Method for baking natural gas furnace with small fire

Abstract

The invention discloses a method for baking a natural gas furnace with soft fire. The method comprises the following steps: checking pressure parameters; checking and calibrating air pressure and gas pressure of all burners in advance; setting a valve opening degree on an HMI interface; fan control is set to be in a manual mode, and a large fan is started; ignition fan control and purging control are started; the opening degree of the air pipeline pressure release valve is set to be in an automatic mode; fan control is set to be in a manual mode, an ignition controller is started for manual ignition control, and a natural gas main inlet valve button of the power distribution cabinet is pressed down; setting an oven baking program according to the oven baking curve; when the temperature is lower than 300 DEG C, small fire is ignited by a small ignition burner of a straight flame burner and small fire is ignited by a small ignition burner of a flat flame burner to heat the hearth, and when the temperature is 300-550 DEG C, small fire is ignited by the small ignition burner of the straight flame burner and large fire is ignited by a large ignition burner of the flat flame burner to heat the hearth until the furnace baking procedure is completed; and after furnace baking is finished, the opening degree of the valve is set. According to the invention, the flame is prevented from directly impacting the castable, and each masonry of the hearth shows the optimal physicochemical property after the furnace baking is finished.

Description

Technical Field

[0001] The present invention belongs to the field of natural gas heat treatment furnaces, and particularly relates to a method for baking a natural gas furnace with a small pilot flame. Background Art

[0002] Baking the furnace before calibrating the temperature is an important step in the installation and construction of heat treatment furnaces. Baking the furnace means slowly heating each part of the furnace lining according to a heating curve suitable for the furnace lining, so that the moisture contained therein is gradually precipitated until it is completely dry. During the furnace baking process, a relatively gentle heating process curve should be set to avoid cracking or spalling of the furnace lining due to too rapid heating, which affects its service life. The traditional furnace baking method uses gas or natural gas for baking, because it has the advantages of soft flame, easy temperature control, uniform furnace temperature and convenient installation. The traditional furnace baking method often uses diffusion-type or atmospheric gas burners for furnace baking. After the furnace temperature rises to 600 °C, the combustion device used during normal production of the heat treatment furnace is replaced to continue baking. When these conditions are not available or when gas supply is inconvenient, a small baking stove can be built separately for large heat treatment furnaces, and coal is used as fuel to bake the heat treatment furnace. Sometimes it can also be carried out on the combustion chamber of the heat treatment furnace body, but special attention should be paid to strictly controlling the uniformity of the furnace temperature to prevent damage to the furnace body caused by too rapid local heating.

[0003] For the furnace baking method of natural gas furnace equipment with a similar furnace lining design abroad, the combustion chamber of its own equipment body is used, and natural gas is used as fuel. The highest temperature of the furnace baking process is 1200 °C, the highest heating rate is 32.5 °C / h, and the total duration of the furnace baking process is 122 h. Due to the different materials and properties of its furnace lining materials, the physicochemical reaction of its castable to the surface directly impacted by the flame is small, and cracking or spalling will not occur under the high-temperature furnace baking process. If the natural gas furnace involved in the present invention adopts this furnace baking method, it may damage the refractory layer in the furnace, resulting in cracking, spalling or bulging of the castable, seriously affecting the service life of the refractory layer, and even causing damage to the refractory layer and making it unusable. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for baking a natural gas furnace with a small pilot flame. According to the furnace baking process curve suitable for the furnace lining material, a method combining a small pilot flame and a flat flame burner is adopted to slowly heat up and bake the furnace chamber, so that the moisture contained in each masonry of the furnace chamber is completely precipitated. Avoid direct flame impact on the castable, and ensure that each masonry of the furnace chamber exhibits the best physicochemical properties after the furnace baking is completed.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for baking a natural gas furnace with a small pilot flame includes the following steps:

[0007] S1. Close and press the furnace door tightly, and check the following pressure parameters: the inlet pressure of the natural gas main pipeline, the pressure after decompression of the natural gas main pipeline for the large burner, the pressure after decompression of the natural gas main pipeline for the ignition small burner, the set values of each pressure switch, the air pressure of the blower, and the air pressure of the ignition small blower.

