Method for efficiently utilizing tail gas of powder metallurgy fine reduction furnace

Abstract

The invention relates to a method for efficiently utilizing tail gas of a powder metallurgy fine reduction furnace, which comprises the following steps: collecting reduction tail gas: inserting the end part of a collecting pipe into a tail gas outlet of the reduction furnace, and storing the reduction tail gas in a gas storage cabinet after passing through a cooler and a dust remover under the action of an induced draft fan on the collecting pipe; waste steel is preheated through the reduction tail gas, wherein when the waste steel needs to be preheated, the reduction tail gas in the gas storage cabinet is supplied to a waste steel preheating device through a tail gas output pipe for combustion preheating; separation of the reduction tail gas: purifying hydrogen and carbon monoxide in the reduction tail gas in the gas storage cabinet through a gas purification system; returning to the reduction furnace for gas supply; according to the method, energy waste caused by direct combustion and emission of tail gas is avoided, the influence of iron-containing dust on the environment is reduced, the unit energy purchasing cost is reduced, and the energy utilization rate is increased. The method plays an important role in resource recycling, energy conservation, efficiency improvement and production cost reduction of a powder metallurgy plant.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy technology, specifically to a method for the efficient utilization of tail gas from a powder metallurgy refining furnace. Background Technology

[0002] In the iron powder production process of powder metallurgy, intermediate products need to be refined and reduced to obtain qualified iron powder products. This refinement and reduction is generally carried out in a belt reduction furnace, using hydrogen as the reducing gas. Hydrogen is typically produced by the decomposition of ammonia (H2 + N2 mixture) or by conversion to natural gas (H2 + CO mixture). In the ammonia decomposition reduction system, the tail gas from the refinement and reduction mainly consists of H2, N2, a small amount of water vapor, a small amount of iron powder dust, and trace amounts of acidic gases such as H2S and PH3. In the natural gas conversion and reduction system, the tail gas from the refinement and reduction mainly consists of H2, CH4, CO, CO2, a small amount of water vapor, a small amount of iron powder dust, and trace amounts of acidic gases such as H2S and PH3. Currently, the process for treating the tail gas from the refinement and reduction is to directly burn it, which is undoubtedly a huge waste of energy.

[0003] Therefore, it is necessary to develop a method for the efficient utilization of tail gas from the reduction of iron powder in powder metallurgy. This is of great significance for reducing production costs and promoting the development of a circular economy in iron powder powder plants. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a method for the efficient utilization of tail gas from powder metallurgy refining furnaces.

[0005] This invention is achieved through the following technical solution, providing a method for efficient utilization of tail gas from a powder metallurgy refining furnace, comprising the following steps: a. Reduction tail gas collection: Insert the end of the collection pipe into the tail gas outlet of the reduction furnace. Through the action of the induced draft fan on the collection pipe, the reduction tail gas passes through the cooler and dust collector and is stored in the gas storage tank. b. Preheating scrap steel with reducing tail gas: When scrap steel needs to be preheated, the reducing tail gas in the gas storage tank is supplied to the scrap steel preheating device for combustion preheating through the tail gas output pipe. c. Reduction tail gas separation: The reduction tail gas in the gas storage tank is purified by the gas purification system to remove internal hydrogen and / or carbon monoxide. d. Return the gas to the reduction furnace; the purified hydrogen and / or carbon monoxide are returned to the reduction furnace gas supply system for recycling.

[0006] As an optimization, the scrap steel preheating device uses a mixture of reducing tail gas and converter gas for combustion to preheat the scrap steel.

[0007] As an optimization, the dust collector is a pulse-jet bag filter with PTFE membrane filter media, a filtration accuracy of ≤1µm, and an outlet dust content of ≤10mg / m³.3 .

[0008] As an optimization, the gas purification system is a membrane separation device and / or a pressure swing adsorption separation device.

