Purification apparatus and method

Abstract

The present disclosure relates to a purification system for purifying a gaseous product produced by electrolysis comprising: a separation vessel (10) configured to contain a separating liquid (12), and where the gaseous product is passed through the separating liquid (12) to at least partially remove a contaminant from the gaseous product in use. A condenser vessel (30) operatively connected downstream of the separation vessel (10), the condensing vessel (30) comprising a condenser (24) configured to condense one or more contaminant out from the gaseous product. The separation vessel (10) and the condensing vessel (30) are provided as separate, fluidly connected vessels.

Description

[0001] Purification apparatus and method

[0002] The present disclosure relates an apparatus and method for purifying a gaseous product, in particular, but not limited to a gaseous product produced using alkaline electrolysis.

[0003] Background of the Invention

[0004] A prior art system for purifying a gaseous product produced by electrolysis is shown in figure 1. In the shown example, the gaseous product comprises hydrogen (H2). The hydrogen is produced using an alkaline electrolyte, such as potassium hydroxide (KOH), vapours of which are typically entrained within the produced gaseous product. The H2and KOH are sent to a first scrubbing station A, where the KOH is diluted using water (H2O). The KOH and water are then extracted, whilst the hydrogen passes through the scrubber. However, the hydrogen contains water vapour and thus is still “wet”. The wet hydrogen passes through a dryer B where “dry” hydrogen is produced.

[0005] A further prior art solution is provided in US 2023 / 295824. A separating vessel has liquid and a gas phase part, which are fluidly connected to one another within the vessel. A condenser is provided within the vessel to condense the electrolyte medium from the gas, which then drops back into the liquid part of the vessel. The purified gas may then flow out from the outlet 7 and the electrolyte may be reused.

[0006] The invention has found numerous problems with the prior art arrangement. Having both dryer and a scrubber may be expensive and occupy large amounts of space. The diluted KOH from the scrubber is typically disposed of as it is uneconomical to recover the KOH. The KOH for the electrolysis step may therefore need to be constantly replaced. In the system in US’824, the electrolyte condenses on the condenser, which may cause corrosion thereof. As the electrolyte is reused, contamination from corrosion of the condenser may accumulated within the system. Additionally, given the fixed size of the vessel, the size of the condenser apparatus is fixed accordingly. This provides an inflexible configuration, for example, the fixed size of the condenser may only be suitable for a specific electrolyte.

[0007] It is an aim of the present invention to overcome and / or ameliorate one or more of the above problems.

[0008] Statement of Invention

[0009] According to first aspect, there is provided: a purification system for purifying a gaseous product produced by electrolysis comprising: a separation vessel, and where the gaseous product is passed through the separation vessel to at least partially remove a contaminant from the gaseous product in use; a condenser vessel operatively connected downstream of the separation vessel, the condensing vessel comprising a condenser configuration to condense one or more contaminant out from the gaseous product; and where the separation vessel and the condensing vessel are provided as separate, fluidly connected vessels.

[0010] The separation vessel may comprise a separating liquid. The gaseous product may be configured to pass through separating liquid.

[0011] The separation vessel and the condensing vessel may be detachable / separable. The separation vessel and the condensing vessel may be modular / interchangeable. The separation vessel and the condensing vessel may be spaced from one another.

[0012] The system may comprise a holding tank. The holding tank may be operatively connected to the condenser vessel to receive the condensed contaminant. The holding tank may be operatively provided between the condenser vessel and the separation vessel. The holding tank may feed condensed contaminant back to the separation vessel.

[0013] The system may comprise a cooling system to provide a cooling fluid to the condenser. The cooling system may comprise a refrigeration system. The condenser may comprise a conduit for cooling fluid. The conduit may be coiled, serpentine and / or tortuous. The condenser may provide a heat exchanger.

[0014] The system may comprise a sensor configured to detect byproducts of corrosion of the condenser.

