Abstract: In an acid alkylation process wherein a fresh isobutane stream is combined with an olefin stream to form a combined isobutane olefin feed stream, a control system maintains a desired ratio of isobutane to olefin in the combined feed stream by manipulating the flow rate of the fresh isobutane stream. In addition, the controller automatically compensates for the effect of changes in the fresh isobutane feed stream by making equal changes in the flow rate of reactor effluent. Thus, the liquid level in the alkylation reactor is unaffected by changes made in the fresh isobutane stream to maintain the desired isobutane to olefin ratio.

Abstract: A desired unreacted monomer concentration is maintained in the reaction effluent removed from a polymerization reactor by manipulating the catalyst feed rate to the polymerization reactor based on a non-linear control signal derived from a comparison of actual and desired unreacted monomer concentration.

Abstract: A variable limit is utilized to prevent a position controller which requires a velocity set point signal from overdriving a stuck control valve. Control based on a comparison of the actual position to desired position is utilized unless the valve is stuck. If the valve is stuck, the variable limit controls the velocity set point provided to the position controller until such time as the valve becomes unstuck.

Abstract: A control system for a fluid catalytic cracking unit is provided in which either the wet gas compressor or the air blower is selected for base loading. After the device selected for base loading has been base loaded, load is shifted to the device which was not base loaded. The feed flow rate is forced to continue to increase until both the wet gas compressor and the air blower are loaded so as to substantially maximize the production of the desired product.

Abstract: Method and apparatus are disclosed for the automatic adjustment of the fractionation column pressure in a fractionator system which employs total condensation of overhead vapor and a liquid full reflux accumulator to thus float the column pressure above minimum column pressure. The set point of a condensder fan pitch controller, which manipulates the blade pitch of the condenser fan, is automatically adjusted in response to a desired offset of condensate subcooling from the overhead bubble point temperature which is repeatedly automatically calculated in response to analysis of the overhead product composition and pressure. The set point of a pressure controller, which manipulates the overhead product control valve to adjust column pressure, is automatically adjusted in response to a fan pitch signal from the condenser fan pitch controller and a desired fan pitch set point. Appropriate limits and overrides are also disclosed to prevent sudden changes in column pressure which might upset system operation.