A coal-fired boiler prying type gas ammonia direct supply combustion stabilizing system and combustion stabilizing method

Abstract

The application discloses a coal-fired boiler prying type gas ammonia direct supply combustion stabilizing system based on low valley electricity price and load linkage, which comprises a prying type gas ammonia preparation unit, a gas ammonia conveying pipeline, a boiler burner and a distributed control system, wherein the prying type gas ammonia preparation unit is integrated by a prying type synthetic ammonia reactor and a PEM electrolytic cell; hydrogen gas prepared by the PEM electrolytic cell is mixed with nitrogen gas provided by an air separation device and then input into the prying type synthetic ammonia reactor; the gas ammonia conveying pipeline directly conveys the gas ammonia generated by the prying type synthetic ammonia reactor to the boiler burner without liquefaction or storage; the boiler burner is provided with a first ammonia injection channel and a second pulverized coal injection channel; and the distributed control system is integrated with a multi-objective optimization algorithm. The application achieves significant progress in economy, response speed, environmental protection, safety and combustion stability through system integration and multi-objective optimization, and provides a low-carbon, efficient and reliable solution for deep peak regulation of a coal-fired unit.

Description

Technical Field

[0001] This invention relates to a skid-mounted gaseous ammonia direct supply stable combustion system and method for coal-fired boilers based on off-peak electricity prices and load linkage, belonging to the field of energy, power and chemical coupling technology. Background Technology

[0002] Coal-fired power plants face key technical challenges in deep peak-shaving operation, including poor combustion stability under low-load conditions, high risk of flameout, and high auxiliary fuel consumption. Existing combustion stabilization solutions generally rely on oil or natural gas injection for combustion assistance. Their core components include oil / gas storage tanks, burner modifications, and automatic control systems, maintaining combustion by increasing the calorific value of the auxiliary fuel. While such systems can achieve stable combustion in the short term, they have the following inherent drawbacks: Firstly, the cost of using oil / gas is high, and it is accompanied by an increase in emissions of pollutants such as CO2 and NOx; Secondly, the fuel supply system is complex, requiring additional storage tanks and pipelines, resulting in high investment costs and fire risks. Third, traditional ammonia preparation equipment requires the purchase of hydrogen sources and has a long preparation cycle (>2 hours), which cannot meet the immediate demand for ammonia supply under low load conditions.

[0003] Furthermore, existing ammonia supply systems mostly employ liquid ammonia storage and vaporization processes, requiring high-pressure storage tanks (>2 MPa) and complex vaporization equipment. This not only results in high investment costs (approximately 5 million RMB per set) but also poses a risk of leakage, making it difficult to achieve a closed-loop response of "off-peak electricity price triggering - immediate ammonia production and injection." More importantly, existing technologies do not link grid electricity price fluctuation signals with boiler load dynamic models, leading to overlap between ammonia production periods and peak electricity prices, resulting in persistently high overall costs. The aforementioned technological systems share three major pain points: Firstly, the methods for stabilizing combustion are limited and rely on high-carbon auxiliary fuels; Secondly, ammonia production and supply are disconnected, lacking local production and direct supply capabilities; Third, a collaborative optimization mechanism for power dispatch and combustion control has not been established.

[0004] This invention aims to overcome the aforementioned technical bottlenecks and proposes a skid-mounted low-temperature and low-pressure ammonia synthesis device driven by off-peak electricity prices. It synthesizes ammonia on-site by producing hydrogen through water electrolysis and combines staged combustion technology for direct low-load stable combustion in boilers, thereby solving the core defects of existing technologies in terms of economy, response speed and safety. Summary of the Invention

