Determination of combustibles in coal

Determination of the combustibility of coal; I’m hearing about this concept for the first time and look forward to an answer.

There is no such thing as a lab technician’s handbook. It is divided into two volumes: upper and lower. Edited by Liu Zhen.

Bookstores sell textbooks for laboratory technicians; you can go to a bookstore to look for them. They seem to be available on forums as well – I remember having seen them before; you can try searching for them. This post was last edited by Happy Bird on 2009-3-19 at 11:39

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It doesn’t seem to contain any content on this topic!

On the industrial analysis of coal: Knowledge of coal testing and analysis. The industrial analysis of coal, also known as its technical or practical analysis, serves as the basic basis for evaluating coal quality. 　　In **standard species, the industrial analysis of coal involves the determination of parameters such as moisture, ash, volatile matter, and fixed carbon in coal. Generally, the determination of parameters such as moisture, ash, volatile matter, and fixed carbon in coal. Typically, the moisture, ash, and volatile matter content of coal are measured directly, while fixed carbon is calculated by subtraction. Broadly speaking, the industrial analysis of coal also includes the determination of the total sulfur content and calorific value of coal, which is also known as the comprehensive industrial analysis of coal. 1. Moisture content of coal: The moisture content of coal is an auxiliary indicator used in the pricing of coal. The moisture content of coal directly affects its use, transportation, and storage. As the moisture content in coal increases, the useful components in it decrease relatively. Moreover, moisture turns into steam during combustion, absorbing heat in the process, which reduces the calorific value of the coal. An increase in the moisture content of coal also leads to more ineffective transportation and poses difficulties in unloading. The characteristic is that in cold regions during winter, vehicle freezing often occurs, which affects unloading, production, and the turnover of freight cars, thereby exacerbating transportation constraints. The moisture content in coal can also cause it to stick to the silo walls, reducing the silo’s capacity and even leading to silo blockages. As mining depths increase, along with the development of mechanization in mining operations and improved safety measures underground, as well as the implementation of measures such as spray watering, coal seam injection, and comprehensive dust control, the moisture content of raw coal tends to increase. To this end, in addition to implementing measures to reduce the moisture content of coal in the mining design and throughout various stages of mining such as coal extraction, tunneling, ventilation, and transportation, coal mines should also take actions to reduce coal moisture during its processing on the surface. (1) Free water and bound water in coal: The water content in coal is divided into two categories based on its form of existence, namely free water and bound water. Free water is the moisture that is adsorbed in the capillaries within coal particles and attached to the surface of those particles in a physical state ； Combined water, also known as crystalline water, is the water that is bound to the minerals in coal through chemical bonds. Such as the crystalline water in calcium sulfate (NaSO4.2H2O) and aging soil (AL2O3.2SiO2.2H2O). Free water can be evaporated at a temperature of 105–110°C over 1–2 hours, whereas crystalline water usually requires a temperature above 200°C to be separated out. In the industrial analysis of coal, only free water is tested, not crystalline water. (2) External and internal moisture of coal: The free moisture in coal is further divided into external moisture and internal moisture. External moisture is the moisture attached to the surface of coal particles. External moisture evaporates easily in dry air at room temperature; evaporation stops when the vapor pressure of water on the surface of the coal particles reaches equilibrium with the humidity of the air. Intrinsic moisture is the water adsorbed in the capillaries within coal particles. The internal moisture needs to be exposed to a temperature above 100°C for a certain period of time before it can evaporate. Maximum internal moisture: This occurs when the amount of water adsorbed in the capillaries within the coal particles reaches its saturation point; at this stage, the coal’s internal moisture content is at its highest value, which is referred to as the maximum internal moisture. The maximum internal moisture is related to the porosity of coal, and the porosity of coal in turn is related to its degree of coalification. Therefore, the maximum internal moisture content can, to a considerable extent, indicate the degree of coalification of coal, especially helping to distinguish coals with lower degrees of coalification. For example, the highest inherent moisture content of young lignite is usually above 25%, with a few cases such as the lignite from Mile in Yunnan having a highest inherent moisture content of 31%. Bituminous coals with the highest internal moisture content of less than 2% are almost always highly cohesive and high-calorific coking coals as well as main coking coals. The maximum internal moisture of anthracite is lower than that of