the present invention relates to a method and apparatus for reducing the maximum water concentration in multi - phase reactors operating at fischer - tropsch conditions . in a preferred embodiment of the present invention , a method of reducing the maximum concentration of water in a multi - phase reactor containing an expanded slurry bed and a water - rich slurry region for fisher - tropsch synthesis includes changing the flow structure of a predetermined region in the reactor . the flow structure may be changed by introducing a mixing enhancing fluid into the predetermined region , installing baffles into the predetermined region , or by other methods known in the art . preferably the predetermined region is located between ½ h and h and between ½ r and r , where h is the height of the expanded slurry bed and r is the radius of the reactor .