A METHOD OF INCREASING THE PERFORMANCE OF A CARBONACEOUS FUEL COMBUSTING BOILER SYSTEM

摘要

A method of increasing the power of a carbonaceous fuel combusting boiler system. The method includes the steps of (a) feeding carbonaceous fuel (16) into a furnace (14) of the boiler plant at a fuel feeding rate, (b) feeding oxidant gas (18) into the furnace for combusting the fuel to produce exhaust gas, (c) discharging the exhaust gas from the furnace via an exhaust gas channel (20), (d) conveying a stream of feedwater from a boiler economizer (38) 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 (50) for generating power, (f) extracting steam (74) 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 (36) arranged in the exhaust gas channel for generating reheated steam, (h) expanding the reheated steam in an intermediate pressure steam turbine (52) 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 (42). The method also includes increasing the heat exchange surface area of at least one of the reheater and the boiler economizer and/ or adding a high pressure economizer downstream of the boiler economizer and upstream of the gas heater.