CN204412040U - A kind of combined type Gas Purification Factory low concentration acid gas processing device - Google Patents

Abstract

A kind of combined type Gas Purification Factory low concentration acid gas processing device provided by the utility model, comprise solid phase direct oxidation reaction and liquid phase oxidation reaction, described solid phase direct oxidation reaction and liquid phase oxidation reaction are connected in series, and the secondary sulphur condensation separator of described solid phase direct oxidation reaction is connected with the tail gas condenser in described liquid phase oxidation reaction.Solve the problem that Gas Purification Factory process low concentration acid gas process sulfur recovery rate is low and operating cost is high, total sulfur recovery reaches 99.9%, makes full use of novel oxidized catalyst choice, improves sulfur recovery rate, reclaims high-quality sulphur; Low Sulfur capacity acid gas ensures discharge gas reduction operating cost up to standard by liquid phase oxidation technique.

Description

A combined low-concentration acid gas treatment device in a natural gas purification plant

Technical field:

The utility model relates to a low-concentration acid gas treatment device for a combined natural gas purification plant.

Background technique:

Sour gas refers to the acid gas mixture extracted from sour natural gas, its main components are H ₂ S and CO ₂ , and contain a small amount of hydrocarbons.

Low-concentration acid gas with H ₂ S content less than 15% cannot be treated by Claus method sulfur recovery and extension process. At present, low-concentration acid gas natural gas purification plants mostly use traditional solid-phase catalyst direct oxidation method or liquid-phase catalyst direct oxidation method. The traditional solid-phase catalyst Claus has good activity, poor selectivity, side reaction of generating SO ₂ , and the highest sulfur recovery rate is about 90%, which is difficult to meet the current emission standards. The sulfur recovery rate of the liquid-phase catalyst direct oxidation method can reach 99.9%, but the product is sulfur cake with 60.0% (wt) of water and impurities. The sulfur is of poor quality and difficult to sell. Because the traditional low-concentration acid gas treatment technology has problems such as unqualified tail gas emissions or unqualified sulfur products and high operating costs of the device, low-concentration sour gas treatment in natural gas purification plants is currently a difficult point.

With the increasingly stringent national environmental protection requirements, various industries have formulated stricter air pollutant emission standards. At present, the control of SO ₂ emissions in natural gas purification plants is mainly achieved through production process measures to increase the recovery rate of sulfur, which is also a common practice in foreign natural gas purification industries. At present, high-concentration acid gas in natural gas purification plants at home and abroad usually adopts the Claus method to recover sulfur. In order to meet the emission standards and further improve the sulfur recovery rate, tail gas treatment processes are added, mainly including extended Claus method, reduction absorption method and catalyst direct oxidation method.

Conventional Claus method sulfur recovery process and its extended Claus process are generally used to treat acid gas with H ₂ S content greater than 15% due to the limitation of reaction temperature. This method is already a very mature process technology. The Claus reaction is a slightly exothermic reaction, and it is a reversible reaction from the perspective of a small equilibrium constant. The highest sulfur recovery rate of this type of process is only 99.2%. Due to the limitation of the conversion rate, the introduction has been stopped, or the built devices have been modified to meet the new environmental protection emission requirements.

The reduction and absorption tail gas treatment process is mature, and the total sulfur recovery rate can reach more than 99.8%. However, due to its complicated process flow and high investment and operating costs, it is generally used for tail gas treatment of larger-scale Claus units.

Sour gas with H ₂ S content less than 15% currently has no effective treatment methods in China. At present, the traditional treatment methods mostly use catalyst direct oxidation method, which is divided into liquid phase oxidation and solid oxidation process. Under the action of the catalyst, H ₂ S is directly oxidized to elemental sulfur.

