WO2011141221A1

WO2011141221A1 - Method for producing hydrogen from water by means of a high temperature electrolyzer

Info

Publication number: WO2011141221A1
Application number: PCT/EP2011/054768
Authority: WO
Inventors: Martin Ise; Harald Landes
Original assignee: Siemens Aktiengesellschaft
Priority date: 2010-05-11
Filing date: 2011-03-29
Publication date: 2011-11-17
Also published as: EP2569463A1; CN102884226A; US20130126360A1; DE102010020265A1

Abstract

The invention relates to methods for producing hydrogen from water by means of a high temperature electrolyzer and comprises the following steps: heating the water to a process temperature of the electrolyzer (2) of more than 500° C, electrolyzing the water in the electrolyzer (2) to form product gases hydrogen (H₂) and oxygen (O₂), compressing the product gas hydrogen (H₂) by means of a compressing apparatus (4), cooling the compressed hydrogen (H₂) by means of a cooling medium (6) and feeding the thermal energy augmented in the cooling medium (6) to the heating process of the water.

Description

description

Process for producing hydrogen from water by means of a high-temperature electrolyzer

The invention relates to a process for the production of hydrogen from water using a high-temperature electric ^¬ lyseurs according to claim 1 and a device for generating hydrogen, comprising a high-temperature electric lyseur, according to the preamble of patent claim 11.

The storage of large amounts of electrical energy from renewable sources (eg wind energy, solar power) is required by the rapid expansion of renewable energies. This involves short-term buffering due to the daily fluctuation as well as long-term storage due to the seasonal fluctuations in regenerative energy production and the demand for electrical energy. If the storage of electrical energy by high temperature electrolysis of water vapor is carried out, which is advantageous because of the low electrolysis cell voltage, additional energy must be expended for the evaporation of liquid water and for the compression of the product gases hydrogen and oxygen. This energy expenditure must be minimized in order to maximize the efficiency for the storage of electrical energy.

As far as the storage of electrical energy is performed by high-temperature electrolysis of water vapor, a liquid water evaporator has been used at the system inlet and compressors for the product gases at the system outlet so far. The evaporation enthalpy for the required educt water vapor must be made available to the evaporator and the compression energy for the product gases hydrogen and oxygen to the compressors.

The invention is therefore based on the object to provide a Vorrich ^¬ tion and a method by the water is umgewan ^¬ punched through a high-temperature electrolysis to hydrogen, which has a significantly improved energy balance over the prior art. The object is achieved in a method for generating hydrogen with the features of claim 1 and in a device for generating hydrogen with the features of claim 11. The inventive method for generating hydrogen from water by means of a high-temperature electrolyzer comprises following steps:

First, the water is brought to a process temperature of

Electrolyzer heated, the process temperature is usually higher than 500 ° C, in particular between 600 ° C and 800 ° C. In the next step, an electrolysis of What ^¬ sers takes place in the electrolyzer, wherein the product gases hydrogen and oxygen are formed from the educt of water. In addition, the product gas is compressed hydrogen with a Verdichtungsvor ^¬ direction and the compressed hydrogen is cooled with ^¬ means of a cooling medium. The thermal energy enriched in the cooling medium during cooling is fed into the heating process of the water forming the starting material of the process.

The compression of the product gas hydrogen produced is necessary or expedient to temporarily store the hydrogen in the smallest possible volume until it is used again for energy recovery. However, compression introduces work into the product gas hydrogen (H ₂ ). As a result of this introduced compression work, the hydrogen is strongly heated, so that it can have temperatures of more than 400 ° C., depending on the external frame conditions, at a pressure which is, for example, 100 bar after compression.

According to the invention, this energy is transmitted in the form of heat and what ^¬ serstoffes to a cooling medium, with the cooling medium heats and in turn the heat energy of the now off carries cooled hydrogen in itself. This heat energy is expediently used again to heat the water which forms the starting material, that is to say the educt of the electrolysis process. Thus, the energy balance of the overall process is significantly improved.

