Liquid desiccant lithium chloride regeneration by membrane distillation for air conditioning

Liquid desiccant air conditioning (LDAC) has emerged as an attractive technology for improving indoor air quality and thermal comfort. Regeneration of liquid desiccants is critical to sustain the process efficiency of LDAC. This study explores membrane distillation (MD) for regeneration of lithium chloride (LiCl) desiccant solution commonly used in LDAC. The results demonstrate the viability of MD for LiCl regeneration. The MD process at the feed temperature of 65 °C could increase the LiCl concentration up to 29 wt.% without any observable LiCl loss. Given the high concentration of the LiCl solution feed, unlike traditional desalination applications, the impact of concentration polarisation on the process water flux was significant. Indeed, the calculated water flux obtained by excluding the concentration polarisation effect was more than twice the experimentally measured water flux from a concentrated LiCl solution (>20 wt.%). The regeneration process can be optimised in terms of regeneration capacity (ΔC) and specific thermal energy consumption (α) by regulating several operating conditions, including LiCl concentration, feed temperature, and circulation cross flow velocity. Increasing feed temperature and circulation cross flow velocity was beneficial to the process efficiency, enhancing water flux and ΔC while reducing α. On the other hand, increasing LiCl concentration resulted in a linear decrease in both water flux and ΔC, but an increase in α following a hyperbolic function.