WO2012142996A2

WO2012142996A2 - Water treatment for the electrolysis of water

Info

Publication number: WO2012142996A2
Application number: PCT/DE2012/000384
Authority: WO
Inventors: Dietrich Karl WERNER
Original assignee: Werner Dietrich Karl
Priority date: 2011-04-19
Filing date: 2012-04-10
Publication date: 2012-10-26
Also published as: DE102011017491A1; DE112012001785A5; WO2012142996A3

Abstract

Currently, the electrolysis of water is used primarily for producing pure hydrogen. In the future, however, hydrogen produced by the electrolysis of water will gain increasing importance as a secondary energy carrier for renewable energies. Thus, there is a necessity to make the electrolysis of water as economical as possible. According to the current prior art, the efficiency of the electrolysis of water is approximately an 80% hydrogen yield. 20% of the electric energy is lost as thermal energy. Additionally, salt-free or distilled water that is produced from freshwater by means of ion exchangers must be continuously added for a trouble-free operation. When converting the electric energy directly into hydrogen in offshore wind parks, sea water must be desalinated if freshwater is not supplied. The same applies to solar power plants in desert areas in the vicinity of coasts. It has now been determined that 4.4 - 4.6 KW, 0.8 to 0.9 KW of which must be discharged as thermal energy by cooling the electrolysis device, are required to electrolytically produce 1 Nm of hydrogen. Treated (distilled) water, for the heating and distillation of which 0.8 to 0.9 KW of "waste heat" may suffice, must be introduced into the electrolysis device in order to produce 1 Nm of hydrogen 0.8 l (802 g). By integrating the treatment of water into the electrolysis process, the water electrolysis is suitable for bringing into physical proximity to the location where wind or solar power is harvested, said power then being directly producible as direct current with the voltage that is appropriate for the electrolysis device. This is a substantial simplification of the total system, both in the electrolysis process as well as in the harvesting, transportation, and conversion of wind or solar power. The hydrogen produced according to the invention can likewise be introduced as combustible gas into natural gas and brought into circulation together with the natural gas. At the use point, however, the highly different physical, chemical, and fire safety properties between hydrogen and natural gas must be taken into consideration. It is also possible to use the hydrogen to hydrogenate carbon dioxide or carbon monoxide and to reconstruct methane from the combustion gases thereof. If the electrolysis device and the system for hydrogenating carbon dioxide are coupled to a gas power plant, the power plant can first dispense natural gas in a sequence of operating states, wherein carbon dioxide can be separated from the fumes. In the subsequent operating state, the carbon dioxide is hydrogenated with hydrogen provided by the electrolysis device into methane. The first operating state is used to stabilize the power grid, and excess wind and solar power is converted into hydrogen and then into methane in the second operating state. The methane is conducted back into the natural gas grid. Such a system can be used as a storage power plant. Said simplification of the accessibility of highly purified feed water for the electrolysis of water, whether it is for reconverting the hydrogen or for reconstructing methane, is of economic significance specifically with the use of natural gas.

Description

Water treatment for water electrolysis

Today, water electrolysis is mainly used to produce pure hydrogen. In the future, however, hydrogen produced by electrolysis of water will become increasingly important as a secondary source of energy for renewable energies.

This results in the need to make the water electrolysis as economical as possible. According to the state of the art, the efficiency of water electrolysis is about 80% hydrogen yield. 20% of the electrical energy is lost as heat energy. In addition, for trouble-free operation, continuously salt-free or distilled water must be added, e.g. Is processed by means of an ion exchanger Depending on the quality of the available water, the cleaning must be done several times.

If you want to convert electrical energy directly into hydrogen in "offshore" wind farms, you do not want to bring in fresh water, you have to desalinate sea water.

It has now been found that for the electronic production of 1Nm hydrogen 4.4 - 4.6 KW. are needed, from which 0.8 to 0.9 KW must be dissipated as heat energy by cooling the electrolyzer. On the other hand, for the production of 1 Nm of hydrogen, 0.8 l (802 g) of treated (distilled) water must be introduced into the electrolyzer, for the heating and distillation of which 0.8 to 0.9 kW of "waste heat" should suffice.