The absorption of heat energy by a coolant may also be referred to as a heat exchange process. In order to make the heat exchange process as efficient as possible, it may be expedient to design the compression process and the associated heat exchange or cooling process in several stages, ie in a cascaded manner.

In the heat exchange process, it is expedient that the compression device, for example a compressor, is already cooled by the cooling medium. The heat exchange device is thus an integral part of the compression device.

On the other hand, it may also be expedient to isolate the compression device against its environment at least partially in the highly temperature-stressed areas, and to cool the compressed gas, for example in the subsequent Gaslei ^¬ tion by means of a heat exchange device. In principle, it is expedient in all alternatives to run through the compression device with cooling channels, so that the heat obtained in the compacting device can already be used appropriately. In a further expedient embodiment of the cooling medium that cools the compressed product gas is hydrogen from ^¬ and is part of the heat exchange device, the water which in turn is the starting material for the electrolysis process includes. In this case, the educt water (process water) as coolant is passed through the heat exchange devices and finally introduced in vaporized form into the electrolyzer with the corresponding temperature. Also expedient has been found, the water ^¬ material, exiting the electrolyser, which also comprises the process temperature of the electrolyzer of about 500 ° C to 800 ° C, to cool before it is compacted. This cooling process before compression is expedient in order not to unnecessarily thermally stress the compression device. It is expedient that the hot product gas hydrogen and / or the hot product gas oxygen enter into a heat exchange process with the reactant water in vapor form. Through this heat exchange process, which is preferably also used in the form of a counterflow heat exchanger, the waste heat of the product gases can be used directly for heating the starting material. With a particularly good insulation of the electrolyzer per se and with an effective heat exchange of the products and educts, the energy loss of the high-temperature electrolyzer is extremely low.

In the method described so far, in particular the hydrogen is compressed as product gas and the resulting energy is added back to the heating process of the water. In principle, it may also be expedient to compress the oxygen and store it temporarily in a specially provided tank. If the oxygen is also compressed, the resulting heat of compression can also be dissipated analogously to the previously described and added to the heating of the water, which increases the efficiency of the process even more.

Another component of the invention is a device for generating hydrogen. This device comprises egg ^¬ NEN high temperature electrolyzer for converting water into hydrogen. The device further comprises a compaction ^¬ processing apparatus for compressing the produced hydrogen. The compression device, in turn, comprises a heat exchange device which serves to transfer the heat of compression, which arises in the compression process, to the educt ^{water of} the high-temperature electrolyzer. The compact Processing device is preferably configured in the form of a compres- sor ^¬ sors.

The device according to claim 11 is used in particular for carrying out a method according to one of claims 1 to 9 and has the same already explained Vortei ^¬ le on.

It may be expedient that the compression device is insulated in its surroundings, in particular in the areas subject to high temperatures. In this case, the compression device does not ^release the resulting heat of compression to the environment, the resulting heat of compression can be removed from the hydrogen by a subsequent heat exchange device after the compression process.

Alternatively or additionally, it may be expedient that the heat exchange device partly surrounds the compacting device, for example by cooling channels run through the compression device and thus withdraw introduced by the compression unit heat energy of the compression ^¬ device.

Further embodiments and further features of the invention will be explained in more detail with reference to the following drawings. In this case, features that have the same name, but different configurations, provided with the same reference numerals. Show it:

FIG. 1 shows a schematic sequence of a hydrogen production by means of a high-temperature electrolyzer with subsequent compression of the hydrogen,

FIG. 2 shows a schematic representation of a process sequence as in FIG. 2, wherein a cooling medium in the form of the educt water is designed, Figure 3 shows a compression device, which is traversed by cooling channels and

Figure 4 shows a compression device with an insulation and a subsequent heat exchanger.

