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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
  • 133 Downloads

Abstract

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.

Keywords

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

Abbreviations

AFTs

Ash fusion temperatures

BE

Boiler efficiency

C

The carbon content in the pellet

CE

Combustion efficiency

Cpmd

The dry flue gases specific heat

CpmH2O

The water vapor specific heat

Cpw

Calorific capacity of liquid water

Cr

The unburned carbon content passing through ash

DT

Deformation temperature

DTG

Derivative thermogravimetric

FC

Fixed carbon

FT

Flow temperature

H

The hydrogen content in the pellet

HHV

Higher heating value

HT

Hemisphere temperature

LHV

Lower heating value

M

The moisture content in the pellet fuel

MBB

Medium-scale biomass boiler

PC

The heat power content in the fuel

PM

Particulate matter

PN

The heat power gain of water in the exchanger

Qa

The thermal heat loss

Qb

The unburned gaseous heat loss

Qcomb

The pellet mass flow

Qr

The unburned carbon heat loss

Qw

The mass flow of water in the heat exchanger

SBB

Small-scale biomass boiler

SCO

Selective catalytic oxidation

SCR

Selective catalytic reduction

SNCR

Selective noncatalytic reduction

r

Pearson coefficients

ST

Softening temperature

Ta

The temperature of supply air

Tg

The temperature of the exhaust gases

Tin

The inlet water temperature in the exchanger

Tout

The outlet water temperature in the exchanger

TG

Thermogravimetric analysis

Th

The temperature with burning rate being equal to 0

Ti

Ignition temperature

Tmax

The temperature with maximum burning rate

toe

Tons of oil equivalent

VCO

The concentration in the dry flue gases

VCO2

The concentration in the dry flue gases

VM

Volatile matter

Vp

Primary air supply volume

Vs

Secondary air supply volume

Yi

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

α

The ratio between air mass flow and fuel feed mass flow

αst

Stoichiometric air value

ε

Air excess

λ

Secondary to primary air flow ratio

λtotal

Primary to total air flow ratio

Notes

Acknowledgements

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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