Biogas fermentation system and method

Abstract

The invention belongs to the technical field of biomass energy utilization, and particularly relates to a biogas fermentation system and method. The biogas fermentation system comprises a pretreatment section, a desulfurization section, a hydrolysis section, an acid production section and a methane production section which are sequentially arranged from top to bottom. A discharge pipe at the bottom of the pretreatment section penetrates through the liquid distributor to reach the middle part of the desulfurization section; the return pipe is connected with the liquid distributor through the pump; gas in the hydrolysis section enters the desulfurization section for desulfurization through a gas guide pipe and a floating valve group in the desulfurization section; gas in the acid production section enters the hydrolysis section through a gas guide pipe and a floating valve group in the hydrolysis section to be hydrolyzed; and gas in the methane production section enters the acid production section through a gas guide pipe and a floating valve group in the acid production section to be subjected to acid production treatment. According to the invention, CO2 removal, H2S removal, oxygen removal, ammonia removal, mercaptan removal, halogenated hydrocarbon removal and siloxane removal are carried out on the fermentation system through a plurality of strengthening means, so that high-quality biogas and functionalized biogas slurry are obtained.

Description

Technical Field

[0001] This invention belongs to the field of biomass energy utilization technology, specifically relating to a biogas fermentation system and method. Background Technology

[0002] Biogas projects convert waste organic matter into renewable biogas, realizing the resource utilization of waste and sustainable energy production. The biogas produced can replace coal-fired power generation and heating, and after further purification, it can also serve as a substitute for natural gas. To obtain high-quality biogas (typically high in methane, low in impurities, stable in calorific value, and low in corrosivity), it is necessary to systematically optimize the pretreatment methods of fermentation raw materials, fermentation processes, process control, and purification treatment. Although biogas purification can remove a large amount of CO2 and a small amount of H2S and H2O, existing purification methods only purify the produced biogas, resulting in high purification costs and high energy consumption.

[0003] In addition, fermentation is the core biochemical process for producing high-quality biogas. In existing technologies, although the quality of biogas has been improved to some extent by strengthening the pretreatment of raw materials, designing new reactors and dynamically controlling the reaction process, the following problems still exist: (1) The CH4 concentration in biogas is low and it usually contains impurities such as H2S, oxygen, ammonia, thiols, halogenated hydrocarbons and siloxanes. Among them, H2S is a highly toxic gas with a putrid, rotten egg-like odor, which can damage the central nervous system even at very low concentrations; H2S will be oxidized to sulfuric acid when it meets water, which corrodes the production equipment and must be removed before biogas is used. Ammonia is a toxic gas with a strong, pungent odor that is harmful to the environment and equipment. Ammonia removal is generally required during biogas purification. Biogas produced by large-scale biogas projects is mainly used for combustion power generation. Siloxanes are converted into microcrystalline silica during biogas combustion. Microcrystalline silica has chemical and physical properties similar to glass, which can reduce the effectiveness of combustion catalysts and lubricants. It can also deposit on the inner wall of the engine combustion chamber and on the surface of engine components such as pistons and valves, hindering heat conduction and causing wear on the engine and components, shortening the service life of equipment, and seriously affecting the efficient utilization of biogas. Therefore, it is necessary to remove siloxanes before using biogas. In addition, the low pressure of biogas and the presence of thiols and halogenated hydrocarbons are not conducive to the utilization of biogas; (2) the added value of biogas residue and biogas liquid is low and the utilization is difficult, resulting in poor efficiency of biogas projects and problems such as emission reduction without efficiency improvement; (3) biogas fermentation containers need to be disinfected regularly to ensure the cleanliness and sterility of their internal environment, thereby ensuring the smooth progress of biogas fermentation and efficient biogas production; (4) biogas fermentation containers are large in volume and occupy a large area; (5) the temperature of fermentation raw materials is low in winter, and additional energy needs to be added to increase the temperature of fermentation raw materials in order to achieve a higher fermentation rate, but this increases energy consumption.

[0004] The above problems have, to some extent, limited the industrial-scale promotion and application of biogas, or increased the difficulty of utilizing biogas. Summary of the Invention

[0005] The purpose of this invention is to provide a biogas fermentation system and method to solve the problems of low biogas quality, high impurities, low pressure, low added value of biogas residue and biogas slurry, and high energy consumption in winter due to low temperature of fermentation raw materials.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a biogas fermentation system, comprising a pretreatment section, a desulfurization section, a hydrolysis section, an acid production section and a methanogenic section arranged sequentially from top to bottom; The pretreatment section has a first discharge pipe at the bottom, the desulfurization section has a liquid distributor at the top and a return pipe at the bottom. The first discharge pipe passes through the liquid distributor and is located inside the desulfurization section. The return pipe is connected to the liquid distributor via a pump. The bottom of the desulfurization section, hydrolysis section and acid production section are all equipped with float valve groups, discharge pipes and gas guide pipes; Packing material is also installed in the desulfurization section, hydrolysis section, acid production section and methanogenesis section; The packing material is composed of a mixture of packing material A, packing material B, and packing material C; Packing A, packing B, and packing C all have a core-shell structure. Packing A includes porous plastic balls and a stainless steel porous spherical shell attached to its surface; packing B includes porous plastic balls supported by silica gel and a stainless steel porous spherical shell attached to its surface; and packing C includes porous plastic balls co-supported by silica gel / TiO2 and a polytetrafluoroethylene porous spherical shell attached to its surface.

[0007] In some other embodiments, the packing volume accounts for 75-85% of the volume of the desulfurization section, hydrolysis section, acid-producing section, and methanogenic section, respectively; The packing material used in the desulfurization section is a packing material for desulfurization bacteria to attach to biofilm; The packing material for desulfurization bacteria biofilm formation in the desulfurization section was prepared according to the following reference: Xu Haipeng, Li Yan, Mu Hui, et al. Characteristics of H2S removal from gas by immobilized Thiobacillus thiocyanate [J]. Journal of Environmental Engineering, 2018, 12(11): 3109-3115; the desulfurization bacteria used were Thiobacillus thiocyanate (accession number ATCC 8158), which is suitable for growth in a neutral environment.

[0008] Biofilm-based desulfurization systems are highly efficient, low-cost, and environmentally friendly, making them particularly suitable for biogas projects with medium to high sulfur loads.

[0009] The packing material in the desulfurization section is composed of packing material A, packing material B and packing material C mixed in a volume ratio of (5-6):(2-3):(2-3); the packing material in the desulfurization section is a packing material for desulfurization bacteria to attach to biofilm. The packing material in the hydrolysis section is composed of packing material A, packing material B and packing material C mixed in a volume ratio of (2-3):(3-4):(3-4); The packing material in the acid-producing section is composed of packing material A, packing material B and packing material C mixed in a volume ratio of (2-3):(3-4):(4-5); The packing material in the methanogenic section is composed of packing material A, packing material B and packing material C mixed in a volume ratio of (3-4):(3-4):(4-5); The volume ratio of packing materials A, B, and C in the desulfurization, hydrolysis, acid production, and methanogenesis sections serves two purposes: first, it ensures uniform mixing and distribution of the packing materials; second, it allows the mixed packing materials to better adsorb substances such as H2S, oxygen, ammonia, thiols, halogenated hydrocarbons, and siloxanes, thereby enhancing gas-liquid mass transfer and chemical reactions. Packing material A adsorbs a significant amount of hydrophobic substances such as halogenated hydrocarbons and siloxanes, while packing materials B and C adsorb a significant amount of hydrophilic substances such as H2S, oxygen, ammonia, and thiols. Packing material C also plays a photocatalytic role (primarily including photocatalytic fermentation for hydrogen production and photocatalytic conversion of hydrogen and carbon dioxide into methane). Furthermore, packing material A constitutes a larger proportion in the desulfurization section to avoid excessive accumulation of hydrophilic substances in the fermentation feedstock on the packing material, which could lead to poor biofilm formation by desulfurizing bacteria.

[0010] The density of the porous plastic balls in filler A is 0.95-1.05 g / cm³. 3 Specific surface area greater than 200 m² 2 / m 3 Diameter is 10-20 mm, opening ratio is 15%-35%, and aperture is 3-4 mm; The density of the porous plastic spheres supported on silica gel in filler B is 0.96-1.05 g / cm³. 3 Specific surface area greater than 200 m² 2 / m 3 The diameter is 10-20 mm, the porosity is 15%-35%, and the pore size is 3-4 mm; the loading of silica gel is 2wt%-8wt%. The density of porous plastic spheres supported on silica gel and TiO2 in filler C is 0.95-1.05 g / cm³. 3 Specific surface area greater than 200m² 2 / m 3 The diameter is 10-20 mm, the porosity is 15%-35%, and the pore size is 3-4 mm; among which, the loading of silica gel is 1.5wt%-6wt%, and the loading of TiO2 is 0.5wt%-2wt%.

[0011] The porosity of a porous plastic ball refers to the proportion of its surface pores to the total surface area of ​​the ball.

[0012] Using different packing volume ratios is to make the packings have different densities, specific surface areas, etc., so that they can form a uniform distribution in the upper, middle and lower layers of the desulfurization section, hydrolysis section, acid production section and methanogenesis section, rather than floating in the upper layer or settling in the lower layer.

