System for preparing metal oxide through nitrate pyrolysis and recycling nitric acid step by step

Abstract

The utility model discloses a system for preparing metal oxide through nitrate pyrolysis and recycling nitric acid step by step. The system comprises a heating melting tank, an atomization pyrolysis furnace, a first dust collector, a first heat exchanger, a dynamic pyrolysis furnace, a second dust collector, a second heat exchanger and a nitric acid regeneration device. Nitrate is heated and melted to obtain nitrate hot fluid, the nitrate hot fluid is atomized and pyrolyzed at low temperature to obtain a precursor, and then the precursor is fed into a dynamic pyrolyzing furnace for thermal decomposition to obtain metal oxide powder. Condensing the dust-collected gas of the atomization pyrolyzing furnace through a heat exchanger to directly collect a first part of finished product nitric acid; the tail gas of the dynamic pyrolyzing furnace passes through a heat exchanger and then is sent to a nitric acid regeneration device to recover a second part of finished nitric acid. According to the system, the size of the atomization pyrolyzing furnace is obviously reduced, the pyrolyzing temperature is reduced, the heat energy utilization efficiency is improved, and the energy cost is greatly reduced. The treatment capacity of the nitric acid regeneration device is remarkably reduced, and the nitric acid regeneration and recovery cost is reduced, so that energy conservation and emission reduction are realized.

Description

Technical Field

[0001] The utility model provides a system for stepwise recovering nitric acid by pyrolyzing metal nitrates to prepare metal oxides, belonging to the cross field of inorganic chemical industry and metallurgical engineering. Background Technique

[0002] Most metal nitrates can be decomposed into metal oxides, nitrogen dioxide and oxygen under heating conditions. The released oxygen and nitrogen dioxide can be absorbed by water under certain conditions to generate nitric acid. Metal oxides can also be recycled in hydrometallurgy of non-ferrous metals and other chemical fields to achieve a low-cost production process. This way of recovering nitric acid and metal oxides by pyrolyzing metal nitrates has attracted more and more attention.

[0003] In practical applications, a rotary kiln is a conventional device for pyrolysis. However, when directly transporting metal nitrates into the rotary kiln for heating and decomposition, the nitrates will melt to form a fluid that adheres to the inner wall of the decomposition furnace, causing caking, uneven heating of the nitrates, and incomplete decomposition of the nitrates. As a result, the operating energy consumption of the system is high and the decomposition rate of the nitrates is not high. For this reason, people have developed a fluidized pyrolysis method using high-temperature gas as a heat source, which can make the nitrates heated evenly and decomposed sufficiently, and greatly improve the recovery rate of nitric acid.

[0004] For example, Chinese Patent CN109721038A discloses a method and device system for recovering nitric acid by pyrolyzing metal nitrates. The metal nitrates are transported to at least two-stage preheating devices for heating and liquefaction. Then, the hot fluid of the metal nitrates is transported to a decomposer and heated by high-temperature gas to decompose the metal nitrates to produce a mixed gas and solid powder. The mixed gas and the solid powder are separated. Part of the mixed gas is transported to a nitric acid recovery tank, and the other part of the mixed gas is heated to 500 - 800 °C and then returned to the decomposer to heat the hot fluid of the metal nitrates to make it efficiently decomposed by heating. However, this method also has some drawbacks. First, since it is necessary to ensure that the concentration of nitrogen oxides in the decomposed gas is high enough, indirect heating of the circulating gas is required, and the indirect heating has low thermal efficiency. In addition, the available heating methods such as electric heating (electric energy) or heating furnace heating (gas fuel) all have the problem of too high operating heat source cost. Second, in order to ensure that the metal nitrates in the pyrolysis furnace are decomposed as thoroughly as possible and increase the residence time of the material in the furnace, the furnace body is usually designed to be relatively large, resulting in an increase in fixed investment and large heat dissipation of the equipment. Finally, all the gases after pyrolysis are recycled and regenerated through a nitric acid regeneration device, resulting in a large processing capacity of the nitric acid regeneration equipment, and both the fixed investment and the operating cost are increased.

[0005] Chinese Patent CN213060214U discloses a system device for the thermal decomposition of nitrates. First, the nitrates are converted into nitrate thermal fluid, and the high-temperature gas generated by the combustion of natural gas is used as the heat source to pyrolyze the nitrates. Then, the high-temperature gas is transported to a nitric acid recovery tank for nitric acid recovery. Although this patent increases the thermal energy utilization rate by adopting a direct combustion pyrolysis method, this method greatly reduces the concentration of nitrogen oxide gas after pyrolysis, and then greatly increases the burden on subsequent nitric acid regeneration equipment. The process is difficult to implement and has poor feasibility.

