Fuel rich combustor, operating

One operating concern for a rich combustor is the occurrence of high combustor wall temperatures. In a fuel-rich combustor, air cannot be used to film-cool the walls and other techniques (e.g., fin cooling) must be employed. The temperature rise of the primary combustor coolant was measured and normalized to form a heat flux coefficient which included both convective and radiative heat loads. Figure 7 displays the dependence of this heat flux coefficient on primary combustor equivalence ratio. These data were acquired in tests in which the combustor airflow was kept constant. If convective heat transfer were the dominant mechanism a constant heat flux coefficient of approximately 25 Btu/ft -hr-deg F would be expected. The higher values of heat flux and its convex character indicate that radiative heat transfer was an important mechanism. 

Control of SO is intrinsic to the MHD process because of the strong chemical affinity of the potassium seed in the flow for the sulfur in the gas. Although the system is operated fuel-rich from the primary combustor to the secondary combustor, the predominant sulfur compound in the gas is sulfur... 

When a turbo pump is used to obtain high oxidizer fuel flow, this is also operated by the fuel-rich gas generated in the primary combustor. Since the fuel-rich gas is at a higher pressure than the pressure in the secondary combustor, it is used to operate the oxidizer pump and is then used as a fuel component in the secondary... 

Fuel-rich propellants (FRPs) with high metal content find use in ram-rockets which operate with the combustion of fuel-rich hot gases generated in the primary chamber or combustor and ram air inducted from atmosphere to a secondary chamber or combustor for full combustion. The rocket system where energy for propulsion is derived in such a manner is termed an integrated rocket-ramjet (IRR). The major benefit of a ram-rocket is substantial reduction in the weight of rocket or missile as the oxidizer need not be carried along with the propellant fuel. Fuel-rich propellant formulations for ram-rockets consist of metal fuels, binder... 

Although gas turbine combustion systems operate with overall air/fuel ratios which are quite fuel-lean, perhaps three times stoichiometric, stabilization of the combustion process requires that a portion of the combustor, the primary zone, operate stoichiometric or fuel-rich. Under fuel-lean conditions, fuel-bound nitrogen can be converted directly to N0X. Under fuel-rich conditions, fuel-bound nitrogen can be converted to HCN and NH3 in addition to N0X. Of course, in either case, the most desirable product of converted fuel nitrogen would be molecular nitrogen,... 

Figures 4 and 5 present model calculations for a Montana Rosebud coal-fired, potassium carbonate seeded combustor operated under slightly fuel-rich conditions (equivalence ratio = 1.09). Note that KPO2 and KPO3 are the dominant neutral phosphorus species at all temperatures. Negative ion chemistry is dominated by PO2 and PO3 below 2000 K, phosphorus species negative ions outnumber free electrons. The only negative ion which Is comparable in concentration to PO2 is Fe02 and then only at the upper temperature range. The sharp temperature falloff of Fe02 Is caused by the stability of condensed Iron containing species.

Under normal operating conditions, in which the combustor is sufficiently warm and operated under fuel rich conditions, virtually no NOx is formed, although the formation of ammonia is possible. Most hydrocarbons are converted to carbon dioxide (or methane if the reaction is incomplete) however, trace levels of hydrocarbons can pass through the fuel processor and fuel cell. The shift reactors and the preferential oxidation (PrOx) reactor reduce CO in the product gas, with further reduction in the fuel cell. Thus, of the criteria pollutants (NOx, CO, and non-methane hydrocarbons [NMHC]), NOx CO levels are generally well below the most aggressive standards. NMOG concentrations, however, can exceed emission goals if these are not efficiently eliminated in the catalytic burner. 

Different design concepts have been proposed to match the severe requirements of catalytic combustors. A main classification criterion is based on fuel/air stoichiometry in the catalyst section, which has a dominant effect on the selection of catalytic materials and on the operating characteristics of the combustor. In this section, only configurations based on lean catalytic combustion will be described. The peculiar characteristics of rich catalytic combustion will be described in a separate section. 

COMBUSTOR INLET AIR PRESSURE. The effect of decreasing inlet static pressure has been shown to decrease efficiency at an accelerating rate, decrease maximum stable temperature rise, and narrow the operable fuel-air ratio range (rich to lean blowout... 

The NO levels obtained from the staged combustion investigation were substanially less than obtained from a lean combustor (Figure 12). At exit temperatures representative of baseload operation, the rich-lean combustor produced N0X levels approximately one-third the levels associated with the lean combustor. Unlike the staged combustor emissions increased with increased fuel-bound nitrogen. 

The data acquired in the evaluation of a subscale, rich-lean staged combustor indicated a substantial tolerance for fuel property variations while retaining a low emissions operation characteristic. In particular, it was observed that ... 

Gas turbine engines with a conventional natural gas combustion system or water injection combustion system can operate on H2 or H2-rich fuels with little or no modifications to the core injectors. Modifications to the fuel delivery system and injectors are required. The volumetric heating value of hydrogen is 10,787 kJ/N-m3 (274 Btu per standard cubic foot [scf]> as compared with 35,786 kJ/N-m3 (909 Btu/scf) for methane. In order to supply the required energy input rate to the gas turbine, approximately 3.32 times the volume of hydrogen fuel has to be injected into the primary zone of the combustor to provide the same heating value as that of natural gas fuel. 

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