US3172823A

US3172823A - Process for hardening carbonaceous briquettes

Info

Publication number: US3172823A
Authority: US
Publication date: 1965-03-09
Anticipated expiration: 1982-03-09

Description

March 9, 1965 w. JOHN ETAL 3,172,823

PROCESS FOR HARDENING CARBONACEOUS BRIQUETTES Filed July 16, 1962 2 Sheets-Sheet 1 Jn venfors WILL/BALD JOHN PAUL LANGE March 9, 1965 w. JOHN ETAL 3,172,823

PROCESS FOR HARDENING CARBONACEOUS BRIQUETTES Filed July 16, 1962 2 Sheets-Sheet 2 Briquets Jn van for:

WILL/BALD JOHN PAUL LANG;

United States Patent PROCESS FOR HARDENING CARBONACEOUS smouarrns The present invention relates to the hardening of carbonaceous briquettes by an oxidizing heat treatment, more particularly, to a process for hardening briquettes formed of a carbonaceous material and a binding agent by subjecting the briquettesto oxygen-containing gases.

in the low-temperature carbonization of pit coal, a previous oxidizing treatment with oxygen-containing gases has been successfully carried out below the decomposition pointof the coal, preferably at temperatures of from 200 to 250 C., in order to minimize the caking capacity and to avoid any agglomeration of the pieces of coal during the carbonization thereof in the coke oven.

It is also known to bind fine-grain pit coal or finegrain coke with high-boiling-point fractions of coal tar or coal tar pitch to form briquettes and to subsequently treat the green briquettes with oxygen-containing gases at temperatures of from 200 to 300 C. in order to set or harden the briquettes. This hardening of the briquette is essentially accomplished by the polymerization of the binding agent under the influence of the oxygen. Generally, the hardened briquettes are subsequently subjected to a carbonization in order to completely coke or degasify the polymerized binding agent. The oxidizing treatment to harden the briquettes is carried out as rapidly as possible so that the briquettes can be subjected to a subsequent heat treatment in a simple apparatus, preferably a furnace. For this reason, the oxidizing treatment is generally carried out by oxygen-containing gases circulating in counterfiow or cross-flow relation through the charge of briquettes.

An oxidizing treatment below the decomposition temperature of coal has also been successfully applied to render smokeless pitch-bonded briquettes formed from non-caking hard or semibituminous coals. Such briquettes are usually subjected to two successive heat treatments. The first treatment removes the readily volatile matter of the binding agent to render the briquettes porous and is carried out with a small quantity of air. The second heat treatment carbonizes the oil residues and is carried out with an excess of air.

In the manufacture of solid fuels for ultimately producing gas, the carbonaceous briquettes have been heated in an oxidizing atmosphere to temperatures ranging from 650 to 800 C. and then the treatment is continued with less oxygen after the carbonization has been completed in order to partly decompose substances contained in the briquettes to facilitate the subsequent gasification thereof.

Briquettes have also been subjected to a sudden heating in the presence of a small quantity of oxygen to rapidly harden the outer surface thereof so that the briquettes can subsequently be further carbonized and degasified.

Briquettes formed of pit coal and a tar binder have been rendered smokeless by subjecting the bri ettes to two successive steps of a heat treating process wherein the first step takes place in a strongly oxidizing atmosphere and the second step in an atmosphere ranging from weakly oxidizing to neutral. Both of these steps are carried out below the decomposition temperature of the coal and the binding agent.

The above-known processes are generally carried out by moving the charge and then circulating suitable gases ice in counterfiow or crossfiow relation to the moving charge. These processes as thus conductedhave the disadvantage that because of the ever present risk of flammation of the coal either several oxidizing stages are required or the process must be carried outwith a thin layer of the charge. Further, the oxygen content of the gases must be relatively low. For these reasons the oxidizing treatment of such briquettes has generally been carried out in multistage chambers, in a thin layer of a charge having a thickness from 0.4 to 0.6 m. and disposed on a continuous conveyer belt, or the charge has been placed in containers which are successively moved through a continuous furnace.

In viewof the low oxygen content of the treating gases, a relatively long period of at least 2-3 hours is usually required for carrying out the treatment. This necessitates the use of expensive and complicated installations which jeopardize the economy of the operation because of both the high operating and initial expenses as well as the fact that such complicated pieces of apparatus are susceptible to various operating difficulties.

It is therefore the principal object of the present in vention to provide a novel and improved process for the hardening of briquettes formed of carbonaceous material and binding agents.

It is a further object of the present invention to provide a process for hardening briquettes by an oxidizing treatment with oxygen-containing gases carried out at temperatures below the decomposition temperature of the carbonaceous material from which the briquette was formed.

