Abstract:
The invention relates to a facility for grinding inorganic material comprising: a means ( 1 ) for supplying raw material; a means ( 2 ) for detecting metal material coupled to a discharge circuit ( 3 ); a first static separator ( 4 ); a roller press ( 5 ); a dynamic separator ( 6 ); a ventilation circuit ( 7 ); and a circuit ( 8 ) for circulating the finished product. The press is connectable by means of a conveyance system ( 25 ) having a diverting circuit ( 26 ) or a second static separator ( 27 ), at least one of the outlets ( 28 ) of which is connected to the dynamic separator ( 6 ).

Description:
TECHNICAL FIELD 
       [0001]    This invention concerns a facility for grinding inorganic matter, intended in particular to be installed in a concrete mixing plant. 
       BRIEF DESCRIPTION OF RELATED ART 
       [0002]    The manufacture of concrete includes various steps, each of which consumes a significant amount of energy. These steps include, in particular, two grinding steps, one at the beginning, the other at the end of the manufacturing process. These steps are energy-intensive. The first grinding step is the grinding of the raw material, representing 20-30% of the total electrical power consumption of the manufacture of concrete. It also carries out the mixing and drying of this matter, known as raw meal, before cooking it at a temperature of approximately 1450° C. The second grinding step is carried out on the product resulting from the cooking: the clinker. It represents 30-50% of the total electrical power consumption of the manufacture of concrete, and is an essential step in the production of concrete. In fact, this is the step that, by adding gypsum and additives, determines the composition and granulometry of the final product, and thus the technical characteristics of the cement. This invention, more specifically, concerns this second grinding step, that of the clinker, but can also concern the first grinding step in which the raw meal is obtained. 
         [0003]    In the constant desire to reduce the operating costs and environmental impact of the manufacture of concrete, the facilities used in the grinding steps, in particular that of the clinker, have developed over the past roughly twenty years. Thus, until the 1980s, this type of facility used ball mills according to a grinding method consisting of passing the matter to be ground through a horizontal rotating tube that contains metal discs. This means of grinding the matter has very low energy efficiency. Later, grinding facilities developed progressively in the direction of pressing the matter, which provides better energy efficiency. This initially took the form of using roller mills, either vertical or horizontal. The substantial increase in energy efficiency that accompanied these technologies is cancelled out by the increased complexity of the facility, and, in the case of vertical roller mills, the need to wet the matter to be ground, which entails an additional step of drying, in which a great deal of heat energy is expended. 
         [0004]    Simultaneously, both metallurgical improvements and improved granulometric separation methods for the matter allowed for the development of roller press grinding. This type of mill, which also presses the matter, uses gravity for the intake of the matter, reduces energy consumption, and simplifies the grinding facility. 
         [0005]    Thus, the current grinding facilities, which comprise a roller press, generally comprise a static separator, usually cascade-type, serving to remove and dry the raw material, and to break and remove the agglomerated material (or discs) resulting from press-grinding, a roller press allowing for reduction of the granulometry of the matter, and a dynamic separator to select the particles having the desired granulometry. The connection of the cascade-type static separator to the roller press in this type of facility allows for recycling of material having excessive granulometry even following a first pass through the roller press. This type of facility, though perfectly suited to ensure adequate granulometry of the final product, still consumes a substantial amount of energy, due in particular to the recycling in the roller press of low-granulometry matter which should have gone to the final product. 
       BRIEF SUMMARY 
       [0006]    The disclosure provides a facility for grinding inorganic matter having a roller press, which both has the grinding and drying characteristics of the current facilities, and requires a reduced amount of energy per dedicated tonnage of inorganic matter to be processed. 
