WO2024089424A1

WO2024089424A1 - Catalytic heater

Info

Publication number: WO2024089424A1
Application number: PCT/GB2023/052797
Authority: WO
Inventors: Simon Bateson; Thomas Mcgee
Original assignee: X-Heat Limited
Priority date: 2022-10-27
Filing date: 2023-10-26
Publication date: 2024-05-02
Also published as: GB2623798A; GB202215939D0

Abstract

Disclosed herein is a catalytic heater comprising: a porous catalyst; and a fuel disperser arranged to supply gaseous fuel into the catalyst such that the fuel is catalysed within the catalyst in the presence of oxygen to generate heat. Resistive heating wire is embedded within the catalyst to pre-heat the catalyst to an initial operating temperature when supplied with an electric current.

Description

Catalytic Heater

Technical Field

The present invention relates to catalytic heaters. In particular, but not exclusively, the present invention relates to catalytic space heaters.

Background

Catalytic heaters generate heat by passing gaseous fuel, such as natural gas or liquefied petroleum gas (LPG), through a porous catalyst in the presence of oxygen. The fuel undergoes a flameless combustion reaction within the catalyst to generate heat. Catalytic heaters release most of their heat in the form of long wavelength infrared radiation. This makes catalytic heaters particularly efficient as space heaters for heating people or animals in certain applications because the infrared radiation they generate directly heats organic matter rather than the surrounding air. Catalytic heaters are commonly used as industrial or agricultural personnel space heaters.

Before fuel can safely be supplied to the catalyst of a catalytic heater, the catalyst needs to be pre-heated to an initial operating temperature at which the catalytic process can begin to operate effectively. Supplying fuel to the catalyst when it is below the initial operating temperature risks unburned fuel being released from the catalyst into the local environment. In a catalytic space heater, the catalyst typically needs to be pre-heated to a temperature of approximately 120-300°C before fuel can be safely introduced into it.

Existing catalytic heaters pre-heat the catalyst using a heating element secured to an outer surface of the catalyst. The heating element used in such existing heaters is typically a composite heating element composed of a spiral shaped length of resistive heating wire enclosed within a ceramic insulating outer tube. This type of composite heating element is commonly used in domestic ovens. Such catalytic heaters are typically connected to a mains electricity supply which supplies electric current to the heating element.

A disadvantage of such catalytic heaters is that pre-heating the catalyst takes a significant amount of time and uses a significant amount of electrical energy. This is at least in part because the heating element has a high thermal mass due to its insulating outer layer, and because only one side of the heating element is in contact with the catalyst which means that a significant amount of heat generated by the heating element does not heat the catalyst. For example, an existing catalytic space heater of a type described above may require approximately 1 kW of power to be supplied to the heating element for approximately 30 minutes before the catalyst reaches a suitable initial operating temperature. This is undesirable because it takes a long time for such heaters to start providing heat after they have been powered on by a user. This makes them less attractive to users compared with other types of space heater, such as electric space heaters, that can provide heat on demand.

Additionally, the significant power and energy that needs to be supplied to the heating element during the pre-heating process means that such catalytic heaters need to be connected to a mains electricity supply capable of supplying a sufficiently high current, and consume a large amount of electrical energy during the pre-heating process.

A further disadvantage of such catalytic heaters is that having a large composite heating element secured to an outer surface of the catalyst reduces the flow of fuel to parts of the catalyst that are located behind the heating element. This reduces the overall efficiency and heat output of the catalyst.

Summary of the Invention

In accordance with a first aspect of the invention, there is provided a catalytic heater comprising: a porous catalyst; and a fuel disperser arranged to supply gaseous fuel into the catalyst such that the fuel is catalysed within the catalyst in the presence of oxygen to generate heat. Resistive heating wire is embedded within the catalyst to pre-heat the catalyst to an initial operating temperature when supplied with an electric current.

Optionally, the resistive heating wire is uninsulated such that an outer surface of the resistive heating wire is in contact with the catalyst.

Optionally, the catalyst comprises two or more layers and the resistive heating wire is located between adjacent layers.

Optionally, the resistive heating wire comprises one or more elongate lengths of wire.

Optionally, the catalytic heater further comprises a mesh embedded within the catalyst, wherein the resistive heating wire is threaded through the mesh.

Optionally, the mesh extends across a substantial portion of the surface area of the catalyst.

Optionally, the mesh is composed of a thermally conductive material.

Optionally, the catalytic heater further comprises a control unit operable to control an amount of current supplied to the resistive heating wire and an amount of fuel supplied to the fuel disperser.

