A level control system for controlling a liquid level in a vessel containing a two-phase fluid includes a plurality of sensors configured to measure parameters related to the vessel. The parameters include liquid level in the vessel, vapor flow rate leaving the vessel, pressure in the vessel, temperature of the vessel, and feed-liquid flow rate entering the vessel indicative of a state of the vessel. A predictive controller is configured to receive output signals from the plurality of sensors and predict a volume of liquid over a predetermined time period in the vessel based on output signals from the plurality of sensors and a variation in pressure, thermal load, or combinations thereof in the vessel. The controller is configured to generate a liquid level set point of the vessel based on the predicted volume of liquid in the vessel; and further control a liquid level in the vessel based on the generated liquid level set point by manipulating one or more control elements coupled to the vessel.