Low-nitrogen castable for combustion chamber of circulating fluidized bed boiler and preparation method thereof

Abstract

The present application relates to circulating fluidized bed boiler combustion technical field, specifically is related to a kind of low nitrogen castable for circulating fluidized bed boiler combustion chamber and preparation method, castable is made of the following mass percentage of raw materials: 10~20wt% sintered magnesium-aluminum spinel, 5~12wt% active α-Al2O3 micro powder, 3~5wt% binder a, 0.1~0.4wt% water reducing agent, 4~15wt% water, 1~5wt% nitrogen reduction compound and 2~6wt% aggregate, the balance of white fused alumina by electric melting;Its preparation method is: S1, preparation main mixture according to formula;S2, preparation main castable;S3, preparation nitrogen reduction compound;S4, preparation functional castable;S5, cast construction;The raw material of the present application uses white fused alumina by electric melting and sintered magnesium-aluminum spinel as raw material has excellent high-temperature resistance;By active α-Al2O3 micro powder and white fused alumina by electric melting, castable has good corrosion resistance;By urea particle wrapping binder b and alumina powder form sustained-release microspheres, so that castable realizes sustained nitrogen reduction effect.

Description

Technical Field

[0001] This invention relates to the field of circulating fluidized bed boiler combustion technology, specifically to a low-NOx castable for the combustion chamber of a circulating fluidized bed boiler and its preparation method. Background Technology

[0002] A circulating fluidized bed boiler is a type of boiler that utilizes circulating fluidized bed technology for combustion. Circulating fluidized bed is an advanced combustion technology that uses a high-speed airflow to suspend solid particles (usually coal, biomass, or waste) in a bed, creating a fluid-like state, hence the name "fluidized bed." During combustion, the fuel particles are impacted and agitated by the high-temperature airflow within the bed, allowing for thorough mixing and reaction with oxygen, thus achieving highly efficient combustion.

[0003] The combustion chamber of a circulating fluidized bed (CFB) boiler refers to the area inside the boiler used for combustion. In a CFB boiler, the combustion chamber typically consists of a specially designed bed and nozzles. The nozzles inject fuel and gas to maintain the fluidization of the bed. By controlling parameters such as bed temperature, airflow velocity, and fuel input, precise control of the combustion process can be achieved, thereby improving combustion efficiency, reducing emissions, and decreasing energy consumption.

[0004] The existing castable refractory materials used in the combustion chambers of circulating fluidized bed boilers are only used to coat or cover the internal surface of the combustion chamber to enhance its heat resistance, but they cannot reduce the emission of nitrogen oxides (NOx) generated during combustion. The existing NOx reduction method is to achieve the effect of spraying NOx reducing agent after the nitrogen is discharged from the combustion chamber, which consumes additional power energy and cannot achieve NOx reduction from the castable refractory itself. If the NOx reducing agent is added directly to the castable refractory, it will affect the heat resistance and strength of the castable refractory. However, the effect of spraying NOx reducing agent on the surface of the castable refractory after demolding is not practical and cannot achieve a continuous NOx reduction effect during high-temperature combustion. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a low-NOx castable for the combustion chamber of a circulating fluidized bed boiler and its preparation method.

[0006] The technical solution of the present invention is: a low-NOx castable for combustion chamber of a circulating fluidized bed boiler, comprising the following raw materials in the following mass percentages: 10-20 wt% sintered magnesium aluminum spinel, 5-12 wt% active α-Al2O3 micro powder, 3-5 wt% binder a, 0.1-0.4 wt% water-reducing agent, 4-15 wt% water, 1-5 wt% NOx-reducing compound, and 2-6 wt% aggregate, with the balance being fused white corundum;

[0007] The nitrogen-reducing complex comprises, by mass parts: 20-30 parts urea, 15-20 parts ammonium sulfate, 5-9 parts alumina, 3-8 parts ethanolamine, 4-6 parts dimethyl silicone oil, 3.5-5.5 parts potassium chloride, 1-2 parts binder b, 0.3-2 parts alkyl glucoside, and 100 parts water.

