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CFD Provides Value to Solutia
Posted Thu December 19, 2002 @04:02PM
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Application by Dave Davidson,
Nylon Technology, Solutia Inc, USA

(Dave Davidson passed away in late October. He was an asset to the CFD community and a great friend who will be sorely missed by all who knew him.)

Early in 1995, Monsanto implemented a CFD Initiative leading to a concerted application of the technology throughout the company. By standardizing on CFX-4, we simplified the learning process and made it trivial to share models across the organization. Since then, the CFD group has been closely monitored, checking cost against economic benefits for each case. Consequently, we have a large dataset of industrial CFD applications from which we can extract performance statistics on the benefits of CFD.

Economic impact

Because of the manner in which CFD adds value, it is impossible to precisely quantify this. However, we can estimate a lower bound to be the cumulative net income derived from all projects where CFD made the difference between success and failure; a conservative estimate is $35 million. In fact, one project’s return is in excess of $10 million of cumulative net income. Total cumulative investment in CFD is about $6 million, including salaries; therefore a conservative estimate of the payback ratio is in excess of 580%. This estimate excludes any contributions from technical service work. One such project, involving CFD and structural analysis at a customer site, helped prevent loss of a key customer who provided $40 million of annual revenue. The customer was convinced that we were to blame for low yields, and was threatening to bring in a competitor. The project results showed them that their equipment was at fault, they cancelled the competitor trial and we retained the entire sales volume. Subsequently we were able to use the results to suggest process modifications aimed at improving yield.

Since 1995, we have maintained approximately 1 full-time CFD practitioner per billion dollars of annual sales and the same ratio of CFD practitioners to enterprise employees (0.035%). Both the annual net income of about $4 million per user and the rate of return are continuing to increase.

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The keys to success

Our CFD Initiative has been very successful; we identify the most important reasons for that success as follows: Firstly, what we call the industrial problem solving perspective. CFD is of interest only as an efficient means of accomplishing business objectives, (i.e. solving problems associated with new product and process development, existing process optimization, cost reduction, technical support, etc.). Once the problem is resolved, the project must finish. While additional work could be done, say to refine the calculations or to publish the work, this has no immediate return.

The practitioner’s approach to CFD is important. The customer has a problem in which the relevant physical phenomena are identified. The CFD expert then simulates these and helps engineer a solution that will correct the problem. Key to this process is the expert’s ability to identify the essential physics that must be solved by CFD and that which should be ignored.

The distributed nature of the CFD Initiative has been an ingredient essential to its success. Rather than place all CFD practitioners in a centralized group, we located them close to the projects and problems. CFD Team members have the responsibility of contributing to the business objectives by participating in all of the problem solving activities of the enterprise.

The use of an Engineer-on-Site for the first year of the initiative was valuable. A CFX employee brought most of our users up to speed quickly on CFX-4, and was available for consulting and problem solving. The first substantial success was to a great extent due to his involvement with the CFD Team.

The use of in-house software in conjunction with CFX has contributed substantially to our success. We have used CFX-4 since the beginning and CFX-5 for about two years, but we rarely use them alone. We have integrated in-house codes with CFX to reduce problem definition time.

Finally, maintaining a business model for the CFD Initiative and continually communicating its status to potential customers and managers throughout the enterprise was essential. By making conservative estimates of return on investment and by developing a track record of successfully solved problems, the credibility of the CFD Initiative was established and has been maintained until this day.

Digital experts

While CFX has become much more user friendly over the last decade, it still requires a time commitment and level of understanding greater than most of our employees will accept. Nevertheless, the potential for widespread application is large. Consider the impact if all of the engineers, whether in design engineering, R&D, manufacturing or technical service, could apply CFD to all their projects and problems. Decisions that are made today based on inadequate information, misguided intuition, unsubstantiated process lore, dominant personalities and guessing (all of these methods of decision making are practiced at Solutia!) could be made based upon the conservation laws that govern every product and process.

The solution lies in what we call digital experts. Digital experts are stand-alone CFD applications that are integrated into CFX and wrapped in interfaces that speak the language of the industrial application. They automate the geometry construction, mesh generation, solver selection and convergence criteria specification, etc. They then extract the essential ingredients from the complete CFD solution and present them in a convenient and relevant manner.

One such digital expert is SpinExpert™, a tool for the solution of CFD problems associated with fiber spinning. SpinExpert™ customizes CFX-4 and provides a user interface in the language of fiber spinning. The code addresses the problems associated with melt spinning of fibers, where the polymers are filtered, distributed and extruded into fibers, and in the quench zone where they are solidified. SpinExpert™ has been applied to more than 120 industrial fiber-spinning applications in the last five years. It has become the tool for melt spinning pack design within Solutia.

Another digital expert is FinExpert, a tool for the simulation of two-phase flow of polymer melts in polymer finishers. Finishers are used to build molecular weight to product specifications. Molten low-molecular-weight polymer is fed to one end of the finisher and flows by gravity to the opposite end. Multiple flights supported by a rotating mandrel are used to pull polymer from the melt into the vapor space above, enhancing mass transfer of water out of the melt and thereby increasing molecular weight. The final-molecular-weight polymer falls into the sump and is pumped downstream for further processing into pellets or fibers. The design and positioning of the flights has an important impact on polymerization rate and operability of the vessel.

From-scratch CFD simulation of this vessel is possible but tedious, due to the complexity of geometry and grid construction. Consequently, FinExpert was created to allow the user to rapidly construct the geometry and grid, specify physics of interest, and initiate and monitor the CFD simulation. After building the geometry for each unique type of flight (a simple task), the user constructs a table that describes the flight positions and types, making it a simple matter to experiment with these parameters. Once the flight geometries are constructed, the user can define the simulation and initiate it in about 60 seconds.

CFD has lead to major benefits within Monsanto and Solutia over the past six years. It is our view that its utility has just begun to be realized, but that great increases in that utilization may not occur until CFD applications are routinely embedded within digital experts. That’s why we have recently bought EASA, which will help us to create as many digital experts as necessary.

Reactor vapor disengagement
Reactor overflow vapor disengagement. Most of the vapor in the inflowing mixture flows to the next reactor via the overflow line. Solutia engineer, Ralph Goodwin, solved this two-phase problem in order to modify an existing process to accommodate higher production rates. © 2002 Solutia Inc.

Filtration cavity
Transient filling of a filtration cavity used in melt fibre spinning. This analysis is one component of a regiment of CFD analyses we use to look for sources of performance problems and yield losses. © 2002 Solutia Inc.

Horizontal finisher
Horizontal finisher used for condensation polymerization. Solutia engineer, Greg Bush, used CFX to help us understand hydraulics and mass transfer in this geometrically complicated multiphase vessel, used to produce nylon-66 polymer and fiber. © 2002 Solutia Inc.

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