In recent years, with the continuous tightening of environmental protection policies, the emission standards for boiler flue gas have become increasingly stringent, and the nitrogen oxide emissions have been reduced again and again. In most areas, the nitrogen oxide content has been controlled at 30mg/Nm³, exceeding the standards. Many companies' existing boiler equipment can no longer meet such strict emission standards, making ultra-low emission retrofits for gas thermal oil boilers an urgent necessity.
Regarding the need for design in the ultra-low emission retrofitting of gas-fired thermal oil boilers, it depends on the actual performance of the existing boiler. The general process for ultra-low emission retrofitting of gas-fired boilers is: determine retrofitting standards, develop a retrofitting plan, begin the retrofitting, and conduct the acceptance.
Ultra-Low Emission Retrofit Plan for Gas Boilers
The ultra-low emissions retrofit for gas-fired boilers primarily involves upgrading the burners and increasing the furnace chamber size of the boiler. To help companies save costs, configuring appropriate low-NOx burners with分级 combustion technology and flue gas recirculation (FGR) can achieve low-NOx retrofitting, controlling emissions to less than 30 mg/Nm³. The current ultra-low emissions retrofit plan for gas-fired boilers includes: FGR low-NOx combustion technology, which is the mainstream and mature low-NOx emission technology for natural gas boilers, utilizing分级 combustion and flue gas recirculation. By adopting FGR low-NOx combustion technology, the air excess coefficient of the newly introduced cold air into the boiler is reduced to the lowest possible level, ultimately achieving energy-saving and emission-reduction effects by reducing flue gas heat loss and lowering NOx content in the flue gas. The principle of FGR low-NOx combustion technology involves using the pressure head of the combustion air to draw part of the combustion flue gas back into the burner, where it mixes with air for combustion. Due to the flue gas recirculation, the combustion flue gas has a high heat capacity, lowering combustion temperature and reducing NOx. Another self-recirculation burner directly recirculates part of the flue gas within the burner and incorporates it into the combustion process, providing both NOx suppression and energy-saving effects. The FGR low-NOx flue gas recirculation process involves mixing part of the flue gas with air and then sending it to the combustion chamber for combustion assistance. The mixed combustion air effectively reduces the temperature and oxygen concentration in the combustion chamber. Since the combustion reaction activation energy of gas with oxygen is significantly lower than that of oxygen with nitrogen, gas combusts with oxygen first. Only when oxygen is in excess does gas react with nitrogen to form nitrogen oxides; however, the lower reaction zone temperature makes the reaction with nitrogen extremely slow, effectively suppressing the formation of thermal nitrogen oxides.