[0005] The purpose of this invention is to provide a skid-mounted ammonia direct supply stable combustion system for coal-fired boilers based on off-peak electricity prices and load linkage, and to provide a multi-objective optimized stable combustion method based on off-peak electricity prices and load linkage. This invention is used to solve key technical problems faced by coal-fired power plants in deep peak shaving processes, such as unstable combustion under low load, high risk of flameout, and large consumption of auxiliary fuel. By performing multi-objective collaborative optimization of power system dispatch signals, boiler combustion control, and distributed ammonia synthesis processes, the invention achieves spatiotemporal matching and efficient utilization of energy.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a skid-mounted gasified ammonia direct supply stable combustion system for coal-fired boilers based on off-peak electricity prices and load linkage, comprising: The skid-mounted ammonia production unit integrates a skid-mounted ammonia synthesis reactor and a PEM electrolyzer. The input end of the skid-mounted ammonia synthesis reactor is connected to the PEM electrolyzer and an air separation unit. The PEM electrolyzer is used to electrolyze deionized water to produce hydrogen during off-peak or negative electricity price periods. The hydrogen is then mixed with nitrogen provided by the air separation unit at a set molar ratio and fed into the skid-mounted ammonia synthesis reactor, where it synthesizes ammonia under the action of a catalyst. The skid-mounted installation method facilitates mobility, allowing for on-site electrolysis of water to produce hydrogen and synthesize ammonia during negative electricity price or off-peak periods, achieving a closed-loop conversion of "green electricity-ammonia-fuel". The skid-mounted ammonia production unit eliminates the need for liquid ammonia storage, transportation, and gasification, significantly reducing system investment and safety risks. The gaseous ammonia conveying pipeline is made of corrosion-resistant alloy material and directly conveys the gaseous ammonia produced by the skid-mounted ammonia synthesis reactor to the boiler burner without liquefaction or storage. The boiler burner is equipped with a first ammonia injection channel and a second pulverized coal injection channel. The first ammonia injection channel is located in the root area of ​​the flame of the micro-oil ignition gun and is used to inject gaseous ammonia to form an ammonia-rich atmosphere. The active free radicals generated by the high-temperature cracking of ammonia are used to enhance ignition, achieving immediate use and rapid response, breaking through the bottleneck of response lag in traditional stable combustion methods. The second pulverized coal injection channel is located 150mm axially from the center of the flame and is used to inject lean coal powder. The low-volatile coal powder is ignited in the high-temperature zone of rich ammonia, which significantly improves the combustion stability under low load conditions of 20%-35% THA and avoids flameout. The distributed control system integrates a multi-objective optimization algorithm to collect real-time grid electricity price signals, boiler load data, and ammonia production capacity information. The distributed control system is electrically connected to the PEM electrolyzer and the skid-mounted ammonia synthesis reactor, respectively, and is used to dynamically adjust the start-up and shutdown of the PEM electrolyzer and the skid-mounted ammonia synthesis reactor, as well as the ammonia injection parameters. It is linked in real-time with grid electricity price, unit load, and ammonia production capacity, and automatically starts and stops the electrolysis and synthesis units to achieve dynamic matching between economic efficiency and stable combustion requirements.

[0007] In the aforementioned system, the PEM electrolyzer has a rated power of 100kW, a hydrogen production capacity of 1.2 Nm³ / h, an electrolysis voltage of 57–59V, and a current of 1650–1750A.

[0008] In the aforementioned system, the skid-mounted ammonia synthesis reactor operates at a pressure of 7.5–8.0 MPa, a catalyst bed temperature of 380–390 °C, a space velocity of 5800–6200 h⁻¹, and uses an iron-based catalyst with a particle size of 3–5 mm.

[0009] In the aforementioned system, the ammonia gas delivery pipeline is made of Inconel 625 alloy with an inner diameter of 15mm. The ammonia gas in the pipeline is cooled to 40°C and then delivered to the boiler burner.

[0010] In the aforementioned system, the ammonia flow rate injected into the first ammonia injection channel is 1.6–1.9 Nm³ / h; the coal powder fineness R90 injected into the second pulverized coal injection channel is 7.8%–9.2%, and the flow rate is 0.43–0.46 kg / min.

[0011] In the aforementioned system, the molar ratio of hydrogen to nitrogen in the mixed input gas of the skid-mounted ammonia synthesis reactor is 3:1.

[0012] A multi-objective optimization method for stable fuel supply based on off-peak electricity prices and load linkage includes the following steps: S1. During periods of low electricity prices or negative electricity prices, start the PEM electrolyzer and the skid-mounted ammonia synthesis reactor. The PEM electrolyzer electrolyzes deionized water to produce hydrogen, which is then mixed with nitrogen supplied by the air separation unit to synthesize ammonia. S2. The synthesized gaseous ammonia is directly transported to the boiler burner through a corrosion-resistant alloy pipeline without liquefaction or storage. S3. A staged combustion mode is adopted in the boiler burner. First, gaseous ammonia is injected into the root of the flame of the micro-oil ignition gun through the first ammonia injection channel to form an ammonia-rich atmosphere. Then, lean coal powder is injected into the second powder injection channel at an axial distance of 150mm from the center of the flame to achieve ammonia-rich ignition and lean coal stable combustion. S4. Real-time data collection of grid electricity price, boiler load and ammonia production capacity is achieved through a distributed control system. Electrolysis, synthesis and ammonia injection parameters are dynamically adjusted using a multi-objective optimization algorithm to achieve synergistic optimization of economic efficiency and stable combustion requirements.

[0013] The aforementioned method uses the following reaction conditions for synthesizing ammonia: pressure 7.5–8.0 MPa, temperature 380–390 °C, space velocity 5800–6200 h⁻¹, and a hydrogen to nitrogen molar ratio of 3:1.

[0014] In the aforementioned method, the ammonia injection flow rate is 1.6–1.9 Nm³ / h, the pulverized coal injection flow rate is 0.43–0.46 kg / min, and the pulverized coal fineness R90 is 7.8%–9.2%.

