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A Seamless PTFE Liner Protects Scrubbing Tower From HF and H2SO4
Product: |
PTFE lined carbon steel column |
Service: |
Boron trifluoride, sulfur trioxide, hydrofluoric acid and sulfuric acid @ 200°F |
Benefit: |
Estimated 20 year service life cuts costs. |
History: |
Problem: The Allied Chemical  Company Delaware Valley Works in Claymont redesigned the environmental control system for the borontrifluoride (BF,) unit early in 1982 and needed a scrubbing tower that could withstand extremely corrosive vapors and fumes, and high negative pressure. The tower was designed with a series of water sprays and a mist eliminator to remove residual BF" sulfuric acid and hydrofluoric acid present in gases from the absorbing tower, process vessels and storage tanks. The gas stream at temperatures from 95 to 200'F is drawn through the tower by an induced draft fan which creates a negative pressure, or vacuum of 36" H,O. The mist eliminator has a collection efficiency of 100% with particles larger than three microns, and up to 99.5% with smaller particles as gas flow through the bed decreases. It operates with 4-20" H,O pressure drop, is self-cleaning, and has unlimited turndown capacity. The 30" ID by 13' tall tower consists of six flanged sections fabricated from carbon steel to minimize the cost, but the interior had to be coated or lined with an inert material to protect the metal from the corrosive fluids and vapors.
Solution: Each section was fitted with a seamless 3/8" thick liner of PTFE. This high density, high molecular weight fluoropolymer was selected because it is non-porous and resists attack by a broad spectrum of organic and inorganic chemicals and solvents. It also exhibits high compressive and tensile strength, and flexfatique resistance at temperatures from cryogenic to 500'F. The TFE liner was isostatically molded with inlet and outlet nozzles, and with an integral flange which serves as a gasket and provides a leak tight seal for . Possible displacement of the liner, even under high vacuum conditions, is eliminated by the heavy wall construction and compression by the flange bolts.
Results: The scrubbing tower was placed in service in July 1983, and examination of the interior during several shutdowns has revealed no signs of attack by the highly acidic fumes, gases and vapors. The chemically inert TFE liner is projected to last throughout the 20 year or more design life of the tower, eliminating any maintenance due to corrosion on the interior of the carbon steel shell.
Reprinted from August 1984 CHEMICAL PROCESSING |
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