A method and system for stable combustion of hydrogen gas by ammonia cracking with low load in a coal-fired boiler

Abstract

The present invention relates to a method and system for stable combustion of hydrogen produced by ammonia cracking with ammonia addition at low load in a coal-fired boiler, including a coal-fired boiler, an ammonia production device, an air pre-mixer, and an ammonia lance. The output end of the ammonia production device is connected to the air pre-mixer, and the output end of the air pre-mixer is connected to the ammonia lance. A plurality of ammonia cracking hydrogen modules are sequentially arranged in the middle of the coal-fired boiler. The plurality of ammonia cracking hydrogen modules sequentially include secondary air fans, burners, ammonia lances, and burners from bottom to top, and a plurality of secondary air fans are arranged in the upper part. The coal-fired boiler is provided with an on-line oxygen concentration analyzer, a thermocouple temperature sensor, an on-line hydrogen concentration analyzer, a pressure sensor, and a flue gas analyzer connected to a controller. By optimizing the structure of the coal-fired boiler and adjusting the ammonia addition amount through a method for stable combustion of hydrogen produced by ammonia cracking with ammonia addition at low load in the coal-fired boiler, and precisely controlling the local oxygen concentration, the overall combustion efficiency and stability are improved, and the nitrogen oxide emissions are reduced.

Description

Technical Field

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

[0002] As a key equipment in thermal power plants, coal-fired boilers play an important role in power production. However, when operating at low load, there are some problems with coal-fired boilers, especially when using ammonia-doped combustion technology. The ammonia-doped combustion technology aims to use ammonia to replace part of the coal to reduce carbon emissions and improve combustion efficiency, such as a pulverized coal boiler system and an ammonia-doped combustion method disclosed in CN113432117A. However, due to the different combustion characteristics of ammonia and coal, the following problems exist in the ammonia-doped combustion technology under low load operating conditions:

[0003] 1. Combustion stability problem: Under low load conditions, coal-fired boilers with ammonia-doped combustion often face the problem of poor combustion stability, especially when the ammonia ratio is relatively high. This is mainly because the combustion characteristics of ammonia are different from those of coal, resulting in difficult control of the combustion process, which may cause flame extinction or incomplete combustion.

[0004] 2. Nitrogen oxide emission problem: Even when the combustion conditions are optimized, ammonia-doped combustion may still lead to an increase in nitrogen oxide emissions. This is because ammonia is prone to react with oxygen at high temperatures to form nitrogen oxides, and nitrogen oxides are one of the important sources of air pollution.

[0005] 3. Boiler combustion efficiency problem: When ammonia-doped combustion is carried out, if the ammonia ratio is too high, it may lead to a decrease in the boiler combustion efficiency, thereby affecting the overall performance of the coal-fired boiler.

[0006] Therefore, there is an urgent need for a system and method for stable combustion of ammonia-doped and cracked hydrogen in a coal-fired boiler at low load. Summary of the Invention

[0007] In order to solve the problems of unstable ammonia-doped combustion and generation of air pollutants in a coal-fired boiler under low load conditions, the present invention provides a method and system for stable combustion of ammonia-doped and cracked hydrogen in a coal-fired boiler at low load. By optimizing the structure of the coal-fired boiler, adjusting the ammonia addition amount, and precisely controlling the local oxygen concentration, the overall combustion efficiency and stability are improved, and nitrogen oxide emissions are reduced.

[0008] To solve the above problems, a stable combustion system for low-load ammonia-doped cracking hydrogen in a coal-fired boiler is proposed in the first aspect of the present invention, which includes a coal-fired boiler, and also includes an ammonia generation device, an air pre-mixer and an ammonia gun. The output end of the ammonia generation device is connected to the air pre-mixer, the output end of the air pre-mixer is connected to the ammonia gun, and the ammonia gun is arranged in the coal-fired boiler. The coal-fired boiler includes an upper part, a middle part and a bottom part. A secondary air blower, a burner, an oil gun and a burner are sequentially arranged from bottom to top at the bottom part. A plurality of ammonia-doped cracking hydrogen modules are sequentially arranged in the middle part. The plurality of ammonia-doped cracking hydrogen modules sequentially include a secondary air blower, a burner, an ammonia gun and a burner from bottom to top. A plurality of secondary air blowers are arranged in the upper part;

[0009] The coal-fired boiler is provided with a plurality of on-line oxygen concentration analyzers, a plurality of thermocouple temperature sensors, an on-line hydrogen concentration analyzer, a pressure sensor and a flue gas analyzer. The plurality of thermocouple temperature sensors are arranged at equal intervals. The on-line oxygen concentration analyzers, the plurality of thermocouple temperature sensors, the on-line hydrogen concentration analyzer, the pressure sensor and the flue gas analyzer are connected to a controller.

