Release of Potentially Corrosive Constituents from the Grate of a Waste-to-Energy Boiler

摘要

Due to corrosion issues on superheater surfaces of waste boilers a relatively low 20 % of the waste lower heating value can be converted to electricity with present technology. Ash species released from the grate combustion zone form boiler deposits with high concentrations of Cl, Na, K, Zn, Pb, and S that cause high corrosion rates. The Cl-content in waste is one of the key-factors for volatilisation of alkali and heavy metals in waste boilers. Little is known about the release of Cl and ash species along the grate in waste incineration plants. The 26 tonnes/h grate-fired WtE-plant Vestforbraending unit 5 in Denmark was used for measurements of temperature, gas concentrations O_2/CO/CO_2. Local sampling was also performed for Cl, Na, K, Pb, Zn, and S in 6 ports evenly distributed along the grate. The ports were placed 1.5-1.8 meters above the grate. The maximum release of Cl and alkali metals was observed in port 2, and lower concentrations were measured further away from the fuel inlet. The flue gas temperature reached a maximum in port 3. Levels below 0.1 % of oxygen were measured at port 2 with average CO and CO_2 levels of 6.6 % and 15.5 % respectively. Only slight changes were measured at port 3 with near atmospheric levels at port 4.