EP4288588A1

EP4288588A1 - Method for treating process fluids, and filter device for carrying out the method

Info

Publication number: EP4288588A1
Application number: EP22713623.1A
Authority: EP
Inventors: Sebastian König
Original assignee: Hydac International GmbH
Current assignee: Hydac International GmbH
Priority date: 2021-03-27
Filing date: 2022-03-09
Publication date: 2023-12-13
Also published as: WO2022207261A1; JP2024514463A; AU2022249449A1; CN117136254A; KR20230167054A; CA3213540A1; DE102021001631A1

Abstract

The invention relates to a method for treating process fluids, such as those which are produced when a process liquid is separated into different process gases using an electric current in an electrolysis cell (10), comprising at least one fluid circuit in which at least one of the process gases is contained in the process liquid, thereby forming the process fluid, wherein at least one fluid storage tank (22) is provided as part of the fluid circuit. The invention is characterized in that the fluid storage tank (22) is equipped with at least one filter device (24), by means of which the process fluid is cleaned of any possible particulate contamination and simultaneously the contained process gas is separated from the process fluid while the process liquid is retained.

Description

Method for treating process fluids and filter device for

performing the procedure

The invention relates to a method for the treatment of process fluids as they arise when a process liquid is broken down into different process gases with the aid of electricity in an electrolytic cell, with at least one fluid circuit in which at least one of the process gases is contained in the process liquid with formation of the process fluid is present, with at least one fluid storage tank being present as part of the fluid circuit. The invention further relates to a device for carrying out the method. WO 2011/012507 A1 discloses a method and a device for generating hydrogen and oxygen, it being possible in particular to use excess electrical energy from wind turbines for this purpose. The associated device for carrying out the process uses a reversible polymer electrolyte fuel cell (PEMFC) with a proton exchange membrane (PEM) as an electrolyzer. By reversing the fuel cell process, such a fuel cell can also be used to produce hydrogen on the one hand and oxygen on the other hand as the different process gases from water as the process liquid. The fuel cell then works as a Electrolyser and must be supplied with electrical power, with several fuel cells can be combined as a fuel cell stack. The electricity required for this can come from generators in wind turbines, for example. The commonly used electrolysis devices in the form of electrolysis cells for generating hydrogen and oxygen are those that are usually operated at atmospheric pressure or as part of a pressure electrolysis. The proton exchange membrane of the presented reversible fuel cell separates a negative side from a positive side. Due to the electrolysis that takes place in the reversible fuel cell when electricity is applied, a water molecule is broken down into hydrogen and oxygen on the positive side or anode side, with the hydrogen migrating as a proton through the proton exchange membrane to the negative side or cathode side , while the oxygen remains on the positive side.

For the reaction to take place, water must be present as the process liquid on the positive side, with the relevant water supply being produced via an independent circuit. The water used as the process liquid is actually pure water and is therefore free of any foreign substances as far as possible. The amount of water that is required in the course of the recycling depends not only on the amount of water that is needed for the electrolysis reaction (the production of 1 kg of hydrogen usually requires 9 kg of water), but also on the cooling requirements of the Electrolytic cell or the electrolytic cell stack, since the process water also serves as a cooling medium for the electrolysis operation. Thus, every PEM electrolysis regularly has a water circuit on the positive side or the oxygen side.

The oxygen generated as a process gas dissolves and mixes with water as the process liquid, which is routed in the associated supply circuit, to form a process fluid. This will be more or less large Gas bubbles in the form of oxygen are entrained in the water cycle and the relevant water cycle is followed by a so-called gravity separator, which normally consists of a horizontal fluid storage tank that is large in size and into which the process fluid water with the dissolved oxygen flows. The process gas oxygen is given sufficient time to outgas from the process fluid in the storage tank in order to recover pure water as the process liquid in this way. Due to the fact that large-volume, horizontally lying fluid storage tanks are used, a large fluid surface is created in the tank as the fluid level in order to give the process gas the opportunity to effectively outgas. Although there is a desire to get pure water as the process liquid again after the process fluid has outgassed, the equipment used and, for example, the piping layout, can result in an unwanted entry of particles into the process liquid and thus contamination and a residual content of incomplete outgassed process gas, which makes a renewed use of the sensitive electrolytic cell or the electrolytic cell stack appear questionable.

