Stora Enso

Crystallisable Cooking Chemicals A Nuisance In The Flue Gas Channel

The heat transfer surfaces and the gas flues in recovery boilers have traditionally been difficult to clean. Stora Enso Fluting Mill in Heinola, Finland, is no exception. The cooking chemicals in the form of salt in the exhaust gases used to create a sticky salt bank in the bend of the smoke flue. Quickly reaching the thickness of dozens of centimetres, the salt deposit gradually clogged the flue and considerably weakened the draught, resulting in smoke streaming into the boiler room.

The clogs and slag were removed out of the flue at intervals of approx. one and half weeks by spraying expensive desalinated water into the flue at 140 bar pressure. Water causes erosion in the flue and corrosion in the electro filters. All in all, the effect of the laborious water and steam cleaning was insufficient.

First Approach

Having been assigned to solve the cleaning problem of the factory’s recovery boiler, the first thing to try was the traditional 150 dB NI250 pneumatic acoustic cleaner, which have performed well in many different applications. It was not, however, effective enough to remove the salt layer sticking to the surface, although the cleaning interval got longer.

Success Through Product Development

For difficult environments, Nirafon had developed a new, more powerful, 3rd generation continuous operation acoustic cleaner at the production stage. The NCSD^® cleaner was installed in the bend of the flue. The cleaner was programmed to emit 170 dB sound pulses in thirty pulse series, repeated at a few minutes’ intervals.

The frequent pulse series of the cleaner prevented the salt granules from clinking to the structures of the flue and the desired level of cleanness was achieved.