Low temperature sulfur recovery

Vaporized elemental sulfur is recovered from a gaseous stream by cooling said stream in a first heat exchanger to condense elemental sulfur and then cooling said stream in a second heat exchanger to solidify the remaining elemental sulfur. The plugging of the heat exchanger is avoided by switching the operating conditions of the two exchangers and reversing the sequence of the flow through these two heat exchangers. The process and apparatus are especially useful in treating the tail gas and the intermediate streams in the Claus process or in the modified Claus process. Instead of reversing the flow, the plugging can be avoided by using two two-zone heat exchangers. One of the heat exchangers is operated to effect the condensation of elemental sulfur in the first zone and melting the solidified sulfur deposited in the second zone. The second heat exchanger is operated to effect condensation of sulfur in the first zone and solidification of sulfur in the second zone. The operating conditions in the second zones are continually reversed before the flow through the heat exchanger is restricted by solidified sulfur.