[0006] Chinese Patent CN 115490249 A discloses a method and system for the stepwise thermal decomposition of nitrates to prepare metal oxide powders and nitric acid regeneration. This method first atomizes and pyrolyzes the nitrates at a low temperature to granulate, obtaining a basic nitrate precursor with controllable particle size and morphology and good fluidity. Then, the precursor is sent to a dynamic pyrolysis furnace for long-term thermal decomposition to obtain metal oxide powders. The gas after cyclone dust removal in the atomization pyrolysis furnace and the tail gas of the dynamic pyrolysis furnace are subjected to high-temperature deep dust removal. The small amount of collected materials is returned to the dynamic pyrolysis furnace for pyrolysis. The tail gas after dust removal is divided into two parts. One part is sent to the atomization pyrolysis furnace for low-temperature pyrolysis granulation of nitrates after circulating and supplementary heating. The other part is directly sent to a nitric acid absorption and regeneration device to obtain regenerated nitric acid. This system significantly reduces the volume of the atomization pyrolysis furnace, reduces the pyrolysis temperature, avoids unnecessary heat loss, improves the comprehensive thermal efficiency, and significantly reduces the comprehensive operation cost, thus achieving energy conservation and emission reduction. Although this patent optimizes the decomposition furnace by adopting a two-stage pyrolysis method, the heating method of the pyrolysis furnace still requires indirect heat exchange and can only use electric heating or indirect heat exchange for heating. The energy consumption cost remains high and the thermal efficiency is low. In addition, the two pyrolysis tail gases are mixed and then enter the nitric acid regeneration device, and the regeneration device still has a heavy burden and the nitric acid regeneration and recovery cost is high. Utility Model Content

[0007] The utility model discloses a system for the stepwise recovery of nitric acid by the thermal decomposition of nitrates to prepare metal oxides. First, the nitrates are atomized and pyrolyzed at a low temperature to form a precursor (basic nitrate or hydroxide), and then the precursor is sent to a dynamic pyrolysis furnace for long-term thermal decomposition to obtain metal oxide powders. The gas after dust collection in the atomization pyrolysis furnace is directly condensed through a first heat exchanger to collect the first part of the finished nitric acid; the gas after dust collection in the tail gas of the dynamic pyrolysis furnace is cooled through a second heat exchanger and the waste heat is recovered, and then sent to a nitric acid regeneration device for regenerative recovery of the second part of the finished nitric acid. The tail gas after the recovery of the two parts of nitric acid is discharged after deep absorption treatment. This system significantly reduces the volume of the atomization pyrolysis furnace, reduces the pyrolysis temperature, improves the thermal energy utilization efficiency, and greatly reduces the energy cost. And the processing capacity of the nitric acid regeneration device is significantly reduced, and the nitric acid regeneration and recovery cost is decreased, thus achieving energy conservation and emission reduction.

[0008] The utility model is realized through the following technical solutions:

[0009] A system for step - by - step recovering nitric acid by pyrolyzing nitrate to prepare metal oxide, comprising a heating and melting tank, an atomizing pyrolysis furnace, a first dust collector, a first heat exchanger, a dynamic pyrolysis furnace, a second dust collector, a second heat exchanger and a nitric acid regeneration device. Among them,

[0010] The heating and melting tank serves as a carrier for the nitrate to be treated, and is used to heat the nitrate to a molten state;

[0011] The discharge port of the heating and melting tank is connected to the feed port of the atomizing pyrolysis furnace. The atomizing pyrolysis furnace is equipped with an atomizing nozzle, which is used to atomize the nitrate and pyrolyze the nitrate at a certain temperature in the atomizing pyrolysis furnace to generate a precursor;

[0012] The discharge port of the atomizing pyrolysis furnace is connected to the feed port of the first dust collector. The first dust collector is used to perform gas - solid separation on the output material of the atomizing pyrolysis furnace to obtain a solid - phase discharge and a first mixed gas;

[0013] The gas - phase outlet of the first dust collector is connected to the feed port of the first heat exchanger. The first heat exchanger is used to reduce the temperature of the first mixed gas, condense the nitric acid into a liquid, and discharge it from the condensate outlet of the first heat exchanger to obtain a first part of finished nitric acid;

[0014] The gas - phase outlet of the first heat exchanger is connected to the feed port of the tail gas absorption device;

[0015] The solid - phase discharge port of the first dust collector is connected to the feed port of the dynamic pyrolysis furnace. The dynamic pyrolysis furnace is used to calcine the precursor output from the atomizing pyrolysis furnace at a certain temperature for a long time to obtain a more thoroughly decomposed metal oxide, and output the metal oxide from the solid - phase discharge port of the dynamic pyrolysis furnace;

[0016] The gas - phase outlet of the dynamic pyrolysis furnace is connected to the feed port of the second dust collector. The second dust collector is used to perform gas - solid separation on the tail gas of the dynamic pyrolysis furnace to obtain a small amount of solid - phase discharge and a second mixed gas;

