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Show will be fired in the future, and even more emphasis will be placed on cleaner burning, easier to use refinery fuel gas. In a further example, the economics of cogeneration is becoming more and more attractive, particularly if some old oil fired boilers can be shut down to help satisfy NOx reduction mandates, as is the case in a recent installation in one of our refineries. Not only have we shut down some ancient, less efficient, more polluting oil fired equipment, but the gas turbines and duct burners in the new cogeneration trains are gas fired. Thus do economics and environment force us away from the utilization of alternative fuels and toward "better" use of the traditional gaseous fuels, which means more conservation and less emission, particularly of the oxides of nitrogen. Let us now explore further the implications of the dual imperatives of NOx reduction and fuel conservation. NOx Reduction and Fuel Conservation When expanded use of the traditional gaseous fuels displaces nitrogenous fuel oils, that brings with it reduced production of the oxides of nitrogen, there being no fuel-bound nitrogen to augment the inevitable thermal fixation. Beyond that, until good low NOx burners came along, the only real alternatives for meaningful NOx reduction were the enormously expensive selective catalytic reduction flue gas treatment plants. The fuel-staged low NOx burner came to the attention of American refiners toward the end of the 1970s. Today, even while refiners are busily installing it, U. S. researchers are busily optimizing the staging technique, and I should like to suggest a small shift in emphasis. Why fuel-staged gas burners do so much better than their air-staged predecessors is an interesting question. But the researchers have long since confirmed that they do, so I am not entirely sure that we need much more help there. However, there is the matter of "combination" (gas or oil) firing where we can use some help. If you are required to retrofit NOx reduction, today's choice is the following. You can retain your oil firing capability, assuming you have it to begin with, and install a selective catalytic reduction flue gas treatment plant, or you can give up oil firing and install fuel-staged low NOx gas burners, hole for hole, at about one-tenth the cost per pound of NOx removed. Considering also that you will have to find a place to put the flue gas plant and, once built, you will have to operate and maintain it, I leave it to you to figure out which is the better deal. Thus do the environmental imperative and sensible economics conspire to influence both expanded and better use of the traditional gaseous refinery fuels. The reason you have to give up oil firing is that fuel-staged low NOx burners aren't really compatible with combination oiVgas firing. In the standard combination oil/gas burner, the oil gun occupies the central position with a surrounding ring of gas nozzles. But in the fuel-staged low NOx gas burner's Simplest, most practical and most effective configuration, the central position is occupied by the primary gas gun and the combustion air annulus, while the peripheral positions are occupied by the staged fuel nozzles. It is true that combination oil/gas low NOx burners are offered, fuel-staged on gas but air-staged on oil because today fuel-staging doesn't work very well on nitrogenous fuel oils. But they are big and clumsy, offering little possibility of simple, inexpensive retrofits. The development of fuel-staged low NOx burners for gas firing is an example of how the combustion R&D community has already helped us in a very important way to make better use of the traditional gaseous fuels. Naturally, we would like to have our cake and eat it, too . We would like to be able to provide "substantial" NOx reduction by hole for hole burner retrofits and retain the combination oil/gas firing capability, where we have it. "Substantial" means reductions approaching those attributable to flue gas treatment plants (on either gas or oil firing) like we can get from today's fuel-staged gas burners. That is where we could use some help from the combustion R&D community today, and I am pleased to acknowledge that, just recently, a major stop in that direction has been taken by the introduction of a "2nd generation" fuel-staged burner in which the central position ~ available for the introduction of a standard (not low NOx) oil gun. "Uhra" Low-NOx Burners Many ordinary gas fired refinery heaters with standard burners produce around 0.16 Ib of NOx per million Btu of gas fired. In Southern California, a stringent new limit of 0.03 Ib/mmBtu has been imposed, requiring over 80% reduction. We reliably got down "only" to about 0.06-0.07 Ib/mmBtu with the "1 st generation" fuel-staged low NOx burners. That's really good but unfortunately |