Patent Application
20250116398
The present invention relates to a catalytic burner and a hydrogen boiler for water heating. More particularly, the present invention relates to a new technical solution of a burner for combustion or transformation into water of hydrogen with oxygen by means of a catalyst for production of hot water for heating or sanitary use and to the related boiler or generator plant.
Catalytic burners or heaters for boilers or hot water generators are known in the state of the art to use mixtures with a low content or concentration of hydrogen in the gaseous state as fuel.
In these types of generators or boiler plants, with preliminary reference to
In these known hydrogen burners, unlike traditional fossil-fuel burners, the catalytic reaction takes place without flame and without carbon dioxide (CO2) emissions, at a temperature in the range of 300° C., avoiding the formation of environmentally and health-damaging gases such as nitrogen oxides (NOx), obtaining steam as the only product of the reaction, which can be released into the atmosphere without any problems.
The heat generated is sufficient to power a domestic heating system, especially in cooperation with well-known radiant plants that improve thermal efficiency.
An example of these known types of catalytic hydrogen combustion burner and related boiler plant is described in document EP 1 899 642 (B1) on behalf of one of the Applicants describing a method and burner for hydrogen by low-temperature oxidation wherein the catalyst, arranged in the oxidation chamber of the burner, comprises a catalyst combined with a self-priming catalyst to trigger the hydrogen oxidation in air at room temperature, with a mixing ratio below the flash point thereof, without supplying energy from the outside and with one or more catalysts arranged downstream. To avoid clogging of the catalyst pores, the mixing air is purified and supplied via a compressor. The burner according to this document can safely provide a heat source for hot water and heating plants, e.g., for domestic use.
Another example of these known types of catalytic hydrogen combustion burner is described in document EP 2 529 157 (A2), on behalf of one of the Applicants, which describes a burner for the combustion of hydrogen by means of a catalyst having a body, a first self-priming catalyst and a subsequent series of oxidation catalysts, as well as a heat exchanger heated by the combustion gases produced. In the burner, the heat exchanger is a conventional heat exchanger arranged outside the burner body housing the catalysts. A header housing the auto-ignition catalyst may be separable from a body housing the oxidation catalysts.
A second heat exchanger through which cold water flows allows the production of high purity distilled water. A first part of the boiler houses the burner modules, while another part houses the conventional common heat exchanger and any additional heat exchanger for the production of distilled water.
These aforementioned catalytic hydrogen burners and their boiler or generation plants have however drawbacks and operational limitations.
One limitation of these mentioned hydrogen boiler plants is due to that they have a lower thermal efficiency than conventional commercial natural gas boiler plants due to the difficulty in condensing the water vapour produced by combustion. In addition, a large amount of air is required per unit of heat output produced.
Another limitation of these well-known catalytic hydrogen burners is due to the fact that the size of the catalysts required to ensure adequate combustion efficiency generates high fluid-dynamic pressure drops located mainly in the catalytic section of the burner.
A further limitation of the well-known catalytic hydrogen burners is that they require a high-pressure hydrogen supply by means of pressurised tanks or cylinders which are not compatible with conventional public fuel gas distribution plants.
The purpose of the present invention is to overcome and obviate, at least in part, the above-mentioned drawbacks and operating limitations.
More particularly, the scope of the present invention is to make available to the user a catalytic burner and related hydrogen boiler plant with improved efficiency or overall thermal efficiency and no or reduced emission of harmful gases into the atmosphere.
A further scope of the present invention is also to realise a hydrogen catalytic burner having a catalyst with improved fluid dynamics such as to reduce the flow pressure losses when passing through the catalyst.
Last but not least, the scope of the present invention is to make available to the user a hydrogen catalytic burner and a related boiler plant capable of being easily installed and adaptable to already existing plants and with hydrogen supply pressures compatible with those of traditional public gas distribution networks.
