Preparation method and device of green biochar-based slow release fertilizer

Abstract

The invention discloses a preparation method and device of a green biochar-based slow release fertilizer, and the preparation method comprises the following steps: carrying out pyrolysis carbonization on biomass to obtain biochar and byproducts, and treating the byproducts to obtain wood vinegar, heavy oil and non-condensable gas; mixing biochar with wood vinegar, and carrying out upgrading modification to obtain modified biochar; the modified biochar and a compound fertilizer are mixed, adsorbed and dried to obtain a fertilizer, and the fertilizer and heavy oil are subjected to low-temperature forming treatment according to a certain proportion to obtain the green biochar-based slow release fertilizer. Wherein the non-condensable gas is used for supplying heat to the low-temperature forming process. By utilizing the surface modification effect of the biomass pyrolysis byproduct wood vinegar and the polycondensation carbonization effect of the heavy oil, the wood vinegar is used as a green modifier, the heavy oil is used as a binder, the green preparation method of the carbon-based slow-release fertilizer is innovatively provided, secondary utilization of the byproduct is realized, environmental pollution is reduced, and the environment-friendly effect is achieved. And economic and environment-friendly benefits are obviously obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of high-value utilization of biomass and green circular agriculture, and in particular to a preparation method and a device for a green biochar-based slow-release fertilizer. Background Art

[0002] With the help of biomass pyrolysis technology, agricultural waste can be processed into related products for reuse in agricultural production, which is of great significance for realizing the high value and resource utilization of waste and developing green circular agriculture.

[0003] Modern agriculture relies heavily on chemical fertilizers to improve soil fertility and crop yields, but the low utilization rate of traditional chemical fertilizers often leads to excessive nutrient leaching, causing pollution problems in the farmland ecological environment. For this reason, researchers are increasingly paying attention to the development of green and environmentally friendly slow-release fertilizers to replace traditional chemical fertilizers. Among many options, biochar has a dense porous structure and rich functional groups, and is itself a soil conditioner. It is widely considered to be one of the most promising fertilizer carriers. Therefore, biochar-based slow-release fertilizers (BSRFs) have great potential in simultaneously improving fertilizer utilization efficiency and improving soil.

[0004] At present, the industrial preparation methods of biochar-based slow-release fertilizers mainly include: blending method, coating method, mixed granulation method, etc. Although these methods are widely used, they usually rely on chemical reagents as modifiers, binders or coating materials to ensure the slow-release effect and complete the formation of slow-release fertilizer particles, which have the defects of complex process, high cost and easy to cause secondary pollution.

[0005] In addition to biochar, by-products such as wood vinegar and heavy oil are also separated from the biomass pyrolysis products. The heavy oil has a complex composition and is difficult to use, but its high carbon content and easy carbonization and polycondensation make it have the function of bonding and molding. In the prior art, a preparation method of sludge straw composite biomass activated carbon with publication number CN111453727B discloses that when preparing biomass activated carbon, wood tar is mixed with sludge and agricultural waste for granulation, so that the wood tar can be used as both a carbon enhancer and a binder. However, in this method, although the wood tar can have a bonding effect to a certain extent, it can easily block the pores and affect the pore structure of the biomass activated carbon to a certain extent.

[0006] In view of this, it is necessary to design a preparation method and device of green biochar-based slow-release fertilizer to solve the above problems. Summary of the invention

[0007] The object of the present invention is to provide a method and device for preparing a green biochar-based slow-release fertilizer which can realize the secondary utilization of by-products while reducing environmental pollution, improving economic and environmental benefits, and improving the slow-release effect.

