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Major category, Sub-category: Coal; Moisture, ash, volatile matter, fixed carbon. 1 Scope of application: This standard specifies the methods for determining moisture, ash, and volatile matter in coal, as well as the method for calculating fixed carbon. This standard applies to lignite, bituminous coal, and anthracite. 2 Determination of moisture: This standard specifies two methods for determining the moisture content in coal. Among them, Method A is applicable to all types of coal, while Method B is only applicable to bituminous coal and anthracite. In arbitration analysis, when it is necessary to correct for the moisture content of air-dried coal samples and to convert bases, Method A should be used to determine the moisture content of air-dried coal samples. 2.1 Method A (Nitrogen-flushed drying method) 2.1.1 Method overview: A certain amount of air-dried coal sample is placed in a drying oven at 105–110°C and dried under nitrogen until its mass remains constant. Then, the mass fraction of moisture is calculated based on the mass loss of the coal sample. 2.1.2 Reagents 2.1.2.1 Nitrogen: purity of 99.9%, with an oxygen content of less than 0.01%. 2.1.2.2 Anhydrous calcium chloride (HGB 3208): chemically pure, granular. 2.1.2.3 Color-changing silica gel: Industrial supplies. 2.1.3 Instruments and Equipment 2.1.3.1 Small-space drying oven: The chamber is airtight, has limited free space, includes gas inlets and outlets, and is equipped with an automatic temperature control system that maintains the temperature within the range of 105–110°C. 2.1.3.2 Glass weighing flask: diameter 40 mm, height 25 mm, with a tight ground glass stopper. 2.1.3.3 Desiccator: Filled with color-changing silica gel or granular anhydrous calcium chloride. 2.1.3.4 Drying tower: capacity 250 mL, equipped with a desiccant. 2.1.3.5 Flow meter: Range is 100–1000 mL/min. 2.1.3.6 Analytical balance: sensitivity of 0.1 mg. 2.1.4 Analysis steps 2.1.4.1 Weigh 1±0.1 g of air-dried coal samples with a particle size of less than 0.2 mm into a pre-dried and weighed weighing vessel, to an accuracy of 0.0002 g, and spread them evenly in the vessel. 2.1.4.2 Open the lid of the weighing flask and place it in the drying oven (3.1.3.1) that has been filled with dry nitrogen and heated to 105–110°C. Lignite is dried for 1.5 hours, while bituminous coal and anthracite are dried for 2 hours. Note: Nitrogen gas should be introduced 10 minutes before placing the weighing bottle in the drying oven, with a flow rate sufficient to achieve 15 air exchanges per hour. 2.1.4.3 Remove the weighing flask from the drying oven, cover it immediately, place it in a desiccator to cool to room temperature (approximately 20 min), and then weigh it. 2.1.4.4 Perform check drying for 30 minutes each time, until the mass loss of the dried coal sample in two consecutive trials is no more than 0.0010 g, or until an increase in mass occurs. In the latter case, the mass from the previous iteration before the increase is used as the basis for calculation. When the moisture content is below 2.00%, no test drying is required. 2.2 Method B (Air Drying Method) 2.2.1 Method Summary: A certain amount of air-dried coal sample is weighed and placed in an oven at 105–110°C, where it is dried in an airflow until its mass remains constant. The mass fraction of moisture is calculated based on the mass loss of the coal sample. 2.2.2 Instruments and Equipment 2.2.2.1 Forced-air drying oven: Equipped with an automatic temperature control system that maintains the temperature within the range of 105–110°C. 2.2.2.2 Glass weighing flask: Same as 3.1.3.2. 2.2.2.3 Drier: Same as 3.1.3.3. 2.2.2.4 Analytical balance: Same as 3.1.3.6. 2.2.3 Analysis steps 2.2.3.1 Weigh 1±0.1 g of air-dried coal sample with a particle size of less than 0.2 mm into a pre-dried and weighed weighing bottle, to an accuracy of 0.0002 g, and spread it evenly in the bottle. 2.2.3.2 Open the stopper of the weighing bottle and place it in the drying oven (2.2.2.1) that has been pre-ventilated and heated to 105–110°C. Under continuous air supply, bituminous coal is dried for 1 hour, while lignite and anthracite are dried for 1–1.5 hours. Note: Pre-ventilating is done to ensure even temperature; ventilation begins 3–5 minutes before placing the weighing bottle containing the coal sample into the drying oven. 2.2.3.3 Remove the weighing flask from the drying oven, cover it immediately, place it in a desiccator to cool to room temperature (about 20 min), and then weigh it. 2.2.3.4 Perform check drying for 30 minutes each time, until the mass loss of the dried coal sample in two consecutive trials is no more than 0.0010 g, or until an increase in mass occurs. In the latter case, the mass from the previous iteration before the increase is used as the basis for calculation. When the moisture content is below 2.00%, no test drying is required. 