Following trials of alternative valve stem packing materials, BP Chemicals Limited significantly reduced unscheduled reactor shutdowns and saved an estimated 56.000 £ annually for each reactor control valve at its Hull, UK, plant by switching from PTFE packing to DuPont™ Kalrez® Valve Stem Packings (KVSP™). In addition to environmental and safety benefits due to improved leak prevention, the company reports much improved valve hysterisis and control, less “sticktion”, and longer service life for valve stem and bore parts.
The Kalrez® Valve Stem Packing set, supplied and fitted by Authorized Kalrez® Distributor James Walker & Co. Ltd, operates in an aggressive process environment involving 60 per cent pentane and 40 per cent butane, hexane, acetone and water acid at –30 °C (-22°F), at a specific pressure. These conditions caused annual attention to the previously fitted PTFE packings in order to prevent leakage, damage to valve parts and unscheduled reactor shutdowns.
“In the past, preventing product leakage from valve glands on the separator four levels at the company’s DF3 plant in order to avoid outages into the atmosphere and surrounding area was a major effort,” said Ken Foster, Line Manager Maintenance Services – Control Valve Department, BP Chemicals, Hull. “Also, valve stems became damaged beyond repair, necessitating costly replacement.”
Each time a valve has to be overhauled, whether scheduled or unscheduled, it is recorded on the valve history. The valves in question had been overhauled at least once per year over the past ten years.
Previous attempts to remedy the problem with varying packing configurations and chromed stems were not successful. The solution was to fit a Kalrez® KVSP™ set supplied by James Walker & Co. Ltd, in conjunction with a ceramic coated stem.
DuPont™ Kalrez® Valve Stem Packing is recognized as the leading packing-based solution to help reduce fugitive air emissions and valve leakage in chemical and petroleum manufacturing processes. The systems have been used successfully in hundreds of different chemicals including benzene, vinyl chloride, chlorine, fluorine, steam, hot water and heat transfer fluids.
“At BP Chemicals we estimate that an unscheduled shutdown due to a valve leak can cost the plant as much as 56.000 £ annually per reactor. With four reactors, possible annual savings by converting to KVSP at this plant could total approximately 225.000 £,” Foster adds.