Patent ID: 9663896
Date: 2017-05-30
CPC Classifications: D21C

Claim:
1. A method for recovering a first treatment liquid in a displacement batch pulping process in a digester filled with comminuted cellulosic material and equipped with a bottom, a top and a middle liquid exchange position, said method comprising: filling the digester with a first treatment liquid during or after a steam prehydrolyzina step wherein the process continues by, after filling the digester with the first treatment liquid during or after the prehydrolyzing step, subjecting the first treatment liquid contained in the digester to circulation within the digester by withdrawing the first treatment liquid from the middle liquid exchange position and reintroducing the withdrawn first treatment liquid to a top and a bottom of the digester, passing the first treatment liquid through the comminuted cellulosic material disposed in the digester at least once, and washing out the carbohydrates dissolved in the hydrolysate; in a first draining phase, draining the first treatment liquid from the digester via one of the middle or bottom liquid exchange positions to obtain a strong first liquid; and sending at least a part of the strong first liquid to a dedicated processing position either for use in a different phase of the batch pulping process or for further processing wherein at least a part the strong first liquid is used for recovering by-products wherein the first treatment liquid is used during prehydrolysis of the comminuted cellulosic material to produce an acidic hydrolysate containing the carbohydrates dissolved in the hydrolysate during the prehydrolysis and wherein after the first draining phase at least a part of the strong first liquid is sent to further processing in a sugar recovery process by using the carbohydrates dissolved in the hydrolysate, and wherein the first draining phase is assisted by displacing steam or gases through the digester, the steam or gases being added via the top liquid exchange position and wherein a pressure and a temperature of the strong first liquid is maintained.