The role of thermophoresis during deposit build-up on a superheater tube

Most studies on modelling ash deposition in pulverised fuel boilers focus on inertial impaction as the main deposition mechanism. Effects, such as thermophoresis or heterogeneous condensation, are often neglected. However, there are several studies indicating that thermophoresis plays a key role during the early stages of deposit build-up on a superheater tube. Presented results obtained by numerical simulation show the dominant role of thermophoresis for small particle diameters, below 20 µm. It is shown that the capture efficiency increases by more than three orders of magnitude for particles in this size range and a temperature gradient of 380 K/mm in the boundary layer of the superheater tube. Furthermore, it is predicted that small iron-rich particles do not deposit due to the increased thermal conductivity, compared to aluminosilicate particles. This behaviour was confirmed by measurements in a power plant.      «

Most studies on modelling ash deposition in pulverised fuel boilers focus on inertial impaction as the main deposition mechanism. Effects, such as thermophoresis or heterogeneous condensation, are often neglected. However, there are several studies indicating that thermophoresis plays a key role during the early stages of deposit build-up on a superheater tube. Presented results obtained by numerical simulation show the dominant role of thermophoresis for small particle diameters, below 20 µm. I...     »