(48b) Session Keynote: Low-Carbon Power Generation with Methane Fueled SOFCs

LOW-CARBON POWER GENERATION WITH METHANE FUELED SOFCs

Introduction

Natural
gas fueled power generation systems, such as large scale thermal power plants
and solid oxide fuel cells (SOFCs), are promising technologies with high electrical
efficiencies of higher than 50% (LHV), and give high temperature exhaust heats¹. While the CO₂ emission coefficient of the electrical power with a
natural gas fuel will decrease with increasing the electrical efficiency, it
remains to have non-negligible value even at the considerably high efficiency.
Methane is a main component of natural gas. Recently thermal decomposition and
catalytic thermal decomposition of methane have attracted attentions as
advanced technologies producing COx-free hydrogen,
which are simple ways to reduce the CO₂ emission caused by methane fuel².

Abstract

As a fuel of the SOFCs, methane is typically mixed
with steam and reformed to hydrogen and carbon monoxide by steam-reforming
reaction before supplied to SOFC stacks. The thermal energy needed for the
endothermic steam-reforming reaction is supplied by the heat generated as a
co-product accompanied by power generation from SOFCs. Methane fueled SOFCs
have high electrical efficiencies, however, they
accompany CO₂ emission
of 0.198 η^-1 kg-CO₂ / kWh, where η is electrical efficiency. While
the CO₂ emission
coefficient decreases with increasing the electrical efficiency, the reduction
of the coefficient has a lower limit of 0.198 kg-CO₂ / kWh by means of merely increasing the electrical
efficiency.

We
have conducted feasibility study of the innovative low-carbon methane-fueled
power generation, in which methane was partly decomposed to form hydrogen and
solid carbon before power generation, and a mixture of the generated hydrogen
and undecomposed methane was used as a fuel. Figure 1 shows the schematic
illustration of the system designed for the low-carbon power generation with
the methane fueled SOFC. In the SOFC system, partially replacing the
steam-reforming methane fuel by the decomposed methane fuel was found to result
in a lower CO₂ emission
coefficient of the electrical power generated in the system without a serious
increase of the thermal energy needed for the fuel processing. The coefficient
had strong dependence on the ratio of the decomposition to the steam-reforming.

The solid carbon deposited by the decomposition will
be able to be utilized as carbon materials such as carbon black and carbon
fiber, or source material of syngas which leads to liquid chemicals. Thus by
using this system, carbon fixation in methane fueled power generation will be
materialized through forming the co-products such as solid carbon, syngas,
and/or liquid organic compounds.

Fig. 1.
Schematics of the system used in this study,

Acknowledgement

This research is supported by The Japan Science and
Technology Agency (JST) through its “Center of Innovation Science and
Technology-based Radical Innovation and Entrepreneurship Program (COI Program).

References

1. Yoshio Matsuzaki,
Yuya Tachikawa, Takaaki Somekawa, Toru Hatae, Hiroshige Matsumoto, Shunsuke
Taniguchi, Kazunari Sasaki (2015)., “Effect of
proton-conduction in electrolyte on electric efficiency of multi-stage solid
oxide fuel cells”, Sci. Rep. 5, 12640, pp 1-10

2. Hazzim F. Abbas, W.M.A. Wan Daud
(2010), “Hydrogen production by methane decomposition: A review”, Int. J. Hydrog. Energy 35 (3) pp. 1160-1190