Device for recovering metal oxides and nitric acid by decomposing nitrate solution

Abstract

The present invention provides a device and method for recovering metal oxides and nitric acid by decomposing nitrate solutions. It includes: a decomposition device, a dust collection device, an acid production device, and a combustion device. The decomposition device is provided with a nitrogen-containing soot discharge port; the dust collection device is provided with a soot inlet, a nitrogen-containing flue gas discharge port, and a dust outlet, and the soot inlet is connected to the nitrogen-containing soot discharge port through a soot transmission pipeline; the acid production device is provided with a nitrogen-containing flue gas inlet and a recycle gas outlet, the nitrogen-containing flue gas inlet is connected to the nitrogen-containing flue gas discharge port through a nitrogen-containing flue gas transmission pipeline, and the recycle gas outlet is connected to the fuel gas inlet through a recycle gas transmission pipeline; the combustion device is provided with a fuel inlet, an auxiliary combustion gas inlet, and a fuel gas outlet, the auxiliary combustion gas inlet is connected to the recycle gas outlet through a recycle gas transmission pipeline, and the fuel gas outlet is connected to the fuel gas inlet through a combustion gas transmission pipeline. It can well solve the problems of flue gas corrosion of equipment and limited selection of materials for transmission pipelines, and reduce investment and carbon recovery costs.

Description

Technical Field

[0001] The present invention relates to the field of smelting of laterite nickel ore, and in particular, to a device for decomposing nitrate solution to recover metal oxides and nitric acid. Background Art

[0002] The hydrometallurgical technology is one of the mainstream processes for treating laterite nickel ore. It usually uses inorganic acid to leach the ore, so that metal ions enter the acidic solution, and then uses an alkaline neutralizer to neutralize and precipitate the acidic solution to obtain products such as iron concentrate and MHP (nickel-cobalt-manganese hydroxide precipitate). Finally, MHP can be further processed through operations such as acid leaching, neutralization precipitation, extraction, and crystallization. When magnesium oxide is used as the neutralizer, magnesium elements will enter the solution to replace the valuable metals therein, and at the same time, a relatively high proportion of magnesium elements contained in the laterite nickel ore itself will also enter the solution during leaching. Therefore, a large amount of magnesium salt solution will be generated during the smelting process. It can be seen that the leaching process consumes a large amount of inorganic acid, and the neutralization precipitation process consumes a large amount of magnesium oxide, resulting in a large consumption of acid and alkali auxiliaries and a high cost of acid and alkali auxiliaries. The produced magnesium salt solution is mainly sold as by-products such as magnesium salt through evaporation and crystallization, and its economic value is not high.

[0003] The recovery and reuse of nitric acid and magnesium oxide can be realized by decomposing magnesium salts, which can greatly reduce the cost of acid and alkali auxiliaries, reduce the output of low-quality salt by-products, reduce the generation of waste water and solid waste, and improve economic and environmental benefits. However, the process concept of the existing magnesium nitrate decomposition technology still stays in the stage of passively treating CO2 tail gas. The CO2 concentration in the tail gas is low, making the recovery of CO2 difficult and the recovery cost high.

[0004] The existing literature (CN112744792A) provides a method for decomposing nitrate to prepare metal oxide powder and nitric acid. In this method, the nitrate solution is added to a pyrolysis furnace to decompose into high-temperature dust gas. The dust gas is separated by a high-temperature dust collector to obtain metal oxide powder and high-temperature flue gas. A part of the high-temperature flue gas is sent to a nitric acid preparation device through a hot air blower, and a part is mixed with oxygen-rich air and used as a combustion-supporting gas. The combustion-supporting gas is mixed with fuel to burn to obtain high-temperature flue gas, which is sent back to the pyrolysis furnace for use. This technology improves the heat utilization efficiency by direct combustion heating, but has the following problems: (1) It directly mixes the dust-containing flue gas with high concentration of NO X after dust collection with fuel and burns it, resulting in that at the high temperature of combustion, NO XIt reacts with components such as CH4, CO, or H2 in the fuel to produce adverse side reactions to generate N2, NO, etc., affecting the stability of the flue gas components and the stable operation of the nitric acid preparation system, and reducing the nitric acid production to a certain extent. And NO is a toxic gas, and the increase in its concentration leads to an increased safety risk of the system. (2) It uses the flue gas after dust collection for circulation, and the equipment and pipelines after the circulation fan operate under positive pressure, with a high risk of flue gas leakage, and the flue gas contains a high concentration of NO X Acidic toxic gas, and at the same time contains a large amount of H2O. When leakage occurs, the condensation of the acidic gas will corrode the equipment, and the toxic NO X gas diffusion will endanger the surrounding environment and personnel. (3) It uses the flue gas after dust collection for circulation, and the flue gas contains a high concentration of NO X and H2O. The flue gas temperature is usually about 300 - 350 °C to ensure that the acidic gas does not condense. Such high-temperature, high-acid, and high-humidity flue gas makes it difficult to select materials for equipment such as circulation fans, heat exchangers, burners and related pipelines, and the material cost is relatively high. (4) It uses oxygen-enriched combustion, which improves the concentration of CO2 to a certain extent, and also considers the recovery of CO2, but it uses the flue gas after dust collection containing NO X for circulation and concentration control, making it impossible to effectively enrich CO2. Therefore, the recovery of carbon dioxide is difficult and the recovery cost is relatively high. Summary of the Invention

[0005] The main object of the present invention is to provide a device for decomposing nitrate solution to recover metal oxides and nitric acid, so as to solve the problems of serious corrosion of equipment and transmission pipelines, high risk of toxic gas leakage, and high carbon recovery cost in the tail gas when using the existing method to decompose nitrate solution to recover metal oxides due to the circulating flue gas containing high-temperature, high-humidity, and high-concentration NO x acidic gas.

