A system and method for deep purification of ammonia feed gas

Abstract

A kind of synthesis ammonia raw material gas deep purification treatment system and method, the system includes fine desulfurization tower, raw material gas inlet pipeline, purification gas outlet pipeline, pulse backwashing system and backwashing waste gas recovery pipeline.Fine desulfurization tower is filled with mesoporous zinc oxide desulfurizer with mesopore ratio ≥70%, pore size 2-50nm;Pulse backwashing system includes nitrogen storage tank, nitrogen heater, pulse valve group and PLC time sequence controller, PLC is electrically connected with outlet online total sulfur analyzer and pulse valve group, realizes automatic trigger of regeneration.The method comprises: after wet desulfurization, raw material gas is imported into fine desulfurization tower for adsorption desulfurization;When outlet total sulfur reaches preset threshold, hot nitrogen is imported for pulse backwashing regeneration, and waste gas returns to wet desulfurization system.The present application breaks through the bottleneck of traditional micropore desulfurizer easy to block and non-regeneration by mesoporous structure regulation and coordination with pulse regeneration, realizes normal temperature deep desulfurization and on-line regeneration, and has high desulfurization precision, long service life, low energy consumption and environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of syngas purification technology, specifically referring to a deep purification system and method for synthetic ammonia feedstock gas. Background Technology

[0002] Ammonia synthesis is a pillar industry of the national economy, with an annual production capacity of over 80 million tons in my country. Refined desulfurization of the feed gas is a core process ensuring the long-term operation of ammonia synthesis catalysts. Iron-based catalysts for ammonia synthesis are extremely sensitive to sulfur, requiring the total sulfur content in the feed gas to remain consistently below 0.01 ppm. High-end low-pressure ammonia synthesis catalysts, in particular, require a total sulfur content of ≤0.005 ppm.

[0003] Currently, the industry generally adopts the "wet coarse desulfurization + zinc oxide fine desulfurization" process. Wet desulfurization technologies such as low-temperature methanol washing and NHD can reduce the total sulfur in the raw gas from thousands of ppm to 0.1-0.5 ppm. However, due to the limitation of gas-liquid balance, deep purification cannot be achieved, and a zinc oxide fine desulfurization process must be added.

[0004] Existing commercial zinc oxide desulfurizers have two major drawbacks: First, their pore structure is unreasonable, mainly consisting of micropores. Sulfates generated during the desulfurization process and impurities carried by the raw gas easily clog the micropore channels, preventing the internal active sites from contacting sulfides. This leads to rapid deactivation of the desulfurizer, and the desulfurization accuracy can only be stabilized at around 0.01 ppm, which cannot meet the requirements of high-end catalysts. Second, they are completely non-renewable. Deactivated desulfurizers can only be disposed of as hazardous waste in landfills and require frequent replacement. This not only significantly increases operating costs but also causes unplanned shutdowns of the plant, resulting in huge losses.

[0005] While alternative technologies such as activated carbon and molecular sieves have been studied, they suffer from problems such as low desulfurization precision, high regeneration energy consumption, and poor adaptability to operating conditions, and cannot replace the mainstream position of zinc oxide. Therefore, developing an ultra-precision desulfurization technology based on optimized pore structure of zinc oxide desulfurizer and capable of low-cost online regeneration has become a key issue that urgently needs to be addressed in this field. Summary of the Invention

[0006] In view of the above situation and to overcome the defects of the prior art, the present invention provides a deep purification system and method for synthetic ammonia feed gas, which at least partially solves the above problems.

[0007] In a first aspect, the present invention provides a deep purification treatment system for synthetic ammonia feed gas, including a fine desulfurization tower, a feed gas inlet pipeline, a purified gas outlet pipeline, a pulse backflushing system, and a backflushing waste gas recovery pipeline.

[0008] The fine desulfurization tower is filled with a mesoporous zinc oxide desulfurizing agent bed, which has a mesoporous content of ≥70% and a mesoporous pore size of 2-50 nm. The raw gas inlet pipeline is connected to the top of the fine desulfurization tower and is equipped with an online total sulfur analyzer at the inlet; the purified gas outlet pipeline is connected to the bottom of the fine desulfurization tower and is equipped with an online total sulfur analyzer at the outlet.