The liquid-phase oxidation process is mainly the complex iron liquid-phase oxidation technology (LO-CAT process). The complex iron liquid-phase oxidation process uses an iron-based catalyst to complete the oxidation reaction and recover sulfur. Its core equipment is the absorption/oxidation reactor. It is mainly suitable for the treatment of acid gas or waste gas with relatively small sulfur content. The LO-CAT device can achieve a sulfur removal efficiency of over 99.9%. The complex iron liquid phase oxidation technology needs to add 5 kinds of chemical solvents, and the solvent consumption is large; the solvent supply system is complex, the operating cost is high, and the production of sulfur chemicals and energy consumption per ton is about 3500-4000 yuan. The product of the liquid phase oxidation process is a sulfur cake containing 60.0% (wt) of water and impurities. The quality of the sulfur is poor and it is difficult to sell.

In the direct oxidation method of solid-phase catalysts, the catalysts are mostly those with Claus activity. Due to the low-temperature activity and poor selectivity of the catalysts, the catalysts not only catalyze the reaction of H ₂ S oxygen to generate elemental S, but also catalyze the side reactions of generating SO ₂ , reducing the sulfur yield, the sulfur yield is less than 90%, it is difficult to meet the increasingly stringent emission requirements, and the existing equipment is currently undergoing device transformation.

Utility model content

The utility model is a combined low-concentration sour gas treatment device developed for natural gas purification plants for the problems of low sulfur recovery rate and high operating cost in the treatment of low-concentration acid gas in current natural gas purification plants. It adopts a new type of high-selectivity solid-phase catalyst oxidation process in series with liquid-phase oxidation process, which successfully solves the problems of low sulfur recovery rate and high operating cost in natural gas purification plants for low-concentration acid gas treatment.

The technical scheme that the utility model adopts:

A combined low-concentration acid gas treatment device in a natural gas purification plant, including a solid-phase oxidation reaction device and a liquid-phase oxidation reaction device, the solid-phase oxidation reaction device and the liquid-phase oxidation reaction device are connected in series;

The solid phase oxidation reaction device includes an isothermal reactor, the upper inlet of the isothermal reactor is connected with an acid gas separator through a pipeline, the upper inlet of the acid gas separator is connected with an acid gas pipeline, and the acid gas separator An acid gas booster fan and an acid gas preheater are sequentially connected between the isothermal reactor and the isothermal reactor, and an air preheater and an air blower are connected in series at the upper inlet of the isothermal reactor, and the upper inlet of the air blower An air pipeline is connected, the outlet at the lower end of the isothermal reactor is connected with a primary sulfur condenser, and the outlet of the primary sulfur condenser is connected with a primary sulfur condensation separator;

The liquid-phase oxidation reaction device includes an absorption oxidation tower, the inlet end of the absorption oxidation tower is connected with a gas-liquid separator, and the inlet end of the gas-liquid separator is connected with a tail gas condenser;

The outlet of the upper end of the primary sulfur condensation separator of the solid-phase oxidation reaction device is connected with the inlet of the tail gas condenser of the liquid-phase oxidation reaction device.

An adiabatic reactor and a secondary sulfur condensation separator are sequentially connected between the primary sulfur condensation separator and the tail gas condenser, and a secondary sulfur condensation separator is connected between the adiabatic reactor and the secondary sulfur condensation separator. sulfur condenser.

The upper inlet of the isothermal reactor is connected to a gas bag, the bottom outlet of the gas bag is connected to the lower outlet of the warm reactor, and the inlet of the gas bag is connected to a boiler water supply pipe.

A filter is connected to the upper outlet of the absorption oxidation tower, and an air blower is arranged between the filter and the absorption oxidation tower.

The absorption and oxidation tower is conical, and the outlet of the conical bottom of the absorption and oxidation tower is connected with a sulfur slurry pump.

It also includes a heat exchanger, the two ends of the heat exchanger are connected to the absorption oxidation tower, and a solution circulation pump is arranged between the heat exchanger and the absorption oxidation tower.

