Feeding biomass into pressure and related safety engineering

Malfunctions in the fuel feed and handling equipment could be cause for biomass gasification process upsets, and are of major concern for pressurized gasification processes. One precondition for the development of handling and feed equipment for solid fuels and wastes and for the design of novel systems is a good knowledge of the characteristics and flowability of bulk materials, because the requirements for the equipment reliability, adjustability, economy, and lifetime are becoming more demanding. Different methods of feeding biomass fuels into pressurized gasifiers, as well as limitations and special features of these methods, are discussed in this literature review. Examples of different systems for fuel feed and ash removal in pressurized gasification and combustion plants are given, and the available plant operational data are surveyed for a better understanding of the handling characteristics of bulk materials in biomass gasification plants. Unfortunately, there are only a few references to long-term operating experience with biomass feeders in the literature. Safety engineering, including fuel flow characteristics, and dust explosion and spontaneous ignition properties, is also discussed with special attention given to the conditions in pressurized feeding systems. Results from dust explosion and spontaneous ignition tests with biofuels at elevated pressures are presented.