[0009] The pulse backflushing system includes a nitrogen storage tank, a nitrogen heater, a pulse valve assembly, and a PLC timing controller. The nitrogen storage tank, nitrogen heater, and pulse valve assembly are sequentially connected and then connected to the bottom of the fine desulfurization tower. The PLC timing controller is electrically connected to the online total sulfur analyzer at the outlet, the pulse valve assembly, and the feed gas inlet valve of the fine desulfurization tower. One end of the backflushing exhaust gas recovery pipeline is connected to the top of the fine desulfurization tower, and the other end is connected to the feed gas inlet pipeline of the wet desulfurization system.

[0010] Furthermore, the desulfurization tower adopts a single-tower structure or a dual-tower parallel switching operation structure; a pressure transmitter and a flow transmitter are also installed on the raw gas inlet pipeline, and the PLC timing controller is electrically connected to the above transmitters and the nitrogen heater. The PLC timing controller has a built-in interlock protection module, which automatically terminates the pulse backflushing program and issues an alarm signal when the nitrogen pressure is lower than 0.3MPa or the nitrogen temperature is lower than 100℃.

[0011] Secondly, the present invention also provides a method for deep purification of ammonia synthesis feedstock gas, comprising the following steps: S1: A mesoporous zinc oxide desulfurizer is used as the adsorbent, wherein the mesoporous content of the desulfurizer is ≥70%, and the mesoporous pore size is 2-50 nm. Preferably, the mesoporous content is 70%-90%, the pore size is concentrated in the range of 10-30 nm, the specific surface area is ≥120 m² / g, and the particle size is 2-6 mm.

[0012] S2: The raw gas after wet desulfurization is passed into a fine desulfurization tower filled with the above-mentioned desulfurizing agent, and adsorption desulfurization is carried out at 40-80℃. The total sulfur content of the raw gas is ≤0.2ppm, the pressure is 2.0-5.0MPa, and the space velocity is 600-1400h. -1 Furthermore, the raw gas passes through the desulfurizing agent bed from top to bottom.

[0013] S3: When the total sulfur content at the outlet of the fine desulfurization tower reaches or exceeds the preset threshold, hot nitrogen is introduced into the tower for pulse backflushing regeneration. The preset threshold is preferably 0.009-0.01 ppm. When the online total sulfur analyzer at the outlet detects total sulfur ≥ 0.009 ppm, the PLC timing controller automatically triggers the pulse backflushing program, first closing the raw material gas inlet valve, and then starting the pulse valve group for backflushing. The hot nitrogen pressure is 0.4-0.8 MPa, and the temperature is 120-180℃; the pulse backflushing parameters are a single pulse duration of 0.3-1.0 s, an interval of 5-15 s, and a total number of purging cycles of 20-40. The waste gas generated by backflushing is returned to the raw material gas inlet pipeline of the wet desulfurization system for treatment via a recovery pipeline.

[0014] S4: After regeneration, the raw material gas is reintroduced to continue adsorption and desulfurization.

[0015] Furthermore, the method also includes an impurity protection step: when the chlorine content in the feed gas is >0.05ppm or the arsenic / heavy metal content is >0.01ppm, the feed gas is first passed into a pre-chlorination tank and / or an arsenic removal tank for impurity removal before entering the fine desulfurization tower. It also includes a sulfate accumulation control step: the sulfate content in the primary wet desulfurization system is periodically monitored, and when the content exceeds 5%, the waste liquid discharge is increased to control sulfate accumulation.

[0016] Compared with existing technologies, this invention overcomes the industry bottlenecks of traditional microporous desulfurizers, such as easy clogging and non-renewability, by precisely controlling the pore structure of the mesoporous zinc oxide desulfurizer and synergistically combining it with a pulsed airflow regeneration process. This achieves deep desulfurization at room temperature and online regeneration. The system and method significantly improve desulfurization accuracy, greatly extend the service life of the desulfurizer, and reduce regeneration energy consumption and hazardous waste emissions, combining the advantages of high precision, long-cycle operation, and environmental friendliness. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the deep purification system for synthetic ammonia feed gas according to an embodiment of the present invention.

