(563b) Optimal Production of Light Olefins from "Wet" Shale Gas: An Integrated NGL Cracking and Dry Gas Reforming Approach
High levels of natural gas production that stemmed from the shale gas industry lowered this feedstock price significantly . Therefore, 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 . In some wet shale plays, the combined ethane and propane composition can exceed 30% . These recent trends motivate industrial effort to build several new ethane crackers with a combined ethylene production capacity of 12.5 million tonnes/year in the United States .
Light olefins including ethylene, propylene, and butene isomers are valuable petrochemical intermediates and make up two-thirds of the petrochemicals market . These olefins can be produced from alternative feedstocks such as biomass and natural gas via thermochemical conversion and reforming . However, extraction of NGLs prior to methane conversion is an opportunity for refineries to maximize carbon conversion and avoid high reforming costs. A demethanizer column is utilized [5,6] to recover more than 83% of ethane and more than 99% of higher hydrocarbons in the NGL stream. The NGLs can be cracked or further separated for C3 and C4 dehydrogenation processes. A rigorous mathematical model is developed for the hydrocarbon cracker using the well-established cracking kinetics in the literature [7,8]. Dry gas is converted via reforming or direct conversion processes introduced into a process superstructure [4,9]. The light olefins are produced and purified to product quality with an extensive superstructure that considers multiple production, conversion, and purification technologies.
The process superstructure that is developed 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 and dry gas conversion plant. A techno-economic 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 for various NGL compositions.
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