Boiler Room Design
There is a mandatory separation of the burner and the fuel store- usually the boiler is located a minimum of 1m away from the silo. A firewall of non-combustable material is required if the silo is closer to the boiler. Systems over 60kW require a water quench at the boiler. Flammable products should not be stored in a boiler room.
Burn Back Protection
There a 2 passive safety functions on the pellet delivery; one in the small metal store itself and one in the drop tube.
The Ecotec burners all have a small internal store (0.5kg – 1.0kg) into which pellets are fed from an auger that is delivering fuel from a bulk store when the burner needs fuel. There is rotary valve (gate) which allows the pellets in but has a tight seal to prevent air coming back from the boiler.
The internal store is only partially filled at any time by the external auger. In this way, in the event of a back burn, the embers will burn out in this small chamber. If that were to fail, the drop tube, which by design we allow for a metre in length, will act as a second fire break as that is always empty.
There are also 2 mechanical devices for safety. One is a heat sensor located on the shaft of the internal auger that delivers fuel to the burner. If this gets hot, +55 deg. C, the external feed is immediately stopped and the internal screw feeds the fuel already in the burner, into the boiler. A non-volatile lock-out occurs that requires a manual reset.
The second is the level sensors which are able to optically detect back pressure in the event of changes in the chimney pressure. The dust in the internal store of the burner will become airborne and the level sensors will activated to stop the external feed screw.
The burner control unit is linked to the boiler’s operating and maximum thermostats.
If as fault occurs in the operating thermostat, the maximum thermostat will cut out and prevent the boiler overheating.
The burner is designed so that it returns to normal operation after disruptions such as power cuts and disruptions to fuel supply etc.
The burner is turned on according to the operating thermostat in the boiler thermal store or the buffer tank. The programming in the PLC, which has evolved over the past 15 years, turns on the combustion fan and electric ceramic element to allow flash point to occur, at which point there are steps in the combustion process that allow the burner to begin and then function at the desired settings that are best suited for the site in question. When the upper operating temperature of the boiler is reached, the feeding of pellets is halted and the fan will have an after run function and then cease. As the burner has a rotary valve seal which prevents back burning, the combustion of the pellets in the burn pot (underfed combustion) die down and the fire and embers die out.
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