GB1577212A

GB1577212A - Process of continuously producing formed coke

Info

Publication number: GB1577212A
Application number: GB23031/78A
Authority: GB
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1977-06-17
Filing date: 1978-05-26
Publication date: 1980-10-22
Also published as: AU3674178A; ZA783135B; FR2394598A1; BR7803833A; DE2825691A1; CA1118207A; JPS5416505A; IN147339B; BE868083A

Description

(54) IMPROVED PROCESS OF CONTINUOUSLY PRODUCING FORMED COKE (71) We, ALLIS-CHALMERS COR PORATION, 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 process of continuously producing formed coke, and more specifically metallurgical coke, and involves the continuous treatment of coals based on agglomeration with a separate hardening stage that combines preheating and charmaking with final carbonization and cooling of the coke.

The carbonization of coal materials is well documented and as known the coal is heated.

This accomplishes rhe melting of the tars with the lighter ingredients passing off as gas. Pitch is formed within the fuel body and carbonization of the pitch serves as a binder to the particles of cooling coal.

It is also known to follow the carbonization process by the briquetting of non-coking coal.

However, it has been believed that to attain a satisfactory result, a high proportion of coking coal must be induded. It is also known to submit coking coal to a precoking step before briquetting. It has also been believed that low grade coal or non-coking coal could not be subjected to a preheating stage to a temperature below the point of actual decomposition followed thereafter by carbonization.

This invention provides a process for continuously producing coke with characteristics considered desirable both from an economic and a technical standpoint. The process provides for an inexpensive, continuous treatment of coals and continuous output of coke and is amenable to simple control, while generating byproduct gases of high BTU content. The process is based on an agglomeration step and a separate hardening stage which combines preheating and charmaking of the coal raw material with final carbonization and cooling of the coke.

It is, therefore, an object of this invention to provide a process of continuously producing formed coke which is relatively inexpensive and simple, and which overcomes the disadvantages of the prior art in a practical and satisfactory manner, including the following respects: (a) It entails a minimum number of process steps consistent with product gravity; (b) It offers an effective environmental control of gaseous and solid emissions; (c) It is amenable to simple control although continuous; (d) It yields a high-gravity by-product gas; (e) It is relatively flexible in regard to the raw material requirements.

According to the invention there is provided a process of continuously producing formed coke, which is characterized by the steps of: introducing a mixture of fine coal, char, and non-coke agglomeration into a vertical shaft furnace for movement of said mixture downwardly through successive preheating, devolatilization, and cooling sections of said furnace, preheating the mixture in the preheating section of the furnace to a temperature of 700"F. to 1000"F. to form char and initiate devolatilization of the coal, raising the temperature of the preheated mixture within said lower devolatilization section of the furnace to a temperature of 1200"F. to 2400"F. to complete devolatilization and form discrete coke agglomerates having a plastic consistency, cooling the plastic-consistency coke agglomerates in said lower cooling section with cool CO2 gas reclaimed from the furnace to reduce the temperature of the coke agglomerates to a range of 6000F. to 1000F. to harden the coke agglomerates, and screening the downwardly moving hardened coke and char to separate the formed coke agglomerates from the char which is recycled through the furnace leaving the coke agglomerates as the desired product to be continuously discharged from the furnace.

Preferably said cooling is accomplished by introducing an oxidizing gas along with said cool CO, gas into the cooling section of said furnace to flow countercurrent to the movement of the material mixture in said cooling section.

Preferably the process includes the further steps of crushing and screening the separated char to form a coarse fraction and a fine fraction, agglomerating the fine char fraction in a separate agglomeration section, and introducing a mixture of clean fine coal, the coarse fraction of char, and the agglomerated char into said vertical shaft furnace.

Preferably there are included the further steps of collecting the gases given off by said coal during the degasifying step, cooling said gases to condense distillates, and supplying said distillates to said agglomeration section to be mixed with said fine char.

Preferably there are also included the further steps of cooling the collected gases to precipitate carbon black, removing the carbon black precipitation and applying the carbon black precipitation to the char agglomerates.

Preferably the process includes uniformly dispersing the char in the mixture progressing downwardly through the vertical shaft furnace to reduce direct contact between coal particles and prevent agglomeration between said particles.

Preferably the process includes controlling the rate of downward flow of the mixture through the furnace to suit the characteristics of the mixture materials, and adjusting the proportions of char and coal to provide sufficient char to surround and support the formed coke agglomerates as they reach plastic consistency to prevent exessive swelling and subsequent physical degradation thereof due to internal pressure of gases evolved in the agglomerates.