2.3 Calculation of results The moisture content of the air-dried coal sample is calculated using equation (1): Mad = ………………………………… (1) In this equation, Mad represents the moisture content of the air-dried coal sample, expressed as a percentage (%) ； m----is the mass of the air-dried coal sample taken, in grams (g) ； m1----The mass lost by the coal sample after drying, in grams (g). 2.4 Precision of moisture determination The repeatability of moisture determination is specified in Table 1: Table 1 Moisture (Mad)/% Repeatability limit/% <5.00 0.20 5.00–10.00 0.30 >10.00 0.40 3 Determination of ash This standard includes two methods for determining the ash content in coal—the slow ashing method and the rapid ashing method. The slow ashing method is the reference method. 3.1 Slow ashing method 3.1.1 Method summary: A certain amount of air-dried coal sample is weighed and placed in a muffle furnace, where it is heated at a constant rate to (815±10)°C to undergo ashing and burning until its mass remains constant. The ash content of the coal sample is expressed as the percentage of the mass of residues relative to the mass of the coal sample. 3.1.2 Instruments and Equipment 3.1.2.1 Muffle furnace: The furnace chamber possesses a sufficient constant-temperature zone capable of maintaining a temperature of (815±10)°C. The upper part of the rear wall of the furnace is equipped with a chimney with a diameter of (25–30) mm, and a hole for inserting a thermocouple is located at a distance of (20–30) mm from the bottom of the furnace chamber. The furnace door has a ventilation hole with a diameter of 20 mm. The constant temperature zone of the muffle furnace should be measured with the furnace door closed, and at least once a year. Thermometers (including millivoltmeters and thermocouples) should be calibrated at least once a year. 3.1.2.2 Ashtray: porcelain, rectangular, with a bottom length of 45 mm, a bottom width of 22 mm, and a height of 14 mm. 3.1.2.3 Drier: Same as 3.1.3.3. 3.1.2.4 Analytical balance: Same as 3.1.3.6. 3.1.2.5 Heat-resistant ceramic plates or asbestos plates. 3.1.3 Analysis steps 3.1.3.1 In a ash dish that has been pre-ignited until its mass remains constant, weigh 1±0.1 g of air-dried coal sample with a particle size of less than 0.2 mm, to an accuracy of 0.0002 g. Spread the sample evenly in the ash dish so that the mass per square centimeter does not exceed 0.15 g. 3.1.3.2 Place the ashtray in the constant-temperature zone of a muffle furnace with a temperature not exceeding 100°C, close the furnace door, leaving a gap of about 15 mm in it. The furnace temperature was slowly raised to 500°C over a period of not less than 30 minutes, and maintained at this temperature for 30 minutes. Continue to heat to (815±10)°C, and burn at this temperature for 1 hour. 3.1.3.3 Remove the ash tray from the furnace, place it on a heat-resistant porcelain plate or asbestos plate, cool it in air for about 5 minutes, then transfer it to a desiccator to cool to room temperature (about 20 minutes), and subsequently weigh it. 3.1.3.4 Perform check burns for 20 minutes each time, until the mass change after two consecutive burns is no more than 0.0010 g. The mass after the last burning is used as the basis for calculation. When the ash content is below 15.00%, a test burning is not necessary. 3.2 Rapid ashing methods This standard includes two rapid ashing methods: Method A and Method B. 3.2.1 Method A 3.2.1.1 Summary of the method: The ashing dish containing the coal sample is placed on the conveyor belt of the rapid ash determination apparatus, which has been preheated to (815±10)°C; the coal sample is then automatically fed into the apparatus where it is completely ashed, after which it is discharged. The ash content of the coal sample is expressed as the percentage of the mass of residues relative to the mass of the coal sample. 3.2.1.2 Special instruments: Rapid ash analyzer (see Appendix A). 3.2.1.3 Analysis procedure: Preheat the rapid ash analyzer to (815±10)°C. Start the conveyor and adjust its transfer speed to around 17 mm/min or some other appropriate speed. Note: For new rapid ash determinators, comparative tests should be conducted with the slow ashing method using different types of coal. Based on the results of these comparative tests and the ashing characteristics of the coal, the conveying speed of the conveyor belt should be adjusted. In a ash dish pre-heat-dried to a constant mass, weigh 0.5±0.01 g of air-dried coal sample with a particle size of less than 0.2 mm, accurate to 0.0002 g, and spread it evenly in the ash dish so that the mass per square centimeter does not exceed 0.08 g. Place the ash cup containing the coal sample on the conveyor belt of the rapid ash analyzer, and the ash cup will be automatically fed into the furnace. When the ash tray is removed from the furnace, it is taken out and placed on a heat-resistant porcelain plate or asbestos sheet, where it is cooled in air for about 5 minutes. After that, it is transferred to a desiccator to cool to room temperature (approximately 20 minutes), after which it is weighed. 