GB2611789A

GB2611789A - Apparatus for heating a fluid

Info

Publication number: GB2611789A
Application number: GB2114695.6A
Authority: GB
Inventors: R Mcgee Thomas
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-10-14
Filing date: 2021-10-14
Publication date: 2023-04-19
Also published as: WO2023062384A3; GB202114695D0; WO2023062384A2

Abstract

Apparatus 10 for heating a fluid comprises an outer housing and at least one catalytic emitter 12 located within the outer housing. The catalytic reacts gaseous fuel with atmospheric oxygen. An outlet 22 allows exhaust gases to exit the outer housing, and an exhaust gas pathway extends between the outlet and the at least one catalytic emitter. An air inlet to allows air to enter the outer housing. A primary heat exchanger 14 is configured to absorb heat energy from at least one catalytic emitter, and a secondary heat exchanger 26 is positioned within the exhaust gas pathway and configured to absorb heat energy from the exhaust gases. The or each catalytic emitter includes a catalyst support (36, figure 2), a catalyst (38), a fuel delivery system (40) and an heating element (44). At least one air inlet pathway 20 connects the air inlet of the outer housing to the or each catalytic emitter and includes a fan 24 configured to draw air through the or each air inlet pathway towards the or each catalytic emitter, whilst the or each catalytic emitter includes a cowling (46) shaped to direct air flow from the air inlet pathway towards the catalyst support.

Description

Apparatus for heating a fluid

Field of the Invention

The present invention relates to apparatus for heating a fluid, and in particular, to a boiler in which the fluid is heated by the catalytic oxidation of a gaseous fuel in air utilising a catalytic emitter of electromagnetic radiation.

Background of the Invention

Conventional boilers use the heat provided by the burning of a liquid or gaseous fuel to heat a fluid, such as water. The flame temperatures in such boilers are extremely high, typically somewhere between 10000C and 1900.C. Such high temperature combustion produces pollutant gases such as nitrogen oxides, and the boilers themselves are not energy efficient. Incomplete combustion also leads to production of harmful carbon monoxide.

US5,851,498 describes a boiler heated by catalytic organic oxidation. The boiler includes one or more catalytic emitters, positioned around a fluid-containing chamber. The chamber, and the fluid within it, is heated predominantly by infrared radiation from the catalytic emitters. Air is drawn into the outer boiler housing via a concentric flue from the external atmosphere by negative pressure. Internal fan or fans, components of the catalytic emitters, draw the air into the oxidation process, and vent via an exhaust gas pathway, ultimately venting to the external atmosphere via concentric flue.

It would be desirable to provide an improved boiler.

Summary of the Invention

According to a first aspect of the invention there is provided apparatus for heating a fluid comprising: an outer housing; at least one catalytic emitter of electromagnetic radiation located within the outer housing, the catalytic emitter configured for reaction of a gaseous fuel and atmospheric oxygen; an outlet for exhaust gases to exit the outer housing, and an exhaust gas pathway extending between the outlet and the at least one catalytic emitter; means for delivering a gaseous fuel to the at least one catalytic emitter; an air inlet to allow air to enter the outer housing; a primary heat exchanger, having a fluid pathway therethrough, located within the outer housing, the primary heat exchanger configured to absorb heat energy from the electromagnetic radiation emitted by the at least one catalytic emitter; a secondary heat exchanger, having a fluid pathway therethrough, positioned within the exhaust gas pathway and configured to absorb heat energy from the exhaust gases; wherein the or each catalytic emitter includes a catalyst support, a catalyst, means for delivering fuel to the catalyst and means for pre-heating the catalyst; wherein the apparatus further comprises at least one air inlet pathway, the or each air inlet pathway connecting the air inlet of the outer housing to the or each catalytic emitter, and wherein the or each air inlet pathway includes a fan configured to draw air through the or each air inlet pathway towards the or each catalytic emitter; and wherein the or each catalytic emitter includes a cowling shaped to direct air flow from the air inlet pathway towards the catalyst support.

Catalytic emitters operate at much lower temperatures, typically between around 2000C and 5000C, meaning that construction of the boiler can be greatly reduced in weight and cost.

Catalytic emitters generate radiant, infrared heat which is far more efficient compared to an open-flame heater.

Catalytic oxidation of a fuel produces only carbon dioxide and steam. The production of carbon monoxide, nitric oxides and unburnt hydrocarbons is much reduced compared to open-flame heaters.

The provision of a secondary heat exchanger located within the exhaust gas pathway allows heat energy from the exhaust gases to be reclaimed. Fluid warmed by the secondary heat exchanger may be returned to the primary heat exchanger for further heating.