The following is the sequence of the method to produce hydrogen from water will be explained with ^¬ means of high-temperature electrolysis schematically with reference to FIG. 1 First, liquid water is characterized by H ₂ 0 _{f passed} through a water supply 18 in a heat exchanger 10. In this heat exchanger 10 is already a heated cooling medium 6, the heating will be discussed in the further course, through which the liquid water is heated to a temperature in the range of the boiling point and evaporated.

In the next step, the evaporated water, which is designated H ₂ 0 _g , ie gaseous water, brought into another heat exchanger 10 '. Through this heat exchanger 10 'of the water vapor and the gaseous water is Annae ^¬ hernd heated H ₂ 0 _g to the process temperature of the high temperature electric ^¬ lyseurs. 2 The gaseous water H ₂ 0 _g , which is introduced into the high-temperature electrolyzer 2, has a temperature of about 500 to 800 ° C. In the electrolyzer 2, which is also referred to as solid-oxide electrolyzer (SOE), the water H ₂ 0 _g in a conventional manner in the product gases hydrogen (H ₂ ) and oxygen (0 ₂ ) is converted. The product gases, of which in particular is being treated ^¬ What serstoff hereinafter, step out of the electrolyzer 2 and also in this case have nearly the process temperature of

Electrolyzers on. The product gases, in particular the water ^¬ material are in turn cooled in a heat exchanger 10 'to a temperature under 100 ° C, particularly preferably at about room temperature or at elevated room temperature (about 50 °) is preferred.

The two heat exchangers 10 'are in a circuit, but in separate, for purely graphical reasons in Figure 1 Positions shown. Preferably, a so-called countercurrent heat exchanger is used for the heat exchanger 10 ', wherein in two intertwined channels on the one hand, the relatively cool cooling medium, in this case the gaseous water, and on the other side of the hot medium, in this case from the Electrolyzer leaking hydrogen, a ^¬ are passed, with these two media each other, although separated from the system, heat up each other. This means that the approximately 100 ° hot steam enters on one side of the countercurrent heat exchanger 14 and there meets the approximately 600 to 800 ° C hot hydrogen. When this heat exchanger against each derdurchströmen cools the hydrogen H ₂ further and further down until it has the temperature output ^¬ structure of the inflowing water vapor, ie about 100 ° C, up to about. In return, the water vapor H ₂ 0 _g heats up more and more on passing through the countercurrent heat exchanger 14 until it almost has the temperature of emerging from the electrolyzer 2 hydrogen H ₂ at the exit from the heat exchanger 14.

Certainly, there are some heat losses in this heat exchanger, but these are relatively low in itself with a good insulation of the total ^¬ system, so the incoming and outgoing gases and the electro ^¬ lyseur 2, when the total system once on process temperature between 600 ° C and 800 ° C is heated. The energy loss of the high-temperature electrolyzer is thus relatively low by the above-described heat exchange process and a good per se isolation of the overall device.

It should be noted at this point that the educt of water from process engineering reasons small amounts of hydrogen, which is diverted to the exiting product hydrogen, is led to ^¬ .

The now cooled to a temperature of 100 ° hydrogen, which can also continue to cool down or can be cooled with another heat exchanger must be further compressed to an economic storage. It may be expedient to carry out a compression of the hydrogen to about 100 bar. At a

The volume of the gas is reduced by a factor of 100 times over 100 times the pressure of the atmospheric pressure. The aim is to save the hydrogen in a storage tank as space-saving as possible. A storage pressure of approximately 100 bar (preferably between 50 bar and 200 bar) has been found to be ^¬ tech nically useful and economically ALISE to re-.