Optionally, the control unit is operable to determine a temperature of the resistive heating wire based on a change in resistance of the resistive heating wire.

Optionally, the catalytic heater further comprises a fuel valve arranged to control fuel supplied to the fuel disperser.

Optionally, a position of the valve is controllable by pulse-width-modulation (PWM).

Optionally, the catalytic heater further comprises a battery, and electrical power required to operate the catalytic heater is supplied by the battery. Optionally, the catalytic heater is a space heater for heating occupants of an environment local to the heater.

Optionally, the catalytic heater further comprises a wireless receiver arranged to receive wireless control signals from a remote control, and wherein the control unit is arranged to control the operation of the catalytic heater based on the control signals.

Optionally, the wireless control signals comprise one or more of: a power on signal, a power off signal, a heat increase signal, and a heat decrease signal.

In accordance with a second aspect of the invention there is provided a method of operating a catalytic heater, the method comprising: supplying an electric current to resistive heating wire embedded within a porous catalyst of the catalytic heater to pre-heat the catalyst to an initial operating temperature; determining that the catalyst has been pre-heated to the initial operating temperature; and supplying gaseous fuel into the catalyst using a fuel disperser such that the fuel is catalysed within the catalyst in the presence of oxygen to generate heat.

Advantageously, resistive heating wire is embedded within the catalyst and has a low thermal mass compared with “domestic oven style” composite heating elements that are commonly used in existing catalytic heaters. Advantageously, the resistive heating wire heats up quickly when supplied with an electric current, and the heat from the resistive heating wire directly heats the inside of the catalyst. In contrast with existing heaters that use a composite heating element located on the outside of the catalyst, heat energy is not required to heat an insulating outer layer, and all of the heat energy from the resistive heating wire is supplied to the catalyst.

Advantageously, this significantly reduces both the time and electrical energy needed to preheat the catalyst. For example, in certain embodiments, the catalyst can be pre-heated to a suitable temperature by supplying approximately 70W of power to the resistive heating wire for approximately 1 minute. In comparison, an equivalent catalytic heater that uses a composite heating element located on an outer surface of the catalyst may require approximately 1 kW of power to be supplied to the heating element for approximately 30 minutes to pre-heat the catalyst to the same temperature.

Advantageously, faster pre-heating means that the heater can start providing heat more quickly after it is switched on by a user. Additionally, the low power and energy requirements for the pre-heating process mean that, in certain embodiments, the heater does not need to be connected to a mains electricity supply and can be provided as a battery-operated portable free-standing unit. In such embodiments, the heater can be powered by a small battery (for example a 12V, 7Ah lead acid or Li-Fe-Phosphate battery). This makes the heater particularly suitable for use as a mobile industrial or domestic outdoor heater (also known as a patio heater).

Advantageously, embedding the resistive heating wire within the catalyst means that the resistive heating wire does not need to include an electrically insulating outer layer. This can improve safety and reliability of the heater compared with existing heaters because in existing heaters, the electrically insulating outer layer of a composite heating element can degrade over time and cause an electrical short circuit.

Various further features and aspects of the invention are defined in the claims.

Brief Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings where like parts are provided with corresponding reference numerals and in which:

Figure 1 provides a simplified cross-sectional diagram of a catalytic heater in accordance with embodiments of the invention;

Figure 2 provides a simplified diagram showing an isometric view of the catalytic heater of Figure 1 in use;

Figure 3 provides a simplified diagram showing resistive heating wire embedded within a catalyst in accordance with embodiments of the invention;

Figure 4 provides a simplified diagram showing resistive heating wire embedded within a catalyst together with a mesh in accordance with embodiments of the invention;

Figure 5 provides a schematic diagram of a system that includes a catalytic heater control unit and a remote control in accordance with embodiments of the invention; and

Figure 6 is a flow diagram depicting a method of operating a catalytic heater in accordance with embodiments of the invention.

Detailed Description

Figure 1 provides a simplified cross-sectional diagram of a catalytic heater in accordance with embodiments of the invention.

The catalytic heater 100 comprises a housing 101 that encloses other components of the catalytic heater 100. The housing 101 is composed of a suitable material such as aluminium. The housing 101 includes a first enclosed end that provides a fuel dispersal chamber 102 and a second open end that is exposed to the local environment of the catalytic heater 100.

