How to Analyze Biochar

Abstract

To provide a method for analyzing biochar suitable for efficiently analyzing the quality of the carbon. [Solution] A method for analyzing biochar using thermogravimetry, comprising the steps of heating a sample made of biochar to a first temperature zone of 900°C or higher in an atmosphere of a non-oxygen-containing gas, cooling the sample to a second temperature zone of 300°C or lower, heating the sample to a third temperature zone of 900°C or higher in an atmosphere of an oxygen-containing gas and combusting it, estimating the carbonization temperature of the sample based on the change in weight of the sample in the step of heating to the first temperature zone, and estimating the amount of carbon dioxide stored in the sample based on the change in weight of the sample in the step of heating to the third temperature zone and combusting it.

Description

[Technical field]

[0001] The present invention relates to a method for analyzing biochar. [Background technology]

[0002] In recent years, carbon capture and storage (CCS) through the application of biochar to soil, etc., has attracted worldwide attention as a simple method for reducing atmospheric carbon dioxide. The report of the Intergovernmental Panel on Climate Change (IPCC) includes an example of a formula for calculating the amount of carbon dioxide stored by the application of biochar, and it is possible to calculate the amount of carbon dioxide stored using values ​​classified by the type of biochar and the carbonization method. However, this method does not allow the amount of carbon dioxide stored to be calculated unless the quality of the biochar used is clearly known. Therefore, in order to calculate the amount of carbon dioxide stored, we are currently performing coal quality analysis based on JIS M8812 (Coals and cokes - proximate analysis method). However, problems with coal quality analysis based on JIS M8812 include the time required for analysis and the large error due to differences in analysts because the analysis is done manually. In the analysis of coals and cokes, a method is known in which moisture, volatile matter, fixed carbon, and ash are measured using a thermobalance device with a temperature profile similar to that of JIS 8812, without relying on manual analysis (see, for example, Patent Document 1). In the analysis of biochar, it is important to understand the coal quality, such as the carbonization temperature, but it has been difficult to obtain information on the coal quality of biochar using conventional methods. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 61-191950 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention was devised under the above circumstances, and its main objective is to provide a biochar analysis method suitable for efficiently analyzing carbon quality. [Means for solving the problem]

[0005] As a result of intensive research by the inventors into the above-mentioned problems, they discovered that when measuring the weight and analyzing biochar by thermogravimetry, it is possible to estimate the carbon quality (carbonization temperature and amount of carbon dioxide stored) by heating the sample under specified conditions, then cooling it, and then heating it again and burning it, which led to the completion of the present invention.

[0006] A method for analyzing biochar provided by a first aspect of the present invention is a method for analyzing biochar by thermogravimetry, comprising the steps of heating a sample made of biochar to a first temperature zone of 900°C or higher in an atmosphere of an oxygen-free gas, cooling the sample to a second temperature zone of 300°C or lower, heating the sample to a third temperature zone of 900°C or higher in an atmosphere of an oxygen-containing gas and combusting it, estimating the carbonization temperature of the sample based on the change in weight of the sample in the step of heating to the first temperature zone, and estimating the amount of carbon dioxide stored in the sample based on the change in weight of the sample in the step of heating to the third temperature zone and combusting it.

[0007] In a preferred embodiment of the first aspect of the present invention, in the step of estimating the carbonization temperature of the sample, data analyzing the relationship between the carbonization temperature and the pyrolysis temperature in the oxygen-free gas atmosphere for each type of biochar raw material is accumulated in advance, and the pyrolysis temperature of the sample in the oxygen-free gas atmosphere is compared with the data to estimate the carbonization temperature of the sample.

[0008] A method for analyzing biochar provided by a second aspect of the present invention is a method for analyzing biochar by thermogravimetry, comprising the steps of heating a sample made of biochar to a first temperature zone of 900°C or higher in an atmosphere of an oxygen-free gas, cooling the sample to a second temperature zone of 300°C or lower, heating the sample to a third temperature zone of 900°C or higher in an atmosphere of an oxygen-containing gas and combusting it, estimating the raw material type and carbonization temperature of the sample based on the change in weight of the sample in the steps of heating to the first temperature zone, cooling to the second temperature zone, and heating to the third temperature zone and combusting it, and estimating the amount of carbon dioxide stored in the sample based on the change in weight of the sample in the step of heating to the third temperature zone and combusting it.

