PURPOSE: To utilize effectively heat energy and concentrate a solution by evaporating the water content of solution by jetting combustion gas into the solution, and discharging automatically a formed residual concentrate.

CONSTITUTION: A combustion cylinder 2 is disposed on the center of an upper part of a conical main body 1, under which a combustion gas jetting cylinder 3 is provided, and further a screen conveyor 13 connected with a residual concentrate discharge outlet 4 is provided on the conical lower section. A plurality of small diameter holes 15 are formed on the jetting cylinder 3 slightly above the water level 20 of the solution in the main body 1. Then combustion gas is jetted into the solution to evaporate and concentrate the water content, and the whole sensible heat of combustion gas is utilized. A residual concentrate is discharged automatically the screw conveyor opened on the height of adjusted water level.