Alumina calcination furnace flue gas waste heat recycling system

Abstract

The utility model provides a kind of alumina calcination furnace flue gas waste heat recycling system, including fluidization mechanism, fluidized heat preservation reactor, preheating unit and venturi dryer connected with chimney in turn, venturi dryer is connected preheating unit by cyclone separator, preheating unit connects calcination furnace main furnace;Fluidized heat preservation reactor is connected to the outlet of calcination furnace main furnace;Cyclone separator's flue gas outlet end is connected chimney;Cooling unit connects calcination furnace main furnace air inlet, preheating unit discharge port connects cooling unit feed inlet.The utility model passes through fluidization mechanism and fluidized heat preservation reactor, so that flue gas and the material of calcination furnace main furnace come out heat exchange, return to preheating system again;Through flue gas in venturi drying against aluminium hydroxide dry, and after separating by cyclone separator, aluminium hydroxide and flue gas heat exchange again in preheating unit, enter calcination furnace main furnace and carry out decomposition reaction production alumina;And flue gas returns chimney and is recycled, improve waste heat recovery efficiency, reduce the loss of system.

Description

Technical Field

[0001] This utility model relates to the field of calcining furnace technology, and in particular to an alumina calcining furnace flue gas system. Background Technology

[0002] In the alumina production process, the conventional process flow is as follows: the flue gas from the cyclone separator passes through the dust collector and the induced draft fan, and is then directly discharged into the atmosphere through the chimney. The flue gas temperature is generally 130~170℃, and the waste heat of the flue gas is wasted.

[0003] Currently, there are also new processes for utilizing flue gas waste heat: a flue heat exchanger is added between the dust collector and the induced draft fan, using circulating demineralized water as the cooling medium to recover waste heat from the flue gas. This waste heat is then used to heat the pan wash water, circulating mother liquor, and evaporate secondary water, reducing the temperature of the roasting flue gas to 110-120℃, thus achieving waste heat utilization. However, the roasting furnace uses high-value-added fuel gas. On the one hand, the recovered heat can only be used externally for low-value hot water resources; on the other hand, the recovered heat cannot be returned to the roasting furnace system. Therefore, it cannot reduce the fuel gas resource loss in the roasting furnace.

[0004] Chinese invention patent CN 113461040 A, published on October 1, 2021, describes a novel aluminum hydroxide steam-producing suspension roasting furnace device. The device includes a bucket elevator and a roasting furnace. The bucket elevator is connected to a feeding hopper. A heat exchanger is located below the feeding hopper's discharge port. The heat exchanger's discharge port is connected to the inlet of a first cyclone separator. The first cyclone separator's outlet is connected to the roasting furnace. The roasting furnace's flue gas outlet is connected to a third cyclone separator. The third cyclone separator's flue gas outlet is connected to the heat exchanger's flue gas inlet. The heat exchanger's flue gas outlet is connected to a second cyclone separator. The second cyclone separator's flue gas outlet is connected to a waste heat boiler. The waste heat boiler's flue gas outlet is connected to a dust collector. The waste heat boiler has a cooling water inlet and a steam outlet. However, this patent cannot recover waste heat to reduce the fuel consumption of the roasting furnace. Summary of the Invention

[0005] To address the aforementioned technical problems, this utility model proposes a waste heat recycling system for alumina calcining furnace flue gas, which solves the problem that existing technologies for utilizing waste heat from alumina calcining furnace flue gas cannot reduce the loss of fuel gas resources in the calcining furnace.

[0006] To achieve the above objectives, the technical solution of this utility model is implemented as follows: A waste heat recycling system for flue gas from an alumina calcining furnace includes a fluidizing air mechanism connected to a chimney, a fluidized bed reactor connected to the fluidizing air mechanism, a preheating unit connected to a Venturi dryer with a raw material inlet, a cyclone separator connected to the preheating unit, and the preheating unit connected to the main furnace of the calcining furnace. This allows the raw material and preheated flue gas to exchange heat and increase in temperature in the Venturi dryer and preheating unit before entering the main furnace for reaction. One outlet of the main furnace is connected to the fluidized bed reactor, and the flue gas outlet of the cyclone separator is connected to the chimney.

