A method for regulating low-pollution stable combustion of ammonia-doped fuel based on carbon-nitrogen separation combustion organization

Abstract

The present application relates to the technical field of low pollution combustion of ammonia-doped fuel, in particular to a low pollution stable combustion regulation method of ammonia-doped fuel based on carbon-nitrogen separation combustion organization, which comprises fuel grading supply, wherein carbon-hydrogen fuel such as CH4, coal powder and NH3 are injected into a combustion zone in layers through independent channels, wherein NH3 can be injected from the center of a burner, and carbon-hydrogen fuel is distributed in the outer layer of NH3, and mixing is realized through the action of swirl shear; air grading combustion, wherein a main air path and a secondary air path are set, the main air path adopts rich premixing, and the secondary air path supplements air to realize grading combustion; NH3 pre-decomposition treatment, wherein part of NH3 is pre-decomposed during combustion, and the pre-decomposition rate is controlled at 20%-40%; carbon-nitrogen path separation is realized through fuel layer injection, and reduction intermediates are generated by combining NH3 pre-decomposition, thereby synergistically inhibiting NO x generation and CO emission, and equivalence ratio is dynamically regulated based on a Damkohler number cross-scale model, so that industrial application is realized.

Description

Technical Field

[0001] This invention relates to the field of low-pollution combustion technology of ammonia-blended fuels, and more specifically, to a method for controlling low-pollution stable combustion of ammonia-blended fuels based on carbon-nitrogen separation combustion organization. Background Technology

[0002] Ammonia-blended fuels refer to a technology that mixes NH3 with traditional fossil fuels (such as coal and natural gas) in a certain proportion for use as fuel. Ammonia is a zero-carbon compound, and its combustion products are mainly nitrogen and water, thus it has the characteristics of being clean and having low carbon emissions. The application of ammonia-blended fuels is mainly to reduce carbon emissions from traditional fuels and achieve low-carbon combustion.

[0003] Ammonia fuel, as a zero-carbon energy carrier, produces nitrogen oxides (NOx) during combustion. x The core bottlenecks are high emissions and poor flame stability. Traditional ammonia-blended combustion technologies employ premixing or staged combustion strategies, but these cannot effectively address the NO emissions caused by the coupling of carbon and nitrogen reaction pathways. x Problem arising from combustion: The reactive free radicals (such as OH) released from hydrocarbon fuels, such as CH4 and pulverized coal, accelerate the oxidation of ammonia (NH3). When the equivalence ratio Φ > 1.2, nitrogen is converted to NO. x The conversion rate exceeds 3%; while air staged combustion can reduce local temperature, but the lag in dynamic control causes a surge in CO emissions (>100ppm). Existing technologies such as catalytic pre-decomposition can improve the combustion rate, but when the decomposition rate exceeds 50%, the concentration of hydrogen free radicals (H2) is too high and can easily induce backfire. Moreover, due to the lack of real-time feedback linkage with the combustion state, it is difficult to balance the contradiction between emissions and stability. Summary of the Invention

[0004] This invention provides a method for controlling the low-pollution and stable combustion of ammonia-blended fuels based on carbon-nitrogen separation combustion organization. Through a three-level innovation of "fuel stratified injection - pre-decomposition synergy - free radical closed-loop control," it enables NO... x While achieving a conversion rate of <0.5%, it also ensures CO emissions of <50ppm and megawatt-level combustion chamber stability, thereby solving the problems mentioned in the background technology, namely:

[0005] In existing technologies, NO is caused by the coupling of carbon and nitrogen reaction pathways. x High generation rate (>3%), delayed dynamic control leading to a surge in CO emissions (>100ppm), high pre-decomposition rate (>50%) causing backfire risk, and lack of real-time feedback and cross-scale matching mechanism make it difficult to achieve efficient and clean ammonia-blended combustion.

[0006] To achieve the above objectives, the ammonia-blended fuel low-pollution stable combustion control method based on carbon-nitrogen separation combustion organization includes the following steps:

[0007] (1) Fuel staged supply: hydrocarbon fuel and NH3 are injected into the combustion zone through independent channels in a stratified manner. NH3 is injected from the center of the burner, and hydrocarbon fuel is distributed around the outer layer of NH3. Mixing is achieved through swirling shearing action.

[0008] (2) Staged combustion of air is achieved by setting up a main air path and a secondary air path. The main air path adopts fuel-rich premixing (equivalence ratio Φ>1), and the secondary air path supplements air to achieve staged combustion.

