Method for preparing a litter-based biochar and method for soil carbon sequestration

Abstract

The application discloses a preparation method of litter-based biochar and a soil carbon fixation method. The preparation method of the litter-based biochar comprises the following steps: (1) collecting litter as coarse material, and crushing the coarse material to obtain fine material; (2) drying the fine material, and then forming the fine material into particles; and (3) pyrolyzing the particles after the particle forming, so as to obtain the litter-based biochar. The litter and other waste biomasses with small bulk density are first formed into particles and then pyrolyzed, so that the yield, stability and the carbon fixation and emission reduction potential in soil of the biochar are significantly increased. Through technical means, the carbon fixation rate of the litter for producing the biochar and the stability of the litter-based biochar are enhanced, and then the carbon fixation and emission reduction potential of the litter-based biochar in soil is improved. The particle biochar produced by the application has better yield, carbon content, carbon stability and soil carbon fixation and emission reduction potential compared with the biochar without particle forming.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbon neutralization, and particularly relates to a preparation method of litter-based biochar and a soil carbon sequestration method. BACKGROUND

[0002] Plants fix carbon dioxide in the atmosphere through photosynthesis, and the fixed carbon is released back into the atmosphere through respiration and decomposition, forming a macro carbon cycle. This process maintains the overall carbon balance. A large amount of litter is produced every year, and most of the carbon in the litter enters the atmosphere in the form of carbon dioxide after short-term decomposition. If the carbon in the litter is locked in the form of biochar and added to the soil for carbon sequestration, it can prevent them from returning to the atmosphere after rapid decomposition, thereby reducing the concentration of atmospheric carbon dioxide and playing a role in carbon sequestration and emission reduction.

[0003] The litter has a small bulk density, and most of it becomes ash after direct pyrolysis. The carbon elements contained therein are mostly returned to the atmosphere in the form of carbon dioxide. The biochar produced by such burning has a low yield, poor aromaticity and stability. Therefore, it is of great significance to improve the carbon sequestration and emission reduction potential of litter-based biochar in the soil, mainly including improving the carbon locking capacity of biochar pyrolysis and reducing the potential of soil carbon dioxide and other greenhouse gas emissions.

[0004] The carbon content, aromatic carbon content, H / C org , and defects of biochar are important indicators for measuring carbon stability. Carbon stability will affect the decomposition of biochar in the soil system and the induced soil organic carbon priming effect, thereby disturbing the apparent carbon and nitrogen related greenhouse gas emission flux of the soil, and further affecting the carbon sequestration potential of litter-based biochar in the soil. The commonly used biomass raw materials for producing biochar at present mainly include crop straw, forest waste, poultry manure, sludge, algae and the like.

[0005] For example, the application with the publication number CN109775684A discloses a method for preparing biochar by using rice straw, which comprises the following steps: selecting the straw after harvesting and stacking and airing. The application uses straw with extremely low cost as the raw material of biochar, and pre-crushes and dries the straw. Then, the straw is burned by a dry distillation type carbonization furnace, and the conveying device and the cooling device are matched with the furnace, so that the burning and cooling of the straw can form a flow line operation. Then, the wood vinegar liquid produced by burning the straw is diluted with pure water according to a proportion to form a modified liquid, which greatly reduces the modification cost of biochar. Finally, the biochar is sieved to reach the specified particle size.

[0006] The invention with publication number CN113526808A provides a preparation method of sludge-based biochar and sludge-based biochar, comprising the following steps: S1, adding acid and water to the sludge and stirring, and injecting into the sludge chamber; S2, placing the electrolyte in the cathode chamber and the water in the anode chamber, and adjusting the pH of the cathode chamber to be acidic; wherein the cathode chamber, the sludge chamber and the anode chamber are sequentially separated by a hole-containing partition plate and filter paper; S3, inserting the electrodes into the cathode chamber and the anode chamber respectively, connecting the power supply, and stirring the sludge in the sludge chamber; S4, centrifugal dewatering, drying and grinding the sludge obtained in step S3; S5, pyrolyzing the sludge obtained in step S4 under the protection of inert gas, cooling, and obtaining sludge-based biochar.

[0007] Although litter is abundant in resources, its bulk density is small, and it is basically burned into ash in the natural environment without oxygen, so its utilization rate is very low. If the yield of litter-based biochar and the stability of litter-based biochar can be enhanced through technical means, the abundant resource of litter can be used for soil carbon sequestration and emission reduction, providing an important technical means for carbon neutralization and relieving the atmospheric greenhouse effect. SUMMARY

[0008] The present application provides a preparation method of litter-based biochar and a soil carbon sequestration method to overcome the shortcomings of using litter to prepare biochar and utilize carbon sequestration and emission reduction in the prior art.

