DE3603005A1 - Method of producing compacted coal pellets - Google Patents

Abstract

The invention relates to a method of producing compacted coal pellets having improved physical properties, the coal being subjected to a shearing and a tridgerating stage followed by extrusion and drying stages. The method is characterised in that an additive is incorporated in the coal which is subjected to the shearing and tridgerating stage, the additive being selected from one or more constituents of the following group: Alkali-metal hydroxides, Alkaline-earth-metal hydroxides Ammonium hydroxide, alkali metal carbonates, Alkaline-earth-metal carbonates, Oxides of base metals, Oxides of transition metals and Carbonyl compounds having small molecules.

Description

The invention relates to a method of manufacture

of compacted coal pellets with improved strength and abrasion or wear resistance.

Applicant's co-pending patent application AU-24294/84 and Application as supplement thereto, PG 9283, filed February 14, 1985, becomes a process for refining or processing lignite to harder, relatively denser forms a solid fuel with smaller residual water contents and considerably increased Calorific value or calorific value per unit weight disclosed. The disclosed method has important technical and economic advantages over the known Briquetting and sun drying processes for refining lignite.

Essentially, this involves the process of the copending application three stages: 1. The first stage is a trituration or trituration stage, in which the coal is mainly exposed to shear forces, as opposed to grinding forces.

This is done in a mixing or kneading device or another Machine that shear the soft materials instead of breaking them or sanding down can be achieved.

2. The second stage involves a compaction of the wet plastic Mass produced in the first stage by extrusion into pellets in one Extrusion or similar compression device.

3. In the third stage of the above process, the extruded Pellets dried at or near ambient temperature, depending on but preferably not necessarily with the help of an air flow around the developed To remove water vapor.

It is believed that in the compression process, there is a mechanism chemical bond formation takes place. This is based on irreversibility towards a dispersion in water, the changed behavior towards solvent extraction, Changes in the pyrolysis behavior, the sensitivity of the process to the pH and dissolved species in the aqueous medium, as well as noticeable changes in the spectral properties of the compacted solids. All of these factors indicate the development of strong covalent and electrostatic bonds between the coal particles and, in particular, that these bonds are created by small molecules and polyvalent ions between reactive sites on neighboring ones The sides of the coal particles form bridges. An analog but not identical situation for one of the types of bond is the one in which formaldehyde bridges between phenols forms and thermosetting phenol-formaldehyde resins are produced.

In the above co-pending application, the holding was of the molecular species in the carbon structure in the binding process in a natural one Acid ionization - typically phenols and / or carboxylic acids - mentioned. The reactivity of covalent bonds in such species depends on the ionization state of the acid groups depending on which decreases when the acidity of the medium increases and vice versa.

It has been found that alkali and alkaline earth carbonates (despite the relative insolubility of the latter) comparatively effective additives for the most types of coal are to increase their bond strength.

This suggests that, in addition to the alkalinity of these additives, the carbonate ion or an aqueous species derived therefrom plays an important role in the binding process. Possible species are those included in the following equilibria: Carbon dioxide is of course an integral part of all types of carbon, so that the effect due to the added carbonate is in addition to that which is naturally present.

Of the major known species in lignite species, such as by pyrolysis gas chromatography and other processes shown are the phenols and especially the polyhydroxyphenols probably the most reactive towards carbon dioxide or related molecular ones Species at normal temperatures and pressures in an aqueous medium.

A significant reaction here is that in which carbon dioxide participates in electrophilic substitution in an activated position on the benzene ring of the phenol. This is the following type of reaction: Pressure is required to achieve reaction with monohydroxyphenol; however, if the activation of the ring positions is enhanced with two or three hydroxyl groups, as in the polyhydroxyphenols, then the reaction proceeds under ordinary conditions. The electron densities at different ring positions in hydroquinone, resorcinol and catechol show this: Of these three dihydroxyphenols, resorcinol is apparently the most reactive towards electrophilic substitution because it has three positions with very high electron densities. Carboxylation with carbon dioxide gives the following two resorcylic acids: In general, the electron densities at the ring positions of the phenols are remarkably influenced by the ionization state of the hydroxyl groups.

As the pH of the medium increases, the hydroxyl groups undergo ionization closer and the electronic charge flow to the benzene ring increases accordingly. One Increasing the pH therefore favors electrophilic substitution at suitable ones Ring positions.

