Boiler tail gas treatment device and method

Abstract

According to the boiler tail gas treatment device and method, a low-nitrogen combustor of a gas boiler is provided with a main combustion chamber and an outer-layer combustion chamber, a fuel gas pipeline comprises a main feeding pipeline and an auxiliary feeding pipeline which are connected in parallel, the main feeding pipeline communicates with the main combustion chamber, and the auxiliary feeding pipeline communicates with the outer-layer combustion chamber; the low-nitrogen combustor is communicated with an air inlet pipeline; the flue gas circulating pipeline is communicated with the preheated air pipeline and is provided with a variable-frequency fan and a valve; the tail gas treatment method comprises the following steps: closing a stop valve of an auxiliary feeding pipeline and a valve of a flue gas circulation pipeline, starting a frequency conversion fan after the gas-fired boiler normally operates for 30-60 minutes, slowly increasing the frequency of the frequency conversion fan, stabilizing the oxygen content value at 4%, opening the stop valve, adjusting the opening degree of the stop valve according to the NOx concentration value in a flue gas analyzer, and controlling the oxygen content value at 4%. The NOx concentration value meets the emission standard. According to the scheme, tail gas emission meets the current emission standard, the tail gas treatment effect is remarkable, and ultralow emission of tail gas NOx can be achieved.

Description

Technical Field

[0001] The present invention relates to the field of tail gas treatment, and in particular to a boiler tail gas treatment device and method. Background Art

[0002] Boilers are one of the important equipment in the chemical industry. During the operation of the boiler, a large amount of exhaust gas will be generated, which will cause serious harm to the environment and human health. With the improvement of environmental awareness, the country's exhaust gas emission standards are becoming more and more stringent. Starting from January 1, 2020, Shandong Province began to implement the new standard, the "Shandong Boiler Air Pollutant Emission Standard" (DB37 / 2374-2018), among which the concentration of nitrogen oxides emitted from flue gas from gas boilers in key control areas is ≤100mg / m³. In order to cope with the impact of boiler emission pollutants on the environment, it is urgent to transform some gas boilers. How to effectively control the low emission of nitrogen oxides NOx in flue gas is of great significance to the long-term operation of environmentally friendly treatment of gas boiler exhaust.

[0003] At present, common low-nitrogen transformation technology solutions include burner transformation / replacement, SCR technology, SNCR technology, full combustion technology, etc. The transformation technologies are relatively complex and costly. The low-nitrogen transformation technology solution needs to be selected and adjusted according to the specific situation of the boiler. It must match the existing boiler combustion technology and take into account the increasingly stringent environmental protection standards to ensure that the transformed boiler can meet the requirements of low-nitrogen emissions and ensure that the effect of low-nitrogen transformation is lasting and stable.

[0004] Some gas boilers in the existing technology that do not meet the exhaust emission requirements can reduce the nitrogen oxide content in the flue gas by reducing the workload, adjusting the excess air coefficient or one of the above-mentioned common technologies to meet the new flue gas emission indicators, but at the same time waste the company's existing resources. As the country continues to pay attention to environmental protection work, a single technology and simple process adjustments can no longer meet the ever-changing new environment, ultimately resulting in the company's environmental emissions failing to meet standards. Summary of the invention

[0005] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a boiler exhaust gas treatment device and method, which can meet the current emission standards and have significant exhaust gas treatment effects and achieve ultra-low exhaust NOx emissions.

[0006] To solve the above problems, the present invention provides the following technical solutions: A boiler tail gas treatment device comprises a fuel gas intake pipeline, a gas boiler, an air preheater and a chimney which are connected in sequence, the gas boiler is provided with a low-nitrogen burner, and the low-nitrogen burner is provided with a main combustion chamber and an outer combustion chamber; the fuel gas pipeline comprises a main feed pipeline and an auxiliary feed pipeline connected in parallel, the main feed pipeline is connected to the main combustion chamber, the auxiliary feed pipeline is connected to the outer combustion chamber, and the auxiliary feed pipeline is provided with a stop valve; the low-nitrogen burner is connected to an air intake pipeline, the air intake pipeline comprises a blower, the air outlet end of the blower is connected to the air inlet of the air preheater, and the air outlet of the air preheater is connected to the air intake end of the low-nitrogen burner through the preheating air pipeline; a circulating gas outlet is provided on one side of the chimney, the circulating gas outlet is connected to the preheating air pipeline through a flue gas circulation pipeline, and the flue gas circulation pipeline is provided with a variable frequency fan and a valve.

