A flue gas denitration and dust removal system and process for an aluminum alloy smelting furnace holding furnace

Abstract

The application discloses a flue gas denitration and dust removal system and process for an aluminum alloy smelting furnace holding furnace, comprising an aluminum smelting furnace and an aluminum holding furnace, wherein the aluminum smelting furnace hearth flue of the aluminum smelting furnace and the aluminum holding furnace hearth flue of the aluminum holding furnace are both communicated with a flue gas heat exchanger first inlet flue, the flue gas heat exchanger first inlet flue is communicated with a flue gas heat exchanger, and through flue gas cooling and temperature adjustment, flue gas preheating and flue gas heating, the system can adapt to all flue gas working conditions in the whole aluminum smelting and holding furnace production process, that is, the denitration and dust removal system can operate at high and low temperature of flue gas, the generation of ammonium bisulfate during denitration can be inhibited when the system operates at high temperature of flue gas, and the generated ammonium bisulfate during operation at low temperature of flue gas can also be decomposed, the phenomenon of catalyst adhesion to ammonium bisulfate can be avoided compared with traditional flue gas denitration and dust removal technology for an aluminum smelting and holding furnace, the service life of the catalyst and the flue gas heat exchanger is prolonged, and the system operation cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of flue gas denitrification and dust removal technology, specifically to a flue gas denitrification and dust removal system and process for an aluminum alloy smelting furnace and its holding furnace. Background Technology

[0002] With the increasing domestic demand for aluminum alloys, aluminum alloy production capacity is also continuously rising. Aluminum melting and casting is a crucial step in the entire aluminum alloy processing, and the aluminum melting and casting furnace is a key piece of equipment. With the increasing availability of natural gas in China, aluminum melting and casting furnaces primarily use natural gas as fuel. The pollutants in the flue gas produced during production are mainly particulate matter and NO. x With increasingly stringent national and local pollutant emission standards, the minimum emission limit for particulate matter from aluminum melting furnaces has been reduced to ≤10 mg / Nm³; NO x It is a more harmful pollutant than particulate matter, and its emission limit is already required to be ≤50mg / Nm³. Therefore, particulate matter and NO from aluminum melting furnaces... x The treatment of [the pollutants] is the focus of environmental protection work in the aluminum processing industry now and in the future.

[0003] The production of aluminum melting and holding furnaces is cyclical, with significant fluctuations in flue gas volume, temperature, and pollutant content throughout the production cycle. This fluctuation is particularly pronounced when the number of furnaces in a combination is small. Flue gas temperature ranges from 130 to 450℃; dust content is generally 300-400 mg / Nm³, with a maximum of 1200 mg / Nm³, and fine dust particles ranging from 1 to 50 μm in size; NO in the flue gas... x The NO content is basically synchronized with temperature changes; when the flue gas temperature is high, NO... x The content is high, reaching up to 500 mg / Nm³ or more, while it is only 100~150 mg / Nm³ when the flue gas temperature is low. The characteristics of the flue gas from aluminum melting furnaces have a significant impact on the methods and processes used for flue gas denitrification and dust removal, especially the flue gas temperature.

[0004] Among the various denitrification methods currently available, the ammonia-based SCR (Selective Catalytic Reduction) method, although requiring a relatively high investment, is technologically mature and has low operating costs. It works as long as the nitrogen content is within acceptable limits. x The flue gas can meet the conditions for ammonia-based SCR denitrification, or some auxiliary means can be adopted to achieve the conditions for ammonia-based SCR denitrification. Ammonia-based SCR is the preferred flue gas denitrification method, and it is also suitable for aluminum smelting furnace flue gas. However, even when natural gas is used as fuel, aluminum smelting furnace flue gas still contains SO2. Therefore, when ammonia-based SCR denitrification is applied to aluminum smelting furnace flue gas denitrification, it is also necessary to consider how to minimize the impact of ammonium bisulfate on the flue gas denitrification and dust removal system to ensure the stable and reliable operation of the system.

[0005] Baghouse dust collectors are a mature and reliable dust removal technology. As a purification device that ensures ultra-low emissions of particulate matter in the flue gas of aluminum smelting furnaces, they have more obvious advantages than other ultra-low emission dust collectors. They are well adapted to flue gas fluctuations, can effectively remove fine particulate matter in the flue gas, and do not cause secondary pollution.

[0006] Traditional aluminum smelting furnace flue gas denitrification and dust removal technologies focus on the low-temperature conditions of the flue gas. Using low-temperature denitrification technology, the flue gas is first cooled, followed by sequential baghouse dust collection and ammonia-based SCR denitrification. The baghouse dust collector uses a filter capable of withstanding temperatures ≤250℃. The flue gas temperature entering the denitrification reactor is low, with a maximum of only 250℃. Particulate ammonium bisulfate is continuously generated within the reactor. This ammonium bisulfate adheres to the catalyst, making soot removal difficult. Furthermore, the ammonium bisulfate particles blown off the catalyst and emitted with the flue gas easily lead to excessive particulate matter emissions. Simultaneously, long-term adhesion of ammonium bisulfate to the denitrification catalyst can cause catalyst poisoning, leading to frequent catalyst regeneration, high system energy consumption, shortened catalyst lifespan, and high system operating costs. Moreover, frequent catalyst regeneration often results in excessive levels of ammonia and acidic gases, placing significant environmental pressure on aluminum processing enterprises. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the existing defects and provide a flue gas denitrification and dust removal system and process for aluminum alloy smelting furnace holding furnace. Compared with the traditional aluminum smelting furnace flue gas denitrification and dust removal technology, it can avoid the phenomenon of ammonium bisulfate adhering to the catalyst, extend the service life of the catalyst and flue gas heat exchanger, reduce the system operating cost, and effectively solve the problems in the background technology.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a flue gas denitrification and dust removal system for an aluminum alloy smelting furnace and an aluminum holding furnace, comprising an aluminum smelting furnace and an aluminum holding furnace, wherein the flue gas duct of the aluminum smelting furnace and the flue gas duct of the aluminum holding furnace are both connected to the first inlet flue gas duct of a flue gas heat exchanger, the first inlet flue gas duct of the flue gas heat exchanger is connected to the flue gas heat exchanger, the first outlet flue gas duct of the flue gas heat exchanger is connected to a flue gas heating furnace, the flue gas heating furnace is connected to a flue gas ammonia mixer through the flue gas heating furnace outlet flue gas duct, the flue gas heating furnace outlet flue gas duct is also connected to an ammonia conveying assembly, the flue gas ammonia mixer is connected to an SCR denitrification reactor through the inlet flue gas duct of the SCR denitrification reactor, the SCR denitrification reactor is connected to the flue gas heat exchanger through the second inlet flue gas duct of the flue gas heat exchanger, and the flue gas heat exchanger is connected to a metal filter bag dust collector through the second outlet flue gas duct of the flue gas heat exchanger.

