A method for detecting the vitrinite reflectance of coal

Abstract

The present invention discloses a method for detecting the vitrinite reflectance of coal, which mainly solves the technical problems in the prior art that the detection accuracy of the vitrinite reflectance of coal is low, it depends on the experience of the inspector, and the vitrinite reflectance of coal with a particle size of less than 0.2 mm cannot be detected. The technical scheme is a method for detecting the vitrinite reflectance of coal, comprising the following steps: 1) preparing a coal sample to be tested; 2) performing dry distillation on the coal to be tested, weighing a certain mass of the coal sample to be tested, loading it into a high-temperature furnace, controlling the high-temperature furnace to heat the coal sample to be tested from room temperature to the dry distillation temperature of the coal at a heating rate of 3 to 10°C / min, using a hydrogen analyzer to measure the volume of hydrogen generated in the whole process of heating the coal sample to be tested from room temperature to the dry distillation temperature of the coal, and calculating the hydrogen generation index n of the coal to be tested, in units of ml / mg; 3) calculating the vitrinite reflectance of coal. The method of the present invention detects the vitrinite reflectance of coal quickly and accurately, and is not affected by the particle size of the coal.

Description

Technical Field

[0001] The invention relates to a coal quality analysis method, in particular to a method for detecting the vitrinite reflectance of coal, and belongs to the technical field of coal chemical industry. Background Art

[0002] Under the current global energy shortage, the application field of coal is constantly expanding and the demand is increasing day by day. In order to make reasonable and comprehensive use of coal, it is necessary to strengthen the research on the material composition of coal. Through the determination of the reflectivity of the vitrinite group of coal, the coking property of coal can be predicted, the coking coal can be selected, and the basis for coke production can be provided.

[0003] The Chinese standard GB / T 6948-2008 "Method for Determination of Coal Vitrinite Reflectance by Microscope" stipulates the determination method of coal vitrinite reflectance; its determination principle is based on the principle that the reflected light intensity received by the photomultiplier tube is proportional to its electrical signal. When irradiated with incident light of a certain intensity under a microscope, the light signal of the vitrinite group with known reflectance is compared to determine it. This method uses a photomultiplier tube to perform a single-point test on the vitrinite group. Its test accuracy is affected by the fluctuation of the optical signal and the electrical signal, especially the voltage fluctuation. Since the single-point test takes a long time, it will cause fluctuations in the determination of the vitrinite reflectance of the coal; in addition, this determination method requires manual determination of the vitrinite components before determination, and the determination accuracy is also affected by the determination person's experience in component determination.

[0004] The Chinese patent document with application publication number CN101846623A discloses a device for detecting the vitrinite reflectance of coal or organic rock, including a stage for placing coal or organic rock vitrinite samples, an imaging device for imaging the samples, and an image acquisition device for acquiring images formed by the imaging device, and a vitrinite reflectance measurement device for performing image call, measurement point arrangement, vitrinite reflectance measurement, linking, statistics and result output on the images collected by the image acquisition device. This method detects the vitrinite reflectance of coal by collecting images and then analyzing the images. The accuracy of the measurement is affected by the camera system and light fluctuations. In addition, the collected images are processed to determine which are vitrinite groups before their reflectance can be measured. Therefore, the results depend on the software algorithm, and different software may obtain different results.

[0005] The Chinese patent document with application publication number CN102928340A discloses a method for measuring the vitrinite reflectance of coal based on image analysis. It combines microscopic digital technology with computer image processing technology, uses a microscopic digital camera to collect images under a polarizing microscope and transfers them to a computer, and uses a vitrinite reflectance measuring device to call out and process the images. The operator measures the reflectance of the vitrinite on the computer, and establishes a database link in real time to record the measured object, position, area, and original measured value of each measuring point, so that the measurement result is traceable and the measurement accuracy is improved. At the same time, the time occupied by the microscope is reduced during the measurement process, the measurement efficiency is greatly improved, and more samples can be measured in the same time. The method uses the relationship between image grayscale and reflectance to measure the vitrinite reflectance of coal. Multiple images can be collected through an automated stage, and the vitrinite is determined on the computer after collection, and then the vitrinite reflectance of coal is measured. The method still manually determines the components, and the test results are affected by the judgment experience. Moreover, since it is not a real-time measurement, the measurement results are also affected by the image quality.

