When the thermal fluid it was using was discontinued, one chemical manufacturer was forced to reevaluate its heat transfer system. While the fluid changeout was not planned, the shift has resulted in reduced fluid degradation, increased fluid operating life and improved product yield.

Heat transfer fluid is heated in large tanks and then circulated through the process system as the heat source.

With little warning, Stepan Co., Elwood, Ill., learned that its heat transfer fluid supplier was discontinuing the fluid Stepan had been using to produce pthallic anhydride. This left Stepan, a manufacturer of specialty and intermediate chemicals, without a fluid for its pthallic anhydride system, which requires 40,000 gal of heat transfer fluid.

"We started researching fluids and looked closely at the current fluid, and we realized it wasn't the best fluid for us, even though it was the least expensive," said Paul Heckert, polymer operation superintendent for Stepan. "We were pushing the fluid to the limit of its operating temperature."

As a result of the constant cycling between 374 and 122oF (190 and 50oC), Stepan was experiencing tremendous fluid degradation, which in turn negatively impacted its productivity.

"The thermal fluid was degrading rapidly, and this reduced its ability to effectively transfer heat," Heckert said. "Our operations depend on the fluid to both impart heat and pull heat away. In doing this, we capture our product. The heat transfer fluid wasn't doing a good job, and we were losing yield."

While using the discontinued material, the polymers manufacturing team was forced to replace the fluid every three to five years. As the team began to research potential replacement fluids, it looked for a fluid that would perform at least as well as the previous fluid in the process.

"Even though our previous fluid didn't last a long time, it did work," said Marc Cieslak, polymers manufacturing specialist at Stepan. "We wanted to find a fluid that would maintain at least that level of performance while at the same time not degrade as rapidly."

A research team worked together to set priorities for the new fluid. The resulting matrix included characteristics such as viscosity, heat transfer and cost. The team met with about eight vendors to get more information, and decided to work with St. Louis-based Solutia Inc., manufacturer of Therminol heat transfer fluids.

"We were aware that the heat transfer fluid Stepan previously had been using was discontinued and knew that it represented a big opportunity for Solutia," said Nancy Wall, Therminol sales specialist. "Therminol has properties very similar to Stepan's previous fluid, especially with respect to its viscosity at operating temperature, which was the key parameter ensuring continued reliable system operation."

Having made the decision to use Therminol 59, Stepan decided to change out the fluid early in November 1997. Changeout took three to four days. In the months since the change, Stepan has already seen increased yields, and the team has noticed that the system performs better.

"It runs more efficiently with Therminol 59, which has increased our yields," Cieslak said. "Even though it has been in the system about a year and a half, the fluid still acts like new. This is a big difference for us. It's obvious we are not having the same degradation problems we had previously."

While Therminol 59 is a more expensive fluid than the one previously used, given Stepan's operating conditions, the company anticipates reducing costs in the future. The performance of Therminol 59 is expected to reduce changeover downtime and increase product yield.

"At our initial meeting, Solutia's technical support staff told us that because we weren't pushing the limit on the fluid's operating temperature, we shouldn't have anything to worry about -- the fluid would last 10 to 15 years," Heckert said. "At first, I didn't really believe them."

Time has proved them right, however. Since the changeover, Stepan has experienced less downtime, which allows the company to manufacture more product. In addition, the company is saving money because it has not purchased new fluid. Overall, the performance of Therminol 59 has exceeded the team's expectations.

"It has certainly performed just as we were told, and them some," Cieslak said. "So much so that we have purchased another product in the Therminol family for use in a different system."

For more information on Therminol heat transfer fluids from Solutia Inc., call (800) 426-2463 or visit www.therminol.com.