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 material flow diagram.

Referring to the drawing, incoming raw material coal 10 is first beneficiated in a system indicated generally at 11 which is shown comprising crushing, grinding, screening and washing. The clean fine coal is delivered to a mixer 12 by a conveyor or other means indicated generally at 14 and is introduced into a vertical shaft furnace 16 through a top feeder 31 together with char particles and non-coked agglomerates.

Char to be mixed with the clean fine coal particles, preferably of minus 10 Tyler mesh size, may be obtained from the shaft furnace from the discharge end thereof where cool hardened furnace coke is discharged over an internally arranged furnace screen 17 which preferably is a No. 10 Tyler mesh size. The fine char drops through the furnace screen 17 into discharge chutes 18 and onto a conveyor 19 which delivers the char to means for crushing and screening the char, indicated generally at 21.

It is to be understood that rhe char is used to form char agglomerate which is basically non-coke in its composition. However, trace amounts of coke fines will pass through the furnace screen 17 and become part of the char agglomerate.

The crushed and screened char is discharged from the crushing and screening system in two streams, one stream being a coarse char fraction and the other stream being a fine char fraction. The coarse char fraction is deposited on a coarse char conveyor 22 which carries the char upwardly for introduction into the mixture 12. The fine char is fed to an agglomeration section, generally indicated at 26, for agglomeration and thence is passed to a pelletizing or briquetting system, generally indicated at 27, where the fine char agglomerates are formed into pellets or briquettes, preferably od a size that will pass a No. 2 or No. 3 Tyler mesh screen. The formed pellets or briquettes are then passed to a conveyor 28 for delivery to the mixer.

Thus, in this way, clean fine coal, coarse char, and fine char pellets or briquettes are mixed together in the mixer 12, and the mixture is introduced into the top feeder 31.

The crushing and screening system 21, the agglomeration section 26, and the pelletizing or briquetting system 27 may be of any of the well-known commercially available systems.

The fine coal introduced into the top of the shaft furnace is subject to gradual heating as it passes downwardly through the furnace and becomes progressively devolatilized and charred. The feed mix is preheated to a temperature of 700"F. to 1()000F. to commence the devolatilization. During the downward passage through the devolatllizing section of the furnace, devolatilization is completed and the fine coal particles are prevented from agglomerating with each other by operation of the surrounding coarse char and fine char briquettes which break down during processing. The char will surround the coal and reduce direct contact between the coal particles. Upon reaching the final coking temperature range of 1200"F.

to 2400 F., depending on rhe coal, the fine coal particles will soften and form discrete coke agglomerates that minimize subsequent dusting problems. It has also been determined that, as the coal preheats and is devolatilized it enriches the coal reducing gas which is admitted to the cooling section for upward flow through the furnace, as will be more fully described hereinafter.

The gases given off during the coking processes are recovered through conduits 36 and 37 located in the upper portion of the furnace.

These recovered gases are subjected to a cool ing process effected in a cooling and condensing system, indicated generally at 38. In the system 38, the distillations are condensed and the condensed distillates are re-introduced into the coking process through the agglomeration section 26.

The cool gases from the cooling section 38 are processed through a gas compositionadjustment section, generally indicated at 39, and oxidizing gases are reclaimed. These oxidizing gases are re-introduced into the furnace 16 through a pipe 41 which is located at the bottom of the devolatilization or final coking stage of the furnace 16.

Also reclaimed from the gas-adjustment section 39 are cool CO2 gases which are utilized as reducing cooling gases for hardening the coke in the lowest portion of the furnaceprior to being discharged therefrom. The cooling gases are introduced into the bottom of the furnace through a pipe 42. The cooling gases lower the temperature of the coke from approximately the coking temperature range of 1200 F. to 2400"F. down to a range of from 6000 F. to 1000F. At this lower temperature the coke is hardened and is discharged over the screen 17 with the fine char falling into the collecting chutes 18.

As previously mentioned, the char is subsequently separated from the cool hardened coke product by operation of the screen 17, and is after crushing divided into coarse and fine char fractions, the coarse fraction being recirculated, via the conveyor 22 or other suitable means for introduction into the mixer 12, whilst the fine char fraction serves as the raw material to make a coal char agglomerate in the system 26.

The use of devolatilized char for coke agglomeration permits the use of a wide range of raw material coals.

