Preparation method of straw-derived fulvic acid liquid fertilizer and directional regulation process thereof

Abstract

The application belongs to the field of fertilizer preparation, and particularly relates to a preparation method and a directional regulation process of a straw source fulvic acid liquid fertilizer, which comprises the following steps: raw material pretreatment: after being crushed, dry straw is put into a reaction kettle, mixed with water, and heated to a preset temperature for hydrothermal pretreatment to obtain a mixed liquid; stepwise alkaline hydrolysis: alkali is added to the mixed liquid after S1 treatment in sections, and pH value, reaction temperature and reaction time are controlled in each stage to gradually degrade lignin in the straw into fulvic acid and dissolve it into a liquid phase to obtain an alkaline hydrolysis mixed material; solid-liquid separation: the alkaline hydrolysis mixed liquid obtained in S2 is sent into a plate and frame filter for solid-liquid separation to obtain a fulvic acid liquid phase and a solid phase residue; liquid phase blending: the fulvic acid liquid phase obtained in S3 is sent into a blending tank, corresponding trace elements or fermentation bacterial liquid are added according to the nutrient requirements of target crops, and a liquid fertilizer product is obtained after uniform mixing.

Description

Technical Field

[0001] This invention relates to the field of fertilizer preparation, specifically a method for preparing straw-derived humic acid liquid fertilizer and its targeted regulation process. Background Technology

[0002] Fulvic acid possesses multiple biological functions, including promoting plant root development, enhancing nutrient absorption efficiency, improving crop resistance to adverse conditions, and improving soil physical and chemical properties. Compared to solid fulvic acid fertilizers, straw-derived liquid fulvic acid fertilizers have significant advantages such as better nutrient uniformity, higher crop absorption and utilization rates, and ease of mechanized application, showing broad application prospects in the cultivation of cash crops such as rice, lychee, and bananas.

[0003] The typical preparation process of existing straw-derived humic acid liquid fertilizer is as follows: First, the dried straw collected from the field is crushed to a certain particle size by a pulverizer and then put into a reaction vessel. Water is added and mixed, and an alkali agent is added. The pH of the reaction system is adjusted to 11.0-12.5 in one go. The temperature is raised to 75-85℃ for heat preservation and alkaline hydrolysis reaction. The reaction time is 2-4 hours. After the alkaline hydrolysis reaction is completed, the mixed liquid is sent to a plate and frame filter press for solid-liquid separation to obtain a liquid phase rich in humic acid and a solid phase mainly composed of undegraded cellulose, hemicellulose and residual lignin. The liquid phase is collected in a storage tank for temporary storage and then transferred to a mixing tank. Necessary trace elements or auxiliary materials are added according to product requirements. After stirring and mixing, it is bottled as a finished liquid fertilizer product. The solid filter residue is discharged as waste residue or low-value by-product.

[0004] The existing technology has the following technical defects: the existing process adds all the alkali agent at the beginning of the alkaline hydrolysis reaction, so that the pH of the system rises to the target high level all at once. As the alkaline hydrolysis reaction proceeds, the alkali agent is continuously consumed by the lignin degradation reaction. In the later stage of the reaction (usually after 1.5 hours), the pH of the system has dropped to 9.0-10.0 or even lower. The continuous decline of pH results in a serious lack of driving force for the reaction in the later stage of alkaline hydrolysis. A large amount of lignin fails to be effectively converted into fulvic acid and remains in the filter residue in an undegraded state. This not only results in a low yield of the target product fulvic acid, but also leads to insufficient comprehensive utilization of organic matter in straw raw materials.

[0005] Therefore, a method for preparing straw-derived humic acid liquid fertilizer and its targeted regulation process are proposed to address the above problems. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0007] The technical solution adopted by this invention to solve its technical problem is: a method for preparing straw-derived humic acid liquid fertilizer and its targeted regulation process, comprising the following steps: S1. Raw material pretreatment: Dry straw is crushed and put into a reaction vessel, water is added and mixed, and the temperature is raised to a preset temperature for hydrothermal pretreatment to obtain a mixed liquid. S2, stepped alkaline hydrolysis: Alkali agent is added to the mixture liquid after S1 treatment in stages. The pH value, reaction temperature and reaction time are controlled at each stage to gradually degrade the lignin in the straw into fulvic acid and dissolve it into the liquid phase, resulting in an alkaline hydrolyzed mixture. S3. Solid-liquid separation: The alkaline hydrolysis mixture obtained in S2 is sent to a plate and frame filter press for solid-liquid separation to obtain humic acid liquid phase and solid filter residue. S4. Liquid phase preparation: The humic acid liquid phase obtained in S3 is sent to the preparation tank. According to the nutrient requirements of the target crop, the corresponding trace elements or fermentation liquid are added. After mixing evenly, the liquid fertilizer product is obtained.

