A sulfuric acid plant for producing acid from a mineral by a double absorption process recovering low level heat

Abstract

This application relates to a sulfuric acid production system for sulfuric acid by recovering low-grade heat from a secondary absorption process. It includes a primary absorption tower and a secondary absorption tower. Flue gas is fed into the primary absorption tower by a fan connected to it via an inlet pipe. A converter is installed between the fan and the primary absorption tower. Flue gas passes through the converter as it is pumped into both towers, which are connected by a conversion pipe. A heat exchange component is installed at the bottom of the secondary absorption tower, connected to it via a heat exchange pipe. The fan outlet is connected to the heat exchange component, which is located between and connected to the conversion pipe. Flue gas flows from the primary absorption tower, passes through the heat exchange component, and then flows into the secondary absorption tower. This application features a system where flue gas in both the primary and secondary flue gas pipes is simultaneously heated by acid in the acid pipe. The heating temperature of the two flue gas streams is uniform, and the temperature difference of the heated flue gas after heat exchange is small, thus not affecting the subsequent acid production process.

Description

Technical Field

[0001] This application relates to the field of sulfuric acid preparation, and in particular to a sulfuric acid production system for sulfuric acid ore that recovers low-grade heat from the secondary absorption process. Background Technology

[0002] Sulfuric acid is an important industrial raw material, generally produced using sulfur or acidic waste gas. When using acidic waste gas to produce acid, a two-stage conversion and two-stage absorption acid production system is typically employed.

[0003] One related technology involves a two-stage absorption-to-acid production system. This system designs the acid loading rate of the second absorption tower and re-selects the packing specifications. While ensuring the SO3 absorption rate of the second absorption process, it increases the acid temperature exiting the tower, thus enabling the utilization of the heat from the acid. Furthermore, by setting up a first preheater and a second preheater, the heat from the acid exiting the second absorption process is used to preheat the smelting flue gas entering the blower or the air entering the fluidized bed furnace and smelting furnace, as well as to preheat the flue gas exiting the first absorption tower. This achieves the recycling of the heat from the acid exiting the tower back into the flue gas-to-acid production system, realizing the recovery and utilization of heat from the acid temperature at the second absorption tower. By connecting a demineralized water preheater to the outlet ends of the first and second preheaters, partial energy recovery from the acid exiting the second absorption process is further achieved. Sulfuric acid is cooled to a suitable temperature via the first preheater, the second preheater, and the demineralized water preheater before being recycled back into the second absorption tower, achieving the recycling of sulfuric acid.

[0004] The outlet ends of the first and second preheaters are connected to the demineralized water preheater to further realize partial energy recovery of the acid exiting the tower in the two-absorption process. Although the heat recovery of the acid exiting the tower is realized, due to the adoption of the two-to-two-absorption process, a set of preheaters needs to be set up at the first and second absorptive towers to heat the flue gas entering the first and second absorptive towers respectively. The whole system is large in volume, and due to the different positions of the two heat exchangers, the initial temperature of the acid entering the two heat exchangers is actually different, and the temperature of the flue gas after the heat exchange is different, which affects the entire acid production process. Summary of the Invention

[0005] To address the issue of initial temperature differences when acid enters the heat exchanger, this application provides a sulfuric acid production system that recovers low-grade heat from the secondary absorption process.

[0006] This application provides a sulfuric acid production system for recovering low-grade heat from a secondary absorption process, employing the following technical solution:

[0007] A sulfuric acid production system for recovering low-grade heat from a secondary absorption process includes a primary absorption tower and a secondary absorption tower. Flue gas is sent into the primary absorption tower by a blower. The blower and the primary absorption tower are connected by an inlet pipe. A converter is provided between the blower and the primary absorption tower. When the flue gas is pumped into the primary and secondary absorption towers, it passes through the converter respectively. The primary and secondary absorption towers are connected by a conversion pipe.

[0008] The bottom of the second suction tower is equipped with a heat exchange component. The second suction tower and the heat exchange component are connected by a heat exchange pipe. The air outlet of the fan is connected to the heat exchange component. The heat exchange component is located between the conversion pipes and is connected to the conversion pipes. Flue gas flows from the first suction tower, passes through the heat exchange component, and flows into the second suction tower.