bituminous coal, as the porosity of anthracite is higher than that of bituminous coal. (3) Total moisture of coal: Total moisture is an auxiliary indicator for coal, calculated on a basis related to the ash content. a. The meaning of total moisture in coal. The total moisture content in coal refers to all the free moisture present in the coal, that is, the sum of the external moisture and the internal moisture in the coal. It must be noted that the external and internal moisture of coal measured in laboratories when testing its total moisture content are completely different from the external and internal moisture of coal in various structural states mentioned above. The external moisture measured in the laboratory refers to the moisture lost by the coal sample when it is in contact with air and reaches equilibrium with the air humidity (as a result, some of the internal moisture adsorbed in the coal’s capillaries is also lost, and the amount of this lost moisture increases as air humidity decreases and temperature rises); the moisture remaining in the coal at this point is the internal moisture. Obviously, the external and internal moisture measured in laboratory tests are related not only to the external and internal moisture in different structural states of coal, but also to the humidity and temperature of the air used in the testing. b. Key points of the testing method for the total moisture content of coal are specified in the national standard GB212-91 for coal testing. 2. Ash content of coal: The ash content of coal refers to the residue that remains after the coal has been completely burned. Since this residue is the product of complete combustion of the combustible components in coal, with the minerals in coal (all inorganic substances except water) undergoing a series of decomposition and combination reactions during complete combustion, ash should technically be referred to as the ash yield. (1) Minerals in coal: Minerals in coal are divided into inherent minerals and extrinsic minerals. a. Intrinsic minerals, which are further divided into primary minerals and secondary minerals. Primary minerals are the minerals contained within the coal-forming plants themselves, and their content generally does not exceed 1–2% ； Secondary minerals are those that remain in coal as a result of the mixing of minerals from peat swamp waters with the remains of coal-forming plants during the coal formation process. The content of secondary minerals is generally not high either, but it varies considerably. The ash formed by the inherent minerals is called inherent ash, and it can only be separated from coal using chemical methods. b. Foreign minerals refer to the gangue from the roof, floor, and intercalated strata that gets mixed into the coal during its formation and transportation. The ash resulting from the formation of external minerals is called external ash, and external ash can be separated from coal through washing methods. (2) Ash in coal: The ash in coal originates from minerals. Minerals in coal form ash upon combustion. Minerals such as clay, gypsum, carbonates, and pyrite undergo decomposition and chemical reactions during the combustion of coal; some of them turn into gases and escape, while the residue that remains is ash. Ash content is usually lower than that of the original substance; therefore, based on the ash content and using appropriate formulas for correction, the mineral content can be approximated. (3) Impact of ash content in coal ash on industrial utilization. Ash content in coal is one of the indicators used for pricing coal. In a ash meter, the ash content is the key indicator used for pricing ； In calorimeters, ash content is an auxiliary indicator for pricing. Ash is a harmful substance in coal, which also affects its use, transportation, and storage. When coal is used as a fuel, the ash content increases, while the proportion of combustible substances in the coal decreases relatively. Minerals absorb heat during combustion and ashing, and the large amount of slag produced takes away heat as well, thereby reducing the calorific value of the coal. This affects boiler operation (such as increased tendency to form slag and shutdowns), accelerates equipment wear, and increases slag discharge. When coal is used for coking, the ash content increases, and as a result the ash content of the coke also rises, thereby reducing the utilization efficiency of blast furnaces. It must also be pointed out that an increase in ash content in coal leads to more unnecessary transportation, exacerbating the strain on China’s railway transport system. (4) Determination of ash content in coal: Refer to the national standard for coal testing GB212-91. 3. Volatiles in coal: The volatiles in coal refer to the content of substances (gases or liquids) that escape when coal is heated at a certain temperature in an air-free environment, after deducting the moisture content. The remaining residue is called cinder. Since volatiles are not inherent in coal but are products of pyrolysis at specific temperatures, it should more accurately be called the volatiles yield. (1) The volatiles content of coal is not only an indicator to be considered in coking and gasification, but also an important parameter for coal used as fuel; it serves as an auxiliary indicator for pricing thermal coal based on its calorific value. Volatile matter is an important indicator for coal classification. The volatiles content of coal reflects its degree of metamorphism; as the volatiles content decreases, the degree of metamorphism increases. For example, the volatiles content in peat can be as high as 70%, while it is generally 40–60% in lignite, 10–50% in bituminous coal, and less than 10% in highly metamorphosed anthracite. The volatiles content of coal is related to its petrographic composition; kerinite has the highest volatiles content, followed by vitrine and inertinite, with filamentite having the lowest. Therefore, countries around the world and our own country use the volatiles content of coal as the most important indicator for classifying coal. (2) The key points for testing the volatiles content of coal are specified in the national standard GB212-91 for coal testing and analysis. 