[0008] To achieve the above-mentioned object of the invention, the present invention provides a method for preparing a green biochar-based slow-release fertilizer, comprising the following steps: S1. Pyrolyzing and carbonizing biomass to obtain biochar and by-products, and treating the by-products to obtain wood vinegar, heavy oil and non-condensable gas; S2, mixing the biochar obtained in step S1 with wood vinegar in a certain proportion to improve the quality of the biochar to obtain modified biochar; S3. Mix the modified biochar obtained in step S2 with a certain amount of compound fertilizer for adsorption and then dry to obtain fertilizer, and perform low-temperature molding treatment on the fertilizer and the heavy oil obtained in step S1 in a certain proportion to obtain green biochar-based slow-release fertilizer; wherein the non-condensable gas obtained in step S1 is used to provide heat for the low-temperature molding process.

[0009] As a further improvement of the present invention, in step S1, the biomass is any one of rice straw, wheat straw, cotton straw and soybean straw, or a combination of several of them.

[0010] As a further improvement of the present invention, the temperature of the pyrolysis carbonization is 400-700° C. and the time is 10-60 min.

[0011] As a further improvement of the present invention, in step S1, the by-products are condensed and separated to obtain wood vinegar, heavy oil and non-condensable gas.

[0012] As a further improvement of the present invention, in step S2, the mass ratio of the wood vinegar to the biochar is (10-20):1.

[0013] As a further improvement of the present invention, in step S3, the mass ratio of the compound fertilizer to the modified biochar is (0.4-0.8):1.

[0014] As a further improvement of the present invention, in step S3, the mass ratio of the heavy oil to the fertilizer is (0.05-0.2):1.

[0015] As a further improvement of the present invention, in step S3, the low temperature molding process is specifically: mixing and granulating at 200-400°C.

[0016] The present invention also provides a device for the preparation method of the green biochar-based slow-release fertilizer, comprising: A pyrolysis unit, comprising a pyrolysis reactor and a biochar storage bin connected to the pyrolysis reactor; A condensing unit, comprising a condenser connected to the pyrolysis reactor for condensing by-products and a separator connected to the liquid outlet of the condenser, wherein the condenser is also provided with a non-condensable gas outlet, and the separator is connected to a wood vinegar storage bin and a heavy oil storage bin; A slow-release fertilizer preparation unit comprises a quality improvement and modification mechanism, a fertilizer adsorption mechanism and a low-temperature molding mechanism which are connected in sequence, wherein the quality improvement and modification mechanism is connected to the biochar storage bin and the wood vinegar storage bin, and the low-temperature molding mechanism comprises a molding chamber and an external combustion chamber connected to the non-condensable gas outlet for providing heat to the molding structure.

[0017] As a further improvement of the present invention, an exhaust gas treatment mechanism is connected to the external combustion chamber.

[0018] As a further improvement of the present invention, the compound fertilizer includes nitrogen fertilizer, phosphorus fertilizer and potassium fertilizer.

[0019] The beneficial effects of the present invention are: 1. The present invention modifies biochar by wood vinegar, optimizes the pore structure of biochar, increases the surface functional groups of biochar, strengthens the adsorption capacity of biochar to nutrients such as N, P, and K, improves the adsorption capacity, and can reduce the slow release rate. In addition, by mixing heavy oil with the modified biochar that has adsorbed the composite fertilizer, i.e., fertilizer, for low-temperature molding, the bonding molding function of heavy oil can be fully utilized, and by low-temperature molding, heavy oil can be secondary cracked in this step to form several small pores, so that heavy oil, while having cohesiveness, will not only not block the original pore structure of biochar, but also form a new pore structure, which can enhance the bonding and curing effect while also being conducive to improving the slow release effect of slow-release fertilizer.

[0020] 2. The present invention utilizes the surface modification effect of wood vinegar, a by-product of biomass pyrolysis, and the condensation carbonization effect of heavy oil, and uses wood vinegar as a green modifier and heavy oil as a binder to replace traditional chemical reagents, innovatively proposes a green preparation method for carbon-based slow-release fertilizer, realizes the secondary utilization of by-products, reduces environmental pollution, and significantly achieves economic and environmental benefits.

[0021] 3. The present invention proposes a new path for the resource utilization of agricultural waste, reduces the difficulty of agricultural waste disposal, promotes the directional transformation of straw into high-performance green biochar-based slow-release fertilizer, and realizes the green circular agriculture of "taking from the field and giving back to the field".