[0015] In the aforementioned method, the multi-objective optimization algorithm is the MINLP algorithm, the system response time from the triggering of the electricity price signal to the injection of ammonia into the combustion zone is less than 5 minutes, and the combustion stability index (CSI) is greater than 0.90.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The economic efficiency of the system of the present invention is significantly improved. It utilizes the off-peak hours or negative electricity price periods to produce ammonia on-site, reducing the stable operation cost to RMB 0.019-0.023 / kWh, which is more than 60% lower than the traditional oil injection or external purchase of liquid ammonia scheme; it adopts skid-mounted integrated equipment, eliminating the liquid ammonia storage, transportation and gasification links, with an initial investment of about RMB 1.8 million, which is about 80% lower than the external purchase of liquid ammonia system; (2) The system of the present invention has a fast response capability, and the gaseous ammonia is produced and used immediately. It is directly supplied to the burner through alloy pipeline, and the entire process response time from the triggering of the electricity price signal to the injection of ammonia into the combustion zone is less than 5 minutes, which is much faster than the 18 minutes of the traditional liquid ammonia gasification scheme, thus meeting the instantaneous demand of deep peak shaving of the power grid. (3) The present invention has excellent environmental performance. It adopts the staged combustion mode of "rich ammonia gas-poor coal powder". Under the low load conditions of 20% to 35% THA, the NOx emission concentration is reduced to 232 to 245 mg / Nm³, which is 20% to 30% lower than the traditional oil combustion. The ammonia gas is produced and used immediately, with no risk of storage leakage. The ammonia escape concentration is less than 3 ppm, which is far below the national standard limit and the purchased liquid ammonia system. (4) This invention has higher operational safety, eliminates the need for high-pressure liquid ammonia storage tanks and gasification equipment, and fundamentally eliminates the major safety risk of ammonia leakage; the system integrates DCS and MINLP optimization algorithms to realize automatic start-up and shutdown and parameter adjustment, reduce manual intervention and improve operational safety; (5) The combustion stability of the present invention is significantly enhanced. Under ultra-low load conditions of 20% to 35% THA, the combustion stability index is increased to 0.90 to 0.94, and the flame temperature is stabilized at 1350 to 1390℃, effectively avoiding flameout and pulsation; (6) The energy utilization efficiency improvement of the present invention is achieved by converting low-cost green electricity into high-value fuel through the closed-loop coupling of "electricity-ammonia-fuel", improving the energy spatiotemporal matching efficiency, providing a new path for green electricity consumption, and using the MINLP multi-objective optimization algorithm to dynamically match electricity price, load and ammonia production capacity, thereby maximizing the synergy between energy and economy. Attached Figure Description

[0017] Figure 1 is a flowchart of the overall system flow and multi-objective optimization control of the present invention; Figure 2 is a multi-objective optimization control logic diagram of the present invention; Figure 3 is a timing diagram of the "electricity price-load-ammonia production" response of the present invention. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0019] Embodiment 1 of the present invention: A skid-mounted ammonia direct supply and stable combustion system for coal-fired boilers based on off-peak electricity prices and load linkage, comprising a skid-mounted ammonia preparation unit, ammonia delivery pipeline, a boiler burner, and a distributed control system, wherein: The skid-mounted ammonia production unit integrates a skid-mounted ammonia synthesis reactor and a PEM electrolyzer. The input end of the skid-mounted ammonia synthesis reactor is connected to both the PEM electrolyzer and an air separation unit. The PEM electrolyzer is used to electrolyze deionized water to produce hydrogen during off-peak or negative electricity price periods. This hydrogen is then mixed with nitrogen supplied by the air separation unit at a set molar ratio and fed into the skid-mounted ammonia synthesis reactor, where it synthesizes ammonia under the action of a catalyst. Specifically, during off-peak or negative electricity price periods (-0.06 to -0.15 yuan / kWh), the PEM electrolyzer electrolyzes deionized water to generate hydrogen with a purity of 99.99%. The rated power of the PEM electrolyzer is 100kW, and its hydrogen production capacity is 1.2 kWh. The electrolysis rate is Nm³ / h, the electrolysis voltage is 57–59V, and the current is 1650–1750A. The generated hydrogen is mixed with high-purity nitrogen provided by the air separation unit and then enters the skid-mounted ammonia synthesis reactor. The molar ratio of hydrogen to nitrogen in the mixed input gas of the skid-mounted ammonia synthesis reactor is 3:1. The reactor is filled with commercially available iron-based catalyst (Fe3O4-Al2O3, particle size 3–5 mm). Under the conditions of system pressure 7.5–8.0 MPa, bed temperature 380–390℃, and space velocity 5800–6200 h⁻¹, gaseous ammonia is directly synthesized. The ammonia gaseous pipeline is made of corrosion-resistant alloy material and directly transports the ammonia gaseous produced by the skid-mounted ammonia synthesis reactor to the boiler burner without liquefaction or storage. The ammonia gaseous pipeline is made of Inconel 625 alloy and has an inner diameter of 15mm. The ammonia gaseous in the pipeline is cooled to 40°C before being transported to the boiler burner. The boiler burner is equipped with a first ammonia injection channel and a second pulverized coal injection channel. The first ammonia injection channel is located at the root region of the flame of the micro-oil ignition gun and is used to inject gaseous ammonia to form an ammonia-rich atmosphere. The high-temperature cracking of ammonia gas generates active free radicals to enhance ignition, achieving immediate production and use, and rapid response, breaking through the bottleneck of response lag in traditional stable combustion methods. The second pulverized coal injection channel is located 150 mm axially from the center of the flame and is used to inject lean coal powder. The high-temperature zone rich in ammonia ignites the low-volatile coal powder, significantly improving the combustion stability under low-load conditions of 20%-35% THA and avoiding flameout. The ammonia gas flow rate injected into the first ammonia injection channel is 1.6-1.9 Nm³ / h; the coal powder fineness R90 injected into the second pulverized coal injection channel is 7.8%-9.2%, and the flow rate is 0.43-0.46 kg / min. The distributed control system integrates a multi-objective optimization algorithm to collect real-time grid electricity price signals, boiler load data, and ammonia production capacity information. The distributed control system is electrically connected to the PEM electrolyzer and the skid-mounted ammonia synthesis reactor, respectively, and is used to dynamically adjust the start-up and shutdown of the PEM electrolyzer and the skid-mounted ammonia synthesis reactor, as well as the ammonia injection parameters. It is linked in real-time with grid electricity price, unit load, and ammonia production capacity, and automatically starts and stops the electrolysis and synthesis units to achieve dynamic matching between economic efficiency and stable combustion requirements.

