Process for operating a steam power plant with a coal-fired steam generator as well as a steam power plant

Abstract

A process and apparatus for operating a steam power plant having a coal-fired steam generator, in which at least two partial air streams are heated by means of the exchange of heat in at least one exhaust gas/air heat exchanger with hot exhaust gases that are obtained in the steam generator by the combustion of coal. The coal is dried in a milling-drying system with a first partial air stream of the heated air supplied as a primary air stream and a second partial air stream of the heated air is supplied to the steam generator as a secondary air stream for the combustion of the coal. The secondary air stream is preheated in an air/air heat exchanger upstream from the exhaust gas/air heat exchanger, with respect to the direction in which the secondary air stream flows, by the exchange of heat with the heated primary air stream.

1 . A process for operating a steam power plant having a coal-fired steam generator, the process comprising:
 heating at least first and second partial air streams in at least one exhaust gas/air heat exchanger by the transfer of heat from hot exhaust gases produced in a steam generator by the combustion of the coal, producing a heated primary air stream and a heated secondary air stream;   drying the coal with the heated primary air stream in a milling-drying system;   supplying the heated secondary air stream to the steam generator for the combustion of the coal; and   preheating the second partial air stream in an air/air heat exchanger by a transfer of heat from the heated primary air stream, the air/air heat exchanger being upstream to the exhaust gas/air heat exchanger relative to a direction of flow of the second partial air stream.   
   
   
       2 . The process of  claim 1  further comprising:
 transporting a bypassed partial amount of the heated primary air stream around the air/air heat exchanger with a bypass line that bypasses the air/air heat exchanger; and   controlling the bypassed partial amount of the heated primary air stream with a control device.   
   
   
       3 . The process of  claim 1  further comprising:
 removing a portion of the first partial air stream at a position that is upstream from the exhaust gas/air heat exchanger with respect to a direction of flow of the first partial air stream;   adding the portion of the first partial air stream with the heated primary air stream at a position downstream from the air/air heat exchanger with respect to the direction of flow of the heated primary air stream; and   controlling the portion of the first partial air stream with a control device.   
   
   
       4 . The process of  claim 1  further comprising:
 providing steam or hot water from a water/steam circuit of the steam power plant or from an source external to the steam power plant to a secondary preheater located intermediate the air/air heat exchanger and the exhaust gas/air heat exchanger in the direction of flow of the second partial air stream; and   preheating the second partial air stream by the transfer of heat from the steam or the hot water in the secondary preheater.   
   
   
       5 . The process of  claim 3  further comprising:
 providing steam or hot water from a water/steam circuit of the steam power plant or from an source external to the steam power plant to a primary preheater located intermediate the exhaust gas/air heat exchanger and the position where the portion of the first partial air stream is removed, in the direction of flow of the first partial air stream; and   preheating the first partial air stream by the transfer of heat from the steam or the hot water in the primary preheater.   
   
   
       6 . The process of  claim 1  wherein heating at least first and second partial air streams comprises
 transferring heat from a first controlled exhaust gas partial flow to a first partial air stream in a first exhaust gas/air heat exchanger, producing a heated primary air stream; and   transferring heat from a second controlled exhaust gas partial flow to a second partial air stream in a second exhaust gas/air heat exchanger, producing a heated secondary air stream.   
   
   
       7 . The steam power plant comprising:
 a coal-fired steam generator;   at least one exhaust gas/air heat exchanger having a gas side and an air side, the gas side receiving hot exhaust gas from the steam generator, the air side having first and second air stream flow paths, the first air stream flow path being separate from the second air stream flow path, a first air stream being received at an inlet of the first air stream flow path, a primary air stream being discharged at an outlet of the first air stream flow path, a second air stream being received at an inlet of the second air stream flow path, a secondary air stream being discharged at an outlet of the second air stream flow path;   an air/air heat exchanger having a first inlet in fluid communication with the exhaust gas/air heat exchanger first air stream flow path outlet receiving the primary air stream and a first outlet discharging the primary air stream, a second inlet receiving the first air stream and a second outlet in fluid communication with the exhaust gas/air heat exchanger second air stream flow path inlet; and   at least one milling-drying system having an inlet in fluid communication with the air/air heat exchanger first outlet and an outlet in fluid communication with the steam generator.   
   
   
       8 . The steam generating system of  claim 7  further comprising:
 a primary air line including:
 a first segment providing fluid communication between the exhaust gas/air heat exchanger first air stream flow path outlet and the air/air heat exchanger first inlet, 
 a second segment providing fluid communication between the air/air heat exchanger first outlet and the at least one milling-drying system inlet, and 
 a first bypass line providing fluid communication between the first and second segments; and 
   a first control device controlling flow through the first bypass line.   
   
   
       9 . The steam generating system of  claim 8  wherein the primary air line also includes a third segment providing fluid communication with the exhaust gas/air heat exchanger first air stream flow path inlet and a second bypass providing fluid communication between the third segment and the second segment, the steam generator system further comprising a second control device controlling flow through the second bypass line. 
   
   
       10 . The steam generating system of  claim 7  further comprising a steam or hot water/air heat exchanger in fluid communication with the air/air heat exchanger second outlet and the exhaust gas/air heat exchanger second air stream flow path inlet. 
   
   
       11 . The steam generating system of  claim 9  further comprising a steam or hot water/air heat exchanger disposed in the third segment of the primary air line intermediate the exhaust gas/air heat exchanger and the second bypass. 
   
   
       12 . The steam generating system of  claim 7  wherein the at least one exhaust gas/air heat exchanger includes first and second exhaust gas/air heat exchangers, each of the exhaust gas/air heat exchangers having a gas side and an air side, the air side of the first exhaust gas/air heat exchanger including the first air steam flow path and the air side of the second exhaust gas/air heat exchanger including the second air stream flow path. 
   
   
       13 . The steam generating system of  claim 12  wherein each of the exhaust gas/air heat exchangers has a heat transfer capacity, the heat transfer capacity of the first exhaust gas/air heat exchanger being different from the heat transfer capacity of the second exhaust gas/air heat exchanger. 
   
   
       14 . The steam generating system of  claim 12  wherein each of the exhaust gas/air heat exchangers has a design type, the design type of the first exhaust gas/air heat exchanger being different from the design type of the second exhaust gas/air heat exchanger. 
   
   
       15 . The steam generating system of  claim 12  wherein each of the exhaust gas/air heat exchangers has a design size, the design size of the first exhaust gas/air heat exchanger being different from the design size of the second exhaust gas/air heat exchanger.