The catalytic heater 100 comprises a fuel disperser 103. The fuel disperser 103 comprises a fuel inlet 104 fluidly connected to a fuel dispersal arm. The fuel dispersal arm is located within the fuel dispersal chamber 102 and comprises an elongate fluid conduit with a plurality of apertures that provide fuel outlets. In use, the fuel inlet 104 is connected to an external fuel supply. The fuel supplied to the fuel disperser 103 is typically natural gas or liquefied petroleum gas (LPG). The catalytic heater 100 further comprises a fuel valve 109 configured to control the flow of fuel from the fuel inlet 104 to the fuel disperser 103.

The catalytic heater 100 comprises a plurality of layers of material that are arranged in series within the housing 101 including a fuel dispersal layer 105, a catalyst layer 106 with embedded resistive heating wire 107, and a retaining layer 108.

A first surface of the fuel dispersal layer 105 is exposed to the fuel dispersal chamber 102 and a second surface of the fuel dispersal layer 105 is in contact with the catalyst layer 106. The fuel dispersal layer 105 distributes fuel so it enters the catalyst layer 106 more evenly. The fuel dispersal layer 105 can be provided by a glass fibre material.

A first surface of the catalyst layer 106 is in contact with the fuel dispersal layer 105 and a second surface of the catalyst layer 106 is in contact with the retaining layer 108.

The catalyst layer 106 is a porous layer of material that allows gaseous fuel and air to pass through it. In certain embodiments, the catalyst layer 106 itself comprises a plurality of layers. In certain embodiments, the catalyst layer 106 comprises a porous support with an active phase provided by nano particles that are disposed on the support. It will be understood that any suitable catalyst can be used. For example, in certain embodiments the catalyst comprises a glass fibre support with a platinum group active phase. Alternatively, in certain embodiments, the catalyst comprises an alumina support with a palladium, ruthenium and rhodium active phase. In certain embodiments, the catalyst layer 106 is approximately 20mm in thickness between the first surface and the second surface.

The resistive heating wire 107 is arranged to pre-heat the catalyst layer 106 when supplied with an electric current. The resistive heating wire 107 is uninsulated such that an outer surface of it is in contact with the catalyst layer 106. Advantageously, this means that heat from the resistive heating wire 107 passes directly into the catalyst layer 106. The resistive heating wire 107 has a low thermal mass such that it heats up quickly when supplied with an electric current.

The resistive heating wire 107 can be embedded within the catalyst layer 106 using any suitable technique. For example, as noted above, in certain embodiments the catalyst layer

106 is itself composed of a plurality of layers. In such embodiments, the resistive heating wire

107 is positioned between adjacent layers within the catalyst.

Alternatively, in certain embodiments the resistive heating wire 107 can be embedded within the catalyst layer during synthesis of the catalyst. Advantageously, in such embodiments the resistive heating wire can provide additional structural support to the catalyst layer. This can also further increase heat transfer from the resistive heating wire to the catalyst layer due to the increased area of contact between the resistive heating wire and the catalyst layer.

As shown in Figure 1 , the resistive heating wire 107 is arranged in a substantially planar layer within the catalyst layer 106. It will be understood that various shapes and configurations of resistive heating wire can be provided. Examples of suitable configurations of resistive heating wire are described in more detail herein with reference to Figure 3.

In certain embodiments, the resistive heating wire 107 is an iron-chromium-aluminium wire such as KANTHAL® D (Sandvik AB, Sweden). Alternatively, in certain embodiments the resistive heating wire 107 is a nickel-chromium wire such as Nikrothal® (Sandvik AB, Sweden). Advantageously, such materials have a low thermal mass, are resistant to oxidation, are low cost and low energy to manufacture.

In certain embodiments, the resistive heating wire 107 has a diameter of approximately 1mm and a resistance of approximately 1.74 ohms per metre. In certain embodiments, the resistive heating wire 107 has a specific heat capacity at room temperature of approximately 0.46 kJ kg’¹ K’¹. A first surface of the retaining layer 108 is in contact with the catalyst layer 106 and a second surface of the retaining layer 108 is exposed to the environment of the catalytic heater 100. The retaining layer 108 is composed of a porous heat-resistant fabric and is used to secure the catalyst layer 106 within the housing 101 and to direct heat energy generated within the catalyst layer 106 out of the catalytic heater 100.

The layers are arranged within the housing 101 such that during use the catalyst layer 106 receives gaseous fuel from the fuel dispersal layer 105 and air from the retaining layer 108.

The catalytic heater 100 will now be described in use.

