The removal of sulfur dioxide from flue gas using fly ash in a spray dryer/fabric filter system

During the summer of 1981, an investigation on behalf of the Department of Energy was begun at The University of Tennessee, Knoxville. The purpose of this study was to investigate the reactivity of fly ash with SO₂ in the University's pilot plant spray dryer/fabric filter removal system.

The study commenced with the collection of 22 fly ashes (including lignite, subbituminous and bituminous eastern and western ashes) from the Gulf Coast, Rocky Mountains, and Northern Great Plains regions. These ashes were then used to investigate methods of enhancing SO₂ removal capability due to alkaline fly ash placed in a water based slurry and pumped to a spinning disk atomizer located on a slipstream from a stoker-fired boiler.

It was demonstrated that SO₂ removal efficiencies as high as 30 percent could be achieved by several of the fly ashes tested. It was also demonstrated by one fly ash that ball milling, prior to production of the slurry, increased the SO₂ removal efficiency from 18 to 46 percent. It is believed that the 62 percent increase in slurry alkalinity and the 17 percent increase in surface area for the milled ash caused this improvement in efficiency.

Using the concept of total sulfur retention as a function of surface area and slurry alkalinity, four modeling equations were produced. A complete model consisting of all the ashes collected yielded an R² of 0.82. In addition, separation of the ashes by rank, i.e., bituminous, lignite, and subbituminous, yielded R² values of 0.96, 0.95, and 0.89, respectively.