Combustion

A wheel-loader transports the wood chips, bark and sawdust from the storage into the "moving floor". The walking floor transports the fuel into the boiler. The boiler, grate, combustion zone, afterburner zone and heat exchanger are the key components of the system in terms of combustion quality. Optimal combastion of biomass is extremely tricky as the composition and moisture content of the fuel constantly varies.

Key system components:

Grate zones, each with its own speed-controlled primary air fan
Ember bed control
Speed-controlled secondary air fans
Speed-controlled recirculation fans
Sensors for burning temperature, flue gas temperatures
Water temperatures
Subpressure sensor
O2 sensor
A digital controller evaluates all the readings and controls the individual system components accordingly.

Phases of combustion:

Heat-up phase: Embers or pilot burner heat up the wood.

Drying phase: Water is vaporised out of the wood. The speed of drying depends on heat conductors, specific heat, density, piece size and water content.

Disintegration phase: At approx. 150 °C, the main components begin to disintegrate. First the hemicellulose and cellulose and then, at 250 °C, the lignin. Intermediate levoglocosan is formed, immediately producing compounds such as acetic acid, acetone, phenols and others.

Degassing phase: At a process temperature of more than 250 °C, the first combustion gases and smouldering gases form. Above 280 °C the reaction becomes more violent, the escaping gases contain easily combustible materials such as CO, CH4, H2, methanol, tars and oils. Degassing reaches a maximum level at approx. 350 °C. In order to utilise the substances created during degas-sing, it is necessary to burn the gases. This requires temperatures of approx. 500 °C and admixing a sufficient quantity of air. 


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900°C is the ideal temperature for
burning wood chips.