Flue gas waste heat utilization system and flue gas preheating magnesium nitrate raw material processing method and preheating air method

Abstract

The present invention belongs to the field of waste heat utilization of metallurgical solid waste, and particularly relates to a flue gas waste heat utilization system and a method for preheating raw materials and preheating air. The waste heat utilization system includes a regenerative hot blast furnace, a raw material heater, a jet tube, a chimney, a reversing valve, and an air preheater; the method for preheating magnesium nitrate raw materials includes the high-temperature flue gas generated by the regenerative chamber hot blast furnace being connected to the raw material heater through a reversing valve; the high-temperature flue gas entering the raw material heater is divided into two paths; the method for preheating combustion-supporting air includes the high-temperature flue gas generated by the regenerative hot blast furnace being connected to the air preheater through a reversing valve, the high-temperature flue gas is connected to the high-temperature flue gas inlet of the air preheater, and the combustion-supporting air is introduced into the regenerative hot blast furnace for fuel combustion. The present invention solves the technical problems existing in the prior art that the exhaust temperature is high, an external heat source is required, or the heat optimization is imperfect. The thermal efficiency of the hot blast furnace is improved, fuel is saved, and the heat is optimized and improved.

Description

Technical field:

[0001] The invention belongs to the field of waste heat utilization of metallurgical solid waste, and in particular relates to a flue gas waste heat utilization system and a method for preheating raw materials and preheating air. Background technology:

[0002] The research and technical transformation of the traditional laterite nickel ore pressure acid leaching process are completed in a sulfuric acid system. However, pressure acid leaching in a sulfuric acid system has the following disadvantages: leaching requires high temperature and high pressure (230℃~260℃, 4~5MPa); high requirements for equipment; high sulfuric acid consumption, which has become the main indicator restricting the economic efficiency of the process. The leached slag is difficult to be comprehensively utilized due to its high sulfur content, and sulfate is easy to scale and requires regular descaling. In view of the disadvantages of the traditional sulfuric acid leaching process, the nitric acid leaching process currently used has mild leaching conditions; the leaching agent can be recycled; and the scaling problem is avoided. The calcium and magnesium content in laterite nickel ore is relatively high, and the leaching process will lead to an increase in the consumption of nitric acid. If the reaction solution is not recycled, it will lead to increased costs, and the nitrate concentration in the residual waste liquid of the leaching reaction is relatively high, which poses a risk of environmental damage. If it is directly discharged and resources are wasted, it is not conducive to environmental protection.

[0003] At present, the method of comprehensive treatment of laterite nickel ore using nitric acid medium can effectively separate Ni and Co. At the same time, whether the byproduct magnesium nitrate can be effectively utilized has become a bottleneck of the metallurgical process of the nitric acid system. In view of the comprehensive utilization of magnesium nitrate, people have been studying the pyrolysis technology of magnesium nitrate in recent years. As for the prior art: the spray pyrolysis method has solved the technical problems such as uneven heating of magnesium nitrate in the furnace, incomplete decomposition, and corrosion in the furnace in the rotary kiln. The spray pyrolysis method has also been widely used. However, in the pyrolysis process of magnesium nitrate in recent years, it only stays on the simple idea of ​​separating the decomposed gas from the generated oxide. In order to realize the reuse of nitric acid in the decomposition process of magnesium nitrate, there are certain requirements for the concentration of nitrogen dioxide produced by the decomposition of magnesium nitrate. The clean reuse of the decomposed gas has become the key to whether the magnesium nitrate pyrolysis system can be operated continuously in industrialization.

[0004] In recent years, a system using regenerative cycle heating for magnesium nitrate atomization pyrolysis has been developed with patent number CN 110342497 A. The main feature of this technology is that according to the system acid production process requirements for nitrogen dioxide concentration in the treatment gas and the magnesium nitrate atomization characteristics, a regenerative hot blast furnace heating method is adopted. The hot blast furnace heating gas is the material decomposition gas, and no combustion gas or other gas is mixed in, so the nitrogen dioxide gas concentration is improved. The acid production cost is reduced and the equipment investment is reduced. The gas heated by the regenerative hot blast furnace is the material decomposition gas, which has a high temperature and can be recycled. Although the regenerative heating furnace is adopted, it is well achieved that there is no mixing of other gases in the pyrolysis furnace, and the decomposition gas is recycled. However, there are problems such as high flue gas temperature at the outlet of the regenerative heating furnace; the heating method of the raw material (magnesium nitrate atomization) also requires an external heat source; the heat optimization has not been improved, resulting in a huge waste of waste heat resources.

[0005] The magnesium nitrate pyrolysis method provided by the existing patent has the following problems:

[0006] (1) The flue gas temperature at the outlet of the regenerative hot blast furnace reaches 400°C, and the exhaust gas temperature is too high;

[0007] (2) The raw material heating method (magnesium nitrate atomization) uses an external heat source;

[0008] (3) The combustion air temperature at the regenerative furnace inlet is low and the heat optimization is imperfect;

[0009] (4) A large amount of nitrogen oxides will be generated in the system, and there is no necessary denitrification process.