[0022] 4. The preparation device of the present invention fully utilizes the three-phase products of biomass pyrolysis, further improves the utilization rate of products and energy, and realizes coupling between devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the overall structure of a device for preparing green biochar-based slow-release fertilizer.

[0024] Figure 2 Schematic diagram of the structure of the pyrolysis reactor.

[0025] Figure 3 Schematic diagram of the condenser structure.

[0026] Figure 4 This is a schematic diagram of the structure of the slow-release fertilizer preparation unit.

[0027] Reference numerals 10. Silo; 11. First feed screw; 20. Pyrolysis reactor; 21. Pyrolysis zone; 211. Material inlet; 212. Biochar outlet; 213. Pyrolysis gas outlet; 214. Bio-oil outlet; 22. Insulation layer; 30. Biochar storage bin; 31. Second feed screw; 40. Condenser; 41. Condensation zone; 411. Gas-liquid inlet; 412. Liquid outlet; 413. Non-condensable gas outlet; 42. Condenser; 421. Condensate inlet; 422. Condensate outlet; 50. Separator; 61. Wood vinegar storage bin; 62. Heavy oil storage bin; 71. Quality improvement and modification mechanism; 72. Fertilizer adsorption mechanism; 731. Molding chamber; 732. External combustion chamber; 733. Gas inlet; 734. Exhaust gas outlet; 735. Exhaust gas treatment mechanism; 75. Slow-release fertilizer storage bin; 76. Third feed screw; 77. Fourth feed screw; 78. Fifth feed screw. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0030] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0031] Example 1 like Figure 1 and Figure 3 As shown, the present invention provides a device for preparing green biochar-based slow-release fertilizer, comprising: A pyrolysis unit, comprising a pyrolysis reactor 20 and a biochar storage bin 30 connected to the pyrolysis reactor 20; A condensing unit, comprising a condenser 40 connected to the pyrolysis reactor 20 for condensing by-products and a separator 50 connected to a liquid outlet 412 of the condenser 40, wherein the condenser 40 is further provided with a non-condensable gas outlet 413, and the separator 50 is connected to a wood vinegar storage bin 61 and a heavy oil storage bin 62; The slow-release fertilizer preparation unit includes a quality improvement and modification mechanism 71, a fertilizer adsorption mechanism 72 and a low-temperature molding mechanism which are connected in sequence, wherein the quality improvement and modification mechanism 71 is connected to the biochar storage bin 30 and the wood vinegar storage bin 61, and the low-temperature molding mechanism includes a molding chamber 731 and an external combustion chamber 732 connected to the non-condensable gas outlet 413 for providing heat to the molding structure.

[0032] Specifically, it also includes a feeding unit, which includes a silo 10 for storing biomass raw materials and a first feeding screw 11 for conveying the biomass raw materials in the silo 10 to the pyrolysis reactor 20 .

[0033] Specifically, Figure 2 As shown, the pyrolysis reactor 20 includes a pyrolysis zone 21 and an insulation layer 22 wound around the pyrolysis zone 21, and the pyrolysis zone 21 is provided with a material inlet 211, a biochar outlet 212, a pyrolysis gas outlet 213 and a bio-oil outlet 214, wherein the biochar outlet 212 is connected to the biochar storage bin 30 through a second feed screw 31.

[0034] Specifically, Figure 3 As shown, the condenser 40 includes a condensation zone 41 and a condensation pipe 42 wound around the condensation zone 41, wherein the condensation zone 41 is provided with a gas-liquid inlet 411, a liquid outlet 412 and a non-condensable gas outlet 413, wherein the pyrolysis gas outlet 213 and the bio-oil outlet 214 on the pyrolysis zone 21 are both connected to the gas-liquid inlet 411. The condensation water inlet 421 and the condensation water outlet 422 of the condensation pipe 42 are both provided at the left end of the condensation zone 41.

