Method for correcting bituminous coal air-dry basis moisture system error

Abstract

The invention mainly relates to the technical field of coal detection tests. The invention provides a method for correcting bituminous coal air-dry basis moisture system errors, which comprises the following steps: S1, preparing a standard sample, and after air-dry basis balance, obtaining the air-dry basis calorific value 0 of the standard sample; s2, taking the standard sample, performing air-dry basis balance again in the test environment, and obtaining the air-dry basis calorific value 1 of the standard sample in the test environment; s3, calculating a humidity correction coefficient K based on the air-dry basis heating value 0 and the air-dry basis heating value 1; s4, obtaining the air-dry basis calorific value 2 of the sample to be tested in the test environment; according to the air-dry basis calorific value 2 of the to-be-detected sample and the humidity correction coefficient K, obtaining the corrected air-dry basis calorific value of the to-be-detected sample, eliminating the system error of the bituminous coal air-dry basis moisture affected by the environment, performing conversion to obtain the more accurate as-received basis lower calorific value, improving the reproducibility of the bituminous coal industrial analysis result, and improving the quality of the bituminous coal. And tracing and management of bituminous coal industrial analysis results are facilitated.

Description

Technical Field

[0001] The invention mainly relates to the technical field of coal detection test, and in particular to a method for correcting the error of bituminous coal air-dry basis moisture system. Background Art

[0002] At present, in order to avoid the influence of environmental humidity on the test results and make the settlement results fair, just and traceable, the low calorific value on the received basis is used for commodity trading settlement in the industry. The received basis is the analysis result obtained based on the coal in the received state. However, the received basis low calorific value cannot be directly obtained through test detection, but needs to be converted according to the following formula through the air-dried basis low calorific value result of the coal sample.

[0003] (unit: J / g);

[0004] (unit: Cal / g);

[0005] Where: Q net,ar : Received base low heat, J / g; Q net,ad : Low calorific value on air-dry basis, J / g; M ar : received base moisture, %; M ad : Air-dried basis moisture, %.

[0006] However, in practical applications, even after conversion, the calorific value results of the same coal sample still have large deviations in different laboratories. If the geographical span is large, the test results of laboratories in the south and the north will differ even more. This is because the moisture content of coal includes external moisture and internal moisture. The external moisture of coal is the moisture attached to the surface of coal particles; the internal moisture of coal is the moisture adsorbed in the capillaries inside coal particles; the external moisture is easy to evaporate in dry air at room temperature, but the water vapor pressure evaporated to the surface of coal particles will no longer evaporate when it is in equilibrium with the humidity of the air. Obviously, the air-dried basis moisture content has a great relationship with the air humidity of the test environment. Experimental data show that when the air humidity differs by 5%, the air-dried basis moisture content of coal will differ by 0.3%, the air-dried basis low calorific value will differ by 50 kcal, and the received basis low calorific value will differ by 30 kcal. It can be seen that it is difficult to truly objectively and fairly express the low calorific value of coal using the received basis. When the coal is settled on the received basis, disputes often arise between suppliers and users. Summary of the invention

[0007] Technical Problems to be Solved by the Invention

[0008] A method for correcting the system error of air-dried basis moisture of bituminous coal is provided, aiming to eliminate the system error of air-dried basis low calorific value of bituminous coal affected by ambient humidity and more accurately convert the received basis low calorific value of bituminous coal.

[0009] The present invention solves the technical solution adopted by the above technology

[0010] A method for correcting a system error of air-dried basis moisture of bituminous coal comprises:

[0011] Step S1, prepare a standard sample, perform air-dry basis balance, and obtain the air-dry basis low calorific value of the standard sample as 0 as a reference value;

[0012] Step S2, after re-balancing the standard sample on an air-dry basis in the test environment, obtain the air-dry basis low calorific value 1 of the standard sample in the test environment;

[0013] Step S3, calculating a humidity correction coefficient K based on the air-dry basis lower calorific value 0 and the air-dry basis lower calorific value 1;

[0014] Step S4, obtaining the air-dry basis lower calorific value 2 of the sample to be tested in the test environment; and obtaining the corrected air-dry basis lower calorific value of the sample to be tested according to the air-dry basis lower calorific value 2 of the sample to be tested and the humidity correction coefficient K.