[0008] Explanation: Alkyl glucosides can enhance the dispersibility of urea, strengthen its surface activity, increase the amount of ammonia produced by urea decomposition, improve the conversion rate of nitrogen oxides, and produce ammonia with ammonium sulfate at high temperatures. They can also have a synergistic effect with the ammonia produced by urea decomposition, greatly improving the conversion rate of catalytic reduction of nitrogen oxides. At high temperatures, potassium chloride can catalyze the thermal decomposition of urea, promote ammonia production, and potassium chloride can form a low eutectic point with urea, thereby further improving the conversion rate of nitrogen oxides. Alumina can enhance the sustained nitrogen-reducing effect of the nitrogen-reducing complex.

[0009] Furthermore, the water-reducing agent uses 0-10 wt% carbon nanotubes and the balance is allyl polyoxyethylene ether maleic anhydride.

[0010] Explanation: Carbon nanotubes are nanomaterials with extremely high specific surface area, which can improve the flowability of castables at the microscale, making them easier to construct and mold; allyl polyoxyethylene ether maleic anhydride has excellent dispersibility and stability, which can effectively prevent the castable from separating or unevenly dispersing during construction, ensuring the integrity and stability of the castable; due to the action of the water-reducing agent, the amount of cement used can be reduced to a certain extent, lowering costs, while maintaining the performance and effect of the castable; improving the flowability and plasticity of the castable can reduce energy consumption during construction, increase work efficiency, and save energy costs.

[0011] Furthermore, the water-reducing agent comprises 0-5 wt% nano-silica, 0-5 wt% nano-alumina, and the remainder being FS-10 water-reducing agent.

[0012] Note: Nano-silica and nano-alumina have extremely small particle size and high specific surface area, which can effectively improve the fluidity and plasticity of castables, making them easier to construct and mold. The addition of nanomaterials helps to improve the stability and durability of castables, prevents segregation or uneven dispersion during construction, and ensures construction quality and castable performance. Due to the action of water-reducing agents, the amount of cement used can be reduced to a certain extent, thereby reducing costs while maintaining the performance and effect of castables.

[0013] Furthermore, the binder a is one or more of Secar71 cement, active p-Al2O3 micro powder, and magnesium phosphate cement; the aggregate is one or more of clay particles, perlite, and shale ceramic.

[0014] Explanation: Clay particles, perlite, and shale ceramics all have hollow structures and rough surfaces, which can increase the contact surface area, allowing the aggregates to bond tightly with fused white corundum, active α-Al2O3 micro powder, and sintered magnesia-alumina spinel. These aggregates have good mechanical properties, which can enhance the strength and stability of the castable, and improve its load-bearing capacity and durability. Perlite is widely used in thermal insulation and refractory materials. The addition of this lightweight aggregate can reduce the density of the castable, reduce the self-weight of the structure, and help reduce the pressure on the foundation and supporting structure. Aggregates such as shale ceramics have good thermal insulation properties, which can reduce heat conduction and improve the thermal efficiency of the combustion chamber of circulating fluidized bed boilers.

[0015] Furthermore, the preparation method of the low-NOx castable for the combustion chamber of the circulating fluidized bed boiler includes the following steps:

[0016] S1. Weigh out the fused white corundum, sintered magnesium aluminum spinel, active α-Al2O3 micro powder, water-reducing agent, aggregate and binder a according to the formula, grind them thoroughly and evenly to obtain the main mixture, and store it in moisture-proof packaging.

[0017] S2. Pour the main mixture into the mixer and mix for 5-10 minutes. Divide the water into 10-20 equal parts and add them in batches until the mixture is uniform. The interval between each addition of water is 8-15 minutes to obtain the main casting material.

[0018] S3. Preparation of nitrogen-reducing complex;

[0019] S4. Weigh out 5-10% of the main casting material by its total mass and mix it evenly with the prepared nitrogen-reducing compound. After exporting, let it stand for 5-10 minutes to obtain the functional casting material.

[0020] S5. Pour the remaining main castable material and allow it to dry and harden naturally. Then, pour the functional castable material again and bake it at 100-120℃ for 48 hours. Then, slowly increase the temperature to the working temperature at 10-20℃ / h.

