JPS61180819A - Denitration of burnt exhaust gas in waste heat recovery boiler - Google Patents

Abstract

PURPOSE:To keep high denitration power and reduce NOx concentration in exhaust gas by installing a denitration device in such a manner that reducing agent is injected into exhaust gas from many jet nozzles and then mixed fluid of reducing agent and exhaust gas is denitrated by passing through a reactor. CONSTITUTION:A denitration device is composed of reducing agent injection nozzles 32 which inject reducing agent such as ammonia gas from reducer system into exhaust gas and a reactor where exhaust gas with injected reducing agent is reacted through the catalyst layer of iron oxide system and said gas is reduced and decomposed into nitrogen and steam. Dampers 38 control the flow rate of gas passing through it and make uniform the flowing volume into the catalyst layer 41. The reactor 31 is composed of the catalyst layer 41 loaded with catalyst of iron oxide system, support members 35 and partition plate 37. When the exhaust gas flowing down from the dampers 38 flows up through the catalyst layer 41 from the under side of support members 35, NOx is decomposed by the action of catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for denitrating combustion exhaust gas in an exhaust heat recovery boiler that uses the combustion exhaust gas of a gas turbine device as a heat source to generate driving steam for another steam motor.

FIG. 1 shows a combined cycle plant comprising a conventional gas turbine device 10, an exhaust heat recovery boiler 20 that generates steam using its combustion exhaust gas as a heat source, and a steam turbine device W40 that uses the generated steam as driving steam. It shows. Here, the exhaust heat recovery boiler 20 is connected to a superheater 21 . It is equipped with an evaporator 229, a economizer 23, and a chimney 24, and the steam generated in the superheater 21 is transferred to the pipe 2.
Through the steam turbine installation! ! 40 and a generator 41 takes a load thereon, and feed water from the steam turbine device 40 is led to the economizer 23 through the pipe 1.

The gas turbine device 1o also includes a compressor 11 that pressurizes introduced air 4, a combustor 14 that adds fuel supplied from a fuel system 5 to the pressurized air, and combusts the fuel, and a combustion gas generated by combustion. It comprises a turbine 12 to be operated, a generator 13 to take up the load, and a water or steam injection system 7 to reduce the NOx concentration in the combustion gases. In a combined cycle plant having these configurations, water or steam is introduced into the combustor 14 through the system 7 as a measure to reduce the concentration of NOx contained in the exhaust gas discharged from the gas turbine system [10]. .

However, as shown in FIG. 2, if the amount of injected water or steam is increased in order to reduce NOx emissions, the gas turbine equipment f! The thermal efficiency at 10 will be reduced. Furthermore, when the total amount of NOx emissions is regulated, it becomes difficult to achieve the regulated value using NOx reduction means such as steam injection. For this purpose, it has been considered to install a denitrification device in the combustion gas stream, but one method of denitration, the dry catalytic reduction cracking method, involves injecting ammonia into the combustion gas and using an iron oxide catalyst. This method reduces and decomposes NOx into harmless nitrogen and water vapor by passing it through a filled reactor. In this denitrification method, as shown in FIG. 3, it is known that the denitrification efficiency largely depends on the reaction temperature of the catalyst layer, that is, the temperature of the combustion gas passing through the catalyst layer of the denitrification device. In other words, as is clear from Fig. 3, the denitrification efficiency increases rapidly as the reaction temperature rises from 200°C to 300°C;
At 0°C, the denitrification efficiency approaches the highest, and
It is said that if the temperature exceeds 00°C, there will be a problem with the life of the catalyst.

On the other hand, in the exhaust heat recovery boiler 20 of the combined cycle plant shown in FIG. 1, as shown in FIG.
1. The heat is recovered by sequentially flowing down the evaporator 229 and the economizer 23, and the temperature is lowered to about 200° C. before being discharged. Conversely, boiler feed water is heated and converted to steam at approximately 450°C.

Therefore, even if the denitrification device is installed on the outlet side of the waste heat recovery boiler, the exhaust gas temperature is around 200°C, so the denitrification efficiency will be low, as is clear from the temperature characteristics of the denitrification device shown in Figure 3. If the temperature is too high, the desired NOx reduction value cannot be achieved.

