US20110180396A1

US20110180396A1 - Hydrogen generator system for a catalytic hydrogen burner

Info

Publication number: US20110180396A1
Application number: US12/875,160
Authority: US
Inventors: Corrado Giacomini
Original assignee: Giacomini SpA
Current assignee: Giacomini SpA
Priority date: 2010-01-27
Filing date: 2010-09-03
Publication date: 2011-07-28
Also published as: WO2011092540A1; ITCO20100003A1; IT1397855B1; EP2529444A1

Abstract

A hydrogen generator system (1) for a hydrogen powered unit or user (3), such as for example a catalytic hydrogen burner or a fuel cell, includes an electrolyzer (2) for the electrolysis of distilled water, producing hydrogen and oxygen, provided with a demineralizer device (5) and an A/C transformer/converter unit (7) for supplying electrical power for the electrolysis process and, on the outlet side, a device for purifying the hydrogen produced, such system (1) further includes:

- a device (10) for recovering the heat generated by the electrolysis process
- and/or a device (17) for storing the hydrogen produced,
  such hydrogen generator system (1) is accommodated in a casing (20) which has—externally—inlet and outlet connection fittings.

Description

DESCRIPTION OF THE INVENTION

1. Field of Application
The present invention refers to a hydrogen generator system for a catalytic hydrogen burner according to the preamble of claim 1.
2. Technological Background and State of the Art
Recently developed, as an alternative to the known liquid fuel or gas heaters for producing heat, respectively for heating systems, were burners for catalytic hydrogen combustion with the ignition of the reaction at ambient temperature, without the formation of a flame, with reaction below the temperature of formation of NO_x, with exhaust product solely made up of hot moist air, and with the heat transferred entirely to a heat exchanger for heating water of a heating system, for example of the radiant type, in particular for residential buildings, i.e. with surfaces for example up to about 250-300 m². Hydrogen catalytic burners of the indicated type are disclosed, for example, by document WO 2005/024301 of the applicant. The supply of hydrogen therein is provided for at low pressures, for example in the order of 2-5 bars, where the supply of hydrogen must be ensured in a reliable, safe and continuous manner.
Production of hydrogen at industrial level is obtained through electrolysis of distilled water in alkaline electrolysers, obtaining oxygen and hydrogen. Suitably demineralised supply system water is supplied to the electrolysers and the required electrical energy is supplied from the electrical supplky supply system using an A/C transformer/converter unit, generally supplied with three-phase current following the high current values and low voltage values required, wherein heat is developed during the electrolysis process. For practical use of the abovementioned hydrogen catalytic burners it is necessary to provide a suitable supply of hydrogen, i.e. continuous, at low pressure and with a suitable degree of purity of hydrogen. One such supply is currently available with plants or systems solely for generating hydrogen and oxygen assembled with devices or components available in the market, generally provided for industrial production of hydrogen.
Thus, such systems reveal the following drawbacks:

- they are generally made up of components or devices recovered occasionally on the market, possibly modified and not designed in function of the unit in question,
- these systems are generally quite complex for the hydraulic and electric installation technicians, in that they require quite long assembly and installation times, errors may occur and they require a lot of space,
- performance thereof is improvable,
- often used are proton exchange membrane (PEM) electrolytic cells, which actually provide higher purity of hydrogen with respect to the use of electrolytic cells provided for according to the invention, but have correspondingly higher costs and a more limited duration,
- heat is developed during electrolysis, hence lowering the performance of the system,
- an interruption of the electrical energy entails an interruption of the production of hydrogen,
- provided for is the sole production of hydrogen and oxygen,