[0006] To achieve the above object, on the one hand, the present invention provides a device for decomposing nitrate solution to recover metal oxides and nitric acid. The device for decomposing nitrate solution to recover metal oxides and nitric acid includes: a decomposition device, a dust collection device, an acid making device, and a combustion device. The decomposition device is provided with a nitrate solution inlet, a fuel gas inlet, and a nitrogen-containing dust discharge port; the dust collection device is provided with a dust inlet, a nitrogen-containing flue gas discharge port, and a dust outlet, and the dust inlet is communicated with the nitrogen-containing dust discharge port through a dust conveying pipeline; the acid making device is provided with a nitrogen-containing flue gas inlet, a nitric acid discharge port, and a circulating gas outlet, the nitrogen-containing flue gas inlet is communicated with the nitrogen-containing flue gas discharge port through a nitrogen-containing flue gas conveying pipeline, and the circulating gas outlet is communicated with the fuel gas inlet through a circulating gas conveying pipeline; the combustion device is provided with a fuel inlet, an auxiliary combustion gas inlet, and a fuel gas outlet, the auxiliary combustion gas inlet is communicated with the circulating gas outlet through a circulating gas conveying pipeline, and the fuel gas outlet is communicated with the fuel gas inlet through a combustion gas conveying pipeline.

[0007] Further, the device for decomposing nitrate solution to recover metal oxide and nitric acid further includes: a primary preheating device and a secondary preheating device. The primary preheating device is provided with a primary raw material inlet to be preheated, a primary preheated raw material outlet, and a heat medium inlet, and is used for preheating the nitrate solution; the secondary preheating device is arranged on the circulating gas pipeline, and is provided with a secondary raw material inlet to be preheated and a secondary preheated raw material outlet. The secondary raw material inlet to be preheated is communicated with the primary preheated raw material outlet, and the secondary preheated raw material outlet is communicated with the nitrate solution inlet through a secondary preheated raw material pipeline.

[0008] Further, the device for decomposing nitrate solution to recover metal oxide and nitric acid further includes: at least one concentration device, and the concentration device is arranged on the secondary preheated raw material pipeline.

[0009] Further, the concentration device is further provided with a first steam outlet, and the first steam outlet is communicated with the heat medium inlet.

[0010] Further, the device for decomposing nitrate solution to recover metal oxide and nitric acid further includes a mixing device, the mixing device is arranged on the circulating gas pipeline, and the mixing device is provided with an oxygen inlet.

[0011] Further, the device for decomposing nitrate solution to recover metal oxide and nitric acid further includes a gas distribution device and an atomization device. The gas distribution device is arranged on the combustion gas pipeline, and the atomization device is arranged at the nitrate solution inlet.

[0012] Further, the concentration device is further provided with a heat source inlet. The device for decomposing nitrate solution to recover metal oxide and nitric acid further includes a waste heat recovery device. The waste heat recovery device is arranged on the dust pipeline, and the waste heat recovery device is provided with a second steam outlet, and the second steam outlet is communicated with the heat source inlet.

[0013] Further, the decomposition device is provided with a solid material outlet and a return material port. The solid material outlet and the return material port are communicated through a return material pipeline. The device for decomposing nitrate solution to recover metal oxide and nitric acid further includes a return material device, and the return material device is arranged on the return material pipeline.

[0014] Further, the device for decomposing nitrate solution to recover metal oxide and nitric acid further includes a powder collection device. The powder collection device further includes a dust collection port, and the dust collection port is respectively communicated with the return material device, the waste heat recovery device and the dust collection device, and is used for recovering the dust discharged from the return material device, the waste heat recovery device and the dust collection device.

[0015] Further, the apparatus for decomposing a nitrate solution to recover metal oxides and nitric acid further includes: a tail gas scrubbing device and a carbon dioxide collection device. The tail gas scrubbing device is provided with a tail gas inlet and a purified gas discharge outlet, and the tail gas inlet and the recycle gas outlet are connected through a tail gas pipeline; the carbon dioxide collection device is arranged on the tail gas pipeline.

[0016] The second aspect of the present application further provides a method for decomposing a nitrate solution to recover metal oxides and nitric acid. The method for decomposing a nitrate solution to recover metal oxides and nitric acid includes: performing a decomposition reaction on the nitrate solution and the fuel gas to obtain nitrogen-containing soot and metal oxides; performing dust collection on the nitrogen-containing soot to obtain nitrogen-containing flue gas and first dust; mixing the nitrogen-containing flue gas with water to produce nitric acid and flue gas; burning at least part of the flue gas with fuel to obtain fuel gas.

[0017] Further, the method for decomposing a nitrate solution to recover metal oxides and nitric acid further includes: performing a first preheating on the nitrate solution to obtain a first-stage preheated raw material; performing heat exchange between the first-stage preheated raw material and the flue gas to enable the first-stage preheated raw material to perform a second heat exchange; preferably, the nitrate solution is heated to 90 - 99 °C after the first preheating, and then heated to 110 - 120 °C after the second preheating, and the temperature of the flue gas drops to 150 - 250 °C.

[0018] Further, the method for decomposing a nitrate solution to recover metal oxides and nitric acid further includes: concentrating the nitrate solution after the second heat exchange to obtain a concentrated nitrate solution; and performing a decomposition reaction on the concentrated nitrate solution.

[0019] Further, the product of the concentration process includes first steam. The method for decomposing a nitrate solution to recover metal oxides and nitric acid further includes: using the first steam as the heat source for the first preheating process.

[0020] Further, the method for decomposing a nitrate solution to recover metal oxides and nitric acid further includes: performing a decomposition reaction on the fuel gas after passing through a gas distribution device.

