DuPont: Flue gas coolers with AlWaFlon® pressure hoses based on Teflon® PTFE maximize power plant efficiency

A new 858 MW-rated generating unit is being built at the site of Europe’s largest lignite-fired power station in Belchatów, Poland. Upon completion at the end of 2010, it will be one of the country’s most productive and efficient lignite-fired plants with an efficiency rating of around 42 percent, and one of the world’s most modern installations. Two innovative flue gas coolers, equipped with heat exchangers using the AlWaFlon® pressure hose system based on DuPont™ Teflon® PTFE (www.dupont.com), will make a considerable contribution to the plant’s comparatively low fuel consumption, reduced emissions and high sustainability. The flue gas coolers are developed and supplied by the engineering company Wallstein of Recklinghausen, Germany. The prime contractor for the specification, construction and commissioning of the new power plant is Alstom.

The two units, scheduled for delivery in the first half of 2009, are each equipped with five heat exchanger modules in which a total of approximately 500,000 meters of AlWaFlon® pressure hoses are integrated. After commissioning, they will reduce the temperature of the flue gas by about 50 K and, in doing so, generate two times 32 MW of heat energy. This will contribute towards the feed water heating at the power plant, while the surplus steam will be used for energy production, thereby significantly improving the overall energy balance of the plant.

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AlWaFlon® is defined by the interaction of an almost entirely chemically-inert fluoropolymer, designed for use in highly corrosive and reactive gases, and the use of complementary processing methods. Joint developers are Wallstein, DuPont (Geneva/Sweitzerland), as manufacturers of the base material Teflon® PTFE, and Fluortubing (Utrecht/the Netherlands), as the supplier of installation-ready, pre-formed pressure hoses. “We chose AlWaFlon® because – in contrast to the previously all-prevailing nickel-based alloys – it even resists highly corrosive mixed acids of SO2, SO3, HF and HCl, which condense on the hose surface during cooling of the flue gases,” explains Peter Dittmann, technical manager at Wallstein.

“The AlWaFlon® concept combines cost-efficient processing and application benefits with exceptional consistency in terms of its properties over long production periods, from charge to charge and for the entire hose length,” adds Alex Soeterbroek, managing director of Fluortubing. “Compared to many other fluoropolymer grades, the application attributes of AlWaflon® include higher upper service temperatures of up to 260 °C, a significant increase in the Vicat softening temperature to between 130 °C and 140 °C, as well as high flexural fatigue strength and stress cracking resistance.”

Successfully completed internal pressure creep rupture tests, conducted over 10,000 hours at laboratories belonging to BASF, confirm the following: AlWaFlon® pressure hoses provide long-term resistance to the combination of internal pressure, high temperatures and corrosive media, and exceed the performance of comparable products made of a range of other fluoropolymers. For this reason, they can be used at lower wall thicknesses than pressure hoses made, for example, from the equally corrosion-resistant fluoropolymer PFA, whilst providing the same levels of safety and being exposed to the same mechanical stress. Accordingly, larger amounts of heat energy can be coupled out at the same length, or alternatively the number/length of pressure hoses used can be reduced to achieve the same level of heat exchange performance. The German TÜV Süd has produced a positive report on the use of the AlWaFlon® system as a pressure hose at elevated temperatures.

Dittmann finds particular advantage in the excellent non-stick properties and self-cleaning effect of the fluoropolymer: “Compared with metal hoses, considerably fewer deposits form on their exterior, and those that do can be removed both quickly and thoroughly, and therefore cost-efficiently. This extends maintenance intervals and increases the overall availability of the plant.”

DuPont de Nemours (Deutschland) GmbH, Neu-Isenburg, Germany

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