[0009] (3) NH3 pre-decomposition treatment: Before combustion, some NH3 is pre-decomposed to generate NH2 and H2. The pre-decomposition rate is controlled at 20%-40%. Among them, NH2, as an intermediate product, further inhibits NO through the reduction reaction pathway (NH2 + NO → N2 + H2O). x H2 is generated, and H2 enhances combustion stability by increasing the flame propagation speed;

[0010] (4) Combustion dynamic control: Based on the real-time monitoring of OH / NH2 free radical concentration distribution, the flow ratio of the main and secondary gas paths is adjusted to maintain the overall equivalence ratio at Φ=0.9~1.35.

[0011] In the above technical solution, the spatiotemporal decoupling of the carbon-nitrogen reaction pathway is achieved through fuel stratified injection: the central NH3 is pre-decomposed (20%-40%) to generate NH2 / H2, reducing nitrogen activity; and the direct oxidation of NH3 to NO is inhibited. x (Reaction pathway: NH3→NH2→N2), while the outer layer of hydrocarbon fuel swirls and shears to form a fuel-rich barrier (CH4+O2→CO / H2O), blocking the conversion of NH3 to NO by competitively consuming oxygen free radicals (O) and regulating the temperature field. x The chain reaction (NH + O → NO).

[0012] Staged air combustion with coordinated control of the primary and secondary gas paths to achieve an equivalence ratio (Φ=0.9~1.35), with the primary gas path using fuel-rich conditions to suppress NO. x Generation (Zeldovich mechanism thermodynamic NO) x (Suppressed), secondary gas path afterburning enhances CO oxidation (CO+OH→CO2+H) by increasing OH concentration (monitoring feedback adjustment);

[0013] Based on the Damköhler number (Da=τ) m / τ r The cross-scale model matches the mixing and reaction time scales in real time, avoiding CO2 accumulation (τ) caused by dynamic regulation lag. m Optimizing (shortening CO residence time) and abrupt changes in pre-decomposed H2 concentration (synchronous mixing reaction when Da≈1) ultimately achieves NO reduction in a megawatt-level combustion chamber. xA multi-objective balance between conversion rate <0.5% (carbon-nitrogen decoupling inhibits generation), CO emission <50ppm (free radical closed-loop accelerated oxidation), and flame stability (H2 concentration gradient and shear flow field work together to prevent flashback).

[0014] Secondly, this invention provides a method for pre-decomposition of NH3, which can be implemented through any of the following methods:

[0015] (a) High-temperature flue gas recirculation: The flue gas at 800-1200℃ at the combustion chamber outlet is recirculated to the NH3 fuel inlet to decompose NH3 by high-temperature pyrolysis;

[0016] (b) Embedded catalytic decomposition: An insert tube loaded with a nickel-based catalyst is installed in the NH3 delivery pipeline, and NH3 is catalytically decomposed at 500-700℃.

[0017] The high-temperature flue gas recirculation pyrolysis utilizes the high-temperature enthalpy (ΔH≈+46 kJ / mol NH3) of the flue gas at the combustion chamber outlet (800-1200℃) to control the degree of NH3 decomposition (NH3→NH2+H2) through thermodynamic equilibrium. By controlling the temperature gradient (decomposition rate decreases sharply as temperature decreases) and residence time of the recirculated flue gas, the decomposition rate is limited to 20%-40%, avoiding sudden changes in H2 concentration (H2 generation is proportional to the decomposition rate). Simultaneously, the low-oxygen environment in the recirculated flue gas (fuel-rich conditions in the main combustion zone) inhibits further oxidation of NH2 to NO. x This ensures the passivation of nitrogen activity in pre-decomposition products (NH2→N2 pathway is dominant) and forms a thermo-chemical synergy with the outer hydrocarbon fuel-rich barrier to suppress thermodynamic NO. x With fast NO x Dual generation;

[0018] Secondly, the embedded catalytic decomposition uses a nickel-based catalyst (Ni / Al2O3) to reduce the activation energy of NH3 decomposition, achieving controllable catalytic cracking (NH3→NH2+H2) under medium-temperature conditions of 500-700℃. Through dual regulation of catalyst active site density and reaction temperature, the decomposition kinetics and combustion requirements are precisely matched: the low-temperature section (500℃) suppresses side reactions (such as NH2→NH→N free radical chains), while the medium-temperature section (700℃) accelerates the main reaction without triggering excessive decomposition (<40%). The insert structure is integrated into the fuel pipeline, and through dynamic matching of fuel flow rate and catalyst contact time (Damköhler number Da≈1), it ensures that the H2 generation rate is synchronized with the combustion chamber equivalence ratio adjustment, avoiding local enrichment of H2 that could cause backfire. At the same time, the endothermic reaction of the catalytic reaction (ΔH>0) compensates for the temperature drop of the pipeline and maintains the thermal balance of the system.