[0021] Explanation: Thorough grinding and mixing of raw materials ensures the homogeneity of the main mixture, which guarantees the uniform distribution of various raw materials in subsequent preparation processes, thereby improving the consistency and stability of the preparation process; Part of the main castable is mixed with the nitrogen-reducing compound to form a functional castable. The nitrogen-reducing compound can effectively reduce the amount of nitrogen oxides emitted during the use of the castable, which is beneficial to environmental protection and reducing air pollution.

[0022] The main castable is dried before the functional castable is cast. The functional castable is then coated on the main castable. This achieves the nitrogen reduction function of the castable without affecting the original strength and heat resistance of the castable. After baking, the two are promoted to be tightly integrated. The baking and slow heating treatment of the castable also helps to enhance the thermal stability and high temperature resistance of the castable, ensuring its long-term stable operation in the combustion chamber of the circulating fluidized bed boiler.

[0023] Furthermore, according to the preparation method of low-NOx castable for combustion chambers of circulating fluidized bed boilers, the preparation method of the NOx-reducing compound is as follows:

[0024] S3-1. High-purity ammonia and carbon dioxide are prepared and reacted in a reactor under heat and pressure. The reaction temperature is 170–180℃, and the pressure is 3 × 10⁻⁶. 4 kPa, after repeated compression reaction, urea melt is obtained;

[0025] S3-2. Cool the urea melt to room temperature, and mix it with ammonium sulfate, ethanolamine, dimethyl silicone oil, alkyl glucoside, potassium chloride and water according to the formula ratio, and stir evenly to obtain a urea solution composition.

[0026] S3-3. Place the urea solution composition into a multi-stage liquid film crystallizer to crystallize and obtain urea crystals. Put the urea crystals into a crusher to crush them into particles, and after sieving, obtain urea particles. Put the urea particles into a coating machine, adjust the speed and tilt angle and start it. Spray atomized binder b on the rotating urea particles to make the urea particles evenly coated with binder b. Then add alumina powder in multiple batches to coat the urea particles. The amount of alumina powder added each time accounts for 10-20% of the total mass of the particles. Repeat the cycle until all the alumina powder is added. After drying, obtain the nitrogen-reducing complex.

[0027] Explanation: The use of high-purity ammonia and carbon dioxide ensures the quality and purity of the produced urea, improving the quality and performance of the prepared product; the urea particles are sprayed with a mist binder b in a coating machine, so that the urea particles can be uniformly coated with binder b, and then alumina powder is added for coating, ensuring the uniformity and stability of the nitrogen-reducing complex.

[0028] Potassium chloride can lower the melting point of urea and increase the activity of ammonia production under surface thermal reaction. Alkyl glucoside and ammonium sulfate generate ammonia under high temperature environment and can play a synergistic role with the ammonia produced by urea decomposition, thereby improving the conversion rate of catalytic reduction of nitrogen oxides. By coating urea particles with binder b and alumina powder in a coating machine, urea can be formed into slow-release microspheres. The prepared nitrogen-reducing complex, after drying, has good stability and storage resistance, and can be used stably in the combustion chamber of circulating fluidized bed boilers for a long time, improving the reliability and stability of the equipment, achieving a slow-release effect, and realizing the continuous nitrogen reduction effect during high-temperature combustion.

[0029] The prepared urea melt contains carbon dioxide and ammonia. After crystallization, tiny air bubbles are present inside, and the coating process also causes these bubbles to be incorporated. Therefore, after the prepared nitrogen-reducing compound is mixed with some castable to obtain functional castable, the nitrogen-reducing compound will float on the outer surface of the functional castable after casting due to buoyancy, thus further enhancing the nitrogen-reducing effect inside the boiler combustion chamber.

[0030] Furthermore, the atomized binder b is one or a combination of polylactic acid or polyvinyl alcohol.

[0031] Note: Both polylactic acid and polyvinyl alcohol are biodegradable materials, which are environmentally friendly. After use, they can be naturally degraded into water and carbon dioxide, without causing long-term pollution to the environment. Both materials can form a uniform film covering the surface of urea particles, effectively encapsulating the particles and maintaining stability, which is conducive to achieving the slow-release effect of the nitrogen-reducing compound.

