A low-temperature waste heat recovery system and method for zinc smelting off-gas acid production

Abstract

The present application relates to non-ferrous smelting flue gas treatment technical field, especially to a kind of zinc smelting flue gas acid low-temperature waste heat recovery system and recovery method.The recovery system includes the cooling and dust removal component, purification and heat exchange component, drying and circulating component, conversion component and dry absorption acid low-temperature waste heat recovery component in turn along the zinc smelting flue gas flow direction.The recovery system in zinc smelting process, not only can the high humidity flue gas of low SO2 concentration is converted to produce 98wt% mass concentration sulfuric acid and low pressure saturated steam, and the yield of low pressure saturated steam is more than 0.3 times of sulfuric acid ton, also can realize the total conversion rate of SO2 gas in zinc smelting flue gas is greater than 99.9%, the total absorption rate of converted SO3 gas is greater than 99.99%.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal smelting flue gas treatment technology, and in particular to a low-temperature waste heat recovery system and method for acid production from zinc smelting flue gas. Background Technology

[0002] The main process flow for sulfuric acid production from zinc smelting flue gas is as follows: First, the smelting flue gas is purified and then discharged through a drying tower. Subsequently, it is introduced into a conversion process by an SO2 main blower to obtain flue gas rich in SO3. Finally, the flue gas rich in SO3 is subjected to a dry absorption process to desulfurize the discharged tail gas. The smelting flue gas contains high-temperature heat energy (>500℃), accounting for 51.45% of the total heat release. This heat can be used in waste heat boilers to generate medium-pressure saturated steam and is easily recovered. The reaction heat generated in the conversion process is medium-temperature heat energy (250~500℃), accounting for 17.27% of the total heat release. This heat can be used to generate steam or assist high-temperature heat energy in heating the feedwater of waste heat boilers or to superheat the medium-pressure saturated steam generated therefrom. When SO3 is absorbed by sulfuric acid, it releases a large amount of heat, and the increased acid temperature is low-temperature heat energy (<250℃), accounting for 31.28% of the total heat release. The waste heat carrier is concentrated sulfuric acid, which has strong oxidizing and corrosive properties. Traditionally, circulating cooling water is used to remove the low-temperature waste heat generated in the dry absorption process and finally discharge it into the atmosphere through a cooling tower. This not only wastes waste heat resources but also exacerbates environmental thermal pollution. In addition, the oxygen produced by the cryogenic oxygen production station built in conjunction with the zinc smelting process is used for zinc sulfide leaching and side-blown furnace smelting, while most of the by-product low-temperature nitrogen is directly discharged into the atmosphere, also causing significant energy loss.

[0003] Currently, low-temperature waste heat recovery systems for sulfuric acid production from smelting flue gas can not only produce concentrated sulfuric acid but also recover low-temperature waste heat (such as generating low-pressure steam). However, these systems have the following problems: 1) They are suitable for smelting flue gas containing a high concentration of SO2 (e.g., a volume fraction of 10%~12%). However, zinc smelting flue gas has a high moisture content and a low SO2 concentration (generally a volume fraction of 7.5%~8%). After purification, the flue gas temperature is high, and the saturated water content is high, resulting in a low SO2 concentration. During dry absorption conversion in the high-temperature absorption tower, the amount of SO3 gas that can be absorbed and converted into sulfuric acid is small, while the amount of water absorbed is large. This leads to the inability to stably maintain the circulating acid (i.e., sulfuric acid) in the high-temperature absorption tower within the sulfuric acid production system. 1) A mass concentration greater than 98.5% (which causes the acid production system to "swell") makes the high-temperature absorption tower susceptible to corrosion, shortens its service life, or even causes it to shut down; 2) The waste heat carrier is concentrated sulfuric acid, which has strong oxidizing and corrosive properties and is at a high temperature. Existing waste heat recovery methods mostly use pumps to directly pump high-temperature concentrated sulfuric acid into the evaporator for waste heat recovery. This method is not only prone to corrosion of the pump, but also prone to excessively lowering the temperature of the concentrated sulfuric acid, resulting in the concentrated sulfuric acid being too cold. If the concentrated sulfuric acid at too low a temperature is directly returned to the high-temperature absorption tower to absorb SO3, it will cause serious corrosion to the high-temperature absorption tower.

[0004] Therefore, it is necessary to provide a low-temperature waste heat recovery system and method for sulfuric acid production from zinc smelting flue gas to solve the following problems in the existing technology: 1) The high moisture content and low SO2 concentration in zinc smelting flue gas cause the sulfuric acid production system to "swell" with water, resulting in easy corrosion of the high-temperature absorption tower, shortened service life, or even shutdown; 2) Using a pump to directly pump high-temperature concentrated sulfuric acid into the evaporator for waste heat recovery will result in the concentrated sulfuric acid temperature being too low, which will cause serious corrosion to the high-temperature absorption tower. Summary of the Invention

[0005] The purpose of this invention is to provide a low-temperature waste heat recovery system and method for acid production from zinc smelting flue gas. The specific technical solution is as follows:

[0006] In a first aspect, the present invention provides a low-temperature waste heat recovery system for acid production from zinc smelting flue gas, comprising a cooling and dust removal component, a purification heat exchange component, a drying and circulation component, a conversion component, and a dry absorption acid production low-temperature waste heat recovery component arranged sequentially along the flow direction of zinc smelting flue gas.

[0007] The purification heat exchange assembly includes a pre-purification device, a gas cooling tower, a nitrogen cooling device, and a post-purification device. A first packing layer is provided within the gas cooling tower, along with a first air inlet located below the first packing layer and a first air outlet located above it. The front-end cooling and dust removal assembly is connected to the first air inlet via the pre-purification device. The first air outlet is connected to the rear-end drying and circulation assembly via the post-purification device. A first nozzle is also provided within the gas cooling tower, positioned above the first packing layer. A liquid return channel is also provided below the first packing layer within the gas cooling tower.

[0008] A jacketed liquid delivery chamber and a heat exchange pipe are provided inside the nitrogen cooling device; the heat exchange pipe is located inside the jacketed liquid delivery chamber; the inlet of the jacketed liquid delivery chamber is lower than the outlet of the jacketed liquid delivery chamber, and its outlet is connected to the first nozzle, while its inlet is connected to the return liquid channel; the heat exchange pipe includes a second air inlet connected to the nitrogen outlet of the nitrogen supply equipment and a second air outlet connected to the nitrogen inlet of the nitrogen supply equipment.

[0009] Optionally, the drying circulation assembly includes a drying tower and a first circulation tank;

[0010] A second packing layer is provided inside the drying tower; the drying tower includes a third air inlet below the second packing layer and a third air outlet above it; the post-purification equipment is connected to the third air inlet; the third air outlet is connected to the conversion component via an SO2 main fan; a first drain outlet is provided at the bottom of the drying tower, and a first inlet is provided at its top; a second nozzle connected to the first inlet is provided inside the drying tower.

[0011] The first circulation tank is located below the drying tower and is connected to the first drain port; a first delivery pump is installed in the first circulation tank and is connected to the first inlet via a delivery pipeline; a second drain port is installed on the delivery pipeline and is connected to the dry absorption acid production low-temperature waste heat recovery component.

[0012] Optionally, the drying circulation assembly further includes a degassing tower; a third packing layer is provided inside the degassing tower, and a fourth air inlet is respectively provided below the third packing layer, a fourth air outlet is provided above the third packing layer, and a second liquid inlet is provided above the third packing layer; the fourth air inlet is connected to air; the second liquid inlet is connected to a branch pipe of the liquid delivery pipeline; the fourth air outlet is connected to the third air inlet; and a third drain outlet is provided at the bottom of the degassing tower, which is connected to the dry absorption acid production low-temperature waste heat recovery assembly.

