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Show discussion is pertinent to retrofit situations in other regions as well. A key factor in the choice of the Southern California region is its present status as being the most tightly regulated region of the country. Therefore, it is serving as a testing ground for many of the technologies, strategies, and concepts of NOx reduction that will no doubt apply later in other parts of the country. Another factor is that unlike regulations that apply in many regions that "grandfather" existing units, the SCAQMD regulations apply to existing heaters not new equipment. Thus, it presents some of the most difficult challenges for the retrofit engineer. Retrofitting existing units to reduce their emissions subject to various other constraints is often a demanding task for the engineer and designer. It is also a subject that has not received adequate exposure in the literature where most of the discussion is limited to technology applicability in new designs. After briefly discussing the relevant SCAQMD regulations, this paper describes the various aspects of the retrofit situation that should be considered, including heater evaluation and other constraints. This is followed by a brief review of the available NOx reduction technologies. These are described only insofar as their characteristics impact the retrofit situation. Finally, two case studies are presented to illustrate the applications of the control technologies discussed. 2. SCAQMD NOX RULES Two major rules of the SCAQMD affect the NOx emissions from refinery heaters [4]. These are Rule 1146 and Rule 1109. Together, they impact almost all of the fired units operating in the Southern California Basin, numbering in the hundreds. Rule 1146 applies to heaters that have firing rates in the range of 5 to 40 million BTU per hour, on a HHV basis. It essentially mandates that, by September 1991, the NOx emission (as N02) from such units be reduced to no greater than 0.05 pounds per million BTU (HHV) fired. Corrected to 3 percent oxygen, this corresponds to a NOx concentration of approximately 40 ppmvd (dry basis) in the fluegas. Rule 1109 applies to heaters having firing rates greater than 40 million BTU per hour, on a HHV basis. It requires that the NOx emissions (as N02) from such units should not exceed 0.03 pounds per million BTU (HHV) fired. Corrected to 3 percent oxygen, this corresponds to a NOx concentration of approximately 24 ppmvd in the fluegas. The implementation of this Rule is in two phases, with a final compliance deadline of December 31, 1995. 3. HEATEREVALUATION The first step in the retrofitting of an existing heater is a thorough evaluation of its current operation. Compared with its original design basis using computer model simulations, this operating data evaluation provides invaluable insight into various factors that might be affecting the heater's performance. In many ways this corresponds to a calibration of the heater. This evaluation helps to point out potential deficiencies, if any, that exist in the heater and its auxiliary equipment (such as burners, heat transfer surfaces, refractory, fans, air preheater, stack, and dampers). This information, in conjunction with the other constraints and considerations discussed below, helps to define the design basis for future operation of the heater. 2 |
