Abstract
This study quantifies the cost of cellulosic sugar production using a fully-mechanical pretreatment process and fuel pellets as a co-product. The pretreatment reduces softwood forest harvest residuals to micron-sized amorphous particles. Energy consumption is minimized using a three-stage milling process. A techno-economic analysis was completed for a milling facility with saccharification and wood pellet manufacture. For the base case, concentrated sugar syrup can be produced for $0.496/kg of sugar. Sensitivity analyses were used to determine cost controlling variable, optimize the sugar cost and found that siting for this technology needs to strongly consider electricity cost and to a lesser extent local feedstock availability. If the sugar produced in this process is used to generate biofuel and is qualified for RIN credits through a life-cycle analysis, the effective cost could be reduced by $0.04-$0.06/kg of sugar. An additional $0.067/kg savings is possible if the biofuel facility is located adjacent or on-site; the finished sugar syrup would not have to be concentrated for transportation. An optimized scenario, including the RIN credit, dilute sugar syrup, and favorable energy costs and consumption, could reduce the cost to $0.34/kg sugar compared to $0.496/kg for the base case.
Highlights
Conversion of non-food lignocellulosic material into clean sugars or transportation fuels has been widely studied, with researchers citing abundant and low-cost feedstocks
The current paper examines the economics of a mechanical pretreatment process that uses three stages of milling to produce clean feedstock for saccharification
The final product is called micronized wood and is transferred to the saccharification department to be processed into a concentrated sugar syrup; the lignin residuals are manufactured into fuel pellets
Summary
Conversion of non-food lignocellulosic material into clean sugars or transportation fuels has been widely studied, with researchers citing abundant and low-cost feedstocks They present caution regarding lower yields and more difficult processes, especially with high lignin feedstocks (Piccolo and Bezzo, 2009; He and Zhang, 2011; Dutta et al, 2015). Pretreatment before a bioconversion process is required to disrupt the intricate hierarchical structures, thereby allowing enzymes access to the cellulose and hemicellulose for saccharification (Cadoche and López, 1989; McMillan, 1994; Sun and Cheng, 2002; Zhu et al, 2008) Disrupting this crystalline microstructure is difficult and requires complex, high-cost pretreatment options (Mosier et al, 2005; Crawford, 2013; Zhang et al, 2013; MYPP BETO, 2016). These compounds are toxic to the fermentation organisms and their removal adds cost to the process
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