[0015] Furthermore, the humidity correction coefficient K = air-dry basis lower heating value 0 ÷ air-dry basis lower heating value 1.

[0016] Furthermore, the method for calculating the air-dry basis lower calorific value of the standard sample or the sample to be tested is: obtaining the air-dry basis moisture, ash, volatile matter, and coke residue characteristics of the standard sample or the sample to be tested; and calculating the air-dry basis lower calorific value of the standard sample or the sample to be tested based on the air-dry basis moisture, ash, volatile matter, and coke residue characteristics of the standard sample or the sample to be tested.

[0017] Furthermore, the preparation of the standard sample in step 1 includes: crushing the air-dried coal into 80 meshes, spreading it flat to a thickness of no more than 0.2 cm, and placing it at a temperature of 20±2° C. and an ambient humidity of 70%±2% for at least 8 hours.

[0018] Furthermore, the prepared standard sample is subjected to air-dry basis equilibrium and then stored in a sealed bottle, wherein a corrosion-resistant and oxidation-resistant ceramic ball with a diameter of 5 mm is arranged in the sealed bottle.

[0019] Furthermore, the method also includes: using GB / T214-2007 "Determination of Total Sulfur in Coal" to perform multiple total sulfur result tests on the prepared standard sample. If the deviations of the multiple test results are all within the set range, the uniformity of the prepared standard sample is qualified.

[0020] Furthermore, it is characterized in that the specific method for obtaining the air-dried basis moisture of the standard sample or the sample to be tested is:

[0021] Take 1g±0.1g sample, accurate to 0.0001g, and spread it evenly in a weighing bottle;

[0022] Open the weighing bottle cap and put it into a drying oven that has been blown and heated to 105℃-110℃ in advance. Dry the bituminous coal for 1 hour under the condition of continuous blowing.

[0023] Take out the weighing bottle from the drying oven, cover it immediately, put it in the drying oven to cool to room temperature, and then weigh it;

[0024] Then put the weighing bottle into a drying oven heated to 105℃-110℃ and dry it for 30 minutes under the condition of continuous blowing, until the difference in the mass of the sample weighed twice in a row does not exceed 0.0001g;

[0025] Air-dried basis moisture is: m2-the mass of the sample reduced after drying, g; m1-the mass of the sample before drying, g.

[0026] Furthermore, the ash content of the standard sample or the sample to be tested is calculated as follows:

[0027] In an ash dish that has been pre-burned to a constant mass, weigh 1g±0.01g of sample, accurate to 0.0001g, and spread it evenly in a special ash dish for coal industry analysis so that the sample per square meter does not exceed 0.15g;

[0028] Place the ash dish into the muffle furnace, close the furnace door and leave a 15mm gap, raise the furnace temperature from room temperature to 500℃ in no less than 30min, and keep it at this temperature for 30min, then continue to raise it to 815℃±10℃, and burn it at this temperature for 1h;

[0029] Take out the ash dish, cool it in the air for 5 minutes, move it into a dryer, cool it to room temperature and weigh it; then put it into a furnace at 815℃±10℃ and burn it for 20 minutes, until the mass change after two consecutive burnings does not exceed 0.0010g;

[0030] The air-dried ash content is: m3-the mass of the sample residue after ignition, g; m4-the mass of the sample before ignition, g.