[0018] The components include: 1. Fine desulfurization tower; 2. Mesoporous zinc oxide desulfurizing agent bed; 3. Raw material gas inlet pipeline; 4. Purified gas outlet pipeline; 5. Nitrogen storage tank; 6. Heater; 7. Pulse valve group; 8. PLC controller; 9. Inlet online total sulfur analyzer; 10. Outlet online total sulfur analyzer; 11. Backflush waste gas recovery pipe; 12. Inlet valve; 13. Purified gas outlet valve; 14. Pressure transmitter; 15. Flow transmitter; 16. Storage tank outlet valve; and 17. Pre-protection unit.

[0019] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] like Figure 1 The synthetic ammonia feed gas deep purification system provided by this invention includes a fine desulfurization tower 1, a feed gas inlet pipeline 3, a purified gas outlet pipeline 4, a pulse backflushing system, and a backflushing waste gas recovery pipeline 11. The fine desulfurization tower 1 is a vertical fixed-bed reactor, made of sulfur-resistant 304 stainless steel or composite steel plate, with a design pressure rating of 6.0 MPa and a tower height-to-diameter ratio controlled between 3:1 and 5:1. The tower is filled with a mesoporous zinc oxide desulfurizing agent bed 2, with wire mesh and ceramic ball support layers laid above and below the bed to ensure uniform airflow distribution. The feed gas inlet pipeline 3 connects to the top of the fine desulfurization tower 1, and is sequentially equipped with an inlet valve 12, an online total sulfur analyzer 9, a pressure transmitter 14, and a flow transmitter 15. The online total sulfur analyzer 9 uses ultraviolet fluorescence or lead acetate paper tape method for trace sulfur analysis, with a detection limit of 0.001 ppm and a response time of less than 30 seconds. The purified gas outlet pipeline 4 is led out from the bottom of the fine desulfurization tower 1. The pipeline is equipped with a purified gas outlet valve 13 and an online total sulfur analyzer 10 at the outlet. Its specifications are consistent with those of the inlet analyzer to ensure uniform detection accuracy.

[0022] The pulse backflushing system includes a nitrogen storage tank 5, a nitrogen heater 6, a pulse valve assembly 7, and a PLC timing controller 8. The nitrogen storage tank 5 has a volume configured to be 3 to 5 times the volume of gas used in a single backflushing cycle, and a design pressure of not less than 1.0 MPa. The nitrogen heater 6 is electrically heated, with its power calculated based on the heat required to heat nitrogen from room temperature to 120-180℃, and a temperature control accuracy of ±5℃. The pulse valve assembly 7 consists of several rapidly opening and closing electromagnetic pulse valves, with a single valve's opening and closing response time not exceeding 0.1 seconds. These valves are evenly arranged circumferentially along the bottom of the desulfurization tower, with at least two valves per meter of tower diameter. The PLC timing controller 8 is an industrial-grade programmable controller, equipped with analog input modules and digital output modules, and features timing programming, logic interlocking, and alarm output functions. One end of the backflushing exhaust gas recovery pipeline 11 is connected to the top outlet pipeline of the fine desulfurization tower 1, and the other end is connected to the main feed gas inlet pipeline 3 of the wet desulfurization system. This allows the sulfate in the backflushing exhaust gas to enter the thermal regeneration system along with the rich liquid from the wet desulfurization process, and ultimately be discharged as acidic wastewater. Furthermore, when the feed gas contains high levels of impurities such as chlorine and arsenic, a pre-protection unit 17 can be added before the fine desulfurization tower, including a dechlorination tank and / or an arsenic removal tank. The dechlorination tank is filled with modified activated carbon or alumina-supported copper dechlorinating agent, and the operating space velocity is 1000-2000 h⁻¹. -1 The arsenic removal tank is filled with copper-zinc or lead-zinc arsenic removal agents, and the operating space velocity is 800-1500 h⁻¹. -1 .

