Process and system for recovering nitric oxide in spray roasting nitric acid tail gas

Abstract

The invention discloses a process and a system for recovering nitric oxide in spray roasting nitric acid tail gas, and relates to the technical field of tail gas recovery. The recovery process comprises the following steps: S1, introducing NOx-containing flue gas into a cooling-multi-stage absorption system to form regenerated acid; s2, introducing the residual NOx-containing gas after the primary absorption into a VPSA coarse denitration system, and adsorbing NO2 and water vapor through an adsorbent; s3, the gas obtained after VPSA rough NOx removal treatment is introduced into a TSA fine denitration system, residual NOx is adsorbed through a catalytic adsorbent, and purified tail gas is obtained; and S4, part of purified tail gas is taken and heated to serve as a regeneration gas source, the catalytic adsorbent is flushed to desorb and regenerate NOx, and recovered gas 2 formed after cooling is returned to the cooling-multi-stage absorption system. The traditional SCR denitration technology is replaced with VPSA coarse denitration and TSA fine denitration, the concentration of NOx in exhausted tail gas is smaller than or equal to 50 mg / Nm < 3 >, and the problem that NOx emission exceeds the standard in the traditional technology is effectively solved.

Description

Technical Field

[0001] This invention relates to the field of exhaust gas recovery technology, specifically to a process and system for recovering nitrogen oxides from spray-roasted nitric acid exhaust gas. Background Technology

[0002] Spray roasting, as an advanced material preparation technology, has been widely applied in various materials science fields, including ceramic materials, catalyst supports, and nanoparticles, due to its significant advantages in controllable particle size, high purity, good dispersibility, and low-temperature processing. For example, in the preparation of lithium-ion battery cathode materials, spray roasting can precisely control the morphology and particle size distribution of lithium iron phosphate particles, significantly improving the electrochemical performance of the electrode material. In the production of environmentally friendly catalysts, this process can effectively avoid the agglomeration problem of active components caused by traditional solid-state methods, increasing the specific surface area of ​​the catalyst by more than 30%. However, this process generates a large amount of roasting furnace exhaust gas containing nitrogen oxides (NOx) during the high-temperature decomposition of nitrates. If not effectively treated, this will not only cause serious environmental pollution but also lead to a large loss of nitrogen resources.

[0003] Traditional processes primarily employ "low-temperature water absorption + SCR denitrification" to treat nitric acid tail gas. First, a multi-stage spray absorption tower uses water or dilute nitric acid to absorb NO2 from the tail gas, forming regenerated nitric acid that is recycled back into the production system. However, due to the chemical equilibrium in the NOx system (3NO2 + H2O = 2HNO3 + NO), the absorption process is accompanied by the generation of NO gas. Since NO has extremely low solubility in water, the theoretical absorption rate of NOx is limited to 85%-93%. The unabsorbed 7%-15% of NOx (mainly NO) must then enter the SCR denitrification system, where it undergoes a reduction reaction with a reducing agent (urea or ammonia) under the action of a catalyst to produce N2 and water. This treatment method has significant drawbacks: firstly, SCR denitrification consumes a large amount of energy and chemical raw materials, resulting in high operating costs; secondly, this process directly converts recoverable NOx into nitrogen gas for emission, leading to a waste of nitrogen resources.

[0004] Given the increasing cost pressures on the manufacturing industry, developing a new technology that can simultaneously achieve deep NOx purification and efficient resource recovery has become a critical issue that the spray roasting nitric acid production industry urgently needs to address. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a process and system for recovering nitrogen oxides from nitric acid tail gas by spray roasting, which can effectively achieve deep purification of NOx (emission concentration ≤50mg / Nm³) and efficient resource recovery.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A process for recovering nitrogen oxides from nitric acid tail gas by spray roasting includes: S1, Primary Absorption: NOx-containing flue gas is introduced into a cooling-multi-stage absorption system to form regenerated acid; S2 introduces the NOx-containing gas remaining after primary absorption into the VPSA crude denitrification system, where NO2 and water vapor are adsorbed by the adsorbent, and the desorbed recovery gas 1 is returned to the cooling-multi-stage absorption system. S3, the gas after the VPSA crude NOx removal treatment is introduced into the TSA fine denitrification system, and the remaining NOx is adsorbed by the catalytic adsorbent to obtain purified tail gas; S4, TSA regeneration: Take part of the purified tail gas, heat it and use it as the regeneration gas source. Rinse the catalytic adsorbent to desorb and regenerate NOx, and obtain regeneration gas. The recovered gas 2 formed after cooling is returned to the cooling-multi-stage absorption system. S5, Recycling: The cooling-multi-stage absorption system absorbs NOx from recovery gas 1 and recovery gas 2 and converts it into regenerated acid.