[0017] The solid - phase outlet of the second dust collector is connected to the feed port of the dynamic pyrolysis furnace, and is used to return a small amount of incompletely decomposed metal basic nitrate or hydroxide to the dynamic pyrolysis furnace for complete pyrolysis;

[0018] The gas - phase outlet of the second dust collector is connected to the feed port of the second heat exchanger. The second heat exchanger is used to reduce the temperature of the second mixed gas and recover waste heat, and the waste heat can be used to heat the melting tank to melt nitrate;

[0019] The gas - phase outlet of the second heat exchanger is connected to the inlet of the nitric acid regeneration device, and the output gas of the second heat exchanger is sent to the nitric acid regeneration device;

[0020] The nitric acid regeneration device is used to obtain regenerated nitric acid, i.e., the second part of the finished nitric acid, by pressurized absorption of the second mixed gas after recovering waste heat.

[0021] Optionally, the system further includes a heating device, the outlet of which is connected to the top inlet of the atomization pyrolysis furnace. The heating device is used to heat air or steam and then send it to the atomization pyrolysis furnace to supply the heat required for pyrolysis.

[0022] Optionally, the system further includes an induced draft fan, the inlet of which is connected to the gas phase outlet of the second heat exchanger, and the outlet of which is connected to the inlet of the nitric acid regeneration device. The induced draft fan is used to send the second mixed gas after recovering waste heat output by the second heat exchanger into the nitric acid regeneration device.

[0023] Optionally, the gas phase outlet of the second heat exchanger is connected to the feed inlet of the tail gas absorption device. That is, the gas phase outlet of the second heat exchanger can be either connected to the nitric acid regeneration device or to the feed inlet of the tail gas absorption device, and the gas phase outlet of the second heat exchanger is switched between the inlet of the nitric acid regeneration device and the feed inlet of the tail gas absorption device according to the working conditions.

[0024] Optionally, the system further includes a tail gas absorption device, the feed inlet of which is connected to the gas phase outlet of the nitric acid regeneration device. The tail gas absorption device is used to absorb NO in the tail gas x gas, and the outlet of the tail gas absorption device is connected to the atmosphere.

[0025] Optionally, the atomization pyrolysis furnace is one of a two-fluid spray atomization pyrolysis furnace, a pressure atomization pyrolysis furnace, and a rotary centrifugal atomization pyrolysis furnace, or a combination of at least two of them.

[0026] Optionally, the type of the dynamic pyrolysis furnace is various types of rotary kilns and tunnel kilns.

[0027] Optionally, the first dust collector and the second dust collector are one of cyclone dust collection, electrostatic dust collection, high-temperature metal membrane dust collection, porous ceramic dust collection, and high-temperature metal wire dust collection, or a combination of at least two of them.

[0028] The present invention also provides a method for stepwise recovering nitric acid using the system, including the following steps:

[0029] (1) Adding nitrate into a heating and melting tank to obtain a molten nitrate hot fluid;

[0030] (2) Spray the nitrate hot fluid into the atomization pyrolysis furnace for low-temperature pyrolysis. After the low-temperature pyrolysis products are subjected to gas-solid separation by the first dust collector, a precursor (basic nitrate or hydroxide) and a first mixed gas are obtained;

[0031] (3) Input the precursor (basic nitrate or hydroxide) into the dynamic pyrolysis furnace for calcination pyrolysis. After gas-solid separation by the second dust collector, a completely decomposed metal oxide powder and a second mixed gas are obtained;

[0032] (4) The first mixed gas is condensed by the first heat exchanger, and the first part of the finished nitric acid is directly collected; the second mixed gas is cooled by the second heat exchanger and the waste heat is recovered, and then sent to the nitric acid regeneration device to obtain the second part of the finished nitric acid;

[0033] After the first mixed gas and the second mixed gas recover nitric acid, the tail gas obtained is discharged after deep absorption treatment.

[0034] During long-term scientific research and exploration, the applicant found that nitrates can generate basic nitrates, water, nitric acid, and nitrogen oxides during the fluidized bed pyrolysis process. If the temperature is controlled properly and the type of nitrate is selected appropriately (especially nitrates with a metal activity sequence lower than calcium among metal nitrates), basic nitrates, water, nitric acid, and nitrogen oxides (trace amounts, 100 - 1000 ppm) can be generated during the fluidized bed pyrolysis process. In addition, the basic nitrate does not melt during the pyrolysis process, so a rotary kiln dynamic pyrolysis can be used. If the content of water vapor in the atmosphere is increased, the hydrolysis of the basic nitrate can be further promoted to obtain hydroxide and nitric acid. In this process, more than 65% of the nitrogen element exists in the form of nitric acid in the first mixed gas, and the energy consumption of the first-step atomization pyrolysis is also the largest, accounting for more than 69.5%. Based on this discovery, the applicant further optimized the two-step pyrolysis process, that is, there are two situations:

[0035] (1) Hot air heating

[0036] In the first step, the nitrate generates nitric acid, basic nitrate, water, and nitrogen oxides (trace amounts) in the atmosphere of hot air. After dust removal, the condensed nitric acid is obtained through condensation, and the remaining gas is discharged up to standard after treatment.

