A solid bleached sulphate mill in North America, when asked to sum up their first impressions of the drying equipment that they had bought from Compact Engineering, said that it delivered everything they expected and “it does what it said on the box!”

The mill makes coated bleached board on a single Fourdrinier machine with a BelBond, between 210 gsm and 440 gsm, at speeds of up to 450m/min.

The machine displayed a typical composite profile, a central hump of about 3% as well as the normal peak-to-peak spread of about 3.5%, indicating a problem with the pocket ventilation in the main bank as well as variable CD drying, which is not uncommon on board.

Rather than use IR to flatten the hump and the normal moisture spread, which is not energy efficient, Compact Engineering recommended a more cost effective solution, by making use of their BlaCbox ventilator to replace the existing pocket ventilation system while using the existing ventilation infrastructure to remove the hump and save energy and use the Corona IR profile control dryers to control the moisture profile spread.

The BlaCbox ventilators removed the 3% hump while the Corona moisture profile control system provided a peak-to-peak reduction of 3% on the average and between them they produced an average production increase of 11% on all heavyweight products, at an average cost of about 35 kWh/ton: the lighter weights being limited in other areas.

The Corona profile control dryers were installed between the 4th and 5th dryer sections, to take advantage of their ability to bring the moisture from the middle of the sheet to the surface and improve the 5th section drying performance. In profiling before the last section, the surface fibres are re-moisturised by the water from the middle of the sheet and are therefore able to pick up more heat from the following cylinders, further increasing the overall thermal efficiency of the dryers and contributing to a swift recovery of the capital invested in the project.

Today, with the speed increases the Corona dryers are controlling at an average of 18% with a peak-topeak of just 1% after the 5th section.

The next drying bottleneck was the dryers after the wetstack, so Compact replaced existing IR dryers and installed a pair of Corona 480 IR moisture profile control dryers to augment the capacity of the afterdryers. Flattening the CD and ‘Z’ direction profile ensured a better quality sheet going into the coaters, which improved the coating holdout. These dryers were originally intended for use only on the lightweight sheets, but the improvement in coating quality means that the dryers are now used across the range.

The BlaCbox uses a novel method to control the boundary layer activity, which reduces sheet temperature and so improves heat transfer from the cylinders while improving ventilation in the pockets.

The Corona dryers transfer more energy/m² into the sheet than any other short wave IR system available. This is because of the combination of their unique lamp design and the curved lamp and reflector assembly, which fits neatly over the drying cylinders and radiates the IR energy normal to the sheet surface on the cylinder for optimum absorption and minimum losses.

The new range of Compact super efficient lamps, which are designed and manufactured in house, produce the optimum wavelength for absorption by cellulose fibre through the thickness of the sheet, even when run at maximum output. Compact claims they are the only lamps to do so.

Compact Engineering Ltd., www.compact.co.uk

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