[0031] Furthermore, the volatile matter of the standard sample or the sample to be tested is calculated as follows:

[0032] Weigh 1g±0.01 sample into a crucible that has been pre-burned to a constant volatile content, vibrate the crucible to flatten the coal sample, cover the crucible with a lid, and place it on a crucible stand;

[0033] Preheat the muffle furnace to about 920℃, open the furnace door, quickly put the crucible stand with the crucible into the constant temperature zone, immediately close the furnace door and start timing, heating for 7 minutes accurately; and after the crucible and the stand are placed in, restore the furnace temperature to 900℃±10℃ within 3 minutes;

[0034] Take the crucible out of the furnace, cool it in air for 5 minutes, then move it into a desiccator and cool it to room temperature before weighing;

[0035] The volatile matter on air-dried basis is: m5-the weight of the sample reduced after heating, g; m6-the weight of the sample before heating, g; M ad -Air-dry basis moisture, %.

[0036] Furthermore, the low calorific value on an air-dried basis is: Q net,ad =8575.63-17.63V ad -94.64A ad -167.89M ad +41.52CRC, where Q net,ad - Low calorific value on air-dry basis, J / g; V ad - Volatile matter on air-dried basis, %; A ad -Ash content on air-dried basis, %; M ad -Moisture content on air-dried basis, %; CRC—coke residue characteristics.

[0037] Beneficial effects of the present invention

[0038] The method for correcting the systematic error of air-dry basis moisture content of bituminous coal disclosed in the present invention determines a humidity correction coefficient K based on the air-dry basis low calorific value of a prepared bituminous coal standard sample under standard test conditions and the air-dry basis low calorific value of the standard sample under the same test environment as the sample to be tested. The air-dry basis low calorific value of the sample to be tested in the test environment is corrected by the humidity correction coefficient K, which can effectively reduce the systematic error of the air-dry basis low calorific value of the sample to be tested caused by the ambient humidity during industrial analysis of the bituminous coal. A more accurate bituminous coal received basis calorific value result can be converted based on the corrected air-dry basis low calorific value, which is beneficial to improving the reproducibility of the bituminous coal industrial analysis results and the traceability and management of the bituminous coal industrial analysis results. DETAILED DESCRIPTION

[0039] Step S1: Prepare a standard sample, perform air-dry basis balance, obtain the air-dry basis low calorific value of the standard sample, record it as air-dry basis low calorific value 0, and use it as the reference value for humidity correction. The preparation process of the standard sample specifically includes:

[0040] 1) The air-dried bituminous coal is crushed into 80 meshes, passed through a sieve with an aperture of 0.2 mm, and then spread flat in a flat-bottomed container. The thickness of the coal powder spread flat is not more than 0.2 cm, and placed in a standard environment with a temperature of 20±2°C and a humidity of 70%±2% for air-dry basis equilibrium. The preferred equilibrium time is 8 hours;

[0041] 2) Weigh the coal powder twice in succession. If the weight difference is less than 0.0003g, it means that the prepared coal powder has reached the air-dried state. The air-dried coal powder is immediately put into a sealed bottle and the bottle cap is covered to prevent the coal powder from absorbing moisture in the air. A ceramic ball with a smooth surface and corrosion resistance and oxidation resistance of 5mm in diameter is set in the sealed bottle to ensure the stability of the coal powder in the sealed bottle;

[0042] 3) Shake the sealed bottle back and forth to mix the coal powder evenly in the sealed bottle;

[0043] 4) Conduct uniformity and stability tests on the uniformly mixed coal powder, take ten samples for total sulfur test, and test the total sulfur results of the ten samples in parallel. If the deviation of the total sulfur test results of the ten samples is within the range of ±0.4%, it means that the uniformity and stability of the prepared coal powder samples are qualified;

[0044] 5) For the coal powder with qualified test results in 4), the air-dried basis moisture, ash, volatile matter and coke slag characteristic results are determined; the certification value and uncertainty are calculated after mathematical and statistical processing of all the fixed value experimental data, the certification result is taken as the reference value, and the reference result is marked as air-dried basis moisture 0, ash 0, volatile matter 0 and coke slag characteristic 0, and then the air-dry basis low calorific value 0 is calculated according to the formula of the low calorific value of bituminous coal.

