Method of and System For Generating Power By Oxyfuel Combustion

Abstract

An oxyfuel combustion system for generating power that includes a furnace for combusting carbonaceous fuel and substantially pure oxygen to produce exhaust gas including mainly carbon dioxide and water. An exhaust gas channel system discharges the exhaust gas from the furnace. The exhaust gas channel system has an upstream channel, an outlet channel and a gas recycling channel. The upstream channel recycles a recycling portion of the exhaust gas through the recycling channel to the furnace, and conveys an end portion of the exhaust gas through the outlet channel for final processing. The upstream channel is divided between a first divider piece and a connecting piece into a first exhaust gas channel portion and a second exhaust gas channel portion. A gas-gas heat exchanger arranged in the first exhaust gas channel portion transfers heat from exhaust gas in the first exhaust gas channel portion to gas in the gas recycling channel. A first economizer arranged in the second exhaust gas channel portion transfers heat from exhaust gas in the second exhaust gas channel portion to a flow of feedwater in a feedwater line, and a second economizer arranged in the exhaust gas channel system downstream of the connecting piece transfers heat from gas in the exhaust gas channel system to the flow of feedwater in the feedwater line.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a method of and a system for generating power by oxyfuel combustion. The invention especially relates to a dual-firing or flexi-burn combustion system, i.e., to a system which can be easily switched between the modes of oxyfuel combustion and combustion with air.[0003]2. Description of the Related Art[0004]Oxyfuel combustion is one of the methods suggested for removing CO2 from the combustion 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, without having to separate it from a gas stream having nitrogen as its main component, suc...

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Benefits of technology

[0022]Typically, a majority of the exhaust gas, for example, about 80%, flows through the first exhaust gas channel portion, and a smaller portion, for example, about 20%, flows through the second exhaust gas channel portion. Thus, when the first exhaust gas stream is cooled in the gas-gas heat exchanger, for example, from about 310° C. to about 210° C., and the second exhaust gas stream is cooled in the first economizer, for example, to about 170° C., the combined exhaust gas will have downstream of the connecting piece a temperature of about 200° C. Thereby, the combined exhaust gas stream is advantageously cooled in a second economizer arranged in the upstream channel from about 200° C., for example, to about 150° C. This arrangement of the economizers provides the possibility of simultaneously heating both the recycling gas, in the gas-gas exchanger, and the feedwater, in the economizers, to their optimal temperatures, without risk of acid condensation on the economizers or the downstream dust separator.

[0023]According to another preferred embodiment of the present invention, which is especially advantageous when the outlet channel comprises an exhaust gas cooler connected to an oxygen heater, the second economizer is arranged in the gas recycling channel instead of the upstream channel. Thereby, the second economizer transfers heat only from the recycling portion of the exhaust gas to the feedwater. This arrangement provides the advantage that the temperature of the exhaust gas remains relatively high, typically, about 200° C., when the exhaust gas enters the exhaust gas cooler, and the oxygen stream can correspondingly be heated by the oxygen heater to a relatively high temperature. Naturally, it is a

Problems solved by technology

Generating power by oxyfuel combustion is more complicated than conventional combustion by air, because of the need of an oxygen supply, for example, a cryogenic or membrane based air separation unit (A

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