System and process for coupling methane purification, deacidification and fly ash reduction in a waste incineration plant

Abstract

This invention belongs to the field of resource utilization technology for waste incineration plants, and relates to a system and process for biogas purification coupled with acid removal and fly ash reduction in waste incineration plants. The process includes the following steps: S1, leachate biogas is sequentially processed through a biogas buffer tank, a water washing tower, a complexing iron wet desulfurization tower, and an iron oxide dry fine desulfurization tower; S2, after fine desulfurization, the biogas is processed through a dehydration device, a biogas compressor, and a deep dehydration device, and then CO2 and CH4 are separated by a pressure swing adsorption system to produce biomethane; S3, the sulfur-rich liquid produced by the complexing iron wet desulfurization tower enters the regeneration system for regeneration and is returned to the complexing iron wet desulfurization tower for recycling. The precipitated sulfur slurry is dehydrated by a sulfur slurry dehydration device to form sulfur paste, which is sent to the waste incinerator for co-incineration with municipal solid waste; S4, the CO2 separated by the pressure swing adsorption system is fed into a CO2 conversion reactor to generate sodium bicarbonate slurry, which is then transported to a semi-dry acid removal system; S5, all wastewater generated in steps S1 to S4 is recycled back to the leachate treatment system.

Description

Technical Field

[0001] This invention belongs to the field of resource utilization technology of waste incineration plants, and relates to a system and process for biogas purification coupled with acid removal and fly ash reduction in waste incineration plants. Background Technology

[0002] Biogas produced from the anaerobic digestion of leachate from waste incineration plants can be purified to produce biomethane. Currently, biogas purification technologies are relatively mature, mainly including water washing, pressure swing adsorption (PSA), membrane separation, and chemical absorption. Conventional process routes typically include two main stages: desulfurization and decarbonization. Meanwhile, domestic waste incineration plants generally use semi-dry processes for flue gas acid removal, employing slaked lime (Ca(OH)2) as the acid removal agent. However, slaked lime acid removal suffers from low efficiency and reacts with CO2 in the flue gas to produce CaCO3, increasing fly ash production and burdening subsequent treatment.

[0003] Existing technologies have attempted to couple waste incineration with biogas utilization. For example, utility model patent CN211230591U discloses a waste incineration and biogas coupled complementary power generation system, and utility model patent CN220684688U discloses a coupling system for waste incineration and biogas hydrogen production. However, these technologies all focus on the direct utilization of biogas as an energy source and do not involve the purification of biogas to produce biomethane or the resource utilization of byproducts.

[0004] Siloxanes, a characteristic impurity in biogas, are present in high concentrations in leachate biogas. If not removed, they will generate silica during subsequent combustion, causing wear and tear on equipment. Conventional purification processes often lack dedicated removal units. Regarding the treatment of sulfur paste generated from complexed iron desulfurization, existing technologies primarily focus on purification and external sales, failing to achieve a closed-loop system within the plant.

[0005] In summary, the existing technology has the following problems: (1) The sulfur paste produced by wet desulfurization lacks on-site harmless disposal methods; (2) The CO2 captured by biogas purification was not utilized as a resource; (3) Semi-dry deacidification uses hydrated lime, which has low deacidification efficiency and large fly ash production; (4) There is a lack of specific purification measures for siloxanes in leachate biogas.

[0006] Therefore, how to couple biogas purification byproducts with the existing system of the incineration plant to achieve "waste treatment with waste" and at the same time increase the incineration plant's revenue and achieve carbon emission reduction through the production of biogas is an urgent problem to be solved in this field. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a system and process for biogas purification coupled with acid removal and fly ash reduction in waste incineration plants, in order to solve the problems in the existing technology of high outsourcing disposal of sulfur paste, lack of resource utilization of captured CO2, low efficiency and large fly ash production of semi-dry acid removal using quicklime, and lack of purification measures for siloxanes in leachate biogas during the purification process of waste incineration plants; thereby realizing closed-loop in-plant disposal of sulfur paste, resource utilization of CO2, improving acid removal efficiency, reducing fly ash production, increasing incineration plant revenue and achieving carbon emission reduction through the production of biogas.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A biogas purification coupled with acid removal and fly ash reduction system for a waste incineration plant includes a biogas purification main process system, a sulfur closed-loop treatment system, and a CO2 resource utilization treatment system. The biogas purification main process system includes a biogas buffer tank, a water washing tower, a complexed iron wet desulfurization tower, an iron oxide dry fine desulfurization tower, a dehydration device, a biogas compressor, a deep dehydration device, a modified activated carbon adsorption tower, and a pressure swing adsorption system connected in sequence, which are used to purify leachate biogas into biomethane. The closed-loop sulfur treatment system includes a regeneration system and a sulfur slurry dewatering device connected in sequence. The sulfur-rich liquid outlet of the complexed iron wet desulfurization tower is connected to the regeneration system. The solution regenerated by the regeneration system is returned to the complexed iron wet desulfurization tower for recycling. The sulfur paste outlet of the sulfur slurry dewatering device is connected to a waste incinerator. The SO2 generated after the sulfur paste is mixed and incinerated with municipal solid waste enters the semi-dry deacidification system with the flue gas for removal. The CO2 resource utilization system includes a CO2 conversion reactor. The CO2-rich desorbed gas outlet of the pressure swing adsorption system is connected to the CO2 conversion reactor. The CO2-rich desorbed gas in the CO2 conversion reactor reacts with sodium carbonate solution to generate sodium bicarbonate slurry. The sodium bicarbonate slurry is directly transported to the slurry preparation and supply system of the semi-dry deacidification system, replacing lime slurry as a deacidifying agent, and is injected into the deacidification reaction tower of the semi-dry deacidification system to react with acidic gases in the flue gas.

