RU2829457C1 - Birch bark processing method - Google Patents

Abstract

FIELD: woodworking industry.

SUBSTANCE: invention relates to woodworking and wood-chemical industry, namely to a method of processing birch bark. Method of processing birch bark includes the following stages: selection of birch bark without impurities of wood, drying of the bark, crushing of bark on a hammer crusher at a shaft rotation speed of not more than 1,800 rpm, sieving of the obtained crushed mass, wherein selected birch bark is subjected to coarse grinding to size of not more than 35 mm and brought to moisture content of 42÷52%; crushing of bark on a hammer crusher is carried out for 1÷2 min, separating crushed particles through 5 mm holes; which are further sieved through a set of sieves to obtain three fractions: coarse with particle size 2÷5 mm, average with particle size 1÷2 mm and fine with particle size less than 1 mm; remaining in hammer crusher mass is mixed with coarse fraction and ground in rotor-knife mill to size 1÷2 mm; middle fraction is mixed with water and separated into birch bark and bast in gravity settler for 5-10 minutes; ground mass from the rotary knife mill and birch bark from the gravity settler are separated by extraction into betulin, raffinate and extractant; bast from gravity settler and raffinate from extractor are dried, mixed with fine fraction and used as filler for production of wood-composite materials.

EFFECT: use of the above method enables to obtain birch bark with increased output.

1 cl, 1 dwg, 1 tbl, 4 ex

Description

The invention relates to the woodworking and forest chemical industries and can be used to obtain birch bark from birch bark, which is one of the waste products of production, in particular plywood and pulp and paper mills.

Birch bark is currently a large-tonnage waste product of plywood and pulp and paper mills. At one pulp and paper mill alone, the bark dump is filled with 50 thousand tons annually. At the same time, the outer layer of birch bark (birch bark) contains a large number of valuable triterpene compounds: betulin, betulinic acid, etc., which are biologically active substances and can be used in other industries, in particular, in the food, veterinary, perfumery and cosmetics and pharmaceutical industries. The presence of useful substances in birch bark, combined with the serious environmental damage caused to the environment by waste dumps of unutilized birch bark, determines the exceptional relevance of the problem of processing birch bark to obtain birch bark from it.

A method is known for separating birch bark from birch bark by boiling it in water until the bast is completely softened, followed by scraping or rolling the bark in a drum.

[A.S. 78328 published 12.03.1949].

The disadvantages of the known method are: low productivity, labor-intensive process with manual scraping and poor separation of birch bark from bast when rolling the bark in a drum.

A method for processing birch bark into birch bark and bast is also known, which includes debarking the log with the removal of the bark and simultaneous grinding to obtain a mixture of birch bark and bast of the required fraction, and then milling the fraction in order to separate the birch bark from the bast. [SU 1428576 published 10/07/1988].

The known method involves the use of special energy-intensive equipment to separate birch bark from bast and does not ensure complete separation of birch bark from bast.

A method is known, taken as a prototype, for obtaining birch bark, in which birch bark without wood admixture is selected, the selected bark is withered and dried to a moisture content of 30-35%, the bark is crushed in a hammer mill at a shaft rotation speed of no more than 1800 rpm and the crushed mass is sifted through a sieve with a cell size of no more than 3 mm to separate the birch bark from the bast.

The disadvantage of the prototype is the low yield of separated birch bark, due to poor separation of birch bark from bast during sifting of crushed bark.

The technical problem is to increase the yield of birch bark.

The solution to the technical problem is achieved in that the method for processing birch bark includes the stages of selecting birch bark without wood admixture, drying the selected bark, crushing the bark in a hammer crusher at a shaft rotation speed of no more than 1800 rpm, sifting the resulting crushed mass through a sieve, in which, according to the invention, the selected birch bark is subjected to coarse crushing to a size of no more than 35 mm and brought to a moisture content of 42-52%; crushing the bark in a hammer crusher is carried out for 1-2 minutes, separating the crushed particles through 5 mm openings; sifting which is then carried out through a set of sieves and three fractions are obtained: a large fraction of 2-5 mm, a medium fraction of 1-2 mm, a small fraction of less than 1 mm; the mass remaining in the hammer mill is mixed with the large fraction and crushed in a rotary knife mill to a size of 1-2 mm; the medium fraction is mixed with water and separated into birch bark and bast in a gravity settler for 5-10 minutes; the crushed mass from the rotary knife mill and birch bark from the gravity settler are separated by extraction into betulin, raffinate and extractant; bast from the gravity settler and raffinate from the extractor are dried, mixed with the small fraction and used as a filler for the production of wood-composite materials.