Furthermore, if the denitrification device is installed on the inlet side of the exhaust heat recovery boiler, the exhaust gas temperature will be as high as 500° C. or higher, which will cause problems such as the heat resistance of the reactor filled with the catalyst and a reduction in the life of the catalyst.

On the other hand, there is a problem in that sufficient denitrification performance cannot be obtained unless the reducing agent is uniformly mixed in the exhaust gas passing through the reactor.

An object of the present invention is to provide a denitrification method that maintains high denitrification performance and reduces the NOx concentration in exhaust gas in an exhaust heat recovery boiler having a denitrification device.

A feature of the present invention is that in an exhaust heat recovery boiler device equipped with an evaporator that guides combustion exhaust gas discharged from a gas turbine device as a heat source and uses the exhaust gas to evaporate feed water, a portion immediately downstream of the evaporator contains nitrogen in the exhaust gas. A reactor having a catalyst layer for removing Ox components is installed, a reducing agent injection nozzle having a large number of nozzles in a plane intersecting the flow of exhaust gas is provided on the upstream side of the reactor, and a reducing agent injection nozzle is installed in the exhaust gas from the many nozzles. After a reducing agent is injected into the reactor, a mixed fluid of the reducing agent and exhaust gas is introduced into the reactor for denitrification.

Next, an example of a combined cycle plant equipped with an exhaust heat recovery boiler that implements the method of the present invention will be described.

In FIG. 5, the combined cycle plant includes a gas turbine device 10, an exhaust heat recovery boiler 20 that generates steam using exhaust gas discharged from the gas turbine device as a heat source,
A steam turbine device j40 that is driven by steam generated in a boiler and a gas turbine device! ! The denitrification device 30 removes NOx from the exhaust gas discharged from the fio.

The gas turbine device 10 includes a compressor 11 that pressurizes introduced air, a combustor 14 that uses pressurized air to combust fuel supplied from a combustion system, a gas turbine 12 that is driven by combustion gas generated by combustion, and a load. Generator 1 that takes
It has 3.

Further, the exhaust heat recovery boiler 20 includes a superheater 21 along the upstream to downstream of the exhaust gas flow led from the gas turbine device 1o.
．． It has an evaporator 221, a economizer 23, and a chimney 24,
The steam generated in the superheater 21 is passed through the pipe 2 to the steam turbine! 40, and a generator 41 takes the load. And a steam turbine! ! From 40, the water supply is led to the economizer 23 through the pipe 1. Furthermore, a denitrification device 30 is installed immediately downstream of the evaporator 22 of the exhaust heat recovery boiler device 20, that is, between it and the economizer 23. The structure of this denitrification device 30 will be explained using FIG. 6.

Denitration bag! l! 30 is a reducing agent injection nozzle 32 that spouts a reducing agent such as ammonia gas from a reducing agent system 36 into the exhaust gas from a large number of nozzles, and the exhaust gas injected with the reducing agent is reacted through an iron oxide catalyst layer 41 to generate nitrogen. The reactor 31 is equipped with a reactor 31 for reductive decomposition into water vapor and water vapor. That is,
A nozzle 32 for spouting a reducing agent is installed downstream of the exhaust gas flow from the evaporator 22 in the exhaust heat recovery boiler 20, and the exhaust gas mixed with the reducing agent here is divided into three flow paths by three dampers 38. and flows down to the catalyst layer 41. The damper 38 controls the amount of exhaust gas flowing down through the damper 38 to
The amount of inflow into the area is made uniform.

In addition, the reactor 31 has a catalyst layer 4 filled with an iron oxide catalyst.
1, a supporting member 35, and a partition plate 37. When the exhaust gas flowing down from the damper 38 flows upward through the catalyst layer 41 from below the support member 35, NOx is decomposed by the action of the catalyst.

The exhaust gas from which NOx has been removed in the reactor 31 then flows down to the economizer 23 through an expansion joint. The operation of the exhaust heat recovery boiler having the above configuration will be explained.

