The present invention relates to a gas generator and more particularly to an apparatus for generating pressurised gas on demand employing chemical reactions initiated by contact in a high shear environment; these batch reactions occurring sequentially and delivering continuous generated gas and pressure via a common gas rail connecting each reactor.

Background of the Invention

It is well known that certain chemical reactions produce a range of gases during contact between various materials. Such reactions in an enclosed vessel will also generate pressure as gas evolves, and may also create an exothermic product, whilst other reactions may require the introduction of heat in order to initiate the appropriate environment for a successful reaction to take place.

With regard to volatile gases in particular, there are a number of advantages to be gained by avoiding the space requirements, safety considerations, delivery challenges and associated costs of distributing and using pressurised gases in a highly compressed format. Equipment is generally large and cumbersome, and does not adapt easily to existing engineering architecture when in either a mobile or static application.

In many instances, the pressure required at the point of use is many orders of magnitude less than that required to economically transport and store a given gas.

Previous apparatuses intended to generate gas at the point of use have tended to suffer either from a lack of efficiency, or the need for compressors in multiple configurations and numerous components, with the resultant regular maintenance required for such parts. This, in turn, leads to higher costs to produce robust components, higher assembly costs to construct the apparatus, and reliability issues unless a strict maintenance regime is observed.

WO2014/013246 (Prometheus Wireless Limited) discloses a fuel cell apparatus and a hydrogen generator for use with the fuel cell. The fuel cell and hydrogen generator are intended primarily for mobile use. The hydrogen generator uses the reaction between a chemical hydride and water to produce water. WO2014/013246 discloses that a plurality of reactor vessels may be connected in parallel and may be used in a staggered manner in order to provide a continuous supply of gas. The reactor vessels used in the hydrogen generator of WO2014/013246 do not make use of mixing devices but, instead, mixing is achieved by vigorously shaking the reactor vessel to mix and initiate reaction between the reactants. Mixing is apparently also facilitated by convection currents and the upward movement of hydrogen gas bubbles within the reactor. The reactor vessels used in the apparatus of WO2014/013246 are relatively small in size and it is disclosed that a hydrogen generator for use with a 50W fuel cell apparatus would require a reactor vessel of 2 litre capacity.

Korean patent application KR1020180031996 (Daewoo Shipbuilding & Marine) discloses a hydrogen generator and fuel cell combination for use in underwater vehicles. The hydrogen generator may comprise several reactor vessels in parallel thereby enabling maintenance and repair of one reactor whilst maintaining constancy of hydrogen supply to the fuel cells. Whilst Figure 3 in KR1020180031996 shows each of the three parallel reactors as having what appears to be mechanical mixers, KR1020180031996 is otherwise silent as to the nature of the mixers and their mode of operation.

The Invention

It is an object of the present invention to provide an apparatus which mitigates or obviates at least one of the disadvantages of known methods and devices.

It is also an object of the invention to provide an apparatus for generating gas which is flexible in design when integrating with pre-existing engineering architecture and allows specified volumes of gas at desired pressures to be produced at will according to the requirements of the specific application, using a number of reactors of a specified size on a common gas rail linking the reactors.

It is a further object of the invention to provide an apparatus for generating gas and exothermic heat together for useful deployment on a mobile platform, where the apparatus can be flexibly and easily integrated into extant engineering designs.

It is another object of the invention to reduce the dangers inherent in the storage of volatile gases in particular by eliminating insofar as possible the presence of pressurised gas when immediate supply is not required and in any event holding such gas in far smaller volumes and far lower pressures than present volume gas storage equipment.

The present invention makes use of a plurality of chemical reactors each linked to a common gas rail, wherein each reactor is provided with a high shear mixer to allow rapid mixing of reactants and therefore rapid evolution of a desired gas which is then fed into the common gas rail. The reactors can be activated in a desired sequence and at desired intervals to provide a desired pressure of gas within the common gas rail. Because the reactors are provided with high shear mixers, the chemical reactions taking place in the reactors can be brought to completion rapidly and the spent reactants (i.e. chemical waste) removed from the reactors and fresh reactants charged into the reactor if desired.

