Hydrogen Electrolysis: Flow and Pressure Guide

Scientists and engineers worldwide are diligently engaged in the refinement of the electrolysis process for hydrogen production. It presents many challenges, including fluctuating power inputs from renewable energy sources and the ongoing pursuit of cost reductions. The following guide addresses the common flow and pressure challenges encountered in electrolyser development and provides solutions to tackle those issues.

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Diagram of CODA controllers and Alicat back pressure regulators for electrolysis hydrogen generation regulation & testing.

Back Pressure Control Challenges

Maximizing electrolysis efficiency requires fast and responsive pressure control to maintain the differential or balanced pressures between oxygen and hydrogen.

1. Process conditions change quickly and pressure is difficult to hold steady.
  • Custom sized valves on back pressure controllers provides the steadiest of control, given process conditions.
  • PID tuning gives users in-field precision control on how fast a setpoint is reached as well as control stability. 
2. Wet gases corrode instrumentation.
  • Anti-corrosive pressure controllers resist corrosion, even when exposed to high humidity. 
3. Hot gases degrade electronics in electronic back pressure controllers.
  • High temperature builds include modifications to the electronics and temperature compensation for device longevity and top performance between 60°C and 100°C. Remote displays protect electronics while providing quick monitoring and system service.
4. Extremely high temperatures and pressures and highly corrosive gases require industrial-grade instruments.
Pressure Controllers Family

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Flow Validation Challenges

Validation of the resultant H2 and O2 flows is critical to determining electrolyzer performance, but barriers can stand between engineers and dependable results.

1. Pressures or flow rates oscillate through production cycle.
  • Mass flow meters with integrated totalizers and flow averaging provide easy monitoring and remove guesswork
2. Wet gases (or a failed dehumidifier) corrode instrumentation.
  • Anti-corrosive mass flow meters provide long-term resistance to corrosion.
  • Placing the mass flow meter in a warm water bath helps avoid water vapor condensing within the mass flow meter.
  • Differential-pressure-based mass flow instruments must only be cleaned when exposed to water, compared to thermal mass flow instruments that must be replaced. 
3. Humidity changes, affecting mass flow readings.
  • Relative humidity compensation on mass flow meter offers additional accuracy, even when humidity levels change. RH sensors can be integrated into Alicat mass flow meters, or data from a remote sensors can be reported data digitally. 
4. Hot gases degrade electronics in digital mass flow meters.
  • A high temperature build option includes modifications to the electronics and temperature compensation for device longevity and top performance between 60°C and 100°C.
  • Remote displays protect electronics, but still allow quick monitoring and system service.

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DI Water Control Challenge

1. Flow rates are low, but precision is essential.
  • Coriolis mass flow technology is compatible with liquids, and measures flow rates as low as 0.08 g/h, while maintaining an incredibly high accuracy (±0.2% of reading or ±0.05% of full scale).

See Coriolis and back pressure controllers in process:


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Alicats in Action

Maximize electrolyser efficiency with real-time hydrogen and oxygen measurement

Use mass flow meters to verify hydrogen and oxygen gas flows in PEM electrolysers.

Nel hydrogen setup with mass flow meter

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