[0007] Furthermore, in step S2, the adsorption pressure is 20-100 kPa and the adsorption temperature is 10-50 °C; the adsorbent is a combination bed formed by two or three of activated alumina, silica gel and molecular sieve, and each component accounts for 10%-60%.

[0008] Furthermore, in step S2, the desorption process is as follows: NOx is extracted from the adsorbent by a vacuum pump with a vacuum regeneration pressure of -50 to -90 kPa under conditions of 10-50°C.

[0009] Furthermore, in step S3, the catalytic adsorbent is one of 13X, ZSM-5, 10X, or a molecular sieve carrying a metal oxide; the metal oxide is one or more oxides of Pt, Pd, Rh, Cu, Mn, or Ti.

[0010] Furthermore, in step S4, 5%-20% of the purified exhaust gas is heated to 180-250℃ and used as a regeneration gas source.

[0011] The present invention also provides a system for implementing the above-mentioned recovery process, comprising: a spray roasting system capable of generating NOx-containing gas; a cooling-multi-stage absorption system connected to the spray roasting system for primary absorption of NOx and generation of regenerated nitric acid; a VPSA crude denitrification system connected to the cooling-multi-stage absorption system for coarse NOx removal and outputting recovered gas 1; and a TSA fine denitrification system connected to the VPSA crude denitrification system for fine NOx removal and outputting recovered gas 2.

[0012] Furthermore, the VPSA coarse denitrification system and the TSA fine denitrification system are each equipped with 2-6 adsorption towers.

[0013] Furthermore, the TSA denitrification system is equipped with a heater for heating the regeneration gas source and a cooler for cooling the regeneration gas to form the recovery gas 2.

[0014] Furthermore, a booster fan is provided between the cooling-multi-stage absorption system and the VPSA coarse denitrification system; a vacuum pump is connected to the VPSA coarse denitrification system to desorb the NOx and water vapor adsorbed on the adsorbent and form recovery gas 1; and an outlet pressure regulating programmable valve is provided at the exhaust port of the TSA fine denitrification system.

[0015] Furthermore, the output ends of the vacuum pump and the cooler are both connected to the cooling-multi-stage absorption system.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses “VPSA coarse denitrification + TSA fine denitrification” to replace the traditional SCR denitrification technology, so that the NOx concentration in the exhaust gas is ≤50mg / Nm 3 This effectively solves the problem of excessive NOx emissions in traditional processes.

[0017] (2) The high-concentration NOx gas (recovery gas 1 and recovery gas 2) desorbed by the VPSA and TSA systems of this invention is returned to the cooling-multi-stage absorption system and finally converted into nitric acid product. The NOx resource utilization rate exceeds 99.9%, which is significantly improved compared with the traditional process (85%-93%), and avoids the waste of nitrogen resources.

[0018] (3) This invention eliminates the need for reducing agents such as urea and natural gas and energy consumption required by traditional SCR denitrification, which greatly reduces operating costs. In addition, this invention generates nitric acid products by recovering NOx, which can reduce energy and raw material consumption at the same time, achieving a win-win situation for environmental protection and economic benefits.

[0019] (4) In the VPSA coarse denitrification process, this invention uses a combination of activated alumina, silica gel, and molecular sieve adsorbents, which can efficiently remove NO2 and water vapor and reduce the risk of corrosion in subsequent systems. In the TSA fine denitrification process, an adsorbent with both adsorption and catalytic functions (such as molecular sieves or metal oxide-supported molecular sieves) is used to catalyze the oxidation of NO to NO2, enhance adsorption capacity, and ensure purification accuracy. In both the VPSA coarse denitrification system and the TSA fine denitrification system, this invention sets up multiple towers to operate alternately (2-6 adsorption towers) to achieve continuous and stable operation.

