From the Trenches: Distillation Columns – Internal Reflux Control

Posted by Jim Ford on June 6, 2012 @ 8:31 am

Distillation columns are one of the most often used unit operations for separation and purification in the process industries.  They can also be some of the most complex to operate and control, because they involve two-phase, multi-stage, counter-current mass and heat transfer (each tray or segment of packing is a theoretical equilibrium stage).  The greater the number of trays, the longer the time constants related to composition changes. For a two-product distillation column (top and bottom product), there are typically five degrees of control freedom (control valves):

  • Reflux flow
  • Top product flow
  • Reboiler heat input flow
  • Bottom product flow
  • Pressure control valve (the specific location depends upon how the pressure is controlled).
Three of these valves are needed for inventory control (reflux drum, column bottom... Continue Reading

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Fine-Tuning Your Alarm Management System

Posted by Bruce Brandt on June 5, 2012 @ 10:45 am

In the wake of the Deepwater Horizon disaster, alarm management has moved once again into the forefront for many companies as they ask: “What is the best way to keep an operator from missing a key alarm when things start to go wrong? What are the obstacles to having an effective alarm management system?” In my experience, the decision to have, or not have, an alarm is more often cultural than it is based on a good operational analysis of the process. That’s why the alarm rationalization process is so necessary and beneficial. It strips away the cultural, “I want the operator to know about…” and replaces it with, “This is the most important thing the operator has to do.” Many plant personnel do not appreciate just how significant this change is. Almost from the introduction of the DCS, its ability to generate more alarms than a human can effectively deal with was not ap... Continue Reading

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Getting More Out of Your Historian, Part 2

Posted by John Clemons on May 31, 2012 @ 8:29 am

In the last post I mentioned that you probably had lots of data that you might not even know about all over the place just waiting to be collected and put into your historian. I suggested that if you collected that data you could put the data to work and would probably find out that the data was actually very valuable and quite worth it to have collected. In this post, I’d like to suggest another idea to get more out of your historian. You probably have a data warehouse of some kind somewhere. It’s probably part of a business intelligence initiative and it’s almost certainly owned by the IT department. And, you may not even know it’s there and might never have even used it. And, it probably has no manufacturing data in it and almost certainly has no data from the historian in it. But, it’s probably there. And, there’s probably a lot of people that use it. And, if they k... Continue Reading

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MOC for Plant Control Systems

Posted by Jason Montroy on May 30, 2012 @ 7:52 am

Management of change (MOC) can apply to nearly anything from organizations to projects to IT infrastructure. But does it apply to plant control systems? Considering that control systems need to change over time - process optimization drives changes in control logic and software updates occur on at least a monthly basis – the answer is: MOC is essential for plant control systems. You will make at least a handful of changes to your control systems on a monthly basis. It pays to approach these changes in a consistent manner. After all, if your SCADA system fails, your operators find themselves flying blind, without a means to control the system. If your PLC or DCS fails, plant production will come to a screeching halt. Most plants have some form of MOC process. But not every plant’s process is well-reasoned and documented – or effective. Processes range from simply “asking Joe... Continue Reading

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Ten Tips for Successful Team Leadership, Part 2

Posted by Control Engineering Team on May 29, 2012 @ 9:34 am

Here are the final suggestions to get the most out of a leadership role by creating an enjoyable and productive experience for you and your team. 5. Keep in touch. Peters and Waterman popularized the concept of “management by wandering around” in their 1982 book “In Search of Excellence.” Email is a great tool, but informal communication such as face-to-face, voice-to-voice, or even chat-to-chat provides much more information about how the work is progressing. Most of us are hesitant to voice our frustrations in a email that can live forever and be forwarded, but a simple, “How’s it going?” may elicit a lengthy and detailed description of any current frustrations or roadblocks that might adversely affect progress. Sometimes shooting the breeze clears the air. 6. Give them what they need. Make sure your team members have everything they need to keep moving forward, be ... Continue Reading

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