The biomass feedstock moisture and ash content have an effect on the gasification product composition, the process energy balance, and the reactor operating condi­tion. Different gasification processes require different moisture levels; high moisture content in biomass will, however, reduce the gasifier temperature and have negative effects on gasification efficiency and the quality of the products. To reduce moisture, driers are used and the most common type is the rotary drier. Nevertheless, the use of steam drying techniques is also increasing due to its easy integration into existing sys­tems. Other techniques, such as biomass mechanical dewatering and leaching with water, have been demonstrated to reduce ash content efficiently [3]. Since water va­por plays an essential role in the chemical reactions of the gasification process, there is a trade-off between moisture removal (beneficial to the process energy balance) and syngas composition.

Biomass particle-size reduction techniques include milling, grinding, and pulver­ization, which make drying, transfer, and biomass storage easier. Their use depends mainly on the requirements of the gasification system as well as the biomass char­acteristics. For example, to pulverize particles to an average size below 0.2 mm, a vibration mill is recommended [4]. There are also some new methods being de­veloped, like freezing pulverization or explosion disintegration, which are suitable for materials that could not be pulverized by conventional methods; however, their power consumption is relatively high.