Low-load ammonia-doped cracking hydrogen stable combustion method and system for coal-fired boiler

Abstract

The coal-fired boiler low-load ammonia-doped cracking hydrogen stable combustion system comprises a coal-fired boiler, an ammonia gas generating device, an air premixer and an ammonia gun, the output end of the ammonia gas generating device is connected with the air premixer, the output end of the air premixer is connected with the ammonia gun, and a plurality of ammonia-doped cracking hydrogen modules are sequentially arranged in the middle of the coal-fired boiler. The ammonia-doped hydrogen cracking modules sequentially comprise secondary fans, combustors, ammonia guns and combustors from bottom to top, and the secondary fans are arranged at the upper parts of the ammonia-doped hydrogen cracking modules; the coal-fired boiler is provided with an online oxygen concentration analyzer, a thermocouple temperature sensor, an online hydrogen concentration analyzer, a pressure sensor and a flue gas analyzer which are connected with a controller. According to the invention, the structure of the coal-fired boiler is optimized, the addition amount of ammonia gas is adjusted through the low-load ammonia-doped cracking hydrogen stable combustion method for the coal-fired boiler, and the local oxygen concentration is accurately controlled, so that the overall combustion efficiency and stability are improved, and the emission of nitrogen oxides is reduced.

Description

Technical Field

[0001] The invention belongs to the field of coal-fired boiler combustion, and in particular relates to a method and system for stable combustion of low-load ammonia-blended cracked hydrogen in a coal-fired boiler. Background Art

[0002] As a key equipment in thermal power plants, coal-fired boilers play an important role in electricity production. However, there are some problems with coal-fired boilers when operating at low loads, especially when ammonia-blended combustion technology is used. Ammonia-blended combustion technology aims to replace part of the coal with ammonia to reduce carbon emissions and improve combustion efficiency, such as a coal-fired boiler system and an ammonia-blended combustion method disclosed in CN113432117A. However, due to the differences in the combustion characteristics of ammonia and coal, the ammonia-blended combustion technology under low-load operating conditions has the following problems: 1. Combustion stability problem: Under low load conditions, coal-fired boilers that burn with ammonia often face the problem of poor combustion stability, especially when the ammonia ratio is high. This is mainly because the combustion characteristics of ammonia are different from those of coal, which makes the combustion process difficult to control and may cause flame extinguishing or incomplete combustion.

[0003] 2. Nitrogen oxide emission problem: Even if the combustion conditions are optimized, ammonia combustion may still lead to increased nitrogen oxide emissions. This is because ammonia easily reacts with oxygen at high temperatures to form nitrogen oxides, which are one of the important sources of air pollution.

[0004] 3. Boiler combustion efficiency problem: When ammonia is mixed and burned, if the ammonia ratio is too high, it may cause the boiler combustion efficiency to decrease, thereby affecting the overall performance of the coal-fired boiler.

[0005] Therefore, there is an urgent need for a system and method for stably burning hydrogen gas cracked by ammonia in a coal-fired boiler under low load. Summary of the invention

[0006] In order to solve the problem that ammonia-doped combustion is unstable and generates atmospheric pollutants in a coal-fired boiler under low load, the present invention provides a method and system for stable combustion of hydrogen by cracking with ammonia in a coal-fired boiler under low load. By optimizing the structure of the coal-fired boiler, adjusting the amount of ammonia added, and accurately controlling the local oxygen concentration, the overall combustion efficiency and stability are improved, and nitrogen oxide emissions are reduced.

[0007] In order to solve the above problems, the first aspect of the present invention proposes a coal-fired boiler low-load ammonia cracking hydrogen stable combustion system, comprising a coal-fired boiler, and also comprising an ammonia generating device, an air premixer and an ammonia gun, wherein the output end of the ammonia generating device is connected to the air premixer, and the output end of the air premixer is connected to the ammonia gun, which is arranged in the coal-fired boiler, and the coal-fired boiler comprises an upper part, a middle part and a bottom part, wherein the bottom part is provided with a secondary fan, a burner, an oil gun and a burner in sequence from bottom to top, wherein the middle part is provided with a plurality of ammonia cracking hydrogen modules in sequence, wherein the plurality of ammonia cracking hydrogen modules include a secondary fan, a burner, an ammonia gun and a burner in sequence from bottom to top, and wherein the upper part is provided with a plurality of secondary fans; The coal-fired boiler is provided with a plurality of online oxygen concentration analyzers, a plurality of thermocouple temperature sensors, an online hydrogen concentration analyzer, a pressure sensor and a flue gas analyzer. The plurality of thermocouple temperature sensors are equidistantly arranged. The online oxygen concentration analyzer, the plurality of thermocouple temperature sensors, the online hydrogen concentration analyzer, the pressure sensor and the flue gas analyzer are connected to a controller.