[0009] A preparation method of litter-based biochar, comprising the following steps:

[0010] (1) collecting litter as coarse material, and crushing the coarse material to obtain fine material;

[0011] (2) drying the fine material, and then forming into granules;

[0012] (3) pyrolyzing the granules after granulation to prepare litter-based biochar.

[0013] The litter is at least one of fallen leaves, branches and straws.

[0014] Preferably, in step (1), the diameter of the fine material obtained after crushing is 1-2 mm, and the length is 1-20 mm. If the particle size of the fine material obtained during crushing is too large, it may lead to poor granulation effect.

[0015] Preferably, in step (2), the drying temperature is 120-160℃, and the moisture content after drying is controlled at 15%-20%.

[0016] Preferably, in step (2), a granulator is used for granulation, and the pressure during granulation is controlled at 70-200Mpa.

[0017] Preferably, in step (2), the density of the pellets obtained after the pelletizing is 1.1-1.4 kg / m 3 . The density before the pelletizing is about 0.10-0.25 kg / m 3 .

[0018] Preferably, in step (3), the temperature for the pyrolysis is 300-700℃. In an alternative way, the temperature for the pyrolysis is 300-500℃. In an alternative way, the temperature for the pyrolysis is 600-700℃. Limited oxygen is needed during the pyrolysis, but no absolute oxygen is needed, so no nitrogen is needed to be introduced, which can save cost.

[0019] The yield of the biochar refers to the mass of the biochar produced per unit mass of the biomass. The carbon sequestration potential of the biochar in the soil includes the following two aspects: one is the carbon sequestration amount of the biochar itself (m 锁碳量 = m 生物质使用量 × biochar yield % × biochar carbon content %); and the other is the influence of the biochar on the flux of carbon dioxide, methane or nitrous oxide (converted into carbon dioxide equivalent) in the soil within a certain time boundary.

[0020] The application further provides a method for carbon sequestration in soil, comprising the following steps:

[0021] (1) preparing litter-based biochar from litter by using the method for preparing litter-based biochar;

[0022] (2) applying the litter-based biochar to farmland soil.

[0023] The prepared litter-based biochar pellets are applied to farmland soil, which can optimize soil properties as a soil conditioner and perform carbon sequestration, thereby playing a role in carbon sequestration and emission reduction. In general, the litter-based biochar is uniformly mixed into the surface soil, and the soil depth is 10-20 cm.

[0024] The application significantly increases the yield, stability and carbon sequestration and emission reduction potential in soil of the biochar by first pelletizing the litter and other waste biomass with a small bulk density and then pyrolyzing. The carbon sequestration rate of the litter-based biochar and the stability of the litter-based biochar are enhanced by technical means, thereby improving the carbon sequestration and emission reduction potential in soil of the litter-based biochar. The pelletized biochar produced by the application has better yield, carbon content, carbon stability and carbon sequestration and emission reduction potential in soil than the biochar without pelletizing. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The figure is a comparison result graph of different biochar yields (a), different biochar carbon contents (b) and different biochar carbon sequestration rates (c).

[0026] Figure 2 H / C for different biochar org (a) Comparison of carbon element defects (b) of different biochar.

[0027] Figure 3 (a-e) Time series of CO2 emission flux induced by different biochar in soil, (f) Comparison of cumulative CO2 emission value induced by different biochar in soil. DETAILED DESCRIPTION

[0028] Example 1

[0029] Collect the litter of a certain forest in Zunyi, Guizhou, and crush the coarse litter into fine materials with a diameter range of 1-2 mm and a length range of 1-20 mm using a crusher, which is recorded as "biomass raw material A without compression". After drying the fine materials at 120-160°C (water content controlled at 15%-20%), compress and form them into particles using a compression machine, which is recorded as "compressed biomass raw material B" (granulator model: XGJ560, pressure controlled at about 120 Mpa, particle density after compression at 1.1-1.4 kg / m 3 ). Prepare 10 different types of biochar at 300°C, 400°C, 500°C, 600°C, and 700°C using raw materials A and B, respectively, which are recorded as BC300-A, BC400-A, BC500-A, BC600-A, BC700-A, BC300-B, BC400-B, BC500-B, B600C-B, and BC700-B.

[0030] Char production steps: 1. Fill the biomass raw material into the crucible cup and send it to the pyrolysis furnace for thermal cracking; 2. First, preheat the pyrolysis furnace to 80°C, and then increase the temperature to the target temperature at a rate of 5°C / min; 3. Stop heating after 2 hours of pyrolysis at the target temperature, and take out the produced biochar after cooling. No nitrogen gas is needed throughout the process.

[0031] Determine the yield, carbon content, carbon sequestration rate (carbon fixation rate), H / C org , and defects of each biochar, respectively.

