Prevention Of Combustion Chamber Overfilling; Reignition Protection; Back Burning Protection, Fuel Supply (Rse); Shut-Off Gate Valve - Viessmann KOB PYROTEC Technical Manual

Design information
(cont.)

Prevention of combustion chamber overfilling

In accordance with TRVB 118, a fill level monitor should be installed
to prevent overfilling of the combustion chamber. The boiler has two
light barriers for incandescence monitoring. A sensor directly on the
insert pipe is used to detect any sign of a burn-back risk and to coun-
teract this early on by means of a short-term output increase (increas-
ing in material feed).

Reignition protection

In accordance with TRVB 118, reignition protection is prescribed for
all systems over 150 kW. If a spark detection and extinguishing facility
is not used, TRD 414 prescribes a constantly available separating
barrier (TRD 414 relates primarily to waste wood from the preparation
and distribution of wood and wood materials). There are simpler ways
of achieving this for woodchips from the forestry and sawmill sector.

Back burning protection, fuel supply (RSE)

Additional "material transportation back burning protection" depends
on the relevant requirements (location, size of the fuel store, material,
pressure, regulations) and is a separate item from the standard deliv-
ery ordered from KÖB Holzfeuerungen GmbH.

Shut-off gate valve

The shut-off gate valve is permissible in all unpressurised fuel stores
and is considered suitable back burning protection in accordance with
TRVB 118 (test certificate BV 2979/89).

Rotary lock valve

If the wood remnants are introduced with fans in fuel storage rooms,
due to the pressure load, at least one rotary lock valve is required to
reduce pressure between the fuel store and the boiler. The rotary lock
valve is suitable for reducing pressure and at the same time is con-
sidered suitable back burning protection in accordance with TRVB 118
(test certificate BV 2979/89).

Dual rotary lock valve with pressure compensation

If, due to special circumstances, mechanically generated underpres-
sure or extremely high overpressure can be expected in the fuel store,
then in accordance with the relevant project plan, two rotary lock valves
with a pressure compensation to outside should be installed in the
material transport path.
The maximum pressures that can be expected are to be confirmed by
the supplier of the chip extraction system. Leaks may occur in the
rotary lock valve under the silo discharge system as a result of wearing
of the sealing elements or due to larger pieces of wood that cannot be
transported. Such leaks may allow the back flow of low temperature
carbonisation gases from the combustion system into the silo.
Between the rotary lock valve and the silo discharge system, a flue gas
alarm should be installed, which, when responding, switches off the
system causing the silo underpressure.

Low water indicator

EN 12828 specifies that boilers must be equipped with a low water
indicator (water level limiter). Tests have verified that the burner will
be automatically switched OFF in the event of water shortage due to
a leak in the heating system and oil burner operation, before the boiler
or the flue system reach unacceptably high temperatures.

Maximum pressure limiter

If the rated output of the wood boiler is more than 300 kW, a maximum
pressure limit is required for each boiler in a system.
PYROTEC
As a result, any prescribed protection device does not come into effect
and normal operation is maintained with regard to the greatest possible
heat supply reliability.
The boiler is equipped with a separating barrier and is operated per-
manently with underpressure. The boiler is then equipped with reig-
nition protection in accordance with both TRVB 118 and TRD 414.
For this boiler, we recommend installing a rotary lock valve. In addition
to the back burning protection, the penetration of infiltrating air via the
supply screw conveyor is also prevented.
■ Max. permissible overpressure in the fuel store: + 500 Pa
■ Max. permissible underpressure in the fuel store: + 0 Pa
■ Max. permissible overpressure in the fuel store: + 3000 Pa
■ Max. permissible underpressure in the fuel store: - 3000 Pa
For installation purposes, the wood boilers have a R½ connector on
top of the boiler.
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