Method for processing grass for manufacturing paper, paperboard and cardboard

Abstract

The present invention relates to a method for processing grass or hay as paper pulp having the steps of pre-reducing the grass or hay with a bale breaker and/or a shredder to an average fiber length between 500 mm and 10 mm, preferably between 120 mm and 10 mm, removing impurities and foreign or extraneous substances by means of a cyclone; reducing and fibrillating the grass or hay in a fiber mill, fraying the grass or hay; and screening and/or sifting the grass or hay by means of a circulating-air separator and/or a cyclone screener.

Claims

1. A method for processing grass or hay having the steps comprising: a) Pre-reducing the grass or hay with a bale breaker and/or a shredder to an average fiber length between 500 mm and 10 mm; b) Removing impurities and foreign or extraneous substances by a cyclone; c) Reducing and fibrillating the grass or hay in a fiber mill; d) After milling, pulling apart and/or isolating fibers of the grass or hay with shape rollers; and e) Screening and/or sifting the grass or hay by a circulating-air separator and/or a cyclone screener.

2. The method for processing grass or hay according to claim 1, wherein pelleting is performed by a pellet press after the grass or hay has been screened and/or sifted.

3. The method for processing grass or hay according to claim 1, wherein the reduction and fibrillation of the grass or hay is accomplished in a hammer mill for coarse fiber lengths, in an edge mill for medium fiber lengths and/or in a fine grinding mill for short fiber lengths.

4. The method for processing grass or hay according to claim 1, wherein following the removal of impurities, the shredded and cleaned grass or hay is temporarily stored in a storage container before being subjected to further reduction or grinding.

5. The method for processing grass or hay according to claim 1, wherein coarse fiber lengths have an average fiber length between 10 mm and 3 mm, medium fiber lengths have an average fiber length between 3 mm and 0.5 mm and short fiber lengths have an average fiber length under 0.5 mm.

6. The method for processing grass or hay according to claim 1, wherein the bale breaker is a container having a blade rotor.

7. The method for processing grass or hay according to claim 3, wherein the precut and cleaned grass or hay is fed to the hammer mill, edge mill and/or fine grinding mill by a material-metering screw.

8. The method for processing grass or hay according to claim 3, wherein the edge mill has at least one roller which continuously grind the pulp against a die.

9. The method for processing grass or hay according to claim 1, wherein following the screening and/or sifting of the grass or hay, a predefined fraction is removed and packed away in a filling unit.

10. The method for processing grass or hay according to claim 1, wherein the grass or hay is separated into at least three fiber length fractions by screening and/or sifting, wherein the coarse fraction has an average fiber length between 10 and mm and 3 mm, the medium fraction an average fiber length between 3 mm and 0.5 mm and the short fraction an average fiber length below 0.5 mm.

11. The method for processing grass or hay according to claim 2, wherein following the screening and/or sifting of the grass or hay, accepted stock is transported by a conveying screw and/or mixing screw for pelleting.

12. The method for processing grass or hay according to claim 2, wherein different fiber length fractions, in particular coarse, medium and/or short fiber lengths of the grass or hay are mixed in predefined portions following screening and/or sifting and before pelleting.

13. The method for processing grass or hay according to claim 2, wherein the grass or hay is moistened by a water-dosing system prior to pelleting.

14. The method for processing grass or hay according to claim 2, wherein to produce the pellets, the pellet press presses the pulp through a die, in particular a perforated die, by at least one edge roller.

15. The method for processing grass or hay according to claim 14, wherein the basic shape of the pellets is cylindrical, with a diameter measuring roughly between 40 mm and 2 mm.

16. The method for processing grass or hay according to claim 2, wherein the pellets are conveyed out of the pellet press by a rotary feeder.

17. The method for processing grass or hay according to claim 2, wherein the pellets are packed at a dispensing station.

18. The method for processing grass or hay according to claim 1, wherein the device is explosion-proof, at least with respect to dust.

