Marine auxiliary boiler is only used in port and the exhaust boiler caters for all heating and steam needs while at sea. Generally if the burner routines are carried out religiously and the filters are cleaned, there is no major maintenance or routine that needs to be done
In this article the author is relating a problem faced on one ship and the troubleshooting done.
One day the boiler shut down after flame failure alarm came. After many futile attempts to restart the boiler on HFO, the boiler was changed over to diesel and manually fired. The auto firing mode was non operational and the FO pressure low alarm was coming and fuel pumps stopping.
The following checks were done that helped to restart the boiler:
- Correct pressure setting of the boiler: Generally the Fuel Oil pressure at the burner must be between 2 to 4 bars. In case the pressure is too high more fuel will be sent and the air fuel ratio disturbed. Less fuel pressure will give a lean mixture and flame will be unsteady and fail.
- The fuel pump might trip on overload. Check the pump for mechanical damage and jamming. It should be free to turn by hand.
- The over current relay may be at fault. Check the OCR setting and try increasing it if not correct. There is generally a test lever at back of OCR for testing.
- The fine filter also called as dirt trap on the burner may be dirty.
- The pressure transmitter may be giving wrong pressure feedback, check the wires.
- The pressure transmitter for DO is normally different from FO line, Check this pressure transmitter.
- The PLC will give command to stop due to pressure transmitter fault. Try calibrating the transmitter with the Master calibrator and check output. Output should be between 4 to 20 mA.
- The fuel oil line may be choked and blocked. This can be ascertained by high back pressure.
- The fuel oil temperature should be around 90 deg C. Check heater for correct functioning. High temperature can cause vapor lock that can lead to ignition failure.
- The PLC (Programmable Logic Controller) has a reset buttons and resetting it restores the default values, often solving the problem.
- Check any error code flashing on the display of the PLC or logic module and consult the manufacturer.
- If a fuel oil (FO) low pressure alarm is generated it may be due to restriction in the line going to the pressure transmitter. There are also valves for isolation, they must be open.
- Local FO pressure gauge may be replaced with a new / calibrated one to get correct picture.
- If the boiler is firing on diesel oil (DO) then the burner should be generally ok, however if filters are partially dirty or the nozzle is partially choked, it may lead to this problem. Overhauling the burners may give correct picture. If the nozzle is choked it will create a back pressure.
- There are two fuel oil (FO) pumps, try starting the second pump.
- Check supply and return lines for correct functioning of valves.
- Check the megger reading of the pump motor.
- Check the suction line change over and return line change over valves.
- In case the system includes separate pressure control valves for HFO and MDO, change over the three way valve from MDO position to HFO position or close the stop valve before the MDO pressure control valve.
- Near the FO change over valves and near the burner assembly, there are pressure regulating valves on MDO and HFO line, try to adjust the pressure within 3 to 4 bars for HFO. Moreover there may be another pressure regulating valve near the pressure gauge of burner assembly. Use this for fine adjustment.
- If the fuel pumps are tripping in manual firing then there is pump problem or back pressure.
- In manual mode PLC should not be involved and as still pump is tripping there is some other fault.
- Check the input voltage to the pump and also the current by clamp meter.
- If both the pumps are tripping then it indicates Pressure switch or back pressure problem.
The information was related to Saacke boiler on board but may slightly differ with the make of the boiler and the piping system and automation on board.