[0021] Further, the method for decomposing a nitrate solution to recover metal oxides and nitric acid further includes: recovering the waste heat of the heat in the nitrogen-containing soot; preferably, the product of the waste heat recovery process further includes second steam, and using the second steam as the heat source for the concentration process.

[0022] Further, the method for decomposing a nitrate solution to recover metal oxides and nitric acid further includes: using the unreacted material in the decomposition reaction process as a reaction raw material to perform a decomposition reaction again.

[0023] Further, the method for decomposing a nitrate solution to recover metal oxides and nitric acid further includes: recovering at least part of the carbon dioxide in the flue gas to obtain tail gas; washing the tail gas and then discharging it.

[0024] Applying the technical solution of the present invention, in the decomposition device, magnesium nitrate dehydrates and decomposes to generate dust containing magnesium oxide powder and pyrolysis flue gas. After the above-mentioned dust is collected by the dust collection device, nitrogen-containing flue gas is discharged. The nitrogen-containing flue gas is transported to the acid-making device, and after the nitrogen-containing compounds are absorbed, nitric acid is made, and the remaining flue gas without acidic compounds such as nitrogen-containing oxides is discharged from the acid-making device. A large amount of carbon dioxide and oxygen are contained in the above-mentioned flue gas, which will be used as recycle gas and transported through the recycle gas pipeline to the combustion-supporting gas inlet and then enter the combustion device for combustion. The above device can remove acidic gases such as nitrogen-containing compounds in the flue gas, thus well solving the problems of flue gas corrosion of equipment and limited selection of pipeline materials, and reducing the investment cost. At the same time, the flue gas discharged from the acid-making device can be recycled to the combustion device and directly mixed with the fuel for combustion, without adverse side reactions, so it does not affect the flue gas composition after nitrate decomposition, and can greatly improve the operation stability and safety of the system. Using the above device can increase the concentration of CO2 in the tail gas, which is beneficial to reducing the carbon recovery cost. Description of the Drawings

[0025] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0026] Figure 1 It is a schematic structural diagram of a preferred device for decomposing a nitrate solution to recover metal oxides and nitric acid provided by this application.

[0027] Among them, the above-mentioned drawings include the following reference numerals:

[0028] 10. Decomposition device; 11. Combustion device; 12. Mixing device; 13. Gas distribution device; 14. Atomization device; 15. Waste heat recovery device; 101. Solid material discharge port; 102. Return port;

[0029] 20. Dust collection device;

[0030] 30. Acid-making device; 301. Recycle gas outlet; 31. Recycle fan; 32. Nitric acid storage device;

[0031] 40. Primary preheating device; 401. Primary raw material to be preheated inlet; 402. Primary preheated raw material discharge port; 403. Heat medium inlet; 41. Secondary preheating device; 411. Secondary raw material to be preheated inlet; 412. Secondary preheated raw material discharge port; 43. Concentration device; 431. First steam outlet;

[0032] 50. Return material device; 60. Powder collecting device; 61. Metal oxide collecting device; 70. Tail gas scrubbing device; 80. Carbon dioxide collecting device; 90. Condenser. Detailed implementation manners

[0033] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0034] As described in the background art, when recovering metal oxides by decomposing nitrate solutions using existing methods, there are problems such as serious corrosion of equipment and transmission pipelines due to high temperature, high humidity, and high-concentration NOx acidic gases in the recycled flue gas, high risk of leakage of toxic gases, and high carbon recovery cost in the tail gas. To solve the above technical problems, this application provides a device for recovering metal oxides and nitric acid by decomposing nitrate solutions, as Figure 1 shown, including: a decomposition device 10, a dust collection device 20, an acid making device 30, and a combustion device 11. The decomposition device 10 is provided with a nitrate solution inlet, a fuel gas inlet, and a nitrogen-containing dust discharge outlet; the dust collection device 20 is provided with a dust inlet, a nitrogen-containing flue gas discharge outlet, and a dust outlet, and the dust inlet is communicated with the nitrogen-containing dust discharge outlet through a dust conveying pipeline; the acid making device 30 is provided with a nitrogen-containing flue gas inlet, a nitric acid discharge outlet, and a recycle gas outlet 301, the nitrogen-containing flue gas inlet is communicated with the nitrogen-containing flue gas discharge outlet through a nitrogen-containing flue gas conveying pipeline, and the recycle gas outlet 301 is communicated with the fuel gas inlet through a recycle gas conveying pipeline; the combustion device 11 is provided with a fuel inlet, an auxiliary combustion gas inlet, and a fuel gas outlet, the auxiliary combustion gas inlet is communicated with the recycle gas outlet 301 through a recycle gas conveying pipeline, and the fuel gas outlet is communicated with the fuel gas inlet through a combustion gas conveying pipeline.

[0035] In the decomposition device 10, magnesium nitrate dehydrates and decomposes to generate dust containing magnesium oxide powder and pyrolysis flue gas. After the above-mentioned dust is collected by the dust collection device 20, the nitrogen-containing flue gas is discharged. The nitrogen-containing flue gas is conveyed to the acid making device 30, and the nitrogen-containing compounds are absorbed to make nitric acid, and the remaining flue gas without acidic compounds such as nitrogen oxides is discharged from the acid making device 30. A large amount of carbon dioxide and oxygen are contained in the above-mentioned flue gas, and it will be used as recycle gas and conveyed through the recycle gas conveying pipeline to the auxiliary combustion gas inlet and then enter the combustion device 11 for combustion. By using the above device, acidic gases such as nitrogen-containing compounds in the flue gas can be removed, thus well solving the problems of corrosion of equipment by flue gas and limited material selection for transmission pipelines, and reducing the investment cost. At the same time, the flue gas discharged from the acid making device 30 can be recycled to the combustion device 11 and directly mixed with the fuel for combustion, and no adverse side reactions will occur, so it does not affect the flue gas composition after nitrate decomposition, and can greatly improve the operation stability and safety of the system. By using the above device, the concentration of CO2 in the tail gas can be increased, which is beneficial to reducing the carbon recovery cost.Figure 1 The raw material A is a nitrate solution, such as one or more of magnesium nitrate solution, aluminum nitrate solution, copper nitrate solution or zinc nitrate solution.

