Vertical multistage pumps for alkaline water electrolysis 

Here’s a project we were involved in to support the large scale production of green hydrogen using alkaline water electrolysis. 

Hydrogen is one of the most important chemicals on the planet and it’s made from various techniques using renewable and non-renewable energy. 

Making greener hydrogen 

At the moment, it’s mainly produced from fossil fuels, which obviously has a negative impact on the environment. In contrast, hydrogen produced using alkaline water electrolysis can result in zero greenhouse gas emissions, if renewable energy is used to generate it.  

So, the process of alkaline water electrolysis can produce greener hydrogen and is an important step towards environmentally friendlier energy production.  

This is why North Ridge Pumps were excited to take part in this project by supplying two high pressure vertical multistage pumps. 

What is alkaline water electrolysis? 

It’s a chemical process that uses an electrolyser to separate water molecules (H2O) into hydrogen gas (H2) and oxygen gas (O2) using electricity. 

Alkaline water electrolysis is crucial for the future of large-scale hydrogen production. That’s because it offers a proven, cost-effective technology which can produce large quantities of green hydrogen. 

What’s more, when generated using renewable energy sources like wind, solar and tidal power for the electrolysis process, hydrogen production can be completely carbon emission-free.  

This clearly makes a major contribution to net zero efforts which are taking place around the world, to address climate change and transition to a more viable energy future. 

What’s the process? 

The electrolyser has two electrodes - one positively charged anode and one negatively charged cathode. These are immersed in a 30% potassium hydroxide (KOH) caustic aqueous solution, and separated by a diaphragm or membrane. 

During electrolysis with KOH, water is split into hydrogen and oxygen. When an electric current is applied to the electrolyte, it induces the reduction of water molecules at the negative electrode, resulting in the production of hydrogen gas. Simultaneously, oxidation of hydroxyl ions occurs at the positive electrode, producing oxygen gas.  

The resulting mixture of hydrogen and oxygen gases can be utilized to generate electricity or as a fuel source. The only by-product of this electrolysis process is water, making alkaline water electrolysis with KOH a sustainable and environmentally friendly solution for green energy generation. 

Advantages of alkaline water electrolysis 

Other electrolysis technologies are available including proton exchange membrane electrolysis (PEM), solid oxide electrolysis (SOEC) and anion exchange membrane electrolysis (AEM). However, alkaline water electrolysis (AWE) offers significant advantages over all of these other processes: 

• Energy efficient 

With AWE, a large part of the electricity put in is converted into hydrogen gas. The level of efficiency depends on the composition of the electrolyte solution usually a 30% potassium hydroxide (KOH) caustic aqueous solution, the temperature and the electrode material used. Generally, it’s around 70% to 80%  

• Environmental friendly 

AWE can be powered by renewable energy sources such as wind, tidal or solar, making it truly green hydrogen that has a negligible contribution to greenhouse gas emissions 

• Scalable 

AWE can be easily scaled right up to megawatt-range production levels. This means it offers outstanding flexibility to meet varying consumer energy demand through the year 

• Cost-effective 

AWE uses catalysts that are cheaper and last longer than those used in PEM electrolysis. This makes it a more cost-effective way to produce green hydrogen 

• Safer 

AWE is a clean and environmentally friendly process using a proven technology with little risk of gas crossover problems or catalyst poisoning 

• Purer hydrogen 

Thanks to the better separation of the hydrogen and oxygen gases, AWE produces high purity hydrogen gas, which is essential for some applications like fuel cells 

Our project specification 

Here at North Ridge Pumps, we can specify a large range of pumps for a wide variety of industrial applications and sectors. 

What’s more, we’re not restricted to just one pump technology. Our experienced technical team enables us to deliver a bespoke solution for your needs, so we can always select the most cost-effective pump for any particular client, project or application.  

For this particular hydrogen gas generation project which used alkaline water electrolysis, we specified two high pressure vertical multistage pumps.  Alternative pump designs and systems are available, including horizontal pumps, so why did we choose this specific design? 

Vertical multistage pumps vs horizontal centrifugal pumps 

Taking into account the requirements of this application, and the area available to house the processing system, a vertical multistage pump was selected over a horizontal pump due to its smaller footprint. 

Another factor was that the vertical multistage pump had an overall casing pressure that would be able to take up to 63 bar of pressure. Vertical pumps also have a sleeve bearing at the pump end lubricated by the pumped medium, ensuring continuous and efficient operation.  In contrast, horizontal pumps feature a heavy duty thrust bearing located at the opposite end to the drive end which was not required. 

What does multistage mean?

Centrifugal pumps, whether horizontal or vertical, typically feature a single impeller, while multistage pumps incorporate multiple impellers arranged in sequence.  

Adding extra impellers allows the pump to generate significantly higher pressures than a single impeller of maximum diameter could achieve. This is because as an impeller increases in diameter, the side friction also increases, reducing overall pump efficiency. To overcome this limitation and achieve high pressures, additional impellers are added along the shaft in stages, known as ring sections. 

More impellers for higher pressure 

These additional ring sections increase the total head and shaft power proportionally to the number of stages added, without negatively impacting the flow rate. In essence, multistage pumps are highly efficient and can offer multiple duty points through the use of a variable speed drive or multiple outlets on the same pump.  

They excel in applications requiring high-pressure circulation, boiler feed, and pressure boosting of clean fluids. Additionally, they can handle slightly contaminated fluids if the pumps are larger and designed with sufficient clearance to allow solids to pass through. 

For this hydrogen generation project, we selected vertical multistage pumps with an inlet pressure of 40 bar and a differential pressure capability of up to 10 bar. Crafted from robust stainless steel, these pumps achieved flow rates ranging from 50L/min to 150L/min. 

If you have a fluid transfer application requiring the movement of sensitive fluids, solids or viscous materials and aren’t sure which pump to specify, speak to North Ridge Pumps to see how we can help.