3.2.2 Method B 3.2.2.1 Method Summary: The ash dish containing the coal sample is gradually introduced from outside the furnace into a muffle furnace preheated to (815±10)°C, where it is ashed and burned until its mass remains constant. The ash content of the coal sample is expressed as the percentage of the mass of residues relative to the mass of the coal sample. 3.2.2.2 Instruments and equipment: Same as 4.1.2. 3.2.2.3 Analysis procedure: In a ash dish that has been pre-ignited until its mass remains constant, weigh 1±0.1 g of air-dried coal sample with a particle size of less than 0.2 mm, to an accuracy of 0.0002 g. Spread the sample evenly in the ash dish so that the mass per square centimeter does not exceed 0.15 g. The ash trays containing the coal samples are placed in advance on heat-resistant porcelain plates or asbestos plates. Heat the muffle furnace to 850°C, open the furnace door, and slowly insert the heat-resistant porcelain plate or asbestos plate containing the ash trays into the muffle furnace, so as to ash the coal samples in the first row of ash trays first. After waiting 5 to 10 minutes until the coal sample no longer emits smoke, push the remaining ash trays into the hot part of the furnace at a speed of no more than 2 cm per minute (if the coal sample catches fire and explodes, the test shall be invalidated). Close the furnace door and burn at a temperature of (815±10)°C for 40 minutes. Remove the ash tray from the furnace, allow it to cool in the air for about 5 minutes, then transfer it to a desiccator to cool to room temperature (approximately 20 minutes), after which it is weighed. Perform inspection burns for 20 minutes each time, until the mass change after two consecutive burns is no more than 0.0010 g. The mass after the last burning is used as the basis for calculation. If the results are unstable during exploratory burning, re-determination should be performed using the slow ashing method. When the ash content is below 15.00%, a test burning is not necessary. 3.3 Calculation of results The ash content of air-dried coal samples is calculated using equation (2): Aad = ………………………………… (2) Where: Aad ---- Ash content of air-dried coal samples, expressed as a percentage (%) ； m----is the mass of the air-dried coal sample taken, in grams (g) ； m1---the mass of the residue after burning, in grams (g). 3.4 Precision of ash determination The repeatability and reproducibility of ash determination are specified in Table 2: Table 2 Ash/% Repeatability limit Aad/% Reproducibility critical difference Ad/% <15.00 0.20 0.30 15.00–30.00 0.30 0.50 >30.00 0.50 0.70 4 Determination of volatile matter 4.1 Method summary A certain amount of air-dried coal sample is weighed and placed in a covered porcelain crucible; it is then heated at (900±10)°C in an oxygen-free environment for 7 minutes. The volatiles of a coal sample are calculated as the percentage of the reduced mass relative to the mass of the coal sample, minus the moisture content of that coal sample. 4.2 Instruments and Equipment 4.2.1 Volatiles crucible: A porcelain crucible with a tightly fitting lid. The total mass of the crucible is 15–20 g. 4.2.2 Muffle furnace: Equipped with a pyrometer and temperature control device, capable of maintaining a temperature of (900±10)°C, and having a sufficient constant-temperature zone at (900±5)°C. The heat capacity of the furnace is such that, when the initial temperature is 920°C and a crucible holder along with several crucibles at room temperature are placed inside, it returns to (900±10)°C within 3 minutes after the furnace door is closed. The rear wall of the furnace has an exhaust hole and a hole for inserting a thermocouple. The position of the small hole should be such that, after the thermocouple is inserted into the furnace, its hot junction lies between the bottom of the crucible and the bottom of the furnace, at a distance of 20–30 mm from the furnace bottom. The constant temperature zone of the muffle furnace should be measured with the furnace door closed, and at least once a year. Thermometers (including millivoltmeters and thermocouples) should be calibrated at least once a year. 4.2.3 Crucible holder: Made of nichrome wire or other heat-resistant metal wires. Its dimensions are such that all crucibles can be placed within the constant-temperature zone of the muffle furnace, with the bottom of the crucibles positioned directly above the thermocouple junction. 4.2.4 Crucible holder clamp. 4.2.5 Drier: Same as 2.1.3.3. 4.2.6 Analytical balance: Same as 2.1.3.6. 4.2.7 Compactor: A spiral or lever-type compactor capable of compressing coal samples with a diameter of 10 mm. 4.2.8 Stopwatch. 