Which is the coal with the highest energy available per unit to burn: lignite, subbituminous, bituminous, or anthracite?

●lignite coal
colorific value of less than 5 kw/kg approximately.
● sub bituminous coal
calorific values ranging from 5 - 6.8 kw/kg approximately.
● bituminous coal
calorific values ranging from 6.8 - 9 kw/kg approximately.
● anthracite coal
calorific values of around 9 kw/kg or above.

from this it is clear that anthracite coal has the highest calorific value.