[0009] By adopting the above technical solution, the flue gas used for heat exchange in the first and second absorption towers actually enters the same heat exchange component for heat exchange. Therefore, whether it is the acid (mainly sulfuric acid) used as the heat exchange medium or the flue gas flowing to the first and second absorption towers as the heat exchange medium, the heat exchange efficiency is the same because the contact time with the acid is the same. Ultimately, the temperature difference of the heated flue gas after heat exchange is small, which does not affect the subsequent acid production process.

[0010] Optionally, the heat exchange assembly includes a housing and a heat exchange section. The heat exchange section is fixed inside the housing. The housing is provided with a first flue gas inlet, a second flue gas inlet, a first flue gas outlet, a second flue gas outlet, an acid inlet, and an acid outlet. The first flue gas inlet, the second flue gas inlet, the first flue gas outlet, the second flue gas outlet, the acid inlet, and the acid outlet are respectively connected to the heat exchange section.

[0011] By adopting the above technical solution, the heat exchange section is the core component of the heat exchange assembly. It uses the two flue gas streams of the heat exchange section to exchange heat and raise the temperature, so that the residual heat in the acid solution is fully utilized. During the heat exchange process, there will be basically no uneven heating of the two flue gas streams. The temperature of the two flue gas streams is uniform. The temperature difference of the heated flue gas after heat exchange is small and does not affect the subsequent acid production process.

[0012] Optionally, the heat exchange section includes an acid pipe, a first flue gas pipe, and a second flue gas pipe. The acid pipe, the first flue gas pipe, and the second flue gas pipe are all spiral-shaped. One side of each spiral of the acid pipe abuts against the first flue gas pipe, and the other side of each spiral of the acid pipe abuts against the second flue gas pipe. One end of the acid pipe is connected to an acid inlet, and the other end of the acid pipe is connected to an acid outlet. The acid outlet is connected to the second absorption tower through a pipe.

[0013] One end of the first flue gas duct is connected to the first flue gas inlet, and the other end of the first flue gas duct is connected to the first flue gas outlet. One end of the second flue gas duct is connected to the second flue gas inlet, and the other end of the second flue gas duct is connected to the second flue gas outlet.

[0014] By adopting the above technical solution, there is only one acid pipe in the heat exchange section. Both flue gas streams exchange heat with this acid pipe. The first flue gas pipe, the acid pipe, and the second flue gas pipe are spirally stacked on top of each other, so that the higher temperature acid liquid can fully contact the first and second flue gas pipes in the acid pipe, improving the heat exchange efficiency. At the same time, the flue gas in the first and second flue gas pipes is heated by the acid liquid in the acid pipe simultaneously. The temperature of the two flue gas streams is uniform, and the temperature difference of the heated flue gas after heat exchange is small, which does not affect the subsequent acid production process.

[0015] Optionally, the heat exchange section includes an outer sleeve and an inner sleeve. The inner sleeve is fitted inside the outer sleeve. A partition is provided on the outer wall of the inner sleeve, which divides the outer sleeve into a first channel and a second channel that are not connected to each other. One end of the inner sleeve is connected to the acid inlet, and the other end of the inner sleeve is connected to the acid outlet. The acid outlet is connected to the second absorption tower through a pipeline.

[0016] One end of the first channel is connected to the first flue gas inlet, and the other end of the first channel is connected to the first flue gas outlet. One end of the second channel is connected to the second flue gas inlet, and the other end of the second channel is connected to the second flue gas outlet.

[0017] By adopting the above technical solution, the space between the outer sleeve and the inner sleeve is used for flue gas flow, and the area between the inner and outer sleeves is divided into two non-communicating regions by a partition. This allows the two flue gas streams to enter the area between the outer and inner sleeves independently. Once inside, since the fluid flowing between the inner sleeves is acid, and the flue gas is only separated from it by the outer wall of the inner sleeve, the heat exchange efficiency is high.

[0018] Optionally, the secondary absorption tower includes a tower body, an acid separator disposed at the top of the tower body, packing material disposed below the acid separator, and an acid circulation tank disposed at the bottom of the tower body. The acid circulation tank is connected to the acid inlet, and the acid outlet is connected to the acid separator.