[0009] In a preferred embodiment of the second aspect of the present invention, in the step of estimating the carbonization temperature and raw material type of the sample, data analyzing the relationship between the carbonization temperature and five parameters, i.e., the pyrolysis temperature in the oxygen-free gas atmosphere, the weight loss rate in the oxygen-free gas atmosphere, the pyrolysis temperature in the oxygen-containing gas atmosphere, the weight loss rate in the oxygen-containing gas atmosphere, and the residue ratio, for each type of raw material of biochar is accumulated in advance, and the raw material type and carbonization temperature of the sample are estimated by comparing the five parameters of the sample with the data. Effect of the Invention

[0010] According to the biochar analysis method of the present invention, it is possible to estimate the carbon quality (carbonization temperature and carbon dioxide storage amount) of biochar. In carbon sequestration by the use of biochar, the carbonization temperature of the biochar is an important factor in evaluating the carbon quality, and according to the present invention, it is possible to appropriately estimate the carbonization temperature of biochar.

[0011] Other features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0012] [Figure 1] 1 is a graph showing the relationship between temperature change and sample weight by a thermogravimetric method in the first embodiment of the biochar analysis method according to the present invention. [Diagram 2] 1 is a graph showing an example of a change in sample weight for each carbonization temperature in a process of increasing the temperature to a first temperature zone. [Diagram 3] 1 is a graph showing the relationship between the carbonization temperature and the pyrolysis temperature in an oxygen-free gas atmosphere depending on the type of biochar raw material in the process of raising the temperature to the first temperature zone. [Figure 4] 1 is a graph showing the relationship between fixed carbon in proximate analysis and weight loss rate in air in thermogravimetry. [Diagram 5] 1 is a graph showing the relationship between temperature change and sample weight by a thermogravimetric method in the second embodiment of the biochar analysis method according to the present invention. [Figure 6] This is a graph showing the relationship between temperature change and sample weight when the type of biochar raw material is different. [Figure 7] This is a graph showing the relationship between temperature change and sample weight when the carbonization temperature of biochar is different. [Figure 8] This is a graph showing the relationship between temperature change and sample weight when the carbonization temperature of biochar is different. [Figure 9] FIG. 11 is a diagram showing an example of various parameters derived from the relationship between temperature change and sample weight. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[0014] First Embodiment A first embodiment of the biochar analysis method according to the present invention will be described. In this embodiment, a biochar sample was prepared, and the weight of the sample was measured by thermogravimetry while changing the temperature of the sample, and the measurement results were analyzed. In addition, the components of the sample were analyzed by industrial analysis, which is a conventional method, and compared with this analysis method (thermogravimetry). Here, "biochar" refers to any carbonized material obtained by carbonizing organic matter (biomass) derived from living organisms. There are many types of raw materials for biochar, such as carbonized materials derived from wood, herbs, rice husks and rice straw, wheat husks, wheat straw, buckwheat husks, bean husks, bagasse, nuts, sludge, and livestock manure, and bamboo charcoal.

[0015] <Sample preparation> Biomass, which is the raw material for biochar, was carbonized at a specified temperature to prepare samples. Specifically, the biomass raw material was heat-treated at a specified temperature of 300-800°C in a semi-closed iron container placed in an electric furnace to obtain biochar samples. Biochar samples were prepared for each type of raw material for biochar, with carbonization temperatures of 300°C, 350°C, 400°C, 500°C, 600°C, 700°C, and 800°C.

