JP2002221091A - Exhaust gas boiler and combustion method in exhaust gas boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas boiler producing less NOx utilizing the remaining oxygen in the exhaust gas in a diesel engine or a gas turbine. SOLUTION: A heat regenerator set consisting of two units is mounted on either side of a boiler combustion chamber, and the exhaust gas of a diesel engine or a gas turbine is fed to the heat regenerators on both sides of the boiler combustion chamber alternately at prescribed intervals by switching a selector valve. As the fuel is fed alternately, the exhaust gas boiler performs low-NOx combustion with high temperature and low oxygen concentration. In another case, a primary combustion chamber and a secondary combustion chamber are made to communicate with each other via a restrictor to perform fuel rich combustion in the primary combustion chamber and the combustion with high temperature and low oxygen concentration in the secondary combustion chamber by feeding air.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler using a combustion gas obtained by reburning exhaust gas of a diesel engine or a gas turbine as a driving heat source.

[0002]

2. Description of the Related Art Conventionally, the residual heat of exhaust gas of a diesel engine or a gas turbine has been recovered by an exhaust gas boiler.
It is around 00 ° C. In particular, since the exhaust gas of a diesel engine has a high NOx concentration, exhaust gas treatment such as denitration using a catalyst is performed.

[0003]

Since the temperature of the exhaust gas of a diesel engine or gas turbine is as low as about 400 ° C. to 550 ° C., the amount of heat energy per unit volume is small, and a large amount of power is required to increase the output of the boiler. The boiler must be large because it requires exhaust gas, and when driving the steam turbine with the steam output from the boiler, it is necessary to secure sufficient steam temperature and pressure to increase the efficiency of the steam turbine. could not. Further, since the exhaust gas of a diesel engine has a high NOx concentration, there is a problem in that the residual heat is recovered and recovered as it is in an exhaust gas boiler.

[0004] Diesel engines are burned under excess air to achieve complete combustion of the injected liquid fuel,
In addition, gas turbines require excessive air in order to suppress the temperature of the combustion gas from the viewpoint of the heat resistance of the turbine blades.Therefore, excess air not involved in combustion remains in the exhaust gas, In addition, the exhaust gas is adiabatically expanded in the diesel engine cylinder or the turbine cascade, and its temperature is lowered. The present invention provides a boiler capable of utilizing a residual air in the exhaust gas to burn fuel in a method of generating less NOx to raise the temperature of the exhaust gas again to obtain a large output with a small displacement. The purpose is to provide.

[0005]

According to a first aspect of the present invention, there is provided a tubular boiler combustion chamber provided with a water pipe, having a passage communicating with the boiler combustion chamber at both ends. First and second regenerative heat exchangers each having a heat storage body are provided, and both of these heat storage type heat exchangers have a fuel supply valve for supplying fuel to the boiler combustion chamber side of the heat storage body. An exhaust gas boiler is provided, wherein an exhaust gas passage of a diesel engine or a gas turbine is connected to the two regenerative heat exchangers via a switching valve.

According to a second aspect of the present invention, the exhaust gas is communicated to the first regenerative heat exchanger or the second regenerative heat exchanger by switching the switching valve. The temperature of the exhaust gas communicated with the heat exchanger is increased by heat exchange with the heat storage body of the heat exchanger, and the heated exhaust gas is supplied with fuel from the fuel supply valve to increase the temperature of the exhaust gas. The gas is blown into the boiler combustion chamber together with the gas to perform combustion in the heated high-temperature, low-oxygen concentration gas, and the combustion gas releases heat to the water pipe provided in the boiler combustion chamber, and the other gas is cooled down. When the temperature reaches the regenerative heat exchanger and passes through the regenerative heat exchanger, the temperature is further reduced by heat exchange with the heat storage body, and then discharged through the switching valve.The switching of the switching valve and the fuel supply are performed in a predetermined manner. Exhaust gas boiler characterized by alternate operation at time intervals It is the definitive combustion method.