From the preceding description, it is apparent that the fine char fractions are utilized to coke manufacture, using either a pelletized or a briquette method with the coal char agglomerates being introduced into the shaft furnace with the coal particles which are heated to form a coke agglomerate and hardened. The concept of creating char and recyding the char as a feed material permits an increase in the amount of low grade noncoking coal that heretofore could be used with high grade coking coal to produce a formed coke agglomerate.

One specific advantage is the use of a threecomponent mixture comprised of fine char agglomerates, coarse char, and coal fines and the ability to change the rate of descent of the burden provide the flexibility with respect to the heating cycle of both charmaking and coking operations. Another advantage is the ability to change the ratio of the fine char agglomerates, coarse char, and coal fines in the burden which permits control of the gas permeability of the burden. A third advantage is the ability to prevent coke degradation during the hardening stage. This advantage is related to the use of char and coal in varying proportions to support the coke agglomerates during their descent through the furnace. Coke agglomerates can spall, swell and otherwise physically degrade during coking due to the internal pressure of gases that evolve during coking.However, as set forth, the use of nonreactive char that surrounds the formed coke agglomerate provides a firm support and prevents the coke swelling excessively. Also, the use of coal particles that can soften within the interstices of the bed transfers thermal stresses from the coke agglomerates to the coal. This provides for firm but moderately plastic support that can absorb minor dimensional changes in the agglomerates without physical degradation occurring, thereby forming a strong desirable coke product.

The use of a cooling stage, based on circulating reductant gases, prevents excessive heat loss in an energy efficient system associated with the circulating load of char in the system.

In addition, the combination of charmaking and coking operations in a single vessel eliminates the need for multiple solid and gas transfer operations and provides for effective environmental control of gaseous and solid emissions. A cooling method found to be extremely beneficial is set forth herein as a preferred application.

The cooling method herein disclosed is particularly well adapted for countercurrent vessels, which can be either vertically or horizontally arranged, but which in the present invention is described and claimed as a vertical shaft furnace into the bottom of which a stream of CO2 rich gas is injected, as shown in the drawing. The cool CO2 gas does not react with the agglomerates being discharged because at the discharge end such products are sufficiently cool already; at this point the cooling stream of CO2 simply provides a final cooling stage so that the fuel products can be handled without significant re-oxidation.

As the CO2 enters the cooling vessel, it becomes heated due to heat exchange between the warm fuel and the gas. At temperatures of several hundred degrees F., however, the gas reacts with the carbon-rich fuel according to the following reaction: Reaction (1) CO2 + C

2 CO And, since the reaction becomes exothermic at high temperatures, 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 or hardening step in carbonization. At the same time, since the chemical reaction shifts toward the right at higher temperatures, the gas becomes CO rich and CO2 poor; this prevents further COO conversion, while providing a relative stable temperature regime during final carbonization.An important feature at this stage is that the chemical reaction occurs preferentially, that is, reacts with unreacted portions 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.

Thus, 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 vessel, it transfers heat to the solids that move countercurrently. To provide sufficient heat so as to maintain carbonization as well as to raise the temperature to the carbonization temperature range of from 1290 F. to 1830 F. it becomes necessary to oxidize the gas injecting by air, oxygen, or similar gases (such as blast furnace top gases) containing sufficient oxidizing constituents. The chemical reaction would then be: Reaction (2) CO + 1/2 O2

Co2 which, again, permits reaction 1 to take place.

Because these two reactions are strongly exothermic, the result is that sufficient heat is 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 a third reaction expressed by the equation: H20 + CO e H2 + CO2 which tends to enrich the gas in hydrogen. The water derives from moisture elimination near the feed end of the vessel.

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 exit point will then consist of coal volatiles, CO2, plus vary ing amounts of hydrogen and CO depending on the gas temperature.

It is expected that the entrained carbon black particles would be removed in convent tional dust control systems. These carbon black particles will be available for re-use dur ing fuel agglomeration, both to achieve higher agglomerate densities (leading to higher pro duct strength) and also because of their low impurity levels. The gas would also be cooled by heat exchange for steam or power genera tion and to permit recycling into the vessel.