Beneficial effects of the utility model:

For the low H ₂ S concentration (H ₂ S<15%) acid gas treatment process, it can meet the increasingly stringent emission standards. By adopting the solid-phase direct oxidation series liquid-phase oxidation technology, the solid-phase direct oxidation catalyst selects a new domestic catalyst with good low-temperature activity and high selectivity, and selects direct selective oxidation and direct oxidation two-stage reactor or direct selection according to the level of acid gas concentration. 99.6% of the H ₂ S in the primary oxidation reactor is converted into high-quality sulfur.

During the process, the acid gas enters the complex iron liquid phase oxidation reactor after being cooled, and the remaining H ₂ S is directly oxidized into sulfur slurry through liquid phase oxidation, and the total sulfur recovery rate reaches 99.9%. Most of the sulfur is recovered through the solid-phase catalytic oxidation method, which greatly reduces the total sulfur capacity of the liquid-phase oxidation reactor and reduces the operating cost of the liquid-phase oxidation technology.

Through the combination of selective oxidation method and liquid phase oxidation method, make full use of the selectivity of the new oxidation catalyst, improve the sulfur recovery rate, and recover high-quality sulfur; low sulfur capacity acid gas through the liquid phase oxidation process to ensure that the tail gas discharge meets the standard and reduce operating costs.

Further description will be made below in conjunction with the accompanying drawings.

Description of drawings:

Figure 1 is a process schematic diagram of a low-concentration acid gas treatment device in a combined natural gas purification plant.

In the figure: 1. Acid gas separator; 2. Acid gas booster fan; 3. Acid gas preheater; 4. Air blower; 5. Air preheater; 6. Isothermal reactor; 7. Primary sulfur condensation 8. Primary sulfur condensation separator; 9. Secondary reaction preheater; 10. Adiabatic reactor; 11. Secondary sulfur condenser; 12. Secondary sulfur condensation separator; 13. Gas bag; 14. Exhaust gas cooler; 15. Gas-liquid separator; 16. Absorption oxidation tower; 17. Filter; 18. Air blower; 19. Sulfur slurry pump; 20. Solution circulation pump; 21. Heat exchanger.

a, acid gas pipeline; b, air pipeline; c, boiler water supply pipeline; d, medium pressure steam pipeline; e, acid condensate to sewage treatment pipeline; f, tail gas pipeline; g, defoamer pipeline; h, KOH solution Pipeline; i, chemical solution pipeline; j, desalinated water pipeline; k, vacuum belt filter; m, storage tank.

Detailed ways:

Example 1:

The utility model is a combined low-concentration sour gas treatment device developed for natural gas purification plants for the problems of low sulfur recovery rate and high operating cost in the treatment of low-concentration acid gas in current natural gas purification plants. It adopts a new type of high-selectivity solid-phase catalyst oxidation process in series with liquid-phase oxidation process, which successfully solves the problems of low sulfur recovery rate and high operating cost in natural gas purification plants for low-concentration acid gas treatment.

The utility model provides a combined type natural gas purification plant low-concentration acid gas treatment device and method as shown in Figure 1. The low H ₂ S concentration (H ₂ S<15%) acid gas treatment process satisfies the current increasing more stringent emission standards.

As shown in Figure 1, it includes a solid-phase oxidation reaction device and a liquid-phase oxidation reaction device, and the solid-phase oxidation reaction device and the liquid-phase oxidation reaction device are connected in series;

The solid-phase oxidation reaction device includes an isothermal reactor 6, the upper end inlet of the isothermal reactor 6 is connected with an acid gas separator 1 through a pipeline, and the upper end inlet of the acid gas separator 1 is connected with an acid gas pipeline a, An acid gas booster fan 2 and an acid gas preheater 3 are sequentially connected between the acid gas separator 1 and the isothermal reactor 6, and an air preheater 5 is connected in series at the inlet of the upper end of the isothermal reactor 6 , air blower 4, the upper inlet of described air blower 4 is connected with air duct b, the outlet of the lower end of described isothermal reactor 6 is connected with primary sulfur condenser 7, and the outlet of described primary sulfur condenser 7 is connected with primary sulfur condensation Separator 8;

The liquid-phase oxidation reaction device includes an absorption oxidation tower 16, the inlet end of the absorption oxidation tower 16 is connected with a gas-liquid separator 15, and the inlet end of the gas-liquid separator 15 is connected with a tail gas condenser 14;

The outlet at the upper end of the primary sulfur condensation separator 8 of the solid-phase oxidation reaction device is connected to the inlet of the tail gas condenser 14 of the liquid-phase oxidation reaction device.

