Improvement of SO2 removal with application of wall rings and advanced CFD modeling. The case of FGD unit Megalopolis

Megalopolis SES is a lignite-fired steam-electric power plant (850 MW) located in southern Greece. The plant consists of four units. Unit III is retrofitted with a WFGD unit in order to meet the emission values of LCP 2001/80/EC. The WFGD flue gas treatment system removes SO2 by scrubbing the flue gas with a limestone / gypsum process. Flue gas is treated in the absorber by passing the flue gas stream through proper spray levels. The gas flows upward through the absorber countercurrent to the spray liquor flowing downward through the absorber. Slurry is pumped through banks of spray nozzles to atomize it to fine droplets and uniformly contact the gas. The droplets absorb SO2 from the gas, facilitating the reaction of the SO2 with reagent in the slurry. The quantity of liquid sprayed relative to flue gas is related to the SO2 collection efficiency needed and is referred to as liquid-to-gas (L/G) ratio. Higher L/G ratios improve SO2 removal by exposing the gas to more absorbing liquor. However, higher L/G ratios also consume more power. A CFD modelling of the absorber has been used to define gas and liquid distribution inside of the absorber with the purpose to combine the optimised SO2 removal with the lowest possible power consumption. The paper shows the results of the CFD study on Megalopolis III WFGD containing the fluid dynamic optimisation of the nozzles arrangement including the wall ring (patented by Alstom) location.