When the catalytic heater 100 is turned on, a pre-heating process begins. The operation of the catalytic heater 100 during pre-heating and subsequent operation is typically controlled by a control unit of the catalytic heater 100. A suitable control unit is described in more detail with reference to Figure 5. During the pre-heating process, an electric current is supplied to the resistive heating wire 107. The resistive heating wire 107 releases heat into the catalyst layer 106 which increases the temperature of the catalyst layer 106.

The catalyst layer 106 is heated to a predetermined initial operating temperature. Depending on the catalyst material being used, the initial operating temperature is typically at least 120°C. The initial operating temperature is a temperature where fuel can be effectively catalysed within the catalyst layer 106. The temperature of the catalyst layer 106 can be determined using a thermocouple. The temperature of the catalyst layer 106 is typically measured close to the location of the resistive heating wire 107.

Once the catalyst layer 106 reaches the initial operation temperature, the fuel valve 109 is opened. Gaseous fuel flows from the fuel inlet 104 through the fuel disperser 103 into the fuel dispersal chamber 102. The fuel passes through the fuel dispersal layer 105 and enters the catalyst layer 106. Air (containing oxygen) is also present within the catalyst layer 106 because the catalyst layer 106 is exposed to the local environment of the catalytic heater 100 via the retaining layer 108. The fuel is catalysed within the catalyst layer 106 through a flameless combustion reaction to generate heat energy. In certain embodiments, electric current is supplied to the resistive heating wire 107 during the pre-heating process until all or at least a substantial portion of the catalyst layer 106 reaches the initial operating temperature.

Alternatively, to reduce the time and energy required for the pre-heating process, in certain embodiments electric current is supplied to the resistive heating wire 107 until parts of the catalyst layer 106 adjacent to the resistive heating wire 107 reach the initial operating temperature. In such embodiments, the parts of the catalyst layer 106 adjacent to the resistive heating wire 107 provide local high temperature regions of catalyst where the catalysis process can be initiated when fuel is first introduced. Once fuel is introduced, the heat generated by catalysis at the locally pre-heated regions spreads through the catalyst layer 106 to quickly raise the temperature of the remainder of the catalyst layer 106 to above the initial operating temperature. In such embodiments, typically the fuel valve 109 is controlled to initially introduce fuel into the catalyst at a lower flow rate to ensure unburned fuel is not released into the local environment.

During normal operation, fuel continues to be supplied through the fuel disperser 103 and the heat energy generated within the catalyst layer 106 is directed through the retaining layer 108 into the local environment of the catalytic heater 100, predominantly in the form of long wavelength infrared radiation. Depending on the catalyst and fuel supplied, during normal operation the catalyst layer 106 typically reaches a temperature of approximately 400-500°C.

While the fuel disperser described with reference to Figure 1 includes a fuel dispersal arm, it will be understood that different arrangements of fuel disperser can be provided. For example, in certain embodiments, the fuel disperser can be provided by a suitable chamber that is shaped to supply fuel to the catalyst.

In certain embodiments, a retaining screen, for example provided by a stainless-steel mesh or a perforated sheet, can be provided at the open end of the housing 101 to secure the retaining layer 108 within the housing 101.

As described above, in certain embodiments the fuel supplied to the catalyst is a hydrocarbon such as natural gas or liquefied petroleum gas (LPG). However, it will be understood that hydrogen is an alternative renewable fuel that could be used, for example alone or mixed with hydrocarbon fuels. Typically, the catalytic heater 100 is a space heater for heating occupants of an environment local to the heater 100.

Advantageously, as described, embodiments of the invention can reduce the pre-heating time and temperature, thereby reducing degradation of the resistive heating wire. This can reduce the risk of the resistive heating wire deforming after repeated pre-heating cycles.

Advantageously, the resistive heating wire is composed of a material that is resistant to oxidation. For example, nickel-chromium wire such as Nikrothal® can be particularly resistant to oxidation. This can be particularly useful if hydrogen is used as a fuel because of the increased amount of water present within the catalyst when hydrogen is catalysed.

Advantageously, the catalytic heater 100 significantly reduces both the time and electrical energy needed to pre-heat the catalyst layer 106. For example, in certain embodiments, the catalyst layer 106 can be pre-heated to a suitable temperature by supplying approximately 70W of power to the resistive heating wire 107 for approximately 1 minute. In comparison, an equivalently sized catalytic heater that uses a composite heating element located on an outer surface of the catalyst layer may require approximately 1 kW of power to be supplied to the heating element for approximately 30 minutes to pre-heat the catalyst to a state where fuel can be safely introduced.

