Geosyntec’s client, a large Eastern utility, plans to burn higher sulfur coals in the future, and the fuel change has the potential to increase sulfur trioxide (SO3) and sulfuric acid (H2SO4) concentrations in the flue gas. Besides impacting air emissions, the acid gases could increase equipment corrosion and pluggage in the air preheater (APH) through condensation of sulfuric acid and sulfate salts. Previous test results from a third party stack tester for SO3 and H2SO4 concentrations in the flue gas were inconsistent and appeared to be biased low. To meet their goals and regulatory requirements, the utility retained Geosyntec to assist in the follow-up round of stack testing in determining accurate SO3 and H2SO4 concentrations across the scrubber.
In addition, the client also asked us to help them understand how process changes to unit operations between the boiler and the stack impact generation and removal of SO3 and H2SO4 within the flue gas stream.
Geosyntec’s Scope of Services
Geosyntec worked with our client’s third-party stack tester by adapting NCASI Method 8A (controlled condensation), modifying the tester’s procedures and providing training, and upgrading test equipment to more fully capture SO3 and H2SO4 species. We also designed a test program to analyze the impacts to SO3 and H2SO4 concentrations through changes to the operation of the selective catalytic reduction (SCR) unit, injection of boiler additives to control slagging, coal types, and scrubber operating parameters.
Due to Geosyntec’s stack testing experience for these species that are traditionally difficult to quantify in the flue gas, the measured SO3 and H2SO4 concentrations were more consistent and reproducible. The results also agreed with predicted concentrations based on fuel type, expected sulfur dioxide (SO2) oxidation in the boiler across the SCR, and removal in the air preheater. In addition, our engineering tests gave the utility tools to predict and reduce the concentration of SO3 and H2SO4 at the stack through changes to operating parameters of air emission control devices including the scrubber and SCR to decrease APH pluggage and sulfuric acid stack emissions.