[0019] By adopting the above technical solution, the acid from the acid outlet circulates in the secondary absorption tower and participates in the sulfide absorption step in flue gas treatment, thereby improving the utilization efficiency of the acid solution.

[0020] Optionally, the acid outlet of the heat exchange component is connected to the demineralized water preheater. The acid cooled by the heat exchange component enters the demineralized water preheater. The outlet of the demineralized water preheater is connected to the acid separator. The acid solution further cooled by the demineralized water preheater flows back to the acid separator.

[0021] By adopting the above technical solution, the acid solution, after heat exchange by the heat exchange components, is further cooled by the demineralized water preheater and flows back to the acid separator. The acid outlet circulates in the secondary absorption tower, participating in the sulfide absorption step in flue gas treatment, thereby improving the utilization efficiency of the acid solution.

[0022] Optionally, the converter includes a first conversion layer, a second conversion layer, a third conversion layer, a fourth conversion layer, and a fifth conversion layer, wherein the first to third conversion layers are connected in sequence, and the fourth and fifth conversion layers are connected in sequence.

[0023] The flue gas inlet of the first conversion layer is connected to the flue gas outlet of the fan; the flue gas outlet of the third conversion layer is connected to the flue gas inlet of the first suction tower; the flue gas outlet of the first suction tower is connected to the flue gas inlet of the fourth conversion layer; and the flue gas outlet of the fifth conversion layer is connected to the flue gas inlet of the second suction tower.

[0024] By adopting the above technical solution, the converter converts sulfur dioxide in the flue gas into sulfur trioxide, thus preparing for the next step of acid production.

[0025] Optionally, the spray density of the acid separator is 2–3.5 m³ / s. 3 / m 2 ·h, the packing material is a ceramic packing material with a diameter of φ20~50mm.

[0026] By adopting the above technical solution and using ceramic packing of this specification, the gas-liquid contact area is increased, thereby improving the acid production efficiency.

[0027] The packing material is a rectangular saddle ring ceramic packing, a heterosaddle ring ceramic packing, a Raschig ring ceramic packing, or a cross ring ceramic packing.

[0028] By adopting the above technical solutions, these ceramic fillers possess the advantage of high corrosion resistance.

[0029] Optionally, the flue gas outlet of the second suction tower is connected to a tail gas treatment device, and the tail gas treatment device is connected to a flue gas pipe.

[0030] By adopting the above technical solutions, exhaust gas can be treated by the exhaust gas treatment device to meet the standards before being discharged, thereby reducing environmental pollution.

[0031] In summary, this application includes at least one of the following beneficial effects:

[0032] 1. The heat exchange section has only one acid pipe, and both flue gas lines exchange heat with this acid pipe. The first flue gas pipe, the acid pipe, and the second flue gas pipe are spirally stacked on top of each other, so that the higher temperature acid liquid can fully contact the first flue gas pipe and the second flue gas pipe in the acid pipe, improving the heat exchange efficiency. At the same time, the flue gas in the first flue gas pipe and the second flue gas pipe are heated by the acid liquid in the acid pipe simultaneously. The temperature of the two flue gas lines is uniform, and the temperature difference of the heated flue gas after heat exchange is small, which does not affect the subsequent acid production process.

[0033] 2. The space between the outer sleeve and the inner sleeve is used for flue gas flow, and the area between the inner and outer sleeves is divided into two non-connected areas by a partition. This allows the two flue gas streams to enter the area between the outer and inner sleeves independently. Once inside, since the fluid flowing between the inner sleeves is acid, and the only barrier between the acid and the flue gas is the outer wall of the inner sleeve, the heat exchange efficiency is high.

[0034] 3. After heat exchange by the heat exchange components, the acid solution, further cooled by the demineralized water preheater, flows back to the acid separator. The acid outlet circulates in the secondary absorption tower, participating in the sulfide absorption step of flue gas treatment, thereby improving the utilization efficiency of the acid solution. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the principle of the sulfuric acid production system for recovering low-grade heat from the secondary absorption process in the embodiments of this application;

[0036] Figure 2 This is a schematic diagram of the structure of the heat exchange component in the first embodiment of this application.

[0037] Figure 3 This is a schematic cross-sectional view of the heat exchange component according to a first embodiment of this application.

