SE466550B - Process for drying material in fibre or particle form - Google Patents

Abstract

The invention relates to a process for drying and shaping material in fibre or particle form. Material which has been wet-shaped but not dried is defibred 1, dispersed and transported to an endless movable wire 6. Warm gas flows through the wire, thereby drying the material. After the shaping and partial drying, the material is compressed to a higher density. Suitable materials for drying are lignocellulose fibres such as sulphate and sulphite pulp fibres or so-called mechanical pulp of the ground pulp, thermomechanical pulp (TMP) and chemomechanical pulp type. <IMAGE>

Description

466 550. For optimization of the density, it is not desirable to start from a material with high initial density and strong bonding forces. In the wet forming method, the initial density is high after the mechanical pressing. Therefore, even at low dry temperatures, strong hydrogen bonds develop between fi brema. High density leads i.a. to poor air permeability and high strength in the material structure. This complicates both mechanical dewatering and drying. The crucial argument for having a high initial density in the drying part is that it is considered energy optimal to mechanically dewater the pulp.

Technical solution The disadvantages of the prior art are reduced by applying the present invention.

This is due i.a. that the invention is a combination of dry and wet forming.

This results in a better energy exchange during drying and production of products with specific properties. 'Wet-shaped but not dried material e.g. pulses with a dry content varying from 20% up to 65 96 they are mechanically removed so that the fibers are exposed without the shortening of the branches at the same time. The lubrication is performed using a special type of hammer mill manufactured by ROTOM AB, Sundsvall, Sweden. Modified disc lubricators can also be used. In special cases, it may be compulsory to combine hammer mill and disc raffin butter. Fibers and / or particles are dispersed, transported and partially dried in a gas stream which compulsorily consists of air. Also other gases e.g. superheated water vapor can be used. The temperature of the gas need not be higher than 20-50 ° C. Nothing prevents the use of higher temperatures. The main thing is that the gas pours low moisture content. The material dispersed in the gas passes through a storage system in which a part of the loosely bound moisture is evaporated with the part of the gas which is separated from the storage system.

According to the invention, it is possible to form wide layers. A floor mat with a width of 1 to 6 m is thus within the scope of the invention. This step is achieved b1.a by using a so-called transverse or spiral formers and which are described in Swedish patent 82 07097. By using this special apparatus, the expansion of the members is avoided. In addition, an expulsion of moisture is obtained from the material amounting to 5-25% of the original dry content. The degree of moisture escape depends on the type of goods, density and dry matter content at the entrance of the fibers to the device.

Exposed beams are laid on a movable gas-permeable wire cloth which can be made of different materials and can also consist of layers. The fibers or particles form a mat having a basis weight in the range of 10 grams per square meter up to 1500 grams per square meter. The web of material obtained by the invention is blown through with a gas, suitably conditioned to a certain dry content, whereby moisture is evaporated without energy being added to evaporate the moisture. This gas fate is diverted via a central filter. Depending on the dry matter content obtained, heated gas is then added in a partially closed and combined flow and surface drying system. The drying becomes more dominant with increased compaction of the material mat. To achieve high density, the material is subjected to successive compression and addition of moisture. Pressure pressures up to 250 bar can be used to obtain the desired density and strength. Other properties such as surface strength and evenness are also affected by the conditions of the compaction. Advantages According to the present invention, the mechanical dewatering is operated to a dry content which is optimal for the process in terms of economy and product quality. By using gas dynamic effects in the debrisation of e.g. fi glazing When laying the fi glazing on the wire cloth, an evaporation of moisture is obtained without the addition of extra evaporation energy. The energy in the gas fl fate is sufficient. Obtained dewatering within the dry matter range up to the fiber saturation point for pulps, i.e. 60-75%, is even greater than the evaporation that can be obtained with only the engine power installed in the system. In addition, this technique can be used for dry-drying under optimal conditions. Thanks to the fact that gas is used as a storage medium, it is easy to control density and basis weight (weight per square meter). Furthermore, the air permeability during drying and pressing can be regulated. The invention is very flexible in terms of the process and the possibility of influencing the properties of the finished product. The method facilitates mixing different materials with each other. Examples of mixtures are pulp and synthetic fibers. Such a mixture can be provided with adhesives or chemicals which make the product resistant to, for example, fire and / or water.

With the method according to the invention, the energy consumption becomes relatively low and the plant and the process are easy to start up. In addition, little staffing is required. An additional advantage is that the process is extremely environmentally friendly due to low energy consumption and no emissions of pollutants.

