Abstract:
The present invention relates to a system for dry extracting and cooling incinerator clinkers, mainly comprising an extraction-cooling unit and means for separating the environment of the combustion chamber from that of said unit. The system is able to reduce the final temperature of the extracted clinkers, without exceeding the air quantity that can be admitted at the entrance to the combustion chamber of the incinerator (FIG.  1 ). When the air flow needed for cooling process exceeds said quantity that can be admitted, the system allows exceeding air to be sent in the most appropriate point of the boiler downstream of the combustion chamber, by suitable control means.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a system and method for dry extracting/cooling heavy ashes coming from the combustion of waste inside of incineration plants. 
       BACKGROUND OF THE INVENTION 
       [0002]    Current systems for extracting heavy ashes coming from the combustion of waste in incinerators provide for the use of wet systems. 
         [0003]    Heavy ashes outlet from incinerators are discharged into a water-filled tank located downstream of the last combustion grate. The collection tank has the double function of cooling the ash clinkers and of water seal, thereby preventing the entrance in the boiler of ambient air resucked by the value of depression existing therein, which would disturb the combustion process. 
         [0004]    The clinkers thus cooled are removed from the collection tank by scrapers or pushers, causing the reascending of the ash along a slope, and the subsequent discharging thereof in downstream apparatuses. 
         [0005]    The use of systems for wet extracting causes remarkable inconveniences to the system on itself and to the surrounding environment. The main drawbacks are related to:
       Irreversible loss of chemical energy and sensible heat contained in the water-cooled ashes. Once the ashes precipitate in the collection tank, the combustion processes of unburnt material present therein stop. Moreover, all the thermal content of the ashes is transferred to the cooling water.   High costs of wet ashes transportation and storage, due to their higher weight, proportional to the humidity content therein.   Consumption of water needed for cooling the clinkers.   Need to purify the clinkers-contaminated cooling water, prior to its discharge in the environment.   Difficulty of separating the metallic fractions present in the wet ash, owing to cohesion phenomena between the ash itself and the metallic fractions to be recovered.   Energy expenditure for moving the cooling water, which requires continuous additions to limit its thermal rise and recover its losses.   High maintenance costs, due to the high corrosion rate of the apparatuses and pipelines in which the water flows.       
 
         [0013]    The present invention is based instead on the adoption of systems for dry extracting and cooling said clinkers. The adoption of a system for dry extracting incinerator clinkers poses the problem of controlling the entrance of air (air inlet) in the boiler from the section for discharging heavy ashes downstream of the last combustion grate. In fact, an uncontrolled and oversized entrance of air from said section would entail altering the combustion phenomena in the boiler, with a strong and negative impact on the combustion efficiency, the distribution of the heat flow on exchange surfaces, and the formation of pollutants (NO x ) and particulate matter. 
         [0014]    Moreover, said clinkers, due to the very nature of the fuel used, are heterogeneous and can contain extraneous bodies of remarkable size; this renders advisable the use of environment separation systems alternative to the typical ones used in other applications (e.g., double-clapet valves), which might be at risk of mechanical blocking at the closing and therefore cause the uncontrolled inlet in the combustion chamber of remarkable quantities of air. 
         [0015]    Therefore, the technical problem underlying and solved by the present invention is to provide a system and method for extracting and cooling incinerator clinkers which allow obviating the drawbacks disclosed hereto in connection with the known art. 
       SUMMARY OF THE INVENTION 
       [0016]    The above-mentioned problem is solved by a system according to claim  1  and a method according to claim  11 . 
         [0017]    Preferred features of the invention at issue are present in the claims depending from the invention itself. 
         [0018]    The present invention provides some important advantages, some of which are summarized in the following and will be appreciated in full in the light of the detailed description reported hereinafter. In general terms, important advantages of the invention with respect to the known art are the elimination of all problems related to the use of cooling water, the fact of making easier and more economical the processes of clinkers separation and storage, and the fact of allowing the recovery of the thermal and chemical energy contained in the high-temperature ashes. 