A further aim of the present invention is to provide a catalytic hydrogen burner and a relative boiler plant capable of ensuring a high level of resistance and reliability over time, such that it can be easily and economically realized.
These and other purposes are achieved by the hydrogen catalytic burner and the related boiler plant subject matter of the present invention in accordance with the independent claim.
The structural and functional features of the catalytic hydrogen burner and boiler plant which are the subject matter of the present invention may be better understood from the detailed description which follows, in which reference is made to the appended drawing plates which represent some preferred and non-limiting embodiments thereof, wherein:
In the following description, it will be apparent to a person skilled in the art how by the term “burner” is meant a heat generator within which the combustion and water production reaction is a hydrogen-oxygen molecular oxidation reaction which takes place by means of a catalyst element with a hydrogen concentration below that of the flammability limit of combustible hydrogen and without a combustion flame, at a temperature below the auto-ignition point of the hydrogen-oxygen mixture (H2+O2).
It will also be evident to the person skilled in the art that the terms “exhaust fumes”, “combustion gases” or “reaction products” refer to the reaction product exiting the catalytic section comprising water (H2O) in the form of predominantly liquid water, water vapour or a saturated mixture of liquid water and water vapour (1+v) produced by the oxidation reaction of hydrogen with oxygen contained in atmospheric air.
With initial reference to
Still with reference to the same figures and in particular to
Again with particular reference to the embodiment of
The fan 40 can be defined as and preferably comprises a centrifugal machine, which is also used in conventional natural gas condensing boilers and is capable of generating high flow rates and heads. Said fan 40 also allows adjustment of the rotation speed of the centrifugal impeller in order to allow the boiler plant 100 to operate at partial load, and can be sized according to the required heat output of the boiler and consequently the flow rate of hydrogen to be processed. The air flow rate is typically calculated to obtain at the burner inlet a mole fraction of hydrogen in the mixture of between 1% and 3.5%, measured under nominal conditions downstream of the fan.
The fan 40, configured to also operate with gaseous mixtures, may also be defined as or comprise a blower or an axial fan capable of generating head and flow rate values necessary for proper operation of the hydrogen boiler. The head of the fan 40 required to provide the catalytic burner 10 with the nominal air-hydrogen mixture flow rate is typically between 3 and 50 millibars [mbar].
Said fan 40 being configured to work with a combustible mixture can also advantageously be a fan for combustible substances or gases comprising conventional non-sparking devices or plants.
Referring to
With reference to the variant embodiments of
Referring again to
The catalytic burner 10 may also be configured to convey into the inlet port 11 through the manifold 14 the inlet flow through a recirculation port 13 from a recirculation recovery line, as in the example of
With particular reference to
In the latter case oxygen inlet port 11 degenerates and coincides with the inlet port of fan 40, as in the example in
The burner 10 can also be configured to connect and feed directly into the inlet port (not shown) of the fan 40 also the inlet flow from a recirculation port 13 coming from a recirculation recovery line, as in the example of
Still with reference to
These further intake openings may be formed in the fan housing 40 and may be arranged side-by-side in fluid connection with the intake chamber or may be arranged concentrically in fluid connection with the intake chamber of the fan 10 itself.
Referring again to the same figures, the catalytic burner 10 may also comprise a diffuser 20 element arranged downstream of the fan 40, with respect to the direction or direction of flow, and configured to convey the air-hydrogen mixture through said catalytic section 30. Said diffuser element is also advantageously capable of equalising the flow velocity of the fluid air-hydrogen mixture prior to entering said catalytic section 30.
The catalytic section 30 of the catalytic burner 10 generally comprises at least one self-priming catalyst 31 and may comprise at least one finishing catalyst 32.
The self-priming catalyst 31 is preferably made in a conventional quadrangular panel geometry having generally a thickness of the order of a few centimetres [cm]. The thickness can advantageously be optimised in such a way as to achieve a conversion of hydrogen to water of more than 95% estimated through both theoretical calculations and experimental tests.
