Biomass Feedstock Production and Provision: Overview, Current Status, and Challenges - Engineering and Science of Biomass Feedstock Production and Provision - page 9

1.3.5 Processing

The biomass processing and conversion facilities will typically have a buffer storage
containing biomass suffi cient to meet the demand for 7-10 days. The biomass
received from the farms or removed from the buffer storage will fi rst be ground to
achieve the desired particle size. The optimal particle size is not yet known, and it
will depend on the processing option selected. However, in general, a smaller parti-
cle size will improve the conversion effi ciency by increasing the total surface area for
thermal, chemical, or enzymatic reactions. The quality parameters such as moisture
and ash content are not yet standardized. Hence, these parameters often differ for
different pilot- and demonstration-scale biorefi neries currently operational.

1.4 Challenges in Biomass Feedstock Production

Although the tasks within the feedstock production system described above are com-
mon to most agricultural products, there are challenges specifi c to bioenergy crops.
In general, expert knowledge about the appropriate production and provision prac-
tices is not readily available, because the bioenergy feedstock sector is relatively
young with very little large-scale, commercial production. Another equally impor-
tant issue is the mismatch between supply and demand. Given the year-round demand
for fuel, biorefi neries would require an uninterrupted supply of the feedstock.
Harvesting of the energy crops, though, is typically done over a period of 2-3 months.
This means that the supply system must account for intermediate storage and should
do so at minimum cost and quality degradation. The biomass feedstock also has very
low bulk and energy densities. The bulk density of a typical baler used for agricul-
tural residue currently is about 25 % of the bulk density of coal. Similarly, the energy
density of a typical lignocellulosic material in MJ/Mg is about 30 % of that of coal.
This highlights the magnitude of the challenges in handling and provisioning the
feedstock for large biorefi neries. The logistical complexity of biomass production
systems is further characterized by a wide distribution of sources, time- and weather-
sensitive crop maturity, and competition from concurrent harvest operations. In addi-
tion to these broad challenges that pervade all stages of feedstock production, each
of the stages mentioned earlier also has specifi c challenges that need to be addressed:

• Agronomy: For many novel energy crops, such as Miscanthus and energy cane,
the establishment and management techniques are not well understood and,
therefore, not optimized. This includes row spacing, plantation density, fertiliza-
tion and irrigation, pest control, and maturation schedules. The selection of the
appropriate energy crop for each region is also a major challenge in this area. It
is a function of regional attributes such as soil, weather, and rainfall in addition
to the crop properties.
• Preharvest crop monitoring: As mentioned before, precision agriculture and
remote sensing operations must be used to improve crop management and the