DE2256385A1 - PROCESS AND DEVICE FOR CONTINUOUS HEATING OF FINE-GRAIN MATERIALS, IN PARTICULAR COAL, TO AN EQUAL, EXACTLY CONTROLLED FINAL TEMPERATURE - Google Patents

Description

METALIGESELLSCHAFT Frankfurt / Main, November 6th, 1972 Aktiengesellschaft ~ Wgn / HSz-

Method and device for continuously heating fine-grained materials, in particular coal, on a even, precisely controlled final temperature.

The invention relates to a method and the associated one Device for the continuous heating of fine-grained materials, especially baking coal, to a uniform, precisely controlled final temperature by means of hot gases which are brought into direct contact with the material to be heated.

It is known to use fluidized beds for heating coal, Insofar as the heating is used to dry the coal, the exhaust gas temperatures are low and therefore heat-efficient advantageous solution that has already found its way into practice. With increasing heating temperatures of the coal However, the thermal efficiency of a fluidized bed decreases more and more, and the apparatus becomes at the same time . always more complex. It is only at treatment temperatures above 500 to 600 ° C. that more favorable efficiencies can be achieved again come because in many cases it is then possible to work with a combustion within the fluidized bed. At these temperatures, coal is already subjected to considerable degassing, which is often the aim of heating.

For heating coal to temperatures just below the beginning of the degassing, i.e. at temperatures Isis approx. 300 C, two-stage and multi-stage fluidized bed systems have therefore been proposed to improve the heat economy, in which

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the exhaust gas of the respectively hotter fluidized bed than heating and Fluidization medium is used in the next colder fluidized bed and the coal in the various stages Direction of increasing temperature. Such facilities result in a better utilization of the heat, but remain structurally very complex, especially when treating relatively fine material, which is low Prescribes fluidization rates. They also have the disadvantage of one corresponding to the number of stages multiplied pressure loss.

Other methods provide for the heating of coal, the use of the lift pipe before ^ in which the coal during heat is supplied to the pneumatic conveying »This principle has been used for treatment at low temperatures very well proven and is available in a variety of ways in the form of numerous air dryers for coal and many other materials Use. It has also been proposed as so-called blow coking for the degassing of coal, here again using internal combustion, i.e. combustion in the presence of coal.

Average treatment temperatures are also problematic for this principle above about 250 C. For the same reasons as with the fluidized bed process, this is also the case with lift pipe a two-stage mode of operation has been proposed, whereby coal and conveying gas are gradually guided in countercurrent to one another. The same disadvantages arise here that apply to multi-stage fluidized bed systems. In addition, there is a further, considerable disadvantage that the final temperature the coal is subject to much greater fluctuations. When heating charcoal, one must therefore avoid it of malfunctions in lift pipe systems keep a greater distance from the softening temperature of the coal than in fluidized bed systems in order to avoid disruptive caking of the coal particles with one another and on the wall.

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German patent specification 1 160 823 describes a method for degassing non-baking coal, in which the coal has been dried in a flight dryer is heated in several cyclones connected in series, with coal and heat-carrying conveying gas in stages are guided in countercurrent to each other. This process also has the disadvantage that the treatment temperature is subject to major fluctuations and an unevenly degassed finished product is obtained. To alleviate this deficiency a modified version is found in German Offenlegungsschrift 1 671 320 Procedure described. The change from the older one The main method is that the upstream flight dryer is operated by a separate system of cyclones is replaced, which are hereinafter referred to as heat exchange cyclones. This method also has the disadvantage part fluctuating treatment end temperatures because the for the very short treatment times, which are characteristic and advantageous in themselves, have a correspondingly small inventory Condition of coal in the system, so that there are unwanted, small changes in the operating conditions, for example the feed quantity, have an immediate effect on the final temperature.

