Adsorption

, Volume 20, Issue 1, pp 201–210

Microwave assisted vacuum regeneration for CO2 capture from wet flue gas

Article

DOI: 10.1007/s10450-013-9563-y

Cite this article as:
Webley, P.A. & Zhang, J. Adsorption (2014) 20: 201. doi:10.1007/s10450-013-9563-y

Abstract

Small scale processing of flue gas with the goal of enriching the stream in CO2 for sequestration or use is an interesting application area for adsorption technology. For example, boiler flue gas which may contain up to 10 % (v/v) CO2 in air can be readily enriched to a stream containing >70 % CO2 which may be ideal for use within a process such as acidification, precipitation, stripping, etc. The challenge in these applications is producing high purity CO2 without excessive energy use and handling high concentrations of water vapor without the added complication of a pre-drying stage. In this study we have examined the use of microwave assisted vacuum as a way of rapidly directing thermal energy to the adsorbent surface to liberate water and CO2. Preliminary “proof-of-concept” pump down experiments were conducted on a small transparent adsorption column of 13X zeolite pre-saturated with a 12 % CO2 in N2 gas mixture. Both wet and dry gas tests were conducted. The addition of microwave radiation improved the rapid desorption of CO2 and water and improved the integrated CO2 purity in the blowdown stream from 60 to 80 %. In the case of dry CO2 mixtures, the enhancement is due to microwave heating of the 13X zeolite facilitated by the high cation density in the faujasite structure. In the case of water and CO2 desorption, the temperature rise of the adsorbent upon microwave heating was much lower than that predicted by simple heating suggesting that the microwave radiation is absorbed primarily by the adsorbed water. A simplified energy analysis suggests that brief exposure of an adsorbent to microwave radiation will raise the required vacuum level for regeneration of high humidity flue gas streams and may lead to an overall lower energy penalty. The selective ability of microwave radiation to target different species provides scope for optimized, compact, flue gas treatment systems.

Keywords

CO2 capture Microwave regeneration Zeolite 13X Vacuum swing adsorption 

List of symbols

C

Total gas concentration (mol/cm3)

Ci

Concentration of species i (mol/cm3)

t

Time (s)

\(\varepsilon_{b}\)

Bed voidage

\(\rho_{\text{ads}}\)

Adsorbent density (g/cm3)

\(\bar{n}_{i}\)

Loading of component i (mol/g)

\(\bar{n}_{T}\)

Total loading (mol/g)

\(\bar{n}_{i}^{*}\)

Equilibrium loading of component i (mol/g)

u

Gas interstitial velocity (cm/s)

z

Axial distance (cm)

ki

Linear driving force constant (1/s)

Deff

Effective diffusion coefficient for i in the adsorbent (cm2/s)

Rp

Pellet radius (cm)

Cp, ads

Adsorbent specific heat (J/g K)

Cp,gas

Gas specific heat (J/mol K)

T

Temperature (K)

ΔHi

Isosteric heat of component i (J/mol)

\(\dot{Q}_{gen}\)

Rate of heat generation by external means (W/g)

hw

Bed-wall heat transfer coefficient (W/cm2 K)

Tw

Wall temperature (K)

D

Bed inner diameter (cm)

m1i, m2i

Isotherm parameters (mol/g)

b10i, b20i

Isotherm parameters (1/bar)

Q1i, Q2i

Isotherm parameters (J/mol)

P

Pressure (bar)

PMW

Microwave power per unit volume (W/m3)

\(\omega\)

Microwave frequency (rd/s)

\(\varepsilon_{\text{o}}\)

Dielectric permittivity of vacuum (F/m)

\(\varepsilon^ {\prime \prime}\)

Dielectric loss coefficient

E

Microwave electric field (V/m)

Copyright information

© Springer Science+Business Media New York 2013

Authors and Affiliations

  1. 1.Department of Chemical and Biomolecular EngineeringThe University of MelbourneParkvilleAustralia

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