[0045] The determination of air-dried basis moisture specifically includes: weigh (1±0.1)g of the prepared standard sample in a weighing bottle for coal industry analysis that has been pre-dried to a constant mass, accurate to 0.0001g, and spread it evenly in the weighing bottle. Open the bottle cap and put it in a drying oven that has been pre-blown and heated to 105℃-110℃. Dry the bituminous coal for 1h under the condition of continuous blowing. Take out the weighing bottle from the drying oven, cover it immediately, put it in the drying oven to cool to room temperature and weigh it. Put it in a drying oven that has been heated to 105℃-110℃ and dry it for 30min under the condition of continuous blowing until the mass of the dried coal sample decreases by no more than 0.0010g or increases for two consecutive times. When the mass increases, the mass before the mass increase is used as the basis for calculation.

[0046] The air-dried basis moisture of the standard sample is calculated as follows: m2-the mass reduced after the standard sample is dried, g; m1-the mass of the standard sample before drying.

[0047] The determination of ash content specifically includes: in an ash dish that has been pre-burned to a constant mass, weigh (1±0.01)g of the prepared standard sample, accurate to 0.0001g, and evenly spread it in a special ash dish for coal industry analysis, not exceeding 0.15g per square meter. Send the ash dish into the muffle furnace, close the furnace door and leave a 15mm gap in the furnace door. From room temperature, slowly raise the furnace temperature to 500℃ in no less than 30min, and keep it at this temperature for 30min. Continue to raise it to (815±10)℃ and burn it at this temperature for 1h. Take out the ash dish from the furnace, cool it in the air for 5min, move it into a dryer, cool it to room temperature and weigh it. Put it into the (815±10)℃ muffle furnace again and burn it for 20min until the mass change between two consecutive burnings does not exceed 0.0010g, and the mass after the last burning is used as the basis.

[0048] The coal ash content of the standard sample is calculated as follows: m3-the mass of the residue after ignition of the standard sample, g; m4-the mass of the standard sample before ignition, g.

[0049] The determination of volatile matter specifically includes: weigh (1±0.01)g of coal sample in a crucible that has been pre-burned to a constant volatile content, accurate to 0.0001g, then gently vibrate the crucible to flatten the coal sample, cover the crucible lid, and place it on the crucible stand. Preheat the muffle furnace to about 920℃. Open the furnace door, quickly send the crucible stand with the crucible into the constant temperature zone, immediately close the furnace door and start the timer, and heat accurately for 7 minutes. After the crucible and the bracket are placed, the furnace temperature is required to return to (900±10)℃ within 3 minutes, otherwise the test will be scrapped. The heating time includes the temperature recovery time. Take out the crucible from the furnace, cool it in the air for 5 minutes, then move it into the dryer to cool to room temperature and weigh it.

[0050] The volatile matter of the standard sample is calculated as follows: m6-the mass of the standard sample reduced after heating, g; m7-the mass of the standard sample before heating, g; M ad -Air-dry basis moisture, %.

[0051] Judgment of coke slag characteristics CRC:

[0052] The coke residue obtained after the determination of the volatile matter shall be judged according to the following requirements.

[0053] Powdery - All powdery, without particles sticking to each other. In this case, the slag characteristic value is 1.

[0054] Adhesive: It turns into powder or is basically powder when touched lightly with fingers. Larger lumps turn into powder when touched lightly. At this time, the characteristic value of the coke residue is 2.

[0055] Weakly bonded - crushed into small pieces with fingers, the slag characteristic value is 3.

[0056] Non-melting adhesion - it breaks into small pieces only when pressed hard with fingers. The upper surface of the slag is dull, and the lower surface has a slight silvery white luster. At this time, the characteristic value of the slag is 4.