         [0019]    In more specific terms, the main advantage of the invention consists in that it allows the dry extracting of the clinkers, providing and adequate, effective and efficient cooling of the same without use of cooling water, by operating an effective control on the air inlet in the combustion chamber to which the extracting system is connected. 
         [0020]    This is mainly obtained by the use of separating means internal to the extractor and comprised between the extraction zone and the discharge point. Said separating means cause the entrance in the combustion chamber of a predefined quantity of air useful to the cooling of the clinkers and such as not to influence the combustion process. 
         [0021]    According to a preferred and particularly advantageous embodiment, said separation is carried out by the use of a series of movable air locks overhung and hinged to the cover of the extractor in a direction substantially perpendicular to the direction of transport, implementing a sort of labyrinth seal with regard to air, allowing anyhow the passage of clinkers in transit on the belt. 
         [0022]    In case the quantity of clinkers extracted is such that the quantity of cooling air required and inlet into the combustion chamber exceeds the minimum percent of combustion air that would negatively influence the combustion efficiency, the present invention equips the extracting system with a device for transferring excess cooling air downstream of the combustion chamber. Said device connects the extractor portion downstream of the separating means to a suitable zone of the boiler downstream of the combustion chamber, and it is sized so as to effect load losses sufficient to render the pressure of the extractor portion to which it is connected equal to or higher than the pressure in the combustion chamber. This feature prevents the danger of combustion fumes passing through the extractor. 
         [0023]    According to a preferred embodiment, said device for transferring excess air is constituted by a suitable duct, optionally equipped with a dedusting system and a regulation valve in line. 
         [0024]    In some system configurations the extracting function and the cooling one can be entrusted to two distinct conveyors, the first one positioned at the combustion chamber and the second one downstream thereof; the environments of the two conveyors being connected by a hopper for feeding the clinkers from the first belt to the second belt. All of this does not alter the concept at the basis of the present invention, since the environments of the two conveyors form a single environment and therefore a single extracting/cooling unit as described above according to a preferred embodiment. 
         [0025]    Upon summarizing the detailed description of preferred embodiments reported hereinafter, the present invention relates to a system for dry extracting and cooling incinerator clinkers, able to reduce the final temperature of the extracted clinkers, without exceeding the air flow that can be admitted at the entrance to the combustion chamber of the incinerator. When the air flow needed for cooling process exceeds said quantity that can be admitted, the system allows exceeding air to be sent in the most appropriate point of the boiler downstream of the combustion chamber, by suitable control means. 
         [0026]    The proposed system, upon use, is mainly constituted by the following members: 
         [0027]    1. a connection hopper between extractor and incinerator, through which clinkers are discharged on the extractor belt, the latter of the type subject of Patent EP 0 471 055 B1; 
         [0028]    2. the above-mentioned extractor/cooler, receiving ash in size and fines, the latter coming from the hoppers underlying the combustion grate; at the loading zone, the pitch of the load-bearing rolls of the conveyor belt is thicker in order to better distribute the load deriving from the impact of the free-falling material; the extracting and transport section is sized so as to facilitate the extracting also of maximum-size clinkers; 
         [0029]    3. a system for recovering fines, positioned on the bottom of the extractor and constituted by components resisting to high temperatures; 
         [0030]    4. separating means present inside the extractor, to limit the entrance of ambient air in the combustion chamber, forming to this end a separation zone between the combustion chamber and the discharge point of the extractor; 
         [0031]    5. means for feeding cooling air inside the extractor, positioned on the side walls of the extractor itself, such as to prevent, in case of overpressure, the outlet of hot gases; 
         [0032]    6. optionally, a connecting pipeline or duct for the connection between the extractor portion downstream of the separating means and the point of the boiler downstream of the combustion chamber most suitable for the outlet of the cooling air exceeding the maximum acceptable by the combustion chamber; said pipeline may be equipped with a cyclone dedusting system and a regulation valve in line; 
         [0033]    7. optionally, a control logic for the pressure existing upstream and downstream of the extractor section equipped with separating means, through the adjustment of the valve located on the mentioned duct. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    Other advantages, features and application modes of the present invention will be evident from the following detailed description of some preferred embodiments, shown by way of example and not for limitative purposes. The figures of the enclosed drawings will be referred to, wherein:
         FIG. 1  shows a general layout exemplifying a preferred embodiment of the invention system, in an operation mode which provides the entrance in the combustion chamber of all the cooling air;     FIG. 2  shows a general layout exemplifying an embodiment of the invention system, in an operation mode which provides to send exceeding cooling air in the boiler downstream of the combustion chamber;     FIG. 3  shows a general layout exemplifying an embodiment of the invention system, in an operation mode which provides to send exceeding cooling air in the atmosphere, upon filtering treatment;     FIG. 4  shows a schematic cross-sectional view according to the line A-A of  FIG. 1  ;     FIG. 5  shows a detail of  FIG. 3  highlighting the section for the passage of cooling air inside the extractor;     FIG. 6  shows a schematic cross-sectional view according to the line B-B of  FIG. 2  ;       
 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    By firstly referring to  FIG. 1 , a system for dry extracting/cooling incinerator clinkers is designated as a whole with  1 . 