[0007] Furthermore, the flue gas outlet end of the cyclone separator is connected to a dust collector, which is connected to the chimney via an induced draft fan.

[0008] Furthermore, in order to exchange heat between the material coming out of the main furnace of the roasting furnace and the flue gas and air, a cooling unit is connected to the preheating unit and the main furnace of the roasting furnace.

[0009] Furthermore, the preheating unit includes a primary cyclone preheater, a secondary cyclone preheater, and a tertiary cyclone preheater. The bottom outlet of the cyclone separator is connected to the inlet of the primary cyclone preheater. One outlet of the primary cyclone preheater is connected to the Venturi dryer, and the other outlet is connected to the inlet of the secondary cyclone preheater. The bottom outlet of the secondary cyclone preheater is connected to the main furnace of the roasting furnace, and the top outlet is connected to the primary cyclone preheater. The outlet of the main furnace of the roasting furnace is connected to the tertiary cyclone preheater. One outlet of the tertiary cyclone preheater is connected to the secondary cyclone preheater, and the other outlet is connected to the cooling unit.

[0010] Furthermore, the cooling unit is equipped with an air inlet and is connected to the bottom inlet of the main furnace of the roasting furnace, so that the air is heated by heat exchange in the cooling unit and then enters the main furnace of the roasting furnace as combustion air.

[0011] Furthermore, the chimney is connected to the preheating unit via a flue gas pipeline. A fluidized bed preheating reactor is installed on the flue gas pipeline, and the three-stage cyclone preheater is connected to the fluidized bed preheating reactor via a cooling unit, so that the material after the flue gas reacts with the main furnace of the roasting furnace reacts in the fluidized bed preheating reactor. One outlet of the fluidized bed preheating reactor is connected to one inlet of the two-stage cyclone preheater, so that the flue gas enters the preheating unit.

[0012] Furthermore, the fluidizing air mechanism includes a pressurized fan for generating fluidizing air within the fluidized insulated reactor.

[0013] Furthermore, the precooling unit includes a primary cyclone cooler, a secondary cyclone cooler, a tertiary cyclone cooler, and a quaternary cyclone cooler. One outlet of the tertiary cyclone preheater is connected to the inlet of the primary cyclone cooler. The two outlets of the primary cyclone cooler are respectively connected to the bottom of the main furnace of the calcining furnace and one inlet of the fluidized bed reactor. The other outlet of the fluidized bed reactor is connected to the secondary cyclone cooler. One outlet of the secondary cyclone cooler is connected to the inlet of the primary cyclone cooler, and the other outlet is connected to the inlet of the quaternary cyclone cooler. One outlet of the quaternary cyclone cooler is used to discharge the product, and the other outlet is connected to the tertiary cyclone cooler. One outlet of the tertiary cyclone cooler is connected to the inlet of the secondary cyclone cooler, and the other outlet is connected to the inlet of the quaternary cyclone cooler.

[0014] Furthermore, an air duct is provided between one outlet of the three-stage cyclone cooler and one inlet of the four-stage cyclone cooler; an air input pipe is connected to the air duct.

[0015] Furthermore, a circulating flue gas dust collector is installed on the flue gas pipeline between the pressurized blower and the chimney. The bottom outlet of the circulating flue gas dust collector is connected to the inlet of the secondary cyclone cooler, so that the flue gas also reacts with the solid materials collected by the circulating flue gas dust collector.

[0016] Furthermore, a flue gas dust collector is connected between the flue gas outlet end of the cyclone separator and the chimney, and the bottom outlet of the flue gas dust collector is connected to the inlet end of the first-stage cyclone cooler.