[0006] The Chinese patent document with publication number CN1123910A discloses an automatic method for coal quality analysis and determination of the reflectivity of vitrinite in coal, which is used for coal quality analysis of a sample composed of crushed coal and coated with resin, including scanning the surface of the sample with a microscope and measuring the reflectivity of vitrinite, forming a digital image with several gray levels for each field of view of the microscope; deleting the field of view with high resin content by defining a threshold; performing the following steps for each field of view that has not been deleted: a) determining the distribution and gradient of the gray level; b) forming a binary image by giving a threshold to the gray gradient to determine the vitrinite area; c) determining the distribution or density of the gray level of the obtained vitrinite area. d) calculating the reflectivity of vitrinite. This method belongs to the image method for determining the reflectivity of the vitrinite group of coal, and the key point is to determine the threshold of the gray gradient of the image, and the vitrinite reflectivity is screened out by this threshold. However, the reflectivity of the vitrinite group of coal is not fixed. How to determine this threshold directly affects the detection result, and artificial determination of this threshold also brings uncertainty to the measurement result.

[0007] In summary, the methods for measuring the vitrinite reflectance of coal in the literature can be divided into two categories: one is to first determine the vitrinite of coal, and then measure the vitrinite reflectance of coal based on the relationship between the light signal and the reflectance or the relationship between the grayscale of the image and the reflectance; the other is to first measure the reflectance of all components of coal, and then use program software to process and obtain the vitrinite reflectance of coal. Both of these measurement methods rely on the experience of the measurer or the software program based on the experience of the measurer. The measurement results are uncertain and are affected by the measurer, resulting in poor comparability between different measurers and different equipment. Summary of the invention

[0008] The purpose of the present invention is to provide a method for detecting the vitrinite reflectance of coal, which mainly solves the technical problems in the prior art that the detection accuracy of the vitrinite reflectance of coal is low, relies on the experience of the inspector, and the vitrinite reflectance of coal with a particle size of less than 0.2 mm cannot be detected; the method of the present invention realizes the accurate detection of the vitrinite reflectance of coal with a particle size of less than 0.2 mm, and avoids the interference of the particle size of the coal on the detection of the vitrinite reflectance of the coal.

[0009] The present invention calculates the hydrogen generation index per unit mass of coal by measuring the amount of hydrogen generated by the test coal when it is heated to a certain temperature in an air-tight state; based on the correlation equation between the hydrogen generation index and the vitrinite reflectance, the hydrogen generation index is used to characterize the metamorphic degree of the coal and determine the vitrinite reflectance of the coal.

[0010] The technical solution adopted by the present invention is a method for detecting the vitrinite reflectance of coal, comprising the following steps:

[0011] 1) Prepare the coal sample to be tested according to the provisions of the coal sample preparation method of the Chinese standard GB / T 474-2008, and reduce and crush the coal to be tested to obtain the coal sample to be tested with a particle size of less than 0.2 mm;

[0012] 2) Carry out dry distillation on the coal to be tested, weigh a certain mass of the coal sample to be tested, load it into a high-temperature furnace, operate the high-temperature furnace to heat the coal sample to be tested from room temperature to the dry distillation temperature of the coal, detect the volume v of hydrogen generated in the whole process of heating the coal sample to be tested from room temperature to the dry distillation temperature of the coal, and calculate the hydrogen generation index n of the coal to be tested, the unit is ml / mg;