[0015] The separation vessel and the condenser vessel may be operatively connected via a conduit (e.g. a hose or pipe). The conduit may be detachable from one or both of the separation vessel and the condenser vessel. The separation vessel and the condenser vessel may comprise an outlet. The conduit may be connected to the outlet.

[0016] The separating vessel may comprise an inlet for the gaseous product. The inlet may be provided below the liquid level of the separating fluid. The separating vessel may comprise an outlet for the gaseous product. The outlet may be provided below the liquid level of the separating fluid.

[0017] The condensing vessel may comprise an outlet for egress of purified gas. The gaseous product may comprise hydrogen and / or nitrogen.

[0018] According to a further aspect, there is provided: an electrolysis apparatus comprising the purification system of the previous aspect.

[0019] The separation vessel and / or the holding tank may be operatively connected to an electrolysis cell to provide an electrolyte there to (i.e. electrolyte recirculated to the electrolysis cell). The condensate may be recirculated to the electrolysis cell. The apparatus may comprise an alkaline water electrolysis apparatus. The electrolysis apparatus may be configured to produce at least two gaseous products. A respective purification system may be provided for at least two of the gaseous products. At least two of the purification systems may share a common cooling system.

[0020] According to a further aspect, there is provided: a method of purifying a gaseous product produced by electrolysis comprising: passing the gaseous product through a separation vessel to at least partially remove a contaminant from the gaseous product; condensing one or more contaminant out from the gaseous product using a condenser provided downstream of the separation vessel; and where the separation vessel and the condensing vessel are provided as separate, fluidly connected vessels.

[0021] The gaseous product may be passed through a separating liquid contained in a separation vessel.

[0022] The gaseous product may be bubbled the through the separating liquid. The gaseous product may separated using a gravity separation (i.e. gas flow upward and the liquid flows downward)

[0023] The contaminant may comprise a vapour. The contaminant may comprise an electrolysis electrolyte. The contaminant may comprise an alkaline electrolyte and / or water. The separating liquid may comprise an alkaline electrolyte. The separating liquid may comprise the same substance as the electrolyte. The alkaline electrolyte may comprise sodium hydroxide and / or potassium hydroxide. The alkaline electrolyte may comprise lithium hydroxide. The alkaline electrolyte may comprise 25-35% potassium hydroxide and / or sodium hydroxide. The alkaline electrolyte may comprise 30% potassium hydroxide and / or sodium hydroxide. The separating liquid may comprise sodium hydroxide and / or potassium hydroxide. According to a further aspect, there is provided: a method of electrolysis comprising the method of purifying a gaseous product according to the previous aspect.

[0024] The separating liquid and / or condensed contaminant may be recirculated to an electrolysis cell of an electrolysis apparatus.

[0025] Any aspect of the invention may be combined with any other aspect of the invention where practicable.

[0026] Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings:

[0027] An electrolysis system 2 is shown in figure 2. The system 2 comprises an electrolysis cell 4. The cell 4 may comprise electrodes (not shown), electrolyte and / or diaphragm / membrane. The electrodes may comprise a metallic alloy, for example, a transition metal alloy. The electrodes may comprise nickel. It can be understood that the cell is conventional and will not be described in detail. Typically, multiple cells 4 are provided. The cells 4 may be provided in series and / or parallel. Such an arrangement may be referred to as a “stack” of cells.

[0028] In the present embodiment, the cell 4 comprise an alkaline water electrolysis cell. The electrolyte therefore comprises an alkaline material. Typically, the alkaline material comprises hydroxide (OH-) ions, for example potassium hydroxide (KOH), sodium hydroxide (NaOH) or combinations thereof. The electrolyte is pumped into / through the cell 4 to ensure adequately supply thereof. A pump or like (not shown) may pump the electrolyte. The electrolyte is supplied to the cell via an inlet 6. In other embodiments, the cell 4 comprises a proton-exchange membrane (PEM) cell. In such embodiments, it can be understood that the electrolyte is provided by the membrane itself. In some embodiments, the cell may comprise an anion exchange membrane (AEM) electrolysis cell.