Proceeding from this state of the art, the object of the invention is to provide an improved method and device that help to facilitate the outgassing process of a process gas while at the same time keeping the process liquid clean for renewed use in electrolytic cell operation. A task in this regard is solved by a method with the features of patent claim 1 and a filter device with the features of patent claim 6.

The method according to the invention is characterized in that at least one filter device is accommodated in the fluid storage tank, by means of which the process fluid is cleaned of any particle contamination and at the same time the dissolved process gas is separated from the process fluid while retaining the process liquid. In this way, the process using the filter device ensures that even finely dispersed process gas in the process fluid can be released onto the gas side of the fluid storage tank, with small-volume gas bubbles merging to form larger gas bubbles due to surface tension, which means that the process fluid is discharged relieved. What remains on the liquid side of the fluid storage tank is the process liquid, which has been cleaned of any particle contamination by the filter device for a new extraction process in electrolysis cell operation.

This has no equivalent in the prior art. In this way, degassing of process water on the oxygen side of PEM electrolyzers in a fluid storage tank is ensured. In particular, it is possible to remove the smallest gas bubbles from the fluid using a filter medium of the filter device that is suitable for this purpose. In this way, even the smallest gas bubbles, which could otherwise accumulate in the process liquid, are effectively removed. If the claim states that at least one process gas is contained in the process liquid, this means a loose bond between gas and liquid in which the gas is carried along with the liquid in an unbound manner, for example being entrained with the fluid flow; but also means that the gas in the liquid is at least partially present in a dissolved form, for example in a finely dispersed form.

In terms of process technology, it is not absolutely necessary for an additional liquid circuit to be used on the negative side as part of hydrogen production. The hydrogen atoms (protons) that reach the negative side during the operation of the electrolytic cell always take a few water molecules with them; but in principle Sometimes the negative side of a PEM electrolysis can be run "dry", ie there is no separate liquid circuit on the cathode side.

However, the negative side or cathode side can also be run as part of a liquid circuit that is independent of the liquid circuit on the oxygen side. This enables more even cooling and the water can easily carry the hydrogen out of the electrolytic cell. This means that the method mentioned above can also be used in addition to the device for degassing process water on the hydrogen side of PEM electrolyzers. The hydrogen, in the form of gas bubbles, is in turn entrained in more or less dissolved form as a process fluid by the process water and brought into an independent fluid storage tank, where the hydrogen can now outgas by means of the filter device.

In addition to the PEM electrolysis shown, there is also the option of carrying out alkaline electrolysis to obtain hydrogen and oxygen gas, in which a so-called diaphragm is used as the separating element instead of a proton exchange membrane, which regularly consists of a fine metal lattice structure. The actual electrolysis reaction now takes place here on the negative side, where the hydrogen produced remains and only the oxygen produced migrates as a so-called hydroxide molecule through the diaphragm to the positive side, where it recombines with electrons to form oxygen. In order for this process to work, there must be sufficient hydroxide ions in the process liquid. This is achieved by not using pure water here, but using a potassium hydroxide solution, preferably a 30% potassium hydroxide solution. This contains a large number of the required ions and thus ensures good conductivity and thus a very efficient electrolysis process. Since the hydroxide ions on the positive side recombine to form oxygen they must be able to swim in the liquid up to the positive electrode or anode. In the case of alkaline electrolysis with a diaphragm, it is therefore basically not possible to work with electrodes without a liquid circuit of their own, as is the case with PEM electrolysis for hydrogen, but there are always two liquid circuits; one on the oxygen side and one on the hydrogen side. Instead of a diaphragm, a so-called anion exchange membrane (AEM) is also used with comparable results. Analogous to PEM electrolysis, alkaline systems with AEM instead of a diaphragm can also be carried out with a "dry" hydrogen side without a separate fluid circuit.

Both liquid circuits contain after the electrolytic cell stack as well as the fluid storage tanks in which the liquid can be freed from oxygen on the positive side and from hydrogen on the negative side by means of the respective filter device. The two process gases are transported away again by the liquids from the respective cells as gas bubbles of different sizes, and the creation of two separate liquid circuits, each with a fluid storage tank and a filter device arranged therein, results in an accelerated degassing process and the actual operation of the electrolytic cells is then available high-purity process liquid that has been cleaned of particle contamination and gas bubbles is available again in the respective liquid circuit. In this way, therefore, degassing of electrolyte liquid (potassium liquor) is accomplished both on the oxygen soap and on the hydrogen side of alkaline electrolyzers.

