Low NOx Burners
For over a decade, Japan and Europe have faced the necessity of reducing NOx emissions. Although the Bloom baffle burner is inherently a low NOx design, modifications were made which lowered NOx even further to meet the challenges presented by the clean air requirements of Japan and Europe. With the development of regenerative burners, the low NOx baffle concept was successfully applied to these designs. To improve air quality with radiant tube burners, several changes to the basic design have been developed.
Bloom Engineering's Low NOx Burners
Bloom's low NOx burner products cover the spectrum from cold air to hot air, small to large, and include direct fired burners, radiant tube fired, conventional and regenerative burners.
Among the Low NOx burner products are:
- 1060-, 1070-, 1080-, 1440-, 1500-, 1550-, 1560-, 1570-, and 1610- Series large capacity hot and cold air fabricated low NOx direct fired baffle burners.
- 2000-,2070-, 2100- and 2170- Series hot and cold air high thermal release (HTR) direct fired burners.
- 1360-, 1400-and 1430-Seriessmall capacity, low NOx baffle burners.
- 1440-, 1500- and 1550- Series small capacity hot air low NOx direct fired baffle burners with air staging.
- 1080-, 1000-, 1100- and 1150 Series low NOx direct fired regenerative baffle burners utilizing various methods of NOx suppression.
- Type 'F 2370- Series low NOx recuperative radiant tube burners which, use recirculated products of combustion to reduce NOx. Radiant tube burners using staging are also available.
What is NOx?
The two oxides of nitrogen related to combustion are nitric oxide (NO) and nitrogen dioxide (NOJ. NOx refers to either one of these gases, which playa major role in the formation of smog and ozone.
NO and NO2 are considered toxic, with NO2 being one of the most toxic of commonly found atmospheric gases. NO2 contributes to the formation of acid rain and several airborne carcinogens.
Thermal NOx
NOx formed during combustion using nitrogen and oxygen in the combustion air is referred to as "thermal NOx :'Several important variables influencing thermal
NOx are:
- Flame temperature . Air preheat
- Furnace temperature . Excess air
- Chemical environment within the flame
Flame temperature is the most important variable. The higher the flame temperature, the higher the NOx concentration. Air preheat and furnace temperature are related to flame temperature and, as a consequence, have a major influence on NOx generation. As excess air is increased above stoichiometric, the amount of NOx produced begins increasing. The amount of NOx produced will start decreasing when excess air continues to increase because the suppressed combustion temperature begins having a major influence. For practical and economic reasons, it is generally not feasible or desirable to reduce NOx by using excess air.
Thermal NOx Control
There are a variety of methods for controlling thermal NOx . Among them are:
. Burner design
. Exhaust or Flue Gas Recirculation (EGR or FGR) . Chemical additives (e.g., ammonia) . Catalyst aided
Burner manufacturers utilize designs such as low NOx baffles and air staging as well as flue gas recirculation. Flue gas recirculation may be achieved by inducing products of combustion (POC) into the flame from the furnace or by using POC from the exhaust system to mix with air or fuel which reduces flame temperature. Oxygen, which controls the reaction rate, is also diluted, reducing the probability that the available oxygen will enter Into the NOx generating reactions.
Air staging controls flame temperature and the chemical environment to reduce NOx formation.
Low NOx Burner Summary
Bloom's low NOx burner product line spans the input range commonly used in industrial applications. It includes direct fired and radiant tube fired burners which can be designed for cold air or hot air produced by recuperators or with regenerators.
The heart of the direct fired burners is the well proven baffle concept. With regenerative applications, efficiencies and emissions levels which reduce NOx , CO and CO2 below the levels expected even from modern cold air burners are achieved.
In radiant tube designs, Bloom uses unique engineering approaches to provide exhaust gas recirculation to the burner with only insignificant or very small losses in thermal efficiency.