WHAT WE CLAIM IS: 1. A process of continually producing formed coke, characterized by the steps of: introducing a mixture of fine coal, char, and non-coke agglomerates into a vertical shaft furnace for movement of said mixture downwardly through successive preheating, devolatilization, and cooling sections of said furnace, preheating the mixture in the preheating section of the furnace to a temperature of 700"F. to 1000 F. to form char and initiate devolatilization of the coal, raising the temperature of the preheated mixture within said lower devolatilization section of the furnace to a temperature of 12000F. to 2400 F.

to complete devolatilization and form discrete coke agglomerates having a plastic consistency, cooling the plastic-consistency coke agglomerates in said lower cooling section with cool CO2 gas reclaimed from the furnace to reduce the temperature of the coke agglomerates to a range of 600"F. to 100 F. to harden the coke agglomerates, and screening the downwardly moving hardened coke and char to separate the formed coke agglomerates from the char which is recycled through the furnace leaving the coke agglomerates as the desired product to be continuously discharged from the furnace.

2. A process of continuously producing formed coke according to claim 1, character-- ized in that said cooling is accomplished by introducing an oxidizing gas along with said cool CO2 gas into the cooling section of said furnace to flow countercurrent to the movement of the material mixture in said cooling section.

3. A process of continuously producing formed coke according to claim 1 or 2, characterized by the further steps of: crushing and screening the separated char to form a coarse fraction and a fine fraction, agglomerating the fine char fraction in a separate agglomeration section, and introducing a mixture of clean fine coal, rhe coarse fraction of char, and the agglomerated char into said vertical shaft furnace.

4. A process of continuously producing formed coke according to claim 3, characterized by the further steps of collecting the gases given off by said coal during the degasifying step, cooling said gases to condense distillates, and supplying said distillates to said agglomeration section to be mixed with said fine char.

5. A process of continuously producing formed coke according to claim 3 or 4, characterized by the further steps of cooling the collected gases to precipitate carbon black, removing the carbon black precipitation and applying the carbon black precipitation to the char agglomerates.

6. A process of continuously producing formed coke according to any one of claims 1 to 5, characterized by uniformly dispersing the char in the mixture progressing downwardly through the vertical shaft furnace to

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. important feature at this stage is that the chemical reaction occurs preferentially, that is, reacts with unreacted portions 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. Thus, 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 vessel, it transfers heat to the solids that move countercurrently. To provide sufficient heat so as to maintain carbonization as well as to raise the temperature to the carbonization temperature range of from 1290 F. to 1830 F. it becomes necessary to oxidize the gas injecting by air, oxygen, or similar gases (such as blast furnace top gases) containing sufficient oxidizing constituents. The chemical reaction would then be: Reaction (2) CO + 1/2 O2 Co2 which, again, permits reaction 1 to take place. Because these two reactions are strongly exothermic, the result is that sufficient heat is 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 a third reaction expressed by the equation: H20 + CO e H2 + CO2 which tends to enrich the gas in hydrogen. The water derives from moisture elimination near the feed end of the vessel. 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 exit point will then consist of coal volatiles, CO2, plus vary ing amounts of hydrogen and CO depending on the gas temperature. It is expected that the entrained carbon black particles would be removed in convent tional dust control systems. These carbon black particles will be available for re-use dur ing fuel agglomeration, both to achieve higher agglomerate densities (leading to higher pro duct strength) and also because of their low impurity levels. The gas would also be cooled by heat exchange for steam or power genera tion and to permit recycling into the vessel. WHAT WE CLAIM IS:

1. A process of continually producing formed coke, characterized by the steps of: introducing a mixture of fine coal, char, and non-coke agglomerates into a vertical shaft furnace for movement of said mixture downwardly through successive preheating, devolatilization, and cooling sections of said furnace, preheating the mixture in the preheating section of the furnace to a temperature of 700"F. to 1000 F. to form char and initiate devolatilization of the coal, raising the temperature of the preheated mixture within said lower devolatilization section of the furnace to a temperature of 12000F. to 2400 F.

reduce direct contact between coal particles and prevent agglomeration between said particles.

7; A process of continuously producing formed coke according to any one of claims 1 to 6, characterized by controlling the rate of downward flow of the mixture through the furnace to suit the characteristics of the mixture materials, and adjusting the proportions of char and coal to provide sufficient char to surround and support the formed coke agglomerates as they reach plastic consistency to prevent excessive swelling and suibsequent physical degradation thereof due to internal pressure of gases evolved in the agglomerates.

8. A process of continuously producing formed coke as set forth in claim 1, sub stantially as herein described with reference to the accompanying drawing.

9. Formed coke when produced by the process set forth in any one of claims 1 to 8.