EP0023455B1 - Process and installation for drying and/or preheating coal to be coked - Google Patents

Description

The invention relates to a process for drying and / or preheating by entrainment and / or fluidization of coking coal by means of a neutral coolant or reducing gas partially recycled and maintained at an appropriate temperature of 250 to 650 ° C. , in which the coal to be dried and / or preheated is introduced into a drying and / or preheating chamber by means of an introduction device with known and / or adjustable flow rate. The invention also relates to an installation for implementing the method.

Almost all of the steel coke is produced in traditional coke ovens where the load is brought to around 1000 ° C. The cooling of the coke in the discharge is very generally carried out by massive sprinkling of water in an extinguishing tower. The sensible heat of the coke thus lost represents 40 to 45% of the heat used to heat the ovens, which is 550 to 600 therms per tonne of dry charcoal placed. This is the most important heat loss item in the heat balance of coking. Consideration has long been given to recovering the sensitive heat of coke by means of dry extinction, the principle of which is as follows. The hot coke is cooled by circulation of inert gases in a closed cycle, by direct contact. The sensible heat recovered by the gases is used to make steam.

However, dry extinguishing processes are generally criticized for providing steam which is generally not used. The use of this heat in the coking plant itself would obviously be much preferable to the installation of turbines allowing the production of electricity. Coal preheating could be an application, as has already been described in patent DE-4 53 464, and more recently in patent FR-2173997 and its equivalents DE-2304541 and US-3843458 and 3728230 which propose use for the drying of the coal a gas heated in a heat exchanger by extinguishing gas, when the latter has already supplied part of its heat to a steam generator.

In patent DE-453464, the heat exchange is only imperfect. In the other aforementioned process, an attempt has been made to isolate the two extinction and heat-transfer gas circuits by a set of complex gas-gas and gas-liquid exchangers, by supplying heat to the coal at two distinct stages of drying and heating and introducing water vapor condensers. But then, if we put already dried coal in contact with gases at more than 350 ° C, we will degrade it.

In French patent 2,225,503, the extinguishing gases circulate in a closed circuit which contains a heat exchanger and a boiler; from the heat exchanger there are three separate secondary circuits including an inert gas circuit for preheating carbon, an open gas circuit for drying coal, a closed fluid circuit for drying coal but without contact direct with the latter. Although this circuit is complex and expensive, it does not include anything that is provided to ensure the start-up of the installation.

In French Patent No. 2,265,840, the extinguishing gases circulate in a circuit which contains a heat exchanger from which there is a single secondary circuit for a gas which is used for preheating and then drying the coal after which this gas is sent to two steam condensers. According to this patent, the condensation of water vapor is essential. For start-up there is no provision for preheating and drying the coal.

The main object of the invention is to achieve a simplified process and installation allowing good regulation of the temperature of the heat transfer gas and eliminating all the difficulties due to the corrosion caused by water vapor in known installations.

A secondary object of the invention is to provide a method and an installation of the above type admitting the installation and the use of means which can be used at the time of start-up in order to avoid any start-up with cold, undried coal.

According to the method of the invention, a single closed circuit is used in which the heat transfer gas is enriched in water vapor until it becomes substantially water vapor, while maintaining its temperature at a value greater than 250 ° C by acting on the fraction of extinguishing smoke sent through the heat exchanger.

It is advantageous for the flow rate of extinguishing smoke which is introduced into the heat exchanger to be controlled by the flow rate of the device for introducing the coal to be dried and / or preheated in the drying and / or preheating chamber.

According to other advantageous characteristics of the invention, the fraction of the extinguishing fumes used for heating the heat transfer gas and the unused fraction are used for the production of heat by heat exchange, and part of the heat necessary for drying and / or preheating of the coal is provided in addition by a combustion chamber whose caloric flow is controlled by the temperature measured in the drying and / or preheating chamber.

By the above means, which are very simple, it can be seen that the fitting of complicated apparatuses is avoided and that the problems of water condensation are freed, since it is not bothersome, only at the limit , the heat transfer gas is no more than water vapor, whereas it would be harmful if it were the recycled extinguishing fumes containing it.

