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Show the burners selected be reliable and be able to meet the emissions limit of 40 ppmvd NOx, consistently under various operating conditions. There were further constraints on the limited downtime available to implement the changes. The first option, standard staged fuel burners, was considered but disregarded due to the burners' inability to consistently control NOx at below 40 ppmvd. The second option, staged fuel burners with external flue gas recirculation (FGR), was capable of achieving the NOx level of less than 40 ppmvd. However, it was not implemented due to its high cost. Staged fuel burners with steam injection was the third option to be considered. This option was also disregarded, due to its dependence on steam injection to achieve the required NOx emissions level of below 40 ppmvd. The injection of steam impacts flame characteristics and flame control with steam injection has prov.en generally difficult. The option that was finally selected was staged fuel burners WIth internal flue gas recirculation (IFGR) based on reliability, cost and control reasons. Based on all these considerations, the staged fuel burner with internal fluegas recirculation (IFGR) was selected. Not only would this burn.er meet the emissions limit without further treatment, the emissions could actually be lowered even further, if required, by future steam injection. Table 2 shows a cost comparison between the FGR and IFGR options. The second step in the implementation was to ensure that the burner would fit in the existing heater floor. The IFGR burner was inherently larger, for the same heat release, as compared to the original standard burners. Therefore the substitution could not be made without a floor replacement. The next hurdle was the burner to tube distance. The quoted burner circle diameter for the IFGR was over 50 inches, leaving a mere 30 inches from the burner center to the tubes (which could not be moved). This was unacceptable [5]. However, after much consultation with the burner manufacturer, an IFGR burner with burner circle diameter of 31 inches (as existing) was redesigned. This was made possible by offsetting the burner throats, thereby allowing the tips to be installed closer together as in a cluster. An important lesson to be learnt from this is that there is often flexibility in burner designs without affecting their performance. The last step was to ensure that compliance and performance objectives would be met with these burners. A critical factor was the fuel supply to the burner. Typically, petroleum refineries obtain their fuel from a central fuel blending facility. Therefore, depending on the status of sources of that fuel supply (often process units), the fuel composition can vary widely (fable 3). The IFGR, therefore had to be designed to be compatible with the range of fuel compositions shown. Naturally, the impact of the fuel composition fluctuation on the burner NOx emission was examined in great detail. NOx emissions are likely to be greater with the increased presence of either hydrogen or other "heavy" components (such as butane and unsaturated hydrocarbons). Once the decision to purchase the IFGR burners for this heater was finalized, it was recommended that each burner manufacturer arrange burner performance tests at the manufacturers' test facilities prior to vendor selection. This test typically included a demonstration of the burners' flame pattern, flame height, pressure drop (fuel and combustion air), and most importantly, the NOx emissions rates at different firing rates depending on the expected range of operation (25 - 100 percent of load). The effect of steam injection on flame quality was also tested. Throughout the test, fuel compositions that were typically to be expected during actual operation were used. Upon the successful completion of the tests and other contractual negotiations, the burners were procured and installed. It is expected that the installation of the IFGR 10 |