The quality index system of coking coal in Dashang Institute includes industrial analysis index, lithofacies analysis index and small coke oven experiment index, in which the industrial analysis index includes ash, sulfur, volatile matter, maximum thickness of colloidal layer, adhesion index and moisture, the lithofacies analysis index includes standard deviation of vitrinite random reflectance, and the small coke oven experiment index includes the strength index of coke produced by small coke oven experiment.
1. Grey
Ash is not an inherent component of coking coal, but all comes from minerals. Untreated coking raw coal has high ash content and must be washed to remove impurities. In coke production, almost all the ash of coking coal is transferred to coke, which has an adverse effect on coke and affects ironmaking production.
In GB/T397-2009 Technical Specification for Coking Coal, the ash content is divided into 14 grades on average between 5%- 14%, and the ash content of most enterprises is not allowed to exceed 12%. According to the test data, 84.2% of the sample data are below 1 1.5%. According to the actual production demand of coking plant and the range of coke substitutes, coking coal with ash below 1 1.5% (inclusive) can be used as delivery coal, that is, coking coal with ash below 13 can be used for delivery. According to the production habits of steel mills and coking plants, the ash content of substitute delivery products is divided into two grades: [9.0%, 10.0%] coking coal with high ash content is Grade I, and coking coal with ash content lower than 9.0% is Grade II.
According to the conversion relationship between coking coal and coke ash, and the influence of coke ash on ironmaking process, the ash premium is calculated. According to production statistics, for every 0. 1% increase in ash content of one ton of coking coal, the cost of consuming one ton of coking coal increases by 7.2-8.28 yuan/ton, and the lower limit is 7.20 yuan/ton. Assume that the proportion of coking coal in coal blending is 30% higher, which is about 2 yuan/ton. Therefore, if the ash content is reduced by 0. 1%, the water will be 2 yuan/ton. Considering that the inspection index of small coke oven is not set for the time being, in order to make the quality index system close to the actual spot trade, it is not appropriate to set too much moisture for the ash index, so the lowest interval of ash moisture is set to 9.0%, and if it is lower than 9.0%, it is regarded as 9.0%, and no water is added.
2. Sulfur content
Sulfur is the main harmful element in coal, and 70%-90% of sulfur in coke is converted from sulfur in coking raw coal. Sulfur content affects the quality of coking coal and coking products, corrodes equipment and makes pig iron brittle. The maximum allowable sulfur content of pig iron is 0.074%. According to statistics, for every 0.65438 0% increase in sulfur content in coke, the ratio of limestone to coke increases by 2.0% respectively, and the pig iron output decreases by 2%-2.5%.
In GB/T397-2009 Technical Specification for Coking Coal, the sulfur content is divided into six grades within the range of 0.3 1- 1.75%. The sulfur content of coking coal futures standard product is set to [1. 10%, 1.40%], and the sulfur content of substitute delivery product is less than 1. 10%, which is divided into two grades, and the sulfur content is [0.80%,/kloc].
The setting of sulfur content and premium mainly considers the influence of sulfur content on production. According to statistics, for every 0.0 1% increase in sulfur content per ton of coking coal, the cost will increase by 3.9 1-4.18 yuan/ton, and the lower limit will be 3.9 1 yuan/ton, which is equivalent to coking coal. Therefore, if the sulfur content decreases by 0.0 1%, the premium will be 1 yuan/ton. Considering that the inspection index of small coke oven is not set for the time being, in order to make the quality index system close to the actual spot trade, it is not appropriate to set too much water for sulfur index, so the lowest interval of sulfur water is set at 0.80%, and if it is lower than 0.80%, it is regarded as 0.80%, and no water is added.
3. Volatiles
Volatile matter is an important index to judge the degree of coalification of coal. In the coking process, in addition to coke, coal tar, crude benzene, ammonia, coke oven gas and other chemical products are also formed. The output of chemical products affects the overall income of coking enterprises. The higher the volatile matter, the higher the yield of chemical products. The volatile matter of coke is an index to judge the maturity of coke. If the volatile content of coke is greater than 1.5%, the coke is green; if the volatile content is less than 0.5%-0.7%, the coke is overheated and easily broken.
According to statistics, the average and median value of volatile matter is 2 1%. In order to unify with the national standard, the volatilization range of coking coal standard is 16%-28%. The influence of volatile matter on coking production is difficult to quantify. High volatile matter affects the quality of coke, but increases the output and income of chemical products, so there is no substitution and premium.
