Method and system for producing nitric acid from ammonia-containing tail gas

Abstract

According to the method and system for producing nitric acid from ammonia-containing tail gas, after the ammonia-containing tail gas and compressed air are mixed, a large amount of ammonia-containing tail gas can be digested through oxidation of the oxidation furnace, absorption of the absorption tower and bleaching of the bleaching tower, emission of the ammonia-containing tail gas is reduced, the production cost is reduced, and the product quality is improved; and the profit level of the product is improved, and the ammonia-containing tail gas is utilized in a high-valued manner.

Description

Technical Field

[0001] The invention belongs to the technical field of nitric acid preparation, and relates to a method and system for producing nitric acid from ammonia-containing tail gas. Background Art

[0002] The coal chemical industry's melamine production process usually produces a large amount of tail gas containing ammonia as a by-product. This ammonia-containing tail gas generally needs to be sent to the coal chemical plant for recycling and utilization. However, the coal chemical industry's recovery of ammonia-containing tail gas is limited, which affects the operation of the entire plant. Summary of the Invention

[0003] The purpose of the present invention is to provide a method and system for producing nitric acid from ammonia tail gas to solve the problem of To achieve the above object, the present invention adopts the following technical solutions: The present application provides a system for producing nitric acid from ammonia-containing tail gas, comprising: an oxidation furnace and an ammonia-air mixer, an air compressor and a tail gas reheater respectively connected to the oxidation furnace; The ammonia-air mixer is connected to the ammonia filter and the tail gas filter in sequence; The air compressor is respectively connected to the air filter, the ammonia-air mixer and the secondary air cooler; The tail gas reheater is connected in sequence to an economizer, a condensation separation bleaching device, a NOx fine separator, a NOx compressor, a tail gas preheater, a high-pressure reaction water cooler, an absorption tower, a bleaching tower and a nitric acid storage tank; The condensation separation bleaching device is also connected to the absorption tower through a dilute acid cooler.

[0004] Preferably, the secondary air cooler is connected to the tail gas reheater through the tail gas preheater, and the secondary air cooler is also connected to the absorption tower through a tail gas separator; the secondary air cooler is also connected to the bleaching tower.

[0005] Preferably, the tail gas reheater is also connected to an ammonia reduction reactor, a tail gas turbine, a tail gas muffler and a tail gas heat exchanger in sequence.

[0006] The present application provides a method for producing nitric acid from ammonia-containing tail gas, comprising: The ammonia-containing tail gas is filtered, mixed with air, and then undergoes an ammonia oxidation reaction in the oxidation furnace to form nitrogen oxide gas; Part of the nitrogen oxide gas is mixed with cooling water to form dilute nitric acid, and the other part of the process gas is compressed and enters the absorption tower to form dilute nitric acid; The two dilute nitric acids are mixed with secondary air, and the NOx gas dissolved in the dilute nitric acid is removed in the bleaching tower to obtain dilute nitric acid with HNO2 less than 0.001%.

[0007] Preferably, the ammonia-containing tail gas is filtered successively through a tail gas filter with a filtration precision of 10 μm and a 0.5 μm, and a gas ammonia filter.

[0008] Preferably, the nitrogen oxide gas and the secondary air are compressed to 1.1 MPa.

[0009] Preferably, the temperature and pressure of the ammoxidation reaction are 850-870° C. and 0.35 MPa, respectively.

[0010] The present invention has the following beneficial effects: The system and method provided in the present application can absorb and digest a large amount of ammonia-containing tail gas through oxidation in an oxidation furnace, absorption in an absorption tower, and bleaching in a bleaching tower, thereby reducing the emission of ammonia-containing tail gas, lowering production costs, improving product quality, increasing product profitability, and enabling high-value utilization of ammonia-containing tail gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a structural diagram of the system for producing nitric acid from ammonia-containing tail gas provided in an embodiment of the present application. DETAILED DESCRIPTION

[0012] The technical solution of the present invention is further explained and illustrated by means of specific embodiments below.

