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1. Scope of application This standard specifies the method for determining the high calorific value of coal and the method for calculating its low calorific value. This standard applies to peat, lignite, bituminous coal, anthracite, coke, and carbonaceous shale. 2 Method Summary 2.1 Higher heating value The heating value of coal is determined using an oxygen bomb calorimeter. A certain amount of the analytical sample is burned in an oxygen bomb calorimeter, within an oxygen bomb filled with excess oxygen. The heat capacity of the oxygen bomb calorimeter is determined by burning a certain amount of a reference calorimeter substance, benzoic acid, under similar conditions. The calorific value of the sample in a bomb can be determined by considering the temperature rise in the thermal system before and after combustion of the sample, and by correcting for additional heat sources such as spark heat. The higher heating value is obtained by deducting the heat of formation of nitric acid and the sulfuric acid correction value (the difference between the heat of formation of sulfuric acid and sulfur dioxide) from the calorific value of the cartridge. 2.2 Lower heating value: The constant-volume lower heating value and the constant-pressure lower heating value of coal can be calculated from the higher heating value of the sample. To determine the constant-volume lower heating value, it is necessary to know the moisture and hydrogen content in the coal sample. In principle, to calculate the constant-pressure lower heating value, it is also necessary to know the contents of oxygen and nitrogen in the coal sample. 3. Laboratory conditions —— The laboratory in which calorimetric measurements are carried out should be a separate room; no other testing procedures shall be conducted in the same room at the same time. ———The room temperature should remain relatively stable; the change in room temperature during each measurement should not exceed 1°C. It is advisable for the room temperature to be within the range of 15°C to 30°C. ———There should be no strong air convection indoors; therefore, there should be no strong heat sources, cold sources, or fans, and doors and windows should be kept closed during the testing process. ———The laboratory should preferably face north to avoid sunlight; otherwise, the calorimeter should be placed in a location free from direct sunlight. 4. Reagents and materials 4.1 Oxygen (GB 3853), with a purity of 99.5%, free of flammable components; electrolytic oxygen is not permitted. 4.2 Sodium hydroxide standard solution: c(NaOH) ≈ 0.1 mol/L. Weigh 4 g of reagent-grade sodium hydroxide (GB/T 629), dissolve it in 1000 mL of water that has been boiled and then cooled, mix well, and transfer the mixture into a plastic bottle or container, securing the lid tightly. It is then calibrated using high-purity potassium hydrogen phthalate (GB/T 1257). 4.3 Methyl red indicator: 2 g/L. Weigh 0.2 g of methyl red (HG 3-958-7 6) and dissolve it in 100 mL of water. 4.4 Benzoic acid – reference calorimetric substance, grade II or higher. It has had its standard calorific value determined by an authorized metrological institution or an institution authorized to conduct such determinations. 4.5 Ignition wire: A platinum, copper, nickel wire, or another metal wire with a known heat value, with a diameter of around 0.1 mm; or cotton thread. If cotton thread is used, it should be white and of uniform thickness, without any wax coating. The heat released when various ignition wires are ignited is as follows: Iron wire: 6700 J/g; Nickel-chromium wire: 6000 J/g; Copper wire: 2500 J/g; Cotton thread: 17500 J/g. 6.6 Acid-washed asbestos fluff should be burned at 800°C for 30 minutes before use. 6.7 Wiping paper: Determine its heat of combustion before use: Take 3 to 4 sheets of paper, roll them into a ball, and weigh their mass accurately. Place it in a combustion crucible, and then determine the heat of combustion using conventional methods. The average of the 3 results is taken as the calorific value of the lens cleaning paper. 5 Instrumentation and Equipment 5.1 Calorimeter 5.1.1 General Provisions A calorimeter consists of a combustion oxygen bomb, an inner cylinder, an outer cylinder, a stirrer, temperature sensors, a sample ignition device, a temperature measurement and control system, and water. There are two types of general calorimeters: constant-temperature and adiabatic types, whose calorimetry systems are enclosed in a double-jacketed (outer tube) filled with water. The only difference between them lies in the outer cylinder and the attached automatic temperature control device; there are no significant differences in the rest of the components. The inner cylinder, stirrer, and water of the anhydrous calorimeter are replaced by a metal block. The oxygen bomb is made of double-layer metal. It contains a temperature sensor, and the oxygen bomb itself constitutes the calorimetry system. In principle, automatic oxygen bomb calorimeters should be designed and constructed in accordance with the principles and provisions in Chapters 7 and 8 of this standard, and the bomb heat and constant-volume high-heating value of the test sample should be calculated and analyzed in accordance with the provisions of 9.3. The calorific value results should be expressed in units of joules per gram (J/g) or megajoules per kilogram (MJ/kg). In each test, the automatic oxygen bomb calorimeter must specify the required parameters in detail. The information from each test, whether printed or recorded in some other way, includes the temperature rise, cooling correction values (for constant-temperature conditions), effective heat capacity, sample mass, ignition energy, and other additional heats; all calculations performed based on this data can be verified manually, and the formulas used should be provided in the instrument’s operating instructions. The additional heat used in the calculation must be clearly defined, and the