[0020] (5) In this invention, all NOx-containing desorbed gases (recovered gas 1 and recovered gas 2) are returned to the absorption system for recycling and treatment, with no secondary waste gas emissions; the regenerated nitric acid can be transported to an off-site nitric acid storage tank for recycling or other uses, forming a closed loop of "tail gas treatment - resource recovery - recycling", which is in line with the development direction of green chemical industry. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of the recycling device provided by the present invention; Figure 2 This is a schematic diagram of the VPSA crude denitrification system in this invention; Figure 3 This is a schematic diagram of the TSA denitrification system in this invention.

[0022] The corresponding names of the attached figures are: 1-spray roasting system, 2-cooling-multi-stage absorption system, 3-VPSA coarse denitrification system, 4-TSA fine denitrification system, 5-heater, 6-boost fan, 7-vacuum pump, 8-cooler, 9-outlet pressure regulating programmable valve. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments of the present invention include, but are not limited to, the following embodiments.

[0024] In this embodiment, a VPSA coarse NOx removal section and a TSA fine NOx removal section are set up after the flue gas cooling and multi-stage absorption tower of the spray roaster (nitric acid production) to replace the traditional SCR denitrification technology, so that the NOx in the exhaust gas is ≤50mg / Nm³. 3 The high-concentration NOx desorbed gas from the VPSA crude NOx removal section and the TSA fine NOx removal section is returned to the nitric acid multi-stage absorption system for absorption, becoming nitric acid products, thus achieving a NOx resource utilization rate of over 99.9%.

[0025] The nitrogen oxide recovery process in the spray roasting nitric acid tail gas provided in this embodiment includes: (1) Primary absorption stage: NOx-containing gas (NOx content 5-12%) generated by spray roasting furnace (or nitric acid production) is introduced into cooling-multi-stage absorption system to absorb 85%-93% of the NOx and form regenerated nitric acid; (2) VPSA coarse NOx removal stage: The NOx-containing gas (NOx content 0.5%-3%) remaining after primary absorption is introduced into the VPSA coarse denitrification system. The adsorbent adsorbs part of the NOx (mainly NO2) and water vapor. The adsorption pressure is 20-100KPa and the temperature is 10-50℃. The adsorbed NOx is extracted from the adsorbent by a vacuum pump (vacuum regeneration pressure -50 to -90KPa) to form recovery gas 1 (containing NOx and water vapor, etc.). Recovery gas 1 is returned to the cooling-multi-stage absorption system. The adsorbent is a combination bed formed by two or three of the following: activated alumina, silica gel, and molecular sieve (each component accounts for 10%-60%). (3) TSA NOx Removal Stage: NOx gas (containing 0.4%-2.8% NOx) after being degassed by VPSA to remove NO2 and water vapor is introduced into the TSA denitrification system. The remaining NOx is adsorbed by the catalytic adsorbent in the TSA system. The adsorbent must have both adsorption and catalytic functions and be able to catalyze the reaction 2NO + O2 = 2NO2 to enhance NOx adsorption capacity and purification accuracy. Preferably, the catalytic adsorbent is a molecular sieve (such as 13X, ZSM-5, 10X) or a molecular sieve loaded with specific metal oxides (Pt, Pd, Rh, Cu, Mn, Ti). The NOx content in the purified tail gas after treatment is ≤50mg / Nm³. 3 It can be discharged directly; (4) TSA regeneration stage: Take 5%-20% of the purified tail gas, heat it to 180-250℃ through the heating system and then pass it into the TSA system to flush the adsorbent so that NOx is regenerated at high temperature. The high temperature regeneration gas is cooled by the cooler to form recovery gas 2 (NOx content 5%-12%). The recovery gas 2 is returned to the cooling-multi-stage absorption system. (5) Recycling: The cooling-multi-stage absorption system converts the absorbed NOx (including NOx absorbed in the primary absorption stage, as well as NOx in recovery gas 1 and recovery gas 2) into regenerated nitric acid, which is then sent to an off-site storage tank for recycling or other purposes.