[0010] Therefore, it is currently hoped that a pyrolysis system can be developed to at least solve the above problem. Summary of the invention:

[0011] Purpose of the invention:

[0012] The present invention aims to provide a flue gas waste heat utilization system and a method for preheating raw materials and preheating air to solve the technical problems existing in the prior art such as high exhaust temperature, the need for an external heat source or imperfect heat optimization.

[0013] Technical solution:

[0014] A flue gas waste heat utilization system, wherein a regenerative hot blast furnace is connected to a raw material heater through an outlet at one end of a reversing valve, and the raw material heater is connected to a jet pipe and a chimney in sequence; the outlet at the other end of the reversing valve is connected to an air preheater; the flue gas outlet of the air preheater is connected to the jet pipe; the internal circulation and external circulation inlets and outlets of the raw material heater are respectively connected to the reversing valve and the jet pipe.

[0015] Furthermore, the external circulation of the raw material heater is provided with an external jacket, and the spiral external jacket is vertically welded to the outer wall of the raw material storage tank in the axial direction of the tank body, and the high-temperature flue gas in the external jacket is introduced from the bottom and discharged from the top; a thermal insulation structure is added to the outside of the external jacket; the internal circulation of the raw material heater is provided with an inner jacket, and the spiral internal jacket is arranged parallel to the axial direction of the tank body; the high-temperature flue gas in the inner jacket is introduced from the top and discharged from the bottom; the raw material storage tank is a hollow cylindrical tank body; a raw material inlet and a raw material outlet are provided at the upper end of the hollow cylindrical tank body, and a stirring paddle is provided inside the tank body; the stirring paddle is connected to an externally arranged motor; the raw material outlet is connected to a raw material transport pump; the raw material inlet of the raw material storage tank is connected to the raw material magnesium nitrate inlet, and the raw material outlet of the raw material storage tank is connected to the molten magnesium nitrate outlet pipe.

[0016] Furthermore, the jet pipe is a pipe that first contracts and then diffuses. The jet pipe is composed of an inlet contraction section, a throat, and an outlet diffusion section. A spray pipe bundle is vertically welded directly above the central axis of the throat, and a drain valve is welded vertically directly below the central axis of the throat. The horizontal direction of the jet pipe is the flue gas inlet, and the vertical direction of the jet pipe is provided with an ammonia inlet for introducing flue gas denitrification.

[0017] Furthermore, the inlet contraction section of the jet tube is a conical tube with a cone angle of 21±2°, the cone angle of the conical outlet diffusion section is 8-15°, the diameter of the throat is 0.3 to 0.75 times the maximum tube diameter of the inlet contraction section, the length of the inlet contraction section is 1 to 1.5 times the maximum tube diameter of the inlet contraction section, the length of the outlet diffusion section is 1.5 times the length of the inlet contraction section, and the diameter of the ammonia port is 1 / 3 to 1 / 4 of the maximum tube diameter of the inlet contraction section.

[0018] A method for preheating magnesium nitrate raw materials with flue gas waste heat, wherein the high-temperature flue gas generated by a hot blast furnace in a heat storage chamber is connected to a raw material heater through a reversing valve; the high-temperature flue gas entering the raw material heater through the reversing valve is divided into two paths: in a first path, the high-temperature flue gas is sent to the high-temperature flue gas inlet of an outer pipe of an outer jacket of the raw material heater through a high-temperature flue gas branch pipe, and flows through a spiral tube bundle welded to the outer wall of a raw material storage tank; in a second path, the high-temperature flue gas flows in a direction opposite to that of the flue gas in the first path through a heat exchange tube bundle of an inner jacket arranged in the raw material heater; the high-temperature flue gas is connected to the high-temperature flue gas inlet of an inner pipe of the inner jacket through a high-temperature flue gas branch pipe, and the high-temperature flue gas exchanges heat with the magnesium nitrate raw material in the raw material storage tank through the inner jacket and the outer jacket, and a stirring paddle in the raw material storage tank is used to further evenly exchange the heat of the magnesium nitrate, thereby obtaining molten magnesium nitrate.

[0019] Furthermore, the high-temperature flue gas is generated by the combustion of natural gas, and the high-temperature flue gas generated is 400-500°C; the high-temperature flue gas generated by the regenerative hot blast furnace heats the magnesium nitrate of the raw material heater to 130-150°C.

[0020] A method for preheating combustion air with flue gas waste heat, wherein the high-temperature flue gas generated by a regenerative hot blast furnace is connected to an air preheater through a reversing valve, and the high-temperature flue gas is connected to a high-temperature flue gas inlet of an external pipeline of the air preheater to preheat the combustion air, and the preheated combustion air is introduced into the regenerative hot blast furnace through a post-preheating combustion air pipeline for combustion of fuel.

[0021] Furthermore, the combustion air inlet temperature of the air inlet pipeline of the air preheater is 25-30°C, and the combustion air outlet temperature after being heated by the air preheater is maintained at 100-150°C and is passed into the regenerative hot air furnace.