The present invention thus provides a process for the treatment of water for the electrolysis of water, characterized in that the heat energy released during the electrolysis of water is used to evaporate water.

According to this method it is possible, for example in an "offshore" wind farm, to connect the production of wind power directly to the electrolysis and to use seawater.As the electrical energy then no longer has to be transported, direct current at the wind turbine can be obtained and convert it into hydrogen on-site by electrolysis, which means that electrical energy no longer needs to be reconnected, rectified, transported in submarine cables as high-voltage direct current and then reversed and reconnected to be transformed. Instead, the energy at the wind turbine is converted into hydrogen and this is passed as energy gas in gas lines to the collection point and then to the consumer.

The same applies to systems for solar power, which can be fed directly to the electrolyzer in photovoltaic systems, the inevitable resulting direct current.

The present invention thus further the treatment of water for electrolysis of water is characterized in that the liberated in the electrolysis of water heat energy for the distillation of sea and brackish water is used.

Coupling the water cooling of an electrolyzer in such a way with a device for the evaporation of water that evaporates the heated water during cooling and the water vapor is condensed, you get directly the feed water for electrolysis.

Another object of the present invention is thus the treatment of water for electrolysis of water characterized in that the cooling of the electrolyzer heated cooling water, then condensed and used as feed water for electrolysis, preferably sea or brackish water according to the invention are used as cooling water ,

The use of sea water as cooling and feed water (distilled water) for the electrolyzer allows the construction of the electrolyzer, e.g. Directly in an "offshore" wind farm, since every windmill has its own electrolysis unit with water treatment in the immediate vicinity, directly from the windmill direct low-voltage direct current, suitable for water electrolysis, can be provided Instead of this, hydrogen is recovered "in situ" as renewable energy and, like other fuel gases (eg natural gas), is reclaimed, converted to DC and inversion, as is usually necessary for the transport and use of renewable energies ) and stored. The important thing here is that the electrical energy (direct current, low voltage, high current density) only has to be transported to the e-jetting device over a short distance.

Thus, the real advantage of this rather simple technique of water treatment lies in the possibility of decentralized generation of hydrogen directly next to the source of renewable electrical energy. The advantage of this process becomes obvious when one considers the need for distilled water in the electrolysis of water in the here considered Magnitude considered. As already mentioned, for 1 Nm3 of hydrogen you need 802g or 0.81 water. In a fictitious comparison, the demand for natural gas in Germany is now to be replaced by hydrogen at around 100 billion cbm / year. It should also be considered that natural gas has approximately three times the energy content of hydrogen. The bill tautly:

0.8 x 100 billion x 3 = 240 billion

That is, to produce a quantity of hydrogen corresponding to the German natural gas demand by electrolysis of water, one needs 240 billion liters of distilled water. If this calculation is applied to natural gas producing countries such as Qatar or Algiers, where one day hydrogen could replace natural gas because of the available solar energy and where only seawater is available as feedwater for electrolysis, the significance of the present substitution process becomes more fossil Energy sources through renewable energy significantly.

Providing such an amount of distilled water by other means in desert areas would challenge the economics of renewable energy there. As an alternative to the secondary energy carrier hydrogen, the electrical energy e.g. From the Persian Gulf to the consumers in Europe and the Far East is also not very promising.

The present invention thus further a method for the treatment of water for the electrolysis of water is characterized in that the liberated during the water electrolysis heat is used to evaporate water, from the water vapor after condensation distilled water is obtained as feed water for an electrolyzer and both the water treatment as well as the water electrolysis is connected with wind turbine or solar system, preferably wind or solar power for direct use for the electrolysis is generated as a direct current with tuned to the electrolyzer voltage.