[0009] Furthermore, it also includes a wastewater treatment system, which includes a wastewater return pipeline. The wastewater outlets of the dewatering device, the deep dewatering device, and the sulfur slurry dewatering device are all connected to the leachate treatment system of the waste incineration plant through the wastewater return pipeline.

[0010] Furthermore, the pressure swing adsorption system is equipped with multiple adsorption towers and adopts a cyclic operation mode of multi-tower adsorption, multi-tower pressure equalization, and multi-tower regeneration. The adsorption pressure is 0.2 to 1.0 MPa (g), the desorption pressure is -0.02 to -0.09 MPa (g), and the methane concentration of the produced biogas is ≥97%.

[0011] Furthermore, the CO2 conversion reactor is a bubble column structure, in which sodium carbonate solution is injected. CO2-rich desorbed gas is bubbled in and reacts with the sodium carbonate solution to generate sodium bicarbonate slurry. The reaction conversion rate is 80% to 90%, and the sodium bicarbonate slurry has a solid content of 10% to 20%. It can be directly transported to the semi-dry deacidification system through pipeline without drying.

[0012] Furthermore, the modified activated carbon adsorption tower is filled with coconut shell-based modified activated carbon, and the adsorption temperature is controlled at 20–35°C, with a space velocity of 200–500 h⁻¹. -1 The removal rate of siloxanes is ≥95%.

[0013] Furthermore, the complexed iron wet desulfurization tower uses a complexed iron catalyst for circulating spray desulfurization, controls the solution pH to 7.5-9.0, oxidizes H2S in biogas to elemental sulfur, and achieves an H2S removal rate of ≥99%.

[0014] Furthermore, the deacidification reaction tower of the semi-dry deacidification system uses a rotary atomizer to atomize and spray sodium bicarbonate slurry into the flue gas. The slurry reacts with HCl and SO2 in the flue gas to generate sodium salt, which is then captured and replaced with quicklime slurry for flue gas deacidification, thereby reducing fly ash production by more than 25%.

[0015] This invention also provides a process for biogas purification coupled with acid removal and fly ash reduction in waste incineration plants using the above-mentioned system, comprising the following steps: S1. After the leachate biogas is pressure stabilized in the biogas buffer tank, it is sequentially passed through a water washing tower to remove water-soluble impurities and trace amounts of ammonia, a complexed iron wet desulfurization tower to oxidize H2S into elemental sulfur, and an iron oxide dry fine desulfurization tower for fine desulfurization, so that the total sulfur content meets the intake requirements of the subsequent pressure swing adsorption system. S2. After fine desulfurization, the biogas is dehydrated to remove free water. After being pressurized by the biogas compressor, it is then passed through a deep dehydration device to lower the gas dew point and remove residual moisture, a modified activated carbon adsorption tower to remove impurities such as siloxanes, and a pressure swing adsorption system to separate CO2 and CH4 to obtain biogas. S3. The sulfur-rich liquid produced by the complexed iron wet desulfurization tower enters the regeneration system for regeneration. The regenerated solution is returned to the complexed iron wet desulfurization tower for recycling. The sulfur slurry precipitated during the regeneration process is dehydrated by the sulfur slurry dehydration device to form sulfur paste. The sulfur paste is sent to the waste incinerator and mixed with municipal solid waste for incineration. The sulfur paste decomposes into SO2 at high temperature in the incinerator and enters the semi-dry desulfurization system with the flue gas to be removed. S4. The CO2-rich desorbed gas separated by the pressure swing adsorption system is fed into the CO2 conversion reactor and reacts with the sodium carbonate solution to generate sodium bicarbonate slurry. The sodium bicarbonate slurry is directly transported to the slurry preparation and supply system of the semi-dry deacidification system to replace lime slurry as a deacidification agent and react with acidic gases in the flue gas to achieve deacidification. S5. All wastewater generated in steps S1 to S4 is returned to the leachate treatment system for centralized treatment through the wastewater return pipeline.

[0016] Further, in step S1, the pH of the solution in the complexed iron wet desulfurization tower is controlled at 7.5–9.0, and the H2S concentration in the biogas is 10000 mg / Nm³. 3 After wet desulfurization with complexed iron, the H2S concentration decreased to 50 mg / Nm³. 3 Next, the total sulfur is removed to ≤5mg / m³ using a dry iron oxide desulfurization tower. 3 .

