Abstract: In a process in which a first process variable is manipulated so as to maintain a second process variable substantially equal to a desired value for the second process variable, a set point for the first process variable is generated based on the difference between the actual value of the second process variable and the set point for the second process variable. The magnitude of the set point is determined by the probability that the second process variable may reach an undesirable value and thus control using the set point takes into the consideration the fact that large control actions may be required under some circumstances and minimal control actions may be required under other circumstances in a process.

Abstract: The heat supplied to an ethylene process cracking furnace is manipulated so as to maintain a desired ethylene production rate while the flow of feed to the ethylene process cracking furnace is manipulated so as to substantially maximize the selectivity of the ethylene process cracking furnace to the production of ethylene. In this manner a desired ethylene production rate is maintained while the process economics are improved in the case where the cost of the feed is a more important economic consideration than the cost of the energy required for the cracking furnace by substantially minimizing the conversion of the feed to undesired byproducts.

Abstract: In a method and apparatus for control of a reaction system in which a plurality of feedstock-containing streams are combined to form a total reactor feed stream, the desired ratio of relative reactant concentrations and the total flow of feed material to a reaction zone are controlled in response to a total production rate set point signal and a reactant concentration set point signal. In addition, the temperature of material introduced into one or more reaction zones can be controlled in response to a conversion rate set point signal. The recycle flow of effluent around a reaction zone can also be controlled in response to a residence time set point signal.

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 temperature requirement signal is utilized to provide a required heat signal which is representative of the direction and magnitude of any change necessary in the heat input to the fractionation column to maintain the required temperature. The required heat signal is utilized to provide fast changes in the heat input to the fractionation column in response to pressure fluctuations in the fractionation column.

Abstract: The flow rate of the absorption medium entering an absorption column and the flow rate of steam into a reboiler associated with a stripping column are controlled in response to the flow rate of a feed stream into the absorption column, the concentration of impurities in the feed stream, and the flow rate of the absorption medium containing the impurity removed from the feedstream into the stripping column in such a manner that the efficiency of the absorption process is optimized. A computer system is utilized to simulate the flow of materials inside the absorption and stripping columns. Feed forward control, based on the simulations, is utilized to maximize the energy efficiency of the absorption/stripping process by reducing the amount of steam required by the stripping process and reducing the energy consumption of the pumping system utilized to return the absorption medium to the absorption column.

Abstract: Control of a process for producing free sulfur from hydrogen sulfide is accomplished by manipulating the flow rate of a feed stream containing oxygen to a furnace in such a manner that a desired proportion of the hydrogen sulfide fed to the furnace is converted to sulfur dioxide. The flow rate of a feed stream containing hydrogen sulfide to a tail gas cleanup process is also manipulated utilizing feedforward and feedback control to maintain the hydrogen sulfide and sulfur dioxide concentrations in the gas stream from the tail gas cleanup process at acceptable levels to avoid environmental polution.

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: Bumpless transfer of control of a process parameter from control in response to a conventional controller set point to automatic control in responseto a supervisory set point is accomplished by substituting an alignment set point for the conventional set point and subsequently substituting the supervisory set point of the alignment set point.

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.