Method and apparatus to produce pulp using pre-hydrolysis and Kraft cooking

摘要

A pulp cooking system including: a cellulosic material feed system, a pre-hydrolysis reactor vessel and a Kraft cooking reactor vessel. The feed material system includes a steaming chip bin and a high pressure transfer device. The pre-hydrolysis reactor vessel maintains the feed material in a mildly acidic condition and allows hydrolysate to be extracted through screens below a hydrolysis zone in the vessel. A wash zone is below the screens and allows wash liquid to flow through the feed material in a cross-current direction. The wash liquid and hydrolysate removed from the feed material is extracted through the screens. The feed material is maintained in a mildly acidic condition through the pre-hydrolysis reactor vessel until the material enters the Kraft cooking vessel where the feed material is treated with alkaline cooking liquors.

主权项

1. A method to produce pulp using a feed system, a prehydrolysis reactor vessel and Kraft cooking vessel, the method comprising:
steaming cellulosic fibrous organic feed material in a material feed system; adding to the feed material liquor extracted from the prehydrolysis reactor vessel before the feed material enters the prehydrolysis reactor vessel; pressurizing the feed material from the chip feed system in a high pressure transfer device before the feed material enters the prehydrolysis vessel and transferring the pressurized feed material to an upper inlet to the prehydrolysis reactor vessel; subjecting the feed material to a hydrolysis reaction in a hydrolysis zone in the prehydrolysis reactor vessel, the feed material and a liquor flow concurrently in the hydrolysis zone, wherein hydrolysate is generated by the hydrolysis reaction; extracting a hydrolysate-containing liquor through a screen in the prehydrolysis reactor vessel into a conduit, wherein the screen is adjacent a lower portion of the hydrolysis zone; separating the extracted hydrolysate-containing liquor into at least a first portion and a second portion by forming at least a first flow path and a second flow path in the conduit; discharging the first portion of the extracted hydrolysate-containing liquor in the first flow path from the prehydrolysis reactor vessel such that the discharged first portion does not return to the prehydrolysis reactor vessel; returning the second portion of the extracted hydrolysate-containing liquor in the second flow path to one or more elevations of the hydrolysis zone upstream of the screen; adding a wash liquid to a wash zone in the prehydrolysis reactor vessel; as the feed material flows downward past the screen and through the wash zone, washing the feed material with the wash liquid flowing upward through the wash zone to the screen; discharging the washed feed material from the prehydrolysis reactor vessel and transporting the washed feed material to an upper inlet to the Kraft cooking vessel; changing the pH of the washed feed material to alkaline after the feed material is in the Kraft cooking vessel, and Kraft cooking the washed feed material in the Kraft cooking vessel to produce the pulp; wherein the steps of the method are performed continuously and simultaneously as the feed material flows through the feed system, prehydrolysis reactor vessel and Kraft cooking vessel.