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With a firm understanding of how the formation of NOX occurs, various methods of inhibiting its formation or breaking down the compound can be investigated.
Low nitrogen fuels
Approximately 60–80 percent of NOX formation results from fuel-bound nitrogen. With the majority of NOX emissions coming directly from fuel combustion, the most logical approach to reducing NOX emissions is to use fuels containing less available nitrogen for conversion. Approximately 60–80 percent of NOX formation results from fuel bound nitrogen. Results would be immediate and no plant downtime would be required. However, there are several potential problems in switching to lower nitrogen fuels. Ash compositions might change and additional boiler slagging might be observed. The fuel cost could be significantly greater than that of the existing fuel, leading to a continuing expense for the NOX reduction. Additionally, if a plant is burning a bituminous coal and implements a switch to a sub-bituminous coal
Upgrades of combustion instrumentation and controls
Better control of fuel and airflow rates into the boiler will result in better combustion control, which can effectively decrease NOX emissions. Controlling the amount of primary and secondary air, as well as precise measurements of coal flow through pipes, will lead to a more favorable fuel-to-air mixture and reduced NOX generation. Installation of updated instrumentation and controls to air ducts, coal pipes, etc., is a fairly simple approach with short lead times. Immediate results can be obtained, as well as better historical documentation of combustion in case there are future issues with boiler operations. Real-time measurements result in instantaneous adjustments to account for variations in fuel or airflow.
Instrumentation to support real-time measurement capabilities are available for all boiler types and are compatible for almost all boiler control systems. However, some problems might be encountered when upgrading an existing control system. Better measurement devices might reveal that additional systems will need to be upgraded or replaced. Better seals, dampers and valves are critical to a fully operational control system. Also, when newer, more precise measurement devices are put in place, continuing maintenance and calibration is required to maintain the accuracy intended.
Boiler tuning will result in better combustion operation and lower NOX generation. Short equipment downtime, if any, makes this a desirable option for low-cost NOX control. However, similar to instrumentation and control upgrades, boiler tuning will degrade with time and require additional tuning to achieve the same results. Additionally, if operations staff does not follow any new protocols implemented from a recent tuning, NOX reduction might not be as effective as intended.
Low-NOX burners have become a popular option for reduction of NOX generation. Changing the fuel and air distribution in the combustion zone will directly affect the amount of NOX generated by combustion. In addition to reducing the formation of NOX, other benefits might be realized by installing low-NOX burners. Some of these include:
- Reducing CO generation along the sidewalls
- Coal roping can be broken up into a better fuel air distribution
- Slagging and corrosion control can be increased
- Low operating costs are observed