[0008] Furthermore, the ammonia generating equipment is provided with an ammonia concentration sensor, a pressure sensor and a temperature and humidity sensor, and the ammonia concentration sensor, pressure sensor and temperature and humidity sensor are connected to the controller, and the controller adjusts the power of the ammonia generating equipment according to the detection parameters of the ammonia concentration sensor, pressure sensor and temperature and humidity sensor.

[0009] Ammonia concentration sensors, pressure sensors, and temperature and humidity sensors are set up to monitor the ammonia generation equipment, and the intelligent adjustment of the ammonia concentration sensor is realized in combination with the controller.

[0010] The second aspect of the present invention provides a method for stable combustion of hydrogen from low-load ammonia-blended cracking of a coal-fired boiler, comprising: Step 1: Clean the furnace to ensure there is no residue in the furnace, and adjust the coal-fired boiler to low-load operation; Step 2: Open the ammonia gun to add ammonia into the furnace, and disperse the ammonia evenly into the furnace through multiple ammonia-doped hydrogen cracking modules; Step 3: Use an online hydrogen concentration analyzer to detect the hydrogen content in the furnace, and control the ammonia gun through the controller to adjust the amount of ammonia added; Step 4: Use multiple online oxygen concentration analyzers to detect the local oxygen concentration in the furnace, and adjust the local oxygen concentration by controlling the power of the secondary fan through the controller; Step 5: Use multiple thermocouple temperature sensors to detect the temperature in the combustion chamber, and the controller records the temperature in the combustion chamber. Use the pressure sensor to detect the pressure in the combustion chamber, and the controller records the pressure in the combustion chamber. The controller evaluates the combustion stability through the pressure parameter and the temperature parameter. Step 6: Use a flue gas analyzer to detect nitrogen oxide emissions. The controller is set with a standard value for nitrogen oxide emissions. The controller compares the detected value with the standard value. If the detected value is greater than the standard value, the ammonia addition amount and the local oxygen concentration are adjusted through steps 3 and 4 to reduce the detected value.

[0011] Furthermore, the step 3 specifically includes: Set the ammonia addition ratio, detect the hydrogen content in the furnace through the online hydrogen concentration analyzer, calculate the theoretical ammonia demand based on the ratio value and the real-time hydrogen content, and compare the theoretical ammonia demand with the actual ammonia addition to obtain the ammonia deviation value; According to the ammonia amount deviation value, the flow rate of the ammonia gun is adjusted through PID control to form a closed-loop control system to ensure that the ammonia addition amount is always within the optimal range.

[0012] Furthermore, the optimal range of the amount of ammonia added is 10% to 20% of the hydrogen content.

[0013] Furthermore, step 4 specifically includes: Set a local oxygen concentration range, detect the local oxygen concentration in the furnace through an online oxygen concentration analyzer, compare the set local oxygen concentration range with the actual local oxygen concentration, and obtain the oxygen concentration range deviation value; According to the oxygen concentration range deviation value, the power of the secondary fan is adjusted through the PID controller to ensure that the oxygen concentration is always within the optimal range.

[0014] Furthermore, the optimal range of oxygen concentration is 1.5% to 2.5%.

[0015] Through the above technical solution, the beneficial effects of the present invention are: (1) The present invention optimizes the structure of the coal-fired boiler to provide a basis for uniform dispersion of ammonia into the furnace and control of local oxygen concentration. A plurality of ammonia-doped hydrogen cracking modules are arranged in sequence in the middle of the coal-fired boiler. The ammonia-doped hydrogen cracking modules include a secondary fan, a burner, an ammonia gun and a burner from bottom to top to ensure temperature stability, which is conducive to the cracking of ammonia.

