MARINE STEAM BOILER -FUEL OIL SYSTEMS

     
                   

  A.   Fuel Oil header
The 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 filters
Clean 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 valves
Shut off valves for cleaning of the filters. The valves should normally be open.

D.   Fuel Oil pumps
Each 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 than being started upon a pump motor failure.

E.    Shut off non return valves
These 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 heater
The 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


      1.     Change over valve, Heavy Fuel Oil to Diesel Oil

      The 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 control

     The pressure control loop adjusts the fuel oil pressure by means of the pressure controller and the fuel oil return valve. 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 control
The 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 control
On 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 valves
Almost 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 valve
This 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 120ºC and water that might occur at the bottom of the tank will vaporize and in worst-case cause damage to the tank.

 Fuel oil drain valve
Some 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