EP0030376B1 - Process and apparatus for drying and preheating moist coal - Google Patents

Description

The invention relates to a method for drying and heating moist coal, in particular fine and very fine coal, in which the coal to be dried is supplied with heat via an inert gas circuit, which can be heated with the aid of a heat exchanger, and the dried and heated coal with a Partial circuit of the inert gas is protected from the entry of oxygen. The invention also shows an apparatus for performing this method.

DE-A 28 10 694 shows a method of the type described in the introduction, in which fine-grained hard coal is pre-dried and further processed to high-quality hard coal coke. The fine-shaped hard coal is dried in a drying device by means of a low-oxygen cycle gas, which essentially consists of water vapor. Water vapor is used as the inert gas for the cycle, which develops when the coal to be dried is heated from the moisture that is carried in by the moist coal. The inert gas circuit is indirectly heated by a heat exchanger. The inert gas circuit must also be cleaned with a dedusting system, whereby the entrained coal particles must be separated. If a cyclone is used as the dedusting system, the low weight of the coal and the high fines content result in insufficient cleaning. In addition, the fine parts of the coal are also deposited on the heat exchanger and considerably impair the heat transfer. If, on the other hand, a cloth filter is used, temperature problems arise, particularly when starting up and shutting down the system. If the temperature of the inert gas in the cloth filter is too high, there is a risk that the filter cloths will burn. If, on the other hand, the temperature is too low, condensate forms and the carbon particles are deposited with the condensate on the filter cloths, so that the filter resistance increases.

Furthermore, there are major problems with starting and stopping the system in the known method; because moist coal is first introduced into the hot drying device. When starting up, only hot air is initially available in the circulation, so that its oxygen content can very easily lead to self-ignition of the coal. As a result, deflagrations and explosions can occur. If the system is still too cold when starting up, there is a risk that the water initially expelled from the coal will condense again on another part of the system and thus in particular impair a cloth filter dedusting. If, on the other hand, the temperature in the system is too high, the filter cloths can burn. Similar difficulties arise when switching off the system. Local temperature increases due to interrupted coal entry can also disturb the sensitive cloth filter system. On the other hand, condensate can accumulate as a result of the temperature drop in the cloth filter system and contamination can occur.

The known method works on the countercurrent principle. This is disadvantageous insofar as the inert gas heated in the heat exchanger hits the already dried coal at the outlet of the drying system with its hottest temperature. Symptoms of overheating can occur here. In addition, the hot fines from the coal are taken in countercurrent. These migrate back to the entrance of the drying facility and can be deposited there again on the wet coal particles. This results in an accumulation of the fine particles in the drying device, so that their resistance increases. This affects the inert gas cycle.

From US-A 4 008 042 a single-stage entrained flow dryer is known which is continuously heated with a hot gas generator. If coal production fails, water should be injected into the circuit to prevent the temperature from rising and subsequent destruction of the plant. The hot gas generator can be operated with coke oven gas and usually has to be operated with excess air in order not to let the temperatures rise too high and to achieve complete combustion. When the system is started up, it therefore seems at best possible to reduce the oxygen content in the cycle gas to about 5% before moist coal is introduced. It is described that the oxygen content should normally be kept below 1%, but it is not clear how this could be achieved.

DE-A 16 29 117 shows a method and a device for the gentle and accelerated drying of oxidation-sensitive substances, in which a preheated inert gas, preferably nitrogen, is used. Even in the presence of the dry material, the air in the system is to be displaced by spraying water vapor and the water vapor is to be discharged via condensers. To an equivalent extent, the inert gas, preferably nitrogen, should be blown into the space of the dryer which has been freed by the condensation of the water vapor. In this known system, a heater is used, from which it is not possible to see how it should work.