[0007] The concentration of residual oxygen in the exhaust gas of an internal combustion engine is determined by the following equation. Residual oxygen concentration (% by weight) = 23 · L ₀ · (λ−1) / (1 + λ · L ₀ ) (1) where λ is the excess air ratio, and L ₀ is the theoretical air amount, that is, 1 kg of fuel is completely used. It is the amount of air (kg) required to burn. The value of L ₀ is determined by the composition of the fuel. When the petroleum-based fuel is represented by CnHm and m / n is 1.9, L ₀ =
14.5. 23 is the oxygen concentration (% by weight) of the air.

In the equation (1), the theoretical air amount L ₀ = 1
At 4.5 kg / kg, the relationship between the residual oxygen concentration (% by weight) and the excess air ratio λ is plotted as shown in FIG. Combustion in a diesel engine is diffusion combustion, and the excess air ratio must be increased to some extent in order to achieve complete combustion of the fuel. The excess air ratio of a diesel engine varies depending on the combustion chamber type, load, etc.
At full load, λ = 1.35 to 2, and becomes larger as the load becomes lower. In the case of gas turbines, those that perform a simple cycle have a low load of about λ = 3 to 3.5 at full load, and those with a reheater and a reheat cycle have a low load of about λ = 1.2 to 1.5 at full load. It becomes bigger. Therefore, the oxygen concentration of the exhaust gas of a diesel engine or a gas turbine is about 5% or more.

[0009] In normal combustion in air, the temperature distribution in the flame is very uneven, there are locally very high temperature portions, and even if the average temperature is not so high, NOx is generated in the local high temperature portions. Is generated in large quantities. When burning in high-temperature, low-oxygen gas, the flame combustion area becomes larger than when burning in normal air, and as the combustion area increases, the average heat flux increases and the combustion gas temperature becomes more uniform. In addition, since the oxygen concentration is low, combustion with little NOx generation is performed. The increase in flame volume is more significant at higher temperatures and lower oxygen concentrations.

According to the present invention, the exhaust gas of a diesel engine or a gas turbine is guided to the first regenerative heat exchanger, the temperature of the exhaust gas is increased by heat exchange with the heat storage body, and fuel is supplied to the heated exhaust gas. When the fuel is injected into the boiler combustion chamber, mixing of the fuel and the heated exhaust gas at the time of injection proceeds, and the fuel is burned in the high-temperature, low-oxygen concentration gas that is the heated exhaust gas. Combustion with less NOx generation is performed. A boiler water pipe is provided in the boiler combustion chamber, and the combustion gas burns, while radiating heat to the boiler water pipe, that is, while being cooled by the boiler water pipe,
The heat reaches the second regenerative heat exchanger disposed on the side opposite to the first regenerative heat exchanger, radiates heat to the heat storage body of the second regenerative heat exchanger, and cools down to the switching valve. , Are discharged to the flue via the switching valve.

After a predetermined period of time, the switching valve is switched to raise the temperature of the exhaust gas through the heat storage element of the second regenerative heat exchanger heated by the combustion gas. When fuel is supplied to the boiler combustion chamber and injected into the boiler combustion chamber, the mixing of the fuel and the heated exhaust gas at the time of injection proceeds, and the fuel is burned in the high-temperature low-oxygen gas, which is the heated exhaust gas. Therefore, the combustion with little NOx generation as described above is performed. As the combustion gas burns,
On the other hand, while radiating heat to the boiler water pipe, that is, while being cooled by the boiler water pipe, the heat reaches the first regenerative heat exchanger disposed on the side opposite to the second regenerative heat exchanger, and The heat is radiated to the heat storage body of the heat storage type heat exchanger, and the temperature is lowered to reach the switching valve, and is discharged to the flue via the switching valve.

As described above, the exhaust gas of a diesel engine or a gas turbine is alternately heated at predetermined time intervals from both sides of the boiler combustion chamber and is injected into the boiler combustion chamber together with the fuel. always performed except time, also, the combustion high temperatures because performed under a low oxygen concentration less combustion of NOx generation is performed, NOx which has been present in the exhaust gas HCN, intermediate, such as NH ₃ The boiler exhaust gas discharged from the boiler combustion chamber via the switching valve becomes low NOx exhaust gas because it is partially reduced to N ₂ via the product. Then, the fluid passing through the water pipe provided in the boiler combustion chamber is heated and supplied to a use such as a turbine.