SUMMARY OF THE INVENTION

Thus, the task on which the present invention is based is that of providing a hydrogen generator system for obtaining hydrogen catalytic burners of the indicated type capable of overcoming the drawbacks of the prior art systems and capable of providing hydrogen produced with sufficient degree of purity in a reliable and continuous manner as well as obtainable in an inexpensive manner and with an improved performance.
A hydrogen generator system simplifying construction and installation thereof falls within the task of this invention
The abovementioned task is obtained by means of a hydrogen generator system for hydrogen catalytic burners having the characteristics of claim 1. Further advantageous developments and embodiments are observable from the dependent claims.
The hydrogen generator system according to the invention allows attaining various important advantages obtained starting from the known production of hydrogen through electrolysis of distilled water and by using more rational formation criteria for the single blocks into which the proposed hydrogen generator system may be divided as illustrated more in detail hereinafter.
Another advantage of the proposed hydrogen generator lies in the exploitation of the heat that is developed inside the electrolyser during the electrolysis process, such heat being advantageously useable as an integration of the pre-existent system for heating and/or producing domestic hot water.
Reliable continuous supply of the produced hydrogen, even during possible interruptions of the electrolysis process, may be guaranteed in a further development of the base hydrogen generator.
Obtained in a further development of the hydrogen generator according to the invention is a suitable purification of hydrogen using simple and inexpensive means.
Furthermore, a common advantage for all embodiments of the hydrogen generator according to the invention lies in the fact of providing a choice, targeted design and dimensions of the single components required for obtaining the proposed hydrogen generator, hence said circuit may be advantageously assembled in a compact manner and accommodated in an installable casing inside or outside the house.
Such casing shall thus be provided—externally—with inlet fittings and outlet fittings alone, thus further facilitating the connection of said casing, i.e. of the hydrogen generator according to the invention, during the execution of the respective connections.
Providing for a supply of electrical energy produced from renewable sources (solar, wind energy, biogas) alongside the presence of storage of hydrogen, allows obtaining an independent, continuous and inexpensive operation, wherein hydrogen may be produced substantially continuously when the renewable source is available and stored for use thereof when actually required.
Furthermore, it is advantageous to provide a plurality of embodiments of the proposed hydrogen generator, which are capable of meeting the various characteristics to be taken into account depending on the function of the unit to be supplied with hydrogen, for example depending on the degree of purity of hydrogen, which is fundamental should one decide to supply the catalytic burner or any other unit, for example a fuel cell, or even the pressure or flow rate.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics, advantages and details of the hydrogen generator system for a hydrogen-powered unit, such as for example a catalytic hydrogen burner, are observable from the following description of some preferred embodiments, illustrated for exemplifying purposes in the attached drawings, to which reference shall be made even for possible details not outlined in detail in the description that follows, and wherein:

FIG. 1 schematically shows an embodiment of a hydrogen generator system for a hydrogen-powered unit, and