Advantageously, faster pre-heating means that the catalytic heater 100 can start providing heat more quickly after it is switched on by a user. Additionally, the low power and energy requirements for the pre-heating process mean that, in certain embodiments, the catalytic heater 100 does not need to be connected to a mains electricity supply and can be provided as a battery-operated portable free-standing unit. In such embodiments, the heater 100 can be powered by a small battery.

Advantageously, embedding the resistive heating wire 107 within the catalyst layer 106 means that the resistive heating wire 107 does not need to include an electrically insulating outer layer. This can improve safety and reliability of the heater 100 compared with existing heaters because in existing heaters, the electrically insulating outer layer of a composite heating element can degrade over time and cause an electrical short circuit. In contrast, the resistive heating wire 107 is safely located within the catalyst layer 106. Figure 2 provides a simplified diagram showing an isometric view of the catalytic heater 100 of Figure 1 in use. As shown, during operation, heat energy, predominantly in the form of infrared radiation, is released from the catalytic heater 100 into its local environment.

Figure 3 provides a simplified diagram showing resistive heating wire embedded within a catalyst in accordance with embodiments of the invention.

The resistive heating wire 300 is of a type described herein. The resistive heating wire 300 is located between a first layer 301 and a second layer 302 of the catalyst.

The resistive heating wire 300 is a continuous elongate length of wire that follows a serpentine path through the catalyst. The path of the resistive heating wire 300 is such that it extends across a substantial portion of the catalyst. When electric current is supplied to the resistive heating wire 300 during the pre-heating process, the resistive heating wire 300 heats the inner regions of the catalyst that are immediately adjacent to the resistive heating wire 300. These high temperature regions of catalyst provide regions where catalysis can be initiated when fuel is first introduced into the catalyst.

Advantageously, arranging the resistive heating wire 300 as a continuous elongate length of wire through the catalyst provides sufficient high temperature regions of catalyst to initiate the catalytic reaction while minimising the amount of electrical energy that needs to be supplied to the resistive heating wire 300 during the pre-heating process.

The resistive heating wire 300 comprises a first electrical connection 303 and a second electrical connection 304 for connecting the resistive heating wire 300 to a source of electric current.

It will be understood that alternative shapes of resistive heating wire could be used. For example, the resistive heating wire could be arranged in a spiral shape.

Figure 4 provides a simplified diagram showing resistive heating wire embedded within a catalyst together with a mesh in accordance with embodiments of the invention.

Similar to Figure 3, the resistive heating wire 400 is of a type described herein. The resistive heating wire 400 is located between a first layer 401 and a second layer 402 of the catalyst. The resistive heating wire 400 comprises a first electrical connection 403 and a second electrical connection 404 for connecting it to a source of electric current.

In the embodiment shown in Figure 4, the resistive heating wire 400 has substantially the same shape as the resistive heating wire described with reference to Figure 3. It will be understood, however, that different shapes of resistive heating wire 400 can be used.

In addition to the resistive heating wire 400, a mesh 405 is also provided. The mesh 405 is located between the first and second layers 401 402 of the catalyst. The mesh 405 comprises wire arranged in a lattice shape. The mesh 405 extends across a substantial portion of the surface area of the catalyst.

The resistive heating wire 400 is threaded through holes in the mesh 405. In this way, the mesh 405 physically supports the resistive heating wire 400.

The mesh 405 is composed of a thermally conductive material. In certain embodiments, the mesh 405 is composed of an alloy comprising copper or aluminium and graphene. For example, in certain embodiments, the alloy comprises 10-50% graphene by weight. In other embodiments, the mesh 405 comprises copper or aluminium coated with a nanographene formulation. In certain embodiments, the mesh wire has a diameter of approximately 0.5- 1.5mm.

When electric current is supplied to the resistive heating wire 400 during the pre-heating process, the resistive heating wire 400 heats the regions of the catalyst that are immediately adjacent to it. Additionally, the resistive heating wire 400 also heats the regions of the mesh 405 that are immediately adjacent to it. Due to the high thermal conductivity of the mesh 405, the mesh 405 distributes the heat from the resistive heating wire 400 across the catalyst.