The mixed gas enters the isothermal reactor 6, where a selective oxidation reaction is carried out, most of the H ₂ S is directly oxidized into sulfur vapor, and the sulfur vapor after the isothermal reaction enters the primary sulfur condenser 7, and is cooled to Enter the primary sulfur condensation separator 8 at 125°C to separate the liquid sulfur, the liquid sulfur enters the storage tank m, and the tail gas exiting the primary sulfur condensation separator 8 is heated to 160°C by the secondary reaction preheater 9 and then enters the adiabatic reactor 10 Carry out direct oxidation reaction, the reacted sulfur vapor enters the secondary sulfur condenser 11 and cools to 125°C, enters the secondary sulfur condensation separator 12 to separate the liquid sulfur, and the liquid sulfur enters the storage tank m; the isothermal reactor 6 is equipped with a heat exchange plate The tube takes away the heat generated by the chemical reaction, and the steam and water generated by the heat exchange coil are separated into steam and water in the air bag 13, and part of the generated steam is used as the heat source of the acid gas preheater 3 and the air preheater 5, and the rest The medium-pressure steam exits the device, and the generated water enters the isothermal reactor 6 for heat exchange coil circulation.

An adiabatic reactor 10, a secondary sulfur condenser 11, and a secondary sulfur condensation separator 12 are sequentially connected between the primary sulfur condensation separator 8 and the tail gas condenser 14.

The upper inlet of the isothermal reactor 6 is connected to a gas bag 13, the bottom outlet of the gas bag 13 is connected to the lower outlet of the warm reactor 6, and the inlet of the gas bag 13 is connected to a boiler water supply pipe c.

Example 2:

The upper outlet of the absorption oxidation tower 16 is connected with a filter 17 , and an air blower 18 is arranged between the filter 17 and the absorption oxidation tower 16 .

The tail gas exiting the secondary sulfur condensation separator 12 is cooled to 50°C through the tail gas cooler 14 and enters the absorption oxidation tower 16 through the gas-liquid separator 15, and the H ₂ S gas in the tail gas reacts with the alkaline solution in the absorption oxidation tower 16 Absorption, oxidation reaction with the chelated iron in the absorption oxidation tower 16 to generate sulfur element; the air enters the air blower 18 through the filter 17 for pressurization and then enters the absorption oxidation tower 16 to oxidize and regenerate iron ions for recycling.

Example 3:

The absorption and oxidation tower 16 is conical, and the outlet of the conical bottom of the absorption and oxidation tower 16 is connected with a sulfur slurry pump 19.

It also includes a heat exchanger 21 , the two ends of the heat exchanger 21 are connected to the absorption oxidation tower 16 , and a solution circulation pump 20 is arranged between the heat exchanger 21 and the absorption oxidation tower 16 .

When the concentration of the sulfur slurry at the bottom of the vertebral body of the absorption and oxidation tower 16 reaches more than 5%, it is pumped by the sulfur slurry pump 19 to a belt filter to remove moisture to obtain 60.0% (wt) sulfur cake. The concentration of SO ₂ and H ₂ S in the up-to-standard tail gas discharged from the absorption oxidation tower 16 is less than 10ppm (v). The solution in the absorption oxidation tower enters the heat exchanger 21 through the solution circulation pump 20 to maintain a constant temperature in the absorption oxidation tower. The KOH solution and chemical solution consumed by the reaction are replenished to the absorption oxidation tower 16 through the solution storage tank.