DE-A 26 59 335 shows a coal drying and heating system that works with an entrained-flow dryer and a downstream entrained-current heater for the coal and in which a directly fired gas circuit is initially operated by the entrained-current heater and gas circuit, first by the entrained-current heater and then by the entrained-air dryer because it is conducted in direct current. Air in the form of combustion air is also introduced into the gas-operated combustion chamber, so that the oxygen content in the circuit of the heat transfer medium is difficult to control. In spite of vapor recirculation, deflagration phenomena and explosions cannot be avoided with this known coal heating system. The system also works with an electrostatic precipitator, whereby the coal separated there is added to the dried coal. In the circuit of the heat transfer medium, two short-circuit lines are arranged, both of which bridge the entrained-flow dryer and serve to raise or regulate the temperature in a cyclone separator and in the electrostatic filter. The fan provided in the circuit of the heat transfer medium conveys in addition to the vapor return immediately into the electrostatic filter and then into the chimney, so that there is an additional risk that air at leaky points in the system and thus oxygen will get into the circuit of the heat transfer medium.

From DE-B 26 26 653 a two-stage single-tube entrained flow dryer is known, which of course is also operated in direct current. Here, too, the heat transfer circuit is heated directly, excess oxygen being introduced via the combustion air of the gas burner. Here, too, there is a risk that the oxygen content in the heat transfer medium will easily accumulate to such an order of magnitude that deflagration, fires and explosions can occur. This is particularly the case during the start-up process when there is only hot air with the known high oxygen content in the heat transfer circuit.

In DE-A 2415 758 it is recommended to fill the drying gas circuit with inert gas when starting up. This inert gas is generated as combustion gas by a burner that only works in the start-up phase. The exhaust gases generated by the burner should displace the air in the system until an oxygen limit value not mentioned is reached. This permissible limit was set at 2% on the mining side around mid-1980. In order to achieve such a limit, the burner of the known system would have to be operated without excess air and without mixed gas. The exhaust gases then have a temperature of 1,200 to 1,300 ° C. However, this temperature is beyond the permissible thermal load on the system. In addition, if coal was introduced into the plant, overheating of the coal grain would certainly occur.

A limit value of 14% is known for thermal drying systems from the “Preparation Technology”, Issue 12, 1978, pages 581 to 586 (584). H. the maximum permissible oxygen content in the hot gas is limited to 14%. In order to reach this limit, it is recommended to first fill the system with steam and then inject water, which is to be gradually replaced by coal sludge to be dried. This method of operation is problematic in that the water vapor condenses in the cold system and the water subsequently injected only increases the amount of water or condensate. A reduction in the oxygen content to less than 2% is hardly conceivable in this way and is not even attempted according to the limit value of 14% recommended there.

From DE-A2748423 it is known to flush a coal heating system and also the transport and bunker system part with an inert gas before starting in order to obtain a limit value of approximately 2% oxygen. This inert gas is to be taken from a neighboring heating system in operation. However, a second plant will usually not be available. In addition, it is not shown how the first of several neighboring plants should be approached.

Despite these diverse proposals, attempts and efforts to reduce the oxygen content, no practical way has been shown how a low oxygen content, as is now required by the mining authorities, can be achieved when starting up a single drying and heating system.

The invention has for its object to develop the method of the type described in such a way that a system can be started up and shut down without the risk of deflagration, burns and explosions, the coal and the system is not damaged by overheating and a lowering of the temperature with the risk of condensation of water vapor is also avoided. Furthermore, the problems associated with dedusting and maintaining the filter effect must be solved in such a coal drying plant.

The method according to the invention is characterized in that during the start-up process before the introduction of moist coal in the system, air present in the circuit is heated and thereby heated via a heat exchanger that the parts of the system coming into contact with the circuit by means of the heated air circuit to condensation of water vapor avoiding temperature are warmed up before water is sprayed into the heated air circuit or water vapor is introduced and the air circuit is enriched with water vapor, the oxygen content being reduced below 2% and the inert gas circuit being formed before moist coal is dried in cocurrent for drying Inert gas circuit is introduced. The air in the system with its known oxygen content is thus initially heated indirectly and without coal coming into contact with it, so that all system parts that come into contact with the air circuit are heated to such an extent that condensation of water vapor is avoided that will. Water is sprayed into this heated air circuit, i.e. introduced in a very fine distribution with a large surface area, so that this water actually has the possibility of evaporating and thus causing an enrichment with water vapor without a substantial reduction in the temperature of the air circuit, as a result of which the oxygen content of the Recycle gas is lowered. This reduction can be carried out safely for the plant until the oxygen content in the cycle gas has dropped below 2% and the vast majority of the cycle gas is formed from water vapor. It goes without saying that circulating gas must be continuously removed from the circuit during this start-up process because the volume increases while the oxygen content is continuously reduced by spraying in the water or introducing the water vapor. It is also necessary to measure this limit value of 2% oxygen content, which is now mandatory on the mining side, namely on the undried cycle gas. Only after this limit has been fallen below is the moist coal brought in for drying. During this start-up process, the temperature of the cycle gas and thus also the temperature of the system parts to which it is exposed already remains approximately constant, namely at a temperature level which corresponds to the continuous operation of the system. As a result, there is no impairment of these system parts, in particular the cloth filter dedusting.