[0009] As an optimization, the operating pressure of the membrane separation device is 1.0-2.5 MPa, the membrane material is selected as polyimide or polysulfone hollow fiber membrane, the working temperature is 30-60℃, and the purity of the purified hydrogen is above 95%.

[0010] As an optimization, the operating pressure of the pressure swing adsorption separation device is 0.8-3.0 MPa, the vacuum desorption pressure is 0.02-0.1 MPa, the adsorbent is zeolite molecular sieve, the operating temperature is 20-40℃, and the purity of hydrogen + carbon monoxide after purification is above 95%.

[0011] As an optimization, a heat exchanger is installed on the exhaust gas output pipe. The heat exchanger includes a housing wrapped around the exhaust gas output pipe. An end pipe is connected to the end of the collection pipe. The end pipe is a double-layered hollow pipe, and the two sides of the double-layered hollow cavity are respectively connected to a third water pipe and a second water pipe. The second water pipe is connected to the coolant outlet of the cooler, the third water pipe is connected to one end of the housing, and the other end of the housing is connected to the coolant inlet of the cooler through a first water pipe.

[0012] As an optimization, multiple inner and outer finned tubes are fixedly connected inside the box, the finned tubes are coaxial with the exhaust gas output pipe, and multiple heat-conducting rods are connected between the finned tubes and the exhaust gas output pipe.

[0013] As an optimization, the spacing between adjacent finned tubes gradually decreases along the flow direction of the exhaust gas output pipe, and the third water pipe and the first water pipe are connected at both ends of the box along the flow direction of the exhaust gas output pipe.

[0014] As an optimization, multiple heat-conducting rods are arranged along the length of the exhaust gas output pipe.

[0015] The beneficial effects of this invention are as follows: This invention provides a method for the efficient utilization of tail gas from a powder metallurgy reduction furnace. By collecting, cooling, removing dust, and pressurizing the tail gas, it can be used to preheat scrap steel or, after further purification, returned to the reduction gas supply system of the reduction furnace for recycling. This ensures that all combustible components of the tail gas are fully utilized and iron-containing dust is recovered. This avoids energy waste caused by direct combustion and emission of tail gas, reduces the environmental impact of iron-containing dust, and lowers the unit energy procurement cost. It plays an important role in resource recycling, energy saving and efficiency improvement, and cost reduction in powder metallurgy plants. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is an internal sectional view of the heat exchanger box of the present invention; Figure 3 For the present invention Figure 2 Sectional view of plane AA; Figure 4 This is an internal sectional view of the end tube of the present invention; As shown in the figure: 1. Gas storage tank; 2. Collection pipe; 3. End pipe; 4. Heat exchange box; 41. Box body; 42. Finned tube; 43. Heat transfer rod; 5. Exhaust gas output pipe; 6. Cooling water pump; 7. Cooler; 8. Dust collector; 9. Exhaust fan; 10. First water pipe; 11. Second water pipe; 12. Third water pipe; 13. Gas purification system. Detailed Implementation

[0017] To clearly illustrate the technical features of this solution, the following detailed implementation method will be used to explain the solution.

[0018] like Figures 1-4 As shown, the present invention provides a method for efficient utilization of tail gas from a powder metallurgy refining furnace, comprising the following steps: a. Collection of reduction tail gas: Insert the end of the collection pipe 2 into the tail gas outlet of the reduction furnace. Through the action of the induced draft fan 9 on the collection pipe 2, the reduction tail gas passes through the cooler 7 and the dust collector 8 and is stored in the gas storage tank 1.

[0019] The collecting pipe 2 is made of ordinary carbon steel with a diameter of 5cm-20cm. Since the end of the collecting pipe 2 is inserted into the tail gas outlet of the reduction furnace, there is an open flame and the temperature is high at this location. In order to prevent the collecting pipe 2 from deforming or being damaged at high temperature, and at the same time to achieve a certain amount of heat collection, in this embodiment, an end pipe 3 is connected to the end of the collecting pipe 2. The inner diameter of the end pipe 3 is larger than the inner diameter of the collecting pipe 2, and the end pipe 3 is a flat pipe to adapt to the flat shape of the tail gas outlet of the reduction furnace.

