I remember reading that some coal-carrying bulk cargo ships were being built -- or at least proposed -- with coal-fired steam plants (probably turbines, not triple expansion or uniflow engines) into the late 1970s.
Of course, coal-burning diesel and gas turbine engines were (are?) an active area of R&D. I believe Sulzer had some test low-speed engines burning powdered coal, and I believe GE had some gas turbines doing so. I think the latter were given up on as the coal ash pretty quickly destroyed the hot end.
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