Water Online

MAR 2017

Water Innovations gives Water and Wastewater Engineers and end-users a venue to find project solutions and source valuable product information. We aim to educate the engineering and operations community on important issues and trends.

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By Paul Brake W e live in a world where automation is now the center of plant engineering. Automation enables better controls, safer operation, environmental compliance, lower manpower requirements, and data logging. It has provided us with nearly hands-free operation of most systems. It gives operators virtually instantaneous reporting, feedback, and control of the process. It warns us when things are not going along with our plans and warns us of dangers to avert catastrophes. Automation is truly a blessing to everyone involved, until we go overboard. Then we curse its inception. It is essential that our automation, controls, and sensors be designed and built to give the operator a real-time, complete, and accurate picture of the entire process. It's also necessary for that automation to identify problems and warn the operator before they escalate. Furthermore, automation must be empowered to take over and control or even cease certain operations based on imminent hazards perceived by the sensors and interpreted by the control program. Imperfect Starts Recently we were commissioning an oil/water separation unit with three serial stages and three serial coalescing tanks. The emulsion is pumped through a separator module into a coalescing tank. The recovered hydrocarbon is pumped off the top. The underflow water is pumped from below. Levels are maintained by controlling the pump rates and measured through pressure differentials — three times over. So you have a whole bunch of pumps, a crate or two of flow meters, dozens of automated valves, variable frequency drives (VFDs), level indicators, gas detectors, pressure switches and indicators, temperature sensors, fire monitors, etc., etc. To top it off, the whole system was under a controlled-flow natural gas blanket with a vapor recovery unit because the influent contains hydrogen sulfide gas. A long list of instrumentation and automated equipment is all tied back to the client's distributed control system (DCS). When the system is up and running properly and tuned in to the flow, temperature, and variations of the process, it hums along beautifully with no problems for years. The issue, of course, is getting to that perfect running state. That agonizing, sometimes torturous process is called commissioning. Commissioning demonstrates, quite painfully, that it is very easy to engineer too many sensors, too many alarms, and too many shutdown keys into the process. It became almost impossible to commission our system, because during commissioning — while filling tanks and adjusting levels and flows — we were not within the preset program limits. As we were working, lights were flashing, alarms were ringing, and numerous times the system shut down because some sensor's limit had been breached. We learned our lesson. We learned from our mistakes. It is better, and cheaper, to learn from the mistakes of others. So now, when you go to design your next system, learn from our mistakes. When setting alarms, care should be taken to alarm only those things that are truly critical to your process. Get It Right By Setting It Right There are numerous industry protocols that you can reference and use as your design guides. But to simplify things, try using a Failure Mode Effects Analysis (FMEA) on your system. There are numerous models out there — an internet search will reveal dozens that can help you. The FMEA will help you determine what can go wrong, how it can go wrong, what the possible 22 wateronline.com n Water Innovations The Bells And Whistles Of Automation: What To Expect When You're Commissioning Commissioning demonstrates, quite painfully, that it is very easy to engineer too many sensors, too many alarms, and too many shutdown keys into the process. Getting systems online is tough enough without unnecessary alarms and shutdowns, but the safety and visibility of operations are also paramount. During the commissioning process, balance is critical.

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