Fluoropolymer products in various high corrosive sulphuric acid applications –an update on new applications and long term references

摘要

Sulphuric acid(H2SO4)can lead to corrosion problems,in particular if high temperatures and high concentrations are combined.This can be a major problem resulting in lots of maintenance/repair and production loss for sulphuric acid production plants,acid storage and piping systems.A superb option to solve these corrosion problems are linings made from fully fluorinated melt-extruded thermoplastics like FEP and PFA.Partially fluorinated thermoplastics like PVDF and ECTFE,are successfully used for numerous sulphuric acid storage solutions and sulphuric acid handling at lower temperatures.In this paper,the chemical resistance to sulphuric acid is described.On the one hand a laboratory study shows that PFA can withstand highly concentrated H2SO4 up to 260°C(500°F).On the other hand,different applications are described,confirming these test results.A special focus is put on 3 different successful projects for corrosion protective linings and pipes made from PFA and ECTFE.1.First,a new high-end PFA steel lining application in the copper CCR Refinery,Montreal Canada is discussed in detail.In this project,Electro Chemical lined an acid recovery unit with operation temperatures up to 150°C(300°F)with PFA sheets.The old lining of the ventilation pipe could not withstand the harsh combination of corrosive gases,high temperatures,temperature fluctuations and vacuum.These conditions soon led to cracks,pinholes and leaks in the pipe lining causing the shutdown of one of two affected production lines every 2 to 3 months to repair the lining.The costs for the repair and loss of productivity made CCR's engineers look for an alternative solution.After two years of operation using the PFA lined equipment,CCR has not had to do any maintenance to the lining.The decision to use the new PFA lining system resulted in notable savings in repair costs and equipment downtime,thereby also increasing the plant productivity and workplace safety.According to an engineer from CCR,the PFA lining"has already more than paid for itself in terms of saved maintenance costs and less downtime."2.The second case study is demonstrating the long-term resistance of a 20 years old PFA"fix point lined"wet sulphuric acid(WSA)plant in Sweden which was constructed and planed by P&P Industries AG.In this plant,the PFA is used as a corrosion resistance lining in the area of the heat exchanger(condensation of highly concentrated sulphuric acid),with temperatures up to 260°C(500°F).The lifetime of more than 20 years impressively shows the excellent performance of PFA when exposed to H2SO4,even at high temperatures.3.In the third positive reference a sulphuric acid double-containment pipe is presented.It is used for the transportation of 98% sulphuric acid in the"Surat next Generation Project"in Sugen(India).All in all more than 1800 m of ECTFE double containment pipes were installed and they are successfully in operation since 2011.