Flue gas circulation system for coal-fired power plant boiler

Abstract

The utility model provides a flue gas circulation system for a coal-fired power plant boiler, and relates to the technical field of coal-fired power generation, the flue gas circulation system comprises a cyclone separator, a first flue gas extraction pipeline, a second flue gas extraction pipeline and a flue gas distribution branch, an inlet of the first flue gas extraction pipeline communicates with an inlet of a tail flue, and an outlet of the second flue gas extraction pipeline communicates with an outlet of a tail flue; an outlet of the first flue gas extraction pipeline is communicated to a first inlet of the cyclone separator, an inlet of the second flue gas extraction pipeline is communicated to a flue of an air preheater outlet of a tail flue, an outlet of the second flue gas extraction pipeline is communicated to a second inlet of the cyclone separator, and an outlet of the cyclone separator is communicated to an inlet of the flue gas distribution branch; and an outlet of the flue gas distribution branch is communicated to the main combustor. According to the coal-fired unit, the air temperature and the oxygen content during pulverized coal combustion are adjusted by using the flue gas after the tail flue at the outlet of the hearth and the air preheater, and safe and stable combustion of the pulverized coal under the full-load working condition of the coal-fired unit is achieved.

Description

Technical Field

[0001] This utility model relates to the technical field of coal-fired power generation, and in particular to a flue gas recirculation system for a coal-fired power plant boiler. Background Technology

[0002] With the continuous expansion of installed capacity of fluctuating new energy sources such as wind power and photovoltaics, the intermittency and randomness of their power output pose a severe challenge to grid stability. Against this backdrop, coal-fired power units need to transition to a flexible operating mode, freeing up power generation space for new energy consumption through deep peak shaving. However, a sudden drop in pulverized coal concentration under deep peak shaving conditions can easily lead to combustion instability. The existing solution involves installing a pulverized coal separator before the burner to separate the primary air pulverized coal into concentrated and diluted phases, increasing the pulverized coal concentration at the main burner inlet and promoting continuous and stable combustion. The separated diluted pulverized coal is then fed into the furnace via a waste gas burner, ensuring the total heat provided by the pulverized coal entering the furnace. However, this technology has significant drawbacks: when operating at high loads, if the separator continues to run, the concentration of pulverized coal entering the main combustion zone increases, which intensifies combustion, leading to overheating and coking, as well as a surge in NOx generation. If the valve of the light phase branch of the external pulverized coal separator is closed to prevent it from operating, the valve cannot be completely closed, resulting in air leakage, which will also increase the concentration of pulverized coal entering the main combustion zone. If a conventional flue gas recirculation system is used to extract low-temperature, low-oxygen flue gas to cool the main combustion zone, although coking under high loads can be suppressed, it will affect the stable combustion capability under low loads. Utility Model Content

[0003] In view of this, this application provides a flue gas recirculation system for coal-fired power plant boilers, aiming to develop anti-coking technology that is compatible with external pulverized coal separators and can also take into account their low-load stable combustion function, so as to achieve safe and stable combustion of pulverized coal under full load of coal-fired units.

[0004] This application provides a flue gas recirculation system for a coal-fired power plant boiler. The coal-fired power plant boiler includes an external pulverized coal separator, a main burner, a furnace body, and a tail flue. The inlet of the external pulverized coal separator is connected to a primary air / pulverized coal flow pipeline, and the concentrated pulverized coal outlet of the external pulverized coal separator is connected to the pulverized coal flow inlet of the main burner. The main burner is located in the furnace chamber of the furnace body. The inlet of the tail flue is connected to the furnace chamber outlet of the furnace body. The flue gas recirculation system includes a cyclone separator, a first flue gas extraction pipeline, a second flue gas extraction pipeline, and a flue gas distribution branch. The inlet of the first flue gas extraction pipeline... The first flue gas extraction pipe is connected to the inlet of the tail flue, the outlet of the first flue gas extraction pipe is connected to the first inlet of the cyclone separator, the inlet of the second flue gas extraction pipe is connected to the flue of the air preheater outlet of the tail flue, the outlet of the second flue gas extraction pipe is connected to the second inlet of the cyclone separator, the outlet of the cyclone separator is connected to the inlet of the flue gas distribution branch, the outlet of the flue gas distribution branch is connected between the pulverized coal airflow inlet of the main burner and the concentrated pulverized coal outlet of the external pulverized coal separator, and / or, the outlet of the flue gas distribution branch is connected to the secondary air inlet of the main burner.