When the lignite treated by the process of the co-pending application is in its wet plastic state, it consists of many small fragments dispersed in an aqueous phase, each fragment having freshly cleaved faces with exposed phenols which become attached to the main polymer backbone of the coal. If the carbon faces are in close proximity, the electrophilic substitution with carbon dioxide could involve a phenol pair, one on each side, creating a bridging structure rather than a carboxylic acid group attached to only one ring. The reaction can be represented as follows: H OH OH II ou OH O OH Coal t Coal Kohl u - Ot ohle + c + - CEI + H2 II OHH O If the coal sides are not close enough to each other, a reaction can still occur; however, it is expected that this will result in inactivation of the phenolic sites without achieving densification bond.

There is always sufficient carbon dioxide in the various types of carbon for a substantial response to occur. The aqueous medium is important in the plastic state of coal to facilitate bridge bonding, such as in other chemical reactions the solvents.

The object of the present invention is both the speed as well as increasing the degree of compaction of lignite. According to the invention this is achieved through careful selection and controlled use of additives. In a preferred embodiment, the invention relates to the use of additives for the refinement of lignite, which according to the co-pending patent application 24294/84 has been treated.

The brown coal can also by the method, which is shorter Treatment times used as in the above-mentioned supplementary application PG 9283, including a method in which the coal is subjected to shear forces and extruding in a continuous manner, for example in a Sigma kneader HKS 50, manufactured by Janke and Kunkel GmbH & Co.

KG, IKA-Werk Biengen, is suspended.

A wide range of additives are suitable and effective for improvement the rate and extent of compaction, such as by means of crush strength and abrasion resistance of the produced densified material was measured.

It should be noted that different types of lignite have different Show responsiveness to additives.

These responsibilities are different because of the special Properties of the coals, the most important of which is probably the natural one pH of a particular coal is.

Although the advantages achieved by various additives are special advantageous in lignite refining processes, as in the above co-pending Patent application disclosed, can also benefit from these additives other lignite refining processes, for example a process carried out by The State Electricity Commission of Victoria is investigating which is the manufacture a pumpable coal slurry, which is sun-dried for several months will be expected.

Suitable additives according to the invention can generally be of the following Kind of be: 1. Additives to increase the pH.

2. Additives to improve bridge bonding.

3. Additives which provide electrostatic bridging capacity in the form of divalent cations, as are present in magnesium and calcium compounds, for example according to the formula Coal 0 mm O t coal Xg O) ftQ The addition of lime to peat during drying and briquetting is known. According to the invention, lime is not regarded as an additive.

Preferred additives are alkali metal hydroxides, ammonium hydroxide, Alkali metal carbonates, the oxides of base metals and transition metals, aldehydes and certain carbonyl compounds.

It has been found that alkali metal hydroxides, preferably in the range from 0.05 to 5% by weight, particularly preferably in the range of 2% by weight, the strength and remarkably increase the abrasion resistance of compacted lignite pellets.

Ammonium hydroxide - a weak base -, preferably in the range of 0.05 to 5.0% by weight, particularly preferably in the range from 0.5 to 2% by weight similar beneficial effects as alkali metal hydroxides. In this case it won't only neutralizes the acidity of the coal with the advantages described above, but it is also possible that the aqueous ammonia phase has an increased activity such dissolved species, based on carbon dioxide, which act as bridging molecules between Coal particles are active, supplies.

This addition is particularly beneficial in cases where the end use the compressed coal excludes the addition of metal ions. Using a Ammonia gas atmosphere during the kneading of the coal is also very beneficial.

Alkali metal carbonates, for example sodium carbonate, also increase the hardening rate, the crushing strength and the abrasion resistance of the lignite pellets, the amounts added being preferably 0.05 to 5.0% by weight, particularly preferably 1 to 2% by weight. This addition has a twofold effect, since it reduces the acidity of the acidic coals and also provides a considerably increased activity of the aqueous species with respect to the carbonate ion, ie

Alkaline earth hydroxides have an effect similar to that above mentioned additives, if they are added preferably in concentrations of 1 to 5 wt .-% will. This also applies to alkaline earth carbonates (either precipitated or natural), in this case the concentration range is preferably 1 to 20% by weight.

Finely divided magnesium and calcium hydroxides are very effective Additions with a double effect. The pH of the acidic coals becomes beneficial increased, while the divalent cations under electrostatic bridge bonds Use of acidic (including phenolic) groups on neighboring coal particles form.