[0026] In the above process, the number of adsorption towers in both the VPSA coarse denitrification system and the TSA fine denitrification system can be set to 2-6, with a minimum of 2, so that one tower performs adsorption and the other tower performs regeneration and desorption. The exhaust gas after the above process has NOx ≤ 50 mg / Nm³. 3 Furthermore, the recovery rate of nitric acid formed from NOx recovery is greatly increased, from 85-93% in the traditional process to over 99.9%.

[0027] like Figure 1 As shown, this embodiment also provides a system for implementing the above-mentioned recycling process, including a spray roasting system 1, a cooling-multi-stage absorption system 2, a VPSA coarse denitrification system 3, and a TSA fine denitrification system 4.

[0028] The spray roasting system 1 is the source of NOx-containing gas, producing flue gas with a NOx concentration of approximately 5%-12%, which serves as the feed gas source for the entire system. The cooling-multi-stage absorption system 2 consists of a cooling device (such as a heat exchanger) and a multi-stage absorption tower (usually a spray absorption tower). It is used to cool the NOx-containing gas from the spray roasting system 1 and absorb 85%-93% of the NOx in the gas through multi-stage absorption (using water or dilute nitric acid as the absorbent), forming regenerated nitric acid. The outlet of the cooling-multi-stage absorption system 2 is divided into two paths: one path transports the incompletely absorbed NOx-containing gas (concentration 0.5%-3%) to the VPSA crude denitrification system 3; the other path transports the generated regenerated nitric acid to an off-site nitric acid storage tank for recycling or other uses.

[0029] The VPSA coarse denitrification system consists of 2-6 adsorption towers (e.g., Figure 2 As shown, the system consists of at least two adsorbent cells (for alternating adsorption and regeneration) and internally filled adsorbent, primarily used to adsorb NO2 and water vapor to reduce the impact and corrosiveness of moisture on the subsequent TSA system. The VPSA coarse denitrification system 3 performs coarse denitrification treatment on NOx-containing gas (concentration 0.5%-3%) from the cooling-multi-stage absorption system 2, removing some NOx (mainly NO2) and water vapor. After treatment, the NOx concentration in the gas is reduced to 0.4%-2.8%. A vacuum pump 7 is connected to the adsorption tower of the VPSA coarse denitrification system 3. By drawing a vacuum (pressure -50 to -90 kPa), the NOx and water vapor adsorbed on the adsorbent can be desorbed, forming recovered gas 1. The output of the vacuum pump 7 is connected to the cooling-multi-stage absorption system 2 to transport the recovered gas 1 to the cooling-multi-stage absorption system 2. In this VPSA coarse denitrification system, the adsorption pressure of VPSA coarse denitrification system 3 is 20-100 kPa, and the adsorption and desorption temperatures are 10-50℃. The single-tower cycle is typically 2-30 minutes, and the switching frequency of the adsorption towers is controlled according to the NO2 concentration and H2O content at the VPSA outlet. The operation process of VPSA coarse denitrification system 3 is shown in the table below: Table 1. Operation process of VPSA coarse denitrification system The TSA denitrification system consists of 2-6 adsorption towers (e.g., Figure 3As shown, the system consists of at least two adsorption and regeneration units (to achieve alternating adsorption and regeneration operation) and an internally filled catalytic adsorbent. The TSA fine denitrification system 4 performs fine denitrification treatment on the gas (NOx concentration 0.4%-2.8%) from the VPSA coarse denitrification system 3, adsorbing the remaining NOx to ensure the NOx concentration in the purified tail gas is ≤50mg / Nm³. An outlet pressure regulating valve 9 is installed at the purified tail gas discharge port of the TSA fine denitrification system 4 to control the pressure of both the TSA fine denitrification system 4 and the VPSA coarse denitrification system 3. Additionally, a heater 5 is installed within the TSA fine denitrification system 4 to heat 5-20% of the flue gas in the purified tail gas to 180-250℃, serving as the regeneration gas source for the TSA fine denitrification system. This regeneration process desorbs and regenerates the NOx by flushing the adsorbent. A cooler 8 is installed at the regeneration gas outlet of the TSA fine denitrification system 4 to cool the high-temperature NOx-containing regeneration gas generated by desorption, forming a normal-temperature recovery gas 2 (NOx concentration 5%-12%). The output of cooler 8 is connected to cooling-multi-stage absorption system 2, used to transport the recovered gas 2 to cooling-multi-stage absorption system 2 for reabsorption. In this TSA denitrification system, a single adsorption tower completes one full cycle of "adsorption-desorption regeneration" in 2-8 hours; the single tower cycle is typically 120-180 minutes, depending on the NO content. x The concentration, throughput, and adsorbent performance can be adjusted based on the NOx content at the TSA outlet to control the switching frequency of the adsorption tower. The operation process of the TSA fine denitrification system is shown in Table 2. Table 2. Operation Procedures of the TSA Fine Denitrification System Furthermore, a booster fan 6 is installed between the cooling-multi-stage absorption system 2 and the VPSA coarse denitrification system 3 to provide the conveying pressure for NOx-containing gas to enter the VPSA coarse denitrification system 3 and the TSA fine denitrification system 4, ensuring smooth gas flow.

