EISA (Energy Independence and Security Act) compliant ethanol fuel from corn stover in a depot‐based decentralized system

Abstract

Cellulosic biofuels face significant problems of feedstock aggregation and logistics leading to poor economies of scale. The current model is for relatively small biorefineries using feedstock gathered locally. Here a depot‐based decentralized biorefinery system is explored to estimate the US Energy Independence and Security Act (EISA) compliant corn stover ethanol production potential in the US Midwest. Depots serve to aggregate, pretreat, and densify biomass (via pellets) and thereby enable very large biorefineries using a decentralized system to collect these pellets. Such a corn‐stover based decentralized system using depots would establish one or two very large‐scale decentralized biorefineries capable of processing about 8–12% of the total corn stover available in the US Midwest. These decentralized biorefineries are economically competitive with the centralized biorefineries. About 55–153 depots could supply the pretreated pellets to the individual decentralized biorefineries leading to an annual production of 1.02–2.91 billion liters of cellulosic ethanol fuel. Most of the participating depots are located in Illinois and Iowa. The total EISA‐compliant ethanol fuel produced in the decentralized system is 2.82–4.07 billion liters per year. The ethanol selling price in the depot‐based decentralized biorefinery system varies between US$0.67 and US$0.72 L−1. The greenhouse gas (GHG) savings from cellulosic ethanol in the decentralized system compared to gasoline are 3.35–4.84 Tg CO2 year−1. Importantly, the total capital investment per annual volume of ethanol in the decentralized biorefinery ranges from US$0.71 L1 to US$1.15 L1, while the total capital investment per annual ethanol volume in the centralized biorefinery is US$1.98 L−1. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd

Integration in a depot‐based decentralized biorefinery system: Corn stover‐based cellulosic biofuel

“…Depot facilities are assumed to be located at existing grain elevators in the U.S. Midwest (Kim & Dale, ; Kim et al, ). In this analysis, the depot facility locations are determined based on the following two assumptions: (1) the collection radius for the depot facilities is less than 16.1 km, and (2) the depot facility size ranges from 90 to 200 dry Mg/day.…”

“…The price of pretreated pellets estimated by Kim et al () is used in this analysis. The minimum biofuel selling price (MBSP) is estimated by regression equations based on results from the modified Aspen Plus model (see Figure S1).…”

“…In this study, marginal analysis was used to assign SOC changes over the entire soil profile and also soil N 2 O emissions to corn stover. The process data estimated for the depot (Kim et al, ) are used to calculate GHG emissions associated with the depot. The GHG emissions associated with the IDB and energy consumption (i.e., electricity and thermal energy) are estimated based on the mass and energy balance resulting from the modified Aspen Plus model, and the GHG emissions associated with biomethane losses (assumed to be 1%, Saur & Jalalzadeh‐Azar, ) are also included.…”

“…The minimization function in both systems is solved by mixed integer nonlinear programming algorithms. Previous studies (Kim & Dale, 2016;Kim et al, 2018) show that the sequence of the biorefineries affects the overall supply chain system. Following the energy demand-oriented supply chain approach (Kim & Dale, 2016), the first supply chain is assumed to be established for an IDB located in the Chicago area, the highest gasoline consumption area among the urban areas considered here.…”

“…The capital investment costs for on‐site energy generation facility account for 28%–34% of the total capital investment in both centralized and decentralized biorefinery systems (Humbird et al, ; Kim et al, ). Greenhouse gas (GHG) credits associated with the excess electricity are a major cause of reduced lifecycle GHG emissions of cellulosic ethanol fuels and equal approximately 6–22 g CO 2 /MJ in the centralized biorefinery system (Kim et al, ) and 32–45 g CO 2 /MJ in the decentralized (depot‐based) biorefinery system (Kim et al, ). In this analysis, the GHG credits refer to avoided GHG emissions.…”