KR20110022634A - Method of and system for generating power by oxyfuel combustion - Google Patents

Abstract

The present invention relates to a method of generating electric power by pure oxygen combustion. Carbonaceous fuel and oxidant gas are supplied to the furnace. In a first mode of operation, the oxidant gas comprises a stream of substantially pure oxygen carried from an oxygen supply to combust oxygen and fuel to produce an exhaust gas comprising primarily carbon dioxide and water. The exhaust gas is discharged from the furnace and divided into a recycle portion and an end portion. The recycle section is recycled to the furnace. Heat is transferred from the end portion to the substantially pure flow of oxygen by circulating the liquid heat transfer medium in the passage between the exhaust gas cooler and the oxygen heater.

Description

METHOD OF AND SYSTEM FOR GENERATING POWER BY OXYFUEL COMBUSTION}

The present invention relates to a method and system for generating power by pure oxygen combustion. The present invention relates in particular to a flexi-burn or double-ignition combustion system, ie a system in which the oxyfuel combustion mode and the combustion mode with air can be easily switched.

Pure oxygen combustion is one of the proposed methods for removing CO ₂ from the combustion gas of a power generating boiler, such as a pulverized coal (PC) boiler or a circulating fluidized bed (CFB) boiler. Pure oxygen combustion is based on burning carbonaceous fuel with oxygen that is substantially pure, typically about 95% pure, to have water and carbon dioxide as the main components of the exhaust gases emitted from the boiler. Thereby, carbon dioxide can be collected relatively easily without the need to separate it from the gas stream having nitrogen as its main component, such as when burning fuel with air.

Generating power by pure oxygen combustion is more complicated than conventional combustion by air, since it requires an oxygen supply, for example a cryogenic or membrane-based air separation unit (ASU), where oxygen is Separated from other components of air. The resulting exhaust gas is then ready to extract CO ₂ when water is removed from the oxidant, fuel and air-leakage. Such purification is typically accomplished by condensing CO ₂ at low temperatures under high pressure. CO ₂ can be separated from the exhaust gas, for example, by cooling it to a relatively low temperature while compressing it to a pressure of at least 110 bar.

In order to avoid very high combustion temperatures resulting from combustion with pure oxygen, it is advantageous to use pure oxygen combustion boilers, in which the combustion conditions are arranged close to the conditions of air-ignition combustion. This can be done by recycling the exhaust gas to the furnace to provide an average O ₂ content of the oxidant gas, for example from about 20 to about 28%. Such oxy-fuel boilers can advantageously be constructed by modifying existing air-ignition boilers. Because of the many uncertainties regarding the capture and storage of carbon dioxide in oxy-fuel combustion, there is a need for dual ignition boilers, ie boilers that can be switched back from oxy-fuel to air-ignition as easily as possible without any change in the actual configuration. Do. In such dual ignition boilers, it is possible to have maximum power output by using air-ignition combustion when demanding high load requirements, such as summer or weekdays, and by applying oxy-fuel combustion with CO ₂ removal under other conditions. It is also possible, for example, to use a dual ignition boiler in the air-ignition mode when the separation unit or the CO ₂ removal unit has failed.

U. S. Patent No. 6,202, 574 proposes a combustion system for igniting fossil fuels with substantially pure oxygen to produce exhaust gases having water and carbon dioxide as the two largest components. A portion of the exhaust gas is recycled to the combustion chamber and the remainder of the exhaust gas is compressed and removed to produce liquid carbon dioxide. The recycled exhaust gas and substantially pure oxygen flow are preheated by the exhaust gas in each gas-gas heat exchanger.

DE 103 56 703 A1 discloses a oxy-fueled boiler system comprising a gas-gas heat exchanger and a feed water heater which act as an oxygen heater arranged to cool exhaust gases downstream of the recycle gas take-off. Seems.

In order to generate electricity more economically when minimizing carbon dioxide emissions, there is a need for improved methods and systems for burning pure oxygen, in particular using dual ignition combustion systems.

It is an object of the present invention to provide a novel method and system for pure oxygen combustion.

