Coal-fired boiler economizer wide load denitration bypass device

Abstract

The utility model discloses a kind of coal-saving device wide load denitration bypass device of coal-fired boiler, including the main flue of boiler, economizer and denitration reactor are sequentially arranged in the main flue along flue gas flow direction, bypass device is arranged outside main flue, the entrance and exit of bypass device are all connected on main flue, entrance is located in front end of economizer, exit is located between denitration reactor and economizer, U-shaped dust collection bin is arranged in series on the transverse flue section of bypass device, high-temperature flue gas flows out after being folded by U-shaped dust collection bin. The utility model device can stabilize the SCR inlet flue gas temperature in efficient interval at low load, avoid the denitration efficiency drop and catalyst poisoning caused by temperature fluctuation, guarantee standard discharge;Promote flue gas mixing to be fully and evenly, create stable environment for denitration;With the function of recycling large particle dust, avoid fly ash accumulation, prevent flue ash accumulation, guarantee long-term stable operation, reduce failure and maintenance cost.

Description

Technical Field

[0001] This utility model relates to the field of flue gas denitrification, and in particular to a wide-load denitrification bypass device for economizers of coal-fired boilers. Background Technology

[0002] Environmental protection requirements are becoming increasingly stringent, requiring thermal power plants to meet emission standards for nitrogen oxide emissions and for denitrification devices to operate stably under full load. Due to the volatility brought about by the grid connection of clean energy sources such as wind power and photovoltaics, coal-fired power units are required to undertake peak-shaving tasks and have the ability to operate stably under wide loads and deep low loads.

[0003] The SCR denitrification technology commonly used in coal-fired power units requires a high-efficiency reaction in the 310-420℃ range. However, when the unit is under low load, the flue gas temperature is often below 300℃, which leads to a sharp drop in denitrification efficiency, catalyst poisoning, and emissions that are prone to exceeding standards.

[0004] To improve the inlet flue gas temperature of the flue gas denitrification system at low loads and achieve stable operation of the SCR denitrification unit under wide load conditions, most coal-fired power plants adopt an economizer bypass modification scheme. This scheme involves installing a bypass flue in the boiler tail flue, allowing some flue gas to bypass the economizer and other heating surfaces, mixing with the low-temperature flue gas at the tail outlet to increase the inlet flue gas temperature of the SCR reactor. However, in actual operation, not only does the flue gas contain fly ash, but the low flue gas velocity at low loads also makes fly ash easily accumulate in the flue, forming ash caking over time, increasing the flue load, affecting the flow of high-temperature flue gas, and in severe cases causing the damper doors to jam and fail to open; moreover, under the traditional bypass flue design, the high-temperature bypass flue gas and the low-temperature flue gas in the main flue are mostly in a laminar flow state, making it difficult to mix fully, resulting in uneven flue gas mixing and further exacerbating local temperature deviations. These problems collectively lead to limited flue gas temperature improvement, poor adjustability, and increased resistance in the main flue, failing to meet the requirements for stable and efficient operation of the full-load denitrification system. Utility Model Content

[0005] To address the aforementioned issues, this utility model provides a wide-load denitrification bypass device for economizers in coal-fired boilers. It features a simple structure, the ability to recover large particulate dust to prevent fly ash accumulation, and promotes thorough and uniform mixing of flue gas. This solves the temperature problem in SCR denitrification and ensures efficient operation of the denitrification system.

[0006] This utility model is implemented as follows:

[0007] A wide-load denitrification bypass device for an economizer in a coal-fired boiler includes the main flue of the boiler. An economizer and a denitrification reactor are sequentially arranged in the main flue along the flue gas flow direction. A bypass device is installed outside the main flue. The inlet and outlet of the bypass device are both connected to the main flue. The inlet is located at the front end of the economizer, and the outlet is located between the denitrification reactor and the economizer. The main body of the bypass device is a set of flue components, including a horizontal section and a vertical section, used to introduce high-temperature flue gas that has not been cooled by the economizer. U-shaped dust collection bins are arranged in series on the horizontal flue section of the bypass device. The U-shaped dust collection bins have a U-shaped structure and a dust collection chamber at the bottom of the U-shaped bin. After the high-temperature flue gas is folded by the U-shaped dust collection bins, it flows out, which can trap large dust particles carried in the flue gas in the U-shaped dust collection bins. The folding structure of the U-shaped dust collection bins causes the flue gas flow to be turbulent, which can break the laminar flow state and improve uniformity when mixed with the flue gas in the main flue.