In many commercially available devices for electrolysis of water, the decomposition of the water proceeds at normal or low overpressure and 70 ° C to 90 ° C. This temperature would then correspond to the cooling water temperature of the electrolyzer. The vapor pressure of the water is then at 308 to 698 mbar. In these conditions, the cooling water z. B. by lowering the pressure to boiling (vacuum distillation) and by cooling the water vapor to bring the (distilled) water to condensation. In the technical implementation, you can use the usual flash evaporation plants .. Here, the distilled water, which serves as feed water of the electrolysis and is diverted from the cooling water, constantly be replaced by fresh water (eg sea water) from the outside. In addition, when using seawater or highly mineral-containing waters as cooling water always a part of the cooling water be replaced in order to avoid Überlalzung and crystallization of the cooling liquid. Equipped so a combination of solar system or wind turbine and electrolyzer with integrated seawater desalination work for a long time maintenance-free.

With the initially calculated heat energy, as it is released in the electrolysis of water, can be prepared by sophisticated desalination techniques also an excess of desalted water, which, for example. can be used for agriculture. However, this requires the use of large scale equipment such as preceded by a multi-stage flash evaporator, possibly requiring centralized water treatment. However, this means that either electrolysis and water treatment or electrolysis and power generation must be separated. In the first case, the heated water, in the second case, the electrical energy (DC low voltage!) Must be conducted over a longer distance. Both would be associated with energy losses and increased technical complexity.

For the quality of the feed water, it is very important to ensure that only fully demineralised or distilled water, which can be disassembled residue-free, is used for trouble-free continuous operation during electrolysis.

At a water vapor pressure of 300 to 700 mbar, it is also possible to direct the heated cooling water over an evaporation surface and to contrast this with a cooled surface for the condensation of the water vapor. In practice, these are two upright concentrically arranged tubes. On the inner wall of the outer tube, the heated cooling water runs down. The resulting water vapor condenses on the outer wall of the inner tubes, which is flowed through by a cooling medium.

In electrolysis plants operating at higher temperatures, heat exchangers may have to be used to transfer the heat energy to the water treatment plant.

The advantage of the process according to the invention over the water treatment with ion exchangers otherwise customary in water electrolysis is particularly evident in the desalination of seawater or brackish water. When using ion exchangers, the passage of seawater would exhaust the capacity with an average of 33g of salt per liter of seawater very quickly. But even with the use of fresh water with about 1, 5g minerals per liter of water, the ion exchanger must be regenerated regularly This eliminates in the present process for water treatment, so that even on landside wind turbines, which are mostly remote in the landscape and the largely maintenance-free are (as well as the electrolyzer), the use of the method according to the invention worthwhile.

The decentralized renewable energy produced by hydrogen is sent to a collection point and can then be transported and stored as an energy source such as natural gas. It is also possible to introduce the hydrogen as a flammable gas in a gas pipeline or a natural gas deposit or a natural gas storage and transport or store together with the natural gas. Plenty of solar energy in the vicinity of natural gas pipelines and natural gas deposits z. As in North Africa and the Persian Gulf invite to apply there the method of the invention and to use the natural gas as a carrier for the hydrogen.

If the hydrogen, which originates from naturally fluctuating renewable energies, is introduced into natural gas, the result is a fluctuation in the hydrogen content of the natural gas / hydrogen mixture. Because of the differences between hydrogen and natural gas (methane) with regard to their combustion, physical and chemical properties (for example, gas has three times the calorific value of hydrogen, needs four times more oxygen and eight times the gas density), then a gas mixture that fluctuates in relation to the gases can not be consumed unchecked. The control can be achieved by measuring the hydrogen content in the gas mixture at the point of consumption and adjusting the metering of the mixture in the combustion site to the determined hydrogen content.

The mentioned problems with fluctuating gas mixtures when introducing hydrogen into natural gas are avoided if the hydrogen is converted into methane and this is introduced into natural gas. Natural gas consists mainly of methane.

