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By Greg McMillan and Stan Weiner
Greg McMillan and Stan Weiner bring their wits and more than 66 years of process control experience to bear on your questions, comments, and problems. Write to them at firstname.lastname@example.org.
Stan: The success of a retrofit that upgrades an existing production unit or an automation project for a new production unit depends on the experience of the design team.
Greg: There also is a huge opportunity to take advantage of the best of what new field devices and control systems have to offer. The newest sensor and process/installation compensation technologies, control valves with low-friction packing, direct tight connections, higher diaphragm actuator pressures and digital positioners, and DCSs with more flexible configurable basic control, model-predictive control and neural networks all make investing in new technology worthwhile, but implementing such systems requires careful planning.
Stan: For the rest of the year, we will be interviewing Hunter Vegas, a senior project leader for Avid Solutions Inc., a system integrator in Winston Salem, N.C., and a veteran of many such retrofits and upgrades. He provided the best answers when Control Talk posed puzzlers years ago and is on Béla Lipták's exclusive list of experts that answer questions worldwide.
Greg: In Part 1, we'll discuss control system design and implementation for retrofit and automation projects. What are the challenges in meeting plant and corporate requirements?
Hunter: The main challenge for the integration team stems from the fact that:
A new system can be terrifying for the more experienced operators, who are accustomed to walking down the panel board and immediately seeing how everything is running. Now they have to find the information and control the plant on a PC they have never used. If the plant has a DCS, then the operators have grown very accustomed to the existing graphics and functionality, and want the new system to behave exactly the same way. The cultural and psychological aspects of this transition are often overlooked.
Stan: How do you get operators to accept and effectively use PCs for their interface?
Hunter: Get them heavily involved in the development of the graphics. There is almost always one operator whom the other operators respect. Find this operator and have him/her provide the lead role officially or unofficially.
Greg: How do you get operators proficient on the new system?
Hunter: That can be a real challenge. The key is to create real-time simulations of the plant during configuration. The simulation does not need to be high-fidelity—simple tie backs on the valves, pumps and PIDs will often provide enough realism for the operators to "run the plant" during the acceptance testing.
We also always invite a new operator who grew up with computers and a seasoned operator with clout. The seasoned operator looks over the shoulder of the new operator and sees how easily and quickly he navigates and controls the plant. If the operators ask for something on a graphic, we try to give it to them immediately to facilitate ownership and buy in. The net result is that the seasoned operator goes back and gives the other operators the impression that this new and fancy system is actually going to work. The fully simulated system is then sent to the plant a few weeks in advance of the start-up and used for extensive operator training on overtime.
Stan: How do you deal with the wiring maze of retrofits?
Hunter: The whole experience is intense, but can be painless if you do enough homework up-front. But that means you have to have a very thorough understanding of all of the electrical details of the old and the new system, and know exactly what field devices you are wired to. Unidentified differences in grounds, card impedances, leakage current, etc. can turn a retrofit into a nightmare of epic proportions. Nobody is happy when a three-day start-up turns into a three-week death march.
Greg: How is the control functionality concisely and accurately defined?
Hunter: Most clients are familiar with the ISA-88 standard for batch processes. If not, we do most of the definition using ISA-88, and train the clients how to review and update the batch documentation.
Stan: What is particularly important when using ISA-88?
Hunter: Where you draw the line in the definition of the phases will often determine the success or failure of the system. Ideally, you are trying to create phase "puzzle pieces" that are easily arranged at the recipe level to perform the operations you need. If you make the phases too simple, you end up with inordinately complex recipes that can bog the system down. Conversely, if you create very complicated phases that do a variety of operations, you end up with spaghetti code that is impossible to troubleshoot, and requires a complete rewrite every time you want to change something. The initial decisions are critical—and any plant considering a batch installation needs to get the right person to help them understand and make those decisions.
Greg: How do you improve the process definition?
Hunter: We will help most clients by creating the initial flowcharts and pointing out areas where cycle time reductions and/or process improvements are possible. Some clients know exactly what they want and we do that. Others are looking to us to suggest a path forward. Either way, we collectively review everything and get everyone on the same page, so system configuration can progress smoothly with minimal rework.
Stan: What are the benefits achieved in a successful retrofit project?
Hunter: Labor reduction is almost always cited, but is rarely where the money comes from. Operators that are "eliminated" are usually not let go, just reassigned elsewhere in the plant, so the actual plant costs are not reduced. The big benefits come from capacity, quality and flexibility for new products. For one plant producing 70 recipes on five different reactors, "first time right" went from 60% to above 90% within a week of installing the new batch system. This was made possible by the repeatability of the automated system that allowed the plant to home in on the best operating sequence and conditions. Increased capacity is another major benefit of batch automation, since an upgraded system will often allow the same number of operators to control two and even three times the reactors as before. The key to this is enhanced phase messaging that not only tells the operator the system has gone to hold, but why. The operator can resolve issues immediately rather than having to call in maintenance and hold production until they arrive.
Greg: Hunter and I have come up with following list of scary stuff in time for Halloween.
10 We never really could figure out what the old system was doing.
9 Do I have a system backup?!? I thought you were making backups!
8 They want to make our start-up into a reality show.
7 The displays are fine and dandy, but where are the panel boards?
6 We have changed our mind. We want the old system back.
5 Can you reprogram it so the wrong valve still works?
4 Didn't you get the revised batch sheets?
3 Is a blue screen bad?
2 What is that burning smell?
1 We are out of coffee!