correction for the heat of the spark ignition and side reactions should be explicitly stated. This standard also allows the use of other oxygen bomb calorimeters, provided that their calibration conditions, the similarity of conditions during calibration and calorimetry, the sample mass and the volume of the oxygen bomb, the oxygen filling pressure, the amount of water added to the oxygen bomb, as well as the precision and accuracy of the measurements, all meet the basic requirements of this standard. The precision and accuracy requirements for the calorimeter are as follows: testing precision: the relative standard deviation of the results from 5 benzoic acid tests shall not be greater than 0.20% ； Accuracy: The difference between the test results for standard coal and the standard values is within the range of uncertainty; or when benzoic acid is used as a sample for 5 calorimetric measurements, the difference between its average value and the standard calorific value does not exceed 50 J/g. Note: Except for the results resulting from incomplete combustion, none of the test results can be discarded arbitrarily. 5. 1.2 Oxygen bombs are made of heat-resistant and corrosion-resistant nickel-chromium or nickel-chromium-molybdenum alloy steels. They need to possess three main properties: a) resistance to thermal effects caused by the high temperatures and corrosive substances generated during combustion ； b) Able to withstand oxygenation pressure and the instantaneous high pressures generated during combustion; c) Maintain complete airtightness during testing. The cartridge volume ranges from 250 mL to 350 mL, and the projectile should be equipped with valves for oxygen supply and exhaust, as well as a wiring plate for the ignition power source. Oxygen bombs, as well as those with newly replaced components (cylinders, projectiles, connecting rings), must undergo a hydrostatic test at 20.0 MPa; they can be used only after it is proven that there are no issues. In addition, regular attention should be paid to the components related to the strength of the oxygen bomb, such as the threads of the cylinder and connecting rings, the inlet valve, the outlet valve, and the connections between the electrodes and the warhead. If any significant wear or loosening is detected, repairs should be carried out, and the device must pass a hydrostatic test before it can be used again. The oxygen bomb should also undergo pressure tests on a regular basis; after each such test, its usable life generally should not exceed 2 years. When multiple designs are used to manufacture the same oxygen bomb, each oxygen bomb must be used as a complete unit. The interchange and reuse of oxygen bomb components can lead to serious accidents. 5.1.3 The inner cylinder is made of red copper, brass, or stainless steel, and its cross-section can be oval, rhombus, or any other appropriate shape. Fill the cylinder with 2000 mL to 3000 mL of water, sufficient to submerge the oxygen bomb (excluding the inlet and outlet valves and electrodes). The outer surface of the inner cylinder should be highly polished to reduce radiation between it and the outer cylinder. 5. 1.4 The outer cylinder is a double-walled container made of metal, with an upper cover. The outer wall is circular, while the shape of the inner wall depends on the shape of the inner cylinder ； The outer tube should completely enclose the inner tube, with a gap of 10 mm to 12 mm between them. The bottom of the outer tube is equipped with insulating supports for placing the inner tube. a) Constant-temperature outer cylinder: A constant-temperature calorimeter is equipped with a constant-temperature outer cylinder. For the externally heated cylinder, during the entire testing process, the temperature variation of the water in the cylinder should be kept within ±0.1 K or less; in the case of a non-externally heated cylinder, that is, a static cylinder, its heat capacity after being filled with water should be at least 5 times that of the calorimeter, so as to maintain a relatively constant temperature in the cylinder throughout the testing process. The heat capacity of the outer cylinder should be such that, when the cooling constant is approximately 0.0020 min-1, the temperature change of the outer cylinder from the moment the sample is ignited until the end of the process is less than 0.16K ； When the cooling constant is approximately 0.0030 min-1, this temperature change should be less than 0.11K. An insulating protective layer can be added outside the outer cylinder to reduce the impact of room temperature fluctuations. The thermometer used for the outer cylinder should have a minimum resolution of 0.1 K. b) Insulated outer cylinder: An insulated calorimeter is equipped with an insulated outer cylinder. The outer cylinder is equipped with a heating device, and through an automatic temperature control system, the water temperature in the outer cylinder can be kept closely in line with the temperature of the inner cylinder. The water in the outer cylinder should also circulate within a special double-layered cover. The sensitivity of the automatic temperature control device should be sufficient to maintain a stable temperature in the inner cylinder before ignition and after completion of the process (with an average temperature change of no more than 0.0005 K/min over 5 minutes) ； During the heating phase of a test, the heat exchange between the inner and outer cylinders should not exceed 20 J. 5.1.5 Agitator: propeller-type or other types. An appropriate rotation speed is (400–600) r/min. And it should remain constant. Effective thermal insulation measures should be employed between the stirrer shaft and the outside environment to minimize heat exchange between the calorimetry system and the surroundings. The mixing efficiency of the stirrer should ensure that the time from ignition to completion in the heat capacity calibration does not exceed 10 minutes, while also preventing the generation of excessive mixing heat (when the temperatures of the inner and outer cylinders are equal to the room temperature, the heat generated by continuous mixing for 10 minutes should not exceed 120 J). 