According to one aspect, the present invention provides a method for generating power by pure oxygen combustion, the method supplying carbonaceous fuel to a furnace and oxidant gas to a furnace, wherein in the first mode of operation, the oxidant The gas comprises a stream of substantially pure oxygen carried from an oxygen supply to combust oxygen and fuel to produce an exhaust gas comprising primarily carbon dioxide and water, exhaust the exhaust gas from the furnace, and return the exhaust gas to the recycle section and Splitting into an end portion, recycling the recycle portion of the furnace and transferring heat from the end portion to the flow of substantially pure oxygen by circulating a liquid heat transfer medium such as water in the passage between the oxygen heater and the exhaust gas cooler It includes.

According to another feature, the present invention provides a system for generating electric power by pure oxygen combustion, which system uses oxygen and fuel to generate an exhaust for the combustion of carbonaceous fuel, mainly exhaust of water and carbon dioxide. An oxygen channel for supplying substantially pure oxygen from the oxygen supply to the furnace for combustion, an exhaust gas channel connected to the furnace for exhausting the exhaust gas from the furnace, branch pipes for dividing the exhaust gas into the recirculation and end portions, exhaust A flow of substantially pure oxygen from the end portion by means of a gas recycle channel for supplying the recycled portion of the gas to the furnace, an exhaust gas cooler disposed in the exhaust gas channel downstream of the branch piping, and a liquid heat transfer medium circulating in the passageway Oxygen heating disposed in an oxygen channel connected by a passage for transferring heat Contains groups.

The process of transferring heat from the exhaust gas to the oxidant gas improves the efficiency of the boiler and the process as a whole. The present invention discloses, for example, that the pure oxygen flow is heated by low grade heat obtained from the end portion of the exhaust gas emitted from the system, not from the exhaust gas upstream of the outlet point of the recycled gas. It is different from the prior art solution shown in 6,202,574. This improves the thermal efficiency of the process. Although the exhaust gas cooler is in the cold portion of the exhaust gas channel, it can be cooled below the acidic condensation temperature during heat transfer. Therefore, the exhaust gas cooler is advantageously of a corrosion resistance type, such as a plastic gas cooler.

The recycle portion of the exhaust gas comprises, in pure oxygen combustion, the majority of the exhaust gas emitted from the furnace, typically about 65 to about 80%, so that the end portion of the exhaust gas is about one third or less of the exhaust gas flow. to be. On the other hand, the terminal portion is always as large as the oxygen flow. Therefore, the arrangement of the exhaust gas cooler downstream of the point that divides the recirculation part is such that the oxygen flow and the gas flow at the distal end of the exhaust gas are as large, thus achieving an energy balance between the two flows at an advantageous temperature level. Another advantage is that it is relatively easy. In practice, the distal end of the exhaust gas is virtually dust free, but located downstream of the electronic dust separator (ESP) or bag house. This provides the conditions for placing an effective and compact heat exchanger. In addition, this increases the safety of the system, with very little ignition or explosive dust present.

According to the invention, heat is transferred from the exhaust gas to the oxygen flow by means of a liquid heat transfer medium, instead of transferring heat directly in the gas-gas heat exchanger. This feature provides the advantage that leakage in the exhaust gas cooler, which can occur especially when the heat exchanger is used below the acidic dew point temperature, can only cause the leakage of water, not the leakage of explosive oxygen in the exhaust gas channel.

Another advantage of transferring heat from the exhaust gas to the oxygen by the liquid heat transfer medium is that in reality, the system looks more complex, but generally provides a relatively simple configuration. The reason is that an oxygen supply, typically an air separation unit (ASU), is typically placed in a part of the power plant other than the final exhaust gas treatment system that includes a unit for cleaning, trapping and storing carbon dioxide. Therefore, the heat transfer distance can be relatively long, making it easy to heat transfer this long distance in a relatively small water tube by making additional excursions into larger channels carrying hot exhaust gases or explosive oxygen gas.

According to a preferred embodiment of the invention, the method further comprises transferring heat from the exhaust gas to the recycle portion of the exhaust gas to produce a stream of heated recycle gas in the gas-gas heat exchanger. The recirculating gas stream and the substantially pure oxygen flow can be guided separately to the furnace, but in accordance with a preferred embodiment of the present invention, the substantially pure oxygen flow is provided with an oxygen channel downstream of the oxygen heater and a gas-gas heat exchanger. Mixed with a stream of heated recycle gas in a mixer arranged to connect a gas recycle channel downstream of the. Therefore, a flow of mixed gas is formed and supplied to the furnace as oxidant gas through the channel.

