Table of Contents
ISRN Environmental Chemistry
Volume 2013, Article ID 514751, 7 pages
Research Article

Emissions of SO3 from a Coal-Fired Fluidized Bed under Normal and Staged Combustion

1Department of Chemical Engineering, Nazarbayev University, 53 Kabanbay Batyr Avenue, Astana 010000, Kazakhstan
2Department of Fuel and Energy, University of Leeds, Leeds LS2 9JT, UK

Received 26 February 2013; Accepted 28 March 2013

Academic Editors: N. Fontanals, F. Long, and K. L. Smalling

Copyright © 2013 Wasi Z. Khan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


This paper reports the measurements of SO3 emissions with and without limestone under unstaged and staged fluidized-bed combustion, carried out on a  m2 and 2 m high stainless-steel combustor at atmospheric pressure. The secondary air was injected 100 cm above the distributor. SO3 emissions were monitored for staging levels of 85 : 15, 70 : 30, and 60 : 40, equivalent to a primary air/coal ratio (PACR) of ~0.86, 0.75, and 0.67. Experiments were carried out at 0%–60% excess air level, 1-2 m/s fluidizing velocity, 800–850°C bed temperature, and 20–30 cm bed height. During unstaged combustion runs, SO3 emissions were monitored for a wide range of Ca/S ratios from 0.5 to 13. However, for the staged combustion runs, the Ca/S ratio was fixed at 3. SO3 was retained to a lesser extent than SO2, suggesting that SO2 reacts preferentially with CaO and that SO3 is involved in the sulphation process to a lesser degree. The SO3 emissions were found to be affected by excess air, whereas the fluidizing velocity and bed temperature had little effect. SO3 was depressed on the addition of limestone during both the staged and unstaged operations, and the extent of the reduction was higher under staged combustion.