[0005] Preferably, the external coal pulverizer includes: a waste steam burner, the inlet of which is connected to the light coal pulverizer outlet of the external coal pulverizer, the outlet of which is connected to the furnace of the furnace body, and the waste steam burner is located above the main burner.

[0006] Preferably, the external pulverized coal separator includes at least two, the main burner includes at least two, and the flue gas distribution branch includes at least two, wherein the number of external pulverized coal separators is the same as the number of main burners, the number of flue gas distribution branches is the same as the number of main burners, the outlet of each flue gas distribution branch is connected to the pulverized coal airflow inlet of the main burner and the concentrated pulverized coal outlet of the external pulverized coal separator, and / or, the outlet of each flue gas distribution branch is connected to the secondary air inlet of the main burner, and the inlets of all flue gas distribution branches are connected to the outlet of the cyclone separator.

[0007] Preferably, the tail flue includes a tail vertical flue and an SCR denitrification system. The inlet of the tail vertical flue is connected to the furnace outlet, and the outlet of the tail vertical flue is connected to the inlet of the SCR denitrification system. The air preheater is arranged downstream of the SCR denitrification system.

[0008] Preferably, the air preheater is located downstream of the SCR denitrification system along the flue gas flow direction.

[0009] Preferably, the flue gas recirculation system further includes: a first fan, installed on the first flue gas extraction pipeline, for extracting flue gas from the furnace outlet and transporting it to the cyclone separator; and a second fan, installed on the second flue gas extraction pipeline, for extracting flue gas from the downstream side of the air preheater and transporting it to the cyclone separator.

[0010] Preferably, the flue gas recirculation system further includes a valve disposed on the flue gas distribution branch for controlling the flow rate of flue gas drawn from the cyclone separator.

[0011] Preferably, the main burner is a swirl burner or a direct-flow burner.

[0012] Preferably, the boiler combustion method of the coal-fired power plant boiler is tangential combustion or counter-firing combustion.

[0013] This application provides a flue gas recirculation system for a coal-fired power plant boiler, relating to the technical field of coal-fired power generation. The system includes a cyclone separator, a first flue gas extraction pipeline, a second flue gas extraction pipeline, and a flue gas distribution branch. The inlet of the first flue gas extraction pipeline connects to the inlet of the tail flue, and the outlet of the first flue gas extraction pipeline connects to the first inlet of the cyclone separator. The inlet of the second flue gas extraction pipeline connects to the flue at the outlet of the air preheater in the tail flue, and the outlet of the second flue gas extraction pipeline connects to the second inlet of the cyclone separator. The outlet of the cyclone separator connects to the inlet of the flue gas distribution branch, and the outlet of the flue gas distribution branch connects to the main burner. This application, by using the flue gas from the furnace outlet tail flue and the air preheater, regulates the air temperature and oxygen content during pulverized coal combustion, aiming to achieve safe and stable pulverized coal combustion in coal-fired units under full load conditions.

[0014] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This invention provides a schematic diagram of the structure of a flue gas recirculation system for a coal-fired power plant boiler, according to an embodiment of this application.

[0017] Figure 2This is a second schematic diagram of the structure of a flue gas recirculation system for a coal-fired power plant boiler provided in an embodiment of this application.