[0019] Secondly, this invention provides a burner required for the low-pollution stable combustion control method of ammonia-blended fuels based on carbon-nitrogen separation combustion organization:

[0020] The fuel staged supply structure adopts a double-pipe fuel nozzle, with the inner pipe conveying NH3 and the outer annular gap conveying hydrocarbon fuel. The outlet of the outer annular gap is equipped with swirl blades with a swirl intensity S=0.6-1.2, which realizes the stratified shear mixing of hydrocarbon fuel and NH3.

[0021] The air grading control component has a built-in Venturi mixer in the main air passage to generate a fuel-rich premixed gas, and the secondary air passage adjusts the amount of supplemental gas through an electric regulating valve.

[0022] The NH3 pre-decomposition unit is equipped with a high-temperature flue gas reflux chamber or a tube-type catalytic reactor along the NH3 conveying path, and the pre-decomposition rate is controlled at 20%-40%.

[0023] The combustion control execution unit is equipped with an OH radical laser detection probe and an NH2 spectral sensor on the combustion chamber wall. The sensor signal is input to the controller, and the controller output is connected to the electric regulating valve and the fuel flow valve to perform the dynamic adjustment of the equivalence ratio in step (4).

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] By coordinating fuel staging and air staging, the combustion pathways of hydrocarbon fuels and ammonia (NH3) are separated, cutting off the N-HCN-NO combustion path. x The conversion chain inhibits NO x Generation; Pre-decomposition technology is used to decompose some ammonia (NH3) into NH2 and H2, which preferentially participate in the reduction reaction, further reducing NO. x Emissions (target conversion rate <0.5%);

[0026] By employing independent control of the primary and secondary gas paths, with the primary path using fuel-rich premixing (Φ>1) and the secondary path supplementing air to achieve staged combustion, mixing efficiency and flame stability are enhanced. Combined with high-temperature recirculation zone and swirl intensity adjustment, fuel residence time is extended, promoting complete NH3 decomposition, while suppressing localized high-temperature zones to reduce thermal NO. x ;

[0027] Ammonia fuel is injected from the center of the burner and supplied in stratified layers with hydrocarbon fuel. Rapid mixing is achieved through swirling shearing, reducing local equivalence ratio fluctuations and avoiding combustion oscillations. Based on real-time monitoring of combustion parameters (such as OH / NH2 radical distribution), the optimal equivalence ratio window (Φ=0.9~1.35) is maintained by adjusting the flow ratio of the primary and secondary gas paths, thus balancing low NO levels. x In line with the demand for stable fuel supply;

[0028] By establishing the Damköhler number (Da=τ) m / τ r The amplification model, with τ as its core, utilizes a hybrid time scale (τ) m) and reaction time scale (τ) r Matching ensures the performance consistency between laboratory-scale (100kW) and industrial megawatt-scale (5000kW) burners. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of the swirl burner of the present invention;

[0030] Figure 2 The suppression pathways show the different reducing properties of NH2 under swirling flames and direct current flames. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] In current technologies, NO is caused by the coupling of carbon and nitrogen reaction pathways. x High formation rate (>3%), delayed dynamic control leading to a surge in CO emissions (>100ppm), and high pre-decomposition rate (>50%) causing backfire risk, coupled with the lack of real-time feedback and cross-scale matching mechanisms, make it difficult to achieve efficient and clean ammonia-blended combustion. This invention provides a low-pollution, stable combustion control method for ammonia-blended fuels based on carbon-nitrogen separation combustion organization, comprising the following steps:

[0033] (1) Fuel staged supply: hydrocarbon fuel and NH3 are injected into the combustion zone through independent channels. NH3 can be injected from the center of the burner, and hydrocarbon fuel is distributed around the outer layer of NH3. Mixing is achieved through swirling shearing action.

[0034] (2) Staged combustion of air is achieved by setting up a main air path and a secondary air path. The main air path adopts fuel-rich premixing (equivalence ratio Φ>1), and the secondary air path supplements air to achieve staged combustion.

[0035] (3) NH3 pre-decomposition treatment: Before combustion, some NH3 is pre-decomposed to generate NH2 and H2. The pre-decomposition rate is controlled at 20%-40%. This is combined with the dimensionless tempering index design to take into account low NO. x Emissions and fuel stability requirements;

[0036] (4) Combustion dynamic control: Based on the real-time monitoring of OH / NH2 free radical concentration distribution, the flow ratio of the main and secondary gas paths is adjusted to maintain the overall equivalence ratio at Φ=0.9~1.35.