[0038] Figure 4 This is a schematic diagram of the second embodiment of the heat exchange component in this application.

[0039] Figure 5 This is a schematic cross-sectional view of the heat exchange component according to a second embodiment of the present application.

[0040] In the diagram: 1. First suction tower; 2. Second suction tower; 21. Tower body; 22. Acid separator; 23. Packing; 24. Acid circulation tank; 3. Fan; 4. Heat exchange components; 41. Outer shell; 411. First flue gas inlet; 412. Second flue gas inlet; 413. First flue gas outlet; 414. Second flue gas outlet; 415. Acid inlet; 416. Acid outlet; 42. Heat exchange section; 421. Acid pipe; 422. First flue gas pipe; 423. Second flue gas pipe; 424. Outer shell; 425. Inner shell; 426. Baffle; 5. Converter; 51. First conversion layer; 52. Second conversion layer; 53. Third conversion layer; 54. Fourth conversion layer; 55. Fifth conversion layer. Detailed Implementation

[0041] The following is in conjunction with the appendix Figures 1-5 This application will be described in further detail.

[0042] This application discloses a sulfuric acid production system for sulfuric acid ore that recovers low-grade heat from a secondary absorption process. (Refer to...) Figure 1 The system includes a primary absorption tower 1, a secondary absorption tower 2, and a converter 5. A blower 3 blows smelting flue gas containing sulfides into the primary absorption tower 1. The smelting flue gas undergoes pretreatment in the primary absorption tower 1, primarily to remove impurities. The impurity-removed smelting flue gas then enters the converter 5 to convert the sulfides into SO3, which is then converted into sulfuric acid in the secondary absorption tower 2. A heat exchange assembly 4 is fixed to the bottom of the secondary absorption tower 2, and the secondary absorption tower 2 and the heat exchange assembly 4 are connected via heat exchange pipes. The outlet of the blower 3 is connected to the heat exchange assembly 4, which is located between and connected to the conversion pipes. Flue gas flows from the primary absorption tower 1, passes through the heat exchange assembly 4, and then flows into the secondary absorption tower 2. The heat exchange function of the heat exchange assembly 4 is mainly due to the high temperature of the acid outlet 416 of the secondary absorption tower 2. The acid from the secondary absorption tower 2 is used as the heat exchange medium for the heat exchange assembly 4. After the smelting flue gas enters the heat exchange assembly 4, it undergoes heat exchange, raising the temperature of the smelting flue gas to facilitate acid production, while simultaneously lowering the temperature of the acid production process.

[0043] Reference Figure 1 and Figure 2The heat exchange component 4 includes a housing 41 and a heat exchange section 42, which is fixed inside the housing 41. The housing 41 is provided with a first flue gas inlet 411, a second flue gas inlet 412, a first flue gas outlet 413, a second flue gas outlet 414, an acid inlet 415, and an acid outlet 416. The first flue gas inlet 411, the second flue gas inlet 412, the first flue gas outlet 413, the second flue gas outlet 414, the acid inlet 415, and the acid outlet 416 are respectively connected to the heat exchange section 42. The smelting flue gas enters through the first flue gas inlet 411 and the second flue gas inlet 412, respectively. Before the flue gas enters the first absorption tower 1 and the second absorption tower 2, it is heat-exchanged by the heat exchange section 42. The heat exchange medium enters through the acid inlet 415 to exchange heat with the flue gas and reduce the temperature of the acid liquid. At the same time, the high temperature of the acid liquid is used to preheat the smelting flue gas, accelerating the acid production process and making good use of the waste heat in the acid production process.