Accordingly, in a first aspect, the invention provides an apparatus for generating gas, the apparatus comprising: a plurality of chemical reactors, each chemical reactor comprising a reactor vessel equipped with a high shear mixer; the reactor vessel having at least one inlet for introducing one or more chemicals into the reactor, from which chemical or chemicals a gas can be generated; at least one waste discharge outlet through which chemical waste can exit the reactor vessel; and a gas outlet through which generated gas can exit the reactor; a common gas rail linked to the gas outlets of each of the chemical reactors; and an electronic controller operatively linked to each of the chemical reactors and being programmed or programmable to control the timing and rate of evolution of gas within the chemical reactors to maintain a desired pressure of gas within the common gas rail.

Further aspects and embodiments of the invention are as set out below and the claims appended hereto.

Each chemical reactor comprises a reactor vessel equipped with a high shear mixer. High shear mixers typically have a drive motor and a high shear mixing head which rotates at very high speeds, for example in the range from about 500 rpm up to about 10,000 rpm, more usually in the range from about 750 rpm up to about 9,000 rpm, for example in the range from about 1 ,000 rpm to about 8,500 rpm.

High shear mixers typically comprise a rotor (rotating mixing head) and a stator (a stationary structure) within which the rotor rotates. The radial gap between the rotor and stator is relatively small such that fluids present in the gap (shear zone) are subjected to high shearing forces as the rotor rotates.

High shear mixers are typically able to provide very high torque outputs, for example up to 4000 newton-metres.

Examples of high shear mixers are the mixers available from Joshua Greaves & Sons Ltd of Ramsbottom, United Kingdom, and Silverson Machines Ltd of Chesham, United Kingdom.

In some embodiments of the invention, the high shear mixer in each reactor has its own drive motor. In other embodiments of the invention, the high shear mixers of several reactors may be linked via a common drive shaft to a common drive motor. In this embodiment, the reactors may be vertically stacked so that a common drive shaft passes down through each reactor in the stack.

An electronic controller is operatively linked to each of the chemical reactors and is programmed or programmable to control the timing and rate of evolution of gas within the chemical reactors to maintain a desired pressure of gas within the common gas rail.

The electronic controller can be operatively linked to each of the chemical reactors by means of hard wiring, or by wireless connection, or by a combination of hard wiring and wireless connection. Electronic controllers suitable for use controlling the operation of the chemical reactors will be well known to the skilled person.

The electronic controller is linked to at least one pressure sensor for determining whether a pressure of gas within the common gas rail is the desired pressure.

The desired pressure may be a constant pressure or a pressure that fluctuates between predetermined limits, depending on the use to which the generated gas is to be put.

The electronic controller is also typically linked to one or more sensors or gauges for measuring other operational and reaction parameters such as gas flow rates, temperatures, indicators of reaction progress such as pH meters and spectrophotometers, as well as any valves, metering devices, fans or pumps required to control the movement of materials through the apparatus and to distribute the gas produced in the reactors.

The electronic controller is typically programmed to bring two or more reactors into operation in a sequential manner, such that each reactor is operated on a batch basis by the introduction into the reactor of amounts of reactants needed to produce a desired amount of gas. The operation of the reactors may be on a staggered basis so that there are always several reactors in operation, typically at different stages of progress, or the operation of one reactor may be initiated once the reaction in another reactor has finished. Thus, the number and sequence of reactor operations and the intervals between the activation of different reactors can be determined according to the desired gas output.

The electronic controller may be programmed to perform a flushing step at the end of each batch reaction in a reactor so as to ready the reactor for the next batch reaction. The reactor vessels forming part of the chemical reactors used in the apparatus of the invention can vary widely in size, depending on the volumes and pressures of gases that are desired to be generated in a given situation. By way of example, reactor vessel volumes can be between 0.5 litres and forty litres in size.