[0032] Furthermore, the coating machine has a rotation speed of 30-70 r / m, a coating time of 10-20 min, and a temperature environment controlled at 30-45℃.

[0033] Explanation: By controlling the rotation speed and coating time of the coating machine, it is possible to ensure that the urea granules are evenly covered during the coating process, allowing the binder b and alumina powder to adhere evenly to the granule surface, thus improving the stability and uniformity of the nitrogen-reducing compound. Controlling the coating time ensures that the urea granules are in full contact with the binder b and alumina powder during the coating process, ensuring the coating effect while avoiding over-coating and waste that may result from excessively long coating times. Controlling the temperature environment ensures temperature stability during the coating process, which helps maintain the fluidity and viscosity of the binder b, allowing it to evenly cover the granule surface, and also facilitates the subsequent drying process. Controlling the rotation speed, coating time, and temperature environment is relatively simple, and operators can adjust them according to the actual situation, reducing the difficulty of operation and the error rate.

[0034] Furthermore, the average particle size of the alumina powder is 10–100 μm; and the average thickness of the alumina powder coating on the urea particles is controlled to be 20–900 μm.

[0035] Explanation: By controlling the average particle size of alumina powder, it is possible to ensure that the particle size is moderate, which is conducive to forming a uniform coating layer on the surface of urea particles. The average particle size of alumina powder is between 10 and 100 μm, which is conducive to forming a uniform coating layer without affecting the physical properties and flowability of urea particles. The coating thickness can be controlled to adjust the slow-release effect of the nitrogen-reducing compound. It can be reasonably adjusted according to actual needs to improve the stability and controllability of the nitrogen-reducing effect. An appropriate coating thickness can slow down the release rate of nitrogen-reducing substances, making them more persistent and stable during combustion, thereby effectively and continuously reducing nitrogen oxide emissions.

[0036] The beneficial effects of this invention are:

[0037] (1) The raw materials used in this invention are fused white corundum and sintered magnesium aluminum spinel, which have excellent high temperature resistance and can withstand the high temperature environment in the combustion chamber of a circulating fluidized bed boiler, ensuring the stability and reliability of the castable. The active α-Al2O3 micro powder and fused white corundum give the castable good corrosion resistance, which can resist the erosion of the castable by the corrosive substances generated in the combustion chamber and extend its service life. The addition of binder a helps to improve the bonding force and plasticity of the castable, making it easier to construct and form. The addition of water-reducing agent helps to control the fluidity of the castable, ensuring that it has appropriate fluidity and plasticity during construction. The components containing nitrogen-reducing compound can reduce the emission of nitrogen oxides generated during combustion and promote environmental protection.

[0038] (2) The process of this invention achieves the nitrogen reduction function of the castable by coating the main castable with a functional castable without affecting the original strength and heat resistance of the castable. The urea solution composition is prepared by mixing urea with ammonium sulfate, ethanolamine, dimethyl silicone oil, alkyl glucoside, potassium chloride and water according to the formula ratio, which can increase the ammonia output at high temperature. The urea particles are coated with binder b and alumina powder in the coating machine to form slow-release microspheres, so that the castable can achieve a continuous nitrogen reduction effect. After the nitrogen reduction complex is mixed with part of the castable to obtain the functional castable, the nitrogen reduction complex can float on the outer surface of the functional castable after casting, ensuring the effective role of the nitrogen reduction complex. Attached Figure Description

[0039] Figure 1 This is a bar chart showing the nitrogen reduction performance of Experimental Examples 1-9 and Control Examples 1 and 3 of this invention;

[0040] Figure 2This is a bar chart showing the compressive strength properties of Experimental Examples 1, 6, and 7 and Control Example 2 of this invention;

[0041] Figure 3 This is a bar chart showing the corrosion resistance performance of Experimental Examples 1, 6, and 7 and Control Example 2 of this invention. Detailed Implementation

[0042] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0043] Example 1: A low-NOx castable for the combustion chamber of a circulating fluidized bed boiler, comprising the following raw materials by mass percentage: 15wt% sintered magnesium aluminum spinel, 8.5wt% active α-Al2O3 micro powder, 4wt% binder a, 0.25wt% water-reducing agent, 9.5wt% water, 3wt% NOx-reducing compound, and 4wt% aggregate, with the balance being fused white corundum;

