METHOD AND APPARATUS TO PRODUCE PULP USING PRE- HYDROLYSIS AND KRAFT COOKING

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.