[0009] As a preferred embodiment of the present invention, a flue gas temperature regulating valve and a flue gas temperature sensor at the first inlet of the flue gas heat exchanger are respectively provided on the first inlet flue gas duct of the flue gas heat exchanger. Both the flue gas temperature regulating valve and the flue gas temperature sensor at the first inlet of the flue gas heat exchanger are electrically connected to the control system.

[0010] As a preferred embodiment of the present invention, a flue gas heat exchanger soot blower is provided inside the flue gas heat exchanger, the flue gas heat exchanger soot blower is connected to the flue gas heat exchanger soot blower compressed air pipe, and a flue gas heat exchanger soot blower compressed air valve is provided on the flue gas heat exchanger soot blower compressed air pipe.

[0011] As a preferred embodiment of the present invention, the flue gas heating furnace is connected to one end of the flue gas heating furnace burner, and the other end of the flue gas heating furnace burner is connected to the combustion air pipe. The combustion air pipe is equipped with a combustion air flow regulating valve, and a combustion air fan is provided at the end of the combustion air pipe.

[0012] As a preferred embodiment of the present invention, the flue gas heating furnace burner is connected to a gas pipe, and a gas flow regulating valve is provided on the gas pipe.

[0013] As a preferred embodiment of the present invention, the ammonia conveying assembly includes an ammonia water storage tank, the outlet of which is connected to an ammonia water conveying pipe via an ammonia water conveying pump, the ammonia water conveying pipe being connected to the flue gas heating furnace outlet flue via a dual-fluid spray gun, and an ammonia water flow regulating valve being provided on the ammonia water conveying pipe, the dual-fluid spray gun being connected to a dual-fluid spray gun compressed air pipe.

[0014] As a preferred embodiment of the present invention, the SCR denitrification reactor is provided with a plurality of SCR denitrification reactor soot blowers, the SCR denitrification reactor soot blowers are connected to the SCR denitrification reactor soot blower compressed air pipes, and the SCR denitrification reactor soot blower compressed air valves are provided on the SCR denitrification reactor soot blower compressed air pipes.

[0015] As a preferred embodiment of the present invention, the metal filter bag dust collector is provided with a dust collector cleaner, which is connected to the dust collector cleaning compressed air pipe, and a dust collector unloading valve is provided on the lower side of the metal filter bag dust collector.

[0016] As a preferred embodiment of the present invention, the metal filter bag dust collector is connected to the fan through the dust collector outlet flue, and the fan is connected to the exhaust stack through the exhaust stack inlet flue.

[0017] This invention also provides a flue gas denitrification and dust removal process for an aluminum alloy smelting furnace holding furnace, which adopts the above-mentioned flue gas denitrification and dust removal system for an aluminum alloy smelting furnace holding furnace, and includes the following steps: S1) When the temperature of the flue gas discharged from the aluminum melting furnace exceeds a certain set value, the flue gas is first cooled and its temperature adjusted to be within the temperature limit of the denitrification and dust removal system and the temperature range where the denitrification catalyst has high activity. Then, the flue gas flows through the flue gas heat exchanger and the flue gas heater (no heating is required at this time) before entering the outlet flue of the flue gas heater. Atomized ammonia water is injected into the outlet flue of the flue gas heater. The ammonia water decomposes at high temperature and mixes with the flue gas. The mixture of flue gas and ammonia then enters the ammonia-flue gas mixer. In the ammonia-flue gas mixer, strong turbulence occurs, uniformly mixing the ammonia in the flue gas, which is beneficial for improving denitrification efficiency and reducing ammonia escape. The mixture of flue gas and ammonia then enters the SCR denitrification reactor. In the denitrification reactor, the NO in the flue gas... x The gas reacts with ammonia in the presence of a catalyst to produce harmless nitrogen and water, thus achieving denitrification. After denitrification, the flue gas passes through a flue gas heat exchanger and then enters a metal bag filter dust collector, where particulate matter is removed. At this point, the particulate matter and NO in the flue gas are... x The concentrations were all below the emission limits and met the emission requirements. The qualified flue gas was then discharged into the atmosphere through the fan and exhaust stack.

[0018] S2) When the temperature of the flue gas discharged from the aluminum melting furnace is lower than a certain set value but higher than a certain set value, the flue gas does not need to be cooled or adjusted, nor does it need to be heated in the flue gas heating furnace. The flue gas purification process is the same as S1).

[0019] S3) When the temperature of the flue gas discharged from the aluminum melting furnace is lower than a certain set value, the flue gas does not need to be cooled and adjusted, but it needs to be heated in the flue gas heater. The flue gas discharged from the aluminum melting furnace first enters the flue gas heat exchanger, where the high-temperature flue gas after denitrification is used to preheat the aluminum melting furnace flue gas, aiming to save on the fuel consumption of the flue gas heater. After being preheated in the flue gas heat exchanger, the aluminum melting furnace flue gas enters the flue gas heater, where the fuel gas combustion is used to heat the flue gas to a temperature slightly higher than the minimum activity temperature requirement of the denitrification catalyst, ensuring that the denitrification effect is achieved while saving fuel consumption and reducing system operating costs. The subsequent process is the same as S1).

