GB1595825A - Method of producing and cooling hot agglomerates of fuel - Google Patents

Description

(54) IMPROVED METHOD OF PRODUCING AND COOLING HOT AGGLOMERATES OF FUEL (71) We. ALLIS-CHALMERS CoRPOICTION. a Corporation organized under the laws of the State of Delaware.

United States of America, of 1126 South 70th Street, West Allis 14, Wisconsin, United States of America. do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention is concerned with an improved method of producing and cooling hot agglomerates of the type used for fuel in industrial application and processes such as, for example, the production of iron and steel, and in foundries.

More specifically, the invention is concerned with a method of producing and cooling hot agglomerates in a continuous coking operation in which the hot agglomerates are produced from a fuel material such as, for example, coking coal, or a mixture of fine coal, char, and non-coking agglomerates, and the hot agglomerates are then cooled so that the resulting product will not oxidize with the atmosphere and will, therefore. provide a product of lower chemical reactivity with respect of CO2 so as to render the produced product more attractive to industrial use.

The method of the invention utilizes a counter-current furnace into which a stream of cool CO2 rich gas is injected. The cool CO2 gas does not react with the formed agglomerates being discharged from the furnace because at the discharge end the products are sufficiently cool so that the cooling stream of C02 gas provides a final cooling stage wherein the fuel products can be handled without significant re-oxidation.

Metallurgical coke is an essential material in an industrial society; it is indispensable for ironmaking operations in blast furnaces - the most important source of iron for steel production. It is also utilized in selected steelmaking processes and in the foundry industry.

Conventional coke is produced primarily in so-called "by-product coke ovens" where a blend of various coals is introduced and subjected to distillation to remove the volatile constituents from the coal. The end product is a porous mass that must be cooled to prevent burning during storage under atmospheric conditions. The principal method to acccomplish this cooling is a quenching with water, although dry quenching methods have recently been introduced as well.

These techniques suffer from the following disadvantages: a) There is significant pollution associated with quenching operations, particularly with the most commonly practiced techniques of water quenching.

b) The heat released in cooling operations is not recoverable and represents a significant fraction of the heat losses in cokemaking operations.

c) Such cooling operations cause thermal shock which in turn leads to product degradation, thereby increasing operating costs in ironmaking and in steelmaking.

d) Normally, the methods used for cooling permit moisture pickup in the product and this must be removed in subsequent operations, thus again increasing thermal inefficiencies.

However, interest in coke cooling technology need not be limited to conventional cokemaking applications. In recent years, the general scarcity of good quality coking coals plus the attendant price increases experienced by the industry have caused much interest in the so-called "formed coke" technology which does not require quality coking coals as raw materials. These new processes reportedly operate with low-rank coals but provide a uniform metallurgical coke that can replace the conventional product in most industrial applications. Unfortunately, formed coke technology suffers from the same problems associated with conventional cokemaking applications, i.e., cooling of the final product.In addition, it has been found that formed coke tends to be more reactive with respect of CO2 than conventional coke and this leads to lower productivity in blast furnaces.

It is an object of the present invention to provide an improved method to cool formed coke which avoids the above-stated problems, and overcomes the disadvantages of the prior art in a practical and satisfactory manner by not only eliminating the drawbacks of conventional cooling methods but also reduces the chemical reactivities in the formed coke product.

The invention described herein is intended to accomplish these goals and has potential for providing additional benefits.

The concept is based on utilizing CO2 gas which initially reacts with carbon at high temperatures but which ceases to react once converted to CO. As a result of this conversion, the most active sites in the fuel are removed during chemical reaction, thus decreasing the reactivity of the material as part of the cooling operation. Also the concept will permit the generation of high quality by-product gas, a definite advantage with respect to known formed coke processes.

