Cooling system for the dry extraction of heavy ashes from boilers

Abstract

The present invention relates to an additional cooling system ( 1 ) for the dry extraction of large flow of heavy ashes produced by boilers ( 100 ) with solid fuel apt to decrease the temperature of the ashes. The system comprises an extractor with metallic belt ( 2 ) gathering the ash which deposits onto the bottom of the boiler ( 100 ), a crushing system ( 3 ), having the purpose of increasing the thermal exchange surface of the material, one or more metallic conveyors ( 4, 6 ) having the cooling function by introducing countercurrent air-flow running through transported ashes, an in-line cooling device ( 5 ) having the function of putting into contact the ash several times with additional countercurrent air in order to increase the possible exchange without necessarily increasing the air-flow entering the combustion chamber. Such additional air can be sent preferably upstream of the air heater or in atmosphere upon fines' captation.

1 . A system ( 1 ) for extracting and dry cooling combustion residues of the type apt to be used in association with a combustion chamber, in particular for significant flows of heavy ashes deriving for example from fossil fuel in an energy-production plant, which extraction and cooling system ( 1 ) comprises:
 means for extracting and transporting ( 2 ,  4 ,  6 ) combustion residues from the combustion chamber ( 100 ,  105 );   a system ( 5 ,  13 ,  14 ,  17 ) for cooling combustion residues, apt to determine a feeding of cooling air at said extraction and transport means ( 9 ,  6 ,  13 ), the overall arrangement being such that part of said cooling air is introduced into the combustion chamber ( 100 ) from the bottom thereof; and   means ( 20 ,  15 ;  200 ,  150 ;  201 ,  151 ) for feeding another part of the cooling air, downstream of the ash cooling process by the air itself, in atmosphere or in a fume duct ( 101 ) associated with the combustion chamber ( 100 ).   
     
     
         2 . The system ( 1 ) according to  claim 1 , wherein said cooling system ( 5 ,  13 ,  14 ,  17 ) comprises a dedicated air/ash heat exchanger ( 5 ), arranged in line with said extraction and transport means ( 2 ,  4 ,  6 ). 
     
     
         3 . The system ( 1 ) according to the preceding claim, wherein said feeding means ( 20 ,  15 ;  200 ,  150 ;  201 ,  151 ) is apt to feed into the fume duct ( 101 ) or into the atmosphere the cooling air crossing said exchanger ( 5 ). 
     
     
         4 . The system ( 1 ) according to  claim 2  or  3 , comprising one or more dedicated air entrances ( 14 ,  17 ) apt to feed into the system ( 1 ) the cooling air which crosses said exchanger ( 5 ). 
     
     
         5 . The system ( 1 ) according to the preceding claim, wherein said dedicated cooling air entrance or entrances ( 14 ,  17 ) are equipped with means for adjusting the flow of entering air. 
     
     
         6 . The system ( 1 ) according to  claim 4  or  5 , wherein said or at least one ( 17 ) of said dedicated entrances of cooling air is arranged immediately downstream of said exchanger ( 5 ). 
     
     
         7 . The system ( 1 ) according to anyone of the  claims 4  to  6 , wherein said or at least one ( 14 ) of said dedicated cooling air entrances is arranged at an area for discharging the ashes ( 11 ) of the system ( 1 ). 
     
     
         8 . The system ( 1 ) according to anyone of  claims 2  to  7 , wherein the whole arrangement is such that said dedicated exchanger ( 5 ) is crossed in countercurrent by the cooling air. 
     
     
         9 . The system ( 1 ) according to anyone of  claims 2  to  8 , comprising control means apt to adjust the air flow crossing said dedicated exchanger ( 5 ). 
     
     
         10 . The system ( 1 ) according to anyone of  claims 2  to  9 , wherein said dedicated exchanger ( 5 ) is of a gravitational type. 
     
     
         11 . The system ( 1 ) according to the preceding claim, wherein said gravitational exchanger ( 5 ) is of the type with multiple falls. 
     
     
         12 . The system ( 1 ) according to  claim 10  or  11 , wherein said gravitational exchanger ( 5 ) is of the type having multiple plates ( 19 ). 
     
     
         13 . The system ( 1 ) according to anyone of the preceding claims, wherein said feeding means ( 20 ,  15 ) is apt to feed part of the cooling air upstream of an air/fume exchanger ( 102 ) of the fume duct ( 101 ) apt to pre-heat the combustion air. 
     
     
         14 . The system ( 1 ) according to anyone of the preceding claims, wherein is said feeding means ( 20 ,  15 ) is apt to feed part of the cooling air in the economizers' area associated with the combustion chamber ( 100 ). 
     
     
         15 . The system ( 1 ) according to anyone of the preceding claims, comprising dust removing means ( 7 ) of the cooling air portion associated with said feeding means ( 20 ,  15 ;  200 ,  150 ;  201 ,  151 ). 
     
     
         16 . The system ( 1 ) according to the preceding claim, wherein said dust removing means ( 7 ) is of the cyclone-like type. 
     
     
         17 . The system ( 1 ) according to anyone of the preceding claims, comprising means for crushing the combustion residues ( 3 ,  10 ) arranged in line with said extraction and transport means ( 2 ,  4 ,  6 ). 
     