[0016] <Measurement of samples by thermogravimetry> Measurement or analysis of a sample by the thermogravimetry is performed using, for example, a thermobalance device. In this embodiment, the thermobalance device is used to analyze the sample in conjunction with an autosampler. First, a sample made of biochar is heated to 900°C or higher (a step of heating to the first temperature zone), then the sample is cooled to 300°C or lower and cooled (a step of lowering the temperature to the second temperature zone), and then heated again to 900°C or higher and combusted (a step of heating to the third temperature zone and combusting). The steps of heating the sample to 900°C or higher (a step of heating to the first temperature zone) and then lowering the temperature to 300°C or lower (a step of lowering the temperature to the second temperature zone) are performed in an atmosphere of a non-oxygen-containing gas (e.g., nitrogen gas). The steps of heating the sample to 900°C or higher and combusting it (a step of heating to the third temperature zone and combusting it) are performed in an atmosphere of an oxygen-containing gas (e.g., air). Then, the sample weight (TG) was continuously measured during the process of changing the temperature of the sample as described above.

[0017] <Industrial analysis> The proximate analysis for the comparative study was carried out in accordance with JIS M8812 (coals and cokes - proximate analysis method), and the weight ratios of volatile matter, fixed carbon, and ash were obtained.

[0018] FIG. 1 is a graph showing an example of the relationship between the temperature change and the weight of a sample measured by a thermogravimetric method. In the example shown in FIG. 1, a sample made of biochar was first heated from room temperature to about 950°C in a nitrogen gas atmosphere (a step of heating to the first temperature zone). The heating rate was 10°C / min. After heating, the high temperature state of about 950°C was maintained for about 10 minutes. Next, the sample was cooled to about 260°C (a step of cooling to the second temperature zone). The heating rate was 10°C / min. After cooling, the low temperature state of about 260°C was maintained for about 10 minutes. After that, the sample was heated to about 950°C in an air atmosphere and burned (a step of heating to the third temperature zone and burning). The heating rate was 10°C / min. The thin line in FIG. 1 represents the temperature of the sample.

[0019] In the example shown in FIG. 1, the sample is biochar of red pine (derived from wood), and the carbonization temperature of the sample is 500°C. The thick line in FIG. 1 represents the sample weight (TG). The sample weight is expressed as a percentage, which is the ratio of the weight of the sample at the time of measurement to the weight of the sample before the start of the measurement. Note that the temperature change of the sample shown in FIG. 1 is one example, and the present analysis method is not limited to this. The temperature increase rate and temperature decrease rate of the sample are also not limited to the example shown in the figure.

[0020] <Estimation of carbonization temperature of sample> The results of the measurements obtained by heating, lowering, and burning the sample at elevated temperature as described above using the thermogravimetry method were analyzed. In the process of heating the sample in a nitrogen gas atmosphere (the process of heating to the first temperature zone), the sample undergoes thermal decomposition as the temperature is raised, resulting in a decrease in weight. Here, the thermal decomposition temperature of the sample in a nitrogen gas atmosphere is considered to be approximately the same as or higher than the carbonization temperature of the sample. Here, the change in sample weight at each carbonization temperature in the process of heating the sample in a nitrogen gas atmosphere was analyzed.

[0021] FIG. 2 is a graph showing an example of the change in sample weight for each carbonization temperature in the process of heating the sample under a nitrogen gas atmosphere. FIG. 2 shows the weight change of a sample made of red pine (wood-derived) biochar. Specifically, the relationship between the sample temperature and the sample weight (TG) for each carbonization temperature is shown. When the sample temperature exceeds about 200°C, the weight gradually starts to decrease due to the thermal decomposition of the volatile matter. The temperature of the inflection point of the sample weight curve at the start of the weight decrease (the inflection point is plotted in FIG. 2) was determined as the thermal decomposition temperature of the sample under a nitrogen gas atmosphere. From the graph shown in FIG. 2, the following findings (1) and (2) were obtained. (1) As the carbonization temperature of the sample becomes higher, the thermal decomposition temperature also shifts to the higher temperature side. (2) As the carbonization temperature of the sample becomes higher, the amount of thermal decomposition decreases.

