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POSSIBILITY OF ACTIVE CARBON RECYCLE ENERGY SYSTEM
ACRES with CO
The η of CO is 104%. This demonstrates that CO has a higher energy density than H 2 . CO is a popular
energy material in conventional chemical, steel and other manufacturing industries. Then, ACRES for
CO was evaluated secondary. Figure 7 shows a structure of ACRES for CO. In the CO process, oxidation
of CO [Eq. (10)] for heat output and shift reaction of CO for H 2 production [Eq. (11)] are available.
CO can also be converted into polymeric materials by polymerisation [Eq. (12)]:
CO + 1/2O 2 → CO 2 (10)
CO + H 2 O → H 2 + CO 2 (11)
xCO + yH 2 + zO 2 → C x H 2y O (2z+x) (12)
CO is regenerative from CO 2 by electrolysis [Eq. (13)] using a solid oxide fuel cell (Jensen, 2007).
CO 2 → CO + 1/2O 2 (13)
A two-step reaction of hydrogen production by water electrolysis and reduction of CO 2 with the
hydrogen [Eqs. (14) and (15)] is a practical process for CO regeneration.
H 2 O → H 2 + 1/2O 2 (14)
CO 2 + H 2 → CO + H 2 O (15)
The enthalpy balance of ACRES for CO is shown in Figure 7. Required enthalpies per one
molecule of CO for the processes of usage and regeneration are depicted in HHV. The regeneration
process is assumed to use hydrogen for CO regeneration using the two-step reaction in Eqs. (14) and (15).
Figure 7: Structure of ACRES with CO
Recovery and
separation
Physical and chemical sorptions
Recov./Sep. energy
Effluent CO 2
Usage
Materials
Energy
CO
CO 2
Regen. energy
(H 2 O)
Regeneration
(H 2 O+)1/2O 2
Production of H 2 of 1 mol needs an enthalpy of 242 kJ/mol-CO. Reduction of CO 2 into CO with H 2 is
endothermic reaction required heat input of 41 kJ/mol-CO. Because CO has higher energy density than
H 2 , CO is one of the most popular media in chemical processes.
A chemical reaction equilibrium for CO 2 /CO system of Eqs. (14) and (15) is shown in Figure 9.
It was assumed in the evaluation that the reaction proceeded under an equivalent ratio and a
pressure of 100 kPa. CO 2 /CO is reversible around 700°C.
CO regeneration in Figure 8 needs heat input over 700°C in Figure 8. Because η of ACRES for CO
was 104%, the ACRES for CO can recover all of enthalpy of H 2 . Waste heat at high temperature around
700°C generated from high-temperature processes can be utilised in the reaction. Energy saving of the
high-temperature processes is achievable by ACRES with CO. CO is quite acceptable for conventional
chemical and manufacturing industries. Thus, it is expected that CO is the most appropriate
candidate for a regenerative media in ACRES.
350 NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010