[0010] Furthermore, the ammonia generation device is provided with an ammonia concentration sensor, a pressure sensor and a temperature and humidity sensor. The ammonia concentration sensor, the pressure sensor and the temperature and humidity sensor are connected to the controller. The controller adjusts the power of the ammonia generation device according to the detection parameters of the ammonia concentration sensor, the pressure sensor and the temperature and humidity sensor.

[0011] An ammonia concentration sensor, a pressure sensor and a temperature and humidity sensor are set to monitor the ammonia generation device, and intelligent adjustment of the ammonia concentration sensor is realized in combination with the controller.

[0012] A stable combustion method for low-load ammonia-doped cracking hydrogen in a coal-fired boiler is proposed in the second aspect of the present invention, which includes:

[0013] Step 1: Clean the furnace to ensure that there is no residue in the furnace, and adjust the coal-fired boiler to a low-load operation state;

[0014] Step 2: Open the ammonia gun to add ammonia into the furnace, and make the ammonia evenly disperse into the furnace through a plurality of ammonia-doped cracking hydrogen modules;

[0015] Step 3: Use the on-line hydrogen concentration analyzer to detect the hydrogen content in the furnace, and control the ammonia gun through the controller to adjust the ammonia addition amount;

[0016] Step 4: Use a plurality of on-line oxygen concentration analyzers to detect the local oxygen concentration in the furnace, and control the power of the secondary air blower through the controller to adjust the local oxygen concentration;

[0017] Step 5: Use multiple thermocouple temperature sensors to detect the temperature inside the combustion chamber. The controller records the temperature inside the combustion chamber. Detect the pressure inside the combustion chamber through a pressure sensor. The controller records the pressure inside the combustion chamber. The controller evaluates the combustion stability based on the pressure parameters and temperature parameters;

[0018] Step 6: Use a flue gas analyzer to detect the nitrogen oxide emissions. A standard value of nitrogen oxide emissions is set in the controller. The controller compares the detected value with the standard value. If the detected value is greater than the emissions standard value, adjust the ammonia addition amount and the local oxygen concentration through Step 3 and Step 4 to reduce the detected value.

[0019] Further, the specific steps of Step 3 are as follows:

[0020] Set the ammonia addition ratio. Detect the hydrogen content in the furnace through an on-line hydrogen concentration analyzer. Calculate the theoretically required ammonia amount based on the ratio value and the real-time hydrogen content. Compare the theoretically required ammonia amount with the actual ammonia addition amount to obtain the ammonia amount deviation value;

[0021] According to the ammonia amount deviation value, adjust the flow rate of the ammonia gun through PID control to form a closed-loop control system to ensure that the ammonia addition amount is always within the optimal range.

[0022] Further, the optimal range of the ammonia addition amount is 10% - 20% of the hydrogen content.

[0023] Further, the specific steps of Step 4 are as follows:

[0024] Set the local oxygen concentration range. Detect the local oxygen concentration in the furnace through an on-line oxygen concentration analyzer. Compare the set local oxygen concentration range with the actual local oxygen concentration to obtain the oxygen concentration range deviation value;

[0025] According to the oxygen concentration range deviation value, adjust the power of the secondary fan through a PID controller to ensure that the oxygen concentration is always within the optimal range.

[0026] Further, the optimal range of the oxygen concentration is 1.5% - 2.5%.

