A direct reduction rotary kiln flue gas treatment process

Abstract

This invention discloses a direct reduction rotary kiln flue gas treatment process. The production process is as follows: The iron ore direct reduction rotary kiln flue gas treatment system mainly consists of an air supply system, a flue gas treatment chamber, a feeding system, and a flue gas main pipe. The 500-600℃ flue gas discharged from the feed end of the rotary kiln first enters the gravity settling chamber. During the change of flow direction of the flue gas, the coarse dust particles it contains are separated from the flue gas. After coarse dust removal, the flue gas continues to flow from bottom to top in the flue gas treatment chamber, and the fine dust particles contained in the flue gas continue to separate from the flue gas under the action of gravity. When the flue gas flows to the combustible component treatment chamber, the flue gas mixes with the air ejected from the air outlet and burns, which can clean the combustible components in the flue gas.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical and mineral engineering technology, and specifically relates to a direct reduction rotary kiln flue gas treatment process. Background Technology

[0002] In the direct reduction process of iron ore in a rotary kiln, the high-temperature flue gas discharged from the feed end of the rotary kiln contains certain combustible components such as CO and H2. If this part of the flue gas is not treated and is directly discharged after dust removal by a dust collector and desulfurization by a desulfurization device, the flue gas cannot meet the emission standards due to the high CO content.

[0003] To ensure that the flue gas discharged from the rotary kiln for direct reduction of iron ore meets emission standards, the common practice both domestically and internationally is to first introduce the high-temperature flue gas discharged from the feed end of the rotary kiln into the kiln tail hood. Most of the coarse dust particles in the flue gas are removed under gravity. The flue gas after coarse dust removal then enters the secondary combustion chamber through the exhaust pipe. The high-temperature flue gas mixes with the combustion air supplied by the air supply system and then undergoes combustion. The high-temperature flue gas after secondary combustion then passes through a waste heat recovery device to recover heat and cool down, a dust removal system to remove dust, a fan system to pressurize it, a desulfurization system to desulfurize it, and finally, it is discharged into the atmosphere through the chimney.

[0004] Figure 1 This diagram illustrates an existing direct reduction rotary kiln flue gas treatment system. The secondary combustion chamber of the rotary kiln consists of an air supply system, a main exhaust pipe, exhaust ports, ash collection points, and exhaust ducts. The air supply system comprises a blower, a main air pipe, an air distribution pipe, regulating valves, and air nozzles. Air blown in by the blower enters the air distribution pipe through the main air pipe, and is then injected into the secondary combustion chamber according to process requirements via the air distribution pipe and regulating valves. During the horizontal jet flow within the secondary combustion chamber, the air mixes with the upward-flowing high-temperature flue gas, causing combustion of the combustible components in the flue gas. Currently, the main problems with direct reduction rotary kiln flue gas treatment systems include:

[0005] 1) In the secondary combustion chamber of the rotary kiln, due to the poor mixing conditions between high-temperature flue gas and ambient air, the combustible components in the flue gas are difficult to burn completely. The CO content in the flue gas discharged from the secondary combustion chamber is as high as 1-3%, which cannot meet the emission standards.

[0006] 2) Inside the kiln tail hood of the rotary kiln, during the horizontal flow of flue gas, since the flue gas and dust flow in the same direction, the flue gas velocity does not change much, and the dust removal efficiency in the flue gas is low. Most dust particles are carried into the secondary combustion chamber by the high-temperature flue gas. Under the action of combustion air, the combustible components in the flue gas are burned, and the dust particles easily generate a low-melting-point liquid phase. The molten liquid phase adheres to the inner wall of the secondary combustion chamber, affecting the long-term stable operation of the rotary kiln.

[0007] 3) A kiln tail hood and a secondary combustion chamber are installed at the feed end of the rotary kiln. The two devices occupy a certain amount of production space, which brings some difficulties to production and equipment layout.

[0008] 4) A kiln tail hood and a secondary combustion chamber are installed at the feed end of the rotary kiln. The ash generated by these two devices requires two sets of ash removal devices.

