CASE STUDY

Recovering a Chemical Manufacturer’s Productivity with Batch Cycle Time Reduction

The completed project made the process safer and recovered 30% of the lost cycle time, giving an ROI of well under one year.

OBJECTIVE: The chemical manufacturer needed to recover productivity losses caused by an unexpected increase in cycle time after a migration of the plant’s legacy Emerson PROVOX™ to a DeltaV™ distributed control system (DCS).

The third-party migration from legacy Emerson PROVOX™ to DeltaV™ DCS increased the cycle time on a train of eight chemical reactors by approximately 6%, costing the end user more than one million dollars per month in lost productivity. The objective was to investigate where time was being lost in the batch process due to logic changes during migration and recover as much time as possible to increase productivity.

CHALLENGE: A safety issue required a project pivot and scope change during the project. A potentially dangerous safety hazard associated with the original migration was identified and the system was operating in an unknown state.

The DeltaV™ logic was skipping over the task of confirming valve positions before moving to the next step in the batch. This issue needed to be addressed before moving forward with the cycle time reclamation aspect of the project. Addressing the lack of valve position confirmation, the additional logic forcing the DeltaV™ to wait for the valve positions to confirm caused even slower cycle times than the project started with, so the gains shown in the initial proof of concept became unattainable.

BACKGROUND: A vinyl derived chemical manufacturer in the greater Houston area operating a fully batch process had undergone a migration from Provox to Emerson DeltaV. After the migration was completed, the cycle time of each reactor batch was up approximately 18%. Hargrove was called to assist with returning the process to its pre-migration cycle time.

A review of the new logic was undertaken and it was discovered that the logic was migrated in a manner that kept the original phase structure intact from PROVOX™ into DeltaV™. Unfortunately, key differences in PROVOX™ and DeltaV™ system architecture on how phases are loaded and executed was causing long pauses in the new DeltaV™ batch process.

The pauses occurred where devices in the unit were idle while waiting for DeltaV™ to unload the current phase and load the next phase. This issue was exacerbated by the fact that the new DeltaV™ controllers were operating beyond the ideal loading capacity, so unloading and loading phases were taking longer than they normally would. A lack of available controller processing capacity prevented the phases from being permanently loaded into memory or being allowed to execute at a faster scan rate.