US2359581A - Method of and mixture for coking - Google Patents

Description

Patented Oct. 3, 1944 Horace. 0. Porter, Philadelphia, Pa.

No Drawing. Application November 26, 1940,.

Serial No. 367,232

3 Claims. ((31. 202-.33)

This invention relates to coking coal, and more particularly to an improved process for coking coal and to animproved coal mixture for coking purposes to improve the quality and yield of the coking operation and to eliminate destructive expansion properties of coking coal.

In carrying out a coking operation bituminous coal is subjected to heat to drive off volatile constituents of the coal and to transform. the coal into a form called coke. The products of the distillation .are generally recovered as coke oven gas, tar, ammonia, and other products. The coke itself is used primarily for metallurgical purposes and its physical structure must be so strong that it does not deteriorate in handling nor crush under the weight of the material being treated with the coke. Also, the coke must me sufficiently porous to provide a larg contact surface with gases passed through the coke during the process of utilization.

During the coking operation the coal is heated and its .temperature is raised to the-point where decomposition and distillation of materials making up the coal takes place. At this temperature some of the materials fuse or softenso that the coalbecomes afluid mass. As the volatile constituents form in and escape from this fluid mass, gas pockets form in it and as the heat treatment continues, the mass solidifies in a porous condition. Coal which has the property of thus agglutinatin during the heating operation is called coking coal and such property is neces sary in order to obtain a coke which has a strong physical structure.

The degree of the fluidity of the mass during the coking operation is important and difierent coals have different degrees of fluidity. As a general rule, th higher the percent of Volatile constituents in the coking coal the greater will be its fluidity durin the coking operation. If the fluidity is not sufllciently high the gas formed during the coking treatment is not able to pass 01f freely from the mass and creates a pressure which causes the mass to expand or create expansion pressure, largely sidewards, so as to crack, bulge, distort or weaken th walls of the coke oven. Coking coals having such a low fluidity characteristic during coking are called expansive coals. Although these coals give a higher percent yield of coke per ton of coal charged (because of the relatively small loss of volatile matter) they are undesirable when coked alone because of the damage they cause to the coke ovens. Hence coking coal having a low percentage (for example 14-23%) of volatile constituents. are. generally. considered as, unuseable for coking, except in mixture with contracting coals.

Coking .coals having, more than a small expansive characteristic are generally mixed with-a so-called contracting or shrinking? coking coal to insure suflicient fluidity to avoid dangerous expansion and to improve coke quality. Such a shrinking? coal is a coal having a relatively highvolatile content, i. e. 23-38% and acorrespondingly high fluidity characteristic. Th useof this'shrinking coal, however, reduces thecoke yield per ton of coal chargedbecause of the distillation of the volatile constituents.

By .the practic of the present invention it is possible to use normally highly. expansive coals in coking ovens without damaging. the oven and.

without admixing coals of higher volatile content and greater fluidity. With such use. of expansive 10w volatile coal the quality and yield of a the coke is improved.

I have discovered that the normally destructive expansive. properties of alow volatile coking coalhaving .a low fluidity characteristic may be eliminated by admixing with it a certain .typeef naturally. alteredlow-volatile coal that is non.-.

coking (non-agglutinating) or only lightly coking coal and that such a coal mixture gives a high coke yield of good physical structure without damaging the oven walls. Such expansive coals are found in many coal fields such as, for example, the Huntingdon-Broadtop field, Rockhill, and others, in Pennsylvania; several fields in Cambria, Clearfield and Indiana counties in Pennsylvania; in the Pocahontas field and others of West Virginia; and many other fields.

