currently accounting for only a small proportion of the supply curve. This is changing and in
many respects, the biomass industries of today are, in fact, renewable carbon managers —
gaining the maximum utility from these residual streams prior to the return of the carbon as CO 2
to the atmosphere.
The bioenergy potential is the subject of much debate due to the limited land area and the
competition that is perceived with the food and fiber sectors. A summary of recent projections
for the biomass primary energy supply suggests a potential range between 1 and 40 TW (IEA
2004a). The central value is about 14 TW. Assuming liquid fuel production at today’s 40%
thermal conversion efficiency, this would produce 80 million Bbl/day of refined products.
Biomass Supply Issues. Given that most of today’s biomass is derived from cascading, it is
useful to look at the biomass material flows, as shown in Figure 68. At the terminal ends, the
majority of biomass today is used to provide energy services mainly as heat, and the technical
term used by the combustion engineering profession is that these fuels are opportunity fuels^
(Tillman and Harding 2004) — thus, much of the biomass conversion technology consists of
adaptations of fossil fired units, including coal, oil, and gas.
Figure 68 Biomass material flowsEstimating future biomass supply has proved to be rather complex. There are basically four
different approaches to establishing the biomass resource:
(1) Biomass surveys at a fixed point in time;(2) Estimation of residues, using two parameters — the actual production of the
desired crop or product and residue factor that is empirically derived from
measurement of, say, the corn stover and cob mass in relation to the yield of
corn;