[0032] Table 1 Comparison of yield, carbon fixation rate, and defect data of different biochar

[0033]

[0034] Note: 1. The values in parentheses represent the standard deviation of the sample (confidence level 95% CI); 2. The letters a, b, c, etc. after the parentheses represent the restrictive difference, and the same letters indicate that there is no significant difference between groups, and different letters indicate that there is a significant difference between groups, P<0.05.

[0035] Experimental results are as follows Figure 1 , Figure 2 As shown in Table 1. Figure 1 It has been fully demonstrated that pelleting can significantly improve the biochar yield for biochar produced at any temperature from low temperature (300℃) to high temperature (700℃), thereby greatly increasing the base amount of biochar available for soil carbon sequestration each year; pelleting can significantly improve the carbon content of biochar produced at medium and high temperatures (600℃ and 700℃); pelleting can significantly improve the production carbon sequestration rate or thermal decomposition carbon sequestration rate (yield multiplied by carbon content) of biochar produced at all temperatures, and this effect is most significant at medium and high temperatures (600℃ and 700℃). Figure 2 a indicates that pelletizing increases the H / C ratio of low-temperature biochar (300–500°C). org H / C ratio of medium- and high-temperature biochar org No significant impact. Figure 2 b indicates that pelletizing reduces carbon defects in biochar at various temperatures (the reduction is most significant for high-temperature biochar), thereby enhancing the stability and antioxidant properties of carbon in biochar and ultimately increasing its carbon sequestration potential in soil.

[0036] Example 2

[0037] Ten types of biochar prepared in Example 1 (including BC300-A, BC400-A, BC500-A, BC600-A, BC700-A, BC300-B, BC400-B, BC500-B, B600C-B, and BC700-B) were added to a typical paddy soil from the Jiangsu and Zhejiang regions as experimental groups. Soil columns containing only paddy soil without biochar were used as control groups. A soil column carbon fixation simulation experiment was conducted, and the CO2 emission flux from the soil surface of different groups of soil columns was measured to investigate and verify that granulated biochar has a better performance in reducing soil CO2 emissions than fragmented biochar.

[0038] Table 2 shows the short-term effects of high-temperature biochar on soil CO2 release flux.

[0039]

[0040] Note: 1. The value in parentheses represents the standard deviation of the sample (95% confidence level CI); 2. The letters a, b, c, etc. after the parentheses indicate the limiting difference. The same letter indicates that there is no significant difference between groups, and different letters indicate that there is a significant difference between groups (P<0.05).

[0041] Experimental results are as follows Figure 3 And as shown in Table 2. From Figure 3 As can be seen from a, 3b, and 3c, for low-temperature biochar (300–500℃), there is no significant difference in soil CO2 emission flux between granulated biochar and fragmented biochar.Figure 3 d、3eIt can be seen that, for medium-high temperature biochar (600℃ and 700℃), the pelletized biochar has better and more significant performance of reducing soil CO2 emission than the fragmented biochar. Figure 3 fThe comparison of the soil cumulative CO2 emission values induced by different biochars can further prove that the pelletization can effectively reduce the soil CO2 emission in the presence of medium-high temperature biochar, thereby enhancing the carbon sequestration and emission reduction potential of biochar in soil.

[0042] In summary, the results of Example 1 and Example 2 can fully prove that the pelletization can significantly increase the yield of the biochar in the oxygen-limited pyrolysis process at each temperature, the carbon sequestration rate of the biochar produced at each temperature or the pyrolysis carbon sequestration rate (yield multiplied by carbon content), thereby greatly increasing the base of the amount of biochar available for soil carbon sequestration per year. At the same time, the pelletization can significantly increase the carbon content of medium-high temperature biochar (600℃ and 700℃), reduce the defects of carbon and reduce the soil CO2 emission in the short term. In summary, the biochar produced by pelletization before pyrolysis of biomass can effectively improve the carbon sequestration rate of litter-based biochar and its soil carbon sequestration and emission reduction potential.

Claims

1. A method for soil carbon sequestration, characterized in that, Includes the following steps: S1: Prepare litter-based biochar from litter; S2: Apply the litter-based biochar to farmland soil; The preparation method of litter-based biochar in step S1 includes the following steps: (1) Collect fallen leaves as coarse material, and crush the coarse material to obtain fine material; (2) Dry the fine material at a temperature of 120~160℃, and control the moisture content after drying to 15%~20%; then granulate it using a pellet mill, and control the pressure at 70~200MPa; the density of the granules obtained after granulation is 1.1~1.4kg / m³. 3 ; (3) The granulated particles are subjected to thermal pyrolysis to prepare litter-based biochar; the thermal pyrolysis temperature is 600~700℃.

2. The soil carbon sequestration method according to claim 1, characterized in that, The fallen material is at least one of fallen leaves, dead branches, and straw.

3. The soil carbon sequestration method according to claim 1, characterized in that, In step (1), the fine material obtained after crushing has a diameter of 1~2mm and a length of 1~20mm.

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