[0022] Furthermore, the flue gas generated after preheating the magnesium nitrate raw material and the air includes a process of flue gas tail denitrification. The exhaust gas generated by preheating the air and heating the magnesium nitrate raw material enters the jet tube through the exhaust gas outlet pipe. The exhaust gas flows horizontally into the jet tube and passes through the inlet contraction section. Due to the change in the cross-sectional area of ​​the jet tube, the flow velocity of the exhaust gas gradually increases, and the local pressure at the throat is reduced, so that the ammonia in the vertical direction of the jet tube is sucked into the throat of the jet tube. The exhaust gas in the jet tube is denitrified by the spray tube bundle arranged above the jet tube. After denitrification, it flows through the outlet diffusion section and is discharged into the atmosphere through the chimney.

[0023] Furthermore, the exhaust gas from the jet tube denitrification is discharged into the atmosphere at a temperature of 160-200°C.

[0024] Advantages and effects:

[0025] The present invention has the following advantages and beneficial effects:

[0026] (1) The present invention provides a flue gas waste heat utilization system, which includes a regenerative hot blast furnace, a raw material heater, a jet tube, a chimney, a reversing valve, an air preheater, a high-temperature flue gas outlet pipe, and a spent flue gas outlet pipe. The system recovers the latent heat of the high-temperature flue gas at the outlet of the regenerative hot blast furnace, thereby eliminating the need for an external heat source of magnesium nitrate and lowering the exhaust temperature, thereby reducing the heat loss of the exhaust gas from the regenerative hot blast furnace and improving the thermal efficiency of the regenerative hot blast furnace, thereby achieving the purpose of energy saving.

[0027] (2) The present invention also provides a method for preheating combustion air of a hot blast furnace using flue gas waste heat, which is composed of a heat storage hot blast furnace, an air preheater, a high-temperature flue gas pipeline, and a reversing valve; the high-temperature flue gas is used to preheat the combustion air, and the combustion air entering the heat storage hot blast furnace is preheated, thereby achieving the purpose of saving fuel. The arrangement of the reversing valve can realize that the high-temperature flue gas preheats the decomposition gas and the combustion air at the same time.

[0028] (3) The present invention also provides a magnesium nitrate pyrolysis process method, which applies the above-mentioned flue gas waste heat utilization system to the magnesium nitrate pyrolysis process to realize the recovery and utilization of exhaust flue gas waste heat, and the raw material heating device does not need an external heat source; the heat of the flue gas is used to preheat the combustion air through the reversing valve, thereby achieving the purpose of saving fuel. The magnesium nitrate pyrolysis system is also optimized and improved in terms of heat. Description of the drawings:

[0029] Figure 1 This is a schematic diagram of a flue gas waste heat utilization system provided in Example 1 of the present invention;

[0030] Figure 2 It is a front view and a cross-sectional view of the raw material heater in Example 1 of the present invention;

[0031] Figure 3 A schematic diagram of the jet tube in Example 1 of the present invention;

[0032] Figure 4 This is a schematic diagram of a magnesium nitrate pyrolysis process system of the present invention;

[0033] Figure 5 It is a system schematic diagram of a magnesium nitrate pyrolysis process in a comparative example of the present invention which does not utilize flue gas waste heat and preheat combustion-supporting air.

[0034] Description of reference numerals:

[0035] 1-regenerative hot blast furnace, 2-raw material heater, 3-jet tube, 4-chimney, 5-reversing valve, 6-air preheater, 7-high-temperature flue gas pipeline, 7-1 high-temperature flue gas branch pipeline, 7-2 high-temperature pipeline, 8-exhaust flue gas outlet pipeline, 9-preheated combustion air pipeline, 10-air inlet pipeline, 11-raw material inlet, 12-raw material outlet, 2-1 high-temperature flue gas inlet of outer pipeline, 2-2 high-temperature flue gas inlet of inner pipeline, 2-3 raw material magnesium nitrate inlet, 2-4 outlet pipeline of molten magnesium nitrate, 2-5 outer jacket, 2-6 inner jacket, 2-7 stirring paddle; 3-1 inlet contraction section, 3-2 throat, 3-3 outlet diffusion section, 3-4 spray tube bundle, 3-5 flue gas inlet, 3-6 ammonia outlet; 13-pyrolysis furnace, 14-acid making system; 4a-ordinary pyrolysis furnace, 5a-acid making device. Specific implementation method:

[0036] The present invention will be further described below in conjunction with the accompanying drawings:

[0037] Embodiment 1:

[0038] like Figure 1As shown, the present invention relates to a waste heat utilization system, the regenerative hot blast furnace 1 is connected to the raw material heater 2 through the outlet of one end of the reversing valve 5, the raw material heater 2 is connected to the jet pipe 3 and the chimney 4 in sequence; the other end outlet of the reversing valve 5 is connected to the air preheater 6; the flue gas outlet of the air preheater 6 is connected to the jet pipe 3; the internal circulation and external circulation inlets and outlets of the raw material heater 2 are respectively connected to the reversing valve 5 and the jet pipe 3.

