Mechanical/thermal dewatering of lignite. Part 2: A rheological model for consolidation and creep process

A rheological model is presented for the description of the dynamic behaviour of lignite during mechanical/thermal dewatering (MTE). The dewatering during the MTE-process is described depending on the process parameters time, temperature, pressure and the initial height of the coal filling in a press. The model was verified by comparing the calculations with experimental data in a wide range of process parameters. The comparison for three different lignites shows an excellent agreement. Therefore the model is also applicable for the technical process design. Additional experiments and calculations have been performed for a detailed analysis of the hydraulic pressure drop during the expression of water from lignite. It was found that the differences in geological history result in large variations of the lignite permeability and have remarkable influence on the duration of the primary consolidation (early stage dewatering). The theoretical and experimental results offer a deeper understanding of the influence of process parameters and lignite properties on the consolidation process and the kinetics.