Feeding system having pumps in parallel for a continuous digester
The feed system is for a continuous digester where at least two pumps are arranged in parallel at the bottom of a pre-treatment vessel. The outlets of the pumps are combined at a merging point before a common transfer line extends to the top of the digester. The system makes it possible to provide a feed system with an improved accessibility and operational reliability, and to operate the main part of the pumps at optimal efficiency even if the production capacity is reduced.
1. A feed system for a continuous digester wherein wood chips are continuously fed into a top of the digester and fed out from a bottom of the digester, comprising:
a liquor line connected to a vessel for suspending the wood chips, that are to be fed into the top of the digester, to create a chips suspension,
at least two pumps connected in parallel to a bottom of the vessel,
the chips suspension being pumpable by the at least two pumps through first sections of a transfer line, each first section extending from each pump, each first section being combined at a merging point to form a combined second section of the transfer line, the combined second section extending from the merging point to the top of the digester, and
a dilution line connected to the merging point.
2. The feed system according to claim 1 wherein at least three pumps are connected in parallel to the bottom of the vessel.
3. The feed system according to claim 2 wherein at least four pumps are connected in parallel to the bottom of the vessel.
4. The feed system according to claim 2 wherein at least a second section of the transfer lines from at least two pumps in a first pump group are combined with another section of the transfer lines from at least one pump in a second pump group at a merging point to a common third section of the transfer line before the third section extends towards the top of the digester.
5. The feed system according to claim 1 wherein the pumps are connected symmetrically to the bottom of the vessel.
6. The feed system according to claim 1 wherein in the vessel is arranged a supply line for the addition of fluid controlled by a level transmitter that is adapted to establish a liquid level (LIQ LEV ) in the vessel.
7. The feed system according to claim 1 wherein the outlet of the transfer line opens directly into the top of the digester.
8. The feed system according to claim 1 wherein a bucket-shaped outlet is connected to the bottom of the vessel, the bucket-shaped outlet having an upper inlet defined therein, a cylindrical mantle surface, and a bottom, at least two pumps in parallel having pump inlets and pump outlets defined therein,
the pump inlets being connected to the cylindrical mantle surface,
the pump outlets being connected to a transfer line that extends to the top of the digester,
a stirrer disposed at the bottom of the vessel and arranged to rotate in the bucket-shaped outlet, and
the stirrer having at least two scraper arms that are adapted to sweep over the pump inlets arranged in the mantle surface of the bucket-shaped outlet.