Comprehensive environmental impact assessment of a combined petroleum coke and natural gas to Fischer-Tropsch diesel process

Abstract

In this study, a well-to-wheels life cycle assessment was conducted to determine the environmental impacts from disposing of petroleum coke by converting it into liquid fuel. Specifically, this work is an extension of the life cycle assessment of the petcoke standalone gasification to diesel study which also includes two new pathways for converting petroleum coke and natural gas to Fischer Tropsch diesel operated with and without carbon capture and sequestration (CCS). Impact categories were calculated using the EPA’s TRACI 2.1 US-Canada 2008 midpoint method in SimaPro software. In addition, the impact of grid emissions on the overall process was assessed using two representative Canadian locations with high (Alberta) and low (Ontario) grid emissions. The results of each impact category were compared among the designs and against conventional petroleum and oil sands derived diesel. Key findings showed that the proposed designs when operated with CCS in the low-emissions-grid location had life cycle GHG emissions between 281–291 gCO2-eq/km compared to the conventional petroleum and oil sands derived diesel with GHG emissions of 305 and 348 gCO2-eq/km respectively. Nevertheless, the various tradeoffs between processes indicated that there was no clearly superior design among the candidates. However, the design which uses a natural gas reformer that is integrated directly into the radiant syngas cooler of a petcoke gasification unit has the lowest cost of CO2 avoided ($144/tCO2-eq), and so is likely the best choice for reducing environmental impacts.