(721b) Feasibility Study of Production of Methanol and Dimethyl Ether From Flare Gas

We studied the feasibility of effectively utilizing gas associated with oil production (APG), including the economics of producing methanol and dimethyl ether from APG. Detailed estimates indicate that the internal rate of return (IRR) of these processes is >10%, indicating potential for success.

  When crude oil is produced, APG comes to the surface from the oil reservoirs. In most cases, this APG is used as generator fuel onsite or transported by pipeline and sold elsewhere. However, in some areas far from gas markets, much of the APG is ignited and released into the atmosphere due to the high cost of constructing pipelines. In remote areas and/or at small-scale oil fields, it is difficult to recover construction costs through sales. Globally, APG comprises 150 billion m³/yr, equivalent to 25% of the USA’s gas consumption. CO₂ emissions due to flaring of APG are 400 billion tons/yr, equivalent to about 1.2% of global CO₂ emissions. CO₂emissions have serious consequences to the environment; thus, reducing the amount of APG flared at oil fields without using pipelines is a priority.

  Heavy hydrocarbons such as liquid petroleum gas (LPG) can be separated by cooling, compression, or absorption. Separated gases can be liquefied easily and transported by truck. Considering the cost of constructing a pipeline, we assumed that transporting the gas by truck was more feasible. If all of the APG could be separated and trucked, construction of a pipeline would not be needed. However, APG consists of light hydrocarbons, which are not easy to liquefy through physical phase changes. Thus, we considered chemical reactions to liquefy APG.

  Methanol and dimethyl ether are liquid chemicals produced from hydrocarbons. Methanol is used in the manufacture of various chemicals and liquid fuels and is globally in demand. On the other hand, the market for dimethyl ether is not currently large. However, it has the potential to increase, because dimethyl ether is expected to become a substitute for LPG. Accordingly, methanol and/or dimethyl ether could be manufactured from APG and trucked to market. We developed a process flow based on the concepts above and the actual conditions at one oil field. Production of methanol requires producing syngas from hydrocarbons through various possible reactions. We evaluated the production of syngas through steam reforming and partial oxidation. Thus, we considered the following four cases consisting of two reactions for producing syngas and two final products:

Case A: Methanol synthesis via syngas production by partial oxidation

Case B: Dimethyl ether synthesis via syngas production by partial oxidation

Case C: Methanol synthesis via syngas production by steam reforming

Case D: Dimethyl ether synthesis via syngas production by steam reforming

  We estimated the feasibility of these processes based on operating expenses, capital expenses, and the actual conditions at one oil field. The price of the ingredient gas was considered to be $0 US, because the chemicals are produced from the oil field’s own APG. The results of the economic analysis indicated that the IRR of these processes was >10% and thus they had the potential for success. Comparison of the four cases indicated that use of partial oxidation was superior to use of steam reforming for larger facilities, because the reactor for partial oxidation is smaller than that for steam reforming. Considering the IRR for dimethyl ether production, Case B or Case D may be successful depending on the size of the market. The comparison reveals the feasible conditions for each case. The effects of conditions and details of the process flow are discussed.