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I. Working principle of low-NOx burners: Many low-NOx burners incorporate additional flue gas recirculation (FGR), which can further reduce and minimize nitrogen oxide emissions. The FGR rate typically accounts for 5% to 30% of the total flue gas flow rate of the boiler. FGR can be introduced into the FD fan (commonly referred to as IFGR) and mixed with the combustion air before entering the burner/hood. The addition of IFGR increases the mass flow rate requirements for the FD (and ID) fans, while also increasing the pressure drop in the furnace and the system. It is very important to inspect the existing FD fans (and ID fans, if applicable) to ensure that the existing combustion air and flue gas systems can meet the requirements of the new equipment and performance levels. In applications where the existing fans in operation are not sufficient to meet and exceed the new performance requirements, it is necessary to consider using larger fans and motors, employing separate FGR fans, or reducing the capacity of the heating furnace. Check the dynamics of the existing fan capacity in the surrounding area. Most low-emission burners today require a relatively high air-side pressure drop in order to achieve the desired fuel/air stratification within the burner itself. Based on this design consideration, the pressure drop may be significantly higher than that designed for the original burner. The dynamic of voltage drop is commonly referred to as “register draft loss” or RDL. The new RDL requires that existing forced-draft fans be inspected to ensure that they can provide the static pressure necessary to accommodate the new burner system. It should be the responsibility of the burner supplier to verify the functionality of the existing FD fans, by examining the boiler operation data that shows the system pressure drop based on the fan curve, or by assessing the performance of the existing fans through static pressure tests. The retrofitting of low-nitrogen burners can help the petrochemical industry reduce the excess air coefficient; moreover, suppressing excessive combustion can lower the oxygen concentration around the fuel. In environments with less residual air, reduce the peak temperature to lower thermally reflected nitrogen oxides ； In low-oxygen environments, the residence time of combustibles in the flame front and reaction zone increases. II. Considerations for retrofitting low-nitrogen burners: When compared directly with many existing burner designs, low-nitrogen burners exhibit significant differences in terms of the fuel/air mixing design, internal dimensions, pressure drop requirements, flame geometry, and control requirements. When budgeting for, selecting, and installing new burners, all of these aspects need to be thoroughly examined and reviewed.