[0013] 3) Calculate the vitrinite reflectance of the coal. The vitrinite reflectance of the coal is calculated according to Formula 1: R = a + b × n Formula 1, wherein R is the vitrinite reflectance of the coal to be tested, in %; n is the volume of hydrogen produced by heating the unit mass of the coal to be tested from room temperature to the coal distillation temperature, in ml / mg; a is the conversion constant, in %; b is the conversion of the vitrinite reflectance of the coal to the hydrogen generation index, in % / (ml / mg); the conversion constant a and the conversion b of the vitrinite reflectance of the coal to the hydrogen generation index are obtained by dividing the vitrinite reflectance of the coal by the hydrogen generation index. The working curve equation of the relationship between the vitrinite reflectance and the hydrogen generation index of each coal is determined, specifically: weigh five kinds of standard coal with vitrinite reflectance of 0.8%, 1.0%, 1.2%, 1.4% and 1.6% respectively, put each kind of standard coal into a high-temperature furnace respectively, control the high-temperature furnace to heat each kind of standard coal from room temperature to the coal distillation temperature, detect the volume of hydrogen generated by each kind of coal in the whole process of heating from room temperature to the coal distillation temperature, calculate the hydrogen generation index of each kind of coal, and calculate the univariate linear regression equation R of the working curve of the relationship between the vitrinite reflectance and the hydrogen generation index of the coal by computer. 标=a+b×n 标 Determine the values ​​of a and b; in the regression equation, R 标 is the reflectance of the vitrinite group of standard coal, in %; a is the conversion constant, in %; b is the conversion of the vitrinite reflectance of coal to the hydrogen generation index, in % / (ml / mg); n 标 It is the volume of hydrogen produced when a unit mass of standard coal is heated from room temperature to the coal's dry distillation temperature, and the unit is ml / mg.

[0014] Further, in step 2), the high temperature furnace heats the coal sample to be tested from room temperature to the coal distillation temperature at a heating rate of 3 to 10°C / min; in step 3), the high temperature furnace heats each standard coal from room temperature to the coal distillation temperature at a heating rate of 3 to 10°C / min, and the effect is good.

[0015] The carbonization temperature of the coal described in the present invention is 950-1050°C.

[0016] The hydrogen generation index n of the coal described in the present invention is the volume of hydrogen generated by heating a unit mass of coal from room temperature to the dry distillation temperature of the coal, and the unit is ml / mg.

[0017] The vitrinite reflectance of the standard coal described in the present invention is measured according to the Chinese standard GB / T 6948-2008 "Method for measuring the vitrinite reflectance of coal by microscope".

[0018] The present invention adopts a hydrogen analyzer to detect the volume of hydrogen.

[0019] The reasons for determining the parameter control parameters of the present invention are as follows:

[0020] 1. Setting the heating rate of coal during coal distillation

[0021] During the process of coal dry distillation, it will go through stages such as softening, fusion, expansion, solidification and contraction, and complex physical and chemical changes will occur. Since physical and chemical changes require a certain amount of time, if the heating rate is too fast, there will not be enough time for a full reaction, and if the heating rate is too slow, the test time will be too long. After comprehensive consideration, the heating rate of coal during coal dry distillation is set to 3-10℃ / min.

[0022] 2. Setting of coal distillation temperature

[0023] The dry distillation temperature refers to the temperature T at which coke matures. In the process of forming coke by dry distillation, small molecules are continuously removed, and gases such as hydrogen and methane are produced. When the temperature is below 950℃, the amount produced is large. When the temperature is above 950℃, the volatile matter of coke is less than 1.2%, and the amount of hydrogen produced is very small. Therefore, the temperature is set not lower than 950℃; when it reaches 1050℃, there is still a little hydrogen precipitation in the coke, but its content is low and can be ignored. After comprehensive consideration, the dry distillation temperature of coal is set to 950~1050℃.

[0024] The above-mentioned method of predicting the reflectivity of coal by the amount of hydrogen produced is based on the study of the composition structure of coal. The organic matter in coal is a mixture of a large number of similar compounds with different relative molecular masses and similar but not completely the same molecular structures. Most of them are macromolecular compounds with aromatic structures as the main component, and a small part are low molecular compounds with chain structures as the main component.

[0025] During the coking process, as the temperature rises, the carbon content continues to increase, and the organic matter in the coal is continuously removed, mainly generating hydrogen and methane. During the process of removing hydrogen, part of the hydrogen enters hydrogen, and part enters methane and other alkanes. Whether hydrogen enters hydrogen or methane is affected by the structure of the coal. In low-metamorphic coal, most of the hydrogen enters methane, and a small part enters hydrogen, while in high-metamorphic coal, the proportion of hydrogen entering hydrogen increases, and the proportion entering methane decreases. This is because there are more small molecular organic matter with chain structure in the structure of low-metamorphic coal, which is easy to break during the dry distillation process to form methane, and a small amount enters hydrogen; while in high-metamorphic coal, there are more macromolecular compounds with aromatic structure in the coal structure, and this part of hydrogen is more likely to generate hydrogen.