[0009] 5) Installing a kiln tail hood and a secondary combustion chamber at the feed end of the rotary kiln lengthens the flue gas flow path, increases exhaust resistance, and raises equipment maintenance and operating costs. Summary of the Invention

[0010] This invention addresses the aforementioned problems in the treatment of flue gas discharged from traditional rotary kilns for direct reduction of iron ore. To achieve compliant emissions of the discharged flue gas, reduce the dust content of the flue gas before the treatment of combustible components, reduce the number of ash removal devices, and shorten the flue gas flow path, this invention proposes a flue gas treatment process for direct reduction rotary kilns.

[0011] Therefore, the present invention adopts the following technical solution:

[0012] A direct reduction rotary kiln flue gas treatment process is disclosed, wherein the feed end of the rotary kiln is connected to a vertical flue gas treatment chamber, the feed end of the rotary kiln is flexibly sealed to the side wall of the flue gas treatment chamber, and the cross-section of the flue gas treatment chamber is more than three times the cross-sectional area of ​​the kiln tail hood of the rotary kiln; the feed pipe of the rotary kiln is vertically inserted downward from the top of the flue gas treatment chamber and into the rotary kiln.

[0013] The flue gas treatment chamber is equipped with an ash discharge port at the bottom and a main exhaust pipe at the top; the lower part of the flue gas treatment chamber is a gravity settling chamber and the upper part is a combustible component treatment chamber. The gravity settling chamber is used to settle particulate matter in the flue gas, and the combustible component treatment chamber is used to burn combustible components in the flue gas; a gas supply system is installed in the combustible component treatment chamber.

[0014] In this invention, the 500-600℃ flue gas discharged from the feed end of the rotary kiln first enters the gravity settling chamber of the flue gas treatment chamber. The flue gas changes from horizontal to upward flow. During this change in flow direction, coarse dust particles are separated from the flue gas under the influence of inertia and gravity and deposited at the bottom of the flue gas treatment chamber. The flue gas, after coarse dust removal, continues to flow upward within the flue gas treatment chamber, where fine dust particles continue to separate under gravity and also deposit at the bottom. When the flue gas flows into the combustible component treatment chamber, it mixes with and combusts with air ejected from the air outlet, raising the flue gas temperature to 900-1000℃. The high-temperature flue gas is finally discharged from the top of the flue gas treatment chamber.

[0015] To improve the dust removal effect of flue gas in the flue gas treatment chamber, this invention adopts a flue gas treatment chamber with a cross-sectional area of ​​flue gas flow that is more than three times larger than the cross-sectional area of ​​the kiln tail hood. This can effectively reduce the flow velocity of flue gas in the flue gas treatment chamber and prolong the flow time of flue gas in the flue gas treatment chamber.

[0016] This invention includes a blower installed outside the flue gas treatment chamber. The blower outlet is connected to one end of an air main pipe, and the other end of the air main pipe is connected to the middle of an air distribution pipe. The air distribution pipe is installed vertically, and air jet pipes are evenly installed along the length of the air distribution pipe. A regulating valve is installed on the air jet pipes, and an air outlet is provided at the other end of the air jet pipes. The air outlet is located in the middle of the flue gas treatment chamber, which can evenly blow air into the combustible component treatment chamber in a circumferential direction.

[0017] The present invention places the feeding port at the top of the flue gas treatment chamber, and the lower part of the feeding port is connected to the upper end of the feeding pipe. The lower end of the feeding pipe is located at the bottom of the kiln tail inside the rotary kiln. In the part of the feeding pipe located inside the kiln, since the feeding pipe needs to withstand the effect of high temperature radiation, in order to extend the service life of the feeding pipe, a refractory castable with a thickness of 30-50mm is provided on the outside of the pipe wall.

[0018] This invention aims to completely remove combustible components from flue gas. It includes 8-12 air nozzles installed in a combustible component treatment chamber, each vertically aligned. As the flue gas flows upwards, the combustible components are uniformly mixed with the air, ensuring complete combustion and achieving compliant emissions.

[0019] The present invention has an ash collection bin at the bottom of the flue gas treatment chamber. The ash that settles down from the high-temperature flue gas falls into the ash collection bin for temporary storage. The ash in the ash collection bin is discharged periodically through the ash discharge port set at the bottom.

