METHOD FOR OPERATING AN ELECTROLYSIS PLANT

Description

[0001] The invention relates to an electrolysis plant with an electrolyzer for producing hydrogen with the aid of electrical current, wherein a cooling device with a cooling circuit is used in order to be able to dissipate the waste heat generated during the process in the electrolyzer.

[0002] Electrolysis systems are known in various designs. The central component of the electrolysis system is the electrolyzer, which is typically either an alkaline electrolyzer or a PEM electrolyzer. In both cases, it is necessary that pure water, preferably non-conductive, be supplied to the electrolyzer for electrolysis. For this purpose, water treatment with deionization is usually used. Deionization inevitably produces highly contaminated wastewater containing ions, which is also discharged as "wastewater."

[0003] The electrolysis process generates waste heat, which is typically caused by a coolant flowing through the electrolyzer. This coolant is then cooled down in a cooling system.

[0004] In larger systems, a significant amount of waste heat is generated, so that sufficient cooling capacity of the cooling system is required.

[0005] To solve this problem, electrically powered fans are used, for example, to support convection. However, the disadvantage is the additional power consumption required for electrolysis. Furthermore, the ambient temperature limits the achievable temperature of the coolant, which can be particularly problematic in areas with typically high outside temperatures.

[0006] An advantageous utilization of the heat generated during electrolysis is described in WO 2013 / 113631 A1. It proposes that the waste heat from the electrolyzer be fed directly to a water treatment system. This waste heat is used to heat the raw water supplied to support deionization. Depending on local conditions, the high water consumption of this solution can be an advantage or disadvantage. Therefore, this solution can be used effectively if the additional water can be used for another purpose. CH 137 203 A discloses diverting the wastewater to the bottom and feeding only pure distilled water into the closed cooling system.

[0007] In alternative designs, evaporative cooling is preferred, which allows for high cooling performance without significant energy consumption. In particular, this makes it possible to cool the coolant to temperatures below ambient. Obviously, this requires a water supply to enable wet cooling.

[0008] The use of electrolysis systems is particularly suitable when electricity generated from renewable energy sources, particularly photovoltaics, can be used. Accordingly, larger electrolysis systems are used primarily in areas with high levels of solar radiation. This is often associated with high ambient temperatures and a limited water supply. This poses the problem that convection cooling causes high power losses due to the fans used. Furthermore, a desired low coolant temperature is sometimes not achievable with convection cooling. Therefore, evaporative cooling is generally used, which, however, exacerbates the problem of water scarcity and results in high water costs.

[0009] The object of the present invention is to improve the yield of hydrogen in relation to the costs.

[0010] A method according to the invention for operating an electrolysis plant with improved efficiency is specified in claim 1. Advantageous embodiments are the subject of the subclaims.

[0011] The generic electrolysis plant comprises an electrolyzer as an essential element in which hydrogen and oxygen are produced from water using electrical energy during operation of the electrolysis plant.

[0012] This first requires a water supply that provides process water. Since high purity and minimal conductivity requirements are placed on the system, water treatment is also required. This is connected to the water supply so that process water is pumped for water treatment during operation of the electrolysis plant. During water treatment, the process water is cleaned if necessary and, in any case, deionized. Accordingly, deionized ultrapure water—hereinafter referred to as deionized water—is produced.

[0013] It should be noted that the deionized water is not necessarily pure H2O. Rather, the deionized water has the water quality that meets the necessary purity requirements for use in electrolysis, and in particular, the lowest possible presence of conductive ions.

[0014] During the process of de-ionization and thus the separation of ions from the process water, wastewater containing ions is inevitably produced.

[0015] The water treatment is obviously connected to the electrolyzer, whereby the deionized water is fed to the electrolyzer during operation of the electrolysis plant.

[0016] Furthermore, the electrolysis system of this type includes a cooling device. During operation, the electrolyzer generates waste heat, which must be dissipated. For this purpose, the electrolyzer is connected to the cooling device in such a way that the waste heat generated in the electrolyzer can be dissipated by the cooling device.

[0017] According to the invention, it is now provided that the water treatment is also connected to the cooling device, wherein the ion-containing wastewater arising in the water treatment is fed to the cooling device for cooling purposes.

[0018] Until now, it has been fundamentally rejected as inadmissible to further use the ion-containing wastewater generated during water treatment within the electrolysis plant, as the quality is considered completely inadequate.