Although the start-up process only takes a few minutes, it can also be operated without further ado that the oxygen content in the inert gas circuit is reduced to below 1% by enriching with water vapor before moist coal is introduced for drying.

When the plant is switched off, the inert gas circuit is initially maintained until the last coal has left the plant; water is sprayed in or water vapor is introduced to avoid local overheating on the system. The burner is switched off and then the inert gas is gradually replaced by air until the system has cooled to 80 ° C.

The device for carrying out the method has a drying device, an inert gas circuit which can be heated indirectly via a heat exchanger and which is passed once through the drying device and in a partial circuit via a mixer for dried coal, such as a dedusting device, in the inert gas circuit and a heat source connected to the heat exchanger on. It is characterized by the fact that the drying device is a driven drying drum connected in direct current to the inert gas circuit, which is followed by a pre-separator and cooler as well as a cloth filter dedusting device in the inert gas circuit, and that the inert gas circuit has a shut-off supply line for water or water vapor and another lockable supply line for air having. The gas circuit is also passed through the plant in direct current during the start-up process, that is in the same direction in which the coal to be dried is also guided during the operating phase of the plant. This then has the advantage during the operating phase that depletion of the fine fractions of coal in the drying device is avoided. At the same time, this means gentle treatment of the coal and, in contrast to drying in the entrained flow process, the circulation of considerable amounts of gas and the mechanical stress on the coal are thereby avoided. By using a drying drum in a direct current process as a drying device, the coal is gently dried, the highest temperature of the inert gas circuit acting on the wet coal, so that overheating at the outlet of the drying drum on the dried coal is avoided and the temperature profiles can be controlled more easily and better. This also applies during the start-up process and when the system is switched off. The lockable supply line for water or steam and a further lockable supply line for air make a significant contribution to this. The first line is used for the start-up process, while the further lockable supply line for air is required when the system is switched off. The better controllability of the temperatures also makes it possible to use a pre-separator and cooler in the inert gas circuit, as well as a cloth filter dedusting device, which, when working dry, can achieve the required cleaning of the inert gases.

The inert gas circuit has two short-circuit lines, each provided with controllable shut-off devices, one of which is connected between the heat exchanger and the drying drum and leads into the line between the drying drum and the pre-separator and cooler, while the other branches off after the cloth filter dedusting and after the downstream fan and in front of the heat exchanger and bridges the heat exchanger. While the first short-circuit line is used to increase the temperature in the cloth filter dedusting, the second short-circuit line serves to lower the temperature in the cloth filter dedusting. It is understood that in this way the cloth filter dedusting can be carried out in an optimal temperature range, so that the temperature falls below the dew point and thus the formation of sulphurous acid and the condensation of water are avoided. Such a temperature control can be necessary in particular if, for example, there is a defect in the water supply during the start-up process. The upstream pre-separator and cooler can also be used to reduce the temperature in the cloth filter dedusting will. The cooling device on the pre-separator expediently consists of several fans which can be switched on or off accordingly.

