JPH0694212A - Fossil fuel combustion boiler - Google Patents

Abstract

PURPOSE:To economically recover CO2 from waste gas of a CO2/O2 combustion type boiler and to improve a thermal efficiency of the boiler by heating feedwater of the boiler and O2 by part of combustion waste gas, mixing the residual waste gas with O2 after heating, supplying it to the boiler, and liquefying to recover CO2 from the combustion waste gas cooled by itself. CONSTITUTION:After 20-40% of dust-removed combustion waste gas is denitrified, it is distributed to an O2 heater 5 and a waste gas feedwater heater 6. The combustion waste gas fed through the heaters 5 and 6 is cooled by heating O2 and boiler feedwater by its sensible heat, and recovered as liquid CO2 by a CO2 recovery unit having a cooler 8, a dehumidifier 9 and a CO2 liquefying unit 10. The residual 60-80% of the waste gas is fed to a gas mixer 12, uniformly mixed with the O2 fed from the heater 5, and supplied to a burner of a boiler 2. Thus, the CO2 can be economically recovered from the waste gas of the boiler, and performance of the boiler is also improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for effectively and economically recovering carbon dioxide in exhaust gas in a fossil fuel combustion boiler of a thermal power plant.

[0002]

2. Description of the Related Art Carbon dioxide (hereinafter referred to as CO ₂ ) emission control, which is one of the greenhouse gases that cause global warming and has a large impact on the environment, has become an international issue. There is. Among the CO ₂ emissions in Japan, fossil fuel-based thermal power plants account for a large amount of weight, and by removing and recovering CO ₂ from these exhaust gases, the amount released to the atmosphere is reduced. That is extremely important.

Currently, as a CO ₂ removal / recovery technology in a thermal power plant that burns fossil fuels, an adsorption method in which CO ₂ is adsorbed by a special adsorbent, or CO ₂ is absorbed / separated by using an absorbing liquid such as amine. It is considered to add equipment such as a chemical absorption method. However, when burning fossil fuel with air, the CO ₂ concentration in the exhaust gas is low, which is in the range of 5 to 23%. Therefore, it is necessary to increase the partial pressure of CO _{2 in} the adsorption method, which consumes a large amount of power for gas compression.

On the other hand, in the chemical absorption method, a large amount of vapor is required to regenerate the absorbing solution due to the low CO ₂ concentration. Further, equipment such as a CO ₂ absorption tower, an absorption liquid regeneration tower, an absorption liquid storage tank, etc. will be specially added, and the equipment cost and operating cost are required. Further, since the cost and the operation labor are required for supplying the chemical absorbing liquid and treating the waste liquid, the cost of the separated and recovered CO ₂ is relatively high, and it is hard to say that it is excellent in economic efficiency.

Therefore, CO in the exhaust gas₂Purpose of collecting
Proposes a power generation system using carbon dioxide / oxygen combustion
Has been done. The basic diagram is shown in FIG. This combustion method
Is oxygen (hereinafter O₂Will be written)
Combustion of fossil fuels with a mixture of
According to this method, CO in exhaust gas is₂9
It can be concentrated to a high concentration of 0% or more. According to
CO in exhaust gas₂Without the need for extensive equipment
Can be collected. In this combustion method, the gas supplied to the combustion is also used.
Nitrogen (N₂) No components are included, so when burning at high temperature
Nitrogen oxide (NO _x) Does not occur. Therefore,
The concentration of nitrogen oxides in the gas becomes extremely low,
Not only the equipment is compact, but also the amount of catalyst to be filled.
Can be significantly reduced.

[0006]

Even in the CO ₂ / O ₂ combustion system, economic evaluation and effects can be achieved by selecting the combination of the devices and equipment constituting the power plant and the extraction position of the recirculated exhaust gas used for combustion. Are significantly different.

An object of the present invention is to use a CO ₂ / O ₂ combustion type power generation plant on the premise of recovering CO ₂ , a fossil fuel combustion boiler which is a highly economical and energy-saving method and which is highly safe and reliable. Is to provide.

[0008]

The present invention achieves the above objects.
O to make₂And CO₂Mixed gas containing
Therefore, a combustion device for burning fossil fuel, and the above combustion device
The boiler that evaporates water by the heat generated in the
Combustion exhaust generated by the above combustion device
Exhaust gas feed water heater that heats by a part of gas, above
O which heats oxygen by another part of the combustion exhaust gas₂
Heater and O₂O above the heater ₂Above combustion exhaust
The gas mixture is mixed with the rest of the gas and supplied to the combustion device.
Gas mixer and the above exhaust gas feed water heater and
Note O₂CO in the combustion exhaust gas leaving the heater₂Collect
CO₂Fossil fuel characterized by having a recovery device
Combustion boilers; and, in addition to the above requirements, the above fossil fuels
Is a fine powder solid, and O ₂And CO₂Mixed with
Transported and supplied to the above combustion device by combined gas
To propose a fossil fuel combustion boiler characterized by
It

[0009]

[Action]