[0057] Non-expansion molten bonding: the slag forms flat blocks, the boundaries of coal particles are difficult to distinguish, the upper surface of the slag has a distinct silvery-white metallic luster, and the silvery-white luster of the lower surface of the slag is more obvious. At this time, the characteristic value of the slag is 5.

[0058] Slightly expanded molten bonding: it cannot be crushed by fingers, and the upper and lower surfaces of the slag have a silvery-white metallic luster, but there are smaller expansion bubbles or small bubbles on the surface of the slag. At this time, the characteristic value of the slag is 6.

[0059] Expansion fusion bonding: the upper and lower surfaces of the slag have a silvery white metallic luster and are obviously expanded, but the height does not exceed 15 mm. At this time, the characteristic value of the slag is 8.

[0060] Strong expansion fusion bonding: the upper and lower surfaces of the slag have a silvery white metallic luster, the slag height is greater than 15 mm, and the slag characteristic value is 9.

[0061] The specific calculation formula of the low calorific value of the standard sample on an air-dry basis is:

[0062] Q net,ad =8575.63-17.63V ad -94.64A ad -167.89M ad +41.52CRC (unit: cal / g)

[0063] Where Q net,ad -Air-based low calorific value, J / g; V ad - Volatile matter on air-dried basis, %; A ad -Ash content on air-dried basis, %; M ad -Moisture content on air-dried basis, %; CRC—coke residue characteristics.

[0064] Step S2: Before conducting industrial analysis of coal powder each time, the user takes out 10 g of the prepared standard sample from the sealed bottle and places it in the air together with the industrial analysis sample to be tested with a particle size of 0.2 mm, with the spreading thickness being no more than 0.2 cm and the spreading time being 8 hours. After reaching air-dry basis equilibrium in the test environment of the sample to be tested, the industrial analysis is conducted to obtain the air-dry basis moisture 1, ash 1, volatile matter 1 and coke residue characteristic 1 of the standard sample, and obtain the air-dry basis low calorific value 1 of the standard sample in the test environment in the same manner as in step 1.

[0065] Step S3: Divide the air-dry basis lower calorific value 0 by the air-dry basis lower calorific value 1 to obtain a humidity correction coefficient K.

[0066] Step S4: Perform industrial analysis on the industrial analysis sample with a particle size of 0.2 mm in the same manner as in step S2, record the industrial analysis results of the sample as air-dried basis moisture 2, ash 2, volatile matter 2 and coke residue feature 2, and calculate the air-dried basis low calorific value 2 of the sample in the test environment. Multiply the air-dried basis low calorific value 2 of the sample by the humidity correction coefficient K to obtain the corrected air-dried basis low calorific value of the sample, and convert the received basis low calorific value based on the corrected air-dried basis low calorific value.

[0067] Example 1

[0068] The standard sample prepared in this embodiment is subjected to air-dried basis equilibrium under standard environmental conditions of temperature of 20±2°C and humidity of 70%±2% for no less than 8 hours, and then the air-dried basis moisture content, ash content, and volatile matter content are tested according to step S1.

[0069] The results of the calculated low calorific value (Qnet,ad) on an air-dry basis and the coke slag characteristics are shown in Table 1:

[0070] Table 1 Industrial analysis results of standard samples

[0071]

[0072] 10g of standard samples were taken out from sealed bottles in laboratory A and laboratory B respectively, and the flattening thickness was no more than 0.2cm, and the flattening time was 8 hours, so that the standard samples reached air-dry basis equilibrium in laboratory A and laboratory B. The air-dry basis moisture 1, ash 1, volatile matter 1, coke residue characteristics 1, and air-dry basis low calorific value 1 of the standard samples in laboratory A and laboratory B were calculated and measured, as shown in Table 2.