[0008] Preferably, the specific method of adding alkali in stages in S2 is as follows: at least two alkali addition nodes are set along the reaction time axis, with a predetermined time interval between each node. The alkali added at the later node is used to compensate for the amount of alkali consumed in the previous stage of alkali hydrolysis reaction and to raise the pH of the reaction system to the range required for the next stage, so that the pH value of each stage changes in a stepwise manner.

[0009] Preferably, the target crop in S4 includes at least one of rice, lychee, and banana; the trace elements include at least one of zinc, boron, magnesium, iron, and manganese; and the fermentation broth includes at least one of phosphate-solubilizing bacteria, potassium-solubilizing bacteria, and nitrogen-fixing bacteria.

[0010] Preferably, it also includes: S5, waste heat recovery: before the high-temperature fulvic acid liquid phase discharged from the plate and frame filter in S3 is sent into the storage tank, it is preheated by exchanging heat with the new feed liquid through a heat exchanger.

[0011] This invention also provides a targeted control process for straw-derived fulvic acid liquid fertilizer, used to realize the above-described method for preparing straw-derived fulvic acid liquid fertilizer. This process is achieved through the following apparatus: a steam boiler, a preheater, a reactor, a plate and frame filter, a storage tank, a mixing tank, a preparation tank, a seed tank group, a fermentation tank, and a control unit. The steam boiler is connected to the preheater and the reactor to provide heat energy. The preheater is located upstream of the reactor to preheat the newly fed liquid. The reactor is equipped with an alkali addition unit to add alkali at each stage of the stepwise alkali hydrolysis process. Alkali is added in stages inside the reactor; a plate and frame filter is connected to the outlet of the reactor for solid-liquid separation of the alkaline hydrolysis mixture; a storage tank is connected between the liquid phase outlet of the plate and frame filter and the inlet of the mixing tank for temporary storage of fulvic acid liquid phase; the mixing tank is used to add trace elements or fermentation liquid according to the needs of the target crop; the preparation tank, seed tank group and fermentation tank are connected in sequence to the inlet of the mixing tank for injecting the prepared functional liquid into the mixing tank; the control unit is electrically connected to the reactor and the alkali addition unit for controlling the reaction conditions and the timing of alkali addition.

[0012] Preferably, the seed tank group includes a No. 1 seed tank and a No. 2 seed tank connected sequentially along the flow direction of the bacterial culture, wherein: the outlet of the seed tank is connected to the inlet of the No. 1 seed tank, the outlet of the No. 1 seed tank is connected to the inlet of the No. 2 seed tank, and the outlet of the No. 2 seed tank is connected to the inlet of the fermentation tank, for two-stage progressive culture of the bacterial culture.

[0013] Preferably, it also includes a heat exchanger, which is disposed between the liquid phase outlet of the plate and frame filter and the liquid inlet of the storage tank.

[0014] Preferably, the plate and frame filter includes alternately arranged filter plates and filter frames, the surface of the filter plates is covered with filter cloth, and the filter frames form a filtration chamber inside.

[0015] The advantages of this invention are: The present invention discloses a method for preparing straw-derived fulvic acid liquid fertilizer. By adopting a stepwise alkaline hydrolysis strategy of adding alkali in stages, alkali is added at different stages of the reaction process to compensate for the reaction consumption, so that the reaction system is maintained within the target pH range at each stage. This prevents the reaction from stalling due to excessively low pH in the later stage and significantly improves the conversion rate of lignin to fulvic acid. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Specific implementation examples are given below.

