A system includes sensors configured to measure vessel parameters. A signal processing unit receives sensor output signals and generates a first, second, third, fourth, and fifth filtered output signals representative of liquid level, gas flow rate, feed-liquid flow rate, vessel pressure, and vessel temperature, respectively. A flow demand control unit receives the first filtered output signal and generates an output signal representative of feed-liquid flow demand. A shaping unit receives the second, fourth, and fifth filtered output signals and generates an output signal representative of shaped gas flow rate. A liquid level control unit controls the liquid level within predetermined limits by controlling one or more components based on the output signals from the flow demand control unit, the shaping unit, and the third filtered output signal.