Patent Publication Number: US-4840561-A

Title: Apparatus for the heat treatment of fine-grained material

Description:
The invention relates to apparatus for the heat treatment of fine-grained material, such as cement raw material. 
     Apparatus of the general class disclosed herein is known for example from DE-A-24 51 197 and 27 37 992. Such apparatus facilitates precalcination (deacidification) of the preheated material in a combustion chamber supplied with exhaust air from a cooler (tertiary air), and the material which has already been greatly heated in this way and largely deacidified is then introduced into the furnace exhaust gas pipe and here undergoes further deacidification by means of the hot furnace exhaust gases and possibly additional fuel before it passes into the rotary drum furnace after separation in the lowest cyclone of the preheater. 
     In the known apparatus of this type the cover of the combustion chamber which is of cylindrical construction in the upper region is substantially level and provided in the region of its centre with the fuel supply. Practical experience with such apparatus show it to be desirable to improve the combustion conditions in the combustion chamber and the start of the combustion. 
     This object is achieved by apparatus constructed according to the invention. Advantageous embodiments of the invention are disclosed in the drawings wherein: 
    
    
     FIG. 1 shows a schematic representation of a first embodiment of the apparatus according to the invention. 
     FIGS. 2 and 3 show partial representations of the elements of the apparatus according to FIG. 1 which are essential to the invention. 
     FIG. 4 shows a section through the combustion chamber according to FIGS. 1 to 3. 
     FIGS. 5 to 7 show schematic representations (corresponding to FIG. 2) of three further embodiments of the invention. 
    
    
     The apparatus illustrated in FIGS. 1 to 4 for the heat treatment of fine-grained material, particularly cement raw material, contains a multi-stage preheater 1 which is only shown quite schematically and serves to preheat the material. This preheater 1 preferably consists of a plurality of cyclones which are connected to one another by their gas and material pipes and in which the material is preheated in stages by the hot exhaust gases from the combustion and precalcination zone which is described below. 
     The apparatus according to FIG. 1 also contains a combustion chamber 2, a cyclone 3, a rotary drum furnace 4 and a cooler 5. 
     The combustion chamber 2 which is shown in detail in FIG. 4 contains an upper region 6 of cylindrical construction and a lower region constructed as a hopper 7. The cover 8 of the combustion chamber is provided with a downwardly-directed central recess 9, the base 9a of which is provided with a fuel supply 10. 
     In addition the combustion chamber 2 contains a tangential combustion air supply 11 in the upper region at the level of the central recess 9. The base 9a of the central recess 9 is somewhat lower than the the underside of the tangential combustion air supply 11. 
     In the central part of the level of the upper cylindrical region 6 of the combustion chamber two diametrically opposed material supplies 12, 13 (for example in the form of dispersion boxes) are provided in the peripheral wall of the combustion chamber. 
     The ratio of the length L to the diameter D of the upper cyclindrical region 6 of the combustion chamber is advantageously between 2 and 2.5. 
     In the embodiment illustrated in FIGS. 1 to 4 a pipe 14 which is connected to the cooler 5 and conducts exhaust air from the cooler (so-called tertiary air) branches into one pipe 14a which is connected to the combustion chamber 2 and two pipes 14b, 14c which are connected directly to the furnace exhaust gas pipe 15 connecting the rotary drum furnace to the cyclone 3. 
     The pipe 14a opens via the aforementioned combustion air supply 11 into the combustion chamber 2, whilst the pipes 14b and 14c--as can be seen from FIG. 2--open with a downwards inclination into the furnace exhaust gas pipe 15. Valves 16a, 16b, 16c are provided in the said three pipes 14a, 14b and 14c to adjust the air streams introduced into the combustion chamber 2 into the furnace exhaust gas pipe 15. 
     The hopper 7 of the combustion chamber 2 is connected to the furnace exhaust gas pipe 15, and the point at which this hopper 7 opens into the furnace exhaust gas pipe 15 can lie at the same level, above or below the point at which the pipes 14b and 14c open. 
     Shortly before the point at which they open into the furnace exhaust gas pipe 15 the pipes 14b and 14c are provided with connections 17b, 17c for the supply of fuel and with connections 18b, 18c for the supply of preheated material (cf FIG. 2). The material pipes leading from the preheater 1 to the connections 18b18c are designated schematically by 18&#39;b and 18&#39;c respectively in FIG. 1. In a corresponding manner the pipes leading to the material supplies 12, 13 of the combustion chamber 2 are designated by 12&#39; and 13&#39; respectively. The material pipe leading from the hopper 7 to the furnace exhaust gas pipe 15 is designated by 7&#39;. 
     The apparatus advantageously contains arrangements (not illustrated in the drawings) to enable the material streams introduced into the combustion chamber 2 and directly into the furnace exhaust gas pipe 15 to be adjusted as required. 
     The illustrated apparatus functions as follows: 
     The fine-grained material is preheated in the preheater 1 with the hot exhaust gases from the rotary drum furnace 4 and the combustion chamber 2. An adjustable proportion of the preheated material passes from the preheater 1 via the pipes 12&#39;, 13&#39; into the combustion chamber 2 where it is further heated and greatly deacidified by the additional fuel supplied at 10. The central recess 9 provided in the cover of the combustion chamber 2 serves for spin stabilisation of the combustion air which is supplied tangentially. The fuel is introduced centrally into the combustion chamber 2 via the supply pipe 10 and ignites in pure air. At approximately half the height of the cylindrical upper region 6 of the combustion chamber 2 the material passes via the supply pipes 12, 13 into the combustion chamber 2. At the same time the temperature in the combustion chamber is controlled. 
     The material which is greatly deacidified in the combustion chamber 2 then passes via the pipe 7&#39; into the furnace exhaust gas pipe 15 and is there mixed together with the material streams which in the illustrated embodiment are introduced via the pipes 18&#39;b, 18&#39;c into the tertiary air pipes 14b, 14c which open directly into the furnace exhaust gas pipe 15. For the deacidification of these material streams further fuel is introduced via the connections 17b, 17c into the pipes 14b, 14c (immediately before the points at which they open into the furnace exhaust gas pipe 15). 
     The material separated off in the cyclone 3 is then delivered via a pipe 19 to the rotary drum furnace 4 where it is burnt to clinker and is then cooled in the cooler 5. The gas stream which is free of material is delivered via a pipe 20 to the further stages of the preheater 1. 
     FIG. 5 shows in schematic form an embodiment in which the pipe 14 conducting the exhaust air from the cooler only branches into two pipes 14a, 14&#39;a which are each connected to a combustion chamber 2 or 2&#39; respectively. The hoppers of these combustion chambers 2, 2&#39; are connected at different points to the furnace exhaust gas pipe 15 (the points at which they open do not have to be at the same level but can be offset in terms of height). The combustion chambers 2, 2&#39; are constructed in the same manner as has already been described with the aid of FIG. 4. 
     FIG. 6 shows a variant in which the pipe 14 conducting the tertiary air is not branched, but is connected to one single combustion chamber 2, the hopper 7 of which is connected to the furnace exhaust gas pipe 15. In this embodiment the total quantity of material coming from the preheater 1 is generally introduced into the combustion chamber 2. 
     Finally, a variant of the construction according to FIG. 6 is shown in FIG. 7, in which the hopper 7 of the single combustion chamber 2 branches into two pipes 7&#39;a, 7&#39;b which open into the furnace exhaust gas pipe 15 at different points. 
     Otherwise the construction of the combustion chamber 2 corresponds to that of the embodiment according to FIG. 4.