[0044] Reference Figure 2 and Figure 3 One implementation of the heat exchange section 42 includes an acid pipe 421, a first flue gas pipe 422, and a second flue gas pipe 423. All three pipes are spiral-shaped, with one side of each spiral of the acid pipe 421 abutting against the first flue gas pipe 422 and the other side against the second flue gas pipe 423. This ensures that the acid pipe 421 is always positioned with the first and second flue gas pipes on either side, thus improving heat exchange efficiency. The spiral shape of the first and second flue gas pipes 422 and the acid pipe 423 within the confined outer casing 41 ensures sufficient contact between the two flue gas pipes and the acid pipe 421, resulting in more efficient heat exchange. One end of acid pipe 421 is connected to acid inlet 415, and the other end of acid pipe 421 is connected to acid outlet 416. Acid outlet 416 is connected to the second suction tower 2 via a pipe. One end of the first flue gas pipe 422 is connected to the first flue gas inlet 411, and the other end of the first flue gas pipe 422 is connected to the first flue gas outlet 413. One end of the second flue gas pipe 423 is connected to the second flue gas inlet 412, and the other end of the second flue gas pipe 423 is connected to the second flue gas outlet 414. The entire heat exchange section 42 contains only one acid pipe 421. Both flue gas streams exchange heat with this acid pipe 421. The first flue gas pipe 422, the acid pipe 421, and the second flue gas pipe 423 are spirally stacked on top of each other, allowing the higher-temperature acid liquid to fully contact the first flue gas pipe 422 and the second flue gas pipe 423 within the acid pipe 421, thus improving heat exchange efficiency. At the same time, the smelting flue gas in the first flue gas pipe 422 and the second flue gas pipe 423 is simultaneously heated by the acid liquid in the acid pipe 421. The heating temperature of the two flue gas streams is uniform, and the temperature difference of the heated flue gas after heat exchange is small, which does not affect the subsequent acid production process.

[0045] Reference Figure 4 and Figure 5 Another implementation of the heat exchange section 42 is as follows: the heat exchange section 42 includes an outer sleeve 424 and an inner sleeve 425. The inner sleeve 425 is fitted inside the outer sleeve 424. A partition 426 is provided on the outer wall of the inner sleeve 425, dividing the outer sleeve 424 into a first channel and a second channel that are not interconnected. One end of the inner sleeve 425 is connected to the acid inlet 415, and the other end of the inner sleeve 425 is connected to the acid outlet 416. The acid outlet 416 is connected to the second suction tower 2 through a pipe. The area between the wall of the outer sleeve 424 and the inner sleeve 425 is used for flue gas to flow, and the area between the inner sleeve 425 and the outer sleeve 424 is divided into two non-interconnected areas by the partition 426. This allows the two flue gas streams to enter the area between the outer sleeve 424 and the inner sleeve 425 independently. After entering, since the fluid flowing between the inner sleeve 425 is acid, and there is only the outer wall of the inner sleeve 425 separating it from the flue gas, the heat exchange efficiency is high. One end of the first channel is connected to the first flue gas inlet 411, and the other end is connected to the first flue gas outlet 413. One end of the second channel is connected to the second flue gas inlet 412, and the other end is connected to the second flue gas outlet 414. The connection between the first flue gas inlet 411 and the first channel, and the connection between the second flue gas inlet 412 and the second channel, allows the two smelting flue gases to independently enter the area between the inner sleeve 425 and the outer sleeve 424, where they exchange heat with the acid liquid inside the inner sleeve, improving heat exchange efficiency. At the same time, the two independent smelting flue gases are simultaneously heated by the acid liquid in the acid pipe 421, resulting in uniform heating temperatures for both flue gases. The temperature difference of the heated flue gases after heat exchange is small and does not affect the subsequent acid production process.

[0046] Reference Figure 1 After the smelting flue gas enters converter 5, converter 5 has a multi-layer structure, specifically including converter layer 51, converter layer 52, converter layer 53, converter layer 54, and converter layer 55. Converter layers 51 to 53 are connected sequentially, and converter layers 54 and 55 are connected. The flue gas inlet of converter layer 51 is connected to the flue gas outlet of blower 3, the flue gas outlet of converter layer 53 is connected to the flue gas inlet of first suction tower 1, the flue gas outlet of first suction tower 1 is connected to the flue gas inlet of fourth suction tower 54, and the flue gas outlet of fifth suction tower 55 is connected to the flue gas inlet of second suction tower 2. After conversion in converter 5, the smelting flue gas that has been purified in first suction tower 1 can be converted into SO3, which is convenient for subsequent scrubbing in second suction tower 2 for acid production.

