) of the water-filled gas riser column (110), the electrolysis unit (120) configured to have a water inlet (121) and at least one gas outlet (122), the electrically driven electrolysis unit (120) configured, in use, to decompose water into hydrogen gas and oxygen gas in an electrolysis process during which process waste heat is generated; at least one gas transport vessel (210; 310) having at least one cavity (212) and a gas inlet (223) and a gas outlet (225) communicating with said cavity (212), configured to receive a predetermined amount of hydrogen gas in said cavity (212) and transport said hydrogen gas from the bottom to the top of said gas riser column (110) by buoyancy provided by the transported gas; a gas connection means (125) provided at the lower end (111) of the water-filled gas riser column (110) and configured to provide a removable gas transport connection between the electrolysis unit (120) and the gas inlet (223) of the gas transport vessel (210; 310); and a gas delivery means (125) provided at the upper end (112) of the water-filled gas riser column (110) and configured to provide a removable gas transport connection between the gas outlet (225) and a gas collector (170). A system (100) for producing hydrogen gas, comprising: the electrolysis unit (120); and a heat transfer unit (130) connected to the gas connection means (125) or the gas transport vessel (210; 310), and configured to transfer at least a portion of waste heat from the electrolysis unit (120) to hydrogen gas in the gas delivery means (125) or the gas transport vessel (210; 310).

2. 2. The system for producing hydrogen gas according to claim 1, wherein the heat transfer unit comprises: a first thermal circuit arranged in contact with a heat-generating portion of the electrolysis unit, thereby cooling the electrolysis unit; a second thermal circuit configured to heat the gas produced by the electrolysis unit; and a heat exchanger configured to transfer heat from the first thermal circuit to the second thermal circuit.

3. 3. The system (100) for producing hydrogen gas as recited in claim 2, wherein the heat transfer unit (130) comprises a flow-through gas heater (134) disposed between the electrolysis unit (120) and the gas connection means (125).

4. 3. The system (100) for producing hydrogen gas as recited in claim 2, wherein the heat transfer unit (130) comprises an internal heating device (230) disposed within the gas transport vessel (210) and forming part of the second thermal circuit (133).

5. 5. The system (100) for producing hydrogen gas as recited in claim 4, wherein the internal heating device (230) comprises a coil (230b) disposed inside the gas transport vessel (210).

6. 5. The system (100) for producing hydrogen gas as recited in claim 4, wherein the internal heating device (230) comprises a heating mantle (230c) disposed on at least a portion of a wall of the gas transport vessel (210).

7. 2. The system for producing hydrogen gas according to claim 1, wherein the gas transport vessel comprises a pressure regulator configured to control the gas pressure in the cavity of the gas transport vessel relative to an external pressure, thereby controlling the buoyancy of the gas transport vessel while the gas transport vessel is filled with heated gas received from the electrolysis unit and ascends through the gas riser column.

8. The pressure adjusting device (229) a control valve (225:1; 343) configured to provide fluid communication between the cavity (212) and the exterior of the gas transport vessel (210) or to a gas container separate from the cavity (212); an internal pressure sensor (227) configured to provide a measurement of the pressure of a gas contained within said cavity (212); an external pressure sensor (228) configured to provide a measurement of the pressure of the water surrounding the gas transport vessel (210); 8. The system (100) for producing hydrogen gas as described in claim 7, wherein the internal pressure sensor (227) and the external pressure sensor (228) are configured to affect adjustment of the control valve (225:1; 343) to control the pressure inside the cavity (212) relative to the pressure outside the gas transport vessel (210) so that a predetermined buoyancy is achieved.

9. 9. The system for producing hydrogen gas according to claim 8, wherein the pressure regulator further comprises a control unit configured to receive measurement data from the internal pressure sensor and the external pressure sensor and to control the control valve, the control unit having a stored pressure profile and configured to adjust the control valve according to the stored pressure profile.

10. The gas transport vessel (310) an incompressible container (310:1) provided with a main cavity (312); an expansion vessel (310:2) capable of varying its volume and configured to be affected by both internal and external pressure; a pipe (340) connecting the incompressible container (310:1) and the expansion vessel (310:2), the pipe (340) being provided with a control valve (343); an internal pressure sensor (327) configured to provide a measurement of the pressure of the gas contained within the main cavity (312); and an external pressure sensor (328) configured to provide a measurement of the pressure of the water surrounding the gas transport vessel (310); 8. The system (100) for producing hydrogen gas as recited in claim 7, wherein the internal pressure sensor (327) and the external pressure sensor (328) are configured to affect adjustment of the control valve (343), thereby controlling the flow of gas between the main cavity (312) and the expansion vessel (310:2).

11. the incompressible container (310:1) is double-walled, providing an insulating space (342) between an inner wall (343) and an outer wall (344) of the incompressible container (310:1); 11. The system for producing hydrogen gas as recited in claim 10, wherein the incompressible container is provided with a differential pressure sensor configured to provide a measurement of a difference in gas pressure between the main cavity and the insulating space, and a second volume and pressure regulating valve configured to equalize the pressure between the main cavity and the insulating space.

12. 10. The system (100) for producing hydrogen gas as recited in claim 1, further comprising a belt (180) having a plurality of gas transport vessels (210; 310) attached thereto, the belt (180) being configured to drive a generator (190).

