PROCESS FOR DRY COOLING OF COKE WITH CARBON DIOXIDE WITH SUBSEQUENT USE OF THE CARBON MONOXIDE PRODUCED

Abstract

A process for dry cooling of coke with carbon dioxide with subsequent use of the carbon monoxide produced, in which the coal is cyclically converted to coke and the coke, after the coking oven has been unloaded, is introduced into a cooling apparatus, and carbon dioxide is introduced in the cooling apparatus for dry cooling, such that a Boudouard reaction gives rise to carbon monoxide, and the carbon monoxide produced is used to heat the coking oven. The process allows utilization of the heat which arises in the course of coking for production of carbon monoxide, which in turn is used in the heating, such that a very balanced heat budget of the overall process can be achieved overall.

Description

The invention relates to a method for the dry quenching of coke by means of carbon dioxide with subsequent use of the carbon monoxide produced, said method involving the cyclic coking of coal to coke with the coke being sent to a quenching device after being discharged from the coke oven and carbon dioxide being introduced into the quenching device for dry quenching, thus creating carbon monoxide via a Boudouard reaction and the carbon monoxide produced being used to heat the coke oven. This method allows the heat generated during coking to be used for the production of carbon monoxide which, in turn, can be used in the heating process, thus on the whole achieving an extremely even heat balance throughout the entire process.

Most methods for the production of coke take place in large coke oven batteries or coke oven banks that comprise conventional coke oven chambers or coke oven chambers of the “heat recovery” or “non-recovery” type. In conventional coke oven chambers the coking gas is collected and processed, while the coking gas in “heat recovery” or “non-recovery”-type coke oven banks is combusted in the coke oven in order to heat said oven. Here, in many embodiments the heating of the coke oven is carried out in several steps in a gas space above the coke cake and in a coke oven sole below the coke oven chamber.

The coking process is performed cyclically, the cycles being charging, coking, discharging and quenching. After coking, the coke is pushed out of the coke oven chamber at a temperature of approximately 1100° C. It is pushed out into a quenching car that collects the coke cake and transports it to a quenching device. In many embodiments this is a wet quench tower, where the coke cake is sprayed with water which evaporates and cools the coke cake to a temperature below the kindling temperature of the coke so that it can be transported in the open air without posing a hazard. After quenching, the temperature of the coke is unevenly distributed in the coke cake but is usually less than 100° C.

DE19614482C1 gives one embodiment of a wet quench tower. This teaching describes a plant for the wet quenching of hot coke in a method for the coking of coal using a coke sluice and a coke transfer chute that is located in a quench tower with a water feed device. On the other side, the chute fits onto a coke quenching car equipped at the bottom end with a coke discharge device and water discharge flaps. The water feed system is located directly at the transfer chute and empties into the coke quenching car, which can be sealed watertightly and is equipped with a control system which keeps the coke discharge flaps closed watertightly while the water is being fed in and opens the water discharge flaps once the water feed has been completed. When water is used for quenching, all of the thermal energy stored in the coke cake is lost without being used.

For this reason, increasing efforts have recently been made to dry quench hot coke using gases instead of water. Here, the gases are passed through the hot coke and collected or extracted until the coke has cooled to a temperature below its kindling temperature. The hot gas is usually passed through a heat recovery unit in which steam is generated, thus recovering the thermal energy. In turn, the steam can be used to drive auxiliary units or to generate electric power. For these purposes, inert gases, such as nitrogen or blast furnace gas, are often used.

WO9109094B1 describes a method for the dry quenching of coke in a quenching chamber with the aid of circulating quenching gas, said method allowing the velocity of the gas coming from the coke to be adjusted so that the grain size of the entrained coke dust particles is less than 3 mm and when the hot quenching gas enters the waste heat boiler the grain size of the entrained coke dust is less than 1 mm, said method involving this gas being passed through a device that consists of a quenching chamber and an antechamber with a round cross section of about equal size and a cylindrical outer casing made of metal, and in particular the roof of the quenching chamber being in an inclined position so that it rises to the hot gas channel, thus increasing the cross section of the annular gas channel above the coke pile enough to allow the gas velocity of the hot quenching gas to be adjusted during quenching so that it remains virtually uniform across the length.

