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The proposed design utilizes 750,000 metric dry tons per year of woodchip biomass obtained from the local sawmill and forestry industries. The woodchips are processed and dried before being fed to a gasification system. The gasifiers produce a hydrogen-rich syngas, which is routed through a monoethanol amine (MEA) absorption section to remove the coproduced CO2. The syngas then enters a novel microchannel reactor where the equilibrium between the synthesis gas, methanol, and dimethyl ether results in a high overall conversion and efficient heat removal. Conversions were modeled using recent experimental data from PNNL. The DME product is removed from the reactor effluent using a water absorption tower and separated from the water via distillation. The DME and methanol byproduct are then routed to another reactor section where propylene, ethylene, and other hydrocarbon byproducts are produced. This reactor section was designed with near 100% feed conversion. Propylene and ethylene are separated from the other effluents to be sold as products. The byproduct hydrocarbons are routed back to a steam cracking reactor to form additional propylene and ethylene, which are also feed to the separation train.
145,000 metric tons per year of propylene and 35,000 metric tons per year of ethylene are produced. An initial total permanent investment of $525 million is required, as well as annual fixed and variable costs amounting to $62 million. The project has an NPV of $88 million at a 15% discount rate and an IRR of 17.5%.
The materials handling and gasification sections of the project require large initial investments and continuing operating and maintenance expenses. The project is sensitive to the price and availability of biomass, requiring further detailed siting and supply contracts. The economics of this plant are compared to the economics of a traditional methanol-to-olefin (MTO) process.
Date Posted: 24 July 2012