[0008] Furthermore, the bypass device includes a bypass control valve, and a main flue control valve is installed in the main flue between the front end of the economizer and the inlet of the bypass device.

[0009] Furthermore, the bypass control valve and the main flue control valve are electrically connected to the valve master control device. The valve master control device includes a valve interlock controller. The valve master control device can control the opening and closing of the bypass control valve and the main flue control valve, as well as the valve opening degree. The valve interlock control device can realize the linkage control of the relevant valves, namely the bypass control valve and the main flue control valve, through preset logic and real-time monitoring, so as to forcibly avoid the dangerous state of flue blockage caused by the simultaneous closure of the two valves.

[0010] Furthermore, the U-shaped dust collection bin is equipped with a dust cleaning door, and the bottom is equipped with an electric valve and a screw conveyor, which can automatically discharge dust to an external collection device at regular intervals to complete the entire self-cleaning process.

[0011] Furthermore, a flow guiding device is provided at the outlet of the bypass device.

[0012] Furthermore, the front end of the denitrification reactor is equipped with multiple temperature sensors.

[0013] Furthermore, the main flue section between the bypass device and the denitrification reactor is a mixed flue, and a bend guide plate is provided at the bend of the mixed flue.

[0014] Furthermore, the bypass device flue is equipped with multiple high-temperature expansion joints.

[0015] Furthermore, the bypass control valve and the main flue control valve include an electrically operated shut-off damper that serves as a seal and an adjusting damper that regulates the flue gas flow.

[0016] The beneficial effects of this utility model are as follows: A wide-load denitrification bypass device for economizers in coal-fired boilers can significantly increase the inlet flue gas temperature of the SCR denitrification system at low loads, and the flue gas temperature adjustability is better. It can stably control the flue gas temperature within the high-efficiency reaction range of 310-420℃, avoiding the problem of sudden drop in denitrification efficiency and catalyst poisoning caused by excessively low flue gas temperature, and ensuring that nitrogen oxide emissions meet environmental protection standards. Regarding the problem of uneven flue gas mixing, it breaks the laminar flow state of high-temperature bypass flue gas and low-temperature flue gas in the main flue in traditional designs, promoting full mixing of the two, reducing local temperature deviations, and making the flue gas temperature entering the SCR reactor more uniform, creating a stable temperature environment for the denitrification reaction. In solving the problem of ash accumulation, it can prevent fly ash from accumulating and forming caking in the flue, thereby reducing the flue load, ensuring smooth flow of high-temperature flue gas, ensuring long-term stable operation of the bypass flue, and reducing equipment failures and maintenance costs caused by ash accumulation.

[0017] The present invention will be explained in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the wide-load denitrification bypass device for the economizer of a coal-fired boiler, which is a utility model.

[0019] In the diagram: 1-Main flue, 2-Economizer, 3-Bypass control valve, 4-Main flue control valve, 5-U-shaped dust collection bin, 6-Dust cleaning door, 7-Flow guiding device, 8-Denitrification reactor, 9-High temperature expansion joint, 10-Temperature sensor, 11-Elbow guide plate, 12-Mixing flue, 100-Bypass device. Detailed Implementation

[0020] This embodiment describes a wide-load denitrification bypass device for an economizer in a coal-fired boiler, such as... Figure 1 As shown, the boiler includes a main flue 1, in which an economizer 2 and a denitrification reactor 8 are arranged sequentially along the flue gas flow direction. The economizer 2 is used to cool the flue gas, and the denitrification reactor 8 needs to achieve a high-efficiency denitrification reaction in the range of 310-420℃.

[0021] The main body of the bypass device 100 is a set of flue components, which includes a horizontal section and a vertical section. Its core function is to bypass the economizer 2 and directly introduce the high-temperature flue gas into the front end of the denitrification reactor 8. After mixing with the cooled low-temperature flue gas in the main flue, it enters the denitrification reactor 8 to increase the denitrification reaction temperature. A U-shaped dust collection bin 5 is arranged in series on the horizontal flue section of the bypass device 100. The dust collection bin is made of corrosion-resistant and high-temperature resistant steel plate welded into a U-shaped structure. The two side bin walls are set vertically, and the bottom is a smooth arc transition. A special dust collection cavity is provided at the bottom of the U-shaped bin to ensure that there is enough space to hold the trapped dust.

