Valmet Chip Bin is a buffer that acts as a feeding device to the plug screw feeder. It can act both as a buffer and pre-steaming bin, but also Whilst the chips are inside the bin, they will undergo equalization of moisture and temperature to create a highly homogenous chip content.
The homogenous chip content can be further processed by combining the Valmet Chip Bin with pre-steaming, this will result in an increased temperature and moisture level of the chip content to facilitate the upcoming process step like dewatering, refining and reducing the amount of natural wood resins. Ensuring proper dewatering starts with the removal of trapped gases inside the chips and replacing them with steam. Allowing that steam to condensate inside the chip completes the replacement of a non-compressible media with a compressible one, water. This change will allow for a far more effective dewatering when the chips are moving forward to the dewatering zone of the plug screw feeder.
Valmet offers two types of chip bins, the Chip Bin VB (Vibrating Bin) that uses gravity and vibrational energy to control the feeding and the Chip Bin DB (Discharge Bin) which uses a screw conveyor and agitator to actively control the feeding.
Valmet Chip bin VB is a conical chip bin primarily designed to handle raw materials with favorable flow characteristics, normally seen with a even sizes and shape distribution. It should also be relatively free from impurities such as sawdust, shavings, bark and pin chips since their presence greatly increases the risk of bridging, especially when used with pre-steaming.
Valmet Chip Bin VB consists of an upper shell, a bottom part with an internal cone acting both as a chip stack pressure relief system and a steam distribution device, this then is finished off with an outlet part of variable sizes to match the following machines.
With springs and drawbars the bottom part is freely suspended from the upper shell and sealed off with a flexible rubber cloth. This setup allows the bottom part to be externally vibrated with a electrical vibrator to improve the material flow considerably by reducing the bridging tendencies in the chip bin.
The internal SteamCone that serves to evenly distribute steam in the center of the chip stack also acts to relief the chip stack pressure exerted on the outlet part to ensure an even material flow with the purpose to optimize the dewatering performance of the plug screw feeder which results in less moisture entering the dryer.
Valmet Chip Bin DB is designed to handle most types of raw materials, regardless of the amount of impurities such as sawdust, shavings, bark and pin chips that in other chip bins greatly increases the risk of bridging, especially with gravity-controlled feeding systems.
Valmet Chip Bin DB is a agitator equipped flat-bottomed chip bin fitted with a screw conveyor for an actively controlled discharge of raw material. Paired with a slightly conical upper shell narrowing towards the top and with one central and multiple peripheral insertion points for adding steam the Valmet Chip Bin DB is highly suitable to use for pre-steaming of the chips. Together with the agitator that rotates in full revolutions along the bottom to avoid any stagnant material that may cause unwanted build-ups and bridging problems. The agitator directs the material towards the discharge screw which can be fitted with a dewatering box to further optimize the dewatering performance of the plug screw feeder which will results in less moisture entering the dryer.