[0013] The drying circulation assembly further includes a first heat exchanger disposed on the liquid delivery pipeline, and the first heat exchanger is disposed between the second drain port of the liquid delivery pipeline and a branch pipe of the liquid delivery pipeline.

[0014] Optionally, the dry absorption acid production low-temperature waste heat recovery assembly includes a second absorption tower, a second circulation tank, a high-temperature absorption tower, a third circulation tank, an acid-acid heat exchanger, a diluent, and a waste heat recovery steam generation assembly.

[0015] The high-temperature absorption tower includes an upper packing layer and a lower packing layer arranged vertically. The high-temperature absorption tower also includes a fifth air inlet located below the lower packing layer, a fifth air outlet and a third liquid inlet located above the upper packing layer, and a fourth liquid inlet located between the upper and lower packing layers. The fifth air inlet is connected to the SO3 gas generated by the primary conversion of the conversion component. The fifth air outlet is connected to the air inlet of the conversion component, used to send residual SO2 gas in the gas into the conversion component for secondary conversion. A third nozzle connected to the third liquid inlet and a fourth nozzle connected to the fourth liquid inlet are provided within the high-temperature absorption tower. The third nozzle is located above the upper packing layer. The fourth nozzle is located between the upper and lower packing layers.

[0016] A fourth drain outlet is provided at the bottom of the high-temperature absorption tower, and the fourth drain outlet is connected to the third circulation tank through a pipeline; the inlet end of the third circulation tank is higher than the outlet end; a second transfer pump is provided at the outlet end of the third circulation tank, and the second transfer pump is connected to the inlet of the acid-acid heat exchanger through a first main pipeline; a first branch pipeline is provided on the first main pipeline; the first branch pipeline is connected to the fourth inlet through the diluent; the second drain outlet is connected to the diluent through the acid-acid heat exchanger.

[0017] The outlet of the acid-acid heat exchanger is connected to the inlet of the second circulation tank after exchanging heat with the deoxygenated water preheater and the demineralized water preheater in sequence through pipelines; a third delivery pump is installed in the second circulation tank, and the third delivery pump is connected to the fifth liquid inlet located at the top of the second suction tower through the second main pipeline; a second branch pipeline for connecting with the third liquid inlet and a third branch pipeline for connecting with the inlet of the first circulation tank are installed on the second main pipeline.

[0018] A fourth packing layer is provided inside the secondary absorption tower; the secondary absorption tower includes a sixth gas outlet above the fourth packing layer and a sixth gas inlet below it; the sixth gas inlet is connected to SO3 gas after secondary conversion by the conversion component; the exhaust gas discharged from the sixth gas outlet is treated by a desulfurization device to meet standards before being discharged into the atmosphere; a fifth nozzle is provided above the fourth packing layer inside the secondary absorption tower; the fifth nozzle is connected to the fifth liquid inlet; a fifth liquid outlet is provided at the bottom of the secondary absorption tower, and the fifth liquid outlet is connected to the second circulation tank located below the secondary absorption tower; the third liquid outlet at the bottom of the degassing tower is connected to the inlet of the second circulation tank; process water is also connected to the inlet of the second circulation tank;

[0019] The waste heat recovery steam generation assembly includes a demineralized water preheater, a deaerator, a first circulating water pump, a deoxygenated water preheater, a steam drum, and a second circulating water pump arranged sequentially along the flow direction of the demineralized water. The steam drum is provided with an outlet, a first inlet, a second inlet, and a steam generation port. The outlet is connected to the inlet of the second circulating water pump. The outlet of the second circulating water pump is connected to the first inlet via a first pipeline and to the second inlet via a second pipeline. Both the first and second pipelines extend from the outlet end of the third circulating tank to the inlet end.

[0020] Optionally, the dry absorption acid production low-temperature waste heat recovery assembly further includes flow regulating valves installed on both the first pipeline and the second pipeline;

[0021] It also includes installing a second heat exchanger on the second main pipeline, and the second heat exchanger is located at the front end of the second branch pipeline and the third branch pipeline.

[0022] Optionally, the dry absorption acid production low-temperature waste heat recovery assembly further includes a steam ejector; the steam ejector is located at the fifth air inlet of the high-temperature absorption tower and is connected to the fifth air inlet.

[0023] Optionally, the pre-purification equipment includes a primary high-efficiency scrubber;

[0024] The post-purification equipment includes a two-stage high-efficiency scrubber, a first electrostatic precipitator, and a second electrostatic precipitator arranged in sequence.

[0025] Optionally, the cooling and dust removal assembly includes a waste heat boiler and a dust collection system arranged sequentially along the flow direction of zinc smelting flue gas;

[0026] The conversion assembly includes a first conversion layer, a second conversion layer, a third conversion layer, and a fourth conversion layer arranged sequentially from top to bottom. The first, second, third, and fourth conversion layers have identical structures and each includes, from top to bottom, a catalyst layer, heat-resistant ceramic balls, stainless steel wire mesh, a grate plate, a column, and a support beam. The catalyst layer is a catalyst-filled layer. The first, second, and third conversion layers combine to form a primary conversion unit, used to complete a primary conversion of the gas supplied to the conversion assembly by the SO2 main blower. An inlet communicating with the SO2 main blower is provided on the first conversion layer, and an outlet communicating with the fifth inlet of the high-temperature absorption tower is provided on the third conversion layer. Furthermore, circulating heat exchange pipelines connected to external heat exchange equipment are provided on the first conversion layer, the second conversion layer, and the third conversion layer; the outlet on the third conversion layer is located on the return pipeline of the circulating heat exchange pipeline on the third conversion layer; a secondary conversion unit is formed by the fourth conversion layer for secondary conversion of residual SO2 gas in the gas not absorbed by the high-temperature absorption tower; an inlet connected to the fifth outlet of the high-temperature absorption tower and an outlet connected to the sixth inlet of the secondary absorption tower are provided on the fourth conversion layer; a circulating heat exchange pipeline connected to external heat exchange equipment is provided on the fourth conversion layer; the outlet on the fourth conversion layer is located on the return pipeline of the circulating heat exchange pipeline on the fourth conversion layer.

[0027] In a second aspect, the present invention provides a method for recovering waste heat from the zinc smelting flue gas used in acid production at low temperatures, comprising:

[0028] Step S1: After the zinc smelting flue gas is treated by the cooling and dust removal component, a cooled and dust-removed flue gas is obtained, with a temperature ≤320℃ and a dust concentration ≤500 mg / Nm³. 3 The flue gas contains 6%~7% water by volume and 7.5%~8% SO2 by volume.

[0029] Step S2: The cooled and dust-removed flue gas is sent into the purification heat exchange component. After being purified by the pre-purification equipment, the flue gas flows in through the first inlet below the gas cooling tower and undergoes heat exchange with the spray acid sprayed by the first packing layer and the first nozzle within the gas cooling tower. This reduces the flue gas temperature to below 30°C, the water content to less than 4.8% of the flue gas volume, and the SO2 content to 8.5%~8.7% of the flue gas volume. Subsequently, the flue gas flows into the post-purification equipment for further purification through the first outlet above the gas cooling tower. The nitrogen cooling device continuously provides a cold source to the spray acid in the jacketed liquid delivery chamber through heat exchange pipes, used to cool the spray acid that has heated up after exchanging heat with the flue gas.

