An experimental pressure swing adsorption unit has been
constructed and used to investigate the separation of carbon dioxide
from carbon dioxide enriched air using both an activated carbon and
a type 5A molecular sieve adsorbent. Continuous, cyclic operation
was achievedusing a pair of fixed bed adsorbers. At any one time
the feed gas entered one bed at a high pressure and part of the
purified gas was returned to the other bed at a reduced pressure
to provide countercurrent regeneration of the adsorbent.
The beds of adsorbent used were each nominally 0.165m diameter
and Im. deep. Separations were carried out at approximately ambient
temperature using air flow rates in the range 0.15 to 0.95 kg/m2s and inlet carbon dioxide concentrations'in the range 0.1 to 1.5% v/v.
Adsorption pressures of 2 to 6.4 bar were examined, the desorption
pressure being maintained throughout at essentially 1.0 bar. The
period time was varied from 30 to 900 seconds and the revert ratio
(i. e. the ratio of the product gas returned for desorption to the
total feed rate to the unit) was varied from 0 to 1.0.
The carbon dioxide separation efficiency was found to increase
markedly as the adsorption pressure and the revert ratio were
increased whereas it was relatively insensitive to variations in feed
rate and, more particularly, feed concentration. The performance of
the molecular sieve adsorbent was found to be very sensitive to the
presence of moisture in the feed gas. In contrast the carbon dioxide
efficiencies observed with Lhe activated carbon were unaffected by the
presence of small amounts (circa 100 ppm) of moisture in the feed.
A theoretical model has been proposed for predicting the
performance of pressure swing adsorption systems of the type
investigated and approximate analytical equations and more precise
numerical techniques have been established to represent its solution.
The approximate analytical solutions were found to give close agreement
with the more precise methods examined under conditions corresponding
to low values of a dimensionless period time parameter. The proposed
theoretical model incorporates an effective irean mass transfer
coefficient to represent the diffusion process within the adsorbent
particles. Methods for estimation of the value of this coefficient
based on the limiting conditions of a periodic constant surface flux
or a periodic constant surface concentration are presented.
The experimental performance data were analysed in terms of the
proposed analytical solution to give values of the apparent solid phase
mass transfer coefficient for comparison with those predicted theoretically.
In general the apparent experimental values were consistently
less than the predicted values. In addition the relationship between
the experimental and predicted coefficients was found to be dependent
on both the nature of the adsorbent and a parameter formed by the
product of the revert ratio and the adsorption to desorption pressure
ratio. Empirical correlating equations which incorporate this
dependence are presented.
| Identifer | oai:union.ndltd.org:BRADFORD/oai:bradscholars.brad.ac.uk:10454/4351 |
| Date | January 1973 |
| Creators | Ellis, David I. |
| Contributors | Granville, W.H. |
| Publisher | University of Bradford, Postgraduate School of Studies in Chemical Engineering |
| Source Sets | Bradford Scholars |
| Language | English |
| Detected Language | English |
| Type | Thesis, doctoral, PhD |
| Rights | <a rel="license" href="http://creativecommons.org/licenses/by-nc-nd/3.0/"><img alt="Creative Commons License" style="border-width:0" src="http://i.creativecommons.org/l/by-nc-nd/3.0/88x31.png" /></a><br />The University of Bradford theses are licenced under a <a rel="license" href="http://creativecommons.org/licenses/by-nc-nd/3.0/">Creative Commons Licence</a>. |
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