Wood Gasification Boilers
First, let me tell you a little about how they work. The wood is loaded into the top chamber and air is injected from the top down. There is no escape for the burning gases except down through a "nozzle" or slot at the bottom of the ceramic chamber. The fire is actually rather small and only burning the wood on the bottom of the wood chamber. The burning gases are pushed down through the slot and mixed with super-heated oxygen that is forced through the ceramics below the wood. The introduction of the hot oxygen mixed with the "wood gas" from the top "explodes" into the lower chamber and burns violently at temperatures exceeding 2000F.At those temperatures all creosote is eliminated, smoke becomes almost non-existent, and very little ash is left. Dont let anyone tell you they have a gasification burner that burns in one chamber. Believe me, if you had this kind of fire near the wood the entire load of firewood would be consumed in minutes.The 2000 + gases then pass to the rear of the boiler and pass through a series of "fire tubes"simply, a series of tubes that take the hot gases from the bottom of the stove, through the water, toward the chimney vent. These gases exit the boiler at temperatures usually less than 400. All the heat possible is pulled from the fire into the water through these tubes.
A wood gasification boiler is a central heating boiler which produces its useful heat through combustion of wood gas. This generator gas is produced by the thermal transformation of wood fuel i.e. the wood fuel is first converted to gas then the resulting charcoal is then also converted to gas.
A wood gasification boiler differs from a standard wood boiler by way of the combustion process. In a standard wood boiler, direct combustion of the wood fuel takes place, whereas in a wood gasification boiler, combustion of wood-gas takes place following thermal conversion of the wood fuel to gas.
Accumulator Tank An accumulator tank (heat storage tank) should be installed in conjunction with your wood gasification boiler to ensure the efficient operation of your boiler. Accumulator tanks are important heat storage devices, especially for wood gasification boilers. These boilers can only be operated efficiently when combined with an accumulator since controlled operation at part load is more difficult. This is due to the nature of the fuel (generally wood logs). Once combustion take place, the fuel will continue to burn irrespective of whether the dwellings heat load is met. Consequently the storage or accumulator tank in a domestic biomass heating installation is the primary heat storage/distribution device, which is heated by the boiler to a set temperature and can store the resulting high temperature water for long system standstill periods, until heating or hot water is required. The accumulator capacity should be calculated in accordance with your manufacturers recommendations. A rough guideline for establishing the volume of the buffer is available from EN303-5 and from the REIA training manual and is in the region of 55 to 65 L/kW of the rated boiler size.
Flues - The flue is used for the exhaust of the boiler or stove. It can be installed through a chimney or outside the building. The flue must be installed to current Building Regulations. Some things to look for would be:
Constructional Hearth - A constructional hearth should be placed under a stove to separate the stove from combustible material and to provide protection from the threat of fire. The constructional hearth could be a metal, cement, tile, or a non-combustible plate. The appliance should not be placed close to the edge of a hearth or any combustible material.
Air Supply - A stove or boiler must have a secure air supply for safe operation. This can be either in the form of a controlled dedicated air supply directly to the appliance, or in the form of a permanent ventilation opening to the room in which the appliance is located. Best practice is to rely upon dedicated ventilation and not on air infiltration and/or leakage in the room. The size of the opening depends on the size of the appliance. Your installer should be able to size this correctly. In addition, extractor fans may interfere with the operation of the appliance causing smoke to spill out of the appliance into the room so please consult with your installer.
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