[0030] Step S3: The flue gas purified by the post-purification equipment flows into the third air inlet below the drying tower, and is then dried by being sprayed with 93% sulfuric acid by the second packing layer and the second nozzle inside the drying tower, achieving a moisture content of 0.1 g / Nm³ in the flue gas. 3 Subsequently, the dried flue gas is discharged through the third outlet and transported by the SO2 main blower to the conversion component to complete one conversion; the sulfuric acid sprayed by the second nozzle is provided by the first circulation tank and the first delivery pump; the sulfuric acid discharged from the first drain outlet of the drying tower flows back into the first circulation tank, and the returned sulfuric acid flows through the first delivery pump, the liquid delivery pipeline and the second inlet, and after heat exchange in the first heat exchanger, it flows into the degassing tower, and after degassing by the third packing layer and the air convection introduced by the fourth inlet, the SO2 gas in the returned sulfuric acid is removed, and then it is introduced into the drying tower through the fourth outlet and the third inlet in sequence; the sulfuric acid discharged from the third drain outlet of the degassing tower flows back into the second circulation tank;

[0031] Step S4: The SO3 gas generated by the primary conversion of the conversion component is injected into the high-temperature absorption tower through the steam ejector and the fifth inlet. It is first absorbed by sulfuric acid sprayed at 190°C (99% concentration) by the lower packing layer and the fourth nozzle within the high-temperature absorption tower. Then, it is absorbed again by sulfuric acid sprayed at 55°C (98.5% concentration) by the upper packing layer and the third nozzle within the high-temperature absorption tower. The remaining SO2 gas in the unabsorbed gas from the high-temperature absorption tower is then sent back into the conversion component through the fifth outlet for secondary processing. The sulfuric acid sprayed by the fourth nozzle is supplied by mixing sulfuric acid returned to the diluent from the third circulation tank and the second transfer pump, and sulfuric acid returned to the diluent from the second drain outlet via the acid-acid heat exchanger; the sulfuric acid sprayed by the third nozzle is supplied by the second circulation tank, the third transfer pump, the second main pipeline and the second branch pipeline, and undergoes heat exchange via the second heat exchanger; the sulfuric acid sprayed by the third and fourth nozzles is returned to the third circulation tank via the fourth drain outlet; the mass concentration of sulfuric acid in the third circulation tank is 99.4%~99.6%;

[0032] The SO3 gas generated from the secondary conversion of the conversion component flows into the secondary absorption tower through the sixth inlet. After being absorbed by sulfuric acid with a mass concentration of 98% and a temperature of 55°C sprayed by the fourth packing layer and the fifth nozzle, the resulting tail gas is discharged through the sixth outlet and then discharged into the atmosphere after being treated by the desulfurization equipment to meet the standards. The sulfuric acid sprayed by the fifth nozzle is supplied by the second circulation tank, the third transfer pump, and the second main pipeline, and undergoes heat exchange through the second heat exchanger. The sulfuric acid sprayed by the fifth nozzle flows back into the second circulation tank through the fifth drain outlet.

[0033] Process water is added to the second circulation tank to regulate the sulfuric acid mass concentration in the second circulation tank to 98%.

[0034] The demineralized water sequentially passes through the demineralized water preheater, the deaerator, the first circulating water pump, the deoxygenated water preheater, the steam drum, the second circulating water pump, and then returns to the steam drum via the first and second pipelines to generate low-pressure saturated steam. The third circulating tank, the acid-acid heat exchanger, the deoxygenated water preheater, and the demineralized water preheater provide heat to the demineralized water, converting it into the low-pressure saturated steam. The output of the low-pressure saturated steam is at least 0.3 times the amount of 98% sulfuric acid produced in the second circulating tank, and the steam pressure is 0.4~0.8 MPa.

[0035] Optionally, the spraying acid is sulfuric acid with a mass concentration of 8% to 10%.

[0036] The application of the technical solution of the present invention has at least the following beneficial effects:

[0037] (1) The present invention provides a low-temperature waste heat recovery system for acid production from zinc smelting flue gas. By combining a gas cooling tower and a nitrogen cooling device in the purification heat exchange components, nitrogen can be used to cool the sprayed acid that has heated up after exchanging heat with the flue gas in real time. This facilitates continuous heat exchange of the sprayed acid with the flue gas, controls the volume of water in the flue gas to be reduced to less than 4.8%, and reduces the water volume ratio of the low-content SO2 gas in the zinc smelting flue gas. This makes it easier for the gas to directly enter the conversion process and be converted into SO3. This solves the problem that the existing zinc smelting flue gas has a high water content and a low SO2 concentration, which causes the acid production system to "swell" with water, resulting in easy corrosion of the high-temperature absorption tower, shortened service life, or even shutdown. The nitrogen gas that has heated up after exchanging heat with the sprayed acid can be used as an instrument protection gas to protect the instruments.

[0038] (2) The zinc smelting flue gas acid production low-temperature waste heat recovery system provided in this invention, by adopting a dry absorption acid production low-temperature waste heat recovery component, facilitates the recovery of low-temperature waste heat and achieves a low-pressure saturated steam output that is more than 0.3 times the amount of sulfuric acid with a mass concentration of 98% produced in the second circulation tank. In addition, the liquid inlet end of the third circulation tank is higher than the liquid outlet end. This height difference facilitates enhanced convective heat transfer between the first and second pipelines of the waste heat recovery steam generation component, thereby achieving acid temperature control and low-pressure saturated steam production. Therefore, the dry absorption acid production low-temperature waste heat recovery component of this invention can solve the problem in the prior art where the use of a pump to directly pump high-temperature concentrated sulfuric acid into the evaporator for waste heat recovery leads to excessively low concentrated sulfuric acid temperature, which in turn causes severe corrosion to the high-temperature absorption tower.

[0039] (3) The recovery method of the low-temperature waste heat recovery system for acid production from zinc smelting flue gas adopted in this invention can not only achieve a low-pressure saturated steam output that is more than 0.3 times the amount of sulfuric acid with a mass concentration of 98% produced in the second circulating tank, but also achieve a total conversion rate of SO2 gas in zinc smelting flue gas greater than 99.9% and a total absorption rate of SO3 gas after conversion greater than 99.99%.

[0040] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the process of the low-temperature waste heat recovery system for acid production from zinc smelting flue gas in the embodiment.

[0043] Figure 2 This is a schematic diagram of the nitrogen cooling device in the embodiment (the diagram shows a partial perspective view of the heat exchange pipe).

[0044] Explanation of reference numerals: 1. First-stage high-efficiency scrubber; 2. Gas cooling tower; 3. Nitrogen cooling device; 3.1. Heat exchange pipe; 3.2. Inlet of the jacketed liquid delivery chamber; 3.3. Outlet of the jacketed liquid delivery chamber; 4. Second-stage high-efficiency scrubber; 5. First electrostatic precipitator; 6. Second electrostatic precipitator; 7. Drying tower; 8. First circulation tank; 9. Degassing tower; 10. First heat exchanger; 11. Second absorption tower; 12. Second circulation tank; 13. Second heat exchanger; 14. High-temperature absorption tower; 15. Third circulation tank; 16. Acid-acid heat exchanger; 17. Diluent; 18. Demineralized water preheater; 19. Deaerator; 20. First circulating water pump; 21. Deoxygenated water preheater; 22. Steam drum; 23. Second circulating water pump; 24. Steam ejector.