Nevertheless, it is in the compression of the hydrogen compression work or compression work in the gas, so the hydrogen (or in analog application in the second product gas oxygen) introduced. This compression work is converted into heat in the compressed gas system, which is why the compressed hydrogen heats up strongly. Depending externa ^¬ ßeren conditions, the compressed hydrogen at a pressure of usually 100 bar to a temperature of 200 to 600 ° C. Essentially, this thermal energy of the gas is the energy that was previously introduced in the form of electrical energy into the compressor and that would be lost in itself, the gas would, as is übli ^¬ cherweise sistatten be cooled. This energy would be released to the environment. However, this is an uneconomical process, which is why at this point a heat exchange process is likewise introduced in an expedient manner, which extracts the heat energy from the compressed gas and supplies this extracted heat energy to the educt water, in particular the liquid water , This is illustrated in Figure 1 by the two heat exchangers ^¬ 10 at the beginning of the process and at the end of the process. The heat exchangers 10 at the lower part of FIG. 1, that is to say in the region of the liquid water H20 _f and the heat exchanger 10 in the upper region of FIG. 1 in the region of the hydrogen H ₂ to be compressed, form a unit, they are connected via lines 7, the corresponding cooling medium. 6 transport, interconnected and are therefore provided with a reference numeral.

The heat exchanger 10 in the upper area encloses a compression device 4, which can be ausgestal ^¬ tet, for example, as shown in Figure 3 and Figure 4, in the form of a compressor 12, and withdraws the compression device 4, the heat energy. This can be done in a cooling step, but it can also be done cascaded by a plurality of compression devices 4 are connected in series with heat exchange devices 10, as shown by way of example in Figure 1.

The finished compressed product gas, here for example the hydrogen, is now stored compressed in a schematically illustrated tank 16. On the right side, in addition to the course of the hydrogen, the exit of the oxygen O _{2 is} shown as an example, which is usually not ver ^¬ sealed, since the storage of oxygen is worthwhile in only a few cases, but in principle it would be possible with the oxygen as well as with the hydrogen, which would make the energy balance of the heat exchanger in the vorbeschriebe ^¬ nen system even more efficient. In the process described in Figure 1, the Kühlme ^¬ medium 6 runs in each case in a closed circuit, another course takes the process medium, ie the water that enters the electrolyser 2 as starting material and is converted to hydrogen. In Figure 2, an alternative to this is shown, wherein the cooling medium 6 is configured in the form of the process ^¬ water. In the upper right area of Figure 2, the liquid water, characterized by H ₂ O _f , is fed into the cooling line system of the cooling lines 7 as the cooling medium 6, it passes through the heat exchanger 10, which extracts the heat from the compressed hydrogen. In this case, the water is already heated, preferably to a temperature above 100 °, it is now further in a gaseous state and is along the line 7 in the next heat exchanger 10 ' brought, which in turn can be configured in a favorable embodiment in the form of a countercurrent heat exchanger. Here, the water (H ₂ 0 _g) is confronted with the very hot pro ^¬ duktgas H ₂ (> 500 ° C) and exchanges data with this heat content from. After running of this heat exchanger 10 'or 14, the gaseous water, which has already been preheated almost to the process temperature of about 600 ° to 800 ° C., is introduced into the electrolyzer 2 and is then converted into hydrogen in a manner known per se. Of course, an additional thermal heating can be done to compensate for heat losses to the environment.

The hydrogen exits the electrolyzer, is cooled in the heat exchanger 14 as described, then again reaches temperatures between room temperature and 100 ° and is compressed by the compression device 4. Furthermore, in this example according to FIG. 2, unlike in FIG. 1, the compression device is not directly cooled but, as will be mentioned later, isolated, so that the hot hydrogen is cooled as described in the heat exchanger 10 as described. There may be a further cascaded compression in a further compression device 4, after which the now completely compressed hydrogen is again stored in a corresponding tank 16. An isolation of the compression device and the subsequent heat exchange is of course applicable to the embodiment in Figure 1.

In FIGS. 3 and 4, exemplary schematic representations of a compression device 4 are given, each having a compression space 20 and a reciprocating piston 26. The compression process is shown here very schematically and Figures 3 and 4 are not exhaustive. Both compressors 12 in Figure 3 and Figure 4, it is inherent that they have both a WasserstoffZu ^¬ leadership 22 and a hydrogen discharge 23. The reciprocating piston 26 is moved up and down in the compression space 20, which is indicated by the double arrow on the side of the reciprocating piston. is is. The reciprocating piston 26 is preferably tervorrichtung by a Excen-, for example, by a camshaft is driven ^¬. In FIG. 3, the compressor 12, that is to say a special Ausges ^¬ taltungsform the general compression device 4, crossed by cooling channels 8. These cooling channels 8 absorb the heat generated during the compression process and carry it off. The cooling channels 8 are thus part of the heat exchange device 10 in a specific embodiment.

