Dynamics of soot formation by turbulent combustion and thermal decomposition of natural gas

Abstract

This study investigates the formation process of soot particles in turbulent flows within fuel-rich natural gas flames. Research on carbon formation from relatively simple hydrocarbons under real process conditions and harsh environments allows new insights into the general understanding of soot formation. Experimental work was undertaken on a small-scale gas furnace based on the design of a modern oil-fired carbon black furnace. The combustion system investigated is fired by a nonpremixed, swirl stabilized, confined methane-air flame. The study comprises establishing conditions under which the production of soot particles takes place, progressing toward quantified analysis. A large number of process parameters have been investigated, and the relative role of incomplete combustion and thermal decomposition in the process of carbon particulate formation has been illustrated. Maximum solid carbon formation was realized at maximum air temperature and maximum furnace temperature. Experimental investigations, using carbon particle concentration measurements coupled with on-line gas analysis showed that slightly fuel rich conditions are governed by incomplete combustion only, whereas richer combustion systems are governed by thermal decomposition processes. Both processes are found to be strongly temperature dependent, whereby an increase in temperature reduces particle production in the former process, but enhances it in the latter. A 3-D simulation of the simultaneous processes of incomplete fuel combustion and fuel decomposition in turbulent combustion systems, using a novel integration of fluid mechanics, chemical kinetics, and a standard soot model, facilitates discrimination between the two main sources of carbonaceous particulate matter, and indicates reasonable agreement with experimental trends.