[0023] One of the core aspects of this invention lies in the precise control of the pore structure of the desulfurizing agent. The following explanation uses the template method for preparing mesoporous zinc oxide desulfurizing agent as an example. Zinc nitrate is dissolved in deionized water to prepare a zinc salt solution with a concentration of 0.5-1.2 mol / L. Polyethylene glycol or hexadecyltrimethylammonium bromide is added as a template agent at a zinc to template agent molar ratio of 1:0.05-0.2. After stirring evenly, ammonium carbonate solution is slowly added dropwise to adjust the pH value to 7.5-9.0, forming a precipitate. After aging, filtration, and washing, the precipitate is dried at 110℃ for 12 hours and then calcined at 450-550℃ for 4 hours to obtain the mesoporous zinc oxide product. By adjusting the type and amount of template agent, the mesoporous content can be controlled between 70% and 90%, and the average pore size can be within the range of 10-30 nm. The obtained desulfurizing agent, determined by nitrogen adsorption-desorption method, has a specific surface area ≥120 m² / g, a mesoporous content of 75%-85%, and a pore volume of 0.25-0.40 cm³ / g. X-ray diffraction analysis shows that the zinc oxide crystal form is mainly hexagonal wurtzite, with a grain size of 15-25 nm. The product is formed into spherical or strip-shaped particles with a Φ3-5 mm diameter, a bulk density of 0.8-1.1 g / cm³, and a radial compressive strength ≥60 N / cm.

[0024] In actual operation, the mesoporous zinc oxide desulfurizing agent is first uniformly loaded into the fine desulfurization tower 1, with a bed height of 2.0-3.0m, preferably 2.5m. After loading, nitrogen is introduced for an airtightness test. After confirming no leakage, the feed gas is switched. The feed gas after wet desulfurization treatment such as low-temperature methanol washing has a total sulfur content ≤0.2ppm, a temperature of 40-80℃, a pressure of 2.0-5.0MPa, and a space velocity of 600-1400h⁻¹. -1 The gas passes through the desulfurizing agent bed from top to bottom. Sulfur-containing components in the feed gas, such as hydrogen sulfide, carbonyl sulfide, and mercaptans, undergo chemical adsorption on the surface of mesoporous zinc oxide, generating stable zinc sulfide and a small amount of sulfate, thus achieving deep removal. During operation, online total sulfur analyzers at the inlet and outlet monitor the total sulfur content in the gas in real time, and the data is synchronously transmitted to the PLC timing controller 8 and the DCS system (distributed control system) in the central control room. Under normal operating conditions, the total sulfur content at the outlet is stable at 0.003-0.005 ppm.

[0025] When the online total sulfur analyzer 10 detects that the total sulfur content of the outlet gas has risen to 0.009 ppm, it indicates that the desulfurizing agent bed is close to penetration, and the PLC timing controller 8 automatically triggers the pulse backflushing regeneration program. This threshold is adjustable within the range of 0.009-0.01 ppm, and the specific setting can be flexibly determined according to the requirements of the downstream synthesis catalyst. After the regeneration program is started, the PLC first closes the raw material gas inlet valve 12 and the purified gas outlet valve 13 of the fine desulfurization tower 1, isolating the desulfurization tower from the operating system. Then, the storage tank outlet valve 16 of the nitrogen storage tank 5 is opened. After the nitrogen is heated to 120-180℃ by the nitrogen heater 6, it is blown in from the bottom of the tower in a pulse form by the pulse valve group 7. The pulse backflushing parameters are set as follows: nitrogen pressure 0.4-0.8 MPa, single pulse duration 0.3-1.0 s, pulse interval 5-15 s, and total number of purging cycles 20-40. Preferably, the nitrogen pressure is 0.6 MPa, the temperature is 150°C, the pulse width is 0.5 s, the interval is 10 s, and the purging is performed 30 times. Under the high-speed impact of the pulsed airflow, the sulfates and physical adsorbates attached to the surface and outer pores of the desulfurizing agent particles are instantly blown off and carried upwards to the top of the tower by the airflow, and then discharged through the backflushing waste gas recovery pipeline 11. Because the mesoporous structure provides a smooth diffusion channel, the airflow can penetrate deep into the interior of the particles, and the purging effect is far superior to the continuous backflushing method of traditional microporous desulfurizing agents. The PLC timing controller 8 has a built-in interlock protection module that monitors the nitrogen pressure and temperature in real time. If the nitrogen pressure drops below 0.3 MPa or the temperature drops below 100°C during the regeneration process, the interlock module will automatically terminate the pulse backflushing program, shut down the nitrogen heater and pulse valve group 7, and issue an audible and visual alarm signal to prevent incomplete regeneration of the desulfurizing agent or damage to the bed due to insufficient regeneration conditions. After regeneration is complete, close pulse valve group 7 and let it stand for 5 minutes to allow the bed temperature to become uniform. Then, sequentially open the purified gas outlet valve 13 and the raw material gas inlet valve 12 to resume adsorption desulfurization operation. The total time for a single regeneration process is approximately 15-20 minutes.