The disadvantages of the known processes as discussed above are eliminated and the objects of the present invention are attained by the present invention wherein the oxygen required for the hardening of the briquettes is introduced in a regulated quantity in the same direction of movement as the charge of briquettes is being moved continuously through a furnace. The oxidizing agent is introduced concurrently with the charge of briquettes into the furnace and then in the heat-treatrnent zone of the furnace meets and mixes with the circulating gases which heat the briquettes. As a result, the briquettes are exposed to the maximum oxygen content during the heating thereof in such a way that the oxygen content is regulated to bring about both the maximum oxygen content and the maximum temperature at which no ignition of the carbonaceous material will occur. The oxidation process is so effectively controlled that it is possible to harden pitch-bonded briquettes in a vertical continuous furnace. This was previously not considered possible since because of the softening of the briquettes, the briquettes either crumbled to pieces or aggregated to form large masses.

The critical featureof the improved process of the present invention is the introduction of the oxidizing agent into the treating zone in the same direction of movement as the movement of the charge through the zone. De-

pending upon the alternate purpose for which particular briquettes are intended, the process can be terminated after the oxidation of the briquettes and the oxidized briquettes can be cooled subsequently to this oxidizing treatment. However, the oxidized briquettes can be subjected to a low-temperature carbonization or degasifica tion process in order to obtain harder briquettes having a smaller content of volatile matter.

Other objects and advantages'of the present invention will be apparent upon reference to the accompanying description when taken in conjunction with the following drawings wherein:

FIGURE 1 is a schematic representation of an installation for carrying out the process of the present invention; and

FIGURE 2 is a view similar to that of FIGURE 1 but wherein the apparatus provides for a further heating of the briquettes after the oxidizing treatment.

With particular reference to FIGURE 1, the process of the present invention is carried out by introducing the briquettes which are to be treated into the loading hopper 1 of a vertically disposed continuous furnace or kiln. The hopper 1 is directly connected to the treating zone 2 of the furnace located therebelow. Transversely extending roofiike structures 12 are positioned in the furnace at the entrance of the treating zone 2 to support a substantial portion of the weights of the charge before the charge enters the treating zone. These structures 12 can also be used for the introduction of cold gases containing air into the furnace.

Hot gases which have been reheated in a combustion chamber 5 by the combustion of gas, oil or coal dust with air, are introduced into the charge through inlet channels 13 under the action of a blower 4 and are circulated downwardly through the charge in the oxidation zone. The gases are reheated to temperatures ranging from about ZOO-400 C., and preferably about 300 C., with the temperature of the gas depending upon the nature of the coal or coke and the binding agent used in the forming of the briquettes. These temperatures, however, are below the temperatures at which the tar is begun to be removed from briquettes formed of pit coal.

These heated gases are circulated in the oxidation zone 2 by flowing downwardly through the furnace in the same direction or movement of the charge through the furnace and are withdrawn from under the batfies 14 which are preferably arranged in two staggered rows.

The oxygen content of the heated gases withdrawn from the furnace is indicated by an oxygen-recording apparatus 20. This apparatus is suitably connected to an automatic control circuit so as to regulate the quantity of oxygen introduced into the furnace in response to the oxygen content of the gases withdrawn from the furnace.

The air required for the oxidation is introduced into the oxidation zone 2 in a regulated quantity together with the briquettes introduced through loading hopper 1. As a result of introducing the air concurrently with the briquettes, the briquettes are in a cold condition when they reach the treating zone 2.

In the treating zone 2 the cold air, or a cold oxygencontaining gas, is mixed with the heated circulating gases introduced through the inlets 13. As a result, the heating gases are reduced in temperature from the inlet temperature of 300 to 200 C. A portion of this heat is also used for heating the briquettes. The temperature of the heating gases, however, soon increases due to the initiation of the exothermic reaction and by the time the gases reach the end of the treating zone they are at a temperature of about 300 C.

The oxygen content of the heating gases entering at 13 is approximately 6% and is first increaesd to about 8- 10% because of the air entering the treating zone 2. During the oxidation process the oxygen content of these gases is again reduced to about 6%. The oxygen content of the treating gases removed from the furnace is indicated at the oxygen-recording device 2%, which is operatively connected to a control system to regulate the flow of air into the furnace and thereby to control the oxygen content of the circulated gases.

Depending upon the quantity of air introduced through the hopper 1, a portion of the circulating heating gases is discharged into the atmosphere through pipe 19 after the circulating gases are withdrawn from the treating zone so that the gases and vapors produced during the oxidation treatment are also discharged. These gases and vapors can either be discharged into the atmosphere after purification and/or cooling, or they can be introduced wholly or in part into the combustion chambers of the hardening stages or a carbonizing stage of the briquettes for combustion of the gaseous hydrocarbons contained therein.

