Numerical investigation to assess the possibility of utilizing a new type of mechanically thermally dewatered (MTE) coal in existing tangentially-fired furnaces

The mechanical and thermal expression (MTE) process can be used to remove the moisture from high moisture coal such as lignite by applying the thermal energy and mechanical force. The moisture content of lignite at Yallourn, VIC, Australia is around 60-70%. Two-third of the water from the lignite can be removed at 150 degrees C and 5.1 MPa by this process. In the conventional drying process, moisture is driven off by evaporation when the lignite passes through the mill. This process is inefficient from a thermodynamic point of view, because the latent heat of evaporation has to be supplied from the hot flue gas. This paper presents computational fluid dynamics (CFD) investigation of fluid flow and combustion of conventional lignite and MTE lignite in a tangentially fired full-scale industrial furnace. The idea is to investigate the aerodynamics and combustion effect of using MTE lignite in existing furnaces. The furnace investigated was Yallourn stage-2 in Victoria, Australia. CFD software CFX-4 (User Guide, CFX-4-Solver. AEA Technology. Harwell Laboratory, Oxfordshire, 1997) was used in this investigation. The MTE process is under development and has not been used in the real power station for the commercial production of electricity, hence no experimental data is available for comparison with the numerical predictions. To gain confidence in the MTE lignite simulations, the temperature contours and oxygen concentration at different furnace level of the conventional lignite combustion were validated first against the available experimental data. Then the predicted results of MTE lignite combustion were compared with conventional lignite combustion to assess the possibility of burning MTE lignite in existing tangentially fired furnaces.