[0027] Through the above technical solutions, the beneficial effects of the present invention are as follows:

[0028] (1) The present invention optimizes the structure of the coal-fired boiler to provide a basis for the uniform dispersion of ammonia into the furnace and the control of the local oxygen concentration. A plurality of ammonia-doped cracking hydrogen modules are sequentially arranged in the middle of the coal-fired boiler. The ammonia-doped cracking hydrogen modules sequentially include a secondary fan, a burner, an ammonia gun from bottom to top, and the burner ensures stable temperature, which helps the cracking of ammonia.

[0029] (2) A method for stable combustion of hydrogen produced by ammonia cracking with low load in a coal-fired boiler of the present invention realizes efficient cracking of ammonia under locally oxygen-deficient conditions by precisely controlling the ammonia addition amount and local oxygen concentration, generating hydrogen to assist the stable combustion of the coal-fired boiler during low-load operation. This method can not only improve the combustion efficiency but also significantly reduce nitrogen oxide emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a structural diagram of a system for stable combustion of hydrogen produced by ammonia cracking with low load in a coal-fired boiler of the present invention;

[0031] Figure 2 It is a step flow chart of a method for stable combustion of hydrogen produced by ammonia cracking with low load in a coal-fired boiler of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The present invention will be further described below in conjunction with the drawings and specific embodiments: Embodiment 1

[0033] As Figures 1 - 2 shown, a system for stable combustion of hydrogen produced by ammonia cracking with low load in a coal-fired boiler includes a coal-fired boiler, and further includes an ammonia generation device, an air pre-mixer, and an ammonia gun. The output end of the ammonia generation device is connected to the air pre-mixer, the output end of the air pre-mixer is connected to the ammonia gun, and the ammonia gun is arranged in the coal-fired boiler. The coal-fired boiler includes an upper part, a middle part, and a bottom part. A secondary air blower, a burner, an oil gun, and a burner are sequentially arranged from bottom to top at the bottom part. A plurality of ammonia cracking hydrogen modules are sequentially arranged in the middle part. The plurality of ammonia cracking hydrogen modules sequentially include a secondary air blower, a burner, an ammonia gun, and a burner from bottom to top. A plurality of secondary air blowers are arranged in the upper part;

[0034] The coal-fired boiler is provided with a plurality of on-line oxygen concentration analyzers, a plurality of thermocouple temperature sensors, an on-line hydrogen concentration analyzer, a pressure sensor, and a flue gas analyzer. The plurality of thermocouple temperature sensors are arranged at equal intervals. The on-line oxygen concentration analyzer, the plurality of thermocouple temperature sensors, the on-line hydrogen concentration analyzer, the pressure sensor, and the flue gas analyzer are connected to a controller.

[0035] The ammonia generation device is provided with an ammonia concentration sensor, a pressure sensor, and a temperature and humidity sensor. The ammonia concentration sensor, the pressure sensor, and the temperature and humidity sensor are connected to the controller. The controller adjusts the power of the ammonia generation device according to the detection parameters of the ammonia concentration sensor, the pressure sensor, and the temperature and humidity sensor.

[0036] A method for stable combustion of hydrogen produced by ammonia cracking with low load in a coal-fired boiler includes:

[0037] Step 1: Clean the furnace to ensure that there is no residue in the furnace, and adjust the coal-fired boiler to the low-load operation state;

[0038] Step 2: Open the ammonia gun to add ammonia into the furnace, and make the ammonia evenly disperse into the furnace through multiple ammonia-diluted hydrogen cracking modules;

[0039] Step 3: Use an on-line hydrogen concentration analyzer to detect the hydrogen content in the furnace, and control the ammonia gun through a controller to adjust the ammonia addition amount;

[0040] Step 4: Use multiple on-line oxygen concentration analyzers to detect the local oxygen concentration in the furnace, and control the power of the secondary fan through a controller to adjust the local oxygen concentration;

[0041] Step 5: Use multiple thermocouple temperature sensors to detect the temperature in the combustion chamber, the controller records the temperature in the combustion chamber, use a pressure sensor to detect the pressure in the combustion chamber, the controller records the pressure in the combustion chamber, and the controller evaluates the combustion stability through the pressure parameter and the temperature parameter;

[0042] Step 6: Use a flue gas analyzer to detect the nitrogen oxide emission amount. A nitrogen oxide emission standard value is set in the controller. The controller compares the detected value with the standard value. If the detected value is greater than the emission standard value, adjust the ammonia addition amount and the local oxygen concentration through Step 3 and Step 4 to make the detected value decrease.

