Method for preparing biochar by blending and hydrothermally carbonizing sludge and straw

Abstract

The present invention relates to the technical field of municipal sludge and industrial sludge treatment methods. Disclosed is a hydrothermal carbonization-based method for comprehensively treating iron-containing sludge and straw, comprising the following steps: 1) crushing and sieving straw, primarily dehydrating iron-containing sludge, and adding a catalyst for catalytic wet oxidation treatment; 2) adding wet-oxidized iron-containing sludge and a crushed and sieved fiber to a raw material storage tank and adding a dehydrating agent for dehydration treatment; 3) preheating a raw material conveying tank and then feeding the material into a reactor for a hydrothermal carbonization reaction; 4) collecting the resulting biochar slurry to a collecting tank for cooling; and 5) adding an appropriate amount of pulverized coal to the material and then carrying out plate press dehydration, or directly carrying out plate press dehydration, the material being used as a solid fuel. The present invention integrates two techniques, i.e., anaerobic digestion and hydrothermal carbonization, for sludge treatment, and the process is optimized from material and energy balance perspectives, so that the solid fuel and biochar substances are generated while sludge reduction is realized; moreover, the operation cost of the process is reduced, and the generated hydrothermal carbon can be either returned to the field for use or be used as an additive to promote anaerobic digestion, and also exhibits magnetism and can be recycled.

Description

A method for preparing biochar by hydrothermal carbonization of sludge and straw Technical Field

[0001] This invention relates to the fields of iron-containing sludge, straw, and hydrothermal carbonization technology, specifically to a method for preparing biochar by hydrothermal carbonization of iron-containing sludge and straw. Background Technology

[0002] In industrial wastewater treatment, the frequent use of iron-containing flocculants and conditioners leads to the generation of large amounts of iron-rich sludge, posing a significant challenge to its comprehensive disposal and utilization. Simultaneously, the large quantities of biomass residues such as straw generated during agricultural production urgently require proper treatment and disposal. Lignocellulose waste is mainly composed of lignocellulose, including cellulose, lignin, and hemicellulose. The lignin structure encapsulates the surface of cellulose and hemicellulose, limiting their utilization. Collectible and usable lignocellulose waste mainly includes crop straw, rice husks, sugarcane bagasse, and corn cobs. While some are used as livestock feed, papermaking, and fuel, the vast majority is discarded in farmland or burned on-site, polluting the environment and wasting significant amounts of natural resources.

[0003] Hydrothermal carbonization is a commonly used technology for treating sludge. It involves completely mixing biomass and water in a specific ratio and placing them in a reactor for a hydrothermal reaction under controlled temperature, reaction time, and pressure. The main product obtained is hydrothermal char, a solid product with quality similar to peat and lignite, which can be directly burned as a composite solid fuel. Currently, there is no method for preparing fuel by co-carbonizing sludge and wood fiber waste. Therefore, there is an urgent need to develop a method for preparing biochar through hydrothermal carbonization of sludge and straw, to achieve the recycling and reuse of sludge and wood fiber waste, avoid resource waste, and protect the environment. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing biochar by hydrothermal carbonization of iron-containing sludge and straw, so as to solve the problems existing in the prior art, reduce the environmental impact of sludge and straw treatment, improve the recycling of biomass, avoid resource waste, and protect the environment.

[0005] To achieve the above objectives, the present invention provides a method for preparing biochar by hydrothermal carbonization of iron-containing sludge and straw, the method comprising the following steps:

[0006] a. The straw is crushed and screened, the iron-containing sludge is initially dewatered, and a catalyst is added to the iron-containing sludge for catalytic wet oxidation treatment, wherein the catalyst includes active components and / or ozone;

[0007] b. Pump the iron-containing sludge after wet oxidation to the raw material storage tank, add the crushed and screened fibrous material to the raw material storage tank, mix, and then add a dewatering agent for dewatering treatment;

[0008] c. The raw material is preheated in the feed tank and then enters the reactor for hydrothermal carbonization reaction, during which concentrated nitric acid is added;

[0009] d. Collect the generated biochar slurry into a collection tank for cooling. The heat generated in the reactor and collection tank can be recovered and reused.

