Halar® ECTFE dual-laminate stack for a sulphuric acid plant

About the ECTFE liner project

The purpose of this project was the construction of a stack within a sulphuric acid plant in a refinery in Talara, Peru. By processing the flue gases, the formation of highly aggressive media such as SO2 and H2SO4, can occur. Since these media are very corrosive to metals and many other plastics, a dual-laminate solution using Halar® ECTFE liner material and fibre reinforced plastic (FRP) was chosen.

Applications made of fibre-reinforced plastic are lined with fabric backed sheets to maintain chemical resistance and leak-tightness. Like an ECTFE piping system, the stack is also equipped against most aggressive media. The FRP ensures the compressive and mechanical strength. This ensures safe operation of the system (even under vacuum).

Halar® ECTFE as a lining material

Halar® ECTFE possesses a unique combination of properties that are the result of its chemical structure, which consists of a copolymer with ethylene and chlorotrifluoroethylene arranged alternately. Halar® ECTFE has an excellent chemical resistance and shows almost no property changes over a wide range of temperature. Furthermore, Halar® ECTFE is known for its good permeation barrier, which ensures, together with the highly chemical resistant fabric backing system “SK+”, the durability and longevity of the bonding strength in dual-laminate applications.

The solution and its design

The stack was constructed out of five parts installed via flange connections. For the subcomponents within each part, 2.3 mm ECTFE fabric backed sheets were bent and hot-gas welded as shown in Figure 3. After this first step, the cylinders have been laminated with fibre-reinforced plastic. During this process a conductive element had to be placed in the welding area which was later used for spark testing to ensure the leak-tightness of each weld seam (Figure 4). Subsequently, the cylinders were aligned to each other, welded and laminated.

Advantages of ECTFE SK+ fabric backed sheets and dual-laminate constructions

• ECTFE has an excellent chemical resistance to both alkaline and acid solvents
• ECTFE shows almost no property changes over a wide temperature range of up to 140 °C
• ECTFE is known for its good permeation barrier for many chemicals
• The excellent chemical resistance of the SK+ fabric backing system ensures the durability and expected lifetime of the dual-laminate construction
• In general dual-laminate applications are suitable for operation temperatures of up to 180 °C (depending on material and chemical), even under vacuum

Finally, AGRU would like to thank PH Technology and Agruquero for the good cooperation!