Experimental research of fouling layer and prediction of acid condensation outside heat exchanger used in coal-fired boiler

Research on the fouling layer covering heat exchangers is of practical value to increase the efficiency of heat exchangers and even that of boiler, especially when considering coupled effects of ash deposition and acid condensation. The field experiments are carried out using a special designed pipe in a 300 MW sub-critical unit. The effects of internal Reynolds number of water (Rewater), inlet temperature of water (Tin), flue gas temperature (Tgas) and external Reynolds number of flue gas (Regas) on heat transfer efficiency have been analyzed via the calculation of fouling factor (ε) as well as external Nusselt number of flue gas (Nugas). Apart from this, the 1-D model to describe the acid condensation has been built in light of the thermodynamic results of water vapor and sulfuric acid vapor obtained by former research. In this model, both gas-liquid equilibrium effect and multi-component diffusion effect have been well considered. Furthermore, the acid condensation can be influenced to different extents by the exterior wall temperature of the pipe, acid vapor and water vapor contents of flue gas. Consequently, the efficiency of heat exchangers is enhanced by the rise of exterior wall temperature according to the experimental results and acid condensation analysis.