The supply rate of relatively pure oxygen is determined based on the fuel supply rate to provide sufficiently complete combustion of the fuel. In general, the oxygen feed rate is controlled by monitoring the residual oxygen content of the exhaust gas, which should be maintained at an appropriate level, typically about 3%. By mixing the recycle gas heated in the gas-gas heat exchanger with the pure oxygen stream heated by the heat transfer medium as described above, effectively controlling the temperature, flow rate and oxygen content of the mixed gas used as the oxidant gas in the furnace can do.

The recycle gas channel and the oxygen channel can advantageously be divided into multiple parallel lines, which form several streams of mixed gas, which can be used, for example, as primary and secondary oxidant gases in a furnace. The mixers are individually connected. By controlling the gas flow in the parallel recirculation gas line and the oxygen line separately, it is possible to control the flow and oxygen content of the oxidant gas stream separately.

According to a preferred embodiment of the present invention, the gas feed rate from air-ignition to boilers refurbished with pure oxygen combustion is modified so that the original gas velocity in the furnace is maintained so that the oxygen content of the oxidant gas is advantageously the content of air, Typically, it is modified to be about 18% to about 28%. The furnace temperature or heat flux of the refurbished boiler should advantageously be maintained near the original level to avoid, for example, material strength problems or corrosion of the furnace walls.

Due to the high heat capacity of the exhaust gas produced in the oxy-fuel combustion process, which has carbon dioxide as the main component, compared to conventional exhaust gas having nitrogen as its main component, the same volume flow rate of the exhaust gas at the same temperature results in air-ignition combustion It carries more heat in the case of pure oxygen combustion than in. Therefore, when converting the air-ignition steam generation process to pure oxygen combustion, the fuel supply rate can be increased by at least 10% and maintains the original furnace temperature or heat flux. Thereby, increased amounts of heat are available, for example for steam generation and heating of the oxidant gas.

According to a particularly advantageous embodiment of the invention, the first mode of operation is carried out differently than the second mode of operation, the so-called air-ignition mode, wherein the recycle portion is minimized by, for example, a damper and the oxidant gas Includes the air flow. Advantageously, this system includes an air inlet for introducing air into the gas recycle line upstream of the gas-gas heat exchanger. Gas-gas heat exchangers are used in the second mode of operation to transfer heat from the exhaust gas to the air stream.

In the second mode of operation, the combustion system is advantageously separated from the oxygen supply and the exhaust gas comprises nitrogen, carbon dioxide and water as its main components. Therefore, the system is also separated from the carbon dioxide capture and storage unit, and exhaust gases are released to the environment through the stack. One of the main ideas of the present invention is a net that can be easily switched back to air-ignition combustion, even on-line, without stopping power generation during change and without any modification to the actual configuration. It is to provide an oxygen combustion method.

In the second mode of operation, the oxygen supply is not used because the content of exhaust gas is not purified and removed in the conventional combustion of carbon dioxide in the exhaust gas. Therefore, the additional power consumption of this process is minimized, and the system provides a higher total efficiency than in oxy-combustion at the cost of releasing carbon dioxide into the environment. The air-ignition mode of operation is advantageously used when the power demand is particularly high, for example summer or daytime. Alternatively, the air-ignition mode can be used temporarily, for example, based on various economic conditions, or when the oxygen supply or carbon dioxide capture and storage system is unavailable for some reason.

The method advantageously comprises in the second mode of operation, circulating a liquid heat transfer medium in a passage between the exhaust gas cooler and the air heater to transfer heat from the exhaust gas to the air stream. Since the exhaust gas flow rate is much higher than the flow rate of the distal portion of the exhaust gas in the second mode of operation, typically in the first mode of operation, advantageously one or more other channels with an exhaust gas cooler are used for the oxyfuel combustion mode. It may be formed in parallel to the exhaust gas channel portion comprising the exhaust gas cooler. Thereby, the heat transfer medium is circulated in the air-ignition mode between the air heater and the two or more parallel exhaust gas coolers. Therefore, the air stream, which has a much larger flow rate than in the oxygen flow in the oxy-fuel combustion mode, can be effectively heated by the exhaust gas.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing brief description of the invention, as well as further objects, features, and advantages, is, in conjunction with the accompanying drawings, more fully understood with reference to the following detailed description of the presently preferred but exemplary embodiments of the invention.

The present invention has the effect of providing an improved method and system for burning pure oxygen using a dual ignition combustion system.

1 is a schematic view of a oxy-fuel combustion power plant according to the present invention.