[0010] e. Depending on the nature of the material source and the required calorific value, add an appropriate amount of pulverized coal and then dehydrate it by plate pressing, or directly dehydrate it by plate pressing, as solid fuel.

[0011] The present invention discloses the following technical effects:

[0012] 1. The biochar preparation device for hydrothermal carbonization of sludge and straw provided by the present invention achieves the crushing and screening of straw by setting up a raw material storage system and an internal crushing and screening mechanism, ensuring the degree of crushing and screening. At the same time, the water content in the sludge can be reduced by mixing straw with iron-containing sludge, thereby reducing the consumption in the sludge dewatering process and saving resources.

[0013] 2. The biochar preparation device for hydrothermal carbonization of sludge and straw provided by the present invention realizes the recovery of heat during the reaction process by setting up a gas collection mechanism. The recovered heat is used to preheat the mixed sludge in the raw material conveying system, avoiding heat waste and realizing resource reuse.

[0014] 3. The biochar preparation device for hydrothermal carbonization of sludge and straw provided by the present invention realizes the recovery and reuse of heat during the cooling of materials after reaction by setting up a heat exchange mechanism. The heat generated when the materials are cooled by static placement is used to preheat the mixed sludge in the raw material conveying system, which further improves the preheating efficiency and saves energy consumption.

[0015] 4. The biochar preparation device for sludge and straw mixing and hydrothermal carbonization provided by the present invention realizes the hydrothermal carbonization process by setting microwave heating, which is clean and efficient in energy, avoids the large amount of harmful gases generated in traditional processes, and reduces the cost of waste gas treatment. Attached Figure Description

[0016] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0017] Figure 1 is a schematic flowchart of a method for preparing biochar by hydrothermal carbonization of sludge and straw according to an embodiment of the present invention. Detailed Implementation

[0018] Preferred embodiments of the present invention will now be described in more detail. While preferred embodiments of the present invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be more thorough and complete, and will fully convey the scope of the invention to those skilled in the art. To enable those skilled in the art to fully understand the technical solutions and beneficial effects of the present invention, further description is provided below in conjunction with specific embodiments.

[0019] Example 1

[0020] This invention provides a method for preparing biochar by hydrothermal carbonization of sludge and straw, as shown in Figure 1. The method includes the following steps:

[0021] S1. The straw is crushed and screened, and a catalyst is added to the sludge for catalytic wet oxidation treatment. The catalyst includes active components and / or ozone. The sludge is pumped to the raw material storage tank, and the crushed and screened fiber is added to the raw material storage tank. After mixing, a dehydrating agent is added for dehydration treatment.

[0022] S2. The reactor is heated to produce a hydrothermal carbonization reaction.

[0023] Wet oxidation is an effective water treatment technology for treating toxic, harmful, and high-concentration organic wastewater. In wet oxidation, sludge is passed through a reactor equipped with a highly efficient oxidizing catalyst, where organic matter and substances containing nitrogen and sulfur are catalytically oxidized into harmless substances such as CO2, H2O, N2, and SO4 before being discharged, thereby removing volatile suspended solids from the sludge. During the process, ozone and active ingredients are used to catalytically oxidize and treat ammonia nitrogen in the sludge.

[0024] Hydrothermal carbonization is a simple, efficient, and mild reaction method that uses biomass from sludge as raw material and water as the reaction medium, making it a green and sustainable sludge treatment method. The hydrothermal process mainly consists of the following stages: 1. Hydrolysis of precursors into monomers; 2. Dehydration of monomers and induction of polymerization; 3. Aromatization leading to the formation of the final product, biochar. After wet oxidation treatment, hydrothermal carbonization converts sludge into biochar and liquid-phase products, achieving harmless and reduced-volume treatment of sludge and minimizing sludge carbon emissions.

[0025] As a further improvement to the above technical solution, the mass ratio of catalyst to sludge in step S1 is 1:30. A mass ratio of catalyst to sludge between 1 and 4:30 allows the sludge to undergo sufficient catalytic wet oxidation without wasting catalyst.

[0026] As a further improvement to the above technical solution, in step S1, the catalyst includes ozone. Under high temperature and high pressure conditions, using ozone as a catalyst, organic pollutants in sludge can be oxidized into inorganic substances such as CO2 and water, or small-molecule organic substances.

