GB2066285A - Binder for coal briquettes - Google Patents

Abstract

A binder for use in briquetting coal-containing material is obtained by disintegrating comminuted coal and/or similar carbonaceous raw material with a hydrocarbon mixture as solvent using elevated temperature and pressure conditions, distilling off between 5 and 20% of readily volatile fractions from the resultant high aromatic, coke oven pitch-like by-product to give a hard pitch-like product having a softening point (according to Kramer-Sarnow) of 120 to 200 DEG C, and adjusting the softening point to 50 to 100 DEG C with a hydrocarbon fraction boiling in the boiling point range 220 to 450 DEG C obtained from coal tar and/or by pyrolysis of petroleum fractions.

Description

SPECIFICATION Binder for coal briquettes The invention relates to the use of thermoplastic, pitch-like coke oven by-products for producing coal briquettes.

On account of the long-term increasing scarcity of petroleum and natural gas; coal will in the future become more important as a fuel. Coal is conveniently employed in briquette form for heating buildings and for other heat provision purposes.

Coaltar pitch in particular was used in the past as a briquetting agent. Coaltar pitch occurs as a residue of tar distillation in the form of a thermoplastic product having a Krämar-Sarnow softening point (hereinafter termed S.P.) of about 68-75"C (see H.-G. Franck, G. Collin, Steinkohlenteer, Berlin 1968, P. 96). This pitch has excellent binding properties and can thus be used as a briquetting pitch for producing coal briquettes. The briquettes produced with coaltar pitch have however the disadvantage that they produce too much smoke when burnt.

Attempts have therefore not been lacking to replace coaltar pitch by a relatively smokeless binder.

In particular, binders based on oil asphalt (see Zakar, Toth, Brennstoff-Chemie 39, 1958, P.373) are of practical importance as substitution products for coaltar pitch in producing coal briquettes. Briquettes made using oil asphalt as binder produce less smoke but have the following disadvantages compared with briquettes bound with coaltar pitch: binders based on asphalt generally have a higher sulphur content and thus give rise to a higher sulphur dioxide emission compared with coaltar pitch. Also, on account of the flatter viscosity-temperature curve of the asphalt, a longer cooling time is necessary after the briquetting process in order to impart the necessary cold compressive strength to the briquette. A further disadvantage of asphaltbound briquettes is the lower hot compressive strength compared to pitch-bound briquettes.

Thus, when the briquettes are burnt in a furnace there is a marked tendency for them to disintegrate, which interferes with a regulated and efficient combustion.

A further disadvantage is the uncertainty as regards longterm availability of asphalt.

The described disadvantages do not arise in the case of the binder described in German Offenlegungsschrift 2708495. This binder is obtained by adjusting a coaltar hard pitch to a S.P.

of 50-100"C, in particular 65-75"C, with hydrocarbon fractions obtained from coaltar or by pyrolysis of petroleum fractions.

Since the availability of coaltar pitch, which also serves as the basis for the production of improved briquette pitch according to German Offenlegungsschrift 2708495, is limited for briquetting purposes, there is a need for binders having the recognised good binding property of coaltar pitch and which moreover are sufficiently smokeless with regard to environmental factors. It was therefore the object of the present invention to find a binder for coal briquetting which combines the good binding properties of coaltar pitch with the advantages of low smoke emission, and whose Isiig-term availability is ensured.

According to the invention this objective is achieved by using a binder for briquetting coals and coal-containing materials which is obtained by distilling off between 5 and 20%, preferably 8-1 5% of readily volatile constituents from a high aromatic, pitch-like coke oven by-product obtained by disintegrating comminuted coal and/or similar coal-containing raw materials with hydrocarbon mixtures as solvent using elevated temperature and pressure conditions, and the hard pitch-lik.3 product obtained, which has a S.P. aSP. of 120-200"C, preferably 130-160"C, is adjusted to a .P. of 50-1 00C, preferably 65-75"C, with hydrocarbon fractions having a boiling point range of 220-450"C, preferably 260-400"C, derived from coaltar or obtained by pyrolysis of petroleum fractions.