[0020] Compared with the prior art, the beneficial effects of the present invention are: the use of metal filter bag dust collectors for flue gas dust removal ensures that the particulate matter emission concentration in the flue gas is lower than the emission limit, and its temperature resistance limit can adapt to all flue gas operating conditions in the system. The selection of this type of dust collector, which is different from conventional filter bag types, is for two reasons: first, to shorten the flue gas denitrification and dust removal process and reduce investment and operating costs; second, this type of filter bag dust collector can even operate safely at 500℃, so that the temperature of the flue gas entering the dust collector is almost the same as the temperature of the flue gas in the denitrification reactor, which can effectively inhibit the filter bags from being blocked by ammonium bisulfate.

[0021] By employing flue gas cooling and temperature regulation, flue gas preheating, and flue gas heating, the system can adapt to all flue gas conditions throughout the entire aluminum smelting furnace production process. This means the denitrification and dust removal system can operate at both high and low flue gas temperatures. When the flue gas temperature is too low and heating is required, it only needs to be heated to slightly above the minimum temperature necessary for denitrification, ensuring effective denitrification while saving operating costs. During high-temperature operation, the system can suppress the formation of ammonium bisulfate during denitrification and decompose ammonium bisulfate generated during low-temperature operation. Compared to traditional aluminum smelting furnace flue gas denitrification and dust removal technologies, this avoids the phenomenon of ammonium bisulfate adhering to the catalyst, extending the service life of the catalyst and flue gas heat exchanger, and reducing system operating costs. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention.

[0023] In the diagram: 1. Aluminum smelting furnace; 2. Aluminum holding furnace; 3. Aluminum smelting furnace furnace flue valve; 4. Aluminum holding furnace furnace flue valve; 5. Aluminum smelting furnace furnace flue; 6. Aluminum holding furnace furnace flue; 7. First inlet flue of flue gas heat exchanger; 8. Flue gas temperature regulating valve; 9. Flue gas heat exchanger; 10. Flue gas heat exchanger soot blower; 11. Flue gas heat exchanger soot blower compressed air pipe; 12. Flue gas heat exchanger soot blower compressed air valve; 13. First outlet of flue gas heat exchanger. 14 Flue gas heater, 15 Combustion fan, 16 Combustion air pipe, 17 Combustion air flow regulating valve, 18 Flue gas heater burner, 19 Gas pipe, 20 Gas flow regulating valve, 21 Flue gas heater outlet flue, 22 Dual-fluid spray gun, 23 Ammonia storage tank, 24 Dual-fluid spray gun compressed air pipe, 25 Ammonia delivery pump, 26 Ammonia delivery pipe, 27 Ammonia flow regulating valve, 28 Flue gas ammonia mixer, 29 SCR denitrification reactor inlet flue, 30 SCR denitrification reactor, 31 SCR denitrification reactor soot blower, 32 SCR denitrification reactor soot blower compressed air pipe, 33 SCR denitrification reactor soot blower compressed air valve, 34 flue gas heat exchanger second inlet flue, 35 flue gas heat exchanger second outlet flue, 36 metal filter bag dust collector, 37 dust collector cleaner, 38 dust collector cleaning compressed air pipe, 39 dust collector ash discharge valve, 40 dust collector outlet flue, 41 fan, 42 exhaust stack inlet flue, 43 exhaust stack, 44 flue gas heat exchanger first inlet flue gas temperature sensor, 45 flue gas heat exchanger first outlet flue gas temperature sensor, 46 flue gas heater outlet flue gas temperature sensor, 47 SCR denitrification reactor inlet NO x Online monitoring instrument, 48 SCR denitrification reactor inlet flue gas temperature sensor, 49 flue gas pressure sensor, 50 SCR denitrification reactor differential pressure sensor, 51 SCR denitrification reactor outlet flue gas temperature sensor, 52 SCR denitrification reactor outlet NO. xOnline detector, 53 Ammonia escape online detector, 54 Differential pressure sensor for the second inlet and outlet of flue gas heat exchanger, 55 Flue gas temperature sensor for the second outlet of flue gas heat exchanger, 56 Differential pressure sensor for dust collector, 57 Gas flow meter, 58 Ammonia water flow meter, 59 Ammonia water storage tank level gauge. Detailed Implementation

[0024] 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.

[0025] Please see Figure 1 The present invention provides a technical solution: a flue gas denitrification and dust removal system for an aluminum alloy smelting furnace and a holding furnace, comprising an aluminum smelting furnace 1 and an aluminum holding furnace 2. The aluminum smelting furnace 1 is used to melt and remelt aluminum ingots, etc., and the furnace chamber discharges flue gas generated by fuel combustion during the production process. The aluminum holding furnace 2 performs static, refining, and heat preservation of the aluminum liquid, etc., and the furnace chamber discharges flue gas generated by fuel combustion during the production process.

[0026] The aluminum smelting furnace flue 5 of the aluminum smelting furnace 1 and the aluminum holding furnace flue 6 of the aluminum holding furnace 2 are both connected to the first inlet flue 7 of the flue gas heat exchanger. The first inlet flue 7 of the flue gas heat exchanger is connected to the flue gas heat exchanger 9. The flue gas generated by the aluminum smelting furnace 1 enters the flue gas heat exchanger 9 through the aluminum smelting furnace flue 5 and the first inlet flue 7 of the flue gas heat exchanger. The flue gas generated by the aluminum holding furnace 2 enters the flue gas heat exchanger 9 through the aluminum holding furnace flue 6 and the first inlet flue 7 of the flue gas heat exchanger. The flue gas heat exchanger 9 preheats the flue gas from the aluminum smelting furnace under low temperature conditions (temperature between 130°C and 180°C), reducing the gas consumption of the flue gas heating furnace and ensuring that the system operates energy-savingly while achieving the denitrification effect.