In an installation where there is a heat exchanger through which a circuit of coolant gas for drying and preheating and a separate circuit of dry extinction, according to the invention, for implementing the method, the circuit of the coolant gas is a single circuit passing through the exchanger, the extinguishing smoke circuit comprises a pipe passing through the exchanger and a bypass pipe with respect to the latter, however, servo valves mounted on at least one of these pipes regulate the fraction of extinguishing fumes passing through the exchanger by the pipe so as to maintain the temperature of the heat transfer gas at a value greater than 250 ° C.

• - les canalisations d'entrée et de sortie des fumées de l'échangeur thermique soient réunies par une dérivation,
• - un jeu de vannes permette de régler la répartition du débit des fumées d'extinction en deux fractions respectivement entre l'échangeur et la dérivation,
• - des moyens soient prévus pour asservir le débit de la fraction de fumées d'extinction traversant l'échangeur au débit du dispositif d'introduction du charbon dans l'enceinte.

It is in accordance with the invention that:

• - the flue gas inlet and outlet pipes of the heat exchanger are joined by a bypass,
• - a set of valves makes it possible to adjust the distribution of the flow rate of the extinguishing smoke into two fractions respectively between the exchanger and the bypass,
• - Means are provided for controlling the flow rate of the fraction of extinguishing smoke passing through the exchanger to the flow rate of the device for introducing coal into the enclosure.

According to other characteristics, the common pipe bringing together the pipe for the outlet of the fumes from the exchanger and the bypass brings the fumes to another device for thermal use, the means for introducing the heat-transfer gas into the drying enclosure and / or preheating further comprises a combustion chamber interposed between the outlet pipe of the heat transfer gas from the exchanger and the means for introducing the heat transfer gas into the drying and / or preheating chamber.

In an installation in which the drying and / or preheating chamber comprises means for measuring the temperature, it is advantageous for the combustion chamber to include means for regulating the caloric flow controlled by the means for measuring the temperature in the drying and / or preheating enclosure, or at its outlet, as it is known per se.

Other characteristics and adventures will emerge from the description, which will be given below only by way of example, of an embodiment of the invention. For this purpose, reference is made to the single appended drawing which is a diagram of an installation in accordance with the invention.

An installation for the pretreatment of coking coal comprises a preheater mill 1 for grinding and preheating in a fluidized bed. This grinder-preheater 1 comprises a fluidization enclosure 2 inside which rotates a hammer mill 3. The fluidizing and heating gas for the 'fluidization and preheating of the coal is produced in part in a combustion chamber 4 by combustion of gas brought to its burner 5 by a pipe 6 with air forced by a fan 7. In addition, the fumes from the prior treatment of the coal are recycled, through a heat exchanger 13 and a pipe 14, into the combustion chamber by a fan 8. The exchanger 13 is of a heat exchange type through a partition wall, for example tubes or a coil, avoiding any communication between the two gas circuits which must exchange heat. The hot gases coming from the heat exchanger 13 and from the combustion chamber 4 are brought, through a venturi 10, to a vertical pipe 9 for pneumatic transport and pre-drying, into which opens, from a conveyor screw 11, the coal stored in a hopper 12. The vertical pipe 9 opens out, it is known per se, in the enclosure 2 for fluidization and grinding and preheating. From the top of the enclosure 2 leaves a pipe 15 for pneumatic transport of the ground coal and preheated by the fluidization gas again acting as a gaseous transport vector. Line 15 brings the carrier gas and the coal transported to a battery of cyclones 16 to the vortex 17 of the last or the last group of which is connected a line 18 serving to collect the gases which are then distributed between an extraction line 19 and a recycling line 20, having a flow measurement throttle 28 and connected to the fan 8. At the tips 21 of the cyclones 16, the preheated coal is collected ready to be placed in a coke oven, for which it is brought by an assembly conveyor 22 to a hot coal hopper 23.

