What are the commonly used coal quality indicators?

The symbol of moisture: m, unit:%, is an important coal quality index, and the moisture of coal has great influence on its processing, utilization, trade, transportation and storage. Generally speaking, high water content will affect the quality of coal. In the utilization of coal, the first problem is coal crushing, and coal with high moisture content is difficult to break; In boiler combustion, high water content affects combustion stability and heat conduction; When coking, too high moisture will reduce coke yield; Moreover, because a large amount of water evaporates to take away heat, the coking period is prolonged; In coal trade, moisture is also a qualitative and quantitative index, so when signing a coal sales contract, users generally put forward the limit value of moisture in coal.

The moisture of coal can be simply divided into total moisture, internal moisture, external moisture, crystallization water and decomposition water. In actual measurement, only the total moisture, internal moisture, external moisture and maximum internal moisture of coal can be measured, but not the water of crystallization and decomposition.

The water content of coal in daily life refers to the part of water lost (external water) and the internal water left when the coal and the atmosphere are close to balance under the ambient temperature and humidity, and their measured values change with the change of temperature and humidity in the measuring environment, which is why the water content of coal produced in mines is often very different from that of users.

The commonly used moisture indicators in coal transportation and marketing are: total moisture (symbol: Mt), which includes external moisture and internal moisture; General analysis of coal sample moisture (also known as air-dried base moisture, symbol: Mad) refers to the analysis of coal samples (

② Ashes

The symbol of ash in coal: a, unit:%, is another index that plays an important role in coal quality characteristics and utilization, and it depends on carbon content, calorific value, slagging and grindability to varying degrees. In coal combustion and gasification, the possible corrosion, pollution and slagging problems in coal combustion and gasification are predicted according to the ash content, ash fusibility, ash viscosity, electrical conductivity and chemical composition of coal, and the furnace type is selected accordingly. In coking, the ash content of coal should be used to predict the ash content in coke. When the ash content of coal is high, the effective carbon content is low and the calorific value is generally low. In business, the price should be graded according to the ash content of coal (coking coal is now priced according to ash content, while thermal coal has been changed to calorific value).

The definition of coal ash in coal analysis is: the residue left after coal is completely burned, which is not an inherent mineral in coal, but a solid residue generated by various chemical reactions at high temperature. Commonly used ash indexes in coal transportation and marketing are: empty dry basis (also known as analytical basis) ash (symbol: Aad), dry basis ash (symbol: ad) and received basis ash (symbol: Aar).

(iii) Volatile substances (full name: volatile substances)

The volatile symbol of coal: V, unit:%, is the product of thermal decomposition of organic matter and some minerals in coal; It is not an inherent substance in coal; It is the product of thermal decomposition of coal at a specific temperature, so the volatile matter is accurately called volatile matter yield. The volatile matter of coal has a great relationship with the metamorphic degree of coal. With the increase of coalification degree, the volatile matter decreases. For example, the volatile matter of lignite is generally 38%-65%, that of bituminous coal is generally 10%-55%, and that of anthracite is ≤ 10%. Volatile matter is an important index to determine the utilization rate of coal. When burning coal, the combustion equipment or coal source suitable for specific equipment should be selected according to the volatile matter (the volatile matter score has been set in a certain range when designing the boiler, so users should emphasize the volatile matter index when purchasing coal); The proportion of coal blending should be determined according to volatile matter in coking, because bituminous coal with moderate volatile matter has good cohesiveness and is suitable for coking; Volatiles also play an important role in the selection of gasification and liquefaction conditions; In environmental protection, volatile substances are also used as the basis for formulating smoke laws and regulations.

The volatile matter of coal has a good correlation with other coal quality indexes such as calorific value, carbon and hydrogen content.

The commonly used volatile indexes in coal transportation and marketing are: air-dried volatile (symbol: Vad), dry volatile (symbol: Vd), received volatile (symbol: Var) and dry ashless volatile (symbol: Vdaf).

