"In the case of environmental processes, consistent reduction in the variance of controlled variables with large through-put processes is of particular interest. Accordingly, this report utilizes current understanding of limestone scrubbers for flue gas desulfurization (FGD) to develop an effort into the optimization of automatic control for the recirculating slurry processes. To this end the acknowledged methods of mathematical modeling, computer simulation, and experimental proofing are applied to the design of slurry limestone addition, slurry density, and absorber liquid-to-gas ratio control systems. Three automatic control methods are analyzed for dense limestone feedrate to the recirculating slurry including experimental results. Stoichiometric control is based on material balance considerations, but is compromised by the lack of slurry reaction measurements. Control of pH is geared to accommodate variations in the slurry reactions, but requires a high slurry reaction gain (ApH/A limestone feedrate) for stable and responsive control. Stoichiometric-assisted pH control offers additional process disorder reduction than either Stoichiometric or pH control separately, but its additional complexity is warranted only under conditions of low slurry reaction gain. Absorber liquid-to-gas ratio control for minimizing scrubber energy requirements while maintaining an SOz exit target is also designed based on a feedforward SO2 removal law and slurry pump selection."