4. Fixed carbon in coal: After removing moisture, ash, and volatile matter from coal, what remains is the fixed carbon. Like volatile matter, the fixed carbon in coal is also an indicator of the degree of coal metamorphism, increasing as the degree of metamorphism increases. So, fixed carbon is used as an indicator for classifying coal. Fixed carbon is an important source of the calorific value of coal; therefore, some use fixed carbon as the main parameter for calculating the calorific value of coal. Fixed carbon is also an important indicator for coal used in ammonia synthesis. Formula for calculating fixed carbon: (FC)ad = 100 – (Mad + Aad + Vad). When the carbonate CO2 content in the coal sample is between 2-12%, the formula becomes: (FC)ad = 100 – (Mad – Aad + Vad) – CO2,ad (coal). When the carbonate CO2 content in the coal sample is greater than 12%, the formula is: (FC)ad = 100 – (Mad + Aad + Vad). Where: (FC)ad represents the fixed carbon content in the analyzed coal sample, in % ； Mad — Analysis of moisture content in coal samples, % ； Aad — Analysis of ash content in coal samples, % ； Vad —— Analysis of volatile matter in coal samples, % ； CO2,ad (coal) — Analysis of carbonate CO2 content in coal samples, % ； CO2,ad (cokemass) — Percentage of CO2 in the cokemass relative to that in coal, % ； 5 Sulfur content in coal (1) Forms of sulfur present in coal: The sulfur content in coal can be divided into organic sulfur and inorganic sulfur based on its form of existence. Some coals also contain a small amount of elemental sulfur. Organic sulfur in coal exists in the form of organic compounds; it is structurally complex, and not enough is known about it to date. The main functional groups include thioalcohols, R-SH (–SH represents a thiol group) ； Thiophenes, such as thiophene and benzothiophene; thioquins, such as p-thioquinone; thioethers, R-S-R’; thianthrenes, etc. Inorganic sulfur in coal is the residue present in coal in inorganic form. Inorganic sulfur is further divided into sulfide sulfur and sulfate sulfur. The vast majority of sulfur in sulfides is pyrite sulfur, with a small portion being marcasite sulfur; the two are polymorphs of the same substance. There are also small amounts of ZnS, PbS, etc. Sulfate sulfur is mainly present in CaSO4. Sulfur in coal is classified into combustible sulfur and non-combustible sulfur based on its ability to burn in air. Organic sulfur, pyrite sulfur, and elemental sulfur can all burn in air; they are all combustible forms of sulfur. Sulfate sulfur cannot burn in air; it is non-flammable sulfur. Sulfur remaining in the ash after coal combustion (primarily as sulfate sulfur), or sulfur remaining in coke after coking (primarily as organic sulfur, calcium sulfide, ferrous sulfide, etc.), is referred to as solid sulfur. Sulfur released during coal combustion, or sulfur that emerges along with gas and tar during coal coking, is known as volatile sulfur (primarily in the form of hydrogen sulfide and carbon monoxide sulfide (COS)). The fixed sulfur and volatile sulfur in coal are not constant; they vary depending on factors such as the combustion or coking temperature, the rate of temperature increase, and the nature and quantity of mineral components. The sum of sulfur in all its forms in coal is called the total sulfur content of coal (St). The total sulfur in coal typically includes the sulfate sulfur (Ss), pyrite sulfur (Sp), and organic sulfur (So) of the coal. St = Ss + Sp + So; if there is elemental sulfur present in the coal, it should also be included in the total sulfur amount. (2) The impact of sulfur in coal on industrial utilization: Sulfur is one of the harmful substances in coal. When coal is burned as a fuel, it produces SO2 and SO3, which not only corrode equipment but also pollute the air and even cause acid rain, posing a serious threat to plant growth and human health. When coal is used to produce semi-water gas for ammonia synthesis, gases such as hydrogen sulfide are present in large amounts in the gas and are difficult to remove completely; this can poison the synthesis catalyst and affect production. Coal is used for coking, and the sulfur in coal ends up in the coke, making steel brittle. Steel becomes scrap when its sulfur content exceeds 0.07%. To reduce sulfur in steel, limestone is added during blast furnace ironmaking, which reduces the effective volume of the blast furnace and also increases the slag discharge volume. During storage and transportation, when coal contains high levels of substances such as iron sulfide, it can catch fire spontaneously due to oxidation and rising temperatures. The sulfur content in coal fields in our country varies. The sulfur content in coal fields in