[0037] In step (1), see Figure 1NH3 is injected from the center of the burner, and the outer layer of hydrocarbon fuel forms a high-speed shear flow (injection velocity difference 5-15 m / s) through a cyclone separator (cyclone intensity S=0.6-1.2). A radial mixing gradient is generated by the interaction of centrifugal force and viscous force. Figure 2 The study demonstrates different suppression pathways for the reducing power of NH2 under swirling and direct-flow flames. Under fuel-rich conditions (Φ>1), the outer hydrocarbon fuels preferentially oxidize to CO / H2O, simultaneously consuming oxygen radicals (O) to form a low-oxygen, fuel-rich barrier. After the central NH3 pre-decomposes to NH2 / H2, the heat released from the combustion of the outer hydrocarbon fuels (ΔT≈300K) accelerates its denitrification reaction (NH2→N2+H2), blocking the direct contact between NH3 and O radicals, thereby inhibiting the rapid NO reaction (NH+O→NO). x Generate path;

[0038] In step (2), the fuel-rich conditions in the main gas path (Φ=1.2-1.35) reduce the local oxygen concentration and suppress the Zeldovich thermal NO. x The reaction rate is proportional to the square of the O2 concentration; simultaneously, the high-temperature zone (1400-1550K) promotes the cracking of hydrocarbon fuels, generating a large number of H / OH free radicals. After air is introduced into the secondary gas path, the OH concentration gradient increases (as detected in real time by laser detection), accelerating CO oxidation (CO + OH → CO2 + H, reaction rate constant k = 2.5 × 10⁻⁶). 13 cm 3 CO emissions were reduced to below 50 ppm by adjusting the flow ratio of the primary and secondary gas paths, keeping the equivalence ratio Φ within the 0.9-1.35 window, thus avoiding NO emissions under oxygen-rich conditions (Φ<1). x The surge in CO concentration, while preventing excessive fuel enrichment (Φ>1.35) from causing incomplete CO oxidation, is also a concern.

[0039] The NH3 pre-decomposition treatment in step (3) is achieved through high-temperature flue gas recirculation (800-1200℃) or tube catalysis (Ni / Al2O3, 500-700℃). The core of this process is controlling the matching of NH3 decomposition kinetics with combustion requirements. During the pre-decomposition process, NH3 first decomposes into NH2 and H2 (2NH3 → N2 + 3H2, NH2 being an intermediate product). Subsequently, NH2 undergoes a reduction reaction (NH2 + NO → N2 + H2O) to convert the generated NO into NO. x It is reduced back to N2, further reducing final emissions.

[0040] It includes a high-temperature flue gas recirculation path, and the high-temperature flue gas recirculation utilizes thermodynamic equilibrium (NH3). (NH2 + H2, ΔH = +46 kJ / mol) The decomposition rate was controlled by a temperature gradient. When the flue gas temperature decreased from 1200℃ to 800℃, the decomposition rate constant k decreased from 1.2 × 10⁻⁶ kJ / mol. 8s -1 Reduced to 3.5×10 6 s -1 Limiting the decomposition rate to 20%-40% is preferred;

[0041] Catalytic decomposition achieves controllable decomposition at lower temperatures by reducing the activation energy (Ea from 360 kJ / mol to 210 kJ / mol), avoiding excessive H2 generation (the risk of backfire increases dramatically when the concentration is >10 vol.%). The NH2 generated from pre-decomposition preferentially participates in the reduction reaction (NH2 + NO → N2 + H2O), while H2 increases the flame propagation speed (S L (Increased from 0.15 m / s to 0.35 m / s), enhancing combustion stability;

[0042] In step (4), τ is calibrated using PIV. m (Laboratory grade 15ms, industrial grade 52ms) and CHEMKIN simulation τ r (Laboratory grade 15.8ms, industrial grade 49.5ms) ensuring Da≈1 (deviation ≤10%), synchronizing H2 generation rate with combustion chamber equivalence ratio adjustment. OH / NH2 free radical concentration distribution is monitored in real-time using TDLAS and PLIF technology. When OH concentration decreases by 10%, the feedback controller adjusts the secondary gas path valve opening (flow rate change ±15%) within 50ms, reducing Φ by 0.1-0.3 to prevent CO accumulation. When the local temperature exceeds 1600K, the main gas path fuel flow rate is increased (Φ increases by 0.2-0.5) to suppress thermal NO. x .

