Abstract
The ease and thus mode of dewatering for a given material is highly dependent on the material's physical and chemical properties. For example, in lignite, which has in the order of 60% water, a significant proportion of the water is contained within the porous lignite structure, thus making lignite difficult to dewater. To express the water from the lignite, elevated temperatures and pressures are required. The CRC for Clean Power from Lignite is investigating Mechanical Thermal Expression (MTE) as a process with the potential to economically dewater lignite. In the MTE process, the lignite is mechanically pressed at moderate temperature (150-200°C) and held at sufficient pressure to ensure that the water is expressed from the lignite matrix as a liquid. The upgraded product can be used to increase the efficiency of existing power plants, or alternatively can be used as the feed to advanced technology generating processes which enable more efficient power generation with significantly reduced greenhouse gas emissions. Analogous to lignite, materials including biosolids (from sewage sludge) and bagasse (sugar cane waste) are notorious for being difficult to dewater, with conventional dewatering methods producing cakes with high moisture contents. The major focus of this paper is therefore to investigate the dewatering of a range of 'difficult to dewater' materials using MTE. Testing is completed in a laboratory scale compression cell at a range of processing temperatures (20-200°C) and compressive pressures (3-12MPa). It is illustrated that MTE is adaptable to a range of materials, with the moisture reduction significantly enhanced relative to conventional dewatering methods.
