By Enes Tunagur LONDON (Reuters) -Fuel oil used in ships and power plants is seeing unexpected demand, with efforts to curb its use more than offset by an expanding shadow fleet of oil tankers serving Russia and others, and longer shipping routes as vessels avoid the Red Sea. Instead of switching to cleaner-burning alternatives such as marine gasoil and low-sulphur fuel oil, many shippers have installed exhaust gas cleaning devices known as scrubbers to continue using high-sulphur fuel oil. Western sanct ...