Processing technology for preparing fuel particles by using pig and cow dung

Abstract

The invention relates to a processing technology for preparing fuel particles from pig and cow dung, and belongs to the technical field of biomass energy. The process solves the problems of low calorific value and high slagging rate of the traditional excrement fuel through the core steps of solid-liquid separation, gradient high-temperature drying, moisture regulation and control, extrusion forming, cooling and screening and the like. A two-stage drying strategy is innovatively adopted, and specific moisture interval control and circular model parameter optimization are combined, so that the particle combustion performance is remarkably improved. Energy self-circulation and pollution control are achieved in the whole process, excrement derived biogas is used for supplying heat, and waste gas is prepared into liquid fertilizer through ammonia nitrogen recovery. The calorific value of the obtained fuel particles reaches 3500-4200 kcal / kg, the ash content is smaller than or equal to 15%, the slagging rate is smaller than 5%, the fuel particles can directly replace fossil fuel to be used for industrial boiler combustion, and an efficient path is provided for large-scale excrement resource utilization.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass energy, and in particular to a processing technology for preparing fuel particles by utilizing pig and cow manure. Background Art

[0002] Traditional methods for treating pig and cattle manure, such as composting and biogas fermentation, are plagued by long cycles, extensive land use, and high greenhouse gas emissions. Direct combustion, however, suffers from low calorific value due to the high moisture content of manure, and undegraded antibiotic residues can be dispersed in the flue gas. Existing manure pellet technologies often rely on adding fossil fuels (such as coal sludge) to increase calorific value, which violates carbon neutrality goals. Alternatively, they neglect chloride and alkali metal control, leading to slagging and corrosion in boilers.

[0003] Some processes attempt to pelletize straw using a single drying or blending method, but these methods fail to address the synergistic mechanism between moisture gradient removal and lignin plasticization, resulting in insufficient pellet strength and unstable combustion efficiency. Furthermore, existing technologies lack systematic design for pollution control steps, such as the biological removal of antibiotics from feces and the recovery of ammonia nitrogen from waste gas, hindering large-scale application. Summary of the Invention

[0004] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0005] In view of the above problems in the prior art, the inventors proposed the present invention.

[0006] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a process for preparing fuel particles using pig and cow manure.

[0007] To solve the above technical problems, the present invention provides the following technical solution: a process for preparing fuel pellets using pig and cow manure, comprising the following steps:

[0008] (1) A mixed raw material of pig and cow manure with a moisture content of 85-90% is subjected to solid-liquid separation by a screw extrusion separator with a sieve aperture of 0.5 mm to obtain a solid manure residue with a moisture content of 60-70%;

[0009] (2) The solid manure residue is sent to a belt dryer for gradient high-temperature drying: the first stage is 60-80℃ hot air drying for 30-50 minutes, the wind speed is 3-4m / s; the second stage is 100-130℃ drying for 20-40 minutes, the wind speed is 5-6m / s, and the moisture content of the final dry manure is controlled at 20-25%;

[0010] (3) The dry manure was pretreated with a microwave at a power of 800-1200 W for 5-10 min and then fed into a ring die pellet extruder for extrusion molding at a ring die aperture of 8-10 mm, an aspect ratio of 6:1-8:1, and a pressure of 30-50 MPa;

[0011] (4) The formed particles are cooled to room temperature by a negative pressure air cooling system at a wind speed of 2-4 m / s, and the debris is removed by a 20-mesh vibrating screen to obtain a density of 1.1-1.3 g / cm 3 , fuel particles with a length of 10-30mm.

[0012] As a preferred solution of the processing technology for preparing fuel particles using pig and cow manure described in the present invention, the heat source for the gradient high-temperature drying is the heat energy generated by the combustion of manure biogas, and the flue gas is discharged after being dust-removed by a bag and deodorized by a biological filter.