5.1.6 Calorimetric thermometers: The calorimetric thermometers used for measuring the temperature of the inner cylinder should have a resolution of at least 0.001 K, so as to enable the determination of temperature increases in the range of 2 K to 3 K with a resolution of 0.002 K or better; the absolute temperature they indicate should be able to reach accuracy levels of around 0.1 K. Calorimetric thermometers must be linear or linearized within each temperature range they measure. They must all be calibrated by a metrological authority to prove that they meet the aforementioned requirements. There are two types of thermometers that can be used for this purpose. a) Glass-mercury thermometers: There are two common types of glass-mercury thermometers: one is a precision thermometer with a fixed temperature measurement range, and the other is a Beckman thermometer that allows for varying temperature measurements. The minimum resolution for both should be 0.01K. When in use, necessary corrections should be made according to the correction values in the calibration certificate issued by the metrology authority. Both types of thermometers require temperature calibration (Bekman thermometers require aperture calibration); in addition to this correction value, Bekman thermometers also need another correction value known as the \"average division value\". To achieve the required resolution, a 5x magnifying glass is needed to read the temperature; to prevent the mercury column from sticking to the glass, a mechanical oscillator is usually required to shake the thermometer. If there is no mechanical oscillator, the temperature probe should be tapped manually before reading the temperature. b) Digital display thermometers: Digital display thermometers can replace traditional glass mercury thermometers. These thermometers are composed of elements such as platinum resistors, thermistors, and quartz crystal resonators, along with appropriate bridges, zero-point controllers, frequency counters, or other electronic devices; they should be capable of providing the required level of resolution. The short-term repeatability of such thermometers should be 0.001K or better, while their long-term drift over a period of 6 months should not exceed 0.05K. Linear temperature sensors cause less bias in heat generation measurements compared to nonlinear temperature sensors. 5.2 Auxiliary Equipment 5.2.1 Burner Pots Platinum products are the most ideal; nickel-chromium steel products can generally be used as alternatives. The specifications can be: height of 17 mm to 18 mm, bottom diameter of 19 mm to 20 mm, upper diameter of 25 mm to 26 mm, and thickness of 0.5 mm. Other combustion cells made of alloy steel or quartz can also be used, provided that they ensure complete combustion of the sample without suffering from corrosion or generating heat effects. 5.2.2 Pressure gauges and oxygen tubes The pressure gauge consists of two dials: one indicates the pressure in the oxygen cylinder, and the other indicates the pressure inside the oxygen bomb during oxygen filling. A pressure relief valve and a safety valve should be installed on the gauge head. The pressure gauge should be calibrated by a metrology department every 2 years to ensure accurate readings and safe operation. The pressure gauge is connected to the oxygen bomb via seamless copper tubes with an inner diameter of 1 mm to 2 mm, or to the oxygen filling device via high-strength nylon tubes, in order to introduce oxygen. Pressure gauges and all connection parts must not come into contact with grease or lubricants. If it gets contaminated accidentally, it must be cleaned sequentially with benzene and alcohol, and used only after it has dried. 5.2.3 Ignition device: The ignition is powered by a 12 V–24 V power supply, which can be provided by a 220 V AC supply via a transformer. A rheostat for adjusting the voltage and an indicator light or ammeter to show the ignition status should be connected in series in the circuit. The ignition voltage should be determined through preliminary testing. Method: Connect the ignition wire and conduct an electrical test in air. In the case of fuse-type ignition, adjust the voltage so that the ignition wire reaches a bright red color within 1 to 2 seconds ； With the cotton thread ignited, adjust the voltage so that the ignition wire reaches a dark red color within 1 to 5 seconds. Once the voltage and time have been determined, it is necessary to accurately measure the voltage, current, and duration of power application in order to calculate the heat generated by electrical energy. If cotton thread is used for ignition, a nickel-chromium wire with a diameter of about 0.05 is connected between the two electrode posts above the fire shield; the middle part of the wire is pre-coiled into several spirals to concentrate heat generation. 5. 2. 4 Presses: Screw-type, lever-type, or other types of presses. It can compress coal cakes or benzoic acid cakes with a diameter of 10 mm. The molds and pressure rods are made of hard steel, with a smooth surface that is easy to wipe clean. 5. 2. 5 Stopwatch or other timer capable of indicating 10 seconds 5. 3 Balance 5. 3.1 Analytical balance: sensitivity of 0.1 mg. 5. 3.2 Industrial balance: loading capacity of 1 kg to 5 kg, sensitivity of 1 g. 6 Measurement Steps 6.1 Overview The determination of calorific value consists of two separate tests, namely the combustion test of a reference calorimetric substance under specified conditions (heat capacity calibration) and the combustion test of the sample. To eliminate systematic errors caused by uncontrolled heat exchange, it is required that the conditions of the two tests be as similar as possible. The experiments involve quantitatively carrying out the combustion reaction to defined products and measuring the temperature changes caused by the entire combustion process. The experimental process is divided into the initial stage, the main stage (reaction stage), and the final stage. For adiabatic calorimeters, the initial and final stages are used to determine the starting temperature and the ending temperature for ignition ； For constant-temperature calorimeters, the initial and final measurements are used to determine the heat exchange characteristics of the calorimeter, so as to correct for the heat exchange between the inner and outer cylinders of the calorimeter during the combustion reaction. The initial and final periods should be long enough. 