According to invention there is provided a method producing and cooling hot agglomerates of the type used for fuel to prevent oxidization of the agglomerates upon contact with atmosphere and to regenerate process gas, wherein a fuel material, such as coking coal or a mixture of fine coal, char, and non-coking agglomerates, continuously moved through a furnace in a direction counter to the flow therethrough of process gases which serve to preheat the material to form char, and then continue to heat the material to devolatize the coal and form coak agglomerates of plastic consistency, characterized by the steps of:: (a) introducing CO2 rich gas into the formed agglomerates at a cooling stage in their production where the agglomerates are at a temperature in the range of 100" to 600OF., (b) heating the C02 gas in the cooling stage to a temperature to initiate the reaction CO2 + C2 CO to cause unreacted carbon in the hot agglomerate to react and elevate the agglomerate4s to a final carbonization temperature not exceeding 2350OF (c) moving the gas to a heat-hardening and carbonization zone wherein the temperature of the agglomerates does not exceed 2000OF, (d) introducing oxidizing gases into the agglomerates in the heat hardening and carbonization zone, (e) continuing the heating of the gas for a duration to cause the reaction CO + 1/2 02 CO2 and to maintain the temperature of the agglomerate in the zone of step (c) in a range of 1200OF to 20000F., (f) collecting the C02 gas produced by step (e), and (g) re-introducing the CO2 gas as cooling gas into the process according to step (a).

Preferably there is included the further steps of: continuing the reaction of step (b) until a temperature is reached where the reaction becomes exothermic.

Preferably the C02 gas is introduced into the agglomerates at a zone of the furnace where the agglomerates have a temperature of 600 F.

Preferably there is included the still further steps of: processing said gas through drying, preheating and incipient carbonization zones of the furnace at a rate which will enrich the gas in hydrogen according to the reaction (3) H,O + CO < H2 + CQ It will be seen that, in subsequent stages of the gas phase composition according to the method of the invention, several reactions occur.

These are:- (1) CO2 + C 2C0 (2) C0+1/20,ICO, (3) H2 + CO = CO2 As a result, the gas becomes progressively enriched in H2 and CO2 until the temperature drops sufficiently to reverse such reactions with the eventual precipitation of carbon black and moisture pickup.

However, since the uncarbonized fuel consists primarily of chars and coal fractions with significant volatile content, such volatiles are incorporated into the gas stream.

The final gas composition of the gas at the exit point will then consist of coal volatiles, C02 plus varying amounts of hydrogen and CO depending on the gas temperature. It is expected that the entrained carbon black particles would be removed in conventional dust control systems; they are valuable for re-use during fuel agglomeration, both to achieve higher product strength and also because of their low impurity levels. The gas would also be cooled by heat exchange for steam or power generation and to permit recycling into the vessel.

The invention will now be described in detail, with reference, by way of example, to the accompanying diagrammatic drawing which is a schematic view of a vertical shaft furnace and associated gas and solid flow diagram.

Referring to the drawing, a fuel material, such as coking coal, or a mixture of fine coal, char, and non-coking agglomerates, to be used in artificial and conventional fuel production, is fed into the top of a vertical shaft furnace 10, through a normal bellhopper-type seal, and progresses downwardly through the furnace, undergoing as it does heating at various temperatures as shown on the drawing and various chemical reactions to produce hot formed coke agglomerates which are discharged at the bottom of the furnace after cooling.

In the method of the invention, the hot agglomerates are cooled so that the resulting product will not react (oxidize) with the atmosphere, whilst concurrently providing a product of lower chemical reactivity with respect ot CO2 so as to render such product more attractive for industrial use.

It is to be understood that whilst the method of the invention is depicted as being utilized in the vertical shaft furnace 10 in which process gases flow upwardly in counter-current to the progressive downward movement of the fuel material, the method is not limited to such a vertical arrangement of process vessel and a horizontally-arranged vessel could be utilized to plrovide flow of material in one direction and counter-current flow of gases in the other direction.

In the method of the invention, a stream of CO2 rich gas is injected through pipes 11 into the formed coke agglomerates produced within the furnace 10. The cool CO2 gas does not react with the agglomerates at the lower portion of the furnace because the agglomerates are sufficiently cool already in this portion of the furnace, and at this point the cooling stream of CO2 gas simply provides a final cooling stage so that the produced fuel agglomerates discharged from the furnace can be handled without significant re-oxidization.

As the CO2 gas enters the cooling section of the furnace, the gas becomes heated due to heat exchange between the warm fuel and the gas. At temperatures of several hundred degrees Fahrenheit, however, the gas reacts wuth the carbon-rich fuel according to the following reaction: (a) CO2+C#2C0.