[0022] After entering from the front end of the horizontal flue section, the high-temperature flue gas first flows through the series-connected U-shaped dust collection bins 5. Inside the bins, it completes the downward flow to the bottom and then reverses upward. It then continues to flow through the remaining part of the horizontal flue section and finally merges into the vertical flue section for discharge, and is transported to the front end of the denitrification reactor 8 in the main flue 1.

[0023] The inlet of the bypass device 100 is connected to the main flue 1 at the front end of the economizer 2, specifically located at the rear wall of the boiler turning chamber. During the modification, the tail wall fins are cut off to form the flue gas outlet. The outlet is connected to the main flue section between the economizer 2 and the denitrification reactor 8. The connection between the inlet of the bypass device 100 and the tail wall tube is made of 12Cr1MoV plate. After the comb plate and the wall tube are fully welded, they need to be inspected by coloring (to ensure that there are no defects such as cracks). In order to avoid the scouring and wear of flue gas, the windward side of the wall tube at the inlet is wrapped with wear-resistant tiles, and the leeward side is fixed by upper and lower wear-resistant pressure plates.

[0024] The main flue section 1 between the outlet of the bypass device 100 and the denitrification reactor 8 is a mixing flue 12. An elbow guide plate 11 is installed at the bend to effectively avoid flue gas eddies and reduce pressure loss.

[0025] The bypass device 100 is equipped with two-stage control valves. A set of electrically operated shut-off dampers is installed at the inlet to provide a seal. The double spring-loaded seal ensures a tight seal. A set of electrically operated regulating dampers is installed in the middle to regulate the flue gas flow. Together, they constitute the bypass control valve 3.

[0026] A main flue control valve 4 is installed in the main flue 1 between the front end of the economizer 2 and the bypass inlet, which also includes an electrically shut-off damper and an electrically adjustable damper.

[0027] The U-shaped dust collection bin 5, as the core functional component of the bypass device 100, is connected in series in the bypass flue. When the flue gas flows through it, large dust particles are trapped inside due to inertia and gravity. An electric valve and a screw conveyor are installed at the bottom of the bin to automatically discharge dust to an external collection device at regular intervals. A dust removal door 6 is also provided for manual inspection and cleaning. The structure of the U-shaped dust collection bin 5 creates a turbulent flow pattern in the flue gas, breaking the laminar flow state when mixed with the main flue gas, significantly improving mixing uniformity. A flow guide device 7 is installed at the outlet of the bypass device 100 to guide the high-temperature bypass flue gas into the mixing flue 12 at a reasonable angle, avoiding collision with the main flue gas and preventing laminar flow after mixing.

[0028] Multiple high-temperature expansion joints 9 (located in the vertical and horizontal sections respectively) are also arranged on the flue to absorb the thermal expansion stress generated by flue gas flow and temperature changes, and to prevent the flue from deforming.

[0029] One set of temperature sensors 10 is installed at the inlet and outlet of the bypass device 100. Multiple sets of temperature sensors 10 are installed at the front end of the denitrification reactor 8. The temperature monitored by multiple temperature sensors can reflect the mixing degree of flue gas. Their signals are connected to the central control system to monitor the inlet flue gas temperature in real time. The central control system adjusts the valve opening according to the monitoring data: when the temperature is below 310℃, the system commands to increase the opening of the bypass regulating damper and decrease the opening of the main flue regulating damper to introduce more high-temperature flue gas; when the temperature is above 420℃, the bypass opening is decreased and the main flue opening is increased. The temperature is balanced by low-temperature flue gas to ensure that the denitrification reaction always takes place in the high-efficiency range.

[0030] Both the bypass control valve 3 and the main flue control valve 4 are electrically connected to the valve master control device, which includes a valve interlock controller. Through preset logic and real-time monitoring, the valve achieves linkage control. When one valve is closed, the other valve opens proportionally to prevent the risk of flue blockage caused by the simultaneous closure of both valves, thus ensuring the safety of boiler operation. All status signals of regulating dampers and shut-off dampers, as well as temperature measurement data, are connected to the central control system. The central control room can remotely operate, monitor status, and trigger fault alarms, enabling the bypass system to operate independently without on-site supervision.

[0031] The bypass device 100's flue uses a combination of spring hangers and supports. When the vertical section passes through the inner side of the horizontal truss at the boiler's tail, a specialized support design ensures it is fixed and prevents interference with the truss. For ease of maintenance, the system has four manholes, and maintenance platforms are located near the inlet door and electric actuator. The platform position where the vertical section passes through is adjusted to ensure unobstructed passage. Based on the temperature characteristics of the diversion chamber, the high-temperature section of the bypass flue uses a 320mm thick insulation layer, while the remaining sections use a 240mm thick insulation layer to reduce heat loss. Except for the anti-wear treatment of the flue outlet, easily eroded parts such as flue bends and guide plates have had their service life improved through material optimization (e.g., using wear-resistant alloy steel).

