WO2005017251A1 - Method for the production of fiberboards made of moist biomass - Google Patents

Abstract

Disclosed is a method for producing fiberboards made of moist biomass, comprising the following steps: (a) the raw material is prepared and reduced to fibers; and (b) the boards are produced from the plant fibers. The inventive method is characterized in that the boards are produced according to the following procedure: b1) the fiber lumps are at least almost fully opened; b2) a fiber bed having a uniform thickness is formed; b3) the fiber bed is pressed to a desired thickness or density; b4) the fiber bed is uniformly vaporized until a temperature of more than 60 DEG C, preferably more than 80 DEG C, has been reached across the entire cross section. Said method is suitable for producing insulating boards having a density of 50 to 180 kg/m<3> and structural panels having a density of 130 to 300 kg/m<3>. The method has the advantage of producing mechanically stable low-density insulating boards while conserving drying energy. Said advantages are obtained especially by said vaporizing process.

Description

Process for the production of fiberboard from moist biomass

Definition of the field of invention

The present invention is in the field of processing moist biomass into industrially usable products, in particular for the production of fiberboard for the construction sector.

The term "moist biomass" encompasses vegetable material that is processed in the ^' moist state. This includes monocotyledonous plants, in particular all types of grasses, including cereals which have been harvested moist (ie before ripening) such as wheat, barley, oats, rye and millet as well as sugar cane, millet and maize. Also included are broad-leaved plants such as alfalfa, clover and others, as well as products or residues from processing plants such as wood fibers or bagasse from the processing of sugar cane or millet. The definition "moist" refers to a dry matter content of the biomass from 10-50%. The biomass can be processed fresh from the harvest, withered or temporarily stored (also ensiled).

The term "fiberboard" is used to summarize panels of different thicknesses and densities, which are used as insulation materials to protect against cold and heat or as mechanically resilient panels of higher density. To express the desired properties, these panels are sometimes made into 2 or 3-layer panels edited.

State of the art

The production of boards of different thicknesses and densities from wood fibers has been an established industry worldwide for decades. Usually the treated raw material wood is treated with steam and the fibers are then ground in a refiner. The plates are produced by placing the fibers in a non-dewatered state as an endless fleece on a screen belt, followed by dewatering, pressing and drying the plates. The panel strength is due to the adhesive effect of the lignin contained in the raw material, which is heated above its softening point by the steam treatment and an adhesive effect when cooling or solidifying

page 1 unfolded. The continuous fiber fleece is pressed by pressing rollers, which results in mechanical dewatering to only 20-25% dry matter. Plate drying is therefore very complex.

The production of fiberboard by the likewise industrially customary drying process is not relevant to the present invention and is therefore not described further. Various processes for the production of high and medium density fiberboard from wood-like raw materials or straw as well as insulation boards made of flax, hemp, waste paper, sheep's wool or mixtures thereof are also carried out using the dry process and are therefore not relevant to the invention.

The production of insulation boards from agricultural raw materials that were fiberized in a wet digestion is not yet known.

Numerous processes have been developed for the processing and fiberization of biomass, some of which aim to obtain fibers and partly to hydrolise the fibers as far as possible. • Janson et al. (Nordic Pulp and Paper Research Journal 11; 4-14 (1996) describe a digestion process for grasses using trisodium phosphate as an alkali source. • DE 3433508 describes a chemo-thermo-mechanical process for the production of cellulose from plant fiber material. The raw material is first described in Addition of organic solvents dissolved in a pulper, then further comminuted in a sealant pulper and a de-stipper, and then further delignified with the addition of ethanol or methanol, oxygen, anthraquinone and alkali • WO 01/45523 describes a process for separating plant biomass in a liquid phase and a solid-containing phase with a fibrous consistency. The basis is the generation of a speed gradient in a flowing suspension. A macerator is described for carrying out the method.

The above documents do not contain instructions for the further processing of the fibers produced into fiberboard.

