Method of Increasing the Performance of a Carbonaceous Fuel Combusting Boiler System

Abstract

A method of increasing the power of a carbonaceous fuel combusting boiler system includes the steps of (a) feeding carbonaceous fuel into a furnace of the boiler system, (b) feeding oxidant gas into the furnace for combusting fuel to produce exhaust gas, (c) discharging the exhaust gas from the furnace via an exhaust gas channel, (d) conveying a stream of feedwater from a boiler economizer arranged in the exhaust gas channel to evaporating and superheating heat exchange surfaces arranged in the furnace and in the exhaust gas channel for converting the feedwater to superheated steam, (e) expanding the superheated steam in a high-pressure steam turbine for generating power, (f) extracting steam from the high-pressure steam turbine at a decreased rate for preheating the feedwater, (g) conveying steam from the high-pressure steam turbine at an increased rate to a reheater arranged in the exhaust gas channel for generating reheated steam, (h) expanding the reheated steam in an intermediate pressure steam turbine for generating power, and (i) conveying the exhaust gas in the exhaust gas channel from the reheater through a boiler economizer to a gas heater. The heat exchange surface area of at least one of the reheater and the boiler economizer is increased and/or a high pressure economizer is added downstream of the boiler economizer and upstream of the gas heater.

1 . A method of increasing the power of a carbonaceous fuel combusting boiler system, the method comprising the steps of:
 (a) feeding carbonaceous fuel into a furnace of the boiler system at a fuel feeding rate;   (b) feeding oxidant gas into the furnace for combusting the fuel to produce exhaust gas;   (c) discharging the exhaust gas from the furnace via an exhaust gas channel;   (d) conveying a stream of feedwater from a boiler economizer arranged in the exhaust gas channel to evaporating and superheating heat exchange surfaces arranged in the furnace and in the exhaust gas channel, for converting the feedwater to superheated steam;   (e) expanding the superheated steam in a high-pressure steam turbine for generating power;   (f) extracting steam from the high-pressure steam turbine at a decreased rate for preheating the feedwater;   (g) conveying steam from the high-pressure steam turbine at an increased rate to a reheater arranged in the exhaust gas channel for generating reheated steam;   (h) expanding the reheated steam in an intermediate pressure steam turbine for generating power;   (i) conveying the exhaust gas in the exhaust gas channel from the reheater through a boiler economizer to a gas heater; and   (j) effecting at least one of (i) increasing the heat exchange surface area of at least one of the reheater and the boiler economizer and (ii) adding a high pressure economizer downstream of the boiler economizer and upstream of the gas heater.   
     
     
         2 . The method according to  claim 1 , further comprising feeding carbonaceous fuel into the furnace at an increased fuel feeding rate. 
     
     
         3 . The method according to  claim 1 , wherein at least one of (i) the decreased steam extraction rate and increased steam conveying rate and (ii) the increased fuel feeding rate are as compared to a typical earlier use of the same boiler. 
     
     
         4 . The method according to  claim 1 , wherein at least one of (i) the decreased steam extraction rate and increased steam conveying rate and (ii) the increased fuel feeding rate are as compared to a typical use of a similar boiler. 
     
     
         5 . The method according to  claim 1 , further comprising stopping the extracting of steam from the high-pressure steam turbine for preheating the feedwater. 
     
     
         6 . The method according to  claim 1 , wherein the boiler system is a retrofitted boiler and the increase of the heat exchange surface area of the boiler economizer or the heat exchange area of the added high pressure economizer is at least 50% of the original heat exchange surface area of the boiler economizer. 
     
     
         7 . The method according to  claim 1 , wherein the increase of the heat exchange surface area of the boiler economizer or the heat exchange area of the added high pressure economizer is at least 50% of a typical heat exchange surface area of the boiler economizer of a similar boiler system. 
     
     
         8 . The method according to  claim 1 , further comprising adding a high pressure economizer downstream of the boiler economizer and upstream of the gas heater, and arranging an NOx catalyst in the exhaust gas channel downstream of the boiler economizer and upstream of the high pressure economizer. 
     
     
         9 . The method according to  claim 8 , further comprising arranging a controllable feedwater line bypassing the high pressure economizer. 
     
     
         10 . The method according to  claim 2 , wherein at least one of (i) the decreased steam extraction rate and increased steam conveying rate and (ii) the increased fuel feeding rate are as compared to a typical earlier use of the same boiler. 
     
     
         11 . The method according to  claim 2 , wherein at least one of (i) the decreased steam extraction rate and increased steam conveying rate and (ii) the increased fuel feeding rate are as compared to a typical use of a similar boiler. 
     
     
         12 . The method according to  claim 2 , further comprising stopping the extracting of steam from the high-pressure steam turbine for preheating the feedwater.