The 1990 Amendments to the U.S. Clean Air Act require the regulation o
f hazardous air pollutants (HAPs). The combined system of air-blow bla
ck liquor oxidation and recovery boilers with direct-contact evaporato
rs and wet-bottom precipitators constitutes one of the major sources o
f HAP emissions in a pulp and paper mill. This paper summarizes the re
sults of laboratory studies and field tests to investigate the formati
on, release, and destruction of HAP compounds, particularly methanol a
nd hydrogen chloride, in recovery boiler systems with direct-contact e
vaporators.