Careful control of the excess O2 content (often
monitored by a lambda sensor) and gas oxidation
zone combustion temperature at stage 4 is
required to minimise the formation of soot,
CO and NO
x and maximise thermal efficiency.
However, as complete oxidation of
the wood gases usually requires
a slightly higher combustion
temperatur e than in fossil
fuelled boilers, the quantity
of NO
x produced by biomass
boilers per unit of heat generated
is usually greater than that from
gas fuelled boilers