The Influence\nof Sulfuric Acid Injection on Deposit\nFormation in a Waste-to-Energy Plant

Waste-to-Energy (WtE) technology is the most competitive\nand mature\ntechnology for producing heat and electricity from municipal solid\nwaste (MSW). However, the electrical efficiency of WtE plants is constrained\nby the formation of corrosive deposits on the superheaters. The present\nwork deals with the sulfur recirculation technology, which was aimed\nat reducing the corrosion rate of the superheaters and dioxin formation\nin WtE plants, by recirculating the sulfur from the wet flue gas cleaning\nback to the boiler in the form of sulfuric acid. To improve the understanding\nof how sulfuric acid injection influences the ash chemistry and deposition\nrate, full-scale measurements in a WtE plant equipped with sulfur\nrecirculation were carried out by using an advanced deposit probe\nsystem. The sulfuric acid was injected into two different positions,\nA (flue gas temperature ∼1000 °C) and B (flue gas temperature\n∼730 °C) inside the boiler. Compared to the reference\noperation without sulfuric acid injection, injecting sulfuric acid\nequivalent to 170–920 mg SO<sub>2</sub>/Nm<sup>3</sup> reduced\nthe Cl/S molar ratio in fly ash from 2.3 to a minimum of 0.6, and\nin deposits from 0.8 to a minimum of 0.2. The short-term (14–15\nh) deposition rate also decreased from 19 g/h/m<sup>2</sup> to a minimum\nof 7 g/h/m<sup>2</sup>. The reduction in both the Cl/S ratio and the\nshort-term deposition rate was more effective with sulfur injection\nat position B compared with position A. This was attributed to the\nincreased generation of SO<sub>3</sub> at position B, which facilitated\nthe sulfation of alkali chlorides. This phenomenon was supported by\nchemical kinetic modeling. A long-term (1 week) deposition test was\nconducted with a sulfur dosage of ∼200 mg of SO<sub>2</sub>/Nm<sup>3</sup> at position B after 60 h of reference operation.\nThis resulted in a higher deposition rate of 22 g/h/m<sup>2</sup> compared\nto the short-term deposition rate (7–13 g/h/m<sup>2</sup>).\nThis suggests that the deposition rate increases over time, indicating\nthe need for further research to understand this phenomenon.