Technical Paper on Industrial Analysis of Coal —— On Industrial Analysis of Coal
This paper briefly discusses the key points, principles and matters needing attention in the analysis of coal industry, and briefly introduces the application of test results in practical work.
Keywords: moisture, ash, volatile matter, fixed carbon
This paper briefly discusses the methods, principles and points for attention in the process of coal industry analysis, and briefly introduces its application in practical work and test results.
Keywords volatile moisture ash fixed carbon
China Library Classification Number: TQ52 Document Identification Number: A
Text:
Industrial analysis of coal is also called technical analysis or practical analysis of coal. In the national standard, the industrial analysis of coal refers to the determination of four analysis items: moisture (M), ash (A), volatile matter (V) and fixed carbon (Fc). The industrial analysis of coal is the main index to understand the characteristics of coal quality and the basic basis to evaluate coal quality. Usually, the moisture, ash and volatile matter of coal are measured directly, while the fixed carbon is calculated by difference subtraction. Broadly speaking, the industrial analysis of coal also includes the determination of total sulfur and calorific value of coal, which is also called industrial analysis of coal. Industrial analysis is a standard quantitative analysis method, which is the measured value under specific conditions.
1, coal moisture
The moisture content of coal is one of the most basic indexes in coal pricing. Coal is a porous solid containing a certain amount of water. Water is an inorganic component in coal, and its content and existing state are related to the internal structure and external environment of coal. Generally speaking, the existence of moisture is not conducive to the processing and utilization of coal.
According to its existing state and physical and chemical properties, the moisture in coal can be divided into three types: external moisture, internal and external moisture and bound water.
The moisture content of coal directly affects the use, transportation and storage of coal. When the moisture content of coal increases, the useful components in coal decrease, and the moisture becomes steam to absorb heat during combustion, thus reducing the calorific value of coal. The increase of coal moisture also increases invalid transportation, which brings difficulties to unloading. Its characteristic is that cars are often frozen in cold areas in winter, which affects unloading, production, car turnover and transportation. The moisture of coal is also easy to cause coal to stick to the coal bunker, reduce the capacity of the coal bunker, and even cause coal bunker blockage accidents.
Water in coal can be divided into two types according to different forms of existence, namely free water and bound water. In the industrial analysis of coal, only free water is tested, not crystal water.
The free moisture of coal is divided into external moisture and internal moisture. The total moisture of coal refers to the total free moisture of coal quality, that is, the sum of internal moisture and external moisture in coal, abbreviated as MT.
There are four methods to determine the total moisture of coal, namely, nitrogen drying, air drying, microwave drying, one-step and two-step air drying. In our practical work, the air drying method is adopted, that is, a certain amount of coal samples with particle size less than 6mm are weighed and dried in the air flow of 105- 1 10℃ until the quality is constant, and then the total moisture content is calculated according to the mass loss of coal samples.
2. Ash content of coal
The ash content of coal is not an inherent component in coal, but a residue after coal is completely burned under specified conditions. The abbreviation symbol of ash is A, which also indicates the mass fraction of ash. That is, the minerals in coal are formed through a series of complex reactions such as decomposition and combination under certain conditions, and are derivatives of coal-based minerals. Ash all comes from minerals, and its composition and quality are different from those of minerals. The ash content of coal is closely related to the minerals in coal and has a direct impact on the utilization of coal. Ash yield is usually used in industry to estimate mineral content in coal.
The ash content of coal can be used to indicate the mineral content in coal. By measuring the ash yield in coal, we can study other properties of coal, such as carbon content, calorific value and slagging properties, so as to determine the quality and use value of coal.
China standard GB/T2 12-200 1 stipulates that ash determination methods include slow ashing method and fast ashing method. The slow ashing method is an arbitration method.
When measured by slow ashing method, air-dry coal sample (1? 0. 1)g (calibrated to 0.0002g), evenly spread it in the ash dish, put it in the muffle furnace, push the ash dish into the high temperature part of the furnace at a speed of less than 2cm per minute, that is, the constant temperature area (if the coal sample is on fire and exploded, the experiment is invalid), close the oven door, and put it in the muffle furnace at (8 15). Take out the ash dish from the furnace at 65438 00)℃, cool it for about 5 minutes, move it into a dryer, cool it to room temperature, weigh it, and conduct inspection combustion. If the test results are unstable during combustion, the slow ashing method should be used for re-determination. When the ash content is lower than 15.00%, there is no need to check the combustion.
3. Volatile matter and fixed carbon of coal
(1) volatile matter of coal
The concept of volatile matter The yield of volatile matter is called the volatile matter after the coal sample is heated in isolation from air and corrected for moisture under specified conditions. The abbreviation is V. The volatile matter of coal is mainly composed of water, carbon, hydroxide and carbohydrate (mainly CH4), but does not include physically adsorbed water and carbon dioxide in minerals. It can be seen that the volatiles are not inherent in coal, but the products of thermal decomposition of coal under certain conditions, so it is more accurate to call the volatiles of coal volatile yield. The results of volatile matter determination vary with heating temperature, heating time, heating speed, the form of experimental equipment, the material and size of sample container. Therefore, the determination of volatile matter is a highly standardized experimental project, and only under certain standardized conditions can the obtained volatile matter data be comparable.
According to the national standard GB/T2 12-200 1, the volatile matter was determined. The key points of the volatile matter determination method are as follows: Weigh a certain amount of air-dried coal samples, put them in a covered porcelain crucible, and put them in a (900? At 65438 00)℃
(2) Fixed carbon of coal
The concept of fixed carbon of coal The residue after deducting ash from coke residue after volatile matter determination of coal sample is called fixed carbon, and the abbreviation symbol is FC. Fixed carbon, like volatile matter, is not an inherent component in coal, but a product of thermal decomposition. In terms of composition, fixed carbon contains hydrogen, oxygen, nitrogen, sulfur and other elements besides carbon. Therefore, fixed carbon and carbon content of organic matter in coal are two different concepts and must not be confused. Generally speaking, the content of fixed carbon in coal is less than that of carbon element, and the two are close only in coal with high degree of coalification.
Calculation of fixed carbon In the industrial analysis of coal, fixed carbon is generally not measured directly, but obtained by calculation. After the moisture, ash and volatile matter of air-dried coal samples are determined, the mass fraction of remaining fixed carbon is calculated according to the following formula.
Wad(FC)= 100-(Mad+Aad+Vad)
Where Wad(FC) mass fraction of fixed carbon in air-dried coal sample,%
Average mass fraction of moisture in air-dried coal samples,%
Mass fraction of ash in Aad air-dried coal sample,%
Mass fraction of volatile matter in Vad air-dried coal sample,%
Conclusion: With the increase of coalification degree of coal, the moisture content in coal began to decrease rapidly, but it changed little in the later period. Fixed carbon content gradually increased; The output of volatile substances first increased and then decreased. If calculated by dry ash-free, the yield of volatile matter decreases linearly with the increase of coalification degree.
refer to
1 Zhu Coal Chemical Industry Press, August 2004
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