Goals of the low-volatile, non-agglutinating (or slightly agglutinating) type are coals which have been weathered or oxidized and so have a higher oxygen content than the usual low-volatile agglutinating coals and have other differences. Such coals are best obtained from coal seam located near the earth surface and subject to infiltration of oxygen from the air. Such nonagglutinating or slightly agglutinating coals, slowly oxidized and altered over a period of many years, are more completely and uniformly oxidized, and, being oxidized without heat and in the presence of moisture, are chemically altered in different fashion through a greater degree of additive oxygenation than are coals artificially oxidized in known ways. Seam-oxidized nonagglutinating or slightly agglutinating coal of this type are found in many coal fields such as, for example, the Huntingdon-Broadtop and seam-oxidized Cambria fields of Pennsylvania, the Pocahontas field of West Virginia, and others.

By way of illustration, a satisfactory coal mixture is 65-50 parts of underground mine Rockhill coal (Pennsylvania) with 35-50 parts of strip-mined low-volatile coal taken-from a seam 8-20 feet beneath the surface. Such coals have the following analysis:

Rockhill:

Moisture 1.0, volatile 16.0, ash 6.5, sulphur 1.1, oxygen 2.9%-

Seamoxidized Moisture 3.5, volatile 15.7, ash 5.5, sulphur .65, oxygen 6.2%

'Examples of other mixtures are:

(a) 25 parts Pittsburgh-seam, high-volatile coking coal, 55 parts Rockhill (Pennsylvania) low-volatile coking coal, 20 parts seam-oxidized strip-mine low-volatile coal;

(b) '75 parts Cambria Co. (Pennsylvania) Lower Kittanning seam, low-volatile coking coal,

with 25 parts seam-oxidized Cambria low-volatile coal.

The two coals should be crushed to a size under f andthen blended'or mixed in any suit- 7 able thorough manner. and the mixture charged to coke ovens of the by-product recovery type andcoked in the usual manner. The destructive expansion quality of the coking coal is eliminated and the coke obtained has a physical structure superior to that obtained by coking the coking coal alone. It is superior also in.many respects to coke obtained from coals or coal mixtures having higher fluidity characteristics and th yield is greater than that obtained from coal of higher volatile content. Further, be-

cause oxidized non agglutinating coalshave at equal oven heats ahigher rate of coke formation, the.coking operation proceeds in a shorter period of time than that required by coking coals or coking coal mixtures of the usual non-oxidized type.

If more volatile matter. is desired, as when the coking operation is carried out by coke plants producing coke oven gas for outside sale, a highvolatile coal may be added in suitably regulated amount to the coking and non-coking coal mixture above. described. Also heavy petroleum oils may be added to the mixture to increase the distillation products without reducing the coke yield or the quality of the coke.

I claim:

1. The method of manufacturing metallurgical coke comprising making a blend consisting of -85 parts of a coking coal having a volatile component of 14-23% on a dry ash-free basis and 15-50 parts of a non-coking, or poorly coking, seam-oxidized coal having a volatile content of 15-20% and an oxygen content of 35-45% on a dry ash-free basis, coking said blend in a byproduct oven at temperatures exceeding 900 C. to distill off the by-products and convert the blend into coke.

2. The method of manufacturing metallurgical coke comprising making a blend consisting of a low volatile coal having a volatile component of 14-23% on a dry ash-free basis and objectionable expansion characteristics and a noncoking, or poorly coking, seam-oxidized coal havinga volatile content of 15-20% and an oxygen content of 35-45% on a dry ash-free basis, said latter coal being present in sufiicient quantity to eliminate the objectionable expansion characteristic of the low volatile coking coal, and coking said blend in a by-product' coke oven at temperatures exceeding 900 C. to distill off the byproducts and convert the blend into coke,

3. The method of manufacturing metallurgical coke comprising making a blend consisting of a low volatile coking coal having a volatile component of 14-23% on a dry ash-free basis and objectionable expansion characteristics and a non-coking, or poorly coking, seam-oxidized coal having a volatile content of 15-20% and an oxygen content of 3.645% on a dry ash-free basis said seam-oxidized coal being present in an amount sufficient to offset the expansive char- 900 C. to distill off the by-products and convert theblend into coke.

HORACE C. PORTER.