Carburization of High-Temperature Alloys during Steam Cracking: The Impact of Alloy Composition and Temperature

Abstract

Prior studies found that the carburization tendency is negligible for technically developed materials at temperatures below 900 °C, especially for Al-containing alloys compared to non-Al-containing alloys applied in steam cracking reactors. However, it is unclear whether this benefit remains at higher temperatures. This work compared coke deposition tendencies of recently developed alloys to each other and to a conventional material when cracking ethane at a higher temperature (950 °C) than previously reported. Under the studied experimental conditions, coking rates vary in the range of 1.22 × 10 −6 to 20.5 × 10 −6 kg/(m 2 • s) for Al-containing alloys, while for non-Al-containing alloys, coke deposition rates fall in a range of 4.95 × 10 −6 to 33 × 10 −6 kg/ (m 2 •s). In general, aluminum-containing alloys showed less coke formation and improved stability against aging after five cracking cycles compared to the non-aluminum-containing materials. The results also showed that substantially less, if any, carburization could be detected in developed alloys even at high temperatures, in contrast to the results from a reference conventional alloy of 27/ 34 Cr−Ni. At higher temperatures, the protective oxide surface layer of the Al-containing alloys remained noticeably durable and integrated with negligible spallation compared to the ones of non-Al-containing alloys. In fact, the 27/34 Cr−Ni alloy showed the highest coking rate and carburization, implying the most vulnerable oxide surface layer relative to the other alloys. However, energydispersive X-ray (EDX) results showed no signs of carburization or deterioration of the surface of 27/34 Cr−Ni after experiments at 880 °C, indicating that both the temperature and matrix composition can play significant roles in determining the suitability of an alloy for application in steam crackers.

Effect of Reactor Alloy Composition on Coke Formation during Butane and Ethane Steam Cracking

“…The Al-Boosted, demonstrated higher resistance to coke formation compared to the aluminum-free alloys, Spinel-Coated and 35/45 Cr–Ni. This finding aligns with previous experimental studies on ethane steam cracking, ,, which also highlighted the superior fouling resistance of Al-containing alloys.…”

“…As shown in Section , the preoxidation step was not performed with the Spinel-Coated alloy because the alloy is already preoxidized during the manufacturing process. These results show that additional preoxidation might be needed for this alloy, as well …”

“…EDX mapping analysis performed on the cross-sectional area of Al-Boosted after five cracking cycles with ethane and butane feeds illustrates why the amount of coke and the catalytic coking rate are lower for this alloy than for the other nonaluminum materials. Carbon did not diffuse into the bulk, and no evidence of internal oxidation was observed, a detrimental phenomenon in cracking of aluminum-containing alloys that results in poor resistance to carburization . The integrity of the alumina layer formed during preoxidation is still visible after several coking/decoking cycles, indicating the excellent resistance of this alloy to carburization.…”

“…Carbon did not diffuse into the bulk, and no evidence of internal oxidation was observed, a detrimental phenomenon in cracking of aluminum-containing alloys that results in poor resistance to carburization. 38 The integrity of the alumina layer formed during preoxidation is still visible after several coking/decoking cycles, indicating the excellent resistance of this alloy to carburization. This thin (ca.…”

Carburizing Rate of Pyrolysis Furnace Tube in Long-term Service

“…Causes of pyrolysis furnace failure include carburization, creep, high-temperature oxidation, thermal fatigue, thermal shock, and other damage. Failures caused by carburization are especially common [1][2][3][4]. The statistical results of the investigation of ethylene pyrolysis furnace tube failure in Japan [5] showed that more than half of pyrolysis furnace tube damage was caused by carburization pyrolysis.…”