Numerical simulation using single- and double-mixture-fraction / PDF( Probability Density Function)transport model was carried out to evaluate the characteristics of coal burning alone and with domestic sludge on a420 t / h tangentially coal-fired boiler. The flow

combustion and NOxemission properties were investigated. The simulation results were consistent with the field test under the same working condition

when the coal was burned alone and the load is 70% and 100%. Under 100% load condition

the NOxemission reduced after co-combustion. With the increasing mass ratio of sludge

the burn out rate of coal decreased slightly. Temperature distribution and flue gas composition distribution in the furnace were roughly the same. All these above indicated that the co-combustion had little influence on characteristics of flow

combustion and NOxemission of this boiler.