[0036] In a preferred embodiment, as Figure 1 shown, the device for recovering metal oxides and nitric acid by decomposing nitrate solution further includes: a primary preheating device 40 and a secondary preheating device 41. The primary preheating device 40 is provided with a primary raw material inlet to be preheated 401, a primary preheated raw material discharge outlet 402 and a heat medium inlet 403, and the primary preheating device 40 is used for preheating the nitrate solution; the secondary preheating device 41 is arranged on the circulating gas pipeline, and the secondary preheating device 41 is provided with a secondary raw material inlet to be preheated 411 and a secondary preheated raw material discharge outlet 412. The secondary raw material inlet to be preheated 411 is communicated with the primary preheated raw material discharge outlet 402, and the secondary preheated raw material discharge outlet 412 is communicated with the nitrate solution inlet through a secondary preheated raw material pipeline.

[0037] Since the temperature in the decomposition device 10 is relatively high, for the purpose of saving energy, the nitrate solution participating in the decomposition can be preheated. The flue gas discharged from the acid-making device 30 mainly contains CO2, O2 and a small amount of H2O, and almost no NO x . And the above flue gas has a certain temperature when discharged. By setting the secondary preheating device 41, the above flue gas can be heat-exchanged with the nitrate solution obtained after primary preheating, so as to further recover and utilize the heat in the above flue gas.

[0038] In a preferred embodiment, as Figure 1 shown, the device for recovering metal oxides and nitric acid by decomposing nitrate solution further includes at least one concentration device 43, and the concentration device 43 is arranged on the secondary preheated raw material pipeline. Concentrating the secondary preheated raw material is beneficial to increasing the concentration of nitrate, thereby increasing the concentration of carbon dioxide in the flue gas discharged from the decomposition device 10, which is convenient for recovery.

[0039] In a preferred embodiment, as Figure 1 shown, the concentration device 43 is further provided with a first steam outlet 431, and the first steam outlet 431 is communicated with the heat medium inlet 403. A certain amount of high-temperature steam will be generated during the concentration process. Using it as the heat medium of the primary preheating device 40 is beneficial to further improving the energy utilization rate and reducing energy consumption.

[0040] In a preferred embodiment, as Figure 1As shown, the device for decomposing nitrate solution to recover metal oxide and nitric acid further includes a mixing device 12, which is arranged on the circulating gas pipeline, and the mixing device 12 is provided with an oxygen inlet. The circulating gas humidified in the secondary preheating device 41 is sent to the mixer, mixed with oxygen to form oxygen-rich combustion-supporting gas (preferably with an oxygen concentration of 15-40 vol%), and then sent to the decomposition device 10 together. Mixing with oxygen for combustion without introducing inert gases such as nitrogen can increase the concentration of carbon dioxide in the flue gas discharged from the decomposition device 10, facilitating the recovery of carbon dioxide; at the same time, it reduces the content of nitrogen oxides in the flue gas and relieves the operating pressure of the subsequent acid-making device 30.

[0041] In a preferred embodiment, as Figure 1 shown, the device for decomposing nitrate solution to recover metal oxide and nitric acid further includes a gas distribution device 13, which is arranged on the combustion gas pipeline. Fuel, circulating gas and oxygen are combusted in the combustion device 11 to form combustion gas, and then it is evenly sent to the decomposition device 10 through the gas distribution device 13. This is beneficial to improving the utilization efficiency of fuel gas during the decomposition process.

[0042] Preferably, the temperature of the combustion gas discharged from the combustion device 11 is 850-1300 °C, and it enters the decomposition device 10 through the gas distribution device 13. At the same time, through multi-stage temperature increase, the nitrate solution undergoes dehydration and decomposition in the presence of the above combustion gas, generating magnesium oxide powder and pyrolysis flue gas (about 400-700 °C), and the decomposition rate of nitrate can reach 95-99%.

[0043] Preferably, in order to further improve the pyrolysis efficiency in the decomposition device, an atomizing device 14 is arranged at the nitrate solution inlet position. After atomizing the nitrate solution, it enters the decomposition device 10 in the form of small droplets, which can make its decomposition more complete.

[0044] In a preferred embodiment, as Figure 1 shown, the concentration device 43 is further provided with a heat source inlet, and the device for decomposing nitrate solution to recover metal oxide and nitric acid further includes a waste heat recovery device 15, which is arranged on the soot pipeline, and the waste heat recovery device 15 is provided with a second steam outlet, and the second steam outlet is communicated with the heat source inlet.

[0045] After the soot containing magnesium oxide powder and pyrolysis flue gas enters the waste heat recovery device 15, the heat of the flue gas is recovered, and part of the magnesium oxide powder settles and is collected. Preferably, the above waste heat recovery device 15 is a pyrolysis boiler. Using water to heat the boiler feed water with the pyrolysis flue gas (nitrogen-containing flue gas) to obtain heat exchange and generate steam. Part of the steam is sent to the concentration device 43 for use as a heat source.

