DE4007541C1 - Direct conversion of heat into electrical energy - using solar collector to transfer hydrogen from stove to high pressure chamber bounded by foil coated electrolyte - Google Patents

Abstract

For direct conversion of heat (150-300 deg.C) into electrical energy, heat from a solar collector (14) is used to drive out H2 from a H store (10), which passes into a high pressure chamber (6), bounded by a proton-conducting solid electrolyte (4), coated with metal foils as electrodes. The H+ diffuses through the metal foils and the electrolyte and recombines with electrons in the low pressure chamber. Electrical voltage is produced between the electrodes. The H2 passes to a second store (13) from which it can be recovered by heat. ADVANTAGE - Low temp. system can use solar energy.

Description

The present invention relates to a method for direct conversion of heat in the (order of magnitude: 150-300 ° C) in electrical energy using at least one proton-conducting, layered solid state electrolyte, on the bilaterally hydrogen-permeable, mutually insulated Partial layers are attached as electrodes.

A method for direct energy conversion is as so-called. AMTEC process - the alkali metal thermoelectrical converter - (see T. Cole, Thermoelectric Energy Conversion with Solid Electrolytes, Science 221/1983/1915). The principle of this Process is the separation of sodium ions and electrons by means of β-alumina in a cell. The β-Al₂O₃ electrolyte is coated with a porous electrode. The cell consists essentially of a housing which is defined by the β- Al₂O₃ electrolyte with the electrode in two electrically isolated Rooms is divided. By introducing sodium at higher temperatures in a subspace becomes a differential pressure generated. The sodium ions, and only the ones, migrate through the electrolyte and cause a charge difference between the electrode side with high and the electrode side with low sodium partial pressure. On the side with higher Sodium particle pressure is an electron surplus before and therefore, this electrode becomes negative. With open circuit turns according to the pressure difference a maximum Tension.

A disadvantage of this method, however, is working with the reactive alkali metals. Besides, the stability is of the β-Al₂O₃ electrolyte for the required high operating temperature questionable and the problem of the positive Electrode not yet solved satisfactorily. Operation of the  AMTEC-Systems sets temperatures on the low pressure side greater than 300 ° C ahead, otherwise the volume flows of the sodium vapor at the then prevailing low saturated steam pressure too large pressure drops and thus high losses of efficiency to lead. That means the AMTEC process needed on the hot Side a temperature of at least 800 ° C to a thermodynamic To achieve efficiency of about 35%. Should solar energy are used, this temperature level is very high high demands on the solar system.

The present invention now has for its object a method for direct conversion of heat into electrical energy too create, which at considerably lower temperatures than so far works, so that for heat production with him also simpler Solar collectors can be used.

As a solution, the present invention proposes a method before, by the method steps a) to f) in the claim 1 is marked.

Further advantageous individual features of the method according to the invention arise from the characteristics of the dependent claims. 2 till 9.

According to the new method, by maintaining a Pressure and / or temperature difference of the hydrogen gas electric Generates energy, with the gas in two rooms. The rooms are separated by a proton conductor. The Proton conductor is from both sides of hydrogen permeable Metal foils enclosed, the rooms are electric isolated from each other. The pressure gradient now drives hydrogen as ion through the solid electrolyte or the foil-like Layers. There is a voltage potential between the inlet and outlet side, so that a useful electrical power tapped can be. The pressure gradient is preferably formed by Discharge a hydrogen storage, at high temperatures  and the higher pressure or loading at lower temperatures and with the low pressure. As a heat source can advantageously Solar energy can be used.

After the procedure, good efficiencies already under 200 ° C can be achieved. With 250 ° C can be used for dehydration Efficiencies are achieved that are better than those of the state the technology. With suitable coupling with different Storage materials is also possible with a two-step process corresponding profit of useful power. Organic hydrogen storage media allow closed circuits with lower Pump powers. The lower temperature level allows the coupling of the process with the known parabolic trough solar collectors.

The advantages of the process with the hydrogen energy generator are in its simple function and the resulting simple design of a plant and easy integration to see the use of solar energy. In construction The plant does not require any new, high-tech processes. The energy conversion process is environmentally friendly and is suitable for a wide range of applications on.