FIGS. 2 to 5 schematically show further embodiments of the hydrogen generator system according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the various figures identical or functionally equivalent components of the proposed system have identical reference numbers.
First, reference is made to a base embodiment illustrated in FIG. 1,
wherein the hydrogen generator system according to the invention is indicated in its entirety with 1. The proposed system 1 comprises an electrolyser 2, i.e. an electrolytic cell, containing a base alkaline solution (KOH) for the process of electrolysis of distilled water for the production of oxygen and hydrogen. Alkaline electrolysers are convenient in terms of costs. Also alternatively used may be PEM electrolysers, i.e. having a proton exchange membrane, such electrolysers being more expensive but obtaining higher purity of the supplied hydrogen. Hydrogen, in case of a catalytic burner 3, is supplied for example at the pressure of 5 bars, where the control of the production occurs through the value of the pressure.
The produced oxygen 4 may be released into the atmosphere.
The water to be subjected to electrolysis is obtained from the supply network and demineralised in a demineralizer 5, advantageously of the reverse osmosis type, which provides high purity of the distilled water suitable for the water electrolysis requirements.
Advantageously, the demineralizer 5 is connected to a tank 6, which automatically requires filling thereof with demineralised water when the level of the water therein drops beneath an adjustable minimum threshold level. Even the dimensioning of the tank 6, provided to have the desired operation autonomy, is performed to have a smallest overall dimension possible. The tank 6 allows obtaining a constant operating safety even in case of possible interruption of the water of the supply system.
The electrical energy required for the electrolysis process may be drawn from the supply system, for example from a three-phase power supply system following the high absorptions of the electrolysis process (about 5 KW per cubic meter of the produced hydrogen), by means of an A/C transformer/converter intermediate unit 7 provided with a control system, not illustrated.
Alternatively provided for may be drawing electrical energy from a renewable source, such as for example a solar, wind energy or biogas system, not illustrated.
As mentioned beforehand, hydrogen is produced at a much lower pressure, for example 5 bars due to reasons related to the safety and duration of the system, wherein the hydrogen produced through alkaline electrolysis may have traces of a base solution, however having a purity exceeding 99%, and thus sufficient for a catalytic burner, while the remaining part is formed by water in vapour state or very slight traces of oxygen. It should be herein observed that such impurities are uninfluential should one decide to store hydrogen at low pressures (as illustrated more in detail hereinafter) or in case of use of hydrogen in combustion processes, as in the case of catalytic burners, while they are influential in case of power supplying the fuel cells, which require purities of higher degree, to avoid occurrence of damage thereon.
Further purification of the gases may require, as known, a step 8 for the condensation of hydrogen through a chiller, not illustrated, which may allow attaining an extremely high degree of purity of 4.5 (99.995%). These chillers are however extremely cumbersome and have high electrical energy consumptions to reduce possible water residues, which are actually uninfluential for the combustion, which generates water vapour.
However, as mentioned above in the case of hydrogen catalytic burners, lower purity is required, for example at least 99.5%, which is doubtlessly obtainable through the mentioned steps of condensation 8 supplied by a chiller.
According to the invention one may waiver the use of chillers and add to the stage of condensation 8—instead—an active carbon and teflon filter 9 for eliminating possible electrolytic residues. This allows obtaining a less expensive and more compact solution. Possible traces of oxygen are actually uninfluential, given that hydrogen is intended for a combustion process.
A further teaching of the invention lies in the recovery of the heat generated in the electrolyser, i.e. in the electrolytic cell 2 during the electrolysis process, providing for a heat exchanger device 10 associated to the electrolyser 2. The primary circuit 11 of the heat exchanger 10 is inserted into the electrolyser 2 and contains a circulation pump 12. The secondary circuit 13 has a delivery 14 and a return 15 means associated to a heating system 16. This heat exchanger device 10 constitutes a source of heat which allows boosting the performance and energy balance of the hydrogen generator system 1, wherein the heat exchanger 10 also serves for cooling the electrolyser 2.
It should be observed that regarding this, generally, 1 Nm³of hydrogen are required for producing about 5.3 KW of electrical energy, 3.5 KW of which are actually used for electrolysis, while the rest is substantially dissipated in heat and by the hydrogen generator system 1 itself, for example through its electric control panel, sensors, fans and so on and so forth. The recovery illustrated above allows the performance of the electrolytic cell 2 to exceed 90%.
Provided for according to a further important teaching of the present invention is the storage of the produced hydrogen, FIGS. 2, 3, 4 and 5. Due to reasons related to the space and simultaneously to the purification of hydrogen, the storage device provided for may either be based on a pressure storage, possibly increased by means of a compressor, or on a storage based on the absorption of hydrogen through metal hydrides, which have the capacity to absorb hydrogen thereinto then releasing it, wherein this solution allows having low-pressure storage devices and having an optimal capacity with respect to the volume.
As known, metal hydrides must be cooled when they absorb hydrogen while they develop heat when they release it. This development of heat may be more or less relevant depending on the composition of the alloy of the abovementioned metal hydrides, wherein the ideal solution would be operating at ambient temperature, or slightly higher with respect thereto. According to the invention the required supply of heat may come from the heat recovery 10 of the electrolysis process, hence—in this sense—the system 1 may be autonomous, FIGS. 2 and 3. Provided for in this case are electrically actuated three-way valves 22 and 23, of which the first (22) serves for by-passing the storage device 17 while the second (23) regulates the temperature according to the needs mixing the water. As an alternative to this, heat may be produced through an external source of heat, for example by means of an electric resistance, not illustrated.
Another important advantage attained through the storage of hydrogen on a solid base, i.e. metal hydrides, lies in the fact that, alongside storing a good amount of hydrogen therein, the metal hydrides also allow further purification of hydrogen, advantageous for combustion thereof, wherein this allows obtaining a purification unit per se included in the storage device 17.
Therefore, in cases where the unit or user does not require particular purity, like in the case of a catalytic burner 3, the unit may directly draw hydrogen from the electrolyser 2 and/or from the storage device 17. Therefore, the hydrogen generator system 1 may have two outlets for the gas, FIG. 3, i.e. an outlet 18 for purified hydrogen solely from the filter 9 and no longer from the storage device 17 directly provided by the electrolyser 2, and an outlet 19 for purer hydrogen, i.e. purified both by the filter 9 and by the storage device 16, and coming from the latter. The two outlets 18 and 19 may supply the same unit or, as illustrated, two units requiring different degrees of purity of hydrogen.
Alternatively, the storage of hydrogen may be obtained by means of a container under pressure, which may be the same one provided by the electrolyser 2 or it may be increased by a compressor, not illustrated, FIG. 5. The embodiment of FIG. 4 shows a hydrogen generator system 1 with separate heat management and storage system.
The embodiment of FIG. 5 illustrates a hydrogen generator system 1 according to the invention with storage of hydrogen under pressure, without a compressor.
In all the embodiments illustrated above, improving performance and consumptions requires a more rational management of all circuit components and devices of the proposed system 1. Thus, proposed according to the invention is the use of a logic, assisted by a software, suitable to run the entire system, wherein for example the production of hydrogen should function only if the storage of sterilized water in the tank 6 of the demineralizer 5 and the storage of hydrogen in the storage device 17 drop below the preset thresholds. Provided for the production of hydrogen and management of the storage of hydrogen is a pressure control; wherein—up to a given level or lower threshold—hydrogen is drawn from the storage device 17, after which rechargeing thereof is performed and/or the unit 3 is supplied with con hydrogen directly by the electrolyser 2. Such solutions are provided for exemplifying purposes and they are made using corresponding circuit arrangements of the hydrogen generator systems 1 as illustrated in the drawings.
A further teaching of the present invention lies in accommodating—in a casing 20—a preassembled circuit or hydrogen generation system 1 according to the invention, made in the most compact manner possible according to the criteria illustrated further above. In such manner, said casing 20 and the hydrogen generator system 1 accommodated therein form a unit 21 that is compact and installable in a simple and quick manner and excluding possible errors related to the formation of the various circuits provided for. The unit 21 shall externally be solely provided with the required inlet and outlet fittings. Thus this shall also allow quick and safe performance of the various connections, for example to the water supply system pipe, to the source of electrical power, as well as to the hydrogen outlet pipe/ s 18, 19 for the units in question, as well as for the delivery 14 and return 15 pipes of the exchanger 10 to be connected to a heating system 16, for example of the radiant type for a residential building, completed with a solar system.
From the structural and functional description outlined above it is observable that the hydrogen generator systems for catalytic burners according to the invention allow an efficient fulfilment of the indicated task and attaining the aforementioned advantages.
What has been described above related to a catalytic burner is obviously valid even for other hydrogen-powered units, like in the case of fuel cells, which may be advantageously used for producing electrical energy as a back-up service, for example in hospitals to replace the common batteries, wherein also used in such hospitals may be the produced oxygen and, for heating purposes, if combined with a catalytic burner likewise supplied with the produced hydrogen.
Following are two examples regarding the dimensioning of a hydrogen generator system 1 according to the criteria and of the invention illustrated above, respectively for a catalytic burner and for a fuel cell.

