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

Abstract

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

A method for aggregating external operating conditions in multi-generation system optimization models

“…In the rewritten optimization problem, the constraint (19) is slacked and replaced by a new constraint 569 stating that the total heat production over the entire period must equal the total heat consumption 570 Given equations (15)- (19) and (23)-(27), the optimization problem with thermal energy storage can be 576 written in condensed form as 577 (16), (17), (25), (26), (27) ℎ : , ∈ ℝ + (28) 578…”

“…As constraints (26) and (27) require knowledge of the time chronology of the data points, the optimization 579 problem (28) cannot be solved using the CHOP-reduced dataset. Therefore, constraints (26) and (27) were 580 slacked, and the resulting error was evaluated a posteriori. Results obtained from solving the problem (28) 581 using the full EOC dataset and the revised CHOP dataset are presented in Table 11.…”

“…However, neither monthly-nor annually-averaged operating 100 parameter values provide information on short-term relations and variations between various operating 101 conditions. While it may be acceptable to neglect this information for static operating facilities, it can be 102 critical to the economy and thermodynamic performance of flexible facilities such as combined heat and 103 power (CHP) plants [24] and FMGs [25] [26]. Failing to consider short-term relations between relevant 104 operating parameters may lead to sub-optimal solutions in the design optimization of FMGs [27].…”

A polygeneration from a dual-gas partial catalytic oxidation coupling with an oxygen-permeable membrane reactor

“…Base on these advantages, a number of polygeneration systems on the basis of different energy resources types (such as coal, natural gas, solar and biomass) with various configurations and products (eg. methanol (MeOH), dimethyl ether (DME), dimethyl carbonate (DMC), Fischer-Tropsch oil and electricity) are proposed and investigated [5][6][7][8][9][10].…”

Simulation of Polygeneration Systems

“…Other studies used polygeneration systems in order to produce a specific product. For example, Lythcke-Jørgensen et al [14] integrated biofuel production in a polygeneration system in order to reduce the operating costs and increase the energy efficiency. In particular, they integrated a Rankine steam cycle within an ethanol facility using steam extracted from the turbine to supply the heat required for ethanol production.…”