Heed the Warning

Optimizing plant performance requires more than running within alarm limits

By Chris Stearns, Honeywell Process Solutions

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Without this broader view, each role is working with data that lack the larger context.

For example, planners who can't validate the weekly production plan against limits potentially could overdrive equipment that may have units operating in alarm, leading to damage and possibly even failure. The ripple effect of planning without an understanding of all limits (e.g., operating, environmental, design and reliability) can result in injury to plant workers, harm to other equipment, shutdowns and environmental releases.

Operations management products can effectively manage information such as planning targets, key performance indicators, standard operating limits and procedures, safety and environmental limits, and the causes of deviations. They improve plant performance by systematically setting and communicating operating plans, monitoring process data against limits, and highlighting the priorities of deviations. By providing a better understanding of performance versus industry norms, and knowledge of true operating limits for better reliability and agility, they help reduce energy usage while improving yield, product consistency and run lengths.

Moreover, they impose a standard, structured way to activate the operating plan, thus improving coordination between the planning and operating staffs. Once the plan is in place, actual data are systematically evaluated against operating targets. Plant personnel gain access to the information needed to determine the causes of downtime and production inefficiencies, so they can make appropriate changes.

Some tools even display safe operating limits for multiple applications and assets in real-time and in context — regardless of their source — within the plant human-machine interface. This enables operators to know the operating envelope for a particular monitored point or asset, and proactively take action before an excursion occurs. A single data model of the limit space (e.g., variables, boundaries, constraints, operating limits and modes) also allows limits to be consistently managed for storage and retrieval.

The development of a "limit repository" helps plant personnel monitor and maintain consistency between applications in the business and control networks. For example, if modification of a limit used by the planner application makes it inconsistent with the limit in any other application, the limit repository can serve to notify the other application of the problem. This includes informing the application how the limit is inconsistent and what steps are needed to re-establish consistency. The application then executes the appropriate changes or actions based on the input. Reports to engineering or management identify unresolved inconsistencies and the responsible entities. This allows operations to continue without inconsistent or conflicting limits (Figure 3).

With a single limit repository, inconsistency becomes a non-issue — all the limits can be managed, even those owned by another source. Plus, this approach eliminates the need to determine which limit is valid (i.e., if there's only one limit, it must be the correct one).

An operations management initiative also can give engineers the means to develop a boundary hierarchy, to detect and report deviations such as an alarm setting that's higher than a safety-instrumented-system trip point. This provides additional assurance that modifications to configuration parameters, including alarm limits and instrument ranges, remain within the safe operating envelope.

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