[0045] exist Figure 1 In the diagram, purple-red arrows indicate the direction of flue gas flow; green arrows indicate the direction of acid flow (such as sprayed acid and sulfuric acid); and red arrows indicate the direction of demineralized water flow. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0047] Example:

[0048] See Figures 1-2 A low-temperature waste heat recovery system for acid production from zinc smelting flue gas includes a cooling and dust removal component, a purification and heat exchange component, a drying and circulation component, a conversion component, and a dry absorption acid production low-temperature waste heat recovery component arranged sequentially along the flow direction of zinc smelting flue gas.

[0049] The purification heat exchange assembly includes a pre-purification device, a gas cooling tower 2, a nitrogen cooling device 3, and a post-purification device. A first packing layer is provided within the gas cooling tower 2, along with a first air inlet located below the first packing layer and a first air outlet located above it. The front-end cooling and dust removal assembly is connected to the first air inlet via the pre-purification device. The first air outlet is connected to the rear-end drying and circulation assembly via the post-purification device. A first nozzle is also provided within the gas cooling tower 2, located above the first packing layer. A liquid return channel is also provided below the first packing layer in the gas cooling tower 2.

[0050] A jacketed liquid delivery chamber and a heat exchange pipe 3.1 are provided inside the nitrogen cooling device 3; the heat exchange pipe 3.1 is located inside the jacketed liquid delivery chamber; the inlet 3.2 of the jacketed liquid delivery chamber is lower than the outlet 3.3 of the jacketed liquid delivery chamber, and its outlet is connected to the first nozzle, while its inlet is connected to the return liquid channel; the heat exchange pipe 3.1 includes a second air inlet connected to the nitrogen outlet of the nitrogen supply equipment and a second air outlet connected to the nitrogen inlet of the nitrogen supply equipment.

[0051] The drying circulation assembly includes a drying tower 7 and a first circulation tank 8;

[0052] A second packing layer is provided inside the drying tower 7; the drying tower 7 includes a third air inlet below the second packing layer and a third air outlet above it; the post-purification equipment is connected to the third air inlet; the third air outlet is connected to the conversion component via an SO2 main fan; a first drain outlet is provided at the bottom of the drying tower 7, and a first inlet is provided at its top; a second nozzle connected to the first inlet is provided inside the drying tower 7.

[0053] The first circulation tank 8 is located below the drying tower 7 and is connected to the first drain port; a first delivery pump is installed in the first circulation tank 8 and is connected to the first inlet via a delivery pipeline; a second drain port is installed on the delivery pipeline and is connected to the dry absorption acid production low-temperature waste heat recovery component.

[0054] The drying circulation assembly further includes a degassing tower 9; a third packing layer is provided inside the degassing tower 9, and a fourth air inlet is respectively provided below the third packing layer, a fourth air outlet is provided above the third packing layer, and a second liquid inlet is provided above the third packing layer; the fourth air inlet is connected to air; the second liquid inlet is connected to a branch pipe of the liquid delivery pipeline; the fourth air outlet is connected to the third air inlet; a third liquid outlet is provided at the bottom of the degassing tower 9 and is connected to the dry absorption acid production low-temperature waste heat recovery assembly;

[0055] The drying circulation assembly further includes a first heat exchanger 10 disposed on the liquid delivery pipeline, and the first heat exchanger 10 is disposed between the second drain port of the liquid delivery pipeline and a branch pipe of the liquid delivery pipeline.

[0056] The dry absorption acid production low-temperature waste heat recovery assembly includes a second absorption tower 11, a second circulation tank 12 (the second circulation tank 12 is lined with Q235A bricks), a high-temperature absorption tower 14 (the high-temperature absorption tower 14 is a vertical cylindrical packed tower without an inner lining; the material selected for the high-temperature absorption tower 14 is XDS-8 high-temperature resistant high-concentration sulfuric acid alloy material from the XDS series special alloys; under concentrated sulfuric acid conditions with a mass concentration of 98.5%~99.9% and a temperature of 200~220℃, the annual corrosion rate of this alloy material is far less than 0.1mm, thus ensuring the normal operation of the high-temperature absorption tower 14), a third circulation tank 15 (the third circulation tank 15 is lined with Q235A bricks), an acid-acid heat exchanger 16, a diluent 17, and a waste heat recovery steam generation assembly;

[0057] The high-temperature absorption tower 14 includes an upper packing layer and a lower packing layer arranged vertically. The high-temperature absorption tower 14 also includes a fifth air inlet located below the lower packing layer, a fifth air outlet and a third liquid inlet located above the upper packing layer, and a fourth liquid inlet located between the upper and lower packing layers. The fifth air inlet is connected to the SO3 gas generated by the primary conversion of the conversion component. The fifth air outlet is connected to the air inlet of the conversion component, used to send residual SO2 gas in the gas into the conversion component for secondary conversion. The high-temperature absorption tower 14 is equipped with a third nozzle connected to the third liquid inlet and a fourth nozzle connected to the fourth liquid inlet. The third nozzle is located above the upper packing layer. The fourth nozzle is located between the upper and lower packing layers.

[0058] A fourth drain outlet is provided at the bottom of the high-temperature absorption tower 14, and the fourth drain outlet is connected to the third circulation tank 15 through a pipeline; the inlet end of the third circulation tank 15 is higher than the outlet end (the height difference is greater than 300mm, which on the one hand avoids the second circulation tank 12 from dry suction and the liquid level fluctuation of the third circulation tank 15; on the other hand, it is convenient to accumulate the heat flowing out of the high-temperature absorption tower 14, so that the temperature of the third circulation tank 15 is about 200℃; furthermore, the height difference facilitates the strengthening of convective heat exchange between the first and second pipelines of the waste heat recovery steam generation component, so as to realize acid temperature control and low-pressure saturated steam production); a second delivery pump is provided at the outlet end in the third circulation tank 15, and the second delivery pump is connected to the inlet of the acid-acid heat exchanger 16 through the first main pipeline; a first branch pipeline is provided on the first main pipeline; the first branch pipeline is connected to the fourth inlet through the diluent 17; the second drain outlet is connected to the diluent 17 through the acid-acid heat exchanger 16;

[0059] The outlet of the acid-acid heat exchanger 16 is connected to the deoxygenated water preheater 21 and the demineralized water preheater 18 in sequence through pipelines, and then connected to the inlet of the second circulation tank 12; a third delivery pump is installed in the second circulation tank 12, and the third delivery pump is connected to the fifth liquid inlet installed at the top of the second suction tower 11 through the second main pipeline; a second branch pipeline for connecting to the third liquid inlet and a third branch pipeline for connecting to the inlet of the first circulation tank 8 are installed on the second main pipeline;

[0060] A fourth packing layer is provided inside the secondary absorption tower 11; the secondary absorption tower 11 includes a sixth gas outlet above the fourth packing layer and a sixth gas inlet below the fourth packing layer; the sixth gas inlet is connected to SO3 gas after secondary conversion by the conversion component; the exhaust gas discharged from the sixth gas outlet is treated by the desulfurization equipment to meet the standards before being discharged into the atmosphere; a fifth nozzle is provided inside the secondary absorption tower 11 above the fourth packing layer; the fifth nozzle is connected to the fifth liquid inlet; a fifth liquid outlet is provided at the bottom of the secondary absorption tower 11, and the fifth liquid outlet is connected to the second circulation tank 12 located below the secondary absorption tower 11; the third liquid outlet at the bottom of the degassing tower 9 is connected to the inlet of the second circulation tank 12; process water is also connected to the inlet of the second circulation tank 12;

[0061] The waste heat recovery steam generation assembly includes a demineralized water preheater 18, a deaerator 19, a first circulating water pump 20, a deoxygenated water preheater 21, a steam drum 22, and a second circulating water pump 23 arranged sequentially along the flow direction of the demineralized water. The steam drum 22 is provided with an outlet, a first inlet, a second inlet, and a steam generation port. The outlet is connected to the inlet of the second circulating water pump 23. The outlet of the second circulating water pump 23 is connected to the first inlet via a first pipeline and to the second inlet via a second pipeline. Both the first and second pipelines extend from the outlet end of the third circulating tank 15 to the inlet end.