[0007] This device introduces the chimney exhaust gas into the low-nitrogen burner through a variable frequency fan, realizing controllable flue gas recirculation. At the same time, a secondary feed pipeline for fuel gas is set to enter the outer combustion chamber to realize combustion grading. Fuel grading is to first mix a part of the fuel with air for combustion to form a pre-combustion zone, and then add the remaining fuel to complete the main combustion process, which can reduce the formation of local high-temperature zones and reduce the generation of NOx. Flue gas circulation is to reintroduce part of the burned flue gas into the combustion zone and mix it with fresh air before burning. The inert gas in the flue gas (such as carbon dioxide and water vapor) can dilute the oxygen concentration and reduce the combustion temperature, thereby reducing the generation of NOx. The dual design of combustion grading and flue gas recirculation of this device can significantly reduce the emission level of nitrogen oxides NOx in the flue gas, achieve ultra-low emissions of NOx, significantly lower than the emission standards, and solve the problem of excessive flue gas emissions.

[0008] The technical solution of the present invention also includes that the outlet end of the stop valve of the auxiliary feed pipeline is provided with a pressure gauge and a flame arrester in sequence. The gas intake amount in the auxiliary feed pipeline can be adjusted by adjusting the opening of the stop valve, and the pressure gauge and the flame arrester are used to improve the safety of the pipeline.

[0009] The technical solution of the present invention also includes that the air inlet and air outlet of the variable frequency fan are both provided with valves. The purpose of providing valves at the air inlet and air outlet of the variable frequency fan is to control and optimize the operating state of the fan and ensure the safe and efficient operation of the system, wherein the function of the air inlet valve is to control the air intake volume and the fan inlet pressure, and at the same time facilitate cutting off the air source to ensure safety, and the function of the air outlet valve is to control the air outlet volume and the fan outlet pressure and prevent the air flow from flowing back to the fan.

[0010] In order to improve the convenience of valve adjustment, the technical solution of the present invention also includes that the valves at the air inlet and outlet ends of the variable frequency fan are one or a combination of butterfly valves and pendulum valves.

[0011] In order to achieve more accurate control of exhaust gas composition, the technical solution of the present invention also includes that the boiler exhaust gas device is provided with a flue gas analyzer, the flue gas analyzer includes a sampling probe fixed in the chimney, the sampling probe is connected to the gas analyzer through a sampling pipeline, and the gas analyzer is electrically connected to the controller. The controller and the flue gas analyzer can monitor and adjust the ratio of air and fuel in real time, monitor the exhaust gas composition and content, and ensure the best combustion conditions. The flue gas analyzer is a device for continuous and real-time monitoring of flue gas composition, which can measure NOx, SOx, CO, CO 2 , O 2 The flue gas analyzer in this device is mainly used to realize the concentration value of oxygen in the exhaust gas, and based on this concentration value, the frequency of the variable frequency fan and the opening of the stop valve are adjusted, and then the flue gas circulation volume and the fuel gas intake volume of the auxiliary feed pipeline are adjusted to achieve standard exhaust gas emissions.

[0012] The technical solution of the present invention also includes that the variable frequency fan and valve of the flue gas circulation pipeline, and the blower of the air intake pipeline are all electrically connected to the controller.

[0013] As a preferred embodiment, the technical solution of the present invention further includes that the stop valve is a butterfly valve or a pendulum valve, the stop valve is provided with a position sensor, and the stop valve is electrically connected to the controller. The controller and the position sensor can monitor and adjust the intake amount of the fuel gas in real time, thereby adjusting the optimal combustion conditions.

[0014] The second object of the present invention is to provide a method for treating boiler tail gas using the above device, comprising the following steps: (1) Close the stop valve of the auxiliary feed pipeline and the valve of the flue gas circulation pipeline, start the gas boiler and the flue gas analyzer, and the tail gas after the fuel gas is burned in the boiler is discharged from the chimney after the waste heat is recovered by the air preheater; (2) After the gas boiler has been running normally for 30-60 minutes, open the valve of the flue gas circulation pipeline, adjust the frequency of the variable frequency fan to 0 Hz, start the variable frequency fan, and slowly increase the frequency of the variable frequency fan according to the oxygen content value in the flue gas analyzer to stabilize the oxygen content value at 4%; (3) Open the stop valve of the auxiliary feed pipeline, and a part of the fuel gas enters the outer combustion chamber through the auxiliary feed pipeline. Adjust the opening of the stop valve according to the NOx concentration value in the flue gas analyzer until the NOx concentration value meets the emission standards.