6.2 Constant-temperature calorimetry method 6.2.1 Install and adjust the calorimeter according to the instruction manual. 6.2.2 Weigh 0.9 g to 1.1 g of air-dried coal sample with a particle size of less than 0.2 mm in a combustion crucible (with accuracy to 0.0002 g). For specimens that are prone to splashing during combustion, they can be tightly wrapped in lens cleaning paper of known mass before testing, or they can first be compressed into pellets using a pelletizer and then cut into pieces ranging from 2 mm to 4 mm in size for use. For samples that do not burn completely, an asbestos pad can be placed at the bottom of the combustion dish, or asbestos wool (4.6) can be used as a lining (first lay a layer of asbestos wool at the bottom of the dish and then compress it with your hand). Quartz burners do not require any lining. If incomplete combustion still occurs even with the use of a padding, the oxygen pressure can be increased to 3.2 MPa; alternatively, the weighed sample can be wrapped in lens cleaning paper of known mass and calorific value and compressed by hand before being placed in the combustion chamber. 6.2.3 Take a section of ignition wire of known mass, connect its ends to two electrode posts respectively, bend the ignition wire close to the sample, making sure to maintain good contact with it or keeping a small distance (for coal that is prone to spattering and burning easily) ； Be careful not to let the ignition wire touch the combustion crucible, to avoid a short circuit that could cause failure to ignite or even damage the crucible. At the same time, care should be taken to prevent short circuits between the two electrodes, as well as between the combustion cell and the other electrode. When igniting with a cotton thread, fix one end of the thread to the ignition wire that is already connected to the two electrode posts (it is best to clamp it in the spiral of the ignition wire), and place the other end over the sample; adjust the degree of overlap depending on how easily the sample ignites. For coal samples that are prone to splashing, a small distance should be maintained. Add 10 mL of distilled water to the oxygen bomb. Carefully tighten the oxygen bomb lid, being careful not to cause any changes in the position of the combustion chamber and the ignition wire due to vibrations. Slowly fill the oxygen bomb with oxygen until the pressure reaches 2.8 M Pa to 3.0 M Pa; the oxygen filling process should take no less than 15 seconds ； If oxygen is filled accidentally and the pressure exceeds 3.3 MPa, stop the test, release the oxygen, and then refill it to below 3.2 MPa. When the oxygen pressure in the cylinder drops below 5.0 MPa, the oxygen filling time should be appropriately extended; when the pressure falls below 4.0 MPa, a new cylinder of oxygen should be used. 6.2.4 Add sufficient distilled water to the inner cylinder so that the top surface of the oxygen bomb lid (excluding the protruding inlet, outlet valves, and electrodes) is submerged 10 mm to 20 mm below the water surface. The amount of water used in each test should be the same as that used when calibrating the heat capacity (with a difference of within 1 g). The water volume is best determined by weighing. If the volumetric method is used, temperature variations need to be corrected. Be sure to adjust the temperature of the inner cylinder appropriately, so that at the end point its temperature is about 1 K higher than that of the outer cylinder, thereby causing a significant drop in the temperature of the inner cylinder at that point. The temperature of the outer cylinder should be as close as possible to room temperature, with a difference not exceeding 1.5 K. 6.2.5 Place the oxygen bomb into the inner cylinder filled with water. If no bubbles escape from the oxygen bomb, it indicates good airtightness, and the inner cylinder can then be placed on the insulating stand of the outer cylinder. If bubbles appear, it signifies a leak; the cause must be identified and corrected, followed by recharging the oxygen bomb. Then connect the ignition electrode plug, install the stirrer and calorimetric thermometer, and close the lid of the outer cylinder. The mercury bulb of the thermometer (or temperature sensor) should be aligned with the center of the oxygen bomb body (excluding the inlet and outlet valves and electrodes); neither the thermometer nor the stirrer shall come into contact with the oxygen bomb or the inner cylinder. Near the part of the mercury column that is exposed near the calorimetric thermometer (when a glass mercury thermometer is used), another ordinary thermometer should be hung separately to measure the temperature of the exposed column. 6.2.6 Start the stirrer; 5 minutes later, begin timing and measure the temperature of the inner cylinder (t0), and immediately turn on the power to ignite it. Then record the outer cylinder temperature (t) and the exposed column temperature (t). The temperature of the outer cylinder is read to at least 0.05 K, while the temperature of the inner cylinder is read to 0.001 K with the help of a magnifying glass. When reading the temperature, the line of sight, the center line of the magnifier, and the top of the mercury column should be on the same horizontal level to avoid the impact of parallax on the reading. Before each reading, the oscillator should be operated to vibrate for 3 s to 5 s. 6.2.7 Monitor the temperature of the inner cylinder (Note: Do not extend any part of your body above the calorimeter within 20 seconds after ignition). If the temperature rises sharply within 30 seconds, it indicates successful ignition. Read the temperature inside the inner cylinder once at 1’40” after ignition (t1’40’’); a value of 0.01 K is sufficient. 