The partial circuit of the inert gas circuit intended to protect the dried coal branches off after the fan and is returned to the inert gas circuit, bridging the drum between the drying drum and the pre-separator and cooler. The dried coal is thus effectively protected against the entry of atmospheric oxygen even after it has left the drying drum until it has been subjected to a desired processing. Thus, e.g. B. inert the material silo, the weighing and mixing device and the conveyor line of the coal. This can be done by depositing in a silo. It is also possible to coat the dried coal with a binder, preferably a bituninous binder, this is particularly useful if the coal is then to be coked. Starting from the fan, a controllable shut-off device is arranged in the inert gas circuit in front of the heat exchanger and in front of the branching of one short-circuit line, as well as in the branching circuit. These two shut-off devices control the quantity distribution of the inert gas for the inert gas circuit on the one hand and for the partial circuit on the other. It goes without saying that this quantity control can also influence the temperatures at the respective parts of the system. A mixer, a weighing device and an intermediate silo can be provided in the partial circuit of the inert gas. It goes without saying that other devices for the dried coal can also be provided here, which are then expediently also included in the partial circuit, provided that the temperature of the dried coal is still in a dangerous range in such plant parts.

The lockable supply line for water or water vapor is expediently provided at the entrance to the drying drum. In this case, all you need is a water supply line and a shut-off device, while the drying drum itself can be used to evaporate the water, as will happen later for the main purpose of the system, namely the drying of the coal. The shut-off supply line for air, on the other hand, is expediently connected to the inert gas circuit between the dust filter and the fan, so that here air is sucked in and mixed with the inert gas in a simple manner. The temperature in the dedusting system is initially not reduced, so that no condensation can occur.

The heat exchanger connected to the inert gas circuit is, on the other hand, connected to a heating circuit which has an exhaust gas recirculation system in which a controllable shut-off element is provided. In this way, the heat of the exhaust gases of this heating circuit can be used by recirculation and, in this sense, the temperature control of the heating circuit can be influenced.

• Die Vorrichtung zum Trocknen und Erhitzen von feuchter Kohle weist ein Materialsilo 1 mit Dosiereinrichtung auf, von dem über einen Gutförderer 2 feuchte Kohle abgezogen werden kann. Am Ende des Gutförderers 2 befindet sich eine Zellenradschleuse 3 im Bereich des Einlauftrichters der Trockentrommel4, die um ihre Längsachse drehbar gelagert ist und angetrieben ist, so daß sich die Kohle beim Durchgang durch die Trockentrommel 4 immer in einer kaskadenförmigen Bewegung befindet.

The invention is illustrated and further described on the basis of a system shown schematically in the drawing:

• The device for drying and heating moist coal has a material silo 1 with a metering device, from which 2 moist coal can be drawn off via a material conveyor. At the end of the material conveyor 2 there is a cellular wheel sluice 3 in the area of the inlet funnel of the drying drum 4, which is rotatably mounted about its longitudinal axis and is driven so that the coal is always in a cascade-shaped movement as it passes through the drying drum 4.

The system also has a pre-separator and cooler 5, and a cloth filter dedusting device 6 connected downstream of this. A fan 7 is provided downstream for circulating the heat transfer medium or the inert gas circuit and the partial circuit. A heat exchanger8 is used for indirect heating of the inert gas circuit. The heat exchanger 8, on the other hand, is connected to a heating circuit 9, 11 from the line sections 9 and 11, which ultimately leads to the exhaust stack 10. A mixed gas fan 12 and a controllable shut-off device 13 are arranged in this line section 11. A burner 14 is heated with gas or another medium which is drawn off via a line or a storage tank 15. The combustion air for the burner 14 is brought in via the air fan 16. As can be seen, a return of the exhaust gases after passing through the heat exchanger and mixing in a mixing chamber 17 with the combustion exhaust gases can take place via the line section 11.

The inert gas circuit leads with a line 18 from heat exchanger 8 to the entrance to the drying drum 4. After passing through the drying drum4, the inert gas circuit is completed by the line sections 19, 20, 21, 22 and 23. As can be seen, the line piece 19 is connected between the output of the drying drum 4 and the input of the pre-separator and cooler 5, which, moreover, can be blown with cooling air by a blower (not shown) according to the arrows 24 and thus the temperature of the inert gas can be reduced. The line piece 20 connects the outlet of the pre-separator and cooler 5 with the cloth filter dedusting 6; the output of which is connected to the blower 7 via the line piece 21. From this the line piece 22 leads to a controllable shut-off _'25, of which the line piece 23 leads to the Wärmetauscher8. The inert gas circuit 18 to 23 is formed from the line 18 and the line sections 19, 20, 21, 22 and 23. In the inert gas circuit, two short-circuit lines 26 and 27 are provided, in which controllable shut-off organs ne 28 and 29 are arranged. By opening the shut-off device 28, the temperature of the inert gas in the pre-separator 5 and in the cloth filter dedusting 6 can be increased. By opening the short-circuit line 27 or the shut-off device 29, on the other hand, the temperature in question can be lowered, even in the drying drum 4.