the Northeast and North China is relatively low, while coal mines such as Xiaocao Coal in Zaozhuang, Shandong, Wuda in Inner Mongolia, Fenshi in Shanxi, and Tongchuan in Shanxi have a higher sulfur content. The sulfur content in coal mines in Guizhou and Sichuan is even higher. In some coal mines in Sichuan, the sulfur content is as high as 4–6%, and it is difficult to reduce it to even 2% even after washing. Removing sulfur from coal is an important issue in coal utilization. In this regard, Western countries such as the United States have made great progress in research on clean coal. First, they develop coal washing and processing (the proportion of raw coal that is washed ranges from 0 to over 80%, while in China it is less than 20%); through washing, the ash content in coal is reduced, and inorganic sulfur in coal is removed (organic sulfur cannot be removed by washing) ； The second is desulfurization during coal combustion and desulfurization of flue gas. This undoubtedly increases the cost of using coal. We are also conducting research on clean coal. Given that the capacity utilization rate of coal washing plants for thermal coal in our country is only slightly over 50%, it is necessary to formulate and implement environmental protection laws related to coal use as soon as possible, in order to promote the development of coal washing processes and the application of clean coal technologies. (3) Key points in the testing of sulfur in coal. The testing of sulfur in coal includes the determination of total sulfur, pyrite sulfur, and sulfate sulfur. Refer to the national standard for coal testing GB214-83. 6 Determination of the calorific value of coal The calorific value of coal, also known as its heat value, refers to the amount of heat generated when a unit mass of coal burns completely. The calorific value of coal is the basic indicator for pricing coal based on its heat content. As a power fuel, coal is utilized primarily based on its calorific value; the higher this value, the greater its economic value. At the same time, calorific value is also the basis for calculating heat balance, thermal efficiency, and coal consumption, as well as a parameter in boiler design. The calorific value of coal indicates the degree of its metamorphism (degree of coalification). The calorific value referred to here is that of the float coal after separation using a 1.4 specific gravity liquid (or that of the raw coal with an ash content of no more than 10%). Peat formed during the latest stages of coal formation, with the lowest degree of coalification, has the lowest calorific value, typically ranging from 20.9 to 25.1 MJ/kg. Lignite, which formed earlier than peat, has a higher calorific value of 25 to 31 MJ/kg. The calorific value of bituminous coal increases further; in the case of coking coal and lean coal, although the carbon content is higher, the volatile matter content is reduced, and in particular the hydrogen content is much lower than that of bituminous coal—sometimes less than 1%, which is equivalent to 1/6 of the hydrogen content in bituminous coal. Therefore, the coal with the highest calorific value is still certain types of bituminous coal. Given that the calorific value of coal with low degree of carbonization varies significantly depending on the degree of carbonization, the constant-moisture, ash-free higher heating value of some **commonly used coals is used as an indicator to classify coal with low degrees of carbonization. In our country, lignite and long-flame coal are classified based on the constant-moisture, ash-free higher heating value of coal. (1) Units of calorific value: The main units used to express calorific value are joule (J), calorie (cal), and the British thermal unit Btu. Joule is a unit of energy. 1 joule is equal to the work done by a force of 1 Newton (N) over a displacement of 1 meter in the direction of that force. 1 J = 1 N × 0 J; 1 MJ = 1000 KJ. The joule is the unit of heat adopted by the International Organization for Standardization (ISO), and it was also established in China in 1984, becoming the official unit for measuring heat as of July 1, 1986. The units for expressing the heat content of coal are J/g, KJ/g, and MJ/kg. Calories (cal) is a unit of heat that has been widely used in China since the establishment of the country. 1 cal refers to the amount of heat absorbed by 1 g of pure water when heated from 19.5°C to 20.5°C. In some European and American countries, 15 Ccal is commonly used, which refers to the amount of heat absorbed when 1 gram of pure water is heated from 14.5°C to 15.5°C. 1 cal (20 Ccal) = 4.1816 J; 1 cal (15 Ccal) = 4.1855 J. The temperature values on the international steam table adopted at the International Conference on the Properties of Steam held in London in 1956 are lower than 15 Ccal, and their values are as follows: 1 cal == 4.1866 J. It can be seen from this that each cal in 15 Ccal contains more thermal energy than in 20 Ccal. Countries such as the UK and the US **still use the imperial unit of heat, the Btu, which is defined as 1/180 of the amount of heat required to raise 1 pound of pure water from 32°F to 212°F.