Finely ground, natural magnesite and calcite, although they are relative are insoluble are also effective additives. They cause a neutralization of the acids found in some types of carbon, magnesium and calcium ions provide available for electrostatic bridge bonding and provide a further feed of carbon dioxide species in solution.

Simple aldehydes and other small molecules of carbonyl compounds in connection with different bases also improve the hardening speed, the strength and abrasion resistance of the compacted lignite pellets, where the concentration of the additive is preferably in the range from 1 to 5% by weight. Loading preferred aldehydes are formaldehyde and acetaldehyde, in particular the former.

In this case, small molecules of carbonyl compounds should be in be able to use carbon dioxide in providing bridges between to add the coal particles. The effectiveness is a function of the pH, which the activity of the polyhydroxyphenol towards electrophilic substitution certainly.

Other suitable carbonyl compounds are urea and formamide. Bases for use with these additives include the alkali hydroxides and ammonium hydroxide a. = wexamethylefltetramill, hexamine (derived from formaldehyde and ammonium hydroxide) improves the curing speed, strength and abrasion resistance of the compacted lignite pellets, the added amounts preferably from 1 to 5 % lie.

Hexamine, which slowly yields ammonium hydroxide and formaldehyde on hydrolysis, should provide both a neutralizing effect and a supply of bridging molecules: Base metal and transition metal oxides can also be used as additives, preferably in the range 5 to 70% by weight, and result in dried products which are often hard, dark, glassy solids and in some cases a significant increase in strength compared to the original coal.

The following examples illustrate preferred embodiments of the Invention. All relate to each other Percentages based on dry weight.

Example 1 (alkali metal hydroxides) Loy-Yang charcoal from the medium-dark Lithotype has a pH of 3.2 when wet, plastic, and it's closed expect it to be particularly suitable for base addition. 200 g of this coal were triturated for 5 h in a Sigma kneader with 2% by weight of sodium hydroxide added. The plastic mass obtained (pH 5.7) was in a hand-operated screw extruder extruded to make rods 3mm in diameter cut into lengths of 5 mm and dried in still air at 20 ° C. for one week became. Compressive strength measurements on the dried, cylindrical pellets resulted average values of 48 MPa. In contrast, pellets resulted in which under identical Conditions established, but without the addition of sodium hydroxide, were an average Strength of 11 MPa.

Morwell coal has a natural pH of about 5.4. When treating, as described above for the Loy-Yang charcoal, with the addition of 2% sodium hydroxide, the resulting material cured quickly and was difficult to extrude. A repetition of the experiment with an addition of 2% water and a reduction in the kneading time from 5 to 1.5 h allowed an extrusion before pellets, which after drying a possessed an average compressive strength of 41 MPa.

Pellets without addition gave an average compressive strength of 29 MPa.

Maddingley charcoal has a natural pH of 7.1.

Pellets obtained therefrom by the same treatment as above for the Loy Yang charcoal described showed little improvement the Compressive strength compared to pellets which had no added Contained sodium hydroxide.

Example 2 (ammonium hydroxide) 200 g of medium-dark Loy-Yang charcoal Lithotype (natural pH 3.2 in the wet plastic state) was made in a Sigma kneader for 5 h triturated with 1% aqueous ammonia (specific weight 0.880) as an additive. The pH was increased to 6.2 by this treatment. Then pellets (diameter 10 mm, length 10 mm) by extrusion with a hand-operated screw extruder and dried in calm air at 20 ° C. for one week. These pellets gave an average Compressive strength of 35 MPa compared to similar pellets without the addition which had an average compressive strength of 5 MPa. Smaller pellets (diameter 3 mm, length 5 mm during extrusion) even resulted greater compressive strengths, being the average compressive strength for the material with 1% ammonium hydroxide addition was 63 MPa. Similar pellets with no additive resulted an average compressive strength of 11 MPa.

The increased compressive strength of pellets with a smaller diameter, compared to those of a larger diameter, can be applied to the considerably larger ones Pressure which develops in the extrusion device when the nozzle is pushed with a large Diameter is replaced by a nozzle with a smaller diameter be.

200 g Morwell charcoal (N 3372 dark lithotype) with a pH of 4.0 when kneaded in an atmosphere of ammonia gas resulted in an increase in pHs to 7.6. However, the hardening took place very quickly and the plastic mass became too stiff to extrude. In the kneading machine machine became a considerable one Developed heat, which not only broke the original coal structure, but also destroyed new structures that became apparent as the compaction process progressed formed.

