US3918929A

US3918929A - Process for post-treating hot briquettes and the like

Info

Publication number: US3918929A
Application number: US389052A
Authority: US
Inventors: Paul Schmalfeld; Helmut Hahn; Joachim Lehmann; Kurt Kleisa
Original assignee: Metallgesellschaft AG
Current assignee: GEA Group AG
Priority date: 1972-09-26
Filing date: 1973-08-16
Publication date: 1975-11-11
Anticipated expiration: 1992-11-11
Also published as: DE2247101A1; IT995483B; ZA735185B; BR7307428D0; JPS4970803A; FR2200349A1; CA994276A; JPS5717040B2; FR2200349B1; GB1411496A

Abstract

Hot briquettes formed at temperatures in the range of 350*-550*C are conveyed through a shaft zone countercurrent to oxygencontaining gases. The oxygen-containing gases are preferably recycled through the process and admixed with air as a source of oxygen. This results in a combustion of carbon on the surface of the briquettes and of the gases and tar vapors released by the briquettes when so heated. Briquettes post-treated according to the invention have an optimum crushing strength and abrasion resistance making them easily transportable and useful in blast furnaces.

Description

United States Patent Schmalfeld et al.

[ PROCESS FOR POST-TREATING HOT BRIQUETTES AND THE LIKE [75] Inventors: Paul Schmalfeld, Bad Homburg;

Helmu. Hahn, Hunau; Joachim Lehmann, Essen-Haarzopf; Kurt Kleisa, Essen-Frintrop, all of Germany [73] Assignee: Metallgesellschaft Aktiengesellschaft,

Frankfurt am Main Germany [22] Filed: Aug. 16, 1973 [21] Appl. No: 389,052

[30] Foreign Application Priority Data Sept, 16. I972 Germany 2247l0l {52} US. Cl. 44/10 K; 44/l0 H [51] Int. Cl. ClOL 5/00 [58] Field of Search 44/l0 K 10 R, l R. 10 H, 44/ 10 J [56] References Cited UNITED STATES PATENTS 1357396 12/]967 Gusior et a] 44/] R NOV. 11,1975

3.384557 5/l968 Saller 44/) R 3.663J86 5/1972 Dzhaparidze et al.. 44/10 H 3.67%449 7/1973 Schmalfeld et al, H 44/IU R Primal)- E.\'anlilwrCarl F. Dees Attorney, Agent. or Firm-Dinklage, Dinklage 84 Sprung [57] ABSTRACT Hot briquettes formed at temperatures in the range of 3S0550C are conveyed through a shaft zone countercurrent to oxygencontaining gases, The oxygencontaining gases are preferably recycled through the process and admixed with air as a source of oxygen. This results in a combustion of carbon on the surface of the briquettes and of the gases and tar vapors released by the briquettes when so heated. Briquettcs post-treated according to the invention have an optimum crushing strength and abrasion resistance making them easily transportable and useful in blast furnaces.

6 Claims. 1 Drawing Figure US. Patent Nov. 11, 1975 PROCESS FOR POST-TREATING HOT BRIQUETTES AND THE LIKE BACKGROUND This invention relates to a process of aftertreating hot briquettes or similar shaped bodies which contain caking coal and have been made at a temperature between about 350 and 550C.

Hot briquettes are preferably made by pressing a mixture of caking coal and non-softening solids, partic ularly fine-grained coke, at temperatures in the plastic region of the caking coal. The coke is heated to such a temperature that the mixture of coke and predried and possibly preheated caking coal has a mixed temperature in the range of 400 550C. and at this temperature is fed to a briquetting press. The ratio of coke to caking coal varies widely in dependence on the nature and the caking capacity of the coal which is used and above all on the porosity and also the strength of the hot coke. Conventional ratios are 60-75% coke to 40-25% caking coal by weight. The temperature of the mixture is preferably kept within the range of 4405 20C., particularly between 450 and 480C.

SUMMARY It is an object of the invention to provide a process to make briquettes which have an optimum crushing strength and abrasion resistance and which are highly suitable for being transported, handled before the blast furnace and used as a reducing agent in the blast furnace. This is accomplished according to the invention by conveying hot briquettes through a shaft zone, countercurrent to oxygen-containing gases. In this operation, the presence of these gases, which preferably contain admixed air, results in a combustion of carbon on the surface of the briquettes and of the gases and tar vapors released by the briquettes when heated. To heat the briquettes by, e.g., lC., about l.2% of the carbon of the hot briquettes or an equivalent amount of volatile constituents must be burnt. The combustion on the surface of the hot briquettes may be suppressed to a high degree by an addition of combustible gases unless this effect is produced by the volatile constituents which have been released from the briquettes.