6.2.8 As the end of the period approaches, start reading the inner cylinder temperature at 1-minute intervals. Start the oscillator before taking the temperature reading, and ensure the accuracy is up to 0.001 K. Use the first temperature drop as the end temperature (t). The main phase of the experiment is now complete. Note: The time from ignition to the end point for one calorimeter is 8 min to 10 min. For a specific calorimeter, it can be appropriately determined based on experience. 6.2.9 Stop stirring, remove the inner cylinder and oxygen bomb, open the vent valve to release the combustion exhaust gases, open the oxygen bomb, and carefully inspect the interior of the bomb cylinder and combustion crucible; if there are signs of incomplete combustion of the sample or carbon black present, the test must be discarded. Measure the length of the unburned ignition wire in order to calculate the actual amount consumed. Thoroughly rinse all parts of the oxygen bomb, the vent valve, the inside and outside of the combustion crucible, and the combustion residues with distilled water. Collect all the wash solutions (approximately 100 mL in total) in a beaker for sulfur determination (see 7.3.2 of this standard). 6.3 Adiabatic Calorimetry Method 6.3.1 Install and adjust the calorimeter in accordance with the instruction manual. 6.3.2 Weigh the sample in accordance with the steps in 6.2.2 of this standard. 6.3.3 Prepare the oxygen bomb according to the steps in 6.2.3 of this standard. 6.3.4 Weigh the required amount of water in the inner cylinder according to the steps in 6.2.4 of this standard. Adjust the water temperature to be as close as possible to room temperature. The difference should not exceed 5K, with a value slightly below room temperature being ideal. If the temperature of the inner cylinder is too low, water vapor tends to condense on the outer wall of the inner cylinder; if the temperature is too high, excessive evaporation of water from the inner cylinder occurs. All of this is unfavorable for obtaining accurate measurement results. 6.3.5 Place the inner cylinder, oxygen bomb, stirrer, and thermometer in accordance with the steps in 6.2.5 of this standard. 6.3.6 Start the agitator and the external cylinder circulation water pump, and activate the cooling water and heater for the external cylinder. Once the temperature of the inner cylinder stabilizes, adjust the cooling water flow rate so that the outer cylinder heater is activated automatically 3 to 5 times per minute (as observed via an ammeter or indicator light). If thyristors are used instead of relays in the automatic temperature control circuit, the adjustment of the cooling water should be based on a weak current flowing in the heater. After adjusting the cooling water, start reading the temperature of the inner cylinder; using a magnifying glass, the temperature can be read to 0.001K. Before each reading, operate the oscillator for 3 to 5 seconds. When the range of three consecutive temperature readings taken at 1-minute intervals does not exceed 0.001 K, power can be applied for ignition; this temperature is then the ignition temperature t. Otherwise, adjust the balance knob of the bridge until the temperature of the inner cylinder stabilizes, and then ignite. 6 to 7 minutes after ignition, the temperature of the inner cylinder is read at 1-minute intervals until the difference between three consecutive readings is no more than 0.001 K. Take the highest reading as the final temperature t. 6.3.7 Turn off the mixer and heater (keep the circulation water pump running), and then terminate the test according to step 6.2.9 of this standard. 6.4 Automatic Oxygen Bomb Calorimetry 6.4.1 Install and adjust the calorimeter in accordance with the instrument’s instructions. 6.4.2 Weigh the sample in accordance with step 6.2.2 of this standard. 6.4.3 Prepare the oxygen bomb according to step 6.2.3 of this standard. 6.4.4 Conduct the remaining test steps in the chamber in accordance with the instrument’s operation manual, and then conclude the test following step 6.2.9 of these guidelines. 6.4.5 After the test results are printed or displayed, verify the input parameters; once they are confirmed to be correct, the results are reported. 7 Calculation of measurement results 7.1 Temperature correction 7.1.1 Calibration of thermometers When glass thermometers are used, the ignition temperature and end temperature must be corrected according to the calibration certificate. a) Thermometer scale calibration: The ignition temperature t0 and the end temperature tn are corrected using the aperture correction values provided in the calibration certificate. The temperature rise is then calculated from the corrected temperatures (t0 – h0) and (tn – hn), where h0 and hn represent the aperture correction values for t0 and tn, respectively. b) If a Beckman thermometer is used, correction for the average division value is required. After setting the base temperature, the average division value H0 corresponding to the exposed column temperature at that base temperature (calculated based on the exposed column temperature given in the calibration certificate) should be calculated using the average division value provided in the calibration certificate. In the test, when the temperature of the exposed column during testing, te, differs from the standard exposed column temperature by more than 3°C, the average division value H is calculated using the following formula: ……………………………(1) Where: H0 —— the average division value corresponding to the standard exposed column temperature at that reference temperature ； ——The standard exposed column temperature corresponding to this base temperature, in degrees Celsius (℃) ； ——Actual exposed column temperature in the test, in degrees Celsius (℃) ； 0.00016 —— The relative coefficient of thermal expansion of mercury with respect to glass. 