In the field of classic chamber coking, a new development has emerged in recent years, the consists in the fact that the coking coal is dried and heated before being used in the chambers. This measure is in view on increasing the performance of the batteries, broadening the coking coal base and improving the coke quality all the more more effective the higher the coal is preheated, i.e. the closer it is in practice, one can bring the coal to the temperature at which it begins to soften, that is between and 350 ° C. It can also be advantageous in the process of producing molded coke by hot briquetting or hot pelleting or it may be necessary to prepare the baking component in advance

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heats up giving up. The points of view for choosing the level of the preheating temperature are different. Frequently Here, too, there is the requirement for the highest possible preheating.

The invention has the object, in particular baking coal or other fine-grained materials such. B. not baking To heat coal with high thermal efficiency to a precisely controllable temperature while reducing the structural effort can be kept low.

According to the invention this is achieved in that the material to be heated with hot conveying gases passed through one or more heat exchange cyclones and preheated in one downstream fluidized bed is brought to the final temperature. The heat exchange cyclones are advantageously fed with the exhaust gas of the fluidized bed. The residence times of the material to be heated in the fluidized bed are a few minutes up to about half an hour; in most cases they are approximately in the range from 5 to 20 minutes. When used For moist material, a dryer, preferably an air dryer, is advantageously connected upstream of the heat exchange cyclones.

The inventive method circuit is useful for the initial Warming the advantages of the heat exchange cyclones, which because of the gradual countercurrent low exhaust gas temperatures and thus ensure a high degree of heat utilization and which because of the high heating rates allow short dwell times of the material to be heated and thus a low structural effort. For the power amplifier the heating uses the invention the advantages of the extremely rapid temperature equalization within a Fluidized bed. This guarantees even heating of the items to be treated without local temperature differences and at the same time yaucn with heat-sensitive material,

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like ζ. B. "Baking coal, relatively high gas inlet temperatures compared to other ways of working. The additional dwell time of the material to be heated in the fluidized bed from a few minutes to about half an hour ensures that the coarser grain fractions, which in the rapid passage through the heat exchange cyclones may not have been fully warmed through, come to the same temperature as the finer fractions. In addition, the due to the relatively long residence times, the considerable content of the fluidized bed of material to be heated leads to a certain, desired inertia of the overall system in its reactions to unavoidable operating fluctuations. This is additional For uniformity in terms of location and grain fraction, a temporal stability of the heating is also guaranteed. The heating system according to the invention with the fluidized bed as the final stage also offers the advantage that in many cases because of the capacity of the fluidized bed, an intermediate bunker for the heated material can be dispensed with by its use, for example the mixing part of a shaped coke plant, is fed directly from the fluidized bed.

Fine coal is usually wet. Other materials are also only exceptionally free of moisture. It will deshaUy in in most cases it will be advantageous to connect a dryer upstream of the heating system according to the invention, unless drying can be carried out with advantage in the uppermost heat exchange cyclone put, which comes into consideration in particular when tar- or oil-free feedstocks at temperatures are to be heated above 500 to 600 ° C.

In the interest of lower investment costs is of the various Dryer types in the present case the flight dryer is particularly advantageous. That made up of several cyclones with a downstream The existing fluidized bed heating system according to the invention usually has a fine grain flow going from top to bottom, i.e. it requires a high-level delivery point

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for the input material. The flight dryer, its dryer tube, if necessary, for drying reasons required length can also be increased, connects the drying with the promotion and can therefore Combine very easily with the heating system according to the invention without the interposition of mechanical conveyors.

According to a further development of the invention, the exhaust gases from the fluidized bed are at approximately the same temperature as the final treatment temperature of the material to be heated is used in the heat exchange cyclones as a conveying gas and heat carrier. With little abrasion-resistant feed, it can happen that a relatively large amount of dusty material from the gases from the Fluidized bed is entrained. In this case, it is useful to assign a cyclone to the fluidized bed, which the fluidized bed exhaust gases dedusted before they flow through the heat exchange cyclones installed above. That in this dedusting cyclone Depressed solid good is either in returned to the fluidized bed or admixed with the fine-grained product withdrawn from the fluidized bed or withdrawn separately.