[0017] The beneficial effects of this utility model are: 1. This utility model, by setting up a Venturi dryer and a cyclone separator, allows the flue gas from the chimney to dry aluminum hydroxide in the Venturi dryer, and then separate it in the cyclone separator. The dried aluminum hydroxide then enters the main furnace of the calcining furnace for decomposition reaction to produce alumina; while the flue gas is returned to the chimney for recycling, which improves the waste heat recovery efficiency and reduces the system loss. 2. This utility model, by setting up a fluidized bed heat-insulating reactor, enables the flue gas from the chimney to not only exchange heat with the alumina and unreacted aluminum hydroxide after the reaction in the main furnace of the roasting furnace, thus fully recovering and utilizing the waste heat of the product, but also to undergo a chemical dehydration reaction to generate alumina. 3. This utility model cools the alumina of the product through a cooling unit. At the same time, air enters the cooling unit to exchange heat with the alumina and is heated before entering the main furnace of the calcining furnace to assist combustion. Afterward, the alumina is discharged from the system, so that some of the heat of the alumina remains in the system, which plays an energy-saving role. 4. This utility model uses a preheating unit to exchange heat between flue gas and dried aluminum hydroxide. After the aluminum hydroxide is heated, it enters the main furnace of the calcination furnace for reaction, while the flue gas is cooled down to dry the aluminum hydroxide entering the Venturi dryer, thus recycling the flue gas. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of this utility model.

[0020] In the diagram: 1. Venturi dryer, 2. Cyclone separator, 3. First-stage cyclone preheater, 4. Second-stage cyclone preheater, 5. Third-stage cyclone preheater, 6. Main furnace of suspension roasting furnace, 7. First-stage cyclone cooler, 8. Second-stage cyclone cooler, 9. Third-stage cyclone cooler, 10. Fourth-stage cyclone cooler, 11. Fluidized bed insulated reactor, 12. Recovered flue gas dust collector, 13. Pressurized blower, 14. Circulating flue gas dust collector, 15. Main induced draft fan, 16. Chimney. Detailed Implementation

[0021] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0022] like Figure 1 As shown in Embodiment 1 of this utility model, a waste heat recycling system for alumina calcining furnace flue gas includes a circulating flue gas dust collector 14, a pressurized fan 13, and a fluidized bed reactor 11 connected in sequence to a chimney 16. A preheating unit is connected to one outlet end of the fluidized bed reactor 11, i.e., the flue gas outlet end. A Venturi dryer 1 is connected to the preheating unit. A cyclone separator 2 is connected to the outlet end of the Venturi dryer 1. The flue gas outlet end of the cyclone separator 2 is connected to the chimney 16 via a recovery flue gas dust collector 12. An induced draft fan 15 is installed between the recovery flue gas dust collector 12 and the chimney 16. After being preheated by the preheating unit, the flue gas and aluminum hydroxide entering the Venturi dryer 1 are dried in the Venturi dryer 1 and then enter the cyclone separator 2 for gas-solid separation. The separated flue gas exits from the exhaust pipe outlet of the cyclone separator 2, is purified by the recovery flue gas dust collector 12, and then returns to the chimney 16.

[0023] The solid material end of cyclone separator 2 is connected to the preheating unit. The preheating unit preheats the raw materials and cools the flue gas. The preheating unit includes the main furnace 6 of the calcining furnace. The solid material from cyclone separator 2, namely aluminum hydroxide, is heated by heat exchange with the flue gas in the preheating unit before entering the main furnace 6 of the calcining furnace, where it undergoes a decomposition reaction to produce alumina. The preheating unit includes a primary cyclone preheater 3, a secondary cyclone preheater 4, and a tertiary cyclone preheater 5. The bottom solid material outlet of cyclone separator 2 is connected to the inlet of the primary cyclone preheater 3. One outlet of the primary cyclone preheater 3 is connected to the Venturi dryer 1, and the other outlet is connected to the inlet of the secondary cyclone preheater 4. The bottom outlet of the secondary cyclone preheater 4 is connected to the main furnace 6 of the calcining furnace, and the top outlet is connected to the primary cyclone preheater 3. The outlet of the main furnace 6 of the calcining furnace is connected to the tertiary cyclone preheater 5. One outlet of the three-stage cyclone preheater 5, namely the exhaust pipe, is connected to the two-stage cyclone preheater 4, and the other outlet, namely the feed pipe, is connected to the cooling unit. This allows the alumina produced by the decomposition reaction in the main furnace 6 of the calcining furnace to be preheated by the three-stage cyclone preheater 5, then enter the cooling unit to exchange heat with the combustion air before being output from the system.