[0020] By replacing liquid ammonia storage and transportation with on-demand gaseous ammonia production (ammonia escape <3 ppm), the risk of leakage from high-pressure storage tanks is eliminated; the staged combustion mode reduces NOx emissions by 20%-30%, while the utilization of green electricity improves energy efficiency. The synergistic effect of these technical features achieves a multi-dimensional breakthrough in economy, safety and environmental protection.

[0021] Embodiment 2 of the present invention: A multi-objective optimized stable combustion method based on off-peak electricity prices and load linkage, comprising the following steps: S1. During periods of low electricity prices or negative electricity prices, start the PEM electrolyzer and the skid-mounted ammonia synthesis reactor. The PEM electrolyzer electrolyzes deionized water to produce hydrogen, which is then mixed with nitrogen supplied by the air separation unit to synthesize ammonia. S2. The synthesized gaseous ammonia is directly transported to the boiler burner through a corrosion-resistant alloy pipeline without liquefaction or storage. S3. A staged combustion mode is adopted in the boiler burner. First, gaseous ammonia is injected into the root of the flame of the micro-oil ignition gun through the first ammonia injection channel to form an ammonia-rich atmosphere. Then, lean coal powder is injected into the second powder injection channel at an axial distance of 150mm from the center of the flame to achieve ammonia-rich ignition and lean coal stable combustion. S4. Real-time data collection of grid electricity price, boiler load and ammonia production capacity is achieved through a distributed control system. Electrolysis, synthesis and ammonia injection parameters are dynamically adjusted using a multi-objective optimization algorithm to achieve synergistic optimization of economic efficiency and stable combustion requirements.

[0022] Specifically, the reaction conditions for synthesizing ammonia are: pressure 7.5-8.0 MPa, temperature 380-390℃, space velocity 5800-6200 h⁻¹, and molar ratio of hydrogen to nitrogen 3:1.

[0023] Specifically, the ammonia injection flow rate is 1.6–1.9 Nm³ / h, the pulverized coal injection flow rate is 0.43–0.46 kg / min, and the pulverized coal fineness R90 is 7.8%–9.2%.

[0024] Specifically, the multi-objective optimization algorithm is the MINLP algorithm, the system response time from the triggering of the electricity price signal to the injection of ammonia into the combustion zone is less than 5 minutes, and the combustion stability index (CSI) is greater than 0.90.

[0025] The present invention will be further described below with reference to specific embodiments and comparative examples.

[0026] Embodiment 3 of the present invention: The experimental system consists of a proton exchange membrane (PEM) electrolyzer (rated power 100 kW, hydrogen production 1.2 Nm³ / h), a skid-mounted low-temperature and low-pressure ammonia synthesis reactor (inner diameter 120 mm, length 2.8 m, filled with 3.6 kg of commercially available iron-based catalyst), an Inconel 625 alloy gaseous ammonia delivery pipeline (inner diameter 15 mm, length 8 m), a micro-flow control valve group (minimum adjustment accuracy 0.5 L / min), a boiler combustion simulation section (thermal power 100 kW, adjustable load range 15%-100%), and a DCS integrated control system.