[0044] The binder a is a mixture of Secar71 cement, active ρ-Al2O3 micro powder and magnesium phosphate cement of equal mass;

[0045] The nitrogen-reducing compound comprises, by weight parts: 25 parts urea, 17.5 parts ammonium sulfate, 7 parts alumina, 5.5 parts ethanolamine, 5 parts dimethyl silicone oil, 4.5 parts potassium chloride, 1.5 parts binder b, 1.2 parts alkyl glucoside, and 100 parts water; the water-reducing agent is composed of 5 wt% carbon nanotubes and the balance being allyl polyoxyethylene ether maleic anhydride.

[0046] The aggregate is a mixture of clay particles, perlite and shale ceramic of equal mass;

[0047] The method for preparing the low-NOx castable for the combustion chamber of the circulating fluidized bed boiler is characterized by comprising the following steps:

[0048] S1. Weigh out the fused white corundum, sintered magnesium aluminum spinel, active α-Al2O3 micro powder, water-reducing agent, aggregate and binder a according to the formula, grind them thoroughly and evenly to obtain the main mixture, and store it in moisture-proof packaging.

[0049] S2. Pour the main mixture into the mixer and mix for 7.5 minutes. Divide the water into 15 equal parts and add them in batches until they are mixed evenly. The interval between each addition of water is 11.5 minutes to obtain the main casting material.

[0050] S3. Preparation of nitrogen-reducing complex;

[0051] S3-1. Prepared ammonia and carbon dioxide (99.8% purity) are heated and pressurized in a reaction vessel at a temperature of 175℃ and a pressure of 3 × 10⁻⁶.4 kPa, after repeated compression reaction, urea melt is obtained;

[0052] S3-2. Cool the urea melt to room temperature, and mix it with ammonium sulfate, ethanolamine, dimethyl silicone oil, alkyl glucoside, potassium chloride and water according to the formula ratio, and stir evenly to obtain a urea solution composition.

[0053] S3-3. The urea solution composition is placed in a multi-stage liquid film crystallization kettle for crystallization to obtain urea crystals. The urea crystals are then fed into a crusher to be crushed into granules, which are then sieved to obtain urea granules. The urea granules are fed into a coating machine, and the rotation speed and tilt angle are adjusted before starting the machine. A mist-like binder b is sprayed onto the rotating urea granules to evenly coat them with binder b. Then, alumina powder is added in multiple batches to coat the urea granules. The amount of alumina powder added each time accounts for 15% of the total mass of the alumina powder. This process is repeated until all the alumina powder is added. After drying, a nitrogen-reducing complex is obtained. The mist-like binder b is polylactic acid. The rotation speed of the coating machine is 50 r / m, the coating time is 15 min, and the temperature environment is controlled at 37.5℃. The average particle size of the alumina powder is 55 μm. The average thickness of the alumina powder coating on the urea granules is controlled to be 460 μm.

[0054] S4. Weigh 7.5% of the main castable material by its total mass and mix it evenly with the prepared nitrogen-reducing compound. After exporting, let it stand for 7.5 minutes to obtain the functional castable material.

[0055] S5. Pour the remaining main castable material and allow it to dry and harden naturally. Then, pour the functional castable material again and bake it at 110℃ for 48 hours. Then, slowly increase the temperature to the working temperature at 15℃ / h. When pouring the functional castable material, take the material from the bottom of the container holding the settled functional castable material and take it out from the bottom to the top to pour the combustion chamber. Control the top layer of the settled functional castable material to be poured on the outermost surface of the combustion chamber.

[0056] Example 2: This example is basically the same as Example 1, except that in S4, 5% of the main casting material is weighed and mixed evenly with the prepared nitrogen-reducing compound, and then left to stand for 5 minutes after being exported to obtain the functional casting material.

[0057] Example 3: This example is basically the same as Example 1, except that in S4, 10% of the main casting material is weighed and mixed evenly with the prepared nitrogen-reducing compound, and then left to stand for 10 minutes after being exported to obtain the functional casting material.