1 shows a schematic diagram of a power plant 10 according to a preferred embodiment of the present invention. The power plant 10 includes a boiler 12, which may be, for example, a pulverized coal (PC) boiler or a circulating fluidized bed (CFB) boiler. The furnace 14 of the boiler comprises a conventional fuel supply means 16, a means for supplying oxidant gas 18 to the furnace, and an exhaust gas channel 20 for discharging the exhaust gas generated by burning fuel with oxygen of the oxidant gas. ). The details and type of some members of the boiler 12, such as fuel supply means 16 and oxidant gas supply means 18, naturally depend on the type of boiler. However, such details, such as burners, coal mills, and means for separately supplying primary and secondary inlet gases, are not shown in FIG. 1 because they are not important to the present invention.

The oxidant gas is a mixture of a portion of the exhaust gas that is recycled through the exhaust gas recirculation channel 26 and the substantially pure oxygen generated from the air stream 22 in the air separation unit 24 (ASU). The exhaust gas recirculation channel 26 advantageously comprises a flow controller, such as a controllable fan 28 and / or a damper 30, for controlling the exhaust gas recirculation rate. The recycle rate of the exhaust gas is advantageously modified such that the average O ₂ content of the oxidant gas is close to the air content, preferably from about 18% to about 28%. In some applications of the present invention, the streams of recycled exhaust gas and substantially pure oxygen can be introduced separately, or several streams with different O ₂ contents, for example, in different parts of the furnace 14.

As conventionally, the furnace 14 generally comprises an evaporation surface, not shown in FIG. 1, and the exhaust gas channel 20 further comprises heat exchanger surfaces 32, 34, for example a superheater and an economizer. do. For simplicity, FIG. 1 shows only two heat exchanger surfaces 32, 34, but in practice, the exhaust gas channel 20 generally has several superheat, reheat, and coalescer surfaces to recover heat from the exhaust gas. Include. Between the heat generating heat exchanger surfaces 32, 34, a gas-gas heat exchanger 36, generally a regenerative heat exchanger, is arranged to transfer heat directly from the exhaust gas to the recycle portion of the exhaust gas.

The exhaust gas channel 20 generally comprises a conventional unit for cleaning the exhaust gas from particulates and gaseous contaminants, which are schematically represented only with a dust separator 38 in FIG. 1. The vibration suppressor 38 and other possible gas cleaning units are advantageously arranged upstream of the branch point 40 of the exhaust gas recirculation channel 26. At the bifurcation, the exhaust gas flows back to the furnace 14 through the recycle gas channel 26 and to the end portion carried through the distal portion 42 of the exhaust gas channel 20 for final processing. Divided.

As the primary purpose of pure oxygen combustion, namely recovering carbon dioxide from exhaust gas, the distal portion 42 of the exhaust gas channel 20 is provided by a carbon dioxide capture unit 44 for cooling, cleaning and compressing the carbon dioxide. Schematically, with a device. The unit 44 generally includes a dryer for completely drying all the water from the exhaust gas, and a separator for separating the flow of non-condensable gases such as oxygen 50 from the carbon dioxide and other possible impurities. The stream of carbon dioxide 46 is typically collected in a liquid or supercritical state, for example at a pressure of about 110 bar, and can be transported for storage at a suitable location or for later use. 1 individually shows a condensation gas cooler 48 located upstream of the carbon dioxide capture unit 44 for initially removing water from the exhaust gas.

In order to transfer energy from the end portion of the exhaust gas to the flow of substantially pure oxygen, the end portion 42 of the exhaust gas channel 20 has, according to the invention, a gas cooler 52, which is an oxygen supply. Connected by circulation of a liquid heat transfer medium to an oxygen heater 54 disposed in an oxygen channel 56 downstream of 24. The heat transfer medium, generally water, is preferably circulated by the pump 58 in the piping 60 extending between the gas cooler 52 and the oxygen heater 54, which is generally practically a power plant 10. Is located in the far part of).

The oxygen channel 56 may be connected directly to the furnace 14, but according to a preferred embodiment of the present invention, both the oxygen channel 56 and the exhaust gas recirculation channel 26 are connected to the mixer 62 and mixed The flow of gas is sent through the oxidant gas supply means 18 to the furnace as oxidant gas. This system allows individual control of the temperature, flow rate and oxygen content of the oxidant gas.

