Chemical Processing - January 2008 - (Page 40) >> MAKING IT WORK so I don’t want to take any chances and have an upset.” An upset could mean anywhere from four to eight hours of lost production. It took a while but the operators nally developed enough con dence in the new MPC. Immediate benefits and future plans When you add up the savings in engineering coverage, operator interventions and time necessary both for testing and analyzing data — all cut by approximately 50% — the real bottom-line bene t of implementing an MPC in this compressed time frame is enormous. This is in addition to the well-known industry-proven advantages of having a reliable well-modeled MPC. The Hartford site gained a number of important bene ts: • increased LPC stability, which leads to better CLAR recovery, reduced operator intervention, and less downtime or fewer loss-producing events; • the ability to change production rates very quickly, without upsetting the plant and the key purities; • optimization of the evaporation tower; • improved control of power demand — the MPC is set up such that it can drive production while also maintaining the power demand targets set by the power company; • better load-following on pipelines — the MPC can quickly adjust plant production to meet changes in pipeline demand; • enhanced constraint handling; and • improved ramping — overall average ramp rate improvement of 220 to 650%. “LMPC [Linear Model Predictive Control] has done a much better job than our previous APC [Advanced Process Control] system in maintaining the ever-so-critical low pressure column purity control,” says Golinsky. “The LMPC system has been in place ve months now, and our downtime on argon has been reduced by over 75%. The plant will run for weeks or longer without operator intervention being necessary on the LPC purity.” The old underperforming MPC didn’t provide any of these bene ts. While speci c numbers for the Hartford plant aren’t yet available, Golinsky estimates a $20,000/ year savings from reduction in upsets alone. Industry experience shows that a solid MPC implementation will provide $80,000 to $85,000 annual bene t to a plant. After the demonstrated success at Hartford, Linde is implementing this methodology at other eight plants. We have nished two already and are currently are in the process of doing three more. CP Zul Bandali is an advanced controls engineer for Matrikon in Edmonton, Alberta. Reach him via e-mail at Zul.bandali@matrikon.com. www.chemicalprocessing.com http://www.intersystems.net http://www.intersystems.net http://www.westernstates.com http://www.westernstates.com http://www.chemicalprocessing.com
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