Evaluation of bed-to-tube heat transfer in a fluidized bed heat exchanger in a 75 MWth CFB boiler for municipal solid waste fuels

•Heat transfer has been investigated for a fluidized bed heat exchanger in a Circulating Fluidized Bed.•Analysis is based on historical data for several years of operation with waste-derived fuels.•Two different heat exchanger designs and two different bed materials are investigated.•It is found that heat transfer coefficient varies over season and is lower than expected.•Tube fouling, bed agglomeration and poor mixing are identified as contributing factors.