According to a third aspect of the present invention, a primary combustion chamber is provided in an exhaust gas passage of a diesel engine or a gas turbine, and the primary combustion chamber is connected to a secondary combustion chamber via a throttle passage. The fuel is supplied to the primary combustion chamber to perform primary combustion with excess fuel, and the secondary combustion is performed by supplying air to the primary combustion gas that exits the throttling portion and is injected into the secondary combustion chamber. The secondary combustion gas is used as a heating source for a boiler water pipe.

According to the invention, the temperature is from 400.degree.
Exhaust gas from a diesel engine or gas turbine having an oxygen concentration of at least about 5% or more at about 50 ° C. is introduced into the primary combustion chamber, and fuel is supplied in excess of an amount corresponding to the amount of residual oxygen, resulting in less NOx generation. Cause excessive combustion. The combustion gas is injected into the secondary combustion chamber through the throttle,
Expands adiabatically, lowering temperature and pressure. Mixing of the combustion gas at the time of ejection into the secondary combustion chamber is promoted, and uniformity of the distribution of unburned fuel and the temperature distribution is promoted. The temperature drop depends on the degree of restriction of the restrictor, but the temperature of the gas having been homogenized is sufficiently high also in the secondary combustion chamber, and by supplying secondary air to the secondary combustion chamber, 800 fuel
NOx in a high-temperature, low-oxygen concentration atmosphere at
Generating less combustion is performed, the NOx in the exhaust gas HCN, and partially via an intermediate product, such as NH ₃ N ₂
The combustion gas discharged from the secondary combustion chamber becomes exhaust gas having a low NOx concentration. The low NOx combustion gas is introduced into the boiler, where the high temperature combustion gas provides a higher output with the same amount of exhaust gas. Further, a boiler water pipe may be provided in the secondary combustion chamber.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to an embodiment shown in the drawings. However, dimensions, materials, shapes, relative positions, and the like described in the embodiments are not intended to limit the scope of the present invention, but are merely illustrative examples, unless otherwise specified.

FIG. 1 relates to a first embodiment of the present invention.
1 shows a schematic configuration of an exhaust gas boiler. In the figure, 10 is
Boiler combustion chamber, 11 boiler water pipes, 12 and 13
First and second regenerative heat exchangers. The regenerative heat exchanger
Heat storage bodies 12a and 13a and fuel supply valves are respectively provided in 12 and 13.
12b and 13b are provided. Exhaust gas not shown
From diesel engines and gas turbines
Exhaust gas g₁Is the line L ₁Is guided to the four-way valve 14 by
You. When the switching position of the four-way valve 14 is as shown in FIG.
Note exhaust gas g₁Is a line L from the four-way valve 14₂By
The heat is led to the first regenerative heat exchanger 12
a into the boiler combustion chamber 10 through
When passing through the body 12a, heat is received from the heat storage body 12a to increase the temperature.
The exhaust gas heated in the mixing chamber 12c immediately after the heat storage body 12a
Fuel is supplied to the gas from the fuel supply valve 12b.
The fuel supplied to the mixing chamber 12c is
And the exhaust gas is heated to 800-1000 ° C. or more.
Squirt into boiler combustion chamber 10
₂It is burned under high temperature and low oxygen concentration,
Flame area widens greatly, no local high temperature part, NOx
Combustion with less generation.

The combustion gas g ₃ advances toward the boiler combustion chamber 10 to the second regenerative heat exchanger 13, boiler water pipe disposed on the inner wall of the combustion chamber 10 primarily by thermal radiation between them (radiation) 11 is heated to heat water and / or steam passing through the water pipe 11. The combustion gas g ₄ which is lowered around 1200 ° C. by the heat release for heating is lowered by heating the heat storage member 13a when passing through the regenerator 13a of the second regenerative heat exchanger 13, boiler exhaust gas g ₅ which is the temperature drop is led to the four-way valve 14 through line L _3, it is through discharge line L ₄ through the four-way valve. N in the exhaust gas supplied from the exhaust gas source
Because Ox is HCN, is reduced to partially N ₂ via the intermediate products such as NH _3, boiler exhaust gas through discharging the line L ₄ is a a low NOx concentration exhaust gas.

