Nuclear Production of Hydrogen, Fourth Information Exchange ...

HEAT PUMP CYCLE BY HYDROGEN-ABSORBING ALLOYS TO ASSIST HTGR IN PRODUCING HYDROGEN
Introduction
Hydrogen is a secondary (and transportable) energy resource as well as electricity. At present, the
major part of the secondary energy is electricity produced from oil, coal and natural gas. On the other
hand, hydrogen can be effectively produced from water by the primary resources of nuclear energy
and so on from the global viewpoints of less carbon emission and reliable energy resources. In order
to promote the change of the major energy resources from oil to nuclear energy, it is inevitable to
develop a new hydrogen production technology that can utilise nuclear reactors more efficiently.
Kyushu University has been selected as one of the Centre of Excellence (COE) programmes by
the Japanese Ministry of Education, Culture, Sports, Science and Technology. We also involved in the
hydrogen project that is financially supported to promote hydrogen research. An overview of
hydrogen-related research performed at Kyushu University is schematically illustrated in Figure 1.
Our research group has been investigating hydrogen science and technology from the field of energy
chemical engineering. Our recent experimental or analytical results on the overall hydrogen system
(Fukada, 2006, 2009; Nishikawa, 2006), on hydrogen-absorbing alloys (Fukada, 2004a, 2004b, 2005), on
hydrogen production by steam-methane reforming (Fukada, 2004, 2007a), ceramic fuel cells (Fukada,
2007, 2009a), proton-conducting membrane fuel cells (Hatakenaka, 2008; Takata, 2007), molten salt
working as high temperature (Fukada, 2006a, 2007b, 2008), etc., are published in scientific journals.
Figure 1: Kyushu University hydrogen project
Technology for directly converting nuclear heat to electricity has been fully developed. At present,
around 30% of the total electricity used in Japan comes from nuclear power stations. The heat to
electricity conversion ratio by means of a He gas turbine of the high-temperature gas-cooled reactor
(HTGR) is expected maximally 50%. The electricity to hydrogen conversion ratio by electrolysis of
more than 90% is achieved. Therefore, if HTGR conjugated with thermochemical splitting of water
such as the S-I cycle is utilised for hydrogen production in the future, the overall heat to hydrogen
conversion ratio should be more than 50%, and the efficiency of 55% is targeted at the S-I cycle in
Japan. If not, there is no advantage in converting the primary energy of nuclear heat to the secondary
energy of hydrogen. The present heat to hydrogen production efficiency based on the S-I cycle is
estimated to be 43%. Therefore, it is inevitable to enhance the heat utilisation efficiency. It is very
important to elevate the heat utilisation in the HTGR system.
Figure 2 shows our proposal for utilising nuclear heat more efficiently. This is a proposal to
combine hydrogen production with direct electricity production using ceramic fuel cells through
high-temperature coolant. Hydrogen in the system is produced by the steam-methane reforming or
the S-I cycle, the heat for which will be supplied from HTGR. Hydrogen after purification is utilised to
generate electricity by means of proton-conducting ceramic fuel cells or is used for hydrogen cars. In the
former Information Exchange Meeting held at Oarai, Japan in 2005 (Fukada, 2006), we presented our
experimental results of direct energy conversion by proton-conducting ceramic fuel cell supplied with
CH 4 and H 2 O at 600-800°C. From the viewpoint of less CO 2 emission and better environmental safety,
water-splitting reaction by the S-I cycle is promising for the future energy resources. In the present
study, a heat pump system working at high temperature is introduced.
408 NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010