Heat exchanger for rapid cooling of gas - which is fed up water:cooled tubes which are periodically de:coked by steam under conditions minimising thermal shock

摘要

The vertical exchanger has a bottom inlet and a top outlet for gas, and a bottom boiling chamber connected by a bundle of tubes to a top boiling chamber; both chambers are made of thin plates, Inside each tube is a coaxial tube through which the gas flows upwards; whereas a coolant, e.g. pressurised water, flows up the annular gap between tubes. The bundle of double tubes is surrounded by a thermally-insulating casing. The exchanger is pref. used in conjunction with a cracking furnace, and steam or steam and air are periodically fed up tubes at max. 750 deg.C to remove coke which has deposited inside tubes. The coolant is removed from tubes to control the temp. of the decoking operation, which may be simultaneously employed for decoking the cracking furnace. Thermal stresses on the tubes are reduced.