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Marine Boilers Heavy Fuel Oil

A. Fuel Oil headerThe Fuel Oil header should be a standing up relatively large pipe with a deaeration pipe to a higher level than the

fuel oil service tanks; some times it's connected to the top of the diesel oil service tank.

B. Fuel Oil filtersClean the Fuel Oil filter frequently. If the filters are clogged the fuel oil might vaporize in the pump and cause

damage. A differential pressure meter across the filter would be a good help to have the filters cleaned in time.

C. Shut off valvesShut off valves for cleaning of the filters. The valves should normally be open.

D. Fuel Oil pumpsEach pump should have sufficient capacity to run both boilers on maximum load. Normally one pump is running

and the other is standing-by. The stand-by pump should start upon low pressure in the process line rather thanbeing started upon a pump motor failure.

E. Shut off non return valvesThese valves have to be non-return type, or a shut off valve and a non-return valve. The valves should always be

open on both pumps, so the stand-by pump can start automatically.

F. Fuel Oil heaterThe fuel oil heater is a heat exchanger that must have a safety relief valve.

Always install a safety relief valve if a fuel oil volume can be shut up and heated.

G. Burners

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7/28/2019 Marine Boiler Heavy F.O

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Marine Boilers Heavy Fuel Oil

H. Make-up water pumpFrom softener unit.

1. Change over valve, Heavy Fuel Oil, HFO, to Diesel Oil, DOThe three-way valve ought to be provided with a limit switch that breaks the electric circuit and shut off the fuel

oil heating valve, in the control loop 3 , avoiding the diesel oil from being heated over its flashpoint.

2. Fuel oil pressure controlThe pressure control loop adjusts the fuel oil pressure by means of the pressure controller and the fuel oil returnvalve. The pressure is measured after the fuel oil heater to get accurate pressure to the burners. The return valve

before the fuel oil heater recycles cold fuel to protect the pumps from overheating.

3. Fuel oil temperature controlThe temperature control loop adjusts the fuel oil temperature by means of the temperature controller and the

steam inlet control valve. The temperature controller's set point should be set to assure an adequate fuel oil

viscosity for the actual burners.

Sometimes the control valve is installed in the condensate outlet line. This requires a smaller control valve and

the control function works even better. However, this installation is for some reason not so very common.

4. Fuel oil flow controlOn large boilers the fuel oil flow controller gets its setpoint from the burner management system or the airflow

controller to achieve a proper air-fuel mixture.

On smaller boilers the fuel oil flow control valve often is connected to the combustion air damper by means of a

metal rod or wire.In both cases the steam pressure in the boiler sets a suitable fuel oil flow.

5. Fuel oil shut of valvesAlmost every classification society and other authorities requires two shut of valves for the fuel oil, mechanically

in series and electrically in parallel.

6. Fuel oil recirculation valveThis valve does not always exist, but if it does, the valve should open when the fuel oil shut of valves closes. The

recirculation has advantages and disadvantages.

The advantage is that it keeps the fuel oil line warm when the burner is off. The disadvantages is that it will, in the long run, heat up the fuel oil passing through the oil pump that

might cause problem with cavitations.

Leading the recirculation fuel oil back to the fuel oil service tank wouldn't be wise. The fuel oil's temperature

often exceeds 120C and water that might occur at the bottom of the tank will vaporize and in worst-case cause

damage to the tank.

7. Fuel oil drain valveSome authorities require a drain valve to be installed between the shut off valves. The burner management

program mustn't open the drain valve before the shut off valves are totally closed and it should close the drain

valve before the shut off valves open.

8. Smoke density meterHigh smoke density indicates deficiency of air.

9. Oxygen meterThe smoke duct from the boiler to the funnel is designed with respect to the pressure drop and smoke velocity at

maximum firing. At minimum firing the smoke velocity can be very low and along the sides of the smoke duct a

downdraught can occur. Therefore the O2 probe ought to be located as close to the centre of the smoke duct as

possible.

10.

ThermometerNormally a thermocouple or a resistance-thermometer. This temperature should be recorded since a slowly

increasing temperature indicates accumulation of soot on the boilers heating surfaces and a rapid rise in

temperature might indicate a soot fire.

11. Difference pressure transmitterThis difference pressure should be recorded since increasing difference pressure indicates accumulation of soot

on the boilers heating surfaces.

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