The loop type of a scrubber changes the washwater, and that changes the demands on the monitor. Open loop systems pass seawater through once, closed loop systems recirculate it, and hybrid systems can do either.
A summary of the scrubber types is on the exhaust scrubber washwater discharge page.
How do the three scrubber types differ?
| Type | How it works | Monitoring implication |
|---|---|---|
| Open loop | Seawater passes over the exhaust once and is discharged | Generally the cleanest water, but constant discharge is a problem where discharge is prohibited |
| Closed loop | Seawater is recirculated and cleaned as it cycles | No discharge needed, but the water gets dirtier and more aggressive, which makes cleaning and monitoring harder |
| Hybrid | Can run in open or closed loop | The vessel can choose the better mode, so monitoring must suit both |
Why is closed loop washwater harder to monitor?
Recirculated water carries more of what the scrubber removes and is more aggressive to the equipment. Wetted parts and sample handling matter more. The SMART ESM wetted parts include stainless steel, glass, PVC-u, acetal, nylon, Delrin and acrylic tube (see the SMART ESM technical overview).
What does a hybrid scrubber change?
A hybrid vessel can switch to closed loop where open loop discharge is banned. The monitor should work in either mode and the system should report which mode is active. The SMART ESM control module warns if its flow switch status does not match the scrubber operating state.
| Key point: On a hybrid scrubber, check that the monitor and the scrubber control system agree on the operating mode. |
How does the discharge ban affect this?
Port and coastal bans push vessels towards closed loop operation, so the washwater monitoring must still be reliable in that mode. Read more in our open loop scrubber discharge ban article.
Frequently asked questions
Is closed loop washwater monitored differently?
The same parameters apply, but recirculated water is dirtier and more aggressive, which makes cleaning and monitoring harder.
What is a hybrid scrubber?
A scrubber that can run in either open loop or closed loop, so the vessel can choose the better method.
Can the SMART ESM be used on all scrubber types?
The product page states it suits open loop, closed loop and hybrid scrubbers, for new builds or retrofits.
What happens if the monitor and scrubber state disagree?
The SMART ESM control module warns if the flow switch status does not match the scrubber operating state.
Which Rivertrace products are relevant?
| Product | Technology and use |
|---|---|
| SMART ESM | Washwater monitor for PAH, turbidity, pH and temperature. Open loop, closed loop and hybrid scrubbers |
| Calibration Check Kits | Used to check the PAH and turbidity readings onboard |