The heat storage body 1 of the second heat storage type heat exchanger 13
When 3a is sufficiently heated, the four-way valve 14 is turned off.
(B) When the position is switched to the position shown in FIG.
Gas g ₁Is the line L₃Through the second regenerative heat
800-1 when guided by the exchanger 13 and passing through the heat storage body 13a.
000 ° C., and the mixing chamber 13 immediately after the heat storage body 13a
The exhaust gas whose temperature has been increased in FIG.
Fees are supplied. Fuel supplied to the mixing chamber 13c
Is heated to 800 to 100 in the mixing chamber 13c.
Exhaust gas of 0 ° C or higher burns a part while burning
Spout into the combustion chamber 10₂Under high temperature and low oxygen concentration
Combustion takes place in the
There is no target high temperature part, and combustion with little NOx generation is achieved.

The combustion gas g ₃ travels in the boiler combustion chamber 10 toward the first regenerative heat exchanger 12, during which the boiler water pipe disposed on the inner wall of the combustion chamber 10 mainly by heat radiation (radiation) 11 is heated to heat water and / or steam passing through the water pipe 11. The combustion gas g ₄ which is lowered around 1200 ° C. by the heat release for heating is lowered by heating the heat storage member 12a when passing through the regenerator 12a of the first regenerative heat exchanger 12, boiler exhaust gas g ₅ which is the temperature drop is led to the four-way valve 14 through line L _2, it is through discharge line L ₄ through the four-way valve. N in the exhaust gas supplied from the exhaust gas source
Because Ox is HCN, is reduced to partially N ₂ via the intermediate products such as NH _3, boiler exhaust gas through discharging the line L ₄ is a a low NOx concentration exhaust gas.

As described above, by switching the four-way valve 14 at predetermined time intervals, the heat storage bodies 12a and 13a are alternately heated and cooled, and the high-temperature combustion gas in the boiler combustion chamber 10 is filled with the first heat storage type. From the heat exchanger 12 side to the second regenerative heat exchanger 13 side, or alternately from the second regenerative heat exchanger 13 side to the first regenerative heat exchanger 12 side, the boiler combustion chamber The boiler water pipes arranged in the boiler are always heated by the hot combustion gas. Combustion is always performed except for an extremely short time when the four-way valve 14 is switched.In addition, since combustion is performed under a high temperature and low oxygen concentration, combustion with little NOx generation is performed, and the combustion is performed in the exhaust gas. NOx that was present is H
CN, since it is reduced to partially N ₂ via the intermediate products such as NH _3, boiler exhaust gas through discharging the line L ₄ is a a low NOx concentration exhaust gas. Then, the fluid passing through the water pipe provided in the boiler combustion chamber is heated and supplied to a use such as a turbine. In addition, the said heat storage body 1
For 2a and 13a, a ceramic or metal formed into a honeycomb shape having a small gas passage resistance and excellent heat exchange performance is suitable.

In FIG. 1, the first and second regenerative heat exchangers are respectively provided at both ends of the boiler combustion chamber 10, but it is needless to say that a plurality of heat exchangers may be provided respectively. It is. The exhaust gas g _1, in order not to increase the back pressure of the exhaust gas generating source, preferably send four-way valve 14 in the blower, not shown. Incidentally, boiler exhaust gas g ₅ discharged through line L ₄ are discharged from the chimney, which has been subjected to the boiler feed water heating or the like.