[0024] The fluidized bed reactor 11 is connected to the cooling unit. The cooling unit cools the product material and preheats the air to form combustion air. The cooling unit includes a primary cyclone cooler 7, a secondary cyclone cooler 8, a tertiary cyclone cooler 9, and a quaternary cyclone cooler 10. One outlet of the tertiary cyclone preheater 5 is connected to the inlet of the primary cyclone cooler 7. The two outlets of the primary cyclone cooler 7 are respectively connected to the bottom of the main furnace 6 of the roasting furnace and one inlet of the fluidized bed reactor 11. One outlet of the fluidized bed reactor 11 is connected to one inlet of the secondary cyclone preheater 4, allowing flue gas to enter the preheating unit; the other outlet of the fluidized bed reactor 11 is connected to the secondary cyclone cooler 8. One outlet of the secondary cyclone cooler 8 is connected to the primary cyclone cooler 7, and the other outlet is connected to the quaternary cyclone cooler 10. One outlet of the quaternary cyclone cooler 10 is used to discharge the product alumina, and the other outlet is connected to the tertiary cyclone cooler 9. One outlet of the three-stage cyclone cooler 9 is connected to the inlet of the two-stage cyclone cooler 8, and the other outlet is connected via a pipe to one inlet of the four-stage cyclone cooler 10, with air supplied through this pipe. Additionally, the bottom outlet of the circulating flue gas dust collector 14 is connected to the cooling unit. The bottom outlet of the recovery flue gas dust collector 12 is also connected to the cooling unit.

[0025] The usage process of this utility model is as follows: During the baking process of the alumina calcining furnace, the waste heat recycling system of the alumina calcining furnace flue gas needs to be shut off through a valve. Before normal operation, the pressurizing fan 13 for circulating flue gas is turned on to ensure the normal operation of the waste heat recycling system. Part of the flue gas is drawn out from the exhaust chimney 16, purified by the circulating flue gas dust collector 14, and then pressurized by the pressurizing fan 13. After pressurization, it serves as fluidizing air for fluidized bed reactor 11. At the same time, the flue gas, the mixture of alumina and unreacted aluminum hydroxide from the main furnace 6 of the calcining furnace, and the solid powder collected by the two dust collectors pass through the fluidized bed reactor 11 for heat exchange and reaction. The mixed powder is transformed into product alumina while being cooled. The heated flue gas enters the preheating unit to heat the aluminum hydroxide from the cyclone separator 2. Through the flue gas waste heat recycling system, the heat from the cooling of alumina and the heat brought in by the circulating flue gas can be used to heat the raw materials, reduce the amount of high-temperature flue gas from the three-stage cyclone preheater, reduce fuel consumption, and achieve the purpose of energy saving and consumption reduction. Specifically, the opening degree and frequency of the circulating flue gas pressurizing fan 13 are determined based on the exhaust temperature at the chimney 16 outlet, the material flow conditions within the fluidized bed insulated reactor 11, and the loss on ignition index of the finished alumina product. The aim is to ensure that the flue gas participating in fluidization within the fluidized bed insulated reactor 11 enters the inlet of the secondary cyclone preheating separator 4 through the circulating flue gas exhaust pipe as much as possible.

[0026] During operation, aluminum hydroxide enters the Venturi dryer 1 and exchanges heat with the high-temperature flue gas from the exhaust pipe of the first-stage cyclone preheater 3 within the Venturi dryer 1. Inside the Venturi dryer 1, the flue gas exchanges heat with the low-temperature aluminum hydroxide. After the heat exchange, a certain temperature difference still exists between the solid aluminum hydroxide powder and the flue gas. After heat exchange in the Venturi dryer 1, the gas and solid phases are discharged from the outlet of the Venturi dryer 1. The flue gas and aluminum hydroxide then enter the cyclone separator 2 for gas-solid separation. The separated aluminum hydroxide enters the inlet of the first-stage cyclone preheater 3 through the discharge pipe of the cyclone separator 2. The separated flue gas exits from the exhaust pipe outlet of the cyclone separator 2 and is purified by the flue gas dust collector 12. Finally, under the action of the induced draft fan 15, it returns to the chimney 16.

