JPS6176803A - Waste-heat recovery boiler - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to an exhaust heat recovery boiler equipped with a denitrification device.

[Background of the invention]

With recent changes in electricity demand, there is a growing trend toward the adoption of combined cycle plants that use gas turbines, which are easy to start, stop, and operate at low loads, and are suitable for intermediate load operation. In other words, the main purpose of conventional thermal power plants was base load operation, but with the rise of nuclear power, nuclear couplers are in charge of base load operation, and thermal power plants are required to shut down at night and operate at extremely low loads5. Became. In this case, for thermal power plants,
There is a strong demand for compliance with environmental regulations, that is, nitrogen oxide (1'JOX) control, not only during low-load operation but also when restarting after a shutdown. Normally, high-temperature gas is discharged from the gas turbine, and an exhaust heat recovery boiler is used to utilize this exhaust gas. However, since the exhaust gas contains a large amount of NQx, the exhaust heat recovery boiler is has a built-in denitrification device to reduce NO in flue gas.

Such an exhaust heat recovery boiler will be explained with reference to the drawings.

FIG. 7 is a system diagram of a conventional exhaust heat recovery boiler.

In the figure, 1 is a gas turbine, 2 is a silencer for extinguishing exhaust gas discharged from the gas turbine 1, and 3 is a duct of an exhaust heat recovery boiler into which the exhaust gas from the silencer 2 is introduced. 4 is a superheater that superheats steam; 5a and 5b are high-pressure evaporators that evaporate canned water; and 6 is a denitrification unit that removes NO from exhaust gas.

7 is a high-pressure economizer, 8 is a low-pressure evaporator that evaporates canned water, 9
& completed low-pressure economizers, and these are arranged in order in duct 3.
It has been fixed. For example, 10 is 60 Yu/c! D class high pressure drum, 11 leads canned water of high pressure drum 10<11 main pipe, 1
The second high-pressure water supply '11 and 13 are high-pressure riser pipes. 14 is, for example, a 9/i class low pressure drum, and 15 is a downcomer. In the exhaust heat recovery boiler π, a high-pressure system is constituted by a superheater 4, a high-pressure evaporator 5a + 5b, a high-pressure economizer 7, a drum 10, etc., a low-pressure evaporator 8, a low-pressure economizer 9, a drum 14 A low-pressure system is constructed by these high-pressure systems and low-pressure systems.
``q has been completed.

Here, an outline of the operation of the high pressure system of the exhaust heat recovery boiler will be explained. Exhaust gas discharged from the gas turbine 1 is supplied to a duct 3 via a silencer 2. On the other hand, the water supply
It is heated by exhaust gas in the low-pressure economizer 9Vc, supplied to the high-pressure economizer 7, further heated, and then introduced into the drum IOK. The canned water in the drum 10 is introduced into the high-pressure evaporators 5a, 5b via the downcomer pipe 11 and the high-pressure water supply pipe 12, where it is heated by exhaust gas and evaporated. The evaporated steam is introduced into the drum 10 via the high pressure riser pipe 13. The steam in the drum 10 is sent to the superheater 4, where it is heated and turned into superheated steam, which is then supplied to the steam turbine. The denitrification device 6 is installed between the two divided high-pressure evaporators 5a and 5b, and removes NOx contained in the passing exhaust gas, reduces NOx in the exhaust gas, and suppresses it below a regulation value.

By the way, the denitrification characteristics of the denitrification device 6 are largely dependent on the exhaust gas temperature. This is shown in FIG. In FIG. 8, the horizontal axis represents the exhaust gas temperature, and the vertical axis represents the denitrification rate. As is clear from the figure, effective denitrification occurs when the exhaust gas temperature is within a certain range (for example, about 00°C to about 400°C), and when the exhaust gas temperature is not within the above range, the denitrification rate of VC is extremely low. , and effective denitrification becomes impossible.

On the other hand, the characteristics of the exhaust gas emitted from gas turbines are
As shown in Figure 9, compared to the exhaust gas characteristics of conventional thermal power plants,
The amount of exhaust gas is large in the low load range, and.

