DE3604146A1 - Process for the treatment of brown coal - Google Patents

Abstract

The invention relates to a process for the treatment of brown coal, in which the coal is subjected to shearing forces in order to produce a plastic mass which can be converted by subsequent compaction and drying into a fuel of increased density and increased gross calorific value, which is characterised in that the water content of the coal amounts to more than 54% and the shearing forces are applied for less than 1h, shorter times being preferred, for example less than 30s. A preferred embodiment provides a continuous process in which the coal is treated in a machine in which it is successively subjected to shearing and extrusion stages in a continuous way. After drying, the extruded product yields the fuel of increased density and increased gross calorific value. The desired effect can likewise be obtained by treating part of a quantity of brown coal and mixing the treated part with the untreated remaining quantity.

Description

description

The invention relates to an improved method for refining or processing lignite, as it is in of Australian Patent Application 24294/84.

Lignite species usually have a total moisture content of more than 60% and in the raw state are soft, friable materials with lower Density, which represent a low quality fuel.

Processes for upgrading lignite include briquetting and sun drying processes.

Briquetting is a widespread and long-known technology for converting lignite into a hard fuel with a higher calorific value Use of thermal energy. A water content of 18% is generally considered to be optimal for the subsequent briquetting. After cooling to a temperature of 40 to 50 ^° C., the dried coal is pressed in an extrusion press or a roller briquetting machine.

Much thermal energy is required to dry the coal in this process, and a considerable amount mechanical work with associated wear is associated with the briquetting operation. Follow the briquettes, although they are a high quality fuel, are correspondingly expensive to produce.

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} Λ / Sun drying of the lignite Vv was recently proposed in order to produce a hard product with a water content of the order of 5 to 10%. In this process, the raw lignite is mixed with 20 to 25% water in a ball mill for up to 16 h ground long. The thixotropic slurry so produced is then placed in shallow basins to lose water with the help of the sun. As it dries, the slurry becomes hard, dark in appearance, and water resistant (ie, the solid does not degrade significantly when contacted with liquid water). The drying time varies with the weather, but can take several months. This process gives an essentially satisfactory product which varies somewhat in quality. It takes a long time in both milling and sunbathing of the slurry. Long grinding is of course energy-intensive.

The invention described in copending application 24294/84 which provides a method for converting Brown coal species in a hard, relatively dense ^ solid fuel form with a much smaller residual water content and provides a substantially enhanced calorific value per unit weight has important advantages compared to known briquetting and sun drying processes for refining lignite.

As stated, raw coal often has a water content holds above 60%, and their calorific value is correspondingly low. Compared to known briquetting processes In this process, no added thermal energy is required to remove the water.

Compared to known sun drying processes, there is no gg requires additional water to grind up the degraded Coal, the time required for attrition is considerably reduced and the final drying step takes time 3 to 5 days instead of several months (depending on

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on weather conditions). Alternative methods to this are therefore relatively ineffective and uneconomical.

The invention of the co-pending application is characterized in that the coal is in a first attrition stage Shear forces, in contrast to grinding forces, is exposed. This treatment compacts the coal into a mass that can be compacted, for example by extrusion, into a coherent, solid form, which is very suitable for efficient drying and handling. Extruded manufactured in this way Pellets can be dried by mere exposure to the atmosphere, preferably at or near ambient temperature will.

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Although the disclosure of the co-pending patent application does not refer to a minimum attrition time for lignite, crushed in a kneading / shearing type apparatus, it was believed at the time that it was needed Time for this stage would and has been on the order of hours rather than minutes suggested that attrition times above 1 to 1 1/2 hours would be suitable. In a specific example, the Coal exposed to attrition in a kneader for 5 hours.

It has now surprisingly been found that shorter treatment times for this stage are also effective and may even be more effective than the previous comparable ₃ Q used longer times.

The minimum time it takes to scissor-grind the raw lignite required in the compaction process is that which is sufficient to produce a significant amount of moisture ability and a plastic character in the coal mass. In practice this condition is due visual observation controlled on the basis of experience. The length of time is a function of the

the speed of the attritor , the intensity of the shear achieved by the machine, and the effectiveness of the machine in constantly moving the coal into the shear zone.