In one embodiment, each reactor vessel has a volume of between 3 litres and 40 litres in size, for example from 5 litres up to 40 litres.

Each reactor is typically provided with a thermal exchange jacket through which either a coolant or a warming liquid can be passed in order to cool the reactor (in the case of an exothermic reaction) or warm the reactor (in the case of an endothermic reaction or a reaction with a high activation energy).

The thermal exchange jacket may take the form of a coil formed from a heat conducting material such as a metal (e.g. copper) wound around the reactor vessel. The thermal exchange jacket is typically connected to a heat exchanger which either extracts heat or provides heat to a thermal exchange fluid in the thermal exchange jacket.

In one embodiment of the invention, the reaction carried out in the reactors is an exothermic reaction and the heat produced by the reaction is extracted by a heat exchanger connected to the thermal exchange jacket and directed to a point of use.

Each reactor is provided with one or more inlets through which reactants can be introduced into the reactor vessel. The inlets are typically connected to metering devices for metering controlled amounts of reactants into the reactors. The metering devices are typically connected to the electronic controller. By way of example, reactants can be introduced into the reactors in the form of liquids, gels, slurries, granulates, powders, pellets or gases.

The inlets are typically provided with pressure seals to prevent back-flow of gases generated in the reactor vessels.

In one embodiment of the invention, the inlets are connected to PTFE-coated helical screws which meter and deliver the required materials in the required amounts into the reactor vessel whilst maintaining a pressure seal.

In preferred embodiments of the invention, reactants are taken from separate tanks which each may be removably attached to the apparatus as sealed cassettes containing reactants, thereby bypassing the necessity for removal or other handling of the materials therein directly. Each reactor is provided with a gas outlet. The gas outlet, or pipework leading to the common gas rail, or the connection to the common gas rail, are typically provided with an isolator valve to enable the reactor to be isolated from the common gas rail when desired or necessary. The isolator valve is typically linked electronically (by wiring or wirelessly) to the electronic controller.

In some embodiments of the invention, the pressure of gas leaving each reactor is governed by a valve which is actuated by mechanical means and controlled either directly by pressure within the vessel or via the electronic controller.

The common gas rail may be formed from a number of materials, provided that they are inert and substantially impermeable to the gases generated in the reactors. As such, they may be formed from a material selected from plastics, metals, alloys and rubber compounds and mixtures thereof.

In one embodiment, the common gas rail is formed from a plastics material.

The common gas rail may be formed from a laminar material wherein one layer provides mechanical strength and another layer provides enhanced resistance to permeation by the gas.

In a preferred embodiment, the common gas rail will pass through gas drying or other conditioning filters or apparatus to remove moisture or other contaminants from the evolved gas stream.

The common gas rail may also be connected to one or more buffer tanks in order to smooth pressure and gas flow fluctuations. For example, in one embodiment, the common gas rail is attached to one or more diaphragm expansion tanks.

In certain embodiments the apparatus comprises a plurality of common gas rails.

In one embodiment, each reactor will have a plurality (e.g. two or three) or gas outlets linked to a plurality of different common gas rails. Each gas outlet is provided or connected to a valve so that control can be exerted over which common gas rail the gas outlet vents into.

In some embodiments, the gas produced in a given reactor will only vent into one common gas rail at a given time. In other embodiments, a given reactor may vent into several different common gas rails simultaneously. An advantage of having a plurality of common gas rails is that they have the capability for accommodating larger volumes and flow rates of gas for variable demand and they offer redundancy in the event of a pipe failure.