[0008] S2. Check and calibrate the air pressure and gas pressure of all burners in advance to ensure that all burners can be ignited normally.

[0009] S3. Set the valve opening degree on the HMI interface.

[0010] S4. Set the blower control to manual mode, set the blower speed to 35 Hz, and start the large blower.

[0011] S5. Start the ignition blower control and purge control.

[0012] S6. After purging, set the opening degree of the air pipeline pressure relief valve to automatic mode; set the blower control to manual mode, and set the blower speed to 25 Hz; start the manual ignition control of the ignition controller, and press the button of the total inlet valve of natural gas in the power distribution cabinet.

[0013] S7. Set the oven drying program according to the oven drying curve.

[0014] S8. Below 300 °C, use the direct flame burner ignition small burner and the flat flame burner ignition small burner to ignite small fires to heat the furnace chamber. From 300 °C to 550 °C, use the direct flame burner ignition small burner to ignite small fires and the flat flame burner large burner to ignite large fires to heat the furnace chamber until the oven drying program is completed.

[0015] S9. After oven drying, keep the furnace door closed and pressed tightly, and set the valve opening degree.

[0016] Preferably, in S1, the inlet pressure of the natural gas main pipeline is 25 - 30 kPa, the pressure after decompression of the natural gas main pipeline for the large burner is 10 kPa, and the pressure after decompression of the natural gas main pipeline for the ignition small burner is 6 kPa; the minimum pressure switch set value of the natural gas main pipeline for the large burner is 30 mbar, and the maximum pressure switch set value is 142 mbar; the minimum pressure switch set value of the natural gas main pipeline for the ignition small burner is 30 mbar, and the maximum pressure switch set value is 120 mbar; the air pressure of the blower is 3 - 5 kPa, and the air pressure of the ignition small blower is not less than 8 kPa.

[0017] Preferably, in S2, the air pressure of the ignition small burner in the direct flame burner system is 40 - 50 mbar, and the gas pressure is 25 mbar. The air pressure of the ignition small burner in the flat flame burner system is 35 - 40 mbar, and the gas pressure is 30 mbar.

[0018] Preferably, in step S3, the opening degree of the furnace pressure valve is 90%, the opening degree of the air pipeline pressure relief valve is 0%, and the opening degrees of all air valves of the flat flame burner system and the straight flame burner system are 100%.

[0019] Preferably, in step S7, the oven drying curve is specifically as follows: in the first stage, it is heated from room temperature to 150°C at a heating rate of 10°C / h and then kept warm for 72 hours; in the second stage, it is heated from 150°C to 250°C at a heating rate of 10°C / h and then kept warm for 72 hours; in the third stage, it is heated from 250°C to 400°C at a heating rate of 20°C / h and then kept warm for 60 hours; in the fourth stage, it is heated from 400°C to 550°C at a heating rate of 20°C / h and then kept warm for 60 hours; after completion, it is naturally cooled at a rate of 20°C / h.

[0020] Preferably, in step S8, during the whole oven drying process, a special person records the actual furnace temperature of the three temperature zones every half an hour until the recorded actual furnace temperature drops to 100 degrees Celsius.

[0021] Preferably, the specific steps of step S9 are as follows: keep the furnace door closed and tightened, set the opening degree of the furnace pressure valve to 0%; keep the blower and the ignition small blower in the operating state; set the opening degree of the air pipeline pressure relief valve to 100%; set the opening degree of the heat exchanger protection valve to 100%.

[0022] The beneficial effects of the present invention are as follows:

[0023] (1) Based on the natural gas furnace combustion system, the present invention combines an ignition small burner and a flat flame burner to ignite and heat the refractory layer of the furnace lining by ignition, effectively removing the free water, combined water and even crystal water in the refractory layer. According to a certain oven drying process curve, the baking of the refractory layer is completed. The straight flame burner system of the natural gas furnace combustion system involved in the present invention is located directly above the castable in the lower part of the side wall. The straight flame burner has a high flame outlet speed and a long flame length. Using the ignition small burner and the flat flame burner for ignition heating can effectively avoid the direct impact of the flame on the surface of the castable. After the oven drying is completed using this method and the natural cooling ends, the surface of the castable is flat, without cracking, spalling and bulging caused by its own thermal expansion and contraction.

