Valve controls keep variables on a leash

INEOS Chlor has reduced process variability by 5% at its Runcorn chlor-alkali and chlorine derivatives plant by replacing traditional butterfly valves with Fisher Control-Disk valves.

The tighter control provided by the Fisher valves has increased plant throughput and avoided several unplanned shutdowns that could have cost as much as €450,000 (£379,000), reports supplier Emerson Process Management.

The project also helped achieve a 96% OEE (overall equipment effectiveness) rating for the unit where the valves were installed, according to the vendor.

“For a plant this size, even a modest reduction in variability can have a significant payback,” said Barry Makepeace, INEOS Chlor control and instrumentation engineer. The new valve applications “also enabled us to optimise process control without sacrificing flow capacity or needing to re-pipe,” he added.

The Runcorn plant had previously used traditional butterfly valves to control the temperature and flow of cooling water to the primary condensers. Tight control is essential because if the condensers’ temperature is too low, there will be residual chlorine in the system, which has to be removed.

If the temperature is too high, there is an increased risk of a safety trip or plant shutdown. Each trip and subsequent unplanned shutdown can cost INEOS Chlor up to €75,000.

The traditional valves had a small control range and a large deadband, which reduced their ability to respond to temperature changes. In the previous 12 months, the plant had experienced 23 trips, leading to a significant loss of production.

INEOS Chlor, therefore, replaced four traditional butterfly valves with the new Fisher Control-Disk design. Its effective control range - between 15% and 70% of travel - approaches that of a segmented ball valve.

The enhanced valve control, said Emerson, enabled plant operators to optimise temperature set points and avoid at least six unplanned shutdowns.