Example 4:

A method for treating low-concentration acid gas in a combined natural gas purification plant, the specific steps are as follows,

(1) In the solid-phase direct oxidation separator, the acid gas from the device enters the acid gas separator 1 through the acid gas channel a and is separated and then pressurized by the acid gas booster fan 2. The heater 3 is heated to 180°C; at the same time, the air enters the air blower 4 through the air channel b to pressurize, and after the pressurization, it is heated to 180°C by the air preheater 5 and then mixed with the acid gas passing through the acid gas preheater 3;

(2) When the mixed gas enters the isothermal reactor 6, a selective oxidation reaction is carried out in the isothermal reactor 6, and the H ₂ S is directly oxidized into sulfur vapor, and the sulfur vapor after the isothermal reaction enters the first-stage sulfur condenser 7 for cooling Enter the primary sulfur condensation separator 8 to separate the liquid sulfur at 125°C, and the liquid sulfur enters the storage tank m;

(3) The tail gas exiting the primary sulfur condensation separator 8 is heated to 160°C by the secondary reaction preheater 9 and enters the adiabatic reactor 10 for direct oxidation reaction. The reacted sulfur vapor enters the secondary sulfur condenser 11 and is cooled to Enter the secondary sulfur condensation separator 12 at 125°C to separate the liquid sulfur, and the liquid sulfur enters the storage tank m;

(4) A heat exchange coil is installed in the isothermal reactor 6 to take away the heat generated by the chemical reaction. The steam and water generated by the heat exchange coil are separated in the air drum 13 to separate the steam and water, and part of the generated steam is used as acid gas preheating 3 and the heat source of the air preheater 5, the rest of the medium-pressure steam goes out of the device, and the generated water enters the isothermal reactor 6 for heat exchange coil circulation;

(5) The tail gas from the secondary sulfur condensation separator 12 is cooled to 50°C through the tail gas cooler 14 and enters the absorption oxidation tower 16 through the gas-liquid separator 15. The H ₂ S gas in the tail gas and the alkalinity in the absorption oxidation tower 16 The solution is reacted and absorbed, and reacts with the chelated iron oxidation reaction in the absorption oxidation tower 16 to generate sulfur element;

(6) In the liquid-phase oxidation separator, the air passes through the air pipe b, passes through the filter 17, enters the air blower 18 for pressurization, and then enters the absorption oxidation tower 16 to oxidize and regenerate iron ions for recycling;

(7) When the concentration of the sulfur slurry at the bottom of the vertebral body of the absorption and oxidation tower 16 reaches more than 5%, it is pumped by the sulfur slurry pump 19 to the belt filter to remove water, and 60.0% (wt) sulfur cake is obtained, and the exhaust gas is passed out of the absorption and oxidation tower 16 The concentration of SO ₂ and H ₂ S in the up-to-standard tail gas discharged from pipeline f is less than 10ppm (v);

(8) The solution in the absorption oxidation tower enters the heat exchanger 21 through the solution circulation pump 20 to maintain a constant temperature in the absorption oxidation tower 16, and supplies the absorption oxidation tower 9 through the solution storage tank through the KOH solution pipeline h and the chemical solution pipeline i to supplement the reaction consumption KOH solution and chemical solution.

Both the acid gas separator and the gas-liquid separator 15 are treated by the acid condensate through the sewage treatment pipeline e to the sewage treatment system, and the boiler water supply pipeline c and the medium-pressure steam pipeline d are connected to the gas bag 13 to ensure sufficient water source. The defoamer pipeline g is connected to the solution circulation pump 20 to ensure that the solution passes through the solution circulation pump 20 smoothly.