Advantageously, the mesh 405 can improve the pre-heating process by reducing the time needed to pre-heat the catalyst and by ensuring that the catalyst is heated more evenly across its surface. For example, the mesh 405 can enable a large surface area of the catalyst to be heated to the initial operating temperature in a short period of time. This is advantageous because when fuel is introduced into the catalyst, a larger portion of the catalyst will be at a high enough temperature to begin catalysing fuel. This results in the remainder of the catalyst heating up more quickly. Advantageously, the mesh 405 has a high level of thermal conductivity. The mesh 405 is also resistant to fatigue and oxidation. This is particularly advantageous when hydrogen is used as a fuel because the water released during catalysis risks increasing the rate of breakdown of materials. The mesh 405 is also physically resilient and thereby supports the resistive heating wire 400.

Figure 5 provides a schematic diagram of a system that includes a catalytic heater control unit and a remote control in accordance with embodiments of the invention.

The system 500 comprises a control unit 501 and a remote control 502. The control unit 501 is provided as part of a catalytic heater of a type described herein in accordance with embodiments of the invention.

The control unit 501 comprises a processor unit 503 connected to a memory unit 504. The memory unit 504 is used to store data associated with operation of the catalytic heater.

The control unit 501 comprises an I/O port 505 connected to the processor unit 503. The I/O port 505 provides an externally accessible port that allows a technician to connect an external diagnostic device to interact with the components of the control unit 501. In certain embodiments, the I/O port 505 is an RS232 port.

The control unit 501 comprises a wireless receiver 506 connected to the processor unit 503. The wireless receiver 506 is operable to receive control signals from the remote control 502 using a suitable wireless control protocol such as infrared (IR) and to transmit the control signals to the processor unit 503.

The remote control 502 comprises an interface that allows a user to select a control signal to transmit to the control unit 501 . The remote control 502 is arranged to transmit control signals via a suitable wireless control protocol such as I R. In certain embodiments, the remote control 502 is operable to transmit a “power on” signal, a “power off” signal, a “heat increase” signal and/or a “heat decrease” signal.

The control unit 501 comprises a power unit 507 which provides power to the components of the catalytic heater. Typically, the power unit 507 is provided by a battery. For example, in certain embodiments the battery is a 12V, 7Ah lead acid or Li-Fe-Phosphate battery. However, additionally, or alternatively, the power unit 507 can provide a connection for connecting the control unit 501 to an external power supply, for example a mains electrical power supply.

The control unit 501 comprises a fuel valve controller 508. The fuel valve controller 508 controls the position of the fuel valve that supplies fuel to the fuel disperser of the catalytic heater in response to control signals received from the processor unit 503. In certain embodiments, the fuel valve controller 508 is a proportional valve controller that allows the fuel flow rate to be adjusted by driving a valve coil with a pulse-width-modulated (PWM) waveform with a suitable duty cycle. Advantageously, using PWM to control the fuel valve can reduce the duty cycle and reduce power consumption because the power required to open a solenoid valve is significantly greater than the power needed to hold it open.

The control unit 501 comprises a resistive heating wire controller 509 arranged to control the supply of electric current to the resistive heating wire in response to control signals received from the processor unit 503. In certain embodiments, the resistive heating wire controller 509 comprises a field-effect transistor (FET).

The control unit 501 comprises a catalyst temperature sensor analogue to digital converter (ADC) 510. The catalyst temperature sensor ADC 510 is connected to the processor unit 503 and to a catalyst temperature sensor and is arranged to measure the current and voltage across the catalyst temperature sensor in response to control signals received from the processor unit 503. In certain embodiments, the catalyst temperature sensor is a thermocouple positioned within the catalyst of the catalytic heater.

Alternatively, in certain embodiments, the resistive heating wire is used as a temperature sensor to measure the temperature of the catalyst. In such embodiments, the resistive heating wire is composed of a material that has a known temperature coefficient of resistance. The catalyst temperature sensor ADC 510 measures the current and voltage across the resistive heating wire to determine the resistance. The resistance is used to determine the temperature of the resistive heating wire based on stored data about the resistance-temperature characteristics of the resistive heating wire. For example, such stored data can include stored temperature values associated with measured resistances.

Advantageously, using the resistive heating wire as a temperature sensor avoids the need for providing separate thermocouples within the catalyst. Further, since the resistive heating wire is embedded within the catalyst, it provides an accurate temperature measurement from within the catalyst.

As described in more detail below, during pre-heating, current is typically supplied continuously to the resistive heating wire. This means that during pre-heating the catalyst temperature sensor ADC 510 can take regular current and voltage readings to determine the resistance (and therefore temperature) of the catalyst. However, during normal operation once pre-heating has finished, current is not typically supplied to the resistive heating wire. Therefore, during normal operation, to take a temperature measurement using the resistive heating wire, current is briefly supplied to the resistive heating wire (for example for a few milliseconds every few seconds). Advantageously, this reduces power consumption of the catalytic heater but still allows the temperature of the catalyst to be measured during operation.