[0016] (2) The present invention provides a method for the stable combustion of coal-fired boilers by cracking hydrogen with ammonia at low load, which achieves efficient cracking of ammonia under local oxygen-deficient conditions by precisely controlling the amount of ammonia added and the local oxygen concentration, thereby generating hydrogen to assist the stable combustion of coal-fired boilers at low load. This method can not only improve combustion efficiency, but also significantly reduce nitrogen oxide emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a structural diagram of a low-load ammonia-blended cracking hydrogen stable combustion system for a coal-fired boiler according to the present invention; Figure 2 The present invention is a flow chart of the steps of a method for stable combustion of hydrogen by cracking with ammonia in a coal-fired boiler at low load. DETAILED DESCRIPTION

[0018] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments: Example 1

[0019] like Figure 1~2 As shown, a low-load ammonia-blended cracking hydrogen stable combustion system for a coal-fired boiler comprises a coal-fired boiler, and also comprises an ammonia generating device, an air premixer and an ammonia gun, wherein the output end of the ammonia generating device is connected to the air premixer, and the output end of the air premixer is connected to the ammonia gun, and the ammonia gun is arranged in the coal-fired boiler, and the coal-fired boiler comprises an upper part, a middle part and a bottom part, and the bottom part is provided with a secondary fan, a burner, an oil gun and a burner in sequence from bottom to top, and the middle part is provided with a plurality of ammonia-blended cracking hydrogen modules in sequence, and the plurality of ammonia-blended cracking hydrogen modules include a secondary fan, a burner, an ammonia gun and a burner in sequence from bottom to top, and the upper part is provided with a plurality of secondary fans; The coal-fired boiler is provided with a plurality of online oxygen concentration analyzers, a plurality of thermocouple temperature sensors, an online hydrogen concentration analyzer, a pressure sensor and a flue gas analyzer. The plurality of thermocouple temperature sensors are equidistantly arranged. The online oxygen concentration analyzer, the plurality of thermocouple temperature sensors, the online hydrogen concentration analyzer, the pressure sensor and the flue gas analyzer are connected to a controller.

[0020] The ammonia generating device is provided with an ammonia concentration sensor, a pressure sensor and a temperature and humidity sensor, and the ammonia concentration sensor, the pressure sensor and the temperature and humidity sensor are connected to the controller, and the controller adjusts the power of the ammonia generating device according to the detection parameters of the ammonia concentration sensor, the pressure sensor and the temperature and humidity sensor.

[0021] A method for stable combustion of low-load ammonia-blended cracked hydrogen in a coal-fired boiler, comprising: Step 1: Clean the furnace to ensure there is no residue in the furnace, and adjust the coal-fired boiler to low-load operation; Step 2: Open the ammonia gun to add ammonia into the furnace, and disperse the ammonia evenly into the furnace through multiple ammonia-doped hydrogen cracking modules; Step 3: Use an online hydrogen concentration analyzer to detect the hydrogen content in the furnace, and control the ammonia gun through the controller to adjust the amount of ammonia added; Step 4: Use multiple online oxygen concentration analyzers to detect the local oxygen concentration in the furnace, and adjust the local oxygen concentration by controlling the power of the secondary fan through the controller; Step 5: Use multiple thermocouple temperature sensors to detect the temperature in the combustion chamber, and the controller records the temperature in the combustion chamber. Use the pressure sensor to detect the pressure in the combustion chamber, and the controller records the pressure in the combustion chamber. The controller evaluates the combustion stability through the pressure parameter and the temperature parameter. Step 6: Use a flue gas analyzer to detect nitrogen oxide emissions. The controller is set with a standard value for nitrogen oxide emissions. The controller compares the detected value with the standard value. If the detected value is greater than the standard value, the ammonia addition amount and the local oxygen concentration are adjusted through steps 3 and 4 to reduce the detected value.

[0022] The step 3 specifically includes: Set the ammonia addition ratio, detect the hydrogen content in the furnace through the online hydrogen concentration analyzer, calculate the theoretical ammonia demand based on the ratio value and the real-time hydrogen content, and compare the theoretical ammonia demand with the actual ammonia addition to obtain the ammonia deviation value; According to the ammonia amount deviation value, the flow rate of the ammonia gun is adjusted through PID control to form a closed-loop control system to ensure that the ammonia addition amount is always within the optimal range.

[0023] The optimal range of the amount of ammonia added is 10% to 20% of the hydrogen content.

[0024] Step 4 specifically includes: Set a local oxygen concentration range, detect the local oxygen concentration in the furnace through an online oxygen concentration analyzer, compare the set local oxygen concentration range with the actual local oxygen concentration, and obtain the oxygen concentration range deviation value; According to the oxygen concentration range deviation value, the power of the secondary fan is adjusted through the PID controller to ensure that the oxygen concentration is always within the optimal range.