         [0042]    For greater illustration clarity, the different components of the system  1  will be described hereinafter by referring to the path followed by the clinkers from the extraction thereof from the combustion chamber, designated with  100 , to the disposal thereof. 
         [0043]    Immediately downstream of the combustion chamber  100 , the system  1  provides an extracting and cooling unit  9 , based on a dry extractor mainly made of steel with high thermal resistance. Such extractor  9  is of the kind known on itself and described for example in EP 0 252 967, herein incorporated by means of this reference. 
         [0044]    The extractor  9  gathers the heavy ashes which precipitate downwards from a combustion grate  101  of the chamber  100  through a transition hopper  102 . 
         [0045]    The fines are instead transported on the extractor  9  by collection hoppers  8 , arranged at the bottom of the combustion grate  101 , the latter ones being equipped with double-clapet valves  5  (or equivalent means), apt to separate the environments upstream and downstream thereto, and being positive-pressure hoppers. 
         [0046]    The extractor  9 , at the side walls of its own casing  98 , has a plurality of entrance holes for the outer cooling air, distribuited in a substantially regular way along the development of the extractor  9  itself and each one designated with  10 . Such entrances  10  can be equipped with means for adjusting the flow or can be made active or deactivated. They serve as check valves, i.e. prevent, in case of overpressure in the extractor, the outlet of hot gases in the environment. 
         [0047]    Inside the extractor  9 , stationary  91  and movable  92  separating means are present, apt to cause a substantial pressure separation of the environments upstream and downstream thereof. 
         [0048]    The stationary separating means  91  is preferably constituted by metal baffles, preferably arranged at the transmission head of the extractor  9 , in a zone upstream of the clinkers loading point. The means  91 , by occupying all the available section between the conveyor belt and the related metal container  98 , have the function of preventing air entering the extractor  9  from re-entering in the combustion chamber  100  by passing around the transmission drum  931 . 
         [0049]    The movable separating means  92  is preferably constituted by air locks overhung and hinged to the cover of the extractor  9 , arranged in series along the transport section. The number of air locks is such as to assure a remarkable load loss at the entrance of air resucked from the discharge point of the extractor, so as to let in the combustion chamber a known and predefined maximum quantity of air. 
         [0050]    As shown in greater detail in  FIG. 4 , the air locks  92  are preferably with a pivoting multiple body, i.e. constituted by parallel bands  93  hinged therebetween, so as to accompany the contour of the layer of material travelling on the belt. Said parallel bands  93  may be sized so that those more proximal to the conveyor have greater weight to operate a levelling of the layer upon passage of more compressible material. This function, operated mainly by the air locks more proximal to the combustion chamber  100 , make more effective the air seal function of the air locks nearer to the discharge point of the extractor  9 . 
         [0051]    To guarantee the confinement of clinkers extracted in the transport region, the extractor  9 , along all of its length, has metal boards  94  for containing the material. Said containing boards  94  provide a minimum vertical distance from the belt, needed to prevent contact and interference therewith. 