As shown in Figure 1, the acid gas from the device is preliminarily separated by the acid gas separation tank 1, then pressurized, heated to 180°C by the acid preheater 3, and then pressurized by the air blower 4 and air preheater 5 The air b heated to 180°C is mixed, and the mixed gas O ₂ /H ₂ S=0.6-0.8 is ensured, and the mixed gas enters the isothermal reactor 6 . The acid gas undergoes selective oxidation reaction through the new selective oxidation catalyst in the isothermal reactor 6, and oxidizes most of the H ₂ S into sulfur. During the constant temperature reaction, steam is generated in the heat exchange tube 21, and the heat generated by the reaction is taken away. , part of the steam is used as the heat source of the reactor inlet heater, and the rest is out of the device. The gas after the isothermal reaction enters the primary sulfur condenser 7 and is cooled to 125°C to separate liquid sulfur. After the liquid sulfur is separated, the tail gas still contains a small amount of H ₂ S gas, and a deep adiabatic reaction is required. The gas is heated to 160° C. by the secondary reaction preheater 9 and enters the adiabatic reactor 10 for direct oxidation reaction. The reacted gas is cooled to 125° C. through the secondary sulfur condenser 11 , and then the liquid sulfur is separated in the secondary sulfur condensation separator 12 . When the concentration of H ₂ S in the acid gas is low, the first-order isothermal reaction can be directly adopted.

Using a novel selective direct oxidation catalyst, the reaction equation is as follows:

The core technology of the selective oxidation desulfurization process is its selective oxidation catalyst. The selective oxidation catalyst is HS-35. Its appearance and shape are cylindrical. The main components are TiO ₂ , Fe ₂ O ₃ , Al ₂ O ₃ , and the specification is mm Φ4 ×5～15(L), crushing strength N/cm ≥120, bulk density kg/m ³ 900～1100, specific surface m ² /g 100～120, sulfur yield % ≥95.0, service life ≥3.0 years.

The deep oxidation catalyst is HS-38, its shape is cylindrical, the main components are TiO ₂ , MoO, Fe ₂ O ₃ , the specification is mm Φ4×5～15 (L), the crushing strength is N/cm ≥120, and the bulk density is kg/ m ³ 950～1050, sulfur yield % ≥ 95.0, service life ≥ 3.0 years.

The catalyst has good low-temperature activity and selectivity, can be used at 130°C, has no Claus reaction activity, has stable activity, and its selective oxidation is an irreversible reaction. The reaction is a non-equilibrium reaction, so the outlet H ₂ S concentration is not affected by thermodynamic equilibrium, and the total sulfur recovery rate is high.

The separated tail gas is cooled to 50°C and enters the liquid phase oxidation reactor (LO-CAT device). Acid gas enters the bottom of the absorption and oxidation tower 16 of the main reactor, and air is passed into the bottom of the absorption and oxidation tower 16 of the main reactor by an air blower 18 . The reactor absorbs the solution in the oxidation tower 16, mainly demineralized water j, chelates, iron ions, KOH solution h, and chemical solution i.

The hydrogen sulfide in the acid gas is dissolved and ionized by the density difference in the reactor, and reacts with the chelated iron in the reactor to form sulfur element, and the reduced iron ions are regenerated under the oxidation of air. When the concentration of the sulfur slurry at the bottom of the reactor cone reaches more than 5%, it is pumped by the sulfur slurry pump 19 to the vacuum belt filter k to remove water and obtain 60.0% (wt) sulfur cake.

The Lo-cat process is a sulfur recovery process carried out under normal temperature and low pressure conditions. It is carried out in the liquid phase, usually with alkaline aqueous solution, and the catalyst uses water-soluble chelated iron ions. The whole reaction can be divided into absorption reaction and regeneration reaction. , side effects also occur. Alkaline solution can inhibit the occurrence of side reactions. The chemical formula is as follows:

Absorption chamber: H ₂ S(g)+H ₂ O→H ₂ S(aq)+H ₂ O (dissolution of H ₂ S gas)

H ₂ S(aq) →H ⁺ +HS ^- (electrolytic reaction)

HS ^- +2Fe ³⁺ →S(s)+H ⁺ +2Fe ²⁺ (sulfur formation reaction)

