New Life for a Dual Loop Wet FGD System

摘要

Indianapolis Power & Light (IP&L) installed a dual-loop, limestone, inhibited-oxidation wet flue gas desulfurization (FGD) system in 1986 on its Petersburg Unit 4. The unit has a capacity of 550 MW and fires high sulfur coal. The wet FGD system included three modules, each with an integral quencher section and tank plus a separate absorber section with an external absorber reaction tank. The wet FGD installation did not include a wet stack and, instead, bypassed 6% of the hot flue gas around the absorber modules to reheat the treated flue gas to allowable stack temperatures. With addition of sodium formate, the wet FGD system achieved approximately 84% sulfur dioxide (SO_2) removal from the remaining 94% of the flue gas passing through the system. In 2008, IP&L began working with the Babcock & Wilcox Power Generation Group (B&W PGG) to convert the absorbers to a modern, state-of-the-art single loop limestone wet FGD system with forced oxidation while increasing SO_2 removal without gas bypass or sodium formate. Major modifications included raising the gas inlet, cross-tying the integral quencher tank to the external absorber reaction tank, installing an upgraded absorber tray, modifying the spray levels and adding a forced oxidation air system. The limestone slurry preparation and slurry bleed dewatering systems were also upgraded to support the higher SO_2 removal rates and processing of high quality gypsum. B&W PGG provided most of the process design for the new system. Balance-of-plant (BOP) upgrades and expansions required to support the wet FGD process changes and conversion to a wet stack. The upgraded equipment was started up in November 2011 and performance testing was conducted in February 2012. Test data indicates SO_2 removal is in excess of 95% while operating within expected pressure drop and gypsum quality requirements.