Embodiments In the following, the application of the invention will be demonstrated by means of the fl diagram Figure 1.

Exemrgl 1 For the experiments, chemically mechanical spruce pulp was used from a factory for the manufacture of e.g. cardboard. The dry matter content of the pulp was measured at 47% and its drainage properties according to Canadian Standard Freeness (according to SCAN-C 21:65) were measured at 415 ml.

At the same time, chemical mechanical spruce pulp was extracted from the same plant, which had been dried to a dry matter content of 88% in a conventional dryer. The freeness of this mass was also 415 C.S.F. ml. The mass-dried mass is referred to as reference sample 1: A. Sampled pulps were transported to the test plant for forming and drying in accordance with the method of the invention.

In the pilot plant, the wet mass was ground in a specially modified hammer mill 1.

The exposed brakes were conveyed via line 2 to a cyclone-like device 3. From device 3, pulp brakes were conveyed by line 4 to the cross-feeder 5, which disintegrates the yokes, disperses the fiber stream and disposes of the transport air during the laying of the brakes. From the cross former, the wires were formed into an endless continuous moving wire cloth 6.

Sample 1: B was taken from the wire, which was analyzed for dry matter, see Table 1. A visual assessment of the sample showed that the sample's content of fiber knots (fiber creeps) was practically 466,550 virtually zero, which was very surprising given that the dry matter content of the pulp was as high as 47 96. The dry matter content had been achieved by mechanical pressing of the r berr material.

A bed of just over 10 mm thick made of porous and fl uf fi g fi berm rug was laid on the wire. The basis weight was 708 g / m 2 calculated as absolutely dry pulp. The carpet thus formed was conveyed by means of the wire to a double wire section 7 in which the carpet was blown through, partially dried and deaerated in both the bottom and top layer. the mat was compressed to increase the density. In the experiment, the contact pressure was measured at 5 MPa. The temperature of the surfaces 9 of the sheet metal press was measured at 160 ° C. The passage through the sheet metal press lasted for 8 seconds and the speed was 15 m / min. It should be emphasized that the stated performance applies to this experimental facility.

During the passage through the sheet metal belt press, a certain drying effect was maintained. After the treatment in the belt press, a 1: C sample was taken, which was analyzed for freeness, dry matter content and density, see Table 1.

Table 1 Sample designation Reference sample l: A Sample 1: B Sample 1: C Dry content,% 88.0 69.0 89.5 Freeness, CSF, rnl 415 --- 415 Density, kg / m3 505 --- 690 The results show that the mass fi brema on which the wire was applied, sample 1: B, had a surprisingly high dry matter content, given that the only energy stored in the transport stream consisted of energy from installed motors and the entalpiirmehâlleti outdoor air. Even if all installed engine power excluding heating power is converted to evaporation power, this does not correspond to the total degree of dewatering obtained during the process according to the invention. the venting takes place.

Particularly positive and surprising is the high density obtained in dried pulp. In sample 1: C, the burst index according to SCAN P 24:77 was measured at 0.15 kPa m2, which is an extremely low value in relation to the density of the dried and pressed sheet. Wet-formed sheets of the same mass have a burst index of 1.4 kPa / g. An explanation for the large difference is probably that the establishment of hydrogen bonds is significantly greater in wet forming than in tone forming.

Sample 1: A and sample 1: C were de- berted in an ordinary hammer mill to so-called fl uff. During the debriefing, it was found that the electrical energy consumption amounted to only 29 kWh per tonne, while the conventionally dried pulp required an electrical energy consumption of 37 kWh per tonne of pulp.

The obtained fl uff was tested for bulk and absorption properties. Results table 2.

TABLE 2 Reference test According to invention 1: A 1: C Bulk, cmS / g 14.2 15.1 Absorption rate, secsmder 5.3 5.6 Absorption capacity, g / g 9.1 9.1 466 550 From the values in Table 2 it appears that the pulp produced according to the invention has given higher bulk and otherwise the same properties as the reference pulp.

EXAMPLE 2 Experiments were performed with the same type of pulp as used in Example 1. In this experiment, two cross-formers (5) were used for laying the fibers on the wire (6). This resulted in the weight of the pulp bed becoming high or 1248 g / m 2. In order to increase the drying capacity, the circulating gas flow was increased. Furthermore, the temperature in the belt press (8) was raised to 180 ° C. Otherwise, the experiment was carried out as described under Example 1. The mass obtained, Sample 2A, was analyzed for dry matter and density. After debrisation, bulk and absorption properties were measured. The properties have been compared with conventionally shaped and dried pulp. 3 Table 1 shows the results.