The self-priming catalyst 31 of the catalytic section 30, having to trigger the reaction at low temperature, must comprise noble metals, typically Platinum (Pt 78) and Palladium (Pd 46), capable of triggering the air-hydrogen mixture even at room temperature. The self-priming catalyst 31 must be able to activate the reaction by processing a gas stream at room temperature and with a hydrogen concentration of approximately 1.5% to 3.5%. The average temperature generally reached inside the self-priming catalyst 31 is typically between 150° C. and 320° C., with localised temperature peaks that can generally reach temperatures of around 500-600° C., which is in any case lower than the temperatures required for the formation of nitrogen oxides (NOx).
The self-priming catalyst 31 may advantageously comprise a plant with low fluid dynamic pressure drop, such as, for example, a conventional catalyst having a honeycomb geometry and a cell density in the range of 100-1200 CPSI (cells per square inches), more preferably in the range of 200-600 CPSI.
Said catalytic burner section 30 of the catalytic burner 10 may also advantageously comprise at least one finishing catalyst 32 capable of ensuring complete combustion of the residual hydrogen. Said finishing catalyst 32 is typically capable of operating at a mixture inlet temperature indicatively between 150 and 320° C., a temperature sufficient to cause the reaction to take place with a catalyst having moderate activity characteristics.
The finishing catalyst 32 generally comprises a support formed in metal foam capable of allowing a gas phase mass exchange (air and hydrogen) between the different regions of the finishing catalyst 32 itself, so as to allow complete conversion of the fuel mixture.
Said support of the catalyst constitutes an obstacle to the flow and generates a fluid-dynamic pressure drop of the fuel mixture, consequently requiring a greater head to the fan 40, therefore, the smaller the dimensions of the finishing catalyst 32 and the lower the fluid-dynamic pressure drop of the catalytic section 30, the lower the power consumption of the fan 40.
Said finishing catalyst 32 may also comprise a plant with any geometry capable of distributing the reactants over its cross-section, but imposing moderate fluid dynamic pressure losses.
The finishing catalyst 32 may contain minimal amounts of noble metals or be formed from mixed oxides. In general, the composition of the finishing catalyst 32 must be necessary for the conversion of a very large part of the unburnt hydrogen present downstream of the self-priming catalyst 31.
The finishing catalyst 32 is a device used to maximise the conversion of hydrogen supplied to the boiler plant 100 during the combustion reaction, but is not strictly necessary for the operation of the boiler plant 100. The loss of reaction yield associated with the lower hydrogen conversion achieved in the absence of the finishing catalyst 32 can be avoided by appropriate sizing of the self-priming catalyst 31.
With reference now to
In the following description, all the various embodiments of the boiler plant 100 comprising a burner 10 according to the present invention provided with a single inlet port 11 configured to receive the supply of both air and hydrogen via the respective air (oxygen) supply line 15 and hydrogen inlet line 15′ will be considered for clarity and simplicity of description.
It will be clear to the person skilled in the art how the same air inlet line 15 and hydrogen inlet line 15′ can be connected in an obvious manner to the further inlet ports 11′ 11′ of the catalytic burner 10.
With initial reference to
Preferably said heat exchanger 50 may be a conventional finned pack air-water exchanger. This heat exchanger 50 is designed to ensure condensation of the water vapour produced by the reaction at the last ranks of the exchanger encountered by the exhaust fumes or reaction products.
Through the outlet port 12 of the burner from the catalytic section 30, a stream of moist air at a temperature of approximately 150 to 320° C. passes into the heat exchanger 50. The heat exchanger 50 may also be defined by or comprise heat exchange systems based on different technologies, provided that they are capable of fully dissipating the heat generated by the combustion of the hydrogen in the catalytic section 30 of the catalytic burner 10 and handling the condensation of part of the water vapour contained in the reaction products, and provided that they are capable of operating with minimal fluid dynamic pressure losses.