[0027] The experimental raw material was deionized water (conductivity <0.1 μS / cm), which was electrolyzed in a PEM electrolyzer at a DC voltage of 58.3 V and a current of 1720 A to obtain hydrogen with a purity of 99.99%, while the oxygen side was vented. The hydrogen was mixed with high-purity nitrogen (purity 99.999%) provided by the air separation unit at a molar ratio of H2:N2=3:1 and then fed into the ammonia synthesis reactor. The reaction was carried out under the conditions of a system pressure of 7.8 MPa, a bed temperature of 385℃, and a space velocity of 6000 h⁻¹. The product was gaseous ammonia, which was cooled to 40℃ by heat exchange and then directly transported to the combustion simulation section.

[0028] The combustion system is equipped with a dedicated spray gun and adopts a staged combustion mode of "rich ammonia gas - lean coal powder": in the root area of ​​the flame of the micro oil ignition gun, ammonia gas is injected through the first ammonia injection channel (flow rate controlled at 1.8 Nm³ / h) to form an ammonia-rich atmosphere with an equivalent ratio of 1.3; at a distance of 150 mm from the center of the flame, lean coal powder with a fineness of R90=8.5% (flow rate 0.45 kg / min) is injected through the second powder injection channel to achieve ignition and stable combustion of coal powder in the high-temperature ammonia core.

[0029] The DCS system collects real-time grid electricity price signals (simulating a negative electricity price of 0.06 yuan / kWh for 30 minutes) and boiler load (simulating 25% THA), triggering the MINLP optimization algorithm to start ammonia production. The total response time from signal issuance to ammonia injection into the combustion zone is 4 minutes and 12 seconds.

[0030] The test results show that under 25% THA load, the boiler combustion stability index (CSI) is 0.93 (>0.8 indicates stability), the flame temperature is maintained above 1380℃, and the NOx emission concentration is 241 mg / Nm³, which is significantly improved compared with pure coal combustion (CSI 0.52, NOx 315 mg / Nm³).

[0031] Example 4 of the present invention: Starting the system under the conditions of a simulated negative electricity price of -0.06 yuan / kWh for 30 minutes and a simulated boiler load of 30% THA: The PEM electrolyzer is input with a DC voltage of 57.8 V and a current of 1680 A. It electrolyzes deionized water to produce hydrogen, with a purity of 99.99%. The flow rate is stable at 1.15 Nm³ / h, and oxygen is vented. Hydrogen is precisely mixed with high-purity nitrogen (99.999%) supplied by the air separation unit at a molar ratio of H₂:N₂ = 3:1 before entering the skid-mounted ammonia synthesis reactor. The system operating pressure is 7.8 MPa, the catalyst bed temperature is 385℃, and the gas hourly space velocity is 6000 h⁻¹. The reactor is loaded with 3.6 kg of commercially available iron-based catalyst (Fe₃O₄-Al₂O₃, particle size 3-5 mm). The ammonia gas generated in the reaction is not absorbed or liquefied by water, but is directly transported to the combustion simulation section through an Inconel 625 alloy pipe (15 mm inner diameter). After being cooled to 40°C, it is adjusted to 1.7 Nm³ / h by a micro-flow control valve group and injected into the root of the flame of the micro-oil ignition gun through the first ammonia injection channel of a dedicated spray gun, forming a local ammonia-rich zone (equivalent ratio 1.25). At a distance of 150 mm axially from the flame center, a second powder injection channel simultaneously injects lean coal powder with a fineness of R90=8.5% at a flow rate of 0.44 kg / min, achieving staged ignition.

[0032] The system took 4 minutes and 18 seconds from receiving the electricity price and load signals to injecting ammonia into the combustion zone. It operated continuously and stably for 60 minutes without any flameout or backfire. The combustion stability index (CSI) reached 0.91, the average flame temperature was 1375℃, the NOx concentration in the exhaust gas was 238 mg / Nm³, and the ammonia slip was less than 2 ppm. The entire process required no external ammonia source, achieving a closed-loop operation of "off-peak electricity price triggering—on-demand production and use—co-firing and stable combustion".

