Numerical Study of Thermochemistry and Trace Element Behavior during the Co-Combustion of Coal and Sludge in Boiler

Abstract

Sludge is one of the main pollutants from sewage treatment and contains a high content of water and organic matter. The co-combustion of sludge and coal can bring about the energy conversion of sludge. However, the high moisture content in sludge and the inorganic pollutants generated by co-combustion have adverse effects on combustion and the environment. In this work, through experimentation, it was demonstrated that co-combustion does not release obvious toxic elements or create an environmental hazard. On the basis of the TG/DTG curves, the ignition points of sludge and coal and the temperature of each group were obtained, which provided boundary conditions for a numerical simulation. Co-combustion with various mixing ratios and moisture contents was studied via the numerical simulation of a 330 MW boiler. The numerical results show that a high mixing ratio reduced the boiler temperature and created more moisture and fuel NOx. When the mixing ratio reached 40%, the boiler temperature became less than the combustion temperature. Sludge drying improved the internal temperature of the boiler, but it created thermal NOx. When the moisture content decreased to 40%, the temperature in the boiler rose, which improved combustion.