EP1899642B1

EP1899642B1 - Method for burning hydrogen and burner therefor

Info

Publication number: EP1899642B1
Application number: EP06762035.1A
Authority: EP
Inventors: Corrado Giacomini
Original assignee: Giacomini SpA
Current assignee: Giacomini SpA
Priority date: 2005-06-21
Filing date: 2006-06-13
Publication date: 2018-04-25
Anticipated expiration: 2026-06-13
Also published as: ES2677893T3; WO2006136316A1; EP1899642A1; DK1899642T3; PT1899642T; ITCO20050019A1

Description

Background of the invention

The present invention relates to a method and burner for burning/oxidating hydrogen on a catalyzer according to the preambles of claims 1 and 4.

Background of the invention

A burner for burning a hydrogen-air mixture is already known from the document EP 1 179 709 A2 . In this burner, for priming the hydrogen oxidation, a primary operating step and related catalyzer are provided, in which a hydrogen/air mixing ratio much larger than its flash point (about 4% by volume of the hydrogen/air mixing ratio) and which can also approach to very dangerous detonation conditions (a hydrogen/air mixing ratio up to 12.5% by volume) is used.
Said primary operating step and related catalyzer, in addition to requiring a two-stage adjusting system for adjusting the hydrogen flow-rate to the mixing chamber, or a first flow-rate for said primary or pre-burning step and a second flow-rate for the operating burning or combustion operation, represents a self-evident unsafe condition for people, the encompassing environment and the burner itself, and susceptible to damage the catalyzer.
Moreover, in said prior burner, for priming the hydrogen oxidation, it is necessary to provide an outside power supply.
To the above it is furthermore to be added that the mixing air is supplied through a tangential fan, which must also operate to convey the oxidation hot gases through the heat exchanger to heat the thermal carrier fluid.
A method according to the preamble of claim 1 and a burner according to the preamble of claim 4 are known from WO2005/024301A .

Summary of the invention

Accordingly, the aim of the present invention is to provide a method and burner or combustor for burning/oxidating hydrogen which are very simplified and adapted to operate under highly safe conditions.
This aim is achieved, according to the invention, by a method and burner for burning/oxidating hydrogen having the characterizing features of claims 1 and 4 respectively. The burning method and burner for safely burning hydrogen according to the invention, provide the following very important advantages.
Firstly, the hydrogen oxidating primary priming step and related catalyzer are eliminated; moreover are also eliminated the two stage adjusting circuit for adjusting the hydrogen flow-rate and any outside energy supply for performing the mentioned primary oxidation step; in addition a hydrogen/air mixture greatly less than 4% by volume, i.e. much smaller than the flash point is used, thereby providing highly safe conditions.
The low operating temperature is selected in a range from about 200 to about 560°C, which corresponds to the self-priming or self-igniting hydrogen flame temperature. Said operating temperature being preferably of about 300°C. In this temperature range of < 650°C, moreover, air nitrogen oxides are prevented from forming, thereby allowing to carry out a "zero emission" burning process. In such a no-flame hydrogen oxidation process, impurities contained in the supplied air, such as powders, are not burned thereby they could clog the catalyzer pores to hinder an efficient operation of the latter and generate unsafe conditions due to the presence of un-oxided hydrogen. This, however, advantageously prevented from occurring since mixing air is preliminarily purified, thereby increasing the operating safety; moreover, by using a hydrogen/air mixture in a ratio less than that of the flash point, it is advantageously possible to operate the subject burner even in closed environments such as residential buildings and the like. Furthermore, it is not necessary to store oxygen from oxidating hydrogen, as in prior art burners.
Further advantageously, the prior fan is replaced by a compressor, operating to purify said feeding air, and adapted to safely provide the required high pressure head to "propel" hot gases from the oxidation process through the heat exchanger, that will be more efficient the more labyrinth passages are performed therein. Thus, an improved heat transmission to the thermal carrier fluid, such as water, is obtained, allowing said thermal carrier fluid to be used with an optimum yield, for example in domestic heating and/or hot water producing systems.
By priming the hydrogen oxidation on a room temperature catalyzer no preheating and related outside energy supply is required.
Yet another advantage is that the burner according to the invention provides a modular unit to be used in any desired numbers for forming a target power boiler, for example of about 30 - 35 kW, as conventionally used in domestic heating applications.
By providing a water to be heated exchanger in the form of a candle longitudinally extending through the hot gas conducting and collecting chamber, and using turbulator elements for guiding said hot gas and water through the burner or combustor jacket, it is moreover possible to operate with a very high thermal efficiency.

Brief description of the drawings

Further characteristics, advantages and details of the hydrogen burning method and burner according to the invention, will become more apparent hereinafter from the following disclosure of an exemplary embodiment of a burner according to the invention, and a boiler using it, as schematically shown in the accompanying drawings, where:

Figure 1 is a schematic view illustrating the constructional and operating principle for making and operating the burner according to the invention;
Figure 2 is a middle longitudinal cross-sectional view of an exemplary embodiment of a modular burner according to the invention;
Figure 3 is a cross-sectional view, analogous to figure 2, of a simplified burner construction and related designing parameters; and
Figure 4 is a cross-sectional view of an exemplary boiler including burners as shown in figure 2 and with a power adapted for a domestic use.