[0013] The packing volume accounts for 75-85% of the volume of the desulfurization section, hydrolysis section, acid production section, and methanogenesis section, respectively. Such a large packing volume fraction is not used in conventional biogas fermentation, nor is it necessary. The present invention uses such a large packing volume fraction so that the packing can act as a packing tower to promote gas-liquid mass transfer, and the entire system can achieve the purpose of simultaneous fermentation and biogas purification. When the fermentation liquid comes into contact with the static packing, blockage can easily occur. Therefore, the present invention uses spherical wear-resistant packing, which can not only act as a packing tower under the action of stirring, but also allows the deposits generated on the wear-resistant packing to fall off quickly, making blockage less likely.

[0014] Considering the complex composition and diverse properties of the fermentation raw materials, some components might be toxic to the desulfurizing bacteria if directly introduced into the desulfurization stage. Pre-treated fermentation raw materials, however, are more uniform and have a more stable dissolved oxygen concentration before entering the desulfurization stage, providing a foundation for stable operation. Using the fermentation raw materials directly as the fermentation substrate for biological desulfurization not only reduces the cost of raw material consumption during standalone biological desulfurization but also allows for the degradation of difficult-to-degrade substances such as lignocellulose in the fermentation raw materials, reducing the difficulty of degradation in the hydrolysis, acid production, and methanogenesis stages. The desulfurization stage consumes dissolved oxygen from the fermentation raw materials while desulfurizing biogas, thus reducing the dissolved oxygen concentration in the fermentation raw materials and consequently lowering the oxygen content in the biogas. A small number of desulfurizing bacteria inevitably end up in the hydrolysis, acid production, and methanogenesis stages, continuing to perform desulfurization in these stages and reducing the H2S concentration in the biogas and the oxygen concentration in the fermentation broth.

[0015] Specifically, the gas in the hydrolysis section enters the desulfurization section through the gas guide pipe and float valve group of the desulfurization section for desulfurization treatment; the gas in the acid production section enters the hydrolysis section through the gas guide pipe and float valve group of the hydrolysis section for hydrolysis treatment; and the gas in the methanogenesis section enters the acid production section through the gas guide pipe and float valve group of the acid production section for acid production treatment.

[0016] In some other embodiments, the biogas digester corresponding to the pretreatment section is provided with a feed pipe and a first level gauge on the side wall, a safety valve is provided at the top of the biogas digester corresponding to the pretreatment section, a top-entry agitator is provided at the top inside the pretreatment section, and a first filter is provided at the bottom of the pretreatment section, and the first filter is located at the upper end of the first discharge pipe. The first discharge pipe is equipped with a first control valve, which is connected to the first control line group.

[0017] In some other embodiments, a feed pipe is provided on the side wall of the biogas digester corresponding to the desulfurization section, and the feed pipe is connected to a liquid distributor; a first agitator is provided on the other side wall of the desulfurization section, and the first agitator is used to improve the uniformity of material dispersion in the desulfurization section. The top side wall of the desulfurization section is also equipped with a biogas discharge pipe, which is connected to the back pressure valve, the gas outlet valve and the gas storage tank in sequence. The bottom of the desulfurization section is equipped with a second filter, a first float valve group and a second discharge pipe from top to bottom. The second discharge pipe is equipped with a second control valve, which is connected to the second control line group.

[0018] In some other embodiments, a feed pipe and a second level gauge are provided on the side wall of the hydrolysis section, a second stirrer is provided on the other side wall of the hydrolysis section, and a third filter, a second float valve group and a third discharge pipe are provided from top to bottom at the bottom of the hydrolysis section. A third control valve is provided on the third discharge pipe and the third control valve is connected to a third control line group.

[0019] In some other embodiments, a feed pipe and a third level gauge are provided on the side wall of the acid-producing section, a third stirrer is provided on the other side wall of the acid-producing section, and a fourth filter, a third float valve group and a fourth discharge pipe are provided from top to bottom at the bottom of the acid-producing section. A fourth control valve is provided on the fourth discharge pipe and the fourth control valve is connected to a fourth control line group. In some other embodiments, a feed pipe and a fourth level gauge are provided on the side wall of the methanogenic section, a fourth agitator is provided on the other side wall of the methanogenic section, and a fifth filter and a discharge pipe are provided at the bottom of the methanogenic section; a discharge valve is provided on the discharge pipe, and the discharge pipe is connected in sequence to a discharge pump and a biogas slurry storage tank. In a second aspect, the present invention provides a biogas fermentation method, employing the biogas fermentation system of the first aspect, comprising the following steps: The fermentation raw materials are mixed with water to make a suspension, and the suspension is added to the pretreatment section for hydrolysis and fermentation to obtain a slurry; Add papermaking black liquor into the desulfurization section, add the pretreated slurry into the desulfurization section, so that the slurry and biogas come into countercurrent contact for desulfurization treatment, add the desulfurized slurry into the desulfurization section for circulating desulfurization treatment and discharge the desulfurized biogas. Papermaking black liquor and desulfurized slurry are added to the hydrolysis section for hydrolysis to obtain hydrolyzed slurry; when the pressure of the gas in the hydrolysis section is greater than the set pressure of the float valve group, the gas in the hydrolysis section enters the desulfurization section through the gas guide pipe and the float valve group for desulfurization treatment. Acclimated anaerobic sludge and hydrolyzed slurry are added to the acid-producing section for acid production treatment to obtain acid-producing slurry; when the pressure of the gas in the acid-producing section is greater than the set pressure of the bottom floating valve group of the hydrolysis section, the gas in the acid-producing section enters the hydrolysis section through the gas guide pipe and the bottom floating valve group of the hydrolysis section. Acclimated anaerobic sludge and acidified slurry are added to the methanogenic section for methanogenic treatment to produce biogas slurry. When the gas pressure in the biogas slurry is greater than the set pressure of the bottom float valve group of the acidogenic section, the gas in the biogas slurry enters the acidogenic section through the gas guide pipe and the bottom float valve group of the acidogenic section.

[0020] In some other embodiments, packing material is also provided in the desulfurization section, hydrolysis section, acid production section and methanogenesis section, wherein the packing material in the desulfurization section is a packing material for desulfurization bacteria to attach to a biofilm; the packing material is a mixture of packing material A, packing material B and packing material C in a volume ratio; The filler is prepared by mixing filler A, filler B and filler C; the porous plastic ball in filler A is prepared as follows: polypropylene powder, polystyrene powder and sodium chloride powder are mixed, stirred evenly and heated, and then molded. After cooling and demolding, it is washed with water until no precipitate is added with silver nitrate aqueous solution. After drying, the porous plastic ball is obtained. The preparation method of porous plastic balls loaded with silica gel in filler B is as follows: The porous plastic balls are put into a sealed container, vacuum is drawn, sodium silicate aqueous solution is added to the container, stirred and mixed, filtered to obtain porous plastic balls containing sodium silicate aqueous solution, hydrochloric acid solution is added, stirred and mixed, filtered, washed until neutral, and dried to obtain porous plastic balls loaded with silica gel. The preparation method of porous plastic balls loaded with silica gel and TiO2 in filler C is as follows: Add the porous plastic balls loaded with silica gel to a cyclohexane solution of tetrabutyl titanate, soak and filter, take them out and place them in air atmosphere at room temperature for natural hydrolysis, and dry them to obtain porous plastic balls loaded with silica gel and TiO2.

[0021] In some other embodiments, the mixing mass ratio of polypropylene powder and polystyrene powder in the preparation method of porous plastic balls in filler A is (1-9):5, the amount of sodium chloride powder added is 15-20% of the total mass of polypropylene powder and polystyrene powder; the heating temperature is 235-245℃, the concentration of silver nitrate aqueous solution is 0.008-0.012 mol / L, and the drying is carried out at 75-85℃ for 20-24 h; In the preparation method of porous plastic balls loaded with silica gel in filler B, the pressure after vacuuming is less than -0.099 MPa, the concentration of sodium silicate aqueous solution is 20-25 wt%, the volume ratio of sodium silicate aqueous solution to porous plastic balls is (2-3):1, the concentration of hydrochloric acid solution is 3.5-3.5 wt%, the volume ratio of hydrochloric acid solution to porous plastic balls containing sodium silicate aqueous solution is (2-3):1, and the stirring time is 5-7 h; In the preparation method of porous plastic balls supported by silica gel and TiO2 in filler C, the concentration of cyclohexane solution of tetrabutyl titanate is 25-35%, the volume ratio of cyclohexane solution of tetrabutyl titanate to porous plastic balls supported by silica gel is (2-3):1, the soaking time is 5-7h, the natural hydrolysis time is 40-50h, and the drying is carried out at 75-85℃ for 20-24h.