[0047] Reference Figure 1SO3 enters the secondary adsorption tower 2 and is then washed by the acid separator 22 within it. Specifically, the secondary adsorption tower 2 includes a tower body 21, an acid separator 22 located at the top of the tower body 21, packing material 23 located below the acid separator 22, and an acid circulation tank 24 located at the bottom of the tower body 21. The acid circulation tank 24 is connected to the acid inlet 415, and the acid outlet 416 is connected to the acid separator 22. Inside the secondary adsorption tower 2, the acid separator 22 is used to spray concentrated sulfuric acid, typically a sulfuric acid solution of 70% or higher. During acid production, the acid solution flowing from the acid outlet 416 into the acid circulation tank 24 at the bottom of the tower body 21 also flows into the acid separator 22 for washing. The spray density of the acid separator 22 is 2–3.5 m³ / s. 3 / m 2 •h, the packing 23 is a ceramic packing 23 with a diameter of φ20~50mm. Preferably, the ceramic packing 23 can be selected from one of the following: rectangular saddle ring ceramic packing 23, heterosaddle ring ceramic packing 23, Raschig ring ceramic packing 23, and cross ring ceramic packing 23. The acid outlet 416 circulates in the secondary absorption tower 2, participating in the sulfide absorption step in the flue gas treatment, thereby improving the utilization efficiency of the acid solution. At the same time, the use of ceramic packing 23 increases the liquid contact time and improves the reaction efficiency.

[0048] The acid outlet 416 of the heat exchange assembly 4 can be connected to a demineralized water preheater. Acid cooled by the heat exchange assembly 4 enters the demineralized water preheater, whose outlet is connected to an acid separator 22. Acid further cooled by the demineralized water preheater flows back to the acid separator 22. The acid outlet 416 circulates in the secondary absorption tower 2, participating in the sulfide absorption step of flue gas treatment, thus improving the efficiency of acid utilization.

[0049] The second suction tower 2 also has a flue gas outlet to discharge the desulfurized flue gas (i.e., tail gas). After being discharged, the flue gas can enter the tail gas treatment device for treatment. Conventional tail gas treatment devices, such as the combination of a demister and alkaline solution, actually use alkaline solution to further neutralize the tail gas, so that the tail gas can be discharged harmlessly.

[0050] In this application, the flue gas used for heat exchange in the first and second absorption towers 1 and 2 actually enters the same heat exchange component 4 for heat exchange. Therefore, whether it is the acid (mainly sulfuric acid) used as the heat exchange medium or the flue gas flowing to the first and second absorption towers 1 and 2 as the heat exchange medium, the heat exchange efficiency is the same because the contact time with the acid is the same. Ultimately, the temperature difference of the heated flue gas after heat exchange is small and does not affect the subsequent acid production process.

[0051] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A sulfuric acid production system for recovering low-grade heat from a secondary absorption process, comprising a primary absorption tower (1) and a secondary absorption tower (2), wherein flue gas is fed into the primary absorption tower (1) by a blower (3), the blower (3) and the primary absorption tower (1) are connected by an air inlet pipe, a converter (5) is provided between the blower (3) and the primary absorption tower (1), and the flue gas passes through the converter (5) when pumped into the primary absorption tower (1) and the secondary absorption tower (2), and the primary absorption tower (1) and the secondary absorption tower (2) are connected by a conversion pipe; The bottom of the second suction tower (2) is provided with a heat exchange component (4). The second suction tower (2) and the heat exchange component (4) are connected by a heat exchange pipe. The air outlet of the fan (3) is connected to the heat exchange component (4). The heat exchange component (4) is located between the conversion pipes and is connected to the conversion pipes. The flue gas flows from the first suction tower (1) through the heat exchange component (4) into the second suction tower (2). The heat exchange assembly (4) includes a shell (41) and a heat exchange section (42). The heat exchange section (42) is fixed inside the shell (41). The shell (41) is provided with a first flue gas inlet (411), a second flue gas inlet (412), a first flue gas outlet (413), a second flue gas outlet (414), an acid inlet (415), and an acid outlet (416). The first flue gas inlet (411), the second flue gas inlet (412), the first flue gas outlet (413), the second flue gas outlet (414), the acid inlet (415), and the acid outlet (416) are respectively connected to the heat exchange section (42). The heat exchange section (42) includes an acid pipe (421), a first flue gas pipe (422), and a second flue gas pipe (423). The acid pipe (421), the first flue gas pipe (422), and the second flue gas pipe (423) are all spiral-shaped. One side of each spiral of the acid pipe (421) abuts against the first flue gas pipe (422), and the other side of each spiral of the acid pipe (421) abuts against the second flue gas pipe (423). One end of the acid pipe (421) is connected to the acid inlet (415), and the other end of the acid pipe (421) is connected to the acid outlet (416). The acid outlet (416) is connected to the second absorption tower (2) through a pipe. One end of the first flue gas duct (422) is connected to the first flue gas inlet (411), and the other end of the first flue gas duct (422) is connected to the first flue gas outlet (413). One end of the second flue gas duct (423) is connected to the second flue gas inlet (412), and the other end of the second flue gas duct (423) is connected to the second flue gas outlet (414).

