1. In coal-fired suspension burners the fuel has to be
pretreated in such a way that full combustion within
the short residence time (2–3 s) in the combustion
chamber is realized. Lumpy biomass fuel, which has
not been pretreated, will need a longer time to burn out
depending on the size and the moisture content. If the
agricultural residue is inhomogeneous, the combustion
process is difficult to control.
2. The combustion temperature of coal fired boilers is 850–
9008C for fluidized bed combustors and 1000–12008C
for suspension burners. The melting points of ashes of
agricultural residues are often lower which could lead to
slagging or fouling.
3. Some agricultural residues have a high chlorine content
which causes high-temperature corrosion at heat
exchanger surfaces with wall temperatures above 4008C.
4. Many coal-fired power stations are equipped with the
selective catalytic reduction of the nitric oxides (SCR).
Alkalis supplied with the burnt biomass can deactivate
the DeNOx-catalyst.
5. In Europe, ash from coal combustors is often used as
inert material in the cement industry. The co-combustion
of agriculture waste changes the composition of the ash,
which may hinder its utilization in the cement industry.