[0033] Example 5 of the present invention: Starting the system under extreme low load conditions: a simulated negative electricity price of -0.15 yuan / kWh for 30 minutes and a simulated boiler load of 20% THA. The PEM electrolyzer operates at 59.1 V and 1750 A, electrolyzing deionized water to produce 99.99% pure hydrogen at a stable flow rate of 1.22 Nm³ / h, with oxygen directly vented. Hydrogen and high-purity nitrogen (99.999%) are mixed at a molar ratio of H₂:N₂ = 3:1 and then fed into a skid-mounted ammonia synthesis reactor. The system pressure is controlled at 8.0 MPa, the catalyst bed temperature is maintained at 390℃, and the space velocity is 5800 h⁻¹. The reactor is loaded with 3.6 kg of commercially available iron-based catalyst (Fe₃O₄-Al₂O₃). The generated ammonia gas is cooled to 40℃ via heat exchange and then directly transported to the combustion simulation section through Inconel 625 alloy piping. A micro-flow control valve group precisely adjusts the ammonia flow rate to 1.9 Nm³ / h, and the ammonia is injected into the base of the micro-oil ignition gun flame through the first ammonia injection channel of a dedicated spray gun, creating an ammonia-rich atmosphere with an equivalence ratio of 1.3. At an axial distance of 150 mm from the flame center, a second powder injection channel injects finer lean coal powder (R90=7.8%) at a flow rate of 0.46 kg / min, achieving staged coupled combustion of "rich ammonia ignition - lean coal stable combustion". The system response time is 4 minutes and 8 seconds. During continuous operation for 45 minutes, combustion was stable without pulsation or flameout. The combustion stability index (CSI) was 0.94, the average flame temperature was 1350℃, the NOx emission concentration in the exhaust gas was 245 mg / Nm³, and the ammonia slip detection value was less than 3 ppm, verifying that the invention still has reliable stable combustion capability under ultra-low load conditions.

[0034] Example 6 of the present invention: The system is started under the following conditions: a simulated negative electricity price of -0.08 yuan / kWh for 30 minutes and a simulated boiler load of 35% THA. The PEM electrolyzer operates at an input voltage of 57.5 V and a current of 1650 A, electrolyzing deionized water to produce hydrogen with a purity of 99.99%, with a stable production rate of 1.12 Nm³ / h. The oxygen side is directly vented. Hydrogen and high-purity nitrogen (99.999%) are mixed at a molar ratio of H₂:N₂ = 3:1 and then fed into a skid-mounted low-temperature, low-pressure ammonia synthesis reactor. The system operating pressure is 7.5 MPa, the catalyst bed temperature is controlled at 380℃, and the space velocity is 6200 h⁻¹. The reactor is loaded with a commercially available iron-based catalyst (Fe₃O₄-Al₂O₃, 3.6 kg). The ammonia gas generated in the reaction, without liquefaction or water absorption, is directly cooled to 40°C via an Inconel 625 alloy pipeline and then transported to the combustion simulation section. The flow rate is precisely adjusted to 1.6 Nm³ / h using a micro-flow control valve group. It is then injected into the root of the flame in the micro-oil ignition gun through the first ammonia injection channel of a dedicated spray gun, forming an ammonia-rich zone with an equivalence ratio of 1.2. Simultaneously, at an axial distance of 150 mm from the flame center, a second powder injection channel injects lean coal powder with a fineness of R90=9.2% at a flow rate of 0.43 kg / min, achieving staged combustion organization. The system took 4 minutes and 25 seconds from signal triggering to ammonia injection into the combustion zone, and operated continuously and stably for 90 minutes. The combustion process was smooth, without flameout or severe pulsation. The combustion stability index (CSI) was 0.90, the average flame temperature was 1390°C, the NOx concentration in the exhaust gas was 232 mg / Nm³, and the ammonia slip was less than 2 ppm, verifying the reliability and stability of this invention during long-term operation in the low-to-medium load range.

[0035] Comparative Example 1: The traditional oil-fired combustion method was adopted, operating under a boiler load of 25% THA. The experimental system was a combustion simulation section of the same model (100 kW thermal power), equipped with an oil burner (rated power 150 kW, mechanical atomization type oil gun), and 0# light diesel oil (density 830 kg / m³, lower heating value 42.7 MJ / kg). The operating parameters were set as follows: fuel oil pressure 2.5 MPa, injection rate 120 kg / h (equivalent to a flow rate of 14.4 L / min), excess air coefficient 1.2, and combustion air temperature 30℃. During operation, the boiler load was maintained stably through the DCS system. Continuous oil injection was required during 60 minutes of continuous operation. No flameout occurred, but significant flame pulsation (frequency 2-3 Hz) was observed. Monitoring data shows that the combustion stability index (CSI) is 0.68 (<0.8 indicates instability), the average flame temperature is 1310℃, the NOx concentration in the exhaust gas is 305 mg / Nm³, and CO2 emissions increase by 1.8 t / h. The system operating cost is 144 yuan / h (calculated based on an oil price of 1.2 yuan / kg), and there is a risk of oil tank leakage (oil vapor concentration of 0.8 ppm was detected in the simulation test). Compared with the technical solution of this invention, traditional oil-based stable combustion is significantly degraded in terms of economy (10 times higher cost), environmental protection (3 times higher CO2 emissions), and safety (potential fire hazard), and cannot achieve linkage optimization with the grid electricity price signal. This verifies the comprehensive advantages of this invention in low-load stable combustion scenarios.