[0017] Further, in step S2, the biogas compressor pressurizes the biogas to 0.2-1.0 MPa (g); the deep dehydration device uses a freeze dehydration method to reduce the dew point of the pressurized biogas to -40°C to -50°C.

[0018] The beneficial effects of this invention are as follows: 1. Significantly reduce operating costs and increase revenue.

[0019] The sulfur paste produced by wet desulfurization will be recycled and incinerated on-site instead of being outsourced for disposal, thus reducing the cost of hazardous waste treatment. At the same time, the purified biogas will be integrated into the natural gas pipeline network or stored and sold externally, creating a new source of income for the waste incineration plant and comprehensively improving the economic benefits of the project.

[0020] 2. Achieve carbon resource utilization and material closed-loop.

[0021] The CO2 captured by biogas purification is reacted with sodium carbonate solution to convert it into sodium bicarbonate slurry, which is directly recycled into the semi-dry deacidification system to replace the purchased lime slurry, realizing the recycling of carbon resources within the plant. All process wastewater is recycled to the leachate treatment system, and the three types of by-products, sulfur paste, CO2, and wastewater, are all disposed of in the plant, forming a complete material closed loop.

[0022] 3. Reduce fly ash production and improve deacidification efficiency.

[0023] Using sodium bicarbonate slurry instead of quicklime for deacidification avoids the side reaction of quicklime reacting with CO2 in flue gas to form CaCO3, thus reducing fly ash production at the source. At the same time, sodium bicarbonate has a higher deacidification efficiency than traditional quicklime, achieving better flue gas purification and providing technical support for incineration plants to meet more stringent environmental standards in the future.

[0024] 4. Ensure equipment safety and product quality.

[0025] An additional siloxane removal unit is added to improve adsorption efficiency by using the increased pressure conditions after pressurization. This removes characteristic impurities from the leachate biogas, preventing the formation of silica that can wear down equipment during subsequent combustion, thus ensuring the quality of biogas and the safety of subsequent equipment.

[0026] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of a biogas purification coupled with acid removal and fly ash reduction system in a waste incineration plant, as shown in the embodiment.

[0028] Figure labels: 1. Biogas buffer tank; 2. Water washing tower; 3. Complexed iron wet desulfurization tower; 4. Iron oxide dry fine desulfurization tower; 5. Dehydration device; 6. Biogas compressor; 7. Deep dehydration device; 8. Modified activated carbon adsorption tower; 9. Pressure swing adsorption system; 10. Regeneration system; 11. Sulfur slurry dehydration device; 12. Waste incinerator; 13. Semi-dry deacidification system; 14. CO2 conversion reactor; 15. Leachate treatment system. Detailed Implementation

[0029] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0030] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0031] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0032] Example 1 This embodiment uses a waste incineration plant as an example to describe the system and process of the present invention in detail. This waste incineration plant processes 1000 tons of municipal solid waste per day and is equipped with a leachate treatment system, producing approximately 7500 Nm³ of biogas per day. 3 The main components of biogas are: CH4 content 65% (volume fraction), CO2 content 32% (volume fraction), and H2S concentration 10000 mg / Nm³. 3 The siloxane content is approximately 50 mg / m³. 3 .

[0033] like Figure 1 As shown, the waste incineration plant biogas purification coupled with desulfurization and fly ash reduction system in this embodiment includes four parts: a biogas purification main process system, a sulfur closed-loop treatment system, a CO2 resource utilization treatment system, and a wastewater treatment system. The composition and working process of each part are described in detail below.

[0034] (I) Biogas purification main process system The biogas purification main process system is the core system of this invention. Its function is to gradually remove impurities from the leachate biogas, ultimately purifying it into biogas that meets natural gas standards. This system includes, in sequence, a biogas buffer tank 1, a water washing tower 2, a complexed iron wet desulfurization tower 3, an iron oxide dry fine desulfurization tower 4, a dehydration device 5, a biogas compressor 6, a deep dehydration device 7, a modified activated carbon adsorption tower 8, and a pressure swing adsorption system 9. The functions and process parameters of each piece of equipment are described below.

[0035] Biogas Buffer Tank 1: The biogas produced from the anaerobic digestion of leachate is first introduced into Biogas Buffer Tank 1. The function of the buffer tank is to stabilize the biogas inlet pressure and flow rate, eliminating the impact of gas production fluctuations during anaerobic digestion on the operation of subsequent equipment. The buffer tank acts as a "peak shaving and valley filling" mechanism, ensuring that subsequent processing units can operate under stable conditions. The biogas stays briefly in the buffer tank, and after the pressure fluctuations are smoothed out, it is output to the next stage at a relatively stable flow rate.

[0036] Water Scrubber 2: Biogas from the buffer tank enters water scrubber 2. The water scrubber uses a counter-current spray method, with a spray water volume of 1.5 m³ / h. 3 The main function of the water scrubbing tower is to remove water-soluble impurities and trace amounts of ammonia (NH3) from biogas by utilizing the dissolving effect of water. Ammonia is highly soluble in water and is absorbed by the sprayed water during the scrubbing process; simultaneously, some water-soluble organic impurities in the biogas are also washed away. The improved cleanliness of the biogas after scrubbing is beneficial for the stable operation of subsequent desulfurization processes. The wastewater containing impurities discharged from the bottom of the water scrubbing tower is transported to the leachate treatment system for centralized disposal through a wastewater return pipeline.