[0058] Example 4: This example is basically the same as Example 1, except that the raw material ratio for preparing the urea solution composition includes: 20 parts urea, 15 parts ammonium sulfate, 5 parts alumina, 3 parts ethanolamine, 4 parts dimethyl silicone oil, and 3.5 parts potassium chloride.

[0059] Example 5: This example is basically the same as Example 1, except that the raw material ratio for preparing the urea solution composition includes: 30 parts urea, 20 parts ammonium sulfate, 9 parts alumina, 8 parts ethanolamine, 6 parts dimethyl silicone oil, and 5.5 parts potassium chloride.

[0060] Example 6: This example is basically the same as Example 1, except that the remainder is fused white fused alumina, 10 wt% sintered magnesium aluminum spinel, 5 wt% active α-Al2O3 micro powder, 3 wt% binder a, 0.1 wt% water-reducing agent, 4 wt% water, and 2 wt% aggregate, with the remainder being fused white fused alumina.

[0061] Example 7: This example is basically the same as Example 1, except that the remainder is fused white fused alumina, 20 wt% sintered magnesium aluminum spinel, 12 wt% active α-Al2O3 micro powder, 5 wt% binder a, 0.4 wt% water-reducing agent, 15 wt% water and 6 wt% aggregate, and the remainder is fused white fused alumina.

[0062] Example 8: This example is basically the same as Example 1, except that the average particle size of the alumina powder is 10 μm; and the average thickness of the alumina powder coating on the urea particles is controlled to be 20 μm.

[0063] Example 9: This example is basically the same as Example 1, except that the average particle size of the alumina powder is 10 μm; and the average thickness of the alumina powder coating on the urea particles is controlled to be 900 μm.

[0064] Example 10: This example is basically the same as Example 1, except that the average particle size of the alumina powder is 100 μm; and the average thickness of the alumina powder coating on the urea particles is controlled to be 900 μm.

[0065] Example 11: This example is basically the same as Example 1, except that the average particle size of the alumina powder is 100 μm; and the average thickness of the alumina powder coating on the urea particles is controlled to be 300 μm.

[0066] Example 12: This example is basically the same as Example 1, except that the water-reducing agent used is 2.5wt% nano-silica, 2.5wt% nano-alumina and the balance FS-10 water-reducing agent.

[0067] Comparative Example 1: Referring to Example 1, no preparation or casting of functional castable was performed.

[0068] Comparative Example 2: Referring to Example 1, no aggregate is added to the raw materials of the main castable.

[0069] Comparative Example 3: Referring to Example 1, the urea particles were not coated with binder b and alumina powder.

[0070] Experimental Example: To investigate the performance of the castables produced in each embodiment and control example, the main raw materials were determined and weighed according to the experimental formula, poured into an NRJ-4111A type cement mortar mixer and dry-mixed for 180s, then wet-mixed with water for 270s, and then vibrated and cast on an HCZT type vibrating table to form crucible samples with external dimensions of Φ100 / 90mm×100mm and internal hole dimensions of Φ50 / 45mm×60mm. The samples were naturally cured at room temperature for 24h, then demolded, naturally cured in air for 6h, and then baked in an oven at 110℃ for 24h to obtain crucible samples for performance testing. The maximum temperature in the combustion test was controlled at 1600℃. The compressive strength test method referred to GB / T5072-2008, and the acid resistance test method referred to GBT 17601. The specific investigation is as follows:

[0071] Figure 1 In the above, condition 1 is to measure the NOx density in the flue gas 1 hour after combustion;

[0072] Condition 2 involves measuring the NOx density in the flue gas 3 hours after combustion;

[0073] Condition 3 involves burning for 3 hours per day for 10 consecutive days, after which the NOx density in the flue gas is measured.

[0074] Figure 2 In the above, condition 4 is to test the compressive strength of the sample at 1300℃;

[0075] Condition 5 is to test the acid resistance of the samples at 1100℃.