[0035] Specifically, Figure 4 As shown, the low-temperature molding mechanism is also connected to a slow-release fertilizer storage bin 75; the quality improvement and modification mechanism 71 is connected to the fertilizer adsorption mechanism 72 via a third feed screw 76, the fertilizer adsorption mechanism 72 is connected to the low-temperature molding mechanism via a fourth feed screw 77, and the low-temperature molding mechanism and the slow-release fertilizer storage bin 75 are connected via a fifth feed screw 78.

[0036] Specifically, a fuel gas inlet 733 and a tail gas outlet 734 are provided on the external combustion chamber 732 . The fuel gas inlet 733 is connected to the non-condensable gas outlet 413 , and the tail gas outlet 734 is connected to a tail gas treatment mechanism 735 .

[0037] Specifically, the feeding screws in this embodiment are all connected to a motor for driving the feeding screws to rotate.

[0038] During operation, the biomass raw materials in the silo 10 are fed into the pyrolysis reactor 20 via the first feeding screw 11, and are pyrolyzed and carbonized to generate biochar, pyrolysis gas and bio-oil, wherein the biochar is fed into the biochar storage bin 30 via the second feeding screw 31, and the pyrolysis gas flows to the gas-liquid inlet 411 of the condensation zone 41 via the pyrolysis gas outlet 213 of the pyrolysis reactor 20, and the bio-oil also flows to the gas-liquid inlet 411 of the condensation zone 41 via the bio-oil outlet 214; thereafter, the pyrolysis gas and the bio-oil are condensed into liquid and flow to the separator 50 via the liquid outlet 412, and are separated by the separator 50 to obtain wood vinegar and heavy oil, which are stored in the wood vinegar storage bin 61 and the heavy oil storage bin 62 respectively, and the non-condensable gas and liquid in the condensation zone 41 flows to the external combustion chamber 732 via the non-condensable gas outlet 413; Then, the biochar and wood vinegar are respectively transported from the biochar storage bin 30 and the wood vinegar storage bin 61 to the upgrading and modification mechanism 71 for upgrading and modification to obtain modified biochar. The modified biochar is transported to the fertilizer adsorption mechanism 72 via the third feeding screw 76 to be mixed with the compound fertilizer for adsorption to obtain fertilizer; the fertilizer is then transported to the molding chamber 731 via the fourth feeding screw 77. At the same time, the heavy oil is also transported from the heavy oil storage bin 62 to the molding chamber 731, so that the fertilizer and the heavy oil are low-temperature molded in the molding chamber 731 to obtain a green biochar-based slow-release fertilizer and transported to the slow-release fertilizer storage bin 75 via the fifth feeding screw 78. During the molding process, the non-condensable gas is used as fuel to provide heat for the molding chamber 731, and the exhaust gas generated by the combustion flows to the exhaust gas treatment mechanism 735 through the external combustion chamber exhaust gas outlet 734 and is safely discharged after treatment.

[0039] Example 2 The present invention also provides a method for preparing a green biochar-based slow-release fertilizer. The preparation method in this embodiment is described in detail in conjunction with a device for preparing the green biochar-based slow-release fertilizer.

