PURPOSE: To make heat transfer of a heat transfer tube excellent, to decrease contamination of the inside face of the heat transfer tube and to enable to evaporate main components of the feed stream in the upstream side of the inlet of a vacuum distillation tower by increasing an inner diameter of the heat transfer tube and an inner diameter of a connecting conduit by respective specific values along the lengths.
CONSTITUTION: The inner diameter of the heat transfer tube 27 of the heating furnace 2 increases by 2.4-3 times the inner diameter of the tube inlet 28, and also the inner diameter of a connecting conduit 3 to the vacuum distillation tower 1 increases by 2.5-5.4 times the inner diameter of the tube outlet 29 along the lengths in the directions of the flows of respective fluids. Thus, a portion of the feed stream evaporates in the heat transfer tube 27 but since a liquid portion is always present on in the heat transfer tube 27, and excellent heat transfer is surely performed between the inner face of the heat transfer tube 27 and the feed, hot spots on the inner wall surface of the heat transfer tube 27 decrease and portions changing the feed stream to cokes decrease, then a contamination quantity decreases. Also while the inner diameter of the connected tube 3 gradually increases, a liquid portion of the feed is evaporated in the connecting conduit 3, then a large volume of the feed stream becomes vapor.
KORUNERISU YOZUA FUAN DERU BUR
DEIRUKU KANBIEERU
PIITERU FUAN DERU HEIDEN
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