[0024] (2) Below 300°C, both the straight flame burner and the flat flame burner are ignited with small flames for oven drying, and from 300°C to 550°C, the straight flame burner is ignited with a small flame and the flat flame burner is ignited with a large flame, which can save gas consumption compared with using only large burners for ignition heating. The present invention provides a safe, reliable, energy-saving and efficient oven drying method suitable for low-temperature (up to 550°C) oven drying process. This method is suitable for the furnace design form where the heat-resistant layer is directly exposed to the burner flame, is suitable for the castable whose surface cannot directly contact the flame, and is suitable for the natural gas furnace equipment with an ignition small burner and a flat flame burner in the combustion system design. Description of the Drawings

[0025] Figure 1 It is a flowchart of a method for baking a small fire in a natural gas furnace.

[0026] Figure 2 It is a schematic diagram of the components of a direct flame burner.

[0027] Figure 3 It is a schematic diagram of the A-A section of the furnace refractory lining.

[0028] Figure 4 It is a schematic diagram of the C-C section of the furnace refractory lining.

[0029] Figure 5 It is a schematic diagram of the baking process curve of 300-100mm castable for a natural gas furnace.

[0030] Among them, 1. Manual butterfly valve; 2. Direct flame burner; 3. Burner control box assembly; 4. Orifice valve; 5. Quick-opening solenoid valve; 6. Slow-opening solenoid valve; 7. Proportional valve; 8. Manual proportional regulating valve; 9. Quick-opening solenoid valve; 10. Electric butterfly valve; 11. SUV flame detector; 12. Standard aluminosilicate fiber backing board; 13. 23-grade mullite brick; 14. 45% Al2O3 lightweight insulation castable; 15. 60% Al2O3 low-cement castable; 16. Microcrystalline fiber module; 17. Alumina fiber crystal shield versatile module. Specific embodiments

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention.

[0032] Such as Figure 2As shown in the figure, the existing natural gas furnace combustion system consists of two different types of burners, namely the straight flame burner system and the flat flame burner system. Among them, a total of 16 burner systems are set on the furnace top, 6 straight flame burner systems with a power of 250 kW are set on each side, and 4 flat flame burner systems with a power of 230 kW are set in the middle. The straight flame burner system and the flat flame burner system are equipped with ignition electrodes and SUV flame detectors. The straight flame burner system consists of a manual butterfly valve 1, a straight flame burner 2, a burner control box assembly 3, an orifice valve 4, a quick-opening solenoid valve 5, a slow-opening solenoid valve 6, a proportional valve 7, a manual proportional regulating valve 8, a quick-opening solenoid valve 9, an electric butterfly valve 10, and an SUV flame detector 11. The flat flame burner system has the same structure as the straight flame burner system. The straight flame burner system is a super-high-speed burner. The flame length of the straight flame burner is 380 mm, and the maximum outlet speed of the burner flame can reach 180 m / s. An ignition small burner is installed on the straight flame burner system and used for ignition detection. The purpose of installing the ignition small burner is: during ignition, only the small fire solenoid valve is opened, and ignition is carried out under a small power state. After successful ignition, the large fire gas solenoid valve is opened to achieve the pulse control of large and small fires. The ignition principle of the flat flame burner system is the same as that of the straight flame burner system. The flat flame burner has a flat flame, a high radiation temperature, no gas flow scouring during combustion, and a uniform flame temperature distribution.