[0037] In the second step, the basic nitrate undergoes calcination pyrolysis to produce metal oxides and nitrogen oxides. The nitrogen oxides enter the nitric acid regeneration device through dust removal to obtain regenerated nitric acid.

[0038] (2) Water vapor heating

[0039] In the first step, the nitrate generates nitric acid, hydroxide, water, and nitrogen oxides (trace amounts) in the atmosphere of hot air. After dust removal, the condensed nitric acid is obtained through condensation, and the remaining gas is discharged up to standard after treatment.

[0040] In the second step, if necessary, the metal hydroxide can be calcined to produce metal oxide, nitrogen oxides (trace amounts), and the gas after dust removal can be discharged up to standard after treatment without passing through the nitric acid absorption and regeneration device.

[0041] Based on this, the applicant optimized the two-step pyrolysis process, reduced the system operation cost and nitric acid regeneration cost, greatly increased the economy of the process, improved the thermal efficiency, and achieved energy conservation and emission reduction.

[0042] The beneficial effects of the present utility model are as follows:

[0043] (1) In the two-step pyrolysis, the present utility model uses hot air or steam as the heating atmosphere for atomization pyrolysis, enriches the fuel types, and greatly reduces the heat source cost.

[0044] (2) By recycling nitric acid in two steps, the present utility model greatly reduces the processing capacity of the nitric acid regeneration device, reduces the nitric acid regeneration and recovery cost, and thus realizes energy conservation and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present utility model. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0046] Figure 1 It is a schematic structural diagram of a system for pyrolyzing nitrate to prepare metal oxide and stepwise recovering nitric acid provided by the present utility model;

[0047] Among them, 1 - heating and melting tank, 2 - heating device, 3 - atomization pyrolysis furnace, 4 - first dust collector, 5 - first heat exchanger, 6 - dynamic pyrolysis furnace, 7 - second dust collector, 8 - second heat exchanger, 9 - induced draft fan, 10 - nitric acid regeneration device, 11 - tail gas absorption device. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] In order to make the technical problems, technical solutions and advantages to be solved by the present utility model clearer, the following will be described in detail with reference to the drawings and specific embodiments.

[0049] The present utility model provides a system for pyrolyzing nitrate to prepare metal oxide and stepwise recovering nitric acid, as Figure 1 shown, including a heating and melting tank 1, a heating device 2, an atomization pyrolysis furnace 3, a first dust collector 4, a first heat exchanger 5, a dynamic pyrolysis furnace 6, a second dust collector 7, a second heat exchanger 8, an induced draft fan 9, a nitric acid regeneration device 10, and a tail gas absorption device 11. Among them,

[0050] The heating and melting tank 1 serves as a carrier for nitrates to be processed, used to heat the nitrates to a molten state to obtain a nitrate thermal fluid, and the heating or not and the heating temperature are selected as appropriate;

[0051] The discharge port of the heating and melting tank 1 is connected to the feed port of the atomization pyrolysis furnace 3. The atomization pyrolysis furnace 3 is equipped with an atomization nozzle for atomizing the nitrates, and the nitrates are pyrolyzed to form precursors (basic nitrates or hydroxides) at a certain temperature in the atomization pyrolysis furnace 3;

[0052] The outlet of the heating device 2 is connected to the top feed port of the atomization pyrolysis furnace 3. The heating device 2 is used to heat air or steam and then send it to the atomization pyrolysis furnace 3 to supply the heat required for pyrolysis;

[0053] The discharge port of the atomization pyrolysis furnace 3 is connected to the feed port of the first dust collector 4. The first dust collector 4 is used to separate the gas and solid of the output material of the atomization pyrolysis furnace 3 to obtain a solid-phase discharge and a first mixed gas;

[0054] The gas-phase outlet of the first dust collector 4 is connected to the feed port of the first heat exchanger 5. The first heat exchanger 5 is used to reduce the temperature of the first mixed gas and condense the nitric acid into a liquid, and then discharge it from the condensate outlet of the first heat exchanger 5 to obtain the first part of the finished nitric acid;

[0055] The gas-phase outlet of the first heat exchanger 5 is connected to the feed port of the tail gas absorption device 11;

[0056] The solid-phase discharge port of the first dust collector 4 is connected to the feed port of the dynamic pyrolysis furnace 6. The dynamic pyrolysis furnace 6 is used to calcine the precursors (basic nitrates or hydroxides) output from the atomization pyrolysis furnace at a certain temperature for a long time to obtain a more thoroughly decomposed metal oxide, and the metal oxide is output from the solid-phase discharge port of the dynamic pyrolysis furnace 6;

