Models Take off

Process simulation historically has taken place within proprietary modeling environments. However, the ability of simulators to more accurately handle demanding tasks continues to evolve.

By Mark Rosenzweig

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Firms also are focusing on how to get more engineers to use models. EPCON’;s Willman says that only about 30% of site-based engineers use simulators. Many operating companies still generally consign simulation to specialists, which limits the broader application of the models. Dolsinek’;s goal is to have operating people, not specialists, able to use the system.

Microsoft’;s Excel may excel in that role. Since most engineers use it, simulator vendors are working to make it easier to work through Excel. For instance, Chau-Chyun Chen, a technical fellow at Aspen Technology, Cambridge, Mass., expects AspenPlus to accept properties through Excel within a year. More and more tools will be available via Excel, adds AspenTech’;s chairman Larry Evans.

Advancing into control
Dolsinek aims to develop a process control strategy for NOVA that takes advantage of rigorous process simulation models. He now has put in place a company-wide structure. “It’;s 10% technical challenge, 90% people challenge,” he says. Specialists have favored specific software systems but that’;s not cost effective, he explains. Instead, he plans to implement consistent, standardized tools. He expects to use the models for advanced process control (APC) within a couple of years.

He is targeting selected APC applications where throughput or product consistency clearly could benefit from the sophistication of the first-principles models. After that, he plans to integrate the models into the supply-chain system.

Bill Tchir, research manager for Sclairtech process R&D in Calgary, hopes to implement such models for control of NOVA’;s large Sclairtech high-density polyethylene units in Joffre, Alberta, within a couple of years. This should provide extra output and smoother grade transitions. He also cites the benefit of having the same physical properties model for simulation and control.

Honeywell’;s Henderson definitely sees a role for rigorous Hysys models in APC and expects products to debut during 2005. The company will add tools to enable use of Hysys in its Experion Application Profit Controller, which now uses linear models. This should improve the fidelity of advanced strategies, he explains.

Massey of Chemstations believes that most distributed control system (DCS) vendors are on the path to converting from empirical to first-principles models. By the end of the year he expects at least one DCS firm to sign a pact to use ChemCAD. The first application will be for feed-forward control of a pressure-swing process with fast gas-phase dynamics, he says.

However, Chen cautions that first-principles simulation won’;t always make sense for APC. “While rigorous models can provide additional benefits, these have to be very significant versus what can be achieved with empirical models for control.” He adds, “A promising direction is the combination of empirical and first-principles models, which could lead to a merger of advanced control and real-time optimization into a single discipline and the ability to handle steady-state optimization and dynamic optimization/control problems in a consistent way.”
    
Sighting on the site
Expanding the scope of simulation models from analysis of a single process to analysis of an entire site represents a major opportunity, says Suresh Sundaram, Cambridge-based director of product marketing, engineering and innovation for AspenTech. “A process plant never operates in isolation. Changes in a process affect other processes and have an impact on the utilities and site-wide infrastructure,” he explains. “To get the overall site optimum requires gauging the impact of one process on another.”

It now is possible to simulate and optimize a whole site, says Larry Evans, AspenTech’;s chairman. “Being able to do this will bring big benefits,” he adds. Fraser of SimSci agrees. He says integrated refineries are leading the way.

Seiji Terado, senior control engineer in the Process System Technology Center of Idemitsu Kosan Co., Tokyo, feels that site-wide simulation is beneficial, not just for more accurate modeling of existing operations but for assessing refinery-wide product balance when adding or removing units.

Axel Polt, director, conceptual process engineering for BASF AG, Ludwigshafen, Germany, says that the company now is working to achieve site-wide simulations at all its plants around the world.

Chemstations’; Massey, however, doesn’;t see a groundswell of interest from clients for site-wide simulation. “Their caution is wise,” he says, “because a site-wide simulation requires a very good understanding of each process and how to put them together.”
 
Extending to the enterprise
Many operating companies would like to leverage their investment in these models even more broadly, such as for scheduling and planning. Integration with information technology is becoming more of a focus, says Harpreet Gulati, director of product marketing for simulation, optimization and advanced control at SimSci in Lake Forest, Calif. “Agility for a process is the key to success. So, simulation will play a wider role.” There is a clear need for faster decision-making and execution based on what is most profitable for the company, not a given plant or department, adds Sundaram of AspenTech. This demands a change in the way simulation is deployed, he says (Figure 3).

"The process industries utilize numerous other modeling and optimization tools for specific business problems, such as production planning, scheduling and distribution. Each application has been approached from a different viewpoint, using the most appropriate technology and devising a user paradigm specific to the business task at hand,” Chen says.

Planning and scheduling now typically rely on linear-programming models. However, Terado of Idemitsu notes that first-principles simulations overcome limitations posed by linear-programming models and that rigorous simulations can be used selectively and can be simplified as appropriate.

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