Examples of Control Performance Improvement

An important part of a smooth running plant is optimizing the performance of the control loops. Emerson’s Mark Coughran, a senior process control consultant, describes and shares examples of how loop optimization is a part of a control performance program in regulated industries including pharmaceutical and biotech. Control performance along with operational excellence, regulatory compliance, and Process Analytical Technology (PAT) are important areas of focus for these manufacturers.

As a member of the Control Performance consulting team, they work with Life Science manufacturers in many capacities including streamlining startups, solving control problems in existing operations, and preparing the control loops to respond properly to the PAT. Examples of project objectives are to have loops move to new setpoints smoothly without oscillation or operator intervention, to minimize consumption of utilities, to implement advanced controls, and to train the plant staff ways to do the same. The team works with plant staff to isolate the limits to the plant production, whether it’s in the control algorithm, controller tuning, or the selection of instruments such as control valves.

The team’s areas of experience include both batch and continuous control for chemical reactors, bioreactors, and centrifuges to name a few. For bioreactors, Mark has worked with plants to maximize production from cultures of mammalian cells, algae, and bacteria. The team has worked on many types of fermentors: from 1-liter to 200000 liters; glass, steel, and bag (single-use); stirred and airlift; electrically heated and jacketed.

For biotech manufacturers, the loops critical to cell viability typically include temperature, Dissolved Oxygen (DO), and pH. Mark highlighted examples of the “as-left” performance after working to optimize control performance.

Bioreactor temperature control

The controller OUT is limited to 30% maximum. On a SP increase, the controller holds the OUT to maximum until just the right moment, then backs off so the PV curves right onto SP.

The reactor controller OUT (jacket temperature SP) is limited to 100 degC. Note initially the maximum heatup rate, followed by smooth approach of PV to SP, and no oscillation.

DeltaV trend chart. Lambda Tuning applied to the slave flow loops (self-regulating dynamics) and the master DO loop (integrating dynamics). The PV moves to the new SP with the appropriate speed and no oscillation.

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