Catalytic and Gas-Solid Reactions Involving HCN over Limestone

Anker Jensen, Jan Erik Johnsson, Kim Dam-Johansen

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

In coal-fired combustion systems solid calcium species may be present as ash components or limestone added to the combustion chamber. In this study heterogeneous reactions involving HCN over seven different limestones were investigated in a laboratory fixed-bed quartz reactor at 873-1,173 K. Calcined limestone is an effective catalyst for oxidation of HCN. Under conditions with complete conversion of HCN at O-2 concentrations above about 5,000 ppmv the selectivity for formation of NO and N2O is 50-70% and below 5%, respectively. Nitric oxide can be reduced by HCN to N-2 in the absence of O-2 and to N-2 and N2O in the presence of O-2. At low O-2 concentrations or low temperatures. HCN may react with CaO, forming calcium cyanamide, CaCN2. The selectivities for formation of NO and N2O from oxidation of CaCN2 is 20-25% for both species. The catalytic activity of limestone for oxidation of HCN decreases with increasing degree of sulfation. Simultaneously the selectivity for formation of NO decreases while that for N2O increases. The catalytic activity of sulfated limestone increases with decreasing SO2 concentration indicating a competition between SO2 and HCN for sites on the surface. The results indicate that heterogeneous oxidation of HCN is important in calciners and fluidized-bed combustors with limestone addition or when burning coals with an ash with a high catalytic activity.
Original languageEnglish
JournalA I Ch E Journal
Volume43
Issue number11
Pages (from-to)3070-3084
ISSN0001-1541
DOIs
Publication statusPublished - 1997

Fingerprint Dive into the research topics of 'Catalytic and Gas-Solid Reactions Involving HCN over Limestone'. Together they form a unique fingerprint.

Cite this