WO2003026859A1

WO2003026859A1 - Method for recovering chips and fibers from timber-derived products

Info

Publication number: WO2003026859A1
Application number: PCT/DE2002/002618
Authority: WO
Inventors: Andreas Michanickl; Christian Boehme
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2001-09-12
Filing date: 2002-07-17
Publication date: 2003-04-03
Also published as: DE10144793A1

Abstract

The invention relates to a method for recovering chips and fibers from timber-derived products that are glued with urea-formaldehyde binders or other binders that can be hydrolyzed or chemically disintegrated, old pieces of furniture, production residues, wastes and other materials containing timber-derived products. The aim of the invention is to improve the cost-effectiveness of such a method. According to the invention, this aim is attained by a method that comprises the following steps: a) filling a digestion container, provided in its top section with a relief valve and its interior subjected to an atmospheric pressure, with timber-derived product pieces and closing it with the relief valve open; b) introducing vapor into the lower section of the interior of the digestion container so filled under a slight excess pressure until said vapor has at least substantially displaced the air from the digestion container via the opened relief valve and until, in the interior of the container, a temperature of approximately 100 to 120 °C and a pressure slightly above atmospheric pressure is attained; c) guiding the vapor discharged from the relief valve into an impregnation solution together with the air displaced from the interior of the container in order to heat said solution; d) feeding the pre-heated impregnation solution to the digestion container until the material filled in the digestion container is completely covered with the impregnation solution; e) discharging the remaining impregnation solution when the timber-derived product pieces have absorbed at least 50 % of their dry substance of impregnation solution; f) heating the timber-derived product pieces, with the relief valve closed, to 80° to 120 °C by introducing vapor into the digestion container, thereby breaking up the pieces to chips and/or fibers.

Description

Process for the recovery of chips and fibers from wood-based material residues

The invention relates to a process for the recovery of chips and fibers from wood-based material residues, old furniture, production residues, waste and other wood-based materials containing glue that is glued with urea-formaldehyde binders or with other hydrolyzable or chemically digestible binders.

Such a method is described in EP 0 697 941 B1. Then, in a first step, an excess of an impregnation or impregnation solution is added to the wood material pieces. after the

Pieces of wood material have absorbed at least 50% of their own weight in impregnation solution, the remaining liquid is drained off. The wood material pieces impregnated in this way are heated to 80 ° C - 120 ° C; the wood-based material thus broken up is then sorted by sieving and / or air separation. According to a modified method, the wood-based material pieces are soaked. Impregnation solution added, which is dimensioned such that the entire liquid is absorbed by the wood material pieces when the wood material pieces have absorbed at least 50% of their own weight of impregnation solution. The wood material pieces impregnated in this way are then heated to 80-120 ° C. Impregnation and the effects of temperature take place in a digestion tank in which an overpressure of up to 2 bar can prevail.

DE 196 40 503 C1 describes a method and an apparatus for the extraction of secondary chips and fibers. Here, old furniture and production waste are shredded into a lumpy raw material, from which fines are then separated. In a first digestion step, the starting material is evacuated from the Reaction container and by the vacuum generated thereby, the air trapped in cavities. In a second digestion step, the material is mixed with a preheated impregnation solution, which causes swelling and weight gain to almost twice the weight of the material used during a given swelling period, after which excess impregnation solution added is drained off. In a third digestion step, this pre-swollen material is subjected to hot water vapor at excess pressure and decomposed into a crumbly digestion mass essentially formed from chip and fiber components. In the second digestion step, the swelling time of the material used is between 10 and 20 minutes, while the reaction vessel has a swelling temperature of 75-90 ° C. In the third digestion step, the steam is introduced with a steam temperature between 1 20-140 ° C and a steam pressure of 1.9-3.6 bar evenly distributed over the interior of the container into the reaction container.

DE 42 24 629 A1 discloses a method for recycling wood-based materials, in which the fragments previously produced are exposed to a preferably saturated water vapor atmosphere under high pressure and at high temperature in a digestion step over a certain digestion time. The digestion step uses a temperature between 1 20 ° C and 180 ° C and a pressure between 2 and 1 1 bar. The hot steam from the digestion step can be used in a preheating step at normal pressure to preheat and dampen the fragments.