At the entrance of the drying drum 4 there is a feed line 30 for water or steam and a control device 31 which is required for start-up purposes. A further supply line 32 for air, in which a shut-off element 33 is arranged, opens into the line section 21. The feed line 32 is required when the system is switched off. The dried coal passes from the exit of the drying drum 4 via an encapsulated conveyor device 34 into a bucket elevator 35 and from there into an intermediate silo 36, from which it can be transferred in batches to a weighing device 37, from which the coal in turn reaches the mixer 38. The coal can then finally be deposited in a silo 39 or be used for the corresponding purpose. In the mixer 38 it is possible to coat the dried coal with a binder, preferably a bituminous binder. This is fed from the binder tank 40 into the mixer 38 via the injection device 41. The binder tank 40 is kept at the desired processing temperature by a thermal oil heating unit 42.

In addition to the inert gas circuit 18 to 23 as the main circuit, the partial circuit 43 to 47 formed from the line sections 43 to 47 branches off from the line section 22. This subcircuit 43 to 47 of the inert gas protects the dried coal and the relevant parts of the plant over which it is guided.

Not only the short-circuit line 27 branches off from the line piece 23, but also the inert gas outlet line 48, in which the adjustable pressure relief valve 49 is provided and which ultimately leads to the exhaust gas chimney 10. An overpressure is always maintained in the inert gas circuit 18 to 23 and in the partial circuit 43 to 47 via this pressure relief valve 49. At the same time, gas is continuously released to the exhaust gas chimney 10 via the pressure relief valve 49 both during the start-up phase and during the operation of the installation, because water vapor is continuously enriched by the water introduced or by the water carried in by the coal.

The pre-separator and cooler 5 as well as the cloth filter dedusting 6 are connected to the bucket elevator 35 via screw conveyors 50, so that the dry coal separated in the pre-separator 5 and the cloth filter dedusting 6 is added again to the dried coal brought up via the conveying line 34.

To start up the system, starting from system parts filled with air, the fan 7, the drying drum 4 and various other system parts are started. The heating circuit 9, 11 is then released by igniting the burner 14 for the development of heat, the associated system parts such as air fan 16 and mixed gas fan 12 also having to be switched on. Heat is transferred to the air-filled circuit via the heat exchanger. When a temperature of 180 ° C. in front of the pre-separator and cooler 5 is reached, water is sprayed into the drying drum 4 by the control device 31 for water via the feed line 30. The water evaporates through the hot inlet gases. The resulting steam increases the amount of vapors in circulation. When a certain overpressure on the drying drum is reached, the controllable overpressure valve 49 is made ready for opening so that it can discharge a partial gas flow into the exhaust gas stack 10. The amount of water supplied is measured so that the water vapor produced is sufficient to reduce the oxygen content in the circulating vapors below 2%, preferably below 1%. This start-up process will take about 5 minutes. The drying of the coal can then be started by switching on the material conveyor 2 and removing moist coal from the material silo 1 and feeding it to the drying drum 4 via the cellular wheel sluice 3. It goes without saying that at this point in time no more water is inserted via the feed line 30. The moist coal to be dried reaches the material silo 1 in some way, for example with the aid of a shovel loader. The material conveyor 2 is equipped with a direct current control drive. The quantity discharged can be measured volumetrically by hand or set manually from a control center. The amount of coal to be dried should be kept constant during operation. The interior of the drying drum 4 is largely airtight against the environment. Above all, no atmospheric oxygen can penetrate, since the inert gas circuit 18 to 23 is operated at the sealing points of the drying drum under a corresponding excess pressure. The temperature of the dried coal present at the end of the drying drum 4 is specified as a setpoint and compared in a controller. When the value falls below the setpoint, the shut-off device 25 on the pressure side of the fan 7 is opened, so that the amount of vapors in the inert gas circuit 18 to 23 is increased. If the target value of the temperature of the coal at the outlet of the drying drum 4 is exceeded, the amount of vapors is reduced by the control devices described above.

