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POSSIBILITY OF ACTIVE CARBON RECYCLE ENERGY SYSTEM
Figure 8: Enthalpy balance of ACRES with CO
Thermally
regenerative
+41
CO 2 +H 2 , +1/2O 2
CO+H 2 O, +1/2O 2
CO production
Electricity
+242
Water decomposition
Work/Heat/
Reductant
-283
Oxidation
CO 2 +H 2 O(g)
[HHV-kJ/mol-CO 2 ]
Figure 9: Chemical reaction equilibrium for CO 2 /CO system
Partial pressure in equilibrium
0.6
0.5
0.4
0.3
0.2
0.1
H 2 O
CH 4
CO 2 rich
CO 2
H 2
CO
CO rich
H 2 +CO 2 CO+H 2 O
P ini,CO2 =50 kPa
P ini,H2 =50 kPa
Total P=100 kPa
0
0 500 1000 1500
Reaction temperature [ o C]
Value of ACRES
The value of ACRES is that the system uses carbon cyclically, and does not emit CO 2 into the
atmosphere. Non-carbon primary energy sources are essential for ACRES. ACRES with CO was the
most effective recycle system in this study. CO regeneration in Eq. (15) needs heat at a temperature
above 700°C. High-temperature gas reactor (HTGR) was the most suitable energy source for ACRES
because of high temperature output up to 950°C with non-carbon emission and sufficient fuel for a
country demand (Fujikawa, 2004). Thermochemical reduction of CO 2 is ideal process for reduction
method like water reduction. Electrolysis of CO 2 with an electric output from a power plant of a HTGR
is also one of the candidates. High-temperature electrolysis of CO 2 using both heat and electricity
outputs from HTGR is expected to have higher efficiency than atmospheric electrolysis like water
high-temperature electrolysis.
ACRES is an energy transformation system with energy consumption. Direct use of primary
energy in energy demanding process without through ACRES has the highest efficient with the
smallest energy loss. When recycling hydrocarbon in ACRES has higher benefit for energy demanding
process than a direct use of a primary energy, the ACRES will have a practical value. In conventional
chemical, steel and other high-temperature manufacturing industries, CO has a higher affinity with
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