Using sewage sludge as a denitration agent and secondary fuel in a cement plant: A case study

• Using sewage sludge as denitration agent in a cement plant was studied.
• The optimum condition for DeNOX was determined.
• CH4, HCN, and NH3 play a decisive role for the reduction of NOX.
• The method can reduce resources consumption and NOX emission in cement industry.

The influences of sludge feed rate, feed point, feed method, and air-staged combustion were systematically investigated in a Chinese cement plant with emphasis on NOX removal. Results indicate that the use of sludge as a secondary fuel is conducive to NOX reduction, which depends primarily on the feed rate and feed point. Moreover, both feed method and air-staged combustion influence NOX removal to some extent. Nonetheless, these factors have little effects on CO removal. When the sludge feed rate is 9 t·h− 1 in a precalciner reburning zone in the combustion temperature range from 850 to 1000 °C, NOX removal reached 75.82% in the air-staged combustion condition. The NOX concentration easily met the national emission standards. Finally, the use of sludge as alternative fuel does not affect clinker quality negatively. This method utilizes sludge effectively and reduces NOX emissions; hence, the application of sewage sludge as a denitration agent and secondary fuel in cement production is a worthy option.