Page 2 Presentation of the invention

The invention therefore has the following objects:

(a) Development of a binding system which develops sufficiently strong binding forces between the fibers to give the fiberboard the necessary mechanical strength. The density, insulation value and load-bearing capacity of the panels should be in a relationship that is customary in practice (e.g. similar to stone wool panels or wood fiber panels). The starting point is that fibers from gramineae and legumes have a low lignin content, especially when cut early, and lignin or heat-softened lignin (in contrast to wood fiber boards) can therefore make little contribution to the mechanical strength of fiber boards made from these raw materials.

(b) Provision of a system of aggregates that gives the panels the necessary fire resistance and resistance to mold.

(c) Limitation of the effort for drying the plates

(d) Provision of engineering technology that is suitable for implementation on a small and medium scale. Due to restrictions in the provision, interim storage and logistics of moist biomass, processing from approx. 1,000 to approx. 50,000 tons of dry matter per year is realistic. With a fiber content of 50% of the dry matter content, this results in a product output of 50% of the acceptance weight. In contrast, industrial plate production today usually has a production capacity of 50,000-500,000 tons per year.

(e) Provision of a fiberization technique which provides fibers which are best suited for the developed binding system (cf. (a)). The fiber length and the fiber separation are decisive for this.

According to the invention, these objects are achieved by a method, an apparatus, and by plates in accordance with the independent claims.

The method according to the invention therefore has the following steps: (a) raw material preparation and metering; (b) defibration of the raw material; (c) fiber removal and mechanical dewatering to 30-45% dry matter; (d) Plate making from the mechanically dewatered fibers. The plate production follows the following procedure:

Page 3 e) at least approximately complete opening of the fiber lumps after the mechanical dewatering; f) metering and mixing in of aggregates; g) formation of a fiber bed with a uniform layer thickness; h) pressing the fiber bed to a desired thickness or density; i) Uniform vapor deposition of the fiber bed until a temperature of over 60 ° C., preferably of 80-100 ° C., is reached over the entire cross section.

The method according to the invention thus has two sub-methods, namely

(a) the defibration of the moist biomass and the removal of fibers from accompanying substances contained in the raw material, and

(b) the processing of the moist fibers into fiberboard.

The advantages of the method according to the invention are achieved in particular by the vapor deposition described. This makes it possible to produce low-density insulation boards that can withstand mechanical loads without the addition of binders. Another significant advantage of the invention lies in the greatly reduced or even obsolete effort for drying the fibers with air.

The device according to the invention comprises: a preferably rectangular frame (1) for receiving a fiber bed (2), the frame being able to be arranged above an air-permeable support means (3), a pressing device (8) for pressing the fiber bed (2) against the support means ( 3), the device having means for introducing steam (5,7) and means for introducing drying air (6,7) into the fiber bed and means for extracting steam or drying air (9,10) from the fiber bed (2) ,

With the method according to the invention or the device, for example, insulation boards and building boards as well as non-woven fabrics can be produced.

Insulation boards have a lower density, for example 50-180 kg / m ³ , preferably 70-130 kg / m ³ . Building boards have a higher density, for example 130-300 kg / m ³ , preferably 150-250 kg / m ³ . The length and width of the panels are between 50 and 200 cm. The thickness of the plates is between 30 and 200 mm. In a further processing step, these plates can also be used to produce, for example, 2- or 3-layer plates that are mechanically very robust.

page 4 Further preferred embodiments emerge from the dependent patent claims.

Brief description of the drawings

The subject matter of the invention is explained in more detail below on the basis of preferred exemplary embodiments which are illustrated in the accompanying drawings. FIG. 1 shows a block diagram of a process sequence according to the invention; and FIG. 2: an apparatus for producing plates according to the invention.

Ways of Carrying Out the Invention

Provision and preparation of the fibers

The fibers are prepared and processed in accordance with the following procedure (cf. FIG. 1). The specific information relates to the tested raw materials fresh grass, grass silage and corn silage.