In the above mentioned figures, like or equivalent elements have been shown by like references.

Description of the preferred embodiment

With reference at first to figure 1, the reference number 1 generally shows a burner or combustor for air burning/oxidating hydrogen without flame on a catalyzer 2 to provide "zero emission" heat by operating at low temperatures from about 200 to 560°C, for example about 300°C, under highly safe conditions, with a hydrogen/air mixing ratio much less than 4% by volume, which represents the flash point of this mixture.
The catalyzer 2 is designed as a composite catalyzer including a sequence of at least two series catalyzers, of which the first catalyzer 3, at the hydrogen-air mixture inlet side, as indicated by dashed lines, is adapted to prime the hydrogen oxidation without requiring outside power supply means.
This self-priming or self-igniting catalyzer 3 comprises, in an exemplary embodiment a monolithic graphite construction using, as oxidating catalyzer elements, palladium (Pd 46) and platinum (Pt 78), and being adapted to prime or ignite the hydrogen oxidation at room air temperature, with the above mentioned hydrogen/air mixing ratio less than 4% by volume. Upon priming the hydrogen oxidation on the self-priming catalyzer 3, oxidation will continue on the downstream catalyzer 4 arranged in a series relationship with the first, and provided as one or more tandem arranged catalyzers, as shown in dashed lines, so as to provide an overall composite catalyzer 2. The catalyzer/catalyzers 4 is/are constituted, for example, by palladium (Pd 46), platinum (Pt 78) or other suitable metals and alloys thereof on a support, for example alumina, or in a monolithic form, such as small balls, granules and the like.
The hydrogen-air mixture, with a mixing ratio less than 4% by volume, is fed by a compressor 6 leading to a mixing chamber 7, to which also leads a low-pressure hydrogen delivery duct, the pressure of which is in a 16 to 25 millibars range, preferably of about 20 millibars. Through a mixing nozzle 9 and duct 10, the hydrogen-air mixture impinges on the composite catalyzer 2, by flowing, at first, on the self-priming catalyzer 3, at room temperature, and then on the downstream arranged catalyzers 4.
The hydrogen oxidation heat is removed by a heat exchanger having substantially the shape of a toroidal jacket 11, therethrough water to be heated is caused to pass; said water coming from an inlet duct 12 and exiting through the outlet 13, where said jacket 11 can also include therein a tube sheet assembly, not shown, for conveying exhaust gases exiting a tube 14, for example, to a first outside air-water exchanger, not shown, for further exploiting the exhaust gas heat. The reference number 16 shows a process water outlet and collecting element, said process water being advantageously re-conveyed to an electrolyzer, not shown, for making hydrogen.
In figures 2 and 3, water to be heated is supplied through a duct 12A which longitudinally extends in an exchanger 5 in the form of a candle, which in turn longitudinally extends in the hot gas conducting and collecting chamber 15, and the outlet 12 of which communicates with the toroidal jacket or chamber 11, in which said water is caused to pass through a scroll turbulator 18. In particular, hot gases are conveyed through the exchanger 5 via a further turbulator 19. Thus, by using said turbulators 18 and 19, a high efficiency gas/water or thermal carrier fluid heat exchange is obtained.
In a practical use of a domestic boiler, the heated water outlet 13 is coupled to the delivery side of a hot water and heating system (for example of a radiating floor type), whereas the inlet duct 12A is coupled to the return side of said system, which preferably contains an accumulating vessel therein.
With respect to environment air to be mixed with hydrogen, said air is purified by an air purifying device 17 arranged upstream of the compressor 6, and designed for performing, for example filtering, demoistening, oil eliminating operations and so on, while simultaneously removing powder materials, for preventing the composite catalyzer 2 pores from being clogged; thus operating failures of said catalyzer, and a risk of continuously providing a non-oxidated hydrogen flow are also prevented.
Moreover, said compressor will provide the pressure head necessary to efficiently propel the oxidation hot gas through a heat exchanger assembly provided in the jacket 11, thereby improving heat transmission to the thermal carrier fluid, i.e. to water to be heated.
The above disclosed burner, with it designing exemplary size parameters hereinbelow shown, provide a comparatively low power modular burner, having, for example, a power of about 6 kW, which can be used for making larger power boilers, for example of about 30 - 35 kW, like those which are conventionally used for domestic heating applications.
Said designing parameter and sizes, for a burner and boiler according to the invention, could be as follows:

Burner

Air flow-rate: 830 l/min
H₂ flow-rate: 30 l/min (≈3.5% by volume in the mixture) → 1.8 nm³
H₂ high heating value (the water steam produced by burning is condensed and the related heat is exploited): 3.050 kcal/nm³ $Thermal power = 1.8 \frac{{nm}^{3}}{h} \times 3,050 \frac{kcal}{nm} \times \frac{4,186}{3,600} \frac{kW . h}{kcal} = 6.38 kW$
Water side example:
- Tin: 39°C (return to the radiating floor)
- Tout: 45°C (delivery from the radiating floor)
  ≈ 15 l/min