There is, on the other hand, a dry extinguishing installation of the hot coke discharged, the main apparatus of which is a dry extinguishing chamber 30, of known type, which comprises a pre-chamber 31, constituting an introductory airlock. coke to be extinguished and which is introduced through an opening 32. From the prechamber 31, the coke descends into the cooling chamber 33 which constitutes a heat exchanger between the hot solid constituted by the coke and neutral or reducing fumes brought to the chamber cooling 33 by a fan 34 and a pipe 35 and evacuated to the thermal use of their sensible heat by a pipe 36. The gases and the vapor released by the coke in the prechamber 31 are extracted by an extraction pipe 37. The refoid cole is extracted at 38. The neutral or reducing fumes are used in a closed circuit from the pipe 36 to the fan 34. At the outlet of a dust separator 39, a pipe 40 conducts these fumes to the exchange eur 13 through a pipe 41, 42 the flow rate of which is controlled by a valve 43 or a set of valves. Upstream of the valve 43, .a pipe 41, 42 is looped by a bypass pipe 44 which may include a valve 45 contributing with the valve 43 to regulate the distribution of the hot smoke flow rates between the exchanger 13 and the pipe 44. At their junction the pipes 42 and 44 open into a pipe 45 'for supplying to a boiler 46, the outlet from which the extinction fumes, now cold, are brought back to the fan 34 through a dust collector 47 and the pipe 48. We see the very great simplicity of the combined installation, the exclusion of any risk of disturbance. one by the other of the two basic installations, the simplicity of their uncoupling by simply closing the valve 43.

The installation of the invention also includes regulation devices.

It comprises, as is known per se, a regulation circuit R ₂ ensuring stoichiometric combustion at the burner 5. The installation also has a regulation circuit R ₁ for the flow of gas to line 6 to control the caloric flow of make-up to the temperature measured in enclosure 2, or at its outlet, by a thermometric probe 24. The flow of recycled heat transfer gas is adjusted at the outlet of the exchanger 13 by valves 25 and / or 26 controlled by the pressure at vortex 17 by a regulation circuit R ₃ .

Finally, and in accordance with a preferred feature of the invention, the distribution of the flow of hot extinguishing fumes between the exchanger 41 and the bypass 44 is ensured by the valve 43 whose adjustable flow control is controlled by a circuit regulation valve R ₄ , at the rate of the coal supply screw 11 for the dryer and / or preheater 1.

For a quenching unit 30 of 56 t / h of coke cooled from 1000 ° C to 220 ° C, the quantity of steam produced is 26.1 t / h having as characteristic: 440 ° C, 40 kg / cm ² . The amount of heat recovered is around 325 therms per tonne of coke, or 240 therms per tonne of dry coal. For a preheating unit at 200 ° C, it is estimated that 210 to 240 th / t of coke are required. At 260 ° C it takes about 300 th / t of coke. The heat balance is therefore favorable to the process according to the invention. For a 56 t / h dry extinguisher unit, the smoke flow rate is 90,000 m ³ N / h at a temperature of 750 to 800 ° C. We can therefore combine an extinguishing installation of 56 t / h of coke and a preheater of 80 t / h of wet coal.

In the installation described, the temperature of 260 ° C can be taken as the set temperature for the temperature probe 24.

The preheating temperature will therefore be maintained at 260 ° C with good finesse by automatic action on the gas flow rate to the burner 5 of the combustion chamber 4. The regulation circuit R ₂ will accordingly adjust the air flow rate so that the combustion remains stoichiometric. The speed of the gases in the preheating chamber 2 will be kept constant by acting on the flow of neutral fumes recycled into the combustion chamber, by the circuit R ₃ , which keeps the pressure drop of the secondary cyclones constant by adjusting the flow recycled smoke. The coal flow rate is set to a constant value, chosen between 1/2 capacity and nominal capacity. If the coal flow rate is voluntarily changed, or if the humidity of the coal is variable, the preheating temperature and the speed of the gases are automatically maintained at their set value as just explained. The handling of the device is therefore extremely flexible.

