Boiler

Abstract

In a boiler, a heat exchanger provided in one of two flow paths formed by partitioning a downstream portion of a flow path for exhaust gas discharged from a furnace has a smaller total heat transfer area than a heat exchanger provided in the other of the two flow paths; the exhaust gases discharged from the flow paths to outside the boiler are introduced, without being mixed, into an air heater downstream of the boiler; and, in the air heater, the heat of the exhaust gases is transferred to the primary air and the secondary air so as to heat combustion air.

1 . A boiler comprising: a furnace for burning solid fuel; a fuel mill for pulverizing the solid fuel; a solid fuel feeding pipe for conveying the solid fuel from the fuel mill to the furnace; a burner for igniting the solid fuel; an air port for introducing air into the furnace; an air heater for recovering heat from exhaust gas and heating primary air and secondary air to be supplied to the furnace; a primary combustion air supply duct for introducing the primary air from the air heater to the fuel mill; a secondary combustion air supply duct for introducing the secondary air from the air heater into the burner and the air port; an air duct for introducing air into the air heater; an exhaust gas duct for introducing exhaust gas into the air heater; a partition wall for partitioning a downstream portion of a flow path for exhaust gas discharged from the furnace; and a plurality of heat exchangers which are provided in the flow paths formed on both sides of the partition wall, recover heat from the exhaust gases flowing through the flow paths and heat steam using the recovered heat,
 wherein the heat exchanger provided in the flow path on a first side of the partition wall has a smaller total heat transfer area than the heat exchanger provided in the flow path on a second side of the partition wall; wherein the exhaust gases discharged from the flow paths to outside the boiler are introduced, without being mixed, into the air heater downstream of the boiler; and wherein, in the air heater, the heat of the exhaust gases is transferred to the primary air and the secondary air so as to heat combustion air.   
     
     
         2 . The boiler according to  claim 1 ,
 wherein the air heater comprises a low-temperature air heater which is provided downstream of the heat exchanger having a larger heat transfer area and which heats the primary air and a high-temperature air heater which is provided downstream of the heat exchanger having a smaller heat transfer area and which heats the secondary air.   
     
     
         3 . The boiler according to  claim 1 ,
 wherein the heat exchanger having a larger heat transfer area is used to heat reheat steam and the heat exchanger having a smaller heat transfer area is used to heat main steam.   
     
     
         4 . The boiler according to  claim 2 ,
 wherein the heat exchanger having a larger heat transfer area is used to heat reheat steam and the heat exchanger having a smaller heat transfer area is used to heat main steam.   
     
     
         5 . The boiler according to  claim 2 , further comprising a de-NOx device which the exhaust gas flowing through the flow path provided with the heat exchanger having a larger heat transfer area enters before passing through the low-temperature air heater and which removes nitrogen oxide contained in the exhaust gas,
 wherein the secondary air enters, after being heated by the low-temperature air heater, the high-temperature air heater to be heated therein by the exhaust gas flowing through the flow path provided with the heat exchanger having a smaller heat transfer area.   
     
     
         6 . The boiler according to  claim 4 , further comprising a de-NOx device which the exhaust gas flowing through the flow path provided with the heat exchanger having a larger heat transfer area enters before passing through the low-temperature air heater and which removes nitrogen oxide contained in the exhaust gas,
 wherein the secondary air enters, after being heated by the low-temperature air heater, the high-temperature air heater to be heated therein by the exhaust gas flowing through the flow path provided with the heat exchanger having a smaller heat transfer area.   
     
     
         7 . The boiler according to  claim 5 ,
 wherein, after entering the high-temperature air heater and being heat-exchanged therein, the exhaust gas flowing through the flow path provided with the heat exchanger having a smaller heat transfer area enters the de-NOx device and, along with the exhaust gas flowing through the flow path provided with the heat exchanger having a larger heat transfer area, has nitrogen oxide removed therein before entering the low-temperature air heater.   
     
     
         8 . The boiler according to  claim 6 ,
 wherein, after entering the high-temperature air heater and being heat-exchanged therein, the exhaust gas flowing through the flow path provided with the heat exchanger having a smaller heat transfer area enters the de-NOx device and, along with the exhaust gas flowing through the flow path provided with the heat exchanger having a larger heat transfer area, has nitrogen oxide removed therein before entering the low-temperature air heater.   
     
