Energy Efficiency Assessment and Exergy Analysis for Lignite Pyrolysis Process System

The exergy calculation model was established to evaluate the energy consumption and exergy assessment of a typical coal pyrolysis process system with a capacity of 1000 kg/h for raw lignite. The results indicate that although the drying unit consumes more energy, it is the pyrolysis unit that exist the maximum exergy loss because of great temperature gradient at the first reaction stage. In addition, the energy quality factor of fuel was defined to evaluate the pyrolysis yield grade. It is found the tar energy quality factor is higher than that of semi-coke and syngas. Besides, the waste steam from drying unit contains plenty of exergy, which could be used to preliminary heat raw lignite in order to reduce the energy consumption and exergy loss of drying unit.