(448d) High-Purity Hydrogen from Biogas with a Combined Reformer and Fixed-Bed Chemical Looping System

Authors: 
Bock, S., Graz University of Technology
Zacharias, R., Graz University of Technology
Malli, K., Graz University of Technology
Hacker, V., Graz University of Technology
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High-Purity Hydrogen from Biogas with a
Combined Reformer and Fixed-Bed Chemical Looping System

The
decentralized allocation of high-purity hydrogen plays a crucial role for a
future hydrogen-based economy. Hydrogen will act as secondary energy carrier
and temporary storage between fluctuating renewables as primary energy and the
volatile demand from private and commercial consumers. The RESC process is
proposed as a combination of a steam reformer and a fixed-bed chemical looping
system within a single, compact reactor system for hydrogen generation by
Hacker [1]. Depending on the syngas generation (i.e. reforming, gasification),
different renewable and fossil feedstocks can be utilized. High pressure
hydrogen generation was demonstrated in smaller lab systems reaching a hydrogen
release pressure of up to 100 bar by Zacharias et al. [2].

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Figure 1: Schematic of RESC process (right) and
exemplary hydrogen product gas in oxidation phase (left).

As part of
the research activities, an experimental plant capable of hydrogen generation
with an output power of 10 kW (LHV-based) from methane and 18 kg total
inventory of oxygen carrier was presented by Bock et al. [3]. The system was
capable of high purity hydrogen generation exceeding 99.999% from methane
feedstock with carbon monoxide and carbon dioxide being the main contaminants.
Ongoing research especially focuses on the utilization of biogenic resources as
biogas or gasified biomass for hydrogen generation. Within the experimental
research, the applicability of synthetic biogas mixtures was proved by Bock et
al. [4]. Therefore, several biogas compositions were investigated regarding
their suitability for hydrogen generation. The results confirm the high
potential of biogas as potential source for high-purity hydrogen generation
between 99.99%-99.999% purity as demanded by low temperature fuel cells (see
Figure 1). Nevertheless, the application of synthetic biogas also led to
increased carbon contamination compared to earlier experiments with methane as
feedstock. The degree of utilization for hydrogen generation from synthetic
biogas exceeded 40% within the experimental series, depending on the biogas
composition. In addition, a variation of the process temperature was investigated
in order to determine the influence on hydrogen purity as suggested by other
research groups [5].

Long-term
employment of the oxygen carrier also gives fundamental insights into the
behavior for the proposed system. The applied material in the experimental
plant featured a high resistance towards mechanical and thermal stress from
cyclic reduction and oxidation in long-term operation throughout 70 cycles and
more than four months of uninterrupted high-temperature exposure.

In addition,
several trace gas compounds in biogas are prone to significantly affect the
product gas purity. To investigate the impact of these compounds, the main
impurities in common biogas and gasified biomass feedstocks were identified and
tested. Their influence on carbon deposition and hence also on the product gas
impurities in hydrogen generation phase was investigated in a fixed-bed system.
Model compounds were defined for alkanes, cycloalkanes and alcohols and
investigated in a fixed-bed system. Carbon depositions were identified
especially from co-feeding alcohols and cyclic compounds at higher relative
shares applied in reduction phase, although additional steam was applied to
enable full conversion the compounds.

Acknowledgements

Financial
support by the Klima- and Energiefonds
through the Energy Research Program 2015 is gratefully acknowledged.

[1]          V. Hacker, A novel process for
stationary hydrogen production: The reformer sponge iron cycle (RESC), J. Power
Sources. 118 (2003) 311–314. doi:10.1016/S0378-7753(03)00076-4.

[2]          R. Zacharias, S. Visentin,
S. Bock, V. Hacker, High-pressure hydrogen production with inherent
sequestration of a pure carbon dioxide stream via fixed bed chemical looping,
Int. J. Hydrogen Energy. (2019) 1–15. doi:10.1016/j.ijhydene.2019.01.257.

[3]          S. Bock, R. Zacharias, V. Hacker, High
purity hydrogen production with a 10kWthRESC prototype system, Energy Convers. Manag. 172 (2018) 418–427.
doi:10.1016/j.enconman.2018.07.020.

[4]          S. Bock, R. Zacharias, V. Hacker,
Experimental study on pure hydrogen production from biogas in a combined
fixed-bed reformer and chemical looping system, in review (2019).

[5]          J. Lachén,
P. Durán, J.A. Peña, J. Herguido,
High purity hydrogen from coupled dry reforming and steam iron process with
cobalt ferrites as oxygen carrier: Process improvement with the addition of
NiAl2O4catalyst, Catal. Today. 296 (2017) 163–169.
doi:10.1016/j.cattod.2017.04.046.