On-site experimental study on fouling and heat transfer characteristics of flue gas heat exchanger for waste heat recovery

A large number of fly ash particles in flue gas easily cause the fouling problem of heat exchangers, which seriously affects the efficient utilization of flue gas waste heat. In this study, experimental and numerical investigations on fouling and heat transfer characteristics in cross flow heat exchangers were carried out. The on-site experimental system was established, and the heat transfer coefficients for different heat-transfer surfaces at the fouling state were monitored in real time. The weakened degree of heat transfer coefficient and fouling thermal resistance are adopted to assess the effect of fouling on the heat transfer performance and compare the practicality of four different heat-transfer surfaces under dusty conditions. Numerical investigation was performed with the fouling model established in previous work to model the thermal-hydraulic and fouling processes. Numerical results are compared with experimental measurements and a good agreement is achieved. Results showed that compared with the aligned circular tube bundle, using H-type fins or honeycomb tube bundle both improve the anti-fouling performance, especially for the honeycomb H-type finned tube bundle, which has the lowest fouling thermal resistance. Therefore, due to the characteristics of easily soot-blowing and lower fouling thermal resistance, honeycomb heat exchangers are suitable for waste heat utilization of dusty flue gas.