A Model based analysis in applying Anderson–Schulz–Flory (ASF) equation with CO2 Utilisation on the Fischer Tropsch Gas-to-liquid Process

Abstract

Abstract Industrial emissions of CO2 have observed a rapid increase since the industrial revolution and is accepted as a major contributor towards global warming. Despite the low market demand for the captured CO2, carbon capture and storage has not seen commercial deployment due to questions regarding economic feasibility. As such, carbon capture and utilisation (CCU) is considered as an alternative and commercially viable CO2 reduction approach, which can contribute effectively to the economy and environment. In CCU systems, captured CO2 is utilised as a feedstock in other processes which require CO2. This includes the synthesis of chemicals and materials such as Fischer-Tropsch Gas-to-liquid (GTL) production. The purpose of this paper is to evaluate the production of LPG, gasoline, diesel and wax using a Fischer-Tropsch (FT) GTL process model utilising mainly synthetic and captured CO2 as a raw material. The aim is to assess the effects of reforming methods, recycle ratio of syngas mixture on the process efficiency. The reforming unit of this study includes both; auto-thermal reforming (ATR) and steam-methane reforming (SMR), to form synthesis gas (syngas). Moreover, the application of the Anderson–Schulz–Flory (ASF) equation on the product distribution of FT synthesis is studied to investigate the growth probability of hydrocarbons (α) affected by CO2 utilisation. This GTL process is modelled using Aspen HYSYS software, and mainly includes a feeding unit, a reforming unit, an FT synthesis unit, upgrading and separation units and recycling units. The unreacted syngas mixture is recycled to the FT synthesis unit to enhance process efficiency and reduce the required amount of fresh feed. This work indicates that the optimal application of ASF with CO2 captured can increase the production rates of paraffin’s and olefins depending on the variation of α and H2/CO. Initial results demonstrated promising results for an SMR case with around 27% and 4% increase in CO and H2 production; respectively, when introducing CO2 with around 38% mass flowrate of natural gas. The ATR case demonstrated less potential with only 9% increase in CO production when introducing the same flow rate of CO2. The findings of this study include the effect of this increase on the production of fuel liquids such as gasoline and diesel and the optimization of ASF and H2/CO ratio when introducing the captured CO2. These results can have a positive impact on enhancing the overall process efficiency and reduce significantly the environmental impact.