TABLE 3 Reference test According to invention 1: A 2: A Dry content% 88.0 90.1 Density kg / m3 505 921 Fluffed pulp Bulk cm3 / g 14.2 15.3 Absorption rate sects 5.3 5.4 Absorption capacity g / g 9 The results show that the pulp produced according to the invention has equivalent or even better properties than pulp formed and dried according to known technology. Particularly surprising is the high density of sample 2: A before defibration.

EXAMPLE 3 In this third experiment the same type of pulp was used as in previous experiments. The pulp was dried to a dry matter content of 88% and taken out before the belt press (8), after which it was ground in a conventional hammer mill to fl ingor. The flakes were fed to a plate press which is used for drying. The resulting plates were further compressed in a baler used in conventional drying. After the plate press, Sample 3: A was taken as they were fi brated in a standard hammer mill to obtain the properties of the ff uffFluff pulp have been compiled in Table 4.

TABLE 4 Reference test!: A Sample 3: A Density kg / m3 505 570 Bulk cm3 / g 14.2 15.2 Absorption rate seconds 5.3 5.5 Absorption capacity g / g 9.1 9.2 466 550 6 Despite the mass pressed in the same way, the pulp according to the invention has a higher density than the reference sample. It is therefore particularly surprising that Sample 3: A obtained as good properties as the reference sample.

EXAMPLE 5 In this experiment, the pine sulphate pulp whose dry content was measured to be 42% was measured. After passing through the cross former, the dry matter content had risen to 58% when the fibers were applied to the wire cloth.

By means of another cross-former, polypropylene fibers were fed, the proportion of which by total mass and polypropylene fibers was 10%. After shaping and drying the fi ber mixture, a fi bone night with high strength was obtained.

EXAMPLE 6 The purpose of this example was to demonstrate the possibility of mixing in chemical binders. In the experiment, pulps of pine sulphate pulp were used which were pulverized in the specially built hammer kiln and then fed to the cross former. In addition, the binder water glass (sodium silicate) was added to the former in an amount of 3% based on the dry weight of the pulp. To increase the durability of the product 0,5 0.5% potassium dihydrogen phosphate was also added.

The product obtained a dry content of 92%.

When testing the product's resistance to fire, it turned out that it was completely resistant to fire insofar as it did not catch fire but only glowed very slowly.

In addition to the näm bres mentioned in the examples may be mentioned polyethylene, polyamide and polyester. Binders include phenolic glue, bone glue, starch and urea. With regard to pulp bridges, it is advantageous to use bridges which have been obtained by means of so-called fi berfractionation. In this methodology, short bridges are separated from long bridges. In the practice of the present invention, short and long strips can be laid on the wire in different layers. Thus, a first layer of long fibers can be laid on the bottom of the wire and the next layer can consist of short fibers. On top of these layers a third layer consisting of long fi bricks can be laid. The fibers in each layer can of course consist of mixtures containing synthetic fibers or peat fibers. fl l

Claims (1)

1,466,550 PATENT REQUIREMENTS 1. A process for forming and drying materials in the form of fibers and / or particles, characterized in that the material is distributed at a dry content of 20-75%, dispersed, partially dried and transported in a gas stream so that the dry content increases by at least 5% (expressed in actual terms) before applying a gas-permeable wire cloth to form a coherent unit while simultaneously gas-dynamically expelling moisture and drying by means of convection heat and mechanically compressing the formed unit to a higher density. Method according to claim 1, characterized in that the material forming the dried unit consists of pulp fibers of the chemical pulp or mechanical pulp type or intermediate types of said pulps. Process according to Claims 1 and 2, characterized in that synthetic fibers are mixed with the pulp brems. Process according to claims 1-3, characterized in that binder is added during the formation of the fibers into a coherent unit. Method according to claims 1-4, characterized in that the material is dehumidified in a cyclone-like device in which the material has a speed of at least 15 m per second. Method according to claims 1-5, characterized in that the material is dehumidified to a dry content of 50-90 96 before the formed unit is compressed. Method according to claims 1-6, characterized in that the unit formed after forming and drying is compressed to a higher density. Method according to claims 1-7, characterized in that one or more of your materials are applied to the wire in your layers. Process according to Claims 1 to 8, characterized in that protective materials chemically protect the applied material.