Environmental Science and Pollution Research

, Volume 26, Issue 10, pp 9717–9729 | Cite as

Control of NOx emissions by air staging in small- and medium-scale biomass pellet boilers

  • Yuening Li
  • Yingchao Lin
  • Jingbo Zhao
  • Boyang Liu
  • Ting WangEmail author
  • Peng WangEmail author
  • Hongjun MaoEmail author
Research Article


The effect of air staging strategies on NOx control was investigated on a 210-kW small-scale biomass boiler (SBB) and a 1.4-MW medium-scale biomass boiler (MBB). Considering the de-NOx effect, as well as the convenience and economy for future wide use, the structures of the secondary air duct and the fuel feed tube were innovatively designed to solve the problems of the traditional prototype. The preliminary experiment showed that the lowest NOx emission was achieved when the air excess (ε) was equal to 2.04. Then, additional operating modes were conducted on the MBB to further optimize the air staging strategies. The optimal air staging strategy of the MBB (the secondary to primary air flow ratio (λ) and the ε were equal to 0.13 and 0.76, respectively) could decrease the NOx emission from 338.12 to 148.14 mg/m3. Furthermore, the SO2 emissions and the lowest NOx emission of the SBB and the MBB could meet most emission standards of China and some developed countries. The thermogravimetric analysis (TG) and combustion characteristics of the wood fuel showed that the air staging was a suitable de-NOx technology for wood combustion, and the slagging was less likely to occur under the selected condition. Hence, the air staging technology was an effective and low-cost method for the emission reduction of biomass boilers. This study provided a practical basis for future research on the gas emission control of biomass boilers.


Biomass boiler Small-scale Medium-scale Air staging NOx reduction 



Ash fusion temperatures


Boiler efficiency


The carbon content in the pellet


Combustion efficiency


The dry flue gases specific heat


The water vapor specific heat


Calorific capacity of liquid water


The unburned carbon content passing through ash


Deformation temperature


Derivative thermogravimetric


Fixed carbon


Flow temperature


The hydrogen content in the pellet


Higher heating value


Hemisphere temperature


Lower heating value


The moisture content in the pellet fuel


Medium-scale biomass boiler


The heat power content in the fuel


Particulate matter


The heat power gain of water in the exchanger


The thermal heat loss


The unburned gaseous heat loss


The pellet mass flow


The unburned carbon heat loss


The mass flow of water in the heat exchanger


Small-scale biomass boiler


Selective catalytic oxidation


Selective catalytic reduction


Selective noncatalytic reduction


Pearson coefficients


Softening temperature


The temperature of supply air


The temperature of the exhaust gases


The inlet water temperature in the exchanger


The outlet water temperature in the exchanger


Thermogravimetric analysis


The temperature with burning rate being equal to 0


Ignition temperature


The temperature with maximum burning rate


Tons of oil equivalent


The concentration in the dry flue gases


The concentration in the dry flue gases


Volatile matter


Primary air supply volume


Secondary air supply volume


The mass fraction of the i-th component in the fuel


The ratio between air mass flow and fuel feed mass flow


Stoichiometric air value


Air excess


Secondary to primary air flow ratio


Primary to total air flow ratio



This work was financially supported by Key Technologies R&D Program of Tianjin [18YFZCNC01410, 16YFZCSF00410], Natural Science Foundation of Tianjin [15JCQNJC15200], National Natural Science Foundation of China [21806082], and the Fundamental Research Funds for the Central Universities.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Center for Urban Transport Emission Research, State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention and Control, College of Environmental Science and EngineeringNankai UniversityTianjinChina
  2. 2.QES Department, Novozymes (China) Biotechnology LtdTianjinChina
  3. 3.Zachry Department of Texas A&M UniversityCollege StationUSA

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