7.1.2 Cooling correction: The heat loss in adiabatic calorimeters is negligible, hence no cooling correction is required. During the test, heat exchange continuously occurs between the inner cylinder and the outer cylinder of a constant-temperature calorimeter; this lost heat must be corrected by adding a correction value C to the temperature increase. This correction value is known as the cooling correction value, and its calculation method is as follows: First, based on the temperature differences between the inner and outer cylinders at the start and end of the test, namely t0–tj and tn–tj, the corresponding values of v0 and vn are determined from the v–(t–tj) relationship curve (calibrated according to sections 8.1–8.4), or v0 and vn can be calculated using the pre-calculated equations (2) and (3): ………………………（2） ………………………（3） Where: V0 – the rate of temperature decrease of the inner cylinder due to the temperature difference between the inner and outer cylinders at the start of the test, expressed in Kelvin per minute, K/min ； Vn —— The cooling rate of the inner cylinder at the end point due to the temperature difference between the inner and outer cylinders, K/min ； k —— the cooling constant of the calorimeter (calibrated according to clauses 8.3–8.4), in minutes per minute (min-1) ； A —— Comprehensive constant of the calorimeter (calibrated according to clauses 8.3–8.4), in units of per minute (min-1) ； t0–tj —— the temperature difference between the inner and outer cylinders at ignition, in Kelvin (K) ； tn-tj — the temperature difference between the inner and outer cylinders at the end point, in Kelvin (K) ； tj——outer cylinder temperature, in Kelvin (K). Then, the cooling correction value is calculated using the following formula: ………………………（4）Where: C —— Cooling correction value, in Kelvin (K) ； n —— the time from ignition to the end point, in minutes (min) ； a —— When △/△₁′40″ ≤ 1.20, a = △/△₁′40″ – 0.10 ； When △/△₁′40″ > 1.20, a = △/△₁′40″; where △ is the total temperature rise during the main period (△ = tn – t0), and △₁′40″ is the temperature rise at 1′40″ after ignition (△₁′40″ = t₁′40″ – t0). In an oxygen bomb calorimeter, or in cases where it is necessary, the Regnault-Pfandler formula can be used: ………………………(5) Where: ti – the temperature of the inner cylinder at minute i during the main period. The meanings of the remaining symbols are the same as before. The Ray-Fang formula is applicable; according to the procedure, the temperature must be measured at least once per minute after ignition until the end point is reached. 7.2 In the spark ignition calibration for the fuse-type pyrometric method, the heat released by the ignition wire during the test should be calculated based on the actual consumption of the ignition wire (the original amount minus the remaining amount) and the heat of combustion of the ignition wire. In the cotton thread ignition method, first, the heat of combustion of a single cotton thread is calculated (a certain amount of cotton thread of appropriate length is cut off, its mass is measured; from this, the mass of one thread is determined, and then this value is multiplied by the specific heat value of the cotton thread). After that, the heat generated by the electrical energy consumed each time is determined. Note: The heat generated by electrical energy (J) = voltage (V) × current (A) × time (S). The total heat released by the two is the spark heat. 7.3 Calculation of the bomb calorific value and the high-temperature calorific value 7.3.1 Calculation of the bomb calorific value Qb,ad of air-dried coal samples using equation (6) or equation (7) a) Constant-temperature calorimeter: ………………(6) In this equation, Qb,ad represents the bomb calorific value of the sample under analysis, expressed in joules per gram (J/g); E represents the heat capacity of the calorimeter, expressed in joules per kelvin (J/K) ； q1 —— Heat input, in joules (J) ； q2 —— Total heat generated by additives (such as wrapping paper, etc.), in joules (J) ； m —— sample mass, in grams (g) ； H — the average division value of the Beckman thermometer. h0 —— the capillary pore size correction value for t0; when a digital thermometer is used, h0 = 0 ； hn——the capillary pore size correction value for tn; when a digital thermometer is used, hn = 0. b) Adiabatic calorimeter ……………… (7) 7.3.2 The constant-volume high heating value Qgr,ad of air-dried coal is calculated using equation (8) ……………………… (8) Where: Qgr,ad – the constant-volume high heating value of the air-dried coal sample, in joules per gram (J/g) ； Qb,ad —— adiabatic calorific value of air-dried coal samples, in joules per gram (J/g) ； Sb,ad —— The sulfur content of coal as determined by the cartridge wash solution, expressed in percent (%) ； When the total sulfur content is below 4.00%, or the calorific value is greater than 14.60 MJ/kg, total sulfur (determined according to GB T214) is used in place of Sb,ad ； ? 94.1——Correction factor for every 1.00% of sulfur in air-dried coal samples, in joules (J) ； α — Nitric acid correction factor: When Qb,ad ≤ 16.70 MJ/kg, α = 0.0010 ； When 16.70MJ/kg＜Qb,ad ≤25.10MJ/kg, α=0.0012 ； When Qb,ad > 25.10 MJ/kg, α = 0.0016. When an oxidizer is added, it should be considered in terms of the total heat release. When it is necessary to determine Sb,ad in the cartridge wash solution (6.2.9), the wash solution is boiled for 2 to 3 minutes; after it has cooled slightly, it is titrated using a sodium hydroxide standard solution (4.2) with methyl red (4.3) (or an appropriate mixed indicator) as an indicator, in order to determine the total acid content in the wash solution. The sulfur content of the cartridge wash solution, expressed as Sb,ad (%), is then calculated using equation (9): ………………………（9）Where: c —— the molar concentration of the sodium hydroxide standard solution (4.2), in units of moles per liter (mol/L) ； V — Volume of sodium hydroxide solution used in titration, in milliliters (mL) ； 60 —— the enthalpy of formation of l m mol of nitric acid, in joules (J) ； m —— the mass of the sample taken, in grams (g) ； 1.6 —— The conversion factor for converting 1/2(H2SO4) per mole of sulfuric acid to the mass fraction of sulfur. 