[0076] 1. Investigate the influence of process parameters in the preparation of functional castables on nitrogen reduction effect:

[0077] like Figure 1As shown, a comparison between Examples 1-3 and Control Example 1 reveals that: Example 1 exhibits a stable nitrogen reduction effect; compared to Control Example 1, Examples 1-3 show no nitrogen reduction effect; the sample of the castable functional castable shows a significant nitrogen reduction effect in combustion exhaust; the sample of the castable functional castable can clearly achieve the effect of removing nitrogen oxides; the nitrogen reduction effect of Example 2 is worse than that of Examples 1 and 3, while the nitrogen reduction effect of Example 3 is the best and has better sustainability. This indicates that the longer the functional castable is left to stand, the greater the density of the nitrogen reduction complex that slowly floats to the upper layer, and the denser the nitrogen reduction complex that adheres to the surface of the sample after casting, i.e., the closer it is to the high temperature of the combustion chamber, the more ammonia is produced, and the better the nitrogen reduction effect is achieved.

[0078] 2. Investigate the effect of the raw material ratio in the preparation of urea solution composition on the nitrogen reduction effect:

[0079] like Figure 1 As shown, comparing Examples 1, 4, and 5 reveals that: Example 1 showed better nitrogen reduction effects after 1 hour and 3 hours of continuous use, although the nitrogen reduction effect decreased after a period of continuous use, the reduction value was still good. Compared with Examples 1 and 3, Example 4 showed the worst nitrogen reduction effects after 1 hour and 3 hours of continuous use, although the nitrogen reduction effect decreased after a period of continuous use, the reduction value was still the best. Compared with Examples 1 and 4, Example 5 showed the best nitrogen reduction effects after 1 hour and 3 hours of continuous use, and still had a nitrogen reduction effect after a period of continuous use, but the reduction in nitrogen reduction was the greatest. It can be seen that the best overall result was achieved when the raw material ratio of the urea solution composition was selected using the method of Example 1.

[0080] 3. Investigate the influence of the raw material ratio of the main castable on the strength and corrosion resistance of the castable:

[0081] like Figure 2 , 3 As shown, comparing Examples 1, 6, 7 and Control Example 2, it can be seen that the castable sample prepared using the raw material ratio of Example 1 has the best compressive strength and acid resistance. The test results of Examples 6 and 7 are not significantly different. The compressive strength of the castable sample prepared using the raw material ratio of Control Example 2 is significantly lower than that of Examples 1, 6, and 7. It can be seen that adding aggregate is beneficial to increasing the strength of castables.

[0082] 4. Investigate the influence of process parameters in preparing the nitrogen-reducing compound on the nitrogen-reducing effect:

[0083] like Figure 1As shown, comparing Examples 1, 8 to 11 reveals that: in Example 1, the alumina particles coated by the urea particles have a moderate size and a moderate average coating thickness; in Example 8, the alumina particles coated by the urea particles have the smallest size and the thinnest average coating thickness. Examples 1 and 8 have better nitrogen reduction effects, which decrease after a period of time, but the reduction value is still relatively good.

[0084] In Example 9, the alumina particles coated by the urea particles were the smallest in size and the average coating thickness was the largest. In Example 10, the alumina particles coated by the urea particles were the largest in size and the average coating thickness was the thickest. The nitrogen reduction effect of Examples 9 and 10 was poor at the beginning and continued to decrease after a period of time, but the nitrogen reduction value was the best.

[0085] In Example 11, the urea particles coated with the largest alumina particles and the smallest average coating thickness exhibited the best initial nitrogen reduction effect, and the effect persisted for a period of time, although the nitrogen reduction effect decreased the most. This demonstrates that under a thinner coating layer, urea particles can release nitrogen-reducing substances more quickly, which is beneficial for rapidly exerting nitrogen reduction during combustion. Conversely, a thicker coating layer can slow down the degradation rate, making the nitrogen reduction effect more durable. Therefore, controlling the coating layer thickness allows for adjustment of the degradation rate according to specific needs, improving the adjustability of the nitrogen reduction effect.

[0086] A comparison of Examples 1, 8-11 and Control Example 3 shows that: Control Example 3 did not coat the urea granules, and its initial nitrogen reduction effect was the best. After a period of time, the nitrogen reduction effect was still weak, and the nitrogen reduction effect decreased significantly over time, with the worst sustainability.

