(66b) Higher Productivity by Using the New Grade Sandvik ΑPMT as Radiant Tube in Ethylene Cracking Furnaces

Abstract. The Sandvik grade Kanthal®APMT has properties that provides ethylene producers with increased flexibility regarding how to utilize their furnaces in the most economical way. ? Long production runs before decoking ? High conversion conditions possible, less need for recycling ? Increased feed rates and improved production yields ? Lower operating costs Obtaining longer run length between decoking and operating the ethylene furnaces at higher temperatures are major challenges for the ethylene producers in order to improve their productivity. Depending of the feed stock, ethane or naphtha, the selected furnace tube material can be of major importance to obtain longer run lengths.

In the case of ethane feed stock, catalytic coke formation is the dominant coke forming mechanism and material selection then becomes important in order to prevent coke formation. Besides the ability to prevent coke formation, carburization resistance and high temperature strength are properties that must be regarded in order to reach increased productivity and less maintenance.

Kanthal®APMT is an alumina forming FeCrAl alloy that shows excellent properties when it comes to prevent coke formation and carburization. Conventional FeCrAl-alloys suffer from relatively poor mechanical properties at elevated temperatures which limits the use of the alloys in highly stressed components.

However, powder metallurgy, in form of mechanical alloying and rapid solidification from melt has been shown to offer effective means to bypass this weakness. Kanthal®APMT is an advanced example of application of rapid solidification to introduce dispersion strengthening in FeCrAl to allow the use of the material in highly stressed components at high temperature.

High temperature mechanical data, coke formation resistance and carburization properties are presented and discussed in relation to other alloys.

Results from up to 2.5 years cracking service in commercially operated furnaces are reviewed and joining techniques are discussed.