[0013] As a preferred embodiment of the processing technology for preparing fuel pellets using pig and cow manure according to the present invention, 5-10 wt% of a molding aid is added to the dry manure obtained in step (2), wherein the aid is at least one of pine sawdust, rice husk powder or sugarcane bagasse, and the particle size is ≤2 mm.

[0014] As a preferred solution of the processing technology for preparing fuel particles using pig and cow manure described in the present invention, the rice husk powder needs to be calcined at 600° C. to increase its SiO2 content to more than 60%.

[0015] As a preferred embodiment of the process for preparing fuel pellets using pig and cow manure according to the present invention, in step (2), the waste gas is dried and passed through a condensation tower to recover ammonia nitrogen compounds, which are then concentrated and reacted with phosphoric acid to form ammonium phosphate liquid fertilizer.

[0016] As a preferred embodiment of the processing technology for preparing fuel pellets using pig and cow manure described in the present invention, the solid manure residue is treated with an immobilized bacterial agent of the white rot fungus Trametes versicolor before gradient drying, with a mass ratio of the bacterial agent to the manure residue of 1:2, and aerobic fermentation is carried out at 28°C for 48 hours to degrade antibiotic residues.

[0017] As a preferred embodiment of the processing technology for preparing fuel particles using pig and cow manure according to the present invention, kaolin of 3-5% by weight of the dry manure is added before extrusion molding in step (3), wherein the kaolin has an Al2O3 content of ≥35% and a particle size of ≤50 μm.

[0018] As a preferred solution of the processing technology for preparing fuel pellets using pig and cow manure described in the present invention, the die temperature of the ring die pellet extruder is dynamically monitored by an infrared thermometer and maintained in the range of 85-90°C.

[0019] As a preferred solution of the processing technology for preparing fuel particles using pig and cow manure described in the present invention, after cooling, the surface of the particles is sprayed with a lignin sulfonate solution, with the spraying amount being 1-2% of the particle mass, to form a moisture-proof coating layer.

[0020] The invention discloses fuel particles prepared by using a process for preparing fuel particles from pig and cow dung, with a calorific value of ≥3500kcal / kg, an ash content of ≤15%, a combustion slagging rate of <5%, and a chloride ion content of ≤0.3%.

[0021] The present invention achieves beneficial effects: This process precisely controls moisture phase transitions through gradient drying. The first stage removes free water to prevent surface hardening, while the second stage uses high temperature to break down bound water and inactivate pathogens, stabilizing the moisture content of the dry manure within the optimal plasticizing range of 20-25% for lignin. Combined with optimized die aspect ratios and microwave pretreatment, the process significantly improves pellet density and crushing strength.

[0022] The addition of kaolin synergistically elevates the ash melting point to over 1200°C, effectively inhibiting slagging caused by potassium and sodium fusion. White-rot fungus pretreatment degrades over 99% of antibiotic residues, eliminating environmental risks. Waste gas ammonia nitrogen recovery and biogas energy self-circulation form a closed-loop treatment system, achieving near-zero pollutant emissions. The resulting pellet fuel combines high combustion efficiency with low maintenance costs, providing an industrially viable solution for the resource utilization of livestock and poultry manure. DETAILED DESCRIPTION

[0023] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0024] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0025] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it designate a separate or selective embodiment that is mutually exclusive with other embodiments.

[0026] Example 1

[0027] This embodiment provides a basic processing technology for preparing fuel pellets using pig and cow manure.

[0028] Rheological Control of Solid-Liquid Separation

[0029] Specific operation: 10 tons of pig and cow dung mixture (pig dung: cow dung = 6:4, moisture content 88%) was processed by LX-350 screw extruder, the screen aperture was 0.5mm, and the extrusion pressure was 2.0MPa.

[0030] Optimization principle: A mesh pore size of 0.5mm or less can retain >90% of the cellulose skeleton (particle size distribution tests show that 0.3-1.2mm fibers account for 82%), which provides the structural foundation for subsequent plasticization. A pore size that is too large (e.g., >1mm) will result in a fiber loss rate of >30%, reducing pellet strength.

[0031] Results: The moisture content of solid manure residue was 65%±2%, and the COD value of liquid component was >15,000 mg / L, which was suitable for biogas fermentation.

[0032] Phase Transition Kinetics Analysis of Gradient Drying

[0033] Specific temperature:

[0034] The first stage (60-80℃): constant temperature at 70℃ for 40 minutes, wind speed 3m / s;

[0035] Mechanism of action: Free water is removed in this stage, and the water diffusion coefficient D = 2.1×10 -9 m 2 / s (calculated according to Fick's second law), there is no crusting on the material surface.

[0036] The second stage (100-130℃): constant temperature at 120℃ for 30 minutes, wind speed 6m / s;

[0037] Mechanism of action: removal of bound water, activation energy Ea = 35.2 kJ / mol (fitted by Arrhenius equation), protein denaturation releases hydroxyl groups, and enhances the reaction activity of lignin.

[0038] Comparative proof:

[0039] Drying method Moisture content% E. coli killing rate Extrusion energy consumption (kWh / t) Single stage 100℃ 28％ 92％ 48.5 This embodiment has two stages 22％ ＞99.9％ 32.7

[0040] Optimization of rheological parameters for extrusion molding

[0041] The preferred ring die structure has an aspect ratio of 7:1 (compared to the standard 5:1), and the calculated material residence time t = 3.2s (formula: t = L / v, v = linear velocity 0.8m / s). The basis: When t > 3s, the lignin melt degree reaches above 75% (DSC glass transition enthalpy ΔH = 28J / g).

[0042] Microwave pretreatment mechanism: 1000W treatment for 8 min reduced the crystallinity of cellulose from 52% to 39% (XRD analysis), and the hydrogen bond rupture reduced the extrusion resistance by 15%.

[0043] Die temperature control: Infrared thermometer dynamically adjusts the pressure to maintain 88℃±2℃ (below this temperature, the particle density is less than 1.1g / cm 3 , pyrolysis and carbonization occur above 95℃).

[0044] Industrial verification of product performance: When continuously operated in a 4t / h boiler for 72h, the slagging rate was 4.7% and the thermal efficiency reached 78% (compared to 82% for lignite).

[0045] Example 2

[0046] This embodiment provides a processing technology for preparing fuel pellets using pig and cow manure.

[0047] This embodiment adds water washing dechlorination and additive strengthening steps based on embodiment 1, focusing on solving the corrosion problem caused by high chlorine content.

[0048] Water washing dechlorination

[0049] Specifically, the fecal residue after solid-liquid separation was mixed with water at a ratio of 1:8 (g / mL), stirred at 30°C for 40 min, and vacuum filtered;

[0050] The water washing solution was further added with a CaO-NaAlO2 composite dechlorination agent (molar ratio 6:3:1), reacted for 2 hours, and the filtrate was recycled. Effect: Chloride ion removal rate >45%.

[0051] Additive blending

[0052] The following components are preferably added to the dry manure:

[0053] 5% calcined rice husk powder (treated at 600℃ for 2h, SiO2 content 62%, particle size ≤50μm);

[0054] 4% kaolin (Al2O3 38%, particle size 45μm).

[0055] Rice husk ash increases the ash melting point, and Al2O3 in kaolin reacts with potassium to form KAlSi3O8, which inhibits slagging.

[0056] Gradient drying and extrusion molding

[0057] Same as in Example 1, the moisture content of the dry material was controlled at 23%±1%.

[0058] Product performance comparison:

[0059] Ash melting point: 1210℃ (XRD shows potassium feldspar accounts for 42%);

[0060] Slagging rate: 3.1% (34% lower than Example 1);

[0061] Chloride ion: 0.15% (meeting the safety standard of coal-fired boilers).

[0062] Example 3

[0063] This embodiment provides a processing technology for preparing fuel pellets using pig and cow manure.

[0064] As a comprehensive implementation method, this embodiment integrates white rot fungus pretreatment and surface moisture-proofing technology, and is suitable for large-scale manure treatment containing antibiotic residues.

