The invention relates to a hydrogen generator which can be a hydrogen generator comprising a container for containing an aqueous solution of at least one metal hydride, a reactor chamber containing a catalyst, a pump for pumping the aqueous solution from the container to the reactor chamber, a first liquid collecting area communicating with the reactor chamber for collecting the reaction exhaust products, an exhaust products outlet exiting from the collecting area and a gas outlet for extracting the gaseous products, or a hydrogen generator comprising a container for containing a liquid reaction agent, a reactor chamber containing at least one metal hydride in solid form, a pump for pumping the liquid reaction agent from the container to the reactor chamber, a first liquid collecting area communicating with the reactor chamber for collecting the reaction exhaust products, an exhaust products outlet exiting from the collecting area and a gas outlet for extracting the gaseous products, and to a method of operating it.
Hydrogen generators of the kind mentioned above usually serve to supply fuel cells with gaseous hydrogen, e.g. for vehicles such as small aircrafts. Particularly for this purpose low volume and light weight are essential. Hydrogen is chemically generated by a following reaction
where MBH4 and MBO2 respectively represent a metal borohydride and a metal metaborate. While H2 is the useful product, MBO2 and residual water, partly in the form of steam, are exhaust products. These exhaust products, dissolved in aqueous solution, have a high tendency to crystallize.
According to US 2004/0009379 A1 the exhaust product is separated into dry residuals which are collected in a special vessel, and steam which can be vented to the atmosphere. The drying equipment and the mentioned vessel lead to a bulky and heavy construction.
According to US 2006/0225350 A1, the exhaust is processed in a gas/liquid separator and the exhaust is drained to a collecting tank. Again, the construction is unfavourable with respect to size and weight. This prior art, further, uses a closed loop control of the pressure and the temperature in the reaction chamber, mentioned pressures are from 0 to 41 kPa and mentioned temperatures are 20 to 50° C.
Due to U.S. Pat. No. 7,083,657 B2, the exhaust product is separated into its gaseous and liquid components, the liquid component being fed back to the reaction chamber. In this prior art, the problem is further discussed that in the reaction exhaust products the salt product tends to crystallize, thereby clogging the reaction chamber or the downstream conduits and apparatus.
It is an object of the invention to provide for a compact, lightweight hydrogen generator. For such compact generators with small sized element, it is particularly necessary to avoid crystallization of the reaction exhaust products which, in this case hypercritically congests the conduits. For preventing the crystallization, the conduit extending from the exhaust products outlet via the controllable valve to a conduit end carries heating devices at least along part of its length, an elevated temperature counteracts the crystallization.
To obtain such compact and lightweight generator, according to the invention, in the generator the exhaust products outlet opens to the environment via a controllable valve. By such disposals, the components for separating or drying the exhaust products are no longer necessary.
A further aspect with reference to the compactness is the fact that the saturation water vapour partial pressure depends on the temperature but keeps materially constant if the gas pressure of the mixture containing the water vapour in the reaction chamber is increased. Upon hydrolyses, it is possible to generate the hydrogen under a high pressure in the reaction chamber by controlling the flow rate of the pump and the power of heating devices of the reaction chamber, where a preferred temperature is at least 70° C. For this reason, the reactor chamber preferably contains temperature and pressure sensors, it is coupled to temperature adjusting devices, and the sensors are connected to a control unit controlling the pump and the temperature adjusting devices.
For maintaining the desired pressure in the reaction chamber the first liquid collecting area contains first liquid level sensors coupled to a control unit controlling the controllable valve which opens and closes in intervals.
In the generator the gas outlet is coupled via a cooling device to a gas/liquid separator containing a second liquid collecting area including second liquid level sensors, as is known in the prior art; To said area a discharging conduit is connected which leads via a controllable valve, which opens and closes in intervals, alternatively to the environment or to a point upstream of the pump. The liquid is almost pure water which, if conducted to the environment, is discharged similarly as the reaction exhaust products, and if conducted to a point upstream of the pump, can be used for diluting the fuel, similarly to the prior art U.S. Pat. No. 7,083,657 B2, or for a cleaning cycle
For avoiding crystallization of the reaction exhaust products in the reaction chamber and its downstream elements, high pressure and high temperature according to mutual relations are preferably used, as characterized in claims 9 to 11.
The foregoing and further objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings.
A hydrogen generator 1 according to
The hydrogen escapes the reaction chamber through a gas outlet 13, flows through a cooling coil 14 and is fed into a gas/liquid separator 19. In this separator, the hydrogen is withdrawn through filter units 20 and a pressure regulator 21 and fed via a conduit 22 to a fuel cell system 23.
The reaction chamber 7 contains a pressure sensor 27 and temperature sensors 28. A control unit 29 in the hydrogen generator 1 picks up the values of the pressure sensor 27 and the temperature sensors 28 and regulates the flow rate of the pump 5 as well as the power of the heater 11 and of the fans 12 according to a given program.
In the lower part of the reaction chamber 7 there is a first liquid collecting area 30 wherein the slurry like exhaust products 31 accumulate. An exhaust products outlet 32 at the bottom of area 30 extends to a conduit 36 and further via a controllable valve 37 to a conduit end 38 that is located outside the casing of the hydrogen generator 1. In area 30 two liquid level sensors 39, 40 are arranged at slightly different level heights and are connected to the control unit 29, which controls the valve 37. When the higher liquid level sensor 40 gives a signal, the control unit 29 opens the valve 37 between conduit 36 and conduit end 38, discharging the exhaust products 31 through end 38 into the surrounding environment. As surrounding environment the atmosphere is usually defined; also the surrounding environment can be a collection container open to atmosphere, that is no part of the hydrogen generator and not shown in the figures, wherein the exhaust products are accumulated. When the lower liquid level sensor 39 gives a signal, the control unit 29 closes the valve 37. To maintain the predefined pressure in the reaction chamber 7 the level difference between the sensors 39,40 is small as well as the discharged amount, keeping the gas volume in chamber 7 almost constant. The frequency of opening the valve 37 is rather high and the duty rate can be in the order of 1:10. The path from the outlet 32 to the conduit end 38 is short and does not contain complex elements, thereby almost preventing the danger of crystallization. As a further measure the conduit 36 and the valve 37 are at least partially heated.
In the lower part of gas/liquid separator 19, the water condensed from the mixture of hydrogen and steam and cooled in the cooling coil 14 accumulates in a second liquid collecting area 45. In the bottom of area 45, a discharging conduit 46 is connected that leads to the valve 37. Two level sensors 47, 48 are placed in the area 45 and connected to the control unit 29, working similar to level sensors 39, 40. The valve 37, controlled by control unit 29, can block the exit of the liquid through the discharging conduit 46, can connect the discharging conduit 46 to the conduit end 38 so as to discharge the condensed water or can connect the discharging conduit 46 to a conduit 49, located to a point upstream of the pump 5 either into the fuel container 2 or directly into pump 5. The latter can be suitable for a cleaning cycle for restarting the generator after an interruption, thus preventing clogging of the system by crystallization; or for diluting the solution of the metal hydride.
According to different embodiment shown in
In the graph of
Number | Date | Country | Kind |
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201100904-0 | Feb 2011 | SG | national |