[0073] Table 2 Humidity correction coefficient K of standard samples in different experiments

[0074]

[0075] Based on the air-dry basis lower calorific value of the standard sample of 0 in Table 2 and the air-dry basis lower calorific value of the standard sample in laboratory A and laboratory B of 1, the humidity correction coefficient K in laboratory A is calculated to be 1.0107, and the humidity correction coefficient K in laboratory B is calculated to be 0.9928.

[0076] The mixed bituminous raw coal samples 1#, 2#, 3#, and 4# were crushed to less than 6 mm to detect the received basic moisture content, and then ground to 0.2 mm and divided into two parts. 10 g was taken from each of them for air-dry basis balance in laboratory A and laboratory B. The flattening thickness was not more than 0.2 cm, and the flattening time was 8 hours. After reaching air-dry basis balance, industrial analysis was performed on the samples to be tested in the same manner as in step S1, and the air-dry basis moisture content 2, ash content 2, volatile matter 2, coke residue characteristics 2 and air-dry basis low calorific value 2 of the samples to be tested in laboratory A and laboratory B were obtained respectively as shown in Table 3.

[0077] Table 3 Industrial analysis results of the samples to be tested based on the correction factor K

[0078]

[0079] The air-dried low calorific value of the 1# sample to be tested in laboratory A without humidity coefficient correction was 6343 cal / g, and the received low calorific value based on the air-dried low calorific value was 6004 cal / g; the air-dried low calorific value of the 1# sample to be tested in laboratory B without humidity coefficient correction was 6514 cal / g, and the received low calorific value based on the air-dried low calorific value was 6106 cal / g. After humidity coefficient correction, the air-dried low calorific value was 6467 cal / g, and the received low calorific value based on the air-dried low calorific value was 6062 cal / g. Before humidity coefficient correction, the difference in air-dried low calorific value of the same sample in two different laboratories was 171 cal / g, and the difference in received low calorific value was 101 cal / g. After the humidity coefficient correction, the low calorific value of the air-dry basis of the 1# test sample in laboratory A is 6479cal / g, and the low calorific value as received is 6068cal / g. The low calorific value of the air-dry basis in laboratory B is 6467cal / g, and the low calorific value as received is 6062cal / g. After the humidity coefficient correction of the same sample, the difference in the low calorific value of the air-dry basis is 12cal / g, and the difference in the low calorific value as received is 6cal / g. Similarly, after the humidity coefficient correction of the 2# test sample, the 3# test sample, and the 4# test sample, the errors of the low calorific value of the air-dry basis and the low calorific value as received measured in laboratories A and B are reduced to varying degrees, proving that the correction of the air-dry basis moisture system error of bituminous coal based on the humidity coefficient in the present invention can effectively reduce the influence of environmental humidity on the calorific value.

[0080] Embodiment 2:

[0081] The standard sample prepared in this embodiment is subjected to air-dried basis equilibrium for no less than 8 hours under standard environmental conditions of temperature of 20±2°C and humidity of 70%±2%, and then the results of testing air-dried basis moisture 0, ash 0, volatile matter 0, coke residue characteristics 0, and air-dried basis low calorific value 0 in step S1 are shown in Table 4:

[0082] Table 4 Industrial analysis results of standard samples

[0083] Serial number <![CDATA[M ad ]]> <![CDATA[A ad ]]> <![CDATA[V ad ]]> CRC <![CDATA[Q net,ad (cal / g)]]> Ambient humidity Benchmark value 3.32 13.62 26.3 2 6349 70％

[0084] In laboratory A, 10g of standard sample was taken out from a sealed bottle on different test dates and placed in the air together with 10g of the sample to be tested, with a flat thickness of no more than 0.2cm and a flat time of 8 hours, so that the standard sample and the sample to be tested reached air-dry basis equilibrium. Then, the coal industrial analysis was performed, and the industrial analysis results of the standard sample were calculated as air-dry basis moisture 1, ash 1, volatile matter 1, coke slag characteristics 1 and air-dry basis lower calorific value 1, and the specific values ​​are shown in Table 5.