DESCRIPTION OF THE DRAWING The present invention will be more fully understood from the following description taken in conjunction with the accompanying drawing which is a schematic flow diagram of apparatus suitable for carrying out the process of the invention.

DESCRIPTION The combustion in the shaft is controlled in such a manner that the hot briquettes are heated to a certain temperature which is 50200C., preferably about 100C., above the briquetting temperature. As a result, substantially all of the residual tar contained in the hot briquettes is removed and their content of volatile con stituents is reduced to or below 5% by weight. The briquettes having this composition now posses the desired crushing strength and abrasion resistance.

An essential feature of the invention resides in admixing air at a controlled rate to gases which are recirculated through the shaft zone. As soon as the ignition temperature has been reached and the combustion temperature is sufficient to effect a higher temperature rise of the recirculated gases and of the hot briquettes, this air causes the combustion of the recirculated gases which flow through the briquette charge in the shaft zone and are subjected to a temperature rise. The air is added to the recirculated gases at such a rate that the combustion on the surface of the hot briquettes or of the combustible components of the recirculated gases just results in the desired temperature. It will be desirable to admix the air to the recirculated gases before they enter the briquette charge. Alternatively, the air may be added through distributing means in the top half of the briquette charge where the recirculated gases and briquettes are at a higher temperature.

An example of the process according to the invention will now be explained with reference to the drawing:

The hot mixture of coke and caking coal is pressed in a doubleroll press I to form hot briquettes. The temperature of the mixture is in the range of 4005 50C., preferably between 450 and 480C. From the briquetting press l, the briquettes move by a horizontal conveyor 2 and a steep conveyor 3 to a feed chute 4, which delivers them into shaft zone 5. The chute 4 is suitably provided with a grate or screen 6 for a removal of fines abraded from the briquettes and any undersize particles.

Under the action of gravity, the briquettes move through the shaft zone 5 as a closed charge continuously from top to bottom. The valve member 8 associated with the shaft is controlled so that the shaft is always entirely filled with briquettes up to the distributing chutes 7.

At the lower end of the shaft 5, recirculated gases at a low temperature are fed into the shaft 5 through a conduit 9. These gases will be referred to hereinafter as recirculated gases. The recirculated gases consist normally of the exhaust gases which have been formed as a result of the addition of air and the combustion and which still contain oxygen. Water vapor from the means for the direct-contact cooling of the recirculated gases with water or from the means for the final cooling of the hot briquettes may be admixed to the recirculated gases. Air flowing through the conduit 10 at a metered rate is admixed to the recirculated gases when they are at a temperature between 30 and 200C. before they enter the shaft 5 via conduit 9.

In the shaft zone 5, the mixture of recirculated gas and air flows from bottom to top through the hot briquette charge so that the latter is cooled in the lower portion 5a of the shaft while the countercurently flowing gases are heated. In In the upper portion 5b of the shaft, the ignition temperature is reached and the air in the recirculated gases supports the combustion of carbon on the surface of the hot briquettes and the combustion of the gases and tar vapors which are released from the briquettes as they were heated.

The air is added to the recirculated gases at such a rate that the combustion results just in the desired temperature at the hot briquettes. When briquetted at a temperature of, e.g., 450C, the hot briquettes may cool to, e.g., 420C. until they enter the shaft zone 5 and are then heated in the shaft to about 500C. by the partial combustion in the charge. The temperature may be increased to 550600 or more if combustion air is added at a suitable rate. It is important to heat the briquettes to such an adjusted temperature that virtually all residual tar in the hot briquettes is eliminated and their content of volatile constituents is reduced below 5% by weight.

Owing to the relatively low 0, content of the recirculated gases and the low combustion temperatures, the combustion is slow and takes place in an extended zone (5b) of the briquette charge. The recirculated gases which leave the shaft 5 at the upper end thereof always contain still a certain amount of unconsumed oxygen. A number ofthermocouples (not shown) which are distributed in the shaft zone 5 over the height of the briquette charge and serve to monitor the cooling, combustion and temperature rise of the briquettes. The temperature of the recirculated gases emerging from the briquettes charge also furnishes an indication of the temperature to which the hot briquettes have been heated.

The residence time of the hot briquettes which descend in the shaft 5 is generally -20 minutes in the heating zone 5b and about 20-40 minutes in the cooling zone 5a. In the case of a high temperature in the heating zone 5 b, a short residence time will be suffcient. The success of the process is desirably checked by a determination of the contents of residual tar and volatile constituents in the treated hot briquettes. The air rate may be controlled to ensure a suitable combus tion and a heating of the hot briquettes to the desired temperature in the top part of the briquette charge.