4.3 Analysis steps 4.3.1 In a covered porcelain crucible that has been pre-burned at 900°C until its mass remains constant, weigh 1±0.01 g of air-dried coal sample with a particle size of less than 0.2 mm, to an accuracy of 0.0002 g. Then gently shake the crucible to spread the coal sample evenly, cover it, and place it on the crucible stand. Lignite and bituminous coal should be pre-pressed into pellets and cut into small pieces of about 3 mm. 4.3.2 Preheat the muffle furnace to around 920°C. Open the furnace door, quickly insert the rack with the crucible into the constant temperature zone, close the furnace door immediately and start timing to ensure an exact heating time of 7 minutes. After the crucible and stand are placed in, the furnace temperature must be restored to (900±10)°C within 3 minutes, and must remain at (900±10)°C thereafter; otherwise, this test is invalid. The heating time includes the temperature recovery time. 4.3.3 Remove the crucible from the furnace, allow it to cool in the air for about 5 minutes, then transfer it to a desiccator to cool to room temperature (approximately 20 minutes), after which it is weighed. 4.4 Classification of slag characteristics The characteristics of the slag obtained by measuring the volatile content are classified according to the following rules: (1) Powderous——entirely in powder form, with no particles sticking together. (2) Adhesiveness——Upon gentle touching with a finger, it turns into powder or is essentially powder, with larger clumps also turning into powder with a light touch. (3) Weak adhesion ---- It breaks into small pieces when gently pressed with a finger. (4) Non-melting adhesion——It breaks into small pieces only when pressed firmly with fingers; the upper surface of the slag has no luster, while the lower surface has a slight silver-white luster. (5) Non-expanding molten bonding——The cokemass forms flat lumps, with the boundaries between coal particles being difficult to distinguish; the upper surface of the cokemass has a distinct silver-white metallic luster, and this luster is even more pronounced on the lower surface. (6) Slightly expanded molten bond – it cannot be crushed with fingers; both the upper and lower surfaces of the slag have a silver-white metallic luster, but the surface of the slag features small expansion bubbles (or tiny gas bubbles). (7) Expansive molten bonding – The upper and lower surfaces of the slag have a silvery-white metallic luster, showing significant expansion, but the height does not exceed 15 mm. (8) Strongly expanded molten bonding – the upper and lower surfaces of the cinder have a silvery-white metallic luster, and the height of the cinder is greater than 15 mm. For simplicity, the sequence numbers listed above are commonly used as codes for various cinder characteristics. 4.5 Calculation of results The volatiles in air-dried coal samples are calculated using equation (3): Vad = …………………………………… (3) Where: Vad ---- Volatiles in air-dried coal samples, expressed as a percentage (%) ； m----the mass of the air-dried coal sample, in grams (g) ； m1----The mass loss of the coal sample after heating, in grams (g) ； Mad----The moisture content of air-dried coal samples, expressed as a percentage (%). 4.6 Precision of volatiles determination The repeatability and reproducibility of volatiles determination are specified in Table 3: Table 3 Volatiles/% Repeatability limit Vad/% Reproducibility critical difference Vd/% <20.00 0.30 0.50 20.00–40.00 0.50 1.00 >40.00 0.80 1.50 5 Calculation of fixed carbon The fixed carbon on an air-dried basis is calculated using Equation (4): FCad = …………………………(4) Where: FCad – Fixed carbon on an air-dried basis, expressed as a percentage (%) ； Mad----Moisture content of air-dried coal samples, expressed as a percentage (%) ； Aad----Ash content of air-dried coal samples, expressed as a percentage (%) ； Vad ---- the volatiles content of air-dried coal samples, expressed as a percentage (%). 6 Conversion of volatile matter on an air-dried basis to volatile matter on a dry, ash-free basis and on a dry, mineral-free basis 6.1 Dry, ash-free basis volatile matter: Vdaf = …………………………(5) When the mass fraction of carbon dioxide from carbonates in the air-dried coal sample is between 2% and 12%, then Vdaf = …………………………(6). When this mass fraction is greater than 12%, then Vdaf = ………………(7). In these equations, Vdaf represents the volatile matter on a dry, ash-free basis, expressed as a percentage (%) ； (CO2)ad——The mass fraction of carbonate carbon dioxide in air-dried coal samples (determined according to GB/T 218), expressed as a percentage (%) ； (CO2)ad (coking slag) – The mass fraction of carbon dioxide in the coking slag relative to the mass of the coal sample, expressed as a percentage (%). 7.2 Volatiles on a dry, mineral-free basis, Vdmmf = …………………… (8) When the mass fraction of carbon dioxide derived from carbonates in the air-dried coal sample is 2% to 12%, then Vdmmf = …………………… (9). When this mass fraction is greater than 12%, then Vdmmf = ……………… (10). In these equations, Vdmmf represents the volatiles on a dry, mineral-free basis, expressed as a percentage (%) ； MMad----The mineral mass fraction of the air-dried coal sample (determined in accordance with GB/T 7560), expressed as a percentage (%). 8 Source of the method ； The method is derived from GB/T212-2001 Methods for industrial analysis of coal.