Technoeconomic Analysis of Biofuel Production and Biorefinery Operation Utilizing Geothermal Energy

Abstract

A technoeconomic study is conducted to assess the feasibility of integrating geothermal energy into a biorefinery for biofuel production. The biorefinery is based on a thermochemical platform that converts low-value lignocellulosic biomass into biofuels via gasification and fuel reforming. Geothermal energy is utilized in the refinery to generate process steam for gasification and steam-methane reforming in addition to providing excess electricity via the organic Rankine cycle. A process simulation model is developed to simulate the operation of the proposed biorefinery, and corresponding economic analysis tools are utilized to predict the product value. The biorefinery uses 2000 metric tons of corn stover per day, and the products include gasoline, diesel fuel, hydrogen, and electricity. Implementation of geothermal energy into the proposed biorefinery is analyzed through two studies. In the first study, process steam at 150 °C with a flow rate of approximately 16 kg/s is assumed to be generated through a heat exchanger process by utilizing the heat from geothermal resources, producing a geothermal liquid at 180 °C and a total flow rate of 105 kg/s which is used to provide steam for gasification and steam-methane reforming within the biorefinery. In the second study, additional geothermal capacity of 204 kg/s is assumed to be available and is separated into two phases (liquid and steam) via a flash column. The steam produced is utilized in the same manner as the initial study while the geothermal liquid is used for electricity production via the organic Rankine cycle to add to the profitability of the biorefinery. This analysis considers that the technology is feasible in the near future with a high scope of technology development and the end products are compatible with the present fuel infrastructure. The total capital investment, operating costs, and total product values are calculated considering an operating duration of 20 years for the plant, and the data are reported based on the 2012 cost year. Simulation results show that the price of the fuel obtained from the present biorefinery utilizing geothermal energy ranges from $5.17 to $5.48 per gallon gasoline equivalent, which is comparable to $5.14 using the purchased steam. One important incentive for using geothermal energy in the present scenario is the reduction of greenhouse gas emissions resulting from the combustion of fossil fuels used to generate the purchased steam. Geothermal energy is an important renewable energy resource, and this study provides a unique way of integrating geothermal energy into a biorefinery to produce biofuels in an environmentally friendly manner.