DYNAMIC INSTABILITIES OF TWO PARALLEL INTEGRAL SUPERHEATERS TO VAPORIZE NGL FEED TO OLEFINS CRACKING FURNACES

摘要

Cracking butane in ethylene furnaces requires that the liquid feed first be vaporized to a superheated temperature before being introduced into the olefins furnaces. Conventionally, superheating NGL liquid feeds was performed in a two-unit operation, namely, a kettle-type vaporizer unit to generate a saturated condition, followed by a superheater unit to achieve the desired degree of superheating. The vaporizer and the superheater are two separate units that are physically separated from each other and arranged in tandem. When vaporizing refinery butane streams, extensive fouling occurs in the kettle vaporizer due to heavy hydrocarbon fractions present in the refinery feed stream. A new methodology has recently been adopted to mitigate this problem, in which the two units were combined in one shell and tube-type heat exchanger, where the inlet liquid feed on the shell side is vaporized then superheated in one path. This method has been implemented to keep the full process stream flowing forward, thus reducing the tendency of fouling present in the kettle-type vaporizer.