[0039] The waste heat utilization system includes a regenerative hot blast furnace 1, a raw material heater 2, a jet pipe 3, a chimney 4, a reversing valve 5, an air preheater 6, a high-temperature flue gas pipeline 7, and a spent flue gas outlet pipeline 8. The reversing valve 5 is a three-way reversing valve, which is respectively connected to the regenerative hot blast furnace 1, the air preheater 6, and the raw material heater 2. The reversing valve 5 is connected to the regenerative hot blast furnace 1 through a high-temperature flue gas branch pipeline 7-1, and the reversing valve 5 is connected to the regenerative hot blast furnace 1 through a high-temperature pipeline 7-2; the jet pipe 3 is connected to the outlet of the raw material heater 2 at one end through the spent flue gas outlet pipeline 8, and the other end is connected to the chimney 4 through a pipeline; the flue gas outlet of the air preheater 6 is merged into the spent flue gas outlet pipeline 8 through a pipeline and enters the jet pipe 3; the air preheated by the air preheater 6 returns to the regenerative hot blast furnace 1.

[0040] The regenerative hot blast furnace 1 adopts the method of "two burning and one sending", uses natural gas as fuel, heats the decomposed gas after dust removal from the pyrolysis furnace 13, and serves as a high-temperature heat source for the pyrolysis furnace 13. The high-temperature flue gas generated by the combustion of the natural gas used to heat the decomposed gas is connected to the inlet of the raw material heater 2 through the high-temperature flue gas pipeline 7, and after sufficient heat exchange with the raw material magnesium nitrate inlet 2-3, the generated exhaust gas is sent to the horizontal inlet of the jet tube 3 through the exhaust gas outlet pipeline 8, and the horizontal outlet of the jet tube 3 is connected to the chimney 4 and discharged to the outside atmosphere. The outlet pipeline 2-4 of the preheated molten magnesium nitrate is sent to the pyrolysis furnace 13 by a transport pump.

[0041] The regenerative hot blast furnace 1 uses natural gas as fuel, and the temperature of the exhaust gas at the outlet is 200°C; the combustion air inlet of the air inlet pipe 10 of the air preheater 6 is fed with air at a temperature of 25-30°C, and the outlet temperature of the combustion air heated by the air preheater 6 is maintained at 100-150°C and passed into the regenerative hot blast furnace 1. High-temperature flue gas is generated by the combustion of natural gas, and the high-temperature flue gas generated is 400-500°C. The high-temperature flue gas generated by the regenerative hot blast furnace 1 heats the magnesium nitrate of the raw material heater 2 to 130-150°C.

[0042] like Figure 1As shown, compared with the prior art, the significance of the present invention lies firstly in that the flue gas at the outlet of the regenerative hot blast furnace 1 is used as a heat carrier to heat the raw material magnesium nitrate inlet 2-3 in the raw material heater 2, without the need for an external heat source, thereby lowering the exhaust gas temperature and reducing the exhaust gas heat loss, thereby improving the thermal efficiency of the regenerative hot blast furnace, and a jet tube 3 is arranged on the pipeline to denitrate the flue gas.

[0043] In order to explain the implementation method of the present invention more clearly, Figure 2 The structure and working principle of the raw material heater 2 are further technically explained. Figure 2 Including the main view and the cross-sectional view, it illustrates the heat exchange method between the high-temperature flue gas and the magnesium nitrate raw material.

[0044] Figure 2 It is a typical implementation case with high heat transfer efficiency and effective realization of efficient utilization of flue gas. The raw material heater 2 includes an outer jacket 2-5, which is a spiral, semicircular cross-section hollow tube bundle welded longitudinally on the raw material storage tank; the high-temperature flue gas of the outer jacket 2-5 enters from the bottom and is discharged from the top; the outer jacket 2-5 has an external insulation structure, and a thermal insulation layer is added to the outside of the heater. Rock wool insulation board is selected, and an iron sheet protective layer is added on the outside. The inner jacket 2-6 is a circular cross-section tube bundle spirally wound around the inside of the tank body of the raw material heater 2; the high-temperature flue gas of the inner jacket 2-6 enters from the top and is discharged from the bottom.

[0045] The external circulation of the raw material heater 2 is provided with an external jacket 2-5, and the spiral external jacket 2-5 is vertically welded on the outer wall of the raw material storage tank in the axial direction of the tank body, and the high-temperature flue gas in the external jacket 2-5 is introduced from the bottom and discharged from the top; an insulation structure is added to the outside of the external jacket 2-5; the internal circulation of the raw material heater 2 is provided with an internal jacket 2-6, and the spiral internal jacket 2-6 is arranged parallel to the axial direction of the tank body; the high-temperature flue gas of the inner jacket 2-6 is introduced from the top and discharged from the bottom; the raw material storage tank is a hollow cylindrical tank body; a raw material inlet 11 and a raw material outlet 12 are provided at the upper end of the hollow cylindrical tank body, and a stirring paddle 2-7 is provided inside the tank body; the stirring paddle 2-7 is connected to an externally arranged motor; the raw material outlet 12 is connected to a raw material transport pump; the raw material inlet 11 of the raw material storage tank is introduced into the raw material magnesium nitrate inlet 2-3, and the raw material outlet 12 of the raw material storage tank is connected to the molten magnesium nitrate outlet pipe 2-4. The raw material heater 2 includes internal and external circulation heating, which heats the raw material storage tank both inside and outside at the same time, and cooperates with the stirring paddles 2-7 to fully heat the raw material storage tank.

