Abstract: A heat exchanger 10 comprises a pressure vessel 14 having a feed inlet 11 in an upper part thereof for particulate material to be subjected to heat exchange and an outlet 13 at a lower part thereof for the outflow of particulate material from the vessel 14. A plurality of heat exchange elements, such as heat exchange plates 12, arranged in spaced relationship inside the pressure vessel 14 to define flow passages between adjacent heat exchange elements 12 is provided for particulate material to flow therethrough under the force of gravity. The pressure vessel 14 has an inside wall extending around the heat exchange elements 12 and further comprises a trap, such as a baffle 22, between the heat exchange elements 12 and the inside wall for trapping particulate material leaking from the flow passages between the heat exchange elements 12 to form a gas barrier 26 between the heat exchange elements 12 and the pressure vessel 14.