A gas desulfurization scrubbing system for removing sulfur oxides from gases, such as those of fossil fuel burning operations or other manufacturing process emitting sulfur oxides, and for collecting reaction products of the desulfurization chemical reactions. A quenching section is disposed in a gas duct upstream of a gas desulfurization scrubbing tower and a scrubbing slurry is provided at that section for quenching and chemically reacting with the gas. A quench reaction product is collected, at a location between the quenching section and the scrubbing tower, for use in making commercial by-products, such as gypsum.