[0037] Complexed iron wet desulfurization tower 3: The biogas after water washing enters complexed iron wet desulfurization tower 3. This desulfurization tower is the main equipment for biogas desulfurization, using a complexed iron catalyst solution for circulating spray desulfurization. The basic principle of complexed iron wet desulfurization is: H2S in the biogas is absorbed by the complexed iron solution during gas-liquid contact, and H2S in Fe... 3+ Under oxidation, it is converted into elemental sulfur (S), while Fe is converted into elemental sulfur (S). 3+ Reduced to Fe 2+ .

[0038] In this embodiment, the H2S concentration in the biogas is as high as 10000 mg / Nm³. 3 This is a high-sulfur biogas. By controlling the pH value of the solution in the complexed iron wet desulfurization tower within the range of 7.5 to 9.0, and preferably within the range of 8.0 to 8.5 in this embodiment, the activity and stability of the complexed iron catalyst can be maintained, achieving highly efficient desulfurization. After complexed iron wet desulfurization, the H2S removal rate can reach over 99.5%, and the H2S concentration in the effluent is reduced to 50 mg / Nm³. 3 the following.

[0039] Complexed iron wet desulfurization has advantages such as high desulfurization efficiency, mild operating conditions, and elemental sulfur as a byproduct. Elemental sulfur exists in the form of sulfur slurry in the rich desulfurization solution and is discharged from the desulfurization tower along with the rich solution, entering the subsequent closed-loop sulfur treatment system.

[0040] Iron oxide dry desulfurization tower 4: After wet desulfurization with complexed iron, a small amount of H2S and other forms of sulfides remain in the biogas. To meet the stringent requirements of the subsequent pressure swing adsorption (PSA) system for inlet sulfur content, the biogas needs further desulfurization through iron oxide dry desulfurization tower 4. Iron oxide dry desulfurization utilizes the chemical reaction between iron oxide (Fe2O3) and H2S to convert residual sulfides into iron sulfide, which is then fixed in the desulfurizing agent, thus achieving deep desulfurization. After desulfurization, the total sulfur content of the biogas can be reduced to ≤5 mg / m³, meeting the inlet requirements of the PSA system.

[0041] As a supplementary link to wet desulfurization, the iron oxide dry desulfurization tower plays a "gatekeeping" role, ensuring that the sulfur content of biogas entering subsequent equipment meets the standards and preventing sulfides from poisoning or damaging the adsorbent in the pressure swing adsorption system.

[0042] Dehydration Unit 5: The biogas after fine desulfurization contains a certain amount of free water. If this water is not removed, it may cause corrosion of pipes and equipment during subsequent compression, and may also affect the normal operation of the pressure swing adsorption system. Therefore, the biogas first passes through dehydration unit 5 to remove free water. The dehydration unit can use mechanical separation or low-temperature condensation to remove most of the free water from the biogas. The wastewater discharged from the dehydration unit is transported to the leachate treatment system through the wastewater return pipeline.

[0043] Biogas compressor 6: The biogas after free water removal enters the biogas compressor 6 for pressurization. The compressor increases the biogas pressure to 0.2–1.0 MPa (g), preferably 0.6–0.8 MPa (g) in this embodiment, where (g) represents gauge pressure. The pressurization serves two purposes: first, to provide the necessary operating pressure for the subsequent pressure swing adsorption (PSA) system, which requires a certain pressure to effectively separate CO2 and CH4; second, the high pressure conditions after pressurization are beneficial to the operational efficiency of subsequent deep dehydration and siloxane removal processes.

[0044] Deep Dehydration Unit 7: The pressurized biogas enters the deep dehydration unit 7. This unit employs cryogenic dehydration to further remove residual moisture from the pressurized biogas, lowering the gas dew point to -40℃ to -50℃. The necessity of deep dehydration lies in the fact that pressure swing adsorption (PSA) systems have strict requirements on the moisture content of the incoming gas. Excessive moisture will occupy adsorption sites on the adsorbent, reducing CO2 adsorption efficiency and thus affecting the quality of the biogas. Deep dehydration effectively ensures the operational performance of the PSA system and the quality of the product.

[0045] It is worth noting that the present invention places the deep dehydration device 7 and the modified activated carbon adsorption tower 8 after the biogas compressor 6 and before the pressure swing adsorption system 9. This arrangement has a dual advantage: on the one hand, the high pressure conditions after pressurization are conducive to improving the adsorption capacity and removal efficiency of the adsorbent for siloxanes; on the other hand, pressurizing before deep dehydration can effectively avoid the influence of moisture on the pressure swing adsorption system and ensure the quality of biogas.

[0046] Modified activated carbon adsorption tower 8: The biogas after deep dehydration enters the modified activated carbon adsorption tower 8. The adsorption tower is filled with coconut shell-based modified activated carbon as an adsorbent. The activated carbon removes siloxanes from the biogas by physically adsorbing organosilicon compounds such as siloxanes.