[0020] like Figure 4 As shown, in order to facilitate the cooling of the end tube 3, the end tube 3 in this embodiment is a double-layer hollow tube. Therefore, there is an annular double-layer hollow cavity between the inner and outer layers, which can be circulated with coolant.

[0021] The induced draft fan 9 ensures a stable atmosphere and production within the reduction furnace, and also facilitates the unobstructed delivery of the refined reduction tail gas to the gas storage tank. In this embodiment, the induced draft fan 9 is a variable frequency Roots blower with a frequency range of 30%-100%.

[0022] The cooler is a shell-and-tube type, with circulating water as the cooling material. It can cool the reduction exhaust gas to below 40°C, thereby preventing aging of the gas tank seals or degradation of the membrane material.

[0023] The dust collector 8 is a pulse-jet bag filter, with PTFE membrane filter bags, a filtration accuracy of ≤1µm, and an outlet dust content of ≤10mg / m³. 3 .

[0024] Gas storage tank 1 is a dual-mode gas storage tank with a volume of 1000m³. 3 -10000m 3 The working pressure is 1kPa-10kPa, and the membrane material is selected as butyl rubber composite membrane or PVDF membrane that is resistant to H2 permeation.

[0025] b. Preheating scrap steel with reduction tail gas: When scrap steel needs to be preheated, the reduction tail gas in the gas storage tank 1 is supplied to the scrap steel preheating device for combustion preheating through the tail gas output pipe 5. Since hydrogen has a low density, it floats to the upper layer of the gas storage tank 1. Therefore, the tail gas output pipe 5 is set at the upper end of the gas storage tank 1, so that the gas with a higher hydrogen concentration in the upper layer can be transported to the scrap steel preheating device. The scrap steel preheating device uses the mixed combustion of reduction tail gas and hydrogen to achieve scrap steel preheating.

[0026] In this embodiment, the gas in the exhaust gas outlet pipe 5 is preheated by the coolant flowing through the cooler 7 and the end pipe 3, thereby improving the preheating effect of the subsequent scrap steel. At the same time, it can also realize the utilization of heat and cool the coolant. Therefore, a heat exchanger 4 is installed on the exhaust gas outlet pipe 5.

[0027] like Figure 2 As shown, the heat exchanger 4 includes a housing 41 wrapped around the exhaust gas outlet pipe 5. The housing 41 is a cylindrical strip and is coaxially arranged with the exhaust gas outlet pipe 5. The length of the housing 41 is generally set between 2 meters and 5 meters to improve the heat exchange effect.

[0028] The two sides of the double-layer hollow cavity of the end pipe 3 are respectively connected to the third water pipe 12 and the second water pipe 11. The second water pipe 11 is connected to the coolant outlet of the cooler 7, the third water pipe 12 is connected to one end of the box 41, and the other end of the box 41 is connected to the coolant inlet of the cooler 7 through the first water pipe 10.

[0029] The first water pipe 10 is equipped with a cooling water pump 6. Therefore, after the coolant flows through the cooler 7 to cool the reduction exhaust gas, it flows through the end pipe 3, where the temperature is the highest. Then it flows through the box 41 to preheat the gas in the exhaust gas output pipe 5, at which point the coolant temperature decreases.

[0030] To improve heat exchange efficiency, such as Figure 2 , 3 As shown, multiple inner and outer finned tubes 42 are fixedly connected inside the housing 41. The finned tubes 42 are coaxial with the exhaust gas output pipe 5. In this embodiment, six finned tubes 42 are provided, and the thickness of the finned tubes 42 is between 0.5-1.5mm.

[0031] Multiple heat-conducting rods 43 are connected between the finned tube 42 and the exhaust gas output pipe 5. Multiple heat-conducting rods 43 are arranged along the length of the exhaust gas output pipe 5 and multiple are also arranged circumferentially. On the one hand, they are used to support the finned tube 42, and on the other hand, they are used to transfer heat to the exhaust gas output pipe 5.