In certain embodiments, the resistive heating wire is an iron-chromium-aluminium resistive heating wire. Such heating wire has a resistance that increases by approximately 3% from 0°C to 500°C. Due to the small change in resistance, a suitably high-resolution ADC should be used to measure voltage and current across the resistive heating wire. For example, in certain embodiments a 24-bit 2-channel ADC can be used.

In embodiments where the resistive heating wire is used as a catalyst temperature sensor, when the control unit 501 is first powered on, the processor unit 503 is arranged to control the components of the control unit 501 to perform an initial calibration measurement to determine the resistance of the resistive heating wire and to store the calibration data in the memory unit 504 to use when calculating the temperature of the resistive heating wire. Advantageously this can improve the accuracy of temperature measurements by accounting for differences in the material properties and/or manufacturing of the catalytic heater.

The system 500 will now be described in use.

The control unit 501 is initially in a standby mode. A user presses the “power on” button on the remote control 502. The remote control 502 sends a wireless control signal, which is received by the processor unit 503 via the wireless receiver 506.

The control unit 501 then enters a pre-heating mode. The processor unit 503 sends a control signal to the resistive heating wire controller 509 to direct the resistive heating wire controller 509 to supply an electric current to the resistive heating wire. As described with reference to Figure 1 , the resistive heating wire releases heat into the catalyst which increases the temperature of the catalyst.

During the pre-heating process, the processor unit 503 monitors the temperature of the catalyst by sending regular control signals to cause the catalyst temperature sensor ADC 510 to take voltage and current measurements across thermocouples embedded within the catalyst and/or across the resistive heating wire itself.

Based on the voltage and current measurements from the catalyst temperature sensor ADC 510, the processor unit 503 determines when the catalyst reaches a pre-determined initial operating temperature (for example, at least 120°C). When the catalyst reaches the predetermined initial operating temperature, the processor unit 503 sends a control signal to the fuel valve controller 508 to cause the fuel valve controller 508 to open the fuel valve to initiate the supply of gaseous fuel to the catalyst.

In certain embodiments, the processor unit 503 controls the resistive heating wire controller 509 to stop supplying current to the resistive heating element at the same time as initiating the supply of fuel to the catalyst. Alternatively, in certain embodiments, the controller is operable to ensure current continues to be supplied to the resistive heating wire for a pre-determined period of time after fuel is supplied to the catalyst, and/or until one or more pre-determined conditions are met (for example, the temperature of the catalyst reaches a certain temperature).

In certain embodiments, the processor unit 503 controls the fuel valve controller 508 such that the fuel valve initially supplies fuel into the catalyst at a lower flow rate than the normal operation flow rate until the catalyst reaches a full operation temperature.

The processor unit 503 then enters a heating mode. Fuel continues to be supplied through the fuel valve and the catalyst generates heat energy.

In certain embodiments, the amount of heat provided by the catalytic heater can be controlled by a user. In such embodiments, the user can press a “heat increase” or “heat decrease” button on the remote control 502. In response, the remote control 502 sends a corresponding control signal to the processor unit 503 via the wireless receiver 506. On receipt of the control signal, the processor unit 503 is operable to control the fuel valve controller 508 to actuate the fuel valve to increase or decrease the flow of fuel into the catalyst. The processor unit 503 monitors the temperature of the catalyst when fuel is initially introduced into the catalyst and during normal operation to ensure that safe combustion is taking place within the catalyst. The processor unit 503 is operable to determine a fault condition and in response to send a control signal to the fuel valve controller 508 to cause the fuel valve controller 508 to close the fuel valve. The processor unit 503 is operable to determine various fault conditions for example based on the temperature of the catalyst (high or low) or the health of components of the catalytic heater.

At the end of operation, a user presses the “power off’ button on the remote control 502. The remote control 502 sends a corresponding wireless control signal, which is received by the processor unit 503 via the wireless receiver 506. The control unit 501 then enters a cooling mode. The control unit 501 controls the fuel valve controller 508 to close the fuel valve to stop the supply of fuel to the catalyst. The processor unit 503 monitors the temperature of the catalyst during cooling to ensure the catalytic heater is safely shut down. The control unit 501 then enters the standby mode.