The anthracene oil obtained after separating the crude anthracene by crystallisation is preferably used as the hydrocarbon fraction for adjusting the desired S.P. of the binder pitch (see H.-G. Franck, G. Collin, loc. cit. 1, P. 57). The boiling point range of this solvent is from 300 to 460 C. Appropriate petroleum-derived fractions obtained from cracking or refining processes may likewise be used to adjust the desired S.P.

The type of coal to be formed into briquettes may vary over a wide range. Thus, brown coals, bituminous coals and anthracite may be briquetted.

The binders used according to the invention impart, during the coal briquetting, comparably good cold compressive strengths compared with coaltar pitch or the binders obtained from coaliar hard pitch according to German Offenlegungsschrift 2708495, which correspond to a force according to the described experimental conditions of > 2500 N.

It has however surprisingly been found that the binders that can be produced on the basis of disintegrated coal also have extremely low smoke emission levels and thus ensure an environmentally satisfactory combustion. A further advantage is the markedly reduced smell experienced when handling briquettes produced from disintegrated coal.

The preparation of the binders is described in Examples 1 to 3. The preparation of the high aromatic coke oven by products used as starting pitch is the subject of an earlier patent application P 29 35 039.8 in the name of the applicants. It thus follows that coal containing a higher or lower content of volatiles is disintegrated with aromatised residues obtained from the steam pyrolysis of petroleum fractions in combination with coal-derived aromatic mixtures having an average boiling point above 350"C as complementary solvent, optionally with the addition of further solvents. In order to adjust the desired S.P., the filtered anthracene oil formed during the anthracene processing is used in the following examples (loc. cit. 1, P. 57).

Examples 4 and 5 illustrate the advantages of the binders according to the invention.

In the Table the smoke figures for the binders produced according to the invention are compared with the hitherto recommended coal-based briquetting agents. The favourable smoke behaviour of the binder according to the invention can be seen by comparison with traditional coaltar pitch as binder. To determine the cold compressive strengths and smoke figures, cylindrical briquettes (diameter 4 cm, height 4 cm) were produced by intimately mixing 94.5 parts of anthracene (screening analysis: 0-05 mm = 3%; 0.05-2 mm = 17%; 0.2-0.5 mm = 25%; 0.5-2.0 mm = 55%) and 5.5 parts of binder, and compacting the briquettes in a stamping press for 1 second at 150 C using a pressure of 4000 N/cm2. The cold compressive strengths were determined in an apparatus for measuring compressive strength, by measuring the force required to destroy the briquettes.

The nephelometric method has proved suitable for determining the smoke figures. In this method the turbidity of a constant air stream at 600"C in a smoke-stack draught is optically measured. The smoke behaviour of the briquettes can be quantitatively described by this method.

Example 1 In accordance with the method described in the earlier patent application P 29 35 039.8, a pitch-like coke oven by-product is produced by disintegrating 30 parts by weight of open burning coal (Westerholt type, Ruhr) with 5 parts by weight of pitch distillate, 35 parts by weight of pyrolysis residue obtained from the cracking of gas oil, 10 parts by weight of coaltar pitch, and 20 parts by weight of pitch distillate from the heat/pressure treatment of coaltar pitch.The mixture is subjected to a reaction temperature of 370 C, a maximum pressure of 36 bars, and a reaction time of 3 hours. 1 5 parts by weight of the pitch obtained in this way was topped as a light boiling fraction and 72 parts by weight of the hard pitch thus formed and having a S.P. of 145or were adjusted to a softening point of 70"C with 28 parts by weight of filtered anthracene oil.

The nephelometrically determined smoke figure was 1843 + 247. The sulphur content is 1.25%. The cold compressive strength is > 2500 N.