[0027] A furnace flue valve 3 is installed on the furnace flue 5 of the aluminum smelting furnace to open and close the furnace flue gas of the aluminum smelting furnace; a furnace flue valve 4 is installed on the furnace flue 6 of the aluminum heat preservation furnace to open and close the furnace flue gas of the aluminum heat preservation furnace.

[0028] The first outlet flue duct 13 of the flue gas heat exchanger 9 is connected to the flue gas heating furnace 14. When the flue gas temperature from the aluminum melting furnace is low and does not meet the minimum activity temperature (180°C) requirement of the ammonia-based SCR denitrification catalyst, the flue gas is heated by the flue gas heating furnace 14 to make the flue gas temperature higher than the minimum activity temperature (180°C) of the ammonia-based SCR denitrification catalyst.

[0029] A flue gas temperature sensor 45 is installed on the first outlet flue duct 13 of the flue gas heat exchanger to measure the flue gas temperature at the first outlet of the flue gas heat exchanger and control the operation of the gas supply system and combustion air system of the flue gas heater.

[0030] The flue gas heater 14 is connected to the ammonia-flue gas mixer 28 through the flue gas heater outlet flue 21. The mixed gas of flue gas and ammonia undergoes strong turbulent flow in the ammonia-flue gas mixer 28, which makes the ammonia and flue gas fully mixed and distributes the ammonia evenly in the flue gas, which is beneficial to improving the denitrification efficiency and reducing ammonia escape.

[0031] A flue gas temperature sensor 46 is installed on the flue gas outlet duct 21 of the flue gas heater. The flue gas temperature sensor 46 is used to measure the flue gas temperature at the outlet of the flue gas heater. When the flue gas temperature at the outlet of the flue gas heater exceeds a certain set value (the reason for the excessively high temperature may be that the gas heating system is out of control, such as exceeding 400°C), an alarm is triggered and the denitrification and dust removal system is shut down.

[0032] The ammonia-fume mixer 28 is connected to the SCR denitrification reactor 30 via the inlet flue 29 of the SCR denitrification reactor. The SCR denitrification reactor 30 is the core equipment for ammonia-based SCR denitrification, and it is responsible for removing NO from the flue gas of the aluminum melting furnace. x Under the action of a catalyst, NH3 reacts with NH3 to produce harmless N2 and H2O.

[0033] An SCR denitrification reactor inlet flue gas temperature sensor 48 is installed on the inlet flue duct 29 of the SCR denitrification reactor. This sensor is used to measure the inlet flue gas temperature of the SCR denitrification reactor and to control the opening of the gas flow regulating valve 20 and to shut down the gas system and combustion air system.

[0034] A flue pressure sensor 49 is also installed on the inlet flue 29 of the SCR denitrification reactor to measure the flue pressure (negative pressure). When the flue pressure exceeds a certain set value, an alarm is triggered through the external control system and alarm system.

[0035] The SCR denitrification reactor 30 is equipped with an SCR denitrification reactor differential pressure sensor 50, which measures the differential pressure of the catalyst layer in the SCR denitrification reactor. When the differential pressure exceeds a certain set value, an alarm is triggered through the external control system and alarm system.

[0036] The SCR denitrification reactor 30 is connected to the flue gas heat exchanger 9 via the second inlet flue duct 34. The flue gas heat exchanger 9 is connected to the metal bag filter dust collector 36 via the second outlet flue duct 35. The gas generated by the SCR denitrification reactor 30 enters the flue gas heat exchanger 9 through the second inlet flue duct 34 and is then sent to the metal bag filter dust collector 36 for dust removal from the second outlet flue duct 35, ensuring that the particulate matter emission concentration in the flue gas is below the emission limit. The temperature resistance limit of the metal bag filter dust collector 36 can adapt to all flue gas operating conditions in the system. This type of dust collector, which is different from the conventional bag filter type, is chosen for two reasons: first, to shorten the flue gas denitrification and dust removal process (eliminating the need to connect a flue gas cooler in series before the bag filter), reducing investment and operating costs; second, this type of bag filter dust collector can even operate safely at 500℃, making the temperature of the flue gas entering the dust collector almost the same as the temperature of the flue gas in the denitrification reactor, which can effectively inhibit the filter bags from being blocked by ammonium bisulfate.

[0037] A flue gas temperature sensor 51 is installed on the second inlet flue duct 34 of the flue gas heat exchanger to measure the flue gas temperature at the outlet of the SCR denitrification reactor.

[0038] The second inlet flue duct 34 of the flue gas heat exchanger is also equipped with an SCR denitrification reactor outlet NO. x Online detector 52 and online ammonia slip detector 53, NO at the outlet of SCR denitrification reactor x Online detector 52 is used to measure NO at the outlet of SCR denitrification reactor. x The concentration, in conjunction with the online ammonia slip detector, controls the opening of the ammonia flow regulating valve, thereby controlling the ammonia flow rate into the system. This ensures denitrification efficiency while keeping the ammonia slip concentration below a certain limit. (SCR denitrification reactor outlet NO...) x An alarm is triggered when the concentration exceeds a certain set value. The ammonia slip online detector 53 measures the ammonia slip concentration in the SCR denitrification reactor and the NO concentration at the SCR denitrification reactor outlet. x The online monitoring instrument, in conjunction with the ammonia water flow regulating valve, controls the opening degree of the ammonia water flow into the system, thereby controlling the ammonia water flow rate and ensuring denitrification efficiency while keeping the ammonia slip concentration below a certain limit. An alarm is triggered when the ammonia slip concentration exceeds a certain set value.

[0039] A second inlet and outlet differential pressure sensor 54 is installed between the second inlet flue duct 34 and the second outlet flue duct 35 of the flue gas heat exchanger to measure the pressure difference between the second inlet and outlet of the flue gas heat exchanger. An alarm is triggered when the pressure difference exceeds a certain set value.

[0040] A flue gas temperature sensor 55 is installed on the second outlet flue duct 35 of the flue gas heat exchanger to measure the flue gas temperature at the second outlet of the flue gas heat exchanger.

