Application of liquid desiccant dehumidification to amine-based carbon capture systems

Liquid desiccant-based dehumidification with water recovery is an effective and robust method to remove excess moisture from process gas streams and recover relatively high quality product water. A study was undertaken to determine if desiccant-based technology could be applied to the benefit of an amine-based CO2 capture system since the addition of CO2 capture to a coal-fired power plant can significantly increase the plant's consumptive water use. Test data with a pilot flue gas moisture recovery system are presented to illustrate the characteristics of the process, including the water recovery potential, product water quality, and thermal energy consumption. The process is then evaluated theoretically under conditions typical of a monoethanolamine-based CO2 capture process. The analysis indicates that there is less opportunity for moisture recovery compared to a plant without CO2 capture because of the cooler processing temperatures associated with CO2 absorption and stripping. However, a desiccant-based dehumidification system might be useful as a heat-driven moisture management tool since desiccant-based moisture removal is more effective than dew point cooling for a given heat rejection temperature. Dehumidifying the CO2 product stream prior to compression might offer incremental power consumption savings compared to other options of moisture vapor management.