Mercury and SO3 measurements on the fabric filter at the Callide Oxy-fuel Project during air and oxy-fuel firing transitions

The Callide Oxy-fuel Project is the world's largest operating oxy-fuel plant. This work details an experimental test campaign at the Callide Oxy-fuel Project monitoring mercury and SO3 levels exiting the fabric filter during transitions between air and oxy firing conditions. The measurements were taken using two custom built probes; the first allowing combined collection of SO3 and mercury over short time intervals; the second allowing on-line measurements of Hg-total and Hg-0 with SOx removal. Total mercury emissions in oxy-firing measured a maximum of 6-7 mu g/m(3) of which 89% was in oxidised form (Hg2+). The use of low NOx burners had an overriding influence on the mercury measurements reducing the total mercury levels to 0.13 and 0.15 mu g/m3 (air, oxy respectively) with no Hg2+ being measured. The SO3 concentrations were also lower than expected, estimated at similar to 0.5-0.8 ppm (based on a practical estimate of 1% conversion of SO2). Overall mercury capture in either operating mode was estimated at 92-93% for the existing burners and 98-99% with the low NOx burners used (being 2 of the 4 burners operating). Total SOx captured from the flue gas was 16% in oxy-mode and 19% in air firing. These findings suggest that operational conditions have a primary impact on capture of Hg and SOx during transitions with a secondary impact of firing mode (i.e. air or oxy). (C) 2016 Elsevier Ltd. All rights reserved.