[0046] Generally, there will still be some unreacted raw materials after pyrolysis in the decomposition device 10. In order to improve the recovery rate of the raw materials, in a preferred embodiment, as Figure 1 shown, the decomposition device 10 is provided with a solid material discharge port 101 and a return material port 102. The solid material discharge port 101 and the return material port 102 are connected through a return material conveying pipeline. The device for decomposing nitrate solution to recover metal oxide and nitric acid further includes a return material device 50, which is arranged on the return material conveying pipeline. The return material device 50 can return the unreacted solid materials in the decomposition device 10 back to the decomposition device 10 for pyrolysis reaction again, thereby further improving the decomposition rate of magnesium nitrate and the purity of the metal oxide. The decomposition rate of nitrate can reach up to 99%.

[0047] In a preferred embodiment, as Figure 1 shown, the device for decomposing nitrate solution to recover metal oxide and nitric acid further includes a powder collection device 60, which includes a dust collection port. The dust collection port is respectively connected to the return material device 50, the waste heat recovery device 15 and the dust collection device 20, and is used to recover the soot discharged from the return material device 50, the waste heat recovery device 15 and the dust collection device 20. The return material device 50, the waste heat recovery device 15 and the dust collection device 20 will generate a certain amount of dust during operation. The dust collection device can recover it and transport it to the metal oxide collection device 61 for storage and use. Preferably, the above-mentioned dust collection device 20 includes but is not limited to a bag filter, an electrostatic precipitator or a metal membrane dust collector.

[0048] In a preferred embodiment, as Figure 1 shown, the device for decomposing nitrate solution to recover metal oxide and nitric acid further includes: a tail gas washing device 70 and a carbon dioxide collection device 80. The tail gas washing device 70 is provided with a tail gas inlet and a purified gas discharge port. The tail gas inlet and the recycle gas outlet 301 are connected through a tail gas conveying pipeline; the carbon dioxide collection device 80 is arranged on the tail gas conveying pipeline. A part of the flue gas discharged from the acid-making device 30 is used as recycle gas, and the other part can be transported to the carbon dioxide collection device 80 to recover carbon dioxide for the purpose of carbon emission reduction (the purity of carbon dioxide can reach 99.5 - 99.9 wt%), and the remaining tail gas is directly discharged through the chimney 72 under the action of the tail gas fan 71 after passing through the tail gas washing device 70, or the remaining tail gas is transported to the tail gas washing device 70 by the tail gas fan 71 for washing and then directly discharged through the chimney 72.

[0049] The flue gas after dust collection still has a certain amount of heat. In order to further recover and utilize its heat, it is heat-exchanged with the recycle gas discharged from the acid-making device 30 in the condenser 90 to cool the flue gas obtained after dust collection, and then enter the acid-making device 30. At the same time, the recycle gas is preliminarily heated and then enters the secondary preheating device 41. The number of condensers 90 can be one or more, and their functions are the same. When there are multiple ones, they are arranged in series. The nitric acid produced by the acid-making device 30 is stored in the nitric acid storage device 32.

[0050] Preferably, at least one recycle fan 31 is provided on the recycle gas pipeline to increase the flow rate of the flue gas discharged from the acid-making device 30 during the flow process to the condenser 90. More preferably, a first pressure detection device P1 is provided on the gas distribution device 13, and a second pressure detection device P2 is provided on the dust conveying pipeline of the decomposition device 10. P1 and P2 are interlocked with the outlet valve of the recycle fan 31 to control the pressure of P1 at about 50 - 100 Pa and the pressure of P2 at about -100 - -50 Pa. By interlockingly controlling the first pressure detection, the second pressure detection and the outlet valve of the recycle fan, the pressure balance point of the recycle system can be controlled within the decomposition device 10, and the front section of the flue gas containing NO X (the part between the decomposition device 10 and the recycle fan 31) is controlled under negative pressure operation to avoid the leakage of toxic NO X flue gas, and the rear section of the flue gas containing CO2 (the part from the recycle fan 31 to the decomposition device 10) is controlled under positive pressure operation to reduce the difficulty and cost after preventing flue gas leakage, so as to minimize the leakage risk and harm of the entire system.

[0051] The second aspect of the present application also provides a method for decomposing a nitrate solution to recover metal oxides and nitric acid, including: performing a decomposition reaction on the nitrate solution and the fuel gas to obtain nitrogen-containing dust and metal oxides; performing dust collection treatment on the nitrogen-containing dust to obtain nitrogen-containing flue gas and first dust; mixing the nitrogen-containing flue gas with water to obtain nitric acid and flue gas; burning at least part of the flue gas with the fuel to obtain fuel gas.

[0052] The fuel gas refers to the reducing gas obtained after fuel combustion. The fuel is a hydrocarbon fuel, including but not limited to one or more of natural gas, water gas, blast furnace gas, coal gas, and liquid hydrocarbon.

[0053] In the presence of fuel gas, the nitrate solution undergoes thermal decomposition to form nitrogen-containing soot containing metal oxide dust and nitrogen oxides; after dust collection treatment of the above-mentioned nitrogen-containing soot, the flue gas containing nitrogen oxides is mixed with water to prepare nitric acid, which can remove the acidic gas in the nitrogen-containing soot, thus well solving the problems of flue gas corrosion of equipment and limited selection of pipeline materials, and reducing the investment cost. And the remaining flue gas after acid production contains a large amount of carbon dioxide and oxygen, so at least part of it can be burned with fuel to prepare fuel gas. This process does not produce side reactions that generate acidic nitrogen oxides, so it does not affect the flue gas composition after nitrate decomposition, and can greatly improve the operational stability and safety of the system.

[0054] Preferably, the nitrate solution used in the above method includes, but is not limited to, one or more of magnesium nitrate solution, aluminum nitrate solution, copper nitrate solution or zinc nitrate solution.

