Process for the comminution of materials and plants for carrying out the process

#Reference is made to U.S. patent application Ser. No. 203,907 filed Jun. 8, 1988 in the name of Sbaschnigg, Baumgartner and Mausser for "Mixer for Pulp and Bleaching Chemicals", U.S. Pat. No. 4,913,358.

#The invention relates to a process and plant for the comminution, in particular defibrillation, of fibrous materials of high consistency, i.e., having high dry solids content, which separates bundles of fibers into individual fibers or loose fiber structures, with the addition of a medium comprising a circulating gas composed of carrier gas, reaction agent, chemicals or a combination thereof.

#In recent years, increasing efforts have been made to effect bleaching of pulp with substances free of chlorine. The bleaching agent used is usually ozone, but NO.sub.x, in particular NO.sub.2, is also used. Bleaching with ozone is frequently carried out in the gaseous phase which requires comparatively high consistencies of fibrous materials. It is very important that pulp and ozone be intimately mixed to provide uniform delignification with a reduced amount of chemicals. The pulp fibers must be rendered freely accessible to ozone. This can be achieved, as is known in the art, by using a fluffer, or defibrator, in which the pulp is fluffed, i.e., separated into small bundles of fibers, by means of rotating elements.

#The invention is explained on the basis of exemplary embodiments with reference to the accompanying drawings.

#FIG. 1 shows a schematic process and plant diagram of the invention with the defibrator in partial longitudinal section;

#FIGS. 2a and 2b each represent a side elevation in partial longitudinal section of the defibrator showing a modification of the sealing assembly according to the invention;

#Referring to FIG. 1, fibrous material, i.e., pulp, having a consistency of 20-60%, preferably 30-40%, is introduced via process line 10 to a sealed conveying means 24. Fresh gaseous mixture, including carrier gas, reaction gas and optional promotor chemicals, may be jointly introduced with the fibrous material at line 10 through sealed conveying means 24. The infiltration of secondary air to the system during the introduction of material is largely prevented by using sealed conveying means 24, in particular packing screw 59 as shown in FIG. 1. Alternatively, the sealed conveying means 58 shown in FIG. 4 having a cellular wheel sluice 58 can be used. The system is closed and operates at about atmospheric pressure (1 bar absolute). To prevent leakage, a pressure of slightly less than atmospheric may be used. Reaction agent, carrier gas and chemical promotors can be introduced with the pulp by line 10 at this stage. The material is then conveyed to inlet orifice 8 of fluffer or defibrator 1 by entrance chute 33 shown as process lines 33, 33a, and 33b in FIG. 1. Entrance chute 33 has side access pipes for introducing recycled circulating gas via process lines 29 or 31. FIGS. 3a and 3b show alternative side access pipes which can accommodate a relatively small flow of circulating gas, see FIG. 3a, or a large flow of gas, see FIG. 3b, into chute 33.

#FIGS. 2a and 2b show a vertical sectional view of the comminuting device 1 according to the invention, in particular defibrator 1. As shown in FIGS. 2a and 2b, inlet orifice 8 serves for the introduction of fibrous material and circulating medium to defibrator 1 axially to grinding plates 20 and 22 by entrance chute 33. In addition, ventilation openings 12 in chamber 50 serve for the introduction of circulating medium in the direction of process lines 14 or 27 perpendicularly to the axis of rotation of grinding plates 20 and 22.

#In defibrator or mixer 1, the fibrous material is comminuted and begins to be bleached by the reaction agent. Defibrator or mixer 1 has a structure similar to that shown in U.S. Pat. No. 4,913,358 to Sbaschnigg et al, which patent is hereby incorporated by reference. In one embodiment, ozone, O.sub.3, is used as the reaction gas. However, other known bleaching agents may be used such as NO, NO.sub.2, or NO.sub.3. Another embodiment uses hydrogen peroxide, H.sub.2 O.sub.2, as the reaction agent. It is noted that peroxide is a liquid, yet the circulating gas, according to the equilibrium of gaseous and liquid phase, contains peroxide vapor which is recirculated. When bleaching with ozone, oxygen is normally used as the carrier gas. If NO, NO.sub.2, or NO.sub.3 is used as the bleaching agent, carbon dioxide, CO.sub.2, is used as carrier gas. Hydrogen peroxide bleaching uses air as carrier gas. Optional promotor chemicals are used to enhance bleaching. Hydrogen peroxide, H.sub.2 O.sub.2, can be used as a chemical promotor in conjunction with ozone.