This invention relates in general to heat exchangers, and in particular to a new and useful heat exchanger for operation at high gas temperatures and high jacket pressures, especially a cracked gas cooler tubular heat exchanger with a tube sheet at the gas inlet side and at the gas outlet side, and with heat exchange tubes arranged in graduated circles.
Tubular heat exchangers of this type include a cylindrical jacket that is sealed off by two tube sheets. The cooling tubes, through which the gas flows parallel to the axis of the jacket are, set into the tube sheets. The flow is around the cooling tubes from the outside. Vertical and horizontal heat exchangers are differentiated according to their positions.
The design of the tube sheets presents no particular difficulties. In cracked gas coolers, however, in which the gas inlet temperature is above 800.degree. C. and are subjected to jacket pressures of above 100 bar, the tube sheet on the gas inlet side becomes very hot and therefore has to be made extremely thin to keep the temperature stresses occurring in the sheet small, so that jacket cooling is guaranteed. The protective layer of magnetic forming on the water side during operation, which protects the steel to a great extent against further oxidation, must be retained. Care must therefore be taken that the deformations are kept within limits in spite of high stress to which the tube sheet is exposed, so that this protective magnetic layer is not destroyed.
In cracked gas coolers that have to operate under the aforementioned conditions, and which have been designed with very thin "hot" tube sheets because of the temperature stresses that occur, in order to be able to absorb the loads, tie bolts have been welded to the so-called hot tube sheet perpendicular to its central plane. The bolts are distributed uniformly over the tube sheet surface in tube gases passing through, which were fastened at the other end to very rigid cross bars that are supported on appropriately heavy duty forged rings on the tank jacket.
The so-called cold tube sheet of the cracked gas cooler had thick walls corresponding to its loads. Design calculation on this basis is very tedious.