Additional remarks may be made to show other adventures of the invention. The final dust removal of dewatering fumes will be greatly facilitated. In fact, the quantity of smoke discharged into the atmosphere will be substantially equivalent to the volume of water vapor coming from the humidity of the coal, i.e. 9000 m ³ N / h for a unit of 80 t / h of capacity. In the classic version of the preheater, the volume of smoke released to the atmosphere is 25,000 m ³ N / h. It should also be noted that the coal preheating fumes, from the moment that equilibrium is reached, will essentially contain water vapor, coming from the humidity of the coal. The dewatering fumes could therefore possibly be condensed, which would make it possible to eliminate releases to the atmosphere. As for dry extinction fumes, they can still produce around 2 t / h of steam by yielding their residual sensible heat in the boiler 46.

Claims (10)

1. A process for drying-preheating coal to be coked in a suitable enclosure by means of a heat-carrying gas to which the necessary heat is supplied by recovery by traverse of a wall of a heat exchanger the heat from at least a fraction of the dry extinguishing smoke of the discharged hot coke, characterised in that a single closed circuit is used in which enrichment of the heat-carrying gas with steam is permitted until it becomes substantially steam, while its temperature is maintained at a value greater than 250°C by acting on the fraction of extinguishing smoke conveyed through the heat exchanger.

2. A process according to Claim 1, characterised in that the flow rate of extinguishing smoke which is introduced into the heat exchanger is governed by the flow rate of the device for introducing the coal to be dried and/or preheated into the drying and/or preheating enclosure.

3. A process according to Claim 1, characterised in that the fraction of extinguishing smoke used in heating the heat-carring gas and the unused fraction are used for generating heat by means of heat exchange.

4. A process according to Claim 1, characterised in that some of the heat necessary for drying and/or preheating the coal is provided additionally be a combustion chamber whose thermal output is governed by the temperature measured in the drying and/or preheating enclosure.

5. An installation for drying-preheating coal to be coked, associated with an installation for dry extinguishing of the discharged hot coke, the two installations having in common a heat exchanger (13) in which a drying-preheating heat-carrying gas follows a circuit separate from the circuit for the dry extinguishing smoke, characterised by a combination of the following means: the circuit for the heat-carrying gas is a single circuit passing through the exchanger (13), the circuit for the extinguishing smoke comprises a pipeline (41,42) passing through the exchanger (13) and a pipeline (44) branched in relation to the latter, whilst servo-valves (43, 45) mounted on at least one of these pipelines (40, 41, 44) regulate the fraction of extinguishing smoke passing through the exchanger (13) via the pipeline (41, 42) so as to maintain the temperature of the heat-carrying gas at a value greater than 250° C.

6. An installation according to Claim 5, characterised in that:

- the inlet pipeline (41) and outlet pipeline (42) for the smoke of the heat exchanger (13) are connected by a branch (44),

- a set of valves (43, 45) permit regulation of the distribution of the flow of extinguishing smoke in two fractions respectively between the exchanger (13) and the branch (44),

- means (R₄) are provided for the flow of the fraction of extinguishing smoke passing through the exchanger (13) governed by the delivery of the device (11) for introducing the coal into the enclosure (2).

7. An installation according to Claim 6, characterised in that the common pipeline connecting the outlet pipeline for the smoke of the exchanger and the branch conveys the smoke to another heat utilisation apparatus.

8. An installation according to Claim 6, characterised in that the means (9) for introducing the heat-carrying gas into the drying and/or preheating enclosure (2) includes a combustion chamber (4).

9. An installation according to Claim 8, characterised in that the combustion chamber (4) is interposed between the outlet pipeline (14) for the heat-carrying gas of the exchanger (13) and the means for introducing the heat-carrying gas into the drying and/or preheating enclosure. 10. An installation according to Claim 8, in which the drying and/or preheating enclosure (2) incorporates temperature measuring means (24), characterised in that the combustion chamber (4) incorporates means for regulating the heat output (R₁), governed by the temperature-measuring means (24) in the drying and/or preheating enclosure (2) or at its outlet so as to maintain the latter temperature at a value greater than 250° C.

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