** The relationship between joules, calories, and Btu: 1 Btu = 1055.79 J (≈1.055×1000 J); 1 J = 9471.58×10 to the power of minus 7 Btu. The conversion formula between 20 Ccal/g and Btu/1lb is as follows: Since 1 Btu = 1055.79 J and 1 lb = 453.6 g, then 1 Btu/1lb = 1/1.8 cal/g; 1 cal/g = 1.8 Btu/1lb. As the calorific value expressed in cal/g varies depending on whether it is 15 Ccal or 20 Ccal, etc., in international trade and scientific exchanges, especially when using imported benzoic acid (with its cal/g value indicated) to determine the heat capacity of a calorimeter, it is essential to know the calorific value under what temperature (in degrees C) and conditions; otherwise, the measured combustion calorific value may be systematically too high or too low. To standardize heat units both domestically and internationally, there is no need to replace cal with J as the unit for expressing the calorific value of coal. (2) Meanings of the various calorific values of coal a. Calorific value of coal in a bomb (Qb) The calorific value of coal in a bomb is the heat generated when a unit mass of coal sample burns inside a bomb-type calorimeter under excessive high-pressure oxygen (around 25–35 atmospheres); the final temperature of the combustion products is specified at 25°C. Since the coal sample was burned in a cylinder filled with high-pressure oxygen, thermochemical reactions that do not occur when coal burns in air took place. For example, nitrogen in coal and nitrogen in the air inside the cartridge before oxygen is introduced generally escapes as gaseous nitrogen when burning in air, whereas when burning in the cartridge, nitrogen oxides such as N2O5 or NO2 are formed. These nitrogen oxides dissolve in the cartridge tax to form nitric acid; this chemical reaction is exothermic. Furthermore, when the combustible sulfur in coal burns in air, it produces SO2 gas that escapes, whereas when it burns in the cartridge, it is oxidized to SO3; SO3 then dissolves in the water in the cartridge to form sulfuric acid. The dissolution of SO2, SO3, and H2SO4 in water to form sulfate hydrates are all exothermic reactions. Therefore, the calorific value of coal in a bomb is higher than the actual heat generated when the coal burns in air or in industrial boilers. To this end, in practice, the heat release of the cartridge must be converted into a value corresponding to that of coal burning in air. b. High calorific value of coal (Qgr) The high calorific value of coal refers to the heat generated when coal burns in air at atmospheric pressure. In fact, it is the heat obtained by subtracting the heat of formation of sulfuric acid and nitric acid from the bomb calorific value of coal measured in the laboratory. It should be noted that the calorific value of coal in a bomb is measured under constant volume conditions (i.e., with the volume of the combustion chamber inside the bomb remaining unchanged), which is why it is also known as the constant-volume bomb calorific value. The higher heating value calculated from the heat released in a constant-volume bomb is also known as the constant-volume higher heating value. Coal burns under atmospheric pressure in air under conditions of constant humidity and pressure (with the atmospheric pressure remaining unchanged); its high calorific value is the high calorific value at constant humidity and pressure. There is a difference between the constant-volume higher heating value and the constant-pressure higher heating value. Generally, the high-heating value at constant volume is 8.4–20.9 J/g lower than that at constant pressure; in practice, when high precision is not required, no correction is usually made. c. Lower heating value of coal (Qnet): The lower heating value of coal refers to the heat generated when coal burns under atmospheric pressure in air, minus the latent heat of vaporization (evaporation heat) associated with the moisture in the coal – namely, the water formed by the combustion of hydrogen in the organic components of the coal, as well as the free water and bound water present in it – leaving behind the actual heat that can be utilized. Similarly, the lower heating value calculated from the constant-volume high heating value is also known as the constant-volume lower heating value, and there is as well a slight difference between it and the constant-pressure lower heating value obtained when combustion takes place under atmospheric pressure in air. d. The constant-humidity ash-free higher heating value (Qmaf) of coal: Constant humidity refers to the moisture content (or maximum inherent moisture) of the coal sample, as measured at a temperature of 30°C and a relative humidity of 96%. The constant-humidity ash-free higher heating value of coal does not actually exist; it refers to the constant-volume higher heating value of coal measured under constant-humidity conditions, which is the heating value calculated after taking the effect of ash into account. The constant humidity ash-free higher heating value is an indicator for classifying coals with low degree of coalification. (3) Testing of the calorific value of coal in a bomb – key points are specified in the national standard for coal testing GB213-87. (4) Calculation of the high calorific value of coal: The formula for calculating the high calorific value of coal is: Qgr,ad = Qb,ad – 95 × Sb,ad – a × Qb,ad. Where: Qgr,ad represents the high calorific value of the analyzed coal sample, in J/g; Qb,ad represents the bomb calorific value of the analyzed coal sample, in J/g; Sb,ad represents the sulfur content of the coal as determined from the wash solution obtained from the bomb test, in % ； 95 —— Correction factor for every 1% (0.01 g) of sulfur in coal, J/g; a —— Nitric acid correction coefficient. Qb,ad≤16700J/g, a=0.001 16700J/g