Since the reaction becomes exothermic at high temperature, both the gas and the solids will show a steep but transient temperature increase. Such a stage provides the necessary heat for the final induration step in carbonization. At the same time, since the chemical reaction shifts towards the right at higher temperatures the gas becomes CO rich and CO2 poor. This prevents further CO2 conversion while providing a relatively stable temperature regime during final carbonization.

An important feature at this stage is that the chemical reaction occurs preferentially at those sites where there is an excess of free energy, i.e., at those points that are responsible for the high chemical reactivity of the fuel agglomerates. Therefore, the initial reaction of CO2 with carbon not only provides the heat for temperature induration but also removes much of the excess reactivity in the product.

As the gas stream progresses inside the furnace 10 the gas transfers heat to the solids that are moving counter-currently. To provide sufficient heat so as to maintain carbonization as well as to raise the temperature to the carbonization range (1290"F.--1830"F.), it becomes necessary to oxidize the gas by injecting air, oxygen, or similar gases (such as blast furnace top gases) through the pipes 14 containing sufficient oxidizing constituents. The chemical reaction is: (2) C0+1/20,=CO,; which again permits reaction (1) to take place. Because these two reactions are strongly exothermic the result is sufficient heat being released into the solid phase, thus increasing the temperature to the point of incipient carbonization and beyond.

In subsequent stages, the gas phase composition is regulated by reactions (1) and (2), plus: (3) H,O+COH,+ CO,; which tends to enrich the gas in hydrogen.

The water, of course, derives from moisture elimination near the feed end of the furnace 10.

As a result of these reactions, the gas becomes progressively enriched in H2 and CO until the temperature drops sufficiently to reverse such reactions with the eventual precipitation of carbon black and moisture pickup. However, since the uncarbonized fuel consists primarily of chars and coal fractions with significant volatile content, such volatiles are incorporated into the gas stream.

The final gas composition of the gas at the gas exit or take-off points will then consist of coal volatiles, CO2, plus varying amounts of hydrogen and CO, depending on the gas temperature. The entrained carbon black particles will be removed in conventional dust control systems and will be reused during fuel agglomeration, both to achieve higher agglomerate densities (leading to higher product strength) and also because of their low impurity levels.

The gas would also be cooled by heat exchange for steam or power generation, and to permit recycling into the furnace 10.

WHAT WE CLAIM IS: 1. A method of producing and cooling hot agglomerates of the type used for fuel to prevent oxidization of the agglomerates upon contact with atmosphere and to regenerate process gas, wherein a fuel material, such a coking coal or a mixture of fine coal, char, and non-coking agglomerates, is continuously moved through a furnace in a direction counter to the flow therethrough of process gases which serve to preheat the material to form char, and then continue to heat the material to