[0062] The dry absorption acid production low-temperature waste heat recovery component also includes flow regulating valves installed on both the first pipeline and the second pipeline to ensure safe system operation and facilitate maintenance.

[0063] The dry absorption acid production low-temperature waste heat recovery assembly also includes a second heat exchanger 13 installed on the second main pipeline, and the second heat exchanger 13 is installed at the front end of the second branch pipeline and the third branch pipeline.

[0064] The dry absorption acid production low-temperature waste heat recovery assembly also includes a steam ejector 24; the steam ejector 24 is located at the fifth air inlet of the high-temperature absorption tower 14 and is connected to the fifth air inlet.

[0065] A mist trap is installed inside the drying tower 7. The mist trap is made of a woven metal wire mesh made of 20# alloy and F4.

[0066] High-efficiency fiber mist traps are installed in both the secondary absorption tower 11 and the high-temperature absorption tower 14.

[0067] The pre-purification equipment includes a primary high-efficiency scrubber 1;

[0068] The post-purification equipment includes a two-stage high-efficiency scrubber 4, a first electrostatic precipitator 5, and a second electrostatic precipitator 6, which are connected in sequence.

[0069] The cooling and dust removal assembly includes a waste heat boiler and a dust collection system arranged sequentially along the flow direction of zinc smelting flue gas.

[0070] The conversion assembly includes a first conversion layer, a second conversion layer, a third conversion layer, and a fourth conversion layer arranged sequentially from top to bottom. The first, second, third, and fourth conversion layers have identical structures and each includes a catalyst layer, heat-resistant ceramic balls, stainless steel wire mesh, a grate plate, a column, and a support beam arranged sequentially from top to bottom. The catalyst layer is a catalyst (vanadium catalyst) filling layer. The first, second, and third conversion layers combine to form a primary conversion unit for completing a primary conversion of the gas supplied to the conversion assembly by the SO2 main blower. An inlet communicating with the SO2 main blower is provided on the first conversion layer, and a fifth air inlet communicating with the high-temperature absorption tower 14 is provided on the third conversion layer. The fourth conversion layer has an outlet, and circulating heat exchange pipelines connected to external heat exchange equipment are provided on the first conversion layer, the second conversion layer, and the third conversion layer; the outlet on the third conversion layer is located on the return pipeline of the circulating heat exchange pipeline on the third conversion layer; the fourth conversion layer forms a secondary conversion unit for secondary conversion of the residual SO2 gas in the gas not absorbed by the high-temperature absorption tower 14; the fourth conversion layer has an inlet connected to the fifth outlet of the high-temperature absorption tower 14 and an outlet connected to the sixth inlet of the secondary absorption tower 11; the fourth conversion layer has a circulating heat exchange pipeline connected to external heat exchange equipment; the outlet on the fourth conversion layer is located on the return pipeline of the circulating heat exchange pipeline on the fourth conversion layer.

[0071] The total amount of catalyst used in the conversion assembly is 100 parts, of which 15-25 (specifically 20) parts are used on the first conversion layer, 15-25 (specifically 20) parts are used on the second conversion layer, 20-30 (specifically 25) parts are used on the third conversion layer, and 30-40 (specifically 35) parts are used on the fourth conversion layer.

[0072] The recovery method of the zinc smelting flue gas acid production low-temperature waste heat recovery system includes:

[0073] Step S1: After the zinc smelting flue gas is treated by the cooling and dust removal component, a cooled and dust-removed flue gas is obtained, with a temperature ≤320℃ and a dust concentration ≤500 mg / Nm³. 3 The flue gas contains 6.571% water by volume and 7.925% SO2 by volume.

[0074] Step S2: The cooled and dust-removed flue gas is sent into the purification heat exchange component. After being purified by the pre-purification equipment, the flue gas flows in through the first inlet below the gas cooling tower 2, and after heat exchange with the spray acid sprayed by the first packing layer and the first nozzle in the gas cooling tower 2, the flue gas temperature is reduced to below 30°C, the flue gas water volume is less than 4.8%, and the flue gas SO2 volume is 8.7%. Subsequently, the flue gas flows into the post-purification equipment for purification through the first outlet above the gas cooling tower 2. The nitrogen cooling device 3 continuously provides a cold source to the spray acid in the jacketed liquid delivery chamber through the heat exchange pipe 3.1 to cool down the spray acid that has heated up after exchanging heat with the flue gas. Specifically, the nitrogen inlet temperature is 13°C, the outlet temperature is less than 22°C, the inlet pressure is greater than 2KPa, the gas-liquid ratio is 10~20, and the nitrogen outlet area is 5% of the inlet area, ensuring the uniformity of nitrogen distribution and residence time in the nitrogen cooling device 3.

[0075] Step S3: The flue gas purified by the post-purification equipment flows into the third air inlet below the drying tower 7, and is then dried by being sprayed with 93% sulfuric acid by the second packing layer and the second nozzle inside the drying tower 7, achieving a moisture content of 0.1 g / Nm³ in the flue gas. 3 Subsequently, the dried flue gas is discharged through the third outlet and then by the SO2 main blower (the flue gas parameters at the SO2 main blower outlet are as follows: flue gas volume is 43641.38 Nm³). 3The sulfuric acid (SO2 volume fraction of 9.143% and O2 volume fraction of 10.855%) is transported to the conversion component to complete one conversion (specifically, 94% of SO2 gas can be converted into SO3 gas in one conversion); the sulfuric acid sprayed by the second nozzle is provided by the first circulation tank 8 and the first delivery pump; the sulfuric acid discharged from the first drain port of the drying tower 7 is returned to the first circulation tank 8, and the returned sulfuric acid flows through the first delivery pump, the liquid delivery pipeline and the second liquid inlet, and flows into the degassing tower 9 after heat exchange through the first heat exchanger 10. After degassing by the third packing layer and the air convection introduced by the fourth air inlet, the SO2 gas in the returned sulfuric acid is removed, and then it is introduced into the drying tower 7 in sequence through the fourth air outlet and the third air inlet; the sulfuric acid discharged from the third drain port of the degassing tower 9 is returned to the second circulation tank 12;

[0076] Step S4: The SO3 gas (approximately 200°C) generated by the primary conversion of the conversion component is humidified by the steam injector 24 and injected into the high-temperature absorption tower 14 through the fifth inlet. It is first absorbed by sulfuric acid sprayed at a concentration of 99% and a temperature of approximately 190°C by the lower packing layer and the fourth nozzle within the high-temperature absorption tower 14. Then, it is absorbed by sulfuric acid sprayed at a concentration of 98.5% and a temperature of approximately 55°C by the upper packing layer and the third nozzle within the high-temperature absorption tower 14. The remaining SO2 gas (temperature < 80°C, specifically 78°C) in the unabsorbed gas from the high-temperature absorption tower 14 is then sent through the fifth outlet. The conversion component performs a secondary conversion; the sulfuric acid sprayed by the fourth nozzle is supplied by mixing the sulfuric acid returned to the diluent 17 from the third circulation tank 15 and the sulfuric acid returned to the diluent 17 from the second drain port via the acid-acid heat exchanger 16; the sulfuric acid sprayed by the third nozzle is supplied by the second circulation tank 12, the third transfer pump, the second main pipeline and the second branch pipeline, and undergoes heat exchange via the second heat exchanger 13; the sulfuric acid sprayed by the third and fourth nozzles is returned to the third circulation tank 15 via the fourth drain port; the mass concentration of sulfuric acid in the third circulation tank 15 is 99.4%~99.6%;

