(259c) Energy Optimization of Hydrogen Production From Biomass

Energy
optimization of Hydrogen production from biomass

Mariano Martín^a,b,
Ignacio E. Grossmann^b[1]

mariano.m3@usal.es; grossmann@cmu.edu

^a Departamento
de Ingeniería Química yTextil. Universidad de Salamanca. Plz. Caidos 1-5 37008,
Salamanca (Spain)

^bDepartment of Chemical
Engineering. Carnegie Mellon University 5000 Forbes Avd. Pittsburgh PA 15213 

Hydrogen is a promising source of energy for the
transportation sector. It is clean and the technology is becoming available as
many car manufactures plan to offer it in the future (Cole 2007). However, its
deployment in the market is not ready due to the strength and convenience of
the liquid fuels industry (the energy density of liquid fuels is much higher),
as well as the  lack of infrastructure for hydrogen distribution, handling and
storage, resulting in high production costs using current technologies such as
reforming of natural gas ($2.6/kg) or water electrolysis ($2.6?$4.2/kg)
(Levene, Kroposki, & Sverdrup, 2006). The key issue to make hydrogen an
attractive alternative fuel for the transportation sector is to optimize the
production process from renewable raw materials instead of the more common
processes such as natural gas reforming or electrolysis of water (Rand &
Dell, 2008).

Although biomass has been traditionally regarded as
a source of liquid biofuels (i.e. bioethanol, green diesel), it can in fact
also be considered as a source of hydrogen as has been reported recently. Gasification
of biomass generates a fair amount of H₂ which has to be purified
and/or separated from the other gases resulting from the gasification
(Tanksale, Beltramini, & Lu, 2010). Therefore, recent studies have
evaluated the production of hydrogen from gasification of biomass using a
simulation-based approach selecting the technologies involved with good potential
in terms of yield and energy consumption (Feng, Wang,&Min, 2009; Gao,
Aimin,&Quan, 2009; Hamelinck & Faaij, 2002; Ji, Feng, & Chen,
2009a, 2009b; Lau et al., 2002; Li, Zeng, & Fan, 2010; Mueller-langer,
Tzimas, Kalschmitt, & Peteves, 2007).

In this paper we address the conceptual design for
the production of hydrogen from lignocellulosic raw materials. The optimization
of the process is formulated as an MINLP using short-cut models, design and
empirical correlations for modeling a superstructure embedding two different
gasification technologies, direct and indirect gasification, and two reforming
modes, partial oxidation or steam reforming. Finally, following recent trends,
a water gas shift reactor (WGSR) with membrane separation is used to obtain
pure hydrogen.

The problem is solved by constraining the binary
variables of the MINLP so as to select each gasifier and reforming mode
yielding four NLP's. The operating conditions in the gasifiers and at the WGSR
are optimized for hydrogen production in the solution of each NLP. Next, the
energy is integrated, and finally, an economic evaluation is performed to
determine the production cost of each of the four alternatives. It is shown
that indirect gasification with steam reforming is the preferred technology
providing higher production yields than the ones reported in the literature for
hydrogen from natural gas and at a potentially lower and promising production
cost 0.67 $/kg with a yield of 0.11 kg/kg wet
biomass.

Finally, an important issue to
point out is the fact that this process generates CO₂, 1.2 kg/kg_Biomass
together with  0.11
kgH₂ /kg_Biomass.
It has recently been reported that the production of biodiesel from algae is a
promising technology with a yield to biodiesel 10?100 times higher than using
the current raw materials like soy bean or rapeedseed (Yusuf, 2007). However,
it needs plenty of CO₂. This process could be a source for growing
the algae. Biodiesel production requires in the range of 3.6 kg of CO₂
per kg of biodiesel (Pate, 2008; Sazdanoff, 2006). Thus, on a kg of biomass
basis, it would be possible to obtain 0.33 kg_Biodiesel/kg_Biomass
together with the hydrogen produced which provides full use of the biomass
while producing short-term and long term biofuels with good integration of
different processes.  According to the DOE, by using algae for the production
of biodiesel it would be possible to meet the demand for biodiesel with 2?5% of
the current cropland and with no consumption of water, since salt water can
also be used.

Keywords: Energy, Biofuels,
Alternative fuels, Fuel cells, Water

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