Fluidized Catalytic Cracking to Convert Biomass to Fuels

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Senior Design Reports (CBE)
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Biochemical and Biomolecular Engineering
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Boust, Stephen
Green, Mo
Machi, Serena

The process of biomass fluidized catalytic cracking (BFCC) has been adapted from the traditional fluidized catalytic cracking of crude oil in petroleum refineries. Instead of a naphtha feedstock, BFCC can accommodate various types of biomass that is cracked into more valuable aromatic and olefinic compounds. This plant inputs forest biomass and will be located in southwestern Louisiana, where wood output exceeds 100 million kg/yr in over ten counties. Biomass, procured in the form of wood chips, must first be dried to a moisture content below 10 wt% and crushed to a particle size of 100-500 micron. The wood sawdust is then fed to a circulating fluidized bed riser, where it undergoes catalytic fast pyrolysis (CFP) in the presence of a ZSM-5 catalyst. CFP occurs at a high temperature of 600 °C, producing an effluent syngas composed of aromatics, olefins, and volatiles. The biogas is separated from water and volatiles, produced by deoxygenation processes, in a three phase pressure vessel. The more valuable products of benzene, toluene, and xylenes are then separated from the high-boiling components. The proposed design converts 400,000 metric tons of wood to 17.4 million kilograms of a BTX mixture per year, including 4.6, 7, and 3.3 million kilograms per year of benzene, toluene, and xylenes, respectively. In addition, 345 GWh of electricity is produced yearly as a byproduct. The required total permanent investment for this project is $93 MM. At a discount rate of 10% and BTX sale price of $1.1/kg, the base case net present value (NPV) is $(157 MM) and the expected ROI is -20%. The result of this base case analysis suggests that this project should not be further pursued. The best case scenario assumed double the yield of BTX at a sale price of $1.54/kg and a renewable fuel credit of $1.01/gal, resulting in a NPV of $506 MM, an IRR of 70%, and a ROI of 81 %. The economic feasibility of this project is also sensitive to the availability and price of biomass, as well as the catalyst degeneration rate within the system.

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