[0057] The gas-phase outlet of the dynamic pyrolysis furnace 6 is connected to the feed port of the second dust collector 7. The second dust collector 7 is used to separate the gas and solid of the tail gas of the dynamic pyrolysis furnace 6 to obtain a small amount of solid-phase discharge and a second mixed gas;

[0058] The solid-phase outlet of the second dust collector 7 is connected to the feed port of the dynamic pyrolysis furnace 6, and is used to return a small amount of incompletely decomposed basic nitrates or hydroxides to the dynamic pyrolysis furnace 6 for thorough pyrolysis;

[0059] The gas-phase outlet of the second dust collector 7 is connected to the feed port of the second heat exchanger 8. The second heat exchanger 8 is used to reduce the temperature of the second mixed gas and recover the waste heat, and the waste heat can be used to heat the melting tank to melt the nitrates;

[0060] The gas-phase outlet of the second heat exchanger 8 is connected to the inlet of the induced draft fan 9 and sent to the nitric acid regeneration device 10; the gas-phase outlet of the second heat exchanger 8 is also connected to the feed port of the tail gas absorption device 11 and is switched according to the working conditions.

[0061] The inlet of the nitric acid regeneration device 10 is connected to the outlet of the induced draft fan 9. The nitric acid regeneration device 10 is used to obtain regenerated nitric acid, that is, the second part of the finished nitric acid, by pressurized absorption of the second mixed gas after recovering waste heat.

[0062] The gas-phase outlet of the nitric acid regeneration device 10 is connected to the feed port of the tail gas absorption device 11.

[0063] The tail gas absorption device 11 is used to absorb NO in the tail gas. x The gas, and the outlet of the tail gas absorption device 11 is connected to the atmosphere.

[0064] The present utility model also provides a method for stepwise recovering nitric acid by pyrolyzing nitrate to prepare metal oxide, and the method uses the above pyrolysis regeneration system, including the following steps:

[0065] (1) Add nitrate into the heating and melting tank to obtain a molten nitrate thermal fluid.

[0066] (2) Spray the nitrate thermal fluid into the atomizing pyrolysis furnace for low-temperature pyrolysis. After the low-temperature pyrolysis products are subjected to gas-solid separation through the first heat exchanger, a precursor (basic nitrate or hydroxide) and a first mixed gas are obtained.

[0067] (3) Input the precursor (basic nitrate or hydroxide) into the dynamic pyrolysis furnace for calcination pyrolysis. After gas-solid separation through the second heat exchanger, a completely decomposed metal oxide powder and a second mixed gas are obtained.

[0068] (4) The first mixed gas directly collects the first part of the finished nitric acid through condensation in the first heat exchanger; the second mixed gas is cooled in the second heat exchanger and the waste heat is recovered, and then sent to the nitric acid regeneration device to regenerate the second part of the finished nitric acid. The tail gas after recovering the two parts of nitric acid is discharged after deep absorption treatment.

[0069] In an embodiment of the present utility model, in step (1), the nitrate type is one or a mixture of aluminum nitrate, iron nitrate, manganese nitrate, nickel nitrate, cobalt nitrate, and scandium nitrate, and the heating temperature range of the melting tank is from room temperature to 140 °C.

[0070] In an embodiment of the present utility model, in step (2), the nitrate thermal fluid is sprayed into the atomizing pyrolysis furnace for low-temperature pyrolysis, the temperature range is 150 °C - 300 °C, and the atomizing method is one or a combination of at least two of two-fluid spray atomization, pressure atomization, and rotary centrifugal atomization.

[0071] In one embodiment of the present utility model, in step (3), the precursor (basic nitrate or hydroxide) is input into a dynamic pyrolysis furnace for calcination pyrolysis. The temperature range in the dynamic pyrolysis furnace is 300°C - 700°C, and the pyrolysis time is 0.5 h - 3 h. The types of dynamic pyrolysis furnaces are various types of rotary kilns, tunnel kilns, etc.

[0072] In one embodiment of the present utility model, in step (3), there are a small amount of uncompletely decomposed basic nitrates or hydroxides in the tail gas generated after pyrolysis in the dynamic pyrolysis furnace. After collecting this part of the basic nitrates or hydroxides by a second dust collector, they are returned to the dynamic pyrolysis furnace for pyrolysis.

[0073] In one embodiment of the present utility model, in step (4), the tail gases generated after pyrolysis in the atomization pyrolysis furnace and the dynamic pyrolysis furnace are dust collected to obtain a first mixed gas and a second mixed gas, wherein the dust collection method is one or a combination of at least two of cyclone dust collection, electrostatic dust collection, high-temperature metal membrane dust collection, porous ceramic dust collection, and high-temperature metal wire dust collection.

[0074] In one embodiment of the present utility model, using hot air as the heat medium, after the second mixed gas in step (3) is cooled and its waste heat is recovered by a second heat exchanger, it is sent to a nitric acid regeneration device to obtain a second part of finished nitric acid.