[0020] The preparation method and targeted regulation process of straw-derived humic acid liquid fertilizer according to the embodiments of the present invention include the following steps: S1. Raw material pretreatment: Dry straw is crushed and put into a reaction vessel, water is added and mixed, and the temperature is raised to a preset temperature for hydrothermal pretreatment to obtain a mixed liquid. S2, stepped alkaline hydrolysis: Alkali agent is added to the mixture liquid after S1 treatment in stages. The pH value, reaction temperature and reaction time are controlled at each stage to gradually degrade the lignin in the straw into fulvic acid and dissolve it into the liquid phase, resulting in an alkaline hydrolyzed mixture. S3. Solid-liquid separation: The alkaline hydrolysis mixture obtained in S2 is sent to a plate and frame filter press for solid-liquid separation to obtain humic acid liquid phase and solid filter residue. S4. Liquid phase preparation: The humic acid liquid phase obtained in S3 is sent into the preparation tank. According to the nutrient requirements of the target crop, the corresponding trace elements or fermentation liquid are added. After mixing evenly, the liquid fertilizer product is obtained. In specific implementation, in S1, the dried straw is crushed by a pulverizer and then fed into the reaction vessel. Water is added for dilution, and the temperature is raised to about 80°C for hydrothermal pretreatment to destroy the straw fiber structure and make lignin easier to degrade with alkali. In S2, alkali (KOH or NaOH) can be added in 2-3 batches, with different pH values ​​and temperatures controlled at each stage to achieve stepwise degradation of lignin. In S3, the lignin is separated into a fulvic acid liquid phase and an undegraded solid filter residue under pressure using a plate and frame filter press. In S4, according to the target crop (rice requires zinc and silicon, lychee requires boron and magnesium, and banana requires potassium and calcium), corresponding trace elements and functional bacterial solutions are added to the liquid phase. By adopting a stepwise alkali degradation strategy of adding alkali in stages, alkali is added at different stages of the reaction process to compensate for the reaction consumption, so that the reaction system is maintained within the target pH range at each stage. This prevents the reaction from stalling due to excessively low pH in the later stages and significantly improves the conversion rate of lignin to fulvic acid.

[0021] The specific method of adding alkali in S2 is as follows: at least two alkali addition nodes are set along the reaction time axis, with a predetermined time interval between each node. The alkali added at the next node is used to compensate for the amount of alkali consumed in the previous stage of alkaline hydrolysis reaction and to raise the pH of the reaction system to the range required for the next stage, so that the pH value of each stage changes in a stepwise manner. Taking the three-stage addition of alkali as an example, 50-60% of the total alkali can be added at the beginning of the reaction to raise the pH to 11.5-12.0 and initiate alkaline hydrolysis. After 1-1.5 hours of reaction, the pH drops to 9.5-10.0. At this time, 60-70% of the remaining alkali is added to bring the pH back to 11.0-11.5 to continue the reaction. After another 0.5-1 hour, the remaining alkali is added to maintain the pH at 10.5-11.0 until the reaction ends. By adding alkali in stages as described above, the increased side reactions caused by excessively high initial pH due to a single addition of alkali and the reaction stagnation caused by excessively low pH in the later stages can be avoided.

[0022] The target crop in S4 includes at least one of rice, lychee, and banana; the trace elements include at least one of zinc, boron, magnesium, iron, and manganese; and the fermentation liquid includes at least one of phosphate-solubilizing bacteria, potassium-solubilizing bacteria, and nitrogen-fixing bacteria. In specific implementation, for rice, to promote tillering and resist lodging, zinc and silicon (in silicate form) are added, along with nitrogen-fixing bacteria and phosphate-solubilizing bacteria; for lychee, to promote flowering and fruit retention and increase sugar content, boron and magnesium are added, along with phosphate-solubilizing bacteria and potassium-solubilizing bacteria; for banana, to promote robust stems and leaves and fruit enlargement, potassium and calcium are added, along with potassium-solubilizing bacteria. In addition, trace elements are added in the form of soluble salts, while humic acid is used as a protectant and nutrient for the strain to improve the survival rate of the strain.

[0023] It also includes: S5, waste heat recovery: before the high-temperature fulvic acid liquid phase discharged from the plate and frame filter in S3 is sent into the storage tank, it is preheated by exchanging heat with the new feed liquid through a heat exchanger. The fulvic acid liquid phase discharged from the plate and frame filter press still contains residual heat. This high-temperature filtrate is introduced into a heat exchanger to exchange heat with the new feed liquid in a countercurrent manner. After the high-temperature fulvic acid liquid phase is cooled down, it is sent to a storage tank for temporary storage (low-temperature storage is beneficial to the stability of fulvic acid). The new feed liquid is preheated and then sent to the reactor, which reduces the amount of heat required for heating, thereby reducing the heating energy consumption.