[0047] The siloxane content in the leachate biogas is approximately 50 mg / m³. 3If not removed, siloxanes will generate silicon dioxide (SiO2) during subsequent combustion, which will be deposited on the surface of combustion equipment, engine cylinders and other components, causing wear and tear on the equipment, and in severe cases affecting the normal operation and service life of the equipment.

[0048] In this embodiment, the adsorption temperature of the modified activated carbon adsorption tower is controlled at 25–30°C, and the space velocity is 300 h⁻¹. -1 Under these operating conditions, the modified activated carbon can achieve a siloxane removal rate of over 95%, reducing the siloxane concentration in the effluent to 2.5 mg / m³. 3 The following conditions must be met to ensure the safe operation of subsequent equipment. Coconut shell-based modified activated carbon has advantages such as large specific surface area, reasonable pore size distribution, and high adsorption capacity, and exhibits good selective adsorption capacity for siloxanes.

[0049] Pressure Swing Adsorption System 9: After undergoing deep purification through the above-mentioned stages, the biogas finally enters the Pressure Swing Adsorption System 9 (PSA system). The PSA system is the core unit for biogas purification, and its function is to separate CO2 and CH4 in the biogas to obtain high-purity methane gas (i.e., biomethane).

[0050] The basic principle of pressure swing adsorption (PSA) is as follows: Under high pressure, the adsorbent (such as activated carbon, molecular sieves, etc.) has a much stronger adsorption capacity for CO2 than for CH4. CO2 is preferentially adsorbed onto the adsorbent, while CH4 flows out as a permeate gas, thus achieving the separation of CO2 and CH4. When the adsorbent reaches saturation, the system pressure is reduced for desorption and regeneration. The adsorbed CO2 is discharged with the desorbed gas, the adsorbent regains its adsorption capacity, and enters the next cycle.

[0051] In this embodiment, the pressure swing adsorption (PSA) system consists of six adsorption towers, employing a cyclical operation mode of two towers for adsorption, two towers for pressure equalization, and two towers for regeneration. The adsorption pressure is 0.6 MPa (g), and the desorption pressure is -0.06 MPa (g). Through a reasonable pressure equalization process, CH4 in the adsorption towers can be effectively recovered, increasing the methane yield. The PSA system produces CH4-rich gas (biogas) with a methane concentration exceeding 98%, meeting the requirements of the "Natural Gas" (GB 17820-2018) standard. This gas can be integrated into urban natural gas pipelines for sale or stored for future use.

[0052] The CO2-rich desorbed gas generated during the desorption stage of the pressure swing adsorption system is then guided to the CO2 resource recovery and treatment system for processing.

[0053] (ii) Sulfur closed-loop treatment system The sulfur closed-loop treatment system is an important component of this invention in realizing the "waste-to-waste" concept. Its function is to treat the sulfur-containing byproducts generated during the wet desulfurization process of complexed iron in a closed-loop manner within the plant, replacing the traditional outsourced treatment model. The system includes a regeneration system 10 and a sulfur slurry dewatering device 11 connected in sequence.

[0054] Regeneration System 10: During the operation of the complexed iron wet desulfurization tower, the desulfurization rich liquor (containing elemental sulfur and reduced Fe) 2+ The solution is discharged from the bottom of the desulfurization tower and enters the regeneration system 10. The regeneration system has two functions: one is to remove Fe from the solution. 2+ Re-oxidized to Fe³ + The first step is to restore the activity of the complexed iron catalyst so that the regenerated solution can be returned to the desulfurization tower for recycling; the second step is to preliminarily enrich the elemental sulfur suspended in the solution.

[0055] The regeneration system employs an air oxidation regeneration method, which involves blowing air into the sulfur-rich solution to utilize the oxygen in the air to regenerate Fe. 2+ Oxidized to Fe³ + The regenerated solution regains its desulfurization activity and is recycled back to the complexed iron wet desulfurization tower via pipeline, achieving the recycling of the desulfurization liquid and reducing operating costs. During the regeneration process, due to changes in solution conditions, elemental sulfur particles in the solution further aggregate and precipitate, forming sulfur slurry.

[0056] Sulfur slurry dewatering unit 11: The sulfur slurry precipitated during the regeneration process enters the sulfur slurry dewatering unit 11 for dewatering treatment. In this embodiment, a plate and frame filter press is used to remove the water from the sulfur slurry, forming sulfur paste with a moisture content of about 30%. The daily output of sulfur paste is about 100 kg.

[0057] The dehydrated sulfur paste is transported by vehicle to the waste storage pit via mechanical conveying or packaged conveying. It is then mixed with municipal solid waste through a waste grab bucket and fed into the waste incinerator 12. The sulfur paste decomposes into SO2 in the high-temperature environment of the waste incinerator (850-950℃). The SO2 enters the semi-dry desulfurization system 13 along with the flue gas and is captured and removed by the desulfurization agent.

[0058] Through the aforementioned closed-loop treatment method, sulfur paste does not require outsourcing for transportation and disposal, which reduces operating costs and eliminates the environmental risks that may arise during the transportation and storage of sulfur paste. The sulfur in the sulfur paste is ultimately converted into SO2 in the incinerator and captured as solid salts in the desulfurization system, which are discharged with the fly ash, achieving closed-loop in-plant treatment of sulfur.

