- shutdown and startup procedures that are infrequently executed;
- product grade changes that require moving the plant from one mode of operation to another;
- abnormal situation management to bring the plant to a safe holding point from which operations can resume or a shutdown can take place; and
- periodic activities such as regeneration, pump changeover or furnace decoking.
For instance, polymer plants commonly transition between products without stopping the process. This requires the operator to adjust operating parameters in a specific sequence while carefully observing the process response. While many transitions are similar, there can be significant differences in the procedure depending upon the product pair involved.
Executing the changeover as quickly as possible minimizes output of transitional material, which generally is less valuable or may even have to be discarded. In most plants today, the success of the transition often depends upon the particular operator’s experience, familiarity and “feel” for the process.
Even for plants that make fairly frequent transitions, any given operator may handle a specific transition only once every few months. As a result, the time taken to complete the transition and the amount of transition material made will vary.
A key area of focus for implementing automated procedures here is the reactor. Often, polymers manufacturers rely on sophisticated advanced control strategies that must be guided through the transition. Procedural operations are able to interact with the advanced control solution and coordinate these interactions with changes that are required in other parts of the plant, including feed, catalyst preparation and finishing areas — and so can significantly improve plant agility.
Automated procedures also promise sizable benefits for cyclic activities or periodic maintenance. For instance, an ethylene plant typically will sequentially take each of the furnaces that crack naphtha into ethylene and propylene offline every 45 days or so for decoking.
During continuous operation, coke forms on the inner surface of the cracking coils. Left unchecked, this coking can lead to decreased productivity, furnace system failure and safety issues. Decoking requires the furnace to be isolated from the process. A flow of steam or a steam/air mixture is passed through the furnace coils. This converts the hard solid carbon layer to carbon monoxide and carbon dioxide. Once the carbon/coke is removed, the furnace can be returned to service.
Automating these procedures (and providing manual interactions that are required) can ensure that they are carried out consistently while capturing detailed information about their execution that may provide insights for improvements.
State-of-the-art DCSs can readily accommodate automating of procedures, typically though use of a sequential function control notation. The procedures consist of a series of steps with outputs (Open Valve V1101), instructions (“Take a lab sample”) and transitions (wait for T101.PV > 85.5). In addition, the procedures can be configured to react (e.g., hold or abort) to abnormal conditions.
Implementation must be done as part of a broader exercise for determining and updating best practices and must incorporate a comprehensive process for designing, reviewing and modifying procedures. Failed procedural-operations implementations often stem from poor scoping and planning. Keys to success include:
- scoping — evaluating current procedural operations needs, prioritizing procedures, defining a timeline and determining the financial value of converting manual procedures;
- procedure evaluation and design — leveraging best practices for implementing and documenting automated procedures;
- best practice benchmarking — identifying and fixing gaps within departmental procedures;
- automated procedure value analysis — measuring performance of procedure execution and identifying areas with opportunity for additional improvement;
- procedure workflow — reviewing the overall steps required in the procedure and looking for bottlenecks;
- simulation and verification — checking the procedures before implementation is completed to ensure the solution functions properly and achieves the desired results; and
- full lifecycle support — leveraging batch reporting tools to capture execution history and support problem resolution and continuous improvement.
Specific implementation pointers appear in the sidebar.
Integration of automated procedures into a DCS can ensure that operators execute procedures in the correct and validated way. This can significantly reduce the risk of human-error-induced incidents, improving safety and achieving more consistent operations and reduced downtime. Additionally, the technology can capture the knowledge of retiring operators by moving it into a traceable and improvable system. Implementation of just a few key procedures as part of a wider operator-effectiveness program can provide sizable savings.
Patrick Kelly is chemicals market segment leader for Honeywell Process Solutions, Phoenix, Ariz. E-mail him at Patrick.Kelly@Honeywell.com.