Rolling out BESPOKE BENEFITS
15 Jan 2000
When a company is prepared to invest around £300 000 on a process temperature control system, it generally is not looking for just an off-the-shelf product. What it wants for its money is a tailor-made solution, which is exactly what Crane Heatex recently supplied to Weston Vinyls for its PVC film calendering plant in Frome, Somerset.
Formerly part of the Marley group, and more recently a division of EVC (European Vinyls), Weston is now an independent company specialising in the production of PVC film and sheeting. As part of this change in emphasis, two years ago it wanted to transfer a complete Berstorff calendering line from a then-sister EVC company in Austria to Weston's Frome factory.
Shipped over in 26 truck loads of machinery, the line, though generally serviceable, proved to be some way short of the exact specifications that Weston's senior project manager John Oswin had in mind for its new use.
Of particular concern were the safety features of the original plant which involves a PVC compounding station, extrusion and grinding operations, and the multi-roll, high temperature calendering line itself. The safety improvements since made by Oswin and his team not only comply fully with current legislation, but also won the praise of the local HSE inspector as 'one of the best examples of a plant of its type'.
TEMPERATURE CHANGES
On a specific process engineering level, the new use for which Weston wanted the line also required considerable changes to the original operating specifications. Instead of the 38 C maximum temperatures at which the plant was run in Austria, Oswin specified operating temperatures ranging from 9 to 205 C with temperatures on the calendering and stretching rolls capable of being controlled to within +/-1degC.
Having already installed systems on other Weston lines, Crane Heatex's general manager Tony Judd thought his company could tackle the job. What it didn't know about the new project, however, were any of the original design data or thermal loadings involved.
The first step therefore was to undertake a survey and evaluation of the proposed system, which comprises an eight-stream temperature control system for the Berstorff line.
'The toughest part of the job,' says Judd, 'was getting the boiler size right.' This was solved by supplying a skid-mounted package of 27barg, dual fuel steam generator, complete with all ancillary plant such as water softeners and blowdown. On top of temperature control, the control system is also interfaced with sophisticated gauging and monitoring software and can be remotely programmed.
The end result was a system specification agreed between Weston and Crane Heatex. From this Heatex designed, manufactured, installed and commissioned the whole system. This consists of a dedicated heater, cooler, pump and controller for each main calender roll, together with the whole control system and ancillary equipment.
For controlling and adjusting the temperature of the heat transfer medium, a total of 14 separate and independent heat exchangers is used a combination of shell-and-tube and plate designs depending on individual output requirements.
According to Heatex, its approach to the problem is adaptable to many other processes requiring tight temperature control over a wide range.