[0018] Reference numerals: 101-Furnace body; 102-Tail flue; 201-Cyclone separator; 202-First flue gas extraction pipeline; 203-Second flue gas extraction pipeline; 204-Flue gas distribution branch; 205-Pulverized coal external separator; 206-Main burner; 207-Exhaust steam burner; 208-Two high-temperature superheaters; 209-Air preheater; 210-First fan; 211-Second fan; 212-Low-temperature reheater; 213-High-temperature reheater; 214-Economizer; 215-SCR denitrification system; 216-Two screen-type superheaters; 217-Low-temperature superheater; 218-Valve. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0020] In the description of the embodiments of this application, it should be noted that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the utility model product is in use. They are only for the convenience of describing the utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the utility model. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0021] Furthermore, terms such as "horizontal" and "vertical" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0022] In the description of the embodiments of this application, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0023] like Figure 1 As shown in the figure, this application provides a flue gas recirculation system for a coal-fired power plant boiler. The coal-fired power plant boiler includes an external pulverized coal separator 205, a main burner 206, a furnace body 101, and a tail flue 102. The inlet of the external pulverized coal separator 205 is connected to the primary air pulverized coal flow pipeline, and the pulverized coal flow inlet of the main burner 206 is connected to the concentrated pulverized coal outlet of the external pulverized coal separator 205. The main burner 206 is installed on the furnace chamber of the furnace body 101.

[0024] The flue gas recirculation system includes a cyclone separator 201, a first flue gas extraction pipeline 202, a second flue gas extraction pipeline 203, and a flue gas distribution branch 204.

[0025] Here, the inlet of the first flue gas extraction pipe 202 is connected to the inlet of the tail flue 102, and the outlet of the first flue gas extraction pipe 202 is connected to the first inlet of the cyclone separator 201 for dust removal and mixing. The inlet of the second flue gas extraction pipe 203 is connected to the downstream side of the air preheater of the tail flue 102, and the outlet of the second flue gas extraction pipe 203 is connected to the second inlet of the cyclone separator 201. The outlet of the cyclone separator 201 is connected to the inlet of the flue gas distribution branch 204, and the outlet of the flue gas distribution branch 204 is connected between the pulverized coal airflow inlet of the main burner 206 and the concentrated pulverized coal outlet of the external pulverized coal separator 205, and / or, the outlet of the flue gas distribution branch 204 is connected to the secondary air inlet of the main burner 206.

[0026] The flue gas recirculation system also includes: exhaust steam burner 207, air preheater 209, and SCR denitrification system 215.

[0027] The inlet of the exhaust steam burner 207 is connected to the light pulverized coal outlet of the external pulverized coal separator 205, and the outlet of the exhaust steam burner 207 is connected to the furnace of the furnace body 101. The exhaust steam burner 207 is located above the main burner 206.

[0028] As an example, this application can extract flue gas from the furnace body 101 and return it to the primary air pulverized coal flow of the main burner 206 equipped with an external pulverized coal separator 205. By adjusting the temperature and flow rate of the circulating flue gas to cope with different furnace body 101 loads, the high-temperature flue gas returned under low load promotes the thermal desorption of volatiles from the primary air pulverized coal flow and provides reaction activation energy for pulverized coal ignition, thereby promoting stable combustion. Under high load, the low-temperature flue gas returned reduces the combustion temperature and dilutes the combustion oxygen, thereby inhibiting coking and NOx formation. Under low load conditions, the temperature of the circulating flue gas returned to the primary air pulverized coal flow is above 600°C, while under high load conditions, the temperature of the circulating flue gas returned to the primary air pulverized coal flow is below 400°C.

[0029] As an example, the main burner 206 is a swirl burner or a direct-flow burner, and the boiler combustion method of the coal-fired power plant boiler is tangential combustion or counter-current combustion.

[0030] In a preferred embodiment of this application, the external coal pulverizer separator 205 includes at least two, the main burner 206 includes at least two, and the flue gas distribution branch 204 includes at least two. The number of external coal pulverizer separators 205 is the same as the number of main burners 206, and the number of flue gas distribution branches 204 is the same as the number of main burners 206. The outlet of each flue gas distribution branch 204 is connected between the coal pulverizer airflow inlet of the main burner 206 and the concentrated coal pulverizer outlet of the external coal pulverizer separator 205, and / or, the outlet of each flue gas distribution branch 204 is connected to the secondary air inlet of the main burner 206. The inlets of all flue gas distribution branches 204 are connected to the outlet of the cyclone separator 201.

[0031] In a preferred embodiment of this application, the tail flue 102 includes a tail vertical flue and an SCR denitrification system 215. The inlet of the tail vertical flue is connected to the outlet of the furnace body, and the outlet of the tail vertical flue is connected to the inlet of the SCR denitrification system. The air preheater 209 is arranged downstream of the SCR denitrification system 215.