The fluidized bed technology has experienced an expansion in the direction of a thin-phase fluidized bed in recent years, from which, due to the relatively high fluidization speeds, a comparatively large amount of material is discharged with the gas stream will. In order to ensure a sufficient residence time of the solid in the bed temperature range, one switches such beds are followed by a cyclone, the solids discharge of which is returned to the fluidized bed. This technique results in reduced capital costs and is if it has the properties allow the material to be heated, also applicable in the present case. It leads to the one described in the previous section Circulation circuit, consisting of a fluidized bed and a cyclone, whose solids drain is fed back into the fluidized bed.

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The invention is based on a. Example further explained. It is based on the simplified, schematic Reference is made to illustration in Fig. 1. The example concerns the heating of moist, fine-grain coking coal to 320 ° C to provide the preheated baking component for the continuous production of shaped coke.

The fine-grain, baking charcoal with 9% moisture and outside temperature comes from the feed bunker 1 into the air dryer 2. The dryer 2 is designed in the present example as a circulating dryer with a sifter hood 3 and coarse grain return 3a. A hammer mill 4 is switched into the return 3a. The dryer 2 receives hot combustion gas from a combustion chamber 5, which is fed with air L and gaseous fuel G. The combustion chamber 5 is operated with a slight excess pressure and a precisely controlled ratio of fuel gas to air, so that the combustion gas contains only very small amounts of free oxygen. The temperature of the gas at the outlet from the combustion chamber 5 is adjusted to 570 ° C. by recycling cooled gas from the line 18. On the way up through the tube of the dryer 2, the gas cools down to 140 ° C., at the same time the coal carried along is heated to approximately 100 ° C. and dried to a residual water content of 1%. It is separated from the dryer gases in the coal separation cyclone 6 and then immediately fed to further heating.

Since the heat transfer takes place in the air dryer 2 during the pneumatic conveying, the coal separation cyclone 6 is on top and no further conveying device is required to bring the coal to the feed device in front of the uppermost heat exchange cyclone. The one from the '. Dryer vapors freed from coal are sucked in by the fan 7 and pressed into the electrostatic precipitator 8 for further dedusting. The dry coal coming from the cyclone separator 6 passes through it

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Derivation 6a and enters the line 10a. On the line 10a, the coal becomes a heat exchanger cyclone by means of hot conveying gases 9 and reaches the line 10b via its discharge line 9a. Hot gases in line 10b with a higher temperature than in the line 10 a promote the coal in the second heat exchange cyclone 10, the Heating of the coal continues,

The coal finally runs through the line 11a to the fluidized bed 11, in which it has a residence time of 12 minutes is brought to its final temperature of 320 ° C. At this temperature, it is delivered as a finished product via line 20 withdrawn and immediately supplied for further use. Because of the storage capacity of the fluidized bed, there is an intermediate bunker not mandatory.

The fluidized bed 11 is heated with combustion gases from the combustion chamber 12, which, like the combustion chamber 5, with precisely controlled Gas / air ratio is operated to ensure that the combustion gases are only trace free Contain oxygen. This is important because otherwise the baking capacity of the charcoal will be significantly impaired by oxidation could be. The temperature of the gases is raised by adding 140 ° C. before they enter the fluidized bed Return gas set to 460 ° C. The return gas is behind the electrostatic precipitator 8 from the exhaust gas flow of the system through the line branched off and brought to the required pressure by the fan 13. The remaining exhaust gas is discharged into the open at 19.

After flowing through the coal bed, the fluidizing gas leaves the fluidized bed 11 at approx. 320 ° C. and passes through isolated Pipes 17 in the cyclones arranged above. It first flows through the separating cyclone 14, in which it is entrained Dust is deposited. This dust will vary depending on the Requirements either through line 15 into the vortex

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returned bed or added via line 16 to the coarser grain withdrawn as a finished product from the fluidized bed. The cyclone dust has approximately the temperature of the coarser material.