[0059] (III) CO2 Resource Utilization System The CO2 resource utilization system is another core innovation of this invention. Its function is to utilize the CO2 separated by the pressure swing adsorption system and convert it into a deacidifying agent to replace traditional quicklime for flue gas deacidification. The core equipment of this system is the CO2 conversion reactor 14.

[0060] CO2 Conversion Reactor 14: The CO2-rich desorbed gas generated during the desorption stage of the pressure swing adsorption system is guided to the CO2 conversion reactor 14. The CO2 conversion reactor is a bubble column structure, into which a saturated sodium carbonate (Na2CO3) solution is injected. The CO2-rich desorbed gas is bubbled into the sodium carbonate solution from the bottom of the reactor, where the CO2 reacts chemically with the sodium carbonate solution to produce sodium bicarbonate (NaHCO3) slurry. The chemical reaction equation is as follows: Na₂CO₃ + CO₂ + H₂O → 2NaHCO₃ In this embodiment, the reaction temperature is controlled at 35°C, and the reaction conversion rate is approximately 85%. The generated sodium bicarbonate slurry has a solids content of approximately 15% and is in a suspended slurry state. This slurry does not require drying treatment and is directly transported through pipelines to the slurry preparation and supply system of the semi-dry deacidification system 13.

[0061] The advantages of setting the CO2 conversion reactor as a bubble column structure are: the bubble column structure allows for full contact between the gas and liquid phases, increasing the contact area and contact time between CO2 and sodium carbonate solution, which is beneficial to improving the reaction conversion rate; at the same time, the bubble column structure is simple, easy to operate and maintain, and suitable for long-term stable operation in the industrial environment of waste incineration plants.

[0062] 2. Application of sodium bicarbonate slurry in semi-dry deacidification systems After being transported to the semi-dry deacidification system 13, sodium bicarbonate slurry replaces the original lime slurry as the deacidification agent. The deacidification reaction tower of the semi-dry deacidification system uses a rotary atomizer to atomize and spray the sodium bicarbonate slurry into the tower, so that it can fully contact and react with the acidic gases (mainly HCl and SO2) in the flue gas.

[0063] Sodium bicarbonate first decomposes under high temperature conditions inside the deacidification reaction tower: 2NaHCO3→ Na2CO3+ CO2+ H2O The generated sodium carbonate then reacts with acidic gases in the flue gas: Reaction with SO2: Na2CO3 + SO2 + 1 / 2O2 → Na2SO4 + CO2 Reaction with HCl: Na₂CO₃ + 2HCl → 2NaCl + CO₂ + H₂O The sodium sulfate (Na2SO4) and sodium chloride (NaCl) produced in the reaction are solid salts that are collected in subsequent dust removal equipment along with the flue gas, thereby achieving flue gas deacidification.

[0064] Using sodium bicarbonate instead of quicklime for deacidification has the following significant advantages: First, it avoids the problem of increased fly ash. In traditional quicklime desulfurization processes, quicklime reacts with CO2 in flue gas in the following side reactions: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O The generated CaCO3 mixes into the fly ash, leading to a significant increase in fly ash production. According to industry measurement data, in waste incineration plants using slaked lime for semi-dry deacidification, the measured CaCO3 content in fly ash is as high as 30%. By replacing slaked lime with sodium bicarbonate, this side reaction is eliminated at the source, reducing fly ash production by more than 25% and significantly alleviating the burden of fly ash disposal.

[0065] Secondly, it has higher deacidification efficiency. Sodium carbonate, which is produced by the thermal decomposition of sodium bicarbonate, has high reactivity and reacts quickly and completely with acidic gases, resulting in higher deacidification efficiency than traditional quicklime and achieving better flue gas purification.

[0066] Third, it realizes the resource utilization of CO2. The CO2 captured by the pressure swing adsorption system is a kind of waste gas that needs to be treated. Through the coupling process of this invention, the CO2 is converted into a useful raw material for deacidification agent, realizing the recycling of carbon resources within the plant and turning waste into treasure.

[0067] The original deacidification system used quicklime slurry, consuming approximately 10 kg of quicklime per ton of waste, or 10,000 kg per day, with an effective utilization rate of about 50%, resulting in an actual effective deacidification output of 5,000 kg / day. According to the stoichiometric relationship of the deacidification reaction, 2 mol NaHCO3 (168 g) and 1 mol Ca(OH)2 (74 g) have the same neutralization capacity, with a mass ratio of 2.27:1. To achieve the same deacidification effect, approximately 11,350 kg / day of sodium bicarbonate is required. Considering an 80% effective utilization rate of sodium bicarbonate, the actual amount of sodium bicarbonate to be added is approximately 14,188 kg / day.

[0068] Based on the calculation data of this embodiment, the daily biogas processing capacity is 7500 Nm³. 3 The biogas contains 32% CO2 by volume, with a total CO2 volume of approximately 4750 kg / d. The pressure swing adsorption (PSA) system has a CO2 capture efficiency of approximately 90%, resulting in an actual CO2 capture of approximately 4275 kg / d. Each ton of CO2 can generate approximately 3.82 tons of NaHCO3, and with a daily CO2 capture of approximately 4.275 tons, approximately 16.33 tons of NaHCO3 can be produced, which is sufficient to meet the acid removal agent requirements of the existing semi-dry acid removal system in the waste incineration plant.

[0069] (iv) Wastewater treatment system The wastewater treatment system is the key component ensuring zero wastewater discharge throughout the plant, a crucial aspect of this invention. During the operation of this process, wastewater is generated at multiple stages, including: (1) Drainage generated by the dehydration device 5 before the biogas compressor 6; (2) Condensate produced by the deep dehydration device 7 after the biogas compressor 6; (3) The filtrate produced by the sulfur slurry dewatering device 11 during the sulfur slurry dewatering process.

[0070] The total wastewater generated in the above-mentioned stages is approximately 12m³. 3 All wastewater is transported via a wastewater return pipeline to the existing leachate treatment system 15 at the waste incineration plant for centralized treatment. The leachate treatment system has the capacity and technological conditions to treat this wastewater, eliminating the need for additional wastewater treatment facilities. This method achieves zero wastewater discharge for the entire plant.

[0071] (v) Closed-loop material management throughout the system By combining the above four subsystems, this invention constructs a complete closed-loop material system, as detailed below: (1) Closed loop of sulfur: The sulfur-rich liquid produced by the complexed iron wet desulfurization → regeneration system → dehydration of sulfur slurry to form sulfur paste → sulfur paste sent to the incinerator for combustion → SO2 enters the deacidification system with the flue gas → is captured by the deacidification agent as solid salts → discharged with fly ash. The regenerated desulfurization liquid is returned to the desulfurization tower for recycling.

[0072] (2) Closed loop of carbon: CO2 captured by pressure swing adsorption system → CO2 conversion reactor reacts with sodium carbonate to generate sodium bicarbonate slurry → replaces lime slurry for semi-dry deacidification → CO2 generated by sodium bicarbonate decomposition is discharged with flue gas.

[0073] (3) Closed loop of water: wastewater generated in each dehydration stage → wastewater return pipeline → leachate treatment system for centralized treatment.

[0074] All three types of by-products are processed and recycled within the factory, eliminating the need for external transportation and forming a complete material closed loop, embodying the design concept of "treating waste with waste".

[0075] (vi) Operational Results Through actual operation and verification, this embodiment has achieved the following results: (1) The sulfur paste can be disposed of in a closed loop within the plant, eliminating the need for outsourcing and thus eliminating the costs and environmental risks associated with outsourcing the disposal of sulfur paste. (2) The CO2 captured by biogas purification can fully meet the sodium bicarbonate requirements for flue gas deacidification, realizing the in-plant recycling of carbon resources, and CO2 is no longer emitted as waste gas. (3) Using sodium bicarbonate instead of quicklime for deacidification reduces fly ash production by more than 30%, significantly reducing the burden and cost of fly ash disposal. (4) All process wastewater is reused in the leachate treatment system to achieve zero wastewater discharge for the entire plant; (5) Biogas production is approximately 4800 Nm³. 3 / d, with a methane concentration of over 98%, meeting national standards, it can be connected to the natural gas pipeline network for external sale, adding a new source of revenue for the incineration plant; (6) The added siloxane removal unit effectively removes siloxane impurities from biogas, ensuring the quality of biogas and the safety of subsequent equipment.

[0076] In summary, this invention couples biogas purification byproducts with the existing system of a waste incineration plant, achieving closed-loop in-plant treatment of three types of byproducts: sulfur paste, CO2, and wastewater. At the same time, it increases the incineration plant's revenue by producing biogas, resulting in significant environmental and economic benefits.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A biogas purification coupled with acid removal and fly ash reduction system for waste incineration plants, characterized in that, This includes a biogas purification main process system, a sulfur closed-loop treatment system, and a CO2 resource utilization treatment system. The biogas purification main process system includes a biogas buffer tank, a water washing tower, a complexed iron wet desulfurization tower, an iron oxide dry fine desulfurization tower, a dehydration device, a biogas compressor, a deep dehydration device, a modified activated carbon adsorption tower, and a pressure swing adsorption system connected in sequence, which are used to purify leachate biogas into biomethane. The closed-loop sulfur treatment system includes a regeneration system and a sulfur slurry dewatering device connected in sequence. The sulfur-rich liquid outlet of the complexed iron wet desulfurization tower is connected to the regeneration system. The solution regenerated by the regeneration system is returned to the complexed iron wet desulfurization tower for recycling. The sulfur paste outlet of the sulfur slurry dewatering device is connected to a waste incinerator. The SO2 generated after the sulfur paste is mixed and incinerated with municipal solid waste enters the semi-dry deacidification system with the flue gas for removal. The CO2 resource utilization system includes a CO2 conversion reactor. The CO2-rich desorbed gas outlet of the pressure swing adsorption system is connected to the CO2 conversion reactor. The CO2-rich desorbed gas in the CO2 conversion reactor reacts with sodium carbonate solution to generate sodium bicarbonate slurry. The sodium bicarbonate slurry is directly transported to the slurry preparation and supply system of the semi-dry deacidification system, replacing lime slurry as a deacidifying agent, and is injected into the deacidification reaction tower of the semi-dry deacidification system to react with acidic gases in the flue gas.

