Gas molten salt furnace with multiple combustors arranged cooperatively

Abstract

The invention discloses a fuel gas molten salt furnace with multiple combustors arranged cooperatively, and relates to the technical field of industrial heating equipment, the fuel gas molten salt furnace comprises a furnace body, a plurality of groups of fuel gas combustors, a fuel gas supply system, a combustion-supporting air system, an electrical control system and a pipeline heat tracing system; the furnace body is of a horizontal structure, a spiral salt pipe is arranged in the furnace body, and a steel plate, a first ceramic fiber plate, second high-alumina bricks and castable are sequentially laid on the furnace body from inside to outside. According to the fuel gas molten salt furnace with the multiple combustors arranged cooperatively, the concept of multipoint uniform heat release is applied to combustor arrangement, the multiple sets of combustors are vertically installed at reserved positions of the furnace bottom in rows, the adjacent distance is precisely matched with the flame diameter, full coverage of hearth flames is achieved, the flame fullness reaches 95% or above, environmental protection comprehensively reaches the standard, and productivity is efficiently recovered; the heat efficiency is improved by 5%-10%, the total heat energy consumption is reduced, and the high-temperature heating requirement of melamine production is met.

Description

Technical Field

[0001] This invention relates to the field of industrial heating equipment technology, specifically to a gas-fired molten salt furnace with multiple burners arranged in a coordinated manner. Background Technology

[0002] A gas-fired molten salt furnace is an industrial heating device that uses gas (such as natural gas or liquefied petroleum gas) as a heat source to heat molten salt (usually a mixture of nitrates) as a heat transfer and storage medium. Molten salt has high thermal stability, high specific heat capacity, and good heat transfer performance at high temperatures, and is often used in solar thermal power generation, chemical industry, and materials heat treatment.

[0003] However, traditional molten salt furnaces mostly use coal, which has problems such as failing to meet environmental emission standards, serious ash accumulation in the furnace, and low thermal efficiency. With the tightening of environmental policies, the conversion of coal-fired molten salt furnaces to gas-fired molten salt furnaces has become an industry trend. However, in the existing conversion schemes, the burners are mostly arranged in a single or two-unit centralized configuration. The two existing coal-fired molten salt furnaces (models RYL-7600MA and RYL-7200MA) still have the following core problems: 1. Environmental protection standards not met: Coal combustion produces a large amount of pollutants. The fuel consumption is 1.8t / h and 1.3t / h of standard coal respectively. The emissions of particulate matter, sulfur dioxide and nitrogen oxides far exceed the current standards and do not meet the clean energy upgrade requirements for industrial kilns under 35 tons. 2. Limited production capacity: After trying to burn biomass fuel, the calorific value of biomass is only 3900-4200 kcal / ton, and the capacity utilization rate is only 65% ​​of the design value. In addition, the furnace needs to be shut down every week to clean the molten salt tubes and heat exchangers, resulting in a monthly production capacity loss of 955 tons for P1 furnace and 605.25 tons for P2 furnace, which cannot meet the daily production targets of 70 tons and 45 tons respectively. 3. Low thermal efficiency and safety hazards: Traditional coal-fired furnaces have serious ash accumulation in the furnace, and the system thermal efficiency is only about 70%. If one or two gas burners are simply replaced, flame concentration and local overheating damage to the molten salt tube (material 12Cr1MoVG) are likely to occur. Moreover, the flame coverage is less than 70%, which cannot meet the requirements for uniform heating of molten salt. At the same time, the flame coverage of the centrally arranged burners is limited, and airflow dead zones are likely to form in the furnace, affecting the heating efficiency of molten salt. 4. Operation is dependent on manual labor and the load regulation is poor: The existing heating process requires manual restarting and stopping of the burner for preheating and heating, which is not only labor-intensive, but also prone to safety accidents due to misoperation. In addition, the preheating and heating speed is slow and the production efficiency is low. At the same time, the load regulation ratio of a single burner is limited, making it difficult to adapt to the heat load requirements of the molten salt furnace under different operating conditions. Especially during the molten salt heating stage, the problem of excessive temperature fluctuation is likely to occur. 5. Existing gas-fired molten salt furnace retrofit schemes mostly adopt a single high-power burner top-mounted arrangement, without designing a multi-burner collaborative structure to meet the production capacity requirements of melamine production. Furthermore, they lack automated temperature control and precise exhaust gas treatment schemes, and there is no optimized scheme for the multi-group collaborative arrangement of gas-fired molten salt furnace burners. Therefore, they cannot effectively solve the core contradiction between flame distribution, thermal efficiency, and production capacity and environmental protection. Summary of the Invention