1) By heating the combustion O ₂ and boiler feed water with a part of the combustion exhaust gas of fossil fuel, the sensible heat of the combustion exhaust gas is effectively recovered, and the heat energy loss of the plant is reduced to improve the economic efficiency. Let 2) The rest of the combustion exhaust gas is heated O ₂ for combustion.
The flame temperature is controlled by mixing it with and supplying it to the combustion device. 3) CO ₂ is recovered by a simple device from the combustion exhaust gas (main component CO ₂ ) obtained by heating the combustion O ₂ and the boiler feed water. 4) If the fossil fuel is finely divided solid, as a medium for conveying it from the mill or pulverized coal reservoir grinding the coal to the combustion device of the boiler, using the above 2) of the CO ₂ / O ₂ mixed gas, CO ₂ By adjusting and controlling the mixing ratio of O ₂ and O _{2 according} to the properties of the fuel, in particular the volatile content, fuel ratio, ash content and fineness, atmospheric temperature, etc., spontaneous ignition or explosion of the fuel in the fuel supply system can be prevented. To prevent.

[0010]

FIG. 1 is a block diagram showing an embodiment of the present invention. In this figure, coal is pulverized by a mill (1) and supplied as pulverized coal to a combustion device of a boiler (2). Then, it is burned by a mixed gas containing O ₂ and CO ₂ as main components, and the water supplied to the boiler (2) is converted into steam by the generated heat. The steam is sent to a steam turbine or the like (not shown).

Combustion exhaust gas (CO) produced in the boiler (2)
₍₂ Concentration 90% or more) is removed by the dust remover (3). 20 to 40% of the dust-removed combustion exhaust gas is distributed to the O ₂ heater (5) and the exhaust gas feed water heater (6) after nitrogen oxides are removed by the denitration device (4).

In the O ₂ heater (5), the O ₂ supplied to the boiler combustion is heated by the combustion exhaust gas and sent to the gas mixer (12). On the other hand, in the exhaust gas feed water heater (6), the boiler feed water is heated, and the heated feed water is further heated in the feed water heater (16) by extraction steam or the like from a steam turbine (not shown), and then the boiler (2 )
Is supplied to.

O₂Heater (5) and exhaust gas feed water heater
The combustion exhaust gas that has passed through (6) is O due to its sensible heat.₂Oh
And it is cooled by heating the boiler feedwater. That
The sulfur oxide in the gas is removed by the desulfurization device (7).
CO that does not contain impurities₂The cooling device (8) is removed
Wetting device (9), CO₂CO consisting of liquefier (10) ₂
Liquid CO₂Will be collected as.

The remaining 60 to 80% of the combustion exhaust gas is branched from the exhaust gas passage between the dust remover (3) and the O ₂ heater (5) (inlet of the denitration device (4) in the illustrated example), and CO as a recycle gas ₂ as a main component, the recycle gas fan (1
It is sent to the gas mixer (12) by 1) and is uniformly mixed with O ₂ sent from the O ₂ heater (5). This mixed gas is supplied to the combustion device of the boiler (2).

On the other hand, a part of the mixed gas is branched to the carrier gas mixer (13), and the heat exchanger (1 for reducing the temperature is used.
After 4), the mill (1) is operated by the carrier gas fan (15).
Sent to. Then, it is supplied to the boiler (2) together with the pulverized coal as a pulverized coal carrier medium (carrier gas) of the coal supply system. Here, in order to control and adjust the O ₂ concentration of the carrier gas,
A part of the recirculation gas from the outlet of the recirculation gas fan (11) is introduced into the carrier gas mixer (13) by a signal such as pulverized coal properties.

Next, the operation of this embodiment will be described including the research results on the mass balance of the system.

CO₂/ O₂In the combustion type boiler,
Adiabatic flame temperature equivalent to conventional air combustion is obtained
The results of examining the exhaust gas recirculation ratio are shown in Fig. 4. Over air
The adiabatic flame temperature when coal is burned at a surplus rate of 5% is usually
It is about 2100 ° C. (indicated by diagonal lines in FIG. 4). Same as this
Fig. 4 shows the exhaust gas recirculation ratio at which a similar adiabatic flame temperature can be obtained.
From 60 to 80%. Therefore, the boiler
Mouth) 60-80% of exhaust gas is recycled to the boiler for combustion
CO₂As CO2 and the remaining 20-40% is CO ₂Liquefaction equipment
Liquid CO₂To collect.

The boiler exhaust gas temperature is usually 350 to 38.
It is 0 ° C., and it is necessary to cool it to -15 ° C. or lower for liquefying CO ₂ . Therefore, effective use of the amount of heat possessed by this gas greatly affects the performance and economic efficiency of the plant. Therefore, in this embodiment, the sensible heat of the combustion exhaust gas is used as a means for heating the O ₂ used for combustion to the same level as the recirculated exhaust gas temperature. Here, if expensive O ₂ leaks to the combustion exhaust gas side, not only an economic loss but also an accident such as explosion or flame may occur in terms of safety, so the structure of the O ₂ heater (5) is Is preferably a non-leak type.