[0046] The jacket is spiral, and is wound around a raw material storage tank with a semicircular cross-section hollow tube bundle, a raw material storage tank, and a raw material heater composed of stirring paddles 2-7. That is, the flue gas tangent passes through the inner and outer spiral tube bundles, which increases the flue gas flow rate and the contact area between the flue gas and the raw material. The flue gas flow directions of the inner and outer tube bundles are different, the purpose is to reduce the temperature difference, which is conducive to uniform heat exchange. In order to improve the heat transfer coefficient on the raw material side, the setting of the stirring paddle 2-7 in the raw material storage tank increases the internal turbulence and improves the heat transfer effect. The preheated molten magnesium nitrate is transported by a pump above the tank body to provide raw materials for the pyrolysis process.

[0047] Working principle of raw material heater 2: In order to improve the heat transfer coefficient on the flue gas side, the flue gas tangent passes through the inner and outer spiral tube bundles to increase the flue gas flow rate; welding is used to form a closed space between the outer spiral tube and the raw material storage tank body. The cross-section of the spiral tube is semicircular. The flue gas passes through the spiral channel to increase the flue gas travel, which is beneficial to heat exchange. The inner spiral tube bundle is parallel to the axial direction of the tank body and is circular in cross-section. It is placed inside the cylinder. The flue gas flow directions of the inner and outer tube bundles are different in order to reduce the temperature difference and facilitate uniform heat exchange. In order to improve the heat transfer coefficient on the raw material side, the setting of the stirring paddle in the raw material storage tank increases the internal turbulence and improves the heat transfer effect. The preheated molten magnesium nitrate is transported by the pump above the tank body to provide raw materials for the pyrolysis process.

[0048] The diameter of the semicircular cross section of the spiral tube is 50 mm, and the spacing between the spiral tubes is 30 mm.

[0049] The raw material storage tank is a hollow cylindrical tank body; a raw material inlet 11 and a raw material outlet 12 are provided at the upper end of the hollow cylindrical tank body, and a stirring paddle 2-7 is provided inside the tank body; the stirring paddle 2-7 is connected to an externally arranged motor; the raw material outlet 12 is connected to a raw material transport pump; the raw material inlet 11 of the raw material storage tank is connected to the raw material magnesium nitrate inlet 2-3, and the raw material outlet 12 of the raw material storage tank is connected to the outlet pipe 2-4 of the molten magnesium nitrate.

[0050] In order to explain the implementation method of the present invention more clearly, Figure 3 The structure and working principle of the jet tube 3 are further described in detail.

[0051] Figure 3The jet tube is a pipe that contracts first and then expands, and is divided into an inlet section, which is a short cylindrical section with a diameter equal to the diameter of the pipe. The contraction part is a conical tube, that is, the inlet contraction section 3-1, with a cone angle of 21±2°, and the outlet diffusion section 3-3 has a cone angle of 8-15°. A spray tube bundle 3-4 is vertically welded directly above the central axis of the throat 3-2 of the jet tube 3. Exhaust gas is introduced into the jet tube 3 in the horizontal direction, and ammonia NH3 is introduced into the jet tube 3 in the vertical direction. The inlet contraction section 3-1 of the jet tube 3 is a conical tube with a cone angle of 21±2°, the cone angle of the outlet diffusion section 3-3 is 8-15°, the diameter of the throat 3-2 is 0.3 to 0.75 times the maximum diameter of the inlet contraction section 3-1, that is, the diameter of the pipe, the length of the inlet contraction section 3-1 is 1 to 1.5 times the maximum diameter of the inlet contraction section 3-1, the length of the outlet diffusion section 3-3 is 1.5 times the length of the inlet contraction section 3-1, and the diameter of the ammonia port 3-6 is 1 / 3 to 1 / 4 of the maximum diameter of the inlet contraction section 3-1. The ammonia port 3-6 can be arranged above or below the throat 3-2, and a drain valve is also arranged vertically below.

[0052] The setting of the jet tube 3 utilizes the gradual contraction and then expansion of the nozzle, so that the flow velocity in the throat 3-2 of the jet tube 3 is increased and the static pressure is reduced. The middle tube in the throat realizes the suction of the denitrification catalyst ammonia NH3, thereby realizing the tail denitrification of the flue gas, simplifying the denitrification device, and having the advantage of preventing blockage.

[0053] The diameter of the throat 3-2 is 0.3 to 0.75 times the maximum diameter of the inlet contraction section 3-1, which can reduce local resistance loss. The cone angle of the outlet diffusion section 3-3 is smaller than that of the inlet contraction section 3-1 to avoid flow classification and reduce pressure head loss.