With particular reference to the embodiments of
Said external air air preheater 70 may comprise a finned tube air-to-air heat exchanger or more preferably a plate air-to-air heat exchanger.
Said air preheater 70 is configured to recover part of the residual energy of the exhaust fumes or reaction products exiting the catalytic section 30 downstream of the main heat exchanger 50 and to heat the inlet air of the catalytic burner 10 from the air inlet line 15, in such a way as to avoid condensation of water upstream of the self-priming catalyst 31 of the catalytic section 30.
Said air preheater 70 may also be defined by or comprise any air-to-air heat exchanger or device capable of heating the atmospheric air inlet to the catalytic burner 10 by extracting heat from the fraction of combustion gases conveyed in the exhaust fumes discharge line 60, with a layout such as to ensure a more compact circuit.
Again with reference to the same figures, the boiler plant 100 may advantageously comprise a water-rich exhaust fumes recirculation recovery line or water recirculation line, more briefly said recirculation recovery line 60′ for recirculating in the burner 10 a fraction of the combustion products and configured to connect the exhaust fumes exhaust fumes discharge line 60 before or upstream of the air preheater with the inlet port 11 of the burner 10, said recirculation recovery line 60′ being configured to be connected with the air inlet line 15 after or downstream of said air preheater 70.
With reference again to
With particular reference to the variant embodiments of
With particular reference to the variant embodiments of
With particular reference again to
The extractor fan 64 may also be replaced by a three-way control valve 65 arranged on the traditional a T-joint connecting the branches of the boiler plant lines 100.
Said at least one regulating valve 65 may be arranged on the flue exhaust fumes discharge line 60 at the junction point with the recirculation recovery line 60′, as in the examples of boiler plant of
Referring again to
From the description of the catalytic burner 10 and the related hydrogen boiler plant 100 object of the present invention, the operation described below is obvious.
With initial reference again to
Referring also to
Said air flow rate processed by the fan 40 refers to a mixture of fresh external air, taken either from the external environment or from recirculated exhaust fumes, generally under-oxygenated and rich in water, the latter in a vapour state.
With reference again to the same
With particular reference to
Referring again to
The fan 40 also has the important function of uniformly and efficiently mixing the air and hydrogen in such a way that a homogeneous flow with a uniform concentration is obtained at the inlet to the catalytic section 30 and the reaction surface between hydrogen and oxygen is maximised.
Downstream or after the fan 40 is arranged the diffuser 20 which has the function of make uniform the flow velocity of the fluid air-hydrogen mixture before entering the catalytic section 30, as well as that of conveying the flow of the mixture towards and through the catalytic section 30.
This catalytic section 30 is typically composed of two catalysts in sequence. The air-hydrogen mixture first encounters the self-priming catalyst 31, which comprises materials with enough noble metal concentration to trigger the reaction at room temperature and with a low hydrogen concentration, even below the flammability limit.
Subsequently, the air-hydrogen mixture, largely converted by the combustion reaction in the self-priming catalyst 31, encounters the finishing catalyst 32 which allows the conversion of the remaining hydrogen present in the feed stream to be completed. Said finishing catalyst 32 comprises materials with a low concentration of noble metals or is generally formed from chemically less active mixed oxides, said finishing catalyst 32 having to process a higher temperature stream (about 250° C. under nominal conditions) than the self-priming catalyst 31.
The entire catalytic section 30, whether provided with or without the finishing catalyst 32, may comprise and be made of one or more elements or panels.
The catalytic section 30 is generally adiabatic and the use of an exchanger dedicated to the catalytic section 30 itself is not necessary.
Thanks to a more uniform and homogeneous mixing of the hydrogen with the air obtained in the fan 40, it is possible to optimise the size and volume of the elements or panels forming the self-priming catalyst 31 and the possible finishing catalyst 32, thus advantageously reducing the fluid-dynamic pressure drop in the entire catalytic section 30, thereby decreasing the head and energy consumption of the fan 40.
