A flue gas recirculation system for low nitrogen boilers

Abstract

The present invention relates to a flue gas recirculation system for a low-nitrogen boiler, comprising a fan, a burner, a boiler, and an economizer. The air inlet of the fan is connected to a mixing cylinder, and a flue gas circulation pipeline is provided on the flue gas outlet pipeline of the boiler, and the flue gas circulation pipeline is connected to the mixing cylinder; a flow regulating mechanism is provided on the flue gas circulation pipeline; the flow regulating mechanism comprises a rotating shaft on the central axis parallel to the cross section of the flue gas circulation pipeline, a baffle matching the cross section of the flue gas circulation pipeline, and a servo motor controlling the axial rotation of the rotating shaft; the two ends of the rotating shaft pass through two circular holes corresponding to two positions on the pipe wall of the flue gas circulation pipeline, and the baffle is placed inside the flue gas circulation pipeline. Compared with the prior art, the present invention has the advantages of accurate and convenient adjustment of the flue gas circulation volume and effective reduction of nitrogen oxide emission values.

Description

Technical Field

[0001] The invention relates to the field of thermal power and boilers, and in particular to a flue gas recirculation system for a low-nitrogen boiler. Background Art

[0002] In order to effectively control the emission of nitrogen oxides from gas boilers and reduce the secondary generation of PM2.5, many regions have clearly stated that the emission standard of nitrogen oxides in boiler flue gas cannot be higher than 50mg / cubic meter, and the exhaust temperature of boiler flue gas should be lower than 110℃. The emission standards of many boilers in use cannot meet the emission standards stipulated by the latest regions, and it is difficult to reduce the exhaust temperature below the standard value. The most basic technology at present is to replace the boiler or the burner as a whole. On the one hand, this will cause the overall replacement of equipment and facilities to have high transformation costs and a long construction period; on the other hand, the boiler exhaust temperature is too high, resulting in heat energy waste. In addition, the existing boiler flue gas circulation device cannot flexibly adjust the flue gas circulation volume, and cannot be adaptively adjusted according to different emission standards. Although some circulation devices adjust the circulating flue gas volume through butterfly valves, the butterfly valve adjustment accuracy is poor, and the use of high-precision valves is expensive and cannot meet economic and practical requirements. Summary of the invention

[0003] The purpose of the present invention is to overcome the difficulty in regulating the flue gas volume in the above-mentioned prior art and to provide a flue gas recirculation system for low-nitrogen boilers that is easy to regulate the flue gas.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] A flue gas recirculation system for a low-nitrogen boiler comprises a fan, a burner, a boiler and an economizer, wherein a mixing cylinder is connected to the air inlet of the fan, a flue gas circulation pipe is provided on the flue gas outlet pipeline of the boiler, and the flue gas circulation pipe is connected to the mixing cylinder; a flow regulating mechanism is provided on the flue gas circulation pipe; the flow regulating mechanism comprises a rotating shaft on the central axis parallel to the cross section of the flue gas circulation pipe, a baffle matching the cross section of the flue gas circulation pipe, and a servo motor controlling the axial rotation of the rotating shaft; both ends of the rotating shaft pass through circular holes corresponding to two positions on the pipe wall of the flue gas circulation pipe, and the baffle is placed inside the flue gas circulation pipe.

[0006] The present invention is designed on the original burner, and by adding a flue gas recirculation (FGR) device, the effect of effectively controlling the nitrogen oxide emission value can be achieved without the need to replace the entire equipment and facilities, thereby greatly saving costs.

[0007] The present invention designs an adjustment plate with a simple structure, changes the flow cross-sectional area of ​​the smoke circulation duct by the rotation angle of the adjustment plate, and controls the rotation angle of the adjustment plate by a servo motor. The servo motor can control the speed and position accuracy very accurately, thereby realizing precise adjustment of the smoke circulation amount, which is beneficial to improving the adjustment accuracy.

