aNG = Natural gas.
bNMOG = Non-methane organic gases.
Source: ANL, Bechtel.
In this study, care was taken to identify power requirements within the fuel production facility. Compressors for gas circulation and oxygen plants require significant amounts of power. However, excess steam is still produced in some processes. FTD production results in more excess energy as the hydrogen to carbon content in the fuel is lower than that of methanol. After all power requirements in the production facility are taken into account, excess energy is provided a credit equivalent to electric power generation from natural gas. Essentially, a synthetic fuels facility can serve to coproduce fuel and electric power. Such designs have frequently been considered. The Coolwater coal gasification facility was almost converted to coproduce methanol and electric power in 1996.
Synthesis gas can also be produced through a partial oxidation (POX) process. Oxygen or air is reacted with natural gas to produce synthesis gas. The hydrogen to carbon ratio of the POX product gas is lower than that of a steam reforming process. An important advantage of the POX process is that the reforming process is simplified through direct contact of the POX products in the feed gas stream. Industrial POX processes generally use pure oxygen from an air separation plant; however POX operation with air is also possible. Operation on pure oxygen has the advantage of eliminating nitrogen from the gas stream. Nitrogen acts as a dilute that increases the requirement for compression recirculation, and catalyst volumes.
Steam reforming and POX plants can be combined as shown in Figure 4-2 or combination POX and steam reforming systems are also possible. Combining steam reforming and POX operation allows for the production of a synthesis gas that has an optimal ratio of hydrogen to CO to improve plant efficiency. The ratio depends on the fuel being produced and the process. Combined POX and steam reformer systems are referred to as autothermal reformers. (ATR).
4.5 Methanol Production from Natural Gas
Methanol was first produced by heating wood and distilling the products. In 1913, methanol was produced by passing CO and H2 over an iron catalyst. Currently, almost all of the methanol in the world is made by dissociating natural gas, primarily CH4, into CO and H2 with the addition of steam or oxygen (referred to as steam reforming or partial oxidation, respectively). Some CO2, CH4, and light hydrocarbons are also produced. This gas mixture produced through steam reforming or partial oxidation is called synthesis gas or syngas. Methanol is produced under pressure in a reactor