Whole-process SCR (Selective Catalytic Reduction) denitration system

Abstract

The invention discloses a whole-process SCR denitration system, and relates to the technical field of coal-fired power plant boiler denitration systems. The system comprises a boiler and an SCR denitration reactor, the boiler and the SCR denitration reactor are connected through a flue, a boiler hearth is composed of a water cooling wall, the system further comprises a whole-process SCR denitration bypass system, and the whole-process SCR denitration bypass system comprises a bypass pipeline, a bypass ash discharging system and a bypass adjusting system; the bypass pipeline comprises a flue gas bypass interface, a denitration flue gas bypass branch pipe, a denitration flue gas bypass mother pipe and a denitration flue gas injection branch pipe; the bypass adjusting system comprises a turn-off baffle and an adjusting baffle. The whole-process investment of the SCR denitration system from boiler ignition to BMCR load can be realized, the investment time of the denitration system is shortened, the problem of flue gas nitrogen oxide pollutant emission during the period from boiler ignition to unit grid connection is solved, the nitrogen oxide emission is reduced, the pollutant emission level of a power plant is improved, and certain social and environmental benefits are achieved.

Description

Technical Field

[0001] This invention relates to the field of denitrification systems for coal-fired power plant boilers, and more specifically, to a full-process SCR denitrification system. Background Technology

[0002] Article 5.1.3 of the "Technical Specification for Design of Flue Gas Denitrification in Thermal Power Plants" (DL / T 5480-2013) requires that "the denitrification system should be able to operate safely and continuously between the minimum stable combustion load of the boiler and the BMCR. When the flue gas temperature cannot reach the minimum operating temperature of the catalyst under the minimum stable combustion load of the boiler, corresponding measures should be taken to increase the reactor inlet temperature." According to this specification, the boiler of a thermal power plant should be able to put the denitrification system into operation between the minimum stable combustion load (generally 20%-30% of the boiler load) and the BMCR.

[0003] In actual operation, thermal power plants generally follow the requirements of local environmental protection departments and put the denitrification system into operation from the moment the unit is connected to the grid (zero boiler load). That is, the denitrification system continues to operate safely under any operating conditions from grid connection to BMCR.

[0004] However, even if the unit is put into operation with the SCR denitrification system immediately after grid connection, the heating rate of the boiler body is limited, and there is still a heating process of 8 hours or even longer between boiler ignition and unit grid connection. During this period, the inlet flue gas temperature of the SCR denitrification system does not meet the denitrification input requirements, and a large amount of flue gas generated by boiler combustion is discharged into the ambient atmosphere without being treated by the denitrification system, resulting in the emission of a large amount of nitrogen oxide pollutants in the flue gas, which has a certain impact on the environment.

[0005] Therefore, it is necessary to develop a full-process SCR denitrification system that can increase the inlet flue gas temperature of the SCR system and enable the SCR denitrification system to be continuously put into operation from boiler ignition. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the above-mentioned background technology and provide a full-process SCR denitrification system. This invention solves the problem that the existing coal-fired boiler SCR denitrification system cannot be put into operation during the period from boiler ignition to unit grid connection, effectively increases the inlet flue gas temperature of the SCR denitrification system, shortens the denitrification system commissioning time, reduces nitrogen oxide emissions during boiler start-up, and realizes full-process denitrification from boiler ignition to BMCR operation.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: a full-process SCR denitrification system, comprising a boiler and an SCR denitrification reactor, wherein the boiler and the SCR denitrification reactor are connected by a flue, and the boiler furnace is composed of water-cooled walls, characterized in that: it further comprises a full-process SCR denitrification bypass system, wherein the full-process SCR denitrification bypass system comprises a bypass pipeline, a bypass ash discharge system and a bypass regulation system; The bypass pipeline includes a flue gas bypass interface connected to the water-cooled wall, a denitrification flue gas bypass branch pipe connected to the flue gas bypass interface, a denitrification flue gas bypass main pipe connected to the denitrification flue gas bypass branch pipe, and a denitrification flue gas injection branch pipe connected to the denitrification flue gas bypass main pipe; the denitrification flue gas injection branch pipe is connected to a flue near the SCR denitrification reactor. The bypass ash discharge system includes an ash discharge port located at the lowest point of the denitrification flue gas bypass branch pipe, an ash discharge pipeline connected to the ash discharge port, an ash discharge shut-off baffle plate installed on the ash discharge pipeline, and a silo pump conveying system connected to the ash discharge pipeline. The bypass regulation system includes a shut-off baffle and a regulating baffle located at the denitrification flue gas bypass main pipe, and sequentially arranged between the connection point of the denitrification flue gas bypass branch pipe and the denitrification flue gas bypass main pipe and the denitrification flue gas injection branch pipe.