[0026] Experimental studies have shown that the amount of hydrogen produced has a good correlation with the reflectivity of coal rock and is one of the effective indicators for quickly determining the degree of coalification.

[0027] The method of the invention can detect the vitrinite reflectance of coal quickly and accurately, is not affected by the particle size of the coal, and realizes the accurate detection of the vitrinite reflectance of coal with a particle size less than 0.2 mm.

[0028] Compared with the prior art, the present invention has the following positive effects: 1. The method of the present invention can quickly detect the vitrinite reflectance of coal, and can obtain the vitrinite reflectance without using a special measuring device, and it is not affected by the technical level and skills of the measurer. 2. The method of the present invention can quickly detect the vitrinite reflectance of a powdered coal sample, while the prior method requires the coal sample to be made into a particle sample smaller than 1.5 mm for measurement under a microscope, and cannot accurately measure a powder sample smaller than 0.2 mm. The present invention avoids the interference of the coal particle size on the detection of the vitrinite reflectance of the coal. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with Example 1.

[0030] Embodiment 1, a method for predicting the vitrinite reflectance of coal, comprising the following steps:

[0031] A method for detecting the vitrinite reflectance of coal comprises the following steps:

[0032] 1) Prepare the coal sample to be tested according to the provisions of the coal sample preparation method of the Chinese standard GB / T 474-2008, and reduce and crush the coal to be tested to obtain the coal sample to be tested with a particle size of less than 0.2 mm;

[0033] 2) The coal to be tested is subjected to dry distillation. 50 mg of the coal sample to be tested is weighed and loaded into a high-temperature furnace. The high-temperature furnace is controlled to heat the coal sample to be tested from room temperature to 1000° C. at a heating rate of 10° C. / min. The volume of hydrogen v generated in the whole process of heating the coal sample to be tested from room temperature to 1000° C. is detected by a hydrogen analyzer, and the volume v is 28.5 ml. The hydrogen generation index n of the coal to be tested is obtained to be 0.57 ml / mg;

[0034] 3) Calculate the vitrinite reflectance of the coal. The vitrinite reflectance of the coal is calculated according to Formula 1: R = a + b × n Formula 1, wherein R is the vitrinite reflectance of the coal to be tested, in %; n is the volume of hydrogen produced by heating the unit mass of the coal to be tested from room temperature to the coal distillation temperature, which is 0.57 ml / mg; a is the conversion constant term, in %; b is the conversion of the vitrinite reflectance of the coal to the hydrogen generation index, in % / (ml / mg); the conversion constant term a and the conversion b of the vitrinite reflectance of the coal to the hydrogen generation index are determined by the working curve equation of the relationship between the vitrinite reflectance of the coal and the hydrogen generation index, specifically: weigh five kinds of vitrinite reflectances of 0.8%, 1.0%, 1.2%, 1.4%, and 1.6%, respectively. 50 mg of each standard coal was loaded into a high-temperature furnace, and the high-temperature furnace was controlled to heat each standard coal from room temperature to 1000°C at a heating rate of 10°C / min. The volume of hydrogen produced by each coal during the whole process from room temperature to 1000°C was detected by a hydrogen analyzer, which were 21.5 ml, 23.2 ml, 27.4 ml, 30.4 ml and 33.0 ml respectively, which were converted into hydrogen generation index of 0.430 ml / mg, 0.464 ml / mg, 0.548 ml / mg, 0.608 ml / mg and 0.660 ml / mg respectively; the univariate linear regression equation R of the working curve of the relationship between the vitrinite reflectance of the coal and the hydrogen generation index was calculated by computer 标 =3.27×n 标 -0.57, a is determined to be -0.57%, b is 3.27% / (ml / mg), and the vitrinite reflectance R of the tested coal is calculated to be 1.29%.

[0035] The accuracy and precision of the method of the present invention are confirmed by comparison and precision experiments of adjusting the heating rate.

