CFD simulations were performed to assist the design of a more efficient grit collection system so as to reduce the amount of grit entering the air heater and subsequently prevent blockage.
Presently, flue gases from the super-heater and re-heater banks of the rear convection pass are turned through 90 degrees before passing to the air heaters. Hoppers are positioned directly underneath the bend, to collect the coarse particles (grit) which fall out in the turning gas flow. Originally, a set of screw conveyors (not modelled) were installed at the trailing edges of the guide vanes to mechanically carry the grit that fall onto the upper surface of the guide vanes out of the system. But the plant operator had found it unreliable and costly to maintain.
By rearranging the floor and the air-heater duct, the new unit is able to achieve a more efficient gas-solid separation without the need for guide vanes and other mechanical devices.
The ash particles from the superheater are coarser than that from the reheater. The grit collector is thus less efficient in capturing the yellow tracks which represent fine ash particles. The animation compares the performance of two grit collection systems in capturing coarse ash particles. The system on the top is an existing grit collection unit at Callide Power Station and the one below is a reconfigured grit collector.
If the animation does not load or is of poor quality, try running this compiled Smacker file: c10.exe (0.5MB).
Note that this is an executable file, and should be suitable for all PCs running Win95 or later. For more information about Smacker and its compiled executables, please follow this link.
CFD