47
SPECIFIC INSTRUCTIONS FOR IGNITING A MIXED FUEL BURNER
It is advisable to first ignite the burner using liquid fuel, as this feed depends on the nozzle available, whereas the
methane delivery can be regulated at will, by operating the relative flow regulator.
DESCRIPTION THE WORKING OF THE HEAVY OIL TWO-FLAME COMIST 122 N BURNER
(See BT 8726/1)
During the pre-heating stage of the heavy oil, the tension crosses the preheater’s regulating thermostat and reaches
the coil of the resistors’ contactor.
This contactor closes and takes the current to the resistors of the pre-heater which heats the fuel it contains. The pre-
heater’s minimum thermostat closes when the temperature reaches the value it is set at. The equipment is only
switched on when, the temperature is reached in the pre-heater at which the resistors switch off (with the opening of
the regulation thermostat contact), and thus with heavy oil in the pre-heater at the maximum temperature. The
burner’s command and control equipment (cyclical relay) is then switched on by the pre-heater thermostat when it
cuts off the resistors, switching off the corresponding contactor.
Control box Specifications
The cyclic relay equipment executes the ignition program, switching on the fan motor for the pre-ventilation phase.
If the air pressure provided by the fan is enough to trigger the corresponding pressure switch, the pump motor for the
pre-circulation of the hot oil in the burner’s ducts is also immediately switched on.
The pump delivers the oil to the pre-heater, it crosses it and heats up to the set temperature and exits through a filter
to go to the atomisation unit. During the “pre-wash” and “pre-ventilation” stages the air damper is moved to the 2nd
flame position by the air adjustment servo motor (pre-ventilation with air open (see BT 8653/1). The air adjustment
servo motor door then moves the air damper to the position for the 1st flame. Subsequently, the equipment supplies
voltage to solenoid 1 (open in the idle position) which, on closing, stops the free discharge of oil towards the tank.
When solenoid 1 closes, the pressure rises in the delivery ducts.
When this pressure reaches 15 bar, the mechanical value opens in the atomisation unit so that the oil can reach the
1st flame nozzle and from here is expelled in a fine spray into the combustion chamber. The pressure stabilises at
about 18 bars because the 1st flame’s pressure regulator is set at this value. As soon at the atomised oil leaves the
nozzle it is ignited by the discharge from the electrodes that is already present from the closing of the 1st flame’s
valve. During ignition of the 1st flame, the air damper is in the position that is registered according to the quantity of
fuel burnt. If the UV photo-electric cell detects the flame, the ignition transformer is switched off and the block position
is passed. The equipment switches on the air adjustment servo motor that moves the air damper into the set position
(see BT 8653/1) for the second flame. During the movement of the air adjustment servo motor, a cam closes a
microswitch that supplies voltage to solenoid 2 normally open). This solenoid closes and cuts of the flow of oil through
the 1st flame’s pressure regulator. The pressure regulator for the 1st flame is thus excluded and the pressure increases
to the setting of the pressure regulator incorporated in the pump (25 bar). The pressure of 25 bar also acts on the
mechanical value up to a pressure of 22 bars and prevents the flow of fuel to the second nozzle. This valve is thus
opened by the pressure itself and the second nozzle starts working. The pressure of 25 bar now acts on both nozzles.
When the equipment is working at a pressure of 25 bar it is working at maximum capacity.
Control box or
Safety
Preventilation
Pre-ignition
Post-ignition
Time between opening
programmer
time
time
1
st
flame valve
and 2
nd
flame valve
s
s
s
s
s
LFL 1.333
3
31,5
6
3
12
Cyclic relay
