Biomass Handling - Biomass Gasification, Pyrolysis and Torrefaction - page 407

12.3 BIOMASS-HANDLING SYSTEM
A typical biomass conversion plant comprises a large number of process
units, of which the biomass-handling unit is the most important. Unlike coal-
fired boiler plants, an ash-handling system is not a major component of a
biomass plant because biomass contains a relatively small amount of ash.
Also a biomass plant does not produce a large volume of spent catalysts or
sorbents like in a coal-based plant. The transportation and handling of bio-
mass are the main focus of a biomass plant; as transportation, feed prepara-
tion, and feeding are more important for biomass than they are for coal- or
oil-gas-fired units. There is, however, a major challenge in the design of a
biomass conversion plant due to the large variability of bulk density of bio-
mass. It varies from species to species. For example, loosely piled straw has
bulk density of 32 160 kg/m 3 , while that

of sawdust is 256 577 kg/m 3 (Susawa, 1989). Delivered form (chopped vs.
loose, pelletized vs. dust) could also affect the bulk density.
The biomass-handling system could typically comprise of the following
units or components:

48 kg/m 3 , loose bagasse has 112

Receiving unit
Storage and screening unit
Feed preparation unit
Conveying system
Feeding system

While the biomass conversion unit may vary widely depending on the
system used, the design of the biomass-handling system is very similar,
and is equal to that of a biomass-fired steam plant. Figure 12.2 illustrates
the layout of a typical plant showing receiving, screening, storage, and
conveying.
Major considerations for the design of feeding and handling systems are
transportation, sealing, and injection of the feed into the reactor. The feed
should be transported smoothly from the temporary storage to the feed sys-
tem, which must be sealed against the conversion unit's pressure and temper-
ature, and is then injected into the reactor. Metering or measurement of the
fuel feed rate is an important aspect of the feed system, as it is a key parame-
ter in the control of the entire process.
The following subsections discuss the individual components of a solids-
handling system for biomass. They assume the biomass to be solid, although
some biomass, such as sewage sludge, is in slurry or semisolid form.

12.3.1 Receiving
Biomass is brought to the plant typically by truck, barge, or by rail car. For
large biomass plants, unloading from the truck or rail car is a major task.
Manual unloading can be strenuous and uneconomical in terms of manpower