[0036] Comparative Example 2: The ammonia gasification technology using purchased liquid ammonia was employed to verify its stable combustion performance under a boiler load of 25% THA. The experimental system consisted of a 10 m³ liquid ammonia storage tank (design pressure 2.5 MPa, investment approximately 4.8 million RMB), a gasifier (rated gasification capacity 2 t / h), and a supporting pipeline network. Operating parameters were set as follows: liquid ammonia storage tank pressure 1.6 MPa, gasification temperature 60℃, gasification energy consumption 180 kWh / t-NH3, and the gasified ammonia was transported via pipeline to the combustion simulation section (150 m away). During the experiment, it took 18 minutes from receiving the stable combustion command to the ammonia injection into the combustion zone, during which the gasifier needed to be manually started and the flow rate adjusted to 1.8 Nm³ / h. After 60 minutes of continuous operation, the combustion stability index (CSI) was 0.75, the average flame temperature was 1330℃, the NOx concentration in the exhaust gas was 280 mg / Nm³, and the ammonia slip detection value was 12 ppm (exceeding the limit of the "Emission Standard for Air Pollutants from Thermal Power Plants"). The annual operating cost of the system includes the purchase cost of liquid ammonia (at 25,000 yuan / ton), gasification energy consumption, and equipment depreciation, with a comprehensive cost of 0.089 yuan / kWh. Compared with the technical solution of this invention, the externally purchased liquid ammonia system has three major drawbacks: firstly, high investment cost (liquid ammonia storage tank accounts for 70% of the total investment); secondly, long response delay (18 minutes vs. 4 minutes and 12 seconds), which cannot adapt to the dynamic triggering demand of grid electricity prices; and thirdly, ammonia slip exceeds the standard (12 ppm vs. <3 ppm), posing a risk of secondary pollution. The above data fully verify the significant advantages of this invention in terms of economy, response speed, and environmental protection.

[0037] Table 1. Comparison of operating parameters and performance between the embodiments of the present invention and the comparative examples.

[0038]

[0039] Conclusion: The above comparison shows that the present invention, by constructing an integrated system of "off-peak electricity price - skid-mounted ammonia production - staged combustion", achieves efficient and stable combustion of coal-fired boilers under low load conditions, and its technical effect is significantly better than the existing solutions.

[0040] In terms of economics, utilizing negative electricity price periods (-0.06 to -0.15 yuan / kWh) for on-site ammonia production reduces operating costs to 0.019 to 0.023 yuan / kWh (more than 60% lower than traditional oil-based / purchased liquid ammonia), and the initial investment for skid-mounted equipment is only 1.8 million yuan (80% lower than liquid ammonia systems). Regarding response speed, the direct ammonia supply technology achieves a rapid response of less than 5 minutes via Inconel 625 alloy pipelines (traditional liquid ammonia vaporization requires 18 minutes), meeting the instantaneous demands of grid dispatch. The system takes 4 minutes and 12 seconds from electricity price triggering to ammonia injection (comparative example 2 requires 18 minutes).

[0041] In terms of environmental protection, the "ammonia-rich gas-lean coal powder" staged combustion mode reduces NOx emissions by 20%-30% (232-245 mg / Nm³ vs. 305 mg / Nm³), and ammonia slip is <3 ppm (national standard limit of 15 ppm), which is better than the purchased liquid ammonia system (12 ppm).

[0042] In terms of safety, the liquid ammonia storage tank and high-pressure vaporization process are eliminated, thus removing the risk of leakage (comparative example 2 has a high risk). Through the MINLP multi-objective optimization algorithm, electricity price, load, and ammonia production capacity are dynamically matched, achieving a combustion stability index (CSI) of 0.90–0.94 under 20%–35% THA conditions (compared to only 0.68 for traditional oil injection), and maintaining a flame temperature of 1350–1390℃, thus achieving stable operation under ultra-low load.

[0043] The synergistic effect of the above-mentioned technical features enables this invention to overcome the bottlenecks of existing technologies in terms of economy, response speed, environmental protection, and safety, providing a low-carbon and economical solution for deep peak shaving in thermal power plants. The core differences between this invention and existing technologies are shown in the table below: Table 2 Comparison of core differences between the present invention and existing technologies .

