Wood Chip Boiler

Heat and hot water are produced using an Austrian Köb Pyrot boiler which has an output of 300kW. Annual wood chip consumption is anticipated to fall in the range 250 to 450 tonnes. Locally-grown wood chip fuel from Kielder Forest is supplied from the Forest Enterprise depot in the village. The main fuel store can hold up to 450 cubic metres (between 80 and 120 tonnes) of wood chip. Conversion factors between volume, weight and energy content of wood chip vary with moisture content and packing density. Wood chips supplied to the Kielder system have moisture content in the range 25 to 35%. The volume of one tonne of wood chip at this moisture content may range from 3 to 4 to as much as 6 cubic metres, depending on chipping method and the resulting particle size distribution. The Kielder wood chips are supplied as approx. one-inch (25 mm) chunks of sitka spruce.

The Fliegl wood chip delivery trailer holds about 16 cubic metres (2 to 3 tonnes) of fuel, and has a “push off” action to empty the chips into the boiler house fuel store. Inside the boiler house, a “walking floor” moves the wood chips form the storage area to the screw augers, which then convey the wood chips into the boiler where they are burned.


Cutaway of Köb Boiler

Wood Chip

The Köb boiler uses a maximum of 80kg of wood chips per hour. It has a special rotating firebox, designed to burn all kinds of dry or damp wood fuels (chips, sawdust shavings, pellets, briquettes, forestry wood shavings). The boiler has an efficiency of 87% (measured as heat output to wood fuel energy input). The boiler house also incorporates a back-up system (an oil-fired burner) that can be used if the primary system requires maintenance.

The boiler produces very little noise, smoke or ash. Emissions from the chimney are mainly composed of water vapour: total emissions are expected to be less than a single household coal fire. The few wheelbarrow loads of ash produced each year are used as fertiliser to mix with compost for the village gardens and allotments.

Compared to alternative fossil fuels (which in this case would be heating oil), the Kielder district heating system saves about 57 tonnes of carbon dioxide emissions per year.