Once-through steam generator for burning dry brown coal

Abstract

The invention relates to a forced-flow steam generator for burning dry brown coal without assistance from recirculated waste gas in the combustion chamber thereof. Said forced-flow steam generator ( 1 ) comprises a combustion chamber ( 2 ) and a waste gas flue ( 3 ) connected to the upper end thereof, and peripheral walls ( 4 ) surrounding said flue. Said walls ( 4 ) are formed from tubular walls ( 5 ), the tubes thereof guiding the water/steam working medium. The combustion chamber ( 2 ) comprises at least one burner ( 6 ), and downstream heating surfaces ( 7 ) are arranged in the waste gas flue ( 3 ). Part of the peripheral walls ( 4 ) is covered in the region of the combustion chamber ( 2 ) by at least one bulkhead heating surface ( 8 ), the size of which on the surface side being determined such that the heat absorption of the peripheral walls ( 4 ) and therefore the temperature thereof are reduced to a value enabling the formation of the peripheral walls ( 4 ) from modified, heat-resistant 2.25-2.5% chrome steel that does not require any heat aftertreatment following the welding treatment thereof.

1 . A once-through steam generator for burning dry brown coal without the aid of recycled flue gas in its combustion chamber, the once-through steam generator ( 1 ) having a combustion chamber ( 2 ), a flue gas pass ( 3 ) which adjoins the upper end of said combustion chamber ( 2 ), and enclosure walls ( 4 ) which enclose them, the enclosure walls ( 4 ) being formed from tube walls ( 5 ), the tubes of which conduct the working medium water/steam, the combustion chamber ( 2 ) having at least one burner ( 6 ), and heating surfaces ( 7 ) being arranged in the flue gas pass ( 3 ), part of the enclosure walls ( 4 ) being covered in the region of the combustion chamber ( 2 ) by at least one platen heating surface ( 8 ), the surface-side size of which is defined such that the heat absorption of the enclosure walls ( 4 ) and, as a consequence, their temperature are reduced to a value which permits the configuration of the enclosure walls ( 4 ) from modified, heat-resistant 2.25-2.5% chromium steels which do not require any thermal post-treatment after they have been processed using welding technology. 
     
     
         2 . The once-through steam generator as claimed in  claim 1 , characterized in that the platen heating surface ( 8 ) which covers part of the enclosure walls ( 4 ) in the region of the combustion chamber ( 2 ) is arranged between the upper edge of the uppermost burner ( 6 ) and the lower edge of the lowermost heating surface ( 7 ). 
     
     
         3 . The once-through steam generator as claimed in  claim 1 , characterized in that at least part of the enclosure walls ( 4 ) is formed from one of the materials T23, T24 or another material with a similar chemical composition. 
     
     
         4 . The once-through steam generator as claimed in  claim 1 , characterized in that the platen heating surface ( 8 ) is formed from martensitic steels with a 9-12% chromium proportion, austenitic steels or nickel-based alloys. 
     
     
         5 . The once-through steam generator as claimed in  claim 1 , characterized in that the platen heating surface ( 8 ) is configured as a superheater heating surface. 
     
     
         6 . The once-through steam generator as claimed in  claim 1 , characterized in that the platen heating surface ( 8 ) is configured as a reheater heating surface. 
     
     
         7 . The once-through steam generator as claimed in  claim 1 , characterized in that the platen heating surface ( 8 ) is arranged parallel to the enclosure wall ( 4 ). 
     
     
         8 . The once-through steam generator as claimed in one of the preceding claims  claim 1 , characterized in that the platen heating surface ( 8 ) extends such that it bears against the enclosure wall ( 4 ).