Example 2 The procedure of Example 1 is adopted , but the following solvent mixture is however used for the disintegration: 10 parts by weight of pitch distillate, 20 parts by weight of residue pitch from naphtha pyrolysis (S.P. 88 C), 10 parts by weight of pyrolysis oil from the steam cracking of gas oil, and 30 parts by weight of pyrolpsis oil from the steam cracking of naphtha. 1 3 parts by weight of readily volatile constituents are topped from the pitch obtained in this way. The hard pitch having a S.P. of 135"C was adjusted to a softening point of 69"C with 37 parts by weight of filtered anthracene oil. The nephelometrically determined smoke figure was 1615 + 250. The sulphur content is 0.99%.The cold compressive strength is > 2500 N.

Example 3 The procedure of Examples 1 and 2 is adopted. 30 parts by weight of free-burning coal ("Ensdod" type, Saar) is used as coal. The solvent mixture consists of 10 parts by weight of pitch distillate from the heat/pressure treatment of coaltar pitch, 30 parts by weight of pyrolysis oil from the steam cracking of naphtha, and 10 parts by weight of pyrolysis oil residue from the steam cracking of naphtha (S.P. 88"C). A hard pitch having a S.P. of 132"C is obtained by topping 8 parts by weight of light boiling constituents. This hard pitch was adjusted to a S.P. of 72"C by adding 27 parts by weight of filtered anthracene oil.

The smoke figure is 1446 + 240. The sulphur content is 0.67%. The cold compressive strength is > 2500 N.

Example 4 (Comparison Example) A pitch produced according to Patent Specification DT-OS 2708495 on a coaltar basis from hard pitch and filtered anthracene oil and having a S.P. of 70"C is used as briquetting agent.

The smoke figure was found to be 1520 f 250.

Example 5 (Comparison Example) A coaltar pitch obtained from the primary distillation of coaltar and having a S.P. of 73"C gave a smoke figure of 3100 + 500.

Table--Smoke figures of briquette binders Binder according to Example 1: (coal disintegration) 1 843 + 247 Binder according to Example 2: (coal disintegration) 1 61 5 i 250 Binder according to Example 3: (coal disintegration) 1446 + 240 Binder according to Example 4: (DT-OS 2708495) 1520 + 250 Binder according to Example 5: (coaltar pitch) 3100 + 500 The patent application no. P 29 35 039.8 is a German patent application corresponding to British patent application no. 8021603.

Claims (4)

1. A method for briquetting coal-containing material using a binder, wherein the binder is obtained by disintegrating comminuted coal and/or similar carbonaceous raw material with a hydrocarbon mixture as solvent using elevated temperature and pressure conditions, distilling off between 5 and 20% of readily volatile fractions from the resultant high aromatic, pitch-like coke oven by-product to give a hard pitch-like product having a softening point (according to Kramer Sarnow) of 1 20 to 200"C, and adjusting the softening point to 50 to 100"C with a hydrocarbon fraction boiling in the boiling point range 220 to 450"C obtained from coaltar and/or by pyrolysis of petroleum fractions.

2. A method according to claim 1, in which from 8 to 15% of readily volatile components is distilled off from the high aromatic, pitch-like coke oven by-product.

3. A method according to claim 1 or 2, in which the pitch-like coke oven by-product is obtained by disintegrating coal or like carbonaceous material with an aromatic residue from the steam pyrolysis of petroleum fractions in combination with a coal-derived aromatic mixture having an average boiling point above 350"C as complementary solvents, optionally with the addition of further solvents, using a pressure of up to 50 bars and a temperature between 250 and 420 C.

4. A binder obtained by disintegrating comminuted coal and/or similar carbonaceous raw material with a hydrocarbon mixture as solvent using elevated temprature and pressure conditions, distilling off between 5 and 20% of readily volatile fractions from the resultant high aromatic, pitch-like coke oven by-product to give a hard pitch-like product having a softening point (according to Kramer-Sarnow) of 1 20 to 200 C, and adjusting the softening point to 50 to 100"C with a hydrocarbon fraction boiling in the boiling point range 220 to 450 C obtained from coltar and/or by pyrolysis of petroleum fractions.