The raw material is metered into a stirred storage tank and processed into a suspension of 0.5-2% (fresh grass, grass silage) or 3-7% dry matter (corn silage). This suspension is fed to a stripper. De-strippers are used in many places in the fiber industry to dissolve fiber knots.

After one or more passes through a stripper, the raw material is sufficiently well separated with a fiber length of 5-50 mm. In Fig. 1, two deflashers connected in series are shown to illustrate this situation. After fiber separation, the fibers are removed from the suspension and mechanically dewatered to a dry matter content of 30-50%. The liquid phase is partly reused as process water and partly used for further use (e.g. biogas or ethanol production, animal feed). The dewatered fiber lumps are broken up by a suitable device (e.g. impact mill, card, or a combination thereof).

page 5 Alternatively, the defibration can also be carried out by another method described in the literature. The choice of another process may be necessary if the raw material is further lignified and if a purely mechanical pulping process does not result in satisfactory defibrillation.

One way of carrying out the method is to provide and process a mixture of fibers of different origins. Basically suitable for admixing to the fibers produced according to the invention are e.g. Wood fibers, other fibers of agricultural origin (e.g. flax fibers, hemp fibers, others) or other materials that are used for the production of insulation material.

The further processing of the fibers and production of fiberboard is the main subject of the invention.

Further processing of the fibers and production of fiberboard

Following the dissolution of the fiber lumps, additives are added (if necessary), which are mixed into the moist fiber material as dry powder and adhere directly and permanently there. Suitable additives are substances which have a flame-retardant or a fungus-suppressing effect. Furthermore, it can be substances that give the plate a specific expression, e.g. Additives that increase the strength of the panels and thus open up further application options. In particular, clay powder, gypsum, boron-containing flame retardants, synthetic fibers, sodium nitrite, cellulose derivatives, starch and adhesives made therefrom, and others are suitable.

The basis of plate production from the individual fibers, which have been freed from knots and equipped with additives, is the fact known in the technical field that hydrogen bridges are formed during the drying of cellulose fibers, which develop an adhesive effect. This effect is e.g. used in the manufacture of paper. It is crucial for the present invention to observe that the adhesive effect of isolated, cleaned grass fibers is strongly temperature-dependent. However, it is not the drying temperature that is decisive, but the temperature when wet. If the fibers in the fiber bed are heated to over 70-80 ° C with steam, the natural fiber fibers are after drying

page 6 Binding forces much higher than without steam treatment. This finding was verified with the following apparatus (see FIG. 2) and used for the production of fiberboard:

A frame 1 with the desired dimensions of length and width is filled uniformly with a predetermined mass of moist, open fibers, whereby a fiber bed 2 is created. The frame has no floor, so that the fiber bed 2 comes to lie directly on an air-permeable support means 3 located under the frame. A press plate 4 is installed above the frame 1 so that it can be sunk into the frame 1. The press plate 4 is equipped with: • a connection 5 for the supply of steam • a connection 6 for the supply of drying air • recessed nozzles 7, which are evenly distributed over the entire contact surface of the plate 4 and with the supply of steam and drying air in one here Connections or distribution lines not defined in more detail are • a pressing device 8, via which the fiber bed 2 is compressed and thus compressed to the desired plate thickness x.

Under the perforated plate 3 there is a chamber 9, with which an air extraction fan 10 is connected.

Probes for pressure, temperature and flow measurement are for a targeted use of the

Device useful, but are not shown in Fig.2.

The press plate 4 can be specifically designed so that the steam dries before being introduced and thus the formation of condensate is prevented. Preventing condensation is desirable because the moisture content of the panel will facilitate subsequent processing

Drying should not be increased unnecessarily.

Furthermore, it has been shown that the vapor deposition of the fibers with simultaneous supply of

Hot air can take place. This heats the fiber material more quickly and the formation of

Condensate is reduced or completely prevented.