[0025] The optimal range of oxygen concentration is 1.5% to 2.5%. Example 2

[0026] In order to prove that a method for stable combustion of hydrogen by mixing ammonia with low load in coal-fired boiler has good use effect, the following four experiments were conducted: Experiment 1: Ammonia addition: 10% of the total fuel, local oxygen concentration: 1.5%, furnace temperature: 1350°C, combustion time: 2 hours; Experimental results: combustion efficiency: 97.5%, nitrogen oxide emissions: 50mg / Nm³, combustion stability: good.

[0027] Under low load conditions, the local oxygen concentration was set to 1.5%, which successfully cracked ammonia and produced enough hydrogen to improve combustion efficiency. Through real-time monitoring, the furnace temperature was stabilized at 1350°C. The furnace temperature was stabilized at 1350°C, which was conducive to the cracking of ammonia, and at such a temperature, the hydrogen produced by the cracking of ammonia and the gases such as CO produced by the combustion of pulverized coal worked together to improve the combustion efficiency. The good combustion stability proved that under local oxygen-deficient conditions, the hydrogen produced by the cracking of ammonia could burn stably and the nitrogen oxide emissions were effectively controlled.

[0028] Experiment 2: Ammonia addition: 15% of the total fuel, local oxygen concentration: 2%, furnace temperature: 1350°C, combustion time: 2 hours; Experimental results: combustion efficiency: 97.2%, nitrogen oxide emissions: 45mg / Nm³, combustion stability: good.

[0029] The amount of ammonia added was increased to 15% of the total fuel amount, and the local oxygen concentration was controlled at 2%. Under this condition, the amount of hydrogen produced by ammonia cracking was further increased, which helped to improve the combustion efficiency. The experimental results showed that even with the increase in the amount of ammonia added, good combustion stability could be maintained by controlling the local oxygen concentration, and nitrogen oxide emissions were further reduced to 45mg / Nm³. Compared with Experiment 1, the combustion efficiency of Experiment 2 decreased slightly, but nitrogen oxide emissions were further reduced, indicating that by adjusting the amount of ammonia added and the local oxygen concentration, more efficient combustion can be achieved under low-load operating conditions and pollutant emissions can be reduced.

[0030] Experiment 3: Ammonia addition: 20% of the total fuel, local oxygen concentration: 2.5%, furnace temperature: 1350°C, combustion time: 2 hours; Experimental results: combustion efficiency: 96.8%, nitrogen oxide emissions: 40mg / Nm³, combustion stability: good.

[0031] In this experiment, the amount of ammonia added was further increased to 20% of the total fuel amount, and the local oxygen concentration was controlled at 2.5%. Under this condition, the amount of hydrogen produced by ammonia cracking continued to increase, which helped to improve the combustion efficiency. The experimental results show that even if the amount of ammonia added is further increased, good combustion stability can be maintained by controlling the local oxygen concentration, and nitrogen oxide emissions are further reduced to 40mg / Nm³. Compared with Experiments 1 and 2, the combustion efficiency of Experiment 3 decreased slightly, but nitrogen oxide emissions were further reduced, indicating that by adjusting the amount of ammonia added and the local oxygen concentration, more efficient combustion can be achieved under low-load operating conditions and pollutant emissions can be reduced.

[0032] Experiment 4: Ammonia addition: 0%, local oxygen concentration: 3%, furnace temperature: 1350℃, combustion time: 2 hours; Experimental results: combustion efficiency: 96%, nitrogen oxide emissions: 70mg / Nm³, combustion stability: general.

[0033] In this experiment, no ammonia was added and the local oxygen concentration was controlled at 3%. Under this condition, there was no hydrogen generated by ammonia cracking to assist combustion, and the combustion efficiency was low. The experimental results showed that when no ammonia was added, the combustion efficiency was low and the nitrogen oxide emissions were high, at 70mg / Nm³. Compared with Experiments 1, 2, and 3, the combustion stability of Experiment 4 was average, and the nitrogen oxide emissions were significantly higher than when ammonia was added.

[0034] By comparing the results of Experiment 4 with those of Experiments 1 to 3, it can be seen that under low-load operating conditions, by adding ammonia and controlling the local oxygen concentration environment, ammonia can be thermally cracked to produce hydrogen under local oxygen-deficient conditions, significantly improving combustion stability and reducing nitrogen oxide emissions.