[0043] The specific content of Step 3 includes:

[0044] Set the ammonia addition ratio, use an on-line hydrogen concentration analyzer to detect the hydrogen content in the furnace, calculate the theoretically required ammonia amount according to the ratio value and the real-time hydrogen content, and compare the theoretically required ammonia amount with the actual ammonia addition amount to obtain the ammonia amount deviation value;

[0045] According to the ammonia amount deviation value, adjust the flow rate of the ammonia gun through PID control to form a closed-loop control system, ensuring that the ammonia addition amount is always within the optimal range.

[0046] The optimal range of the ammonia addition amount is 10% - 20% of the hydrogen content.

[0047] The specific content of Step 4 includes:

[0048] Set the local oxygen concentration range, use an on-line oxygen concentration analyzer to detect the local oxygen concentration in the furnace, compare the set local oxygen concentration range with the actual local oxygen concentration to obtain the oxygen concentration range deviation value;

[0049] According to the oxygen concentration range deviation value, adjust the power of the secondary fan through a PID controller to ensure that the oxygen concentration is always within the optimal range.

[0050] The optimal range of the oxygen concentration is 1.5% - 2.5%. Embodiment 2

[0051] In order to prove that a method for stable combustion of hydrogen produced by ammonia cracking with low load in a coal-fired boiler has good application effects, the following four experiments were carried out:

[0052] Experiment 1:

[0053] Ammonia addition amount: 10% of the total fuel amount, local oxygen concentration: 1.5%, furnace temperature: 1350 °C, combustion time: 2 hours;

[0054] Experiment results: Combustion efficiency: 97.5%, nitrogen oxide emission: 50 mg / Nm³, combustion stability: good.

[0055] Under the low load condition, the local oxygen concentration was set at 1.5%, and the cracking of ammonia was successfully achieved, generating sufficient hydrogen to improve the combustion efficiency. Through real-time monitoring, the furnace temperature was stable at 1350 °C. The stable furnace temperature at 1350 °C contributed to the cracking of ammonia, and at such a temperature, the hydrogen produced by ammonia cracking and gases such as CO produced by pulverized coal combustion acted together to improve the combustion efficiency. The combustion stability was good, proving that under local oxygen-deficient conditions, the hydrogen produced by ammonia cracking could burn stably, and the nitrogen oxide emissions were effectively controlled.

[0056] Experiment 2:

[0057] Ammonia addition amount: 15% of the total fuel amount, local oxygen concentration: 2%, furnace temperature: 1350 °C, combustion time: 2 hours;

[0058] Experiment results: Combustion efficiency: 97.2%, nitrogen oxide emission: 45 mg / Nm³, combustion stability: good.

[0059] The ammonia addition amount was increased to 15% of the total fuel amount, and the local oxygen concentration was controlled at 2%. Under such conditions, the amount of hydrogen produced by ammonia cracking further increased, which helped to improve the combustion efficiency. The experiment results showed that even when the ammonia addition amount increased, by controlling the local oxygen concentration, good combustion stability could still be maintained, and the nitrogen oxide emissions were further reduced to 45 mg / Nm³. Compared with Experiment 1, the combustion efficiency of Experiment 2 decreased slightly, but the nitrogen oxide emissions were further reduced, indicating that by adjusting the ammonia addition amount and local oxygen concentration, more efficient combustion can be achieved under low load operating conditions and pollutant emissions can be reduced.

[0060] Experiment 3:

[0061] Ammonia addition amount: 20% of the total fuel amount, local oxygen concentration: 2.5%, furnace temperature: 1350 °C, combustion time: 2 hours;

[0062] Experimental results: Combustion efficiency: 96.8%, Nitrogen oxide emissions: 40 mg / Nm³, Combustion stability: Good.