2. The sulfuric acid production system for recovering low-grade heat from a secondary absorption process according to claim 1, characterized in that, The heat exchange section (42) includes an outer sleeve (424) and an inner sleeve (425). The inner sleeve (425) is fitted inside the outer sleeve (424). A partition (426) is provided on the outer wall of the inner sleeve (425). The partition (426) divides the outer sleeve (424) into a first channel and a second channel that are not connected to each other. One end of the inner sleeve (425) is connected to the acid inlet (415), and the other end of the inner sleeve (425) is connected to the acid outlet (416). The acid outlet (416) is connected to the second absorption tower (2) through a pipe. One end of the first channel is connected to the first flue gas inlet (411), and the other end of the first channel is connected to the first flue gas outlet (413). One end of the second channel is connected to the second flue gas inlet (412), and the other end of the second channel is connected to the second flue gas outlet (414).

3. The sulfuric acid production system for recovering low-grade heat from a secondary absorption process according to claim 1, characterized in that, The two-absorption tower (2) includes a tower body (21), an acid separator (22) disposed on the upper part of the tower body (21), a packing (23) disposed below the acid separator (22), and an acid circulation tank (24) disposed at the bottom of the tower body (21). The acid circulation tank (24) is connected to the acid inlet (415), and the acid outlet (416) is connected to the acid separator (22).

4. A sulfuric acid production system for recovering low-grade heat from a secondary absorption process according to claim 3, characterized in that, The acid outlet (416) of the heat exchange component (4) is connected to the demineralized water preheater. The acid cooled by the heat exchange component (4) enters the demineralized water preheater. The outlet of the demineralized water preheater is connected to the acid separator (22). The sulfuric acid further cooled by the demineralized water preheater flows back to the acid separator (22).

5. A sulfuric acid production system for recovering low-grade heat from a secondary absorption process according to claim 1, characterized in that, The converter (5) includes a first conversion layer (51), a second conversion layer (52), a third conversion layer (53), a fourth conversion layer (54), and a fifth conversion layer (55). The first conversion layer (51) to the third conversion layer (53) are connected in sequence, and the fourth conversion layer (54) and the fifth conversion layer (55) are connected in sequence. The flue gas inlet of the first conversion layer (51) is connected to the flue gas outlet of the fan (3), the flue gas outlet of the third conversion layer (53) is connected to the flue gas inlet of the first suction tower (1), the flue gas outlet of the first suction tower (1) is connected to the flue gas inlet of the fourth conversion layer (54), and the flue gas outlet of the fifth conversion layer (55) is connected to the flue gas inlet of the second suction tower (2).

6. A sulfuric acid production system for recovering low-grade heat from a secondary absorption process according to claim 3, characterized in that, The spray density of the acid separator (22) is 2 to 3.5 m3 / m2·h, and the packing (23) is φ20 to 50 mm ceramic packing (23).

7. A sulfuric acid production system for recovering low-grade heat from a secondary absorption process according to claim 6, characterized in that, The packing (23) is a rectangular saddle ring ceramic packing, a heterosaddle ring ceramic packing, a Raschig ring ceramic packing, or a cross ring ceramic packing.

8. A sulfuric acid production system for recovering low-grade heat from a secondary absorption process according to claim 1, characterized in that, The flue gas outlet of the second suction tower (2) is connected to a tail gas treatment device, and the tail gas treatment device is connected to a flue pipe.

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