Destruction of alkali chlorides using sulphur and ferric sulphate during grate combustion of corn stover and wood chip blends

Sulphur containing additives were used to destroy alkali chlorides in the furnace of a 100 kW grate reactor during combustion of a blend containing 40 ± 4% (based on energy content) corn stover with wood chips. Ferric sulphate spray, when added to zones where alkali chlorides have already been formed and gas temperature is < 1000 °C, can destroy a significant portion of alkali chlorides in the furnace even at dosage S/Cl = 0.4–0.6 and prevent high temperature chlorine corrosion of superheaters. This dosage can increase SO₂ emissions from about 100 (without additives) to 250–350 mg/Nm³ 6% O₂. Additive costs can be estimated at 0.4–1 €/MW h electricity with blends containing 40–100% corn stover, assuming a 30% efficiency in electricity production. Mixing ferric sulphate with fuel feed had little effectiveness compared to spraying it into the upper furnace. Elemental sulphur mixed with the fuel feed was much less effective than the ferric sulphate spray. The minimum dosage of elemental sulphur needed to prevent Cl deposition (S/Cl = 3) lead to high SO₂ formation (≈2000 mg/Nm³ 6% O₂).