④ Fixed carbon

Fixed carbon symbol: FC, unit:%, which is also a coal quality index frequently requested by some users. This index is different from the carbon in the elemental analysis of coal (measured). It is calculated according to the moisture, ash and volatile matter of coal, and FC = 100-(m+a+v). Commonly used fixed carbon indicators are: dry fixed carbon (symbol: FCd) and fixed carbon (FCar).

⑤ Total sulfur

Generally speaking, the sulfur content in coal refers to the symbol of total sulfur content: St, unit:%, and the direct measurement is the total sulfur on air dry basis (symbol: St, ad). The commonly used sulfur indexes in coal transportation and marketing are: empty dry basis total sulfur, dry basis total sulfur (St, D) and base total sulfur (St, ar).

Sulfur is one of the harmful elements in coal. Sulfur in coal includes organic sulfur and inorganic sulfur dominated by pyrite. Generally speaking, inorganic sulfur in coal can be mostly removed by washing. Organic sulfur is difficult to remove. In the process of coal combustion, most of the sulfur in coal is converted into SO2 and discharged into the atmosphere, which causes serious pollution to the environment and even acid rain. According to statistics, from 65438 to 0998, the national SO2 emission was 20.9 million tons, of which SO2 emission from coal combustion accounted for about 80%-90%. With the whole society paying more and more attention to the living environment, the state has imposed restrictions on the production and use of high-sulfur coal, such as burning sulfur in the urban area of Beijing.

Below 0.5%, the sulfur content of coal in coastal cities such as Shanghai is required to be lower than 0.6% or 0.8%. Therefore, all users put forward strict limits on the sulfur content in coal when purchasing coal. The good sales of Shenhua coal and its low sulfur content (generally less than 0.5%) are also one of the main reasons. However, sulfur in coal can also play a good role in some utilization ways, such as when coal is liquefied, sulfur can also play the role of catalyst; For example, sulfur recovered from high-sulfur coal after washing can be used to produce sulfur and sulfuric acid.

[6] calorific value

Symbol of calorific value of coal: Q, unit: J/g (Joule/g) and MJ/kg (Megajoule/kg), and cal/g (Cal/g) and kcal/kg (kilocalories/kg) are also used customarily; Conversion relation: 1 calorie =4. 18 16 joules, which is an important index to measure coal quality. First of all, it is the basis of thermal calculation of combustion equipment; The calculation of heat balance, coal consumption and thermal efficiency in the process of coal combustion is based on the calorific value of coal used. In the design of power plant boilers, the type, model and combustion mode of boilers are also considered according to the average received calorific value of coal. Secondly, the calorific value of coal is a comprehensive index to characterize various characteristics of coal. The calorific value (Qgr, daf) of coal is closely related to the metamorphic degree of coal, and generally increases with the deepening of metamorphic degree. For example, lignite has a low calorific value, while bituminous coal has the highest calorific value among coking coal and fat coal. After coking coal, it decreases slightly with the deepening of coal metamorphism, which is the reason why the calorific value of anthracite is lower than that of bituminous coal.

Because of the importance of calorific value index of coal, users first consider whether calorific value can meet the requirements of coal-fired equipment when purchasing coal, and also take calorific value as the settlement basis when pricing thermal coal.

Commonly used calorific value indicators in coal transportation and marketing include: air drying cylinder calorific value (symbol: Qd, ad), air drying high calorific value (symbol: Qgr, ad), dry high calorific value (symbol: Qgr, D) and low calorific value of receiving base (symbol: Qnet, ar) (formerly called application base), and sometimes dry ashless high calorific value (symbol: QGR, AD) is also used. In the current coal purchase and sale contract, domestic northern users generally use the received basic low calorific value (Qnet, ar), while southern users (such as Guangdong) and foreign customers generally use the air-dried basic high calorific value (Qgr, ad). For Shenhua coal, there is a big difference between the two calorific value expression methods (600kcal/kg- 1000kcal/kg), so it is necessary to sign a contract.

(7) grindability (grindability)

The grindability often mentioned in coal transportation and marketing refers to "Hargreaves grindability index", symbol: HGI.

