Biomass Combustion and Co-firing

Biomass fuels available

Biomass fuels available

A mobile
chipper with crane efficiently collects roadside thinnings for fuel (Courtesy
of Bruins and Kwast, Netherlands)

The characteristics and quality of biomass as a fuel depend on the kind
of biomass and the pre-treatment technologies applied. For example, the
moisture content of the fuel as fed into the furnace may vary from 25 to
55 wt% for bark and sawmill by?products, and be less than 10 wt% for
pellets. Also, the ash sintering temperatures of biofuels used cover a
wide range (800 to 1200°C), as do particle shapes and sizes. Fuel quality
can be improved by suitable pre-treatment technologies, but this increases
costs.

Different combustion technologies are available to deal with various
fuel qualities – less homogeneous and low-quality fuels need more
sophisticated combustion systems. Therefore, and for “economy of
scale” reasons, only medium and large-scale systems are suitable for
low-quality and cheap biofuels. The smaller the combustion plant, the
greater the need for fuel quality and homogeneity.

 

Clean and dry woodpellets are an
ideal fuel for combustion in small-scale installations

The chemical fuel composition has a direct influence on combustion
characteristics, ie energy content, ash deposition, emissions, corrosion
mechanisms, as well as ash behaviour inside a boiler. It is therefore
important to know probable variations in chemical fuel composition. Task
32 has prepared a database covering the chemical composition of fuel, ash,
and condensate samples of fuels really used in installations, and this can
be accessed through the internet.