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

The modernization of a sulfuric acid plant in Talara, Peru by PH Technology (Spain) also included the design and manufacture of this acid-resistant stack made with ECTFE dual-laminate from AGRU Kunststofftechnik.

ECTFE dual-laminate part of the stack
Figure 1: ECTFE dual-laminate part of the stack during the lamination process

Distributor: Agruquero
Manufacture of a OD 1600 mm ECTFE dual-laminate stack with a height of 46 m
Product: 2.3 mm ECTFE SK+ fabric backed sheets, ECTFE welding rod and ECTFE cap-strips
Medium: Sulphur Dioxide (SO2), Sulphuric Acid (H2SO4)
Design pressure: -0.1 to +0.1 bar relative to ambient pressure
Design temperature: 110 °C
Manufacturer: PH Technology (Spain)

ECTFE/FRP dual-laminate part
Figure 2: Finished ECTFE/FRP dual-laminate part

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.

Hot-gas welding of ECTFE fabric backed sheets
Figure 3: Hot-gas welding of ECTFE fabric backed sheets

Welding training at AGRU Bad Hall

AGRU was able to carry out a welding training with the staff from PH Technology and Agruquero who was in charge of the project. The main focus of the AGRU welding experts, who are certified according to DVS (German Association for Welding), was the processing of Halar® ECTFE. In addition, the design and implementation of the project was discussed in detail.

ECTFE sheets
Figure 4: ECTFE sheets including a conductive element in the welding area

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.

FRP Stack from the inside
FRP Stack from the inside

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!

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