Further details of the method according to the invention are described in the following and with reference to the figure, which is schematic the circuit diagram of the new method shows.

The figure shows schematically the hydrogen-energy generator 1 in a circuit. The arrangement causes the hydrogen atoms to be absorbed on a metal foil 3 in the region 6 of higher hydrogen pressure and thereafter migrate as hydrogen ions through the proton conductor 4 to recombine with electrons in the metal foil 5 in the space 7 at lower pressure. At operating temperatures above 100 ° C, a solid proton conductor 4 will be used. At lower temperatures, an aqueous electrolyte can be used, it must only be ensured that the metal foils 3 and 4 by their insulating border 8 close the electrolyte 4 tight. The entire layer 2 can be supported and stabilized by a suitable mesh because of the pressure difference. The mesh can serve as an electrical conductor at the same time. The pressure difference between the spaces 6 and 7 separated by the permeation layers 2 is achieved by a type of "pumping off" and "compression" by means of hydride reservoirs. The process proves to be particularly suitable for the use of solar energy, to the hydrogen energy generator is combined with a hydrogen storage in metal hydrides or in liquid organic compounds, it being known that certain metals and metal alloys chemically bond the hydrogen and thereby form hydrides. This chemical bonding takes place with evolution of heat. To release hydrogen heat must again be supplied, which can be done by coupling solar energy through solar panels.

This process is represented by the following equation:

To get a continuous release of hydrogen from the Ensuring metal hydride must therefore constantly supplied heat become.

The metal hydrides with a decomposition pressure above 1 bar at Temperatures below 100 ° C are considered low-temperature Hydrides and the hydrides, where the pressure limit of 1 bar at higher temperatures than high temperature hydrides designated.  

The low-pressure hydrides are characterized by:

AH 30 kJ / mol H₂ Pressure range: about 1 to 20 bar memory capacity: about 1 to 2 wt .-% H₂ Temperature range: about -20 ° C to 100 ° C

The high temperature hydrides show approximately the following values:

AH 60-80 kJ / mol H₂ Pressure range: about 1 to 10 bar memory capacity: 3 to 6 wt .-% H₂ Temperature range: 250 to 400 ° C

In the figure, the coupling of the solar energy to the hydrogen-energy generator is shown schematically in the circuit schematically. By the decomposition z. As a metal hydride 9 in the memory 10 as a storage material by the coupling of solar energy 11 via collectors 14 hydrogen is released under higher pressure in the H₂-energy generator 1 . By loading another hydride 12 in the hydride storage 13 with simultaneous cooling 15 (discharge for hydride formation heat, ΔH is effected between the two chambers 6 and 7 of the hydrogen-energy generator 1, a pressure difference and thus a voltage 11 between the two metal foils 3 and 5 By alternately loading and unloading the hydrogen in the hydride reservoirs 9 and 12 , an approximately continuous operation of the generator can be achieved.

In an analogous manner, the generator 1 can be coupled as a further example with liquid organic H₂ stores. The system is known

The characteristic values in this MTW system (methylcyclohexane) Toluene-hydrogen) are:

ΔH of dehydrogenation: 70 kJ / mol H₂ (210 kJ / mol C₇H₁₄) Pressure range: 0.07-some bar memory capacity: 6.1 wt .-% H₂ Temperature range: 20-420 ° C.

The generated rest voltage of the generator is the higher, depending greater the pressure difference, therefore, is in the operation of the plant according to the method by pumping the hydrogen and increasing the pressure in the negative charge space another heat input by solar energy also possible in this investment zone. When incorporating H₂ memory in the power generation system can be the effective pressure difference between the two rooms by introducing inert gas in the H₂-low pressure zone opposite the H₂-high pressure zone are degraded. For the building up Tension between the two metal foils and the proton conductor is decisive only the actual H₂ difference Partial pressure of the two rooms. By the effective Pressure equalization can reduce the stress on the separation membrane become:

The new process thus includes the following essential process steps:

• a) expulsion of hydrogen bound in a hydrogen storage through the heat to be converted creating a hydrogen pressure is produced,  
• b) introducing the hydrogen pressure into a space through delimited one of the two metal layers of the electrolyte becomes,
• c) diffusion of hydrogen through a metal layer in the proton conductor,
• d) charge separation by migration of the hydrogen ions through the proton conductor,
• e) diffusion of the hydrogen through the second metal layer, under recombination of hydrogen ions and electrons in the layer, in the low-pressure zone of a room through the other of the two metal layers is bounded,
• f) picking up the electrical voltage or generated electrical energy at the two electrodes,
• g) introducing the hydrogen into a hydrogen storage, from which it is expelled again by means of heat can.

In this case, the hydrogen in the low pressure zone acc. the Step g) chemically bound in a hydrogen storage and this further gem. Step a) are treated. It can too gem. the steps a) and g) uses two hydrogen storage be connected to the system, which are mutually be charged with hydrogen and discharged again, the release of hydrogen from the hydrogen storage by coupling solar energy follows. The hydrogen pressure in the zone of higher pressure can by additional Coupling of solar energy by means of temperature increase also increase. Finally, still in the low pressure side for pressure equalization with the high pressure side of an inert gas, z. As nitrogen or noble gas, at constant hydrogen partial pressure be added. Ultimately, as an example of  the electrolyte layer Ta₂O₅ be used, which on both sides with palladium, nickel, platinum or alloys or Multilayer structure of these metals is coated.

LIST OF REFERENCE NUMBERS

1 hydrogen energy generator
2 layer
3 metal foil
4 solid electrolyte, proton conductor
5 metal foil
6 room of high pressure
7 room of low pressure
8 border
9 hydride
10 memory
11 solar energy
12 hydride
13 memory
14 solar panel
15 cooling

Claims (9)

1. A method for the direct conversion of heat (order of magnitude: 150-300 ° C) into electrical energy using at least one proton-conducting, layered solid electrolyte, on both sides of the hydrogen-permeable, mutually insulated metal layers are mounted as electrodes, comprising the following steps:

• a) expelling hydrogen bound in a hydrogen storage by the heat to be converted, whereby a hydrogen pressure is generated,
• b) introduction of the hydrogen pressure into a space bounded by one of the two metal layers of the electrolyte,
• c) diffusion of the hydrogen through the one metal layer into the proton conductor,
• d) charge separation by migration of the hydrogen ions through the proton conductor,
• e) diffusion of the hydrogen through the second metal layer, with recombination of the hydrogen ions and electrons in the layer, into the low pressure zone of a space bounded by the other of the two metal layers,
• f) picking up the electrical voltage or the generated electrical energy at the two electrodes,
• g) introducing the hydrogen into a hydrogen storage, from which it can be expelled by means of heat again.

2. The method according to claim 1, characterized in that the Hydrogen in the low pressure zone acc. Step g) in one Hydrogen storage chemically bound and this gem. Step a) is treated again. 3. The method according to claim 1 or claim 2, characterized that as hydrogen storage gem. Step g) Metal, a metal alloy hydride, a liquid organic Used compound or a glass bead hydrogen storage becomes. 4. The method according to any one of claims 1 to 3, characterized that gem. the steps a) and g) two hydrogen storage used or connected to the system which are alternately charged and discharged with hydrogen become. 5. The method according to claim 1 or claim 4, characterized that the hydrogen from the hydrogen storage by releasing solar energy or heat released becomes. 6. The method according to claim 1, characterized in that in Step b) in the zone of higher pressure, the hydrogen pressure by additional coupling of solar energy and the resulting temperature increase is increased. 7. The method according to claim 1 or claim 4, characterized that the waste heat of the zone of higher pressure to expelling the hydrogen is used from the memory. 8. The method according to any one of claims 1 to 7, characterized that in the low pressure side for pressure equalization with the high pressure side of an inert gas, in particular N₂ and / or noble gas, at constant hydrogen partial pressure is added.   9. The method according to claim 1, characterized in that the Solid electrolyte layer of Ta₂O₅, which on both sides with Pd, nickel, platinum or an alloy or a Multilayer structure of these metals coated as electrodes is formed.