Preferably, the apparatus further comprises at least one exhaust gas recirculation pathway connecting the exhaust pathway to the or each air inlet pathway and configured to redirect a proportion of the exhaust gases back towards the or each catalytic emitter. Recirculation of a proportion of the exhaust gases improves efficiency of the apparatus by reclaiming convectional waste heat which is produced from the rear of the catalyst. Preferably the amount of exhaust gas that is recirculated via the recirculation pathway is in the range 10-15% of the total volume of exhaust gases. More preferably, the amount of exhaust gas that is recirculated via the recirculation pathway is approximately 10% of the exhaust gases.

Preferably the air inlet pathway is configured to absorb heat energy from the exhaust gases. By locating the air inlet pathway adjacent to the exhaust flue, the incoming air stream is pre-warmed by any residual heat in the exhaust gases, rendering the boiler more efficient.

Preferably, the means for pre-heating the catalyst comprises an electric heating element. More preferably the heating element is a rigid element. A particularly preferred heating element is an 8mm diameter Incoloy (TM) heating element.

Preferably, the air inlet is located adjacent to the exhaust outlet.

Preferably, the apparatus comprises two catalytic emitters.

Preferably, the primary heat exchanger is oriented substantially parallel to the or each catalytic emitter.

Preferably, the catalyst includes noble metals selected from the group comprising rhodium, palladium and platinum.

Preferably, the catalyst support comprises woven fibres of crystalline silica or crystalline alumina. Alternatively, the catalyst support may have a porous, sponge-like structure.

Preferably, the primary heat exchanger has at least one heat absorbing face and the at least one heat absorbing face includes an array of protrusions. The protrusions may have a pyramid shape or a truncated pyramid shape. These shapes have been found to be more efficient at absorbing medium to long wavelength infra-red waves.

Preferably the fluid pathway of the primary heat exchanger lies in a plane which is parallel to the at least one heat absorbing face and preferably the fluid pathway is arranged in a spiral configuration.

Preferably the electromagnetic radiation emitted by the catalytic emitter is infra-red radiation, preferably medium to long wavelength infra-red waves.

According to a further aspect of the invention, there is provided a heat exchanger apparatus comprising at least one heat absorbing face and a fluid pathway, the fluid pathway lying in a plane which is substantially parallel to a plane containing the at least one heat absorbing face, wherein the least one heat absorbing face includes an array of protrusions and wherein the fluid pathway is arranged in a spiral configuration.

Preferably the protrusions have the shape of a pyramid or a truncated pyramid.

The apparatus of the invention provides a more efficient means for heating a fluid and a more efficient heat exchanger for use in said apparatus.

Brief Description of the drawings

In the Drawings, which illustrate preferred embodiments of the apparatus for heating a fluid of the invention: Figure 1 is a schematic cross-sectional view of a catalytic boiler; Figure 2 is a schematic cross-sectional view of a catalytic emitter of the boiler of Figure 1.

Figure 3a is a perspective view of a primary heat exchanger suitable for use in the catalytic boiler of Figure 1; Figure 3b is a side view of the primary heat exchanger of Figure 3a; Figure 4a is a perspective view of a part of the primary heat exchanger of Figure 3a, illustrating the fluid pathway therethrough; and Figure 4b is a plan view of the part of the primary heat exchanger illustrated in Figure 4a.

Detailed Description of the Preferred Embodiments

Figure 1 is a schematic cross section through a boiler 10 according to the present invention. The boiler incorporates a pair of catalytic emitters of electromagnetic radiation 12 which are described in more detail in relation to Figure 2. The catalytic emitters are preferably catalytic heaters which emit infra-red radiation. The boiler 10 includes a primary heat exchanger 14 which absorbs radiation emitted by the catalytic emitters 12 to heat water passing through the primary heat exchanger Cold water is introduced to the primary heat exchanger via an inlet 16 towards the bottom and warmed water exits the primary heat exchanger via an outlet 18.

Air enters the boiler 10 through a pathway 20 which lies adjacent to the exhaust outlet 22. The air inlet pathway 20 extends around the exhaust outlet towards the emitters 12 and air is drawn towards the emitters 12 by a fan 24 associated with each emitter 12. Preferably the air flow through the boiler is in the range 2350 to 4000 litres per minute.

Figure 2 is a schematic cross section through one of the catalytic emitters 12. Catalytic emitters are flameless heaters in which fuel, oxygen and a catalyst react together, producing heat at much lower temperatures compared to conventional open-flame heaters. The emitters include a layer 36 of a catalyst support, the catalyst support is porous with a high surface area and may be in the form of a woven support comprising woven fibres of crystalline silica or crystalline alumina. Alternatively, the catalyst support may have a porous, sponge-like structure. Suitable catalytic media is available from specialist catalytic manufacturers. The surface area of the catalyst support is preferably around 720crm. The catalyst support has a front face and a rear face. A catalyst is supported on the catalyst support, represented schematically by dots 38. The emitter also includes a fuel delivery system 40, including a number of outlets 42 for delivery of gaseous fuel to the rear face of the catalyst support. The catalyst 38 preferably comprises noble metals, for example rhodium, palladium and platinum. Other suitable catalysts include cobalt chromium oxide spine!.