[0022] FIG. 3 is a graph showing the relationship between the carbonization temperature of biochar and the pyrolysis temperature in a nitrogen gas atmosphere depending on the type of raw material of the biochar in the process of increasing the temperature of the sample in a nitrogen gas atmosphere.

[0023] The relationship between the carbonization temperature for each type of biochar raw material and the pyrolysis temperature under a nitrogen gas atmosphere thus obtained is stored as known sample data. Then, a new biochar sample to be analyzed is similarly measured using the thermogravimetric method of the present embodiment. The pyrolysis temperature under a nitrogen gas atmosphere calculated from the weight change during the process of heating the sample under a nitrogen gas atmosphere (the process of heating the sample to the first temperature zone) is compared with the known sample data to estimate the carbonization temperature of the biochar sample to be analyzed.

[0024] <Estimation of carbon dioxide retention in samples> Based on the measurement results by the thermogravimetry described above with reference to FIG. 1, the weight loss rate of biochar under air was determined. In the example shown in FIG. 1, the arrow "A" corresponds to the weight loss rate under a nitrogen gas atmosphere (hereinafter, appropriately referred to as "weight loss rate under nitrogen"), and the arrow "B" corresponds to the weight loss rate under an air atmosphere (hereinafter, appropriately referred to as "weight loss rate under air"). In the case of the biochar shown in FIG. 1 (raw material is red pine and carbonization temperature is 500°C), the weight loss rate under nitrogen is about 20%, and the weight loss rate under air is about 79%. Note that weight loss is observed in the early stage of the process of heating the biochar sample under a nitrogen gas atmosphere (the process of heating to the first temperature zone), and this weight loss corresponds to the moisture remaining in the biochar sample. The weight loss rate under nitrogen and the weight loss rate under air are expressed as percentages based on the sample weight after moisture has been removed. This is also true in the second embodiment described below.

[0025] The weight loss rate under nitrogen measured by thermogravimetry is the weight loss due to thermal decomposition and corresponds to the volatile matter in proximate analysis (JIS M8812). The weight loss rate under air measured by thermogravimetry is the weight loss due to combustion and corresponds to the fixed carbon in proximate analysis.

[0026] According to the methodology (AG-004) of the J-Credit Scheme certified by the government, the carbonization temperature of the charred material must be estimated to calculate the amount of carbon dioxide stored in the credit generated by biochar application, and a carbonization temperature of 350°C or higher must be confirmed. In addition, it is possible to calculate the amount of carbon dioxide stored based on the amount of fixed carbon using a predetermined calculation formula for each raw material and carbonization method. In this embodiment, for each of the samples with different carbonization temperatures for multiple types of raw materials for biochar, the fixed carbon measured by industrial analysis (JIS M8812) and the weight loss rate under air measured by thermogravimetry were measured and compared.

[0027] Figure 4 is a graph showing the relationship between fixed carbon in proximate analysis (JIS M8812) and the weight loss rate in air in the thermogravimetric method. As shown in Figure 4, the types of biochar measured were many, including bamboo charcoal, red pine charcoal, oak charcoal, rice husk charcoal, sludge charcoal, and feces charcoal. The measurement results shown in Figure 4 show that for each of these many types of biochar, the fixed carbon (%) and weight loss rate in air (%) were close to each other, and a high correlation was observed between the two.

[0028] This makes it possible to estimate the amount of carbon dioxide stored by applying the weight loss rate under air calculated from the change in weight of a biochar sample during the process of heating and combusting the sample in an air atmosphere in the thermogravimetry (the process of heating to the third temperature zone and combusting) to the calculation formula for carbon dioxide storage based on the amount of fixed carbon in proximate analysis (JIS M8812).

[0029] Next, the operation of this embodiment will be described.