[0041] The SCR denitrification reactor inlet NO is installed on flue gas heater outlet flue 21. x Online detector 47 is used to measure NO at the inlet of the SCR denitrification reactor. x concentration.

[0042] In a preferred embodiment, a flue gas temperature regulating valve 8 and a flue gas temperature sensor 44 at the first inlet of the flue gas heat exchanger are respectively installed on the first inlet flue gas duct 7 of the flue gas heat exchanger. Both the flue gas temperature regulating valve 8 and the flue gas temperature sensor 44 at the first inlet of the flue gas heat exchanger are electrically connected to the control system.

[0043] The flue gas temperature regulating valve 8 automatically opens when the flue gas temperature 44 at the first inlet of the flue gas heat exchanger exceeds a certain set temperature value (e.g., 380℃), mixing in a small amount of outside cold air to cool the flue gas. When the flue gas temperature 44 at the first inlet of the flue gas heat exchanger falls below a certain set temperature value (e.g., 340℃), the flue gas temperature regulating valve 8 automatically closes. Its main functions are: firstly, to protect the equipment from damage caused by the flue gas temperature exceeding its temperature resistance limit; for example, if the flue gas temperature entering the ammonia-based SCR denitrification reactor exceeds 420℃, it will burn the catalyst inside. Secondly, for flue gas from high-temperature conditions (e.g., flue gas temperature exceeding 380℃) in the aluminum smelting furnace, this valve regulates the flue gas temperature at the first inlet of the flue gas heat exchanger to stabilize it within a certain high-temperature range. This ensures that the flue gas temperature entering the ammonia-based SCR denitrification reactor is within the optimal activity temperature range of the SCR denitrification catalyst (320~360℃), which is beneficial for improving denitrification efficiency and reducing NO. x The emission concentration should be controlled, while also suppressing the formation of ammonium bisulfate during ammonia denitrification, which could lead to equipment blockage (such as blockage of the catalyst, flue gas heat exchanger, and dust collector in the ammonia SCR denitrification reactor) and catalyst failure.

[0044] The flue gas temperature sensor 44 at the first inlet of the flue gas heat exchanger is used to measure the flue gas temperature at the first inlet of the flue gas heat exchanger and control the opening and closing of the flue gas temperature regulating valve. When the flue gas temperature at the first inlet of the flue gas heat exchanger exceeds a certain set value (e.g., exceeding 400℃), an alarm is triggered, and the denitrification and dust removal system is shut down.

[0045] In a preferred embodiment, the flue gas heat exchanger 9 is equipped with a flue gas heat exchanger soot blower 10, which is used to blow away the accumulated ash on the surface of the heat exchange element in the second flue gas channel of the flue gas heat exchanger, to prevent dust and ammonium bisulfate, a product of ammonia denitrification, from clogging the flue gas heat exchanger and to ensure stable operation of the system.

[0046] In a further preferred embodiment, the flue gas heat exchanger sootblower 10 is connected to the flue gas heat exchanger sootblower compressed air pipe 11, and the flue gas heat exchanger sootblower compressed air pipe 11 is provided with a flue gas heat exchanger sootblower compressed air valve 12. The flue gas heat exchanger sootblower compressed air pipe 11 is opened and closed by the flue gas heat exchanger sootblower compressed air valve 12, and the pipe is automatically opened at regular intervals to blow away the ash accumulated on the surface of the heat exchange element of the second flue gas channel of the flue gas heat exchanger.

[0047] In a preferred embodiment, the flue gas heater 14 is connected to one end of the flue gas heater burner 18, and the other end of the flue gas heater burner 18 is connected to the combustion air pipe 16. A combustion air fan 15 is installed at the end of the combustion air pipe 16 to provide combustion air to the flue gas heater burner. The system automatically starts when the flue gas temperature at the first outlet of the flue gas heat exchanger (flue gas temperature sensor 45 at the first outlet of the flue gas heat exchanger) is lower than a certain set temperature value (e.g., 190°C) and continues to operate throughout the entire flue gas heating process. It automatically stops when the flue gas temperature at the inlet of the ammonia-based SCR denitrification reactor (flue gas temperature sensor 48 at the inlet of the SCR denitrification reactor) is higher than a certain set value (e.g., 220°C). This ensures that the flue gas temperature entering the ammonia-based SCR denitrification reactor during operation is always higher than the minimum activation temperature (180°C) required by the ammonia-based SCR denitrification catalyst, with a margin of safety, which is beneficial for denitrification.

[0048] Optionally, the combustion air pipe 16 is equipped with a combustion air flow regulating valve 17, which automatically opens and closes with the start and stop of the combustion air blower 15, and adjusts the combustion air flow according to the change in the gas flow supplied to the burner of the flue gas heating furnace during the flue gas heating process.

[0049] In a preferred embodiment, the flue gas heater burner 18 is connected to a gas pipe 19, which is connected to an external gas supply device to supply gas to the flue gas heater burner. A gas flow regulating valve 20 is installed on the gas pipe 19, which automatically opens when the flue gas temperature at the first outlet of the flue gas heat exchanger (flue gas temperature sensor 45 at the first outlet of the flue gas heat exchanger) is lower than a certain temperature set value (e.g., 190°C). During the flue gas heating process, the gas flow is adjusted according to the flue gas temperature at the inlet of the ammonia-based SCR denitrification reactor (flue gas temperature sensor 48 at the inlet of the SCR denitrification reactor) to stabilize the temperature of the heated flue gas and ensure that the flue gas temperature is higher than the minimum activity temperature (180°C) required by the ammonia-based SCR denitrification catalyst. When the inlet flue gas temperature of the ammonia-based SCR denitrification reactor (SCR denitrification reactor inlet flue gas temperature sensor 48) is higher than a certain temperature set value (e.g., 220℃), it will automatically shut down to ensure that the flue gas temperature entering the ammonia-based SCR denitrification reactor during the operation of the denitrification and dust removal system is always higher than the minimum activation temperature requirement (180℃) of the ammonia-based SCR denitrification catalyst, with a margin, which is beneficial to denitrification.