[0024] Please see Figure 1As shown, this invention also provides a targeted regulation process for straw-derived fulvic acid liquid fertilizer, used to realize the above-described method for preparing straw-derived fulvic acid liquid fertilizer. This is achieved through the following apparatus: a steam boiler, a preheater, a reactor, a plate and frame filter, a storage tank, a mixing tank, a preparation tank, a seed tank group, a fermentation tank, and a control unit. The steam boiler connects the preheater and the reactor to provide heat energy; the preheater is located upstream of the reactor to preheat the newly fed liquid; the reactor is equipped with an alkali additive unit to add alkali at each stage of the cascade alkali hydrolysis process. The alkaline agent should be added in stages inside the reactor; a plate and frame filter is connected to the outlet of the reactor for solid-liquid separation of the alkaline hydrolysis mixture; a storage tank is connected between the liquid phase outlet of the plate and frame filter and the inlet of the mixing tank for temporary storage of the fulvic acid liquid phase; the mixing tank is used to add trace elements or fermentation liquid according to the needs of the target crop; the preparation tank, seed tank group and fermentation tank are connected in sequence to the inlet of the mixing tank for injecting the prepared functional liquid into the mixing tank; the control unit is electrically connected to the reactor and the alkaline agent addition unit to control the reaction conditions and the timing of alkaline agent addition. In practice, steam generated by the steam boiler is diverted to the preheater and the reactor. The preheater preheats the cold liquid and then sends it to the reactor to reduce the heating load. The control unit in the reactor controls the alkali addition unit to inject alkali in stages to complete the step-by-step alkali hydrolysis. After the alkali hydrolysis is completed, the liquid is sent to the plate and frame filter for solid-liquid separation. The liquid phase enters the storage tank for temporary storage and then is sent to the mixing tank. The nutrient solution is prepared in the mixing tank and then expanded by the seed tank group and deeply fermented in the fermentation tank to obtain the functional bacterial solution. It is then injected into the mixing tank along with trace elements to obtain the finished liquid fertilizer.

[0025] The seed tank group includes a No. 1 seed tank and a No. 2 seed tank connected sequentially along the flow direction of the bacterial culture. The outlet of the preparation tank is connected to the inlet of the No. 1 seed tank, the outlet of the No. 1 seed tank is connected to the inlet of the No. 2 seed tank, and the outlet of the No. 2 seed tank is connected to the inlet of the fermentation tank. This is used for two-stage progressive culture of the bacterial culture. In practice, the nutrient solution prepared in the preparation tank is sterilized and then pumped into the No. 1 seed tank for primary expansion culture to obtain primary seed liquid. The primary seed liquid is then transferred to the No. 2 seed tank at an inoculation rate of 5-10% for secondary expansion culture to obtain secondary seed liquid. Finally, the secondary seed liquid is transferred to the fermenter at an inoculation rate of 5-10% for deep fermentation. The two-stage expansion culture system allows the strain to gradually adapt to the fermentation environment, shortens the fermenter cycle, improves equipment turnover rate, and ensures stable fermentation results.

[0026] It also includes a heat exchanger, which is disposed between the liquid phase outlet of the plate and frame filter and the liquid inlet of the storage tank. By setting up a separate heat exchanger (specifically a plate heat exchanger) specifically for recovering the waste heat from the filtrate discharged from the plate and frame filter, the high-temperature humic acid liquid phase discharged from the plate and frame filter enters the hot liquid channel of the heat exchanger, while the new feed liquid enters the cold liquid channel in the opposite direction for countercurrent heat exchange. After heat exchange, the high-temperature filtrate is cooled and sent to the storage tank, while the new feed liquid is preheated and sent to the reactor. The preheater uses boiler steam to preheat the new feed liquid initially, and the heat exchanger uses the waste heat from the filtrate for secondary preheating. This two-stage preheating achieves cascaded utilization of thermal energy, further reducing boiler steam consumption.

[0027] The plate and frame filter includes alternately arranged filter plates and filter frames, the surface of the filter plates is covered with filter cloth, and the filter frames form a filtration chamber inside; The plate and frame filter consists of a fixed end plate, a clamping end plate, and filter plates and filter frames arranged alternately between the two. The surface of the filter plates is covered with filter cloth, and the filter frames have a hollow structure. A closed filtration chamber is formed between adjacent filter plates and filter frames. The alkaline hydrolysis liquid is pressurized and sent into each filtration chamber by a feed pump. The liquid phase (humic acid solution) passes through the guide grooves on the surface of the filter cloth and filter plates under pressure, and is discharged from the liquid phase outlet after collection. Solid particles are trapped in the filtration chamber by the filter cloth to form a filter cake. After filtration is completed, the hydraulic system releases the clamping end plate, the filter plates and filter frames separate, and the filter cake is automatically unloaded and discharged through the solid phase outlet.