With regard to the latter, the water content of the coal can be critical; if it is too low, it worsens the machine efficiency increases drastically. Experience shows that lignite species with water contents above 60% by weight show optimal shear-attrition characteristics, whereas water contents in the range of 54% (or less) are unsatisfactory.

Using a Sigma kneader at kneading shaft speeds of 40 and 20 Upre and a rotor-wall distance of 0.3 mm were different types of lignite of Victorian and German descent successful converted into extrudable plastic masses by shear-frictional forces over periods of 30 s. 30 s should not, however, be regarded as a minimum time '.-.', because the time required depends very much on the effectiveness of the machine available. Any time that is enough to convert the raw lignite into an extrudable plastic state is suitable.

It should be noted that in practice short shear

Can be compensated Zerreibzeiten which provide a limited reduction in size of the coal particles to a certain degree by the subsequent use of high extrusion _"0 print. A relatively dry plastic mass leads to the development of high pressures in the nozzle area of the extruder.

Another preferred embodiment of the invention represents a continuous shear extrusion process to disposal. The very short grinding times that are described allow continuous operation, in the case of lignite in small lumps (5 mm or

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ι smaller) continuously in a shear triturator is fed at low speed (20 to 40 rpm) of the sigma type. The configuration of the machine is designed to provide a residence time for the coal in the shear zone of the order of magnitude required (as above defined) before they can be removed by a suitably arranged discharge screw or - auger is pulled out. The discharge screw feeds the moist, grated coal into an extrusion head, which is designed to provide the required extrusion pressure and pellets available establish which are sufficiently strong to withstand considerable stress immediately after formation.

The present invention accordingly provides an improvement on the method of the co-pending application 24394/84 available and is characterized in that the coal is exposed to shear forces for less than 1 hour is, with particularly advantageous effects being achieved with treatment times of 1 minute or less.

The machine that performs the functions described above and one discharge screw and one Containing integrally fitted extruder is a Sigma kneading machine HKS 50 manufactured by Janke & Kunkel GmbH & Co. KG, IKA plant in Biengen.

Although the present invention should not be limited by any statement Q ₃ of the advantageous effect, it is believed that a compression begins with an appreciable speed, split / trimmed coal surfaces are sufficient as soon as available. This leads to a further improvement which provides a gg continuous process in which the coal has a residence time in the attrition (shear) zone which is sufficient to produce material which is effective in a high pressure extrusion or compression device.

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can be extruded.

The following examples illustrate the invention.

example 1

Dark lithotype coal from the Loy Yang deposit in the Latrobetal (Loy Yang 1276) was subjected to attrition for different times, and the average Compressive strength of the extruded pellets obtained from the resulting mass was measured. The results are shown in FIG. The results show that

Pellets with good strength are made using attrition times of 5 minutes or less can,

~ The EvtrurfopFdruck is very effective for reinforcement the pellet strength (an extruder with a diameter of 3 mm gives pellets which are about three times as are solid like those from an extruder with a diameter of 10 mm),

- there are signs of the absence of additives

Existence of maxima and minima in the pellet strength versus attrition time curves.

gQ A visual observation during the course of this Experiments showed that while charcoal kneaded for 5 to 10 minutes did not have a wet plastic consistency, it had become damp anyway and had a plastic character, which is an effective extrusion

gg was sufficient. Shorter grinding times should also be feasible be. The high extrusion prints made with the 3mm diameter extruder are occasionally sufficient to have a separate water

phase to occur. The extruded pellets are quite coherent and do not stick together, indicating that they can be stacked without adverse effects.

On the basis of the above data and observations, it can be concluded that compacted pellets are of good quality can be produced from coal that is moist during storage using attrition times of only a few minutes, provided that an efficient machine is used which keeps the coal constantly in the shear zone and wherein the separation of the fixed moving surfaces is small enough (on the order of 0.3 mm) to give a high shear and that

! 5 relatively high extrusion pressures can be used to produce the Forcing coal fragments into close proximity.