The filter device used to carry out the method according to the invention has a preferably replaceable filter element through which the process fluid can flow from the inside to the outside, the filter element being spaced apart while maintaining a definable radial distance and forming a fluid flow space is surrounded by a housing wall, which is designed as a discharge pipe, has a plurality of passage points, part of which is arranged below the variable fluid level in the fluid storage tank and the other part above this fluid level. However, it is also possible to achieve effective bubble discharge via the respective filter medium without an additional housing wall.

For an improved gas separation process, it is provided that the respective passage points in the housing wall of the filter device are designed like windows. The gas bubbles collect at the edge of the housing wall at these particularly window-like passage points and individual gas bubbles increase in gas volume, so that they receive increased buoyancy and are promptly separated from the process fluid. Although in the fluid storage tank there is a fluid-level delivery along the surface of the process liquid, there is no foaming of the same, so that the process liquid can be removed undisturbed for further electrolytic cell operation. With a corresponding gradient structure for the filter medium, an improved discharge of bubbles from the fluid can also take place on the hollow-cylindrical inside of the filter element.

Particularly preferably, the filter device according to the invention can be fixed by means of its cover part inside the fluid storage tank, with the inflow for the process fluid into the interior of the filter element taking place from the opposite, bottom-side housing wall of the fluid storage tank. If necessary, several such filter devices can also be accommodated in a fluid storage tank and a used filter element can be exchanged for a new element by releasing it through the cover part. Due to the shorter residence time in the fluid storage tanks caused by the invention, these tanks can be reduced in volume, which is technically referred to as downsizing. In this way, the container costs for the tank can be reduced and the gas space above the fluid level in the tank is also reduced, so that there is less dead volume, which increases the dynamics of the overall system. Accordingly, less process liquid, such as water or caustic potash, is required, which improves the so-called cold-start behavior in electrolysis cell operation.

At least a smaller gas space on the hydrogen delivery side is helpful for safety reasons, since hydrogen is known to be highly flammable, particularly when so-called oxyhydrogen gas formation occurs in connection with the oxygen in the air. In reality, some hydrogen always diffuses through the respective membrane (PEM or AEM) or the diaphragm to the oxygen side, which can lead to the formation of such an ignitable oxyhydrogen mixture on the oxygen side in the partial load range of electrolysis cell operation. A smaller volume of gas in the fluid storage tank on the oxygen side is also definitely helpful in this respect.

The process solution according to the invention using a filter device according to the drawing is explained in more detail below. Here, in principle and not to scale representation show the

Figure 1 in a schematically greatly simplified form

Electrolysis process together with degassing based on a basic process diagram;

Figures 2 and 3 each in a perspective view, once in plan view and once in longitudinal section, one in the flow diagram according to FIG. 1 uses a filter device.

In FIG. 1, an electrolytic cell or an electrolytic cell stack (stack) is denoted as a whole by 10 in the manner of a black box representation. The electrolytic cell 10 is connected via a power line 12 to a power source (not shown), such as a wind turbine generator. Furthermore, the electrolytic cell 10 has a supply line 14 for a process liquid in the form of water or potassium hydroxide solution. The cooling circuit for the electrolytic cell 10 is omitted for the sake of simplicity.

