Evaluation and extension of the load and fuel flexibility limits of a stratified downdraft gasifier

Angelika Michaela Zachl*, Markus Buchmayr, Johann Gruber, Andres Anca-Couce, Robert Scharler, Christoph Hochenauer

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The small-scale biomass gasifiers' application for CHP in conventional households is still inhibited by their inflexible operating conditions, which do often not meet the user's desires of yielding varying loads and switching between any available fuels. Thus, the present work aims to identify the gasifier's flexibility limits by investigating sudden steps in load and fuel water content in a woodchips-driven, stratified downdraft gasifier with a 90-kW nominal fuel load. In contrast to former work, the focus was set on the transient processes, during which the product gas composition and the gasifier bed temperatures were continuously monitored. The evaluations revealed that the gasifier produces a continuously high and almost load independent product gas quality in the range of ±20% of the nominal load, even throughout sudden load changes. Steps of 8 m% fuel water content from dry to wet fuel turned out to be the maximum manageable step size without additional measures. Switches from wet to dry fuel required the previously introduced methods of exhaust gas recirculation and water injection. These methods successfully enlarged the allowable step to over 8 m% fuel water content. These promising results will allow a future more versatile and user-optimized operation of stratified downdraft gasifiers.
Original languageEnglish
Article number122279
Number of pages12
Issue numberPart D
Publication statusPublished - 15 Jan 2022


  • Biomass downdraft gasification
  • Flexibility limits
  • Fuel water content variation
  • Load variation
  • Transient operation

ASJC Scopus subject areas

  • Mechanical Engineering
  • Pollution
  • Energy Engineering and Power Technology
  • Energy(all)
  • Electrical and Electronic Engineering
  • Industrial and Manufacturing Engineering
  • Management, Monitoring, Policy and Law
  • Building and Construction
  • Fuel Technology
  • Renewable Energy, Sustainability and the Environment
  • Civil and Structural Engineering
  • Modelling and Simulation

Fields of Expertise

  • Sustainable Systems


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