[0015] The beneficial effects of the present invention are as follows: compared with the prior art, the purpose of the present invention is to provide a boiler tail gas treatment device and method that meets the current emission standards and has a significant tail gas treatment effect, and can achieve ultra-low tail gas NOx emissions. This device introduces the chimney exhaust gas into the low-nitrogen burner through a variable frequency fan, realizing controllable flue gas recirculation. At the same time, a secondary feed pipeline for fuel gas is set to enter the outer combustion chamber to achieve combustion grading. This device is a dual design of fuel grading and flue gas recirculation, which can achieve ultra-low emissions of NOx in gas boiler flue gas. On the one hand, it has a significant effect in reducing pollution, being green, and energy-saving. On the other hand, it can control the gas boiler flue gas emission value within the standard, and the nitrogen oxide concentration is far lower than 100mg / m3, providing a long-term solution for the needs of gas boiler transformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 It is a structural schematic diagram of a boiler tail gas treatment device in a specific implementation manner.

[0018] Among them, 1 is a gas boiler, 2 is an air preheater, 3 is a chimney, 4 is a low-nitrogen burner, 5 is a main combustion chamber, 6 is an outer combustion chamber, 7 is a main feed pipeline, 8 is an auxiliary feed pipeline, 9 is a stop valve, 10 is a pressure gauge, 11 is a flame arrester, 12 is a controller, 13 is a blower, 14 is a preheated air pipeline, 15 is a flue gas circulation pipeline, 16 is a variable frequency fan, 17 is a butterfly valve, 18 is a sampling probe, and 19 is a gas analyzer. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0020] In the description of the present invention, it should be understood that the terms "center", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only intended to simplify the description of the present invention, rather than to indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0021] As can be seen from the accompanying drawings, a boiler exhaust gas treatment device includes a fuel gas intake pipeline, a gas boiler 1, an air preheater 2 and a chimney 3 connected in sequence, the gas boiler 1 is provided with a low-nitrogen burner 4, and the low-nitrogen burner 4 is provided with a main combustion chamber 5 and an outer combustion chamber 6; the fuel gas pipeline includes a main feed pipeline 7 and an auxiliary feed pipeline 8 connected in parallel, the main feed pipeline 7 is connected to the main combustion chamber 5, the auxiliary feed pipeline 8 is connected to the outer combustion chamber 6, the auxiliary feed pipeline 8 is provided with a stop valve 9, the stop valve 9 is a pendulum valve, and the gas outlet end of the stop valve 9 is provided with a pressure gauge 10 and a flame arrester 11 in sequence.

[0022] The low-nitrogen burner 4 is connected to an air intake pipeline, which includes a blower 13. The air outlet of the blower 13 is connected to the air inlet of the air preheater 2, and the air outlet of the air preheater 2 is connected to the air intake end of the low-nitrogen burner 4 through the preheating air pipeline 14. A circulating air outlet is provided on one side of the chimney 3, and the circulating air outlet is connected to the preheating air pipeline 14 through a flue gas circulation pipeline 15. The flue gas circulation pipeline 15 is provided with a variable frequency fan 16, and butterfly valves 17 are provided at both the air inlet and the air outlet of the variable frequency fan 16.

[0023] The boiler tail gas device is provided with a flue gas analyzer, which includes a sampling probe 18 fixed in the chimney, the sampling probe 18 is connected to a gas analyzer 19 through a sampling pipeline, and the gas analyzer 19 is electrically connected to the controller 12. The variable frequency fan 16 and butterfly valve 17 of the flue gas circulation pipeline 15, the stop valve 9, and the blower 13 of the air intake pipeline are all electrically connected to the controller.

