Energy company Enterprise Products is systematically converting existing process control systems over to APC on its pipelines, natural gas processing plants, NGL and propylene fractionators, and import/export terminals. They use Honeywell's Profit Controller and Profit Controller Express multi-variable control and optimization. "We plan to have APC running all our major facilities in the coming years," says staff engineer Tom Lyndrup.
"We've been monitoring our APC installations constantly to ensure the benefits are achieved and maintained over time," he says. "Once we were successful with the first few APC installations, and we saw how well they performed, APC became our assumed method of control in each new facility, and we are aggressively working towards upgrading existing facilities to APC."
Enterprise Products justifies APC projects by looking at historical data and estimating how much better they can run after significantly reducing normal PID control variations and running closer to process limits. "Justification has been easy on each project, and we have achieved or exceeded the estimated benefits immediately after each APC controller was turned on," Lyndrup says. "These improvements include increased throughput, more consistent product spec and improved operability."
"We maximize profit of the plants by constantly pushing up against real plant limits rather than operating conservatively," he adds. "To do this we sometimes need to take full advantage of custom programming features available in the APC software to force the plant to its true limits, while simultaneously reducing the chance of a process upset."
Enterprise developed numerous software tools to help monitor its APC facilities and keep the process control and operations people informed of their unit's APC performance on a regular basis.
Most projects start with step testing. "The Enterprise APC engineer works closely with Honeywell in every phase of each APC project, including controller design, step testing and implementation," says Lyndrup. "Honeywell performs the initial model identification from the step-test data. The Enterprise APC engineer supports the APC controllers after implementation, with technical support from Honeywell as needed.
Although they recommend step testing where possible, Enterprise has implemented two APC controllers without any step testing when the new processes were similar enough to existing APC processes.
"We have not found it necessary to perform any step testing after a project has been completed," he adds. "We make occasional minor model adjustments and other changes to settings on-line. That has been sufficient to keep the plants running smoothly and at their optimum performance."
Years of experience with APC is paying off. "Step testing is already dramatically improved," says Lyndrup. "Our first APC about 15 years ago took one month to step-test, and now it takes a week for a similar process. We expect this to be even further reduced, and more off-the-shelf components have driven the cost down. Our oldest APC system, which ran on Honeywell's AxM node, now runs on a server. The install is much easier and more integrated with the Honeywell DCS."