[0032] The spacing between adjacent finned tubes 42 gradually decreases along the flow direction of the exhaust gas output pipe 5. The third water pipe 12 and the first water pipe 10 are connected to both ends of the housing 41 along the flow direction of the exhaust gas output pipe 5. Furthermore, the outermost finned tube 42 has the largest outer diameter and is attached to the inner wall of the housing 41.

[0033] When the coolant temperature is highest, it flows through the position where the spacing between adjacent finned tubes 42 is smallest. At this point, the heat-conducting rod 43 is shortest, so the hottest coolant is closest to the inner wall of the exhaust gas outlet pipe 5, and the flow velocity is also fastest. The coolant then flows in the opposite direction to the flow direction inside the exhaust gas outlet pipe 5, thus flowing between adjacent finned tubes 42. At this point, the spacing between adjacent finned tubes 42 increases, the coolant temperature decreases, but the flow velocity slows down, achieving a better heat exchange effect. This avoids the problem of incomplete heat exchange caused by uniform flow velocity in some heat exchangers.

[0034] c. Separation of reduction tail gas: The atomization of iron powder in powder metallurgy plants is a non-continuous process, and the heating of scrap steel is also non-continuous. In order to make full use of the excess reduction tail gas, the tail gas output pipe 5 is closed at this time, and the internal hydrogen and / or carbon monoxide are purified by the gas purification system 13. The gas purification system 13 is connected to the lower end of the gas storage tank 1, and the part with the least hydrogen content at the bottom is purified, thereby increasing the hydrogen content in the upper part.

[0035] The gas purification system 13 is a membrane separation device and / or a pressure swing adsorption separation device.

[0036] The membrane separation device operates at a pressure of 1.0-2.5 MPa, uses polyimide or polysulfone hollow fiber membrane as the membrane material, operates at a temperature of 30-60℃, and the purified hydrogen has a purity of over 95%.

[0037] The pressure swing adsorption separation device operates at a pressure of 0.8-3.0 MPa, with a vacuum desorption pressure of 0.02-0.1 MPa. The adsorbent is zeolite molecular sieve, and the operating temperature is 20-40℃. After purification, the purity of hydrogen + carbon monoxide is above 95%.

[0038] d. Return the gas to the reduction furnace; the purified hydrogen and / or carbon monoxide are returned to the reduction furnace gas supply system for recycling.

[0039] Taking a powder metallurgy plant with an annual output of 40,000 tons of atomized iron powder and 60,000 tons of reduced iron powder as an example, preheating 1 ton of scrap steel to 250°C can save approximately 8-12 yuan in electricity / fuel costs for steelmaking. Assuming that 50% of the preheating of scrap steel is done using reduction tail gas instead of purchased heat sources, the plant can process 20,000 tons of scrap steel annually, saving 160,000-240,000 yuan in costs each year. Excess refined reduction tail gas can be purified to obtain 20,000-50,000 Nm³ of refined iron powder. 3 Based on an industrial natural gas price of 4 yuan / Nm3, this translates to annual cost savings of 80,000 to 400,000 yuan. The efficient use of exhaust gas from the reduction furnace also reduces the environmental impact of dust in the exhaust gas.

[0040] Of course, the above description is not limited to the examples above. Technical features not described in this invention can be implemented by or using existing technology, and will not be repeated here. The above embodiments and drawings are only used to illustrate the technical solutions of this invention and are not intended to limit this invention. This invention has been described in detail with reference to preferred embodiments. Those skilled in the art should understand that any changes, modifications, additions or substitutions made by those skilled in the art within the scope of this invention do not depart from the spirit of this invention and should also fall within the scope of protection of the claims of this invention.

