Oxyfuel Combusting Boiler System and a Method of Generating Power By Using the Boiler System

Abstract

Carbonaceous fuel is combusted with an oxidant gas in a furnace of a boiler system to generate power. Oxidant gas is fed into the furnace for combusting the fuel to produce exhaust gas, the exhaust gas is discharged from the furnace via an exhaust gas channel, a stream of feedwater is conveyed from a final 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, the superheated steam is converted in a high-pressure steam turbine for generating power, a first portion of steam is extracted from the high-pressure steam turbine for preheating the feedwater, a second portion of steam is conveyed from the high-pressure steam turbine to reheating heat exchange surfaces arranged in the exhaust gas channel for generating reheated steam, and the reheated steam is expanded in an intermediate pressure steam turbine for generating power. The oxidant gas can be a mixture of substantially pure oxygen and recycled exhaust gas, and the ratio of the first and second portions of steam can be controlled to obtain a desired flue gas temperature in the exhaust gas channel downstream of the final economizer.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an oxyfuel combusting boiler system and a method of generating power by using the boiler system. The invention relates especially to a dual-firing boiler system, i.e., a boiler system which can be operated by using either air or a mixture of substantially pure oxygen and recycled exhaust gas as the oxidant gas, i.e., as the oxygen carrier gas.

[0003] 2. Description of the Related Art

[0004] Oxyfuel combustion is one of the methods suggested for removing CO2 from the exhaust gases of a power generating boiler, such as a pulverized coal (PC) boiler or a circulating fluidized bed (CFB) boiler. Oxyfuel combustion is based on combusting carbonaceous fuel with substantially pure oxygen, typically, of about 95% purity, so as to have carbon dioxide and water as the main components of the exhaust gas discharged from the boiler. Thereby, the carbon dioxide can be captured relatively easily from the ex...

Images