[0032] This device achieves dual functions of dust recovery and flue gas disturbance through a U-shaped dust collection bin, solving the problem of fly ash accumulation. With the help of multi-stage valve linkage and closed-loop temperature control, it ensures that the flue gas temperature at the denitrification inlet is stable in the range of 310-420℃. At the same time, through wear-resistant reinforcement, structural optimization and remote control design, it significantly improves the system reliability and ease of operation and maintenance, providing a strong guarantee for efficient denitrification of boilers.

[0033] The above description is only used to illustrate the technical solution of this utility model and is not intended to limit it. Although this utility model has been described in detail with reference to the preferred arrangement, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of this utility model (such as the connection method, the shape of each element, etc.) without departing from the spirit and scope of the technical solution of this utility model.

Claims

1. A wide-load denitrification bypass device for an economizer in a coal-fired boiler, comprising a main flue (1) of the boiler, wherein an economizer (2) and a denitrification reactor (8) are sequentially arranged in the main flue (1) along the flue gas flow direction, characterized in that... A bypass device (100) is provided outside the main flue (1). The inlet and outlet of the bypass device (100) are connected to the main flue (1). The inlet is located at the front end of the economizer (2), and the outlet is located between the denitrification reactor (8) and the economizer (2). The main body of the bypass device (100) is a set of flue components, including a horizontal section and a vertical section, which are used to introduce high-temperature flue gas that has not been cooled by the economizer (2). The bypass device (100) has a U-shaped dust collection chamber (5) arranged in series on the horizontal flue section. The U-shaped dust collection chamber (5) has a U-shaped structure and a dust collection cavity at the bottom of the U-shaped chamber. After the high-temperature flue gas is folded by the U-shaped dust collection chamber (5), it flows out and can trap large dust particles carried in the flue gas in the U-shaped dust collection chamber (5). The folding structure of the U-shaped dust collection chamber (5) makes the flue gas flow turbulent. When it mixes with the flue gas in the main flue (1), it can break the laminar flow state and improve the uniformity.

2. The wide-load denitrification bypass device for economizers in coal-fired boilers according to claim 1, characterized in that, The bypass device (100) includes a bypass control valve (3), and a main flue control valve (4) is provided between the front end of the economizer (2) in the main flue (1) and the inlet of the bypass device (100).

3. The wide-load denitrification bypass device for economizers in coal-fired boilers according to claim 2, characterized in that, The bypass control valve (3) and the main flue control valve (4) are electrically connected to the valve master control device. The valve master control device can control the opening and closing of the bypass control valve (3) and the main flue control valve (4) as well as the valve opening degree. It can also perform linkage control on the bypass control valve (3) and the main flue control valve (4) to avoid the dangerous situation of flue blockage caused by the simultaneous closure of the two valves.

4. The wide-load denitrification bypass device for economizers in coal-fired boilers according to claim 1, characterized in that, The U-shaped dust collection bin (5) is equipped with a dust cleaning door (6) and an electric valve and a screw conveyor at the bottom, which can automatically discharge dust to an external collection device at regular intervals.

5. The wide-load denitrification bypass device for economizers in coal-fired boilers according to claim 1, characterized in that, A flow guiding device (7) is provided at the outlet of the bypass device (100).

6. The wide-load denitrification bypass device for economizers in coal-fired boilers according to claim 1, characterized in that, The front end of the denitrification reactor (8) is equipped with multiple temperature sensors (10).

7. The wide-load denitrification bypass device for economizers in coal-fired boilers according to claim 1, characterized in that, The main flue (1) section between the bypass device (100) and the denitrification reactor (8) is a mixing flue (12), and a bend guide plate (11) is provided at the bend of the mixing flue (12).

8. The wide-load denitrification bypass device for economizers in coal-fired boilers according to claim 1, characterized in that, The bypass device (100) has multiple high-temperature expansion joints (9) installed on its flue.

9. The wide-load denitrification bypass device for economizers in coal-fired boilers according to claim 2, characterized in that, The bypass control valve (3) and the main flue control valve (4) include an electrically operated shut-off damper that provides a sealing function and an adjusting damper that regulates the flow of flue gas.

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