[0043] Example 1: (Laboratory-scale burner, 100kW, embedded catalytic decomposition)

[0044] Experimental conditions:

[0045] Burner structure: such as Figure 1 As shown, the concentric double-tube nozzle has an inner tube of NH3 (99.9% purity) and an outer ring of hydrocarbon fuel (95% purity). The swirl intensity S = 0.8 (U θ =12m / s, U axial =15m / s);

[0046] Pre-decomposition method: Tubular catalytic reactor (Ni / Al2O3, catalyst loading 20 g / m³) 2 ), NH3 inlet temperature 600℃, fuel flow rate 2m / s;

[0047] Air classification: main air path Φ=1.25 (CH4 volume percentage 70%), secondary air path make-up air volume accounts for 20% of the total air volume;

[0048] Control parameter: Da = 0.95 (τ) m =15ms via PIV calibration, τ r =15.8ms simulated using CHEMKIN).

[0049] Experimental results:

[0050]

[0051] Example 2: (Megawatt-class combustion chamber, 5000kW, high-temperature flue gas recirculation decomposition)

[0052] Experimental conditions:

[0053] Combustion chamber design: High-temperature recirculation zone size L = 1.2m, swirl intensity S = 1.0 (U θ =25m / s, U axial =25m / s), residence time τ residence =55ms;

[0054] Pre-decomposition method: flue gas recirculation temperature 1100℃, NH3 flow rate 8m / s, oxygen concentration ≤2% (fuel-rich environment);

[0055] Air classification: main air path Φ=1.35 (CH4 volume percentage 80%), secondary air path make-up air volume accounts for 25% of the total air volume;

[0056] Control parameter: Da = 1.05 (τ) m =52ms, τ r =49.5ms).

[0057] In this embodiment, the size of the high-temperature reflux zone L = 1.2m and the mixing time τ m =52ms matching derivation:

[0058] Mixed timescales τ m Determined by the hydrodynamic characteristics of the recirculation region, its calculation formula is as follows: In the formula: L = 1.2m, which is the characteristic length of the recirculation zone (calibrated through PIV flow field diagnosis); , where is the swirl synthesis velocity; S=0.1 is the swirl intensity, S= ;

[0059] Experimental corrections revealed that, due to turbulent dissipation and viscous drag in actual flow, the effective mixing time τ could be calculated using the measured velocity field from the PIV (Precision Injection) method. m =52ms, which deviates from the theoretical value by 22.9% (in line with engineering error <25%), indicating that the formula is applicable to industrial-grade combustion chamber design.

[0060] In addition, the reaction time scale τ r=49.5ms was obtained through CHEMKIN-PRO simulation, using the GRI-Mech 3.0 reaction mechanism, with the following boundary conditions: pressure P =1 atm, temperature T= 1100K (reflux zone inlet); fuel composition is pre-decomposed NH3 (28% NH2 + 14% H2 + 58% NH3). Simulation results show that 95% of the NH3 is oxidized to N2. T 95% =49.5ms, and τ m The matching degree reached in 52ms: Da=τ m / τ r =1.05, which satisfies the cross-scale control target of Da≈1 (deviation ≤8.6%).

[0061] Experimental results:

[0062]

[0063] Comparative Example 1: (Traditional ammonia-blended combustion, without carbon-nitrogen separation)

[0064] Experimental conditions:

[0065] Combustion method: hydrocarbon fuels, such as CH4, pulverized coal and NH3 premixed injection (volume ratio 1:1), equivalence ratio Φ=1.2, non-staged combustion;

[0066] Control parameters: No free radical monitoring and dynamic feedback.

[0067] Comparison results:

[0068]

[0069] Comparison of the nitrogen element reaction pathway between traditional ammonia-blended combustion technology and Example 1 of this invention:

[0070]

[0071] Conclusion: By combining carbon-nitrogen separation combustion organization with pre-decomposition, the nitrogen reaction pathway can be shifted from NH3→NO. x The process transforms into NH3→NH2→N2, where NH2 further eliminates the previously generated NO through a reduction reaction (NH2 + NO → N2 + H2O). x The competitive consumption of O radicals by the outer hydrocarbon fuel-rich barrier makes NO... x The conversion rate decreased from 3.2% to 0.42%, and the experimental data were in high agreement with the chemical reaction kinetic model (deviation <10%), confirming the effectiveness of the chemical mechanism of the present invention.

[0072] In megawatt-level verification experiments, under different carbon-nitrogen separation rates, the experimental conditions were: heat load ≥ 1.0 MW (1.0 MW) and ammonia blending ratio ≥ 30% (30%). Experiments were conducted comparing NH3 and hydrocarbon fuel blending, partial carbon-nitrogen separation, complete carbon-nitrogen separation (with internal hydrocarbon fuel), and complete carbon-nitrogen separation (with internal NH3). A detailed comparison was also made between using only carbon-nitrogen separation and using both carbon-nitrogen separation and multi-stage decomposition conditions formed by air staging. x Emission concentration experimental data show that, under the same pre-decomposition rate, the NO from complete carbon-nitrogen separation (internal hydrocarbon fuel) is significantly lower. x The emission concentration was the lowest, from >2700 mg / m³ in the mixed state. 3 Reduced to <2000mg / m 3 ;

[0073] Furthermore, under multi-stage decomposition conditions and equipped with OFA to adjust the equivalence ratio Φ, the scheme for complete carbon-nitrogen separation (internal hydrocarbon fuel) adopts a concentration of <2000 mg / m³. 3 Reduced to 393 mg / m 3 To achieve NO x Ultra-low conversion of emissions.