It will be understood that in certain embodiments, in addition to or instead of using a remote control, the catalytic heater can comprise an interface with buttons that can be pressed by a user. Alternatively or additionally, in certain embodiments the catalytic heater can comprise a wired remote control. The wired remote control can be connected to the processor unit by a suitable electrical connection such as a five-core electrical connection.

It will be understood that in certain embodiments, in addition to or instead of using a dedicated remote control or an interface with buttons, the catalytic heater can be controlled by a remote app such as a smartphone or tablet app. In such embodiments, the catalytic heater can comprise a Bluetooth and/or WiFi module and associated transceiver connected to the processor.

It will be understood that the control unit 501 includes additional suitable safety and fail-safe features to ensure safe operation of the catalytic heater. For example, the processor unit 503 can be operable to perform pre-start health checks and continuous monitoring of fault conditions. It will be understood that in certain embodiments, the control unit 501 can include an externally facing LED array connected to the processor unit 503 and operable to display the status of the device to a user.

Figure 6 is a flow diagram depicting a method of operating a catalytic heater in accordance with embodiments of the invention. The method is typically performed by a control unit of the heater such as a control unit of a type described with reference to Figure 5. The method can include further steps as described herein.

At step S601 , an electric current is supplied to resistive heating wire embedded within a porous catalyst of a catalytic heater to pre-heat the catalyst to an initial operating temperature.

At step S602, it is determined that the catalyst has been pre-heated to the initial operating temperature.

At step S603, upon determining that the catalyst has been pre-heated to the initial operating temperature, gaseous fuel is supplied into the catalyst using a fuel disperser such that the fuel is catalysed within the catalyst in the presence of oxygen to generate heat.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, means at least two recitations, or two or more recitations).

It will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope being indicated by the following claims.

Claims

1 . A catalytic heater comprising: a porous catalyst; a fuel disperser arranged to supply gaseous fuel into the catalyst such that the fuel is catalysed within the catalyst in the presence of oxygen to generate heat; wherein resistive heating wire is embedded within the catalyst to pre-heat the catalyst to an initial operating temperature when supplied with an electric current.

2. A catalytic heater as claimed in claim 1 , wherein the resistive heating wire is uninsulated such that an outer surface of the resistive heating wire is in contact with the catalyst.

3. A catalytic heater as claimed in any preceding claim, wherein the catalyst comprises two or more layers and the resistive heating wire is located between adjacent layers.

4. A catalytic heater as claimed in any preceding claim, wherein the resistive heating wire comprises one or more elongate lengths of wire.

5. A catalytic heater as claimed in any preceding claim, further comprising a mesh embedded within the catalyst, wherein the resistive heating wire is threaded through the mesh.

6. A catalytic heater as claimed in claim 5, wherein the mesh extends across a substantial portion of the surface area of the catalyst.

7. A catalytic heater as claimed in claim 5 or 6, wherein the mesh is composed of a thermally conductive material.

8. A catalytic heater as claimed in any preceding claim, further comprising a control unit operable to control an amount of current supplied to the resistive heating wire and an amount of fuel supplied to the fuel disperser.

9. A catalytic heater as claimed in claim 8, wherein the control unit is operable to determine a temperature of the resistive heating wire based on a change in resistance of the resistive heating wire.

10. A catalytic heater as claimed in any preceding claim, further comprising a fuel valve arranged to control fuel supplied to the fuel disperser.

11. A catalytic heater as claimed in claim 10, wherein a position of the valve is controllable by pulse-width-modulation (PWM).

12. A catalytic heater as claimed in any preceding claim, wherein the catalytic heater comprises a battery, and electrical power required to operate the catalytic heater is supplied by the battery.

13. A catalytic heater as claimed in any preceding claim, wherein the catalytic heater is a space heater for heating occupants of an environment local to the heater.

14. A catalytic heater as claimed in any of claims 8 to 13, further comprising a wireless receiver arranged to receive wireless control signals from a remote control, and wherein the control unit is arranged to control the operation of the catalytic heater based on the control signals.

15. A catalytic heater as claimed in claim 14, wherein the wireless control signals comprise one or more of: a power on signal, a power off signal, a heat increase signal, and a heat decrease signal.

16. A method of operating a catalytic heater, the method comprising: supplying an electric current to resistive heating wire embedded within a porous catalyst of the catalytic heater to pre-heat the catalyst to an initial operating temperature; determining that the catalyst has been pre-heated to the initial operating temperature; and supplying gaseous fuel into the catalyst using a fuel disperser such that the fuel is catalysed within the catalyst in the presence of oxygen to generate heat.