[0033] The straight flame burner system of the natural gas furnace combustion system is located directly above the castable in the lower part of the furnace side wall. As Figure 3 and Figure 4 shown, a furnace chamber built with a variety of castables (refractory materials), which is composed of a composite of a variety of castables. The refractory materials for the furnace door, the upper part of the furnace wall, and the furnace top are in the form of fiber modules. The lower part of the furnace wall, the furnace bottom, the furnace door columns, the upper crossbeam, and the smoke exhaust duct adopt a composite masonry form of refractory fiber boards, lightweight mullite bricks, high-temperature castables, and low-cement castables. The smoke exhaust duct is an arch roof structure. Castables are built on both sides of the lower part of the furnace wall, and the inclined plane forms a 20° angle with the furnace wall. The furnace refractory materials consist of a standard back lining board of aluminosilicate fiber 12, 23-grade mullite bricks 13, 45% Al2O3 lightweight insulation castable 14, 60% Al2O3 low-cement castable 15, microcrystalline fiber modules 16, and alumina fiber crystal shield variable modules 17.

[0034] Based on the natural gas furnace combustion system and the furnace chamber, the present invention provides a method for igniting a small fire and baking the natural gas furnace. As Figure 1 shown, a method for igniting a small fire and baking the natural gas furnace includes the following steps:

[0035] S1, close and press the furnace door tightly. Check the following pressure parameters: the intake pressure of the natural gas main pipeline, the pressure after decompression of the natural gas main pipeline of the large burner, the pressure after decompression of the natural gas main pipeline of the ignition small burner, the set values of each pressure switch, the air pressure of the fan, and the air pressure of the ignition small fan.

[0036] Among them, the inlet pressure of the natural gas main pipeline is 25 - 30 kPa, the pressure of the natural gas main pipeline of the large burner after pressure reduction is about 10 kPa, and the pressure of the natural gas main pipeline of the ignition small burner after pressure reduction is about 6 kPa; the set value of the minimum pressure switch of the natural gas main pipeline of the large burner is 30 mbar, and the set value of the maximum pressure switch is 142 mbar; the set value of the minimum pressure switch of the natural gas main pipeline of the ignition small burner is 30 mbar, and the set value of the maximum pressure switch is 120 mbar; the air pressure of the fan is 3 - 5 kPa, and the air pressure of the ignition small fan is not less than 8 kPa.

[0037] S2. Check and calibrate the air pressure and gas pressure of all burners (including the ignition small burner) in advance to ensure that all burners can be ignited normally.

[0038] Among them, the gas pressure and air pressure of the ignition small burner in the direct flame burner system are adjusted and calibrated through the manual proportional regulating valve 8. The operation steps for adjusting and calibrating the gas pressure and air pressure of the ignition small burner in the flat flame burner system are the same. The air pressure of the ignition small burner in the direct flame burner system is 40 - 50 mbar, and the gas pressure is about 25 mbar. The air pressure of the ignition small burner in the flat flame burner system is 35 - 40 mbar, and the gas pressure is about 30 mbar.

[0039] Turn the slow - opening solenoid valve 6 (the opening speed of the slow - opening solenoid valve is adjustable) to the second grid scale, and turn the manual proportional regulating valve 8 of the same gas pipeline to the maximum to complete the calibration of the gas pressure of the direct flame large burner. The operation steps for calibrating the gas pressure of the flat flame large burner are the same. Turn the electric butterfly valve 10 to the fourth grid scale to complete the calibration of the air pressure of the direct flame large burner. The operation steps for calibrating the air pressure of the flat flame large burner are the same. The electric butterfly valve 10 of the air pipeline of the direct flame large burner and the proportional valve 7 of the gas pipeline are connected through a pressure - guiding pipe. During ignition, after the electric butterfly valve 10 of the air pipeline is opened, the proportional valve 7 of the gas pipeline opens accordingly. The operation steps for opening the proportional valve of the flat flame large burner are the same.

[0040] S3. Set the valve opening in the HMI interface.

[0041] The opening of the furnace pressure valve is 90% (the purpose is to maintain good air flow in the furnace during the furnace drying process to facilitate the timely discharge of water vapor), the opening of the air pipeline pressure - relief valve is 0%, and the opening of all air valves in the flat flame burner system and the direct flame burner system is 100%.

[0042] S4. Set the fan control to manual mode in the fan control interface of the HMI interface, set the fan speed to 35 Hz, and start the large fan.

[0043] S5. Start the ignition fan control and purge control.