[0020] The portion of the air ejector pipe in this invention located within the flue gas treatment chamber needs to withstand the radiation from high-temperature flue gas at 900-1000℃. To extend its service life, a 30-50mm layer of refractory castable is installed on the outer wall of the portion of the air ejector pipe within the flue gas treatment chamber.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. This invention eliminates the kiln tail hood and secondary combustion chamber of the existing direct reduction rotary kiln for iron ore, and adds a flue gas treatment chamber at the feed end of the rotary kiln, thereby reducing the number of production equipment and shortening the flue gas production process.

[0023] 2. In the dust removal of high-temperature flue gas discharged from rotary kiln, the present invention adopts a method combining airflow disturbance and gravity dust removal, which can remove the ash in the flue gas as cleanly as possible and make the clean flue gas burn in the combustible component treatment chamber, thereby preventing the dust in the flue gas from melting and adhering to the inner wall of the flue gas treatment chamber, so as to ensure the continuous and stable operation of the production line.

[0024] 3. The present invention has multiple air outlets arranged vertically in the combustible component treatment chamber of the rotary kiln, which can enable the combustible components in the flue gas to be combusted in layers, thus achieving the emission of flue gas in compliance with standards. Attached Figure Description

[0025] Figure 1 Diagram of the existing direct reduction rotary kiln flue gas treatment system;

[0026] Figure 2 This is a diagram of the direct reduction rotary kiln flue gas treatment system of the present invention;

[0027] In the diagram: 1-Flue gas treatment chamber, 101-Gravity settling chamber, 102-Combustible component treatment chamber;

[0028] 2-Feeding pipe, 3-Exhaust main pipe, 4-Air supply system, 41-Blower, 42-Air main pipe, 43-Air distribution pipe, 44-Regulating valve, 45-Air ejection pipe. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0030] like Figure 2 As shown, a direct reduction rotary kiln flue gas treatment process is described, wherein a vertical flue gas treatment chamber 1 is connected to the feed end of the rotary kiln, and the feed end of the rotary kiln is flexibly sealed to the side wall of the flue gas treatment chamber 1. The cross-section of the flue gas treatment chamber 1 is more than three times the cross-sectional area of ​​the kiln tail hood of the rotary kiln. The feed pipe 2 of the rotary kiln is vertically inserted downward from the top of the flue gas treatment chamber 1 and then inserted into the rotary kiln.

[0031] The flue gas treatment chamber 1 is equipped with an ash discharge port at the bottom and a main exhaust pipe 3 at the top; the lower part of the flue gas treatment chamber 1 is a gravity settling chamber 101 and the upper part is a combustible component treatment chamber 102. The gravity settling chamber 101 is used to settle particulate matter in the flue gas, and the combustible component treatment chamber 102 is used to burn combustible components in the flue gas; a gas supply system 4 is installed in the combustible component treatment chamber 102. The gas supply system 4 includes a blower 41, an air main duct 42, an air distribution duct 43, and an air ejector duct 45. The blower 41 is located outside the flue gas treatment chamber 1. The outlet of the blower 41 is connected to one end of the air main duct 42, and the other end of the air main duct 42 is connected to the middle of the air distribution duct 43. The air distribution duct 43 is installed vertically, and air ejector ducts 45 are evenly installed along the length of the air distribution duct 43. The air ejector duct 45 is horizontally inserted into the combustible component treatment chamber 102, and the air ejector outlet is located in the middle of the combustible component treatment chamber 102. A regulating valve 44 is installed on the air ejector duct 45, and an air ejector outlet is provided at the other end of the air ejector duct 45, which can blow air evenly into the combustible component treatment chamber 102 in a circumferential direction.

[0032] 1) The flue gas treatment system of the rotary kiln for direct reduction of iron ore mainly consists of an air supply system, a flue gas treatment chamber 1, a feeding system, and a main flue gas pipe. The air supply system consists of a blower 41, a main air pipe 42, an air distribution pipe 43, a regulating valve 44, an air ejector pipe 45, and an air ejector outlet; the flue gas treatment chamber 1 consists of a gravity settling chamber 101, a combustible component treatment chamber 102, a sealing device, a flue gas outlet, an ash discharge outlet, and an ash collection point; the feeding system consists of a feeding port, a feeding pipe 2, and refractory materials.

