Biomass Conversion and Biorefinery

, Volume 9, Issue 1, pp 99–116 | Cite as

Impact of adhering soil and other extraneous impurities on the combustion and emission behavior of forest residue wood chips in an automatically stoked small-scale boiler

  • Thomas ZengEmail author
  • Daniel Kuptz
  • Kathrin Schreiber
  • Claudia Schön
  • Fabian Schulmeyer
  • Volker Zelinski
  • Annett Pollex
  • Herbert Borchert
  • Achim Loewen
  • Hans Hartmann
  • Volker Lenz
  • Michael Nelles
Original Article


Within six case studies, different drying and sieving process steps were employed for the removal of adhering soil and other extraneous impurities from wood chips. Consequently, it was systematically investigated to which extent this strategy can be used to jointly mitigate the risk of bottom ash slagging and high pollutant emission levels during combustion in an automatically stoked small-scale boiler. Throughout all combustion tests, slag and emission formation were recorded. Formation of agglomerates in the bottom ash was not observed in the fuel bed. However, fuel processing resulted in an increase of the ash shrinking–softening range up to 230 K indicating a lower slagging risk in the bottom ash. An asymptotic trend for the ash melting temperatures was observed as a function of the molar (Si + P + K)/(Ca + Mg) ratio. It was also found that potassium is less efficiently retained in the bottom ash with lower Si content in the fuel. Lower moisture contents in the wood chips typically resulted in lower CO emissions and higher boiler efficiencies for the investigated range of moisture content. The sieving of the unprocessed wood chips reduced NOx emission levels up to 28%. However, fuel processing did not necessarily reduce the level of particulate matter emissions.


Wood chip Combustion Emission Sieving Drying Ash agglomeration 



As received


Dry basis


Detrital/authigenic index


Ash deformation temperature (°C)


Processed wood chips (i.e., end product)


ENplus is an international acknowledged wood pellet certification scheme which was established in 2011. ENplus introduced quality classes and stronger requirements to those set by the European and international product standards for solid biofuels.


Ash flow temperature (°C)


High pressure liquid chromatography


Ash hemisphere temperature (°C)


Unprocessed wood chips (i.e., raw material)


Standard deviation


Ash shrinkage starting temperature (°C)


Standard temperature and pressure (i.e., 293.15 K and 1013 mbar, respectively)


Total particulate matter [mg/m3]


Volume percent


Weight percent



Boiler efficiency (%)


Specific heat capacity for water (kJ/(kg K))


Net calorific value on as received basis (MJ/kg ar)


Net calorific value on dry basis (MJ/kg db)


Energy input of the fuel during the combustion test (kW)


Heat transferred to the water heating circuit during the combustion test (kW)


Consumed fuel mass (kg/s)


Water mass flow (kg/s)


Auxiliary energy consumed during the test (kW)


Water return temperature (K)


Water outlet temperature (K)


Maximum measurement uncertainty.


Water return temperature from the heat circuit into the boiler (K)


Average moisture content of the fuel determined out of three analyses per combustion test (wt%)



The work presented here was funded under grant agreement numbers 22031814, 22035714, 22035814, and 22005815 of the Agency for Renewable Resources (Fachagentur Nachwachsende Rohstoffe e.V., FNR) in the name of the German Federal Ministry of Food and Agriculture (BMEL) on the basis of a resolution of the German Federal Parliament. Funds have also been received from the Federal Ministry of Food and Agriculture (BMEL) based on a decision of the Parliament of the Federal Republic of Germany via the Federal Office for Agriculture and Food (BLE) under the innovation support programme. Special thanks go to our colleagues from the Bundesverband Bioenergie e. V. (German Federal Association of Bioenergy, BBE). The contribution of the industrial partners is gratefully acknowledged.

Supplementary material

13399_2018_368_MOESM1_ESM.docx (60 kb)
ESM 1 (DOCX 36 kb)


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Copyright information

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

Authors and Affiliations

  • Thomas Zeng
    • 1
    Email author
  • Daniel Kuptz
    • 2
  • Kathrin Schreiber
    • 3
  • Claudia Schön
    • 2
  • Fabian Schulmeyer
    • 3
  • Volker Zelinski
    • 4
  • Annett Pollex
    • 1
  • Herbert Borchert
    • 3
  • Achim Loewen
    • 4
  • Hans Hartmann
    • 2
  • Volker Lenz
    • 1
  • Michael Nelles
    • 1
    • 5
  1. 1.DBFZ Deutsches Biomasseforschungszentrum Gemeinnützige GmbH (DBFZ)LeipzigGermany
  2. 2.Technologie- und Förderzentrum im Kompetenzzentrum für Nachwachsende Rohstoffe (TFZ), Solid Biofuels DepartmentStraubingGermany
  3. 3.Bavarian State Institute of Forestry (LWF)FreisingGermany
  4. 4.Faculty of Resource ManagementUniversity of Applied Sciences and Arts (HAWK)GöttingenGermany
  5. 5.Faculty of Agricultural and Environmental Sciences, Chair of Waste ManagementUniversity of RostockRostockGermany

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