[0027] Aluminum hydroxide passes sequentially through a primary cyclone preheater 3 and a secondary cyclone preheater 4, where it undergoes heating and decomposition. It then enters the main furnace 6 of the calcining furnace through the feed pipe of the secondary cyclone preheater 4, where it undergoes a decomposition reaction to produce alumina. The alumina, along with the flue gas from the combustion chamber, enters the tertiary cyclone preheater 5. After gas-solid separation in the tertiary cyclone preheater 5, the alumina enters the cooling unit through the feed pipe of the tertiary cyclone preheater 5. The flue gas then circulates through the exhaust pipe of the tertiary cyclone preheater 5 into the secondary cyclone preheater 4 of the preheating unit.

[0028] Alumina enters the cooling unit, where it first undergoes rapid heat exchange with the combustion air exiting from the exhaust pipe of the secondary cyclone cooler 8. After heat exchange, the combustion air and alumina sequentially pass through the primary cyclone cooler 7, the secondary cyclone cooler 8, the tertiary cyclone cooler 9, and the quaternary cyclone cooler 10, experiencing progressively lower temperatures while the combustion air experiences progressively higher temperatures. The alumina is then discharged from the system, while the combustion air enters the main furnace 6 of the calcining furnace.

[0029] The flue gas temperature before entering the circulating flue gas dust collector is 130~170℃. If the flue gas temperature exceeds the requirement, the circulating flue gas pressurizing fan must be stopped.

[0030] Furthermore, the temperature of the powder material inside the fluidized bed reactor 11 is 500~750℃, the inlet temperature is 600~750℃, and the outlet temperature is controlled at 500~600℃. The inlet temperature of the circulating flue gas inside the fluidized bed reactor 11 is 170~200℃, and the outlet temperature is 400~500℃.

[0031] Furthermore, to ensure the safe operation of the circulating flue gas pressurization fan and the equipment inside the fluidized bed insulated reactor, the dust concentration entering the pressurization fan is controlled at 1 mg / Nm³. 3 the following.

[0032] Furthermore, the inlet dust concentration of the circulating flue gas dust collector is ≤10mg / Nm³. 3 The inlet flue gas temperature is 130~170℃, and the inlet pressure is -0.5~0.3kPa. Furthermore, through the waste heat recycling system of the alumina calcining furnace flue gas, the temperature of the flue gas discharged from the chimney 16 can be controlled at 110~120℃, and the alumina discharge temperature is 150~200℃.

[0033] Furthermore, in the alumina calcining furnace flue gas waste heat recycling system, the amount of high-temperature flue gas discharged from the three-stage cyclone preheater 5 is reduced by 2-4%, and the overall heat consumption of the system is reduced by 2-4%.

[0034] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Although the present utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions of some or all of the technical features therein, within the spirit and principles of the present utility model, shall not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present utility model, and shall all be included within the protection scope of the present utility model.

Claims

1. A waste heat recycling system for flue gas from an alumina calcining furnace, characterized in that, The system includes a fluidizing air mechanism connected to a chimney (16), which is connected to a fluidized bed reactor (11). The fluidized bed reactor (11) is connected to a Venturi dryer (1) with a raw material inlet via a preheating unit. The Venturi dryer (1) is connected to the preheating unit via a cyclone separator (2). The preheating unit is connected to the main furnace of the roasting furnace (6), so that the raw material and the preheated flue gas exchange heat and are heated by the Venturi dryer (1) and the preheating unit before entering the main furnace of the roasting furnace (6). One outlet of the main furnace of the roasting furnace (6) is connected to the fluidized bed reactor (11). The flue gas outlet end of the cyclone separator (2) is connected to the chimney (16).

2. The alumina calcining furnace flue gas waste heat recycling system according to claim 1, characterized in that, The flue gas outlet end of the cyclone separator (2) is connected to the flue gas dust collector (12), and the flue gas dust collector (12) is connected to the chimney (16) through the induced draft fan (15).