[0008] In addition, fresh air and recycled flue gas are mixed through a mixing barrel before entering the burner, which improves the uniformity of the gas entering the burner and ensures the combustion quality. After the flue gas is premixed with fresh air, the oxygen content of the combustion wind is reduced, thereby reducing the combustion temperature, and the flue gas emission temperature will also be reduced accordingly, reducing heat energy waste.

[0009] The flue gas circulation duct is a circular duct, and the baffle is a circular baffle.

[0010] The housing of the servo motor is fixed to the outer side of the pipe wall of the flue gas circulation pipe, and the output shaft of the servo motor is connected to the rotating shaft.

[0011] A connecting rod is fixed on the rotating shaft located outside the flue gas circulation duct, and the connecting rod is perpendicular to the rotating shaft; a connecting bolt is fixed below the end of the connecting rod, and the connecting bolt is parallel to the rotating shaft; a fan-shaped connecting plate is fixedly connected to the flue gas circulation duct, and a long strip through hole arranged along the arc direction of the fan is provided on the surface of the fan-shaped connecting plate; the connecting bolt passes through the long strip through hole and is fixed to the fan-shaped connecting plate through matching nuts located on the upper and lower surfaces of the fan-shaped connecting plate.

[0012] When the servo motor is positioned, the connecting rod and the rotating shaft are fixed by connecting bolts and matching nuts, so that the baffle is kept at a fixed rotation angle, preventing the servo motor from being opened for a long time and being stressed, which affects the life of the servo motor.

[0013] The fan, burner, boiler, economizer and flue gas circulation pipe are each provided with two sets, and the two sets of devices are arranged symmetrically.

[0014] The flow regulating mechanism is arranged at one end of the smoke circulation duct close to the mixing cylinder.

[0015] The flue gas circulation duct is provided with an insulation layer to perform insulation treatment on the FGR, thereby effectively preventing the generation of flue gas condensation water.

[0016] The present invention also includes a PLC controller, a nitrogen oxide sensor is provided on the smoke exhaust pipe of the boiler, and the PLC controller is connected to the servo motor and the nitrogen oxide sensor signal. Through the PLC controller, the system automatically adjusts according to the nitrogen oxide sensor content of the smoke exhaust.

[0017] The air inlet of the mixing cylinder is connected to the air heater, air is introduced into the tube side of the air heater, the shell side inlet of the air heater is connected to the water outlet pipe of the boiler, and the shell side outlet of the air heater is connected to the water inlet pipe of the boiler.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The servo motor drives the adjustment plate to achieve efficient and accurate adjustment of the flue gas circulation volume, which is conducive to improving the adjustment accuracy and can meet different emission requirements by controlling the recirculation volume of the flue gas;

[0020] (2) The circulating flue gas and air are premixed first, so that the gas entering the burner is more uniform, which is conducive to the uniformity of combustion and improves the combustion quality;

[0021] (3) When the system is stable, the position of the adjustment plate is stable, and the position of the adjustment plate is fixed by matching connecting rods, connecting bolts, nuts, and fan-shaped connecting plates to prevent the servo motor from working for a long time, causing energy waste and damage to the servo motor;

[0022] (4) Insulate the flue gas circulation pipe FGR to effectively prevent the generation of flue gas condensation water;

[0023] (5) Using hot water or steam generated by the boiler to preheat the fresh air ensures the gas temperature entering the burner, which is beneficial to improving the combustion effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the present invention;

[0025] Figure 2 It is a working principle diagram of the present invention;

[0026] Figure 3 It is a schematic diagram of the main structure of the flow regulating mechanism in the present invention;

[0027] Figure 4 It is a schematic diagram of the structure of the fan-shaped connecting plate in the present invention;

[0028] In the figure, 1 is a boiler, 2 is a mixing cylinder, 3 is a fan, 4 is a burner, 5 is an economizer, 6 is a baffle, 7 is a rotating shaft, 8 is a servo motor, 9 is a connecting rod, 10 is a connecting bolt, 11 is a nut, 12 is a fan-shaped connecting plate, 13 is a flue gas circulation duct, 14 is a long strip through hole, 15 is an air inlet, 16 is flue gas, and 17 is circulating flue gas. DETAILED DESCRIPTION

