Drying high-moisture coals before liquefaction or gasification

A new system of drying high-moisture coals is put forward and the requirements of the new system discussed. A fluidized-bed dryer, heated by condensing steam in tubes, and fluidized by superheated steam is employed in a power-station system. High pressure steam after expansion through the high pressure turbine is fed to the dryer tubes and used for drying as much coal as possible, some of the dried coal being used for combustion, achieving greatly increased thermal efficiency and a cheaper boiler. Vapour produced in the dryer is cleaned by cyclones and used to generate clean steam in a steam generator which is then fed to low-pressure turbines. Calculations show that (17% w/w moisture) dry coal can probably be produced at a drying cost of $1.12 Aust. per tonne dry coal, in 1970 dollars, from a brown coal containing 2 te water/te dry coal. Allowing for contingencies a cost of $2.5-$3/tonne dry coal seems a reasonable estimate for a 1980 plant. Two tonnes water are evaporated to produce one tonne dry coal. If drying is to 3% w/w moisture, there is additional cost of about 10%.