[0004] This invention provides a gas-fired molten salt furnace with multiple burners arranged in a coordinated manner, which solves the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: a gas-fired molten salt furnace with multiple burners arranged in a coordinated manner, the gas-fired molten salt furnace including a furnace body, several sets of gas burners, a gas supply system, a combustion air system, an electrical control system and a pipeline heat tracing system; The furnace body is configured as a horizontal structure, and the interior of the furnace body is equipped with a spiral salt pipe. The furnace body is laid with steel plate, first ceramic fiber board, second high alumina brick and castable material in sequence from the inside to the outside. Ceramic fiber insulation material is filled between the steel plate and the second high alumina brick. The interior of the furnace body is provided with several second high alumina bricks. The second high alumina bricks are built into a grid wall. A combustion chamber is formed between two adjacent grid walls. The side wall of the furnace body is laid with second ceramic fiber board and first high alumina brick in sequence from the inside to the outside. The burners in several groups are vertically installed in multiple rows through the reserved mounting holes at the bottom of the furnace body, and each burner corresponds to a combustion chamber. Each burner is equipped with a detachable conical burner. The gas supply system includes a main pipe, branch pipes, two sets of pressure reducing devices, a metering device, and a valve assembly. The combustion air system includes a blower, combustion air duct, frequency converter, and heat pipe air preheater; The electrical control system includes a controller, a molten salt temperature sensor, a flame detector, an exhaust gas oxygen content sensor, and an interlocking protection module. The pipeline heat tracing system uses electric heating tape, which is wrapped around the outer wall of the spiral salt pipe.

[0006] Optionally, the working medium inside the spiral salt tube is set as a mixed molten salt of potassium nitrate, sodium nitrite, and sodium nitrate, and the mixing ratio of the mixed molten salt of potassium nitrate, sodium nitrite, and sodium nitrate is 53%:40%:7%.

[0007] Optionally, the top of the furnace body is fitted with a diamond mesh to fix a ceramic fiber blanket, and the surface is coated with a high-temperature finishing material. The top of the furnace body is provided with a viewing hole, and the viewing hole is equipped with high-temperature resistant glass.

[0008] Optionally, the burner is composed of a first conical short tube, a straight short tube, and a second conical short tube connected by a flange.

[0009] Optionally, the main pipe is connected to an external gas pipeline network, and after being reduced in pressure by a pressure reducing device and measured by a metering device, it is divided into multiple branch pipes connected to the corresponding burners. The valve assembly integrates a filter, flame arrester, safety valve, pilot flame valve, main flame valve, and gas pressure switch, and is installed at the burner inlet. A gas leak detector is installed every 20m along the branch pipe.

[0010] Optionally, the output end of the blower is connected to a combustion air duct, the combustion air duct is connected to the burner and has a combustion air inlet, the combustion air duct is equipped with a frequency converter, and the combustion air duct is equipped with a metering point, which is equipped with a temperature sensor, a humidity sensor and an absolute pressure transmitter.

[0011] Optionally, the electrical control system is equipped with a touch screen.

[0012] Optionally, the gas-fired molten salt furnace also includes a denitrification system, which uses denitrification nozzles to spray ammonia water into the furnace.

[0013] The present invention has the following beneficial effects: 1. This gas-fired molten salt furnace with multi-burner coordinated arrangement applies the concept of multi-point uniform heat release to the burner arrangement. Multiple sets of burners are vertically installed in rows at the reserved positions at the bottom of the furnace. The adjacent spacing is precisely matched with the flame diameter to achieve full flame coverage in the furnace chamber, achieving a flame filling degree of more than 95%. It fully meets environmental protection standards, efficiently restores production capacity, improves thermal efficiency by 5%-10%, and reduces total heat energy consumption, thus meeting the high-temperature heating requirements of melamine production.

[0014] 2. This gas-fired molten salt furnace with multiple burners working together, by adopting clean gas fuel combined with low-NOx combustion and precise denitrification technology, ensures that the exhaust emissions meet the requirements of particulate matter ≤5mg / m³, sulfur dioxide ≤35mg / m³, and nitrogen oxides ≤50mg / m³ after the modification. This completely solves the environmental compliance problem of coal-fired furnaces, meets the requirements of the national clean energy transformation policy, and achieves comprehensive environmental protection results.

[0015] 3. This gas-fired molten salt furnace with multiple burners working together achieves a flame coverage of over 95% through a collaborative structure of "multiple burners + multiple combustion chambers," improving the uniformity of molten salt heating and restoring production capacity to 70 tons and 45 tons per day. Compared to burning biomass fuel, it increases monthly production by 1560.25 tons and annual production by 18723 tons, achieving a highly efficient production capacity.

[0016] 4. This gas-fired molten salt furnace with multiple burners working together, through a four-layer insulation structure for the furnace body and waste heat recovery from the air preheater, increases the system's thermal efficiency from 70% to over 78%, reduces total heat energy consumption by about 13%, and reduces flue gas heat loss. A single furnace saves approximately 100,000 Nm³ of gas consumption per year. The frequency conversion modification of the induced draft fan reduces energy consumption to 1 / 2 to 1 / 3 of the original, saving 132,000 yuan in labor and machinery costs per year, achieving the effect of improving both thermal efficiency and energy saving.

[0017] 5. This gas-fired molten salt furnace with multiple burners arranged in a coordinated manner achieves full flame coverage within the furnace by evenly arranging multiple sets of burners and precisely matching flame parameters. The flame diameter and length are 500mm and 2000mm respectively. This avoids the local overheating problem caused by traditional centralized arrangement, protects the molten salt heat exchange tube bundle, and extends the service life of the equipment, achieving the effect of uniform flame distribution and extended equipment life.