[0022] In some other embodiments, the fermentation raw materials are one or both of kitchen waste and fruit and vegetable processing waste; The solid content of the suspension is 3-8%; the water is one or both of tap water and wastewater. The wastewater has a pH of 5.0-5.5, CODcr of 15000-20000 mg / L, BOD5 of 5000-10000 mg / L, and SS of 2500-3500 mg / L; specifically, the solid content of the suspension is 3%, 4%, 5%, 6%, 7%, or 8%; the water is one or both of tap water and wastewater. The wastewater is starch processing wastewater with a pH of 5.1, CODcr of 18000 mg / L, BOD5 of 8000 mg / L, and SS of 3000 mg / L. The safety valve is set to discharge pressure of 0.25-0.45 MPa. The safety valve is set to discharge pressure 0.05 MPa higher than that of the back pressure valve.

[0023] In some other embodiments, the pH value of the desulfurization section is 7.0-7.5; the pH value of the hydrolysis section is 8.0-8.5; the pH value of the acid production section is 6.0-6.5; and the pH value of the methanogenesis section is 7.0-7.5.

[0024] The acclimation method for the acclimated anaerobic sludge added to the acidogenic or methanogenic stage is as follows: Nitrogen and phosphorus sources are added to the anaerobic sludge raw material, and the mixture is inoculated into a serum bottle and cultured at 30-35℃ for 4 fermentation cycles to obtain the final product. The nitrogen and phosphorus sources are provided in the form of NH4Cl and KH2PO4, respectively, with a COD:N:P ratio of 100:(4-5):1 and one fermentation cycle is 30 days.

[0025] In some other embodiments, the volume concentration of CH4 in the biogas is greater than 64.50%, the volume concentration of CO2 is less than 33.10%, the volume concentration of H2S is less than 0.02%, the volume concentration of oxygen is less than 0.04%, the volume concentration of ammonia, thiols, halogenated hydrocarbons and siloxanes is 0.00%, and the volume content of other gases is less than 2.34%; the elemental sulfur content in the biogas slurry is less than 0.082 g / L.

[0026] The beneficial effects of this invention are: (1) The biogas fermentation process is designed in a segmented manner, that is, the gas-liquid phase environment of each segment of the biogas fermentation process, namely the pretreatment segment, desulfurization segment, hydrolysis segment, acid production segment and methanogenesis segment, is matched with the reaction conditions suitable for the pretreatment, desulfurization, hydrolysis, acid production and methanogenesis segments, which improves the biogas fermentation efficiency.

[0027] The pretreatment, desulfurization, hydrolysis, acid production, and methanogenesis stages work together to achieve better fermentation and biogas purification effects. This is reflected in the following: the fermentation feedstock has a complex composition and diverse properties. If it were to directly enter the desulfurization stage, some components might be toxic to the desulfurizing bacteria. However, the fermentation feedstock treated in the pretreatment stage is more uniform and has a more stable dissolved oxygen concentration when it enters the desulfurization stage, which provides a foundation for the stable operation of the desulfurization stage. Using the fermentation feedstock directly as the fermentation substrate for biological desulfurization not only reduces the cost of feedstock consumption in the separate implementation of biological desulfurization, but also... Furthermore, substances that are difficult to degrade, such as lignocellulose in the fermentation raw materials, will also be degraded in the biological desulfurization unit, reducing the difficulty of degradation in the hydrolysis, acid production, and methanogenesis stages. While desulfurizing biogas, the desulfurization stage also consumes dissolved oxygen in the fermentation raw materials, thereby reducing the dissolved oxygen concentration in the fermentation raw materials and thus reducing the oxygen content in the biogas. A small number of desulfurizing bacteria in the biological desulfurization unit are inevitably discharged into the hydrolysis, acid production, and methanogenesis stages, where they continue to play a desulfurization role, thereby reducing the H2S concentration in the biogas and the oxygen concentration in the fermentation liquid.

[0028] (2) The present invention performs biogas fermentation and biogas purification simultaneously in one device, saving the cost of subsequent biogas purification process; the use of wear-resistant functional packing and stirring not only strengthens the gas-liquid mass transfer process, but also allows the deposits generated on the wear-resistant functional packing to fall off quickly, avoiding the clogging problem caused by using ordinary packing towers. Biogas enters the acidification, hydrolysis, and desulfurization sections in a countercurrent contact process. By adjusting the pH values ​​of these sections using papermaking black liquor, CO2 is effectively removed from the biogas. The dissolved CO2 reacts with H2 in the biogas to form CH4. The countercurrent flow of biogas into the acidification and hydrolysis sections effectively removes ammonia, mercaptans, siloxanes, and halogenated hydrocarbons, with wear-resistant packing material enhancing the removal process. The countercurrent flow into the desulfurization section consumes oxygen during desulfurization, effectively removing H2S and oxygen. Furthermore, moderate pressurization (0.2-0.4 MPa) not only effectively enhances the removal of these impurity gases but also avoids excessive acidification. Therefore, this invention's process system effectively purifies biogas to obtain high-quality biogas, overcoming the problems of low-quality biogas, high impurity content, and low pressure that hinder its utilization.

[0029] The hollow plastic spheres in packings A, B, and C are made of a blend of polypropylene and polystyrene. Different mass ratios are used to make the packings have different densities, so that they can form a uniform distribution in the upper, middle, and lower layers of the desulfurization, hydrolysis, acid production, and methanogenesis sections, rather than floating entirely in the upper layer or settling in the lower layer.

[0030] The filler material, made primarily of hollow plastic spheres, is hydrophobic and can adsorb hydrophobic substances such as halogenated hydrocarbons and siloxanes. Under pressure, the adsorption capacity is even greater. The adsorbed halogenated hydrocarbons undergo hydrolysis under the action of acids, alkalis, or fermentation microorganisms to produce hydrogen halides. These hydrogen halides are then converted into halide salts in the fermentation broth and discharged with the biogas slurry. The adsorbed siloxanes undergo hydrolysis under the action of acids, alkalis, or fermentation microorganisms to produce silanols and silicic acid. The filler material loaded with silica gel and / or TiO2 is hydrophilic and can adsorb H2S, oxygen, ammonia, thiols, and silicic acid from biogas. The adsorption capacity is even greater under pressure. Among them, silanols and silicic acid further react to form silica and are discharged with biogas slurry. Thiols react under the action of acid, alkali, or fermentation microorganisms to produce H2S. Ammonia in biogas slurry is converted into nitrogen fertilizer and discharged with biogas slurry. Loading with TiO2 can also promote photochemical reactions between fermentation broth and gas. (3) In the desulfurization section, H2S is converted into sulfur elemental powder, which can play a role in sterilization and disinfection in the biogas fermentation system, reducing the frequency of regular disinfection required for the biogas fermentation system and improving the stability of system operation. The sulfur elemental powder is discharged from the system with the biogas liquid. This biogas liquid containing sulfur elemental powder has a sterilization and disinfection effect and can be used as a functional fertilizer for agricultural pest control and soil improvement, thereby increasing the added value of biogas liquid.

[0031] (4) When biogas flows back into the acid production section, hydrolysis section and desulfurization section, it can transfer the heat of biogas itself to the fermentation raw materials, and the heat generated in the desulfurization process can also be transferred to the fermentation raw materials. This overcomes the problem that the fermentation raw materials are cold in winter and need to be supplemented with extra energy, thus reducing the energy consumption of biogas projects.

[0032] (5) Pressurization can increase the solubility of CO2, H2S, oxygen, ammonia, mercaptan, halogenated hydrocarbons and siloxanes in the fermentation broth, thereby increasing the concentration of these impurities in the fermentation broth and improving the removal efficiency of these impurities; pressurization can also increase the pressure of biogas products, which is more conducive to the efficient utilization of biogas products.

[0033] In summary, this invention utilizes various enhancement methods, such as pressurization, silica gel adsorption, resin adsorption, addition of photocatalysts, and pH adjustment, to achieve CO2 removal, H2S removal, oxygen removal, ammonia removal, mercaptan removal, dehalogenated hydrocarbon removal, and desiloxane removal in the fermentation system, thereby obtaining high-quality biogas and functional biogas slurry. Attached Figure Description

[0034] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0035] Figure 1 This is a schematic diagram of the fermentation system structure in this invention; The components are as follows: 1. Feed pump; 2. First feed valve; 3. Pretreatment section; 4. Top-entry agitator; 5. First level gauge; 6. Safety valve; 7. First filter; 8. Desulfurization section; 9. Second feed valve; 10. Return pump; 11. Liquid distributor; 12. First discharge pipe; 13. Return pipe; 14. Second filter; 15. First control line assembly; 16. Back pressure valve; 17. Gas outlet valve; 18. Gas storage tank; 19. First control valve; 20. First agitator; 21. First float valve assembly; 22. Third feed valve; 23. Second level gauge; 24. Hydrolysis section; 25. Second control valve; 26. Second control line assembly. 27. Second agitator; 28. Third filter; 29. ​​Second float valve assembly; 30. Fourth feed valve; 31. Third level gauge; 32. Acid production section; 33. Third control valve; 34. Third control line assembly; 35. Third agitator; 36. Fourth filter; 37. Third float valve assembly; 38. Fifth feed valve; 39. Fourth level gauge; 40. Methanogenic section; 41. Fourth control valve; 42. Fourth control line assembly; 43. Fourth agitator; 44. Fifth filter; 45. Discharge valve; 46. Discharge pump; 47. Biogas slurry storage tank; 48. First gas guide pipe; 49. Second gas guide pipe; 50. Third gas guide pipe. Detailed Implementation

[0036] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Specific conditions not specified in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Components whose manufacturers are not specified are all commercially available conventional products.