The entry temperature of the hot vapors into the drying drum 4 should be about 450 ° C. If the value falls below this target value, the gas supply to the burner 14 is increased. By introducing more energy, the exhaust gas temperature of the heating circuit 9, 11 increases, so that the temperature of the inert gas circuit 18 to 23 is raised via the heat exchanger 8. When the setpoint of the temperature of the heating circuit 9, 11 is exceeded at the entrance to the heat exchanger, which is approximately 1 100 ° C., the shut-off element 13 in the heating circuit 9, 11 is opened. As a result, an increased recirculation of the exhaust gases at approximately 300 ° C. is initiated, whereby the exhaust gas temperature in the mixing chamber 17 is reduced to the setpoint.

Water vapor is generated continuously during the drying process. Inert gas must therefore be blown off continuously or in batches at the overflow valve 49 into the exhaust gas stack 10. The fan 7 can, for example, be designed in such a way that it produces a total pressure difference of 70 mbar at 20 ° C., so that this pressure cannot be exceeded at any point in the inert gas circuit.

The vapors and the inert gas circuit are cleaned with the cloth filter dedusting device 6 and the upstream indirect pre-separator and cooler 5. Two control circuits are required to protect the filter cloths from over and under temperature. If the specified setpoint temperature of z. B. 128 ° C in the line section 20, the first half of the cooling fans is switched on according to the arrows 24. If the temperature continues to rise and reaches z. B. 132 ° C, all cooling fans are turned on. Nevertheless, the temperature continues to rise and reaches z. B. 135 ° C, the gas supply in the burner 14 is switched off and the shut-off device 29 in the short-circuit line 27 is opened. As a result, the temperature in the inert gas circuit 18 to 23 is lowered with certainty. The temperatures specified above depend on the permissible temperature for the filter cloth used in each case. If the specified setpoint temperature of 115 ° C. on the line section 20 is undershot, the shut-off device 28 in the short-circuit line 26 is opened, the material conveyor 2 being switched off at the same time. As a result, the temperature in the pre-separator and cooler 5 and in the cloth filter dedusting 6 is raised again to such a value that critical conditions with regard to falling below the dew point cannot occur.

The dried coal present at the end of the drying drum 4 is conveyed into the intermediate silo 36 via the conveying device 34 and via a bucket elevator 35. At the same time, the coal, which is also dry and separated in the pre-separator 5 and in the cloth filter dedusting 6, is fed via the conveyor screws 50. The coal is removed from the intermediate silo 36 by means of cellular wheel locks and fed to the weighing device 37. When the specified weight is reached, the cellular wheel sluices are switched off and the coal is introduced into the mixer38. Simultaneously with the mixing of the mixer 38 with coal, the binder is injected into the mixer 38 by the injection device 41. After the prescribed mixing time has expired, the mixer opens and the dried coated material, namely the coal, falls into a silo 39 or is used for further use. As can be seen, the partial circuit 43-47 made of inert gas protects the other parts of the system after the drying drum4 and the heated, dry coal contained in them. The ratio of the inert gas, which is introduced into the inert gas circuit 18 to 23 after the fan 7, in relation to the amount of inert gas of the partial circuit 43 to 47 is achieved by the settings of the shut-off devices 25 and 51.

When the system is switched off, the material conveyor 2 is first stopped. Since the drying drum 4 no longer consumes as much heat, the temperature of the dry coal rises at the outlet of the drying drum. Likewise, the temperature of the inert gas in line piece 19 also rises. Water is now input into drying drum 4 via control device 31 for water. Even now, atmospheric oxygen is prevented from entering the system. After the mixing of the coal in the mixer 38 has ended, the water supply to the drying drum 4 is switched off and the air supply via the second feed line 32 is made possible by opening the shut-off device 33. The amount of vapors circulating increases further by sucking in air. Exhaust gas is continuously released into the exhaust stack 10 via the open pressure relief valve 49. The proportion of water vapor is now constantly decreasing, while the proportion of air is increasing. Condensation of water vapor is prevented because the system is still at temperature. Finally, the gas supply to the burner 14 is switched off, so that no further energy is supplied and the temperature of the circuits can also be reduced with hot air. This is carried out until the temperature of the air has dropped below about 80 ° C. at all temperature measuring points. Then the control drives of the individual parts of the system, if they are not already shut down, are switched off.