Example 1

Catalytic Burner

Project Data:
User: 5.8 kW catalytic burner, 1.67 Nm3/h hydrogen consumption
Storage duration: 12 hours
Duration of recharge cycle: 12 hours
Hypothesis for drawing solely from the storage and not directly from the producer.
Dimensioning:
$Minimum dimension of the storage means = 1.67 \frac{m^{3}}{h} \cdot 12 h = 20 m^{3} = 20000 l$ $Minimum electrolyser flow rate = 2 \frac{m^{3}}{h}$
Where the required flow rate was rounded off to the higher number for a safety factor and to near the flow rates available in the market.
Amount of distilled water required to fill the
$storage means = 20 m^{3} \cdot 0.87 \frac{l}{m^{3}} = 17.4 l$
Where 0.87 represents the standard consumption of the electrolyser. A 20 litre storage means is assumed for the sake of safety.
$Minimum water treatment flow rate = 20 l \div 12 h = 1.67 \frac{l}{h}$
N.B. In this calculation example, the m³shall be considered under normal conditions.
Results:
Water treatment (minimum flow rate)=1.67 l/h
Demineralised water storage=20 litres
Electrolysis (recommended flow rate)=2 Nm3/h
Hydrogen storage=20000 litres

Example 2

Fuel Cell

Project Data:
User: 1 kW fuel cell, 14 litres/minute hydrogen consumption
Storage duration: 8 ore
Duration of recharge cycle: 12 ore
Hypothesis for drawing solely from the storage and not directly from the electrolyser.
Dimensioning:
$User = 14 \frac{litres}{\min} \cdot \frac{60}{1000} = 0.84 \frac{m^{3}}{h} ≃ 1 \frac{m^{3}}{h}$
In this dimensioning, the maximum consumption of hydrogen was rounded off to the higher value so as to have a safety margin.
$Minimum dimension of the storage means = 1 \frac{m^{3}}{h} \cdot 8 h = 8 m^{3} = 8000 l$ $Minimum flow rate of the electrolyser = 8 m^{3} \div 12 h = 0.67 \frac{m^{3}}{h}$
Amount of distilled water required to fill the
$storage means = 8 m^{3} \cdot 0.87 \frac{l}{m^{3}} = 6.96 l$
Where 0.87 is the standard consumption of an electrolyser. A 10 litre storage means is assumed for the sake of safety.
$Minimum water treatment flow rate = 10 l \div 12 h = 0, 83 \frac{l}{h}$
In this calculation example, the m³shall be considered under normal conditions.

