The research on utilizing renewable energy, which emits less greenhouse gas compare to fossil fuels, is getting noticed as environmental problems arise. Hydrogen energy and biomass as well as natural energy sources such as solar heat, wind power, geothermal heat, etc. are attracting attention as new and renewable energy sources. For efficient usage of biomass, several pre-treatment process is needed. The torrefaction process removes moisture and volatile gases to produce a solid fuel with a high ratio of fixed carbon. The bio-drying process using the metabolic heat of microorganisms charges less operating costs compared to commercial thermal drying processes. The biomass based power plant applying bio-drying process was modeled with a process simulator and the effect on energy saving was compared with the plant applying thermal drying process. By replacing the thermal drying process to the bio-drying process, heat recovery was needed to use waste heat. In the case applying bio-drying process, boiler feed water preheating and additional steam generation was considered for heat recovery. The required energy for bio-drying process was reduced about 500 kW and required feed stock was reduced about 13%. Though the simulated process has simple heat exchanger network, energy was saved as applying bio-drying process. The bio-drying process is expected to be effective for processes utilizing biomass to save energy.