[0030] As described above, according to this embodiment, it is possible to estimate the quality of biochar (carbonization temperature and carbon dioxide storage amount). In carbon sequestration by the application of biochar, the carbonization temperature of the biochar is an important factor in evaluating the quality of the biochar, and according to this embodiment, it is possible to appropriately estimate the carbonization temperature of the biochar. As a result, when evaluating the quality of biochar, it is possible to determine whether the carbonization temperature of the biochar is in the low temperature range (350°C or more and less than 450°C), the medium temperature range (450°C or more and less than 600°C), or the high temperature range (600°C or more). In addition, the measurement time required by conventional industrial analysis (JIS M8812) was about 10 hours, and errors may have occurred due to manual analysis. In contrast, the measurement time required by the thermogravimetric method of this embodiment is about 4 hours, and it is expected to shorten the measurement time and increase accuracy. Furthermore, in the thermogravimetric method of this embodiment, sample analysis can be performed more efficiently by linking it to an autosampler.

[0031] <Second embodiment> A second embodiment of the biochar analysis method according to the present invention will be described. In this embodiment, the preparation of a biochar sample, the measurement of the sample by thermogravimetry, and the proximate analysis for comparative analysis are the same as those in the first embodiment.

[0032] FIG. 5 is a graph showing an example of the relationship between the temperature change and the weight of a sample measured by a thermogravimetric method. In the example shown in FIG. 5, the sample is rice husk biochar, and the carbonization temperature of the sample is 300°C. The conditions of the temperature change of the sample shown in FIG. 5 were the same as those of the above embodiment shown in FIG. 1. Specifically, first, the sample made of biochar was heated from room temperature to about 950°C in a nitrogen gas atmosphere (step of heating to the first temperature zone). The heating rate at this time was 10°C / min. After the heating, the high temperature state of about 950°C was maintained for about 10 minutes. Next, the sample was cooled to about 260°C (step of cooling to the second temperature zone). The heating rate at this time was 10°C / min. After the cooling, the low temperature state of about 260°C was maintained for about 10 minutes. Thereafter, the sample was heated to about 950°C in an air atmosphere and burned (step of heating to the third temperature zone and burning). The heating rate at this time was 10°C / min. The thin line in FIG. 5 represents the temperature of the sample. The thick line in FIG. 5 represents the weight of the sample (TG). The weight of the sample is expressed as a percentage of the weight of the sample at the time of measurement relative to the weight of the sample before the start of the measurement. Note that the temperature change of the sample shown in FIG. 5 is an example, and the present analysis method is not limited to this. The heating rate and cooling rate of the sample are also not limited to the example shown in the figure.

[0033] <Estimation of carbonization temperature and raw material type of sample> The measurement results obtained by increasing the temperature, decreasing the temperature, and burning the sample at the increased temperature as described above by the thermogravimetric method were analyzed. In this embodiment, from the change in sample weight shown in FIG. 5, five parameters A to E shown in the figure were focused on. "A" indicated by an arrow corresponds to the weight loss rate in a nitrogen gas atmosphere. "B" indicated by an arrow corresponds to the weight loss rate in an air atmosphere. "C" indicated by an arrow corresponds to the proportion of residue (ash). "D" in the figure indicates the pyrolysis temperature in a nitrogen gas atmosphere. As described in the first embodiment, the pyrolysis temperature in the nitrogen gas atmosphere is the inflection point temperature of the sample weight curve in a nitrogen gas atmosphere (the step of increasing the temperature to the first temperature zone) and is the temperature at which weight loss begins. "E" in the figure indicates the pyrolysis temperature in an air atmosphere. The pyrolysis temperature in the air atmosphere is the inflection point temperature of the sample weight curve in an air atmosphere (the step of increasing the temperature to the third temperature zone and burning the sample) and is the temperature at which weight loss begins.

