Synthetic heat transfer fluids improve high temperature operations for two manufacturers.

Reliable heat transfer fluids are vital for efficient operation and productivity. When pushed to their limits, some heat transfer fluids can degrade rapidly, resulting in deteriorating performance, increased operating costs and poor finished product quality. With these risks, how can users find a heat transfer fluid that prevents such problems?

The main applications using heat transfer fluids are manufacturing processes involving industrial chemicals, paper and wood, resin preheating, natural gas treatment, and oil pipeline preheating. These processes normally operate at temperatures from 428 to 572°F (220 to 300°C), or higher. In this temperature range, there are two main categories of product that are used for heat transfer:
  • Mixtures of petroleum distillates, or mineral oils.
  • Fluids consisting of synthetic aromatic compounds.
Therminol 55, 62 and 66 from Solutia Inc. are examples of the latter. The fluids have been used with success by customers who have converted from mineral oil-based systems. This article profiles the experiences of two such customers.

Polimeri Europa

Polimeri Europa is an Italian petrochemical company wholly owned and operated by Eni SpA. Its three divisions -- basic chemicals, polyethylene, and elastomers and styrenes -- offer a portfolio of products, and its many production plants have heat transfer fluid systems operating at various temperature ranges. The company has successfully operated with two different Therminol fluids, and has been using Therminol in the styrene monomer process system, for more than 10 years.

In 1975, the plant’s ethyl benzene distillation column, which is a key part of the styrene monomer process, was started up using a mineral oil-based fluid, nominally rated to 608°F (320°C) but operated at bulk temperatures up to only 500°F (260°C). Although the heat transfer system performed adequately at this temperature, all the mineral oil, approximately 27,000 gal (90 metric tons) had to be changed due to product degradation. The fluid replacement was made during a scheduled plant shutdown when degradation products, consisting mainly of sludge and tar, were observed at the pump inline filters.

A requirement to increase the distillation rate in the early 1980s meant that the maximum temperature of the mineral oil heating the distillation column was raised to 554°F (290°C). The higher temperature caused the fluid degradation to increase exponentially, and Polimeri Europa had to increase the top-up rates and repeatedly clean the filters.

Given this experience of disruptive thermal instability, the company decided to switch to a synthetic heat transfer fluid offering similar heating performance but with higher thermal stability. Therminol synthetic heat transfer fluid manufactured by Solutia was selected to replace the mineral-oil-based fluid. Since this replacement in 1995, Therminol has been operating continuously, reaching bulk temperatures up to 572°F (300°C). Today, the bulk temperature of the fluid at the heater outlet is maintained successfully between 561 and 572°F (294 and 300°C).

As an added benefit, within the first six months of operation, Therminol’s solvency power (provided by the superior aromatic base), eliminated a high proportion of solids left behind from the previous fluid via new bypass filters installed in a side-stream installation. Today, these filters continue to remove previous product residues during normal operation.

Indicators of fluid performance and routine analysis have shown no significant deviation in fluid quality over time. In addition, since the plant was filled with Therminol, no major unplanned shutdowns have been needed due to problems with the heat transfer fluid condition. Polimeri Europa’s Therminol fluid condition now is regularly monitored in Solutia’s Louvain La Neuve Therminol Laboratories in Belgium, performing specific analysis for heat transfer fluids, with results and guidance provided by Solutia. This type of analytical service is also available through Solutia in North America, South America, India and China as the cornerstone of its “TLC Total Lifecycle Care” program.

Polimeri Europa representatives report that during 11 years of operation using Therminol heat transfer fluid, the company has experienced lower maintenance, lower top-up rates, potential to reach higher temperatures to allow better operating margins, and much longer fluid life at higher temperatures.

Gutta Werke, Italy

Founded in 1965 in Switzerland, Gutta Group is a multinational company with production sites and offices in several European locations. Production covers a range of building materials and garden products, including bituminous and insulated roofing sheets, waterproofing membranes, nets, grass gratings and draining membranes. The nature of Gutta products, based mainly on bitumen and high-density polyethylene (HDPE), means that heat and heat transfer factors are vital to the company’s success.

In its production site at Filago in northern Italy, Gutta produces membranes and bituminous sheets. In 1996, Gutta installed a new heat transfer fluid system serving both asphalt heating and delivering heat to drying machines. The system initially was filled with mineral oil, and the heater’s normal operating temperature was 509°F (265°C) with peaks of 536°F (280°C). The system had an open expansion vessel.

Within three years of system startup, the operators found that the heat transfer fluid circuit was dirty and that several mechanical seals were damaged. In addition, there were insoluble deposits, and fuel consumption had increased.

Due to the success of Gutta products, in 2000 a new higher temperature rated heater was installed to satisfy the higher production requirements. The amount of mineral oil top-ups then increased continuously, forcing the system to a standstill for cleaning and repair. In 2002, Gutta engineers researched the heat transfer fluid market to find a product that would meet its operational criteria. The company opted for Therminol synthetic high temperature heat transfer fluid.

At the time, the Filago site was at maximum production capacity with increasing demand. As a result, production management required that the maintenance outage to change the fluid be minimized. With the support of Solutia’s technical department, a change-over fluid strategy that avoided system cleaning was devised, which allowed the direct substitution of used mineral oil with Therminol, minimizing the production break.

The benefits of the fluid change were clear:
  • Over time, the solvency power of Therminol synthetic fluid cleaned the system internally, including heat exchange surfaces, resulting in a better heat transfer coefficient.
  • Less heat was required to reach the desired production capacity, leading to a consistent reduction of fuel consumption.
  • After four years of continuous operation, maintenance and fluid top-up are now reduced to a minimum. The operation of Therminol is being monitored regularly through Solutia’s analytical service program.
Angelo Rota, utility manager for the Filago production units said, “The reduction of fuel consumption and maintenance operations in the HTF [heat transfer fluid] system implied a return of Therminol capital investment in less than one year. Now, thanks to Therminol, heat transfer system down times and heavy maintenance works belong to the past.”

Therminol and TLC Total Lifecycle Care are registered trademark of Solutia Inc.