Retrofit Injection of Humid Gas From Sludge Dryer and Secondary Air in WTE Furnaces of Que´bec City

This paper discusses the retrofit injection of humid gas from sludge dryer with secondary air in the WTE furnaces in Que´bec City. In 1992, a municipal sludge treatment plant was added in the WTE building. Three sludge dryers, each connected to a furnace, were added. Direct contact with hot furnace gas was used to dry sludge in a rotary drum. Humid gas from the dryer was returned to the rear wall of the furnace just above the finishing grate. CFD modeling showed cold flow of humid gas on the rear furnace wall, restriction of the combustion area on the principal grate, and stratification of the flow inside the boiler. A retrofit of the first chamber of the boiler was designed using injection of humid gas from the sludge dryer with secondary air on the front and rear walls. The main purpose of the retrofit was to maintain CO levels of under 57 mg/m³ on a 4 hour mobile average. The first boiler was retrofitted in winter 2008 and results have been very encouraging.