Emission of oxygen, sulphur and nitrogen containing heterocyclic polyaromatic compounds from lignite combustion

Maritza-East Bulgarian lignite was burnt in an atmospheric fluidised bed pilot plant, laboratory scale, at conditions close to the real ones used in power generation (850 degreesC, 3% oxygen excess, limestone with ratio Ca/S = 3.25) in order to analyse in a qualitative way the polycyclic aromatic compounds (PAC) emissions. The samples studied were collected by flowing an aliquot of the combustion gases through a sampling system, consisting of cyclones, nylon and teflon filters and an XAD-2 resin, Before sample analysis by gas chromatography with mass spectrometry detection (GC-MS), ligand exchange chromatography on PdCl2 impregnated silicagel was used to separate PAC with different heteroatoms, concretely, oxygen (O-PAC), sulphur (S-PAC) and nitrogen (N-PAC) of the polycyclic aromatic hydrocarbon (PAH) fraction, For all samples studied, the highest PAC emissions were due to compounds containing three and four aromatic rings in their structure. The O-PAC constituted carbonyl-containing compounds Z(O) = - 18 to - 22, with carbon numbers n = 13 - 17; anthraquinones, Z(O-2) = - 20, n = 14 and 15, phenols, phenanthroaldehyde, and furans, Z(O) = - 22, n = 16, where concentration of quinones far predominated. A peculiar group of C-19-C-23 alkylbenzones, with a maximum at C-20-C-21, was found as well. Dibenzothiophenes, phe-nanthro-thiophene and benzonaphthothiophenes, Z(S) = - 16 to - 20, were the major constituents of the S-PAC, while the N-PAC were determined at trace levels, (C) 2002 Elsevier Science B.V All rights reserved.