Application of plasma burners for char combustion in a pulverized coal-fired (PC) boiler – Experimental and numerical analysis

This study considers the combustion of pulverized coal with unburned char recovered from ash of the industrial boiler. The concept of char combustion with coal is implemented by installing two plasma burners on the front wall of the combustion chamber. The main objective is to improve the boiler's efficiency by reducing the amount of unburned fuel. The behavior of the combustion process is investigated using CFD modeling of the combustion chamber with tangentially-fired burners and two plasma burners. Thermogravimetric analysis and laboratory-scale tests in a drop tube furnace are performed to obtain the combustion characteristics of the investigated char and, eventually, to assess the validity of co-firing with coal the unburned char. The CFD simulation of the non-retrofitted boiler with twelve pulverized-fired burners results in the excessive movement of coal particle streams toward the chamber walls outside of the designed swirl diameter caused by a high centrifugal force, thereby contributing to a decreased level of fuel burnout. The CFD results with plasma burners indicated that the swirl diameter is reduced improving the degree of mixing resulting in a more uniform temperature and velocity distributions. The average temperature at the combustion chamber outlet increases by approximately 40 °Creaching 1260 °C.