In-situ monitoring of agglomeration and defluidisation in a biomass FB combustor (Scientific Council Collaboration Fund)

UKCCSRC Scientific Council Collaboration Award winners, Hao Liu (University of Nottingham) and Gang Lu (University of Kent), have completed the visualisation and characterisation of agglomeration and defluidisation in a biomass FB combustor.

Given the UK 2050 targets, and the significant roles that bioenergy and CCS are expected to make, it is vital that the UK quickly develops its bioenergy technologies with CCS (BECCS). In fluidised bed boilers burning biomass, whether under conventional air combustion or oxy-combustion conditions, agglomeration and defluidisation is a particular concern. Biomass fuels often contain high levels of alkali and alkaline metals (AAMs) which can interact with bed materials to form low melting point potassium-rich silicates, that can adhere to the bed material particles.

Under the UKCCSRC Scientific Council Collaboration Award, research teams at the University of Nottingham and the University of Kent conducted an experimental study on a 20kWth biomass-fired BFB (bubbling fluidised bed) combustor to investigate the fluid dynamic characteristics of biomass fuels and bed materials, as well as the formation process of agglomerates through digital imaging and signal/image processing. The Kent’s flame imaging system was modified and installed on the Nottingham’s BFB combustor for visualising burning biomass particles on the bed surface. Rig operation data, including pressure drops and furnace temperature, were collected under a range of operation conditions.

Kent’s flame imaging system installed on Nottingham’s fluidised bed biomass combustion test facility

The results obtained suggested that there is a strong correlation between the defluidisation/agglomeration and the pressure drop across the combustion bed zone. In particular, the rate of the pressure drop change can potentially be a better indicator for severe agglomeration/defluidisation in the combustor. It has also been proven that digital imaging is a promising technique for visualising the combustion behaviours of biomass particles and bed materials inside the BFB combustor. The findings of the research have led to an improved understanding of the fundamental aspects of biomass combustion in BFB combustors, and thus the energy conversion, agglomeration formation and defluidisation process.

Despite being severely disrupted by the COVID-19 pandemic and several unavoidable non-cost extensions to the completion date, the results obtained indicate clearly that the project teams have achieved the proposed research objectives and measurable outputs. More comprehensive data processing is in progress in order to quantify the combustion behaviours of different biomass materials (e.g. colour, and spectral intensities of biomass flames) under different operating conditions. A technical paper has been planned to report the research results with a reputable journal such as Fuel, Biomass and Bioenergy in the near future.


Prof Hao Liu, Faculty of Engineering, University of Nottingham, email:

Dr Gang Lu, School of Engineering, University of Kent, email: