Production method for preparing biomass natural gas from straw and co-producing organic fertilizer
The method addresses inefficiencies in straw biogas production by employing steam explosion and high-temperature fermentation with biogas slurry recycling, achieving efficient biogas and organic fertilizer production with reduced environmental impact.
Patent Information
- Application Number
- CN202411447969.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-17
- Publication Date
- 2025-01-03
AI Technical Summary
The existing straw biogas production technologies face issues such as inefficient straw pretreatment, low cellulose hydrolysis rates, long fermentation times, low biogas yield, and environmental pollution from biogas residue, limiting the rapid and large-scale development of biogas and organic fertilizer production.
A method involving steam explosion, continuous cooking, and full-mixed high-temperature liquid fermentation of straw without chemical additives, coupled with biogas slurry recycling and direct use of filter residues as organic fertilizer, to enhance biogas production and reduce environmental impact.
This method achieves high methane content biogas production, reduces chemical pollution, conserves energy by recycling heat, and eliminates the need for secondary composting of biogas residues, thereby enhancing scalability and environmental sustainability.
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of straw agricultural byproduct processing, and particularly relates to a method for producing organic fertilizer by co-producing biomass natural gas from straw. Background Art
[0002] Biogas is a green, low-carbon, clean and renewable natural gas produced by anaerobic fermentation and purification of various urban and rural organic wastes such as crop straw, livestock and poultry manure, kitchen waste, and wastewater from agricultural and sideline product processing. At the same time, the sludge and liquid produced in the anaerobic fermentation process can be used to produce organic fertilizer.
[0003] The main reason is that the straw biogas technology, especially the unreasonable straw pretreatment technology and anaerobic fermentation technology, has limited the development speed of biogas. Among them, straw pretreatment generally adopts straw crushing and then composting for pre-hydrolysis or crushing and directly inoculating in a pool (tank), solid or semi-solid anaerobic fermentation, low cellulose hydrolysis rate, long fermentation time, short 20-30 days, long two months, low biogas yield, biogas residue needs to be composted for secondary fermentation (biogas residue contains live eggs and pathogens) before it can be used as organic fertilizer, and the large amount of biogas produced by semi-solid fermentation is difficult to digest, etc., all of which have limited the rapid and large-scale development of biogas. Summary of the invention The purpose of the present invention is to solve the problems existing in the process of producing biogas by processing straw in the background technology, and to provide a method for producing organic fertilizer by co-producing biomass natural gas from straw.
[0004] A method for producing organic fertilizer by co-producing biomass natural gas from straw comprises the following steps: Step 1: Remove the sand from the straw, keep the leaves, skin and pith, and cut the whole straw into small pieces with a length of 1-5 cm using a grass cutter; Step 2: Adjust the moisture content of the cut straw to 35-40%. If the moisture content of the straw is lower than 35%, add water. If the moisture content of the straw is higher than 40%, dry it in the sun to make the moisture content of the straw between 35-40%. Step 3: squeeze the water-adjusted straw with a screw extruder and send it into a continuous cooker, add saturated steam with a pressure of 0.8-1.1Mpa, heat the straw in the continuous cooker to 175-190°C, and cook for 20-30 minutes. No acid, alkali or other chemicals are added during the whole cooking process; Step 4: continuously decompress the steamed straw and spray it into a steam explosion material receiver. The pressure of the steam explosion material receiver is maintained at a slightly negative pressure state. The secondary steam generated by flash evaporation in the steam explosion material receiver is recovered by a hydraulic ejector with the returned biogas slurry. While the biogas slurry recovers the heat of the secondary steam, it also recovers the organic gas taken away by the secondary steam into the biogas slurry. Step 5: Send the steam-exploded straw into a mixing tank, dilute and mix the material with the biogas slurry that has recovered the heat of the secondary steam, and adjust the pH value and temperature. Adjust the solid content of the diluted material to 8-12%, the pH value to 5-6, and the temperature to 55-60°C. At the same time, add 0.05-0.1% of cellulase and 0.2-0.3% of urea based on the absolute dry straw to the mixing tank, or add 0.05-0.1% of cellulase and 3-5% of cow dung based on the absolute dry straw to the mixing tank; Step 6: Put the materials in the mixing tank into a pre-hydrolysis tank with an insulation layer and a stirrer, and hydrolyze the materials in the pre-hydrolysis tank for 18-24 hours; Step 7: The pre-hydrolyzed material is pumped into an anaerobic fermentation tank with an insulation layer and a stirrer. The temperature of the anaerobic fermentation tank is maintained at 53-55°C and the residence time in the tank is 8-10 days. Step 8: Send the biogas coming out of the air duct at the top of the anaerobic fermentation tank into the biogas cabinet, and then send it from the biogas cabinet to the biogas purification device by a fan. After removing water, hydrogen sulfide and carbon dioxide, the biogas with a methane content of more than 95% is compressed and enters the CNG or LNG storage tank; Step nine, the effluent from the anaerobic tank is filtered to intercept the undegraded long fibers and sent back to the mixing tank, the water after filtering out the undegraded long fibers is separated into solid and liquid by a plate and frame filter press with a 150-200 mesh filter cloth, and the filter residue obtained after separation can be directly used as an organic fertilizer without secondary composting and fermentation; all the filtrate after separation is returned to the hydraulic ejector in step four for recovering secondary steam.
[0005] The length of the straw after steam explosion in step 4 is 0.1-1 cm.
[0006] The absolute pressure of the slight negative pressure in step 4 is 0.09-0.095Mpa.
[0007] In the process of the present invention, there is no need to remove leaves, skin and pith from the straw, and the whole straw is cooked without adding chemicals such as acid and alkali.
[0008] In the present invention, the heat taken away by the secondary steam generated in the straw explosion process is all recycled by the biogas slurry; the heat required to maintain the high-temperature anaerobic fermentation temperature is all from the heat brought by the secondary steam of the straw explosion flash, and no fresh steam needs to be consumed.
[0009] The present invention adopts the method of adding 3-5% of cow dung in terms of absolute dry straw or 0.2-0.3% of urea in terms of absolute dry straw to ensure the nitrogen source required for anaerobic fermentation.
[0010] The present invention adopts full-mixed high-temperature liquid fermentation, and the fermentation time does not exceed 10 days.
[0011] The filter residue separated from the anaerobic effluent of the present invention can be directly used as an organic fertilizer without secondary composting and fermentation.
[0012] In the present invention, all the biogas slurry is refluxed for mixing with materials, and no biogas slurry is discharged during the whole fermentation process.
[0013] Beneficial effects of the present invention: 1. The whole cooking process of the present invention does not add any chemicals, thus reducing the possibility of chemical pollution.
[0014] 2. In the present invention, the heat taken away by the secondary steam generated in the straw explosion process is all recycled and utilized by the biogas slurry; the heat required to maintain the high-temperature anaerobic fermentation temperature is all from the heat brought by the secondary steam of the straw explosion flash, and there is no need to consume fresh steam, thus saving energy.
[0015] 3. The filter residue separated from the anaerobic effluent of the present invention can be directly used as organic fertilizer without secondary composting and fermentation, thereby reducing the pollution of composting and fermentation to the environment.
[0016] 4. In the present invention, all the biogas slurry is returned to mix with the feed, and no biogas slurry is discharged during the entire fermentation process, which will not cause pollution to the environment and also save the cost of pollutant treatment. DETAILED DESCRIPTION
[0017] Embodiment 1 of the present invention.
