For a miniaturised high-pressure stack electrolyser, MARCH PUMPEN configured a magnetic-drive external gear pump to deliver a 30 percent potassium hydroxide solution (KOH, caustic potash). The project-specific TEF-MAG® 201 is designed for process temperatures of 70 to 90 °C, a system pressure of 25 bar and flow rates of 20 to 250 l/h.
The wetted parts are made of chemically resistant non-metallic materials such as electrically conductive PEEK, silicon carbide (SSiC), graphite and FFKM. For use in a hydrogen environment, the pump design was configured to ATEX II 2G, Zone 1, in line with the project requirements.
The challenge: pumping hot caustic potash at high system pressure
In alkaline electrolysis, an aqueous potassium hydroxide solution serves as the electrolyte. In this project the pump has to deliver 30 wt% KOH under demanding pressure and temperature conditions. A low flow rate meets a high inlet and differential pressure.
In addition, chemical resistance to hot caustic potash, non-metallic wetted parts and explosion protection requirements had to be taken into account. The pump design therefore had to combine chemical resistance, temperature resistance, pressure resistance, low flow rates and the project-specific ATEX design.
| Medium | Potassium hydroxide solution (KOH, caustic potash) |
|---|---|
| Concentration | 30 Gew.-% KOH |
| Process temperature | 70–90 °C |
| Inlet pressure | 16 bar |
| Differential pressure | 9 bar |
| Pump system pressure | 25 bar |
| Flow rate | 20–250 l/h |
| Hydrostatic pressure test | 37,5 bar |
| Explosion protection | ATEX II 2G, Zone 1 |
| Operation | Frequency converter |
| Pump type | TEF-MAG® 201 |
| Pump casing | PEEK, electrically conductive |
|---|---|
| Containment shell | PEEK, electrically conductive |
| Pressure reinforcement of the containment shell | external stainless steel sleeve |
| Shafts | SSiC |
| Gears | PEEK-HPV |
| Gear cage | PEEK-HPV |
| Plain bearings | Graphite |
| O-rings | FFKM |
| Inner magnet | PEEK, electrically conductive |
The external stainless steel sleeve increases the pressure resistance of the containment shell but does not come into contact with the pumped medium. The wetted parts therefore remain non-metallic.
The solution: magnetic-drive TEF-MAG® 201 made of conductive PEEK
The customer-specific pump solution is based on the patented magnetic-drive external gear pump TEF-MAG®. External gear pumps are suited to applications in which small, defined flow rates have to be pumped at comparatively high differential pressures. The TEF-MAG® delivers an almost pulsation-free flow.
Power is transmitted via a magnetic coupling. The pump therefore needs no dynamic shaft seal between the pump chamber and the environment. A typical potential leakage point is thus avoided by design, an important advantage when handling aggressive and safety-relevant media.
For the required combination of chemical resistance, mechanical strength, temperature and pressure load and the electrical requirements of the project-specific ATEX design, an electrically conductive PEEK material was selected together with a material manufacturer.
Why a gear pump for KOH in alkaline electrolysis?
The combination of a low flow rate and a high differential pressure places special demands on pump technology. In this electrolysis project, the pump has to deliver a flow rate of 20 to 250 l/h while coping with an inlet pressure of 16 bar and a differential pressure of 9 bar. This results in a system pressure of 25 bar.
For this application, the TEF-MAG® 201 combines several decisive properties:
- pumping 30 wt% KOH at 70–90 °C
- low flow rates of 20–250 l/h
- pumping against 9 bar differential pressure at 25 bar system pressure
- almost pulsation-free flow
- magnetic-drive design without a dynamic shaft seal
- chemically resistant, non-metallic wetted materials
- electrically conductive PEEK for the project-specific design
- ATEX II 2G for use in Zone 1
- flow rate adjustment via a frequency converter
What is the function of KOH in alkaline electrolysis?
In alkaline water electrolysis, water is split into hydrogen and oxygen using electrical energy. An aqueous potassium hydroxide solution serves as the alkaline electrolyte and enables ion transport between the electrodes.
At the negatively charged cathode, water is reduced. This produces hydrogen and hydroxide ions (OH−). The hydroxide ions move through the alkaline electrolyte or separator to the positively charged anode, where they are oxidised and oxygen is formed.