During operation of the cell 10, the electric current and the use of a proton exchange membrane (not shown) breaks down the process liquid water into hydrogen and oxygen, with the hydrogen via a hydrogen line 16 and the dissolved in the process liquid, alternatively fine Dispersed oxygen, which is also entrained in the flow, is fed out as process fluid via the discharge line 18 from the electrolysis cell 10 . The discharge line 18 is fluid-conveying to a gear 20 of a fluid storage tank 22 connected, which receives a designated as a whole with 24 filter device. The fluid storage tank 22 also has an outlet 26 located below a fluid level 26 as well as a further outlet 30 for the process gas oxygen at the top. The fluid outlet 28 for process liquid is connected to the supply line 14 to form a circuit guide (not shown) in order to receive the cleaned process liquid for the electrolytic cell operation. The process fluid (water and oxygen) present at the inlet 20 is cleaned of any particle contamination by means of the filter device 24 and at the same time the dissolved process gas oxygen is removed from the process fluid, while the process liquid water is retained. divorced The process water cleaned in this way is then returned from the liquid side 31 of the tank 22 via the outlet 26 and the separated gas in the form of oxygen leaves the fluid storage tank 22 via its gas side 33 and via the other outlet 30 at the top. As shown in particular in the figure 1 further shows, the degassing and cleaning process is controlled in such a way that the fluid level 28 in the fluid storage tank 22 only partially covers the filter device 24, so that the filter device 24 protrudes beyond the fluid level 28 by a definable axial length.

If, contrary to the illustration in Figure 1, the hydrogen electrode is not run "dry" without its own fluid circuit, but is operated as a so-called wet electrode with its own liquid circuit, a corresponding after-treatment device can be connected to the hydrogen line 16, consisting of the components fluid storage tank 22 and filter device 24.

Furthermore, instead of water, caustic potash can be used as the process liquid, which is then supplied to the electrolytic cell 10 via the supply line 14 . Also in this respect, oxygen is then separated via the line 18 and hydrogen via the line 16. A diaphragm (not shown in detail) serves as the separating element in the cell 10, for example in the form of a fine metal grid or an anion exchange membrane. In this case, both liquid circuits are now provided with an aftertreatment device as shown in FIG. 1, both on the oxygen side and on the hydrogen side.

The filter device shown in FIGS. 2 and 3 is of particular importance for the cleaning and degassing processes. The filter device designed as a so-called in-tank solution is shown in Figures 2 1 and 3 in its entirety and has a filter housing, designated as a whole by 32, which has a cover part 34 on the head side and also a housing wall 36, which is designed in the manner of an outflow pipe. The housing wall 36 has fluid passages in the form of windows 38 (FIG. 2), it being possible for a perforation 40 shown in FIG. 3 to be made in the housing wall 36 instead of the window-like passage points 38. The perforation 40 in question consists of individual circular through-holes 41 in the housing wall 36, preferably in the form of through-holes. Instead of the filter device shown, a different type of filter device can also be used, which carries out the gas separation exclusively via the filter medium, also on its inner side, and does not require any winding of the housing with passage windows. 3 shows the part of the filter housing 32 which extends from the cover part 34 into the interior of the fluid storage tank 22 and consists of a structural unit formed from a filter element 44 as an integral part of the outflow pipe 36. The filter element 44 has as usual, a hollow cylindrical element material 46 which extends between an upper end cap 50 and a lower end cap 52 together with an external support tube 48 which is provided with fluid passage points. The upper end cap 50 assigned to the cover part 34 can be connected to the cover part 34 via individual locking webs 54 . The cover part 34 can be releasably connected to the upper side 56 of the storage tank 22 via a thread section (not shown in detail). The support tube 48 having fluid passages is formed from individual partial segments 58 of longitudinal and transverse rods that are latched to one another, and the housing wall 36 provided with passages 38, 41 surrounds the filter element 44 with its support tube 48 with a definable radial distance, so that a fluid flow space lies in between 60 is formed. FIG. 3 also shows the design of the lower end cap 52 via which process fluid can get into the inner filter cavity 62 for the filtration and degassing operation, for which purpose the lower end cap 52 is provided with a central opening 64 . Contrary to the basic depiction according to FIG. 1, the fluid access occurs via an inlet which does not extend laterally through the tank wall of the storage tank 22, but rather from below via an access opening on the floor, which is not shown in detail and which engages in the interior of the filter device like a socket and from an enclosure 66 is included with the upper end stop.

The respective process fluid therefore flows into the filter cavity 62 via the lower central opening 64 and then flows through the element material 46 of the filter element 44 from the inside to the outside entrained gas bubbles and reaches the interior of the tank 22 via the fluid flow space 60 after flowing through the window-like passage openings 38 (Figure 2) or the hole-type perforation 40 (Figure 3) of the associated housing wall 36, so that in this respect the cleaned process fluid can reach the Filtrate side of the filter device reaches and thus on the liquid side 31 of the fluid storage tank 22 with changing fluid level 28.