The grindability of coal indicates the grinding difficulty of coal. The greater the grindability index of coal, the easier it is to grind coal, and vice versa. As power coal in power plant and cement plant, grindability index is a very important index for designing and improving pulverizing system and estimating output and power consumption of coal mill. In the briquette industry dominated by non-coking coal, it is necessary to determine the grindability of coal in advance, so as to understand the crushing situation of coal used and determine the series of pulverizing system and the type of pulverizer. Because of the complexity of coal, different coals often have different grindability. Even for the coal in the same mining area and coal seam, the same grindability measurement results cannot be obtained because of the different properties and quantities of minerals and the differences in coal structure, volatile matter and moisture. In view of this, at present, users also require the grindability index of coal when purchasing coal.

(8) the fusibility of coal ash (usually called ash fusibility)

Coal ash fusibility, unit℃. It includes four characteristic temperatures: ① deformation temperature, symbol DT, originally called t1; ② Softening temperature, symbol: ST, formerly known as T2; ③ Hemispheric temperature, symbol HT; ④ Flow temperature, symbol: FT, formerly known as T3. Among the four indexes of ash fusibility, the most commonly used one is the softening temperature, namely ST(T2).

Ash fusibility is an important index of power coal and gasification coal, which is mainly used in the design of solid slag boiler and gasifier, and can guide the actual production operation. It can also be used as a reference for the design of liquid slag discharge furnace. Generally, the higher the melting point of coal ash, the better, so as to avoid slagging in the furnace and difficult to discharge. For coal with low melting point, the slag will wrap the coal and lead to incomplete combustion, which will increase the carbon content of the ash. In serious cases, it will block the grate, make it difficult to discharge slag, and even cause boiler shutdown accidents. Slag will also corrode the refractory lining of the furnace, especially when the slag is acidic and the lining refractory brick is alkaline or the slag is alkaline (Shenhua cinder is alkaline) and the lining refractory brick is acidic, the melting situation will be more serious. For chain furnace, the ash melting point needs to be lower, so that proper slag can be reserved to protect the grate. Liquid slag discharge furnace requires ash melting point to be as low as possible. Due to the high content of CaO and Fe2O3 in coal, the ash melting point of Shenhua coal is low, which is one of the reasons why many domestic and foreign users are critical of Shenhua coal. At present, the group and the company have taken measures such as blending coal and adding additives to improve the ash melting point. However, if users require a higher ash melting point (greater than 1350℃) in sales, it needs careful consideration, and even if it can be realized, its economic benefits will be lost.

(9) Ignition point of coal (also called ignition point)

Heating coal to the temperature at which it starts to burn is called the ignition point of coal, and the unit is℃, which has no representative symbol. This is one of the characteristics of coal. The ignition point of coal is obviously related to the metamorphic degree of coal. Coal with low metamorphic degree has low ignition point (that is, it is easy to catch fire), while coal with high metamorphic degree has high ignition point. In coal quality analysis, the determination results of the same coal type are divided into raw coal sample, raw coal sample and oxidized coal sample. Generally speaking, the spontaneous combustion tendency of coal can be inferred from the difference of ignition points between raw coal and oxidized coal. The ignition points of raw coal and oxidized coal with low ignition point are quite different (△T= ignition point of raw coal sample-oxidized coal sample), such as △ t >; Coal is prone to spontaneous combustion at 40℃, △T< <

Shenhua coal has a low ignition point (

10) the density of coal

The density of coal is divided into: true relative density (formerly called true specific gravity), symbol: TRD；; ; Apparent relative density (formerly known as bulk density), symbol: ARD, without units; Pile density, unit: ton/m3 (ton/m3).

The true relative density of coal is an index to calculate the average quality of coal seam and study the properties of coal. Apparent relative density of coal is needed in calculation of coal reserves, transportation, crushing, combustion and design of coal storage bunker. The bulk density of coal is used to design coal bunker and estimate the coal loading capacity of coking furnace.