It has a tendency to be low temperature. In Figure 9, the horizontal axis shows the load, and the vertical axis shows the exhaust gas amount and exhaust gas temperature.
Also, real iA, +'! Gas turbine exhaust gas amount, broken line A, +
2 Exhaust gas amount of conventional thermal power generation, solid line B1 is the gas turbine exhaust gas temperature, and broken line Bx is the exhaust gas temperature of conventional thermal power generation.

As mentioned in r4i1, gas turbines in particular are often started and stopped and operated at low load, and during the initial startup and low load operation, the amount of exhaust gas is large and the exhaust gas temperature is low, as shown in Figure 9 of iC&2. Become. In particular, at the initial stage of startup, the temperature of the gas turbine 1, silencer 2, inlet of the duct 3, superheater 4, high-pressure evaporator 5a, and denitrification device 6 itself, which are arranged upstream of the denitrification device 6, is decreasing.
The heat of the exhaust gas is taken away by these devices, and the non-gas temperature (1
Significant decline. Therefore, the exhaust gas temperature at the initial stage of startup and during low-load operation is outside the temperature range for effective denitrification shown in Figure 8, and effective denitrification is not performed, and combined with the large amount of exhaust gas, the total amount of NOx in the flue gas is reduced. The result is a dog-like scene that far exceeds the regulation value.

In order to eliminate such drawbacks, it is possible to install the denitrification device 6 in a high temperature range, but in that case, when operating in a steady load zone, the exhaust gas temperature will exceed the above effective denitrification temperature range. As in the case of low temperatures, effective denitrification is not performed, and since the denitrification equipment is installed in a high temperature area,
This results in the inconvenience that a high temperature resistant material must be used as the material constituting the.

[Purpose of the invention]

The present invention was made in view of these circumstances, and its purpose is to provide an exhaust heat recovery boiler that can effectively reduce NOx contained in exhaust gas even at the initial startup stage or during low-load operation. There is something to do.

[Summary of the invention]

In order to achieve the above object, the present invention is characterized in that the exhaust heat recovery boiler is provided with a steam supply means for supplying steam to the canned water entering the evaporator.

[Embodiments of the invention]

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a diagram of a waste heat recovery boiler according to a first embodiment of the present invention. In the figure, the same part If as shown in FIG.
( is given the same number 71 and the explanation is omitted.

16 is a boost pump used in a mixed pressure boiler, 17
A circulation connection d connecting the Hadram 10 and the boost pump 16, 18 is a mixing heater connected by the outlet VC line of the boost pump 16, and 19 is a steam system drawn from other systems. Steam from steam system 19 is supplied to mixing heater 18 and drum 10.

Before starting the boiler or during low-load operation, high-temperature canned water in the drum 10 is supplied to the boost pump 16. This canned water is pressurized by a boost pump 16 and sent to a mixing heater 18 . The sent canned water is mixed with steam from the steam system 19 in the mixing heater 18 to raise its temperature, and the heated canned water enters the drum 10 through the high-pressure evaporators 5a and 5b. In this way, the drum IO1 circulation connecting pipe 17, the boost pump 1
6, mixing heater 18, high pressure evaporator 5a, 5b,
To continue the circulation of the drum IO, the denitrification device 6
The temperature of the entire system including the high-pressure evaporator 5a and superheater 4 upstream of can be increased.

On the other hand, although it is easy to raise the temperature of canned water to a latg saturation temperature of 100°C, it takes time to raise the temperature and pressure to 200°C and about 16atg by simply injecting steam into the mixing heater 18. Therefore, from the steam system 19 to the drum 1
By supplying steam to the drum, the temperature can be raised quickly without increasing the drum pressure. Note that when the amount of canned water in the drum 10 increases due to steam injection, this is blown out of the system using a canned water reduction valve or the like.

Thus, the exhaust gas temperature at the inlet of the denitrification device 60 is sufficiently high (
Therefore, early injection of NH into the denitrification device 6 becomes possible, and NOx can be effectively removed.

