Evaluation of the controlled condensation method for flue gas SO3/H2SO4 measurement

Controlled condensation method (CCM) is widely accepted for detecting sulfur trioxide (SO3)/sulfuric acid (H2SO4) in flue gas. However, this method cannot be calibrated accurately because of the absence of the standard gas that contains H2SO4 vapor. We attempted to calibrate CCM by adopting another SO3/H2SO4 detection method that has been proven accurate. The following conclusions have been derived. The performance of the core component of CCM (i.e., the condenser) is acceptable. However, H2SO4 still escaped from the condenser, thereby confirming its negative errors. The filter set behind the condenser can prevent most of, but not all of, the escaping H2SO4 by intercepting aerosol H2SO4. Any flue gas cooling processes that occur in the sampling probe and the connecting pipe under 260 °C before the condenser can possibly cause negative errors because of acid condensation. The ash layer that formed during the ash filtration process cannot only intercept the aerosol H2SO4 but can also absorb the gaseous H2SO4, thereby resulting in negative errors. Errors caused by the accessories (i.e., the sampling probe, the connecting pipe, and the ash filtration) may be greater than those caused by the condenser, which may make the measurement invalid.