Each reactor is also provided with at least one waste discharge outlet through which waste materials such as spent reactants and reaction products can be removed from the reactor. The waste discharge outlets can be used to remove liquids, gels, slurries, granulates, pellets and other solids either together or separately. In one embodiment, the waste discharge outlet comprises a pipe which extends down to a lower end of the reactor vessel so that waste materials accumulating in the bottom of the reactor vessel can be extracted (e.g. sucked or pumped out or, employing pressure within the reactor, partially or wholly ejected).

The progress of the reaction in a given reactor and its degree of completion can be determined by measuring one or more parameters such as the pressures of gases being generated and/or the pH of the reaction mixture in the reactor and/or changes in the temperature of the reaction mixture and/or changes in the colour of the reaction mixture by one or more sensors or probes suitable for measuring each such parameter. A reaction may be judged to be complete once certain reaction parameters meet predefined values, at which point the contents of the reactor vessel may be discharged through the waste outlet.

The exit of waste material from the reactor vessel is typically governed by a valve which may be actuated by mechanical or electromechanical means and may be controlled either directly by pressure within the vessel or by the electronic controller.

In preferred embodiments of the invention, waste materials are discharged through the waste outlet to a waste storage tank which may subsequently be removed from the apparatus as a sealed cassette containing the spent reactants. Such an arrangement thereby bypasses the necessity for removal or other handling of the waste materials directly.

In some embodiments of the invention, the same chemical reaction may be used in each of the plurality of chemical reactors.

In other embodiments of the invention, differing reactive materials are combined sequentially in separate reactors, wherein the heat harvested from one reaction may be employed to provide necessary heat to another reaction and thereby promote its efficient progress in evolving gas.

In one embodiment, the plurality of reactors making up the apparatus of the invention are arranged side by side, with each reactor having its own drive motor for its high shear mixer. In another embodiment, the plurality of reactors making up the apparatus of the invention are stacked one upon another. In this embodiment, a common drive shaft connected to a common motor drive may be used to drive the high shear mixing heads of the reactors in the stack.

In some embodiments of the invention, two or more of the plurality of chemical reactors may be in fluid contact with each other. For example, where a multistage reaction sequence is used to generate a desired gas, the chemical waste from one reactor may serve as one of the reactants for a next reaction in a sequence, in which case the waste outlet of one reactor may be linked to an inlet of the next reactor in a chain.

More usually, however, each of the chemical reactors will operate independently and will not be in fluid communication with the other reactors.

In each of the foregoing aspects and embodiments of the invention, the common gas rail may be connected to a gas-storage or gas-consuming device for storing or consuming the gas generated in the plurality of reactors.

In one particular embodiment, the common gas rail is connected to a device for storing the gas, such as a gas-reservoir or tank or a device for liquifying the gas.

In another particular embodiment, the common gas rail is connected directly or indirectly to a device for consuming the gas. For example, when the generated gas is hydrogen, the common gas rail may be connected directly or indirectly to a device such as a hydrogen- powered electricity generator.

In a further aspect of the invention, there is provided a process for the generation of a gas, which process comprises the use of the apparatus as defined herein.

In one embodiment, the process comprises the use of the apparatus to perform a sequence of batch reactions at intervals, the length of the intervals being controlled in accordance with the pressures and volumes of gas desired.

The individual chemical reactors may be activated in a staggered manner so that there are at least two reactors in operation at a given time.

Alternatively, the individual chemical reactors may be activated in sequence so that only one reaction is in use at a given time. In between reactions, a chemical reactor and its associated pipework may be purged or flushed to remove unwanted materials from the apparatus.

Thus, in one embodiment, the electronic controller can be programmed to initiate a flushing or purging cycle after each batch reaction or a predetermined number of batch reactions.

The apparatus and processes of the invention may be used to generate desired gases on demand from a range of chemical reactions. One such gas is hydrogen and one such reaction comprises the generation of hydrogen by the reaction of aluminium with water in the presence of a catalyst such as sodium hydroxide.

Brief Description of the Drawings

Figure 1 is an isometric view of a chemical reactor forming part of an apparatus according to one embodiment of the invention.

