Device and method for disaggregating derived timber products

Solid material comminution or disintegration – Processes – With application of fluid or lubricant material

Reexamination Certificate

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Details

C241S023000, C241S029000, C241S066000, C241S152100, C241S260100

Reexamination Certificate

active

06648251

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a device for disaggregating derived timber products according to the preamble of the main claim and to a method for implementing the same.
A device of this type has been disclosed (DE 198 19 988). In this device, a screw feeder functions as the transport device for conveying the disaggregation material through the impregnation and pre-swell shaft, while the function of the second screw feeder is to discharge the already disaggregated material from the disaggregation shaft. In the disaggregation shaft itself, the disaggregation material is not conveyed by screw feeders. The disadvantage of this device is the fact that, during disaggregation under pressure, appropriate measures must be taken to make the filling shaft pressure-sealable.
DISCLOSURE OF THE INVENTION
The object he present invention is thus to create a device and a method which permit continuous, and therefore simple and economical disaggregation of derived timber products.
This object is achieved by a device for disaggregating pieces of derived timber products made from cellulose-containing and/or lignocellulose-containing materials, specifically particle board, medium-density fiberboard and the like, with a transport device and at least one disaggregation vessel, characterized in that the disaggregation vessel and the transport device are designed as at least one combined-function plug screw feeder with an outer casing attached to the housing and a drivable shaft located therein provided with helices of a predefined pitch, the pieces of derived timber products being conveyed in the plug screw feeder from a feed opening in the outer casing to an end-face discharge opening in the axial direction (direction of conveyance), and characterized in that a delivery opening for steam is provided in the outer casing between the feed opening and the discharge opening.
The object is also achieved by a process for disaggregating pieces of derived timber products made from cellulose-containing and/or lignocellulose-containing materials, specifically particle board, medium-density fiberboard and other residual materials and waste produced from lignocellulose-containing materials, using a conveyance device as well as a disaggregation vessel, characterized in that the derived timber products are conveyed continuously through pressure-sealed, sequentially arranged plug screw feeders, thereby undergoing the action of shearing and frictional forces occurring in the plug screw feeder, and in that steam is forced into at least one of the plug screw feeders which is neither the first nor the last plug screw feeder.
The surprising determination was made that an arrangement of preferably at least three plug screw feeders in tandem permits the passage of the disaggregation material such that the feedstock is able to seal the plug screw feeders to the degree necessary for performing the disaggregation process under pressure. Here the steam is introduced, preferably at a pressure of 2 bars, into one of the plug screw feeders which is neither the first nor the last one in the sequence of plug screw feeders. Arrangements of, for example, five or more plug screw feeders are preferred, the steam being introduced into the middle section of the sequentially arranged plug screw feeders, for example, into the third in a sequence of five plug screw feeders. While in the side plug screw feeder[s] here, a pressure drop reaching atmospheric pressure may be observed, the arrangement results in the working pressure being sustained in the middle section, said pressure being up to 11 bars but at least 2 to 3 bars of overpressure.
A fundamental advantage of a method thus implemented on a completely continuous basis according to the invention lies specifically in the fact that complex and expensive measures to seal the system may be dispensed with and that continuous processing is nevertheless possible. Processing is thus possible without the opening and subsequent sealing of system components, and as a result there is no concomitant loss of energy or discharge of pollutants from the system. Thus from both the standpoint of economy and ecology, the device may thus operated at an optimal level.
In the method according to the invention, specifically when at least five plug screw feeders are used, disaggregation pressures of 2 bars to 11 bars of overpressure may be sustained, the range of operation being preferably between 3 bars and 8 bars, and especially between 2 bars and 6 bars. When steam is introduced at an overpressure of 4 bars, the disaggregation temperature at the steam inlet is approximately 143° C.
Since passage through the screw feeder entails not only the conveyance of the disaggregation material but also its homogenization, the friction of the particles against each other results in a continuous comminution mechanically and facilitates chemical hydrolysis. The result is that the disaggregation of the particles is accelerated such that a residence time of only a few minutes is sufficient to produce a high level of disaggregation. In the event the derived timber products are more hydrolysis-resistant, appropriate means may be employed to accelerate hydrolysis such as raising or lowering the pH.
The disaggregation process from the addition of the comminuted particleboard fragments through the completely disaggregated, moist wood pulp is thus effected by multiple, at least three, sequentially arranged screw feeders. These pressure-sealed plug screw feeders perform multiple functions: conveyance as well as continuous comminution and hydrolysis of the pre-swollen wood pulp, initially by the friction of the particles against each other, and the actual disaggregation process under the action of water, steam and absorption of heat within the tubular screw feeder system. Use of a modular design is possible here in which multiple identical screw feeders and drive systems are employed, which use significantly reduces cost.
The independently controllable plug screw feeders and drive systems allow the feed rate to be adapted to existing process conditions, the maximum limits being set only by the dimensioning of the conveyance systems and the reaction speed of disaggregation.
Since the entire process proceeds under pressure, the entire system must be pressure-sealed, a feature which has the advantage of preventing any harmful emissions emanating from the disaggregation process from entering the environment.
Since the system is operated without generating effluents, environmental considerations have been accorded a high priority.
It has proven useful to fill the first plug screw feeder into which the disaggregation material has been introduced with preheated water. The water temperature here can range between approximately 20° C. and 95° C.
Conveyance by the screw feeder within the system allows for homogenization of the wood pulp, and the constant friction caused by the conveyance creates desirable and continuous comminution, thereby facilitating wetting of the surface. The result is that the enthalpy of the steam may be utilized over the entire length of the tube since the friction continuously separates the solubilized layers mechanically and exposes the underlying, not-yet-separated layers which are then readily acted upon by the steam. The process may be further accelerated by using higher process pressures.
Waste gas heat can be almost completely utilized and is thus not lost as is the case with the discontinuous process of the prior art. The heat provided by the moist disaggregated wood pulp is also utilized by the fact that the conveyance path from the point after the material has exited the last screw feeder to the drier is extremely short. This feature minimizes heat loss and drying cost.
The absorption of water, steam and heat by the disaggregation material may be very precisely adjusted by controlling the rate of feed—a feature which facilitates additional optimization of the process parameters, especially energy consumption, and optimal process control.
The plug screw feeders may

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