[0029] The cell comprises an outlet 8 to allow egress of gases produced in electrolysis process. Typically, an outlet 8 for each of the respective gases produced. For example, where electrolysis is performed on water, a separate outlet 8 is provided for the hydrogen and the oxygen respectively.

[0030] The outlet 8 is fluidly connected to a separation vessel 10. Valves 11 or the like may be provided to control flow of fluids from the separation vessel 10. The separation vessel 10 is configured to at least partially remove electrolyte from the produced gases. For example, the separation vessel 10 may be configured to remove KOH or NaOH from the produced gas. A separation liquid 12 is provided in the separation vessel 10. The separation vessel 10 comprises an inlet 14 to allow ingress of the gas. The inlet 14 is provided below the liquid level (i.e. submerged therein), such that produced gas flows / bubbles through the separation liquid 12. During flow through the separation liquid 12, the electrolyte in the gas becomes entrained within the separation liquid 12.

[0031] In the present embodiment, the separation liquid 12 comprises the same substance as the electrolyte. For example, where the electrolyte comprises KOH, then the separation liquid 12 comprises KOH accordingly. This allows the separated electrolyte to be recycled / reused. The separation vessel 10 comprises a first outlet 16 to allow egress of the separated electrolyte. Valves 18 or the like are provided to control egress thereof. Where the electrolyte is recycled, the electrolyte and separation liquid 12 mixture are cycled back to the electrolysis cell 4. In some embodiments, the separation liquid 12 comprises a different fluid to the electrolyte. The separation liquid 12 and the separated electrolyte may simply be disposed of once used.

[0032] A second outlet 20 is provided to allow egress of the partially cleaned gas. The second outlet 20 is provided near a top end of the separation vessel 10 to ensure separation liquid does not egress therefrom. A headspace (i.e. a space with no liquid) may be provided. The gas typically contains water vapour.

[0033] The second outlet 20 is fluidly connected to a condenser system 22. The condenser system 22 is configured to condense electrolyte, moisture, or other impurities out from the gas. The condenser system 22 comprises a condenser 24. The condenser 24 comprises a channel, tube or the like configured to receive a cooling fluid (e.g. to provide a heat exchanger). The condenser 24 may be coiled, serpentine, or otherwise tortuous to increase the effective surface area thereof. The condenser 24 is operatively connected to a cooling system 26. The cooling system 26 may comprise a refrigeration system to cool the cooling fluid. In some embodiments, the cooling system 26 may simply draw cooling fluid from a reservoir of cooling fluid (e.g. mains water, river, lake or other water body). The cooling system may provide a heat sink. However, it can be appreciated that a dedicated refrigeration system can provided greater cooling power and / or more consistent / controllable cooling temperatures. Valves 28 or the like are operatively provided between the condenser 24 and the cooling system 26. The condenser 24 may be provided at a temperature between 0 and 10 degrees, preferably, between 4 and 6 degrees.

[0034] The separation vessel 10 and the condenser system 22 are directly connected to one another (i.e. no intermediate vessel or processing apparatus is provided therebetween). Direct connection between the separation vessel 10 and the condenser system 20 helps to ensure easier condensation of liquid from the gas and helps to prevent contamination of any intermediate processing apparatus. In some embodiments, the cooling system 26 may provide a cooling fluid at least partially cooled by the environment. For example, the cooling system 26 may cold introduce air / cooling fluid cooled outside (e.g. fresh air or a liquid cooled in a closed loop system). This may reduce power consumption, for example, in large scale systems. Such systems may be provided in cold climates (e.g. Nordic or arctic environments).

