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Show On the technology side, the last two decades produced a bewildering array of NO! reduction alternatives: over-fire-air, burners-out-of-service and other approaches to off-stoichiometric firing ; flue gas recirculation both external with ducts and internal with lances; fuel switching; reduced excess air; oxygen-enriched combustion; water and steam injection; air staging, fuel staging, and' exquisitely convoluted, multiple combinations of air and fuel staging; premixed surface combustion; the injection of various ammonia compounds at multiple locations in the flue gas stream; selective catalytic NO! reduction and simultaneous SOx/NOx flue gas treatment plants. The list goes on and on . Least cost optimization of a technology mix for refinery NO! reduction can be accomplished only by treating the whole refinery as a single source with a specific performance goal in view. Importantly, South Coast Air Quality Management District's Rules 1109 and 11 ~6 do not dictate technology but rather specify NOx emission limits for broad classes of refinery combustion sources. Based upon Chevron and other experience, we have concluded that an optimized technology mix for refinery NOx reduction includes mainly fuel switching (no oil firing); natural-draft, fuelstaged, self-recirculating ultra low NO! burners; and selective catalytic flue gas treatment. We have long since lost count of the number of burner tests, conducted over the last fifteen years at a dozen test facilities all over the world, in which we have participated. The test furnaces of the burner designers are great places in which to experiment with combustion modifications for NOx reduction and that is the source of a good deal of the experience upon which we rely. Not to be overlooked as a continuing and important source of guidance are the various NO! reduction initiatives carried out over the past fifteen years by the International Flame Research Foundation . The combustion fluid mechanics near-field aerodynamics trials have been particularly useful in helping us to appreciate both the potential and limitations of combustion modification for NO! reduction . Another source of experience has been a number of extensive visits over the past fifteen years to study the evolution and application of NOx reduction technology in japan. While that background has been exceedingly helpful in forming our jUdgements, it is useful to recognize that South Coast Air Quality Management District's Rule 1109 is more than twice as restrictive as the most stringent of japanese limits. Most refiners don 't think of their plant as a laboratory in which to experiment with various approaches to anything and, ordinarily, neither do we. Yet as we look back over the past fifteen years, it nevertheless appears that we have tried at least one version of just about every imaginable approach to NO! reduction. We experimented with water, steam, and ammonia injection . We varied excess oxygen and firing rates. We installed self-recirculation gasification burners, air-staged burners, and fuel-staged burners. We put in selective noncatalytic reduction, selective catalytic reduction, and water-injected gas turbines. We even installed Chevron 's proprietary denitrification technology at the CO boiler. In short, you name it, we tried it. P~rhaps the centerpiece of our proactive refinery experimentation with advanced NO! reduction technology was the Petroleum Environmental Research Forum project on premixed surface combustion that was proposed and carried out by Chevron at its E1 Segundo Refinery. A great success as a demonstration of advanced technology, the project attracted not only refiner and contractor partners, but the South Coast Air Quality Management District as well. But its most important contribution was not entirely anticipated. Chevron's advanced technology demonstration project stimulated a remarkable martet response among burner manufacturers that produced significant NO! reductions through combustion modification which, in turn , reduced the number of SCRs which the refinery has to install to comply with mandated emission limits, thus providing significant cost savings. Burner Evolution The evolution of today's ultra low NO! burners beaan in the late 1970s. We can remember, in 1978 or 1979, jawboning a leading burner manufacturer's consummate wizard about the virtues of fuel-staging , a then obscure japanese development that had demonstrated around 70 percent NO! reduction . Remember that the burner state-of-the-art had evolved with great 2 |