[0040] The specific steps are as follows: adding biomass raw materials to the silo 10, the first feeding screw 11 conveys the biomass to the pyrolysis zone 21 of the pyrolysis reactor 20, pyrolysis and carbonization are carried out at 500°C, the generated biochar is conveyed to the biochar storage bin 30 through the second feeding screw 31 for cooling, the generated pyrolysis gas and bio-oil are conveyed to the condensation zone 41 through the pyrolysis gas outlet 213 and the bio-oil outlet 214 for condensation, the liquid phase components obtained by condensation flow through the liquid outlet 412 to the separator 50 to be separated into wood vinegar and heavy oil, and conveyed to the wood vinegar storage bin 61 and the heavy oil storage bin 62 respectively; the non-condensable gas in the pyrolysis gas is discharged to the external combustion chamber 732 through the non-condensable gas outlet 413, and is used as fuel to provide heat for the low-temperature molding process; Then, the wood vinegar and biochar with a mass ratio of 15:1 are transported from the biochar storage bin 30 and the wood vinegar storage bin 61 to the quality improvement and modification mechanism 71, mixed for 10 minutes for quality improvement and modification to obtain modified biochar; thereafter, the modified biochar is transported to the fertilizer adsorption mechanism 72, the compound fertilizer and the modified biochar are mixed and adsorbed at a mass ratio of 0.6:1, and then dried to obtain fertilizer; the fertilizer is transported to the molding chamber 731, and the heavy oil is transported from the heavy oil storage bin 62 to the molding chamber 731, the heavy oil and fertilizer are subjected to low-temperature molding treatment at a mass ratio of 0.1:1 to obtain a green biochar-based slow-release fertilizer, wherein non-condensable gas is used to provide heat for the low-temperature molding process, the temperature during the low-temperature molding process is 300°C, and the time is 30 minutes.

[0041] Embodiment 3-4 Examples 3 and 4 respectively provide a method for preparing a green biochar-based slow-release fertilizer. Compared with Example 2, the low-temperature molding temperature in Examples 3 and 4 is adjusted from 300°C to 200°C and 400°C, respectively. The remaining steps are consistent with Example 2 and are not repeated here.

[0042] Embodiment 5-6 Examples 5 and 6 respectively provide a method for preparing a green biochar-based slow-release fertilizer. Compared with Example 2, the mass ratio of heavy oil to fertilizer in Examples 5 and 6 is adjusted from 0.1:1 to 0.05:1 and 0.2:1, respectively. The remaining steps are consistent with Example 2 and are not repeated here.

[0043] Comparative Example 1-2 Comparative Examples 1 and 2 respectively provide a method for preparing a green biochar-based slow-release fertilizer. Compared with Example 2, the low-temperature molding temperature in Comparative Examples 1 and 2 is adjusted from 300°C to 150°C and 450°C, respectively, and the remaining steps are consistent with Example 2 and are not repeated here.

[0044] Comparative Examples 3-4 Comparative Examples 3 and 4 respectively provide a method for preparing a green biochar-based slow-release fertilizer. Compared with Example 2, the mass ratio of heavy oil to fertilizer in Comparative Examples 3 and 4 is adjusted from 0.1:1 to 0.05:1 and 0.3:1, respectively. The remaining steps are consistent with Example 2 and are not repeated here.

[0045] Examples 2-6 can all prepare green biochar-based slow-release fertilizers with good slow-release effects. Since the molding process is carried out at a certain temperature, the heavy oil can undergo secondary cracking to form new pores, thereby avoiding the situation where the heavy oil blocks the original pore structure of the biochar. As a result, while utilizing the adhesion of the heavy oil to bond the fertilizer into shape, the slow-release effect of the slow-release fertilizer can also be improved. The cracking change of the heavy oil can also have a solidification effect to a certain extent, thereby ensuring the molding effect of the slow-release fertilizer.

[0046] Compared with Example 2, in Comparative Example 1, when the low-temperature molding temperature is too low, it will affect the cracking of heavy oil, further causing the heavy oil to block the original pores of the biochar and affect the slow-release effect of the slow-release fertilizer. In addition, too low a temperature will also affect the solidification effect of the heavy oil, resulting in a poor molding effect of the slow-release fertilizer obtained in the end, which will deform under a slight external force, affecting the subsequent use of the slow-release fertilizer. In Comparative Example 2, when the low-temperature molding temperature is too high, the biochar will undergo a reduction reaction, affecting the modification effect of the wood vinegar on the biochar in the early stage, resulting in a poor slow-release effect of the slow-release fertilizer obtained in the end.

[0047] In comparative examples 3 and 4, when the proportion of heavy oil is too low, the bonding effect is poor, and when the proportion of heavy oil is too high, the subsequent slow-release effect will be affected. In particular, compared with the existing method of directly mixing biochar with compound fertilizer and a binder for simultaneous fertilizer adsorption and molding, the present invention first completes the adsorption of fertilizer and then uses heavy oil for low-temperature molding, which can avoid the poor uniformity of compound fertilizer loading on biochar while ensuring the bonding and molding effect of slow-release fertilizer, so that the slow-release fertilizer can be uniformly and stably released, thereby improving the slow-release effect.

