Heat transfer in the external heat exchanger of oxy-fuel fluidized bed boilers
Artikel i vetenskaplig tidskrift, 2014

The external heat exchanger (EHE) plays an essential role in the adequate control of the heat balance in large-scale oxy-fuel circulating fluidized bed (CFB) boilers. However, the EHE of an oxy-fuel CFB presents two particularities compared to the known air-combustion case: the composition of the fluidizing gas and the higher flow of recycled solids. Both these issues are addressed in this paper: Firstly, heat transfer coefficients are measured in a 90 kW bubbling fluidized bed, operated at different temperatures, with air and with a wide range of O-2/CO2 mixtures. Thereafter, experiments are also carried out in a cold scaled-down EHE in order to assess the influence of an increment in the solids flow across the EHE on heat transfer. Based on the results of these experiments, an expression for the heat transfer coefficient is proposed which accounts for gas composition and solids flow rate. Finally, a model for the EHE is integrated into a large oxy-fuel CFB model in order to quantify the influence of oxy-fuel operation mode on the heat transfer surfaces required in the EHE.


cfb boiler

enriched atmosphere

horizontal tube


loop seal


particle migration


Irene Bolea

Research Centre for Energy Resources and Consumption

Luis M. Romeo

Research Centre for Energy Resources and Consumption

David Pallarès

Chalmers, Energi och miljö, Energiteknik

Applied Thermal Engineering

1359-4311 (ISSN)

Vol. 66 1-2 75-83





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