[0077] The SO3 gas generated from the secondary conversion of the conversion component flows into the secondary absorption tower 11 through the sixth inlet. After being absorbed by sulfuric acid with a mass concentration of 98% and a temperature of 55°C sprayed by the fourth packing layer and the fifth nozzle, the resulting tail gas is discharged through the sixth outlet and then discharged into the atmosphere after being treated by the desulfurization equipment to meet the standards. The sulfuric acid sprayed by the fifth nozzle is supplied by the second circulation tank 12, the third transfer pump, and the second main pipeline, and undergoes heat exchange through the second heat exchanger 13. The sulfuric acid sprayed by the fifth nozzle flows back into the second circulation tank 12 through the fifth drain outlet.

[0078] Process water is added to the second circulation tank 12 (the specific standard for process water is referred to in "GB / T 12145-2016 Water and Steam Quality of Thermal Power Generating Units and Steam Power Equipment") to regulate the sulfuric acid mass concentration in the second circulation tank 12 to 98%;

[0079] The demineralized water sequentially passes through the demineralized water preheater 18, the deaerator 19, the first circulating water pump, the deoxygenated water preheater 21, the steam drum 22, the second circulating water pump, and then flows back to the steam drum 22 via the first pipeline and the second pipeline to generate low-pressure saturated steam; wherein, the third circulating tank 15, the acid-acid heat exchanger 16, the deoxygenated water preheater 21, and the demineralized water preheater 18 provide heat to the demineralized water to convert it into the low-pressure saturated steam. In this heat conversion process, the sulfuric acid is cooled from the third circulation tank 15 through the acid-acid heat exchanger 16 (heating the 93% sulfuric acid discharged from the first circulation tank 8 from 58.9℃ to 142℃), the deoxygenated water preheater 21 (heating the deoxygenated water from 104℃ to 125℃), and the demineralized water preheater 18 (heating the demineralized water from 25℃ to 98℃), reaching a temperature of 114.6℃ before flowing into the second circulation tank 12. The output of the low-pressure saturated steam is more than 0.3 times the amount of 98% sulfuric acid produced in the second circulation tank 12, and the steam pressure is 0.4 MPa. Specifically, the zinc smelting flue gas sulfuric acid production low-temperature waste heat recovery system can stably produce 16.26 tons of 98% sulfuric acid per hour, and the low-pressure saturated steam output is 5.58 tons / hour.

[0080] The spraying acid is sulfuric acid with a mass concentration of 8.5%.

[0081] The recovery method of the low-temperature waste heat recovery system for acid production from zinc smelting flue gas used in this embodiment can achieve a total conversion rate of SO2 gas in zinc smelting flue gas greater than 99.9% and a total absorption rate of SO3 gas after conversion greater than 99.99%.

[0082] The zinc smelting flue gas sulfuric acid production low-temperature waste heat recovery system uses tower equipment configured 2-3 meters lower than conventional systems, achieving low-level high efficiency. Furthermore, a high-temperature absorption tower 14 replaces the conventional primary absorption tower, facilitating low-temperature waste heat recovery and achieving a low-pressure saturated steam output that is more than 0.3 times the amount of 98% sulfuric acid produced in the second circulation tank 12.

[0083] In step S2, the water content of the flue gas is controlled to be less than 4.8%. On the one hand, the low-temperature nitrogen gas discharged from the oxygen production station of the zinc smelting system is used for refrigeration. On the other hand, the output of low-pressure steam in the high-temperature absorption tower 14 is increased to achieve a low-temperature heat recovery of more than 0.3t of low-pressure saturated steam per ton of acid. Finally, the traditional acid concentration control method is changed to use steam ejector 24 instead of adding liquid water, which extends the service life of diluent 17.

[0084] The zinc smelting flue gas acid production low-temperature waste heat recovery system employs heat exchange within the third circulation tank 15, which not only improves heat exchange efficiency and reduces project costs, but also achieves heat exchange before the second transfer pump, facilitating the extension of the second transfer pump's service life. The system utilizes a combination of degassing tower 9 and drying tower 7, along with the first circulation tank 8 and the second circulation tank 12, to ensure the concentration of the finished acid (i.e., the sulfuric acid concentration in the second circulation tank 12) and the SO2 concentration in the exhaust gas.

[0085] Comparative Example 1:

[0086] Unlike Example 1, the heat exchange pipe 3.1 in the nitrogen cooling device 3 was shut off, i.e., the nitrogen supply was stopped to cool the sprayed acid that had heated up after exchanging heat with the flue gas. This resulted in a 72% reduction in the amount of steam added to the steam injector 24 during operation of the zinc smelting flue gas acid production low-temperature waste heat recovery system, with the low-pressure saturated steam output at 2.88 tons / hour. Corrosion appeared on the inner wall of the high-temperature absorption tower 14. The reasons are as follows: the high moisture content in the flue gas after drying in the drying tower 7 reduces the amount of steam that can be added, decreases the heat of dilution, and reduces the recoverable waste heat, thus reducing the low-pressure saturated steam output. In addition, the high moisture content in the flue gas results in a lower SO2 concentration, reducing the amount of SO3 gas that can be absorbed and converted into sulfuric acid during dry absorption conversion in the high-temperature absorption tower 14. This makes it impossible to stably maintain a sulfuric acid mass concentration greater than 98.5% in the high-temperature absorption tower 14 (i.e., causing the acid production system to "swell" with water), making the high-temperature absorption tower 14 susceptible to corrosion.

[0087] Comparative Example 2:

[0088] Unlike Example 1, steam was stopped from being added to steam ejector 24, and water was added to diluter 17 instead. This resulted in the steam production of the zinc smelting flue gas acid production low-temperature waste heat recovery system being reduced to 4.99 tons / hour, a decrease of 10.5%, and corrosion appeared on the inner wall of diluter 17. The reasons for this are: uneven acid concentration occurred during the water addition process to diluter 17, leading to localized corrosion; in addition, the cessation of steam addition from steam ejector 24 resulted in water phase change endothermic heat, reducing the recoverable waste heat and lowering the low-pressure saturated steam production.

[0089] Comparative Example 3:

[0090] Unlike Embodiment 1, the first and second pipelines, which are connected to the steam drum 22 and pass through the third circulation tank 15, are located outside the third circulation tank 15. A steam generator connected to the steam drum 22 is also added. This results in the zinc smelting flue gas acid production low-temperature waste heat recovery system producing only 4.98 tons / hour of steam, a reduction of 10.8%. The reason for this is that heat loss occurs during the process of hot acid entering the evaporator, reducing the recoverable waste heat and thus lowering the low-pressure saturated steam production.

[0091] The above description is only a preferred embodiment of the present invention and does not limit the scope of the present invention. All equivalent structural transformations made under the inventive concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included within the protection scope of the present invention.