[0065] Antibiotic degradation

[0066] Specifically, the feces after solid-liquid separation were inoculated with white rot fungus Trametes versicolor immobilized bacteria (bacteria: feces = 1:2) and aerobically fermented at 28°C for 48 hours;

[0067] Test results: The degradation rate of tetracycline antibiotics is >99%, and that of sulfonamides is >98% (HPLC-MS test).

[0068] Composite bonding reinforcement

[0069] Preferably, 8% pine sawdust (rosin content > 5%) is added as a natural plasticizer, which reduces extrusion energy consumption by 15%;

[0070] Post-molding treatment: Spray 1.5% lignin sulfonate solution on the particle surface to form a hydrophobic film.

[0071] Gradient drying and waste gas recovery

[0072] Same as Example 1, the ammonia nitrogen recovery rate is greater than 85%.

[0073] Product advantages:

[0074] Moisture resistance: After being placed in an environment with 80% humidity for 7 days, the moisture content only increased by 2.1% (the untreated group increased by 8.7%).

[0075] Durability: ASTM D440 standard test crushing strength> 99%;

[0076] Environmental safety: No antibiotics were detected (detection limit 0.01 mg / kg).

[0077] Through comparative analysis of the above three embodiments, the following comprehensive conclusions can be drawn:

[0078] Universality of gradient drying mechanism: All three examples prove that two-stage drying (70℃+120℃) can accurately control the moisture content to the range of 20-25%. Under this condition, the plasticization efficiency of lignin is the best, and the pellet density is stable at 1.2-1.3g / cm 3(When the moisture content is greater than 30%, the cracking rate of the particles is greater than 15%, and when the moisture content is less than 20%, the compressive strength decreases by 40%). When the moisture content is higher than the critical value, the vapor pressure generated by the phase change of free water during the extrusion process will destroy the integrity of the particle structure; on the contrary, insufficient moisture will lead to an increase in the energy barrier of the glass transition of lignin, and it will be difficult for the cellulose molecular chain to fully stretch. The examples show that the material in a specific water content range exhibits ideal viscoelastic behavior, which not only ensures the fluidity during the extrusion process, but also allows the particles to form a dense network structure after cooling. This control mechanism is generally applicable to all types of livestock and poultry manure raw materials, because the natural ratio of lignin to cellulose in pig and cow manure can just meet the requirements of melt bonding, without relying on exogenous additives, and fundamentally guarantees the scale stability of the process.

[0079] Additive synergistic efficiency rule: Rice husk powder (SiO2>60%) and kaolin (Al2O3>35%) are compounded in a ratio of ≥4%, which increases the ash melting point to above 1200°C and reduces the slagging rate to <3.5%; when pine sawdust is added at a rate of 5-10%, the extrusion energy consumption is reduced by 10-15%, and the calorific value is increased by 8-12%. The essence of the additive compounding strategy lies in reconstructing the ash melting characteristics. The slagging of traditional dung fuel is due to the low-temperature eutectic effect of alkali metals, while the siliceous components rich in calcined rice husks and the aluminum of kaolin cooperate to promote the transformation of ash into a high-melting-point aluminosilicate phase. This phase change not only inhibits slag formation, but also converts volatile alkali metals into thermally stable mineral phases through a chemical locking mechanism. From the perspective of industrial application, this design significantly extends the boiler operation cycle, avoids energy loss caused by frequent shutdowns for slag removal, and is particularly suitable for industrial production scenarios that require continuous heating.

[0080] Feasibility of a closed-loop pollution control system: The integrated design of biogas heating → waste gas ammonia recovery → water wash liquid dechlorination reduces carbon emissions by 62kg CO2-eq per ton of pellet production, and ensures that heavy metal and antibiotic residues meet the GB 36600-2018 soil safety standard.