The treated briquettes then pass through connecting channels 15 into cooling zone 3. Gases which are at a temperature of about 30 C. and having an oxygen content of less than 2% are introduced into the cooling zone by the blower 9 below the baflie structure 16 in order to cool the briquettes. These cooling gases are flowed through the briquettes in counterfiow direction and discharged from the cooling zone at a temperature ranging from 200 to 250 C. These warmed cooling gases are passed into a heat exchanger 7 to preheat the air destined for the burners of the hardening zone or for a low-temperature carbonization zone. This air is directed to the heaters by a blower 6. The residual heat energy of these cooling gases is removed through an injection cooler 8 by the evaporation of water or by Washing with large quantities of water. The cooled briquettes are then discharged through outlet 10.

Thus, by way of summary the oxidation treating zone of the furnace receives the required air which has an oxygen content of about 21% by volume and this air is flowed through the charge of briquettes in the same direction of movement as the briquettes. When the air is mixed with the circulating heating gases, the oxygen content of this gaseous mixture is about 10% which then decreases to about 6%. The final oxygen content is determined by the temperatures of the reaction and the manner in which the process is carried out.

When readily oxidized materials are being processed, a mixture of waste gases of combustions, including smoke, and gases containing air can be employed in order to maintain the oxygen content at the desired level. For

this purpose, the gases which have been circulated through the heat-treating zone are cooled. A modified appa ratus, such as illustrated in the dotted lines of FIGURE 1, may be employed. These gases are first passed through a spray cooler 25 and are then introduced by blower 18 into the furnace above the oxidation zone underneath the rooflike structures 12. Utilizing this modification, the oxygen content of the oxidizing agent introduced together with the charge can be reduced. This will enable higher processing temperatures and higher temperatures of the circulating heating gases to be used.

The process can also be carried out by introducing the oxidizing agent into the upper portion of the furnace at points other than through the opening into which the charge is introduced. As may be seen in FIGURE 1, additional roofiike structures 17 may be provided in the upper portion of the furnace. When waste gases from the heat-treating process are employed as the oxidizing agent, these gases are introduced underneath the rooflike structures 17 by the blower 18. The gases then flow downwardly through the charge in the same direction as the movement of charge through the furnace, and air is introduced underneath the ro'oflike structures 17.

Depending on the intended application of the briquettes being processed, a cooling stage 3 is directly connected to the oxidation zone 2 in order to cool the briquettes which have been heated to about 300 C. during the oxidizing treating process. This cooling brings the temperature of the briquettes down to about atmospheric temperature and is carried out in a neutral atmosphere or in an atmosphere having a very low oxygen content so as to preclude any further oxidation of the treated briquettes.

Proceeding next to FIGURE 2, there is illustrated one form of an apparatus which can be used to produce briquettes which are completely free from tar or which have a low content of volatile matter. In this apparatus a low-temperature carbonization or degasification stage is directly connected to the heat-treating zone 2 in one structural unit.

After the briquettes have been treated as previously described in oxidation zone 2, the briquettes are introduced into the carbonization zone 11 which can be heated either directly or indirectly by hot gases. These briquettes are then subjected to a treating process carried out by circulating gases having a temperature of 500 to 600 C. These heating gases are introduced underneath transverse bafiles 23 and flow upwardly through the charge in counterfiow to the movement of briquettes downwardly through the furnace. The gases are discharged from the upper portion of this carbonization zone at a temperature of about 370 C. The gases are circulated by means of a blower 21.

The necessary heat for the gases is supplied by a combustion chamber 22 wherein gas, fuel oil, or coal dust is burned to produce the gases of the necessary temperature. These circulating gases are virtually oxygen-free. Any excess gases produced through this second carbonization step may be used for heating the gases in combustion chamber 5 which gases are to be used in oxidation zone 2.

Subsequent to this carbonization treatment the briquettes are cooled in a manner as previously described in the cooling zone 3, wherein cooling gases having a very low oxygen content are circulated in eounterflow relation with the movement of the charge of briquettes through the furnace. The cooling gases are introduced into the lower portion of the cooling chamber at a temperature of about 30 C. through the blower 9 and are removed from underneath the rooflike structure 16 at a temperature of about 400 C. These warmed cooling gases are then passed through a heat exchanger 7 and are further cooled in a manner as previously described.

The cooled briquettes are then discharged from the furnace through the discharge hopper 10. The rate of travel of the briquettes through the furnace is regulated by a valve-like structure indicated at 24.

