Some properties of cokes produced from high pressure carbonisation of coals
The British Gas Lurgi slagging gasifier is a counter-current fixed bed gasifier operating at high pressure. Coal descending the gasifier is pyrolysed to form coke which is then gasified. Properties of such coke affect the gasifier in its efficiency of operation. This thesis describes a) the carbonisation of cokes from coal under simulated gasifier conditions, b) the characterisation of the resultant cokes in terms of structure and physical properties and, c) the formulation of relationships between coal thermoplasticity and coke properties. Three high-volatile bituminous coals Manvers Barnburgh NCB 702, and Gedling (Manton NCB 502, NCB 802) were carbonised in an autoclave under a range of pressures (0.5- 8.0 MPa), using two different heating regimes, shock heating to 700 °c and slow heating to 700 °c at 5 °C/min. Physical characterisation of the resultant cokes was carried out using optical and mechanical techniques. Optical anisotropy and image analysis were used to determine coke structure and porosity respectively. Tensile strength, microstrength and abrasion resistance were measured to establish the cokes' resistance to various forms of breakage. High pressure dilatometry and plastometry were used to measure the effects of pressure and heating rate on coal thermoplastic properties. Relationships between coal thermoplastic properties and coke properties are very complex. This work has shown that these relationships are highly dependent on carbonisation conditions with heating rate rather than pressure being the more dominant parameter.