[0033] 2) The 500-600℃ flue gas discharged from the feed end of the rotary kiln first enters the gravity settling chamber 101 of the flue gas treatment chamber 1. The flue gas changes from horizontal to upward flow. During this change in flow direction, coarse dust particles are separated from the flue gas under the influence of inertia and gravity and deposited at the bottom of the flue gas treatment chamber 1. The flue gas, after coarse dust removal, continues to flow upward within the flue gas treatment chamber 1. Fine dust particles continue to separate from the flue gas under gravity and also deposit at the bottom of the flue gas treatment chamber 1. When the flue gas flows to the combustible component treatment chamber 102, it mixes with and combusts with air ejected from the air outlet, raising the flue gas temperature to 900-1000℃. The high-temperature flue gas is finally discharged from the top of the flue gas treatment chamber 1.

[0034] 3) In the flue gas treatment chamber 1, the cross-sectional area of ​​the flue gas flow is more than 3 times larger than that of the existing kiln tail hood. This can reduce the flow velocity of the flue gas in the flue gas treatment chamber 1 and prolong the flow time of the flue gas in the flue gas treatment chamber 1.

[0035] 4) A blower 41 is installed outside the flue gas treatment chamber 1. The outlet of the blower 41 is connected to one end of the air main pipe 42, and the other end of the air main pipe 42 is connected to the middle of the air distribution pipe 43. The air distribution pipe 43 is installed vertically, and air jet pipes 45 are evenly installed along the length of the air distribution pipe 43. A regulating valve 44 is installed on the air jet pipe 45, and an air outlet is provided at the other end of the air jet pipe 45. The air outlet is located in the middle of the flue gas treatment chamber 1, which can blow air evenly into the combustible component treatment chamber 102 in a circumferential direction.

[0036] 5) In the flue gas treatment chamber 1, the feeding port is set at the top of the flue gas treatment chamber 1, and the lower part of the feeding port is connected to the upper end of the feeding pipe 2. The lower end of the feeding pipe 2 is located at the bottom of the kiln tail in the rotary kiln. In the part of the feeding pipe 2 located in the kiln, a refractory castable with a thickness of 40mm is provided on the outside of the pipe wall of the feeding pipe 2.

[0037] 6) Ten air nozzles are installed in the combustible component treatment chamber 102. Each air nozzle is installed vertically. During the upward flow of flue gas, the combustible components in the flue gas can be evenly mixed with the air, so that the combustible components in the flue gas can be completely burned.

[0038] 7) An ash collection bin is provided at the bottom of the flue gas treatment chamber 1. The ash that settles from the high-temperature flue gas falls into the ash collection bin for temporary storage. The ash in the ash collection bin is discharged periodically through the ash discharge port provided at the bottom.

[0039] 8) The portion of the air ejector pipe 45 located inside the flue gas treatment chamber 1 shall have a 50mm layer of refractory castable on its outer wall.

[0040] Comparison of the effects of this invention with traditional solutions:

[0041] 1. The effect of CO treatment in flue gas

[0042] In a traditional rotary kiln for direct reduction of iron ore, air blown in by a blower 41 enters the air distribution pipe 43 through the air main 42 in the secondary combustion chamber. The air is then injected into the secondary combustion chamber according to process requirements via the air distribution pipe 43 and regulating valve 44. During the horizontal jet flow of the air injected into the secondary combustion chamber, it mixes with the high-temperature flue gas flowing upwards. Due to the poor mixing conditions between the combustible components in the flue gas and the air, coupled with the flue gas temperature of only 500-600℃, the combustible components in the flue gas are difficult to completely burn at this low temperature. As a result, the CO content in the flue gas discharged from the secondary combustion chamber is as high as 1-3%, failing to meet emission standards.

[0043] Example of traditional rotary kiln implementation: A large-scale direct reduction rotary kiln for iron ore in China has a secondary combustion chamber at the kiln tail. The CO content in the flue gas discharged from the secondary combustion chamber is as high as 2.5%.