[0074] Comparative Example 2: (High pre-decomposition rate catalytic decomposition, decomposition rate 50%)

[0075] Experimental conditions:

[0076] Pre-decomposition method: Tube catalytic reactor (Ni / Al2O3), NH3 inlet temperature 700℃, fuel flow rate 1m / s (extended contact time);

[0077] Other parameters: Same as in Example 1.

[0078] Comparison results:

[0079]

[0080] Experimental verification of Example 2:

[0081] By adjusting the main air path Φ=1.35 (CH4 accounting for 80%) and the secondary air path supplement (25% air volume), the maximum temperature of the combustion chamber is controlled at 1540K (average measured by thermocouples T1-T3).

[0082] Based on CHEMKIN simulations, at 1540K, the thermal NO x The generation rate at 1600K is 8.6%, which is consistent with the measured N→NO x The conversion rate of 0.48% is consistent (85% lower than the 3.2% of Comparative Example 1).

[0083] Temperature field uniformity (standard deviation σ = 45K) further suppresses local hot spots and avoids chain triggering of the Zeldovich path.

[0084] Technical Effect Comparison Analysis:

[0085]

[0086] According to the comparative analysis table, in Examples 1 and 2, NO was achieved through staged combustion and cross-scale Da number control, respectively. x Conversion rate 0.42%-0.48% (85%-89% lower than Comparative Example 1), CO emissions 38-45ppm (63%-68% lower than Comparative Example 1), and stable flame with no backfire;

[0087] In Comparative Example 1, the lack of staged combustion and the absence of the Da model led to NO... x / CO dual high and flame oscillation;

[0088] In Comparative Example 2, the excessively high pre-decomposition rate, the excessively fast H2 generation rate, and the mismatch with the mixing time led to CO accumulation and the risk of tempering.

[0089] When implementing ammonia-blended combustion systems with high pre-decomposition rates (>50%), strict limits must be placed on the flashback critical conditions to ensure operational safety. This invention quantifies flashback risk by establishing a Flashback Index (FI), specifically defined as follows:

[0090] The formula for calculating the tempering index FI is: ,

[0091] In the formula: H2 is the volume concentration of hydrogen in the pre-decomposed gas (vol.%), which is generated by the pre-decomposition reaction of NH3 (NH3→ 1.5H2+0.5N2);

[0092] S L Flame propagation velocity (m / s) was calculated using CHEMKIN software in conjunction with the GRI-Mech 3.0 mechanism.

[0093] τ residence Residence time of fuel in the premixing section (ms);

[0094] K Let m be an empirical constant (%·m). K =0.1%·m was determined experimentally by the ratio of flow rate to premixed chamber volume (τ = V / Q, where V is the chamber volume and Q is the volumetric flow rate). The critical judgment criterion is that when FI>1.2, the system has a risk of backfire; when FI≤1.2, the combustion stability is controllable.

[0095] In Example 2, [H2] = 7 vol.% (corresponding to a 28% pre-decomposition rate); S L = 0.35 m / s (calculated based on equivalent ratio Φ=1.35); τ residence =0.055s, empirical constant K =0.1%·m, premixing chamber volume V=0.55 m³, volumetric flow rate Q=10m³ 3 / min);

[0096] in K =0.1%·m, determined through laboratory burner calibration experiments: within the pre-decomposition rate range of 20%-40%, different [H2] and S... L τ residence The tempering critical point under the combined conditions was obtained by fitting.

[0097] Substitute into the aforementioned formula In actual operation, due to the enhanced mixing uniformity caused by the swirling shearing effect, the effective value of FI dropped to below 1.2. No flashback was observed during continuous operation, and no flashback was observed after 120 hours of continuous operation. The flame stability coefficient (fluctuation rate <2%) meets the industrial burner standard (GB / T 36699-2018).

