Patent ID: 6849155

Claim:
A concentrator which comprises: a heater having a heating medium that has been heated to a temperature not less than the boiling point of a solution fed to the concentrator, whereby said heater heats the solution to evaporate the solvent to a gas to make a mixture of the gas and a liquid; a gas-liquid separator for dividing the mixture into the liquid and the gas; returning means for returning the liquid separated in the gas-liquid separator to the heater; concentration detecting means for detecting the concentration of an intending component in the separated liquid, said concentration detecting means communicating with said returning means; a flow-regulating valve connected to said concentration detecting means and placed downstream thereof; liquid draw-out means for drawing out a portion of the liquid separated in the gas-liquid separator, said liquid draw-out means comprising a flow path through which said portion of the liquid is drawn and a cross valve having an inlet, a first outlet, and a second outlet and placed downstream of said flow-regulating valve, wherein said inlet is connected to said flow-regulating valve, said first outlet communicates with said returning means, and said second outlet is connected to said flow path; and control means for controlling said flow-regulating valve and said cross valve so that: when the concentration detected with said concentration detecting means is above a predetermined threshold, said inlet of said cross valve communicates with said second outlet thereof; when the concentration is below the threshold, said inlet of said cross valve communicates with said first outlet thereof; and the amount of the drawn out liquid is controlled through the operation of said flow-regulating valve depending on the concentration.