Economic comparison model

The composition of poplar wood was usedasamodel for the feedstock composition however, as used in this simulation, the poplar is modeled as consisting of only cellulose, xylan, and lignin, with compositions of 49.47, 27.26, and 23.27%, respectively. Laboratory results for carbonic acid pretreatment are relatively scarce, so for the purpose of this comparative study, stoichiometry of pretreatment reactions was assumed to be equal to those used in the comparison model (3) cellulose conversion to glucose 6.5% xylan conversion to xylose 75 and lignins solubilized 5%. Thus, economic comparisons made with this model assess different equipment and operating costs but not product yields. For the successful convergence of the carbonic acid model, the simulation required initial specification of several variables. These variables included initial estimates for stream variables and inputs for the unit operation blocks. 

Inits economic model (3), NRELused the discounted cash flow method to calculate the yearly total equipment cost for different process sections. To simplify economic comparisons between the two pretreatment designs,... 

L6pez, C., Moreira, M.T., Feijoo, G. and Lema, J. M. 2011. Economic comparison of enzymatic reactors and advanced oxidation processes applied to the degradation of phenol as a model compound. Biocatalysis and Biotransformation, 29, 344-353. 

Initially, the combined model was huge, containing more than 1.2 million non-zero terms in its matrix of variables. To allow the model to run in a reasonable amount of time on a Pentium III computer, we made some simplifications. In the reduced model, the four catalyst bed models are still fully rigorous. However, the hydrogen furnaces are represented with a heat-exchanger model, quench valves are modeled with mixers, a component splitter model is used for the wash-water system, and a group of component splitters is used for the fractionation section. These changes reduce the number of equations and non-zeros to 130,000 and 680,000 respectively. Despite these simplifications, the slimmed-down model remains, in our collective opinion, a useful tool for offline what-if studies and for economic comparisons of different process options. 

The purpose of this book is to present a comprehensive treatment of both steady-state design and dynamic control of reactive distillation systems using rigorous nonlinear models. Both generic ideal chemical systems and actual chemical systems are studied. Economic comparisons between conventional multiunit processes and reactive distillation are presented. Reactive distillation columns in isolation and in plantwide systems are considered. There are many parameters that affect the design of a reactive distUlation column. Some of these effects are counterintuitive because they are different than in conventional distillation. This is one of the reasons reactive distillation is such a fascinating subject. 

In many process-design calculations it is not necessary to fit the data to within the experimental uncertainty. Here, economics dictates that a minimum number of adjustable parameters be fitted to scarce data with the best accuracy possible. This compromise between "goodness of fit" and number of parameters requires some method of discriminating between models. One way is to compare the uncertainties in the calculated parameters. An alternative method consists of examination of the residuals for trends and excessive errors when plotted versus other system variables (Draper and Smith, 1966). A more useful quantity for comparison is obtained from the sum of the weighted squared residuals given by Equation (1). 

In a comparison of nine economic models, estimated costs to the United States as of the late 1990s ranged from a loss in gross domestic product from 40 billion to 180 billion, with assumptions of no emission trading from 20 billion to 90 billion with trading only among developed countries and from... 

Water Potentials. The ST2 (23), MCY (24), and CF (2J5) potentials are computationally tractable and accurate models for two-body water-water interaction potentials. The ST2, MCY and CF models have five, four, and three interaction sites and have four, three and three charge centers, respectively. Neither the ST2 nor the MCY potentials allow OH or HH distances to vary, whereas bond lengths are flexible with the CF model. While both the ST2 and CF potentials are empirical models, the MCY potential is derived from ab initio configuration interaction molecular orbital methods (24) using many geometrical arrangements of water dimers. The MCY+CC+DC water-water potential (28) is a recent modification of the MCY potential which allows four body interactions to be evaluated. In comparison to the two-body potentials described above, the MCY+CC+DC potential requires a supercomputer or array processor in order to be computationally feasible. Therefore, the ST2, MCY and CF potentials are generally more economical to use than the MCY+CC+DC potential. 

Figure 5 The iterative optimization process. An initial model is developed, used to predict process performance, tested by comparison with experiment, refined, and used to improve prediction. The process naturally accommodates changes in economic or regulatory constraints.

The models may be used to compare performance between several units or unit types. For example, a week of production data from the above-mentioned modified cascade unit was compared with simulated Stratco performance. The agreement between Amoco s Stratco simulation model predictions and material balance and performance predictions provided by the Stratford Engineering Corporation had been confirmed earlier. Model adjustments allowed a comparison at constant operating conditions to be made. Table I compares the performance of the modified cascade unit with the Stratco simulation model predictions. Acid consumption is 36% lower in the modified cascade unit. The Stratco unit does show a slight research octane advantage over the cascade. However, overall economics favor the modified cascade. in this case. 

Secondary as well as tertiary recovery (without or with prior water flooding) processes were simulated in both lab model and computer simulation experiments. In every case, injection of the carbon dioxide slug was followed by a final waterflood until an assumed economically limiting oil cut of 2 % was reached. The extra oil for secondary 002 floods was determined 1 subtracting from the over-all oil yield the recovery which could have been obtained by a prior water flood. The secondary and tertiary extra oil yields are therefore comparable. A comparison of the extra oil recovery by computer simulation with that obtained in the laboratory model is idiown in Table II, on the next page. 

Figures 1 and 4 show the water flood matches to the water-wet and oil-wet lab model curves, respectively. The carbon dioxide flooding runs in the lab model were then matched by computer simulation. In the simulations, as in the lab model, the carbon dioxide slug was followed by waterflooding to an assumed economically limiting water cut of 98%, and the enhanced oil recovery was calculated as the difference between the ultimate total recovery at this point and that of a water flood starting from initial oil saturation and continued until a 98% water cut was reached. Secondary carbon dioxide floods started from the same initial oil saturation, while tertiary carbon dioxide floods started with the condition at the 98% water cut point in the simple water flood. Since the foam or emulsion tests involved a 1 1 ratio of water and carbon dioxide, comparisons are shown only for the case of 1 1 WAG operation vs foam.

Based on the potential benefits for source densification an economic analysis was performed to quantify the dollar savings (2). A model of the collection process was developed that allowed comparison of the cost of conventional waste collection with proposed densified waste collection. 

P.V. Grootenhorst, A comparison of alternative models of prescription drug utilization, Health Economics 4 (1995), 183-198. 

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