EP0022018B1 - Process and plant for the production of coke or semi-coke - Google Patents

Abstract

In the continuous production of coke or semicoke from coal grains and/or fines an inclined air-tight rotating tubular oven is fed with coal grains and/or fines from a hopper. As the coal grains and/or fines progress down the rotating oven they are heated by a stoichiometric mixture from a burner and converted into coke or semicoke having a volatile content of from 1% to 20%. During the heating of the coal grains and/or fines the interior of the oven is maintained under a slightly elevated pressure in relation to the atmosphere. The coke or semicoke is then extracted from the oven and passed to an extinguishing device where the coke or semicoke is extinguished to prevent recombustion.

Description

The subject of the invention is a process for the continuous production of coke or semi-coke by means of a rotary kiln.

In French patent application 7422402 (Publication No. 2,284,662), a process has been described which allows the manufacture of a reactive coke, but which is however fairly well cooked with a volatile matter content usually less than 8%, in which volatile materials are used to produce in situ the heat necessary for carbonization and in which the sensible heat of the fumes as well as the remaining combustible gases can be used for the production of steam. Such a process is almost autothermal and in practice leads to a coke of 1 to 8% of volatile matter.

This process is effective for obtaining more or less reactive cokes with a low volatile matter content, but does not allow, without significant modifications, to obtain cokes or semi-cokes baked at relatively low temperature, for example below 600 °. C and still having a fairly high content of volatile matter, for example up to 20%.

Such cokes or semi-cokes can have many direct or indirect applications. They can be recovered as they are for electrometallurgy, electrochemistry, gasification. They can be used as an adjunct in the manufacture of molded coke or in carbonized coke pastes with charging processes using preheating and / or compacting.

The object of the invention is to propose a new process and a new installation making it possible to obtain, with good adjustment flexibility, a wide range of cokes differentiated by their volatile matter contents, for example in the game from 1 to 20% volatile matter. Another object is to avoid the combustion of by-products in situ, in order to recover a maximum amount of tar and gas.

These objects are achieved, according to the invention, in a process for the continuous production of coke or semi-coke with a volatile matter content of between 1% and 20% from grains or coal fines of more than 15%. of volatile matter and a swelling index of less than 8, into which the fines and / or grains are introduced upstream of a slightly sloping tubular rotary kiln, where the product progresses, during its treatment, upstream end to the downstream end, which is supplied with heat by a hot gas generator and from which the coke or semi-coke produced is extracted, in which the supply of the hot gas generator is controlled so that it produces neutral or reducing hot fumes, by the fact that the oven enclosure is kept in slight gas overpressure relative to the atmosphere by controlled injection of an auxiliary ballast fluid.

In practice, the hot gas generator may for example be a burner installed at the end of the rotary kiln, as is known per se.

We see that the process achieves the goal we set. By renouncing the partial in situ combustion of coal, it preserves the by-products, and in particular the tars. The overpressure by avoiding any presence of oxidizing gas also contributes to preserving the by-products from degradation. Of course this overpressure must be accompanied by the usual measures, in such a circumstance, by achieving a good seal of the installation and in particular of the joints of the rotary kiln. Baffle seals will be fitted to the furnace's heating and supply hoods, to avoid the release of tarry gases to the outside.

To obtain a setting at the desired carbonization temperature, for example at a set temperature between 450 and 1100 ° C, the heat output of the hot gas generator is controlled by the difference between the temperature of the coke or semi-coke at the end of the oven and a set cooking temperature. In this way, carbonization is obtained at the set temperature, which, indirectly, makes it possible to obtain the desired content of volatile matter. Controlling the carbonization temperature is essential according to the invention.

The overpressure in the oven enclosure can be adjusted by action on a valve located upstream of the production gas dewatering fan. A finer adjustment can be obtained in addition by injecting an auxiliary ballast fluid, such as steam and / or combustion fumes of the lean gas from the recycled carbonization and / or nitrogen, directly in the rotating oven.

According to an advantageous means, the coke or semi-coke is quenched by introduction into an inclined rotating tube fitted with water sprayers and the coke or semi-coke is quenched immediately after its extraction from the rotary kiln. The process leading, depending on the settings, to highly flammable semi-cokes, the immediate extinction of these semi-cokes constitutes an important means.

To reduce the formation of agglutinated coke balls, it is possible, during the carbonization of agglutinating coals, to add to the fines and / or grains a recycled part of the finest fraction of the cokes or semi-cokes obtained. By thus reducing the formation of such balls, the re-ignition of the semi-coke is avoided, since these balls are difficult to extinguish at heart. Applicant's tests have shown that the proposed method considerably reduces the proportion of balls.

