초록 ▼

A method and apparatus are provided for the treatment of comminuted cellulosic fibrous material to effect prehydrolysis, and then subsequently kraft digestion, thereof, to produce paper pulp. The material is steamed, entrained in liquid to form a suspension, and transferred by a high pressure feeder

A method and apparatus are provided for the treatment of comminuted cellulosic fibrous material to effect prehydrolysis, and then subsequently kraft digestion, thereof, to produce paper pulp. The material is steamed, entrained in liquid to form a suspension, and transferred by a high pressure feeder in a first circulation loop to the top of a first vertical vessel. At the top of the vessel, a liquid/solids separator is provided, and the liquid withdrawn from the top of the first vessel into the return conduit of the first circulation loop includes recoverable hydrolysate (which contains hemicellulose, sugars, and the like). In the first vessel, countercurrent acid hydrolysis takes place in the top of the vessel, and a countercurrent wash is effected in the bottom of the vessel. A part of the liquid in the return conduit of the first circulatory loop is diverted to one or more flash tanks, to produce steam and a liquid with a high concentration of hydrolysate. After hydrolysis and washing, the material is withdrawn from the bottom of the first vessel and passed through a second circulatory loop to the top of a kraft digester, preferably one having a steam phase at the top.

대표청구항 ▼

A method of prehydrolyzing comminuted cellulosic fibrous material to remove hemi-cellulose and sugars therefrom, and utilizing a generally vertical substantially liquid-filled vessel, comprising the steps of: (a) feeding comminuted cellulosic fibrous material suspended in liquid to a top portion of

A method of prehydrolyzing comminuted cellulosic fibrous material to remove hemi-cellulose and sugars therefrom, and utilizing a generally vertical substantially liquid-filled vessel, comprising the steps of: (a) feeding comminuted cellulosic fibrous material suspended in liquid to a top portion of the vessel; (b) effecting countercurrent acid hydrolysis in a top zone of the vessel, as the material passes downwardly in the vessel; (c) withdrawing liquid containing hydrolysate, including hemi-cellulose and sugars, from the top of the acid hydrolysis zone of the vessel, and recirculating the liquid to be fed back to the top of the vessel in step (a); (d) diverting a part of the liquid, containing hydrolysate, withdrawn in step (c); (e) flashing the diverted liquid from step (d) to produce steam and a high concentration hydrolysate liquid; (f) effecting countercurrent washing of the material after the acid hydrolysis zone; wherein the washing takes place in the vessel in a washing zone below the acid hydrolysis zone; and wherein step (d) is practiced by: withdrawing liquid from a central portion of the vessel, between the hydrolysis reaction zone and the washing zone thereof; adding fresh mineral acid to the liquid withdrawn at the central portion of the vessel; heating the withdrawn liquid; and reintroducing the withdrawn liquid in the vessel at the interface between the hydrolysis reaction zone and the wash zone, so that the acid flows upwardly in the hydrolysis reaction zone, countercurrent to the material.