Example 3 (alkali metal carbonates) 200 g of medium-dark Loy Yang charcoal Lithotyp (pH 3.4) were 5 h in a Sigma kneader with the addition of 0.2 wt .-% sodium carbonate kneaded. The product was extruded in a hand-operated screw extruder, to give pellets 3mm in diameter and 5mm in length, which were air-dried at 20 OC for one week. The average compressive strength the pellet was 19 MPa compared to a value of 11 MPa for pellets without Additive. For pellets produced under similar conditions with an addition of 0.4% Na2C03 the average value was 33 MPa.

Maddingley charcoal has a natural pH of around 7.1. When pellets with a diameter of 3 mm using the above conditions, however with 2% addition of sodium carbonate, the average compressive strength was 38 MPa compared to 29 MPa for no additive pellets.

Example 4 (alkaline earth hydroxides) 200 g of medium-dark Loy Yang charcoal Lithotype was made in a Sigma kneader for 5 hours with 5% by weight of fine, precipitated magnesium hydroxide kneaded. The product was extruded in a hand-operated screw extruder, to give pellets 3mm in diameter and 5mm in length, which were dried in calm air at 20 ° C. for one week. The average liche Compressive strength was 61 MPa compared to 11 MPa for similar pellets which did not contain any additive. When calcium hydroxide was used as an additive, were the average compressive strengths 39 and 65 MPa for pellets which are 2% and Contained 5% calcium hydroxide.

Example 5 (alkaline earth carbonates) 200 g of medium-dark Loy Yang charcoal Lithotyp was kneaded in a Sigma kneader for 5 hours with 5% by weight of fine magnesite. The extruded pellets (3 x 5 mm), after drying in still air at 20 OC an average compressive strength of 20 MPa over a week. In contrast similar pellets with no added magnesite had an average compressive strength of 11 MPa.

200 g of Morwell carbon (H 1317 bore, pH 4.6) were through the above Process converted into compacted pellets with a diameter of 10 mm (during extrusion).

These pellets gave an average compressive strength of 23 MPa. When similar pellets by kneading the coal with 20% fine, precipitated Magnesium carbonate were produced, the average compressive strength was at 36 MPa.

Similar tests were carried out on Morwell coal from an N 3372 well. In two separate tests, 5 z of fine magnesite and fine calcite were found used as additives, and pellets with a diameter of 10 mm were extruded. The dried pellets gave an average compressive strength in both cases of 39 MPa. In contrast, similar pellets without addition gave an average value of 22 MPa.

Example 6 (formaldehyde and other simple aldehydes) in the following The process measures described in Examples 1 to 5 were used used (i.e.

H. Kneading, extrusion to produce pellets of either 3 or 10mm diameter followed by air drying).

Medium-dark lithotype Loy-Yang charcoal (pH 3.2) gave pellets with an average compressive strength of 5 and 11 MPa, each for 10 mm and 3 mm pellets. An addition of 2% sodium hydroxide while mixing increased these values to 18 and 48 MPa, respectively.

More samples in which 5% formaldehyde was added as well 2% sodium hydroxide, increased these values to 32 and 60 MPa, respectively. The latter mixes hardened very quickly and in some cases were impossible to extrude. These products took the form of very tough, resinous solids.

When acetaldehyde was substituted for formaldehyde, the average were Compressive strengths 22 resp.

51 MPa for 10 mm or 3 mm pellets.

The neutral Maddingley charcoal (pH 7.1) did not require pH adjustment, when aldehydes were used as additives. For example, it has been found that 1% formaldehyde alone accounts for the average crush strength of 3 mm pellets 46 MPa, while it was 29 MPa for pellets with no additives.

As an alternative measurement of the strength of the compacted types of coal An attrition test was carried out in which a 5 g sample of the pellets in 30 ml of water Hurled 16,000 times in a closed 250 ml cylinder or

was filmed. Loy-Yang charcoal of the medium-dark lithotype resulted a recovery of only 9% of the fragments larger than 1 mm. When adding 2 % Sodium hydroxide increased the recovery of the fragments greater than 1 mm to 81%, and with further addition of 5% formaldehyde increased the recovery to 96%. The corresponding values for Morwell coal were 79, 86 and 91%.

