Heat exchange apparatus and process

A process wherein a process fluid is subjected to a heat exchange step and then a processing step comprising feeding a process fluid to a process fluid feed zone separated from a heat exchange zone by dividing means, passing said process fluid from said process fluid feed zone through a plurality of heat exchange tubes extending through said heat exchange zone wherein said process fluid is subjected to heat exchange with a heat exchange medium in said heat exchange zone, passing the process fluid from said heat exchange tubes to a process fluid off-take zone separated from said heat exchange zone by second dividing means, subjecting the process fluid from said process fluid off-take zone to said processing step, and passing the resultant processed process fluid through the heat exchange zone as the heat exchange medium, said heat exchange tubes being fastened to one of said dividing means and, for each heat exchange tube, there is provided a seal tube fastened to the other of said dividing means, each seal tube being disposed substantially coaxially with its associated heat exchange tube such that each seal tube is in sliding engagement with its associated heat exchange tube thereby defining an overlapping region where the heat exchange and seal tubes overlap one another whereby thermal expansion of the heat exchange tubes can be accommodated within the overlapping region, the inner tube of said heat exchange tube and its associated seal tube being provided with (i) an interior constriction of reduced cross sectional area forming, within said inner tube and said overlapping region, a low pressure region, (ii) an expansion region, within said inner tube, of cross sectional area greater than that of the constriction downstream of said low pressure region, and (iii) one or more passages through the wall of the inner tube connecting said low pressure region to the exterior of the inner tube, said passages being located within said overlapping region thereby providing a flow path for fluid from the heat exchange zone through said overlapping region into said low pressure region within said inner tube, said process being operated such that the pressure of the processed process fluid fed to the heat exchange zone is greater than the pressure in the low pressure region, whereby part of the processed process fluid fed to the heat exchange zone passes through said overlapping region and said passages into said low pressure region.