         [0007]    To this end, the invention concerns a facility for grinding inorganic matter having a roller press, including a first static separator having an intake for raw material, comprising two outputs, the first for low-granulometry matter and the second for matter with larger granulometry, whereby the latter is connected to a roller press, and the first output of the first static separator is connected to the intake of a dynamic separator comprising two outputs, a first output for particles having the desired granulometry and the second for matter with larger granulometry, connected to the intake of the roller press, in which a ventilation circuit is provided through the first static separator and the dynamic separator in order to participate in the separation, drying, and transport of the low-granulometry particles, which facility comprises a second static separator having an intake that is solely connected to the output of the roller press, and at least one of the outputs of which, for low-granulometry particles, is connected to the dynamic separator, which first static separator is fed only with raw material and through which the ventilation circuit passes. 
         [0008]    The use of a second static separator dedicated to the output of the roller press allows for better distribution of the load between the two static separators, with the first static separator dedicated solely to receiving the raw material. This results not only in improved drying of the raw material and the ground matter, but also in better disintegration and separation of the particles of the discs resulting from the grinding in the roller press, and thus better performance of the facility (reduced amount of low-granulometry particles returning to the press). This improvement in the performance of the press and reduction in the load borne by each separator, which results in reduced differential pressure needed by the ventilation circuit, allows for a reduction in energy consumption per ton of inorganic matter processed. 
         [0009]    Advantageously, the facility comprises a deballasting circuit. 
         [0010]    When the roller press is started or adjusted, such a circuit allows for deballasting of the matter that has passed through the press, and, which, due to constrains related to the roller press grinding technology, has only been very slightly ground. This reduces the load borne by the press in the essential start-up and adjustment periods, thus allowing for increased useful life of the press and the dynamic separator. 
         [0011]    Preferably, the deballasting circuit comprises a hopper, the intake of which can be temporarily connected to the output of the roller press, and the output of which is connected to the first static separator. 
         [0012]    Thus, upon starting the press, the matter coarsely ground by the press can be stored in the hopper and gradually reintroduced with the raw material, thus limiting the load borne by the press at start-up. 
         [0013]    According to an alternative embodiment, the deballasting circuit comprises a hopper, the intake of which can be temporarily connected to the second output of the second static separator, that of the high-granulometry matter. 
         [0014]    Such an alternative allows during the deballasting phase for recovery of the low-granulometry particles arising from this partial grinding, whilst ensuring that the high-granulometry matter is not reintroduced into the dynamic separator, but stored in the deballasting hopper. Once the normal operation of the press has been attained, the coarsely ground matter is reintroduced gradually with the raw material. 
         [0015]    Advantageously, at least one of the static separators is of the cascade type. 
         [0016]    Such separators, by design, are robust, and can process coarse material, and have high disintegration and drying capacity. This type of separator is thus ideal both for processing the raw material and carrying out an initial sorting of the material once it has been ground. 
         [0017]    The raw feed of the first static separator comprises several hoppers, a means of weighted dosing associated with each hopper, and a means for conveying the matter into the first static separator. 
         [0018]    Feeding the first static separator, and thus the grinding facility, in this manner allows for the desired mixture constituting the final product, i.e. the concrete or raw meal (for a facility adapted for the first grinding step of the manufacture of cement) to be determined in the grinding stage by the operation of various hoppers containing different components and using means of dosing. 
         [0019]    Preferably, the facility comprises means for detecting metallic matter, which means cause the rejection of such matter via a reject circuit. 
         [0020]    The existence of means for detecting metallic matter coupled with a reject circuit for such matter allows for the elimination of the risk of damage to the grinding facility, which may arise from the presence of this type of matter, thus guaranteeing better composition of the finished product. 
         [0021]    Advantageously, the first output of the dynamic separator is connected to a filtration device that allows for separation of the low-granulometry particles from the air of the ventilation circuit, and the filtration device is connected to a system for transporting the granular product. 
         [0022]    The use of such a filtration device coupled with a transportation system allow for recovery of particles having the desired granulometry and the transportation of these particles to a storage area, or directly to the conditioning step for the final product. 
         [0023]    Preferably, the intake of the roller press is equipped with a feed hopper. 