Catalyzer " pack " thickness = 1 \times 35 + 11 \times 22 = 277 mm

Boiler

$POWERS AND FLOW - RATES = 6 \times power and flow - rates of a single burner$
Circumscribed "circumference" size = 410 mm
Longitudinal extension = Burner length = 800 mm
By using a single boiler 20 for six burners 1, good results have been obtained by a pentagonal casing 21 with spaced away burners 1 located at the pentagon corners and a central burner separated by thermally insulating material.
From the constructional and operational disclosure of the burner according to the invention and its hydrogen oxidation method, it should be apparent that, by said burner and method, it is possible to operate in highly safe conditions, thereby efficiently achieving the above mentioned aim and providing the mentioned advantages.
Those skilled in the art could made modifications and variations, for example by replacing the self-priming graphite catalyzer or the other continuously operating catalyzers of palladium, platinum or the like by other functionally equivalent catalyzer, and provide said burner with additional functional circuits with measuring, adjusting, shutting-off components and the like, without departing from the scope of the invention.

Claims

A method for catalytically oxidating a hydrogen and low temperature environment air mixture, in a burner, without forming flames,
wherein said hydrogen/air mixture has a mixing ratio less than a flash point thereof and is at first conveyed onto a self- priming catalyzer, adapted to self-prime an oxidation of said mixture, and then onto one or more downstream catalyzers for providing a continued operating oxidation at "zero emissions", and

wherein hydrogen oxidation heat is removed by a heat exchanger having substantially the shape of a toroidal jacket (11) therethrough water to be heated is caused to pass,
characterized

in that water to be heated is supplied through a duct (12A) which longitudinally extends in an heat exchanger (5) in the form of a candle, which in turn longitudinally extends in a hot gas conducting and collecting chamber (15), the outlet (12) of the heat exchanger (5) communicating with the toroidal jacket (11),

in that water exiting from the heat exchanger (5) is caused to pass through the toroidal jacket by a scroll turbulator (18) placed in the toroidal jacket (11), and

in that hot gases produced by hydrogen oxidation are conveyed through the heat exchanger (5) via a further turbulator (19) being placed in the hot gas conducting and collecting chamber (15) between the heat exchanger (5) and the toroidal jacket (11).
Method according to claim 1, wherein water to be heated is stored in a tank and used, for example, for heating and/or making hot water for sanitary applications.
Method according to claim 1 or 2, wherein said air is purified, before forming said oxidation mixture, for removing therefrom moisture and polluting substances, such as powder materials, for preventing said polluting substances from depositing on said catalyzers and clogging the catalyzer pores.
A burner for oxidating hydrogen by a method according to claim 1, comprising:
- a bumer body having, in its inside, a hydrogen oxidating chamber containing a low-temperature hydrogen oxidating catalyzer (2) and, on its outside, a toroidal jacket (11) operating as a heat exchanger for heating a thermal carrier fluid by the burnt hot gases,

- a hydrogen and air mixing chamber for forming said hydrogen-air mixture, said mixing chamber being coupled to a hydrogen supply duct and an air supply duct with associated air supply means,
wherein said catalyzer comprises a composite catalyzer comprising a first self-priming catalyzer, adapted to prime the oxidation of hydrogen in room temperature air, with a mixing ratio less than the flash-point thereof, and without supplying outside power, and one or more downstream arranged catalyzers for performing a continuous hydrogen oxidation operation,
characterized in that
- the burner comprises a duct (12A) for conveying water to be heated, the duct (12A) extending longitudinally in a heat exchanger (5) in the form of a candle,

- the heat exchanger (5) longitudinally extends through a hot gas collecting and conveying chamber (15), and is provided with an outlet (12) communicating with the toroidal jacket (11), for conveying water from the heat exchanger to the toroidal jacket (11) to be further heated,

- the toroidal jacket (11) comprises a scroll turbolator (18),

- a further turbulator (19) is placed in the hot gas conducting and collecting chamber (15) between the heat exchanger (5) and the toroidal jacket (11) for conveying hot gases produced by hydrogen oxidation through the heat exchanger (5).
Method according to claim 4, characterized in that said mixing air supplying means comprise a compressor (6) and that, upstream of said compressor (6), an air purifying device (17), for eliminating from said air moisture, powder and other extraneous substances is provided.
A burner, according to claim 4, characterized in that said self-priming catalyzer (3) comprises a graphite porous monolithic construction including, as oxidation catalyzer elements, palladium (Pd 46) and platinum (Pt 78), said catalyzer (4) for continuously oxidating hydrogen comprising palladium (Pd 46), platinum (Pt 78), or other suitable metal materials and alloys thereof, on a support, such as alumina, or in a monolithic form, such as small balls, granules and the like.
A boiler for heating and/or hot water systems, characterized in that said boiler (20) comprises a plurality of burners (1) according to one or more of claims 4 to 6, housed in a casing and being spaced and thermally insulated from one another, for example six burners in a casing having a pentagonal cross-section.