[0027] Therefore, this method also includes:

[0028] S12. Test the pH value of the sludge;

[0029] S13. When the sludge is detected to be acidic, ozone is added and the oxidation is mainly carried out by direct O3 oxidation. The reactions that occur are: O3 + OH → HO2 + O2; O3 + HO2 → OH + O2 + O2.

[0030] Sludge undergoes different reactions upon the addition of ozone at different pH values. When the sludge is detected to be alkaline, the wet catalytic oxidation process of ozone under alkaline conditions is a relatively effective technology for treating wastewater containing ammonia nitrogen. It can be used as a pretreatment for wastewater containing both organic and inorganic pollutants, or as a deep post-treatment for further degradation of NH3-N pollutants in the wastewater. After the addition of ozone, oxidation is mainly by OH free radicals, and the reactions are: O3 + OH → HO2 + O2; O3 + HO2 → OH + O2 + O2; O3 + NH3 → Qs; where Qs is a product containing NO3 or NO2.

[0031] Understandably, in this embodiment, active components can also be added simultaneously during the wet oxidation reaction to improve the degradation efficiency of organic matter by the wet oxidation reaction.

[0032] As a further improvement to the above technical solution, in step S1, the catalyst is a mixture of one or more active components selected from Fe2O3, CuO, MnO2, or ZnO. This has advantages such as high activity, easy separation, and good stability, and also exhibits better catalytic activity.

[0033] As a further improvement to the above technical solution, the mixture includes Fe2O3, CuO, MnO2 and ZnO, and the mixture is prepared in a mass ratio of 4:3:3:1.

[0034] As a further improvement to the above technical solution, step S1 may also include the following steps:

[0035] S11. Adjust the sludge moisture content to 95-98%; the wet oxidation reaction is most complete and efficient when the moisture content is 95-98%.

[0036] S12. Test the pH value of the sludge;

[0037] S13. When the sludge is detected to be acidic, ozone is added and the oxidation is mainly carried out by direct O3 oxidation; when the sludge is detected to be alkaline, ozone is added and the oxidation is mainly carried out by OH free radicals.

[0038] S14. Adjust the temperature in the reactor to 250℃ and the pressure in the reactor to 5MPa;

[0039] S15. The catalytic wet oxidation treatment time for sludge is 1 hour.

[0040] Wet oxidation reactions can be divided into two stages: the initial stage is controlled by oxygen mass transfer, while the latter stage is controlled by reaction kinetics. Higher temperatures result in faster chemical reaction rates. Furthermore, increased temperature can increase the oxygen mass transfer rate and reduce the viscosity of the liquid. Pressure primarily serves to ensure the liquid-phase reaction, maintaining the partial pressure of oxygen within a certain range to guarantee a high dissolved oxygen concentration in the liquid phase. Higher temperatures lead to more complete oxidation of organic matter; however, increased temperature also increases the total pressure, resulting in greater energy consumption and higher requirements for the reactor. Therefore, from an economic perspective, setting the wet oxidation reaction temperature to 250-300℃ and the pressure to 5-8 MPa in this invention is the preferred reaction condition, and the wet oxidation reaction process is completed within 1-2 hours.

[0041] As a further improvement to the above technical solution, step S2 also includes the following steps:

[0042] S21. First, adjust the sludge moisture content to 85%–90%;

[0043] S22. Add citric acid to the reactor as a catalyst for the hydrothermal carbonization reaction;

[0044] S23. Adjust the temperature in the reactor to 150℃ and the pressure in the reactor to 1.5MPa;

[0045] S24. The hydrothermal carbonization reaction time is 5 hours to obtain carbonized products;

[0046] S25. The carbonization product obtained in step S24 is subjected to solid-liquid separation to obtain biochar and liquid phase product respectively. At the same time, the obtained liquid phase product can also be used as a supplementary carbon source for the next processing.

[0047] The hydrothermal carbonization process typically involves hydrolysis, dehydration, decarboxylation and aromatization, and condensation, accompanied by deoxygenation and dehydrogenation. The hydrothermal reaction is completed within 5-6 hours. As the hydrothermal temperature increases, the biochar production initially rises and then falls, with the largest increase occurring between 150℃ and 200℃.