[0026] For large-scale ammonia synthesis plants, to achieve online, non-stop regeneration, the desulfurization tower 1 can adopt a dual-tower parallel switching operation structure. One tower is in operation while the other is on standby. When the total sulfur content at the outlet of the operating tower approaches the threshold, the PLC automatically switches that tower out of the system for pulse regeneration, while simultaneously putting the standby tower into operation. The switching process is seamlessly connected through a programmable valve group, with a switching time not exceeding 2 minutes, ensuring a continuous and stable gas supply to the downstream synthesis process.

[0027] Considering the risk of permanent poisoning from impurities such as chlorine and arsenic in the raw gas, it is essential to install a pre-protection unit 17 before the fine desulfurization tower 1 when analytical data shows a chlorine content > 0.05 ppm or an arsenic / heavy metal content > 0.01 ppm. The dechlorination tank is filled with modified activated carbon dechlorinating agent, and the operating space velocity is 1500 h⁻¹. -1It can reduce the chlorine content to below 0.01 ppm; the arsenic removal tank is filled with copper-zinc based arsenic removal agent, and the operating space velocity is 1000 h⁻¹. -1 This can reduce arsenic content to below 0.005 ppm. Sulfate in the backflushing exhaust gas enters the thermal regeneration tower along with the rich liquid from the wet desulfurization process, ultimately entering the acidic water system. To control sulfate accumulation, the sulfate content in the circulating solution of the wet desulfurization system is sampled and analyzed every three months. If the accumulated sulfate mass fraction exceeds 5%, it is controlled by increasing the waste liquid discharge or raising the regeneration temperature to prevent sulfate crystallization and blockage of equipment and pipelines.

[0028] Even after deactivation, the mesoporous zinc oxide desulfurizer still possesses high resource utilization value. The waste desulfurizer is discharged from the tower, pulverized to below 200 mesh, and dissolved in 1-2 mol / L dilute sulfuric acid at 60-80℃ with stirring for 2 hours. Insoluble impurities are removed by filtration. An appropriate amount of template agent is added to the filtrate, and the pH is adjusted to approximately 8.0 with sodium carbonate solution, precipitating basic zinc carbonate. The precipitate is filtered, washed, and dried, then calcined at 500℃ for 3 hours to regenerate the mesoporous zinc oxide product. The mesoporous structure and desulfurization activity of the recovered product are essentially equivalent to the virgin product, with a recovery rate exceeding 90%, and the preparation cost is reduced by approximately 40% compared to the virgin desulfurizer.

[0029] As can be clearly seen from the above embodiments, the present invention achieves significant progress in desulfurization accuracy, service life, operational economy, and environmental friendliness through precise control of the mesoporous structure and synergy with the pulse regeneration process.