WO8602939A1 describes a method for dry coke quenching using quenching gas, said method involving the coke and the quenching gas being fed in countercurrent direction through a two-stage quencher, the first stage involving quenching to coke temperatures of approximately 800° C. and the quenching gas fed through the second quenching stage containing steam, the quenching gas loop thus being directly coupled with a thermal treatment step in which steam is added so that there is essentially no char burnout, which is achieved by the quenching in the first quenching stage taking place solely by indirect heat exchange between the coke and a coolant via heat exchanger walls and the quenching in the second stage being carried out solely by means of the steam-containing quenching gas.

State-of-the-art methods for dry coke quenching may include a variety of embodiments. EP0317752A2 describes a method for improving the performance of coke dry quenchers which involves hot coke being broken up before entering the quenching shaft. DE3030969A1 describes a method for the dry quenching of hot raw coke that is pushed out of the chambers of a coke oven battery and discharged in a quenching chamber, where it is quenched by means of direct or indirect contact, or both, with a quenching agent, and therefore the raw coke is preclassified into two or more size fractions before entering the quenching chamber and the individual size fractions are subjected to quenching in separate quenching chambers.

Further embodiments relate to the heat recovery or cleaning of the quenching gas. DE2435500A1 describes a method for preheating coking coal using superheated waste heat steam which is generated in a dry coke quencher by the coke releasing, at its highest temperature level, some of its heat to the walls of a steam jacket. DE3217146A1 describes a device for dedusting the loop gas of a coke dry quencher in which the gas inlet channel and the gas outlet channel are located at right angles to each other, the gas outlet channel being directly connected, via a conical expansion, with the inlet opening of the waste heat recovery boiler integrated into the gas loop and a dust collection chamber with an inclined dust discharge area being positioned on the opposite side to the gas inlet channel.

However, the said methods and their embodiments have the disadvantage that during quenching the heat of the coke either cannot be recovered or the heat of the coke can only be inefficiently recovered as during quenching a large gas volume is generated and this needs to be passed through a heat recovery unit, making quenching technically difficult or economically inefficient. For this reason, it would be advantageous to utilise the heat that exists in the pushed coke via an endothermic chemical reaction that makes this energy available in chemical form.

One suitable endothermic chemical reaction is the Boudouard reaction. To conduct this reaction carbon dioxide (CO₂) is passed through the hot coke, which reacts with the carbon dioxide to form carbon monoxide (CO). This reaction is endothermic and reads:

C+CO₂2 CO; ΔH=+172.45 kJ/mol

The carbon monoxide is then contained in the gas heated by the quenching of the coke and can be used to heat the coke oven. Quenching hot coke with carbon dioxide using the Boudouard equilibrium is described in GB245702A. Although the application describes the use of carbon monoxide as a fuel gas, it does not propose quenching the coke in a quenching device using carbon dioxide, subsequently collecting the carbon monoxide and then heating a coke oven chamber with the carbon monoxide.

Therefore, the objective is to provide a method that cyclically carbonises coal and uses carbon dioxide (CO₂) to dry quench hot coke after a coking cycle, with the carbon dioxide thus reacting at least partially with the coke to form carbon monoxide (CO) according to the Boudouard equilibrium and the carbon monoxide obtained being collected and used to heat at least one coke oven.

