05Maintenance

Before you start

The check lists

Daily or per shift

• Scan the stack and the external loop: no electrolyte, water or gas leaking at the ports, the fittings or the cell edges.
• No white crystals around the ports or fittings, which can be dried KOH.
• The electrolyte flow and temperature are stable near target.
• The stack voltage is stable for the current setpoint.
• The hydrogen outlet and the oxygen and electrolyte return are unobstructed, and the two paths are not mixed.

Weekly

• Review the records and trends: stack voltage against current, the spread between cells, the stability of flow and temperature, and any recurring abnormal events.
• Inspect the tubing, fittings and supports for wear, discolouration, crystal residue, weeping leaks, and any load on the ports.
• Inspect the DC cable routing and the terminal area for discolouration or signs of heat, looseness and corrosion.

Monthly

• Check the electrolyte condition, and replace it if any criterion in the next section applies.
• Update the maintenance and operating records: run hours, start-stop cycles, electrolyte replacement dates, observations and corrective actions.

Changing the electrolyte

KOH is not consumed by electrolysis. Water is, and you make that up during operation. The electrolyte is therefore replaced by its condition and the performance trend rather than on a fixed interval. Consider replacing it when any of the following appears.

• Cell voltage rises continuously at the same current compared with earlier operation.
• Where you measure individual cells, the spread between them widens over time.
• The colour or clarity changes, or precipitate appears in the tank or the loop.

The procedure

1. Perform a normal shutdown and let it cool to a safe temperature by your site practice.
2. Depressurise the external loop and drain the loop and tank into labelled, alkali-compatible containers.
3. Dispose of the used electrolyte to regulation and your site procedures.
4. Make up fresh 0.1 M electrolyte, refill the tank and purge air from the loop.
5. Restart circulation, check for leaks at every fitting and port, then resume electrolysis.

Cleaning

• Wipe the exterior with a soft cloth dampened with clean water.
• Wipe white crystals off with a water-dampened cloth, since KOH is water-soluble, then wipe again with clean water and dry.
• Deal with a spill by your site spill response procedure.

Reading the performance trend

Stack voltage rises over time. The point of watching the trend is to separate gradual change from an abnormal change caused by off-nominal conditions.

• Record the stack voltage periodically at one or more fixed operating points. Conditions that change every time give you noise, not a trend.
• If you can measure individual cell voltages, record the spread between cells too. A widening spread matters even when the average holds.
• Keep the run hours, start-stop cycles, setpoints and any abnormal events with it.