[0030] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0031] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A deep purification system for synthetic ammonia feed gas, characterized in that, include: A fine desulfurization tower (1) is filled with a mesoporous zinc oxide desulfurizing agent bed (2), wherein the mesoporous zinc oxide desulfurizing agent has a mesoporous content of ≥70% and a mesoporous pore size of 2nm-50nm; The raw gas inlet pipeline (3) is connected to the top of the fine desulfurization tower (1); The purified gas outlet pipeline (4) is connected to the bottom of the fine desulfurization tower (1), and an online total sulfur analyzer (10) is installed on the pipeline. The pulse backflushing system is connected to the bottom of the fine desulfurization tower (1), and the pulse backflushing system is connected to the outlet online total sulfur analyzer (10) via signal. The backflushing exhaust gas recovery pipeline (11) is connected at one end to the top of the fine desulfurization tower (1) and at the other end to the raw material gas inlet pipeline (3) of the wet desulfurization system.

2. The system according to claim 1, characterized in that: The pulse backflushing system includes a nitrogen storage tank (5), a nitrogen heater (6), a pulse valve group (7), and a PLC timing controller (8); the nitrogen storage tank (5), the nitrogen heater (6), and the pulse valve group (7) are connected in sequence and then connected to the bottom of the fine desulfurization tower (1); the PLC timing controller (8) is electrically connected to the outlet online total sulfur analyzer (10), the pulse valve group (7), and the inlet valve (12) of the fine desulfurization tower (1).

3. The system according to claim 2, characterized in that: The fine desulfurization tower (1) adopts a single tower structure or a dual tower parallel switching operation structure; the raw gas inlet pipeline (3) is equipped with an inlet online total sulfur analyzer (9), a pressure transmitter and a flow transmitter, and the PLC timing controller (8) is electrically connected to the inlet online total sulfur analyzer (9), the pressure transmitter, the flow transmitter and the nitrogen heater (6).

4. The system according to claim 3, characterized in that: The PLC timing controller (8) has a built-in interlock protection module. When the nitrogen pressure is <0.3MPa or the nitrogen temperature is <100℃, the pulse backflushing program will be automatically terminated and an alarm signal will be issued.

5. A method for deep purification of ammonia synthesis feedstock gas, applied to the system described in any one of claims 1-4, characterized in that, Includes the following steps: S1: Mesoporous zinc oxide desulfurizer is used as the adsorbent, wherein the mesoporous content of the mesoporous zinc oxide desulfurizer is ≥70%, and the mesoporous pore size is 2nm-50nm; S2: The raw gas after wet desulfurization is passed into a fine desulfurization tower filled with the mesoporous zinc oxide desulfurizing agent, and adsorption desulfurization is carried out at 40℃-80℃. S3: When the total sulfur content at the outlet of the fine desulfurization tower reaches or exceeds the preset threshold, hot nitrogen is introduced into the fine desulfurization tower for pulse backflushing regeneration, and the waste gas generated by backflushing is returned to the raw material gas inlet pipeline (3) of the wet desulfurization system for treatment. S4: After regeneration, the raw material gas is reintroduced to continue adsorption and desulfurization.

6. The method according to claim 5, characterized in that: In step S1, the mesoporous zinc oxide desulfurizer has a mesoporous content of 70%-90%, a pore size concentrated in the range of 10nm-30nm, a specific surface area ≥120m² / g, and a particle size of 2mm-6mm.

7. The method according to claim 5, characterized in that: In step S2, the total sulfur content of the feed gas is ≤0.2 ppm, the pressure is 2.0 MPa to 5.0 MPa, the space velocity is 600 h -1 -1400 h -1 and the feed gas passes through the bed of mesoporous zinc oxide desulfurizer from top to bottom.

8. The method according to claim 5, characterized in that: In step S3, the pressure of the hot nitrogen gas is 0.4MPa-0.8MPa, and the temperature is 120℃-180℃; the parameters of the pulse backflushing are: single pulse duration 0.3s-1.0s, pulse interval 5s-15s, and total number of purging cycles 20-40.

9. The method according to claim 5, characterized in that: In step S3, the preset threshold is 0.009ppm-0.01ppm.

10. The method according to claim 5, characterized in that, It also includes an impurity protection step: when the chlorine content in the raw gas is >0.05ppm or the arsenic / heavy metal content is >0.01ppm, the raw gas is first passed into the pre-chlorination tank and / or arsenic removal tank for impurity removal, and then enters the fine desulfurization tower.

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