[0044] In this scheme, the 500-600℃ flue gas discharged from the feed end of the rotary kiln mixes and combusts with the air ejected from the air outlet when it flows into the combustible component treatment chamber 102, raising the flue gas temperature to 900-1000℃. The high-temperature flue gas is finally discharged from the top of the flue gas treatment chamber 1. To improve the dust removal effect of the flue gas in the flue gas treatment chamber 1, a flue gas treatment chamber 1 with a cross-sectional area more than three times larger than the cross-sectional area of ​​the kiln tail hood is used. This can effectively reduce the flow velocity of the flue gas in the flue gas treatment chamber 1 and prolong the flow time of the flue gas in the flue gas treatment chamber 1.

[0045] In this invention, a blower 41 is installed outside the flue gas treatment chamber 1. The outlet of the blower 41 is connected to one end of the air main pipe 42, and the other end of the air main pipe 42 is connected to the middle of the air distribution pipe 43. The air distribution pipe 43 is installed vertically, and air jet pipes 45 are evenly installed along the length of the air distribution pipe 43. A regulating valve 44 is installed on the air jet pipe 45, and an air outlet is provided at the other end of the air jet pipe 45. The air outlet is located in the middle of the flue gas treatment chamber 1, which can blow air evenly into the combustible component treatment chamber 102 in a circumferential direction.

[0046] The present invention aims to clean the combustible components in flue gas. It provides 8-12 air nozzles in the combustible component treatment chamber 102, with each air nozzle installed vertically. As the flue gas flows from bottom to top, the combustible components in the flue gas can be evenly mixed with the air, so that the combustible components in the flue gas can be completely burned, achieving the standard emission of the flue gas.

[0047] Example of this invention: In a large-scale iron ore direct reduction rotary kiln in China, after implementing this method, the CO content in the flue gas was reduced to below 1%.

[0048] 2. Dust treatment effect in flue gas

[0049] In traditional rotary kilns for direct reduction of iron ore, the high-temperature flue gas discharged from the feed end of the rotary kiln first enters the kiln tail hood. Most of the coarse dust particles in the flue gas are removed by gravity. The flue gas, after coarse dust removal, then enters the secondary combustion chamber through the exhaust pipe. Inside the kiln tail hood, the flue gas flows horizontally. Because the flue gas and dust flow in the same direction, the flue gas velocity does not change much, resulting in low dust removal efficiency. Most dust particles are carried into the secondary combustion chamber by the high-temperature flue gas. Under the action of combustion air, the combustible components in the flue gas burn. Dust particles easily generate a low-melting-point liquid phase. The molten liquid phase adheres to the inner wall of the secondary combustion chamber, affecting the long-term stable operation of the rotary kiln.

[0050] Traditional rotary kiln example: The dust content in the flue gas discharged from the rotary kiln is as high as 20-25 g / Nm³, and the dust content in the flue gas discharged from the secondary combustion chamber is as high as 3-5 g / Nm³.

[0051] In this invention, a vertical flue gas treatment chamber 1 is connected to the feed end of the rotary kiln, and the cross-section of the flue gas treatment chamber 1 is more than three times the cross-sectional area of ​​the kiln tail hood of the rotary kiln.

[0052] In this invention, the flue gas discharged from the feed end of the rotary kiln first enters the gravity settling chamber 101 of the flue gas treatment chamber 1. The flue gas changes from horizontal flow to upward flow. During this change in flow direction, the coarse dust particles contained within the flue gas separate from it under the action of inertia and gravity, and deposit at the bottom of the flue gas treatment chamber 1. The flue gas, after coarse dust removal, continues to flow upward within the flue gas treatment chamber 1, and the fine dust particles contained within it continue to separate from the flue gas under the action of gravity, also depositing at the bottom of the flue gas treatment chamber 1.

[0053] To improve the dust removal effect of flue gas in the flue gas treatment chamber 1, this invention adopts a flue gas treatment chamber 1 with a cross-sectional area of ​​flue gas flow that is more than three times larger than the cross-sectional area of ​​the kiln tail hood. This can effectively reduce the flow velocity of flue gas in the flue gas treatment chamber 1 and extend the flow time of flue gas in the flue gas treatment chamber 1.

