5
1
CONSTRUCTIONAL-DIMENSIONAL
TECHNICAL CHARACTERISTICS
1.1 - CONSTRUCTION
OF THE TRIOPREX-N
BOILERS
The TRIOPREX-N, three pass boilers, are
of
horizontal
type (oval shape from model 65
to 380 and the model 840;
eight
shape from
model 500 to 730 and cylindrical shape from
model 1100 to 1900), with direct flame in the
combustion chamber.
The construction completely satisfies the
requirements of the EN 303- part 1.
The sheet metal parts of the pressure vessel
are manufactured of certified carbon steel,
type S235JRG2, according to EN 10025, with
melting certificate 3.1.B, according EN
10024; whereas the pipes are of steel ST 37.0
according to DIN 1626.
The welders and the WPS (Welding
Procedures Specifications) have been
approved according to EN 287 and EN 288
by TUEV (DE). These boilers have been also
approved by - ISCIR (RO).
Up to the model TX-N 380 the furnace is
linked to the rear tube plate.
For larger models (TX-N 500 to TX-N 3500)
the furnace is free to dilatate (it is supported
only by the double welding seam (inner and
outer) to the front tube plate.
The boilers are equipped with a reversible
hinged door, which can be opened, for this
reason, from L.H. or R.H. side.
The outer shell is insulated with a glass wool
matress, thick 100 mm (80 mm for models
TX-N65 & TX-N 85), protected by a textile
in mineral fiber.
The upper part of the outer shell is equipped
with uplift hook(s).
fig. 1
Note
: The TRIOPREX-N boilers are to be
equipped with ON/OFF burner; alternatively
they can be equipped with a two stage or
modulating burner, provided the minimum
reachable heat input is not lower than the figure
shown on the data plate for the fuel used on
site.
For two stage or modulating burner see
paragraph 2.7.1.
1.2 - WORKING PRINCIPLE
The NOx formation process is strongly
affected by:
-
the flame temperature;
-
the time during which the combustion gases
stay in a high temperature zone.
-
oxygen partial pressure and its
concentration.
The provisions to be adopted for the NOx
reduction are then:
-
reduction of combustion temperature;
-
reduction of the specific thermal input;
-
permanence time reduction of the gases
in the combustion chamber;
-
reduction of oxygen concentration.
UNICAL, to reduce the NOx formation on the
TRIOPREX-N range of boilers, has adopted
the following construction solutions:
-
three pass
the furnace is of direct flame type and not
of reversal type any more; the burner flame
results more compact and shorter, thus
The boilers are provided with two 1/2" bulb
holders with inner diameter of 15 mm (for 3
bulbs each), suitable to locate the thermostats
and thermometer bulbs.
The casing side panels are provided with
holes for the cables of the electrical supply,
of the pumps, of the burner and any other
auxiliary equipment.
reducing the permanence time at high
temperature;
the direct pass allows a quicker flame
cooling down by the water cooled furnace
surfaces;
-
specific thermal input reduction
the combustion chamber volume has been
increased if compared with standard boilers
of the same capacity.
With the adoption of the modern Low NOx
burners a further reduction of the NOx
emissions can be obtained with:
-
reburning
a part of the combustion gases is taken
and sent again to the combustion chamber
with the combustion air.
In this way the partial oxygen pressure is
reduced and the flame temperature is
reduced too.
-
reduction of the partial oxygen pressure
thanks to an air excess reduction
During the operation of the burner within the
output range of the boiler, the combustion
chamber is always under positive pressure.
For the value of this pressure see tables on
pages 6 to 10 under the column "Smoke side
pressure losses".
The chimney has to be calculated in such a
way that at its base there is no positive
pressure.
