(i) Running (5 marks)

When the main engine is running, the gas side of the waste heat boiler/economiser is cleaned by soot blowing (on-load cleaning):

1. The soot blowers (steam or compressed air) are operated in sequence, blowing steam/air through the tubes to remove the soot and deposits from the gas side.
2. The soot blowing is done at regular intervals (as per the maker's schedule) and when the boiler pressure is adequate.
3. The soot blowers are operated one at a time, in the correct sequence, to avoid overloading the boiler.
4. The boiler water level and pressure are monitored during soot blowing.
5. The soot is collected in the hopper and removed.

This is done while the engine is running because the exhaust gas flow helps to carry the soot away and the boiler is at operating temperature.

(ii) Stopped (5 marks)

When the main engine is stopped, the gas side is cleaned by:

1. Isolating the boiler (closing the gas inlet/outlet dampers) and allowing it to cool.
2. Opening the access doors/cleaning ports.
3. Removing the soot and deposits manually (by brushing, scraping, or using compressed air/water) from the tubes and the gas passages.
4. Inspecting the tubes for damage (corrosion, erosion, leaks) and cleaning the soot hopper.
5. Re-closing the access doors and restoring the boiler to service.

This is a more thorough cleaning than on-load soot blowing and is done during a port stay or when the engine is stopped.

If the waste heat boiler/economiser cannot be operated due to a tube failure (e.g. a leaking tube), the main engine can still be operated by:

1. Isolating the boiler/economiser from the exhaust gas system: closing the gas inlet/outlet dampers (or by-passing the boiler) so the exhaust gas flows directly to the funnel, and the boiler is taken out of the gas circuit.
2. Isolating the boiler from the steam/water system: closing the steam and water valves so the boiler is isolated from the steam system, and draining the water if necessary.
3. Ensuring the boiler is safe: the failed tube is isolated (or the boiler is blanked off) so that no water can leak into the exhaust gas system.
4. Operating the main engine normally, with the exhaust gas going directly to the funnel (the boiler is by-passed).
5. Monitoring the engine and the exhaust system; the engine can run at full load because the exhaust gas is not restricted by the boiler.
6. Arranging for the repair of the boiler at the next opportunity (port stay), and providing alternative steam generation (e.g. an auxiliary boiler) if steam is needed.

The engine is operated with the boiler isolated and by-passed, so the tube failure does not affect the engine operation.