3. The alumina calcining furnace flue gas waste heat recycling system according to claim 2, characterized in that, The preheating unit includes a primary cyclone preheater (3), a secondary cyclone preheater (4), and a tertiary cyclone preheater (5). The bottom outlet of the cyclone separator (2) is connected to the inlet of the primary cyclone preheater (3). One outlet of the primary cyclone preheater (3) is connected to the Venturi dryer (1), and the other outlet is connected to the inlet of the secondary cyclone preheater (4). The bottom outlet of the secondary cyclone preheater (4) is connected to the main furnace of the roasting furnace (6), and the top outlet is connected to the primary cyclone preheater (3). The outlet of the main furnace of the roasting furnace (6) is connected to the tertiary cyclone preheater (5). One outlet of the tertiary cyclone preheater (5) is connected to the secondary cyclone preheater (4), and the other outlet is connected to the cooling unit.

4. The alumina calcining furnace flue gas waste heat recycling system according to claim 3, characterized in that, The cooling unit is equipped with an air inlet and is connected to the bottom inlet of the main furnace (6) of the roasting furnace, so that the air is heated by heat exchange in the cooling unit and then enters the main furnace (6) of the roasting furnace.

5. The alumina calcining furnace flue gas waste heat recycling system according to claim 4, characterized in that, The chimney (16) is connected to the fluidized bed reactor (11) through the flue gas pipeline. The fluidizing air mechanism is set on the flue gas pipeline, and the three-stage cyclone preheater (5) is connected to the fluidized bed reactor (11) through the cooling unit, so that the flue gas reacts with the main furnace (6) of the roasting furnace and the material reacts in the fluidized bed reactor (11). One outlet of the fluidized bed reactor (11) is connected to one inlet of the two-stage cyclone preheater (4), so that the flue gas enters the preheating unit.

6. The alumina calcining furnace flue gas waste heat recycling system according to claim 5, characterized in that, The fluidizing air mechanism includes a pressurizing fan (13) for generating fluidizing air within the fluidized insulated reactor (11).

7. The alumina calcining furnace flue gas waste heat recycling system according to claim 6, characterized in that, The precooling unit includes a primary cyclone cooler (7), a secondary cyclone cooler (8), a tertiary cyclone cooler (9), and a quaternary cyclone cooler (10). One outlet of the tertiary cyclone preheater (5) is connected to the inlet of the primary cyclone cooler (7). The two outlets of the primary cyclone cooler (7) are respectively connected to the bottom of the main furnace (6) of the roasting furnace and one inlet of the fluidized bed reactor (11). One outlet of the fluidized bed reactor (11) is connected to the secondary cyclone cooler (8). One outlet of the secondary cyclone cooler (8) is connected to the inlet of the primary cyclone cooler (7), and the other outlet is connected to the inlet of the quaternary cyclone cooler (10). One outlet of the quaternary cyclone cooler (10) is used to discharge the product, and the other outlet is connected to the tertiary cyclone cooler (9). One outlet of the tertiary cyclone cooler (9) is connected to the inlet of the secondary cyclone cooler (8), and the other outlet is connected to the inlet of the quaternary cyclone cooler (10).

8. The alumina calcining furnace flue gas waste heat recycling system according to claim 7, characterized in that, An air duct is provided between one outlet of the three-stage cyclone cooler (9) and one inlet of the four-stage cyclone cooler (10); an air input pipe is connected to the air duct.

9. The alumina calcining furnace flue gas waste heat recycling system according to claim 7 or 8, characterized in that, A circulating flue gas dust collector (14) is installed on the flue gas pipeline between the pressurized blower (13) and the chimney (16). The bottom outlet of the circulating flue gas dust collector (14) is connected to the inlet of the secondary cyclone cooler (8), so that the flue gas also reacts with the solid materials collected by the circulating flue gas dust collector (14).

10. The alumina calcining furnace flue gas waste heat recycling system according to claim 7 or 8, characterized in that, The bottom outlet of the flue gas dust collector (12) is connected to the inlet of the primary cyclone cooler (7).

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