[0008] In the above technical solution, when the boiler is a π-type boiler, the flue includes a horizontal flue connected to the top of the boiler and a tail shaft connected to the horizontal flue; The denitrification flue gas injection branch pipe is connected to the flue between the tail shaft and the SCR denitrification reactor.

[0009] In the above technical solution, a screen-type superheater, a high-temperature superheater, and a high-temperature reheater are sequentially arranged between the top of the boiler and the horizontal flue; the tail shaft includes a front shaft and a rear shaft; a low-temperature reheater is arranged in the front shaft, and a front shaft flue gas baffle is provided at the outlet of the front shaft; a low-temperature superheater and an economizer are arranged sequentially from top to bottom in the rear shaft, and a rear shaft flue gas baffle is provided at the outlet of the rear shaft; The connection between the flue gas bypass interface and the water-cooled wall is located below the screen-type superheater.

[0010] In the above technical solution, when the boiler is a tower boiler, a heating surface is provided in the upper part of the boiler and a flue gas baffle is provided at the top of the boiler. The connection between the flue gas bypass interface and the water-cooled wall is located below the heated surface.

[0011] In the above technical solution, the left and right walls of the water-cooled wall are connected to multiple flue gas bypass interfaces; the denitrification flue gas injection branch pipes are provided at intervals.

[0012] Compared with the prior art, the present invention has the following advantages: 1) Compared with conventional full-load SCR denitrification systems, this invention can realize the full-process operation of the SCR denitrification system from boiler ignition to BMCR load, shorten the denitrification system operation time, solve the problem of flue gas nitrogen oxide pollutant emissions during the period from boiler ignition to unit grid connection, reduce nitrogen oxide emissions, improve the pollutant emission level of power plants, and has certain social and environmental benefits.

[0013] 2) Even if the unit is limited by the type of coal used by different units and cannot put the SCR denitrification system into operation immediately after boiler ignition, the present invention can shorten the SCR denitrification system start-up time, enabling the SCR denitrification system to be put into operation as early as possible, reducing the nitrogen oxide emission concentration before the unit is connected to the grid, which also has certain social and environmental benefits. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of the present invention when the boiler is a π-type boiler.

[0015] Figure 2 This is a schematic diagram of the structure of the present invention when the boiler is a tower boiler.

[0016] Figure 3 for Figure 1 Sectional view shown in AA.

[0017] Figure 4 This is a schematic diagram of the structure of a conventional coal-fired boiler in a thermal power plant.

[0018] Figure 5 This is a schematic diagram of a conventional tower boiler.

[0019] Figure 6 This is a graph showing the actual operating data of a power plant when using existing technology.

