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POSSIBILITY OF ACTIVE CARBON RECYCLE ENERGY SYSTEM
Introduction
Energy supply security is an important matter for industrial and economical development of a society.
Steep change and instability of the market prices of primary energy sources is causing economic
confusion in any ages. This paper discusses the establishment of energy supply security from the
standpoint of carbon recycle use. Carbon is the most important energy media for manufacturing
industry and social life of human beings. Carbon supply security is an essential condition for a
sustainable society. In Japan, the supply of fossil fuels of primary energy depends almost entirely on
imports. Enthalpy of import fuel is 82% (18.9 × 10 18 J) of all of using primary energy in Japan (METI,
2007). Seventeen per cent (17%) of fossil fuel is converted into plastics products, and the remainder is
consumed for heat sources. The Kyoto protocol came into effect in 2005. Japan has undertaken an
obligation to follow the protocol, and is thus required to drastically reduce its carbon dioxide (CO 2 )
emissions. However, CO 2 reduction is inextricably linked to restricted use of carbon resources and
leads to depression of activity of manufacturing and service industries. Co-establishment of carbon
supply security and reduction of CO 2 emissions is an important subject for a development of a
modern society.
A new energy system in which carbon is reused cyclically was discussed. A carbon recycle
system has already existed in nature as a natural carbon neutral system. In this paper, a concept of an
Active Carbon Neutral Energy System (ACRES) was proposed against the natural system. CO 2 is
regenerated artificially into hydrocarbons consuming a primary energy source with no CO 2 emission,
and re-used cyclically in ACRES. ACRES recycles carbon, and transform energy without CO 2 emission.
Because ACRES was expected to solve the above carbon problems, the feasibility of ACRES was
discussed thermodynamically.
Proposal of ACRES
Conventional water energy systems and ACRES
ACRES is compared with conventional recycle energy systems in this section. A conventional recycle
energy system based on water is depicted in Figure 1. Figure 1(a) shows a conventional steam engine
in which water/vapour phase change is use for energy conversion. The primary energy is used for
evaporation of water, and a phase change from steam to water provides energy output. Figure 1(b)
indicates a hydrogen system in which water is decomposed into hydrogen (H 2 ) and oxygen by energy
input, and oxidation of H 2 provides energy output. The H 2 energy system is superior to vapour system
at long-term energy storage with small loss and higher energy density. However, H 2 needs quite large
work for compression up to 700 bars in storage, high-cost security in terms of explosion prevention
and system complexity for energy conversion for energy output like fuel cells. Those requirements are
still subject to market development of H 2 energy system.
Figure 1: Conventional recycle energy systems using water
(a) Steam engine system
H 2 O(v)
(b) Hydrogen system
H 2 + O 2
Energy,
E
Work, W
E
W
H 2 O(l)
Water phase change
Water decomposition /
oxidation
A concept of the proposed ACRES is shown in Figure 2. Carbon dioxide (CO 2 ) with/without water
is the ground state of carbon. CO 2 is converted into hydrocarbons and alcohols by energy input using
some catalytic technologies (Kusama, 1996). Produced hydrocarbon is useful for co-production process.
The hydrocarbon provides thermal and electricity energies during oxidation into CO 2 . The hydrocarbons
can be used as raw materials for industrial materials. The hydrocarbon is easily stored and transferred
under lower compression pressure with small risk of explosion as compared with H 2 . The hydrocarbons
H 2 O
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