An electrically conductive element 44 runs parallel with the catalyst support 36. The element 44 is used to heat the catalyst 38 in order to initiate combustion of the fuel. Running a current of between approximately 2.8 and 3.8 amps through the element for around 120 seconds is typically sufficient to preheat the catalyst to a temperature of 150°C needed to initiate combustion. After combustion has been initiated the current through the element is no longer required since the combustion reaction is self-supporting. The heating element 44 is preferably a rigid heating element as this eliminates any twisting or bending during repeated heating and cooling cycles. Any twisting or bending of the heating element would result in uneven pre-heating of the catalyst which could cause gas slippage on start up.

Gaseous fuel is conveyed through a gas train which delivers fuel to the rear of the catalyst support, this fuel then permeates through the catalyst support where it meets oxygen and the catalyst.

Oxygen from the air and fuel react on the surface of the catalyst, heating the catalyst support to a temperature typically between 2000C and 500.C. The surface temperature of the catalyst support depends on a variety of factors including the pressure of the gaseous fuel and the speed of the air flow. The fuel is preferably a gaseous hydrocarbon fuel, such as natural gas, methane, ethane, propane or butane. The particular choice of fuel may affect the temperature of the catalytic emitter Each fuel will operate at a different pressure to compensate for its calorific value.

The front side of the catalyst support emits infrared radiation, predominantly at a wavelength of between 4 and 8 microns, as the fuel and oxygen react on the catalyst. The front sides of the catalyst supports are positioned to face the primary heat exchanger 14. A preferred example of a primary heat exchanger 14' is illustrated in Figures 3 to 4. As illustrated in Figures 3a and 3b, both external, heat absorbing faces of the preferred primary heat exchanger 14' comprise an array of pyramidal or truncated pyramidal protrusions 48 spaced apart, preferably in a regular pattern. In the illustrated example the dimensions of the heat exchanger 14' are approximately 30cm x 22cm and the base of each truncated pyramidal protrusion 48 is approximately 1.5cm2 and 5 mm in height. Protrusions are preferably spaced apart by 5mm. This array of pyramidal protrusions provides a greater surface area for absorption of infrared radiation. The protrusions are preferably solid rather than hollow and constructed as part of the whole heat exchanger, from heat conductive metal such as copper or aluminium. The protrusions are preferably located on both sides of the heat exchanger, enabling the heat exchanger to be located between two catalytic emitters, as shown in Figure 1.

The inside of the primary heat exchanger 14' is preferably provided with a fluid channel arranged in a spiral configuration as illustrated in Figures 4a and 4b. This fluid channel lies in a plane which is parallel to the plane containing each of the heat absorbing faces 50, 51. Water enters the primary heat exchanger 14' via the inlet 16' and follows a spiral path, as indicated by the arrows on Figure 4b, exiting the exchanger at 18'. The spiral design provides a large surface area for water flowing therethrough to trap the heat radiation, maximising absorption of heat into the water. The spiral channel includes thin internal walls 54 which allow for fluid-to-fluid transfer of heat. The primary heat exchanger 14' is preferably cast in two halves which are then welded together, with each half comprising an array of protrusions on one side, and part of the spiral fluid channel on the other so that the fluid channel is sandwiched between the two heat absorbing faces 50, 51.

Fluid flowing within the primary heat exchanger is heated predominantly by the infrared radiation emitted from the emitters. The output of the emitters is typically between around 1.5 and 3kW. The temperature of the water within the primary heat exchanger is monitored via a thermistor. If the sensed temperature of the water decreases then gas pressure and air flow is increased to increase the output of the emitters.

Exhaust gases exit the boiler through the exhaust flue 22. Exhaust gases exiting the boiler pass over a secondary heat exchanger 26 which reclaims remaining heat energy from the exhaust gases. Water warmed by the secondary heat exchanger 26 is preferably returned to the primary heat exchanger for further heating. Alternatively, water heated by the primary heat exchanger is routed via the secondary heat exchange for further heating. By drawing air into the boiler 10 adjacent the exhaust flue 22, any heat energy left in the exhaust gases is transferred to the incoming air, minimising heat losses.

The emitters 12 include a cowling 46 which directs air from the pathway 20 around the emitter and towards the front face of the catalyst support. Directing the air around the rear of the emitter allows the collection of waste heat to be blown onto the heat exchanger. Blowing air across the surface of the catalyst also provides for a more consistent delivery for oxidation to take place.

