Method and arrangement for adding treatment liquors to cellulose raw material in a continuous process using down flow vessels
The method and arrangement is for adding treatment liquor to comminuted cellulose material, preferably wood chips, during the manufacture of chemical pulp in a continuous process. The process uses a down-flow vessel where chips are descending down the vessel in a plug-flow and where treated chips are continuously fed out at the bottom of the vessel. By arranging more than two parallel pipes offset from the center of the vessel a better distribution of treatment liquor is obtained. Any disturbance of the chip plug flow descending down the vessel is reduced to a minimum.
1. A method for adding a hot treatment liquor and steam to un-steamed comminuted cellulose material during a manufacture of chemical pulp in a continuous process, comprising:
providing a down-flow continuous treatment vessel having at least two vertical pipes being arranged parallel to a direction of a plug-flow of chips continuously descending down the vessel, the vertical pipes having open lower ends disposed below a chip level (CH_LEV) of the chips of a chip volume inside the treatment vessel,
adding the treatment liquor via the at least two vertical pipes, the treatment liquor having a temperature exceeding a boiling temperature at a prevailing pressure at the outlets so that a flashing effect is obtained in the chip volume located above a liquid level (LIQ_LEV) established in the treatment vessel below the chip level (CH_LEV),
distributing the treatment liquor in parallel flows and flashed steam at multiple points over a plug flow area with the at least two vertical pipes located at a radial position of a radius R 1 in the treatment vessel, the radius R 1 being smaller than a radius R 2 of the treatment vessel at a height of the open lower ends of the two vertical pipes,
reducing interference of the plug-flow to a minimum by distributing the treatment liquor via the at least two vertical pipes,
locating the outlets of the open lower ends above the liquid level (LIQ_LEV) but below the level (CH_LEV) of the chips in the treatment vessel, and
continuously feeding out treated chips at a bottom of the treatment vessel.
2. The method according to claim 1 wherein a withdrawal of the treatment liquor takes place at a position in a wall of the treatment vessel and inducing a radial displacement flow of treatment liquor from the outlets of the at least two vertical pipes and further through the chips in a liquid volume.