[0050] Optionally, a gas flow meter 57 is installed on the gas pipe 19 to measure the instantaneous and cumulative flow of gas for the flue gas heater, providing a basis for optimizing system operating parameters and energy-saving operation.

[0051] In a preferred embodiment, the flue gas heater outlet flue 21 is also connected to an ammonia conveying assembly. The ammonia conveying assembly includes an ammonia water storage tank 23, which stores ammonia water as a denitrification agent in the ammonia-based SCR process. The outlet of the ammonia water storage tank 23 is connected to an ammonia water conveying pipe 26 via an ammonia water conveying pump 25. The ammonia water conveying pipe 26 is connected to the flue gas heater outlet flue 21 via a dual-fluid spray gun 22. The ammonia water is atomized with compressed air and sprayed into the flue through the dual-fluid spray gun 22 to provide ammonia gas as a denitrification agent for the ammonia-based SCR denitrification process.

[0052] Furthermore, the dual-fluid spray gun 22 is connected to the dual-fluid spray gun compressed air pipe 24 to provide compressed air for the ammonia atomization of the dual-fluid spray gun.

[0053] Furthermore, an ammonia flow regulating valve 27 is installed on the ammonia water delivery pipe 26, which adjusts the flow rate according to the NO outlet of the ammonia-based SCR denitrification reactor. x Adjust the ammonia water flow rate to reduce NO concentration at the outlet of the ammonia-based SCR denitrification reactor. x The concentration must be below the emission limit. At the same time, the concentration of ammonia gas that has not been fully reacted at the outlet of the denitrification reactor (ammonia slip concentration) must be below a certain limit (such as 3 ppm) to prevent excessive ammonia water from causing ammonia emissions to exceed the standard and to reduce the amount of ammonium bisulfate (ammonium bisulfate can clog equipment and cause catalyst failure), which is detrimental to the stable operation of the system.

[0054] Optionally, an ammonia flow meter 58 is installed on the ammonia water delivery pipe 26 to measure the instantaneous and cumulative flow of ammonia water added to the system, providing a basis for optimizing system operating parameters and energy-saving operation.

[0055] Optionally, an ammonia storage tank 23 is equipped with an ammonia storage tank level gauge 59 to measure the ammonia storage tank level and to trigger an alarm when the ammonia level is lower than a certain set value.

[0056] In a preferred embodiment, the SCR denitrification reactor 30 is equipped with several SCR denitrification reactor soot blowers 31, which are used to blow away the dust accumulated on the surface and inside the catalyst in the SCR denitrification reactor, preventing dust and ammonium bisulfate, a product of ammonia denitrification, from clogging the catalyst and ensuring stable operation of the system.

[0057] The soot blower 31 of the SCR denitrification reactor is connected to the compressed air pipe 32 of the soot blower of the SCR denitrification reactor, and supplies compressed air to the soot blower of the ammonia-based SCR denitrification reactor.

[0058] The compressed air pipe 32 of the soot blower of the SCR denitrification reactor is equipped with a compressed air valve 33, which is used to open and close the pipeline of the compressed air pipe 32 of the soot blower of the SCR denitrification reactor and automatically open at regular intervals to blow away the ash accumulated on the catalyst in the ammonia-based SCR denitrification reactor.

[0059] In a preferred embodiment, the metal filter bag dust collector 36 is equipped with a dust collector cleaner 37. During operation, the dust collector cleaner 37 cleans the dust adhering to the surface of the filter bag, reducing the operating resistance of the dust collector and the load on the filter bag. It is a component that ensures the continuous and stable operation of the dust collector.

[0060] The dust collector cleaner 37 is connected to the dust collector cleaning compressed air pipe 38 to supply compressed air for dust collector cleaning.

[0061] The lower side of the metal filter bag dust collector 36 is equipped with a dust collector discharge valve 39, which is used to remove the dust removed from the filter bag by the dust collector cleaning system. It is a component that ensures the continuous and stable operation of the dust collector.

[0062] In the preferred embodiment, the metal filter bag dust collector 36 is connected to the fan 41 through the dust collector outlet flue 40. The fan is used to transport flue gas and is frequency-controlled. The fan speed is controlled according to the furnace production conditions (such as the size of the furnace burners, the number of burners in operation, and the furnace pressure), so that the fan operating parameters are adapted to the actual production conditions of the aluminum melting furnace. This can stabilize the furnace pressure, reduce unnecessary fuel consumption of the aluminum melting furnace, and reduce production costs. At the same time, the frequency-controlled operation of the fan can also save energy consumption of the flue gas treatment system and reduce the operating cost of the flue gas treatment system.

[0063] The blower 41 is connected to the exhaust pipe inlet flue 42 and the exhaust pipe 43, and discharges the aluminum melting furnace flue gas that has been denitrified and dust removed and meets the standards through the exhaust pipe 43.

[0064] Optionally, a dust collector differential pressure sensor 56 is installed between the second outlet flue 35 of the flue gas heat exchanger and the outlet flue 40 of the dust collector to measure the differential pressure of the dust collector. An alarm is triggered when the differential pressure exceeds a certain set value.

[0065] All sensors, valves, and detectors in this invention are controlled by an external control system and powered by an external power source. Their specific structures, working principles, and circuit connections are all well-known technologies and will not be described in detail here.