[0048] Example 2

[0049] This invention provides a method for preparing biochar by hydrothermal carbonization of sludge and straw, as shown in Figure 1. The method includes the following steps:

[0050] S1. The straw is crushed and screened, and a catalyst is added to the sludge for catalytic wet oxidation treatment. The catalyst includes active components and / or ozone. The sludge is pumped to the raw material storage tank, and the crushed and screened fiber is added to the raw material storage tank. After mixing, a dehydrating agent is added for dehydration treatment.

[0051] S2. The reactor is heated to produce a hydrothermal carbonization reaction.

[0052] As a further improvement to the above technical solution, the mass ratio of the catalyst to the sludge in step S1 is 1:30.

[0053] As a further improvement to the above technical solution, in step S1, the catalyst is a mixture of one or more active components selected from Fe2O3, CuO, MnO2 or ZnO.

[0054] As a further improvement to the above technical solution, the mixture includes Fe2O3, CuO and MnO2 mixed in a mass ratio of 4:3:3.

[0055] Understandably, if it contains only CuO, MnO2 and ZnO, then its mass ratio is 3:3:1, and other similar cases are treated similarly.

[0056] As a further improvement to the above technical solution, step S1 also includes the following steps:

[0057] S11. Adjust the sludge moisture content to 95-98%;

[0058] S12. Test the pH value of the sludge;

[0059] S13. When the sludge is detected to be acidic, ozone is added and the oxidation is mainly carried out by direct O3 oxidation; when the sludge is detected to be alkaline, ozone is added and the oxidation is mainly carried out by OH free radicals.

[0060] S14. Adjust the temperature in the reactor to 300℃ and the pressure in the reactor to 8MPa;

[0061] S15. The catalytic wet oxidation treatment time for sludge is 1 hour.

[0062] As a further improvement to the above technical solution, step S2 also includes the following steps:

[0063] S21. First, adjust the sludge moisture content to 85%–90%;

[0064] S22. Add citric acid to the reactor as a catalyst for the hydrothermal carbonization reaction;

[0065] S23. Adjust the temperature in the reactor to 200℃ and the pressure in the reactor to 2MPa;

[0066] S24. The hydrothermal carbonization reaction time is 6 hours to obtain carbonized products;

[0067] S25. The carbonization product obtained in step S24 is subjected to solid-liquid separation to obtain biochar and liquid phase product respectively.

[0068] Example 3

[0069] In step S1, a catalyst is added to the sludge, wherein the mass ratio of the catalyst to the sludge is 2.5:30; at the same time, Fe2O3 is used as an active component to catalyze the wet oxidation treatment.

[0070] In step S14, the reactor temperature is adjusted to 280℃ and the pressure is adjusted to 6.5MPa;

[0071] In step S15, the catalytic wet oxidation treatment of the sludge takes 1.5 hours;

[0072] In step S23, the temperature in the reactor is adjusted to 180°C and the pressure in the reactor is adjusted to 1.8 MPa;

[0073] In step S24, the hydrothermal carbonization reaction takes 5.5 hours to obtain the carbonized product.

[0074] S25. The carbonization product obtained in step S24 is subjected to solid-liquid separation to obtain biochar and liquid phase product respectively.

[0075] Example 4

[0076] In step S1, a catalyst is added to the sludge, wherein the mass ratio of the catalyst to the sludge is 3:30; at the same time, Fe2O3 and CuO are used as active components to catalyze the wet oxidation treatment, wherein the mass ratio of Fe2O3 to CuO is 4:3.

[0077] In step S14, the reactor temperature is adjusted to 300℃ and the pressure is adjusted to 8MPa;

[0078] In step S15, the catalytic wet oxidation treatment of the sludge takes 2 hours;

[0079] In step S23, the temperature in the reactor is adjusted to 200°C and the pressure in the reactor is adjusted to 2MPa.

[0080] In step S24, the hydrothermal carbonization reaction takes 6 hours to obtain the carbonized product.