[0081] Compared with existing technologies, the breakthrough of this solution lies in transforming contradictory demands into a synergistic mechanism: the drying stage requires both rapid dehydration and the avoidance of crusting → segmented temperature control resolves the mass transfer contradiction; the extrusion process requires both low energy consumption and high strength → moisture regulation activates lignin self-adhesion; the product requires both high calorific value and low pollution → additive design reconstructs ash chemical behavior.

[0082] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A process for preparing fuel pellets using pig and cow manure, characterized by: The following steps are involved: (1) A mixed raw material of pig and cow manure with a moisture content of 85-90% is subjected to solid-liquid separation by a screw extrusion separator with a sieve aperture of 0.5 mm to obtain a solid manure residue with a moisture content of 60-70%; (2) The solid manure residue is sent to a belt dryer for gradient high-temperature drying: the first stage is 60-80℃ hot air drying for 30-50 minutes, the wind speed is 3-4m / s; the second stage is 100-130℃ drying for 20-40 minutes, the wind speed is 5-6m / s, and the moisture content of the final dry manure is controlled at 20-25%; (3) The dry manure was pretreated with a microwave at a power of 800-1200 W for 5-10 min and then fed into a ring die pellet extruder for extrusion molding at a ring die aperture of 8-10 mm, an aspect ratio of 6:1-8:1, and a pressure of 30-50 MPa; (4) The formed particles are cooled to room temperature by a negative pressure air cooling system at a wind speed of 2-4 m / s, and the debris is removed by a 20-mesh vibrating screen to obtain a density of 1.1-1.3 g / cm 3 , fuel particles with a length of 10-30mm.

2. The process for preparing fuel pellets using pig and cow manure as claimed in claim 1, characterized in that: The heat source for the gradient high-temperature drying is the heat energy generated by the combustion of manure and biogas, and the flue gas is discharged after being dust-removed by bags and deodorized by biological filters.

3. The process for preparing fuel pellets using pig and cow manure as claimed in claim 2, characterized in that: 5-10 wt% of a forming aid is added to the dry manure obtained in step (2), wherein the aid is at least one of pine sawdust, rice husk powder or sugarcane bagasse, and the particle size is ≤2 mm.

4. The process for preparing fuel pellets using pig and cow manure as claimed in claim 1, characterized in that: The rice husk powder needs to be calcined at 600° C. to increase its SiO2 content to more than 60%.

5. The process for preparing fuel pellets using pig and cow manure as claimed in claim 1, characterized in that: In step (2), the drying waste gas is passed through a condensation tower to recover ammonia nitrogen compounds, which are then concentrated and reacted with phosphoric acid to form ammonium phosphate liquid fertilizer.

6. The process for preparing fuel pellets using pig and cow manure as claimed in claim 1, characterized in that: The solid feces residue is treated with a white rot fungus Trametes versicolor immobilized bacterial agent before gradient drying, with the bacterial agent and feces residue mass ratio being 1:2, and aerobic fermentation is carried out at 28° C. for 48 hours to degrade antibiotic residues.

7. The process for preparing fuel pellets using pig and cow manure as claimed in claim 1, characterized in that: Step (3) Before extrusion molding, 3-5% of the mass of dry feces is added with kaolin, wherein the Al2O3 content of the kaolin is ≥35% and the particle size is ≤50 μm.

8. The process for preparing fuel pellets using pig and cow manure as claimed in claim 1, characterized in that: The die temperature of the ring die pellet extruder is dynamically monitored by an infrared thermometer and maintained in the range of 85-90°C.

9. The process for preparing fuel pellets using pig and cow manure as claimed in claim 1, characterized in that: After cooling, the surface of the particles is sprayed with lignin sulfonate solution, with the spraying amount being 1-2% of the mass of the particles, to form a moisture-proof coating layer.

10. The fuel pellets prepared by the process for preparing fuel pellets using pig and cow manure according to any one of claims 1 to 9, characterized in that: Calorific value ≥3500kcal / kg, ash content ≤15%, combustion slagging rate <5%, chloride ion content ≤0.3%.