[0054] Working principle of jet tube 3: the flue gas after heat exchange by raw material heater 2 flows into jet tube 3 in horizontal direction, passes through inlet contraction section 3-1, and due to the change of cross-sectional area of ​​jet tube 3, the flow velocity of exhaust gas gradually increases, and local pressure is reduced when reaching the throat position, and ammonia gas in the vertical direction of jet tube 3 is sucked into the throat part of jet tube 3, and the flue gas of jet tube 3 is denitrated through spray tube bundle 3-4 above jet tube 3. The flue gas after denitration flows through the gradual expansion section, which reduces the turbulence problem of tail flue gas and discharges it into the atmosphere.

[0055] Embodiment 2:

[0056] Figure 4A flue gas waste heat preheating combustion air system is shown, comprising a regenerative hot blast furnace 1, an air preheater 6, a high-temperature flue gas pipeline 7, and a reversing valve 5; the air preheater 6 is provided with an outer pipeline high-temperature flue gas inlet 2-1, an inner pipeline high-temperature flue gas inlet 2-2, a combustion air inlet, and a combustion air outlet; the high-temperature flue gas generated by the regenerative hot blast furnace 1 is connected to the air preheater 6 through the reversing valve 5, and the high-temperature flue gas is connected to the outer pipeline high-temperature flue gas inlet 2-1 of the air preheater 6 to preheat the combustion air, and the preheated combustion air is introduced into the regenerative hot blast furnace 1 through the preheated combustion air pipeline 9 for fuel combustion. The raw material outlet 12 and the regenerative hot blast furnace 1 are connected to the pyrolysis furnace 13, and the regenerative hot blast furnace 1 and the pyrolysis furnace 13 are also connected to the existing acid production system 14.

[0057] like Figure 1 As shown, the working principle of the regenerative hot blast furnace 1 is as follows: three existing regenerative hot blast furnaces adopt a two-burning and one-delivery working mode. The regenerative hot blast furnace uses natural gas and combustion-supporting air when burning to generate high-temperature flue gas, which is used as the heat storage material in the regenerative hot blast furnace. The heat storage material is checker bricks. During the air supply cycle, the burner is turned off and the cold decomposition furnace is passed to decompose and produce NO x Mixed gas with O2, cold decomposition gas comes from part of NO at the outlet of the decomposition furnace x and O2, are heated by the burner of the regenerative hot blast furnace to between 1150-1200°C, and are sent to the pyrolysis furnace 13 to provide heat source for decomposition of magnesium nitrate. The reason for using three regenerative hot blast furnaces is that when one is used for maintenance, the other two can also be used to maintain production.

[0058] Working principle of the reversing valve 5: The reversing valve 5 selects an existing DC reversing valve with a reversing cycle of 0.1-0.3 seconds. The reversing valve is respectively connected to the high-temperature flue gas waste heat raw material heating system and the high-temperature flue gas preheating combustion air system.

[0059] The regenerative hot blast furnace 1 uses natural gas as fuel, and the temperature of the exhaust gas at the outlet is 200°C; the combustion air inlet of the air inlet pipe 10 of the air preheater 6 is fed with air at a temperature of 25-30°C, and the outlet temperature of the combustion air heated by the air preheater 6 is maintained at 100-150°C and passed into the regenerative hot blast furnace 1. High-temperature flue gas is generated by the combustion of natural gas, and the high-temperature flue gas generated is 400-500°C. The high-temperature flue gas generated by the regenerative hot blast furnace 1 heats the magnesium nitrate of the raw material heater 2 to 130-150°C.

[0060] Figure 4 This is a flow chart of the magnesium nitrate pyrolysis process system using flue gas waste heat provided by the present invention, referring to Figure 4 The specific operation method of magnesium nitrate pyrolysis process using flue gas waste heat is as follows:

[0061] Step 1: The high-temperature flue gas generated by the regenerative hot blast furnace 1 is connected to the reversing valve 5 through the outlet of the regenerative hot blast furnace 1. The reversing valve 5 changes direction every 0.1-0.3 seconds. One side is connected to the raw material heater 2, and the other side is connected to the air preheating system.

[0062] Step 2: In the part connected to the raw material heater, the high-temperature flue gas is divided into two paths. In the first path, the high-temperature flue gas is sent to the high-temperature flue gas inlet 2-1 of the outer pipe of the outer jacket 2-5 of the raw material heater 2 through the high-temperature flue gas branch pipe 7-1, and flows out from the jacket outlet through the longitudinal spiral flow; in the second path, the high-temperature flue gas passes through the heat exchange tube bundle arranged in the raw material heater 2 in the opposite direction of the flue gas flow direction of the first path, and the high-temperature flue gas is connected to the high-temperature flue gas inlet 2-2 of the inner pipe of the inner jacket 2-2 through the high-temperature flue gas branch pipe 7-1. The high-temperature flue gas exchanges heat with the magnesium nitrate in the raw material storage tank through the inner and outer spiral jackets. The stirring paddle in the raw material storage tank is used to further evenly exchange the heat of the magnesium nitrate, and then obtain molten magnesium nitrate. The molten magnesium nitrate is sprayed into the pyrolysis furnace 13 through atomization to provide raw materials for the pyrolysis of magnesium nitrate.