After dedusting in the cyclone 14, the gas withdrawn from the fluidized bed is successively discharged via the lines 10b and 10a passed through the heat exchange cyclones 10 and 9. It transfers its heat to the lines 9a and 6a Gradually counter-flowing coal and cools to 140 ° C away. At this temperature it enters the electrostatic precipitator 8 together with the dryer vapors, in which it removes dust will. In the present example, the dust separated out in the filter is added to the finished product through line 21.

The method example described above can be applied in various ways Way to be modified. So there is no B, the dryer 2 for input material with a very low moisture content. The generation of practically oxygen-free vortex and conveying gas emphasized in the above example can be dispensed with be if you z. B. heated fine coal then wants to smolder or coke. In this case, the Combustion chamber 12 in front of the fluidized bed 11 is omitted and the fluidized bed can be operated with cold or preheated air generates the heat required for the process directly through partial combustion of coke and volatile components in the fluidized bed. A fluidized bed with internal combustion can also be used when heating non-combustible materials. These technology known per se is described in German patent specification 1 758 244; it is based on fuel and air to be introduced through mixing nozzles in the bottom of the fluidized bed and the combustion gases produced in the area of the nozzles as fluidizing gas to use. If you heat coal to temperatures in the loading. rich of degassing, then it would have to take the place of the in the figure shown electrostatic precipitator connect a condensation device.

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Claims (13)

Patent claims 1) A method for continuously heating fine-grained materials, in particular baking coal, to a uniform, precisely controlled final temperature by means of hot gases which are brought into direct contact with the material to be heated, characterized in that the material to be heated with hot conveying gases through one or more heat exchange cyclones passed and preheated and brought to the final temperature in a downstream fluidized bed. 2) Method according to claim 1, characterized in that the residence time of the material to be heated in the fluidized bed is a few minutes up to about half an hour and preferably 5 to 20 minutes. 3) Method according to claim 1 or 2, characterized in that the exhaust gas from the fluidized bed is passed as a hot conveying gas into the heat exchange cyclones. 4) Method according to claim 1 or one of the following, characterized in that the hot conveying gases are passed in parts against the direction of gravity and flow of the material to be heated. 5) Method according to claim 1 or one of the following, characterized in that the exhaust gas from the fluidized bed is first dedusted in a separating cyclone before it flows through the heat exchange cyclones as a conveying gas, and that the precipitated dust in the separating cyclone is removed or into the Fluidized bed is returned, - 11 - 409821/0629 6) Method according to one of claims 1 to 5 » characterized in that when using moist material, a dryer, preferably a flight dryer, is connected upstream. 7) Method according to claim 6, characterized in that the dryer vapor is subjected to fine dust removal together with the exhaust gas from the heating system. 8) Method according to one of claims 1 to 5, characterized gekennaichnet that when using moist material and final treatment temperatures above 500 ° C, the drying is carried out in the top heat exchange cyclone. 9) Method according to one of claims 1 to 8, characterized in that the fluidizing gas required for the fluidized bed is generated in an upstream combustion chamber with an almost stoichiometric fuel gas / air ratio and is tempered by recycling cooled exhaust gas. 10) Method according to one of claims 1 to 8, characterized in that at final treatment temperatures above 500 ° C a We Use comes. 500 ° C a fluidized bed with internal combustion as the final stage for 11) Device for performing the method according to claim. 1 or one of the following, characterized by one or more heat exchange cyclones as the preheating stage, a fluidized bed with fluidizing gas supply as the final stage, pipes for transferring the exhaust gas from the fluidized bed into the heat exchange cyclones and a filter for fine dust removal of the exhaust gas from the top heat exchange Cyclone. 12) Device according to claim 11, characterized in that the fluidized bed contains an internal combustion. 13) Apparatus according to claim 11 or 12, characterized marked 'is characterized in that in the pipeline between the fluidized bed and the lowermost heat exchange cyclone a deposition cyclone single is switched. 4098 2 1/0629 Il Blank page