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Performance of ethanol-fuelled solid oxide fuel cells: Proton and oxygen ion conductors
(2007-09-15)
Jamsak, W.
;
Assabumrungrat, S.
;
Douglas, P. L.
;
Laosiripojana, N.
;
Suwanwarangkul, R.
This paper investigates the performance of ethanol-fuelled solid oxide fuel cells (SOFCs) with two types of solid electrolytes, namely oxygen ion-conducting (SOFC-O2-) and proton-conducting electrolytes (SOFC-H+). Our previous work reported that the SOFC-H+ shows superior theoretical performance over the SOFC-O2- electrolyte. However, in this work when all resistances are taken into account, the actual performance of the SOFC-O2- (Ni-YSZ|YSZ|YSZ-LSM) becomes significantly better than that of SOFC-H+ (Pt|SCY|Pt). The maximum power density of the SOFC-O2- is about 34 times higher than that of the SOFC-H+ when operated at an inlet H<inf>2</inf>O:EtOH ratio of 3, a fuel utilization factor of 80% and a temperature of 1200 K. Then the required values of the total resistance of the SOFC-H+ to achieve the same power density as the SOFC-O2- were determined. It was found that due to the superior theoretical performance of the SOFC-H+, it is not necessary to reduce the SOFC-H+ total resistance to the same values as the one for SOFC-O2-. The study also indicates that reduction of only the electrolyte resistance is not sufficient to improve the SOFC-H+ performance and, therefore, the other resistances including activation, electrodes and interconnect resistances need to be reduced simultaneously. Finally, the improvement of the electrolyte resistance by changing its resistivity and thickness is discussed. © 2007 Elsevier B.V. All rights reserved.
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Synthesis of rice processing plants. II. MINLP optimization
(2003-10-01)
Phongpipatpong, M.
;
Douglas, P. L.
A systematic design approach was applied to develop the optimal process flowsheet for a rice processing plant. The optimization problem was formulated as a Mixed-Integer NonLinear Programme, MINLP, consisting of vectors of binary and continuous variables. A superstructure flowsheet comprising all serial structures of drying, cooling, and tempering units in the process was postulated. The set of optimum decision variables including the number of drying, cooling, and tempering units, temperature and relative humidity of drying air, drying time, cooling time, and tempering time were determine as the solution of the corresponding MINLP. Six objective functions were investigated as possible performance criteria: production time, number of the operating units, energy consumption, total operating cost, head rice yield, and the profit. The choice of objective function was found to have a significant effect on the optimal solution. Comparison with typical design and operating conditions, the MINLP results showed that a 22% reduction in energy consumption was possible along with a 2.4% increase in head rice yield. These savings, if applied to the world-wide rice industry, translate into more than $3 billion dollars/year increase in profit.
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Synthesis of rice processing plants. I. Development of simplified models
(2003-10-01)
Phongpipatpong, M.
;
Douglas, P. L.
This article, the first of three articles on the synthesis of rice processing plants, focuses on the development of simplified mathematical models necessary for use in optimizing rice processing plants. The second concentrates on the optimal synthesis of a rice plant and the third on the sensitivity of the optimization to uncertainty in model parameters. Existing models for rice processing unit operations are not suitable for flowsheet optimization and new models need to be developed to overcome numerical difficulties that occur in optimization applications, specifically in mixed integer nonlinear programming (MINLP) applications. Simplified models of the drying, cooling, and tempering units are developed. In addition head rice yield models, used as a quality indicator, energy consumption, and economic models were also developed. Naturally, the new models exhibit some mismatch with respect to the existing models from which they were developed. However, a sensitivity analysis, presented in Part III, has shown that the optimal flowsheet structure was not sensitive to a lack of fit between the simplified and complex models. The simplified models were found adequate to be appropriate for use at the synthesis stage.
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Synthesis of rice processing plants. III. Sensitivity analysis
(2003-10-01)
Phongpipatpong, M.
;
Douglas, P. L.
An optimal process flowsheet for a rice processing plant has been developed. The optimization problem was formulated as a Mixed-Integer Nonlinear Programme, MINLP, consisting of a vector of binary and continuous variables. The set of optimum decision variables including the number of drying, cooling, and tempering units, temperature and relative humidity of drying air, drying time, cooling time, and tempering time were determined as the solution of the MINLP problem. Six objective functions were investigated as performance criteria. A sensitivity analysis of each model parameter was conducted to determine its influence on the optimal flowsheet. The MINLP approach is an efficient tool for optimization and the simplified models were adequate for use at the synthesis stage. The solution is insensitive to uncertainty in the models. However, due to the nonconvex nature of MINLPs, the solution was found to depend on the initial starting values, especially for the maximum profit flowsheet.

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