Case Study of a Cellulose-Based Bioethanol Plant

Abstract:
In this study a cellulose-based bioethanol plant is investigated. The goal is to develop a base-case design which will be further considered and optimized via heat integration and mathematical programming techniques in a successive study. First, different technologies for the conversion of cellulose biomass to bioethanol are considered in order to determine the most promising alternative. Here, the thermochemical manufacture of ethanol via gasification of biomass is selected. In the following, flowsheet alternatives are investigated and unit operations with their corresponding operating conditions are presented for the thermochemical conversion of switchgrass as a representative of lignocellulosic biomass. For each process block appropriate unit operations and operating conditions are chosen for the base-case design. Finally, operating conditions, flowrates and heat requirements are determined. This is accomplished through the formulation of a shortcut model by means of simplified mass and energy balances. In order to produce 61.29Mgal/yr of ethanol of required purity a feed of 129,633 lb/hr of switchgrass is needed. The total heating and cooling duties are determined to Qheating, total = 303,247 kW and Qcooling, total = 319,030 kW. The base-case design is compared to an optimized corn-based bioethanol plant by Karruppiah et al. [6.1]. The results indicate that the design developed for a cellulose-based bioethanol plant is competitive to the corn-based bioethanol plant, though it is more energy extensive. Hence, an optimized design via heat integration and mathematical programming techniques is worthwhile to investigate.

Keywords:
bioethanol