Results:

Water treatment (minimum flow rate)=0.83 l/h
Demineralised water storage=10 litres
Electrolysis (minimum flow rate)=0.67 Nm³/h
Hydrogen storage=8000 litres
In this case, considering the substantial storage of hydrogen, the storage device may be provided for outside the casing 20, i.e. unit 21.
In practice, those skilled in the art may introduce various modifications and variants, such as for example providing for some components outside the described casing 20 of unit 21, replacing some components with other substantially functionally equivalent elements, same case applying to providing different fields of application, such as for example heating systems for industrial use, such us for example heating greenhouses, or using oxygen for oxygenating water for fish tanks in fish farming and so on and so forth, without departing from the scope of protection of the present invention as described and claimed in the attached claims.

Claims

1. Hydrogen generator system for a hydrogen powered unit, such as for example a hydrogen catalytic burner or a fuel cell, comprising an electrolyser for the electrolysis of distilled water, producing hydrogen and oxygen, containing, on the inlet side, an associated demineralizer device and an associated A/C transformer/converter unit for supplying electrical power for the electrolysis process and, on the outlet side, a device for purifying the hydrogen produced with the subsequent exit of the hydrogen to be supplied to the hydrogen powered unit, as well as production of oxygen, characterised in that it also comprises:

a device (10) for recovering the heat generated by the electrolysis process associated to the electrolyser (2),

and/or a device (17) for storing the hydrogen produced, and in that the entire system (1) for generating hydrogen is accommodated in a casing (20), which has—externally—inlet connection fittings, for the water and electrical power supply systems for feeding the electrolyser (2), and outlet fittings for the generated hydrogen and for delivery and return pipes of a heating system, for example that of a house, to be connected to said heat recovery device (10).

2. Hydrogen generator system (1), according to claim 1, characterised in that the device (10) for recovering the electrolysis heat is formed by a heat exchanger (10), whose primary circuit (11) is arranged in the electrolyser (2) and whose secondary circuit (13) is connected to a heat user (16), for example to a household or industrial heating system.

3. Hydrogen generator system (1) according to claim 1, characterised in that the device (17) for storing hydrogen is a tank under pressure or contains metal hydrides and forms or comprises a hydrogen storage tank, wherein said storage of hydrogen occurs at low pressure, for example at 6 bars maximum.

4. Hydrogen generator system (1), according to claim 1, characterised in that the hydrogen storage device (17) is a pressure storage device with or without compressor.

5. Hydrogen generator system (1), according to claim 1, characterised in that it provides for a direct outlet of the hydrogen produced, which is associable to a hydrogen inlet/outlet of a hydrogen storage device (17) with metal hydrides, and in that it provides for—in the secondary circuit (13) of the heat exchanger (10)—a diversion for supplying heat to the storage device (17). (FIG. 2)

6. Hydrogen generator system (1) according to claim 1, characterised in that it provides for a double hydrogen outlet, i.e. a first outlet derived directly from the electrolyser (2) at low pressure and purified preliminarily, as well as a second hydrogen outlet coming from the hydrogen storage device (16) with metal hydrides and having a higher degree of purification, metals, and in that it provides for—in the secondary circuit (17) of the heat exchanger (10)—a diversion for supplying heat to the storage device (17). (FIG. 3)

7. Hydrogen generator system (1), according to claim 1, characterised in that it comprises a centralised control device supported by a programmable software and suitable to manage—in the most rational manner possible—the control and adjustment of all controllable circuit devices and components to obtain utmost efficiency and consumption.

8. Hydrogen generator system (1), according to claim 3, characterised in that it uses an alloy of metal hydrides which during the step of releasing hydrogen it requires a heat supply capable of operating at ambient temperature or slightly higher, wherein said amount of heat is preferably derived from the recovery of the electrolysis heat.

9. Hydrogen generator system (1), according to claim 2, characterised in that the device (10) heat exchanger cools the electrolyser (2).

10. Hydrogen generator system (1), according to claim 1, characterised in that it forms—with said casing (20) for accommodating the system (1)—a preassembled unit (21) ready to be installed and connected directly with the inlet and outlet lines.