Referring again to
Heat exchange with the fluid in the consumer circuit 50 takes place in this section of the boiler plant 100. Heat exchanger 50 preferably has a counterflow configuration to maximise heat exchange efficiency.
In the heat exchanger 50, partial condensation of the water contained in the exhaust fumes in the vapour state also takes place, which maximises energy recovery from the exhaust fumes stream, thereby increasing the thermal efficiency of the boiler plant 100. Condensation in the heat exchanger 50 occurs over a wide range of operating conditions, this is possible due to the water-rich mixture supplied to the catalytic burner 10 by the fan 40 by means of the recirculation of combustion gases through the recirculation recovery line 60′.
The fan 40 therefore also has the function of advantageously mixing the recirculation water fraction into the air-hydrogen mixture so as to further reduce the risk of condensation in the catalytic section 30.
The condensation water produced in the heat exchanger 50 is subsequently collected in the condensate collection tank 66′ via a further discharge line 66 and discharged externally to the boiler.
With reference to the embodiments of the boiler plant 100 of
Said air preheater 70, has the function of recovering heat from the combustion or exhaust fumes in order to heat the outside air entering the boiler plant 100 via the air inlet line 15. In this way, the thermal efficiency is maximized and a hot flow is introduced into the inlet to avoid condensation phenomena of the water contained in the atmospheric air and that introduced by the recirculation recovery line 60′ in the air-hydrogen mixture entering the burner in the catalytic section 30 of the burner 10.
In order to better control and regulate the fraction of water contained in the exhaust fumes and recirculated in the recirculation recovery line 60′, with particular reference to
After the air preheater 70, the combustion gases or exhaust fumes can be extracted by an extractor fan 64 and expelled from the exhaust fumes exhaust fumes discharge line 60 into the atmosphere by means of a chimney, as in the examples of boiler plant 100 of
With particular reference also to
The boiler plant 100 comprising the catalytic burner 10 according to the present invention, comprises the fan 40 also capable of processing an air-hydrogen mixture outside the self-ignition limits for temperature and flammability limits for hydrogen concentration. In the example, the diffuser 20 is provided to have as uniform a velocity profile as possible at the inlet catalytic section 30.
The experimental data shown in
For simplicity of description, the structural and functional elements of the two compared plants are shown with the same numerical references as the boiler plant 100 subject matter of the present invention represented in the accompanying drawing tables.
The parameters being compared between the two hydrogen boiler plants are the amount of hydrogen present in the exhaust fumes and the concentration of hydrogen present in three different zones or parts of the diffuser 20 arranged upstream of the catalytic section 30. The diffuser 20 is placed horizontally and the three different measurement zones are: the upper extreme point of the diffuser (called the upper extreme part), the middle point (called the middle part), and finally a point in the lower part close to the lower extreme (called the lower part). The measurements of the three parts are obtained by means of a gas chromatograph and are normalised with respect to the concentration at the suction of the fan 40, where this concentration is obtained from the measurement of the air and hydrogen flows detected by means of suitable instrumentation.
The catalytic section 30 in the catalytic burner 10 of the boiler plant 100 is the same as in a conventional boiler plant, according to the known art (
Said catalytic section 30 comprises a self-priming catalyst 31 and a finisher catalyst 32. The self-priming catalyst 31 is made by means of a 600 CPSI (cells per square inch) honeycomb ceramic matrix having a diameter of 76.5 mm. The thickness of said self-priming catalyst 31 matrix is 30 mm.
Finishing catalyst 32 is made of metal foam on which the catalytic material is deposited; it consists of 10 discs, each with a diameter of 75 mm and a thickness of 11 mm. The total thickness of the catalyst finisher 32 is thus 110 mm.
Samples of the air-hydrogen mixture taken in the three different zones upstream of the catalytic section 30 of both the hydrogen boiler plant 100 of the present invention and the hydrogen boiler plant according to the known art were then analysed.
