Biomass Handling - Biomass Gasification, Pyrolysis and Torrefaction - page 405

Chapter 12
Biomass Handling
12.1 INTRODUCTION
Handling of solid biomass poses some special challenges that are not present
for liquid or gaseous fuels. Liquids and gases are relatively easy to handle,
because they are fluid, which continuously deforms under a shear stress.
Fluid easily takes the shape of any vessel they are kept in and flow easily
under gravity, if they are heavier than air. For these reasons, storage, han-
dling, and feeding of gases or liquids do not generally pose a major problem.
However, solids can support shear stress without continuously deforming
and, it thus does not flow freely. This problem is most evident when they are
stored in a conical bin, and are withdrawn from its bottom. Because they do
not deform under shear stress, solids can form a bridge over the cone and
cease to flow.
Biomass is particularly notorious in this respect, because of its fibrous
nature and nonspherical shape. The exceptionally poor flow characteristic of
biomass poses a formidable challenge to both designers and operators of bio-
mass plants. The cause of many shutdowns in these plants incidents can be
traced to the failure of some parts of the biomass-handling system.
This chapter describes the design and operating issues involved in the
flow of biomass through the system. It discusses options for the handling
and feeding of biomass in a biomass conversion plant that include gasifica-
tion, pyrolysis, and torrefaction plants.
12.2 DESIGN OF A BIOMASS ENERGY SYSTEM
A typical biomass energy system comprises farming, collection, transporta-
tion, preparation, storage, feeding, and conversion. This is followed by trans-
mission of the energy produced to the point of use. The concern here is with
the handling of biomass upstream of a conversion system. The production of
biomass through biomass farming is a subject by itself and is beyond the
scope of this chapter.
Biomass has two major ( Figure 12.1 ) applications: (1) energy production
and (2) production of chemicals and fiber-based items (e.g., paper). In either