The influence of bed-region stoichiometry on nitric oxide formation in fixed-bed coal combustion

✍ Scribed by G.P. Starley; F.W. Bradshaw; C.S. Carrel; D.W. Pershing; G.B. Martin

• Publisher: Elsevier Science
• Year: 1985
• Tongue: English
• Weight: 853 KB
• Volume: 59
• Category: Article
• ISSN: 0010-2180
• DOI: 10.1016/0010-2180(85)90025-2

✦ Synopsis

A 15.3 cm by 25.4 cm thick-bed reactor with refractory walls was used to investigate the influence of bedregion (first-stage) stoichiometry on fuel nitrogen evolution and reaction in coal-fired, mass-burning stokers. The combustor operated in a batch mode providing a Lagrangian simulation of the time/temperature/ environmental history of a small bed segment traveling through a larger combustion facility. A southern Utah bituminous coal, sized at 13 mm through 25 mm, was fired in a 15.3 cm deep bed in all experiments. Typically, as a run proceeded, both the superficial burning rate and NO exhaust emissions increased, reached a maximum, and then decreased toward the run termination. However, under locally fuel-rich conditions the NO emissions peaked prior to the maximum combustion rate. In-flame measurements suggested that fuel nitrogen evolution probably occurs at approximately the same rate as carbon oxidation. The decay in exhaust NO emissions with time under staged combustion was attributed to both a shift in flame-zone nitrogen speciation to unoxidized intermediates (HCN and NH3) and an associated NO reduction mechanism. Homogeneous gas-phase reactions appeared to control fuel-rich NO formation. Overall, staging the combustion air resulted in a substantial decrease in exhaust NO emissions. Exhaust concentrations decreased approximately linearly with decreasing bed-region stoichiometry. Fuel nitrogen conversion to NO decreased by 67%, from 12%, under excess-air burning to 4% during staged firing.