Plant-Wide Modeling, Techno-Economic Analysis and Optimization of the Shale-Gas to Dimethyl Ether (DME) Process Via Direct and Indirect Synthesis Route

Due to the uncertainty in supply and prices of petroleum-based fuels, various alternative, clean fuels are being investigated. Dimethyl ether (DME) is a potential alternative to petroleum-based fuel because it is non–toxic, eco- friendly, has minimal particulate emissions, and has properties similar to LPG and diesel with a very high cetane number (55- 60)¹. DME can be produced from a variety of feed stocks like coal, biomass, natural gas, and shale gas via direct or indirect synthesis route. Studies have shown that direct synthesis route has a higher DME production compared to indirect synthesis route. Currently, majority of the DME is produced commercially from coal via indirect synthesis route in the Asia-pacific region. However, in the United States, shale gas is available in abundance and seems to be a more attractive feedstock. Very limited studies are available in the open literature on techno-economic evaluation and optimization of shale gas-to-DME process via direct and indirect synthesis routes. The focus of this presentation will be on the process synthesis, economic evaluation, and optimization of the shale gas-to-DME process via direct and indirect synthesis in a multi-software environment.

In this study, plant-wide models for shale gas-to-DME synthesis processes via direct and indirect routes are first developed in Aspen Plus V8.4^®. Kinetic models of the pre-reforming reactor, autothermal reforming reactor and DME synthesis reactors are developed and validated with the experimental data. For acid gas removal (AGR), two technologies, namely the Rectisol and MDEA/PZ technologies, are evaluated. A novel DME separation process that can efficiently separate DME, syngas and CO₂ has been developed. Binary interaction parameters for the vapor liquid equilibrium (VLE) model of the methanol-CO₂, DME-CO₂, DME-H₂O and DME-CO mixtures are regressed using the experimental data. Aspen Energy Analyzer V8.4^® is used to design an optimal heat exchanger network by pinch analysis and the heat exchangers are sized rigorously using Aspen Exchanger Design and Rating V8.4^®. The modeled equipment is mapped using the Icarus database in Aspen Process Economic Analyzer V8.4^® (APEA) and economic evaluation is performed. An optimal design of the process is obtained by maximizing the Net Present Value (NPV) by using a multi-software platform comprising of Matlab, Microsoft Excel, Visual Basic, Aspen Plus, and APEA.

To summarize, the presentation will focus on the following aspects:

• Synthesis of the plant-wide models for DME synthesis following direct and indirect routes
• System level energy analysis of shale gas-to-DME production processes for varying H₂/CO ratio, CO₂ capture rate, and AGR technology
• Uncertainty analysis due to the raw materials price, product price and scale of the plant
• Optimal design of the process by maximizing NPV

References

Ogawa, T.; Inoue, N.; Shikada, T.; Inokoshi, O.; Ohno, Y. Direct Dimethyl Ether (DME) Synthesis from Natural Gas. Studies in Surface Science and Catalysis Natural Gas Conversion VII, Proceedings of the 7th Natural Gas Conversion Symposium. 2004, 379–384.