Document Version Peer reviewed versionLink back to DTU Orbit Citation (APA): Lythcke-Jørgensen, C. E., Münster, M., Ensinas, A. V., & Haglind, F. (2016). A method for aggregating external operating conditions in multi-generation system optimization models. Applied Energy, 166, 59-75. Abstract 10This paper presents a novel, simple method for reducing external operating condition datasets to be used 11 in multi-generation plant optimization models. The method, called the Characteristic Operating Pattern 12 (CHOP) method, is a visually-based aggregation method that clusters reference data based on parameter 13 values rather than time of occurrence, thereby preserving important information on short-term relations 14 between the relevant operating parameters. This is opposed to commonly used methods where data are 15 averaged over chronological periods (months or years), and extreme conditions are hidden in the averaged 16 values. 17The CHOP method is tested in a case study where the operation of a fictive Danish combined heat and 18 power plant is optimized over a historical 5-year period. The optimization model is solved using the full 19 external operating condition dataset, a reduced dataset obtained using the CHOP method, a monthly-20 averaged dataset, a yearly-averaged dataset, and a seasonal peak/off-peak averaged dataset. The 21 *Revised Manuscript with No Changes Marked economic result obtained using the CHOP-reduced dataset is significantly more accurate than that obtained 22 using any of the other reduced datasets, while the calculation time is similar to those obtained using the 23 monthly averaged and seasonal peak/off-peak averaged datasets. The outcomes of the study suggest that 24 the CHOP method is advantageous compared to chronology-averaging methods in reducing external 25 operating condition datasets to be used in the design optimization models of flexible multi-generation 26 plants. 27

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.

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10A promising way to increase the energy efficiency and reduce costs of biofuel production is to 11 integrate it with heat and power production in polygeneration plants. This study treats the 12 retrofitting of a Danish combined heat and power plant by integrating lignocellulosic ethanol 13 production based on wheat straw with the aim of minimizing specific ethanol production cost. 14 Previously developed and validated models of the facilities are applied in the attempt to solve the 15 design optimization problem. Straw processing capacities in the range of 5 kg/s to 12 kg/s are 16 considered, while plant operation is optimized over the year with respect to maximal income and 17 with the limitations that the reference hourly district heating production has to be met while 18 reference hourly power export cannot be exceeded. 19 *Revised Manuscript with no changes marked Click here to view linked References 2The results suggest that the specific ethanol production cost increased continuously from 0.958 20Euro/L at a straw processing capacity of 5 kg/s to 1.113 Euro/L at a capacity of 12 kg/s, indicating 21 that diseconomies-of-scale applies for the suggested ethanol production scheme. A thermodynamic 22 evaluation further discloses that the average yearly exergy efficiency decreases continuously with 23 increasing ethanol production capacity, ranging from 0.746 for 5 kg/s to 0.696 for 12 kg/s. This 24 trend results from operating constraints that induce expensive operation patterns in periods of high 25 district heating loads or shut-down periods for the combined heat and power plant. A sensitivity 26 analysis indicates that the found optimum is indifferent to major variations in fossil fuel prices. The 27 results question the efficiency of the suggested retrofitting scheme in the present energy system, and 28 they further point towards the importance of taking operating conditions into consideration when 29 developing flexible polygeneration plant concepts as differences between design-point operation 30and actual operation may have a significant impact on overall plant performance. 31

 Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.