This is the 10106th most frequent Japanese word.
選炭
"選炭" means "coal selection" or "sorting coal."
選炭 is used here to refer to the technical process and skills involved in selecting coal.
彼は選炭の技術を学びました。
He learned the techniques of coal selection.
選炭 is employed here to describe an activity that influences the quality of the end product.
選炭によって製品の品質が向上します。
Product quality improves through coal selection.
選炭 pertains to the specialized machinery used for coal selection in this sentence.