Page 311 - Biofuels for a More Sustainable Future

Key issue, challenges, and status quo of models for biofuel supply chain design 277

centralized (e.g., industrial scale) biogas digestors (Ma et al., 2005). At the
same time, biomethane after upgradation can be stored and distributed
through existing natural gas infrustructure, which may influence the selec-
tion of biogas plant locations, inventory planning, and end distribution
(H€ohn et al., 2014).
Thermochemical conversion of biomass is a high-temperature process.
Pyrolysis and gasification are the most common types of thermochemical
conversion (Patel et al., 2016). Various types of feedstocks can be used,
including energy crops, crop residues, woody biomass, municipal solid waste
(MSW) (Dutta et al., 2011; Ringer et al., 2006). Pyrolysis is usually operated
around 500°C in oxygen absence environment (Graham et al., 1984). For
effective heat transfer during the pyrolysis, the size of biomass needs to be
reduced depending on reactor size and design (Bridgwater et al., 1999)
and the particles are dried to the moisture content of 5–10wt% (Ringer
et al., 2006). This requirement can affect the BSC configuration as decen-
tralized preprocessing sites may be used to enhance feedstock quality and
reduce transportation cost (Lamers et al., 2015; You et al., 2012). The pri-
mary products, bio-oil, can be used in combustion (Wornat et al., 1994) and
biodiesel blending (Solantausta et al., 1993). Bio-oil can be further upgraded
to drop-in biofuel by deoxygenation and reforming the remaining hydro-
carbons (e.g., by catalytic cracking and hydrotreating) (Diebold and Scahill,
1987; Baker and Elliott, 1987). Some biofuels can be used as “drop-in” fuels
that take advantage of existing petroleum infrastructure (An et al., 2011a;
Tong et al., 2013).
Gasification process decomposes biomass in a limited oxygen environ-
ment to syngas (CO and H 2 ), tars, and char with a temperature range of
700–900°C(Dutta et al., 2011). Following is the gas cleanup process where
tars, methane, and other hydrocarbons are reformed to CO and H 2 when
particulates and other contaminants are quenched out (McKendry, 2002).
Further processes lowering sulfur and acid levelmay also be used. The syngas
in BSC can be further used by Fischer-Tropsch (FT) synthesis to produce
hydrocarbon fuels and alcohol synthesis to produce bioethanol (Dutta
et al., 2011; Liu et al., 2014; Tong et al., 2014). Gasification process and syn-
gas cleaning up process can be designed at different locations or integrated
into one biorefinery (Li and Hu, 2014).
In addition to two main types of biomass conversion technologies, sev-
eral other processes have been developed in the past decades. One of the
commercially successful processes is transesterification to produce