Performance index analysis of coal

                                                   Performance index analysis of coal

1. Moisture: it is a useless component in coal, and it also affects the calorific value and grindability of coal. Therefore, whether for coking coal or steam coal, it is an important indicator. For users, it is of practical significance to apply base moisture, which is the moisture contained in the coal when it is transported from the coal washing plant to the plant. There is no unified limit on the moisture content of coal. The size of moisture depends on local conditions and transportation distance. For export coal, the allowable moisture content during shipment is generally 6-8%. Since moisture is ineffective for coking coal, it also needs heat to evaporate it, and at the same time, it will reduce the coal loading capacity of coking furnace, so the lower the better. The preheating of some new coking furnaces before coal loading can significantly improve the productivity, although it increases the cost. On the other hand, if the coal is too dry. There will also be problems; Especially in windy areas, pulverized coal will pollute the environment during loading and unloading.
2. Volatile matter: volatile matter on combustible basis is almost one of the indicators used for coal classification in countries all over the world. It is generally believed that coal with volatile content less than 14% will not be coking, or only poor quality coke can be produced; If it is too high, it cannot be coking. Although there is no fixed limit, 38% is considered as the upper limit, and some limit the upper limit to 43%. Generally, 15-31% of coal is considered to be good coking coal; There is a coke oven in the United States, which requires the most ideal volatile content to be 28-30%. Due to the limited amount of single coal that meets the ideal, we have to mix several different coals to make the most ideal coke.
3. Fixed carbon: fixed carbon is a common indicator of coal classification. Since fixed carbon is all real carbon, its content is very important for coke. For coal suitable for coking, the fixed carbon is limited to 69-78%.
4. Element analysis: with the increase of coal rank, that is, the deepening of coalification degree, the carbon content gradually increases and the oxygen content gradually decreases. The hydrogen content of lignite and low-grade bituminous coal is stable at about 5%; The hydrogen content of higher grade bituminous coal and anthracite is reduced to 3-4%. The hydrogen content decreases with the increase of coal rank, which is related to the decrease of volatile matter. The nitrogen content of bituminous coal is the highest, about 1.7%; The nitrogen content of lower coal rank and higher coal rank is lower. Carbon is the most important element in coal. It is the carbon content that improves the value of coke. However, high oxygen coal can only produce coke of inferior quality.
5. Sulfur: because sulfur can enter coke and endanger the quality of metals, it will enter the atmosphere with coal combustion and pollute the environment. Therefore, both metallurgical coal and steam coal need to be given great attention. During coking, about 80-85% of the sulfur content in coal enters coke, which is more harmful to blast furnace than ash. In order to prevent sulfur from entering the iron and let it be removed with the slag, the amount of slag will be increased, that is, more Coke will be consumed. According to some calculations, the sulfur content in Coke will increase from 1.0% to 1.5%, and 15% more Coke will be consumed. The upper limit of sulfur used as coking coal is generally 1.0%. However, some coals with slightly higher sulfur content can also be used if their average sulfur content is not more than 1% when they are mixed with low sulfur coal for coking. Some articles pointed out that if the sulfur of coal cannot be reduced to less than 1.5% after washing, it is not suitable for blending as coking coal.
As for the sulfur content of steam coal, in the international coal market, it mainly depends on the local environmental protection law. If some areas limit it to 1%. In addition, some users also care about the sulfur content in coal from the perspective of boiler fouling. In order to evaluate the sulfur content in coal, it is necessary to determine various forms of sulfur. The main forms of sulfur in coal are sulfate sulfur, iron sulfide sulfur and organic sulfur. The normal value of sulfate sulfur should be very small, generally not more than 0.1%. If it exceeds, it is likely that the coal has been oxidized. Sulfide sulfur is mainly pyrite and white iron ore, which are generally fine-grained and nodular. After crushing, grinding and washing the coal, more than half of the sulfur can be removed. Organic sulfur is a part of hydrocarbon structure, which can only be separated with expensive solvents, and generally can only volatilize with the combustion process. Therefore, when estimating the possible content of sulfur in coal washing in the future, half of sulfide sulfur can be added with organic sulfur. Then, more accurate data will be obtained through the optional test.
6. Phosphorus: for coking coal, phosphorus is a harmful component, so it is very important to clarify its content. All phosphorus in blast furnace burden can be reduced into molten iron. Therefore, the phosphorus content in molten iron depends on coke consumption, ash and ore. The phosphorus content in coal ash is usually very low. For coke with a coke consumption rate of 900 pounds and ash content of 7%, the maximum allowable limit is that the phosphorus content in the ash of coke is 0.09%, and the phosphorus content in molten iron is 0.073%, which is the average level most steel mills will accept. Since the ash content of coke is mostly higher than 7%, the best safety limit for phosphorus content in coal should be 0.05-0.06%.