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. reactions to produce hot formed coke agglomerates which are discharged at the bottom of the furnace after cooling. In the method of the invention, the hot agglomerates are cooled so that the resulting product will not react (oxidize) with the atmosphere, whilst concurrently providing a product of lower chemical reactivity with respect ot CO2 so as to render such product more attractive for industrial use. It is to be understood that whilst the method of the invention is depicted as being utilized in the vertical shaft furnace 10 in which process gases flow upwardly in counter-current to the progressive downward movement of the fuel material, the method is not limited to such a vertical arrangement of process vessel and a horizontally-arranged vessel could be utilized to plrovide flow of material in one direction and counter-current flow of gases in the other direction. In the method of the invention, a stream of CO2 rich gas is injected through pipes 11 into the formed coke agglomerates produced within the furnace 10. The cool CO2 gas does not react with the agglomerates at the lower portion of the furnace because the agglomerates are sufficiently cool already in this portion of the furnace, and at this point the cooling stream of CO2 gas simply provides a final cooling stage so that the produced fuel agglomerates discharged from the furnace can be handled without significant re-oxidization. As the CO2 gas enters the cooling section of the furnace, the gas becomes heated due to heat exchange between the warm fuel and the gas. At temperatures of several hundred degrees Fahrenheit, however, the gas reacts wuth the carbon-rich fuel according to the following reaction: (a) CO2+C#2C0. Since the reaction becomes exothermic at high temperature, both the gas and the solids will show a steep but transient temperature increase. Such a stage provides the necessary heat for the final induration step in carbonization. At the same time, since the chemical reaction shifts towards the right at higher temperatures the gas becomes CO rich and CO2 poor. This prevents further CO2 conversion while providing a relatively stable temperature regime during final carbonization. An important feature at this stage is that the chemical reaction occurs preferentially at those sites where there is an excess of free energy, i.e., at those points that are responsible for the high chemical reactivity of the fuel agglomerates. Therefore, the initial reaction of CO2 with carbon not only provides the heat for temperature induration but also removes much of the excess reactivity in the product. As the gas stream progresses inside the furnace 10 the gas transfers heat to the solids that are moving counter-currently. To provide sufficient heat so as to maintain carbonization as well as to raise the temperature to the carbonization range (1290"F.--1830"F.), it becomes necessary to oxidize the gas by injecting air, oxygen, or similar gases (such as blast furnace top gases) through the pipes 14 containing sufficient oxidizing constituents. The chemical reaction is: (2) C0+1/20,=CO,; which again permits reaction (1) to take place. Because these two reactions are strongly exothermic the result is sufficient heat being released into the solid phase, thus increasing the temperature to the point of incipient carbonization and beyond. In subsequent stages, the gas phase composition is regulated by reactions (1) and (2), plus: (3) H,O+COH,+ CO,; which tends to enrich the gas in hydrogen. The water, of course, derives from moisture elimination near the feed end of the furnace 10. As a result of these reactions, the gas becomes progressively enriched in H2 and CO until the temperature drops sufficiently to reverse such reactions with the eventual precipitation of carbon black and moisture pickup. However, since the uncarbonized fuel consists primarily of chars and coal fractions with significant volatile content, such volatiles are incorporated into the gas stream. The final gas composition of the gas at the gas exit or take-off points will then consist of coal volatiles, CO2, plus varying amounts of hydrogen and CO, depending on the gas temperature. The entrained carbon black particles will be removed in conventional dust control systems and will be reused during fuel agglomeration, both to achieve higher agglomerate densities (leading to higher product strength) and also because of their low impurity levels. The gas would also be cooled by heat exchange for steam or power generation, and to permit recycling into the furnace 10. WHAT WE CLAIM IS:

1. A method of producing and cooling hot agglomerates of the type used for fuel to prevent oxidization of the agglomerates upon contact with atmosphere and to regenerate process gas, wherein a fuel material, such a coking coal or a mixture of fine coal, char, and non-coking agglomerates, is continuously moved through a furnace in a direction counter to the flow therethrough of process gases which serve to preheat the material to form char, and then continue to heat the material to

devolatilize the coal and form coke agglomerates of plastic consistency, characterized by the steps of: (a) introducing CO2 rich gas into the formed agglomerates at a cooling stage in their production where the agglomerates are at a temperature in the range of 100" to 600OF., (b) heating the CO2 gas in the cooling stage to temperature to initiate the reaction C02 + C = 2 CO to cause unreacted carbon in the hot agglomerate to react and elevate the agglomerates to a final carbonization temperature not exceeding 2350OF (c) moving the gas to a heat-hardening and carbonization zone wherein the temperature of the agglomerates does not exceed 2000OF (d) introducing oxidizing gases into the agglomerates in the heat hardening and carbonization zone, (e) continuing the heating of the gas for a duration to cause the reaction CO + 1/2 03 CO2 and to maintain the temperature of the agglomerate in the zone of step (c) in a range of 1200OF to 2000OF., (f) collecting the C02 gas produced by step (e) and (g) re-introducing the CO2 gas as cooling gas into the process according to step (a).

2. A method of producing and cooling hot agglomerates according to Claim 1, characterized by the step of' continuing the reaction of step (b) until a temperature is reached where the reaction becomes exothermic.

3. A method of producing and cooling hot agglomerates according to Claim 1 or Claim 2, characterized in that the CO2 gas is introduced into the agglomerates at a zone of the furnace where the agglomerates have a temperature of 600OF.

4. A method of producing and cooling hot agglomerates according to any of Claims 1 to 3, characterized by the further step of: processing said gas through drying, preheating and incipient carbonization zones of the furnace at a rate which will enrich the gas in hydrogen according to the reaction (3) H2O + C0 H2+ CO2..

5. A method of producing and cooling hot agglomerates of the type used for fuel as set forth in Claim 1 substantially as herein described with reference to the accompanying drawing.

6. Cooled agglomerates of fuel when produced by the method set forth in any one of Claims 1 to 6.