Claims

1. A method for efficient utilization of a powder metallurgy fine reduction furnace tail gas, characterized in that, It comprises the following steps: a. Reducing tail gas collection: the end of the collection pipe (2) is inserted into the tail gas outlet of the reducing furnace, and the reducing tail gas is stored in the gas storage tank (1) after passing through the cooler (7) and the dust collector (8) by the action of the induced draft fan (9) on the collection pipe (2); b. Reducing tail gas preheating scrap steel: when the scrap steel needs to be preheated, the reducing tail gas in the gas storage tank (1) is supplied to the scrap steel preheating device through the tail gas output pipe (5) for combustion preheating; c. Reducing tail gas separation: the reducing tail gas in the gas storage tank (1) is purified by the gas purification system (13) to separate the hydrogen and / or carbon monoxide inside; d. Return to the reducing furnace gas supply; the purified hydrogen and / or carbon monoxide is returned to the reducing furnace gas supply system for recycling.

2. The method for efficient utilization of tail gas of a powder metallurgy fine reduction furnace according to claim 1, characterized in that: The scrap steel preheating device uses reducing tail gas and hydrogen mixed combustion to achieve scrap steel preheating.

3. The method for efficient utilization of tail gas of a powder metallurgy fine reduction furnace according to claim 1, characterized in that: The dust collector (8) is selected as a pulse bag type dust collector, the filter bag material is PTFE coated filter material, the filtering precision is less than or equal to 1 um, and the outlet dust content is less than or equal to 10 mg / m 3 .

4. The method for efficient utilization of tail gas of a powder metallurgy fine reduction furnace according to claim 1, characterized in that: The gas purification system (13) is a membrane separation device and / or a pressure swing adsorption separation device.

5. The method for efficient utilization of tail gas of a powder metallurgy fine reduction furnace according to claim 4, characterized in that: The operating pressure of the membrane separation device is 1.0-2.5 MPa, the membrane material is polyimide or polysulfone hollow fiber membrane, the working temperature is 30-60℃, and the purity of the purified hydrogen is more than 95%.

6. The method for efficient utilization of tail gas of a powder metallurgy fine reduction furnace according to claim 4, characterized in that: The operating pressure of the pressure swing adsorption separation device is 0.8-3.0 MPa, the vacuum desorption pressure is 0.02-0.1 MPa, the adsorbent is zeolite molecular sieve, the operating temperature is 20-40℃, and the purity of the purified hydrogen+carbon monoxide is more than 95%.

7. The method for efficient utilization of tail gas of a powder metallurgy fine reduction furnace according to claim 1, characterized in that: The tail gas output pipe (5) is provided with a heat exchanger (4), the heat exchanger (4) comprises a box (41) wrapped around the tail gas output pipe (5), the end of the collection pipe (2) is connected with an end pipe (3), the end pipe (3) is a double-layer hollow pipe and the two sides of the double-layer hollow cavity are respectively communicated with a third water pipe (12) and a second water pipe (11), the second water pipe (11) is communicated with the cooling liquid outlet of the cooler (7), the third water pipe (12) is communicated with one end of the box (41), and the other end of the box (41) is communicated with the cooling liquid inlet of the cooler (7) through a first water pipe (10).

8. The method for efficient utilization of tail gas of a powder metallurgy fine reduction furnace according to claim 7, characterized in that: A plurality of finned tubes (42) are fixedly connected in the box (41), the finned tubes (42) are coaxial with the tail gas output pipe (5), and a plurality of heat conduction rods (43) are connected between the finned tubes (42) and the tail gas output pipe (5).

9. The method for efficient utilization of tail gas of a powder metallurgy fine reduction furnace according to claim 8, characterized in that: The spacing between adjacent finned tubes (42) gradually decreases along the flow direction of the tail gas output pipe (5), and the third water pipe (12) and the first water pipe (10) are connected at both ends of the box (41) along the flow direction of the tail gas output pipe (5).

10. The method for efficient utilization of tail gas of a powder metallurgy fine reduction furnace according to claim 8, characterized in that: The heat conduction rods (43) are arranged in multiple along the length direction of the tail gas output pipe (5).

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