         [0024]    This hopper ensures both continuous supply and control of the quantity of the matter fed into the press. 
         [0025]    Advantageously, the second static separator comprises two outputs, one for the low-granulometry particles and one for the high-granulometry matter, the output for high-granulometry matter being connected to the dynamic separator. 
         [0026]    Such a coupling allows for the dynamic separator to be supplied with the ground matter that has already passed through the second static separator, and has thus been acceptably disintegrated. This sequence ensures good separation of low-granulometry particles and high-granulometry matter, and thus allows for the press to be supplied with a reduced amount of matter with high granulometry (fewer low-granulometry particles in the matter reintroduced into the press), thus reducing the load on the press, which allows for an increased raw material load. This results in a significant increase in the performance of the facility as a whole for an equivalent quantity of energy. In fact, the performance to be applied for the separation of the pressed matter is that of the dynamic separator (85-90%) and not that of the first static separator (40-50%). 
         [0027]    According to an alternative embodiment, the second static separator comprises two outputs, one for low-granulometry particles and one for the high-granulometry matter, the output for high-granulometry matter being connected to the intake of the first static separator. 
         [0028]    Such a coupling of the second output of the second static separator with the intake of the first separator allows for the ground matter to pass through two separators, and thus for an optimization of the disintegration of the discs arising from the grinding, and optimal recovery of low-granulometry particles after each grinding. 
         [0029]    According to another embodiment, the second static separator comprises two outputs, one for low-granulometry particles and one for the high-granulometry matter, the output for high-granulometry matter being directly connected to the roller press. 
         [0030]    Advantageously, at least one intake and/or output of at least one separator is equipped with sealing. 
         [0031]    Such a sealing allows for limitation of “false air” that may arise at the level of the separators. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The invention will be better understood using the following description, which refers to the attached schematic, showing three exemplary embodiments of this facility for grinding inorganic matter. 
           [0033]      FIG. 1  is a schematic representation of a known-art grinding facility; 
           [0034]      FIG. 2  is a schematic representation of a first embodiment of a grinding facility according to the invention; 
           [0035]      FIG. 3  is a schematic representation of a second embodiment of a grinding facility according to the invention; 
       
    
    
     DETAILED DESCRIPTION 
       [0036]      FIG. 1  shows a facility for grinding inorganic raw material having a roller press according to the state of the art. 
         [0037]    Such a facility comprises a means of supplying raw material  1 , means of detecting metallic matter  2 , coupled with a reject circuit  3 , a static separator  4 , a roller press  5 , a dynamic separator  6 , a ventilation circuit  7 , and a circulation circuit  8  for the finished product. 
         [0038]    During operation, the inorganic matter, e.g., clinker, gypsum, and additives such as blast furnace slag or ash, is injected into the circuit of the facility. This is carried out by means of several hoppers  9 , each containing one of the components necessary for the manufacture of the concrete. Each hopper is associated with a weighted dosing means  10  so as to obtain a mixture having the given composition, e.g., for CEMI concrete, 95% clinker and 5% gypsum, when the various components are introduced into the circuit of the facility. 
         [0039]    This raw material is then transported by a conveyor  11  such as a conveyor belt, a bucket elevator, or a chain conveyor. This conveyor, in the schematic representation of  FIG. 1 , is a conveyor belt  11 . During this transport, the raw material passes through a metallic particle detection system  2 , which redirects the matter to a reject circuit  3  if the raw material contains such particles. The reject circuit  3 , following a filtration procedure to selectively recover the metallic particles in a reject hopper  12 , allows the sorted raw material to be redirected to the conveyor  11 , which transports it, with the rest of the raw material, to the intake  13  of a static separator  4 . 
