Transportation - Engineering and Science of Biomass Feedstock Production and Provision - page 137

current fossil fuels by 2030 is to be reached, the annual transported volume of
biomass would be three times that of the 2011 US corn yield.
This chapter reviews the literature on research that addresses biomass feedstock
provision including transportation and identifies challenges that must be addressed
in the near future.

6.1 Introduction

The US Biomass R&D Technical Advisory Committee has recommended a 30 %
replacement of the current US oil consumption with biofuels by 2030 [ 1 , 3 ]. This is
motivated by the desire to move towards sustainable sources of energy to address
looming problems such as climate change and energy security. The sources of bio-
mass feedstock are highly distributed because high biomass yielding energy crops
are limited to specific growth regions characterized by land use policy, water avail-
ability, soil type, climate, and latitude.
In first-generation biofuels, corn starch and sugar cane are converted into etha-
nol, while vegetable oil, soybean oil, palm oil, and similar sources are converted
into biodiesel. Since these sources are conventional agricultural products, the trans-
portation of first-generation biofuel feedstock can employ the infrastructure built
for corn, soybean, and other field crops. A drawback of first-generation biofuels is
that the crops used as feedstock compete with food production. In contrast, second-
generation (advanced) biofuels are produced from lignocellulosic nonfood sources,
such as agricultural residues, energy grasses, forest residues, and woody plants.
With the emergence of second-generation biofuels, new challenges have arisen,
since crops such as Miscanthus, switchgrass, and energy cane need to be efficiently
harvested, preprocessed, stored, and transported. Since these are not conventional
agricultural products, the existing infrastructure is not optimized for their transport.
Firstly, size reduction (comminution) is required, because no conversion process
can process uncut material directly. Secondly, the energy density of the crop in the
field is very low, and compression beyond baling is needed for long-distance trans-
portation [ 4 ]. Thirdly, the scale of feedstock provision is huge: The goal of a 30 %
replacement of the current US oil consumption by 2030 will increase the annual
demand for feedstock to one billion dry tons of cellulosic feedstock, which is more
than threefold the 2011 US corn production [ 1 , 2 , 5 ]. Biomass can be combusted
directly (either for domestic heating or commercial power generation) or in combi-
nation with fossil fuels such as coal, but even here challenges arise, mainly because
of the biomass' high ash content. The logistics of direct combustion are relatively
straightforward. For domestic heating, the biomass is preprocessed into pellets, bri-
quettes, woody chips, or bundled firewood logs, which are also produced from prai-
rie grass feedstock, sugar cane bagasse (a by-product of sugar cane ethanol
production), or agricultural residues (e.g., corn stover). For commercial power gen-
eration, biomass can be co-combusted through blending with coal, converted into a
gas, or fed directly into a furnace.