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This combustion system is designed to supply two oil fired steam boilers
with Heavy Fuel Oil for normal operation and Diesel Oil for the start up
procedure when no steam is available for fuel oil heating.
- 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.
- 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.
- Shut off valves
Shut off valves for cleaning of the filters. The valves should normally be
open.
- 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.
- 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.
- 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.
- Fuel Oil Burners
The burners must be capable of running on diesel oil as well as heavy fuel oil.
- Make-up water pump
From softener unit.
- Change over valve, Heavy Fuel Oil, HFO, to Diesel
Oil, DO
A three-way-valve to choose between the Heavy Fuel Oil service tank and the
Diesel Oil service tank. The three-way valve ought to be provided with a limit
switch that breaks the electric circuit and shut off the fuel oil pipe heating
to avoid the diesel oil from being heated over its flashpoint.
- 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.
- Heavy 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.
- 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.
- 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.
- 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.
- Smoke density meter
High smoke density indicates deficiency of air.
- Oxygen meter
The 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.
- Thermometer
Normally 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.
- Difference pressure transmitter
This difference pressure should be recorded since increasing difference
pressure indicates accumulation of soot on the boilers heating surfaces.
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