Transfer Line Exchangers (TLX) in olefin cracking furnaces: reliability, different design combinations and cock formation

Mehdi Yosefinejad¹ Bahare Akbari² Atieh khorami³ Ali Noushad⁴ Keyvan Mokhtari⁵

1) 1. Sharif university of technology, chemical engineering department, Azadi Ave.Tehran, Iran
2) Iran university of science and technology, chemical engineering department, Tehran, Iran
3) Razavi Khorasan Gas Company, Mashhad, Iran
4) Bandar Imam Petrochemical Company, Mahshahr, Iran
5) ilam petrochemical company, ilam, Iran

Publication : 2nd. International Congress on science & Engineering - paris(parisconf.com)
Abstract :
Ethylene is the basic product for the fabrication of plastics. Ethylene (C2H4) and some other byproducts like propylene are produced by thermal cracking of hydrocarbons in pyrolysis furnaces in the presence of steam. Predominantly ethane, naphtha and other mineral oil fractions are used as feedstocks. The gas produced by cracking, which leaves the furnace at a temperature of around 850 °C, must be cooled down rapidly (quenching) after leaving the reaction zone of the furnace to prevent secondary reactions and to stabilize the gas composition in order to obtain the optimum product yield. In all modern ethylene processes this rapid cooling of the cracked gas is done with Transfer Line Exchangers (also known as quench coolers or TLEs) thereby producing high pressure steam. Product gas (typically at 775–885 °C) exits the furnace and is cooled in an Ultra-Selective Exchange (USX) followed by a Transfer Line Exchanger (TLE) to prevent side reactions There are one or more parallel TLEs per furnace cell, which are connected by riser and down comer piping with one common, elevated steam drum thereby forming the so called quench system. The transfer-line exchangers with commercial importance are the Borsig exchangers (shell-and tube and a double pipe closed coupled linear exchanger), Alstom (multi double pipe and a double pipe linear exchanger), the Shaw USX exchanger and the KBR exchanger (similar to the USX). The objectives of this paper are to present the fundamentals of transfer line exchangers in olefin plant, to introduce transfer line exchangers design and their arrangement in different licensor to discuss their effects on production yield, coil outlet temperature(COT), residence time, coke formation and product distribution
Keywords : olefin cracking furnace transfer line exchanger TLX USX coke