[0020] Among them, 100-boiler, 110-water-cooled wall, 111-left wall, 112-right wall, 120-screen superheater, 130-high-temperature superheater, 140-high-temperature reheater, 150-heating surface, 160-flue gas damper, 200-SCR denitrification reactor, 300-flue, 310-horizontal flue, 320-tail shaft, 321-front shaft, 3211-low-temperature reheater, 3212-front shaft flue gas damper, 322-rear shaft, 3221-low-temperature superheater, 3222-... - Economizer, 3223 - Rear shaft flue gas damper, 400 - Full-process SCR denitrification bypass system, 410 - Bypass pipeline, 411 - Flue gas bypass interface, 412 - Denitrification flue gas bypass branch pipe, 413 - Denitrification flue gas bypass main pipe, 414 - Denitrification flue gas injection branch pipe, 420 - Bypass ash discharge system, 421 - Ash discharge port, 422 - Ash discharge pipeline, 423 - Ash discharge shut-off damper, 424 - Silo pump ash conveying system, 430 - Bypass regulation system, 431 - Shut-off damper, 432 - Regulation damper. Detailed Implementation

[0021] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but these descriptions are not intended to limit the invention and are merely illustrative. The advantages of the present invention will become clearer and easier to understand through this description.

[0022] Referring to the accompanying drawings, a full-process SCR denitrification system includes a boiler 100 and an SCR denitrification reactor 200, which are connected by a flue 300. The furnace of the boiler 100 is composed of membrane water-cooled walls 110. The system is characterized by further including a full-process SCR denitrification bypass system 400, which includes a bypass pipe 410, a bypass ash discharge system 420, and a bypass regulating system 430. The bypass pipe 410 includes a flue gas bypass interface 411 connected to the water-cooled wall 110, a denitrification flue gas bypass branch pipe 412 connected to the flue gas bypass interface 411, a denitrification flue gas bypass main pipe 413 connected to the denitrification flue gas bypass branch pipe 412, and a denitrification flue gas injection branch pipe 414 connected to the denitrification flue gas bypass main pipe 413; the denitrification flue gas injection branch pipe 414 is connected to the flue duct 300 near the side of the SCR denitrification reactor 200; The bypass ash discharge system 420 includes an ash discharge port 421 located at the lowest point of the denitrification flue gas bypass branch pipe 412, an ash discharge pipe 422 connected to the ash discharge port 421, an ash discharge shut-off baffle 423 located on the ash discharge pipe 422, and a silo pump ash conveying system 424 connected to the ash discharge pipe 422. The ash discharge port 421 is located at the lowest point of the denitrification flue gas bypass branch pipe 412, and a level gauge is installed on the ash discharge pipe 422. The ash discharge shut-off baffle 423 is mainly used to isolate the bypass pipe 410 and the silo pump ash conveying system 424 when the bypass ash discharge system 420 is under maintenance, and is kept fully open during normal operation. When the unit is running, the silo pump ash conveying system 424 is automatically started according to the material level in the ash discharge pipe 422 to discharge the accumulated ash in the ash discharge pipe 422 in a timely manner and transport it to the boiler dust collector system or ash silo.

[0023] The bypass regulation system 430 includes a shut-off baffle 431 and a regulating baffle 432 located at the denitrification flue gas bypass main pipe 413, and sequentially arranged between the connection point of the denitrification flue gas bypass branch pipe 412 and the denitrification flue gas bypass main pipe 413 and the denitrification flue gas injection branch pipe 414.

[0024] When the boiler 100 is a π-type boiler, the flue 300 includes a horizontal flue 310 connected to the top of the boiler 100 and a tail shaft 320 connected to the horizontal flue 310. The denitrification flue gas injection branch pipe 414 is connected to the flue 300 between the tail shaft 320 and the SCR denitrification reactor 200.

[0025] A screen-type superheater 120, a high-temperature superheater 130, and a high-temperature reheater 140 are sequentially arranged between the top of the boiler 100 and the horizontal flue 310; the tail shaft 320 includes a front shaft 321 and a rear shaft 322; a low-temperature reheater 3211 is arranged in the front shaft 321, and a front shaft flue gas baffle 3212 is provided at the outlet of the front shaft 321; a low-temperature superheater 3221 and an economizer 3222 are arranged sequentially from top to bottom in the rear shaft 322, and a rear shaft flue gas baffle 3223 is provided at the outlet of the rear shaft 322; The connection between the flue gas bypass interface 411 and the water-cooled wall 110 is located below the screen-type superheater 120.