[0032] like Figure 2 As shown, in a preferred embodiment of this application, the flue gas recirculation system further includes: two high-temperature superheaters 208, a first fan 210, a second fan 211, a valve 218, a high-temperature reheater 213, a low-temperature reheater 212, an economizer 214, two screen-type superheaters 216, and a low-temperature superheater 217.

[0033] Two high-temperature superheaters 208 are installed in the vertical flue at the rear and arranged side by side along the flue gas flow direction in the vertical flue at the rear.

[0034] Air preheater 209 is installed on the third vertical flue.

[0035] The inlet of the first flue gas extraction pipe 202 is connected to the two high-temperature superheaters 208 in the tail vertical flue, and the inlet of the second flue gas extraction pipe 203 is connected to the air preheater 209 and the outlet of the third vertical flue.

[0036] The first fan 210 is installed on the first flue gas extraction pipeline 202 to extract flue gas from the tail vertical flue and transport it to the cyclone separator 201.

[0037] The second fan 211 is installed on the second flue gas extraction pipeline 203 to extract flue gas downstream of the air preheater 209 and deliver it to the cyclone separator 201.

[0038] Valve 218 is installed on flue gas distribution branch 204 to control the flow rate of flue gas drawn from cyclone separator 201.

[0039] The high-temperature reheater 213 is installed in the vertical flue at the tail end.

[0040] The low-temperature reheater 212 is installed in the tail vertical flue and is arranged sequentially with the high-temperature reheater 213 along the flue gas flow direction in the tail vertical flue. The low-temperature reheater 212 is located downstream of the high-temperature reheater 213.

[0041] Economizer 214 is installed in the vertical flue at the tail end and is located downstream of low-temperature reheater 212.

[0042] Two screen-type superheaters 216 are installed at the outlet of the furnace body 101 and are arranged sequentially along the flue gas flow direction.

[0043] The low-temperature superheater 217 is located in the tail vertical flue and at the same height as the low-temperature reheater 212 and the economizer 214 in the tail vertical flue.

[0044] As an example, the flue gas recirculation system also includes a third flue gas extraction pipeline and a fourth flue gas extraction pipeline.

[0045] The inlet of the third flue gas extraction pipeline is connected to the tail vertical flue and is located between the high-temperature reheater 213 and the low-temperature reheater 212. The outlet of the third flue gas extraction pipeline is connected to the third inlet of the cyclone separator 201, and a fan is installed on the third flue gas extraction pipeline for extracting flue gas.

[0046] The fourth flue gas extraction pipeline has its inlet connected between the economizer 214 and the SCR denitrification system 215, and its outlet connected to the fourth inlet of the cyclone separator 201. A fan is installed on the fourth flue gas extraction pipeline to extract flue gas.

[0047] In actual operation, the circulating flue gas entering the furnace can be controlled by adjusting the output of the fans on multiple flue gas extraction pipelines to control the amount of flue gas extracted, thereby regulating the temperature of the mixed flue gas. The amount of circulating flue gas fed into the primary air pulverized coal thickener is adjusted by valve 218 on the circulating flue gas branch after the cyclone separator 201, thereby adjusting the temperature and oxygen concentration of the primary air pulverized coal flow into the furnace, and thus regulating the combustion temperature inside the furnace.

[0048] Compared to other technologies, this application can improve the flexible operation capability of coal-fired power units. When the unit is operating at high load, the flue gas can be controlled to be returned to the primary air-enriched pulverized coal flow before entering the main burner at a lower temperature, thereby cooling the main combustion zone and diluting the oxygen content in the main combustion zone, preventing coking caused by excessively high temperature in the main combustion zone, and reducing NOx generation. When the unit is operating at low load, the flue gas can be controlled to be returned to the primary air-enriched pulverized coal flow before entering the main burner at a higher temperature. At this time, the temperature of the primary air flow before entering the burner is higher. Although the pulverized coal concentration and oxygen concentration are slightly reduced, the high flue gas temperature can promote the pyrolysis and volatilization of pulverized coal, producing a certain pre-combustion effect. At the same time, the high flue gas temperature can also provide sufficient reaction activation energy for pulverized coal combustion, thereby promoting stable combustion at low load.

