Technoeconomic analysis of a low CO2 emission dimethyl ether (DME) plant based on gasification of torrefied biomass

Two models of a dimethyl ether (DME) fuel production plant were designed and analyzed in DNA and Aspen Plus. The plants produce DME by either recycle (RC) or once through (OT) catalytic conversion of a syngas generated by gasification of torrefied woody biomass. Torrefication is a mild pyrolysis process that takes place at 200–300 °C. Torrefied biomass has properties similar to coal, which enables the use of commercially available coal gasification processing equipment. The DME plants are designed with focus on lowering the total CO2 emissions from the plants; this includes e.g. a recycle of a CO2 rich stream to a CO2 capture plant, which is used in the conditioning of the syngas. The plant models predict energy efficiencies from torrefied biomass to DME of 66% (RC) and 48% (OT) (LHV). If the exported electricity is included, the efficiencies are 71% (RC) and 64% (OT). When accounting for energy loss in torrefaction, the total efficiencies are reduced to 64% (RC) and 58% (OT). The two plants produce DME at an estimated cost of $11.9/GJLHV (RC) and $12.9/GJLHV (OT). If a credit is given for storing the CO2 captured, the future costs may become as low as $5.4/GJLHV (RC) and $3.1/GJLHV (OT).