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Make the most of automation upgrades

By John Dolenc, Emerson Process Management

ChemicalProcessing.com

Keywords: automation, process control and control systems

Avoid common mistakes that undermine projects.

Many plants rely on outdated process control systems — ranging from panel-based pneumatic controllers to Distributed Control Systems (DCS) installed in the 1980s — and now need to consider updating them. However, new technology for its own sake can’t justify capital spending — you must find compelling economic reasons for modernization.

Using obsolescence for justification isn’t easy. While maintenance costs probably are rising and spare parts may be getting scarce and expensive, true maintenance savings normally aren’t large enough to justify the capital investment. Obsolescence is a viable approach only if you can show an increasing risk of control equipment failure shutting down a critical process. Establishing the risk factor becomes the challenge.

It’s difficult to convince management that a system is about to fail when it has no history of failures. Predicting failure is a tough task. Mean Time Between Failure (MTBF) data for older, especially obsolete, equipment are hard to obtain. Plus, MTBF data normally are component-based, not system-based — making it hard to use these data to estimate control system life because a control system consists of multiple components.

Fortunately, modernization can provide considerable financial benefits and thus significant incentives for a project. Whether these benefits will suffice to justify an upgrade, of course, depends on the company’s capital-spending payback policy. Some firms demand a one-year-or-less payback, others allow two-to-three-year paybacks, while a few factor in reduced risk of system failure in determining an acceptable period.

Past financial failures

Unfortunately, many control-system modernization projects haven’t provided the economic benefits that were initially expected. While engineering is happy to have the newest technology to implement and operations personnel view the process as easier to run, management may see the new system as a financial failure.

Several factors can contribute to an automation upgrade project not bringing the expected economic value:

• The process control system was chosen based on technology instead of how well it allows operations to improve the manufacturing process.

When DCSs first became available, the process control engineering department chose or at least strongly drove the choice of system. Selection was centered on the ability of the control system to meet certain technical standards and the initial sales price.

Operations wasn’t involved much if at all in specification and selection, and real analysis of operational improvements wasn’t done.

Leaving operations out of the selection process usually led to a system that wasn’t friendly to the operator. Related process information was scattered on numerous graphic pages, causing the operator to have to toggle among several graphics. While this may be tolerable during normal operation, it can become time consuming and frustrating when abnormal situations arise and the operator needs to manipulate the process and closely monitor measurement readings.

Modifying the system may be difficult and may need the assistance of a system engineer. So, operations management may resist changes in graphics suggested by the operator. Also, it’s very likely that any complex control strategy will be abandoned if it’s not easy to use and troubleshoot without the presence of a system engineer and the process run in a manual mode.

• Process problems weren’t fixed because the control system was expected to overcome them.

Modern control systems, along with properly installed instruments and valves, can allow major improvements in operations. However, faults in process design or equipment may negate the advantages of automation. Performance after the implementation of a new system may be disappointing if a thorough review isn’t done to identify the existence of process or mechanical issues — e.g., related to agitation, heat exchange, undersized units and shared equipment. A control scheme sometimes can overcome a process-related issue but generally the robustness of the control strategy will be low and circumstances will occur that will cause poor operating performance.

Be leery of promises made by sales people in competitive situations. The system vendor may oversell the features of the control system when a bid specification focuses on them and low cost.

• The existing process control system was replaced in-kind.

There are many excuses for why systems get replaced in-kind. Two stand out. First is the desire by management to keep the cost of the replacement as low as possible. This typically means system obsolescence was used to justify the replacement, which, as mentioned earlier, usually is a dubious approach. Driving down the cost of the new system becomes the primary goal of management. No process or operations reviews are conducted to assess areas of poor performance and to design in new control strategies or instrumentation to improve operations.

The second reason is operations management’s desire to not alter the “look and feel” of the system so the operators aren’t confused. This really is unfair to most operators. Sure, there’ll always be the operator who doesn’t want change. He’s the one who goes through the local gauges and the single loop controllers and marks the normal operating point with a grease pencil. Such an operator tends to run the plant by rote rather than by really understanding the operation and the actual impact of his actions.