Biomass Torrefaction Process Review and Moving Bed Torrefaction System Model Development
Torrefaction is gaining attention as an important preprocessing step to improve the quality of biomass in terms of physical properties and chemical composition. Torrefaction is a slow heating of biomass in an inert or reduced environment to a maximum temperature of approximately 300°C. Torrefaction can also be defined as a group of products resulting from the partially controlled and isothermal pyrolysis of biomass occurring in a temperature range of 200-280ºC. Thus, the process can be called a
... mild pyrolysis as it occurs at the lower temperature range of the pyrolysis process. At the end of the torrefaction process, a solid uniform product with lower moisture content and higher energy content than raw biomass is produced. Most of the smoke-producing compounds and other volatiles are removed during torrefaction, which produces a final product that will have a lower mass but a higher heating value. There is a lack of literature on the design aspects of torrefaction reactor and a design sheet for estimating the dimensions of the torrefier based on capacity. This study includes (a) a detailed review of biomass torrefaction in terms of understanding the process, product properties, off-gas compositions, and methods used, and (b) a methodology for designing a moving bed torrefier, taking into account the basic fundamental heat and mass transfer calculations. Specific objectives include establishing a set of basic calculations for configuring a torrefaction system, like the diameter and height of the moving packed bed for different capacities, and the heat loads and gas flow rates of the system. Develop Excel© worksheet so a user can define design specifications. In this report, 25-1000 kg/hr are used in equations for the design of the torrefier. Examples of calculations and specifications for the torrefier are included. iv This page intentionally left blank.