Techno-Economic Aspects of Biomass Gasification Process
A number of researchers have studied the techno-economic aspects of the biomass gasification process to cellulosic ethanol discussed in Part 3 of this book [19-25]. There are considerable variations in gasifier types and methods used to convert syngas to ethanol, making it difficult to compare individual studies. Villanueva Perales and coworkers have studied the techno-economic aspects of the production of ethanol via entrained flow gasification of biomass and subsequent catalytic synthesis by considering current and future scenarios [22]. In the current scenarios are plants making use of available technologies and state-of-the-art mixed alcohol catalysts (Rh-Mn/SiO2 and KCoMoS2 catalysts). In the future scenarios, the
|
MESP ($/gal) |
Feedstock |
Scale (dry ton/day) |
Feed Price ($/dry ton) |
Ethanol Yield (gal/dry ton) |
Notes |
Reference |
|
1.49 |
Corn stover |
2200 |
51 |
90 |
Dilute acid pretreatment, SSCF process, electricity co-product |
[12] |
|
2.15 |
Corn stover |
2200 |
59 |
79 |
Dilute acid pretreatment, SHF process, electricity co-product |
[2] |
|
3.40-4.44 |
Corn stover |
2200 |
75 |
42-72 |
Varying pretreatment options and downstream process assumptions |
[4] |
|
1.42-1.87 |
Aspen, poplar, corn stover, switchgrass |
2200 |
58-100 |
83-111 |
Dilute acid pretreatment |
[11] |
|
1.03-1.41 |
Corn stover |
2200 |
40 |
70 |
AFEX pretreatment, SSCF process, varying process conditions |
[13] |
|
Table 17.2 A survey of recent techno-economic analysis studies on biochemical cellulosic ethanol [2]. |
|
534 Handbook of Cellulosic Ethanol |
|
Table 17.3 Breakdown of the MESP for a corn stover ethanol plant using dilute acid pretreatment with enzymatic hydrolysis and co-fermentation; ethanol production capacity, yield, feedstock + handling cost, internal rate of return, and equity percent of total investment [2].
|
|
Table 17.4 Some key process parameters used to calculate minimum ethanol selling price (MESP) in the, "Enzymatic Hydrolysis of Corn Stover," Technical Report NREL/TP-5100-47764 May 2011 [2].
|
|
Feedstock — Corn stover, 20% moisture content |
|
|
Conversions Overall |
|
|
Cellulose to Glucose |
9.9% |
|
Xylan to Xylose |
90% |
|
Mannan to Mannose |
90% |
|
Arabinan to Arabinose |
90% |
|
Lignin to Soluble Lignin |
5% |
|
Enzymatic Hydrolysis |
|
|
Enzyme Loading (mg/g cell) |
19.9 |
|
Total Solids (wt%) |
20.0% |
|
Insoluble Solids (wt%) |
10.6% |
|
Temperature (°C) |
32 |
|
Pressure (atm) |
1.0 |
|
Residence Time (days) |
3.5 |
|
Conversions Overall |
|
|
Cellulose to Glucose |
90% |
|
Conditioning, Ammonia Loading (g/L hydrolyzate) |
4.7 |
|
Fermentation |
|
|
Total Solids (wt%) |
19.8% |
|
Insoluble Solids (wt%) |
5.1% |
|
Temperature (°C) |
32 |
|
Pressure (atm) |
1.0 |
|
Residence Time (days) |
1.5 |
|
Conversions Overall |
|
|
Glucose to Ethanol |
95% |
(Continued)
|
Table 17.4 (Cont.)
|
effects of improvements in MoS2 catalyst performance and the availability of pressurized solid biomass feeding systems are assessed. A plant size of 2140 dry tonnes/day of wood chip (500 MWth) is considered in this study with the criteria of being energy self-sufficient. The analysis revealed that although the rhodium catalyst presents better performance than MoS2 catalysts in terms of selectivity to ethanol, the high price of the rhodium catalyst leads to higher production costs. For current catalysts, the minimum ethanol selling price (including 10% rate of return) is in the range of $0.90-1.25/L ($3.41-4.73/US gallon). According to the analysis of Villanueva Perales and coworkers, in a future scenario, expected improvements in MoS2 catalyst performance would lead to a decrease in price to about $0.71 /L ($2.69/US gallon).
Prior to the study of Villanueva Perales et al., Dutta and Biddy of NREL reported a study based on an entrained flow slagging gasifier,
1.4
-I
where the MESP was 0.66 $/L ($2.50/US gallon) for a biomass price of $53/dry tonne [26]. The lower MESP reported by Dutta et al. may be largely due to the use of a piston feeder, which allows feeding solid biomass to pressurized gasifiers without needing a flash pyrolysis pretreatment as compared to Villanueva Perales and coworkers study. This comparison of the studies shows the high impact of the feed handling system on process economics in the case of pressurized entrained flow gasifiers [26].
In the gasification route, the catalyst plays a very important role in the overall process economics and MESP. A comparison of MESPs of ethanol produced using three different catalysts, Rh-Mn/SiO2 (PNNL), KCoMoS2 catalysts from Dow Chemical, and KCoMoS2 catalysts from ABNT is shown in Figure 17.1. In this comparison KCoMoS2 catalysts showed lower MESP than Rh-based catalyst.