GB2161175A - Improvements in the production of metallurgical coke - Google Patents

Abstract

Pellets of metallurgical coke are produced from a mixture comprising a material of less than 2 mm and selected from non-coking coal, slightly coking coal, oxidised coking coal, coal and coal dust, coking coal of less than 4 mm and coal tar.

Description

SPECIFICATION Improvements in the production of metallurgical coke This invention relates to improvements in the production of metallurgical coke. More particularly it concerns improvements in the production of pellets for the charging of coke ovens which ensures a higher quality product.

There are several important advantages in using pellets for the production of metallurgical coke. Firstly, this practice permits the density of the charge to be increased, thus increasing the production of the ovens. Secondly it enables types of carbonaceous material to be used which could not otherwise be used for charging of coke ovens, either because of their poor quality or because of their fine particle size.

With the difficulties affecting the steel industry and the rising costs of good coking coals, these are certainly important advantages. Numerous attempts have been made to increase the density of coke oven charges and/or even to use non-coking coals. The approaches adopted have involved briquetting or pelletizing the coal before supplying it to the ovens, but they have not been very successful chiefly because of the high cost of briquetting and because of the types of binders used for pelletizing.

The present invention overcomes these drawbacks by providing several ways of cutting production costs, whilst improving the properties of the end product.

According to this invention, there is provided a process for the production of metallurgical coke, in which pellets are prepared from materials selected from the group including non-coking coals, slightly-coking coals, oxidized coking coals, coking coals and coal and coke dusts, using a coal distillation derivative as a bridging liquid, in which process the bridging liquid comprises from 7 to 15% by weight of coal tar, and in which, in the preparation of the pellets, at least one coal selected from non-coking coal, slightly-coking coal, oxidized coking coal and coal and coke dust, all of particle size finer than 2 mm, is mixed at a concentration of from 50 to 90% with a coking coal of particle size finer than 4 mm, the pellets thus produced ranging in size from 5 to 20 mm and preferably being mixed with coking coal for supply to the coke ovens so that the concentration of non-coking coal in the mix amounts to from 30 to 50% by weight.

The pellets produced in this manner are conveniently mixed with coking coal in proportions such that the concentration of non-coking coal in the final mix is from 30 to 50% by weight.

By employing this mixture of pellets and coking coal in the coke ovens, an increase in charge density of up to 20% can be achieved as compared with a charge containing no pellets, thus increasing production and, surprisingly, productivity also (kg m-3h-1).

It has also been found, surprisingly, that the quality of the coke produced in this way is better than that resulting from a charge consisting solely of coking coal or from a charge containing only pellets of non-coking coal.

If it is desired solely to increase the charge density and perhaps make use of fine or very fine fractions of coking coal and coke, it is also possible to form pellets exclusively from these salvaged materials. However, owing to the unfavourable expansion characteristics and gas pressures developed by pellets made from coking coal along, these should preferably form not more than 10 to 40% of the coke oven charge, to avoid the occurrence of dangerous conditions during coking, such as excessive pressure on the walls of the ovens, for instance, and decreased shrinkage of the coke cake.

Of the various salvaged products which can be used in this invention, special importance attaches to coal and coke dusts collected by equipment installed in modern pollution control plants, charging and discharging points and in dry-process coke-quenching plants.

It should be stressed that, in the coking phase, most of the tar used in the pelletizing process is recovered. The only additional costs incurred, therefore, are those concerned with the mechanical aspect of the pelletizing operation, and these are more than covered by the higher productivity of the coke ovens and the fact that coals can be used which could not otherwise be considered due to their quality or particle size.

In order that the invention may be more fully understood, reference will now be made to some examples of coke production processes, given purely by way of example. These examples are in no way intended to be restrictive as regards the scope and range of the invention.

EXAMPLE 1 By way of comparison, a coking coal having the following characteristics-mean size 2.4 mm, volatile matter 25.2% by weight, ash 5.9%, total sulphur 0.83%, free swelling index 7, maximum Giesler fluidity 310 ddpm and maximum expansion 35%-was supplied to a coke oven at a dry charge density of 695 kg/m3.

After conventional coking (in a pilot oven with a charge width of 450 mm, wall temperature of 1030"C and distillation time of 18.7 hours) and quenching, a coke with Micum indices of M40=79.2, M,o = 7.8 was obtained, productivity being 26.2 kg m-3h-1.

EXAMPLE 2 A non-coking coal having the following characteristics-mean size 0.35 mm, volatile matter 31.4% by weight, ash 4.65%, total sulphur 1.2%, free swelling index 0, maximum Giesler fluidity 1 ddpm and expansion = contraction only-was mixed with the coal as per Example 1 in quantities of 50%, 75% and 90% by weight, and the mixtures were pelletized using 9.5% coal tar and 1 % coal tar pitch (by weight of the final weight of the pellets produced) as a bridging liquid.

Pelletization was performed in a 3m diameter pan, rotating at 12 rpm and inclined at 45" to the horizontal. Pellets ranging from 7 to 18 mm in size were obtained.

Each of the pellet compositions produced was mixed with the coal as per Example 1, so that the non-coking coal accounted for 30%, 40% and 50% of the charge, by weight.

After coking under the same conditions as in Example 1, cokes having the characteristics indicated in the following table were obtained.

Percent Percent Charge X Productivity non-coking non-coking density coal in coal in N pellets charge kg/m3 kg/m3h M40 10 30 710 26.4 81.3 6.4 50 40 730 27.2 80.7 6.6 50* 742 27.5 80.4 6.6 30 710 26.4 81.0 6.8 75 40 730 27.3 80.4 6.8 50 746 27.0 80.3 6.9 30 710 26.4 80.8 6.9 90 40 730 27.3 80.3 7.0 50 746 27.6 79.9 7.2 i * Charge = 100% pellets

Claims (4)

1. A process for the production of metallurgical coke, in which pellets are prepared from materials selected from the group including non-coking coals, slightly-coking coals, oxidized coking coals, coking coals and coal and coke dusts, using a coal distillation derivative as a bridging liquid, in which process the bridging liquid comprises from 7 to 15% by weight of coal tar, and in which, in the preparation of the pellets, at least one coal selected from non-coking coal, slightly-coking coal, oxidized coking coal and coal and coke dust, all of particle size finer than 2 mm, is mixed at a concentration of from 50 to 90% with a coking coal of particle size finer than 4 mm, the pellets thus produced ranging in size from 5 to 20 mm and preferably being mixed with coking coal for supply to the coke ovens so that the concentration of noncoking coal in the mix amounts to from 30 to 50% by weight.

2. A process according to claim 1, wherein the bridging liquid used in the pelletizing operation includes coal tar pitch in a concentration of less than 2% by weight.

3. A process according to claim 1 or 2, wherein pellets consisting wholly of coking coal are used in the mix for supply to the coke ovens in a concentration of from 10 and 40% by weight.

4. A process for the production of metallurgical coke, substantially as hereinbefore described with reference to Example 2.