5 and 6, the gas turbine inlet air 4
After being pressurized by the compressor 11, the fuel is combusted in the combustor 14 to become high-temperature combustion gas, which drives the gas turbine 12. After that, the combustion exhaust gas is introduced into the exhaust heat recovery boiler 2o, but this exhaust gas flows into the superheater 21 at about 550°C, and after passing through the evaporator 23, the temperature reaches about 330°C, and then enters the denitrification device 3o. There will be an influx. Inside the denitrification device 3o, the reducing agent is first injected into the exhaust gas from multiple nozzles of the nozzle 32 to mix it uniformly, and then the exhaust gas flowing into the reactor 31 is made to flow into the reactor 31 through the damper 38. The flow rate is controlled by the damper 38,
It flows into each of the multistage catalyst layers 41 almost uniformly. In this catalyst layer 41, N in the exhaust gas is
Ox is reduced and decomposed into harmless nitrogen and water vapor by the action of the catalyst, and the exhaust gas from which most of the NOX components have been removed passes through the downstream energy saver and is discharged from the chimney 24.

The boiler 20 uses this exhaust gas as a heat source to vaporize feed water and drive the steam turbine device 40.

In the denitrification device 30, the exhaust gas temperature is as high as approximately 330°C, so as is clear from Fig. 3, the denitrification rate is 90%.
It gets higher than that. This shows that the denitrification device can be downsized if the NOx emission standards are at the same level as conventional ones. Additionally, the amount of water or steam injected can be reduced to reduce NOx.

The thermal efficiency of combined cycle plants can also be improved.

Furthermore, as shown in FIG. 6, the reducing agent such as ammonia gas is injected into the exhaust gas from a nozzle 32 having a large number of nozzles in a plane that intersects with the exhaust gas flow, so that the reducing agent can be easily mixed with the exhaust gas evenly. , the denitrification performance within the reactor 31 is improved.

According to the method of the present invention, the exhaust gas is introduced into the reactor at a temperature position where the denitrification efficiency of the catalyst is maximized;
Combined with the fact that the reducing agent is uniformly mixed with the exhaust gas, high denitrification efficiency can be achieved.

[Brief explanation of the drawing]

Figure 1 is a system diagram of a known combined cycle plant, Figure 2 is a characteristic diagram showing the relationship between water injection amount and thermal efficiency, and Figure 3 is a diagram showing the relationship between water injection amount and thermal efficiency.
Figure 4 is a temperature characteristic diagram of denitrification efficiency, and Figure 5 is a characteristic diagram showing the relationship between exhaust gas temperature and feed water temperature in the exhaust heat recovery boiler.
6 and 6 show an exhaust heat recovery boiler for carrying out the method of the invention. Figure 5 is a system diagram of a combined cycle plant, and Figure 6 is:
It is a partial structural diagram of an exhaust heat recovery boiler. 10... Gas turbine device, 20... Exhaust heat recovery boiler. 21... Superheater, 22... Evaporator, 23... Carbon saver, 30... Denitration device, 31... Reactor, 32...
- Reducing agent injection nozzle, 41...catalyst layer. 12th side ・′:ze Iji・2in・・shi] No. 1 Country's first tongue 9λ travel distance 1: God 1'6 = ratio of injection amount (oA) No. 3 → reaction temperature (°C) No. ! 5th Procedural Amendment Form C) Showa 6 Ru 8137

Claims (1)

[Claims] 1. In an exhaust heat recovery boiler having an evaporator that guides combustion exhaust gas discharged from a gas turbine device as a heat source and evaporates feed water using the amount of heat contained in the exhaust gas, with respect to the flow of the exhaust gas, A reactor with a catalyst layer for removing NOx components in exhaust gas is installed on the side,
A reducing agent injection nozzle having a large number of nozzles in a plane intersecting the flow of the exhaust gas is provided on the upstream side of the reactor, and after the reducing agent is injected into the exhaust gas from the multiple nozzles, a mixed fluid of the reducing agent and the exhaust gas is injected. A method for denitrating combustion exhaust gas in an exhaust heat recovery boiler, characterized in that the denitration is performed by introducing the nitrogen into the reactor.