2. The system according to claim 1, characterized in that, It also includes a wastewater treatment system, which includes a wastewater return pipeline. The wastewater outlets of the dewatering device, the deep dewatering device, and the sulfur slurry dewatering device are all connected to the leachate treatment system of the waste incineration plant through the wastewater return pipeline.

3. The system according to claim 1, characterized in that, The pressure swing adsorption system is equipped with multiple adsorption towers and adopts a cyclic operation mode of multi-tower adsorption, multi-tower pressure equalization, and multi-tower regeneration. The adsorption pressure is 0.2 to 1.0 MPa (g), the desorption pressure is -0.02 to -0.09 MPa (g), and the methane concentration of the produced biogas is ≥97%.

4. The system according to claim 1, characterized in that, The CO2 conversion reactor is a bubble column structure. Sodium carbonate solution is injected into the column, and CO2-rich desorbed gas is bubbled in and reacts with the sodium carbonate solution to generate sodium bicarbonate slurry. The reaction conversion rate is 80% to 90%, and the sodium bicarbonate slurry has a solid content of 10% to 20%. It can be directly transported to the semi-dry deacidification system through pipeline without drying.

5. The system according to claim 1, characterized in that, The modified activated carbon adsorption tower is filled with coconut shell-based modified activated carbon, and the adsorption temperature is controlled at 20–35°C, with a space velocity of 200–500 h⁻¹. -1 The removal rate of siloxanes is ≥95%.

6. The system according to claim 1, characterized in that, The complexed iron wet desulfurization tower uses a complexed iron catalyst for circulating spray desulfurization, controls the solution pH to 7.5-9.0, oxidizes H2S in biogas to elemental sulfur, and achieves an H2S removal rate of ≥99%.

7. The system according to claim 1, characterized in that, The semi-dry deacidification system uses a rotary atomizer to atomize and spray sodium bicarbonate slurry into the deacidification reaction tower, which reacts with HCl and SO2 in the flue gas to generate sodium salts that are captured and replaced quicklime slurry for flue gas deacidification, thereby reducing fly ash production by more than 25%.

8. A waste incineration plant biogas purification coupled with acid removal and fly ash reduction process using the system described in any one of claims 1-7, characterized in that, Includes the following steps: S1. After the leachate biogas is pressure stabilized in the biogas buffer tank, it is sequentially passed through a water washing tower to remove water-soluble impurities and trace amounts of ammonia, a complexed iron wet desulfurization tower to oxidize H2S into elemental sulfur, and an iron oxide dry fine desulfurization tower for fine desulfurization, so that the total sulfur content meets the intake requirements of the subsequent pressure swing adsorption system. S2. After fine desulfurization, the biogas is dehydrated to remove free water. After being pressurized by the biogas compressor, it is then passed through a deep dehydration device to lower the gas dew point and remove residual moisture, a modified activated carbon adsorption tower to remove impurities such as siloxanes, and a pressure swing adsorption system to separate CO2 and CH4 to obtain biogas. S3. The sulfur-rich liquid produced by the complexed iron wet desulfurization tower enters the regeneration system for regeneration. The regenerated solution is returned to the complexed iron wet desulfurization tower for recycling. The sulfur slurry precipitated during the regeneration process is dehydrated by the sulfur slurry dehydration device to form sulfur paste. The sulfur paste is sent to the waste incinerator and mixed with municipal solid waste for incineration. The sulfur paste decomposes into SO2 at high temperature in the incinerator and enters the semi-dry desulfurization system with the flue gas to be removed. S4. The CO2-rich desorbed gas separated by the pressure swing adsorption system is fed into the CO2 conversion reactor and reacts with the sodium carbonate solution to generate sodium bicarbonate slurry. The sodium bicarbonate slurry is directly transported to the slurry preparation and supply system of the semi-dry deacidification system to replace lime slurry as a deacidification agent and react with acidic gases in the flue gas to achieve deacidification. S5. All wastewater generated in steps S1 to S4 is returned to the leachate treatment system for centralized treatment through the wastewater return pipeline.

9. The process according to claim 8, characterized in that, In step S1, the pH of the solution in the complexed iron wet desulfurization tower is controlled at 7.5–9.0, and the H2S concentration in the biogas is 10000 mg / Nm³. 3 After wet desulfurization with complexed iron, the H2S concentration decreased to 50 mg / Nm³. 3 Next, the total sulfur is removed to ≤5mg / m³ using a dry iron oxide desulfurization tower. 3 .

10. The process according to claim 8, characterized in that, In step S2, the biogas compressor pressurizes the biogas to 0.2-1.0 MPa (g); the deep dehydration device uses a freeze dehydration method to reduce the dew point of the pressurized biogas to -40°C to -50°C.

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