     
         18 . The system ( 1 ) according to the preceding claim and according to anyone of  claims 2  to  12 , wherein said crushing means ( 3 ,  10 ) is arranged upstream of said dedicated exchanger ( 5 ). 
     
     
         19 . The system ( 1 ) according to  claim 17  or  18 , wherein said crushing means ( 3 ,  10 ) comprises a pair of crushers, arranged spaced and in line with said extraction and transport means ( 2 ,  4 ,  6 ). 
     
     
         20 . The system ( 1 ) according to anyone of the preceding claims, comprising control means apt to adjust the flow of cooling air entering the combustion chamber ( 100 ) from the bottom and/or conveyed by said feeding means ( 20 ,  15 ;  200 ,  150 ;  201 ,  151 ). 
     
     
         21 . The system ( 1 ) according to the preceding claim, wherein said control means is apt to carry out said adjustment so that the flow of cooling air entering the combustion chamber ( 100 ) from the bottom does not exceed a predetermined amount of the total combustion air. 
     
     
         22 . The system ( 1 ) according to the preceding claim, wherein said predetermined amount is equal to about 1.0-1.5%. 
     
     
         23 . The system ( 1 ) according to anyone of  claims 20  to  22  or according to  claim 9 , wherein said control means carries out said adjustment depending upon the temperature and/or quantity of the combustion residues. 
     
     
         24 . The system ( 1 ) according to anyone of the preceding claims, comprising pressure control means, arranged in line with said extraction and transport means ( 2 ,  4 ,  6 ) and downstream of said feeding means ( 20 ,  15 ;  200 ,  150 ;  201 ,  151 ) with respect to the cooling air flow, apt to prevent an uncontrolled entrance of air towards the bottom of the combustion chamber ( 100 ). 
     
     
         25 . The system ( 1 ) according to the preceding claim, wherein said pressure control means comprises one or more members selected in a group comprising a valve with double clapet and a differential pressure transmitter. 
     
     
         26 . The system ( 1 ) according to anyone of the preceding claims, wherein said extraction and transport means ( 2 ,  4 ,  6 ) comprises a plurality of extraction and/or transport units arranged in sequence. 
     
     
         27 . The system ( 1 ) according to anyone of the preceding claims, comprising an extractor/cooler belt ( 2 ) applied to the bottom of the combustion chamber ( 100 ) directly or by transition hopper means ( 105 ), one or more crushers ( 3 ,  10 ), one or more conveyors/coolers ( 4 ,  6 ), an in-line gravity air/ash exchanger ( 5 ) having the purpose of cooling the ash with countercurrent air by means of falls created with specific plates ( 19 ) to increase the exchange surface between ash and air, a cyclone ( 7 ) for the duct collection of the cooling air current, a pipeline system ( 20 ) for connecting between gravity air/ash exchanger ( 5 ) and the fume duct ( 101 ), a conveyor belt ( 6 ) downstream of the gravity air/ash exchanger for the ash transport to an end gathering silo ( 11 ), and eventually a dedicated fan ( 16 ) and filter ( 9 ) for entering the air outcoming from the cyclone ( 7 ) into the atmosphere. 
     
     
         28 . A method for extracting and dry cooling combustion residues coming from a combustion chamber, in particular for significant flows of heavy ashes deriving for example from fossil fuel in an energy production plant, which method comprises the steps of:
 (a) extracting the combustion residues from the combustion chamber ( 100 ,  105 );   (b) cooling such combustion residues along an extraction and transport path ( 2 ,  4 ,  6 ) by means of feeding cooling air along the latter, introducing, downstream of the cooling process, part of said air into the combustion chamber ( 100 ,  105 ) from the bottom thereof; and   (c) feeding another part of the cooling air, downstream of the cooling process of the ashes thereby, in atmosphere or in a fume duct ( 101 ) associated with the combustion chamber ( 100 ).   
     
     
         29 . The method according to  claim 28 , wherein said cooling step (b) provides the use of an air/ash dedicated thermal exchanger ( 5 ), arranged along said extraction and transport path ( 2 ,  4 ,  6 ). 
     
     
         30 . The method according to the preceding claim, wherein said feeding step (c) provides the feeding into the fume duct ( 101 ) or in atmosphere of the cooling air crossing said exchanger ( 5 ). 
     
     
         31 . The method according to  claim 29  or  30 , providing a regulation of the air flow crossing said dedicated exchanger ( 5 ). 
     
     
         32 . The method according to anyone of the  claims 28  to  31 , providing regulation of the cooling air-flow entering the combustion chamber ( 100 ) from the bottom and/or which is involved by said feeding step. 
     
     
         33 . The method according to the preceding claim, wherein said regulation is carried out so that the flow of cooling air entering the combustion chamber ( 100 ) from the bottom does not exceed a predetermined amount of the total combustion air. 
     
     
         34 . The method according to the preceding claim, wherein said predetermined amount is equal to about 1.0-1.5%. 
     
     
         35 . The method according to anyone of the  claims 31  to  34 , wherein said regulation is carried out depending upon the temperature and/or flow of the combustion residues.