Overall reaction: 2 H2O → 2 H2 + O2
A separator or diaphragm divides the electrode compartments and reduces the mixing of the product gases formed at the cathode and anode. KOH is used as the electrolyte and is not consumed stoichiometrically. In the high-pressure electrolyser described here, the concentration of the potassium hydroxide solution is 30 wt%.
If the electrolyser is operated with electricity from renewable energy, the hydrogen produced can be classified as renewable or green hydrogen.
Why are the materials of the KOH pump decisive?
Concentrated caustic potash at elevated temperatures places high demands on the materials of a pump. At the same time, the pressure load, explosion protection and the requirement for non-metallic wetted components had to be taken into account in this project.
Whether a material is suitable for the application always depends on the specific combination of medium, concentration, temperature, pressure, mechanical stress and plant requirements. A blanket division into unsuitable metals and suitable plastics would not be technically correct.
A specific combination of materials was therefore chosen for this application. The pump casing and other key components of the TEF-MAG® 201 are made of electrically conductive PEEK. In addition there are components made of SSiC, PEEK-HPV, graphite and FFKM.
Why is electrically conductive PEEK used?
PEEK combines high mechanical strength, temperature resistance and chemical resistance. For this pump application, a controlled electrical conductivity was also required. An electrically conductive PEEK variant was therefore selected together with a material manufacturer.
This made it possible to realise a pump design with non-metallic wetted parts that is at the same time matched to the mechanical, thermal and electrical requirements of the project. It shows that in demanding hydrogen and electrolysis applications, chemical resistance alone does not decide the choice of material. Pressure, temperature, explosion protection and structural load have to be considered together.
Result: customer-specific pump solution for the high-pressure electrolyser
With the TEF-MAG® 201, a pump configuration was designed for the specific requirements of the miniaturised high-pressure stack electrolyser. The solution combines pumping 30 wt% KOH at 70 to 90 °C with a system pressure of 25 bar and low flow rates between 20 and 250 l/h.
Magnetic coupling, pumping principle, electrically conductive PEEK materials and the design for ATEX Zone 1 were deliberately matched to the project requirements. The project shows that for pumps in alkaline electrolysis, it is above all the interplay of pumping principle, material selection, pressure resistance, temperature resistance and explosion protection that determines a suitable solution.
Frequently asked questions about KOH pumps for alkaline electrolysis
Which pump is suitable for KOH in alkaline electrolysis?
The choice of pump depends on the KOH concentration, temperature, flow rate, inlet and differential pressure and the requirements for materials and explosion protection. In the application described here, a magnetic-drive TEF-MAG® 201 external gear pump is used for 30 wt% KOH at 70–90 °C and a system pressure of 25 bar.
Which materials come into contact with 30 percent caustic potash?
In this application, the wetted components are made of, among others, electrically conductive PEEK, PEEK-HPV, SSiC, graphite and FFKM. The actual suitability of a material must always be assessed on the basis of concentration, temperature, pressure and other operating conditions.
Why is a magnetic-drive pump used?
With a magnetic coupling, power is transmitted to the inside of the pump without a drive shaft with a dynamic shaft seal passing through the pump casing. A potential leakage point is thus avoided by design. This is a particular advantage with aggressive or safety-relevant pumped media.
What flow rate does the KOH pump achieve?
In this application, the TEF-MAG® 201 is designed for a flow rate of 20 to 250 l/h. Operation via a frequency converter makes it possible to adjust the flow rate within the intended operating range.
What pressure is the pump designed for?
In this application the inlet pressure is 16 bar and the differential pressure is 9 bar. This results in a pump system pressure of 25 bar. The hydrostatic pressure test is carried out at 37.5 bar.
Can the pump be used in an ATEX area?
The project-specific pump design described here was designed for ATEX II 2G and use in Zone 1. For other applications, the required design must be checked against the respective zone and operating conditions.
Other suitable pump types
Which pump is suitable for an electrolysis or hydrogen application depends on the pumped medium, concentration, flow rate, pressure, temperature, material requirements and plant concept. Besides the TEF-MAG®, other MARCH PUMPEN series can be considered depending on the process conditions:
Pump sizing for alkaline electrolysis and KOH applications
Are you planning an electrolyser or a comparable plant and looking for a pump for potassium hydroxide, caustic potash or other demanding process media? MARCH PUMPEN supports you in selecting and customising the right pump technology.
Please send us the relevant process data: pumped medium and concentration, operating and maximum temperature, flow rate, inlet and outlet pressure, material requirements and the required ATEX zone. On this basis we will check the suitable pump and material configuration for your application.