The technical result consists in obtaining birch bark with an increased yield compared to the prototype due to higher-quality separation of birch bark from bast.

The proposed invention is explained by drawings, where Fig. 1 shows a diagram of a line for separating birch bark from bast.

The line for separating birch bark from bast consists of a chipping machine 1 with a sluice dispenser 2; a shaft-type drying chamber 3, equipped with a slide gate 4, a gas blower 5, a steam heater 6, a valve 7 for feeding wet water vapor; a hammer crusher 8 with a slide gate 9 for unloading uncrushed particles and with a perforated shell 10 for removing crushed particles; a vibrating separator 11 with sieves - 12; buffer accumulators 13, 15; a rotary knife mill 14; a mixer 16; a gravity precipitator - florentine - 17, filter devices 18, 19; an extractor 20, a separator 21, a centrifugal pump 22; Pseudo-fluid dryers of another layer 23, extruder 24.

The line for separating birch bark from bast operates as follows. Birch bark after coarse grinding in chipper 1 to a size of no more than 35 mm is fed to drying chamber 3, where it is processed with recirculating heat carrier supplied by blower 5 through heater 6, in case of fresh raw material. When processing dry bark, the raw material is first treated with wet saturated steam, and then dried. A portion of dried birch bark with moisture content of 42÷52% is fed by opening damper 4 to hammer crusher MD - 2x2 with outlet opening size of 5 mm, where it is processed for 1÷2 minutes. During this time, bast has time to separate from birch bark. If the processing time is more than 2 minutes, the total yield of large fraction of birch bark decreases, if the processing time is less than one minute, insufficient separation of bast from birch bark is observed.

The crushed mass is fed from the hammer mill to the vibrating separator 11. As a result, three fractions are obtained: a large fraction, 2÷5 mm in size; a medium fraction, 1÷2 mm in size, consisting of birch bark; a small fraction, with a particle size of less than 1 mm, consisting mainly of bast.

If the size of the average fraction exceeds 1÷2 mm, then energy costs increase due to an unjustified increase in the share of the average fraction. If the size is less than 1 mm, the crushed mass with a predominant content of bast is retained in the average fraction; if the size is more than 2 mm, separated birch bark from the large fraction gets into the average fraction.

The uncrushed mass that remains in the hammer crusher, as well as the large fraction, consists of birch bark, so it is removed from the hammer crusher by opening the valve 9 and accumulates together with the large fraction in the buffer tank 13. The medium fraction from the vibratory separator 11 accumulates in the buffer tank 15

The accumulated mass from the buffer tank 15 is separated into bast and birch bark by mixing with water in the mixer 16, and then gravity settling in the florentine 17 for 5 hours - 10 minutes. With an increase in the settling time to more than 10 minutes, the yield of birch bark decreases, due to the fact that some of the small particles of birch bark that have floated up are saturated with water and begin to settle. With a settling time of less than 5 minutes, the quality of separation deteriorates, since large particles of bast do not manage to get sufficiently moistened and precipitate. From the florentine, the birch bark suspension is fed to the filter 19, and then to the extractor 20 with the separator 21 for extracting betulin using a known method (RU Patent No. 2801732 published on 15.08.2023). The bast suspension is discharged into filter 19, water from filters 18, 19 is returned by pump 22 to mixer 16.

The birch bark accumulated in the buffer tank 15 is crushed in a rotary knife mill to sizes of 1÷2 and is also fed to the extractor 20 for betulin extraction. If the birch bark particle size is less than 1 mm, the extraction process slows down due to a decrease in the porosity of the birch bark layer in the extractor and deterioration of the hydrodynamics of the mass exchange process. If the birch bark size is more than 2 mm, the duration of the extraction process will increase due to an increase in diffusion resistance.