• - un four tournant tubulaire à légère pente comportant, en son point le plus haut, des moyens sensiblement étanches d'introduction de charbon en grains et/ou en fines et des moyens étanches d'extraction des gaz du four et, en son point le plus bas, des moyens d'introduction ou de génération de gaz chauds et des moyens sensiblement étanches d'extraction de coke ou semi-coke, et
• - un dispositif d'extinction de coke ou semi-coke avec des moyens de projection d'eau, l'entrée dudit dispositif d'extinction étant raccordée aux moyens d'extraction du coke ou semi-coke du four tournant,
• - ledit four tournant tubulaire étant étanche et comportant des moyens d'introduction de vapeur et un moyen de réglage du débit de vapeur asservi à un capteur de pression gazeuse dans le four.

The aims of the invention are also achieved by an installation which comprises:

• - a tubular rotary furnace with a slight slope, at its highest point, substantially sealed means for introducing coal in grains and / or in fines and sealed means for extracting gases from the oven and, at its point the below, means for introducing or generating hot gases and substantially sealed means for extracting coke or semi-coke, and
• a device for quenching coke or semi-coke with means for spraying water, the inlet of said quenching device being connected to means for extracting coke or semi-coke from the rotary kiln,
• - Said tubular rotary oven being sealed and comprising means for introducing steam and a means for adjusting the steam flow rate controlled by a gas pressure sensor in the oven.

According to another characteristic, the coke or semi-coke extinguishing device comprises means for spraying water.

It is also in accordance with the invention that the extinguishing device is an inclined rotating tube and that said rotating tube is open at its discharge end.

Other characteristics and advantages will emerge from the description, which will be given below by way of example only, of an embodiment of the invention. For this purpose, reference is made to the single appended drawing which represents an installation according to the invention.

An installation according to the invention for the implementation of the method according to the invention comprises a tubular rotary oven 1, sealed and inclined by 2 ° on the horizontal downwards from right to left in the figure. At its two ends, the rotary kiln communicates by rotary joints 2 and 3 with baffles respectively with a feed cover 4 and a heating cover 5. A feed hopper 6 makes it possible to bring the coal upstream of the oven by a inclined chute 7 by means of a honeycomb distributor 8. The hot gases of the rotary kiln are extracted from the feed cover 4, the walls of which are rinsed with water to avoid any fouling, by a pipe 9 to be brought to a first washer 10, then to a second washer 11, in which are arranged batteries of water sprayers 12. At the outlet of the washer 11, the gases are sucked in by a dewatering fan 13 and sent to a pipe 14 provided with a register 15 allowing these gases to be wholly or partially sent to a storage capacity and / or to a pipe recycling 16. The gas washing waters are sent to a decanter 17 communicating with an overflow tank 18, from where a pump 19 recycles them to the sprayers 12.

On the downstream side of the oven, the heating cover 5 opens onto a chute 20 opening directly into the cover 21 of a rotating extinguishing tube 22 inclined 2 ° down from left to right, in the figure. This tube 22 is provided with a ramp 23 of water sprayers. The tube 22 is open at its lower or downstream end and the quenched coke in the tube can fall on a screen 24 whose passers-by falls on a conveyor belt 25.

The heating of the rotary kiln 1 is provided by a burner 26 supplied by a line 27 of liquid or gaseous fuel and an air line 28. A regulator 29 provides a stoichiometric adjustment of the proportion of fuel and air or, at will , a depleted air setting. The fuel flow rate is also regulated by the regulator 29 controlled, by a circuit 30, at a set temperature to be observed in the mass of incandescent coke or semi-coke, the true temperature there being measured by a thermometric probe 31 placed in the oven in the vicinity of the cover 5. It is also possible to introduce water vapor into the oven through a cane 32 opening into the cover 5. The water vapor flow rate can be adjusted by a controlled pressure switch 33, by a circuit 34 , at a set pressure to be observed in the actual enclosure of the oven, the true pressure being measured by a pressure sensor 35 placed in the oven at an upstream point, for example.

The hot gases recycled through the line 16 can be reintroduced into the burner 26, either directly or by mixing with the fuel supplied by the line 27 if this fuel is gaseous.

The oven is sealed by. injections of water vapor by means of the injectors 36 in the rotary joints 2 and 3.

The pressure sensor 35 is used to regulate by a logic circuit 37 the vacuum created by the dewatering fan 13, this logic circuit also being able to open or close a bypass valve 38 and / or to regulate a draft register 39.

The use of the installation is as follows.

The coal is brought into the carbonization furnace via the hopper 6 provided with a protective screen and the anti-pinch cellular distributor 8. This device makes it possible to supply the installation independently of the rotation speed and the slope of the revolving oven 1.

The coal, by traversing the rotary furnace 1 of carbonization, loses its volatile matters thanks to the contribution of calories supplied by the burner 26 operating in stoichiometry.

The rotary carbonization oven 1 operates at slight overpressure (- 10 Pa), this in order to avoid parasitic air inlets liable to degrade the quality of the gas produced by dilution or combustion of volatile materials. The baffle seals 2 and 3 and steam injection 36 fitted to the heating and supply hoods of the oven thus prevent the discharge of tarry gases towards the outside. Steam injection ducts allow eventual artificially increase the pressure.