According to the invention, coke quenching using carbon dioxide takes place in a quenching device that is preferably designed as a quenching shaft. Following coking of the coal and completion of the coking process, the coke cake is taken to, or tipped onto, a quenching car, which transports the coke cake to the quenching device. Here, the coke cake is sealed off from the surrounding atmosphere and carbon dioxide is passed through it. Preferably, this is done in a vertically upward gas flow direction so that the specifically heavier carbon dioxide is displaced by the lighter carbon monoxide during the quenching process. The carbon dioxide may be a gas mixture in any state and even be in a mixture with other gases, but is preferably used cooled and dried in pure form.

What is claimed in particular is a method for the dry quenching of coke, in which

• • coal is heated in a coke oven via heating by means of a high calorific gas and coke is obtained via cyclic coking, said coke being pushed out into a coke quenching car on completion of the coking, and
  • the incandescent coke is transported to a coke quenching device in a coke quenching car in which said incandescent coke is quenched to a temperature below the kindling temperature by means of a quenching gas, and
  • carbon dioxide (CO₂), which reacts at least partially with the incandescent coke to form carbon monoxide (CO) according to the Boudouard reaction, is used as the quenching gas,

said method being characterised in that

• • due to the dry quenching being carried out in a coke quenching device the carbon monoxide-containing quenching gas obtained is collected, and
  • the gas mixture obtained is at least partially returned to the coke oven in order to heat said oven with the carbon monoxide (CO).

The carbon dioxide added for quenching purposes may be dried or undried. So as to avoid the production of undesired by-products, the carbon dioxide added is usually dried and in pure form. For this, the carbon dioxide can be taken from any source and in an exemplary embodiment comes from gas scrubbing processes. Said carbon dioxide can be used without being cleaned, but may also be cleaned prior to use. Other inert gases, such as nitrogen, may also be added to the carbon dioxide.

For addition, the carbon dioxide may be temporarily stored in a storage tank. The carbon monoxide obtained during quenching of the coke may also be temporarily stored. Part streams of these two gases may also be diverted and used for purposes unrelated to the coke production plant. Meters for measuring the concentration of the gases may be installed in the carbon dioxide or the carbon monoxide lines. These readings may be referred to in order to decide on the use of these gases at various times. This may be done manually or by computer.

In a further embodiment steam (H₂O) is added to the carbon dioxide as quenching gas. The steam then reacts with the coke to form hydrogen (H₂) and carbon monoxide (CO), from which synthesis gas is generated with the carbon monoxide which is formed by the carbon dioxide reacting with the coke. The synthesis gas can be used solely for heating or a part stream can also be diverted and used for any further purpose.

The steam may be added to the carbon dioxide used for quenching at any point. It may, for example, be added to the carbon dioxide before said carbon dioxide is used to quench the coke. It may, however, also be fed to the quenching device or to the shaft above the feed point for the carbon dioxide separately from said carbon dioxide and downstream in the direction of flow. For this, the water may also be injected into the carbon dioxide stream in liquid form. It is also possible to add the steam to the coke cake via side feed nozzles directly downstream in the direction of flow when part of the coke has already reacted with the carbon dioxide.

Steam can also be added to the carbon monoxide after quenching by the carbon dioxide in order to carry out a separate carbon monoxide (CO) shift and thus achieve conversion into synthesis gas. The steam is then added after the carbon dioxide has been passed through the coke. For this, liquid water may also be added. In a typical embodiment this is then sprayed into the quenching gas after it has passed through the coke cake. After the Boudouard reaction has been carried out, the carbon monoxide is then cooled and passed though a conversion reactor to convert the carbon monoxide (CO) into carbon dioxide (CO₂) and hydrogen (H₂) via the water-gas shift reaction.

An excess of steam may also be added prior to quenching and passage through the coke cake so that a reaction for converting surplus steam and carbon monoxide into hydrogen can subsequently be carried out. In this case, part of the steam (H₂O) may already react with the hot coke in a water-gas reaction to form carbon monoxide (CO) and hydrogen (H₂). Liquid water can also be used instead of steam. This is sprayed into the carbon monoxide stream before its passage through the coke. This procedure can also be carried out in combination with feeding steam to the quenching gas.

