Technoeconomic analysis of biorefinery based on multistep kinetics and integration of geothermal energy

摘要

In this work, 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 conversion platform that converts 2,000 metric tons of corn stover per day into biofuels via gasification. Geothermal heat is utilized in the biorefinery to generate process steam for gasification and steam-methane reforming. 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. Process steam at 150 ºC with a flow rate of approximately 16 kg/s is assumed to be generated by utilizing the heat from geothermal resources producing a geothermal liquid at 180 °C and a total flowrate of 105 kg/s. In addition to the use for gasification and steam-methane reforming, additional geothermal capacity at 100 kg/sec from multiple wells is used for electricity production via Organic Rankine Cycle to add to the profitability of the biorefinery. 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 $5.18 to $5.50 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.In the other part of the study, the simulation of biomass gasification is carried out using multistep kinetics under various oxygen-enriched air and steam conditions. The oxygen percentage is increased from 21% to 45% (by volume). Five different kinds of biomass feedstocks including pine wood, maple-oak mixture (50/50 by weight), seed corn, corn stover, and switchgrass are used in this study. The bed temperature is maintained at 800 oC. Different conditions such as flowrates of biomass and different oxygen-enriched air and steam ratios are used to simulate different cases. The simulation results for different species are in good agreement with the experimental data.. From the results, it is evident that the proposed gasification kinetics model can predict the syngas compositions. The model is able to capture the effects of biomass feedstock and oxygen and steam concentrations. The model is able to predict the concentrations of H2, CO, CO2, H2O, CH4, N2 in the syngas; nonetheless, more rigorous simulation has to be carried out to model NOx, NH3, and other higher alkane and alkenes such as C2H4, C2H2, C2H6 etc.