[0049] Finally, it should be noted that the above-described embodiments are merely specific implementations of this application, used to illustrate the technical solutions of this application, and not to limit them. The scope of protection of this application is not limited thereto. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the scope of the technology disclosed in this application. Such modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of protection of the claims.

Claims

1. A flue gas recirculation system for a coal-fired power plant boiler, characterized in that, The coal-fired power plant boiler comprises a pulverized coal external separator, a main burner, a furnace body, and a tail flue, The inlet of the pulverized coal external separator is connected with a primary air pulverized coal gas flow pipeline, and the dense pulverized coal outlet of the pulverized coal external separator is connected with the pulverized coal gas flow inlet of the main burner, the main burner is arranged on the hearth of the furnace body, and the inlet of the tail flue is connected with the hearth outlet of the furnace body, The flue gas circulation system comprises a cyclone separator, a first flue gas extraction pipeline, a second flue gas extraction pipeline, and a flue gas distribution branch, The inlet of the first flue gas extraction pipeline is communicated to the inlet of the tail flue, the outlet of the first flue gas extraction pipeline is communicated to the first inlet of the cyclone separator, the inlet of the second flue gas extraction pipeline is communicated to the flue at the air preheater outlet of the tail flue, the outlet of the second flue gas extraction pipeline is communicated to the second inlet of the cyclone separator, the outlet of the cyclone separator is communicated to the inlet of the flue gas distribution branch, the outlet of the flue gas distribution branch is communicated between the pulverized coal gas flow inlet of the main burner and the dense pulverized coal outlet of the pulverized coal external separator, and / or the outlet of the flue gas distribution branch is communicated to the secondary air inlet of the main burner.

2. The flue gas recirculation system of claim 1, wherein, The pulverized coal external separator comprises: A spent steam burner, the inlet of the spent steam burner is connected with the dilute pulverized coal outlet of the pulverized coal external separator, the outlet of the spent steam burner is connected with the hearth of the furnace body, and the spent steam burner is located above the main burner.

3. The flue gas recirculation system of claim 1, wherein, The pulverized coal external separator comprises at least two, the main burner comprises at least two, and the flue gas distribution branch comprises at least two, The number of the pulverized coal external separators is the same as the number of the main burners, the number of the flue gas distribution branches is the same as the number of the main burners, the outlet of each flue gas distribution branch is communicated between the pulverized coal gas flow inlet of the main burner and the dense pulverized coal outlet of the pulverized coal external separator, and / or the outlet of each flue gas distribution branch is communicated to the secondary air inlet of the main burner, and the inlets of all the flue gas distribution branches are connected with the outlet of the cyclone separator.

4. The flue gas recirculation system of claim 1, wherein, The tail flue comprises a tail vertical flue and an SCR denitration system, the inlet of the tail vertical flue is communicated with the hearth outlet, the outlet of the tail vertical flue is communicated with the inlet of the SCR denitration system, and the air preheater is arranged on the downstream side of the SCR denitration system.

5. The flue gas recirculation system of claim 4, wherein, The air preheater is arranged on the downstream side of the SCR denitration system along the flue gas flow direction.

6. The flue gas recirculation system of claim 1, wherein, The flue gas circulation system further comprises: A first fan arranged on the first flue gas extraction pipeline and used for extracting the flue gas in the hearth outlet and conveying the flue gas into the cyclone separator; A second fan arranged on the second flue gas extraction pipeline and used for extracting the flue gas on the downstream side of the air preheater and conveying the flue gas into the cyclone separator.

7. The flue gas recirculation system of claim 1, wherein, The flue gas circulation system further comprises: A valve arranged on the flue gas distribution branch and used for controlling the flow of the flue gas extracted from the cyclone separator.

8. The flue gas recirculation system of claim 1, wherein, The main burner is a swirl burner or a straight-flow burner.

9. The flue gas recirculation system of claim 1, wherein, The boiler combustion mode of the coal-fired power plant boiler is tangentially firing or opposed firing.

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