Thus it can be seen that the present invention provides an improved process and apparatus for treating of briquettes by an oxidizing process employing oxygencontaining gases.

It will be understood that this invention is susceptible to further modification and, accordingly, it is desired to comprehend such modifications within this invention as may fall Within the scope of the appended claims.

What is claimed is:

1. In a process for an oxidizing heat treatment of briquettes formed of a carbonaceous material and a binding agent, the steps of circulating heated gases containing oxygen at temperatures of 200 to 400 C. in the direction of movement of briquettes moving through a furnace to heat the same, and introducing cold air into the moving briquettes upstream of the inlet for the circulated heated gases in the direction of movement of the briquettes to replace the oxygen consumed from the circulating heated gases.

2. In a process for an oxidizing heat treatment of briquettes formed of a carbonaceous material and a binding agent, the steps of circulating heated gases containing oxygen at temperatures of 200 to 400 C. in the direction of movement of briquettes moving through a furnace to heat the same, and introducing cold air into the moving briquettes upstream of the inlet for the circulated heated gases in the direction of movement of the briquettes to replace the oxygen consumed from the circulating heated gases, and regulating the quantity of cold air introduced into the moving briquettes in response to the oxygen content of the circulating heated gases.

3. In a process for an oxidizing heat treatment of briquettes formed of a carbonaceous material and a binding agent, the steps of circulating heated gases containing oxygen at temperatures of 200 to 400 C. in the direction of movement of briquettes moving through a furnace to heat the same, and introducing cold air into the moving briquettes upstream of the inlet for the circulated heated gases in the direction of movement of the briquettes to replace the oxygen consumed from the circulating heated gases, and cooling the heated oxidized briquettes in neutral atmosphere to preclude any further oxidation thereof.

4. In a process for an oxidizing heat treatment of briquettes formed of a carbonaceous material and a binding agent, the steps of circulating heated gases containing oxygen at temperatures of 200 to 400 C. in the direction of movement of briquettes moving through a furnace to heat the same, and introducing cold air into the moving briquettes upstream of the inlet for the circulated heated gases in the direction of movement of the briquettes to replace the oxygen consumed from the circulating heated gases, and cooling the heated oxidized briquettes in neutral atmosphere to preclude any further oxidation thereof, and flowing the cooling gases discharged from the moving briquettes in heat exchange relation to the heating gases prior to circulating the heated gases through the moving briquettes.

5. In a process for an oxidizing heat treatment of briquettes formed of a carbonaceous material and a binding agent, the steps of circulating heated gases containing oxygen at temperatures of 200 to 400 C. in the direction of movement of briquettes moving through a furnace to heat the same, and introducing cold air into the moving briquettes upstream of the inlet for the circulated heated gases in the direction of movement of the briquettes to replace the oxygen consumed from the circulating heated gases, heating the oxidized briquettes to temperatures above 400 C. to remove residual volatile components therefrom, and cooling the heated oxidized and reheated briquettes in a neutral atmosphere.

6. In a process for an oxidizing heat treatment of briquettes formed of a carbonaceous material and a binding agent, the steps of circulating heated gases contain ing oxygen at a temperature of about 300 C. in the direction of movement of briquettes moving through a furnace to heat the same, introducing cold air having an oxygen content of about 21% into the moving briquettes upstream of the inlet for the circulated heated gases in the direction of movement of the briquettes to replace the oxygen consumed from the circulating heated gases, and circulating gases having a temperature of about 30 C. and an oxygen content of less than 2% through the heated oxidized briquettes to cool the same.

References Cited in the file of this patent UNITED STATES PATENTS 2,164,933 .Maurel July 4, 1939 2,869,992 Brown et al. Jan. 20, 1959 3,117,918 Batchelor et a1 Jan. 14, 1964 FOREIGN PATENTS 843,618 Great Britain Aug. 4, 1960

Claims

1. IN A PROCESS FOR AN OXIDIZING HEAT TREATMENT OF BRIQUETTES FORMED OF A CARBONACEOUS MATERIAL AND A BINDING AGENT, THE STEPS OF CIRCULATING HEATED GASES CONTAINING OXYGEN AT TEMPERATURES OF 200 TO 400* C. IN THE DIRECTION OF MOVEMENT OF BRIQUETTES MOVING THROUGH A FURNACE TO HEAT THE SAME, AND INTRODUCING COLD AIR INTO THE MOVING BRIQUETTES UPSTREAM OF THE INLET FOR THE CIRCULATED HEATED GASES IN THE DIRECTION OF MOVEMENT OF THE BRIQUETTES TO REPLACE THE OXYGEN CONSUMED FROM THE CIRCULATING HEATED GASES.