Claims

1. A low-temperature waste heat recovery system for acid production from zinc smelting flue gas, characterized in that, It includes a cooling and dust removal component, a purification and heat exchange component, a drying and circulation component, a conversion component, and a dry absorption acid production low-temperature waste heat recovery component arranged sequentially along the flow direction of zinc smelting flue gas; The purification heat exchange assembly includes a pre-purification device, a gas cooling tower (2), a nitrogen cooling device (3), and a post-purification device; a first packing layer is provided in the gas cooling tower (2), and a first air inlet and a first air outlet are respectively provided below and above the first packing layer; the cooling and dust removal assembly at the front end is connected to the first air inlet via the pre-purification device; the first air outlet is connected to the drying and circulation assembly at the rear end via the post-purification device; a first nozzle is also provided in the gas cooling tower (2); the first nozzle is located above the first packing layer; a return liquid channel is also provided in the gas cooling tower (2) below the first packing layer; A jacketed infusion chamber and a heat exchange pipe (3.1) are provided inside the nitrogen cooling device (3); the heat exchange pipe (3.1) is located inside the jacketed infusion chamber; the inlet (3.2) of the jacketed infusion chamber is lower than the outlet (3.3) of the jacketed infusion chamber, and its outlet is connected to the first nozzle, while its inlet is connected to the return liquid channel; the heat exchange pipe (3.1) includes a second air inlet connected to the nitrogen outlet of the nitrogen supply equipment and a second air outlet connected to the nitrogen inlet of the nitrogen supply equipment; The drying circulation assembly includes a drying tower (7) and a first circulation tank (8); A second packing layer is provided inside the drying tower (7); the drying tower (7) includes a third air inlet below the second packing layer and a third air outlet above it; the post-purification equipment is connected to the third air inlet; the third air outlet is connected to the conversion component via an SO2 main fan; a first drain outlet is provided at the bottom of the drying tower (7), and a first inlet is provided at its top; a second nozzle connected to the first inlet is provided inside the drying tower (7); The first circulation tank (8) is located below the drying tower (7) and is connected to the first drain port; a first delivery pump is installed in the first circulation tank (8) and the first delivery pump is connected to the first inlet via a delivery pipeline; a second drain port connected to the dry absorption acid production low-temperature waste heat recovery component is installed on the delivery pipeline. The drying cycle assembly also includes a degassing tower (9); a third packing layer is provided in the degassing tower (9), and a fourth air inlet, a fourth air outlet and a second liquid inlet are respectively provided below the third packing layer; the fourth air inlet is connected to air; the second liquid inlet is connected to a branch pipe of the liquid delivery pipeline; the fourth air outlet is connected to the third air inlet; a third drain outlet connected to the dry absorption acid production low-temperature waste heat recovery assembly is provided at the bottom of the degassing tower (9); The drying circulation assembly further includes a first heat exchanger (10) disposed on the liquid delivery pipeline, and the first heat exchanger (10) is disposed between the second drain port of the liquid delivery pipeline and a branch pipe of the liquid delivery pipeline. The dry absorption acid production low-temperature waste heat recovery assembly includes a second absorption tower (11), a second circulation tank (12), a high-temperature absorption tower (14), a third circulation tank (15), an acid-acid heat exchanger (16), a diluent (17), and a waste heat recovery steam generation assembly. The high-temperature absorption tower (14) includes an upper packing layer and a lower packing layer arranged vertically. The high-temperature absorption tower (14) also includes a fifth air inlet located below the lower packing layer, a fifth air outlet and a third liquid inlet located above the upper packing layer, and a fourth liquid inlet located between the upper and lower packing layers. The fifth air inlet is connected to the SO3 gas generated by the primary conversion of the conversion component. The fifth air outlet is connected to the air inlet of the conversion component, used to send residual SO2 gas in the gas into the conversion component for secondary conversion. The high-temperature absorption tower (14) is equipped with a third nozzle connected to the third liquid inlet and a fourth nozzle connected to the fourth liquid inlet. The third nozzle is located above the upper packing layer. The fourth nozzle is located between the upper and lower packing layers. A fourth drain outlet is provided at the bottom of the high-temperature absorption tower (14), and the fourth drain outlet is connected to the third circulation tank (15) through a pipeline; the inlet end of the third circulation tank (15) is higher than the outlet end; a second delivery pump is provided at the outlet end of the third circulation tank (15), and the second delivery pump is connected to the inlet of the acid-acid heat exchanger (16) through a first main pipeline; a first branch pipeline is provided on the first main pipeline; the first branch pipeline is connected to the fourth inlet through the diluent (17); the second drain outlet is connected to the diluent (17) through the acid-acid heat exchanger (16); The outlet of the acid-acid heat exchanger (16) is connected to the inlet of the second circulation tank (12) after exchanging heat with the deoxygenated water preheater (21) and the demineralized water preheater (18) in sequence through pipelines; a third delivery pump is installed in the second circulation tank (12), and the third delivery pump is connected to the fifth liquid inlet installed at the top of the second suction tower (11) through the second main pipeline; a second branch pipeline for connecting with the third liquid inlet and a third branch pipeline for connecting with the inlet of the first circulation tank (8) are installed on the second main pipeline; A fourth packing layer is provided inside the second absorption tower (11); the second absorption tower (11) includes a sixth gas outlet above the fourth packing layer and a sixth gas inlet below the fourth packing layer; the sixth gas inlet is connected to SO3 gas after secondary conversion by the conversion component; the tail gas discharged from the sixth gas outlet is discharged into the air after being treated by the desulfurization equipment to meet the standards; a fifth nozzle is provided inside the second absorption tower (11) above the fourth packing layer; the fifth nozzle is connected to the fifth liquid inlet; a fifth liquid outlet is provided at the bottom of the second absorption tower (11), and the fifth liquid outlet is connected to the second circulation tank (12) located below the second absorption tower (11); the third liquid outlet at the bottom of the degassing tower (9) is connected to the inlet of the second circulation tank (12); process water is also connected to the inlet of the second circulation tank (12); The waste heat recovery steam generation assembly includes a demineralized water preheater (18), a deaerator (19), a first circulating water pump (20), a deoxygenated water preheater (21), a steam drum (22), and a second circulating water pump (23) arranged sequentially along the flow direction of the demineralized water. The steam drum (22) is provided with an outlet, a first inlet, a second inlet, and a steam generation port. The outlet is connected to the inlet of the second circulating water pump (23). The outlet of the second circulating water pump (23) is connected to the first inlet through a first pipeline and to the second inlet through a second pipeline. Both the first pipeline and the second pipeline are arranged to pass through the outlet end of the third circulating tank (15) to the inlet end.

2. The low-temperature waste heat recovery system for acid production from zinc smelting flue gas as described in claim 1, characterized in that, The dry absorption acid production low-temperature waste heat recovery component also includes flow regulating valves installed on both the first pipeline and the second pipeline; It also includes providing a second heat exchanger (13) on the second main pipeline, and the second heat exchanger (13) is located at the front end of the second branch pipeline and the third branch pipeline.

3. The low-temperature waste heat recovery system for acid production from zinc smelting flue gas as described in claim 2, characterized in that, The dry absorption acid production low-temperature waste heat recovery assembly also includes a steam ejector (24); the steam ejector (24) is located at the fifth air inlet of the high-temperature absorption tower (14) and is connected to the fifth air inlet.