[0037] Example 1 A biogas fermentation system, such as Figure 1 As shown, the biogas fermentation system includes, from top to bottom, a pretreatment section 3, a desulfurization section 8, a hydrolysis section 24, an acid production section 32, and a methanogenic section 40.

[0038] The pretreatment section 3 has a cylindrical cavity structure for pretreating raw materials, including soaking, mild hydrolysis, and mild fermentation. The top of the pretreatment section 3 is equipped with an inlet and a safety valve 6. The inlet is connected to the feed pump 1 via a pipe equipped with a first feed valve 2. The safety valve 6 is used for venting, and its set venting pressure is 0.25-0.45 MPa. A top-entry agitator 4 is located at the top of the pretreatment section 3, a first level gauge 5 is located on the side wall of the pretreatment section 3, and a first filter 7 is located at the bottom of the pretreatment section 3. The top-entry agitator 4 is an existing structure and can be a turbine agitator or a paddle agitator to improve the mixing uniformity of the raw materials. The first level gauge 5 is an existing structure used to monitor changes in the liquid level within the pretreatment section 3. The first filter 7 is an existing structure used to filter impurities from the pretreated raw materials. The bottom of the pretreatment section 3 is provided with a first discharge pipe 12, and the first discharge pipe 12 is provided with a first control valve 19, which is connected to the first control line group 15. The first discharge pipe 12 is used to transport the pretreated raw materials in the pretreatment section 3 to the desulfurization section 8 for desulfurization treatment.

[0039] The desulfurization section, hydrolysis section, and acid-producing section are all equipped with an outer bottom shell. A first gas guide pipe 48 for gas passage is provided between the desulfurization section 8 and the hydrolysis section 24. The two ends of the first gas guide pipe 48 are connected to the outer bottom shell of the desulfurization section 8 and the top of the hydrolysis section 24, respectively. A second gas guide pipe 49 for gas passage is provided between the hydrolysis section 24 and the acid-producing section 32. The two ends of the second gas guide pipe 49 are connected to the outer bottom shell of the hydrolysis section 24 and the top of the acid-producing section 32, respectively. A third gas guide pipe 50 for gas passage is provided between the acid-producing section 32 and the methanogenic section 40. The two ends of the third gas guide pipe 50 are connected to the outer bottom shell of the acid-producing section 32 and the top of the methanogenic section 40, respectively.

[0040] The desulfurization section 8 has a cylindrical cavity structure for desulfurizing the pretreated raw materials. It also consumes dissolved oxygen in the fermentation raw materials, thus reducing the dissolved oxygen concentration and consequently lowering the oxygen content in the biogas. A liquid distributor 11 is located at the top of the desulfurization section 8. The liquid distributor 11 improves the uniform dispersion of the fermentation raw materials. The first discharge pipe 12 at the bottom of the pretreatment section 3 passes through the liquid distributor 11 to the middle of the desulfurization section 8, allowing the material to come into countercurrent contact with the feed and biogas in the lower layer of the desulfurization section 8, thereby improving the desulfurization effect. A first agitator 20 is located on the side wall of the desulfurization section 8 to improve the uniformity of material dispersion within the desulfurization section 8. The bottom of the desulfurization section 8 is equipped with a second filter 14, a second discharge pipe, a return pipe 13, and a first float valve assembly 21. A second control valve 25 is installed on the second discharge pipe, and the second control valve 25 is connected to a second control line assembly 26. The second discharge pipe is used to transport the desulfurization products to the hydrolysis section 24 for hydrolysis treatment. The return pipe 13 is connected in sequence to the return pump 10 and the liquid distributor 11. In addition, a feed pipe is provided at the top of the desulfurization section 8, with a second feed valve 9 on it. The feed pipe is connected to the liquid distributor 11, thereby achieving countercurrent contact between the feed and biogas, thus improving the desulfurization effect. Furthermore, the desulfurization process in the lower layer of the desulfurization section 8 has already consumed most of the dissolved oxygen in the fermentation feedstock. The recirculated feedstock discharged from the bottom of the desulfurization section 8 is used for the desulfurization of the fermentation feedstock in the desulfurization section 8, preventing dissolved oxygen in the fermentation feedstock from entering the biogas, thus making the desulfurization more complete.

[0041] The H2S is circulated back to the inlet of desulfurization section 8 and mixed with the mainstream low-concentration biogas, which can significantly dilute the inlet H2S concentration, allowing the desulfurization system to operate under more stable and efficient conditions. A biogas discharge pipe is also installed on the top side wall of desulfurization section 8, which is connected in sequence to back pressure valve 16, outlet valve 17, and gas storage tank 18. The set discharge pressure of back pressure valve 16 is 0.2-0.4 MPa; the set discharge pressure of safety valve 6 is 0.05 MPa higher than that of back pressure valve 16.

[0042] The hydrolysis section 24 has a cylindrical cavity structure, used to decompose the desulfurized fermentation raw materials into small molecules that can be directly utilized by microorganisms. The reactions occurring in this stage mainly include physical crushing, chemical hydrolysis, and biological acidification. A feed inlet is located on the top side wall of the hydrolysis section 24, connected to a pipe equipped with a third feed valve 22. A second level gauge 23 is also located on the side wall of the hydrolysis section 24 to monitor the liquid level within it. A second agitator 27 is located on the other side wall of the hydrolysis section 24 to improve the uniformity of material dispersion within it. The bottom of the hydrolysis section 24 is equipped with a third filter 28, a second float valve assembly 29, and a third discharge pipe; a third control valve 33 is located on the third discharge pipe and connected to a third control line assembly 34. The third filter 28 is used to filter impurities within the hydrolysis section 24. The second gas guide pipe 49 and the second float valve assembly 29 are used to return biogas from the top of the acid-producing section 32 to the hydrolysis section 24. The third discharge pipe is used to transport the hydrolyzed material in the hydrolysis section 24 to the acid-producing section 32 for acid production treatment.

[0043] The acid-producing section 32 has a cylindrical cavity structure, used to further convert the hydrolyzed material into volatile fatty acids, alcohols, hydrogen, and carbon dioxide, providing direct substrates for subsequent methanogenic bacteria. An inlet is located on the top side wall of the acid-producing section 32, connected to a pipe equipped with a fourth feed valve 30. A third level gauge 31 is also located on the side wall of the acid-producing section 32, used to monitor the liquid level within the section. A third agitator 35 is located on the other side wall of the acid-producing section 32, used to improve the uniformity of material dispersion within the section. The bottom of the acid-producing section 32 is equipped with a fourth filter 36, a third float valve assembly 37, and a fourth discharge pipe; a fourth control valve 41 is located on the fourth discharge pipe, connected to a fourth control line assembly 42. The fourth filter 36 is used to filter impurities within the acid-producing section 32. The third gas guide pipe 50 and the third float valve assembly 37 are used to return biogas from the top of the methanogenic section 40 to the acidogenic section 32. The fourth discharge pipe is used to transport the material after acidification in the acidogenic section 32 to the methanogenic section 40 for methanogenic treatment.

[0044] The methanogenic section 40 has a cylindrical cavity structure for converting the acidified material into methane. An inlet is located on the top side wall of the methanogenic section 40, connected to a pipe equipped with a fifth feed valve 38. A fourth level gauge 39 is also located on the side wall of the methanogenic section 40 to monitor the liquid level within it. A fourth agitator 43 is located on the other side wall of the methanogenic section 40 to improve the uniformity of material dispersion within it. A fifth filter 44 and a discharge pipe are located at the bottom of the methanogenic section 40; the discharge pipe is equipped with a discharge valve 45 and is connected in sequence to a discharge pump 46 and a biogas slurry storage tank 47.

[0045] Among them, the pretreatment section 3, desulfurization section 8, hydrolysis section 24, acid production section 32 and methanogenic section 40 have the same internal diameter of 1.0 meter and volumes of 1.5 cubic meters, 3.0 cubic meters, 1.5 cubic meters, 1.5 cubic meters and 2.5 cubic meters respectively.

[0046] The first filter 7, the second filter 14, the third filter 28, the fourth filter 36, and the fifth filter 44 are all existing structures. They can be bottom-up porous stainless steel cup-shaped filters with a diameter of 0.20 meters, a height of 0.10 meters, an aperture of 10 mm, and an opening rate of 30%.

[0047] The float valve structure of the first float valve group 21, the second float valve group 29, and the third float valve group 37 can adopt the float valve components in a conventional float valve tower. When the pressure at the bottom of the float valve is greater than the pressure at the top of the float valve, the float valve is in the open state to allow the gas at the bottom to pass through. When the pressure at the bottom of the float valve is less than the pressure at the top of the float valve, the float valve is in the closed state. The first control line group 15, the second control line group 26, the third control line group 34, and the fourth control line group 42 include power lines and signal lines.

[0048] It also includes packing material for adsorbing gases and enhancing gas-liquid mass transfer.

