As shown in Fig. 2(b), major operations in this area include zinc
oxide/activated carbon gas polishing, syngas booster compression,
steam methane reforming (SMR), WGS, pressure swing adsorption
(PSA), FT synthesis, FT product separation, and unconverted syngas
recycle (Swanson et al., 2010).
Appropriate pretreatment must be taken so that the syngas
entering FT synthesis contaminants below 200 ppb sulfur and
10 ppm ammonia at a pressure of 25 bar (Spath and Dayton,
2003). First, a zinc oxide and activated carbon gas polishing is used
to polish sulfur and trace contaminants. The zinc oxide catalyst
cost is assumed to be 4.67 dollar per pound with a catalyst density
of 64 pound per cubic feet, and the catalyst replacement cycle is
3 years (Swanson et al., 2010). Next, the syngas stream is compressed to 25 bar in syngas booster compression unit.
Experimental data indicate that there is a significant amount of
methane and ethane in the syngas stream in the low temperature
bio-oil gasification scenario. Thus, a SMR is utilized to reduce those
components. As mentioned, a WGS unit is included to adjust syngas H2 =CO ratio to just above the optimal value for FT synthesis.
After that, PSA is used to provide hydrogen for the hydroprocessing
section. Next, the syngas reacts over a cobalt-based catalyst in a
fixed-bed FT reactor at 200 C. The Anderson–Schulz–Flory alpha