     
         9 . The boiler according to  claim 1 ,
 wherein the air duct is provided with an air flow regulator, the exhaust gas duct is provided with an exhaust gas flow regulator, and the primary combustion air supply duct is, at an intermediate portion thereof, provided with an air thermometer; and   wherein the air flow regulator and the exhaust gas flow regulator operate to adjust an air flow and an exhaust gas flow based on the output of the air thermometer so as to keep the temperature measured by the air thermometer of the primary combustion air flowing through the primary combustion air supply duct at a desired level.   
     
     
         10 . The boiler according to  claim 2 ,
 wherein the air duct is provided with an air flow regulator, the exhaust gas duct is provided with an exhaust gas flow regulator, and the primary combustion air supply duct is, at an intermediate portion thereof, provided with an air thermometer; and   wherein the air flow regulator and the exhaust gas flow regulator operate to adjust an air flow and an exhaust gas flow based on the output of the air thermometer so as to keep the temperature measured by the air thermometer of the primary combustion air flowing through the primary combustion air supply duct at a desired level.   
     
     
         11 . The boiler according to  claim 3 ,
 wherein the air duct is provided with an air flow regulator, the exhaust gas duct is provided with an exhaust gas flow regulator, and the primary combustion air supply duct is, at an intermediate portion thereof, provided with an air thermometer; and   wherein the air flow regulator and the exhaust gas flow regulator operate to adjust an air flow and an exhaust gas flow based on the output of the air thermometer so as to keep the temperature measured by the air thermometer of the primary combustion air flowing through the primary combustion air supply duct at a desired level.   
     
     
         12 . The boiler according to  claim 4 ,
 wherein the air duct is provided with an air flow regulator, the exhaust gas duct is provided with an exhaust gas flow regulator, and the primary combustion air supply duct is, at an intermediate portion thereof, provided with an air thermometer; and   wherein the air flow regulator and the exhaust gas flow regulator operate to adjust an air flow and an exhaust gas flow based on the output of the air thermometer so as to keep the temperature measured by the air thermometer of the primary combustion air flowing through the primary combustion air supply duct at a desired level.   
     
     
         13 . The boiler according to  claim 5 ,
 wherein the air duct is provided with an air flow regulator, the exhaust gas duct is provided with an exhaust gas flow regulator, and the primary combustion air supply duct is, at an intermediate portion thereof, provided with an air thermometer; and   wherein the air flow regulator and the exhaust gas flow regulator operate to adjust an air flow and an exhaust gas flow based on the output of the air thermometer so as to keep the temperature measured by the air thermometer of the primary combustion air flowing through the primary combustion air supply duct at a desired level.   
     
     
         14 . The boiler according to  claim 6 ,
 wherein the air duct is provided with an air flow regulator, the exhaust gas duct is provided with an exhaust gas flow regulator, and the primary combustion air supply duct is, at an intermediate portion thereof, provided with an air thermometer; and   wherein the air flow regulator and the exhaust gas flow regulator operate to adjust an air flow and an exhaust gas flow based on the output of the air thermometer so as to keep the temperature measured by the air thermometer of the primary combustion air flowing through the primary combustion air supply duct at a desired level.   
     
     
         15 . The boiler according to  claim 7 ,
 wherein the air duct is provided with an air flow regulator, the exhaust gas duct is provided with an exhaust gas flow regulator, and the primary combustion air supply duct is, at an intermediate portion thereof, provided with an air thermometer; and   wherein the air flow regulator and the exhaust gas flow regulator operate to adjust an air flow and an exhaust gas flow based on the output of the air thermometer so as to keep the temperature measured by the air thermometer of the primary combustion air flowing through the primary combustion air supply duct at a desired level.   
     
     
         16 . The boiler according to  claim 8 ,
 wherein the air duct is provided with an air flow regulator, the exhaust gas duct is provided with an exhaust gas flow regulator, and the primary combustion air supply duct is, at an intermediate portion thereof, provided with an air thermometer; and   wherein the air flow regulator and the exhaust gas flow regulator operate to adjust an air flow and an exhaust gas flow based on the output of the air thermometer so as to keep the temperature measured by the air thermometer of the primary combustion air flowing through the primary combustion air supply duct at a desired level.