[0055] In a preferred embodiment, the method for decomposing a nitrate solution to recover metal oxides and nitric acid further includes: preheating the nitrate solution for the first time to obtain a first-stage preheated raw material; exchanging heat between the first-stage preheated raw material and the flue gas to enable the first-stage preheated raw material to undergo a second heat exchange. Preheating the nitrate solution can reduce the energy consumption during the decomposition process, and at the same time, using the high-temperature flue gas obtained after acid production as the heat source for preheating can also realize the reuse of heat energy, thereby improving the energy utilization rate.

[0056] Preferably, the nitrate solution is heated to 90-99 °C after the first preheating, and then heated to 110-120 °C after the second preheating, while the flue gas as the circulating gas obtained after acid production is cooled to 150-250 °C.

[0057] In a preferred embodiment, the method for decomposing a nitrate solution to recover metal oxides and nitric acid further includes: concentrating the nitrate solution after the second heat exchange to obtain a concentrated nitrate solution; and carrying out a decomposition reaction on the concentrated nitrate solution. Concentrating the nitrate solution after the second heat exchange is beneficial to increasing the concentration of nitrate, thereby increasing the concentration of carbon dioxide in the flue gas discharged from the decomposition device 10, which is convenient for recovery.

[0058] In a preferred embodiment, the product of the concentration process includes first steam, and the method for decomposing a nitrate solution to recover metal oxides and nitric acid further includes: using the first steam as the heat source for the first preheating process. A certain amount of high-temperature steam is generated during the concentration process, and using it as the heat medium for the first preheating process is beneficial to further improving the energy utilization rate and reducing the energy consumption.

[0059] In a preferred embodiment, the method for recovering metal oxides and nitric acid by decomposing a nitrate solution further includes: mixing oxygen and the flue gas obtained after acid production as recycle gas, and then burning the mixture with fuel. Mixing with oxygen for combustion assistance without introducing inert gases such as nitrogen can increase the concentration of carbon dioxide in the flue gas discharged during the decomposition process, facilitating the recovery of carbon dioxide and realizing the concept of carbon emission reduction; at the same time, it can reduce the content of nitrogen oxides in the flue gas and relieve the operating pressure in the subsequent nitric acid production process.

[0060] In a preferred embodiment, the method for recovering metal oxides and nitric acid by decomposing a nitrate solution further includes: subjecting the fuel gas to a decomposition reaction after passing through a gas distribution device. After passing through the gas distribution device, the fuel gas becomes more dispersed and homogenized, and subsequent decomposition reaction is conducive to further improving the utilization efficiency of the fuel gas during the decomposition process.

[0061] The temperature of the nitrogen-containing soot discharged after the decomposition reaction is 400 - 700 °C. To further reduce heat loss, preferably, the method for recovering metal oxides and nitric acid by decomposing a nitrate solution further includes: recovering the waste heat of the heat in the nitrogen-containing soot. Preferably, the temperature of the nitrogen-containing soot drops to 300 - 500 °C after heat exchange. More preferably, the product of the waste heat recovery process further includes a second steam, and the second steam is used as the heat source for the concentration process.

[0062] In a preferred embodiment, the method for recovering metal oxides and nitric acid by decomposing a nitrate solution further includes: using the unreacted material during the decomposition reaction process as a reaction raw material to carry out the decomposition reaction again, which is conducive to further increasing the decomposition rate of the nitrate and improving the purity of the metal oxide. The highest decomposition rate of the nitrate can reach 99%.

[0063] The concentration of nitric acid obtained after acid production is about 50 - 70 wt%. The temperature of the flue gas after acid production is about 50 - 100 °C, and the CO2 concentration is about 20 - 80%. To recover the heat in the nitrogen-containing flue gas obtained after dust removal, it is heat-exchanged with the flue gas after acid production. After heat exchange, the temperature of the flue gas after acid production rises to 250 - 350 °C.

[0064] In a preferred embodiment, the method for recovering metal oxides and nitric acid by decomposing a nitrate solution further includes: recovering at least part of the carbon dioxide in the flue gas to obtain tail gas; washing the tail gas and then discharging it. A part of the flue gas obtained after preparing nitric acid is used as recycle gas, and the remaining part of the flue gas can be directly discharged from the chimney after carbon emission reduction through carbon dioxide recovery and then tail gas washing. After recovery, the purity of carbon dioxide can reach 99.5 - 99.9 wt%.

[0065] Example 1

[0066] The method for recovering metal oxides and nitric acid by decomposing a nitrate solution adopts asFigure 1 The device shown includes:

[0067] The 25% magnesium nitrate raw material liquid produced by the hydrometallurgical system enters the first-stage preheating device 40 for preheating. In the first-stage preheating device 40, the magnesium nitrate solution exchanges heat with the secondary steam generated by the concentration device 43 and is heated up. The magnesium nitrate solution is heated to 95 °C, and the heated magnesium nitrate solution enters the second-stage preheating device 41.

[0068] The magnesium nitrate solution after the first-stage preheating enters the second-stage preheating device 41, where it contacts and exchanges heat with the circulating gas at a temperature of about 300 °C sent by the cooler 90. The circulating gas is humidified and cooled down to 200 °C, and the magnesium nitrate solution is heated to 115 °C.

[0069] The preheated magnesium nitrate solution enters the concentration device 43, and the humidified circulating gas is sent to the mixing device 12.

[0070] The concentration device 43 is heated by the steam generated by the waste heat recovery device 15 (waste heat boiler). The magnesium nitrate solution is concentrated to a concentration of about 78% in the concentration device 43 and secondary steam is generated. The secondary steam is sent to the first-stage preheating device 40 for heat exchange and cooling. The concentrated magnesium nitrate solution enters the atomization device 14 (atomizing nozzle).

[0071] The circulating gas after being humidified and cooled enters the mixing device 12, where it is mixed with oxygen with a concentration of 95% to form an oxygen-enriched combustion-supporting gas with an oxygen concentration of about 30%. The oxygen-enriched combustion-supporting gas enters the combustion device 11.