Example 7 (hexamine) The reagent hexamine gives slowly on hydrolysis Ammonium hydroxide and formaldehyde and should therefore both have a neutralizing effect as well as a supply of bridging molecules. The attempts were made with Loy Yang medium dark charcoal using those described in Examples 1-6 Process carried out with 5% hexamine as additive. The addition caused an increase the pH of the mixtures from 3.2 to 5.1 and an increase in the average Compressive strength of the 3 mm pellets from 11 to 29 MPa. The abrasion resistance of the compacted pellets was also greatly increased, from a 9% recovery of fragments larger than 1 mm to a 68% recovery.

Example 8 (base metal and transition metal oxides) It has been shown that that it is possible to use very high amounts of certain finely divided metal oxides in Lignite species during the compaction process as described in Examples 1 to 7 are to be incorporated. The dried products are often hard, dark, glassy solids, and in some cases show a substantial increase their strength compared to the original coal.

Morwell carbon (N 3372) (pH 3.8) with 20% additional water Pellets (10 mm diameter) with a Compressive strength of about 21 MPa. When 10% cobalt oxide was added, the strength increased to about 25 MPa and increased further to about 31 MPa on pyrolysis to 500 OC in an inert The atmosphere. The coal alone shows no increase in strength upon pyrolysis.

Loy Yang (dark) charcoal (pH 3.2) yielded pellets (3 mm in diameter) with a compressive strength of about 11 MPa.

With 10% CuO, the dried pellets gave a compressive strength of about 47 MPa.

Loy Yang (dark) coal with 10% fine Fe 2 O 3 gave compressive strengths of about 22 MPa (pellets with a diameter of 3 mm). More samples, the 30, Containing 50 and 75% Fe203 all gave hard, coherent pellets, indicating that the bond is still effective in spite of the large proportions of inorganic Material.

Claims (14)

Process for the production of compressed coal pellets Patent claims 1. Process for the production of compressed coal pellets with improved physical Properties in which the coal passes a shear attrition stage followed by extrusion and drying stages, characterized in that an additive in the coal which is subjected to the shear attrition stage is incorporated, wherein the additive is selected from one or more components of the following group becomes: alkali metal hydroxides, alkaline earth metal hydroxides, ammonium hydroxide, alkali metal carbonates, Alkaline earth metal carbonates, oxides of base metals, oxides of transition metals and carbonyl compounds of small molecules. 2. The method according to claim 1, characterized in that the additive is selected from alkali metal hydroxides and / or alkali metal carbonates and in in an amount of 0.05 to 5% based on the dry weight of the coal will. 3. The method according to claim 2, characterized in that the additive Sodium hydroxide and the charcoal in an amount of about 2% based on that Dry weight of coal, is added. 4. The method according to claim 2, characterized in that the additive comprises an alkali metal carbonate which is used in an amount of 1 to 2% will. 5. The method according to claim 1, characterized in that the additive aqueous ammonia, which the coal in an amount of 0.05 to 5% ammonia per dry weight of coal is added. 6. The method according to claim 4, characterized in that the amount of ammonia is 0.05 to 2%. 7. The method according to claim 1, characterized in that the additive an alkaline earth hydroxide, which in an amount of 1 to 5% based on the dry weight of the coal, is used. 8. The method according to claim 7, characterized in that the additive finely divided magnesium hydroxide and / or calcium hydroxide. 9. The method according to claim 1, characterized in that the additive an alkaline earth carbonate, which in an amount of 1 to 20% based on the dry weight of the coal, is used. 10. The method according to claim 9, characterized in that g e k e n n -z e i c h n e t that the additive includes finely divided magnesite or calcite. 11. The method according to claim 1, characterized in that g e k e n n -z e i c h n e t that the addition of formaldehyde and / or acetaldehyde in an amount of 1 - 5%, based on the dry weight of the coal. 12. The method according to claim 1, characterized in that g e k e n n -z e i c h n e t that the additive includes urea and / or formamide, which together with a or more alkali metal hydroxides and / or ammonia is used. 13. The method according to claim 1, characterized in that g e k e n n -z e i c h n e t that the additive includes hexamine. 14. The method according to claim 1, characterized in that g e k e n n -z e i c h n e The fact that the addition was chosen from base metal oxides and / or transition metal oxides which is in an amount of 5 to 70%, based on the dry weight of the coal, be used.