Completed Research
Techno-Economic Assessment of Fischer-Tropsch and Direct Methane To Methanol Processes In Modular GTL Technologies
Gustavo Santos, MS, 2016
(Thesis: University of Pittsburgh ETD)
In 2014, about 3.5% of the global gas production was flared, of which 0.289 TCF were in the US alone. This increase of natural gas flaring in the US has been exacerbated by the drilling and fracking activities in the shale gas plays. Improper flaring of natural gas leads to emissions of methane and other organic volatile compounds, sulfur oxides (SOX) and carbon dioxide (CO2). In fact, by 2020 the total gas volume flared is projected to be up to 60% greater than that in 2000, which is problematic. Thus, there is a great and pressing need for curbing or eliminating the flared natural gas and fugitive methane from remote reservoirs in order to protect the environment and avoid global warming.
This study aims at investigating the potential use of the Fischer-Tropsch (F-T) synthesis process, in a microchannel reactor (MCR), and the Direct Methane to Methanol (DMTM) process in a compact plant footprint for curbing or eliminating natural gas flaring. The two processes were modeled using the process simulator Aspen HYSYS v7.2 and their operational and economic performances were evaluated in terms of the products yield, net present value (NPV), payback period (PBP) and internal rate of return (IRR). In addition, the effects of tailgas and methane recycle ratios on these process performances are investigated.
The simulation results showed that the unit cost of the DMTM process was very sensitive to the methane recycle ratio, however, that of the F-T in MCR was less sensitive to the tail gas recycle ratios. In order to maintain an IRR > 10%, which is the minimal acceptable value, the tail gas recycle ratio for the F-T in MCR had to be greater than 8 and 30%, at CO conversions of 80% and 72%, respectively, whereas for the DMTM process, a minimum methane recycle ratio of 60% was required to achieve any profitability. In addition, the DMTM process appeared to have significantly higher net energy requirements per product yield when compared with those of the F-T in MCR process; however, both processes had higher energy requirements than those of conventional GTL technologies.