Abstract: A shell-and-tube apparatus, more specifically, a shell-and-tube reactor, which includes a vessel, at least one intermediate tube plate sectioning the interior of the vessel into at least two compartments having different temperatures, a number of heat transferring tubes penetrating the intermediate tube plate or plates, and a fluid passing through the tubes which is heated or cooled by a heat transfer medium surrounding the tubes. At least one insulation plate or plates are provided on one or both sides of the intermediate tube plate so that the space between the intermediate tube plate or plates and, if two or more insulation plates are used, the space or spaces between the insulation plates may be utilized as a stagnation zone for the heat transfer medium, so as to make the temperature gradient through the intermediate tube plate or plates gentle and relax the thermal stress occurring in the body wall.