462457 Shale Gas to Light Olefins: Global Optimization of an Integrated NGL Recovery, Steam Cracking, and Methane Conversion Superstructure

Tuesday, November 15, 2016: 2:05 PM
Monterey II (Hotel Nikko San Francisco)
Onur Onel1,2,3, Alexander M. Niziolek1,2,3 and Christodoulos A. Floudas1,2, (1)Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX, (2)Texas A&M Energy Institute, Texas A&M University, College Station, TX, (3)Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ

Due to the decreased prices of natural gas in recent years [1], production of “wet” gas that contains natural gas liquids (NGLs), such as ethane, propane, butane, and natural gasoline, is favorable to extract for commercial purposes [2]. In some wet shale plays, the combined ethane and propane composition can exceed 30% [3]. These recent trends motivate industrial efforts to build several new ethane crackers with a combined ethylene production capacity of 12.5 million tonnes/year in the United States [4]. Although the NGLs can be effectively used as petrochemical feedstocks toward light olefins, the optimal processing technology (catalytic and/or thermal), feed composition (mixed feed or a pure feed), and operating conditions are unknown.

Previous work has shown that light olefins including ethylene, propylene, and butene isomers can be produced from natural gas via reforming in a profitable manner out of a superstructure of process alternatives [5]. However, extraction of NGLs prior to methane conversion is an untapped opportunity for these refineries that can simultaneously maximize carbon conversion and avoid high reforming costs. This NGL recovery section is introduced to the existing superstructure of novel/competing process alternatives. A demethanizer column is utilized [6,7] to recover more than 83% of ethane and more than 99% of higher hydrocarbons in the NGL stream. The NGLs can be further separated and sent to steam cracking or catalytic dehydrogenation alternatives. Several steam cracking reactors incorporate a pure or mixture of hydrocarbon feed to produce olefins. The operating conditions and reactor topologies of the steam cracking alternatives are dynamically optimized using the well-established cracking kinetics in the literature [8,9]. Catalytic dehydrogenation process alternatives incorporate commercially available catalysts for propane and/or isobutane dehydrogenation. The methane rich gas from the demethanizer is converted via reforming or direct conversion processes introduced into the process superstructure [5].

The mathematical model of the overall process superstructure is solved using a novel branch and bound global optimization framework. The objective is to maximize the profit of light olefin production from the integrated NGL extraction, cracking, catalytic dehydrogenation, and methane conversion refinery. A technoeconomic analysis will be presented with major topological decisions across several case studies. Different natural gas compositions will be shown to present the topological trade-offs in the NGL recovery section. The net present values can be significantly improved (>10%) through the use of the integrated superstructure.

[1]: Floudas, C. A.; Niziolek, A. M.; Onel, O.; Matthews, L. R. Multi-scale systems engineering for energy and the environment: Challenges and opportunities. AIChE Journal 2016, 62 (3), 602-623.

[2]: Kopalek, M.; High value of liquids drives U.S. producers to target wet natural gas resources, 2014, Energy Information Administration

[3]: Hill, R. J.; Jarvie, D. M.; Zumberge, J.; Henry, M.; Pollastro, R. M.; Oil and gas geochemistry and petroleum systems of the Fort Worth Basin, 2007, AAPG Bulletin, 91(4), 445-473.

[4]: Chang, J.; New projects may raise US ethylene capacity by 52%, PE by 47%, 2014, ICIS Petrochemicals.

[5]: Onel, O.; Niziolek, A. M; Floudas, C. A Optimal Production of Light Olefins from Natural Gas via the Methanol Intermediate. Industrial & Engineering Chemistry Research 2016, 55 (11), 3043-3063.

[6]: Luyben, W. L.; NGL Demethanizer Control, 2013, Industrial and Engineering Chemistry Research, 52, 11626-11638.

[7]: Luyben, W. L.; Effect of Natural Gas Composition on the Design of Natural Gas Liquid Demethanizers, 2013, Industrial and Engineering Chemistry Research, 52, 6513-6516.

[8]: Sundaram, K. M.; Froment, G. F.; Modeling of thermal cracking kinetics – I: Thermal cracking of ethane, propane and their mixtures, 1977, Chemical Engineering Science, 32(6), 601-608.

[9]: Sundaram, K. M.; Froment, G. F.; Modeling of thermal cracking kinetics – II: Cracking of iso-butane, of n-butane, and of mixtures ethane-propane-n-butane, 1977, Chemical Engineering Science, 32(6), 609-617.

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