Chemical links between different pollutant emissions from a small bubbling FBC

A laboratory size bubbling fluidized bed reactor, with continuous coal fuel combustion, has been used to study the kinetic links between the emissions of selected gaseous pollutants. Iodine catalyzes gas phase recombination of the active free radicals (H, OH, O) and its addition was employed to depress their concentration levels, without appreciably affecting the main gas phase component, CO2 and H2O vapor. The iodine was introduced under various experimental conditions: with different SO2 concentration levels achieved by burning a low or a high sulfur coal or by elemental sulfur addition, with or without a Ca-based SO2 sorbent, at atmospheric pressure and at about 400 kPa. The additives were introduced mostly by the batch method, but intermittent addition was also employed. With iodine addition (at a level of less than 18 by volume of atomic iodine in the gas phase) the strongest effects observed were those on CO and hydrocarbon concentrations which usually rose by an order of magnitude. The NO concentration increased slightly when the free radical concentrations were lowered, but the effect was not kinetically linked to that on the CO or hydrocarbon concentrations. Both types of effect were qualitatively similar at atmospheric pressure and at 400 kPa. The SO2 level or the presence of anhydrite in the bed did not appear to influence either the CO or NO concentrations. The NO concentration, lower at increased pressure, rose slightly in the presence of free CaO. A number of other effects were also observed, but these could not be satisfactorily accounted for and would need confirmation. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.