[0054] In this embodiment of the invention, the dust content in the flue gas discharged from the rotary kiln is as high as 20-25 g / Nm³, and the dust content in the flue gas discharged from the secondary combustion chamber is as high as less than 2 g / Nm³.

Claims

1. A direct reduction rotary kiln flue gas treatment process, characterized in that, The rotary kiln has a vertical flue gas treatment chamber (1) connected to its feed end. The feed end of the rotary kiln is flexibly sealed to the side wall of the flue gas treatment chamber (1). The cross-section of the flue gas treatment chamber (1) is more than three times the cross-sectional area of ​​the rotary kiln tail hood. The feed pipe (2) of the rotary kiln is vertically inserted into the top of the flue gas treatment chamber (1) and into the rotary kiln. The flue gas treatment chamber (1) is equipped with an ash discharge port at the bottom and a main exhaust pipe (3) at the top; the lower part of the flue gas treatment chamber (1) is a gravity settling chamber (101) and the upper part is a combustible component treatment chamber (102). The gravity settling chamber (101) is used to settle particulate matter in the flue gas, and the combustible component treatment chamber (102) is used to burn combustible components in the flue gas; a gas supply system (4) is installed in the combustible component treatment chamber (102). The rotary kiln flue gas treatment process is as follows: In the direct reduction rotary kiln for iron ore, the 500-600℃ flue gas discharged from the feed end of the rotary kiln first enters the gravity settling chamber (101). During the change of the flow direction of the flue gas, the coarse dust particles contained in the flue gas are separated from the flue gas and settle downwards. After coarse dust removal, the flue gas continues to flow from bottom to top in the gravity settling chamber (101). The fine dust particles contained in the flue gas continue to be separated from the flue gas and settle downwards under the action of gravity. When the flue gas flows upwards to the combustible component treatment chamber (102), the flue gas mixes with the air sprayed from the air supply system (4) and burns, so that the combustible components in the flue gas are fully burned. The exhaust gas after combustion meets the emission standards and is discharged through the exhaust manifold (3). The air supply system (4) includes a blower (41), an air main pipe (42), an air distribution pipe (43), and an air ejection pipe (45). A blower (41) is located outside the flue gas treatment chamber (1). The outlet of the blower (41) is connected to one end of the air main pipe (42), and the other end of the air main pipe (42) is connected to the middle of the air distribution pipe (43). The air distribution pipe (43) is installed vertically, and air jet pipes (45) are evenly installed along the length of the air distribution pipe (43). The air jet pipes (45) are horizontally inserted into the combustible component treatment chamber (102), and the air jet outlet is located in the middle of the combustible component treatment chamber (102). A regulating valve (44) is installed on the air jet pipe (45), and an air jet outlet is provided at the other end of the air jet pipe (45), which can blow air evenly into the combustible component treatment chamber (102) along the circumferential direction.

2. The direct reduction rotary kiln flue gas treatment process according to claim 1, characterized in that, The feeding port of the feeding pipe (2) is located at the top of the flue gas treatment chamber (1), and the lower part of the feeding port is connected to the upper end of the feeding pipe (2). The lower end of the feeding pipe (2) is located at the bottom of the kiln tail inside the rotary kiln. The part of the feeding pipe (2) located inside the kiln is provided with a refractory castable with a thickness of 30-50mm on the outside of the pipe wall.

3. The direct reduction rotary kiln flue gas treatment process according to claim 1, characterized in that, The combustible component treatment chamber (102) is equipped with 8-12 air nozzles. Each air nozzle is installed vertically. During the upward flow of flue gas, the combustible components in the flue gas can be fully and evenly mixed with the air, so that the combustible components in the flue gas can be fully combusted.

4. The direct reduction rotary kiln flue gas treatment process according to claim 1, characterized in that, The portion of the air ejector pipe (45) located inside the flue gas treatment chamber (1) has a 30-50mm layer of refractory castable on its outer wall.

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