Abstract
Advanced coal-powered power stations utilising combined cycles of both combustion and gasification are currently under development throughout the world. The fuel gas derived from coal gasification contains gaseous species such as CO/CO2, H2/H2O and CH4, as well as gaseous compounds of sulphur, nitrogen and chlorine and entrained solids of char and ash. On exiting the gasifier vessel temperatures can be between 673 K and 1273 K with oxygen pressures as low as 10−20 atm. and sulphur pressures as high as 10−7atm. making the environment extremely reducing and sulphidising. In this area, high temperature particulate control filters are required to meet environmental and turbine equipment requirements.
The aim of this research is to evaluate the effect of a simulated gasification atmosphere on the mechanical properties of a clay-bonded SiC and to consider the thermodynamic stability of the possible gaseous and solid chemical reactions. Temperatures between 873 K and 1273 K were employed for up to 200 hours with 3-point bend tests used to measure changes in strength. Analytical techniques (XRD, EDX and SEM) coupled with thermodynamic calculations allowed the investigation of the corrosion mechanisms for these materials under simulated gasification conditions. It was found that a severe strength degradation of the filter material occurred due to volatilisation of clay-binder constituents and crack formation due to stresses induced by devitrification.