[0075] In one embodiment of the present utility model, using water vapor as the heat medium, in step (2), the second mixed gas can directly lead to a tail gas absorption device after recovering its waste heat, and after being treated to meet the standards, it is discharged, and the discharged NO x concentration is lower than 50 ppm.

[0076] In one embodiment of the present utility model, in step (4), the first mixed gas passes through a heat exchanger for condensation to directly collect the first part of finished nitric acid, and the mass fraction of nitric acid is 15 - 60%. The second mixed gas passes through a heat exchanger for cooling and recovering its waste heat, and then is sent to a nitric acid absorption device to regenerate the second part of nitric acid, and the mass fraction of nitric acid is 40 - 60%. The proportion of the first part of finished nitric acid in the total recovered nitric acid is 65 - 99%.

[0077] In one embodiment of the present utility model, in step (4), the NO in the tail gas after the two parts of recovered nitric acid x concentration is lower than 1000 ppm, and after being deeply absorbed and treated to meet the standards, it is discharged, and the discharged NO x concentration is lower than 50 ppm.

[0078] Examples 1 to 4 all adopt Figure 1 the system for stepwise recovering nitric acid by pyrolyzing nitrate to prepare metal oxides as shown.

[0079] Example 1

[0080] Place ferric nitrate crystals in a heating and melting tank, heat to 110 °C to melt them into a hot fluid, and then atomize the ferric nitrate through a rotary centrifugal atomizer and send it into an atomization pyrolysis furnace. The heat source gas is direct combustion hot air, and the fuel is natural gas. The temperature in the atomization pyrolysis furnace is 200 °C. The ferric nitrate undergoes rapid low-temperature thermal decomposition in the atomization pyrolysis furnace to obtain a mixed dust gas containing basic ferric nitrate precursor, H2O, HNO3, NO x (trace), after dust collection by the first dust collector, basic ferric nitrate and the first mixed gas are obtained. The first mixed gas passes through the first heat exchanger for condensation to directly collect the first part of the finished nitric acid with a concentration of 50%, and the recovery rate of this part of nitric acid is 66.7%. The basic ferric nitrate is then sent to a dynamic pyrolysis furnace (externally heated rotary kiln) and calcined at 350 °C for 2 h to obtain iron oxide, nitrogen oxides, H2O and oxygen, and the decomposition rate of iron oxide is greater than 99%. After the tail gas of the dynamic pyrolysis furnace undergoes electrostatic deep dust removal, the second mixed gas is obtained. After the second mixed gas passes through the second heat exchanger to cool down and recover waste heat, it is sent to a nitric acid regeneration device to regenerate and recover the second part of the finished nitric acid with a concentration of 55%. The tail gas after condensation of the first mixed gas and the tail gas after nitric acid regeneration absorption are treated by a tail gas absorption device and then discharged, and the total recovery rate of nitric acid is greater than 98%.

[0081] Example 2

[0082] Place ferric nitrate crystals in a heating and melting tank, heat to 110 °C to melt them into a hot fluid, and then atomize the ferric nitrate through a rotary centrifugal atomizer and send it into an atomization pyrolysis furnace. The heat source gas is high-temperature steam, and the fuel is coke oven gas. The temperature in the atomization pyrolysis furnace is 200 °C. The ferric nitrate undergoes rapid low-temperature thermal decomposition in the atomization pyrolysis furnace to obtain a mixed dust gas containing iron hydroxide precursor, H2O, HNO3, NO x (trace), after dust collection by the first dust collector, iron hydroxide and the first mixed gas are obtained. The first mixed gas passes through the first heat exchanger for condensation to directly collect the finished nitric acid with a concentration of 17.07%, and the recovery rate of this part of nitric acid is 99%. The iron hydroxide is then sent to a dynamic pyrolysis furnace (externally heated rotary kiln) and calcined at 350 °C for 2 h to obtain iron oxide, water, oxygen and NO x (trace), and the decomposition rate of iron oxide is greater than 99%. After the tail gas of the dynamic pyrolysis furnace undergoes electrostatic deep dust removal, the second mixed gas is obtained. After the tail gas after condensation of the first mixed gas and the second mixed gas recover waste heat, the tail gas is treated by a tail gas absorption device and then discharged.

