Environmental Engineering Reference
In-Depth Information
Yields from high-density slash pine stands peaked at 9800 trees/ha at 80 mt/ha at age 6 years and
98 mt/ha at 10 years at 6200 trees/ha (Campbell 1983; Campbell et al. 1983). Through three years
on a site with a higher P level, slash pine yields nearly tripled when stand densities tripled even up
to 43,300 trees/ha, but on a less fertile site, a similar tripling of yield only extended up to 14,600
trees/ha (Rockwood et al. 1983). High density sand pine appeared less productive and required
longer rotations, with maximum yields up to 8 mt/ha per year at almost 20 years. In spite of favor-
able energy output/input ratios of as high as 28 and 26 for slash and sand pine SRWCs with 5-20
year rotations, respectively, only slash pine SRWC systems generated suitable break-even prices
(Rockwood et al. 1985). Although biomass yields from these early SRWC tests were low, genetic
variation within slash and sand pines for traits including survival and tree biomass quantity and
quality may be utilized to increase their SRWC productivity (Frampton and Rockwood 1983). Still,
because southern pines do not coppice, they are not well suited to SRWC systems.
Combustion, pyrolysis, gasification, and bioconversion convert wood into heat, electricity and
liquid fuel (Peter 2007). The well-established infrastructure and extensive plantations in the forest
products industry are huge advantages for using southern pine for bioenergy. European demand for
renewable sources of electricity is driving wood pellet production using southern pine roundwood
(Kotra 2007), and the U.S. forest products industry is actively researching integrated forest biore-
fineries (Amidon 2006; Larson et al. 2006; Van Heiningen 2006; Chambost et al. 2007a, 2007b;
Towers et al. 2007).
Wood gasification facilities to convert wood into energy and power are planned in the Southeast.
For example, a northern Florida facility to produce electricity and gas began construction in 2008.
Also in 2008, a facility to produce ethanol from syngas was begun in south Georgia. Oglethorpe
Power Corporation (OPC), the United States' largest power supply cooperative, is planning to build
as many as three 100 MW biomass-fired electric generating facilities in Georgia. The facilities will
provide power to OPC's members, which supply electricity to nearly 50% of Georgia's population.
The steam-electric power plants will use fluidized bed boiler/steam turbine technology for a woody
biomass mixture.
Other pine species elsewhere in the world that exemplify additional bioenergy opportunities
from natural stands and plantations include radiata pine (
P. radiata
), jack pine (
P. banksiana
), and
P. halepensis
. Radiata pine is widely planted as an exotic in New Zealand, Chile, and other temper-
ate regions. Jack pine is a wide ranging species in northern North America.
P
.
halepensis
is com-
mon to semiarid Mediterranean areas.
Renewable energy, particularly bioenergy, can be important for reducing New Zealand's green-
house gas emissions back to 1990 levels by 2012 (Hall et al. 2001). Currently, biomass provides less
than 5% (28 PJ) of New Zealand's primary energy supply. However, large quantities of current and
future forest residues have potential to fuel biomass power generation. New Zealand has approxi-
mately 1.7 million ha of forest plantations of which 91% is
P. radiata
. By 2010, the annual log
harvest is expected to be over 30 million m
3
. Residue delivery costs largely depended on the deliv-
ery system chosen, the site characteristics and the transport distance. The cheapest system ranged
from 22 to 37 NZ$/ton (1.2-2.0 NZ$/GJ) for residues at the landing and from 29 to 42 NZ$/ton
(1.6-2.2 NZ$/GJ) for residues collected from the cutover. The cheapest option was the simplest
system because extra handling added cost. Use of landing residues for the generation of heat and/or
electricity could be feasible, particularly for sites with short transport distances on private roads that
have no legal restrictions for payloads. Biomass delivery systems have also been assessed elsewhere
for forest residues (Bjorheden 2000), willow short rotation coppice (Gigler et al. 1999), and biomass
fuel mixes (Allen et al. 1997; Sims and Culshaw 1998).
Potential forest bioenergy costs in central Chile were estimated (Faundez 2003), as approxi-
mately 70% of Chile's energy comes from imported fossil fuels, and approximately 70% of its
electricity comes from hydroelectricity. Biomass does contribute 19% of the total energy (mainly
as firewood from native forests), but increasing its share would have economic and environmental
benefits. Sustainable production of firewood would reduce the use of native forests.
