(564e) Process Intensification of Biogas to Liquid (BGTL) Processes: A Techno-Economic Study

Benard Nyawanga*, Ahmed Naqi (co-author), Babu Joseph, and John Kuhn

Department of Chemical and Biomedical Engineering, University of South Florida.

*Presenting author. Email: nyawanga@mail.usf.edu , Tel : (954)632 0931

ABSTRACT

Industrial conversion of biogas to liquid fuel has been a subject of study for some time now. In current technology, biogas is converted into liquid fuel through two major steps: tri-reforming step to produce syngas (a mixture of CO and H2), and Fischer-Tropsch Synthesis (FTS) step to convert the syngas to a spectrum of hydrocarbons [1]. Separation and upgrading of the produced hydrocarbon mixture allows production of synthetic transportation fuels. Currently efforts are underway to create catalysts that can convert biogas directly to liquids in a single reactor. The objective of this paper is to compare the process economics of such an intensified process with the current two step BGTL process.

A detailed modeling of the two-step process is carried out using ASPEN Plus process design software package. Data for the process is based on literature, combined with laboratory results on the biogas to liquid conversion process. The current commercial diesel prices is used to evaluate the potential revenue from selling the product in the open market. The total capital investment to construct the plant with a capacity of handling 100,000 ton per year of wet biomass is $16.2 million with a potential of producing 2.60 million gallons of diesel [2].Corn stover is used as the biomass, which is then converted into biogas through anaerobic digesters. The annual operating cost to run the plant is estimated to be $8.81 million [3]. An annual revenue from selling the diesel product is estimated to be $14.6 million taking into account a green energy incentive of $3.00/gallon of diesel sold. The net present worth at the end of the plant life is $8.76 million with a discounted cash flow of return of 26.2%. The breakeven cost of diesel is determined to be $4.34/gallon assuming no tipping fees are charged for handling the waste [3].

The major challenge of the Industrial two steps method is the cost of production. In this process, there is considerable energy demand from the reformer. FTS produces energy but it is not enough possible to recycle this energy due to the low operating temperature of the FTS unit. The reformer operates at higher temperatures (~1073 K) and lower pressure (~3 bars) while the FTS reactor operates at lower temperature (~700 K) and higher pressure (~10 bars). In the proposed intensified process, both the reformer and the FTS are combined into a single reactor. This way, an average optimal temperature and pressure conditions can be used in the presence of a novel catalyst. The combined process will be modeled using ASPEN Plus software and economic analysis will be done in order to estimate the feasibility of a such a process. A comparison between this new process and the two step process will be done to determine the potential payback from an intensified process.

• Williams. Bioenergy Conversion Technologies. Madison, WI: University of Wisconsin. Accessed Date:02/18/2018.Available:http://www.wgbn.wisc.edu/conversion/bioenergy-conversion-technologies
• EIA. (2018). Weekly Retail Gasoline and Diesel Prices. Accessed Date: 02/10/2018. Available: https://www.eia.gov/dnav/pet/pet_pri_gnd_dcus_nus_m.htm.
• A. Naqi, “Conversion of Biomass to Liquid Hydrocarbon Fuels via Anaerobic Digestion: A Feasibility Study” Masters of Science in Chemical Engineering M.S. Thesis, Department of Chemical and Biomedical Engineering, University of South Florida, Tampa, Florida, 2018.