Among the variety of industrial burners, the low NOx burner or low NOx boiler is basically utilized in the utility boilers to regenerate steam and electricity. These burners are said to be uniquely regenerative which modifies the fuel before the combustion process which then forms and burns the soot within the flame.
“The increasing heat transfer rate and declined flame temperature results in the inclined furnace production and thereby efficiency of the thermal”
NOx are defined either as the flame temperature, furnace temperature or are related to the chemical environment within the flame. The key variable among the three is the flame temperature, i.e. where the flame temperature is high, NOx concentration is also reported as high. Concerning the furnace temperature and air preheat, it ultimately assist in the generation of NOx. The amount of NOx produced starts increasing once the excess air increases over the stoichiometric. In the same manner, the amount of NOx production begins to decrease as soon as the air continues to increase as a result of suppressed combustion temperature starts off.
“It is not considered as a feasible decision to make a reduction in NOx especially by consuming the excess air”
With regards to the aim of designing behind the low NOx burner, these specifically control the fuel and air mixing at every burner/boiler to produce much larger and branched flames. Hence, this reduces the peak flame temperature and ultimately results in less NOx formation. The improvement in the flame structure then declines the amount of oxygen which is available within the hottest flame part thereby bringing improvement in the efficiency of burning.
Working of low NOx burners/boilers
Where a conventional low NOx boiler is consumed, activities including combustion at first, reduction as second and burnout as the third are achieved within three distinctive stages as mentioned below:
- As far as the very first stage is concerned, the combustion takes place within the fuel-rich and oxygen-deficient zone where the NOx is said to be formed.
- Concerning the second stage, i.e. reduction, this takes place as the reducing atmosphere. It includes the formation of hydrocarbons that reacts with the NOx that is already formed.
- Where the third stage is concerned, the internal air staging completes the process of combustion that also results in some more NOx formation. The stage can be minimized via the completion of the combustion process within an air lean environment.
“Where low NOx burner is combined with several other primary measures, the plant experience results in approximately 74% NOx removal efficiency.”
Where does the low NOx technology come from?
When low NOx boiler technology is being utilized, it exactly means that the heat would be consumed to regenerate hot water as well as steam. In the process of combustion, NOx (nitrous oxide) is actually produced as a byproduct. It comes from the three main sources as below:
- The prompt NOx- it happens when the nitrogen bounds back to the fuel.
- The thermal NOx- it takes place as a result of higher temperature combustion. When it comes to the overall NOx emissions, the thermal NOx is said to be one of the greatest contributor.
- The fuel-bound NOx- lack of concern with the natural gas.
“NOx refers to either the nitric oxide (NO) or nitrogen dioxide (NOJ) that plays a major role in the formation of ozone and smog”
How to control thermal NOx?
When it comes to controlling the thermal NOx, it can be done via burner design, exhaust gas recirculation (EGR)/ fuel gas recirculation (FGR) and via the chemical additives which includes ammonia. This takes place in a way that the burner/boiler manufacturers such as burnertec.com consumes the designs (e.g. low NOx baffles), flue gas recirculation as well as the air staging. If it’s more about achieving the FGR (flue gas recirculation), it requires induction of POC (products of combustion) within the flames or via making use of the POC from the exhausting system to mix it up with either fuel or air. Hence, reducing the temperature of the flame.
*Note that during the NOx generating reaction, it may also be required to keep control over the oxygen so that it is diluted, minimizing the certain probability.