         [0040]    This static separator  4 , usually of cascade type, is connected to the ventilation circuit  7 . This circuit  7 , either open or recirculating, allows for adjustment of the temperature of the air passing through this circuit. This adjustment is made by combining an air heater such as a hot gas generator or the heat connected to the equipment of the concrete factory such as the exhaust gases of a kiln or a cooler, and means of cooling such as the injection of outside air. Thus, according to the mode of operation of the cascade separator, i.e., the matter falling, cascade-fashion, onto several inclined walls around which the air flow of the ventilation circuit  7  circulates, the material is disintegrated by means of the collision with the inclined walls, and the low-granulometry particles that detach themselves are carried off by the air flow. The low-granulometry particles are directed by the air flow to a first output  14  of the cascade separator  4 , whilst the rest of the matter is directed to the second output  15 , connected to a feed hopper  16  for the roller press  5 . The passage of the high-granulometry matter through this hopper  16  allows for the supply to the roller press  5  to be regulated. The high-granulometry matter is then ground by the roller press  5 , and exits in a mixture of fine particles and discs of agglomerated matter. The matter thus ground is then reintroduced by means of the conveyor  18 , generally a bucket elevator, into the static separator  4  at the output  17  of the press  5 . 
         [0041]    During this second passage, the discs, mixed with the raw material, are disintegrated, allowing for partial release of the low-granulometry particles, which are transported by the air flow to the first output  14  of the static separator  4 . This first output  14  is connected to the intake  19  of a second, dynamic, separator  6 . This separator  6 , which is preferably a third-generation vertical-axle squirrel cage, allows for the selection of the particles having the required size, which are carried by the air flow to a first output  20 . The rest of the matter is sent through a second output  21  and a conveyor  22 , generally a conveyor belt, to the feed hopper  16  of the press  5  reduce its granulometry. The particles selected, which thus pass through the first output of the dynamic separator, are transported by the ventilation circuit  7  to a filtration device  23 , which allows for collection of the finished product having the required composition and granulometry. This product is then transported by a transportation system  24  for granular products, such as an air chute  24 , to be stored in storage silos before being packaged for sale or sent to the kiln following homogenization (for a facility adapted to obtain raw meal). 
         [0042]      FIG. 2  shows a first embodiment of a grinding facility according to the invention. Such a grinding facility differs from a prior-art facility in that the output of the press can be connected by a conveyor system  25  either to a deballasting circuit  26 , or to a second static separator  27 , also of cascade type, having two outputs  28 , 29  connected to the dynamic separator  6 . 
         [0043]    Thus, when the facility is started up, the feed hoppers  9  supply the facility with inorganic matter. As with the facility shown in  FIG. 1 , this raw material is sent by a conveyor system  11  to the first cascade separator  4 , which carries out a first sorting of the raw material; the high-granulometry matter is sent to the press  5  through the intake hopper  16  of the press  5 . When the press  5  is started up or being adjusted, the raw material, upon passing through the roller press  5 , is only slightly ground. Thus, in order not to overload the press  5 , the raw material, with this very slightly ground matter, is transported by the conveyor  25  to a deballasting circuit  26  comprising a deballasting hopper  30  and a means of weighted dosing  31  connected to the first cascade separator  4 . The matter is then stored in the deballasting hopper  30  whilst the roller press  5  is reaching its specific rated grinding power value, e.g., a value on the order of 2 kWh/t. Once this level has been attained, the slightly ground matter stored in the deballasting hopper  30  is gradually mixed with the raw material via the first static separator  4 . It thus passes again through the roller press  5  to be properly ground. 
