Patent ID: 9328458
Filing Date: 2016-05-03
CPC Classification: D21C

Claim Text:
1. A continuous digester for producing delignified cellulosic material comprising: an outer digester shell designed for withstanding the pressure applied in the digester, a bottom with a central outlet for the delignified cellulosic material, and a bottom scraper including scraper arms with scraper blades, and a cone diverter driven by a rotating shaft, the scraper arms are angled at an angle α in relation to the horizontal plane in the range between 5°-30°, a wash zone in the digester bottom with nozzles (HN, VN, CP) adding wash or dilution liquid to bottom of digester and a wash screen (WS) located at a distance above the bottom scraper, with no other withdrawal screens between the scraper and the wash screen (WS), for withdrawing at least a part of the added wash or dilution liquid after a displacement trough the delignified cellulosic material, said distance providing for a wash zone having a retention time of 5-45 minutes of the delignified material, a wash extraction chamber (WEC) located behind the wash screen, and between the digester shell and the wash screen, said wash extraction chamber having an radial extension (A) as seen in the radial direction of the digester, below the wash screen (WS) is arranged an vertical extension (VE) of the interior digester wall down towards the end of the outer arm of the bottom scraper, said vertical extension (VE) ending at a distance (D) shorter than three times the radial extension (A) of the wash extraction chamber above the outer end of the scraper arms, and with a radial extension (R) between the digester shell (DS) and the inner wall (IW) of the vertical extension of the interior digester wall being in the range of 50-100% of the radial extension (A) of the wash extraction chamber.