Management

Test caseLower olefins, primarily ethylene, propylene, and butadiene are produced by pyrolysis of hydrocarbon feedstock within furnace tubes in the presence of steam. The amount of olefins that this process yields depends on feedstock composition and pyrolysis conditions.

2. Steam does not participate directly in the pyrolysis reactions but acts as an inert diluent. The steam reduces the hydrocarbon partial pressure and this promotes higher yields of the lower olefins. Reduction of hydrocarbon partial pressure also retards coke formation on the interior surfaces of furnace tubes and this reduces fouling of downstream quench coolers and carburization of equipment.

3. A small amount of steam is normally converted to carbon oxides, (CO and CO2) by non-pyrolytic coke gasification reactions that take place at the surface of coke deposits in the equipment.

4. The pyrolysis process has been the most widely used for commercial production of lower olefins in the last 50+ years. During this time, the process has been continuously developed and optimized by many contractors and operating companies. This has resulted in a wide range of furnace designs. All of them use the same basic principles to produce lower olefins.

5. Pyrolysis of hydrocarbons to produce high yields of lower olefins is a highly endothermic process requiring a high rate of heat transfer to sustain it. The process is sustained by the generation of free radicals and a propagation of chain reactions that require that temperatures above approximately 1000°F, (538°C) be maintained.

6. To selectively produce lower olefins by pyrolysis, the residence time above approximately 1000 °F is minimized so that primary thermal decomposition reactions are favoured and secondary recombination reactions are minimized. This is done by very rapid heating of the feedstock and steam mixture to temperatures above 1400°F, (760°C) followed by rapid quenching to non-reactive temperatures.