In the embodiment according to Figure 4, the compression device 4 and the compressor 12 is provided with an insulation 28, wherein also a hydrogen supply 22 of a hydrogen discharge 23 is provided, the compressor 12 itself operates at an elevated process temperature and the hydrogen, which is already in Compressed form comes out of line 23 is now cooled by a separate heat exchanger 10. The case extracted heat energy is used to heat up the process ^¬ water as previously described. Of course, the compres sion ^¬ device 4 may include insulation from Figure 3, whereby the heat energy produced is focused through the cooling channels 8 ^¬ dissipated.

Claims

claims

A process for producing hydrogen from water by means of a high temperature electrolyzer, comprising the following

Steps:

Heating the water to a process temperature of

Electrolyzers (2) of more than 500 ° C,

- Electrolysis of the water in the electrolyzer (2) too

Product gases hydrogen (H ₂ 0) and oxygen (0 ₂ ),

Compressing the product gas hydrogen (H ₂ ) by means of a compression device (4),

- Cooling of the compressed hydrogen (H ₂ ) by means of a cooling medium (6) and

- Feeding the enriched in the cooling medium (6) heat energy in the heating process of the water.

2. The method according to claim 1, characterized in that the compression of the hydrogen (H ₂ ) takes place in several compression steps, which in turn several cooling processes are affiliated.

3. The method according to claim 1 or 2, characterized in that the compression device (4) by the cooling medium (6) is cooled, the heat energy is supplied to the heating process of the water sers.

4. The method according to any one of claims 1 to 3, characterized in that the compression device (4) is at least partially isolated from their environment.

5. The method according to claim 3 or 4, characterized in that the compression device (4) with cooling channels (8) is traversed.

6. The method according to any one of the preceding claims, characterized in that the water which is supplied to the electrolyzer (2) for reaction, at least partially comprises the Kühlme ^¬ dium.

7. The method according to any one of the preceding claims, characterized in that the hydrogen (H ₂ ) is cooled after exiting the electrolyzer (2) and before the compression by means of a heat exchange process.

8. The method according to claim 7, characterized in that the hydrogen (H ₂ ) after exiting the electrolyzer (2) is cooled by a countercurrent heat exchanger.

9. The method according to claim 7 or 8, characterized in that the water, which is supplied to the electrolyzer (2), in the form of a vapor cooling medium in the heat exchange process, the hydrogen (H ₂ ) cools and is heated.

10. The method according to any one of the preceding claims, characterized in that in addition to the product gas hydrogen (H ₂ ) oxygen (0 ₂ ) as further product gas is also ver ^¬ seals, is cooled and the thereby dissipated heat energy is supplied to the heating process of the water ,

11. An apparatus for producing hydrogen comprising a high-temperature electrolyzer (2) for converting water into hydrogen (H ₂ ) and a compression device (4) for compressing the generated hydrogen, wherein the compression device (4) comprises a heat exchange device (10) for transferring the compression heat occurring in the compression process to the water to be supplied to the high-temperature electrolyzer (2).

12. The device according to claim 11, characterized in that the compression device (4) in the form of a compressor (12) is configured.

13. The apparatus of claim 11 or 12, characterized in that the compression device (4) is at least partially isolated.

14. Device according to one of claims 11 to 13, characterized in that the compression device (4) is at least partially surrounded by the heat exchange device (10).

15. Device according to one of claims 11 to 14, characterized in that the heat exchange device (10) at least partially in the form of cooling channels (8) passes through the compression ^¬ device (4).