After the extraction process, the products are separated into betulin, birch bark raffinate and extractant. The extractant is returned for recirculation to the extractor - 20. The bast with birch bark raffinate is dried in the fluidized bed apparatus - 23, mixed with a small fraction from the vibration separator and fed to the extruder for the production of wood-polymer composite materials according to a known method (RU Patent No. 2800911 published on July 31, 2023). Water from filter devices 18, 19 is returned by a centrifugal pump - 33 and a mixer 16.

The essence of the claimed invention is explained by specific examples of its implementation.

Example 1. Obtaining birch bark from "raw" bark

Fresh bark was crushed by chopping to a size of 30-35 mm and dried to a moisture content of 42%. The resulting bark (1000 g (based on dry weight)) was placed in a hammer crusher with a rotation speed of 1800 rpm and an outlet opening of 5 mm. After 1 minute, the crusher was turned off, the crushed mass was sifted through a set of sieves of 2 mm; 1.0 mm and three fractions were obtained (based on dry weight): 50 grams of large fraction, from 2 to 5 mm in size; 320 grams of medium fraction, from 1 to 2 mm in size; 330 grams of small fraction, less than 1 mm in size.

290 grams of uncrushed mass larger than 5 mm, extracted from a hammer crusher, were added to the resulting large fraction. The total yield of the large fraction was 350 grams.

The middle fraction was mixed with water and loaded into a separatory funnel. After 5 minutes of settling, the sediment from the bast was poured into the first filter funnel. The remaining part of the funnel contents was poured into the second filter funnel. After drying the sediment, 192 grams of bast and 128 grams of birch bark were obtained.

The combined large fraction was crushed in a rotary knife mill to a size of 1-2 mm, mixed with the dried sediment of birch bark filtrate and betulin was extracted using a known method (Patent RU No. 2801732 published 08/15/2023) and 124 grams of betulin and 353 grams of raffinate were obtained.

The dried bast sediment, raffinate and fine fraction with a total weight of 875 grams were mixed with polyethylene and additives using a known method (RU Patent No. 2800911 published on July 31, 2023) and a wood-polymer-polymer board weighing 1500 grams was obtained.

Example 2. Obtaining birch bark from "dry bark"

The dry bark was treated with saturated water vapor at a temperature of 100°C for 30 minutes, followed by drying to a moisture content of 47%. The remaining process parameters are given in the table.

Example 3 is similar to example 1.

Example 4 is carried out in accordance with the prototype.

Analysis of the results shows that the average fraction, even after short-term grinding for 1-2 minutes, contains "40% birch bark. Separating it from the average fraction and settling the prepared suspension allows for a significant increase in the yield of birch bark compared to the prototype.

It should also be noted that during long-term grinding, in accordance with the prototype, most of the birch bark is crushed and falls into a small fraction and is not used to extract biologically active substances.

In addition, moistening dry birch bark with saturated steam significantly reduces the duration of this stage.

Claims (5)

A method for processing birch bark, comprising the following stages: selecting birch bark without wood admixture, drying the selected bark, crushing the bark in a hammer crusher at a shaft speed of no more than 1800 rpm, sifting the resulting crushed mass, characterized in that the selected birch bark is subjected to coarse crushing to a size of no more than 35 mm and brought to a moisture content of 42-52%; crushing the bark in a hammer crusher is carried out for 1-2 minutes, separating the crushed particles through 5 mm openings; sifting which is then carried out through a set of sieves to obtain three fractions: large with a particle size of 2-5 mm, medium with a particle size of 1-2 mm and small with a particle size of less than 1 mm; the mass remaining in the hammer crusher is mixed with a large fraction and crushed in a rotary knife mill to a size of 1÷2 mm; the middle fraction is mixed with water and separated into birch bark and bast in a gravity settling tank for 5-10 minutes; the crushed mass from the rotary knife mill and birch bark from the gravity settling tank are separated by extraction into betulin, raffinate and extractant; The bast from the gravity settling tank and the raffinate from the extractor are dried, mixed with a fine fraction and used as a filler for the production of wood composite materials.