[0028] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for preparing straw-derived humic acid liquid fertilizer, characterized in that: Includes the following steps: S1. Raw material pretreatment: Dry straw is crushed and put into a reaction vessel, water is added and mixed, and the temperature is raised to a preset temperature for hydrothermal pretreatment to obtain a mixed liquid. S2, stepped alkaline hydrolysis: Alkali agent is added to the mixture liquid after S1 treatment in stages. The pH value, reaction temperature and reaction time are controlled at each stage to gradually degrade the lignin in the straw into fulvic acid and dissolve it into the liquid phase, resulting in an alkaline hydrolyzed mixture. S3. Solid-liquid separation: The alkaline hydrolysis mixture obtained in S2 is sent to a plate and frame filter press for solid-liquid separation to obtain humic acid liquid phase and solid filter residue. S4. Liquid phase preparation: The humic acid liquid phase obtained in S3 is sent to the preparation tank. According to the nutrient requirements of the target crop, the corresponding trace elements or fermentation liquid are added. After mixing evenly, the liquid fertilizer product is obtained.

2. The method for preparing straw-derived humic acid liquid fertilizer according to claim 1, characterized in that: The specific method of adding alkali in S2 is as follows: at least two alkali addition nodes are set along the reaction time axis, with a predetermined time interval between each node. The alkali added at the next node is used to compensate for the amount of alkali consumed in the previous stage of alkali hydrolysis reaction and to raise the pH of the reaction system to the range required for the next stage, so that the pH value of each stage changes in a stepwise manner.

3. The method for preparing straw-derived humic acid liquid fertilizer according to claim 2, characterized in that: The target crop in S4 includes at least one of rice, lychee, and banana; the trace elements include at least one of zinc, boron, magnesium, iron, and manganese; and the fermentation broth includes at least one of phosphate-solubilizing bacteria, potassium-solubilizing bacteria, and nitrogen-fixing bacteria.

4. The method for preparing straw-derived humic acid liquid fertilizer according to claim 3, characterized in that: Also includes: S5. Waste heat recovery: Before the high-temperature fulvic acid liquid phase discharged from the plate and frame filter in S3 is sent into the storage tank, it is preheated by exchanging heat with the new feed liquid through a heat exchanger.

5. A targeted regulation process for straw-derived fulvic acid liquid fertilizer, used to achieve the preparation method of straw-derived fulvic acid liquid fertilizer according to any one of claims 1 to 4, characterized in that: This is achieved through the following device: Steam boiler, preheater, reactor, plate and frame filter, liquid storage tank, mixing tank, preparation tank, seed tank group, fermentation tank and control unit, including: A steam boiler connects a preheater and a reaction vessel to provide thermal energy; The preheater is located upstream of the reactor and is used to preheat the new feed liquid; The reactor is equipped with an alkali addition unit, which is used to add alkali to the reactor in stages at each stage of the step-by-step alkaline hydrolysis. The plate and frame filter is connected to the outlet of the reactor and is used for solid-liquid separation of the alkaline hydrolysis mixture. The storage tank is connected between the liquid phase outlet of the plate and frame filter and the liquid inlet of the mixing tank, and is used to temporarily store the fulvic acid liquid phase; The mixing tank is used to add trace elements or fermentation liquid according to the needs of the target crop; The preparation tank, seed tank group and fermentation tank are connected in sequence to the feed inlet of the mixing tank, and are used to prepare functional bacterial liquid and then inject it into the mixing tank; The control unit is electrically connected to the reaction vessel and the alkali addition unit to control the reaction conditions and the timing of alkali addition.

6. The targeted regulation process for straw-derived humic acid liquid fertilizer according to claim 5, characterized in that: The seed tank assembly includes Seed Tank No. 1 and Seed Tank No. 2 connected sequentially along the direction of bacterial culture flow, wherein: The outlet of the preparation tank is connected to the inlet of the first seed tank, the outlet of the first seed tank is connected to the inlet of the second seed tank, and the outlet of the second seed tank is connected to the inlet of the fermentation tank, which is used for two-stage progressive propagation of the strain.

7. The targeted regulation process for straw-derived humic acid liquid fertilizer according to claim 5, characterized in that: It also includes a heat exchanger, which is disposed between the liquid phase outlet of the plate and frame filter and the liquid inlet of the storage tank.

8. The targeted regulation process for straw-derived humic acid liquid fertilizer according to claim 5, characterized in that: The plate and frame filter includes alternately arranged filter plates and filter frames, the surface of the filter plates is covered with filter cloth, and the filter frames form a filtration chamber inside.

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