[0034] Figure 6 shows the relationship between temperature change and sample weight when the raw materials of the biochar samples are different. In the example shown in Figure 6, the raw materials of the biochar samples are chicken manure, red pine, oak, and rice husk, and the carbonization temperature of each sample is 500°C. As shown in Figure 6, when the raw materials of the biochar samples are different, the sample weight curves are clearly different even when the carbonization temperature is the same. When the raw material is chicken manure, the weight loss rate under nitrogen (parameter A) is 38.8%, the weight loss rate under air (parameter B) is 9.9%, the residue (ash) ratio (parameter C) is 51.3%, the pyrolysis temperature under nitrogen gas atmosphere (parameter D) is 681.1°C, and the pyrolysis temperature under air atmosphere (parameter E) is 334.5°C. When the raw material was red pine, the weight loss rate under nitrogen (parameter A) was 20.1%, the weight loss rate under air (parameter B) was 79.1%, the residue (ash) ratio (parameter C) was 0.8%, the pyrolysis temperature under nitrogen gas atmosphere (parameter D) was 541.7°C, and the pyrolysis temperature under air atmosphere (parameter E) was 483.6°C. When the raw material was oak, the weight loss rate under nitrogen (parameter A) was 17.4%, the weight loss rate under air (parameter B) was 80.4%, the residue (ash) ratio (parameter C) was 2.3%, the pyrolysis temperature under nitrogen gas atmosphere (parameter D) was 541.7°C, and the pyrolysis temperature under air atmosphere (parameter E) was 477.8°C. When the raw material was rice husk, the weight loss rate under nitrogen (parameter A) was 10.4%, the weight loss rate under air (parameter B) was 45.4%, the residue (ash) ratio (parameter C) was 44.3%, the pyrolysis temperature under nitrogen gas atmosphere (parameter D) was 540.3°C, and the pyrolysis temperature under air atmosphere (parameter E) was 414.0°C. In particular, when the raw material was chicken manure, the residue (ash) ratio (parameter C) was significantly large. For rice husk, the residue (ash) ratio (parameter C) was also relatively large.

[0035] Figure 7 shows the relationship between temperature change and sample weight when the carbonization temperature of the biochar sample is different. In the example shown in Figure 7, the raw material of the biochar sample is Quercus serrata, and the carbonization temperatures of the sample are 300°C, 500°C, and 700°C. As shown in Figure 7, when the carbonization temperature is different, the sample weight curves are clearly different even if the raw material type of the biochar sample is the same. When the carbonization temperature is 300°C, the weight loss rate under nitrogen (parameter A) is 45.0%, the weight loss rate under air (parameter B) is 54.1%, the residue (ash) ratio (parameter C) is 0.9%, the pyrolysis temperature under nitrogen gas atmosphere (parameter D) is 352.8°C, and the pyrolysis temperature under air atmosphere (parameter E) is 477.8°C. When the carbonization temperature was 500°C, the weight loss rate under nitrogen (parameter A) was 17.4%, the weight loss rate under air (parameter B) was 80.4%, the residue (ash) ratio (parameter C) was 2.3%, the pyrolysis temperature under nitrogen gas atmosphere (parameter D) was 541.7°C, and the pyrolysis temperature under air atmosphere (parameter E) was 477.8°C. When the carbonization temperature was 700°C, the weight loss rate under nitrogen (parameter A) was 6.1%, the weight loss rate under air (parameter B) was 88.6%, the residue (ash) ratio (parameter C) was 5.3%, the pyrolysis temperature under nitrogen gas atmosphere (parameter D) was 750.0°C, and the pyrolysis temperature under air atmosphere (parameter E) was 476.3°C. As can be seen from the above results, as the carbonization temperature of the biochar sample (oak charcoal) increased, the weight loss rate under nitrogen (parameter A) decreased and the weight loss rate under air (parameter B) increased.

