Greg: Real-time process simulation is a powerful tool. From engineering testing to operator training, having a virtual plant to test and train helps reduce risks in manufacturing facilities.
Originally designed for site acceptance testing (SAT), operator training systems (OTS) and process control improvement (PCI), simulators focus on automation system details, such as inputs, outputs and dynamic relationships, all of which affect control system and operator performance. OTS, SAT and PCI simulations are as simple as tieback models that use analog output (AO) from a control system, pass the signal through an open-loop gain, deadtime and time-constant, and connect the results as the analog input (AI) signal that becomes the process variable (PV) used by the control system and seen by the operator.
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These models are readily adaptable to become step-response models (experimental models) by identifying dynamics using an adaptive tuner and rapid modeler. It’s particularly important to correctly ascertain the dead time, which is the most important and easiest dynamic parameter to identify. Many tieback models don’t include dead time. If the dead time is zero, any tuning or strategy works and control performance is viewed as unrealistically tight. The ISA technical report, ISA-TR5.9-2023, “Proportional-integral-derivative (PID) algorithms and performance” offers perspective on PID performance and simulation requirements. ISA standards and technical reports are freely viewable by ISA members.
In a previous Control Talk column, “Modeling and control opportunities,” I talked with José María Ferrer about the value of different simulators and their various applications. We’re fortunate this month to have Marsha Wisely’s insightful and diverse experience to provide a multidisciplinary perspective on this technical topic.
She started as a process simulation engineer before joining Emerson to configure control systems, working as a part of fleet-wide modernization projects, commissioning greenfield polymer facilities, and working as the lead automation engineer in the Emerson Interactive Plant Environment at the Rosemount office in Shakopee, Minn. Her experience includes working in multiple industries, primarily supporting chemical, pulp and paper, and life sciences, and as a business development manager and product marketing specialist for Emerson’s Mimic product line. Today, she is president and lead process simulation consultant for PlantWise Industrial Consulting LLC.
She joins us in this two-part series to discuss making a simulation project a reality. In Part 1, we discuss how to right size the scope of a dynamic process simulation and get a project funded. Next month, Part 2 looks at the lifecycle of a dynamic process simulation and how to stay current with production.
Marsha, what are some barriers to entry that people face when trying to get a dynamic process simulation of their facility?
Marsha: There are three things that come to mind: scope, funding and lifecycle maintenance.
Greg: Tell me more about the challenges when it comes to scope.
Marsha: Process simulation excites many engineers and executives. As a virtual version of your plant, there’s so much you can do with it. People get excited, see the possibilities and think they need the highest-tech tools, but their actual need may be simpler.
Imagine shopping for car—you can get swept away by the features and glamor of a Ferrari, even though all you need is a car (or maybe a bike).
In dynamic process simulation, you can model all the reactions and kinetics for a high-fidelity model, or create a model with simple tiebacks so valves open and pumps start, but that’s about it.
I’ve seen projects end up in limbo for this reason. You don’t have to skip the car because you can’t afford or don’t need the Ferrari. The car will still get you to where you need to go.
Greg: How is scope set correctly?
Marsha: I recommend identifying the problem you’re trying to solve and your timeline. For example, say you want to start a training program and you know that, in the first year, you’ll focus on standard operating procedures, and by the third year, you’ll train operators on malfunctions and more complicated scenarios. You can start small and build each year, helping to lower the initial investment and reducing maintenance, while you build your system. It allows your requirements to change (if needed) as you learn how you’re going to use your training system.
Scoping simulation projects is an area where consulting can add a lot of value. Every situation, every manufacturing plant has unique processes, equipment and needs. Consultants help you work through all the pieces, and ensure you maximize the return on your process simulation investment.
Greg: Sometimes, you still want or need the Ferrari. I’ve extensively used high-fidelity, first-principle, dynamic simulations to find the best boiler, compressor surge control, pH control, exothermic reactor control, furnace pressure control and biochemical reactor control. Eliminating shutdowns of boilers, compressors, exothermic reactors and furnaces saved several plants millions of dollars per year. Reducing exothermic batch reactor cycle time increased capacity and profitability by millions of dollars per year. For pH systems, the savings in pH reagent is less than $1 million a year, but eliminating pH violations covered by the Resource Conservation and Recovery Act (RCRA) was critical for continued operation under existing environmental agreements. For these simulations, or any others, how do you solve the funding challenge?
Marsha: Think about who holds the purse strings in your organization. There may be technical decision makers with a lot of influence, but more often, the funding for simulation projects comes from a plant manager or someone who cares about profitability.
Every day, every hour that the plant isn’t producing good product, there’s an opportunity cost for the price of the material that could have been made. So, the same reasons you try to justify a simulator are the same reasons your executives will fund it. You need to translate those reasons into the language they understand, which is dollars.
Your experience with high-fidelity simulation illustrate this. Let’s consider your example of reducing downtime. Once you identifiy the downtime reduced at a facility, you can calculate the impact in saved days/hours and/or product price to determine the opportunity production cost. There are additional expenses to consider as well—from contractors to customer commitment risks to possible safety/environmental remedy costs—so, the dollars add up. Consultants can ensure you capture all the costs and present numbers that will be well understood by your executives (or whoever writes the checks).
Greg: What if management doesn’t agree with the justification or your site is on a tight budget?
Marsha: In cases where funding is more difficult or the business justification is a challenge, I suggest you start with a small simulation and grow it. A good example is a greenfield project. Budgets get tight, and you may not have the operational data to build your business justification.
Start with a simpler process simulation—medium fidelity or material balance, plus some dynamics where you really need them—so you can begin training operations and test your code prior to startup. Because your process model is less rigorous, it’s less expensive, but now you have a simulation license. When you have operational data and can identify areas where you’ll get the most return from a high-fidelity simulation, you already have licensing (reduced costs) and you have a tight scope, which will also keep cost lower.
Another lever to pull for price is licensing. Simulation software companies get more flexible pricing options with subscription offerings, which helps reduce capital investment.
Greg: But subscription mean a recurring cost.
Marsha: True. There’s an annual need to rejustify the ongoing expense, but if you have a maintenance plan that keeps the model in lockstep with production and use your simulation, it’s just a matter of articulating the ROI from using the simulator.
Subscription is also an opportunity for cost-restricted teams. We mentioned earlier that the upfront capital cost is less, helping you land the project. The subscription justification reminds management, and opens the door to more simulation projects, if the business justification is there, of course.
Greg: Next month, we’ll continue our discussion with Marsha, focusing on how to maintain your dynamic process simulation.
The following recent ISA books detail the use and value of simulations with breakthroughs. (Use promo code ISAGM10 for a 10% discount on Greg’s ISA books.):
Since so many of my colleagues are of retirement age, I thought the ISA book I wrote, The funnier side of retirement for engineers and people of the technical persuasion, with cameo appearances by the late Stan Weiner and cartoons by Ted Williams, would be a good source of Top 10 lists for the next several months.
