A novel approach to the dry desulfurization process by means of sodium bicarbonate: A full-scale study on SO₂ emission and geochemistry of fly ash

The application of Dry Sorbent Injection (DSI) desulfurization with sodium bicarbonate was investigated to reduce SO₂ emission from power sector. The sorbent was injected directly into the combustion chamber of the 29 MW_th grate boiler, into a non-standard area of high temperature (approximately 700 °C), while generally the DSI method is carried out in the flue gas duct with a temperature below 250 °C. Unique nozzle design for injecting powdery sorbents was implemented and two stoichiometric ratios were tested: NSR = 1.1 and NSR = 3.0. The reduction of SO₂ from a base level of 1580 mg SO₂/Nm³ to 301 mg SO₂/Nm³ at 6% O₂ was achieved, resulting in a process efficiency of 81%. The chemical properties of fly ash were determined in terms of its safe storage and potential use according to the principles of the circular economy. Ash formed during the desulfurization process shows a different chemical composition than the reference sample. A significant increase in the concentrations of the following components and parameters was indicated: S, Na, Zn, Cu, As, Mo, Pb, loss of ignition (LOI) and total organic carbon (TOC). The change in chemical composition led to an increase of total dissolved matter (TDS) in water leachate as well as sulphates, chlorides, fluorides, As, PB, Cu and Zn concentrations.