the combustion technology selection process. The industry
trend is now driving permit levels to lower and lower values.
This suggests a potential break point where the CFB may
have an advantage by being able to achieve a given nitrogen
oxides (NOx) limit without the use of selective catalytic
reactor (SCR) technology.
Biomass firing requires the control of carbon monoxide
(CO), volatile organic compounds (VOCs), NOx, and at
times sulfur dioxide (SO2) and hydrochloric acid (HCl).
With BFB technology, CO and VOCs are controlled by
good fluidization, uniform fuel distribution and a properly
designed overfire air system. NOx is controlled by bed
stoichiometry. A staged overfire air system provides approximately
15 to 25% NOx reduction.
For the CFB, high furnace solids recirculation rates,
deep staging, low excess air (below 3% O2) coupled with
a uniform furnace temperature profile, result in low carbon
losses and low uncontrolled NOx formation. Like the BFB,
a CFB’s CO and VOC emissions are controlled by good
fluidization and uniform air/fuel distribution, supplemented
by high solids recirculation rates.