Abstract: In a fractionation system in which pressure fluctuations within the fractionation vessel can result in alteration of the fractionator product composition, fractionation column pressure is monitored and converted to a temperature requirement signal representative of the temperature required within a preselected portion of the fractionation column in order to provide the desired product constituent distribution. The heat input to the fractionation column is controlled in response to the temperature requirement signal, corrected as necessary by actual analysis of the product. In a preferred embodiment, control of a demethanizer column in a cryogenic natural gas liquids separation process can be practiced advantageously.

Abstract: In a poymerization system having first and second feed streams, diluent and recycled diluent streams, and a modifier stream controllably fed to a reactor, a resultant product stream is passed from the reactor, and a gas stream is removed from the resultant bottoms product of the reactor. The gas stream is analyzed and signals are delivered in response to the analysis. The signals are modified and compared to a modified signal responsive to one of the flow rates of the recycled diluent stream or the second feed stream that has been modified by the flow rate of the diluent stream for providing a resultant control signal for relatively controlling the flow of the modifier stream.