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Show ) not good enough to comply with that stringent new rule in Southern California. Selective catalytic reduction flue gas treatment plants reliably produce 80 to 90% reductions. But the cost per pound of NOx reduced for SCR retrofits is about 1 O-times that of low NOx burners! Nevertheless, faced with a mandated 80%+ reduction, it seems (in Southern California) that we are stuck with the technically feasible but outrageously expensive selective catalytic reduction flue gas treatment plants. Or are we? As long as there is no nitrogen in the fuel gas, all the NOx comes from thermal fixation of the nitrogen in the combustion air. That process is reaction rate limited so if we could keep the reaction temperature below 2000oF, we could get below 0.03 Ib-NOxlmmBtu. Surface combustion can do that! That is why we championed the innovative development of surface combustion burners for refinery process heaters, recently completing a most successful demonstration. Even more recently, fuel-staged gas burners incorporating flue gas recirculation have been introduced that do that, too. SCR-reductions at a burner price! That is our hope. This is another example . of how the combustion R&D community is already helping us to make better use of the traditional gaseous fuels. Fuel Conservation Another way that we can make "bette(' use of the traditional gaseous refinery fuels is to use less. However, in that connection, it may be useful to observe that reduced excess air is generally thought to reduce fuel consumption and put that "axiom" into perspective. In brief, while "reduced excess air" may be a laudable operating goal and a commendable pursuit for the combustion R&D community, it isn't necessarily a big deal. It all depends on the flue gas temperature in the stack. As long as the stack temperature is low, most of the energy has been extracted from the flue gas no matter what the excess air. For example, even at a stack temperature of 7000F, which is pretty hot, a decrease in excess air from twenty-five to ten percent produces only about one percent increase in fuel efficiency. On the other hand, if you employ waste heat recovery to reduce the stack temperature to 400°F, you get a whopping eight percent increase in the efficiency of fuel use in the furnace. Your fuel savings are eight times as great! The hot flue gas is the problem, not the excess air. The way to make substantial cuts in the refinery fuel bill, which today dominates the refinery annual operating cost, is to recover more of the heat that goes up the stacks. Although the petroleum refining sector consumes about 60 percent of the industrial furnace fuel, we do so at an efficiency of over 70 percent, whereas the steel, glass and aluminum industries consume fuel at less than 30 percent efficiency. Particularly in those industries, one might think that waste heat recovery would be attractive, but there do not exist the same opportunities for utilizing waste heat that are found in petroleum refineries. But even in petroleum refineries, furnace waste heat recovery projects often have only moderately attractive rates of return compared with other opportunities for capital use. It might be "good" to recover more stack heat and thus use less fuel, but it won't be done if it isn't good business, and many furnace waste heat recovery projects simply are not. That suggests that some R&D directed toward improving the cost-effectiveness of stack waste heat recovery would be a good idea. Cogeneration Most of the cogeneration systems that are being installed in the United States today employ gas turbines fueled on natural gas. Of course, that supports the main thesis of this discussion, that economic and environmental pressures force greater emphasis on the traditional gaseous fuels rather than on the alternative fuels. But if the energy future were to include expanded use of, say, residual fuels or heavy crudes to fuel refineries and petrochemical plants, cogeneration might offer away. Distinguished from the aircraft derivative designs, there are robust heavy duty gas turbines with external combustors that are capable of burning low grade fuels with controlled NOx emissions. The external combustor design is offered by several gas turbine makers. It inherently employs the rich burn quick quench staged combustion concept which deals with the high nitrogen content of the typical low grade liquids. As in other deSigns, steam or water injection effectively suppresses thermal NOx. Of course, the attractiveness of low grade fueling depends on how much less the fuel costs as against how much more the system costs. If, in addition to the cost-effective NOx reductions provided by the staged combustor and water (or |