19. The method for processing grass or hay according to claim 1, wherein the hay has a moisture content between 0% and 15%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In what follows, preferred embodiments of the invention are explained in more detail with reference to the drawings, in which:

(2) FIG. 1 is a schematic diagram illustrating possible method steps for preparing grass or hay according to the present invention;

(3) FIG. 2 shows the diagram of FIG. 1 with additional requirements for the grass or hay at the time of harvesting;

(4) FIG. 3 shows the sieve analysis of the end product of Sub-test A2;

(5) FIG. 4 shows the sieve analysis of the end product of Sub-test A3;

(6) FIG. 5 shows the light fraction of Sub-test P4; and

(7) FIG. 6 shows the medium fraction of Sub-test P4.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

(8) In the process of prior studies, in particular conventional hay from an agricultural operation was used and processed into grass pellets with a machine suited for the production of wood pellets. In this process, it was not possible to clean the hay, and the cut was limited to 6 mm. In addition, the various requirements in paper production were analyzed, thereby allowing the requirements for grass or hay fibers to be defined. In other words, different properties of grass or hay fibers must be achieved in the production process depending on paper type (paperboard, graphic paper or toilet paper).

(9) Basically, these properties concern: Eliminating impurities and foreign objects and ensuring a defined degree of purity Eliminating fine dust to reduce the portions that act as filler in paper and thus change the technical characteristics Cutting/shredding the stalks to the particular length required according to the requirements of paper production Grinding the stalks to increase the surface structure of the fibers according to the requirements of paper production Ensuring fiber length distribution within a defined fraction. Ensuring a consistent quality standard.

(10) Additional goals that should be achieved during production include, among others: Compressing into pellets for simpler storage, Dispensing into paper bags, big bags or a silo for ease of feeding into the paper production process and Reducing volume to reduce the cost of transport.

(11) From this it is clear that the basic principles for the method of preparing grass or hay for use in paper, paperboard or cardboard production are the end user's requirements for the end product, i.e. paper. In this context, the initial situation is additionally determined by the quality and the condition of the hay being prepared.

(12) If, for example, the paper needs to be highly tear-resistant, a certain minimum fiber length must be maintained to make optimal use of the strength potential of the pulp. Different properties of the grass or hay pulp can be achieved by appropriate method steps.

(13) In this context, in the three columns, FIG. 1 shows the procedure or technique to be used for preparing grass or hay while factoring in the key paper-production requirement parameters for the pulp to be used.

(14) Grass is a raw material that is available in large quantities and, above all, locally. Grass grows quickly and in central Europe can thus be harvested in two to five annual cuttings.

(15) The method comprises the processing steps such as shredding, cleaning, cutting, grinding, screening, sifting, moistening and pelleting. It is not mandatory to employ all method steps in the processing of the pulp. Moreover, it is also possible to combine the individual method steps with one another in different ways. In addition, it is also possible to adapt, within the individual process steps, the target variables according to the profile of paper production requirements. For example, the pulp can be cut long, medium or short during the cutting process, or it can be further shortened or fibrillated during grinding. The two method steps of cutting and grinding differ fundamentally from one another such that the quality of the pulp to be achieved can be affected across a wide range.

(16) Equipment for executing the aforementioned method steps includes, among other items, shredders, cyclones, hammer mills, edge mills, fine grinding mills, air separators, screens, moisteners and pellet presses.

(17) Paper-production requirements depend essentially on the particular use of the paper. In this regard, distinction is made among the following core requirements: Grammage/weight per m.sup.2 Increases strength and opacity Volume For making a stronger material/thicker paper Tear-resistance Important for papers subject to great stress and wear Stability, flexural strength Important for making cardboard boxes and packaging Printability Requires a smooth surface

(18) These requirements should also be assured with the method for preparing grass or hay and can be achieved as detailed below: Grammage/weight per unit area The natural property of grass or hay results in higher volume. If necessary, the weight/grammage can be reduced, while other properties remain the same. Opacity increases as grass or hay content increases all the way to opaque. Low surface weight thus requires a very homogenous distribution of fibers, for which the pulp must also have enough short fibers in addition to long fibers to achieve the desired pulp distribution and homogeneity in the paper. Volume In addition to the natural property, volume is achieved by increasing the surface structure, i.e. by grinding the grasses. Tear-resistance Tear-resistance is a function of fiber length and/or fiber length distribution. The fiber length (mm) is achieved by cutting in the corresponding mill. Depending on the mill or on the combination of multiple mills employed, grass fibers of short, medium or long length are produced. If the proportion of a certain fiber length and thereby the tear-resistance of the paper is to be as high as possible, this can be achieved by subsequent sifting or removal of the fine substance. The tear-resistance of the paper is substantially determined by the average length of the grass or hay fibers, which, in addition to the actual length, is critical for the strengthening surface. This surface is affected not only by the actual length of the fibers when cut, but also by grinding. Fibrillating can thus considerably increase the binding-active surface of the fibers. This is achieved essentially by exposing the binding-active fibers from the outer area of the fiber lattice. Stability, flexural strength The required stability or flexural strength is achieved through the appropriate fiber length and surface structure of the grass or hay fibers. Printability Printability requires a smooth surface that is free of unevenness. To this end, a good cleaning process and fibers that are as short and uniform as possible are imperative. The uniform fibers are obtained by using an air separator followed by sifting. When it comes to printability, the paper surface is especially critical. Considering the printing process, it must be as smooth and even as possible to facilitate optimally even ink trapping and color distribution, thereby making it possible to produce an appealing printed image. In addition, there may also be special requirements for the bonding of fibers in the surface to prevent fibers from separating and thereby contaminating the printing machine.

