Environmental Engineering Reference
In-Depth Information
promoting poplar biomass as an energy source. Tillman (1976) reviewed the potential of wood as
an alternative fuel at that time. Clearly, high biomass yields of plantations were needed to make fuel
plantations feasible.
Zavitkovski et al. (1976) outlined the potential of using poplar hybrids as a source of wood
and energy. Soon after, Isebrands et al. (1979) examined the potential of an integrated utilization
strategy for biomass from short rotation poplars. The strategy provided alternatives, including 1)
pulp only, 2) energy only, 3) pulp and fuel and 4) pulp, fuel and animal feed. The case study used
was a 5-year-old hybrid poplar plantation grown at 1.2m spacing. The biomass yield was 8.4 mt/ha
per year for pulp or 200 MKcal/ha for energy. Energy values determined for NE poplar clones in
Wisconsin (Strong 1980) were used to calculate the high heating value of the biomass. The caloric
values of poplar clones were relatively similar, ranging from 4636 to 4755 cal/g or 1.9-2.0 × 10 4 J/g
(i.e., 19 MJ/kg). These results are similar to those of Bowersox et al. (1979) with other clones. Their
values also agreed closely with those provided by Sastry and Anderson (1980) for juvenile poplar
clones grown in Canada and more recent findings (Klasnja et al. 2006). There are 4.2 joules in a
calorie in biomass. So, the poplar biomass plantation produced over 200 Mkcal/ha (8.4 × 10 4 J/ha).
A high heating value of 200 Mkcal/ha in 5 years is equivalent to 40 Mkcal/ha per year or 27 barrels
of oil equivalent per ha. Their analysis assumed each barrel of oil equals 1.48 Mkcal or 6.1 × 10 9 J.
With each ton of poplar biomass equating to more than 3 barrels of oil equivalent, 30 mt/ha equals
90 barrels of oil!
For the energy plantation concept to work successfully, the energy output/input ratio must be
positive. Therefore, biomass energy produced must exceed the energy spent on production and har-
vesting (Anderson et al. 1983). Zavitkovski and Isebrands (1985) analyzed the energy output/input
ration in short rotation hybrid poplar and found them favorable. Anderson et al. (1983) in a thorough
review of energy plantations concluded that one must maximize bioecological factors, genetic mate-
rials, and cultural factors to maximize biomass yields of an energy plantation. Therefore, there is a
premium placed upon achieving as much biomass per ha as possible to be successful. Kauter et al.
(2003) conducted an analysis of quantity and quality of Populus short rotation coppice systems for
energy in European systems. Notably, their energy content was very similar to those found in the
North American studies. And, the energy content of the short rotation poplar biomass was similar
to caloric values of native aspen stands in Canada (Peterson et al. 1970). Christersson (2008) made
an energy comparison of short rotation poplar with agricultural crops in Sweden. According to his
analysis, the poplar biomass crops compare more favorably in energy balance than sugar beet and
wheat in Sweden.
15.4.4 l imitationS and c hallEngES
Despite the promise of using poplar biomass for bioenergy, there are many limitations and chal-
lenges that must be overcome. These limitations can be classified into several categories includ-
ing biological, technical, economic, political and psychological (Anderson et al. 1983; Hoffman
and Wieh 2005; van Rees 2008). These categories are closely interrelated and often have mul-
tiple interactions. Despite the huge genetic gains that have been made in biomass yields through
genetic hybridization and cloning programs, the major factor affecting the production costs of
bioenergy is biomass yield. Thus, the emphasis placed on biomass production in this chapter.
The consensus is that biomass yields will have to be at least 15-20 mt/ha per year to compete
with fossil fuels (Anderson et al. 1983), and some analysts believe 20 mt/ha per year may not be
enough given recent economic conditions (Gallagher et al. 2006). They concluded that yields
will need to be increased by 40% through improvements in genetics and silvicultural practices to
make short rotation biomass plantations cost effective. Genetic improvements take considerable
time, but “best management practices” for growing poplars have recently been developed (van
Oosten 2006; Isebrands 2007). However, climate effects and diseases are also very important
(Anderson et al. 1983; Kauter et al. 2003). Other important variables in economic analysis of
Search WWH ::




Custom Search