an apparatus for flamelessly reconcentrating liquid desiccant including vertically disposed upper and lower enclosed reboiler chambers having an enclosed heating section interposed therebetween . water - rich liquid desiccant is continuously recirculated between the upper and lower reboiler drums through riser conduits disposed within the heating section and return conduits exterior thereof . simultaneously with the recirculation of the water - rich liquid desiccant an exhaust gas stream from a prime mover is passed through the heating section to convectionally heat the liquid desiccant within the riser conduits causing disengagement of water vapors therefrom . the upper drum includes an outlet for the disengaged water vapors and also an outlet for the resultant water - lean liquid desiccant .