[0013] Example 1 The present invention provides a system for producing nitric acid from ammonia-containing tail gas, which includes an oxidation furnace and an ammonia-air mixer, an air compressor and a tail gas reheater connected to the oxidation furnace, as shown in the attached figure. Figure 1 As shown, the ammonia-air mixer is connected to the ammonia filter and the exhaust filter in sequence, the air compressor is connected to the air filter, the ammonia-air mixer, and the secondary air cooler respectively, the exhaust reheater is connected to the economizer, the condensation separation bleacher, the NOx fine separator, the NOx compressor, the exhaust preheater, the high-pressure reaction water cooler, the absorption tower, the bleaching tower, and the nitric acid storage tank in sequence, and the condensation separation bleacher is also connected to the absorption tower through the dilute acid cooler.

[0014] The secondary air cooler is connected to the exhaust gas reheater via the exhaust preheater, and to the absorption tower via the exhaust gas separator. The secondary air cooler is also connected to the bleaching tower. The exhaust gas reheater is also connected in sequence to the ammonia reduction reactor, exhaust gas turbine, exhaust muffler, and exhaust gas heat exchanger.

[0015] Example 2 The present invention provides a method for producing nitric acid from ammonia-containing tail gas, the method comprising: S01: The ammonia-containing tail gas is filtered, mixed with air, and then undergoes an ammonia oxidation reaction in the oxidation furnace to form nitrogen oxide gas.

[0016] The ammonia-containing tail gas from the outside with a pressure of 0.45MPa and a temperature of 105-130°C is filtered successively through a tail gas filter with a filtration accuracy of 10μm and 0.5μm, and a gas ammonia filter to remove impurities in the tail gas. In this application, in addition to ammonia, the ammonia-containing tail gas also contains about 30% CO2 and trace water vapor. After the air is filtered through the air filter, it is compressed to a pressure of 0.4MPa and a temperature of about 200°C by an air compressor to form compressed air. The compressed air is divided into two air streams, one air stream is the primary compressed air, and the other air stream is the secondary compressed air. The majority of the compressed air enters the oxidation furnace to participate in the oxidation reaction, and the other part enters the secondary air cooler for use in the post-system bleaching tower.

[0017] The filtered ammonia-containing tail gas is mixed with primary compressed air in an ammonia-air mixer at an ammonia-air ratio of 8.5-10.5% to form a mixed gas. The ammonia-air ratio is the volume ratio of ammonia in the ammonia-containing tail gas to the total volume of ammonia and primary compressed air. The mixed gas enters the oxidation furnace and is evenly distributed on the platinum mesh. Ammonia oxidation occurs at a temperature of 860°C and a pressure of 0.35 MPa, forming nitrogen oxide gas.

[0018] The heat released during the ammonia oxidation reaction and the sensible heat generated during mixing in the ammonia-air mixer raise the temperature of the nitrogen oxide gas to approximately 860°C. The heat carried by the nitrogen oxide gas is recovered by the steam superheater and heat recovery device installed below the oxidation furnace, at which point the temperature of the nitrogen oxide gas is reduced to 380-400°C.

[0019] S02: Part of the nitrogen oxide gas is mixed with cooling water to form dilute nitric acid, and the other part of the process gas is compressed and enters the absorption tower to form dilute nitric acid.

[0020] The nitrogen oxide gas, whose temperature is reduced to 380-400℃, passes through the tail gas reheater and economizer and then enters the condensation separation bleaching device. While being cooled, the NO in the nitrogen oxide gas is oxidized to NO2.

[0021] After the nitrogen oxide gas enters the heat exchange section of the condensation separation bleacher, it contacts with the cooling water in countercurrent. The nitrogen oxide gas is cooled to 30-50 ° C. During the countercurrent contact process, part of the NO2 reacts with the cooling water to generate dilute nitric acid with a concentration of 40-50%. This part of the dilute nitric acid is cooled in the dilute nitric acid cooler and then sent to the tower plate with the corresponding acid concentration in the absorption tower.

[0022] After entering the secondary air cooler, the secondary compressed air is cooled to 100-120°C by the nitrogen oxide gas. A portion of this cooled secondary compressed air enters the bleaching tower, while the remaining portion enters the dilute acid bleaching section of the condensation separation bleaching unit to bleach the resulting dilute nitric acid. In the condensation separation bleaching unit, the nitrogen oxide gas that is not absorbed by the cooling water enters the NO2 fine separator for separation. After being compressed by the NO2 compressor to a pressure of 1.1 MPa and a temperature of 190°C, it enters the tail gas preheater and then the high-pressure reaction water condenser. In the high-pressure reaction water condenser, the nitrogen oxide gas is cooled to 30-50°C by cooling water in the upper and lower heat exchange sections before entering the bottom of the absorption tower. Process water is introduced to the top of the absorption tower, and cooling coils are installed between the absorption tower trays to remove the heat of absorption and oxidation. The nitrogen oxide gas is absorbed by the water on the absorption tower trays, forming dilute nitric acid with a concentration of 55-65% and a temperature of 50-55°C at the bottom of the tower.