[0018] 6. This multi-burner coordinated gas-fired molten salt furnace replaces manual operation with a fully automatic preheating-heating program, which not only reduces the burden on operators but also avoids the risk of misoperation. Combined with a multi-level interlocking protection and leakage detection system, the safety of equipment operation is significantly improved. The accident frequency factor can be reduced from 3.72 to below 0.46. The multi-level interlocking protection (gas leakage, flame extinguishing, over-temperature, over-pressure) and the micro-negative pressure operating environment further ensure the safe operation of the equipment, reduce the risk of accidents, and achieve the effect of operation automation and safety upgrade.

[0019] 7. This gas-fired molten salt furnace with multiple burners arranged in a coordinated manner, through strict matching of the rated parameters of the two molten salt furnaces, does not break through the furnace body structure and is simple and easy to construct; the burners adopt detachable burners and the combustion chamber is independently separated, which facilitates local fault diagnosis and maintenance and reduces the difficulty of operation and maintenance; the 10:1 burner load regulation ratio and multiple sets of coordinated control are adapted to the different operating conditions of molten salt furnace such as heating and heat preservation, improve production stability, and achieve the effect of adaptability, maintainability and load regulation optimization. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the side of the furnace body of the present invention; Figure 2 This is a schematic diagram of the front of the furnace body of the present invention; Figure 3 This is a top view schematic diagram of the burner arrangement on the front of the molten salt furnace of the present invention; Figure 4 This is a top view of the valve assembly on the front of the molten salt furnace of the present invention; Figure 5 This is a schematic diagram of the burner of the present invention; Figure 6 This is a schematic diagram of the gas valve assembly of the present invention; Figure 7 This is a flowchart of the electrical control system of the present invention.

[0021] In the diagram: 11. Second ceramic fiber board; 12. First high alumina brick; 13. Combustion chamber; 14. Burner; 15. Steel plate; 16. First ceramic fiber board; 17. Second high alumina brick; 18. Castable refractory; 19. Spiral salt pipe; 27. Grid wall; 41. Combustion air duct; 52. Combustion air inlet; 54. Burner; 61. Filter; 62. Safety valve; 63. Flame arrester. Detailed Implementation

[0022] 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.

[0023] Please see Figure 1 and Figure 6 The present invention provides a technical solution: a gas-fired molten salt furnace with multiple burners arranged in a coordinated manner, the gas-fired molten salt furnace including a furnace body, several sets of gas burners 14, a gas supply system, a combustion air system, an electrical control system and a pipeline heat tracing system; The furnace body is designed as a horizontal structure, and its interior is equipped with a spiral salt pipe 19 made of 12Cr1MoVG material. From the inside out, the furnace body is laid with a steel plate 15, a 200mm thick first ceramic fiber board 16, a 24mm thick second high-alumina brick 17, and a castable refractory 18. A 16mm thick steel plate 15 seals the furnace bottom. The first ceramic fiber board 16 is 200mm thick, and the castable refractory 18 is 150mm thick. Ceramic fiber insulation material is filled between the steel plate 15 and the second high-alumina brick 17, with an 80-100mm gap between them, which is filled with ceramic fiber insulation material. The furnace body is equipped with several second high-alumina bricks 17 inside, which are used to build a grid wall 27. The grid wall 27 is 230mm thick and can withstand a temperature of ≥1700℃. It is divided into multiple independent combustion chambers 13. The total height of the furnace body is 2276mm, the height of the combustion chamber 13 area is 1200mm, and the height of the bottom concrete foundation is 600mm. A combustion chamber 13 is formed between two adjacent grid walls 27. The side wall of the furnace body is covered with a second ceramic fiber board 11 and a first high-alumina brick 12 from the inside to the outside. The thickness of the second ceramic fiber board 11 is set to 150mm, and the thickness of the first high-alumina brick 12 is set to 150mm. Several groups of burners 14 are vertically installed in multiple rows through pre-drilled mounting holes in the steel plate at the bottom of the furnace body. Each burner 14 corresponds to a combustion chamber 13, and each burner 14 is equipped with a detachable conical burner 54. The burner 14 is model ZXOQM-QER-2.8. The single row of burners 14 is evenly distributed along the length of the furnace body, with an adjacent burner spacing of 800-1000mm, which is adapted to the 500mm diameter of the output flame of the burner 14, ensuring that adjacent flames do not overlap and cover the bottom of the furnace. The thermal power of a single burner 14 is 1100KW, and the gas consumption is 210Nm³. 3 / h, combustion air demand 16118-19717Nm 3 / h, flame length 2000mm, diameter 500mm, combustion efficiency ≥99.9%, the connection between burner 14 and the bottom steel plate of the furnace body is sealed with high temperature refractory castable, the sealing layer thickness is ≥50mm, and the temperature resistance is ≥1200℃; The gas supply system includes a φ159×7 main pipe, a φ108×6 branch pipe, two pressure reducing devices, one metering device, and valve assemblies. When the leak detector of the gas supply system triggers an alarm, the PLC system immediately cuts off the emergency shut-off valve of the main gas pipeline and starts the purging procedure of the combustion air duct 41, with a purging time of ≥300s. The combustion air system includes a 45KW blower, a combustion air duct 41, a frequency converter, and a heat pipe air preheater. The selection of the blower for the combustion air system is reserved with a margin of 10%-15%. The air-fuel ratio is adjusted by feedback from the exhaust gas oxygen content sensor to ensure that the exhaust gas oxygen content is maintained at 4%-4.5% when the load is 80%-90%. In addition, the heat pipe air preheater uses the waste heat of the flue gas to heat the combustion air, so that the exhaust gas temperature is reduced to ≤180℃. The electrical control system includes a Mitsubishi PLC controller (model FX3U-64MT / ES-A), a molten salt temperature sensor (measuring range 0-500℃, accuracy ±1℃), a flame detector (ultraviolet type, detection distance 0-3m), a tail gas oxygen content sensor (measuring range 0-25%), and an interlock protection module. The gradient heating program of the electrical control system includes an empty tube preheating stage: the burner runs at minimum load for 300s and then stops, purging for 300s, repeating the operation at 30s intervals, until the temperature of the outer coil under the molten salt furnace reaches 240℃, at which point it automatically switches to gradient heating mode. The system includes a temperature sensor that collects molten salt temperature signals, a PLC controller that adjusts the burner load through PID calculations, and a built-in gradient temperature rise control program: using the initial temperature T0 as a base point, the set temperature is linearly increased at a rate of 30℃ / h; combustion stops when the difference between the measured temperature and the set temperature is ≥25℃, and restarts when the difference is ≤2℃. The interlock protection module includes high and low gas pressure interlock (10-20 kPa), flame extinguishing interlock, high and high molten salt temperature interlock (shutdown when the temperature exceeds 460℃), and induced draft fan interlock (induced draft fan starts first and then stops, with a 5-10 minute delay before shutdown). It supports front-of-machine operation and remote monitoring in the control room, and is interconnected with the central control system. The pipeline heat tracing system uses electric heating tape, which is wrapped around the outer wall of the spiral salt pipe 19. The heat tracing power is matched according to the pipe diameter to ensure that the temperature of the molten salt inside the pipe is not lower than 180℃, thus avoiding solidification and blockage.