[0044] Start the manual ignition fan control on the ignition control interface of the HMI interface to start the ignition small fan. Start the manual purge control of the ignition controller part of the ignition controller and start the purge. After purging for one hour, turn off the purge.

[0045] The purpose of purging is to clean the flue gas system and various pipelines and eliminate all blockages.

[0046] S6, after the purge is completed, set the opening of the air pipeline pressure relief valve to the automatic mode. Set the fan control to the manual mode on the fan control interface of the HMI interface, and set the fan speed to 25 Hz; start the manual ignition control of the ignition controller on the ignition control interface of the HMI interface and press the button of the total natural gas intake valve of the power distribution cabinet.

[0047] S7, according to Figure 5 the oven drying curve to set the oven drying procedure.

[0048] After the castable is poured and cured for 5 - 7 days, start the oven drying. The temperature control thermocouples are buried in the holes pre-set in the fiber module on the right side wall, a total of three, all located at the representative positions where the castable is heated in the three temperature control zones.

[0049] Set the oven drying procedure according to Figure 5 the oven drying curve on the Eurotherm 3504 temperature controller or the process curve setting interface of the HMI interface.

[0050] The oven drying curve of the 300 - 400 mm castable is as follows:

[0051] Among them, in the first stage, heat up from room temperature to 150 °C at a heating rate of 10 °C / h and then hold for 72 hours; in the second stage, heat up from 150 °C to 250 °C at a heating rate of 10 °C / h and then hold for 72 hours; in the third stage, heat up from 250 °C to 400 °C at a heating rate of 20 °C / h and then hold for 60 hours; in the fourth stage, heat up from 400 °C to 550 °C at a heating rate of 20 °C / h and then hold for 60 hours; after completion, cool down naturally at a rate of 20 °C / h.

[0052] S8, below 300 °C, use the direct flame burner ignition small burner and the flat flame burner ignition small burner to light small fires to heat the furnace chamber, and from 300 °C to 550 °C, use the direct flame burner ignition small burner to light small fires and the flat flame burner large burner to light large fires to heat the furnace chamber until the oven drying procedure is completed.

[0053] The 45% Al2O3 lightweight heat-insulating castable 14 and the 60% Al2O3 low-cement castable 15 cannot be directly impacted by the flame. The direct-flame burner system of the natural gas furnace combustion system is located directly above the castable at the lower part of the furnace side wall, and the flat-flame burner system is located in the middle part of the furnace. Start the ignition of the small ignition burner. Below 300°C, use the direct-flame burner 2 to ignite the small ignition burner and the flat-flame burner small ignition burner to bake the furnace with small flames. When the direct-flame burner small ignition burner and the flat-flame burner small ignition burner are all turned on, the maximum temperature that the furnace can reach is 300°C. Therefore, when the temperature controller and the furnace temperature reach 300°C, about 171.5 h after the furnace drying starts, perform the following operations:

[0054] Manually close the butterfly valve 1 of the air pipeline of the direct-flame burner large burner. Start heating on the main interface of the system working condition in the HMI interface, and start the ignition of the flat-flame burner. Start using the direct-flame burner 2 small burner to ignite with a small flame and the flat-flame burner large burner to ignite with a large flame to heat the furnace to bake the furnace until the furnace drying procedure is completed. The flame of the flat-flame burner large burner is in a slow scattering shape, and it will not cause flame impact on the castable during ignition heating.

[0055] During the entire furnace drying process, a special person records the actual temperature of the furnace in three temperature zones every half hour until the recorded actual temperature of the furnace drops to 100 degrees Celsius.

[0056] S9, after the furnace drying is completed, keep the furnace door closed and tightened, and set the valve opening.

[0057] Keep the furnace door closed and tightened, set the opening of the furnace pressure valve to 0%; keep the fan and the small ignition fan in the operating state; set the opening of the air pipeline pressure relief valve to 100%; set the opening of the heat exchanger protection valve to 100%. The purpose is to allow the furnace to cool naturally in a closed state to avoid damage to the castable caused by rapid cooling and the entry of cold air.

