Steam deicing in the debarking drum - LESS ENERGY, LESS WATER, MORE SAVINGS

Antti Haapalainen, Head of Wood Processing Product Group at ANDRITZ explains, “The traditional way to deice logs in the woodyard is by using warm water – at around 50 °C – which is sprayed in a long tunnel onto the log bundles on a moving conveyor. In this case, the warm water melts the ice and snow on the surface logs; however, the logs in the middle of the bundle do not get so much heat energy and can often remain frozen.

“In the case of the ANDRITZ steam injection deicing system in the debarking drum, multiple injectors are housed in the drum itself, and the energy transfer of hot steam is much more efficient than warm water, and therefore super-efficient when it comes to deicing the logs. At the same time, the steam injection system has a much smaller footprint and has markedly less auxiliary equipment required for operation.”

The operating principle from ANDRITZ first involves a steam injection to melt ice and snow in the entrance of the drum, followed by a second injection of steam spread directly on the surface of the logs during debarking using special log lifters. Steam injected directly onto rotating logs ensures that all logs are properly deiced. Furthermore, the amount of energy and thus the whole deicing process is easier to control and can be accurate according to the requested debarking degree, thereby saving energy.

“This constant steam injection sequence in the drum is crucial to the debarking process as it makes sure that the frozen core of the logs does not cause the surface bark to freeze again, resulting in a much more efficient debarking process,” says Haapalainen. “In the case of the warm water deicing system, energy input stops at the entrance of the drum and frozen cores can re-freeze the surface bark. Ultimately, this means the debarking process needs more warm water and the drum needs to rotate harder to get the required result, which increases energy costs and the possibility of white wood loss.”

SAVINGS: FRESH WATER, EFFLUENT, ENERGY, AND WOOD LOSS

Calculations by ANDRITZ indicate that an average size pulp mill, with a warm water deicing system can save around 1.5 MEUR a year by installing a steam injection system on a typical nordic debarking line.

These savings are made in the areas of fresh water, wood losses, steam and power consumption:

• Fresh water consumption savings of up to 40%
• Lower emissions and carbon footprint
• Electricity consumption up to 240 kW lower installed power
• Steam consumption up to 20% saving
• Less wood losses, at medium sized mills (more than 100 KEUR annually)
• Lower investment cost (equipment and civil works)
• Efficient layout of the plant
• Lower life cycle costs (less equipment to maintain)

“There are many savings to be made by installing a steam injection system,” says Haapalainen. “First of all, with a warm water deicing system, fresh water needs to be constantly added as the water becomes full of soil, mud, and bark residue. With the steam injection deicing system in the debarking plant, 40% less fresh water is required, which also means there is much less effluent.”

“Also, there are generally lower emissions considering reduced effluent and we need less equipment due to the smaller footprint. Electricity consumption is much lower due to less energy being used in the debarking process and, of course, there is less wood consumption due to more accurate debarking efficiency. In addition to these savings, “over-debarking” can be avoided and drum rotation can be kept optimum for the purpose.”

Furthermore, due to exposure in the long tunnel of conventional deicing conveyor, some 2 MW of heat loss occurs during winter months on the warm water deicing system, representing a 23% energy loss. As the steam injection system is contained in the debarking drum and energy transfer to logs is more accurate, much less energy is wasted.