[0026] When the boiler 100 is a tower boiler, a heating surface 150 is provided in the upper part of the boiler 100, and a flue gas baffle 160 is provided at the top of the boiler 100. The connection between the flue gas bypass interface 411 and the water-cooled wall 110 is located below the heating surface 150. The tower boiler and the π-type boiler have slightly different structural types. The heating surface 150 is arranged in the upper part of the furnace of the boiler 100. After combustion, the flue gas passes through the upper heating surface 150 of the furnace in sequence, and then turns into the SCR denitrification reactor 200 after passing through the flue gas baffle 160.

[0027] To ensure a uniform flue gas flow field, the left wall 111 and right wall 112 of the water-cooled wall 110 are both connected to multiple flue gas bypass interfaces 411; the flue gas bypass interfaces 411 adopt a multi-branch pipe type, and the number of branch pipes is determined according to the furnace size, unit capacity and flue gas volume at ignition. Multiple denitrification flue gas injection branch pipes 414 are provided at intervals. In order to ensure the uniformity of the flue gas flow field at the SCR inlet, the denitrification flue gas injection branch pipes 414 are also considered to be of the multi-branch type. The number and diameter of the denitrification flue gas injection branch pipes 414 are determined by flow field simulation based on the size of the SCR inlet flue and the unit capacity.

[0028] Each boiler 100 is equipped with two bypass regulation systems 430, which are used to regulate the flow of denitrification flue gas bypass branch pipes 412 of the left wall 111 and the right wall 112 to ensure uniformity. The shut-off damper 431 is used to shut off the flue gas when the whole process SCR denitrification bypass system 400 is not in operation. The regulating damper 432 is used to regulate the bypass flue gas flow by adjusting the opening of the damper 432, while ensuring that the bypass flue gas volume from the left wall 111 and the right wall 112 is balanced. The shut-off damper 431 and the regulating damper 432 are connected in series. The flue gas first passes through the shut-off damper 431 and then flows through the regulating damper 432.

[0029] In actual use, such as Figure 4The flue gas flow of a conventional coal-fired boiler (π-type boiler) in a thermal power plant is as follows: After pulverized coal is burned in the furnace of boiler 100, the generated flue gas flows upward through the furnace of boiler 100, passing successively through the screen-type superheater 120, high-temperature superheater 130, and high-temperature reheater 140 at the top of the furnace, and then enters the tail shaft 320 through the horizontal flue 310; the tail shaft 320 is divided into a front shaft 321 and a rear shaft 322, where the front shaft 321 is generally equipped with a low-temperature reheater 3211, and the rear shaft 322 is generally equipped with a low-temperature superheater 3221 and an economizer 3222; the flue gas flows through each heating surface of the tail shaft 320 in sequence, and then mixes with the front shaft flue gas baffle 3212 at the outlet of the front shaft 321 and the rear shaft flue gas baffle 3223 at the outlet of the rear shaft 322. The mixed flue gas enters the SCR denitrification reactor 200 for denitrification; the denitrified flue gas enters the subsequent flue gas system.

[0030] like Figure 5 The conventional tower boiler shown has a slightly different structure from the conventional π-type boiler. The heating surfaces 150 are all arranged in the upper part of the furnace of the boiler 100. After combustion, the flue gas passes through the heating surfaces 150 in the upper part of the furnace, and then turns into the SCR denitrification reactor 200 after passing through the flue gas baffle 160.