8 Heat Capacity and Instrument Constants Calibration 8.1 The heat capacity E required to calculate the heat of combustion, as well as the v～(t-tj) relationship curve needed to determine the cooling correction in the constant-temperature calorimetry method, or the instrument constants k and A, are all calibrated through the same experiment. 8.2 Weigh the dried and **benzoic acid (4.4) in an unlined combustion vessel; the appropriate mass of benzoic acid is 0.9 g to 1.1 g. Benzonic acid should be ground finely in advance and dried in concentrated sulfuric acid for 3 days, or in an oven at 60°C–70°C for 3–4 hours; after cooling, it is compressed into tablets. Benzoic acid can also be used after being melted in a combustion dish. Melting can be carried out by placing the sample in an oven at 121°C to 126°C for 1 hour, or over a low flame on an alcohol lamp; it is then cooled in a desiccator before use. The needle-like crystals that appear on the surface of the melt should be removed with a small brush to prevent incomplete combustion. 8.3 Depending on the type of calorimeter used (constant-temperature or adiabatic), prepare the oxygen bomb and the inner and outer cylinders according to the corresponding steps for calorimetric determination, then ignite it and measure the temperature rise. In the constant-temperature calorimeter, the temperature of the inner cylinder (T0) is measured accurately once 5 minutes after stirring begins, and again after 10 minutes (To). Subsequently, ignition is carried out according to the calorimetry procedure; the temperature of the outer cylinder (tj) and the temperature of the exposed column (te) are recorded, and the process continues until the final temperature (tn) is obtained (see Sections 6.2.6–6.2.8 of this standard). Then continue stirring for 10 minutes and record the temperature of the inner cylinder (Tn); the test is then complete. In the case of an adiabatic calorimeter, follow the same steps as in 6.3. Open the oxygen bomb, carefully inspect its interior, and record the temperature of the inner cylinder; if carbon black is found, the test must be discarded. 8.4 Based on the observed data, dv0 and vn, as well as the corresponding temperature differences between the inner and outer cylinders (t – tj), are calculated and shown in Table 1. The aforementioned tj is the value obtained by correcting the base point of the Beckman thermometer for the measured outer tube temperature, using the method specified in Note 7.1 of this standard. After the heat capacity calibration test is completed, list v0, vn, as well as the corresponding temperature differences between the inner and outer cylinders: v (t–tj)… Table 1. Using v as the vertical axis and t–tj as the horizontal axis, a graph of the relationship between v and (t–tj) is drawn as shown below; alternatively, k and A can be calculated using linear regression. 8.5 In the calibration of heat capacity, the enthalpy of formation of nitric acid can be determined using equation (10): ………………………………（10）Where: qn —— the enthalpy of formation of nitric acid, in joules (J) ； Q — Standard heat value of benzoic acid, in joules per gram (J/g) ； m – the amount of benzoic acid, in grams (g) ； 0.0015——Correction factor for the heat of formation of nitric acid during the combustion of benzoic acid. 8.6 Perform all necessary corrections in accordance with the methods specified in clauses 7.1 and 7.2 of this standard. 8.7 The heat capacity E is calculated using equation (11): ………………………………（11） Here, v0 and vn used in the calculation of C should be obtained from the relationship curve v～(t-tj) by using the values (t0-tj) and (tn-tj) measured in each experiment, or they can be calculated using equations (2) and (3); these values are then substituted into the cooling correction formula to determine the value of C. Note: When the Reifel formula is used to calculate the cooling correction in routine measurements, the same formula must also be used for the calculation of heat capacity. 8.8 Five replicate tests should generally be conducted for calorimetric calibration. Calculate the mean ( ) and standard deviation S of the results from 5 repeated trials. Its relative standard deviation should not exceed 0.20% ； If it exceeds 0.20%, another test shall be conducted. The average of the 5 results that meet the requirements (rounded to 1 mJ) is taken as the heat capacity of the instrument. If the relative standard deviation of any 5 results exceeds 0.20%, the test conditions and operating techniques should be carefully examined; any issues found must be corrected before recalibration is performed, and all existing results must be discarded. 8.9 Before using a new type of calorimeter, it is necessary to determine its effective operating range for heat capacity. The method is as follows: Perform heat capacity calibration tests using benzoic acid at least 8 times; the mass of the benzoic acid tablets is generally between 0.7 g and 1.3 g, or it can be determined based on the range of heat values (temperature rise) associated with the sample being tested. At both endpoints, at least 2 repeated measurements should be performed respectively. Then, a graph showing the relationship between the temperature rise and the heat capacity is plotted, with the temperature rise Δt (tn–t0) on the horizontal axis and the heat capacity E on the vertical axis. If the heat capacity values observed from the graph show no significant systematic variation over the entire range, the heat capacity of this calorimeter can be considered constant. If there is a significant correlation between the heat capacity values observed in the graph and the temperature increase, then a graph showing the relationship between E and △t should be drawn, or the relationship between E and △t can be determined using simple linear regression: ………………………………(12). The estimated variance S2 of the linear regression equation should not exceed 0.20%; the method for calculation is given in Appendix A.2. All results should be included in the calculations, except for those from tests with incomplete combustion, which must be discarded. If the precision meets the requirements, when determining the heat of combustion of the sample, the value of heat capacity to be used can be determined using equation (12) based on the actual temperature rise Δt. (Check the chart or calculate using the formula). If the precision does not meet the requirements, the cause should be identified; after the problem is resolved, a new set of calibrations should be performed. 