Reply to floor 7: Bro, where is the analysis of combustible materials such as coal in yours? ? ? What Caiyun wants is the principles and methods for analyzing the combustibility of coal. This post was last edited by Happy Bird on 2009-3-19 at 15:45.]

Thank you very much for providing the comprehensive analysis of the coal; although there is no combustible material present. I learned more knowledge from it.

Isn’t it the calorific value determination of coal? There is the **standard GB/T213-2003 for the calorific value of coal**.

Generally speaking, the main analysis parameters for coal include moisture, ash content, volatile matter, fixed carbon, and calorific value. If there is no calorimetry device. Conversion can be carried out using the coal research formula and the previous analysis results.

The original poster invented a new term, “combustible matter of coal,” which actually refers to the measurement of coal’s calorific value; it’s a rather complicated way of putting it.

Are combustibles and calorific value the same thing? I heard about this for the first time. I think combustibles refer to substances that can burn, while heat generation should include combustibles as well. Besides the heat produced by the combustion of combustibles, are there not also certain reactions that generate heat? Therefore, I believe combustibles are part of the heat generation; it cannot be said that combustibles are equivalent to heat generation. What do you all think?

In the original question, if a chemical reaction is involved, it refers to exothermic reactions in which both volatile substances and fixed carbon can burn. According to national standards, these are treated as separate parameters. Does the term \"combustible materials\" mentioned by the original poster refer to the total amount of volatile substances and fixed carbon? The determination of calorific value should include the heat released from the combustion of both volatile matter and fixed carbon.