A blending control system in a refinery comprising a splitter and a blender for implementing blending operations in rundown components supplied from the splitter without intermediate storage tanks, the blending control system comprising a computer modeling apparatus deploying a nonlinear optimization problem solver component acting on nonlinear parameters and discrete variables, the computer modeling apparatus comprising: an input module enabling user specification of inventory information including at least one rundown component, and user specification of refinery product commitments; and a processor routine executable by a computer and coupled to the input module and responsive to the user specification by sequencing refinery operation events into a schedule that matches the refinery product commitments with inventory and unit rundown blending operations, wherein the refinery operation events include blend events; and the processor routine determining for the schedule the sequence and timing of refinery operation events, including the number and duration of event periods, optimizing event volumes simultaneously with recipes for product blends for the rundown blending operations of at least one rundown component supplied to the blender from the splitter; and determining the split ratio of the splitter, for splitting rundown component blending operations between refinery products and changing qualities of component streams wherein the processor routine implements a mathematical model which implements a series of optimizations and which applies penalties to encourage the sequence of blends to remain the same from one optimization and the next, and to minimize the number of changes in the split ratio for the or each splitter the blending control system using the schedule to provide a new value range to parameters and variables of the blending control system to control the blending operations wherein the sequence of timing of blend events is determined as well as the blend recipes while ensuring that the entire volume of the at least one rundown component is used as it becomes available. an input module enabling user specification of inventory information including at least one rundown component, and user specification of refinery product commitments; and a processor routine executable by a computer and coupled to the input module and responsive to the user specification by sequencing refinery operation events into a schedule that matches the refinery product commitments with inventory and unit rundown blending operations, wherein the refinery operation events include blend events; and the processor routine determining for the schedule the sequence and timing of refinery operation events, including the number and duration of event periods, optimizing event volumes simultaneously with recipes for product blends for the rundown blending operations of at least one rundown component supplied to the blender from the splitter; and determining the split ratio of the splitter, for splitting rundown component blending operations between refinery products and changing qualities of component streams wherein the processor routine implements a mathematical model which implements a series of optimizations and which applies penalties to encourage the sequence of blends to remain the same from one optimization and the next, and to minimize the number of changes in the split ratio for the or each splitter the blending control system using the schedule to provide a new value range to parameters and variables of the blending control system to control the blending operations wherein the sequence of timing of blend events is determined as well as the blend recipes while ensuring that the entire volume of the at least one rundown component is used as it becomes available.