[0024] The working medium inside the spiral salt tube 19 is set as a mixed molten salt of potassium nitrate, sodium nitrite and sodium nitrate, and the mixing ratio of potassium nitrate, sodium nitrite and sodium nitrate is 53%:40%:7%, melting point 142℃, rated working pressure 1.0-1.9Mpa, and maximum medium temperature 450℃.

[0025] The top of the furnace body is fixed with a diamond mesh to a 200mm thick ceramic fiber blanket, and the surface is coated with a 150mm thick high-temperature finishing material. The top of the furnace body is equipped with a viewing hole, which is fitted with high-temperature resistant glass.

[0026] The burner 54 is composed of a first conical short tube, a straight connecting short tube, and a second conical short tube connected by a flange.

[0027] The main pipe is connected to the external gas pipeline network, and the pressure is reduced to 10-20 kPa by the pressure reducing device. After being metered by the metering device, it is divided into multiple branch pipes and connected to the corresponding burners 14. The valve assembly integrates a filter 61 (filtration accuracy ≤5μm), a flame arrester 63 (explosion-proof rating Exd IIB T4), a safety valve 62 (opening pressure 25kpa), a small fire valve (DN40), a large fire valve (DN50), and a gas pressure switch (range 0-30kpa), which is installed at the inlet end of the burner 14. A gas leak detector (with a detection accuracy of ≤0.1% LEL) is installed every 20m along the branch pipe.

[0028] The blower output is connected to a combustion air duct 41, which is connected to the combustion air inlet 52 of the burner. A frequency converter (frequency adjustment range 0-50Hz) is installed on the combustion air duct 41. The blower speed is adjusted by the frequency converter to match the 10:1 load adjustment ratio of the burner 14, so that the combustion air temperature is maintained at 90-120℃. A metering point is set on the combustion air duct 41, and the metering point is equipped with a temperature sensor, a humidity sensor and an absolute pressure transmitter to monitor the parameters in real time and dynamically calculate the combustion air flow rate through a formula. The induced draft fan is adjusted by a frequency converter to maintain a slight negative pressure of -50~-100Pa in the furnace, reducing energy consumption to 1 / 2-1 / 3 of that before the modification.

[0029] The electrical control system is equipped with a 10-inch touch screen, enabling parameter setting, status display, and manual operation, with molten salt temperature fluctuations controlled within ±5℃.

[0030] The gas-fired molten salt furnace also includes a denitrification system, which uses denitrification nozzles to inject ammonia water into the furnace, with the ammonia water usage controlled at 0.35m³. 3 For shifts of less than one, using a low-NOx burner will reduce NOx emissions to ≤50mg / m³. 3 .

