Method of estimating surface tension of coal inert material, method of estimating surface tension of coal, and method of producing coke

A method of producing coke comprising:

• blending coals having surface tensions estimated by
• determining in advance a first relational expression representing a relationship between a surface tension of coal inert material and a physical property value representing a coal rank;
• measuring the physical property value representing the coal rank of a coal for which the surface tension of coal inert material is to be estimated, and calculating the surface tension of the coal inert material by using the measured physical property value representing the coal rank and the first relational expression, and
• determining a blending ratio of different coals based on the calculated surface tension to form a coal blend;
• wherein the first relational expression is represented by formula (2);
• γ100=−14.791Ro+59.324 (2)
• wherein, γ is the surface tension, γ100 is the surface tension of inert material at 100% inert material and Ro is the physical property value representing coal rank and is a mean maximum vitrinite reflectance in JIS M 8816
• to form a coal blend;
• and
• carbonizing the coal blend to produce coke;
• wherein the resulting strength of the coke made from the coal blend containing a mixture of coals with a similar γ is higher than that of a coke made from a coal blend containing a mixture of coals with different γ.