In the case of this embodiment, combustion by air
Compared with the case of ₂The amount of at least
Nitrogen contained in air (N₂) (About 79% by volume)
There are few cases. Therefore, the heated O₂The amount of and the heating source
Planning design of the heater in terms of mass balance with a certain amount of exhaust gas
Inconvenience occurs. There O₂Discharge in parallel with the heater (5)
Install a gas water heater (6)₂Pair with heater (5)
And use excessive amount of exhaust gas as a heating source for boiler feed water.
Enables effective thermal energy while maintaining calorie balance
To collect. Thus O₂6 for heater (5)
0 ~ 70%, 30 ~ 4 in the exhaust gas feed water heater (6)
About 0% of combustion exhaust gas is passed through.

Next, where to extract the recirculated gas mixed with the heated O ₂ from the combustion exhaust gas flow path has a great influence on the economical efficiency of the plant. In the present embodiment, the recirculation gas extraction point is at least upstream of the O ₂ heater. For example, as shown in FIG. 2, if considering the case where the extraction point of the recycle gas provided downstream of the O ₂ heater (5), the amount of gas passing through O ₂ heater (5), the present embodiment As compared with the example, the amount of O ₂ heater (5) increases at least by the amount corresponding to the gas to be recirculated, so that not only the equipment cost increases but also the pressure capacity and operating consumption of the aerator are inevitably increased. Power will increase, and it will be inferior both in terms of economy and energy saving. Also, considering the flame stability and combustion efficiency improvement of pulverized coal combustion in the boiler,
Combustion air (O ₂ ) is desired to be at a high temperature, usually 3
A temperature of about 00 to 400 ° C is adopted. Therefore, the above extraction point is the most appropriate extraction position also from this meaning.

Combustion of pulverized coal from mill or pulverized coal storage tank
Air has traditionally been used as the medium to be transported to the device.
It was However, depending on the properties of the pulverized coal and the conditions of the atmosphere,
Accidents such as spontaneous combustion or explosion may occur in the coal supply system.
There was. Therefore, to ensure safety, inert gas such as nitrogen
Gas was sometimes supplied instead of air, but an inert gas was used.
To supply gas from outside the system requires special equipment and gas costs.
It has a drawback that it requires a burden and is inferior in economic efficiency. Implementation
In the example, CO is used as the carrier for the pulverized coal.₂/ O₂For mixed gas
CO depending on the properties of pulverized coal and atmospheric conditions₂/ O₂Ratio of
Adjust rate. The main component of the recirculation gas is CO₂And inactive
Therefore, increasing the amount of coal in the coal supply system
It prevents fire or explosion before it happens, and it is economical.
It will be a safe and reliable coal supply system. Figure 5
O₂CO₂O in the atmosphere when diluted with₂Versus concentration
It is a figure which shows the relationship between the explosion pressure and the pressure rising speed which occur. C
O ₂This means that increasing the amount of
Can be understood from the figure.

[0022]

EFFECTS OF THE INVENTION According to the present invention, CO ₂ which is a global warming effect gas is effectively extracted from the exhaust gas of a fossil fuel combustion boiler by a safe and reliable energy saving method which is excellent in economic efficiency. Can be recovered and the boiler performance is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a reference block diagram for comparing the effects of the present invention.

FIG. 3 is a basic block diagram of a conventional CO ₂ / O ₂ combustion type boiler.

FIG. 4 is a diagram showing a relationship between a recirculation gas ratio and an adiabatic flame temperature.

FIG. 5 is a diagram showing the relationship between the O ₂ concentration in the atmosphere and the explosion pressure and pressure rise rate.

[Explanation of symbols]

(1) Mill (2) Boiler (3) Dust removal device (4) Denitration device (5) O ₂ heater (6) Exhaust gas feed water heater (7) Desulfurization device (8) Cooling device (9) Dehumidification device (10) CO ₂ liquefier (11) Recirculation gas fan (12) Gas mixer (13) Carrier gas mixer (14) Heat exchanger (15) Carrier gas fan (16) Feed water heater

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junsuke Miyake 5-3, Atsunoura-cho, Nagasaki-shi Nishinihon Hishijukosan Building 4F Nagaro Design Co., Ltd.

Claims (2)

[Claims] 1. A combustion device that burns fossil fuel with a mixed gas containing oxygen and carbon dioxide as main components, a boiler that evaporates water by heat generated in the combustion device, and a feed water supplied to the boiler. An exhaust gas feed water heater that is heated by part of the combustion exhaust gas generated in the combustion device,
An O ₂ heater for heating the oxygen by another part of the combustion exhaust gas, and a mixed gas supplied to the combustion device by mixing the oxygen discharged from the O ₂ heater with the remainder of the combustion exhaust gas. A fossil fuel combustion boiler, comprising: a gas mixer that performs the above; and a CO ₂ recovery device that recovers carbon dioxide in the combustion exhaust gas that has exited from the exhaust gas feed water heater and the O ₂ heater. 2. The fossil fuel is a fine powder solid, and is conveyed and supplied to the combustion device by a mixed gas containing oxygen and carbon dioxide as main components.
Fossil fuel combustion boiler described.