When water is added to the quenching gas or during a subsequent conversion reaction, synthesis gas is obtained. It is possible to divert a part stream thereof and use the synthesis gas for any other purpose. In one embodiment of the invention it can be used at least partially to heat the coke oven.

Before being fed to the coke oven the carbon monoxide used to heat the coke oven can be mixed with a fuel gas. In one embodiment this is hydrocarbonaceous and so a hydrocarbonaceous fuel gas is mixed with the carbon monoxide. In one embodiment of the invention, the fuel gas is natural gas. This is mixed with the carbon monoxide before it is fed into the coke oven and used to heat said oven. It is also possible for the carbon monoxide for heating the coke oven to be mixed with fuel gases that are generated as byproducts in other processes and still have a certain calorific value. For example, it is possible to add blast furnace gas from a blast furnace process to the carbon monoxide before it is added to the coke oven. In a further embodiment of the invention it is also possible for additional heating to feed coke oven gas to the carbon monoxide before it is added to the coke oven.

The carbon monoxide that is generated by the Boudouard reaction and to which a fuel gas has been added as required can be used directly for heating without further treatment before it is fed to the coke oven. However, it can also be subjected to a heat recovery process before being used for heating in a coke oven. In an advantageous embodiment, the carbon monoxide is passed through the coke cake at a temperature of approximately 1000° C. After being passed through the coke cake the temperature of the carbon monoxide is usually still approximately 900° C. as the Boudouard reaction almost ceases below this temperature threshold.

This temperature is adequate for heat recovery and so in an advantageous embodiment the carbon monoxide is passed through a heat recovery unit before being fed into the coke oven for combustion. For example, it is possible to use this heat to preheat, in countercurrent, the carbon dioxide gas stream that is fed in. It is also possible to use the heat for various purposes but it is advantageously used to generate steam. The steam can also be used for various purposes but is usually used to generate mechanical energy. In a typical embodiment this is, in turn, used to drive a turbine and to generate electric power.

After quenching, the coke cake usually has a temperature of 500 to 900° C. To finally bring the coke down to a temperature below the kindling temperature after quenching, final quenching is carried out using state-of-the-art methods following the quenching operation with the carbon dioxide within the scope of the invention.

The carbon dioxide for quenching the coke can simply be directed into the coke cake in a stream. It may however also be split into any number of part streams. In one embodiment of the method according to the invention the carbon dioxide stream that is fed in is split into at least two part streams, with one carbon dioxide part stream being fed into the coke quenching device from below and a further carbon dioxide part stream being fed in in a part of the shaft in which the coke to be quenched has a temperature of 500 to 900° C. The carbon dioxide part stream can be fed in at any point in the quenching device, but is preferably done at this point as utilisation of the heat is thus optimum. An additional part stream of carbon dioxide can also be fed in at any time in order to achieve complete quenching of the coke. The part streams can generally be fed into the coke at any point in the hot coke cake.

For use in implementing the method, the coke oven battery or coke oven bank may be of any design and configured in any way. The coke oven battery from which the coke comes and which is heated by the carbon monoxide may, for example, be a coke oven battery in which the coking gas is collected and processed. The coke oven bank from which the coke comes and which is heated by the carbon monoxide may, for example, be a “heat-recovery”-type coke oven battery. Finally, the coke oven bank from which the coke comes and which is heated by the carbon monoxide may also be a “non-recovery”-type coke oven battery. Even the coke ovens that are located in a coke oven battery or bank may ultimately be of any design as long as they are suitable for the production of coke and for being heated by carbon monoxide. The coke pushing may also be carried out at a different coke oven battery or bank from that to which the carbon monoxide obtained during quenching is fed, but this is not usual practice.

