Utilization of Water Utility Lime Sludge for Flue Gas Desulfurization in Coal-Fired Power Plants: Part III. Testing at a Higher Scale and Assessment of Selected Potential Operational Issues

The feasibility of lime sludge utilization for flue gas desulfurization was evaluated by continuing the previous laboratory-scale studies at a higher scale and investigating two potential operational issues, namely, viscosity and metal corrosion. Two lime sludge samples and a baseline limestone sample, which were previously characterized and tested for SO₂ capture from a simulated flue gas at a laboratory scale, were first tested at a tenfold scale with a simulated flue gas and then tested with a slipstream of flue gas from a coal-fired power plant. The tested lime sludge and limestone slurries reduced the SO₂ concentration of the simulated flue gas from 2000 to <1 ppm and they demonstrated similar Hg re-emission profiles. Field-testing results revealed that the limestone and lime sludge slurries reduced the SO₂ concentration of the flue gas from ∼1500 to <1 ppm. These experiments confirmed our previous smaller scale laboratory results that lime sludge can function as a suitable substitute for limestone for SO₂ removal from the flue gas of coal-fired power plants without negatively affecting Hg re-emission. Two operational issues, namely, viscosity and metal corrosion, were investigated to evaluate practical issues in the transition from limestone to lime sludge at power plants. Results of Marsh funnel viscosity experiments conducted at different solid contents and temperatures indicated that the limestone and lime sludge slurries and their gypsum counterparts had similar flow characteristics. Carbon-steel, stainless-steel, and Hastelloy coupons were tested for corrosion by lime sludge and limestone slurries. Both stainless steel and Hastelloy were resistive to corrosion in slurries made from lime sludge or limestone samples or their gypsum counterparts. A considerable but similar amount of corrosion was observed for carbon-steel coupons exposed to lime sludge and limestone slurries. Adding 5000 ppm of Cl^- to slurries considerably increased the corrosion rate of carbon steel.