LU83261A1 - PROCESS FOR PRODUCING METALLURGICAL COKE - Google Patents

Description

i ♦ * ', BL-3116 -ΙΟ 2110/8103.

METALLURGICAL RESEARCH CENTER -CENTRUM V00R RESEARCH IN DE METALLURGIE,

Non-profit association -Vereniging zonder winstoogmerk, in BRUXELLES, (Belgium).

Process for manufacturing metallurgical coke.

The present invention relates to a process for manufacturing metallurgical coke of good quality, from coke pastes in which the so-called coking coals have been replaced, in whole or in part, by so-called little or non-coking coals.

Currently, metallurgical coke, which can be used in particular as a feedstock for blast furnaces, is generally manufactured by charging raw materials,> 10 mainly so-called coking coal, in cells, for carbonization and by heating these materials which, by distillation and agglutination, give a product having the well known properties of coke used in steel factories.

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The generally used carbonization cells are made of refractory bricks and are heated externally-vjk ment by hot fumes. These carbonization cells do not

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- 2 - * are never completely waterproof. Consequently, in order to avoid any entry of air into the ovens, while limiting gas losses to the outside, the pressure of the distillation gases must be constantly maintained at a value slightly above the atmospheric pressure. (overpressure of a few millimeters of water column).

Another drawback of carbonization cells operating according to the conventional process results from the external heating of these cells. In fact, in this way, the thermal trans-v iron used during the process depends on the nature of the walls. The efficiency of this heat transfer is reduced, which has an unfavorable impact on the productivity of the ovens.

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The material used in conventional metallurgical coke manufacturing processes is generally used in the pulverulent state, which has the well-known drawbacks of such a state from the point of view of at-20-mospheric pollution and the safety of work to which staff are assigned.

The various modalities of the manufacture of metallurgical coke according to the conventional methods impose a discontinuous operation with the troubles inherent in such a kind of operation; numerous repetitions, interrupted cadences, more frequent monitoring, higher costs, variation in the quality of the coke produced and above all lower energy efficiency, because the opening of the doors at the time of unloading generates high heat losses.

With regard to the control of the operation, the manufacture of metallurgical coke according to conventional methods is carried out in an extremely rigid framework with the possibility of action on a very limited number of parameters. Therefore Λ-.

- 3 - 4 * quence, the manufacture of coke according to the conventional process can only be done from certain so-called coking coals having well defined properties. These coals are becoming increasingly rare, their cost increases 5 and the cost price of the coke produced from these coals increases. In some cases, the reduction in the supply of so-called coking coals can make it difficult, if not impossible, to regularly supply production facilities.

10 'In order to remedy these various drawbacks, the industry has developed, for several years, methods such as pounding, preheating, partial briquetting which make it possible, under certain conditions, to manufacture metallurgical coke in better conditions and from lower quality coals. However, with all these improvements, the coking process always takes place at a pressure close to atmospheric pressure.

In this perspective, the applicant has also recommended a new process for the manufacture of coke from so-called little or non-coking coals. This process is based in particular on the observation that the coke produced in a cell inside which there is a gaseous pressure 25 substantially higher than that commonly used hitherto (atmospheric pressure + a few millimeters of water column) is almost always of high quality- | improved.

The results obtained with such a process have proved to be very satisfactory and the object of the present invention is to define the operating procedures for such a manufacture of pressurized coke.

The process which is the subject of the present invention is essentially characterized in that after having prepared the yrL coke paste by one or more of the following operations: grinding, drying, preheating and addition of a binder -solvent, this coke paste is subjected to compaction in a selected form, preferably followed by surface cooking, then to coking under a gas pressure which is appreciably higher than atmospheric pressure, by means of distillation gases which are preferably recycled and pulsed through the aggregate bed and whose temperature and pressure are maintained at adequate predetermined values / and finally at extinction of the coke thus obtained.

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Regarding compaction, the possible forms are as follows: balls (ovoids, spheroids, pads, bananas, orange wedges, horse saddles etc ...), splits, granules, etc ... Preference is given to the forms giving a high vacuum index to the bulk material after compaction.

With regard to the coking operation, the necessary heat supply is ensured by carrying the distillation gases at high temperature in an external heat exchanger before their recycling and their impulsion through the aggregate bed.

As the applicant has already recommended in the luxem-25 bourgeois patent No. 82.773, the gas pressure in the enclosure is maintained at the appropriate value depending in particular on the nature of the coal and the quality of coke sought.

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According to an advantageous embodiment of the invention, the coking operation is carried out in two stages, the first of which with circulation of low-quality distillation gases, that is to say containing various products, whether or not troublesome, such as for example tar, benzol, etc. These latter products are preferably extracted from the distillation gases before their recycling which takes place after reheating and evacuation of noble distillation, that is to say rich in and CO.

With such gases, the fraction recycled after reheating does not require any purification treatment, while the fraction discharged to maintain the pressure at an adequate value 5 can be used in particular as synthesis gas for the chemical industry.

As regards the coke quenching operation, it can be carried out wet with water or dry (gas).

10 * In the case of dry extinction, this operation can be carried out following the second coking step, by means of an inert gas from which the therms are preferably recovered to carry out other phases of the process such as drying, preheating, external cooking and coking.

