Techno-Economic Aspects of Biomass Hydrolysis Process
The majority of current cellulosic ethanol pilot plants and commercial-scale operations under construction around the world are based on the aqueous-phase biomass hydrolysis process described in Part 2 of this book. Evidently, these investments are based on a series of techno-economic analysis of the aqueous-phase biomass hydrolysis path to cellulosic ethanol. The most noticeable publication is the May, 2011, NREL report titled, "Process Design and Economics for Biochemical Conversion of Lignocellulosic Biomass to Ethanol Dilute-Acid Pretreatment and Enzymatic Hydrolysis of Corn Stover" — Technical Report NREL/TP-5100-47764 May 2011 [2]. In addition to this, techno-economic aspects of the biochemical cellulosic ethanol process is discussed in some recent publications as well [3-11].
As discussed in earlier chapters, unlike in many other industrial processes, a very wide range of raw materials can be used to make
cellulosic ethanol. Additionally, there are numerous pretreatment, saccharification and fermentation technologies that can be used in the biomass hydrolysis process. Therefore, a comparison of different routes can be complicated, but the ultimate goal is to identify the technology that can yield the minimum ethanol selling price (MESP) in dollars per gallon. In addition to $/gallon criteria there are factors like environmental considerations, employment opportunities, long-term stability of the feedstock supply, and the effect on the local economy, that are also vital to a comprehensive technoeconomic analysis. A survey of recent techno-economic analysis studies on biochemical cellulosic ethanol is shown in Table 17.2.
The lowest MESP value of $0.63-0.83/gallon is found in a process economics analysis by Laser and Larson for a plant using switchgrass as feedstock, AFEX pretreatment, and consolidated bioprocessing (CBP) path. Then, Sendich and Laser predicted $0.8-0.9/gallon for a corn stover-ethanol plant based on similar technology. However, these values look to be too far off from the NREL 2011 report prediction of $2.15/gallon for corn stover-cellulosic ethanol [2].
Among several techno-economic analysis reports, Humbbird and Hsu’s NREL reports provide the best insight to analysis technique. According to their analysis feedstock cost ($0.74/gal), enzymes ($0.34/gal), and non-enzyme conversion costs ($1.08/gal) contribute to the MESP value of $2.15/gal, as shown in Table 17.3.
This NREL MESP value ($2.15/gal) is based on a series of process parameters. Some of the critical parameters used by NREL analysis are shown in Table 17.4.