[0023] The exhaust gas generated at the top of the absorption tower enters the exhaust gas separator to remove entrained mist. It then enters the secondary air cooler, where it is heated to 40-60°C by secondary compressed air. The heated exhaust gas is then heated to 100-120°C by the high-pressure nitrogen oxide gas in the exhaust gas preheater, and then heated to 350-380°C in the exhaust gas reheater. The heated exhaust gas enters the ammonia reduction reactor, where it undergoes a reduction reaction with ammonia under the action of an internal catalyst, reducing the nitrogen oxide gas content in the exhaust gas to ≤20ppm(v). The exhaust gas is finally discharged into the atmosphere after heat exchange through the exhaust muffler and exhaust heat exchanger.

[0024] S03: The two dilute nitric acids are mixed with secondary air, and the NOx gas dissolved in the dilute nitric acid is removed in a bleaching tower to obtain nitric acid with HNO2 < 0.001%.

[0025] The dilute nitric acid discharged from the dilute acid cooler into the absorption tower and the dilute nitric acid absorbed in the absorption tower after being discharged from the static high-pressure reaction water cooler are both discharged into the bleaching tower. Secondary compressed air, which has undergone heat exchange in the secondary air cooler, enters the bottom of the bleaching tower. This secondary compressed air removes the nitric oxide gas dissolved in the dilute nitric acid, completing the bleaching process. After bleaching, the HNO2 content in the finished nitric acid is less than 0.001%, and the finished nitric acid is discharged into the nitric acid storage tank for storage.

[0026] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A system for producing nitric acid from ammonia-containing tail gas, characterized in that: include: An oxidation furnace and an ammonia-air mixer, an air compressor and a tail gas reheater respectively connected to the oxidation furnace; The ammonia-air mixer is connected to the ammonia filter and the tail gas filter in sequence; The air compressor is respectively connected to the air filter, the ammonia-air mixer and the secondary air cooler; The tail gas reheater is connected in sequence to an economizer, a condensation separation bleaching device, a NOx fine separator, a NOx compressor, a tail gas preheater, a high-pressure reaction water cooler, an absorption tower, a bleaching tower and a nitric acid storage tank; The condensation separation bleaching device is also connected to the absorption tower through a dilute acid cooler.

2. The system for producing nitric acid from ammonia-containing tail gas according to claim 1, characterized in that: The secondary air cooler is connected to the tail gas reheater through the tail gas preheater, and the secondary air cooler is also connected to the absorption tower through a tail gas separator; the secondary air cooler is also connected to the bleaching tower.

3. The system for producing nitric acid from ammonia-containing tail gas according to claim 1, characterized in that: The tail gas reheater is also connected in sequence to an ammonia reduction reactor, a tail gas turbine, a tail gas muffler and a tail gas heat exchanger.

4. A method for producing nitric acid from ammonia-containing tail gas, characterized in that: include: The ammonia-containing tail gas is filtered, mixed with air, and then undergoes an ammonia oxidation reaction in the oxidation furnace to form nitrogen oxide gas; Part of the nitrogen oxide gas is mixed with cooling water to form dilute nitric acid, and the other part of the process gas is compressed and enters the absorption tower to form dilute nitric acid; The two dilute nitric acids are mixed with secondary air, and the NOx gas dissolved in the dilute nitric acid is removed in the bleaching tower to obtain dilute nitric acid with HNO2 less than 0.001%.

5. The method for producing nitric acid from ammonia-containing tail gas according to claim 4, characterized in that: The ammonia-containing tail gas is filtered successively through a tail gas filter with a filtration precision of 10 μm and a 0.5 μm, and a gas ammonia filter.

6. The method for producing nitric acid from ammonia-containing tail gas according to claim 4, characterized in that: The nitrogen oxide gas and the secondary air are compressed to 1.1 MPa.

7. The method for producing nitric acid from ammonia-containing tail gas according to claim 4, characterized in that: The temperature and pressure of the ammoxidation reaction are 850-870° C. and 0.35 MPa, respectively.

Images