flow controller 30 continually adjusts a valve 31 in conduit 1 to control the flow rate of water into the top of column 3 the set point of flow controller 30 is continually adjusted by a flow ratio controller 32 to maintain a ratio of the flow of water in conduit 1 to the flow of incoming purge gas in conduit 19 such that the blended ammonia product will have a water concentration between desired minimum and maximum water concentrations as an alternative mode of operation the set point of flow controller 30 may be continually adjusted by a liquid density controller 33 thereby controlling and maintaining the flow of water to absorber 3 at a rate which will result in a constant density in the aqueous ammonia solution leaving the system in conduit 18 which in turn maintain an approximately constant ammonia concentration in the aqueous solution such that the blended ammonia product will have a water concentration between desired minimum and maximum water concentrations the ratio set point of ratio controller 32 and or the density set point of density controller 33 are adjusted from time to time to maintain a concentration in the anhydrous ammonia product of the plant at a desired level high enough for corrosion protection in the product storage equipment and low enough to meet product specifications fig2 shows in.