Abstract
Many potential diversification and conversion options are available for utilization of natural gas resources, and several design configurations and technology choices exist for conversion of natural gas to value-added products. Therefore, a detailed mathematical model is desirable for selection of optimal configuration and operating mode among the various options available. In this study, we present a simulation-optimization framework for the optimal selection of economic and environmentally sustainable pathways for natural gas downstream utilization networks by optimizing process design and operational decisions. The main processes (e.g., LNG, GTL, and methanol production), along with different design alternatives in terms of flow-sheeting for each main processing unit (namely syngas preparation, liquefaction, N2 rejection, hydrogen, FT synthesis, methanol synthesis, FT upgrade, and methanol upgrade units), are used for superstructure development. These processes are simulated using ASPEN Plus V7.3 to determine the yields of different processing units under various operating modes. The model has been applied to maximize total profit of the natural gas utilization system with penalties for environmental impact, represented by CO2eq emission obtained using ASPEN Plus for each flowsheet configuration and operating mode options. The performance of the proposed modeling framework is demonstrated using a case study.
Highlights
Many potential diversification and conversion options are available for utilization of natural gas resources
Hydrogen is produced in three main steps: (i) Syngas preparation using steam reforming of natural gas, which accounts for more than half of the worldwide hydrogen production [26,27]; (ii) Water-shift reaction where CO reacts with steam producing hydrogen, CO2, and some impurities such as unconverted CH4 and CO; (iii) Separation where CO2 is removed using alkanolamines via chemical absorption producing hydrogen-rich gas purified via pressure swing adsorption (PSA)
We first present some of the results from the simulation analysis with Aspen Plus to illustrate the yield values we used for the key production units, and the results of the overall framework when we focus on a single product (e.g., liquefied natural gas (LNG), gas to liquids (GTL), or methanol) at a time
Summary
Many potential diversification and conversion options are available for utilization of natural gas resources. The utilization system that we consider in this work includes three main natural gas conversion options: LNG, GTL, and methanol. We propose a superstructure design approach through rigorous simulation, modeling, and optimization of natural gas downstream utilization network considering several technology alternatives and operating modes for the considered processing units. The main unique features of this work are as follows: It analyses different production processes namely LNG, GTL, and methanol along with different design alternatives for each of the main processing units. It considers both the maximization profit to reflect the economic perspective, and minimization of CO2 emission to reflect the environmental perspective.
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