The material for the parts touching the product must be selected so that in the

There is no caking and the panels can be easily removed from the frame. Between the fiber bed 2 and the perforated plate 3 can

Prevent caking a tissue to be inserted.

When the apparatus is operating, the press plate 4 is first set to the desired plate thickness x via the press device 8. Then 5 steam is in via the steam feed line

Page 7 and blown through the fiber bed and the air or steam exhaust fan 10 turned on. This causes the fiber bed to heat up without drying out. When the required temperature has been reached and the desired drying effect has been achieved with the steam supply line, the steam supply line is terminated. The fibers have now become softer and more resilient, so that the fiber bed 2 can optionally be further compacted with a low pressing pressure. The drying air supply line 6 is then opened. This will initiate the drying cycle. After drying is complete, the press plate 4 is retracted and the now stable fiberboard is removed from the frame 1.

1 is of course only a schematic representation of the facilities and processes according to the invention. For example, drying with air can become obsolete if there is sufficient vaporization and sufficient ventilation. Media supply and discharge can just as easily be implemented in reverse as shown in Fig. 1 (i.e. supply of steam and air from below). The process steps "vapor deposition" and "drying" can equally well take place in two separate apparatuses, the drying e.g. can also be supported by the use of microwaves. For applications with high throughput, the above principle can also be implemented as a continuous plate line.

Results achieved

The following types of insulation boards were produced using the process described above:

Raw material density (kg / m) additive vaporization breaking strength

Fresh grass 72 no no not enough 101 yes no not enough 76 no yes good 89 no yes good 108 yes yes very good 156 yes yes very good

Grass silage 54 yes yes good 90 yes yes very good

page 8 120 yes, very good

Corn silage 181 little no bad 252 much no bad 175 little yes enough 234 little yes good

Sugar millet 152 yes no insufficient 152 yes yes good

With increased addition of mineral additives (e.g. clay powder, gypsum, others), very resilient, porous plates with higher density can also be produced. The results show very clearly that steaming is the quality-determining process step, and binders and board density only have a subordinate influence on the breaking strength of the boards.

The fibers made from corn silage also contain bast that has broken down into fine particles and fragments of the spindles. This material is mainly because of these accompanying substances in the present form for the production of light insulation boards much less suitable than grass fibers. A separation of fine material, fibers and fragments, e.g. by means of airflow sieving, will significantly improve the usability of the fiber fraction for plate production. The fibers made from millet also contain decaying bast with a relatively small grain diameter. A separation from the bast is advisable for the use of these fibers.

The invention has the following advantages:

a) With the described method, plates with a density of up to over 50 kg / m ³ can be produced. These boards are comparable to rock wool of similar density in terms of breaking strength and compressive strength.

b) The described method is well compatible with some of the common additives that are used to ensure fire resistance and fungus resistance. It has been found that these additives can lead to a further improvement in plate strength as a side effect. The chosen metering process works without loss and leads to a good material connection (no segregation).

Page 9 c) The effort for drying the plates with air is significantly reduced by the described method. This reduction results on the one hand from the fact that water vapor-saturated air and condensate are drawn off from the plate during the steaming and the moisture content of the plate drops in the course of the steaming. On the other hand, the vaporization results in an increase in the temperature of the fiber material and the moisture contained therein to 80-100 ° C. and thus a reduction in the heat of vaporization to be used for drying. It is conceivable that after steaming, no further drying of the fibers with air is necessary.

d) The described method can be implemented in batch operation or in continuous operation. Batch operation (1 plate = 1 batch) is more suitable for decentralized small systems. In contrast to continuous operation, the plates are shaped before the plate is stamped and dried. The manufacturing units are inexpensive and can be supplemented with additional units as the product demand increases. The implementation of the process in a continuously operated plate line is advantageous for larger to large production capacities.

e) The process described for defibering leads to good fiber separation when processing suitable raw material qualities, a very low proportion of fiber fragments and an optimal fiber length of 15-30 mm for the board production. It is not necessary to add chemicals to improve the digestibility.