[0029] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0030] Example

[0031] A flue gas recirculation system for a low nitrogen boiler, such as Figure 1 As shown, along the air flow direction, it includes a mixing cylinder 2, a fan 3, a burner 4, a boiler 1, and an economizer 5 connected in sequence. The flue gas outlet pipeline of the boiler 1 is provided with a flue gas circulation pipe 13, which is connected to the mixing cylinder 2. The mixing cylinder 2 is provided with an air inlet 15, and fresh air enters the system from the air inlet 15; the fan 3, the burner 4, the boiler 1, the economizer 5 and the flue gas circulation pipe 13 are each provided with two sets, and the two sets of devices are arranged symmetrically. The air inlet of the mixing cylinder 2 is connected to the air heater, and the air is introduced into the tube side of the air heater. The shell side inlet of the air heater is connected to the water outlet pipe of the boiler 1, and the shell side outlet of the air heater is connected to the water inlet pipe of the boiler 1.

[0032] like Figure 2 As shown, the principle of the present invention is that the circulating flue gas 17 from the air and flue gas circulation duct 13 is mixed and enters the burner 4 to provide oxygen for the fuel, which is burned in the furnace of the boiler 1. Then, part of the generated flue gas 16 passes through the flue gas circulation duct 13 and is mixed with fresh air, and part is discharged.

[0033] The flue gas circulation duct 13 is a circular duct, and a heat preservation layer is provided on the flue gas circulation duct 13. A flow regulating mechanism is provided on the circular duct, and the flow regulating mechanism is provided at one end of the flue gas circulation duct 13 close to the mixing cylinder 2. Figure 3 As shown, the flow regulating mechanism includes a rotating shaft on the central axis parallel to the cross section of the smoke circulation pipe 13, a circular baffle 6 matching the cross section of the smoke circulation pipe 13, and a servo motor 8 for controlling the axial rotation of the rotating shaft; both ends of the rotating shaft pass through two corresponding circular holes on the pipe wall of the smoke circulation pipe 13, and the baffle 6 is placed inside the smoke circulation pipe 13; the casing of the servo motor 8 is fixed to the outside of the pipe wall of the smoke circulation pipe 13, and the output shaft of the servo motor 8 is connected to the rotating shaft; a connecting rod 9 is fixed on the rotating shaft outside the smoke circulation pipe 13, and the connecting rod 9 is perpendicular to the rotating shaft; a connecting bolt 10 is fixed below the end of the connecting rod 9, and the connecting bolt 10 is parallel to the rotating shaft; as shown Figure 4As shown, a fan-shaped connecting plate 12 is fixedly connected to the flue gas circulation duct 13, and a long strip through hole 14 arranged along the arc direction of the fan is provided on the surface of the fan-shaped connecting plate 12; the connecting bolt 10 passes through the long strip through hole 14, and is fixed to the fan-shaped connecting plate 12 through the matching nuts 11 located on the upper and lower surfaces of the fan-shaped connecting plate 12. By setting a baffle fixing component in the matching adjustment mechanism, the baffle position can be mechanically fixed after the system is running stably, thereby avoiding long-term operation of the servo motor.

[0034] A PLC controller is provided in the system of this embodiment, and a nitrogen oxide sensor is provided on the smoke exhaust duct of the boiler 1. The PLC controller is connected with the servo motor 8 and the nitrogen oxide sensor signal, and can realize automatic adjustment in the adjustment stage. If the nitrogen oxide sensor detects that the nitrogen oxide content is high and does not meet the emission standards, the servo motor 8 is controlled to increase the amount of circulating flue gas to reduce the nitrogen oxides to below the emission standards; the nitrogen oxide sensor is an online nitrogen oxide detector, which is suitable for continuous online detection of nitrogen oxide concentration in various industrial environments and special environments, and a commercially available machine can be selected, such as the OS6-NOx online nitrogen oxide detector of the manufacturer OUSJ; the PLC controller can adopt the controller commonly used in the field of chemical automation.