[0031] like Figure 4 and Figure 5 The process for starting up a conventional coal-fired boiler and putting the SCR denitrification system into operation in a conventional thermal power plant is as follows: Boiler 100 is started and ignited, and the furnace and heating surfaces heat up according to the start-up curve. The flue gas after combustion enters the SCR denitrification reactor 200 after passing through the heating surfaces inside the furnace. Before the unit is connected to the grid, the flue gas temperature at the inlet of the SCR denitrification reactor 200 is low and does not meet the conditions for putting the denitrification system into operation. The flue gas enters the subsequent flue gas process directly without denitrification. As the amount of boiler fuel increases and the temperature of the heating surfaces rises, the flue gas temperature at the inlet of the SCR denitrification reactor 200 continues to rise. When the denitrification system operation temperature is met (for conventional denitrification catalysts, operation is possible after the flue gas temperature is ≥300℃; for wide-temperature catalysts, operation is possible after the flue gas temperature is ≥240℃), the denitrification system is started, the denitrification catalyst is injected, and the flue gas enters the subsequent flue gas system after denitrification.

[0032] For example Figure 1 Taking the π-type boiler shown as an example, the operation mode of the present invention includes the following steps: Step 1, from boiler startup and ignition to unit grid connection: Before boiler 100 is ignited, the front vertical shaft flue gas damper 3212 and the rear vertical shaft flue gas damper 3223 at the tail vertical shaft outlet 320 are closed, and the shut-off damper 431 and the regulating damper 432 are opened; boiler 100 is ignited, and the flue gas enters the SCR denitrification reactor 200 through the full-process SCR denitrification bypass system 400; when the SCR inlet flue gas temperature meets the commissioning requirements, the SCR denitrification reactor 200 is put into operation; as the flue gas temperature continues to rise, the front vertical shaft flue gas damper 3212 and the rear vertical shaft flue gas damper 3223 are gradually opened. The vertical shaft flue gas damper 3223 is closed, and the regulating damper 432 is adjusted to ensure that the temperature of the two flue gas streams after mixing always meets the SCR inlet flue gas temperature requirements. Following this procedure, the amount of flue gas entering the tail shaft 320 is gradually increased, and the amount of flue gas entering the entire SCR denitrification bypass system 400 is reduced, until the regulating damper 432 is completely closed, and the flue gas enters the SCR denitrification reactor 200 through the tail shaft 320. After the unit parameters meet the grid connection requirements, the unit is connected to the grid.

[0033] During the operation of the whole process SCR denitrification bypass system 400, the bypass ash discharge system 420 automatically starts to operate according to the material level to ensure that the ash accumulated in the bypass pipeline 410 is discharged in a timely manner.

[0034] Step 2, Unit connection to BMCR operating conditions: When the shut-off damper 431 of the full-process SCR denitrification bypass system 400 is closed, the bypass pipeline 410 is shut down. The flue gas enters the SCR denitrification reactor 200 after passing through the heating surface at the top of the furnace of the boiler 100 and the heating surface at the tail shaft 320. After denitrification, the flue gas enters the subsequent flue gas process. The bypass ash discharge system 420 is automatically activated. According to the ash accumulation in the bypass flue 410, the silo pump ash conveying system 424 is automatically activated to transport the ash accumulated in the bypass flue 410 to the boiler dust collector system or ash silo.

[0035] The above operating method is for, for example Figure 2 The tower boiler shown is also applicable.

[0036] like Figure 6 As shown, taking the actual operating data of a power plant as an example, it takes 8.5 hours (05:29-14:05) between the ignition of boiler 100 and the grid connection of the unit. Eight hours after the boiler ignition (13:30), the temperature of the flue gas at the SCR denitrification inlet reaches the conditions for commissioning, and the SCR denitrification system is put into operation. During this 8-hour period, the flue gas of boiler 100 is directly discharged into the atmosphere without denitrification.

[0037] According to actual operating data, after the boiler is ignited (05:29), the flue gas temperature at the inlet of the 120-type superheater is 231℃, and it can reach 300℃ 1 hour after ignition (06:30).

