NOVELTY - The method involves taking out the portion of boiler (1) waste gas of the devulcanizer exit duct (47) of the boiler waste gas processing facility in thermal-power-generation plant. The taken-out boiler waste gas is heated using the solar heat energy collected with the solar-heat collecting apparatus (54). The low grade coal is heated indirectly and dried, using the heated hot boiler waste gas.    USE - Method for drying low grade coal such as wood coal for use in thermal-power-generation plant.    ADVANTAGE - The output of the thermal-power-generation plant and decline in efficiency can be suppressed. The sulfuric corrosion can be reduced. The thermal efficiency of the thermal power-generation plant can be improved effectively.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a thermal-power-generation plant which includes boiler waste gas transfer piping system branches from piping of the exit side of the devulcanizer (46) of boiler waste gas processing facility, and extended to solar heat collecting apparatus. The high temperature dry-gas transfer piping system extends to the wood-coal drying apparatus (23) from the exit of solar-heat collecting apparatus. Piping connected to wood-coal drying apparatus and wood-coal mill (25). Transfer piping connects wood-coal mill and combustion burner of boiler. The dry-gas storage tank entrance piping is branched from high temperature dry-gas transfer piping system, and is extended in dry-gas storage tank. Compressor is provided in the middle of dry-gas storage piping system. Wood-coal drying apparatus is comprised from rotary dryer provided with heat exchanger tube in splitter. Wood-coal transfer piping is set to supply wood coal before drying in heat exchanger tube at rotary dryer. Splitter entrance piping is set to transfer substance containing the wood coal heated within heat exchanger tube to splitter. Wood-coal drying-apparatus entrance piping is set to connect with high temperature dry-gas transfer piping system or dry-gas storage tank exit piping system, and introduced into high temperature dry gas into rotary dry machine. Low-temperature dry-gas transfer piping is set to connect with piping of waste gas processing facility. The water vapor and fine powder wood-coal transfer pipe are connected with upper portion of boiler are attached to splitter upper portion. Wood-coal mill is attached to splitter at the splitter lower portion. Low-temperature dry-gas transfer piping is set to connect with piping of the waste gas processing facility behind devulcanizer, and discharges the low-temperature dry gas in heat exchanger tube is attached.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the thermal-power-generation plant. (Drawing includes non-English language text)    Boiler (1)    Wood-coal drying apparatus (23)    Wood-coal mill (25)    Devulcanizer (46)    Devulcanizer exit duct (47)    Solar-heat collecting apparatus (54)