[0049] Packing material is also provided in desulfurization section 8, hydrolysis section 24, acid production section 32, and methanogenesis section 40. The packing material is used to adsorb gas and enhance gas-liquid mass transfer. Among them, the packing material in desulfurization section 8 is pre-coated with desulfurizing bacteria. The coating method is in accordance with the reference: Xu Haipeng, Li Yan, Mu Hui, et al. Characteristics of H2S removal from gas by immobilized sulfur-depleting bacteria [J]. Journal of Environmental Engineering, 2018, 12(11): 3109-3115. The height of the packing material in desulfurization section 8 is 1.5 meters. The desulfurization section is filled with packing material A, packing material B, and packing material C in a volume ratio of 6:2:2, and the total volume of the three packing materials accounts for 75% of the volume of the desulfurization section.

[0050] In the hydrolysis section, packing material A, packing material B, and packing material C are added in a volume ratio of 2:4:4, and the total volume of the three packing materials accounts for 75% of the volume of the desulfurization section.

[0051] The packing material in the acid-producing section consists of packing material A, packing material B, and packing material C added in a volume ratio of 2:3:5, with the total volume of the three packing materials accounting for 75% of the volume of the desulfurization section.

[0052] The packing material in the methanogenic section consists of packing material A, packing material B, and packing material C added in a volume ratio of 3:3:4, with the total volume of the three packing materials accounting for 75% of the desulfurization section volume.

[0053] Filler A: The outer layer is a porous wear-resistant layer, and the inner layer is a hollow plastic sphere. The porous wear-resistant layer is formed by two interlocking porous hemispheres of 304 stainless steel, with a layer thickness of 0.5 mm, an inner diameter of 20 mm, an opening diameter of 4 mm, and an opening rate of 30%. Filler A is composed of 20% filler A1, 20% filler A2, 20% filler A3, 20% filler A4, 10% filler A5, and 10% filler A6. The diameters of fillers A1, A2, A3, A4, A5, and A6 are all 20 mm, and the opening diameters are all 4 mm. Other parameters are shown in Table 1. Table 1 Performance parameters of packings A1-A6

[0054] Filler B: The outer layer is a porous wear-resistant layer, and the inner layer is a hollow plastic sphere loaded with silicone. The porous wear-resistant layer is formed by two interlocking porous hemispheres of 304 stainless steel, with a layer thickness of 0.5 mm, an inner diameter of 20 mm, an opening diameter of 4 mm, and an opening rate of 30%. The diameter of the hollow plastic sphere is 20 mm. Filler B is composed of 30% filler B1, 30% filler B2, 20% filler B3, 10% filler B4, and 10% filler B5. The diameters of fillers B1, B2, B3, B4, and B5 are all 20 mm, and the opening diameters are all 4 mm. Other parameters are shown in Table 2. Table 2 Performance parameters of packings B1-B5

[0055] The method for making hollow plastic spheres loaded with silica gel is as follows: Add sodium silicate aqueous solution to a container containing hollow plastic spheres in proportion, filter, add the hollow plastic spheres to dilute hydrochloric acid, stir, filter out the hollow plastic spheres, wash with water until neutral, and then dry.

[0056] Filler C: The outer layer is a porous wear-resistant layer, and the inner layer is a hollow plastic sphere loaded with silica gel and TiO2. The porous wear-resistant layer is formed by two interlocking polytetrafluoroethylene porous hemispheres, with a layer thickness of 1.0 mm, an inner diameter of 20 mm, an opening diameter of 3 mm, and an opening rate of 30%. Filler C is composed of 40% filler C1, 30% filler C2, 20% filler C3, 5% filler C4, and 5% filler C5. The diameters of fillers C1, C2, C3, C4, and C5 are all 20 mm, and the opening diameters are all 4 mm. Other parameters are shown in Table 3. Table 3 Performance parameters of packings C1-C5

[0057] The manufacturing method of the plastic hollow spheres in fillers A, B, and C is as follows: Polypropylene powder, polystyrene powder, and sodium chloride powder are added to a container in proportion, wherein the mass of sodium chloride powder is 20% of the sum of the masses of polypropylene powder and polystyrene powder; the mixture is heated to 240℃ under thorough stirring, then molded, cooled and demolded, washed with water until no precipitate is observed when added dropwise with a 0.01 mol / L silver nitrate aqueous solution, and then dried at 80℃ for 24 hours. Sodium chloride powder is added during processing to increase the specific surface area of ​​the filler; the diameter of the plastic hollow spheres is 20 mm.

[0058] The method for preparing silicone-loaded hollow plastic spheres is as follows: Vacuum the container containing the hollow plastic spheres to -0.099 MPa. Add a 25% sodium silicate aqueous solution through a separatory funnel, with a volume ratio of sodium silicate aqueous solution to hollow plastic spheres of 2:1. After stirring for 6 hours, filter out the hollow plastic spheres and add them to a 3.0% dilute hydrochloric acid solution, with a volume ratio of dilute hydrochloric acid to hollow plastic spheres of 2:1. After stirring for 6 hours, filter out the hollow plastic spheres and wash them with deionized water until neutral, then dry them.

[0059] The method for preparing hollow plastic spheres loaded with silica gel and TiO2 is as follows: First, prepare hollow plastic spheres loaded with silica gel according to the method described in "Preparation Method of Filler B"; add the dried hollow spheres to a 30% cyclohexane solution of tetrabutyl titanate, with a volume ratio of solution to hollow spheres of 2:1, soak for 6 hours, filter, remove and allow to hydrolyze naturally in air at room temperature for 48 hours, and then dry at 80℃ for 24 hours.

[0060] Loading a silica gel layer onto the hollow plastic spheres is to adsorb more hydrophilic gases; loading TiO2 is to promote photochemical reactions between the fermentation broth and the gases.

[0061] The hollow plastic spheres in packings A, B, and C are made of a blend of polypropylene and polystyrene and are manufactured by compression molding. Different mass ratios are used to make the packings have different densities, so that they can form a uniform distribution in the upper, middle, and lower layers of the desulfurization, hydrolysis, acid production, and methanogenesis sections, rather than floating entirely in the upper layer or settling in the lower layer.

[0062] The packing volume accounts for 75-85% of the volume of the desulfurization section, hydrolysis section, acid production section, and methanogenesis section, respectively. Such a large packing volume fraction is not used in conventional biogas fermentation, nor is it necessary. The present invention uses such a large packing volume fraction so that the packing can act as a packing tower to promote gas-liquid mass transfer, and the entire system can achieve the purpose of simultaneous fermentation and biogas purification. When the fermentation liquid comes into contact with the static packing, it is easy to cause blockage. Therefore, the present invention uses spherical wear-resistant packing, which can not only act as a packing tower under the action of stirring, but also allows the deposits generated on the wear-resistant packing to fall off quickly, making it less prone to blockage.

[0063] Example 2 A biogas fermentation system is described in this embodiment. The similarities to Embodiment 1 will not be repeated here, but the differences are as follows: The desulfurization section is filled with packing material A, packing material B, and packing material C in a volume ratio of 6:2:2, and the total volume of the three packing materials accounts for 85% of the volume of the desulfurization section.

[0064] In the hydrolysis section, packing material A, packing material B, and packing material C are added in a volume ratio of 2:4:4, and the total volume of the three packing materials accounts for 85% of the volume of the desulfurization section.

[0065] The packing material in the acid-producing section consists of packing material A, packing material B, and packing material C added in a volume ratio of 2:3:5, with the total volume of the three packing materials accounting for 85% of the volume of the desulfurization section.

[0066] The packing material in the methanogenic section consists of packing material A, packing material B, and packing material C added in a volume ratio of 3:3:4, with the total volume of the three packing materials accounting for 85% of the desulfurization section volume.

[0067] Example 3 A biogas fermentation system is described in this embodiment. The similarities to Embodiment 1 will not be repeated here, but the differences are as follows: The desulfurization section is filled with packing material A, packing material B, and packing material C in a volume ratio of 6:2:2, and the total volume of the three packing materials accounts for 80% of the volume of the desulfurization section.

[0068] In the hydrolysis section, packing material A, packing material B, and packing material C are added in a volume ratio of 2:4:4, and the total volume of the three packing materials accounts for 80% of the volume of the desulfurization section.

[0069] The packing material in the acid-producing section consists of packing material A, packing material B, and packing material C added in a volume ratio of 2:3:5, with the total volume of the three packing materials accounting for 80% of the volume of the desulfurization section.

[0070] The packing material in the methanogenic section consists of packing material A, packing material B, and packing material C added in a volume ratio of 3:3:4, with the total volume of the three packing materials accounting for 80% of the volume of the desulfurization section.

[0071] Example 4 A biogas fermentation system is described in this embodiment. The similarities between this embodiment and Embodiment 3 will not be repeated here, but the differences are as follows: The pretreatment section 3, desulfurization section 8, hydrolysis section 24, acid production section 32, and methanogenesis section 40 are all made of plexiglass, with the same internal diameter of 0.1 meters and a volume of 3.5 liters. There are no first control line group 15, second control line group 26, third control line group 34, or fourth control line group 42; no first filter 7, second filter 14, third filter 28, fourth filter 36, or fifth filter 44; no first level gauge 5, second level gauge 23, third level gauge 31, or fourth level gauge 39; and no top-entry agitator 4, first agitator 20, second agitator 27, third agitator 35, or fourth agitator 43.