[0072] The fuel and the oxygen-enriched combustion-supporting gas burn fully in the combustion device 11 to generate high-temperature gas (fuel gas), and the flue gas temperature is about 1000 °C. The high-temperature gas enters the gas distribution device 13.

[0073] The magnesium nitrate solution forms tiny droplets after passing through the atomization device 14 (atomizing nozzle) and enters the decomposition device 10. The high-temperature gas enters the decomposition device 10 evenly after passing through the gas distribution device 13. In the decomposition device 10, the high-temperature flue gas and the magnesium nitrate droplets contact and exchange heat fully. The magnesium nitrate dehydrates and decomposes to produce nitrogen-containing dust containing magnesium oxide powder and pyrolysis flue gas. The temperature of the nitrogen-containing dust at the outlet of the decomposition device 10 is about 550 °C. The solid collected at the bottom of the decomposition device 10 is sent back to the decomposition device 10 through the return device 50 for continuous decomposition, and the magnesium nitrate decomposition rate reaches 99%.

[0074] Magnesium oxide powder and pyrolysis flue gas (containing nitrogen oxides) enter the waste heat recovery device 15 (waste heat boiler). Part of the magnesium oxide powder settles and is collected. The pyrolysis flue gas heats the boiler feed water to obtain the heat-exchanged flue gas and generate steam. Part of the steam is sent to the concentration device 43 for heating use, and the other steam is sent out of the system for use. The temperature of the heat-exchanged flue gas is about 350 °C. The heat-exchanged flue gas and the remaining magnesium oxide powder enter the dust collection device 20 for further gas-solid separation to obtain the post-dust collection flue gas and magnesium oxide powder. The magnesium oxide powder produced at the decomposition device 10, the waste heat recovery device 15, and the dust collection device 20 is collected by the powder collection device 60 and transported to the powder collection device 60 (magnesium oxide powder silo) for storage and use. The post-dust collection flue gas enters the cooler 90, exchanges heat with the circulating gas produced by the acid-making device 30, cools down to 100 °C, and then enters the acid-making device 30 after cooling.

[0075] In the acid-making device 30, NO in the flue gas X gas is absorbed by water or nitric acid to produce nitric acid and obtain the post-acid-making flue gas. The nitric acid enters the nitric acid storage device 32 for storage. The concentration of nitric acid produced by the acid-making device 30 is about ~70%. The temperature of the post-acid-making flue gas is about 50 °C, and it is sent into the cooler 90 through the circulating fan 31 for heat exchange and heated to 250 °C. Part of the post-acid-making flue gas enters the carbon dioxide collection device 80, and after collection and treatment, carbon dioxide products are obtained. The purity of carbon dioxide is about 99.9%. The treated tail gas enters the tail gas scrubber 70. Magnesium oxide produced by the system is used for absorption treatment in the tail gas scrubber 70. A small amount of magnesium nitrate produced is sent to the magnesium nitrate storage tank. The treated tail gas is sent to the chimney 72 through the tail gas fan 71 for up-to-standard discharge. A first pressure monitoring device P1 is set on the gas distribution device 13, and a second pressure monitoring device P2 is set on the gas outlet pipeline of the decomposition device 10. P1 and P2 are interlocked with the outlet valve of the circulating fan 31 to maintain a slightly positive pressure of P1 at 50 Pa to 100 Pa and a slightly negative pressure of P2 at -100 Pa to -50 Pa.

[0076] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0077] (1) Using flue gas containing a relatively high concentration of CO2, containing a small amount of H2O, and almost no NO X for circulating heat transfer, realizing the cyclic enrichment and efficient recovery of CO2, reducing the X circulation of NO, improving safety and environmental protection, and reducing material costs.

[0078] (2) Utilizing cascade heat exchange to utilize heat of different grades, and simultaneously achieving the recovery of heat released during nitric acid preparation, the preheating of circulating gas, the concentration of magnesium nitrate solution, etc. The entire process can achieve cascade step-by-step heat exchange, and when there is a leak, acid condensation will not occur, the toxicity of the flue gas is very low, and the risk of leakage causing harm to the environment and personnel is relatively low.

[0079] It should be noted that the terms "first", "second", etc. in the description and claims of this application are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that such terms can be interchanged under appropriate circumstances so that the embodiments of this application described herein can, for example, be implemented in an order other than those described herein.

[0080] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An apparatus for recovering metal oxides and nitric acid by decomposing a nitrate solution, characterized in that The device for decomposing nitrate solution to recover metal oxide and nitric acid includes: A decomposition device (10) provided with a nitrate solution inlet, a fuel gas inlet, and a nitrogen-containing soot discharge outlet; A dust collection device (20) provided with a soot inlet, a nitrogen-containing flue gas discharge outlet, and a dust outlet, and the soot inlet is communicated with the nitrogen-containing soot discharge outlet through a soot conveying pipeline; An acid making device (30) provided with a nitrogen-containing flue gas inlet, a nitric acid discharge outlet, and a recycle gas outlet (301), the nitrogen-containing flue gas inlet is communicated with the nitrogen-containing flue gas discharge outlet through a nitrogen-containing flue gas conveying pipeline, and the recycle gas outlet (301) is communicated with the fuel gas inlet through a recycle gas conveying pipeline; A combustion device (11) provided with a fuel inlet, an auxiliary combustion gas inlet, and a fuel gas outlet, the auxiliary combustion gas inlet is communicated with the recycle gas outlet (301) through a recycle gas conveying pipeline, and the fuel gas outlet is communicated with the fuel gas inlet through a combustion gas conveying pipeline; A primary preheating device (40) provided with a primary raw material to be preheated inlet (401), a primary preheated raw material discharge outlet (402), and a heat medium inlet (403), and the primary preheating device (40) is used for preheating the nitrate solution; A secondary preheating device (41) arranged on the recycle gas conveying pipeline, the secondary preheating device (41) is provided with a secondary raw material to be preheated inlet (411) and a secondary preheated raw material discharge outlet (412), the secondary raw material to be preheated inlet (411) is communicated with the primary preheated raw material discharge outlet (402), and the secondary preheated raw material discharge outlet (412) is communicated with the nitrate solution inlet through a secondary preheated raw material conveying pipeline; Wherein, the device for decomposing nitrate solution to recover metal oxide and nitric acid further includes: at least one concentration device (43) arranged on the secondary preheated raw material conveying pipeline; The concentration device (43) is further provided with a first steam outlet (431), and the first steam outlet (431) is communicated with the heat medium inlet (403); The concentration device (43) is further provided with a heat source inlet, and the device for decomposing nitrate solution to recover metal oxide and nitric acid further includes a waste heat recovery device (15) arranged on the soot conveying pipeline, and the waste heat recovery device (15) is provided with a second steam outlet, and the second steam outlet is communicated with the heat source inlet.