[0035] The condenser 24 is contained within the condensing vessel 30. The vessel 30 comprises a first outlet 32 to allow egress of the condensate. The condensate may comprise a mixture of water, electrolyte and separation fluid 12 (where different from the electrolyte). In an example, the condensate comprises a mixture of KOH and water. The first outlet 32 is operatively connected to a holding vessel 34 to a store the condensate. The holding vessel 34 is operatively connected to the separation vessel 10 to allow return of the electrolyte thereto (e.g. to be recycled or disposed of, as required). In some embodiments, the condensate may simply be disposed of.

[0036] The condensing vessel comprises a second outlet 36 to allow egress of the clean and dry gas. The clean / dry gas may then be stored and / or processed as required.

[0037] The condensing vessel 30 and the separation vessel 10 are provided as separate / discrete vessels (i.e. they are not contained with a single vessel or other housing). This is in contrast the prior art system, where the condenser is provided within a separation vessel. Providing the condensing vessel 30 and the separation vessel 10 as separate vessels reduces expose of the condenser 24 to corrosive substances (e.g. corrosive electrolyte). Furthermore, any corrosion that does occur on the condenser 24 is contained within the separate condensing vessel 30, and thus does not directly contaminate the separation vessel 10. The condensing vessel 30 and the separation vessel 10 may be operatively connected via tubing or hoses etc. This allows flexible positioning of condensing vessel 30 and the separation vessel 10 (e.g. they can be moved independently, provided in any configuration, or provided in separate areas). The condensing vessel 30 and the separation vessel 10 are separable / detachable. This allows interchangeability of the condensing vessel 30 and / or the separation vessel 10 within the system. For example, is greater cooling capacity is required, a large condenser system 22 can be provided within significant modification of the system. The system is therefore modular / interchangeable. Such a configuration is not possible in the prior art system, as the size of the condenser is limited by the size of the separation vessel.

[0038] The presence of the corrosive substances (e.g. the electrolyte) may cause some corrosion of the condenser 24. Filters or the like may be provided in the fluid pathway between the condensing vessel 30 and the separation vessel 10 to filter corrosion particulate. For example, filters may be provided within or adjacent the holding vessel 34. In some embodiments, the sensors may be provided in the fluid pathway between the condensing vessel 30 and the separation vessel 10 to detect corrosion particular or byproducts. The system may then be cleaned or purged in the event such corrosion products are detected.

[0039] In the present arrangement, the condensing system 20 provides both drying, cooling and condensing of the gas. Thus, separate units are not required to performed drying, cooling and condensing accordingly. For example, a drying unit may not be provided. The gas from the condensing system 20 is pure enough that further filtering or processing is not required. For example, a filtering unit may not be provided.

[0040] In some embodiments, processing apparatus may be provided to ensure that the recycled electrolyte comprises the desired characteristics. It can be appreciated that such apparatus may be provided at any point in the fluid pathway between the condenser 24 and the electrolysis cell 4. For example, the processing apparatus may monitor and / or control the pH levels of the electrolyte (i.e. the concentration of the alkaline components).

[0041] It can be appreciated that the above cleaning and drying system may be applied to two or more gaseous products from the electrolysis cell 4. For example, for electrolysis of water, a first cleaning / drying system is provided for the produced hydrogen and a second cleaning / drying system is provided for the produced oxygen. In some embodiments, the first and second cleaning / drying system may comprise one or more shared component. For example, first and second cleaning / drying system may use a single cooling system 26.

[0042] Operation of the system is shown in figure 3. In the present example, the system comprises alkaline electrolysis system using a KOH electrolyte to produce hydrogen and oxygen. It can be understood that such an arrangement is merely exemplary.

[0043] A 30% KOH is provided in the electrolysis cell 4. Electrolysis is performed, and hydrogen and oxygen gas are produced. Both cases contain KOH vapours. Processing of the hydrogen is described, however, it can be appreciated that a similar process will be provided with the oxygen gas. The hydrogen with KOH is provided to the separation vessel 10 and bubbled through 30% KOH separation liquid 12. KOH is filtered out from the hydrogen gas. The filter KOH mixes with the 30% KOH and is then recirculated back to the electrolysis cell 4. Processing may be performed to ensure the concentration of KOH remains at 30%.