Figure 2 is another isometric view of the chemical reactor of Figure 1 , but with the outer cooling coil omitted for clarity and the side wall partially cut away to show the interior of the reactor.

Figure 3 shows three of the chemical reactors of Figures 1 and 2 arranged in a vertical stack.

Figure 4 shows three of the chemical reactors of Figures 1 and 2 connected together by a common gas rail.

Figure 5 is a schematic illustration showing four chemical reactors connected together by a common gas rail and linked to an electronic controller.

Detailed Description of the Invention

In order that the invention can be easily understood and readily carried into effect, reference will now be made, by way of example only, to the accompanying drawings.

Figure 1 shows a chemical reactor (2) forming part of an apparatus according to a first embodiment of the invention. The reactor (2) comprises a reactor vessel body (4) and a top (6) securely fastened (fastenings not shown) to the vessel body (4). The reactor vessel is typically formed from stainless steel or another suitably resistant (to the reactants/products) material. The top (6) can be removed for cleaning and maintenance purposes. The bottom (7) of the reactor vessel may also be removable (fastenings not shown in the Figures) to facilitate cleaning and maintenance.

Attached to the side wall of the reactor vessel body (4) are a pair of brackets (8) which enable the reactor to be connected to a support structure or to other reactors.

A cooling/heating jacket (10) comprising a coil of a suitable heat conducting material such as copper is coiled around the mid to lower part of the reactor vessel body (4). The jacket (10) is connected to a source of coolant/heating fluid (not shown) and typically also a heat exchanger (not shown).

The top (6) of the reactor vessel is provided with a gas outlet pipe (12) which is connected to a common gas rail (14), as shown in Figure 4. The top (6) of the reactor vessel is also provided with a plurality of inlet tubes (15) which can be used to introduce chemical reactants into the reactor vessel, and an outlet tube (16) which extends down through the vessel and terminates near to the bottom of the vessel. The outlet tube (16) can be used to remove reaction products and spent reactants (waste materials) from the reactor vessel.

Mounted in the centre of the top (6) is a high shear mixer comprising a high torque axial flux motor (18) and a high shear mixing head (20) (see Figure 2). The motor (10) is capable of providing torque in the range of up to 4000 newton-metres and rotational speeds of up to 8,400 rpm. An example of such a high shear mixer is the Silverson Model RBX400 manufactured by Silverson Machines Limited of Chesham, England, fitted with an axial flux motor and gearbox.

The high shear mixing head (20) comprises a stator (22) mounted on supporting rods (24) extending down from the upper end of the mixer. A drive shaft (26) is connected to the motor and is provided at its lower end with a rotor/impeller (28). The radial gap between the rotor (28) and the stator (22) is narrow and therefore provides a high shear zone in which very high shear forces act on the reactant materials. Although not shown in Figure 2, the stator can be provided with holes, baffles and other surface features in order to increase the level of shear exerted on the reactants in the high shear zone.

In use, a plurality of the reactors will be connected together via a common gas rail (14) as shown in Figure 4, with T-connectors (32) connecting the gas outlet pipes (12) of each reactor with the common gas rail (14). The T-connectors contain valves (not shown) to allow the reactors to vent into the common gas rail or be isolated from the common gas rail as necessary, in order to allow the reactors to in a sequential batch process. In the arrangement shown in Figure 4, each of the reactors operates independently (although under common control). In an alternative arrangement, as shown in Figure 3, a single motor (34) drives the high shear mixing heads of a vertical stack of three separate reactors via a common drive shaft (not shown).