FIG. 2 shows an example of temperature and pressure increase in this example. In the figure, the horizontal axis represents the time since startup, and the vertical axis represents the amount of exhaust gas, the total amount of NOx, and the temperature of the exhaust gas at the entrance of the denitrification device. In the figure, solid line C, Hatram pressure is 3
The exhaust gas temperature when the drum pressure is 0 atg is shown, and the dashed line C2 is the exhaust gas temperature when the drum pressure is 10 atg. Note that, taking into account the heat capacity of one can of water and metal, the required steam savings required to raise the temperature and pressure of the drum from atmospheric pressure to LOatg is approximately 1,000 tons. Two songs? /M C+ As is clear from C2, the higher the drum pressure, the higher the can water temperature and the higher the exhaust gas temperature at the inlet of the denitrification device 60. When the drum pressure is set to 30 atg, the exhaust gas temperature exceeds 200°C at startup, which is within the effective denitrification range. On the other hand, when the drum pressure is 10 atg, the exhaust gas temperature is 2
The temperature is below 00°C, and the temperature exceeds 200°C after a considerable amount of time has elapsed.

The broken line D+) indicates the amount of exhaust gas supplied via the gas turbine 1 and silencer 2. Also, real #j! F is the NO discharged from the boiler outlet when the drum pressure is 30 atg.
, total amount, and the dashed line F indicates the total amount of NOx when the drum pressure is 10 atg. E is the N0w regulation value. It is clear from the curve F1 that the drum pressure is 3 at startup.
In the case of 0 atg, the exhaust gas temperature exceeds 200° C., so denitrification is effectively performed and the total amount of NOx discharged does not exceed the regulation value. On the other hand, if the drum pressure is 1
If 0atg.

It takes a certain amount of time for the exhaust gas temperature to rise above 200°C, and before that, denitrification cannot be performed effectively.
As shown in the song G FtK, the NO and i-views emitted at the initial stage of startup will significantly exceed the regulation values. That is,
The higher the drum pressure, the faster the temperature rises, allowing for a quicker start-up. Incidentally, even when the drum pressure is 10 atg, the boiler can be started more quickly compared to conventional devices.

Figures 3 (al to (C)) are diagrams showing the characteristics of various quantities when the can water temperature at the time of boiler startup is room temperature.
In both cases, time is plotted on the horizontal axis, and time is plotted on the vertical axis.

In Figures 3(a) and (C), the total amount of NOx discharged (indicated by curve G') is shown, and in Figures 3(b) and (d), the exhaust gas temperature at the inlet of the denitration equipment (curve I, I') and exhaust gas amount (song #iiH, H')
It's great. Time T1 on the horizontal axis is when the gas turbine is ignited, time T, # "t" is when the gas turbine is added, and time '13 +T,' +s is when the plant is under full load. Figures 3 (a) and (b) This is the characteristic when the gas turbine is installed early. In this case, as is clear from the curve G, the total amount of N (J

After that, the NOx standard value indicated by 4g was exceeded for a considerable period of time. FIGS. 3(C) and 3(d) are characteristic diagrams when the turbine entry time is adjusted so that the total amount of NOx discharged does not exceed the NOx regulation value. In this case, the gas turbine joining time T2' is such that the exhaust gas temperature is 200
It must be adjusted when the temperature exceeds ℃.

Comparing this with the characteristics of this example, we can see that the NO
In the case of this embodiment, the startup time for starting the gas turbine while suppressing the NOx emissions to below the NOx regulation value can be reduced by about 3 hours compared to the conventional device.

In this example, a circulation system is provided in which canned water in the drum is circulated through a circulation connection pipe, a boost pump, a mixing heater, and a high-pressure evaporation pipe, and steam is supplied to the drum and mixing heater. Since the temperature inside the system is raised, the exhaust gas temperature at the denitrification equipment inlet can be kept within the denitrification effective range during startup or low-load operation, making it possible to effectively reduce NOx. , the startup time of the gas turbine can be significantly reduced. Furthermore, since the above-mentioned circulation system was installed and steam was introduced into this system, the amount of steam in the system (compared to when hot water was directly supplied to the evaporator) was reduced without installing a circulation system. Heating can be done uniformly and sufficiently.Furthermore, since the mixing heater is heated by 4 people instead of 5 people, it is possible to suppress the need to photograph the structure.

