In many advanced coal-fired plant the gases being passed to the gas turbine will contain low levels of small particles. These particles may deposit on, or cause erosion of, the turbine blades, affecting the economic and technical viability of such systems. Modelling work has been undertaken to assess the effects of particulate contamination in coal-fired systems.
A number of different models for the particle behaviour have been developed and used, depending on the particular application involved. The behaviour of particles of a few microns in size and upwards is dominated by inertial effects and has been modelled by performing particle trajectory calculations in the turbine flow field, this having been first calculated with a turbine flow code.
Smaller particles tend to be deposited by a process of diffusion through the turbine blade boundary layers. Two modelling approaches have been undertaken for diffusive deposition. The simpler approach is based on a heat transfer analogy combined with extra prescriptions for thermophoresis and eddy impaction effects. The more complicated approach involves a numerical solution of the particle diffusion equation within the boundary layer, including the effects of thermophoresis and using a stopping distance model for eddy impaction effects.
Predictions from the models have been compared with experimental results at realistic conditions obtained in a PFBC rig at Grimethorpe and with laboratory results at ambient conditions.