Oxidation chamber: O ₂ (g)+2H ₂ O→O ₂ (aq)+ 2H ₂ O (dissolution of oxygen)

O ₂ (aq)＋4H ⁺ +4Fe ²⁺ → 2H ₂ O+4Fe ³⁺ (dissolved oxygen oxidizes Fe ³⁺ )

By adopting solid-phase direct oxidation and liquid-phase oxidation (LO-CAT device) combined acid gas treatment technology, the concentration of SO ₂ and H ₂ S in the exhaust tail gas is guaranteed to be less than 10ppm (v). It overcomes the inability of the traditional Claus and its extended process to handle low H ₂ S concentration (H ₂ S<15%) sour gas, and solves the problem of low sulfur recovery rate in the treatment of low concentration sour gas by the direct oxidation method, reducing sulfur capacity and liquid phase oxidation (LO-CAT device) Operating costs.

Claims (6)

1. A low-concentration acid gas treatment device in a combined natural gas purification plant, characterized in that: it comprises a solid-phase oxidation reaction device and a liquid-phase oxidation reaction device, and the solid-phase oxidation reaction device and the liquid-phase oxidation reaction device are connected in series; The solid-phase oxidation reaction device includes an isothermal reactor (6), the inlet of the upper end of the isothermal reactor (6) is connected to an acid gas separator (1) through a pipeline, and the upper end of the acid gas separator (1) An acid gas pipeline (a) is connected to the inlet, and an acid gas booster fan (2) and an acid gas preheater (3) are sequentially connected between the acid gas separator (1) and the isothermal reactor (6) , the upper inlet of the isothermal reactor (6) is connected in series with an air preheater (5) and an air blower (4), the upper inlet of the air blower (4) is connected with an air pipe (b), and the isothermal The outlet at the lower end of the reactor (6) is connected with a primary sulfur condenser (7), and the outlet of the primary sulfur condenser (7) is connected with a primary sulfur condensation separator (8); The liquid-phase oxidation reaction device includes an absorption oxidation tower (16), the inlet end of the absorption oxidation tower (16) is connected with a gas-liquid separator (15), and the inlet end of the gas-liquid separator (15) is connected with a tail gas condensing device (14); The outlet at the upper end of the primary sulfur condensation separator (8) of the solid-phase oxidation reaction device is connected to the inlet of the tail gas condenser (14) of the liquid-phase oxidation reaction device. 2. A combined low-concentration acid gas treatment device in a natural gas purification plant according to claim 1, characterized in that: the first-stage sulfur condensation separator (8) and the tail gas condenser (14) are sequentially An adiabatic reactor (10) and a secondary sulfur condensation separator (12) are connected, and a secondary sulfur condenser (11) is connected between the adiabatic reactor (10) and the secondary sulfur condensation separator (12). ). 3. A combined type natural gas purification plant low-concentration acid gas treatment device according to claim 1, characterized in that: the upper end inlet of the isothermal reactor (6) is connected to a gas bag (13), and the gas bag The outlet at the bottom of (13) communicates with the outlet at the lower end of the warm reactor (6), and the inlet of the air bag (13) is connected with a boiler water supply pipe (c). 4. A combined type natural gas purification plant low-concentration acid gas treatment device according to claim 1, characterized in that: the upper outlet of the absorption oxidation tower (16) is connected with a filter (17), and the filter An air blower (18) is provided between (17) and the absorption oxidation tower (16). 5. A combined type natural gas purification plant low-concentration acid gas treatment device according to claim 1, characterized in that: the absorption and oxidation tower (16) is conical, and the bottom of the absorption and oxidation tower (16) is conical The outlet is connected with a sulfur slurry pump (19). 6. A combined type natural gas purification plant low-concentration acid gas treatment device according to claim 1, characterized in that it also includes a heat exchanger (21), and the two ends of the heat exchanger (21) are connected to the absorption oxidation The tower (16) is connected, and a solution circulation pump (20) is arranged between the heat exchanger (21) and the absorption oxidation tower (16).