[0083] Example 3

[0084] Place aluminum nitrate crystals in a heating and melting tank, heat to 95 °C to melt them into a hot fluid, and then atomize the aluminum nitrate through a two-fluid atomizer and send it into an atomization pyrolysis furnace. The heat source gas is directly combusted hot air, and the fuel is natural gas. The temperature in the atomization pyrolysis furnace is 180 °C. The aluminum nitrate undergoes rapid low-temperature thermal decomposition in the atomization pyrolysis furnace to obtain a mixed dust gas containing basic aluminum nitrate precursor, H2O, HNO3, and NO (trace amounts). x After dust collection by the first dust collector, basic aluminum nitrate and the first mixed gas are obtained. The first mixed gas passes through the first heat exchanger for condensation to directly collect the first part of the finished nitric acid with a concentration of 57.3%, and the recovery rate of this part of nitric acid is 83.3%. The basic aluminum nitrate is then sent to a dynamic pyrolysis furnace (externally heated rotary kiln) and calcined at 500 °C for 1 h to obtain γ-aluminum oxide, nitrogen oxides, H2O, and oxygen, and the decomposition rate of aluminum oxide is greater than 99.5%. After the tail gas of the dynamic pyrolysis furnace undergoes electrostatic deep dust removal, the second mixed gas is obtained. After the second mixed gas passes through the second heat exchanger to cool down and recover waste heat, it is sent to a nitric acid regeneration device to regenerate and recover the second part of the finished nitric acid with a concentration of 50%. The tail gas after condensation of the first mixed gas and the tail gas after absorption and regeneration of nitric acid are discharged after being treated by a tail gas absorption device.

[0085] Example 4

[0086] Place aluminum nitrate crystals in a heating and melting tank, heat to 95 °C to melt them into a hot fluid, and then atomize the aluminum nitrate through a two-fluid atomizer and send it into an atomization pyrolysis furnace. The heat source gas is high-temperature steam, and the fuel is coke oven gas. The temperature in the atomization pyrolysis furnace is 250 °C. The aluminum nitrate undergoes rapid low-temperature thermal decomposition in the atomization pyrolysis furnace to obtain a mixed dust gas containing aluminum hydroxide precursor, H2O, HNO3, and NO (trace amounts). x After dust collection by the first dust collector, aluminum hydroxide and the first mixed gas are obtained. The first mixed gas passes through the first heat exchanger for condensation to directly collect the first part of the finished nitric acid with a concentration of 20.6%, and the recovery rate of this part of nitric acid is 99%. The aluminum hydroxide is then sent to a dynamic pyrolysis furnace (externally heated rotary kiln) and calcined at 500 °C for 1 h to obtain γ-aluminum oxide, water, oxygen, and NO (trace amounts), and the decomposition rate of aluminum oxide is greater than 99.5%. After the tail gas of the dynamic pyrolysis furnace undergoes electrostatic deep dust removal, the second mixed gas is obtained. The tail gas after condensation of the first mixed gas and the tail gas after recovering waste heat from the second mixed gas are discharged after being treated by a tail gas absorption device. x After electrostatic deep dust removal of the tail gas of the dynamic pyrolysis furnace, the second mixed gas is obtained. The tail gas after condensation of the first mixed gas and the tail gas after recovering waste heat from the second mixed gas are discharged after being treated by a tail gas absorption device.

[0087] The heat source gas in Examples 1 and 3 is directly combusted hot air. The atomization pyrolysis furnace uses hot air as the heat source, and the nitrate decomposition yields hydroxides, H2O, HNO3, and NO. xThe first mixed gas containing (trace) mixed dust gas, H2O and HNO3 can be directly condensed to obtain nitric acid, and most of the nitric acid can be recovered. Only the second mixed gas needs to be sent to the nitric acid regeneration device, greatly reducing the burden on the regeneration device.

[0088] In Examples 2 and 4, the heat source is high-temperature steam. The atomization pyrolysis furnace uses high-temperature steam as the heat source, and the nitrate decomposes to obtain hydroxides, H2O, HNO3 and NO x , the first mixed gas containing H2O and HNO3 can be directly condensed to obtain nitric acid, and the recovery rate of the first part of nitric acid is greater than 99%. Therefore, the second mixed gas can directly pass through the tail gas absorption device after recovering waste heat, and be discharged after reaching the standard after treatment, without generating the second part of finished nitric acid. This heating method does not require the use of a nitric acid regeneration device.

[0089] Comparative Example

[0090] Taking 1 ton of aluminum nitrate nonahydrate as an example, the comprehensive operating costs of the single atomization pyrolysis process, the two-step pyrolysis one-step nitric acid recovery process, the two-step pyrolysis two-step nitric acid recovery (hot air-natural gas), the two-step pyrolysis two-step nitric acid recovery (hot air-coal), and the two-step pyrolysis two-step nitric acid recovery process (steam-coal) will be calculated respectively. The results are shown in Table 1 (the operating cost is converted to 3 yuan / Nm 3 Natural gas, calorific value 8000 kcal / Nm 3 . The price of coal is 900 yuan / ton, and the calorific value is 7000 kcal / kg. The single atomization pyrolysis process and the two-step pyrolysis one-step nitric acid recovery process respectively use the nitrate pyrolysis nitric acid recovery devices in CN 109721038 A and CN 218523945 U, and are compared with the different methods of the present invention).