A slight leakage flow takes place between the rotary charring furnace 1 and the tube 22 for extinguishing the incandescent coke.

The coke flows freely between tubes 1 and 2, the pressure difference between carbonization tube 1 and extinguishing tube 22 is less than 10 Pa. A hot coke guard also makes it possible to limit ironing.

The control of the pressure as well as the measurement and the regulation of the temperature in the carbonization furnace 1 are carried out as previously stated.

The incandescent coke flows, via the chute 20 which is broadly dimensioned and sufficiently sloping to avoid any accidental blockage by agglomerates, in the quenching tube 22 where the coke is quenched by water spraying. The extinction is favored by a sweeping with natural air of the extinction tube by effect of air call of the sprayers. It is known, in fact, that to obtain a good extinction of a semi-coke, it is advisable that during its cooling it fixes a sufficient quantity of oxygen.

The production gas passes, as has been said, in the supply hood 4, the walls of which, to avoid any fouling, are rinsed with water, then in a series of washers 10, 11, where it undergoes watering. . Almost all of the tars are thus trapped and recovered at the base in the decanter 17.

In normal operation, there is practically no floating tars in the decanter 17 and at the same time a plunging tar which is not very humid and little dusty is obtained.

In order to obtain the best possible tar quality, the residence time of volatile materials in the oven should be controlled in order to avoid their thermal dissociation. This is achieved by the steam serving as the ballast gas in the oven and by the appropriate washing system for the production gases to prevent fouling. It is also obtained by recycling the fumes that make ballast.

The means of the invention therefore make it possible to control the carbonization temperature, which is essential, due to the risks of runaway well known in the manufacture of semi-coke or reactive coke.

We will now give a table of the experimental conditions of the invention on a Wendel 1-11 carbon without and with recycling of the finest fraction of the cokes obtained.

It can thus be seen that recycling leads to a reduction in "balls" (3.3% compared to 11.8%) and to a reduction in "fines" (13.6% from 0-5 against 17.4%).

Claims (11)

1. Process for continuously producing a coke or semi-coke product having a content of volatile matters from 1% to 20% from coal fines and/or coal grains or from coal fines containing more than 15% of volatile matters and having a swelling index less than 8, wherein the fines and/or the grains are introduced into the upstream end of a rotary tubular oven having a slight inclination, where the product progresses, in the course of its treatment, from the upstream end to the downstream end, said downstream end being supplied with heat from a hot gas generator and the coke or semi-coke produced being extracted from said downstream end the supply of heat from the hot gas generator being regulated to produce neutral or reducing hot gases, characterised in that the oven is maintained under a slight gaseous overpressure with respect to the atmosphere by a controlled injection of an auxiliary ballast fluid.

2. Process according to Claim 1, characterised in that the auxiliary ballast fluid comprises water vapour.

3. Process according to Claim 1, operated with a set coking temperature between 450 and 1100°C, characterised in that the calorific output of the hot gas generator is regulated by the difference between the temperature of the coke or semi-coke at the downstream end of the oven and the set coking temperature.

4. Process according to any one of Claims 1 to 3, characterised in that the tightness of the furnace is maintained by injecting a neutral gaseous fluid, such as water vapour, into the joints of the rotary oven.

5. Process according to Claim 1, wherein the coke or semi-coke is extinguished by introduction into an inclined rotating tube, characterised in that the rotating tube is provided with water atomizers and the coke or semi-coke is extinguished therein immediately after its extraction from the rotary oven.

6. Process according to Claim 1, characterised in that the fines and/or the grains are introduced into the rotary oven with addition, by recycling, of the finest fraction of the cokes or semi-cokes obtained.

7. Installation for carrying out the process according to any one of Claims 1 to 6, comprising:

-a rotary tubular oven with a slight inclination comprising, at its highest point, substantially tight means for introduction of coal grains and/or coal fines and tight means for extraction of the gases from the oven and, at its lowest point, means for introduction or generation of hot gases and substantially tight means for extraction of coke or semi-coke, and

- device for extinction of coke or semi-coke, the inlet of said extinction device being connected to the means for extraction of the coke or semi-coke from the rotary oven, characterised in that the rotary tubular oven (1) is tight and comprises steam introduction means (32) and a means for regulating the flow of steam (33) in dependence on a gas pressure sensor (35) detecting the gas pressure in the oven (1).

8. Installation according to Claim 7, characterised in that the device (22) for extinguishing coke or semi-coke comprises water spraying means (23).

9. Installation according to Claim 8, in which the extinction device is an inclined rotatable tube, characterised in that said rotating tube (22) is open at its discharge end.

10. Installation according to Claim 7, characterised in that it comprises means (13) for pumping gas from the oven at a adjustable output controlled by the means (35) sensing the overpressure in the oven (1).

11. Installation according to Claim 7, characterised in that it comprises means (36) for injecting a neutral gaseous fluid such as water vapour in the joints (2, 3) of the rotary oven (1).

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