[0085] Table 5 Humidity correction coefficient K of standard samples at different times in the same experiment

[0086]

[0087] Based on the air-dry basis low calorific value of the standard sample of 0 and the air-dry basis low calorific value of the standard sample in laboratory A of 1, the humidity correction coefficient K on January 19 was calculated to be 1.0107, and the humidity correction coefficient K on February 7 was calculated to be 0.9928.

[0088] On January 19 and February 7, two samples were tested on the as-received basis moisture and industrial analysis tests in Laboratory A, respectively, and the as-received basis moisture of the samples, as well as the air-dried basis moisture2, ash2, volatile matter2, coke residue characteristics2 and air-dried basis low calorific value2 of the samples were obtained as shown in Table 6.

[0089] Table 6 Results of calibration of the samples by the same laboratory based on the calibration coefficient K

[0090]

[0091] The ambient humidity in Laboratory A was 75% on January 19, and 45% on February 7. Before the humidity coefficient correction was performed on sample 1# in Laboratory A, the difference in air-dry basis lower calorific value between January 19 and February 7 was 139 cal / g, and the difference in received basis calorific value based on received basis moisture content and air-dry basis lower calorific value was 74 cal / g; after humidity coefficient correction, the difference in air-dry basis lower calorific value between January 19 and February 7 was 74 cal / g, and the difference in received basis lower calorific value based on air-dry basis calorific value and received basis moisture content was 18 cal / g. Compared with before the humidity coefficient correction, the difference in air-dry basis lower calorific value and the difference in received basis lower calorific value on the two test dates in the same laboratory were significantly reduced. Similarly, compared with the difference in the air-dry basis low calorific value and the as-received basis low calorific value of sample 2# in laboratory A before the humidity coefficient correction on January 19 and February 7, the difference was also greatly reduced, which can prove that the method for correcting the system error of bituminous coal air-dry basis moisture content described in the present invention can significantly eliminate the influence of ambient humidity on the air-dry basis moisture content of coal.

Claims

1. A method for correcting the system error of air-dry basis moisture of bituminous coal, characterized in that: include: Step S1, prepare a standard sample, perform air-dry basis balance, and obtain the air-dry basis low calorific value of the standard sample 0; Step S2, after re-balancing the standard sample on an air-dry basis in the test environment, obtain the air-dry basis low calorific value 1 of the standard sample in the test environment; Step S3, calculating a humidity correction coefficient K based on the air-dry basis lower calorific value 0 and the air-dry basis lower calorific value 1; Step S4, obtaining the air-dry basis lower calorific value 2 of the sample to be tested in the test environment; and obtaining the corrected air-dry basis lower calorific value of the sample to be tested according to the air-dry basis lower calorific value 2 of the sample to be tested and the humidity correction coefficient K.

2. A method for correcting the system error of air-dried coal moisture content according to claim 1, characterized in that: Humidity correction coefficient K = air-dry basis lower heating value 0 ÷ air-dry basis lower heating value 1.

3. A method for correcting the system error of air-dried coal moisture content according to claim 1 or 2, characterized in that: The calculation method of the air-dry basis lower calorific value of the standard sample or the sample to be tested is as follows: obtaining the air-dry basis moisture, ash, volatile matter and coke residue characteristics of the standard sample or the sample to be tested; The air-dry basis lower calorific value of the standard sample or the sample to be tested is calculated according to the air-dry basis moisture, ash, volatile matter and coke residue characteristics of the standard sample or the sample to be tested.

4. A method for correcting the system error of air-dried coal moisture content according to claim 1 or 2, characterized in that: The preparation of the standard sample in step 1 includes: crushing the air-dried coal into 80 meshes, spreading it flat with a thickness of no more than 0.2 cm, and placing it at a temperature of 20±2° C. and an ambient humidity of 70%±2% for at least 8 hours.