[0022] In FIG. 1, since it varies the temperature distribution of the boiler combustion chamber 10 axially of the combustion gas g ₃ by the traveling direction of the combustion gas g _3, switching of the four-way valve is carried out in a relatively short time interval, The temporal change of the temperature distribution is not large, and an average temperature distribution is determined. The boiler combustion chamber may be divided into sections according to the averagely determined temperature, and a water pipe having an inlet / outlet may be provided for each section. Also,
Although water tube 11 in Figure 1 are arranged in a ring shape on the inner wall of the boiler combustion chamber 10 may be disposed so as to face in the axial direction of the boiler combustion chamber 10, further contact with the combustion gas g ₃ There may be a water pipe traversing the combustion chamber 10 to effect heat transfer.

FIG. 2 shows a schematic configuration of an exhaust gas boiler according to a second embodiment of the present invention. In FIG. 1, exhaust gas from a diesel engine or a gas turbine as an exhaust gas supply source 8 is sent to a primary combustion chamber 1 via a blower 9, and fuel is supplied from the burner 3 to the primary combustion chamber 1. Then, excess fuel combustion is performed. Excessive fuel combustion does not necessarily mean that the amount of oxygen existing in the primary combustion chamber is excessive, but that excess combustion is performed in the combustion region. That is, low NOx combustion in the reduction combustion region is performed.

Although the temperature distribution and the unburned fuel distribution of the combustion gas in the primary combustion chamber are not uniform, the combustion gas is adiabatically expanded and injected into the boiler combustion chamber, that is, the secondary combustion chamber through the throttle portion 2. The mixing is promoted to make it more uniform and the temperature drops,
The squeezing degree is set so that the temperature of 800 ° C. to 1000 ° C. or more is maintained even when the temperature is lowered. Secondary air is supplied from the air nozzle provided at the outlet of the throttle unit 2 to the relatively uniform high-temperature gas containing unburned fuel to perform combustion at a high temperature and low oxygen concentration. In the combustion in the chamber, the flame 5a greatly spreads, and there is no local high-temperature portion, resulting in low NOx combustion. In particular, NOx, which is largely present in the exhaust gas of a diesel engine, is HCN, NH ₃
And the like, and is partially reduced to N ₂ via an intermediate product such as the above, and the exhaust gas from the outlet 7 of the boiler combustion chamber becomes an exhaust gas with low NOx.

A boiler water pipe 5 is provided in the boiler combustion chamber (secondary combustion chamber) 4, and mainly includes a high-temperature flame 5a.
The water and / or steam flowing through the water pipe 5 is heated by the radiation (radiation) heat from the water pipe. In the figure, the water pipe 5 is arranged in an annular shape on the furnace wall of the boiler combustion chamber 4, but may be arranged so as to face in the axial direction of the furnace, and also for contact heat transfer with the flame 5a. Therefore, it goes without saying that there may be a pipe crossing the inside of the combustion chamber 4.

The boiler water pipe may not be disposed in the boiler combustion chamber 4, but may be disposed downstream of the combustion gas. It is preferable that a plurality of the air nozzles 6 for ejecting the secondary air are arranged in a position and a direction so that the secondary air causes an appropriate swirling flow in the combustion chamber 4. Although the burner 3 is disposed opposite to the direction in which the exhaust gas flows into the primary combustion chamber in the drawing, it is also disposed with an optimum position and direction determined.
It goes without saying that the shape of the primary combustion chamber is also optimized.

With the above configuration, the so-called two-stage combustion consisting of primary combustion and secondary combustion is performed by using residual oxygen in the exhaust gas of a diesel engine or a gas turbine as an oxidizing agent for combustion. The boiler output can be increased with the same displacement as the boiler, and the exhaust gas can have a lower NOx concentration.

[0028]

The present invention is embodied in the form described above, and has the following effects.

First and second regenerative heat exchangers are disposed on both sides of the boiler combustion chamber, respectively, and the exhaust gas of a diesel engine or a gas turbine is supplied to the first heat exchanger via a switching valve at predetermined time intervals.
And alternately lead to the second regenerative heat exchanger, and supply the fuel when the exhaust gas is heated by the regenerator of the regenerative heat exchanger and ejects the exhaust gas into the boiler combustion chamber. It is possible to provide an exhaust gas boiler that performs combustion at a low concentration and generates less NOx.