[0038] Based on existing power plant operating data, the operational status after adopting this invention is evaluated. After adopting this invention, if the SCR denitrification system is equipped with a wide-temperature catalyst, the denitrification system can be put into operation immediately after the boiler is ignited at 100°C. If the SCR denitrification system is equipped with a conventional catalyst, the denitrification system can be put into operation 1 hour after the boiler is ignited at 100°C. Both of these schemes are earlier than the conventional denitrification system, which can only be put into operation 8 hours after the boiler is ignited. This effectively shortens the denitrification start-up time and reduces nitrogen oxide emissions during boiler startup, resulting in good social and environmental benefits.

[0039] All other unspecified parts belong to the prior art.

Claims

1. A full-process SCR denitrification system, comprising a boiler (100) and an SCR denitrification reactor (200), wherein the boiler (100) and the SCR denitrification reactor (200) are connected by a flue (300), and the furnace of the boiler (100) is composed of membrane water-cooled walls (110), characterized in that: It also includes a full-process SCR denitrification bypass system (400), which includes a bypass pipeline (410), a bypass ash discharge system (420), and a bypass regulation system (430); The bypass pipe (410) includes a flue gas bypass interface (411) connected to the water-cooled wall (110), a denitrification flue gas bypass branch pipe (412) connected to the flue gas bypass interface (411), a denitrification flue gas bypass main pipe (413) connected to the denitrification flue gas bypass branch pipe (412), and a denitrification flue gas injection branch pipe (414) connected to the denitrification flue gas bypass main pipe (413); the denitrification flue gas injection branch pipe (414) is connected to the flue (300) on the side near the SCR denitrification reactor (200); The bypass ash discharge system (420) includes an ash discharge port (421) located at the lowest point of the denitrification flue gas bypass branch pipe (412), an ash discharge pipeline (422) connected to the ash discharge port (421), an ash discharge shut-off baffle (423) installed on the ash discharge pipeline (422), and a silo pump ash conveying system (424) connected to the ash discharge pipeline (422); The bypass regulation system (430) includes a shut-off baffle (431) and a regulating baffle (432) located at the denitrification flue gas bypass main pipe (413), and sequentially arranged between the connection between the denitrification flue gas bypass branch pipe (412) and the denitrification flue gas bypass main pipe (413) and the denitrification flue gas injection branch pipe (414).

2. The full-process SCR denitrification system according to claim 1, characterized in that: When the boiler (100) is a π-type boiler, the flue (300) includes a horizontal flue (310) connected to the top of the boiler (100) and a tail shaft (320) connected to the horizontal flue (310); The denitrification flue gas injection branch pipe (414) is connected to the flue (300) between the tail shaft (320) and the SCR denitrification reactor (200).

3. The full-process SCR denitrification system according to claim 2, characterized in that: Between the top of the boiler (100) and the horizontal flue (310), a screen-type superheater (120), a high-temperature superheater (130), and a high-temperature reheater (140) are arranged in sequence; the tail shaft (320) includes a front shaft (321) and a rear shaft (322); a low-temperature reheater (3211) is arranged in the front shaft (321), and a front shaft flue gas baffle (3212) is provided at the outlet of the front shaft (321); a low-temperature superheater (3221) and an economizer (3222) are arranged in the rear shaft (322) from top to bottom, and a rear shaft flue gas baffle (3223) is provided at the outlet of the rear shaft (322); The connection between the flue gas bypass interface (411) and the water-cooled wall (110) is located below the screen-type superheater (120).

4. The full-process SCR denitrification system according to claim 1, characterized in that: When the boiler (100) is a tower boiler, a heating surface (150) is provided in the upper part of the boiler (100), and a flue gas baffle (160) is provided on the top of the boiler (100). The connection between the flue gas bypass interface (411) and the water-cooled wall (110) is located below the heated surface (150).

5. The full-process SCR denitrification system according to claim 1, characterized in that: The left wall (111) and right wall (112) of the water-cooled wall (110) are both connected to multiple flue gas bypass interfaces (411); the denitrification flue gas injection branch pipe (414) is provided with multiple intervals.

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