The recirculated gases which emerge from the briquette charge at the top end of the shaft zone 5 are fed by a conduit 11 into a cyclone zone 12, where the dust which has been entrained from the briquette charge is removed. The gases are then cooled in a cooler 13 to a temperature between 30 and 200C The cooler may be a waste heat boiler for the generation of steam, a water-evaporating spray cooler, or an indirectly cooled cooler using air or water. The cooled recirculated gases and the admixed air are returned into the shaft 5 by a blower 14. Any surplus recirculated gas is withdrawn at 16.

The hot briquettes discharged from the shaft 5 at its discharge end 15 may be postcooled quickly to avoid selfignition, which might otherwise be possible. This postcooling may be accomplished in various ways, e.g., by an aftertreatment with water, which may be sprayed or may be contained in dip basins, or by a mere air cooling.

In the process described hereinbefore, the air conducted in the conduit 10 is admixed to the recirculated gases before they enter the briquette charge in the shaft 5. In an alternative process, the air may be added through distributing means in the top half of the shaft 5. The distributing means consist, e.g., of a multiplicity of parallel horizontal tubes having uniformly spaced air outlet openings.

The air is fed to the tubes 20 through a supply conduit manifold 22. The distributing tubes 20 may be disposed under downwardly open rooflike elements 21, which serve to stiffen the tubes 20 and also simultaneously to premix the air with the recirculated gases. This may be accomplished in the space under the roofs 21 outside the briquette charge. These distributing members may be used to provide over the height of the shaft a temperature profile which differs somewhat from that obtained when air is supplied through conduit 10. The supply of air through the distributing tubes 20 may be combined with the admixing of air through the conduit 10.

If the recirculated gases which emerge from the briquette charge through the conduit 11 still contain unburnt or undecomposed tar vapors which may form undesired deposits in the cyclone or cooler it will be suitable to admix air at a controlled rate to the recirculated gases before or after the cyclone in order to cause the combustion of these tar vapors and of any permanent gases which are still present. If this combustion is not sufficiently intense because the temperatures are too low, it will be suitable to admix not only air but to admix hot combustion gases and an excess of air so that the recirculated gases are sufficiently heated.

The process is applicable not only to hot briquettes which have been made at a temperature of 400550C. from a mixture of fine-grained coke and caking fine coal, but also to hot briquettes which have been made by pressing from coal or a coal mixture which has been heated to a temperature between 350450C. whereas hot coke has not been added. The process is also applicable to the aftertreatment of hot pellets which have been made in a rotary drum from a mixture of hot, fine-grained coke with predried or preheated, caking fine coal with or without an addition of tar pitch.

We claim:

1. Process for post-treating hot briquettes or similar shaped bodies containing caking coal which have been made at temperatures between about 350 and 550C, which comprises conveying the hot briquettes through a shaft zone countercurrent to oxygen-containing gases, thereby raising the temperature of said briquettes to from 50-200C above said shaping temperature by combustion within said shaft zone of carbon of the briquettes and of gases and tar released by the briquettes when so heated.

2. Process of claim 1 wherein air is admixed at a controlled rate to said gases which are recirculated through the shaft zone.

3. Process of claim 2 wherein the air is admixed before the recirculated gases enter the briquettes in the shaft zone.

4. Process of claim 2 wherein the air is admixed by distributing means arranged in the top half of the briquettes in the shaft zone.

5. Process of claim 4 wherein the air is added at such a rate that the combustion of combustible constituents of the recirculated gases and a partial combustion of the hot briquettes at their surface result in a heating of the hot briquettes to a temperature which exceeds the briquetting temperature by about C.

6. Process of claim 1 wherein air is admixed to recirculated gases when they have left the shaft zone and/or when subjected to dust collection in a cyclone zone following the shaft zone, and said admixed air results in a substantial combustion or decomposition of tar vapors entrained in the recirculated gases.

* k r w

Claims

1. PROCESS FOR POST-TREATING HOT BRIQUETTE OR SIMILAR SHAPED BODIES CONTAINING CAKING COAL WHICH HAVE BEEN MADE AT TEMPERATURES BETWEEN ABOUT 350* AND 550*C., WHICH COMPRISES CONVEYING THE HOT BRIQUETTES THROUGH A SHAFT ZONE CONTERCURRENT TO A OXYGEN-CONTAINING GASES, THEREBY RAISING THE TEMPERATURE OF SAID BRIQUETTES TO FROM 50$-200$C ABOVE SAID SHAPING TEMPERATURE BY COMBUSTION WITHIN SAID SHAFT ZONE OF CARBON OF THE BRIQUETTES AND OF GASES TAR RELEASED BY THE BRIQUETTES WHEN SO HEATED.

5. Process of claim 4 wherein the air is added at such a rate that the combustion of combustible constituents of the recirculated gases and a partial combustion of the hot briquettes at their surface result in a heating of the hot briquettes to a temperature which exceeds the briquetting temperature by about 100*C.