Existing NOx-reduction technologies such as external flue gas recirculation (EFGR) and selective catalytic reduction (SCR) are well-established systems for hitting emission targets. But these post-combustion approaches entail high capital and operating costs stemming from their more complex upfront designs, equipment requirements, and planned-unplanned maintenance cycles. In an effort to avert issues that can accompany EFGR and SCR systems, a California refiner recently opted to implement Duplex, a front-end, fuel-combustion technology developed by ClearSign Combustion Corp., Seattle, Wash. Retrofitted into a multiple-burner, vertical-cylindrical (VC) production process heater at the refinery, the technology has proven effective at reducing NOx emissions to levels that meet or exceed California's regional regulatory requirements, some of the most stringent in the US. Completed in August 2016, the southern California refinery retrofit involved installation of the technology in a VC reformer-splitter reboiler process heater with a maximum firing capacity of 11.25 MMbtu/hr. The heater's radiant section included a 9.65-ft diameter, 17.85-ft high outside shell. Previously equipped with three natural-draft 3.75-MMbtu/hr ultralow-NOx (ULN) burners installed on the furnace floor, the VC furnace heats fluid it receives from a distillation tower to fractionate process fluid from a reforming unit. The system implementation met and exceeded the refiner's objective of NOx emissions ≤ 6 ppm, corrected at 3% O2, with actual emissions during the 6-week evaluation averaging 3.7 ppm, corrected at 3% O2.

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• ClearSign Combustion Corporation

• Burner

• NOx

• Article