[0030] The following is a description using specific embodiments: (1) Primary absorption stage: The NOx-containing gas generated by the spray roasting system enters the cooling-multi-stage absorption system, where a large amount of NOx is absorbed to form regenerated nitric acid; the material data of each material in the NOx-containing gas generated by the spray roasting system is shown in Table 3, and the material data of each material in the NOx-containing gas after treatment by the cooling-multi-stage absorption system is shown in Table 4.

[0031] Table 3. Data on materials in NOx-containing gases produced by the spray roasting system Table 4. Material data of NOx-containing gas after cooling-multi-stage absorption system treatment (2) VPSA coarse NOx removal stage: The remaining NOx-containing gas (NOx content 0.5%-3%) after primary absorption enters the VPSA coarse denitrification system, where NO2 and water vapor are removed under conditions of 50 kPa and 25°C. The adsorbed NOx is extracted from the adsorbent by a vacuum pump (vacuum regeneration pressure -60 kPa) to form recovery gas 1 (containing NOx and water vapor, etc.), which is returned to the cooling-multi-stage absorption system. The VPSA coarse denitrification system has two adsorption towers, and the adsorbent is a combined bed of activated alumina and silica gel with a mass ratio of 1:1. Data on each material in the NOx-containing gas discharged into the next process after VPSA coarse NOx removal are shown in Table 5, and data on each material in recovery gas 1 are shown in Table 6.

[0032] Table 5. Data on the components in the NOx-containing gas remaining after VPSA crude NOx removal treatment. Table 6 Data of each material in recovered gas 1 (3) TSA fine NOx removal stage: The NOx-containing gas after crude denitrification enters the TSA fine denitrification system, where NOx is catalytically adsorbed. The purified tail gas contains NOx ≤ 50 mg / Nm³. 3 It can be directly discharged. The system is equipped with two adsorption towers, and the catalytic adsorbent is 13X molecular sieve. The data of each material in the purified tail gas after TSA NOx removal are shown in Table 7.

[0033] Table 7. Data on various materials in the purified exhaust gas obtained after TSA NOx removal treatment. (4) The purified exhaust gas after treatment by the TSA denitrification system contains NOx ≤ 50 mg / Nm³. 3 15% of the flue gas in the purified exhaust gas is heated to 200℃ and returned to the TSA denitrification system as the regeneration gas source for the TSA. The high-concentration NOx desorbed gas generated after regeneration is cooled to form recovery gas 2, which is then returned to the cooling-multi-stage absorption system. The data of each material in recovery gas 2 are shown in Table 8.

[0034] Table 8 Data on each material in recovered gas 2 (5) The regenerated nitric acid is discharged off-site as a product for system recycling or other uses. The NOx content in the treated roasting furnace tail gas is low and can be discharged into the atmosphere. Data for each material in the regenerated nitric acid are shown in Table 9.

[0035] Table 9 Data on each material in regenerated nitric acid Note: In the cooling-multi-stage absorption system, NOx is absorbed to form nitric acid. The excess H2O and O2 required are supplemented by external units. The concentration of regenerated nitric acid can be adjusted by the amount of H2O supplemented as needed.

[0036] The process provided in this embodiment is used to treat the NOx-containing exhaust gas generated by the spray roasting system. After NOx recovery and utilization, the NOx emission concentration in the purified exhaust gas is ≤50mg / Nm³. 3 The costs of electricity, urea, and natural gas consumed when replacing the above process with traditional SCR technology are shown in Table 10: Table 10 By replacing this process with traditional SCR technology, the recovery rate of NOx (nitrogen oxides) is reduced by 15% because some NOx reacts with urea in SCR to generate N2.