[0031] In summary, this multi-burner coordinated gas-fired molten salt furnace, when in use: 1. Furnace body structure The furnace body has a horizontal structure and is compatible with the rated parameters of two molten salt furnaces: the working medium is a mixed molten salt of potassium nitrate, sodium nitrite, and sodium nitrate (mixing ratio 53%:40%:7%). This molten salt has a melting point of only 142℃ and can operate stably in the range of 350-600℃. The circulating molten salt volume is 350m³. 3 / h, the furnace modification strictly follows these steps: (1) Foundation demolition: Remove the grate and wind chamber angle iron of the original coal-fired furnace, remove the ash and soot in the furnace, and conduct ball and hydraulic tests on the original spiral salt pipe 19 to ensure that the spiral salt pipe 19 is unobstructed and leak-free. After the front row of furnace arches of the furnace body is demolished, lay 200mm first ceramic fiber board 16 and build 24mm second high alumina refractory bricks 17. (2) Furnace bottom reconstruction: The furnace bottom is sealed with a 16mm thick steel plate 15, and multiple sets of burner 14 installation holes are reserved (in multiple rows, each row corresponding to the number of combustion chambers). A 200mm thick first ceramic fiber board 16 (thermal conductivity ≤0.1W / (m・K)) and a high alumina refractory second high alumina brick 17 (withstanding ≥1700℃) are laid on the steel plate 15 in sequence. A 150mm thick corundum refractory castable 18 (compressive strength ≥50MPa) is poured on top to form a four-layer furnace bottom structure. An 80-100mm gap is reserved between the steel plate 15 and the refractory second high alumina brick 17, which is filled with ceramic fiber insulation material to reduce heat loss. (3) Combustion chamber 13 division: The furnace body is divided into multiple independent combustion chambers 13 by a 230mm thick high alumina brick grid wall 27. Each combustion chamber 13 corresponds to a burner 14, which not only avoids flame crosstalk, but also enhances heat exchange efficiency through space constraint, and the flame filling degree is increased to more than 95%. (4) Furnace wall and furnace top modification: The original furnace wall is demolished, and a 150mm second ceramic fiber board 11 is laid on the inner side and a 150mm first high alumina brick 12 is built on the outer side to form a double fire-resistant and heat-insulating structure. The furnace top is fixed with a diamond mesh to a 200mm ceramic fiber blanket and coated with high-temperature plastering material to ensure that the temperature of the outer wall of the furnace does not exceed the ambient temperature +15℃. A fire observation hole (equipped with high-temperature resistant glass) is set on the top of the furnace to facilitate observation of the flame status inside the furnace.

[0032] 2. Multi-burner coordinated arrangement The collaborative structure of "multiple burners + multiple combustion chambers" is inspired by the difference between the "single-point centralized heat dissipation" of radiators and the "multi-point uniform heat dissipation" of underfloor heating. It applies the concept of "multi-point uniform heat release" to the burner arrangement and is designed strictly according to flame parameters and production capacity requirements. (1) Selection of burner 14: The ZXOQM-QER-2.8 type fully automatic proportional adjustment burner 14 is adopted, with a single unit heat power of 1100KW, which is suitable for the heating demand of a single combustion chamber 13. The total heat power of multiple sets can meet the rated heat load of two molten salt furnaces. The burner 54 of the burner 14 adopts a detachable conical combination structure, which is composed of a first conical short pipe, a straight short pipe and a second conical short pipe connected by a flange, which is convenient for later disassembly and cleaning of combustion impurities on the inner wall; (2) Arrangement: Each molten salt furnace is equipped with multiple sets of burners 14, which are installed vertically in multiple rows in the reserved holes of the bottom steel plate of the furnace. Each burner 14 corresponds to an independent combustion chamber 13. The single row of burners 14 is evenly distributed along the length of the furnace body, with an adjacent spacing of 800-1000mm. This spacing is designed based on a flame diameter of 500mm to ensure that adjacent flames do not overlap and fully cover the bottom of the furnace, avoiding local overheating damage to the spiral salt tube 19. (3) Sealing treatment: The connection between the burner 14 and the steel plate 15 is sealed with high-temperature refractory castable 18 (thickness ≥50mm, withstand ≥1200℃) to prevent flue gas leakage and ensure the stability of the furnace micro negative pressure environment.

[0033] 3. Gas supply system The gas supply system is designed according to pressure ratings and safety requirements to ensure stable and reliable gas delivery: Gas from the gas company's pipeline at 0.8 MPa is reduced to 10-20 kPa through a two-stage pressure reduction process and then sent to the bottom burners 14 of the P1 and P2 molten salt furnaces. In burners 14, the gas mixes with combustion air and is burned to heat the molten salt to 430±5℃. The combustion flue gas then sequentially passes through a nitrogen preheater, a carrier gas preheater, a medium-temperature denitrification system, a waste heat boiler, an air preheater, a bag filter, and an induced draft fan. Finally, it passes through a flue gas desulfurization tower for desulfurization absorption before being discharged into the atmosphere. The process is as follows: (1) Pipeline specifications: The main pipe is made of φ159×7 seamless steel pipe and the branch pipe is made of φ108×6 seamless steel pipe. The branch pipe of P1 furnace is about 70m long and the branch pipe of P2 furnace is about 130m long. The main pipe is connected to the furnace body through the workshop pipe rack (48m) and the road bridge section (34m). The pipe connection is made by argon arc welding. After welding, annealing treatment is performed and radiographic inspection is carried out. (2) Pressure reduction and metering: Configure two pressure reducing devices (to reduce the municipal gas pressure to 10-20 kPa) and one high-precision metering device (accuracy ≤ 1%) to ensure stable gas pressure and accurate metering of usage; (3) Safety assurance: Each branch pipe end is equipped with an integrated valve group, including filter 61, flame arrester 63, safety valve 62 (starting pressure 25kpa) and pressure switch, to achieve triple protection of filtration, explosion prevention and overpressure; a leak detector is installed every 20m of the branch pipe, with a detection accuracy of ≤0.1% LEL. In case of leakage, the main emergency shut-off valve is immediately shut off and the audible and visual alarm is activated. At the same time, the combustion air duct 41 is linked to purge for 300s to remove residual gas.