[0036] Figure 8 shows the relationship between temperature change and sample weight when the carbonization temperature of the biochar sample is different. In the example shown in Figure 7, the raw material of the biochar sample is chicken manure, and the carbonization temperatures of the sample are 300°C, 500°C, and 700°C. As shown in Figure 8, when the carbonization temperature is different, the sample weight curves are clearly different even if the raw material type of the biochar sample is the same. When the carbonization temperature is 300°C, the weight loss rate under nitrogen (parameter A) is 47.2%, the weight loss rate under air (parameter B) is 11.2%, the residue (ash) ratio (parameter C) is 41.6%, the pyrolysis temperature under nitrogen gas atmosphere (parameter D) is 356.7°C, and the pyrolysis temperature under air atmosphere (parameter E) is 349.1°C. When the carbonization temperature was 500°C, the weight loss rate under nitrogen (parameter A) was 38.8%, the weight loss rate under air (parameter B) was 9.9%, the residue (ash) ratio (parameter C) was 51.3%, the pyrolysis temperature under nitrogen gas atmosphere (parameter D) was 681.1°C, and the pyrolysis temperature under air atmosphere (parameter E) was 334.5°C. When the carbonization temperature was 700°C, the weight loss rate under nitrogen (parameter A) was 36.8%, the weight loss rate under air (parameter B) was 7.6%, the residue (ash) ratio (parameter C) was 55.6%, the pyrolysis temperature under nitrogen gas atmosphere (parameter D) was 684.2°C, and the pyrolysis temperature under air atmosphere (parameter E) was 331.6°C. As can be seen from the above results, as the carbonization temperature of the biochar sample (chicken manure charcoal) increased, the weight loss rate under nitrogen (parameter A) decreased and the weight loss rate under air (parameter B) increased. Furthermore, as can be seen by comparing with the case shown in Figure 7 above (where the raw material for the biochar sample was oak), even if the carbonization temperature of the biochar sample was the same, there were clear differences in the weight loss rate under nitrogen (parameter A), the weight loss rate under air (parameter B), the proportion of residue (ash) (parameter C), and the pyrolysis temperature in an air atmosphere (parameter E), etc., depending on the type of raw material for the biochar.

[0037] Fig. 9 shows an example of the above parameters A to E derived from the sample weight curve in the process of heating the sample in a nitrogen gas atmosphere (heating to a first temperature zone), the process of lowering the temperature of the sample (lowering the temperature to a second temperature zone), and the process of heating and combusting the sample in an air atmosphere (heating to a third temperature zone and combusting). Fig. 9 shows data on multiple samples with different carbonization temperatures for multiple types of biochar raw material. It can be seen that there is a large difference in the pyrolysis temperature (parameter E) in an air atmosphere between the raw material types of red pine and oak, rice husk, and chicken manure.

[0038] For each type of raw material of the biochar obtained in this manner, sample weight curves (parameters A to E) at multiple carbonization temperatures are stored as known sample data. Then, a new biochar sample to be analyzed is similarly measured by the thermogravimetric method of the present embodiment. For the biochar sample to be analyzed, the sample weight curves (parameters A to E) in the process of heating the sample in a nitrogen gas atmosphere (heating to a first temperature zone), the process of cooling the sample (cooling to a second temperature zone), and the process of heating and combusting the sample in an air atmosphere (heating to a third temperature zone and combusting) are collated with the known sample data, thereby making it possible to estimate the raw material type and carbonization temperature of the biochar sample to be analyzed.

[0039] <Estimation of carbon dioxide retention in samples>

[0040] The weight loss rate under nitrogen measured by thermogravimetry is the weight loss due to thermal decomposition and corresponds to the volatile matter in proximate analysis (JIS M8812). The weight loss rate under air measured by thermogravimetry is the weight loss due to combustion and corresponds to the fixed carbon in proximate analysis.

[0041] According to the methodology of the J-Credit Scheme (AG-004), the condition for crediting the amount of carbon dioxide stored by applying biochar is that the carbonization temperature during the production of biochar is 350°C or higher. In this embodiment, for each of the multiple types of raw material for biochar, samples with different carbonization temperatures were measured for fixed carbon by industrial analysis (JIS M8812) and weight loss rate under air by thermogravimetry, and compared.

[0042] As explained with reference to FIG. 4 in the first embodiment above, the measurement results shown in FIG. 4 show that for each of the many types of biochar, such as bamboo charcoal, red pine charcoal, oak charcoal, rice husk charcoal, sludge charcoal, and faeces charcoal, the fixed carbon (%) and the weight loss rate under air (%) were close to each other, and a high correlation was observed between the two.

