(404c) Carbon Dioxide Capture by Adsorption of Carbonaceous Materials with Direct-Electrothermal Desorption

Abstract:

Some
recent studies have highlighted the potential of adsorption technology for greenhouse
gas CO₂ capture from the flue gases. The
pressure/vacuum swing adsorption (PSA/VPSA), temperature swing adsorption (TSA)
and electrical swing adsorption (ESA) have attracted much research effort with
the development of the novel CO₂ adsorbents materials. Carbonaceous
materials are the promising candidate adsorbents, since they have high BET
surface area, better CO₂ adsorption capacity and novel morphologies
(monolith, bead, fiber). Moreover, these adsorbents materials are also unique to
undergo direct-electrothermal regeneration.

In this paper, carbonaceous materials with four
morphologies (granular, monolith, fiber and bead) are used to capture CO₂
from the flue gas. Activated carbon beads were made in our laboratory with
2000-3000 m²/g BET surface area and better electrical conductivity.
The research contents include the adsorption equilibrium isotherms, breakthrough
curves, electrical energy consumption at direct-electrothermal desortpion, and the
optimization of the cycle adsorption/ desorption processes.  

The experimental apparatus for the optimization of the cycle
adsorption/ Direct-electrothermal desorption process comprise  an adsorber
with 40-100mm height  and 25-50mm diameter, an electricity heating unit, a
cooling unit, a vacuum unit, a gas detection unit, a data acquisition and
control system. The heating step by electricity is very fast, about 2-5 minutes
to raise the temperature of adsorbents from 30^oC to 150^oC
when using 50 V voltages. But the cooling step is very slow due to the poor
heat conductivity of porous adsorbents, so the alternative cooling units are designed,
one using the direct cooling unit with air or nitrogen passing through the column,
the other one as the indirect cooling unit by the medium of water or heat
transfer oil indirect cooling adsorbents.  

Three processes of the cycle adsorption/desorption to
capture CO₂ from the flue gases using carbonaceous materials are investigated,
which included the conventional vacuum swing adsorption process, the electrical
swing adsorption process, and the combined process of vacuum swing adsorption
and direct-electrothermal regeneration. The mathematical models are proposed
for different capture processes using activated carbons with four morphologies
(granular, monolith, fiber, beads). Based on the experimental and theoretical
investigations, the product recovery, purity, and the energy consumption of the
adsorption processes for CO₂ capture from the flue gas are compared,
and the feasibilities of the capture processes using carbonaceous materials are
evaluated comprehensively.

Keywords: CO₂ capture, adsorption, VPSA, ESA, Combined VPESA
process, CO₂ mitigation, carbonaceous
materials, direct-electrothermal
desorption, modeling.