Cracking tube having helical fins

Abstract

A cracking tube (50) for use in thermal cracking furnaces for producing ethylene or the like has fins (1) formed on an inner surface thereof and inclined with respect to an axis of the tube for stirring a fluid inside the tube. The fins are arranged discretely on one or a plurality of helical loci, and the tube inner surface has regions (ZB) wherein no fins are present over the entire axial length of the tube from one axial end of the tube to the other axial end thereof.

Description

TECHNICAL FIELD [0001] The present invention relates to cracking tubes for use in thermal cracking reactors for producing ethylene or the like, and more particularly to a cracking tube which is provided on the inner surface thereof with fins for stirring the fluid therein and which is adapted to suppress pressure losses to the greatest possible extent while effectively promoting heat transfer to the fluid therein. BACKGROUND ART [0002] Olefins such as ethylene, propylene or the like are produced by thermally cracking material gases of hydrocarbons (naphtha, natural gas, ethane, etc.). The thermal cracking reaction is conducted by introducing the hydrocarbon material gas and steam into a cracking coil disposed within a heating furnace supplied with heat from outside, and heating the mixture to a reaction temperature range while the mixture flows through the coil at a high velocity. [0003] Typically, the cracking coil comprises a plurality of (straight) tubes which are connected into ...

AI Technical Summary

Benefits of technology

[0013] The tube of this construction is adapted to minimize the pressure loss of the fluid inside the tube while permitting the helical fins to transfer heat to the inside fluid with a high efficiency.

Problems solved by technology

If the gas is heated at a high temperature over a prolonged period of time, lighter fractions of hydrocarbons (methane, free carbons, etc.) will be produced in excessive amounts or the product of cracking will undergo, for example, a polycondensation reaction to reduce the yield of the desired product.

Promoted coking (deposition of free carbon on the tube inner wall) will also result to lower the coefficient of heat transfer, giving rise to a need to perform decoking frequently.

These examples have a great effect to stir the fluid within the tubes and are highly efficient in heat transfer to the fluid within the tubes, whereas the internal pressure of the fluid inside the tubes builds up owing to a great pressure loss of the fluid, entailing the drawback that the cracking operation produces ethylene, propylene or the like in a lower yield.

However, the fins positioned in parallel to the tube axis fail to produce a sufficient effect to stir the fluid inside the tubes and to achieve the desired heat transfer performance.

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