[0018] A method for producing organic fertilizer by co-producing biomass natural gas from straw comprises the following steps: Step 1: Remove the sand from the straw, keep the leaves, skin and pith, and cut the whole straw into small pieces with a length of 3 cm using a grass cutter; Step 2: Adjust the moisture content of the cut straw to 35-40%. If the moisture content of the straw is lower than 35%, add water. If the moisture content of the straw is higher than 40%, dry it in the sun to make the moisture content of the straw between 35-40%. Step 3: The moisture-adjusted straw is squeezed by a screw extruder and then sent to a continuous digester, and saturated steam with a pressure of 0.9 MPa is added at the same time, the straw in the continuous digester is heated to 185° C. and boiled for 28 minutes; Step 4: continuously decompress the cooked straw and spray it into a steam explosion material receiver. The pressure of the steam explosion material receiver is maintained at a slightly negative pressure state. The secondary steam generated by flash evaporation in the steam explosion material receiver is used to recover the returned biogas slurry through a hydraulic ejector. While the biogas slurry recovers the heat of the secondary steam, it also recovers the organic gas taken away by the secondary steam into the biogas slurry. Step 5: Send the steam-exploded straw into a mixing tank, dilute and mix it with biogas slurry that has recovered the heat of secondary steam, and adjust the pH value and temperature. The solid content of the diluted material is adjusted to 10%, the pH value is adjusted to 6, and the temperature is adjusted to 55°C. At the same time, 0.05-0.1% of cellulase based on the amount of absolute dry straw and 0.2-0.3% of urea based on the amount of absolute dry straw are added to the mixing tank; Step 6: Put the materials in the mixing tank into a pre-hydrolysis tank with an insulation layer and a stirrer, and hydrolyze the materials in the pre-hydrolysis tank for 20 hours; Step 7: The pre-hydrolyzed material is pumped into an anaerobic fermentation tank with an insulation layer and a stirrer. The temperature of the anaerobic fermentation tank is maintained at 55°C and the residence time in the tank is 10 days. Step 8: Send the biogas coming out of the air duct at the top of the anaerobic fermentation tank into the biogas cabinet, and then send it from the biogas cabinet to the biogas purification device by a fan. After removing water, hydrogen sulfide and carbon dioxide, the biogas with a methane content of more than 95% is compressed and enters the CNG storage tank; Step nine, the effluent from the anaerobic tank is filtered to intercept the undegraded long fibers and sent back to the mixing tank, the water after filtering out the undegraded long fibers is used for solid-liquid separation by a plate and frame filter press with a 200-mesh filter cloth, and the filter residue obtained after separation can be directly used as an organic fertilizer without secondary composting and fermentation; the filtrate after separation is all returned to the hydraulic ejector in step four for recovery of secondary steam.
[0019] The length of the straw after steam explosion in step 4 is 0.1-1 cm.
[0020] The absolute pressure of the slight negative pressure in step 4 is 0.09 MPa.
[0021] Embodiment 2 of the present invention.
[0022] A method for producing organic fertilizer by co-producing biomass natural gas from straw comprises the following steps: Step 1: Remove the sand from the straw, keep the leaves, skin and pith, and cut the whole straw into small pieces with a length of 2 cm using a grass cutter; Step 2: Adjust the moisture content of the cut straw to 35-40%. If the moisture content of the straw is lower than 35%, add water. If the moisture content of the straw is higher than 40%, dry it in the sun to make the moisture content of the straw between 35-40%. Step 3: squeeze the moisture-adjusted straw with a screw extruder and send it into a continuous digester, add saturated steam with a pressure of 1.0 MPa, heat the straw in the continuous digester to 180°C, and cook for 25 minutes; Step 4: continuously decompress the cooked straw and spray it into a steam explosion material receiver. The pressure of the steam explosion material receiver is maintained at a slightly negative pressure state. The secondary steam generated by flash evaporation in the steam explosion material receiver is used to recover the returned biogas slurry through a hydraulic ejector. While the biogas slurry recovers the heat of the secondary steam, it also recovers the organic gas taken away by the secondary steam into the biogas slurry. Step 5: Send the steam-exploded straw into a mixing tank, dilute and mix it with biogas slurry that has recovered the heat of secondary steam, and adjust the pH value and temperature. The solid content of the diluted material is adjusted to 10%, the pH value is adjusted to 5, and the temperature is adjusted to 60°C. At the same time, 0.05-0.1% of cellulase based on the absolute dry straw and 3-5% of cow dung based on the absolute dry straw are added to the mixing tank; Step 6: Put the materials in the mixing tank into a pre-hydrolysis tank with an insulation layer and a stirrer, and hydrolyze the materials in the pre-hydrolysis tank for 22 hours; Step 7: The pre-hydrolyzed material is pumped into an anaerobic fermentation tank with an insulation layer and a stirrer. The temperature of the anaerobic fermentation tank is maintained at 60°C and the residence time in the tank is 9 days. Step 8: Send the biogas coming out of the air duct at the top of the anaerobic fermentation tank into the biogas cabinet, and then send it from the biogas cabinet to the biogas purification device by a fan. After removing water, hydrogen sulfide and carbon dioxide, the biogas with a methane content of more than 95% is compressed and enters the LNG storage tank; Step nine, the effluent from the anaerobic tank is filtered to intercept the undegraded long fibers and sent back to the mixing tank, the water after filtering out the undegraded long fibers is separated into solid and liquid by a plate and frame filter press with a 180-mesh filter cloth, and the filter residue obtained after separation can be directly used as an organic fertilizer without secondary composting and fermentation; the filtrate after separation is all returned to the hydraulic ejector in step four for recovering secondary steam.
