BIOREFINERIES: INTEGRATION OF DIFFERENT TECHNOLOGIES - Biomass as a Sustainable Energy Source for the Future - page 481

Lignin conversion by biochemical techniques is not straightforward — remember

that one of its functions in plants is to protect them from microbial attack and is still

under investigation. Thus, in most (bio)chemical processes developed so far, the car-
bohydrate part of biomass is converted using (enzymatic) hydrolysis and subsequent
or simultaneous sugar fermentation. Thermochemical conversion of the lignin part is
usually carried out in industrial practice by combustion to generate steam as the
simplest technology; this combination of techniques is already current practice.
A more advanced development is to gasify (part of ) the lignin to generate syngas
or hydrogen that can be used in the plant or can be sold. Hydrothermal conversion
is even more promising as the residue streams contain high amounts of water. An
example of such a detailed hybrid plant based on the above generic scheme is given
by De Wild (2011) (Figure 15.7).
Another approach in hybrid biorefining is that a thermochemical conversion
process is placed upfront (bio)chemical conversion. In this case, gasification and
gas cleaning are used to produce a product gas or synthesis gas, which in a subsequent
step is biochemically converted to, e.g., ethanol. This configuration makes use of the
advantage of thermochemical conversion to convert the largest part of biomass
(including lignin), while ensuring selective biofuel production (in particular ethanol)
by fermentation, a biochemical process. A good overview of such a biorefinery con-
stellation is given by Mohammadi et al. (2011).
There are microbes that ferment syngas under anaerobic conditions so as to per-
form effectively a water

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gas shift reaction aimed at H 2 production (see, e.g., Jung
et al., 1999; Merida et al., 2004; Younesi et al., 2008) and conversion of syngas into
a mixture of acetic acid and ethanol (see, e.g., Allen et al., 2010; Lorowitz and Bryant,
1984; Sakai et al., 2004; Tanner et al., 1993); yet other microbes produce mixtures of
ethanol, butanol, acetic acid, and butyric acid from syngas components (see, e.g.,
Grethlein et al., 1990; Heiskanen et al., 2007; Liou et al., 2005). Methane can also
be formed from syngas using microbes (see, e.g., Klasson et al., 1991). Industrial
application is currently developed by the company Coskata based on multifuel input
(tinyurl.com/les4tw4).

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15.2.4 Examples of Current Biorefineries

Table 15.2 gives examples of biorefineries that are currently running (not exhaustive;
the reader is encouraged to look up and evaluate novel developments; see also, e.g.,
tinyurl.com/nl7qt3n).

15.3 ECONOMIC CONSIDERATIONS EVALUATING BIOREFINERY
CONCEPTS: BASIC METHODS FOR ASSESSING INVESTMENTS
AND COST PRICES

One can imagine and design a myriad of different biorefineries, for sure, for gener-
ation III types given their multioutput multi-input nature. How to evaluate these
from an economical point of view? There are extensive ways of making economic