7. Chlorine: it is harmful to coking and steam coal (corroding pipes and furnace walls). Therefore, attention should be paid to the measured value of chlorine content in various coals. The chlorine content in most coals is very low, generally less than 0.1%. Although there is no upper limit, any coal with high chlorine content should be considered suspicious.
8. Grindability: Generally speaking, the size of the final product of modern coal production is very small. This is due to: (1) in terms of coal utilization, more and more pulverized coal is required. For example, for boilers that produce steam, pulverized coal is injected into the combustion furnace with strong pressure when loading coal; Pulverized coal injection into metallurgical blast furnace; In recent years, the development of coal pipeline transportation requires that the coal be ground into pulverized coal before it can be sent away with coal slurry in the pipeline. (2) Through grinding, a part of mineral impurities can be separated, and then washed to reduce ash, sulfur and other harmful impurities, so as to reduce transportation costs and improve the utilization efficiency of coal. (3) Different coal, such as coal from different coal seams in the same mine (mining area), can be blended as required after grinding and washing, and different levels of coal products can be obtained for users with different purposes, so as to achieve the best utilization effect of coal. The grindability of coal is needed when designing and improving the pulverizing system and estimating the output and power consumption of the coal mill. Therefore, the grindability of coal is one of the important control parameters to evaluate the technological performance of coal. The larger the grindability index is, the softer the coal is and the easier it is to be broken. Generally, Hardgrove grindability index is required to be greater than 50. In general, most bituminous coals have the largest grindability index, while lignite and anthracite are relatively small. The water content and impurities of coal can affect the grindability index.
9. Screening test: it is a problem to be considered in the design of coal washing plant, and it is also very important in coke production. Therefore, it is not only required to take large samples of coal seams for testing in the production of coal mines and sampling projects, but also required to take samples from boreholes with a diameter of 6 inches or 8 inches for such testing. Most coking coal users are willing to receive coal less than 35-50 mm. Some coal purchase contracts limit the quantity of materials less than 0.5mm to 20-25%. Generally, before entering the coke oven, the coal is crushed to 90% of the coal grade passing 3.3 mm (1/8 inch).
10. Coal washability: after screening, the coal samples of each particle size shall be subject to floating and sinking test to understand the washability of coal. Provide technical data of coal preparation method, process flow and equipment selection for the design of coal washing plant. After coal washing, in addition to reducing harmful components, reducing transportation volume and improving the utilization of heat energy as described in the previous "grindability", some coking coal can also be obtained: (1) from other coal considered as steam coal or non coking coal. In the international coal market, the price of coking coal is much higher than that of non coking coal. At the same time, it can also give full play to the potential of coal resources, especially in areas lacking coking coal resources. Therefore, for non coking coals close to coking coals, it is necessary to carry out coking tests such as free expansion number and Kirschner plastometer. (2) Since the ash, sulfur and calorific value of each specific gravity grade are measured, if combined with coking test and coal rock analysis data, it is possible to calculate the best percentage of coke that can be refined after mixing two or more kinds of coal. (3) For mines (or mining areas) with many coal seams, we can calculate how to mix them according to the washing data, so as to balance the strength of all kinds of coal. To meet the needs of the market and obtain the maximum economic benefits. (4) It can supply or sell a variety of coal products. In particular, the percentage of high-quality products can be calculated. In addition, at present, equipment with high horsepower is used, which has the ability to cut any material encountered. The material it cuts is not only the product of small size, but also mixed with non combustible materials. This also increases the necessity of washing.
11. Ash content and coal ash properties: Ash in coal is a harmful component. The main harm is to increase the transportation volume and slag volume. In order to reduce the transportation volume, it is generally transported out after washing in the world. The properties of coal ash refer to its composition, melting temperature and viscosity. The composition of coal ash is to understand its chemical properties by chemical analysis. The melting temperature and viscosity of coal ash are to determine the physical properties of coal ash, and the chemical composition of coal ash affects the physical properties of coal ash. The state of coal ash burning in the furnace has a very important relationship with the design, type selection, efficiency and determination of technical parameters of steam boilers. Practical boilers are designed with special coal, that is, the physical and chemical properties of coal should be in line with the special scope. In this way, the boiler manufacturer can improve the boiler design according to the characteristics of coal ash. Thus, when signing the purchase and sale contract, the characteristics of coal ash is one of the contents of the contract. At the same time, the contract period is generally about 30 years to ensure the service life of the equipment, and then select new equipment and coal sources. The combustion state of coal ash in the furnace depends on the chemical composition. Slaggingindex and fouling index can be calculated according to the chemical composition of coal ash.