[0023] The length of the straw after steam explosion in step 4 is 0.1-1 cm.
[0024] The absolute pressure of the slight negative pressure in step 4 is 0.095 MPa.
Claims
1. A method for producing organic fertilizer by co-producing biomass natural gas from straw, characterized in that: The steps include: Step 1: Remove the sand from the straw, keep the leaves, skin and pith, and cut the whole straw into small pieces with a length of 1-5 cm using a grass cutter; Step 2: Adjust the moisture content of the cut straw to 35-40%. If the moisture content of the straw is lower than 35%, add water. If the moisture content of the straw is higher than 40%, dry it in the sun to make the moisture content of the straw between 35-40%. Step 3: squeeze the moisture-adjusted straw with a screw extruder and send it into a continuous digester, add saturated steam with a pressure of 0.8-1.1Mpa, heat the straw in the continuous digester to 175-190°C, and cook for 20-30 minutes; Step 4: continuously decompress the steamed straw and spray it into a steam explosion material receiver. The pressure of the steam explosion material receiver is maintained at a slightly negative pressure state. The secondary steam generated by flash evaporation in the steam explosion material receiver is recovered by a hydraulic ejector with the returned biogas slurry. While the biogas slurry recovers the heat of the secondary steam, it also recovers the organic gas taken away by the secondary steam into the biogas slurry. Step 5: Send the steam-exploded straw into a mixing tank, dilute and mix the material with the biogas slurry that has recovered the heat of the secondary steam, and adjust the pH value and temperature. Adjust the solid content of the diluted material to 8-12%, the pH value to 5-6, and the temperature to 55-60°C. At the same time, add 0.05-0.1% of cellulase and 0.2-0.3% of urea based on the absolute dry straw to the mixing tank, or add 0.05-0.1% of cellulase and 3-5% of cow dung based on the absolute dry straw to the mixing tank; Step 6: Put the materials in the mixing tank into a pre-hydrolysis tank with an insulation layer and a stirrer, and hydrolyze the materials in the pre-hydrolysis tank for 18-24 hours; Step 7: The pre-hydrolyzed material is pumped into an anaerobic fermentation tank with an insulation layer and a stirrer. The temperature of the anaerobic fermentation tank is maintained at 53-55°C and the residence time in the tank is 8-10 days. Step 8: The biogas coming out of the air duct at the top of the anaerobic fermentation tank passes through a biogas purification device, and the biogas with a methane content of more than 95% after removing water, hydrogen sulfide and carbon dioxide is compressed and enters a CNG or LNG storage tank; Step nine, the effluent from the anaerobic tank is filtered to intercept the undegraded long fibers and sent back to the mixing tank, the water after filtering out the undegraded long fibers is separated into solid and liquid by a plate and frame filter press with a 150-200 mesh filter cloth, and the filter residue obtained after separation can be directly used as an organic fertilizer without secondary composting and fermentation; all the filtrate after separation is returned to the hydraulic ejector in step four for recovering secondary steam.
2. The method for producing organic fertilizer by co-producing biomass natural gas from straw according to claim 1, characterized in that: The length of the straw after steam explosion in step 4 is 0.1-1 cm.
3. The method for producing organic fertilizer by co-producing biomass natural gas from straw according to claim 1, characterized in that: The absolute pressure of the slight negative pressure in step 4 is 0.09-0.095Mpa.