Page 10

Claims

Expectations: 1. A process for the production of fiberboard from moist biomass, consisting of the steps (a) raw material preparation and defibration, and (b) board production, characterized in that the board production from the plant fibers is carried out according to the following procedure: bl) at least approximately complete openings of fiber lumps ; b2) formation of a fiber bed with a uniform layer thickness; b3) pressing the fiber bed to a desired thickness or density; b4) Uniform vapor deposition of the fiber bed until a temperature of over 60 ° C., preferably over 80 ° C., is reached over the entire cross section. 2. The method according to claim 1, characterized in that the fiberization of the biomass takes place as follows: a) creating an aqueous suspension with a consistency of 0.5-6%; b) defibering by targeted action of striking elements that are not equipped with cutting tools; c) Optimization of the fiber separation through multiple passes through the striking elements. 3. The method according to claims 1 or 2, characterized in that the fibers are metered in and mixed in after the mechanical dewatering and before the formation of a fiber bed 4. The method according to any one of claims 1-3, characterized in that, after the vaporization of the fiber bed, drying is carried out with air and this drying is preferably carried out by forced flow of hot air through the fiber bed. 5. The method according to any one of claims 1 to 4, characterized in that the raw material belongs to the family of gramineae or legumes and the preparation includes the following steps: a) treatment in a hammer mill or a crusher; Side il b) squeezing plant sap; c) Preparation of the plant sap with a view to suitable utilization. 6. The method according to any one of claims 1-5, characterized in that corn or cereal starch, cellulose or cellulose derivatives, ground clay, synthetic fibers and / or boron-containing flame retardants are used as additives for the production of plates. 7. The method according to any one of claims 1-6, characterized in that the vapor deposition of the fiber bed is carried out with a vapor pressure of 0-15 bar, preferably 4-10 bar. 8. The method according to any one of claims 1-7, characterized in that steam or condensate and drying air are drawn through the fiber bed with a vacuum pump. 9. A method for carrying out the method in batches according to one of claims 1- 8, characterized in that the fiber bed 2 is fitted into a frame 1 with predetermined dimensions before the steaming and the supply of steam and drying air takes place via the same press plate 13. 10. Process for the batch-wise implementation of the process according to claim 9, characterized in that the steaming and drying process steps take place in two process steps that are spatially and temporally separate from one another. 11. The method for continuously carrying out the method according to any one of claims 1-8, characterized in that the fiber bed is moved by a conveyor belt and the process steps lb2) to lb4) are carried out successively on this belt. 12. Device for the production of flat sheets or fleece mats, comprising a preferably rectangular frame (1) for receiving a fiber bed (2), the frame being able to be arranged over an air-permeable support means (3), a pressing device (8) for pressing the fiber bed ( 2) against the support means (3), the device means for introducing steam (5,7) and means for introducing drying air (6,7) into the page 12 Has fiber bed and means for extracting steam or drying air (9, 10) from the fiber bed (2). 13. The method according to any one of claims 1-12, characterized in that the fibers produced from moist biomass for plate manufacture are also mixed with fibers of other origin and composition and the admixing of these fibers takes place before the compression of the fiber bed to the desired thickness and density. 14. Insulation boards with a density of 50-180 kg / m3, which were produced by the method according to any one of claims 1-13. 15. Porous building boards with a density of 120-300 kg / m ³ , which were produced by the method according to any one of claims 1-13 and with the use of increased amounts of additives. 16. Multi-layer panels with one-sided or double-sided coating, the core layer of which was produced by the method according to one of claims 1-13. 17. Nonwoven fabric with a thickness of less than 30 mm and a density between 30-180 kg / m ³ , which were produced by the method according to any one of claims 1-13. Page 13