[0037] The above embodiments are merely one of the preferred embodiments of the present invention and should not be used to limit the scope of protection of the present invention. Any modifications or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but solve the same technical problem as the present invention, should be included within the scope of protection of the present invention.

Claims

1. A process for recovering nitrogen oxides from nitric acid tail gas after spray roasting, characterized in that, include: S1, Primary Absorption: NOx-containing flue gas is introduced into a cooling-multi-stage absorption system to form regenerated acid; S2 introduces the NOx-containing gas remaining after primary absorption into the VPSA crude denitrification system, where NO2 and water vapor are adsorbed by the adsorbent, and the desorbed recovery gas 1 is returned to the cooling-multi-stage absorption system. S3, the gas after the VPSA crude NOx removal treatment is introduced into the TSA fine denitrification system, and the remaining NOx is adsorbed by the catalytic adsorbent to obtain purified tail gas; S4, TSA regeneration: Take part of the purified tail gas, heat it and use it as the regeneration gas source. Rinse the catalytic adsorbent to desorb and regenerate NOx, and obtain regeneration gas. The recovered gas 2 formed after cooling is returned to the cooling-multi-stage absorption system. S5, Recycling: The cooling-multi-stage absorption system absorbs NOx from recovery gas 1 and recovery gas 2 and converts it into regenerated acid.

2. The process for recovering nitrogen oxides from nitric acid tail gas by spray roasting according to claim 1, characterized in that, In step S2, the adsorption pressure is 20-100 kPa and the adsorption temperature is 10-50℃; the adsorbent is a combination bed formed by two or three of activated alumina, silica gel and molecular sieve, and each component accounts for 10%-60%.

3. The process for recovering nitrogen oxides from nitric acid tail gas by spray roasting according to claim 2, characterized in that, In step S2, the desorption process is as follows: NOx is extracted from the adsorbent by a vacuum pump with a vacuum regeneration pressure of -50 to -90 kPa under conditions of 10-50℃.

4. The process for recovering nitrogen oxides from nitric acid tail gas by spray roasting according to claim 3, characterized in that, In step S3, the catalytic adsorbent is one of 13X, ZSM-5, 10X, or a molecular sieve loaded with a metal oxide; the metal oxide is one or more oxides of Pt, Pd, Rh, Cu, Mn, or Ti.

5. The process for recovering nitrogen oxides from nitric acid tail gas by spray roasting according to claim 4, characterized in that, In step S4, 5%-20% of the purified exhaust gas is heated to 180-250℃ and used as a regeneration gas source.

6. A system for implementing the recycling process according to any one of claims 1 to 5, characterized in that, include: A spray roasting system (1) capable of generating NOx-containing gas, a cooling-multi-stage absorption system (2) connected to the spray roasting system (1) for primary absorption of NOx and generation of regenerated nitric acid, a VPSA crude denitrification system (3) connected to the cooling-multi-stage absorption system (2) for crude NOx removal and output of recovered gas 1, and a TSA fine denitrification system (4) connected to the VPSA crude denitrification system (3) for fine NOx removal and output of recovered gas 2.

7. The system according to claim 6, characterized in that, The VPSA coarse denitrification system (3) and the TSA fine denitrification system (4) are each equipped with 2-6 adsorption towers.

8. A system according to claim 7, characterized in that, The TSA denitrification system (4) is equipped with a heater (5) for heating the regeneration gas source and a cooler (8) for cooling the regeneration gas to form the recovery gas 2.

9. A system according to claim 8, characterized in that, A booster fan (6) is provided between the cooling-multi-stage absorption system (2) and the VPSA coarse denitrification system (3); a vacuum pump (7) is connected to the VPSA coarse denitrification system (3) to desorb the NOx and water vapor adsorbed on the adsorbent and form the recovery gas 1; an outlet pressure regulating control valve (9) is provided at the exhaust port of the purified tail gas of the TSA fine denitrification system (4).

10. A system according to claim 9, characterized in that, The output ends of the vacuum pump (7) and the cooler (8) are both connected to the cooling-multi-stage absorption system (2).

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