According to a preferred embodiment of the invention, the system comprises an air intake 64 for supplying air to the furnace. The air stream is preferably introduced into the exhaust gas recirculation channel 26 upstream of the gas-gas heat exchanger 36 to transfer heat directly from the exhaust gas to the air stream. The purpose of the air intake 64 is to make it possible to switch from pure oxygen combustion to air-ignition combustion. Therefore, when introducing air into the gas recycle line, the oxygen supply is stopped and the recycle of the exhaust gas is minimized, preferably completely stopped, by the damper. The exhaust gas cannot easily collect carbon dioxide from the exhaust gas, including water and carbon dioxide mixed with a large amount of nitrogen in the air-ignition mode, which in this case is eventually released through the stack 66 to the environment.

When the air flow obtained from the environment is typically at a much lower temperature than the recycle exhaust gas, the heating of air in the gas-gas heat exchanger 36 is generally not sufficient, but more heat is advantageously the air heater 68 By the air stream. The air heater 68 is also advantageous for increasing the inlet temperature of air in the gas-gas heat exchanger 36 to avoid flue gas condensation and related problems at the heat exchanger surface. The air heater 68 is preferably connected to the exhaust gas cooler 52, which is also used in the oxyfuel combustion mode by the heat transfer medium circulation. Therefore, the piping 60 used for the circulation of water in oxy-fuel combustion is connected to the side piping 70, the so-called air heating arm, which includes the circulation pump 72 in the air-ignition mode.

By opening the valve 74 in the air heating arm and closing the valve 76 in the so-called oxygen heating arm in the main line, the heat transfer medium can be switched to circulate through the air heater 68 instead of the oxygen heater 54. have. If the water circulation pump is arranged in a common part of the water pipe 60, it is sufficient to have only one circulation pump in the case described above. Heat transfer, because the flow rate of air in the air-ignition mode is much higher than the flow rate of oxygen in the oxy-combustion mode, and the flow rate of the exhaust gas in the air-ignition mode is much greater than the flow rate of the end portion of the exhaust gas in the oxy-combustion mode. The circulation rate of the medium is advantageously lower in pure oxygen combustion mode than in air-ignition mode.

According to an alternative embodiment of the invention, the parallel channel portion 78 is arranged in parallel at the distal portion of the exhaust gas channel 42. The portion of the flue gas flowing through the parallel channel portion 78 may be varied by, for example, about 0% to about 75% by the damper 80. The parallel channel portion includes another exhaust gas cooler 82, which is connected in parallel to the exhaust gas cooler 52 in an air-ignition mode. Therefore, heat is transferred from the exhaust gas cooler 52 to the oxygen heater 54 in the pure oxygen combustion mode and from the two exhaust gas coolers 52 and 82 to the air heater 68 in the air-ignition combustion mode. . By properly modifying the heat transfer rate, it is possible to obtain sufficient cooling of the exhaust gas and the required inlet gas temperature in both operating modes.

While the present invention has been described herein by way of example of what is presently considered to be the most preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments and is defined within the scope of the invention as defined in the appended claims. It is intended to cover various combinations or modifications of the features involved and some other uses.

10: power plant 12: boiler
14: furnace 16: fuel supply means
18: oxidant gas supply means 20: exhaust gas channel
22: air flow 24: air separation unit
26: exhaust gas recirculation channel 28: fan

Claims (17)