5. A method for correcting the system error of air-dried coal moisture content according to claim 1 or 2, characterized in that: The prepared standard sample is stored in a sealed bottle after being balanced on an air-dry basis. A corrosion-resistant and oxidation-resistant ceramic ball with a diameter of 5 mm is arranged in the sealed bottle.

6. A method for correcting the system error of air-dried coal moisture content according to claim 1 or 2, characterized in that: The method also includes: using GB / T214-2007 "Determination of Total Sulfur in Coal" to perform multiple total sulfur result tests on the prepared standard sample. If the deviations of the multiple determination results are all within the set range, the prepared standard sample is qualified.

7. A method for correcting the system error of air-dried coal moisture content according to claim 3, characterized in that: The specific method for obtaining the air-dry basis moisture of the standard sample or the sample to be tested is: Take 1g±0.1g sample, accurate to 0.0001g, and spread it evenly in a weighing bottle; Open the cap of the weighing bottle and put it into a drying oven that has been pre-blown and heated to 105℃-110℃, and dry it for 1 hour under continuous blowing; Take out the weighing bottle from the drying oven, cover it immediately, put it in the drying oven to cool to room temperature, and then weigh it; Then put the weighing bottle into a drying oven heated to 105℃-110℃ and dry it for 30 minutes under the condition of continuous blowing, until the difference in the mass of the sample weighed twice in a row does not exceed 0.0001g; Air-dried basis moisture is: m2-the mass of the sample reduced after drying, g; m1-mass of the sample before drying, g.

8. A method for correcting the system error of air-dried coal moisture content according to claim 3, characterized in that: The specific methods for obtaining the ash content of the standard sample or the sample to be tested include: Weigh 1g±0.01g of sample in an ash dish that has been pre-burned to a constant mass, accurate to 0.0001g, and spread it evenly in a special ash dish for coal industry analysis, with a maximum of 0.15g per square meter; Place the ash dish into the muffle furnace, close the furnace door and leave a 15mm gap. From room temperature, raise the furnace temperature to 500℃ within 30min, maintain this temperature for 30min, then continue to raise the temperature to 815℃±10℃, and burn at this temperature for 1h. Take out the ash dish, cool it in the air for 5 minutes, move it into a dryer, cool it to room temperature and weigh it; then put it into a furnace at 815℃±10℃ and burn it for 20 minutes, until the mass change after two consecutive burnings does not exceed 0.0010g; The air-dried ash content is: m3-the mass of the sample residue after ignition, g; m4-the mass of the sample before ignition, g.

9. A method for correcting the system error of air-dried coal moisture content according to claim 3, characterized in that: The calculation method of the volatile matter of the standard sample or the sample to be tested is: Weigh 1g±0.01 sample into a crucible that has been pre-burned to a constant volatile content, vibrate the crucible to flatten the coal sample, cover the crucible with a lid, and place it on a crucible stand; Preheat the muffle furnace to about 920℃, open the furnace door, put the crucible stand with the crucible into the constant temperature zone, immediately close the furnace door and start timing, heating for 7 minutes accurately; and after the crucible and the stand are placed in, restore the furnace temperature to 900℃±10℃ within 3 minutes; Take the crucible out of the furnace, cool it in air for 5 minutes, then move it into a desiccator and cool it to room temperature before weighing; The volatile matter on air-dried basis is: m5-the weight of the sample reduced after heating, g; m6-the weight of the sample before heating, g; M ad -Air-dry basis moisture, %.

10. A method for correcting the system error of air-dried coal moisture content according to claim 3, characterized in that: The lowest calorific value on air-dry basis is: Q net,ad =8575.63-17.63V ad -94.64A ad -167.89M ad +41.52CRC, where Q net,ad - Low calorific value on air-dry basis, J / g; V ad - Volatile matter on air-dried basis, %; A ad -Ash content on air-dried basis, %; M ad -Moisture content on air-dried basis, %; CRC—coke residue characteristics.

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