[0072] Example 5 A biogas fermentation method using the biogas fermentation system in Example 1 includes the following steps: (1) The fermentation raw materials enter the pretreatment section 3 for soaking through the feed pump 1 and the first feed valve 2. The top-entry agitator 4 discharges the gas in the fermentation raw materials under the stirring action of 15 revolutions / minute, so that the fermentation raw materials are evenly dispersed and mild hydrolysis and mild fermentation are carried out at the same time. When the pressure of the pretreatment section 3 is greater than the set pressure of the safety valve 6 (the set exhaust pressure is 0.35 MPa), exhaust is performed. When the liquid level displayed by the first liquid level gauge 5 is greater than the liquid level set by the pretreatment section 3 (the set liquid level is 1.2 cubic meters), the first control line group 15 controls the first control valve 19 to open for material discharge.

[0073] The fermentation raw material is kitchen waste (from the canteen of Qilu University of Technology). Paper towels, bones and other materials are selected, the floating oil is removed, and the waste is crushed. During the crushing and discharge process, the waste is passed through a 10-mesh sieve, and the lower layer of material is taken as the fermentation raw material. Before feeding, the waste is diluted with tap water to form a suspension with a solid content of 5%.

[0074] (2) The material discharged from the pretreatment section 3 passes through the first discharge pipe 12 at a flow rate of 25 kg / h, enters the middle of the desulfurization section 8 through the first filter 7, and comes into countercurrent contact with biogas in the lower layer of the desulfurization section 8. Part of the material discharged from the desulfurization section 8 enters the hydrolysis section 24 through the second control valve 25; the other part of the material discharged from the desulfurization section 8 is discharged from the bottom of the desulfurization section 8 and returned to the upper part of the desulfurization section 8 to the liquid distributor 11 via the return pump 10, where it comes into countercurrent contact with biogas in the desulfurization section 8; the biogas is discharged from the upper part of the side wall of the desulfurization section 8 and enters the gas storage tank 18 in sequence via the back pressure valve 16 and the gas outlet valve 17; the set exhaust pressure of the back pressure valve 16 is 0.3 MPa; the second control line group 26 controls the discharge rate of the desulfurization section 8 by controlling the second control valve 25, and the biogas enters the desulfurization section 8 from the top of the hydrolysis section 24 via the first float valve group 21.

[0075] The desulfurization section 8 is stirred by the first agitator 20 at a speed of 15 revolutions per minute.

[0076] The second feed valve 9 is used to transport papermaking black liquor in the desulfurization section 8 to adjust the pH value of the material to 7.4. The papermaking black liquor is provided by the Key Laboratory of Bio-based Materials and Green Papermaking of Qilu University of Technology. It is a high-concentration organic wastewater obtained by using corn stalks as raw material and sulfite pulping process. It is rich in lignin derivatives and has a COD of 62,000 mg / L and a pH value of 12.5.

[0077] The packing material in desulfurization section 8 was pre-coated with desulfurizing bacteria. The coating method followed the reference: Xu Haipeng, Li Yan, Mu Hui, et al. Characteristics of H2S removal from gas by immobilized Thiobacillus thiocyanate [J]. Journal of Environmental Engineering, 2018, 12(11): 3109-3115; the desulfurizing bacteria used were Thiobacillus thiocyanate (accession number ATCC8158), which is suitable for growth in a neutral environment.

[0078] (3) The black liquor from papermaking enters the hydrolysis section 24 through the third feed valve 22 to adjust the pH value of the material to 8.1. The hydrolysis section 24 is stirred by the second agitator 27 at a stirring speed of 15 rpm, and the raw material is hydrolyzed in an alkaline environment. Biogas enters the desulfurization section 8 from the top of the hydrolysis section 24 through the first float valve group 21.

[0079] When the liquid level displayed by the second liquid level gauge 23 is higher than the liquid level set in the hydrolysis section 24 (set liquid level is 1.2 cubic meters), the third control line group 34 controls the third control valve 33 to open for discharge. Biogas enters the hydrolysis section 24 from the top of the acid production section 32 through the second float valve group 29.

[0080] (4) The material discharged from the hydrolysis section 24 enters the acid-producing section 32; 100 kg of acclimated anaerobic sludge and papermaking black liquor are added to the acid-producing section 32. The acclimation method of the anaerobic sludge is as follows: the anaerobic sludge raw material (taken from the anaerobic fermentation device of sugar wastewater of Shandong Xingguang Sugar Industry Co., Ltd.) is acclimated. The nitrogen source and phosphorus source are provided in the form of NH4Cl and KH2PO4, respectively, to meet the COD:N:P=100:5:1. The raw material and inoculum are placed in a 1.0 L serum bottle and cultured under mesophilic conditions (35℃) for 30 days (one fermentation cycle). The gas production is observed. This process is repeated for 4 cycles and then used as the inoculum for the acid-producing section 32. The material discharged from the acid-producing section 32 passes through the fourth filter 36 and the fourth control valve 41 in sequence and enters the methanogenic section 40.

[0081] When the liquid level displayed by the third liquid level gauge 31 is higher than the liquid level set in the acid production section 32 (set liquid level is 1.2 cubic meters), the fourth control line group 42 controls the fourth control valve 41 to open for discharge. Biogas enters the acid production section 32 from the top of the methane section 40 through the third float valve group 37.

[0082] The black liquor from papermaking enters the acid-producing section 32 through the fourth feed valve 30 to adjust the pH value of the material to 6.3. The acid-producing section 32 is stirred by the third agitator 35 at a speed of 15 revolutions per minute.

[0083] (5) The material discharged from the acid-producing section 32 enters the methanogenic section 40; 100 kg of acclimated anaerobic sludge and papermaking black liquor are added to the methanogenic section 40. The acclimation method of anaerobic sludge is as follows: the anaerobic sludge raw material (taken from the anaerobic fermentation device of sugar wastewater of Shandong Xingguang Sugar Industry Co., Ltd.) is acclimated. The nitrogen source and phosphorus source are provided in the form of NH4Cl and KH2PO4 respectively, satisfying COD:N:P=100:5:1. The raw material and inoculum are placed in a 1.0 L serum bottle and cultured under medium temperature conditions (35℃) for 30 days (one fermentation cycle). The gas production status is observed. This process is repeated for 4 cycles and then used as the inoculum for the acid-producing section 32.

[0084] When the liquid level displayed by the fourth liquid level gauge 39 is greater than the liquid level set by the methanogenic section 40 (the set liquid level is 2.0 cubic meters), the fourth control line group 42 controls the fourth control valve 41 to open for discharge. The material passes through the fifth filter 44, the discharge valve 45 and the discharge pump 46 in sequence before reaching the biogas slurry storage tank 47.

[0085] The black liquor from papermaking enters the methanogenic section 40 through the fifth feed valve 38 to adjust the pH value of the material to 7.2. The methanogenic section 40 is stirred by the fourth agitator 43 at a speed of 15 revolutions per minute.

[0086] The biogas fermentation system was run for 480 hours, and the composition of biogas was determined by gas chromatography (the determination method was in accordance with the reference: Bian Wenfan, Wang Yanqin, Zhang Changai, et al. Research on the optimized method of gas chromatography for biogas composition determination [J]. Shandong Agricultural Sciences, 2011, (4): 93-95).

[0087] The results showed that the CH4 concentration in biogas was 64.50% (volume percentage, the same below), CO2 concentration was 33.10%, H2S concentration was 0.02%, oxygen concentration was 0.04%, and the concentrations of ammonia, thiols, halogenated hydrocarbons and siloxanes were 0.00%, with other gases accounting for 2.34%. The elemental sulfur content in biogas slurry was determined by spectrophotometry according to the reference: Li Junxing, Zhang Keqiang, Ji Min, et al. Spectrophotometric determination of elemental sulfur content in microbial treatment of sulfide-containing wastewater [J]. Journal of Agricultural Environmental Science, 2006, 25(1): 261-265. The results showed that the elemental sulfur content in biogas slurry was 0.082 g / L.

[0088] Generally, the methane content in biogas ranges from 50% to 80% depending on the raw materials, and biogas used for power generation typically requires a methane content of no less than 55% to 60%. The biogas produced in this embodiment has a CH4 concentration of 64.50%, which meets the requirements for biogas used in power generation.

[0089] Example 6 The biogas fermentation method of the biogas fermentation system in Example 2 is adopted. The similarities between this example and Example 5 will not be repeated here. The differences are as follows: The fermentation raw material is fruit and vegetable processing waste from a fruit and vegetable planting base in Shouguang City. The waste is crushed and passed through a 10-mesh sieve during the crushing process, with the lower layer used as the fermentation raw material. Before feeding, it is diluted with starch processing wastewater to form a suspension with a solid content of 5%. The starch processing wastewater is generated by a starch production enterprise in Jinan, with a pH of 5.1, CODcr of 18000 mg / L, BOD5 of 8000 mg / L, and SS of 3000 mg / L. The suspension is added to pretreatment section 3 until the material volume in pretreatment section 3 reaches 1.2 cubic meters and the corresponding liquid level is maintained. The set exhaust pressure of safety valve 6 is 0.25 MPa, and the set exhaust pressure of back pressure valve 16 is 0.2 MPa. The stirring speed of the first agitator 20, the second agitator 27, the third agitator 35, and the fourth agitator 43 is all 5 rpm.