[0035] The present invention is designed and studied on the original burner. By adding an FGR flue gas recirculation device, the effect of effectively controlling the nitrogen oxide emission value can be achieved without the need to replace the entire equipment and facilities, which greatly saves costs; the flue gas circulation pipe FGR is insulated to effectively prevent the generation of flue gas condensation water; by adding an FGR baffle and a servo motor, the recirculation amount of flue gas can be controlled to meet different emission requirements; after the flue gas is premixed with fresh air, the oxygen content of the combustion air is reduced, thereby reducing the combustion temperature, and the flue gas emission temperature will also be reduced accordingly, reducing heat energy waste.

[0036] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A flue gas recirculation system for a low-nitrogen boiler, comprising a fan (3), a burner (4), a boiler (1), and an economizer (5), characterized in that: The air inlet of the fan (3) is connected to a mixing cylinder (2); a flue gas circulation pipe (13) is provided on the flue gas outlet pipeline of the boiler (1), and the flue gas circulation pipe (13) is connected to the mixing cylinder (2); a flow regulating mechanism is provided on the flue gas circulation pipe (13), and the flow regulating mechanism is arranged at one end of the flue gas circulation pipe (13) close to the mixing cylinder (2); the flow regulating mechanism comprises a rotating shaft on the central axis parallel to the cross section of the flue gas circulation pipe (13), a baffle (6) matching the cross section of the flue gas circulation pipe (13), and a servo motor (8) for controlling the axial rotation of the rotating shaft; the two ends of the rotating shaft pass through two corresponding circular holes on the pipe wall of the flue gas circulation pipe (13), and the baffle (6) is placed inside the flue gas circulation pipe (13); the flue gas circulation pipe (13) is a circular pipe, and the baffle (6) is a circular baffle; A connecting rod (9) is fixed on a rotating shaft located outside the flue gas circulation duct (13), and the connecting rod (9) is perpendicular to the rotating shaft; a connecting bolt (10) is fixed below the end of the connecting rod (9), and the connecting bolt (10) is parallel to the rotating shaft; a fan-shaped connecting plate (12) is fixedly connected to the flue gas circulation duct (13), and a long strip through hole (14) arranged along the arc direction of the fan is provided on the surface of the fan-shaped connecting plate (12); the connecting bolt (10) passes through the long strip through hole (14) and is fixed to the fan-shaped connecting plate (12) through matching nuts (11) located on the upper and lower surfaces of the fan-shaped connecting plate (12).

2. A flue gas recirculation system for a low-nitrogen boiler according to claim 1, characterized in that: The housing of the servo motor (8) is fixed to the outside of the pipe wall of the flue gas circulation pipe (13), and the output shaft of the servo motor (8) is connected to the rotating shaft.

3. The flue gas recirculation system for a low-nitrogen boiler according to claim 1, characterized in that: The fan (3), burner (4), boiler (1), economizer (5) and flue gas circulation duct (13) are each provided in two sets, and the two sets of devices are arranged symmetrically.

4. The flue gas recirculation system for a low-nitrogen boiler according to claim 1, characterized in that: The flue gas circulation duct (13) is provided with a heat-insulating layer.

5. The flue gas recirculation system for a low-nitrogen boiler according to claim 1, characterized in that: It also comprises a PLC controller. A nitrogen oxide sensor is provided on the smoke exhaust pipe of the boiler (1). The PLC controller is connected to the servo motor (8) and the nitrogen oxide sensor signal.

6. The flue gas recirculation system for a low-nitrogen boiler according to claim 1, characterized in that: The air inlet of the mixing cylinder (2) is connected to an air heater, air is introduced into the tube side of the air heater, the shell side inlet of the air heater is connected to the water outlet pipe of the boiler (1), and the shell side outlet of the air heater is connected to the water inlet pipe of the boiler (1).

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