[0034] 4. Combustion-supporting air system The combustion air system adopts a "precise metering + waste heat recovery" design to improve combustion efficiency and energy saving. Blower system: A 45KW centrifugal blower is selected, with an air volume adapted to the total requirements of multiple burners (16118-19717 Nm³ / h × number of burners), and an air pressure ≥30 kPa. The combustion air duct (41) is equipped with a frequency converter to adjust the speed according to the combustion load, meeting a 10:1 load regulation ratio. Gas pipeline flow meters and air pipeline flow meters are used to adjust the air-fuel ratio in real time to avoid incomplete combustion or excess air. A 10%-15% margin is reserved in the blower selection. ① Regulating loop logic: Target temperature of molten salt furnace ↓ Temperature controller (compared to actual temperature) ↓ ( Deviation signal output) Gas regulating valve → Regulates gas flow ↓┌─────────┐ ││ │ ↓│ │ Gas flow meter → Air regulating valve → Adjust air flow (according to air-fuel ratio) ↓ │ The heat released during combustion in the molten salt furnace changes the actual temperature of the molten salt furnace. ↓ │ Temperature sensor → Feedback to temperature controller ┘ (Negative feedback closed loop: deviation is reduced, temperature is stabilized) ② Explanation of the regulatory mechanism: a. First-level negative feedback regulation (temperature → gas) When the actual temperature is less than the target temperature: the temperature controller outputs an increased signal → the gas regulating valve opens wider → the gas flow increases → the heat released from combustion in the molten salt furnace increases → the actual temperature rises → the deviation gradually decreases. When the actual temperature > the target temperature: the temperature controller outputs a reduced signal → the gas regulating valve opening decreases → the gas flow decreases → heat release decreases → the actual temperature drops → the deviation decreases; b. Two-stage linkage regulation (gas → air) Airflow regulation follows changes in gas flow to ensure the optimal air-fuel ratio and avoid incomplete combustion of gas (wasting fuel and producing pollutants) or excessive air (taking away heat and reducing thermal efficiency). Increased gas flow → Gas flow meter detects increased flow → Signal transmitted to air regulating valve → Air opening increases synchronously → Air flow increases. Reduced gas flow rate → Reduced air opening rate → Reduced air flow rate; (2) Exhaust fan system: The frequency converter is used to adjust the air volume dynamically according to the furnace pressure sensor signal (-50~-100Pa). After the modification, the energy consumption is reduced to 1 / 2-1 / 3 of the original coal-fired furnace. (3) Waste heat utilization: A heat pipe air preheater is added to heat the combustion air to 90-120℃ using the waste heat of flue gas, which not only improves the combustion efficiency, but also reduces the exhaust gas temperature to ≤180℃, and the system thermal efficiency is increased to more than 78%. The air-fuel ratio is adjusted by feedback from the exhaust gas oxygen content sensor to ensure that the exhaust gas oxygen content is maintained at 4%-4.5% when the load is 80%-90%.

[0035] 5. Electrical control system Please see Figure 7 The electrical control system adopts a "PLC+DCS interconnection" architecture to achieve fully automated control of the entire process. (1) Control core: Mitsubishi PLC controller (model FX3U-64MT / ES-A) is adopted, equipped with a 10-inch touch screen and human-machine interface, supports front-of-machine operation and remote monitoring in the control room, can be interconnected with the central control system computer, and transmit parameters such as burner load, molten salt temperature, gas pressure, and tail gas oxygen content in real time, so as to realize parameter setting, status display and manual operation. (2) Detection module: integrates molten salt temperature sensor (accuracy ±1℃), ultraviolet flame detector (detection distance 0-3m), gas pressure sensor, furnace pressure sensor and tail gas oxygen content sensor to ensure comprehensive monitoring of key parameters; (3) Intelligent control function: ①Automatic preheating of empty tubes: Burner 14 runs at minimum load for 300s and then stops, purges for 300s, repeats the operation at 30s intervals until the temperature of the outer coil of the molten salt furnace reaches 240℃ and then automatically stops, waiting for the molten salt pump to start signal; ② Intelligent gradient heating: Taking the initial temperature T0 as the base point, the set temperature is linearly increased at a rate of 30℃ / h. The PLC compares the measured temperature with the set temperature in real time. When the temperature difference is ≥25℃, combustion stops. When the temperature difference is ≤2℃, combustion restarts. This continues until the temperature reaches 450℃±5℃, achieving stable control of the molten salt temperature within the range of ±5℃. ③ Adaptive air-fuel ratio: Based on the exhaust gas oxygen content sensor signal (target 4%-4.5%), automatically adjust the opening of the gas flow valve and damper to ensure complete combustion and minimal heat loss; ④ Flexible load adjustment: The burner supports a load adjustment ratio of 10:1. During the molten salt heating stage (preheating for 3 hours), it can be adjusted to low flame mode and then switched to high flame mode after the heating is completed, adapting to different working conditions.