(19) FIG. 2 shows the chart from FIG. 1 with the addition of the starting raw material components, i.e. grass or hay. From this figure it is clear that, because of the seasonally dictated composition and structure of the grass, it is preferable to use grass from the second cutting and later cuttings of the annual harvest that is free of mold, has no more than 15% residual moisture and has a cut length typical of harvesting that measures between 0.1 mm and 500 mm, for example.

(20) As stated in the description above, this grass or hay is supplied to the method for processing grass or hay for the paper-manufacturing process.

(21) A possible configuration of a plant set-up to produce approximately 2 metric tons of grass or hay per hour is described below in the context of a diagram showing the sequence of operation. 1. Breaking up the hay bales using a bale breaker and shredder in a grinding vat to a length between 1 and 12 cm for a first pre-reduction. This plant is configured for an output of approximately 4 metric tons of grass per hour. 2. Feeding into a cyclone to remove impurities and foreign or extraneous materials such as: Earth, sand and stones Metal objects Plastic parts and sheeting Wood Glass Fine dust In addition to removing solids, dust is removed by a filter from the conveying air. The solids (dust) captured therein are returned to the hay in the supply container, if necessary. 3. Capturing the cleaned hay in a supply container with a capacity of approximately 2.5 m.sup.3 for buffering and continuously supplying the mill and, if necessary, moistening if moisture content is below 8%. 4. Feeding to the mill by means of a pneumatic conveying device. 5. Conveying to the reduction process by means of a hammer mill for a coarse fiber length an edge mill for a medium fiber length a fine grinding mill for a short fiber length Fiber length is determined by the use of various dies or screens. 6. Conveying to the grinding process Grinding is carried out either during the reduction process or, if necessary, in an additional milling process. The particular degree of grinding determines the corresponding enlargement of the surface structure. 7. Conveying to the air separation process Different fractions with different grain size distribution are achieved through air separation. Any remaining foreign objects are separated by screening. 8. Conveying to the sifting process Further refinement of the fraction with primarily homogenous grain sizes is achieved by sifting. 9. Conveying to the pelleting process Pressing the grass fibers into grass pellets. Moisturizing is necessary if moisture is below 8%. To prevent mold and ensure shelf-life, a moisture content of 15% must not be exceeded. Pellet strength is determined by the use of various dies and the pressure generated in the press. The lower the strength, the more easily it dissolves during paper production. 10. Conveying to the filling process, e.g. into paper bags, into big bags or into a silo
Experimental Design

(22) To better illustrate the invention, tests designed according to the invention are described below.

(23) General Description of the Tests

(24) In all of the tests described here, hay was used that had been delivered in the form of two bundled hay bales. This starting material contains long-fiber hay, i.e. having a fiber length between 50 and 80 mm, with dried hay fibers, a raw product moisture of 9.3% and a bulk density of 0.07 kg/dm.sup.3. The flow behavior can be characterized as slow flowing.

(25) The goal of the test was to produce fibers of even length using the edge mill. The ground hay is intended to be later mixed into the paper.

(26) The test results show that the hay was processed very well with the 33-390 press. The 33-390 press was used as an edge mill for reducing the hay. The hay was broken up very evenly in sub-test P4.

