Process for reducing thermal shock in fluidized bed stem coils cycled in and out of service

摘要

The invention provides an improved method and apparatus for operating a fluidized bed chemical processing unit of the type having steam generating coils, so as to reduce the occurrence of thermally-induced stresses in the coils and thereby extend the useful life of the coils. The invention involves causing the tube wall temperature of a coil being brought into service to be lowered from bed temperature prior to initiating water flow in the coil, so as to decrease the thermal shock temperature gradient and thereby reduce the magnitude of thermally-induced stress in the coil. The invention utilizes a base coil in addition to the steam generating coil that is being cycled, and a pair of steam drums which operate at a pressure differential. The method involves generating saturated steam in the base coil and superheating the saturated steam in the coil being brought on line. Steam is directed from one drum to the other in a predetermined manner so as to provide proper temperature control of the coil being cycled.