FIG. 4 is a schematic diagram of the configuration of the header portion of the evaporation tube of the exhaust heat recovery boiler according to the second embodiment of the present invention.

In the figure, 5a and 5b are the same high-pressure evaporators as shown in FIG. 1, 20 is the header of the high-pressure evaporators 5a and 5b, and 21 is each evaporator tube connected to the header. 22 is a steam mixing pipe inserted into the header area, 23 is a steam outlet formed in the steam mixing pipe 4, and 23 is a steam communication pipe.

The steam jet ports are formed at the same pitch toward the inlet of each evaporator pipe 210 at the upper part of the steam mixing pipe section. Canned water from the drum IO shown in FIG. 1 is directly introduced into the header, and steam from the steam system 19 shown in FIG. 1 is directly introduced into the steam communication pipe. That is, in this embodiment, the mixing heater 18 and booster pump 16 shown in FIG. 1 are not used. In this embodiment, the temperature of the canned water is raised by the steam ejected from the steam outlet of the steam mixing pipe 22 at the header J. The other components and operations of 474 are the same as those of the embodiment shown in FIG.

In this way, in this embodiment, canned water is introduced into the header of the evaporator, and steam is mixed into it to raise the temperature, so that the same effect as in the first embodiment (however, the mixing heater In addition, since the boost pump and mixing heater are removed, the configuration can be simplified.

FIG. 5 is a system diagram of a waste heat recovery boiler according to a third embodiment of the present invention. In the figure, parts that are the same as those shown in FIG.

26 is a steam turbine; 27 is a main steam pipe that supplies steam from the superheater 4 to the steam turbine A; and 27 is a steam turbine control valve that adjusts the amount of steam to the steam turbine A.

29 is a turbine bypass pipe that bypasses the steam turbine 26, chrysanthemum is a turbine bypass valve that adjusts the amount of steam in the turbine bypass pipe 29, and 31 is a condenser.

These devices are already installed in the boiler equipment.

During boiler operation, steam superheated in superheater 4 is transferred to main steam pipe 2.
The power is supplied to the steam turbine through the steam turbine control valve 7 to generate electricity. Steam discharged from the steam turbine 26 is sent to the condenser 31, and is supplied as feed water to the low pressure economizer 9 by a condensate pump (not shown). The amount of steam supplied to the steam turbine is adjusted by the steam turbine control valve 28, and excess steam passes through the turbine bypass pipe section and is directly discharged to the condenser 31 via the turbine bypass valve. The main steam pipe, the steam turbine control valve, the turbine bypass pipe section, the turbine bypass valve, and the condenser 31 are all already installed.

Now, as described above, in order for the denitrification device 6 to perform effective denitration, the exhaust gas temperature at the inlet of the denitrification device 60 must be at a high temperature within the eaves.

Here, considering the case when the boiler is restarted after being stopped, if the temperature of the hot water in the pool is quite high at the time of restart, the exhaust gas temperature will also be high, and the steam in the steam system 19 will be used. The exhaust gas temperature can be raised to a high temperature in a short time. This example is.

Not yet 1. In addition to the means of the second embodiment, a method of maintaining the exhaust gas temperature at a high temperature upon restart is also used. This method will be explained below with reference to FIG.

In FIG. 6, the horizontal axis represents time, and the vertical axis represents drum pressure. When the boiler is stopped, in the conventional stopping method, when the gas turbine 1 enters the stopping process, the pressure in the drum 10 decreases from the pressure P0 as shown by the solid line J in FIG. 1, the pressure decreases to P at T4. In this state, the boiler banking state is entered. During banking, the boiler is cooled down by natural heat radiation.

The pressure of the drum [0 is further reduced to the pressure P1.

Therefore, at the boiler restart time T, the drum pressure is at an extremely low pressure P, and the temperature of the canned water is also low.