[0036] (4) Enhanced interlocking protection: ① Gas pressure interlock: The gas supply will be immediately cut off and the furnace will be shut down when the pressure is below 10 kPa or above 20 kPa; ②Flame interlock: The gas supply is cut off within 3 seconds after the flame is extinguished and a 5-minute purging process is initiated; ③ Molten salt over-temperature interlock: When the temperature exceeds 460℃, an emergency shutdown is triggered, and the emergency cooling circuit is opened at the same time; ④ Induced draft fan interlock: The “start first, stop later” logic is adopted. The burner can be ignited 5 minutes after the induced draft fan starts. When the furnace is shut down, the induced draft fan is delayed by 5-10 minutes to ensure that the residual gas is completely removed.

[0037] 6. Auxiliary systems (1) Pipeline heat tracing system: The outer wall of the molten salt conveying pipeline is wrapped with electric heating tape for heat tracing. The heat tracing power is matched according to the pipeline diameter (the heat tracing power of DN300 pipeline is ≥50W / m), and a temperature controller is provided to ensure that the temperature of the molten salt in the pipeline is always maintained above 180℃, so as to avoid the pipeline from being blocked due to solidification caused by temperature drop. (2) Pipeline protection: All exposed metal pipelines, such as molten salt transport pipelines, shall be treated with anti-corrosion measures. First, the pipeline surface shall be sandblasted to remove rust and reach the Sa2.5 standard. Then, two layers of epoxy zinc-rich primer shall be applied, each layer with a thickness of not less than 70 μm. Next, two layers of epoxy micaceous iron oxide intermediate paint shall be applied, each layer with a thickness of not less than 80 μm. Finally, two layers of acrylic polyurethane topcoat shall be applied, each layer with a thickness of not less than 60 μm, to form an effective anti-corrosion barrier and prevent the pipeline from being damaged by corrosion due to external environmental factors. (3) Denitrification system: Denitrification nozzles are installed at the furnace outlet to inject ammonia water into the flue gas. The ammonia injection rate is automatically adjusted by the PLC system based on the nitrogen oxide detection value to control the ammonia water usage at 0.35m³. 3 For shifts of less than one, ensure nitrogen oxide emissions are ≤50mg / m³. 3 .

[0038] Example 1 (Compatible with RYL-7600MA molten salt furnace, P1 furnace) 1. Furnace body reconstruction: Remove the original grate and wind chamber angle iron, seal the furnace bottom with 16mm steel plate 15, and reserve 12 burner holes (divided into 4 rows, 3 holes per row, with a hole spacing of 800mm). Lay 200mm first ceramic fiber board 16, refractory second high alumina brick 17, and 150mm corundum castable 18 in sequence on the furnace bottom. Build 3 grid walls 27 with 230mm thick second high alumina brick 17 to divide it into 12 combustion chambers 13. Lay 150mm second ceramic fiber board 11 + 150mm first high alumina brick 12 on the furnace wall. Lay 200mm ceramic fiber blanket + 150mm plastering material on the furnace top. After the front row of furnace arches is removed, lay 200mm first ceramic fiber board 16 and build 24mm refractory second high alumina brick 17. Perform ball passing and hydraulic tests on the original molten salt heat exchange spiral salt tubes and remove surface soot. 2. Burner 14 installation: Install 12 ZXOQM-QER-2.8 type burners 14, each corresponding to one combustion chamber 13. The gap between the burner 14 and the steel plate 15 is sealed with high-temperature castable refractory 18. 3. System setup: Lay φ159×7 main pipe (48m for workshop pipe rack + 34m for road bridge), φ108×6 branch pipe (70m), install 2 sets of pressure reducing devices (15kpa constant pressure), 1 set of metering device, install 45KW blower (with frequency converter), heat pipe air preheater, induced draft fan (with frequency converter), spiral wound pipe heat tracing system, and install denitrification nozzles; 4. Control system debugging: Connect Mitsubishi PLC (model FX3U-64MT / ES-A), temperature sensor, flame detector, oxygen content sensor, equipped with 10-inch touch screen, debug the automation program: preheat the empty pipe to 240℃, gradient temperature increase of 30℃ / h to 450℃, and control the oxygen content of the exhaust gas at 4%-4.5%.

[0039] 5. Operating parameters after modification (verification target): (1) Molten salt temperature: 450℃±4℃; (2) Production capacity: 70 tons of melamine per day; (3) Emissions: Particulate matter 3.2 mg / m³, sulfur dioxide 22 mg / m³, nitrogen oxides 43 mg / m³; (4) Thermal efficiency: 82%; (5) Energy consumption of the induced draft fan: reduced by 60% compared to before the renovation; (6) Ammonia water usage: 0.32 m³ / shift; (7) Annual operating costs: 8% lower than the cost of coal before the transformation, and 15% lower than the cost of biomass fuel (including capacity loss).

