Karagoz, Secgin (2014-08). Process Design, Simulation and Integration of Dimethyl Ether (DME) Production from Shale Gas by Direct and Indirect Methods. Master's Thesis.
Thesis
As the energy demand is increasing constantly, sustainable energy resources are needed to meet this demand and enable economic stability. In order to attain this goal, researchers continue to develop new technologies and methods in the field of sustainable energy. Over the last decade, the U.S has witnessed substantial growth in shale gas production. Consequently, shale gas has become a competitive feedstock for usage as energy and production of chemicals and petrochemicals.
A valuable product which may be obtained from shale gas is dimethyl ether (DME). Dimethyl ether can be used in many areas such as power generation, transportation fuel, and domestic heating and cooking. Dimethyl ether is currently produced from natural gas, coal and biomass through synthesis gas as an intermediate. Recently, the attention to DME has increased because of its potential in addressing energy security and environmental problems.
DME is produced conventionally through two steps (indirect process) which are methanol synthesis and dehydration of the methanol to DME. Another way to produce DME is the direct synthesis of DME from syngas. In order to use DME as a fuel alternative, it must be produced at low cost in large quantities. The purpose of this study is to develop a process synthesis, simulation, and integration of a shale gas-to-DME plant by direct and indirect methods. Techno-economic analysis is carried out to assess the profitability of the base-case processes under current market conditions. A sensitivity analysis is also conducted to evaluate the process profitability under variable market conditions. Finally, the both methods are compared in terms of the fixed capital cost, operating cost, return on investment, and CO_(2) and water impact.
Indirect and direct process simulation of commercial DME plant was carried out by Aspen Plus. The shale gas feedstock was taken from one of the wells in Barnett shale play. The DME production capacities of the base cases for the direct and indirect processes were set to 3,250 tonnes per day. The direct and indirect process flowsheets were synthesized using five and seven main processing steps, respectively. Pinch analysis was used to conduct heat integration of the process. As a result of study, it was found that the direct method has advantage over the indirect method in terms of the fixed capital cost, operating cost, return on investment, and CO_(2) impact.
The capital investment of the direct production method is 25% less than the indirect method. The direct method is more economically attractive than the indirect method. When a sensitivity analysis is considered, the prices of methanol and shale gas are the most important factors impacting the operating cost. The contribution of energy integration on the ROI of the direct method is approximately 2.25%. The ROI of the indirect method is improved by 1.83% after energy integration. In contrast to the other criteria, the indirect way has significant advantage over the direct way by producing almost 1760 ton/d water. The direct method produces less CO_(2) emission than the indirect method because it uses dry reforming to convert CO_(2) to syngas.