On the other hand, the method of this embodiment employs a method different from the conventional method described above. That is, in the plant shutdown process, the amount of steam dumped to the condenser 31 via the turbine bypass pipe section is reduced by applying a turbine bypass valve. As a result, the pressure in the drum 10 is increased by the two-dot chain line J in FIG.
′, and at time T, when the boiler banking state is entered, the pressure is increased to P. As mentioned above, the boiler is cooled during banking, and the drum pressure also decreases as shown by the two-dot chain line J'. However, the drum pressure that was increased to pressure P3 at the start of boiler banking T4, even if the pressure decreases due to cooling during banking, at the time 1414 when the boiler is restarted,
Pressures P and K are maintained much higher than the conventional pressure P2. As a result, the hot water temperature is maintained at a high temperature, and the amount of heat taken from the exhaust gas when the boiler is restarted is significantly reduced, making it possible to maintain the temperature of the exhaust gas at a high temperature, with a small amount of steam.

Moreover, the exhaust gas temperature can be raised to a high temperature in a short time.

In addition, in order to prevent the increase in drum pressure due to throttling of the turbine bypass valve J from exceeding the allowable pressure, a pressure detector is installed to detect the drum pressure, and the opening between the turbine bypass valves is controlled accordingly. A means may also be provided.

In this way, in this example, since the method of increasing the drum pressure when the boiler is stopped is also used, it not only achieves the same effect as the example in Eki 1, but also reduces the amount of steam used. The exhaust gas temperature can be raised in a short time. Further, even if steam from another system to be supplied to the steam system cannot be obtained for some reason, NO can be sufficiently reduced by using the above method in combination.

In addition, in the description of the above embodiment, a gas turbine has been described as an exhaust gas source, but the exhaust gas source is not limited to a gas turbine, and can be applied to an industrial furnace, an industrial processing facility, or the like. Furthermore, although an example in which a booster pump is used as a circulation pump has been described, a pump is not necessary in the case of natural circulation.

Even when using a pump, it is not limited to a boost pump, and a water supply pump can also be used. Of course, a circulation pump may be used in addition to the existing pump.

〔Effect of the invention〕

As described above, in the present invention, canned water in the drum is circulated through the evaporator, and steam is supplied to the evaporator inlet and the drum to heat the circulating water and increase the drum pressure. Therefore, the temperature of the exhaust gas at the inlet of the denitrification device can be maintained at a high temperature even at the initial stage of startup or during low-load operation, thereby making it possible to effectively reduce NO contained in the exhaust gas.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an exhaust heat recovery boiler according to the first embodiment of the present invention, FIGS. 2 and 3 (a), (b), (C),
(d) is a characteristic diagram of exhaust gas amount, exhaust gas temperature, and total amount of NOx, FIG. 4 is a schematic diagram of a part of the exhaust heat recovery boiler according to the second embodiment of the present invention, and FIG. Fig. 6 is a characteristic diagram of drum pressure, Fig. 7 is a system diagram of a conventional waste heat recovery boiler, Fig. 8 is a characteristic diagram of denitrification rate, Fig. 9 is a characteristic diagram of exhaust gas amount S and exhaust gas temperature. 1... Gas turbine, 4... Superheater,
5a, 5b...Evaporator, 6...Denitration device, 7...High pressure economizer, 9...Low pressure economizer, 10, 14. ...Drums, 16...
... Boosting pump, 17 ... Circulation connecting pipe, 18
...Mixing heater, 19 ... Steam system, m ... Header, 21 ... Evaporator tube,
n...Steam mixing pipe, a...Steam communication pipe. 26...Steam turbine, 28...Steam turbine control valve, 29...Turbine bypass pipe, adjustment...Turbine bypass valve, 31...
・Double water device. Fig. 1 M'1 Fig. 2 □ Drum pressure 3 () atg Face leap (mod) Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 #P push storm ('C) - Chapter Figure 9 Load (%n)

Claims (1)

[Claims] 1. Exhaust heat recovery comprising an evaporator heated by exhaust gas, a drum for steam generation connected to the evaporator, and a denitrification device for removing nitrogen oxides from the exhaust gas. An exhaust heat recovery boiler 2 characterized in that the boiler is provided with a steam supply means for supplying steam to the can water entering the evaporator. An exhaust heat recovery boiler 3 characterized in that it includes a mixing heater for mixing steam into the boiler, and in claim 1, the steam supply means includes a steam mixing pipe inserted into the header of the evaporator. An exhaust heat recovery boiler characterized by