OCR Text |
Show opposed to shale oil, which had high FBN but normal hydrogen content, similar to that of a diesel oil - while EDS served as an intermediate case concerning these properties. NO Emissions The two main sources leading to NO production are the oxidation of molecular nitrogen from the air during the combustion processes (thermal NO ) and the oxidation of FBN. Activation energies for the first NO forming process are high; therefore, these occur at peak flame temperatures, while the conversion of FBN to NO is mainly dependent on oxygen avail ability and less sensitive to temperature. The recognition and identification of the two formation mechanisms is the key to successful NO control. In simple terms, a lowering of the flame temperature reduces thermal NO formation, whereas combustion at high fuel to air equivalence ratios (eO depresses FBN conversion. Lowering of flame temperature is achieved by water or steam injection, dilution with inert gases and burning at very low or high (substoichio-metric) fuel to air equivalence ratios. On the other hand, FBN conversion is minimized by maintaining fuel rich conditions in the primary combustion zone. Recent test data with natural gas combustion in the BBC type 13 gas turbine showed that at very low fuel to air ratios, the requirements of the EPA Standard were successfully met without taking any additional measures [11]. Obviously, the approach has limitations when applied to fuels of high FBN. (It is in order to mention here - that the EPA NO Emission Standard for large (+30 MW) industrial turbines was rescinded in 1982). The present series of tests were carried out in the standard, fuel rich primary combustion zone of the single combustor, under conditions which are beneficial for reduced FBN conversion. These conditions established in the combustor were analyzed and reported earlier by Hanson [12]. For the simple treatment of the experimental data, we introduce here the term of conversion efficiency for FBN, O N ) . This term defines the fraction of the fuel bound nitrogen that is converted to NO under the conditions selected for the combustion of a given nitrogen bearing fuel, (i). To 1.4.7 |