The exhaust gas of a diesel engine or a gas turbine is guided to a primary combustion chamber to perform primary combustion with an excessive amount of fuel, and secondary air is passed through a boiler combustion chamber, which is a secondary combustion chamber communicated via a throttle. To provide an exhaust gas boiler with low NOx generation that performs two-stage combustion of excessive fuel combustion and combustion at a high temperature and low oxygen concentration by using residual air in the exhaust gas by performing secondary combustion by supplying air. Can be.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an exhaust gas boiler according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of an exhaust gas boiler according to a second embodiment of the present invention.

FIG. 3 is a graph showing an excess air ratio and a residual oxygen concentration in a combustion gas.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Primary combustion chamber 2 Throttle part 3 Burner 4 Boiler combustion chamber (secondary combustion chamber) 5 Boiler water pipe 6 Air nozzle 7 Boiler combustion chamber outlet 8 Exhaust gas supply source 9 Blower 10 Boiler 11 Boiler water pipe 12 First regenerative heat exchange Unit 13 Second regenerative heat exchanger 14 Four-way valve

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02C 6/18 F02C 6/18 B 7/00 7/00 B F22B 1/18 F22B 1/18 R F23G 5 / 46 ZAB F23G 5/46 ZABZ 7/06 ZAB 7/06 ZABZ 103 103 F23L 15/02 F23L 15/02 (72) Inventor Kazuhiro Kawai 1-8-1 Koura, Kanazawa-ku, Yokohama-shi Yokohama, Mitsubishi Heavy Industries, Ltd. F term in the laboratory (reference) 3G071 BA10 DA08 FA06 HA05 JA03 3G081 BA11 BA18 BB00 BC07 BD00 DA14 3K023 QA02 QB02 QB10 QC07 3K065 AA23 AB01 AC19 BA04 JA05 JA18 3K078 AA04 BA02 BA10 BA22 CA02 CA09 CA13 CA22

Claims (4)

[Claims] 1. A first heat storage type heat exchanger and a second heat storage type heat exchanger each having a heat storage body having a passage communicating with the boiler combustion chamber at both ends of a cylindrical boiler combustion chamber provided with a water pipe. A fuel supply valve for supplying fuel to the boiler combustion chamber side of the regenerator is provided in each of these regenerative heat exchangers, and the exhaust gas passage of a diesel engine or a gas turbine is connected via a switching valve. An exhaust gas boiler connected to the both heat storage heat exchangers. 2. The switching of the switching valve causes the exhaust gas to communicate with the first regenerative heat exchanger or the second regenerative heat exchanger, and the exhaust gas communicates with one of the regenerative heat exchangers. The temperature of the exhaust gas is increased by heat exchange with the heat storage body of the heat exchanger, and the fuel is supplied from the fuel supply valve to the heated exhaust gas, and is ejected to the boiler combustion chamber together with the heated exhaust gas. Then, the combustion is performed in the high-temperature, low-oxygen-concentration gas whose temperature has been increased, and the combustion gas reaches the other regenerative heat exchanger while radiating heat to the water pipe provided in the boiler combustion chamber and lowering the temperature. After passing through the regenerative heat exchanger, the temperature is further lowered by heat exchange with the heat storage body, then discharged through the switching valve, and the switching of the switching valve and the fuel supply are alternately performed at predetermined time intervals. The fuel in the exhaust gas boiler according to claim 1, wherein Baking method. 3. A primary combustion chamber is provided in an exhaust gas passage of a diesel engine or a gas turbine, the primary combustion chamber is connected to a secondary combustion chamber via a throttle passage, and fuel is supplied to the primary combustion chamber. The primary combustion gas is supplied to perform primary combustion with excess fuel, and air is supplied to the primary combustion gas ejected from the throttle portion and ejected to the secondary combustion chamber to perform secondary combustion. An exhaust gas boiler, which is used as a heating source for a boiler water pipe. 4. The exhaust gas boiler according to claim 3, wherein a boiler water pipe is provided in the secondary combustion chamber.