In the method for generating electric power by pure oxygen combustion,
(a) supplying carbonaceous fuel to the furnace,
(b) supplying an oxidant gas to the furnace wherein, in a first mode of operation, the oxidant gas is substantially conveyed from an oxygen supply to combust oxygen and fuel to produce an exhaust gas comprising primarily carbon dioxide and water. Comprising a flow of pure oxygen,
(c) exhausting the exhaust gas from the furnace,
(d) dividing the exhaust gas into a recycle portion and an end portion;
(e) recycling the recycle portion to the furnace;
(f) circulating the liquid heat transfer medium in the passage between the exhaust gas cooler and the oxygen heater to transfer heat from the end portion to the flow of substantially pure oxygen.
A power generation method by pure oxygen combustion, comprising. The method of claim 1,
(g) transferring heat in the gas-gas heat exchanger from the exhaust gas to the recycle portion to produce a stream of heated recycle gas;
(h) mixing a stream of heated recycle gas and a stream of substantially pure oxygen to form a stream of mixed gas,
(i) supplying the furnace with a flow of mixed gas, which is an oxidant gas,
Further comprising, the power generation method by pure oxygen combustion. The method of claim 1 wherein the liquid heat transfer medium is water. The method of claim 1, wherein the exhaust gas cooler is of a corrosion resistant type. The method of claim 1, wherein the first mode of operation is performed alternately with the second mode of operation, where the recycle portion is minimized and the oxidant gas comprises an air stream. 3. The gas recycle line of claim 2, wherein the first mode of operation is performed alternately with the second mode of operation, where the recycle portion is minimized and the oxidant gas transfers heat from the exhaust gas to the air stream in the gas-gas heat exchanger. A method of generating power by pure oxygen combustion, comprising an air stream introduced to the. 6. The power generation by oxy-combustion of claim 5, wherein the second mode of operation comprises circulating the liquid heat transfer medium in the passage between the exhaust gas cooler and the air heater to transfer heat from an end portion of the air stream. Way. 7. The power generation by oxy-combustion of claim 6, wherein the second mode of operation comprises circulating liquid heat transfer medium in the passage between the exhaust gas cooler and the air heater to transfer heat from an end portion of the air stream. Way. 8. The method of claim 7, wherein the second mode of operation comprises a further step of dividing the parallel flow from the exhaust gas stream and circulating a liquid heat transfer medium between the second exhaust gas cooler and the air heater to transfer heat from the parallel flow to the air stream. A power generation method by pure oxygen combustion, comprising. In a system that generates power by pure oxygen combustion,
Furnace for burning carbonaceous fuel,
An oxygen channel for supplying substantially pure oxygen from the oxygen supply to the furnace to combust the fuel with oxygen to produce an exhaust gas mainly comprising carbon dioxide and water,
An exhaust gas channel connected to the furnace for exhausting the exhaust gas from the furnace,
Branch piping for dividing the exhaust gas into the recirculation portion and the end portion;
A gas recirculation channel for supplying a recirculation portion of the exhaust gas to the furnace,
An exhaust gas disposed in an exhaust gas channel downstream of the branch piping and an oxygen heater disposed in an oxygen channel connected by the passage for circulating a liquid heat transfer medium in the passage to transfer heat from the end portion to the flow of substantially pure oxygen. Chiller
A system for generating power by pure oxygen combustion. The method of claim 10,
A gas-gas heat exchanger for transferring heat from the exhaust gas to the recycle section,
A mixer arranged to connect an oxygen channel downstream of the oxygen heater and a gas recycle channel downstream of the gas-gas heat exchanger to mix substantially pure oxygen flow and the recycle portion to form a flow of mixed gas,
A channel that supplies a stream of mixed gas, which is an oxidant gas,
Further comprising: a system for generating power by pure oxygen combustion. The system of claim 10, wherein the exhaust gas cooler is of a corrosion resistant type. The method of claim 10,
A flow controller disposed in the recycle gas channel for controlling the recycle portion,
An air inlet for introducing an air stream as an oxidant gas instead of substantially pure oxygen
Further comprising: a system for generating power by pure oxygen combustion. 12. The method of claim 11,
A flow controller disposed in the recycle gas for controlling the recycle portion,
An air intake for introducing a flow of air as an oxidant gas instead of substantially pure oxygen to the gas recycle line, the air intake to transfer heat from the exhaust gas to the air flow of the gas-gas heat exchanger. An air intake, disposed upstream of the gas-gas heat exchanger,
Further comprising: a system for generating power by pure oxygen combustion. 14. The net of claim 13, further comprising an air heater connected by the passage to the exhaust gas cooler for circulating the liquid heat transfer medium in the passage between the air heater and the exhaust gas cooler to transfer heat from the end portion to the air flow. A system that generates power by oxygen combustion. 15. The net of claim 14, further comprising an air heater connected by the passage to the exhaust gas cooler for circulating the liquid heat transfer medium in the passage between the exhaust gas cooler and the air heater to transfer heat from the end portion to the air flow. A system that generates power by oxygen combustion. 16. The method of claim 15,
A second branch piping for dividing the parallel flow from the exhaust gas flow in the parallel channel option;
A second exhaust gas cooler disposed in the parallel channel portion for circulating the liquid heat transfer medium in the passage between the second exhaust gas cooler and the air heater to transfer heat from the parallel flow to the flow of air.
Further comprising: a system for generating power by pure oxygen combustion.

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