[0036] The accuracy test of the vitrinite reflectance of coal was compared with the standard coal sample. The standard value of the reflectance of the standard coal sample here refers to the standard value obtained by testing with reference to the method of Chinese standard GB / T 6948-2008. The test results are shown in Table 1 below.

[0037] Table 1 Parameters of standard sample for vitrinite reflectance of coal detected by the method of the present invention

[0038]

[0039] By comparing the test value of the vitrinite reflectance of the coal in the table with the standard value, it can be seen that the difference is 0.02%, which is less than the national standard requirement for reflectance accuracy and meets the detection needs.

[0040] Precision experiment, 11 precision experiments were carried out on the vitrinite reflectance of coal in the two groups of samples, and the analysis results are shown in Table 2.

[0041] Table 2 Experimental parameters of the precision of the method of the present invention %

[0042]

[0043] The above experimental results show that the vitrinite reflectance of coal is similar, RSD is less than 5%, and the detection data has good precision, which proves that the method of the present invention is accurate and reliable and fully meets the requirements for measuring the vitrinite reflectance of coal.

[0044] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A method for detecting the vitrinite reflectance of coal, characterized in that: The method comprises the following steps: 1) Prepare the coal sample to be tested according to the provisions of the coal sample preparation method of the Chinese standard GB / T 474-2008, and reduce and crush the coal to be tested to obtain the coal sample to be tested with a particle size of less than 0.2 mm; 2) Carry out dry distillation on the coal to be tested, weigh a certain mass of the coal sample to be tested, load it into a high-temperature furnace, operate the high-temperature furnace to heat the coal sample to be tested from room temperature to the dry distillation temperature of the coal, detect the volume v of hydrogen generated in the whole process of heating the coal sample to be tested from room temperature to the dry distillation temperature of the coal, and calculate the hydrogen generation index n of the coal to be tested, the unit is ml / mg; 3) Calculate the vitrinite reflectance of the coal. The vitrinite reflectance of the coal is calculated according to Formula 1: R = a + b × n Formula 1, wherein R is the vitrinite reflectance of the coal to be tested, in %; n is the volume of hydrogen produced by heating the unit mass of the coal to be tested from room temperature to the coal distillation temperature, in ml / mg; a is the conversion constant, in %; b is the conversion of the vitrinite reflectance of the coal to the hydrogen generation index, in % / (ml / mg); the conversion constant a and the conversion b of the vitrinite reflectance of the coal to the hydrogen generation index are obtained by dividing the vitrinite reflectance of the coal by the hydrogen generation index. The working curve equation of the relationship between the vitrinite reflectance and the hydrogen generation index of each coal is determined, specifically: weigh five kinds of standard coal with vitrinite reflectance of 0.8%, 1.0%, 1.2%, 1.4% and 1.6% respectively, put each kind of standard coal into a high-temperature furnace respectively, control the high-temperature furnace to heat each kind of standard coal from room temperature to the coal distillation temperature, detect the volume of hydrogen generated by each kind of coal in the whole process of heating from room temperature to the coal distillation temperature, calculate the hydrogen generation index of each kind of coal, and calculate the univariate linear regression equation R of the working curve of the relationship between the vitrinite reflectance and the hydrogen generation index of the coal by computer. 标 =a+b×n 标 Determine the values ​​of a and b; in the regression equation, R 标 is the reflectance of the vitrinite group of standard coal, in %; a is the conversion constant, in %; b is the conversion of the vitrinite reflectance of coal to the hydrogen generation index, in % / (ml / mg); n 标 It is the volume of hydrogen produced when a unit mass of standard coal is heated from room temperature to the coal's dry distillation temperature, and the unit is ml / mg.

2. The method for detecting the vitrinite reflectance of coal according to claim 1, characterized in that: In step 2), the high temperature furnace heats the coal sample to be tested from room temperature to the coal distillation temperature at a heating rate of 3 to 10°C / min; in step 3), the high temperature furnace heats each standard coal from room temperature to the coal distillation temperature at a heating rate of 3 to 10°C / min.

3. The method for detecting the vitrinite reflectance of coal according to claim 1, characterized in that: The carbonization temperature of the coal is 950-1050°C.

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