[0066] This invention also provides a flue gas denitrification and dust removal process for an aluminum alloy smelting furnace holding furnace, which adopts the above-mentioned flue gas denitrification and dust removal system for an aluminum alloy smelting furnace holding furnace, and includes the following steps: (1) When the temperature of the flue gas discharged from the furnace of the aluminum melting furnace is higher than a certain set value (e.g., higher than 380℃), the flue gas is first cooled and its temperature is adjusted to control the flue gas temperature within the temperature limit of the denitrification and dust removal system and the temperature range where the denitrification catalyst has high activity (e.g., 340~380℃). Then, the flue gas flows through the flue gas heat exchanger and the flue gas heater (at this time, the flue gas does not need to be heated) and enters the flue gas heater outlet flue. Atomized ammonia water is sprayed into the flue gas heater outlet flue. The ammonia gas decomposed after the ammonia water is vaporized at high temperature mixes with the flue gas. Then, the mixed gas of flue gas and ammonia gas enters the ammonia-flue gas mixer. In the ammonia-flue gas mixer, the flue gas undergoes strong turbulence, which mixes the ammonia gas evenly in the flue gas, which is beneficial to improving the denitrification efficiency and reducing ammonia gas escape. Then, the mixed gas of flue gas and ammonia gas enters the SCR denitrification reactor. In the denitrification reactor, the NO in the flue gas x The gas reacts with ammonia in the presence of a catalyst to produce harmless nitrogen and water, thus achieving denitrification. After denitrification, the flue gas passes through a flue gas heat exchanger and then enters a metal bag filter dust collector, where particulate matter is removed. At this point, the particulate matter and NO in the flue gas are... x The concentrations were all below the emission limits and met the emission requirements. The qualified flue gas was then discharged into the atmosphere through the fan and exhaust stack.

[0067] (2) When the temperature of the flue gas discharged from the furnace of the aluminum melting furnace is lower than a certain set value but higher than a certain set value (for example, lower than 380°C but higher than 190°C), the flue gas does not need to be cooled and adjusted, nor does it need to be heated in the flue gas heating furnace. The flue gas purification process is the same as (1).

[0068] (3) When the temperature of the flue gas discharged from the furnace of the aluminum melting furnace is lower than a certain set value (e.g., lower than 190°C), the flue gas does not need to be cooled and adjusted, but it needs to be heated in the flue gas heater. The flue gas discharged from the furnace of the aluminum melting furnace first enters the flue gas heat exchanger. In the flue gas heat exchanger, the high-temperature flue gas after denitrification is used to preheat the flue gas of the aluminum melting furnace. The purpose is to save the gas consumption of the flue gas heater. After the flue gas of the aluminum melting furnace is preheated in the flue gas heat exchanger, it enters the flue gas heater. In the flue gas heater, the flue gas is heated to slightly higher than the minimum activity temperature requirement of the denitrification catalyst by the combustion of gas. While ensuring that the denitrification effect can be achieved, the gas consumption is saved and the system operating cost is reduced. The subsequent process is the same as (1).

[0069] To prevent ash accumulation in the denitrification reactor from clogging the catalyst, and ash accumulation on the surface of the heat exchange elements in the second flue gas channel of the flue gas heat exchanger from clogging the flue gas heat exchanger and to slow down catalyst failure, the catalyst and the surface of the heat exchange elements in the second flue gas channel of the flue gas heat exchanger are periodically blew out ash.

[0070] To prevent the dust collector filter bag resistance from increasing and thus reducing the actual air volume required by the system, and to prevent filter bag blockage, compressed air is used to perform timed pulse cleaning of the filter bags. The dust removed from the filter bags is periodically discharged to ensure continuous operation of the dust collector.

[0071] The gas flow rate required for flue gas heating and the ammonia flow rate required for denitrification can be automatically adjusted according to actual needs. Furthermore, when flue gas heating is required, preheating with the high-temperature flue gas after denitrification can significantly reduce gas consumption. All of these measures achieve the goals of reducing system energy consumption and saving operating costs.

[0072] By employing flue gas cooling and temperature regulation, flue gas preheating, and flue gas heating, the system can adapt to all flue gas conditions throughout the entire aluminum smelting furnace production process. This means the denitrification and dust removal system can operate at both high and low flue gas temperatures. When the flue gas temperature is too low and heating is required, it only needs to be heated to slightly above the minimum temperature necessary for denitrification, ensuring effective denitrification while saving operating costs. During high-temperature operation, the system can suppress the formation of ammonium bisulfate during denitrification and decompose ammonium bisulfate generated during low-temperature operation. Compared to traditional aluminum smelting furnace flue gas denitrification and dust removal technologies, this avoids the phenomenon of ammonium bisulfate adhering to the catalyst, extending the service life of the catalyst and flue gas heat exchanger, and reducing system operating costs.

[0073] The dust collector not only removes particulate matter from the raw flue gas but also from the catalyst and flue gas heat exchanger, ensuring that particulate matter emissions do not exceed standards. Additionally, the system's inherent ability to promptly decompose ammonium bisulfate ensures that, during normal operation, not only particulate matter and NOx from the raw flue gas are removed. x The levels are within acceptable limits, and the denitrification byproducts are also within acceptable limits, which can reduce the environmental pressure on aluminum processing enterprises and is of great significance to the sustainable development of enterprises.

[0074] All key parameters of the system are monitored and controlled, and appropriate protection is implemented when the limits are exceeded to ensure the safe and stable operation of the system.

