Subject: Agglomeration, defluidisation and their countermeasures for biomass combustion in fluidised beds

Speaker: Professor Hao Liu,University of Nottingham, U.K.

Abstract: In this study, the combustion of pelletised problematic biomass fuels (wheat straw and miscanthus) was investigated in a 20 kWth bubbling fluidised bed (BFB) combustor using quartz sand as the bed material. The combustion profiles were established for the two fuels at the bed temperature above 820  ？C with regards to the combustion temperature distribution, pressure variance and defluidisation time. The mitigation of bed agglomeration and defluidisation was investigated by the addition of 1.5 wt% lime to fuel, the addition of 5 wt% dolomite and 5 wt% of molochite to bed materials respectively. All the additives successfully maintained the combustion temperature at 900 ？C for both fuels.
The defluidisation time was significantly extended by over 14 times via adding lime to fuel which provided a continuous on-site agglomeration counter action. 5% wt addition of dolomite to the bed material extended the defluidisation time for both fuels by ca.6 times for straw and 2 times for miscanthus. The use of molochite as bed additive doubled the defluidisation time for miscanthus combustion but did not affect that of straw combustion.The impacts of the oxy-fuel combustion atmosphere on the performance of bed additives were investigated by using the synthetic oxidiser of 30 vol% O2 and 70 vol% CO2. The experimental results indicated that the CO2-rich atmosphere significantly hindered the performance of dolomite as a bed material additive on the defluidisation time due to the restrained decomposition of dolomite which resulted in less CaO in the bed to counter the formation of K-rich sticky molten phases.
Ash fusion tests were conducted on an ash fusibility furnace with fuel ashes with and without the additives and the results were used to better understand the fuel ash melting process and the effect of additives on the agglomeration and defluidisation behaviour observed with the BFB tests.

Time: 13:30-14:50 pm, August 16, 2019 (Friday)

Location: 1010 Meeting Room, Energy Saving Building

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