[0090] The biogas fermentation system was run for 480 hours. The composition of biogas was determined by gas chromatography (the determination method was based on the reference: Bian Wenfan, Wang Yanqin, Zhang Changai, et al. Research on the optimized method of gas chromatography for determining biogas components [J]. Shandong Agricultural Sciences, 2011, (4): 93-95). The results showed that the concentration of CH4 in biogas was 64.09% (volume percentage, the same below), the concentration of CO2 was 33.21%, the concentration of H2S was 0.01%, the concentration of oxygen was 0.05%, the concentrations of ammonia, thiols, halogenated hydrocarbons and siloxanes were 0.00%, and the content of other gases accounted for 2.64%. The content of elemental sulfur in biogas slurry was determined by spectrophotometry (the determination method was based on the reference: Li Junxing, Zhang Keqiang, Ji Min, et al. Spectrophotometric determination of elemental sulfur content in microbial treatment of sulfide-containing wastewater [J]. Journal of Agricultural Environmental Science, 2006, 25(1): (261-265), the results showed that the elemental sulfur content in the biogas slurry was 0.047 g / L.

[0091] Example 7 The biogas fermentation method of the biogas fermentation system in Example 3 is used. The similarities between this example and Example 5 will not be repeated here. The differences are as follows: The source and treatment method of kitchen waste are the same as in Example 5, and the source and treatment method of fruit and vegetable processing waste are the same as in Example 6; the source and parameters of starch processing wastewater are the same as in Example 6; the fermentation raw material is a mixture of kitchen waste and fruit and vegetable processing waste in a mass ratio of 6:4, which is diluted with starch processing wastewater to a suspension with a solid content of 5%, and then added to the pretreatment section 3 until the material in the pretreatment section 3 reaches 1.2 cubic meters and is maintained at the corresponding liquid level; the set exhaust pressure of safety valve 6 is 0.25 MPa, and the set exhaust pressure of back pressure valve 16 is 0.2 MPa; the stirring speed of the first stirrer 20, the second stirrer 27, the third stirrer 35, and the fourth stirrer 43 is 10 rpm. The gas generated in the methanogenic section 40 enters the acidogenic section 32 through the third gas guide pipe 50, the gas in the acidogenic section 32 enters the hydrolysis section 24 through the second gas guide pipe 49, and the gas in the hydrolysis section 24 enters the desulfurization section 8 through the first gas guide pipe 48.

[0092] The biogas fermentation system was run for 480 hours, and the composition of biogas was determined by gas chromatography (the determination method was in accordance with the reference: Bian Wenfan, Wang Yanqin, Zhang Changai, et al. Research on the optimized method of gas chromatography for biogas composition determination [J]. Shandong Agricultural Sciences, 2011, (4): 93-95).

[0093] The results showed that the CH4 concentration in biogas was 64.55% (volume percentage, the same below), CO2 concentration was 33.36%, H2S concentration was 0.01%, oxygen concentration was 0.04%, and the concentrations of ammonia, thiols, halogenated hydrocarbons and siloxanes were 0.00%, with other gases accounting for 2.04%. The elemental sulfur content in biogas slurry was determined by spectrophotometry according to the reference: Li Junxing, Zhang Keqiang, Ji Min, et al. Spectrophotometric determination of elemental sulfur content in microbial treatment of sulfide-containing wastewater [J]. Journal of Agricultural Environmental Science, 2006, 25(1): 261-265. The results showed that the elemental sulfur content in biogas slurry was 0.071 g / L.

[0094] In Examples 5, 6, and 7, the larger the proportion of the packing volume to the volume of the desulfurization section, hydrolysis section, acid production section, and methanogenesis section, the greater the resistance to stirring. Therefore, the stirring speed of the first stirrer 20, the second stirrer 27, the third stirrer 35, and the fourth stirrer 43 is also smaller. Thus, the proportion of the packing volume to the volume of the desulfurization section, hydrolysis section, acid production section, and methanogenesis section is controlled at a maximum of 85%. Further increasing this proportion will hinder stirring, leading to the accumulation of products on the packing and consequently causing reactor blockage.

[0095] Example 8 The biogas fermentation method of the biogas fermentation system in Example 4 is used. The similarities between this example and Example 7 will not be repeated here. The differences are as follows: The source and treatment method of kitchen waste are the same as in Example 5, and the source and treatment method of fruit and vegetable processing waste are the same as in Example 6. The fermentation raw material is a mixture of kitchen waste and fruit and vegetable processing waste in a mass ratio of 6:4, which is diluted with tap water to form a suspension with a solid content of 5%. Then, it is added to the pretreatment section 3 until the material in the pretreatment section 3 reaches 3.0 liters and the corresponding liquid level is maintained.

[0096] The liquid levels in the pretreatment section 3, desulfurization section 8, hydrolysis section 24, acid-producing section 32, and methanogenic section 40 are directly observed by manually controlling the first control valve 19, the second control valve 25, the third control valve 33, and the fourth control valve 41. Since there are no top-entry agitators 4, 20, 27, 35, and 43, direct stirring is not possible. Instead, intermittent aeration is performed using an air pump. Gas from the upper part of the pretreatment section 3 is pumped into the lower solution of the pretreatment section 3 using an air pump (diaphragm pump, model AD30KEEDBW12, manufactured by Yuanxun Intelligent Technology (Shanghai) Co., Ltd.) at a gas velocity of 20 liters / minute, for 15 minutes every 24 hours. Gas from the upper part of the desulfurization section 8 is then pumped... Gas is pumped into the lower part of the desulfurization section 8 via an air pump (diaphragm pump, same model and manufacturer as above) at a gas velocity of 20 liters / minute, for 15 minutes every 24 hours; gas from the upper part of the hydrolysis section 24 is pumped into the lower part of the hydrolysis section 24 via an air pump (diaphragm pump, same model and manufacturer as above) at a gas velocity of 20 liters / minute, for 15 minutes every 24 hours; gas from the upper part of the acid-producing section 32 is pumped into the lower part of the acid-producing section 32 via an air pump (diaphragm pump, same model and manufacturer as above) at a gas velocity of 20 liters / minute, for 15 minutes every 24 hours; gas from the upper part of the methanogenic section 40 is pumped into the lower part of the methanogenic section 40 via an air pump (diaphragm pump, same model and manufacturer as above) at a gas velocity of 20 liters / minute, for 15 minutes every 24 hours.

[0097] The material discharged from the pretreatment section 3 enters the desulfurization section 8 at a flow rate of 100 mL / h; Add 0.2 kg of acclimated anaerobic sludge and papermaking black liquor to acid-producing section 32, wherein the acclimation method of the anaerobic sludge is the same as the acclimation method of the anaerobic sludge added to acid-producing section 32 in Example 5. Add 0.2 kg of acclimated anaerobic sludge and papermaking black liquor to the methanogenic section 40, wherein the acclimation method of the anaerobic sludge is the same as the acclimation method of the anaerobic sludge added to the methanogenic section 40 in Example 5. The biogas fermentation system was run for 480 hours, and the composition of biogas was determined by gas chromatography (the determination method was in accordance with the reference: Bian Wenfan, Wang Yanqin, Zhang Changai, et al. Research on the optimized method of gas chromatography for biogas composition determination [J]. Shandong Agricultural Sciences, 2011, (4): 93-95).

[0098] The results showed that the CH4 concentration in biogas was 63.30% (volume percentage, the same below), CO2 concentration was 33.59%, H2S concentration was 0.01%, oxygen concentration was 0.03%, and the concentrations of ammonia, thiols, halogenated hydrocarbons and siloxanes were 0.00%, with other gases accounting for 3.07%. The elemental sulfur content in biogas slurry was determined by spectrophotometry according to the reference: Li Junxing, Zhang Keqiang, Ji Min, et al. Spectrophotometric determination of elemental sulfur content in microbial treatment of sulfide-containing wastewater [J]. Journal of Agricultural Environmental Science, 2006, 25(1): 261-265. The results showed that the elemental sulfur content in biogas slurry was 0.045 g / L.

[0099] In Example 8, the biogas fermentation system device was designed for laboratory use and still achieved good biogas fermentation results.

[0100] Comparative Example 1 Biogas fermentation was carried out using a 2.0 cubic meter conventional fermentation tank (manufacturer: Beijing Mancang Technology Co., Ltd., model MC-MSF-2T), including the following steps: The fermentation raw material is kitchen waste, and the source and treatment method are the same as in Example 5; a suspension with a solid content of 5% is added to the fermentation tank to make the material in the fermentation tank reach 1.5 cubic meters and maintain the corresponding liquid level; Add 100 kg of acclimated anaerobic sludge to the fermenter. Acclimation method: Acclimate the anaerobic sludge raw material (taken from the anaerobic fermentation device of sugar wastewater of Shandong Xingguang Sugar Industry Co., Ltd.). Nitrogen source and phosphorus source are provided in the form of NH4Cl and KH2PO4 respectively, satisfying COD:N:P=100:5:1. Place the raw material and inoculum in a 1.0 L serum bottle and culture it under mesophilic conditions (35℃) for 30 days (one fermentation cycle). Observe the gas production. Repeat this process for 4 cycles and use it as inoculum for acid production section 32. Fermentation was carried out under stirring conditions at a stirring speed of 15 revolutions per minute.