[0044] The hydrogen passes to the top of the separation vessel 10, through the outlet 20 and the condenser system 20. Some residual moisture and / or KOH vapour is contained with the hydrogen. The residual moisture / KOH condenses on the condenser 24 and then flows the holding vessel 34. The water and KOH then flow back to the separation vessel 10 for recirculation. Cleaned and dried hydrogen then passes through the outlet 36.

[0045] The present arrangement mitigates the need for scrubbing and drying apparatus. The present arrangement reduces corrosion of the condenser. This helps to improve the longevity of the system. If corrosion does occur, then corrosion particulate is contained with the condensing vessel or otherwise prevented from entering the separation vessel. This helps to prevent the recirculation of said particulate. The separate separation and condensing vessels provide a flexible and / or modular arrangement. Electrolyte is captured and recirculated back to the electrolyte cell to help avoid wastage thereof. The system may provide particular benefit when used in cold environments.

Claims

Claims:1 . A purification system for purifying a gaseous product produced by electrolysis comprising: a separation vessel (10) configured to contain a separating liquid (12), and where the gaseous product is passed through the separating liquid (12) to at least partially remove a contaminant from the gaseous product in use; a condenser vessel (30) operatively connected downstream of the separation vessel (10), the condensing vessel (30) comprising a condenser (24) configured to condense one or more contaminant out from the gaseous product; and where the separation vessel (10) and the condensing vessel (30) are provided as separate, fluidly connected vessels.

2. A purification system according to claim 1 , comprising a holding tank (34) operatively connected to the condenser vessel (30) to receive the condensed contaminant.

3. A purification system according to any preceding claim, comprising a cooling system (26) to provide a cooling fluid to the condenser.

4. A purification system according to any preceding claim, comprising a sensor configured to detect byproducts of corrosion of the condenser (24).

5. A purification system according to any preceding claim, where the separation vessel (10) and the condenser vessel (30) are operatively connected via a conduit, and the conduit is detachable from one or both of the separation vessel (10) and the condenser vessel (30).

6. An electrolysis apparatus (2) comprising the purification system of any of claims 1-5.

7. An electrolysis apparatus (2) according to claim 6, where the separation vessel (10) and / or the holding tank (34) are operatively connected to an electrolysis cell (4) to provide an electrolyte there to.

8. An electrolysis apparatus according to claim 6 or 7, where the electrolysis apparatus (2) is configured to produce at least two gaseous products, and a respective purification system is provided for at least two of the gaseous products.

9. An electrolysis apparatus according to claim 8, where at least two of the purification systems share a common cooling system (26).

10. A method of purifying a gaseous product produced by electrolysis comprising: passing the gaseous product through separating liquid (12) contained in a separation vessel (10) to at least partially remove a contaminant from the gaseous product; condensing one or more contaminant out from the gaseous product using a condenser (24) provided in a condensing vessel (30) downstream of the separation vessel (10); and where the separation vessel (10) and the condensing vessel (30) are provided as separate, fluidly connected vessels.

11. A method according to claim 10, where passing the gaseous product comprises bubbling the gaseous product through the separating liquid (12).

12. A method according to claim 10 or 11 , where the contaminant is an alkaline electrolyte and / or water.

13. A method according to any of claims 10-12, where the separating liquid comprises an alkaline electrolyte.

14. A method according to claim 13, where the alkaline electrolyte comprises sodium hydroxide and / or potassium hydroxide.

15. A method of electrolysis comprising the method of purifying a gaseous product according to any of claims 10-14, where the separating liquid (12) and / or condensed contaminant are recirculated to an electrolysis cell of an electrolysis apparatus.

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