baltur BT 75 DSNM/D Manual De Instrucciones página 21

TWO - FLAME BURNER OPERATION
IThe two-flame burner always ignites at reduced fuel and air flow
(1st flame) and a few seconds later change to full fuel and air (2nd
flame) flow operation.
Cutting-in of the second flame depends on control box and control
device (pressure switch or thermostat) consent. When the burner
is working at full flow, it stays in this position until the pressure or
temperature level at which the control device (pressure switch or
thermostat) has been set, is reached. The control device is trigge-
red off cutting-off the second flame (fuel and air) when the value at
which the device has been set, is reached.
The burner therefore stays in operation on the first flame only.
The first flame on its own is not usually enough to maintain pressure
or temperature at the desired level and consequently, pressure or
temperature drops until it reaches the level at which the second
flame control device (pressure switch or thermostat) again cuts-in
total air and fuel flow (second flame).
The burner stops operating completely when, with only the first-
flame cut-in, pressure or temperature reaches the level at which
the device being used (pressure switch or thermostat) open contact.
The burner automatically re-ignites when pressure or temperature
drops below the level at which the pressure switch or thermostat
has been set.
WHEN SHOULD TWO-FLAME BURNERS BE USED
A two-flame burner is usually found necessary if it has to be coupled
to boilers producing steam; however there may be other reasons
why two-flame burners are necessary.
For steam boilers, two-flame operation enables, to a certain extent
only, the vapour quantity produced to be in line with the actual
needs of the plant, reducing ignition frequency and thus also boiler
thermal stress.
This is why steam boiler manufacturers specify two-flame burners
for their boilers.
It is also important to note that low pressure steam boilers (max.
0,5 bar) strictly call for two-flame burners in order to keep working
pressure sufficiently constant.
Two-flame burners are required for pressurized boilers (where com-
bustion chamber pressure is higher than atmospheric pressure) in
order to give sufficiently gradual ignition (two-flame burners always
ignite on the first flame only, which means at reduced flow; they only
change to full flow operation later on).
In these kinds of boilers, full flow ignition would cause considerable
damage over a short time due to the excessive pressure the com-
bustion chamber would have to bear.
From what has been said above, it is quite clear that with regard to
pressurized boilers, it is necessary to use burners that can ignite
automatically at reduced flow and only change to full flow operation
later on (after a few seconds).
It is not advisable that a burner operating with a boiler for
!
the production of water for heating purposes be connected
up for two flame operation. In this case, when the burner is
operating on one flame only (this can be over long periods,
too) the boiler is insufficiently fed; consequently, the pro-
ducts of combustion exit at an excessively low temperature
(less than 180 °C) creating soot at the chimney outlet. When
the boiler is not sufficiently fed, acid condensate and soot
formation is very likely in the boiler with the result that the
boiler quickly gets clogged and corroded.
When a two-flame burner is installed in a boiler producing water for
heating purposes, it must be connected to enable two flame full-flow
operation and must stop operation completely, without change-over
to the first flame, when the pre-set temperature is reached.
To achieve this type of operation, the second flame thermometer
must note installed and a direct (bridge) connection as to be effected
between the relevant terminals.
In this way, only the reduced flow ignition capacity of the burner is
used in order to have gradual ignition, which is essential for boilers
with combustion chamber under pressure (pressurized) but it is also
very useful for boilers (negative pressure combustion chamber).
The burner control device (cutting-in and stop) depends on the usual
operation and safety thermostats.
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