[0081] Alternatively, compounds containing Co2O3, NiO, PbO, PbO2, Rh2O3, RuO2, and PtO2 can be used as active components in the implementation.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A comprehensive sludge treatment method based on anaerobic digestion and hydrothermal carbonization, characterized in that... Includes the following steps: Step 1: Crush and screen the straw, perform preliminary dewatering on the iron-containing sludge, and add a catalyst to the iron-containing sludge for catalytic wet oxidation treatment. The catalyst includes active components and / or ozone. Step 2: Pump the iron-containing sludge after wet oxidation into the raw material storage tank, add the crushed and screened fibrous material into the raw material storage tank, mix, and then add a dewatering agent for dewatering treatment; Step 3: The raw material is preheated in the feed tank and then enters the reactor for hydrothermal carbonization reaction, during which concentrated nitric acid is added; Step 4: Collect the generated biochar slurry into a collection tank for cooling. The heat generated in the reactor and collection tank can be recovered and reused. Step 5: Add an appropriate amount of pulverized coal according to the nature of the material source and the required calorific value, and then dehydrate it by plate pressing, or directly dehydrate it by plate pressing, as solid fuel.

2. The comprehensive treatment method for iron-containing sludge and straw based on hydrothermal carbonization according to claim 1, characterized in that... The mass ratio of catalyst to sludge in step one is 1:

30. The mass ratio of catalyst to sludge is typically between 1:10 and 4:

30. The temperature in the wet catalytic oxidation reactor is adjusted to 250℃, and the pressure in the reactor is adjusted to 5MPa. The wet catalytic oxidation treatment time is 1 hour. Citric acid is added simultaneously as a wet oxidation catalyst. Step 3: As the concentration of concentrated nitric acid increases, the amount of biochar produced first increases and then decreases, with the increase reaching its maximum between 150℃ and 200℃.

3. The integrated treatment method for iron-containing sludge and straw based on hydrothermal carbonization according to claim 1, characterized in that... In step three, the digested sludge reacts at a temperature of 300-380℃ in a hydrothermal carbonization tank for 2-6 hours.

4. The integrated treatment method for iron-containing sludge and straw based on hydrothermal carbonization according to claim 1, characterized in that... In step three, add citric acid or acetic acid to adjust the pH of the material in the hydrothermal carbonization tank to 4.0~4.

9.

5. The integrated treatment method for iron-containing sludge and straw based on hydrothermal carbonization according to claim 1, characterized in that... In step one, the high-temperature steam generated by the biogas boiler is transported to the steam distributor, which distributes the high-temperature steam and delivers it to the heat exchanger in step one and the hydrothermal carbonization tank in step three.

6. The integrated treatment method for iron-containing sludge and straw based on hydrothermal carbonization according to claim 1, characterized in that... In step one, the high-temperature steam generated by the biogas boiler is transported to the steam distributor, which then distributes and transports the high-temperature steam to the dryer.

7. The integrated treatment method for iron-containing sludge and straw based on hydrothermal carbonization according to claim 1, characterized in that... The amount of concentrated nitric acid added in step three is 2-5% v / v.

8. The integrated treatment method for iron-containing sludge and straw based on hydrothermal carbonization according to claim 1, characterized in that... The biochar produced in step three is magnetic, with a saturation magnetization ranging from 27 to 33 A·m. 2 / kg.

9. A method for integrated treatment of iron-containing sludge and straw based on hydrothermal carbonization according to claim 1, characterized in that... In step five, the amount of coal powder added is 1 / 5 to 1 / 6 of the material weight.

10. A method for comprehensive treatment of iron-containing sludge and straw based on hydrothermal carbonization according to claim 1, characterized in that... In step five, the specific process of burning the solid separation and generating electricity is as follows: the solid separation is dried; the dried solid separation is used as fuel for combustion to produce high-temperature flue gas; the high-temperature flue gas heats liquid water to obtain high-temperature water vapor; the high-temperature water vapor is vaporized by heating and constant pressure to become superheated steam; the superheated steam is used for expansion to do work, converting chemical energy into mechanical energy; the mechanical energy is converted into electrical energy through a generator.

11. A comprehensive treatment method for iron-containing sludge and straw based on hydrothermal carbonization according to claim 1, characterized in that... The sludge treated contains 5%-30% iron, mainly including FeCl3 and FeSO4.

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