This variability not only impacted the quality of the produced resin, it impacted overall energy usage and the amount of manual efforts required by plant operators to try to keep the produced products within specification limits. Improving the temperature control would mean reduced rework and optimized reaction speed.
The plant contained several reactors which required heating and cooling systems for the jackets surrounding each reactor. The objective was to keep the reactor temperature with 5°C of the setpoint. Additionally, if the temperature exceeded +30°C of the setpoint, the exothermic reaction speed would increase too fast. This would cause a distillation column overload at the top of the reactor.
At this higher temperature, the raw material components exit on the top of the distillation and these components are missed from the chemical reaction. These high temperatures damage the final product by changing its color—one of the quality parameters.
Part of the batch process to make these resins was to perform initial laboratory analysis. If this analysis revealed that the final product was not on track to meet specifications, the reactor needed to be cooled down to add raw materials to the batch. The reactor temperature was then brought back up to original setpoint.
As a consultant on the Process Improvement and Optimization Consulting team, Gergo worked with the plant staff and analyzed the control strategies as well as the tuning of the temperature and other loops involved in the batch reaction process.
The plant had a DeltaV distributed control system to control the process. Gergo and the team tuned the loops in all of the reactors. The cascaded temperature loops were placed into automatic and cascade modes.
The control strategy was also improved to handle the large number of product variations the plant needed to manufacture. With the changes made, the new controls could keep the temperature within 0.5-1°C deviation from the setpoint with very little overshoot.
One immediate benefit was increased energy efficiency. Previously, to keep the reactor temperature stable required using both the heating and cooling systems. Now, the heat demand is stable and the cycles of cooling the jacket temperature have been eliminated. Also, the operators could spend time optimizing the process in other areas instead of manually adjusting the control loops to keep the temperature within the ±5°C range. With the temperature more tightly controlled, the repeatability of on-spec batches increased.
Gergo noted that ongoing assessments are being made as various products are produced to verify that the control strategy and loop tuning parameters perform as well as the initial batches. These assessments will also be used to help identify further improvements which can be made in the future.
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