Tough steaming

Tough steaming can lower tearing resistance

The steaming process of chips is necessary for continuous cooking and is also used frequently during batch cooking. A couple of years ago MoRe discovered a connection between low tearing resistance and a tough steaming process. The reason for this relation was that a too tough steaming process, in combination with high pressure against the bottom of the steaming vessel, could cause fibre ruptures. In order to be able to investigate this phenomenon in pilot scale, a unique testing device was developed.

Pekkala 3 1

If the chips are treated by a too tough steaming process the chip column in the steaming vessel will be too hot. The chips therefore become compact and soft, causing fibre rupture as a result of the mechanical output from the vessel. On the other hand, if the steaming process is too weak, the cooking part is adversely affected as the chips in that case might contain air and thus do not sink through the digester.

"It is important to optimize the steaming for subsequent impregnation and a good cooking result in the digester so that no fibre rupture will occur," says Torbjörn Sjölund, Process Consultant, MoRe Research. “In order to simulate the steaming process, the former MoRe employee Christer Pekkala built the “Pekkala pilot” which in an efficient way simulates the steaming process. “

“By varying the pressure on the chip column and the steam in the apparatus, different steaming conditions can be simulated. The chips from the chosen steaming conditions are cooked simultaneously under the same cooking conditions in our pilot digester, after which strength testing on hand sheets are done. In parallel, microscope studies are conducted to determine the occurrence of fibre ruptures as a consequence of the different steaming conditions. In this way, the right steaming process conditions can be simulated,” concludes Torbjörn Sjölund.

Contact: Lars Sundvall +4670 526 52 21, E-mail