[0098] In Comparative Example 2 (high pre-decomposition rate catalytic decomposition, decomposition rate 50%), the [H2] in the pre-decomposed gas reached 12 vol.%, with a residence time τ. residence =60 ms (due to fuel flow rate decreasing to 1 m / s), flame propagation speed S L =0.45 m / s (calculated under the condition of Φ=1.2), its tempering index is: ,satisfy FI >1.2, the experimental results are consistent with the formula prediction, and the system tempering frequency reaches 3 times / hour, verifying the... FI When the value is >1.2, the risk of tempering increases significantly, further supporting the preferred range of controlling the pre-decomposition rate within 20%-40% (corresponding to...). FI ≤1.2).

[0099] In addition, the deviations of Da and NO in Examples 1 and 2 are as follows: x The direct correlation with low CO emissions demonstrates that cross-scale regulation mechanisms can simultaneously resolve the nitrogen and carbon pollution contradictions in ammonia-blended combustion, meeting the performance consistency requirements of burners from laboratory to industrial levels.

[0100] In Example 1, a dynamic control system based on real-time monitoring of OH radicals was used to control the OH concentration when it fell below a set threshold (1.0 × 10⁻⁶). 15 cm -3 When this occurs, secondary air replenishment is triggered, causing the equivalence ratio Φ to decrease by 0.1-0.3. According to the CO oxidation kinetic equation: k = 2.5 × 10 13 cm 3 / (mol·s), temperature 1500K, a 20% increase in OH concentration can increase the CO oxidation rate by 50%, CO residence time τ m The average OH concentration [OH] was measured by shortening the timeframe from 100ms to 50ms. avg = 1.2×10 15 cm -3 (PLIF measurement, fluctuation range ±15%); CO emission concentration: 38 ppm (actual value measured by flue gas analyzer);

[0101] In the combustion system without OH control in Comparative Example 1, the average OH concentration [OH] was measured. avg = 0.7×10 15 cm -3 CO emission concentration: 120 ppm; and due to mixing delay and insufficient OH concentration, the residence time τ of CO in the high-temperature zone is limited. m =100ms, resulting in significant accumulation;

[0102] Based on the test results of Example 1 and Comparative Example 1 above, the technical effectiveness and contribution rate calculation of real-time monitoring of OH free radicals → inhibition of CO surge are verified:

[0103] Quantification of CO2 emission reduction contribution rate: Contribution rate CO = [(CO 对比例1 - CO 实施例1 ) / CO 对比例1 × 100%;

[0104] Substitute the aforementioned experimental test data: Contribution rate CO = (120 - 38) / 120 × 100% = 68.3%;

[0105] Verification of the correlation between OH concentration and CO emissions:

[0106] OH concentration increased by 71% (from 0.7 × 10⁻⁶). 15 Up to 1.2×10 15 cm -3 ), contributing 68.3% to CO2 emission reduction;

[0107] According to the rate equation d[CO] / dt = -k*[OH]*[CO], k = 2.5×10 13 cm 3 / (mol·s) (reaction rate constant at 1500K), where [OH] is the concentration of hydroxyl radicals, which directly determines the CO oxidation rate.

[0108] Verification: When [OH] increases by 71%, the theoretical CO oxidation rate increases by 71%, which is ≤8% different from the experimental value of 68.3% (due to incomplete and uneven mixing).

[0109] Conclusion: The experimentally obtained CO emission reduction contribution rate (68.3%) deviates from the theoretical prediction value (71%) corresponding to a 71% increase in OH concentration by ≤8%, confirming the effectiveness of the regulation mechanism. The remaining difference is due to local mixing inhomogeneity.

[0110] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling the low-pollution and stable combustion of ammonia-blended fuels based on carbon-nitrogen separation combustion organization, characterized in that, Includes the following steps: (1) Fuel is supplied in stages, and hydrocarbon fuel, CH4, pulverized coal and NH3 are injected into the combustion zone in layers through independent channels. NH3 is injected from the center of the burner, and hydrocarbon fuel is distributed around the outer layer of NH3. Mixing is achieved through swirling shearing action. The swirling shearing action is achieved by setting up a swirler. The injection velocity difference between hydrocarbon fuel and NH3 is 5-15 m / s. (2) Staged combustion of air: a main air path and a secondary air path are set up. The main air path adopts a fuel-rich combustion mode. The flow ratio of the main and secondary air paths is adjusted to maintain the overall equivalence ratio at Φ=0.9~1.

35. The secondary air path supplements air to achieve staged combustion. (3) NH3 pre-decomposition treatment: during combustion, some NH3 is pre-decomposed to generate NH2 and H2, and the decomposition rate is controlled at 20%-40%; (4) Combustion dynamic control, based on real-time monitoring of OH / NH2 free radical concentration distribution and the Damköhler number cross-scale model, is applied to industrial scale-up processes; When a 10% decrease in OH radical concentration or a deviation of >15% in NH2 distribution uniformity is detected, the secondary gas path airflow is increased to reduce the equivalence ratio by 0.1-0.3; when a local temperature peak exceeds 1600K, the main gas path fuel flow is increased to increase the equivalence ratio by 0.2-0.5, in order to avoid thermal NO. x generate.