[0063] Step three: The part connected to the air preheater 6, the high-temperature flue gas is connected to the high-temperature flue gas inlet 2-1 of the outer pipe of the air preheater 6, and the combustion air is preheated through the tail flue gas. The preheated combustion air is introduced into the regenerative hot air furnace 1 for fuel combustion.

[0064] Step 4: The flue gas from the air preheater 6 outlet and the raw material heater 2 outlet are passed into the jet tube 3 through the exhaust gas outlet pipe 8. Due to the low pressure area generated in the throat 3-2 of the jet tube 3, the denitrified ammonia NH3 is sucked into the jet tube 3, spraying the flue gas in the jet tube for denitrification.

[0065] Step 5: The exhaust gas after denitrification is sent to the exhaust gas outlet pipe 8 through the outlet of the jet pipe 3 to the chimney 4 and discharged into the atmosphere.

[0066] Step 6: The decomposition gas generated by the pyrolysis of magnesium nitrate is subjected to dust removal, a part of which is used for acid production in the acid production system 14, and a part of which is returned to the regenerative hot blast furnace 1; a part of the decomposition gas returned to the regenerative hot blast furnace 1 is heated to the required process temperature through the regenerative body to provide a heat source for the decomposition of magnesium nitrate, and the regenerative hot blast furnace 1 is provided with a pipeline for discharging the heated high-temperature decomposition gas.

[0067] In order to more clearly explain the improvement of the magnesium nitrate pyrolysis process using flue gas waste heat, a method for atomizing and pyrolyzing magnesium nitrate by heat storage circulation heating for producing magnesium nitrate is now compared with the present invention.

[0068] Comparative Examples

[0069] Figure 5This is a schematic diagram of a system for atomizing and pyrolyzing magnesium nitrate using regenerative circulating heating, disclosed in the comparative example announcement number CN 110342497 A. The system is mainly composed of a regenerative hot blast furnace 1, a raw material heater 2, a chimney 4, a common pyrolysis furnace 4a, and an acid-making device 5a. 200 kg / h of magnesium nitrate with a content of 99% is put into the raw material heater 2. The raw material is heated to 130°C by an external heat source to heat the magnesium nitrate into a molten state. It is transported to the atomizing nozzle of the common pyrolysis furnace 4a by a transport pump and sprayed into the common pyrolysis furnace to maintain the temperature in the furnace at 500-800°C. The high-temperature gas source required in the common pyrolysis furnace 4a is provided by the regenerative hot blast furnace 1 after heating. During the actual test, the smoke temperature at the outlet of the regenerative hot blast furnace 1 reached 400°C, and the heat loss of the exhaust smoke of the regenerative hot blast furnace was 23.5%, resulting in a large amount of smoke emission and waste of waste heat.

[0070] Example 1 adopts a proposed magnesium nitrate pyrolysis system with energy system optimization, and proposes a flue gas recycling energy optimization method. The 400°C exhaust gas at the outlet of the regenerative hot blast furnace 1 preheats the raw magnesium nitrate. Assuming that the flue gas temperature drops to 200°C after preheating, the raw material is also heated to 130°C. The raw material preheating rate can be increased to 472kg / h, and the exhaust heat loss can be reduced to 10% to 11%. The problems of large exhaust heat loss and unreasonable heat distribution in the original system are greatly improved, and the control of the decomposition reaction is better achieved.

[0071] Example 2 adopts an energy system optimized magnesium nitrate pyrolysis system, and proposes a magnesium nitrate pyrolysis system for preheating combustion air. Before preheating, the combustion air temperature of the regenerative furnace is 25°C. Assuming that the combustion air is 100°C after preheating, the exhaust heat loss can be reduced by 4.38%, and the fuel coal saving is 4.2%, achieving the effect of coal saving.

Claims

1. A flue gas waste heat utilization system, characterized in that: The regenerative hot blast furnace (1) is connected to a raw material heater (2) via an outlet at one end of a reversing valve (5), and the raw material heater (2) is connected to a jet pipe (3) and a chimney (4) in sequence; the outlet at the other end of the reversing valve (5) is connected to an air preheater (6); the flue gas outlet of the air preheater (6) is connected to the jet pipe (3); the internal circulation inlet and outlet of the raw material heater (2) are connected to the reversing valve (5) and the jet pipe (3), respectively, and the external circulation inlet and outlet of the raw material heater (2) are connected to the reversing valve (5) and the jet pipe (3), respectively; The external circulation of the raw material heater (2) is provided with an external jacket (2-5), the spiral external jacket (2-5) is vertically welded to the outer wall of the raw material storage tank in the axial direction of the tank body, and the high-temperature flue gas in the external jacket (2-5) is introduced from the bottom and discharged from the top; a heat preservation structure is added to the outside of the external jacket (2-5); the internal circulation of the raw material heater (2) is provided with an internal jacket (2-6), the spiral internal jacket (2-6) is arranged in parallel with the axial direction of the tank body; the high-temperature flue gas in the internal jacket (2-6) is introduced from the top and discharged from the bottom; The raw material storage tank is a hollow cylindrical tank body; a raw material inlet (11) and a raw material outlet (12) are provided at the upper end of the hollow cylindrical tank body, and a stirring paddle (2-7) is provided inside the tank body; the stirring paddle (2-7) is connected to an externally arranged motor; the raw material outlet (12) is connected to a raw material transport pump; the raw material inlet (11) of the raw material storage tank is connected to a raw material magnesium nitrate inlet (2-3), and the raw material outlet (12) of the raw material storage tank is connected to a molten magnesium nitrate outlet pipe (2-4).