Claims

1. A skid-mounted ammonia direct-supply stable combustion system for coal-fired boilers based on off-peak electricity prices and load linkage, characterized in that, include: The skid-mounted ammonia production unit is an integrated skid-mounted module consisting of a skid-mounted ammonia synthesis reactor and a PEM electrolyzer. The input end of the skid-mounted ammonia synthesis reactor is connected to the PEM electrolyzer and an air separation unit. The PEM electrolyzer is used to electrolyze deionized water to produce hydrogen during off-peak hours or periods of negative electricity prices. The hydrogen is then mixed with nitrogen provided by the air separation unit at a set molar ratio and fed into the skid-mounted ammonia synthesis reactor, where ammonia is directly synthesized under the action of a catalyst. The gaseous ammonia conveying pipeline is made of corrosion-resistant alloy material and directly conveys the gaseous ammonia produced by the skid-mounted ammonia synthesis reactor to the boiler burner without liquefaction or storage. The boiler burner is equipped with a first ammonia injection channel and a second pulverized coal injection channel. The first ammonia injection channel is located in the root area of ​​the micro-oil ignition flame and is used to inject gaseous ammonia to form an ammonia-rich atmosphere so that the ammonia gas is decomposed at high temperature to generate active free radicals. The second pulverized coal injection channel is located 150 mm axially from the center of the flame and is used to inject lean coal powder into the ammonia-rich high-temperature zone to achieve staged combustion of rich ammonia ignition and lean coal stable combustion. The distributed control system integrates the MINLP multi-objective optimization algorithm to collect real-time grid electricity price signals, boiler load data, and ammonia production capacity information. Using the grid electricity price signal as a trigger condition, it automatically starts the PEM electrolyzer and the skid-mounted ammonia synthesis reactor when a low or negative grid electricity price signal is detected. The distributed control system is electrically connected to the PEM electrolyzer and the skid-mounted ammonia synthesis reactor respectively, and is used to dynamically adjust the start-up and shutdown of the PEM electrolyzer and the skid-mounted ammonia synthesis reactor and the ammonia injection parameters to achieve multi-objective collaborative optimization of electricity price signals, load signals, and ammonia production capacity.

2. The system according to claim 1, characterized in that, The PEM electrolyzer has a rated power of 100kW, a hydrogen production capacity of 1.2 Nm³ / h, an electrolysis voltage of 57~59V, and a current of 1650~1750A.

3. The system according to claim 1, characterized in that, The skid-mounted ammonia synthesis reactor operates at a pressure of 7.5~8.0 MPa, a catalyst bed temperature of 380~390°C, and a space velocity of 5800~6200 h⁻¹. The catalyst used is an iron-based catalyst with a particle size of 3~5 mm.

4. The system according to claim 1, characterized in that, The ammonia gas delivery pipeline is made of Inconel 625 alloy and has an inner diameter of 15mm. The ammonia gas in the pipeline is cooled to 40°C and then delivered to the boiler burner.

5. The system according to claim 1, characterized in that, The ammonia flow rate injected into the first ammonia injection channel is 1.6~1.9 Nm³ / h; the coal powder fineness R90 injected into the second pulverized coal injection channel is 7.8%~9.2%, and the flow rate is 0.43~0.46 kg / min.

6. The system according to claim 1, characterized in that, The molar ratio of hydrogen to nitrogen in the mixed input gas of the skid-mounted ammonia synthesis reactor is 3:

1.

7. A method for stabilizing combustion using a skid-mounted ammonia direct-supply combustion stabilization system for a coal-fired boiler according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. During periods of low grid activity or negative electricity prices, start the PEM electrolyzer and skid-mounted ammonia synthesis reactor. The PEM electrolyzer electrolyzes deionized water to produce hydrogen, which is then mixed with nitrogen supplied by the air separation unit to synthesize ammonia. S2. The synthesized gaseous ammonia is directly transported to the boiler burner through a corrosion-resistant alloy pipeline without liquefaction or storage. S3. A staged combustion mode is adopted in the boiler burner. First, gaseous ammonia is injected into the root of the micro-oil ignition flame through the first channel to form an ammonia-rich atmosphere. Then, lean coal powder is injected into the second channel at an axial distance of 150mm from the center of the flame to achieve ammonia-rich ignition and lean coal stable combustion. S4. Real-time data collection of grid electricity price, boiler load and ammonia production capacity is achieved through a distributed control system. Electrolysis, synthesis and ammonia injection parameters are dynamically adjusted using a multi-objective optimization algorithm to achieve synergistic optimization of economic efficiency and stable combustion requirements.

8. The method according to claim 7, characterized in that, The reaction conditions for synthesizing ammonia are: pressure 7.5~8.0 MPa, temperature 380~390°C. The molar ratio of hydrogen to nitrogen is 3:

1.

9. The method according to claim 7, characterized in that, The ammonia injection flow rate is 1.6~1.9 Nm³ / h, the pulverized coal injection flow rate is 0.43~0.46 kg / min, and the pulverized coal fineness R90 is 7.8%~9.2%.

10. The method according to claim 7, characterized in that, The multi-objective optimization algorithm is the MINLP algorithm. The system's response time from the triggering of the electricity price signal to the injection of ammonia into the combustion zone is less than 5 minutes, and the combustion stability index (CSI) is greater than 0.90.

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