3.4. GTL fuel scenarios
Bio gas upgrading and syngas production are two common stages in GTL fuel scenarios. In the present study, bio gas upgrading was assumed to be performed by a chemical scrubber based on an activated methamphetamine (MDEA) system, with an electricity requirement of 0.12–0.14 kWh/Nm3 UG and a heat requirement of 0.55 kWh/Nm3
UG [2]. The chemical scrubber was chosen since the surplus heat generated in the GTL scenarios can be utilized. Methane emissions related to the chemical scrubber are 0.2 g CH4/kWh UG [32]. Upstream of the scrubber unit, an activated carbon filter is used for removing the bulk of the H2S, while traces of H2S are removed in the chemical scrubber. The resulting bio methane is reformed to syn gas by the steam reforming method, modeled here as Gibbs free energy reactors. The steam re- former is externally heated by burning part of the feed. The burner was modeled as a combustion reactor in Aspen Plus setup to provide the energy required in the steam reformer. Temperature in the steam reformer was set to 800 °C and with a pressure drop of 1 bar. After reforming, the gas contains H2, CO, CO2, nitrogen gas (N2) and water va- pour (H2O). To set the ratio between CO and H2 for synthesizing the fuel, CO is shifted with H2O to H2 in the water–gas shift reaction (Eq. (1)).