Multi-Unit Optimization at YNCC

Yeochun NCC Company Ltd. (YNCC) in Yeosu, South Korea is an example illustrating the value of applying both advanced control and optimization to an ethylene complex. YNCC's three large naphtha cracking units had all been expanded. Each unit had a different design and a different DCS. The increasing variability of feedstocks required more flexible operations and automation. Different parts of the plant represented production bottlenecks, depending on the feedstock and the unit. YNCC needed an integrated solution of optimization and multivariable control to maintain optimal conditions during changing operations.

YNCC's objective was to maximize on-spec production across seven furnaces while processing feedstocks of greatly varying quality. There were numerous operating constraints including the capacity of furnaces, refrigeration compressors, and fractionators. The objective was to be met while minimizing energy consumption.

Honeywell designed a solution that consisted of 17 Profit Controller applications on the various process units. A single Profit Optimizer application provided yield predictions and managed the controller gains. Since the cracking process is highly non-linear, a separate process model developed real-time estimates of conversion and coking rates as well as metal temperatures. These estimates were used by the Profit Controllers. Honeywell also provided OPC connectivity for integration of the other plant automation systems.

The project was completed in under a year and YNCC measured the major results as follows:

	3% increase in feed rate
	3.2% decrease in energy consumption per unit of product

The energy savings came from reduced steam to fractionation columns and from reduced loading of refrigeration circuits. Besides these benefits, the plant has gained new flexibility in terms of its operations. The plant model and optimizer allow much more consistent operation of the plant and enables variations in feedstock quality to be handled far more easily. Having chosen Honeywell to optimize their plant because of their "technical superiority and detailed knowledge of various process control solutions", YNCC's plant manager comments that he expects his company to "strengthen its competitiveness in the ethylene business through its APC alliance with Honeywell".