Experience with the kneader, which has been used for about 1 1/2 to 2 years, shows that abrasion in the Attrition machine is very small. Obviously, the moisture in the coal is effective in providing lubrication and the slow machine speed can also help. The same goes for the liquid Water phase, which usually develops and supports the extrusion process considerably.

Example 2

Another series of tests using narraca coal (N3372) was carried out with the water content standardized to 60%. No additive was used. The average compressive strengths at various kneading times are shown in FIG. the Results generally agree with the results for. the dark lithotype Ley Yang charcoal have been matched. Attrition times of 5 to 10 minutes have been used in addition to the previously investigated range.

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seeks. The kneading machine was with the sigma shaped head is used, which gives maximum shear efficiency by ensuring that the carbon is in the all the time Shear zone remains. The extrusion was carried out with a hand-operated screw extruder, alternatively with nozzles a diameter of 10 mm and 3 mm.

Figure 2 shows that pellets of sufficient strength produced in the 5 and 10 minute attrition experiments became. This is especially true for the high extrusion pressures produced with the 3 mm diameter nozzle were, too. Although in these short-term experiments there was not enough time to get the coal a good deal To give it a moist appearance, it could still be extruded satisfactorily and gave coherent ones Pellets that could withstand considerable loads without deformation.

2Q If higher strengths for pellets, which by short If attrition times are required, this can be achieved by using:

(a) a faster grinder to remove smaller particles to give in a given residence time with improved compaction,

(b) from higher extrusion pressures to compensate for less effective attrition to some degree

QQ pause assuming that this is the extrusion process promotes, or

(c) an additive such as ammonium hydroxide (0.1-0.5%).

_{g (_} A further discussion of the general aspects of the present invention can be found in co-pending application 24294/84, the contents of which made the object of the present invention.

Claims (1)

Claims 1. Process for the treatment of lignite, in which the Coal is subjected to shear forces in order to produce a plastic mass, which is through subsequent Convert compression and drying into a fuel with increased density and increased calorific value can, characterized in that the water content of the coal is more than 54% and the shear forces used for less than 1 hour. 2. The method according to claim 1, characterized in that that the shear forces are applied for less than 1 minute. 3. The method according to claim 1, characterized in that that the shear forces are applied for less than 30 seconds. 4. Process for the treatment of a quantity of lignite in order to produce a plastic mass, which extends through subsequent compression and drying into a fuel with increased density and increased calorific value can convert, characterized in that part of the amount is exposed to shear forces for less than 1 hour and the part thus treated is mixed with the rest of the amount to produce the plastic mass. 5. The method according to claim 4, characterized in that that the shear forces are applied for less than 1 minute. 6. The method according to claim 4, characterized in that that the shear forces are applied less than 30 ε. 7. Process for refining lignite, in which the lignite is exposed to shear forces in a first stage is used to create a plastic mass, the plastic mass is compacted in a second stage in order to produce a compacted mass, and the compacted mass is dried in a third stage to give a dried product with increased To establish 3Q density and increased calorific value, characterized in that the water content of the coal is more than 54% and the shear forces are less than 1 hour. ■ 35 ^{8 # Verfanren} according to claim 7, characterized in that _v that the shear forces are applied for less than 1 min the. Π ί: / 3604Η6 9. The method according to claim 7, characterized in that the shear forces are applied for less than 30 s. 10. The method according to any one of claims 7, 8 or 9, characterized in that the compression stage is carried out by extruding the plastic mass will. 11. The method according to any one of claims 7 to 10, characterized in that the drying stage at or is carried out close to ambient temperature. 12. Continuous process for the production of a refined lignite product, which at ambient temperature Can be dried to produce a fuel with increased density and increased calorific value manufacture, characterized in that the raw lignite, which contains more than 54% water, is treated in a machine in which they are consecutive Shear and extrusion levels are continuously exposed to the product to manufacture. 13. A method for refining lignite, characterized in that the raw lignite by the continuous process according to claim 12 is treated and the product thus produced is dried is used to produce a fuel with increased density and increased calorific value.