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...

AI Technical Summary

Benefits of technology

[0015]The recycling portion of the exhaust gas and the stream of substantially pure oxygen may be conducted to the furnace separately, but, according to a preferred embodiment of the present invention, the stream of substantially pure oxygen is mixed with the recycling portion of the exhaust gas in 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. Thus, a stream of combined oxidant gas is formed to be fed via a channel into the furnace. An advantage resulting from heating the oxygen stream prior to mixing with recycling gas is the avoiding of moisture or acid gas condensation from the recycling gas on an O2 injector pipe, which may result if the temperature of the O2 stream is too low. Generally, the mixing of a heated pure oxygen stream with a heated recycling portion of the exhaust gas makes it possible to efficiently control the temperature, flow rate and oxygen content of the combined oxidant gas.

[0029]As described above, in the oxyfuel combustion mode, a large portion of steam extracted from steam turbines is used for driving compressors in the ASU or the CCU. In the air-firing mode, when the ASU and CCU are not in use, this steam is saved for preheating the feedwater, and the need for feedwater preheating in the economizers is greatly reduced. As described above, the present arrangement decreases, in the air-firing mode, automatically, the heat transfer duty of the economizers. The preheating of the feedwater is, in the air-firing mode, also advantageously decreased by using the damper in one of the first and second exhaust gas channel portions, so as to decrease the share of exhaust gas flowing through the second exhaust gas channel portion.

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 (ASU), where oxygen is separated from other components of air.

This system is quite complicated due to the valves and controllers required for controlling the feedwater flow in the oxyfuel combustion mode.

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