According to a particularly advantageous variant of the invention, a first part of the dry extinction 20 is carried out by means of distillation gases produced during the first stage of the coking operation, as follows: these gases, preferably purified, heat up on the incandescent coke before being recycled and transfer the accumulated heat to the aggregates being carbonized.

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It should be noted that the pressures of the various gas circuits used during coking and possibly extinction are to be chosen to avoid excessive mixing of these different gases.

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The possible preliminary operations of grinding, drying, preheating and addition of a binder-solvent are described in detail below.

With regard to grinding, it must be taken into account that the carbon * intended for coking must be at an ade-d-y quate particle size, always less than 10 mm, preferably less, of the inert materials.

After grinding, the carbon is dried using one of the many known methods (rotary kiln, fluidized bed, multitubular dryer, etc.).

The coal is then preheated to a temperature below its softening temperature.

10 At this time, the coal is then intimately mixed with a suitable solvent-binder such as for example: coal pitch, petroleum pitch, tar, bitumen, oils, etc.

'This binder-solvent is preferably injected in liquid form, in order to obtain good dispersion in the mass. 15

It has been found advantageous, according to the invention, to use as binder-solvent, the tar recovered from the distillation gases after possible treatment.

According to an advantageous embodiment of the invention, at the outlet of the compacting machine, the compacted aggregates are baked superficially in an atmosphere at high temperature (above 500 ° C.) so that only their outer surface layer is brought to a temperature higher than the softening temperature of the coal.

The purpose of this cooking is to avoid any subsequent agglutination of the aggregates formed.

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The attached figure is given by way of nonlimiting example, to recall the various operations of the process: 1. grinding 2. drying 3. preheating 4. addition of a binder-solvent 35 5. compaction vi 6 external cooking - 7 - 7. coking 8. extinguishing, only the compacting (5), coking (7) and quenching (8) operations are essential; the others are optional, but nevertheless advantageous.

The process described above constitutes a means of manufacturing metallurgical coke of excellent quality, under the following advantageous conditions: 10 1. continuous production, 2. use of coals known to have little or no coking, which is easier to supply and cheaper, 3. better energy efficiency, 15 4. better recovery of the distillation gases, 5. lower pollution, 6. less arduous work for the staff, 7. flexible driving with possibility of action on a larger number of settings.

20 8. reduced cost price.

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Claims (14)

1. Method for manufacturing metallurgical coke, characterized in that after having prepared the coke paste by one or more of the following operations: grinding, drying, preheating and addition of a binder-solvent, this paste is subjected to coke to a compacting in a selected form, preferably followed by a surface cooking, then to a coking under a gas pressure substantially higher than atmospheric pressure, by means of the distillation gases which are preferably recycled and pulsed through the aggregate bed and the temperature and pressure of which are maintained at suitable predetermined values, and finally to an extinction of the coke thus obtained. 15 2. Method according to claim 1, characterized in that the mixture is compacted in a form giving a high vacuum index to the bulk material after compacting. 3. Method according to either of Claims 1 and 2, characterized in that the heat input necessary for the coking operation is ensured by bringing the distillation gases to high temperature in a heat exchanger outside before their recycling and their drive through the 25 aggregate beds. 4. Method according to either of claims 1 to 3, characterized in that the coking operation is carried out in two stages, the first of which with circulation of low-noble distillation gases is ie containing various products, bothersome or not, such as for example tar, benzol, etc., and the second with circulation of noble gases Il, that is to say rich in H 2 and CO. A - 2 - 5. Method according to claim 4, characterized in that the various products contained in the not very noble distillation gases are extracted before their recycling which takes place after reheating and partial evacuation. 5 6. Method according to either of claims 1 to 5, characterized in that, in the case of dry extinction, this operation can be carried out following the second coking step, garlic by means of an inert gas, the therms of which would be recovered, preferably to carry out "other phases of the process, such as drying, preheating, external cooking and coking. k 7. Method according to either of claims 1 to 15 6, characterized in that a first part of the dry extinction is carried out, by means of distillation gases produced during the first stage of l coking operation, as follows: these gases, preferably purified, heat up on the incandescent coke before being recycled and to transfer the accumulated heat to the aggregates being carbonized. 8. Method according to either of claims 1 to 7, characterized in that the pressures of the various gaseous circuits used during coking and possibly extinction are to be chosen to avoid any excessive mixing of these different gases. ♦ 9. Method according to either of claims 1 to 30 8, characterized in that the possible prior grinding is carried out so that the carbon intended for coking is at an adequate particle size, always less than 10 mm, preferably less than 5 mm and all the more finer than said carbon contains inert materials. - 3 - 10. Method according to either of claims 1 to 9, characterized in that the possible preheating is carried out up to a temperature below the softening temperature of the coal. 5 11. Method according to either of claims 1 to 10, characterized in that after preheating, the coal is intimately mixed with a suitable solvent-binder, such as for example coal tar, petroleum pitch, tar, 10 bitumen, oils, etc ...% 12. Method according to claim 11, characterized in * that this binder-solvent is injected in liquid form. 13. Method according to either of claims 1 to 12, characterized in that the tar recovered from the distillation gases is used as binder-solvent after optional treatment. 14. Method according to either of claims 1 to 13. characterized in that at the outlet of the compacting machine, the compacted aggregates are baked superficially in an atmosphere at high temperature (above 500 ° C) , so that only their surface layer is brought to a temperature higher than the softening temperature of the carbon.