[0101] The biogas fermentation system was run for 480 hours, and the composition of biogas was determined by gas chromatography (the determination method was in accordance with the reference: Bian Wenfan, Wang Yanqin, Zhang Changai, et al. Research on the optimized method of gas chromatography for biogas composition determination [J]. Shandong Agricultural Sciences, 2011, (4): 93-95).

[0102] The results showed that the concentration of CH4 in biogas was 52.74% (volume percentage, the same below), CO2 was 43.25%, H2S was 0.06%, oxygen was 0.31%, ammonia was 0.03%, thiol was 0.02%, halogenated hydrocarbons were 0.05%, siloxane was 0.01%, and other gases accounted for 3.53%. The elemental sulfur content in biogas slurry was determined by spectrophotometry according to the reference: Li Junxing, Zhang Keqiang, Ji Min, et al. Spectrophotometric determination of elemental sulfur content in microbial treatment of sulfide-containing wastewater [J]. Journal of Agricultural Environmental Science, 2006, 25(1): 261-265), and the elemental sulfur content in biogas slurry was 0.002 g / L.

[0103] Comparing Examples 5, 6, 7, 8 and Comparative Example 1, the results show that the fermentation system and method provided by the present invention can obtain high-quality biogas and biogas slurry with high elemental sulfur content. The biogas not only contains a high concentration of CH4 and a low concentration of CO2, but also has low concentrations of H2S, oxygen, ammonia, thiols, halogenated hydrocarbons and siloxanes. The concentration of dissolved H2S in the biogas slurry is also reduced accordingly, which reduces the odor of the biogas slurry. Furthermore, this biogas slurry containing elemental sulfur powder has a bactericidal and disinfecting effect and can be used as a functional fertilizer for agricultural pest control and soil improvement, thereby increasing the added value of the biogas slurry.

[0104] The fermentation systems provided in Examples 1, 2, 3, and 4 are all modular structures. However, the fermentation system of the present invention can also adopt an integrated, segmented structural design, that is, the pretreatment section, desulfurization section, hydrolysis section, acid production section, and methanogenesis section in the biogas fermentation process are integrated into one design to overcome the problems of large volume and large footprint of biogas fermentation containers.

[0105] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A biogas fermentation system, characterized in that, The biogas fermentation system includes, from top to bottom, a pretreatment section, a desulfurization section, a hydrolysis section, an acid production section, and a methanogenesis section; The pretreatment section is equipped with a first discharge pipe at the bottom, the desulfurization section is equipped with a liquid distributor at the top and a return pipe at the bottom, the first discharge pipe passes through the liquid distributor and is located inside the desulfurization section; the return pipe is connected to the liquid distributor. The desulfurization section, hydrolysis section, acid production section and methanation section are equipped with packing materials. The bottom of the desulfurization section, hydrolysis section and acid production section are equipped with a float valve group, a discharge pipe and a gas guide pipe. The filler is composed of porous plastic balls A, silica-supported porous plastic balls B, and silica / TiO2 co-supported porous plastic balls C.

2. The biogas fermentation system according to claim 1, characterized in that, The pretreatment section, desulfurization section, hydrolysis section and acid production section are all equipped with control valves on the bottom discharge pipes, and feed pipes, level gauges and agitators are all equipped on the top side walls. The control valves are connected to the control line group.

3. The biogas fermentation system according to claim 1, characterized in that, The pretreatment section is equipped with a safety valve at the top and a first filter at the bottom, with the first filter located at the upper end of the first discharge pipe; The desulfurization section has a biogas discharge pipe on its side wall, and the feed pipe on the side wall is connected to the liquid distributor; the biogas discharge pipe is connected in sequence to the back pressure valve, the gas outlet valve and the gas storage tank. The side wall of the methanogenic section is equipped with a feed pipe, a level gauge and a stirrer, and the bottom is equipped with a filter and a discharge pipe; the discharge pipe is equipped with a discharge valve, which is connected in sequence to the discharge pump and the biogas slurry storage tank.

4. The biogas fermentation system according to claim 1, characterized in that, The packing volume accounts for 75-85% of the volume of the desulfurization section, hydrolysis section, acid production section, and methanogenesis section, respectively; The packing material in the desulfurization section is a mixture of A, B, and C in a volume ratio of (5-6):(2-3):(2-3); the packing material in the desulfurization section is a packing material for desulfurization bacteria to attach to a biofilm. The packing material in the hydrolysis section is a mixture of A, B, and C in a volume ratio of (2-3):(3-4):(3-4); The packing material in the acid-producing section is a mixture of A, B, and C in a volume ratio of (2-3):(3-4):(4-5); The packing material in the methanogenic section is a mixture of A, B, and C in a volume ratio of (3-4):(3-4):(4-5).

5. The biogas fermentation system according to claim 4, characterized in that, The density of porous plastic A in the filler is 0.95-1.05 g / cm³. 3 Specific surface area greater than 200 m² 2 / m 3 Diameter is 10-20 mm, opening ratio is 15%-35%, and aperture is 3-4 mm; The porous plastic balls B and C in the packing material are the same as those in A. The loading of silica gel in the filler B is 2 wt%-8 wt%; The loading of silica gel in the filler is 1.5 wt%-6 wt%, and the loading of TiO2 is 0.5 wt%-2 wt%.

6. A biogas fermentation method, characterized in that, The biogas fermentation system according to any one of claims 1-5 includes the following steps: Fermentation raw materials are added to the pretreatment section for hydrolysis and fermentation to obtain gas and slurry; Black liquor from papermaking is added to the desulfurization section and the hydrolysis section respectively for desulfurization and hydrolysis treatment, and gas and pulp are obtained respectively. Acclimated anaerobic sludge and papermaking black liquor were added to the acid-producing section and the methanogenic section, respectively, to carry out acid-producing and methanogenic treatments, and to obtain gas and pulp, respectively. When the liquid levels in the pretreatment section, desulfurization section, hydrolysis section, and production section are higher than the set liquid level, the slurry enters the next treatment section; When the gas obtained from hydrolysis, acid production, and methanogenesis exceeds the set pressure of the float valve assembly, the gas enters the upper treatment section through the gas guide pipe and the float valve assembly.

7. The biogas fermentation method according to claim 6, characterized in that, When the gas pressure in the pretreatment section is greater than the set pressure of the safety valve, venting is performed; When the liquid level in the desulfurization section is higher than the set liquid level, part of the desulfurized slurry is discharged to the hydrolysis section; the remaining part is returned to the desulfurization section through the return pipe for circulating desulfurization. When the gas pressure in the desulfurization section exceeds the set pressure of the back pressure valve, biogas is discharged. The desulfurization section, hydrolysis section, acid production section and methanogenesis section are also equipped with packing materials, wherein the packing material in the desulfurization section is a packing material for desulfurization bacteria to attach to a biofilm.

8. The biogas fermentation method according to claim 7, characterized in that, The fermentation raw materials are one or two of kitchen waste and fruit and vegetable processing waste; The safety valve is set to discharge pressure of 0.25-0.45 MPa; The set exhaust pressure of the safety valve is 0.05 MPa higher than that of the back pressure valve; The pH value of the desulfurization section is 7.0-7.5; The pH of the hydrolysis section is 8.0-8.5; The pH value of the acid-producing section is 6.0-6.5; The pH value of the methanogenic phase is 7.0-7.

5.

9. The biogas fermentation method according to claim 6, characterized in that, The preparation method of the porous plastic ball A in the filler is as follows: Polypropylene powder, polystyrene powder and sodium chloride powder are mixed, stirred evenly and heated, molded, cooled and demolded, washed with water and dried to obtain porous plastic balls; The mixing mass ratio of polypropylene powder and polystyrene powder is (1-9):5, and the amount of sodium chloride powder added is 15-20% of the total mass of polypropylene powder and polystyrene powder; the heating temperature is 235-245℃, and the drying is carried out at 75-85℃ for 20-24 hours. The acclimation method for the acclimated anaerobic sludge added to the acidogenic or methanogenic stage is as follows: Nitrogen and phosphorus sources are added to the anaerobic sludge raw material, and the mixture is inoculated into a serum bottle and cultured at 30-35℃ for 4 fermentation cycles to obtain the product. The nitrogen and phosphorus sources are provided in the form of NH4Cl and KH2PO4, respectively, with COD:N:P = 100:(4-5):1, and one fermentation cycle is 30 days.

10. The biogas fermentation method according to claim 6, characterized in that, The biogas contains CH4 at a volume concentration greater than 64.50%, CO2 at a volume concentration less than 33.10%, H2S at a volume concentration less than 0.02%, oxygen at a volume concentration less than 0.04%, ammonia, thiols, halogenated hydrocarbons and siloxanes at a volume concentration of 0.00%, and other gases at a volume concentration less than 2.34%; the biogas slurry contains elemental sulfur.

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