4. The low-temperature waste heat recovery system for acid production from zinc smelting flue gas as described in claim 3, characterized in that, The pre-purification equipment includes a first-stage high-efficiency scrubber (1); The post-purification equipment includes a two-stage high-efficiency scrubber (4), a first electrostatic precipitator (5), and a second electrostatic precipitator (6) connected in sequence.

5. The low-temperature waste heat recovery system for acid production from zinc smelting flue gas as described in claim 4, characterized in that, The cooling and dust removal assembly includes a waste heat boiler and a dust collection system arranged sequentially along the flow direction of zinc smelting flue gas. The conversion assembly includes a first conversion layer, a second conversion layer, a third conversion layer, and a fourth conversion layer arranged sequentially from top to bottom; the first conversion layer, the second conversion layer, the third conversion layer, and the fourth conversion layer have the same structure and each includes a catalyst layer, heat-resistant ceramic balls, stainless steel wire mesh, a grate plate, a column, and a support beam arranged sequentially from top to bottom; the catalyst layer is a catalyst-filled layer; the first conversion layer, the second conversion layer, and the third conversion layer are combined to form a primary conversion unit, which is used to complete a primary conversion of the gas delivered to the conversion assembly by the SO2 main blower; an inlet connected to the SO2 main blower is provided on the first conversion layer, and an outlet connected to the fifth air inlet of the high-temperature absorption tower (14) is provided on the third conversion layer, and in the... The first conversion layer, the second conversion layer, and the third conversion layer are all provided with circulating heat exchange pipelines connected to external heat exchange equipment; the outlet on the third conversion layer is located on the return pipeline of the circulating heat exchange pipeline on the third conversion layer; the fourth conversion layer forms a secondary conversion unit for secondary conversion of the residual SO2 gas in the gas not absorbed by the high-temperature absorption tower (14); the fourth conversion layer is provided with an inlet connected to the fifth outlet of the high-temperature absorption tower (14) and an outlet connected to the sixth inlet of the secondary absorption tower (11); the fourth conversion layer is provided with circulating heat exchange pipelines connected to external heat exchange equipment; the outlet on the fourth conversion layer is located on the return pipeline of the circulating heat exchange pipeline on the fourth conversion layer.

6. A method for recovering waste heat from a low-temperature sulfuric acid production system based on zinc smelting flue gas as described in claim 5, characterized in that, include: Step S1, the zinc smelting flue gas is treated by the cooling and dust removal assembly, and a cooled and dust-removed flue gas is obtained, which has a temperature of ≤320℃ and a dust concentration of ≤500 mg / Nm 3 , the flue gas contains water in a volume of 6%~7%, and the flue gas contains SO2 in a volume of 7.5%~8%; Step S2: The cooled and dust-removed flue gas is sent into the purification heat exchange component. After being purified by the pre-purification equipment, the flue gas flows into the first inlet below the gas cooling tower (2) and exchanges heat with the spray acid sprayed by the first packing layer and the first nozzle in the gas cooling tower (2), thereby reducing the flue gas temperature to below 30°C, the flue gas water volume to less than 4.8%, and the flue gas SO2 volume to 8.5%~8.7%. Subsequently, the flue gas flows into the post-purification equipment for purification through the first outlet above the gas cooling tower (2). The nitrogen cooling device (3) continuously provides a cold source for the spray acid in the jacketed liquid delivery chamber through the heat exchange pipe (3.1) to cool down the spray acid that has heated up after exchanging heat with the flue gas. Step S3, the flue gas after being purified by the post-purification device flows into through the third gas inlet below the drying tower (7), and after being sprayed and dried by the second packing layer in the drying tower (7) and the second spray head spraying 93% sulfuric acid, the moisture in the flue gas is dried to 0.1 g / Nm 3 Subsequently, the dried flue gas is discharged through the third gas outlet and transported by the SO2 main fan to the conversion assembly to complete the first conversion; the sulfuric acid sprayed by the second spray head is provided by the first circulating tank (8) and the first delivery pump; the sulfuric acid discharged from the first liquid outlet of the drying tower (7) flows back into the first circulating tank (8), and the backflowing sulfuric acid flows into the degassing tower (9) after being heated by the first heat exchanger (10) through the first delivery pump, the liquid delivery pipeline and the second liquid inlet, and after being convectively degassed by the third packing layer and air connected through the fourth gas inlet, the SO2 gas in the backflowing sulfuric acid is removed, and in turn flows into the drying tower (7) through the fourth gas outlet and the third gas inlet; the sulfuric acid discharged from the third liquid outlet of the degassing tower (9) flows back into the second circulating tank (12); Step S4: The SO3 gas generated by the primary conversion of the conversion component is injected into the high-temperature absorption tower (14) through the steam ejector (24) and the fifth inlet. It is first absorbed by sulfuric acid sprayed at a concentration of 99% and a temperature of 190°C by the lower packing layer and the fourth nozzle in the high-temperature absorption tower (14). Then, it is absorbed again by sulfuric acid sprayed at a concentration of 98.5% and a temperature of 55°C by the upper packing layer and the third nozzle in the high-temperature absorption tower (14). The remaining SO2 gas in the unabsorbed gas in the high-temperature absorption tower (14) is then sent to the conversion component for secondary conversion through the fifth outlet. The sulfuric acid sprayed by the four nozzles is supplied by mixing the sulfuric acid after it is returned to the diluent (17) by the third circulation tank (15), the sulfuric acid after it is returned to the diluent (17) by the second transfer pump, and the sulfuric acid after it is returned to the diluent (17) by the second drain port through the acid-acid heat exchanger (16); the sulfuric acid sprayed by the third nozzle is supplied by the second circulation tank (12), the third transfer pump, the second main pipeline and the second branch pipeline, and undergoes heat exchange through the second heat exchanger (13); the sulfuric acid after spraying by the third nozzle and the fourth nozzle is returned to the third circulation tank (15) through the fourth drain port; the mass concentration of sulfuric acid in the third circulation tank (15) is 99.4%~99.6%; The SO3 gas generated by the secondary conversion of the conversion component flows into the second absorption tower (11) through the sixth inlet. After being absorbed by sulfuric acid with a mass concentration of 98% and a temperature of 55°C sprayed by the fourth packing layer and the fifth nozzle, the resulting tail gas is discharged through the sixth outlet and discharged into the air after being treated by the desulfurization equipment to meet the standards. The sulfuric acid sprayed by the fifth nozzle is provided by the second circulation tank (12), the third delivery pump and the second main pipeline, and is heat-exchanged through the second heat exchanger (13). The sulfuric acid sprayed by the fifth nozzle flows back into the second circulation tank (12) through the fifth drain port. Process water is added to the second circulation tank (12) to adjust the sulfuric acid mass concentration in the second circulation tank (12) to 98%; The demineralized water is sequentially passed through the demineralized water preheater (18), the deaerator (19), the first circulating water pump, the deoxygenated water preheater (21), the steam drum (22), the second circulating water pump, and then returned to the steam drum (22) via the first pipeline and the second pipeline to generate low-pressure saturated steam; wherein, the third circulating tank (15), the acid-acid heat exchanger (16), the deoxygenated water preheater (21), and the demineralized water preheater (18) provide heat to the demineralized water to convert it into the low-pressure saturated steam; the output of the low-pressure saturated steam is more than 0.3 times the amount of sulfuric acid with a mass concentration of 98% produced in the second circulating tank (12), and the steam pressure is 0.4~0.8 MPa.

7. The recovery method of the low-temperature waste heat recovery system for acid production from zinc smelting flue gas as described in claim 6, characterized in that, The spraying acid is sulfuric acid with a mass concentration of 8% to 10%.

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