Claims (11)

1. Process for drying and heating moist coal, in particular fine coal and fines, in which heat is supplied to the coal to be dried via an inert gas circulation which can be heated by means of a heat exchanger, and the dried and heated coal is protected from the access of oxygen by a part circulation of the inert gas, characterised in that, during the start-up procedure before moist coal is introduced, the air present in the unit is circulated and, during this, heated up via a heat exchanger, that those parts of the unit which come into contact with the circulation are warmed by means of the heated-up air circulation to a temperature which avoids the condensation of water vapour, before water is sprayed, or steam introduced, into the heated-up air circulation and the air circulation is enriched in steam, the proportion of oxygen being lowered to below 2 % by volume and the inert gas circulation thus being formed, before moist coal is introduced in co-current into the inert gas circulation for drying.

2. Process according to Claim 1, characterised in that the proportion of oxygen in the inert gas circulation is lowered to below 1 % by enrichment with steam, before moist coal is introduced for drying.

3. Process according to Claim 1 or 2, characterised in that, when the unit is closed down, initially the inert gas circulation is maintained until the last coal has left the unit, water being sprayed in or steam being introduced, the burner is switched off and the inert gas is then gradually replaced by air until the unit has been cooled to 80 °C.

4. Equipment for carrying out the process according to Claims 1 to 3, having a drying installation, an inert gas circulation which can be heated up indirectly by means of a heat exchanger and which is passed on the one hand through the drying installation and, in a part circulation, through a mixer for dried coal, dust removal equipment in the inert gas circulation and a heat source connected to the heat exchanger, characterised in that the drying installation is a driven drying drum (4) which is connected in co-current to the inert gas circulation (18 to 23) and downstream of which the pre-separator and cooler (5) as well as a filter cloth deduster (6) are arranged in the inert gas circulation, and that the inert gas circulation has a feed line (30), which can be isolated, for water or steam and a further feed line (32), which can be isolated, for air.

5. Equipment according to Claim 4, characterised in that the inert gas circulation (18 to 23) has two short-circuit lines (26, 27) which are each provided with controllable isolation means (28, 29) and one (26) of which is connected between the heat exchanger (8) and the drying drum (4) and leads into the line (19) between the drying drum (4) and the pre-separator and cooler (5), whilst the other (27) branches off after the filter cloth deduster(6) and after the downstream fan (7) and before the heat exchanger (8), and bridges the heat exchanger.

6. Equipment according to Claims4 and 5, characterised in that the part circulation (43 to 47), intended to protect the dried coal, of the inert gas circulation branches off after the fan (7) and is returned into the inert gas circulation, bridging the drum (4), between the drying drum (4) and the pre-separator and cooler (5).

7. Equipment according to Claim 6, characterised in that one controllable isolation means (25, 51) is arranged in each case, starting from the fan (7), in the inert gas circulation (18 to 23) upstream of the heat exchanger (8) and upstream of the branch point of one short-circuit line (27) as well as in the branching part-circulation (43-47).

8. Equipment according to Claim 6 and 7, characterised in that a mixer (38), a weighing device (37) and an intermediate silo (36) are provided in the part circulation (43 to 47) of the inert gas.

9. Equipment according to Claim 4, characterised in that the feed line (30), which can be isolated, for water or steam is provided at the inlet into the drying drum (4).

10. Equipment according to Claim 4, characterised in that the feed line (32), which can be isolated, for air is connected to the inert gas circulation between the filter cloth deduster (6) and the fan (7).

11. Equipment according to Claims 4 and 5 characterised in that the heat exchanger (8) which is connected to the inert gas circulation (18 to 23) is connected with a heat circulation (9, 11) which is provided with a recycling of exhaust gases containing a controllable isolating mean (13).

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