13. A combined system (400) for producing hydrogen gas and oxygen gas, comprising: configured to be disposed within or connected to at least one water volume forming a first water-filled gas riser column (110) having a lower end (111) and an upper end (112), and a second water-filled gas riser column (110') having a lower end (111') and an upper end (112'); an electrically driven electrolysis unit (420) disposed adjacent the lower ends (111) of the first and second water-filled gas riser columns (110), the electrolysis unit (420) being configured to have a water inlet (418), a hydrogen gas outlet (421), and an oxygen gas outlet (422), the electrically driven electrolysis unit (420) being configured, in use, to decompose water into hydrogen gas and oxygen gas in an electrolysis process during which process waste heat is generated; A hydrogen subsystem (410) comprising: at least one hydrogen gas transport vessel (210; 310) having at least one cavity (212) and a gas inlet (223) and a gas outlet (225) communicating with the cavity (212), the vessel being configured to receive a predetermined amount of hydrogen gas in the cavity (212) and transport the hydrogen gas from the bottom to the top of the first gas riser column (110) by buoyancy provided by the transported gas; a hydrogen subsystem (410) comprising: a hydrogen gas connection means (125) disposed at the lower end (111) of the first water-filled gas riser column (110) and configured to provide a removable gas transport connection between the electrolysis unit (120) and a gas inlet (223) of the hydrogen gas transport vessel (210; 310); and a hydrogen gas delivery means (125) disposed at the upper end (112) of the first water-filled gas riser column (110) and configured to provide a removable gas transport connection between the gas outlet (225) and a hydrogen gas collector (170); An oxygen subsystem (411) comprising: At least one oxygen gas transport vessel (210; 310) having at least one cavity (212) and a gas inlet (223) and a gas outlet (225) communicating with the cavity (212), configured to receive a predetermined amount of oxygen gas into the cavity (212) and transport the oxygen gas from the bottom to the top of the second gas riser column (110') by buoyancy provided by the transported gas; an oxygen subsystem (411) comprising: oxygen gas connection means (125) provided at the lower end (111) of the second water-filled gas riser column (110') and configured to provide a removable gas transport connection between the electrolysis unit (120) and the gas inlet (223) of the oxygen gas transport vessel (210; 310); and oxygen gas delivery means (125) provided at the upper end (112) of the second water-filled gas riser column (110') and configured to provide a removable gas transport connection between the gas outlet (225) and an oxygen gas collector (170); a heat transfer unit (430) connected to the electrolysis unit (420) and the hydrogen gas connection means (125) or the hydrogen gas transport vessel (210; 310), the heat transfer unit (430) configured to transfer at least a portion of waste heat from the electrolysis unit (120) to the hydrogen gas in the hydrogen gas delivery means (125) or the hydrogen gas in the hydrogen gas transport vessel (210; 310); The heat transfer unit (430) is further connected to the oxygen gas connection means (125) or the oxygen gas transport vessel (210; 310) and is configured to transfer at least a portion of the waste heat from the electrolysis unit (120) to the oxygen gas in the oxygen gas delivery means (125) or the oxygen gas in the oxygen gas transport vessel (210; 310).

14. The electrolysis unit (120) produces at least hydrogen gas, and in the process, waste heat is generated; a) the gas transport vessel (210; 310) reaches the lower end of the gas riser column (110) and is maintained there; b) transferring a predetermined amount of hydrogen gas from the electrolysis unit (120) to the gas transport vessel (210; 310); c) heating the hydrogen gas during transport or after it is received by a gas transport vessel (210; 310); d) Releasing the gas transport vessel (210; 310) which is moving upward in the hydrogen gas riser column (110) due to buoyancy; e) causing the gas transport vessel (210; 310) to move upwards due to buoyancy, the upward movement being controlled by monitoring the internal gas pressure within the gas transport vessel (210; 310) and the external pressure outside the gas transport vessel (210; 310) and selecting a setting for the control valve (225:1; 343) to provide a predetermined buoyancy; f) delivering the hydrogen gas from the transport vessel (210; 310) to the gas collector (170) at the top of the gas riser column (110); g) transporting the gas transport vessel (210; 310) back to the lower end of the gas riser column (110).

15. 15. The method for producing hydrogen gas according to claim 14, wherein in the step of transporting the gas transport vessel (210; 310) back to the lower end (111) of the gas riser column (110), the gas transport vessel is filled with water and submerged.

16. 15. The method for producing hydrogen gas according to claim 14, further comprising using the system according to claim 12, wherein the buoyancy of the gas transport vessel (210; 310) is utilized to drive the generator (190) during the step of moving the gas transport vessel (210; 310) upward to the top of the gas riser column (110).

17. 15. The method for producing hydrogen gas as described in claim 14 using the system as described in claim 11, wherein the gas transport vessel (310) comprises an incompressible container (310:1) having a main cavity (312), an expansion vessel (310:2) capable of changing its volume and configured to be affected by both internal and external pressures, and piping (340) connecting the incompressible container (310:1) and the expansion vessel (310:2), the piping (340) being provided with a control valve (343), and wherein the step of moving the gas transport vessel (210; 310) upward by buoyancy includes the step of monitoring the internal gas pressure in the gas transport vessel (310) and the external pressure outside the gas transport vessel (310) and controlling the upward movement by selecting a setting of at least the pressure regulating valve (334) to provide a predetermined buoyancy.

18. 18. The method for producing hydrogen gas according to claim 17, wherein the non-compressible container (310:1) is double-walled and provides an insulating space (342) between an inner wall (345) and an outer wall (344) of the non-compressible container (310:1), and in the step of moving the gas transport vessel (210; 310) upward, a pressure regulating means is activated to equalize the air pressure in the main cavity (312) and the insulating space.

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