Method of and system for generating power by oxyfuel combustion

Abstract

A method of generating power by oxyfuel combustion. Carbonaceous fuel and oxidant gas are fed into a furnace. In a first operating mode, the oxidant gas includes a stream of substantially pure oxygen conveyed from an oxygen supply for combusting the fuel with the oxygen to produce exhaust gas including mainly carbon dioxide and water. The exhaust gas is discharged from the furnace and is divided into a recycling portion and an end portion. The recycling portion is recycled to the furnace. Heat is transferred from the end portion to the stream of substantially pure oxygen by circulating a liquid heat transfer medium in a passage between an exhaust gas cooler and an oxygen heater.

1 . A method of generating power by oxyfuel combustion, said method comprising the steps of:
 (a) feeding carbonaceous fuel into a furnace;   (b) feeding oxidant gas into the furnace, wherein, in a first operating mode, the oxidant gas comprises a stream of substantially pure oxygen conveyed from an oxygen supply for combusting the fuel with the oxygen to produce exhaust gas comprising mainly carbon dioxide and water;   (c) discharging the exhaust gas from the furnace;   (d) dividing the exhaust gas into a recycling portion and an end portion;   (e) recycling the recycling portion to the furnace; and   (f) transferring heat from the end portion to the stream of substantially pure oxygen by circulating a liquid heat transfer medium in a passage between an exhaust gas cooler and an oxygen heater.   
   
   
       2 . The method according to  claim 1 , further comprising the steps of:
 (g) transferring heat in a gas-gas heat exchanger from the exhaust gas to the recycling portion to produce a stream of heated recycling gas;   (h) mixing the stream of substantially pure oxygen with the stream of heated recycling gas so as to form a stream of mixed gas; and   (i) feeding the stream of mixed gas as the oxidant gas into the furnace.   
   
   
       3 . The method according to  claim 1 , wherein the liquid heat transfer medium is water. 
   
   
       4 . The method according to  claim 1 , wherein the exhaust gas cooler is of a corrosion resistant type. 
   
   
       5 . The method according to  claim 1 , wherein the first operating mode is performed alternatingly with a second operating mode, in which the recycling portion is minimized, and the oxidant gas comprises a stream of air. 
   
   
       6 . The method of  claim 2 , wherein the first operating mode is performed alternatingly with a second operating mode, in which the recycling portion is minimized, and the oxidant gas comprises a stream of air introduced into the gas recycling line, so as to transfer heat in the gas-gas heat exchanger from the exhaust gas to the air stream. 
   
   
       7 . The method according to  claim 5 , wherein the second operating mode comprises a step of transferring heat from the end portion of the stream of air by circulating a liquid heat transfer medium in a passage between the exhaust gas cooler and an air heater. 
   
   
       8 . The method according to  claim 6 , wherein the second operating mode comprises a step of transferring heat from the end portion of the stream of air by circulating a liquid heat transfer medium in a passage between the exhaust gas cooler and an air heater. 
   
   
       9 . The method according to  claim 7 , wherein the second operating mode comprises further steps of dividing a parallel stream from the exhaust gas stream and transferring heat from the parallel stream into the stream of air by circulating a liquid heat transfer medium between a second exhaust gas cooler and the air heater. 
   
   
       10 . A system for generating power by oxyfuel combustion, said system comprising:
 a furnace for combusting carbonaceous fuel;   an oxygen channel for feeding the substantially pure oxygen from an oxygen supply to the furnace for combusting the fuel with the oxygen to produce exhaust gas comprising mainly carbon dioxide and water;   an exhaust gas channel connected to the furnace for discharging the exhaust gas from the furnace;   branch piping for dividing the exhaust gas into a recycling portion and an end portion;   a gas recycling channel for feeding the recycling portion of the exhaust gas to the furnace; and   an exhaust gas cooler arranged in the exhaust gas channel downstream of the branch piping and an oxygen heater arranged in the oxygen channel connected by a passage for transferring heat from the end portion to the stream of substantially pure oxygen by circulating a liquid heat transfer medium in the passage.   
   
   
       11 . The system according to  claim 10 , further comprising:
 a gas-gas heat exchanger for transferring heat from the exhaust gas to the recycling portion;   a mixer arranged to connect the gas recycling channel downstream of the gas-gas heat exchanger and the oxygen channel downstream of the oxygen heater for mixing the recycling portion with the stream of substantially pure oxygen so as to form a stream of mixed gas; and   a channel for feeding the stream of mixed gas as the oxidant gas into the furnace.   
   
   
       12 . The system according to  claim 10 , wherein the exhaust gas cooler is of a corrosion resistant type. 
   
   
       13  The system according to  claim 10 , further comprising:
 a flow controller arranged in the recycling gas channel for controlling the recycling portion; and   an air intake for introducing a stream of air as the oxidant gas instead of substantially pure oxygen.   
   
   
       14 . The system according to  claim 11 , further comprising:
 a flow controller arranged in the recycling gas channel for controlling the recycling portion; and   an air intake for introducing a stream of air as the oxidant gas, instead of substantially pure oxygen into the gas recycling line, wherein the air intake is arranged upstream of the gas-gas heat exchanger so as to transfer heat from the exhaust gas to the air stream in the gas-gas heat exchanger.   
   
   
       15 . The system according to  claim 13 , further comprising an air heater connected by a passage to the exhaust gas cooler for transferring heat from the end portion to the stream of air by circulating a liquid heat transfer medium in the passage between the exhaust gas cooler and the air heater. 
   
   
       16 . The system according to  claim 14 , further comprising an air heater connected by a passage to the exhaust gas cooler for transferring heat from the end portion to the stream of air by circulating a liquid heat transfer medium in the passage between the exhaust gas cooler and the air heater. 
   
   
       17 . The system according to  claim 15 , further comprising:
 second branch piping for dividing from the exhaust gas stream a parallel stream in a parallel channel option; and   a second exhaust gas cooler arranged in the parallel channel portion for transferring heat from the parallel stream into the stream of air by circulating a liquid heat transfer medium in a passage between the second exhaust gas cooler and the air heater.