4. Maximum thickness of colloidal layer
As the raw material of coke production, it is the basic condition that coal can form colloid during pyrolysis. The maximum thickness of the adhesive layer can reflect the quality of adhesion. The greater the maximum thickness of colloidal layer, the better the caking property of coal, but it is difficult to ensure the coking property of coking coal.
GB/T575 1—2009 China Coal Classification stipulates that the upper limit of the maximum cuticle thickness of coking coal is 25mm, and there is no lower limit. According to the test data, the maximum thickness of colloidal layer of coking coal is widely distributed. Some high-quality Shanxi coking coal is only 10mm, and the proportion below 12mm is 14.3%. Considering that the maximum thickness of the colloidal layer is only an index to characterize the cohesiveness, the value varies greatly. So according to the national standard, there is no lower limit. The maximum thickness of the colloidal layer is more than 25mm, which can be used as a substitute without setting paste-lifting water.
5. Adhesion index
The caking property of coal refers to whether coal can be refined into high-quality coke after being heated in the air under industrial conditions. Coal with good caking property may not be good caking property, but coal with good caking property must be good caking property. Logar index and caking index are the most commonly used indexes to determine the caking property of coal. After analyzing the advantages and disadvantages of Logar index, China put forward the index of caking index, named G, which is one of the main indexes to determine the technical category (abbreviated as brand) of bituminous coal in the new national standard of coal classification in China. According to the investigation, the self-owned coking plants of large steel mills generally require higher strength indexes after coke reaction, and improving the cohesiveness of main coking coal is an important guarantee for the strength and quality indexes after coke reaction.
In the national standard GB/T5751-2009, the lower limit of caking index of coking coal is 50. According to the investigation, the caking index of the main coking coal used in the coking plant is above 65. According to the test data, the average value of the test data of caking index is 78.2, 68.9% of coking coal meets the storage standard, and 89.2% meets the storage standard.
The validity period of the coking coal futures warehouse receipt of Dashang Institute is roughly 1 month, and the caking index of most coking coal may change by 2-3 points during the validity period of the warehouse receipt. Therefore, the setting of outbound and inbound indexes is different. The inbound index of benchmark products is not less than 75, and the outbound index is not less than 65, which can cover the range of adhesion index. Because it is difficult to calculate the influence of caking index on coking income by quantitative method, there is no substitution and premium.
6. Post-reaction strength of experimental coke in small coke oven
Coking is an important index to measure the properties of coking coal. At present, there is no index in China's coal quality evaluation system that can directly judge coking. In actual production, coking enterprises carry out small coke oven experiments to detect coking, which has been widely recognized in China's coking industry and has become the practice of detecting coking.
According to the judgment method of coking in domestic enterprises and the classification habit of foreign coal, the strength test value of 50 after the experimental reaction of small coke oven is taken as the standard. The average inspection data is 64, 96.2% of coking coal meets the requirements of ex-factory standards. In order to meet the minimum coking demand of consumer enterprises and simplify the quality index system, the CSR of coking coal standard small coke oven experiment is set to be higher than 50%, with no premium.
7. Standard deviation of vitrinite random reflectance (S)
Coal petrographic analysis can accurately evaluate coking characteristics of coal, predict coke strength and guide coal blending. According to GB/T6948—2008, the descriptive indexes of vitrinite random reflectance of coking coal include the average value, standard deviation and notch number of frequency histogram. The setting of reference standard quality index of coking coal basically refers to the numerical range specified in the national standard, and the standard deviation of vitrinite random reflectivity is determined to be less than or equal to 0. 13, but the provisions of notch number are not included. The standard deviation of random reflectance of vitrinite in coking coal is the basis for determining the degree of coal blending, without substitution or premium.
8. Total moisture
The moisture in coking coal can be divided into free water and bound water according to different existing forms, and the total moisture in coking coal refers to free water. Moisture has an important influence on coking process. If the water content is too large, the heat absorbed by vaporization will be greater, thus prolonging the coking time and reducing the coke output.
From the inspection data, the average moisture inspection data is 8.78%, and 97. 1% inspection data is in the interval [7, 10]. According to GB/T397-2009 Technical Conditions for Coking Coal, if it is less than 8% (including 8%), it can meet the production needs of coking enterprises. Therefore, the value setting of the national standard is selected, and the premium is not directly set. The excess part is rounded to one decimal place according to the actual moisture.