Preparing for the Unpredictable

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Unpredictability haunts every process. Any number of factors might be responsible, including inappropriate material use, exceeding design conditions, poor care and stewardship of equipment, new use of equipment, new operating conditions or a new retrofit. Unpredictability often leads to unsafe operating conditions, poor performance and other unfavorable results.

What can you do about unpredictability?

First and foremost, do not treat processes as black boxes. Everyone involved with the process should remember: Process understanding is key to good and safe operations.

Prior testing of most processes is essential because it helps avoid surprises. New equipment and operations should be lab tested and field tested before use. When buying a piece of equipment, the plant should make certain the vendor describes how the equipment works, the process physics that occur inside, the material's flow behavior inside the equipment, the power input and the expected power signature if the operation occurs over time. Plant personnel should completely understand the detailed descriptions and performance data.

Proper monitoring and maintenance of equipment and feed are essential. Feed changes occur and should be identified. Well-developed, well-thought-out processing procedures should be in place. These procedures might include how the process is started, how the process is fed and how the process is shut down. Processing scenarios for various equipment failures are needed. These should be practiced. Drills should be developed and practiced, much like routine fire drills.

Pre-planned maintenance is wise ," maintenance and cleaning operations should be included in the design phase of the process to prevent many difficulties later.

Do not wait for catastrophic failure. A wheel balancer ," a device that takes vibrations out of rotating equipment such as a fan or spray dryer wheel ," can be used to illustrate the importance of scheduled maintenance. Imbalances often are caused by material buildup in one portion of the rotating equipment, resulting in vibration. The wheel balancer smooths out this material buildup. However, the wheel balancer does not stop the buildup, which is likely to continue until a catastrophic failure. Maintenance and cleaning performed on schedule can prevent catastrophic failure.

Process control set points and their origin should be clearly understood by everyone. Set points can come from:

Steady-state equations, which describe the process.

Safety considerations.

Process failure boundaries.

Equipment limitations.

The last three of these are directly related to safety and predictability.

The way a process is controlled also impacts the predictability of that process. Process control in plant design often is added in the last two weeks of a process design. It often is added in a hurried manner, which leads to unpredictability in measurements.

Process measurements also should be understood. Measurement locations also are very important. Are the measurements being made in the best spot? How do you know for sure?

Catastrophic failures can happen without warning. Playing "what-happens games" often is necessary. Like the Boy Scouts say, being prepared is a good idea. And remember: "Practice makes perfect."

Failures happen for a reason. Different perspectives are necessary to catch these failures before they happen. By thinking "outside the box," you often can identify and prevent catastrophic failures. However, success is difficult to demonstrate. Although, the accident did not happen, that fact usually raises little praise. Fighting for your point of view might be necessary.

Company cultures and attitudes often are obstructions to progress. The "NIH" (not invented here) attitude should be readjusted. New technology and methods should be incorporated into new processes and plants. Interestingly, problems are not solved forever. They return time and time again as companies evolve. Be prepared.

Tatterson is a technical editor for Chemical Processing. He is a professor at North Carolina A&T State University in Greensboro. Contact him at gbt@ncat.edu. He also teaches short courses for the Center for Professional Advancement, www.cfpa.com.

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