The results are described below, first as obtained from the gas chromatograph and then, normalising as previously explained. The experimental data obtained shows that the hydrogen present in the combustion gases varies from a concentration of 412 ppm (parts per million), average concentration in the known hydrogen boiler plant to 179 ppm average concentration in the hydrogen boiler plant according to the present invention. These values were obtained with the same catalytic section 31, varying only the feed conditions thereof.
The table in
In the boiler plant according to the known art, the normalised hydrogen concentration is highest in the extreme upper part of the diffuser 20, while it is lowest in the lower part of the diffuser 20.
In the boiler plant 100 of the present invention, the concentration of normalised hydrogen is constant, and equal to 1, in the different zones of the diffuser 20 placed upstream of the catalytic section 30, demonstrating the marked improvement in the uniformity of the mixture.
With particular reference to the diagram in
The numerical simulation was carried out by analysing the diagram shown in
In said diagram, the fan 40 processes a flow of air and hydrogen (FAN), which is then sent to the catalytic section 30 (CMB). Downstream of said catalytic section 30, a heat exchanger 50 (HEX) is arranged, in which the condensation of part of the water contained in the exhaust fumes is provided. The condensate is subsequently separated in a liquid separator (FL1).
In the simulation, the water recovery recirculation of the flue or combustion gases via the recirculation recovery line 60′ takes place via the user-settable three-way control valve 65 (SPL) and without extractor fan 64. The exhaust fumes to be expelled are processed by an outside air air preheater 70 (REC). Any additional water condensed in the air preheater 70 in a liquid separator (FL2) is separated before expulsion.
The heated outside air flow, the recirculated exhaust fumes or exhaust fumes flow and the hydrogen flow are conveyed into the inlet port 11, component (MIX), and then drawn in by the fan 40.
In addition to the diagram in
In this way, it is possible to evaluate the advantageous effect of the recirculation of combustion gases on the overall efficiency of the boiler plant 100 according to the present invention, calculated by evaluating the heat generated by the boiler plant 100 and supplied to the cooling water of the heat exchanger 50 (HEX) and the heat supplied to the boiler plant 100 by the combustion of hydrogen in the catalytic burner 10 (CMB) in the two cases analysed with recovery recirculation and preheating and without recovery recirculation and air preheating.
The table in
As can be seen from the foregoing, the advantages that the catalytic burner 10 and the related hydrogen boiler plant 100 of the present invention achieve are obvious.
The catalytic burner 10 and the boiler plant 100 object of the present invention are particularly advantageous compared to conventional catalytic plants because they allow the same boiler plant 100 an improved operating efficiency thanks to a fan 40 capable of introducing a flow rate of air-hydrogen mixture instead of air only, making it possible to feed hydrogen at the low pressure zone upstream of the fan so as to allow a uniform and complete mixing of the mixture within the fan 40 itself.
A further advantage of the catalytic burner 10 and the related boiler plant 100 is represented by the fact that thanks to the better and more uniform mixing of the air-hydrogen flow entering the catalytic section 30 it is possible, with the same reaction yield, to optimise the dimensions of the catalysts (31, 32) by reducing them in such a way as to reduce the fluid-dynamic pressure drop of the flow in the catalytic section 30 and to increase the overall thermal efficiency of the boiler plant 100.
A further advantage of the catalytic burner 10 and the boiler of the present invention is that with this type of configuration, the radial heat losses of the catalytic section of the catalytic burner 10 are negligible and therefore a dedicated heat exchanger for the catalytic section 30 is not required, thus making the boiler plant 100 constructively simpler and cheaper to manufacture.
Although the invention has been described above with particular reference to a preferred embodiment, which is given for illustrative and non-limiting purposes, numerous modifications and embodiments will become apparent to a skilled person in the art in the light of the above description. The present invention is therefore intended to encompass all modifications and variations falling within the protective scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102022000000950 | Jan 2022 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2023/050383 | 1/17/2023 | WO |
