MERCIA 

          ENERGY 

                Ltd

Supplier of automatic wood heating systems


 

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Wood Energy


  Why biomass    How it works     Key features    Useful data 

 

How it works

Automatic wood-fired boilers consist of four key components

 

Boiler: Conventional boilers are used and are similar to those of gas and oil fired systems. They comprise either a simple water jacket or a number of fire tubes positioned horizontally or vertically. The boilers are highly efficient with typical efficiencies of 85% to 92%.

 

 

 

 

 

Burner: A short auger meters the fuel into the combustion zone either below or above the grate. Moving or rotating grates are used in very large systems. Wood typically produces 0.5 % to 1% ash that is collected at the bottom of the grate in ash pans, larger systems have automatic de-ashing devices. Combustion quality is usually monitored to maintain correct fuel/air ratio.

Fuel feed systems: Wood-chip is not a free flowing material and storage bunkers are fitted with agitators. Small systems use two rotating spring loaded arms that drag the material towards an auger. Larger wood-chip storage systems require moving floors that push the material towards an auger at the end of store. Wood-pellets flow very easily and do not need special agitator systems. The fuel is removed from the store by an auger which lifts the fuel and deposits it in a drop cell or zone before it is metered to the burner by another auger. The drop cell is a safety feature that prevents unwanted air being drawn into the boiler, and prevents burn back.

Fuel delivery and storage: Fuel is supplied by an external contractor or as a self supply operation, for example a farm or estate with its own wood harvesting operation. The chips or pellets can be tipped directly from a tipper truck or trailer into an bunker. Other options include using dump bag, front end loaders, purpose built containers, or feed blowers (pellets only). The storage system can account for a large proportion of the cost of installing biomass heating systems.