A proportion of the exhaust gases are recirculated via ducting 32 back to the emitter Preferably 10-15% of the exhaust gases are recirculated. The volume of recirculated exhaust gases is determined by the diameter of the return ducting 32. The system requires a minimum of 75% fresh oxygen to impinge on the catalyst support in order to function correctly. A lambda sensor monitors exhaust oxygen levels. The output of the lambda sensor, indicative of exhaust oxygen levels, coupled with temperature sensor information from the catalytic emitters and the heat exchanger surface, and flow temperature readings, enable the boiler to be operated safely by monitoring oxidation within the boiler. If the sensors indicate that the boiler is operating outside parameter thresholds, the boiler may be shut down or a warning signal may be issued. The software may provide for preheating, and the regulation of gas and air flows to be autonomous.

This recirculated air is preheated so it also helps maintain the temperature of the catalyst bed in the desired range.

The invention provides a heating boiler, which uses considerably less fuel than conventional systems. By running at a lower temperature the apparatus of the invention eliminates NO production and harmful acidic by-products. Carbon monoxide emissions are reduced to negligible levels. The low fuel to heat production ratio also significantly reduces CO2 production and heat waste compared to a conventional boiler.

Claims

Claims 1. Apparatus for heating a fluid comprising: an outer housing; at least one catalytic emitter of electromagnetic radiation located within the outer housing, the catalytic emitter configured for reaction of a gaseous fuel and atmospheric oxygen; an outlet for exhaust gases to exit the outer housing, and an exhaust gas pathway extending between the outlet and the at least one catalytic emitter; means for delivering a gaseous fuel to the at least one catalytic emitter; an air inlet to allow air to enter the outer housing; a primary heat exchanger, having a fluid pathway therethrough, located within the outer housing, the primary heat exchanger configured to absorb heat energy from the electromagnetic radiation emitted by the at least one catalytic emitter; a secondary heat exchanger, having a fluid pathway therethrough, positioned within the exhaust gas pathway and configured to absorb heat energy from the exhaust gases; wherein the or each catalytic emitter includes a catalyst support, a catalyst, means for delivering fuel to the catalyst and means for pre-heating the catalyst; wherein the apparatus further comprises at least one air inlet pathway, the or each air inlet pathway connecting the air inlet of the outer housing to the or each catalytic emitter, and wherein the or each air inlet pathway includes a fan configured to draw air through the or each air inlet pathway towards the or each catalytic emitter; and wherein the or each catalytic emitter includes a cowling shaped to direct air flow from the air inlet pathway towards the catalyst support.
2. Apparatus for heating a fluid according to claim 1, wherein the air inlet is located adjacent to the exhaust outlet.
3. Apparatus for heating a fluid according to Claim 1 or 2 comprising two catalytic emitters.
4. Apparatus for heating a fluid according to any preceding claim, wherein the primary heat exchanger is oriented substantially parallel to the or each catalytic emitter.
5. Apparatus for heating a fluid according to any preceding claim, further comprising at least one exhaust gas recirculation pathway connecting the exhaust pathway to the or each air inlet pathway and configured to redirect a proportion of the exhaust gases back towards the or each catalytic emitter.
6. Apparatus for heating a fluid according to Claim 5, wherein the proportion of the exhaust gases redirected towards the recirculation pathway is in the region of 10% to 15%.
7. Apparatus for heating a fluid according to any preceding claim, wherein the means for pre-heating the catalyst is an electric element.
8. Apparatus for heating a fluid according to any preceding claim, wherein the catalyst includes noble metals selected from the group comprising rhodium, palladium and platinum.
9. Apparatus for heating a fluid according to any preceding claim, wherein the catalyst support comprises woven fibres of crystalline silica or crystalline alumina.
10. Apparatus for heating a fluid according to any preceding claim, wherein the primary heat exchanger has at least one heat absorbing face and the at least one heat absorbing face includes an array of protrusions.
11. Apparatus for heating a fluid according to Claim 10, wherein the protrusions have a shape selected from the group comprising: pyramid and truncated pyramid.
12. Apparatus according to any preceding claim, wherein the fluid pathway of the primary heat exchanger lies in a plane parallel to the at least one heat absorbing face and the fluid pathway is arranged in a spiral configuration.
13. Apparatus according to any preceding claim, wherein the electromagnetic radiation is infra-red radiation.
14. A heat exchanger apparatus comprising at least one heat absorbing face and a fluid pathway, the fluid pathway lying in a plane which is substantially parallel to a plane containing the at least one heat absorbing face, wherein the least one heat absorbing face includes an array of protrusions and wherein the fluid pathway is arranged in a spiral configuration.
15. A heat exchanger apparatus according to Claim 13, wherein the protrusions have a shape selected from the group comprising: pyramid and truncated pyramid.