State-of-the-art of Coke Formation during Steam Cracking: Anti-Coking Surface Technologies

Abstract

Although steam cracking is a mature technology, mitigation of coke formation remains one of the main challenges in the petrochemical industry. To increase the olefin output of existing plants, coil materials that can withstand higher temperatures are desired. This work reviews material technologies that were developed and tested in the past three decades to minimize the rate of coke deposition and extend the furnace run length. The material not only determines the mechanical properties of the coil but also affects the coking rate substantially. In some cases, differences in coking rates by more than a factor 10 have been observed. SiC materials could be operated at significantly higher temperatures, and this leads to higher olefin selectivity if one includes acetylene hydrogenation; however, the mechanical joints make it currently impossible to take advantage of their superior temperature resistance. On the industrial scale, operational improvements have been reported with advanced reactor surface technologies such as high-performance alloys and coatings during the past decade. Catalytic coatings go a step further than barrier coatings by actively removing coke that is deposited on the coils. Another trend is to add aluminum to the coil material, which forms a protective aluminum oxide layer on the reactor wall during operation and results in reduced carburization. To optimize the coking mitigation capabilities of the coils, the state-of-the-art materials and/or coatings should be combined with 3D reactor technologies, which is not always possible for all materials because of the advanced machining that is needed.

Alumina-based Coating for Coke Reduction in Steam Crackers

“…To restrain this financial loss, numerous "anti-coking" technologies have been introduced and suggested in the industrial arena of steam cracking, frequently categorized in various groups: three-dimensional (3D) reactor technologies [9][10][11][12][13][14][15], feed additives [16][17][18][19][20][21][22][23][24] and surface technologies [25][26][27][28][29][30][31]. Surface technologies [18], and in particular coatings, have been claimed to completely solve the coking problem.…”

“…To date, several barrier coatings have been introduced for steam cracking reactors [25,[32][33][34][35]. The performance of an Al/Si barrier coating that is applied in a two-step chemical vapor deposition process and suppress the total amount of coke up to 90% for ethane cracking and up to 80% for naphtha cracking using as reference material HP 40 was commercialized as AlcroPlex ® and evaluated by Zychlinski et al [32].…”

Influence of Sulfur and Water Vapor on High-Temperature Oxidation Resistance of an Alumina-Forming Austenitic Alloy

“…Alumina-forming alloys are known to be stable at higher temperatures than chromia-forming alloys, especially under water vapor conditions [5 -7]. A first patent has been published in 1981 for an alloy based on HP grade [8], but the development was stopped due to creep resistance problems [9]. Better understanding of creep mechanisms in Al-containing austenitic stainless alloys up to 1000-1050°C [10] has contributed to develop a new generation of alloys for steam cracking applications.…”

Effect of Phosphine on Coke Formation during Steam Cracking of Propane

“…The olefins leaving the tubular reactor are quickly degraded by secondary reactions. In order to prevent this, the products are quenched to temperatures of around 550 °C in 0.02–0.1 s [ 4 , 5 , 6 , 7 , 8 ]. Due to the high temperature of the reactor material, the industrial standard is Fe-Ni-Cr alloys, which has high creep and heat-resistant properties.…”