In one embodiment of the invention the waste gas or completely combusted coking gas from the coke oven is subjected to gas scrubbing. This allows the carbon dioxide to be scrubbed from the waste gas and the carbon dioxide obtained to be added to the carbon dioxide for quenching the coke. In this way an even carbon dioxide (CO₂) balance can be achieved for the entire plant as the carbon dioxide from the waste gas is, in turn, used to quench the coke and, after being converted to carbon monoxide, to heat the oven. As a result, the overall emission of carbon dioxide is low and ideally non-existent.

The quenching device for the coke may be of any design for implementing the invention. Preferably, for example, the coke quenching device may be a coke quenching shaft. But the coke quenching device may also be a coke quenching chamber. This may be equipped with auxiliary equipment to improve or optimise quenching. In one embodiment of the invention the coke quenching chamber is equipped with an antechamber in which the gas velocity is evened out. The quenching device or the subsequent transfer line for the carbon monoxide may also be equipped with a dedusting device. This allows the dust to be reduced if a dust-laden coal is used or large amounts of dust are created during quenching.

Furthermore, auxiliary equipment, such as storage tanks for liquids or gases, pumps, valves, heating or quenching equipment, or meters for measuring temperatures or concentrations of gas constituents may be used at any point in the method according to the invention.

The invention has the advantage of utilising the thermal energy of the coke after coking by means of an endothermic chemical reaction and so the thermal energy of the hot coke can be utilised much better than in prior-art methods. In addition, if down-stream gas scrubbing of the waste gas is employed, the invention has the advantage of considerably reducing the carbon dioxide balance or even reducing it to zero in relation to its emission to the atmosphere as the carbon dioxide is fed back into the method. The environmental compatibility of this method can thus be considerably improved.

The invention is further explained by means of a drawing, this drawing merely representing an exemplary embodiment and not being limited thereto.

FIG. 1 shows a coke oven which serves to carbonise coal. It depicts the coke oven chamber (1) with the coal cake (2), the coke oven chamber doors (3), the primary heating space (4) above the coke cake (2) and the secondary heating space (5) below the coke cake (2). The quenching car (6), which collects the coke cake (2) for quenching, is parked in front of the coke oven chamber (1). Said quenching car (6) is brought in front of the coke quenching chamber (7) and the coke cake (2) is emptied into the coke quenching chamber (7) via a feed flap (7a). Said flap (7a) is closed once the coke quenching chamber (7) has been filled. Carbon dioxide (8, CO₂) then flows into the coke quenching chamber (7) from below and reacts with the hot coke cake (2) according to the Boudouard equilibrium to form carbon monoxide (9, CO). This is extracted in an upward direction and, following dedusting in a dedusting unit (10) and a heat exchange for preheating the carbon dioxide (8) in a heat exchanger (11), it is directed into the secondary heating space (5) of the coke oven (1). Here, it is added to the partially combusted coking gas which has already flowed into the secondary heating space (5) from the primary heating space (4) and combusted. As a result, it contributes to the heating of the coke cake (2) through the floor of the coke oven chamber (1). After combustion, the fully combusted coking gas is exported out of the secondary heating space (5) as waste gas (12) and sent to a gas scrubbing device (13). Thereby, carbon dioxide (13a) is obtained. This is used to quench the coke (2) via a storage tank (14) for the carbon dioxide (8). The cleaned waste gas (13b) is exported from the gas scrubbing device (13) and sent to a heat recovery unit (15). Here, a generator (15a) that generates electric power is driven via a turbine. The cooled waste gas (15b) is exported via a flue (16). The quenched coke (5a) is discharged via a discharge flap (7b) and sent for final quenching.