2. A flue gas waste heat utilization system according to claim 1, characterized in that: The jet pipe (3) is a pipe that contracts first and then expands. The jet pipe (3) is composed of an inlet contraction section (3-1), a throat (3-2), and an outlet expansion section (3-3). A spray pipe bundle (3-4) is vertically welded directly above the central axis of the throat (3-2), and a drain valve is vertically welded directly below the central axis of the throat (3-2). The jet pipe (3) has a flue gas inlet (3-5) in the horizontal direction, and an ammonia port (3-6) for introducing flue gas denitrification is provided in the vertical direction of the jet pipe (3).

3. A flue gas waste heat utilization system according to claim 2, characterized in that: The inlet contraction section (3-1) of the jet tube (3) is a conical tube with a cone angle of 21±2°, the cone angle of the conical outlet diffusion section (3-3) is 8-15°, the diameter of the throat (3-2) is 0.3-0.75 times the maximum tube diameter of the inlet contraction section (3-1), the length of the inlet contraction section (3-1) is 1-1.5 times the maximum tube diameter of the inlet contraction section (3-1), the length of the outlet diffusion section (3-3) is 1.5 times the length of the inlet contraction section (3-1), and the diameter of the ammonia port (3-6) is 1 / 3-1 / 4 of the maximum tube diameter of the inlet contraction section (3-1).

4. A method for preheating magnesium nitrate raw materials with flue gas using the flue gas waste heat utilization system as claimed in claim 1, characterized in that: The high-temperature flue gas generated by the regenerative hot blast furnace (1) is connected to the raw material heater (2) via a reversing valve (5); the high-temperature flue gas entering the raw material heater (2) through the reversing valve (5) is divided into two paths: In the first path, the high-temperature flue gas is sent to the high-temperature flue gas inlet (2-1) of the outer jacket (2-5) of the raw material heater (2) through the high-temperature flue gas branch pipe (7-1), and flows through the spiral pipe bundle welded on the outer wall of the raw material storage tank; In the second path, the high-temperature flue gas passes through the heat exchange tube bundle of the inner jacket (2-6) arranged in the raw material heater (2); the high-temperature flue gas is connected to the high-temperature flue gas inlet (2-2) of the inner pipe of the inner jacket (2-6) through the high-temperature flue gas branch pipe (7-1), and the high-temperature flue gas exchanges heat with the magnesium nitrate raw material in the raw material storage tank through the inner jacket (2-6) and the outer jacket (2-5). The stirring paddle (2-7) in the raw material storage tank is used to further uniformly exchange the heat of the magnesium nitrate, thereby obtaining molten magnesium nitrate.

5. The processing method according to claim 4, characterized in that: The high-temperature flue gas is generated by the combustion of natural gas, and the temperature of the high-temperature flue gas is 400-500° C. The high-temperature flue gas generated by the regenerative hot air furnace (1) heats the magnesium nitrate in the raw material heater (2) to 130-150° C.

6. A method for preheating air in a flue gas waste heat utilization system as claimed in claim 1, characterized in that: The high-temperature flue gas generated by the regenerative hot blast furnace (1) enters the air preheater (6) through the reversing valve (5), and the preheated combustion air is passed into the regenerative hot blast furnace (1) through the preheated combustion air pipeline (9) for use in the combustion of fuel.

7. The method for preheating air according to claim 6, characterized in that: The combustion air inlet temperature of the air inlet pipeline (10) of the air preheater (6) is 25-30°C, and the combustion air outlet temperature after being heated by the air preheater (6) is maintained at 100-150°C and is passed into the regenerative hot air furnace (1).

8. The method for preheating air according to claim 6, characterized in that: The flue gas generated after preheating the magnesium nitrate raw material and the air includes a flue gas tail denitrification process. The exhaust gas generated after preheating the air and heating the magnesium nitrate raw material enters the jet pipe (3) through the exhaust gas outlet pipe (8). The exhaust gas flows horizontally into the jet pipe (3) and enters the inlet contraction section (3-1). Due to the change in the cross-sectional area of ​​the jet pipe (3), the flow rate of the exhaust gas gradually increases. When it reaches the throat (3-2), the local pressure decreases, and the ammonia gas in the vertical direction of the jet pipe (3) is sucked into the throat (3-2) of the jet pipe (3). The exhaust gas of the jet pipe (3) is denitrified by the spray pipe bundle (3-4) arranged above the jet pipe (3). After denitrification, it flows through the outlet diffusion section (3-3) and is discharged into the atmosphere through the chimney (4).

9. The method for preheating air according to claim 8, characterized in that: The exhaust gas denitrated by the jet tube (3) is discharged into the atmosphere at a temperature of 160-200°C.

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