Claims

1. A low-NOx castable refractory for the combustion chamber of a circulating fluidized bed boiler, characterized in that, It is composed of the following raw materials in the indicated weight percentages: 10-20 wt% sintered magnesium aluminum spinel, 5-12 wt% active α-Al2O3 micro powder, 3-5 wt% binder a, 0.1-0.4 wt% water-reducing agent, 4-15 wt% water, 1-5 wt% nitrogen-reducing compound, and 2-6 wt% aggregate, with the balance being fused white corundum; the water-reducing agent is composed of 0-10 wt% carbon nanotubes and the balance being allyl polyoxyethylene ether maleic anhydride; The nitrogen-reducing complex comprises, by weight parts: 20-30 parts urea, 15-20 parts ammonium sulfate, 5-9 parts alumina, 3-8 parts ethanolamine, 4-6 parts dimethyl silicone oil, 3.5-5.5 parts potassium chloride, 1-2 parts binder b, 0.3-2 parts alkyl glucoside, and 100 parts water; The preparation method of this low-nitrogen castable includes the following steps: S1. Weigh out the fused white corundum, sintered magnesium aluminum spinel, active α-Al2O3 micro powder, water-reducing agent, aggregate and binder a according to the formula, grind them thoroughly and evenly to obtain the main mixture, and store it in moisture-proof packaging. S2. Pour the main mixture into the mixer and mix for 5-10 minutes. Divide the water into 10-20 equal parts and add them in batches until the mixture is uniform. The interval between each addition of water is 8-15 minutes to obtain the main casting material. S3. Preparation of nitrogen-reducing complex: S3-1. The prepared high-purity ammonia and carbon dioxide are heated and pressurized in a reaction vessel at a temperature of 170~180℃ and a pressure of 3×10⁻⁶. 4 kPa, after repeated compression reaction, urea melt is obtained; S3-2. Cool the urea melt to room temperature, and mix it with ammonium sulfate, ethanolamine, dimethyl silicone oil, alkyl glucoside, potassium chloride and water according to the formula ratio, and stir evenly to obtain a urea solution composition. S3-3. Place the urea solution composition into a multi-stage liquid film crystallizer to crystallize and obtain urea crystals. Put the urea crystals into a crusher to crush them into particles. After sieving, obtain urea particles. Put the urea particles into a coating machine, adjust the speed and tilt angle and start it. Spray atomized binder b on the rotating urea particles so that the urea particles are evenly coated with binder b. Then add alumina powder in multiple batches to coat the urea particles. The amount of alumina powder added each time accounts for 10-20% of its total mass. Repeat the cycle until all the alumina powder is added. After drying, obtain the nitrogen-reducing complex. S4. Weigh out 5-10% of the main casting material by its total mass and mix it evenly with the prepared nitrogen-reducing compound. After exporting, let it stand for 5-10 minutes to obtain the functional casting material. S5. Pour the remaining main castable material and allow it to dry and harden naturally. Then, pour the functional castable material again and bake it at 100~120℃ for 48 hours. Then, slowly increase the temperature to the working temperature at 10~20℃ / h.

2. The low-NOx castable refractory for the combustion chamber of a circulating fluidized bed boiler according to claim 1, characterized in that, The water-reducing agent consists of 0-5 wt% nano-silica, 0-5 wt% nano-alumina, and the remainder is FS-10 water-reducing agent.

3. The low-NOx castable refractory for the combustion chamber of a circulating fluidized bed boiler according to claim 1, characterized in that, The binder a is one or more of Secar71 cement, active p-Al2O3 micro powder, and magnesium phosphate cement; the aggregate is one or more of clay particles, perlite, and shale ceramic.

4. The low-NOx castable refractory for the combustion chamber of a circulating fluidized bed boiler according to claim 1, characterized in that, The atomized binder b is one or a combination of polylactic acid or polyvinyl alcohol.

5. The low-NOx castable refractory for the combustion chamber of a circulating fluidized bed boiler according to claim 1, characterized in that, The coating machine operates at a speed of 30-70 r / m, with a coating time of 10-20 min and a temperature range of 30-45℃.

6. The low-NOx castable refractory for the combustion chamber of a circulating fluidized bed boiler according to claim 1, characterized in that, The average particle size of the alumina powder is 10~100μm; the average thickness of the alumina powder coating on the urea particles is controlled to be 20~900μm.

Images