To achieve this, hydrogen is reacted with carbon monoxide or carbon dioxide to form methane and water. As an energy source eg excess wind and solar power is used with advantage. Carbon monoxide is obtained by coal gasification as synthesis gas (mixture of carbon monoxide and hydrogen in the molar ratio 1: 1 according to reaction 1..

1.) C + H20 = CO + H2

With obtained from the electrolysis of water, additional 2 moles of hydrogen is then obtained according to reaction 2. Methane.

2.) (CO + H2) + 2 H2 = CH4 + H20

According to this process, coal can be produced by electrolysis with excess wind or solar power, and climate-friendly methane. The economy of water electrolysis is also the prerequisite for this technology ..

Carbon dioxide can be separated from the flue gases during the combustion of fossil carbon compounds or coal and is easily accessible and low-priced. Likewise, the excess renewable energy. Only the electrolysis of water requires economic optimization and here the preparation of the feedwater according to the invention brings an important cost advantage.

Coupling the electrolysis process according to the invention on the one hand with the carbon dioxide hydrogenation and on the other hand with a gas power plant, a process combination is produced, according to which one burns methane in a first operating phase, thereby producing electrical energy, and after combustion from the flue gases separates the carbon dioxide. This is hydrogenated in a second phase of operation with hydrogen, which was inventively produced by electrolysis with excess electrical energy, and returned as methane back into the gas network.

The two operating phases alternate;

^■ In the first ^phase of operation, natural gas (methane) is taken from the natural gas grid and emitted in the gas-fired power plant. The electrical energy generated is preferably used for the purpose of stabilizing the power grid. From the flue gases of the power plant, the carbon dioxide is separated and stored for the following second phase of operation.

■ In the second phase of operation, when excess electrical energy is generated in the power network, the water treated according to the invention is converted into hydrogen by electrolysis using this excess energy, and the hydrogen hydrogenates the carbon dioxide generated in the first operating phase to methane. Methane is fed into the natural gas grid. In the balance sheet, natural gas is taken from the natural gas grid during the first phase of operation and an equivalent amount of methane is released into the gas network in the following phase of operation.

In addition, in the second phase of operation with excess energy, the amount of methane generated which is consumed in the subsequent first phase of operation of the gas power plant and delivered as electrical energy to the power grid for stabilization. Here, the methane is always reconstructed from its combustion product carbon dioxide. The gas-fired power plant works thereby emission-free. At equilibrium, no natural gas is consumed and no carbon dioxide is released. In toto this is a "chemical storage power plant" with carbon dioxide storage.

A prerequisite for the success of the reconstruction of methane by hydrogenation of carbon monoxide and carbon dioxide is an economical water electrolysis. The preparation according to the invention of highly purified, salt-free feedwater for electrolysis is an important building block (cf the demand for feedwater for electrolysis in the calculations on page 3).

The inven tion proper method is practiced with advantage where excess electrical energy is generated and connections including transformers for removal from the high-voltage network are available. Nuclear power plants are particularly noteworthy here, which often generate surplus energy due to their low flexibility. Even shut down nuclear power plants, which usually have connections to the high-voltage network, can be retrofitted for the inventive method.

The hydrogen thus obtained from excess electrical energy can be introduced into the natural gas grid. However, it also offers advantages with the hydrogen produced according to the invention in the area of the nuclear power plant for the above-described hydrogenation of carbon monoxide (synthesis gas) or carbon dioxide and thus to recover methane from the surplus energy. The carbon dioxide can be taken from a gas power plant, which results from conversion of the energy part of the nuclear power plant. The conversion to a gas and steam power plant can e.g. about 2/3 of the steam turbines, which are converted into gas turbines. Then you get a gas and steam power plant, The combination of water electrolysis with gas power plant can then emit electrical energy into the network to stabilize it alternately or absorb excess energy and transform it into hydrogen or methane. Downstream nuclear power plants become storage power plants through the production of carbon dioxide from reconstructed methane and the gas network becomes a memory.

