In fluidised-bed heat exchangers, it is necessary to achieve as effective a recirculation as possible of solid particles entrained in the rising tubes in the medium to be treated. It is the object of the invention to use simple structural means to provide a production engineering device favourable in terms of cost for the effective and reliable recirculation of solid particles in conjunction with a simultaneous improvement in the heat transfer characteristics. This object is achieved by respectively providing the return tubes used to return the solid particles with a restrictor. The device according to the invention is successfully used wherever there is a need to heat up a medium which forms crusts and a layer of dirt. <IMAGE>
