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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Tying in the supply chain and information technology is a major theme at AspenTech, Evans says. As a long-term objective, the company’;s new Open Simulation Environment (OSE) will incorporate planning and supply-chain modeling to enable consistent decision-making, Sundaram says. Within a year, it should be able to mix and match first-principles, empirical and statistical models and update one model type with another. The goal is to have data entered only once.

However, SimSci’;s Fraser notes that companies commonly face workflow barriers. “Departments have separate data and don’;t share.” 

The ultimate goal, explains PSE’;s Pantelides, is to develop a general modeling capability that can be used for diverse functions. Specific models tailored for a particular task would be derived automatically from the master model. This would facilitate collaboration and minimize costs of software acquisition and deployment, he adds. It also would avoid problems due to inconsistencies among models and data for various applications.

"The real dream is an equation-based mathematical model that could do everything,” Evans says. This view is seconded by NOVA’;s Dolsinek and Willman of EPCON. No one is expecting this anytime soon, though.

Achieving plug-and-play
Process simulation historically has taken place within proprietary modeling environments. This has limited the users’; ability to “mix and match” components from different vendors. A recent initiative, the development of the so-called CAPE-OPEN (CO) Standard, promises to change that. Open, which is multiplatform and available for free, aims to allow components from one vendor to be used easily with process-modeling software tools from other suppliers.

The initiative is now under the aegis of the CO Laboratories Network (CO-LaN), Rueil-Malmaison, France, which is supported by major operating companies, including Air Liquide, BASF, BP, IFP, Shell International Chemicals and TOTAL.

The thermodynamics part of CO version 1.1 was issued as a draft in September 2002. Minor modifications are under discussion, says Michel Pons, process simulation group leader for ARKEMA, Lyon, France, who will become chief technology officer of CO-LaN in January.

"The key benefit [of CO] will be to be able to use ‘best in breed’; software tools without having to worry about interoperability problems … It won’;t restrict any more end users to one suite provided by a specific vendor.”

“CO is driven by owner-operators who were concerned about the ability to inject their own expertise and use other software without custom coding,” says Willman of EPCON.

Right now, CO-LaN has special interest groups (SIGs) on thermodynamics, unit operations and interoperability, Pons says, and an SIG on solvers may debut in early 2005. The thermodynamics SIG is working on an extension to mixtures involving solids. CO-LaN already has started the development of a logger to monitor all communications going through CO interfaces, to provide detailed information to developers and, ultimately, users.

“Technical obstacles have been overcome,” says PSE’;s Pantiledes, “but wider adoption will depend on continued support of software vendors and end-users.”

In October, Aspen Technology launched aspenONE, a software portfolio for the chemical industry that features OSE and supports CO. “OSE and CO are synergistic … OSE is an important step for AspenTech. We want to embrace third parties’; modeling tools,” Evans says.

A number of operating companies already are telling vendors that they prefer and may even insist upon CO-compliant software from now on, Pons says.
 
Tchir of NOVA says that CO may fit into the company’;s strategy for interconnections. However, it hasn’;t decided on whether to insist on CO since interconnectivity is only part of the issue.

“CO has very strong support in Europe,” says Fraser of SimSci. Massey of Chemstations adds that one major U.S. chemical company stated that it would continue to use the ChemCAD thermodynamics package only if it were made compliant. The package will be compliant no later than the end of the first quarter of 2005, he says.

However, the response to CO at many U.S. companies seems less enthusiastic. Pons is not surprised. “CO is seen as a European initiative … Then, everything that is coming from Europe, and especially France, is looked upon with some suspicion. That is regrettable, but you can’;t help it.”

“Philosophically, CO is doing the right thing,” says Satyro of Virtual Materials. “The real problem is acceptance.” To have CO succeed, the standard has to be widely promoted and companies with money to spend on simulation must insist on compliant software. These companies must be willing to accept that implementation will give worse performance at least in the short term versus a simulator’;s native environment, Satyro says. 

Speed can be an issue, Pons admits. Using the CO interface instead of a simulator’;s native one typically leads to slightly slower performance. Implementations so far give a 3% or worse drop-off. This reflects any inefficiency in the implementation as well as the interface itself, he adds.

The initiative will open up opportunities, but does not represent a step change, Fraser says. Equity in current models will place some barriers in the way of making existing applications compliant, he notes.

CO should allow users to more easily take advantage of niche software from small, specialized vendors, says ProSim’;s Hameury. “Areas such as unit operations and thermodynamics should be the first to emerge,” Pons adds.

Developing new capabilities
The ability of simulators to more accurately handle demanding tasks continues to evolve, both through better methods and via links with other software.


Areas with scope for advances include modeling of larger molecules, like those common in pharmaceuticals and polymers, as well as operations involving solids, says AspenTech’;s Evans.

In the pharmaceutical industry, process design often involves selecting the best solvent or solvent mixture from among hundreds of candidates. To speed that process, AspenTech has developed a model, called NRTL-SAC, for fast, qualitative estimates of the solubility of organic non-electrolytes in common solvents and solvent mixtures, Chen says. It works well not only for small molecules but also for oligomers and polymers. He expects the approach to be extended to organic salts within a couple of years, if not sooner.

The model, which is already being used by several pharmaceutical companies, is accurate enough for phase 1 and phase 2 pharmaceutical trials, Chen says.

“There’;s a huge physical properties data gap,” says Chemstations’; Massey. “Compounds are being developed faster than reliable properties for them.” So, Chemstations has just started offering a service to predict such properties of pure compounds via a novel group-contribution method. The company expects to offer the same service for mixtures by mid-2005 and to release a CO-compliant version for use by non-specialists within 18 months.

Computational fluid dynamics (CFD) has long played a role in equipment analysis. Now, hybrid approaches that link CFD with simulation are emerging. PSE’;s Pantiledes, for instance, cites their value in crystallization, where differing flows in portions of a vessel can dramatically affect nucleation in those areas. PSE this year launched a package combining its gPROMS simulator with CFD software from Fluent. The same approach holds promise for reactors and cracking furnaces, he adds.

Pretty soon, says Polt of BASF, end users — not the software — will become the limiting factor in simulation.

Mark Rosenzweig is editor in chief of Chemical Processing magazine. E-mail him at mrosenzweig@putman.net.

 

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