Claims

claims

1. A process for the treatment of water for the electrolysis of water, characterized in that the released during the water electrolysis heat energy is used to evaporate water

2. A process for the treatment of water for the electrolysis of water according to claim 1, characterized in that the evaporated water is condensed and the desalted condensed water is used as feed water for the electrolysis of water.

3. A process for the treatment of water for the electrolysis of water according to claim 1 and 2, characterized in that seawater or brackish water is desalted.

4. A process for the treatment of water for the electrolysis of water according to one of claims 1 to 3, characterized in that the water used for cooling of the electrolyzer is evaporated by the heating and then condensed again.

5. A process for the treatment of water for the electrolysis of water according to one of claims 1 to 4, characterized in that the electrolysis of water is coupled with the water treatment by the evaporated and recondensed portion of the cooling water is used as feed water for the electrolysis.

6. A process for the treatment of water for the electrolysis of water according to one of claims 1 to 5, characterized in that water treatment and electrolysis water with wind turbine or solar system are connected such that wind or solar electricity for direct use for electrolysis as a DC with for the electrolyzer voltage is generated and the water for cooling and feed water is taken locally.

7. A process for the treatment of water for the electrolysis of water according to one of claims 1 to 6, characterized in that the cooling water is returned after heating and after evaporation back to the cooler of the electrolyzer and this process is repeated several times while filling with fresh water.

8. A process for the treatment of water for the electrolysis of water according to one of claims 1 to 6, characterized in that a flash evaporation plant is used for water treatment.

9. A process for the treatment of water for the electrolysis of water according to one of claims 1 to 9, characterized in that the hydrogen obtained in the electrolysis of water is introduced into a natural gas line or a natural gas deposit and transported or stored together with the natural gas.

10. A process for the treatment of water for the electrolysis of water according to claim 9, characterized in that the hydrogen is separated again from the natural gas.

1 1. A process for the treatment of water for the electrolysis of water according to one of claims 1 to 10, characterized in that the electrolysis is carried out with fluctuating wind and / or solar power and after introducing the obtained hydrogen into natural gas, a fluctuating hydrogen / natural gas mixture is obtained, which is stored or transported and in which the hydrogen content in the gas mixture is determined at the point of consumption before combustion with fluctuating gas composition and the function of the burner with respect to metering of the gas mixture is adapted to the determined hydrogen / natural gas - ratio.

12. A process for the treatment of water for the electrolysis of water according to one of claims 1 to 10, characterized in that the hydrogen obtained in the electrolysis of water obtained in the coal gasification synthesis gas consisting of carbon monoxide and hydrogen in Mo ratio 1: 1, converted to methane , wherein 1 mole of carbon monoxide react with 3 moles of hydrogen to 1 mole of methane and forms next to 1 mole of water.

13. A process for the treatment of water for the electrolysis of water according to one of claims 1 to 10, characterized in that the hydrogen obtained in the electrolysis of water is reacted with carbon dioxide to methane, wherein 1 mol of carbon dioxide with 4 moles of hydrogen to 1 mole of methane and react next to it make 2 moles of water ..

14. A process for the treatment of water for the electrolysis of water according to claim 13, characterized in that the electrolysis of water in combination with a power plant, in which carbonaceous fuels such as coal, wood or natural gas are burned, is carried out in the combustion gases of the power plant, the carbon dioxide separated and with the separated carbon dioxide together with the hydrogen produced by the water electrolysis methane is reconstructed and the methane is introduced into a natural gas line, further that combustion of the fuels takes place in the power plant and the water electrolysis with the reconstruction of methane in two different operating phases.

15. A process for the treatment of water for the electrolysis of water according to one of claims 1 to 14, characterized in that the electrolysis of water is carried out in conjunction with a running or shut down nuclear power plant while doing the remaining connections to the high-voltage network or to the nuclear power plant and the electrotechnical Devices, in particular the transformers, serve for the transmission of excess electrical energy for water electrolysis.