[0063] In this experiment, the ammonia addition was further increased to 20% of the total fuel amount, and the local oxygen concentration was controlled at 2.5%. Under these conditions, the amount of hydrogen generated by the cracking of ammonia continued to increase, which helped to improve the combustion efficiency. The experimental results showed that even if the ammonia addition was further increased, by controlling the local oxygen concentration, good combustion stability could still be maintained, and the nitrogen oxide emissions were further reduced to 40 mg / Nm³. Compared with Experiment 1 and Experiment 2, the combustion efficiency of Experiment 3 decreased slightly, but the nitrogen oxide emissions were further reduced, indicating that by adjusting the ammonia addition and local oxygen concentration, more efficient combustion could be achieved under low-load operating conditions and pollutant emissions could be reduced.

[0064] Experiment 4:

[0065] Ammonia addition: 0%, Local oxygen concentration: 3%, Furnace temperature: 1350 °C, Combustion time: 2 hours;

[0066] Experimental results: Combustion efficiency: 96%, Nitrogen oxide emissions: 70 mg / Nm³, Combustion stability: Moderate.

[0067] In this experiment, no ammonia was added, and the local oxygen concentration was controlled at 3%. Under these conditions, without the hydrogen generated by the cracking of ammonia to assist combustion, 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 70 mg / Nm³. Compared with Experiment 1, Experiment 2, and Experiment 3, the combustion stability of Experiment 4 was moderate, and the nitrogen oxide emissions were significantly higher than those in the case of adding ammonia.

[0068] By comparing the results of Experiment 4 with those of Experiments 1 - 3, it can be seen that under low-load operating conditions, by adding ammonia and controlling the local oxygen concentration environment, ammonia can thermally crack to generate hydrogen under local oxygen-deficient conditions, significantly improving combustion stability and reducing nitrogen oxide emissions.

[0069] The above-described embodiments are only preferred embodiments of the present invention and do not limit the scope of implementation of the present invention. Therefore, any equivalent changes or modifications made according to the structure, features, and principles described in the scope of this invention patent should be included in the scope of the patent application of the present invention.

Claims

1. A method for stable combustion of hydrogen from low-load ammonia-blended cracking of 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, and the output end of the air premixer is connected to the ammonia gun, which is arranged in a coal-fired boiler. The coal-fired boiler includes 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-blended cracking hydrogen modules in sequence, wherein 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, wherein the upper part is provided with a plurality of secondary fans; wherein the coal-fired boiler is provided with a plurality of online oxygen concentration analyzers, a plurality of A thermocouple temperature sensor, an online hydrogen concentration analyzer, a pressure sensor and a flue gas analyzer, the multiple thermocouple temperature sensors are equidistantly arranged, the online oxygen concentration analyzer, the multiple thermocouple temperature sensors, the online hydrogen concentration analyzer, the pressure sensor and the flue gas analyzer are connected to a controller; the ammonia generation device is provided with an ammonia concentration sensor, a pressure sensor and a temperature and humidity sensor, 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 generation device according to the detection parameters of the ammonia concentration sensor, the pressure sensor and the temperature and humidity sensor; include: 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 for emissions, the amount of ammonia added and the local oxygen concentration are adjusted through steps 3 and 4 to reduce the detected value. The optimal range of oxygen concentration is 1.5%~2.5%; The optimal range of the amount of ammonia added is 10% to 20% of the hydrogen content.

2. The method for stable combustion of hydrogen from low-load ammonia-blended cracking of coal-fired boilers according to claim 1, characterized in that: The step 3 specifically includes: setting the ammonia addition ratio in the claims, detecting the hydrogen content in the furnace by an online hydrogen concentration analyzer, calculating the theoretical ammonia demand according to the ratio value and the real-time hydrogen content, and comparing the theoretical ammonia demand with the actual ammonia addition to obtain an ammonia deviation value; according to the ammonia deviation value, adjusting the flow rate of the ammonia gun by PID control to form a closed-loop control system to ensure that the ammonia addition amount is always within the optimal range.

3. The method for stable combustion of hydrogen from low-load ammonia-blended cracking of coal-fired boiler according to claim 1, characterized in that: Step 4 specifically includes: setting a local oxygen concentration range, detecting the local oxygen concentration in the furnace through an online oxygen concentration analyzer, comparing the set local oxygen concentration range with the actual local oxygen concentration, and obtaining an oxygen concentration range deviation value; according to the oxygen concentration range deviation value, adjusting the power of the secondary fan through a PID controller to ensure that the oxygen concentration is always within the optimal range.

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