[0035] The embodiments described above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, any equivalent changes or modifications made according to the structures, features and principles described in the patent scope of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. A low-load ammonia-blended cracking hydrogen stable combustion system for a coal-fired boiler, comprising a coal-fired boiler, characterized in that: It also includes an ammonia generating device, an air premixer and an ammonia gun, wherein the output end of the ammonia generating device is connected to the air premixer, the output end of the air premixer is connected to the ammonia gun, the ammonia gun is arranged in a coal-fired boiler, the coal-fired boiler includes an upper part, a middle part and a bottom part, the bottom part is sequentially provided with a secondary fan, a burner, an oil gun and a burner from bottom to top, the middle part is sequentially provided with a plurality of ammonia-blended cracking hydrogen modules, the plurality of ammonia-blended cracking hydrogen modules sequentially include a secondary fan, a burner, an ammonia gun and a burner from bottom to top, and the upper part is provided with a plurality of secondary fans; The coal-fired boiler is provided with a plurality of online oxygen concentration analyzers, a plurality of thermocouple temperature sensors, an online hydrogen concentration analyzer, a pressure sensor and a flue gas analyzer, wherein the plurality of thermocouple temperature sensors are equidistantly arranged, and the online oxygen concentration analyzer, the plurality of thermocouple temperature sensors, the online hydrogen concentration analyzer, the pressure sensor and the flue gas analyzer are connected with a controller; The ammonia generating device is provided with an ammonia concentration sensor, a pressure sensor and a temperature and humidity sensor, and the ammonia concentration sensor, the pressure sensor and the temperature and humidity sensor are connected to the controller, and the controller adjusts the power of the ammonia generating device according to the detection parameters of the ammonia concentration sensor, the pressure sensor and the temperature and humidity sensor.

2. A method for stable combustion of hydrogen from low-load ammonia-blended cracking of coal-fired boilers, characterized in that: A low-load ammonia-blended cracking hydrogen stable combustion system for a coal-fired boiler as claimed in claim 1 comprises: Step 1: Clean the furnace to ensure there is no residue in the furnace, and adjust the coal-fired boiler to low-load operation; Step 2: Open the ammonia gun to add ammonia into the furnace, and evenly disperse the ammonia into the furnace through multiple ammonia-doped hydrogen cracking modules; Step 3: Use an online hydrogen concentration analyzer to detect the hydrogen content in the furnace, and control the ammonia gun through the controller to adjust the amount of ammonia added; Step 4: Use multiple online oxygen concentration analyzers to detect the local oxygen concentration in the furnace, and adjust the local oxygen concentration by controlling the power of the secondary fan through the controller; Step 5: Use multiple thermocouple temperature sensors to detect the temperature in the combustion chamber, and the controller records the temperature in the combustion chamber. Use the pressure sensor to detect the pressure in the combustion chamber, and the controller records the pressure in the combustion chamber. The controller evaluates the combustion stability through the pressure parameter and the temperature parameter. Step 6: Use a flue gas analyzer to detect nitrogen oxide emissions. The controller is set with a standard value for nitrogen oxide emissions. The controller compares the detected value with the standard value. If the detected value is greater than the standard value, the ammonia addition amount and the local oxygen concentration are adjusted through steps 3 and 4 to reduce the detected value.

3. The method for stable combustion of hydrogen from low-load ammonia-blended cracking of coal-fired boiler according to claim 2, characterized in that: The step 3 specifically includes: Set the ammonia addition ratio, detect the hydrogen content in the furnace through the online hydrogen concentration analyzer, calculate the theoretical ammonia demand based on the ratio value and the real-time hydrogen content, and compare the theoretical ammonia demand with the actual ammonia addition to obtain the ammonia deviation value; According to the ammonia amount deviation value, the flow rate of the ammonia gun is adjusted through PID control to form a closed-loop control system to ensure that the ammonia addition amount is always within the optimal range.

4. The method for stable combustion of hydrogen from low-load ammonia-blended cracking of coal-fired boiler according to claim 3, characterized in that: The optimal range of the amount of ammonia added is 10% to 20% of the hydrogen content.

5. The method for stable combustion of hydrogen from low-load ammonia-blended cracking of coal-fired boiler according to claim 2, characterized in that: Step 4 specifically includes: Set a local oxygen concentration range, detect the local oxygen concentration in the furnace through an online oxygen concentration analyzer, compare the set local oxygen concentration range with the actual local oxygen concentration, and obtain the oxygen concentration range deviation value; According to the oxygen concentration range deviation value, the power of the secondary fan is adjusted through the PID controller to ensure that the oxygen concentration is always within the optimal range.

6. The method for stable combustion of hydrogen from low-load ammonia-blended cracking of coal-fired boiler according to claim 5, characterized in that: The optimal range of oxygen concentration is 1.5% to 2.5%.

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