[0048] The present invention uses biochar as a slow-release fertilizer carrier, uses the by-product wood vinegar as a modifier, and heavy oil as a binder to complete the directional construction of green biochar-based slow-release fertilizer, and uses non-condensable gas as fuel for auxiliary heating, making full use of the three-phase products of biomass pyrolysis, realizing the green and efficient preparation of biochar-based slow-release fertilizer, thereby promoting the green cycle of agricultural waste and achieving both economic and environmental benefits.

[0049] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. 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 solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a green biochar-based slow-release fertilizer, characterized in that: The following steps are involved: S1. Pyrolyzing and carbonizing biomass to obtain biochar and by-products, and treating the by-products to obtain wood vinegar, heavy oil and non-condensable gas; S2, mixing the biochar obtained in step S1 with wood vinegar in a certain proportion to improve the quality of the biochar to obtain modified biochar; S3. Mix the modified biochar obtained in step S2 with a certain amount of compound fertilizer for adsorption and then dry to obtain fertilizer, and perform low-temperature molding treatment on the fertilizer and the heavy oil obtained in step S1 in a certain proportion to obtain green biochar-based slow-release fertilizer; wherein the non-condensable gas obtained in step S1 is used to provide heat for the low-temperature molding process.

2. The method for preparing the green biochar-based slow-release fertilizer according to claim 1, characterized in that: In step S1, the biomass is any one of rice straw, wheat straw, cotton straw and soybean straw, or a combination of several of them.

3. The method for preparing the green biochar-based slow-release fertilizer according to claim 1, characterized in that: The temperature of the pyrolysis carbonization is 400-700° C., and the time is 10-60 minutes.

4. The method for preparing the green biochar-based slow-release fertilizer according to claim 1, characterized in that: In step S1, the by-products are condensed and separated to obtain wood vinegar, heavy oil and non-condensable gas.

5. The method for preparing the green biochar-based slow-release fertilizer according to claim 1, characterized in that: In step S2, the mass ratio of the wood vinegar to the biochar is (10-20):

1.

6. The method for preparing the green biochar-based slow-release fertilizer according to claim 1, characterized in that: In step S3, the mass ratio of the compound fertilizer to the modified biochar is (0.4-0.8):

1.

7. The method for preparing the green biochar-based slow-release fertilizer according to claim 1, characterized in that: In step S3, the mass ratio of the heavy oil to the fertilizer is (0.05-0.2):

1.

8. The method for preparing the green biochar-based slow-release fertilizer according to claim 1, characterized in that: In step S3, the low temperature forming process is specifically: mixing and granulating at 200-400°C.

9. A device for the preparation method of the green biochar-based slow-release fertilizer according to claim 1, characterized in that: include: A pyrolysis unit, comprising a pyrolysis reactor and a biochar storage bin connected to the pyrolysis reactor; A condensing unit, comprising a condenser connected to the pyrolysis reactor for condensing by-products and a separator connected to the liquid outlet of the condenser, wherein the condenser is also provided with a non-condensable gas outlet, and the separator is connected to a wood vinegar storage bin and a heavy oil storage bin; A slow-release fertilizer preparation unit comprises a quality improvement and modification mechanism, a fertilizer adsorption mechanism and a low-temperature molding mechanism which are connected in sequence, wherein the quality improvement and modification mechanism is connected to the biochar storage bin and the wood vinegar storage bin, and the low-temperature molding mechanism comprises a molding chamber and an external combustion chamber connected to the non-condensable gas outlet for providing heat to the molding structure.

10. The device for preparing the green biochar-based slow-release fertilizer according to claim 9, characterized in that: The external combustion chamber is connected with an exhaust gas treatment mechanism.

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