[0019] In contrast, the solution according to the invention uses ion-containing wastewater for cooling. This reduces the water consumption of the electrolysis system, thus improving acceptance of an electrolysis system, particularly in areas with critical water supplies, and thus reducing water supply costs.

[0020] For cooling, a cooling circuit is advantageously used, connecting the electrolyzer to the cooling device. A cooled coolant is fed to the electrolyzer, which heats up as the electrolyzer operates. The heated coolant is fed into the circuit of the cooling device. After being cooled there, it is fed back to the electrolyzer.

[0021] In the process for operating the electrolysis plant, it is particularly advantageous to take into account the higher pollution caused by the ion-containing wastewater. To achieve this, the maintenance interval is preferably shortened by at least 20% compared to a reference period. The reference period is the theoretical maintenance interval that is appropriate if the process water is used directly for cooling instead of the ion-containing wastewater, with the same existing plant technology.

[0022] It may be planned to take additional measures to extend the maintenance interval that would not have been taken if domestic water had been used directly. However, in this case, the system with the additional measures will be used to determine the comparison period.

[0023] Although shortening the maintenance interval leads to higher costs and possibly more frequent downtimes - or, as a result, to higher installation costs and running costs if offset by additional measures - the higher maintenance costs are less significant in areas with scarce water resources than the otherwise required water consumption.

[0024] The following figures show schematically an embodiment of an electrolysis plant according to the state of the art - see Fig. 1 - and an electrolysis plant according to the invention - see Fig. 2 - outlined.

[0025] Both versions of an electrolysis plant 11 according to the state of the art - Fig. 1 - and an electrolysis plant 01 according to the invention comprise the electrolyzer 06 as an essential element. Here, the reactant water H 2 O is split into the products hydrogen H 2 and oxygen O 2 using electrical current. Obviously, water—i.e., deionized water—is required for this process.

[0026] The figures depict a supply of process water 03, which leads to a water treatment system 04. In this system 04, the process water 03 is purified if necessary and, in any case, deionized. This produces a deionized product 05, which is then fed to the electrolyzer 06.

[0027] The electrolysis process generates waste heat that must be dissipated. For this purpose, the electrolyzer 06 is connected to a cooling device 07 via a cooling circuit. In this cooling device 07, a coolant previously heated in the electrolyzer 06 is cooled down again.

[0028] During water treatment, wastewater containing ions (O2, 12) is inevitably produced.

[0029] Here, as the Fig. 1 As outlined, it is standard practice for the wastewater 12 to be discharged from the electrolysis system 11. However, for effective cooling, particularly in hot regions, it is necessary to supply water to the cooling device 07, especially for evaporative cooling. For this purpose, the cooling device 07 is usually connected to the water supply, so that process water 03 is supplied to the cooling device 07.

[0030] In contrast, according to the invention - as in Fig. 2outlined - it is now intended that the ion-containing wastewater 02 from the water treatment is fed to the cooling device 07.

[0031] This will usually require shortening maintenance intervals, but this can reduce water consumption.

Claims

1. Method for producing hydrogen using an electrolysis system (0) wherein - hydrogen and oxygen are produced in an electrolyser (06) from deionized water (05) using electrical energy, and for this purpose - service water (03) is supplied to a water treatment (04) by a water supply, - the service water (03) is purified and deionized in the water treatment (04), wherein the deionized water (05) is produced and ion-containing wastewater (02) arises, - the deionized water (05) is supplied to the electrolyser (06) and at the same time - the ion-containing wastewater (02) is conducted out of the water treatment (04) and supplied to a cooling device (07), and wherein - waste heat arising in the electrolyser (06) is dissipated by means of the cooling device (07).

2. Method according to Claim 1, wherein a coolant flowing in the circuit is heated in the electrolyser (06) and cooled in the cooling device (07).

3. Method according to Claim 1 or 2, wherein the cooling device (07) comprises evaporative cooling.

4. Method according to any one of Claims 1 to 3, wherein deposits are removed in the cooling device (07) at regular maintenance intervals, wherein the maintenance interval is shortened by at least 20% of the duration of a comparison period of time, wherein the comparison period of time is that interval after which deposits are removed if exclusively service water (03) is supplied to the cooling device (07).