[0024] The boiler tail gas treatment method using the above device comprises the following steps: (1) Close the stop valve of the auxiliary feed pipeline and the valve of the flue gas circulation pipeline, start the gas boiler and the flue gas analyzer, and the tail gas after the fuel gas is burned in the boiler is discharged from the chimney after the waste heat is recovered by the air preheater; (2) After the gas boiler has been running normally for 30 minutes, open the valve of the flue gas circulation pipeline, adjust the frequency of the variable frequency fan to 0 Hz, start the variable frequency fan, and slowly increase the frequency of the variable frequency fan according to the oxygen content value in the flue gas analyzer to stabilize the oxygen content value at 4%; (3) Open the stop valve of the auxiliary feed pipeline, and a portion of the fuel gas enters the outer combustion chamber through the auxiliary feed pipeline. The opening of the stop valve is adjusted according to the NOx concentration value in the flue gas analyzer until the NOx concentration value meets the emission standard. In this embodiment, the tail gas NOx concentration is lower than 50 mg / m3.

[0025] The device and method of this embodiment are dual designs of fuel staging and flue gas recirculation, which can achieve ultra-low emissions of nitrogen oxides NOx in the flue gas of gas boilers. On the one hand, it is effective in reducing pollution, being green and energy-saving. On the other hand, it can control the flue gas emission values ​​of gas boilers within the standard, providing a long-term solution for the needs of gas boiler transformation.

[0026] Although the present invention has been described in detail by referring to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art who is familiar with the present invention may easily think of changes or substitutions within the technical scope disclosed by the present invention, and all of these shall be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A boiler tail gas treatment device, comprising a fuel gas intake pipeline, a gas boiler, an air preheater and a chimney connected in sequence, characterized in that: The gas boiler is provided with a low-nitrogen burner, which is provided with a main combustion chamber and an outer combustion chamber; the fuel gas pipeline includes a main feed pipeline and an auxiliary feed pipeline connected in parallel, the main feed pipeline is connected to the main combustion chamber, the auxiliary feed pipeline is connected to the outer combustion chamber, and the auxiliary feed pipeline is provided with a stop valve; the low-nitrogen burner is connected to an air intake pipeline, the air intake pipeline includes a blower, the air outlet of the blower is connected to the air inlet of the air preheater, and the air outlet of the air preheater is connected to the air intake end of the low-nitrogen burner through the preheating air pipeline; a circulating gas outlet is provided on one side of the chimney, the circulating gas outlet is connected to the preheating air pipeline through a flue gas circulation pipeline, and the flue gas circulation pipeline is provided with a variable frequency fan and a valve.

2. The boiler tail gas treatment device according to claim 1, characterized in that: The gas outlet end of the stop valve of the secondary feed pipeline is provided with a pressure gauge and a flame arrester in sequence.

3. The boiler tail gas treatment device according to claim 1, characterized in that: The air inlet and outlet ends of the variable frequency fan are both provided with valves.

4. The boiler tail gas treatment device according to claim 3, characterized in that: The valves at the air inlet and outlet of the variable frequency fan are butterfly valves, pendulum valves or a combination thereof.

5. The boiler tail gas treatment device according to any one of claims 1 to 4, characterized in that: The boiler tail gas device is provided with a flue gas analyzer, which includes a sampling probe fixed in the chimney, the sampling probe is connected to the gas analyzer through a sampling pipeline, and the gas analyzer is electrically connected to the controller.

6. The boiler tail gas treatment device according to claim 5, characterized in that: The variable frequency fan and valve of the flue gas circulation pipeline, and the blower of the air intake pipeline are all electrically connected to the controller.

7. The boiler tail gas treatment device according to claim 5, characterized in that: The stop valve is a butterfly valve or a pendulum valve. The stop valve is provided with a position sensor and is electrically connected to a controller.

8. The method for treating boiler tail gas according to the device of claim 1, characterized in that: The following steps are involved: (1) Close the stop valve of the auxiliary feed pipeline and the valve of the flue gas circulation pipeline, start the gas boiler and the flue gas analyzer, and the tail gas after the fuel gas is burned in the boiler is discharged from the chimney after the waste heat is recovered by the air preheater; (2) After the gas boiler has been running normally for 30-60 minutes, open the valve of the flue gas circulation pipeline, adjust the frequency of the variable frequency fan to 0 Hz, start the variable frequency fan, and slowly increase the frequency of the variable frequency fan according to the oxygen content value in the flue gas analyzer to stabilize the oxygen content value at 4%; (3) Open the stop valve of the auxiliary feed pipeline, and a part of the fuel gas enters the outer combustion chamber through the auxiliary feed pipeline. Adjust the opening of the stop valve according to the NOx concentration value in the flue gas analyzer until the NOx concentration value meets the emission standards.

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