Simulations Invade Model-Predictive, Abnormal Situations on Way to Real-Time

Process Simulations Are Bursting Their Former Boundaries and Storming into Optimization, Model-Predictive Control, Abnormal Situations Management and Closing In on Real-Time Operations

By Jim Montague

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Consequently, RTA Gove picked Honeywell Process Solutions' ( UniSim Operations simulator to do months of operator training prior to start-up on its control system that was developed six months earlier. UniSim Operations is a direct-connect, full-replica, dynamic process simulator, which allows a high-fidelity model of the process to run in real time and appear from the DCS console as though a real plant is being controlled. UniSim's software contains a library of modules that mathematically represent the behavior of process equipment, logic and control components under dynamic conditions. The modules include heat and material balances, operating equations, thermodynamics and physical property calculations. These modules are used as building blocks to create a realistic representation of a specific process, area or plant.

Using these tools, RTA Gove's double-digestion process model includes 135 tank modules, 85 pumps and 1037 control valves. There are 386 field-operated devices and 7370 control points simulated. Training features also include 1242 malfunctions. The process model takes about 0.2 cpu seconds to run, and the model runs every 2 sec, which is more than enough to realistically simulate the plant's process dynamics.

"One of the biggest benefits we've received from UniSim is improved operator effectiveness. Like most operating alumina refineries, our equipment is operated continuously, and many operators are not well-practiced in running under start-up, shutdown or emergency conditions," says Manoj Pandya, Rio Tinto Alcan's alumina projects manager. "Similarly, in new installations, operators may have even fewer skills in managing the process and the knowledge of the equipment limits, even under normal operating conditions. UniSim enabled us to train our operators in advance, so they could practice new skills without hindering the plant."

Immersed in the Future

Of course, one of the most powerful expressions of simulation are displays that go beyond copying flowcharts of processes to duplicating whole facilities on screen. However, pretty pictures aside, a useful simulator must first reproduce real-life processes and situations in great enough detail, with sophisticated enough mathematics, and with sufficient resulting dynamism to be useful to operators on the plant floor.

For example, Invensys Operations Management ( recently introduced its EYEsim immersive, game-style simulator that merges first-principle simulation with augmented reality to help users see and safely interact with control room, field devices, processes and entire plants. Invensys says that control-room operators, field operators and maintenance technicians can use EYEsim to train in tandem and interactively solve problems under trained supervision (Figure 3). EYEsim is driven by Invensys' DYNSIM high-fidelity process simulator, FSIM Plus software, I/A Series control system emulation and other compatible programs.

"The increasing complexity of plants, combined with a changing workforce, demands next-generation tools that can safely and interactively train new operators and engineers without putting them, the community or the environment at risk," added Tobias Scheele, Invensys' advanced applications vice president. "This system provides a stable, realistic environment for learning routine operations and maintenance, as well as practicing rarely performed volatile tasks such as plant shutdowns. In addition, using computer models of real equipment allows endless experimentation without ever taking the equipment off-line, which also mitigates production risks." 

Not Ready for Real-Time—Yet

Despite all the gains and assistance they can give to processes, simulations aren't being used to control operations or field devices directly. "Simulations use starting values to make their calculations, but we haven't reached the point where they're using real-time transmitter data," adds E-Technologies' Gerken.

Though still in the monitoring realm, one of the only substantive links between simulation and the real world is the OPC servers, which can access both real-time operations and simulators. "If you need to prove that the controls in a DCS will react properly in a given scenario, then you can have a substitute simulation engine go through OPC to the controls, look at OPC-based data, and see that the devices are responding appropriated based on what they've been told," says Kevin Wright, system consultant to ABB's Process Automation division ( "This is sort of like partial-stroke valve testing for software. Likewise, there have been a lot of efforts to automate and save on traditional manual testing of safety-instrumented systems, but the Catch-22 is still how to validate the validator? Eventually, it will likely be done in pieces by running an automated test procedure, recording results and then monitoring the final elements."  

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