Mechanisms and strategies for ash deposition reduction in flue gas heat exchanger

Ash deposition in flue gas heat exchanger affects its heat transfer performance and lifecycle, which becomes a crucial factor restricting the efficient recovery and utilization of flue gas waste heat. In this paper, a numerical method was established to investigate the characteristics of ash deposition in tube bundle heat exchangers. An integrated fouling model including transport, rebound, deposition, and removal of particles was employed to predict the behaviour of particles. Then, the effects of particle diameter and flue gas velocity on collision mass, deposition mass, absolute deposition ratio, and relative deposition ratio were studied. At last, the thermal-hydraulic and ash deposition characteristics of three different tube shapes were compared. The results showed that the low-velocity regions on the circumference were the primary locations of particle deposition, and the medium-diameter particles were the main deposition components. With the increase in flue gas velocity, the deposition mass of large-diameter particles decreased, and that of small-diameter particles increased. The use of an elliptical tube and flattened round tube with an apex angle of 60 degrees had also excellent thermal-hydraulic and anti-fouling performances. Consequently, the ash deposition and wear can be reduced by increasing flue gas velocity, filtering medium and large-diameter particles, and using elliptical and flattened round tubes.

Automated summary

The study investigated the factors affecting ash deposition in tube bundle heat exchangers, comparing the performance of different tube shapes. The results indicated that increasing flue gas velocity, filtering specific particles, and using certain tube shapes can reduce ash deposition and wear.