(27) Sub-Test P1

(28) Sub-test P1 was performed using a 33-390 press at a roller number of 2, a rotational speed of 166 rpm and a roller speed of 2.28 m/s. An 82112 die having a press ratio of 1:20 was used. The conveyor belt was fed by shovels after the material had been spread out on the factory floor. Before pressing, the material had a moisture content of 9.3%, a temperature of 20? C. and a bulk density of 0.07 kg/dm.sup.3. Following pressing, the material had a moisture content of 10.0%, a temperature of 59? C. and a bulk density of 0.37 kg/dm.sup.3. The press was operated at an output of 180 kg/h. No cooling was undertaken.

(29) In this sub-test P1, there was fluctuating press capacity (13 and 24 kW) due to intermittent ejection of material through the pockets of the conveyor belt, choppy press operation, some loosely pelleted and unstable pellets and a somewhat unevenly milled product. The material was ejected into a big bag.

(30) Sub-test A2

(31) Sub-test A2 was performed using a press having the parameters: roller diameter 400 mm, fluting 475 flutes/circumference=3.8 F/cm=9.6 F/inch, level 0.1 mm, back angle 41.5?, cutting angle 12.5?, flute depth 1.1 mm, roller speed (left) 8.9 m/s, roller speed (right) 6.4 m/s, lead of 1:1.4, gap 3.4 mm. The press was fed manually.

(32) FIG. 3 shows the sieve analysis of the end product. Grain classes are as follows: below 1 mm 31.2%, the range between 1 to 2 mm 32.6%, for the range between 2 to 3.15 mm 20.1%, for the range between 3.15 to 4.0 mm 8.8%, for the range between 4 to 5 mm 5.5% and above 5 mm 1.8%. The aggregate grain classes are as follows: below 1 mm 31.2%, up to 2 mm 63.8%, up to 3.15 mm 83.9%, up to 4.0 mm 92.7% up to 5.0 mm 98.2% and total 100%.

(33) Sub-Test A3

(34) Compared to sub-test A2, sub-test A3 was performed with a smaller gap of 0.8 mm (as opposed to 3.4 for A2). All other parameters were the same as those used for sub-test A2.

(35) FIG. 4 shows the sieve analysis of the end product. Grain classes were as follows: below 1 mm 35.5%, for the range between 1 to 2 mm 47.0%, for the range between 2 to 3.15 mm 16.0%, for the range between 3.15 to 4.0 mm 1.3%, for the range between 4 to 5 mm 0.1% and above 5 mm 0.1%. The aggregate grain classes are as follows: below 1 mm 35.5%, up to 2 mm 82.5%, up to 3.15 mm 98.5%, up to 4.0 mm 99.8% up to 5.0 mm 99.9% and total 100%.

(36) Sub-Test P4

(37) Sub-test P4 was performed with the same press used for P1.

(38) As with P1, the conveyor belt was loaded by shovel. A smaller bore diameter than that of sub-test P1 was used.

(39) Before pressing, as was the case with P1, the material had a moisture content of 9.3%, a temperature of 20? C. and a bulk density of 0.07 kg/dm.sup.3. Following pressing, the material had a moisture content of 7.7%, a temperature of 47? C. and a bulk density of 0.26 kg/dm.sup.3. In this sub-trial P4, there was fluctuating press performance (6 and 18 kW) due to the intermittent material ejection through the pockets of the conveyor belt, choppy press operation, some loosely pelleted and unstable pellets, but a very evenly milled product. The material was once again ejected into a big bag.

(40) The subsequent screening yielded two fractions, the grain class distribution of which is shown in FIG. 5 as the light fraction and in FIG. 6 as the medium fraction. For the medium fraction, the grain classes are as follows: below 1 mm 24.6%, for the range between 1 and 2 mm 51.3%, for the range between 2 and 3.15 mm 22% and above 3.15 mm 1.9%. The aggregate grain classes are as follows: below 1 mm 24.6%, up to 2 mm 75.9%, up to 3.15 mm 98.1% and total 100%.

(41) For the light fraction, the grain classes are as follows: below 1 mm 45.6%, for the range between 1 and 2 mm 50.1%, for the range between 2 and 3.15 mm 4.2% and above 3.15 mm 0.1%. The aggregate grain classes are as follows: below 1 mm 45.6%, up to 2 mm 95.7%, up to 3.15 mm 99.9% and total 100%.

(42) In summary, the present results establish that a larger die results in longer fibers and lower homogeneity of the grain classes. Reduction with the roller mill is advantageous for separating into different fractions. A smaller die reduces fiber length, results in homogeneous fractions and requires, as the case may be, no reduction by the roller mill.