| 摘要 |
A system to produce ethylene includes, in one embodiment, separately cracking a heavy hydrocarbon feed and a lighter feed, cooling the latter product in a transfer-line exchanger before admixture with the former product and cooling the mixed product in a transfer-line exchanger. Both exchangers are preferably a novel transfer-line exchanger that has a construction including a vertical tank, with a cylindrical intermediate portion and conical bottom entrance and top exit end portions, tube sheets at the top and bottom ends of the intermediate portion of the tank, vertical tubes extending between the tube sheets and in alignment with openings in the tube sheets. The tubes extend downwardly through the lower tube sheet with their ends at openings in a conical shield that is supported in the entrance conical portion of the tank by the tubes or by the conical entrance portion of the tank. The lower tube sheet has an opening to pass steam into the chamber between that sheet and the shield or steam is introduced into that chamber through the wall of the conical entrance portion of the tank and through the shield. The construction provides egress of steam from this chamber to the entrance end of the tubes below the conical shield for mixture with product to be cooled. When using the novel transfer-line exchanger, the system can provide the cooling of the product from the steam-cracking of the heavier feed without prior admixture with cooled product from the steam-cracking of lighter feed.
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