Electrolysis and Electrolyzer Pressure Control - Equilibar

Electrolysis and Electrolyzer Pressure Control

Back pressure regulators for electrolysis

  • schematic of alkaline water electrolysis

What is electrolysis? Electrolysis uses an electric current to energize a chemical reaction that will not occur naturally. Water electrolysis is an electrochemical process using electricity to split water into hydrogen and oxygen. Carbon dioxide electrolysis is the reduction of CO2 into CO. These reactions can occur in an electrolysis cell or an electrolyzer unit containing an electrolytic medium between an anode and cathode. Pressure control during electrolysis is an important consideration and depends on the electrolyzer technology.

Electrolyzer Technology

Technologies using Polymer Electrolyte Membrane stacks, also called Proton Exchange Membranes or PEM, were designed for higher efficiency water electrolysis than the earlier alkaline solution electrolyzer. These PEM electrolysis systems may be designed as a balanced pressure system, where O2 and H2 operate at the same pressure, or as a differential pressure system where O2 and H2 operate at different pressures. The advantage of high pressure electrolysis of H2 is that it minimizes the need for a second stage mechanical compression to pressurize for storage. In either the differential or balanced pressure designs, pressure regulation of the O2 and H2 gases is extremely important to the efficiency and life of the PEM electrolyzer.

In CO2 electrolysis, research is ongoing to find efficient electrolyzer technology to use at large scale. Solid oxide electrolysis cells (SOECs), molten carbonate electrolysis cells (MCECs), and gas diffusion electrodes (GDE) are all being studied. Electrolyzers assisted by catalysts, creating a multilayer electrolyzer stack is also under investigation.

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What are the benefits of the Equilibar electrolyzer solution?

Equilibar has back pressure regulators (BPRs) to control the electrolysis process at a range of pressures, high or low, with extreme precision. The unique multi-orifice design of Equilibar© BPRs allows for stable pressure control within a wide Cv range. This is particularly important for electrolyzer systems which can involve mixed phase (liquid-gas) flow, a wide range of pressures and flows, or varying pressures on the outlet of the BPR.

Oftentimes in production electrolyzer systems it is advantageous to have minimal pressure drop across the BPR, with the pressure downstream being as high as possible to reduce the need for pumping up the gas to a higher pressure for storage or usage. Equilibar BPRs, when sized properly for the required Cv, can maintain stable pressure control with either minimal pressure drop across the BPR, or with a large pressure drop, depending on the case. Traditional control valves and spring-loaded BPRs often cannot operate with a very small dP across the valve. Conversely, large pressure drops across the valve that would normally cause cavitation or otherwise damage traditional single seat valves are no issue for Equilibar BPRs.

Since the pressure control of the Equilibar regulator is not reliant upon an external transducer and PID loop, the BPR reacts nearly instantaneously to changes in flow and adjusts its Cv accordingly to maintain the desired pressure. This stable, precise pressure control is particularly important when dealing with sensitive proton exchange membranes which will rupture if the dP across them is too great. The dome-loaded control of our BPRs also means that that it is possible to control the pressure on both the cathode and anode side of the electrolyzer with one pilot connected to the dome of two BPRs, ensuring that the pressure on both sides of the PEM closely match each other.

The simplicity of the Equilibar design also allows us to easily tailor the materials of construction for the challenges of high pressure electrolysis. The regulator body can be easily machined from high nickel containing alloys like brass, bronze, or Monel to be safely used with high pressure pure oxygen. For alkaline electrolysis, the diaphragm and O-ring materials can be chosen to be compatible with the caustic electrolyte solution. Equilibar valves can be cleaned for oxygen service upon request as well.

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Equilibar technology used for electrolysis to generate oxygen in space

Flow cell electrolysis, which is used for spaceflight applications, uses a flowing water electrolyzer to generate enough oxygen from water to keep up with the crew’s metabolic requirements. Many of the current electrolyzer designs require a downstream gas-liquid separation process, presenting challenges in a microgravity environment. One complication is two-phase flow caused by bubble generation in the electrolyzer. Researchers at the University of Colorado at Boulder proposed an alternative electrolyzer configuration and built a prototype using an Equilibar® vacuum regulator.

Read the case study in the link to the right.

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Equilibar back pressure regulators used in “artificial photosynthesis” to make power from renewable sources

Our partners at Pressure Control Solutions (PCS) in the Netherlands worked with Evonik and Siemens on a project where the two companies combined CO2 electrolysis and gas fermentation in an “artificial photosynthesis” process they call The Rheticus Project. The project links the companies’ innovations in fermentation and electrolysis to make power from renewable energies.

PCS was called upon to find a solution for this project where a range of precision pressure setpoints was required. The customer found the Equilibar BPR technology to be “superior to conventional valve technologies”. Additionally, with the solution PCS designed, the customer was able to avoid crystallization issues related to salt in the electrolysis process. Read more in the case study on PCS website.

What are the products from water and CO2 electrolysis used for?

Energy researchers are optimizing water electrolysis for producing hydrogen as an energy source from renewable resources. Wind turbines and PV cells can be used as electricity sources for the electrolyzer to produce hydrogen for hydrogen fuel cells. The goal is to increase the use of renewable energy and decrease carbon emissions.

Oxygen gas produced in the reaction may be used for a variety of applications, including breathable O2 for space travel and submarines.

Carbon Monoxide is used in a pure form as a source for many industrial and fine chemicals or together with H2 in synthetic gas. When CO2 and H2O are reduced in a co-electrolysis process, syngas is produced and used to make fuels. It’s a win-win process taking CO2 from the atmosphere and using it to make renewable fuel.

About Equilibar back pressure regulators

The Equilibar® back pressure regulator is dome-loaded and, with its novel multiple orifice design, delivers instantaneous reliable control in the most challenging applications. The dome-loaded design means it requires a fluid (typically air or nitrogen) pressure applied to the dome of the BPR matching the desired inlet pressure. This setpoint pressure can be manually or electronically controlled. Learn how Equilibar back pressure valves work.

Our team of experienced engineers offer detailed guidance in choosing the pressure control products for a specific condition. Special considerations are taken into account for oxygen rich processes seen in electrolysis.

Contact an Equilibar engineer to discuss your application in more detail.

schematic of alkaline water electrolysis

GSDM8 high pressure 1 inch back pressure regulator

Equilibar GSDM8 back pressure regulator for electrolyzer pressure control

image of EPR 3000 controlling pilot of Equilibar H3P high pressure back pressure regulator

Equilibar LF back pressure regulator for low flow electrolysis pressure control

Download a brochure
Equilibar EVR used for electrolysis in space for oxygen generation

Case Study: Prototype electrolyzer for generating oxygen in space


Artificial photosynthesis using Equilibar BPR

Case Study: Artificial Photosynthesis using electrolysis and fermentation



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