Gas bubbles collect at the respective passage opening 38, 40 in the housing wall 36, which, combined to form larger bubble packs, then rise on the outside of the housing wall 36 and reach the gas side 33 of the storage tank 22, with the possibility of discharge from the Tank 22 by means of the further outlet 30 on the gas side.

To exchange the filter element 44 for a new element, the cover part 34 must then be unscrewed from the tank 22 on its upper side 56. Ben and the unit shown in FIG. 3 can be removed from the tank 22 together with the cover part 34 . After separating the cover part 34 from the other parts of the filter device via the locking webs 54, the filter element 44 can be removed from the filter housing 32 via the upper discharge opening and exchanged for a new element. The filter device is then reinserted into the tank 22 in a correspondingly reversed sequence. While the particle filtration essentially takes place in a horizontal flow direction (Figure 1), the degassing takes place in a vertical direction along the inside and outside of the housing wall 36, with any entrained fluid being able to run down due to heavy force and to increase the fluid level 28 in the tank 22 then contributes. In this way, the degassing of hydrogen or oxygen from process fluids in the context of electrolysis cell operation is significantly facilitated by means of the filter device 24, with the pertinent device also being able to be used without further ado for alkaline electrolysis. The method described here and the filter device can be used with other electrolysis methods, for example for the production of chlorine, without further ado.

Claims

P atentClaims

1 . Process for the treatment of process fluids as they arise when a process liquid is broken down into different process gases with the aid of electricity in an electrolytic cell (10), with at least one fluid circuit in which at least one of the process gases is contained in the process liquid under formation of the process fluid is present, with at least one fluid storage tank (22) being present as part of the fluid circuit, characterized in that at least one filter device (24) is accommodated in the fluid storage tank (22), by means of which the process fluid of any Particle pollution is cleaned and at the same time the process gas contained is separated from the process fluid with retention of the process liquid.

2. The method according to claim 1, characterized in that water or caustic potash is used as the process liquid, and that hydrogen and oxygen are generated as the process gases.

3. The method according to claim 1 or 2, characterized in that for the generation of the process gases at least one proton exchange membrane is used as a separation element using water as the process liquid, and that the material on the oxygen side of the membrane resulting process fluid by means the filter device (24) arranged in the storage tank (22) is separated again into its components water and oxygen.

4. The method according to any one of the preceding claims, characterized in that the hydrogen formed on the hydrogen side of the proton exchange membrane in water as the process liquid is dissolved to form the process fluid and is separated again into its components water and hydrogen by means of the filter device (24).

5. The method according to any one of the preceding claims, characterized in that for the generation of the process gases at least one diaphragm or an anion exchange membrane (AEM) is used as a separation element, using caustic potash as the process liquid, and that on the oxygen side and the process fluid produced on the hydrogen side of the diaphragm is separated again into its components of potassium hydroxide solution and the respective process gas in the form of oxygen and hydrogen by means of an assignable filter device (24) in the storage tank (22).

6. Filter device for carrying out a method for treating process fluids, according to one of the preceding claims with at least one, preferably replaceable, filter element (44) through which a fluid can flow from the inside to the outside, and that in each case maintaining a predeterminable radial distance and under Formation of a fluid flow space (60), the filter element (44) is surrounded by a housing wall (36), which is designed as an outflow pipe and has several passage points (38, 40), part of which is below the respective variable fluid level (28) in the Fluid storage tank (22) and the other part above this fluid level (28) is arranged.

7. Filter device according to claim 6, characterized in that the respective passage points (38) in the housing wall (36) are designed like windows, and that any gas bubbles in the cleaned fluid can be separated via the window-like passage openings (38) and for a discharge close to the fluid level are collectible.

8. Filter device according to claim 6 or 7, characterized in that the housing wall (36) with the window-like passage openings (38) can be fixed in the fluid storage tank (22) by means of a cover part (34), and that a supply of process fluid in the

Interior of the filter element via an inlet (20) in the fluid storage tank (22) is made.

9. Filter device according to one of claims 6 to 8, characterized in that the opening cross sections for the passage points

(38, 40) are selected in such a way that the volume of the gas bubbles can be enlarged for easier release under the influence of their surface tension.