DE-AS 1 201 045 describes a process for the recovery of chip material from waste, sawdust, garbage etc. interspersed with hardened binders for the production of chipboard or the like. Here, the waste is to be exposed to the action of strained steam, the steam being at an overpressure of 1-5 atm act on the waste for a period of between 0.5 and 4 hours.

The invention has for its object to improve the economy in the method described above for the recovery of chips and fibers.

Based on the method described in the introduction, this object is achieved according to the invention with the following method steps:

a) a digestion tank provided in its upper area with an exhaust gas valve and in its interior under atmospheric pressure is filled with the wood material pieces and then closed with the exhaust gas valve open;

b) Steam is introduced into the lower area of the interior of the digestion tank filled with a slight excess pressure until it has at least largely displaced the air from the digestion tank via the open exhaust gas valve and has reached a temperature of approximately 100-120 ° C. in the interior of the tank and there is a pressure slightly above atmospheric pressure;

c) the steam emerging from the exhaust valve is introduced together with the air it displaces from the interior of the container into an impregnation solution for preheating it;

d) the preheated impregnation solution is then introduced into the digestion tank until the contents in the digestion tank are completely covered with the impregnation solution;

e) after the wood material pieces have taken up at least 50% of their dry substance in impregnation solution, the remaining impregnation solution is drained off; f) When the exhaust gas valve is closed, the wood-based material pieces are heated to 80 ° to 120 ° C. by introducing steam into the digestion tanks, thereby breaking up chips and / or fibers.

The steam displacing the air from the interior of the container leads to a preheating of the wood-based material pieces, but not to their digestion, since there is too little water in the steam for this purpose, or too little water can condense on the latter when the steam flows through the filling material. It is important from the point of view of energy saving that the steam displacing the air from the interior of the container can be used together with the displaced air heated by it to preheat the impregnation solution.

As a result of the fact that the steam is introduced into the digestion tank from below, flows through the interior of the tank from bottom to top and partially exits the exhaust gas valve again at the top, no condensate can collect in the lower part of the digestion tank, since a condensate is immediately present again due to the inflowing steam would be transferred to the vapor phase. This avoids excessive absorption of water or premature, undesirable moistening of the wood material pieces located in the lower part of the digestion tank before they are actually impregnated.

In order to preheat all wood material pieces of the filling material filled into the digester evenly on all sides, the steam is introduced into the interior of the container until a temperature of J> 100 ° C can be determined, the pressure of the introduced steam always being slightly above the surrounding atmospheric pressure to prevent air from flowing back into the interior of the container.

According to the invention, the impregnation solution is introduced into the interior of the container in excess until the contents in the digestion container are completely covered. If the preheated Impregnation solution has a temperature of, for example, 80 ° C, and the wood material pieces are heated to, for example, 60 ° C as a result of the application of steam, the impregnation liquid introduced into the digestion tank cools down somewhat. It can therefore be expedient to maintain the supply of steam into the interior of the container even while the impregnation solution is being introduced and acted upon. The resulting equalization of the decrease in steam also has an advantageous effect, inter alia, for steam generation.

Claims

Expectations:

1 . Process for the recovery of chips and fibers from glued with urea-formaldehyde binders or with other hydrolyzable or chemically digestible binders

Wood material residues, old furniture, production residues, waste and other wood-based materials, with the following process steps:

d) the preheated impregnation solution is then introduced into the digestion tank until the contents in the Digestion tank is completely covered with the impregnation solution;

e) after the wood material pieces have taken up at least 50% of their dry substance in impregnation solution, the remaining impregnation solution is drained off;

f) when the exhaust valve is closed, the wood material pieces are heated to 80 ° to 120 ° C. by introducing steam into the digestion tanks and thereby broken down into chips and / or fibers.

2. The method according to claim 1, characterized in that steam is still fed into the interior of the container while the impregnation solution is being introduced and is acting in the digestion tank with the exhaust gas valve still open.