Claims

1. A method for baking a natural gas furnace with a small flame, characterized in that, It includes the following steps: S1. Close and press the furnace door, and check the following pressure parameters: the inlet pressure of the natural gas main pipeline, the pressure after decompression of the natural gas main pipeline for the large burner, the pressure after decompression of the natural gas main pipeline for the ignition small burner, the set values of each pressure switch, the air pressure of the fan, and the air pressure of the ignition small fan; S2. Check and calibrate the air pressure and gas pressure of all burners in advance to ensure that all burners can be ignited normally; S3. Set the valve opening degree on the HMI interface; S4. Set the fan control to manual mode, set the fan speed to 35 Hz, and start the large fan; S5. Start the ignition fan control and purge control; S6. After the purge is completed, set the opening degree of the air pipeline pressure relief valve to automatic mode; set the fan control to manual mode, and set the fan speed to 25 Hz; start the manual ignition control of the ignition controller, and press the button of the total natural gas inlet valve of the power distribution cabinet; S7. Set the furnace drying program according to the furnace drying curve; S8. Below 300 °C, use the direct flame burner ignition small burner and the flat flame burner ignition small burner to ignite small fires to heat the furnace chamber. From 300 °C to 550 °C, use the direct flame burner ignition small burner to ignite small fires and the flat flame burner large burner to ignite large fires to heat the furnace chamber until the furnace drying program is completed; S9. After the furnace drying is completed, keep the furnace door closed and pressed, and set the valve opening degree.

2. The method for baking a furnace with a small flame of a natural gas furnace according to claim 1, characterized in that, In S1, the inlet pressure of the natural gas main pipeline is 25 - 30 kPa, the pressure after decompression of the natural gas main pipeline for the large burner is 10 kPa, and the pressure after decompression of the natural gas main pipeline for the ignition small burner is 6 kPa; the minimum pressure switch set value of the natural gas main pipeline for the large burner is 30 mbar, and the maximum pressure switch set value is 142 mbar; the minimum pressure switch set value of the natural gas main pipeline for the ignition small burner is 30 mbar, and the maximum pressure switch set value is 120 mbar; the air pressure of the fan is 3 - 5 kPa, and the air pressure of the ignition small fan is not less than 8 kPa.

3. The method for baking the furnace with small fire of the natural gas furnace according to claim 1, characterized in that, In S2, the air pressure of the ignition small burner in the direct flame burner system is 40 - 50 mbar, and the gas pressure is 25 mbar. The air pressure of the ignition small burner in the flat flame burner system is 35 - 40 mbar, and the gas pressure is 30 mbar.

4. The method for baking the furnace with small fire of the natural gas furnace according to claim 1, characterized in that, In S3, the opening degree of the furnace chamber pressure valve is 90%, the opening degree of the air pipeline pressure relief valve is 0%, and the opening degrees of all air valves in the flat flame burner system and the direct flame burner system are 100%.

5. The method for baking a natural gas furnace with a small flame according to claim 1, characterized in that, In S7, the furnace drying curve is specifically as follows: in the first stage, heat up from room temperature to 150 °C at a heating rate of 10 °C / h and then keep it warm for 72 hours; in the second stage, heat up from 150 °C to 250 °C at a heating rate of 10 °C / h and then keep it warm for 72 hours; in the third stage, heat up from 250 °C to 400 °C at a heating rate of 20 °C / h and then keep it warm for 60 hours; in the fourth stage, heat up from 400 °C to 550 °C at a heating rate of 20 °C / h and then keep it warm for 60 hours; after completion, cool down naturally at a rate of 20 °C / h.

6. The method for baking the furnace with small fire of the natural gas furnace according to claim 1, characterized in that In S8, during the whole furnace drying process, a special person records the actual temperature of the furnace chamber in three temperature zones every half hour until the recorded actual temperature of the furnace chamber drops to 100 degrees Celsius.

7. The method for baking the furnace with small fire of the natural gas furnace according to claim 1, characterized in that, The specific steps of S9 are as follows: Keep the furnace door closed and pressed, and set the opening of the furnace pressure valve to 0%; Keep the blower and the ignition blower in the running state; Set the opening of the air pipeline pressure relief valve to 100%; Set the opening of the heat exchanger protection valve to 100%.

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