The operation of the chemical reactors (2) is controlled by means of a control system comprising an electronic controller (36) and associated wiring (38) connecting the electronic controller (36) to each reactor (2), as shown in Figure 5. Instead of, or in addition to, hard wiring, wireless communication may be used. The electronic controller (36) is also linked (links not shown) to various control valves located in the apparatus, such as control valves present in the T-connectors (32), as well as instrumentation such as flow meters, pressure gauges, pH meters, and temperature probes for monitoring the progress of reactions and the amounts of gas produced. The electronic controller will also be linked to pumps, metering valves and dispensers and other devices for introducing controlled amounts of reactants into the reactors, as well as fans and pumps for controlling for controlling the flow of materials into and around the apparatus. Such monitoring, sensing and controlling devices will be well known to the skilled person and do not need to be discussed in detail here.

The electronic controller can be a desk-top or laptop computer containing the appropriate control software or, more usually, it can be any one of many commercially available programmable electronic controllers for process control.

In use, a desired output of a gas can be selected using the electronic controller and the appropriate control signals are then sent to one of the reactors in the system and associated devices such as reactant-metering devices. Under the control of the electronic controller, metered amounts of reactants and any necessary solvents are introduced into the first reactor and the high shear mixer is turned on and set to a suitable speed to being about rapid reaction between the reactants. A thermal exchange fluid is pumped through the cooling/heating jacket either to provide cooling (for exothermic reactions) or a source of heat (for endothermic reactions or reactions having a significantly high activation energy). Gases produced by the reaction are vented through the gas outlet pipe (12) and into the common gas rail. A fan or pump may be used to convey the gases to a desired destination. Once the reaction has proceeded to completion, or as near to completion as is feasible, and once gas evolution has ceased, an isolator valve (which may be in the gas outlet pipe (12) or in the T- connector (32) is closed to isolate the reactor from the common gas rail and the high shear mixer is switched off. Spent reactants and reaction products can then be extracted from the reactor via the outlet tube (16) and one or more optional flushing operations may be carried out using the inlet tubes (15) and outlet tube (16) in order to prepare the reactor for another batch reaction.

While the first reactor is being shut down and prepared for a further batch reaction, the electronic controller instructs a second reactor to commence operation and produce the desired gas. When the second reactor has completed its reaction and is then isolated for removal of waste and flushing, the first reactor may be brough back on stream or a third reactor may be activated, and so on.

Thus, by a sequence of batch reactions taking place in separate reactors, a steady supply of gas into the common gas rail is ensured. The intervals between the individual reactors being activated, and the number of reactors in active use at any one time can be varied according to the volumes of gas required to be produced. For example, in one process, the generation of gas can be achieved by activating reactors in sequence with one reactor shutting down as another is starting up. In another process, reactors can be started up and operated in a staggered fashion so that there may be two, three or even more reactors in operation simultaneously but each at different stages of progression.

In order to smooth out gas pressures and gas flow in the system, one or more buffer tanks (not shown) may be provided for accommodating excess gas pressure at a given point.

Ad advantage of the reactor system of the invention is that it provides a highly versatile method of producing desired volumes of gas which can be switched from producing relatively small volumes of gas up to very large amounts of gas in a relatively short period of time, dependent upon demand.

Each reactor is typically used in a batch process in which set amounts of reactants are introduced into the reactor to produce particular desired volumes of gas. By virtue of the high shear mixing, reaction takes place quickly and completely (or at least near to completion). Once the reaction has finished, the reactor can be emptied and prepared for a fresh reaction. The use of the batch process means that once delivery of a particular volume of gas has been completed, and any flushing operations have been carried out, there is no residual gas in the system which could constitute a hazard. This is particularly important if the gas being produced is flammable or even potentially explosive.

The apparatus of the invention is suitable for use in producing a range of different gases, one example of which is the production of hydrogen by the reaction of metals such as aluminium with water in the presence of a suitable catalyst (sodium hydroxide in the case of aluminium).

The embodiments described above and illustrated in the accompanying drawings are merely illustrative of the invention and are not intended to have any limiting effect. It will readily be apparent that numerous modifications and alterations may be made to the specific embodiments shown without departing from the principles underlying the invention. All such modifications and alterations are intended to be embraced by this application.