[0075] All parts not disclosed in this invention are prior art, and their specific structures, materials, and working principles will not be described in detail. 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 variations 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 flue gas denitrification and dust removal process for an aluminum alloy smelting furnace holding furnace, characterized in that: This is achieved through a flue gas denitrification and dust removal system for an aluminum alloy smelting furnace and a holding furnace. The flue gas denitrification and dust removal system for an aluminum alloy smelting furnace and a holding furnace includes an aluminum smelting furnace (1) and an aluminum holding furnace (2). The flue gas duct (5) of the aluminum smelting furnace (1) and the flue gas duct (6) of the aluminum holding furnace (2) are both connected to the first inlet flue gas duct (7) of the flue gas heat exchanger. The first inlet flue gas duct (7) of the flue gas heat exchanger is connected to the flue gas heat exchanger (9). The first outlet flue gas duct (13) of the flue gas heat exchanger (9) is connected to the flue gas heating furnace (14). The flue gas heating furnace (14) is connected to the ammonia-flue gas mixer (28) through the outlet flue gas duct (21) of the flue gas heating furnace. The flue gas heater outlet flue (21) is also connected to the ammonia conveying assembly. The flue gas ammonia mixer (28) is connected to the SCR denitrification reactor (30) through the SCR denitrification reactor inlet flue (29). The SCR denitrification reactor (30) is connected to the flue gas heat exchanger (9) through the flue gas heat exchanger second inlet flue (34). The flue gas heat exchanger (9) is connected to the metal filter bag dust collector (36) through the flue gas heat exchanger second outlet flue (35). The metal filter bag dust collector (36) is connected to the fan (41) through the dust collector outlet flue (40). The fan (41) is connected to the exhaust stack inlet flue (42) and the exhaust stack (43). The process includes the following steps: S1) When the flue gas temperature discharged from the furnace of the aluminum smelting furnace (1) and the aluminum holding furnace (2) is higher than 380℃, the flue gas is first cooled and regulated to control the flue gas temperature within the temperature limit of the denitrification and dust removal system and the temperature range of high activity of the denitrification catalyst, which is 320~360℃. Then the flue gas flows through the flue gas heat exchanger (9) and the flue gas heating furnace (14) in sequence and enters the flue gas heating furnace outlet flue (21). Atomized ammonia water is sprayed into the flue gas heating furnace outlet flue (21). After the ammonia water is vaporized at high temperature, The decomposed ammonia gas is mixed with the flue gas, and then the mixture of flue gas and ammonia gas enters the ammonia-flue gas mixer (28). In the ammonia-flue gas mixer (28), the flue gas undergoes strong turbulence, which uniformly mixes the ammonia gas in the flue gas. Then the mixture of flue gas and ammonia gas enters the SCR denitrification reactor (30). After denitrification, the flue gas passes through the flue gas heat exchanger (9) and then enters the metal filter bag dust collector (36). In the metal filter bag dust collector (36), particulate matter in the flue gas is removed. At this time, the particulate matter and NO in the flue gas are removed. x The concentrations are all below the emission limits and meet the emission requirements. The qualified flue gas is discharged into the atmosphere through the fan (41) and the exhaust stack (43) in sequence. S2) When the temperature of the flue gas discharged from the furnace of the aluminum smelting furnace (1) and the aluminum holding furnace (2) is lower than 380°C but higher than 190°C, the flue gas does not need to be cooled and adjusted, nor does it need to be heated in the flue gas heating furnace. S3) When the temperature of the flue gas discharged from the furnace of the aluminum smelting furnace (1) and the aluminum holding furnace (2) is lower than 190°C, the flue gas does not need to be cooled and adjusted, but it needs to be heated in the flue gas heating furnace (14). The flue gas discharged from the furnace of the aluminum smelting furnace (1) and the aluminum holding furnace (2) first enters the flue gas heat exchanger (9). In the flue gas heat exchanger (9), the high temperature flue gas after denitrification is used to preheat the flue gas of the aluminum smelting furnace (1) and the aluminum holding furnace (2). After the flue gas of the aluminum smelting furnace (1) and the aluminum holding furnace (2) is preheated in the flue gas heat exchanger (9), it enters the flue gas heating furnace. In the flue gas heating furnace (14), the flue gas is heated to above 220°C by the combustion of gas.

2. The flue gas denitrification and dust removal process for an aluminum alloy smelting furnace holding furnace according to claim 1, characterized in that: The first inlet flue (7) of the flue gas heat exchanger is equipped with a flue gas temperature regulating valve (8) and a flue gas temperature sensor (44) at the first inlet of the flue gas heat exchanger. Both the flue gas temperature regulating valve (8) and the flue gas temperature sensor (44) at the first inlet of the flue gas heat exchanger are electrically connected to the control system.

3. The flue gas denitrification and dust removal process for an aluminum alloy smelting furnace holding furnace according to claim 1, characterized in that: The flue gas heat exchanger (9) is equipped with a flue gas heat exchanger soot blower (10), which is connected to the flue gas heat exchanger soot blower compressed air pipe (11). A flue gas heat exchanger soot blower compressed air valve (12) is provided on the flue gas heat exchanger soot blower compressed air pipe (11).

4. The flue gas denitrification and dust removal process for an aluminum alloy smelting furnace holding furnace according to claim 1, characterized in that: The flue gas heater (14) is connected to one end of the flue gas heater burner (18), and the other end of the flue gas heater burner (18) is connected to the combustion air pipe (16). The combustion air pipe (16) is equipped with a combustion air flow regulating valve (17), and the end of the combustion air pipe (16) is equipped with a combustion air fan (15).

5. The flue gas denitrification and dust removal process for an aluminum alloy smelting furnace holding furnace according to claim 4, characterized in that: The flue gas heating furnace burner (18) is connected to the gas pipe (19), and a gas flow regulating valve (20) is provided on the gas pipe (19).

6. The flue gas denitrification and dust removal process for an aluminum alloy smelting furnace holding furnace according to claim 1, characterized in that: The ammonia delivery assembly includes an ammonia storage tank (23), the outlet of which is connected to an ammonia delivery pipe (26) via an ammonia delivery pump (25), the ammonia delivery pipe (26) is connected to the flue gas heater outlet flue (21) via a dual-fluid spray gun (22), and an ammonia flow regulating valve (27) is provided on the ammonia delivery pipe (26), and the dual-fluid spray gun (22) is connected to the dual-fluid spray gun compressed air pipe (24).

7. The flue gas denitrification and dust removal process for an aluminum alloy smelting furnace holding furnace according to claim 1, characterized in that: The SCR denitrification reactor (30) is equipped with several SCR denitrification reactor soot blowers (31). The SCR denitrification reactor soot blowers (31) are connected to the SCR denitrification reactor soot blower compressed air pipe (32). The SCR denitrification reactor soot blower compressed air valve (33) is installed on the SCR denitrification reactor soot blower compressed air pipe (32).

8. The flue gas denitrification and dust removal process for an aluminum alloy smelting furnace holding furnace according to claim 1, characterized in that: The metal bag dust collector (36) is equipped with a dust collector cleaner (37), which is connected to the dust collector cleaning compressed air pipe (38). The metal bag dust collector (36) is equipped with a dust collector ash discharge valve (39) on its lower side.

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