A Novel Correlation for Considering the Effect of Neighboring Droplets on the Evaporation Rate of Solvent Droplets Used in Carbon Capture Applications

Abstract

The spraying of chemicals such as mono-ethanolamine (MEA) and aqueous ammonia is widely used in spray columns for CO2 removal from the combustion flue gasses. When droplets in the spray interact with flue gas, due to temperature difference, along with the absorption of CO2 from the flue gas, they also undergo evaporation. Also, the presence of other droplets in the vicinity of a given droplet can influence evaporation as well as gas absorption into it. Understanding the droplet evaporation and the influence of the surrounding droplets on the evaporation of droplets are one of the critical aspects to address for developing reliable models for CO2 capture from flue gasses. This work investigates the influence of neighboring droplets on evaporation of a droplet in question and comparison with evaporation of an isolated droplet. Various configurations of suspended droplets of water, aqueous ammonia, and MEA were examined within a temperature range spanning from 75 °C to 125 °C. The droplets, placed on a microfiber grid made up of 100 μm glass fiber, were introduced into a heating chamber, and temporal variation of the droplet size was recorded using backlit imaging. Images were processed using Matlab algorithms to obtain the droplet's evaporation rate. Variation in the evaporation rate is evaluated with respect to the temperature and available surface area for vapor diffusion. The results indicate that the presence of neighboring droplets influences the droplet evaporation, and the magnitude of influence depends both on the number of droplets as well as their proximity. Of the three liquids studied, influence of neighboring droplets found to be more significant in case of MEA. To consider the influence of neighboring droplets and their proximity, a novel independent parameter called surface area ratio (SAR) was introduced by combining both the parameters. The analysis involved investigating the variation in the normalized evaporation rate in relation to the SAR parameter. It was found that the normalized rate of evaporation under different conditions studied varies linearly with SAR. A correlation is developed between the normalized evaporation rate and SAR combining the data from all the cases studied which can be used to correct rate of evaporation in computational models.