8.10 The validity period of the heat capacity calibration values is 3 months; recalibration is required once this period has passed. However, in the following cases, retesting should be carried out immediately: P a) Replace the calorimetric thermometer ； b) Replacing large components of the calorimeter such as the oxygen bomb head and connection rings (small components of the same specifications supplied by the manufacturer or fabricated by oneself, such as seals for the oxygen bomb, electrode posts, nuts, etc., are not included here) ； c) The temperature difference between the inner cylinder during calorimetric heat capacity determination and calorific value measurement exceeds 5 K ； d) After the calorimeter has been moved significantly. If there are no significant changes in the calorimetric system, the recalibrated heat capacity value should differ from the previous value by no more than 0.25%. Otherwise, the testing procedure should be checked, the issue resolved, and then recalibration should be performed. Calibration frequencies should be increased for calorimeters that lack a precise physical definition or are highly automated and deviate from classical methods; when necessary, calibration should be performed daily. 9 Presentation of results: The results for the barrel calorific value and the high-position calorific value are calculated to 1 J/g. The average of the two repeated measurements for the high-position calorific value is taken, and it is rounded to the nearest multiple of 10 J/g in accordance with the rounding rules specified in GB/T 483. The values are then presented in units of J/g or MJ/kg. 10 Precision of the method: The repeatability and reproducibility of calorific value determination are specified in Table 2: Table 2 High calorific value Qgr, M (converted to the same moisture basis)/(J/g) Repeatability limit Reproducibility critical difference 120 300 11 Calculation of low calorific value 11.1 Constant-volume low calorific value Industrially, calculations and designs are carried out based on the low calorific value of coal on an as-received basis. The method for calculating the lower heating value of coal on a received basis at constant volume is given by Equation (13): ………………(13) In this equation: —— represents the lower heating value of coal on a received basis at constant volume, with the unit being joules per gram (J/g) ； ——The constant-volume high heating value of coal on an air-dried basis, expressed in joules per gram (J/g) ； Mt —— Total moisture of coal on a received basis (determined in accordance with GB/T211), expressed as a percentage (%) ； Mad – Moisture content of coal on an air-dried basis (as determined according to GB/T212), expressed as a percentage (%) ； Had – the hydrogen content on an air-dried basis of coal (determined in accordance with GB/T 476 or GB/T 1546), expressed as a percentage (%). 11.2 Lower heating value at constant pressure: Both the higher heating value and the lower heating value calculated from the bomb calorimetry value are determined under constant-volume conditions; in actual industrial combustion, however, the conditions are constant pressure. Strictly speaking, the lower heating value at constant pressure should be used in industrial calculations. If necessary, the constant-pressure lower heating value can be calculated using equation (14): ………(14) In this equation: —— represents the constant-pressure lower heating value of the coal on a received basis, expressed in joules per gram (J/g) ； ——Oxygen content on an air-dried basis of coal (calculated according to GB/T 476), expressed as a percentage (%) ； ——The nitrogen content on an air-dried basis of coal (determined in accordance with GB/T 476), expressed as a percentage (%). The meanings of the remaining symbols are the same as before. Note: It can be calculated from equation (15): ……………(15) 12 Conversion of the calorific value of coal based on various bases 12.1 Conversion based on the high heating value basis The high heating values of coal based on various bases are converted using equations (16), (17), and (18): ………………………(16)…………………………(17) ……………………(18) Where: Qgr – high heating value, in joules per gram (J/g) ； Aad – Ash content of the air-dried coal sample, expressed as a percentage (%) ； ar, ad, d, daf — represent basis on received basis, air-dried basis, dried basis, and dry ash-free basis respectively. The meanings of the remaining symbols are the same as before. 12.2 Conversion based on lower heating value The constant-volume lower heating value of coal at various moisture levels is converted using equation (19): ………………(19) Where: —— is the constant-volume lower heating value of coal with moisture content M, expressed in joules per gram (J/g) ； M — Moisture content of the coal sample, expressed as a percentage (%) ； On a dry basis, M = 0; on an air-dry basis, M = Mad; on a received basis, M = Mt. The meanings of the remaining symbols are the same as before. 13 Test Report The test result report shall include the following information: a) Sample number ； b) Based on standards ； c) Method used ； d) Test results ； e) Any deviation from the standards ； f) Abnormal phenomena that occurred during the test ； 9) Test date.