[0091] Table 1

[0092]

[0093] Calculation shows that the lowest operating cost of this patent is 124.4 yuan, which is a 70.7% decrease compared to the one-step pyrolysis process and a 63% decrease compared to the original two-step pyrolysis process. In addition, the steam coal gas process can save the nitric acid pressurized absorption device, and the fixed investment is greatly reduced. From the above results, it can be seen that this patent saves the nitric acid regeneration cost, greatly reduces the operating cost of the equipment, and has excellent economy.

[0094] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, and all should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A system for stepwise recovering nitric acid by pyrolyzing nitrate to prepare metal oxide, characterized in that, It includes a heating and melting tank, an atomization and pyrolysis furnace, a first dust collector, a first heat exchanger, a dynamic pyrolysis furnace, a second dust collector, a second heat exchanger and a nitric acid regeneration device, and further includes a tail gas absorption device. Among them, the heating and melting tank serves as a carrier for nitrates to be processed, and is used to heat the nitrates to a molten state; the discharge port of the heating and melting tank is connected to the feed port of the atomization and pyrolysis furnace, and the atomization and pyrolysis furnace is provided with an atomization nozzle, which is used to atomize the nitrates and thermally decompose the nitrates to generate precursors at a certain temperature in the atomization and pyrolysis furnace; the discharge port of the atomization and pyrolysis furnace is connected to the feed port of the first dust collector, and the first dust collector is used to perform gas-solid separation on the output materials of the atomization and pyrolysis furnace to obtain solid-phase discharge and a first mixed gas; the gas-phase outlet of the first dust collector is connected to the feed port of the first heat exchanger, and the first heat exchanger is used to lower the temperature of the first mixed gas, condense nitric acid into a liquid, and discharge it from the condensate outlet of the first heat exchanger to obtain a first part of finished nitric acid; the gas-phase outlet of the first heat exchanger is connected to the feed port of the tail gas absorption device; the solid-phase discharge port of the first dust collector is connected to the feed port of the dynamic pyrolysis furnace, and the dynamic pyrolysis furnace is used to calcine the precursors output from the atomization and pyrolysis furnace to obtain completely decomposed metal oxides, and output the metal oxides from the solid-phase discharge port of the dynamic pyrolysis furnace; the gas-phase outlet of the dynamic pyrolysis furnace is connected to the feed port of the second dust collector, and the second dust collector is used to perform gas-solid separation on the tail gas of the dynamic pyrolysis furnace to obtain a small amount of solid-phase discharge and a second mixed gas; the solid-phase outlet of the second dust collector is connected to the feed port of the dynamic pyrolysis furnace, and is used to return a small amount of incompletely decomposed metal basic nitrates or hydroxides to the dynamic pyrolysis furnace for complete thermal decomposition; the gas-phase outlet of the second dust collector is connected to the feed port of the second heat exchanger, and the second heat exchanger is used to lower the temperature of the second mixed gas and recover waste heat, and the waste heat can be used to heat the melting tank to melt nitrates; the gas-phase outlet of the second heat exchanger is connected to the inlet of the nitric acid regeneration device, and the output gas of the second heat exchanger is sent to the nitric acid regeneration device; the nitric acid regeneration device is used to obtain regenerated nitric acid, that is, a second part of finished nitric acid, by pressurized absorption of the second mixed gas after recovering waste heat.

2. The system according to claim 1, wherein It further includes a heating device, the outlet of the heating device is connected to the top feed port of the atomization and pyrolysis furnace, and the heating device is used to heat air or steam and then send it to the atomization and pyrolysis furnace to supply the heat required for pyrolysis.

3. The system according to claim 2, characterized in that, It further includes an induced draft fan, the inlet of the induced draft fan is connected to the gas-phase outlet of the second heat exchanger, and the outlet of the induced draft fan is connected to the inlet of the nitric acid regeneration device. The induced draft fan is used to send the second mixed gas after recovering waste heat output by the second heat exchanger into the nitric acid regeneration device.

4. The system according to claim 3, wherein The gas-phase outlet of the second heat exchanger is connected to the feed port of the tail gas absorption device.

5. The system according to claim 4, wherein The feed inlet of the tail gas absorption device is connected to the gas phase outlet of the nitric acid regeneration device. The tail gas absorption device is used to absorb NO in the tail gas x gas, and the outlet of the tail gas absorption device is connected to the atmosphere.

6. The system according to claim 1, wherein The atomization and pyrolysis furnace is one of a two-fluid spray atomization and pyrolysis furnace, a pressure atomization and pyrolysis furnace, a rotary centrifugal atomization and pyrolysis furnace or a combination of at least two of them.

7. The system according to claim 1, wherein The type of the dynamic pyrolysis furnace is various types of rotary kilns and tunnel kilns.

8. The system according to claim 1, characterized in that, The first dust collector and the second dust collector are in the form of one or a combination of at least two of cyclone dust collection, electrostatic dust collection, high-temperature metal membrane dust collection, porous ceramic dust collection, and high-temperature metal wire dust collection.

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