Excellent process flexibility was demonstrated.
The boiler operated successfully
at load levels as low as 37 MWe (a turndown
ratio of 66%) with bituminous coal
and 41 MWe (a turndown ratio of 63%)
with subbituminous coal. It was found
that accurate and responsive control of
both fuel and air flow rates into the different
operating zones of the boiler was
required.
For optimum NOx control, effective
in-furnace mixing of the gases from the
cyclone and reburning burners is essential.
This was predicted by mathematical
modeling, which proved to be an
extremely useful process design tool.
Measured NOx emissions with bitumi-
nous coal at full load were reduced from
the baseline level of 0.82 lb/million Btu
to 0.39 lb/million Btu, a reduction of
52%. Percentage reductions were somewhat
poorer at reduced load levels, and
slightly better emissions reductions were
achieved with the subbituminous coal.