         [0052]    When needed, in the gap comprised between belt and metal board  94 , brushes  95  of metal or other material resisting to high temperatures can be provided so as to improve the seal and further limit air entrance. 
         [0053]    The quantity of ambient air entering through the entrances  10  on the side walls of the extractor can be controlled by making a prefixed passage section. As shown in greated detail in  FIG. 4 , said entrance section or port may be preferably made by horizontal seal plates  96  connected to the external side of the containing boards  94  and fastened thereto at a determined distance from the fins  97  of the conveyor belt. The presence of said seal plates  96  on both sides of the extractor belt and for all the length of transport assures the entrance of a predetermined quantity of air in the extractor  9  and therefore in the combustion chamber  100 , there being known the passage section and the depression value in the combustion chamber  100 . Of course, such plates  96  can also involve only a portion of the transport (conveying) section of the belt  9 , and in particular only part of the portion downstream of the hopper  102 . 
         [0054]    Therefore, cooling air is resucked into the extractor  9  for the most part through the entrances  10  (and the section determined by the seal plates  96 , when present); and partly it is resucked from the discharge point of the extractor through the labyrinth seal operated by the movable air locks  92 . 
         [0055]    The clinkers cooling on the belt occurs by ambient air that, resucked in such a way by the depression in the combustion chamber, crosses them in countercurrent. Once heated by effect of the thermal exchange with the latter, the air enters the combustion chamber, re-inletting heat therein. 
         [0056]    As previously anticipated, in case the quantity of clinkers to be cooled is such that the cooling air needed exceeds the quantity than can be admitted in the combustion chamber, the invention provides the transfer of exceeding cooling air to a boiler zone downstream of the combustion chamber. 
         [0057]    In such a system configuration, and by referring to  FIG. 2 , the device for transferring exceeding cooling air is constituted by a duct  2 , connected to the extractor portion downstream of the separating means, preferably equipped with a cyclone dedusting system  3  and an automatic regulation valve  4  in line. 
         [0058]    The boiler zone downstream of the combustion chamber  100  being at a lower pressure with respect to the combustion chamber itself, by connecting said zone with the extractor belt  9  there might take place a passage of combustion fumes from the combustion chamber itself to said extractor. To avoid this situation, the duct  2  is sized so as to effect sufficient load losses along the line, such as to obtain in the portion of extractor connected thereto a pressure value equal to that of the combustion chamber. 
         [0059]    For a fine adjustment of this condition, the pressure difference between the extractor portions upstream and downstream of the separating means is constantly monitored by means of suitable sensors  7  and adjusted by means of the actuation of the valve  4  on the duct  2 . 
         [0060]    By referring to  FIG. 3 , optionally the duct for expelling exceeding cooling air may have a connection different from the above-described one. In this case, in fact, the air, instead of being sucked by the depression existing in a boiler zone downstream of the combustion chamber, can be sucked by a dedicated fan  22  or equivalent means along the duct  21  equipped with regulation means  40  analogous to the hereto-described ones, and then discharged in the atmosphere upon passing into a dedicated filter  210  arranged upstream of the fan  22 . 
         [0061]    In these last two system configurations ( FIGS. 2 and 3 ), the air entering the extractor  9 , through the discharge point  99  and the side entrances  10 , provides to complete the cooling in countercurrent of the clinkers present on the belt portion downstream of the separating means, and is then resucked through the duct  2  into a suitable boiler zone downstream of the combustion chamber  100 , by referring to  FIG. 2 , or sent in the atmosphere by the duct  21  and the fan  22 , by referring to  FIG. 3 . 
         [0062]    In addition, as shown also in  FIG. 6 , the extractor  9  is equipped with a system  981  for recovering the fines positioned on the bottom of the metal container  98 , consisting of components resisting to high temperatures. 
         [0063]    To avoid fines entrainment by ambient air re-entering from the discharge point  99 , it is provided the separate discharge  991  of the fines collected from the recovering system, by double-clapet valve  992  or equivalent system for separating the environments. 
         [0064]    The present invention has been so far described referring to preferred embodiments. It is to be meant that other embodiments belonging to the same inventive core may exist, all comprised within the protective scope of the herebelow reported claims.