Numerical investigation on ash fouling characteristics of flue gas heat exchanger

•The increase of fluid velocity can lead to a decrease of the ash fouling.•Smaller particles can hardly reach tubes walls to induce the formation of ashes.•The longitudinal tube pitch is recommended of 2 as a whole.•Oval tubes can avoid loss by pressure drop and make heat transfer enhancement. The particulate deposits on flue gas heat exchanger surfaces can increase thermal resistance, reduce heat transfer efficiency and increase the instability of equipment operation. Reasonable designing of heat exchanger is of vital importance to efficiently avoiding ash fouling. This paper adopted a numerical model to predict the collision, adhesion and rebound of fly ash particles on the surface of flue gas heat exchanger. The effects of flow parameters and geometry parameters on fouling rate were examined for six row tube heat exchangers, and the feasibility of using oval tube was explored for the purpose of fouling reduction. It was confirmed that particle deposits accumulate primarily in the flow stagnation region, recirculation region, the vortex separation and the reattachment regions. Increasing the velocity can lead to a lower deposit rate. The big particles tend to deposit on the front of tubes, and the small particles are easy to follow the fluid and deposit on both the front and the back of tubes. The elliptical tube is recommended for the fouling reduction of heat exchangers, while the arrangement of tube bundles depend on the typical diameter of fly ash to soothe ash fouling.