Introduction
The sulfur content of coal has a major impact on many aspects of the use of coal. Coal combustion and gasification are the two main methods of utilizing coal. In the process of combustion, when the sulfur content is too high, the formed sulfur dioxide will cause environmental pollution. In order to meet environmental protection requirements, it is necessary to reduce sulfur dioxide emissions, usually through the desulfurization facility. The sulfur content of coal also has an important influence on gasification process which requires the sulfur content of coal not to be too high.
In order to better measure the scale of sulfur content of coal, the International Standard ISO recommends coal quality indexing system, that is, the sulfur grade of different coal. Specifically, coal sulfur grade is divided into 6 grade, as following: 0 grade, I grade, II grade, III grade, IV grade, V grade. The grade difference of each grade is 1.5%, from 0 grade meaning the lowest sulfur content to V grade meaning the highest sulfur content.
Classification of Coal Sulfur Grade
According to the sulfur grade of coal indexes, the sulfur content of coal can be divided into 6 grades: 0 grade, I grade, II grade, III grade, IV grade, V grade. The grade gap is 1.5%.
0 grade: Generally, it refers to coal with low sulfur content and high quality coal, which accounts for about 30% to 50% of the sulfur content of air-dried coal.
I grade: Generally, it refers to coal with low sulfur content and medium quality coal, which accounts for about 0.7 to 1.5% of the sulfur content of air-dried coal.
II grade: Generally, it refers to coal with medium sulfur content and medium quality coal, which accounts for about 1.5 to 3% of the sulfur content of air-dried coal.
III grade: Generally, it refers to coal with medium sulfur content and low quality coal, which accounts for about 3 to 4.5% of the sulfur content of air-dried coal.
IV grade: Generally, it refers to coal with high sulfur content and low quality coal, which accounts for about 4.5 to 6% of the sulfur content of air-dried coal.
V grade: Generally, it refers to coal with high sulfur content and very poor quality coal, which accounts for more than 6% of the sulfur content of air-dried coal.
Coal Sulfur Grading Method
Generally, the graying method of coal sulfur grade is based on the measurement of three component, the total sulfur content, ash and volatile matter of coal. The measurement process of these three components is as following:
(1) The Content of Total Sulfur in Coal
Generally speaking, the content of total sulfur in coal is determined by the chemical combined analysis method. First, collect a certain amount of air-dried coal sample, and then put into a high temperature combustion condition, use sulfuric acid dropper to drop the reaction product, then acidity will be measured, thus the sulfuric content of air-dried coal can be calculated.
(2) The Content of Ash and Volatile Matter in Coal
Generally speaking, the content of ash and volatile matter both require to determine the total weight of coal sample, the content of ash and volatile matter can be calculated after measuring the ratio of volatile matter and ash in the sample.
Application of Coal Sulfur Grade
In the combustion process of coal, the sulfur oxide emissions are related to the sulfur content of coal, and the sulfur content can also affect the combustion rate of coal. Therefore, the sulfur grade of coal can be used as an important parameter for the selection of coal. In order to ensure the quality of burning coal and reduce the sulfur oxide emissions, the sulfur content of coal must be strictly controlled, usually selected low-sulfur coal.
Conclusion
The sulfur content of coal has a significant influence on the utilization of coal and the emission of sulfur oxides. In order to better understand the sulfur content of coal, the sulfur content of coal is divided into six grades by sulfur grade. The International Standard ISO recommends a coal quality indexing system, that is, the sulfur grade of different coal. Besides, it is necessary to strictly control the sulfur content of coal when selecting coal to ensure the quality of burning coal and reduce sulfur oxide emissions.