[0043] This makes it possible to estimate the amount of carbon dioxide stored by applying the weight loss rate under air calculated from the change in weight of a biochar sample during the process of heating and combusting the sample in an air atmosphere in the thermogravimetry (the process of heating to the third temperature zone and combusting) to the calculation formula for carbon dioxide storage based on the amount of fixed carbon in proximate analysis (JIS M8812).

[0044] Next, the operation of this embodiment will be described.

[0045] As described above, according to this embodiment, it is possible to estimate the quality of biochar (raw material type, carbonization temperature, and carbon dioxide storage amount). In carbon sequestration by the application of biochar, the raw material type and carbonization temperature of the biochar are important factors in evaluating the quality of the biochar, and according to this embodiment, it is possible to appropriately estimate the raw material type and carbonization temperature of the biochar. As a result, when evaluating the quality of biochar, it is possible to determine whether the carbonization temperature of the biochar is in the low temperature range (350°C or more and less than 450°C), the medium temperature range (450°C or more and less than 600°C), or the high temperature range (600°C or more). In addition, the measurement time required by conventional industrial analysis (JIS M8812) was about 10 hours, and errors may have occurred due to manual analysis. In contrast, the measurement time required by the thermogravimetric method of this embodiment is about 4 hours, and it is expected to shorten the measurement time and increase accuracy. Furthermore, in the thermogravimetric method of this embodiment, sample analysis can be performed more efficiently by linking it to an autosampler.

[0046] Although an embodiment of the present invention has been described above, the scope of the present invention is not limited to the above-described embodiment, and all modifications within the scope of the matters described in each claim are all included in the scope of the present invention.

Claims

1. 1. A method for thermogravimetric analysis of biochar, comprising: A step of heating a sample made of biochar to a first temperature zone of 900° C. or more under an atmosphere of an oxygen-free gas; A step of lowering the temperature of the sample to a second temperature zone of 300° C. or less; a step of heating the sample to a third temperature zone of 900° C. or higher in an oxygen-containing gas atmosphere and combusting the sample; a step of estimating a carbonization temperature of the sample based on a change in weight of the sample during the step of heating the sample to the first temperature zone; and estimating the amount of carbon dioxide stored in the sample based on the change in weight of the sample during the process of heating the sample to the third temperature zone and burning the sample.

2. The biochar analysis method of claim 1, wherein in the step of estimating the carbonization temperature of the sample, data analyzing the relationship between the carbonization temperature and the pyrolysis temperature in the oxygen-free gas atmosphere for each type of biochar raw material is accumulated in advance, and the pyrolysis temperature of the sample in the oxygen-free gas atmosphere is compared with the data to estimate the carbonization temperature of the sample.

3. 1. A method for thermogravimetric analysis of biochar, comprising: A step of heating a sample made of biochar to a first temperature zone of 900° C. or more under an atmosphere of an oxygen-free gas; A step of lowering the temperature of the sample to a second temperature zone of 300° C. or less; a step of heating the sample to a third temperature zone of 900° C. or higher in an oxygen-containing gas atmosphere and combusting the sample; a step of estimating the raw material type and the carbonization temperature of the sample based on a change in weight of the sample during a step of heating the sample to the first temperature zone, a step of cooling the sample to the second temperature zone, and a step of heating the sample to the third temperature zone and burning the sample; and estimating the amount of carbon dioxide stored in the sample based on the change in weight of the sample during the process of heating the sample to the third temperature zone and burning the sample.

4. The biochar analysis method of claim 3, wherein in the process of estimating the carbonization temperature and raw material type of the sample, data analyzing the relationship between the carbonization temperature and five parameters, i.e., the pyrolysis temperature in the oxygen-free gas atmosphere, the weight loss rate in the oxygen-free gas atmosphere, the pyrolysis temperature in the oxygen-containing gas atmosphere, the weight loss rate in the oxygen-containing gas atmosphere, and the residue ratio, for each type of biochar raw material is accumulated in advance, and the raw material type and carbonization temperature of the sample are estimated by comparing the five parameters of the sample with the data.

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