Co-combustion of crude glycerin with natural gas and hydrogen

This study focuses on the co-combustion of crude glycerin with natural gas (NG) and hydrogen. Initially, glycerin sprays produced by two commercial air assisted atomizers, one that produces solid cone sprays and other flat sprays, were characterized under non-reacting conditions. Subsequently, a selection of the characterized glycerin sprays was burnt in co-combustion with NG and hydrogen in a laboratory furnace fired by a swirl burner. Flue gas data were then obtained for various flame conditions to quantify the effects of the atomizer type, atomization quality, excess air and thermal percentage of glycerin in the fuel mixture on combustion performance. In addition, deposits formed at the burner exit and at the furnace walls were collected and analyzed. The results showed that: (1) the spray fineness for both atomizers increases with the atomizing air to glycerin mass ratio (AFR) up to 1, beyond which no significant improvements were obtained; (2) CO and HC emissions reduce as AFR increases up to 1.5, beyond which they increase, and NOx emissions increase with AFR; (3) at low excess air levels, the atomizer that produces solid cone sprays yields higher CO and HC emissions than the atomizer that produces flat sprays, but the differences disappear as the excess air increases; NOx emissions tend to increase with the excess air for both atomizers; (4) for the atomizer that produces flat sprays, NOx emissions remain constant and CO and HC emissions decrease as the thermal percentage of glycerin in the fuel mixture increases up to approximate to 45%, beyond which the emissions increase; (5) acrolein emissions were undetectable for all flames studied; (6) during the co-combustion of high amounts of glycerin with the gaseous fuels, deposits were rapidly formed at the burner exit and at the furnace walls, containing high concentrations of Na, K and Cl, which can endanger long term furnace utilization. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.