2. The method for controlling low-pollution stable combustion of ammonia-blended fuel based on carbon-nitrogen separation combustion organization according to claim 1, characterized in that, The NH3 pre-decomposition in step (3) is achieved in any of the following ways: (a) High-temperature flue gas recirculation: The flue gas at 800-1200℃ at the combustion chamber outlet is recirculated to the NH3 fuel inlet. NH3 is decomposed by high-temperature pyrolysis. The flue gas temperature is controlled at 800-1200℃ and the oxygen concentration is ≤2% by adjusting the opening of the recirculation valve. (b) Embedded catalytic decomposition: An insert tube loaded with a nickel-based catalyst is installed in the NH3 delivery pipeline, and NH3 is catalytically decomposed at 500-700℃.

3. The method for controlling low-pollution stable combustion of ammonia-blended fuels based on carbon-nitrogen separation combustion organization according to claim 1, characterized in that: The main gas path contains 60%-80% hydrocarbon fuel, CH4, and pulverized coal in its fuel-rich gas, and the secondary gas path provides 15%-30% of the total air volume.

4. The method for controlling low-pollution stable combustion of ammonia-blended fuels based on carbon-nitrogen separation combustion organization according to claim 1, characterized in that: The swirl intensity of the hydrocyclone is S = 0.6-1.2, and the calculation formula is: S = (U θ / U axial ) ×(D hub / D tip In the formula, U θ U is the tangential velocity. axial D is the axial velocity; hub D is the hub diameter; tip It is the diameter of the leaf tip.

5. The method for controlling low-pollution stable combustion of ammonia-blended fuels based on carbon-nitrogen separation combustion organization according to claim 1, characterized in that, The parameters monitored in real time in step (4) include: OH radical concentration gradient in the axial / radial direction of the combustion chamber, uniformity of NH2 radical distribution, and local temperature peak.

6. The method for controlling low-pollution stable combustion of ammonia-blended fuels based on carbon-nitrogen separation combustion organization according to claim 1, characterized in that: By adjusting the size and swirl intensity of the high-temperature recirculation zone in the combustion chamber, the fuel residence time in the combustion chamber is ≥50ms, and the temperature of the recirculation zone is maintained at 1400-1550K.

7. The method for controlling low-pollution stable combustion of ammonia-blended fuel based on carbon-nitrogen separation combustion organization according to claim 1, characterized in that: Based on the Damköhler number Da=τ m / τ r Establish a scaled-up model of the burner, where the mixing time scale τ m The reaction time scale τ was calibrated using PIV experiments. r Data was obtained through CHEMKIN simulations, ensuring that the Da number deviation between laboratory-scale and industrial megawatt-level burners was ≤10%. τ was calibrated using PIV velocity field measurements. m CHEMKIN simulation of reaction pathways to obtain τ r Furthermore, the geometric similarity ratio between laboratory-grade and industrial-grade burners remains at 1:

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8. The method for controlling low-pollution stable combustion of ammonia-blended fuel based on carbon-nitrogen separation combustion organization according to claim 1, characterized in that: Through the synergistic effect of carbon-nitrogen pathway separation and pre-decomposition, the N→NO conversion from NH3 combustion is achieved. x The conversion rate is <0.5%, and the CO emission is <50ppm.

9. The method for controlling low-pollution stable combustion of ammonia-blended fuel based on carbon-nitrogen separation combustion organization according to claim 1, characterized in that, Steps (1)-(4) are performed using the following burners: The fuel staged supply structure adopts a double-pipe fuel nozzle, with the inner pipe conveying NH3 and the outer annular gap conveying hydrocarbon fuel. The outlet of the outer annular gap is equipped with swirl blades with a swirl intensity S=0.6-1.2, which realizes the stratified shear mixing of hydrocarbon fuel and NH3. The air grading control component has a built-in Venturi mixer in the main air passage to generate a fuel-rich premixed gas, and the secondary air passage adjusts the amount of supplemental gas through an electric regulating valve. The NH3 pre-decomposition unit is equipped with a high-temperature flue gas reflux chamber or a tube-type catalytic reactor along the NH3 conveying path, and the pre-decomposition rate is controlled at 20%-40%. The combustion control execution unit is equipped with an OH radical laser detection probe and an NH2 spectral sensor on the combustion chamber wall. The sensor signal is input to the controller, and the controller output is connected to the electric regulating valve and the fuel flow valve to perform the dynamic adjustment of the equivalence ratio in step (4).

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