Perhaps a safer approach will be to either pre-heat the biomass feedstock to raise the temperature before pelletization or inject steam into the pelletizer. Hope this helps.
If you need to transfer heat to the biomass material during the pelletizing process, you can use a heater around the mold. The amount of heat and the time is controlled according the time of pelletizing and the required temperature or expose the pellet to stream of steam to heat it before relaxation time.