Mass transfer processes in flow passages of rotating regenerative air preheaters

This investigation was performed in order to provide the knowledge base needed for establishing optimal operating conditions for air preheaters in coal-fired power plants.;A finite difference analysis was developed for predicting the condensation rates of sulfuric acid and water vapor on the flow passage wall. The theoretical Sherwood number distributions were found to be insensitive to the acid and water vapor concentrations and surface temperature over the range of conditions addressed. This conclusion was also obtained from the experimental results.;Theoretical models were developed for analyzing evaporation of a liquid layer of sulfuric acid and water in both fully developed and developing flows, and a superposition technique was introduced to simplify the calculation procedures. Simulations of the evaporation process show that surface temperature, moisture level and Reynolds number have the most significant influences on the evaporation rates. Evaporation experiments were performed, and the measured Sherwood numbers for evaporation were found to be independent of surface temperature and moisture level over the parameter ranges of interest. A comparison between the measured and theoretical Sherwood numbers showed that the average relative difference was 7.8 per cent.;A theoretical model was developed for predicting the condensation rates of sulfuric acid and water vapor on fly ash particles suspended in flue gas. The analytical results showed that the smallest particles play the most important role in influencing the condensation rate of acid vapor at the passage wall.;In the adsorption analysis, a mixed-gas heterogeneous model was applied in analyzing the equilibrium adsorption of the gas mixture containing sulfuric acid, water and a non-adsorbable gas on the surfaces of fly ash particles. The influence of adsorption on the condensation rates towards the passage wall was shown to be small for typical conditions, even though the depletion of the bulk acid and water concentrations had increased due to adsorption. It was also shown that the adsorbed amounts of acid and water on the particle surfaces can not be neglected in comparison to the condensed amounts under the conditions of interest, especially in the region near the center line of a flow passage.