         [0044]    The mixture of raw material and partially ground matter, after passing through the roller press  5 , is then sent in a steady state of operation to the second static separator  27 . This second separator  27 , in the case of this properly ground matter, allows both for disintegration and drying of the discs formed during the grinding by the roller press  5 . The matter thus obtained, a mixture of coarse matter and fine particles, is sent through the two outputs  28 ,  29  of the second separator to the dynamic separator  6 . The low-granulometry particles having been separate from the rest of the matter, the separator  6 , due to its high selectivity, carries out a selective sorting, as a result of which the fine particles having the desired granulometry exit through a first output  20 , and the higher-granulometry matter exists through a second output  21 . The latter matter is sent back to the press  5  for another grinding, disintegration, and sorting cycle, until the desired granulometry is achieved. Particles having the desired granulometry, i.e., of a size lower than a few microns, are transported by the ventilation circuit  7  from the first output  20  of the dynamic separator  6  to a filtration device  23 . This filtration device allows for the finished product with the required composition and granulometry to be collected. This product is then transported by a transportation system  24  for granular products, such as an air chute  24 , to be stored in storage silos before being packaged for sale or sent to the kiln following homogenization (for a facility adapted to obtain raw meal). 
         [0045]    A facility for grinding inorganic matter according to this embodiment, by increasing the amount of low-granulometry matter recovered after each grinding and thus increasing the performance of the entire facility, allows for a reduction in consumption per ton of ground matter of more than 16%, and a reduction by half of the capacity of the feed hopper  16 , as well as the transport system  25 . 
         [0046]      FIG. 3  shows a second embodiment of a grinding facility according to the invention. Such a grinding facility differs from the first embodiment in that an output  29  of the second static separator  27 , the high-granulometry matter output, is connected to a conveyor  32  to the feed hopper  16  of the roller press  5 . 
         [0047]    During operation, the feed circuit  9 ,  10 ,  11 ,  13  of the press and the deballasting circuit  25 ,  26  operate identically to the first embodiment. The change related to this second embodiment only occurs after the material has passed through the second, static, separator  27 . When it does so, the high-granulometry matter, which passes through the second output  29  of the second static separator  27 , is not sent to the dynamic separator  6 , but directly to the feed hopper  16  of the press  5 , by means of a conveyor  32 . Thus, the matter rich in course materials is ground again in order to reduce its granulometry, whilst only the low-granulometry particles originating from the first outputs  24 ,  28  of the two static separators  4 ,  27  pass through the dynamic separator  6 . The particles selected, as in the first embodiment, are transported by the ventilation circuit  7  to a filtration device  23 , which allows for collection of the finished product having the required composition and granulometry. This product is then transported by a transportation system  24  for granular products, such as an air chute  24 , to be stored in storage silos before being packaged for sale or sent to the kiln following homogenization (for a facility adapted to obtain raw meal). 
         [0048]    A third embodiment, not shown here, comprises, for a facility similar to the first embodiment, of connecting the second output  29  of the second cascade separator  27 , corresponding to the high-granulometry matter, to the conveyor  11  supplying the facility. This allows the ground matter to pass through two static separators  2 ,  27 , thus, allowing for optimal recovery of the low-granulometry particles at each grinding by means of optimizing the disintegration of the discs arising from the grinding. 
         [0049]    In the three embodiments shown, the deballasting circuit  26  is connected to the output of the press  17  during the deballasting phase. A possible alternative is to supply the deballasting circuit  26  during this deballasting phase from the second output  29  of the second static separator  27 , which output  29  corresponds to the high-granulometry matter. In this configuration, the output  17  of the roller press  5  is directly connected, as during steady-state operation, to the intake of the second static separator  27 . During this deballasting phase, this alternative allows for recovery of the low-granulometry particles arising from the partial grinding despite the low performance of the press  5 . 
         [0050]    In any embodiment of the invention, as shown by  FIGS. 2 and 3 , sealings  33  can be placed on the intakes  13 ,  34 ,  29  for matter and the outputs  15 ,  29 ,  21  for high-granulometry particles of the various separators  4 ,  27 ,  6 . For example, the second separator has a sealing  33  on its intake  34 . These sealings  33  are installed in order to limit the “false air” that may enter at the level of these separators ( 4 ,  27 ,  6 ). 
         [0051]    Obviously, the invention is not limited to these embodiments of the grinding facility for inorganic matter described above by way of example; rather, it encompasses all possible embodiments. In particular, it can be adapted to be used to grind the raw material before cooking.