Multivariable Constraint Control at Longford
This paper covers the application of multivariable constraint control (MVCC) technology to the three Esso/BHPB gas plants at Longford, Gippsland (Australia). The plants were pneumatically controlled before upgrades to distributed control systems in the 1990s. The first project maximized distributed control systems effectiveness. This project improved plant stability, reduced alarms and operator intervention by using tried-and-true control tool-sets from Exxon Mobil Corporation's and its subsidiaries Refining & Chemicals operations around the globe.
The second project at Longford used MVCC to enhanced recovery of LPG molecules from sales gas (natural gas) in the three gas plants. This was [only] the second time that this technology had been applied [anywhere in the world] by ExxonMobil in the upstream. The MVCC technology created plant models of up to one hundred variables to effective automate the plants. All plants models had a prediction horizon of two hours and a running frequency of one minute. Economic optimization of the plant uses both linear and quadratic programming. All types of variables are controlled including continuous, intermittent and ramp variables.
The MVCC project exceeded expectations. The gas plants now recover more LPG from sales gas and the plants' capacity has increased. Plant stability, alarm and operator intervention frequencies also improved. Looking forward, there are further attractive opportunities for MVCC in ExxonMobil Australia’s Upstream facilities. There are currently plans to apply MVCC technology to three light ends fractionation trains at Long Island Point on Westernport Bay.