2. The apparatus for recovering metal oxide and nitric acid by decomposing nitrate solution according to claim 1, wherein The device for decomposing nitrate solution to recover metal oxide and nitric acid further includes a mixing device (12) arranged on the recycle gas conveying pipeline, and the mixing device (12) is provided with an oxygen inlet.

3. The device for recovering metal oxides and nitric acid by decomposing a nitrate solution according to claim 1, characterized in that, The device for decomposing nitrate solution to recover metal oxide and nitric acid further includes: A gas distribution device (13) arranged on the combustion gas conveying pipeline; An atomizing device (14), the atomizing device (14) being arranged at the nitrate solution inlet.

4. The device for recovering metal oxide and nitric acid by decomposing nitrate solution according to claim 1, characterized in that, The decomposition device (10) is provided with a solid material discharge port (101) and a return material port (102). The solid material discharge port (101) and the return material port (102) are connected through a return material conveying pipeline. The device for decomposing nitrate solution to recover metal oxide and nitric acid further includes a return material device (50), and the return material device (50) is arranged on the return material conveying pipeline.

5. The device for recovering metal oxide and nitric acid by decomposing nitrate solution according to claim 4, characterized in that, The device for decomposing nitrate solution to recover metal oxide and nitric acid further includes a powder collecting device (60). The powder collecting device (60) further includes a dust collecting port, and the dust collecting port is respectively connected to the return material device (50), the waste heat recovery device (15) and the dust collecting device (20) for recovering the soot discharged from the return material device (50), the waste heat recovery device (15) and the dust collecting device (20).

6. The device for recovering metal oxides and nitric acid by decomposing a nitrate solution according to any one of claims 1 to 5, characterized in that, The device for decomposing nitrate solution to recover metal oxide and nitric acid further includes: An exhaust gas washing device (70), the exhaust gas washing device (70) being provided with an exhaust gas inlet and a purified gas discharge port, and the exhaust gas inlet and the circulating gas outlet (301) are connected through an exhaust gas conveying pipeline; A carbon dioxide collecting device (80), the carbon dioxide collecting device (80) being arranged on the exhaust gas conveying pipeline.

7. A method for recovering metal oxides and nitric acid by decomposing a nitrate solution, characterized in that, The method for decomposing nitrate solution to recover metal oxide and nitric acid includes: Performing a decomposition reaction on the nitrate solution and the fuel gas to obtain nitrogen-containing soot and metal oxide; Performing dust collection treatment on the nitrogen-containing soot to obtain nitrogen-containing flue gas and first dust; Mixing the nitrogen-containing flue gas with water to obtain nitric acid and flue gas; Burning at least part of the flue gas with fuel to obtain the fuel gas; wherein, Performing a first preheating on the nitrate solution to obtain a first-stage preheated raw material; Exchanging heat between the first-stage preheated raw material and the flue gas to enable the first-stage preheated raw material to perform a second heat exchange; Concentrating the nitrate solution that has undergone the second heat exchange to obtain a nitrate concentrate; and performing the decomposition reaction on the nitrate concentrate; The product of the concentration process includes first steam. The method for decomposing nitrate solution to recover metal oxide and nitric acid further includes: using the first steam as the heat source for the first preheating process; Recovering the waste heat in the nitrogen-containing soot; the product of the waste heat recovery process further includes second steam, and using the second steam as the heat source for the concentration process.

8. The method for recovering metal oxide and nitric acid by decomposing nitrate solution according to claim 7, characterized in that, The nitrate solution is heated to 90 - 99 °C after the first preheating, and then heated to 110 - 120 °C after the second heat exchange, and the temperature of the flue gas drops to 150 - 250 °C.

9. The method for recovering metal oxide and nitric acid by decomposing nitrate solution according to claim 7, characterized in that, The method for decomposing nitrate solution to recover metal oxide and nitric acid further includes: performing the decomposition reaction on the fuel gas after passing through a gas distribution device.

10. The method for recovering metal oxides and nitric acid by decomposing a nitrate solution according to claim 7, characterized in that, The method for decomposing nitrate solution to recover metal oxide and nitric acid further includes: using the unreacted materials in the decomposition reaction process as reaction raw materials to perform the decomposition reaction again.

11. The method for recovering metal oxide and nitric acid by decomposing nitrate solution according to any one of claims 7 to 10, characterized in that, The method for decomposing a nitrate solution to recover metal oxides and nitric acid further includes: recovering at least part of the carbon dioxide in the flue gas to obtain tail gas; and discharging the tail gas after washing.

Images