LIST OF REFERENCE NUMBERS AND DESIGNATIONS

• 1 Coke oven chamber
• 2 Coal or coke cake
• 3 Coke oven chamber doors
• 4 Primary heating space
• 5 Secondary heating space
• 5a Quenched coke
• 6 Quenching car
• 7 Coke quenching chamber
• 7a Feed flap
• 7b Discharge flap for quenched coke
• 8 Carbon dioxide
• 9 Carbon monoxide
• 10 Dedusting unit
• 11 Heat exchanger
• 12 Waste gas
• 13 Gas scrubbing device
• 13a Carbon dioxide from the gas scrubbing
• 13b Cleaned waste gas
• 14 Storage tank
• 15 Heat recovery unit 15a Generator 15b Cooled waste gas
• 16 Flue

Claims

1. A method for the dry quenching of coke in which

coal is heated in a coke oven via heating by means of a high calorific gas and coke is obtained via cyclic coking, said coke being pushed out into a coke quenching car on completion of the coking, and

the incandescent coke is transported to a coke quenching device in a coke quenching car in which said incandescent coke is quenched to a temperature below the kindling temperature by means of a quenching gas, and

carbon dioxide (CO2), which reacts at least partially with the incandescent coke to form carbon monoxide (CO) according to the Boudouard reaction, is used as the quenching gas,

wherein due to the dry quenching being carried out in a coke quenching device the carbon monoxide-containing quenching gas obtained is collected, and

the gas mixture obtained is at least partially returned to the coke oven in order to heat said oven with the carbon monoxide (CO).

2. The method for the dry quenching of coke according to claim 1, wherein steam is added to the quenching gas.

3. The method for the dry quenching of coke according to claim 2, wherein the steam is added to the coke quenching device above the coke cake and downstream in the direction of flow so that a reaction for converting surplus carbon dioxide into carbon monoxide can subsequently be carried out.

4. The method for the dry quenching of coke according to claim 1 wherein liquid water is sprayed into the quenching gas after it has passed through the coke cake so that a reaction for converting surplus carbon dioxide into carbon monoxide can subsequently be carried out.

5. The method for the dry quenching of coke according to claim 1, wherein a hydrocarbonaceous fuel gas is mixed with the carbon monoxide used to heat the coke oven before said carbon monoxide is fed to the coke oven.

6. The method for the dry quenching of coke according to claim 5, wherein the fuel gas is natural gas.

7. The method for the dry quenching of coke according to claim 5, wherein the fuel gas is blast furnace gas from a blast furnace process.

8. The method for the dry quenching of coke according to claim 5, wherein the fuel gas is coke oven gas.

9. The method for the dry quenching of coke according to claim 1, wherein the carbon monoxide is subjected to a heat recovery process before being fed to the coke oven for heating.

10. The method for the dry quenching of coke according to claim 9, wherein steam is generated during the heat recovery process.

11. The method for the dry quenching of coke according to claim 1, wherein the carbon dioxide for quenching is split into at least two part streams, with one carbon dioxide part stream being fed into the coke quenching device from below and a further carbon dioxide part stream being fed in in a part of the coke quenching device in which the coke to be quenched has a temperature of 500 to 900° C.

12. The method for the dry quenching of coke according to claim 1, wherein the coke oven battery from which the coke comes and which is heated by the carbon monoxide is a “heat-recovery”-type coke oven battery.

13. The method for the dry quenching of coke according to claim 1, wherein the coke oven battery from which the coke comes and which is heated by the carbon monoxide is a “non-recovery”-type coke oven battery.

14. The method for the dry quenching of coke according to claim 1, wherein the coke oven battery from which the coke comes and which is heated by the carbon monoxide is a coke oven battery in which the coking gas is collected and processed.

15. The method for the dry quenching of coke according to claim 1, wherein the waste gas or coking gas from the coke oven is subjected to gas scrubbing in which the carbon dioxide is scrubbed from the waste gas and the carbon dioxide obtained is added to the carbon dioxide for quenching the coke.

16. The method for the dry quenching of coke according to claim 1, wherein the coke quenching device is a coke quenching shaft.

17. The method for the dry quenching of coke according to claim 1, wherein the coke quenching device is a coke quenching chamber.

18. The method for the dry quenching of coke according to claim 1, wherein the coke quenching chamber is equipped with an antechamber.