Performance study and validation of the downdraft biomass gasification process for combined heat & power plants from under-utilised biomass and bio–waste

  • Oisin De Priall

Student thesis: Doctoral Thesis


Improved energy generation methods are required to guarantee sustainable energy sources for the future. Gasification technology allows for waste and low-quality biomass materials to be converted into a producer gas, which can in turn be utilised in a CHP system for sustainable heat and electricity generation. To improve the downdraft gasification process, blends of biomass materials were investigated for their impact on process parameters such as producer gas lower heating value, conversion efficiency, tar production and producer gas application processes. This work was carried out through a combination of experimental and simulation analysis.

Novel work analysing agricultural residues such as poultry litter and anaerobic digestate, along with the bioenergy crop miscanthus showed improvement in gas lower heating value when using blended feedstocks. From previous feedstock blending literature, the blending ratios of interest were identified as 80/20, 60/40 and 40/60 by weight percentage, with wood pellets the blending feedstock introduced. Small–scale experimental analysis was carried out on the Fluidyne downdraft gasification system in Ulster University, using the results collected to validate the computational simulations generated with ECLIPSE simulation software.

Experimental results from the blended feedstocks displayed improvements up to 12.9% in producer gas lower heating value, from the 24% increase in carbon content of the feedstock after the introduction of wood pellets. Increases in the combustible portion of the producer gas led to a 6.1% improvement in thermal efficiencies along with 2.5% increase in electrical efficiency of the simulated CHP process. A cradle to grave life cycle assessment carried out using SimaPro software to evaluate the environmental impact that blending feedstocks for downdraft gasification and the application process had showed improvements in environmental impacts when compared to traditional energy generation methods. Further ECLIPSE software was used to carry out the techno economic analysis of the process and using financial indices to evaluate the impact of blends, decreases in net present value, break even selling price and payback period were found due to the purchasing cost of the wood pellet feedstock.
Date of AwardMay 2022
Original languageEnglish
SupervisorCaterina Brandoni (Supervisor) & Ye Huang (Supervisor)


  • Biowaste
  • Energy from waste
  • Synthesis gas

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