Exergy analysis of a combined heat and power plant with integrated lignocellulosic ethanol production

Abstract

Lignocellulosic ethanol production is often assumed integrated in polygeneration systems because of its energy intensive nature. The objective of this study is to investigate potential irreversibilities from such integration, and what impact it has on the efficiency of the integrated ethanol production.An exergy analysis is carried out for a modeled polygeneration system in which lignocellulosic ethanol production based on hydrothermal pretreatment is integrated in an existing combined heat and power (CHP) plant. The ethanol facility is driven by steam extracted from the CHP unit when feasible, and a gas boiler is used as back-up when integration is not possible. The system was evaluated according to six operation points that alternate on the following three different operation parameters: Load in the CHP unit, integrated versus separate operation, and inclusion of district heating production in the ethanol facility. The calculated standard exergy efficiency of the ethanol facility varied from 0.564 to 0.855, of which the highest was obtained for integrated operation at Complete revised manuscript Click here to view linked References 2 minimum CHP load and full district heating production in the ethanol facility, and the lowest for separate operation with zero district heating production in the ethanol facility. The results suggest that the efficiency of integrating lignocellulosic ethanol production in CHP plants is highly dependent on operation, and it is therefore suggested that the expected operation pattern of such polygeneration system is taken into account when evaluating the potential of the ethanol production.

Technical possibilities of bioethanol production from coffee pulp: a renewable feedstock

“…Another alternative that recommended to be used is energy integration in the entire system (Lythcke-Jørgensen et al 2014). For example, the utilization of excess steams from distillation column to evaporation unit would save at least 10 % of the energy demand (Kravanja et al 2013).…”

Exergy and CO2 Analyses as Key Tools for the Evaluation of Bio-Ethanol Production

“…Based upon this literature survey, the following conclusions can be drawn: (1) Most of the studies focus on specific parts of the process, e.g., water reduction and recycling, integrated energy supply using stillage and/or residual biomass, the use of co-generation systems (CHP (Combined heat and power), gasification, Rankine cycle); (2) Due to the energy-intensive nature of lignocellulosic ethanol production, different studies investigate improvements of the efficiency of ethanol production; (3) The production facilities (e.g., power, heat, lignocellulosic ethanol, and syngas (SNG)) are often integrated in poly-generation systems [61]; (4) The exergy analysis is usually applied to assess the efficiency of an integrated system; (5) Exergy analysis has been performed mainly for thermochemical pathways while fewer studies involve applications of exergy analysis to biochemical pathways [47,62]; (6) Understanding the complex structure of lignocellulose represents an important key to design a sustainable pretreatment process for the production of bioethanol [28].…”

Design optimization of a polygeneration plant producing power, heat, and lignocellulosic ethanol

“…The exergy efficiency of the straw-to-ethanol conversion was markedly higher for integrated 240 operation [27] [15]. 241…”

“…Two other studies by Lythcke-Jørgensen et al [27] [15] investigated six different operation points 227 for the reference PGP and found that within these, the exergy efficiency of the ethanol production 228 varied from 0.564 to 0.855. The highest exergy efficiency was obtained for integrated operation 229 with full DH production in the ethanol facility and lowest possible load in the CHP unit, while the 230 lowest exergy efficiency was obtained for separate operation.…”

“…(37), ߟ ௫, is the hour-wise exergy efficiency of the ethanol production. Using the exergy 452 analysis method described in Lythcke-Jørgensen et al [15] for calculating exergy contents of the 453 flows in the ethanol production, the hourly exergy efficiency is calculated as 454…”