We assisted a major oil refinery in reducing NOx emissions on three 550,000 lb/hr tangentially fired boilers while considering retrofit cost, timeline, and equipment compatibility. The retrofit successfully achieved target emissions, received an award for exceptional performance, and showcased our expertise in optimizing industrial combustion systems.
Objective
A major oil refinery needed to reduce NOx emissions on three 550,000 lb/hr (250,000 kg/h) tangentially fired boilers. The strategy called for the application of low NOx burners with induced flue gas recirculation (IFGR) to provide reliable combustion and achieve target NOx emissions when operating with various refinery gas and load combinations. Additional customer requirements included:
- Minimum retrofit cost
- Short project execution timeline
- Compatibility with existing windbox and No. 2 oil backup system
Solution
The refinery approached us to define and implement the most economical approach. We proposed a burner design that would minimize modifications to the existing windbox geometry, backup fuel oil firing system and ignition equipment.
CFD modeling supported the decision to proceed with the low NOx burners with the IFGR approach as a mechanism to achieve NOx reduction and maintain boiler efficiency. In addition to CFD modeling, a 1/4-scale model of one low NOx corner burner element was tested at our Research & Development Test Center under simulated field conditions. The tests demonstrated reliable low NOx characteristics of the proposed burner over the required burner turndown range.
The impact of increased IFGR rates on the boiler superheater and temperature control was evaluated using CFD and mathematical modeling. The analysis indicated that the superheater would accommodate the IFGR rates and that superheat temperature control could be maintained via existing means. The CFD study of the combustion air ductwork and windboxes indicated that no modifications were necessary to achieve optimum airflow distribution to the burners. Our burner solution kept the retrofit cost to a minimum by replacing only critical burner components with custom-engineered components, while most of the oil burner system remained intact.
The equipment supplied included low NOx gas injectors, new flame stabilizers and replacement of associated windbox air nozzles (buckets). These components were designed to adapt to existing windbox compartments and burner tilt mechanisms, which avoided costly windbox modifications. In designing the replacement windbox air nozzles, care was taken to ensure that the existing oil firing equipment could be reused with minor modifications. The project had a short execution time and was subject to rigorous quality assurance testing during fabrication. It was also imperative that the equipment attained design performance immediately after the installation outage.
Results
All three industrial boilers were successfully retrofitted. The burner modifications were confirmed to provide good flame shape and reliable light-offs over the boiler load range with all gas fuels and IFGR combinations. The NOx emissions were easily achieved while maintaining superheat and boiler efficiency. We received an award for “Exceptional Vendor Performance” from the refinery.