[0040] Example 2 (Compatible with RYL-7200MA molten salt furnace, P2 furnace) 1. Furnace body reconstruction: The spacing of the reserved holes in the furnace bottom steel plate 15 is adjusted to 1000mm (to match the furnace body length), the number of grid walls 27 is adapted to the arrangement of burners 14, and the rest of the structure is the same as in Example 1; 2. Burner 14 and system setup: The model and quantity of burner 14 remain unchanged, the branch pipe length is 130m, the ammonia water nozzle flow rate is adapted and adjusted, and the rest is the same as in Example 1; 3. Debugging: Temperature control target 450℃±5℃, production capacity target 45 tons per day.

[0041] 4. Operating parameters after modification (verification target): (1) Molten salt temperature: 450℃±3℃; (2) Production capacity: 45 tons of melamine per day; (3) Emissions: Particulate matter 2.8 mg / m³, sulfur dioxide 19 mg / m³, nitrogen oxides 41 mg / m³; (4) Thermal efficiency: 80%; (5) Annual cost savings: RMB 132,000 in labor and machinery costs, resulting in an annual profit increase of RMB 4.83 million; (6) Flame filling degree of burner 14: 91%, with no local overheating.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A gas-fired molten salt furnace with multiple burners arranged in a coordinated manner, characterized in that: The gas-fired molten salt furnace includes a furnace body, several sets of gas burners (14), a gas supply system, a combustion air system, an electrical control system, and a pipeline heat tracing system; The furnace body is configured as a horizontal structure, and the interior of the furnace body is provided with a spiral salt pipe (19). The furnace body is laid with steel plate (15), first ceramic fiber board (16), second high alumina brick (17) and castable (18) from the inside out. Ceramic fiber insulation material is filled between the steel plate (15) and the second high alumina brick (17). The interior of the furnace body is provided with several second high alumina bricks (17). The second high alumina bricks (17) are built into a grid wall (27). A combustion chamber (13) is formed between two adjacent grid walls (27). The side wall of the furnace body is laid with second ceramic fiber board (11) and first high alumina brick (12) from the inside out. Several groups of burners (14) are vertically installed in multiple rows on the reserved installation holes at the bottom of the furnace body, and each burner (14) corresponds to a combustion chamber (13). Each burner (14) is provided with a detachable conical burner (54). The gas supply system includes a main pipe, branch pipes, two sets of pressure reducing devices, a metering device, and a valve assembly. The combustion air system includes a blower, a combustion air duct (41), a frequency converter, and a heat pipe air preheater; The electrical control system includes a controller, a molten salt temperature sensor, a flame detector, an exhaust gas oxygen content sensor, and an interlocking protection module. The pipeline heat tracing system uses electric heating tape, which is wrapped around the outer wall of the spiral salt pipe (19).

2. The gas-fired molten salt furnace with multiple burners arranged in a coordinated manner according to claim 1, characterized in that: The working medium inside the spiral salt tube (19) is set as a mixed molten salt of potassium nitrate, sodium nitrite and sodium nitrate, and the mixing ratio of the mixed molten salt of potassium nitrate, sodium nitrite and sodium nitrate is 53%:40%:7%.

3. A gas-fired molten salt furnace with multiple burners arranged in a coordinated manner according to claim 1, characterized in that: The top of the furnace body is made of a diamond mesh to fix a ceramic fiber blanket, and the surface is coated with a high-temperature finishing material. The top of the furnace body is provided with a fire observation hole, which is equipped with high-temperature resistant glass.

4. A gas-fired molten salt furnace with multiple burners arranged in a coordinated manner according to claim 1, characterized in that: The burner (54) is composed of a first conical short tube, a straight short tube, and a second conical short tube connected by a flange.

5. A gas-fired molten salt furnace with multiple burners arranged in a coordinated manner according to claim 1, characterized in that: The main pipe is connected to the external gas pipeline network. After being depressurized by the pressure reducing device and metered by the metering device, it is divided into multiple branch pipes and connected to the corresponding burners (14). The valve group integrates a filter (61), a flame arrester (63), a safety valve (62), a small fire valve, a large fire valve, and a gas pressure switch, and is installed at the inlet end of the burner (14); A gas leak detector is installed every 20m along the branch pipe.

6. A gas-fired molten salt furnace with multiple burners arranged in a coordinated manner according to claim 1, characterized in that: The output end of the blower is connected to a combustion air duct (41), which is connected to the combustion air inlet (52) of the burner. A frequency converter is installed on the combustion air duct (41), and a metering point is installed on the combustion air duct (41). The metering point is equipped with a temperature sensor, a humidity sensor and an absolute pressure transmitter.

7. A gas-fired molten salt furnace with multiple burners arranged in a coordinated manner according to claim 1, characterized in that: The electrical control system is equipped with a touch screen.

8. A gas-fired molten salt furnace with multiple burners arranged in a coordinated manner according to claim 1, characterized in that: The gas-fired molten salt furnace also includes a denitrification system, which uses denitrification nozzles to spray ammonia water into the furnace.

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