Process and economic analysis of pretreatment technologies

doi:10.1016/j.biortech.2005.01.017

Bioresource Technology

Volume 96, Issue 18, December 2005, Pages 2019-2025

https://doi.org/10.1016/j.biortech.2005.01.017 Get rights and content

Abstract

Five pretreatment processes (dilute acid, hot water, ammonia fiber explosion (AFEX), ammonia recycle percolation (ARP), and lime) for the liberation of sugars from corn stover are compared on a consistent basis. Each pretreatment process model was embedded in a full bioethanol facility model so that systematic effects for variations in pretreatment were accounted in the overall process. Economic drivers influenced by pretreatment are yield of both five and six carbon sugars, solids concentration, enzyme loading and hemicellulase activity.

All of the designs considered were projected to be capital intensive. Low cost pretreatment reactors in some pretreatment processes are often counterbalanced by higher costs associated with pretreatment catalyst recovery or higher costs for ethanol product recovery. The result is little differentiation between the projected economic performances of the pretreatment options. Additional process performance data, especially involving the identification of optimal enzyme blends for each pretreatment approach and conditioning requirements of hydrolyzates at process-relevant sugar concentrations resulting from each pretreatment may lead to greater differentiation in projected process economics.

Introduction

Process engineering and economic analysis for the Biomass Refining Consortium for Applied Fundamentals and Innovation (CAFI) USDA Initiative for Future Agriculture and Food Systems (IFAFS) program were conducted via support from the US Department of Energy’s Office of the Biomass Program. The material balance and technoeconomic models were developed early in the USDA IFAFS project for each pretreatment technology in collaboration with each CAFI researcher. Initially, these models were populated with either assumptions or data generated in previous work, if applicable. The models were updated throughout the course of the IFAFS project as process performance data was generated and thus provided important information for guiding the selection of experimental conditions and the interpretation of experimental results. A series of sensitivity cases were also developed for each pretreatment approach to identify the economic impact of sugar and ethanol yields, enzyme loading and cost, capital costs, and other relevant parameters. The details of the various sensitivity analyses are not covered in this paper, but have been provided to each CAFI researcher.

The data generated in the IFAFS project were primarily focused upon determining glucose and xylose sugar yields upon pretreatment and enzymatic hydrolysis using a standard cellulase loading. Less emphasis was placed on downstream process characterization and optimization, such as identifying improved enzyme preparations for each pretreatment or determination of conditioning requirements on hydrolyzates resulting from each pretreatment to allow for efficient fermentation at process-relevant sugar concentrations. Therefore, this paper is focused on identifying the process economic impact of the different pretreatment approaches as related to capital and operating cost investment and baseline glucose and xylose sugar yields from each pretreatment.

Section snippets

Methods

An ASPEN Plus 10 (Aspen Technology, Inc., Cambridge, MA) simulation model was assembled for each pretreatment process using performance data supplied by each CAFI researcher. Detailed descriptions for each pretreatment process can be found in this volume (Kim and Lee, 2005, Teymouri et al., 2005, Mosier et al., 2005, Lloyd and Wyman, 2005, Kim and Holtzapple, 2005). Appropriate pretreatment reactor design and materials of construction for each pretreatment technology were developed that are

Results and discussion

Table 1 compares the capital costs for each case. The pretreatment area direct fixed capital for the dilute acid, AFEX, ARP, and lime cases are roughly the same. The contribution of the pretreatment reactor dominates pretreatment area cost for the dilute acid case, whereas for AFEX, ARP and lime, other equipment items dominate, with the pretreatment reactor cost being significantly lower than for dilute acid. Much of this other equipment is related to recovery of the pretreatment catalyst,

Conclusions

The pretreatment processes were compared on a consistent basis. Each pretreatment process model was embedded in a full facility model so that systematic effects for variations in pretreatment were accounted in the overall process. Economic drivers influenced by pretreatment are yield of both five and six carbon sugars, solids concentration, enzyme loading and hemicellulase activity.

All of the designs considered were projected to be capital intensive. Low cost pretreatment reactors are often

Acknowledgements

•
The United States Department of Energy—Office of the Biomass Program.
•
The United States Department of Agriculture—Initiative for Future Agricultural and Food Systems/Cooperative State Research, Education and Extension Service (Contract Number 00-52104-9663).
•
Biomass Refining Consortium for Applied Fundamentals and Innovation (CAFI).

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